National Library of Energy BETA

Sample records for disk brakes rear

  1. Braking the Gas in the beta Pictoris Disk

    E-Print Network [OSTI]

    Fern'andez, R; Wu, Y; Brandeker, Alexis; Fern\\'andez, Rodrigo

    2006-01-01

    (Abridged) The main sequence star beta Pictoris hosts the best studied circumstellar disk to date. Nonetheless, a long-standing puzzle has been around since the detection of metallic gas in the disk: radiation pressure from the star should blow the gas away, yet the observed motion is consistent with Keplerian rotation. In this work we search for braking mechanisms that can resolve this discrepancy. We find that all species affected by radiation force are heavily ionized and dynamically coupled into a single fluid by Coulomb collisions, reducing the radiation force on species feeling the strongest acceleration. For a gas of solar composition, the resulting total radiation force still exceeds gravity, while a gas of enhanced carbon abundance could be self-braking. We also explore two other braking agents: collisions with dust grains and neutral gas. Grains surrounding beta Pic are photoelectrically charged to a positive electrostatic potential. If a significant fraction of the grains are carbonaceous (10% in t...

  2. Use of an auditory signal in a rear-end collision warning system: effects on braking force and reaction time 

    E-Print Network [OSTI]

    Hopkins, Jennifer Susan

    1995-01-01

    This simulator experiment is a preliminary study examining the effects of different auditory signals on braking force and reaction time in a rear-end collision warning system. A driving simulator was built in which subjects operated a computer...

  3. Braking the Gas in the beta Pictoris Disk

    E-Print Network [OSTI]

    Rodrigo Fernández; Alexis Brandeker; Yanqin Wu

    2006-01-11

    (Abridged) The main sequence star beta Pictoris hosts the best studied circumstellar disk to date. Nonetheless, a long-standing puzzle has been around since the detection of metallic gas in the disk: radiation pressure from the star should blow the gas away, yet the observed motion is consistent with Keplerian rotation. In this work we search for braking mechanisms that can resolve this discrepancy. We find that all species affected by radiation force are heavily ionized and dynamically coupled into a single fluid by Coulomb collisions, reducing the radiation force on species feeling the strongest acceleration. For a gas of solar composition, the resulting total radiation force still exceeds gravity, while a gas of enhanced carbon abundance could be self-braking. We also explore two other braking agents: collisions with dust grains and neutral gas. Grains surrounding beta Pic are photoelectrically charged to a positive electrostatic potential. If a significant fraction of the grains are carbonaceous (10% in the midplane and larger at higher altitudes), ions can be slowed down to satisfy the observed velocity constraints. For neutral gas to brake the coupled ion fluid, we find the minimum required mass to be $\\approx$ 0.03 $M_\\earth$, consistent with observed upper limits of the hydrogen column density, and substantially reduced relative to previous estimates. Our results favor a scenario in which metallic gas is generated by grain evaporation in the disk, perhaps during grain-grain collisions. We exclude a primordial origin for the gas, but cannot rule out the possibility of its production by falling evaporating bodies near the star. We discuss the implications of this work for observations of gas in other debris disks.

  4. DOES MAGNETIC-FIELD-ROTATION MISALIGNMENT SOLVE THE MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION?

    SciTech Connect (OSTI)

    Li Zhiyun [Astronomy Department, University of Virginia, Charlottesville, VA (United States); Krasnopolsky, Ruben; Shang, Hsien [Academia Sinica, Theoretical Institute for Advanced Research in Astrophysics, Taipei, Taiwan (China)

    2013-09-01

    Stars form in dense cores of molecular clouds that are observed to be significantly magnetized. In the simplest case of a laminar (non-turbulent) core with the magnetic field aligned with the rotation axis, both analytic considerations and numerical simulations have shown that the formation of a large, 10{sup 2} AU scale, rotationally supported protostellar disk is suppressed by magnetic braking in the ideal MHD limit for a realistic level of core magnetization. This theoretical difficulty in forming protostellar disks is termed the ''magnetic braking catastrophe''. A possible resolution to this problem, proposed by Hennebelle and Ciardi and Joos et al., is that misalignment between the magnetic field and rotation axis may weaken the magnetic braking enough to enable disk formation. We evaluate this possibility quantitatively through numerical simulations. We confirm the basic result of Joos et al. that the misalignment is indeed conducive to disk formation. In relatively weakly magnetized cores with dimensionless mass-to-flux ratio {approx}> 4, it enabled the formation of rotationally supported disks that would otherwise be suppressed if the magnetic field and rotation axis are aligned. For more strongly magnetized cores, disk formation remains suppressed, however, even for the maximum tilt angle of 90 Degree-Sign . If dense cores are as strongly magnetized as indicated by OH Zeeman observations (with a mean dimensionless mass-to-flux ratio {approx}2), it would be difficult for the misalignment alone to enable disk formation in the majority of them. We conclude that, while beneficial to disk formation, especially for the relatively weak field case, misalignment does not completely solve the problem of catastrophic magnetic braking in general.

  5. No Keplerian Disk >10 AU around the Protostar B335: Magnetic Braking or Young Age?

    E-Print Network [OSTI]

    Yen, Hsi-Wei; Koch, Patrick M; Aso, Yusuke; Koyamatsu, Shin; Krasnopolsky, Ruben; Ohashi, Nagayoshi

    2015-01-01

    We have conducted ALMA cycle 2 observations in the 1.3 mm continuum and in the C18O (2-1) and SO (5_6-4_5) lines at a resolution of ~0.3" toward the Class 0 protostar B335. The 1.3 mm continuum, C18O, and SO emission all show central compact components with sizes of ~40-180 AU within more extended components. The C18O component shows signs of infalling and rotational motion. By fitting simple kinematic models to the C18O data, the protostellar mass is estimated to be 0.05 Msun. The specific angular momentum, on a 100 AU scale, is ~4.3E-5 km/s*pc. A similar specific angular momentum, ~3E-5 to 5E-5 km/s*pc, is measured on a 10 AU scale from the velocity gradient observed in the central SO component, and there is no clear sign of an infalling motion in the SO emission. By comparing the infalling and rotational motion, our ALMA results suggest that the observed rotational motion has not yet reached Keplerian velocity neither on a 100 AU nor even on a 10 AU scale. Consequently, the radius of the Keplerian disk in ...

  6. Gravity brake

    DOE Patents [OSTI]

    Lujan, Richard E. (Santa Fe, NM)

    2001-01-01

    A mechanical gravity brake that prevents hoisted loads within a shaft from free-falling when a loss of hoisting force occurs. A loss of hoist lifting force may occur in a number of situations, for example if a hoist cable were to break, the brakes were to fail on a winch, or the hoist mechanism itself were to fail. Under normal hoisting conditions, the gravity brake of the invention is subject to an upward lifting force from the hoist and a downward pulling force from a suspended load. If the lifting force should suddenly cease, the loss of differential forces on the gravity brake in free-fall is translated to extend a set of brakes against the walls of the shaft to stop the free fall descent of the gravity brake and attached load.

  7. Braking system

    DOE Patents [OSTI]

    Norgren, D.U.

    1982-09-23

    A balanced braking system comprising a plurality of braking assemblies located about a member to be braked. Each of the braking assemblies consists of a spring biased piston of a first material fitted into a body of a different material which has a greater contraction upon cooling than the piston material. The piston is provided with a recessed head portion over which is positioned a diaphragm and forming a space therebetween to which is connected a pressurized fluid supply. The diaphragm is controlled by the fluid in the space to contact or withdraw from the member to be braked. A cooling means causes the body within which the piston is fitted to contract more than the piston, producing a tight shrink fit therebetween. The braking system is particularly applicable for selectively braking an arbor of an electron microscope which immobilizes, for example, a vertically adjustable low temperature specimen holder during observation. The system provides balanced braking forces which can be easily removed and re-established with minimal disturbance to arbor location.

  8. A mathematical model for air brake systems in the presence of leaks 

    E-Print Network [OSTI]

    Ramaratham, Srivatsan

    2008-10-10

    of leaks. Brake systems in trucks are crucial for ensuring the safety of vehicles and passengers on the roadways. Most trucks in the US are equipped with S-cam drum brake systems and they are sensitive to maintenance. Brake defects such as leaks are a major... and schematic of operation. . . . . . . . . . . . . 7 3 A typical drum brake assembly. . . . . . . . . . . . . . . . . . . . . . 8 4 Front and rear brake chambers. . . . . . . . . . . . . . . . . . . . . . 8 5 Automatic slack adjuster construction...

  9. Hybrid: Braking

    Alternative Fuels and Advanced Vehicles Data Center [Office of Energy Efficiency and Renewable Energy (EERE)]

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels Data Center Home Page on Delicious Rank EERE: Alternative Fuels Data Center HomeVehicle Replacement VouchersBraking

  10. Heavy and Overweight Vehicle Brake Testing: Five-Axle Combination Tractor-Flatbed Final Report

    SciTech Connect (OSTI)

    Lascurain, Mary Beth; Capps, Gary J; Franzese, Oscar

    2013-10-01

    The Federal Motor Carrier Safety Administration, in coordination with the Federal Highway Administration, sponsored the Heavy and Overweight Vehicle Brake Testing (HOVBT) program in order to provide information about the effect of gross vehicle weight (GVW) on braking performance. Because the Federal Motor Carrier Safety Regulations limit the number of braking system defects that may exist for a vehicle to be allowed to operate on the roadways, the examination of the effect of brake defects on brake performance for increased loads is also relevant. The HOVBT program seeks to provide relevant information to policy makers responsible for establishing load limits, beginning with providing test data for a combination tractor/trailer. This testing was conducted on a five-axle combination vehicle with tractor brakes meeting the Reduced Stopping Distance requirement rulemaking. This report provides a summary of the testing activities, the results of various analyses of the data, and recommendations for future research. Following a complete brake rebuild, instrumentation, and brake burnish, stopping tests were performed from 20 and 40 mph with various brake application pressures (15 psi, 25 psi, 35 psi, 45 psi, 55 psi, and full system pressure). These tests were conducted for various brake conditions at the following GVWs: 60,000, 80,000, 91,000, 97,000, 106,000, and 116,000 lb. The 80,000-lb GVWs included both balanced and unbalanced loads. The condition of the braking system was also varied. To introduce these defects, brakes (none, forward drive axle, or rear trailer axle) were made inoperative. In addition to the stopping tests, performance-based brake tests were conducted for the various loading and brake conditions. Analysis of the stopping test data showed the stopping distance to increase with load (as expected) and also showed that more braking force was generated by the drive axle brakes than the trailer axle brakes. The constant-pressure stopping test data revealed a linear relationship between brake application pressure and was used to develop an algorithm to normalize stopping data for weight and initial speed.

  11. Full Hybrid: Braking

    Alternative Fuels and Advanced Vehicles Data Center [Office of Energy Efficiency and Renewable Energy (EERE)]

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels Data Center Home Page on Delicious Rank EERE: Alternative Fuels Data Center HomeVehicle Replacement VouchersBraking button highlighted Stopped

  12. Combined hydraulic and regenerative braking system

    DOE Patents [OSTI]

    Venkataperumal, Rama R. (Troy, MI); Mericle, Gerald E. (Mount Clemens, MI)

    1981-06-02

    A combined hydraulic and regenerative braking system and method for an electric vehicle, with the braking system being responsive to the applied hydraulic pressure in a brake line to control the braking of the vehicle to be completely hydraulic up to a first level of brake line pressure, to be partially hydraulic at a constant braking force and partially regenerative at a linearly increasing braking force from the first level of applied brake line pressure to a higher second level of brake line pressure, to be partially hydraulic at a linearly increasing braking force and partially regenerative at a linearly decreasing braking force from the second level of applied line pressure to a third and higher level of applied line pressure, and to be completely hydraulic at a linearly increasing braking force from the third level to all higher applied levels of line pressure.

  13. Solar tracker motor having a fixed caliper and a translating caliper each with an electromagnetic brake system

    DOE Patents [OSTI]

    Rau, Scott James

    2013-01-29

    Concepts and technologies described herein provide for an accurate and cost-effective method for rotating a solar array disk for tracking the movement of the sun. According to various aspects, a motor includes a fixed caliper and a translating caliper positioned adjacent to one another. Electromagnetically controlled brakes on the translating caliper grip the solar array disk while adjacent, but spaced apart, electromagnets on the fixed caliper and the translating caliper are energized to create an attractive force that pulls the translating caliper with the solar array disk toward the fixed caliper. After reaching the fixed caliper, brakes on the fixed caliper are engaged with the disk, brakes on the translating caliper are released from the disk, and the translating caliper is pushed back to the starting location where the process repeats until the desired rotation is completed.

  14. Regenerative braking device

    DOE Patents [OSTI]

    Hoppie, Lyle O. (Birmingham, MI)

    1982-01-12

    Disclosed are several embodiments of a regenerative braking device for an automotive vehicle. The device includes a plurality of rubber rollers (24, 26) mounted for rotation between an input shaft (14) connectable to the vehicle drivetrain and an output shaft (16) which is drivingly connected to the input shaft by a variable ratio transmission (20). When the transmission ratio is such that the input shaft rotates faster than the output shaft, the rubber rollers are torsionally stressed to accumulate energy, thereby slowing the vehicle. When the transmission ratio is such that the output shaft rotates faster than the input shaft, the rubber rollers are torsionally relaxed to deliver accumulated energy, thereby accelerating or driving the vehicle.

  15. Variable ratio regenerative braking device

    DOE Patents [OSTI]

    Hoppie, Lyle O. (Birmingham, MI)

    1981-12-15

    Disclosed is a regenerative braking device (10) for an automotive vehicle. The device includes an energy storage assembly (12) having a plurality of rubber rollers (26, 28) mounted for rotation between an input shaft (36) and an output shaft (42), clutches (38, 46) and brakes (40, 48) associated with each shaft, and a continuously variable transmission (22) connectable to a vehicle drivetrain and to the input and output shafts by the respective clutches. The rubber rollers are torsionally stressed to accumulate energy from the vehicle when the input shaft is clutched to the transmission while the brake on the output shaft is applied, and are torsionally relaxed to deliver energy to the vehicle when the output shaft is clutched to the transmission while the brake on the input shaft is applied. The transmission ratio is varied to control the rate of energy accumulation and delivery for a given rotational speed of the vehicle drivetrain.

  16. Brake System Modeling, Control And Integrated Brake/throttle Switching Phase I

    E-Print Network [OSTI]

    Hedrick, Karl; Et. al.,

    1997-01-01

    and vacuum chambers, the intake manifold, the secondary brake line at the master cylinder and the front brake on the same hydraulic

  17. Brake Defect Causation and Abatement Study (BDCAS)

    E-Print Network [OSTI]

    cost with proper re- pairs being made the first time and reduction in out-of-service vehicles #12; corrective actions and validate true abatement of initial out-of- service causation the FMCSA began the BDCAS brake efficiency data as new brakes are burnished; and where possible, collect brake efficiency data

  18. Commercial Motor Vehicle Brake Assessment Tools

    E-Print Network [OSTI]

    Commercial Motor Vehicle Brake Assessment Tools Commercial Motor Vehicle Roadside Technology to deceleration in g's ­ Passing score: BE43.5 · Enforcement tool for only 3 years. · Based solely on brake Brake Research · CMVRTC research built on these enforcement tools ­ Correlation Study ­ Level-1 / PBBT

  19. Brake blending strategy for a hybrid vehicle

    DOE Patents [OSTI]

    Boberg, Evan S. (Hazel Park, MI)

    2000-12-05

    A hybrid electric powertrain system is provided including a transmission for driving a pair of wheels of a vehicle and a heat engine and an electric motor/generator coupled to the transmission. A friction brake system is provided for applying a braking torque to said vehicle. A controller unit generates control signals to the electric motor/generator and the friction brake system for controllably braking the vehicle in response to a drivers brake command. The controller unit determines and amount of regenerative torque available and compares this value to a determined amount of brake torque requested for determining the control signals to the electric motor/generator and the friction brake system.

  20. Commercial Motor Vehicle Brake-Related Research

    E-Print Network [OSTI]

    Commercial Motor Vehicle Brake-Related Research Commercial Motor Vehicle Roadside Technology Corridor Safety Technology Showcase October 14, 2010 Commercial Motor Vehicle Roadside Technology Corridor

  1. Multidisciplinary design optimization of an automotive magnetorheological brake design

    E-Print Network [OSTI]

    Park, Edward

    Multidisciplinary design optimization of an automotive magnetorheological brake design Edward J to the elec- tromagnet. Key issues involved in the initial design of the automotive MR brake are presented: Magnetorheological fluid; Automotive brake; Finite element analysis; Computational fluid dynamics; Multidisciplinary

  2. A diagnostic system for air brakes in commercial vehicles 

    E-Print Network [OSTI]

    Coimbatore Subramanian, Shankar Ram

    2007-09-17

    ............. 14 4 The S-cam foundation brake ....................... 15 5 A schematic of the drum brake ..................... 16 6 A schematic of the experimental setup ................. 24 7 A sectional view of the treadle valve .................. 26 8 A layout... the disc brake and the drum brake. In this dissertation, the main focus will be restricted to air brake systems that use S-cam drum foundation brakes. A. Background and motivation The safety of vehicles operating on the road depends amongst other things...

  3. Svendborg Brakes | Open Energy Information

    Open Energy Info (EERE)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels Data Center Home Page on QA:QA J-E-1 SECTION J APPENDIX E LIST OFAMERICA'SHeavyAgencyTendo New Energy EquipmentSvendborg Brakes Jump to:

  4. TMV Technology Capabilities Brake Stroke Monitor

    E-Print Network [OSTI]

    TMV Technology Capabilities Brake Stroke Monitor Brake monitoring systems are proactive maintenance This technology allows for CMV operators to have knowledge of their steer, drive, and tandem axle group weights setup is required. Current Safety/Enforcement Technologies EOBR (electronic on-board recorder) On

  5. An engine air-brake integration study

    E-Print Network [OSTI]

    Mulchandani, Hiten

    2011-01-01

    The feasibility of operating an engine air-brake (EAB) integrated with a pylon duct bifurcation in a realistic aircraft engine environment has been analyzed. The EAB uses variable exit guide vanes downstream of a high ...

  6. Method and apparatus for wind turbine braking

    DOE Patents [OSTI]

    Barbu, Corneliu (Laguna Hills, CA); Teichmann, Ralph (Nishkayuna, NY); Avagliano, Aaron (Houston, TX); Kammer, Leonardo Cesar (Niskayuna, NY); Pierce, Kirk Gee (Simpsonville, SC); Pesetsky, David Samuel (Greenville, SC); Gauchel, Peter (Muenster, DE)

    2009-02-10

    A method for braking a wind turbine including at least one rotor blade coupled to a rotor. The method includes selectively controlling an angle of pitch of the at least one rotor blade with respect to a wind direction based on a design parameter of a component of the wind turbine to facilitate reducing a force induced into the wind turbine component as a result of braking.

  7. Contactless magnetic brake for automotive applications 

    E-Print Network [OSTI]

    Gay, Sebastien Emmanuel

    2009-05-15

    MAGNETIC BRAKE FOR AUTOMOTIVE APPLICATIONS A Dissertation by SEBASTIEN EMMANUEL GAY Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY... May 2005 Major Subject: Electrical Engineering CONTACTLESS MAGNETIC BRAKE FOR AUTOMOTIVE APPLICATIONS A Dissertation by SEBASTIEN EMMANUEL GAY Submitted to Texas A&M University in partial fulfillment of the requirements...

  8. CMV Brake Wear and Performance Test Little is known about the brake

    E-Print Network [OSTI]

    inspections were due to brake defects. Additionally, brake maintenance and repair present a significant cost as part of an 18-month Field Operational Test. Parameters Being Measured The PBBT machine uses in Data, Statistical Analysis Geo-Spatial Information Tools Defense Transportation Energy Policy Analysis

  9. Adaptive controller for regenerative and friction braking system

    DOE Patents [OSTI]

    Davis, Roy I. (Ypsilanti, MI)

    1990-01-01

    A regenerative and friction braking system for a vehicle having one or more roadwheels driven by an electric traction motor includes a driver responsive device for producing a brake demand signal having a magnitude corresponding to the level of braking force selected by the driver and friction and regenerative brakes operatively connected with the roadwheels of the vehicle. A system according to this invention further includes control means for operating the friction and regenerative braking subsystems so that maximum brake torques sustainable by the roadwheels of the vehicle without skidding or slipping will not be exceeded.

  10. Adaptive controller for regenerative and friction braking system

    DOE Patents [OSTI]

    Davis, R.I.

    1990-10-16

    A regenerative and friction braking system for a vehicle having one or more road wheels driven by an electric traction motor includes a driver responsive device for producing a brake demand signal having a magnitude corresponding to the level of braking force selected by the driver and friction and regenerative brakes operatively connected with the road wheels of the vehicle. A system according to this invention further includes control means for operating the friction and regenerative braking subsystems so that maximum brake torques sustainable by the road wheels of the vehicle without skidding or slipping will not be exceeded. 8 figs.

  11. ORBITAL AND MASS RATIO EVOLUTION OF PROTOBINARIES DRIVEN BY MAGNETIC BRAKING

    SciTech Connect (OSTI)

    Zhao, Bo; Li, Zhi-Yun

    2013-01-20

    The majority of stars reside in multiple systems, especially binaries. The formation and early evolution of binaries is a longstanding problem in star formation that is not yet fully understood. In particular, how the magnetic field observed in star-forming cores shapes the binary characteristics remains relatively unexplored. We demonstrate numerically, using an MHD version of the ENZO AMR hydro code, that a magnetic field of the observed strength can drastically change two of the basic quantities that characterize a binary system: the orbital separation and mass ratio of the two components. Our calculations focus on the protostellar mass accretion phase, after a pair of stellar 'seeds' have already formed. We find that in dense cores magnetized to a realistic level, the angular momentum of the material accreted by the protobinary is greatly reduced by magnetic braking. Accretion of strongly braked material shrinks the protobinary separation by a large factor compared to the non-magnetic case. The magnetic braking also changes the evolution of the mass ratio of unequal-mass protobinaries by producing material of low specific angular momentum that accretes preferentially onto the more massive primary star rather than the secondary. This is in contrast with the preferential mass accretion onto the secondary previously found numerically for protobinaries accreting from an unmagnetized envelope, which tends to drive the mass ratio toward unity. In addition, the magnetic field greatly modifies the morphology and dynamics of the protobinary accretion flow. It suppresses the traditional circumstellar and circumbinary disks that feed the protobinary in the non-magnetic case; the binary is fed instead by a fast collapsing pseudodisk whose rotation is strongly braked. The magnetic braking-driven inward migration of binaries from their birth locations may be constrained by high-resolution observations of the orbital distribution of deeply embedded protobinaries, especially with ALMA and JVLA.

  12. Electric vehicle regenerative antiskid braking and traction control system

    DOE Patents [OSTI]

    Cikanek, S.R.

    1995-09-12

    An antiskid braking and traction control system for an electric or hybrid vehicle having a regenerative braking system operatively connected to an electric traction motor, and a separate hydraulic braking system includes one or more sensors for monitoring present vehicle parameters and a processor, responsive to the sensors, for calculating vehicle parameters defining the vehicle behavior not directly measurable by the sensors and determining if regenerative antiskid braking control, requiring hydraulic braking control, or requiring traction control are required. The processor then employs a control strategy based on the determined vehicle state and provides command signals to a motor controller to control the operation of the electric traction motor and to a brake controller to control fluid pressure applied at each vehicle wheel to provide the appropriate regenerative antiskid braking control, hydraulic braking control, and traction control. 10 figs.

  13. Electric vehicle regenerative antiskid braking and traction control system

    DOE Patents [OSTI]

    Cikanek, Susan R. (Wixom, MI)

    1995-01-01

    An antiskid braking and traction control system for an electric or hybrid vehicle having a regenerative braking system operatively connected to an electric traction motor, and a separate hydraulic braking system includes one or more sensors for monitoring present vehicle parameters and a processor, responsive to the sensors, for calculating vehicle parameters defining the vehicle behavior not directly measurable by the sensors and determining if regenerative antiskid braking control, requiring hydrualic braking control, or requiring traction control are required. The processor then employs a control strategy based on the determined vehicle state and provides command signals to a motor controller to control the operation of the electric traction motor and to a brake controller to control fluid pressure applied at each vehicle wheel to provide the appropriate regenerative antiskid braking control, hydraulic braking control, and traction control.

  14. Design Restrictions Ground clearance Brake components cannot contact

    E-Print Network [OSTI]

    Provancher, William

    of Mechanical Engineering, University of Utah Test Results Heat Test ­ apply pressure to the rotating brake. The truck and brake must be strong but not heavy. · Temperature ­ The brake will generate a lot of heat. The epoxy, wheels and bearings must all be able to withstand high heat. · Testing of Realistic Conditions

  15. Engine brake control in automatic transmission

    SciTech Connect (OSTI)

    Hayasaki, K.; Sugano, K.

    1988-09-13

    This patent describes an engine braking control for a transmission for an automotive vehicle having an engine, the transmission including an input member drivingly coupled to the engine and an output member subject to load from driving wheels of the automotive vehicle, the transmission also including a first rotary member, a second rotary member, a hydraulically operated clutch selectively establishing a drive connection between the first rotary member and the second rotary member, and a one-way clutch arranged in parallel to the hydraulically operated clutch such that when the hydraulically operated clutch is released, the one-way clutch transmits forward torque from the first rotary member to the second rotary member, but interrupts transmission of revers torque to the first rotary member from the second rotary member, the engine braking control comprising: means for providing an engine braking command fluid pressure signal when demanded by a vehicle operator; a valve means for normally discharging hydraulic fluid from the hydraulically operated clutch to deactivate the hydraulically operated clutch, the valve means being fluidly connected to the hydraulically operated clutch, the engine braking command fluid pressure signal providing means and a drain port. The valve means including a valve spool having a first position where the hydraulically operated clutch is allowed to communicate with the drain port to permit discharge of hydraulic fluid therefrom and thus the hydraulically operated clutch is caused to be deactivated and a second position where the hydraulically operated clutch is disconnected from the drain port and allowed to communicate with the engine braking command fluid pressure signal.

  16. Hybrid Braking System for Non-Drive Axles | Department of Energy

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Braking System for Non-Drive Axles Hybrid Braking System for Non-Drive Axles A hybrid braking system is designed to conserve diesel fuel (or alternative fuels) by using...

  17. Braking system for use with an arbor of a microscope

    DOE Patents [OSTI]

    Norgren, Duane U. (Orinda, CA)

    1984-01-01

    A balanced braking system comprising a plurality of braking assemblies located about a member to be braked. Each of the braking assemblies consists of a spring biased piston of a first material fitted into a body of a different material which has a greater contraction upon cooling than the piston material. The piston is provided with a recessed head portion over which is positioned a diaphragm and forming a space therebetween to which is connected a pressurized fluid supply. The diaphragm is controlled by the fluid in the space to contact or withdraw from the member to be braked. A cooling device causes the body within which the piston is fitted to contract more than the piston, producing a tight shrink fit therebetween. The braking system is particularly applicable for selectively braking an arbor of an electron microscope which immobilizes, for example, a vertically adjustable low temperature specimen holder during observation. The system provides balanced braking forces which can be easily removed and re-established with minimal disturbance to arbor location.

  18. Development of Diagnostic Algorithms for Air Brakes in Trucks 

    E-Print Network [OSTI]

    Dhar, Sandeep

    2011-10-21

    In this dissertation, we focus on development of algorithms for estimating the severity of air leakage and for predicting the out-of-adjustment of pushrod in an air brake system of heavy commercial vehicles. The leakage of air from the brake system...

  19. A pressure control scheme for air brakes in commercial vehicles 

    E-Print Network [OSTI]

    Bowlin, Christopher Leland

    2007-04-25

    This research is focused on developing a control scheme for regulating the pressure in the brake chamber of an air brake system found in most commercial vehicles like trucks, tractor-trailers and buses. Such a control scheme can be used...

  20. Laboratory rearing of the cottonwood twig borer on artificial diets 

    E-Print Network [OSTI]

    Mastro, Victory Carl

    1973-01-01

    several advantages over rearing them on their natural food such as: (1) simplification of the maintenance of an insect colony; (2) a capability to rear insects during the dormant season; (3) reduction in contamination from natural food; (4) production...) has successfully reared the cottonwood twig borer on its natural food. The purpose of this thesis is to describe attempts to rear the insect on artificial diets and develop a rearing technique for handling various stages of the insect. The research...

  1. Airbus A320 Braking as Predicate-Action Peter B. Ladkin

    E-Print Network [OSTI]

    Ladkin, Peter B.

    to interest us and others in the design of the A320 braking system [FI.93a, FI.93b, FI.93c]. This paper]. The Braking System Design of the A320. The braking system design of the A320 is described in the A320 Flight). The brakes and anti-skid system are described in [FCOM, 1.32.30: Landing Gear: Brakes and Anti

  2. Regenerative braking on bicycles to power LED safety flashers

    E-Print Network [OSTI]

    Collier, Ian M

    2005-01-01

    This work develops a method for capturing some of the kinetic energy ordinarily lost during braking on bicycles to power LED safety flashers. The system is designed to eliminate: (a) battery changing in popular LED flashers, ...

  3. Disk filter

    DOE Patents [OSTI]

    Bergman, W.

    1985-01-09

    An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

  4. Disk filter

    DOE Patents [OSTI]

    Bergman, Werner (Pleasanton, CA)

    1986-01-01

    An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

  5. The Vela pulsar with an active fallback disk

    SciTech Connect (OSTI)

    Özsükan, Gökçe; Ek?i, K. Yavuz [Faculty of Science and Letters, Department of Physics, ?stanbul Technical University, Maslak 34469, ?stanbul (Turkey); Hambaryan, Valeri; Neuhäuser, Ralph; Hohle, Markus M.; Ginski, Christian [Astrophysikalisches Institut und Universitäts-Sternwarte, Universität Jena, Schillergäßchen 2-3, 07745 Jena (Germany); Werner, Klaus, E-mail: eksi@itu.edu.tr [Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, D-72076 Tübingen (Germany)

    2014-11-20

    Fallback disks are expected to form around young neutron stars. The presence of these disks can be revealed by their blackbody spectrum in the infrared, optical, and UV bands. We present a re-reduction of the archival optical and infrared data of the Vela pulsar, together with the existing infrared and UV spectrum of Vela, and model their unpulsed components with the blackbody spectrum of a supernova debris disk. We invoke the quiescent disk solution of Sunyaev and Shakura for the description of the disk in the propeller stage and find the inner radius of the disk to be inside the light cylinder radius. We perform a high-resolution X-ray analysis with XMM-Newton and find a narrow absorption feature at 0.57 keV that can be interpreted as the K {sub ?} line of He-like oxygen (O VII). The strength of the line indicates an element over-abundance in our line of sight exceeding the amounts that would be expected from interstellar medium. The spectral feature may originate from the pulsar wind nebula and may be partly caused by the reprocessed X-ray radiation by the fallback disk. We discuss the lower-than-three braking index of Vela as partially due to the contribution of the propeller torques. Our results suggest that the pulsar mechanism can work simultaneously with the propeller processes and that the debris disks can survive the radiation pressure for at least ?10{sup 4} yr. As Vela is a relatively close object, and a prototypical pulsar, the presence of a disk, if confirmed, may indicate the ubiquity of debris disks around young neutron stars.

  6. Design considerations for an automotive magnetorheological brake Kerem Karakoc, Edward J. Park *, Afzal Suleman

    E-Print Network [OSTI]

    Park, Edward

    Design considerations for an automotive magnetorheological brake Kerem Karakoc, Edward J. Park *, Afzal Suleman Department of Mechanical Engineering, University of Victoria, P.O. Box 3055, STN CSC February 2008 Available online xxxx Keywords: Mechatronic design Magnetorheological fluid Automotive brake

  7. Modeling the pneumatic relay valve of an s-cam air brake 

    E-Print Network [OSTI]

    Vilayannur Natarajan, Shankar

    2005-08-29

    Statistics indicate that defects in brake system contribute significantly to fatal crashes involving commercial vehicles. Hence there is a need for developing preventive and active safety measures for assessing the performance of an air brake system...

  8. Fuzzy logic electric vehicle regenerative antiskid braking and traction control system

    DOE Patents [OSTI]

    Cikanek, S.R.

    1994-10-25

    An regenerative antiskid braking and traction control system using fuzzy logic for an electric or hybrid vehicle having a regenerative braking system operatively connected to an electric traction motor, and a separate hydraulic braking system includes sensors for monitoring present vehicle parameters and a processor, responsive to the sensors, for calculating vehicle parameters defining the vehicle behavior not directly measurable by the sensor and determining if regenerative antiskid braking control, requiring hydraulic braking control, and requiring traction control are required. The processor then employs fuzzy logic based on the determined vehicle state and provides command signals to a motor controller to control operation of the electric traction motor and to the brake controller to control fluid pressure applied at each vehicle wheel to provide the appropriate regenerative braking control, hydraulic braking control, and traction control. 123 figs.

  9. Fuzzy logic electric vehicle regenerative antiskid braking and traction control system

    DOE Patents [OSTI]

    Cikanek, Susan R. (Wixom, MI)

    1994-01-01

    An regenerative antiskid braking and traction control system using fuzzy logic for an electric or hybrid vehicle having a regenerative braking system operatively connected to an electric traction motor, and a separate hydraulic braking system includes sensors for monitoring present vehicle parameters and a processor, responsive to the sensors, for calculating vehicle parameters defining the vehicle behavior not directly measurable by the sensor and determining if regenerative antiskid braking control, requiring hydraulic braking control, and requiring traction control are required. The processor then employs fuzzy logic based on the determined vehicle state and provides command signals to a motor controller to control operation of the electric traction motor and to the brake controller to control fluid pressure applied at each vehicle wheel to provide the appropriate regenerative braking control, hydraulic braking control, and traction control.

  10. Regenerative braking device with rotationally mounted energy storage means

    DOE Patents [OSTI]

    Hoppie, Lyle O. (Birmingham, MI)

    1982-03-16

    A regenerative braking device for an automotive vehicle includes an energy storage assembly (12) having a plurality of rubber rollers (26, 28) mounted for rotation between an input shaft (30) and an output shaft (32), clutches (50, 56) and brakes (52, 58) associated with each shaft, and a continuously variable transmission (22) connectable to a vehicle drivetrain and to the input and output shafts by the respective clutches. In a second embodiment the clutches and brakes are dispensed with and the variable ratio transmission is connected directly across the input and output shafts. In both embodiments the rubber rollers are torsionally stressed to accumulate energy from the vehicle when the input shaft rotates faster or relative to the output shaft and are torsionally relaxed to deliver energy to the vehicle when the output shaft rotates faster or relative to the input shaft.

  11. Aalborg Universitet Disturbance Control of the Hydraulic Brake in a Wind Turbine

    E-Print Network [OSTI]

    Yang, Zhenyu

    Aalborg Universitet Disturbance Control of the Hydraulic Brake in a Wind Turbine Jepsen, Frank Brake in a Wind Turbine. In Energy Conference and Exhibition (EnergyCon), 2010 IEEE International . (pp from vbn.aau.dk on: juli 07, 2015 #12;Disturbance Control of the Hydraulic Brake in a Wind Turbine

  12. The Chinese brake fern (Pteris vittata L.), native to China, is widely naturalized in

    E-Print Network [OSTI]

    Ma, Lena

    The Chinese brake fern (Pteris vittata L.), native to China, is widely naturalized in many areas and anatomical aspects of Chinese brake fern (Pteris vittata; Pteridaceae) Bhaskar Bondada1, Cong Tu, and Lena Ma-0290, U.S.A.; e-mail: lqma@ifas.ufl.edu). Sur- face structure and anatomical aspects of Chinese brake fern

  13. Regenerative Braking for an Electric Vehicle Using Ultracapacitors and a Buck-Boost Converter

    E-Print Network [OSTI]

    Catholic University of Chile (Universidad Católica de Chile)

    Regenerative Braking for an Electric Vehicle Using Ultracapacitors and a Buck-Boost Converter Juan situation (regenerative braking), the battery voltage goes up, and then the control needs to activate regenerative braking can be avoided #12;with the help of ultracapacitors. Besides, ultracapacitors allow

  14. Emission Factor for Antimony in Brake Abrasion Dusts as One of the

    E-Print Network [OSTI]

    Short, Daniel

    112-8551, Japan, and Akebono Brake Industry, Co., Ltd., 5-4-71 Higashi, Hanyu, Saitama 348-8509, Japan, and shape distributions, automotive brake abrasion dusts were suspected as one of the important sources factor that originates from automotive braking in order to quantitatively evaluate the contribution

  15. Tyre curve estimation in slip-controlled braking

    E-Print Network [OSTI]

    Miller, Jonathan I.; Cebon, David

    2015-06-09

    identifying a Kalman filter observer for vehicle handling dynamics. IMECHE Part D – J. of Auto. Eng. 2006; 220: 1063–1072. 27. Yi J et al. Emergency braking control with an observer-based dynamic tire/road friction model and wheel angular velocity... also used by Shim et al.15, and Hong et al.16 Unsal and Kachroo17 compared an EKF with a sliding mode observer to estimate vehicle velocity, using this estimated velocity with a nominal slip-friction curve to determine the braking force. The authors...

  16. Hall-effect-controlled gas dynamics in protoplanetary disks. I. Wind solutions at the inner disk

    SciTech Connect (OSTI)

    Bai, Xue-Ning

    2014-08-20

    The gas dynamics of protoplanetary disks (PPDs) is largely controlled by non-ideal magnetohydrodynamic (MHD) effects including Ohmic resistivity, the Hall effect, and ambipolar diffusion. Among these the role of the Hall effect is the least explored and most poorly understood. In this series, we have included, for the first time, all three non-ideal MHD effects in a self-consistent manner to investigate the role of the Hall effect on PPD gas dynamics using local shearing-box simulations. In this first paper, we focus on the inner region of PPDs, where previous studies (Bai and Stone 2013; Bai 2013) excluding the Hall effect have revealed that the inner disk up to ?10 AU is largely laminar, with accretion driven by a magnetocentrifugal wind. We confirm this basic picture and show that the Hall effect modifies the wind solutions depending on the polarity of the large-scale poloidal magnetic field B{sub 0} threading the disk. When B{sub 0}??>0, the horizontal magnetic field is strongly amplified toward the disk interior, leading to a stronger disk wind (by ?50% or less in terms of the wind-driven accretion rate). The enhanced horizontal field also leads to much stronger large-scale Maxwell stress (magnetic braking) that contributes to a considerable fraction of the wind-driven accretion rate. When B{sub 0}??<0, the horizontal magnetic field is reduced, leading to a weaker disk wind (by ? 20%) and negligible magnetic braking. Under fiducial parameters, we find that when B{sub 0}??>0, the laminar region extends farther to ?10-15 AU before the magnetorotational instability sets in, while for B{sub 0}??<0, the laminar region extends only to ?3-5 AU for a typical accretion rate of ?10{sup –8} to10{sup –7} M {sub ?} yr{sup –1}. Scaling relations for the wind properties, especially the wind-driven accretion rate, are provided for aligned and anti-aligned field geometries.

  17. Braking index of isolated pulsars: open questions and ways forward

    E-Print Network [OSTI]

    Hamil, Oliver

    2015-01-01

    Isolated pulsars are rotating neutron stars with accurately measured angular velocities $\\Omega$, and their time derivatives which show unambiguously that the pulsars are slowing down. Although the exact mechanism of the spin-down is a question of debate, the commonly accepted view is that it arises either through emission of magnetic dipole radiation (MDR) from a rotating magnetized body, through emission of a relativistic particle wind, or via higher order magnetic multipole or gravitational quadrupole radiation. The calculated energy loss by a rotating pulsar is model dependent and leads to the power law $\\dot{\\Omega}$ = -K $\\Omega^{\\rm n}$ where $n$ is called the braking index. The theoretical value for braking index is $n = 1, 3, 5$ for wind, MDR, quadrupole radiation respectively. The accepted view is that pulsar braking is strongly dominated by MDR. Highly precise observations of isolated pulsars yield braking index values in the range $1 < n < 2.8$ which are consistently less than the value pred...

  18. Active Pedestrian Safety by Automatic Braking and Evasive Steering

    E-Print Network [OSTI]

    Gavrila, Dariu M.

    1 Active Pedestrian Safety by Automatic Braking and Evasive Steering C. Keller, T. Dang, H. Fritz of crashes. This paper presents a novel active pedestrian safety system, which combines sensing, situation two complementary approaches for added robustness: motion-based object detection and pedestrian

  19. Catalog of Waters Important for the Spawning, Rearing or Migration...

    Open Energy Info (EERE)

    Spawning, Rearing or Migration of Anadromous Fishes Organization Alaska Department of Fish and Game Published Divisions of Sport Fish and Habitat, 2012 Report Number 12-05 DOI...

  20. Energy Efficiency in Heavy Vehicle Tires, Drivetrains, and Braking Systems

    SciTech Connect (OSTI)

    Peter J. Blau

    2000-04-26

    This document was prepared to support the primary goals of the Department of Energy, Office of Heavy Vehicle Technologies. These were recently stated as follows: ''Develop by 2004 the enabling technologies for a class 7-8 truck with a fuel efficiency of 10 mpg (at 65 mph) which will meet prevailing emission standards. For Class 3-6 trucks operating on an urban driving cycle, develop by 2004 commercially viable vehicles that achieve at least double the fuel economy of comparable current vehicles (1999), and as a research goal, reduce criteria pollutants to 30% below EPA standards. Develop by 2004 the diesel engine enabling technologies to support large-scale industry dieselization of Class 1 and 2 trucks, achieving a 35 % fuel efficiency improvement over comparable gasoline-fueled trucks, while meeting applicable emissions standards.'' The enabling technologies for improving the fuel efficiency of trucks, include not only engine technologies but also technologies involved with lowering the rolling resistance of tires, reducing vehicle aerodynamic drag, improving thermal management, and reducing parasitic frictional losses in drive train components. Opportunities also exist for making better use of the energy that might ordinarily be dissipated during vehicle braking. Braking systems must be included in this evaluation since safety in truck operations is vital, and braking requirements are greater for vehicles having lowered resistance to rolling. The Office of Heavy Vehicle Technologies has initiated a program to improve the aerodynamics of heavy vehicles through wind tunnel testing, computational modeling, and on-road evaluations. That activity is described in a separate multi-year plan; therefore, emphasis in this document will be on tires, drive trains, and braking systems. Recent, dramatic fluctuations in diesel fuel prices have emphasized the importance of effecting savings in truck fuel economy by implementing new component designs and materials.

  1. SPINDOWN OF ISOLATED NEUTRON STARS: GRAVITATIONAL WAVES OR MAGNETIC BRAKING?

    SciTech Connect (OSTI)

    Staff, Jan E.; Jaikumar, Prashanth; Chan, Vincent; Ouyed, Rachid

    2012-05-20

    We study the spindown of isolated neutron stars from initially rapid rotation rates, driven by two factors: (1) gravitational wave emission due to r-modes and (2) magnetic braking. In the context of isolated neutron stars, we present the first study including self-consistently the magnetic damping of r-modes in the spin evolution. We track the spin evolution employing the RNS code, which accounts for the rotating structure of neutron stars for various equations of state. We find that, despite the strong damping due to the magnetic field, r-modes alter the braking rate from pure magnetic braking for B {<=} 10{sup 13} G. For realistic values of the saturation amplitude {alpha}{sub sat}, the r-mode can also decrease the time to reach the threshold central density for quark deconfinement. Within a phenomenological model, we assess the gravitational waveform that would result from r-mode-driven spindown of a magnetized neutron star. To contrast with the persistent signal during the spindown phase, we also present a preliminary estimate of the transient gravitational wave signal from an explosive quark-hadron phase transition, which can be a signal for the deconfinement of quarks inside neutron stars.

  2. Real-Time Dynamic Brake Assessment Proof of Concept Final Report

    SciTech Connect (OSTI)

    Lascurain, Mary Beth [ORNL; Franzese, Oscar [ORNL; Capps, Gary J [ORNL

    2011-11-01

    This proof-of-concept research was performed to explore the feasibility of using real-world braking data from commercial motor vehicles to make a diagnosis of brake condition similar to that of the performance-based brake tester (PBBT). This was done by determining the relationship between pressure and brake force (P-BF), compensating for the gross vehicle weight (GVW). The nature of this P-BF relationship (e.g., low braking force for a given brake application pressure) may indicate brake system problems. In order to determine the relationship between brake force and brake application pressure, a few key parameters of duty cycle information were collected. Because braking events are often brief, spanning only a few seconds, a sample rate of 10 Hz was needed. The algorithm under development required brake application pressure and speed (from which deceleration was calculated). Accurate weight estimation was also needed to properly derive the braking force from the deceleration. In order to ensure that braking force was the predominant factor in deceleration for the segments of data used in analysis, the data was screened for grade as well. Also, the analysis needed to be based on pressures above the crack pressure. The crack pressure is the pressure below which the individual brakes are not applied due the nature of the mechanical system. This value, which may vary somewhat from one wheel end to another, is approximately 10 psi. Therefore, only pressures 15 psi and above were used in the analysis. The Department of Energy s Medium Truck Duty Cycle research has indicated that under the real-world circumstances of the test vehicle brake pressures of up to approximately 30 psi can be expected. Several different types of data were collected during the testing task of this project. Constant-pressure stopping tests were conducted at several combinations of brake application pressure (15, 20, 25, and 30 psi), load conditions (moderately and fully laden), and speeds (20 and 30 mph). Data was collected at 10 Hz. Standard and stepped-pressure performance-based brake tests with brake pressure transducers were performed for each loading condition. The stepped-pressure test included the constant-pressure intervals of brake application at 15, 20, 25, and 30 psi. The PBBT data files included 10 Hz streaming data collected during the testing of each axle. Two weeks of real-world duty cycle (driving and braking) data was also collected at 10 Hz. Initial analysis of the data revealed that the data collected in the field (i.e., day-to-day operations) provided the same information as that obtained from the controlled tests. Analysis of the data collected revealed a strong linear relationship between brake application pressure and deceleration for given GVWs. As anticipated, initial speed was not found to be a significant factor in the deceleration-pressure relationship, unlike GVW. The positive results obtained from this proof of concept test point to the need for further research to expand this concept. A second phase should include testing over a wider range of speeds and include medium brake application pressures in addition to the low pressures tested in this research. Testing on multiple vehicles would also be of value. This future phase should involve testing to determine how degradation of braking performance affects the pressure-deceleration relationship.

  3. EA-1111: K Pool Fish Rearing, Hanford Site, Richland, Washington

    Office of Energy Efficiency and Renewable Energy (EERE)

    This EA evaluates the environmental impacts of the proposal to enter into a use permit or lease agreement with the Yakama Indian Nation or other parties who would rear fish in the 100-K Area Pools.

  4. THE MAGNETIC FIELD IN THE CLASS 0 PROTOSTELLAR DISK OF L1527

    SciTech Connect (OSTI)

    Segura-Cox, Dominique M.; Looney, Leslie W.; Stephens, Ian W.; Fernández-López, Manuel; Crutcher, Richard; Kwon, Woojin; Tobin, John J.; Li, Zhi-Yun

    2015-01-01

    We present subarcsecond (?0.''35) resolved observations of the 1.3 mm dust polarization from the edge-on circumstellar disk around the Class 0 protostar L1527. The inferred magnetic field is consistent with a dominantly toroidal morphology; there is no significantly detected vertical poloidal component to which observations of an edge-on disk are most sensitive. This suggests that angular momentum transport in Class 0 protostars (when large amounts of material are fed down to the disk from the envelope and accreted onto the protostar) is driven mainly by magnetorotational instability rather than magnetocentrifugal winds at 50 AU scales. In addition, with the data to date there is an early, tentative trend that R > 30 AU disks have so far been found in Class 0 systems with average magnetic fields on the 1000 AU scale strongly misaligned with the rotation axis. The absence of such a disk in the aligned case could be due to efficient magnetic braking that disrupts disk formation. If this is the case, this implies that candidate Class 0 disk systems could be identified by the average magnetic field direction at ?1000 AU spatial scales.

  5. Tachyon cosmology, supernovae data and the Big Brake singularity

    E-Print Network [OSTI]

    Z. Keresztes; L. Á. Gergely; V. Gorini; U. Moschella; A. Yu. Kamenshchik

    2009-04-21

    We compare the existing observational data on type Ia Supernovae with the evolutions of the universe predicted by a one-parameter family of tachyon models which we have introduced recently in paper \\cite{we-tach}. Among the set of the trajectories of the model which are compatible with the data there is a consistent subset for which the universe ends up in a new type of soft cosmological singularity dubbed Big Brake. This opens up yet another scenario for the future history of the universe besides the one predicted by the standard $\\Lambda$CDM model.

  6. Adaptive Torque Control of Electro-Rheological Fluid Brakes Used in Active Knee Rehabilitation Devices

    E-Print Network [OSTI]

    Mavroidis, Constantinos

    1 Adaptive Torque Control of Electro-Rheological Fluid Brakes Used in Active Knee Rehabilitation-rheological fluid (ERF) based variable resistance brakes that are used in compact and portable rehabilitation Control, Actuators for Rehabilitation Robotics I. INTRODUCTION Electro-rheological fluids (ERFs

  7. Modeling the pneumatic subsystem of a S-cam air brake system 

    E-Print Network [OSTI]

    Coimbatore Subramanian, Shankar

    2004-09-30

    The air brake system is one of the critical components in ensuring the safe operation of any commercial vehicle. This work is directed towards the development of a fault-free model of the pneumatic subsystem of the air brake system. This model can...

  8. On The Use of Eddy Current Brakes as Tunable, Fast Turn-On Viscous Dampers For Haptic Rendering

    E-Print Network [OSTI]

    Hayward, Vincent

    On The Use of Eddy Current Brakes as Tunable, Fast Turn-On Viscous Dampers For Haptic RenderingGill University, Montr´eal, Canada ABSTRACT We describe the use of eddy current brakes as fast turn-on, tunable, linear dampers for haptic rendering using a prototype haptic device outfitted with eddy current brakes

  9. CIRCUMPLANETARY DISK FORMATION

    SciTech Connect (OSTI)

    Ward, William R.; Canup, Robin M.

    2010-11-15

    The development and evolution of a circumplanetary disk during the accretion of a giant planet is examined. The planet gains mass and angular momentum from infalling solar nebula material while simultaneously contracting due to luminosity losses. When the planet becomes rotationally unstable it begins to shed material into a circumplanetary disk. Viscosity causes the disk to spread to a moderate fraction of the Hill radius where it is assumed that a small fraction of the material escapes back into heliocentric orbit, carrying away most of the excess angular momentum. As the planet's contraction continues, its radius can become smaller than the spatial range of the inflow and material begins to fall directly onto the disk, which switches from a spin-out disk to an accretion disk as the planet completes its growth. We here develop a description of the circumplanetary disk, which is combined with models of the planet's contraction and the inflow rate including its angular momentum content to yield a solution for the time evolution of a planet-disk system.

  10. A nonextensive view of the stellar braking indices

    E-Print Network [OSTI]

    de Freitas, D B; Soares, B B; Silva, J R P

    2015-01-01

    The present work is based on a description for the angular mometum loss rate due to magnetic braking for main-sequence stars on the relationship between stellar rotation and age. In general, this loss rate denoted by $\\mathrm dJ/\\mathrm dt$ depends on angular velocity $\\Omega$ in the form $\\mathrm dJ/\\mathrm dt\\propto\\Omega^{q}$, where $q$ is a parameter extracted from nonextensive statistical mechanics. Already, in context of stellar rotation, this parameter is greater than unity and it is directly related to the braking index. For $q$ equal to unity, the scenario of saturation of the magnetic field is recovered, otherwise $q$ indicates an unsaturated field. This new approach have been proposed and investigated by de Freitas \\& De Medeiros for unsaturated field stars. In present work, we propose a nonextensive approach for the stellar rotational evolution based on the Reiners \\& Mohanthy model. In this sense, we developed a nonextensive version of Reiners \\& Mohanthy torque and also compare this ...

  11. Vortices In Circumstellar Disks

    E-Print Network [OSTI]

    Fred Adams; Richard Watkins

    1995-01-12

    We discuss the physics of vortices in the circumstellar disks associated with young stellar objects. We elucidate the basic physical properties of these localized storm systems. In particular, we consider point vortices, linear vortices, the effects of self-gravity, magnetic fields, and nonlinear aspects of the problem. We find that these vortices can exist in many different forms in the disks of young stellar objects and may play a role in the formation of binary companions and/or giant planets. Vortices may enhance giant planet formation via gravitational instability by allowing dust grains (heavy elements) to settle to the center on a short timescale; the gravitational instability itself is also enhanced because the vortices also create a larger local surface density in the disk. In addition, vortices can enhance energy dissipation in disks and thereby affect disk accretion. Finally, we consider the possibility that vortices of this type exist in molecular clouds and in the disk of the galaxy itself. On all of these size scales, vortices can produce long-lived structures which may correspond to observed structures in these systems.

  12. Evaluation of driver braking performance to an unexpected object in the roadway 

    E-Print Network [OSTI]

    Picha, Dale Louis

    1994-01-01

    ) in 1940, incorporates two components into geometric design, a perception-response time (PRT) component and a braking distance component. Because of the importance of sight distance on highways, previous research has questioned the assumptions of these two...

  13. Injection Timing Effects on Brake Fuel Conversion Efficiency and Engine System's Respones 

    E-Print Network [OSTI]

    McLean, James Elliott

    2011-10-21

    Societal concerns on combustion-based fuel consumption are ever-increasing. With respect to internal combustion engines, this translates to a need to increase brake fuel conversion efficiency (BFCE). Diesel engines are a relatively efficient...

  14. A study of factors affecting foot movement time in a braking maneuver 

    E-Print Network [OSTI]

    Berman, Andrea Helene

    1994-01-01

    The nature of foot movement time (MT) in an actual braking maneuver and in a stationary vehicle was investigated regarding the effects of age and gender of the driver and nature of the stimulus to which the driver was ...

  15. Combined fast valving and braking resistor application to improve transient stability 

    E-Print Network [OSTI]

    Chen, Jen-Yeu Thomas

    1982-01-01

    COMBINED FAST VALVING AND BRAKING RESISTOR APPLICATION TO IMPROVE TRANSIENT STABILITY A Thesis by Submitted to the Graduate College of' Texas A&M University in Partial fulfillment of the requirement for the degree of MASTER OF SCIENCE May... 1982 Major Subjecta Electrical Engineering COMBINED FAST VALVING AND BRAKING RESISTOR APPLICATION TO IMPROVE TRANSIENT STABILITY A Thesis by Approved as to style and content by& herman oY mm ee ad of' De tment Member May 1982 ABSTRACT...

  16. Premixed direct injection disk

    DOE Patents [OSTI]

    York, William David; Ziminsky, Willy Steve; Johnson, Thomas Edward; Lacy, Benjamin; Zuo, Baifang; Uhm, Jong Ho

    2013-04-23

    A fuel/air mixing disk for use in a fuel/air mixing combustor assembly is provided. The disk includes a first face, a second face, and at least one fuel plenum disposed therebetween. A plurality of fuel/air mixing tubes extend through the pre-mixing disk, each mixing tube including an outer tube wall extending axially along a tube axis and in fluid communication with the at least one fuel plenum. At least a portion of the plurality of fuel/air mixing tubes further includes at least one fuel injection hole have a fuel injection hole diameter extending through said outer tube wall, the fuel injection hole having an injection angle relative to the tube axis. The invention provides good fuel air mixing with low combustion generated NOx and low flow pressure loss translating to a high gas turbine efficiency, that is durable, and resistant to flame holding and flash back.

  17. Fuel for Galaxy Disks

    E-Print Network [OSTI]

    M. E. Putman; J. Grcevich; J. E. G. Peek

    2008-04-04

    Halo clouds have been found about the three largest galaxies of the Local Group and in the halos of nearby spirals. This suggests they are a relatively generic feature of the galaxy evolution process and a source of fuel for galaxy disks. In this review, two main sources of disk star formation fuel, satellite material and clouds condensing from the hot halo medium, are discussed and their contribution to fueling the Galaxy quantified. The origin of the halo gas of M31 and M33 is also discussed.

  18. GIANT PLANET FORMATION BY DISK INSTABILITY IN LOW MASS DISKS?

    SciTech Connect (OSTI)

    Boss, Alan P.

    2010-12-20

    Forming giant planets by disk instability requires a gaseous disk that is massive enough to become gravitationally unstable and able to cool fast enough for self-gravitating clumps to form and survive. Models with simplified disk cooling have shown the critical importance of the ratio of the cooling to the orbital timescales. Uncertainties about the proper value of this ratio can be sidestepped by including radiative transfer. Three-dimensional radiative hydrodynamics models of a disk with a mass of 0.043 M{sub sun} from 4 to 20 AU in orbit around a 1 M{sub sun} protostar show that disk instabilities are considerably less successful in producing self-gravitating clumps than in a disk with twice this mass. The results are sensitive to the assumed initial outer disk (T{sub o}) temperatures. Models with T{sub o} = 20 K are able to form a single self-gravitating clump, whereas models with T{sub o} = 25 K form clumps that are not quite self-gravitating. These models imply that disk instability requires a disk with a mass of at least {approx}0.043 M{sub sun} inside 20 AU in order to form giant planets around solar-mass protostars with realistic disk cooling rates and outer-disk temperatures. Lower mass disks around solar-mass protostars must rely upon core accretion to form inner giant planets.

  19. Braking index of isolated uniformly rotating magnetized pulsars

    E-Print Network [OSTI]

    Hamil, Oliver; Urbanec, Martin; Urbancova, Gabriela

    2015-01-01

    Isolated pulsars are rotating neutron stars with accurately measured angular velocities $\\Omega$, and their time derivatives which show unambiguously that the pulsars are slowing down. Although the exact mechanism of the spin-down is a question of debate in detail, the commonly accepted view is that it arises through emission of magnetic dipole radiation (MDR) from a rotating magnetized body. Other processes, including the emission of gravitational radiation, and of relativistic particles (pulsar wind), are also being considered. The calculated energy loss by a rotating pulsar with a constant moment of inertia is assumed proportional to a model dependent power of $\\Omega$. This relation leads to the power law $\\dot{\\Omega}$ = -K $\\Omega^{\\rm n}$ where $n$ is called the braking index. The MDR model predicts $n$ exactly equal to 3. Selected observations of isolated pulsars provide rather precise values of $n$, individually accurate to a few percent or better, in the range 1$ <$ n $ < $ 2.8, which is consi...

  20. DISK DELAY LINES Philip Machanick

    E-Print Network [OSTI]

    Machanick, Philip

    2050 Wits, South Africa philip@cs.wits.ac.za Abstract Latency goals often relate to response times seen performance challenges other than disk latency, it is interesting to develop a model of disk architecture

  1. Disk Encryption Cryptographic Engine

    E-Print Network [OSTI]

    SecureDoc® Disk Encryption Cryptographic Engine Security Policy Abstract: This document specifies Security Policy enforced by the SecureDoc Cryptographic Engine compliant with the requirements of FIPS 140-2 level 1. It includes definition of the SecureDoc Cryptographic Engine as multi-chip standalone

  2. BOOKSHELF Hard Disk Drive

    E-Print Network [OSTI]

    Benmei, Chen

    » BOOKSHELF Hard Disk Drive Servo Systems, 2nd edition by B.M. CHEN, T.H. LEE, K. PENG, and V at Seagate Research working on spinstand microactuator integration, and I continued to work at Sea- gate part 15% of track pitch 3 , leads to fundamental challenges in position detection, while pushing band

  3. The Evolution of Inner Disk Gas in Transition Disks

    E-Print Network [OSTI]

    Hoadley, Keri; Alexander, Richard D; McJunkin, Matthew; Schneider, Christian

    2015-01-01

    Investigating the molecular gas in the inner regions of protoplanetary disks provides insight into how the molecular disk environment changes during the transition from primordial to debris disk systems. We conduct a small survey of molecular hydrogen (H$_2$) fluorescent emission, using 14 well-studied Classical T Tauri stars at two distinct dust disk evolutionary stages, to explore how the structure of the inner molecular disk changes as the optically thick warm dust dissipates. We simulate the observed HI-Lyman $\\alpha$-pumped H$_2$ disk fluorescence by creating a 2D radiative transfer model that describes the radial distributions of H$_{2}$ emission in the disk atmosphere and compare these to observations from the Hubble Space Telescope. We find the radial distributions that best describe the observed H$_2$ FUV emission arising in primordial disk targets (full dust disk) are demonstrably different than those of transition disks (little-to-no warm dust observed). For each best-fit model, we estimate inner a...

  4. Volatiles in protoplanetary disks

    E-Print Network [OSTI]

    Pontoppidan, Klaus M; Bergin, Edwin A; Brittain, Sean; Marty, Bernard; Mousis, Olvier; Oberg, Karin L

    2014-01-01

    Volatiles are compounds with low sublimation temperatures, and they make up most of the condensible mass in typical planet-forming environments. They consist of relatively small, often hydrogenated, molecules based on the abundant elements carbon, nitrogen and oxygen. Volatiles are central to the process of planet formation, forming the backbone of a rich chemistry that sets the initial conditions for the formation of planetary atmospheres, and act as a solid mass reservoir catalyzing the formation of planets and planetesimals. This growth has been driven by rapid advances in observations and models of protoplanetary disks, and by a deepening understanding of the cosmochemistry of the solar system. Indeed, it is only in the past few years that representative samples of molecules have been discovered in great abundance throughout protoplanetary disks - enough to begin building a complete budget for the most abundant elements after hydrogen and helium. The spatial distributions of key volatiles are being mapped...

  5. Initial results using Eddy Current Brakes as Fast Turn-on, Programmable Physical Dampers for Haptic Rendering

    E-Print Network [OSTI]

    Hayward, Vincent

    Initial results using Eddy Current Brakes as Fast Turn-on, Programmable Physical Dampers for Haptic Machines McGill University, Montr´eal, Qu´ebec, Canada ABSTRACT We demonstrate the use of eddy current propose an alternate method to create damping in a haptic interface that uses eddy current brakes. 2 EDDY

  6. Energy-Saving Control of an Unstable Valve with a MR Brake QingHui Yuan and Perry Y. Li

    E-Print Network [OSTI]

    Li, Perry Y.

    as a brake does not imply heat reduction. In this paper, we propose a new type of actuator in which a dual lead to heat reduction. In [6], we use a dual-solenoid actuator and design a controller to minimizeEnergy-Saving Control of an Unstable Valve with a MR Brake QingHui Yuan and Perry Y. Li Abstract

  7. Investigations into the reproductive performance and larval rearing of the Brown shrimp, Farfantepenaeus aztecus, using closed recirculating systems 

    E-Print Network [OSTI]

    Gandy, Ryan Leighton

    2005-02-17

    tanks larval rearing management schedule????????? 54 4.2 Recirculating larval rearing feed and water turnover rate associated with larval developmental stage??????????????????. 56 4.3 Water quality indicators monitored and methods used... of spawning tanks from larval rearing tanks allowed for the hatchery manager to maximize larval rearing productivity by transferring only viable nauplii of known quality and quantity to larval rearing tanks. The use of certain species of unicellular algae...

  8. REPORT on the TRUCK BRAKE LINING WORKSHOP and FLEET OPERATORS' SURVEY

    SciTech Connect (OSTI)

    Blau, P.J.

    2003-02-03

    The report summarizes what transpired during brake linings-related workshop held at the Fall 2003 meeting of the Technology and Maintenance Council (TMC) in Charlotte, NC. The title of the workshop was ''Developing a Useful Friction Material Rating System''. It was organized by a team consisting of Peter Blau (Oak Ridge National Laboratory), Jim Britell (National Highway Traffic Safety Administration), and Jim Lawrence (Motor and Equipment Manufacturers Association). The workshop was held under the auspices of TMC Task Force S6 (Chassis), chaired by Joseph Stianche (Sanderson Farms, Inc.). Six invited speakers during the morning session provided varied perspectives on testing and rating aftermarket automotive and truck brake linings. They were: James R. Clark, Chief Engineer, Foundation Brakes and Wheel Equipment, Dana Corporation, Spicer Heavy Axle and Brake Division; Charles W. Greening, Jr, President, Greening Test Labs; Tim Duncan, General Manager, Link Testing Services;Dennis J. McNichol, President, Dennis NationaLease; Jim Fajerski, Business Manager, OE Sales and Applications Engineering, Federal Mogul Corporation; and Peter J. Blau, Senior Materials Development Engineer, Oak Ridge National Laboratory. The afternoon break-out sessions addressed nine questions concerning such issues as: ''Should the federal government regulate aftermarket lining quality?''; ''How many operators use RP 628, and if so, what's good or bad about it?''; and ''Would there be any value to you of a vocation-specific rating system?'' The opinions of each discussion group, consisting of 7-9 participants, were reported and consolidated in summary findings on each question. Some questions produced a greater degree of agreement than others. In general, the industry seems eager for more information that would allow those who are responsible for maintaining truck brakes to make better, more informed choices on aftermarket linings. A written fleet operator survey was also conducted during the TMC meeting. Twenty-one responses were received, spanning fleet sizes between 12 and 170,000 vehicles. Responses are summarized in a series of tables separated into responses from small (100 or fewer powered vehicles), medium (101-1000 vehicles), and large fleets (>1000 vehicles). The vast majority of fleets do their own brake maintenance, relying primarily on experience and lining manufactures to select aftermarket linings. At least half of the responders are familiar to some extent with TMC Recommended Practice 628 on brake linings, but most do not use this source of test data as the sole criterion to select linings. Significant shortfalls in the applicability of TMC RP 628 to certain types of brake systems were noted.

  9. System for lubrication of a brake air compressor associated with a turbocharged internal combustion engine

    SciTech Connect (OSTI)

    Spencer, J.C.

    1992-10-13

    This patent describes a system for use with a vehicle which includes a turbocharged internal combustion engine having a lubricating system wherein lubricating oil from an engine oil reservoir is circulated within the engine and also to and from an associated brake system air compressor which supplies compressed air for operation of the vehicle air braking system. This patent describes improvement in passing supercharged air to an oil crankcase of the air compressor to cause lubricating oil to drain therefrom and return to the engine oil reservoir.

  10. Achieving Consistent Maximum Brake Torque with Varied Injection Timing in a DI Diesel Engine 

    E-Print Network [OSTI]

    Kroeger, Timothy H

    2013-09-19

    The brake torque of a direct-injection diesel engine is known to plateau over a range of injection timings. Injection timing affects the engine’s ignition delay and the fractions of fuel which burn in premixed and diffusion modes. Therefore...

  11. Disk eccentricity and embedded planets

    E-Print Network [OSTI]

    Wilhelm Kley; Gerben Dirksen

    2005-10-13

    We investigate the response of an accretion disk to the presence of a perturbing protoplanet embedded in the disk through time dependent hydrodynamical simulations. The disk is treated as a two-dimensional viscous fluid and the planet is kept on a fixed orbit. We run a set of simulations varying the planet mass, and the viscosity and temperature of the disk. All runs are followed until they reach a quasi-equilibrium state. We find that for planetary masses above a certain minimum mass, already 3 M_Jup for a viscosity of nu = 10^{-5}, the disk makes a transition from a nearly circular state into an eccentric state. Increasing the planetary mass leads to a saturation of disk eccentricity with a maximum value of around 0.25. The transition to the eccentric state is driven by the excitation of an m=2 spiral wave at the outer 1:3 Lindblad resonance. The effect occurs only if the planetary masses are large enough to clear a sufficiently wide and deep gap to reduce the damping effect of the outer 1:2 Lindblad resonance. An increase in viscosity and temperature in the disk, which both tend to close the gap, have an adverse influence on the disk eccentricity. In the eccentric state the mass accretion rate onto the planet is greatly enhanced, an effect that may ease the formation of massive planets beyond about 5 M_Jup that are otherwise difficult to reach.

  12. ORIGINAL ARTICLE Car safety seats for children: rear facing for best protection

    E-Print Network [OSTI]

    ORIGINAL ARTICLE Car safety seats for children: rear facing for best protection B Henary, C P between rear-facing (RFCS) and forward-facing (FFCS) car seats for children less than 2 years of age riding in passenger cars, sport utility vehicles, or light trucks were included in the study. Logistic

  13. Tectonic wedging along the rear of the offshore Taiwan accretionary prism

    E-Print Network [OSTI]

    Chi, Wu-Cheng

    Tectonic wedging along the rear of the offshore Taiwan accretionary prism Wu-Cheng Chia,b,*, Donald the rear of the offshore Taiwan accretionary prism were studied using seismic reflection profiling and gravity modeling. Deformation between the offshore prism and forearc basin at the point of incipient

  14. Effects of turbulence on cosmic ray propagation in protostars and young star/disk systems

    SciTech Connect (OSTI)

    Fatuzzo, Marco; Adams, Fred C. E-mail: fca@umich.edu

    2014-05-20

    The magnetic fields associated with young stellar objects are expected to have an hour-glass geometry, i.e., the magnetic field lines are pinched as they thread the equatorial plane surrounding the forming star but merge smoothly onto a background field at large distances. With this field configuration, incoming cosmic rays experience both a funneling effect that acts to enhance the flux impinging on the circumstellar disk and a magnetic mirroring effect that acts to reduce that flux. To leading order, these effects nearly cancel out for simple underlying magnetic field structures. However, the environments surrounding young stellar objects are expected to be highly turbulent. This paper shows how the presence of magnetic field fluctuations affects the process of magnetic mirroring, and thereby changes the flux of cosmic rays striking circumstellar disks. Turbulence has two principle effects: (1) the (single) location of the magnetic mirror point found in the absence of turbulence is replaced with a wide distribution of values. (2) The median of the mirror point distribution moves outward for sufficiently large fluctuation amplitudes (roughly when ?B/B {sub 0} > 0.2 at the location of the turbulence-free mirror point); the distribution becomes significantly non-Gaussian in this regime as well. These results may have significant consequences for the ionization fraction of the disk, which in turn dictates the efficiency with which disk material can accrete onto the central object. A similar reduction in cosmic ray flux can occur during the earlier protostellar stages; the decrease in ionization can help alleviate the magnetic braking problem that inhibits disk formation.

  15. Magneto-thermal Disk Wind from Protoplanetary Disks

    E-Print Network [OSTI]

    Bai, Xue-Ning; Goodman, Jeremy; Yuan, Feng

    2015-01-01

    Global evolution and dispersal of protoplanetary disks (PPDs) is governed by disk angular momentum transport and mass-loss processes. Recent numerical studies suggest that angular momentum transport in the inner region of PPDs is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. On the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. We unify the two scenarios by developing a 1D model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. The wind properties largely depend on 1) the magnetic field strength at the wind base, characterized by the poloidal Alfv\\'en speed $v_{Ap}$, 2) the sound speed $c_s$ near the wind base, and 3) how rapidly poloidal field lines diverge (achieve $R^{-2}$ scaling). When $v_{Ap}\\gg c_s$, corotation is enforced near the wind base, resulting in centrifugal acceleration. Otherwise, the wind is accel...

  16. Disks around Brown Dwarfs and Cool Stars

    E-Print Network [OSTI]

    Daniel Apai; Kevin Luhman; Michael Liu

    2007-02-10

    We review the current picture of disks around cool stars and brown dwarfs, including disk fractions, mass estimates, disk structure and dispersal, accretion, dust composition, and the debris disk phase. We discuss these in the framework of recent planet formation models.

  17. Nonlinear analysis of time series of vibration data from a friction brake: SSA, PCA, and MFDFA

    E-Print Network [OSTI]

    Nikolay K. Vitanov; Norbert P. Hoffmann; Boris Wernitz

    2014-10-23

    We use the methodology of singular spectrum analysis (SSA), principal component analysis (PCA), and multi-fractal detrended fluctuation analysis (MFDFA), for investigating characteristics of vibration time series data from a friction brake. SSA and PCA are used to study the long time-scale characteristics of the time series. MFDFA is applied for investigating all time scales up to the smallest recorded one. It turns out that the majority of the long time-scale dynamics, that is presumably dominated by the structural dynamics of the brake system, is dominated by very few active dimensions only and can well be understood in terms of low dimensional chaotic attractors. The multi-fractal analysis shows that the fast dynamical processes originating in the friction interface are in turn truly multi-scale in nature.

  18. Trends for Outer Disk Profiles

    E-Print Network [OSTI]

    Peter Erwin; Michael Pohlen; Leonel Gutierrez; John E. Beckman

    2007-12-10

    The surface-brightness profiles of galaxy disks fall into three main classes, based on whether they are simple exponentials (Type I), bend down at large radii (Type II, "truncations") or bend up at large radii (Type III, "antitruncations"). Here, we discuss how the frequency of these different profiles depends on Hubble type, environment, and the presence or absence of bars; these trends may herald important new tests for disk formation models.

  19. Trends for Outer Disk Profiles

    E-Print Network [OSTI]

    Erwin, Peter; Gutíerrez, Leonel; Beckman, John E

    2007-01-01

    The surface-brightness profiles of galaxy disks fall into three main classes, based on whether they are simple exponentials (Type I), bend down at large radii (Type II, "truncations") or bend up at large radii (Type III, "antitruncations"). Here, we discuss how the frequency of these different profiles depends on Hubble type, environment, and the presence or absence of bars; these trends may herald important new tests for disk formation models.

  20. Design and manufacture of a rear driveline package including limited slip differential for Formula SAE applications

    E-Print Network [OSTI]

    Yazicioglu, Tolga T

    2008-01-01

    This document describes the design and manufacture of a lightweight rear driveline package for a Formula SAE race car. The design focuses on all components needed to transfer power from the chain driven Honda CBR600 F4i ...

  1. Toto the Robot Figure 1. Toto, front view. Figure 2. Toto, rear view.

    E-Print Network [OSTI]

    Indiana University

    Toto the Robot Figure 1. Toto, front view. Figure 2. Toto, rear view. Toto the Robot was created so a robot, helps account for his lack of verbal charm. Second, some younger children may recognize in Toto

  2. Kwangjin Lee J. R. Barber

    E-Print Network [OSTI]

    Barber, James R.

    Kwangjin Lee J. R. Barber Department of Mechanical Engineering and Applied Mechanics, University Instability in Automotive Disk Brakes Under a Drag Brake Application Thermoelastic instability in an automotive disk brake system is investigated exper- imentally underdrag braking conditions. The onset

  3. The Kozai-Lidov Mechanism in Hydrodynamical Disks - II. Effects of binary and disk parameters

    E-Print Network [OSTI]

    Fu, Wen; Martin, Rebecca G

    2015-01-01

    Martin et al. (2014b) showed that a substantially misaligned accretion disk around one component of a binary system can undergo global damped Kozai-Lidov oscillations. During these oscillations, the inclination and eccentricity of the disk are periodically exchanged. However, the robustness of this mechanism and its dependence on the system parameters were unexplored. In this paper, we use three-dimensional hydrodynamical simulations to analyze how various binary and disk parameters affect the Kozai-Lidov mechanism in hydrodynamical disks. The simulations include the effect of gas pressure and viscosity, but ignore the effects of disk self-gravity. We describe results for different numerical resolutions, binary mass ratios and orbital eccentricities, initial disk sizes, initial disk surface density profiles, disk sound speeds, and disk viscosities. We show that the Kozai-Lidov mechanism can operate for a wide range of binary-disk parameters. We discuss the applications of our results to astrophysical disks in...

  4. The Kozai-Lidov mechanism in hydrodynamical disks. II. Effects of binary and disk parameters

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    Fu, Wen; Lubow, Stephen H.; Martin, Rebecca G.

    2015-07-01

    Martin et al. (2014b) showed that a substantially misaligned accretion disk around one component of a binary system can undergo global damped Kozai–Lidov (KL) oscillations. During these oscillations, the inclination and eccentricity of the disk are periodically exchanged. However, the robustness of this mechanism and its dependence on the system parameters were unexplored. In this paper, we use three-dimensional hydrodynamical simulations to analyze how various binary and disk parameters affect the KL mechanism in hydrodynamical disks. The simulations include the effect of gas pressure and viscosity, but ignore the effects of disk self-gravity. We describe results for different numerical resolutions,more »binary mass ratios and orbital eccentricities, initial disk sizes, initial disk surface density profiles, disk sound speeds, and disk viscosities. We show that the KL mechanism can operate for a wide range of binary-disk parameters. We discuss the applications of our results to astrophysical disks in various accreting systems.« less

  5. Why Do Disks Form Jets?

    E-Print Network [OSTI]

    D Lynden-Bell

    2002-03-27

    It is argued that jet modelers have given insufficient study to the natural magneto-static configurations of field wound up in the presence of a confining general pressure. Such fields form towers whose height grows with each twist at a velocity comparable to the circular velocity of the accretion disk that turns them. A discussion of the generation of such towers is preceded by a brief history of the idea that quasars, active galaxies, and galactic nuclei contain giant black holes with accretion disks.

  6. Probability of failure of the waste hoist brake system at the Waste Isolation Pilot Plant (WIPP)

    SciTech Connect (OSTI)

    Greenfield, M.A. [Univ. of California, Los Angeles, CA (United States); Sargent, T.J. [Univ. of Chicago, IL (United States)]|[Stanford Univ., CA (United States). Hoover Institution

    1998-01-01

    In its most recent report on the annual probability of failure of the waste hoist brake system at the Waste Isolation Pilot Plant (WIPP), the annual failure rate is calculated to be 1.3E({minus}7)(1/yr), rounded off from 1.32E({minus}7). A calculation by the Environmental Evaluation Group (EEG) produces a result that is about 4% higher, namely 1.37E({minus}7)(1/yr). The difference is due to a minor error in the US Department of Energy (DOE) calculations in the Westinghouse 1996 report. WIPP`s hoist safety relies on a braking system consisting of a number of components including two crucial valves. The failure rate of the system needs to be recalculated periodically to accommodate new information on component failure, changes in maintenance and inspection schedules, occasional incidents such as a hoist traveling out-of-control, either up or down, and changes in the design of the brake system. This report examines DOE`s last two reports on the redesigned waste hoist system. In its calculations, the DOE has accepted one EEG recommendation and is using more current information about the component failures rates, the Nonelectronic Parts Reliability Data (NPRD). However, the DOE calculations fail to include the data uncertainties which are described in detail in the NPRD reports. The US Nuclear Regulatory Commission recommended that a system evaluation include mean estimates of component failure rates and take into account the potential uncertainties that exist so that an estimate can be made on the confidence level to be ascribed to the quantitative results. EEG has made this suggestion previously and the DOE has indicated why it does not accept the NRC recommendation. Hence, this EEG report illustrates the importance of including data uncertainty using a simple statistical example.

  7. Disks and Planets in Binary Systems

    E-Print Network [OSTI]

    Wilhelm Kley; Andreas Burkert

    2000-04-04

    The star formation process in molecular clouds usually leads to the formation of multiple stellar systems, mostly binaries. Remaining disks around those stars may be located around individual stars (circumstellar disks) or around the entire binary system (circumbinary disk). We shall briefly review the present observational evidence for both types of disks in binary stars, in particular the properties of circumbinary disks. We then present recent results of the theoretical modeling of the collapse and fragmentation of gravitationally unstable molecular cloud cores and their implications for binary and disk formation, and discuss the dynamical influence of the binary companions on disk truncation and gap formation. The presence of binaries may have profound influence on the process of planet formation as well. We present results on the stability and evolution of orbits of planets in disks around binaries.

  8. Three Types of Galaxy Disks

    E-Print Network [OSTI]

    M. Pohlen; P. Erwin; I. Trujillo; J. E. Beckman

    2007-06-26

    We present our new scheme for the classification of radial stellar surface brightness profiles for disk galaxies. We summarize the current theoretical attempts to understand their origin and give an example of an application by comparing local galaxies with their counterparts at high redshift (z~1).

  9. Three Types of Galaxy Disks

    E-Print Network [OSTI]

    Pohlen, M; Trujillo, I; Beckman, J E

    2007-01-01

    We present our new scheme for the classification of radial stellar surface brightness profiles for disk galaxies. We summarize the current theoretical attempts to understand their origin and give an example of an application by comparing local galaxies with their counterparts at high redshift (z~1).

  10. HARMONIC AND SUPERHARMONIC MAJORANTS ON THE DISK

    E-Print Network [OSTI]

    Thomas, Pascal J.

    HARMONIC AND SUPERHARMONIC MAJORANTS ON THE DISK function on the unit disk admits * *a harmonic majorant if and only if a certain explicit upper D denote the open unit disk in the complex plane, and H+ (D) the cone of positive harmonic

  11. Sensitivity-Based Optimization of Disk Architecture

    E-Print Network [OSTI]

    Gurumurthi, Sudhanva

    -end storage systems consume a large amount of power, the bulk of which is due to the disk drives. Optimizing architectures. Index Terms--Disk drives, storage, power, performance, optimization. Ç 1 INTRODUCTION WESensitivity-Based Optimization of Disk Architecture Sriram Sankar, Yan Zhang, Sudhanva Gurumurthi

  12. Development of a Natural Rearing System to Improve Supplemental Fish Quality, 1996-1998 Progress Report.

    SciTech Connect (OSTI)

    Maynard, Desmond J.

    2001-09-13

    This report covers the 1996-1998 Natural Rearing Enhancement System (NATURES) research for increasing hatchery salmon postrelease survival and producing fish with more wild-like behavior, physiology, and morphology prior to release. Experiments were conducted evaluating automatic subsurface feeders; natural diets; exercise systems; seminatural raceway habitat enriched with cover, structure, and substrate; and predator avoidance conditioning for hatchery salmonids. Automatic subsurface feed delivery systems did not affect chinook salmon depth distribution or vulnerability to avian predators. Live-food diets only marginally improved the ability of chinook salmon to capture prey in stream enclosures. A prototype exercise system that can be retrofitted to raceways was developed, however, initial testing indicated that severe amounts of exercise may increase in culture mortality. Rearing chinook salmon in seminatural raceway habitat with gravel substrate, woody debris structure, and overhead cover improved coloration and postrelease survival without impacting in-culture health or survival. Steelhead fry reared in enriched environments with structure, cover, and point source feeders dominated and outcompeted conventionally reared fish. Exposing chinook salmon to caged predators increased their postrelease survival. Chinook salmon showed an antipredator response to chemical stimuli from injured conspecifics and exhibited acquired predator recognition following exposure to paired predator-prey stimuli. The report also includes the 1997 Natural Rearing System Workshop proceedings.

  13. Hybrid: Braking

    Alternative Fuels and Advanced Vehicles Data Center [Office of Energy Efficiency and Renewable Energy (EERE)]

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels Data Center Home Page on Delicious Rank EERE: Alternative Fuels Data Center Home PageBlenderBusiness Case for E85CaliforniaCleanUNITEDNREL

  14. Hybrid: Braking

    Alternative Fuels and Advanced Vehicles Data Center [Office of Energy Efficiency and Renewable Energy (EERE)]

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels Data Center Home Page on Delicious Rank EERE: Alternative Fuels Data Center Home PageBlenderBusiness Case for E85CaliforniaCleanUNITEDNRELButton

  15. Uncertainty-Enabled Design of a Rocket Sled Track Switch Drs. Jordan E. Massad and Matthew R. Brake

    E-Print Network [OSTI]

    Uncertainty-Enabled Design of a Rocket Sled Track Switch Drs. Jordan E. Massad and Matthew R. Brake Sandia National Laboratories, New Mexico Rocket sled tracks provide a dynamically rich environment acceleration profile, the switch closes to complete a circuit for instrument activation. Preliminary tests

  16. CityCarControl : an electric vehicle drive-by-wire solution for distributed steering, braking and throttle control

    E-Print Network [OSTI]

    Brown, Thomas B., M. Eng. Massachusetts Institute of Technology

    2010-01-01

    In this paper, we propose CityCarControl, a system to manage the steering, braking, and throttle of a new class of intra-city electric vehicles. These vehicles have a focus on extreme light-weight and a small parking ...

  17. Energy-Saving Control of an Unstable Valve with a MR Brake QingHui Yuan and Perry Y. Li

    E-Print Network [OSTI]

    Li, Perry Y.

    Energy-Saving Control of an Unstable Valve with a MR Brake QingHui Yuan and Perry Y. Li Abstract controller is then developed to achieve position tracking and energy-saving. Simulation verifies that using. INTRODUCTION Energy-saving is an important issue in fluid power indus- try. The research of energy efficiency

  18. 19.4% -EFFICIENT LARGE AREA REAR-PASSIVATED SCREEN-PRINTED SILICON SOLAR CELLS T. Dullweber*1

    E-Print Network [OSTI]

    -printed cells by 0.2% [6,7]. The electrical and optical losses of the full- area Al-BSF at the rear side can19.4% -EFFICIENT LARGE AREA REAR-PASSIVATED SCREEN-PRINTED SILICON SOLAR CELLS T. Dullweber*1 , S implemented a baseline solar cell process based on today's standard industrially manufactured silicon solar

  19. Improving the Speed of Virtual Rear Projection: A GPU-Centric Architecture Matthew Flagg, Jay Summet, and James M. Rehg

    E-Print Network [OSTI]

    Haro, Antonio

    front projection [15]. In Passive Virtual Rear Projection, dual projectors redun- dantly illuminate square foot in an office building [18]. Figure 1: Players interacting with a game on the BigBoard projected using passive virtual rear projection. currently use passive VRP across a large 17.5Ã?4.5 foot in

  20. DUSTY DISKS AROUND WHITE DWARFS. I. ORIGIN OF DEBRIS DISKS

    SciTech Connect (OSTI)

    Dong Ruobing; Wang Yan; Lin, D. N. C.; Liu, X.-W., E-mail: rdong@astro.princeton.ed, E-mail: yuw123@psu.ed, E-mail: lin@ucolick.or, E-mail: liuxw@bac.pku.edu.c [Kavli Institute of Astronomy and Astrophysics, Peking University, Beijing (China)

    2010-06-01

    A significant fraction of the mature FGK stars have cool dusty disks at least an order of magnitude brighter than the solar system's outer zodiacal light. Since such dusts must be continually replenished, they are generally assumed to be the collisional fragments of residual planetesimals analogous to the Kuiper-Belt objects. At least 10% of solar-type stars also bear gas giant planets. The fraction of stars with known gas giants or detectable debris disks (or both) appears to increase with the stellar mass. Here, we examine the dynamical evolution of systems of long-period gas giant planets and residual planetesimals as their host stars evolve off the main sequence, lose mass, and form planetary nebula around remnant white dwarf cores. The orbits of distant gas giant planets and super-km-size planetesimals expand adiabatically. During the most intense asymptotic giant branch mass-loss phase, sub-meter-size particles migrate toward their host stars due to the strong hydrodynamical drag by the intense stellar wind. Along their migration paths, gas giant planets capture and sweep up sub-km-size planetesimals onto their mean-motion resonances. These planetesimals also acquire modest eccentricities which are determined by the mass of the perturbing planets, and the rate and speed of stellar mass loss. The swept-up planetesimals undergo disruptive collisions which lead to the production of grains with an extended size range. The radiation drag on these particles is ineffective against the planets' resonant barrier and they form 30-50 AU size rings which can effectively reprocess the stellar irradiation in the form of FIR continuum. We identify the recently discovered dust ring around the white dwarf WD 2226-210 at the center of the Helix nebula as a prototype of such disks and suggest such rings may be common.

  1. MAGNETIC BRAKING FORMULATION FOR SUN-LIKE STARS: DEPENDENCE ON DIPOLE FIELD STRENGTH AND ROTATION RATE

    SciTech Connect (OSTI)

    Matt, Sean P.; Pinsonneault, Marc H.; Greene, Thomas P. E-mail: kmac@ucar.edu E-mail: thomas.p.greene@nasa.gov

    2012-08-01

    We use two-dimensional axisymmetric magnetohydrodynamic simulations to compute steady-state solutions for solar-like stellar winds from rotating stars with dipolar magnetic fields. Our parameter study includes 50 simulations covering a wide range of relative magnetic field strengths and rotation rates, extending from the slow- and approaching the fast-magnetic-rotator regimes. Using the simulations to compute the angular momentum loss, we derive a semi-analytic formulation for the external torque on the star that fits all of the simulations to a precision of a few percent. This formula provides a simple method for computing the magnetic braking of Sun-like stars due to magnetized stellar winds, which properly includes the dependence on the strength of the magnetic field, mass loss rate, stellar radius, surface gravity, and spin rate, and which is valid for both slow and fast rotators.

  2. Air-Bearing Shear Force in the Head–Disk Interface of Hard Disk

    E-Print Network [OSTI]

    Liu, Nan; Bogy, David B.

    2009-01-01

    Time evo- lution of lubricant-slider dynamic interactions.3. Ma, Y. , Liu, B. : Lubricant transfer from disk to sliderR. : The physics of disk lubricant in the continuum picture.

  3. Improvements in in vitro rearing methods of Toxoneuron nigriceps (viereck) (Hymenoptera:Braconidae), a larval endoparasitoid of Heliothis virescens (Lepidoptera: Noctuidae) 

    E-Print Network [OSTI]

    Kuriachan, Indira

    2006-08-16

    were incubated in the artificial rearing media. The growth (increase in length and width), development (molting), and survival of the incubated larvae were observed. Changes in osmotic pressure of the rearing media before and after incubation were...

  4. Houses for early weaned piglets : influence of rearing on the floor or in batteries,

    E-Print Network [OSTI]

    Paris-Sud XI, Université de

    Houses for early weaned piglets : influence of rearing on the floor or in batteries, temperature-deck batteries on wire floor divided into 2 compartments : one at I8.!0 y- i°C, relative humidity 61+ io p. roo and in batteries were the following : 148 and z36 (period I), !2S and 495 (period 11), i. e. differences in favour

  5. Tactile Stimulation During Artificial Rearing Influences Adult Function and Morphology in a

    E-Print Network [OSTI]

    Sokolowski, Marla

    Tactile Stimulation During Artificial Rearing Influences Adult Function and Morphology number, size, and dendritic length in adulthood. Reduced maternal licking also produces deficits in adult, the maternal care reper- toire consists of nursing, licking, grooming, incubat- ing, and retrieving of pups

  6. BINOCULAR INTERACTION IN STRIATE CORTEX OF KITTENS REARED WITH ARTIFICIAL SQUINT'

    E-Print Network [OSTI]

    Hubel, David

    BINOCULAR INTERACTION IN STRIATE CORTEX OF KITTENS REARED WITH ARTIFICIAL SQUINT' DAVID H. HUBEL (strabismus or nonparallel visual axes) may suffer a deterioration of vision in one eye (amblyopia ex anopsia. An artificial squint therefore seemed to provide a possible means of obtaining a cortical defect while sparing

  7. A Comparison of Rearing Costs and Returns of Selected Herbivorous, Omnivorous, and

    E-Print Network [OSTI]

    A Comparison of Rearing Costs and Returns of Selected Herbivorous, Omnivorous, and Carnivorous Aquatic Species 'Derived from Table 2. 'Sources: NIH. 1972. and Anonymous, 1964. :lCost of production per k9 ~ (1.000 9 x edible portion x protein in edible portion per g)J " 1.000. [Cost 01 feed

  8. HEATING AND COOLING PROTOSTELLAR DISKS

    SciTech Connect (OSTI)

    Hirose, S. [Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 3173-25 Showamachi, Kanazawa-ku, Yokohama, Kanagawa 236-0001 (Japan); Turner, N. J., E-mail: shirose@jamstec.go.jp, E-mail: neal.turner@jpl.nasa.gov [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

    2011-05-10

    We examine heating and cooling in protostellar disks using three-dimensional radiation-MHD calculations of a patch of the Solar nebula at 1 AU, employing the shearing-box and flux-limited radiation diffusion approximations. The disk atmosphere is ionized by stellar X-rays, well coupled to magnetic fields, and sustains a turbulent accretion flow driven by magnetorotational instability, while the interior is resistive and magnetically dead. The turbulent layers are heated by absorbing the light from the central star and by dissipating the magnetic fields. They are optically thin to their own radiation and cool inefficiently. The optically thick interior in contrast is heated only weakly, by re-emission from the atmosphere. The interior is colder than a classical viscous model and isothermal. The magnetic fields support an extended atmosphere that absorbs the starlight 1.5 times higher than the hydrostatic viscous model. The disk thickness thus measures not the internal temperature, but the magnetic field strength. Fluctuations in the fields move the starlight-absorbing surface up and down. The height ranges between 13% and 24% of the radius over timescales of several orbits, with implications for infrared variability. The fields are buoyant, so the accretion heating occurs higher in the atmosphere than the stresses. The heating is localized around current sheets, caused by magnetorotational instability at lower elevations and by Parker instability at higher elevations. Gas in the sheets is heated above the stellar irradiation temperature, even though accretion is much less than irradiation power when volume averaged. The hot optically thin current sheets might be detectable through their line emission.

  9. COBE's Galactic Bar and Disk

    E-Print Network [OSTI]

    H. T. Freudenreich

    1997-08-04

    A model of the bar and old stellar disk of the Galaxy has been derived from the survey of the Diffuse Infrared Background Experiment (DIRBE) of the Cosmic Background Explorer at wavelengths of 1.25, 2.2, 3.5, and 4.9 microns. It agrees very well with the data, except in directions in which the near- infrared optical depth is high. Among the conclusions drawn from the model: The Sun is located approximately 16.5 pc above the midpoint of the Galactic plane. The disk has an outer edge four kpc from the Sun, and is warped like the HI layer. It has a central hole roughly the diameter of the inner edge of the "three-kiloparsec" molecular cloud ring, and within that hole lies a bright, strong, "early-type" bar, tilted approximately 14 degrees from the Sun-Galactic center line. The model has 47 free parameters. The model is discussed in detail and contour plots and images of the residuals presented.

  10. Siegel disk for complexified Henon map

    E-Print Network [OSTI]

    O. B. Isaeva; S. P. Kuznetsov

    2008-04-26

    It is shown that critical phenomena associated with Siegel disk, intrinsic to 1D complex analytical maps, survives in 2D complex invertible dissipative H\\'{e}non map. Special numerical method of estimation of the Siegel disk scaling center position (for 1D maps it corresponds to extremum) for multi-dimensional invertible maps are developed.

  11. BACKPRESSURE TESTING OF ROTARY MICROFILTER DISKS

    SciTech Connect (OSTI)

    Fowley, M.; Herman, D.

    2011-04-14

    The Savannah River National Laboratory (SRNL), under the Department of Energy (DOE) Office of Environmental Management (EM), is modifying and testing the SpinTek{trademark} rotary microfilter (RMF) for radioactive filtration service in the Department of Energy (DOE) complex. The RMF has been shown to improve filtration throughput when compared to other conventional methods such as cross-flow filtration. A concern with the RMF was that backpressure, or reverse flow through the disk, would damage the filter membranes. Reverse flow might happen as a result of an inadvertent valve alignment during flushing. Testing was completed in the Engineering Development Laboratory (EDL) located in SRNL to study the physical effects of backpressure as well as to determine the maximum allowable back-pressure for RMF disks. The RMF disks tested at the EDL were manufactured by SpinTek{trademark} Filtration and used a Pall Corporation PMM050 filter membrane (0.5 micron nominal pore size) made from 316L stainless steel. Early versions of the RMF disks were made from synthetic materials that were incompatible with caustic solutions and radioactive service as well as being susceptible to delaminating when subjected to backpressure. Figure 1-1 shows the essential components of the RMF; 3 rotating disks and 3 stationary turbulence promoters (or shear elements) are shown. Figure 1-2 show the assembly view of a 25 disk RMF proposed for use at the Savannah River Site (SRS) and at the Hanford Facility. The purpose of the testing discussed in this report was to determine the allowable backpressure for RMF disks as well as study the physical effects of backpressure on RMF disks made with the Pall PMM050 membrane. This was accomplished by pressurizing the disks in the reverse flow direction (backpressure) until the test limit was reached or until membrane failure occurred. Backpressure was applied to the disks with air while submerged in deionized (DI) water. This method provided a visual representation of membrane integrity via bubble flow patterns. Membrane failure was defined as the inability to filter effectively at the nominal filter pore size. Effective filtration was determined by turbidity measurements of filtrate that was produced by applying forward-pressure to the disks while submerged in a representative simulant. The representative simulant was Tank 8F simulated sludge produced for SRNL by Optima Chemical. Two disks were tested. Disk 1 was tested primarily to determine approximate levels of backpressure where membrane failure occurred. These levels were then used to define the strategy for testing the Disk 2; a strategy that would better define and quantify the mode of failure.

  12. Gravitational wave diagnosis of a circumbinary disk

    E-Print Network [OSTI]

    Kimitake Hayasaki; Kent Yagi; Takahiro Tanaka; Shin Mineshige

    2012-01-13

    When binary black holes are embedded in a gaseous environment, a rotating disk surrounding them, the so-called circumbinary disk, will be formed. The binary exerts a gravitational torque on the circumbinary disk and thereby the orbital angular momentum is transferred to it, while the angular momentum of the circumbinary disk is transferred to the binary through the mass accretion. The binary undergoes an orbital decay due to both the gravitational wave emission and the binary-disk interaction. This causes the phase evolution of the gravitational wave signal. The precise measurement of the gravitational wave phase thus may provide information regarding the circumbinary disk. In this paper, we assess the detectability of the signature of the binary-disk interaction using the future space-borne gravitational wave detectors such as DECIGO and BBO by the standard matched filtering analysis. We find that the effect of the circumbinary disk around binary black holes in the mass range $6M_sun\\le{M}\\lesssim3\\times10^3M_sun$ is detectable at a statistically significant level in five year observation, provided that gas accretes onto the binary at a rate greater than $\\dot{M}\\sim1.4\\times10^{17} [gs^{-1}] j^{-1}(M/10M_sun)^{33/23}$ with 10% mass-to-energy conversion efficiency, where j represents the efficiency of the angular momentum transfer from the binary to the circumbinary disk. We show that $O(0.1)$ coalescence events are expected to occur in sufficiently dense molecular clouds in five year observation. We also point out that the circumbinary disk is detectable, even if its mass at around the inner edge is by over 10 orders of magnitude less than the binary mass.

  13. Rotating Disk-Electrode Aqueous Electrolyte Accelerated Stress...

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Rotating Disk-Electrode Aqueous Electrolyte Accelerated Stress Tests for PGM ElectrocatalystSupport Durability Evaluation Rotating Disk-Electrode Aqueous Electrolyte Accelerated...

  14. Microsoft PowerPoint - Advances_Fuller [Compatibility Mode

    Office of Environmental Management (EM)

    to developing rear-end collisions Haptic warning provides short brake pulse which causes drivers to respond faster to imminent rear-end collisions "Always on" at speeds...

  15. Double-Disk Dark Matter

    E-Print Network [OSTI]

    Fan, JiJi; Randall, Lisa; Reece, Matthew

    2013-01-01

    Based on observational tests and constraints on halo structure, dark matter is generally taken to be cold and essentially collisionless. On the other hand, given the large number of particles and forces in the visible world, a more complex dark sector could be a reasonable or even likely possibility. This hypothesis leads to testable consequences, perhaps portending the discovery of a rich hidden world neighboring our own. We consider a scenario that readily satisfies current bounds that we call Partially Interacting Dark Matter (PIDM). This scenario contains self-interacting dark matter, but it is not the dominant component. Even if PIDM contains only a fraction of the net dark matter density, comparable to the baryonic fraction, the subdominant component's interactions can lead to interesting and potentially observable consequences. Our primary focus will be the special case of Double-Disk Dark Matter (DDDM), in which self-interactions allow the dark matter to lose enough energy to lead to dynamics similar ...

  16. Double-Disk Dark Matter

    E-Print Network [OSTI]

    JiJi Fan; Andrey Katz; Lisa Randall; Matthew Reece

    2013-07-31

    Based on observational constraints on large scale structure and halo structure, dark matter is generally taken to be cold and essentially collisionless. On the other hand, given the large number of particles and forces in the visible world, a more complex dark sector could be a reasonable or even likely possibility. This hypothesis leads to testable consequences, perhaps portending the discovery of a rich hidden world neighboring our own. We consider a scenario that readily satisfies current bounds that we call Partially Interacting Dark Matter (PIDM). This scenario contains self-interacting dark matter, but it is not the dominant component. Even if PIDM contains only a fraction of the net dark matter density, comparable to the baryonic fraction, the subdominant component's interactions can lead to interesting and potentially observable consequences. Our primary focus will be the special case of Double-Disk Dark Matter (DDDM), in which self-interactions allow the dark matter to lose enough energy to lead to dynamics similar to those in the baryonic sector. We explore a simple model in which DDDM can cool efficiently and form a disk within galaxies, and we evaluate some of the possible observational signatures. The most prominent signal of such a scenario could be an enhanced indirect detection signature with a distinctive spatial distribution. Even though subdominant, the enhanced density at the center of the galaxy and possibly throughout the plane of the galaxy can lead to large boost factors, and could even explain a signature as large as the 130 GeV Fermi line. Such scenarios also predict additional dark radiation degrees of freedom that could soon be detectable and would influence the interpretation of future data, such as that from Planck and from the Gaia satellite. We consider this to be the first step toward exploring a rich array of new possibilities for dark matter dynamics.

  17. Resolving Protoplanetary Disks at Millimeter Wavelengths by CARMA

    E-Print Network [OSTI]

    Kwon, Woojin; Mundy, Lee G; Welch, William J

    2015-01-01

    We present continuum observations at 1.3 and 2.7 mm using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) toward six protoplanetary disks in the Taurus molecular cloud: CI Tau, DL Tau, DO Tau, FT Tau, Haro 6-13, and HL Tau. We constrain physical properties of the disks with Bayesian inference using two disk models; flared power-law disk model and flared accretion disk model. Comparing the physical properties, we find that the more extended disks are less flared and that the dust opacity spectral index (beta) is smaller in the less massive disks. In addition, disks with a steeper mid-plane density gradient have a smaller beta, which suggests that grains grow and radially move. Furthermore, we compare the two disk models quantitatively and find that the accretion disk model provides a better fit overall. We also discuss the possibilities of substructures on three extended protoplanetary disks.

  18. Laser-accelerated disks for EOS studies

    SciTech Connect (OSTI)

    Harrach, R.J.; Szoke, A.

    1981-09-01

    An indirect method of laser-based equation of state studies, which utilizes shock waves generated by laser-accelerated projectiles rather than ablation shocks from direct laser irradiation of the sample under investigation, is proposed and examined theoretically. We derive simple formulas for the minimum thickness and maximum speed of laser-accelerated disks, comparing them with results of Nd-laser experiments conducted by the Naval Research Laboratory. Our calculations indicate that disks can be accelerated to velocities above 10/sup 7/ cm/s using a wide choice of laser parameters (pulse duration, energy, intensity, wavelength, etc.). The use of shorter wavelengths, e.g., a KrF(0.25 ..mu..m) laser rather than Nd (1.06 ..mu..m), allows thicker disks to be accelerated and faster velocities to be attained, approximately in the ratio (lambda/sub L/(Nd)/lambda/sub L/(KrF))/sup 1/3/ approx. = 1.6. One-dimensional Lasnex computer calculations indicate that the laser-accelerated disk constitutes a useful flyer plate even while disassembling under the force of the laser ablation shock. The calculations predict that the shockwave the projectile disk generates in a second (impact) disk located a suitable distance away has a greater amplitude than the laser shock and is considerably more steady, exhibiting little decay in propagating through the second disk.

  19. Analytical models of relativistic accretion disks

    E-Print Network [OSTI]

    Viacheslav V. Zhuravlev

    2015-09-24

    We present not a literature review but a description, as detailed and consistent as possible, of two analytic models of disk accretion onto a rotating black hole: a standard relativistic disk and a twisted relativistic disk. Although one of these models is much older than the other, both are of topical current interest for black hole studies. The way the exposition is presented, the reader with only a limited knowledge of general relativity and relativistic hydrodynamics can --- with little or no use of additional sources -- gain good insight into many technical details lacking in the original papers.

  20. MPEG-aware disk storage system 

    E-Print Network [OSTI]

    Ren, Qian

    2000-01-01

    Disks. Digital Video Standards Multi-ported Disk Storage System. . . . . 3 . 4 . 4 . 5 III MPEG-A WARE DISK STORAGE SYSTEM. IV IMPLEMENTATION BACKGROUND. . . 10 4. 1 ISO 11172 Standard 4. 2 ISO 11172 System. 4. 2. 1 Overview . 4. 2. 2 Start... Code 4. 2. 3 System Bitstream Overview 4. 3 ISO 11172 Video. . 10 . 10 . 10 . 12 . 14 . 16 V IMPLEMENTATION DETAIL 18 5. 1 Software Structure 5. 2 Processing Center. 5. 3 Implemented Modules. 5. 3. 1 Fast-forwarding 5. 3. 2 Quality...

  1. Hydrodynamic turbulence cannot transport angular momentum effectively in astrophysical disks

    E-Print Network [OSTI]

    Ji, Hantao

    magnetorotational instability2 . Cool disks, such as the planet-forming disks of proto- stars, may be too poorly, pipe flows) at sufficiently large Reynolds numbers. Although planet-forming disks have extreme Reynolds in cool disks. Our experiments involved a novel Taylor­Couette apparatus16 . The rotating liquid (water

  2. Migration of Protoplanets in Radiative Disks

    E-Print Network [OSTI]

    Wilhelm Kley; Aurelien Crida

    2008-06-18

    In isothermal disks the migration of protoplanets is directed inward. For small planetary masses the standard type-I migration rates are so fast that this may result in an unrealistic loss of planets into the stars. We investigate the planet-disk interaction in non-isothermal disks and analyze the magnitude and direction of migration for an extended range of planet masses. We have performed detailed two-dimensional numerical simulations of embedded planets including heating/cooling effects as well as radiative diffusion for realistic opacities. In radiative disks, small planets with M_planet < 50 M_Earth do migrate outward with a rate comparable to absolute magnitude of standard type-I migration. For larger masses the migration is inward and approaches the isothermal, type-II migration rate. Our findings are particularly important for the first growth phase of planets and ease the problem of too rapid inward type-I migration.

  3. Observations of Solids in Protoplanetary Disks

    E-Print Network [OSTI]

    Andrews, Sean M

    2015-01-01

    This review addresses the state of research that employs astronomical (remote sensing) observations of solids ("dust") in young circumstellar disks to learn about planet formation. The intention is for it to serve as an accessible, introductory, pedagogical resource for junior scientists interested in the subject. After some historical background and a basic observational primer, the focus is shifted to the three fundamental topics that broadly define the field: (1) demographics -- the relationships between disk properties and the characteristics of their environments and hosts; (2) structure -- the spatial distribution of disk material and its associated physical conditions and composition; and (3) evolution -- the signposts of key changes in disk properties, including the growth and migration of solids and the impact of dynamical interactions with young planetary systems. Based on the state of the art results in these areas, suggestions are made for potentially fruitful lines of work in the near future.

  4. The Kuiper Belt and Other Debris Disks

    E-Print Network [OSTI]

    David Jewitt; Amaya Moro-Martín; Pedro Lacerda

    2008-08-24

    We discuss the current knowledge of the Solar system, focusing on bodies in the outer regions, on the information they provide concerning Solar system formation, and on the possible relationships that may exist between our system and the debris disks of other stars. Beyond the domains of the Terrestrial and giant planets, the comets in the Kuiper belt and the Oort cloud preserve some of our most pristine materials. The Kuiper belt, in particular, is a collisional dust source and a scientific bridge to the dusty "debris disks" observed around many nearby main-sequence stars. Study of the Solar system provides a level of detail that we cannot discern in the distant disks while observations of the disks may help to set the Solar system in proper context.

  5. Hydraulic/Shock-Jumps in Protoplanetary Disks

    E-Print Network [OSTI]

    A. C. Boley; R. H. Durisen

    2006-03-10

    In this paper, we describe the nonlinear outcome of spiral shocks in protoplanetary disks. Spiral shocks, for most protoplanetary disk conditions, create a loss of vertical force balance in the post-shock region and result in rapid expansion of the gas perpendicular to the disk midplane. This expansion has characteristics similar to hydraulic jumps, which occur in incompressible fluids. We present a theory to describe the behavior of these hybrids between shocks and hydraulic jumps (shock bores) and then compare the theory to three-dimensional hydrodynamics simulations. We discuss the fully three-dimensional shock structures that shock bores produce and discuss possible consequences for disk mixing, turbulence, and evolution of solids.

  6. Exact Relativistic Magnetized halos around Rotating Disks

    E-Print Network [OSTI]

    Antonio C. Gutiérrez-Piñeres; Abraão J. S. Capistrano

    2015-05-15

    The exact relativistic treatment of a rotating disk surrounded by a magnetized material halo is presented. The features of the halo and disk are described by the distributional energy-momentum tensor of a general fluid in canonical form. All the relevant quantities and the metric and electromagnetic potentials are exactly determined by an arbitrary harmonic function only. For instance, the generalized Kuzmin-disk potential is used. The particular class of solutions obtained is asymptotically flat and satisfies all the energy conditions. Moreover, the motion of a charged particle on the halo is described. As far as we know, this is the first relativistic model describing analytically the magnetized halo of a rotating disk.

  7. The Onset of Planet Formation in Brown Dwarf Disks

    E-Print Network [OSTI]

    D. Apai; I. Pascucci; J. Bouwman; A. Natta; Th. Henning; C. P. Dullemond

    2005-11-14

    The onset of planet formation in protoplanetary disks is marked by the growth and crystallization of sub-micron-sized dust grains accompanied by dust settling toward the disk mid-plane. Here we present infrared spectra of disks around brown dwarfs and brown dwarf candidates. We show that all three processes occur in such cool disks in a way similar or identical to that in disks around low- and intermediate-mass stars. These results indicate that the onset of planet formation extends to disks around brown dwarfs, suggesting that planet formation is a robust process occurring in most young circumstellar disks.

  8. Dynamics of the Disks of Nearby Galaxies

    E-Print Network [OSTI]

    B. Fuchs

    2008-10-20

    I describe how the dynamics of galactic disks can be inferred by imaging and spectroscopy. Next I demonstrate that the decomposition of the rotation curves of spiral galaxies into the contributions by the various components of the galaxies is highly degenerate. Constraints on the decomposition can be found by considering implications for the dynamics of the galactic disks. An important diagnostic is the Toomre Q stability parameter which controls the stability of a galactic disk against local Jeans collapse. I also show how the density wave theory of galactic spiral arms can be employed to constrain the mass of a galactic disk. Applying both diagnostics to the example of NGC 2985 and discussing also the implied mass-to-light ratio I demonstrate that the inner parts of the galaxy, where the optical disk resides, are dominated by baryons. When I apply this method to the disks of low surface brightness galaxies, I find unexpectedly high mass-to light ratios. These could be explained by population synthesis models which assume a bottom heavy initial mass function similar to the recently proposed `integrated galactic initial mass function'.

  9. Water vapor distribution in protoplanetary disks

    SciTech Connect (OSTI)

    Du, Fujun; Bergin, Edwin A.

    2014-09-01

    Water vapor has been detected in protoplanetary disks. In this work, we model the distribution of water vapor in protoplanetary disks with a thermo-chemical code. For a set of parameterized disk models, we calculate the distribution of dust temperature and radiation field of the disk with a Monte Carlo method, and then solve the gas temperature distribution and chemical composition. The radiative transfer includes detailed treatment of scattering by atomic hydrogen and absorption by water of Ly? photons, since the Ly? line dominates the UV spectrum of accreting young stars. In a fiducial model, we find that warm water vapor with temperature around 300 K is mainly distributed in a small and well-confined region in the inner disk. The inner boundary of the warm water region is where the shielding of UV field due to dust and water itself become significant. The outer boundary is where the dust temperature drops below the water condensation temperature. A more luminous central star leads to a more extended distribution of warm water vapor, while dust growth and settling tends to reduce the amount of warm water vapor. Based on typical assumptions regarding the elemental oxygen abundance and the water chemistry, the column density of warm water vapor can be as high as 10{sup 22} cm{sup –2}. A small amount of hot water vapor with temperature higher than ?300 K exists in a more extended region in the upper atmosphere of the disk. Cold water vapor with temperature lower than 100 K is distributed over the entire disk, produced by photodesorption of the water ice.

  10. Massive Protoplanetary Disks in the Trapezium Region

    E-Print Network [OSTI]

    J. A. Eisner; John M. Carpenter

    2006-01-02

    (abridged) We determine the disk mass distribution around 336 stars in the young Orion Nebula cluster by imaging a 2.5' x 2.5' region in 3 mm continuum emission with the Owens Valley Millimeter Array. For this sample of 336 stars, we observe 3 mm emission above the 3-sigma noise level toward ten sources, six of which have also been detected optically in silhouette against the bright nebular background. In addition, we detect 20 objects that do not correspond to known near-IR cluster members. Comparisons of our measured fluxes with longer wavelength observations enable rough separation of dust emission from thermal free-free emission, and we find substantial dust emission toward most objects. For the ten objects detected at both 3 mm and near-IR wavelengths, eight exhibit substantial dust emission. Excluding the high-mass stars and assuming a gas-to-dust ratio of 100, we estimate circumstellar masses ranging from 0.13 to 0.39 Msun. For the cluster members not detected at 3 mm, images of individual objects are stacked to constrain the mean 3 mm flux of the ensemble. The average flux is detected at the 3-sigma confidence level, and implies an average disk mass of 0.005 Msun, comparable to the minimum mass solar nebula. The percentage of stars in Orion surrounded by disks more massive than ~0.1 Msun is consistent with the disk mass distribution in Taurus, and we argue that massive disks in Orion do not appear to be truncated through close encounters with high-mass stars. Comparison of the average disk mass and number of massive dusty structures in Orion with similar surveys of the NGC 2024 and IC 348 clusters constrains the evolutionary timescales of massive circumstellar disks in clustered environments.

  11. Disk radii and grain sizes in Herschel-resolved debris disks

    SciTech Connect (OSTI)

    Pawellek, Nicole; Krivov, Alexander V. [Astrophysikalisches Institut und Universitätssternwarte, Friedrich-Schiller-Universität Jena, Schillergäßchen 2-3, 07745 Jena (Germany); Marshall, Jonathan P. [School of Physics, University of New South Wales, Sydney NSW 2052 (Australia); Montesinos, Benjamin [Departmento de Astrofísica, Centro de Astrobiología (CAB, CSIC-INTA), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Ábrahám, Péter; Moór, Attila [Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, P.O. Box 67, H-1525 Budapest (Hungary); Bryden, Geoffrey [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Eiroa, Carlos [Departamento de Física Teórica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid (Spain)

    2014-09-01

    The radii of debris disks and the sizes of their dust grains are important tracers of the planetesimal formation mechanisms and physical processes operating in these systems. Here we use a representative sample of 34 debris disks resolved in various Herschel Space Observatory (Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA) programs to constrain the disk radii and the size distribution of their dust. While we modeled disks with both warm and cold components, and identified warm inner disks around about two-thirds of the stars, we focus our analysis only on the cold outer disks, i.e., Kuiper-belt analogs. We derive the disk radii from the resolved images and find a large dispersion for host stars of any spectral class, but no significant trend with the stellar luminosity. This argues against ice lines as a dominant player in setting the debris disk sizes, since the ice line location varies with the luminosity of the central star. Fixing the disk radii to those inferred from the resolved images, we model the spectral energy distribution to determine the dust temperature and the grain size distribution for each target. While the dust temperature systematically increases toward earlier spectral types, the ratio of the dust temperature to the blackbody temperature at the disk radius decreases with the stellar luminosity. This is explained by a clear trend of typical sizes increasing toward more luminous stars. The typical grain sizes are compared to the radiation pressure blowout limit s {sub blow} that is proportional to the stellar luminosity-to-mass ratio and thus also increases toward earlier spectral classes. The grain sizes in the disks of G- to A-stars are inferred to be several times s {sub blow} at all stellar luminosities, in agreement with collisional models of debris disks. The sizes, measured in the units of s {sub blow}, appear to decrease with the luminosity, which may be suggestive of the disk's stirring level increasing toward earlier-type stars. The dust opacity index ? ranges between zero and two, and the size distribution index q varies between three and five for all the disks in the sample.

  12. Viruses in laboratory-reared cactus moth, Cactoblastis cactorum (Lepidoptera: Pyralidae)

    SciTech Connect (OSTI)

    Marti, O.G.; Myers, R.E.; Carpenter, J.E.; Styer, E.L.

    2007-03-15

    The cactus moth, Cactoblastis cactorum (Lepidoptera: Pyralidae: Phycitinae), is a non-native species threatening a variety of native cacti, particularly endangered species of Opuntia (Zimmerman et al. 2001), on the coast of the Gulf of Mexico. Cactoblastis cactorum populations have expanded from Florida northward along the Atlantic coast as far as Charleston, SC, and westward along the Gulf of Mexico to Dauphin Island, south of Mobile, AL. It is feared that further movement to the west will allow C. cactorum to enter the US desert Southwest and Mexico, particularly the latter. Numerous cactus species, especially those of the genera Opuntia and Nopalea, are native to the U.S. and Mexico. Local economies based on agricultural and horticultural uses of cacti could be devastated by C. cactorum (Vigueras and Portillo 2001). A bi-national control program between the US and Mexico is being developed, utilizing the sterile insect technique (SIT). In the SIT program, newly emerged moths are irradiated with a {sup 60}Co source and released to mate with wild individuals. The radiation dose completely sterilizes the females and partially sterilizes the males. When irradiated males mate with wild females, the F1 progeny of these matings are sterile. In order for the SIT program to succeed, large numbers of moths must be reared from egg to adult on artificial diet in a quarantined rearing facility (Carpenter et al. 2001). Irradiated insects must then be released in large numbers at the leading edge of the invasive population and at times which coincide with the presence of wild individuals available for mating. Mortality from disease in the rearing colony disrupts the SIT program by reducing the numbers of insects available for release.

  13. Chemical evolution of protoplanetary disks - the effects of viscous accretion, turbulent mixing and disk winds

    E-Print Network [OSTI]

    Heinzeller, Dominikus; Walsh, Catherine; Millar, Tom J

    2011-01-01

    We calculate the chemical evolution of protoplanetary disks considering radial viscous accretion, vertical turbulent mixing and vertical disk winds. We study the effects on the disk chemical structure when different models for the formation of molecular hydrogen on dust grains are adopted. Our gas-phase chemistry is extracted from the UMIST Database for Astrochemistry (Rate06) to which we have added detailed gas-grain interactions. We use our chemical model results to generate synthetic near- and mid-infrared LTE line emission spectra and compare these with recent Spitzer observations. Our results show that if H2 formation on warm grains is taken into consideration, the H2O and OH abundances in the disk surface increase significantly. We find the radial accretion flow strongly influences the molecular abundances, with those in the cold midplane layers particularly affected. On the other hand, we show that diffusive turbulent mixing affects the disk chemistry in the warm molecular layers, influencing the line ...

  14. ACCEPTED AUTHORS' DRAFT, THE FINAL VERSION TO APPEAR IN THE IEEE/ASME TRANSACTIONS ON MECHATRONICS, VOL. 13, NO. 6, 669677, 2008. 1 Eddy Current Brakes for Haptic Interfaces

    E-Print Network [OSTI]

    Hayward, Vincent

    , VOL. 13, NO. 6, 669­677, 2008. 1 Eddy Current Brakes for Haptic Interfaces: Design, Identification describe the design of an eddy current brake for use as programmable viscous damper for haptic interfaces actuators for haptic interfaces. We overview the governing physical relationships, and describe design

  15. The Galactic thick and thin disks: differences in evolution

    E-Print Network [OSTI]

    T. V. Nykytyuk; T. V. Mishenina

    2006-05-26

    Recent observations demonstrate that the thin and thick disks of the Galaxy have different chemical abundance trends and evolution timescales. The relative abundances of $\\alpha$-elements in the thick Galactic disk are increased relative to the thin disk. Our goal is to investigate the cause of such differences in thick and thin disk abundances. We investigate the chemical evolution of the Galactic disk in the framework of the open two-zone model with gas inflow. The Galactic abundance trends for $\\alpha$-elements (Mg, Si, O) and Fe are predicted for the thin and thick Galactic disks. The star formation histories of the thin and thick disks must have been different and the gas infall must have been more intense during the thick disk evolution that the thin disk evolution.

  16. Three-dimensional modeling of radiative disks in binaries

    E-Print Network [OSTI]

    Picogna, Giovanni

    2013-01-01

    Circumstellar disks in binaries are perturbed by the companion gravity causing significant alterations of the disk morphology. Spiral waves due to the companion tidal force also develop in the vertical direction and affect the disk temperature profile. These effects may significantly influence the process of planet formation. We perform 3D numerical simulations of disks in binaries with different initial dynamical configurations and physical parameters. Our goal is to investigate their evolution and their propensity to grow planets. We use an improved version of the SPH code VINE modified to better account for momentum and energy conservation. The energy equation includes a flux--limited radiative transfer algorithm and the disk cooling is obtained via "boundary particles". We model a system made of star/disk + star/disk where the secondary star (and relative disk) is less massive than the primary. The numerical simulations performed for different values of binary separation and disk density show that the dis...

  17. Captive Rearing Program for Salmon River Chinook Salmon, 2000 Project Progress Report.

    SciTech Connect (OSTI)

    Venditti, David A.

    2002-04-01

    During 2000, the Idaho Department of Fish and Game (IDFG) continued to develop techniques to rear chinook salmon Oncorhynchus tshawytscha to sexual maturity in captivity and to monitor their reproductive performance under natural conditions. Eyed-eggs were collected to establish captive cohorts from three study streams and included 503 eyed-eggs from East Fork Salmon River (EFSR), 250 from the Yankee Fork Salmon River, and 304 from the West Fork Yankee Fork Salmon River (WFYF). After collection, the eyed-eggs were immediately transferred to the Eagle Fish Hatchery, where they were incubated and reared by family group. Juveniles collected the previous summer were PIT and elastomer tagged and vaccinated against vibrio Vibrio spp. and bacterial kidney disease before the majority (approximately 75%) were transferred to the National Marine Fisheries Service, Manchester Marine Experimental Station for saltwater rearing through sexual maturity. Smolt transfers included 158 individuals from the Lemhi River (LEM), 193 from the WFYF, and 372 from the EFSR. Maturing fish transfers from the Manchester facility to the Eagle Fish Hatchery included 77 individuals from the LEM, 45 from the WFYF, and 11 from the EFSR. Two mature females from the WFYF were spawned in captivity with four males in 2000. Only one of the females produced viable eggs (N = 1,266), which were placed in in-stream incubators by personnel from the Shoshone-Bannock Tribe. Mature adults (N = 70) from the Lemhi River were released into Big Springs Creek to evaluate their reproductive performance. After release, fish distributed themselves throughout the study section and displayed a progression of habitat associations and behavior consistent with progressing maturation and the onset of spawning. Fifteen of the 17 suspected redds spawned by captive-reared parents in Big Springs Creek were hydraulically sampled to assess survival to the eyed stage of development. Eyed-eggs were collected from 13 of these, and survival ranged from 0% to 96%, although there was evidence that some eggs had died after reaching the eyed stage. Six redds were capped in an attempt to document fry emergence, but none were collected. A final hydraulic sampling of the capped redds yielded nothing from five of the six, but 75 dead eggs and one dead fry were found in the sixth. Smothering by fine sediment is the suspected cause of the observed mortality between the eyed stage and fry emergence.

  18. Urat Rear Banner Jihe Orient Wind Energy Co Ltd | Open Energy Information

    Open Energy Info (EERE)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels Data Center Home Page on QA:QA J-E-1 SECTION J APPENDIX ECoop IncIowa (Utility Company) JumpGTZ ClimateFeedUrat Rear Banner Jihe Orient Wind

  19. Water vapor distribution in protoplanetary disks

    E-Print Network [OSTI]

    Du, Fujun

    2014-01-01

    Water vapor has been detected in protoplanetary disks. In this work we model the distribution of water vapor in protoplanetary disks with a thermo-chemical code. For a set of parameterized disk models, we calculate the distribution of dust temperature and radiation field of the disk with a Monte Carlo method, and then solve the gas temperature distribution and chemical composition. The radiative transfer includes detailed treatment of scattering by atomic hydrogen and absorption by water of Lyman alpha photons, since the Lyman alpha line dominates the UV spectrum of accreting young stars. In a fiducial model, we find that warm water vapor with temperature around 300 K is mainly distributed in a small and well-confined region in the inner disk. The inner boundary of the warm water region is where the shielding of UV field due to dust and water itself become significant. The outer boundary is where the dust temperature drops below the water condensation temperature. A more luminous central star leads to a more ...

  20. Efficient proton acceleration and focusing by an ultraintense laser interacting with a parabolic double concave target with an extended rear

    SciTech Connect (OSTI)

    Bake, Muhammad Ali; Xie, Bai-Song; Aimidula, Aimierding [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China)] [Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875 (China); Wang, Hong-Yu [Department of Physics, Anshan Normal University, Anshan 114005 (China) [Department of Physics, Anshan Normal University, Anshan 114005 (China); Shanghai Bright-Tech Information Technology Co. Ltd., Shanghai 200136 (China)

    2013-07-15

    A new scheme for acceleration and focusing of protons via an improved parabolic double concave target irradiated by an ultraintense laser pulse is proposed. When an intense laser pulse illuminates a concave target, the hot electrons are concentrated on the focal region of the rear cavity and they form a strong space-charge-separation field, which accelerates the protons. For a simple concave target, the proton energy spectrum becomes very broad outside the rear cavity because of transverse divergence of the electromagnetic fields. However, particle-in-cell simulations show that, when the concave target has an extended rear, the hot electrons along the wall surface induce a transverse focusing sheath field, resulting in a clear enhancement of proton focusing, which makes the lower proton energy spread, while, leads to a little reduction of the proton bunch peak energy.

  1. The orbital evolution of planets in disks

    E-Print Network [OSTI]

    Wilhelm Kley

    2000-04-04

    The orbital parameters of the observed extrasolar planets differ strongly from those of our own solar system. The differences include planets with high masses, small semi-major axis and large eccentricities. We performed numerical computations of embedded planets in disks and follow their mass growth and orbital evolution over several thousand periods. We find that planets do migrate inwards on timescales of about $10^5$ years on nearly circular orbits, during which they may grow up to about 5 Jupiter masses. The interaction of the disk with several planets may halt the migration process and lead to a system similar to the solar planetary system.

  2. Nanosecond cryogenic Yb:YAG disk laser

    SciTech Connect (OSTI)

    Perevezentsev, E A; Mukhin, I B; Kuznetsov, I I; Vadimova, O L; Palashov, O V [Institute of Applied Physics, Russian Academy of Sciences, Nizhnii Novgorod (Russian Federation)

    2014-05-30

    A cryogenic Yb:YAG disk laser is modernised to increase its average and peak power. The master oscillator unit of the laser is considerably modified so that the pulse duration decreases to several nanoseconds with the same pulse energy. A cryogenic disk laser head with a flow-through cooling system is developed. Based on two such laser heads, a new main amplifier is assembled according to an active multipass cell scheme. The total small-signal gain of cryogenic cascades is ?10{sup 8}. (lasers)

  3. Competitive Parallel Disk Prefetching and Buffer Management

    E-Print Network [OSTI]

    Barve, Rakesh; Kallahalla, Mahesh; Varman, Peter J.; Vitter, Jeffrey Scott

    2000-01-01

    Competitive Parallel Disk Prefetching and Buffer Managementa0 Rakesh Barvea1 Mahesh Kallahallaa2 Peter J. Varmana2 Jeffrey Scott Vittera3 rbarve@cs.duke.edu kalla@rice.edu pjv@rice.edu jsv@cs.duke.edu Dept. of CS Dept. of ECE Dept. of ECE Dept. of CS Duke... descriptions of I/O performance metrics, lookahead models, and parallel disk configura- tions are given in section 1.1. Our parallel prefetching algorithms NOM and GREED are described 3 in section 1.2. In section 2, we discuss practical situations in which...

  4. Jets and Outflows From Advective Accretion Disks

    E-Print Network [OSTI]

    Sandip K. Chakrabarti

    2000-12-29

    Jets and outflows must be produced directly from accretion disks and inflows, especially when the central gravitating objects are compact, such as neutron stars and black holes, and themselves are {\\it not} mass losing. Here, we review the formation of jets from advective inflows. We show that the centrifugal pressure supported boundary layer (CENBOL) of the black holes may play crucial role in producing outflows. CENBOL is not present in Keplerian disks. Thus energetic jet formation is directly connected to sub-Keplerian flows close to compact objects.

  5. Radiative Flow in a Luminous Disk

    E-Print Network [OSTI]

    Jun Fukue

    2006-01-07

    Radiatively-driven flow in a luminous disk is examined in the subrelativistic regime of $(v/c)^1$, taking account of radiation transfer. The flow is assumed to be vertical, and the gravity and gas pressure are ignored. When internal heating is dropped, for a given optical depth and radiation pressure at the flow base (disk ``inside''), where the flow speed is zero, the flow is analytically solved under the appropriate boundary condition at the flow top (disk ``surface''), where the optical depth is zero. The loaded mass and terminal speed of the flow are both determined by the initial conditions; the mass-loss rate increases as the initial radiation pressure increases, while the flow terminal speed increases as the initial radiation pressure and the loaded mass decrease. In particular, when heating is ignored, the radiative flux $F$ is constant, and the radiation pressure $P_0$ at the flow base with optical depth $\\tau_0$ is bound in the range of $2/3 flow terminal speed becomes zero, while, in the limit of $cP_0/F = 2/3$, the loaded mass becomes zero and the terminal speed approaches $(3/8)c$, which is the terminal speed above the luminous flat disk under an approximation of the order of $(v/c)^1$. We also examine the case where heating exists, and find that the flow properties are qualitatively similar to the case without heating.

  6. Radiative Flow in a Luminous Disk II

    E-Print Network [OSTI]

    Jun Fukue

    2006-01-07

    Radiatively-driven transfer flow perpendicular to a luminous disk is examined in the subrelativistic regime of $(v/c)^1$, taking into account the gravity of the central object. The flow is assumed to be vertical, and the gas pressure is ignored, while internal heating is assumed to be proportional to the gas density. The basic equations were numerically solved as a function of the optical depth, and the flow velocity, the height, the radiative flux, and the radiation pressure were obtained for a given radius, an initial optical depth, and initial conditions at the flow base (disk ``inside''), whereas the mass-loss rate was determined as an eigenvalue of the boundary condition at the flow top (disk ``surface''). For sufficiently luminous cases, the flow resembles the case without gravity. For less-luminous cases, however, the flow velocity decreases, and the flow would be impossible due to the existence of gravity in the case that the radiative flux is sufficiently small. Application to a supercritical accretion disk with mass loss is briefly discussed.

  7. Coefficient of restitution for viscoelastic disks

    E-Print Network [OSTI]

    Thomas Schwager

    2007-01-08

    The dissipative collision of two identical viscoelastic disks is studied. By using a known law for the elastic part of the interaction force and the viscoelastic damping model an analytical solution for the coefficient of restitution shall be given. The coefficient of restitution depends significantly on the impact velocity. It approaches one for small velocities and decreases for increasing velocities.

  8. Viscosity prescription for gravitationally unstable accretion disks

    E-Print Network [OSTI]

    Rafikov, Roman R

    2015-01-01

    Gravitationally unstable accretion disks emerge in a variety of astrophysical contexts - giant planet formation, FU Orioni outbursts, feeding of AGNs, and the origin of Pop III stars. When a gravitationally unstable disk is unable to cool rapidly it settles into a quasi-stationary, fluctuating gravitoturbulent state, in which its Toomre Q remains close to a constant value Q_0~1. Here we develop an analytical formalism describing the evolution of such a disk, which is based on the assumptions of Q=Q_0 and local thermal equilibrium. Our approach works in the presence of additional sources of angular momentum transport (e.g. MRI), as well as external irradiation. Thermal balance dictates a unique value of the gravitoturbulent stress \\alpha_{gt} driving disk evolution, which is a function of the local surface density and angular frequency. We compare this approach with other commonly used gravitoturbulent viscosity prescriptions, which specify the explicit dependence of stress \\alpha_{gt} on Toomre Q in an ad hoc...

  9. Methanol Masers as Tracers of Circumstellar Disks

    E-Print Network [OSTI]

    R. P. Norris; S. E. Byleveld; P. J. Diamond; S. P. Ellingsen; R. H. Ferris; R. G. Gough; M. J. Kesteven; P. M. McCulloch; C. J. Phillips; J. E. Reynolds; A. K. Tzioumis; Y. Takahashi; E. R. Troup; K. J. Wellington

    1998-06-25

    We show that in many methanol maser sources the masers are located in lines, with a velocity gradient along them which suggests that the masers are situated in edge-on circumstellar, or protoplanetary, disks. We present VLBI observations of the methanol maser source G309.92+0.48, in the 12.2 GHz transition, which confirm previous observations that the masers in this source lie along a line. We show that such sources are not only linear in space but, in many cases, also have a linear velocity gradient. We then model these and other data in both the 6.7 GHz and the 12.2 GHz transition from a number of star formation regions, and show that the observed spatial and velocity distribution of methanol masers, and the derived Keplerian masses, are consistent with a circumstellar disk rotating around an OB star. We consider this and other hypotheses, and conclude that about half of these methanol masers are probably located in edge-on circumstellar disks around young stars. This is of particular significance for studies of circumstellar disks because of the detailed velocity information available from the masers.

  10. Patterned Magnetic Nanostructures and Quantized Magnetic Disks

    E-Print Network [OSTI]

    -increasing demands in data storage and to new applications of magnetic devices in the field of sensors. NewPatterned Magnetic Nanostructures and Quantized Magnetic Disks STEPHEN Y. CHOU Invited Paper, opens up new opportunities for engineering innovative magnetic materials and devices, developing ultra

  11. A journey across the M33 disk

    E-Print Network [OSTI]

    Edvige Corbelli; Laura Magrini; Simon Verley

    2007-12-21

    The Local Group member M33 is a pure disk galaxy bearing no prominent bulge or stellar halo. It constitutes a challenge for any hierarchical galaxy formation theory and an ideal laboratory for studying quiescent star formation. Using multiwavelength observations of the gas and stellar component in this nearby galaxy we are able to constrain the gas accretion and star formation history. In the centermost region we find kinematical evidence of a weak bar, which explains the central light excess and the enhanced metallicity. In the more extended disk the lack of strong gradients of metal and dust abundances supports the picture that the slow radial decline of the star formation rate is due to a change in the large scale disk perturbations: bright HII regions and giant molecular clouds being born only in the inner disk. The analysis of the infrared Spitzer maps has however revealed hundreds of low luminosity star forming sites in places with a variety of dust content. These are essential ingredients for understanding the overall gas to star formation process in M33 and in more distant late type galaxies.

  12. Hydraulic Drivetrain and Regenerative Braking Team 13: Andrew Brown, Karan Desai, Andrew McGrath, Hurst Nuckols, Grant Wilson Adviser: Dr. Andrew Jackson

    E-Print Network [OSTI]

    Carpick, Robert W.

    Hydraulic Drivetrain and Regenerative Braking Team 13: Andrew Brown, Karan Desai, Andrew Mc Pressure Reservior Filter Variable Vane Pump Motor/Pump Hydraulic Accumulators Solenoid Valve Relief Valve Suction Line Since their development in 2006, hydraulic drivetrain systems have gained considerable

  13. Finite element analysis of the effect of up-armouring on the off-road braking and sharp-turn performance

    E-Print Network [OSTI]

    Grujicic, Mica

    Finite element analysis of the effect of up-armouring on the off-road braking and sharp-mobility multi-purpose wheeled vehicle, off-road vehicle performance, finite element modelling and simulations revision for publication on 15 June 2009. DOI: 10.1243/09544070JAUTO1187 Abstract: A comprehensive finite

  14. HI CLOUDS BEYOND THE GALACTIC DISK Felix J. Lockman

    E-Print Network [OSTI]

    Groppi, Christopher

    HI CLOUDS BEYOND THE GALACTIC DISK Felix J. Lockman National Radio Astronomy Observatory, Green parts of the Milky Way the disk­halo interface is composed of many discrete HI clouds. The clouds lie: the structure of the ISM at the disk­halo interface, and a high­velocity HI cloud which appears

  15. On the Solar System-Debris Disk Connecction

    E-Print Network [OSTI]

    Amaya Moro-Martin

    2007-12-14

    This paper emphasizes the connection between solar and extra-solar debris disks: how models and observations of the Solar System are helping us understand the debris disk phenomenon, and vice versa, how debris disks are helping us place our Solar System into context.

  16. THE COLLISIONAL EVOLUTION OF DEBRIS DISKS

    SciTech Connect (OSTI)

    Gaspar, Andras; Rieke, George H.; Balog, Zoltan E-mail: grieke@as.arizona.edu

    2013-05-01

    We explore the collisional decay of disk mass and infrared emission in debris disks. With models, we show that the rate of the decay varies throughout the evolution of the disks, increasing its rate up to a certain point, which is followed by a leveling off to a slower value. The total disk mass falls off {proportional_to}t {sup -0.35} at its fastest point (where t is time) for our reference model, while the dust mass and its proxy-the infrared excess emission-fades significantly faster ({proportional_to}t {sup -0.8}). These later level off to a decay rate of M{sub tot}(t){proportional_to}t {sup -0.08} and M{sub dust}(t) or L{sub ir}(t){proportional_to}t {sup -0.6}. This is slower than the {proportional_to}t {sup -1} decay given for all three system parameters by traditional analytic models. We also compile an extensive catalog of Spitzer and Herschel 24, 70, and 100 {mu}m observations. Assuming a log-normal distribution of initial disk masses, we generate model population decay curves for the fraction of stars harboring debris disks detected at 24 {mu}m. We also model the distribution of measured excesses at the far-IR wavelengths (70-100 {mu}m) at certain age regimes. We show general agreement at 24 {mu}m between the decay of our numerical collisional population synthesis model and observations up to a Gyr. We associate offsets above a Gyr to stochastic events in a few select systems. We cannot fit the decay in the far-infrared convincingly with grain strength properties appropriate for silicates, but those of water ice give fits more consistent with the observations (other relatively weak grain materials would presumably also be successful). The oldest disks have a higher incidence of large excesses than predicted by the model; again, a plausible explanation is very late phases of high dynamical activity around a small number of stars. Finally, we constrain the variables of our numerical model by comparing the evolutionary trends generated from the exploration of the full parameter space to observations. Amongst other results, we show that erosive collisions are dominant in setting the timescale of the evolution and that planetesimals on the order of 100 km in diameter are necessary in the cascades for our population synthesis models to reproduce the observations.

  17. Why Disks Shine: the Transport of Angular Momentum in Hot, Thin Disks

    E-Print Network [OSTI]

    E. T. Vishniac

    1993-09-28

    I review recent work on the radial transport of angular momentum in ionized, Keplerian accretion disks. Proposed mechanisms include hydrodynamic and MHD local instabilities and long range effects mediated by wave transport. The most promising models incorporate the Velikhov-Chandrasekhar instability, caused by an instability of the magnetic field embedded in a differentially rotating disk. This has the important feature that the induced turbulent motions necessarily transport angular momentum outward. By contrast, convective modes may transport angular momentum in either direction. Combining the magnetic field instability with an $\\alpha-\\Omega$ dynamo driven by internal waves leads to a model in which the dimensionless viscosity scales as $(H/r)^{4/3}$. However, this model has a phenomenology which is quite different from the $\\alpha$ disk model. For example, an active disk implies some source of excitation for the internal waves. In binary systems with a mass ratio of order unity the most likely exciting mechanism is a parametric instability due to tidal forces. This implies that in systems where the accretion stream is intermittent, like MV Lyrae or TT Ari, epochs when the mass flow is absent or very small will be epochs in which the disk shrinks and becomes relatively inactive and dark. This model also implies that forced vertical mixing is important, even in convectively stable disks. I discuss various observational tests of this model and the focus of current theoretical work.

  18. An analysis of the annual probability of failure of the waste hoist brake system at the Waste Isolation Pilot Plant (WIPP)

    SciTech Connect (OSTI)

    Greenfield, M.A. [Univ. of California, Los Angeles, CA (United States); Sargent, T.J.

    1995-11-01

    The Environmental Evaluation Group (EEG) previously analyzed the probability of a catastrophic accident in the waste hoist of the Waste Isolation Pilot Plant (WIPP) and published the results in Greenfield (1990; EEG-44) and Greenfield and Sargent (1993; EEG-53). The most significant safety element in the waste hoist is the hydraulic brake system, whose possible failure was identified in these studies as the most important contributor in accident scenarios. Westinghouse Electric Corporation, Waste Isolation Division has calculated the probability of an accident involving the brake system based on studies utilizing extensive fault tree analyses. This analysis conducted for the U.S. Department of Energy (DOE) used point estimates to describe the probability of failure and includes failure rates for the various components comprising the brake system. An additional controlling factor in the DOE calculations is the mode of operation of the brake system. This factor enters for the following reason. The basic failure rate per annum of any individual element is called the Event Probability (EP), and is expressed as the probability of failure per annum. The EP in turn is the product of two factors. One is the {open_quotes}reported{close_quotes} failure rate, usually expressed as the probability of failure per hour and the other is the expected number of hours that the element is in use, called the {open_quotes}mission time{close_quotes}. In many instances the {open_quotes}mission time{close_quotes} will be the number of operating hours of the brake system per annum. However since the operation of the waste hoist system includes regular {open_quotes}reoperational check{close_quotes} tests, the {open_quotes}mission time{close_quotes} for standby components is reduced in accordance with the specifics of the operational time table.

  19. An Adaptive Finite Element Startegy for Analysis of Air Lubrication in the Head-Disk Interface of a Hard Disk

    E-Print Network [OSTI]

    Müftü, Sinan

    An Adaptive Finite Element Startegy for Analysis of Air Lubrication in the Head-Disk Interface, interface de tête-disque KEYWORDS: air lubrication, finite elements, adaptive mesh, head-disk interface #12). Air lubrication between the rotating disk and the slider is critical to maintain this gap; a delicate

  20. Rear-Facing Car Safety Seats: Getting the Message Marilyn J. Bull, MDa, Dennis R. Durbin, MD, MSCEb

    E-Print Network [OSTI]

    COMMENTARY Rear-Facing Car Safety Seats: Getting the Message Right Marilyn J. Bull, MDa, Dennis R and young children regarding the safest way for them to ride in a car. Child fatalities and injuries and research provided by the National High- way Traffic Safety Administration, the car safety seat

  1. Role of Disk models in Indentifying Astrophysical Black Holes

    E-Print Network [OSTI]

    Sandip K. Chakrabarti

    2005-01-14

    We discuss how disk models may limit the scope of identifying astrophysical black holes. We show that the standard Keplerian thin disk model, the thick disk model, slim disks, ADAFs etc. are fundamentally limited. We present the most complete solution to date called the advective accretion disk and discuss how it has the scope to address every observational aspects of a black hole. Though the magnetic field is not fully self-consistently taken care of yet, the details with which the present model can handle various issues successfully are astounding. We present some of the examples.

  2. Rings in the Planetesimal Disk of Beta Pic

    E-Print Network [OSTI]

    P. Kalas; J. Larwood; B. A. Smith; A. Schultz

    2000-01-13

    The nearby main sequence star Beta Pictoris is surrounded by an edge-on disk of dust produced by the collisional erosion of larger planetesimals. Here we report the discovery of substructure within the northeast extension of the disk midplane that may represent an asymmetric ring system around Beta Pic. We present a dynamical model showing that a close stellar flyby with a quiescient disk of planetesimals can create such rings, along with previously unexplained disk asymmetries. Thus we infer that Beta Pic's planetesimal disk was highly disrupted by a stellar encounter in the last hundred thousand years.

  3. Synthetic spectra of accretion disks in DQ Her binaries

    SciTech Connect (OSTI)

    Mauche, C.W.; Miller, G.S. (Los Alamos National Lab., NM (USA)); Raymond, J.C. (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (USA)); Lamb, F.K. (Illinois Univ., Urbana, IL (USA). Dept. of Physics)

    1989-01-01

    We explore the effect of the stellar magnetic field on the spectrum of the disk by comparing synthesized disk spectra to the observed ultraviolet spectrum of the well-studied DQ Her binary GK Per. We use the parameterized disk-magnetosphere interaction models of Miller and Lamb to calculate the radius of the inner edge of the disk and the local heating rate within the disk as a function of radius. With appropriate choices of parameters, these models can describe the models of Ghosh and Lamb and Wang. Once the local heating rate is determined, we assign an effective temperature to each of a series of disk annuli. The disk spectrum is then calculated by summing the flux contributed by each annulus, assuming that each annulus has the same spectrum as a main-sequence star with the assigned effective temperature. 5 refs., 2 figs.

  4. Eccentric Jupiters via Disk-Planet Interactions

    E-Print Network [OSTI]

    Duffell, Paul C

    2015-01-01

    Numerical hydrodynamics calculations are performed to determine conditions under which giant planet eccentricities can be excited by parent gas disks. Unlike in other studies, Jupiter-mass planets are found to have their eccentricities amplified --- provided their orbits start eccentric. We disentangle the web of co-rotation, co-orbital, and external resonances to show that this finite-amplitude instability is consistent with that predicted analytically. Ellipticities can grow until they reach of order the disk's aspect ratio, beyond which the external Lindblad resonances that excite eccentricity are weakened by the planet's increasingly supersonic epicyclic motion. Forcing the planet to still larger eccentricities causes catastrophic eccentricity damping as the planet collides into gap walls. If the eccentricity driving documented here survives in 3D, it may explain the low-to-moderate eccentricities $\\lesssim 0.1$ exhibited by many giant planets (including Jupiter and Saturn), especially those without plane...

  5. Massive Disks in Low Surface Brightness Galaxies

    E-Print Network [OSTI]

    B. Fuchs

    2002-09-09

    An update of the set of low surface brightness galaxies is presented which can be used to set constraints on the otherwise ambiguous decompositions of their rotation curves into contributions due to the various components of the galaxies. The selected galaxies show all clear spiral structure and arguments of density wave theory of galactic spiral arms are used to estimate the masses of the galactic disks. Again these estimates seem to indicate that the disks of low surface brightness galaxies might be much more massive than currently thought. This puzzling result contradicts stellar population synthesis models. This would mean also that low surface brightness galaxies are not dominated by dark matter in their inner parts.

  6. Terabyte IDE RAID-5 Disk Arrays

    E-Print Network [OSTI]

    D. A. Sanders; L. M. Cremaldi; V. Eschenburg; R. Godang; C. N. Lawrence; C. Riley; D. J. Summers; D. L. Petravick

    2003-06-04

    High energy physics experiments are currently recording large amounts of data and in a few years will be recording prodigious quantities of data. New methods must be developed to handle this data and make analysis at universities possible. We examine some techniques that exploit recent developments in commodity hardware. We report on tests of redundant arrays of integrated drive electronics (IDE) disk drives for use in offline high energy physics data analysis. IDE redundant array of inexpensive disks (RAID) prices now are less than the cost per terabyte of million-dollar tape robots! The arrays can be scaled to sizes affordable to institutions without robots and used when fast random access at low cost is important.

  7. Galactosynthesis: Halo Histories, Star Formation, and Disks

    E-Print Network [OSTI]

    Ari Buchalter; Raul Jimenez; Marc Kamionkowski

    2000-06-01

    We investigate the effects of a variety of ingredients that must enter into a realistic model for disk-galaxy formation, focusing primarily on the Tully-Fisher (TF) relation and its scatter in several wavebands. Our main findings are: (a) the slope, normalization, and scatter of the TF relation across various wavebands is determined {\\em both} by halo properties and star formation in the disk; (b) TF scatter owes primarily to the spread in formation redshifts. The scatter can be measurably reduced by chemical evolution, and also in some cases by the weak anti-correlation between peak height and spin; (c) multi-wavelength constraints can be important in distinguishing between models which appear to fit the TF relation in I or K; (d) successful models seem to require that the bulk of disk formation cannot occur too early (z>2) or too late (z<0.5), and are inconsistent with high values of $\\Omega_0$; (e) a realistic model with the above ingredients can reasonably reproduce the observed z=0 TF relation in {\\em all} bands (B, R, I, and K). It can also account for the z=1 B-band TF relation and yield rough agreement with the local B and K luminosity functions and B-band surface-brightness--magnitude relation. The remarkable agreement with observations suggests that the amount of gas that is expelled or poured into a disk galaxy must be small, and that the specific angular momentum of the baryons must roughly equal that of the halo; there is little room for angular momentum transfer. In an appendix we present analytic fits to stellar-population synthesis models.

  8. Liouville Quantum Gravity on the unit disk

    E-Print Network [OSTI]

    Yichao Huang; Rémi Rhodes; Vincent Vargas

    2015-02-15

    Our purpose is to pursue the rigorous construction of Liouville Quantum Field Theory on Riemann surfaces initiated by F. David, A. Kupiainen and the last two authors in the context of the Riemann sphere and inspired by the 1981 seminal work by Polyakov. In this paper, we investigate the case of simply connected domains with boundary. We also make precise conjectures about the relationship of this theory to scaling limits of random planar maps with boundary conformally embedded onto the disk.

  9. Large vortex state in ferromagnetic disks

    E-Print Network [OSTI]

    Metlov, Konstantin L

    2013-01-01

    Magnetic vortices in soft ferromagnetic nano-disks have been extensively studied for at least several decades both for their fundamental (as a "live" macroscopic realization of a field theory model of an elementary particle) as well as applied value for high-speed high-density power-independent information storage. Here it is shown that there is another vortex state in nano-scale ferromagnetic disks of several exchange lengths in size. The energy of this large vortex state is computed numerically (within the framework of Magnetism@home distributed computing project) and its stability is studied analytically, which allows to plot it on magnetic phase diagram. It is the ground state of cylinders of certain sizes and is metastable in a wider set of geometries. Large vortices exist on par with classical ones, while being separated by an energy barrier, controllable by tuning the geometry and material of ferromagnetic disk. This state can be an excellent candidate for magnetic information storage not only because ...

  10. Molecular emission from GG Car's circumbinary disk

    E-Print Network [OSTI]

    Kraus, Michaela; Nickeler, Dieter; Muratore, Florencia; Fernandes, Marcelo Borges; Aret, Anna; Cidale, Lydia; de Wit, Willem-Jan

    2012-01-01

    The appearance of the B[e] phenomenon in evolved massive stars such as B[e] supergiants is still a mystery. While these stars are generally found to have disks that are cool and dense enough for efficient molecule and dust condensation, the origin of the disk material is still unclear. We aim at studying the kinematics and origin of the disk in the eccentric binary system GG Car, whose primary component is proposed to be a B[e] supergiant. Based on medium- and high-resolution near-infrared spectra we analyzed the CO-band emission detected from GG Car. The complete CO-band structure delivers information on the density and temperature of the emitting region, and the detectable 13CO bands allow us to constrain the evolutionary phase. In addition, the kinematics of the CO gas can be extracted from the shape of the first 12CO band head. We find that the CO gas is located in a ring surrounding the eccentric binary system, and its kinematics agrees with Keplerian rotation with a velocity, projected to the line of si...

  11. Stellar Disk Truncations: Where do we stand ?

    E-Print Network [OSTI]

    M. Pohlen; J. E. Beckman; S. Huettemeister; J. H. Knapen; P. Erwin; R. -J. Dettmar

    2004-07-12

    In the light of several recent developments we revisit the phenomenon of galactic stellar disk truncations. Even 25 years since the first paper on outer breaks in the radial light profiles of spiral galaxies, their origin is still unclear. The two most promising explanations are that these 'outer edges' either trace the maximum angular momentum during the galaxy formation epoch, or are associated with global star formation thresholds. Depending on their true physical nature, these outer edges may represent an improved size characteristic (e.g., as compared to D_25) and might contain fossil evidence imprinted by the galaxy formation and evolutionary history. We will address several observational aspects of disk truncations: their existence, not only in normal HSB galaxies, but also in LSB and even dwarf galaxies; their detailed shape, not sharp cut-offs as thought before, but in fact demarcating the start of a region with a steeper exponential distribution of starlight; their possible association with bars; as well as problems related to the line-of-sight integration for edge-on galaxies (the main targets for truncation searches so far). Taken together, these observations currently favour the star-formation threshold model, but more work is necessary to implement the truncations as adequate parameters characterising galactic disks.

  12. The chemistry of multiply deuterated molecules in protoplanetary disks. I. The outer disk

    E-Print Network [OSTI]

    K. Willacy

    2007-01-16

    We present new models of the deuterium chemistry in protoplanetary disks, including, for the first time, multiply deuterated species. We use these models to explore whether observations in combination with models can give us clues as to which desorption processes occur in disks. We find, in common with other authors, that photodesorption can allow strongly bound molecules such as HDO to exist in the gas phase in a layer above the midplane. Models including this process give the best agreement with the observations. In the midplane, cosmic ray heating can desorb weakly bound molecules such as CO and N$_2$. We find the observations suggest that N$_2$ is gaseous in this region, but that CO must be retained on the grains to account for the observed DCO$^+$/HCO$^+$. This could be achieved by CO having a higher binding energy than N$_2$ (as may be the case when these molecules are accreted onto water ice) or by a smaller cosmic ray desorption rate for CO than assumed here, as suggested by recent theoretical work. For gaseous molecules the calculated deuteration can be greatly changed by chemical processing in the disk from the input molecular cloud values. On the grains singly deuterated species tend to retain the D/H ratio set in the molecular cloud, whereas multiply deuterated species are more affected by the disk chemistry. Consequently the D/H ratios observed in comets may be partly set in the parent cloud and partly in the disk, depending on the molecule.

  13. On the Steady Nature of Line-Driven Disk Winds

    E-Print Network [OSTI]

    Nicolas A. Pereyra; Stanley P. Owocki; D. John Hillier; David A. Turnshek

    2003-11-11

    We perform an analytic investigation of the stability of line-driven disk winds, independent of hydrodynamic simulations. Our motive is to determine whether or not line-driven disk winds can account for the wide/broad UV resonance absorption lines seen in cataclysmic variables (CVs) and quasi-stellar objects (QSOs). In both CVs and QSOs observations generally indicate that the absorption arising in the outflowing winds has a steady velocity structure on time scales exceeding years (for CVs) and decades (for QSOs). However, published results from hydrodynamic simulations of line-driven disk winds are mixed, with some researchers claiming that the models are inherently unsteady, while other models produce steady winds. The analytic investigation presented here shows that if the accretion disk is steady, then the line-driven disk wind emanating from it can also be steady. In particular, we show that a gravitational force initially increasing along the wind streamline, which is characteristic of disk winds, does not imply an unsteady wind. The steady nature of line-driven disk winds is consistent with the 1D streamline disk-wind models of Murray and collaborators and the 2.5D time-dependent models of Pereyra and collaborators. This paper emphasizes the underlying physics behind the steady nature of line-driven disk winds using mathematically simple models that mimic the disk environment

  14. ORBITAL MIGRATION OF PROTOPLANETS IN A MARGINALLY GRAVITATIONALLY UNSTABLE DISK

    SciTech Connect (OSTI)

    Boss, Alan P.

    2013-02-20

    Core accretion and disk instability require giant protoplanets to form in the presence of disk gas. Protoplanet migration models generally assume disk masses low enough that the disk's self-gravity can be neglected. However, disk instability requires a disk massive enough to be marginally gravitationally unstable (MGU). Even for core accretion, an FU Orionis outburst may require a brief MGU disk phase. We present a new set of three-dimensional, gravitational radiation hydrodynamics models of MGU disks with multiple protoplanets, which interact gravitationally with the disk and with each other, including disk gas mass accretion. Initial protoplanet masses are 0.01 to 10 M {sub Circled-Plus} for core accretion models, and 0.1 to 3 M {sub Jup} for Nice scenario models, starting on circular orbits with radii of 6, 8, 10, or 12 AU, inside a 0.091 M {sub Sun} disk extending from 4 to 20 AU around a 1 M {sub Sun} protostar. Evolutions are followed for up to {approx}4000 yr and involve phases of relative stability (e {approx} 0.1) interspersed with chaotic phases (e {approx} 0.4) of orbital interchanges. The 0.01 to 10 M {sub Circled-Plus} cores can orbit stably for {approx}1000 yr: monotonic inward or outward orbital migration of the type seen in low mass disks does not occur. A system with giant planet masses similar to our solar system (1.0, 0.33, 0.1, 0.1 M {sub Jup}) was stable for over 1000 yr, and a Jupiter-Saturn-like system was stable for over 3800 yr, implying that our giant planets might well survive an MGU disk phase.

  15. Nucleosynthesis in the accretion disks of Type II collapsars

    E-Print Network [OSTI]

    Indrani Banerjee; Banibrata Mukhopadhyay

    2013-05-08

    We investigate nucleosynthesis inside the gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, the core collapse of massive stars first leads to the formation of a proto-neutron star and a mild supernova explosion is driven. However, this supernova ejecta lack momentum and falls back onto the neutron star which gets transformed to a stellar mass black hole. In order to study the hydrodynamics and nucleosynthesis of such an accretion disk formed from the fallback material of the supernova ejecta, we use the well established hydrodynamic models. In such a disk neutrino cooling becomes important in the inner disk where the temperature and density are higher. Higher the accretion rate (dot{M}), higher is the density and temperature in the disks. In this work we deal with accretion disks with relatively low accretion rates: 0.001 M_sun s^{-1} \\lesssim dot{M} \\lesssim 0.01 M_sun s^{-1} and hence these disks are predominantly advection dominated. We use He-rich and Si-rich abundances as the initial condition of nucleosynthesis at the outer disk, and being equipped with the disk hydrodynamics and the nuclear network code, we study the abundance evolution as matter inflows and falls into the central object. We investigate the variation in the nucleosynthesis products in the disk with the change in the initial abundance at the outer disk and also with the change in the mass accretion rate. We report the synthesis of several unusual nuclei like {31}P, {39}K, {43}Sc, {35}Cl, and various isotopes of titanium, vanadium, chromium, manganese and copper. We also confirm that isotopes of iron, cobalt, nickel, argon, calcium, sulphur and silicon get synthesized in the disk, as shown by previous authors. Much of these heavy elements thus synthesized are ejected from the disk via outflows and hence they should leave their signature in observed data.

  16. Composite polymer: Glass edge cladding for laser disks

    DOE Patents [OSTI]

    Powell, H.T.; Wolfe, C.A.; Campbell, J.H.; Murray, J.E.; Riley, M.O.; Lyon, R.E.; Jessop, E.S.

    1987-11-02

    Large neodymium glass laser disks for disk amplifiers such as those used in the Nova laser require an edge cladding which absorbs at 1 micrometer. This cladding prevents edge reflections from causing parasitic oscillations which would otherwise deplete the gain. Nova now utilizes volume-absorbing monolithic-glass claddings which are fused at high temperature to the disks. These perform quite well but are expensive to produce. Absorbing glass strips are adhesively bonded to the edges of polygonal disks using a bonding agent whose index of refraction matches that of both the laser and absorbing glass. Optical finishing occurs after the strips are attached. Laser disks constructed with such claddings have shown identical gain performance to the previous Nova disks and have been tested for hundreds of shots without significant degradation. 18 figs.

  17. Composite polymer-glass edge cladding for laser disks

    DOE Patents [OSTI]

    Powell, Howard T. (Livermore, CA); Riley, Michael O. (San Ramon, CA); Wolfe, Charles R. (Palo Alto, CA); Lyon, Richard E. (Livermore, CA); Campbell, John H. (Livermore, CA); Jessop, Edward S. (Tracy, CA); Murray, James E. (Livermore, CA)

    1989-01-01

    Large neodymium glass laser disks for disk amplifiers such as those used in the Nova laser require an edge cladding which absorbs at 1 micrometer. This cladding prevents edge reflections from causing parasitic oscillations which would otherwise deplete the gain. Nova now utilizes volume-absorbing monolithic-glass claddings which are fused at high temperature to the disks. These perform quite well but are expensive to produce. Absorbing glass strips are adhesively bonded to the edges of polygonal disks using a bonding agent whose index of refraction matches that of both the laser and absorbing glass. Optical finishing occurs after the strips are attached. Laser disks constructed with such claddings have shown identical gain performance to the previous Nova disks and have been tested for hundreds of shots without significant degradation.

  18. Accretion disk radiation dynamics and the cosmic battery

    SciTech Connect (OSTI)

    Koutsantoniou, Leela E.; Contopoulos, Ioannis E-mail: icontop@academyofathens.gr

    2014-10-10

    We investigate the dynamics of radiation in the surface layers of an optically thick astrophysical accretion disk around a Kerr black hole. The source of the radiation is the surface of the accretion disk itself, and not a central object as in previous studies of the Poynting-Robertson effect. We generate numerical sky maps from photon trajectories that originate on the surface of the disk as seen from the inner edge of the disk at the position of the innermost stable circular orbit. We investigate several accretion disk morphologies with a Shakura-Sunyaev surface temperature distribution. Finally, we calculate the electromotive source of the Cosmic Battery mechanism around the inner edge of the accretion disk and obtain characteristic timescales for the generation of astrophysical magnetic fields.

  19. THE KOZAI-LIDOV MECHANISM IN HYDRODYNAMICAL DISKS

    SciTech Connect (OSTI)

    Martin, Rebecca G.; Nixon, Chris; Armitage, Philip J. [JILA, University of Colorado and NIST, UCB 440, Boulder, CO 80309 (United States); Lubow, Stephen H. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Price, Daniel J. [Monash Centre for Astrophysics (MoCA), School of Mathematical Sciences, Monash University, Clayton, Vic. 3800 (Australia); Do?an, Suzan [Department of Astronomy and Space Sciences, University of Ege, Bornova, 35100 ?zmir (Turkey); King, Andrew [Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)

    2014-09-10

    We use three-dimensional hydrodynamical simulations to show that a highly misaligned accretion disk around one component of a binary system can exhibit global Kozai-Lidov cycles, where the inclination and eccentricity of the disk are interchanged periodically. This has important implications for accreting systems on all scales, for example, the formation of planets and satellites in circumstellar and circumplanetary disks, outbursts in X-ray binary systems, and accretion onto supermassive black holes.

  20. MEASURING PROTOPLANETARY DISK ACCRETION WITH H I PFUND {beta}

    SciTech Connect (OSTI)

    Salyk, Colette [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Herczeg, Gregory J. [Kavli Institute for Astronomy and Astrophysics at Peking University, Yi He Yuan Lu 5, Hai Dian Qu, Beijing 100871 (China); Brown, Joanna M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Blake, Geoffrey A. [Division of Geological and Planetary Sciences, Mail Code 150-21, California Institute of Technology, Pasadena, CA 91125 (United States); Pontoppidan, Klaus M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Van Dishoeck, Ewine F., E-mail: csalyk@noao.edu [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)

    2013-05-20

    In this work, we introduce the use of H I Pfund {beta} (Pf{beta}; 4.6538 {mu}m) as a tracer of mass accretion from protoplanetary disks onto young stars. Pf{beta} was serendipitously observed in NIRSPEC and CRIRES surveys of CO fundamental emission, amounting to a sample size of 120 young stars with detected Pf{beta} emission. Using a subsample of disks with previously measured accretion luminosities, we show that Pf{beta} line luminosity is well correlated with accretion luminosity over a range of at least three orders of magnitude. We use this correlation to derive accretion luminosities for all 120 targets, 65 of which are previously unreported in the literature. The conversion from accretion luminosity to accretion rate is limited by the availability of stellar mass and radius measurements; nevertheless, we also report accretion rates for 67 targets, 16 previously unmeasured. Our large sample size and our ability to probe high extinction values allow for relatively unbiased comparisons between different types of disks. We find that the transitional disks in our sample have lower than average Pf{beta} line luminosities, and thus accretion luminosities, at a marginally significant level. We also show that high Pf{beta} equivalent width is a signature of transitional disks with high inner disk gas/dust ratios. In contrast, we find that disks with signatures of slow disk winds have Pf{beta} luminosities comparable to those of other disks in our sample. Finally, we investigate accretion rates for stage I disks, including significantly embedded targets. We find that stage I and stage II disks have statistically indistinguishable Pf{beta} line luminosities, implying similar accretion rates, and that the accretion rates of stage I disks are too low to be consistent with quiescent accretion. Our results are instead consistent with both observational and theoretical evidence that stage I objects experience episodic, rather than quiescent, accretion.

  1. Disk Winds and the Accretion--Outflow Connection

    E-Print Network [OSTI]

    Arieh Konigl; Ralph E. Pudritz

    1999-03-11

    We review recent observational and theoretical results on the relationship between circumstellar accretion disks and jets in young stellar objects. We then present a theoretical framework that interprets jets as accretion-powered, centrifugally driven winds from magnetized accretion disks. Recent progress in the numerical simulation of such outflows is described. We also discuss the structure of the underlying magnetized protostellar disks, emphasizing the role that large-scale, open magnetic fields can play in angular momentum transport.

  2. We Brake for Mars Hi! My name is Mike Meacham. I'm an engineer here at the Jet Propulsion Laboratory and

    E-Print Network [OSTI]

    Waliser, Duane E.

    We Brake for Mars Hi! My name is Mike Meacham. I'm an engineer here at the Jet Propulsion a really big parachute. To make these large parachutes you have to test them before you go. You need a way've got to test big here on Earth. You got to be a little crazy sometimes if you want to do crazy things

  3. Testing Disk Instability Models for Giant Planet Formation

    E-Print Network [OSTI]

    Alan P. Boss

    2007-04-09

    Disk instability is an attractive yet controversial means for the rapid formation of giant planets in our solar system and elsewhere. Recent concerns regarding the first adiabatic exponent of molecular hydrogen gas are addressed and shown not to lead to spurious clump formation in the author's disk instability models. A number of disk instability models have been calculated in order to further test the robustness of the mechanism, exploring the effects of changing the pressure equation of state, the vertical temperature profile, and other parameters affecting the temperature distribution. Possible reasons for differences in results obtained by other workers are discussed. Disk instability remains as a plausible formation mechanism for giant planets.

  4. Adaptive Rejection of Narrow Band Disturbance in Hard Disk Drives

    E-Print Network [OSTI]

    Zheng, Qixing

    2009-01-01

    on Advanced Intelligent Mechatronics, Monterey, CA, pp.13-C. Bi. Hard Disk Drive: Mechatronics and Control. CRC Press,new servo method in mechatronics. Trans. Of Japanese Society

  5. Giant planet formation from disk instability; cooling and heating

    E-Print Network [OSTI]

    Lucio Mayer; James Wadsley; Thomas Quinn; Joachim Stadel

    2003-11-03

    We present the results of high resolution SPH simulations of the evolution of gravitationally unstable protoplanetary disks. We report on calculations in which the disk is evolved using a locally isothermal or adiabatic equation of state (with shock heating), and also on new simulations in which cooling and heating by radiation are explicitly modeled. We find that disks with a minimum Toomre parameter $cooling time comparable to the orbital time is needed to achieve fragmentation, for disk masses in the range $0.08-0.1 M_{\\odot}$. After about 30 orbital times, merging between the bound condensations always leads to 2-3 protoplanets on quite eccentric orbits.

  6. Spectral Softening due to Winds in Accretion Disks

    E-Print Network [OSTI]

    Sandip K. Chakrabarti

    1998-12-06

    Accretion flows may produce profuse winds when they have positive specific energy. Winds deplete matter from the inner region of the disk and makes the inner region thinner, optically. Since there are fewer electrons in this region, it becomes easier to Comptonize this part by the soft photons which are intercepted from the Keplerian disk farther out. We present a self-consistent picture of winds from an accretion disk and show how the spectra of the disk is softened due to the outflowing wind.

  7. High average power scaleable thin-disk laser

    DOE Patents [OSTI]

    Beach, Raymond J. (Livermore, CA); Honea, Eric C. (Sunol, CA); Bibeau, Camille (Dublin, CA); Payne, Stephen A. (Castro Valley, CA); Powell, Howard (Livermore, CA); Krupke, William F. (Pleasanton, CA); Sutton, Steven B. (Manteca, CA)

    2002-01-01

    Using a thin disk laser gain element with an undoped cap layer enables the scaling of lasers to extremely high average output power values. Ordinarily, the power scaling of such thin disk lasers is limited by the deleterious effects of amplified spontaneous emission. By using an undoped cap layer diffusion bonded to the thin disk, the onset of amplified spontaneous emission does not occur as readily as if no cap layer is used, and much larger transverse thin disks can be effectively used as laser gain elements. This invention can be used as a high average power laser for material processing applications as well as for weapon and air defense applications.

  8. TIDAL DISRUPTION FLARES: THE ACCRETION DISK PHASE

    SciTech Connect (OSTI)

    Montesinos Armijo, Matias; De Freitas Pacheco, Jose A. [Observatoire de la Cote d'Azur, Laboratoire Cassiopee, Universite de Nice Sophia-Antipolis Bd de l'Observatoire, BP 4229, 06304 Nice Cedex 4 (France)

    2011-08-01

    The evolution of an accretion disk, formed as a consequence of the disruption of a star by a black hole, is followed by solving numerically hydrodynamic equations. The present investigation aims to study the dependence of resulting light curves on dynamical and physical properties of such a transient disk during its existence. One of the main results derived from our simulations is that blackbody fits of X-ray data tend to overestimate the true mean disk temperature. In fact, the temperature derived from blackbody fits should be identified with the color X-ray temperature rather than the average value derived from the true temperature distribution along the disk. The time interval between the beginning of the circularization of the bound debris and the beginning of the accretion process by the black hole is determined by the viscous (or accretion) timescale, which also fixes the rising part of the resulting light curve. The luminosity peak coincides with the beginning of matter accretion by the black hole and the late evolution of the light curve depends on the evolution of the debris fallback rate. Peak bolometric luminosities are in the range 10{sup 45}-10{sup 46} erg s{sup -1}, whereas peak luminosities in soft X-rays (0.2-2.0 keV) are typically one order of magnitude lower. The typical timescale derived from our preferred models for the flare luminosity to decay by two orders of magnitude is about 3-4 yr. Predicted soft X-ray light curves reproduce quite well data on galaxies in which a variable X-ray emission possibly related to a tidal event was detected. In the cases of NGC 3599 and IC 3599, data are reproduced well by models defined by a black hole with mass {approx}10{sup 7} M{sub sun} and a disrupted star of about 1 solar mass. The X-ray variation observed in XMMSL1 is consistent with a model defined by a black hole with mass {approx}3 x 10{sup 6} M{sub sun} and a disrupted star of 1 solar mass, while that observed in the galaxy situated in the cluster A1689 is consistent with a model including a black hole of {approx}10{sup 7} M{sub sun} and a disrupted star of {approx}0.5 M{sub sun}.

  9. Hydrodynamic Models of Line-Driven Accretion Disk Winds II: Adiabatic Winds from Nonisothermal Disks

    E-Print Network [OSTI]

    Nicolas Antonio Pereyra; Timothy R. Kallman; John M. Blondin

    2000-11-03

    We present here numerical hydrodynamic simulations of line-driven accretion disk winds in cataclysmic variable systems. We calculate wind mass-loss rate, terminal velocities, and line profiles for CIV (1550 A) for various viewing angles. The models are 2.5-dimensional, include an energy balance condition, and calculate the radiation field as a function of position near an optically thick accretion disk. The model results show that centrifugal forces produce collisions of streamlines in the disk wind which in turn generate an enhanced density region, underlining the necessity of two dimensional calculations where these forces may be represented. For disk luminosity Ldisk = Lsun, white dwarf mass Mwd = 0.6 Msun, and white dwarf radii Rwd = 0.01 Rsun, we obtain a wind mass-loss rate of dMwind/dt = 8.0E-12 Msun/yr, and a terminal velocity of ~3000 km/s. The line profiles we obtain are consistent with observations in their general form, in particular in the maximum absorption at roughly half the terminal velocity for the blue-shifted component, in the magnitudes of the wind velocities implied by the absorption components, in the FWHM of the emission components, and in the strong dependence in inclination angle.

  10. Hydrodynamic Models of Line-Driven Accretion Disk Winds II Adiabatic Winds from Nonisothermal Disks

    E-Print Network [OSTI]

    Pereyra, N A; Blondin, J M; Pereyra, Nicolas Antonio; Kallman, Timothy R.; Blondin, John M.

    2000-01-01

    We present here numerical hydrodynamic simulations of line-driven accretion disk winds in cataclysmic variable systems. We calculate wind mass-loss rate, terminal velocities, and line profiles for CIV (1550 A) for various viewing angles. The models are 2.5-dimensional, include an energy balance condition, and calculate the radiation field as a function of position near an optically thick accretion disk. The model results show that centrifugal forces produce collisions of streamlines in the disk wind which in turn generate an enhanced density region, underlining the necessity of two dimensional calculations where these forces may be represented. For disk luminosity Ldisk = Lsun, white dwarf mass Mwd = 0.6 Msun, and white dwarf radii Rwd = 0.01 Rsun, we obtain a wind mass-loss rate of dMwind/dt = 8.0E-12 Msun/yr, and a terminal velocity of ~3000 km/s. The line profiles we obtain are consistent with observations in their general form, in particular in the maximum absorption at roughly half the terminal velocity ...

  11. Resolved imaging of the HR 8799 Debris disk with Herschel

    SciTech Connect (OSTI)

    Matthews, Brenda; Booth, Mark; Broekhoven-Fiene, Hannah; Marois, Christian [National Research Council of Canada Herzberg Astronomy and Astrophsyics, 5071 W. Saanich Road, Victoria, BC, V9E 2E7 (Canada); Kennedy, Grant; Wyatt, Mark [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Sibthorpe, Bruce [SRON Netherlands Institute for Space Research, P.O. Box 800, NL-9700 AV Groningen (Netherlands); Macintosh, Bruce [Lawrence Livermore National Labs, 7000 East Ave, Livermore, CA 94550 (United States)

    2014-01-01

    We present Herschel far-infrared and submillimeter maps of the debris disk associated with the HR 8799 planetary system. We resolve the outer disk emission at 70, 100, 160, and 250 ?m and detect the disk at 350 and 500 ?m. A smooth model explains the observed disk emission well. We observe no obvious clumps or asymmetries associated with the trapping of planetesimals that is a potential consequence of planetary migration in the system. We estimate that the disk eccentricity must be <0.1. As in previous work by Su et al., we find a disk with three components: a warm inner component and two outer components, a planetesimal belt extending from 100 to 310 AU, with some flexibility (±10 AU) on the inner edge, and the external halo that extends to ?2000 AU. We measure the disk inclination to be 26° ± 3° from face-on at a position angle of 64° E of N, establishing that the disk is coplanar with the star and planets. The spectral energy distribution of the disk is well fit by blackbody grains whose semi-major axes lie within the planetesimal belt, suggesting an absence of small grains. The wavelength at which the spectrum steepens from blackbody, 47 ± 30 ?m, however, is short compared with other A star debris disks, suggesting that there are atypically small grains likely populating the halo. The PACS longer wavelength data yield a lower disk color temperature than do MIPS data (24 and 70 ?m), implying two distinct halo dust-grain populations.

  12. Does the debris disk around HD 32297 contain cometary grains?

    SciTech Connect (OSTI)

    Rodigas, Timothy J.; Hinz, Philip M.; Bailey, Vanessa; Defrere, Denis; Leisenring, Jarron; Schneider, Glenn; Skemer, Andrew J.; Vaitheeswaran, Vidhya; Debes, John H.; Mamajek, Eric E.; Pecaut, Mark J.; Currie, Thayne; De Rosa, Robert J.; Ward-Duong, Kimberly; Hill, John M.; Skrutskie, Michael

    2014-03-01

    We present an adaptive optics imaging detection of the HD 32297 debris disk at L' (3.8 ?m) obtained with the LBTI/LMIRcam infrared instrument at the Large Binocular Telescope. The disk is detected at signal-to-noise ratio per resolution element ?3-7.5 from ?0.''3 to 1.''1 (30-120 AU). The disk at L' is bowed, as was seen at shorter wavelengths. This likely indicates that the disk is not perfectly edge-on and contains highly forward-scattering grains. Interior to ?50 AU, the surface brightness at L' rises sharply on both sides of the disk, which was also previously seen at Ks band. This evidence together points to the disk containing a second inner component located at ?50 AU. Comparing the color of the outer (50 disk at L' with archival Hubble Space Telescope/NICMOS images of the disk at 1-2 ?m allows us to test the recently proposed cometary grains model of Donaldson et al. We find that the model fails to match this disk's surface brightness and spectrum simultaneously (reduced chi-square = 17.9). When we modify the density distribution of the model disk, we obtain a better overall fit (reduced chi-square = 2.87). The best fit to all of the data is a pure water ice model (reduced chi-square = 1.06), but additional resolved imaging at 3.1 ?m is necessary to constrain how much (if any) water ice exists in the disk, which can then help refine the originally proposed cometary grains model.

  13. Workload-Adaptive Management of Energy-Smart Disk Storage Systems

    E-Print Network [OSTI]

    Otoo, Ekow

    2010-01-01

    of Energy-Smart Disk Storage Systems Ekow Otoo, Doron Rotem,have identi?ed disk storage systems as one of the majorof idle disks) [2, 4] storage systems where only a small

  14. The gas temperature in circumstellar disks: effects of dust settling

    E-Print Network [OSTI]

    Zadelhoff, Gerd-Jan van

    The gas temperature in circumstellar disks: effects of dust settling F. Faas, G.J. van Zadelhoff, E distributions. The disk gas-temperature (T ¢¡¢£ ) is in general assumed to be equal to the dust-temperature (T¤¦¥ £ § ), due to collisions. Dust settling depends on both the gas and dust temperature. T

  15. Layout Transformation Support for the Disk Resident Arrays Framework

    SciTech Connect (OSTI)

    Krishnamoorthy, Sriram; Baumgartner, Gerald; Lam, Chi-Chung; Nieplocha, Jarek; Sadayappan, Ponnuswamy

    2006-05-15

    Global Arrays coupled with Disk Resident Arrays provides a convenient programming model that encourages locality-aware programming while providing high-level abstractions. This paper discusses the addition of layout transformation support to Disk Resident Arrays. Experimental performance data is provide that demonstrates the effectiveness of proposed functionality.

  16. Saving power without compromising disk drive reliability Xenia Mountrouidou

    E-Print Network [OSTI]

    Butt, Ali R.

    Saving power without compromising disk drive reliability Xenia Mountrouidou College of William intervals for power savings within strict constraints: first, it is imperative to contain the delays in service of IO requests that occur during power savings since the time to bring up the disk

  17. Energy Efficient Prefetching with Buffer Disks for Cluster File Systems

    E-Print Network [OSTI]

    Qin, Xiao

    Energy Efficient Prefetching with Buffer Disks for Cluster File Systems Adam Manzanares, Xiaojun the energy- efficiency of large scale parallel storage systems. To address these issues we introduce EEVFS (Energy Efficient Virtual File System), which is able to manage data placement and disk states to help

  18. Neutrinos and Nucleosynthesis in Gamma-Ray Burst Accretion Disks

    E-Print Network [OSTI]

    R. Surman; G. C. McLaughlin

    2003-11-24

    We calculate the nuclear composition of matter in accretion disks surrounding stellar mass black holes as are thought to accompany gamma-ray bursts (GRBs). We follow a mass element in the accretion disk starting at the point of nuclear dissociation and calculate the evolution of the electron fraction due to electron, positron, electron neutrino and electron antineutrino captures. We find that the neutronization of the disk material by electron capture can be reversed by neutrino interactions in the inner regions of disks with accretion rates of 1 M_solar/s and higher. For these cases the inner disk regions are optically thick to neutrinos, and so to estimate the emitted neutrino fluxes we find the surface of last scattering for the neutrinos (the equivalent of the proto-neutron star neutrinosphere) for each optically thick disk model. We also estimate the influence of neutrino interactions on the neutron-to-proton ratio in outflows from GRB accretion disks, and find it can be significant even when the disk is optically thin to neutrinos.

  19. SODA: Sensitivity Based Optimization of Disk Architecture San Diego, CA

    E-Print Network [OSTI]

    Gurumurthi, Sudhanva

    Disk drives, storage, power, performance, optimization. 1. INTRODUCTION We are in the era of dataSODA: Sensitivity Based Optimization of Disk Architecture Yan Zhang Qualcomm San Diego, CA zhangy R Stan ECE Dept., University of Virginia Charlottesville, VA mircea@virginia.edu ABSTRACT Storage

  20. Accretion Disks Around Black Holes: Twenty Five Years Later

    E-Print Network [OSTI]

    Sandip K. Chakrabarti

    1998-07-10

    We study the progress of the theory of accretion disks around black holes in last twenty five years and explain why advective disks are the best bet in explaining varied stationary and non-stationary observations from black hole candidates. We show also that the recently proposed advection dominated flows are incorrect.

  1. Light Scattering and Evolution of Protoplanetary Disks and Planetary Rings

    E-Print Network [OSTI]

    Throop, Henry

    School of the University of Colorado in partial fulfillment of the requirements for the degree of Doctor of terrestrial planets is not affected. I reproduce the observed sharp edge termination in the Orion disks. The existence of Jovian planets within our solar system suggests that our disk is not sharply terminated

  2. Head/disk interface tribology in the nanometer regime

    E-Print Network [OSTI]

    Xu, Jianfeng

    2008-01-01

    magnetic spacing for a number of sliders using a velocity-sensitive air bearingmagnetic spacing for a series of sliders on a single disk using a velocity-sensitive air bearing.bearing pressure and heat flux distribution. In recent hard disk drives, thermal protrusion of the magnetic

  3. Cooling Requirements for the Vertical Shear Instability in Protoplanetary Disks

    E-Print Network [OSTI]

    Lin, Min-Kai

    2015-01-01

    It is difficult to understand how cold circumstellar disks accrete onto their central stars. A hydrodynamic mechanism, the vertical shear instability (VSI), offers a means to drive angular momentum transport in cold accretion disks such as protoplanetary disks (PPDs). The VSI is driven by a weak vertical gradient in the disk's orbital motion. In order to grow, the VSI must overcome vertical buoyancy, a strongly stabilizing influence in cold disks, where heating is dominated by external irradiation. Rapid cooling, via radiative losses, reduces the effective buoyancy and allows the VSI to operate. In this paper, we quantify the cooling timescale, $t_c$, needed for growth of the VSI. We perform a linear analysis of the VSI with cooling in vertically global and radially local disk models. For irradiated disks, we find that the VSI is most vigorous for rapid cooling with $t_c < \\Omega_\\mathrm{K}^{-1} h |q| / (\\gamma -1)$ in terms of the Keplerian orbital frequency, $\\Omega_\\mathrm{K}$, the disk's aspect ratio, ...

  4. DEUTERIUM CHEMISTRY IN PROTOPLANETARY DISKS. II. THE INNER 30 AU

    SciTech Connect (OSTI)

    Willacy, K. [Jet Propulsion Laboratory, California Institute of Technology, MS 169-506, Pasadena, CA 91109 (United States); Woods, P. M., E-mail: Karen.Willacy@jpl.nasa.go, E-mail: Paul.Woods@manchester.ac.u [Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)

    2009-09-20

    We present the results of models of the chemistry, including deuterium, in the inner regions of protostellar disks. We find good agreement with recent gas-phase observations of several (non-deuterated) species. We also compare our results with observations of comets and find that in the absence of other processing, e.g., in the accretion shock at the surface of the disk, or by mixing in the disk, the calculated D/H ratios in ices are higher than measured and reflect the D/H ratio set in the molecular cloud phase. Our models give quite different abundances and molecular distributions to other inner disk models because of the differences in physical conditions in the model disk. This emphasizes how changes in the assumptions about the density and temperature distribution can radically affect the results of chemical models.

  5. The Driving of Decretion by Maxwell Stress in Disks

    E-Print Network [OSTI]

    Hubbard, Alexander; Oishi, Jeffrey S; Lyra, Wladimir; Mac Low, Mordecai-Mark

    2014-01-01

    Radial magnetic fields that resist orbital shear can explain the outwards angular momentum transport required for accretion in non-self-gravitating disks. This generates azimuthal magnetic fields and thus Maxwell stresses that transfer angular momentum radially. Variations on this idea include both the magnetorotational instability and disk winds. We demonstrate here that these transport mechanisms generate dynamically significant radial Poynting flux, so they are inherently not local. Simulations treating this problem typically use either the shear-periodic, shearing sheet approximation, or disk annuli with artificial radial boundary conditions. Spurious energy flows through these boundaries generally control the magnitude and even the sign of angular momentum transport. We then demonstrate that, when dominated by radial stresses, shearing sheets must decrete, as must self-similar regions of disks with power-law variations in physical quantities. Only the innermost edge of the disk, where magnetic energy inc...

  6. The role of an accretion disk in AGN variability

    E-Print Network [OSTI]

    B. Czerny

    2004-09-10

    Optically thick accretion disks are considered to be important ingredients of luminous AGN. The claim of their existence is well supported by observations and recent years brought some progress in understanding of their dynamics. However, the role of accretion disks in optical/UV/X-ray variability of AGN is not quite clear. Most probably, in short timescales the disk reprocesses the variable X-ray flux but at longer timescales the variations of the disk structure lead directly to optical/UV variations as well as affect, or even create, the X-ray variability pattern. We urgently need a considerable progress in time-dependent disk models to close the gap between the theory and the stream of data coming from the AGN monitoring.

  7. Production of Lithium in the Galactic Disk

    E-Print Network [OSTI]

    E; Casuso; J. E. Beckman

    2000-05-03

    We examine the evolution of Li in the Galactic disk,basing our model on the compilation of Li v.Fe observations in stars of iron abundance ranging between halo values,which give a baseline for the disk Li abundance,and 0.2 dex above solar.The upper envelope of these observations is taken to represent the locus of minimum stellar Li depletion,and thus to follow the Galactic IS Li abundance.The most striking feature of this envelope is its steep rise between Fe/H ~ -0.4 and -0.2,corresponding to a relatively late epoch.The Li abundance increases by an order of magnitude,from its halo value of logLi ~2.2 to the "current" value of ~3.2 within this narrow range of Fe abundances.It is well known that spallation reactions between CNO and 4He in the ISM produce Li,but models give a nearly tenfold shortfall for this process.The alpha+alpha fusion reaction appeared to yield too much early Li or too little current Li.These failures led to the exploration of stellar sources:supernovae,novae,and the He flash phase in AGB stars.The Li-Fe envelope is a strong constraint on any process.Our models can account for this in the context of disk chemical evolution with a near constant or growing rate of low metallicity gas infall,and a purely interstellar Li source: alpha-alpha fusion.The Li production rate is found to be proportional to the gas expulsion rate from intermediate and low mass stars.Low-energy alphas,emitted by these stars,but accelerated in more energetic processes associated with SNe,or the bow-shocks of stellar winds,can yield the observed abundance and its variation with Fe or O.Our model is consistent with the cosmic ray spectrum in the few MeV range,corrected for solar modulation and with new 7Li/6Li ratios found by Knauth et al.(2000) in the local ISM.

  8. PAH chemistry and IR emission from circumstellar disks

    E-Print Network [OSTI]

    R. Visser; V. C. Geers; C. P. Dullemond; J. -C. Augereau; K. M. Pontoppidan; E. F. van Dishoeck

    2007-01-22

    Aims. The chemistry of, and infrared (IR) emission from, polycyclic aromatic hydrocarbons (PAHs) in disks around Herbig Ae/Be and T Tauri stars are investigated. The equilibrium distribution of the PAHs over all accessible charge/hydrogenation states depends on the size and shape of the PAHs and on the physical properties of the star and surrounding disk. Methods. A chemistry model is created to calculate this equilibrium distribution. Destruction of PAHs by ultraviolet (UV) photons, possibly in multi-photon absorption events, is taken into account. The chemistry model is coupled to a radiative transfer code to provide the physical parameters and to combine the PAH emission with the spectral energy distribution (SED) from the star+disk system. Results. Normally hydrogenated PAHs in Herbig Ae/Be disks account for most of the observed PAH emission, with neutral and positively ionized species contributing in roughly equal amounts. Close to the midplane, the PAHs are more strongly hydrogenated and negatively ionized, but these species do not contribute to the overall emission because of the low UV/optical flux deep inside the disk. PAHs of 50 carbon atoms are destroyed out to 100 AU in the disk's surface layer, and the resulting spatial extent of the emission does not agree well with observations. Rather, PAHs of about 100 carbon atoms or more are predicted to cause most of the observed emission. The emission is extended on a scale similar to that of the size of the disk. Furthermore, the emission from T Tauri disks is much weaker and concentrated more towards the central star than that from Herbig Ae/Be disks. Positively ionized PAHs are predicted to be largely absent in T Tauri disks because of the weaker radiation field.

  9. Thermal Fly-height Control Slider Dynamics and Slider-Lubricant Interactions in Hard Disk Drives

    E-Print Network [OSTI]

    Vangipuram Canchi, Sripathi

    2011-01-01

    the HDI at extremely low head-disk clearances. ExperimentsHDI reliability at extremely low head-disk clearance. System

  10. Covariant Lyapunov vectors for rigid disk systems

    E-Print Network [OSTI]

    Hadrien Bosetti; Harald A. Posch

    2010-06-30

    We carry out extensive computer simulations to study the Lyapunov instability of a two-dimensional hard disk system in a rectangular box with periodic boundary conditions. The system is large enough to allow the formation of Lyapunov modes parallel to the x axis of the box. The Oseledec splitting into covariant subspaces of the tangent space is considered by computing the full set of covariant perturbation vectors co-moving with the flow in tangent-space. These vectors are shown to be transversal, but generally not orthogonal to each other. Only the angle between covariant vectors associated with immediate adjacent Lyapunov exponents in the Lyapunov spectrum may become small, but the probability of this angle to vanish approaches zero. The stable and unstable manifolds are transverse to each other and the system is hyperbolic.

  11. The Cosmic Battery in Astrophysical Accretion Disks

    E-Print Network [OSTI]

    Contopoulos, Ioannis; Katsanikas, Matthaios

    2015-01-01

    The aberrated radiation pressure at the inner edge of the accretion disk around an astrophysical black hole imparts a relative azimuthal velocity on the electrons with respect to the ions which gives rise to a ring electric current that generates large scale poloidal magnetic field loops. This is the Cosmic Battery established by Contopoulos and Kazanas in 1998. In the present work we perform realistic numerical simulations of this important astrophysical mechanism in advection-dominated accretion flows-ADAF. We confirm the original prediction that the inner parts of the loops are continuously advected toward the central black hole and contribute to the growth of the large scale magnetic field, whereas the outer parts of the loops are continuously diffusing outward through the turbulent accretion flow. This process of inward advection of the axial field and outward diffusion of the return field proceeds all the way to equipartition, thus generating astrophysically significant magnetic fields on astrophysicall...

  12. The OGLE-II event sc5_2859 -- An example of disk-disk microlensing

    E-Print Network [OSTI]

    M. C. Smith

    2003-06-10

    We present a new long-duration parallax event from the OGLE-II database, sc5_2859, which has the second longest time-scale ever identified (tE = 547.6{+22.6}{-7.8} days). We argue that both the lens and source reside in the Galactic disk, making event sc5_2859 one of the first confirmed examples of so-called disk-disk microlensing. We find that the source star is most probably located at a distance of D_S ~ 2 kpc, and from this we conclude that the lens is unlikely to be a main-sequence star due to the strict limits that can be placed on the lens brightness. A simple likelihood analysis is carried out on the lens mass, which indicates that the lens could be another candidate stellar mass black hole. We recommend that spectroscopic observations of the source be carried out in order to constrain the source distance, since this is the main source of uncertainty in our analysis. In addition, we briefly discuss whether there appears to be an excess of long duration microlensing events in the OGLE-II catalogue.

  13. Lateral control of articulated vehicles for automated highway systems under uncertainty in vehicle parameters 

    E-Print Network [OSTI]

    Daud, Omar

    1998-01-01

    is first developed and then the steering controller is augmented with an independent braking controller which provides differential torque for directly controlling the trailer yaw motion by applying unilateral tire braking on the trailer rear wheels...

  14. LOCAL STUDY OF ACCRETION DISKS WITH A STRONG VERTICAL MAGNETIC FIELD: MAGNETOROTATIONAL INSTABILITY AND DISK OUTFLOW

    SciTech Connect (OSTI)

    Bai, Xue-Ning; Stone, James M., E-mail: xbai@cfa.harvard.edu [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States)

    2013-04-10

    We perform three-dimensional, vertically-stratified, local shearing-box ideal MHD simulations of the magnetorotational instability (MRI) that include a net vertical magnetic flux, which is characterized by midplane plasma {beta}{sub 0} (ratio of gas to magnetic pressure). We have considered {beta}{sub 0} = 10{sup 2}, 10{sup 3}, and 10{sup 4}, and in the first two cases the most unstable linear MRI modes are well resolved in the simulations. We find that the behavior of the MRI turbulence strongly depends on {beta}{sub 0}: the radial transport of angular momentum increases with net vertical flux, achieving {alpha} {approx} 0.08 for {beta} = 10{sup 4} and {alpha} {approx}> 1.0 for {beta}{sub 0} = 100, where {alpha} is the height-integrated and mass-weighted Shakura-Sunyaev parameter. A critical value lies at {beta}{sub 0} {approx} 10{sup 3}: for {beta}{sub 0} {approx}> 10{sup 3}, the disk consists of a gas pressure dominated midplane and a magnetically dominated corona. The turbulent strength increases with net flux, and angular momentum transport is dominated by turbulent fluctuations. The magnetic dynamo that leads to cyclic flips of large-scale fields still exists, but becomes more sporadic as net flux increases. For {beta}{sub 0} {approx}< 10{sup 3}, the entire disk becomes magnetically dominated. The turbulent strength saturates, and the magnetic dynamo is fully quenched. Stronger large-scale fields are generated with increasing net flux, which dominates angular momentum transport. A strong outflow is launched from the disk by the magnetocentrifugal mechanism, and the mass flux increases linearly with net vertical flux and shows sign of saturation at {beta}{sub 0} {approx}< 10{sup 2}. However, the outflow is unlikely to be directly connected to a global wind: for {beta}{sub 0} {approx}> 10{sup 3}, the large-scale field has no permanent bending direction due to dynamo activities, while for {beta}{sub 0} {approx}< 10{sup 3}, the outflows from the top and bottom sides of the disk bend towards opposite directions, inconsistent with a physical disk wind geometry. Global simulations are needed to address the fate of the outflow.

  15. The effect of radial migration on galactic disks

    SciTech Connect (OSTI)

    Vera-Ciro, Carlos; D'Onghia, Elena; Navarro, Julio; Abadi, Mario

    2014-10-20

    We study the radial migration of stars driven by recurring multi-arm spiral features in an exponential disk embedded in a dark matter halo. The spiral perturbations redistribute angular momentum within the disk and lead to substantial radial displacements of individual stars, in a manner that largely preserves the circularity of their orbits and that results, after 5 Gyr (?40 full rotations at the disk scale length), in little radial heating and no appreciable changes to the vertical or radial structure of the disk. Our results clarify a number of issues related to the spatial distribution and kinematics of migrators. In particular, we find that migrators are a heavily biased subset of stars with preferentially low vertical velocity dispersions. This 'provenance bias' for migrators is not surprising in hindsight, for stars with small vertical excursions spend more time near the disk plane, and thus respond more readily to non-axisymmetric perturbations. We also find that the vertical velocity dispersion of outward migrators always decreases, whereas the opposite holds for inward migrators. To first order, newly arrived migrators simply replace stars that have migrated off to other radii, thus inheriting the vertical bias of the latter. Extreme migrators might therefore be recognized, if present, by the unexpectedly small amplitude of their vertical excursions. Our results show that migration, understood as changes in angular momentum that preserve circularity, can strongly affect the thin disk, but cast doubts on models that envision the Galactic thick disk as a relic of radial migration.

  16. ALIGNMENT OF PROTOSTARS AND CIRCUMSTELLAR DISKS DURING THE EMBEDDED PHASE

    SciTech Connect (OSTI)

    Spalding, Christopher; Batygin, Konstantin [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Adams, Fred C., E-mail: cspaldin@caltech.edu, E-mail: kbatygin@gps.caltech.edu, E-mail: fca@umich.edu [Department of Physics, University of Michigan, Ann Arbor, MI 48109 (United States)

    2014-12-20

    Star formation proceeds via the collapse of a molecular cloud core over multiple dynamical timescales. Turbulence within cores results in a spatially non-uniform angular momentum of the cloud, causing a stochastic variation in the orientation of the disk forming from the collapsing material. In the absence of star-disk angular momentum coupling, such disk-tilting would provide a natural mechanism for the production of primordial spin-orbit misalignments in the resulting planetary systems. However, owing to high accretion rates in the embedded phase of star formation, the inner edge of the circumstellar disk extends down to the stellar surface, resulting in efficient gravitational and accretional angular momentum transfer between the star and the disk. Here, we demonstrate that the resulting gravitational coupling is sufficient to suppress any significant star-disk misalignment, with accretion playing a secondary role. The joint tilting of the star-disk system leads to a stochastic wandering of star-aligned bipolar outflows. Such wandering widens the effective opening angle of stellar outflows, allowing for more efficient clearing of the remainder of the protostar's gaseous envelope. Accordingly, the processes described in this work provide an additional mechanism responsible for sculpting the stellar initial mass function.

  17. Finite axisymmetric charged dust disks in conformastatic spacetimes

    SciTech Connect (OSTI)

    Gonzalez, Guillermo A.; Gutierrez-Pineres, Antonio C.; Ospina, Paolo A.

    2008-09-15

    An infinite family of axisymmetric charged dust disks of finite extension is presented. The disks are obtained by solving the vacuum Einstein-Maxwell equations for conformastatic spacetimes, which are characterized by only one metric function. In order to obtain the solutions, a functional relationship between the metric function and the electric potential is assumed. It is also assumed that the metric function is functionally dependent on another auxiliary function, which is taken as a solution of the Laplace equation. The solutions for the auxiliary function are then taken as given by the infinite family of generalized Kalnajs disks recently obtained by Gonzalez and Reina [G. A. Gonzalez and J. I. Reina, Mon. Not. R. Astron. Soc. 371, 1873 (2006).], expressed in terms of the oblate spheroidal coordinates and corresponding to a family of well-behaved Newtonian axisymmetric thin disks of finite radius. The obtained relativistic thin disks have a charge density that is equal, except maybe by a sign, to their mass density, in such a way that the electric and gravitational forces are in exact balance. The energy density of the disks is everywhere positive and well behaved, vanishing at the edge. Accordingly, as the disks are made of dust, their energy-momentum tensor agrees with all the energy conditions.

  18. Angular Momentum Transport in Particle and Fluid Disks

    E-Print Network [OSTI]

    Eliot Quataert; Eugene I. Chiang

    2000-08-23

    We examine the angular momentum transport properties of disks composed of macroscopic particles whose velocity dispersions are externally enhanced (``stirred''). Our simple Boltzmann equation model serves as an analogy for unmagnetized fluid disks in which turbulence may be driven by thermal convection. We show that interparticle collisions in particle disks play the same role as fluctuating pressure forces and viscous dissipation in turbulent disks: both transfer energy in random motions associated with one direction to those associated with another, and convert kinetic energy into heat. The direction of angular momentum transport in stirred particle and fluid disks is determined by the direction of external stirring and by the properties of the collision term in the Boltzmann equation (or its analogue in the fluid problem). In particular, our model problem yields inward transport for vertically or radially stirred disks, provided collisions are suitably inelastic; the transport is outwards in the elastic limit. Numerical simulations of hydrodynamic turbulence driven by thermal convection find inward transport; this requires that fluctuating pressure forces do little to no work, and is analogous to an externally stirred particle disk in which collisions are highly inelastic.

  19. Nucleosynthesis in the Outflow from Gamma Ray Burst Accretion Disks

    E-Print Network [OSTI]

    R. Surman; G. C. McLaughlin; W. R. Hix

    2005-09-13

    We examine the nucleosynthesis products that are produced in the outflow from rapidly accreting disks. We find that the type of element synthesis varies dramatically with the degree of neutrino trapping in the disk and therefore the accretion rate of the disk. Disks with relatively high accretion rates such as 10 M_solar/s can produce very neutron rich nuclei that are found in the r process. Disks with more moderate accretion rates can produce copious amounts of Nickel as well as the light elements such as Lithium and Boron. Disks with lower accretion rates such as 0.1 M_solar/s produce large amounts of Nickel as well as some unusual nuclei such as Ti-49, Sc-45, Zn-64, and Mo-92. This wide array of potential nucleosynthesis products is due to the varying influence of electron neutrinos and antineutrinos emitted from the disk on the neutron-to-proton ratio in the outflow. We use a parameterization for the outflow and discuss our results in terms of entropy and outflow acceleration.

  20. The Impact of Dust Evolution and Photoevaporation on Disk Dispersal

    E-Print Network [OSTI]

    Gorti, Uma; Dullemond, Cornelis

    2015-01-01

    Protoplanetary disks are dispersed by viscous evolution and photoevaporation in a few million years; in the interim small, sub-micron sized dust grains must grow and form planets. The time-varying abundance of small grains in an evolving disk directly affects gas heating by far-ultraviolet photons, while dust evolution affects photoevaporation by changing the disk opacity and resulting penetration of FUV photons in the disk. Photoevaporative flows, in turn, selectively carry small dust grains leaving the larger particles---which decouple from the gas---behind in the disk. We study these effects by investigating the evolution of a disk subject to viscosity, photoevaporation by EUV, FUV and X-rays, dust evolution, and radial drift using a 1-D multi-fluid approach (gas + different dust grain sizes) to solve for the evolving surface density distributions. The 1-D evolution is augmented by 1+1D models constructed at each epoch to obtain the instantaneous disk structure and determine photoevaporation rates. The imp...

  1. Warm formaldehyde in the Oph IRS 48 transitional disk

    E-Print Network [OSTI]

    van der Marel, Nienke; Bruderer, Simon; van Kempen, Tim A

    2014-01-01

    Simple molecules like H2CO and CH3OH in protoplanetary disks are the starting point for the production of more complex organic molecules. So far, the observed chemical complexity in disks has been limited due to freeze out of molecules onto grains in the bulk of the cold outer disk. Complex molecules can be studied more directly in transitional disks with large inner holes, as these have a higher potential of detection, through UV heating of the outer disk and the directly exposed midplane at the wall. We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 9 (~680 GHz) line data of the transitional disk Oph IRS 48, previously shown to have a large dust trap, to search for complex molecules in regions where planetesimals are forming. We report the detection of the H2CO 9(1,8)-8(1,7) line at 674 GHz, which is spatially resolved as a semi-ring at ~60 AU radius centered south from the star. The inferred H2CO abundance is ~10^{-8} derived by combining a physical disk model of the source with a non-LTE exc...

  2. PLANETESIMALS IN DEBRIS DISKS OF SUN-LIKE STARS

    SciTech Connect (OSTI)

    Shannon, Andrew; Wu Yanqin

    2011-09-20

    Observations of dusty debris disks can be used to test theories of planetesimal coagulation. Planetesimals of sizes up to a couple of thousand kilometers are embedded in these disks and their mutual collisions generate the small dust grains that are observed. The dust luminosities, when combined with information on the dust spatial extent and the system age, can be used to infer initial masses in the planetesimal belts. Carrying out such a procedure for a sample of debris disks around Sun-like stars, we reach the following two conclusions. First, if we assume that colliding planetesimals satisfy a primordial size spectrum of the form dn/ds{proportional_to}s{sup -q}, observed disks strongly favor a value of q between 3.5 and 4, while both current theoretical expectations and statistics of Kuiper belt objects favor a somewhat larger value. Second, number densities of planetesimals are two to three orders of magnitude higher in detected disks than in the Kuiper belt, for comparably sized objects. This is a surprise for the coagulation models. It would require a similar increase in the disk surface density over that of the Minimum Mass Solar Nebula, which is unreasonable. Both of our conclusions are driven by the need to explain the presence of bright debris disks at a few gigayears of age.

  3. Simple Models for Turbulent Self-Regulation in Galaxy Disks

    E-Print Network [OSTI]

    Curtis Struck; Daniel C. Smith

    1999-07-29

    We propose that turbulent heating, wave pressure and gas exchanges between different regions of disks play a dominant role in determining the preferred, quasi-equilibrium, self-similar states of gas disks on large-scales. We present simple families of analytic, thermohydrodynamic models for these global states, which include terms for turbulent pressure and Reynolds stresses. Star formation rates, phase balances, and hydrodynamic forces are all tightly coupled and balanced. The models have stratified radial flows, with the cold gas slowly flowing inward in the midplane of the disk, and with the warm/hot phases that surround the midplane flowing outward. The models suggest a number of results that are in accord with observation, as well as some novel predictions, including the following. 1) The large-scale gas density and thermal phase distributions in galaxy disks can be explained as the result of turbulent heating and spatial couplings. 2) The turbulent pressures and stresses that drive radial outflows in the warm gas also allow a reduced circular velocity there. This effect was observed by Swaters, Sancisi and van der Hulst in NGC 891, a particularly turbulent edge-on disk. The models predict that the effect should be universal in such disks. 3) They suggest that a star formation rate like the phenomenological Schmidt Law is the natural result of global thermohydrodynamical balance, and may not obtain in disks far from equilibrium. (Abridged)

  4. Type I planet migration in nearly laminar disks

    SciTech Connect (OSTI)

    Li, Hui; Li, Shengtai; Lubow, S H; Lin, D

    2008-01-01

    We describe two-dimensional hydrodynamic simulations of the migration of low-mass planets ({<=}30 M{sub {circle_plus}}) in nearly laminar disks (viscosity parameter {alpha} < 10{sup -3}) over timescales of several thousand orbit periods. We consider disk masses of 1, 2, and 5 times the minimum mass solar nebula, disk thickness parameters of H/r = 0.035 and 0.05, and a variety of {alpha} values and planet masses. Disk self-gravity is fully included. Previous analytic work has suggested that Type I planet migration can be halted in disks of sufficiently low turbulent viscosity, for {alpha} {approx} 10{sup -4}. The halting is due to a feedback effect of breaking density waves that results in a slight mass redistribution and consequently an increased outward torque contribution. The simulations confirm the existence of a critical mass (M{sub {alpha}} {approx} 10M{sub {circle_plus}}) beyond which migration halts in nearly laminar disks. For {alpha} {approx}> 10{sup -3}, density feedback effects are washed out and Type I migration persists. The critical masses are in good agreement with the analytic model of Rafikov. In addition, for {alpha} {approx}> 10{sup -4} steep density gradients produce a vortex instability, resulting in a small time-varying eccentricity in the planet's orbit and a slight outward migration. Migration in nearly laminar disks may be sufficiently slow to reconcile the timescales of migration theory with those of giant planet formation in the core accretion model.

  5. Multi-Terabyte EIDE Disk Arrays running Linux RAID5

    E-Print Network [OSTI]

    D. A. Sanders; L. M. Cremaldi; V. Eschenburg; R. Godang; M. D. Joy; D. J. Summers; D. L. Petravick

    2004-11-19

    High-energy physics experiments are currently recording large amounts of data and in a few years will be recording prodigious quantities of data. New methods must be developed to handle this data and make analysis at universities possible. Grid Computing is one method; however, the data must be cached at the various Grid nodes. We examine some storage techniques that exploit recent developments in commodity hardware. Disk arrays using RAID level 5 (RAID-5) include both parity and striping. The striping improves access speed. The parity protects data in the event of a single disk failure, but not in the case of multiple disk failures. We report on tests of dual-processor Linux Software RAID-5 arrays and Hardware RAID-5 arrays using a 12-disk 3ware controller, in conjunction with 250 and 300 GB disks, for use in offline high-energy physics data analysis. The price of IDE disks is now less than $1/GB. These RAID-5 disk arrays can be scaled to sizes affordable to small institutions and used when fast random access at low cost is important.

  6. Self-gravity in neutrino-dominated accretion disks

    SciTech Connect (OSTI)

    Liu, Tong; Yu, Xiao-Fei; Gu, Wei-Min; Lu, Ju-Fu

    2014-08-10

    We present the effects of self-gravity on the vertical structure and neutrino luminosity of the neutrino-dominated accretion disks in cylindrical coordinates. It is found that significant changes of the structure appear in the outer region of the disk, especially for high accretion rates (e.g., ? 1 M{sub ?} s{sup –1}), and thus cause the slight increase in the neutrino luminosity. Furthermore, the gravitational instability of the disk is reviewed by the vertical distribution of the Toomre parameter, which may account for the late-time flares in gamma-ray bursts and the extended emission in short-duration gamma-ray bursts.

  7. Recent Progresses Of Accretion Disk Models Around Black Holes

    E-Print Network [OSTI]

    Sandip K. Chakrabarti

    1997-03-09

    Accretion disk models have evolved from Bondi flows in the 1950s to Keplerian disks in the 1970s and finally to advective transonic flows in the 1990s. We discuss recent progresses in this subject and show that sub-Keplerian flows play a major role in determining the spectral properties of black holes. Centrifugal pressure supported enhanced density region outside the black hole horizon produces hard X-rays and gamma rays by reprocessing intercepted soft photons emitted by the Keplerian disk terminated farther out from the black holes. Quasi-periodic oscillations can also be understood from the dynamic or thermal resonance effects of the enhanced density region.

  8. Jets and Accretion Disks in Astrophysics - A Brief Review

    E-Print Network [OSTI]

    L. A. Morabito; D. Meyer

    2012-11-15

    The significance of jets and accretion disks in Astrophysics may be growing far beyond any single example of recent finds in the scientific journals. This brief review will summarize recent, significant manifestations of accretion disk powered jets in the universe. We then introduce supplemental contemporary finds in physics and astrophysics which might bear tangential or direct implications for astrophysics toward rethinking the universe with a major role of relativistic jets powered by accretion disks. We conclude with the direction our research will take in order to establish a new perspective on the universe.

  9. Flow visualization in a multiple disk pump for use as an artificial ventricle 

    E-Print Network [OSTI]

    Madigan, Michael Lawrence

    1996-01-01

    diameter and 3.0 inch outer diameter. Four stainless steel pins affix the disks at a constant spacing of .025 inches and terminate in a sixth solid disk. This solid disk couples the pins to a DC motor shaft which rotates the entire disk assembly. A mock...

  10. SmartSaver: Turning Flash Drive into a Disk Energy Saver for Mobile , Song Jiang2

    E-Print Network [OSTI]

    Jiang, Song

    SmartSaver: Turning Flash Drive into a Disk Energy Saver for Mobile Computers Feng Chen1 , Song computer the hard disk consumes a considerable amount of energy. Existing dynamic power management poli- cies usually take conservative approaches to save disk energy, and disk energy consumption remains

  11. Protoplanetary disks including radiative feedback from accreting planets

    E-Print Network [OSTI]

    Montesinos, Matias; Perez, Sebastian; Baruteau, Clement; Casassus, Simon

    2015-01-01

    While recent observational progress is converging on the detection of compact regions of thermal emission due to embedded protoplanets, further theoretical predictions are needed to understand the response of a protoplanetary disk to the planet formation radiative feedback. This is particularly important to make predictions for the observability of circumplanetary regions. In this work we use 2D hydrodynamical simulations to examine the evolution of a viscous protoplanetary disk in which a luminous Jupiter-mass planet is embedded. We use an energy equation which includes the radiative heating of the planet as an additional mechanism for planet formation feedback. Several models are computed for planet luminosities ranging from $10^{-5}$ to $10^{-3}$ Solar luminosities. We find that the planet radiative feedback enhances the disk's accretion rate at the planet's orbital radius, producing a hotter and more luminous environement around the planet, independently of the prescription used to model the disk's turbul...

  12. Numerical and experimental investigations of the head/disk interface

    E-Print Network [OSTI]

    Duwensee, Maik

    2007-01-01

    Dynamics and the E?ect of Lubricant. ASME J. Trib. , 126:Dynamics and the E?ect of Lubricant. ASME J. Trib. , 126:roughness, and the disk lubricant. An experimental setup was

  13. Disk storage management for LHCb based on Data Popularity estimator

    E-Print Network [OSTI]

    Hushchyn, Mikhail; Ustyuzhanin, Andrey

    2015-01-01

    This paper presents a system providing recommendations for optimizing the LHCb data storage. The LHCb data storage system is a hybrid system. All datasets are kept as archives on magnetic tapes. The most popular datasets are kept on disks. The recommendation system takes the dataset usage history and metadata (size, type, configuration etc.) to generate a recommendation report. In this article present how we use machine learning algorithms to predict future data popularity. Using these predictions it is possible to estimate which datasets should be removed from disk. We use regression algorithms and time series analysis to find the optimal number of replicas for datasets that are kept on disk. Based on the data popularity and the number of replicas optimization, the recommendation system minimizes a loss function to find the optimal data distribution. The loss function represents all requirements for data distribution in the data storage system. We demonstrate how the recommendation system helps to save disk ...

  14. Task 8.4 - High Temperature Turbine Disk Development

    SciTech Connect (OSTI)

    NONE

    1997-02-27

    The goal of this task is to demonstrate a bonding technique to produce a dual-alloy turbine disk concept which will satisfy the diverse property requirements of the rim and hub areas of the disk. The program examines methods of attaching a cast superalloy rim with sufficient rupture strength to a fine grain hub materials with the required LCF properties. The goals of the program were established in the context of a preliminary turbine design by Solar Turbines, Inc. designated ATS 5. The initial target for the ATS 5 application was to allow rim operating temperatures in the 1350-1400 {degrees} F range. The life goal of the Dual-Alloy Disk was envisioned to maintain Solar`s standard turbine disk philosophy of 1000,000 hours.

  15. Disk storage management for LHCb based on Data Popularity estimator

    E-Print Network [OSTI]

    Hushchyn, Mikhail; Ustyuzhanin, Andrey

    2015-01-01

    This paper presents an algorithm providing recommendations for optimizing the LHCb data storage. The LHCb data storage system is a hybrid system. All datasets are kept as archives on magnetic tapes. The most popular datasets are kept on disks. The algorithm takes the dataset usage history and metadata (size, type, configuration etc.) to generate a recommendation report. This article presents how we use machine learning algorithms to predict future data popularity. Using these predictions it is possible to estimate which datasets should be removed from disk. We use regression algorithms and time series analysis to find the optimal number of replicas for datasets that are kept on disk. Based on the data popularity and the number of replicas optimization, the algorithm minimizes a loss function to find the optimal data distribution. The loss function represents all requirements for data distribution in the data storage system. We demonstrate how our algorithm helps to save disk space and to reduce waiting times ...

  16. Numerical and experimental investigations of the head/disk interface

    E-Print Network [OSTI]

    Duwensee, Maik

    2007-01-01

    Flying Head Slider Bearings in Magnetic Hard Disk Drives.for Flying Head Slider Bearings in Magnetic Storage. ASME J.Warner et al. Magnetic Head Air Bearing Slider. U.S. Patent

  17. Innovation incentives and competition in the hard disk drive industry

    E-Print Network [OSTI]

    Wu, Xiaohua Sherry

    2011-01-01

    Firms in the hard disk drive industry are continually engaging in R & D and improving the quality of their products. We explore various determinants of the product innovation incentives for firms concerned with both their ...

  18. Thermal Comptonization and Disk Thermal Reprocessing in NGC 3516

    E-Print Network [OSTI]

    James Chiang; Omer Blaes

    2001-07-03

    We present an application of the thermal Comptonization/disk reprocessing model recently proposed by Zdziarski, Lubi\\'nski, & Smith. We show that the absence of strong optical variations in the presence of strong concurrent X-ray variations, similar to those found by HST/RXTE monitoring observations of NGC 3516, can be explained by changing the geometry of the Comptonizing plasma rather than the accretion disk itself. The total X-ray luminosity of the Comptonizing plasma must decrease as its spatial extent increases. In contrast, the disk inner radius must be roughly fixed in order not to produce optical/ultraviolet color variations stronger than observed. By including emission due to internal viscous dissipation in the disk, we can roughly match the optical and X-ray flux levels and variability amplitudes seen from NGC 3516 during the HST/RXTE campaign.

  19. EFFECTS OF DUST FEEDBACK ON VORTICES IN PROTOPLANETARY DISKS

    SciTech Connect (OSTI)

    Fu, Wen; Liang, Edison; Li, Hui; Li, Shengtai; Lubow, Stephen

    2014-11-10

    We carried out two-dimensional, high-resolution simulations to study the effect of dust feedback on the evolution of vortices induced by massive planets in protoplanetary disks. Various initial dust to gas disk surface density ratios (0.001-0.01) and dust particle sizes (Stokes number 4 × 10{sup –4}-0.16) are considered. We found that while dust particles migrate inward, vortices are very effective at collecting them. When dust density becomes comparable to gas density within the vortex, a dynamical instability is excited and it alters the coherent vorticity pattern and destroys the vortex. This dust feedback effect is stronger with a higher initial dust/gas density ratio and larger dust grain. Consequently, we found that the disk vortex lifetime can be reduced up to a factor of 10. We discuss the implications of our findings on the survivability of vortices in protoplanetary disks and planet formation.

  20. Energy Proportionality for Disk Storage Using Replication

    SciTech Connect (OSTI)

    Kim, Jinoh; Rotem, Doron

    2010-09-09

    Energy saving has become a crucial concern in datacenters as several reports predict that the anticipated energy costs over a three year period will exceed hardware acquisition. In particular, saving energy for storage is of major importance as storage devices (and cooling them off) may contribute over 25 percent of the total energy consumed in a datacenter. Recent work introduced the concept of energy proportionality and argued that it is a more relevant metric than just energy saving as it takes into account the tradeoff between energy consumption and performance. In this paper, we present a novel approach, called FREP (Fractional Replication for Energy Proportionality), for energy management in large datacenters. FREP includes areplication strategy and basic functions to enable flexible energy management. Specifically, our method provides performance guarantees by adaptively controlling the power states of a group of disks based on observed and predicted workloads. Our experiments, using a set of real and synthetic traces, show that FREP dramatically reduces energy requirements with a minimal response time penalty.

  1. Misaligned Disks as Obscurers in Active Galaxies

    SciTech Connect (OSTI)

    Lawrence, A.; Elvis, M.; /Edinburgh U., Inst. Astron. /Harvard-Smithsonian Ctr. Astrophys.

    2010-06-02

    We review critically the evidence concerning the fraction of Active Galactic Nuclei (AGN) which appear as Type 2 AGN, carefully distinguishing strict Type 2 AGN from both more lightly reddened Type 1 AGN, and from low excitation narrow line AGN, which may represent a different mode of activity. Low excitation AGN occur predominantly at low luminosities; after removing these, true Type 2 AGN represent 58{-+}5% of all AGN, and lightly reddened Type 1 AGN a further {approx}15%. Radio, IR, and volume-limited samples all agree in showing no change of Type 2 fraction with luminosity. X-ray samples do show a change with luminosity; we discuss possible reasons for this discrepancy. We test a very simple picture which produces this Type 2 fraction with minimal assumptions. In this picture, infall from large scales occurs in random directions, but must eventually align with the inner accretion flow, producing a severely warped disk on parsec scales. If the re-alignment is dominated by tilt, with minimal twist, a wide range of covering factors is predicted in individual objects, but with an expected mean fraction of Type 2 AGN of exactly 50%. This 'tilted disc' picture predicts reasonable alignment of observed nuclear structures on average, but with distinct misalignments in individual cases. Initial case studies of the few well resolved objects show that such misalignments are indeed present.

  2. Characterizing the noise produced by hard disk drives 

    E-Print Network [OSTI]

    Cherniak, Bruce Marshall

    1991-01-01

    CHARACTERIZING THE NOISE PRODUCED BY HARD DISK DRIVES A Thesis by BRUCE MARSHALL CHERNIAK Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE... August 1991 Major Subject: Electrical Engineering CHARACTERIZING THE NOISE PRODUCED BY HARD DISK DRIVES A Thesis by BRUCE MARSHALL CHERNIAK Approved as to style and content by: Karan L. Watson (Chair of Committee) Hosame Abu-Amara (Member...

  3. The Outer Structure of Galactic Disks: Connections Between Bars, Disks, and Environments

    E-Print Network [OSTI]

    Erwin, Peter; Beckman, John E; Gutíerrez, Leonel; Aladro, Rebeca

    2007-01-01

    Surface-brightness profiles for early-type (S0-Sb) disks exhibit three main classes (Type I, II, and III). Type II profiles are more common in barred galaxies, and most of the time appear to be related to the bar's Outer Lindblad Resonance. Roughly half of barred galaxies in the field have Type II profiles, but almost none in the Virgo Cluster do; this might be related to ram-pressure stripping in clusters. A strong \\textit{anti}correlation is found between Type III profiles ("antitruncations") and bars: Type III profiles are most common when there is no bar, and least common when there is a strong bar.

  4. The Outer Structure of Galactic Disks: Connections Between Bars, Disks, and Environments

    E-Print Network [OSTI]

    Peter Erwin; Michael Pohlen; John E. Beckman; Leonel Gutierrez; Rebeca Aladro

    2007-06-26

    Surface-brightness profiles for early-type (S0-Sb) disks exhibit three main classes (Type I, II, and III). Type II profiles are more common in barred galaxies, and most of the time appear to be related to the bar's Outer Lindblad Resonance. Roughly half of barred galaxies in the field have Type II profiles, but almost none in the Virgo Cluster do; this might be related to ram-pressure stripping in clusters. A strong \\textit{anti}correlation is found between Type III profiles ("antitruncations") and bars: Type III profiles are most common when there is no bar, and least common when there is a strong bar.

  5. Stellar and Gaseous Disk Structures in Cosmological Galaxy Equilibrium Models

    E-Print Network [OSTI]

    Rathaus, Ben

    2015-01-01

    We present "radially-resolved-equilibrium-models" for the growth of stellar and gaseous disks in cosmologically accreting massive halos. Our focus is on objects that evolve to redshifts $z\\sim 2$. We solve the time-dependent equations that govern the radially dependent star-formation rates, inflows and outflows from and to the inter- and circum-galactic medium, and inward radial gas flows within the disks. The stellar and gaseous disks reach equilibrium configurations on dynamical time scales much shorter than variations in the cosmological dark matter halo growth and baryonic accretions rates. We show analytically that mass and global angular momentum conservation naturally give rise to exponential gas and stellar disks over many radial length scales. The gaseous disks are more extended as set by the condition Toomre $Q<1$ for star-formation. The disks rapidly become baryon dominated. For massive, $5\\times 10^{12}M_\\odot$ halos at redshift $z=2$, we reproduced the typical observed star-formation rates of ...

  6. Volatile snowlines in embedded disks around low-mass protostars

    E-Print Network [OSTI]

    Harsono, Daniel; van Dishoeck, Ewine

    2015-01-01

    (Abridged*) Models of the young solar nebula assume a hot initial disk with most volatiles are in the gas phase. The question remains whether an actively accreting disk is warm enough to have gas-phase water up to 50 AU radius. No detailed studies have yet been performed on the extent of snowlines in an embedded accreting disk (Stage 0). Quantify the location of gas-phase volatiles in embedded actively accreting disk system. Two-dimensional physical and radiative transfer models have been used to calculate the temperature structure of embedded protostellar systems. Gas and ice abundances of H$_2$O, CO$_2$, and CO are calculated using the density-dependent thermal desorption formulation. The midplane water snowline increases from 3 to 55 AU for accretion rates through the disk onto the star between $10^{-9}$-$10^{-4} \\ M_{\\odot} \\ {\\rm yr^{-1}}$. CO$_2$ can remain in the solid phase within the disk for $\\dot{M} \\leq 10^{-5} \\ M_{\\odot} \\ {\\rm yr^{-1}}$ down to $\\sim 20$ AU. Most of the CO is in the gas phase w...

  7. Volatile depletion in the TW Hydrae disk atmosphere

    E-Print Network [OSTI]

    Du, Fujun; Hogerheijde, Michiel R

    2015-01-01

    An abundance decrease in carbon- and oxygen-bearing species relative to dust has been frequently found in planet-forming disks, which can be attributed to an overall reduction of gas mass. However, in the case of TW Hya, the only disk with gas mass measured directly with HD rotational lines, the inferred gas mass ($\\lesssim$0.005 solar mass) is significantly below the directly measured value ($\\gtrsim$0.05 solar mass). We show that this apparent conflict can be resolved if the elemental abundances of carbon and oxygen are reduced in the upper layers of the outer disk but are normal elsewhere (except for a possible enhancement of their abundances in the inner disk). The implication is that in the outer disk, the main reservoir of the volatiles (CO, water, ...) resides close to the midplane, locked up inside solid bodies that are too heavy to be transported back to the atmosphere by turbulence. An enhancement in the carbon and oxygen abundances in the inner disk can be caused by inward migration of these solid ...

  8. Bulge growth through disk instabilities in high-redshift galaxies

    E-Print Network [OSTI]

    Bournaud, Frederic

    2015-01-01

    The role of disk instabilities, such as bars and spiral arms, and the associated resonances, in growing bulges in the inner regions of disk galaxies have long been studied in the low-redshift nearby Universe. There it has long been probed observationally, in particular through peanut-shaped bulges. This secular growth of bulges in modern disk galaxies is driven by weak, non-axisymmetric instabilities: it mostly produces pseudo-bulges at slow rates and with long star-formation timescales. Disk instabilities at high redshift (z>1) in moderate-mass to massive galaxies (10^10 to a few 10^11 Msun of stars) are very different from those found in modern spiral galaxies. High-redshift disks are globally unstable and fragment into giant clumps containing 10^8-10^9 Msun of gas and stars each, which results in highly irregular galaxy morphologies. The clumps and other features associated to the violent instability drive disk evolution and bulge growth through various mechanisms, on short timescales. The giant clumps can...

  9. CONSTRAINTS ON COMPTON-THICK WINDS FROM BLACK HOLE ACCRETION DISKS: CAN WE SEE THE INNER DISK?

    SciTech Connect (OSTI)

    Reynolds, Christopher S.

    2012-11-01

    Strong evidence is emerging that winds can be driven from the central regions of accretion disks in both active galactic nuclei and Galactic black hole binaries. Direct evidence for highly ionized, Compton-thin inner-disk winds comes from observations of blueshifted (v {approx} 0.05-0.1c) iron-K X-ray absorption lines. However, it has been suggested that the inner regions of black hole accretion disks can also drive Compton-thick winds-such winds would enshroud the inner disk, preventing us from seeing direct signatures of the accretion disk (i.e., the photospheric thermal emission, or the Doppler/gravitationally broadened iron K{alpha} line). Here, we show that, provided the source is sub-Eddington, the well-established wind-driving mechanisms fail to launch a Compton-thick wind from the inner disk. For the accelerated region of the wind to be Compton-thick, the momentum carried in the wind must exceed the available photon momentum by a factor of at least 2/{lambda}, where {lambda} is the Eddington ratio of the source, ruling out radiative acceleration unless the source is very close to the Eddington limit. Compton-thick winds also carry large mass fluxes, and a consideration of the connections between the wind and the disk shows this to be incompatible with magneto-centrifugal driving. Finally, thermal driving of the wind is ruled out on the basis of the large Compton radii that typify black hole systems. In the absence of some new acceleration mechanisms, we conclude that the inner regions of sub-Eddington accretion disks around black holes are indeed naked.

  10. Magneto-Centrifugal Launching of Jets from Accretion Disks. II: Inner Disk-Driven Winds

    E-Print Network [OSTI]

    Ruben Krasnopolsky; Zhi-Yun Li; Roger D. Blandford

    2003-06-25

    We follow numerically the time evolution of axisymmetric outflows driven magneto-centrifugally from the inner portion of accretion disks, from their launching surface to large, observable distances. Special attention is paid to the collimation of part of the outflow into a dense, narrow jet around the rotation axis, after a steady state has been reached. For parameters typical of T Tauri stars, we define a fiducial ``jet'' as outlined by the contour of constant density at 10^4 cm^{-3}. We find that the jet, so defined, appears nearly cylindrical well above the disk, in agreement with previous asymptotic analyses. Closer to the equatorial plane, the density contour can either bulge outwards or pinch inwards, depending on the conditions at the launching surface, particularly the mass flux distribution. We find that even though a dense, jet-like feature is always formed around the axis, there is no guarantee that the high-density axial jet would dominate the more tenuous, wide-angle part of the wind. Specifically, on the 100 AU scale, resolvable by HST and ground-based adaptive optics for nearby T Tauri winds, the fraction of the wind mass flux enclosed by the fiducial jet can vary substantially, again depending on the launching conditions. We show two examples in which the fraction is ~20% and ~45%. These dependences may provide a way to constrain the conditions at the launching surface, which are poorly known at present.

  11. Color Profiles of Disk Galaxies since z~1: Probing Outer Disk Formation Scenarios

    E-Print Network [OSTI]

    Ruyman Azzollini; Ignacio Trujillo; John E. Beckman

    2008-04-15

    We present deep color profiles for a sample of 415 disk galaxies within the redshift range 0.1disk (Type II objects) usually show a minimum in their color profile at the break, or very near to it, with a maximum to minimum amplitude in color of <~0.2 mag/arcsec^2, a feature which is persistent through the explored range of redshifts (i.e. in the last ~8 Gyr). This color structure is in qualitative agreement with recent model expectations (Roskar et al. 2008) where the break of the surface brightness profiles is the result of the interplay between a radial star formation cut-off and a redistribution of stellar mass by secular processes.

  12. Color Profiles of Disk Galaxies since z~1: Probing Outer Disk Formation Scenarios

    E-Print Network [OSTI]

    Azzollini, Ruyman; Beckman, John E

    2008-01-01

    We present deep color profiles for a sample of 415 disk galaxies within the redshift range 0.1disk (Type II objects) usually show a minimum in their color profile at the break, or very near to it, with a maximum to minimum amplitude in color of <~0.2 mag/arcsec^2, a feature which is persistent through the explored range of redshifts (i.e. in the last ~8 Gyr). This color structure is in qualitative agreement with recent model expectations (Roskar et al. 2008) where the break of the surface brightness profiles is the result of the interplay between a radial star formation cut-off and a redistribution of stellar mass by secular processes.

  13. THE EFFECTS OF INITIAL ABUNDANCES ON NITROGEN IN PROTOPLANETARY DISKS

    SciTech Connect (OSTI)

    Schwarz, Kamber R.; Bergin, Edwin A.

    2014-12-20

    The dominant form of nitrogen provided to most solar system bodies is currently unknown, though available measurements show that the detected nitrogen in solar system rocks and ices is depleted with respect to solar abundances and the interstellar medium. We use a detailed chemical/physical model of the chemical evolution of a protoplanetary disk to explore the evolution and abundance of nitrogen-bearing molecules. Based on this model, we analyze how initial chemical abundances provided as either gas or ice during the early stages of disk formation influence which species become the dominant nitrogen bearers at later stages. We find that a disk with the majority of its initial nitrogen in either atomic or molecular nitrogen is later dominated by atomic and molecular nitrogen as well as NH{sub 3} and HCN ices, where the dominant species varies with disk radius. When nitrogen is initially in gaseous ammonia, it later becomes trapped in ammonia ice except in the outer disk where atomic nitrogen dominates. For a disk with the initial nitrogen in the form of ammonia ice, the nitrogen remains trapped in the ice as NH{sub 3} at later stages. The model in which most of the initial nitrogen is placed in atomic N best matches the ammonia abundances observed in comets. Furthermore, the initial state of nitrogen influences the abundance of N{sub 2}H{sup +}, which has been detected in protoplanetary disks. Strong N{sub 2}H{sup +} emission is found to be indicative of an N{sub 2} abundance greater than n{sub N{sub 2}}/n{sub H{sub 2}}>10{sup ?6} in addition to tracing the CO snow line. Our models also indicate that NO is potentially detectable, with lower N gas abundances leading to higher NO abundances.

  14. Non-LTE modeling of supernova-fallback disks

    E-Print Network [OSTI]

    K. Werner; T. Nagel; T. Rauch

    2006-08-24

    We present a first detailed spectrum synthesis calculation of a supernova-fallback disk composed of iron. We assume a geometrically thin disk with a radial structure described by the classical alpha-disk model. The disk is represented by concentric rings radiating as plane-parallel slabs. The vertical structure and emission spectrum of each ring is computed in a fully self-consistent manner by solving the structure equations simultaneously with the radiation transfer equations under non-LTE conditions. We describe the properties of a specific disk model and discuss various effects on the emergent UV/optical spectrum. We find that strong iron-line blanketing causes broad absorption features over the whole spectral range. Limb darkening changes the spectral distribution up to a factor of four depending on the inclination angle. Consequently, such differences also occur between a blackbody spectrum and our model. The overall spectral shape is independent of the exact chemical composition as long as iron is the dominant species. A pure iron composition cannot be distinguished from silicon-burning ash. Non-LTE effects are small and restricted to few spectral features.

  15. Evolution of stellar disk truncations since z=1

    E-Print Network [OSTI]

    Ignacio Trujillo; Ruyman Azzollini; Judit Bakos; John Beckman; Michael Pohlen

    2008-07-26

    We present our recent results on the cosmic evolution of the outskirst of disk galaxies. In particular we focus on disk-like galaxies with stellar disk truncations. Using UDF, GOODS and SDSS data we show how the position of the break (i.e. a direct estimator of the size of the stellar disk) evolves with time since z~1. Our findings agree with an evolution on the radial position of the break by a factor of 1.3+-0.1 in the last 8 Gyr for galaxies with similar stellar masses. We also present radial color gradients and how they evolve with time. At all redshift we find a radial inside-out bluing reaching a minimum at the position of the break radius, this minimum is followed by a reddening outwards. Our results constraint several galaxy disk formation models and favour a scenario where stars are formed inside the break radius and are relocated in the outskirts of galaxies through secular processes.

  16. Evolution of stellar disk truncations since z=1

    E-Print Network [OSTI]

    Trujillo, Ignacio; Bakos, Judit; Beckman, John; Pohlen, Michael

    2008-01-01

    We present our recent results on the cosmic evolution of the outskirst of disk galaxies. In particular we focus on disk-like galaxies with stellar disk truncations. Using UDF, GOODS and SDSS data we show how the position of the break (i.e. a direct estimator of the size of the stellar disk) evolves with time since z~1. Our findings agree with an evolution on the radial position of the break by a factor of 1.3+-0.1 in the last 8 Gyr for galaxies with similar stellar masses. We also present radial color gradients and how they evolve with time. At all redshift we find a radial inside-out bluing reaching a minimum at the position of the break radius, this minimum is followed by a reddening outwards. Our results constraint several galaxy disk formation models and favour a scenario where stars are formed inside the break radius and are relocated in the outskirts of galaxies through secular processes.

  17. Planet Migration through a Self-Gravitating Planetesimal Disk

    E-Print Network [OSTI]

    Alexander J. Moore; Alice C. Quillen; Richard G. Edgar

    2008-09-17

    We simulate planet migration caused by interactions between planets and a planetesimal disk. We use an N-body integrator optimized for near-Keplerian motion that runs in parallel on a video graphics card, and that computes all pair-wise gravitational interactions. We find that the fraction of planetesimals found in mean motion resonances is reduced and planetary migration rates are on average about 50% slower when gravitational interactions between the planetesimals are computed than when planetesimal self-gravity is neglected. This is likely due to gravitational stirring of the planetesimal disk that is not present when self-gravity is neglected that reduces their capture efficiency because of the increased particle eccentricity dispersion. We find that migration is more stochastic when the disk is self-gravitating or comprised of more massive bodies. Previous studies have found that if the planetesimal disk density is below a critical level, migration is "damped" and the migration rate decays exponentially, otherwise it is "forced" and the planet's migration rate could accelerate exponentially. Migration rates measured from our undamped simulations suggest that the migration rate saturates at a level proportional to disk density and subsequently is approximately power law in form with time.

  18. Massive disk outflows mediated by extreme magnetic fields

    E-Print Network [OSTI]

    Shiber, Sagiv; Soker, Noam

    2015-01-01

    We argue that magnetic fields amplified within a very high accretion-rate disk around main sequence stars can lead to the formation of massive bipolar outflows that can remove most of the disk's mass and energy. This efficient directional removal of energy and mass allows the high accretion-rate disk to be built. We construct thick disks where the magnetic fields are amplified by an Alpha-Omega dynamo in the disk, bringing the fluctuating components of the magnetic field to be much stronger than the large-scale component. By examining the possible activity of the magnetic fields we conclude that main sequence stars can accrete mass at very high rates, up to 0.01Mo/yr for solar type stars, and up to 1Mo/yr for very massive stars. Such energetic outflows can account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, such as the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; Red Novae; Red Transi...

  19. Chemistry and line emission from evolving Herbig Ae disks

    E-Print Network [OSTI]

    B. Jonkheid; C. P. Dullemond; M. R. Hogerheijde; E. F. van Dishoeck

    2006-11-07

    Aims: To calculate chemistry and gas temperature of evolving protoplanetary disks with decreasing mass or dust settling, and to explore the sensitivity of gas-phase tracers. Methods: The density and dust temperature profiles for a range of models of flaring and self-shadowed disks around a typical Herbig Ae star are used together with 2-dimensional ultraviolet (UV) radiative transfer to calculate the chemistry and gas temperature. In each model the line profiles and intensities for the fine structure lines of [O I], [C II] and [C I] and the pure rotational lines of CO, CN, HCN and HCO+ are determined. Results: The chemistry shows a strong correlation with disk mass. Molecules that are easily dissociated, like HCN, require high densities and large extinctions before they can become abundant. The products of photodissociation, like CN and C2H, become abundant in models with lower masses. Dust settling mainly affects the gas temperature, and thus high temperature tracers like the O and C+ fine structure lines. The carbon chemistry is found to be very sensitive to the adopted PAH abundance. The line ratios CO/13CO, CO/HCO+ and [O I] 63 um/146 um can be used to distinguish between disks where dust growth and settling takes place, and disks that undergo overall mass loss.

  20. Inferring Planet Mass from Spiral Structures in Protoplanetary Disks

    E-Print Network [OSTI]

    Fung, Jeffrey

    2015-01-01

    Recent observations of protoplanetary disk have reported spiral structures that are potential signatures of embedded planets, and modeling efforts have shown that a single planet can excite multiple spiral arms, in contrast to conventional disk-planet interaction theory. Using two and three-dimensional hydrodynamics simulations to perform a systematic parameter survey, we confirm the existence of multiple spiral arms in disks with a single planet, and discover a scaling relation between the azimuthal separation of the primary and secondary arm, $\\phi_{\\rm sep}$, and the planet-to-star mass ratio $q$: $\\phi_{\\rm sep} = 102^{\\circ} (q/0.001)^{0.2}$ for companions between Neptune mass and 16 Jupiter masses around a 1 solar mass star, and $\\phi_{\\rm sep} = 180^{\\circ}$ for brown dwarf mass companions. This relation is independent of the disk's temperature, and can be used to infer a planet's mass to within an accuracy of about 30% given only the morphology of a face-on disk. Combining hydrodynamics and Monte-Carl...

  1. The Inner Disk Structure, Disk-Planet Interactions, and Temporal Evolution in the Beta Pictoris System: A Two-Epoch HST/STIS Coronagraphic Study

    E-Print Network [OSTI]

    Apai, Daniel; Grady, Carol A; Wyatt, Mark C; Lagrange, Anne-Marie; Kuchner, Marc J; Stark, Christopher J; Lubow, Stephen H

    2015-01-01

    We present deep HST/STIS coronagraphic images of the Beta Pic debris disk obtained at two epochs separated by 15 years. The new images and the re-reduction of the 1997 data provide the most sensitive and detailed views of the disk at optical wavelengths as well as the yet smallest inner working angle optical coronagraphic image of the disk. Our observations characterize the large-scale and inner-disk asymmetries and we identify multiple breaks in the disk radial surface brightness profile. We study in detail the radial and vertical disk structure and show that the disk is warped. We explore the disk at the location of the Beta Pic b super-jupiter and find that the disk surface brightness slope is continuous between 0.5 and 2.0 arcsec, arguing for no change at the separations where Beta Pic b orbits. The two epoch images constrain the disk surface brightness evolution on orbital and radiation pressure blow-out timescales. We place an upper limit of 3% on the disk surface brightness change between 3-5 arcsec, i...

  2. Spectral modeling of gaseous metal disks around DAZ white dwarfs

    E-Print Network [OSTI]

    K. Werner; T. Nagel; T. Rauch

    2008-09-30

    We report on our attempt for the first non-LTE modeling of gaseous metal disks around single DAZ white dwarfs recently discovered by Gaensicke et al. and thought to originate from a disrupted asteroid. We assume a Keplerian rotating viscous disk ring composed of calcium and hydrogen and compute the detailed vertical structure and emergent spectrum. We find that the observed infrared CaII emission triplet can be modeled with a hydrogen-deficient gas ring located at R=1.2 R_sun, inside of the tidal disruption radius, with Teff about 6000 K and a low surface mass density of about 0.3 g/cm**2. A disk having this density and reaching from the central white dwarf out to R=1.2 R_sun would have a total mass of 7 10**21 g, corresponding to an asteroid with about 160 km diameter.

  3. Does Dissipation in AGN Disks Couple to the Total Pressure?

    E-Print Network [OSTI]

    E. T. Vishniac

    1993-08-12

    Recent work on the transport of angular momentum in accretion disks suggests that the Velikhov-Chandrasekhar instability, in which a large scale magnetic field generates small scale eddys in a shearing environment, may be ultimately responsible for this process. Although there is considerable controversy about the origin and maintenance of this field in accretion disks, it turns out that it is possible to argue, quite generally, using scaling arguments, that this process is sensitive to the total pressure in an AGN disk, rather than the pressure contributed by gas alone. We conclude that the resolution of the conceptual difficulties implied by the presence of strong thermal and viscous instabilities in radiation pressure and electron scattering dominated does not lie in models that couple the total dissipation rate to the gas pressure alone, or to some weighted mean of the gas and radiation pressures.

  4. Type I Planet Migration in Nearly Laminar Disks

    E-Print Network [OSTI]

    H. Li; S. H. Lubow; S. Li; D. N. C. Lin

    2008-12-02

    We describe 2D hydrodynamic simulations of the migration of low-mass planets ($\\leq 30 M_{\\oplus}$) in nearly laminar disks (viscosity parameter $\\alpha laminar disks. For $\\alpha \\ga 10^{-3}$, density feedback effects are washed out and Type I migration persists. The critical masses are in good agreement with the analytic model of Rafikov (2002). In addition, for $\\alpha \\la 10^{-4}$ steep density gradients produce a vortex instability, resulting in a small time-varying eccentricity in the planet's orbit and a slight outward migration. Migration in nearly laminar disks may be sufficiently slow to reconcile the timescales of migration theory with those of giant planet formation in the core accretion model.

  5. PROTOSTELLAR DISK FORMATION ENABLED BY WEAK, MISALIGNED MAGNETIC FIELDS

    SciTech Connect (OSTI)

    Krumholz, Mark R.; Crutcher, Richard M.; Hull, Charles L. H.

    2013-04-10

    The gas from which stars form is magnetized, and strong magnetic fields can efficiently transport angular momentum. Most theoretical models of this phenomenon find that it should prevent formation of large (>100 AU), rotationally supported disks around most protostars, even when non-ideal magnetohydrodynamic (MHD) effects that allow the field and gas to decouple are taken into account. Using recent observations of magnetic field strengths and orientations in protostellar cores, we show that this conclusion is incorrect. The distribution of magnetic field strengths is very broad, and alignments between fields and angular momentum vectors within protostellar cores are essentially random. By combining the field strength and misalignment data with MHD simulations showing that disk formation is expected for both weak and misaligned fields, we show that these observations imply that we should expect disk fractions of {approx}10%-50% even when protostars are still deeply embedded in their parent cores, and even if the gas is governed by ideal MHD.

  6. Rotational Line Emission from Water in Protoplanetary Disks

    E-Print Network [OSTI]

    R. Meijerink; D. R. Poelman; M. Spaans; A. G. G. M. Tielens; A. E. Glassgold

    2008-10-09

    Circumstellar disks provide the material reservoir for the growth of young stars and for planet formation. We combine a high-level radiative transfer program with a thermal-chemical model of a typical T Tauri star disk to investigate the diagnostic potential of the far-infrared lines of water for probing disk structure. We discuss the observability of pure rotational H2O lines with the Herschel Space Observatory, specifically the residual gas where water is mainly frozen out. We find that measuring both the line profile of the ground 110-101 ortho-H2O transition and the ratio of this line to the 312-303 and 221-212 line can provide information on the gas phase water between 5-100 AU, but not on the snow line which is expected to occur at smaller radii.

  7. Modeling the Infrared Emission from the Epsilon Eridani Disk

    E-Print Network [OSTI]

    Li, A; Bendo, G J; Li, Aigen

    2003-01-01

    We model the infrared (IR) emission from the ring-like dust disk around the main-sequence (MS) star Epsilon Eridani, a young analog to our solar system, in terms of a porous dust model previously developed for the extended wedge-shaped disk around the MS star $\\beta$ Pictoris and the sharply truncated ring-like disks around the Herbig Ae/Be stars HR 4796A and HD 141569A. It is shown that the porous dust model with a porosity of $\\simali$90% is also successful in reproducing the IR to submillimeter dust emission spectral energy distribution as well as the 850$\\mum$ flux radial profile of the dust ring around the more evolved MS star Epsilon Eridani. Predictions are made for future {\\it SIRTF} observations which may allow a direct test of the porous dust model.

  8. ENERGETIC PROTONS, RADIONUCLIDES, AND MAGNETIC ACTIVITY IN PROTOSTELLAR DISKS

    SciTech Connect (OSTI)

    Turner, N. J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Drake, J. F., E-mail: neal.turner@jpl.nasa.go [Department of Physics, Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742 (United States)

    2009-10-01

    We calculate the location of the magnetically inactive dead zone in the minimum-mass protosolar disk, under ionization scenarios including stellar X-rays, long- or short-lived radionuclide decay, and energetic protons arriving from the general interstellar medium, from a nearby supernova explosion, from the disk corona, or from the corona of the young star. The disk contains a dead zone in all scenarios except those with small dust grains removed and a fraction of the short-lived radionuclides remaining in the gas. All the cases without exception have an 'undead zone' where intermediate resistivities prevent magneto-rotational turbulence while allowing shear-generated large-scale magnetic fields. The mass column in the undead zone is typically greater than the column in the turbulent surface layers. The results support the idea that the dead and undead zones are robust consequences of cold, dusty gas with mass columns exceeding 1000 g cm{sup -2}.

  9. Simulations of eccentric disks in close binary systems

    E-Print Network [OSTI]

    Wilhelm Kley; John Papaloizou; Gordon Ogilvie

    2008-06-24

    We study the development of finite eccentricity in accretion disks in close binary systems using a two-dimensional grid-based numerical scheme. We perform detailed parameter studies to explore the dependence on viscosity, disk aspect ratio, the inclusion of a mass-transfer stream and the role of the boundary conditions. We consider mass ratios 0.05disk that attains a quasi-steady state with mean eccentricity in the range 0.3-0.5 occurs readily. The shortest growth times are ~15 binary orbits for the largest viscosities and the instability mechanism is for the most part consistent with the mode-coupling mechanism associated with the 3:1 resonance proposed by Lubow. However, the results are sensitive to the treatment of the inner boundary and to the incorporation of the mass-transfer stream. In the presence of a stream we found a critical viscosity below which the disk remains circular. Incorporation of a mass-transfer stream tends to impart stability for small enough viscosity (or, equivalently, mass-transfer rate through the disk) and does assist in obtaining a prograde precession rate that is in agreement with observations. For the larger q the location of the 3:1 resonance is pushed outwards towards the Roche lobe where higher-order mode couplings and nonlinearity occur. It is likely that three-dimensional simulations that properly resolve the disk's vertical structure are required to make significant progress in this case.

  10. CONSTRAINTS FROM ASYMMETRIC HEATING: INVESTIGATING THE EPSILON AURIGAE DISK

    SciTech Connect (OSTI)

    Pearson, Richard L. III; Stencel, Robert E., E-mail: richard.pearson@du.edu, E-mail: robert.stencel@du.edu [Department of Physics and Astronomy, The University of Denver, Denver, CO 80208 (United States)

    2015-01-01

    Epsilon Aurigae is a long-period eclipsing binary that likely contains an F0Ia star and a circumstellar disk enshrouding a hidden companion, assumed to be a main-sequence B star. High uncertainty in its parallax has kept the evolutionary status of the system in question and, hence, the true nature of each component. This unknown, as well as the absence of solid state spectral features in the infrared, requires an investigation of a wide parameter space by means of both analytic and Monte Carlo radiative transfer (MCRT) methods. The first MCRT models of epsilon Aurigae that include all three system components are presented here. We seek additional system parameter constraints by melding analytic approximations with MCRT outputs (e.g., dust temperatures) on a first-order level. The MCRT models investigate the effects of various parameters on the disk-edge temperatures; these include two distances, three particle size distributions, three compositions, and two disk masses, resulting in 36 independent models. Specifically, the MCRT temperatures permit analytic calculations of effective heating and cooling curves along the disk edge. These are used to calculate representative observed fluxes and corresponding temperatures. This novel application of thermal properties provides the basis for utilization of other binary systems containing disks. We find degeneracies in the model fits for the various parameter sets. However, the results show a preference for a carbon disk with particle size distributions ?10 ?m. Additionally, a linear correlation between the MCRT noon and basal temperatures serves as a tool for effectively eliminating portions of the parameter space.

  11. Dusty disks around central stars of planetary nebulae

    SciTech Connect (OSTI)

    Clayton, Geoffrey C. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); De Marco, Orsola [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Nordhaus, Jason [Center for Computational Relativity and Gravitation, and National Technical Institute for the Deaf, Rochester Institute of Technology, Rochester, NY 14623 (United States); Green, Joel [Department of Astronomy, The University of Texas, 1 University Station, C1400, Austin, TX 78712-0259 (United States); Rauch, Thomas; Werner, Klaus [Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, D-72076 Tübingen (Germany); Chu, You-Hua, E-mail: gclayton@fenway.phys.lsu.edu, E-mail: orsola@science.mq.edu.au, E-mail: nordhaus@astro.rit.edu, E-mail: joel@astro.as.utexas.edu, E-mail: rauch@astro.uni-tuebingen.de, E-mail: werner@astro.uni-tuebingen.de, E-mail: chu@astro.uiuc.edu [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801 (United States)

    2014-06-01

    Only a few percent of cool, old white dwarfs (WDs) have infrared excesses interpreted as originating in small hot disks due to the infall and destruction of single asteroids that come within the star's Roche limit. Infrared excesses at 24 ?m were also found to derive from the immediate vicinity of younger, hot WDs, most of which are still central stars of planetary nebulae (CSPNe). The incidence of CSPNe with this excess is 18%. The Helix CSPN, with a 24 ?m excess, has been suggested to have a disk formed from collisions of Kuiper belt-like objects (KBOs). In this paper, we have analyzed an additional sample of CSPNe to look for similar infrared excesses. These CSPNe are all members of the PG 1159 class and were chosen because their immediate progenitors are known to often have dusty environments consistent with large dusty disks. We find that, overall, PG 1159 stars do not present such disks more often than other CSPNe, although the statistics (five objects) are poor. We then consider the entire sample of CSPNe with infrared excesses and compare it to the infrared properties of old WDs, as well as cooler post-asymptotic giant branch (AGB) stars. We conclude with the suggestion that the infrared properties of CSPNe more plausibly derive from AGB-formed disks rather than disks formed via the collision of KBOs, although the latter scenario cannot be ruled out. Finally, there seems to be an association between CSPNe with a 24 ?m excess and confirmed or possible binarity of the central star.

  12. Asymmetric evolution of magnetic reconnection in collisionless accretion disk

    SciTech Connect (OSTI)

    Shirakawa, Keisuke Hoshino, Masahiro

    2014-05-15

    An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks, magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand, also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet, which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection, which can be understood by a coupling of the Hall effect and the differential rotation. We also found a migration of X-point whose direction is determined only by an initial sign of J{sub 0}×?{sub 0}, where J{sub 0} is the initial current density in the neutral sheet and ?{sub 0} is the rotational vector of the background Keplerian rotation. Associated with the migration of X-point, we also found a significant enhancement of the perpendicular magnetic field compared to an ordinary MRI. MRI-Magnetic reconnection coupling and the resulting magnetic field enhancement can be an effective process to sustain a strong turbulence in the accretion disk and to a transport of angular momentum.

  13. Searching for circumplanetary disks around LkCa 15

    SciTech Connect (OSTI)

    Isella, Andrea; Carpenter, John M.; Ricci, Luca [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Chandler, Claire J.; Pérez, Laura M., E-mail: isella@astro.caltech.edu [National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801 (United States)

    2014-06-20

    We present Karl G. Jansky Very Large Array (VLA) observations of the 7 mm continuum emission from the disk surrounding the young star LkCa 15. The observations achieve an angular resolution of 70 mas and spatially resolve the circumstellar emission on a spatial scale of 9 AU. The continuum emission traces a dusty annulus of 45 AU in radius that is consistent with the dust morphology observed at shorter wavelengths. The VLA observations also reveal a compact source at the center of the disk, possibly due to thermal emission from hot dust or ionized gas located within a few AU from the central star. No emission is observed between the star and the dusty ring and, in particular, at the position of the candidate protoplanet LkCa 15 b. By comparing the observations with theoretical models for circumplanetary disk emission, we find that if LkCa 15 b is a massive planet (>5 M{sub J} ) accreting at a rate greater than 10{sup –6} M{sub J} yr{sup –1}, then its circumplanetary disk is less massive than 0.1 M{sub J} , or smaller than 0.4 Hill radii. Similar constraints are derived for any possible circumplanetary disk orbiting within 45 AU from the central star. The mass estimates are uncertain by at least one order of magnitude due to the uncertainties on the mass opacity. Future ALMA observations of this system might be able to detect circumplanetary disks down to a mass of 5 × 10{sup –4} M{sub J} and as small as 0.2 AU, providing crucial constraints on the presence of giant planets in the act of forming around this young star.

  14. Kinematic segregation of nearby disk stars from the Hipparcos database

    E-Print Network [OSTI]

    R. E. de Souza; R. Teixeira

    2007-04-25

    To better understand our Galaxy, we investigate the pertinency of describing the sys tem of nearby disk stars in terms of a two-components Schwarzschild velocity distributio n.Using the proper motion and parallax information of Hipparcos database, we determine t he parameters characterizing the local stellar velocity field of a sample of 22000 disk stars. The sample we use is essentially the same as the one described by the criteria ad opted to study the LSR and the stream motion of the nearby stellar population

  15. Dim Matter in the Disks of Low Surface Brightness Galaxies

    E-Print Network [OSTI]

    B. Fuchs

    2002-04-23

    An attempt is made to set constraints on the otherwise ambiguous decomposition of the rotation curves of low surface brightness galaxies into contributions due to the various components of the galaxies. For this purpose galaxies are selected which show clear spiral structure. Arguments of density wave theory of galactic spiral arms are then used to estimate the masses of the galactic disks. These estimates seem to indicate that the disks of low surface brightness galaxies might be much more massive than currently thought. This unexpected result contradicts stellar population synthesis models. This would also mean that low surface brightness galaxies are not dominated by dark matter in their inner parts.

  16. NGC2613, 3198, 6503, 7184: Case studies against `maximum' disks

    E-Print Network [OSTI]

    B. Fuchs

    1998-12-02

    Decompositions of the rotation curves of NGC2613, 3198, 6505, and 7184 are analysed. For these galaxies the radial velocity dispersions of the stars have been measured and their morphology is clearly discernible. If the parameters of the decompositions are chosen according to the `maximum' disk hypothesis, the Toomre Q stability parameter is systematically less than one and the multiplicities of the spiral arms as expected from density wave theory are inconsitent with the observed morphologies of the galaxies. The apparent Q<1 instability, in particular, is a strong argument against the `maximum' disk hypothesis.

  17. The evolution of dusty Debris disks around solar type stars

    SciTech Connect (OSTI)

    Vican, Laura [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Schneider, Adam, E-mail: lvican@astro.ucla.edu, E-mail: aschneid@physast.uga.edu [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)

    2014-01-10

    We used chromospheric activity to determine the ages of 2820 field stars. We searched these stars for excess emission at 22 ?m with the Wide-Field Infrared Survey Explorer. Such excess emission is indicative of a dusty debris disk around a star. We investigated how disk incidence trends with various stellar parameters, and how these parameters evolve with time. We found 22 ?m excesses around 98 stars (a detection rate of 3.5%). Of these 98 excess sources, 74 are presented here for the first time. We also measured the abundance of lithium in eight dusty stars in order to test our stellar age estimates.

  18. Angular Sizes of Faint Field Disk Galaxies: Intrinsic Luminosity Evolution

    E-Print Network [OSTI]

    Laura Cayon; Joseph Silk; Stephane Charlot

    1996-06-07

    In order to explain the small scale-lengths detected in the recent deep field observations performed from large ground-based telescopes and from the Hubble Space Telescope, we investigate the predictions at high redshifts for disk galaxies that formed by infall. Changes with redshift in the observed properties of field galaxies are directly related to the evolution of the disks and of the stellar populations. We see that changes in the rest frame luminosity of a galaxy induce smaller values of half-light radii than are predicted assuming no evolution. Comparisons are presented with two observed samples from Mutz et al. (1994) and Smail et al. (1995).

  19. Investigation of the effect of shock, vibration, surface texture and surface pattern on the dynamics of the head disk interface

    E-Print Network [OSTI]

    Murthy, Aravind N.

    2007-01-01

    Corrections for Very Low Spacing at the Head Disk InterfaceS, "Low Stiction/Low Glide Height Head Disk Interface forCorrections for Very Low Spacing at the Head Disk Interface

  20. The Role of the Cooling Prescription for Disk Fragmentation: Numerical Convergence & Critical Cooling Parameter in Self-Gravitating Disks

    E-Print Network [OSTI]

    Baehr, Hans

    2015-01-01

    Protoplanetary disks fragment due to gravitational instability when there is enough mass for self-gravitation, described by the Toomre parameter, and when heat can be lost at a rate comparable to the local dynamical timescale, described by t_c=beta Omega^-1. Simulations of self-gravitating disks show that the cooling parameter has a rough critical value at beta_crit=3. When below beta_crit, gas overdensities will contract under their own gravity and fragment into bound objects while otherwise maintaining a steady state of gravitoturbulence. However, previous studies of the critical cooling parameter have found dependence on simulation resolution, indicating that the simulation of self-gravitating protoplanetary disks is not so straightforward. In particular, the simplicity of the cooling timescale t_c prevents fragments from being disrupted by pressure support as temperatures rise. We alter the cooling law so that the cooling timescale is dependent on local surface density fluctuations, a means of incorporati...

  1. Thermal Fly-height Control Slider Dynamics and Slider-Lubricant Interactions in Hard Disk Drives

    E-Print Network [OSTI]

    Vangipuram Canchi, Sripathi

    2011-01-01

    the HDI at extremely low head-disk clearances. ExperimentsHDI reliability at extremely low head-disk clearance. Systemextremely low physical spacing at the read-write head. The

  2. Workload-Adaptive Management of Energy-Smart Disk Storage Systems

    SciTech Connect (OSTI)

    Otoo, Ekow; Rotem, Doron; Tsao, Shih-Chiang

    2009-06-19

    Recent studies have identified disk storage systems as one of the major consumers of power in data centers. Many disk power management (DPM) schemes were suggested where the power consumed by disks is reduced by spinning them down during long idle periods. Spinning the disks down and up results in additional energy and response time costs. For that reason, DPM schemes are effective only if the disks experience relatively long idle periods and the scheme does not introduce a severe response time penalty. In this paper we introduce a dynamic block exchange algorithm which switches data between disks based on the observed workload such that frequently accessed blocks end up residing on a few"hot" disks thus allowing the majority of disks to experience longer idle periods. We validate the effectiveness of the algorithm with trace-driven simulations showing power savings of up to 60percent with very small response time penalties.

  3. The Evolution of Debris Disk Systems: Constraints from Theory and Observation 

    E-Print Network [OSTI]

    Smith, Rachel

    2008-01-01

    Debris disks are believed to be the remnants of planet formation; a disk of solid bodies called planetesimals that did not get incorporated into planets. They provide an ideal opportunity for studying the outcome of ...

  4. BIPOLAR JETS LAUNCHED FROM ACCRETION DISKS. II. THE FORMATION OF ASYMMETRIC JETS AND COUNTER JETS

    SciTech Connect (OSTI)

    Fendt, Christian; Sheikhnezami, Somayeh E-mail: nezami@mpia.de

    2013-09-01

    We investigate the jet launching from accretion disks, in particular the formation of intrinsically asymmetric jet/counter jet systems. We perform axisymmetric MHD simulations of the disk-jet structure on a bipolar computational domain covering both hemispheres. We apply various models such as asymmetric disks with (initially) different scale heights in each hemisphere, symmetric disks into which a local disturbance is injected, and jets launched into an asymmetric disk corona. We consider both a standard global magnetic diffusivity distribution and a novel local diffusivity model. Typical disk evolution first shows substantial disk warping and then results in asymmetric outflows with a 10%-30% mass flux difference. We find that the magnetic diffusivity profile is essential for establishing a long-term outflow asymmetry. We conclude that bipolar asymmetry in protostellar and extragalactic jets can indeed be generated intrinsically and maintained over a long time by disk asymmetries and the standard jet launching mechanism.

  5. Brown Dwarf Formation from Disk Fragmentation and Ejection

    E-Print Network [OSTI]

    Joergens, Viki

    irradiation flux 4 r midplane optical depth opacity from Bell & Lin (1990); = 2 + 20tan /3 u u ; , , / 2 , irr & Basu (2006, ApJ, 650, 956) Clump formation (gravitational instability) and migration Long;Migrating Embryo (ME) Scenario Clumps form in outer disk, radius ~ 50 ­ 100 AU, migrate inward (migration

  6. Jet and disk luminosities in tidal disruption events

    E-Print Network [OSTI]

    Piran, Tsvi; Tchekhovskoy, Alexander

    2015-01-01

    Tidal disruption events (TDE) in which a star is devoured by a massive black hole at a galac- tic center pose a challenge to our understanding of accretion processes. Within a month the accretion rate reaches super-Eddington levels. It then drops gradually over a time scale of a year to sub-Eddington regimes. The initially geometrically thick disk becomes a thin one and eventually an ADAF at very low accretion rates. As such, TDEs explore the whole range of accretion rates and configurations. A challenging question is what the corresponding light curves of these events are. We explore numerically the disk luminosity and the conditions within the inner region of the disk using a fully general relativistic slim disk model. Those conditions determine the magnitude of the magnetic field that engulfs the black hole and this, in turn, determines the Blandford-Znajek jet power. We estimate this power in two different ways and show that they are self-consistent. We find, as expected earlier from analytic argu- ments ...

  7. Automated Design, Analysis, and Optimization of Turbomachinery Disks

    E-Print Network [OSTI]

    Cincinnati, University of

    in virtually all axially configured gas turbines. These components are both highly stressed and heavy. A single discussion includes the development of a one dimensional plane stress model, common disk ge- ometry fidelity finite element method. Hardware from the GE E3 high pressure compressor, GE E3 high pressure

  8. Bridge Creek Watershed Volunteer Lake Secchi Disk Monitoring Program

    E-Print Network [OSTI]

    #12;Bridge Creek Watershed Volunteer Lake Secchi Disk Monitoring Program 1996 DOE FRAP 1996-13 Ryan.C. December 1996 #12;ABSTRACT This document summarizes data collected during the first year of the Bridge transparency data from 22 lakes in the Bridge Creek watershed. Secchi depth readings were collected between May

  9. Vortex generation in protoplanetary disks with an embedded giant planet

    E-Print Network [OSTI]

    M. de Val-Borro; P. Artymowicz; G. D'Angelo; A. Peplinski

    2007-06-21

    Vortices in protoplanetary disks can capture solid particles and form planetary cores within shorter timescales than those involved in the standard core-accretion model. We investigate vortex generation in thin unmagnetized protoplanetary disks with an embedded giant planet with planet to star mass ratio $10^{-4}$ and $10^{-3}$. Two-dimensional hydrodynamical simulations of a protoplanetary disk with a planet are performed using two different numerical methods. The results of the non-linear simulations are compared with a time-resolved modal analysis of the azimuthally averaged surface density profiles using linear perturbation theory. Finite-difference methods implemented in polar coordinates generate vortices moving along the gap created by Neptune-mass to Jupiter-mass planets. The modal analysis shows that unstable modes are generated with growth rate of order $0.3 \\Omega_K$ for azimuthal numbers m=4,5,6, where $\\Omega_K$ is the local Keplerian frequency. Shock-capturing Cartesian-grid codes do not generate very much vorticity around a giant planet in a standard protoplanetary disk. Modal calculations confirm that the obtained radial profiles of density are less susceptible to the growth of linear modes on timescales of several hundreds of orbital periods. Navier-Stokes viscosity of the order $\

  10. Periodicity of the solar full-disk magnetic fields

    SciTech Connect (OSTI)

    Xiang, N. B.; Qu, Z. N.; Zhai, Q. [National Astronomical Observatories/Yunnan Observatory, CAS, Kunming 650011 (China)

    2014-07-01

    A full-disk solar magnetogram has been measured each day since 1970 January 19, and the daily Magnetic Plage Strength Index (MPSI) and the daily Mount Wilson Sunspot Index (MWSI) were calculated for each magnetogram at the Mount Wilson Observatory. The MPSI and MWSI are used to investigate the periodicity of the solar full-disk magnetic activity through autocorrelation analyses. Just two periods, the solar cycle and the rotation cycle, are determined in both the MPSI (the solar full-disk weak magnetic field activity) and MWSI (the solar full-disk strong magnetic field activity) with no annual signal found. The solar cycle for MPSI (10.83 yr) is found to be obviously longer than that for MWSI (9.77 yr). The rotation cycle is determined to be 26.8 ± 0.63 sidereal days for MPSI and 27.4 ± 2.4 sidereal days for MWSI. The rotation cycle length for MPSI is found to fluctuate around 27 days within a very small amplitude, but for MWSI it obviously temporally varies with a rather large amplitude. The rotation cycle for MWSI seems longer near solar minimum than at solar maximum. Cross-correlation analyses of daily MPSI and MWSI are carried out, and it is inferred that the MPSI components partly come from relatively early MWSI measurements.

  11. Covariant Lyapunov Vectors for Rigid Disk Systems Hadrien Bosetti

    E-Print Network [OSTI]

    Posch, Harald A.

    Covariant Lyapunov Vectors for Rigid Disk Systems Hadrien Bosetti and Harald A. Posch Computational: October 17, 2010) We carry out extensive computer simulations to study the Lyapunov instability of a two enough to allow the formation of Lyapunov modes parallel to the x-axis of the box. The Oseledec splitting

  12. Lyapunov Modes in HardDisk Systems April 2, 2004

    E-Print Network [OSTI]

    Lyapunov Modes in Hard­Disk Systems April 2, 2004 Jean­Pierre Eckmann 1,2 , Christina Forster 3 the Lyapunov spectrum near the vanishing Lyapunov exponents. To this spectrum are associated ``eigen­directions'', called Lyapunov modes. We carefully analyze these modes and show how they are naturally associated

  13. MEMS-based storage devices and standard disk interfaces

    E-Print Network [OSTI]

    MEMS-based storage devices and standard disk interfaces: A square peg in a round hole? Steven W University Pittsburgh, PA 15213-3890 Abstract MEMS-based storage devices are a new technology works for existing systems, and by showing that these reasons hold for MEMS-based storage. This result

  14. Active Disks -Remote Execution for Network-Attached Storage

    E-Print Network [OSTI]

    , Seagate, Wind River Systems, Siemens, and StorageTek. The views and conclusions contained in this document power on individual disk drives to run application- level code. Moving portions of an application of the optimizations that are possible with more knowl- edge available directly at the devices. It also compares

  15. Active Disks Remote Execution for NetworkAttached Storage

    E-Print Network [OSTI]

    , Seagate, Wind River Systems, Siemens, and StorageTek. The views and conclusions contained in this document of the processing power on individual disk drives to run application­ level code. Moving portions of an application of the optimizations that are possible with more knowl­ edge available directly at the devices. It also compares

  16. POYNTING JETS FROM ACCRETION DISKS R. V. E. Lovelace,1

    E-Print Network [OSTI]

    POYNTING JETS FROM ACCRETION DISKS R. V. E. Lovelace,1 H. Li,2 A. V. Koldoba,3 G. V. Ustyugova,4 jets in which there is a continuous outflow of energy, angular momentum, and toroidal magnetic flux discuss magnetohy- drodynamic simulations that show quasi-stationary collimated Poynting jets similar

  17. Improving Energy Efficiency and Security for Disk Systems

    E-Print Network [OSTI]

    Qin, Xiao

    Improving Energy Efficiency and Security for Disk Systems Shu Yin1 , Mohammed I. Alghamdi2 been focused on data security and energy efficiency, most of the existing approaches have concentrated optimization with security services to enhance the security of energy-efficient large- scale storage systems

  18. A File Allocation Strategy for Energy-Efficient Disk Storage Systems

    E-Print Network [OSTI]

    Geddes, Cameron Guy Robinson

    A File Allocation Strategy for Energy-Efficient Disk Storage Systems E. Otoo #1, A. Pinar #2, D disk storage farms. The provisioning of disk storage farms however, is at the expense of high energy the trend of rising global fuel and energy prices and the high rate of data growth, the challenge

  19. SmartSaver: Turning Flash Drive into a Disk Energy Saver for Mobile Computers

    E-Print Network [OSTI]

    Chen, Feng

    SmartSaver: Turning Flash Drive into a Disk Energy Saver for Mobile Computers Feng Chen The Ohio amount of energy. Existing dynamic power management poli- cies usually take conservative approaches to save disk energy, and disk energy consumption remains a serious issue. Mean- while, the flash drive

  20. Planetary migration in a planetesimal disk: why did Neptune stop at 30 AU?

    E-Print Network [OSTI]

    Levison, Harold F.

    Planetary migration in a planetesimal disk: why did Neptune stop at 30 AU? Rodney S. Gomes GEA 12 gures #12;{ 2 { Running head: Migration in a planetesimal disk Send correspondence to: Rodney S, Brazil Received accepted #12;{ 3 { ABSTRACT We study planetary migration in a gas-free disk

  1. Improving Reliability of Energy-Efficient Parallel Storage Systems by Disk Swapping

    E-Print Network [OSTI]

    Qin, Xiao

    and the Massive Array of Idle Disks (MAID) technique are two effective energy saving schemes for parallel disk [2]. Existing energy conservation techniques can yield significant en- ergy savings in disks. While several energy conservation schemes like cache-based energy saving approaches normally have marginal

  2. MINT: A Reliability Modeling Framework for Energy-Efficient Parallel Disk Systems

    E-Print Network [OSTI]

    Qin, Xiao

    than disks storing cold data. To study reliability impacts of energy-saving techniques on parallel disk this problem, a broad spectrum of energy-saving techniques were proposed to achieve high energy efficiency that existing energy conservation techniques in disk drives can deliver significant energy savings in large

  3. NICMOS CORONAGRAPHIC OBSERVATIONS OF THE GM AURIGAE CIRCUMSTELLAR DISK G. Schneider

    E-Print Network [OSTI]

    Wood, Kenneth

    NICMOS CORONAGRAPHIC OBSERVATIONS OF THE GM AURIGAE CIRCUMSTELLAR DISK G. Schneider Steward of the young star-disk system GM Aurigae. Scattered near-infrared light in two spectral bands (F110W = 1.1 lm star. The midplane of the disk 1>3 from GM Aurigae is revealed in silhouette against the previously

  4. MAGNETIZED ACCRETION AND DEAD ZONES IN PROTOSTELLAR DISKS

    SciTech Connect (OSTI)

    Dzyurkevich, Natalia; Henning, Thomas; Turner, Neal J.; Kley, Wilhelm

    2013-03-10

    The edges of magnetically dead zones in protostellar disks have been proposed as locations where density bumps may arise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically active zones provides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location of the magnetically active regions in a protostellar disk around a solar-type star, varying the disk temperature, surface density profile, and dust-to-gas ratio. We also consider stellar masses between 0.4 and 2 M{sub Sun }, with corresponding adjustments in the disk mass and temperature. The dead zone's size and shape are found using the Elsasser number criterion with conductivities including the contributions from ions, electrons, and charged fractal dust aggregates. The charged species' abundances are found using the approach proposed by Okuzumi. The dead zone is in most cases defined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, including a fish tail pointing away from the star and islands located on and off the midplane. The corresponding accretion rates vary with radius, indicating locations where the surface density will increase over time, and others where it will decrease. We show that density bumps do not readily grow near the dead zone's outer edge, independently of the disk parameters and the dust properties. Instead, the accretion rate peaks at the radius where the gas-phase metals freeze out. This could lead to clearing a valley in the surface density, and to a trap for pebbles located just outside the metal freezeout line.

  5. FAST MODES AND DUSTY HORSESHOES IN TRANSITIONAL DISKS

    SciTech Connect (OSTI)

    Mittal, Tushar; Chiang, Eugene

    2015-01-01

    The brightest transitional protoplanetary disks are often azimuthally asymmetric: their millimeter-wave thermal emission peaks strongly on one side. Dust overdensities can exceed ?100:1, while gas densities vary by factors less than a few. We propose that these remarkable ALMA observations—which may bear on how planetesimals form—reflect a gravitational global mode in the gas disk. The mode is (1) fast—its pattern speed equals the disk's mean Keplerian frequency; (2) of azimuthal wavenumber m = 1, displacing the host star from the barycenter; and (3) Toomre-stable. We solve for gas streamlines including the indirect stellar potential in the frame rotating with the pattern speed, under the drastic simplification that gas does not feel its own gravity. Near corotation, the gas disk takes the form of a horseshoe-shaped annulus. Dust particles with aerodynamic stopping times much shorter or much longer than the orbital period are dragged by gas toward the horseshoe center. For intermediate stopping times, dust converges toward a ?45° wide arc on the corotation circle. Particles that do not reach their final accumulation points within disk lifetimes, either because of gas turbulence or long particle drift times, conform to horseshoe-shaped gas streamlines. Our mode is not self-consistent because we neglect gas self-gravity; still, we expect that trends between accumulation location and particle size, similar to those we have found, are generically predicted by fast modes and are potentially observable. Unlike vortices, global modes are not restricted in radial width to the pressure scale height; their large radial and azimuthal extents may better match observations.

  6. Evolution of Gas and Dust in Circumstellar Disks

    E-Print Network [OSTI]

    David W. Koerner

    1999-12-17

    A clear understanding of the chemical processing of matter, as it is transferred from a molecular cloud to a planetary system, depends heavily on knowledge of the physical conditions endured by gas and dust as these accrete onto a disk and are incorporated into planetary bodies. Reviewed here are astrophysical observations of circumstellar disks which trace their evolving properties. Accretion disks that are massive enough to produce a solar system like our own are typically larger than 100 AU. This suggests that the chemistry of a large fraction of the infalling material is not radically altered upon contact with a vigorous accretion shock. The mechanisms of accretion onto the star and eventual dispersal are not yet well understood, but timescales for the removal of gas and optically thick dust appear to be a few times 10$^6$ yrs. At later times, tenuous ``debris disks'' of dust remain around stars as old as a few times 10$^8$ yrs. Features in the morphology of the latter, such as inner holes, warps, and azimuthal asymmetries, are likely to be the result of the dynamical influence of large planetary bodies. Future observations will enlighten our understanding of chemical evolution and will focus on the search for disks in transition from a viscous accretion stage to one represented by a gas-free assemblage of colliding planetesimals. In the near future, comparative analysis of circumstellar dust and gas properties within a statistically significant sample of young stars at various ages will be possible with instrumentation such as SIRTF and SOFIA. Well-designed surveys will help place solar system analogs in a general context of a diversity of possible pathways for circumstellar evolution, one which encompasses the formation of stellar and brown-dwarf companions as well as planetary systems.

  7. Black Hole, Jet, and Disk: The Universal Engine

    E-Print Network [OSTI]

    Heino Falcke

    1995-12-14

    In this paper I review the results of our ongoing project to investigate the coupling between accretion disk and radio jet in galactic nuclei and stellar mass black holes. We find a good correlation between the UV bump luminosity and the radio luminosities of AGN, which improves upon the usual [OIII]/radio correlations. Taking mass and energy conservation in the jet/disk system into account we can successfully model the correlation for radio-loud and radio-weak quasars. We find that jets are comparable in power to the accretion disk luminosity, and the difference between radio-loud and radio-weak may correspond to two natural stages of the relativistic electron distribution -- assuming that radio weak quasars have jets as well. The distribution of flat- and steep-spectrum sources is explained by bulk Lorentz factors gamma_j ~ 5-10. The absence of radio-loud quasars below a critical optical luminosity coincides with the FR I/FR II break and could be explained by a powerdependent, ``closing'' torus. This points towards a different type of obscuring torus in radio-loud host galaxies which might be a consequence of past mergers (e.g. by the temporary formation of a binary black-hole). Interaction of the jet with the closing torus might in principle also help to make a jet radio-loud. Turning to stellar-mass black holes we find that galactic jet sources can be described with the same coupled jet/disk model as AGN which is suggestive of some kind of universal coupling between jet and accretion disk around compact objects.

  8. IMAGING THE DISK AND JET OF THE CLASSICAL T TAURI STAR AA TAU

    SciTech Connect (OSTI)

    Cox, Andrew W.; Grady, Carol A.; Hammel, Heidi B.; Hornbeck, Jeremy; Russell, Ray W.; Sitko, Michael L.; Woodgate, Bruce E.

    2013-01-01

    Previous studies of the classical T Tauri star AA Tau have interpreted the UX-Orionis-like photo-polarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipole field. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use Hubble Space Telescope (HST)/STIS coronagraphic imagery to measure the V magnitude of the star for both STIS coronagraphic observations, compare these data with optical photometry in the literature, and find that, unlike other classical T Tauri stars observed in the same HST program, the disk is most robustly detected in scattered light at stellar optical minimum light. We measure the outer disk radius, 1.''15 {+-} 0.''10, major-axis position angle, and disk inclination and find that the inner disk, as reported in the literature, is both misinclined and misaligned with respect to the outer disk. AA Tau drives a faint jet, detected in both STIS observations and in follow-on Goddard Fabry-Perot imagery, which is also misaligned with respect to the projection of the outer disk minor axis and is poorly collimated near the star, but which can be traced 21'' from the star in data from 2005. The measured outer disk inclination, 71 Degree-Sign {+-} 1 Degree-Sign , is out of the range of inclinations suggested for stars with UX-Orionis-like variability when no grain growth has occurred in the disk. The faintness of the disk, small disk size, and detection of the star despite the high inclination all indicate that the dust disk must have experienced grain growth and settling toward the disk midplane, which we verify by comparing the observed disk with model imagery from the literature.

  9. TRANSITIONAL DISKS AND THEIR ORIGINS: AN INFRARED SPECTROSCOPIC SURVEY OF ORION A

    SciTech Connect (OSTI)

    Kim, K. H.; Watson, Dan M.; Manoj, P.; Forrest, W. J.; Arnold, Laura; Najita, Joan; Furlan, Elise; Sargent, Benjamin; Espaillat, Catherine; Muzerolle, James; Megeath, S. T.; Calvet, Nuria; Green, Joel D.

    2013-06-01

    Transitional disks are protoplanetary disks around young stars, with inner holes or gaps which are surrounded by optically thick outer, and often inner, disks. Here we present observations of 62 new transitional disks in the Orion A star-forming region. These were identified using the Spitzer Space Telescope's Infrared Spectrograph and followed up with determinations of stellar and accretion parameters using the Infrared Telescope Facility's SpeX. We combine these new observations with our previous results on transitional disks in Taurus, Chamaeleon I, Ophiuchus, and Perseus, and with archival X-ray observations. This produces a sample of 105 transitional disks of ''cluster'' age 3 Myr or less, by far the largest hitherto assembled. We use this sample to search for trends between the radial structure in the disks and many other system properties, in order to place constraints on the possible origins of transitional disks. We see a clear progression of host-star accretion rate and the different disk morphologies. We confirm that transitional disks with complete central clearings have median accretion rates an order of magnitude smaller than radially continuous disks of the same population. Pre-transitional disks-those objects with gaps that separate inner and outer disks-have median accretion rates intermediate between the two. Our results from the search for statistically significant trends, especially related to M-dot , strongly support that in both cases the gaps are far more likely to be due to the gravitational influence of Jovian planets or brown dwarfs orbiting within the gaps, than to any of the photoevaporative, turbulent, or grain-growth processes that can lead to disk dissipation. We also find that the fraction of Class II YSOs which are transitional disks is large, 0.1-0.2, especially in the youngest associations.

  10. Imprinting Hatchery Reared Salmon and Steelhead Trout for Homing, Volume I of III; Narrative, 1978-1983 Final Report.

    SciTech Connect (OSTI)

    Slatick, Emil; Gilbreath, Lyle G.; Harmon, Jerrel R. (Northwest and Alaska Fisheries Science Center, Coastal Zone and Estuarine Studies Division, Seattle, WA)

    1988-02-01

    The National Marine Fisheries Service began conducting homing research on Pacific salmon and steelhead. Over 4 million juvenile salmon and steelhead were marked and released, and 23 individual experiments were conducted. The research had the following objectives: (1) develop the techniques for imprinting homing cues while increasing survival of hatchery reared salmonids and (2) provide fishery managers with the information necessary to increase the returns of salmon and steelhead to the Columbia River system and to effectively distribute these fish to the various user groups. Our imprint methods were grouped into three general categories: (1) natural migration imprint from a hatchery of origin or an alternate homing site (by allowing fish to volitionally travel downstream through the river on their seaward journey), (2) single exposure imprinting (cueing fish to a single unique water supply with or without mechanical stimuli prior to transport and release), and (3) sequential exposure imprinting (cueing fish to two or more water sources in a step-by-step process to establish a series of signposts for the route ''home''). With variations, all three techniques were used with all salmonid groups tested: coho salmon, spring and fall chinook salmon, and steelhead. For the single and sequential imprint, fish were transported around a portion of their normal migration route before releasing them into the Columbia River.

  11. Limits on iron-dominated fallback disk in SN 1987A

    E-Print Network [OSTI]

    K. Werner; T. Nagel; T. Rauch

    2007-03-20

    The non-detection of a point source in SN1987A imposes an upper limit for the optical luminosity of L=2L_sun. This limits the size of a possible fallback disk around the stellar remnant. Assuming a steady-state thin disk with blackbody emission requires a disk smaller than 100,000 km if the accretion rate is at 30% of the Eddington rate (Graves et al. 2005). We have performed detailed non-LTE radiation transfer calculations to model the disk spectrum more realistically. It turns out that the observational limit on the disk extension becomes even tighter, namely 70,000 km.

  12. DUST TRANSPORT IN PROTOSTELLAR DISKS THROUGH TURBULENCE AND SETTLING

    SciTech Connect (OSTI)

    Turner, N. J.; Carballido, A. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Sano, T., E-mail: neal.turner@jpl.nasa.go [Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871 (Japan)

    2010-01-01

    We apply ionization balance and magnetohydrodynamical (MHD) calculations to investigate whether magnetic activity moderated by recombination on dust grains can account for the mass accretion rates and the mid-infrared spectra and variability of protostellar disks. The MHD calculations use the stratified shearing-box approach and include grain settling and the feedback from the changing dust abundance on the resistivity of the gas. The two-decade spread in accretion rates among solar-mass T Tauri stars is too large to result solely from variations in the grain size and stellar X-ray luminosity, but can plausibly be produced by varying these parameters together with the disk magnetic flux. The diverse shapes and strengths of the mid-infrared silicate bands can come from the coupling of grain settling to the distribution of the magnetorotational turbulence, through the following three effects. First, recombination on grains 1 mum or smaller yields a magnetically inactive dead zone extending more than two scale heights from the midplane, while turbulent motions in the magnetically active disk atmosphere overshoot the dead zone boundary by only about one scale height. Second, grains deep in the dead zone oscillate vertically in wave motions driven by the turbulent layer above, but on average settle at the rates found in laminar flow, so that the interior of the dead zone is a particle sink and the disk atmosphere will become dust-depleted unless resupplied from elsewhere. Third, with sufficient depletion, the dead zone is thinner and mixing dredges grains off the midplane. The last of these processes enables evolutionary signatures such as the degree of settling to sometimes decrease with age. The MHD results also show that the magnetic activity intermittently lifts clouds of small grains into the atmosphere. Consequently the photosphere height changes by up to one-third over timescales of a few orbits, while the extinction along lines of sight grazing the disk surface varies by factors of 2 over times down to a tenth of an orbit. We suggest that the changing shadows cast by the dust clouds on the outer disk are a cause of the daily to monthly mid-infrared variability found in many young stars.

  13. A Thickness of Stellar Disks of Edge-on Galaxies and Position of Their Truncation Radii

    E-Print Network [OSTI]

    A. V. Zasov; D. V. Bizyaev

    2002-12-13

    The relationship between the geometrical properties of stellar disks (a flatness and truncation radius) and the disk kinematics are considered for edge-on galaxies. It is shown that the observed thickness of the disks and the approximate constancy of their thickness along the radius well agrees with the condition of their marginal local gravitational stability. As a consequence, those galaxies whose disks are thinner should harbor more massive dark haloes. The correlation between the de-projeced central brightness of the disks and their flatness is found (the low surface brightness disks tend to be the thinniest ones). We also show that positions of observed photometrically determined truncation radii $R_{cut}$ for the stellar disks support the idea of marginal local gravitational stability of gaseous protodisks at $R =R_{cut}$, and hence the steepening of photometric profiles may be a result of too inefficient star formation beyond $R_{cut}$.

  14. Neutrino Interactions in the Outflow from Gamma-Ray Burst Accretion Disks

    E-Print Network [OSTI]

    R. Surman; G. C. McLaughlin

    2004-07-09

    We examine the composition of matter as it flows away from gamma ray burst accretion disks, in order to determine what sort of nucleosynthesis may occur. Since there is a large flux of neutrinos leaving the surface of the disk, the electron fraction of the outflowing material will change due to charged current neutrino interactions. We calculate the electron fraction in the wind using detailed neutrino fluxes from every point on the disk and study a range of trajectories and outflow conditions for several different accretion disk models. We find that low electron fractions, conducive to making r-process elements, only appear in outflows from disks with high accretion rates that have a significant region both of trapped neutrinos and antineutrinos. Disks with lower accretion rates that have only a significant region of trapped neutrinos can have outflows with very high electron fractions, whereas the lowest accretion rate disks with little trapping have outflow electrons fractions of closer to one half.

  15. ORIGIN OF CHEMICAL AND DYNAMICAL PROPERTIES OF THE GALACTIC THICK DISK

    SciTech Connect (OSTI)

    Bekki, Kenji [ICRAR, M468, University of Western Australia, Crawley, Western Australia, 6009 (Australia); Tsujimoto, Takuji [National Astronomical Observatory, Mitaka-shi, Tokyo 181-8588 (Japan)

    2011-09-01

    We adopt a scenario in which the Galactic thick disk was formed by minor merging between the first generation of the Galactic thin disk (FGTD) and a dwarf galaxy about {approx}9 Gyr ago and thereby investigate chemical and dynamical properties of the Galactic thick disk. In this scenario, the dynamical properties of the thick disk have long been influenced both by the mass growth of the second generation of the Galactic thin disk (i.e., the present thin disk) and by its non-axisymmetric structures. On the other hand, the early star formation history and chemical evolution of the thin disk was influenced by the remaining gas of the thick disk. Based on N-body simulations and chemical evolution models, we investigate the radial metallicity gradient, structural and kinematical properties, and detailed chemical abundance patterns of the thick disk. Our numerical simulations show that the ancient minor merger event can significantly flatten the original radial metallicity gradient of the FGTD, in particular, in the outer part, and also can be responsible for migration of inner metal-rich stars into the outer part (R > 10 kpc). The simulations show that the central region of the thick disk can develop a bar due to dynamical effects of a separate bar in the thin disk. Whether or not rotational velocities (V{sub {phi}}) can correlate with metallicities ([Fe/H]) for the simulated thick disks depends on the initial metallicity gradients of the FGTDs. The simulated orbital eccentricity distributions in the thick disk for models with higher mass ratios ({approx}0.2) and lower orbital eccentricities ({approx}0.5) of minor mergers are in good agreement with the corresponding observations. The simulated V{sub {phi}}-|z| relation of the thick disk in models with low orbital inclination angles of mergers are also in good agreement with the latest observational results. The vertical metallicity gradient of the simulated thick disk is rather flat or very weakly negative in the solar neighborhood. Our Galactic chemical evolution models show that if we choose two distinctive timescales for star formation in the thin and thick disks, then the models can explain both the observed metallicity distribution functions and correlations between [Mg/Fe] and [Fe/H] for the two disks in a self-consistent manner. We discuss how the early star formation history and chemical evolution of the Galactic thin disk can be influenced by the pre-existing thick disk.

  16. DEVELOPMENT OF A LAMINATED DISK FOR THE SPIN TEK ROTARY MICROFILTER

    SciTech Connect (OSTI)

    Herman, D.

    2011-06-03

    Funded by the Department of Energy Office of Environmental Management, EM-31, the Savannah River National Laboratory (SRNL) partnered with SpinTek Filtration{trademark} to develop a filter disk that would withstand a reverse pressure or flow during operation of the rotary microfilter. The ability to withstand a reverse pressure and flow eliminates a potential accident scenario that could have resulted in damage to the filter membranes. While the original welded filter disks have been shown to withstand and reverse pressure/flow in the static condition, the filter disk design discussed in this report will allow a reverse pressure/flow while the disks are rotating. In addition, the laminated disk increases the flexibility during filter startup and cleaning operations. The new filter disk developed by SRNL and SpinTek is manufactured with a more open structure significantly reducing internal flow restrictions in the disk. The prototype was tested at the University of Maryland and demonstrated to withstand the reverse pressure due to the centrifugal action of the rotary filter. The tested water flux of the disk was demonstrated to be 1.34 gpm in a single disk test. By comparison, the water flux of the current disk was 0.49 gpm per disk during a 25 disk test. The disk also demonstrated rejection of solids by filtering a 5 wt % Strontium Carbonate slurry with a filtrate clarity of less the 1.4 Nephelometric Turbidity Units (NTU) throughout the two hour test. The Savannah River National Laboratory (SRNL) has been working with SpinTek Filtration{trademark} to adapt the rotary microfilter for radioactive service in the Department of Energy (DOE) Complex. One potential weakness is the loose nature of the membrane on the filter disks. The current disk is constructed by welding the membrane at the outer edge of the disk. The seal for the center of the membrane is accomplished by an o-ring in compression for the assembled stack. The remainder of the membrane is free floating on the disk. This construction requires that a positive pressure be applied to the rotary filter tank to prevent the membrane from rising from the disk structure and potentially contacting the filter turbulence promoter. In addition, one accident scenario is a reverse flow through the filtrate line due to mis-alignment of valves resulting in the membrane rising from the disk structure. The structural integrity of the current disk has been investigated, and shown that the disk can withstand a significant reverse pressure in a static condition. However, the disk will likely incur damage if the filter stack is rotated during a reverse pressure. The development of a laminated disk would have several significant benefits for the operation of the rotary filter including the prevention of a compromise in filter disk integrity during a reverse flow accident, increasing operational flexibility, and increasing the self cleaning ability of the filter. A laminated disk would allow the filter rotor operation prior to a positive pressure in the filter tank. This would prevent the initial dead-head of the filter and prevent the resulting initial filter cake buildup. The laminated disk would allow rotor operation with cleaning fluid, eliminating the need for a recirculation pump. Additionally, a laminated disk would allow a reverse flow of fluid through the membrane pores removing trapped particles.

  17. Characteristics of a multiple disk pump with turbulent rotor flow 

    E-Print Network [OSTI]

    Roddy, Patrick James

    1985-01-01

    of these turbomachines until the early sixties when Rice [4] designed and tested a multiple disk pump and compressor. Since then, the per- formance of these turbomachines operating with laminar rotor flow has been well documented [1-6, 7-12]. In the seventies, Bakke... the Disk Radius (LT'8) [ (8 + |/)/T + ( aH/8)]2 2T/T ruotq. znba [gy] yyzqoznqg g~otTdxa aqua. go surzag u) passaudxa aq uzo zoq. ozg uoTgo)zg 9uxuuzg aqua '(gT'2) uoTgznba uZ (9T'2) (au 2/1 2 2 ( (n) + (& ? &U)) = sz r(s)p aqua Suoyz guxod fiuz gz...

  18. Adaptor assembly for coupling turbine blades to rotor disks

    DOE Patents [OSTI]

    Garcia-Crespo, Andres Jose; Delvaux, John McConnell

    2014-09-23

    An adaptor assembly for coupling a blade root of a turbine blade to a root slot of a rotor disk is described. The adaptor assembly includes a turbine blade having a blade root and an adaptor body having an adaptor root. The adaptor body defines a slot having an open end configured to receive the blade root of the turbine blade such that the adaptor root of the adaptor body and the blade root of the turbine blade are adjacent to one another when the blade root of the turbine blade is positioned within the slot. Both the adaptor root of the adaptor body and the blade root of the turbine blade are configured to be received within the root slot of the rotor disk.

  19. THE MASS DEPENDENCE BETWEEN PROTOPLANETARY DISKS AND THEIR STELLAR HOSTS

    SciTech Connect (OSTI)

    Andrews, Sean M.; Rosenfeld, Katherine A.; Kraus, Adam L.; Wilner, David J., E-mail: sandrews@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2013-07-10

    We present a substantial extension of the millimeter (mm) wave continuum photometry catalog for circumstellar dust disks in the Taurus star-forming region, based on a new ''snapshot'' {lambda} = 1.3 mm survey with the Submillimeter Array. Combining these new data with measurements in the literature, we construct a mm-wave luminosity distribution, f(L{sub mm}), for Class II disks that is statistically complete for stellar hosts with spectral types earlier than M8.5 and has a 3{sigma} depth of roughly 3 mJy. The resulting census eliminates a longstanding selection bias against disks with late-type hosts, and thereby demonstrates that there is a strong correlation between L{sub mm} and the host spectral type. By translating the locations of individual stars in the Hertzsprung-Russell diagram into masses and ages, and adopting a simple conversion between L{sub mm} and the disk mass, M{sub d} , we confirm that this correlation corresponds to a statistically robust relationship between the masses of dust disks and the stars that host them. A Bayesian regression technique is used to characterize these relationships in the presence of measurement errors, data censoring, and significant intrinsic scatter: the best-fit results indicate a typical 1.3 mm flux density of {approx}25 mJy for 1 M{sub Sun} hosts and a power-law scaling L{sub mm}{proportional_to}M{sub *}{sup 1.5-2.0}. We suggest that a reasonable treatment of dust temperature in the conversion from L{sub mm} to M{sub d} favors an inherently linear M{sub d} {proportional_to}M{sub *} scaling, with a typical disk-to-star mass ratio of {approx}0.2%-0.6%. The measured rms dispersion around this regression curve is {+-}0.7 dex, suggesting that the combined effects of diverse evolutionary states, dust opacities, and temperatures in these disks imprint a full width at half-maximum range of a factor of {approx}40 on the inferred M{sub d} (or L{sub mm}) at any given host mass. We argue that this relationship between M{sub d} and M{sub *} likely represents the origin of the inferred correlation between giant planet frequency and host star mass in the exoplanet population, and provides some basic support for the core accretion model for planet formation. Moreover, we caution that the effects of incompleteness and selection bias must be considered in comparative studies of disk evolution, and illustrate that fact with statistical comparisons of f(L{sub mm}) between the Taurus catalog presented here and incomplete subsamples in the Ophiuchus, IC 348, and Upper Sco young clusters.

  20. Microwave study of quantum n-disk scattering

    E-Print Network [OSTI]

    Wentao Lu; Lorenza Viola; Kristi Pance; Michael Rose; S. Sridhar

    1999-09-16

    We describe a wave-mechanical implementation of classically chaotic n-disk scattering based on thin 2-D microwave cavities. Two, three, and four-disk scattering are investigated in detail. The experiments, which are able to probe the stationary Green's function of the system, yield both frequencies and widths of the low-lying quantum resonances. The observed spectra are found to be in good agreement with calculations based on semiclassical periodic orbit theory. Wave-vector autocorrelation functions are analyzed for various scattering geometries, the small wave-vector behavior allowing one to extract the escape rate from the quantum repeller. Quantitative agreement is found with the value predicted from classical scattering theory. For intermediate energies, non-universal oscillations are detected in the autocorrelation function, reflecting the presence of periodic orbits.

  1. Galaxies that Shine: radiation-hydrodynamical simulations of disk galaxies

    E-Print Network [OSTI]

    Rosdahl, Joakim; Teyssier, Romain; Agertz, Oscar

    2015-01-01

    Radiation feedback is typically implemented using subgrid recipes in hydrodynamical simulations of galaxies. Very little work has so far been performed using radiation-hydrodynamics (RHD), and there is no consensus on the importance of radiation feedback in galaxy evolution. We present RHD simulations of isolated galaxy disks of different masses with a resolution of 18 pc. Besides accounting for supernova feedback, our simulations are the first galaxy-scale simulations to include RHD treatments of photo-ionisation heating and radiation pressure, from both direct optical/UV radiation and multi-scattered, re-processed infrared (IR) radiation. Photo-heating smooths and thickens the disks and suppresses star formation about as much as the inclusion of ("thermal dump") supernova feedback does. These effects decrease with galaxy mass and are mainly due to the prevention of the formation of dense clouds, as opposed to their destruction. Radiation pressure, whether from direct or IR radiation, has little effect, but ...

  2. Kinematics of classical Cepheids in the Nuclear Stellar Disk

    E-Print Network [OSTI]

    Matsunaga, N; Yamamoto, R; Kobayashi, N; Inno, L; Genovali, K; Bono, G; Baba, J; Fujii, M S; Kondo, S; Ikeda, Y; Hamano, S; Nishiyama, S; Nagata, T; Aoki, W; Tsujimoto, T

    2014-01-01

    Classical Cepheids are useful tracers of the Galactic young stellar population because their distances and ages can be determined from their period-luminosity and period-age relations. In addition, the radial velocities and chemical abundance of the Cepheids can be derived from spectroscopic observations, providing further insights into the structure and evolution of the Galaxy. Here, we report the radial velocities of classical Cepheids near the Galactic Center, three of which were reported in 2011, the other reported for the first time. The velocities of these Cepheids suggest that the stars orbit within the Nuclear Stellar Disk, a group of stars and interstellar matter occupying a region of 200 pc around the Center, although the three-dimensional velocities cannot be determined until the proper motions are known. According to our simulation, these four Cepheids formed within the Nuclear Stellar Disk like younger stars and stellar clusters therein.

  3. Wet-steam erosion of steam turbine disks and shafts

    SciTech Connect (OSTI)

    Averkina, N. V.; Zheleznyak, I. V.; Kachuriner, Yu. Ya.; Nosovitskii, I. A.; Orlik, V. G.; Shishkin, V. I.

    2011-01-15

    A study of wet-steam erosion of the disks and the rotor bosses or housings of turbines in thermal and nuclear power plants shows that the rate of wear does not depend on the diagrammed degree of moisture, but is determined by moisture condensing on the surfaces of the diaphragms and steam inlet components. Renovating the diaphragm seals as an assembly with condensate removal provides a manifold reduction in the erosion.

  4. On the generation of asymmetric warps in disk galaxies

    E-Print Network [OSTI]

    Kanak Saha; Chanda J. Jog

    2005-10-28

    The warps in many spiral galaxies are now known to asymmetric. Recent sensitive observations have revealed that asymmetry of warps may be the norm rather than exception. However there exists no generic mechanism to generate these asymmetries in warps. We have derived the dispersion relation in a compact form for the S-shaped warps(described by the m=1 mode) and the bowl-shaped distribution(described by the m=0 mode) in galactic disk embedded in a dark matter halo. We then performed the numerical modal analysis and used the linear and time-dependent superposition principle to generate asymmetric warps in the disk. On doing the modal analysis we find the frequency of the $m=0$ mode is much larger than that of the $m=1$ mode. The linear and time-dependent superposition of these modes with their unmodulated amplitudes(that is, the coefficients of superposition being unity) results in an asymmetry in warps of ~ 20 - 40 %, whereas a smaller coefficient for the m=0 mode results in a smaller asymmetry. The resulting values agree well with the recent observations. We study the dependence of the asymmetry index on the dark matter halo parameters. This approach can also naturally produce U-shaped warps and L-shaped warps. We show that a rich variety of possible asymmetries in the z-distribution of the spiral galaxies can naturally arise due to a dynamical wave interference between the first two bending modes(i.e. m=0 and m=1) in the disk. This is a simple but general method for generating asymmetric warps that is independent of how the individual modes arise in the disk.

  5. Verification of runaway migration in a massive disk

    SciTech Connect (OSTI)

    Li, Shengtai

    2009-01-01

    Runaway migration of a proto-planet was first proposed and observed by Masset and Papaloizou (2003). The semi-major axis of the proto-planet varies by 50% over just a few tens of orbits when runaway migration happens. More recent work by D'Angelo et al. (2005) solved the same problem with locally refined grid and found that the migration rate is sharply reduced and no runaway occurs when the grid cells surrounding the planet are refined enough. To verify these two seemly contradictory results, we independently perform high-resolution simulations, solving the same problem as Masset and Papaloizou (2003), with and without self-gravity. We find that the migration rate is highly dependent on the softening used in the gravitational force between thd disk and planet. When a small softening is used in a 2D massive disk, the mass of the circumplanetary disk (CPD) increases with time with enough resolution in the CPD region. It acts as the mass is continually accreted to the CPD, which cannot be settled down until after thousands of orbits. If the planet is held on a fixed orbit long enough, the mass of CPD will become so large that the condition for the runaway migration derived in Masset (2008) will not be satisfied, and hence the runaway migration will not be triggered. However, when a large softening is used, the mass of the CPD will begin to decrease after the initial increase stage. Our numerical results with and without disk-gravity confirm that the runaway migration indeed exists when the mass deficit is larger than the total mass of the planet and CPD. Our simulations results also show that the torque from the co-orbital region, in particular the planet's Hill sphere, is the main contributor to the runaway migration, and the CPD which is lagged behind by the planet becomes so asymmetric that it accelerates the migration.

  6. Laser illuminator and optical system for disk patterning

    DOE Patents [OSTI]

    Hackel, Lloyd A. (Livermore, CA); Dane, C. Brent (Livermore, CA); Dixit, Shamasundar N. (Livermore, CA); Everett, Mathew (Pleasanton, CA); Honig, John (Livermore, CA)

    2000-01-01

    Magnetic recording media are textured over areas designated for contact in order to minimize friction with data transducing heads. In fabricating a hard disk, an aluminum nickel-phosphorous substrate is polished to a specular finish. A mechanical means is then used to roughen an annular area intended to be the head contact band. An optical and mechanical system allows thousands of spots to be generated with each laser pulse, allowing the textured pattern to be rapidly generated with a low repetition rate laser and an uncomplicated mechanical system. The system uses a low power laser, a beam expander, a specially designed phase plate, a prism to deflect the beam, a lens to transmit the diffraction pattern to the far field, a mechanical means to rotate the pattern and a trigger system to fire the laser when sections of the pattern are precisely aligned. The system generates an annular segment of the desired pattern with which the total pattern is generated by rotating the optical system about its optic axis, sensing the rotational position and firing the laser as the annular segment rotates into the next appropriate position. This marking system can be integrated into a disk sputtering system for manufacturing magnetic disks, allowing for a very streamlined manufacturing process.

  7. Nested-grid calculations of disk-planet interaction

    E-Print Network [OSTI]

    Gennaro D'Angelo; Thomas Henning; Wilhelm Kley

    2001-12-18

    We study the evolution of embedded protoplanets in a protostellar disk using very high resolution nested-grid computations. This method allows us to perform global simulations of planets orbiting in disks and, at the same time, to resolve in detail the dynamics of the flow inside the Roche lobe of the planet. The primary interest of this work lies in the analysis of the gravitational torque balance acting on the planet. For this purpose we study planets of different masses, ranging from one Earth-mass up to one Jupiter-mass, assuming typical parameters of the protostellar disk. The high resolution of the method allows a precise determination of the mass flow onto the planet and the resulting torques. The obtained migration time scales are in the range from few times 10^4 years, for intermediate mass planets, to 10^6 years, for very low and high mass planets. Typical growth time scales depend strongly on the planetary mass, ranging from a few hundred years, in the case of Earth-type planets, to several ten thousand years, in the case of Jupiter-type planets.

  8. ECO and RESOLVE: Galaxy Disk Growth in Environmental Context

    E-Print Network [OSTI]

    Moffett, Amanda J; Berlind, Andreas A; Eckert, Kathleen D; Stark, David V; Hendel, David; Norris, Mark A; Grogin, Norman A

    2015-01-01

    We study the relationships between galaxy environments and galaxy properties related to disk (re)growth, considering two highly complete samples that are approximately baryonic mass limited into the high-mass dwarf galaxy regime, the Environmental COntext (ECO) catalog (data release herein) and the B-semester region of the REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey. We quantify galaxy environments using both group identification and smoothed galaxy density field methods. We use by-eye and quantitative morphological classifications plus atomic gas content measurements and estimates. We find that blue early-type (E/S0) galaxies, gas-dominated galaxies, and UV-bright disk host galaxies all become distinctly more common below group halo mass ~10^11.5 Msun, implying that this low group halo mass regime may be a preferred regime for significant disk growth activity. We also find that blue early-type and blue late-type galaxies inhabit environments of similar group halo mass at fixed baryonic mass, con...

  9. Water in protoplanetary disks: Deuteration and turbulent mixing

    SciTech Connect (OSTI)

    Furuya, Kenji; Aikawa, Yuri; Nomura, Hideko; Hersant, Franck; Wakelam, Valentine

    2013-12-10

    We investigate water and deuterated water chemistry in turbulent protoplanetary disks. Chemical rate equations are solved with the diffusion term, mimicking turbulent mixing in a vertical direction. Water near the midplane is transported to the disk atmosphere by turbulence and is destroyed by photoreactions to produce atomic oxygen, while the atomic oxygen is transported to the midplane and reforms water and/or other molecules. We find that this cycle significantly decreases column densities of water ice at r ? 30 AU, where dust temperatures are too high to reform water ice effectively. The radial extent of such region depends on the desorption energy of atomic hydrogen. Our model indicates that water ice could be deficient even outside the sublimation radius. Outside this radius, the cycle decreases the deuterium-to-hydrogen (D/H) ratio of water ice from ?2 × 10{sup –2}, which is set by the collapsing core model, to 10{sup –4}-10{sup –2} in 10{sup 6} yr, without significantly decreasing the water ice column density. The resultant D/H ratios depend on the strength of mixing and the radial distance from the central star. Our finding suggests that the D/H ratio of cometary water (?10{sup –4}) could be established (i.e., cometary water could be formed) in the solar nebula, even if the D/H ratio of water ice delivered to the disk was very high (?10{sup –2}).

  10. An ATCA survey of debris disks at 7 millimeters

    E-Print Network [OSTI]

    Ricci, L; Wilner, D; MacGregor, M A; Ubach, C; Carpenter, J M; Testi, L

    2015-01-01

    We present ATCA continuum observations at a wavelength of 6.8 mm of five debris disks: $\\beta$ Pictoris, q$^1$ Eridani, HD 107146, HD 181327, and HD 95086. These observations provide the detection at the longest wavelengths obtained to date for all these debris disks. By combining our 6.8 mm data with previous detections at shorter sub-millimeter/millimeter wavelengths we measure the long wavelength spectral index of these sources. We then use previous estimates for the temperature of the emitting dust to derive the spectral index of the dust emissivity. Under the assumption that all the detected flux comes from dust only, we constrain the slope of the solid size distribution, assumed to be a power-law. The values that we infer for the slope of the size distribution range between about 3.36 and 3.50. We compare our findings with the case of the Fomalhaut debris disk and use these results to test the predictions of collisional cascades of planetesimal belts.

  11. SNOW LINES AS PROBES OF TURBULENT DIFFUSION IN PROTOPLANETARY DISKS

    SciTech Connect (OSTI)

    Owen, James E. [Canadian Institute for Theoretical Astrophysics, 60 St George Street, Toronto, M5S 3H8, ON (Canada)

    2014-07-20

    Sharp chemical discontinuities can occur in protoplanetary disks, particularly at ''snow lines'' where a gas-phase species freezes out to form ice grains. Such sharp discontinuities will diffuse out due to the turbulence suspected to drive angular momentum transport in accretion disks. We demonstrate that the concentration gradient—in the vicinity of the snow line—of a species present outside a snow line but destroyed inside is strongly sensitive to the level of turbulent diffusion (provided the chemical and transport timescales are decoupled) and provides a direct measurement of the radial ''Schmidt number'' (the ratio of the angular momentum transport to radial turbulent diffusion). Taking as an example the tracer species N{sub 2}H{sup +}, which is expected to be destroyed inside the CO snow line (as recently observed in TW Hya) we show that ALMA observations possess significant angular resolution to constrain the Schmidt number. Since different turbulent driving mechanisms predict different Schmidt numbers, a direct measurement of the Schmidt number in accretion disks would allow inferences to be made about the nature of the turbulence.

  12. The dynamical structure of HR 8799's inner debris disk

    E-Print Network [OSTI]

    Contro, Bruna; Horner, Jonti; Marshall, Jonathan P

    2015-01-01

    The HR 8799 system, with its four giant planets and two debris belts, has an architecture closely mirroring that of our Solar system where the inner, warm asteroid belt and outer, cool Edgeworth-Kuiper belt bracket the giant planets. As such, it is a valuable laboratory for examining exoplanetary dynamics and debris disk-exoplanet interactions. Whilst the outer debris belt of HR 8799 has been well resolved by previous observations, the spatial extent of the inner disk remains unknown. This leaves a significant question mark over both the location of the planetesimals responsible for producing the belt's visible dust and the physical properties of those grains. We have performed the most extensive simulations to date of the inner, unresolved debris belt around HR 8799, using UNSW Australia's Katana supercomputing facility to follow the dynamical evolution of a model inner disk comprising 300,298 particles for a period of 60 million years. These simulations have enabled the characterisation of the extent and st...

  13. Non-azimuthal linear polarization in protoplanetary disks

    E-Print Network [OSTI]

    Canovas, H; de Boer, J; Pinte, C; Avenhaus, H; Schreiber, M R

    2015-01-01

    Several studies discussing imaging polarimetry observations of protoplanetary disks use the so-called radial Stokes parameters Q_phi and U_phi to discuss the results. This approach has the advantage of providing a direct measure of the noise in the polarized images under the assumption that the polarization is azimuthal only, i.e., perpendicular to the direction towards the illuminating source. However, a detailed study of the validity of this assumption is currently missing. We aim to test whether departures from azimuthal polarization can naturally be produced by scattering processes in optically thick protoplanetary disks at near infrared wavelengths. We use the radiative transfer code MCFOST to create a generic model of a transition disk using different grain size distributions and dust masses. From these models we generate synthetic polarized images at 2.2\\mum. We find that even for moderate inclinations (e.g., i = 40degr), multiple scattering alone can produce significant (up to ~4.5% of the Q_phi image...

  14. Interplay between Stellar Spirals and the ISM in Galactic Disks

    E-Print Network [OSTI]

    Wada, Keiichi; Saitoh, Takayuki R

    2011-01-01

    We propose a new dynamical picture of galactic stellar and gas spirals, based on hydrodynamic simulations in a `live' stellar disk. We focus especially on spiral structures excited in a isolated galactic disk without a stellar bar. Using high-resolution, 3-dimensional N-body/SPH simulations, we found that the spiral features of the gas in galactic disks are formed by essentially different mechanisms from the galactic shock in stellar density waves. The stellar spiral arms and the interstellar matter on average corotate in a galactic potential at any radii. Unlike the stream motions in the galactic shock, the interstellar matter flows into the local potential minima with irregular motions. The flows converge to form dense gas clouds/filaments near the bottom of the stellar spirals, whose global structures resemble dust-lanes seen in late-type spiral galaxies. The stellar arms are non-steady; they are wound and stretched by the galactic shear, and thus local densities of the arm change on a time scale of ~ 100 ...

  15. Molecules in the Circumstellar Disk Orbiting BP Piscium

    E-Print Network [OSTI]

    Kastner, Joel H; Forveille, Thierry

    2008-01-01

    BP Psc is a puzzling late-type, emission-line field star with large infrared excess. The star is encircled and enshrouded by a nearly edge-on, dust circumstellar disk, and displays an extensive jet system similar to those associated with pre-main sequence (pre-MS) stars. We conducted a mm-wave molecular line survey of BP Psc with the 30 m telescope of the Institut de Radio Astronomie Millimetrique (IRAM). We detected lines of 12CO and 13CO and, possibly, very weak emission from HCO+ and CN; HCN, H2CO, and SiO are not detected. The CO line profiles of BP Psc are well fit by a model invoking a disk in Keplerian rotation. The mimumum disk gas mass, inferred from the 12CO line intensity and 13CO/12CO line ratio, is ~0.1 Jupiter masses. The weakness of HCO+ and CN (relative to 13CO) stands in sharp contrast to the strong HCO+ and CN emission that characterizes most low-mass, pre-main sequence stars that have been the subjects of molecular emission-line surveys, and is suggestive of a very low level of X-ray-induce...

  16. Searching for debris disks around seven radio pulsars

    SciTech Connect (OSTI)

    Wang, Zhongxiang; Wang, Xuebing [Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China); Ng, C.-Y. [Department of Physics, The University of Hong Kong, Pokfulam Road (Hong Kong); Li, Aigen [Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States); Kaplan, David L. [Physics Department, University of WisconsinMilwaukee, Milwaukee, WI 53211 (United States)

    2014-10-01

    We report on our searches for debris disks around seven relatively nearby radio pulsars, which are isolated sources that were carefully selected as targets on the basis of our deep K{sub s} -band imaging survey. The K{sub s} images obtained with the 6.5 m Baade Magellan Telescope at Las Campanas Observatory are analyzed together with the Spitzer/IRAC images at 4.5 and 8.0 ?m and the WISE images at 3.4, 4.6, 12, and 22 ?m. No infrared counterparts of these pulsars are found, with flux upper limits of ??Jy at near-infrared (? < 10 ?m) and ?10-1000 ?Jy at mid-infrared wavelengths (? > 10 ?m). The results of this search are discussed in terms of the efficiency of converting the pulsar spin-down energy to thermal energy and X-ray heating of debris disks, with a comparison made of the two magnetars 4U 0142+61 and 1E 2259+586, which are suggested to harbor a debris disk.

  17. COLORS OF INNER DISK CLASSICAL KUIPER BELT OBJECTS

    SciTech Connect (OSTI)

    Romanishin, W. [Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States); Tegler, S. C. [Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ 86011 (United States); Consolmagno, G. J., E-mail: wromanishin@ou.ed, E-mail: Stephen.Tegler@nau.ed, E-mail: gjc@specola.v [Vatican Observatory, Specola Vaticana, V-00120 (Vatican City State, Holy See)

    2010-07-15

    We present new optical broadband colors, obtained with the Keck 1 and Vatican Advanced Technology telescopes, for six objects in the inner classical Kuiper Belt. Objects in the inner classical Kuiper Belt are of interest as they may represent the surviving members of the primordial Kuiper Belt that formed interior to the current position of the 3:2 resonance with Neptune, the current position of the plutinos, or, alternatively, they may be objects formed at a different heliocentric distance that were then moved to their present locations. The six new colors, combined with four previously published, show that the ten inner belt objects with known colors form a neutral clump and a reddish clump in B-R color. Nonparametric statistical tests show no significant difference between the B-R color distribution of the inner disk objects compared to the color distributions of Centaurs, plutinos, or scattered disk objects. However, the B-R color distribution of the inner classical Kuiper Belt Objects does differ significantly from the distribution of colors in the cold (low inclination) main classical Kuiper Belt. The cold main classical objects are predominately red, while the inner classical belt objects are a mixture of neutral and red. The color difference may reveal the existence of a gradient in the composition and/or surface processing history in the primordial Kuiper Belt, or indicate that the inner disk objects are not dynamically analogous to the cold main classical belt objects.

  18. Super-spinning compact objects generated by thick accretion disks

    SciTech Connect (OSTI)

    Li, Zilong; Bambi, Cosimo, E-mail: zilongli@fudan.edu.cn, E-mail: bambi@fudan.edu.cn [Center for Field Theory and Particle Physics and Department of Physics, Fudan University, 220 Handan Road, 200433 Shanghai (China)

    2013-03-01

    If astrophysical black hole candidates are the Kerr black holes predicted by General Relativity, the value of their spin parameter must be subject to the theoretical bound |a{sub *}| ? 1. In this work, we consider the possibility that these objects are either non-Kerr black holes in an alternative theory of gravity or exotic compact objects in General Relativity. We study the accretion process when their accretion disk is geometrically thick with a simple version of the Polish doughnut model. The picture of the accretion process may be qualitatively different from the one around a Kerr black hole. The inner edge of the disk may not have the typical cusp on the equatorial plane any more, but there may be two cusps, respectively above and below the equatorial plane. We extend previous work on the evolution of the spin parameter and we estimate the maximum value of a{sub *} for the super-massive black hole candidates in galactic nuclei. Since measurements of the mean radiative efficiency of AGNs require ? > 0.15, we infer the ''observational'' bound |a{sub *}|?<1.3, which seems to be quite independent of the exact nature of these objects. Such a bound is only slightly weaker than |a{sub *}|?<1.2 found in previous work for thin disks.

  19. The Jet-Disk Connection and Blazar Unification

    E-Print Network [OSTI]

    Laura Maraschi; Fabrizio Tavecchio

    2002-05-16

    We discuss the relation between the power carried by relativistic jets and the nuclear power provided by accretion, for a group of blazars including FSRQs and BL Lac objects. They are characterized by good quality broad band X-ray data provided by the Beppo SAX satellite. The jet powers are estimated using physical parameters determined from uniformly modelling their spectral energy distributions (SEDs). Our analysis indicates that for Flat Spectrum Radio Quasars the total jet power is of the same order as the accretion power. We suggest that blazar jets are likely powered by energy extraction from a rapidly spinning black hole through the magnetic field provided by the accretion disk. FSRQs must have large BH masses (10^8 - 10^9 solar masses) and high, near Eddington accretion rates. For BL Lac objects the jet luminosity is larger than the disk luminosity. This can be understood within the same scenario if BL Lac objects have masses similar to FSRQ but accrete at largely subcritical rates, whereby the accretion disk radiates inefficiently. Thus the ``unification'' of the two classes into a single blazar population, previously proposed on the basis of a spectral sequence governed by luminosity, finds a physical basis.

  20. Testing the Disk Regulation Paradigm with Spitzer Observations. II. A Clear Signature of Star-Disk Interaction in NGC 2264 and the Orion Nebula Cluster

    E-Print Network [OSTI]

    L. Cieza; N. Baliber

    2007-07-31

    Observations of PMS star rotation periods reveal slow rotators in young clusters of various ages, indicating that angular momentum is somehow removed from these rotating masses. The mechanism by which spin-up is regulated as young stars contract has been one of the longest-standing problems in star formation. Attempts to observationally confirm the prevailing theory that magnetic interaction between the star and its circumstellar disk regulates these rotation periods have produced mixed results. In this paper, we use the unprecedented disk identification capability of the Spitzer Space Telescope to test the star-disk interaction paradigm in two young clusters, NGC 2264 and the Orion Nebula Cluster (ONC). We show that once mass effects and sensitivity biases are removed, a clear increase in the disk fraction with period can be observed in both clusters across the entire period range populated by cluster members. We also show that the long-period peak (P $\\sim$8 days) of the bimodal distribution observed for high-mass stars in the ONC is dominated by a population of stars possessing a disk, while the short-period peak (P $\\sim$2 days) is dominated by a population of stars without a disk. Our results represent the strongest evidence to date that star-disk interaction regulates the angular momentum of these young stars. This study will make possible quantitative comparisons between the observed period distributions of stars with and without a disk and numerical models of the angular momentum evolution of young stars.

  1. Evolution of the protolunar disk: dynamics, cooling timescale and implantation of volatiles onto the Earth

    E-Print Network [OSTI]

    Charnoz, Charnoz

    2015-01-01

    It is thought that the Moon accreted from the protolunar disk that was assembled after the last giant impact on Earth. Due to its high temperature, the protolunar disk may act as a thermochemical reactor in which the material is processed before being incorporated into the Moon. Outstanding issues like devolatilisation and istotopic evolution are tied to the disk evolution, however its lifetime, dynamics and thermodynamics are unknown. Here, we numerically explore the long term viscous evolution of the protolunar disk using a one dimensional model where the different phases (vapor and condensed) are vertically stratified. Viscous heating, radiative cooling, phase transitions and gravitational instability are accounted for whereas Moon s accretion is not considered for the moment. The viscosity of the gas, liquid and solid phases dictates the disk evolution. We find that (1) the vapor condenses into liquid in about 10 years, (2) a large fraction of the disk mass flows inward forming a hot and compact liquid di...

  2. The molecular composition of the planet-forming regions of protoplanetary disks across the luminosity regime

    E-Print Network [OSTI]

    Walsh, Catherine; van Dishoeck, Ewine F

    2015-01-01

    (Abridged) Near- to mid-IR observations of protoplanetary disks show that the inner regions (chemistry, and initial abundances, are investigated. The composition in the 'observable' atmosphere is compared with that in the midplane where the planet-building reservoir resides. M dwarf disk atmospheres are relatively more molecule rich than those for T Tauri or Herbig Ae disks. The weak far-UV flux helps retain this complexity which is enhanced by X-ray-induced ion-molecule chemistry. N...

  3. Dirichlet integral dual-access collocation-kernel space analytic interpolation for unit disks: DIDACKS I

    E-Print Network [OSTI]

    Alan Rufty

    2007-02-17

    This article presents a technique for analytic interpolation over the exterior of a unit disk using complex poles in the interior--as well as corresponding techniques for the exterior of a real unit disk and for the interior of a real and complex unit disk. This is accomplished by developing special kernel spaces labeled dual-access collocation-kernel spaces. Higher order pole and logarithmic point source kernels are also considered. Relationships to Szego and Bergman kernel theory are addressed.

  4. Oxygen Abundances in Nearby Stars. Clues to the formation and evolution of the Galactic disk

    E-Print Network [OSTI]

    I. Ramirez; C. Allende Prieto; D. L. Lambert

    2007-01-12

    The abundances of iron and oxygen are homogeneously determined in a sample of 523 nearby (d-0.3, we find no obvious indication of a sudden decrease (i.e., a 'knee') in the [O/Fe] vs. [Fe/H] pattern of thick-disk stars that would connect the thick and thin disk trends at a high metallicity. We conclude that Type Ia supernovae (SN Ia) did not contribute significantly to the chemical enrichment of the thick disk. [Abridged

  5. The structure of disks around intermediate-mass young stars from mid-infrared interferometry. Evidence for a population of group II disks with gaps

    E-Print Network [OSTI]

    Menu, J; Henning, Th; Leinert, Ch; Waelkens, C; Waters, L B F M

    2015-01-01

    The disks around Herbig Ae/Be stars are commonly divided into group I and group II based on their far-infrared spectral energy distribution, and the common interpretation for that is flared and flat disks. Recent observations suggest that many flaring disks have gaps, whereas flat disks are thought to be gapless. The different groups of objects can be expected to have different structural signatures in high-angular-resolution data. Over the past 10 years, the MIDI instrument on the Very Large Telescope Interferometer has collected observations of several tens of protoplanetary disks. We model the large set of observations with simple geometric models. A population of radiative-transfer models is synthesized for interpreting the mid-infrared signatures. Objects with similar luminosities show very different disk sizes in the mid-infrared. Restricting to the young objects of intermediate mass, we confirm that most group I disks are in agreement with being transitional. We find that several group II objects have ...

  6. AIR LUBRICATION IN HARD DISK DRIVE Mechanics of Contact and Lubrication

    E-Print Network [OSTI]

    Müftü, Sinan

    AIR LUBRICATION IN HARD DISK DRIVE Mechanics of Contact and Lubrication Department of Mechanical & Industrial Engineering Northeastern University Boston, MA 02115 ...................................................................................................................... 6 3. Lubrication

  7. An inner disk below the ADAF: the intermediate spectral state of black hole accretion

    E-Print Network [OSTI]

    B. F. Liu; ; F. Meyer; E. Meyer-Hofmeister

    2006-06-09

    Aims: The hard and soft spectral states of black hole accretion are understood as connected with ADAF accretion (truncated disk) and standard disk accretion, respectively. However, observations indicate the existence of cool gas in the inner region at times when the disk is already truncated outside. We try to shed light on these not yet understood intermediate states. Methods: The disk-corona model allows to understand the spectral state transitions as caused by changes of the mass flow rate in the disk and provides a picture for the accretion geometry when disk truncation starts at the time of the soft/hard transition, the formation of a gap in the disk filled by an advection-dominated flow (ADAF) at the distance where the evaporation is maximal. We study the interaction of such an ADAF with an inner thin disk below. Results: We show that, when the accretion rate is not far below the transition rate, an inner disk could exist below an ADAF, leading to an intermediate state of black hole accretion.

  8. The Structure and Evolution of Protoplanetary Disks: an infrared and submillimeter view

    E-Print Network [OSTI]

    Cieza, Lucas A

    2015-01-01

    Circumstellar disks are the sites of planet formation, and the very high incidence of extrasolar planets implies that most of them actually form planetary systems. Studying the structure and evolution of protoplanetary disks can thus place important constraints on the conditions, timescales, and mechanisms associated with the planet formation process. In this review, we discuss observational results from infrared and submillimeter wavelength studies. We review disk lifetimes, transition objects, disk demographics, and highlight a few remarkable results from ALMA Early Science observations. We finish with a brief discussion of ALMA's potential to transform the field in near future.

  9. On the Steady Nature of Line-Driven Disk Winds: Application to Cataclysmic Variables

    E-Print Network [OSTI]

    Nicolas A. Pereyra; David A. Turnshek; D. John Hillier

    2005-06-01

    We apply the semi-analytical analysis of the steady nature of line-driven winds presented in two earlier papers to disk winds driven by the flux distribution of a standard Shakura & Sunyaev (1973) disk for typical cataclysmic variable (CV) parameters. We find that the wind critical point tends to be closer to the disk surface towards the inner disk regions. Our main conclusion, however, is that a line-driven wind, arising from a steady disk flux distribution of a standard Shakura-Sunyaev disk capable of locally supplying the corresponding mass flow, is steady. These results confirm the findings of an earlier paper that studied "simple" flux distributions that are more readily analyzable than those presented here. These results are consistent with the steady velocity nature of outflows observationally inferred for both CVs and quasi-stellar objects (QSOs). We find good agreement with the 2.5D CV disk wind models of Pereyra and collaborators. These results suggest that the likely scenario to account for the wind outflows commonly observed in CVs is the line-driven accretion disk wind scenario, as suggested early-on by Cordova & Mason (1982). For QSOs, these results show that the line-driven accretion disk wind continues to be a promising scenario to account for the outflows detected in broad absorption line (BAL) QSOs, as suggested early-on by Turnshek (1984), and analyzed in detail by Murray et al. (1995).

  10. Nano-scale positioning, control and motion planning in hard disk drives

    E-Print Network [OSTI]

    Boettcher, Uwe

    2011-01-01

    C. Bi. Hard disk drive: mechatronics and control. Automationdrive tracking servos. Mechatronics, IEEE/ASME Transactionsin dual-stage hdds. Mechatronics, IEEE/ASME Transactions on,

  11. Advanced Control Algorithms for Discrete Linear Repetitive Processes in Self-servowriting of Hard Disk Drives

    E-Print Network [OSTI]

    Dong, Feng Dan

    2011-01-01

    IEEE/ASME Trans. On Mechatronics, 4(3):312323, 1999. [41] J.in hard disk drives. Mechatronics . 20(1):53-58, 2009. [86

  12. WWW Database of Models of Accretion Disks Irradiated by The Central Star

    E-Print Network [OSTI]

    Paola D'Alessio; Bruno Merin; Nuria Calvet; Lee Hartmann; Benjamin Montesinos

    2004-12-14

    We announce the release of a catalog of physical models of irradiated accretion disks around young stars based on the modelling techniques by D'Alessio et al. The WWW catalog includes ~ 3000 disk models for different central stars, disk sizes, inclinations, dust contents and mass accretion rates. For any of them, radial profiles of disk physical parameters and synthetic spectral energy distributions can be browsed and downloaded to compare with observations. It can be accessed at http://www-cfa.harvard.edu/youngstars/dalessio/ (US), http://www.astrosmo.unam.mx/~dalessio/ (Mexico), and at http://www.laeff.esa.es/models/dalessio/ (Spain).

  13. The Inner Boundary Condition for a Thin Disk Accreting Into a Black Hole

    E-Print Network [OSTI]

    B. Paczy?ski

    2000-04-10

    Contrary to some recent claims the `no torque inner boundary condition' as applied at the marginally stable orbit is correct for geometrically thin disks accreting into black holes.

  14. Constrained Evolution of a Radially Magnetized Protoplanetary Disk: Implications for Planetary Migration

    E-Print Network [OSTI]

    Russo, Matthew

    2015-01-01

    We consider the inner $\\sim$ AU of a protoplanetary disk (PPD), at a stage where angular momentum transport is driven by the mixing of a radial magnetic field into the disk from a T-Tauri wind. Because the radial profile of the imposed magnetic field is well constrained, a deterministic calculation of the disk mass flow becomes possible. The vertical disk profiles obtained in Paper I imply a stronger magnetization in the inner disk, faster accretion, and a secular depletion of the disk material. Inward transport of solids allows the disk to maintain a broad optical absorption layer even when the grain abundance becomes too small to suppress its ionization. Thus a PPD may show a strong middle-to-near infrared spectral excess even while its mass profile departs radically from the minimum-mass solar nebula. The disk surface density is buffered at $\\sim 30$ g cm$^{-2}$: below this, X-rays trigger strong enough magnetorotational turbulence at the midplane to loft mm-cm sized particles high in the disk, followed by...

  15. Primary, secondary instabilities and control of the rotating-disk boundary layer

    E-Print Network [OSTI]

    ;Typical 3D boundary layers rotating disk swept wing Common features: · crossflow component near the wall · inflection point · strong inviscid instability · secondary instabilities ; growth and saturation of crossflow

  16. Origin of chemical and dynamical properties of the Galactic thick disk

    E-Print Network [OSTI]

    Bekki, Kenji

    2011-01-01

    We adopt a scenario in which the Galactic thick disk was formed by minor merging between the first generation of the Galactic thin disk (FGTD) and a dwarf galaxy about 9 Gyr ago and thereby investigate chemical and dynamical properties of the Galactic thick disk. In this scenario, the dynamical properties of the thick disk have long been influenced both by the mass growth of the second generation of the Galactic thin disk (i.e., the present thin disk) and by its non-axisymmetric structures. On the other hand, the early star formation history and chemical evolution of the thin disk was influenced by the remaining gas of the thick disk. Based on N-body simulations and chemical evolution models, we investigate the radial metallicity gradient, structural and kinematical properties, and detailed chemical abundance patterns of the thick disk. Our numerical simulations show that the ancient minor merger event can significantly flatten the original radial metallicity gradient of the FGTD, in particular, in the outer ...

  17. The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks. IV. Simulations with Envelope Irradiation

    E-Print Network [OSTI]

    Kai Cai; Richard H. Durisen; Aaron C. Boley; Megan K. Pickett; Annie C. Mejia

    2007-10-17

    It is generally thought that protoplanetary disks embedded in envelopes are more massive and thus more susceptible to gravitational instabilities (GIs) than exposed disks. We present three-dimensional radiative hydrodynamics simulations of protoplanetary disks with the presence of envelope irradiation. For a disk with a radius of 40 AU and a mass of 0.07 Msun around a young star of 0.5 Msun, envelope irradiation tends to weaken and even suppress GIs as the irradiating flux is increased. The global mass transport induced by GIs is dominated by lower-order modes, and irradiation preferentially suppresses higher-order modes. As a result, gravitational torques and mass inflow rates are actually increased by mild irradiation. None of the simulations produce dense clumps or rapid cooling by convection, arguing against direct formation of giant planets by disk instability, at least in irradiated disks. However, dense gas rings and radial mass concentrations are produced, and these might be conducive to accelerated planetary core formation. Preliminary results from a simulation of a massive embedded disk with physical characteristics similar to one of the disks in the embedded source L1551 IRS5 indicate a long radiative cooling time and no fragmentation. The GIs in this disk are dominated by global two and three-armed modes.

  18. NEUTRINO SPECTRA FROM ACCRETION DISKS: NEUTRINO GENERAL RELATIVISTIC EFFECTS AND THE CONSEQUENCES FOR NUCLEOSYNTHESIS

    SciTech Connect (OSTI)

    Caballero, O. L.; McLaughlin, G. C. [Department of Physics, North Carolina State University, Raleigh, NC 27695 (United States); Surman, R., E-mail: lcaballe@uw.edu, E-mail: olcaball@ncsu.edu, E-mail: gail_mclaughlin@ncsu.edu, E-mail: surmanr@union.edu [Department of Physics and Astronomy, Union College, Schenectady, NY 12308 (United States)

    2012-02-01

    Black hole (BH) accretion disks have been proposed as good candidates for a range of interesting nucleosynthesis, including the r-process. The presence of the BH influences the neutrino fluxes and affects the nucleosynthesis resulting from the interaction of the emitted neutrinos and hot outflowing material ejected from the disk. We study the impact of general relativistic effects on the neutrinos emitted from BH accretion disks. We present abundances obtained by considering null geodesics and energy shifts for two different disk models. We find that both the bending of the neutrino trajectories and the energy shifts have important consequences for the nucleosynthetic outcome.

  19. Neutrino Spectra from Accretion Disks: Neutrino General Relativistic Effects and the Consequences for Nucleosynthesis

    E-Print Network [OSTI]

    O. L Caballero; G. C. McLaughlin; R. Surman

    2011-05-31

    Black hole accretion disks have been proposed as good candidates for a range of interesting nucleosynthesis, including the r-process. The presence of the black hole influences the neutrino fluxes and affects the nucleosynthesis resulting from the interaction of the emitted neutrinos and hot outflowing material ejected from the disk. We study the impact of general relativistic effects on the neutrinos emitted from black hole accretion disks. We present abundances obtained by considering null geodesics and energy shifts for two different disk models. We find that both the bending of the neutrino trajectories and the energy shifts have important consequences for the nucleosynthetic outcome

  20. Ultrasonic detection of residual stress in a turbine disk 

    E-Print Network [OSTI]

    Pathak, Nitin

    1992-01-01

    Photomicrograph of the disk material at the broad side of the rim. . 30 13 Samples for texture studies. 14 Dual element send-receive probe. 33 15 Instrumental set-up used for travel-time measurements. . A typical waveform obtained on PCDAS. Magnified waveform... ) Two identical plexiglas wedges of approximately 63 mm x 25 mm x 24 mm were machined to the required incident angle, which corresponds to the first critical angle needed to excite Lcn waves. The dual element send-receive probe designed is shown...

  1. Benzene formation in the inner regions of protostellar disks

    E-Print Network [OSTI]

    Paul M. Woods; Karen Willacy

    2006-12-08

    Benzene (c-C6H6) formation in the inner 3 AU of a protostellar disk can be efficient, resulting in high abundances of benzene in the midplane region. The formation mechanism is different to that found in interstellar clouds and in protoplanetary nebulae, and proceeds mainly through the reaction between allene (C3H4) and its ion. This has implications for PAH formation, in that some fraction of PAHs seen in the solar system could be native rather than inherited from the interstellar medium.

  2. Conformastationary disk-haloes in Einstein-Maxwell gravity

    E-Print Network [OSTI]

    Antonio C. Gutiérrez-Piñeres

    2015-04-14

    An exact solution of the Einstein-Maxwell field equations for a conformastationary metric with magnetized disk-haloes sources is worked out in full. The characterization of the nature of the energy momentum tensor of the source is discussed. All the expressions are presented in terms of a solution of the Laplace's equation. A "generalization" of the Kuzmin solution of the Laplace's equations is used as a particular example. The solution obtained is asymptotically flat in general and turns out to be free of singularities. All the relevant quantities show a reasonable physical behaviour.

  3. Magnetic Fields are not ignorable in the dynamics of disks

    E-Print Network [OSTI]

    E. Battaner; E. Florido; A. Guijarro

    2000-09-25

    Magnetic fields are considered to be dominant when $\\epsilon_{B}\\geq\\epsilon_{K}$, being $\\epsilon_{B}=B^{2}/8\\pi$ the magnetic energy density and $\\epsilon_{K}=1/2 \\rho\\theta^{2}$ the rotation energy density, for a conventional moderate B= 1 $\\mu$G. They are considered to be negligible when $\\epsilon_{B}<\\epsilon_{K}$ for $B\\sim 10 \\mu$G. With no assumption and no theoretical calculation, we show that magnetic fields cannot be ignored in the outer parts of a galaxy like the Milky Way and in the whole disk of a dwarf galaxy.

  4. Five steps in the evolution from protoplanetary to debris disk

    E-Print Network [OSTI]

    Wyatt, M. C.; Paníc, O.; Kennedy, G. M.; Matrà, L.

    2015-05-13

    of the best studied pro- toplanetary disks in terms of their detailed structure. Most of the known HAe stars were first identified as potentially young intermediate-mass stars by Herbig (1960) using the criteria of emission line spectra, re- gions of heavy... spectral type designation, given that these are often characterised as A0 or B9/A0 stars. We do not claim the plotted star sample to be free from bias, since it simply comprises those in the literature, however it does plot both protoplanetary and debris...

  5. Rapidity gap survival in the black-disk regime

    SciTech Connect (OSTI)

    Leonid Frankfurt; Charles Hyde; Mark Strikman; Christian Weiss

    2007-04-16

    We summarize how the approach to the black-disk regime (BDR) of strong interactions at TeV energies influences rapidity gap survival in exclusive hard diffraction pp -> p + H + p (H = dijet, Qbar Q, Higgs). Employing a recently developed partonic description of such processes, we discuss (a) the suppression of diffraction at small impact parameters by soft spectator interactions in the BDR; (b) further suppression by inelastic interactions of hard spectator partons in the BDR; (c) correlations between hard and soft interactions. Hard spectator interactions substantially reduce the rapidity gap survival probability at LHC energies compared to previously reported estimates.

  6. Upper and lower limits on the Crab pulsar's astrophysical parameters set from gravitational wave observations by LIGO: braking index and energy considerations

    E-Print Network [OSTI]

    Giovanni Santostasi

    2008-07-16

    The Laser Interferometer Gravitational Observatory (LIGO) has recently reached the end of its fifth science run (S5), having collected more than a year worth of data. Analysis of the data is still ongoing but a positive detection of gravitational waves, while possible, is not realistically expected for most likely sources. This is particularly true for what concerns gravitational waves from known pulsars. In fact, even under the most optimistic (and not very realistic) assumption that all the pulsar's observed spin-down is due to gravitational waves, the gravitational wave strain at earth from all the known isolated pulsars (with the only notable exception of the Crab pulsar) would not be strong enough to be detectable by existing detectors. By August 2006, LIGO had produced enough data for a coherent integration capable to extract signal from noise that was weaker than the one expected from the Crab pulsar's spin-down limit. No signal was detected, but beating the spin-down limit is a considerable achievement for the LIGO Scientific Collaboration (LSC). It is customary to translate the upper limit on strain from a pulsar into a more astrophysically significant upper limit on ellipticity. Once the spin-down limit has been beaten, it is possible to release the constraint that all the spin-down is due to gravitational wave emission. A more complete model with diverse braking mechanisms can be used to set limits on several astrophysical parameters of the pulsar. This paper shows possible values of such parameters for the Crab pulsar given the current limit on gravitational waves from this neutron star.

  7. EVIDENCE FOR A SNOW LINE BEYOND THE TRANSITIONAL RADIUS IN THE TW Hya PROTOPLANETARY DISK

    SciTech Connect (OSTI)

    Zhang, K. [Division of Physics, Mathematics and Astronomy, MC 150-21, California Institute of Technology, Pasadena, CA 91125 (United States)] [Division of Physics, Mathematics and Astronomy, MC 150-21, California Institute of Technology, Pasadena, CA 91125 (United States); Pontoppidan, K. M. [Space Telescope Science Institute, Baltimore, MD 21218 (United States)] [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Salyk, C. [National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 (United States)] [National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 (United States); Blake, G. A., E-mail: kzhang@caltech.edu [Division of Geological and Planetary Sciences, MC 150-21, California Institute of Technology, Pasadena, CA 91125 (United States)

    2013-04-01

    We present an observational reconstruction of the radial water vapor content near the surface of the TW Hya transitional protoplanetary disk, and report the first localization of the snow line during this phase of disk evolution. The observations are comprised of Spitzer-IRS, Herschel-PACS, and Herschel-HIFI archival spectra. The abundance structure is retrieved by fitting a two-dimensional disk model to the available star+disk photometry and all observed H{sub 2}O lines, using a simple step-function parameterization of the water vapor content near the disk surface. We find that water vapor is abundant ({approx}10{sup -4} per H{sub 2}) in a narrow ring, located at the disk transition radius some 4 AU from the central star, but drops rapidly by several orders of magnitude beyond 4.2 AU over a scale length of no more than 0.5 AU. The inner disk (0.5-4 AU) is also dry, with an upper limit on the vertically averaged water abundance of 10{sup -6} per H{sub 2}. The water vapor peak occurs at a radius significantly more distant than that expected for a passive continuous disk around a 0.6 M{sub Sun} star, representing a volatile distribution in the TW Hya disk that bears strong similarities to that of the solar system. This is observational evidence for a snow line that moves outward with time in passive disks, with a dry inner disk that results either from gas giant formation or gas dissipation and a significant ice reservoir at large radii. The amount of water present near the snow line is sufficient to potentially catalyze the (further) formation of planetesimals and planets at distances beyond a few AU.

  8. A File Allocation Strategy for Energy-Efficient Disk Storage Systems

    SciTech Connect (OSTI)

    Otoo, Ekow J; Otoo, Ekow J.; Rotem, Doron; Pinar, Ali; Tsao, Shi-Chiang

    2008-06-27

    Exponential data growth is a reality for most enterprise and scientific data centers.Improvements in price/performance and storage densities of disks have made it both easy and affordable to maintain most of the data in large disk storage farms. The provisioning of disk storage farms however, is at the expense of high energy consumption due to the large number of spinning disks. The power for spinning the disks and the associated cooling costs is a significant fraction of the total power consumption of a typical data center. Given the trend of rising global fuel and energy prices and the high rate of data growth, the challenge is to implement appropriateconfigurations of large scale disk storage systems that meet performancerequirements for information retrieval across data centers. We present part of the solution to this challenge with an energy efficient file allocation strategy on a large scale disk storage system. Given performance characteristics of thedisks, and a profile of the workload in terms of frequencies of file requests and their sizes, the basic idea is to allocate files to disks such that the disks can be configured into two sets of active (constantly spinning), and passive (capable of being spun up or down) disk pools. The goal is to minimize the number of active disks subject to I/O performance constraints. We present an algorithm for solving this problem with guaranteed bounds from the optimal solution. Our algorithm runs in O(n) time where n is the number of files allocated. It uses a mapping of our file allocation problem to a generalization of the bin packing problem known as 2-dimensional vector packing. Detailed simulation results are also provided.

  9. Molecular Hydrogen Emission from Protoplanetary Disks II. Effects of X-ray Irradiation and Dust Evolution

    E-Print Network [OSTI]

    H. Nomura; Y. Aikawa; M. Tsujimoto; Y. Nakagawa; T. J. Millar

    2007-02-01

    Detailed models for the density and temperature profiles of gas and dust in protoplanetary disks are constructed by taking into account X-ray and ultraviolet (UV) irradiation from a central T Tauri star, as well as dust size growth and settling toward the disk midplane. The spatial and size distributions of dust grains in the disks are numerically computed by solving the coagulation equation for settling dust particles. The level populations and line emission of molecular hydrogen are calculated using the derived physical structure of the disks. X-ray irradiation is the dominant heating source of the gas in the inner disk region and in the surface layer, while the far UV heating dominates otherwise. If the central star has strong X-ray and weak UV radiation, the H2 level populations are controlled by X-ray pumping, and the X-ray induced transition lines could be observable. If the UV irradiation is strong, the level populations are controlled by thermal collisions or UV pumping, depending on the properties of the dust grains in the disks. As the dust particles evolve in the disks, the gas temperature at the disk surface drops because the grain photoelectric heating becomes less efficient, while the UV radiation fields become stronger due to the decrease of grain opacity. This makes the H2 level populations change from local thermodynamic equilibrium (LTE) to non-LTE distributions, which results in changes to the line ratios of H2 emission. Our results suggest that dust evolution in protoplanetary disks could be observable through the H2 line ratios. The emission lines are strong from disks irradiated by strong UV and X-rays and possessing small dust grains; such disks will be good targets in which to observe H2 emission.

  10. Powerful, Rotating Disk Winds from Stellar-mass Black Holes

    E-Print Network [OSTI]

    Miller, J M; Kaastra, J; Kallman, T; King, A L; Proga, D; Raymond, J; Reynolds, C S

    2015-01-01

    We present an analysis of ionized X-ray disk winds observed in the Fe K band of four stellar-mass black holes observed with Chandra, including 4U 1630-47, GRO J1655-40, H 1743-322, and GRS 1915+105. High-resolution photoionization grids were generated in order to model the data. Third-order gratings spectra were used to resolve complex absorption profiles into atomic effects and multiple velocity components. The Fe XXV line is found to be shaped by contributions from the intercombination line (in absorption), and the Fe XXVI line is detected as a spin-orbit doublet. The data require 2-3 absorption zones, depending on the source. The fastest components have velocities approaching or exceeding 0.01c, increasing mass outflow rates and wind kinetic power by orders of magnitude over prior single-zone models. The first-order spectra require re-emission from the wind, broadened by a degree that is loosely consistent with Keplerian orbital velocities at the photoionization radius. This suggests that disk winds are ro...

  11. Measurements of water surface snow lines in classical protoplanetary disks

    E-Print Network [OSTI]

    Blevins, Sandra M; Banzatti, Andrea; Zhang, Ke; Najita, Joan R; Carr, John S; Salyk, Colette; Blake, Geoffrey A

    2015-01-01

    We present deep Herschel-PACS spectroscopy of far-infrared water lines from a sample of four protoplanetary disks around solar-mass stars, selected to have strong water emission at mid-infrared wavelengths. By combining the new Herschel spectra with archival Spitzer-IRS spectroscopy, we retrieve a parameterized radial surface water vapor distribution from 0.1-100 AU using two-dimensional dust and line radiative transfer modeling. The surface water distribution is modeled with a step model comprising of a constant inner and outer relative water abundance and a critical radius at which the surface water abundance is allowed to change. We find that the four disks have critical radii of $\\sim 3-11$ AU, at which the surface water abundance decreases by at least 5 orders of magnitude. The measured values for the critical radius are consistently smaller than the location of the surface snow line, as predicted by the observed spectral energy distribution. This suggests that the sharp drop-off of the surface water abu...

  12. Water in Protoplanetary Disks: Deuteration and Turbulent Mixing

    E-Print Network [OSTI]

    Furuya, Kenji; Nomura, Hideko; Hersant, Franck; Wakelam, Valentine

    2013-01-01

    We investigate water and deuterated water chemistry in turbulent protoplanetary disks. Chemical rate equations are solved with the diffusion term, mimicking turbulent mixing in vertical direction. Water near the midplane is transported to the disk atmosphere by turbulence and destroyed by photoreactions to produce atomic oxygen, while the atomic oxygen is transported to the midplane and reforms water and/or other molecules. We find that this cycle significantly decreases column densities of water ice at r < 30 AU, where dust temperatures are too high to reform water ice effectively. The radial extent of such region depends on the desorption energy of atomic hydrogen. Our model indicates that water ice could be deficient even outside the sublimation radius. Outside this radius, the cycle decreases the D/H ratio of water ice from 2x10^-2, which is set by the collapsing core model, to 10^-4-10^-2 in 10^6 yr, without significantly decreasing the water ice column density. The resultant D/H ratios depend on the ...

  13. Double Bars, Inner Disks, and Nuclear Rings in Barred Galaxies

    E-Print Network [OSTI]

    Peter Erwin; Linda S. Sparke; Juan Carlos Vega Beltran; John Beckman

    2001-07-07

    We present results of a high-resolution imaging survey of barred S0--Sa galaxies which demonstrate that the central regions of these galaxies are surprisingly complex. We see many inner bars --- small, secondary bars (typically less than a kiloparsec in radius) located inside of, and probably rotating faster than, the large primary bars. These are present in about one quarter to one third of all our sample. In contrast to some theoretical expectations, they do not seem to enhance AGN activity significantly. A third of barred S0's appear to host kiloparsec-scale disks within their bars; but the frequency of such inner disks is much lower in our S0/a and Sa galaxies. In addition, we find one example of a triple barred galaxy, and two cases of purely stellar nuclear rings --- probably the fossil remnants of past circumnuclear starbursts. We comment briefly on results from an ongoing analysis of known double-barred systems, extending to Hubble types as late as Sbc, and discuss their characteristic sizes and orientations.

  14. Testing particle trapping in transition disks with ALMA

    E-Print Network [OSTI]

    Pinilla, P; Pérez, L M; van Dishoeck, E F; Andrews, S; Birnstiel, T; Herczeg, G; Pontoppidan, K M; van Kempen, T

    2015-01-01

    We present new ALMA continuum observations at 336 GHz of two transition disks, SR 21 and HD 135344B. In combination with previous ALMA observations from Cycle 0 at 689 GHz, we compare the visibility profiles at the two frequencies and calculate the spectral index ($\\alpha_{\\rm{mm}}$). The observations of SR 21 show a clear shift in the visibility nulls, indicating radial variations of the inner edge of the cavity at the two wavelengths. Notable radial variations of the spectral index are also detected for SR 21 with values of $\\alpha_{\\rm{mm}}\\sim3.8-4.2$ in the inner region ($r\\lesssim35$ AU) and $\\alpha_{\\rm{mm}}\\sim2.6-3.0$ outside. An axisymmetric ring ("ring model") or a ring with the addition of an azimuthal Gaussian profile, for mimicking a vortex structure ("vortex model"), is assumed for fitting the disk morphology. For SR 21, the ring model better fits the emission at 336 GHz, conversely the vortex model better fits the 689 GHz emission. For HD 135344B, neither a significant shift in the null of the...

  15. Preliminary Investigations of Eddy Current Effects on a Spinning Disk

    SciTech Connect (OSTI)

    Piggott, W T; Walston, S; Mayhall, D

    2006-09-08

    The design of the positron source target for the International Linear Collider (ILC) envisions a Ti6Al4V wheel rotating in a large magnetic field (5-10 Tesla) being impacted by a photon beam to produce positrons. One of the many challenges for this system is determining how large a motor will be needed to spin the shaft. The wheel spinning in the magnetic field induces an eddy current in the wheel, which retards the spinning motion of the wheel. Earlier calculations by Mayhall [1] have shown that those eddy forces could be quite large, and resulted in the preliminary design being moved from a solid disk to a rim and spoke design, as shown in Figure 1. A series of experiments with a spinning metal disk were run at the Stanford Linear Accelerator Center (SLAC) to provide experimental validation of the Maxwell 3D simulations. This report will give a brief outline of the experimental setup and results. In addition, earlier work by Smythe [2] will be used to compare with the experimental results.

  16. GLOBAL DRAG-INDUCED INSTABILITIES IN PROTOPLANETARY DISKS

    SciTech Connect (OSTI)

    Jalali, Mir Abbas, E-mail: mjalali@sharif.edu [Computational Mechanics Laboratory, Department of Mechanical Engineering, Sharif University of Technology, Azadi Avenue, P.O. Box 11155-9567, Tehran (Iran, Islamic Republic of)

    2013-07-20

    We use the Fokker-Planck equation and model the dispersive dynamics of solid particles in annular protoplanetary disks whose gas component is more massive than the particle phase. We model particle-gas interactions as hard sphere collisions, determine the functional form of diffusion coefficients, and show the existence of two global unstable modes in the particle phase. These modes have spiral patterns with the azimuthal wavenumber m = 1 and rotate slowly. We show that in ring-shaped disks, the phase-space density of solid particles increases linearly in time toward an accumulation point near the location of pressure maximum, while instabilities grow exponentially. Therefore, planetesimals and planetary cores can be efficiently produced near the peaks of unstable density waves. In this mechanism, particles migrating toward the accumulation point will not participate in the formation of planets, and should eventually form a debris ring like the main asteroid belt or classical Kuiper Belt objects. We present the implications of global instabilities to the formation of ice giants and terrestrial planets in the solar system.

  17. Datacenter Scale Evaluation of the Impact of Temperature on Hard Disk Drive Failures

    E-Print Network [OSTI]

    Gurumurthi, Sudhanva

    Datacenter Scale Evaluation of the Impact of Temperature on Hard Disk Drive Failures SRIRAM SANKAR rely heavily on their datacenters to serve end users. A large datacenter facility incurs increased, there is very little understanding on the major determinants of disk failures in datacenters. In this work, we

  18. Interplay of Energy and Performance for Disk Arrays Running Transaction Processing Workloads

    E-Print Network [OSTI]

    Gurumurthi, Sudhanva

    centers could grow to over 100 Watts per square foot, and future centers could add 5 GW of demand (whichInterplay of Energy and Performance for Disk Arrays Running Transaction Processing Workloads for these systems. This paper examines the energy and performance ramifications in the design of disk arrays which

  19. ALMA observations of a misaligned binary protoplanetary disk system in Orion

    SciTech Connect (OSTI)

    Williams, Jonathan P.; Mann, Rita K.; Francesco, James Di; Johnstone, Doug; Matthews, Brenda; Andrews, Sean M.; Ricci, Luca; Hughes, A. Meredith; Bally, John

    2014-12-01

    We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a wide binary system in Orion, with projected separation 440 AU, in which we detect submillimeter emission from the protoplanetary disks around each star. Both disks appear moderately massive and have strong line emission in CO 3-2, HCO{sup +} 4-3, and HCN 3-2. In addition, CS 7-6 is detected in one disk. The line-to-continuum ratios are similar for the two disks in each of the lines. From the resolved velocity gradients across each disk, we constrain the masses of the central stars, and show consistency with optical-infrared spectroscopy, both indicative of a high mass ratio ?9. The small difference between the systemic velocities indicates that the binary orbital plane is close to face-on. The angle between the projected disk rotation axes is very high, ?72°, showing that the system did not form from a single massive disk or a rigidly rotating cloud core. This finding, which adds to related evidence from disk geometries in other systems, protostellar outflows, stellar rotation, and similar recent ALMA results, demonstrates that turbulence or dynamical interactions act on small scales well below that of molecular cores during the early stages of star formation.

  20. Tweening Boundary Curves of Non-simple Immersions of a Disk

    E-Print Network [OSTI]

    Meenakshisundaram, Gopi

    to lists, requires prior specific permission and/or a fee. ICVGIP '12, December 16-19, 2012, Mumbai, India. In order to compute this sequence, we require a mapping function between the interiors of the disk triangulation of the disk serves as one such mapping function. Since there are many such triangulations possible

  1. MAGNETIC STAR-DISK COUPLING IN CLASSICAL T TAURI SYSTEMS Manfred Kuker,1,2

    E-Print Network [OSTI]

    MAGNETIC STAR-DISK COUPLING IN CLASSICAL T TAURI SYSTEMS Manfred Ku¨ker,1,2 Thomas Henning,1 of several kilogauss (Guenther & Emerson 1996; Guenther et al. 1999; Johns- Krull, Valenti, & Koresko 1999 al. 1999, 2001). The coupling between an accretion disk and its central object was first discussed

  2. Increasing Disk Burstiness for Energy Efficiency Athanasios E. Papathanasiou and Michael L. Scott

    E-Print Network [OSTI]

    Scott, Michael L.

    The University of Rochester Computer Science Department Rochester, New York 14627 Technical Report 792 AbstractIncreasing Disk Burstiness for Energy Efficiency Athanasios E. Papathanasiou and Michael L. Scott an alternative strategy, in which the operating system deliberately seeks to cluster disk operations in time

  3. GHRS Observations of Molecular Hydrogen in the Gas Disks of PreMain Sequence Stars

    E-Print Network [OSTI]

    Walter, Frederick M.

    ). When this happens, what happens to the gas disk? The gas disk survival time TGS is not known because cold gas is very difficult to detect. The early history of the proto­solar nebula may constrain TGS.g., Podolak et al. 1993). At radial distances of ¸5­10 AU in our protoplanetary nebula, it seems that TGS

  4. Round-like behavior in multiple disks on a bus Phillip B. Gibbons

    E-Print Network [OSTI]

    Gibbons, Phillip B.

    disks, poten- tidly resulting in an aggregate I/O throughput at nearly bus bandwidth. This paper reports on each bus. Previous work related to disk I/O performance and mod- eling (e.g., [RW94, Wil95, HP96, Shr97

  5. DYNAMICAL STABILITY AND ENVIRONMENTAL INFLUENCES IN LOW SURFACE BRIGHTNESS DISK GALAXIES

    E-Print Network [OSTI]

    McGaugh, Stacy

    and starburst activity in these galaxies. Subject heading: galaxies: evolution -- galaxies: interactions in their lifetimes. Indeed, sufficient tidally induced star formation in LSB disks may drive evolution from LSB are significantly different (de Blok & McGaugh 1996, hereafter dBM). In particular, LSB galaxies have lower disk

  6. Probing the electronic structure and optical response of a graphene quantum disk supported on monolayer graphene

    E-Print Network [OSTI]

    Pennycook, Steve

    Probing the electronic structure and optical response of a graphene quantum disk supported on monolayer graphene This article has been downloaded from IOPscience. Please scroll down to see the full text.1088/0953-8984/24/31/314213 Probing the electronic structure and optical response of a graphene quantum disk supported on monolayer

  7. Asymptotic study of film thinning process on a spinning annular disk B. S. Dandapat

    E-Print Network [OSTI]

    Daripa, Prabir

    Asymptotic study of film thinning process on a spinning annular disk B. S. Dandapat Physics consider an axisymmetric flow of a thin liquid film on a rotating annular disk. The effects of surface tension and gravity terms are included. An asymptotic solution for the free surface of the thin film

  8. A Comparison of Alternative Continuous Display Techniques with Heterogeneous Multi-Zone Disks *

    E-Print Network [OSTI]

    Kim, Seon Ho

    are expected to play an important role in applications such as video-on-demand, digital library, news with the intro- duction of 50 gigabyte disk drives, a video library consisting of 1000 MPEG-2 titles (with administrator is forced to buy new disk drives over time and *This research was supported by the National

  9. Conserving Disk Energy in Network Servers Enrique V. Carrera, Eduardo Pinheiro, and Ricardo Bianchini

    E-Print Network [OSTI]

    Bianchini, Ricardo

    ­generation technologies (such as nuclear and coal­based generation) have a negative impact on the environment. A fewConserving Disk Energy in Network Servers #3; Enrique V. Carrera, Eduardo Pinheiro, and Ricardo,edpin,ricardobg@cs.rutgers.edu ABSTRACT In this paper we study four approaches to conserving disk energy in high­performance network

  10. The interaction of chemicals and red light on growth of etiolated bean leaf disks 

    E-Print Network [OSTI]

    Edwards, John Lee

    1960-01-01

    were then separated and opened. The leaf disk was removed from the basal area of the leaf with a sharpened, sterilised cork borer, 5 mm in diameter. The disk was placed in the Petri dish with the lower epidermis upward and with the main lateral vein...

  11. Issues and Challenges in the Performance Analysis of Real Disk Arrays

    E-Print Network [OSTI]

    Varki, Elizabeth

    , parallel I/O, enterprise storage systems, I/O performance evaluation, disk array. æ 1 INTRODUCTION AS computer applications have become more data intensive, the demands on storage systems in terms of efficient Disks) architectures have become the architecture of choice for large storage systems since they employ

  12. Covariant Lyapunov vectors for rigid disk systems Hadrien Bosetti, Harald A. Posch *

    E-Print Network [OSTI]

    Dellago, Christoph

    Covariant Lyapunov vectors for rigid disk systems Hadrien Bosetti, Harald A. Posch * Computational l e i n f o Article history: Available online 10 June 2010 Keywords: Lyapunov instability Hard disks Covariant vectors Statistical mechanics Computer simulation Fluids Lyapunov modes a b s t r a c t We carry

  13. Lyapunov instability of rough hard-disk fluids Jacobus A. van Meel*

    E-Print Network [OSTI]

    Posch, Harald A.

    Lyapunov instability of rough hard-disk fluids Jacobus A. van Meel* FOM Institute for Atomic The dynamical instability of rough hard-disk fluids in two dimensions is characterized through the Lyapunov, measured by the maximum Lyapunov exponent, is only enhanced by the rotational degrees of freedom for high

  14. Bondi-Hoyle Accretion in Dense Star Clusters: Implications for Stars, Disks, and Planets

    E-Print Network [OSTI]

    Throop, Henry

    may take XX years to collapse, accrete mass, and begin fusion. Star formation in the cluster continuesBondi-Hoyle Accretion in Dense Star Clusters: Implications for Stars, Disks, and Planets Draft the Bondi-Hoyle accretion of gas from a GMC onto young star- disk systems in a cluster. This post

  15. The Carbon-Rich Gas in the Beta Pictoris Circumstellar Disk

    E-Print Network [OSTI]

    Aki Roberge; Paul D. Feldman; Alycia J. Weinberger; Magali Deleuil; Jean-Claude Bouret

    2006-04-20

    The edge-on disk surrounding the nearby young star Beta Pictoris is the archetype of the "debris disks", which are composed of dust and gas produced by collisions and evaporation of planetesimals, analogues of Solar System comets and asteroids. These disks provide a window on the formation and early evolution of terrestrial planets. Previous observations of Beta Pic concluded that the disk gas has roughly solar abundances of elements [1], but this poses a problem because such gas should be rapidly blown away from the star, contrary to observations of a stable gas disk in Keplerian rotation [1, 2]. Here we report the detection of singly and doubly ionized carbon (CII, CIII) and neutral atomic oxygen (OI) gas in the Beta Pic disk; measurement of these abundant volatile species permits a much more complete gas inventory. Carbon is extremely overabundant relative to every other measured element. This appears to solve the problem of the stable gas disk, since the carbon overabundance should keep the gas disk in Keplerian rotation [3]. New questions arise, however, since the overabundance may indicate the gas is produced from material more carbon-rich than the expected Solar System analogues.

  16. THE MIGRATION OF GAP-OPENING PLANETS IS NOT LOCKED TO VISCOUS DISK EVOLUTION

    SciTech Connect (OSTI)

    Duffell, Paul C.; MacFadyen, Andrew I.; Farris, Brian D.; Haiman, Zoltan; D'Orazio, Daniel J.

    2014-09-01

    Most standard descriptions of Type II migration state that massive, gap-opening planets must migrate at the viscous drift rate. This is based on the idea that the disk is separated into an inner and outer region and gas is considered unable to cross the gap. In fact, gas easily crosses the gap on horseshoe orbits, nullifying this necessary premise which would set the migration rate. In this work, it is demonstrated using highly accurate numerical calculations that the actual migration rate is dependent on disk and planet parameters, and can be significantly larger or smaller than the viscous drift rate. In the limiting case of a disk much more massive than the secondary, the migration rate saturates to a constant that is sensitive to disk parameters and is not necessarily of the order of the viscous rate. In the opposite limit of a low-mass disk, the migration rate decreases linearly with disk mass. Steady-state solutions in the low disk mass limit show no pile-up outside the secondary's orbit, and no corresponding drainage of the inner disk.

  17. Formation of Sets and Subsets of Informative Features of Information Carriers with Magnetic Hard Disks*

    E-Print Network [OSTI]

    Borissova, Daniela

    . Regardless of the type of the information carrier with hard magnetic disks, the main and most important137 Formation of Sets and Subsets of Informative Features of Information Carriers with Magnetic magnetic disk, new informative features are presented, which form a substantial subset of the informative

  18. The JCMT Gould Belt Survey: SCUBA-2 observations of circumstellar disks in L 1495

    E-Print Network [OSTI]

    Buckle, J V; Greaves, J; Richer, J S; Matthews, B C; Johnstone, D; Kirk, H; Beaulieu, S F; Berry, D S; Broekhoven-Fiene, H; Currie, M J; Fich, M; Hatchell, J; Jenness, T; Mottram, J C; Nutter, D; Pattle, K; Pineda, J E; Salji, C; Tisi, S; Di Francesco, J; Hogerheijde, M R; Ward-Thompson, D; Bastien, P; Butner, H; Chen, M; Chrysostomou, A; Coude, S; Davis, C J; Duarte-Cabral, A; Friberg, P; Friesen, R; Fuller, G A; Graves, S; Gregson, J; Holland, W; Joncas, G; Kirk, J M; Knee, L B G; Mairs, S; Marsh, K; Moriarty-Schieven, G; Rawlings, J; Rosolowsky, E; Rumble, D; Sadavoy, S; Thomas, H; Tothill, N; Viti, S; White, G J; Wilson, C D; Wouterloot, J; Yates, J; Zhu, M

    2015-01-01

    We present 850$\\mu$m and 450$\\mu$m data from the JCMT Gould Belt Survey obtained with SCUBA-2 and characterise the dust attributes of Class I, Class II and Class III disk sources in L1495. We detect 23% of the sample at both wavelengths, with the detection rate decreasing through the Classes from I--III. The median disk mask is 1.6$\\times 10^{-3}$M$_{\\odot}$, and only 7% of Class II sources have disk masses larger than 20 Jupiter masses. We detect a higher proportion of disks towards sources with stellar hosts of spectral type K than spectral type M. Class II disks with single stellar hosts of spectral type K have higher masses than those of spectral type M, supporting the hypothesis that higher mass stars have more massive disks. Variations in disk masses calculated at the two wavelengths suggests there may be differences in dust opacity and/or dust temperature between disks with hosts of spectral types K to those with spectral type M.

  19. Using FUV to IR Variability to Probe the Star-Disk Connection in the Transitional Disk of GM Aur

    E-Print Network [OSTI]

    Ingleby, Laura; Calvet, Nuria; Sitko, Michael; Russell, Ray; Champney, Elizabeth

    2015-01-01

    We analyze 3 epochs of ultraviolet (UV), optical and near-infrared (NIR) observations of the Taurus transitional disk GM Aur using the Hubble Space Telescope Imaging Spectrograph (STIS) and the Infrared Telescope Facility SpeX spectrograph. Observations were separated by one week and 3 months in order to study variability over multiple timescales. We calculate accretion rates for each epoch of observations using the STIS spectra and find that those separated by one week had similar accretion rates (~1E-8 solar masses/yr) while the epoch obtained 3 months later had a substantially lower accretion rate (~4E-9 solar masses/yr). We find that the decline in accretion rate is caused by lower densities of material in the accretion flows, as opposed to a lower surface coverage of the accretion columns. During the low accretion rate epoch we also observe lower fluxes at both far UV (FUV) and IR wavelengths, which trace molecular gas and dust in the disk, respectively. We find that this can be explained by a lower dust...

  20. Investigation of bit patterned media, thermal flying height control sliders and heat assisted magnetic recording in hard disk drives

    E-Print Network [OSTI]

    Zheng, Hao

    2011-01-01

    51   2.2   Rarefaction Effects for Ultra-Low Head/Diska stable and ultra-low head/disk spacing during driveensure a stable and ultra-low head/disk spacing and reliable

  1. arXiv:submit/0922752[astro-ph.SR]27Feb2014 An Observational Perspective of Transitional Disks

    E-Print Network [OSTI]

    Espaillat, Catherine C.

    these mechanisms, particularly planet-induced disk clearing, compare to actual observations. Lastly, we discuss structure. Transitional disk SEDs were first identified by Strom et al. (1989); Skrutskie et al. (1990) from

  2. Herschel photometry of disks around low-mass stars in the R CrA cloud

    SciTech Connect (OSTI)

    Harvey, Paul M. [Astronomy Department, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259 (United States); Henning, Thomas [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Liu, Yao [Purple Mountain Observatory and Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008 (China); Wolf, Sebastian, E-mail: pmh@astro.as.utexas.edu, E-mail: nje@astro.as.utexas.edu, E-mail: henning@mpia.de, E-mail: yliu@pmo.ac.cn, E-mail: wolf@astrophysik.uni-kiel.de, E-mail: yliu@pmo.ac.cn [Institute of Theoretical Physics and Astrophysics, University of Kiel, Leibnizstr. 15, D-24098 Kiel (Germany)

    2014-11-01

    We report photometric results from a subset of a Herschel-PACS program to observe cool dust in disks around low-mass stars as a complement to our earlier program to measure far-infrared emission from brown dwarfs. In this latest study we observed five low-mass objects in the nearby R Corona Australis region and detected at least three at 70 ?m. Using a Monte Carlo radiative transfer code we have investigated the disk masses and geometry based on detailed spectral energy distribution (SED) modeling, and we compare these new results to those from our earlier larger sample of brown dwarfs. In particular, our SED analysis for these five objects shows again that disk geometries of brown dwarfs or low-mass stars are generally similar to their higher mass counterparts like T Tauri disks, but the range of disk mass extends to well below the value found in T Tauri stars.

  3. Alignments Of Black Holes With Their Warped Accretion Disks And Episodic Lifetimes Of Active Galactic Nuclei

    E-Print Network [OSTI]

    Li, Yan-Rong; Cheng, Cheng; Qiu, Jie

    2015-01-01

    Warped accretion disks have attracted intensive attention because of their critical role on shaping the spin of supermassive massive black holes (SMBHs) through the Bardeen-Petterson effect, a general relativistic effect that leads to final alignments or anti-alignments between black holes and warped accretion disks. We study such alignment processes by explicitly taking into account the finite sizes of accretion disks and the episodic lifetimes of AGNs that delineate the duration of gas fueling onto accretion disks. We employ an approximate global model to simulate the evolution of accretion disks, allowing to determine the gravitomagnetic torque that drives the alignments in a quite simple way. We then track down the evolutionary paths for mass and spin of black holes both in a single activity episode and over a series of episodes. Given with randomly and isotropically oriented gas fueling over episodes, we calculate the spin evolution with different episodic lifetimes and find that it is quite sensitive to...

  4. Near-Infrared Imaging Polarmetry of LkCa 15: A Possible Wwarped Inner Disk

    E-Print Network [OSTI]

    OH, Daehyun; Tamura, Motohide; Winsiewski, John; Akiyama, Eiji; Currie, Thayne; Mayama, Satoshi; Takami, Michihiro; Thalmann, Christian; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D; Carson, Joseph C; Egner, Sebastian; Feldt, Markus; Goto, Miwa; Grady, Carol A; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S; Henning, Thomas; Hodapp, Klaus W; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R; Kuzuhara, Masayuki; Kwon, Jungmi; Matsuo, Taro; Mcelwain, Michael W; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Pyo, Tae-Soo; Serabyn, Eugene; Suenaga, Takuya; Suto, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro H; Takato, Naruhisa; Terada, Hiroshi; Turner, Edwin L; Watanabe, Makoto; Yamada, Toru; Takami, Hideki; Usuda, Tomonori

    2016-01-01

    We present high-contrast H-band polarized intensity images of the transitional disk around the young solar-like star LkCa 15. By utilizing Subaru/HiCIAO for polarimetric differential imaging, both the angular resolution and the inner working angle reach 0.07" and r=0.1", respectively. We obtained a clearly resolved gap (width <~ 27 AU) at ~ 48 AU from the central star. This gap is consistent with images reported in previous studies. We also confirmed the existence of a bright inner disk with a misaligned position angle of 13+/-4 degree with respect to that of the outer disk, i.e., the inner disk is possibly warped. The large gap and the warped inner disk both point to the existence of a multiple planetary system with a mass of <~1Mjup.

  5. Can black-hole neutrino-cooled disks power short gamma-ray bursts?

    E-Print Network [OSTI]

    Liu, Tong; Hou, Shu-Jin; Gu, Wei-Min

    2015-01-01

    Stellar-mass black holes (BHs) surrounded by neutrino-dominated accretion flows (NDAFs) are the plausible candidates to power gamma-ray bursts (GRBs) via neutrinos emission and their annihilation. The progenitors of short-duration GRBs (SGRBs) are generally considered to be compact binaries mergers. According to the simulation results, the disk mass of the NDAF has been limited after merger events. We can estimate such disk mass by using the current SGRB observational data and fireball model. The results show that the disk mass of a certain SGRB mainly depends on its output energy, jet opening angle, and central BH characteristics. Even for the extreme BH parameters, some SGRBs require massive disks, which approach or exceed the limits in simulations. We suggest that there may exist alternative magnetohydrodynamic processes or some mechanisms increasing the neutrino emission to produce SGRBs with the reasonable BH parameters and disk mass.

  6. Precession of neutrino-cooled accretion disks in gamma-ray burst engines

    E-Print Network [OSTI]

    Matias M. Reynoso; Gustavo E. Romero; Oscar A. Sampayo

    2006-07-14

    We study the precession of accretion disks in the context of gamma-ray burst inner engines. With an accretion disk model that allows for neutrino cooling, we evaluate the possible periods of disk precession and nutation due to the Lense-Thirring effect. Assuming jet ejection perpendicular to the disk midplane and a typical intrinsic time dependence for the burst, we find possible gamma-ray light curves with temporal microstructure similar to what is observed in some subsamples. We conclude that the precession and nutation of a neutrino-cooled accretion disk in the burst engine might be responsible for some events, especially those with a slow rise and a fast decay.

  7. A Disk of Young Stars at the Galactic Center as Determined by Individual Stellar Orbits

    E-Print Network [OSTI]

    J. R. Lu; A. M. Ghez; S. D. Hornstein; M. R. Morris; E. E. Becklin; K. Matthews

    2008-08-28

    We present new proper motions from the 10 m Keck telescopes for a puzzling population of massive, young stars located within 3.5" (0.14 pc) of the supermassive black hole at the Galactic Center. Our proper motion measurements have uncertainties of only 0.07 mas/yr (3 km/s), which is ~7 times better than previous proper motion measurements for these stars, and enables us to measure accelerations as low as 0.2 mas/yr^2 (7 km/s/yr). Using these measurements, line-of-sight velocities from the literature, and 3D velocities for additional young stars in the central parsec, we constrain the true orbit of each individual star and directly test the hypothesis that the massive stars reside in two stellar disks as has been previously proposed. Analysis of the stellar orbits reveals only one of the previously proposed disks of young stars using a method that is capable of detecting disks containing at least 7 stars. The detected disk contains 50% of the young stars, is inclined by ~115 deg from the plane of the sky, and is oriented at a position angle of ~100 deg East of North. Additionally, the on-disk and off-disk populations have similar K-band luminosity functions and radial distributions that decrease at larger projected radii as \\propto r^-2. The disk has an out-of-the-disk velocity dispersion of 28 +/- 6 km/s, which corresponds to a half-opening angle of 7 +/- 2 deg, and several candidate disk members have eccentricities greater than 0.2. Our findings suggest that the young stars may have formed in situ but in a more complex geometry than a simple, thin circular disk.

  8. Thermal Effects of Circumplanetary Disk Formation around Proto-Gas Giant Planets

    E-Print Network [OSTI]

    Masahiro N. Machida

    2008-10-15

    The formation of a circumplanetary disk and accretion of angular momentum onto a protoplanetary system are investigated using 3D hydrodynamical simulations. The local region around a protoplanet in a protoplanetary disk is considered with sufficient spatial resolution: the region from outside the Hill sphere to the Jovian radius is covered by the nested-grid method. To investigate the thermal effects of the circumplanetary disk, various equations of state are adopted. Large thermal energy around the protoplanet slightly changes the structure of the circumplanetary disk. Compared with a model adopting an isothermal equation of state, in a model with an adiabatic equation of state, the protoplanet's gas envelope extends farther, and a slightly thick disk appears near the protoplanet. However, different equations of state do not affect the acquisition process of angular momentum for the protoplanetary system. Thus, the specific angular momentum acquired by the system is fitted as a function only of the protoplanet's mass. A large fraction of the total angular momentum contributes to the formation of the circumplanetary disk. The disk forms only in a compact region in very close proximity to the protoplanet. Adapting the results to the solar system, the proto-Jupiter and Saturn have compact disks in the region of r < 21 r_J (r < 0.028 r_HJ) and r < 66 r_S (r < 0.061 r_HS), respectively, where r_J (r_HJ) and r_S (r_HS) are the Jovian and Saturnian (Hill) radius, respectively. The surface density has a peak in these regions due to the balance between centrifugal force and gravity of the protoplanet. The size of these disks corresponds well to the outermost orbit of regular satellites around Jupiter and Saturn. Regular satellites may form in such compact disks around proto-gas giant planets.

  9. Modeling self-subtraction in angular differential imaging: Application to the HD 32297 debris disk

    SciTech Connect (OSTI)

    Esposito, Thomas M.; Fitzgerald, Michael P.; Graham, James R.; Kalas, Paul

    2014-01-01

    We present a new technique for forward-modeling self-subtraction of spatially extended emission in observations processed with angular differential imaging (ADI) algorithms. High-contrast direct imaging of circumstellar disks is limited by quasi-static speckle noise, and ADI is commonly used to suppress those speckles. However, the application of ADI can result in self-subtraction of the disk signal due to the disk's finite spatial extent. This signal attenuation varies with radial separation and biases measurements of the disk's surface brightness, thereby compromising inferences regarding the physical processes responsible for the dust distribution. To compensate for this attenuation, we forward model the disk structure and compute the form of the self-subtraction function at each separation. As a proof of concept, we apply our method to 1.6 and 2.2 ?m Keck adaptive optics NIRC2 scattered-light observations of the HD 32297 debris disk reduced using a variant of the 'locally optimized combination of images' algorithm. We are able to recover disk surface brightness that was otherwise lost to self-subtraction and produce simplified models of the brightness distribution as it appears with and without self-subtraction. From the latter models, we extract radial profiles for the disk's brightness, width, midplane position, and color that are unbiased by self-subtraction. Our analysis of these measurements indicates a break in the brightness profile power law at r ? 110 AU and a disk width that increases with separation from the star. We also verify disk curvature that displaces the midplane by up to 30 AU toward the northwest relative to a straight fiducial midplane.

  10. DETECTION OF STRONG MILLIMETER EMISSION FROM THE CIRCUMSTELLAR DUST DISK AROUND V1094 SCO: COLD AND MASSIVE DISK AROUND A T TAURI STAR IN A QUIESCENT ACCRETION PHASE?

    SciTech Connect (OSTI)

    Tsukagoshi, Takashi; Kohno, Kotaro [Institute of Astronomy, Faculty of Science, University of Tokyo, Osawa 2-21-1, Mitaka, Tokyo 181-0015 (Japan); Saito, Masao [National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan); Kitamura, Yoshimi; Ikeda, Norio; Kamegai, Kazuhisa [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Yoshinodai 3-1-1, Sagamihara, Kanagawa 229-8510 (Japan); Momose, Munetake [Institute of Astrophysics and Planetary Sciences, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512 (Japan); Shimajiri, Yoshito; Ezawa, Hajime; Kawabe, Ryohei [Nobeyama Radio Observatory, Nobeyama 462-2, Minamimaki, Minamisaku, Nagano 384-1305 (Japan); Hiramatsu, Masaaki [Academia Sinica Institute for Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China); Wilson, Grant; Yun, Min S.; Scott, Kimberly; Perera, Thushara [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Austermann, Jason [Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309 (United States); Hughes, David; Aretxaga, Itziar [Instituto Nacional de Astrofisica, Optica y Electronica, Luis Enrique Erro 1, Tonantzintla, Puebla (Mexico); Mauskopf, Philip, E-mail: ttsuka@ioa.s.u-tokyo.ac.jp [Department of Physics and Astronomy, Cardiff University, Cardiff CF24 3YB, Wales (United Kingdom)

    2011-01-01

    We present the discovery of a cold massive dust disk around the T Tauri star V1094 Sco in the Lupus molecular cloud from the 1.1 mm continuum observations with AzTEC on ASTE. A compact (r{approx}< 320 AU) continuum emission coincides with the stellar position having a flux density of 272 mJy, which is the largest among T Tauri stars in Lupus. We also present the detection of molecular gas associated with the star in the five-point observations in {sup 12}CO J = 3-2 and {sup 13}CO J = 3-2. Since our {sup 12}CO and {sup 13}CO observations did not show any signature of a large-scale outflow or a massive envelope, the compact dust emission is likely to come from a disk around the star. The observed spectral energy distribution (SED) of V1094 Sco shows no distinct turnover from near-infrared to millimeter wavelengths, can be well described by a flattened disk for the dust component, and no clear dip feature around 10 {mu}m suggestive of the absence of an inner hole in the disk. We fit a simple power-law disk model to the observed SED. The estimated disk mass ranges from 0.03 M{sub sun} to {approx}>0.12 M{sub sun}, which is one or two orders of magnitude larger than the median disk mass of T Tauri stars in Taurus. The resultant temperature is lower than that of a flared disk with well-mixed dust in hydrostatic equilibrium and is probably attributed to the flattened disk geometry for the dust which the central star cannot illuminate efficiently. From these results, together with the fact that there is no signature of an inner hole in the SED, we suggest that the dust grains in the disk around V1094 Sco sank into the midplane with grain growth by coalescence and are in the evolutional stage just prior to or at the formation of planetesimals.

  11. Probing for exoplanets hiding in dusty debris disks: Disk imaging, characterization, and exploration with HST/STIS multi-roll coronagraphy

    SciTech Connect (OSTI)

    Schneider, Glenn; Hinz, Phillip M.; Grady, Carol A.; Hines, Dean C.; Debes, John H.; Perrin, Marshall D.; Moro-Martin, Amaya; Stark, Christopher C.; Kuchner, Marc J.; Woodgate, Bruce E.; Weinberger, Alycia J.; Rodigas, Timothy J.; Wisniewski, John P.; Silverstone, Murray D.; Jang-Condell, Hannah; Henning, Thomas; Serabyn, Eugene; Tamura, Motohide

    2014-10-01

    Spatially resolved scattered-light images of circumstellar debris in exoplanetary systems constrain the physical properties and orbits of the dust particles in these systems. They also inform on co-orbiting (but unseen) planets, the systemic architectures, and forces perturbing the starlight-scattering circumstellar material. Using Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) broadband optical coronagraphy, we have completed the observational phase of a program to study the spatial distribution of dust in a sample of 10 circumstellar debris systems and 1 'mature' protoplanetrary disk, all with HST pedigree, using point-spread-function-subtracted multi-roll coronagraphy. These observations probe stellocentric distances ?5 AU for the nearest systems, and simultaneously resolve disk substructures well beyond corresponding to the giant planet and Kuiper Belt regions within our own solar system. They also disclose diffuse very low-surface-brightness dust at larger stellocentric distances. Herein we present new results inclusive of fainter disks such as HD 92945 (F {sub disk}/F {sub star} = 5 × 10{sup –5}), confirming, and better revealing, the existence of a narrow inner debris ring within a larger diffuse dust disk. Other disks with ring-like substructures and significant asymmetries and complex morphologies include HD 181327, for which we posit a spray of ejecta from a recent massive collision in an exo-Kuiper Belt; HD 61005, suggested to be interacting with the local interstellar medium; and HD 15115 and HD 32297, also discussed in the context of putative environmental interactions. These disks and HD 15745 suggest that debris system evolution cannot be treated in isolation. For AU Mic's edge-on disk, we find out-of-plane surface brightness asymmetries at ?5 AU that may implicate the existence of one or more planetary perturbers. Time-resolved images of the MP Mus protoplanetary disk provide spatially resolved temporal variability in the disk illumination. These and other new images from our HST/STIS GO/12228 program enable direct inter-comparison of the architectures of these exoplanetary debris systems in the context of our own solar system.

  12. On the axisymmetric stability of stratified and magnetized accretion disks

    E-Print Network [OSTI]

    Mohandas, Gopakumar

    2015-01-01

    We conduct a comprehensive axisymmetric, local linear mode analysis of a stratified, differentially rotating disk permeated by a toroidal magnetic field which could provide significant pressure support. In the adiabatic limit, we derive a new stability criteria that differs from the one obtained for weak magnetic fields with a poloidal component and reduces continuously to the hydrodynamic Solberg-H{\\o}iland criteria. Three fundamental unstable modes are found in the locally isothermal limit. They comprise of overstable: (i) acoustic oscillations, (ii) radial epicyclic (acoustic-inertial) oscillations and (iii) vertical epicyclic (or vertical shear) oscillations. All three modes are present for finite ranges of cooling times but they are each quickly quenched past respective cut-off times. The acoustic and acoustic-inertial overstable modes are driven by the background temperature gradient. When vertical structure is excluded, we find that the radial epicyclic modes appear as a nearly degenerate pair. One of ...

  13. Lyapunov Mode Dynamics in Hard-Disk Systems

    E-Print Network [OSTI]

    D. J. Robinson; G. P. Morriss

    2007-09-20

    The tangent dynamics of the Lyapunov modes and their dynamics as generated numerically - {\\it the numerical dynamics} - is considered. We present a new phenomenological description of the numerical dynamical structure that accurately reproduces the experimental data for the quasi-one-dimensional hard-disk system, and shows that the Lyapunov mode numerical dynamics is linear and separate from the rest of the tangent space. Moreover, we propose a new, detailed structure for the Lyapunov mode tangent dynamics, which implies that the Lyapunov modes have well-defined (in)stability in either direction of time. We test this tangent dynamics and its derivative properties numerically with partial success. The phenomenological description involves a time-modal linear combination of all other Lyapunov modes on the same polarization branch and our proposed Lyapunov mode tangent dynamics is based upon the form of the tangent dynamics for the zero modes.

  14. From Lyapunov modes to the exponents for hard disk systems

    E-Print Network [OSTI]

    Tony Chung; Daniel Truant; Gary P. Morriss

    2009-04-08

    We demonstrate the preservation of the Lyapunov modes by the underlying tangent space dynamics of hard disks. This result is exact for the zero modes and correct to order $\\epsilon$ for the transverse and LP modes where $\\epsilon$ is linear in the mode number. For sufficiently large mode numbers the dynamics no longer preserves the mode structure. We propose a Gram-Schmidt procedure based on orthogonality with respect to the centre space that determines the values of the Lyapunov exponents for the modes. This assumes a detailed knowledge of the modes, but from that predicts the values of the exponents from the modes. Thus the modes and the exponents contain the same information.

  15. Thin-disk laser multi-pass amplifier

    E-Print Network [OSTI]

    Schuhmann, K; Graf, T; Hänsch, T W; Kirch, K; Kottmann, F; Pohl, R; Taqqu, D; Voß, A; Weichelt, B; Antognini, A

    2015-01-01

    In the context of the Lamb shift measurement in muonic helium we developed a thin-disk laser composed of a Q-switched oscillator and a multi-pass amplifier delivering pulses of 150 mJ at a pulse duration of 100 ns. Its peculiar requirements are stochastic trigger and short delay time (power scaling with high efficiency. However the single pass gain is small (about 1.2). Hence a multi-pass scheme with precise mode matching for large beam waists (w = 2 mm) is required. Instead of using the standard 4f design, we have developed a multi-pass amplifier with a beam propagation insensitive to thermal lens effects and misalignments. The beam propagation is equivalent to multiple roundtrips in an optically stable resonator. To support the propagation we used an array of 2 x 8 individually adjustable plane mirrors. Astigmatism has been minimized by a compact mirror placement. Precise alignment of the kinematic arra...

  16. Spectral Energy Distributions for Disk and Halo M--Dwarfs

    E-Print Network [OSTI]

    S. K. Leggett; F. Allard; Conard Dahn; P. H. Hauschildt; T. H. Kerr; J. Rayner

    2000-01-07

    We have obtained infrared (1 to 2.5 micron) spectroscopy for 42 halo and disk dwarfs with spectral type M1 to M6.5. These data are compared to synthetic spectra generated by the latest model atmospheres of Allard & Hauschildt. Photospheric parameters metallicity, effective temperature and radius are determined for the sample. We find good agreement between observation and theory except for known problems due to incomplete molecular data for metal hydrides and water. The metal-poor M subdwarfs are well matched by the models as oxide opacity sources are less important in this case. The derived effective temperatures for the sample range from 3600K to 2600K; at these temperatures grain formation and extinction are not significant in the photosphere. The derived metallicities range from solar to one-tenth solar. The radii and effective temperatures derived agree well with recent models of low mass stars.

  17. Adaptor assembly for coupling turbine blades to rotor disks

    SciTech Connect (OSTI)

    Delvaux, John McConnel; Garcia-Crespo, Andres Jose; Joyce, Kilmer Joseph; Tindell, Allan Randall

    2014-06-03

    An adaptor assembly for coupling a blade root of a turbine blade to a root slot of a rotor disk is disclosed. The adaptor assembly may generally include an adaptor body having a root configured to be received within the root slot. The adaptor body may also define a slot having an open end configured to receive the blade root. The adaptor body may further define a channel. The adaptor assembly may also include a plate having an outwardly extending foot. The foot may be configured to be received within the channel. Additionally, the plate may be configured to cover at least a portion of the open end of the slot when the foot is received within the channel.

  18. High frequency nano-optomechanical disk resonators in liquids

    E-Print Network [OSTI]

    Gil-Santos, E; Nguyen, D T; Hease, W; Lemaître, A; Ducci, S; Leo, G; Favero, I

    2015-01-01

    Vibrating nano- and micromechanical resonators have been the subject of research aiming at ultrasensitive mass sensors for mass spectrometry, chemical analysis and biomedical diagnosis. Unfortunately, their merits diminish dramatically in liquids due to dissipative mechanisms like viscosity and acoustic losses. A push towards faster and lighter miniaturized nanodevices would enable improved performances, provided dissipation was controlled and novel techniques were available to efficiently drive and read-out their minute displacement. Here we report on a nano-optomechanical approach to this problem using miniature semiconductor disks. These devices combine mechanical motion at high frequency above the GHz, ultra-low mass of a few picograms, and moderate dissipation in liquids. We show that high-sensitivity optical measurements allow to direct resolve their thermally driven Brownian vibrations, even in the most dissipative liquids. Thanks to this novel technique, we experimentally, numerically and analytically...

  19. Design, Fabrication and Control of Micro-Actuators for Dual-Stage Servo Systems in Magnetic Disk Files

    E-Print Network [OSTI]

    Horowitz, Roberto

    Design, Fabrication and Control of Micro-Actuators for Dual-Stage Servo Systems in Magnetic Disk to achieve such a storage density. A disk drive stores data as magnetic patterns, forming bits, on one of disk on an air-bearing. The VCM actuates the suspensions and sliders about a pivot in the center

  20. Radial disk heating by more than one spiral density wave

    E-Print Network [OSTI]

    I. Minchev; A. C. Quillen

    2005-10-28

    We consider a differentially rotating, 2D stellar disk perturbed by two steady state spiral density waves moving at different patterns speeds. Our investigation is based on direct numerical integration of initially circular test-particle orbits. We examine a range of spiral strengths and spiral speeds and show that stars in this time dependent gravitational field can be heated (their random motions increased). This is particularly noticeable in the simultaneous propagation of a 2-armed spiral density wave near the corotation resonance (CR), and a weak 4-armed one near the inner and outer 4:1 Lindblad resonances. In simulations with 2 spiral waves moving at different pattern speeds we find: (1) the variance of the radial velocity, sigma_R^2, exceeds the sum of the variances measured from simulations with each individual pattern; (2) sigma_R^2 can grow with time throughout the entire simulation; (3) sigma_R^2 is increased over a wider range of radii compared to that seen with one spiral pattern; (4) particles diffuse radially in real space whereas they don't when only one spiral density wave is present. Near the CR with the stronger, 2-armed pattern, test particles are observed to migrate radially. These effects take place at or near resonances of both spirals so we interpret them as the result of stochastic motions. This provides a possible new mechanism for increasing the stellar velocity dispersion in galactic disks. If multiple spiral patterns are present in the Galaxy we predict that there should be large variations in the stellar velocity dispersion as a function of radius.

  1. Disk heating by more than one spiral density wave

    E-Print Network [OSTI]

    I. Minchev; A. C. Quillen

    2005-11-01

    We consider a differentially rotating, 2D stellar disk perturbed by two steady state spiral density waves moving at different patterns speeds. Our investigation is based on direct numerical integration of initially circular test-particle orbits. We examine a range of spiral strengths and spiral speeds and show that stars in this time dependent gravitational field can be heated (their random motions increased).This is particularly noticeable in the simultaneous propagation of a 2-armed spiral density wave near the corotation resonance (CR), and a weak 4-armed one near the inner and outer 4:1 Lindblad resonances. In simulations with 2 spiral waves moving at different pattern speeds we find: (1) the variance of the radial velocity, sigma_R^2, exceeds the sum of the variances measured from simulations with each individual pattern; (2) sigma_R^2 can grow with time throughout the entire simulation; (3) sigma_R^2 is increased over a wider range of radii compared to that seen with one spiral pattern; (4) particles diffuse radially in real space whereas they don't when only one spiral density wave is present. Near the CR with the stronger, 2-armed pattern, test particles are observed to migrate radially. These effects take place at or near resonances of both spirals so we interpret them as the result of stochastic motions. This provides a possible new mechanism for increasing the stellar velocity dispersion in galactic disks. If multiple spiral patterns are present in the Galaxy we predict that there should be large variations in the stellar velocity dispersion as a function of radius.

  2. The decay of debris disks around solar-type stars

    SciTech Connect (OSTI)

    Sierchio, J. M.; Rieke, G. H.; Su, K. Y. L.; Gáspár, Andras, E-mail: sierchio@mit.edu [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

    2014-04-10

    We present a Spitzer MIPS study of the decay of debris disk excesses at 24 and 70 ?m for 255 stars of types F4-K2. We have used multiple tests, including consistency between chromospheric and X-ray activity and placement on the H-R diagram, to assign accurate stellar ages. Within this spectral type range, at 24 ?m, 13.6% ± 2.8% of the stars younger than 1 Gyr have excesses at the 3? level or more, whereas none of the older stars do, confirming previous work. At 70 ?m, 22.5% ± 3.6% of the younger stars have excesses at ?3? significance, whereas only 4.7{sub ?2.2}{sup +3.7}% of the older stars do. To characterize the far-infrared behavior of debris disks more robustly, we doubled the sample by including stars from the DEBRIS and DUNES surveys. For the F4-K4 stars in this combined sample, there is only a weak (statistically not significant) trend in the incidence of far-infrared excess with spectral type (detected fractions of 21.9{sub ?4.3}{sup +4.8}%, late F; 16.5{sub ?3.3}{sup +3.9}%, G; and 16.9{sub ?5.0}{sup +6.3}%, early K). Taking this spectral type range together, there is a significant decline between 3 and 4.5 Gyr in the incidence of excesses, with fractional luminosities just under 10{sup –5}. There is an indication that the timescale for decay of infrared excesses varies roughly inversely with the fractional luminosity. This behavior is consistent with theoretical expectations for passive evolution. However, more excesses are detected around the oldest stars than are expected from passive evolution, suggesting that there is late-phase dynamical activity around these stars.

  3. Lithium Abundances of the Local Thin Disk Stars

    E-Print Network [OSTI]

    David L. Lambert; Bacham E. Reddy

    2004-01-14

    Lithium abundances are presented for a sample of 181 nearby F and G dwarfs with accurate {\\it Hipparcos} parallaxes. The stars are on circular orbits about the Galactic centre and, hence, are identified as belonging to the thin disk. This sample is combined with two published surveys to provide a catalogue of lithium abundances, metallicities ([Fe/H]), masses, and ages for 451 F-G dwarfs, almost all belonging to the thin disk. The lithium abundances are compared and contrasted with published lithium abundances for F and G stars in local open clusters. The field stars span a larger range in [Fe/H] than the clusters for which [Fe/H] $\\simeq 0.0\\pm0.2$. The initial (i.e., interstellar) lithium abundance of the solar neighborhood, as derived from stars for which astration of lithium is believed to be unimportant, is traced from $\\log\\epsilon$(Li) = 2.2 at [Fe/H] = -1 to $\\log\\epsilon$(Li) = 3.2 at $+0.1$. This form for the evolution is dependent on the assumption that astration of lit hium is negligible for the stars defining the relation. An argument is advanced that this latter assumption may not be entirely correct, and, the evolution of lithium with [Fe/H] may be flatter than previously supposed. A sharp Hyades-like Li-dip is not seen among the field stars and appears to be replaced by a large spread among lithium abundances of stars more massive than the lower mass limit of the dip. Astration of lithium by stars of masses too low to participate in the Li-dip is discussed. These stars show little to no spread in lithium abundance at a given [Fe/H] and mass.

  4. Jupiter's composition: sign of a (relatively) late formation in a chemically evolved protosolar disk

    E-Print Network [OSTI]

    Tristan Guillot; Ricardo Hueso

    2006-01-03

    It has been proposed that the enrichment in noble gases found by Galileo in Jupiter's atmosphere can be explained by their delivery inside cold planetesimals. We propose instead that this is a sign that the planet formed in a chemically evolved disk and that noble gases were acquired mostly in gaseous form during the planet's envelope capture phase. We show that the combined settling of grains to the disk midplane in the cold outer layers, the condensation of noble gases onto these grains at temperatures below 20-30K, and the evaporation from high disk altitudes effectively lead to a progressive, moderate enrichment of the disk. The fact that noble gases are vaporized from the grains in the hot inner disk regions (e.g. Jupiter formation region) is not a concern because a negative temperature gradient prevents convection from carrying the species into the evaporating region. We show that the ~2 times solar enrichment of Ar, Kr, Xe in Jupiter is hence naturally explained by a continuous growth of the planet governed by viscous diffusion in the protosolar disk in conjunction with an evaporation of the disk and its progressive enrichment on a million years timescale.

  5. ACCRETION OF GAS ONTO GAP-OPENING PLANETS AND CIRCUMPLANETARY FLOW STRUCTURE IN MAGNETIZED TURBULENT DISKS

    SciTech Connect (OSTI)

    Uribe, A. L. [University of Chicago, Chicago, IL 60637 (United States); Klahr, H.; Henning, Th., E-mail: uribe@oddjob.uchicago.edu [Max-Planck-Institut fuer Astronomie, Heidelberg (Germany)

    2013-06-01

    We have performed three-dimensional magnetohydrodynamical simulations of stellar accretion disks, using the PLUTO code, and studied the accretion of gas onto a Jupiter-mass planet and the structure of the circumplanetary gas flow after opening a gap in the disk. We compare our results with simulations of laminar, yet viscous disks with different levels of an {alpha}-type viscosity. In all cases, we find that the accretion flow across the surface of the Hill sphere of the planet is not spherically or azimuthally symmetric, and is predominantly restricted to the mid-plane region of the disk. Even in the turbulent case, we find no significant vertical flow of mass into the Hill sphere. The outer parts of the circumplanetary disk are shown to rotate significantly below Keplerian speed, independent of viscosity, while the circumplanetary disk density (therefore the angular momentum) increases with viscosity. For a simulation of a magnetized turbulent disk, where the global averaged alpha stress is {alpha}{sub MHD} = 10{sup -3}, we find the accretion rate onto the planet to be M-dot {approx}2 Multiplication-Sign 10{sup -6}M{sub J} yr{sup -1} for a gap surface density of 12 g cm{sup -2}. This is about a third of the accretion rate obtained in a laminar viscous simulation with equivalent {alpha} parameter.

  6. Observational Possibility of the "Snow Line" on the Surface of Circumstellar Disks with the Scattered Light

    E-Print Network [OSTI]

    Akio K. Inoue; Mitsuhiko Honda; Taishi Nakamoto; Akinori Oka

    2008-02-07

    We discuss how we obtain the spatial distribution of ice on the surface of the circumstellar disk around young stars. Ice in the disks plays a very important role in various issues, for instance, on the disk structure, on the planet formation, on the isotopic anomaly in meteorites, and on the origin of the sea on the Earth. Therefore, the spatially resolved observation of the condensation/sublimation front of ice, so-called ``snow line'' is strongly required. Here, we propose a new method for obtaining the spatially resolved ``snow line'' on the circumstellar disks by observing 3 \\micron H$_2$O ice feature in the scattered light. Based on radiative transfer considerations, we show that the feature is clearly imprinted in the spectrum of the scattered light from both optically thick and thin circumstellar disks. We also show that the scattered light and the H$_2$O ice feature from protoplanetary disks are detectable and spatially resolvable with the current instruments through a $H_2O$ narrowband filter around 3 \\micron. Finally, we present a diagnostics of disk dust properties on the $K-H_2O$ and $K-L'$ two color diagram.

  7. Analysis of Trade-Off Between Power Saving and Response Time in Disk Storage Systems

    SciTech Connect (OSTI)

    Otoo, Ekow J; Rotem, Doron; Tsao, Shih-Chiang

    2009-02-03

    It is anticipated that in the near future disk storage systems will surpass application servers and will become the primary consumer of power in the data centers. Shutting down of inactive disks is one of the more widespread solutions to save power consumption of disk systems. This solution involves spinning down or completely shutting off disks that exhibit long periods of inactivity and placing them in standby mode. A file request from a disk in standby mode will incur an I/O cost penalty as it takes time to spin up the disk before it can serve the file. In this paper, we address the problem of designing and implementing file allocation strategies on disk storage that save energy while meeting performance requirements of file retrievals. We present an algorithm for solving this problem with guaranteed bounds from the optimal solution. Our algorithm runs in O(nlogn) time where n is the number of files allocated. Detailed simulation results and experiments with real life workloads are also presented.

  8. Implications of modes of star formation for the overall dynamics of galactic disks

    E-Print Network [OSTI]

    B. Fuchs

    2001-03-22

    One of the present concepts for the onset of massive star formation is the Kennicutt criterion. This relates the onset of massive star formation to a general gravitational instability of the gas disks of spiral galaxies. It is often overlooked, however that such gravitational instabilities of the gas disks have severe implications for the overall stability of the gas and star disks of spiral galaxies. I show by numerical simulations of the evolution of a combined gas and star disk that the violation of the stability condition induces violent dynamical evolution of the combined system. In particular the star disk heats up on time scales less than a Gyr to unrealistic high values of the Toomre stability parameter Q. The morphologies of both the star and gas disk resemble then no longer observed morphologies of spiral galaxies. Star formation of stars on low velocity dispersion orbits would lead to dynamical cooling of the disks to more realistic states. However, the required star formation rate is extremely high.

  9. Anti-Truncation of Disks in Early-Type Barred Galaxies

    E-Print Network [OSTI]

    Peter Erwin; John E. Beckman; Michael Pohlen

    2005-07-24

    The disks of spiral galaxies are commonly thought to be truncated: the radial surface brightness profile steepens sharply beyond a certain radius (3--5 inner-disk scale lengths). Here we present the radial brightness profiles of a number of barred S0--Sb galaxies with the opposite behavior: their outer profiles are distinctly shallower in slope than the main disk profile. We term these "anti-truncations"; they are found in at least 25% of a larger sample of barred S0--Sb galaxies. There are two distinct types of anti-truncations. About one-third show a fairly gradual transition and outer isophotes which are progressively rounder than the main disk isophotes, suggestive of a disk embedded within a more spheroidal outer zone -- either the outer extent of the bulge or a separate stellar halo. But the majority of the profiles have rather sharp surface-brightness transitions to the shallower, outer exponential profile and, crucially, outer isophotes which are not significantly rounder than the main disk; in the Sab--Sb galaxies, the outer isophotes include visible spiral arms. This suggests that the outer light is still part of the disk. A subset of these profiles are in galaxies with asymmetric outer isophotes (lopsided or one-armed spirals), suggesting that interactions may be responsible for at least some of the disklike anti-truncations.

  10. Planetary migration and sources of dust in the Beta Pic disk

    E-Print Network [OSTI]

    A. Lecavelier des Etangs

    1998-06-22

    The dust disk around Beta Pictoris must be produced by collision or by evaporation of orbiting Kuiper belt-like objects. Here we extend the already proposed Orbiting-Evaporating-Bodies (OEB) scenario in which the disk is a gigantic multi-cometary tail supplied by slowly evaporating bodies like Chiron. We show that the number of these OEBs must be several tens of millions, and that this is consistent with the number of bodies needed to explain the presence of CO and CI in the gaseous disk. We explore some possible origin of the required perturbation on the OEBs. If dust is produced by evaporation, a planet with an eccentric orbit can explain the observed asymmetry of the disk, because the periastron distribution of the parent bodies are then expected to be non-axisymmetric. Following Malhotra (1995), we investigate the consequence for the Kuiper belt-like objects of the formation and the migration of an outer planet like Neptune in Fernandez's scheme (Fernandez 1982). We find that bodies trapped in resonance with a migrating planet can significantly evaporate, producing a Beta Pictoris-like disk with similar characteristics like opening angle and asymmetry. We thus show that the Beta Pictoris disk can be a transient phenomenon. The circumstellar disks around main sequence stars can be the signature of the present formation and migration of outer planets.

  11. Probing the terrestrial regions of planetary systems: warm debris disks with emission features

    SciTech Connect (OSTI)

    Ballering, Nicholas P.; Rieke, George H.; Gáspár, András, E-mail: ballerin@email.arizona.edu [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2014-09-20

    Observations of debris disks allow for the study of planetary systems, even where planets have not been detected. However, debris disks are often only characterized by unresolved infrared excesses that resemble featureless blackbodies, and the location of the emitting dust is uncertain due to a degeneracy with the dust grain properties. Here, we characterize the Spitzer Infrared Spectrograph spectra of 22 debris disks exhibiting 10 ?m silicate emission features. Such features arise from small warm dust grains, and their presence can significantly constrain the orbital location of the emitting debris. We find that these features can be explained by the presence of an additional dust component in the terrestrial zones of the planetary systems, i.e., an exozodiacal belt. Aside from possessing exozodiacal dust, these debris disks are not particularly unique; their minimum grain sizes are consistent with the blowout sizes of their systems, and their brightnesses are comparable to those of featureless warm debris disks. These disks are in systems of a range of ages, though the older systems with features are found only around A-type stars. The features in young systems may be signatures of terrestrial planet formation. Analyzing the spectra of unresolved debris disks with emission features may be one of the simplest and most accessible ways to study the terrestrial regions of planetary systems.

  12. Nucleosynthesis in the outflows associated with accretion disks of Type II collapsars

    E-Print Network [OSTI]

    Indrani Banerjee; Banibrata Mukhopadhyay

    2013-09-04

    We investigate nucleosynthesis inside the outflows from gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, massive stars undergo core collapse to form a proto-neutron star initially and a mild supernova explosion is driven. The supernova ejecta lack momentum and subsequently this newly formed neutron star gets transformed to a stellar mass black hole via massive fallback. The hydrodynamics and the nucleosynthesis in these accretion disks has been studied extensively in the past. Several heavy elements are synthesized in the disk and much of these heavy elements are ejected from the disk via winds and outflows. We study nucleosynthesis in the outflows launched from these disks by using an adiabatic, spherically expanding outflow model, to understand which of these elements thus synthesized in the disk survive in the outflow. While studying this we find that many new elements like isotopes of titanium, copper, zinc etc. are present in the outflows. 56Ni is abundantly synthesized in most of the cases in the outflow which implies that the outflows from these disks in a majority of cases will lead to an observable supernova explosion. It is mainly present when outflow is considered from the He-rich, 56Ni/54Fe rich zones of the disks. However, outflow from the Si-rich zone of the disk remains rich in silicon. Although, emission lines of many of these heavy elements have been observed in the X-ray afterglows of several GRBs by Chandra, BeppoSAX, XMM-Newton etc., Swift seems to have not detected these lines yet.

  13. NUCLEOSYNTHESIS IN THE OUTFLOWS ASSOCIATED WITH ACCRETION DISKS OF TYPE II COLLAPSARS

    SciTech Connect (OSTI)

    Banerjee, Indrani; Mukhopadhyay, Banibrata, E-mail: indrani@physics.iisc.ernet.in, E-mail: bm@physics.iisc.ernet.in [Department of Physics, Indian Institute of Science, Bangalore 560 012 (India)

    2013-11-20

    We investigate nucleosynthesis inside the outflows from gamma-ray burst (GRB) accretion disks formed by the Type II collapsars. In these collapsars, massive stars undergo core collapse to form a proto-neutron star initially, and a mild supernova (SN) explosion is driven. The SN ejecta lack momentum, and subsequently this newly formed neutron star gets transformed to a stellar mass black hole via massive fallback. The hydrodynamics and the nucleosynthesis in these accretion disks have been studied extensively in the past. Several heavy elements are synthesized in the disk, and much of these heavy elements are ejected from the disk via winds and outflows. We study nucleosynthesis in the outflows launched from these disks by using an adiabatic, spherically expanding outflow model, to understand which of these elements thus synthesized in the disk survive in the outflow. While studying this, we find that many new elements like isotopes of titanium, copper, zinc, etc., are present in the outflows. {sup 56}Ni is abundantly synthesized in most of the cases in the outflow, which implies that the outflows from these disks in a majority of cases will lead to an observable SN explosion. It is mainly present when outflow is considered from the He-rich, {sup 56}Ni/{sup 54}Fe-rich zones of the disks. However, outflow from the Si-rich zone of the disk remains rich in silicon. Although emission lines of many of these heavy elements have been observed in the X-ray afterglows of several GRBs by Chandra, BeppoSAX, XMM-Newton, etc., Swift seems to have not yet detected these lines.

  14. Method and apparatus for bistable optical information storage for erasable optical disks

    DOE Patents [OSTI]

    Land, C.E.; McKinney, I.D.

    1988-05-31

    A method and an optical device for bistable storage of optical information, together with reading and erasure of the optical information, using a photoactivated shift in a field dependent phase transition between a metastable or a bias-stabilized ferroelectric (FE) phase and a stable antiferroelectric (AFE) phase in a lead lanthanum zirconate titanate (PLZT). An optical disk contains the PLZT. Writing and erasing of optical information can be accomplished by a light beam normal to the disk. Reading of optical information can be accomplished by a light beam at an incidence angle of 15 to 60 degrees to the normal of the disk. 10 figs.

  15. HERSCHEL's ''COLD DEBRIS DISKS'': BACKGROUND GALAXIES OR QUIESCENT RIMS OF PLANETARY SYSTEMS?

    SciTech Connect (OSTI)

    Krivov, A. V.; Loehne, T.; Mutschke, H.; Neuhaeuser, R. [Astrophysikalisches Institut und Universitaetssternwarte, Friedrich-Schiller-Universitaet Jena, Schillergaesschen 2-3, D-07745 Jena (Germany); Eiroa, C.; Marshall, J. P.; Mustill, A. J. [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad Autonoma de Madrid, Cantoblanco, E-28049 Madrid (Spain); Montesinos, B. [Departamento de Astrofisica, Centro de Astrobiologia (CAB, CSIC-INTA), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Del Burgo, C. [Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Apartado Postal 51 y 216, 72000 Puebla, Pue. (Mexico); Absil, O. [Institut d'Astrophysique et de Geophysique, Universite de Liege, Allee du 6 Aout 17, B-4000 Liege (Belgium); Ardila, D. [NASA Herschel Science Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Augereau, J.-C.; Ertel, S.; Lebreton, J. [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d'Astrophysique de Grenoble (IPAG), UMR 5274, F-38041 Grenoble (France); Bayo, A. [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile); Bryden, G. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Danchi, W. [NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics, Code 667, Greenbelt, MD 20771 (United States); Liseau, R. [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992, Onsala (Sweden); Mora, A. [ESA-ESAC Gaia SOC, P.O. Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Pilbratt, G. L., E-mail: krivov@astro.uni-jena.de [ESA Astrophysics and Fundamental Physics Missions Division, ESTEC/SRE-SA, Keplerlaan 1, 2201 AZ Noordwijk (Netherlands); and others

    2013-07-20

    Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around {approx}100 {mu}m or shorter. However, 6 out of 31 excess sources studied in the Herschel Open Time Key Programme, DUNES, have been seen to show significant-and in some cases extended-excess emission at 160 {mu}m, which is larger than the 100 {mu}m excess. This excess emission has been attributed to circumstellar dust and has been suggested to stem from debris disks colder than those known previously. Since the excess emission of the cold disk candidates is extremely weak, challenging even the unrivaled sensitivity of Herschel, it is prudent to carefully consider whether some or even all of them may represent unrelated galactic or extragalactic emission, or even instrumental noise. We re-address these issues using several distinct methods and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the spectral energy distributions and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than {approx}100 {mu}m, even if they are rich in ices or are composed of any other material with a low absorption in the visible. The dearth of small grains is puzzling, since collisional models of debris disks predict that grains of all sizes down to several times the radiation pressure blowout limit should be present. We explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show that such disks can indeed survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but smaller than a few kilometers in size. If larger planetesimals were present, then they would stir the disk, triggering a collisional cascade and thus causing production of small debris, which is not seen. Thus, planetesimal formation, at least in the outer regions of the systems, has stopped before 'cometary' or 'asteroidal' sizes were reached.

  16. The Internal Energy for Molecular Hydrogen in Gravitationally Unstable Protoplanetary Disks

    E-Print Network [OSTI]

    Aaron C. Boley; Thomas W. Hartquist; Richard H. Durisen; Scott Michael

    2007-01-05

    The gas equation of state may be one of the critical factors for the disk instability theory of gas giant planet formation. This letter addresses the treatment of H$_2$ in hydrodynamical simulations of gravitationally unstable disks. In our discussion, we point out possible consequences of erroneous specific internal energy relations, approximate specific internal energy relations with discontinuities, and assumptions of constant $\\Gamma_1$. In addition, we consider whether the ortho/para ratio for H$_2$ in protoplanetary disks should be treated dynamically as if the species are in equilibrium. Preliminary simulations indicate that the correct treatment is particularly critical for the study of gravitational instability when $T = 30$-50 K.

  17. The Internal Energy for Molecular Hydrogen in Gravitationally Unstable Protoplanetary Disks

    E-Print Network [OSTI]

    Boley, A C; Durisen, R H; Michael, S; Boley, Aaron C.; Hartquist, Thomas W.; Durisen, Richard H.; Michael, Scott

    2007-01-01

    The gas equation of state may be one of the critical factors for the disk instability theory of gas giant planet formation. This letter addresses the treatment of H$_2$ in hydrodynamical simulations of gravitationally unstable disks. In our discussion, we point out possible consequences of erroneous specific internal energy relations, approximate specific internal energy relations with discontinuities, and assumptions of constant $\\Gamma_1$. In addition, we consider whether the ortho/para ratio for H$_2$ in protoplanetary disks should be treated dynamically as if the species are in equilibrium. Preliminary simulations indicate that the correct treatment is particularly critical for the study of gravitational instability when $T = 30$-50 K.

  18. Star Formation in Isolated Disk Galaxies. II. Schmidt Laws and Efficiency of Gravitational Collapse

    E-Print Network [OSTI]

    Yuexing Li; Mordecai-Mark Mac Low; Ralf S. Klessen

    2006-02-21

    (Abridged). We model gravitational instability in a wide range of isolated disk galaxies, using GADGET, a three-dimensional, smoothed particle hydrodynamics code. The model galaxies include a dark matter halo and a disk of stars and isothermal gas. The global Schmidt law observed in disk galaxies is quantitatively reproduced by our models. We find that the surface density of star formation rate directly correlates with the strength of local gravitational instability. The local Schmidt laws of individual galaxies in our models show clear evidence of star formation thresholds. Our results suggest that the non-linear development of gravitational instability determines the local and global Schmidt laws, and the star formation thresholds.

  19. Grand Unified Model of Accretion Disks Around Black Holes: the Sub-Keplerian Paradigm

    E-Print Network [OSTI]

    Sandip K. Chakrabarti

    1995-02-06

    We show that viscous, transonic accretion disks which start with sub-Keplerian angular momentum at the outer boundary reproduce the features of the so-called thick, thin, slim and other accretion disk models depending upon the accretion rates and viscosity parameters. These disks are advection dominated in the pre-shock region and rotation dominated in the post-shock region when viscosity is less than a critical value. For a higher viscosity the shock disappears, and the flow has significant radial velocity only close to the black hole.

  20. MILLIMETER IMAGING OF THE {beta} PICTORIS DEBRIS DISK: EVIDENCE FOR A PLANETESIMAL BELT

    SciTech Connect (OSTI)

    Wilner, David J.; Andrews, Sean M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hughes, A. Meredith [Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720 (United States)

    2011-02-01

    We present observations at 1.3 mm wavelength of the {beta} Pictoris debris disk with beam size 4.''3 x 2.''6 (83 x 50 AU) from the Submillimeter Array. The emission shows two peaks separated by {approx}7'' along the disk plane, which we interpret as a highly inclined dust ring or belt. A simple model constrains the belt center to 94 {+-} 8 AU, close to the prominent break in slope of the optical scattered light. We identify this region as the location of the main reservoir of dust-producing planetesimals in the disk.

  1. Building a High Performance Raw Disk Subsystem for Alpha/Linux

    SciTech Connect (OSTI)

    Garlick,J

    2001-07-02

    The Linux kernel version 2.2.19 lacks UNIX-style raw disk support, and its SCSI layer is optimized for small transfer sizes. This report describes kernel patches to add raw disk support and enhance performance in the SCSI layer and QLA2x00 Fibre Channel device driver for large transfer sizes. Benchmarks demonstrate raw disk performance of 191 megabytes/second write, 176 megabytes/second read for one megabyte random I/O on a Compaq ES40 computer system with two QLogic QLA2200F Fibre Channel host bus adapters, each connected to two Ciprico RF7010 arrays on arbitrated loop.

  2. On the Role of Disks in the Formation of Stellar Systems: A Numerical Parameter Study of Rapid Accretion

    E-Print Network [OSTI]

    Kratter, Kaitlin M; Krumholz, Mark R; Klein, Richard I

    2009-01-01

    We study rapidly accreting, gravitationally unstable disks with a series of global, three dimensional, numerical experiments using the code ORION. In this paper we conduct a numerical parameter study focused on protostellar disks, and show that one can predict disk behavior and the multiplicity of the accreting star system as a function of two dimensionless parameters which compare the disk's accretion rate to its sound speed and orbital period. Although gravitational instabilities become strong, we find that fragmentation into binary or multiple systems occurs only when material falls in several times more rapidly than the canonical isothermal limit. The disk-to-star accretion rate is proportional to the infall rate, and governed by gravitational torques generated by low-m spiral modes. We also confirm the existence of a maximum stable disk mass: disks that exceed ~50% of the total system mass are subject to fragmentation and the subsequent formation of binary companions.

  3. Large area high density quantized magnetic disks fabricated using nanoimprint lithography

    E-Print Network [OSTI]

    for fabricating large area quantized magnetic disks QMDs using nanoimprint lithography NIL , electroplating or a via array. The other is that for high resolution an antireflection coating ARC layer is needed, which

  4. Invited Review Article: Review of centrifugal microfluidic and bio-optical disks

    E-Print Network [OSTI]

    Nolte, David D.

    of noninertial pumping for lab-on-a-chip devices using noninertial valves and switches under centrifugalInvited Review Article: Review of centrifugal microfluidic and bio-optical disks David D. Nolte

  5. Slit disk for modified faraday cup diagnostic for determining power density of electron and ion beams

    DOE Patents [OSTI]

    Teruya, Alan T. (Livermore, CA); Elmer; John W. (Danville, CA); Palmer, Todd A. (State College, PA)

    2011-03-08

    A diagnostic system for characterization of an electron beam or an ion beam includes an electrical conducting disk of refractory material having a circumference, a center, and a Faraday cup assembly positioned to receive the electron beam or ion beam. At least one slit in the disk provides diagnostic characterization of the electron beam or ion beam. The at least one slit is located between the circumference and the center of the disk and includes a radial portion that is in radial alignment with the center and a portion that deviates from radial alignment with the center. The electron beam or ion beam is directed onto the disk and translated to the at least one slit wherein the electron beam or ion beam enters the at least one slit for providing diagnostic characterization of the electron beam or ion beam.

  6. Augmentation of Power Output of Axisymmetric Ducted Wind Turbines by Porous Trailing Edge Disks

    E-Print Network [OSTI]

    widnall, sheila

    2014-06-30

    This paper presents analytical and experimental results that demonstrated that the power output from a ducted wind turbine can be dramatically increased by the addition of a trailing edge device such as a porous disk. In ...

  7. Debris Disks in Nearby Young Moving Groups in the ALMA Era

    E-Print Network [OSTI]

    Kóspál, Á

    2015-01-01

    Many members of nearby young moving groups exhibit infrared excess attributed to circumstellar debris dust, formed via erosion of planetesimals. With their proximity and well-dated ages, these groups are excellent laboratories for studying the early evolution of debris dust and of planetesimal belts. ALMA can spatially resolve the disk emission, revealing the location and extent of these belts, putting constraints on planetesimal evolution models, and allowing us to study planet-disk interactions. While the main trends of dust evolution in debris disks are well-known, there is almost no information on the evolution of gas. During the transition from protoplanetary to debris state, even the origin of gas is dubious. Here we review the exciting new results ALMA provided by observing young debris disks, and discuss possible future research directions.

  8. ON THE EVOLUTION OF THE CO SNOW LINE IN PROTOPLANETARY DISKS

    SciTech Connect (OSTI)

    Martin, Rebecca G. [JILA, University of Colorado and NIST, UCB 440, Boulder, CO 80309 (United States); Livio, Mario [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2014-03-10

    CO is thought to be a vital building block for prebiotic molecules that are necessary for life. Thus, understanding where CO existed in a solid phase within the solar nebula is important for understanding the origin of life. We model the evolution of the CO snow line in a protoplanetary disk. We find that the current observed location of the CO snow line in our solar system, and in the solar system analog TW Hydra, cannot be explained by a fully turbulent disk model. With time-dependent disk models we find that the inclusion of a dead zone (a region of low turbulence) can resolve this problem. Furthermore, we obtain a fully analytic solution for the CO snow line radius for late disk evolutionary times. This will be useful for future observational attempts to characterize the demographics and predict the composition and habitability of exoplanets.

  9. Analysis of Trade-Off Between Power Saving and Response Time in Disk Storage Systems

    E-Print Network [OSTI]

    Otoo, Ekow J

    2009-01-01

    of Trade-Off Between Power Saving and Response Time in Diskthe disks are static and power saving can be realized duringopportunities for power saving. To understand the reasoning

  10. Round-like behavior in multiple disks on a bus Rakesh Barve

    E-Print Network [OSTI]

    Matias, Yossi

    . This paper reports on a performance impair- ment that results from a previously unknown form of con- voy.g., RW94, Wil95, HP96, Shr97]) has focused on the disk drive, downplaying the importance of bus con

  11. Global General Relativistic MHD Simulation of a Tilted Black-Hole Accretion Disk

    E-Print Network [OSTI]

    Fragile, P Chris; Anninos, Peter; Salmonson, Jay D

    2007-01-01

    This paper presents a continuation of our efforts to numerically study accretion disks that are misaligned (tilted) with respect to the rotation axis of a Kerr black hole. Here we present results of a global numerical simulation which fully incorporates the effects of the black hole spacetime as well as magnetorotational turbulence that is the primary source of angular momentum transport in the flow. This simulation shows dramatic differences from comparable simulations of untilted disks. Accretion onto the hole occurs predominantly through two opposing plunging streams that start from high latitudes with respect to both the black-hole and disk midplanes. This is due to the aspherical nature of the gravitational spacetime around the rotating black hole. These plunging streams start from a larger radius than would be expected for an untilted disk. In this regard the tilted black hole effectively acts like an untilted black hole of lesser spin. Throughout the duration of the simulation, the main body of the dis...

  12. Does the Collapse of a Supramassive Neutron Star Leave a Debris Disk?

    E-Print Network [OSTI]

    Margalit, Ben; Beloborodov, Andrei M

    2015-01-01

    One possible channel for black hole formation is the collapse of a rigidly rotating massive neutron star as it loses its angular momentum or gains excessive mass through accretion. It was proposed that part of the neutron star may form a debris disk around the black hole. Such short-lived massive disks could be the sources of powerful jets emitting cosmological gamma-ray bursts. Whether the collapse creates a disk depends on the equation of state of the neutron star. We survey a wide range of equations of states allowed by observations and find that disk formation is unfeasible. We conclude that this channel of black hole formation is incapable of producing powerful jets, and discuss implications for models of gamma-ray bursts.

  13. Prospects for obtaining an r-process from Gamma Ray Burst Disk Winds

    E-Print Network [OSTI]

    G. C. McLaughlin; R. Surman

    2004-07-27

    We discuss the possibility that r-process nucleosynthesis may occur in the winds from gamma ray burst accretion disks. This can happen if the temperature of the disk is sufficiently high that electron antineutrinos are trapped as well as neutrinos. This implies accretion disks with greater than a solar mass per second accretion rate, although lower accretion rates with higher black hole spin parameters may provide viable environments as well. Additionally, the outflow from the disk must either have relatively low entropy, e.g. around s = 10, or the initial acceleration of the wind must be slow enough that it is neutrino and antineutrino capture as opposed to electron and positron capture that sets the electron fraction.

  14. Nucleosynthesis of Nickel-56 from Gamma-Ray Burst Accretion Disks

    E-Print Network [OSTI]

    R. Surman; G. C. McLaughlin; N. Sabbatino

    2011-12-12

    We examine the prospects for producing Nickel-56 from black hole accretion disks, by examining a range of steady state disk models. We focus on relatively slowly accreting disks in the range of 0.05 - 1 solar masses per second, as are thought to be appropriate for the central engines of long-duration gamma-ray bursts. We find that significant amounts of Nickel-56 are produced over a wide range of parameter space. We discuss the influence of entropy, outflow timescale and initial disk position on mass fraction of Nickel-56 which is produced. We keep careful track of the weak interactions to ensure reliable calculations of the electron fraction, and discuss the role of the neutrinos.

  15. Phase behavior of disk-coil molecules : from bulk thermodynamics to blends with block copolymers

    E-Print Network [OSTI]

    Kim, Yong-ju

    2013-01-01

    In this thesis, we explore the phase behavior of discotic molecules in various circumstances. We first study the thermodynamics of disk-coil molecules. The system shows rich phase behavior as a function of the relative ...

  16. THE STABILITY OF LOW SURFACE BRIGHTNESS DISKS BASED ON MULTI-WAVELENGTH MODELING

    E-Print Network [OSTI]

    MacLachlan, J. M.

    To investigate the structure and composition of the dusty interstellar medium (ISM) of low surface brightness (LSB) disk galaxies, we have used multi-wavelength photometry to construct spectral energy distributions for ...

  17. Analysis of Trade-Off Between Power Saving and Response Time in Disk Storage Systems

    E-Print Network [OSTI]

    Otoo, Ekow J

    2009-01-01

    to disk-based mass storage systems. In 12th NASA Goddard -to conserve energy in storage systems. SIGMETRICS Perform.in RAID-structured storage system. IEEE Transactions on

  18. An evaluation of the storage systems based on network-attached disks 

    E-Print Network [OSTI]

    Ma, Gang

    1998-01-01

    The emergence of network-attached disks provides the phics. possibility of transferring data between the storage system and the client directly. This offers new possibilities in building a distributed storage system. In this thesis, we examine...

  19. A File Allocation Strategy for Energy-Efficient Disk Storage Systems

    E-Print Network [OSTI]

    Otoo, Ekow J

    2008-01-01

    to conserve energy in storage systems,” SIGMETRICS Perform.in RAID-structured storage system,” IEEE Transac- tions onto disk-based mass storage systems,” in 12th NASA Goddard -

  20. Velocity Profile of the Ionized Disk and the Mass of the Black Hole in M87

    E-Print Network [OSTI]

    Sandip K. Chakrabarti

    1994-11-10

    We present a theoretical model for the ionized disk in M87 which includes spiral shock waves. The line emission profiles computed from this model at various positions on the disk are found to be in agreement with the recent Hubble Space Telescope results. Based on this model, we find that the ionized disk comprises two-armed giant spiral shock waves which extend from around $0.1$ arc sec from the center to at least $1$ arc second or more. Our model requires that the mass of the black hole be $(4 \\pm 0.2) \\times 10^9 M_\\odot$ and the inclination angle to be $(42\\pm 2)^{\\deg}$. We predict the nature of the line profiles at many other locations of the disk which could be verified in future observations.

  1. Gravitational Wave Emission From a Binary Black Hole System in Presence of an Accretion Disk

    E-Print Network [OSTI]

    Sandip K. Chakrabarti

    1996-03-21

    We study time evolution and gravitational wave emission properties of a black hole orbiting {\\it inside} an accretion disk surrounding a massive black hole. We simultaneously solve the structure equations of the accretion disk in presence of heating, cooling and viscosity as well as the equations governing the companion orbit. The deviation from Keplerian distribution of angular momentum of the disk due to pressure and advection effects causes a significant exchange of angular momentum between the disk and the companion. This significantly affects the gravitational wave emission properties from the binary system. We show that when the companion is light, the effect is extremely important and must be taken into account while interpreting gravitational wave signals from such systems.

  2. Imprint of Accretion Disk-Induced Migration on Gravitational Waves from Extreme Mass Ratio Inspirals

    E-Print Network [OSTI]

    Yunes, Nicolas

    We study the effects of a thin gaseous accretion disk on the inspiral of a stellar-mass black hole into a supermassive black hole. We construct a phenomenological angular momentum transport equation that reproduces known ...

  3. Numerical Simulation of the Head/Disk Interface for Patterned Media

    E-Print Network [OSTI]

    Murthy, Aravind N.; Duwensee, Maik; Talke, Frank E.

    2010-01-01

    ying head slider bearings in magnetic hard disk drives. ASMEfor ?ying head slider bearings in magnetic storage. ASME J.slider Á Magnetic data storage Á Slider air bearing Á Finite

  4. SPECTROSCOPIC DIAGNOSTICS OF DISK ACCRETION IN HER BIG AE/BE STARS

    E-Print Network [OSTI]

    Hillenbrand, Lynne

    1 SPECTROSCOPIC DIAGNOSTICS OF DISK ACCRETION IN HER­ BIG AE/BE STARS L. GHANDOUR, S. STROM, S). In this contribution, we present preliminary results using new spectroscopic data to explore whether the last three

  5. r-Process Nucleosynthesis in Hot Accretion Disk Flows from Black Hole - Neutron Star Mergers

    E-Print Network [OSTI]

    R. Surman; G. C. McLaughlin; M. Ruffert; H. -Th. Janka; W. R. Hix

    2008-06-25

    We consider hot accretion disk outflows from black hole - neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three dimensional numerical model of a black hole - neutron star merger and calculate the neutrino and antineutrino fluxes emitted from the resulting accretion disk. We then follow the element synthesis in material outflowing the disk along parameterized trajectories. We find that at least a weak r-process is produced, and in some cases a main r-process as well. The neutron-rich conditions required for this production of r-process nuclei stem directly from the interactions of the neutrinos emitted by the disk with the free neutrons and protons in the outflow.

  6. Role of the gravitomagnetic field in accelerating accretion disk matter to polar jets

    E-Print Network [OSTI]

    J. Poirier; G. J. Mathews

    2015-04-17

    We show that the motion of the neutral masses in an accretion disk orbiting a black hole creates a general-relativistic magnetic-like (gravitomagnetic) field that vertically accelerates neutral particles near the accretion disk upward and then inward toward the axis of the accretion disk. Even though this gravitomagnetic field alone does not achieve collimated jets, it is a novel means to identify one general relativistic effect from a much more complicated problem. In addition, as the accelerated material above or below the accretion disk nears the axis with a nearly vertical direction, a frame-dragging effect twists the trajectories around the axis thus contributing to the formation of collimated bipolar jets.

  7. Off-disk straylight measurements for the Swedish 1-meter Solar Telescope

    E-Print Network [OSTI]

    Löfdahl, Mats G

    2015-01-01

    Context. Accurate photometry with ground based solar telescopes requires characterization of straylight. Scattering in Earth's atmosphere and in the telescope optics are potentially significant sources of straylight, for which the point spread function (PSF) has wings that reach very far. This kind of straylight produces an aureola, extending several solar radii off the solar disk. Aims. Measure such straylight using the ordinary science instrumentation. Methods. We scanned the intensity on and far off the solar disk by use of the science cameras in several different wavelength bands on a day with low-dust conditions. We characterized the far wing straylight by fitting a model to the recorded intensities involving a multi-component straylight PSF and the limb darkening of the disk. Results. The measured scattered light adds an approximately constant fraction of the local granulation intensity to science images at any position on the disk. The fraction varied over the day but never exceeded a few percent. The ...

  8. Spectral Energy Distributions for Disk and Halo M Dwarfs

    SciTech Connect (OSTI)

    Leggett, S. K.; Allard, F.; Dahn, Conard; Hauschildt, P. H.; Kerr, T. H.; Rayner, J.

    2000-06-01

    We have obtained infrared (1-2.5 {mu}m) spectroscopy for 42 halo and disk dwarfs with spectral types M1-M6.5. These data are compared to synthetic spectra generated by the latest model atmospheres of Allard and Hauschildt. Photospheric parameters metallicity, effective temperature, and radius are determined for the sample.We find good agreement between observation and theory except for known problems due to incomplete molecular data for metal hydrides and H2O. The metal-poor M subdwarfs are well matched by the models, as oxide opacity sources are less important in this case. The derived effective temperatures for the sample range from 3600 to 2600 K; at these temperatures grain formation and extinction are not significant in the photosphere. The derived metallicities range from solar to 1/10 solar. The radii and effective temperatures derived agree well with recent models of low-mass stars. The spectra are available in electronic form upon request. (c) 2000 The American Astronomical Society.

  9. Lyapunov instability of rough hard-disk fluids

    E-Print Network [OSTI]

    Jacobus A. van Meel; Harald A. Posch

    2009-04-02

    The dynamical instability of rough hard-disk fluids in two dimensions is characterized through the Lyapunov spectrum and the Kolmogorov-Sinai entropy, $h_{KS}$, for a wide range of densities and moments of inertia $I$. For small $I$ the spectrum separates into translation-dominated and rotation-dominated parts. With increasing $I$ the rotation-dominated part is gradually filled in at the expense of translation, until such a separation becomes meaningless. At any density, the rate of phase-space mixing, given by $h_{KS}$, becomes less and less effective the more the rotation affects the dynamics. However, the degree of dynamical chaos, measured by the maximum Lyapunov exponent, is only enhanced by the rotational degrees of freedom for high-density gases, but is diminished for lower densities. Surprisingly, no traces of Lyapunov modes were found in the spectrum for larger moments of inertia. The spatial localization of the perturbation vector associated with the maximum exponent however persists for any $I$.

  10. Environmental Effects on Gaseous Disks of the Virgo Spiral Galaxies

    E-Print Network [OSTI]

    Hiroyuki Nakanishi; Nario Kuno; Yoshiaki Sofue; Naoko Sato; Naomasa Nakai; Yasuhiro Shioya; Tomoka Tosaki; Sachiko Onodera; Kazuo Sorai; Fumi Egusa; Akihiko Hirota

    2006-10-27

    We found high molecular fractions ($f_{\\rm mol}$; ratio of the molecular to total gas surface densities) in three of five Virgo spiral galaxies in spite of their low total gas column density, based on $^{12}$CO$(J=1-0)$ observations with the Nobeyama 45 m telescope equipped with a multi-beam receiver, BEARS. We interpret this as a result of environmental effects. Combining the CO data with HI data, the relationship between the surface density of the total gas (HI plus H$_2$) and $f_{\\rm mol}$ indicates that the three galaxies near the cluster center have larger $f_{\\rm mol}$ values than expected for field galaxies, while the others show normal $f_{\\rm mol}$. The large $f_{\\rm mol}$ is interpreted as being due either to effective HI gas stripping, even in the inner disks, or to large ISM pressure induced by the high ICM pressure and/or ram pressure, although the possibility of an unusually high metallicity cannot be ruled out.

  11. WIND-DRIVEN ACCRETION IN PROTOPLANETARY DISKS. II. RADIAL DEPENDENCE AND GLOBAL PICTURE

    SciTech Connect (OSTI)

    Bai Xuening, E-mail: xbai@cfa.harvard.edu [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States)

    2013-08-01

    Non-ideal magnetohydrodynamical effects play a crucial role in determining the mechanism and efficiency of angular momentum transport as well as the level of turbulence in protoplanetary disks (PPDs), which are the key to understanding PPD evolution and planet formation. It was shown in our previous work that at 1 AU, the magnetorotational instability (MRI) is completely suppressed when both ohmic resistivity and ambipolar diffusion (AD) are taken into account, resulting in a laminar flow with accretion driven by magnetocentrifugal wind. In this work, we study the radial dependence of the laminar wind solution using local shearing-box simulations. The scaling relation on the angular momentum transport for the laminar wind is obtained, and we find that the wind-driven accretion rate can be approximated as M-dot approx. 0.91 x 10{sup -8}R{sub AU}{sup 1.21}(B{sub p}/10 mG){sup 0.93} M{sub Sun} yr{sup -1}, where B{sub p} is the strength of the large-scale poloidal magnetic field threading the disk. The result is independent of disk surface density. Four criteria are outlined for the existence of the laminar wind solution: (1) ohmic resistivity dominated the midplane region, (2) the AD-dominated disk upper layer, (3) the presence of a (not too weak) net vertical magnetic flux, and (4) sufficiently well-ionized gas beyond the disk surface. All these criteria are likely to be met in the inner region of the disk from {approx}0.3 AU to about 5-10 AU for typical PPD accretion rates. Beyond this radius, the angular momentum transport is likely to proceed due to a combination of the MRI and disk wind, and eventually completely dominated by the MRI (in the presence of strong AD) in the outer disk. Our simulation results provide key ingredients for a new paradigm on the accretion processes in PPDs.

  12. IMAGING DISK DISTORTION OF BE BINARY SYSTEM {delta} SCORPII NEAR PERIASTRON

    SciTech Connect (OSTI)

    Che, X.; Monnier, J. D.; Kraus, S.; Baron, F. [Astronomy Department, University of Michigan, 1034 Dennison Bldg, Ann Arbor, MI 48109-1090 (United States); Tycner, C. [Department of Physics, Central Michigan University, Mount Pleasant, MI 48859 (United States); Zavala, R. T. [US Naval Observatory, Flagstaff Station, 10391 West Naval Observatory Road, Flagstaff, AZ 86001 (United States); Pedretti, E. [European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Muenchen (Germany); Ten Brummelaar, T.; McAlister, H.; Sturmann, J.; Sturmann, L.; Turner, N. [CHARA Array of Georgia State University, Mount Wilson, CA 91023 (United States); Ridgway, S. T., E-mail: xche@umich.edu [National Optical Astronomy Observatory, NOAO, Tucson, AZ (United States)

    2012-09-20

    The highly eccentric Be binary system {delta} Sco reached periastron during early 2011 July, when the distance between the primary and secondary was a few times the size of the primary disk in the H band. This opened a window of opportunity to study how the gaseous disks around Be stars respond to gravitational disturbance. We first refine the binary parameters with the best orbital phase coverage data from the Navy Precision Optical Interferometer. Then we present the first imaging results of the disk after the periastron, based on seven nights of five telescope observations with the MIRC combiner at the CHARA array. We found that the disk was inclined 27.{sup 0}6 {+-} 6.{sup 0}0 from the plane of the sky, had a half-light radius of 0.49 mas (2.2 stellar radii), and consistently contributed 71.4% {+-} 2.7% of the total flux in the H band from night to night, suggesting no ongoing transfer of material into the disk during the periastron. The new estimation of the periastron passage is UT 2011 July 3 07:00 {+-} 4:30. Re-analysis of archival VLTI-AMBER interferometry data allowed us to determine the rotation direction of the primary disk, constraining it to be inclined either {approx}119 Degree-Sign or {approx}171 Degree-Sign relative to the orbital plane of the binary system. We also detect inner disk asymmetries that could be explained by spot-like emission with a few percent of the disk total flux moving in Keplerian orbits, although we lack sufficient angular resolution to be sure of this interpretation and cannot yet rule out spiral density waves or other more complicated geometries.

  13. Global General Relativistic MHD Simulation of a Tilted Black-Hole Accretion Disk

    E-Print Network [OSTI]

    P. Chris Fragile; Omer M. Blaes; Peter Anninos; Jay D. Salmonson

    2007-06-28

    This paper presents a continuation of our efforts to numerically study accretion disks that are misaligned (tilted) with respect to the rotation axis of a Kerr black hole. Here we present results of a global numerical simulation which fully incorporates the effects of the black hole spacetime as well as magnetorotational turbulence that is the primary source of angular momentum transport in the flow. This simulation shows dramatic differences from comparable simulations of untilted disks. Accretion onto the hole occurs predominantly through two opposing plunging streams that start from high latitudes with respect to both the black-hole and disk midplanes. This is due to the aspherical nature of the gravitational spacetime around the rotating black hole. These plunging streams start from a larger radius than would be expected for an untilted disk. In this regard the tilted black hole effectively acts like an untilted black hole of lesser spin. Throughout the duration of the simulation, the main body of the disk remains tilted with respect to the symmetry plane of the black hole; thus there is no indication of a Bardeen-Petterson effect in the disk at large. The torque of the black hole instead principally causes a global precession of the main disk body. In this simulation the precession has a frequency of $3 (M_\\odot/M)$ Hz, a value consistent with many observed low-frequency quasi-periodic oscillations. However, this value is strongly dependent on the size of the disk, so this frequency may be expected to vary over a large range.

  14. FORMATION OF GIANT PLANETS BY DISK INSTABILITY ON WIDE ORBITS AROUND PROTOSTARS WITH VARIED MASSES

    SciTech Connect (OSTI)

    Boss, Alan P.

    2011-04-10

    Doppler surveys have shown that more massive stars have significantly higher frequencies of giant planets inside {approx}3 AU than lower mass stars, consistent with giant planet formation by core accretion. Direct imaging searches have begun to discover significant numbers of giant planet candidates around stars with masses of {approx}1 M{sub sun} to {approx}2 M{sub sun} at orbital distances of {approx}20 AU to {approx}120 AU. Given the inability of core accretion to form giant planets at such large distances, gravitational instabilities of the gas disk leading to clump formation have been suggested as the more likely formation mechanism. Here, we present five new models of the evolution of disks with inner radii of 20 AU and outer radii of 60 AU, for central protostars with masses of 0.1, 0.5, 1.0, 1.5, and 2.0 M{sub sun}, in order to assess the likelihood of planet formation on wide orbits around stars with varied masses. The disk masses range from 0.028 M{sub sun} to 0.21 M{sub sun}, with initial Toomre Q stability values ranging from 1.1 in the inner disks to {approx}1.6 in the outer disks. These five models show that disk instability is capable of forming clumps on timescales of {approx}10{sup 3} yr that, if they survive for longer times, could form giant planets initially on orbits with semimajor axes of {approx}30 AU to {approx}70 AU and eccentricities of {approx}0 to {approx}0.35, with initial masses of {approx}1 M{sub Jup} to {approx}5 M{sub Jup}, around solar-type stars, with more protoplanets forming as the mass of the protostar (and protoplanetary disk) is increased. In particular, disk instability appears to be a likely formation mechanism for the HR 8799 gas giant planetary system.

  15. Accretion Processes Around Black Holes And Neutron Stars: Advective Disk Paradigm

    E-Print Network [OSTI]

    Sandip K. Chakrabarti

    1997-03-09

    We review models which include advective accretion disks onto compact objects and discuss the influence of the centrifugal pressure supported high density region close to the compact objects on the emitted spectra. We show that the stationary and non-stationary spectral properties (such as low and high states, quasi-periodic oscillations, quiescent and rising phases of X-ray novae, etc.) of black hole candidates could be satisfactorily explained by the advective disk models.

  16. Numerical relativity simulations of thick accretion disks around tilted Kerr black holes

    E-Print Network [OSTI]

    Vassilios Mewes; José A. Font; Filippo Galeazzi; Pedro J. Montero; Nikolaos Stergioulas

    2015-06-12

    In this work we present 3D numerical relativity simulations of thick accretion disks around {\\it tilted} Kerr black holes. We investigate the evolution of three different initial disk models with a range of initial black hole spin magnitudes and tilt angles. For all the disk-to-black hole mass ratios considered ($0.044-0.16$) we observe significant black hole precession and nutation during the evolution. This indicates that for such mass ratios, neglecting the self-gravity of the disks by evolving them in a fixed background black hole spacetime is not justified. We find that the two more massive models are unstable against the Papaloizou-Pringle (PP) instability and that those PP-unstable models remain unstable for all initial spins and tilt angles considered, showing that the development of the instability is a very robust feature of such PP-unstable disks. The tilt between the black hole spin and the disk is strongly modulated during the growth of the PP instability, causing a partial global realignment of black hole spin and disk angular momentum in the most massive model with constant specific angular momentum $l$. For the model with non-constant $l$-profile we observe a long-lived $m=1$ non-axisymmetric structure which shows strong oscillations of the tilt angle in the inner regions of the disk. We attribute this effect to the development of Kozai-Lidov oscillations. Our simulations also confirm earlier findings that the development of the PP instability causes the long-term emission of large amplitude gravitational waves, predominantly for the $l=m=2$ multipole mode. The imprint of the BH precession on the gravitational waves from tilted BH-torus systems remains an interesting open issue that would require significantly longer simulations than those presented in this work.

  17. LARGE-SCALE ASYMMETRIES IN THE TRANSITIONAL DISKS OF SAO 206462 AND SR 21

    SciTech Connect (OSTI)

    Pérez, Laura M.; Chandler, Claire J. [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 (United States); Isella, Andrea; Carpenter, John M. [California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)

    2014-03-01

    We present Atacama Large Millimeter/submillimeter Array (ALMA) observations in the dust continuum (690 GHz, 0.45 mm) and {sup 12}CO J = 6-5 spectral line emission of the transitional disks surrounding the stars SAO 206462 and SR 21. These ALMA observations resolve the dust-depleted disk cavities and extended gaseous disks, revealing large-scale asymmetries in the dust emission of both disks. We modeled these disk structures with a ring and an azimuthal Gaussian, where the azimuthal Gaussian is motivated by the steady-state vortex solution from Lyra and Lin. Compared to recent observations of HD 142527, Oph IRS 48, and LkH? 330, these are low-contrast (? 2) asymmetries. Nevertheless, a ring alone is not a good fit, and the addition of a vortex prescription describes these data much better. The asymmetric component encompasses 15% and 28% of the total disk emission in SAO 206462 and SR 21, respectively, which corresponds to a lower limit of 2 M {sub Jup} of material within the asymmetry for both disks. Although the contrast in the dust asymmetry is low, we find that the turbulent velocity inside it must be large (?20% of the sound speed) in order to drive these azimuthally wide and radially narrow vortex-like structures. We obtain residuals from the ring and vortex fitting that are still significant, tracing non-axisymmetric emission in both disks. We compared these submillimeter observations with recently published H-band scattered light observations. For SR 21 the scattered light emission is distributed quite differently from the submillimeter continuum emission, while for SAO 206462 the submillimeter residuals are suggestive of spiral-like structure similar to the near-IR emission.

  18. A parametric modeling approach to measuring the gas masses of circumstellar disks

    SciTech Connect (OSTI)

    Williams, Jonathan P.; Best, William M. J. E-mail: wbest@ifa.hawaii.edu

    2014-06-10

    The disks that surround young stars are mostly composed of molecular gas, which is harder to detect and interpret than the accompanying dust. Disk mass measurements have therefore relied on large and uncertain extrapolations from the dust to the gas. We have developed a grid of models to study the dependencies of isotopologue CO line strengths on disk structure and temperature parameters and find that a combination of {sup 13}CO and C{sup 18}O observations provides a robust measure of the gas mass. We apply this technique to Submillimeter Array observations of nine circumstellar disks and published measurements of six well studied disks. We find evidence for selective photodissociation of C{sup 18}O and determine masses to within a factor of about three. The inferred masses for the nine disks in our survey range from 0.7 to 6 M {sub Jup}, and all are well below the extrapolation from the interstellar medium gas-to-dust ratio of 100. This is consistent with the low masses of planets found around such stars, and may be due to accretion or photoevaporation of a dust-poor upper atmosphere. However, the masses may be underestimated if there are more efficient CO depletion pathways than those known in molecular clouds and cold cores.

  19. Warm Gas in the Inner Disks around Young Intermediate Mass Stars

    E-Print Network [OSTI]

    Sean Brittain; Theodore Simon; Joan Najita; Terrence Rettig

    2006-12-08

    The characterization of gas in the inner disks around young stars is of particular interest because of its connection to planet formation. In order to study the gas in inner disks, we have obtained high-resolution K-band and M-band spectroscopy of 14 intermediate mass young stars. In sources that have optically thick inner disks, i.e. E(K-L)>1, our detection rate of the ro-vibrational CO transitions is 100% and the gas is thermally excited. Of the five sources that do not have optically thick inner disks, we only detect the ro-vibrational CO transitions from HD 141569. In this case, we show that the gas is excited by UV fluorescence and that the inner disk is devoid of gas and dust. We discuss the plausibility of the various scenarios for forming this inner hole. Our modeling of the UV fluoresced gas suggests an additional method by which to search for and/or place stringent limits on gas in dust depleted regions in disks around Herbig Ae/Be stars.

  20. Decoupling of a giant planet from its disk in an inclined binary system

    E-Print Network [OSTI]

    Picogna, Giovanni

    2015-01-01

    We explore the dynamical evolution of a planet embedded in a disk surrounding a star part of a binary system where the orbital plane of the binary is significantly tilted respect to the initial disk plane. Our aim is to test whether the planet remains within the disk and continues to migrate towards the star in a Type I/II mode in spite of the secular perturbations of the companion star. This would explain observed exoplanets with significant inclination respect to the equatorial plane of their host star. We have used two different SPH codes, vine and phantom, to model the evolution of a system star+disk+planet and companion star with time. After an initial coupled evolution, the inclination of the disk and that of the planet begin to differ significantly. The period of oscillation of the disk inclination, respect to the initial plane, is shorter than that of the planet which evolves independently after about 10^4 yr following a perturbed N-body behavior. However, the planet keeps migrating towards the star b...