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Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


1

Integrated vehicle dynamics control via coordination of active front steering and rear braking  

E-Print Network [OSTI]

Integrated vehicle dynamics control via coordination of active front steering and rear brakingComputer and Automation Research Institue, Hungarian Academy of Sciences, Kende u. 13-17, H-1111, Budapest, Hungary, Email front steering and rear braking in a driver- assist system for vehicle yaw control. The proposed control

Paris-Sud XI, Université de

2

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

SciTech Connect (OSTI)

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.

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)

2013-09-01T23:59:59.000Z

3

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

E-Print Network [OSTI]

driving game. Superimposed on the game screen was the image of a car which appeared to the driver to be ahead of him/her. The image enlarged in size, appearing to be a car applying its brakes. The participant was instructed to react as he would in a real...

Hopkins, Jennifer Susan

1995-01-01T23:59:59.000Z

4

Gravity brake  

DOE Patents [OSTI]

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.

Lujan, Richard E. (Santa Fe, NM)

2001-01-01T23:59:59.000Z

5

Braking system  

DOE Patents [OSTI]

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.

Norgren, D.U.

1982-09-23T23:59:59.000Z

6

Why Brake-By-Wire (BBW) ? Advantages of BBW  

E-Print Network [OSTI]

Conventional Brake System http://www.conti-online.com #12;BBW Survey [ SKF (Motor + PGT +Ball Screw)] [ DELPHI (Motor + PGT +Ball Screw)] [Continental Teves (Motor + PGT + Roller Screw)] [Continental Teves installed at wheel] #12;Sectional Drawing of the Electromechanically Actuated Disk Brake From ITT Brake Pads Caliper

Yao, Bin

7

Observations of Infalling and Rotational Motions on a 1,000-AU Scale around 17 Class 0 and 0/I Protostars: Hints of Disk Growth and Magnetic Braking?  

E-Print Network [OSTI]

We perform imaging and analyses of SMA 1.3 mm continuum, C18O (2-1) and 12CO (2-1) line data of 17 Class 0 and 0/I protostars to study their gas kinematics on a 1,000-AU scale. Continuum and C18O (2-1) emission are detected toward all the sample sources and show central primary components with sizes of ~600-1,500 AU associated with protostars. The velocity gradients in C18O (2-1) have wide ranges of orientations from parallel to perpendicular to the outflows, with magnitudes from ~1 to ~530 km/s/pc. We construct a simple kinematic model to reproduce the observed velocity gradients, estimate the infalling and rotational velocities, and infer the disk radii and the protostellar masses. The inferred disk radii range from 500 AU with estimated protostellar masses from 1 Msun. Our results hint that both large and small disks are possibly present around Class 0 protostars, which could be a sign of disk growth at the Class 0 stage. In addition, the directions of the overall velocity gradients in 7 out of the 17 sour...

Yen, Hsi-Wei; Takakuwa, Shigehisa; Ho, Paul T P; Ohashi, Nagayoshi; Tang, Ya-Wen

2014-01-01T23:59:59.000Z

8

Vehicle brake testing system  

DOE Patents [OSTI]

This invention relates to a force measuring system capable of measuring forces associated with vehicle braking and of evaluating braking performance. The disclosure concerns an invention which comprises a first row of linearly aligned plates, a force bearing surface extending beneath and beside the plates, vertically oriented links and horizontally oriented links connecting each plate to a force bearing surface, a force measuring device in each link, a transducer coupled to each force measuring device, and a computing device coupled to receive an output signal from the transducer indicative of measured force in each force measuring device. The present invention may be used for testing vehicle brake systems.

Stevens, Samuel S. (Harriman, TN); Hodgson, Jeffrey W. (Lenoir City, TN)

2002-11-19T23:59:59.000Z

9

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

SciTech Connect (OSTI)

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.

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

2013-10-01T23:59:59.000Z

10

Combined hydraulic and regenerative braking system  

DOE Patents [OSTI]

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.

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

1981-06-02T23:59:59.000Z

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 CenterEnergyAuthorization for(EV) Road User AssessmentNREL is aBraking

12

Oxygen-Diffused Titanium as a Candidate Brake Rotor Material  

SciTech Connect (OSTI)

Titanium alloys are one of several candidate materials for the next generation of truck disk brake rotors. Despite their advantages of lightweight relative to cast iron and good strength and corrosion resistance, titanium alloys are unlikely to be satisfactory brake rotor materials unless their friction and wear behavior can be significantly improved. In this study, a surface engineering process oxygen diffusion was applied to titanium rotors and has shown very encouraging results. The oxygen diffused Ti-6Al-4V (OD-Ti) was tested on a sub-scale brake tester against a flat block of commercial brake lining material and benchmarked against several other Ti-based materials, including untreated Ti-6Al-4V, ceramic particle-reinforced Ti composites (MMCs), and a thermal-spray-coated Ti alloy. With respect to friction, the OD-Ti outperformed all other candidate materials under the imposed test conditions with the friction coefficient remaining within a desirable range of 0.35-0.50, even under the harshest conditions when the disk surface temperature reached nearly 600 ?C. In addition, the OD-Ti showed significantly improved wear-resistance over the non-treated one and was even better than the Ti-based composite materials.

Qu, Jun [ORNL; Blau, Peter Julian [ORNL; Jolly, Brian C [ORNL

2009-01-01T23:59:59.000Z

13

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

DOE Patents [OSTI]

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.

Rau, Scott James

2013-01-29T23:59:59.000Z

14

Regenerative braking device  

DOE Patents [OSTI]

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.

Hoppie, Lyle O. (Birmingham, MI)

1982-01-12T23:59:59.000Z

15

Speciation of Sb in airborne particulate matter, vehicle brake linings, and brake pad wear residues  

E-Print Network [OSTI]

Speciation of Sb in airborne particulate matter, vehicle brake linings, and brake pad wear residues: XAS XANES EXAFS Antimony Particulate matter Brake linings a b s t r a c t Insights into the speciation of Sb in samples of brake linings, brake pad wear residues, road dust, and atmospheric particulate

Short, Daniel

16

Vehicle rear suspension mechanism  

SciTech Connect (OSTI)

A vehicle rear suspension mechanism is described which consists of: a suspension member connected with a vehicle body; wheel hub means supporting a rear wheel having a wheel center plane for rotation about a rotating axis; and connecting means for connecting the wheel hub means with the suspension member. The connecting means include ball joint means having a pivot center located forwardly of and below the rotating axis of the rear wheel and connecting the wheel hub means to the suspension member pivotably about the pivot center, first resilient means located between the wheel hub means and the suspension member rearwardly of and above the rotating axis of the rear wheel, and second resilient means located between the wheel hub means and the suspension member forwardly of and above the rotating axis of the rear wheel.

Kijima, T.; Maebayashi, J.

1986-08-05T23:59:59.000Z

17

Variable ratio regenerative braking device  

DOE Patents [OSTI]

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.

Hoppie, Lyle O. (Birmingham, MI)

1981-12-15T23:59:59.000Z

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]

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.

Boberg, Evan S. (Hazel Park, MI)

2000-12-05T23:59:59.000Z

20

Disturbance Control of the Hydraulic Brake in a Wind Turbine  

E-Print Network [OSTI]

Disturbance Control of the Hydraulic Brake in a Wind Turbine Frank Jepsen, Anders Søborg brake in a wind turbine. Brake torque is determined by friction coefficient and clamp force; the latter brake is one1 of the two independent brake systems in a wind turbine. As a consequence of the gearing

Yang, Zhenyu

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


21

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

22

Contactless magnetic brake for automotive applications  

E-Print Network [OSTI]

consumption due to power assistance, and requirement for anti-lock controls. To solve these problems, a contactless magnetic brake has been developed. This concept includes a novel flux-shunting structure to control the excitation flux generated by permanent...

Gay, Sebastien Emmanuel

2009-05-15T23:59:59.000Z

23

Brake Defect Causation and Abatement Study (BDCAS)  

E-Print Network [OSTI]

Brake Defect Causation and Abatement Study (BDCAS) Oak Ridge National Laboratory managed by UT corrective actions and validate true abatement of initial out-of- service causation the FMCSA began the BDCAS

24

Adaptive controller for regenerative and friction braking system  

DOE Patents [OSTI]

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.

Davis, R.I.

1990-10-16T23:59:59.000Z

25

Adaptive controller for regenerative and friction braking system  

DOE Patents [OSTI]

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.

Davis, Roy I. (Ypsilanti, MI)

1990-01-01T23:59:59.000Z

26

Electric vehicle regenerative antiskid braking and traction control system  

DOE Patents [OSTI]

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.

Cikanek, Susan R. (Wixom, MI)

1995-01-01T23:59:59.000Z

27

Electric vehicle regenerative antiskid braking and traction control system  

DOE Patents [OSTI]

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.

Cikanek, S.R.

1995-09-12T23:59:59.000Z

28

Thermal cracking in disc brakes Thomas J. Mackin *,1  

E-Print Network [OSTI]

Thermal cracking in disc brakes Thomas J. Mackin *,1 , Steven C. Noe, K.J. Ball, B.C. Bedell, D, or hub, which is connected to the wheel and axle, and an inboard and outboard braking surface

Salvaggio, Carl

29

The effect of friction on drum brakes  

SciTech Connect (OSTI)

The boundary element method (BEM) has been developed for a long period of time. Cruse and Wilson developed an isoparametric quadratic element. Rizzo, Cruse, Rizzo and Shippy, and Swedlow and cruse applied the method to various problems. It shows that the BEM can provide a very good analytical result in the linear problem and it can reduce time in preparation of numerical data. Watson and Newcomb pointed out that the pressure distribution on the contact surface of the brake drum and the lining plate do not vary significantly along the axis. The deflection can be reduced by an appropriate design of the web; therefore, two dimensional analysis with the BEM is used in this analysis. Based on the authors` knowledge, this is the first paper to analyze the drum brake by using the BEM. The assumptions are the brake drum to be a rigid body, perfect interface contact between the drum and the shoe, the constant friction coefficient of the friction material and the thermal effect to be neglected. The two dimensional equations are derived based on the Somigliana`s identity. Since there is no shape function and no need of the Jacobin for the coordinate transform, to integrate numerically is easier and to write a computer code is simpler for the constant value element than the second order element. The linear element is inappropriate to treat the comer problem. Using the linear elements or second order elements creates discontinuous phenomena along the irregular boundary. The common nodal point has different normal vector and boundary conditions. It is necessary to have an extra equation to provide a unique solution for the final linear equation. Using the constant value element can get rid of this problem. The effect of the friction on the pressure distribution at the friction interface is studied. The calculated results of the pressure distribution are compared with the available data. The mathematical model can be used as a design tool to predict the performance of drum brakes.

Huang, Y.M.; Shyr, J.S. [National Taiwan Univ. (China)

1995-12-31T23:59:59.000Z

30

Airborne wear particles railway research group FEM Simulation of train disc brake behavior  

E-Print Network [OSTI]

1 Airborne wear particles railway research group FEM Simulation of train disc brake behavior a modern train disc brake with brake caliper and high speed pads. During braking, a considerable amount. A model of train brake caliper Aim The overall aim of the MSc degree project is to develop a thermoelastic

Haviland, David

31

E-Print Network 3.0 - antiskid braking system Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

and Idar Petersen2 Summary: -lock brake systems ABS control the brake torque of each wheel to prevent it from getting locked... in the process of braking. This is important to...

32

Pulsar Braking Index and Mass Accretion  

E-Print Network [OSTI]

I show that the braking index, $N$, a fundamental pulsar experimental quantity, naturally differs from the canonical value of 3 by terms which involve mass accretion. Using the measured values of $N$ for PSR1509-58 and PSR0531+21, I determine that for constant density neutron stars their present mass accretion rates are $(3.10\\pm.51)\\times10^{-5}$ M year$^{-1}$ and $(9.946\\pm.089)\\times10^{-5}$ M year$^{-1}$ respectively, where M is the mass of each pulsar. Finally, I demonstrate that mass accretion removes the outstanding problem of the origin of the big glitches of the Vela Pulsar.

P. D. Morley

1993-11-15T23:59:59.000Z

33

Do Si stars undergo any magnetic braking?  

E-Print Network [OSTI]

The old question of rotational braking of Ap Si stars is revisited on the empirical side, taking advantage of the recent Hipparcos results. Field stars with various evolutionary states are considered, and it is shown that the loose correlation between their rotational period and their surface gravity is entirely compatible with conservation of angular momentum. No evidence is found for any loss of angular momentum on the Main Sequence, which confirms earlier results based on less reliable estimates of surface gravity. The importance of reliable, fundamental Teff determinations of Bp and Ap stars is emphasized.

P. North

1998-02-23T23:59:59.000Z

34

E-Print Network 3.0 - antilock brake systems Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

such as trucks, tractor... -trailers and buses. In these brake systems, compressed air is used as the energy transmitting medium to actuate... the foundation brakes mounted...

35

E-Print Network 3.0 - anti-lock braking system Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

such as trucks, tractor... -trailers and buses. In these brake systems, compressed air is used as the energy transmitting medium to actuate... the foundation brakes mounted...

36

A diagnostic system for air brakes in commercial vehicles  

E-Print Network [OSTI]

to maintenance and hence they require frequent inspections. Current inspection techniques require an inspector to go underneath a vehicle to check the brake system for possible faults, such as leaks, worn brake pads, out-of-adjustment of push rods, etc...

Coimbatore Subramanian, Shankar Ram

2007-09-17T23:59:59.000Z

37

Development of Diagnostic Algorithms for Air Brakes in Trucks  

E-Print Network [OSTI]

causes a reduction in the steady-state pressure in the brake chamber and an increase in the lag of the braking pressure response thereby increasing the stopping distance of the vehicle. Currently a presence of leak in the system is detected...

Dhar, Sandeep

2011-10-21T23:59:59.000Z

38

A pressure control scheme for air brakes in commercial vehicles  

E-Print Network [OSTI]

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...

Bowlin, Christopher Leland

2007-04-25T23:59:59.000Z

39

Braking system for use with an arbor of a microscope  

DOE Patents [OSTI]

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.

Norgren, Duane U. (Orinda, CA)

1984-01-01T23:59:59.000Z

40

Collapse of Magnetized Singular Isothermal Toroids: II. Rotation and Magnetic Braking  

E-Print Network [OSTI]

We study numerically the collapse of rotating, magnetized molecular cloud cores, focusing on rotation and magnetic braking during the main accretion phase of isolated star formation. Motivated by previous numerical work and analytic considerations, we idealize the pre-collapse core as a magnetized singular isothermal toroid, with a constant rotational speed everywhere. The collapse starts from the center, and propagates outwards in an inside-out fashion, satisfying exact self-similarity in space and time. For rotation rates and field strengths typical of dense low-mass cores, the main feature remains the flattening of the mass distribution along field lines -- the formation of a pseudodisk, as in the nonrotating cases. The density distribution of the pseudodisk is little affected by rotation. On the other hand, the rotation rate is strongly modified by pseudodisk formation. Most of the centrally accreted material reaches the vicinity of the protostar through the pseudodisk. The specific angular momentum can be greatly reduced on the way, by an order of magnitude or more, even when the pre-collapse field strength is substantially below the critical value for dominant cloud support. The efficient magnetic braking is due to the pinched geometry of the magnetic field in the pseudodisk, which strengthens the magnetic field and lengthens the level arm for braking. Both effects enhance the magnetic transport of angular momentum from inside to outside. The excess angular momentum is carried away in a low-speed outflow that has, despite claims made by other workers, little in common with observed bipolar molecular outflows. We discuss the implications of our calculations for the formation of true disks that are supported against gravity by rotation.

A. Allen; Z. Y. Li; F. H. Shu

2003-11-17T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


41

Regenerative braking on bicycles to power LED safety flashers  

E-Print Network [OSTI]

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, ...

Collier, Ian M

2005-01-01T23:59:59.000Z

42

Asbestos-free brake-lining materials for hydrogenerators  

SciTech Connect (OSTI)

Three different asbestos-free materials currently considered as new lining materials for hydrogenerator brakes were tested and compared to the original asbestos lining. Results show that these substitutes not only vary greatly from the original material in terms of mechanical properties and physical characteristics but also exhibit significantly different performances in braking tests. Consequently, these new materials are not entirely suitable for the intended application.

Lalonde, S.; Lanteigne, J. [Hydro-Quebec, Varennes, Quebec (Canada)

1995-11-01T23:59:59.000Z

43

Investigation of aerodynamic braking devices for wind turbine applications  

SciTech Connect (OSTI)

This report documents the selection and preliminary design of a new aerodynamic braking system for use on the stall-regulated AWT-26/27 wind turbines. The goal was to identify and design a configuration that offered improvements over the existing tip brake used by Advanced Wind Turbines, Inc. (AWT). Although the design objectives and approach of this report are specific to aerodynamic braking of AWT-26/27 turbines, many of the issues addressed in this work are applicable to a wider class of turbines. The performance trends and design choices presented in this report should be of general use to wind turbine designers who are considering alternative aerodynamic braking methods. A literature search was combined with preliminary work on device sizing, loads and mechanical design. Candidate configurations were assessed on their potential for benefits in the areas of cost, weight, aerodynamic noise, reliability and performance under icing conditions. As a result, two configurations were identified for further study: the {open_quotes}spoiler-flap{close_quotes} and the {open_quotes}flip-tip.{close_quotes} Wind tunnel experiments were conducted at Wichita State University to evaluate the performance of the candidate aerodynamic brakes on an airfoil section representative of the AWT-26/27 blades. The wind tunnel data were used to predict the braking effectiveness and deployment characteristics of the candidate devices for a wide range of design parameters. The evaluation was iterative, with mechanical design and structural analysis being conducted in parallel with the braking performance studies. The preliminary estimate of the spoiler-flap system cost was $150 less than the production AWT-26/27 tip vanes. This represents a reduction of approximately 5 % in the cost of the aerodynamic braking system. In view of the preliminary nature of the design, it would be prudent to plan for contingencies in both cost and weight.

Griffin, D.A. [R. Lynette & Associates, Seattle, WA (United States)

1997-04-01T23:59:59.000Z

44

Magnetic braking of T Tauri stars  

E-Print Network [OSTI]

We construct models for the rotation rates of T Tauri stars whose spin is regulated by magnetic linkage between the star and a surrounding accretion disc. Our models utilise a time-dependent disc code to follow the accretion process and include the effects of pre-main-sequence stellar evolution. We find that the initial disc mass controls the evolution of the star-disc system. For sufficiently massive discs, a stellar field of $\\sim$ 1 kG is able to regulate the spin rate to the observed values during the classical T Tauri phase. The field then acts to expel the disc and the star spins up at constant angular momentum as a weak-line system. Lower mass discs are ejected at an early epoch and fail to brake the star significantly. We extend the model to close binary systems, and find that the removal of angular momentum from the disc by the secondary significantly prolongs the inner disc lifetime. Such systems should therefore be relatively slow rotators. We also discuss the implications of our model for the spectral energy distributions and variability of T Tauri stars.

P. J. Armitage; C. J. Clarke

1995-12-05T23:59:59.000Z

45

Disk filter  

DOE Patents [OSTI]

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.

Bergman, W.

1985-01-09T23:59:59.000Z

46

MAGNETIZED ACCRETION-EJECTION STRUCTURES: 2.5-DIMENSIONAL MAGNETOHYDRODYNAMIC SIMULATIONS OF CONTINUOUS IDEAL JET LAUNCHING FROM RESISTIVE ACCRETION DISKS  

E-Print Network [OSTI]

inside the disk brakes the matter azimuthally and allows for accre- tion, while it is responsible shell of dense material is the natural outcome of the inward advection of a primordial field. Subject optical forbidden lines emitted in the jets (see also Hartigan et al. 1995). In galactic systems

Casse, Fabien

47

Regenerative braking device with rotationally mounted energy storage means  

DOE Patents [OSTI]

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.

Hoppie, Lyle O. (Birmingham, MI)

1982-03-16T23:59:59.000Z

48

Fuzzy logic electric vehicle regenerative antiskid braking and traction control system  

DOE Patents [OSTI]

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.

Cikanek, S.R.

1994-10-25T23:59:59.000Z

49

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

E-Print Network [OSTI]

components, specifically whether the equation accurately reflects driver and vehicle behaviors during a braking maneuver. This research evaluated the two components of the SSD equation. Four field studies were conducted that evaluated driver braking...

Picha, Dale Louis

1994-01-01T23:59:59.000Z

50

Control Engineering Practice 11 (2003) 163170 A mechatronic conception of a new intelligent braking system  

E-Print Network [OSTI]

, residual friction, noise, vibrations, a new brake has been designed according to a modular principle which describes a new intelligent braking system for motor vehicles. A mechatronic approach helped to avoid some

Paris-Sud XI, Université de

51

Fuzzy logic electric vehicle regenerative antiskid braking and traction control system  

DOE Patents [OSTI]

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.

Cikanek, Susan R. (Wixom, MI)

1994-01-01T23:59:59.000Z

52

The expandable network disk  

E-Print Network [OSTI]

This thesis presents a virtual disk cluster called END, the Expandable Network Disk. END aggregates storage on a cluster of servers into a single virtual disk. END's main goals are to offer good performance during normal ...

Muthitacharoen, Athicha, 1976-

2008-01-01T23:59:59.000Z

53

Evaluation of Corrosion Failure in Tractor-Trailer Brake System  

SciTech Connect (OSTI)

As reported to ORNL, concomitant with the introduction of different deicing and anti-icing compounds, there was an increase in the brake failure rate of tractor-trailer trucks. A forensic evaluation of a failed brake system was performed. Optical and scanning electron microscopic evaluation showed corrosion to be mostly confined to the brake table/lining interface. The corrosion is non-uniform as is to be expected for plain carbon steel in chloride environments. This initial analysis found no evidence for the chlorides of calcium and magnesium, which are the newly introduced deicing and antiicing compounds and are less soluble in water than the identified chlorides of sodium and potassium, in the scale. The result could be as a result of non-exposure of the examined brake table to calcium and magnesium chloride. The mechanisms for the increased failure rate are postulated as being an increased rate of corrosion due to positive shifts in the corrosion potential, and an increased amount of corrosion due to an increased ''time of wetness'' that results from the presence of hygroscopic salts. Laboratory scale evaluation of the corrosion of plain carbon steel in simulated deicing and anti-icing solutions need to be performed to determine corrosion rates and morphological development of corrosion product, to compare laboratory data to in-service data, and to rank economically feasible replacement materials for low carbon steel. In addition, the mechanical behavior of the lining attached to the brake shoe table needs to be assessed. It is opined that an appropriate adjustment of materials could easily allow for a doubling of a brake table/lining lifetime. Suggestions for additional work, to clarify the mechanisms of rust jacking and to develop possible solutions, are described.

Wilson, DF

2002-10-22T23:59:59.000Z

54

E-Print Network 3.0 - air brake association Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

... Source: Southwest Region University Transportation Center Collection: Engineering ; Energy Storage, Conversion and Utilization 2 Commercial Motor Vehicle Brake Assessment...

55

Airbus A320 Braking as Predicate-Action Peter B. Ladkin  

E-Print Network [OSTI]

Airbus A320 Braking as Predicate-Action Diagrams Peter B. Ladkin Universitat Bielefeld, Technische of the Airbus A320 braking systems contained in the Flight Crew Operating Manual. This helps identify to interest us and others in the design of the A320 braking system [FI.93a, FI.93b, FI.93c]. This paper

Ladkin, Peter B.

56

Adaptive Rollover Prevention for Automotive Vehicles with Differential Braking  

E-Print Network [OSTI]

Adaptive Rollover Prevention for Automotive Vehicles with Differential Braking Selim Solmaz, switching, and tuning (MMST) paradigm [13, 14, 15] for preventing un­tripped rollover in automotive vehicles performance than its fixed robust counterpart. Keywords: Automotive control; Multiple models; Parameter

Duffy, Ken

57

Many applications require brakes, for instance to decelerate or to  

E-Print Network [OSTI]

an error occurs in the process of a robotic arm. The energy consumption and actuation force of these brakes is very high. A team of TU Delft scientists developed a method to reduce the energy consumption. The energy consumption is high because an actuator has to generate a normal force between two friction

58

aircraft brake materials: Topics by E-print Network  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

brake materials First Page Previous Page 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Next Page Last Page Topic Index 1 26 REDUCTION OF CADMTUM PLATING ON...

59

Braking index of isolated pulsars: open questions and ways forward  

E-Print Network [OSTI]

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...

Hamil, Oliver

2015-01-01T23:59:59.000Z

60

TOWARDS GLOBAL CHASSIS CONTROL BY INTEGRATING THE BRAKE AND  

E-Print Network [OSTI]

. Szab´o*, J. Bokor*, C. Poussot-Vassal**, O. Sename**, L. Dugard** *Computer and Automation Research active suspensions and an active brake is proposed to improve the safety of vehicles. The design is based of the method is demonstrated through a complex simulation example containing vehicle maneuvers. Keywords: LPV

Paris-Sud XI, Université de

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


61

Design and test of a wet type helium turbo-expander with an alternator as a brake  

SciTech Connect (OSTI)

A wet type helium turbo-expander with expected adiabatic efficiency of 70% at inlet pressure, temperature, and outlet pressure of 1.3 MPa, 6.0 K, and 0.2 MPa, respectively, has been developed. An alternator is adopted as a brake where a permanent magnet is held in the turbine shaft. And a self-acting gas bearing is used at thrust and journal bearings. An electromagnet supports thrust bearing to lift up the thrust disk when initiating operation. Design mass flow rate of the turbine is determined to be 60 g/s, corresponding to the JT mass flow rate in the existing helium liquefier/refrigerator. In the cryogenic performance test, the turbine had increased helium liquefaction rate by four times larger than the liquefaction rate without turbine operation.

Kato, T.; Miyake, A.; Kawano, K.; Hamada, K.; Hiyama, T.; Iwamoto, S.; Ebisu, H.; Tsuji, H. [Japan Atomic Energy Research Institute, Ibaraki-ken (Japan); Saji, N.; Kaneko, Y. [Ishikawajima-Harima Heavy Industries Co. Ltd., Tokyo (Japan)] [and others

1994-12-31T23:59:59.000Z

62

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...

63

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

SciTech Connect (OSTI)

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.

Peter J. Blau

2000-04-26T23:59:59.000Z

64

E-Print Network 3.0 - automotive drum brakes Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Biochemistry, Georgia Institute of Technology Collection: Chemistry 3 Commercial Motor Vehicle Brake Assessment Tools Summary: System Visual determination of potentially unsafe...

65

E-Print Network 3.0 - air brakes Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

... Source: Oak Ridge National Laboratory, Center for Transportation Analysis Collection: Energy Storage, Conversion and Utilization 2 CMV Brake Wear and Performance Test Little is...

66

E-Print Network 3.0 - automotive brake materials Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

such as trucks, tractor... -trailers and buses. In these brake systems, compressed air is used as the energy transmitting medium to ... Source: Southwest Region University...

67

Plant and Environment Interactions Arsenic Accumulation in the Hyperaccumulator Chinese Brake and Its Utilization  

E-Print Network [OSTI]

in a greenhouse. At recently, however, has Chinese brake (Pteris vittata L.)harvest, the Chinese brake produced soils (0.47­7.56 mg As kg 1 ),concentration to water-soluble arsenic in soil) of 1450 and a transloca to remediate arsenic contaminated soils. schullat, 2000), soil arsenic concentration (Jiang and Singh, 1994

Ma, Lena

68

Vehicle yaw control via coordinated use of steering/braking systems  

E-Print Network [OSTI]

Vehicle yaw control via coordinated use of steering/braking systems M. Doumiati, O. Sename, J.sename@gipsa-lab.grenoble-inp.fr) Computer and Automation Research Institute, Hungarian Academy of Sciences, Kende u. 13-17, H-1111, Budapest with steer- ing/braking coordination task for vehicle yaw control. For steerability enhancement, only active

Paris-Sud XI, Université de

69

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

E-Print Network [OSTI]

- niques. The design of a model-based diagnostic system requires the development and experimental corroboration of a mathematical model of the evolution of pressure in each brake chamber of a truck in response to the application of brake pedal input...

Vilayannur Natarajan, Shankar

2005-08-29T23:59:59.000Z

70

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

E-Print Network [OSTI]

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...

Coimbatore Subramanian, Shankar

2004-09-30T23:59:59.000Z

71

Fault tolerant control of automatically controlled vehicles in response to brake system failures  

E-Print Network [OSTI]

in the brake system is vital. In this thesis, nonlinear failure detection filters are used for fault detection of sensors and actuators in a class of nonlinear systems. In this thesis, the effects of brake system failures in an AHS where the vehicle steering...

Hsien, Li-Wei

1998-01-01T23:59:59.000Z

72

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

E-Print Network [OSTI]

originating from automobiles. Abrasion dusts from commercially available brake pads (nonasbestos organic type factors originating from automobiles were approximately 32 µg Sb/braking/car for PM10 and 22 µg Sb of automobiles to the atmospheric Sb concen- tration. The emission factors of pollutants from automobiles have

Short, Daniel

73

Wind turbine trailing-edge aerodynamic brake design  

SciTech Connect (OSTI)

This report describes the design of a centrifugally actuated aerodynamic-overspeed device for a horizontal-axis wind turbine. The device will meet the following criteria; (1) It will be effective for airfoil angles of attack 0{degrees} to 45{degrees}. (2) It will be stowed inside the blade profile prior to deployment. (3) It will be capable of offsetting the positive torque produced by the overall blade. (4) Hinge moments will be minimized to lower actuator loads and cost. (5) It will be evaluated as a potential power modulating active rotor-control system. A literature review of aerodynamic braking devices was conducted. Information from the literature review was used to conceptualize the most effective devices for subsequent testing and design. Wind-tunnel test data for several braking devices are presented in this report. Using the data for the most promising configuration, a preliminary design was developed for a MICON 65/13 wind turbine with Phoenix 7.9-m rotor blades.

Quandt, G.

1996-01-01T23:59:59.000Z

74

Glass rupture disk  

DOE Patents [OSTI]

A frangible rupture disk and mounting apparatus for use in blocking fluid flow, generally in a fluid conducting conduit such as a well casing, a well tubing string or other conduits within subterranean boreholes. The disk can also be utilized in above-surface pipes or tanks where temporary and controllable fluid blockage is required. The frangible rupture disk is made from a pre-stressed glass with controllable rupture properties wherein the strength distribution has a standard deviation less than approximately 5% from the mean strength. The frangible rupture disk has controllable operating pressures and rupture pressures.

Glass, S. Jill (Albuquerque, NM); Nicolaysen, Scott D. (Albuquerque, NM); Beauchamp, Edwin K. (Albuquerque, NM)

2002-01-01T23:59:59.000Z

75

Constraints on the Formation and Evolution of Circumstellar Disks in Rotating Magnetized Cloud Cores  

E-Print Network [OSTI]

We use magnetic collapse models to place some constraints on the formation and angular momentum evolution of circumstellar disks which are embedded in magnetized cloud cores. Previous models have shown that the early evolution of a magnetized cloud core is governed by ambipolar diffusion and magnetic braking, and that the core takes the form of a nonequilibrium flattened envelope which ultimately collapses dynamically to form a protostar. In this paper, we focus on the inner centrifugally-supported disk, which is formed only after a central protostar exists, and grows by dynamical accretion from the flattened envelope. We estimate a centrifugal radius for the collapse of mass shells within a rotating, magnetized cloud core. The centrifugal radius of the inner disk is related to its mass through the two important parameters characterizing the background medium: the background rotation rate $\\Omb$ and the background magnetic field strength $\\Bref$. We also revisit the issue of how rapidly mass is deposited onto the disk (the mass accretion rate) and use several recent models to comment upon the likely outcome in magnetized cores. Our model predicts that a significant centrifugal disk (much larger than a stellar radius) will be present in the very early (Class 0) stage of protostellar evolution. Additionally, we derive an upper limit for the disk radius as it evolves due to internal torques, under the assumption that the star-disk system conserves its mass and angular momentum even while most of the mass is transferred to a central star.

Shantanu Basu

1998-08-13T23:59:59.000Z

76

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

Broader source: Energy.gov [DOE]

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.

77

Preliminary survey report: control technology for brake lining at Northwest Local School District, Cincinnati, Ohio  

SciTech Connect (OSTI)

A walk-through survey of control technology for reducing asbestos exposure during maintenance and repair of vehicular brakes was conducted at Northwest Local School District, Cincinnati, Ohio in January, 1986. The primary method for controlling and collecting dust during brake servicing was a wet-washing technique and good work practices, ensuring that exposure to hazardous physical or chemical agents was reduced or eliminated. Also available was an enclosed-type brake assembly cleaner designed to be connected to the shop air and a vacuum system. The brake assembly cleaner did not have a viewing port to examine the area being cleaned. The operator had to remove the unit to inspect the cleaned area potentially exposing himself to any dust remaining on the brake shoes or hub. The unit itself was a potential dust source as it was designed to fit 16-inch wheels and did not form a tight seal on the smaller 15-inch wheels of the newer buses. The authors conclude that the wet wash technique is an excellent method for controlling asbestos emissions during brake maintenance. The vacuum brake-assembly cleaner is inadequate and potentially hazardous. An in-depth survey of the wet technique is recommended.

Cooper, T.C.; McGlothlin, J.D.; Godbey, F.W.; Sheehy, J.W.; O'Brien, D.M.

1986-05-01T23:59:59.000Z

78

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

E-Print Network [OSTI]

, the characteristics of combustion for swept injection timings along the maximum brake torque plateau are determined. The research is conducted by varying injection timing at constant engine speed and load while measuring engine emissions and in-cylinder pressure...

Kroeger, Timothy H

2013-09-19T23:59:59.000Z

79

E-Print Network 3.0 - automotive brake disc Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Please cite this article in press as: F. Massi, et al., Contact surface topography and system dynamics of brake squeal, Wear (2008), Summary: for future work. 487 References 488...

80

E-Print Network 3.0 - automotive disc brakes Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Please cite this article in press as: F. Massi, et al., Contact surface topography and system dynamics of brake squeal, Wear (2008), Summary: for future work. 487 References 488...

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


81

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

E-Print Network [OSTI]

A MATHEMATICAL MODEL FOR AIR BRAKE SYSTEMS IN THE PRESENCE OF LEAKS A Thesis by SRIVATSAN RAMARATHNAM 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 2008 Major Subject: Mechanical Engineering A MATHEMATICAL MODEL FOR AIR BRAKE SYSTEMS IN THE PRESENCE OF LEAKS A Thesis by SRIVATSAN RAMARATHNAM Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment...

Ramaratham, Srivatsan

2008-10-10T23:59:59.000Z

82

Effect of rearing and laying house environments on performance of incross egg production type pullets  

E-Print Network [OSTI]

and 1n conf1nement dur1ng the age per1od of 9 20 weeks. During the laying period the range reared pullets laid at a rate of 41. 5 per cent while the confinement reared pullets laid at a rate of 36. 6 per cent. The eggs from the range reared pullets... feed efficiency of range reared pullets to be significantly better than that of pullets reared 1n conf1nement. Johnson and Davidson (1957)~ Pepper, et al. (1959)~ snd Minter (1957) found that range reared. pullets laid st a slightly higher rate than...

Shupe, William Dale

1960-01-01T23:59:59.000Z

83

Laboratory rearing of the cottonwood twig borer on artificial diets  

E-Print Network [OSTI]

LABORATORY REARING OF THE COTTONWOOD TWIG BORER ON ARTIFICIAL DIETS A Thesis VICTOR CARL MASTRO Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE August... 1973 Ma)or Sub)ect: Entomology LABORATORY REARING OF THE COTTONWOOD TWIG BORER ON ARTIFICIAL DIETS A Thesis by VICTOR CARL MASTRO Approved as to style and conte by (Cha rman of Committee) Head De artment) (He er) ( mber) mber) August 1973...

Mastro, Victory Carl

1973-01-01T23:59:59.000Z

84

Braking index of isolated uniformly rotating magnetized pulsars  

E-Print Network [OSTI]

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...

Hamil, Oliver; Urbanec, Martin; Urbancova, Gabriela

2015-01-01T23:59:59.000Z

85

PLANETESIMAL DISK MICROLENSING  

SciTech Connect (OSTI)

Motivated by debris disk studies, we investigate the gravitational microlensing of background starlight by a planetesimal disk around a foreground star. We use dynamical survival models to construct a plausible example of a planetesimal disk and study its microlensing properties using established ideas of microlensing by small bodies. When a solar-type source star passes behind a planetesimal disk, the microlensing light curve may exhibit short-term, low-amplitude residuals caused by planetesimals several orders of magnitude below Earth mass. The minimum planetesimal mass probed depends on the photometric sensitivity and the size of the source star, and is lower when the planetesimal lens is located closer to us. Planetesimal lenses may be found more nearby than stellar lenses because the steepness of the planetesimal mass distribution changes how the microlensing signal depends on the lens/source distance ratio. Microlensing searches for planetesimals require essentially continuous monitoring programs that are already feasible and can potentially set constraints on models of debris disks, the progeny of the supposed extrasolar analogues of Kuiper Belts.

Heng, Kevin; Keeton, Charles R., E-mail: heng@ias.ed, E-mail: keeton@physics.rutgers.ed [Institute for Advanced Study, School of Natural Sciences, Einstein Drive, Princeton, NJ 08540 (United States)

2009-12-10T23:59:59.000Z

86

Silica in Protoplanetary Disks  

E-Print Network [OSTI]

Mid-infrared spectra of a few T Tauri stars (TTS) taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope show prominent narrow emission features indicating silica (crystalline silicon dioxide). Silica is not a major constituent of the interstellar medium; therefore, any silica present in the circumstellar protoplanetary disks of TTS must be largely the result of processing of primitive dust material in the disks surrouding these stars. We model the silica emission features in our spectra using the opacities of various polymorphs of silica and their amorphous versions computed from earth-based laboratory measurements. This modeling indicates that the two polymorphs of silica, tridymite and cristobalite, which form at successively higher temperatures and low pressures, are the dominant forms of silica in the TTS of our sample. These high temperature, low pressure polymorphs of silica present in protoplanetary disks are consistent with a grain composed mostly of tridymite named Ada found in the cometary dust samples collected from the STARDUST mission to Comet 81P/Wild 2. The silica in these protoplanetary disks may arise from incongruent melting of enstatite or from incongruent melting of amorphous pyroxene, the latter being analogous to the former. The high temperatures of 1200K-1300K and rapid cooling required to crystallize tridymite or cristobalite set constraints on the mechanisms that could have formed the silica in these protoplanetary disks, suggestive of processing of these grains during the transient heating events hypothesized to create chondrules.

B. A. Sargent; W. J. Forrest; C. Tayrien; M. K. McClure; A. Li; A. R. Basu; P. Manoj; D. M. Watson; C. J. Bohac; E. Furlan; K. H. Kim; J. D. Green; G. C. Sloan

2008-11-21T23:59:59.000Z

87

Estimating Rear-End Accident Probabilities at Signalized Intersections: An Occurrence-Mechanism Approach  

E-Print Network [OSTI]

Estimating Rear-End Accident Probabilities at Signalized Intersections: An Occurrence intersections, rear-end accidents are frequently the predominant accident type. These accidents result from to this deceleration. This paper mathematically represents this process, by expressing accident probability

Wang, Yinhai

88

Premixed direct injection disk  

DOE Patents [OSTI]

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.

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

2013-04-23T23:59:59.000Z

89

INTRODUCTION In birds, the quality of rearing conditions is a  

E-Print Network [OSTI]

major, nest- ling condition affected recruitment probability but not reproductive success (Verboven- ling condition and survival better than with repro- ductive success and adult survival. These lifeINTRODUCTION In birds, the quality of rearing conditions is a major determinant of nestling body

Alvarez, Nadir

90

Fuel for Galaxy Disks  

E-Print Network [OSTI]

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.

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

2008-04-04T23:59:59.000Z

91

Extremal black disks in QCD  

E-Print Network [OSTI]

We argue that in the high energy QCD a true black disk wave function necessarily contains many quarks. This corresponds to necessity of non-vacuum reggeon loops in formation of a black disk. The result comes from decomposition of the black disk S-matrix in characters on group manifold.

Alexey V. Popov

2008-05-12T23:59:59.000Z

92

Preliminary survey report: evaluation of brake-drum service controls at Pennsylvania Bureau of Vehicle Management, Vehicle Maintenance Division, Harrisburg, Pennsylvania  

SciTech Connect (OSTI)

Exposure to asbestos during the servicing of brakes on state-owned vehicles at the Bureau of Vehicle Management Maintenance Division, Harrisburg, Pennsylvania, was investigated as part of a study of control technologies. Brakes had been serviced at this garage facility for the previous year using a BCE-1000 Clayton brake-cleaning unit, sized for cars, vans, and pickups. The brake-cleaning unit consisted of a transparent enclosure hood and a HEPA vacuum filter dust collector, designed to contain and collect all brake-lining dust during vehicular brake maintenance and replacement. The authors conclude that the Clayton BCE-1000 dust-control unit appeared to be effective in containing and collecting brake dust during all vehicular brake maintenance and replacement jobs in this situation.

Van Wagenen, H.D.

1987-03-01T23:59:59.000Z

93

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

E-Print Network [OSTI]

On The Use of Eddy Current Brakes as Tunable, Fast Turn-On Viscous Dampers For Haptic Rendering, linear dampers for haptic rendering using a prototype haptic device outfitted with eddy current brakes discuss the results from haptic experiments for rendering viscosity, virtual walls and virtual friction

Hayward, Vincent

94

Neutron scattering residual stress measurements on gray cast iron brake discs  

SciTech Connect (OSTI)

Neutron diffraction was used to investigate the effects of a heat treatment designed to remove internal residual stresses in brake discs. It is believed that residual stresses may change the rate of deformation of the discs during severe braking conditions when the disc temperature is increased significantly. Neutron diffraction was used to map out residual strain distributions in a production disc before and after a stress-relieving heat treatment. Results from these neutron diffraction experiments show that some residual strains were reduced by as much as 400 microstrain by stress relieving. 5 refs., 5 figs., 1 tab.

Spooner, S.; Payzant, E.A.; Hubbard, C.R. [and others

1996-11-01T23:59:59.000Z

95

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

SciTech Connect (OSTI)

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.

Blau, P.J.

2003-02-03T23:59:59.000Z

96

Recycled brake linings as partial aggregate substitute in asphalt paving. Construction and final report. Report for July 1992-August 1996  

SciTech Connect (OSTI)

The purpose of this project was to evaluate the performance of asphalt containing various percentages of brake lining as an aggregate, and compare its performance to that of normal asphalt containing natural aggregate. This project is an effort to explore alternate ways to use waste product. Four test section of FB-2 Modified mix containing brake lining materials were placed in July 1992 along with one control section on SR 3022 in Mercer county. To date all sections are performing satisfactory, and Brake linings should be recommended as a viable partial replacement of aggregate in bituminous materials. This study only considered the performance of only off-spec brake linings, therefore, any performance data or enviromental effects of placement of used brake material should be addressed.

Miller, P.A.; Sukley, R.

1996-09-01T23:59:59.000Z

97

Real-Time Dynamic Brake Assessment Conduct a proof-of-concept  

E-Print Network [OSTI]

Real-Time Dynamic Brake Assessment Purpose Conduct a proof-of-concept test to examine the Federal Motor Carrier Safety Administration's Vehicle and Roadside Operations Division Concept stemming conducted for the National Highway Transportation Safety Administration. Signals to be collected Real

98

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

E-Print Network [OSTI]

Regenerative Braking for an Electric Vehicle Using Ultracapacitors and a Buck-Boost Converter Juan for an Electric Vehicle has been simulated. The purpose of this device is to allow higher accelerations, similar in shape and size to a Chevrolet S-10. This vehicle was already converted to an electric car

Catholic University of Chile (Universidad Catlica de Chile)

99

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

E-Print Network [OSTI]

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 responding. ANOVAs showed...

Berman, Andrea Helene

1994-01-01T23:59:59.000Z

100

Dynamical Evolution of Protoplanetary Disks  

E-Print Network [OSTI]

This paper reviews the theory of protostellar debris disks. After a brief introduction to accretion disk physics, I describe coagulation models of planet formation in the outer regions of planetesimal disks. Coagulation models for the Kuiper Belt produce Pluto-sized objects on timescales of 10-40 Myr. These models yield size distributions which agree with observations of Kuiper Belt objects with red magnitudes, R = 20-27. Velocity stirring models for other debris disk systems demonstrate that 500 km or larger objects can stir the velocities of small objects up to the shattering limit needed to begin a collisional cascade.

Scott J. Kenyon

2000-10-02T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


101

Disk Quota Increase Request  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

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:1 First Use of Energy for All Purposes (Fuel and Nonfuel),Feet) Year Jan Feb Mar Apr May JunDatastreamsmmcrcalgovInstrumentsruc DocumentationP-Series to UserProduct:Directives Templates The Office of Science isDisk Quota

102

Reared microgastrine wasps (Hymenoptera: Braconidae) from Yanayacu Biological Station and environs (Napo Province,  

E-Print Network [OSTI]

(Napo Province, Ecuador): Diversity and host specialization James B. Whitfield, Josephine J. Rodriguez: Whitfield JB, Rodriguez JJ, Masonick PK. 2009. Reared microgastrine wasps (Hymenoptera: Braconidae) from

Whitfield, James B.

103

CONSTRAINTS ON ACCRETION DISK LIFETIMES  

E-Print Network [OSTI]

of stellar mass. #12; METHODOLOGY Constraining disk lifetimes means measuring infrared excesses and stellar ages and masses for large samples of young stellar objects. #12; Infrared excesses: #15; A combination of stellar irradiative and viscous heating in circumstellar disks produces ux excesses at micro

Hillenbrand, Lynne

104

Development of a Natural Rearing System to Improve Supplemental Fish Quality, 1999-2003 Progress Report.  

SciTech Connect (OSTI)

The National Marine Fisheries Service (NMFS) has been conducting Natural Rearing Enhancement System (NATURES) research since the early 1990s. NATURES studies have looked at a variety of mechanisms to enhance production of wild-like salmonids from hatcheries. The goal of NATURES research is to develop fish culture techniques that enable hatcheries to produce salmon with more wild-like characteristics and increased postrelease survival. The development of such techniques is called for in the Columbia Basin Fish and Wildlife Program. This document is the draft report for the Supplemental Fish Quality Contract DE-AI79-91BP20651 Over the history of the project, the effects of seminatural raceway habitats, automated underwater feeders, exercise current velocities, live food diets, and predator avoidance training have been investigated. The findings of these studies are reported in an earlier contract report (Maynard et al. 1996a). The current report focuses on research that has been conducted between 1999 and 2002. This includes studies on the effect of exercise on salmon and steelhead trout, effects of predator avoid training, integration of NATUES protocols into production hatcheries, and the study of social behavior of steelhead grown in enriched and conventional environments. Traditionally, salmon (Oncorhynchus spp.) are reared in barren concrete raceways that lack natural substrate, in-stream structure, or overhead cover. The fish are fed in an unnatural manner with artificial feeds mechanically or hand broadcast across the water surface. This traditional approach has increased the egg-to-smolt survival of hatchery-reared fish by an order of magnitude over that experienced by wild-reared salmon. However, once hatchery-reared fish are released into the wild their smolt-to-adult survival is usually much lower than wild-reared salmon. The reduced postrelease survival of hatchery-reared fish may stem from differences in their behavior and morphology compared to wild-reared salmon. After release, hatchery-reared fish are inefficient foragers and are often found with empty stomachs or stomachs filled with indigestible debris (Miller 1953, Hochachka 1961, Reimers 1963, Sosiak et al. 1979, Myers 1980, O'Grady 1983, Johnsen and Ugedal 1986). Their social behavior also differs, with hatchery-reared fish congregating at higher densities, being more aggressive, and displaying less territory fidelity than wild-reared fish (Fenderson et al. 1968, Bachman 1984, Swain and Riddell 1990). In the natural environment this results in hatchery-reared fish spending more time in high-risk aggressive behavior and less time in beneficial foraging behavior than their wild-reared counterparts. Hatchery-reared fish are also more surface oriented than wild-reared salmonids (Mason et al. 1967, Sosiak 1978). This increases their risk of being attacked by avian predators, such as kingfishers (Ceryle spp.), which search for fish near the surface. Although some of the differences between wild and hatchery-reared fish are innate (Reisenbichler and McIntyre 1977, Swain and Riddell 1990), many are conditioned and can be modified by altering the hatchery rearing environment. NATURES studies are aimed at developing a more natural salmon culture environment to prevent the development of these unnatural attributes in hatchery-reared fish. NATURES fish culture practices are already producing salmon with up to about 50% higher in-stream survival than conventionally-reared fish (Maynard et al. 1996b). When these techniques are incorporated into production releases, they should also translate into increased smolt-to-adult survival. Conservation and supplementation programs can use NATURES-reared salmonids to rebuild stocks currently listed as endangered and threatened into healthy self-sustaining runs more rapidly than traditional programs. Traditional production programs can also use high-survival NATURES-reared fish to reduce their impact on wild populations, while still meeting their adult mitigation goals.

Maynard, Desmond J.

2003-02-25T23:59:59.000Z

105

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

E-Print Network [OSTI]

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.

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

2014-10-23T23:59:59.000Z

106

Resonant relaxation in protoplanetary disks  

E-Print Network [OSTI]

Resonant relaxation is a novel form of two-body relaxation that arises in nearly Keplerian disks such as protoplanetary disks. Resonant relaxation does not affect the semimajor axes of the particles, but enhances relaxation of particle eccentricities and inclinations. The equilibrium state after resonant relaxation is a Rayleigh distribution, with the mean-square eccentricity and inclination inversely proportional to mass. The rate of resonant relaxation depends strongly on the precession rate of the disk. If the precession due to the disk's self-gravity is small compared to the total precession, then the relaxation is concentrated near the secular resonance between each pair of interacting bodies; on the other hand if the precession rate is dominated by the disk's self-gravity then relaxation occurs through coupling to the large-scale low-frequency m=1 normal modes of the disk. Depending on the disk properties, resonant relaxation may be either stronger or weaker than the usual non-resonant relaxation.

Scott Tremaine

1998-05-27T23:59:59.000Z

107

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

E-Print Network [OSTI]

Houses for early weaned piglets : influence of rearing on the floor or in batteries, temperature groups in order to determine the influence of rearing conditions (housing, room temperature) and feeding on the animals performances between weaning at 36 3 days and 70 days of age. Housing characteristics were

Paris-Sud XI, Universit de

108

REAR-SIDE POINT-CONTACTS BY INLINE THERMAL EVAPORATION OF ALUMINUM Christoph Mader  

E-Print Network [OSTI]

REAR-SIDE POINT-CONTACTS BY INLINE THERMAL EVAPORATION OF ALUMINUM Christoph Mader 1 , Jens Müller of point-contacted aluminum rear-sides for silicon solar cells that are metalized by inline thermal evaporation. We deposit aluminum layers of 2 µm thickness at dynamic deposition rates of 1.0, 2.9 and 5.0 µm

109

V2V Wireless Communication Protocol for Rear-End Collision Avoidance on Highways  

E-Print Network [OSTI]

vehicle crashes in the United States annually has never fallen below 35,000, and the number of persons crashes (both fatal and nonfatal), or more than 1.5 million crashes per year, are rear-end collisions [2]. In Washington State, for the year 2005, rear-end crashes were the leading type of collision on state highways

Roy, Sumit

110

Variations in gear fatigue life for different wind turbine braking strategies  

SciTech Connect (OSTI)

A large number of gearbox failures have occurred in the wind industry in a relatively short period, many because service loads were underestimated. High-torque transients that occur during starting and stopping are difficult to predict and may be overlooked in specifying gearbox design. Although these events comprise a small portion of total load cycles, they can be the most damaging. The severity of these loads varies dramatically with the specific configuration of the wind turbine. The large number of failures in Danish-designed Micon 65 wind turbines prompted this investigation. The high-speed and low-speed shaft torques were measured on a two-stage helical gearbox of a single Micon 65 turbine. Transient events and normal running loads were combined statistically to obtain a typical annual load spectrum. The pitting and bending fatigue lives of the gear teeth were calculated by using Miner's rule for four different high-speed shaft brake configurations. Each breaking scenario was run for both a high- and a low-turbulence normal operating load spectrum. The analysis showed increases in gear life by up to a factor of 25 when the standard high-speed shaft brake is replaced with a dynamic brake or modified with a damper. 9 refs., 9 figs., 3 tabs.

McNiff, B.P. (Second Wind, Inc., Somerville, MA (USA)); Musial, W.D. (Solar Energy Research Inst., Golden, CO (USA)); Errichello, R. (GEARTECH, Albany, CA (USA))

1991-06-01T23:59:59.000Z

111

Design Principles of a flywheel Regenerative Braking System (f-RBS) for Formula SAE type racecar and system testing on a Virtual Test Rig modeled on MSC ADAMS  

E-Print Network [OSTI]

momentum in the industry [4]. These vehicles (BEVs and HEVS) use electric motor/generator pairs to propel themselves and to recapture braking energy (electric RBS) and the power source is the battery. The regenerative braking system uses a generator..., aerodynamic and road losses. 4. Improvised Transmission design to reduce losses. 5. Hybrid and Alternative Energy Propulsion systems e.g. the Hybrid Electric Vehicle (HEV), the Fuel Cell Vehicle (FCV). 6. Recycling Braking energy Storage and reuse...

Pochiraju, Anirudh

2012-08-31T23:59:59.000Z

112

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

E-Print Network [OSTI]

be reduced by applying the PERC (passivated emitter and rear cell) solar cell design [8]. The following19.4% -EFFICIENT LARGE AREA REAR-PASSIVATED SCREEN-PRINTED SILICON SOLAR CELLS T. Dullweber*1 , S% in the near future. Keywords: Silicon Solar Cell, Screen Printing, Rear Passivation 1 Introduction About 80

113

Slow modes in Keplerian disks  

E-Print Network [OSTI]

Low-mass disks orbiting a massive body can support "slow" normal modes, in which the eigenfrequency is much less than the orbital frequency. Slow modes are lopsided, i.e., the azimuthal wavenumber m=1. We investigate the properties of slow modes, using softened self-gravity as a simple model for collective effects in the disk. We employ both the WKB approximation and numerical solutions of the linear eigenvalue equation. We find that all slow modes are stable. Discrete slow modes can be divided into two types, which we label g-modes and p-modes. The g-modes involve long leading and long trailing waves, have properties determined by the self-gravity of the disk, and are only present in narrow rings or in disks where the precession rate is dominated by an external potential. In contrast, the properties of p-modes are determined by the interplay of self-gravity and other collective effects. P-modes involve both long and short waves, and in the WKB approximation appear in degenerate leading/trailing pairs. Disks support a finite number---sometimes zero---of discrete slow modes, and a continuum of singular modes.

Scott Tremaine

2000-11-30T23:59:59.000Z

114

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

SciTech Connect (OSTI)

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.

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

1998-01-01T23:59:59.000Z

115

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

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

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:YearRound-UpHeatMulti-Dimensional Subject:Groundto Apply for Weatherization 7HybirdBraking System

116

E-Print Network 3.0 - asian child-rearing attitudes Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Princeton University Collection: Biology and Medicine 13 The New Dad: I th ll b d fIs there really a new breed of Summary: Many Men Want an Equal Share of the Child-rearing...

117

E-Print Network 3.0 - adult rearing diet Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

55:153168 (2004) 2004 Wiley-Liss, Inc. Summary: . The one study employing natural diets (Smith, 1960) used plants reared from seed on media vary- ing... controlled conditions,...

118

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

E-Print Network [OSTI]

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 ...

Yazicioglu, Tolga T

2008-01-01T23:59:59.000Z

119

Flight characteristics of pen-reared and wild prairie-chickens and an evaluation of a greenhouse to rear prairie-chickens  

E-Print Network [OSTI]

, Krauss et al. 1987, Roseberry et al. 1987, Leif 1994) have 4 shown that pen-reared birds had less fear of humans, were more approachable, and displayed improper hiding behavior (were more often seen in open areas) than their wild counterparts..., Hessler et al. 1970, Krauss et al. 1987, Roseberry et al. 1987, Leif 1994) have shown that pen-reared birds had less fear of humans, were more approachable, and displayed improper hiding behavior (were more often seen in open areas) than their wild...

Hess, Marc Frederick

2004-09-30T23:59:59.000Z

120

Why Do Disks Form Jets?  

E-Print Network [OSTI]

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.

D Lynden-Bell

2002-03-27T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


121

Rotational evolution of the Crab pulsar in the wind braking model  

E-Print Network [OSTI]

The pulsar wind model is updated by considering the effect of particle density and pulsar death. It can describe both the short term and long term rotational evolution of pulsars consistently. It is applied to model the rotational evolution of the Crab pulsar. The pulsar is spun down by a combination of magnetic dipole radiation and particle wind. The parameters of the Crab pulsar, including magnetic field, inclination angle, and particle density are calculated. The particle density in acceleration region is about 10^3 times the Goldreich-Julian charge density. The lower braking index between glitches is due to a larger particle density. This may be glitch induced magnetospheric activities in normal pulsars. Evolution of braking index and the Crab pulsar in P-Pdot diagram are calculated. The Crab pulsar will evolve from magnetic dipole radiation dominated case towards particle wind dominated case. Considering the effect of pulsar "death", the Crab pulsar (and other normal pulsars) will not evolve to the clust...

Kou, F F

2015-01-01T23:59:59.000Z

122

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 HomeNew YorkLouisiana Laws andDakota1 Cleanbutton highlighted

123

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 HomeNew YorkLouisiana Laws andDakota1 Cleanbutton highlightedButton

124

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 CenterEnergyAuthorization for(EV) Road User AssessmentNRELhighlightedButton

125

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

E-Print Network [OSTI]

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 ...

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

2010-01-01T23:59:59.000Z

126

Accretion Disks and Eruptive Phenomena  

E-Print Network [OSTI]

This paper describes eruptive phenomena in pre-main sequence stars. The eruptions of FU Orionis stars have much in common with outbursts in other accreting systems, such as dwarf novae and some symbiotic stars. These common features are best understood as increases in the rate material flows through an accretion disk. The spectroscopic properties, decay of the light curves, and outflow phenomena suggest that these outbursts arise from thermal instabilities in the disk. Available data and estimates for recurrence times indicate that young stars can accrete much, perhaps all, of their mass in FU Ori accretion events. Future observations can test this notion and place better constraints on the importance of eruptive events in the early life of a low mass star.

Scott J. Kenyon

1999-04-05T23:59:59.000Z

127

Enhanced quantum efficiency of amorphous silicon thin film solar cells with the inclusion of a rear-reflector thin film  

SciTech Connect (OSTI)

We investigated the growth mechanism of amorphous silicon thin films by implementing hot-wire chemical vapor deposition and fabricated thin film solar cell devices. The fabricated cells showed efficiencies of 7.5 and 8.6% for the samples without and with the rear-reflector decomposed by sputtering, respectively. The rear-reflector enhances the quantum efficiency in the infrared spectral region from 550 to 750?nm. The more stable quantum efficiency of the sample with the inclusion of a rear-reflector than the sample without the rear-reflector due to the bias effect is related to the enhancement of the short circuit current.

Park, Seungil [Department of Mechanical Engineering, Chonbuk National University, Jeonju 561-756 (Korea, Republic of); Energy Conversions Technology Center, Korea Institute of Industrial Technology, Cheonan 331-825 (Korea, Republic of); Yong Ji, Hyung; Jun Kim, Myeong; Hyeon Peck, Jong [Energy Conversions Technology Center, Korea Institute of Industrial Technology, Cheonan 331-825 (Korea, Republic of); Kim, Keunjoo, E-mail: kimk@chonbuk.ac.kr [Department of Mechanical Engineering, Chonbuk National University, Jeonju 561-756 (Korea, Republic of)

2014-02-17T23:59:59.000Z

128

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

SciTech Connect (OSTI)

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.

Maynard, Desmond J.

2001-09-13T23:59:59.000Z

129

Collapse of Magnetized Singular Isothermal Toroids: II. Rotation and Magnetic Braking  

E-Print Network [OSTI]

We study numerically the collapse of rotating, magnetized molecular cloud cores, focusing on rotation and magnetic braking during the main accretion phase of isolated star formation. Motivated by previous numerical work and analytic considerations, we idealize the pre-collapse core as a magnetized singular isothermal toroid, with a constant rotational speed everywhere. The collapse starts from the center, and propagates outwards in an inside-out fashion, satisfying exact self-similarity in space and time. For rotation rates and field strengths typical of dense low-mass cores, the main feature remains the flattening of the mass distribution along field lines -- the formation of a pseudodisk, as in the nonrotating cases. The density distribution of the pseudodisk is little affected by rotation. On the other hand, the rotation rate is strongly modified by pseudodisk formation. Most of the centrally accreted material reaches the vicinity of the protostar through the pseudodisk. The specific angular momentum can b...

Allen, A; Shu, F H

2003-01-01T23:59:59.000Z

130

E-Print Network 3.0 - accretion disks prospects Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

+ accretion disk. Left panel: Disks of various accretion, inner... disk hole, and inclination properties. ... Source: Hillenbrand, Lynne - Astronomy Department, California...

131

E-Print Network 3.0 - accretion disk contamination Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

+ accretion disk. Left panel: Disks of various accretion, inner... disk hole, and inclination properties. ... Source: Hillenbrand, Lynne - Astronomy Department, California...

132

E-Print Network 3.0 - accretion disk size Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

+ accretion disk. Left panel: Disks of various accretion, inner... disk hole, and inclination properties. ... Source: Hillenbrand, Lynne - Astronomy Department, California...

133

Sterrewacht Gas evolution in protoplanetary disks  

E-Print Network [OSTI]

Sterrewacht Leiden Gas evolution in protoplanetary disks W.F. Thi , E.F. van Dishoeck , G are surrounded by 10 ­10 M of gas+dust in disks with sizes of 100­400 AU. This material may form extrasolar planets. 3 Disks have also been imaged around Vega-like stars, but are thought to be gas­poor with "!#$ M

Zadelhoff, Gerd-Jan van

134

HEATING AND COOLING PROTOSTELLAR DISKS  

SciTech Connect (OSTI)

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.

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)

2011-05-10T23:59:59.000Z

135

Author's personal copy What can the braking indices tell us about the nature of pulsars?  

E-Print Network [OSTI]

additional torques by particle outflow or accretion disk, changes in inclination angle or magnetic field's personal copy pole radiation and relativistic particle flow/wind (Dar, 1999; Allen and Horvath, 2000; Xu and Qiao, 2001; Wu et al., 2003; Contopoulos et al., 2006), the models with changing inclination angles (e

Xu, Ren-Xin

136

Stellar-Mass-Dependent Disk Structure in Coeval Planet-Forming Disks  

E-Print Network [OSTI]

Previous studies suggest that the planet-forming disks around very-low-mass stars/brown dwarfs may be flatter than those around more massive stars, in contrast to model predictions of larger scale heights for gas-disks around lower-mass stars. We conducted a statistically robust study to determine whether there is evidence for stellar-mass-dependent disk structure in planet-forming disks. We find a statistically significant difference in the Spitzer/IRAC color distributions of disks around very-low-mass and low-mass stars all belonging to the same star-forming region, the Chamaeleon I star-forming region. We show that self consistently calculated disk models cannot fit the median spectral energy distributions (SEDs) of the two groups. These SEDs can be only explained by flatter disk models, consistent with the effect of dust settling in disks. We find that relative to the disk structure predicted for flared disks the required reduction in disk scale height is anti-correlated with the stellar mass, i.e. disks ...

Sz?cs, Lszl; Pascucci, Ilaria; Dullemond, Cornelis P

2010-01-01T23:59:59.000Z

137

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

E-Print Network [OSTI]

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...

Kuriachan, Indira

2006-08-16T23:59:59.000Z

138

Disk Accretion Onto High-Mass Planets  

E-Print Network [OSTI]

We analyze the nonlinear, two-dimensional response of a gaseous, viscous protoplanetary disk to the presence of a planet of one Jupiter mass (1 M_J) and greater that orbits a 1 solar mass star by using the ZEUS hydrodynamics code with high resolution near the planet's Roche lobe. The planet is assumed to be in a circular orbit about the central star and is not allowed to migrate. A gap is formed about the orbit of the planet, but there is a nonaxisymmetric flow through the gap and onto the planet. The gap partitions the disk into an inner (outer) disk that extends inside (outside) the planet's orbit. For a 1 M_J planet and typical disk parameters, the accretion through the gap onto the planet is highly efficient. For typical disk parameters, the mass doubling time scale is less than 10^5 years, considerably shorter than the disk lifetime. Following shocks near the L1 and L2 Lagrange points, disk material enters the Roche lobe in the form of two gas streams. Shocks occur within the Roche lobe as the gas streams collide, and shocks lead to rapid inflow towards the planet within much of planet's Roche lobe. Shocks also propagate in the inner and outer disks that orbit the star. For higher mass planets (of order 6 M_J), the flow rate onto the planet is considerably reduced, which suggests an upper mass limit to planets in the range of 10 M_J. This rate reduction is related to the fact that the gap width increases relative to the Roche (Hill sphere) radius with increasing planetary mass. The flow in the gap affects planetary migration. For the 1 M_J planet case, mass can penetrate from the outer disk to the inner disk, so that the inner disk is not depleted. The results suggest that most of the mass in gas giant planets is acquired by flows through gaps.

S. H. Lubow; M. Seibert; P. Artymowicz

1999-10-21T23:59:59.000Z

139

Research Report Long lasting effects of rearing by an ethanol-consuming dam  

E-Print Network [OSTI]

Research Report Long lasting effects of rearing by an ethanol-consuming dam on voluntary ethanol rats as subjects, we examined effects of exposure during weaning to a dam consuming ethanol on adolescents' later affinity for ethanol. In a preliminary experiment, we offered rat pups a choice between 8

Galef Jr., Bennett G.

140

Does Pathogen Spillover from Commercially Reared Bumble Bees Threaten Wild Pollinators?  

E-Print Network [OSTI]

Does Pathogen Spillover from Commercially Reared Bumble Bees Threaten Wild Pollinators? Michael C'); yet, we still have little understanding of the cause(s) of bee declines. Wild bumble bees (Bombus spp pathogen commonly found in commercial Bombus. We also monitored wild bumble bee populations near

Thomson, James D.

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


141

Diet-induced phenotypic plasticity in the skull morphology of hatchery-reared Florida  

E-Print Network [OSTI]

for many fish species, Florida largemouth bass, Micropterus salmoides flor- idanus (LeSeuer), reared, was retarded at this size. Post-release, the skulls of hatchery fish converged towards those of wild bass bass, Micropterus salmoides floridanus Un resumen en espan~ol se incluye detras del texto principal de

Motta, Philip J.

142

Development of a Natural Rearing System to Improve Supplemental Fish Quality, 1991-1995 Progress Report.  

SciTech Connect (OSTI)

In this report, the National Marine Fisheries Service (NMFS), in collaboration with the Bonneville Power Administration (BPA), the Washington State Department of Fish and Wildlife (WDFW), and the US Fish and Wildlife Service (USFWS), presents research findings and guidelines for development and evaluation of innovative culture techniques to increase postrelease survival of hatchery fish. The Natural Rearing Enhancement System (NATURES) described in this report is a collection of experimental approaches designed to produce hatchery-reared chinook salmon (Oncorhynchus tshawytscha) that exhibit wild-like behavior, physiology, and morphology. The NATURES culture research for salmonids included multiple tests to develop techniques such as: raceways equipped with cover, structure, and natural substrates to promote development of proper body camouflage coloration; feed-delivery systems that condition fish to orient to the bottom rather than the surface of the rearing vessel; predator conditioning of fish to train them to avoid predators; and supplementing diets with natural live foods to improve foraging ability. The underlying assumptions are that NATURES will: (1) promote the development of natural cryptic coloration and antipredator behavior; (2) increase postrelease foraging efficiency; (3) improve fish health and condition by alleviating chronic, artificial rearing habitat-induced stress; and (4) reduce potential genetic selection pressures induced by the conventional salmon culture environment. A goal in using NATURES is to provide quality fish for rebuilding depleted natural runs.

Maynard, Desmond J.; Flagg, Thomas A.; Mahnken, Conrad V.W.

1996-08-01T23:59:59.000Z

143

Quantitative Measures of Rearing And Spawning Habitat Characteristics For Stream-Dwelling Salmonids  

E-Print Network [OSTI]

for stream-dwelling salmonids: guidelines for habitat restoration. Province of British Columbia, MinistryQuantitative Measures of Rearing And Spawning Habitat Characteristics For Stream-Dwelling Salmonids: Guidelines For Habitat Restoration by E.R. Keeley and P.A. Slaney Watershed Restoration Project Report No. 4

Keeley, Ernest R.

144

COBE's Galactic Bar and Disk  

E-Print Network [OSTI]

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.

H. T. Freudenreich

1997-08-04T23:59:59.000Z

145

Turbine inter-disk cavity cooling air compressor  

DOE Patents [OSTI]

The inter-disk cavity between turbine rotor disks is used to pressurize cooling air. A plurality of ridges extend radially outwardly over the face of the rotor disks. When the rotor disks are rotated, the ridges cause the inter-disk cavity to compress air coolant flowing through the inter-disk cavity en route to the rotor blades. The ridges eliminate the need for an external compressor to pressurize the air coolant.

Chupp, Raymond E. (Oviedo, FL); Little, David A. (Oviedo, FL)

1998-01-01T23:59:59.000Z

146

Turbine inter-disk cavity cooling air compressor  

DOE Patents [OSTI]

The inter-disk cavity between turbine rotor disks is used to pressurize cooling air. A plurality of ridges extend radially outwardly over the face of the rotor disks. When the rotor disks are rotated, the ridges cause the inter-disk cavity to compress air coolant flowing through the inter-disk cavity en route to the rotor blades. The ridges eliminate the need for an external compressor to pressurize the air coolant. 5 figs.

Chupp, R.E.; Little, D.A.

1998-01-06T23:59:59.000Z

147

Molecular Hydrogen Emission from Protoplanetary Disks  

E-Print Network [OSTI]

We have modeled self-consistently the density and temperature profiles of gas and dust in protoplanetary disks, taking into account irradiation from a central star. Making use of this physical structure, we have calculated the level populations of molecular hydrogen and the line emission from the disks. As a result, we can reproduce the observed strong line spectra of molecular hydrogen from protoplanetary disks, both in the ultraviolet (UV) and the near-infrared, but only if the central star has a strong UV excess radiation.

H. Nomura; T. J. Millar

2005-05-06T23:59:59.000Z

148

Resolving Molecular Line Emission from Protoplanetary Disks: Observational Prospects for Disks Irradiated by Infalling Envelopes  

E-Print Network [OSTI]

Molecular line observations that could resolve protoplanetary disks of ~100 AU both spatially and kinematically would be a useful tool to unambiguously identify these disks and to determine their kinematical and physical characteristics. In this work we model the expected line emission from a protoplanetary disk irradiated by an infalling envelope, addressing the question of its detectability with subarcsecond resolution. We adopt a previously determined disk model structure that gives a continuum spectral energy distribution and a mm intensity spatial distribution that are consistent with observational constraints of HL Tau. An analysis of the capability of presently working and projected interferometers at mm and submm wavelengths shows that molecular transitions of moderate opacity at these wavelengths (e.g., C17O lines) are good candidates for detecting disk lines at subarcsecond resolution in the near future. We suggest that, in general, disks of typical Class I sources will be detectable.

Jose F. Gomez; Paola D'Alessio

1999-12-02T23:59:59.000Z

149

Resolving Molecular Line Emission from Protoplanetary Disks Observational Prospects for Disks Irradiated by Infalling Envelopes  

E-Print Network [OSTI]

Molecular line observations that could resolve protoplanetary disks of ~100 AU both spatially and kinematically would be a useful tool to unambiguously identify these disks and to determine their kinematical and physical characteristics. In this work we model the expected line emission from a protoplanetary disk irradiated by an infalling envelope, addressing the question of its detectability with subarcsecond resolution. We adopt a previously determined disk model structure that gives a continuum spectral energy distribution and a mm intensity spatial distribution that are consistent with observational constraints of HL Tau. An analysis of the capability of presently working and projected interferometers at mm and submm wavelengths shows that molecular transitions of moderate opacity at these wavelengths (e.g., C17O lines) are good candidates for detecting disk lines at subarcsecond resolution in the near future. We suggest that, in general, disks of typical Class I sources will be detectable.

Gomes, J F; Gomez, Jose F.; Alessio, Paola D'

1999-01-01T23:59:59.000Z

150

Hydraulic/Shock-Jumps in Protoplanetary Disks  

E-Print Network [OSTI]

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.

A. C. Boley; R. H. Durisen

2006-03-10T23:59:59.000Z

151

Gas Phase diagnostics of Protoplanetary disk extension  

E-Print Network [OSTI]

We investigate the potential of using ratios of fine structure and near-infrared forbidden line transitions of atomic carbon to diagnose protoplanetary disk extension. Using results from 2D photoionisation and radiative transfer modeling of a realistic protoplanetary disk structure irradiated by X-rays from a T Tauri star, we obtain theoretical emission maps from which we construct radial distributions of the strongest emission lines produced in the disk. We show that ratios of fine structure to near-infrared forbidden line emission of atomic carbon are especially promising to constrain the minimum size of gaseous protoplanetary disks. While theoretically viable, the method presents a number of observational difficulties that are also discussed here.

B. Ercolano; J. J. Drake; C. J. Clarke

2008-11-21T23:59:59.000Z

152

Signpost of Multiple Planets in Debris Disks  

E-Print Network [OSTI]

We review the nearby debris disk structures revealed by multi-wavelength images from Spitzer and Herschel, and complemented with detailed spectral energy distribution modeling. Similar to the definition of habitable zones around stars, debris disk structures should be identified and characterized in terms of dust temperatures rather than physical distances so that the heating power of different spectral type of stars is taken into account and common features in disks can be discussed and compared directly. Common features, such as warm (~150 K) dust belts near the water-ice line and cold (~50 K) Kuiper-belt analogs, give rise to our emerging understanding of the levels of order in debris disk structures and illuminate various processes about the formation and evolution of exoplanetary systems. In light of the disk structures in the debris disk twins (Vega and Fomalhaut), and the current limits on the masses of planetary objects, we suggest that the large gap between the warm and cold dust belts is the best si...

Su, Kate Y L

2013-01-01T23:59:59.000Z

153

Dynamics of the Disks of Nearby Galaxies  

E-Print Network [OSTI]

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'.

B. Fuchs

2008-10-20T23:59:59.000Z

154

A closed-loop quasi-optimal dynamic braking resistor and shunt reactor control strategy for transient stability  

SciTech Connect (OSTI)

A control strategy for dynamic braking resistor and shunt reactor is proposed for stabilization of power systems when subject to large disturbances. The time optimal control is derived as a function of synchronous machine power, its rotor angular position and speed deviation. The response for a single machine system with the proposed control has been compared with that from the time optimal solution obtained through the steepest descent method. The strategy has also been tested on two multimachine systems. Results indicate that the proposed strategy provides a simple and effective method of stabilization under transient emergency conditions.

Rahim, A.H.M.A.; Alamgir, D.A.H.

1988-08-01T23:59:59.000Z

155

Hadron collisions at ultrahigh energies: black disk or resonant disk modes?  

E-Print Network [OSTI]

The analysis of current ultrahigh energy data for hadronic total cross sections and diffractive scattering cross sections points to a steady growth of the optical density with energy for elastic scattering amplitudes in the impact parameter space, $b$. At LHC energy the profile function of the $pp$-scattering amplitude, $T(b)$, reaches the black disk limit at small $b$. Two scenarios are possible at larger energies, $\\sqrt{s}\\ga 100$ TeV. First, the profile function gets frozen in the black disk limit, $T(b)\\simeq 1$ while the radius of the black disk $R_{black\\;disk}$ is increasing with $\\sqrt s$, providing $\\sigma_{tot}\\sim \\ln^2s$, $\\sigma_{el}\\sim \\ln^2s$, $\\sigma_{inel}\\sim \\ln^2s$. In another scenario the profile function continues to grow at $\\sqrt{s}\\ga 100$ TeV approaching the maximal value, $T(b)\\simeq 2$, that means the resonant disk mode. We discuss features of the resonant disk mode when the disk radius, $R_{resonant\\;disk}\\,$, increases providing the growth of the total and elastic cross sections $\\sigma_{tot}\\sim \\ln^2s$, $\\sigma_{el}\\sim \\ln^2s$, but a more slow increase of inelastic cross section, $\\sigma_{inel}\\sim \\ln s$.

V. V. Anisovich; V. A. Nikonov; J. Nyiri

2014-08-11T23:59:59.000Z

156

Disk-cylinder and disk-sphere nanoparticles from block copolymer blend solution construction  

SciTech Connect (OSTI)

Researchers strive to produce nanoparticles with complexity in composition and structure. Although traditional spherical, cylindrical and membranous, or planar, nanostructures are ubiquitous, scientists seek more complicated geometries for potential functionality. Here we report the simple solution construction of multigeometry nanoparticles, disk-sphere and diskcylinder, through a straightforward, molecular-level, blending strategy with binary mixtures of block copolymers. The multigeometry nanoparticles contain disk geometry in the core with either spherical patches along the disk periphery in the case of disk-sphere particles or cylindrical edges and handles in the case of the disk-cylinder particles. The portions of different geometry in the same nanoparticles contain different core block chemistry, thus also defining multicompartments in the nanoparticles. Although the block copolymers chosen for the blends are important for the definition of the final hybrid particles, the control of the kinetic pathway of assembly is critical for successful multigeometry particle construction.

Zhu, Jiahua [ORNL] [ORNL; Zhang, Shiyi [Texas A& M University] [Texas A& M University; Zhang, Ke [Northeastern University] [Northeastern University; Wang, Xiaojun [ORNL] [ORNL; Mays, Jimmy [ORNL] [ORNL; Wooley, Karen L [ORNL] [ORNL; Pochan, Darrin [University of Delaware] [University of Delaware

2013-01-01T23:59:59.000Z

157

The Galactic thick and thin disks: differences in evolution  

E-Print Network [OSTI]

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.

T. V. Nykytyuk; T. V. Mishenina

2006-05-26T23:59:59.000Z

158

E-Print Network 3.0 - accretion disk signatures Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

wind to disk accretion rates, the viscosity in the disk... Accretion Disk Evolution with Wind Infall II. Results of 3D Hydrodynamical Simulations... how the evolution and...

159

Signatures of Planets in Spatially Unresolved Disks  

E-Print Network [OSTI]

Main sequence stars are commonly surrounded by debris disks, composed of cold dust continuously replenished by a reservoir of undetected dust-producing planetesimals. In a planetary system with a belt of planetesimals (like the Solar System's Kuiper Belt) and one or more interior giant planets, the trapping of dust particles in the mean motion resonances with the planets can create structure in the dust disk, as the particles accumulate at certain semimajor axes. Sufficiently massive planets may also scatter and eject dust particles out of a planetary system, creating a dust depleted region inside the orbit of the planet. In anticipation of future observations of spatially unresolved debris disks with the Spitzer Space Telescope, we are interested in studying how the structure carved by planets affects the shape of the disk's spectral energy distribution (SED), and consequently if the SED can be used to infer the presence of planets. We numerically calculate the equilibrium spatial density distributions and SEDs of dust disks originated by a belt of planetesimals in the presence of interior giant planets in different planetary configurations, and for a representative sample of chemical compositions. The dynamical models are necessary to estimate the enhancement of particles near the mean motion resonances with the planets, and to determine how many particles drift inside the planet's orbit. Based on the SEDs and predicted $\\it{Spitzer}$ colors we discuss what types of planetary systems can be distinguishable from one another and the main parameter degeneracies in the model SEDs.

A. Moro-Martin; S. Wolf; R. Malhotra

2005-06-27T23:59:59.000Z

160

Variational thermodynamics of relativistic thin disks  

E-Print Network [OSTI]

We present a relativistic model describing a thin disk system composed of two fluids. The system is surrounded by a halo in the presence of a non-trivial electromagnetic field. We show that the model is compatible with the variational multi-fluid thermodynamics formalism, allowing us to determine all the thermodynamic variables associated with the matter content of the disk. The asymptotic behaviour of these quantities indicates that the single fluid interpretation should be abandoned in favour of a two-fluid model.

A C Gutirrez-Pieres; C S Lopez-Monsalvo; H Quevedo

2014-08-18T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


161

The orbital evolution of planets in disks  

E-Print Network [OSTI]

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.

Wilhelm Kley

2000-04-04T23:59:59.000Z

162

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]

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

Carpick, Robert W.

163

Vehicle System Dynamics, Vol. 26, No.4, October 1996, pp.301-320. Traction/Braking Force Distribution for Optimal Longitudinal  

E-Print Network [OSTI]

as the desired level of vehicle yaw motion, and the control system was designed to follow the yaw motion commandVehicle System Dynamics, Vol. 26, No.4, October 1996, pp.301-320. Traction/Braking Force in the past twenty years through the use of electronic devices. Four-wheel-steering (4WS) systems have been

Peng, Huei

164

artemis disk global: Topics by E-print Network  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Summary: Numerical simulations of planet-disk interactions are usually performed with hydro-codes that -- because they consider only an annulus of the disk, over a 2D grid -- can...

165

UNVEILING THE STRUCTURE OF PRE-TRANSITIONAL DISKS  

SciTech Connect (OSTI)

In the past few years, several disks with inner holes that are relatively empty of small dust grains have been detected and are known as transitional disks. Recently, Spitzer has identified a new class of 'pre-transitional disks' with gaps based on near-infrared photometry and mid-infrared spectra; these objects have an optically thick inner disk separated from an optically thick outer disk by an optically thin disk gap. A near-infrared spectrum provided the first confirmation of a gap in the pre-transitional disk of LkCa 15 by verifying that the near-infrared excess emission in this object was due to an optically thick inner disk. Here, we investigate the difference between the nature of the inner regions of transitional and pre-transitional disks using the same veiling-based technique to extract the near-infrared excess emission above the stellar photosphere. However, in this work we use detailed disk models to fit the excess continua as opposed to the simple blackbody fits previously used. We show that the near-infrared excess emission of the previously identified pre-transitional disks of LkCa 15 and UX Tau A in the Taurus cloud as well as the newly identified pre-transitional disk of ROX 44 in Ophiuchus can be fit with an inner disk wall located at the dust destruction radius. We also present detailed modeling of the broadband spectral energy distributions of these objects, taking into account the effect of shadowing by the inner disk on the outer disk, but considering the finite size of the star, unlike other recent treatments. The near-infrared excess continua of these three pre-transitional disks, which can be explained by optically thick inner disks, are significantly different from that of the transitional disks of GM Aur, whose near-infrared excess continuum can be reproduced by emission from sub-micron-sized optically thin dust, and DM Tau, whose near-infrared spectrum is consistent with a disk hole that is relatively free of small dust. The structure of pre-transitional disks may be a sign of young planets forming in these disks and future studies of pre-transitional disks will provide constraints to aid in theoretical modeling of planet formation.

Espaillat, C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); D'Alessio, P. [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, Morelia, Michoacan, Mexico 58089 (Mexico); Hernandez, J. [Centro de Investigaciones de Astronomia (CIDA), Merida, 5101-A (Venezuela, Bolivarian Republic of); Nagel, E. [Departamento de Astronomia, Universidad de Guanajuato, Guanajuato, Gto, Mexico 36240 (Mexico); Luhman, K. L. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States); Watson, D. M. [Department of Physics and Astronomy, University of Rochester, NY 14627-0171 (United States); Calvet, N.; McClure, M. [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Muzerolle, J., E-mail: cespaillat@cfa.harvard.ed, E-mail: p.dalessio@crya.unam.m, E-mail: jesush@cida.v, E-mail: erick@astro.ugto.m, E-mail: kluhman@astro.psu.ed, E-mail: dmw@pas.rochester.ed, E-mail: ncalvet@umich.ed, E-mail: melisma@umich.ed, E-mail: muzerol@stsci.ed [Space Telescope Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2010-07-01T23:59:59.000Z

166

A Flared, Orbiting, Dusty Disk Around HD 233517  

E-Print Network [OSTI]

We find that the infrared excess around HD 233517, a first ascent red giant, can be naturally explained if the star possesses an orbiting, flared dusty disk. We estimate that the outer radius of this disk is 45 AU and that the total mass within the disk is about 0.01 the mass of the Sun. We speculate that this disk is the result of the engulfment of a low mass companion star that occurred when HD 233517 became a red giant.

M. Jura

2002-09-13T23:59:59.000Z

167

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

SciTech Connect (OSTI)

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.

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

1995-11-01T23:59:59.000Z

168

Patterned Magnetic Nanostructures and Quantized Magnetic Disks  

E-Print Network [OSTI]

, opens up new opportunities for engineering innovative magnetic materials and devices, developing ultra of magnetic nanostructures as small as 10 nm; 2) engineering of unique magnetic properties (such as domainPatterned Magnetic Nanostructures and Quantized Magnetic Disks STEPHEN Y. CHOU Invited Paper

169

MPEG-aware disk storage system  

E-Print Network [OSTI]

In the past decades the demand for systems that can process and deliver massive amount of storage has increased. Multimedia applications such as streaming audio and video require large amounts of data to be read from disk and processed for timely...

Ren, Qian

2000-01-01T23:59:59.000Z

170

Dual Accretion Disks in Alternate Gravity Theories  

E-Print Network [OSTI]

The interior of gravitationally collapsed objects in alternate theories of gravity in which event horizons and singularities do not occur in strong field gravity were generically investigated. These objects, called red holes, were found to contain dynamic configurations of matter, radiation and spacetime similar to inside out accretion disks well inside the photon orbit. Applications to astrophysical phenomena are briefly described.

James S. Graber

1997-12-15T23:59:59.000Z

171

Automated Design, Analysis, and Optimization of Turbomachinery Disks  

E-Print Network [OSTI]

Automated Design, Analysis, and Optimization of Turbomachinery Disks A thesis submitted of Cincinnati June 2008 Committee Chair: Dr. Mark G. Turner #12;#12;ABSTRACT Turbomachinery disks are used weight. Proper design and optimization of turbomachinery disks is an important topic that could yield

Cincinnati, University of

172

Geodesic Disks and Clustering in a Simple Magdalene G. Borgelt  

E-Print Network [OSTI]

Geodesic Disks and Clustering in a Simple Polygon Magdalene G. Borgelt Marc van Kreveld Jun Luo.cs.uu.nl ISSN: 0924-3275 #12;Geodesic Disks and Clustering in a Simple Polygon Magdalene G. Borgelt European points lying in the interior of P. A geodesic disk GD(p, r) with center p and radius r is the set

Utrecht, Universiteit

173

On the Solar System-Debris Disk Connecction  

E-Print Network [OSTI]

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.

Amaya Moro-Martin

2007-12-14T23:59:59.000Z

174

Evolution of Giant Planets in Eccentric Disks  

E-Print Network [OSTI]

We investigate the interaction between a giant planet and a viscous circumstellar disk by means of high-resolution, two-dimensional hydrodynamical simulations. We consider planet masses that range from 1 to 3 Jupiter masses (Mjup) and initial orbital eccentricities that range from 0 to 0.4. We find that a planet can cause eccentricity growth in a disk region adjacent to the planet's orbit, even if the planet's orbit is circular. Disk-planet interactions lead to growth in a planet's orbital eccentricity. The orbital eccentricities of a 2 Mjup and a 3 Mjup planet increase from 0 to 0.11 within about 3000 orbits. Over a similar time period, the orbital eccentricity of a 1 Mjup planet grows from 0 to 0.02. For a case of a 1 Mjup planet with an initial eccentricity of 0.01, the orbital eccentricity grows to 0.09 over 4000 orbits. Radial migration is directed inwards, but slows considerably as a planet's orbit becomes eccentric. If a planet's orbital eccentricity becomes sufficiently large, e > ~0.2, migration can reverse and so be directed outwards. The accretion rate towards a planet depends on both the disk and the planet orbital eccentricity and is pulsed over the orbital period. Planet mass growth rates increase with planet orbital eccentricity. For e~0.2 the mass growth rate of a planet increases by approximately 30% above the value for e=0. For e > ~0.1, most of the accretion within the planet's Roche lobe occurs when the planet is near the apocenter. Similar accretion modulation occurs for flow at the inner disk boundary which represents accretion toward the star.

Gennaro D'Angelo; Stephen H. Lubow; Matthew R. Bate

2006-08-17T23:59:59.000Z

175

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

E-Print Network [OSTI]

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.

E. T. Vishniac

1993-09-28T23:59:59.000Z

176

Rings in the Planetesimal Disk of Beta Pic  

E-Print Network [OSTI]

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.

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

2000-01-13T23:59:59.000Z

177

Disk Evolution in Young Binaries: from Observations to Theory  

E-Print Network [OSTI]

The formation of a binary system surrounded by disks is the most common outcome of stellar formation. Hence studying and understanding the formation and the evolution of binary systems and associated disks is a cornerstone of star formation science. Moreover, since the components within binary systems are coeval and the sizes of their disks are fixed by the tidal truncation of their companion, binary systems provide an ideal "laboratory" in which to study disk evolution under well defined boundary conditions. In this paper, we review observations of several inner disk diagnostics in multiple systems, including hydrogen emission lines (indicative of ongoing accretion), $K-L$ and $K-N$ color excesses (evidence of warm inner disks), and polarization (indicative of the relative orientations of the disks around each component). We examine to what degree these properties are correlated within binary systems and how this degree of correlation depends on parameters such as separation and binary mass ratio. These findings will be interpreted both in terms of models that treat each disk as an isolated reservoir and those in which the disks are subject to re-supply from some form of circumbinary reservoir, the observational evidence for which we will also critically review. The planet forming potential of multiple star systems is discussed in terms of the relative lifetimes of disks around single stars, binary primaries and binary secondaries. Finally, we summarize several potentially revealing observational problems and future projects that could provide further insight into disk evolution in the coming decade

J. -L. Monin; C. J. Clarke; L. Prato; C. McCabe

2006-04-03T23:59:59.000Z

178

Turbulence driven diffusion in protoplanetary disks - chemical effects in the outer disk  

E-Print Network [OSTI]

The dynamics and chemistry of protostellar disks are likely to be intricately linked, with dynamical processes altering the chemical composition, and chemistry, in turn, controlling the ionization structure and hence the ability of the magneto-rotational instability to drive the disk turbulence. Here we present the results from the first chemical models of the outer regions (R > 100 AU) of protoplanetary disks to consider the effects of turbulence driven diffusive mixing in the vertical direction. We show that vertical diffusion can greatly affect the column densities of many species, increasing them by factors of up to two orders of magnitude. Previous disk models have shown that disks can be divided into three chemically distinct layers, with the bulk of the observed molecular emission coming from a region between an atomic/ionic layer on the surface of the disk and the midplane regoin where the bulk of molecules are frozen onto grains. Diffusion retains this three layer structure, but increases the depth of the molecular layer by bringing atoms and atomic ions form by photodissociation in the surface layers into the shielded molecular layer where molecules can reform. For other species, notably NH3 and N2H+, the column densities are relatively unaffected by diffusion. These species peak in abundance near the midplane where most other molecules are heavily depleted, rather than in the molecular layer above. Diffusion only affects the abundances of those molecules with peak abundances in the molecular layer. We find that diffusion does not affect the ionization fraction of the disk. We compare the calculated column densities to observations of DM Tau, LkCa 15 and TW Hya and find good agreement for many molecules with a diffusion coefficient of 1e18 cm^2 s^-1.

K. Willacy; W. D. Langer; M. Allen; G. Bryden

2006-03-03T23:59:59.000Z

179

SPH simulations of tidally unstable accretion disks in cataclysmic variables  

E-Print Network [OSTI]

We numerically study the precessing disk model for superhump in the SU~UMa subclass of cataclysmic variables, using a two dimensional SPH code specifically designed for thin disk problems. Two disk simulations for a binary with mass ratio $q=\\frac{3}{17}$ (similar to OY~Car) are performed, in order to investigate the Lubow (1991 a,b) tidal resonance instability mechanism. In the first calculation, a disk evolves under steady mass transfer from $L_1$. In the second simulation, mass is added in Keplerian orbit to the inner disk. The two disks follow similar evolutionary paths. However the $L_1$ stream-disk interaction is found to slow the disk's radial expansion and to circularise gas orbits. The initial eccentricity growth in our simulations is exponential at a rate slightly less than predicted by Lubow (1991a). We do not observe a clearing of material from the resonance region via the disk's tidal response to the $m=2$ component of the binary potential as was described in Lubow (1992). Instead the $m=2$ response weakens as the disk eccentricty increases. Both disks reach an eccentric equilibrium state, in which they undergo prograde precession. The rate of viscous energy dissipation in the disks has a periodic excess with a period matching the disk's rotation. The source is identified as a large region in the outer disk, and the mechanism by which it is produced is identified. The time taken for the periodic excess to develop is consistent with the first appearance of superhumps in a superoutburst.

James R. Murray

1995-11-08T23:59:59.000Z

180

Paru dans Child Abuse and Neglect, 1997, 21, (10):911-927. ADULT OUTCOME OF CHILDREN REARED  

E-Print Network [OSTI]

1 Paru dans Child Abuse and Neglect, 1997, 21, (10):911-927. ADULT OUTCOME OF CHILDREN REARED manuscript, published in "Child Abuse & Neglect 1997;21(10):911-927" #12;2 Abstract : Objective: To study with a stable care environment. An other aim was to determine predictive factors for maladjusted psycho

Paris-Sud XI, Université de

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181

Safety First Safety Last Safety Always Accessible areas within the swing radius of the rear of the  

E-Print Network [OSTI]

Safety First Safety Last Safety Always Accessible areas within the swing radius of the rear is permissible to meet the OSHA barricade requirement. Crane Swing Radius Safety Tip #12 Better to be dead sure on the reverse side of this safety tip sheet. Please refrain from reading the information verbatim

Minnesota, University of

182

Response to IRSP. Project ID 35027: Evaluation of Two Captive Rearing Methods for Assisting with Recovery of Naturally Spawning  

E-Print Network [OSTI]

general procedures cited by Paul Moran and Robin Waples (P.I's.) under Project No. 198909600. The USFWSResponse to IRSP. Project ID 35027: Evaluation of Two Captive Rearing Methods for Assisting. We will store the fin clips at room temperature prior to DNA extraction. Procedures for DNA

183

Massive Disks in Low Surface Brightness Galaxies  

E-Print Network [OSTI]

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.

B. Fuchs

2002-09-09T23:59:59.000Z

184

Secular Evolution of the Galactic Disk  

E-Print Network [OSTI]

In the solar-neighbourhood, older stars have larger random velocities than younger ones. It is argued that the increase in velocity dispersion with time is predominantly a gradual process rather than one induced by discrete events such as minor mergers. Ephemeral spiral arms seem to be the fundamental drivers of disk heating, although scattering by giant molecular clouds plays an important moderating role. In addition to heating the disk, spiral arms cause stars' guiding centres to diffuse radially. The speed of this diffusion is currently controversial. Data from the Hipparcos satellite has made it clear that the Galaxy is by no means in a steady state. This development enormously increases the complexity of the models required to account for the data. There are preliminary indications that we see in the local phase-space distribution the dynamical footprints of long-dissolved spiral waves.

James Binney

2000-09-20T23:59:59.000Z

185

Galactosynthesis: Halo Histories, Star Formation, and Disks  

E-Print Network [OSTI]

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.

Ari Buchalter; Raul Jimenez; Marc Kamionkowski

2000-06-01T23:59:59.000Z

186

Dynamical Constraints on Disk Galaxy Formation  

E-Print Network [OSTI]

The rotation curves of disk galaxies exhibit a number of striking regularities. The amplitude of the rotation is correlated with luminosity (Tully-Fisher), the shape of the rotation curve is well predicted by the luminous mass distribution, and the magnitude of the mass discrepancy increases systematically with decreasing centripetal acceleration. These properties indicate a tight connection between light and mass, and impose strong constraints on theories of galaxy formation.

Stacy McGaugh

1999-09-27T23:59:59.000Z

187

Disk-Planet Interactions During Planet Formation  

E-Print Network [OSTI]

The discovery of close orbiting extrasolar giant planets led to extensive studies of disk planet interactions and the forms of migration that can result as a means of accounting for their location. Early work established the type I and type II migration regimes for low mass embedded planets and high mass gap forming planets respectively. While providing an attractive means of accounting for close orbiting planets intially formed at several AU, inward migration times for objects in the earth mass range were found to be disturbingly short, making the survival of giant planet cores an issue. Recent progress in this area has come from the application of modern numerical techniques which make use of up to date supercomputer resources. These have enabled higher resolution studies of the regions close to the planet and the initiation of studies of planets interacting with disks undergoing MHD turbulence. This work has led to indications of how the inward migration of low to intermediate mass planets could be slowed down or reversed. In addition, the possibility of a new very fast type III migration regime, that can be directed inwards or outwards, that is relevant to partial gap forming planets in massive disks has been investigated.

J. C. B. Papaloizou; R. P. Nelson; W. Kley; F. S. Masset; P. Artymowicz

2006-03-08T23:59:59.000Z

188

INFRARED VARIABILITY OF EVOLVED PROTOPLANETARY DISKS: EVIDENCE FOR SCALE HEIGHT VARIATIONS IN THE INNER DISK  

SciTech Connect (OSTI)

We present the results of a multi-wavelength multi-epoch survey of five evolved protoplanetary disks in the IC 348 cluster that show significant infrared variability. Using 3-8 {mu}m and 24 {mu}m photometry along with 5-40 {mu}m spectroscopy from the Spitzer Space Telescope, as well as ground-based 0.8-5 {mu}m spectroscopy, optical spectroscopy, and near-infrared photometry, covering timescales of days to years, we examine the variability in the disk, stellar, and accretion flux. We find substantial variations (10%-60%) at all infrared wavelengths on timescales of weeks to months for all of these young stellar objects. This behavior is not unique when compared to other cluster members and is consistent with changes in the structure of the inner disk, most likely scale height fluctuations on a dynamical timescale. Previous observations, along with our near-infrared photometry, indicate that the stellar fluxes are relatively constant; stellar variability does not appear to drive the large changes in the infrared fluxes. Based on our near-infrared spectroscopy of the Pa{beta} and Br{gamma} lines we find that the accretion rates are variable in most of the evolved disks but the overall rates are probably too small to cause the infrared variability. We discuss other possible physical causes for the variability, including the influence of a companion, magnetic fields threading the disk, and X-ray flares.

Flaherty, K. M.; Rieke, G. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Muzerolle, J. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States); Gutermuth, R. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Balog, Z. [Max-Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Herbst, W. [Department of Astronomy, Wesleyan University, Middletown, CT 06459 (United States); Megeath, S. T. [Department of Physics and Astronomy, University of Toledo, Toledo, OH (United States); Kun, M., E-mail: kflaherty@as.arizona.edu [Konkoly Observatory, Konkoly Thege ut 15-17, H-1121 Budapest (Hungary)

2012-03-20T23:59:59.000Z

189

The Differential Lifetimes of Protostellar Gas and Dust Disks  

E-Print Network [OSTI]

We construct a protostellar disk model that takes into account the combined effect of viscous evolution, photoevaporation and the differential radial motion of dust grains and gas. For T Tauri disks, the lifetimes of dust disks that are mainly composed of millimeter sized grains are always shorter than the gas disks' lifetimes, and become similar only when the grains are fluffy (density 10 AU), without strong signs of gas accretion nor of millimeter thermal emission from the dust. For Herbig AeBe stars, the strong photoevaporation clears the inner disks in 10^6 yr, before the dust grains in the outer disk migrate to the inner region. In this case, the grains left behind in the outer gas disk accumulate at the disk inner edge (at 10-100 AU from the star). The dust grains remain there even after the entire gas disk has been photoevaporated, and form a gas-poor dust ring similar to that observed around HR 4796A. Hence, depending on the strength of the stellar ionizing flux, our model predicts opposite types of products around young stars. For low mass stars with a low photoevaporation rate, dust-poor gas disks with an inner hole would form, whereas for high mass stars with a high photoevaporation rate, gas-poor dust rings would form. This prediction should be examined by observations of gas and dust around weak line T Tauri stars and evolved Herbig AeBe stars.

Taku Takeuchi; C. J. Clarke; D. N. C. Lin

2005-03-22T23:59:59.000Z

190

Magnetic Rotator Winds and Keplerian Disks of Hot Stars  

E-Print Network [OSTI]

We consider rotating magnetic stars with winds and disks. We establish a theorem that relates the angular velocity of a disk region with no meridional motion to the angular velocity of the star. Also, we show that for a given value of the magnetic field strength, if the rotation rate is too high or the flow velocity into the shock boundary is too low, a Keplerian disk region will not be formed. We develop a model for the formation of disks in magnetic rotators through the processes of fill-up and diffusion into Keplerian orbits. At the end of the fill-up stage the density of the disk increases significantly and the magnetic force in the disk becomes negligible. We derive analytical expressions for the inner and outer radii of Keplerian disks in terms of the stellar rotation rate. A disk can form if the meridional component Bm of the field at the stellar surface is larger than a minimum value. The radial extent of the Keplerian region becomes larger for larger values of Bm and is largest when Bm equals an optimal value. The strengths of the minimum fields required for Keplerian disk formation in B-type stars varies from order 1G to 10G. In O-type stars they must be of order 500G. Also, we suggest that the stellar magnetic fields may be affected by rotationally driven meridional circulation leading to some of the the observed variations of disks with time.

M. Maheswaran

2003-04-30T23:59:59.000Z

191

Angular Momentum Transport in Simulations of Accretion Disks  

E-Print Network [OSTI]

In this paper we briefly discuss the ways in which angular momentum transport is included in simulations of non-self-gravitating accretion disks, concentrating on disks in close binaries. Numerical approaches fall in two basic categories; particle based Lagrangian schemes, and grid based Eulerian techniques. Underlying the choice of numerical technique are assumptions that are made about disk physics, in particular about the angular momentum transport mechanism. Grid-based simulations have generally been of hot, relatively inviscid disks whereas particle-based simulations are more commonly of cool, viscous disks. Calculations of the latter type have been instrumental in developing a model for the superhump phenomenon. We describe how we use an artificial viscosity term to introduce angular momentum transport into our smoothed particle hydrodynamics (SPH) disk code.

James Rhys Murray

1997-03-10T23:59:59.000Z

192

MEASURING PROTOPLANETARY DISK ACCRETION WITH H I PFUND {beta}  

SciTech Connect (OSTI)

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.

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)

2013-05-20T23:59:59.000Z

193

accretion disk winds: Topics by E-print Network  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

and can obtain radiatively driven winds accelerated up to the it relativistic speed. For less luminous cases, disk winds are transonic types passing through saddle type...

194

accretion disk wind: Topics by E-print Network  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

and can obtain radiatively driven winds accelerated up to the it relativistic speed. For less luminous cases, disk winds are transonic types passing through saddle type...

195

Planet Shadows in Protoplanetary Disks. I: Temperature Perturbations  

E-Print Network [OSTI]

Planets embedded in optically thick passive accretion disks are expected to produce perturbations in the density and temperature structure of the disk. We calculate the magnitudes of these perturbations for a range of planet masses and distances. The model predicts the formation of a shadow at the position of the planet paired with a brightening just beyond the shadow. We improve on previous work on the subject by self-consistently calculating the temperature and density structures under the assumption of hydrostatic equilibrium and taking the full three-dimensional shape of the disk into account rather than assuming a plane-parallel disk. While the excursion in temperatures is less than in previous models, the spatial size of the perturbation is larger. We demonstrate that a self-consistent calculation of the density and temperature structure of the disk has a large effect on the disk model. In addition, the temperature structure in the disk is highly sensitive to the angle of incidence of stellar irradition at the surface, so accurately calculating the shape of the disk surface is crucial for modeling the thermal structure of the disk.

H. Jang-Condell

2008-01-29T23:59:59.000Z

196

ae protoplanetary disks: Topics by E-print Network  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

these protoplanetary disks, suggestive of processing of these grains during the transient heating events hypothesized to create chondrules. B. A. Sargent; W. J. Forrest; C....

197

Debris Disk Radiative Transfer Simulation Tool (DDS)  

E-Print Network [OSTI]

A WWW interface for the simulation of spectral energy distributions of optically thin dust configurations with an embedded radiative source is presented. The density distribution, radiative source, and dust parameters can be selected either from an internal database or defined by the user. This tool is optimized for studying circumstellar debris disks where large grains are expected to determine the far-infrared through millimeter dust reemission spectral energy distribution. The tool is available at http://aida28.mpia-hd.mpg.de/~swolf/dds

S. Wolf; L. A. Hillenbrand

2005-06-17T23:59:59.000Z

198

TIDAL DISRUPTION FLARES: THE ACCRETION DISK PHASE  

SciTech Connect (OSTI)

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}.

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)

2011-08-01T23:59:59.000Z

199

PLANETESIMAL AND PROTOPLANET DYNAMICS IN A TURBULENT PROTOPLANETARY DISK: IDEAL STRATIFIED DISKS  

SciTech Connect (OSTI)

Due to the gravitational influence of density fluctuations driven by magneto-rotational instability in the gas disk, planetesimals and protoplanets undergo diffusive radial migration as well as changes in other orbital properties. The magnitude of the effect on particle orbits can have important consequences for planet formation scenarios. We use the local-shearing-box approximation to simulate an ideal, isothermal, magnetized gas disk with vertical density stratification and simultaneously evolve numerous massless particles moving under the gravitational field of the gas and the host star. We measure the evolution of the particle orbital properties, including mean radius, eccentricity, inclination, and velocity dispersion, and its dependence on the disk properties and the particle initial conditions. Although the results converge with resolution for fixed box dimensions, we find the response of the particles to the gravity of the turbulent gas correlates with the horizontal box size, up to 16 disk scale heights. This correlation indicates that caution should be exercised when interpreting local-shearing-box models involving gravitational physics of magneto-rotational turbulence. Based on heuristic arguments, nevertheless, the criterion L{sub h} /R {approx} O(1), where L{sub h} is the horizontal box size and R is the distance to the host star, is proposed to possibly circumvent this conundrum. If this criterion holds, we can still conclude that magneto-rotational turbulence seems likely to be ineffective at driving either diffusive migration or collisional erosion under most circumstances.

Yang, Chao-Chin [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Mac Low, Mordecai-Mark [Department of Astrophysics, American Museum of Natural History, New York, NY 10024 (United States); Menou, Kristen, E-mail: ccyang@ucolick.org, E-mail: mordecai@amnh.org, E-mail: kristen@astro.columbia.edu [Department of Astronomy, Columbia University, New York, NY 10027 (United States)

2012-04-01T23:59:59.000Z

200

Investigations of the cause of fishkills in fish-rearing facilities in Raven Fork watershed  

SciTech Connect (OSTI)

An investigation was undertaken to determine the cause of fishkills in trout-rearing facilities located adjacent to Raven Fork Creek within the Cherokee Indian Reservation in North Carolina. Approximately 50,000 rainbow trout were lost at the Blankenship trout farm-a commercial facility-following eight storm events between March 31 and December 2, 1981. In addition, 524 trophy-size trout died in three ponds operated by the Cherokee tribe for stocking reservation streams. It was found fishkills in the trout farm could be prevented by adding lime to water from the creek as it was pumped into the facility; this strengthened the assumption acidity (H/sup +/) was responsible for the fishkills. Mortality of trophy trout was stopped by routing water from nearby springs to the ponds during and following rain events. Because of concern that these fishkills might be caused by acid rain, TVA was requested by the Cherokee tribe to assist in determining the cause. Limited studies were conducted during March through August 1982 to test two hypotheses: (1) concentrations of H/sup +/ and soluble aluminum in Raven Fork following storm events were high enough to kill rainbow trout and (2) atmospheric deposition was a greater source of stream H/sup +/ than acid-producing geologic formations or the forest soils.

Jones, H.C.; Noggle, J.C.; Young, R.C.; Kelly, J.M.; Olem, H.; Ruane, R.J.; Pasch, R.W.; Hyfantis, G.J.; Parkhurst, W.J.

1983-04-01T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


201

Feasibility study 100 K East Area water purification pools fish-rearing program  

SciTech Connect (OSTI)

As part of the feasibility study, a design analysis was conducted to determine the usefulness of the existing sand filters and associated media for reuse. The sand filters which were studied for potential reuse are located on the northern end of the 100-K East Area water filtration plant on the Hanford Site. This plant is located about one- half mile from the Columbia River. The sand filters were originally part of a system which was used to provide cooling water to the nearby plutonium production K Reactors. This Cold War operation took place until 1971, at which time the K Reactors were closed for eventual decontamination and decommissioning. Recently, it was decided to study the concept of putting the sand filter structures back into use for fish-rearing purposes. Because the water that circulated through the water purification pools (K Pools) and associated sand filters was clean river water, there is little chance of the structures being radioactively contaminated. To date, separate K Pools have been used for raising a variety of cold water fish species, including white sturgeon and fall chinook salmon, as well as for providing potable water to the 100 K Area of the Hanford Site for fire and service water purposes.

Betsch, M.D., Westinghouse Hanford

1996-07-03T23:59:59.000Z

202

Competitive Parallel Disk Prefetching and Buffer Management  

E-Print Network [OSTI]

across the set a167 of a24 disks. A bad phase,a130a137a131a137a133a140a135a120a136a134a54a10a141a61a56 , with bad disk parameter a149a66a28 consists of blocks a142a72a68a50a143a51a144 , a141a61a25a146a145a97a147a102a148a124a54a61a141a34a94a168a104a39a56a...43a25 , laid out such that the first a25a169a163a15a25a170a81a66a64a51a55 a24 blocks a142a78a68 a143 a144 , where a141a61a25a146a145a97a147a102a148a124a54a10a141a80a94a69a104a19a56a153a25a171a163a172a25a170a81a66a64a51a55 a24 , are striped in a round...

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

2000-01-01T23:59:59.000Z

203

Kinematic Density Waves in Accretion Disks  

E-Print Network [OSTI]

When thin accretion disks around black holes are perturbed, the main restoring force is gravity. If gas pressure, magnetic stresses, and radiation pressure are neglected, the disk remains thin as long as orbits do not intersect. Intersections would result in pressure forces which limit the growth of perturbations. We find that a discrete set of perturbations is possible for which orbits remain non-intersecting for arbitrarily long times. These modes define a discrete set of frequencies. We classify all long-lived perturbations for arbitrary potentials and show how their mode frequencies are related to pattern speeds computed from the azimuthal and epicyclic frequencies. We show that modes are concentrated near radii where the pattern speed has vanishing radial derivative. We explore these modes around Kerr black holes as a possible explanation for the high-frequency quasi-periodic oscillations of black hole binaries such as GRO J1655-40. The long-lived modes are shown to coincide with diskoseismic waves in the limit of small sound speed. While the waves have long lifetime, they have the wrong frequencies to explain the pairs of high-frequency quasi-periodic oscillations observed in black hole binaries.

Svetlin Tassev; Edmund Bertschinger

2008-10-14T23:59:59.000Z

204

Research Associate Rearing and Identification of Wood-boring Beetles Intercepted in US Ports Xavier University & USDA APHIS PPQ CPHST Otis Laboratory  

E-Print Network [OSTI]

intercepted insects from ports, and rearing insects in host wood or artificial diets. Identification at Buzzards Bay, Massachusetts. This job requires fine motor skills, and the ability to lift up to 20 pounds

Ferrara, Katherine W.

205

The 22nd International Photovoltaic Science and Engineering Conference, November 05-09, 2012, Hangzhou, China Front side degradation of silicon solar cells by rear side laser  

E-Print Network [OSTI]

wafers without bow for further processing and module integration. [1,2] In this contribution we recombination rate beneath the contacts. A thermal oxide with a thickness of 150 nm serves as a rear side

206

E-Print Network 3.0 - accretion disk properties Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

23 CONSTRAINTS ON ACCRETION DISK LIFETIMES Summary: accretion, inner disk hole, and inclination properties. Compared to the non-accreting no-hole pole-on disk... of various...

207

E-Print Network 3.0 - astrophysical disk models Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

accretion disk models. The Astrophysical... disk material to the outer disk is the X-wind model (Shu et al. 1996). The notion that young stars... of material transported to...

208

CAPTURE OF PLANETESIMALS BY GAS DRAG FROM CIRCUMPLANETARY DISKS  

SciTech Connect (OSTI)

Growing giant planets have circumplanetary disks around them in the late stage of their formation if their mass is sufficiently large. We examine capture of relatively large planetesimals that are decoupled from the gas inflow, due to gas drag from a circumplanetary disk of a growing giant planet. Assuming that the structure of the circumplanetary disk is axisymmetric, and solving the three-body problem including gas drag, we perform analytic and numerical calculations for capture of planetesimals. When planetesimal random velocity is small, planetesimals approaching in the retrograde direction are more easily captured, owing to their larger velocity relative to the gas. Planetesimals with large orbital inclinations interact with the disk for a short period of time and show lower capture rates. The effect of ablation on capture rates seems insignificant, although mass loss due to ablation would be significant in the case of high random velocity. We also examine the effect of non-uniform radial distribution of planetesimals in the protoplanetary disk due to gap opening by the planet. When the random velocity of planetesimals is small, the planetesimal capture rate decreases rapidly as the half width of the gap in the planetesimal disk increases from two planetary Hill radii to three planetary Hill radii; planetesimals with low random velocities cannot approach the planet in the case of a sufficiently wide gap. Our results show that the radial distribution and random velocity of planetesimals in the protoplanetary disk are essentially important for the understanding of capture of planetesimals by circumplanetary disks.

Fujita, Tetsuya; Ohtsuki, Keiji; Suetsugu, Ryo [Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501 (Japan); Tanigawa, Takayuki [Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819 (Japan)

2013-12-01T23:59:59.000Z

209

Energy Conservation Techniques for Disk Array-Based Servers  

E-Print Network [OSTI]

, we introduce a new conser- vation technique, called Popular Data Concentration (PDC), that migrates that takes advantage of PDC. In the context of this server, we compare PDC to the Massive Array of Idle Disks and a wide range of parame- ters. Our results for conventional disks show that PDC and MAID can only conserve

Bianchini, Ricardo

210

Energy Conservation Techniques for Disk ArrayBased Servers  

E-Print Network [OSTI]

, we introduce a new conser­ vation technique, called Popular Data Concentration (PDC), that migrates that takes advantage of PDC. In the context of this server, we compare PDC to the Massive Array of Idle Disks and a wide range of parame­ ters. Our results for conventional disks show that PDC and MAID can only conserve

Bianchini, Ricardo

211

Author Retrospective for Energy Conservation Techniques for Disk  

E-Print Network [OSTI]

Author Retrospective for Energy Conservation Techniques for Disk Array-based Servers Eduardo original paper ti- tled "Energy Conservation Techniques for Disk Array-based Servers", which was published.1145/2591635.2591666 Categories and Subject Descriptors D.4 [Operating systems]: Storage management Keywords Energy conservation

Bianchini, Ricardo

212

The gas temperature in circumstellar disks: effects of dust settling  

E-Print Network [OSTI]

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

Zadelhoff, Gerd-Jan van

213

Neutrinos and Nucleosynthesis in Gamma-Ray Burst Accretion Disks  

E-Print Network [OSTI]

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.

R. Surman; G. C. McLaughlin

2003-11-24T23:59:59.000Z

214

THE SPHERICALIZATION OF DARK MATTER HALOS BY GALAXY DISKS  

SciTech Connect (OSTI)

Cosmological simulations indicate that cold dark matter (CDM) halos should be triaxial. Validating this theoretical prediction is, however, less than straightforward because the assembly of galaxies is expected to modify halo shapes and to render them more axisymmetric. We use a suite of N-body simulations to quantitatively investigate the effect of the growth of a central disk galaxy on the shape of triaxial dark matter halos. In most circumstances, the halo responds to the presence of the disk by becoming more spherical. The net effect depends weakly on the timescale of the disk assembly but noticeably on the orientation of the disk relative to the halo principal axes, and it is maximal when the disk symmetry axis is aligned with the major axis of the halo. The effect depends most sensitively on the overall gravitational importance of the disk. Our results indicate that exponential disks whose contribution peaks at less than {approx}50% of their circular velocity are unable to noticeably modify the shape of the gravitational potential of their surrounding halos. Many dwarf and low surface brightness galaxies are expected to be in this regime, and therefore their detailed kinematics could be used to probe halo triaxiality, one of the basic predictions of the CDM paradigm. We argue that the complex disk kinematics of the dwarf galaxy NGC 2976 might be the reflection of a triaxial halo. Such signatures of halo triaxiality should be common in galaxies where the luminous component is subdominant.

Kazantzidis, Stelios [Center for Cosmology and Astro-Particle Physics, Ohio State University, Columbus, OH 43210 (United States); Abadi, Mario G. [Instituto de Astronomia Teorica y Experimental (IATE), Observatorio Astronomico de Cordoba and CONICET, Laprida 854 X5000BGR Cordoba (Argentina); Navarro, Julio F., E-mail: stelios@mps.ohio-state.ed, E-mail: mario@oac.uncor.ed, E-mail: jfn@uvic.c [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 5C2 (Canada)

2010-09-01T23:59:59.000Z

215

Energy Efficient Prefetching with Buffer Disks for Cluster File Systems  

E-Print Network [OSTI]

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

Qin, Xiao

216

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

SciTech Connect (OSTI)

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.

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)

2009-09-20T23:59:59.000Z

217

USING MEGAMASER DISKS TO PROBE BLACK HOLE ACCRETION  

SciTech Connect (OSTI)

We examine the alignment between H{sub 2}O megamaser disks on subparsec scales with circumnuclear disks and bars on <500 pc scales observed with the Hubble Space Telescope (HST)/WFC3. The HST imaging reveals young stars, indicating the presence of gas. The megamaser disks are not well aligned with the circumnuclear bars or disks as traced by stars in the HST images. We speculate on the implications of the observed misalignments for fueling supermassive black holes in gas-rich spiral galaxies. In contrast, we find a strong preference for the rotation axes of the megamaser disks to align with radio continuum jets observed on {approx}> 50 pc scales, in those galaxies for which radio continuum detections are available. Subarcsecond observations of molecular gas with ALMA will enable a more complete understanding of the interplay between circumnuclear structures.

Greene, Jenny E.; Sun Ailei [Department of Astrophysics, Princeton University, Princeton, NJ 08540 (United States); Seth, Anil; Den Brok, Mark [University of Utah, Salt Lake City, UT 84112 (United States); Braatz, James A.; Impellizzeri, C. M. Violette; Lo, K. Y. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Henkel, Christian [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Peng, Chien Y. [GMTO Corporation, 251 S. Lake Ave., Suite 300, Pasadena, CA 91101 (United States); Kuo, Cheng-Yu [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 16617, Taiwan (China)

2013-07-10T23:59:59.000Z

218

Forced oscillations in magnetized accretion disks and QPOs  

E-Print Network [OSTI]

We propose a new model for these QPOs based on forced oscillations induced in the accretion disk due to the stellar magnetic field. First, it is shown that a magnetized accretion disk evolving in a rotating nonaxisymmetric magnetic field anchored to a neutron star will be subject to three kinds of resonances: a corotation resonance, a Lindblad resonance due to a driving force, and a parametric resonance due to the time varying epicyclic frequencies. In the second part of the paper, we focus on the linear response of a thin accretion disk, developing the density perturbation as the sum of free wave solutions and non-wavelike disturbances. In the last part, we show results of 2D numerical simulations of a simplified version of the accretion disk consisting of a column of plasma threaded by a vertical magnetic field. It is argued that the nearly periodic motion induced in the disk will produce high quality factor QPOs.

J. Ptri

2005-07-06T23:59:59.000Z

219

An Eccentric Disk Model for the Nucleus of M31  

E-Print Network [OSTI]

The nucleus of M31 may be a thick eccentric disk, composed of stars traveling on nearly Keplerian orbits around a black hole or other dark compact object. This hypothesis reproduces most of the features seen in HST photometry of the center of M31; in particular the bright off-center source P1 is the apoapsis of the disk. An eccentric disk can also explain the rotation curve and asymmetric dispersion profile revealed by ground-based observations. The central object must be smaller than 1 pc so that the potential felt by the disk is nearly Keplerian. The disk eccentricity may be excited by a secular instability driven by dynamical friction from the bulge.

Scott Tremaine

1995-02-13T23:59:59.000Z

220

The role of an accretion disk in AGN variability  

E-Print Network [OSTI]

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.

B. Czerny

2004-09-10T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


221

On the stability of a galactic disk in modified gravity  

E-Print Network [OSTI]

We find the dispersion relation for tightly wound spiral density waves in the surface of rotating, self-gravitating disks in the framework of Modified Gravity (MOG). Also, the Toomre-like stability criterion for differentially rotating disks has been derived for both fluid and stellar disks. More specifically, the stability criterion can be expressed in terms of a matter density threshold over which the instability occurs. In other words the local stability criterion can be written as $\\Sigma_0sound speed), $\\kappa$ (epicycle frequency) and $\\alpha$ and $\\mu_0$ are the free parameters of the theory. In the case of a stellar disk the radial velocity dispersion $\\sigma_r$ appears in $\\Sigma_{\\text{crit}}$ instead of $v_s$. We find the exact form of the function $\\Sigma_{\\text{crit}}$ for both stellar and fluid self-gravitating disks. Also, we use a sub-sample of THINGS catalog of spiral galaxies in order to ...

Roshan, Mahmood

2015-01-01T23:59:59.000Z

222

E-Print Network 3.0 - accretion disk flows Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

39 Manuel Gdel Switzerland Summary: II Diagnoses Different Regions Rkm.com.au disk wind, photoevap. flow jet accretion columns 12;END 12;... - stellar? (Taurus) Disk...

223

E-Print Network 3.0 - accretion disks crystalline Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

(MIT) Collection: Physics 87 SPECTRAL ENERGY DISTRIBUTIONS OF PASSIVE T TAURI DISKS: INCLINATION Summary: --- stars: pre- main sequence --- accretion, accretion disks ---...

224

PROTOPLANETARY DISK STRUCTURE WITH GRAIN EVOLUTION: THE ANDES MODEL  

SciTech Connect (OSTI)

We present a self-consistent model of a protoplanetary disk: 'ANDES' ('AccretioN disk with Dust Evolution and Sedimentation'). ANDES is based on a flexible and extendable modular structure that includes (1) a 1+1D frequency-dependent continuum radiative transfer module, (2) a module to calculate the chemical evolution using an extended gas-grain network with UV/X-ray-driven processes and surface reactions, (3) a module to calculate the gas thermal energy balance, and (4) a 1+1D module that simulates dust grain evolution. For the first time, grain evolution and time-dependent molecular chemistry are included in a protoplanetary disk model. We find that grain growth and sedimentation of large grains onto the disk midplane lead to a dust-depleted atmosphere. Consequently, dust and gas temperatures become higher in the inner disk (R {approx}< 50 AU) and lower in the outer disk (R {approx}> 50 AU), in comparison with the disk model with pristine dust. The response of disk chemical structure to the dust growth and sedimentation is twofold. First, due to higher transparency a partly UV-shielded molecular layer is shifted closer to the dense midplane. Second, the presence of big grains in the disk midplane delays the freeze-out of volatile gas-phase species such as CO there, while in adjacent upper layers the depletion is still effective. Molecular concentrations and thus column densities of many species are enhanced in the disk model with dust evolution, e.g., CO{sub 2}, NH{sub 2}CN, HNO, H{sub 2}O, HCOOH, HCN, and CO. We also show that time-dependent chemistry is important for a proper description of gas thermal balance.

Akimkin, V.; Wiebe, D.; Pavlyuchenkov, Ya. [Institute of Astronomy of the RAS, Pyatnitskaya str. 48, Moscow (Russian Federation)] [Institute of Astronomy of the RAS, Pyatnitskaya str. 48, Moscow (Russian Federation); Zhukovska, S.; Semenov, D.; Henning, Th. [Max-Planck-Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany)] [Max-Planck-Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Vasyunin, A. [Department of Chemistry, The University of Virginia, VA (United States)] [Department of Chemistry, The University of Virginia, VA (United States); Birnstiel, T., E-mail: akimkin@inasan.ru, E-mail: dwiebe@inasan.ru, E-mail: pavyar@inasan.ru, E-mail: zhukovska@mpia.de, E-mail: semenov@mpia.de, E-mail: henning@mpia.de, E-mail: anton.vasyunin@gmail.com, E-mail: tbirnstiel@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2013-03-20T23:59:59.000Z

225

PAH chemistry and IR emission from circumstellar disks  

E-Print Network [OSTI]

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.

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

2007-01-22T23:59:59.000Z

226

Snake River Spring/Summer Chinook Captive Broodstock Rearing and Research, 2002 Annual Report.  

SciTech Connect (OSTI)

In 1995, the National Marine Fisheries Service (NMFS), in cooperation with the Idaho Department of Fish and Game (IDFG), the Oregon Department of Fish and Wildlife (ODFW), and the Bonneville Power Administration (BPA) established captive broodstock programs to aid in the recovery of Snake River spring/summer chinook salmon (Oncorhynchus tshawytscha) listed as endangered under the U.S. Endangered Species Act (ESA). These programs were intended to provide safety nets for Salmon and Grande Ronde River Basins spring/summer chinook salmon stocks. They also provide a basis of examining the efficacy of captive rearing and captive breeding programs as tools for recovering listed salmonid populations. In years when no or few naturally produced fish return from the sea, captive fish and their progeny can be used to maintain populations in these two Snake River Basin tributaries. The NMFS facility at Manchester, WA, provides the crucial seawater environment needed to culture anadromous salmonids during the marine phase of their life cycle. At the Manchester Research Station, the fish are cultured in 6.1m diameter circular tanks housed in a fully enclosed and secure building. The tanks are supplied with seawater that has been processed to eliminate most marine pathogens. The fish are fed a commercially prepared diet and held at densities and loading rates designed to maximize fish quality. When fish begin to mature, they are transferred to ODFW or IDFG freshwater facilities in Oregon and Idaho for final maturation. The states then release the mature fish (Idaho) or their progeny (Oregon) back into their native Snake River tributary waters in restoration efforts. In FY 2002, NMFS cultured 1996, 1997, 1998, 1999, and 2000 broodyear fish at its Manchester Facility. This report addresses program activities from September 1, 2001 to August 31, 2002.

McAuley, W. Carlin; Maynard, Desmond J. (National Marine Fishereis Service, Northwest Fisheries Science Center, Seattle, WA)

2003-03-01T23:59:59.000Z

227

Snake River Spring/Summer Chinook Captive Broodstock Rearing and Research, 2003 Annual Report.  

SciTech Connect (OSTI)

In 1995, the National Marine Fisheries Service (NMFS), in cooperation with the Idaho Department of Fish and Game (IDFG), the Oregon Department of Fish and Wildlife (ODFW), and the Bonneville Power Administration (BPA) established captive broodstock programs to aid in the recovery of Snake River spring/summer chinook salmon (Oncorhynchus tshawytscha) listed as endangered under the U.S. Endangered Species Act (ESA). These programs are intended to provide safety nets for Salmon and Grande Ronde River Basins spring/summer chinook salmon stocks. They also provide a basis of examining the efficacy of captive rearing and captive breeding programs as tools for recovering listed salmonid populations. In years when no or few naturally produced fish return from the sea, captive fish and their progeny can be used to maintain populations in these two Snake River Basin tributaries. The NMFS facility at Manchester, WA provides the crucial seawater environment needed to culture anadromous salmonids during the marine phase of their life cycle. At the Manchester Research Station, the fish are cultured in 6.1m diameter circular tanks housed in a fully enclosed and secure building. The tanks are supplied with seawater that has been processed to eliminate most marine pathogens. The fish are fed a commercially prepared diet and held at densities and loading rates intended to maximize fish quality. When fish begin to mature, they are transferred to ODFW or IDFG freshwater facilities in Oregon and Idaho for final maturation. The states then release the mature fish (Idaho) or their progeny (Oregon) back into their native Snake River tributary waters in restoration efforts. In FY 2003, NMFS cultured 1998, 1999, 2000, and 2001 broodyear fish at its Manchester Facility. This report addresses program activities from September 1, 2002 to August 31, 2003.

Maynard, Desmond J.; McAuley, W. Carlin (National Marine Fisheries Service, Northwest Fisheries Science Center, Resource Enhancement and Utilization, Seattle, WA)

2004-08-01T23:59:59.000Z

228

Planetesimal Capture in the Disk Instability Model  

E-Print Network [OSTI]

We follow the contraction and evolution of a typical Jupiter-mass clump created by the disk instability mechanism, and compute the rate of planetesimal capture during this evolution. We show that such a clump has a slow contraction phase lasting ~3x10^5 years. By following the trajectories of planetesimals as they pass through the envelope of the protoplanet, we compute the cross-section for planetesimal capture at all stages of the protoplanet's evolution. We show that the protoplanet can capture a large fraction of the solid material in its feeding zone, which will lead to an enrichment of the protoplanet in heavy elements. The exact amount of this enrichment depends upon, but is not very sensitive to the size and random speed of the planetesimals.

Ravit Helled; Morris Podolak; Attay Kovetz

2006-06-29T23:59:59.000Z

229

The Cosmic Battery in Astrophysical Accretion Disks  

E-Print Network [OSTI]

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...

Contopoulos, Ioannis; Katsanikas, Matthaios

2015-01-01T23:59:59.000Z

230

TESTING CONVERGENCE FOR GLOBAL ACCRETION DISKS  

SciTech Connect (OSTI)

Global disk simulations provide a powerful tool for investigating accretion and the underlying magnetohydrodynamic turbulence driven by magneto-rotational instability (MRI). Using them to accurately predict quantities such as stress, accretion rate, and surface brightness profile requires that purely numerical effects, arising from both resolution and algorithm, be understood and controlled. We use the flux-conservative Athena code to conduct a series of experiments on disks having a variety of magnetic topologies to determine what constitutes adequate resolution. We develop and apply several resolution metrics: (Q{sub z} ) and (Q{sub {phi}}), the ratio of the grid zone size to the characteristic MRI wavelength, {alpha}{sub mag}, the ratio of the Maxwell stress to the magnetic pressure, and /, the ratio of radial to toroidal magnetic field energy. For the initial conditions considered here, adequate resolution is characterized by (Q{sub z} ) {>=} 15, (Q{sub {phi}}) {>=} 20, {alpha}{sub mag} Almost-Equal-To 0.45, and /{approx}0.2. These values are associated with {>=}35 zones per scaleheight H, a result consistent with shearing box simulations. Numerical algorithm is also important. Use of the Harten-Lax-van Leer-Einfeldt flux solver or second-order interpolation can significantly degrade the effective resolution compared to the Harten-Lax-van Leer discontinuities flux solver and third-order interpolation. Resolution at this standard can be achieved only with large numbers of grid zones, arranged in a fashion that matches the symmetries of the problem and the scientific goals of the simulation. Without it, however, quantitative measures important to predictions of observables are subject to large systematic errors.

Hawley, John F.; Richers, Sherwood A.; Guan Xiaoyue [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Krolik, Julian H., E-mail: jh8h@virginia.edu, E-mail: xg3z@virginia.edu, E-mail: jhk@pha.jhu.edu [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)

2013-08-01T23:59:59.000Z

231

FORMING AN O STAR VIA DISK ACCRETION?  

SciTech Connect (OSTI)

We present a study of outflow, infall, and rotation in a {approx}10{sup 5} L{sub Sun} star-forming region, IRAS 18360-0537, with Submillimeter Array and IRAM 30 m observations. The 1.3 mm continuum map shows a 0.5 pc dust ridge, of which the central compact part has a mass of {approx}80 M{sub Sun} and harbors two condensations, MM1 and MM2. The CO (2-1) and SiO (5-4) maps reveal a biconical outflow centered at MM1, which is a hot molecular core (HMC) with a gas temperature of 320 {+-} 50 K and a mass of {approx}13 M{sub Sun }. The outflow has a gas mass of 54 M{sub Sun} and a dynamical timescale of 8 Multiplication-Sign 10{sup 3} yr. The kinematics of the HMC are probed by high-excitation CH{sub 3}OH and CH{sub 3}CN lines, which are detected at subarcsecond resolution and unveil a velocity gradient perpendicular to the outflow axis, suggesting a disk-like rotation of the HMC. An infalling envelope around the HMC is evidenced by CN lines exhibiting a profound inverse P Cygni profile, and the estimated mass infall rate, 1.5 Multiplication-Sign 10{sup -3} M{sub Sun} yr{sup -1}, is well comparable to that inferred from the mass outflow rate. A more detailed investigation of the kinematics of the dense gas around the HMC is obtained from the {sup 13}CO and C{sup 18}O (2-1) lines; the position-velocity diagrams of the two lines are consistent with the model of a free-falling and Keplerian-like rotating envelope. The observations suggest that the protostar of a current mass {approx}10 M{sub Sun} embedded within MM1 will develop into an O star via disk accretion and envelope infall.

Qiu Keping [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Zhang Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Beuther, Henrik; Fallscheer, Cassandra, E-mail: kqiu@mpifr-bonn.mpg.de [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

2012-09-10T23:59:59.000Z

232

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

E-Print Network [OSTI]

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.

M. C. Smith

2003-06-10T23:59:59.000Z

233

Thermal stability of thin disk with magnetically driven winds  

E-Print Network [OSTI]

The absence of thermal instability in the high/soft state of black hole X-ray binaries, in disagreement with the standard thin disk theory, is a long-standing riddle for theoretical astronomers. We have tried to resolve this question by studying the thermal stability of a thin disk with magnetically driven winds in the $\\dot{M}- \\Sigma$ plane. It is found that disk winds can greatly decrease the disk temperature and thus help the disk become more stable at a given accretion rate. The critical accretion rate $\\dot{M}_{\\rm crit}$ corresponding to the thermal instability threshold is increased significantly in the presence of disk winds. For $\\alpha=0.01$ and $B_{\\rm \\phi}=10B_{\\rm _p}$, the disk is quite stable even for a very weak initial poloidal magnetic field [$\\beta_{\\rm p,0}\\sim 2000, \\beta_{\\rm p}=(P_{\\rm {gas}}+P_{\\rm rad})/(B_{\\rm p}^2/8\\pi)$]. But when $B_{\\rm \\phi}=B_{\\rm _p}$ or $B_{\\rm \\phi}=0.1B_{\\rm _p}$, a somewhat stronger (but still weak) field ($\\beta_{\\rm p,0}\\sim 200$ or $\\beta_{\\rm p,0}\\si...

Li, Shuang-Liang

2014-01-01T23:59:59.000Z

234

Simple Models for Turbulent Self-Regulation in Galaxy Disks  

E-Print Network [OSTI]

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)

Curtis Struck; Daniel C. Smith

1999-07-29T23:59:59.000Z

235

On the Structural Differences between Disk and Dwarf Galaxies  

E-Print Network [OSTI]

Gas-rich dwarf and disk galaxies overlap in numerous physical quantities that make their classification subjective. We report the discovery of a separation between dwarfs and disks into two unique sequences in the mass (luminosity) versus scale length plane. This provides an objective classification scheme for late-type galaxies that only requires optical or near-IR surface photometry of a galaxy. Since the baryonic Tully-Fisher relation for these samples produces a continuous relation between baryonic mass and rotational velocity, we conclude that the difference between dwarfs and disks must be because of their distribution of stellar light such that dwarfs are more diffuse than disk galaxies. This structural separation may be due to a primordial difference between low and high mass galaxies or produced by hierarchical mergers where disks are built up from dwarfs. Structural differences between dwarf and disk galaxies may also be driven by the underlying kinematics where the strong rotation in disks produces an axial symmetric object that undergoes highly efficient star formation in contrast to the lower rotation, more disordered motion of dwarfs that produces a diffuse, triaxial object with a history of inefficient star formation.

J. Schombert

2005-09-12T23:59:59.000Z

236

Planet Shadows in Protoplanetary Disks. I: Temperature Perturbations  

E-Print Network [OSTI]

Planets embedded in optically thick passive accretion disks are expected to produce perturbations in the density and temperature structure of the disk. We calculate the magnitudes of these perturbations for a range of planet masses and distances. The model predicts the formation of a shadow at the position of the planet paired with a brightening just beyond the shadow. We improve on previous work on the subject by self-consistently calculating the temperature and density structures under the assumption of hydrostatic equilibrium and taking the full three-dimensional shape of the disk into account rather than assuming a plane-parallel disk. While the excursion in temperatures is less than in previous models, the spatial size of the perturbation is larger. We demonstrate that a self-consistent calculation of the density and temperature structure of the disk has a large effect on the disk model. In addition, the temperature structure in the disk is highly sensitive to the angle of incidence of stellar irradition...

Jang-Condell, H

2008-01-01T23:59:59.000Z

237

Nucleosynthesis in the Outflow from Gamma Ray Burst Accretion Disks  

E-Print Network [OSTI]

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.

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

2005-09-13T23:59:59.000Z

238

Type I planet migration in nearly laminar disks  

SciTech Connect (OSTI)

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.

Li, Hui [Los Alamos National Laboratory; Li, Shengtai [Los Alamos National Laboratory; Lubow, S H [STSI; Lin, D [UCSC

2008-01-01T23:59:59.000Z

239

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

SciTech Connect (OSTI)

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.

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)

2013-04-10T23:59:59.000Z

240

Characteristics of a multiple disk pump with turbulent rotor flow  

E-Print Network [OSTI]

DIRHETER IINIt tl, DISCHARGE OIANETER IINlt 3. CLEARANCE OETHEEN DISKS 0. 13636 IN. TYPE SEALJ PRCKING DISKFLO PUHP; NODEL K03 TOTRL HERO HORSEPOHER X EFFICIENCY + NPSH AVAIL V Figure 12. Performance of the 11 Disk Pump at 890 rpm (Test 2) C& C...: D. 13636 IN 111'E 5EAI. PACK(NO OISKFLD PL'. "P: HDD L 40 TOTAL HERO HDRSEPOHER X EFFICIENCY + NPSH AVAIL Y Figure 14 . Performance of the 1 1 Disk Pump at 1 790 rpm ( Tes t 1 ) CV o O C) CI O C) O \\ C CC C O I-!-W I o O O O 6 )3...

Roddy, Patrick James

1985-01-01T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


241

Identification of the Spawning, Rearing and Migratory Requirements of Fall Chinook Salmon in the Columbia River Basin, Annual Report 1992.  

SciTech Connect (OSTI)

This document is the 1992 annual progress report for selected studies of fall chinook Salmon Oncorhynchus tshawytscha conducted by the National Biological Survey (NBS) and the US Fish and Wildlife Service. The decline in abundance of fall chinook salmon in the Snake River basin has become a growing concern. Effective recovery efforts for fall chinook salmon cannot be developed until we increase our knowledge of the factors that are limiting the various life history stages. This study attempts to identify those physical and biological factors which influence spawning of fall chinook salmon in the free-flowing Snake River and their rearing and seaward migration through Columbia River basin reservoirs.

Rondorf, Dennis W.; Miller, William H.

1994-03-01T23:59:59.000Z

242

Modeling Disk Arrays Using Genetic Programming Evan Kirshenbaum  

E-Print Network [OSTI]

Page Mill Road Palo Alto, CA 94304 kirshenbaum@hpl.hp.com Abstract This paper describes the results to population size but not run length. 1 BACKGROUND In the past decade, enterprises have turned to disk arrays

Fernandez, Thomas

243

Innovation incentives and competition in the hard disk drive industry  

E-Print Network [OSTI]

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 ...

Wu, Xiaohua Sherry

2011-01-01T23:59:59.000Z

244

Nanolithographically defined magnetic structures and quantum magnetic disk (invited)  

E-Print Network [OSTI]

is demonstrated along with a low-cost method for mass producing such disks. Other impacts that nanofabrication can- veloped in a cellosolve and methanol solution to form a re- sist template on the substrate. Ferromagnetic

245

ames disk galaxies: Topics by E-print Network  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

pressure, from both direct opticalUV radiation and multi-scattered, re-processed infrared (IR) radiation. Photo-heating smooths and thickens the disks and suppresses star...

246

STAR CLUSTER POPULATIONS IN THE OUTER DISKS OF NEARBY GALAXIES  

SciTech Connect (OSTI)

We present a Large Binocular Telescope imaging study that characterizes the star cluster component of nearby galaxy outer disks (beyond the optical radius R{sub 25}). Expanding on the pilot project of Herbert-Fort et al., we present deep ({approx}27.5 mag V-band point-source limiting magnitude) U- and V-band imaging of six galaxies: IC 4182, NGC 3351, NGC 4736, NGC 4826, NGC 5474, and NGC 6503. We find that the outer disk of each galaxy is populated with marginally resolved star clusters with masses {approx}10{sup 3} M{sub Sun} and ages up to {approx}1 Gyr (masses and ages are limited by the depth of our imaging and uncertainties are large given how photometry can be strongly affected by the presence or absence of a few stars in such low-mass systems), and that they are typically found out to at least 2 R{sub 25} but sometimes as far as 3-4 R{sub 25}-even beyond the apparent H I disk. The mean rate of cluster formation for 1 R{sub 25} {<=} R {<=} 1.5 R{sub 25} is at least one every {approx}2.5 Myr and the clusters are spatially correlated with the H I, most strongly with higher density gas near the periphery of the optical disk and with lower density neutral gas at the H I disk periphery. We hypothesize that the clusters near the edge of the optical disk are formed in the extension of spiral structure from the inner disk and are a fairly consistent phenomenon and that the clusters formed at the periphery of the H I disk are the result of accretion episodes.

Herbert-Fort, Stephane; Zaritsky, Dennis [Department of Astronomy/Steward Observatory, University of Arizona, 933 N Cherry Avenue, Tucson, AZ 85721 (United States); Moustakas, John [Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA 92093 (United States); Di Paola, Andrea [INAF, Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio (Italy); Pogge, Richard W. [Department of Astronomy, Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210-1173 (United States); Ragazzoni, Roberto, E-mail: s.herbertfort@gmail.com, E-mail: dennis.zaritsky@gmail.com [INAF, Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, I-35122 Padova (Italy)

2012-08-01T23:59:59.000Z

247

Destruction of protoplanetary disks in the Orion Nebula Cluster  

E-Print Network [OSTI]

We use numerical N-body simulations of the Orion Nebula Cluster (ONC) to investigate the destruction of protoplanetary disks by close stellar encounters and UV radiation from massive stars. The simulations model a cluster of 4000 stars, and we consider separately cases in which the disks have fixed radii of 100 AU and 10 AU. In the former case, depending on a star's position and orbit in the cluster over 10^7 years, UV photoevaporation removes at least 0.01 Msol from its disk, and can remove up to 1 Msol. We find no dynamical models of the ONC consistent with the suggestion of Storzer and Hollenbach that the observed distribution and abundance of proplyds could be explained by a population of stars on radial orbits which spend relatively little time near Theta 1C Ori (the most massive star in the ONC). Instead the observations require either massive disks (e.g. a typical initial disk mass of 0.4 Msol) or a very recent birth for Theta 1C Ori. When we consider the photoevaporation of the inner 10 AU of disks in the ONC, we find that planet formation would be hardly affected. Outside that region, planets would be prevented from forming in about half the systems, unless either the initial disk masses were very high or they formed in less than ~ 2 Myr and Theta 1C Ori has only very recently appeared. We also present statistics on the distribution of minimum stellar encounter separations. This peaks at 1000 AU, with less than 10% of stars having had an encounter closer than 100 AU after 10^7 years. We conclude that stellar encounters are unlikely to play a significant role in destroying protoplanetary disks. In the absence of any disruption mechanism other than those considered here, we would thus predict planetary systems like our own to be common amongst stars forming in ONC-like environments.

Aylwyn Scally; Cathie Clarke

2000-12-05T23:59:59.000Z

248

Radiation-Dominated Disks Are Thermally Stable  

E-Print Network [OSTI]

When the accretion rate is more than a small fraction of Eddington, the inner regions of accretion disks around black holes are expected to be radiation-dominated. However, in the alpha-model, these regions are also expected to be thermally unstable. In this paper, we report two 3-d radiation MHD simulations of a vertically-stratified shearing box in which the ratio of radiation to gas pressure is ~ 10, and yet no thermal runaway occurs over a timespan ~ 40 cooling times. Where the time-averaged dissipation rate is greater than the critical dissipation rate that creates hydrostatic equilibrium by diffusive radiation flux, the time-averaged radiation flux is held to the critical value, with the excess dissipated energy transported by radiative advection. Although the stress and total pressure are well-correlated as predicted by the alpha-model, we show that stress fluctuations precede pressure fluctuations, contrary to the usual supposition that the pressure controls the saturation level of the magnetic energy. This fact explains the thermal stability. Using a simple toy-model, we show that independently-generated magnetic fluctuations can drive radiation pressure fluctuations, creating a correlation between the two while maintaining thermal stability.

Shigenobu Hirose; Julian H. Krolik; Omer Blaes

2008-09-10T23:59:59.000Z

249

Spin-Induced Disk Precession in Sagittarius A*  

E-Print Network [OSTI]

In Sgr A* at the Galactic center, by far the closest and easiest supermassive black hole we can study, the observational evidence is increasingly pointing to the presence of a compact, hot, magnetized disk feeding the accretor. In such low-Mach-number plasmas, forces arising, e.g., from pressure gradients in the plasma, can altogether negate the warping of disks around Kerr black holes caused by the Bardeen-Petterson effect and can lead to coherent precession of the entire disk. In this Letter, we present for the first time highly detailed 3D SPH simulations of the accretion disk evolution in Sgr A*, guided by observational constraints on its physical characteristics, and conclude that indeed the Bardeen-Petterson effect is probably absent in this source. Given what we now understand regarding the emission geometry in this object, we suggest that a ~ 50-500-day modulation in Sgr A*'s spectrum, arising from the disk precession, could be an important observational signature; perhaps the ~ 106-day period seen earlier in its radio flux, if confirmed, could be due to this process. On the other hand, if future observations do not confirm this long modulation in Sgr A*'s spectrum, this would be an indication that either the disk size or orientation is very different from current estimates, or that the black hole is not spinning at all (unlikely), or that our current understanding of how it produces its radiative output is incorrect.

Gabriel Rockefeller; Christopher L. Fryer; Fulvio Melia

2005-08-03T23:59:59.000Z

250

FORMATION OF ORGANIC MOLECULES AND WATER IN WARM DISK ATMOSPHERES  

SciTech Connect (OSTI)

Observations from Spitzer and ground-based infrared spectroscopy reveal significant diversity in the molecular emission from the inner few AU of T Tauri disks. We explore theoretically the possible origin of this diversity by expanding on our earlier thermal-chemical model of disk atmospheres. We consider how variations in grain settling, X-ray irradiation, accretion-related mechanical heating, and the oxygen-to-carbon ratio can affect the thermal and chemical properties of the atmosphere at 0.25-40 AU. We find that these model parameters can account for many properties of the detected molecular emission. The column density of the warm (200-2000 K) molecular atmosphere is sensitive to grain settling and the efficiency of accretion-related heating, which may account, at least in part, for the large range in molecular emission fluxes that have been observed. The dependence of the atmospheric properties on the model parameters may also help to explain trends that have been reported in the literature between molecular emission strength and mid-infrared color, stellar accretion rate, and disk mass. We discuss whether some of the differences between our model results and the observations (e.g., for water) indicate a role for vertical transport and freezeout in the disk midplane. We also discuss how planetesimal formation in the outer disk (beyond the snowline) may imprint a chemical signature on the inner few AU of the disk and speculate on possible observational tracers of this process.

Najita, Joan R. [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States); Adamkovics, Mate; Glassgold, Alfred E. [Astronomy Department, University of California, Berkeley, CA 94720 (United States)

2011-12-20T23:59:59.000Z

251

Identification of new transitional disk candidates in Lupus with Herschel  

E-Print Network [OSTI]

New data from the Herschel Space Observatory are broadening our understanding of the physics and evolution of the outer regions of protoplanetary disks in star forming regions. In particular they prove to be useful to identify transitional disk candidates. The goals of this work are to complement the detections of disks and the identification of transitional disk candidates in the Lupus clouds with data from the Herschel Gould Belt Survey. We extracted photometry at 70, 100, 160, 250, 350 and 500 $\\mu$m of all spectroscopically confirmed Class II members previously identified in the Lupus regions and analyzed their updated spectral energy distributions. We have detected 34 young disks in Lupus in at least one Herschel band, from an initial sample of 123 known members in the observed fields. Using the criteria defined in Ribas et al. (2013) we have identified five transitional disk candidates in the region. Three of them are new to the literature. Their PACS-70 $\\mu$m fluxes are systematically higher than thos...

Bustamante, I; Ribas, ; Bouy, H; Prusti, T; Pilbratt, G L; Andr, Ph

2015-01-01T23:59:59.000Z

252

THE PROTOPLANETARY DISK AROUND THE M4 STAR RECX 5: WITNESSING THE INFLUENCE OF PLANET FORMATION?  

SciTech Connect (OSTI)

We present Spitzer Space Telescope low-resolution spectroscopy of the protoplanetary disk around the M4 star RECX 5, a low-mass member of the {approx}8 Myr old {eta} Chamaeleontis star cluster. Two features of the disk around RECX 5 set it apart from other young, low-mass stars with protoplanetary disks: its mineralogy and its disk geometry. Band strengths of the crystalline silicate forsterite are a factor of two higher than that typically observed in T Tauri star disks, indicative of a high forsterite mass fraction. Continuum fluxes of the disk are inconsistent with either a flaring or flattened structure, suggesting a complex disk geometry. Radiative transfer modeling of the spectrum suggests that the disk has a gap at a radius of r = 0.6 AU, and that the disk density at r < 33 AU is a factor of 100 lower than that of a continuous disk. A second disk gap might be centered at r = 24 AU. The RECX 5 disk has properties that are remarkably similar to the disk surrounding the Herbig Be star HD 100546, which is noted for having extreme mineralogy and geometry among Herbig star disks. Similar to a solution proposed for HD 100546, we speculate that the clearance of the RECX 5 disk at r < 33 AU is a consequence of the formation of a Saturn-mass planet, with the planet being responsible for the striking difference in both the spectral energy distribution and chemical composition of the dust around RECX 5.

Bouwman, J.; Juhasz, A.; Henning, Th. [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Lawson, W. A. [School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Australian Defence Force Academy, Canberra ACT 2600 (Australia); Dominik, C.; Waters, L. B. F. M. [Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Kruislaan 403 NL-1098 SJ Amsterdam (Netherlands); Feigelson, E. D. [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park PA 16802 (United States); Tielens, A. G. G. M. [Leiden Observatory, P.O. Box 9513, 2300 RA Leiden (Netherlands)

2010-11-10T23:59:59.000Z

253

Vertical Structure of Neutrino Dominated Accretion Disks and Neutrino Transport in the disks  

E-Print Network [OSTI]

We investigate the vertical structure of neutrino dominated accretion disks by self-consistently considering the detailed microphysics, such as the neutrino transport, vertical hydrostatic equilibrium, the conservation of lepton number, as well as the balance between neutrino cooling, advection cooling and viscosity heating. After obtaining the emitting spectra of neutrinos and antineutrinos by solving the one dimensional Boltzmann equation of neutrino and antineutrino transport in the disk, we calculate the neutrino/antineutrino luminosity and their annihilation luminosity. We find that the total neutrino and antineutrino luminosity is about $10^{54}$ ergs/s and their annihilation luminosity is about $5\\times10^{51}$ ergs/s with an extreme accretion rate $10 M_{\\rm {sun}}$/s and an alpha viscosity $\\alpha=0.1$. In addition, we find that the annihilation luminosity is sensitive to the accretion rate and will not exceed $10^{50}$ ergs/s which is not sufficient to power the most fireball of GRBs, if the accretion rate is lower than $1 M_{\\rm {sun}}$/s. Therefore, the effects of the spin of black hole or/and the magnetic field in the accretion flow might be introduced to power the central engine of GRBs.

Zhen Pan; Ye-Fei Yuan

2012-09-06T23:59:59.000Z

254

Silicate Dust in Evolved Protoplanetary Disks: Growth, Sedimentation, and Accretion  

E-Print Network [OSTI]

We present the Spitzer IRS spectra for 33 young stars in Tr 37 and NGC 7160. The sample includes the high- and intermediate-mass stars with MIPS 24 microns excess, the only known active accretor in the 12 Myr-old cluster NGC 7160, and 19 low-mass stars with disks in the 4 Myr-old cluster Tr 37. We examine the 10 microns silicate feature, present in the whole sample of low-mass star and in 3 of the high- and intermediate-mass targets, and we find that PAH emission is detectable only in the Herbig Be star. We analyze the composition and size of the warm photospheric silicate grains by fitting the 10 microns silicate feature, and study the possible correlations between the silicate characteristics and the stellar and disk properties (age, SED slope, accretion rate, spectral type). We find indications of dust settling with age and of the effect of turbulent enrichment of the disk atmosphere with large grains. Crystalline grains are only small contributors to the total silicate mass in all disks, and do not seem to correlate with any other property, except maybe binarity. We also observe that spectra with very weak silicate emission are at least 3 times more frequent among M stars than among earlier spectral types, which may be an evidence of inner disk evolution. Finally, we find that 5 of the high- and intermediate-mass stars have SEDs and IRS spectra consistent with debris disk models involving planet formation, which could indicate debris disk formation at ages as early as 4 Myr.

Aurora Sicilia-Aguilar; L. W. Hartmann; Dan Watson; Chris Bohac; Thomas Henning; Jeroen Bouwman

2007-01-11T23:59:59.000Z

255

THE TRANSITIONAL PROTOPLANETARY DISK FREQUENCY AS A FUNCTION OF AGE: DISK EVOLUTION IN THE CORONET CLUSTER, TAURUS, AND OTHER 1-8 Myr OLD REGIONS  

SciTech Connect (OSTI)

We present Spitzer 3.6-24 {mu}m photometry and spectroscopy for stars in the 1-3 Myr old Coronet Cluster, expanding upon the survey of Sicilia-Aguilar et al. Using sophisticated radiative transfer models, we analyze these new data and those from Sicilia-Aguilar et al. to identify disks with evidence for substantial dust evolution consistent with disk clearing: transitional disks. We then analyze data in Taurus and others young clusters-IC 348, NGC 2362, and {eta} Cha-to constrain the transitional disk frequency as a function of time. Our analysis confirms previous results finding evidence for two types of transitional disks-those with inner holes and those that are homologously depleted. The percentage of disks in the transitional phase increases from {approx}15%-20% at 1-2 Myr to {>=}50% at 5-8 Myr; the mean transitional disk lifetime is closer to {approx}1 Myr than 0.1-0.5 Myr, consistent with previous studies by Currie et al. and Sicilia-Aguilar et al. In the Coronet Cluster and IC 348, transitional disks are more numerous for very low mass M3-M6 stars than for more massive K5-M2 stars, while Taurus lacks a strong spectral-type-dependent frequency. Assuming standard values for the gas-to-dust ratio and other disk properties, the lower limit for the masses of optically thick primordial disks is M{sub disk} {approx} 0.001-0.003 M{sub *}. We find that single color-color diagrams do not by themselves uniquely identify transitional disks or primordial disks. Full spectral energy distribution modeling is required to accurately assess disk evolution for individual sources and inform statistical estimates of the transitional disk population in large samples using mid-IR colors.

Currie, Thayne [NASA-Goddard Space Flight Center, Greenbelt, MD (United States); Sicilia-Aguilar, Aurora [Max-Planck-Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany)

2011-05-01T23:59:59.000Z

256

Giant disk galaxies : Where environment trumps mass in galaxy evolution  

E-Print Network [OSTI]

We identify some of the most HI massive and fastest rotating disk galaxies in the local universe with the aim of probing the processes that drive the formation of these extreme disk galaxies. By combining data from the Cosmic Flows project, which has consistently reanalyzed archival galaxy HI profiles, and 3.6$\\mu$m photometry obtained with the Spitzer Space Telescope, with which we can measure stellar mass, we use the baryonic Tully-Fisher (BTF) relationship to explore whether these massive galaxies are distinct. We discuss several results, but the most striking is the systematic offset of the HI-massive sample above the BTF. These galaxies have both more gas and more stars in their disks than the typical disk galaxy of similar rotational velocity. The "condensed" baryon fraction, $f_C$, the fraction of the baryons in a dark matter halo that settle either as cold gas or stars into the disk, is twice as high in the HI-massive sample than typical, and almost reaches the universal baryon fraction in some cases,...

Courtois, H M; Sorce, J G; Pomarede, D

2015-01-01T23:59:59.000Z

257

Massive disk outflows mediated by extreme magnetic fields  

E-Print Network [OSTI]

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...

Shiber, Sagiv; Soker, Noam

2015-01-01T23:59:59.000Z

258

On the stability of a galactic disk in modified gravity  

E-Print Network [OSTI]

We find the dispersion relation for tightly wound spiral density waves in the surface of rotating, self-gravitating disks in the framework of Modified Gravity (MOG). Also, the Toomre-like stability criterion for differentially rotating disks has been derived for both fluid and stellar disks. More specifically, the stability criterion can be expressed in terms of a matter density threshold over which the instability occurs. In other words the local stability criterion can be written as $\\Sigma_0sound speed), $\\kappa$ (epicycle frequency) and $\\alpha$ and $\\mu_0$ are the free parameters of the theory. In the case of a stellar disk the radial velocity dispersion $\\sigma_r$ appears in $\\Sigma_{\\text{crit}}$ instead of $v_s$. We find the exact form of the function $\\Sigma_{\\text{crit}}$ for both stellar and fluid self-gravitating disks. Also, we use a sub-sample of THINGS catalog of spiral galaxies in order to compare the local stability criteria. In this perspective, we have compared MOG with Newtonian gravity and investigated the possible and detectable differences between these theories.

Mahmood Roshan; Shahram Abbassi

2015-03-14T23:59:59.000Z

259

RELAXATION OF WARPED DISKS: THE CASE OF PURE HYDRODYNAMICS  

SciTech Connect (OSTI)

Orbiting disks may exhibit bends due to a misalignment between the angular momentum of the inner and outer regions of the disk. We begin a systematic simulational inquiry into the physics of warped disks with the simplest case: the relaxation of an unforced warp under pure fluid dynamics, i.e., with no internal stresses other than Reynolds stress. We focus on the nonlinear regime in which the bend rate is large compared to the disk aspect ratio. When warps are nonlinear, strong radial pressure gradients drive transonic radial motions along the disk's top and bottom surfaces that efficiently mix angular momentum. The resulting nonlinear decay rate of the warp increases with the warp rate and the warp width, but, at least in the parameter regime studied here, is independent of the sound speed. The characteristic magnitude of the associated angular momentum fluxes likewise increases with both the local warp rate and the radial range over which the warp extends; it also increases with increasing sound speed, but more slowly than linearly. The angular momentum fluxes respond to the warp rate after a delay that scales with the square root of the time for sound waves to cross the radial extent of the warp. These behaviors are at variance with a number of the assumptions commonly used in analytic models to describe linear warp dynamics.

Sorathia, Kareem A.; Krolik, Julian H. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Hawley, John F. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States)

2013-05-10T23:59:59.000Z

260

Non-LTE modeling of supernova-fallback disks  

E-Print Network [OSTI]

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.

K. Werner; T. Nagel; T. Rauch

2006-08-24T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
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We encourage you to perform a real-time search of NLEBeta
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261

Chemistry and line emission from evolving Herbig Ae disks  

E-Print Network [OSTI]

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.

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

2006-11-07T23:59:59.000Z

262

Energetic Protons, Radionuclides and Magnetic Activity in Protostellar Disks  

E-Print Network [OSTI]

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^2.

Turner, N J

2009-01-01T23:59:59.000Z

263

Does Dissipation in AGN Disks Couple to the Total Pressure?  

E-Print Network [OSTI]

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.

E. T. Vishniac

1993-08-12T23:59:59.000Z

264

Spectral modeling of gaseous metal disks around DAZ white dwarfs  

E-Print Network [OSTI]

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.

K. Werner; T. Nagel; T. Rauch

2008-09-30T23:59:59.000Z

265

Testing protostellar disk formation models with ALMA observations  

E-Print Network [OSTI]

Abridged: Recent simulations have explored different ways to form accretion disks around low-mass stars. We aim to present observables to differentiate a rotationally supported disk from an infalling rotating envelope toward deeply embedded young stellar objects and infer their masses and sizes. Two 3D magnetohydrodynamics (MHD) formation simulations and 2D semi-analytical model are studied. The dust temperature structure is determined through continuum radiative transfer RADMC3D modelling. A simple temperature dependent CO abundance structure is adopted and synthetic spectrally resolved submm rotational molecular lines up to $J_{\\rm u} = 10$ are simulated. All models predict similar compact components in continuum if observed at the spatial resolutions of 0.5-1$"$ (70-140 AU) typical of the observations to date. A spatial resolution of $\\sim$14 AU and high dynamic range ($> 1000$) are required to differentiate between RSD and pseudo-disk in the continuum. The peak-position velocity diagrams indicate that the...

Harsono, Daniel; Bruderer, Simon; Li, Zhi-Yun; Jorgensen, Jes

2015-01-01T23:59:59.000Z

266

Debris Disks Around White Dwarfs: The DAZ Connection  

E-Print Network [OSTI]

We present near-infrared spectroscopic observations of 20 previously known DAZ white dwarfs obtained at the NASA Infrared Telescope Facility. Two of these white dwarfs (G29-38 and GD362) are known to display significant K-band excesses due to circumstellar debris disks. Here we report the discovery of excess K-band radiation from another DAZ white dwarf, WD0408-041 (GD56). Using spectroscopic observations, we show that the excess radiation cannot be explained by a stellar or substellar companion, and is likely to be caused by a warm debris disk. Our observations strengthen the connection between the debris disk phenomena and the observed metal abundances in cool DAZ white dwarfs. However, we do not find any excess infrared emission from the most metal rich DAZs with $T_{\\rm eff}=$ 16000 -- 20000 K. This suggests that the metal abundances in warmer DAZ white dwarfs may require another explanation.

Mukremin Kilic; Ted von Hippel; S. K. Leggett; D. E. Winget

2006-03-28T23:59:59.000Z

267

POLARIMETRIC IMAGING OF LARGE CAVITY STRUCTURES IN THE PRE-TRANSITIONAL PROTOPLANETARY DISK AROUND PDS 70: OBSERVATIONS OF THE DISK  

SciTech Connect (OSTI)

We present high-resolution H-band polarized intensity (FWHM = 0.''1: 14 AU) and L'-band imaging data (FWHM = 0.''11: 15 AU) of the circumstellar disk around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of 28 AU (0.''2) up to 210 AU (1.''5). In both images, a giant inner gap is clearly resolved for the first time, and the radius of the gap is {approx}70 AU. Our data show that the geometric center of the disk shifts by {approx}6 AU toward the minor axis. We confirm that the brown dwarf companion candidate to the north of PDS 70 is a background star based on its proper motion. As a result of spectral energy distribution fitting by Monte Carlo radiative transfer modeling, we infer the existence of an optically thick inner disk at a few AU. Combining our observations and modeling, we classify the disk of PDS 70 as a pre-transitional disk. Furthermore, based on the analysis of L'-band imaging data, we put an upper limit of {approx}30 to {approx}50 M{sub J} on the mass of companions within the gap. Taking into account the presence of the large and sharp gap, we suggest that the gap could be formed by dynamical interactions of sub-stellar companions or multiple unseen giant planets in the gap.

Hashimoto, J.; Hayashi, M. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Dong, R.; Zhu, Z.; Brandt, T. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Kudo, T.; Egner, S.; Guyon, O.; Hayano, Y. [Subaru Telescope, 650 North A'ohoku Place, Hilo, HI 96720 (United States); Honda, M. [Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293 (Japan); McClure, M. K. [Department of Astronomy, University of Michigan, 500 Church Street, 830 Dennison Building, Ann Arbor, MI 48109 (United States); Muto, T. [Division of Liberal Arts, Kogakuin University, 1-24-2, Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677 (Japan); Wisniewski, J. [University of Washington, Seattle, WA 98195 (United States); Abe, L. [Laboratoire Hippolyte Fizeau, UMR6525, Universite de Nice Sophia-Antipolis, 28, avenue Valrose, F-06108 Nice Cedex 02 (France); Brandner, W.; Carson, J.; Feldt, M. [Max Planck Institute for Astronomy, D-69117 Heidelberg (Germany); Fukagawa, M. [Osaka University, 1-1, Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Goto, M. [Universitaets-Sternwarte Muenchen, Scheinerstr. 1, D-81679 Munich (Germany); Grady, C. A., E-mail: jun.hashimoto@nao.ac.jp [Exoplanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center, Greenbelt, MD 20771 (United States); and others

2012-10-10T23:59:59.000Z

268

EFFECTS OF LOCAL DISSIPATION PROFILES ON MAGNETIZED ACCRETION DISK SPECTRA  

SciTech Connect (OSTI)

We present spectral calculations of non-LTE accretion disk models appropriate for high-luminosity stellar mass black hole X-ray binary systems. We first use a dissipation profile based on scaling the results of shearing box simulations of Hirose et al. to a range of annuli parameters. We simultaneously scale the effective temperature, orbital frequency, and surface density with luminosity and radius according to the standard {alpha}-model. This naturally brings increased dissipation to the disk surface layers (around the photospheres) at small radii and high luminosities. We find that the local spectrum transitions directly from a modified blackbody to a saturated Compton scattering spectrum as we increase the effective temperature and orbital frequency while decreasing midplane surface density. Next, we construct annuli models based on the parameters of a L/L{sub Edd} = 0.8 disk orbiting a 6.62 solar mass black hole using two modified dissipation profiles that explicitly put more dissipation per unit mass near the disk surface. The new dissipation profiles are qualitatively similar to the one found by Hirose et al., but produce strong near power-law spectral tails. Our models also include physically motivated magnetic acceleration support based once again on scaling the Hirose et al. results. We present three full-disk spectra, each based on one of the dissipation prescriptions. Our most aggressive dissipation profile results in a disk spectrum that is in approximate quantitative agreement with certain observations of the steep power-law spectral states from some black hole X-ray binaries.

Tao, Ted [Department of Physics, St. Mary's College of Maryland, St. Mary's City, MD 20686 (United States); Blaes, Omer [Department of Physics, University of California, Santa Barbara, CA 93106 (United States)

2013-06-10T23:59:59.000Z

269

Forced oscillations in relativistic accretion disks and QPOs  

E-Print Network [OSTI]

In this work we explore the idea that the high frequency QPOs observed in LMXBs may be explained as a resonant coupling between the neutron star spin and epicyclic modes of accretion disk oscillations. We propose a new model for these QPOs based on forced oscillations induced in the accretion disk due to a stellar asymmetric rotating gravitational or magnetic field. It is shown that particles evolving in a rotating non-axisymmetric field are subject to three kinds of resonances: a corotation resonance, a Lindblad resonance due to a driving force, and a parametric resonance due to the time varying epicyclic frequencies. These results are extends by means of 2D numerical simulations of a simplified version of the accretion disk. The simulations are performed for the Newtonian gravitational potential, as well as for a pseudo-general relativistic potential, which enables us to explore the behavior of the resonances around both rotating neutron stars and black holes. Density perturbations are only significant in the region located close to the inner edge of the disk near the ISCO where the gravitational or magnetic perturbation is maximal. It is argued that the nearly periodic motion induced in the disk will produce high quality factor QPOs. Finally, applying this model to a typical neutron star, we found that the strongest response occurs when the frequency difference of the two modes equals either the spin frequency (for "slow rotators") or half of it (for "fast rotators"). The two main excited modes may both be connected to vertical oscillations of the disk. We emphasize that strong gravity is not needed to excite the modes.

J. Petri

2006-12-29T23:59:59.000Z

270

Kinematic segregation of nearby disk stars from the Hipparcos database  

E-Print Network [OSTI]

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

R. E. de Souza; R. Teixeira

2007-04-25T23:59:59.000Z

271

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

E-Print Network [OSTI]

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.

B. Fuchs

1998-12-02T23:59:59.000Z

272

Dim Matter in the Disks of Low Surface Brightness Galaxies  

E-Print Network [OSTI]

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.

B. Fuchs

2002-04-23T23:59:59.000Z

273

Chemistry and line emission of outer protoplanetary disks  

E-Print Network [OSTI]

The structure and chemistry of protoplanetary disks depends strongly on the nature of the central star around which it has formed. The dust temperature is mainly set by the stellar luminosity, while the chemistry of the upper disk layers depends on the amount of intercepted UV and X-ray flux. We will study the differences in chemistry, thermal sturcture and line emission around Herbig Ae/Be, T Tauri stars and low mass M dwarfs. Predictions will be made for future observations with SOFIA and Herschel.

Inga Kamp; Cornelis P. Dullemond; Michiel Hogerheijde; Jesus Emilio Enriquez

2005-09-21T23:59:59.000Z

274

INJECTION OF SUPERNOVA DUST IN NEARBY PROTOPLANETARY DISKS  

SciTech Connect (OSTI)

The early solar system contained a number of short-lived radionuclides (SLRs) such as {sup 26}Al with half-lives <15 Myr. The one-time presence of {sup 60}Fe strongly suggests that the source of these radionuclides was a nearby supernova. In this paper, we investigate the 'aerogel' model, which hypothesizes that the solar system's SLRs were injected directly into the solar system's protoplanetary disk from a supernova within the same star-forming region. Previous work has shown that disks generally survive the impact of supernova ejecta, but also that little gaseous ejecta can be injected into the disk. The aerogel model hypothesizes that radionuclides in the ejecta condensed into micron-sized dust grains that were injected directly into the solar nebula disk. Here, we discuss the density structure of supernova ejecta and the observational support for dust condensation in the ejecta. We argue that supernova ejecta are clumpy and describe a model to quantify this clumpiness. We also argue that infrared observations may be underestimating the fraction of material that condenses into dust. Building on calculations of how supernova ejecta interact with protoplanetary disks, we calculate the efficiency with which dust grains in the ejecta are injected into a disk. We find that about 70% of material in grains roughly 0.4 {mu}m in diameter can be injected into disks. If ejecta are clumpy, the solar nebula was struck by a clump with higher-than-average {sup 26}Al and {sup 60}Fe, and these elements condensed efficiently into large grains, then the abundances of SLRs in the early solar system can be explained, even if the disk lies 2 pc from the supernova explosion. The probability that all these factors are met is low, perhaps {approx}10{sup -3}-10{sup -2}, and receiving as much {sup 26}Al and {sup 60}Fe as the solar system did may be a rare event. Still, the aerogel model remains a viable explanation for the origins of the radionuclides in the early solar system, and may be the most plausible one.

Ouellette, N. [Department of Physics, Arizona State University, P.O. Box 871504, Tempe, AZ 85287-1504 (United States); Desch, S. J.; Hester, J. J. [School of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404 (United States)

2010-03-10T23:59:59.000Z

275

The missing cavities in the SEEDS polarized scattered light images of transitional protoplanetary disks: a generic disk model  

E-Print Network [OSTI]

Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 microns in their Spectral Energy Distributions (SED), recently measured by the Spitzer Infrared Spectrograph (IRS), suggesting dust depletion in the inner regions. These disks have been confirmed to have giant central cavities by imaging of the submillimeter (sub-mm) continuum emission using the Submillimeter Array (SMA). However, the polarized near-infrared scattered light images for most objects in a systematic IRS/SMA cross sample, obtained by HiCIAO on the Subaru telescope, show no evidence for the cavity, in clear contrast with SMA and Spitzer observations. Radiative transfer modeling indicates that many of these scattered light images are consistent with a smooth spatial distribution for micron-sized grains, with little discontinuity in the surface density of the micron-sized grains at the cavity edge. Here we present a generic disk model that can simultaneously account for the general features in...

Dong, R; Zhu, Z; Hartmann, L; Whitney, B; Brandt, T; Muto, T; Hashimoto, J; Grady, C; Follette, K; Kuzuhara, M; Tanii, R; Itoh, Y; Thalmann, C; Wisniewski, J; Mayama, S; Janson, M; Abe, L; Brandner, W; Carson, J; Egner, S; Feldt, M; Goto, M; Guyon, O; Hayano, Y; Hayashi, M; Hayashi, S; Henning, T; Hodapp, K W; Honda, M; Inutsuka, S; Ishii, M; Iye, M; Kandori, R; Knapp, G R; Kudo, T; Kusakabe, N; Matsuo, T; McElwain, M W; Miyama, S; Morino, J -I; Moro-Martin, A; Nishimura, T; Pyo, T -S; Suto, H; Suzuki, R; Takami, M; Takato, N; Terada, H; Tomono, D; Turner, E L; Watanabe, M; Yamada, T; Takami, H; Usuda, T; Tamura, M

2012-01-01T23:59:59.000Z

276

accretion-disk outflows ii: Topics by E-print Network  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

field direction in the stellar wind is opposite to that in the disk wind. The maximum speed of the outflow is about the Keplerian speed at the inner disk radius. With the chosen...

277

E-Print Network 3.0 - accretion disk candidates Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

beamed bright spot on the accretion disk around the compact star. The long... the orbital inclination because the contribution of theM . accretion disk to the observed ux is...

278

E-Print Network 3.0 - accretion disk revealed Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

beamed bright spot on the accretion disk around the compact star. The long... the orbital inclination because the contribution of theM . accretion disk to the observed ux is...

279

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

E-Print Network [OSTI]

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 ...

Smith, Rachel

2008-01-01T23:59:59.000Z

280

Thermal Issues in Disk Drive Design: Challenges and Possible Solutions  

E-Print Network [OSTI]

are to adhere to the thermal design envelope. We motivate the need for continued improvements in IDR by showing throttles its activities to remain within the thermal envelope. Categories and Subject Descriptors: B.4Thermal Issues in Disk Drive Design: Challenges and Possible Solutions SUDHANVA GURUMURTHI

Gurumurthi, Sudhanva

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


281

General Relativistic Flux Modulations from Disk Instabilities in Sagittarius A*  

E-Print Network [OSTI]

Near-IR and X-ray flares have been detected from the supermassive black hole Sgr A* at the center of our Galaxy with a (quasi)-period of ~17-20 minutes, suggesting an emission region only a few Schwarzschild radii above the event horizon. The latest X-ray flare, detected with XMM-Newton, is notable for its detailed lightcurve, yielding not only the highest quality period thus far, but also important structure reflecting the geometry of the emitting region. Recent MHD simulations of Sgr A*'s disk have demonstrated the growth of a Rossby wave instability, that enhances the accretion rate for several hours, possibly accounting for the observed flares. In this Letter, we carry out ray-tracing calculations in a Schwarzschild metric to determine as accurately as possible the lightcurve produced by general relativistic effects during such a disruption. We find that the Rossby wave induced spiral pattern in the disk is an excellent fit to the data, implying a disk inclination angle of ~77 deg. Note, however, that if this association is correct, the observed period is not due to the underlying Keplerian motion but, rather, to the pattern speed. The favorable comparison between the observed and simulated lightcurves provides important additional evidence that the flares are produced in Sgr A*'s inner disk.

Maurizio Falanga; Fulvio Melia; Michel Tagger; Andrea Goldwurm; Guillaume Belanger

2007-05-02T23:59:59.000Z

282

A probable giant planet imaged in the Beta Pictoris disk  

E-Print Network [OSTI]

Since the discovery of its dusty disk in 1984, Beta Pictoris has become the prototype of young early-type planetary systems, and there are now various indications that a massive Jovian planet is orbiting the star at ~ 10 AU. However, no planets have been detected around this star so far. Our goal was to investigate the close environment of Beta Pic, searching for planetary companion(s). Deep adaptive-optics L'-band images of Beta Pic were recorded using the NaCo instrument at the Very Large Telescope. A faint point-like signal is detected at a projected distance of ~ 8 AU from the star, within the North-East side of the dust disk. Various tests were made to rule out with a good confidence level possible instrumental or atmospheric artifacts. The probability of a foreground or background contaminant is extremely low, based in addition on the analysis of previous deep Hubble Space Telescope images. The object L'=11.2 apparent magnitude would indicate a typical temperature of ~1500 K and a mass of ~ 8 Jovian masses. If confirmed, it could explain the main morphological and dynamical peculiarities of the Beta Pic system. The present detection is unique among A-stars by the proximity of the resolved planet to its parent star. Its closeness and location inside the Beta Pic disk suggest a formation process by core accretion or disk instabilities rather than a binary-like formation process.

A. -M. Lagrange; D. Gratadour; G. Chauvin; T. Fusco; D. Ehrenreich; D. Mouillet; G. Rousset; D. Rouan; F. Allard; E. Gendron; J. Charton; L. Mugnier; P. Rabou; J. Montri; F. Lacombe

2008-11-21T23:59:59.000Z

283

A Search for Fallback Disks in Four Young Supernova Remnants  

E-Print Network [OSTI]

We report on our search for the optical/infrared counterparts to the central compact objects in four young supernova remnants: Puppis A, PKS 1209-52, RCW 103, and Cassiopeia A. The X-ray point sources in these supernova remnants, likely members of a new class (or classes) of young neutron stars, are attractive targets for probing the existence of supernova ``fallback'' disks. Such disks, which are a general prediction of many supernova models, can form from supernova ejecta that fails to reach escape velocity during the initial explosion. Irradiation of the disk by a central X-ray source may lead to detectable optical/infrared emission from such a disk. We used imaging observations from ground-based telescopes in the optical and near-infrared regimes and from the Spitzer Space Telescope at 4.5 and 8.0 micron, to search for optical/infrared counterparts at the X-ray point source positions measured in these supernova remnants by the Chandra X-Ray Observatory. We did not detect any counterparts, and hence find n...

Wang, Z; Chakraborty, D; Wang, Zhongxiang; Kaplan, David L.; Chakrabarty, Deepto

2006-01-01T23:59:59.000Z

284

Ultrasonic detection of residual stress in a turbine disk  

E-Print Network [OSTI]

technique measured stresses within one standard deviation of 5000 psi. Further, the technique showed that in the as-received condstion stresses in the narrow and broad sides of the turbine disk rim were above 5500 psi tensile and above 20, 000 psi...

Pathak, Nitin

1992-01-01T23:59:59.000Z

285

Vortex generation in protoplanetary disks with an embedded giant planet  

E-Print Network [OSTI]

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 $\

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

2007-06-21T23:59:59.000Z

286

Disk-shaped Compact Tension Test for Asphalt Concrete Fracture  

E-Print Network [OSTI]

Disk-shaped Compact Tension Test for Asphalt Concrete Fracture by M.P.Wagoner, W.G. Buttlar and G geometry is the ability to test cylindrical cores obtained from in-place asphalt concrete pavements finalizing the specimen geometry, a typical asphalt concrete surface mixture was tested at various

Paulino, Glaucio H.

287

Disk Drive Roadmap from the Thermal Perspective: A Case for Dynamic Thermal Management  

E-Print Network [OSTI]

the thermal envelope, and employs dynamic throttling of disk drive activities to remain within this envelopeDisk Drive Roadmap from the Thermal Perspective: A Case for Dynamic Thermal Management Sudhanva The importance of pushing the performance envelope of disk drives continues to grow, not just in the server

Sivasubramaniam, Anand

288

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

E-Print Network [OSTI]

Conserving 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 General Terms Experimentation, measurement Keywords Energy conservation, network servers, disk power 1

Bianchini, Ricardo

289

Unipolar Induction of a Magnetized Accretion Disk around a Black Hole  

E-Print Network [OSTI]

The structure and magnitude of the electromagnetic field produced by a rotating accretion disk around a black hole were determined. The disk matter is assumed to be a magnetized plasma with a frozenin poloidal magnetic field. The vacuum approximation is used outside the disk.

A. A. Shatskiy

2003-01-27T23:59:59.000Z

290

Forced oscillations in a hydrodynamical accretion disk and QPOs  

E-Print Network [OSTI]

This is the second of a series of papers aimed to look for an explanation on the generation of high frequency quasi-periodic oscillations (QPOs) in accretion disks around neutron star, black hole, and white dwarf binaries. The model is inspired by the general idea of a resonance mechanism in the accretion disk oscillations as was already pointed out by Abramowicz & Klu{\\'z}niak (\\cite{Abramowicz2001}). In a first paper (P\\'etri \\cite{Petri2005a}, paper I), we showed that a rotating misaligned magnetic field of a neutron star gives rise to some resonances close to the inner edge of the accretion disk. In this second paper, we suggest that this process does also exist for an asymmetry in the gravitational potential of the compact object. We prove that the same physics applies, at least in the linear stage of the response to the disturbance in the system. This kind of asymmetry is well suited for neutron stars or white dwarfs possessing an inhomogeneous interior allowing for a deviation from a perfectly spherically symmetric gravitational field. We show by a linear analysis that the disk initially in a cylindrically symmetric stationary state is subject to three kinds of resonances: a corotation resonance, a Lindblad resonance due to a driven force and a parametric sonance. The highest kHz QPOs are then interpreted as the orbital frequency of the disk at locations where the response to the resonances are maximal. It is also found that strong gravity is not required to excite the resonances.

J. Petri

2005-09-22T23:59:59.000Z

291

Dynamics of Circumstellar Disks II: Heating and Cooling  

E-Print Network [OSTI]

We present a series of 2-d ($r,\\phi$) hydrodynamic simulations of marginally self gravitating disks around protostars using an SPH code. We implement simple dynamical heating and we cool each location as a black body, using a photosphere temperature obtained from the local vertical structure. We synthesize SEDs from our simulations and compare them to fiducial SEDs derived from observed systems. These simulations produce less distinct spiral structure than isothermally evolved systems, especially in the inner third of the disk. Pattern are similar further from the star but do not collapse into condensed objects. The photosphere temperature is well fit to a power law in radius with index $q\\sim1.1$, which is very steep. Far from the star, internal heating ($PdV$ work and shocks) are not responsible for generating a large fraction of the thermal energy contained in the disk matter. Gravitational torques responsible for such shocks cannot transport mass and angular momentum efficiently in the outer disk. Within $\\sim$5--10 AU of the star, rapid break up and reformation of spiral structure causes shocks, which provide sufficient dissipation to power a larger fraction of the near IR energy output. The spatial and size distribution of grains can have marked consequences on the observed near IR SED and can lead to increased emission and variability on $\\lesssim 10$ year time scales. When grains are vaporized they do not reform into a size distribution similar to that from which most opacity calculations are based. With rapid grain reformation into the original size distribution, the disk does not emit near infrared photons. With a plausible modification to the opacity, it contributes much more.

Andrew F. Nelson; Willy Benz; Tamara Ruzmaikina

1999-08-13T23:59:59.000Z

292

MINERAL PROCESSING BY SHORT CIRCUITS IN PROTOPLANETARY DISKS  

SciTech Connect (OSTI)

Meteoritic chondrules were formed in the early solar system by brief heating of silicate dust to melting temperatures. Some highly refractory grains (Type B calcium-aluminum-rich inclusions, CAIs) also show signs of transient heating. A similar process may occur in other protoplanetary disks, as evidenced by observations of spectra characteristic of crystalline silicates. One possible environment for this process is the turbulent magnetohydrodynamic flow thought to drive accretion in these disks. Such flows generally form thin current sheets, which are sites of magnetic reconnection, and dissipate the magnetic fields amplified by a disk dynamo. We suggest that it is possible to heat precursor grains for chondrules and other high-temperature minerals in current sheets that have been concentrated by our recently described short-circuit instability. We extend our work on this process by including the effects of radiative cooling, taking into account the temperature dependence of the opacity; and by examining current sheet geometry in three-dimensional, global models of magnetorotational instability. We find that temperatures above 1600 K can be reached for favorable parameters that match the ideal global models. This mechanism could provide an efficient means of tapping the gravitational potential energy of the protoplanetary disk to heat grains strongly enough to form high-temperature minerals. The volume-filling nature of turbulent magnetic reconnection is compatible with constraints from chondrule-matrix complementarity, chondrule-chondrule complementarity, the occurrence of igneous rims, and compound chondrules. The same short-circuit mechanism may perform other high-temperature mineral processing in protoplanetary disks such as the production of crystalline silicates and CAIs.

McNally, Colin P. [Niels Bohr International Academy, Niels Bohr Institute, DK-2100 Copenhagen (Denmark); Hubbard, Alexander; Mac Low, Mordecai-Mark [Department of Astrophysics, American Museum of Natural History, New York, NY 10024-5192 (United States); Ebel, Denton S. [Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY 10024-5192 (United States); D'Alessio, Paola, E-mail: cmcnally@nbi.dk, E-mail: ahubbard@amnh.org, E-mail: mordecai@amnh.org, E-mail: debel@amnh.org, E-mail: p.dalessio@crya.unam.mx [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, 58089 Morelia, MICH (Mexico)

2013-04-10T23:59:59.000Z

293

Why we need survey-styleWhy we need survey-style bulge-disk decompositionbulge-disk decomposition  

E-Print Network [OSTI]

Why we need survey-styleWhy we need survey-style bulge-disk decompositionbulge. Using our calibrated dust model we can also compute the photon escape fractions of galaxies at any other of the nearby Universe before (orange) and after (black) correction for the effects of dust. The energy absorbed

Liske, Jochen

294

Limits on iron-dominated fallback disk in SN 1987A  

E-Print Network [OSTI]

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.

K. Werner; T. Nagel; T. Rauch

2007-03-20T23:59:59.000Z

295

THE PHYSICAL STRUCTURE OF PROTOPLANETARY DISKS: THE SERPENS CLUSTER COMPARED WITH OTHER REGIONS  

SciTech Connect (OSTI)

Spectral energy distributions are presented for 94 young stars surrounded by disks in the Serpens Molecular Cloud, based on photometry and Spitzer/IRS spectra. Most of the stars have spectroscopically determined spectral types. Taking a distance to the cloud of 415 pc rather than 259 pc, the distribution of ages is shifted to lower values, in the 1-3 Myr range, with a tail up to 10 Myr. The mass distribution spans 0.2-1.2 M {sub Sun }, with median mass of 0.7 M {sub Sun }. The distribution of fractional disk luminosities in Serpens resembles that of the young Taurus Molecular Cloud, with most disks consistent with optically thick, passively irradiated disks in a variety of disk geometries (L {sub disk}/L {sub star} {approx} 0.1). In contrast, the distributions for the older Upper Scorpius and {eta} Chamaeleontis clusters are dominated by optically thin lower luminosity disks (L {sub disk}/L {sub star} {approx} 0.02). This evolution in fractional disk luminosities is concurrent with that of disk fractions: with time disks become fainter and the disk fractions decrease. The actively accreting and non-accreting stars (based on H{alpha} data) in Serpens show very similar distributions in fractional disk luminosities, differing only in the brighter tail dominated by strongly accreting stars. In contrast with a sample of Herbig Ae/Be stars, the T Tauri stars in Serpens do not have a clear separation in fractional disk luminosities for different disk geometries: both flared and flat disks present wider, overlapping distributions. This result is consistent with previous suggestions of a faster evolution for disks around Herbig Ae/Be stars. Furthermore, the results for the mineralogy of the dust in the disk surface (grain sizes, temperatures and crystallinity fractions, as derived from Spitzer/IRS spectra) do not show any correlation to either stellar and disk characteristics or mean cluster age in the 1-10 Myr range probed here. A possible explanation for the lack of correlation is that the processes affecting the dust within disks have short timescales, happening repeatedly, making it difficult to distinguish long-lasting evolutionary effects.

Oliveira, Isa; Van Dishoeck, Ewine F. [Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands)] [Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Merin, Bruno [Herschel Science Center, European Space Astronomy Centre (ESA), P.O. Box 78, E-28691 Villanueva de la Canada (Madrid) (Spain)] [Herschel Science Center, European Space Astronomy Centre (ESA), P.O. Box 78, E-28691 Villanueva de la Canada (Madrid) (Spain); Pontoppidan, Klaus M., E-mail: oliveira@astro.as.utexas.edu [Space Telescope Science Institute, Baltimore, MD 21218 (United States)

2013-01-10T23:59:59.000Z

296

Merger Histories of Galaxy Halos and Implications for Disk Survival  

SciTech Connect (OSTI)

The authors study the merger histories of galaxy dark matter halos using a high resolution {Lambda}CDM N-body simulation. The merger trees follow {approx} 17,000 halos with masses M{sub 0} = (10{sup 11} - 10{sup 13})h{sup -1}M{sub {circle_dot}} at z = 0 and track accretion events involving objects as small as m {approx_equal} 10{sup 10} h{sup -1}M{sub {circle_dot}}. They find that mass assembly is remarkably self-similar in m/M{sub 0}, and dominated by mergers that are {approx}10% of the final halo mass. While very large mergers, m {approx}> 0.4 M{sub 0}, are quite rare, sizeable accretion events, m {approx} 0.1 M{sub 0}, are common. Over the last {approx} 10 Gyr, an overwhelming majority ({approx} 95%) of Milky Way-sized halos with M{sub 0} = 10{sup 12} h{sup -1}M{sub {circle_dot}} have accreted at least one object with greater total mass than the Milky Way disk (m > 5 x 10{sup 10} h{sup -1}M{sub {circle_dot}}), and approximately 70% have accreted an object with more than twice that mass (m > 10{sup 11} h{sup -1}M{sub {circle_dot}}). The results raise serious concerns about the survival of thin-disk dominated galaxies within the current paradigm for galaxy formation in a {Lambda}CDM universe. in order to achieve a {approx} 70% disk-dominated fraction in Milky Way-sized {Lambda}CDM halos, mergers involving m {approx_equal} 2 x 10{sup 11} h{sup -1}M{sub {circle_dot}} objects must not destroy disks. Considering that most thick disks and bulges contain old stellar populations, the situation is even more restrictive: these mergers must not heat disks or drive gas into their centers to create young bulges.

Stewart, Kyle R.; Bullock, James S.; Wechsler, Risa H.; Maller, Ariyeh H.; Zentner, Andrew R.

2008-05-16T23:59:59.000Z

297

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

E-Print Network [OSTI]

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.

R. Surman; G. C. McLaughlin

2004-07-09T23:59:59.000Z

298

Multiple hot images from an obscuration in an intense laser beam through cascaded Kerr medium disks  

SciTech Connect (OSTI)

We present a theoretical investigation on the formation of hot images in an intense laser beam through cascaded Kerr medium disks, to disclose the distribution and intensity of hot images in high-power disk amplifiers. It is shown that multiple hot images from an obscuration may be formed, instead of one hot image as reported previously in the literature. This gives a clear explanation for the curious damage pattern of hot images, namely, damage sites appearing on alternating optics in periodic trains. Further analysis demonstrates that the distribution and intensity of hot images depend closely on the number of Kerr medium disks, the distance from the obscuration to the front of the first disk downstream, the space between two neighboring disks, and the thickness and B integral of each disk. Moreover, we take two cascaded Kerr medium disks for example to detail multiple hot images from an obscuration and confirm the theoretical results by numerical simulations.

Wang Youwen; Wen Shuangchun; You Kaiming; Tang Zhixiang; Deng Jianqin; Zhang Lifu; Fan Dianyuan

2008-10-20T23:59:59.000Z

299

ORIGIN OF CHEMICAL AND DYNAMICAL PROPERTIES OF THE GALACTIC THICK DISK  

SciTech Connect (OSTI)

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.

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

2011-09-01T23:59:59.000Z

300

THE 0.5-2.22 {mu}m SCATTERED LIGHT SPECTRUM OF THE DISK AROUND TW Hya: DETECTION OF A PARTIALLY FILLED DISK GAP AT 80 AU  

SciTech Connect (OSTI)

We present a 0.5-2.2 {mu}m scattered light spectrum of the circumstellar disk around TW Hya from a combination of spatially resolved Hubble Space Telescope STIS spectroscopy and NICMOS coronagraphic images of the disk. We investigate the morphology of the disk at distances >40 AU over this wide range of wavelengths, and identify the presence of a depression in surface brightness at {approx}80 AU that could be caused by a gap in the disk. Additionally, we quantify the surface brightness, azimuthal symmetry, and spectral character of the disk as a function of radius. Our analysis shows that the scattering efficiency of the dust is largely neutral to blue over the observed wavelengths. We model the disk as a steady {alpha}-disk with an ad hoc gap structure. The thermal properties of the disk are self-consistently calculated using a three-dimensional radiative transfer code that uses ray tracing to model the heating of the disk interior and scattered light images. We find a good fit to the data over a wide range of distances from the star if we use a model disk with a partially filled gap of 30% depth at 80 AU and with a self-similar truncation knee at 100 AU. The origin of the gap is unclear, but it could arise from a transition in the nature of the disk's dust composition or the presence of a planetary companion. Based on scalings to previous hydrodynamic simulations of gap-opening criteria for embedded proto-planets, we estimate that a planetary companion forming the gap could have a mass between 6 and 28 M{sub Circled-Plus }.

Debes, John H. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Jang-Condell, Hannah [University of Wyoming, Laramie, WY 82071 (United States); Weinberger, Alycia J. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 (United States); Roberge, Aki [Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Schneider, Glenn [Steward Observatory, University of Arizona, Tuscon, AZ 85721 (United States)

2013-07-01T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
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301

DEVELOPMENT OF A LAMINATED DISK FOR THE SPIN TEK ROTARY MICROFILTER  

SciTech Connect (OSTI)

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.

Herman, D.

2011-06-03T23:59:59.000Z

302

Fracture toughness measurements with subsize disk compact specimens  

SciTech Connect (OSTI)

Special fixtures and test methods have been developed for testing small disk compact specimens (1.25 mm diam by 4.6 mm thick). Specimens of European type 316L austenitic stainless steel were irradiated to damage levels of about 3 dpa at nominal irradiation temperatures of either 90 or 250 C and tested over a temperature range from 20 to 250 C. Results show that irradiation to this dose level at these temperatures reduces the fracture toughness but the toughness remains quite high. The toughness decreases as the test temperature increases. Irradiation at 250 C is more damaging than at 90 C, causing larger decreases in the fracture toughness. The testing shows that it is possible to generate useful fracture toughness data with a small disk compact specimens.

Alexander, D.J.

1994-12-31T23:59:59.000Z

303

SUBSTRUCTURE IN BULK VELOCITIES OF MILKY WAY DISK STARS  

SciTech Connect (OSTI)

We find that Galactic disk stars near the anticenter exhibit velocity asymmetries in both the Galactocentric radial and vertical components across the midplane as well as azimuthally. These findings are based on Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic velocities for a sample of ?400, 000 F-type stars, combined with proper motions from the PPMXL catalog for which we have derived corrections to the zero points based in part on spectroscopically discovered galaxies and QSOs from LAMOST. In the region within 2 kpc outside the Sun's radius and 2 kpc from the Galactic midplane, we show that stars above the plane exhibit net outward radial motions with downward vertical velocities, while stars below the plane have roughly the opposite behavior. We discuss this in the context of other recent findings, and conclude that we are likely seeing the signature of vertical disturbances to the disk due to an external perturbation.

Carlin, Jeffrey L.; DeLaunay, James; Newberg, Heidi Jo; Gole, Daniel; Grabowski, Kathleen [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States)] [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Deng, Licai; Liu, Chao; Luo, A-Li; Zhang, Haotong; Zhao, Gang; Zhao, Yongheng [Key Lab for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)] [Key Lab for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Jin, Ge [University of Science and Technology of China, Hefei 230026 (China)] [University of Science and Technology of China, Hefei 230026 (China); Liu, Xiaowei; Yuan, Haibo, E-mail: carlij@rpi.edu [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)] [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)

2013-11-01T23:59:59.000Z

304

Adaptor assembly for coupling turbine blades to rotor disks  

DOE Patents [OSTI]

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.

Garcia-Crespo, Andres Jose; Delvaux, John McConnell

2014-09-23T23:59:59.000Z

305

3-D Simulations of Ergospheric Disk Driven Poynting Jets  

E-Print Network [OSTI]

This Letter reports on 3-dimensional simulations of Kerr black hole magnetospheres that obey the general relativistic equations of perfect magnetohydrodynamics (MHD). In particular, we study powerful Poynting flux dominated jets that are driven from dense gas in the equatorial plane in the ergosphere. The physics of which has been previously studied in the simplified limit of an ergopsheric disk. For high spin black holes, $a/M > 0.95$, the ergospheric disk is prominent in the 3-D simulations and is responsible for greatly enhanced Poynting flux emission. Any large scale poloidal magnetic flux that is trapped in the equatorial region leads to an enormous release of electromagnetic energy that dwarfs the jet energy produced by magnetic flux threading the event horizon. The implication is that magnetic flux threading the equatorial plane of the ergosphere is a likely prerequisite for the central engine of powerful FRII quasars.

Brian Punsly

2007-04-05T23:59:59.000Z

306

Controllable stacked disk morphologies of charged diblock copolymers  

SciTech Connect (OSTI)

Monte Carlo simulations are used to demonstrate the controlled stacking of charged block copolymer disk morphologies that can be obtained under certain thermodynamic conditions. We examine a partially charged block copolymer where 75% of the blocks are neutral and 25% of the blocks are charged. The presence of strong electrostatic interactions promotes charge agglomeration thereby changing morphologies in these systems. This study relates different thermodynamic quantities for which disk-like stackings can be obtained. The long-range order can be sustained even if hydrophobicity is increased albeit with lower dimensional structures. Our simulation results agree very well with recent experiments and are consistent with theoretical observations of counterion adsorption on flexible polyelectrolytes.

Goswami, Monojoy [ORNL; Sumpter, Bobby G [ORNL; Mays, Jimmy [ORNL

2010-01-01T23:59:59.000Z

307

Galaxies that Shine: radiation-hydrodynamical simulations of disk galaxies  

E-Print Network [OSTI]

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 ...

Rosdahl, Joakim; Teyssier, Romain; Agertz, Oscar

2015-01-01T23:59:59.000Z

308

THE MASS DEPENDENCE BETWEEN PROTOPLANETARY DISKS AND THEIR STELLAR HOSTS  

SciTech Connect (OSTI)

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.

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)

2013-07-10T23:59:59.000Z

309

Tribo-chemistry at the head/disk interface  

SciTech Connect (OSTI)

Tribo-chemical studies at the head/disk interface (HDI) were conducted on hydrogenated (CH{sub x}), nitrogenated (CN{sub x}), and cathodic-arc amorphous hard carbon disk samples coated with perfluoropolyether ZDOL and X1P/ZDOL lubricant. The studies involved drag tests with uncoated and carbon-coated Al{sub 2}O{sub 3}-TiC sliders and thermal desorption experiments in an ultra-high vacuum (UHV) tribochamber followed with a surface chemistry analysis by X-ray Photo Emission Electron Microscopy (X-PEEM) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The friction and catalytic decomposition mechanisms of ZDOL are described, as well as the tribo-chemical performance of cathodic-arc carbon overcoats coated with ZDOL, and data demonstrating the chemical alteration of the lubricant and carbon overcoat are also presented.

Bhatia, C.S. [SSD/IBM, San Jose, CA (United States)] [SSD/IBM, San Jose, CA (United States); Fong, W.; Chen, C.Y.; Wei, J.; Bogy, D.B. [Univ. of California, Berkeley, CA (United States). Computer Mechanics Lab.] [Univ. of California, Berkeley, CA (United States). Computer Mechanics Lab.; Anders, S.; Stammler, T. [Lawrence Berkeley National Lab., CA (United States)] [Lawrence Berkeley National Lab., CA (United States); Stoehr, J. [IBM Research Div., San Jose, CA (United States)] [IBM Research Div., San Jose, CA (United States)

1999-03-01T23:59:59.000Z

310

Theory of bending waves with applications to disk galaxies  

SciTech Connect (OSTI)

A theory of bending waves is surveyed which provides an explanation for the required amplification of the warp in the Milky Way. It also provides for self-generated warps in isolated external galaxies. The shape of observed warps and partly their existence in isolated galaxies are indicative of substantial spheroidal components. The theory also provides a plausible explanation for the bending of the inner disk (<2 kpc) of the Milky Way.

Mark, J.W.K.

1982-01-01T23:59:59.000Z

311

On the generation of asymmetric warps in disk galaxies  

E-Print Network [OSTI]

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.

Kanak Saha; Chanda J. Jog

2005-10-28T23:59:59.000Z

312

Wet-steam erosion of steam turbine disks and shafts  

SciTech Connect (OSTI)

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.

Averkina, N. V. [JSC 'NPO TsKTI' (Russian Federation); Zheleznyak, I. V. [Leningradskaya AES branch of JSC 'Kontsern Rosenergoatom' (Russian Federation); Kachuriner, Yu. Ya.; Nosovitskii, I. A.; Orlik, V. G., E-mail: orlikvg@mail.ru [JSC 'NPO TsKTI' (Russian Federation); Shishkin, V. I. [Leningradskaya AES branch of JSC 'Kontsern Rosenergoatom' (Russian Federation)

2011-01-15T23:59:59.000Z

313

Disk-averaged Spectra & light-curves of Earth  

E-Print Network [OSTI]

We are using computer models to explore the observational sensitivity to changes in atmospheric and surface properties, and the detectability of biosignatures, in the globally averaged spectra and light-curves of the Earth. Using AIRS (Atmospheric Infrared Sounder) data, as input for atmospheric and surface properties, we have generated spatially resolved high-resolution synthetic spectra using the SMART radiative transfer model, for a variety of conditions, from the UV to the far-IR (beyond the range of current Earth-based satellite data). We have then averaged over the visible disk for a number of different viewing geometries to quantify the sensitivity to surface types and atmospheric features as a function of viewing geometry, and spatial and spectral resolution. These results have been processed with an instrument simulator to improve our understanding of the detectable characteristics of Earth-like planets as viewed by the first generation extrasolar terrestrial planet detection and characterization missions (Terrestrial Planet Finder/Darwin and Life finder). The wavelength range of our results are modelled over are applicable to both the proposed visible coronograph and mid-infrared interferometer TPF architectures. We have validated this model against disk-averaged observations by the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES). This model was also used to analyze Earth-shine data for detectability of planetary characteristics and biosignatures in disk-averaged spectra.

G. Tinetti; V. S. Meadows; D. Crisp; W. Fong; N. Kiang; E. Fishbein; T. Velusamy; E. Bosc; M. Turnbull

2005-02-11T23:59:59.000Z

314

Star Cluster Populations in the Outer Disks of Nearby Galaxies  

E-Print Network [OSTI]

We present a Large Binocular Telescope (LBT) imaging study that characterizes the star cluster component of nearby galaxy outer disks (beyond the optical radius R_25). Expanding on the pilot project of Herbert-Fort et al. (2009), we present deep (~ 27.5 mag V-band point-source limiting magnitude) U- and V-band imaging of six galaxies: IC 4182, NGC 3351, NGC 4736, NGC 4826, NGC 5474, and NGC 6503. We find that the outer disk of each galaxy is populated with marginally-resolved star clusters with masses ~10^3 M_sun and ages up to ~ 1 Gyr (masses and ages are limited by the depth of our imaging and uncertainties are large given how photometry can be strongly affected by the presence or absence of a few stars in such low mass systems), and that they are typically found out to at least 2 R_25 but sometimes as far as 3 to 4 R_25- even beyond the apparent HI disk. The mean rate of cluster formation for 1 R_25<= R <= 1.5R_25 is at least one every ~2.5 Myr and the clusters are spatially correlated with the HI, m...

Herbert-Fort, Stphane; Moustakas, John; Di Paola, Andrea; Pogge, Richard W; Ragazzoni, Roberto

2012-01-01T23:59:59.000Z

315

THE DEBRIS DISK AROUND {gamma} DORADUS RESOLVED WITH HERSCHEL  

SciTech Connect (OSTI)

We present observations of the debris disk around {gamma} Doradus, an F1V star, from the Herschel Key Programme DEBRIS (Disc Emission via Bias-free Reconnaissance in the Infrared/Submillimetre). The disk is well resolved at 70, 100, and 160 {mu}m, resolved along its major axis at 250 {mu}m, detected but not resolved at 350 {mu}m, and confused with a background source at 500 {mu}m. It is one of our best resolved targets and we find it to have a radially broad dust distribution. The modeling of the resolved images cannot distinguish between two configurations: an arrangement of a warm inner ring at several AU (best fit 4 AU) and a cool outer belt extending from {approx}55 to 400 AU or an arrangement of two cool, narrow rings at {approx}70 AU and {approx}190 AU. This suggests that any configuration between these two is also possible. Both models have a total fractional luminosity of {approx}10{sup -5} and are consistent with the disk being aligned with the stellar equator. The inner edge of either possible configuration suggests that the most likely region to find planets in this system would be within {approx}55 AU of the star. A transient event is not needed to explain the warm dust's fractional luminosity.

Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Booth, Mark; Kavelaars, J. J.; Koning, Alice [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P6 (Canada)] [Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 3P6 (Canada); Kennedy, Grant M.; Wyatt, Mark C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)] [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Sibthorpe, Bruce [UK Astronomy Technology Center, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)] [UK Astronomy Technology Center, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Lawler, Samantha M. [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada)] [Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1 (Canada); Qi, Chenruo [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7 (Canada)] [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7 (Canada); Su, Kate Y. L.; Rieke, George H. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)] [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Wilner, David J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)] [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Greaves, Jane S. [School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS (United Kingdom)] [School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS (United Kingdom)

2013-01-01T23:59:59.000Z

316

Lithium in very metal poor thick disk stars  

E-Print Network [OSTI]

A search for lithium is performed on seven metal poor dwarfs with metallicities ranging from [Fe/H]=-1.5 down to [Fe/H]=-3.0 but showing disk-like kinematics. These stars belong to the metal poor tail of the Galactic thick disk and they may be also the result of an accretion event (Beers and Sommer-Larsen 1995). The Li 6707.8 A line is present in all the seven dwarfs. The weighted average of the Li abundance for the stars is A(Li)=2.20 (+/-0.06) and is consistent within the errors with the plateau Li abundance of A(Li)=2.24(+/- 0.012) found in genuine halo stars in the same range of metallicities (Bonifacio and Molaro 1997). One of the stars, CS 22182-24, shows somewhat lower Li abundance (A(Li)=1.6(+/-0.40)) and is a candidate to being a Li-poor star. Whether this group of stars belongs to the oldest stars in the disk or to the old population of an external galaxy accreted by the Milky Way, the present observations provide support to the universality of a pre-Galactic Li abundance as is observed in the Galactic halo stars.

P. Molaro; P. Bonifacio; L. Pasquini

1997-09-25T23:59:59.000Z

317

Stationary Nonaxisymmetric Configurations of Magnetized Singular Isothermal Disks  

E-Print Network [OSTI]

Accepted.... Received...; in original form... We construct both aligned and unaligned (logarithmic spiral) stationary configurations of nonaxisymmetric magnetohydrodynamic (MHD) disks from either a full or a partial razor-thin power-law axisymmetric magnetized singular isothermal disk (MSID) that is embedded with a coplanar azimuthal magnetic field B? of a non-force-free radial scaling r?1/2 and that rotates differentially with a flat rotation curve of speed aD, where a is the isothermal sound speed and D is the dimensionless rotation parameter. Analytical solutions and stability criteria for determining D2 are derived. For aligned nonaxisymmetric MSIDs, eccentric m = 1 displacements may occur at arbitrary D2 in a full MSID but are allowed only with a2D2 = C2 A /2 in a partial MSID (CA is the Alfvn speed), while each case of |m | ? 1 gives two possible values of D2 for purely azimuthal propagations of fast and slow MHD density waves (FMDWs and SMDWs) that appear stationary in an inertial frame of reference. For disk galaxies modeled by a partial MSID resulting from a massive dark-matter halo with a flat rotation curve and a2D2 ? C2 A, stationary aligned perturbations of m = 1 are not allowed. For

Yu-qing Lou

2003-01-01T23:59:59.000Z

318

Laser illuminator and optical system for disk patterning  

DOE Patents [OSTI]

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.

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

2000-01-01T23:59:59.000Z

319

The formation of planetary disks and winds: an ultraviolet view  

E-Print Network [OSTI]

Planetary systems are angular momentum reservoirs generated during star formation. This accretion process produces very powerful engines able to drive the optical jets and the molecular outflows. A fraction of the engine energy is released into heating thus the temperature of the engine ranges from the 3000K of the inner disk material to the 10MK in the areas where magnetic reconnection occurs. There are important unsolved problems concerning the nature of the engine, its evolution and the impact of the engine in the chemical evolution of the inner disk. Of special relevance is the understanding of the shear layer between the stellar photosphere and the disk; this layer controls a significant fraction of the magnetic field building up and the subsequent dissipative processes ougth to be studied in the UV. This contribution focus on describing the connections between 1 Myr old suns and the Sun and the requirements for new UV instrumentation to address their evolution during this period. Two types of observations are shown to be needed: monitoring programmes and high resolution imaging down to, at least, milliarsecond scales.

Ana I. Gomez de Castro

2008-09-02T23:59:59.000Z

320

The dynamical structure of HR 8799's inner debris disk  

E-Print Network [OSTI]

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...

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

2015-01-01T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


321

The Quiescent Accretion Disk in IP Peg at Near-Infrared Wavelengths  

E-Print Network [OSTI]

We present near-infrared, H-band (1.45-1.85 microns) observations of the eclipsing dwarf nova, IP Peg, in quiescence. The light curves are composed of ellipsoidal variations from the late-type secondary star and emission from the accretion disk and the bright spot. The light curves have two eclipses: a primary eclipse of the accretion disk and the bright spot by the companion star, and a secondary eclipse of the companion star by the disk. The ellipsoidal variations of the secondary star were modeled and subtracted from the data. The resulting light curve shows a pronounced double-hump variation. The double-hump profile resembles those seen in the light curves of WZ Sge and AL Com and likely originates in the accretion disk. The primary eclipse was modeled using maximum entropy disk mapping techniques. The accretion disk has a flat intensity distribution and a cool brightness temperature (Tbr=3000 K) in the near-infrared. Superimposed on the face of the disk is the bright spot (Tbr=10,000 K); the position of the bright spot is different from the observed range of visible bright spot positions. The near-infrared accretion disk flux is dominated by optically thin emission. The secondary eclipse indicates the presence of some occulting medium in the disk, but the eclipse depth is too shallow to be caused by a fully opaque accretion disk.

C. S. Froning; E. L. Robinson; William F. Welsh; Janet H. Wood

1999-07-07T23:59:59.000Z

322

Forming Young Bulges within Existing Disks: Statistical Evidence for External Drivers  

E-Print Network [OSTI]

Contrary to traditional models of galaxy formation, recent observations suggest that some bulges form within preexisting disk galaxies. Such late-epoch bulge formation within disks seems to be linked to disk gas inflow and central star formation, caused by either internal secular processes or galaxy mergers and interactions. We identify a population of galaxies likely to be experiencing active bulge growth within disks, using the criterion that the color within the half-light radius is bluer than the outer disk color. Such blue-centered galaxies make up >10% of star-forming disk galaxies within the Nearby Field Galaxy Survey, a broad survey designed to represent the natural diversity of the low-z galaxy population over a wide range of luminosities and environments. Blue-centered galaxies correlate at 99% confidence with morphological peculiarities suggestive of minor mergers and interactions. From this and other evidence, we argue that external drivers rather than internal secular processes probably account for the majority of blue-centered galaxies. We go on to discuss quantitative plausibility arguments indicating that blue-centered evolutionary phases may represent an important mode of bulge growth for most disk galaxies, leading to significant changes in bulge-to-disk ratio without destroying disks. If this view is correct, bulge growth within disks may be a natural consequence of the repeated galaxy mergers and interactions inherent in hierarchical galaxy formation.

Sheila J. Kannappan; Rolf A. Jansen; Elizabeth J. Barton

2003-12-16T23:59:59.000Z

323

OUTER-DISK POPULATIONS IN NGC 7793: EVIDENCE FOR STELLAR RADIAL MIGRATION  

SciTech Connect (OSTI)

We analyzed the radial surface brightness profile of the spiral galaxy NGC 7793 using HST/ACS images from the GHOSTS survey and a new HST/WFC3 image across the disk break. We used the photometry of resolved stars to select distinct populations covering a wide range of stellar ages. We found breaks in the radial profiles of all stellar populations at 280'' ({approx}5.1 kpc). Beyond this disk break, the profiles become steeper for younger populations. This same trend is seen in numerical simulations where the outer disk is formed almost entirely by radial migration. We also found that the older stars of NGC 7793 extend significantly farther than the underlying H I disk. They are thus unlikely to have formed entirely at their current radii, unless the gas disk was substantially larger in the past. These observations thus provide evidence for substantial stellar radial migration in late-type disks.

Radburn-Smith, David J.; Dalcanton, Julianne J. [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Roskar, Rok [Institut fuer Theoretische Physik, Universitaet Zuerich (Switzerland); Debattista, Victor P. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Streich, David; De Jong, Roelof S.; Vlajic, Marija [Leibniz-Institut fuer Astrophysik Potsdam, D-14482 Potsdam (Germany); Holwerda, Benne W. [European Space Agency, ESTEC, 2200 AG Noordwijk (Netherlands); Purcell, Chris W. [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Dolphin, Andrew E. [Raytheon, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Zucker, Daniel B. [Department of Physics and Astronomy, Macquarie University, NSW 2109 (Australia)

2012-07-10T23:59:59.000Z

324

Searching for Planets in Holey Debris Disks with the Apodizing Phase Plate  

E-Print Network [OSTI]

We present our first results from a high-contrast imaging search for planetary mass companions around stars with gapped debris disks, as inferred from the stars' bright infrared excesses. For the six considered stars, we model the disks' unresolved infrared spectral energy distributions (SEDs) in order to derive the temperature and location of the disk components. With VLT/NaCo Apodizing Phase Plate coronagraphic L'-band imaging, we search for planetary mass companions that may be sculpting the disks. We detect neither disks nor companions in this sample, confirmed by comparing plausible point sources with archival data. In order to calculate our mass sensitivity limit, we revisit the stellar age estimates. One target, HD 17848, at 540$\\pm$100 Myr old is significantly older than previously estimated. We then discuss our high-contrast imaging results with respect to the disk properties.

Meshkat, Tiffany; Su, Kate Y L; Kenworthy, Matthew A; Mamajek, Eric E; Hinz, Philip M; Smith, Paul S

2014-01-01T23:59:59.000Z

325

DISK EVOLUTION IN THE THREE NEARBY STAR-FORMING REGIONS OF TAURUS, CHAMAELEON, AND OPHIUCHUS  

SciTech Connect (OSTI)

We analyze samples of Spitzer Infrared Spectrograph spectra of T Tauri stars in the Ophiuchus, Taurus, and Chamaeleon I star-forming regions, whose median ages lie in the <1-2 Myr range. The median mid-infrared spectra of objects in these three regions are similar in shape, suggesting, on average, similar disk structures. When normalized to the same stellar luminosity, the medians follow each other closely, implying comparable mid-infrared excess emission from the circumstellar disks. We use the spectral index between 13 and 31 {mu}m and the equivalent width of the 10 {mu}m silicate emission feature to identify objects whose disk configuration departs from that of a continuous, optically thick accretion disk. Transitional disks, whose steep 13-31 {mu}m spectral slope and near-IR flux deficit reveal inner disk clearing, occur with about the same frequency of a few percent in all three regions. Objects with unusually large 10 {mu}m equivalent widths are more common (20%-30%); they could reveal the presence of disk gaps filled with optically thin dust. Based on their medians and fraction of evolved disks, T Tauri stars in Taurus and Chamaeleon I are very alike. Disk evolution sets in early, since already the youngest region, the Ophiuchus core (L1688), has more settled disks with larger grains. Our results indicate that protoplanetary disks show clear signs of dust evolution at an age of a few Myr, even as early as approx1 Myr, but age is not the only factor determining the degree of evolution during the first few million years of a disk's lifetime.

Furlan, E. [NASA Astrobiology Institute, and Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Los Angeles, CA 90095 (United States); Watson, Dan M.; McClure, M. K., E-mail: Elise.Furlan@jpl.nasa.go, E-mail: dmw@pas.rochester.ed, E-mail: manoj@pas.rochester.ed [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States)

2009-10-01T23:59:59.000Z

326

NEAR-INFRARED DETECTION OF A SUPER-THIN DISK IN NGC 891  

SciTech Connect (OSTI)

We probe the disk structure of the nearby, massive, edge-on spiral galaxy NGC 891 with subarcsecond resolution JHK{sub s}-band images covering {approx} {+-}10 kpc in radius and {+-}5 kpc in height. We measure intrinsic surface brightness (SB) profiles using realistic attenuation corrections constrained from near- and mid-infrared (Spitzer) color maps and three-dimensional Monte Carlo radiative-transfer models. In addition to the well-known thin and thick disks, a super-thin disk with 60-80 pc scale-height-comparable to the star-forming disk of the Milky Way-is visibly evident and required to fit the attenuation-corrected light distribution. Asymmetries in the super-thin disk light profile are indicative of young, hot stars producing regions of excess luminosity and bluer (attenuation-corrected) near-infrared color. To fit the inner regions of NGC 891, these disks must be truncated within {approx}3 kpc, with almost all their luminosity redistributed in a bar-like structure 50% thicker than the thin disk. There appears to be no classical bulge but rather a nuclear continuation of the super-thin disk. The super-thin, thin, thick, and bar components contribute roughly 30%, 42%, 13%, and 15% (respectively) to the total K{sub s}-band luminosity. Disk axial ratios (length/height) decrease from 30 to 3 from super-thin to thick components. Both exponential and sech{sup 2} vertical SB profiles fit the data equally well. We find that the super-thin disk is significantly brighter in the K{sub s}-band than typically assumed in integrated spectral energy distribution models of NGC 891: it appears that in these models the excess flux, likely produced by young stars in the super-thin disk, has been mistakenly attributed to the thin disk.

Schechtman-Rook, Andrew; Bershady, Matthew A., E-mail: andrew@astro.wisc.edu [Department of Astronomy, University of Wisconsin, 475 N. Charter Street, Madison, WI 53706 (United States)

2013-08-10T23:59:59.000Z

327

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]

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.

Giovanni Santostasi

2008-07-16T23:59:59.000Z

328

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

E-Print Network [OSTI]

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.

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

2007-10-17T23:59:59.000Z

329

Radiation-induced solitary waves in hot plasmas of accretion disks  

E-Print Network [OSTI]

It is shown that the existence of radiation-induced solitary waves in hot plasmas of accretion disks depends on the radial temperature profile.

Fedor V. Prigara

2005-07-08T23:59:59.000Z

330

Discovery of a large dust disk around the nearby star AU Microscopium  

E-Print Network [OSTI]

We present the discovery of a circumstellar dust disk surrounding AU Microscopium (AU Mic, GJ 803, HD 197481). This young M star at 10 parsec has the same age and origin as beta Pictoris, another nearby star surrounded by a dust disk. The AU Mic disk is detected between 50 AU and 210 AU radius, a region where dust lifetimes exceed the present stellar age. Thus, AU Mic is the nearest star where we directly observe the solid material required for planet formation. Since 85% of stars are M-type, the AU Mic disk provides new clues on how the majority of planetary systems might form and evolve.

Paul Kalas; Michael C. Liu; Brenda C. Matthews

2004-03-05T23:59:59.000Z

331

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

E-Print Network [OSTI]

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.

B. Paczy?ski

2000-04-10T23:59:59.000Z

332

Structure and Evolution of Circumstellar Disks Around Young Stars: New Views from ISO  

E-Print Network [OSTI]

A question central to understanding the origin of our solar system is: how do planets form in circumstellar disks around young stars? Because of the complex nature of the physical processes involved, multi-wavelength observations of large samples will be required in order to obtain a complete answer to this question. Surveys undertaken with ISO have helped to solve pieces of this puzzle in addition to uncovering new mysteries. We review a variety of studies aimed at understanding; i) the physical structure and composition of circumstellar disks commonly found surrounding young stellar objects; and ii) the evolution of circumstellar disks from the active accretion phase to post-planet building debris disks.

Michael R. Meyer; Steven V. W. Beckwith

2000-01-31T23:59:59.000Z

333

E-Print Network 3.0 - accretion disk surrounding Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Simulations with an Illustrative Application to Summary: Accretion Disk Evolution with Wind Infall II. Results of 3D Hydrodynamical Simulations... how the evolution and...

334

E-Print Network 3.0 - accretion disk emission Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Technology (MIT) Collection: Physics 34 X-rays from classical T Tauri stars Accretion and wind signatures Summary: are actively accreting matter from a circumstellar disk Influence...

335

E-Print Network 3.0 - accretion disk rim Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

disk inner rim, which dominates the continuum flux in the K... an outflow (stellardisk wind) andor from the ... Source: Liske, Jochen - European Southern Observatory...

336

E-Print Network 3.0 - accretion disk instability Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Queen Mary, University of London Collection: Physics 29 Accretion Disk Evolution with Wind Infall II. Results of 3D Hydrodynamical Simulations with an Illustrative Application...

337

E-Print Network 3.0 - agn accretion-disk outflows Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Jet NLR clouds BLR clouds 1 pc Accretion disk 12... .g., Reyolds & Nowak 2003) 2) The inclination ... Source: Evans, Daniel A. - Kavli Institute for Astrophysics and Space...

338

E-Print Network 3.0 - advection-dominated accretion disks Sample...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Universit Paris 7 Denis Diderot Collection: Physics 5 Accretion Disk Evolution with Wind Infall II. Results of 3D Hydrodynamical Simulations with an Illustrative Application...

339

E-Print Network 3.0 - accretion disks formed Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

California Institute of Technology Collection: Physics 36 Accretion Disk Evolution With Wind Infall I. General Solution and Application to Sgr A* Summary: , slowly accreting,...

340

E-Print Network 3.0 - accretion disk structure Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Physics Laboratory Collection: Plasma Physics and Fusion 27 Accretion Disk Evolution With Wind Infall I. General Solution and Application to Sgr A* Summary: and thus change the...

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


341

E-Print Network 3.0 - accretion disk spectra Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

along the magnetic field lines (of stellar andor disk... an outflow (stellardisk wind) andor from the accreting columns. However, because of insufficient spectral......

342

E-Print Network 3.0 - agn accretion disks Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Accretion disk? (pc Rs) 12; Accretion flow surrounded by dusty torus BB... ) The inclination of the accretion ... Source: Evans, Daniel A. - Kavli Institute for...

343

Cloud and Star Formation in Disk Galaxy Models with Feedback  

E-Print Network [OSTI]

We include feedback in global hydrodynamic simulations in order to study the star formation properties, and gas structure and dynamics, in models of galactic disks. We extend previous models by implementing feedback in gravitationally bound clouds: momentum is injected at a rate proportional to the star formation rate. This mechanical energy disperses cloud gas back into the surrounding ISM, truncating star formation in a given cloud, and raising the overall level of ambient turbulence. Propagating star formation can however occur as expanding shells collide, enhancing the density and triggering new cloud and star formation. By controlling the momentum injection per massive star and the specific star formation rate in dense gas, we find that the negative effects of high turbulence outweigh the positive ones, and in net feedback reduces the fraction of dense gas and thus the overall star formation rate. The properties of the large clouds that form are not, however, very sensitive to feedback, with cutoff masses of a few million solar masses, similar to observations. We find a relationship between the star formation rate surface density and the gas surface density with a power law index ~2 for our models with the largest dynamic range, consistent with theoretical expectations for our model of disk flaring. We point out that the value of the "Kennicutt-Schmidt" index depends on the thickness of the disk. With our simple feedback prescription (a single combined star formation event per cloud), we find that global spiral patterns are not sustained; less correlated feedback and smaller scale turbulence appear to be necessary for spiral patterns to persist.

Rahul Shetty; Eve C. Ostriker

2008-05-26T23:59:59.000Z

344

EVIDENCE FOR MAGNESIUM ISOTOPE HETEROGENEITY IN THE SOLAR PROTOPLANETARY DISK  

SciTech Connect (OSTI)

With a half-life of 0.73 Myr, the {sup 26}Al-to-{sup 26}Mg decay system is the most widely used short-lived chronometer for understanding the formation and earliest evolution of the solar protoplanetary disk. However, the validity of {sup 26}Al-{sup 26}Mg ages of meteorites and their components relies on the critical assumption that the canonical {sup 26}Al/{sup 27}Al ratio of {approx}5 x 10{sup -5} recorded by the oldest dated solids, calcium-aluminium-rich inclusions (CAIs), represents the initial abundance of {sup 26}Al for the solar system as a whole. Here, we report high-precision Mg-isotope measurements of inner solar system solids, asteroids, and planets demonstrating the existence of widespread heterogeneity in the mass-independent {sup 26}Mg composition ({mu}{sup 26}Mg*) of bulk solar system reservoirs with solar or near-solar Al/Mg ratios. This variability may represent heterogeneity in the initial abundance of {sup 26}Al across the solar protoplanetary disk at the time of CAI formation and/or Mg-isotope heterogeneity. By comparing the U-Pb and {sup 26}Al-{sup 26}Mg ages of pristine solar system materials, we infer that the bulk of the {mu}{sup 26}Mg* variability reflects heterogeneity in the initial abundance of {sup 26}Al across the solar protoplanetary disk. We conclude that the canonical value of {approx}5 x 10{sup -5} represents the average initial abundance of {sup 26}Al only in the CAI-forming region, and that large-scale heterogeneity-perhaps up to 80% of the canonical value-may have existed throughout the inner solar system. If correct, our interpretation of the Mg-isotope composition of inner solar system objects precludes the use of the {sup 26}Al-{sup 26}Mg system as an accurate early solar system chronometer.

Larsen, Kirsten K.; Trinquier, Anne; Paton, Chad; Schiller, Martin; Wielandt, Daniel; Connelly, James N.; Nordlund, Ake; Krot, Alexander N.; Bizzarro, Martin [Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen DK-1350 (Denmark); Ivanova, Marina A. [Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow 119991 (Russian Federation)

2011-07-10T23:59:59.000Z

345

Rapidity gap survival in the black-disk regime  

SciTech Connect (OSTI)

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.

Leonid Frankfurt; Charles Hyde; Mark Strikman; Christian Weiss

2007-04-16T23:59:59.000Z

346

The Metallicity of Galaxy Disks: Infall versus Outflow  

E-Print Network [OSTI]

Both gas accretion (infall) and winds (outflow) change a galaxy's metallicity and gas fraction, lowering the effective yield. Low effective yields in galaxies with rotation speeds 15% of baryons have been lost by galaxies of any mass. SN feedback is therefore unlikely to be effective for removing large amounts of gas from low mass disk galaxies. In addition, the dependence between metal-loss and galaxy mass is sufficiently weak that massive galaxies dominate metal enrichment of the IGM. The calculations in this paper provide limiting cases for any arbitrary chemical evolution history, as proven in an Appendix.

J. J. Dalcanton

2006-08-28T23:59:59.000Z

347

On the Fractal Distribution of HII Regions in Disk Galaxies  

E-Print Network [OSTI]

In this work we quantify the degree to which star-forming events are clumped. We apply a precise and accurate technique to calculate the correlation dimension Dc of the distribution of HII regions in a sample of disk galaxies. Our reliable results are distributed in the range 1.5fractal dimension among galaxies, contrary to a universal picture sometimes claimed in literature. The faintest galaxies tend to distribute their HII regions in more clustered (less uniform) patterns. Moreover, the fractal dimension for the brightest HII regions within the same galaxy seems to be smaller than for the faintest ones suggesting some kind of evolutionary effect.

Nestor Sanchez; Emilio J. Alfaro

2008-10-02T23:59:59.000Z

348

Disk Space Quota Management | Argonne Leadership Computing Facility  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

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:1 First Use of Energy for All Purposes (Fuel and Nonfuel),Feet) Year Jan Feb Mar Apr May JunDatastreamsmmcrcalgovInstrumentsruc DocumentationP-Series to UserProduct:Directives Templates The Office of Science isDisk Quota

349

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

E-Print Network [OSTI]

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.

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

2007-02-01T23:59:59.000Z

350

REEXAMINATION OF INDUCTION HEATING OF PRIMITIVE BODIES IN PROTOPLANETARY DISKS  

SciTech Connect (OSTI)

We reexamine the unipolar induction mechanism for heating asteroids originally proposed in a classic series of papers by Sonett and collaborators. As originally conceived, induction heating is caused by the 'motional electric field' that appears in the frame of an asteroid immersed in a fully ionized, magnetized solar wind and drives currents through its interior. However, we point out that classical induction heating contains a subtle conceptual error, in consequence of which the electric field inside the asteroid was calculated incorrectly. The problem is that the motional electric field used by Sonett et al. is the electric field in the freely streaming plasma far from the asteroid; in fact, the motional field vanishes at the asteroid surface for realistic assumptions about the plasma density. In this paper we revisit and improve the induction heating scenario by (1) correcting the conceptual error by self-consistently calculating the electric field in and around the boundary layer at the asteroid-plasma interface; (2) considering weakly ionized plasmas consistent with current ideas about protoplanetary disks; and (3) considering more realistic scenarios that do not require a fully ionized, powerful T Tauri wind in the disk midplane. We present exemplary solutions for two highly idealized flows that show that the interior electric field can either vanish or be comparable to the fields predicted by classical induction depending on the flow geometry. We term the heating driven by these flows 'electrodynamic heating', calculate its upper limits, and compare them to heating produced by short-lived radionuclides.

Menzel, Raymond L.; Roberge, Wayne G., E-mail: menzer@rpi.edu, E-mail: roberw@rpi.edu [New York Center for Astrobiology and Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180 (United States)

2013-10-20T23:59:59.000Z

351

Testing Horava-Lifshitz gravity using thin accretion disk properties  

SciTech Connect (OSTI)

Recently, a renormalizable gravity theory with higher spatial derivatives in four dimensions was proposed by Horava. The theory reduces to Einstein gravity with a nonvanishing cosmological constant in IR, but it has improved UV behaviors. The spherically symmetric black hole solutions for an arbitrary cosmological constant, which represent the generalization of the standard Schwarzschild-(anti) de Sitter solution, have also been obtained for the Horava-Lifshitz theory. The exact asymptotically flat Schwarzschild-type solution of the gravitational field equations in Horava gravity contains a quadratic increasing term, as well as the square root of a fourth order polynomial in the radial coordinate, and it depends on one arbitrary integration constant. The IR-modified Horava gravity seems to be consistent with the current observational data, but in order to test its viability more observational constraints are necessary. In the present paper we consider the possibility of observationally testing Horava gravity by using the accretion disk properties around black holes. The energy flux, the temperature distribution, the emission spectrum, as well as the energy conversion efficiency are obtained, and compared to the standard general relativistic case. Particular signatures can appear in the electromagnetic spectrum, thus leading to the possibility of directly testing Horava gravity models by using astrophysical observations of the emission spectra from accretion disks.

Harko, Tiberiu; Kovacs, Zoltan; Lobo, Francisco S. N. [Department of Physics and Center for Theoretical and Computational Physics, University of Hong Kong, Pok Fu Lam Road (Hong Kong); Centro de Fisica Teorica e Computacional, Faculdade de Ciencias da Universidade de Lisboa, Avenida Professor Gama Pinto 2, P-1649-003 Lisboa (Portugal)

2009-08-15T23:59:59.000Z

352

DUST PROPERTIES AND DISK STRUCTURE OF EVOLVED PROTOPLANETARY DISKS IN Cep OB2: GRAIN GROWTH, SETTLING, GAS AND DUST MASS, AND INSIDE-OUT EVOLUTION  

SciTech Connect (OSTI)

We present Spitzer/Infrared Spectrograph spectra of 31 T Tauri stars (TTS) and IRAM/1.3 mm observations for 34 low- and intermediate-mass stars in the Cep OB2 region. Including our previously published data, we analyze 56 TTS and 3 intermediate-mass stars with silicate features in Tr 37 ({approx}4 Myr) and NGC 7160 ({approx}12 Myr). The silicate emission features are well reproduced with a mixture of amorphous (with olivine, forsterite, and silica stoichiometry) and crystalline grains (forsterite, enstatite). We explore grain size and disk structure using radiative transfer disk models, finding that most objects have suffered substantial evolution (grain growth, settling). About half of the disks show inside-out evolution, with either dust-cleared inner holes or a radially dependent dust distribution, typically with larger grains and more settling in the innermost disk. The typical strong silicate features nevertheless require the presence of small dust grains, and could be explained by differential settling according to grain size, anomalous dust distributions, and/or optically thin dust populations within disk gaps. M-type stars tend to have weaker silicate emission and steeper spectral energy distributions than K-type objects. The inferred low dust masses are in a strong contrast with the relatively high gas accretion rates, suggesting global grain growth and/or an anomalous gas-to-dust ratio. Transition disks in the Cep OB2 region display strongly processed grains, suggesting that they are dominated by dust evolution and settling. Finally, the presence of rare but remarkable disks with strong accretion at old ages reveals that some very massive disks may still survive to grain growth, gravitational instabilities, and planet formation.

Sicilia-Aguilar, Aurora; Henning, Thomas; Dullemond, Cornelis P.; Bouwman, Jeroen; Sturm, Bernhard [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany); Patel, Nimesh [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Juhasz, Attila, E-mail: sicilia@mpia.de, E-mail: aurora.sicilia@uam.es [Leiden Observatory, Niels Bohrweg 2, NL-2333 CA Leiden (Netherlands)

2011-11-20T23:59:59.000Z

353

Extraplanar Dust: a Tracer of Cold Dense Gas in the Thick Disks of Spiral Galaxies  

E-Print Network [OSTI]

The interstellar thick disks of galaxies contain not only gas, but significant quantities of dust. Most of our knowledge of extraplanar dust in disk galaxies comes from direct broadband optical imaging of these systems, wherein the dust is identified due to the irregular extinction it produces against the thick disk and bulge stars. This observational technique is sensitive to only the most dense material, and we argue much of the material identified in this way traces a cold phase of the interstellar thick disks in galaxies. The presence of a cold, dense phase likely implies the interstellar pressures in the thick disks of spiral galaxies can be quite high. This dense phase of the interstellar medium may also fueling thick disk star formation, and H-alpha observations are now revealing H II regions around newly-formed OB stars associations in several galaxies. We argue that the large quantities of dust and the morphologies of the structures traced by the dust imply that much of the extraplanar material in disk galaxies must have been expelled from the underlying thin disk.

J. Christopher Howk

2004-10-15T23:59:59.000Z

354

GRAVITATIONAL DRAG ON A POINT MASS IN HYPERSONIC MOTION WITHIN A GAUSSIAN DISK  

SciTech Connect (OSTI)

We develop an analytical model for the accretion and gravitational drag on a point mass that moves hypersonically in the midplane of a gaseous disk with a Gaussian vertical density stratification. Such a model is of interest for studying the interaction between a planet and a protoplanetary disk, as well as the dynamical decay of massive black holes in galactic nuclei. The model assumes that the flow is ballistic, and gives fully analytical expressions for both the accretion rate onto the point mass and the gravitational drag it suffers. The expressions are further simplified by taking the limits of a thick and of a thin disk. The results for the thick disk reduce correctly to those for a uniform density environment. We find that for a thin disk (small vertical scaleheight compared to the gravitational radius), the accretion rate is proportional to the mass of the moving object and to the surface density of the disk, while the drag force is independent of the velocity of the object. The gravitational deceleration of the hypersonic perturber in a thin disk was found to be independent of its parameters (i.e., mass or velocity) and depends only on the surface mass density of the disk. The predictions of the model are compared to the results of three-dimensional hydrodynamical simulations, with reasonable agreement.

Canto, J.; Sanchez-Salcedo, F. J. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Ap. 70-468, 04510 D.F. (Mexico)] [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Ap. 70-468, 04510 D.F. (Mexico); Esquivel, A.; Raga, A. C., E-mail: jsanchez@astro.unam.mx, E-mail: esquivel@nucleares.una.mx, E-mail: raga@nucleares.unam.mx [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, 04510 Mexico D.F. (Mexico)

2013-01-01T23:59:59.000Z

355

Disk Drive Roadmap from the Thermal Perspective: A Case for Dynamic Thermal Management  

E-Print Network [OSTI]

to the thermal envelope of drive design. We present two mechanisms for buying back some of this IDR loss allowing higher RPMs than the thermal envelope, and employs dynamic throttling of disk drive activities to remain within this envelope. Keywords: Disk Drives, Thermal Management, Technology Scaling. 1

Gurumurthi, Sudhanva

356

Understanding the Performance-Temperature Interactions in Disk I/O of Server Youngjae Kim  

E-Print Network [OSTI]

, this study showed that such aggressive scaling of the RPM cannot be sustained within the thermal envelope the first infrastructure for integrated stud- ies of the performance and thermal behavior of storage systems disks. We then analyze the thermal profiles of real workloads that use such disk drives in their storage

Gurumurthi, Sudhanva

357

Accretion Disk Evolution With Wind Infall I. General Solution and Application to Sgr A*  

E-Print Network [OSTI]

The evolution of an accretion disk can be influenced significantly by the deposition of mass and angular momentum by an infalling Bondi-Hoyle wind. Such a mass influx impacts the long-term behavior of the disk by providing additional sources of viscosity and heating. In this paper, we derive and solve the disk equations when these effects are taken into account. We present a survey of models with various wind configurations and demonstrate that the disk spectrum may then differ substantially from that of a standard alpha-disk. In particular, it is likely that a wind-fed disk has a significant infrared bump due to the deposition of energy in its outer region. We apply some of the results of our calculations to the Galactic Center black hole candidate Sgr A* and show that if a fossil disk is present in this source, it must have a very low viscosity parameter (alpha<10^-4) and the Bondi-Hoyle wind must be accreting with a very high specific angular momentum to prevent it from circularizing in the inner disk region where its impact would be most noticeable.

Heino Falcke; Fulvio Melia

1996-11-12T23:59:59.000Z

358

arXiv:astro-ph/0508261v111Aug2005 THE OPACITY OF SPIRAL GALAXY DISKS  

E-Print Network [OSTI]

Figure 2 shows the stacked radial opacity profile of our entire sample of 32 HST/WFPC2 fields. FromarXiv:astro-ph/0508261v111Aug2005 THE OPACITY OF SPIRAL GALAXY DISKS Dust opacity from calibrated Abstract The opacity of foreground spiral disks can be probed from the number of distant galaxies seen

Kruit, Piet van der

359

Structural modal interaction of a four degree of freedom bladed disk and casing model  

E-Print Network [OSTI]

Structural modal interaction of a four degree of freedom bladed disk and casing model Mathias specific interaction phenomenon that may occur in turbo- machines due to radial rub between a bladed disk requirements leading to reduced clearance between blade-tips and casing together with the rotation of the blade

Boyer, Edmond

360

Model reduction applied to multi-stage assemblies of bladed disks  

E-Print Network [OSTI]

consisted in modelling separately each stage of the assembly of bladed disks that compose the rotor of a jetModel reduction applied to multi-stage assemblies of bladed disks A. Sternch¨uss, E. Balm, France e-mail: arnaud.sternchuss@ecp.fr P. Jean, J.-P. Lombard Snecma (Safran Group) Rond-point Ren

Boyer, Edmond

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


361

HYBUD: An Energy-Efficient Architecture for Hybrid Parallel Disk Systems  

E-Print Network [OSTI]

consumption in parallel disk systems has strong impacts on the cost of backup power-generation and cooling consumption and cooling. Although flash memory is very energy- efficient compared to disk drives, flash memory but not limited to, video surveillance [1], remote-sensing database systems [2], and digital libraries [5

Qin, Xiao

362

A Resolved Molecular Gas Disk around the Nearby A Star 49 Ceti  

E-Print Network [OSTI]

The A star 49 Ceti, at a distance of 61 pc, is unusual in retaining a substantial quantity of molecular gas while exhibiting dust properties similar to those of a debris disk. We present resolved observations of the disk around 49 Ceti from the Submillimeter Array in the J=2-1 rotational transition of CO with a resolution of 1.0x1.2 arcsec. The observed emission reveals an extended rotating structure viewed approximately edge-on and clear of detectable CO emission out to a distance of ~90 AU from the star. No 1.3 millimeter continuum emission is detected at a 3-sigma sensitivity of 2.1 mJy/beam. Models of disk structure and chemistry indicate that the inner disk is devoid of molecular gas, while the outer gas disk between 40 and 200 AU from the star is dominated by photochemistry from stellar and interstellar radiation. We determine parameters for a model that reproduces the basic features of the spatially resolved CO J=2-1 emission, the spectral energy distribution, and the unresolved CO J=3-2 spectrum. We investigate variations in disk chemistry and observable properties for a range of structural parameters. 49 Ceti appears to be a rare example of a system in a late stage of transition between a gas-rich protoplanetary disk and a tenuous, virtually gas-free debris disk.

A. M. Hughes; D. J. Wilner; I. Kamp; M. R. Hogerheijde

2008-03-24T23:59:59.000Z

363

The Carbon-Rich Gas in the Beta Pictoris Circumstellar Disk  

E-Print Network [OSTI]

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.

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

2006-04-20T23:59:59.000Z

364

Distributed Mobile Disk Cover A Building Block for Mobile Backbone Networks  

E-Print Network [OSTI]

1 Distributed Mobile Disk Cover ­ A Building Block for Mobile Backbone Networks Anand Srinivas, Gil of Mobile Backbone Networks has been recently studied by a few different approaches. An important subproblem a Geometric Disk Cover (GDC) under mobility. While from the context of static nodes and centralized solutions

Zussman, Gil

365

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

E-Print Network [OSTI]

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

Pennycook, Steve

366

Energy-Aware Prefetching for Parallel Disk Systems Algorithms, Models, and Evaluation  

E-Print Network [OSTI]

system grows, the energy consumed by the I/O system often becomes a large part of the total cost significantly reduce energy consumption in parallel disk systems by up to 50 percent. In addition, we of ownership [16]. Reducing the energy costs of operating these large-scale disk I/O systems often becomes one

Qin, Xiao

367

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

E-Print Network [OSTI]

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

Gurumurthi, Sudhanva

368

HIGH-CONTRAST NEAR-INFRARED IMAGING POLARIMETRY OF THE PROTOPLANETARY DISK AROUND RY TAU  

SciTech Connect (OSTI)

We present near-infrared coronagraphic imaging polarimetry of RY Tau. The scattered light in the circumstellar environment was imaged at the H band at a high resolution ({approx}0.''05) for the first time, using Subaru/HiCIAO. The observed polarized intensity (PI) distribution shows a butterfly-like distribution of bright emission with an angular scale similar to the disk observed at millimeter wavelengths. This distribution is offset toward the blueshifted jet, indicating the presence of a geometrically thick disk or a remnant envelope, and therefore the earliest stage of the Class II evolutionary phase. We perform comparisons between the observed PI distribution and disk models with (1) full radiative transfer code, using the spectral energy distribution (SED) to constrain the disk parameters; and (2) monochromatic simulations of scattered light which explore a wide range of parameters space to constrain the disk and dust parameters. We show that these models cannot consistently explain the observed PI distribution, SED, and the viewing angle inferred by millimeter interferometry. We suggest that the scattered light in the near-infrared is associated with an optically thin and geometrically thick layer above the disk surface, with the surface responsible for the infrared SED. Half of the scattered light and thermal radiation in this layer illuminates the disk surface, and this process may significantly affect the thermal structure of the disk.

Takami, Michihiro; Karr, Jennifer L.; Kim, Hyosun; Chou, Mei-Yin [Institute of Astronomy and Astrophysics, Academia Sinica. P.O. Box 23-141, Taipei 10617, Taiwan (China); Hashimoto, Jun; Kandori, Ryo; Kusakabe, Nobuhiko; Kwon, Jungmi [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Wisniewski, John [H. L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019 (United States); Henning, Thomas; Brandner, Wolfgang [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Grady, Carol A. [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); Hodapp, Klaus W. [Institute for Astronomy, University of Hawaii, 640 North A'ohoku Place, Hilo, HI 96720 (United States); Kudo, Tomoyuki [Subaru Telescope, 650 North A'ohoku Place, Hilo, HI 96720 (United States); Itoh, Yoichi [Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo, 407-2 Nishigaichi, Sayo, Hyogo 679-5313 (Japan); Momose, Munetake [College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan); Mayama, Satoshi [The Center for the Promotion of Integrated Sciences, The Graduate University for Advanced Studies (SOKENDAI), Shonan International Village, Hayama-cho, Miura-gun, Kanagawa 240-0193 (Japan); Currie, Thayne [Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON (Canada); Follette, Katherine B. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson AZ 85721 (United States); Abe, Lyu, E-mail: hiro@asiaa.sinica.edu.tw [Laboratoire Lagrange (UMR 7293), Universite de Nice-Sophia Antipolis, CNRS, Observatoire de la Cote d'Azur, 28 Avenue Valrose, F-06108 Nice Cedex 2 (France); and others

2013-08-01T23:59:59.000Z

369

An evaluation of the storage systems based on network-attached disks  

E-Print Network [OSTI]

show that (a) The advantages of distributing the server's network processing workload to disks may be offset by the decreased cache hit ratios in a file system based on network-attached disks. (b) Performance can be significantly improved in a Web...

Ma, Gang

1998-01-01T23:59:59.000Z

370

Nano-compact disks with 400 Gbit/in2 storage density fabricated  

E-Print Network [OSTI]

Nano-compact disks with 400 Gbit/in2 storage density fabricated using nanoimprint lithography and read with proximal probe Peter R. Kraussa) and Stephen Y. Choub) NanoStructure Laboratory, Department for publication 30 September 1997 Nano-compact disks Nano-CDs with 400 Gbit/in2 topographical bit density nearly

371

Summary of poster at VSS 2002: The vanishing disk; a revealing quirk of the scintillating grid  

E-Print Network [OSTI]

Summary of poster at VSS 2002: The vanishing disk; a revealing quirk of the scintillating grid, IL ABSTRACT Take a Hermann grid of gray alleys on a black background and place white disks of repeating patterns. To assess the importance of a repeating pattern, we tested a Hermann grid with a single

Levine, Michael

372

DESIGN AND IMPLEMENTATION OF DUAL-STAGE TRACK-FOLLOWING CONTROL FOR HARD DISK DRIVES  

E-Print Network [OSTI]

[1], and spindle motor vibration and is hence synchronous with the disk rotation speed. All other categorized into torque disturbance, windage, non-repeatable disk motions and measurement noises. The torque-turbulence impinging on the voice coil motor (VCM), is typically a low frequency disturbance. Windage, which is mainly

Horowitz, Roberto

373

HUBBLE SPACE TELESCOPE ADVANCED CAMERA FOR SURVEYS CORONAGRAPHIC IMAGING OF THE AU MICROSCOPII DEBRIS DISK  

E-Print Network [OSTI]

the midplane is straight and aligned with the star, and beyond that it deviates by $3 , resulting in a bowed . The inclination of the outer disk and moderate forward scattering (g % 0:4) can explain the apparent bow, creating a debris disk that can be detected in thermal emission and scattered light. Without the continual

374

Probing Protoplanetary Disks with Silicate Emission: Where is the silicate emission zone?  

E-Print Network [OSTI]

Recent results indicate that the grain size and crystallinity inferred from observations of silicate features may be correlated with spectral type of the central star and/or disk geometry. In this paper, we show that grain size, as probed by the 10 um silicate feature peak-to-continuum and 11.3-to-9.8 um flux ratios, is inversely proportional to log L_star. These trends can be understood using a simple two-layer disk model for passive irradiated flaring disks, CGPLUS. We find that the radius, R_10, of the 10 um silicate emission zone in the disk goes as (L_star/L_sun)^0.56, with slight variations depending on disk geometry (flaring angle, inner disk radius). The observed correlations, combined with simulated emission spectra of olivine and pyroxene mixtures, imply a grain size dependence on luminosity. Combined with the fact that R_10 is smaller for less luminous stars, this implies that the apparent grain size of the emitting dust is larger for low-luminositysources. In contrast, our models suggest that the crystallinity is only marginally affected, because for increasing luminosity, the zone for thermal annealing (assumed to be at T>800 K) is enlarged by roughly the same factor as the silicate emission zone. The observed crystallinity is affected by disk geometry, however, with increased crystallinity in flat disks. The apparent crystallinity may also increase with grain growth due to a corresponding increase in contrast between crystalline and amorphous silicate emission bands.

J. E. Kessler-Silacci; C. P. Dullemond; J. -C. Augereau; B. Merin; V. C. Geers; E. F. van Dishoeck; N. J. Evans II; G. A. Blake; J. M. Brown

2006-12-15T23:59:59.000Z

375

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

E-Print Network [OSTI]

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.

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

2015-01-01T23:59:59.000Z

376

Modelling and Analysis of Multi-Stage Systems of Mistuned Bladed Disks  

E-Print Network [OSTI]

uncertainty may be due to numerous factors such as material inho- mogeneity, manufacturing processes of uncertainties in complex computational models. In turbine engines rotating components (bladed disks), one of mistuning phenomena in multi- stage systems of bladed disks. Indeed, in modern turbine engines, which

Paris-Sud XI, Universit de

377

Disk-shaped Compact Tension Test for Plain Concrete A. Amirkhanian1  

E-Print Network [OSTI]

Disk-shaped Compact Tension Test for Plain Concrete A. Amirkhanian1 , D. Spring1 , J. Roesler1 , K cracking prediction of concrete pavement systems. The single-edge notched beam test has been used energy in asphalt concrete using the disk-shaped compact tension (DCT) test. The benefit of this specimen

Paulino, Glaucio H.

378

An interferometric study of the Fomalhaut inner debris disk. III. Detailed models of the exozodiacal disk and its origin  

E-Print Network [OSTI]

[Abridged] Debris disks are extrasolar analogs to the solar system planetesimal belts. The star Fomalhaut harbors a cold debris belt at 140 AU as well as evidence of a warm dust component, which is suspected of being a bright analog to the solar system's zodiacal dust. Interferometric observations obtained with the VLTI and the KIN have identified near- and mid-infrared excesses attributed to hot and warm exozodiacal dust in the inner few AU of the star. We performed parametric modeling of the exozodiacal disk using the GRaTeR radiative transfer code to reproduce the interferometric data, complemented by mid- to far-infrared measurements. A detailed treatment of sublimation temperatures was introduced to explore the hot population at the sublimation rim. We then used an analytical approach to successively testing several source mechanisms. A good fit to the data is found by two distinct dust populations: (1) very small, hence unbound, hot dust grains confined in a narrow region at the sublimation rim of carbo...

Lebreton, J; Augereau, J -C; Absil, O; Mennesson, B; Kama, M; Dominik, C; Bonsor, A; Vandeportal, J; Beust, H; Defrre, D; Ertel, S; Faramaz, V; Hinz, P; Kral, Q; Lagrange, A -M; Liu, W; Thbault, P

2013-01-01T23:59:59.000Z

379

The influence of convective heat transfer on flow stability in rotating disk chemical vapor deposition reactors  

SciTech Connect (OSTI)

Flow and heat transfer of NH{sub 3} and He were studied in a rotating disk system with applications to chemical vapor deposition reactors. Flow field and disk heat flux were obtained over a range of operating conditions. Comparisons of disk convective heat transfer were made to infinite rotating disk results to appraise uniformity of transport to the disk. Important operating variables include disk spin rate, disk and enclosure temperatures, flow rate, composition, pressure, and gas mixture temperature at the reactor inlet. These variables were studied over ranges of the spin Reynolds number, Re{omega}; disk mixed convection parameter, MCP{sub w}; and wall mixed convection parameter, MCP{sub w}. Results obtained for NH{sub 3} show that increasing Re{omega} from 314.5 to 3145 increases the uniformity of rotating disk heat flux and results in thinner thermal boundary layers at the disk surface. At Re{omega}=314.5, increasing MCP{sub d} to 15 leads to significant departure from the infinite disk result with nonuniform disk heat fluxes and recirculating flow patterns; flow becomes increasingly complex at larger values of MCP{sub d}. At Re{omega} of 3145, results are closer to the infinite disk for MCP{sub d} up to 15. For large negative (hot walls) and positive (cold walls) values of MCP{sub w}, flow recirculates and there is significant deviation from the infinite disk result; nonuniformities occur at both values of Re{omega}. The influence of MCP{sub w} on flow stability is increased at larger MCP{sub d} and lower Re{omega}. To determine the influence of viscosity and thermal conductivity variation with temperature, calculations were made with He and NH{sub 3}; He transport property variation is low relative to NH{sub 3}. Results show that the flow of NH{sub 3} is less stable than that of He as MCP{sub d} is increased for MCP{sub w}=0 and Re{omega}=314.5. 16 refs., 15 figs., 1 tab.

Winters, W.S.; Evans, G.H. [Sandia National Labs., Livermore, CA (United States); Grief, R. [Univ. of California, Berkeley, CA (United States). Mechanical Engineering Dept.

1997-06-01T23:59:59.000Z

380

Real-Time Parallel Disk Scheduling for VBR Video Servers Ozgur Ertu g Mahesh Kallahalla Peter J. Varman  

E-Print Network [OSTI]

the potential to alleviate this problem by providing a higher disk bandwidth. However harnessing the raw disk J. Varman Department of Electrical and Computer Engineering Rice University Houston TX 77251

Mellor-Crummey, John

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


381

Thermal Effects of Circumplanetary Disk Formation around Proto-Gas Giant Planets  

E-Print Network [OSTI]

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 protoplan...

Machida, Masahiro N

2008-01-01T23:59:59.000Z

382

Mass accretion rates in self-regulated disks of T Tauri stars  

E-Print Network [OSTI]

We have studied numerically the evolution of protostellar disks around intermediate and upper mass T Tauri stars (0.25 M_sun < M_st < 3.0 M_sun) that have formed self-consistently from the collapse of molecular cloud cores. In the T Tauri phase, disks settle into a self-regulated state, with low-amplitude nonaxisymmetric density perturbations persisting for at least several million years. Our main finding is that the global effect of gravitational torques due to these perturbations is to produce disk accretion rates that are of the correct magnitude to explain observed accretion onto T Tauri stars. Our models yield a correlation between accretion rate M_dot and stellar mass M_st that has a best fit M_dot \\propto M_st^{1.7}, in good agreement with recent observations. We also predict a near-linear correlation between the disk accretion rate and the disk mass.

E. I. Vorobyov; Shantanu Basu

2008-02-15T23:59:59.000Z

383

Precession of neutrino-cooled accretion disks in gamma-ray burst engines  

E-Print Network [OSTI]

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.

Matias M. Reynoso; Gustavo E. Romero; Oscar A. Sampayo

2006-07-14T23:59:59.000Z

384

Can black-hole neutrino-cooled disks power short gamma-ray bursts?  

E-Print Network [OSTI]

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.

Liu, Tong; Hou, Shu-Jin; Gu, Wei-Min

2015-01-01T23:59:59.000Z

385

Detection of Keplerian dynamics in a disk around the post-AGB star AC Her  

E-Print Network [OSTI]

So far, only one rotating disk has been clearly identified and studied in AGB or post-AGB objects (in the Red Rectangle), by means of observations with high spectral and spatial resolution. However, disks are thought to play a key role in the late stellar evolution and are suspected to surround many evolved stars. We aim to extend our knowledge on these structures. We present interferometric observations of CO J=2-1 emission from the nebula surrounding the post-AGB star AC Her, a source belonging to a class of objects that share properties with the Red Rectangle and show hints of Keplerian disks. We clearly detect the Keplerian dynamics of a second disk orbiting an evolved star. Its main properties (size, temperature, central mass) are derived from direct interpretation of the data and model fitting. With this we confirm that there are disks orbiting the stars of this relatively wide class of post-AGB objects

Bujarrabal, V; Alcolea, J; Van Winckel, H

2015-01-01T23:59:59.000Z

386

Thermal Effects of Circumplanetary Disk Formation around Proto-Gas Giant Planets  

E-Print Network [OSTI]

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.

Masahiro N. Machida

2008-10-15T23:59:59.000Z

387

The Origin of Jovian Planets in Protostellar Disks: The Role of Dead Zones  

E-Print Network [OSTI]

The final masses of Jovian planets are attained when the tidal torques that they exert on their surrounding protostellar disks are sufficient to open gaps in the face of disk viscosity, thereby shutting off any further accretion. In sufficiently well-ionized disks, the predominant form of disk viscosity originates from the Magneto-Rotational Instability (MRI) that drives hydromagnetic disk turbulence. In the region of sufficiently low ionization rate -- the so-called dead zone -- turbulence is damped and we show that lower mass planets will be formed. We considered three ionization sources (X-rays, cosmic rays, and radioactive elements) and determined the size of a dead zone for the total ionization rate by using a radiative, hydrostatic equilibrium disk model developed by Chiang et al. (2001). We studied a range of surface mass density (Sigma_{0}=10^3 - 10^5 g cm^{-2}) and X-ray energy (kT_{x}=1 - 10 keV). We also compared the ionization rate of such a disk by X-rays with cosmic rays and find that the latter dominate X-rays in ionizing protostellar disks unless the X-ray energy is very high (5 - 10 keV). Among our major conclusions are that for typical conditions, dead zones encompass a region extending out to several AU -- the region in which terrestrial planets are found in our solar system. Our results suggest that the division between low and high mass planets in exosolar planetary systems is a consequence of the presence of a dead zone in their natal protoplanetary disks. We also find that the extent of a dead zone is mainly dependent on the disk's surface mass density. Our results provide further support for the idea that Jovian planets in exosolar systems must have migrated substantially inwards from their points of origin.

Soko Matsumura; Ralph E. Pudritz

2003-08-03T23:59:59.000Z

388

Origin of the Metallicity Dependence of Exoplanet Host Stars in the Protoplanetary Disk Mass Distribution  

E-Print Network [OSTI]

The probability of a star hosting a planet that is detectable in radial velocity surveys increases Ppl(Z) oc 10^2Z, where Z is metallicity. Core accretion models reproduce this trend, since the protoplanetary disk of a high metallicity star has a high density of solids and so forms cores which accrete gas before the primordial gas disk dissipates. This paper considers the origin of the form of Ppl(Z). We introduce a simple model in which detectable planets form when the mass of solids in the protoplanetary disk, Ms, exceeds a critical value. In this model the form of Ppl(Z) is a direct reflection of the distribution of protoplanetary disk masses, Mg, and the observed Ppl(Z) is reproduced if P(Mg>Mg') oc 1/Mg'^2. We argue that a protoplanetary disk's sub-mm dust mass is a pristine indicator of the mass available for planet-building and find the observed sub-mm disk mass distribution is consistent with the observed Ppl(Z) if Ms>0.5M_J is required to form detectable planets. Any planet formation model which imposes a critical solid mass for planet formation would reproduce the observed Ppl(Z), and core accretion models are empirically consistent with a threshold criterion. We identify 7 protoplanetary disks which, by rigid application of this criterion, would be expected to form detectable planets. A testable prediction is that Ppl(Z) should flatten both for Z>0.5dex and as more distant and lower mass planets are discovered. Further, combining this model with one in which the evolution of a star's debris disk is also influenced by the solid mass in its protoplanetary disk, results in the prediction that debris disks detected around stars with planets should be more infrared luminous than those around stars without planets in tentative agreement with recent observations.

M. C. Wyatt; C. J. Clarke; J. S. Greaves

2007-07-18T23:59:59.000Z

389

ON THE EVOLUTION OF DUST MINERALOGY, FROM PROTOPLANETARY DISKS TO PLANETARY SYSTEMS  

SciTech Connect (OSTI)

Mineralogical studies of silicate features emitted by dust grains in protoplanetary disks and solar system bodies can shed light on the progress of planet formation. The significant fraction of crystalline material in comets, chondritic meteorites, and interplanetary dust particles indicates a modification of the almost completely amorphous interstellar medium dust from which they formed. The production of crystalline silicates, thus, must happen in protoplanetary disks, where dust evolves to build planets and planetesimals. Different scenarios have been proposed, but it is still unclear how and when this happens. This paper presents dust grain mineralogy (composition, crystallinity, and grain size distribution) of a complete sample of protoplanetary disks in the young Serpens cluster. These results are compared to those in the young Taurus region and to sources that have retained their protoplanetary disks in the older Upper Scorpius and {eta} Chamaeleontis stellar clusters, using the same analysis technique for all samples. This comparison allows an investigation of the grain mineralogy evolution with time for a total sample of 139 disks. The mean cluster age and disk fraction are used as indicators of the evolutionary stage of the different populations. Our results show that the disks in the different regions have similar distributions of mean grain sizes and crystallinity fractions ({approx}10%-20%) despite the spread in mean ages. Furthermore, there is no evidence of preferential grain sizes for any given disk geometry nor for the mean cluster crystallinity fraction to increase with mean age in the 1-8 Myr range. The main implication is that a modest level of crystallinity is established in the disk surface early on ({<=}1 Myr), reaching an equilibrium that is independent of what may be happening in the disk midplane. These results are discussed in the context of planet formation, in comparison with mineralogical results from small bodies in our own solar system.

Oliveira, Isa; Van Dishoeck, Ewine F. [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Olofsson, Johan [Max-Planck Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany); Pontoppidan, Klaus M. [California Institute of Technology, Division for Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125 (United States); Augereau, Jean-Charles [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d'Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041 (France); MerIn, Bruno, E-mail: oliveira@strw.leidenuniv.nl [Herschel Science Center, European Space Agency (ESA), P.O. Box 78, 28691 Villanueva de la Canada (Madrid) (Spain)

2011-06-10T23:59:59.000Z

390

Power Management in RAID Server Disk System Using Multiple Idle States Hogil Kim, Eun Jung Kim and Rabi N. Mahapatra  

E-Print Network [OSTI]

}@cs.tamu.edu Abstract Energy efficient design for disk devices has become a very important issue, because ever

Mahapatra, Rabinarayan

391

Carbon, nitrogen and $\\alpha$-element abundances determine the formation sequence of the Galactic thick and thin disks  

E-Print Network [OSTI]

Using the DR12 public release of APOGEE data, we show that thin and thick disk separate very well in the space defined by [$\\alpha$/Fe], [Fe/H] and [C/N]. Thick disk giants have both higher [C/N] and higher [$\\alpha$/Fe] than do thin disk stars with similar [Fe/H]. We deduce that the thick disk is composed of lower mass stars than the thin disk. Considering the fact that at a given metallicity there is a one-to-one relation between stellar mass and age, we are then able to infer the chronology of disk formation. Both the thick and the thin disks - defined by [$\\alpha$/Fe] -- converge in their dependance on [C/N] and [C+N/Fe] at [Fe/H]$\\approx$-0.7. We conclude that 1) the majority of thick disk stars formed earlier than did the thin disk stars 2) the formation histories of the thin and thick disks diverged early on, even when the [Fe/H] abundances are similar 3) that the star formation rate in the thin disk has been lower than in the thick disk, at all metallicities. Although these general conclusions remain ...

Masseron, T

2015-01-01T23:59:59.000Z

392

Vibrated polar disks: spontaneous motion, binary collisions, and collective dynamics  

E-Print Network [OSTI]

We study the spontaneous motion, binary collisions, and collective dynamics of "polar disks", i.e. purpose-built particles which, when vibrated between two horizontal plates, move coherently along a direction strongly correlated to their intrinsic polarity. The motion of our particles, although nominally three-dimensional and complicated, is well accounted for by a two-dimensional persistent random walk. Their binary collisions are spatiotemporally extended events during which multiple actual collisions happen, yielding a weak average effective alignment. We show that this well-controlled, "dry active matter" system can display collective motion with orientationally-ordered regions of the order of the system size. We provide evidence of strong number density in the most ordered regimes observed. These results are discussed in the light of the limitations of our system, notably those due to the inevitable presence of walls.

Julien Deseigne; Sbastien Lonard; Olivier Dauchot; Hugues Chat

2012-01-29T23:59:59.000Z

393

Adaptor assembly for coupling turbine blades to rotor disks  

SciTech Connect (OSTI)

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.

Delvaux, John McConnel; Garcia-Crespo, Andres Jose; Joyce, Kilmer Joseph; Tindell, Allan Randall

2014-06-03T23:59:59.000Z

394

On the aerodynamic redistribution of chondrite components in protoplanetary disks  

E-Print Network [OSTI]

Despite being all roughly of solar composition, primitive meteorites (chondrites) present a diversity in their chemical, isotopic and petrographic properties, and in particular a first-order dichotomy between carbonaceous and non-carbonaceous chondrites. We investigate here analytically the dynamics of their components (chondrules, refractory inclusions, metal/sulfide and matrix grains) in protoplanetary disks prior to their incorporation in chondrite parent bodies. We find the dynamics of the solids, subject to gas drag, to be essentially controlled by the "gas-solid decoupling parameter" $S\\equiv \\textrm{St}/\\alpha$, the ratio of the dimensionless stopping time to the turbulence parameter. The decoupling of the solid particles relative to the gas is significant when $S$ exceeds unity. $S$ is expected to increase with time and heliocentric distance. On the basis of (i) abundance of refractory inclusions (ii) proportion of matrix (iii) lithophile element abundances and (iv) oxygen isotopic composition of chon...

Jacquet, Emmanuel; Fromang, Sbastien

2012-01-01T23:59:59.000Z

395

Radial disk heating by more than one spiral density wave  

E-Print Network [OSTI]

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.

I. Minchev; A. C. Quillen

2005-10-28T23:59:59.000Z

396

HALO ORBITS IN COSMOLOGICAL DISK GALAXIES: TRACERS OF FORMATION HISTORY  

SciTech Connect (OSTI)

We analyze the orbits of stars and dark matter particles in the halo of a disk galaxy formed in a cosmological hydrodynamical simulation. The halo is oblate within the inner {approx}20 kpc and triaxial beyond this radius. About 43% of orbits are short axis tubes-the rest belong to orbit families that characterize triaxial potentials (boxes, long-axis tubes and chaotic orbits), but their shapes are close to axisymmetric. We find no evidence that the self-consistent distribution function of the nearly oblate inner halo is comprised primarily of axisymmetric short-axis tube orbits. Orbits of all families and both types of particles are highly eccentric, with mean eccentricity {approx}> 0.6. We find that randomly selected samples of halo stars show no substructure in 'integrals of motion' space. However, individual accretion events can clearly be identified in plots of metallicity versus formation time. Dynamically young tidal debris is found primarily on a single type of orbit. However, stars associated with older satellites become chaotically mixed during the formation process (possibly due to scattering by the central bulge and disk, and baryonic processes), and appear on all four types of orbits. We find that the tidal debris in cosmological hydrodynamical simulations experiences significantly more chaotic evolution than in collisionless simulations, making it much harder to identify individual progenitors using phase space coordinates alone. However, by combining information on stellar ages and chemical abundances with the orbital properties of halo stars in the underlying self-consistent potential, the identification of progenitors is likely to be possible.

Valluri, Monica [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States)] [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Debattista, Victor P. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom)] [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Stinson, Gregory S. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)] [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Bailin, Jeremy [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487-0324 (United States)] [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487-0324 (United States); Quinn, Thomas R. [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States)] [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); Couchman, H. M. P.; Wadsley, James, E-mail: mvalluri@umich.edu [Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1 (Canada)] [Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1 (Canada)

2013-04-10T23:59:59.000Z

397

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 Office of Inspector GeneralDepartmentAUDIT REPORTOpenWende NewSowitec do Brasil EnergiaSur de RenovablesPvt Ltd

398

Gross crack initiation and propagation in brittle thin solid and annular disks subjected to impact loading  

SciTech Connect (OSTI)

This paper derives from a study of grinding wheel break-up behavior due to impact. The impact fracture characteristics of circular disks of plaster of Paris with a concentric central hole were studied experimentally for three types of loading: (a) when the disks were suspended freely and loaded intensely at one point on their circumference by an explosive detonator; (b) when the disks were allowed to fall under gravity from a certain height on to a rigid base; and (c) when a disk, resting on a rigid base, was struck by a flat ended rigid body which was dropped on to it from a certain height. Quasi-static flattening tests on the disks were also carried out. The paper describes a theoretical investigation into the stress analysis of disks under impact, classifies the relevant damage sustained by them and attempts to unify the ''gross'' impact fracture patterns which arise in different modes of dynamic loading. The extent of local flattening of the quasi-statically loaded disks before fracture, is also reported. Good correlation between the theory and experimental results is obtained, especially for rings of diameter ratio (D /SUB i/ /D/sub 0/) of around 0.5.

Johnson, W.; Bai, Y.L.; Ghosh, S.K.

1984-04-01T23:59:59.000Z

399

THE SEEDS DIRECT IMAGING SURVEY FOR PLANETS AND SCATTERED DUST EMISSION IN DEBRIS DISK SYSTEMS  

SciTech Connect (OSTI)

Debris disks around young main-sequence stars often have gaps and cavities which for a long time have been interpreted as possibly being caused by planets. In recent years, several giant planet discoveries have been made in systems hosting disks of precisely this nature, further implying that interactions with planets could be a common cause of such disk structures. As part of the SEEDS high-contrast imaging survey, we are surveying a population of debris-disk-hosting stars with gaps and cavities implied by their spectral energy distributions, in order to attempt to spatially resolve the disk as well as to detect any planets that may be responsible for the disk structure. Here, we report on intermediate results from this survey. Five debris disks have been spatially resolved, and a number of faint point sources have been discovered, most of which have been tested for common proper motion, which in each case has excluded physical companionship with the target stars. From the detection limits of the 50 targets that have been observed, we find that {beta} Pic b-like planets ({approx}10 M{sub jup} planets around G-A-type stars) near the gap edges are less frequent than 15%-30%, implying that if giant planets are the dominant cause of these wide (27 AU on average) gaps, they are generally less massive than {beta} Pic b.

Janson, Markus; Brandt, Timothy D. [Department of Astrophysical Sciences, Princeton University, NJ 08544 (United States); Moro-Martin, Amaya [Department of Astrophysics, CAB (INTA-CSIC), Instituto Nacional de Tecnica Aerospacial, Torrejonde Ardoz, E-28850 Madrid (Spain); Usuda, Tomonori; Kudo, Tomoyuki; Egner, Sebastian [Subaru Telescope, 650 North Aohoku Place, Hilo, HI 96720 (United States); Thalmann, Christian [Astronomical Institute ''Anton Pannekoek'', University of Amsterdam, Science Park 904, 1098-XH Amsterdam (Netherlands); Carson, Joseph C. [Department of Physics and Astronomy, College of Charleston, 58 Coming Street, Charleston, SC 29424 (United States); Goto, Miwa [Universitaets-Sternwarte Muenchen, Ludwig-Maximilians-Universitaet, Scheinerstr. 1, D-81679 Munich (Germany); Currie, Thayne [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, M5S 3H4 Toronto, ON (Canada); McElwain, M. W. [Exoplanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center, Greenbelt, MD 2071 (United States); Itoh, Yoichi [Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo, 407-2 Nishigaichi, Sayo, Hyogo 679-5313 (Japan); Fukagawa, Misato [Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Crepp, Justin [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Kuzuhara, Masayuki; Hashimoto, Jun; Kusakabe, Nobuhiko [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Abe, Lyu [Laboratoire Lagrange, UMR7239, University of Nice-Sophia Antipolis, CNRS, Observatoire de la Cote d'Azur, F-06300 Nice (France); Brandner, Wolfgang; Feldt, Markus, E-mail: janson@astro.princeton.edu [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); and others

2013-08-10T23:59:59.000Z

400

A Survey for Massive Giant Planets in Debris Disks with Evacuated Inner Cavities  

E-Print Network [OSTI]

The commonality of collisionally replenished debris around main sequence stars suggests that minor bodies are frequent around Sun-like stars. Whether or not debris disks in general are accompanied by planets is yet unknown, but debris disks with large inner cavities - perhaps dynamically cleared - are considered to be prime candidates for hosting large-separation massive giant planets. We present here a high-contrast VLT/NACO angular differential imaging survey for eight such cold debris disks. We investigated the presence of massive giant planets in the range of orbital radii where the inner edge of the dust debris is expected. Our observations are sensitive to planets and brown dwarfs with masses >3 to 7 Jupiter mass, depending on the age and distance of the target star. Our observations did not identify any planet candidates. We compare the derived planet mass upper limits to the minimum planet mass required to dynamically clear the inner disks. While we cannot exclude that single giant planets are responsible for clearing out the inner debris disks, our observations constrain the parameter space available for such planets. The non-detection of massive planets in these evacuated debris disks further reinforces the notion that the giant planet population is confined to the inner disk (<15 AU).

D. Apai; M. Janson; A. Moro-Martin; M. R. Meyer; E. E. Mamajek; E. Masciadri; Th. Henning; I. Pascucci; J. S. Kim; L. A. Hillenbrand; M. Kasper; B. Biller

2007-10-01T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
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they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


401

Flux-Limited Diffusion Approximation Models of Giant Planet Formation by Disk Instability  

E-Print Network [OSTI]

Both core accretion and disk instability appear to be required as formation mechanisms in order to explain the entire range of giant planets found in extrasolar planetary systems. Disk instability is based on the formation of clumps in a marginally-gravitationally unstable protoplanetary disk. These clumps can only be expected to contract and survive to become protoplanets if they are able to lose thermal energy through a combination of convection and radiative cooling. Here we present several new three dimensional, radiative hydrodynamics models of self-gravitating protoplanetary disks, where radiative transfer is handled in the flux-limited diffusion approximation. We show that while the flux-limited models lead to higher midplane temperatures than in a diffusion approximation model without the flux-limiter, the difference in temperatures does not appear to be sufficiently high to have any significant effect on the formation of self-gravitating clumps. Self-gravitating clumps form rapidly in the models both with and without the flux-limiter. These models suggest that the reason for the different outcomes of numerical models of disk instability by different groups cannot be attributed solely to the handling of radiative transfer, but rather appears to be caused by a range of numerical effects and assumptions. Given the observational imperative to have disk instability form at least some extrasolar planets, these models imply that disk instability remains as a viable giant planet formation mechanism.

Alan P. Boss

2008-01-28T23:59:59.000Z

402

A SPITZER IRS SURVEY OF NGC 1333: INSIGHTS INTO DISK EVOLUTION FROM A VERY YOUNG CLUSTER  

SciTech Connect (OSTI)

We report on the {lambda} = 5-36 {mu}m Spitzer Infrared Spectrograph (IRS) spectra of 79 young stellar objects in the very young nearby cluster NGC 1333. NGC 1333's youth enables the study of early protoplanetary disk properties, such as the degree of settling and the formation of gaps and clearings. We construct spectral energy distributions (SEDs) using our IRS data as well as published photometry and classify our sample into SED classes. Using 'extinction-free' spectral indices, we determine whether the disk, envelope, or photosphere dominates the spectrum. We analyze the dereddened spectra of objects that show disk-dominated emission using spectral indices and properties of silicate features in order to study the vertical and radial structure of protoplanetary disks in NGC 1333. At least nine objects in our sample of NGC 1333 show signs of large (several AU) radial gaps or clearings in their inner disk. Disks with radial gaps in NGC 1333 show more nearly pristine silicate dust than their radially continuous counterparts. We compare properties of disks in NGC 1333 to those in three other well-studied regions, Taurus-Auriga, Ophiuchus, and Chamaeleon I, and find no difference in their degree of sedimentation and dust processing.

Arnold, L. A.; Watson, Dan M.; Kim, K. H.; Manoj, P.; Remming, I.; Sheehan, P.; Forrest, W. J.; Mamajek, E. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Adame, L.; McClure, M. [Department of Astronomy, University of Michigan, 500 Church Street, Dennison Building, Ann Arbor, MI 48109 (United States); Furlan, E. [Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 264-723, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Espaillat, C. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); Ausfeld, K.; Rapson, V. A., E-mail: laa@pas.rochester.edu, E-mail: dmw@pas.rochester.edu [Center for Imaging Science, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

2012-08-01T23:59:59.000Z

403

ON THE SIZE EVOLUTION OF A GALACTIC DISK IN HIERARCHICAL MERGING OF COLD DARK MATTER HALOS  

SciTech Connect (OSTI)

We investigate the dynamical effects of dark matter subhalos on the structure and evolution of a galactic disk, using the semi-analytic method that includes approximated and empirical relations as achieved in detailed numerical simulations of the cold dark matter model. We calculate the upper limit for the size of a galactic disk at a specific redshift z, based on the orbital properties of subhalos characterized by their pericentric distances from the center of a host halo. We find that this possibly largest size of a disk as determined by the smallest pericentric distances of subhalos shows the characteristic properties, which are basically in agreement with an observed galactic disk at low and high z. Namely, it is found that a massive disk can have a larger size than a less massive one, because of its stability against the destruction effect of subhalos. Also, with fixed mass, the size of a galactic disk at low z can be larger than that at high z, reflecting the orbital evolution of subhalos with respect to a host halo. These results suggest that the presence and structure of a galactic disk may be dynamically limited by the interaction with dark matter substructures, especially at high z.

Hayashi, Hirohito; Chiba, Masashi [Astronomical Institute, Tohoku University, Aoba-ku, Sendai 980-8578 (Japan)

2009-09-10T23:59:59.000Z

404

Implications of modes of star formation for the overall dynamics of galactic disks  

E-Print Network [OSTI]

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.

B. Fuchs

2001-03-22T23:59:59.000Z

405

Evidence for a Snow Line Beyond the Transitional Radius in the TW Hya Protoplanetary Disk  

E-Print Network [OSTI]

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 H2O lines, using a simple step-function parameterization of the water vapor content near the disk surface. We find that water vapor is abundant (~10^{-4} per H2) in a narrow ring, located at the disk transition radius some 4AU from the central star, but drops rapidly by several orders of magnitude beyond 4.2 AU over a scale length of no more than 0.5AU. The inner disk (0.5-4AU) is also dry, with an upper limit on the vertically averaged water abundance of 10^{-6} per H2. The water vapor peak occurs at a radius significantly more distant than that expected fo...

Zhang, K; Salyk, C; Blake, G A

2013-01-01T23:59:59.000Z

406

Doppler-Shift Asymmetry in High-Velocity Maser Emission from Shocks in Circumnuclear Disks  

E-Print Network [OSTI]

SHORT VERSION: The rapidly rotating, masing circumnuclear disk in the central sub-parsec region of the galaxy NGC 4258 is remarkably circular and Keplerian, yet a striking asymmetry appears in the maser spectrum: the red-shifted, high- velocity sources are much more numerous and significantly more intense than the blue-shifted ones. A similar strong asymmetry appears also in the recently discovered, masing, circumnuclear disks in NGC 1068 and NGC 4945, thus suggesting it may be a general phenomenon. We show that the observed Doppler-shift asymmetry can naturally arise due to spiral shocks in circumnuclear disks, independent of the existence of a warp in the disk or the azimuthal direction to the observer. The high velocities of these features reflect the rotational velocities in the disk, and have nothing to do with the shock speed. In NGC 4258 - the currently most well-defined masing disk - the proposed scenario can also account for the intriguing clustering of the high-velocity maser spots in distinct clumps, the restricted spatial distribution of the low-velocity sources, and the dip in the maser spectrum at the systemic velocity of the disk. In this case we infer a disk mass of ~10E4 M_sun and a mass accretion rate of order ~7E-3 M_sun/year, which may be consistent with an advection-dominated accretion flow. The model is consistent with the observed Keplerian rotation, and introduces only negligible corrections to the previously derived black hole mass and galaxy distance. Predictions include slow systematic drifts in the velocity and position of all the high-velocity features, and the existence of circumnuclear disks which are delineated only by high-velocity maser emission.

Eyal Maoz; Christopher F. McKee

1997-04-04T23:59:59.000Z

407

NUCLEOSYNTHESIS IN THE OUTFLOWS ASSOCIATED WITH ACCRETION DISKS OF TYPE II COLLAPSARS  

SciTech Connect (OSTI)

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.

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)

2013-11-20T23:59:59.000Z

408

MODELING THE RESOLVED DISK AROUND THE CLASS 0 PROTOSTAR L1527  

SciTech Connect (OSTI)

We present high-resolution sub/millimeter interferometric imaging of the Class 0 protostar L1527 IRS (IRAS 04368+2557) at {lambda} = 870 {mu}m and 3.4 mm from the Submillimeter Array and Combined Array for Research in Millimeter Astronomy. We detect the signature of an edge-on disk surrounding the protostar with an observed diameter of 180 AU in the sub/millimeter images. The mass of the disk is estimated to be 0.007 M{sub Sun }, assuming optically thin, isothermal dust emission. The millimeter spectral index is observed to be quite shallow at all the spatial scales probed: {alpha} {approx} 2, implying a dust opacity spectral index {beta} {approx} 0. We model the emission from the disk and surrounding envelope using Monte Carlo radiative transfer codes, simultaneously fitting the sub/millimeter visibility amplitudes, sub/millimeter images, resolved L' image, spectral energy distribution, and mid-infrared spectrum. The best-fitting model has a disk radius of R = 125 AU, is highly flared (H{proportional_to}R {sup 1.3}), has a radial density profile {rho}{proportional_to}R {sup -2.5}, and has a mass of 0.0075 M{sub Sun }. The scale height at 100 AU is 48 AU, about a factor of two greater than vertical hydrostatic equilibrium. The resolved millimeter observations indicate that disks may grow rapidly throughout the Class 0 phase. The mass and radius of the young disk around L1527 are comparable to disks around pre-main-sequence stars; however, the disk is considerably more vertically extended, possibly due to a combination of lower protostellar mass, infall onto the disk upper layers, and little settling of {approx}1 {mu}m-sized dust grains.

Tobin, John J. [National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States); Hartmann, Lee; Calvet, Nuria [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Chiang, Hsin-Fang; Looney, Leslie W. [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Wilner, David J. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Loinard, Laurent; D'Alessio, Paola, E-mail: jtobin@nrao.edu [Centro de Radioastronomia y Astrofisica, UNAM, Apartado Postal 3-72 (Xangari), 58089 Morelia, Michoacan (Mexico)

2013-07-01T23:59:59.000Z

409

ON THE POSSIBILITY OF ENRICHMENT AND DIFFERENTIATION IN GAS GIANTS DURING BIRTH BY DISK INSTABILITY  

SciTech Connect (OSTI)

We investigate the coupling between rock-size solids and gas during the formation of gas giant planets by disk fragmentation in the outer regions of massive disks. In this study, we use three-dimensional radiative hydrodynamic simulations and model solids as a spatial distribution of particles. We assume that half of the total solid fraction is in small grains and half in large solids. The former are perfectly entrained with the gas and set the opacity in the disk, while the latter are allowed to respond to gas drag forces, with the back reaction on the gas taken into account. To explore the maximum effects of gas-solid interactions, we first consider 10 cm size particles. We then compare these results to a simulation with 1 km size particles, which explores the low-drag regime. We show that (1) disk instability planets have the potential to form large cores due to aerodynamic capturing of rock-size solids in spiral arms before fragmentation; (2) temporary clumps can concentrate tens of M{sub +} of solids in very localized regions before clump disruption; (3) the formation of permanent clumps, even in the outer disk, is dependent on the grain-size distribution, i.e., the opacity; (4) nonaxisymmetric structure in the disk can create disk regions that have a solids-to-gas ratio greater than unity; (5) the solid distribution may affect the fragmentation process; (6) proto-gas giants and proto-brown dwarfs can start as differentiated objects prior to the H{sub 2} collapse phase; (7) spiral arms in a gravitationally unstable disk are able to stop the inward drift of rock-size solids, even redistributing them to larger radii; and (8) large solids can form spiral arms that are offset from the gaseous spiral arms. We conclude that planet embryo formation can be strongly affected by the growth of solids during the earliest stages of disk accretion.

Boley, Aaron C. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611 (United States); Durisen, Richard H., E-mail: aaron.boley@gmail.co [Department of Astronomy, Indiana University, 727 East 3rd Street, Swain West 319, Bloomington, IN 47405 (United States)

2010-11-20T23:59:59.000Z

410

The Formation and Structure of a Strongly Magnetized Corona above Weakly Magnetized Accretion Disks  

E-Print Network [OSTI]

We use three-dimensional magnetohydrodynamical (MHD) simulations to study the formation of a corona above an initially weakly magnetized, isothermal accretion disk. We also describe a modification to time-explicit numerical algorithms for MHD which enables us to evolve highly stratified disks for many orbital times. We find that MHD turbulence driven by the magnetorotational instability (MRI) produces strong amplification of weak fields within two scale heights of the disk midplane in a few orbital times. About 25 % of the magnetic energy generated by the MRI within two scale heights escapes due to buoyancy, producing a strongly magnetized corona above the disk. Most of the buoyantly rising magnetic energy is dissipated between 3 and 5 scale heights, suggesting the corona will also be hot. The average vertical disk structure consists of a weakly magnetized turbulent core below a strongly magnetized corona which is stable to the MRI. The largescale field structure in both the disk and corona is toroidal. The functional form of the stress is flat within two scale heights, but proportional to the density above two scale heights. For initially weak uniform vertical fields, we find the exponential growth of magnetic field via axisymmetric vertical modes of the MRI produces strongly buoyant sheets of magnetic energy which break the disk apart into horizontal channels. These channels rise several scale heights vertically before the onset of the Parker instability distorts the sheets and allows matter to flow back towards the midplane and reform a disk. We suggest this evolution may be relevant to the dynamical processes which disrupt the inner regions of a disk when it interacts with a strongly magnetized central object.

K. A. Miller; J. M. Stone

1999-12-07T23:59:59.000Z

411

THE BURST MODE OF ACCRETION AND DISK FRAGMENTATION IN THE EARLY EMBEDDED STAGES OF STAR FORMATION  

SciTech Connect (OSTI)

We revisit our original papers on the burst mode of accretion by incorporating a detailed energy balance equation into a thin-disk model for the formation and evolution of circumstellar disks around low-mass protostars. Our model includes the effect of radiative cooling, viscous and shock heating, and heating due to stellar and background irradiation. Following the collapse from the prestellar phase allows us to model the early embedded phase of disk formation and evolution. During this time, the disk is susceptible to fragmentation, depending upon the properties of the initial prestellar core. Globally, we find that higher initial core angular momentum and mass content favors more fragmentation, but higher levels of background radiation can moderate the tendency to fragment. A higher rate of mass infall onto the disk than that onto the star is a necessary but not a sufficient condition for disk fragmentation. More locally, both the Toomre Q-parameter needs to be below a critical value and the local cooling time needs to be shorter than a few times the local dynamical time. Fragments that form during the early embedded phase tend to be driven into the inner disk regions and likely trigger mass accretion and luminosity bursts that are similar in magnitude to FU-Orionis-type or EX-Lupi-like events. Disk accretion is shown to be an intrinsically variable process, thanks to disk fragmentation, nonaxisymmetric structure, and the effect of gravitational torques. The additional effect of a generic {alpha}-type viscosity acts to reduce burst frequency and accretion variability, and is likely to not be viable for values of {alpha} significantly greater than 0.01.

Vorobyov, Eduard I. [Institute for Computational Astrophysics, Saint Mary's University, Halifax, NS B3H 3C3 (Canada); Basu, Shantanu, E-mail: vorobyov@ap.smu.c, E-mail: basu@uwo.c [Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7 (Canada)

2010-08-20T23:59:59.000Z

412

Ruiz-Ponte, C., Cilia, V., Lambert, C., Nicolas, J.L., 1998. Roseobacter gallaeciensis sp. nov., a new marine bacterium isolated from rearings and collectors of the scallop Pecten maximus. International Journal of Systematic Bacteriology 48 Pt 2, 537-542.  

E-Print Network [OSTI]

., a new marine bacterium isolated from rearings and collectors of the scallop Pecten maximus marine bacterium isolated from rearings and collectors of the scallop Pecten maximus. C. Ruiz-Ponte1 , V were isolated from larval cultures and collectors of the scallop Pecten maximus. They showed a high

Paris-Sud XI, Universit de

413

Method and apparatus for bistable optical information storage for erasable optical disks  

DOE Patents [OSTI]

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.

Land, C.E.; McKinney, I.D.

1988-05-31T23:59:59.000Z

414

Method and apparatus for bistable optical information storage for erasable optical disks  

DOE Patents [OSTI]

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 an 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.

Land, Cecil E. (Albuquerque, NM); McKinney, Ira D. (Albuquerque, NM)

1990-01-01T23:59:59.000Z

415

Star Formation in Isolated Disk Galaxies. II. Schmidt Laws and Efficiency of Gravitational Collapse  

E-Print Network [OSTI]

(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.

Yuexing Li; Mordecai-Mark Mac Low; Ralf S. Klessen

2006-02-21T23:59:59.000Z

416

Dark Matter and Stellar Mass in the Luminous Regions of Disk Galaxies  

E-Print Network [OSTI]

We investigate the correlations among stellar mass (M_*), disk scale length (R_d), and rotation velocity at 2.2 disk scale lengths (V_2.2) for a sample of 81 disk-dominated galaxies (disk/total >= 0.9) selected from the SDSS. We measure V_2.2 from long-slit H-alpha rotation curves and infer M_* from galaxy i-band luminosities (L_i) and g-r colors. We find logarithmic slopes of 2.60+/-0.13 and 3.05+/-0.12 for the L_i-V_2.2 and M_*-V_2.2 relations, somewhat shallower than most previous studies, with intrinsic scatter of 0.13 dex and 0.16 dex. Our direct estimates of the total-to-stellar mass ratio within 2.2R_d, assuming a Kroupa IMF, yield a median ratio of 2.4 for M_*>10^10 Msun and 4.4 for M_*=10^9-10^10 Msun, with large scatter at a given M_* and R_d. The typical ratio of the rotation speed predicted for the stellar disk alone to the observed rotation speed at 2.2R_d is ~0.65. The distribution of R_d at fixed M_* is broad, but we find no correlation between disk size and the residual from the M_*-V_2.2 relation, implying that this relation is an approximately edge-on view of the disk galaxy fundamental plane. Independent of the assumed IMF, this result implies that stellar disks do not, on average, dominate the mass within 2.2R_d. We discuss our results in the context of infall models of disk formation in cold dark matter halos. A model with a disk-to-halo mass ratio m_d=0.05 provides a reasonable match to the R_d-M_* distribution for spin parameters \\lambda ranging from ~0.04-0.08, and it yields a reasonable match to the mean M_*-V_2.2 relation. A model with m_d=0.1 predicts overly strong correlations between disk size and M_*-V_2.2 residual. Explaining the wide range of halo-to-disk mass ratios within 2.2R_d requires significant scatter in m_d values, with systematically lower m_d for galaxies with lower $M_*$.

James Pizagno; Francisco Prada; David H. Weinberg; Hans-Walter Rix; Daniel Harbeck; Eva K. Grebel; Eric Bell; Jon Brinkmann; Jon Holtzman; Andrew West

2005-11-02T23:59:59.000Z

417

27th European Photovoltaic Solar Energy Conference, Frankfurt, Germany, 24-28 September 2012, 2AO.1.5 IMPACT OF THE REAR SURFACE ROUGHNESS ON INDUSTRIAL-TYPE PERC SOLAR CELLS  

E-Print Network [OSTI]

-generation industrial solar cells as stated in the International Technology Roadmap [3]. An industrial PERC process flow27th European Photovoltaic Solar Energy Conference, Frankfurt, Germany, 24-28 September 2012, 2AO.1.5 IMPACT OF THE REAR SURFACE ROUGHNESS ON INDUSTRIAL-TYPE PERC SOLAR CELLS C.Kranz1 , S. Wyczanowski1 , S

418

Microwave whirlpools in a rectangular-waveguide cavity with a thin ferrite disk  

E-Print Network [OSTI]

We study a three dimensional system of a rectangular-waveguide resonator with an inserted thin ferrite disk. The interplay of reflection and transmission at the disk interfaces together with material gyrotropy effect, gives rise to a rich variety of wave phenomena. We analyze the wave propagation based on full Maxwell-equation numerical solutions of the problem. We show that the power-flow lines of the microwave-cavity field interacting with a ferrite disk, in the proximity of its ferromagnetic resonance, form whirlpool-like electromagnetic vortices. Such vortices are characterized by the dynamical symmetry breaking. The role of ohmic losses in waveguide walls and dielectric and magnetic losses in a disk is a subject of our investigations.

E. O. Kamenetskii; Michael Sigalov; Reuven Shavit

2007-07-09T23:59:59.000Z

419

HIDING IN THE SHADOWS: SEARCHING FOR PLANETS IN PRE-TRANSITIONAL AND TRANSITIONAL DISKS  

SciTech Connect (OSTI)

Transitional and pre-transitional disks can be explained by a number of mechanisms. This work aims to find a single observationally detectable marker that would imply a planetary origin for the gap and, therefore, indirectly indicate the presence of a young planet. N-body simulations were conducted to investigate the effect of an embedded planet of one Jupiter mass on the production of instantaneous collisional dust derived from a background planetesimal disk. Our new model allows us to predict the dust distribution and resulting observable markers with greater accuracy than previous works. Dynamical influences from a planet on a circular orbit are shown to enhance dust production in the disk interior and exterior to the planet orbit, while removing planetesimals from the orbit itself, creating a clearly defined gap. In the case of an eccentric planet, the gap opened by the planet is not as clear as the circular case, but there is a detectable asymmetry in the dust disk.

Dobinson, Jack; Leinhardt, Zo M. [School of Physics, H. H. Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL (United Kingdom)] [School of Physics, H. H. Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL (United Kingdom); Dodson-Robinson, Sarah E. [Astronomy Department, University of Texas at Austin, Austin, TX 78712 (United States)] [Astronomy Department, University of Texas at Austin, Austin, TX 78712 (United States); Teanby, Nick A. [School of Earth Sciences, Wills Memorial Building, University of Bristol, Bristol, BS8 1RJ (United Kingdom)] [School of Earth Sciences, Wills Memorial Building, University of Bristol, Bristol, BS8 1RJ (United Kingdom)

2013-11-10T23:59:59.000Z

420

Augmentation of Power Output of Axisymmetric Ducted Wind Turbines by Porous Trailing Edge Disks  

E-Print Network [OSTI]

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 ...

widnall, sheila

2014-06-30T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


421

Flux-Limited Diffusion Approximation Models of Giant Planet Formation by Disk Instability  

E-Print Network [OSTI]

Both core accretion and disk instability appear to be required as formation mechanisms in order to explain the entire range of giant planets found in extrasolar planetary systems. Disk instability is based on the formation of clumps in a marginally-gravitationally unstable protoplanetary disk. These clumps can only be expected to contract and survive to become protoplanets if they are able to lose thermal energy through a combination of convection and radiative cooling. Here we present several new three dimensional, radiative hydrodynamics models of self-gravitating protoplanetary disks, where radiative transfer is handled in the flux-limited diffusion approximation. We show that while the flux-limited models lead to higher midplane temperatures than in a diffusion approximation model without the flux-limiter, the difference in temperatures does not appear to be sufficiently high to have any significant effect on the formation of self-gravitating clumps. Self-gravitating clumps form rapidly in the models both...

Boss, Alan P

2008-01-01T23:59:59.000Z

422

E-Print Network 3.0 - accreting protostellar disks Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

<< < 1 2 3 4 5 > >> 1 The University of Western Ontario DEPARTMENT OF PHYSICS AND ASTRONOMY Summary: from the protostellar disk as the jet mass outflow is comparable to the...

423

First optical images of circumstellar dust surrounding the debris disk candidate HD 32297  

E-Print Network [OSTI]

Near-infrared imaging with the Hubble Space Telescope recently revealed a circumstellar dust disk around the A star HD 32297. Dust scattered light is detected as far as 400 AU radius and the linear morphology is consistent with a disk ~10 degrees away from an edge-on orientation. Here we present the first optical images that show the dust scattered light morphology from 560 to 1680 AU radius. The position angle of the putative disk midplane diverges by 31 degrees and the color of dust scattering is most likely blue. We associate HD 32297 with a wall of interstellar gas and the enigmatic region south of the Taurus molecular cloud. We propose that the extreme asymmetries and blue disk color originate from a collision with a clump of interstellar material as HD 32297 moves southward, and discuss evidence consistent with an age of 30 Myr or younger.

P. Kalas

2005-11-08T23:59:59.000Z

424

E-Print Network 3.0 - atomic circumnuclear disk Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

1 2 3 4 5 > >> 1 The Role of Neutral Hydrogen in the Evolution of Nearby Summary: disk of atomic hydrogen in Centaurus A 101 4.1 Introduction... nuclear H I absorption . . . . . ....

425

Nucleosynthesis of Nickel-56 from Gamma-Ray Burst Accretion Disks  

E-Print Network [OSTI]

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.

R. Surman; G. C. McLaughlin; N. Sabbatino

2011-12-12T23:59:59.000Z

426

Slit disk for modified faraday cup diagnostic for determining power density of electron and ion beams  

DOE Patents [OSTI]

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.

Teruya, Alan T. (Livermore, CA); Elmer; John W. (Danville, CA); Palmer, Todd A. (State College, PA)

2011-03-08T23:59:59.000Z

427

Prospects for obtaining an r-process from Gamma Ray Burst Disk Winds  

E-Print Network [OSTI]

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.

G. C. McLaughlin; R. Surman

2004-07-27T23:59:59.000Z

428

E-Print Network 3.0 - accretion disk annulus Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

I. General Solution and Application to Sgr A* Summary: Accretion Disk Evolution With Wind Infall I. General Solution and Application to Sgr A* Heino... (melia@as.arizona.edu)...

429

E-Print Network 3.0 - accretion disk systems Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

accretion disk in SW Sex, assuming a distance to the binary system of 450 pc... the high-inclination systems, suggesting that their origin is not in a at, Keplarian accretion...

430

E-Print Network 3.0 - accretion disk gamma-ray Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

gamma-ray Search Powered by Explorit Topic List Advanced Search Sample search results for: accretion disk gamma-ray Page: << < 1 2 3 4 5 > >> 1 Lecture 4Lecture 4 Galactic...

431

On the Evolution of Dust Mineralogy, From Protoplanetary Disks to Planetary Systems  

E-Print Network [OSTI]

Mineralogical studies of silicate features emitted by dust grains in protoplanetary disks and Solar System bodies can shed light on the progress of planet formation. The significant fraction of crystalline material in comets, chondritic meteorites and interplanetary dust particles indicates a modification of the almost completely amorphous ISM dust from which they formed. The production of crystalline silicates thus must happen in protoplanetary disks, where dust evolves to build planets and planetesimals. Different scenarios have been proposed, but it is still unclear how and when this happens. This paper presents dust grain mineralogy of a complete sample of protoplanetary disks in the young Serpens cluster. These results are compared to those in the young Taurus region and to sources that have retained their protoplanetary disks in the older Upper Scorpius and Eta Chamaeleontis stellar clusters, using the same analysis technique for all samples. This comparison allows an investigation of the grain mineralo...

Oliveira, Isa; Pontoppidan, Klaus M; van Dishoeck, Ewine F; Augereau, Jean-Charles; Merin, Bruno

2011-01-01T23:59:59.000Z

432

Role of bit patterned media in future of hard disk drives  

E-Print Network [OSTI]

The hard disk industry has traditionally stayed competitive by competing on the means of price alone by cutting down aggressively on cost via increase of areal density. Continuing increases in the areal density of hard ...

Aravindakshan, Vibin

2007-01-01T23:59:59.000Z

433

Shadowing of the Nascent Jet in NGC 4261 by a Line-Emitting Supersonic Accretion Disk  

E-Print Network [OSTI]

NGC 4261 (3C 270) is a low-luminosity radio galaxy with two symmetric kiloparsec-scale jets. Earlier Hubble Space Telescope observations indicated the presence of a hundred-parsec scale disk of cool dust and gas surrounding a central, supermassive ($\\sim 4.9\\times 10^8\\msun$) black hole. The recent detection of free-free radio absorption by a small, geometrically-thin disk, combined with earlier studies of the disk's large scale properties, provide the strictest constraints to date on the nature of the accretion process in this system. We show here that a supersonic disk, illuminated by the active galactic nucleus (AGN), can not only account for the observed radio shadowing, but can also produce the optical broad lines emitted from this region. Beyond a critical radius $r_c$, line cooling dominates over gravitational dissipation and the gas is effectively cooled down to temperatures below $10^4$ K. Within $r_c$, however, heating due to the release of gravitational energy overwhelms line cooling and the plasma is heated very quickly to a temperature close to its virial value as it falls toward the central engine. The disk is optically-thin to UV and X-ray radiation within $r_c$, so the ionizing radiation from the AGN is preferentially absorbed near $r_c$, affecting the disk structure significantly. To include the ensuing photoionization effect, we have used the algorithm Cloudy with additional heating introduced by gravitational dissipation to calculate the temperature profile and line emission from the disk in a self-consistent manner. The results of our model calculation are consistent with current multiwavelength observations of the disk in this source.

Siming Liu; Michael J. Fromerth; Fulvio Melia

2003-06-27T23:59:59.000Z

434

MAPPING H-BAND SCATTERED LIGHT EMISSION IN THE MYSTERIOUS SR21 TRANSITIONAL DISK  

SciTech Connect (OSTI)

We present the first near infrared (NIR) spatially resolved images of the circumstellar transitional disk around SR21. These images were obtained with the Subaru HiCIAO camera, adaptive optics, and the polarized differential imaging technique. We resolve the disk in scattered light at H-band for stellocentric 0.''1 {<=} r {<=} 0.''6 (12 {approx}< r {approx}< 75 AU). We compare our results with previously published spatially resolved 880 {mu}m continuum Submillimeter Array images that show an inner r {approx}< 36 AU cavity in SR21. Radiative transfer models reveal that the large disk depletion factor invoked to explain SR21's sub-mm cavity cannot be 'universal' for all grain sizes. Even significantly more moderate depletions ({delta} = 0.1, 0.01 relative to an undepleted disk) than those that reproduce the sub-mm cavity ({delta} {approx} 10{sup -6}) are inconsistent with our H-band images when they are assumed to carry over to small grains, suggesting that surface grains scattering in the NIR either survive or are generated by whatever mechanism is clearing the disk midplane. In fact, the radial polarized intensity profile of our H-band observations is smooth and steeply inwardly-increasing (r {sup -3}), with no evidence of a break at the 36 AU sub-mm cavity wall. We hypothesize that this profile is dominated by an optically thin disk envelope or atmosphere component. We also discuss the compatibility of our data with the previously postulated existence of a sub-stellar companion to SR21 at r {approx} 10-20 AU, and find that we can neither exclude nor verify this scenario. This study demonstrates the power of multiwavelength imaging of transitional disks to inform modeling efforts, including the debate over precisely what physical mechanism is responsible for clearing these disks of their large midplane grains.

Follette, Katherine B.; Close, Laird [Steward Observatory, The University of Arizona, 933 N Cherry Ave, Tucson, AZ 85721 (United States)] [Steward Observatory, The University of Arizona, 933 N Cherry Ave, Tucson, AZ 85721 (United States); Tamura, Motohide; Hashimoto, Jun; Kwon, Jungmi; Kandori, Ryo [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)] [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Whitney, Barbara [Astronomy Department, University of Wisconsin-Madison, 475 N. Charter Street, Madison, WI 53706 (United States)] [Astronomy Department, University of Wisconsin-Madison, 475 N. Charter Street, Madison, WI 53706 (United States); Grady, Carol [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States)] [Eureka Scientific, 2452 Delmer, Suite 100, Oakland, CA 96002 (United States); Andrews, Sean M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)] [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Wisniewski, John [H.L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks St Norman, OK 73019 (United States)] [H.L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks St Norman, OK 73019 (United States); Brandt, Timothy D.; Dong, Ruobing [Department of Astrophysical Sciences, Princeton University, NJ 08544 (United States)] [Department of Astrophysical Sciences, Princeton University, NJ 08544 (United States); Mayama, Satoshi [The Center for the Promotion of Integrated Sciences, The Graduate University for Advanced Studies (Sokendai), Shonan International Village, Hayama-cho, Miura-gun, Kanagawa 240-0193 (Japan)] [The Center for the Promotion of Integrated Sciences, The Graduate University for Advanced Studies (Sokendai), Shonan International Village, Hayama-cho, Miura-gun, Kanagawa 240-0193 (Japan); Abe, Lyu [Laboratoire Lagrange, UMR7293, Universite de Nice-Sophia Antipolis, CNRS, Observatoire de la Cote d'Azur, F-06300 Nice (France)] [Laboratoire Lagrange, UMR7293, Universite de Nice-Sophia Antipolis, CNRS, Observatoire de la Cote d'Azur, F-06300 Nice (France); Brandner, Wolfgang; Feldt, Markus [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany)] [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Carson, Joseph [Department of Physics and Astronomy, College of Charleston, 58 Coming St., Charleston, SC 29424 (United States)] [Department of Physics and Astronomy, College of Charleston, 58 Coming St., Charleston, SC 29424 (United States); Currie, Thayne [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street M5S 3H4, Toronto Ontario (Canada)] [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street M5S 3H4, Toronto Ontario (Canada); Egner, Sebastian E. [Subaru Telescope, 650 North Aohoku Place, Hilo, HI 96720 (United States)] [Subaru Telescope, 650 North Aohoku Place, Hilo, HI 96720 (United States); Goto, Miwa, E-mail: kfollette@as.arizona.edu [Universitats-Sternwarte Munchen, Ludwig-Maximilians-Universitat, Scheinerstr. 1, D-81679 Munchen (Germany)] [Universitats-Sternwarte Munchen, Ludwig-Maximilians-Universitat, Scheinerstr. 1, D-81679 Munchen (Germany); and others

2013-04-10T23:59:59.000Z

435

Extrasolar Planet Eccentricities from Scattering in the Presence of Residual Gas Disks  

E-Print Network [OSTI]

Gravitational scattering between massive planets has been invoked to explain the eccentricity distribution of extrasolar planets. For scattering to occur, the planets must either form in -- or migrate into -- an unstable configuration. In either case, it is likely that a residual gas disk, with a mass comparable to that of the planets, will be present when scattering occurs. Using explicit hydrodynamic simulations, we study the impact of gas disks on the outcome of two-planet scattering. We assume a specific model in which the planets are driven toward instability by gravitational torques from an outer low mass disk. We find that the accretion of mass and angular momentum that occurs when a scattered planet impacts the disk can strongly influence the subsequent dynamics by reducing the number of close encounters. The eccentricity of the innermost surviving planet at the epoch when the system becomes Hill stable is not substantially altered from the gas-free case, but the outer planet is circularized by its interaction with the disk. The signature of scattering initiated by gas disk migration is thus a high fraction of low eccentricity planets at larger radii accompanying known eccentric planets. Subsequent secular evolution of the two planets in the presence of damping can further damp both eccentricities, and tends to push systems away from apsidal alignment and toward anti-alignment. We note that the late burst of accretion when the outer planet impacts the disk is in principle observable, probably via detection of a strong near-IR excess in systems with otherwise weak disk and stellar accretion signatures.

Nickolas Moeckel; Sean N. Raymond; Philip J. Armitage

2008-07-25T23:59:59.000Z

436

A mathematical model for the electrodeposition of amorphous alloys on a rotating disk electrode  

E-Print Network [OSTI]

A MATHEMATICAL MODEL FOR THE ELECTRODEPOSITION OF AMORPHOUS ALLOYS ON A ROTATING DISK ELECTRODE A Thesis by SHIUAN CHEN Submitted to the Graduate College of Texas AAcM University in partial fulfillment of the requirement, for the degree... of MASTER OF SCIENCE December 19B6 Major Subject: Chemical Engineering A MATHEMATICAL MODEL FOR THE ELECTRODEPOSITION OF AMORPHOUS ALLOYS ON A ROTATING DISK ELECTRODE A Thesis by SHIUAN CHEN Approved as to style and content by: alph E. White...

Chen, Shiuan

1986-01-01T23:59:59.000Z

437

Lyapunov instability of rough hard-disk fluids  

E-Print Network [OSTI]

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 $I$.

Jacobus A. van Meel; Harald A. Posch

2009-04-02T23:59:59.000Z

438

Angle-resolved effective potentials for disk-shaped molecules  

E-Print Network [OSTI]

We present an approach for calculating coarse-grained angle-resolved effective pair potentials for uniaxial molecules. For integrating out the intramolecular degrees of freedom we apply umbrella sampling and steered dynamics techniques in atomistically-resolved molecular dynamics (MD) computer simulations. Throughout this study we focus on disk-like molecules such as coronene. To develop the methods we focus on integrating out the van-der-Waals and intramolecular interactions, while electrostatic charge contributions are neglected. The resulting coarse-grained pair potential reveals a strong temperature and angle dependence. In the next step we fit the numerical data with various Gay-Berne-like potentials to be used in more efficient simulations on larger scales. The quality of the resulting coarse-grained results is evaluated by comparing their pair and many-body structure as well as some thermodynamic quantities self-consistently to the outcome of atomistic MD simulations of many particle systems. We find that angle-resolved potentials are essential not only to accurately describe crystal structures but also for fluid systems where simple isotropic potentials start to fail already for low to moderate packing fractions. Further, in describing these states it is crucial to take into account the pronounced temperature dependence arising in selected pair configurations due to bending fluctuations.

Thomas Heinemann; Karol Palczynski; Joachim Dzubiella; Sabine H. L. Klapp

2014-10-22T23:59:59.000Z

439

The Fractal Distribution of HII Regions in Disk Galaxies  

E-Print Network [OSTI]

It is known that the gas has a fractal structure in a wide range of spatial scales with a fractal dimension that seems to be a constant around Df = 2.7. It is expected that stars forming from this fractal medium exhibit similar fractal patterns. Here we address this issue by quantifying the degree to which star-forming events are clumped. We develop, test, and apply a precise and accurate technique to calculate the correlation dimension Dc of the distribution of HII regions in a sample of disk galaxies. We find that the determination of Dc is limited by the number of HII regions, since if there are fractal dimension among galaxies, contrary to a universal picture sometimes claimed in literature. The fractal dimension exhibits a weak but significant correlation with the absolute magnitude and, to a lesser extent, with the galactic radius. The faintest galaxies tend to distribute their HII regions in more clustered (less uniform) patterns. The fractal dimension for the brightest HII regions within the same galaxy seems to be smaller than for the faintest ones suggesting some kind of evolutionary efffect, but the obtained correlation remains unchanged if only the brightest regions are taken into account.

Nestor Sanchez; Emilio J. Alfaro

2008-04-29T23:59:59.000Z

440

air coupled ultrasonic: Topics by E-print Network  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

ultrasonic testing (ACUT) setup for the inspection of commercial carbon-carbon composite aircraft brake disks was developed in Intelligent Measurement and Evaluation...

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


441

E-Print Network 3.0 - annular flow conditions Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Collection: Environmental Sciences and Ecology ; Geosciences 88 225Noise Control Eng. J. 52 (5), 2004 SeptOct Determination of sound radiation from a simplified disk-brake...

442

Gravitational drag on a point mass in hypersonic motion within a Gaussian disk  

E-Print Network [OSTI]

We develop an analytical model for the accretion and gravitational drag on a point mass that moves hypersonically in the midplane of a gaseous disk with a Gaussian vertical density stratification. Such a model is of interest for studying the interaction between a planet and a protoplanetary disk, as well as the dynamical decay of massive black holes in galactic nuclei. The model considers that the flow is ballistic, and gives fully analytical expressions for both the accretion rate onto the point mass, and the gravitational drag it suffers. The expressions are further simplified by taking the limits of a thick, and of a thin disk. The results for the thick disk reduce correctly to those for a uniform density environment (Cant\\'o et al. 2011). We find that for a thin disk (small vertical scaleheight compared to the gravitational radius) the accretion rate is proportional to the mass of the moving object and to the surface density of the disk, while the drag force is independent of the velocity of the object. T...

Cant, J; Raga, A C

2012-01-01T23:59:59.000Z

443

Time-Dependent Disk Models for the Microquasar GRS1915+105  

E-Print Network [OSTI]

We investigate different accretion disk models and viscosity prescriptions in order to provide a basic explanation for the exotic temporal behavior in GRS 1915+105. Based on the fact that the overall cycle times are very much longer than the rise/fall time scales in GRS 1915, we rule out the geometry of ADAF or a hot quasi-spherical region plus a cold outer disk for this source. We thus concentrate on geometrically thin Shakura-Sunyaev type disks (Shakura & Sunyaev 1973; hereafter SS73). We have devised a modified viscosity law that has a quasi-stable upper branch. Via numerical simulations, we show that the model does account for several gross observational features of GRS 1915+105. On the other hand, the rise/fall time scales are not short enough, and no rapid oscillations on time scales $\\simlt$ 10 s emerge naturally from the model. We then consider and numerically test a more elaborate model that includes the cold disk, a corona, and plasma ejections from the inner disk region and show that this model allows us to reproduce several additional observed features of GRS 1915+105. We conclude that the most likely structure of the accretion flow in this source is that of a cold disk with a modified viscosity prescription, plus a corona that accounts for much of the X-ray emission, and unsteady plasma ejections that occur when the luminosity of the source is high.

Sergei Nayakshin; Saul Rappaport; Fulvio Melia

1999-05-27T23:59:59.000Z

444

Origin of the Metallicity Dependence of Exoplanet Host Stars in the Protoplanetary Disk Mass Distribution  

E-Print Network [OSTI]

The probability of a star hosting a planet that is detectable in radial velocity surveys increases Ppl(Z) oc 10^2Z, where Z is metallicity. Core accretion models reproduce this trend, since the protoplanetary disk of a high metallicity star has a high density of solids and so forms cores which accrete gas before the primordial gas disk dissipates. This paper considers the origin of the form of Ppl(Z). We introduce a simple model in which detectable planets form when the mass of solids in the protoplanetary disk, Ms, exceeds a critical value. In this model the form of Ppl(Z) is a direct reflection of the distribution of protoplanetary disk masses, Mg, and the observed Ppl(Z) is reproduced if P(Mg>Mg') oc 1/Mg'^2. We argue that a protoplanetary disk's sub-mm dust mass is a pristine indicator of the mass available for planet-building and find the observed sub-mm disk mass distribution is consistent with the observed Ppl(Z) if Ms>0.5M_J is required to form detectable planets. Any planet formation model which impo...

Wyatt, M C; Greaves, J S

2007-01-01T23:59:59.000Z

445

The Signature of Primordial Grain Growth in the Polarized Light of the AU Mic Debris Disk  

E-Print Network [OSTI]

We have used the Hubble Space Telescope/ACS coronagraph to make polarization maps of the AU Mic debris disk. The fractional linear polarization rises monotonically from about 0.05 to 0.4 between 20 and 80 AU. The polarization is perpendicular to the disk, indicating that the scattered light originates from micron sized grains in an optically thin disk. Disk models, which simultaneously fit the surface brightness and polarization, show that the inner disk (< 40-50 AU) is depleted of micron-sized dust by a factor of more than 300, which means that the disk is collision dominated. The grains have high maximum linear polarization and strong forward scattering. Spherical grains composed of conventional materials cannot reproduce these optical properties. A Mie/Maxwell-Garnett analysis implicates highly porous (91-94%) particles. In the inner Solar System, porous particles form in cometary dust, where the sublimation of ices leaves a "bird's nest" of refractory organic and silicate material. In AU Mic, the grain porosity may be primordial, because the dust "birth ring" lies beyond the ice sublimation point. The observed porosities span the range of values implied by laboratory studies of particle coagulation by ballistic cluster-cluster aggregation. To avoid compactification, the upper size limit for the parent bodies is in the decimeter range, in agreement with theoretical predictions based on collisional lifetime arguments. Consequently, AU Mic may exhibit the signature of the primordial agglomeration process whereby interstellar grains first assembled to form macroscopic objects.

James R. Graham; Paul G. Kalas; Brenda C. Matthews

2006-09-12T23:59:59.000Z

446

Discovery of a candidate protoplanetary disk around the embedded source IRc9 in Orion  

E-Print Network [OSTI]

We report the detection of spatially-extended mid-infrared emission around the luminous embedded star IRc9 in OMC-1, as seen in 8.8, 11.7, and 18.3 micron images obtained with T-ReCS on Gemini South. The extended emission is asymmetric, and the morphology is reminiscent of warm dust disks around other young stars. The putative disk has a radius of roughly 1.5 arcsec (700 AU), and a likely dust mass of almost 10 Earth masses. The infrared spectral energy distribution of IRc9 indicates a total luminosity of about 100 Lsun, implying that it shall become an early A-type star when it reaches the main sequence. Thus, the candidate disk around IRc9 may be a young analog of the planetary debris disks around Vega-like stars and the disks of Herbig Ae stars, and may provide a laboratory in which to study the earliest phases of planet formation. A disk around IRc9 may also add weight to the hypothesis that an enhanced T Tauri-like wind from this star has influenced the molecular outflow from the OMC-1 core.

Nathan Smith; John Bally

2005-02-08T23:59:59.000Z

447

The Total Number of Giant Planets in Debris Disks with Central Clearings  

E-Print Network [OSTI]

Infrared spectra from the Spitzer Space Telescope (SSC) of many debris disks are well fit with a single black body temperature which suggest clearings within the disk. We assume that inside the clearing orbital instability due to planets removes dust generating planetesimal belts and dust generated by the outer disk that is scattered or drifts into the clearing. From numerical integrations we estimate a minimum planet spacing required for orbital instability (and so planetesimal and dust removal) as a function of system age and planet mass. We estimate that a 10^8 year old debris disk with a dust disk edge at a radius of 50 AU hosted by an A star must contain approximately 5 Neptune mass planets between the clearing radius and the iceline in order to remove all primordial objects within it. We infer that known debris disk systems contain at least a fifth of a Jupiter mass in massive planets. The number of planets and spacing required is insensitive to the assumed planet mass. However an order of magnitude higher total mass in planets could reside in these systems if the planets are more massive.

Peter Faber; Alice C. Quillen

2007-06-12T23:59:59.000Z