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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

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

E-Print Network (OSTI)

This simulator experiment is a preliminary study examining the effects of different auditory signals on braking force and reaction time in a rear-end collision warning system. A driving simulator was built in which subjects operated a computer 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 driving situation by applying his/her brakes. Closing velocities of 10 miles per hour and 30 miles per hour were used. Braking times and forces were measured for four different warning sounds: 1) no warning; 2) a pulsed warning sound that increased in repetition rate; 3) a sound that increased in frequency; and, 4) a sound that increased in intensity. Results suggested that an auditory warning signal would decrease reaction time and increase maximum braking force applied. The sound that increased in frequency and the sound that increased in intensity provided the greatest savings in reaction time, approximately one quarter second, when compared to the no warning condition. The pulsed warning sound provided the greatest increase in braking force. Participants preferred the pulsed sound over the other warning sounds. Further research must be done to determine if the warning sounds decrease the reaction time enough to cause a significant reduction in accidents.

Hopkins, Jennifer Susan

1995-01-01T23:59:59.000Z

2

Hybrid: Braking  

NLE Websites -- All DOE Office Websites (Extended Search)

button highlighted Stopped Button subbanner graphic: gray bar BRAKING: PART 1 Regenerative braking converts otherwise wasted energy from braking into electricity and stores it in...

3

Multidisciplinary design optimization of an automotive magnetorheological brake design  

Science Conference Proceedings (OSTI)

This paper presents the development of a new electromechanical brake system using magnetorheological (MR) fluid. The proposed brake system consists of rotating disks immersed in a MR fluid and enclosed in an electromagnet, where the yield stress of the ... Keywords: Automotive brake, Computational fluid dynamics, Electric brake actuator, Finite element analysis, Magnetorheological fluid, Multidisciplinary design optimization

Edward J. Park; Luis Falcão da Luz; Afzal Suleman

2008-02-01T23:59:59.000Z

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

Hybrid: Braking  

Alternative Fuels and Advanced Vehicles Data Center (EERE)

1 1 Regenerative braking converts otherwise wasted energy from braking into electricity and stores it in the battery. In regenerative braking, the electric motor is reversed so that, instead of using electricity to turn the wheels, the rotating wheels turn the motor and create electricity. Using energy from the wheels to turn the motor slows the vehicle down. Go to nextÂ… stage graphic: vertical blue rule Main stage: See through car with battery, engine, and electric motor visible. The car is decelerating. There are arrows flowing from the front wheels to the electric motor to the battery. Main stage: See through car with battery, engine, and electric motor visible. The car is decelerating. There are arrows flowing from the front wheels to the electric motor to the battery.

7

Hybrid: Braking  

Alternative Fuels and Advanced Vehicles Data Center (EERE)

2 2 If additional stopping power is needed, conventional friction brakes (e.g., disc brakes) are also applied automatically. Go backÂ… stage graphic: vertical blue rule Main stage: See through car with battery, engine, and electric motor visible. The car is stopped at an intersection. Main stage: See through car with battery, engine, and electric motor visible. The car is stopped at an intersection. Battery: The battery stores energy generated from the gasoline engine or, during regenerative braking, from the electric motor. Since the battery helps power the vehicle, it is larger and holds much more energy than batteries used to start conventional vehicles. Main stage: See through car with battery, engine, and electric motor visible. The car is stopped at an intersection.

8

Hybrid: Braking  

NLE Websites -- All DOE Office Websites (Extended Search)

Button Stopped button highlighted subbanner graphic: gray bar Button Stopped button highlighted subbanner graphic: gray bar STOPPED When the vehicle is stopped, such as at a red light, the gasoline engine and electric motor shut off automatically so that energy is not wasted in idling. The battery continues to power auxillary systems, such as the air conditioning and dashboard displays. stage graphic: vertical blue rule Main stage: See through car with battery, engine, and electric motor visible. The car is stopped at an intersection. Main stage: See through car with battery, engine, and electric motor visible. The car is stopped at an intersection. Battery: The battery stores energy generated from the gasoline engine or, during regenerative braking, from the electric motor. Since the battery helps power the vehicle, it is larger and holds much more energy than batteries used to start conventional vehicles. Main stage: See through car with battery, engine, and electric motor visible. The car is stopped at an intersection.

9

Hybrid: Braking  

Alternative Fuels and Advanced Vehicles Data Center (EERE)

Button Stopped button highlighted subbanner graphic: gray bar Button Stopped button highlighted subbanner graphic: gray bar STOPPED When the vehicle is stopped, such as at a red light, the gasoline engine and electric motor shut off automatically so that energy is not wasted in idling. The battery continues to power auxillary systems, such as the air conditioning and dashboard displays. stage graphic: vertical blue rule Main stage: See through car with battery, engine, and electric motor visible. The car is stopped at an intersection. Main stage: See through car with battery, engine, and electric motor visible. The car is stopped at an intersection. Battery: The battery stores energy generated from the gasoline engine or, during regenerative braking, from the electric motor. Since the battery helps power the vehicle, it is larger and holds much more energy than batteries used to start conventional vehicles. Main stage: See through car with battery, engine, and electric motor visible. The car is stopped at an intersection.

10

Full Hybrid: Braking  

Alternative Fuels and Advanced Vehicles Data Center (EERE)

Braking button highlighted Stopped button Braking button highlighted Stopped button BRAKING PART 1 Regenerative braking converts otherwise wasted energy from braking into electricity and stores it in the battery. In regenerative braking, the electric motor is reversed so that, instead of using electricity to turn the wheels, the rotating wheels turn the motor and create electricity. Using energy from the wheels to turn the motor slows the vehicle down. Go to nextÂ… stage graphic: vertical blue rule Main stage: See through car with battery, engine, generator, power split device, and electric motor visible. The car is decelerating. There are arrows flowing from the front wheels to the power split device to the electric motor to the battery. Main stage: See through car with battery, engine, generator, power split device, and electric motor visible. The car is decelerating. There are arrows flowing from the front wheels to the power split device to the electric motor to the battery.

11

Vehicle brake testing system  

SciTech Connect

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

12

Svendborg Brakes | Open Energy Information  

Open Energy Info (EERE)

energy Product Denmark-based manufacturer of braking systems for the wind industry, as well as for the oil sector. References Svendborg Brakes1 LinkedIn Connections CrunchBase...

13

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

Science Conference Proceedings (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] ORNL; Capps, Gary J [ORNL] ORNL; Franzese, Oscar [ORNL] ORNL

2013-10-01T23:59:59.000Z

14

Combined hydraulic and regenerative braking system  

DOE Patents (OSTI)

A combined hydraulic and regenerative braking system and method for an electric vehicle is disclosed. The braking system is 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, R.R.; Mericle, G.E.

1979-08-09T23:59:59.000Z

15

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

16

Oxygen-Diffused Titanium as a Candidate Brake Rotor Material  

SciTech Connect

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

17

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

Science Conference Proceedings (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

18

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

19

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

20

Study of Present-Day LED Brightness and Corresponding Rear Signaling Concepts (LED Optimization)  

E-Print Network (OSTI)

Crash database studies have shown that more than 29 percent of all crashes are rear-end crashes. These types of crashes often result from a failure to respond (or delays in responding) to a stopped or decelerating lead vehicle (NHTSA, 2005). The work described here is part of a larger program of research intended to develop and evaluate rear signaling applications designed to reduce the frequency and severity of rear-end crashes by redirecting drivers ’ visual attention to the forward roadway (for cases involving a distracted driver), and/or increasing the saliency or meaningfulness of the brake signal (for attentive drivers).

Round Stop Lamp A; Round Stoplamp A

2009-01-01T23:59:59.000Z

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.


21

Commercial Motor Vehicle Brake Assessment Tools  

E-Print Network (OSTI)

Commercial Motor Vehicle Brake Assessment Tools Commercial Motor Vehicle Roadside Technology Corridor Safety Technology Showcase October 14, 2010 Commercial Motor Vehicle Roadside Technology Corridor #12;Overview · Commercial Motor Vehicle (CMV) Air Brake System · North American Standard Level-1

22

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

23

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

E-Print Network (OSTI)

inspections were due to brake defects. Additionally, brake maintenance and repair present a significant cost Center for Transportation Analysis (CTA) Research Areas Aviation Safety Air Traffic Management Analysis Environmental Policy Analysis Highway Safety Intelligent Transportation Systems Logistics Management Supply

24

Improved braking torque generation capacity of an eddy current brake with time varying magnetic fields: A numerical study  

Science Conference Proceedings (OSTI)

Eddy current brakes (ECB) are electrically controlled and non-contact actuators used as assistive brakes in vehicles. ECBs exhibit insufficient generated braking torque at low speeds. In order to overcome this, the use of AC magnetic fields with fixed ... Keywords: Automotive applications, Brake-by-wire, Eddy current brakes, Finite element analysis, Time-varying magnetic field

Kerem Karakoc; Edward J. Park; Afzal Suleman

2012-10-01T23:59:59.000Z

25

Commercial Motor Vehicle Brake-Related Research  

E-Print Network (OSTI)

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

26

The Application of Fuzzy Logic in Regenerative Braking of EV  

Science Conference Proceedings (OSTI)

Regenerative braking can improve energy usage efficiency and prolong the driving distance of electric vehicle per charge, effectively. In the paper, we design a sugeno’s fuzzy logic controller which has four inputs including driver’s braking ... Keywords: regenerative braking, fuzzy logic control, braking force distribution, ADVISOR

Zijian Zhang; Guoqing Xu; Weimin Li; Liang Zheng

2010-08-01T23:59:59.000Z

27

Method and apparatus for wind turbine braking  

DOE Patents (OSTI)

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

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

2009-02-10T23:59:59.000Z

28

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

29

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

30

Model and Simulation of a Super-capacitor Braking Energy Recovery System for Urban Railway Vehicles  

Science Conference Proceedings (OSTI)

In this paper, a braking energy recovery system based on super-capacitor was presented. The method use super-capacitor and the conventional braking resistance constitute a new braking unit to realize the regenerative energy recovery, when braking, braking ... Keywords: Urban railway transportation, regeneration braking, super-capacitor, energy recovery, electric traction

Chen Xiao-li; Yang Jian; Fang Yu

2010-08-01T23:59:59.000Z

31

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

32

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

33

The Research of Traction Motor Energy-Saving Regenerative Braking Control Technology  

Science Conference Proceedings (OSTI)

In all the motor braking control systems, regenerative braking is the only way of energy-saving braking control mode. It can convert dynamic energy which generate during braking period into electric energy, then return to the grid. In this paper, through ... Keywords: regenerative braking, traction motor, direct torque, stator flux, slip frequency

Yuhua Wang; Jianlin Miao; Yuanfang Wei

2010-05-01T23:59:59.000Z

34

Niobium Alloying in Grey Cast Iron for Vehicle Brake Discs  

Science Conference Proceedings (OSTI)

Presentation Title, Niobium Alloying in Grey Cast Iron for Vehicle Brake Discs. Author(s) ... Microtexture Analysis of a Hot Rolled Silicon Electric Steel · Niobium

35

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

36

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

37

Study on Regenerative Brake Method of Hybrid Electric Drive System of Armored Vehicle  

Science Conference Proceedings (OSTI)

Aiming at characteristics of regenerative brake of hybrid electric drive system of tracked armored vehicle, mechanism of regenerative brake by pulse width modulation is in-depth analyzed, motor speed, brake current, feedback current, feedback energy ... Keywords: hybrid electric drive, motor, regenerative brake

Li Hua; Zhong Meng-chun; Zhang Jian; Xu Da; Lin Hai

2011-10-01T23:59:59.000Z

38

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

39

Computational model design and performance estimation in registration brake control  

Science Conference Proceedings (OSTI)

Electric motorcycles are applicable to both toys and real motorcycles, and also is a reference for constructing larger electrical vehicles. A design computational model of regenerative braking control of electric motorcycles and an experimental identification ...

P. S. Pa; S. C. Chang

2009-06-01T23:59:59.000Z

40

Investigation of aerodynamic braking devices for wind turbine applications  

DOE Green Energy (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

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

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

Energy.gov (U.S. Department of Energy (DOE)) Indexed Site

1: K Pool Fish Rearing, Hanford Site, Richland, Washington EA-1111: K Pool Fish Rearing, Hanford Site, Richland, Washington SUMMARY This EA evaluates the environmental impacts of...

42

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

43

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

44

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

45

Disk Quota Increase Request  

NLE Websites -- All DOE Office Websites (Extended Search)

Disk Disk Quota Increase Disk Quota Increase Request NERSC will consider reasonable requests for changes in disk space and inode limits. Please submit a request through the "Request Forms" section at the NERSC help portal. If you select "Hopper scratch directory" from the "File System" menu below, the quota value requested applies to the combined contents of $SCRATCH and $SCRATCH2. Please ask for the least amount of resources you need, since the sum of disk space and inodes allocated to users already exceeds system capacity. In other words, system resources would be exhausted before all users could use their existing quotas. You can find out the current quotas and usage of disk space and inodes for your home and scratch file systems with the myquota command. You can find

46

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

47

Parents' Expectations about Child Rearing after Divorce: Does Anticipating Difficulty Deter Divorce?  

E-Print Network (OSTI)

Child Rearing after Divorce: Does Anticipating DifficultyChild Rearing after Divorce: Does Anticipating DifficultyChild Rearing after Divorce: Does Anticipating Difficulty

Poortman, Anne-Rigt; Seltzer, Judith A.

2005-01-01T23:59:59.000Z

48

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

DOE Green Energy (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

49

Dust in Protoplanetary Disks  

E-Print Network (OSTI)

We critically examine the best lines of evidence for grain growth in protoplanetary disks, based on modelling of observed spectral energy distributions and images of T Tauri and Herbig Ae stars. The data are consistent with millimeter-sized grains near disk midplanes, and micron-sized grains near disk surfaces. We review three channels by which grains can grow, including direct condensation from the vapor phase, grain-grain collisional sticking, and gravitational instability. The utility of dust in identifying as yet unseen extrasolar planets is highlighted.

Chiang, E I

2003-01-01T23:59:59.000Z

50

Dust in Protoplanetary Disks  

E-Print Network (OSTI)

We critically examine the best lines of evidence for grain growth in protoplanetary disks, based on modelling of observed spectral energy distributions and images of T Tauri and Herbig Ae stars. The data are consistent with millimeter-sized grains near disk midplanes, and micron-sized grains near disk surfaces. We review three channels by which grains can grow, including direct condensation from the vapor phase, grain-grain collisional sticking, and gravitational instability. The utility of dust in identifying as yet unseen extrasolar planets is highlighted.

E. I. Chiang

2003-09-08T23:59:59.000Z

51

Brake rotor design and comparison using finite element analysis : an investigation in topology optimization.  

E-Print Network (OSTI)

??Disc brake technology used for mountain bikes, and mountain bike technology in general, has improved significantly as the sport of mountain biking has evolved. Disc… (more)

Domond, Kenneth

2010-01-01T23:59:59.000Z

52

Numerical Simulation of Brake Discs of CRH3 High-Speed Trains ...  

Science Conference Proceedings (OSTI)

... the research object?the course of emergency brake was simulated by ANSYS. .... Energy X-Ray Diffraction Microscopy Studies of Bulk Polycrystal Responses.

53

Tachyon cosmology, supernovae data, and the big brake singularity  

SciTech Connect

We compare the existing observational data on type Ia supernovae with the evolutions of the Universe predicted by a one-parameter family of tachyon models which we have introduced recently [Phys. Rev. D 69, 123512 (2004)]. Among the set of the trajectories of the model which are compatible with the data there is a consistent subset for which the Universe ends up in a new type of soft cosmological singularity dubbed big brake. This opens up yet another scenario for the future history of the Universe besides the one predicted by the standard {lambda}CDM model.

Keresztes, Z.; Gergely, L. A.; Gorini, V.; Moschella, U.; Kamenshchik, A. Yu. [Department of Theoretical Physics, University of Szeged, Tisza Lajos krt 84-86, Szeged 6720 (Hungary); Department of Experimental Physics, University of Szeged, Dom Ter 9, Szeged 6720 (Hungary); Department of Theoretical Physics, University of Szeged, Tisza Lajos krt 84-86, Szeged 6720 (Hungary); Department of Experimental Physics, University of Szeged, Dom Ter 9, Szeged 6720 (Hungary); Department of Applied Science, London South Bank University, 103 Borough Road, London SE1 OAA (United Kingdom); Dipartimento di Scienze Fisiche e Mathematiche, Universita dell'Insubria, Via Valleggio 11, 22100 Como (Italy); INFN, sezione di Milano, Via Celoria 16, 20133 Milano (Italy); Dipartimento di Fisica and INFN, via Irnerio 46, 40126 Bologna (Italy); L. D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, Kosygin street 2, 119334 Moscow (Russian Federation)

2009-04-15T23:59:59.000Z

54

Observations of Circumstellar Disks  

E-Print Network (OSTI)

The imaging of disks around young stars presents extreme challenges in high dynamic range, angular resolution, and sensitivity. Recent instrumental advances have met these challenges admirably, leading to a marked increase in imaging discoveries. These have opened up a new era in studies of the origin of planetary systems. Questions about our own solar system's formation, and of the prevalence of extra-solar planets, are now addressed with complementary techniques at different wavelengths. Optical and near-infrared images detail scattered light from disks at the highest possible resolution. Mid-infrared, sub-millimeter, and millimeter-wave techniques probe thermal dust continuum radiation. Millimeter-wave interferometry details the small-scale structure of the molecular gas. Kinematic imaging studies affirm the disk interpretation of mm-wave continuum surveys, and the high incidence rate for solar nebula analogs. Inner holes, azimuthal asymmetries, and gaps suggest the presence of underlying planetary bodies. The combined techniques provide a multi-dimensional picture of disks in time and have strengthened our understanding of the connection between disks and planets. Future progress is assured by the presence of much-improved imaging capability looming on the horizon.

David W. Koerner

2001-03-28T23:59:59.000Z

55

Dual-channel Haptic Synthesis of Viscoelastic Tissue Properties using Programmable Eddy Current Brakes  

Science Conference Proceedings (OSTI)

We describe a novel method for haptic synthesis of viscoelastic responses which employs a dual-channel haptic interface. It has motors that generate torque independently of velocity and brakes that generate viscous torque independently of position. ... Keywords: eddy current brakes, haptic simulation, viscoelastic simulation

Andrew H. C. Gosline; Vincent Hayward

2009-10-01T23:59:59.000Z

56

Simulation of PSO Fuzzy Control Stratety for Regenerative Braking of HEV  

Science Conference Proceedings (OSTI)

Based on particle swarm optimization algorithm, a new fuzzy controller was constructed and a fuzzy control strategy of regenerative braking for HEV was proposed. A model of a parallel hybrid electric vehicle was built. The performance of the default ... Keywords: hybrid electric vehicle, fuzzy control, regenerative braking, particle swarm optimization

Wang Chun; Tang Lan

2012-04-01T23:59:59.000Z

57

Operation Pattern Recognition and Control for Super Capacitor Braking Energy Regeneration System of Micro EV  

Science Conference Proceedings (OSTI)

Super capacitor has some advantages of high charge-discharge rate, long life, simple structure and reliable performance, and it is especially suitable as braking energy renewable energy storage device for electric vehicle and hybrid electric vehicle. ... Keywords: Super capacitor, braking energy regeneration, micro EV, pattern recognition and control

Jinyu Qu; Liyan Liang; Zhongyu Yang

2009-12-01T23:59:59.000Z

58

Microsoft PowerPoint - Real-Time Dynamic Brake Assessment poster.ppt [Compatibility Mode]  

NLE Websites -- All DOE Office Websites (Extended Search)

Dynamic Brake Assessment Dynamic Brake Assessment Purpose Conduct a proof-of-concept test to examine the feasibility of developing an on-board system to assess a vehicle's ability to stop based on typical low-pressure in-service braking events. Partnerships H.T. Hackney Company MGM Brakes Overview Funded through the Federal Motor Carrier Safety Administration's Vehicle and Roadside Operations Division Concept stemming from on the Department of Energy's Medium Truck Duty Cycle research as well as previous research conducted for the National Highway Transportation Safety Administration. Signals to be collected Real-time brake application pressure Vehicle speed and acceleration GPS location and grade information Vehicle weight (current load) Engine parameters such as RPM and torque To be conducted October 2010 -

59

Wind turbine trailing-edge aerodynamic brake design  

DOE Green Energy (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

60

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

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
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61

RO-VIBRATIONAL CO DETECTED IN THE {beta} PICTORIS CIRCUMSTELLAR DISK  

SciTech Connect

We present high-resolution near-infrared spectra of {beta} Pictoris-a nearby young star with a debris disk. Fundamental low-J CO absorption lines are detected and strict upper limits are placed on the flux of v = 2-1 low-J CO emission lines. The limit on the UV fluorescent emission flux in the v = 2-1 lines is used to place a tight constraint on the inner extent of the CO gas. Assuming H I is the primary collision partner, the sub-thermal population of the low-J v = 0 rotational levels constrains the density of the gas in the disk to n{sub H} = (2.5{sup +7.1}{sub -1.2}) x 10{sup 5} cm{sup -3}. If the distribution of hydrogen follows that of the other metals in the disk, we find that the mass of the gas in the disk is 0.17{sup +0.47}{sub -0.08} M{sub +}. We compare this mass to the gas mass necessary to brake the metals in the disk through ion-neutral reactions.

Troutman, Matthew R. [Department of Physics and Astronomy, University of Missouri-St. Louis, 8001 Natural Bridge Road, St. Louis, MO 63121 (United States); Hinkle, Kenneth H.; Najita, Joan R. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Rettig, Terrence W. [Center for Astrophysics, University of Notre Dame, Notre Dame, IN 46556 (United States); Brittain, Sean D., E-mail: mtroutm@clemson.edu, E-mail: khinkle@noao.edu, E-mail: najita@noao.edu, E-mail: trettig@nd.edu, E-mail: sbritt@clemson.edu [Department of Physics and Astronomy, 118 Kinard Laboratory, Clemson University, Clemson, SC 29634 (United States)

2011-09-01T23:59:59.000Z

62

Collisional Particle Disks  

E-Print Network (OSTI)

We present a new, simple, fast algorithm to numerically evolve disks of inelastically colliding particles surrounding a central star. Our algorithm adds negligible computational cost to the fastest existing collisionless N-body codes, and can be used to simulate, for the first time, the interaction of planets with disks over many viscous times. Though the algorithm is implemented in two dimensions-i.e., the motions of bodies need only be tracked in a plane-it captures the behavior of fully three-dimensional disks in which collisions maintain inclinations that are comparable to random eccentricities. We subject the algorithm to a battery of tests for the case of an isolated, narrow, circular ring. Numerical simulations agree with analytic theory with regards to how particles' random velocities equilibrate; how the ring viscously spreads; and how energy dissipation, angular momentum transport, and material transport are connected. We derive and measure the critical value of the coefficient of restitution above which viscous stirring dominates inelastic damping and the particles' velocity dispersion runs away.

Yoram Lithwick; Eugene Chiang

2006-07-11T23:59:59.000Z

63

Nonlinear Control Synthesis for a Self-energizing Electro-Hydraulic Brake  

E-Print Network (OSTI)

Nonlinear control algorithm for a self-energizing electro-hydraulic brake is analytically designed. The desired closed-loop system behavior is reached via a synthesized nonlinear controller.

Starykh, Alexey

2010-01-01T23:59:59.000Z

64

Cooperative fish-rearing programs in Hanford Site excess facilities  

Science Conference Proceedings (OSTI)

In, 1993, two successful fish-rearing pilot projects were conducted in Hanford Site 100 K Area water treatment pools (K Pools) that are excess to the US Department of Energy needs. Beginning this spring, two larger cooperative fish programs will be undertaken in the K Pools. One program will involve the Yakama Indian Nation, which will rear, acclimate, and release 500,000 fall chinook salmon. The other program involves the Washington Department of Fish and Wildlife, which will rear warm-water specie (walleye and channel catfish) for planting in state lakes. Renewed economic vitality is the goal expected from these and follow-on fish programs.

Herborn, D.I.; Anderson, B.N.

1994-05-01T23:59:59.000Z

65

The Dispersal of Protoplanetary Disks  

E-Print Network (OSTI)

Protoplanetary disks are the sites of planet formation, and the evolution and eventual dispersal of these disks strongly influences the formation of planetary systems. Disk evolution during the planet-forming epoch is driven by accretion and mass-loss due to winds, and in typical environments photoevaporation by high-energy radiation from the central star is likely to dominate final gas disk dispersal. We present a critical review of current theoretical models, and discuss the observations that are used to test these models and inform our understanding of the underlying physics. We also discuss the role disk dispersal plays in shaping planetary systems, considering its influence on both the process(es) of planet formation and the architectures of planetary systems. We conclude by presenting a schematic picture of protoplanetary disk evolution and dispersal, and discussing prospects for future work.

Alexander, Richard; Andrews, Sean; Armitage, Philip; Cieza, Lucas

2013-01-01T23:59:59.000Z

66

Environmental Assessment K Pool 'Fish Rearing, Hanford Site, Richland, Washington  

Energy.gov (U.S. Department of Energy (DOE)) Indexed Site

DOERA-1 11 1 DOERA-1 11 1 Environmental Assessment K Pool 'Fish Rearing, Hanford Site, Richland, Washington U.S. Department of Emrgy Richland, Washington December 1996 DOEEA-1111 ENVIRONMJ3'NTAL ASSESSMENT K POOL 'F'ISH REARING HANFORD SITE, RICHLAND, WASHINGTON U.S. DEPARTMENT OF ENERGY RICHLAND, WASHINGTON December 1996 This page intentionally left blank. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. 1 ' U.S. Department of Energy summary The U.S. Department of Energy (DOE) has a need to respond to a request to lease facilities at the Hanford Site 100-KE and 100-KW filter plant pools (K Pools) for fish rearing activities. These fish rearing activities would be: (1) business ventures with public h

67

Hook Echoes and Rear-Flank Downdrafts: A Review  

Science Conference Proceedings (OSTI)

Nearly 50 years of observations of hook echoes and their associated rear-flank downdrafts (RFDs) are reviewed. Relevant theoretical and numerical simulation results also are discussed. For over 20 years, the hook echo and RFD have been ...

Paul M. Markowski

2002-04-01T23:59:59.000Z

68

Environmental assessment, K Pool fish rearing, Hanford Site, Richland, Washington  

Science Conference Proceedings (OSTI)

The US Department of Energy (DOE) has a need to respond to a request to lease facilities at the Hanford Site 100-KE and 100-KW filter plant pools (K Pools) for fish rearing activities. These fish rearing activities would be: (1) business ventures with public and private funds and (2) long-term enhancement and supplementation programs for game fish populations in the Columbia River Basin. The proposed action is to enter into a use permit or lease agreement with the YIN or other parties who would rear fish in the 100-K Area Pools. The proposed action would include necessary piping, pump, and electrical upgrades of the facility; cleaning and preparation of the pools; water withdrawal from the Columbia River, and any necessary water or wastewater treatment; and introduction, rearing and release of fish. Future commercial operations may be included.

NONE

1996-12-01T23:59:59.000Z

69

Modelling Accretion in Transitional Disks  

E-Print Network (OSTI)

Transitional disks are protoplanetary disk around young stars that display inner holes in the dust distribution within a few AU, which is accompanied nevertheless by some gas accretion onto the central star. These cavities could possibly be created by the presence of one or more massive planets. If the gap is created by planets and gas is still present in it, then there should be a flow of gas past the planet into the inner region. It is our goal to study the mass accretion rate into the gap and in particular the dependency on the planet's mass and the thermodynamic properties of the disk. We performed 2D hydro simulations for disks with embedded planets. We added radiative cooling from the disk surfaces, radiative diffusion in the disk midplane, and stellar irradiation to the energy equation to have more realistic models. The mass flow rate into the gap region depends, for given disk thermodynamics, non-monotonically on the mass of the planet. Generally, more massive planets open wider and deeper gaps which ...

Müller, Tobias W A

2013-01-01T23:59:59.000Z

70

Control of a dynamic brake to reduce turbine-generator shaft transient torques  

SciTech Connect

A resistive, thyristor-controlled brake is used to damp transient torques in large thermo-electric generators supplying series-compensated transmission lines. Emphasis is placed on developing a suitable control algorithm and testing the algorithm through a wide variety of different operating configurations. Discrete-level Generalized Predictive Control is examined as one possible approach to optimal control of the brake. Some problems with implementation of GPC on the system are discussed. Prony analysis is used to identify system transfer functions which are then related to control design considerations and robustness properties.

Donnelly, M.K.; Smith, J.R.; Johnson, R.M. (Montana State Univ., Bozeman, MT (United States)); Hauer, J.F. (Bonneville Power Administration, Kalispell, MT (United States)); Brush, R.W. (Montana Power Co., Butte, MT (United States)); Adapa, R. (Electric Power Research Inst., Palo Alto, CA (United States))

1993-02-01T23:59:59.000Z

71

Trends for Outer Disk Profiles  

E-Print Network (OSTI)

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

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

2007-12-10T23:59:59.000Z

72

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

Open Energy Info (EERE)

Urat Rear Banner Jihe Orient Wind Energy Co Ltd Urat Rear Banner Jihe Orient Wind Energy Co Ltd Jump to: navigation, search Name Urat Rear Banner Jihe Orient Wind Energy Co Ltd Place Inner Mongolia Autonomous Region, China Sector Wind energy Product Urat Rear Banner Jihe Orient Wind Energy was established by Beijing Keval-East Technology Development in 2006 to develop wind power projects. References Urat Rear Banner Jihe Orient Wind Energy Co Ltd[1] LinkedIn Connections CrunchBase Profile No CrunchBase profile. Create one now! This article is a stub. You can help OpenEI by expanding it. Urat Rear Banner Jihe Orient Wind Energy Co Ltd is a company located in Inner Mongolia Autonomous Region, China . References ↑ "Urat Rear Banner Jihe Orient Wind Energy Co Ltd" Retrieved from "http://en.openei.org/w/index.php?title=Urat_Rear_Banner_Jihe_Orient_Wind_Energy_Co_Ltd&oldid=352581

73

Surface Analysis of the Rear-Flank Downdraft Outflow in Two Tornadic Supercells  

Science Conference Proceedings (OSTI)

The rear-flank downdraft regions of two tornadic supercells were sampled on 12 June 2004 and 9 June 2005 using four “mobile mesonet” probes. These rear-flank downdraft outflows were sampled employing two different data collection routines; ...

Brian D. Hirth; John L. Schroeder; Christopher C. Weiss

2008-07-01T23:59:59.000Z

74

Thermodynamic Analysis of Supercell Rear-Flank Downdrafts from Project ANSWERS  

Science Conference Proceedings (OSTI)

Data collected during Project Analysis of the Near-Surface Wind and Environment along the Rear-flank of Supercells (ANSWERS) provided an opportunity to test recently published associations between rear-flank downdraft (RFD) thermodynamic ...

Matthew L. Grzych; Bruce D. Lee; Catherine A. Finley

2007-01-01T23:59:59.000Z

75

Beta Pictoris Debris Disk is a Proto-planetary Disk  

E-Print Network (OSTI)

Abstract: The debris disk around the star Beta Pictoris is a proto-planetary disk which was caused by a collision of two or more aging stars. Beta Pictoris is shown to possess a large debris disk which glows in the infared. [1] It has been hypothesized that this debris disk is not evidence for the formation of new stars/exoplanets [2] but of the destruction of older stars colliding with each other, thus taking up new orbits around the proto-star Beta Pictoris, which is a very young planet, and leaving a very large debris field similar to our own asteroid belt. [3] The larger stars that collided will stabilize after losing incredible amounts of material and forming rings (like Saturn, Jupiter, Uranus, Neptune). The smaller much more traveled stars will stabilize and take up orbit around the younger stars and form round, undifferentiated objects similar to the moon Callisto [4] , or the many other arrangements of moons around Saturn or Jupiter and smaller objects such as Ceres. This could also explain why they do not possess iron cores but are mostly volatiles such as water, ammonia, methane and sulfur dioxide which have a relatively low equilibrium condensation as opposed to refractory elements and molecules which have a much higher boiling point, and play a large part

Jeffrey J Wolynski

2012-01-01T23:59:59.000Z

76

A cool disk in the Galactic Center?  

E-Print Network (OSTI)

We study the possibility of a cool disk existing in the Galactic Center in the framework of the disk-corona evaporation/condensation model. Assuming an inactive disk, a hot corona should form above the disk since there is a continuous supply of hot gas from stellar winds of the close-by massive stars. Whether the cool disk can survive depends on the mass exchange between the disk and corona. If the disk-corona interaction is dominated by evaporation and the rate is larger than the Bondi accretion rate in the Galactic Center, the disk will be depleted within a certain time period and no persistent disk will exist. On the other hand, if the interaction results in hot gas steadily condensing into the disk, an inactive cool disk might survive. For this case we further investigate the Bremsstrahlung radiation from the hot corona and compare it with the observed X-ray luminosity. Our model shows that, for standard viscosity in the corona (alpha=0.3), the mass evaporation rate is much higher than the Bondi accretion rate and the coronal density is much larger than that inferred from Chandra observations. An inactive disk can not survive such strong evaporation. For small viscosity (alphanature.

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

2004-03-18T23:59:59.000Z

77

Rapid low fidelity turbomachinery disk optimization  

Science Conference Proceedings (OSTI)

Turbomachinery disks are heavy, highly stressed components used in gas turbines. Improved design of turbomachinery disks could yield a significant reduction in engine weight. This paper focuses on rapid low fidelity design and optimization of isotropic ... Keywords: Flywheel, Optimization, Plane stress, Turbomachinery disk

David P. Gutzwiller; Mark G. Turner

2010-05-01T23:59:59.000Z

78

Collapse and Fragmentation of Molecular Cloud Cores. X. Magnetic Braking of Prolate and Oblate Cores  

E-Print Network (OSTI)

The collapse and fragmentation of initially prolate and oblate, magnetic molecular clouds is calculated in three dimensions with a gravitational, radiative hydrodynamics code. The code includes magnetic field effects in an approximate manner: magnetic pressure, tension, braking, and ambipolar diffusion are all modelled. The parameters varied for both the initially prolate and oblate clouds are the initial degree of central concentration of the radial density profile, the initial angular velocity, and the efficiency of magnetic braking (represented by a factor $f_{mb} = 10^{-4}$ or $10^{-3}$). The oblate cores all collapse to form rings that might be susceptible to fragmentation into multiple systems. The outcome of the collapse of the prolate cores depends strongly on the initial density profile. Prolate cores with central densities 20 times higher than their boundary densities collapse and fragment into binary or quadruple systems, whereas cores with central densities 100 times higher collapse to form single...

Boss, Alan P

2009-01-01T23:59:59.000Z

79

How Many CVs are Crossing the Period Gap? A Test for the Disruption of Magnetic Braking  

E-Print Network (OSTI)

We apply population synthesis techniques to calculate the present day number of two types of white dwarf-main sequence star (WDMS) binaries within the cataclysmic variable period gap. The first are post-common envelope binaries with secondary stars that have masses between 0.17 and 0.36 Msun (gPCEBs), such that they will commence mass transfer within the period gap. The second type are systems that were CVs at some point in their past, but detached once they evolved down in orbital period to ~3 h as a consequence of disrupted magnetic braking, and are crossing the period gap via gravitational radiation (dCVs). Full population synthesis calculations are performed where we assume either constant, global values of the common envelope ejection efficiency, or consider the ejection efficiency as a function of secondary mass. Several forms of magnetic braking are also considered. We predict an excess of dCVs over gPCEBs within the period gap of ~4 to ~13 assuming an ejection efficiency between 0.1 and 0.6, and a flat initial mass ratio distribution. This excess is revealed as a prominent peak at the location of the period gap in the orbital period distribution of the combined gPCEB and dCV population. We suggest that if such a feature is observed in the orbital period distribution of an observed sample of short orbital period WDMS binaries, this would strongly corroborate the disruption of magnetic braking.

P. J. Davis; U. Kolb; B. Willems; B. T. Gänsicke

2008-05-30T23:59:59.000Z

80

Variations in gear fatigue life for different wind turbine braking strategies  

SciTech Connect

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

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

Variations in gear fatigue life for different wind turbine braking strategies  

DOE Green Energy (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

82

Energy Proportionality for Disk Storage Using Replication  

E-Print Network (OSTI)

one tenth of the power in standby mode as compared withlower energy mode (sleep/standby mode) after they experiencetransitioning the disk to standby mode. Expected length of

Kim, Jinoh

2010-01-01T23:59:59.000Z

83

PATENT: Nickel Base Superalloy Turbine Disk - TMS  

Science Conference Proceedings (OSTI)

Feb 10, 2007 ... A low solvus, high refractory alloy having unusually versatile processing mechanical property capabilities for advanced disks and rotors in gas ...

84

ON THE TRANSITIONAL DISK CLASS: LINKING OBSERVATIONS OF T TAURI STARS AND PHYSICAL DISK MODELS  

Science Conference Proceedings (OSTI)

Two decades ago 'transitional disks' (TDs) described spectral energy distributions (SEDs) of T Tauri stars with small near-IR excesses, but significant mid- and far-IR excesses. Many inferred this indicated dust-free holes in disks possibly cleared by planets. Recently, this term has been applied disparately to objects whose Spitzer SEDs diverge from the expectations for a typical full disk (FD). Here, we use irradiated accretion disk models to fit the SEDs of 15 such disks in NGC 2068 and IC 348. One group has a 'dip' in infrared emission while the others' continuum emission decreases steadily at all wavelengths. We find that the former have an inner disk hole or gap at intermediate radii in the disk and we call these objects 'transitional disks' and 'pre-transitional disks' (PTDs), respectively. For the latter group, we can fit these SEDs with FD models and find that millimeter data are necessary to break the degeneracy between dust settling and disk mass. We suggest that the term 'transitional' only be applied to objects that display evidence for a radical change in the disk's radial structure. Using this definition, we find that TDs and PTDs tend to have lower mass accretion rates than FDs and that TDs have lower accretion rates than PTDs. These reduced accretion rates onto the star could be linked to forming planets. Future observations of TDs and PTDs will allow us to better quantify the signatures of planet formation in young disks.

Espaillat, C.; Andrews, S.; Qi, C.; Wilner, D. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States); Ingleby, L.; Calvet, N. [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Hernandez, J. [Centro de Investigaciones de Astronomia (CIDA), Merida 5101-A (Venezuela, Bolivarian Republic of); Furlan, E. [National Optical Astronomy Observatory, 950 N. Cherry Ave., Tucson, AZ 85719 (United States); D'Alessio, P. [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, 58089 Morelia, Michoacan (Mexico); Muzerolle, J., E-mail: cespaillat@cfa.harvard.edu, E-mail: sandrews@cfa.harvard.edu, E-mail: cqi@cfa.harvard.edu, E-mail: dwilner@cfa.harvard.edu, E-mail: lingleby@umich.edu, E-mail: ncalvet@umich.edu, E-mail: jesush@cida.ve, E-mail: Elise.Furlan@jpl.nasa.gov, E-mail: p.dalessio@crya.unam.mx, E-mail: muzerol@stsci.edu [Space Telescope Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2012-03-10T23:59:59.000Z

85

Stability and Evolution of Supernova Fallback Disks  

E-Print Network (OSTI)

We show that thin accretion disks made of Carbon or Oxygen are subject to the same thermal ionization instability as Hydrogen and Helium disks. We argue that the instability applies to disks of any metal content. The relevance of the instability to supernova fallback disks probably means that their power-law evolution breaks down when they first become neutral. We construct simple analytical models for the viscous evolution of fallback disks to show that it is possible for these disks to become neutral when they are still young (ages of a few 10^3 to 10^4 years), compact in size (a few 10^9 cm to 10^11 cm) and generally accreting at sub-Eddington rates (Mdot ~ a few 10^14 - 10^18 g/s). Based on recent results on the nature of viscosity in the disks of close binaries, we argue that this time may also correspond to the end of the disk activity period. Indeed, in the absence of a significant source of viscosity in the neutral phase, the entire disk will likely turn to dust and become passive. We discuss various applications of the evolutionary model, including anomalous X-ray pulsars and young radio pulsars. Our analysis indicates that metal-rich fallback disks around newly-born neutron stars and black holes become neutral generally inside the tidal truncation radius (Roche limit) for planets, at \\~10^11 cm. Consequently, the efficiency of the planetary formation process in this context will mostly depend on the ability of the resulting disk of rocks to spread via collisions beyond the Roche limit. It appears easier for the merger product of a doubly degenerate binary, whether it is a massive white dwarf or a neutron star, to harbor planets because it can spread beyond the Roche limit before becoming neutral.[Abridged

Kristen Menou; Rosalba Perna; Lars Hernquist

2001-02-27T23:59:59.000Z

86

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

DOE Green Energy (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

87

On reducing energy management delays in disks  

Science Conference Proceedings (OSTI)

Enterprise computing systems consume a large amount of energy, the cost of which contributes significantly to the operating budget. Consequently, dynamic energy management techniques are prevalent. Unfortunately, dynamic energy management for disks impose ... Keywords: Disk energy management, Peer memory sharing, Spin-up delay reduction

Krish K.R., Guanying Wang, Puranjoy Bhattacharjee, Ali R. Butt, Chris Gniady

2013-06-01T23:59:59.000Z

88

The Structure of Brown Dwarf Circumstellar Disks  

E-Print Network (OSTI)

We present synthetic spectra for circumstellar disks that are heated by radiation from a central brown dwarf. Under the assumption of vertical hydrostatic equilibrium, our models yield scaleheights for brown dwarf disks in excess of three times those derived for classical T Tauri (CTTS) disks. If the near-IR excess emission observed from brown dwarfs is indeed due to circumstellar disks, then the large scaleheights we find could have a significant impact on the optical and near-IR detectability of such systems. Our radiation transfer calculations show that such highly flared disks around brown dwarfs will result in a large fraction of obscured sources due to extinction of direct starlight by the disk over a wide range of sightlines. The obscured fraction for a 'typical' CTTS is less than 20%. We show that the obscured fraction for brown dwarfs may be double that for CTTS, but this depends on stellar and disk mass. We also comment on possible confusion in identifying brown dwarfs via color-magnitude diagrams: edge-on CTTS display similar colors and magnitudes as a face-on brown dwarf plus disk systems.

Christina Walker; Kenneth Wood; C. J. Lada; Thomas Robitaille; J. E. Bjorkman; Barbara Whitney

2004-03-11T23:59:59.000Z

89

Efficient maximal poisson-disk sampling  

Science Conference Proceedings (OSTI)

We solve the problem of generating a uniform Poisson-disk sampling that is both maximal and unbiased over bounded non-convex domains. To our knowledge this is the first provably correct algorithm with time and space dependent only on the ... Keywords: Poisson disk, blue noise, linear complexity, maximal, provable convergence, sampling

Mohamed S. Ebeida; Andrew A. Davidson; Anjul Patney; Patrick M. Knupp; Scott A. Mitchell; John D. Owens

2011-08-01T23:59:59.000Z

90

Redfish Lake Sockeye Salmon Captive Broodstock Rearing and Research, 1993 Annual Report.  

DOE Green Energy (OSTI)

The National Marine Fisheries Service (NMFS), in cooperation with Idaho and BPA, has established captive broodstocks to aid recovery of endangered Snake River sockeye salmon. NMFS is currently maintaining four separate Redfish Lake sockeye Salmon captive broodstocks; all these broodstocks are being reared full-term to maturity in fresh (well) water. Experiments are also being conducted on nonendangered 1990 and 1991-brood Lake Wenatchee (WA) sockeye salmon to compare effects on survival and reproduction to maturity in fresh water and seawater; for both brood-years, fish reared in fresh water were larger than those reared in seawater. Data from captive rearing experiments suggest a ranking priority of circular tanks supplied with pathogen-free fresh water, circular tanks supplied with pumped/filtered/uv-sterilized seawater, and seawater net-pens for rearing sockeye salmon to maturity.

Flagg, Thomas A.

1994-11-01T23:59:59.000Z

91

BACKPRESSURE TESTING OF ROTARY MICROFILTER DISKS  

Science Conference Proceedings (OSTI)

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

Fowley, M.; Herman, D.

2011-04-14T23:59:59.000Z

92

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

93

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

94

Pen Rearing and Imprinting of Fall Chinook Salmon, 1989 Annual Report.  

DOE Green Energy (OSTI)

The goal of this project is to compare net-pen rearing methods to traditional hatchery methods of rearing upriver bright fall chinook salmon (Oncorhynchus tshawvtscha). Fish were reared at several densities in net pens at three Columbia River backwater sites during 1984-1987, and in a barrier net at one site during 1984-1986; methods included both fed and unfed treatments. The purpose of this report is to summarize the results obtained from the unfed treatments and the current return of adults from all fed treatments and the barrier net. Zooplankton were the primary food item of unfed fish. Fish reared in net pens utilized insects colonizing the nets as an additional food source, whereas those reared in the barrier net did not. Growth and production of fish reared in the unfed treatments were low. Instantaneous growth rates of unfed fish were much lower than those of the fed treatments and hatchery controls except when zooplankton densities were high and chironomid larvae were important in the diet of unfed fish reared in pens. Only fish in the barrier net treatment resulted in consistent net gains in growth and production over the rearing periods. Adult returns of fish from all fed and unfed treatments are lower than those of control fish reared at the hatchery. Returns appear to be inversely related to rearing density. Even though adult returns are lower than those of traditional hatchery methods, a cost-benefit analysis, as return data becomes more complete, may prove these methods to be an economical means of expanding current hatchery production, particularly if thinning releases were used.

Beeman, John W.; Novotny, Jerry F.

1990-02-01T23:59:59.000Z

95

Coordinated Garbage Collection for RAID Array of Solid State Disks  

... or it can query the disks to determine the best time to start a global collection . Advantages • Solid state disks have no mechanical moving ...

96

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

E-Print Network (OSTI)

based on eddy current brakes because they are inexpensive, friction- e-mail: andrewg@cim.mcgill.ca e-mail: champ@cim.mcgill.ca e-mail: hayward@cim.mcgill.ca free, capable of fast turn-on time, and linear

Hayward, Vincent

97

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

98

THERMAL RADIATION FROM AN ACCRETION DISK  

E-Print Network (OSTI)

An effect of stimulated radiation processes on thermal radiation from an accretion disk is considered. The radial density waves triggering flare emission and producing quasiperiodic oscillations in radiation from an accretion disk are discussed. It is argued that the observational data suggest the existence of the weak laser sources in a twotemperature plasma of an accretion disk. It was shown earlier that thermal radio emission has a stimulated character and that this statement is probably valid for thermal blackbody radiation in others spectral ranges (Prigara 2003). According to this conception thermal radiation from non-uniform gas is produced by an ensemble of individual emitters.

unknown authors

2004-01-01T23:59:59.000Z

99

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

100

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

E-Print Network (OSTI)

Societal concerns on combustion-based fuel consumption are ever-increasing. With respect to internal combustion engines, this translates to a need to increase brake fuel conversion efficiency (BFCE). Diesel engines are a relatively efficient internal combustion engine to consider for numerous applications, but associated actions to mitigate certain exhaust emissions have generally deteriorated engine efficiency. Conventionally, diesel engine emission control has centered on in-cylinder techniques. Although these continue to hold promise, the industry trend is presently favoring the use of after-treatment devices which create new opportunities to improve the diesel engine's brake fuel conversion efficiency. This study focuses on injection timing effects on the combustion processes, engine efficiency, and the engine system's responses. The engine in the study is a medium duty diesel engine (capable of meeting US EPA Tier III off road emission standards) equipped with common rail direct fuel injection, variable geometry turbo charging, and interfaced with a custom built engine controller. The study found that injection timing greatly affected BFCE by changing the combustion phasing. BFCE would increase up to a maximum then begin to decrease as phasing became less favorable. Combustion phasing would change from being mostly mixing controlled combustion to premixed combustion as injection timing would advance allowing more time for fuel to mix during the ignition delay. Combustion phasing, in turn, would influence many other engine parameters. As injection timing is advanced, in-cylinder temperatures and pressures amplify, and intake and exhaust manifold pressures deteriorate. Rate of heat release and rate of heat transfer increase when injection timing is advanced. Turbocharger speed falls with the advancing injection timing. Torque, however, rose to a maximum then fell off again even though engine speed and fueling rate were held constant between different injection timings. Interestingly, the coefficient of heat transfer changes from a two peak curve to a smooth one peak curve as the injection timing is advanced further. The major conclusion of the study is that injection advance both positively and negatively influences the diesel engine's response which contributes to the brake fuel conversion efficiency.

McLean, James Elliott

2011-08-01T23:59:59.000Z

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.


101

Stochastic oscillations of general relativistic disks  

E-Print Network (OSTI)

We analyze the general relativistic oscillations of thin accretion disks around compact astrophysical objects interacting with the surrounding medium through non-gravitational forces. The interaction with the external medium (a thermal bath) is modeled via a friction force, and a random force, respectively. The general equations describing the stochastically perturbed disks are derived by considering the perturbations of trajectories of the test particles in equatorial orbits, assumed to move along the geodesic lines. By taking into account the presence of a viscous dissipation and of a stochastic force we show that the dynamics of the stochastically perturbed disks can be formulated in terms of a general relativistic Langevin equation. The stochastic energy transport equation is also obtained. The vertical oscillations of the disks in the Schwarzschild and Kerr geometries are considered in detail, and they are analyzed by numerically integrating the corresponding Langevin equations. The vertical displacement...

Harko, Tiberiu

2012-01-01T23:59:59.000Z

102

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

103

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

2005-10-11T23:59:59.000Z

104

The Kuiper Belt and Other Debris Disks  

E-Print Network (OSTI)

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

Jewitt, David; Lacerda, Pedro

2008-01-01T23:59:59.000Z

105

Carbon isotope fractionation in protoplanetary disks  

E-Print Network (OSTI)

We investigate the gas-phase and grain-surface chemistry in the inner 30 AU of a typical protoplanetary disk using a new model which calculates the gas temperature by solving the gas heating and cooling balance and which has an improved treatment of the UV radiation field. We discuss inner-disk chemistry in general, obtaining excellent agreement with recent observations which have probed the material in the inner regions of protoplanetary disks. We also apply our model to study the isotopic fractionation of carbon. Results show that the fractionation ratio, 12C/13C, of the system varies with radius and height in the disk. Different behaviour is seen in the fractionation of different species. We compare our results with 12C/13C ratios in the Solar System comets, and find a stark contrast, indicative of reprocessing.

Woods, Paul M

2008-01-01T23:59:59.000Z

106

Carbon isotope fractionation in protoplanetary disks  

E-Print Network (OSTI)

We investigate the gas-phase and grain-surface chemistry in the inner 30 AU of a typical protoplanetary disk using a new model which calculates the gas temperature by solving the gas heating and cooling balance and which has an improved treatment of the UV radiation field. We discuss inner-disk chemistry in general, obtaining excellent agreement with recent observations which have probed the material in the inner regions of protoplanetary disks. We also apply our model to study the isotopic fractionation of carbon. Results show that the fractionation ratio, 12C/13C, of the system varies with radius and height in the disk. Different behaviour is seen in the fractionation of different species. We compare our results with 12C/13C ratios in the Solar System comets, and find a stark contrast, indicative of reprocessing.

Paul M. Woods; Karen Willacy

2008-12-01T23:59:59.000Z

107

Application of Rarefied Gas Dynamics to the Head-Disk Interface in Hard Disk Drives  

E-Print Network (OSTI)

7.2 Heat conduction between a slider and a disk . . . . . .compared to heat conduction . . . . . 7.4.1 Importance ofof the currently used heat conduction model . . . . . . . .

Liu, Nan

2010-01-01T23:59:59.000Z

108

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 that the nature of the stimulus was not a significant factor in length of MT, but distance between pedals and age-gender levels were found to have significant effects. For the actual braking maneuver, gender and the gender-by-age interaction were significant; in the stationary vehicle portion of the study, they were not. Mean foot MT for both genders over all conditions were 0.28 seconds for women and 0.22 seconds for men. For older drivers, over all conditions, the mean foot MT was 0.25 seconds, and, for the younger drivers, 0.24 seconds. Linear regressions revealed high intra-subject variation in MT, which was corroborated by comparing with data from other parts of the study. Poor r2 values for fitting the data to Fitts' Law and to a modification of Fitts' Law were attributed to this high intra-subject variation and to obtaining data from only two different movement amplitudes. It was found that drivers' foot MTs tended to converge to a common value when controlling the vehicle at 88 km/hr (55 mph) as opposed to sitting in the driver's seat while the vehicle was stationary; mean foot MT for each subject group decreased, and differences between genders and age groups significantly diminished while the car was in motion.

Berman, Andrea Helene

1994-01-01T23:59:59.000Z

109

Disk evaporation in a planetary nebula  

E-Print Network (OSTI)

We study the Galactic bulge planetary nebula M 2-29 (for which a 3-year eclipse event of the central star has been attributed to a dust disk) using HST imaging and VLT spectroscopy, both long-slit and integral field. The central cavity of M 2-29 is filled with a decreasing, slow wind. An inner high density core is detected, with radius less than 250 AU, interpreted as a rotating gas/dust disk with a bipolar disk wind. The evaporating disk is argued to be the source of the slow wind. The central star is a source of a very fast wind (1000 km/s). An outer, partial ring is seen in the equatorial plane, expanding at 12 km/s. The azimuthal asymmetry is attributed to mass-loss modulation by an eccentric binary. M 2-29 presents a crucial point in disk evolution, where ionization causes the gas to be lost, leaving a low-mass dust disk behind.

Gesicki, K; Szyszka, C; Hajduk, M; Lagadec, E; Ramirez, L Guzman

2010-01-01T23:59:59.000Z

110

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

111

A Review of Downdrafts at the Rear of Tropical Squall Lines  

Science Conference Proceedings (OSTI)

The observational evidence for the formation of downdrafts at the rear of tropical squall lines is reviewed. Some mechanisms, which have been proposed for the formation of such downdrafts, also are reviewed. Although the mechanisms are different, ...

Walter Fernandez

1982-11-01T23:59:59.000Z

112

EVOLVING GRAVITATIONALLY UNSTABLE DISKS OVER COSMIC TIME: IMPLICATIONS FOR THICK DISK FORMATION  

Science Conference Proceedings (OSTI)

Observations of disk galaxies at z {approx} 2 have demonstrated that turbulence driven by gravitational instability can dominate the energetics of the disk. We present a one-dimensional simulation code, which we have made publicly available, that economically evolves these galaxies from z {approx} 2 to z {approx} 0 on a single CPU in a matter of minutes, tracking column density, metallicity, and velocity dispersions of gaseous and multiple stellar components. We include an H{sub 2}-regulated star formation law and the effects of stellar heating by transient spiral structure. We use this code to demonstrate a possible explanation for the existence of a thin and thick disk stellar population and the age-velocity-dispersion correlation of stars in the solar neighborhood: the high velocity dispersion of gas in disks at z {approx} 2 decreases along with the cosmological accretion rate, while at lower redshift the dynamically colder gas forms the low velocity dispersion stars of the thin disk.

Forbes, John; Krumholz, Mark [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Burkert, Andreas, E-mail: jforbes@ucolick.org, E-mail: krumholz@ucolick.org, E-mail: burkert@usm.uni-muenchen.de [University Observatory Munich (USM), Scheinerstrasse 1, 81679 Munich (Germany)

2012-07-20T23:59:59.000Z

113

Stochastic oscillations of general relativistic disks  

E-Print Network (OSTI)

We analyze the general relativistic oscillations of thin accretion disks around compact astrophysical objects interacting with the surrounding medium through non-gravitational forces. The interaction with the external medium (a thermal bath) is modeled via a friction force, and a random force, respectively. The general equations describing the stochastically perturbed disks are derived by considering the perturbations of trajectories of the test particles in equatorial orbits, assumed to move along the geodesic lines. By taking into account the presence of a viscous dissipation and of a stochastic force we show that the dynamics of the stochastically perturbed disks can be formulated in terms of a general relativistic Langevin equation. The stochastic energy transport equation is also obtained. The vertical oscillations of the disks in the Schwarzschild and Kerr geometries are considered in detail, and they are analyzed by numerically integrating the corresponding Langevin equations. The vertical displacements, velocities and luminosities of the stochastically perturbed disks are explicitly obtained for both the Schwarzschild and the Kerr cases.

Tiberiu Harko; Gabriela Mocanu

2012-01-11T23:59:59.000Z

114

Antitruncated Stellar Disks via Minor Mergers  

E-Print Network (OSTI)

We use hydrodynamic simulations of minor mergers of galaxies to investigate the nature of surface brightness excesses at large radii observed in some spiral galaxies: antitruncated stellar disks. We find that this process can produce the antitruncation via two competing effects: (1) merger-driven gas inflows that concentrate mass in the center of the primary galaxy and contract its inner density profile; and (2) angular momentum transferred outwards by the interaction, causing the outer disk to expand. In our experiments, this requires both a significant supply of gas in the primary disk, and that the encounter be prograde with moderate orbital angular momentum. The stellar surface mass density profiles of our remnants both qualitatively and quantitatively resemble the broken exponentials observed in local face--on spirals that display antitruncations. Moreover, the observed trend towards more frequent antitruncation relative to classical truncation in earlier Hubble types is consistent with a merger-driven scenario.

Joshua D. Younger; T. J. Cox; Anil C. Seth; Lars Hernquist

2007-07-30T23:59:59.000Z

115

Dynamics of Line-Driven Disk Winds in Active Galactic Nuclei II: Effects of Disk Radiation  

E-Print Network (OSTI)

We explore consequences of a radiation driven disk wind model for mass outflows from active galactic nuclei (AGN). We performed axisymmetric time-dependent hydrodynamic calculations using the same computational technique as Proga, Stone and Kallman (2000). We test the robustness of radiation launching and acceleration of the wind for relatively unfavorable conditions. In particular, we take into account the central engine radiation as a source of ionizing photons but neglect its contribution to the radiation force. Additionally, we account for the attenuation of the X-ray radiation by computing the X-ray optical depth in the radial direction assuming that only electron scattering contributes to the opacity. Our new simulations confirm the main result from our previous work: the disk atmosphere can 'shield' itself from external X-rays so that the local disk radiation can launch gas off the disk photosphere. We also find that the local disk force suffices to accelerate the disk wind to high velocities in the radial direction. This is true provided the wind does not change significantly the geometry of the disk radiation by continuum scattering and absorption processes; we discuss plausibility of this requirement. Synthetic profiles of a typical resonance ultraviolet line predicted by our models are consistent with observations of broad absorption line (BAL) QSOs.

D. Proga; T. R. Kallman

2004-08-16T23:59:59.000Z

116

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

SciTech Connect

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

117

Gravitational influences on magnetic field structure in accretion disks  

E-Print Network (OSTI)

Black holes and compact objects are often surrounded by structures known as accretion disks which consist of ionized plasma. Due to the immense forces present in the disk, interesting and complex magnetic field structures ...

Schneck, Kristiana E. (Kristiana Elizabeth)

2010-01-01T23:59:59.000Z

118

Trading capacity for performance in a disk array  

Science Conference Proceedings (OSTI)

A variety of performance-enhancing techniques, such as striping, mirroring, and rotational data replication, exist in the disk array literature. Given a fixed budget of disks, one must intelligently choose what combination of these techniques to employ. ...

Xiang Yu; Benjamin Gum; Yuqun Chen; Randolph Y. Wang; Kai Li; Arvind Krishnamurthy; Thomas E. Anderson

2000-10-01T23:59:59.000Z

119

Plant Guide to Turbine Disk Rim Inspection  

Science Conference Proceedings (OSTI)

Steam turbine disk rims are one of the most highly stressed areas of the rotor. Periodic inspection of the rims provides information on the operability of the rotor, including the identification of conditions that could result in catastrophic failure of the rotor.

2006-12-18T23:59:59.000Z

120

DUST-DRIVEN WIND FROM DISK GALAXIES  

SciTech Connect

We study gaseous outflows from disk galaxies driven by radiation pressure on dust grains. We include the effect of bulge and dark matter halo and show that the existence of such an outflow implies a maximum value of disk mass-to-light ratio. We show that the terminal wind speed is proportional to the disk rotation speed in the limit of a cold gaseous outflow, and that in general there is a contribution from the gas sound speed. Using the mean opacity of dust grains and the evolution of the luminosity of a simple stellar population, we then show that the ratio of the wind terminal speed (v{sub {infinity}}) to the galaxy rotation speed (v{sub c}) ranges between 2 and 3 for a period of {approx}10 Myr after a burst of star formation, after which it rapidly decays. This result is independent of any free parameter and depends only on the luminosity of the stellar population and the relation between disk and dark matter halo parameters. We briefly discuss the possible implications of our results.

Sharma, Mahavir; Nath, Biman B. [Raman Research Institute, Sadashiva Nagar, Bangalore 560080 (India); Shchekinov, Yuri, E-mail: mahavir@rri.res.in, E-mail: biman@rri.res.in, E-mail: yus@sfedu.ru [Department of Physics, Southern Federal University, Rostov on Don 344090 (Russian Federation)

2011-08-01T23:59:59.000Z

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121

An hydrodynamic shear instability in stratified disks  

E-Print Network (OSTI)

We discuss the possibility that astrophysical accretion disks are dynamically unstable to non-axisymmetric disturbances with characteristic scales much smaller than the vertical scale height. The instability is studied using three methods: one based on the energy integral, which allows the determination of a sufficient condition of stability, one using a WKB approach, which allows the determination of the necessary and sufficient condition for instability and a last one by numerical solution. This linear instability occurs in any inviscid stably stratified differential rotating fluid for rigid, stress-free or periodic boundary conditions, provided the angular velocity $\\Omega$ decreases outwards with radius $r$. At not too small stratification, its growth rate is a fraction of $\\Omega$. The influence of viscous dissipation and thermal diffusivity on the instability is studied numerically, with emphasis on the case when $d \\ln \\Omega / d \\ln r =-3/2$ (Keplerian case). Strong stratification and large diffusivity are found to have a stabilizing effect. The corresponding critical stratification and Reynolds number for the onset of the instability in a typical disk are derived. We propose that the spontaneous generation of these linear modes is the source of turbulence in disks, especially in weakly ionized disks.

B. Dubrulle; L. Marié; Ch. Normand; D. Richard; F. Hersant; J. -P. Zahn

2004-10-08T23:59:59.000Z

122

Protoplanetary Migration and Creation of Scattered Planetismal Disks  

E-Print Network (OSTI)

The relationship between protoplanet migration and the formation of the Kuiper Belt (planetesimal disk scattering) is examined.

Bruce D. Lindsay; Truell W. Hyde

2004-01-28T23:59:59.000Z

123

Model Spectral Energy Distributions of Circumstellar Debris Disks I. Analytic Disk Density Distributions  

E-Print Network (OSTI)

We present results of a study aimed at deriving fundamental properties of circumstellar debris disks from observed infrared to submillimeter spectral energy distributions. This investigation is motivated by increasing telescope/detector sensitivity, in particular the expected availability of the Space Infrared Telescope Facility (SIRTF) followed by the Stratospheric Observatory for Infrared Astronomy (SOFIA), which will enable detailed studies with large source samples of late stage circumstellar disk and planetary system evolution. We base our study on an analytic model of the disk density distribution and geometry, taking into account existing constraints from observations and results of theoretical investigations of debris disks. We also outline the effects of the most profound characteristics of circumstellar dust including the grain size distribution and dust chemical composition. In particular we find that an increasing iron content in silicates mainly causes an increase of the dust absorption effiency and thus increases the dust reemission continuum. Furthermore, the influence of the sp 2 /sp 3 hybridization

Sebastian Wolf; Lynne A. Hillenbr

2003-01-01T23:59:59.000Z

124

Spectral Energy Distributions of Circumstellar Debris Disks I. Analytic Disk Density Distributions  

E-Print Network (OSTI)

We present results of a study aimed at deriving fundamental properties of circumstellar debris disks from observed infrared to submillimeter spectral energy distributions. This investigation is motivated by increasing telescope/detector sensitivity, in particular the expected availability of the Space Infrared Telescope Facility (SIRTF) followed by the Stratospheric Observatory for Infrared Astronomy (SOFIA), which will enable detailed studies with large source samples of late stage circumstellar disk and planetary system evolution. We base our study on an analytic model of the disk density distribution and geometry, taking into account existing constraints from observations and results of theoretical investigations of debris disks. We also outline the effects of the most profound characteristics of circumstellar dust including the grain size distribution and dust chemical composition.

Sebastian Wolf; Lynne Hillenbrand

2003-06-23T23:59:59.000Z

125

Using Hard Disks For Digital Preservation David S. H. Rosenthal  

E-Print Network (OSTI)

Using Hard Disks For Digital Preservation David S. H. Rosenthal Stanford University Libraries the hard disk holding the copy used for access as a preser- vation medium; the cooperative damage detection system as an example of the techniques needed to use hard disks as a medium for long- term preservation

Baker, Mary G.

126

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

127

METALLICITY GRADIENTS OF THICK DISK DWARF STARS  

Science Conference Proceedings (OSTI)

We examine the metallicity distribution of the Galactic thick disk using F, G, and K dwarf stars selected from the Sloan Digital Sky Survey, Data Release 8. Using the large sample of dwarf stars with proper motions and spectroscopically determined stellar parameters, metallicity gradients in the radial direction for various heights above the Galactic plane and in the vertical direction for various radial distances from the Galaxy center have been found. In particular, we find a vertical metallicity gradient of -0.113 {+-} 0.010 (-0.125 {+-} 0.008) dex kpc{sup -1} using an isochrone (photometric) distance determination in the range 1 kpc solar neighborhood. Metallicity gradients in the thin and thick disks are important probes into possible formation scenarios for our Galaxy and a consistent picture is beginning to emerge from results using large spectroscopic surveys, such as the ones presented here.

Carrell, Kenneth; Chen Yuqin; Zhao Gang, E-mail: carrell@nao.cas.cn [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2012-12-01T23:59:59.000Z

128

Terabyte IDE RAID-5 Disk Arrays  

Science Conference Proceedings (OSTI)

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

David A. Sanders et al.

2003-09-30T23:59:59.000Z

129

A preliminary assessment of asbestos awareness and control measures in brake and clutch repair services in Knoxville and Knox County, Tennessee  

SciTech Connect

The pending OSHA standard revision proposed in 1990 to lower the asbestos Permissible Exposure Limit (PEL) and to mandate effective asbestos control measures (ACM) in brake and clutch assembly work may have a profound effect on industries involved in such operations. Health protection of workers will be improved and costs of improved control methods and training will increase. Considering these facts, this preliminary study was designed to assess the level of worker and management awareness of asbestos hazards associated with brake and clutch repair and to determine what ACM had been implemented by businesses in Knoxville and Knox County, Tennessee. The study, in a metropolitan area of approximately 336,000 people, revealed eight different categories of businesses conducting brake and clutch repair work with an estimated 363 potentially exposed employees. Results of the study suggest that managers and employees of the 80 businesses studied were in need of asbestos hazard awareness training and more adequate asbestos control measures.

Phillips, C.C. (Oak Ridge National Lab., TN (United States)); Hamilton, C.B.

1994-04-01T23:59:59.000Z

130

Direct Surface Thermodynamic Observations within the Rear-Flank Downdrafts of Nontornadic and Tornadic Supercells  

Science Conference Proceedings (OSTI)

Despite the long-surmised importance of the hook echo and rear-flank downdraft (RFD) in tornadogenesis, only a paucity of direct observations have been obtained at the surface within hook echoes and RFDs. In this paper, in situ surface ...

Paul M. Markowski; Jerry M. Straka; Erik N. Rasmussen

2002-07-01T23:59:59.000Z

131

Redfish Lake Sockeye Salmon Captive Broodstock Rearing and Research, Annual Report 2001-2002.  

DOE Green Energy (OSTI)

The National Marine Fisheries Service (NMFS) Northwest Fisheries Science Center, in cooperation with the Idaho Department of Fish and Game and the Bonneville Power Administration, has established captive broodstock programs to aid recovery of Snake River sockeye salmon (Oncorhynchus nerka) listed as endangered under the U.S. Endangered Species Act (ESA). Captive broodstock and captive rearing programs are a form of artificial propagation that are emerging as an important component of restoration efforts for ESA-listed salmon populations that are at critically low numbers. Captive broodstocks, reared in captivity for the entire life cycle, couple the salmon's high fecundity with potentially high survival in protective culture to produce large numbers of juveniles in a single generation for supplementation of natural populations. The captive broodstocks discussed in this report were intended to protect the last known remnants of sockeye salmon that return to Redfish Lake in the Sawtooth Basin of Idaho at the headwaters of the Salmon River. This report addresses NMFS activities from 1 September 2001 to 31 August 2002 on the Redfish Lake sockeye salmon captive broodstock and captive rearing program. NMFS currently has broodstocks in culture from year classes 1997, 1998, 1999, 2000, and 2001 in both the captive breeding and captive rearing programs. Offspring from these programs are being returned to Idaho to aid recovery efforts for the species.

Frost, Deborah; McAuley, W.; Maynard, Desmond

2003-04-01T23:59:59.000Z

132

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

DOE Green Energy (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

133

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

E-Print Network (OSTI)

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

K. Willacy

2007-01-16T23:59:59.000Z

134

Nucleosynthesis in the accretion disks of Type II collapsars  

E-Print Network (OSTI)

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

Indrani Banerjee; Banibrata Mukhopadhyay

2013-05-08T23:59:59.000Z

135

STAR FORMATION IN THE OUTER DISK OF SPIRAL GALAXIES  

SciTech Connect

We combine new deep and wide field of view H{alpha} imaging of a sample of eight nearby (d Almost-Equal-To 17 Mpc) spiral galaxies with new and archival H I and CO imaging to study the star formation and the star formation regulation in the outer disk. We find that, in agreement with previous studies, star formation in the outer disk has low covering fractions, and star formation is typically organized into spiral arms. The star formation in the outer disk is at extremely low levels, with typical star formation rate surface densities of {approx}10{sup -5} to 10{sup -6} M{sub Sun} yr{sup -1} kpc{sup -2}. We find that the ratio of the radial extent of detected H II regions to the radius of the H I disk is typically {approx}>85%. This implies that in order to further our understanding of the implications of extended star formation, we must further our understanding of the formation of extended H I disks. We measure the gravitational stability of the gas disk, and find that the outer gaseous disk is typically a factor of {approx}2 times more stable than the inner star-forming disk. We measure the surface density of outer disk H I arms, and find that the disk is closer to gravitational instability along these arms. Therefore, it seems that spiral arms are a necessary, but not sufficient, requirement for star formation in the outer disk. We use an estimation of the flaring of the outer gas disk to illustrate the effect of flaring on the Schmidt power-law index; we find that including flaring increases the agreement between the power-law indices of the inner and outer disks.

Barnes, Kate L.; Van Zee, Liese [Department of Astronomy, Indiana University, Bloomington, IN 47405 (United States); Cote, Stephanie [Canadian Gemini Office, Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria (Canada); Schade, David, E-mail: barneskl@astro.indiana.edu, E-mail: vanzee@astro.indiana.edu, E-mail: Stephanie.Cote@nrc-cnrc.gc.ca, E-mail: David.Schade@nrc-cnrc.gc.ca [Herzberg Institute of Astrophysics, National Research Council of Canada, Victoria (Canada)

2012-09-20T23:59:59.000Z

136

THE DISPERSAL OF PROTOPLANETARY DISKS AROUND BINARY STARS  

SciTech Connect

I present models of disk evolution around young binary stars. I show that the primary factor in determining circumbinary disk lifetimes is the rate of disk photoevaporation. I also find that photoevaporative clearing leaves a signature on the distribution of circumbinary disk lifetimes, with a sharp increase in disk lifetimes for binary separations a {approx}< 0.3-1 AU. Observations of young binary stars can therefore be used to test models of disk evolution, and I show that current data set a strong upper limit to the rate of on-going photoevaporation (<10{sup -9} M{sub Sun} yr{sup -1}). Finally I discuss the implications of these results for planet formation and suggest that circumbinary planets around close (a {approx}< 1 AU) binaries should be relatively common.

Alexander, Richard, E-mail: richard.alexander@leicester.ac.uk [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom)

2012-10-01T23:59:59.000Z

137

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 ? M = 10 M?/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 ? M = 1 M?/s produce large amounts of Nickel as well as some unusual nuclei such as 49 Ti,

R. Surman; G. C. Mclaughlin; W. R. Hix; Zn

2005-01-01T23:59:59.000Z

138

Composite polymer: Glass edge cladding for laser disks  

DOE Patents (OSTI)

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

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

1987-11-02T23:59:59.000Z

139

Captive Rearing Initiative for Salmon River Chinook Salmon, 1998-1999 Progress Report.  

DOE Green Energy (OSTI)

During 1999, the Idaho Department of Fish and Game (IDFG) continued developing techniques for the captive rearing of chinook salmon Oncorhynchus tshawytscha. Techniques under development included protocols for rearing juveniles in freshwater and saltwater hatchery environments, and fieldwork to collect brood year 1998 and 1999 juveniles and eggs and to investigate the ability of these fish to spawn naturally. Fish collected as juveniles were held for a short time at the Sawtooth Fish Hatchery and later transferred to the Eagle Fish Hatchery for rearing. Eyed-eggs were transferred immediately to the Eagle Fish Hatchery where they were disinfected and reared by family groups. When fish from either collection method reached approximately 60 mm, they were PIT tagged and reared separately by brood year and source stream. Sixteen different groups were in culture at IDFG facilities in 1999. Hatchery spawning activities of captive-reared chinook salmon produced eyed-eggs for outplanting in streamside incubation chambers in the West Fork Yankee Fork Salmon River (N=2,297) and the East Fork Salmon River (N=1,038). Additionally, a number of these eggs were maintained at the Eagle Fish Hatchery to ensure adequate brood year 1999 representation from these systems, and produced 279 and 87 juveniles from the West Fork Yankee Fork and East Fork Salmon River, respectively. Eyed-eggs were not collected from the West Fork Yankee Fork due to low adult escapement. Brood year 1998 juveniles were collected from the Lemhi River (N=191), West Fork Yankee Fork Salmon River (N=229), and East Fork Salmon River (N=185). Additionally, brood year 1999 eyed-eggs were collected from the Lemhi River (N=264) and East Fork Salmon River (N=143). Sixty-two and seven maturing adults were released into Bear Valley Creek (Lemhi River system) and the East Fork Salmon River, respectively, for spawning evaluation in 1999. Nine female carcasses from Bear Valley Creek were examined for egg retention, and of these five were spawned out, one was partially spawned, and three died before depositing eggs. However, much of the spawning related behavior observed involved female chinook salmon paired with male bull trout Salvelinus confluentus. Two female carcasses from the East Fork Salmon River were recovered and examined for egg retention. One of these had spawned and one had not.

Hassemer, Peter F.

2001-04-01T23:59:59.000Z

140

Captive Rearing Initiative for Salmon River Chinook Salmon, 1999 Progress Report.  

DOE Green Energy (OSTI)

During 1999, the Idaho Department of Fish and Game (IDFG) continued developing techniques for the captive rearing of chinook salmon Oncorhynchus tshawytscha. Techniques under development included protocols for rearing juveniles in freshwater and saltwater hatchery environments, and fieldwork to collect brood year 1998 and 1999 juveniles and eggs and to investigate the ability of these fish to spawn naturally. Fish collected as juveniles were held for a short time at the Sawtooth Fish Hatchery and later transferred to the Eagle Fish Hatchery for rearing. Eyed-eggs were transferred immediately to the Eagle Fish Hatchery where they were disinfected and reared by family groups. When fish from either collection method reached approximately 60 mm, they were PIT tagged and reared separately by brood year and source stream. Sixteen different groups were in culture at IDFG facilities in 1999. Hatchery spawning activities of captive-reared chinook salmon produced eyed-eggs for outplanting in streamside incubation chambers in the West Fork Yankee Fork Salmon River (N=2,297) and the East Fork Salmon River (N=1,038). Additionally, a number of these eggs were maintained at the Eagle Fish Hatchery to ensure adequate brood year 1999 representation from these systems, and produced 279 and 87 juveniles from the West Fork Yankee Fork and East Fork Salmon River, respectively. Eyed-eggs were not collected from the West Fork Yankee Fork due to low adult escapement. Brood year 1998 juveniles were collected from the Lemhi River (N=191), West Fork Yankee Fork Salmon River (N=229), and East Fork Salmon River (N=185). Additionally, brood year 1999 eyed-eggs were collected from the Lemhi River (N=264) and East Fork Salmon River (N=143). Sixty-two and seven maturing adults were released into Bear Valley Creek (Lemhi River system) and the East Fork Salmon River, respectively, for spawning evaluation in 1999. Nine female carcasses from Bear Valley Creek were examined for egg retention, and of these five were spawned out, one was partially spawned, and three died before depositing eggs. However, much of the spawning related behavior observed involved female chinook salmon paired with male bull trout Salvelinus confluentus. Two female carcasses from the East Fork Salmon River were recovered and examined for egg retention. One of these had spawned and one had not.

Hassemer, Peter F.

2001-04-01T23:59:59.000Z

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.


141

DISK WINDS AND THE ACCRETION–OUTFLOW CONNECTION  

E-Print Network (OSTI)

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

Arieh K Önigl; Ralph E. Pudritz

1999-01-01T23:59:59.000Z

142

Normal Modes of Black Hole Accretion Disks  

SciTech Connect

This paper studies the hydrodynamical problem of normal modes of small adiabatic oscillations of relativistic barotropic thin accretion disks around black holes (and compact weakly magnetic neutron stars). Employing WKB techniques, we obtain the eigen frequencies and eigenfunctions of the modes for different values of the mass and angular momentum of the central black hole. We discuss the properties of the various types of modes and examine the role of viscosity, as it appears to render some of the modes unstable to rapid growth.

Ortega-Rodriguez, Manuel; /Stanford U., Appl. Phys. Dept. /Costa Rica U.; Silbergleit, Alexander S.; /Stanford U., HEPL; Wagoner, Robert V.; /Stanford U., Phys. Dept.

2006-11-07T23:59:59.000Z

143

DISK CHOPPER TIME-OF-FLIGHT SPECTROMETER (DCS)  

Science Conference Proceedings (OSTI)

... almost all of the high energy neutrons and gamma-rays in the initial ... disk choppers that collectively produce clean monochromatic bursts of neutrons ...

144

Development of Gatorized MERL 76 for Gas Turbine Disk Applications  

Science Conference Proceedings (OSTI)

FOR GAS TURBINE DISK APPLICATIONS. R. H. Caless and D. F. Paulonis. Materials. Engineering. Pratt & Whitney. 400 Main Street. East Hartford,. CT 06108.

145

Abundance trends in the thin and thick disks  

E-Print Network (OSTI)

The Milky Way harbours two disks that appear distinct concerning scale-heights, kinematics, and elemental abundance patterns. Recent years have seen a surge of studies of the elemental abundance trends in the disks using high resolution spectroscopy. Here I will review and discuss the currently available data. Special focus will also be put on how we define stars to be members of either disk, and how current models of galaxy formation favour that thick disks are formed from several accreted bodies. The ability for the stellar abundance trends to test such predictions are discussed.

Sofia Feltzing

2004-11-07T23:59:59.000Z

146

PROBABILISTIC LIFE OF DA718 FOR AIRCRAFT ENGINE DISKS  

Science Conference Proceedings (OSTI)

PROBABILISTIC LIFE OF DA718 FOR AIRCRAFT ENGINE DISKS. S.DEYBER. 1. , F.ALEXANDRE. 2. , J.VAISSAUD. 2. , A.PINEAU. 2. 1. Snecma Materials ...

147

Computer disk with personal information of Department of Energy...  

NLE Websites -- All DOE Office Websites (Extended Search)

Computer disk with personal information of Department of Energy's Idaho site employees lost in transit The Department of Energy's Office of Health, Safety and Security has been...

148

P/M AF115 Dual Property Disk Process Development  

Science Conference Proceedings (OSTI)

logs. The logs were sliced to produce disks of thickness ranging from 1 inch .... properties. The data also showed a trend of higher strength and ductility with.

149

Radiation thermo-chemical models of protoplanetary disks I. Hydrostatic disk structure and inner rim  

E-Print Network (OSTI)

This paper introduces a new disk code, called ProDiMo, to calculate the thermo-chemical structure of protoplanetary disks and to interpret gas emission lines from UV to sub-mm. We combine frequency-dependent 2D dust continuum radiative transfer, kinetic gas-phase and UV photo-chemistry, ice formation, and detailed non-LTE heating & cooling balance with the consistent calculation of the hydrostatic disk structure. We include FeII and CO ro-vibrational line heating/cooling relevant for the high-density gas close to the star, and apply a modified escape probability treatment. The models are characterized by a high degree of consistency between the various physical, chemical and radiative processes, where the mutual feedbacks are solved iteratively. In application to a T Tauri disk extending from 0.5AU to 500AU, the models are featured by a puffed-up inner rim and show that the dense, shielded and cold midplane (z/r<0.1, Tg~Td) is surrounded by a layer of hot (5000K) and thin (10^7 to 10^8 cm^-3) atomic ga...

Woitke, Peter; Thi, Wing-Fai

2009-01-01T23:59:59.000Z

150

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

SciTech Connect

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

151

Beta Pictoris Debris Disk is Not a Proto-planetary Disk  

E-Print Network (OSTI)

Abstract: The debris disk around the star Beta Pictoris is not a proto-planetary disk but of the result of a collision of two or more aging stars as a result of the formation of the Proto-star Beta Pictoris. Beta Pictoris is shown to possess a large debris disk which glows in the infared. [1] It has been hypothesized that this debris disk is not evidence for the formation of new stars/exoplanets [2] but of the formation of smaller moons caused by the collision of older stars taking up new orbits around the proto-star Beta Pictoris, which is a very young star. [3] These will stabilize and become round and undifferentiated similar to the moon Callisto [4] , or the many other arrangements of moons around Saturn or Jupiter and smaller objects such as Ceres. This would also explain why they do not possess iron cores but are mostly volatiles such as water, ammonia, methane and sulfur dioxide which have a relatively low equilibrium condensation as opposed to refractory elements and molecules which have a much higher boiling point, and play a large part in the differentiation process. [5] References

Jeffrey J Wolynski

2012-01-01T23:59:59.000Z

152

ICE LINES IN CIRCUMBINARY PROTOPLANETARY DISKS  

Science Conference Proceedings (OSTI)

I examine the position of the ice line in circumbinary disks heated by steady mass accretion and stellar irradiation and compare with the critical semimajor axis, interior to which planetary orbits are unstable. There is a critical binary separation, dependent on the binary parameters and disk properties, for which binaries with separations larger than this critical value have ice lines that lie interior to the boundary of stability. For an equal-mass binary comprised of 1 M{sub Sun} components, this critical separation is Almost-Equal-To 1.04 AU, and scales weakly with mass accretion rate and Rosseland mean opacity ({proportional_to}[ M-dot {kappa}{sub R}]{sup 2/9}). Assuming a steady mass accretion rate of M-dot {approx}10{sup -8} M{sub Sun} yr{sup -1} and a Rosseland mean opacity of {kappa}{sub R} {approx} 1 cm{sup 2} g{sup -1}, I show that {approx}> 80% of all binary systems with component masses M{sub *} {approx}ice lines that lie interior to the critical semimajor axis. This suggests that rocky planets should not form in these systems, a prediction which can be tested by looking for planets around binaries with separations larger than the critical separation with Kepler (difficult) and with microlensing.

Clanton, Christian, E-mail: clanton@astronomy.ohio-state.edu [Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210 (United States)

2013-05-01T23:59:59.000Z

153

The Role of Convectively Generated Rear-Inflow Jets in the Evolution of Long-Lived Mesoconvective Systems  

Science Conference Proceedings (OSTI)

In this study, the structure of convectively generated rear-inflow jets and their role in the evolution of long-lived mesoconvective systems are investigated through an analysis of idealized three-dimensional simulations using a nonhydrostatic ...

Morris L. Weisman

1992-10-01T23:59:59.000Z

154

Photon Bubbles and the Vertical Structure of Accretion Disks  

E-Print Network (OSTI)

We consider the effects of "photon bubble" shock trains on the vertical structure of radiation pressure-dominated accretion disks. These density inhomogeneities are expected to develop spontaneously in radiation-dominated accretion disks where magnetic pressure exceeds gas pressure, even in the presence of magnetorotational instability. They increase the rate at which radiation escapes from the disk, and may allow disks to exceed the Eddington limit by a substantial factor. We first generalize the theory of photon bubbles to include the effects of finite optical depths and radiation damping. Modifications to the diffusion law at low optical depth tend to fill in the low-density regions of photon bubbles, while radiation damping inhibits the formation of photon bubbles at large radii, small accretion rates, and small heights above the equatorial plane. Accretion disks dominated by photon bubble transport may reach luminosities of 10 to >100 times the Eddington limit (L_E), depending on the mass of the central object, while remaining geometrically thin. However, photon bubble-dominated disks with alpha-viscosity are subject to the same thermal and viscous instabilities that plague standard radiation pressure-dominated disks, suggesting that they may be intrinsically unsteady. Photon bubbles can lead to a "core-halo" vertical disk structure. In super-Eddington disks the halo forms the base of a wind, which carries away substantial energy and mass, but not enough to prevent the luminosity from exceeding L_E. Photon bubble-dominated disks may have smaller color corrections than standard accretion disks of the same luminosity. They remain viable contenders for some ultraluminous X-ray sources and may play a role in the rapid growth of supermassive black holes at high redshift.

Mitchell C. Begelman

2006-02-01T23:59:59.000Z

155

Obscuring Active Galactic Nuclei with Nuclear Starburst Disks  

E-Print Network (OSTI)

We assess the potential of nuclear starburst disks to obscure the Seyfert-like AGN that dominate the hard X-ray background at z~1. Over 1200 starburst disk models, based on the theory developed by Thompson et al., are calculated for five input parameters: the black hole mass, the radial size of the starburst disk, the dust-to-gas ratio, the efficiency of angular momentum transport in the disk, and the gas fraction at the outer disk radius. We find that a large dust-to-gas ratio, a relatively small starburst disk, a significant gas mass fraction, and efficient angular momentum transport are all important to produce a starburst disk that can potentially obscure an AGN. The typical maximum star-formation rate in the disks is ~10 solar masses per year. Assuming no mass-loss due to outflows, the starburst disks feed gas onto the black hole at rates sufficient to produce hard X-ray luminosities of 10^{43}-10^{44} erg s^{-1}. The starburst disks themselves should be detectable at mid-infrared and radio wavelengths; at z=0.8, the predicted fluxes are ~1 mJy at 24microns and ~10-30 microJy at 1.4GHz. Thus, we predict a large fraction of radio/X-ray matches in future deep radio surveys. The starburst disks should be easily distinguished from AGN in future 100microns surveys by Herschel with expected fluxes of ~5 mJy. Any AGN-obscuring starbursts will be associated with hot dust, independent of AGN heating, resulting in observable signatures for separating galactic and nuclear star-formation. Finally, because of the competition between gas and star-formation, nuclear starbursts will be associated with lower-luminosity AGN. Thus, this phenomenon is a natural explanation for the observed decrease in the fraction of obscured AGN with luminosity.

D. R. Ballantyne

2008-06-17T23:59:59.000Z

156

Final Environmental Assessment - Idaho Department of Fish and Game Captive Rearing Initiative for Salmon River Chinook Salmon  

Energy.gov (U.S. Department of Energy (DOE)) Indexed Site

Idaho Department of Fish and Game Captive Rearing Initiative for Salmon River Chinook Salmon Final Environmental Assessment DOE/EA-1301 October 2000 Idaho Department of Fish and Game Captive Rearing Initiative for Salmon River Chinook Salmon Final Environmental Assessment - Need and Purpose for Action Bonneville Power Administration i Contents 1. NEED AND PURPOSE FOR ACTION ..................................................................................1 1.1. Introduction ........................................................................................................................1 1.2. Need for Action ...................................................................................................................1 1.3. Purposes (Decision Factors)...............................................................................................2

157

Captive Rearing Program for Salmon River Chinook Salmon : Project Progress Report, 2001 Annual Report.  

SciTech Connect

During 2001, the Idaho Department of Fish and Game continued to develop techniques to rear chinook salmon Oncorhynchus tshawytscha to sexual maturity in captivity and to monitor their reproductive performance under natural conditions. Eyed-eggs were hydraulically collected from redds in the East Fork Salmon River (EFSR; N = 311) and the West Fork Yankee Fork Salmon River (WFYF; N = 272) to establish brood year 2001 culture cohorts. The eyed-eggs were incubated and reared by family group at the Eagle Fish Hatchery (Eagle). Juveniles collected the previous summer were PIT and elastomer tagged and vaccinated against vibrio Vibrio spp. and bacterial kidney disease prior to the majority of them being transferred to the National Marine Fisheries Service, Manchester Marine Experimental Station for saltwater rearing through maturity. Smolt transfers included 210 individuals from the Lemhi River (LEM), 242 from the WFYF, and 178 from the EFSR. Maturing fish transfers from Manchester to Eagle included 62 individuals from the LEM, 72 from the WFYF, and 27 from the EFSR. Additional water chilling capacity was added at Eagle in 2001 to test if spawn timing could be advanced by temperature manipulations, and adults from the LEM and WFYF were divided into chilled ({approx} 9 C) and ambient ({approx} 13.5 C) water temperature groups while at Eagle. Twenty-five mature females from the LEM (11 chilled, 14 ambient) were spawned in captivity with 23 males with the same temperature history in 2001. Water temperature group was not shown to affect the spawn timing of these females, but males did mature earlier. Egg survival to the eyed stage of development averaged 37.9% and did not differ significantly between the two temperature groups. A total of 8,154 eyed-eggs from these crosses were placed in in-stream incubators by personnel from the Shoshone-Bannock Tribe. Mature adults (N = 89) were released into the WFYF to evaluate their reproductive performance. After release, fish distributed themselves throughout the study section and displayed a progression of habitat associations and behavior consistent with progressing maturation and the onset of spawning. Five of the 18 redds spawned by captive-reared parents were hydraulically sampled to assess survival to the eyed stage of development. Eyed-eggs were collected from four of these, and survival to this stage ranged from 0%-89%. Expanding these results to the remaining redds produced an estimate of 15,000 eyed-eggs being produced by captive-reared fish.

Venditti, David A.

2003-10-01T23:59:59.000Z

158

THE THERMAL STRUCTURE OF GRAVITATIONALLY DARKENED CLASSICAL Be STAR DISKS  

Science Conference Proceedings (OSTI)

The effect of gravitational darkening on models of the thermal structure of Be star disks is systematically studied for a wide range of Be star spectral types and rotation rates. Gravitational darkening causes a reduction of the stellar effective temperature toward the equator and a redirection of energy toward the poles. It is an important physical effect in these star-disk systems because the photoionizing radiation from the central B star is the main energy source for the disk. We have added gravitational darkening to the BEDISK code to produce circumstellar disk models that include both the variation in the effective temperature with latitude and the non-spherical shape of the star in the calculation of the stellar photoionizing radiation field. The effect of gravitational darkening on global measures of disk temperature is generally significant for rotation rates above 80% of critical rotation. For example, a B0V model rotating at 95% of critical has a density-averaged disk temperature Almost-Equal-To 2500 K cooler than its non-rotating counterpart. However, detailed differences in the temperature structure of disks surrounding rotating and non-rotating stars reveal a complex pattern of heating and cooling. Spherical gravitational darkening, an approximation that ignores the changing shape of the star, gives good results for disk temperatures for rotation rates less than Almost-Equal-To 80% of critical. However for the highest rotation rates, the distortion of the stellar surface caused by rotation becomes important.

McGill, M. A.; Sigut, T. A. A.; Jones, C. E. [Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7 (Canada)

2011-12-20T23:59:59.000Z

159

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

2003-07-31T23:59:59.000Z

160

Dynamic data reorganization for energy savings in disk storage systems  

Science Conference Proceedings (OSTI)

High performance computing (HPC) systems utilize parallel file systems that are striped over large number of disks to address the I/O performance requirement of data intensive applications. These large number of disks are typically configured into RAID ... Keywords: RAID system configuration, energy saving, energy-aware storage

Ekow Otoo; Doron Rotem; Shih-Chiang Tsao

2010-06-01T23:59:59.000Z

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.


161

Performance directed energy management for main memory and disks  

Science Conference Proceedings (OSTI)

Much research has been conducted on energy management for memory and disks. Most studies use control algorithms that dynamically transition devices to low power modes after they are idle for a certain threshold period of time. The control algorithms ... Keywords: Disk energy management, adaptation algorithms, control algorithms, low-power design, memory energy management, multiple-power mode device, performance guarantee

Xiaodong Li; Zhenmin Li; Yuanyuan Zhou; Sarita Adve

2005-08-01T23:59:59.000Z

162

Dual Structure Turbine Disks Via Partial Immersion Heat Treatment  

Science Conference Proceedings (OSTI)

turbine disk forging. The method is termed partial immersion treatment. It includes ... to improve gas turbine operating efficiencies generally results in increased turbine inlet .... to aid in this manual advance. (Figure lb). ... A second Astroloy disk was ..... engineer. (prime contractor) was Mr. R. M. Gasior, of Cytemp Specialty.

163

B-tries for disk-based string management  

Science Conference Proceedings (OSTI)

A wide range of applications require that large quantities of data be maintained in sort order on disk. The B-tree, and its variants, are an efficient general-purpose disk-based data structure that is almost universally used for this task. The B-trie ... Keywords: B-tree, Burst trie, Data structures, Secondary storage, Vocabulary accumulation, Word-level indexing

Nikolas Askitis; Justin Zobel

2009-01-01T23:59:59.000Z

164

RESOLVING THE CIRCUMSTELLAR DISK OF HL TAURI AT MILLIMETER WAVELENGTHS  

SciTech Connect

We present results of high-resolution imaging toward HL Tau by the Combined Array for Research in Millimeter-wave Astronomy. We have obtained {lambda} = 1.3 mm and 2.7 mm dust continua with an angular resolution down to 0.''13. Through simultaneous model fitting to the two wavelength data sets in Bayesian inference using a flared viscous accretion disk model, we estimate the physical properties of HL Tau, such as density distribution, dust opacity spectral index, disk mass, disk size, inclination angle, position angle, and disk thickness. HL Tau has a circumstellar disk mass of 0.13 M{sub sun}, a characteristic radius of 79 AU, an inclination of 40{sup 0}, and a position angle of 136{sup 0}. Although a thin disk model is preferred by our two wavelength data sets, a thick disk model is needed to explain the high mid- and far-infrared emission of the HL Tau spectral energy distribution. This could imply large dust grains settled down on the midplane with fine dust grains mixed with gas. The HL Tau disk is likely gravitationally unstable and can be fragmented between 50 and 100 AU of radius. However, we did not detect dust thermal continuum supporting the protoplanet candidate claimed by a previous study using observations of the Very Large Array at {lambda} = 1.3 cm.

Kwon, Woojin; Looney, Leslie W. [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Mundy, Lee G., E-mail: wkwon@illinois.edu [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

2011-11-01T23:59:59.000Z

165

Workload-Adaptive Management of Energy-Smart Disk Storage Systems  

E-Print Network (OSTI)

the disks are kept in standby mode until some data residingis requested. Powering up a standby disk to serve a requestto spin up a powered-off (standby) disk as compared with the

Otoo, Ekow

2010-01-01T23:59:59.000Z

166

Molecular and Stellar Disks Galaxies Lisa Young (New Mexico Tech) and Martin Bureau (Oxford)  

E-Print Network (OSTI)

Molecular and Stellar Disks Galaxies Lisa Young (New Mexico Tech) and Martin Bureau (Oxford galaxies contain molecular disks. These internal structures evolution galaxies. to place observational constraints on the formation in early galaxies studying the relationships between embedded disks, molecular

Bureau, Martin

167

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

168

FORMING AN O STAR VIA DISK ACCRETION?  

Science Conference Proceedings (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

169

DiscPOP: Power-aware buffer management for disk accesses  

Science Conference Proceedings (OSTI)

Much research has been conducted on energy efficient cache buffer management for disk based storage systems. Some of them use greedy prefetching technique to artificially increase disk idle intervals if there are a large number of known future requests. ... Keywords: greedy partition, DiscPOP, power-aware buffer management, disk accesses, disk based storage systems, greedy prefetching, I/O access pattern, application pattern, CPU-bound application, energy conservation, efficient prefetching scheme, disk power consumption, performance guarantee, disk reliability, disk characteristic based power-optimal prefetching, energy-efficient cache buffer management, disk I/O system, optimization problem, integer linear programming, divide-and-conquer based offline algorithm

Xiongzi Ge; Dan Feng; David H. C. Du

2011-07-01T23:59:59.000Z

170

STELLAR POPULATIONS AND RADIAL MIGRATIONS IN VIRGO DISK GALAXIES  

SciTech Connect

We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ({sup U}-shapes{sup )} in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third ({<=}36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks ({approx}11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail ({>=}50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely focused on field galaxies, fail to reproduce these results, thus calling for adequate hydrodynamical simulations of dense galaxy environments if we are to understand cluster disks. The current paper highlights numerous constraints for such simulations. In the Appendix, we confirm the claim by Erwin et al. that Type II breaks are absent in Virgo cluster S0s and discuss the detection of Type III breaks in such galaxies.

Roediger, Joel C.; Courteau, Stephane [Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, Ontario (Canada); Sanchez-Blazquez, Patricia [Deptartamento de Fisica Teorica, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); McDonald, Michael, E-mail: jroediger@astro.queensu.ca, E-mail: courteau@astro.queensu.ca, E-mail: p.sanchezblazquez@uam.es, E-mail: mcdonald@space.mit.edu [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology Cambridge, MA (United States)

2012-10-10T23:59:59.000Z

171

Theory of self-assembled smectic-A "crenellated disks"  

E-Print Network (OSTI)

Smectic-A monolayers self-assembled in aqueous solutions of chiral fd viruses and a polymer depletant have been shown to exhibit a variety of structures including large, flat disks and twisted ribbons. The virus particles twist near the edge of the structure in a direction determined by the chirality of the viruses. When fd viruses and their mutants of opposite chirality are mixed together in nearly equal amounts unusual structures referred to as "crenellated disks" can appear. These disks are achiral overall but the twist at the edge alternates between left- and right-handedness. To minimize the mismatch where the two regions of opposing twist meet, the "crenellated" structure exhibits cusps rising out of the plane of the monolayer. We use a phenomenological elastic theory previously applied to flat disks and twisted ribbons to analyze an analytic model proposed to describe the "crenellated" structure . When compared with flat, circular disks, we find that the model "crenellated disks" are stable or at least metastable in a wide region of the phase diagram spanned by the Gaussian curvature modulus and the edge energy modulus, with a large energy barrier separating the two structures. The director pattern and geometric parameters of the "crenellated disks" are found to be in qualitative agreement with experimental observations.

Hao Tu; Robert A. Pelcovits

2013-01-09T23:59:59.000Z

172

Spectral Energy Distributions of Passive T Tauri Disks Inclination  

E-Print Network (OSTI)

We compute spectral energy distributions (SEDs) for passive T Tauri disks viewed at arbitrary inclinations. Semi-analytic models of disks in radiative and hydrostatic equilibrium are employed. Over viewing angles for which the flared disk does not occult the central star, the SED varies negligibly with inclination. For such aspects, the SED shortward of ~80 microns is particularly insensitive to orientation, since short wavelength disk emission is dominated by superheated surface layers which are optically thin. The SED of a nearly edge-on disk is that of a class I source. The outer disk occults inner disk regions, and emission shortward of ~30 microns is dramatically extinguished. Spectral features from dust grains may appear in absorption. However, millimeter wavelength fluxes decrease by at most a factor of 2 from face-on to edge-on orientations. We present illustrative applications of our SED models. The class I source 04108+2803B is considered a T Tauri star hidden from view by an inclined circumstellar ...

Chiang, E I

1999-01-01T23:59:59.000Z

173

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

174

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

Science Conference Proceedings (OSTI)

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

Marti, O.G.; Myers, R.E.; Carpenter, J.E. [United States Department of Agriculture, Agricultural Research Service, Crop Protection and Management Research Laboratory, PO Box 748, Tifton, GA 31794 (United States); Styer, E.L. [University of Georgia, Veterinary Diagnostic and Investigational Laboratory, PO Box 1389, Tifton, GA 31794 (United States)

2007-03-15T23:59:59.000Z

175

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

SciTech Connect

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

Venditti, David A.

2002-04-01T23:59:59.000Z

176

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

177

Energy Proportionality for Disk Storage Using Replication  

Science Conference Proceedings (OSTI)

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

Kim, Jinoh; Rotem, Doron

2010-09-09T23:59:59.000Z

178

PLANET-PLANET SCATTERING IN PLANETESIMAL DISKS  

Science Conference Proceedings (OSTI)

We study the final architecture of planetary systems that evolve under the combined effects of planet-planet and planetesimal scattering. Using N-body simulations we investigate the dynamics of marginally unstable systems of gas and ice giants both in isolation and when the planets form interior to a planetesimal belt. The unstable isolated systems evolve under planet-planet scattering to yield an eccentricity distribution that matches that observed for extrasolar planets. When planetesimals are included the outcome depends upon the total mass of the planets. For M {sub tot} {approx}> 1 M{sub J} the final eccentricity distribution remains broad, whereas for M {sub tot} {approx}< 1 M{sub J} a combination of divergent orbital evolution and recircularization of scattered planets results in a preponderance of nearly circular final orbits. We also study the fate of marginally stable multiple planet systems in the presence of planetesimal disks, and find that for high planet masses the majority of such systems evolve into resonance. A significant fraction leads to resonant chains that are planetary analogs of Jupiter's Galilean satellites. We predict that a transition from eccentric to near-circular orbits will be observed once extrasolar planet surveys detect sub-Jovian mass planets at orbital radii of a {approx_equal} 5-10 AU.

Raymond, Sean N. [Center for Astrophysics and Space Astronomy, 389 UCB, University of Colorado, Boulder, CO 80309 (United States); Armitage, Philip J. [Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States); Gorelick, Noel [Google, Inc., 1600 Amphitheatre Parkway, Mountain View, CA 94043 (United States)], E-mail: sean.raymond@colorado.edu

2009-07-10T23:59:59.000Z

179

Current Production Status of Alloy 718 Turbine Disks in China  

Science Conference Proceedings (OSTI)

For the past few years the production of high quality alloy 7 18 turbine disks has made great strides ... The main technology studies which led to the production of.

180

The Microstructure Prediction of Alloy 720LI for Turbine Disk ...  

Science Conference Proceedings (OSTI)

Applications,” Supemhoys 1996, (1996), 697-703. 3. H.Hattori et al., “Evaluation of PA4 U720 for Gas Turbine. Engine Disk Application,” 2hpxalloys 1996, (1996)  ...

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181

Multiwavelength studies of accretion disks around compact objects  

E-Print Network (OSTI)

(cont.) to the XPS in SNR RCW 103. The multiple IR band measurements of 1E 1048.1-5937 provide marginal evidence for spectral flattening, and cannot rule out an accretion disk scenario for AXPs.

Wang, Zhongxiang, 1968-

2004-01-01T23:59:59.000Z

182

Controlling the collimation and rotation of hydromagnetic disk winds  

E-Print Network (OSTI)

(Abriged) We present a comprehensive set of axisymmetric, time-dependent simulations of jets from Keplerian disks whose mass loading as a function of disk radius is systematically changed. For a reasonable model for the density structure and injection speed of the underlying accretion disk, mass loading is determined by the radial structure of the disk's magnetic field structure. We vary this structure by using four different magnetic field configurations, ranging from the "potential" configuration (Ouyed&Pudritz 1997), to the increasingly more steeply falling Blandford&Payne (1982) and Pelletier&Pudritz (1992) models, and ending with a quite steeply raked configuration that bears similarities to the Shu X-wind model. We find that the radial distribution of the mass load has a profound effect on both the rotational profile of the underlying jet as well as the degree of collimation of its outflow velocity and magnetic field lines. We show analytically, and confirm by our simulations, that the colli...

Pudritz, R E; Ouyed, R; Pudritz, Ralph E.; Rogers, Conrad; Ouyed, Rachid

2006-01-01T23:59:59.000Z

183

Zooming in on quasar accretion disks using chromatic microlensing  

E-Print Network (OSTI)

Observing the temperature profiles of accretion disks around black holes is a fundamental test of an important astrophysical process. However, angular resolution limitations have prevented such a measurement for distant ...

Blackburne, Jeffrey A

2009-01-01T23:59:59.000Z

184

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

E-Print Network (OSTI)

and the functional layers ­ a magnetic coating, anti-corrosion coating, protective coating and a lubricate layer: alterable magnetic disk packages; alterable information modules "Winchester"; magnetic disk packages magnetic disk packages represent in their essence one or more single magnetic disks with a hard substrate

Borissova, Daniela

185

Captive Rearing Program for Salmon River Chinook Salmon, 2002 Annual Report.  

DOE Green Energy (OSTI)

During 2002, the Idaho Department of Fish and Game continued to develop techniques to rear Chinook salmon Oncorhynchus tshawytscha to sexual maturity in captivity and to monitor their reproductive performance under natural conditions. Eyed-eggs were hydraulically collected from redds in the East Fork Salmon River (EFSR; N = 328) and the West Fork Yankee Fork Salmon River (WFYF; N = 308) to establish brood year 2002 culture cohorts. The eyed-eggs were incubated and reared at the Eagle Fish Hatchery, Eagle, Idaho (Eagle). Juveniles collected in 2000 were PIT and elastomer tagged and vaccinated against vibrio Vibrio spp. and bacterial kidney disease prior to being transferred to the NOAA Fisheries, Manchester Marine Experimental Station, Manchester, Washington (Manchester) for saltwater rearing through maturity. Smolt transfers included 203 individuals from the WFYF and 379 from the EFSR. Maturing fish transfers from Manchester to Eagle included 107 individuals from the LEM, 167 from the WFYF, and 82 from the EFSR. This was the second year maturing adults were held on chilled water at Eagle to test if water temperature manipulations could advance spawn timing. Adults from the LEM and WFYF were divided into chilled ({approx} 9 C) and ambient ({approx} 13.5 C) temperature groups while at Eagle. Forty-seven mature females from the LEM (19 chilled, 16 ambient, and 12 ambient not included in the temperature study) were spawned at Eagle with 42 males in 2002. Water temperature group was not shown to affect the spawn timing of these females, but males did mature earlier. Egg survival to the eyed stage averaged 66.5% and did not differ significantly between the temperature groups. Personnel from the Shoshone-Bannock Tribe placed a total of 47,977 eyed-eggs from these crosses in in-stream incubators. Mature adults (N = 215 including 56 precocial males) were released into the WFYF to evaluate their reproductive performance. After release, fish distributed themselves throughout the study section and displayed a progression of habitat associations and behavior consistent with progressing maturation and the onset of spawning. Twenty-six captive-reared females constructed 33 redds in the WFYF in 2002. Eighteen of these were hydraulically sampled, and eggs were collected from 17. The percentage of live eggs ranged from 0-100% and averaged 34.6%. No live eggs were found in redds spawned by brood year 1997 females. Expanding these results to the remaining redds gives an estimate of 22,900 eyed-eggs being produced by captive-reared fish in the WFYF. Additionally, 130 mature adults (including 41 precocial males) were released into the EFSR. Almost all of these fish moved out of the areas shoreline observers had access to, so no spawning behavior was observed. Radio-telemetry indicated that most of these fish initially moved downstream (although three females moved upstream as far as 7 km) and then held position.

Venditti, David; Willard, Catherine; James, Chris

2003-11-01T23:59:59.000Z

186

Final Environmental Assessment - Idaho Department of Fish and Game Captive Rearing Initiative for Salmon River Chinook Salmon  

Energy.gov (U.S. Department of Energy (DOE)) Indexed Site

Department of Fish and Game Department of Fish and Game Captive Rearing Initiative for Salmon River Chinook Salmon Finding of No Significant Impact October 2000 DEPARTMENT OF ENERGY Bonneville Power Administration Idaho Department of Fish and Game Captive Rearing Initiative for Salmon River Chinook Salmon Finding of No Significant Impact Summary: Bonneville Power Administration (BPA), Department of Energy (DOE), is proposing to fund the Idaho Department of Fish and Game (IDFG) Captive Rearing Initiative for Salmon River Chinook Salmon Program (IDFG Program). The IDFG Program is a small-scale research and production initiative designed to increase numbers of three weak but recoverable populations of spring/summer chinook salmon in the Salmon River drainage. This would increase numbers of spring/summer chinook salmon within the Snake River

187

THE GRAVO-MAGNETO LIMIT CYCLE IN ACCRETION DISKS  

Science Conference Proceedings (OSTI)

Previous theoretical studies have found that repeating outbursts can occur in certain regions of an accretion disk due to sudden transitions in time from gravitationally produced turbulence to magnetically produced turbulence. We analyze the disk evolution in a state diagram that plots the mass accretion rate versus disk surface density. We determine steady state accretion branches that involve gravitational and magnetic sources of turbulence. Using time-dependent numerical disk simulations, we show that cases having outbursts track along a nonsteady 'dead zone' branch and some steady state accretion branches. The outburst is the result of a rapid inter-branch transition. The gravo-magneto outbursts are then explained on this diagram as a limit cycle that is analogous to the well-known S-curve that has been applied to dwarf nova outbursts. The diagram and limit cycle provide a conceptual framework for understanding the nature of the outbursts that may occur in accretion disks of all scales, from circumplanetary to protoplanetary to active galactic nucleus accretion disks.

Martin, R. G.; Lubow, S. H. [Space Telescope Science Institute, Baltimore, MD 21218 (United States)

2011-10-10T23:59:59.000Z

188

FORMATION OF ORGANIC MOLECULES AND WATER IN WARM DISK ATMOSPHERES  

Science Conference Proceedings (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

189

VERTICAL STRUCTURE OF NEUTRINO-DOMINATED ACCRETION DISKS AND NEUTRINO TRANSPORT IN THE DISKS  

SciTech Connect

We investigate the vertical structure of neutrino-dominated accretion disks by self-consistently considering the detailed microphysics, such as the neutrino transport, the 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{sup 54} erg s{sup -1} and their annihilation luminosity is about 5 Multiplication-Sign 10{sup 51} erg s{sup -1} with an extreme accretion rate 10 M{sub Sun} s{sup -1} 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{sup 50} erg s{sup -1}, which is not sufficient to power the fireball of most energetic gamma-ray bursts (GRBs) if the accretion rate is lower than 1 M{sub Sun} s{sup -1}. Therefore, the effects of the spin of the black hole or/and the magnetic field in the accretion flow might play a role in powering the central engine of GRBs.

Pan Zhen; Yuan Yefei, E-mail: yfyuan@ustc.edu.cn [Key Laboratory for Research in Galaxies and Cosmology CAS, Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2012-11-10T23:59:59.000Z

190

MAGNETOROTATIONAL-INSTABILITY-DRIVEN ACCRETION IN PROTOPLANETARY DISKS  

Science Conference Proceedings (OSTI)

Non-ideal MHD effects play an important role in the gas dynamics in protoplanetary disks (PPDs). This paper addresses the influence of non-ideal MHD effects on the magnetorotational instability (MRI) and angular momentum transport in PPDs using the most up-to-date results from numerical simulations. We perform chemistry calculations using a complex reaction network with standard prescriptions for X-ray and cosmic-ray ionizations. We first show that whether or not grains are included, the recombination time is at least one order of magnitude less than the orbital time within five disk scale heights, justifying the validity of local ionization equilibrium and strong coupling limit in PPDs. The full conductivity tensor at different disk radii and heights is evaluated, with the MRI active region determined by requiring that (1) the Ohmic Elsasser number {Lambda} be greater than 1 and (2) the ratio of gas to magnetic pressure {beta} be greater than {beta}{sub min}(Am) as identified in the recent study by Bai and Stone, where Am is the Elsasser number for ambipolar diffusion. With full flexibility as to the magnetic field strength, we provide a general framework for estimating the MRI-driven accretion rate M-dot and the magnetic field strength in the MRI active layer. We find that the MRI active layer always exists at any disk radius as long as the magnetic field in PPDs is sufficiently weak. However, the optimistically predicted M-dot in the inner disk (r = 1-10 AU) appears insufficient to account for the observed range of accretion rates in PPDs (around 10{sup -8} M{sub sun} yr{sup -1}) even in the grain-free calculation, and the presence of solar abundance sub-micron grains further reduces M-dot by one to two orders of magnitude. Moreover, we find that the predicted M-dot increases with radius in the inner disk where accretion is layered, which would lead to runaway mass accumulation if disk accretion is solely driven by the MRI. Our results suggest that stronger sources of ionization and/or additional mechanisms such as magnetized wind are needed to explain the observed accretion rates in PPDs. In contrast, our predicted M-dot is on the order of 10{sup -9} M{sub sun} yr{sup -1} in the outer disk, consistent with the observed accretion rates in transitional disks.

Bai Xuening, E-mail: xbai@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2011-09-20T23:59:59.000Z

191

Initiation and Development of Rear Inflow within the 28-29 June 1989 North Dakota Mesoconvective System  

Science Conference Proceedings (OSTI)

Five dual-Doppler analyses spanning a period of 1.5 h are used to document the initiation and development of rear inflow within a High Plains squall line. The squall line developed as part of the 28-29 June 1989 mesoconvective system that passed ...

Brian A. Klimowski

1994-05-01T23:59:59.000Z

192

Development and Forcing of the Rear Inflow Jet in a Rapidly Developing and Decaying Squall Line during BAMEX  

Science Conference Proceedings (OSTI)

This study examines the development, structure, and forcing of the rear inflow jet (RIJ) through the life cycle of a small, short-lived squall line over north-central Kansas on 29 June 2003. The analyses were developed from airborne quad-Doppler ...

Joseph A. Grim; Robert M. Rauber; Greg M. McFarquhar; Brian F. Jewett; David P. Jorgensen

2009-04-01T23:59:59.000Z

193

Disk magnetohydrodynamic power conversion system for NERVA reactor  

Science Conference Proceedings (OSTI)

The combination of a magnetohydrodynamic (MHD) generator of the disk type with a NERVA reactor yields an advanced power system particularly suited to space applications with the capability of producing up to gigawatt pulses and multi-megawatt continuous operation. Several unique features result from the combination of this type of reactor and a disk MHD generator in which hydrogen serves as the plasma working fluid. Cesium seedings is utilized under conditions which enable the generator to operate stably in the non-equilibrium electrical conduction mode. In common with all practical MHD generators, the disk output is DC and voltages in the range 20--100 kV are attainable. This leads to a simplification of the power conditioning system and a major reduction in specific mass. Taken together with the high performance capabilities of the NERVA reactor, the result is an attractively low overall system specific mass. Further, the use of non-equilibrium ionization enables system specific enthalpy extractions in excess of 40% to be attained. This paper reports the results of a study to establish the basis for the design of a cesium seeded hydrogen MHD disk generator. Generator performance results are presented in terms of a stability factor which is related to cesium seeded hydrogen plasma behavior. It is shown that application of the results already obtained with cesium seeded noble gases (argon and helium) to the case of hydrogen as the working fluid in a disk MHD generator enables a high performance power system to be defined.

Jackson, W.D. (HMJ Corporation. 10400 Connecticut Ave., Kensington, Maryland 20895 (United States)); Bernard, F.E. (Westinghouse Corp., P.O. Box 355, Pittsburgh, Pennsylvania 15230 (United States)); Holman, R.R. (HMJ Corporation, 10400 Connecticut Ave., Kensington, Maryland 20895 (United States)); Maxwell, C.D. (STD Research Corp., P.O. Box C, Arcadia, California 91006 (United States)); Seikel, G.R. (SeiTec, Inc., P.O. Box 81264, Cleveland, Ohio 44181 (United States))

1993-01-15T23:59:59.000Z

194

Gas phase water in the surface layer of protoplanetary disks  

E-Print Network (OSTI)

Recent observations of the ground state transition of HDO at 464 GHz towards the protoplanetary disk of DM Tau have detected the presence of water vapor in the regions just above the outer disk midplane (Ceccarelli et al 2005). In the absence of non-thermal desorption processes, water should be almost entirely frozen onto the grain mantles and HDO undetectable. In this Letter we present a chemical model that explores the possibility that the icy mantles are photo-desorbed by FUV (6eV water vapor above the disk midplane over the entire disk. Assuming a photo-desorption yield of 10^{-3}, the water abundance in this layer is predicted to be ~ 3 x 10^{-7} and the average H2O column density is ~ 1.6x 10^{15} cm^{-2}. The predictions are very weakly dependent on the details of the model, like the incident FUV radiation field, and the gas density in the disk. Based on this model, we predict a gaseous HDO/H2O ratio in DM Tau of ~1%. In addition, we predict the ground state transition of water at 557 GHz to be undetectable with ODIN and/or HSO-HIFI.

C. Dominik; C. Ceccarelli; D. Hollenbach; M. Kaufman

2005-10-21T23:59:59.000Z

195

The Relative Age of the Thin and Thick Galactic Disks  

E-Print Network (OSTI)

We determine the relative ages of the open cluster NGC 188 and selected Hipparcos field stars by isochrone fitting, and compare them to the age of the thick disk globular cluster 47 Tuc. The best fit age for NGC 188 was determined to be $6.5 \\pm 1.0$ Gyr. The solar metallicity Hipparcos field stars yielded a slightly older thin disk age, $7.5 \\pm 0.7$ Gyr. Two slightly metal-poor ($\\feh = -0.22$) field stars whose kinematic and orbital parameters indicate that they are members of the thin disk were found to have an age of $9.7\\pm 0.6$ Gyr. The age for 47 Tuc was determined to be $12.5 \\pm 1.5$ Gyr. All errors are internal errors due to the uncertainty in the values of metallicity and reddening. Thus, the oldest stars dated in the thin disk are found to be $2.8\\pm 1.6$ Gyr younger than 47 Tuc. Furthermore, as discussed by \\citet{Chb99} 47 Tuc has a similar age to three globular clusters located in the inner part of the Galactic halo, implying that star formation in the thin disk started within $2.8\\pm 1.6$ Gyr of star formation in the halo.

Wilson M. Liu; Brian Chaboyer

2000-07-13T23:59:59.000Z

196

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

197

FITDisk: A Cataclysmic Variable Accretion Disk Demonstration Tool  

E-Print Network (OSTI)

We present the software tool FITDisk, a precompiled-binary Windows GUI version of our smoothed particle hydrodynamics cataclysmic variable accretion disk research code. Cataclysmic variables are binary star systems in which a compact stellar remnant, typically a white dwarf star, is stripping mass from a lower-main-sequence companion star by way of an accretion disk. Typically the disk is the brightest component of the system, because the plasma is heated dramatically as it spirals down in the gravitational well of the primary white dwarf star. The shortest-period systems can display disk "superhump" oscillations driven by the rotating tidal field of the secondary star. FITDisk models these accretion disk phenomena using a fully three-dimensional hydrodynamics calculation, and data can be visualized as they are computed or stored to hard drive for later playback at a fast frame rate. Simulations are visualized using OpenGL graphics and the viewing angle can be changed interactively. Pseudo light curves of sim...

Wood, M A; Simpson, J C; Wood, Matt A.; Dolence, Josh; Simpson, James C.

2005-01-01T23:59:59.000Z

198

FITDisk: A Cataclysmic Variable Accretion Disk Demonstration Tool  

E-Print Network (OSTI)

We present the software tool FITDisk, a precompiled-binary Windows GUI version of our smoothed particle hydrodynamics cataclysmic variable accretion disk research code. Cataclysmic variables are binary star systems in which a compact stellar remnant, typically a white dwarf star, is stripping mass from a lower-main-sequence companion star by way of an accretion disk. Typically the disk is the brightest component of the system, because the plasma is heated dramatically as it spirals down in the gravitational well of the primary white dwarf star. The shortest-period systems can display disk "superhump" oscillations driven by the rotating tidal field of the secondary star. FITDisk models these accretion disk phenomena using a fully three-dimensional hydrodynamics calculation, and data can be visualized as they are computed or stored to hard drive for later playback at a fast frame rate. Simulations are visualized using OpenGL graphics and the viewing angle can be changed interactively. Pseudo light curves of simulated systems can be plotted along with the associated Fourier amplitude spectrum. FITDisk is available for free download at www.astro.fit.edu/cv/fitdisk.html.

Matt A. Wood; Josh Dolence; James C. Simpson

2005-11-11T23:59:59.000Z

199

SPH Simulations of Accretion Disks and Narrow Rings  

E-Print Network (OSTI)

We model a massless viscous disk using Smoothed Particle Hydrodynamics (SPH) and note that it evolves according to the Lynden-Bell \\& Pringle theory (1974) until a non-axisymmetric instability develops at the inner edge of the disk. This instability may have the same origin as the instability of initially axisymmetric viscous disks discussed by Lyubarskij et al. (1994). To clarify the evolution we evolved single and double rings of particles. It is actually inconsistent with the SPH scheme to set up a single ring as an initial condition because SPH assumes a smoothed initial state. As would be expected from an SPH simulation, the ring rapidly breaks up into a band. We analyse the stability of the ring and show that the predictions are confirmed by the simulation.

Sarah T. Maddison; James R. Murray; Joe J. Monaghan

1995-07-12T23:59:59.000Z

200

Disk Space Quota Management | Argonne Leadership Computing Facility  

NLE Websites -- All DOE Office Websites (Extended Search)

Account Information Accounts and Access FAQ Connect & Log In Using CRYPTOCards SSH Keys on Surveyor Disk Space Quota Management Allocations Decommissioning of BG/P Systems and Resources Blue Gene/Q Versus Blue Gene/P Mira/Cetus/Vesta Intrepid/Challenger/Surveyor Tukey Eureka / Gadzooks Policies Documentation Feedback Please provide feedback to help guide us as we continue to build documentation for our new computing resource. [Feedback Form] Disk Space Quota Management As you manage your project's disk space quota, it's important to remember that users you approve as to be added as project members are also added to the project's Unix Group. Unix Group members have the ability to write to the project directory and to access project data. You can manually add or remove Unix

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201

Disk Planet Interactions and Early Evolution in Young Planetary Systems  

E-Print Network (OSTI)

We study and review disk protoplanet interactions using local shearing box simulations. These suffer the disadvantage of having potential artefacts arising from periodic boundary conditions but the advantage, when compared to global simulations, of being able to capture much of the dynamics close to the protoplanet at high resolution for low computational cost. Cases with and without self sustained MHD turbulence are considered. The conditions for gap formation and the transition from type I migration are investigated and found to depend on whether the single parameter M_p R^3/(M_* H^3), with M_p, M_*, R and H being the protoplanet mass, the central mass, the orbital radius and the disk semi-thickness respectively exceeds a number of order unity. We also investigate the coorbital torques experienced by a moving protoplanet in an inviscid disk. This is done by demonstrating the equivalence of the problem for a moving protoplanet to one where the protoplanet is in a fixed orbit which the disk material flows through radially as a result of the action of an appropriate external torque. For sustainable coorbital torques to be realized a quasi steady state must be realized in which the planet migrates through the disk without accreting significant mass. In that case although there is sensitivity to computational parameters, in agreement with earlier work by Masset & Papaloizou (2003) based on global simulations, the coorbital torques are proportional to the migration speed and result in a positive feedback on the migration, enhancing it and potentially leading to a runaway. This could lead to a fast migration for protoplanets in the Saturn mass range in massive disks and may be relevant to the mass period correlation for extrasolar planets which gives a preponderance of sub Jovian masses at short orbital period.

J. C. B. Papaloizou

2004-12-30T23:59:59.000Z

202

THE STRUCTURE OF GRAVITATIONALLY UNSTABLE GAS-RICH DISK GALAXIES  

Science Conference Proceedings (OSTI)

We use a series of idealized, numerical smoothed particle hydrodynamics simulations to study the formation and evolution of galactic, gas-rich disks forming from gas infall within dark matter halos. The temperature and density structure of the gas is varied in order to differentiate between (1) simultaneous gas infall at a large range of radii and (2) the inside-out buildup of a disk. In all cases, the disks go through phases of ring formation, gravitational instability and break-up into massive clumps. Ring formation can be enhanced by a focal point effect. The position of the ring is determined by the angular momentum distribution of the material it forms from. We study the ring and clump morphologies, the characteristic properties of the resulting velocity dispersion field and the effect of star formation. In the early phases, gas accretion leads to a high vertical velocity dispersion. We find that the disk fragmentation by gravitational instability and the subsequent clump-clump interactions drive high velocity dispersions mainly in the plane of the disk while at the same time the vertical velocity dispersion dissipates. The result is a strong variation of the line-of-sight velocity dispersion with inclination angle. For a face-on view, clumps appear as minima in the (vertical) dispersion, whereas for a more edge-on view, they tend to correspond to maxima. There exists observational evidence of a systematic variation of the velocity dispersion with inclination angle in high-redshift disks, which could be partly explained by our simulation results. Additional energetic sources to drive velocity dispersion that are not included in our models are also expected to contribute to the observational results.

Aumer, Michael; Burkert, Andreas; Johansson, Peter H. [Universitaets-Sternwarte Muenchen, Scheinerstr. 1, D-81679 Muenchen (Germany); Genzel, Reinhard, E-mail: aumer@usm.lmu.d, E-mail: burkert@usm.lmu.d, E-mail: pjohan@usm.lmu.d, E-mail: genzel@mpe.mpg.d [UC Berkeley Department of Physics, Berkeley, CA 94720 (United States)

2010-08-20T23:59:59.000Z

203

MIGRATION OF GAS GIANT PLANETS IN GRAVITATIONALLY UNSTABLE DISKS  

Science Conference Proceedings (OSTI)

Characterization of migration in gravitationally unstable disks is necessary to understand the fate of protoplanets formed by disk instability. As part of a larger study, we are using a three-dimensional radiative hydrodynamics code to investigate how an embedded gas giant planet interacts with a gas disk that undergoes gravitational instabilities (GIs). This Letter presents results from simulations with a Jupiter-mass planet placed in orbit at 25 AU within a 0.14 M{sub sun} disk. The disk spans 5-40 AU around a 1 M{sub sun} star and is initially marginally unstable. In one simulation, the planet is inserted prior to the eruption of GIs; in another, it is inserted only after the disk has settled into a quasi-steady GI-active state, where heating by GIs roughly balances radiative cooling. When the planet is present from the beginning, its own wake stimulates growth of a particular global mode with which it strongly interacts, and the planet plunges inward 6 AU in about 10{sup 3} years. In both cases with embedded planets, there are times when the planet's radial motion is slow and varies in direction. At other times, when the planet appears to be interacting with strong spiral modes, migration both inward and outward can be relatively rapid, covering several AUs over hundreds of years. Migration in both cases appears to stall near the inner Lindblad resonance of a dominant low-order mode. Planet orbit eccentricities fluctuate rapidly between about 0.02 and 0.1 throughout the GI-active phases of the simulations.

Michael, Scott; Durisen, Richard H. [Department of Astronomy, Indiana University, Bloomington, IN 47405 (United States); Boley, Aaron C., E-mail: scamicha@indiana.edu, E-mail: durisen@astro.indiana.edu, E-mail: aaron.boley@gmail.com [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)

2011-08-20T23:59:59.000Z

204

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

205

On Why Disks Generate Magnetic Towers and Collimate Jets  

E-Print Network (OSTI)

We show that accretion disks with magnetic fields in them ought to make jets provided that their electrical conductivity prevents slippage and there is an ambient pressure in their surroundings. We study equilibria of highly wound magnetic structures. General Energy theorems demonstrate that they form tall magnetic towers whose height grows with every turn at a velocity related to the circular velocity in the accretion disk. The pinch effect amplifies the magnetic pressures toward the axis of the towers whose stability is briefly considered.

D Lynden-Bell

2002-08-21T23:59:59.000Z

206

On Why Disks Generate Magnetic Towers and Collimate Jets  

E-Print Network (OSTI)

We show that accretion disks with magnetic fields in them ought to make jets provided that their electrical conductivity prevents slippage and there is an ambient pressure in their surroundings. We study equilibria of highly wound magnetic structures. General Energy theorems demonstrate that they form tall magnetic towers whose height grows with every turn at a velocity related to the circular velocity in the accretion disk. The pinch effect amplifies the magnetic pressures toward the axis of the towers whose stability is briefly considered.

Lynden-Bell, Donald

2002-01-01T23:59:59.000Z

207

The Diskionary: A Glossary of Terms Commonly Used for Disks and Related Objects, First Edition  

E-Print Network (OSTI)

Based on a panel discussion at the meeting "New Light on Young Stars: Spitzer's View of Circumstellar Disks", we provide some definitions of common usage of terms describing disks and related objects.

Evans, Neal; Cieza, Lucas; Forbrich, Jan; Hillenbrand, Lynne; Lada, Charlie; Merín, Bruno; Strom, Steve; Watson, Dan

2009-01-01T23:59:59.000Z

208

Flow and heat transfer in gas turbine disk cavities subject to nonuniform external pressure field  

SciTech Connect

Ingestion of hot gas from the main-stream gas path into turbine disk cavities, particularly the first-stage disk cavity, has become a serious concern for the next-generation industrial gas turbines features high rotor inlet temperature. Fluid temperature in the cavities increases further due to windage generated by fluid drag at the rotating and stationary surfaces. The resulting problem of rotor disk heat-up is exacerbated by the high disk rim temperature due to adverse (relatively flat) temperature profile of the mainstream gas in the annular flow passage of the turbine. This describes an investigation into local convective heat transfer coefficient and cooling effectiveness of the rotor disk, flow field in the disk cavity, computation of the flow field and heat transfer in the disk cavity, and mainstream gas injection and rotor disk cooling effectiveness by mass transfer analogy.

Roy, R.P.; Kim, Y.W.; Tong, T.W. [Arizona State Univ., Tempe, AZ (United States). Dept. of Mechanical and Aerospace Engineering

1995-12-31T23:59:59.000Z

209

Nonlinear fibre-optic devices pumped by semiconductor disk lasers  

Science Conference Proceedings (OSTI)

Semiconductor disk lasers offer a unique combination of characteristics that are particularly attractive for pumping Raman lasers and amplifiers. The advantages of disk lasers include a low relative noise intensity (-150 dB Hz{sup -1}), scalable (on the order of several watts) output power, and nearly diffraction-limited beam quality resulting in a high ({approx}70 % - 90 %) coupling efficiency into a single-mode fibre. Using this technology, low-noise fibre Raman amplifiers operating at 1.3 {mu}m in co-propagation configuration are developed. A hybrid Raman-bismuth doped fibre amplifier is proposed to further increase the pump conversion efficiency. The possibility of fabricating mode-locked picosecond fibre lasers operating under both normal and anomalous dispersion is shown experimentally. We demonstrate the operation of 1.38-{mu}m and 1.6-{mu}m passively mode-locked Raman fibre lasers pumped by 1.29-{mu}m and 1.48-{mu}m semiconductor disk lasers and producing 1.97- and 2.7-ps pulses, respectively. Using a picosecond semiconductor disk laser amplified with an ytterbium-erbium fibre amplifier, the supercontinuum generation spanning from 1.35 {mu}m to 2 {mu}m is achieved with an average power of 3.5 W. (invited paper)

Chamorovskiy, A Yu; Okhotnikov, Oleg G [Optoelectronics Research Center, Tampere University of Technology, Tampere (Finland)

2012-11-30T23:59:59.000Z

210

ACCRETION DISKS IN TWO-DIMENSIONAL HOYLE-LYTTLETON FLOW  

SciTech Connect

We investigate the flip-flop instability observed in two-dimensional planar hydrodynamic simulations of Hoyle-Lyttleton accretion in the case of an accreting object with a radius much smaller than the nominal accretion radius, as one would expect in astrophysically relevant situations. Contrary to previous results with larger accretors, accretion from a homogenous medium onto a small accretor is characterized by a robust, quasi-Keplerian accretion disk. For gas with a ratio of specific heats of 5/3, such a disk remains locked in one direction for a uniform ambient medium. The accretion flow is more variable for gas with a ratio of specific heats of 4/3, with more dynamical interaction of the disk flow with the bow shock leading to occasional flips in the direction of rotation of the accretion disk. In both cases the accretion of angular momentum is determined by the flow pattern behind the accretion shock rather than by the parameters of the upstream flow.

Blondin, John M., E-mail: John_Blondin@ncsu.edu [Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 (United States)

2013-04-20T23:59:59.000Z

211

Optimizing disk storage to support statistical analysis operations  

Science Conference Proceedings (OSTI)

Data stored in spreadsheets and relational database tables can be viewed as "worksheets" consisting of rows and columns, with rows corresponding to records. Correspondingly, the typical practice is to store the data on disk in row major order. While ... Keywords: business intelligence tools, data mining, data warehouses, database systems, statistical tools

Allen Parrish; Susan Vrbsky; Brandon Dixon; Weigang Ni

2005-01-01T23:59:59.000Z

212

VARIABILITY OF THE INFRARED EXCESS OF EXTREME DEBRIS DISKS  

SciTech Connect

Debris disks with extremely large infrared excesses (fractional luminosities >10{sup -2}) are rare. Those with ages between 30 and 130 Myr are of interest because their evolution has progressed well beyond that of protoplanetary disks (which dissipate with a timescale of order 3 Myr), yet they represent a period when dynamical models suggest that terrestrial planet building may still be progressing through large, violent collisions that could yield large amounts of debris and large infrared excesses. For example, our Moon was formed through a violent collision of two large protoplanets during this age range. We report two disks around the solar-like stars ID8 and HD 23514 in this age range where the 24 {mu}m infrared excesses vary on timescales of a few years, even though the stars are not variable in the optical. Variations this rapid are difficult to understand if the debris is produced by collisional cascades, as it is for most debris disks. It is possible that the debris in these two systems arises in part from condensates from silicate-rich vapor produced in a series of violent collisions among relatively large bodies. If their evolution is rapid, the rate of detection of extreme excesses would indicate that major collisions may be relatively common in this age range.

Meng, Huan Y. A.; Rieke, George H. [Department of Planetary Sciences, Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States); Su, Kate Y. L.; Rujopakarn, Wiphu [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Ivanov, Valentin D. [European Southern Observatory, Ave. Alonso de Cordova 3107, Casilla 19, Santiago, 19001 (Chile); Vanzi, Leonardo [Department of Electrical Engineering and Center of Astro Engineering, Pontificia Universidad Catolica de Chile, Ave. Vicuna Mackenna 4860, Santiago (Chile)

2012-05-20T23:59:59.000Z

213

A Simple Family of Models for Eccentric Keplerian Fluid Disks  

E-Print Network (OSTI)

In order to be in a long-lived configuration, the density in a fluid disk should be constant along streamlines to prevent compressional (PdV) work from being done cyclically around every orbit. In a pure Kepler potential, flow along aligned, elliptical streamlines of constant eccentricity will satisfy this condition. For most density profiles, differential precession driven by the pressure gradient will destroy the alignment; however, in the razor-thin approximation there is a family of simple equilibria in which the precession frequency is the same at all radii. These disks may therefore be long-lived at significant eccentricities. The density can be made axisymmetric as r goes to 0, while maintaining the precession rate, by relaxing the requirement of constancy along streamlines in an arbitrarily small transition region near the center. In the limit of small eccentricity, the models can be seen as acoustically perturbed axisymmetric disks, and the precession rate is shown to agree with linear theory. The perturbation is a traveling wave similar to an ocean wave, with the fluid rising and falling epicyclically in the gravitational field of the central mass. The expected emission line profiles from the eccentric disks are shown to be strongly asymmetric in general, and, in extreme cases, prone to misinterpretation as single narrow lines with significant velocity offsets.

T. S. Statler

2001-08-06T23:59:59.000Z

214

A UNIVERSAL NEUTRAL GAS PROFILE FOR NEARBY DISK GALAXIES  

SciTech Connect

Based on sensitive CO measurements from HERACLES and H I data from THINGS, we show that the azimuthally averaged radial distribution of the neutral gas surface density ({Sigma}{sub HI}+ {Sigma}{sub H2}) in 33 nearby spiral galaxies exhibits a well-constrained universal exponential distribution beyond 0.2 Multiplication-Sign r{sub 25} (inside of which the scatter is large) with less than a factor of two scatter out to two optical radii r{sub 25}. Scaling the radius to r{sub 25} and the total gas surface density to the surface density at the transition radius, i.e., where {Sigma}{sub HI} and {Sigma}{sub H2} are equal, as well as removing galaxies that are interacting with their environment, yields a tightly constrained exponential fit with average scale length 0.61 {+-} 0.06 r{sub 25}. In this case, the scatter reduces to less than 40% across the optical disks (and remains below a factor of two at larger radii). We show that the tight exponential distribution of neutral gas implies that the total neutral gas mass of nearby disk galaxies depends primarily on the size of the stellar disk (influenced to some degree by the great variability of {Sigma}{sub H2} inside 0.2 Multiplication-Sign r{sub 25}). The derived prescription predicts the total gas mass in our sub-sample of 17 non-interacting disk galaxies to within a factor of two. Given the short timescale over which star formation depletes the H{sub 2} content of these galaxies and the large range of r{sub 25} in our sample, there appears to be some mechanism leading to these largely self-similar radial gas distributions in nearby disk galaxies.

Bigiel, F. [Institut fuer theoretische Astrophysik, Zentrum fuer Astronomie der Universitaet Heidelberg, Albert-Ueberle Str. 2, D-69120 Heidelberg (Germany); Blitz, L., E-mail: bigiel@uni-heidelberg.de [Department of Astronomy, Radio Astronomy Laboratory, University of California at Berkeley, CA 94720 (United States)

2012-09-10T23:59:59.000Z

215

GALACTIC ULTRACOMPACT X-RAY BINARIES: DISK STABILITY AND EVOLUTION  

SciTech Connect

We study the mass-transfer rates and disk stability conditions of ultracompact X-ray binaries (UCXBs) using empirical time-averaged X-ray luminosities from Paper I and compiled information from the literature. The majority of UCXBs are consistent with evolutionary tracks for white dwarf donors. Three UCXBs with orbital periods longer than 40 minutes have mass-transfer rates above 10{sup -10} M{sub Sun} yr{sup -1}, inconsistent with white dwarf donor tracks. We show that if helium star donors can retain their initial high entropy, they can explain the observed mass-transfer rates of these UCXBs. Several UCXBs show persistent luminosities apparently below the disk instability limit for irradiated He accretion disks. We point out that a predominantly C and/or O disk (as observed in the optical spectra of several) lowers the disk instability limit, explaining this disagreement. The orbital period and low time-averaged mass-transfer rate of 2S 0918-549 provide evidence that the donor star is a low-entropy C/O white dwarf, consistent with optical spectra. We combine existing information to constrain the masses of the donors in 4U 1916-053 (0.064 {+-} 0.010 M{sub Sun }) and 4U 1626-67 (<0.036 M{sub Sun} for a 1.4 M{sub Sun} neutron star). We show that 4U 1626-67 is indeed persistent, and not undergoing a transient outburst, leaving He star models as the best explanation for the donor.

Heinke, C. O.; Ivanova, N.; Engel, M. C.; Pavlovskii, K.; Sivakoff, G. R.; Gladstone, J. C. [Physics Department, University of Alberta, 4-183 CCIS, Edmonton, AB T6G 2E1 (Canada); Cartwright, T. F., E-mail: heinke@ualberta.ca [International Space University, 1 rue Jean-Dominique Cassini, 67400 Illkirch-Graffenstaden (France)

2013-05-10T23:59:59.000Z

216

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

217

Active learning based intervertebral disk classification combining shape and texture similarities  

Science Conference Proceedings (OSTI)

We consider the problem of the computer aided diagnosis on intervertebral disk degeneration in this paper, where a framework of classifying the disks into healthy and degenerated groups is proposed. First, we propose to separately model the shape and ... Keywords: Active learning, Computer aided diagnosis, Intervertebral disk degeneration, Shape, Texture

Shijie Hao; Jianguo Jiang; Yanrong Guo; Hong Li

2013-02-01T23:59:59.000Z

218

Thin superconducting disk with field-dependent critical current: Magnetization and ac susceptibilities  

E-Print Network (OSTI)

Thin superconducting disk with field-dependent critical current: Magnetization and ac of a superconducting thin disk are calculated in the critical-state model assuming a field-dependent critical current for the flux and current distributions Phys. Rev. B 60, 13 112 1999 for a disk placed in a perpendicular

Johansen, Tom Henning

219

MHV Fleet Testing - Maintenance Sheet for 2010 Smart Fortwo  

NLE Websites -- All DOE Office Websites (Extended Search)

472012 47,544 Changed oil and filter 64.33 4112012 47,840 Replaced left front tire (labor) 45.00 4122012 47,847 Replaced front brake pads, adjusted rear brake shoes...

220

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

Science Conference Proceedings (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

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

Dust distribution in disks supplied by small bodies: Is the Beta Pictoris disk a gigantic multi-cometary tail?  

E-Print Network (OSTI)

We have evaluated the spatial distribution of dust in disks supplied by colliding or evaporating bodies spread in a small belt. The gradient of the distribution of dust expelled by radiation pressure is generally steeper than the one observed around \\bp. It follows that, to generate the \\bp\\ disk distribution in such a way, one should extract relatively more small particles in the production process: thanks to radiation forces, these smaller particles have large eccentricities and thus could be seen at very large distances from their injection place. The evaporation process of comet-like bodies moving slowly inwards may yield the necessary particle size distribution. It is interesting to note that this dynamical description is able to account for the main observational properties of the \\bp\\ disk, such as the power law distribution with possibly a change in slope, the asymmetry at large distances, and the total mass, all of which have remained unexplained up to now. If confirmed, this scenario may indicate that the \\bp\\ disk could be looked on as a gigantic multi-cometary tail with its natural constituents: gas and dust.

A. Lecavelier des Etangs; A. Vidal-Madjar; R. Ferlet

1995-08-08T23:59:59.000Z

222

The Bowdle, South Dakota, Cyclic Tornadic Supercell of 22 May 2010: Surface Analysis of Rear-Flank Downdraft Evolution and Multiple Internal Surges  

Science Conference Proceedings (OSTI)

Mobile mesonet sampling in the hook echo/rear-flank downdraft (RFD) region of a tornadic supercell near Bowdle, South Dakota, provided the opportunity to examine RFD thermodynamic and kinematic attributes and evolution. Focused analysis of the ...

Bruce D. Lee; Catherine A. Finley; Christopher D. Karstens

2012-11-01T23:59:59.000Z

223

Merger Histories of Galaxy Halos and Implications for Disk Survival  

Science Conference Proceedings (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

224

Spectral Energy Distributions of T Tauri Stars With Passive Circumstellar Disks  

E-Print Network (OSTI)

We derive hydrostatic, radiative equilibrium models for passive disks surrounding T Tauri stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer re-emits directly to space about half the stellar energy it absorbs. The other half is emitted inward and regulates the interior temperature of the disk. The heated disk flares. As a consequence, it absorbs more stellar radiation, especially at large radii, than a flat disk would. The portion of the spectral energy distribution contributed by the disk is fairly flat throughout the thermal infrared. At fixed frequency, the contribution from the surface layer exceeds that from the interior by about a factor 3 and is emitted at more than an order of magnitude greater radius. Spectral features from dust grains in the superheated layer appear in emission if the disk is viewed nearly face-on.

Chiang, E I

1997-01-01T23:59:59.000Z

225

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

226

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

227

Harrison transformation of hyperelliptic solutions and charged dust disks  

E-Print Network (OSTI)

We use a Harrison transformation on solutions to the stationary axisymmetric Einstein equations to generate solutions of the Einstein-Maxwell equations. The case of hyperelliptic solutions to the Ernst equation is studied in detail. Analytic expressions for the metric and the multipole moments are obtained. As an example we consider the transformation of a family of counter-rotating dust disks. The resulting solutions can be interpreted as disks with currents and matter with a purely azimuthal pressure or as two streams of freely moving charged particles. We discuss interesting limiting cases as the extreme limit where the charge becomes identical to the mass, and the ultrarelativistic limit where the central redshift diverges.

C. Klein

2005-12-22T23:59:59.000Z

228

The Disk and Extraplanar Regions of NGC 2403  

E-Print Network (OSTI)

Wide field images obtained with WIRCam and MegaCam on the Canada-France-Hawaii Telescope are used to probe the spatial distribution of young stars in the Sc galaxy NGC 2403. Bright main sequence stars and blue supergiants are detected out to projected galactocentric distances of ~14 kpc (~7 disk scale lengths) along the major axis. The star formation rate (SFR) in the disk of NGC 2403 during the past 10 Myr has been 1 solar masses per year based on the number of bright main sequence stars. The radially-averaged number density of red supergiants (RSGs) per unit r-band surface brightness is constant throughout the disk, indicating that (1) RSGs follow the integrated r-band light, and (2) the SFR per unit mass has been constant with radius when averaged over time scales of a few tens of millions of years. The mean color of RSGs varies with galactocentric distance, suggesting that there is a metallicity gradient among recently formed stars. A comparison of the radially-averaged number density of bright main sequence stars also indicates that the SFR per unit stellar mass in NGC 2403 has been ~3 times higher than in NGC 247 during recent epochs, and this is in rough agreement with what would be predicted from the far infrared fluxes of these galaxies. Finally, the data are used to investigate the extraplanar regions of NGC 2403. A population of M giants with peak brightness M_K = -8 is detected at projected distances between 12 and 14 kpc above the disk plane, and six new globular cluster candidates are identified.

T. J. Davidge

2007-06-25T23:59:59.000Z

229

Wet-steam erosion of steam turbine disks and shafts  

SciTech Connect

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

230

Controlling the collimation and rotation of hydromagnetic disk winds  

E-Print Network (OSTI)

(Abriged) We present a comprehensive set of axisymmetric, time-dependent simulations of jets from Keplerian disks whose mass loading as a function of disk radius is systematically changed. For a reasonable model for the density structure and injection speed of the underlying accretion disk, mass loading is determined by the radial structure of the disk's magnetic field structure. We vary this structure by using four different magnetic field configurations, ranging from the "potential" configuration (Ouyed&Pudritz 1997), to the increasingly more steeply falling Blandford&Payne (1982) and Pelletier&Pudritz (1992) models, and ending with a quite steeply raked configuration that bears similarities to the Shu X-wind model. We find that the radial distribution of the mass load has a profound effect on both the rotational profile of the underlying jet as well as the degree of collimation of its outflow velocity and magnetic field lines. We show analytically, and confirm by our simulations, that the collimation of a jet depends on its radial current distribution, which in turn is prescribed by the mass load. Models with steeply descending mass loads have strong toroidal fields, and these collimate to cylinders (this includes the Ouyed-Pudritz and Blandford-Payne outflows). On the other hand, the more gradually descending mass load profiles (the PP92 and monopolar distributions) have weaker toroidal fields, and these result in wide-angle outflows with parabolic collimation. We also present detailed structural information about jets such as their radial profiles of jet density, toroidal magnetic field, and poloidal jet speed, as well as an analysis of the bulk energetics of our different simulations.

Ralph E. Pudritz; Conrad Rogers; Rachid Ouyed

2005-08-12T23:59:59.000Z

231

Elliptic and magneto-elliptic instabilities of disk vortices  

E-Print Network (OSTI)

Vortices are the fundamental units of turbulent flow. Understanding their stability properties therefore provides fundamental insights on the nature of turbulence itself. In this contribution I briefly review the phenomenological aspects of the instability of elliptic streamlines, in the hydro (elliptic instability) and hydromagnetic (magneto-elliptic instability) regimes. Vortex survival in disks is a balance between vortex destruction by these mechanisms, and vortex production by others, namely, the Rossby wave instability and the baroclinic instability.

Lyra, Wlad

2013-01-01T23:59:59.000Z

232

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 Alfvén 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

233

GALACTOSEISMOLOGY: DISCOVERY OF VERTICAL WAVES IN THE GALACTIC DISK  

Science Conference Proceedings (OSTI)

We present evidence for a Galactic North-South asymmetry in the number density and bulk velocity of solar neighborhood stars. The number density profile, which is derived from main-sequence stars in the Sloan Digital Sky Survey, shows a (North-South)/(North+South) deficit at |z| {approx_equal} 400 pc and an excess at |z| {approx} 800 pc. The bulk velocity profile, which is derived from the Sloan Extension for Galactic Understanding and Exploration, shows a gradual trend across the Galactic midplane as well as smaller-scale features. We speculate that the North-South asymmetry, which has the appearance of a wavelike perturbation, is intrinsic to the disk. We explore the physics of this phenomenon through an analysis of the linearized Boltzmann and Poisson equations and through one-dimensional simulations. The perturbation may be excited by the passage of a satellite galaxy or dark matter subhalo through the Galactic disk, in which case we are witnessing a recent disk-heating event.

Widrow, Lawrence M. [Department of Physics, Engineering Physics, and Astronomy, Queen's University, Kingston, ON K7L 3N6 (Canada); Gardner, Susan [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055 (United States); Yanny, Brian; Dodelson, Scott [Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States); Chen, Hsin-Yu [Department of Astronomy and Astrophysics, The University of Chicago, Chicago, IL 60637 (United States)

2012-05-10T23:59:59.000Z

234

Request Bridging and Interleaving: Improving the Performance of Small Synchronous Updates under Seek-Optimizing Disk Subsystems  

Science Conference Proceedings (OSTI)

Write-through caching in modern disk drives enables the protection of data in the event of power failures as well as from certain disk errors when the write-back cache does not. Host system can achieve these benefits at the price of significant performance ... Keywords: Request merging, cross-layer optimizations, disk drive, disk scheduling algorithm, trace-driven analysis

Dong In Shin; Young Jin Yu; Hyeong S. Kim; Hyeonsang Eom; Heon Young Yeom

2011-07-01T23:59:59.000Z

235

THE MISSING CAVITIES IN THE SEEDS POLARIZED SCATTERED LIGHT IMAGES OF TRANSITIONAL PROTOPLANETARY DISKS: A GENERIC DISK MODEL  

Science Conference Proceedings (OSTI)

Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 {mu}m in their spectral energy distributions, 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 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 {mu}m-sized grains, with little discontinuity in the surface density of the {mu}m-sized grains at the cavity edge. Here we present a generic disk model that can simultaneously account for the general features in IRS, SMA, and Subaru observations. Particularly, the scattered light images for this model are computed, which agree with the general trend seen in Subaru data. Decoupling between the spatial distributions of the {mu}m-sized dust and mm-sized dust inside the cavity is suggested by the model, which, if confirmed, necessitates a mechanism, such as dust filtration, for differentiating the small and big dust in the cavity clearing process. Our model also suggests an inwardly increasing gas-to-dust ratio in the inner disk, and different spatial distributions for the small dust inside and outside the cavity, echoing the predictions in grain coagulation and growth models.

Dong, R.; Rafikov, R.; Zhu, Z.; Brandt, T.; Janson, M. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Hartmann, L. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48105 (United States); Whitney, B. [Astronomy Department, University of Wisconsin-Madison, 475 N. Charter Street, Madison, WI 53706 (United States); Muto, T. [Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551 (Japan); Hashimoto, J.; Kuzuhara, M. [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Grady, C. [ExoPlanets and Stellar Astrophysics Laboratory, Code 667, Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Follette, K. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Tanii, R.; Itoh, Y. [Graduate School of Science, Kobe University, 1-1 Rokkodai, Nada-ku, Kobe 657-8501 (Japan); Thalmann, C. [Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands); Wisniewski, J. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Mayama, S. [Graduate University for Advanced Studies (SOKENDAI), Shonan International Village, Hayama-cho, Miura-gun, Kanagawa 240-0193 (Japan); Abe, L. [Laboratoire Lagrange, UMR7293, Universite de Nice-Sophia Antipolis, CNRS, Observatoire de la Cote d'Azur, 06300 Nice (France); Brandner, W. [Max Planck Institute for Astronomy, Heidelberg (Germany); Carson, J., E-mail: rdong@astro.princeton.edu [Department of Physics and Astronomy, College of Charleston, 58 Coming Street, Charleston, SC 29424 (United States); and others

2012-05-10T23:59:59.000Z

236

On the Diversity of the Taurus Transitional Disks: UX Tau A & Lk Ca 15  

E-Print Network (OSTI)

The recently recognized class of "transitional disk" systems consists of young starswith optically-thick outer disks but inner disks which are mostly devoid of small dust. Here we introduce a further class of "pre-transitional disks" with significant near-infrared excesses which indicate the presence of an optically thick inner disk separated from an optically thick outer disk; thus, the spectral energy distributions of pre-transitional disks suggest the incipient development of disk gaps rather than inner holes. In UX Tau A, our analysis of the Spitzer IRS spectrum finds that the near-infrared excess is produced by an inner optically thick disk and a gap of ~56 AU is present. The Spitzer IRS spectrum of LkCa 15 is suggestive of a gap of ~46 AU, confirming previous millimeter imaging. In addition, UX Tau A contains crystalline silicates in its disk at radii >~ 56 AU which poses a challenge to our understanding of the production of this crystalline material. In contrast, LkCa 15's silicates are amorphous and pristine. UX Tau A and LkCa 15 increase our knowledge of the diversity of dust clearing in low-mass star formation.

C. Espaillat; N. Calvet; P. D'Alessio; J. Hernandez; C. Qi; L. Hartmann; E. Furlan; D. M. Watson

2007-10-15T23:59:59.000Z

237

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

DOE Green Energy (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

238

The Opacity of Spiral Galaxy Disks: dust opacity from calibrated counts of distant galaxies  

E-Print Network (OSTI)

The opacity of foreground spiral disks can be probed from the number of distant galaxies seen through them. To calibrate this number for effects other than the dust extinction, Gonzalez et al (1998) developed the "Synthetic Field Method". A synthetic field is an extincted Hubble Deep Field added to the science field. The relation between the dimming and the number of retrieved synthetic galaxies calibrates the number found in the science field. Here I present results from counts in 32 HST/WFPC2 fields. The relation between opacity and radius, arm and disk, surface brightness and HI are presented. The opacity is found to be caused by a clumpy distribution of clouds in the disk. The brighter parts of the disk -the center and arms- are also the more opaque ones. The dust distribution in spiral disks is found to be more extended than the stellar disk. A comparison between HI column densities and opacity shows little relation between the two.

B. W. Holwerda; R. A. Gonzalez; Ronald J. Allen; P. C. van der Kruit

2005-08-11T23:59:59.000Z

239

On rapid migration and accretion within disks around supermassive black holes  

E-Print Network (OSTI)

Galactic nuclei should contain a cluster of stars and compact objects in the vicinity of the central supermassive black hole due to stellar evolution, minor mergers and gravitational dynamical friction. By analogy with protoplanetary migration, nuclear cluster objects (NCOs) can migrate in the accretion disks that power active galactic nuclei by exchanging angular momentum with disk gas. Here we show that an individual NCO undergoing runaway outward migration comparable to Type III protoplanetary migration can generate an accretion rate corresponding to Seyfert AGN or quasar luminosities. Multiple migrating NCOs in an AGN disk can dominate traditional viscous disk accretion and at large disk radii, ensemble NCO migration and accretion could provide sufficient heating to prevent the gravitational instability from consuming disk gas in star formation. The magnitude and energy of the X-ray soft excess observed at ~0.1-1keV in Seyfert AGN could be explained by a small population of ~10^{2}-10^{3} accreting stella...

McKernan, B; Lyra, W; Perets, H B; Winter, L M; Yaqoob, T

2011-01-01T23:59:59.000Z

240

Proceedings: Workshop on Corrosion of Steam Turbine Blading and Disks in the Phase Transition Zone  

Science Conference Proceedings (OSTI)

Most outage hours for steam turbines are due to corrosion of low pressure (LP) blades and disks in the phase transition zone (PTZ). EPRI's Workshop on Corrosion of Steam Turbine Blading and Disks in the PTZ critically reviewed the state of knowledge of corrosion fatigue and stress corrosion cracking of LP blade and disk materials, with particular emphasis on the influence of the local environment.

1998-12-17T23:59:59.000Z

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.


241

HUBBLE SPACE TELESCOPE OBSERVATIONS OF THE HD 202628 DEBRIS DISK  

SciTech Connect

A ring-shaped debris disk around the G2V star HD 202628 (d = 24.4 pc) was imaged in scattered light at visible wavelengths using the coronagraphic mode of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The ring is inclined by {approx}64 Degree-Sign from face-on, based on the apparent major/minor axis ratio, with the major axis aligned along P.A. = 130 Degree-Sign . It has inner and outer radii (>50% maximum surface brightness) of 139 AU and 193 AU in the northwest ansae and 161 AU and 223 AU in the southeast ({Delta}r/r Almost-Equal-To 0.4). The maximum visible radial extent is {approx}254 AU. With mean surface brightness of V Almost-Equal-To 24 mag arcsec{sup -2}, this is the faintest debris disk observed to date in reflected light. The center of the ring appears offset from the star by {approx}28 AU (deprojected). An ellipse fit to the inner edge has an eccentricity of 0.18 and a = 158 AU. This offset, along with the relatively sharp inner edge of the ring, suggests the influence of a planetary-mass companion. There is a strong similarity with the debris ring around Fomalhaut, though HD 202628 is a more mature star with an estimated age of about 2 Gyr. We also provide surface brightness limits for nine other stars in our study with strong Spitzer excesses around which no debris disks were detected in scattered light (HD 377, HD 7590, HD 38858, HD 45184, HD 73350, HD 135599, HD 145229, HD 187897, and HD 201219).

Krist, John E.; Bryden, Geoffrey [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Stapelfeldt, Karl R. [Laboratory for Exoplanets and Stellar Astrophysics, Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Plavchan, Peter [NASA Exoplanet Science Institute, California Institute of Technology, 770 S Wilson Ave., Pasadena, CA 91125 (United States)

2012-08-15T23:59:59.000Z

242

CHEMICAL EVOLUTION OF TURBULENT PROTOPLANETARY DISKS AND THE SOLAR NEBULA  

SciTech Connect

We study the influence of transport processes on the chemical evolution of DM Tau-like protoplanetary disks. Turbulent transport of gases and ices is implicitly modeled in full two dimensions (2D), using the mixing-length approximation, along with the time-dependent chemistry. We find that turbulent transport enhances abundances and column densities of many gas-phase species and ices, particularly, complex ones. The influence of turbulent mixing on disk chemistry is more pronounced in the inner, planet-forming disk region where gradients of temperature and high-energy radiation intensities are steeper than in the outer region. The molecules that are unresponsive to transport include, e.g., C{sub 2}H, C{sup +}, CH{sub 4}, CN, CO, HCN, HNC, H{sub 2}CO, OH, as well as water and ammonia ice. Their column densities computed with the laminar and 2D mixing model differ by a factor of {approx}< 2-5. Molecules whose vertical column densities in the laminar and dynamical models differ by up to two orders of magnitude include, e.g., C{sub 2}H{sub 2}, some carbon chains, CS, H{sub 2}CS, H{sub 2}O, HCO{sup +}, HCOOH, HNCO, N{sub 2}H{sup +}, NH{sub 3}, CO ice, H{sub 2}CO ice, CH{sub 3}OH ice, and electrons. Molecules whose column densities are altered by diffusion by more than two orders of magnitude include, e.g., C{sub 2}S, C{sub 3}S, C{sub 6}H{sub 6}, CO{sub 2}, O{sub 2}, SiO, SO, SO{sub 2}, long carbon chain ices, CH{sub 3}CHO ice, HCOOH ice, O{sub 2} ice, and OCN ice. We indicate several observable or potentially detectable tracers of transport processes in protoplanetary disks and the solar nebula, such as heavy hydrocarbon ices, complex organics, CO{sub 2}, O{sub 2}, SO, SO{sub 2}, C{sub 2}S, C{sub 3}S compared to CO and water ice.

Semenov, D. [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Wiebe, D., E-mail: semenov@mpia.de, E-mail: dwiebe@inasan.ru [Institute of Astronomy of the RAS, Pyatnitskaya St. 48, 119017 Moscow (Russian Federation)

2011-10-01T23:59:59.000Z

243

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

244

Depletion and harvesting thermal energy from actuator arm electronics in hard disk drives.  

E-Print Network (OSTI)

??In recent years, thermally assistive magnetic recording (TAMR) has been applied on actuator arm electronics (AE) in hard disk drive (HDD). When HDD operates, temperature… (more)

Wu, Di

2011-01-01T23:59:59.000Z

245

The Development of Direct Age 718 for Gas Turbine Engine Disk ...  

Science Conference Proceedings (OSTI)

as a commercial gas turbine aircraft engine disk material are described. Initial ... Engines (GEAE) in the production of gas turbine engine components (1).

246

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

Science Conference Proceedings (OSTI)

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

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

2012-02-01T23:59:59.000Z

247

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

E-Print Network (OSTI)

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

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

2011-05-31T23:59:59.000Z

248

GLOBAL MODELING OF RADIATIVELY DRIVEN ACCRETION OF METALS FROM COMPACT DEBRIS DISKS ONTO WHITE DWARFS  

Science Conference Proceedings (OSTI)

Recent infrared observations have revealed the presence of compact (radii {approx}rate M-dot{sub PR}{approx}10{sup 8} g s{sup -1}. Here we extend this local analysis by exploring the global evolution of the debris disk under the action of the PR drag for a variety of assumptions about the disk properties. We find that massive disks (mass {approx}> 10{sup 20} g), which are optically thick to incident stellar radiation, inevitably give rise to metal accretion at rates M-dot {approx}>0.2 M-dot{sub PR}. The magnitude of M-dot and its time evolution are determined predominantly by the initial pattern of the radial distribution of the debris (i.e., ring-like versus disk-like) but not by the total mass of the disk. The latter determines only the disk lifetime, which can be several Myr or longer. The evolution of an optically thick disk generically results in the development of a sharp outer edge of the disk. We also find that the low-mass ({approx}< 10{sup 20} g), optically thin disks exhibit M-dot << M-dot{sub PR} and evolve on a characteristic timescale {approx}10{sup 5}-10{sup 6} yr, independent of their total mass.

Bochkarev, Konstantin V. [Department of General and Applied Physics, Moscow Institute of Physics and Technology, Dolgoprudny, 141700 (Russian Federation); Rafikov, Roman R., E-mail: bochkarevkv@gmail.com, E-mail: rrr@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08540 (United States)

2011-11-01T23:59:59.000Z

249

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

E-Print Network (OSTI)

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

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

2004-12-14T23:59:59.000Z

250

Is There a Fundamental Line for Disk Galaxies?  

E-Print Network (OSTI)

We show that there are strong local correlations between metallicity, surface brightness, and dynamical mass-to-light ratio within M33, analogous to the fundamental line of dwarf galaxies identified by Prada & Burkert (2002). Using near-infrared imaging from 2MASS, the published rotation curve of M33, and literature measurements of the metallicities of HII regions and supergiant stars, we demonstrate that these correlations hold for points at radial distances between 140 pc and 6.2 kpc from the center of the galaxy. At a given metallicity or surface brightness, M33 has a mass-to-light ratio approximately four times as large as the Local Group dwarf galaxies; other than this constant offset, we see broad agreement between the M33 and dwarf galaxy data. We use analytical arguments to show that at least two of the three fundamental line correlations are basic properties of disk galaxies that can be derived from very general assumptions. We investigate the effect of supernova feedback on the fundamental line with numerical models and conclude that while feedback clearly controls the scatter in the fundamental line, it is not needed to create the fundamental line itself, in agreement with our analytical calculations. We also compare the M33 data with measurements of a simulated disk galaxy, finding that the simulation reproduces the trends in the data correctly and matches the fundamental line, although the metallicity of the simulated galaxy is too high, and the surface brightness is lower than that of M33.

Joshua D. Simon; Francisco Prada; Jose M. Vilchez; Leo Blitz; Brant Robertson

2006-06-22T23:59:59.000Z

251

Water in Protoplanetary Disks: Deuteration and Turbulent Mixing  

E-Print Network (OSTI)

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

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

2013-01-01T23:59:59.000Z

252

GLOBAL DRAG-INDUCED INSTABILITIES IN PROTOPLANETARY DISKS  

SciTech Connect

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

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

2013-07-20T23:59:59.000Z

253

Why Buckling Stellar Bars Weaken in Disk Galaxies  

E-Print Network (OSTI)

Young stellar bars in disk galaxies experience a vertical buckling instability which terminates their growth and thickens them, resulting in a characteristic peanut/boxy shape when viewed edge on. Using N-body simulations of galactic disks embedded in live halos, we have analyzed the bar structure throughout this instability and found that the outer third of the bar dissolves completely while the inner part (within the vertical inner Lindblad resonance) becomes less oval. The bar acquires the frequently observed peanut/boxy-shaped isophotes. We also find that the bar buckling is responsible for a mass injection above the plane, which is subsequently trapped by specific 3-D families of periodic orbits of particular shapes explaining the observed isophotes, in line with previous work. Using a 3-D orbit analysis and surfaces of sections, we infer that the outer part of the bar is dissolved by a rapidly widening stochastic region around its corotation radius -- a process related to the bar growth. This leads to a...

Martinez-Valpuesta, I

2004-01-01T23:59:59.000Z

254

THE FREQUENCY OF DEBRIS DISKS AT WHITE DWARFS  

SciTech Connect

We present near- and mid-infrared photometry and spectroscopy from PAIRITEL, IRTF, and Spitzer of a metallicity-unbiased sample of 117 cool, hydrogen-atmosphere white dwarfs (WDs) from the Palomar-Green survey and find five with excess radiation in the infrared, translating to a 4.3{sup +2.7} {sub -1.2}% frequency of debris disks. This is slightly higher than, but consistent with the results of previous surveys. Using an initial-final mass relation, we apply this result to the progenitor stars of our sample and conclude that 1-7 M {sub Sun} stars have at least a 4.3% chance of hosting planets; an indirect probe of the intermediate-mass regime eluding conventional exoplanetary detection methods. Alternatively, we interpret this result as a limit on accretion timescales as a fraction of WD cooling ages; WDs accrete debris from several generations of disks for {approx}10 Myr. The average total mass accreted by these stars ranges from that of 200 km asteroids to Ceres-sized objects, indicating that WDs accrete moons and dwarf planets as well as solar system asteroid analogs.

Barber, Sara D.; Patterson, Adam J.; Kilic, Mukremin [Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W. Brooks St., Norman, OK 73019 (United States); Leggett, S. K. [Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720 (United States); Dufour, P. [Departement de Physique, Universite de Montreal, C.P. 6128, Succursale Centre-Ville, Montreal, Quebec H3C 3J7 (Canada); Bloom, J. S.; Starr, D. L., E-mail: barber@nhn.ou.edu [Department of Astronomy, University of California, Berkeley, CA 94720 (United States)

2012-11-20T23:59:59.000Z

255

Accretion disks around black holes in modified strong gravity  

E-Print Network (OSTI)

Stellar-mass black holes offer what is perhaps the best scenario to test theories of gravity in the strong-field regime. In particular, f(R) theories, which have been widely discuss in a cosmological context, can be constrained through realistic astrophysical models of phenomena around black holes. We aim at building radiative models of thin accretion disks for both Schwarzschild and Kerr black holes in f(R) gravity. We study particle motion in f(R)-Schwarzschild and Kerr space-times. We present the spectral energy distribution of the accretion disk around constant Ricci scalar f(R) black holes, and constrain specific f(R) prescriptions using features of these systems. A precise determination of both the spin and accretion rate onto black holes along with X-ray observations of their thermal spectrum might allow to identify deviations of gravity from General Relativity. We use recent data on the high-mass X-ray binary Cygnus X-1 to restrict the values of the parameters of a class of f(R) models.

Daniela Pérez; Gustavo E. Romero; Santiago E. Perez Bergliaffa

2012-12-11T23:59:59.000Z

256

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

SciTech Connect

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

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

2013-04-01T23:59:59.000Z

257

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

258

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

2006-04-19T23:59:59.000Z

259

THE STRUCTURE OF A SELF-GRAVITATING PROTOPLANETARY DISK AND ITS IMPLICATIONS FOR DIRECT IMAGING OBSERVATIONS  

SciTech Connect

We consider the effects of self-gravity on the hydrostatic balance in the vertical direction of a gaseous disk and discuss the possible signature of the self-gravity that may be captured by direct imaging observations of protoplanetary disks in the future. In this paper, we consider a vertically isothermal disk in order to isolate the effects of self-gravity. The specific disk model we consider in this paper is the one with a radial surface density gap, at which the Toomre's Q-parameter of the disk varies rapidly in the radial direction. We calculate the vertical structure of the disk including the effects of self-gravity. We then calculate the scattered light and the dust thermal emission. We find that if the disk is massive enough and the effects of self-gravity come into play, a weak bump-like structure at the gap edge appears in the near-infrared (NIR) scattered light, while no such bump-like structure is seen in the submillimeter (sub-mm) dust continuum image. The appearance of the bump is caused by the variation of the height of the surface in the NIR wavelength. If such a bump-like feature is detected in future direct imaging observations, combined with sub-mm observations, it will give us useful information about the physical states of the disk.

Muto, Takayuki, E-mail: muto@geo.titech.ac.jp [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Oh-okayama, Meguro-ku, Tokyo 152-8551 (Japan)

2011-09-20T23:59:59.000Z

260

Stress and Fracture Analysis of Shrunk-On Steam Turbine Disks  

Science Conference Proceedings (OSTI)

Utilities spend millions of dollars each year to repair or replace cracked shrunk-on disks in low-pressure steam turbines. One reason for cracking, this project concludes, is that stress approaches the yield strength of disks in many current turbine designs.

1984-01-01T23:59:59.000Z

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261

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

262

PLANET-DISK INTERACTION IN THREE DIMENSIONS: THE IMPORTANCE OF BUOYANCY WAVES  

SciTech Connect

We carry out local three-dimensional (3D) hydrodynamic simulations of planet-disk interaction in stratified disks with varied thermodynamic properties. We find that whenever the Brunt-Vaeisaelae frequency (N) in the disk is non-zero, the planet exerts a strong torque on the disk in the vicinity of the planet, with a reduction in the traditional 'torque cutoff'. In particular, this is true for adiabatic perturbations in disks with isothermal density structure, as should be typical for centrally irradiated protoplanetary disks. We identify this torque with buoyancy waves, which are excited (when N is non-zero) close to the planet, within one disk scale height from its orbit. These waves give rise to density perturbations with a characteristic 3D spatial pattern which is in close agreement with the linear dispersion relation. The torque due to these waves can amount to as much as several tens of percent of the total planetary torque, which is not expected based on analytical calculations limited to axisymmetric or low-m modes. Buoyancy waves should be ubiquitous around planets in the inner, dense regions of protoplanetary disks, where they might possibly affect planet migration.

Zhu Zhaohuan; Stone, James M.; Rafikov, Roman R., E-mail: zhzhu@astro.princeton.edu, E-mail: jstone@astro.princeton.edu, E-mail: rrr@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

2012-10-20T23:59:59.000Z

263

Brief paper: Multi-frequency disturbance rejection via blending control technique for hard disk drives  

Science Conference Proceedings (OSTI)

This paper is concerned with the rejection of multiple narrowband disturbances in hard disk drives (HDDs). Inspired by a control blending idea, the multi-frequency disturbance rejection is formulated as a blending control problem. Each disturbance rejection ... Keywords: Blending control, H2 control, Hard disk drives, Servo control, Vibration rejection

Chunling Du; Lihua Xie; F. L. Lewis; Youyi Wang

2009-10-01T23:59:59.000Z

264

A Wind Tunnel Investigation on the Riming of Snowflakes. Part I: Porous Disks and Large Stellars  

Science Conference Proceedings (OSTI)

The effects of porosity on the accretional growth characteristics of ice crystal aggregates (snowflakes) are investigated by riming circular disks of ice in a cloud tunnel. Twelve disk models were used, sized 5 to 6 mm and 10 to 11 mm in diameter,...

Jeffrey K. Lew; Derek C. Montague; Hans R. Pruppacher; Roy M. Rasmussen

1986-11-01T23:59:59.000Z

265

RAID0.5: design and implementation of a low cost disk array data protection method  

Science Conference Proceedings (OSTI)

RAID has long been established as an effective way to provide highly reliable as well as high-performance disk subsystems. However, reliability in RAID systems comes at the cost of extra disks. In this paper, we describe a mechanism that we have termed ... Keywords: Availability, RAID, Reliability, Storage

John A. Chandy

2008-11-01T23:59:59.000Z

266

INNER EDGES OF COMPACT DEBRIS DISKS AROUND METAL-RICH WHITE DWARFS  

SciTech Connect

A number of metal-rich white dwarfs (WDs) are known to host compact, dense particle disks, which are thought to be responsible for metal pollution of these stars. In many such systems, the inner radii of disks inferred from their spectra are so close to the WD that particles directly exposed to starlight must be heated above 1500 K and are expected to be unstable against sublimation. To reconcile this expectation with observations, we explore particle sublimation in H-poor debris disks around WDs. We show that because of the high metal vapor pressure the characteristic sublimation temperature in these disks is 300-400 K higher than in their protoplanetary analogs, allowing particles to survive at higher temperatures. We then look at the structure of the inner edges of debris disks and show that they should generically feature superheated inner rims directly exposed to starlight with temperatures reaching 2500-3500 K. Particles migrating through the rim toward the WD (and rapidly sublimating) shield the disk behind them from strong stellar heating, making the survival of solids possible close to the WD. Our model agrees well with observations of WD+disk systems provided that disk particles are composed of Si-rich material such as olivine, and have sizes in the range {approx}0.03-30 cm.

Rafikov, Roman R.; Garmilla, Jose A., E-mail: rrr@astro.princeton.edu, E-mail: garmilla@astro.princeton.edu [Department of Astrophysical Sciences, Princeton University, Ivy Lane, Princeton, NJ 08540 (United States)

2012-12-01T23:59:59.000Z

267

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

Science Conference Proceedings (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

268

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

E-Print Network (OSTI)

The effects of unilateral eyestalk ablation, diets and sex ratios were evaluated on two wild populations of Farfantepenaeus aztecus in a closed recirculating maturation system. Ovarian development and spawning frequencies of ablated females in both studies were higher than the non-ablated females. Replacement of bloodworms in maturation diet with enriched adult Artemia sp. had no negative effect on the number of eggs spawned and resulted in increased hatch and survival rates from Nauplius I to Zoea I. Life span of ablated females fed enriched Artemia sp. was longer than ablated females fed bloodworms. Replacement of the expensive bloodworm diet component with adult enriched Artemia sp. is possible without negative impact on female reproductive performance. Reducing male to female ratio from 2:1 to 1:1 resulted in a 1.25% decrease in spawning activities of ablated females. The life cycle of pond-raised F1 generation F. aztecus also was completed in the closed recirculating system using unilateral eyestalk ablation as previously described. This study found diets that contained an enriched adult Artemia sp. component performed superior (i.e. hatch rate, nauplii and zoea production) to a diet containing bloodworms. Six consecutive larval rearing trials evaluated changes in select water quality indicators and their effect on growth, survival, and stress tolerance of F. aztecus postlarvae cultured in artificial seawater under closed recirculating and flow-through conditions. The closed recirculating larval rearing system successfully produced five-day-old postlarvae (PL) from Zoea I (Z1) with similar dry weights, lengths and stress resistance to PL produced under standard water exchange practices. The trickling biofilters were found to be a limiting component of this system. A submerged coral biofilter was added to the system and effectively processed culture water for re-use. Addition of the submerged biofilter resulted in improved survival rates in Trials 4, 5 and 6. These studies demonstrate maturation and larval rearing of F. aztecus is feasible in closed recirculating systems. Implementation of these systems in hatcheries bolsters biosecurity while reducing the environmental impact of hatchery effluent. Recirculating and re-use systems are therefore essential in the further development of sustainable hatchery programs for endemic species.

Gandy, Ryan Leighton

2004-12-01T23:59:59.000Z

269

3D Radiative Hydrodynamics for Disk Stability Simulations: A Proposed Testing Standard and New Results  

E-Print Network (OSTI)

Recent three-dimensional radiative hydrodynamics simulations of protoplanetary disks report disparate disk behaviors, and these differences involve the importance of convection to disk cooling, the dependence of disk cooling on metallicity, and the stability of disks against fragmentation and clump formation. To guarantee trustworthy results, a radiative physics algorithm must demonstrate the capability to handle both the high and low optical depth regimes. We develop a test suite that can be used to demonstrate an algorithm's ability to relax to known analytic flux and temperature distributions, to follow a contracting slab, and to inhibit or permit convection appropriately. We then show that the radiative algorithm employed by Meji\\'a (2004) and Boley et al. (2006) and the algorithm employed by Cai et al. (2006) and Cai et al. (2007, in prep.) pass these tests with reasonable accuracy. In addition, we discuss a new algorithm that couples flux-limited diffusion with vertical rays, we apply the test suite, an...

Boley, Aaron C; Nordlund, Aake; Lord, Jesse

2007-01-01T23:59:59.000Z

270

Accretion Disks Around Binary Black Holes: A Simple GR-Hybrid Evolution Model  

E-Print Network (OSTI)

We consider a geometrically thin, Keplerian disk in the orbital plane of a binary black hole (BHBH) consisting of a spinning primary and low-mass secondary (mass ratio q important prior to binary-disk decoupling, when the orbital separation is large and resides in the weak-field regime. The tidal torque on the disk diminishes during late merger and vanishes altogether following merger. By contrast, the viscous torque drives the flow into the strong-field region and onto the primary during all epochs. Following binary coalescence, the viscous torque alone governs the time-dependent accretion onto the remnant, as well as the temporal behavior, strength and spectrum of the aftermath electromagnetic radiation from the disk. We solve our GR-hybrid equation for a representative BHBH-disk system, identify several observable EM signatures of the merger, and compare results obtained for the gas and EM radiation with those found with the Newtonian prescription.

Stuart L. Shapiro

2013-04-22T23:59:59.000Z

271

Transport coefficients for dense hard-disk systems  

E-Print Network (OSTI)

A study of the transport coefficients of a system of elastic hard disks, based on the use of Helfand-Einstein expressions is reported. The self-diffusion, the viscosity, and the heat conductivity are examined with averaging techniques especially appropriate for the use in event-driven molecular dynamics algorithms with periodic boundary conditions. The density and size dependence of the results is analyzed, and comparison with the predictions from Enskog's theory is carried out. In particular, the behavior of the transport coefficients in the vicinity of the fluid-solid transition is investigated and a striking power law divergence of the viscosity in this region is obtained, while all other examined transport coefficients show a drop in that density range.

Ramón García-Rojo; Stefan Luding; J. Javier Brey

2005-11-28T23:59:59.000Z

272

Identification of the Spawning, Rearing, and Migratory Requirements of Fall Chinook Salmon in the Columbia River Basin, Annual Report 1993.  

DOE Green Energy (OSTI)

Recovery efforts for the endangered fall chinook salmon necessitates knowledge of the factors limiting the various life history stages. This study attempts to identify those physical and biological factors which affect spawning of the fish in the free-flowing Snake River and their rearing seward migration through Columbia River basin reservoirs. The spawning was generally a November event in 1993, with some activity in late Oct. and early Dec. Spawning habitat availability was assessed by applying hydraulic and habitat models to known fall chinook salmon spawning sites. Juveniles were seined and PIT tagged in the free-flowing Snake River, and in the Columbia River in he Hanford Reach and in McNary Reservoir. Subyearling fish were marked at McNary Dam to relate river flow and migration patterns of juveniles to adult returns. Hydroacoustic surveys were conducted on McNary and John Day reservoirs and in net pens.

Rondorf, Dennis W.; Tiffan, Kenneth F.

1994-12-01T23:59:59.000Z

273

Why Buckling Stellar Bars Weaken in Disk Galaxies  

E-Print Network (OSTI)

Young stellar bars in disk galaxies experience a vertical buckling instability which terminates their growth and thickens them, resulting in a characteristic peanut/boxy shape when viewed edge on. Using N-body simulations of galactic disks embedded in live halos, we have analyzed the bar structure throughout this instability and found that the outer third of the bar dissolves completely while the inner part (within the vertical inner Lindblad resonance) becomes less oval. The bar acquires the frequently observed peanut/boxy-shaped isophotes. We also find that the bar buckling is responsible for a mass injection above the plane, which is subsequently trapped by specific 3-D families of periodic orbits of particular shapes explaining the observed isophotes, in line with previous work. Using a 3-D orbit analysis and surfaces of sections, we infer that the outer part of the bar is dissolved by a rapidly widening stochastic region around its corotation radius -- a process related to the bar growth. This leads to a dramatic decrease in the bar size, decrease in the overall bar strength and a mild increase in its pattern speed, but is not expected to lead to a complete bar dissolution. The buckling instability appears primarily responsible for shortening the secular diffusion timescale to a dynamical one when building the boxy isophotes. The sufficiently long timescale of described evolution, ~1 Gyr, can affect the observed bar fraction in local universe and at higher redshifts, both through reduced bar strength and the absence of dust offset lanes in the bar.

Inma Martinez-Valpuesta; Isaac Shlosman

2004-08-13T23:59:59.000Z

274

Redeployment as an alternative to decommissioning. Conversion of a US Department of Energy facility to fish rearing  

Science Conference Proceedings (OSTI)

The Hanford Site and the Tri-Cities community have before them an unprecedented opportunity to create an economic renaissance based on the unparalleled environmental cleanup mission. The nation and the world await the emergence of the post-Cold War economy and conversion of the national defense complex into new national economic thrusts. The legacy of the Hanford Site national defense mission must not end up simply with the Site being cleaned up and land being restored to near-original conditions. There also needs to be a future economic legacy of a dynamic Tri-Cities community resulting from the cumulative current activities that will have a positive impact for years to come. In anticipation of the eventual completion of the Hanford Site cleanup mission, the US Department of Energy (DOE) has established the Office of Economic Transition to identify and implement policies and actions that will support the cleanup mission of the Site and the long-term economic development of the Tri-Cities area. In the future, it is envisioned that one phase of a vibrant regional economy with a diversified economic job base will be the capability to compete in national and international environmental services markets. Recently, it was realized that the K Area water treatments facilities might be suitable for the rearing of fish. A `marketing` effort was undertaken to match the facility with potential users. At this time, four fish-rearing projects have either been conducted or are in various stages of progress or implementation. These will be described to explain the participants, the purposes, and the scope of each project.

Anderson, B.N.; Herborn, D.I.

1994-03-01T23:59:59.000Z

275

Numerical Simulation of an Intense Squall Line during 10–11 June 1985 PRE-STORM. Part II: Rear Inflow, Surface Pressure Perturbations and Stratiform Precipitation  

Science Conference Proceedings (OSTI)

An intense rear-inflow jet, surface pressure perturbations, and stratiform precipitation associated with a squall line during 10–11 June 1985 are examined using a three-dimensional mesoscale nested-grid model. It is found that the large-scale ...

Da-Lin Zhang; Kun Gao

1989-09-01T23:59:59.000Z

276

G-SCAN: a novel real-time disk scheduling using grouping and branch-and-bound strategy  

Science Conference Proceedings (OSTI)

For mixed-media workload, disk scheduling strategies have to guarantee the QoS (Quality of Service) of requests with timing constraints while optimizing the disk utilization. In this paper, we present a novel real-time disk scheduling algorithm which ...

Taeseok Kim; Eungkyu Song; Yunji Koh; Youjip Won; Kern Koh

2006-05-01T23:59:59.000Z

277

Spiral Disk Opacity from Occulting Galaxy Pairs in the Sloan Digital Sky Survey  

E-Print Network (OSTI)

A spiral galaxy partially ovelapping a more distant elliptical offers an unique opportunity to measure the dust extinction in the foreground spiral. From the Sloan Digital Sky Survey DR4 spectroscopic sample, we selected 83 occulting galaxy pairs and measured disk opacity over the redshift range z = 0.0-0.2 with the goal to determine the recent evolution of disk dust opacity. The enrichment of the ISM changes over the lifetime of a disk and it is reasonable to expect the dust extinction properties of spiral disks as a whole to change over their lifetime. When they do, the change will affect our measurements of galaxies over the observable universe. From the SDSS pairs we conclude that spiral disks show evidence of extinction to ~2 effective radii. However, no evidence for recent evolution of disk opacity is evident, due to the limited redshift range and our inability to distinguish other factors on disk opacity such as the presence of spiral arms and Hubble type. Such effects also mask any relation between su...

Holwerda, B W; Bolton, A

2007-01-01T23:59:59.000Z

278

Spiral Disk Opacity from Occulting Galaxy Pairs in the Sloan Digital Sky Survey  

E-Print Network (OSTI)

A spiral galaxy partially ovelapping a more distant elliptical offers an unique opportunity to measure the dust extinction in the foreground spiral. From the Sloan Digital Sky Survey DR4 spectroscopic sample, we selected 83 occulting galaxy pairs and measured disk opacity over the redshift range z = 0.0-0.2 with the goal to determine the recent evolution of disk dust opacity. The enrichment of the ISM changes over the lifetime of a disk and it is reasonable to expect the dust extinction properties of spiral disks as a whole to change over their lifetime. When they do, the change will affect our measurements of galaxies over the observable universe. From the SDSS pairs we conclude that spiral disks show evidence of extinction to ~2 effective radii. However, no evidence for recent evolution of disk opacity is evident, due to the limited redshift range and our inability to distinguish other factors on disk opacity such as the presence of spiral arms and Hubble type. Such effects also mask any relation between surface brightness and optical depth that has been found in nearby galaxies. Hence, we conclude that the SDSS spectral catalog is an excellent way to find occulting pairs and construct a uniform local sample. However, higher resolution than the SDSS images is needed to disentangle the effects of spiral arms and Hubble type from evolution since z = 0.2.

B. W. Holwerda; W. C. Keel; A. Bolton

2007-08-08T23:59:59.000Z

279

Analysis of Trade-Off Between Power Saving and Response Time in Disk Storage Systems  

Science Conference Proceedings (OSTI)

It is anticipated that in the near future disk storage systems will surpass application servers and will become the primary consumer of power in the data centers. Shutting down of inactive disks is one of the more widespread solutions to save power consumption of disk systems. This solution involves spinning down or completely shutting off disks that exhibit long periods of inactivity and placing them in standby mode. A file request from a disk in standby mode will incur an I/O cost penalty as it takes time to spin up the disk before it can serve the file. In this paper, we address the problem of designing and implementing file allocation strategies on disk storage that save energy while meeting performance requirements of file retrievals. We present an algorithm for solving this problem with guaranteed bounds from the optimal solution. Our algorithm runs in O(nlogn) time where n is the number of files allocated. Detailed simulation results and experiments with real life workloads are also presented.

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

2009-02-03T23:59:59.000Z

280

VIN# JHMFA36216S019329 Vehicle Specifications  

NLE Websites -- All DOE Office Websites (Extended Search)

16S019329 Vehicle Specifications Engine: 1.3 L 4-cylinder Electric Motor: 15 kW Battery: NiMH Seatbelt Positions: Five Payload: 968 lbs Features: Front disk brakes wEBD brake...

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

VIN# JHMFA36246S018725 Vehicle Specifications  

NLE Websites -- All DOE Office Websites (Extended Search)

46S018725 Vehicle Specifications Engine: 1.3 L 4-cylinder Electric Motor: 15 kW Battery: NiMH Seatbelt Positions: Five Payload: 968 lbs Features: Front disk brakes wEBD brake...

282

Nucleosynthesis in the outflows associated with accretion disks of Type II collapsars  

E-Print Network (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 explosion is driven. The supernova ejecta lack momentum and subsequently this newly formed neutron star gets transformed to a stellar mass black hole via massive fallback. The hydrodynamics and the nucleosynthesis in these accretion disks has been studied extensively in the past. Several heavy elements are synthesized in the disk and much of these heavy elements are ejected from the disk via winds and outflows. We study nucleosynthesis in the outflows launched from these disks by using an adiabatic, spherically expanding outflow model, to understand which of these elements thus synthesized in the disk survive in the outflow. While studying this we find that many new elements like isotopes of titanium, copper, zinc etc. are present in the outflows. 56Ni is abundantly synthesized in most of the cases in the outflow which implies that the outflows from these disks in a majority of cases will lead to an observable supernova explosion. It is mainly present when outflow is considered from the He-rich, 56Ni/54Fe rich zones of the disks. However, outflow from the Si-rich zone of the disk remains rich in silicon. Although, emission lines of many of these heavy elements have been observed in the X-ray afterglows of several GRBs by Chandra, BeppoSAX, XMM-Newton etc., Swift seems to have not detected these lines yet.

Indrani Banerjee; Banibrata Mukhopadhyay

2013-09-04T23:59:59.000Z

283

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

284

MILLIMETER IMAGING OF THE {beta} PICTORIS DEBRIS DISK: EVIDENCE FOR A PLANETESIMAL BELT  

SciTech Connect

We present observations at 1.3 mm wavelength of the {beta} Pictoris debris disk with beam size 4.''3 x 2.''6 (83 x 50 AU) from the Submillimeter Array. The emission shows two peaks separated by {approx}7'' along the disk plane, which we interpret as a highly inclined dust ring or belt. A simple model constrains the belt center to 94 {+-} 8 AU, close to the prominent break in slope of the optical scattered light. We identify this region as the location of the main reservoir of dust-producing planetesimals in the disk.

Wilner, David J.; Andrews, Sean M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Hughes, A. Meredith [Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720 (United States)

2011-02-01T23:59:59.000Z

285

Magnetic shear-driven instability and turbulent mixing in magnetized protostellar disks  

E-Print Network (OSTI)

Observations of protostellar disks indicate the presence of the magnetic field of thermal (or superthermal) strength. In such a strong magnetic field, many MHD instabilities responsible for turbulent transport of the angular momentum are suppressed. We consider the shear-driven instability that can occur in protostellar disks even if the field is superthermal. This instability is caused by the combined influence of shear and compressibility in a magnetized gas and can be an efficient mechanism to generate turbulence in disks. The typical growth time is of the order of several rotation periods.

Bonanno, Alfio

2008-01-01T23:59:59.000Z

286

A.N. Witt, B.T. Draine, & G.C. Clayton Dust in Protoplanetary Disks  

E-Print Network (OSTI)

Abstract. We critically examine the best lines of evidence for grain growth in protoplanetary disks, based on modelling of observed spectral energy distributions and images of T Tauri and Herbig Ae stars. The data are consistent with millimeter-sized grains near disk midplanes, and micron-sized grains near disk surfaces. We review three channels by which grains can grow, including direct condensation from the vapor phase, grain-grain collisional sticking, and gravitational instability. The utility of dust in identifying as yet unseen extrasolar planets is highlighted. 1.

E. I. Chiang

2003-01-01T23:59:59.000Z

287

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

288

Current distribution and nonuniformity effects in MHD disk generators  

DOE Green Energy (OSTI)

Results of an experimental and analytical study of current distribution and nonuniformity effects in combustion driven MHD disk generators are presented. The overall objective of the study was to investigate the importance of these phenomena to baseload power generation. The experimental work consisted of combustion-driven steady state experiments with a peg-wall channel operated in a superconducting magnet. The peg-wall construction allowed current and voltage distributions to be measured. The channel was operated with plasma temperatures up to 2750 K and magnetic field strengths up to 5.5 Tesla. The magnitudes of the currents and voltages were reduced by significant loss mechanisms, primarily electrode losses and current leakage through the wall caused by potassium seed penetration of the castable ceramic between the pegs. A simple circuit model accounting for these losses was developed enabling comparisons to be made with analytical calculations. Under normal uniform electrical loading the distributions measured in the channel were uniform as expected. Nonuniform electrical loading was used to produce and measure effects on the current distribution that occur only in the presence of high magnetic fields as required for MHD power generation.

Roseman, D.F.

1982-08-01T23:59:59.000Z

289

Nanoindentation and nanoscratching of hard carbon coatings for magnetic disks  

DOE Green Energy (OSTI)

Nanoindentation and nanoscratching experiments have been performed to assess the mechanical properties of several carbon thin films with potential application as wear resistant coatings for magnetic disks. These include three hydrogenated-carbon films prepared by sputter deposition in a H{sub 2}/Ar gas mixture (hydrogen contents of 20, 34, and 40 atomic %) and a pure carbon film prepared by cathodic-arc plasma techniques. Each film was deposited on a silicon substrate to thickness of about 300 run. The hardness and elastic modulus were measured using nanoindentation methods, and ultra-low load scratch tests were used to assess the scratch resistance of the films and measure friction coefficients. Results show that the hardness, elastic modulus, and scratch resistance of the 20 and 34% hydrogenated films are significantly greater than the 40% film, thereby showing that there is a limit to the amount of hydrogen producing beneficial effects. The cathodic-arc film, with a hardness of greater than 59 GPa, is considerably harder than any of the hydrogenated films and has a superior scratch resistance.

Tsui, T.Y.; Pharr, G.M. [Rice Univ., Houston, TX (United States). Dept. of Materials Science; Oliver, W.C. [Nano Instruments, Inc., Knoxville, TN (United States); Bhatia, C.S.; White, R.L. [IBM Storage Systems Division, San Jose, CA (United States); Anders, S.; Anders, A.; Brown, I.G. [Lawrence Berkeley Lab., CA (United States)

1995-06-01T23:59:59.000Z

290

Vibrations of Jammed Disk Packings with Hertzian Interactions  

E-Print Network (OSTI)

Contact breaking and Hertzian interactions between grains can both give rise to nonlinear vibrational response of static granular packings. We perform molecular dynamics simulations at constant energy in 2D of frictionless bidisperse disks that interact via Hertzian spring potentials as a function of energy and measure directly the vibrational response from the Fourier transform of the velocity autocorrelation function. We compare the measured vibrational response of static packings near jamming onset to that obtained from the eigenvalues of the dynamical matrix to determine the temperature above which the linear response breaks down. We compare packings that interact via single-sided (purely repulsive) and double-sided Hertzian spring interactions to disentangle the effects of the shape of the potential from contact breaking. Our studies show that while Hertzian interactions lead to weak nonlinearities in the vibrational behavior (e.g. the generation of harmonics of the eigenfrequencies of the dynamical matrix), the vibrational response of static packings with Hertzian contact interactions is dominated by contact breaking as found for systems with repulsive linear spring interactions.

Carl F. Schreck; Corey S. O'Hern; Mark D. Shattuck

2013-09-03T23:59:59.000Z

291

H-Disk Aluminum Prototype Heat Transfer Test Summary  

SciTech Connect

The aluminum H-disk was instrumented with heaters (156 ohm on average) and 100 ohm platinum RTD's. Each heater supplies the heat of a double sided H-wedge. Since the flow splits into two flow directions at the inlet fitting, only half of the cooling channel is fully instrumented with RTD's. The other path has a single RTD to check for flow balancing. These items were installed after Greg Derylo petformed the first pressure drop tests. At the time of the test, the desired adhesive for gluing the two halves of the channel together was not available. Therefore, 5-minute epoxy was used on the inner and outer diameters of the halves. Tape was used to set the gap between the two halves. This form of attachment does not make a strong bond between the two halves so the differential pressure between the inside and the outside of the channel was limited to a couple of psi. Therefore, the tests were not conducted in a vacuum.

Squires, B.; /Fermilab

1998-07-28T23:59:59.000Z

292

ORNL DAAC BOREAS Follow-On CD-ROM Set, 6 disks  

NLE Websites -- All DOE Office Websites (Extended Search)

BOREAS Follow-On CD-ROM Set, 6 disks Get Data BOREAS Follow-On ProjectCampaign Document Summary: The Boreal Ecosystem-Atmosphere Study (BOREAS) Follow-on project extended and...

293

Cold Dark Matter Substructure and Galactic Disks I: Morphological Signatures of Hierarchical Satellite Accretion  

E-Print Network (OSTI)

(Abridged) We conduct a series of high-resolution, dissipationless N-body simulations to investigate the cumulative effect of substructure mergers onto thin disk galaxies in the context of the LCDM paradigm of structure formation. Our simulation campaign is based on a hybrid approach. Substructure properties are culled directly from cosmological simulations of galaxy-sized cold dark matter (CDM) halos. In contrast to what can be inferred from statistics of the present-day substructure populations, accretions of massive subhalos onto the central regions of host halos, where the galactic disk resides, since z~1 should be common occurrences. One host halo merger history is subsequently used to seed controlled numerical experiments of repeated satellite impacts on an initially-thin Milky Way-type disk galaxy. We show that these accretion events produce several distinctive observational signatures in the stellar disk including: a ring-like feature in the outskirts; a significant flare; a central bar; and faint fil...

Kazantzidis, Stelios; Zentner, Andrew R; Kravtsov, Andrey V; Moustakas, Leonidas A

2007-01-01T23:59:59.000Z

294

High-Frequency QPOs as a Product of Inner Disk Dynamics around Neutron Stars  

SciTech Connect

The kHz QPOs observed in a neutron star low mass X-ray binary are likely to be produced in the innermost regions of accretion disk around the neutron star. The rotational dynamics of the inner disk can be characterized by the presence of either sub-Keplerian or super-Keplerian accretion flow depending on the relative fastness of the neutron spin as compared to the Keplerian frequency at the inner disk radius. Within the magnetosphere-disk interaction model, the frequency difference between the two kHz QPOs observed in a given source can be estimated to be slightly higher than or nearly around the neutron star spin frequency if the neutron star is a slow rotator and less than the stellar spin frequency if the neutron star is a fast rotator.

Hakan Erkut, M. [Physics Department, Istanbul Kueltuer University, Atakoey Campus, Bakirkoey 34156, Istanbul (Turkey)

2011-09-21T23:59:59.000Z

295

The WIRED Survey. IV. New Dust Disks from the McCook & Sion White Dwarf Catalog  

E-Print Network (OSTI)

We have compiled photometric data from the Wide-field Infrared Survey Explorer All Sky Survey and other archival sources for the more than 2200 objects in the original McCook & Sion Catalog of Spectroscopically Identified White Dwarfs. We applied color-selection criteria to identify 28 targets whose infrared spectral energy distributions depart from the expectation for the white dwarf photosphere alone. Seven of these are previously known white dwarfs with circumstellar dust disks, five are known central stars of planetary nebulae, and six were excluded for being known binaries or having possible contamination of their infrared photometry. We fit white dwarf models to the spectral energy distributions of the remaining ten targets, and find seven new candidates with infrared excess suggesting the presence of a circumstellar dust disk. We compare the model dust disk properties for these new candidates with a comprehensive compilation of previously published parameters for known white dwarfs with dust disks....

Hoard, D W; Wachter, Stefanie; Leisawitz, David T; Cohen, Martin

2013-01-01T23:59:59.000Z

296

r-Process Nucleosynthesis in Hot Accretion Disk Flows from Black Hole - Neutron Star Mergers  

E-Print Network (OSTI)

We consider hot accretion disk outflows from black hole - neutron star mergers in the context of the nucleosynthesis they produce. We begin with a three dimensional numerical model of a black hole - neutron star merger and calculate the neutrino and antineutrino fluxes emitted from the resulting accretion disk. We then follow the element synthesis in material outflowing the disk along parameterized trajectories. We find that at least a weak r-process is produced, and in some cases a main r-process as well. The neutron-rich conditions required for this production of r-process nuclei stem directly from the interactions of the neutrinos emitted by the disk with the free neutrons and protons in the outflow.

R. Surman; G. C. McLaughlin; M. Ruffert; H. -Th. Janka; W. R. Hix

2008-03-12T23:59:59.000Z

297

NUCLEOSYNTHESIS OF NICKEL-56 FROM GAMMA-RAY BURST ACCRETION DISKS  

Science Conference Proceedings (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 M-dot = 0.05 M{sub Sun} s{sup -1} to M-dot = 1 M{sub Sun} s{sup -1}, 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.

Surman, R.; Sabbatino, N. [Department of Physics and Astronomy, Union College, Schenectady, NY 12308 (United States); McLaughlin, G. C. [Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 (United States)

2011-12-20T23:59:59.000Z

298

Bias in hard disk drive rotary actuator pivot bearings: measurements and lubrication phenomena  

Science Conference Proceedings (OSTI)

Bias in disk drive rotary actuator bearings exhibits complex behavior related to the history of the actuator movement. This paper investigates the hysteresis component of bias present after seeks. Measurements of bias during full stroke actuator movements ...

Daniel Helmick; William Messner; C. Fred Higgs, III

2007-04-01T23:59:59.000Z

299

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

300

Phyllosilicate Emission from Protoplanetary Disks: Is the Indirect Detection of Extrasolar Water Possible?  

E-Print Network (OSTI)

Phyllosilicates are hydrous minerals formed by interaction between rock and liquid water and are commonly found in meteorites originating in the asteroid belt. Collisions between asteroids contribute to zodiacal dust, which therefore reasonably could include phyllosilicates. Collisions between planetesimals in protoplanetary disks may also produce dust containing phyllosilicates. These minerals possess characteristic emission features in the mid-infrared and could be detectable in extrasolar protoplanetary disks. Here we determine whether phyllosilicates in protoplanetary disks are detectable in the infrared using instruments such as those on board the Spitzer Space Telescope and SOFIA (Stratospheric Observatory for Infrared Astronomy). We calculate opacities for the phyllosilicates most common in meteorites and compute the emission of radiation from a protoplanetary disk using a 2-layer radiative transfer model. We find that phyllosilicates present at the 3% level lead to observationally significant differen...

Morris, Melissa A; 10.1089/ast.2008.0316

2013-01-01T23:59:59.000Z

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.


301

Analysis of Trade-Off Between Power Saving and Response Time in Disk Storage Systems  

E-Print Network (OSTI)

long periods of inactivity and placing them in standby mode.A ?le request from a disk in standby mode will incur an I/Oautomatically spun down into a standby mode. A read or write

Otoo, Ekow J

2009-01-01T23:59:59.000Z

302

The Stability of Low Surface Brightness Disks Based on Multi-Wavelength Modeling  

E-Print Network (OSTI)

To investigate the structure and composition of the dusty interstellar medium (ISM) of low surface brightness (LSB) disk galaxies, we have used multiwavelength photometry to construct spectral energy distributions for three low-mass, edge-on LSB galaxies. We use Monte Carlo radiation transfer codes that include the effects of transiently heated small grains and polycyclic aromatic hydrocarbon molecules to model and interpret the data. We find that unlike the high surface brightness galaxies previously modeled, the dust disks appear to have scale heights equal to or exceeding their stellar scale heights. This result supports the findings of previous studies that low mass disk galaxies have dust scale heights comparable to their stellar scale heights and suggests that the cold ISM of low mass, LSB disk galaxies may be stable against fragmentation and gravitational collapse. This may help to explain the lack of observed dust lanes in edge-on LSB galaxies and their low current star formation rates.

MacLachlan, John M; Wood, Kenneth; Gallagher, John S

2011-01-01T23:59:59.000Z

303

Properties of carbon overcoats and perfluoro-polyether lubricants in hard disk drives  

E-Print Network (OSTI)

3 discusses different lubricants and additives used in hardand A. Wakabayashi, "Disk lubricant additives, A20H and C2:lower corner. Both lubricant additives can be mixed with

Brunner, Ralf

2009-01-01T23:59:59.000Z

304

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

305

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

306

DISCOVERY OF CRYSTALLIZED WATER ICE IN A SILHOUETTE DISK IN THE M43 REGION  

SciTech Connect

We present the 1.9-4.2 {mu}m spectra of the five bright (L {<=} 11.2) young stars associated with silhouette disks with a moderate to high inclination angle of 39 Degree-Sign -80 Degree-Sign in the M42 and M43 regions. The water ice absorption is seen toward d121-1925 and d216-0939, while the spectra of d182-316, d183-405, and d218-354 show no water ice feature around 3.1 {mu}m within the detection limits. By comparing the water ice features toward nearby stars, we find that the water ice absorption toward d121-1925 and d216-0939 most likely originates from the foreground material and the surrounding disk, respectively. The angle of the disk inclination is found to be mainly responsible for the difference of the optical depth of the water ice among the five young stars. Our results suggest that there is a critical inclination angle between 65 Degree-Sign and 75 Degree-Sign for the circumstellar disk where the water ice absorption becomes strong. The average density at the disk surface of d216-0939 was found to be 6.38 Multiplication-Sign 10{sup -18} g cm{sup -3}. The water ice absorption band in the d216-0939 disk is remarkable in that the maximum optical depth of the water ice band is at a longer wavelength than detected before. It indicates that the primary carrier of the feature is purely crystallized water ice at the surface of the d216-0939 disk with characteristic size of {approx}0.8 {mu}m, which suggests grain growth. This is the first direct detection of purely crystallized water ice in a silhouette disk.

Terada, Hiroshi [Subaru Telescope, National Astronomical Observatory of Japan, 650 North A'ohoku Place, Hilo, HI 96720 (United States); Tokunaga, Alan T., E-mail: terada@subaru.naoj.org [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu 96822 (United States)

2012-07-01T23:59:59.000Z

307

Ultra-thin overcoats for the head/disk interface tribology  

SciTech Connect

Areal density in magnetic storage is increasing at a blistering pace of 60% annually. Recently IBM announced its mobile product with the industry highest areal density of 2.64 Gb/In{sup 2}. The areal density demonstrations have shown up to 5 Gb/In{sup 2} possible. Reaching higher areal density targets dictate that magnetic spacing between heads and disks be reduced. For the example of a 10 Gb/In{sup 2} areal density goal, the magnetic spacing should be {approx}25 nm. In budgeting this magnetic spacing, it is required that disk and slider air bearing surface overcoats thickness be reduced to 5 nm range. Present choice of carbon overcoat in the magnetic storage hard disk drive industry is sputter deposited, hydrogenated carbon (CH{sub x}) with thickness in the range of 12-15 nm on heads and disks. Novel overcoats such as nitrogenated carbon (CN{sub x}) and cathodic arc carbon films are being developed for future applications. Cathodic arc deposition forms ultra-thin amorphous hard carbon films of high sp{sup 3} content, high hardness, and low coefficient of friction. These properties make it of great interest for head/disk interface application, in particular for contact recording. In many cases, the tribological properties of the head disk interface could be improved by factors up to ten applying cathodic arc overcoats to the slider or disk surface. This paper reviews the results of cathodic arc ultra-thin (2-10 nm) carbon overcoats for head/disk interface tribological applications.

Bhatia, C.S. [SSD/IBM, San Jose, CA (US); Anders, S.; Brown, I.G. [Lawrence Berkeley National Lab., CA (US)] [and others

1997-05-01T23:59:59.000Z

308

Warm Gas in the Inner Disks around Young Intermediate Mass Stars  

E-Print Network (OSTI)

The characterization of gas in the inner disks around young stars is of particular interest because of its connection to planet formation. In order to study the gas in inner disks, we have obtained high-resolution K-band and M-band spectroscopy of 14 intermediate mass young stars. In sources that have optically thick inner disks, i.e. E(K-L)>1, our detection rate of the ro-vibrational CO transitions is 100% and the gas is thermally excited. Of the five sources that do not have optically thick inner disks, we only detect the ro-vibrational CO transitions from HD 141569. In this case, we show that the gas is excited by UV fluorescence and that the inner disk is devoid of gas and dust. We discuss the plausibility of the various scenarios for forming this inner hole. Our modeling of the UV fluoresced gas suggests an additional method by which to search for and/or place stringent limits on gas in dust depleted regions in disks around Herbig Ae/Be stars.

Sean Brittain; Theodore Simon; Joan Najita; Terrence Rettig

2006-12-08T23:59:59.000Z

309

Ultraviolet Spectra of CV Accretion Disks with Non-Steady T(r) Laws  

E-Print Network (OSTI)

An extensive grid of synthetic mid- and far-ultraviolet spectra for accretion disks in cataclysmic variables has been presented by Wade and Hubeny (1998). In those models, the disk was assumed to be in steady-state, that is T_eff(r) is specified completely by the mass M_WD and radius R_WD of the accreting white dwarf star and the mass transfer rate M_dot which is constant throughout the disk. In these models, T_eff(r) is proportional to r^{-3/4} except as modified by a cutoff term near the white dwarf. Actual disks may vary from the steady-state prescription for T_eff(r), however, e.g. owing to outburst cycles in dwarf novae M_dot not constant with radius) or irradiation (in which case T_eff in the outer disk is raised above T_steady). To show how the spectra of such disks might differ from the steady case, we present a study of the ultraviolet (UV) spectra of models in which power-law temperature profiles T_eff(r) is proportional to r^{-gamma} with gamma < 3/4 are specified. Otherwise, the construction of...

Orosz, J A; Orosz, Jerome A.; Wade, Richard A.

2003-01-01T23:59:59.000Z

310

EVOLUTION OF X-RAY AND FAR-ULTRAVIOLET DISK-DISPERSING RADIATION FIELDS  

Science Conference Proceedings (OSTI)

We present new X-ray and far-ultraviolet (FUV) observations of T Tauri stars covering the age range 1-10 Myr. Our goals are to observationally constrain the intensity of radiation fields responsible for evaporating gas from the circumstellar disk and to assess the feasibility of current photoevaporation models, focusing on X-ray and UV radiation. We greatly increase the number of 7-10 Myr old T Tauri stars observed in X-rays by including observations of the well-populated 25 Ori aggregate in the Orion OB1a subassociation. With these new 7-10 Myr objects, we confirm that X-ray emission remains constant from 1 to 10 Myr. We also show, for the first time, observational evidence for the evolution of FUV radiation fields with a sample of 56 accreting and non-accreting young stars spanning 1 Myr to 1 Gyr. We find that the FUV emission decreases on timescales consistent with the decline of accretion in classical T Tauri stars until reaching the chromospheric level in weak T Tauri stars and debris disks. Overall, we find that the observed strength of high-energy radiation is consistent with that required by photoevaporation models to dissipate the disks in timescales of approximately 10 Myr. Finally, we find that the high-energy fields that affect gas evolution are not similarly affecting dust evolution; in particular, we find that disks with inner clearings, transitional disks, have similar levels of FUV emission as full disks.

Ingleby, Laura; Calvet, Nuria; Miller, Jon; Bergin, Edwin; Hartmann, Lee [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Hernandez, Jesus; Briceno, Cesar [Centro de Investigaciones de Astronomia (CIDA), Merida, 5101-A (Venezuela, Bolivarian Republic of); Espaillat, Catherine, E-mail: lingleby@umich.edu, E-mail: ncalvet@umich.edu, E-mail: jonmm@umich.edu, E-mail: ebergin@umich.edu, E-mail: lhartm@umich.edu, E-mail: jesush@cida.ve, E-mail: briceno@cida.ve, E-mail: cespaillat@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-78, Cambridge, MA 02138 (United States)

2011-04-15T23:59:59.000Z

311

Eclipsing Broad Emission Lines in Hercules X-1: Evidence for a Disk Wind?  

E-Print Network (OSTI)

We present disk wind model calculations for the broad emission lines seen in the ultraviolet spectra of the X-ray binary Hercules X-1. Recent HST/STIS observations of these lines suggest that they are kinematically linked to the orbital motion of the neutron star and exhibit a red-shifted to blue-shifted evolution of the line shape during the progression of the eclipse from ingress to egress which is indicative of disk emission. Furthermore, these lines are single-peaked which implies that they may be formed in a disk wind similar to those we have proposed as producing the broad emission lines seen in the UV spectra of active galactic nuclei. We compute line profiles as a function of eclipse phase and compare them to the observed line profiles. Various effects may modify the appearance of the lines including resonant scattering in the wind itself, self-shadowing of the warped disk from the central continuum, and self-obscuration of parts of the disk along the observer's line-of-sight. These latter two effects can cause orbital and precessional phase dependent variations in the emission lines. Hence, examination of the line profiles as a function of these phases can, in principle, provide additional information on the characteristics of the disk warp.

James Chiang

2000-11-05T23:59:59.000Z

312

Design, testing and two-dimensional flow modeling of a multiple-disk fan  

Science Conference Proceedings (OSTI)

A multiple-disk Tesla type fan has been designed, tested and analyzed two-dimensionally using the conservation of angular momentum principle. Experimental results showed that such multiple-disk fans exhibited exceptionally low performance characteristics, which could be attributed to the low viscosity, tangential nature of the flow, and large mechanical energy losses at both suction and discharge sections that are comparable to the total input power. By means of theoretical analysis, local and overall shearing stresses on the disk surfaces have been determined based on tangential and radial velocity distributions of the air flow of different volume flow rates at prescribed disk spaces and rotational speeds. Then the total power transmitted by rotating disks to air flow, and the power acquired by the air flow in the gap due to transfer of angular momentum have been obtained by numerically integrating shearing stresses over the disk surfaces. Using the measured shaft and hydraulic powers, these quantities were utilized to evaluate mechanical energy losses associated with the suction and discharge sections of the fan. (author)

Engin, Tahsin; Oezdemir, Mustafa; Cesmeci, Sevki [Department of Mechanical Engineering, The University of Sakarya, Esentepe Campus, 54187 Sakarya (Turkey)

2009-11-15T23:59:59.000Z

313

DEAD ZONES AS THERMAL BARRIERS TO RAPID PLANETARY MIGRATION IN PROTOPLANETARY DISKS  

Science Conference Proceedings (OSTI)

Planetary migration in standard models of gaseous protoplanetary disks is known to be very rapid ({approx}10{sup 5} years), jeopardizing the existence of planetary systems. We present a new mechanism for significantly slowing rapid planetary migration, discovered by means of radiative transfer calculations of the thermal structure of protoplanetary disks irradiated by their central stars. Rapid dust settling in a disk's dead zone-a region with very little turbulence-leaves a dusty wall at its outer edge. We show that the back-heating of the dead zone by this irradiated wall produces a positive gradient of the disk temperature, which acts as a thermal barrier to planetary migration which persists for the disk lifetime. Although we analyze in detail the migration of a super-Earth in a low-mass disk around an M star, our findings can apply to a wide variety of young planetary systems. We compare our findings with other potentially important stopping mechanisms and show that there are large parameter spaces for which dead zones are likely to play the most important role for reproducing the observed mass-period relation in longer planetary periods.

Hasegawa, Yasuhiro [Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada); Pudritz, Ralph E. [Origins Institute, McMaster University, Hamilton, ON L8S 4M1 (Canada)], E-mail: hasegay@physics.mcmaster.ca, E-mail: pudritz@physics.mcmaster.ca

2010-02-20T23:59:59.000Z

314

THE EPOCH OF DISK SETTLING: z {approx} 1 TO NOW  

SciTech Connect

We present evidence from a sample of 544 galaxies from the DEEP2 Survey for evolution of the internal kinematics of blue galaxies with stellar masses ranging 8.0 < log M {sub *}(M {sub Sun }) < 10.7 over 0.2 < z < 1.2. DEEP2 provides galaxy spectra and Hubble imaging from which we measure emission-line kinematics and galaxy inclinations, respectively. Our large sample allows us to overcome scatter intrinsic to galaxy properties in order to examine trends in kinematics. We find that at a fixed stellar mass, galaxies systematically decrease in disordered motions and increase in rotation velocity and potential well depth with time. Massive galaxies are the most well ordered at all times examined, with higher rotation velocities and less disordered motions than less massive galaxies. We quantify disordered motions with an integrated gas velocity dispersion corrected for beam smearing ({sigma} {sub g}). It is unlike the typical pressure-supported velocity dispersion measured for early type galaxies and galaxy bulges. Because both seeing and the width of our spectral slits comprise a significant fraction of the galaxy sizes, {sigma} {sub g} integrates over velocity gradients on large scales which can correspond to non-ordered gas kinematics. We compile measurements of galaxy kinematics from the literature over 1.2 < z < 3.8 and do not find any trends with redshift, likely for the most part, because these data sets are biased toward the most highly star-forming systems. In summary, over the last {approx}8 billion years since z = 1.2, blue galaxies evolve from disordered to ordered systems as they settle to become the rotation-dominated disk galaxies observed in the universe today, with the most massive galaxies being the most evolved at any time.

Kassin, Susan A.; Gardner, Jonathan P. [Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Weiner, Benjamin J.; Willmer, C. N. A. [Steward Observatory, University of Arizona, Tucson, AZ (United States); Faber, S. M.; Guhathakurta, Puragra; Koo, David C. [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Coil, Alison L. [Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Cooper, Michael C. [Center for Galaxy Evolution, Department of Physics and Astronomy, University of California, Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); Devriendt, Julien [Department of Physics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); Dutton, Aaron A. [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Metevier, A. J. [Department of Physics and Astronomy, Sonoma State University, 1801 East Cotati Avenue, Rohnert Park, CA 94928 (United States); Noeske, Kai G. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Primack, Joel R., E-mail: susan.kassin@nasa.gov [Department of Physics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)

2012-10-20T23:59:59.000Z

315

Evaluation of the Contribution of Fall Chinook Salmon Reared at Columbia River Hatcheries to the Pacific Salmon Fisheries, 1989 Final Report.  

DOE Green Energy (OSTI)

In 1979 this study was initiated to determine the distribution, contribution, and value of artificially propagated fall chinook salmon from the Columbia River. Coded wire tagging (CWT) of hatchery fall chinook salmon began in 1979 with the 1978 brood and was completed in 1982 with the 1981 brood of fish at rearing facilities on the Columbia River system. From 18 to 20 rearing facilities were involved in the study each brood year. Nearly 14 million tagged fish, about 4% of the production, were released as part of this study over the four years, 1979 through 1982. Sampling for recoveries of these tagged fish occurred from 1980 through 1986 in the sport and commercial marine fisheries from Alaska through California, Columbia River fisheries, and returns to hatcheries and adjacent streams. The National Marine Fisheries Service coordinated this study among three fishery agencies: US Fish and Wildfire Service, Oregon Department of Fish and Wildlife, and Washington Department of Fisheries. The objectives of this study were to determine the distribution, fishery contribution, survival, and value of the production of fall chinook salmon from each rearing facility on the Columbia River system to Pacific coast salmon fisheries. To achieve these objectives fish from each hatchery were given a distinctive CWT. 81 refs., 20 figs., 68 tabs.

Vreeland, Robert R.

1989-10-01T23:59:59.000Z

316

Instream Flows Needed for Successful Migration and Rearing of Rainbow and Westslope Cutthroat Trout in Selected Tributaries of the Kootenai River: Final Report FY 1988.  

Science Conference Proceedings (OSTI)

This is the second phase of a two-part study that was conducted by Montana Department of Fish, Wildlife and Parks in contractual agreement with Bonneville Power Administration to address measures of the Northwest Power Planning Council's River Basin Fish and Wildlife Program. Objectives were to determine instream flow needs in Kootenai River tributaries to maintain successful fish migration, spawning and rearing habitat of game fish, evaluate existing resident and rearing fish populations, and compile hydrologic and fishery information required to secure legal reservation of water for the fishery source. The Kootenai River fishery is threatened by microhydro and other water use development which reduce tributary habitat critical for maintaining a healthy spawning and rearing environment. The wetted perimeter method was used to estimate flows required to maintain existing resident and migratory fish populations in 28 tributaries to the Kootenai River. Migrant passage flows were determined using the discharge-average depth relationship at four (usually five) riffle transects. This information will provide the basis to reserve water through application to the Montana Department of Natural Resources and Conservation. 45 figs., 56 tabs.

Marotz, Brian

1988-06-01T23:59:59.000Z

317

PANCHROMATIC OBSERVATIONS AND MODELING OF THE HV TAU C EDGE-ON DISK  

SciTech Connect

We present new high spatial resolution ({approx}<0.''1) 1-5 {mu}m adaptive optics images, interferometric 1.3 mm continuum and {sup 12}CO 2-1 maps, and 350 {mu}m, 2.8 and 3.3 mm fluxes measurements of the HV Tau system. Our adaptive optics images unambiguously demonstrate that HV Tau AB-C is a common proper motion pair. They further reveal an unusually slow orbital motion within the tight HV Tau AB pair that suggests a highly eccentric orbit and/or a large deprojected physical separation. Scattered light images of the HV Tau C edge-on protoplanetary disk suggest that the anisotropy of the dust scattering phase function is almost independent of wavelength from 0.8 to 5 {mu}m, whereas the dust opacity decreases significantly over the same range. The images further reveal a marked lateral asymmetry in the disk that does not vary over a timescale of two years. We further detect a radial velocity gradient in the disk in our {sup 12}CO map that lies along the same position angle as the elongation of the continuum emission, which is consistent with Keplerian rotation around a 0.5-1 M{sub sun} central star, suggesting that it could be the most massive component in the triple system. To obtain a global representation of the HV Tau C disk, we search for a model that self-consistently reproduces observations of the disk from the visible regime up to millimeter wavelengths. We use a powerful radiative transfer model to compute synthetic disk observations and use a Bayesian inference method to extract constraints on the disk properties. Each individual image, as well as the spectral energy distribution, of HV Tau C can be well reproduced by our models with fully mixed dust provided grain growth has already produced larger-than-interstellar dust grains. However, no single model can satisfactorily simultaneously account for all observations. We suggest that future attempts to model this source include more complex dust properties and possibly vertical stratification. While both grain growth and stratification have already been suggested in many disks, only a panchromatic analysis, such as presented here, can provide a complete picture of the structure of a disk, a necessary step toward quantitatively testing the predictions of numerical models of disk evolution.

Duchene, G.; Maness, H. L. [Astronomy Department, University of California, Berkeley, CA 94720-3411 (United States); McCabe, C. [IPAC, MS 220-6, California Institute of Technology, Pasadena, CA 91125 (United States); Pinte, C.; Menard, F.; Duvert, G. [Universite Joseph Fourier - Grenoble 1/CNRS, Laboratoire d'Astrophysique de Grenoble (LAOG) UMR 5571, BP 53, 38041 Grenoble Cedex 09 (France); Stapelfeldt, K. R. [JPL, MS 183-900, California Institute of Technology, Pasadena, CA 91109-8099 (United States); Ghez, A. M. [Division of Astronomy and Astrophysics, UCLA, Box 951547, Los Angeles, CA 90095-1562 (United States); Bouy, H. [Instituto de Astrofisica de Canarias, C/Via Lactea s/n, 38200 - La Laguna, Tenerife (Spain); Barrado y Navascues, D.; Morales-Calderon, M. [Laboratorio de Astrofisica Estelar y Exoplanetas (LAEX-CAB, INTA-CSIC), P.O. Box 78, 28691 Villanueva de la Canada (Madrid) (Spain); Wolf, S. [Christian-Albrechts-Universitaet zu Kiel, Institut fuer Theoretische Physik und Astrophysik, Leibnizstr. 15, 24098 Kiel (Germany); Padgett, D. L.; Brooke, T. Y.; Noriega-Crespo, A., E-mail: gduchene@astro.berkeley.ed [SSC, MS 220-6, California Institute of Technology, Pasadena, CA 91125 (United States)

2010-03-20T23:59:59.000Z

318

Hard Disk/Solid State Drive Synergy in Support of Data-Intensive Computing  

SciTech Connect

Data-intensive applications are becoming increasingly common in high-performance computing. Examples include combustion simulation, human genome analysis, and satellite image processing. Efficient access of data sets is critical to the performance of these applications. Because of the size of the data today's economically feasible approach is to store the data files on an array of hard disks or data servers equipped with hard disks and managed by a parallel file system such as PVFS or Lustre wherein the data is striped over a (large) number of disks for high aggregate I/O throughout. With file striping, a request for a segment of logically contiguous file space is decomposed into multiple sub-requests, each to a different server. While the data unit for this striping is usually reasonably large to benefit disk efficiency, the first and/or last sub-requests can be much smaller than the striping unit if the request does not align with the striping pattern, severely compromising hard disk efficiency and thus application performance. We propose to exploit solid state drives (SSD), whose efficiency is much less sensitive to small random accesses, to enable the alignment of requests to disk with the data striping pattern. In this scheme hard disks mainly serve large, aligned, sequential requests, with SSDs serving small or unaligned requests, thus respecting the relative cost, performance, and durability characteristics of the two media, and thereby achieving synergy in performance/cost. We will describe the design of the proposed scheme, its implementation on CCS-7's Darwin cluster, and performance results.

Liu,Ke [Los Alamos National Laboratory; Jiang, Song [Los Alamos National Laboratory; Davis, Kei [Los Alamos National Laboratory

2012-07-19T23:59:59.000Z

319

Disk Accretion Flow Driven by Large-Scale Magnetic Fields: Solutions with Constant Specific Energy  

E-Print Network (OSTI)

(Abridged) We study the dynamical evolution of a stationary, axisymmetric, and perfectly conducting cold accretion disk containing a large-scale magnetic field around a Kerr black hole, trying to understand the relation between accretion and the transportation of angular momentum and energy. We solve the radial momentum equation for solutions corresponding to an accretion flow that starts from a subsonic state at infinity, smoothly passes the fast critical point, then supersonically falls into the horizon of the black hole. The solutions always have the following features: 1) The specific energy of fluid particles remains constant but the specific angular momentum is effectively removed by the magnetic field. 2) At large radii, where the disk motion is dominantly rotational, the energy density of the magnetic field is equipartitioned with the rotational energy density of the disk. 3) Inside the fast critical point, where radial motion becomes important, the ratio of the electromagnetic energy density to the kinetic energy density drops quickly. The results indicate that: 1) Disk accretion does not necessarily imply energy dissipation since magnetic fields do not have to transport or dissipate a lot of energy as they effectively transport angular momentum. 2) When resistivity is small, the large-scale magnetic field is amplified by the shearing rotation of the disk until the magnetic energy density is equipartitioned with the rotational energy density, ending up with a geometrically thick disk. This is in contrast with the evolution of small-scale magnetic fields where if the resistivity is nonzero the magnetic energy density is likely to be equipartitioned with the kinetic energy density associated with local random motions (e.g., turbulence), making a thin Keplerian disk possible.

Li-Xin Li

2002-12-20T23:59:59.000Z

320

GRAVITATIONAL INSTABILITY OF ROTATING, PRESSURE-CONFINED, POLYTROPIC GAS DISKS WITH VERTICAL STRATIFICATION  

SciTech Connect

We investigate the gravitational instability (GI) of rotating, vertically stratified, pressure-confined, polytropic gas disks using a linear stability analysis as well as analytic approximations. The disks are initially in vertical hydrostatic equilibrium and bounded by a constant external pressure. We find that the GI of a pressure-confined disk is in general a mixed mode of the conventional Jeans and distortional instabilities, and is thus an unstable version of acoustic-surface-gravity waves. The Jeans mode dominates in weakly confined disks or disks with rigid boundaries. On the other hand, when the disk has free boundaries and is strongly pressure confined, the mixed GI is dominated by the distortional mode that is surface-gravity waves driven unstable under their own gravity and thus incompressible. We demonstrate that the Jeans mode is gravity-modified acoustic waves rather than inertial waves and that inertial waves are almost unaffected by self-gravity. We derive an analytic expression for the effective sound speed c{sub eff} of acoustic-surface-gravity waves. We also find expressions for the gravity reduction factors relative to a razor-thin counterpart that are appropriate for the Jeans and distortional modes. The usual razor-thin dispersion relation, after correcting for c{sub eff} and the reduction factors, closely matches the numerical results obtained by solving a full set of linearized equations. The effective sound speed generalizes the Toomre stability parameter of the Jeans mode to allow for the mixed GI of vertically stratified, pressure-confined disks.

Kim, Jeong-Gyu; Kim, Woong-Tae [Center for the Exploration of the Origin of the Universe (CEOU), Astronomy Program, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Seo, Young Min; Hong, Seung Soo, E-mail: jgkim@astro.snu.ac.kr, E-mail: wkim@astro.snu.ac.kr, E-mail: seo3919@email.arizona.edu, E-mail: sshong@astro.snu.ac.kr [FPRD, Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of)

2012-12-20T23:59:59.000Z

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321

PLANETESIMAL DYNAMICS IN INCLINED BINARY SYSTEMS: THE ROLE OF GAS-DISK GRAVITY  

SciTech Connect

We investigate the effects of gas-disk gravity on planetesimal dynamics in inclined binary systems, where the circumprimary disk plane is tilted by a significant angle (i{sub B} ) with respect to the binary disk plane. Our focus is on the Lidov-Kozai mechanism and the evolution of planetesimal eccentricity and inclination. Using both analytical and numerical methods, we find that, on one hand, disk gravity generally narrows down the Kozai-on region, i.e., the Lidov-Kozai effect can be suppressed in certain parts of (or even the whole of) the disk depending on various parameters. In the Kozai-off region, planetesimals would move to orbits close to the midplane of the gas-disk, with the relative angle (i') following a small amplitude periodical oscillation. On the other hand, when we include the effects of disk gravity, we find that the Lidov-Kozai effect can operate even at arbitrarily low inclinations (i{sub B} ), although a lower i{sub B} leads to a smaller Kozai-on region. Furthermore, in the Kozai-on region, most planetesimals' eccentricities can be excited to extremely high values ({approx}1), and such extreme high eccentricities usually accompany orbital flipping, i.e., the planetesimal orbit flips back and forth between anterograde and retrograde. Once a planetesimal reaches very high orbital eccentricity, gas drag damping will shrink the planetesimal orbit, forming a 'hot planetesimal' on a near circular orbit very close to the primary star. Such a mechanism, if replacing the planetesimals and gas drag damping with Jupiters and tidal damping respectively, may lead to a frequent production of hot Jupiters.

Zhao Gang; Xie Jiwei; Zhou Jilin [Department of Astronomy and Key Laboratory of Modern Astronomy and Astrophysics in the Ministry of Education, Nanjing University, Nanjing 210093 (China); Lin, Douglas N. C., E-mail: xiejiwei@gmail.com, E-mail: zhoujl@nju.edu.cn [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)

2012-04-20T23:59:59.000Z

322

AN OBSERVED LINK BETWEEN ACTIVE GALACTIC NUCLEI AND VIOLENT DISK INSTABILITIES IN HIGH-REDSHIFT GALAXIES  

Science Conference Proceedings (OSTI)

We provide evidence for a correlation between the presence of giant clumps and the occurrence of active galactic nuclei (AGNs) in disk galaxies. Giant clumps of 10{sup 8}-10{sup 9} M{sub Sun} arise from violent gravitational instability in gas-rich galaxies, and it has been proposed that this instability could feed supermassive black holes (BHs). We use emission line diagnostics to compare a sample of 14 clumpy (unstable) disks and a sample of 13 smoother (stable) disks at redshift z {approx} 0.7. The majority of clumpy disks in our sample have a high probability of containing AGNs. Their [O III] {lambda}5007 emission line is strongly excited, inconsistent with low-metallicity star formation (SF) alone. [Ne III] {lambda}3869 excitation is also higher. Stable disks rarely have such properties. Stacking ultra sensitive Chandra observations (4 Ms) reveals an X-ray excess in clumpy galaxies, which confirms the presence of AGNs. The clumpy galaxies in our intermediate-redshift sample have properties typical of gas-rich disk galaxies rather than mergers, being in particular on the main sequence of SF. This suggests that our findings apply to the physically similar and numerous gas-rich unstable disks at z > 1. Using the observed [O III] and X-ray luminosities, we conservatively estimate that AGNs hosted by clumpy disks have typical bolometric luminosities of the order of a few 10{sup 43} erg s{sup -1}, BH growth rates m-dot{sub BH}{approx}10{sup -2} M{sub Sun} yr{sup -1}, and that these AGNs are substantially obscured in X-rays. This moderate-luminosity mode could provide a large fraction of today's BH mass with a high duty cycle (>10%), accretion bursts with higher luminosities being possible over shorter phases. Violent instabilities at high redshift (giant clumps) are a much more efficient driver of BH growth than the weak instabilities in nearby spirals (bars), and the evolution of disk instabilities with mass and redshift could explain the simultaneous downsizing of SF and of BH growth.

Bournaud, Frederic; Juneau, Stephanie; Le Floc'h, Emeric; Mullaney, James; Daddi, Emanuele; Duc, Pierre-Alain; Elbaz, David; Salmi, Fadia [CEA, IRFU, SAp, F-91191 Gif-sur-Yvette (France); Dekel, Avishai [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Dickinson, Mark [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)

2012-09-20T23:59:59.000Z

323

SPITZER OBSERVATIONS OF THE {lambda} ORIONIS CLUSTER. II. DISKS AROUND SOLAR-TYPE AND LOW-MASS STARS  

Science Conference Proceedings (OSTI)

We present IRAC/MIPS Spitzer Space Telescope observations of the solar-type and the low-mass stellar population of the young ({approx}5 Myr) {lambda} Orionis cluster. Combining optical and Two Micron All Sky Survey photometry, we identify 436 stars as probable members of the cluster. Given the distance (450 pc) and the age of the cluster, our sample ranges in mass from 2 M{sub sun} to objects below the substellar limit. With the addition of the Spitzer mid-infrared data, we have identified 49 stars bearing disks in the stellar cluster. Using spectral energy distribution slopes, we place objects in several classes: non-excess stars (diskless), stars with optically thick disks, stars with 'evolved disks' (with smaller excesses than optically thick disk systems), and 'transitional disk' candidates (in which the inner disk is partially or fully cleared). The disk fraction depends on the stellar mass, ranging from {approx}6% for K-type stars (R{sub C} - J 4). We confirm the dependence of disk fraction on stellar mass in this age range found in other studies. Regarding clustering levels, the overall fraction of disks in the {lambda} Orionis cluster is similar to those reported in other stellar groups with ages normally quoted as {approx}5 Myr.

Hernandez, Jesus [Centro de Investigaciones de AstronomIa, Apdo. Postal 264, Merida 5101-A (Venezuela, Bolivarian Republic of); Morales-Calderon, Maria [Laboratorio de Astrofisica Estelar y Exoplanetas (LAEX), Centro de Astrobiologia (CAB, INTA-CSIC), LAEFF, P.O. Box 78, E-28691, Villanueva de la canada, Madrid (Spain); Calvet, Nuria; Hartmann, L. [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Muzerolle, J. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Gutermuth, R. [Five Colleges Astronomy Department, Smith College, Northampton, MA 01027 (United States); Luhman, K. L. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States); Stauffer, J., E-mail: hernandj@cida.v, E-mail: muzerol@stsci.ed [Spitzer Science Center, Caltech M/S 220-6, 1200 East California Boulevard, Pasadena, CA 91125 (United States)

2010-10-20T23:59:59.000Z

324

Ecological Dynamics of De Novo and De Alio Products in the Worldwide Optical Disk Drive Industry, 1983-1999  

E-Print Network (OSTI)

Given the extreme capital intensity of optical disk drivethe industries with low capital intensity or industries withof high and low capital intensity (Freeman & Soete, 1999),

Olga M. Khessina; Glenn R. Carroll

2001-01-01T23:59:59.000Z

325

Analysis of asymmetric disk-shaped and flat-plate heat pipes  

SciTech Connect

An analytical investigation and conceptual design of a disk-shaped asymmetric heat pipe is presented in this work. Using the conservative formulations for the steady incompressible vapor and liquid flow for a disk-shaped heat pipe, an in-depth integral analysis is applied. Analytical results for the asymmetric vapor velocity profile, the vapor and liquid pressure distributions, and the vapor temperature distribution in the heat pipe are obtained and compared to those of a rectangular flat-plate heat pipe. The analysis establishes the physics of the process and the intrawick interactions for the disk-shaped heat pipe. The effects of variations in the thicknesses of the vapor channel and the wick as well as the heat pipe on the performance of both disk-shaped and rectangular flat-plate heat pipes are analyzed in detail and compared with each other. The factors limiting heat pipe performance are discussed and the results show that the disk-shaped heat pipe, while utilizing a smaller surface area and being more adaptable to several application areas, significantly increases the heat transfer capability per unit surface area compared to rectangular flat-plate heat pipe. 19 refs., 7 figs.

Vafai, K.; Zhu, N.; Wang, W. (Ohio State Univ., Columbus, OH (United States))

1995-02-01T23:59:59.000Z

326

SPATIALLY RESOLVED SPECTROSCOPIC STAR FORMATION HISTORIES OF NEARBY DISKS: HINTS OF STELLAR MIGRATION  

SciTech Connect

We use the Mitchell Spectrograph (formerly VIRUS-P) to observe 12 nearby disk galaxies. We successfully measure ages in the outer disk in six systems. In three cases (NGC 2684, NGC 6155, and NGC 7437), we find that a downward break in the disk surface brightness profile corresponds with a change in the dominant stellar population with the interior being dominated by active star formation and the exterior having older stellar populations that are best fit with star formation histories that decline with time. The observed increase in average stellar ages beyond a profile break is similar to theoretical models that predict surface brightness breaks are caused by stellar migration, with the outer disk being populated from scattered old interior stars. In three more cases (IC 1132, NGC 4904, and NGC 6691), we find no significant change in the stellar population as one crosses the break radius. In these galaxies, both the inner and outer disks are dominated by active star formation and younger stellar populations. While radial migration can contribute to the stellar populations beyond the break, it appears that more than one mechanism is required to explain all of our observed stellar profile breaks.

Yoachim, Peter [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Roskar, Rok [Institute for Theoretical Physics, University of Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland); Debattista, Victor P., E-mail: yoachim@u.washington.edu [Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE (United Kingdom)

2012-06-20T23:59:59.000Z

327

The gas temperature in flaring disks around pre-main sequence stars  

E-Print Network (OSTI)

A model is presented which calculates the gas temperature and chemistry in the surface layers of flaring circumstellar disks using a code developed for photon-dominated regions. Special attention is given to the influence of dust settling. It is found that the gas temperature exceeds the dust temperature by up to several hundreds of Kelvins in the part of the disk that is optically thin to ultraviolet radiation, indicating that the common assumption that Tgas=Tdust is not valid throughout the disk. In the optically thick part, gas and dust are strongly coupled and the gas temperature equals the dust temperature. Dust settling has little effect on the chemistry in the disk, but increases the amount of hot gas deeper in the disk. The effects of the higher gas temperature on several emission lines arising in the surface layer are examined. The higher gas temperatures increase the intensities of molecular and fine-structure lines by up to an order of magnitude, and can also have an important effect on the line shapes.

B. Jonkheid; F. G. A. Faas; G. -J. van Zadelhoff; E. F. van Dishoeck

2004-08-26T23:59:59.000Z

328

The Cosmic Battery and the Inner Edge of the Accretion Disk  

E-Print Network (OSTI)

The Poynting-Robertson Cosmic Battery proposes that the innermost part of the accretion disk around a black hole is threaded by a large scale dipolar magnetic field generated in situ, and that the return part of the field diffuses outward through the accretion disk. This is different from the scenario that the field originates at large distances and is carried inward by the accretion flow. In view of the importance of large scale magnetic fields in regulating the processes of accretion and outflows, we study the stability of the inner edge of a magnetized disk in general relativity when the distribution of the magnetic field is the one predicted by the Poynting-Robertson Cosmic Battery. We found that as the field grows, the inner edge of the disk gradually moves outward. In a fast spinning black hole with a>0.8M the inner edge moves back in towards the black hole horizon as the field grows beyond some threshold value. In all cases, the inner part of the disk undergoes a dramatic structural change as the field...

Contopoulos, Ioannis

2012-01-01T23:59:59.000Z

329

EXPLORING THE EFFECTS OF STELLAR ROTATION AND WIND CLEARING: DEBRIS DISKS AROUND F STARS  

Science Conference Proceedings (OSTI)

We have conducted a study of debris disks around F stars in order to explore correlations between rotation, stellar winds, and circumstellar disks. We obtained new 24 {mu}m photometry from the Multiband Imaging Photometer for Spitzer (MIPS) camera for a sample of 188 relatively nearby F dwarfs with various rotation rates and optical colors, and combined it with archival MIPS data for 66 more F stars, as well as Wide-field Infrared Survey Explorer data for the entire sample, plus 9 more F stars. Based on the objects' K{sub s} - [24] and [3.4] - [22] colors, we identify 22 stars in our sample as having 22 and/or 24 {mu}m excesses above our detection limit, 13 of which are new discoveries. Our overall disk detection rate is 22/263, or 8%, consistent with previous determinations of disk fractions in the solar neighborhood. While fast-rotating stars are expected to have strong winds capable of efficiently removing dust, we find no correlation between rotational velocity and infrared excess. Similarly, we find no significant difference in excess detection rate between late-type F stars, which have convective surfaces, and early-type F stars, which have fully radiative envelopes. However, the essentially unknown range of ages in this sample may be washing out any effects relating rotation, winds, and disks.

Mizusawa, Trisha F. [Florida Institute of Technology, 150 W. University Boulevard, Melbourne, FL 32901 (United States); Rebull, Luisa M.; Stauffer, John R. [Spitzer Science Center (SSC), 1200 E. California Blvd., California Institute of Technology, Pasadena, CA 91125 (United States); Bryden, Geoffrey [Jet Propulsion Laboratory, 4800 Oak Grove Blvd, Pasadena, CA 91109 (United States); Meyer, Michael [ETH, Zurich (Switzerland); Song, Inseok, E-mail: trisha.mizusawa@gmail.com [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602 (United States)

2012-11-01T23:59:59.000Z

330

Tomographic Simulations of Accretion Disks in Cataclysmic Variables - Flickering and Wind  

E-Print Network (OSTI)

Both continuum and emission line flickering are phenomena directly associated with the mass accretion process. In this work we simulate accretion disk Doppler maps including the effects of winds and flickering flares. Synthetic flickering Doppler maps are calculated and the effect of the flickering parameters on the maps is explored. Jets and winds occur in many astrophysical objects where accretion disks are present. Jets are generally absent among the cataclysmic variables (CVs), but there is evidence of mass loss by wind in many objects. CVs are ideal objects to study accretion disks and consequently to study the wind associated with these disks. We also present simulations of accretion disks including the presence of a wind with orbital phase resolution. Synthetic H-alpha line profiles in the optical region are obtained and their corresponding Doppler maps are calculated. The effect of the wind simulation parameters on the wind line profiles is also explored. From this study we verified that optically thick lines and/or emission by diffuse material into the primary Roche lobe are necessary to generate single peaked line profiles, often seen in CVs. The future accounting of these effects is suggested for interpreting Doppler tomography reconstructions.

Fabiola M. A. Ribeiro; Marcos P. Diaz

2007-11-22T23:59:59.000Z

331

A Spatially Resolved Inner Hole in the Disk around GM Aurigae  

E-Print Network (OSTI)

We present 0.3 arcsec resolution observations of the disk around GM Aurigae with the Submillimeter Array (SMA) at a wavelength of 860 um and with the Plateau de Bure Interferometer at a wavelength of 1.3 mm. These observations probe the distribution of disk material on spatial scales commensurate with the size of the inner hole predicted by models of the spectral energy distribution. The data clearly indicate a sharp decrease in millimeter optical depth at the disk center, consistent with a deficit of material at distances less than ~20 AU from the star. We refine the accretion disk model of Calvet et al. (2005) based on the unresolved spectral energy distribution (SED) and demonstrate that it reproduces well the spatially resolved millimeter continuum data at both available wavelengths. We also present complementary SMA observations of CO J=3-2 and J=2-1 emission from the disk at 2" resolution. The observed CO morphology is consistent with the continuum model prediction, with two significant deviations: (1) ...

Hughes, A Meredith; Espaillat, Catherine; Wilner, David J; Calvet, Nuria; D'Alessio, Paola; Qi, Chunhua; Williams, Jonathan P; Hogerheijde, Michiel

2009-01-01T23:59:59.000Z

332

Can Early Type Galaxies Evolve from Fading the Disks of Late Types?  

E-Print Network (OSTI)

We examine whether early-type galaxies in clusters may have evolved from later types by the fading of their disks (e.g., as a result of ram-pressure stripping or strangulation) or by enhancement of the bulge luminosity (e.g., due to tidal interactions and mergers). For this purpose, we compare the bulge and disk luminosities of early- and late-type galaxies and of galaxies at different radial distances from the cluster center. We find that, in order for early-type galaxies, including S0s, to have evolved from late-type galaxies, their bulge luminosities must have been physically enhanced. Disk fading models cannot explain the differences observed. We then show that galaxy bulges are systematically brighter at small projected distances from the cluster center, while disk luminosities are uncorrelated with cluster-centric distance. Our results suggest that bulge enhancement, not disk fading, distinguishes early from late types and is thus at least partially responsible for the morphology-environment relation of bright cluster galaxies.

Daniel Christlein; Ann Zabludoff

2004-08-02T23:59:59.000Z

333

Eclipsing Broad Emission Lines in Hercules X-1 Evidence for a Disk Wind?  

E-Print Network (OSTI)

We present disk wind model calculations for the broad emission lines seen in the ultraviolet spectra of the X-ray binary Hercules X-1. Recent HST/STIS observations of these lines suggest that they are kinematically linked to the orbital motion of the neutron star and exhibit a red-shifted to blue-shifted evolution of the line shape during the progression of the eclipse from ingress to egress which is indicative of disk emission. Furthermore, these lines are single-peaked which implies that they may be formed in a disk wind similar to those we have proposed as producing the broad emission lines seen in the UV spectra of active galactic nuclei. We compute line profiles as a function of eclipse phase and compare them to the observed line profiles. Various effects may modify the appearance of the lines including resonant scattering in the wind itself, self-shadowing of the warped disk from the central continuum, and self-obscuration of parts of the disk along the observer's line-of-sight. These latter two effects...

Chiang, J

2000-01-01T23:59:59.000Z

334

Reverberation mapping and the disk wind model of the broad line region  

E-Print Network (OSTI)

Using the disk wind model of Murray et al. (1995), we calculate line profiles and frequency-resolved response functions for broad line emission from the surface of an accretion disk in an AGN in the presence of a radiatively driven wind. We find that the combined effects of the shears in the wind and in the disk itself produce anisotropic line emission which solves several well-known problems connected with disk models of the broad line region. In particular, the broadening of resonance lines such as \\Civ, \\Lya, and \\Nv\\/ can be attributed to orbital motion of the disk gas at radii as close as \\sim 10^{16}~cm in Seyferts without requiring unrealistically large emission regions in order to produce single-peaked profiles. Furthermore, the anisotropy of the line emission results in frequency-dependent response functions which are no longer red-blue symmetric so that the time delays inferred for the various red and blue components of the line agree qualitatively with recent reverberation mapping observations of N...

Chiang, J

1995-01-01T23:59:59.000Z

335

SURFACE LAYER ACCRETION IN CONVENTIONAL AND TRANSITIONAL DISKS DRIVEN BY FAR-ULTRAVIOLET IONIZATION  

Science Conference Proceedings (OSTI)

Whether protoplanetary disks accrete at observationally significant rates by the magnetorotational instability (MRI) depends on how well ionized they are. Disk surface layers ionized by stellar X-rays are susceptible to charge neutralization by small condensates, ranging from {approx}0.01 {mu}m sized grains to angstrom-sized polycyclic aromatic hydrocarbons (PAHs). Ion densities in X-ray-irradiated surfaces are so low that ambipolar diffusion weakens the MRI. Here we show that ionization by stellar far-ultraviolet (FUV) radiation enables full-blown MRI turbulence in disk surface layers. Far-UV ionization of atomic carbon and sulfur produces a plasma so dense that it is immune to ion recombination on grains and PAHs. The FUV-ionized layer, of thickness 0.01-0.1 g cm{sup -2}, behaves in the ideal magnetohydrodynamic limit and can accrete at observationally significant rates at radii {approx}> 1-10 AU. Surface layer accretion driven by FUV ionization can reproduce the trend of increasing accretion rate with increasing hole size seen in transitional disks. At radii {approx}<1-10 AU, FUV-ionized surface layers cannot sustain the accretion rates generated at larger distance, and unless turbulent mixing of plasma can thicken the MRI-active layer, an additional means of transport is needed. In the case of transitional disks, it could be provided by planets.

Perez-Becker, Daniel [Department of Physics, University of California, Berkeley, CA 94720 (United States); Chiang, Eugene [Departments of Astronomy and Earth and Planetary Science, University of California, Berkeley, CA 94720 (United States)

2011-07-01T23:59:59.000Z

336

On the Virialization of Disk Winds: Implications for the Black Hole Mass Estimates in AGN  

E-Print Network (OSTI)

[abbreviated] Estimating the mass of a supermassive black hole (SMBH) in an active galactic nucleus (AGN) usually relies on the assumption that the broad line region (BLR) is virialized. However, this assumption seems invalid in BLR models that consists of an accretion disk and its wind. The disk is likely Keplerian and therefore virialized. However, the wind material must, beyond a certain point, be dominated by an outward force that is stronger than gravity. Here, we analyze hydrodynamic simulations of four different disk winds: an isothermal wind, a thermal wind from an X-ray heated disk, and two line-driven winds, one with and the other without X-ray heating and cooling. For each model, we check whether gravity governs the flow properties, by computing and analyzing the volume-integrated quantities that appear in the virial theorem: internal, kinetic, and gravitational energies, We find that in the first two models, the winds are non-virialized whereas the two line-driven disk winds are virialized up to a...

Kashi, Amit; Nagamine, Kentaro; Greene, Jenny; Barth, Aaron J

2013-01-01T23:59:59.000Z

337

UNCOVERING DRIVERS OF DISK ASSEMBLY: BULGELESS GALAXIES AND THE STELLAR MASS TULLY-FISHER RELATION  

SciTech Connect

In order to determine what processes govern the assembly history of galaxies with rotating disks, we examine the stellar mass Tully-Fisher (TF) relation over a wide range in redshift partitioned according to whether or not galaxies contain a prominent bulge. Using our earlier Keck spectroscopic sample, for which bulge/total parameters are available from analyses of Hubble Space Telescope images, we find that bulgeless disk galaxies with z > 0.8 present a significant offset from the local (TF) relation whereas, at all redshifts probed, those with significant bulges fall along the local relation. Our results support the suggestion that bulge growth may somehow expedite the maturing of disk galaxies onto the (TF) relation. We discuss a variety of physical hypotheses that may explain this result in the context of kinematic observations of star-forming galaxies at redshifts z = 0 and z > 2.

Miller, Sarah H.; Sullivan, Mark [Department of Physics (Astrophysics), University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom); Ellis, Richard S., E-mail: smiller@astro.caltech.edu [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)

2013-01-01T23:59:59.000Z

338

A RESOLVED MILLIMETER EMISSION BELT IN THE AU Mic DEBRIS DISK  

SciTech Connect

We present imaging observations at 1.3 mm of the debris disk surrounding the nearby M-type flare star AU Mic with beam size 3'' (30 AU) from the Submillimeter Array. These data reveal a belt of thermal dust emission surrounding the star with the same edge-on geometry as the more extended scattered light disk detected at optical wavelengths. Simple modeling indicates a central radius of {approx}35 AU for the emission belt. This location is consistent with the reservoir of planetesimals previously invoked to explain the shape of the scattered light surface brightness profile through size-dependent dust dynamics. The identification of this belt further strengthens the kinship between the debris disks around AU Mic and its more massive sister star {beta} Pic, members of the same {approx}10 Myr old moving group.

Wilner, David J.; Andrews, Sean M.; MacGregor, Meredith A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Meredith Hughes, A. [Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720 (United States)

2012-04-20T23:59:59.000Z

339

Using Solid State Disk Array as a Cache for LHC ATLAS Data Analysis  

E-Print Network (OSTI)

User data analysis in high energy physics presents a challenge to spinning-disk based storage systems. The analysis is data intense, yet reads are small, sparse and cover a large volume of data files. It is also unpredictable due to users' response to storage performance. We describe here a system with an array of Solid State Disk as a non-conventional, standalone file level cache in front of the spinning disk storage to help improve the performance of LHC ATLAS user analysis at SLAC. The system uses a long period of data access records to make caching decisions. It can also use information from other sources such as a work-flow management system. We evaluate the performance of the system both in terms of caching and its impact on user analysis jobs. The system currently uses Xrootd technology, but the technique can be applied to any storage system.

Yang, W; The ATLAS collaboration; Mount, R

2013-01-01T23:59:59.000Z

340

Thermal-Instability-Driven Turbulent Mixing in Galactic Disks: I. Effective Mixing of Metals  

E-Print Network (OSTI)

Observations show that radial metallicity gradients in disk galaxies are relatively shallow, if not flat, especially at large galactocentric distances and for galaxies in the high-redshift universe. Given that star formation and metal production are centrally concentrated, this requires a mechanism to redistribute metals. However, the nature of this mechanism is poorly understood, let alone quantified. To address this problem, we conduct magnetohydrodynamical simulations of a local shearing sheet of a thin, thermally unstable, gaseous disk driven by a background stellar spiral potential, including metals modeled as passive scalar fields. Contrary to what a simple \\alpha\\ prescription for the gas disk would suggest, we find that turbulence driven by thermal instability is very efficient at mixing metals, regardless of the presence or absence of stellar spiral potentials or magnetic fields. The timescale for homogenizing randomly distributed metals is comparable to or less than the local orbital time in the dis...

Yang, Chao-Chin

2012-01-01T23:59:59.000Z

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341

The effect of heat conduction on the interaction of disk and corona around black holes  

E-Print Network (OSTI)

Heat conduction plays an important role in the balance between heating and cooling in many astrophysical objects, e.g. cooling flows in clusters of galaxies. Here we investigate the effect of heat conduction on the interaction between a cool disk and a hot corona around black holes. Using the one-radial-zone approximation, we study the vertical structure of the disk corona and derive evaporation and coronal mass flow rates for various reduced thermal conductivities. We find lower evaporation rates and a shift in the evaporation maxima to smaller radii. This implies that the spectral state transition occurs at a lower mass flow rate and a disk truncation closer to the black hole. Reductions of thermal conductivity are thought to be magnetically caused and might vary from object to object by a different configuration of the magnetic fields.

E. Meyer-Hofmeister; F. Meyer

2005-12-21T23:59:59.000Z

342

Brake System Modeling and Control  

E-Print Network (OSTI)

of 3447 kPa Upper Left: Volts vs. Angular Position, showingone cycle. Lower Right: Volts vs. Position at several brakewith a magnitude of several volts. The INA118, a precision

Hedrick, J. K.; Uchanski, M.

2001-01-01T23:59:59.000Z

343

Mechanical and Hydraulic Press Brakes  

Science Conference Proceedings (OSTI)

...drives, with mechanical linkages from motor to flywheel to clutch to gears to crankshaft to crank arm to ram (Fig. 4). They all have one thing in common: a crankshaft action that converts rotary motion into straight, reciprocating motion (Fig. 5). During a stroke cycle, the crank arm drives the ram down...

344

SPARSE APERTURE MASKING OBSERVATIONS OF THE FL Cha PRE-TRANSITIONAL DISK  

Science Conference Proceedings (OSTI)

We present deep Sparse Aperture Masking (SAM) observations obtained with the ESO Very Large Telescope of the pre-transitional disk object FL Cha (SpT = K8, d = 160 pc), the disk of which is known to have a wide optically thin gap separating optically thick inner and outer disk components. We find non-zero closure phases, indicating a significant flux asymmetry in the K{sub S} -band emission (e.g., a departure from a single point source detection). We also present radiative transfer modeling of the spectral energy distribution of the FL Cha system and find that the gap extends from 0.06{sup +0.05}{sub -0.01} AU to 8.3 {+-} 1.3 AU. We demonstrate that the non-zero closure phases can be explained almost equally well by starlight scattered off the inner edge of the outer disk or by a (sub)stellar companion. Single-epoch, single-wavelength SAM observations of transitional disks with large cavities that could become resolved should thus be interpreted with caution, taking the disk and its properties into consideration. In the context of a binary model, the signal is most consistent with a high-contrast ({Delta}K{sub S} {approx} 4.8 mag) source at a {approx}40 mas (6 AU) projected separation. However, the flux ratio and separation parameters remain highly degenerate and a much brighter source ({Delta}K{sub S} {approx} 1 mag) at 15 mas (2.4 AU) can also reproduce the signal. Second-epoch, multi-wavelength observations are needed to establish the nature of the SAM detection in FL Cha.

Cieza, Lucas A.; Mathews, Geoffrey S.; Kraus, Adam L. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Lacour, Sylvestre [LESIA, CNRS/UMR-8109, Observatoire de Paris, UPMC, Universite Paris Diderot, 5 place Jules Janssen, F-92195, Meudon (France); Schreiber, Matthias R.; Canovas, Hector [Departamento de Fisica y Astronomia, Universidad de Valparaiso, Valparaiso (Chile); Casassus, Simon; Jordan, Andres; Menard, Francois [Millenium Nucleus 'Protoplanetary Disks in ALMA Early Science', Universidad de Chile, Casilla 36-D, Santiago (Chile); Perez, Sebastian [Departamento de Astronomia, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago (Chile); Tuthill, Peter [School of Physics, University of Sydney, NSW 2006 (Australia); Ireland, Michael J., E-mail: lcieza@ifa.hawaii.edu [Department of Physics and Astronomy, Macquarie University, NSW 2109 (Australia)

2013-01-01T23:59:59.000Z

345

Ultraviolet Spectra of CV Accretion Disks with Non-Steady T(r) Laws  

E-Print Network (OSTI)

An extensive grid of synthetic mid- and far-ultraviolet spectra for accretion disks in cataclysmic variables has been presented by Wade and Hubeny (1998). In those models, the disk was assumed to be in steady-state, that is T_eff(r) is specified completely by the mass M_WD and radius R_WD of the accreting white dwarf star and the mass transfer rate M_dot which is constant throughout the disk. In these models, T_eff(r) is proportional to r^{-3/4} except as modified by a cutoff term near the white dwarf. Actual disks may vary from the steady-state prescription for T_eff(r), however, e.g. owing to outburst cycles in dwarf novae M_dot not constant with radius) or irradiation (in which case T_eff in the outer disk is raised above T_steady). To show how the spectra of such disks might differ from the steady case, we present a study of the ultraviolet (UV) spectra of models in which power-law temperature profiles T_eff(r) is proportional to r^{-gamma} with gamma grid, to allow comparison. We discuss both the UV spectral energy distributions and the appearance of the UV line spectra. We also briefly discuss the eclipse light curves of the non-standard models. Comparison of these models with UV observations of novalike variables suggests that better agreement may be possible with such modified T_eff(r) profiles.

Jerome A. Orosz; Richard A. Wade

2003-05-20T23:59:59.000Z

346

An Unbiased Survey of 500 Nearby Stars for Debris Disks: A JCMT Legacy Program  

E-Print Network (OSTI)

We present the scientific motivation and observing plan for an upcoming detection survey for debris disks using the James Clerk Maxwell Telescope. The SCUBA-2 Unbiased Nearby Stars (SUNS) Survey will observe 500 nearby main sequence and sub-giant stars (100 of each of the A, F, G, K and M spectral classes) to the 850 micron extragalactic confusion limit to search for evidence of submillimeter excess, an indication of circumstellar material. The survey distance boundaries are 8.6, 16.5, 22, 25 and 45 pc for M, K, G, F and A stars, respectively, and all targets lie between the declinations of -40 deg to 80 deg. In this survey, no star will be rejected based on its inherent properties: binarity, presence of planetary companions, spectral type or age. This will be the first unbiased survey for debris disks since IRAS. We expect to detect ~125 debris disks, including ~50 cold disks not detectable in current shorter wavelength surveys. A substantial amount of complementary data will be required to constrain the temperatures and masses of discovered disks. High resolution studies will likely be required to resolve many of the disks. Therefore, these systems will be the focus of future observational studies using a variety of observatories to characterize their physical properties. For non-detected systems, this survey will set constraints (upper limits) on the amount of circumstellar dust, of typically 200 times the Kuiper Belt mass, but as low as 10 times the Kuiper Belt mass for the nearest stars in the sample (approximately 2 pc).

B. C. Matthews; J. S. Greaves; W. S. Holland; M. C. Wyatt; M. J. Barlow; P. Bastien; C. A. Beichman; A. Biggs; H. M. Butner; W. R. F. Dent; J. Di Francesco; C. Dominik; L. Fissel; P. Friberg; A. G. Gibb; M. Halpern; R. J. Ivison; R. Jayawardhana; T. Jenness; D. Johnstone; JJ Kavelaars; J. L. Marshall; N. Phillips; G. Schieven; I. A. G. Snellen; H. J. Walker; D. Ward-Thompson; B. Weferling; G. J. White; J. Yates; M. Zhu

2007-07-03T23:59:59.000Z

347

Generalized Langevin equation description of the stochastic oscillations of general relativistic disks  

E-Print Network (OSTI)

We consider a description of the stochastic oscillations of the general relativistic accretion disks around compact astrophysical objects based on the generalized Langevin equation, which accounts for the general retarded effects of the frictional force, and on the fluctuation-dissipation theorems. The vertical displacements, velocities and luminosities of the stochastically perturbed disks are explicitly obtained for both the Schwarzschild and the Kerr cases. The Power Spectral Distribution of the luminosity it is also obtained, and it is shown that it has non-standard values. The theoretical predictions of the model are compared with the observational data for the luminosity time variation of the BL Lac S5 0716+714 object.

Leung, Chun Sing; Harko, Tiberiu

2013-01-01T23:59:59.000Z

348

Maximal spin and energy conversion efficiency in a symbiotic system of black hole, disk and jet  

E-Print Network (OSTI)

We study the mass and spin evolution in a symbiotic system consisting of a black hole with magnetosphere and jets, surrounded by a steady-state, thin accretion disk. We analyze how the limiting value of the spin parameter and the conversion efficiency of accreted mass into radiation depend on the interplay of electromagnetic radiation reaction, magnetosphere characteristics and jet cross-section. As a main result, we find that the presence of the jets increases the spin limit (basically obstructing the reverse effect of radiation in the innermost region of the accretion disk) and enhances the energy conversion efficiency.

Kovács, Zoltán; Biermann, Peter L

2010-01-01T23:59:59.000Z

349

MASS TRANSFER TO ROTATING DISKS AND ROTATING RINGS IN LAMINAR, TRANSITION, AND FULLY DEVELOPED TURBULENT FLOW  

SciTech Connect

Experimental data and theoretical calculations are presented for the mass-transfer rate to rotating disks and rotating rings when laminar, transition, and fully developed turbulent flow exist upon different portions of the surface. Good agreement of data and the model is obtained for rotating disks and relatively thick rotating rings. Results of the calculations for thin rings generally exceed the experimental data measured in transition and turbulent flow. A y{sup +{sup 3}} form for the eddy diffusivity is used to fit the data. No improvement is noticed with a form involving both y{sup +{sup 3}} and y{sup +{sup 3}}.

Law Jr., C.G.; Pierini, P.; Newman, J.

1980-07-01T23:59:59.000Z

350

OBSERVATIONAL PROPERTIES OF THE METAL-POOR THICK DISK OF THE MILKY WAY AND INSIGHTS INTO ITS ORIGINS  

SciTech Connect

We have undertaken the study of the elemental abundances and kinematic properties of a metal-poor sample of candidate thick-disk stars selected from the Radial Velocity Experiment spectroscopic survey of bright stars to differentiate among the present scenarios of the formation of the thick disk. In this paper, we report on a sample of 214 red giant branch, 31 red clump/horizontal branch, and 74 main-sequence/sub-giant branch metal-poor stars, which serves to augment our previous sample of only giant stars. We find that the thick disk [{alpha}/Fe] ratios are enhanced and have little variation (<0.1 dex), in agreement with our previous study. The augmented sample further allows, for the first time, investigation of the gradients in the metal-poor thick disk. For stars with [Fe/H] < -1.2, the thick disk shows very small gradients, <0.03 {+-} 0.02 dex kpc{sup -1}, in {alpha}-enhancement, while we find a +0.01 {+-} 0.04 dex kpc{sup -1} radial gradient and a -0.09 {+-} 0.05 dex kpc{sup -1} vertical gradient in iron abundance. In addition, we show that the peak of the distribution of orbital eccentricities for our sample agrees better with models in which the stars that comprise the thick disk were formed primarily in the Galaxy, with direct accretion of stars contributing little. Our results thus disfavor direct accretion of stars from dwarf galaxies into the thick disk as a major contributor to the thick-disk population, but cannot discriminate between alternative models for the thick disk, such as those that invoke high-redshift (gas-rich) mergers, heating of a pre-existing thin stellar disk by a minor merger, or efficient radial migration of stars.

Ruchti, Gregory R.; Fulbright, Jon P.; Wyse, Rosemary F. G. [Bloomberg Center for Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Gilmore, Gerard F. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Bienayme, Olivier; Siebert, Arnaud [Observatoire de Strasbourg, 11 Rue de L'Universite, 67000 Strasbourg (France); Bland-Hawthorn, Joss [Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW 2006 (Australia); Gibson, Brad K. [Jeremiah Horrocks Institute for Astrophysics and Super-computing, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Grebel, Eva K. [Astronomisches Rechen-Institut, Zentrum fuer Astronomie der Universitaet Heidelberg, Moenchhofstr. 12-14, 69120 Heidelberg (Germany); Helmi, Amina [Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands); Munari, Ulisse [INAF Osservatorio Astronomico di Padova, Via dell'Osservatorio 8, Asiago I-36012 (Italy); Navarro, Julio F. [Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Station CSC, Victoria, BC V8W 3P6 (Canada); Parker, Quentin A.; Reid, Warren [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Seabroke, George M. [Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking RH5 6NT (United Kingdom); Siviero, Alessandro [Department of Astronomy, Padova University, Vicolo dell'Osservatorio 2, Padova 35122 (Italy); Steinmetz, Matthias; Williams, Mary [Leibniz-Institut fuer Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam (Germany); Watson, Fred G. [Australian Astronomical Observatory, Coonabarabran, NSW 2357 (Australia); Zwitter, Tomaz, E-mail: gruchti@mpa-garching.mpg.de [Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, Ljubljana (Slovenia)

2011-08-10T23:59:59.000Z

351

DRPM: Dynamic Speed Control for Power Management in Server Class Disks Sudhanva Gurumurthi  

E-Print Network (OSTI)

[5] that power densities of data centers could grow to over 100 Watts per square foot and that the ca between disk requests may not be long enough to outweigh the overheads. This pa- per presents a new interest because of the cost of power delivery, cost of cooling the system components, and the impact

Sivasubramaniam, Anand

352

Massive black hole pairs in clumpy, self-gravitating circumnuclear disks: stochastic orbital decay  

E-Print Network (OSTI)

We study the dynamics of massive black hole pairs in clumpy gaseous circumnuclear disks. We track the orbital decay of the light, secondary black hole M_{\\bullet2} orbiting around the more massive primary at the center of the disk, using N-body/SPH simulations. We find that the gravitational interaction of M_{\\bullet2} with massive clumps M_cl erratically perturbs the otherwise smooth orbital decay. In close encounters with massive clumps, gravitational slingshots can kick the secondary black hole out of the disk plane. The black hole moving on an inclined orbit then experiences the weaker dynamical friction of the stellar background, resulting in a longer orbital decay timescale. Interactions between clumps can also favor orbital decay when the black hole is captured by a massive clump which is segregating toward the center of the disk. The stochastic behavior of the black hole orbit emerges mainly when the ratio M_{\\bullet2}/M_cl falls below unity, with decay timescales ranging from ~1 to ~50 Myr. This sugg...

Colpi, Monica

2013-01-01T23:59:59.000Z

353

The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks II. Extended Simulations with Varied Cooling Rates  

E-Print Network (OSTI)

In order to investigate mass transport and planet formation by gravitational instabilities (GIs), we have extended our 3-D hydrodynamic simulations of protoplanetary disks from a previous paper. Our goal is to determine the asymptotic behavior of GIs and how it is affected by different constant cooling times. Initially, Rdisk = 40 AU, Mdisk = 0.07 Mo, M* = 0.5 Mo, and Qmin = 1.8. Sustained cooling, with tcool = 2 orps (outer rotation periods, 1 orp ~ 250 yrs), drives the disk to instability in ~ 4 orps. This calculation is followed for 23.5 orps. After 12 orps, the disk settles into a quasi-steady state with sustained nonlinear instabilities, an average Q = 1.44 over the outer disk, a well-defined power-law Sigma(r), and a roughly steady Mdot ~ 5(-7) Mo/yr. The transport is driven by global low-order spiral modes. We restart the calculation at 11.2 orps with tcool = 1 and 1/4 orp. The latter case is also run at high azimuthal resolution. We find that shorter cooling times lead to increased Mdots, denser and t...

Mejia, A C; Pickett, M K; Cai, K; Mejia, Annie C.; Durisen, Richard H.; Pickett, Megan K.; Cai, Kai

2003-01-01T23:59:59.000Z

354

Slim Disks with Transition Regions and Applications to Microquasars and Narrow Line Seyfert 1 Galaxies  

E-Print Network (OSTI)

Slim disks have been received much attention because of the increasing evidence for the super-critical accreting objects. In this paper, we make an attempt to construct a unified model, in which the viscosity and the dimensionless accretion rate can span rather wide ranges. We replace blackbody radiation under diffusion approximation with a bridged formula, which accounts for both blackbody radiation and thermal bremsstrahlung in optically-thick and -thin cases, respectively. Thus this allows us to investigate the structures of and the emergent spectra from slim disks in a wider parameter space, covering transition regions from optically thick to optically thin. We show that there is a maximum transition radius, roughly $R_{\\rm tr, max}/R_g\\sim 50$ when $\\dot{M}/\\dot{M}_{\\rm C}\\sim 15$. The emergent spectra from the unified model of the accretion disk have been calculated. A simple model of hot corona above the slim disk is taken into account for the hard X-ray spectrum in this paper based on Wang & Netzer (2003). We have applied the present model to the microquasar GRS 1915+105, narrow line Seyfert 1 galaxies RE J1034+396 and Akn 564. Our model can explain well the broadband X-ray spectra of narrow line Seyfert 1 galaxies, microquasars and possible ultra-luminous compact X-ray sources. The present model can be widely applied to the candidates of super-critical accreting objects.

Lin-Hong Chen; Jian-Min Wang

2004-07-07T23:59:59.000Z

355

Modelling and analysis of multi-stage systems of mistuned bladed disks  

Science Conference Proceedings (OSTI)

A stochastic reduced-order modelling technique for multi-stage mistuned bladed disks assemblies is proposed. In a perturbation framework, the base-line reduced-order model is built using multi-stage cyclic symmetry modelling approach. Uncertainties are ... Keywords: Cyclic symmetry, Mistuning, Multi-stage, Reduce-order models, Uncertainties

Denis Laxalde; Christophe Pierre

2011-02-01T23:59:59.000Z

356

February 16, 2010 The dark matter halo shape of edge-on disk galaxies  

E-Print Network (OSTI)

the velocity dispersion of the HI gas (preferably as a function of height from the central plane of the disk, gas and halo potentials, tot = h + s + g. Assuming that the gas velocity dispersion Fig. 5. Rotation of the gas velocity dispersion and the vertical FWHM thickness of the gas, both functions of radius which we

Kruit, Piet van der

357

O and Na abundance patterns in open clusters of the Galactic disk  

E-Print Network (OSTI)

Aims. A global O-Na abundance anti-correlation is observed in globular clusters, which is not present in the Galactic field population. Open clusters are thought to be chemically homogeneous internally. We aim to explore the O and Na abundance pattern among the open cluster population of the Galactic disk. Methods. We combine open cluster abundance ratios of O and Na from high-resolution spectroscopic studies in the literature and normalize them to a common solar scale. We compare the open cluster abundances against the globular clusters and disk field. Results. We find that the different environments show different abundance patterns. The open clusters do not show the O-Na anti-correlation at the extreme O-depletion / Na-enhancement as observed in globular clusters. Furthermore, the high Na abundances in open clusters do not match the disk field stars. If real, it may be suggesting that the dissolution of present-day open clusters is not a significant contribution to building the Galactic disk. Large-scale h...

De Silva, G M; Lattanzio, J; Asplund, M; 10.1051/0004-6361/200912279

2009-01-01T23:59:59.000Z

358

Protoplanetary disk fragmentation with varying radiative physics, initial conditions and numerical techniques  

E-Print Network (OSTI)

We review recent results of SPH simulations of gravitational instability in gaseous protoplanetary disks,emphasizing the role of thermodynamics in both isolated and binary systems. Contradictory results appeared in the literature regarding disk fragmentation at tens of AU from the central star are likely due to the different treatment of radiation physics as well as reflecting different initial conditions. Further progress on the subject requires extensive comparisons between different codes with the requirement that the same initial conditions are adopted. It is discussed how the local conditions of the disks undergoing fragmentation at $R report that radically different adaptive hydrodynamical codes, SPH and adaptive mesh refinement (AMR), yield very similar results on disk fragmentation at comparable resolution in the simple case of an isothermal equation of state. A high number of refinements in AMR codes is necessary but not sufficient to correctly follow fragmentation, rather an initial resolution of the grid high enough to capture the wavelength of the strongest spiral modes when they are still barely nonlinear is essential. These tests represent a useful benchmark and a starting point for a forthcoming code comparison with realistic radiation physics.

Lucio Mayer; Artur Gawryszczak

2007-10-19T23:59:59.000Z

359

Can gas in young debris disks be constrained by their radial brightness profiles?  

E-Print Network (OSTI)

Disks around young stars are known to evolve from optically thick, gas-dominated protoplanetary disks to optically thin, almost gas-free debris disks. It is thought that the primordial gas is largely removed at ages of ~10 Myr, but it is difficult to discern the true gas densities from gas observations. This suggests using observations of dust: it has been argued that gas, if present with higher densities, would lead to flatter radial profiles of the dust density and surface brightness than those actually observed. However, here we show that these profiles are surprisingly insensitive to variation of the parameters of a central star, location of the dust-producing planetesimal belt, dustiness of the disk and - most importantly - the parameters of the ambient gas. This result holds for a wide range of gas densities (three orders of magnitude), for different radial distributions of the gas temperature, and different gas compositions. The brightness profile slopes of -3...-4 we find are the same that were theore...

Krivov, Alexander V; Brandeker, Alexis; Thébault, Philippe

2009-01-01T23:59:59.000Z

360

Migration and growth of giant planets in self-gravitating disks with varied thermodynamics  

E-Print Network (OSTI)

We report on the results of novel global high-resolution three-dimensional simulations of disk-planet interaction which incorporate simultaneously realistic radiation physics and the self-gravity of the gas, as well as allowing the planet to move. We find that thermodynamics and radiative physics have a remarkable effect on both migration and accretion of Jupiter mass planets. In simulations with radiative transfer adopting flux-limited diffusion, inward migration can be decreased by about 30% relative to the isothermal case, while in adiabatic runs migration nearly shuts off after a few tens of orbits. Migration varies because the relative strength of the inner and outer spiral perturbations is affected by thermodynamics, thus changing the net torque acting on the planet. Mass accretion rates on the planet can be reduced by more than an order of magnitude going from isothermal to radiative transfer and adiabatic simulations. A circumplanetary disk always forms except in adiabatic runs. With radiative transfer the disk is sub-keplerian (Vrot/Vkep ~ 0.7) owing to significant pressure support. We discuss the effect of circumplanetary disk structure on the drift of embedded dust grains and planetesimals and thus on the formation of the rocky satellites of giant planets.

Laure Fouchet; Lucio Mayer

2008-06-25T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
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361

A fast iterative solver for the variable coefficient diffusion equation on a disk  

Science Conference Proceedings (OSTI)

We present an efficient iterative method for solving the variable coefficient diffusion equation on a unit disk. The equation is written in polar coordinates and is discretized by the standard centered difference approximation under the grid arrangement ... Keywords: Ginzburg-Landau vortices, iterative method, polar coordinates, variable diffusion equation

Ming-Chih Lai; Yu-Hou Tseng

2005-09-01T23:59:59.000Z

362

[3] Fred Douglis and Brian Marsh. Low power disk management for mobile computers. Technical  

E-Print Network (OSTI)

. In Pro­ ceedings ACM SIGMOD, 1994. [6] Ravi Jain and John Werth. Airdisks and air­ raid, November 1996. [5] T. Imielinski, S. Viswanathan, , and B.R. Badri­ nath. Energy efficient indexing on air 1996. [11] Stanley Zdonik, Michael Franklin, Rafael Alonso, and Swarup Acharya. Are ``Disks in the Air

California at Berkeley, University of

363

[3] Fred Douglis and Brian Marsh. Low power disk management for mobile computers. Technical  

E-Print Network (OSTI)

. In Pro- ceedings ACM SIGMOD, 1994. [6] Ravi Jain and John Werth. Airdisks and air- raid, November 1996. [5] T. Imielinski, S. Viswanathan, , and B.R. Badri- nath. Energy efficient indexing on air 1996. [11] Stanley Zdonik, Michael Franklin, Rafael Alonso, and Swarup Acharya. Are "Disks in the Air

Han, Richard Y.

364

Protoplanetary Disk Turbulence Driven by the Streaming Instability: Linear Evolution and Numerical Methods  

E-Print Network (OSTI)

We present local simulations that verify the linear streaming instability that arises from aerodynamic coupling between solids and gas in protoplanetary disks. This robust instability creates enhancements in the particle density in order to tap the free energy of the relative drift between solids and gas, generated by the radial pressure gradient of the disk. We confirm the analytic growth rates found by Youdin & Goodman (2005) using grid hydrodynamics to simulate the gas and, alternatively, particle and grid representations of the solids. Since the analytic derivation approximates particles as a fluid, this work corroborates the streaming instability when solids are treated as particles. The idealized physical conditions -- axisymmetry, uniform particle size, and the neglect of vertical stratification and collisions -- provide a rigorous, well-defined test of any numerical algorithm for coupled particle-gas dynamics in protoplanetary disks. We describe a numerical particle-mesh implementation of the drag force, which is crucial for resolving the coupled oscillations. Finally we comment on the balance of energy and angular momentum in two-component disks with frictional coupling. A companion paper details the non-linear evolution of the streaming instability into saturated turbulence with dense particle clumps.

Andrew Youdin; Anders Johansen

2007-02-23T23:59:59.000Z

365

To Appear in Astron. Nachr. Suppl. Issue 1/2003 A Relativistic Disk in Sagittarius A*  

E-Print Network (OSTI)

The detection of a mm/Sub-mm “bump ” in Sgr A*’s radio spectrum suggests that at least a portion of its overall emission is produced within a compact accretion disk. This inference is strengthened by observations of strong linear polarization (at the 10 percent level) within this bump. No linear polarization has been detected yet at other wavelengths. Given that radiation from this source is produced on progressively smaller spatial scales with increasing frequency, the mm/Sub-mm bump apparently arises within a mere handful of Schwarzschild radii of the black hole. We have found that a small (10-Schwarzschild-radii) magnetized accretion disk can not only account for the spectral bump via thermal synchrotron processes, but that it can also reproduce the corresponding polarimetric results. In addition, the quiescent X-ray emission appears to be associated with synchrotron self-Comptonization, while X-ray flares detected from Sgr A * may be induced by a sudden enhancement of accretion through this disk. The hardening of the flare-state X-ray spectrum appears to favor thermal bremsstrahlung as the dominant X-ray emission mechanism during the transient event. This picture predicts correlations among the mm, IR, and X-ray flux densities, that appear to be consistent with recent multi-wavelength observations. Further evidence for such a disk in Sgr A*

Siming Liu; Fulvio Melia

2003-01-01T23:59:59.000Z

366

PROTOSTELLAR DISK EVOLUTION OVER MILLION-YEAR TIMESCALES WITH A PRESCRIPTION FOR MAGNETIZED TURBULENCE  

SciTech Connect

Magnetorotational instability (MRI) is the most promising mechanism behind accretion in low-mass protostellar disks. Here we present the first analysis of the global structure and evolution of non-ideal MRI-driven T-Tauri disks on million-year timescales. We accomplish this in a 1+1D simulation by calculating magnetic diffusivities and utilizing turbulence activity criteria to determine thermal structure and accretion rate without resorting to a three-dimensional magnetohydrodynamical (MHD) simulation. Our major findings are as follows. First, even for modest surface densities of just a few times the minimum-mass solar nebula, the dead zone encompasses the giant planet-forming region, preserving any compositional gradients. Second, the surface density of the active layer is nearly constant in time at roughly 10 g cm{sup -2}, which we use to derive a simple prescription for viscous heating in MRI-active disks for those who wish to avoid detailed MHD computations. Furthermore, unlike a standard disk with constant-{alpha} viscosity, the disk midplane does not cool off over time, though the surface cools as the star evolves along the Hayashi track. Instead, the MRI may pile material in the dead zone, causing it to heat up over time. The ice line is firmly in the terrestrial planet-forming region throughout disk evolution and can move either inward or outward with time, depending on whether pileups form near the star. Finally, steady-state mass transport is an extremely poor description of flow through an MRI-active disk, as we see both the turnaround in the accretion flow required by conservation of angular momentum and peaks in M-dot (R) bracketing each side of the dead zone. We caution that MRI activity is sensitive to many parameters, including stellar X-ray flux, grain size, gas/small grain mass ratio and magnetic field strength, and we have not performed an exhaustive parameter study here. Our 1+1D model also does not include azimuthal information, which prevents us from modeling the effects of Rossby waves.

Landry, Russell [Physics Department, University of Texas at Dallas, Richardson, TX 75080 (United States); Dodson-Robinson, Sarah E. [Astronomy Department, University of Texas at Austin, Austin, TX 78712 (United States); Turner, Neal J. [Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA 91109 (United States); Abram, Greg, E-mail: russell.landry@gmail.com [Texas Advanced Computing Center, University of Texas at Austin, Austin, TX 78758 (United States)

2013-07-10T23:59:59.000Z

367

PLANET-PLANET SCATTERING IN PLANETESIMAL DISKS. II. PREDICTIONS FOR OUTER EXTRASOLAR PLANETARY SYSTEMS  

SciTech Connect

We develop an idealized dynamical model to predict the typical properties of outer extrasolar planetary systems, at radii comparable to the Jupiter-to-Neptune region of the solar system. The model is based upon the hypothesis that dynamical evolution in outer planetary systems is controlled by a combination of planet-planet scattering and planetary interactions with an exterior disk of small bodies ('planetesimals'). Our results are based on 5000 long duration N-body simulations that follow the evolution of three planets from a few to 10 AU, together with a planetesimal disk containing 50 M{sub +} from 10 to 20 AU. For large planet masses (M {approx}> M{sub Sat}), the model recovers the observed eccentricity distribution of extrasolar planets. For lower-mass planets, the range of outcomes in models with disks is far greater than that which is seen in isolated planet-planet scattering. Common outcomes include strong scattering among massive planets, sudden jumps in eccentricity due to resonance crossings driven by divergent migration, and re-circularization of scattered low-mass planets in the outer disk. We present the distributions of the eccentricity and inclination that result, and discuss how they vary with planet mass and initial system architecture. In agreement with other studies, we find that the currently observed eccentricity distribution (derived primarily from planets at a {approx}< 3 AU) is consistent with isolated planet-planet scattering. We explain the observed mass dependence-which is in the opposite sense from that predicted by the simplest scattering models-as a consequence of strong correlations between planet masses in the same system. At somewhat larger radii, initial planetary mass correlations and disk effects can yield similar modest changes to the eccentricity distribution. Nonetheless, strong damping of eccentricity for low-mass planets at large radii appears to be a secure signature of the dynamical influence of disks. Radial velocity measurements capable of detecting planets with K {approx} 5 m s{sup -1} and periods in excess of 10 years will provide constraints on this regime. Finally, we present an analysis of the predicted separation of planets in two-planet systems, and of the population of planets in mean-motion resonances (MMRs). We show that, if there are systems with {approx} Jupiter-mass planets that avoid close encounters, the planetesimal disk acts as a damping mechanism and populates MMRs at a very high rate (50%-80%). In many cases, resonant chains (in particular the 4:2:1 Laplace resonance) are set up among all three planets. We expect such resonant chains to be common among massive planets in outer planetary systems.

Raymond, Sean N. [Universite de Bordeaux, Observatoire Aquitain des Sciences de l'Univers, 2 rue de l'Observatoire, BP 89, F-33271 Floirac Cedex (France); Armitage, Philip J. [JILA, University of Colorado, Boulder, CO 80309 (United States); Gorelick, Noel, E-mail: pja@jilau1.colorado.ed [Google, Inc., 1600 Amphitheatre Parkway, Mountain View, CA 94043 (United States)

2010-03-10T23:59:59.000Z

368

CONFIRMING THE PRIMARILY SMOOTH STRUCTURE OF THE VEGA DEBRIS DISK AT MILLIMETER WAVELENGTHS  

SciTech Connect

Clumpy structure in the debris disk around Vega has been previously reported at millimeter wavelengths and attributed to concentrations of dust grains trapped in resonances with an unseen planet. However, recent imaging at similar wavelengths with higher sensitivity has disputed the observed structure. We present three new millimeter-wavelength observations that help to resolve the puzzling and contradictory observations. We have observed the Vega system with the Submillimeter Array (SMA) at a wavelength of 880 {mu}m and an angular resolution of 5''; with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at a wavelength of 1.3 mm and an angular resolution of 5''; and with the Green Bank Telescope (GBT) at a wavelength of 3.3 mm and angular resolution of 10''. Despite high sensitivity and short baselines, we do not detect the Vega debris disk in either of the interferometric data sets (SMA and CARMA), which should be sensitive at high significance to clumpy structure based on previously reported observations. We obtain a marginal (3{sigma}) detection of disk emission in the GBT data; the spatial distribution of the emission is not well constrained. We analyze the observations in the context of several different models, demonstrating that the observations are consistent with a smooth, broad, axisymmetric disk with inner radius 20-100 AU and width {approx}> 50 AU. The interferometric data require that at least half of the 860 {mu}m emission detected by previous single-dish observations with the James Clerk Maxwell Telescope be distributed axisymmetrically, ruling out strong contributions from flux concentrations on spatial scales of {approx}<100 AU. These observations support recent results from the Plateau de Bure Interferometer indicating that previous detections of clumpy structure in the Vega debris disk were spurious.

Hughes, A. Meredith; Plambeck, Richard; Chiang, Eugene [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Wilner, David J.; Andrews, Sean M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Mason, Brian [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States); Carpenter, John M. [California Institute of Technology, Department of Astronomy, MC 105-24, Pasadena, CA 91125 (United States); Chiang, Hsin-Fang [Institute for Astronomy, University of Hawaii, 640 North Aohoku Place, Hilo, HI 96720 (United States); Williams, Jonathan P. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Hales, Antonio [Joint ALMA Observatory, Av. El Golf 40, Piso 18, Santiago (Chile); Su, Kate [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Dicker, Simon; Korngut, Phil; Devlin, Mark, E-mail: mhughes@astro.berkeley.edu [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States)

2012-05-01T23:59:59.000Z

369

SURFACE LAYER ACCRETION IN TRANSITIONAL AND CONVENTIONAL DISKS: FROM POLYCYCLIC AROMATIC HYDROCARBONS TO PLANETS  

SciTech Connect

'Transitional' T Tauri disks have optically thin holes with radii {approx}>10 AU, yet accrete up to the median T Tauri rate. Multiple planets inside the hole can torque the gas to high radial speeds over large distances, reducing the local surface density while maintaining accretion. Thus multi-planet systems, together with reductions in disk opacity due to grain growth, can explain how holes can be simultaneously transparent and accreting. There remains the problem of how outer disk gas diffuses into the hole. Here it has been proposed that the magnetorotational instability (MRI) erodes disk surface layers ionized by stellar X-rays. In contrast to previous work, we find that the extent to which surface layers are MRI-active is limited not by ohmic dissipation but by ambipolar diffusion, the latter measured by Am: the number of times a neutral hydrogen molecule collides with ions in a dynamical time. Simulations by Hawley and Stone showed that Am {approx} 100 is necessary for ions to drive MRI turbulence in neutral gas. We calculate that in X-ray-irradiated surface layers, Am typically varies from {approx}10{sup -3} to 1, depending on the abundance of charge-adsorbing polycyclic aromatic hydrocarbons, whose properties we infer from Spitzer observations. We conclude that ionization of H{sub 2} by X-rays and cosmic rays can sustain, at most, only weak MRI turbulence in surface layers 1-10 g cm{sup -2} thick, and that accretion rates in such layers are too small compared to observed accretion rates for the majority of disks.

Perez-Becker, Daniel [Department of Physics, University of California, Berkeley, CA 94720 (United States); Chiang, Eugene, E-mail: perez-becker@berkeley.edu [Departments of Astronomy and Earth and Planetary Science, University of California, Berkeley, CA 94720 (United States)

2011-01-20T23:59:59.000Z

370

Constraints for the accretion disk evaporation rate in AGN from the existence of the Broad Line Region  

E-Print Network (OSTI)

We analyze the consequences of the hypothesis that the formation of the Broad Line Region is intrinsically connected with the existence of the cold accretion disk. We assume that the Broad Line Region radius is well estimated by the formula of Kaspi et al. (2000). We consider three models of the disappearance of the inner disk which limit the existence of the Broad Line Region: (i) classical ADAF approach, i.e. the inner hot flow develops whenever it can exist (ii) disk evaporation model of Meyer & Meyer-Hofmeister (2002) (iii) generalized disk evaporation model of Rozanska & Czerny (2000b). For each of the models, we determine the minimum value of the Eddington ratio and the maximum value of the broad line widths as functions of the viscosity parameter alpha and the magnetic field parameter beta. We compare the predicted parameter space with observations of several AGN. Weak dependence of the maximum value of the FWHM and minimum value of the Eddington ratio on the black hole mass in our sample is noticeable. It seems to favor the description of the cold disk/hot inner flow transition as in the classical ADAF approach than with the model of disk evaporation due to conduction between the disk and accreting corona.

B. Czerny; A. Rozanska; J. Kuraszkiewicz

2004-03-21T23:59:59.000Z

371

On the temperature profile of radiatively efficient geometrically thin disks in black hole binaries with the ASCA GIS  

E-Print Network (OSTI)

X-ray spectra of black hole binaries(BHBs) in the high/soft state were studied comprehensively by using ASCA GIS data, and partially RXTE PCA data. A mathematical disk model was applied to several BHBs to see if the observed accretion disk temperature profile was consistent with that expected from the standard accretion disk model. This model is called p-free disk, and assumes that the spectrum is composed of multi-temperature blackbody emission of which the local temperature T(r) at radius r is given by T(r) ~ r^-p with p being a positive free parameter. The standard disk roughly requires p~3/4, while a small deviation is expected depending on the inner boundary conditions, general relativistic effects and disk vertical structures.Our sample objects included LMC X-1, LMC X-3, XTE J2012+381, and GRO J1655-40. During the ASCA observations, these BHBs showed characteristics of the standard high/soft state. Under the standard modeling of high-state black hole binaries, the sources show Tin=0.76-1.17keV, the disk...

Kubota, A; Makishima, K; Nakazawa, K; Kubota, Aya; Ebisawa, Ken; Makishima, Kazuo; Nakazawa, Kazuhiro

2005-01-01T23:59:59.000Z

372

THE RISE AND FALL OF PASSIVE DISK GALAXIES: MORPHOLOGICAL EVOLUTION ALONG THE RED SEQUENCE REVEALED BY COSMOS  

Science Conference Proceedings (OSTI)

The increasing abundance of passive 'red-sequence' galaxies since z {approx} 1-2 is mirrored by a coincident rise in the number of galaxies with spheroidal morphologies. In this paper, however, we show in detail, that, the correspondence between galaxy morphology and color is not perfect, providing insight into the physical origin of this evolution. Using the COSMOS survey, we study a significant population of red-sequence galaxies with disk-like morphologies. These passive disks typically have Sa-Sb morphological types with large bulges, but they are not confined to dense environments. They represent nearly one-half of all red-sequence galaxies and dominate at lower masses ({approx}passive disks with M {sub *} {approx}passive disk population has declined since z {approx} 1, likely because they transform into spheroidals. Based on these trends, we estimate that as much as 60% of galaxies transitioning onto the red sequence evolve through a passive disk phase. The origin of passive disks therefore has broad implications for our understanding of how star formation shuts down. Because passive disks tend to be more bulge-dominated than their star-forming counterparts, a simple fading of blue disks does not fully explain their origin. We explore the strengths and weaknesses of several more sophisticated explanations, including environmental effects, internal stabilization, and disk regrowth during gas-rich mergers. While previous work has sought to explain color and morphological transformations with a single process, these observations open the way to new insight by highlighting the fact that galaxy evolution may actually proceed through several separate stages.

Bundy, Kevin; Hopkins, Philip; Ma, Chung-Pei [Astronomy Department, University of California, Berkeley, CA 94705 (United States); Scarlata, Claudia; Capak, Peter [Spitzer Science Center, California Institute of Technology, 314-6, Pasadena, CA 91125 (United States); Carollo, C. M.; Oesch, Pascal [Institute for Astronomy, ETH Zurich, 8092 Zurich (Switzerland); Ellis, Richard S.; Salvato, Mara; Scoville, Nick [Astronomy Department, California Institute of Technology, Pasadena, CA 91125 (United States); Drory, Niv [Max-Planck Institut fur extraterrestrische Physik, Giessenbachstrashe, 85748 Garching (Germany); Leauthaud, Alexie [Physics Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States); Koekemoer, Anton M. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Murray, Norman [Canadian Institute for Theoretical Astrophysics, 60 St George Street, University of Toronto, ON M5S 3H8 (Canada); Ilbert, Olivier [Laboratoire d'Astrophysique de Marseille, BP 8, Traverse du Siphon, 13376 Marseille Cedex 12 (France); Pozzetti, Lucia [Osservatorio Astronomico di Bologna, Via Ranzani, 1, I-40127 Bologna (Italy)

2010-08-20T23:59:59.000Z

373

On the temperature profile of radiatively efficient geometrically thin disks in black hole binaries with the ASCA GIS  

E-Print Network (OSTI)

X-ray spectra of black hole binaries(BHBs) in the high/soft state were studied comprehensively by using ASCA GIS data, and partially RXTE PCA data. A mathematical disk model was applied to several BHBs to see if the observed accretion disk temperature profile was consistent with that expected from the standard accretion disk model. This model is called p-free disk, and assumes that the spectrum is composed of multi-temperature blackbody emission of which the local temperature T(r) at radius r is given by T(r) ~ r^-p with p being a positive free parameter. The standard disk roughly requires p~3/4, while a small deviation is expected depending on the inner boundary conditions, general relativistic effects and disk vertical structures.Our sample objects included LMC X-1, LMC X-3, XTE J2012+381, and GRO J1655-40. During the ASCA observations, these BHBs showed characteristics of the standard high/soft state. Under the standard modeling of high-state black hole binaries, the sources show Tin=0.76-1.17keV, the disk fraction to the total 0.7-10keV flux of 54-98%, and Nh=(0.7--12)E21/cm^2. The best-fit p-values were found in 0.6-0.8, and the standard value of p=3/4 was accepted for all the sources.The obtained p-values are also compared with those expected for the standard accretion disk in the Schwarzschild metric, and they were consistent with those expected from the standard accretion disk.

Aya Kubota; Ken Ebisawa; Kazuo Makishima; Kazuhiro Nakazawa

2005-05-17T23:59:59.000Z

374

Switching a magnetic vortex by interlayer coupling in epitaxially grown Co/Cu/Py/Cu(001) trilayer disks  

SciTech Connect

Epitaxial Py/Cu/Co/Cu(001) trilayers were patterned into micron sized disks and imaged using element-specific photoemission electron microscopy. By varying the Cu spacer layer thickness, we study how the coupling between the two magnetic layers influences the formation of magnetic vortex states. We find that while the Py and Co disks form magnetic vortex domains when the interlayer coupling is ferromagnetic, the magnetic vortex domains of the Py and Co disks break into anti-parallel aligned multidomains when the interlayer coupling is antiferromagnetic. We explain this result in terms of magnetic flux closure between the Py and Co layers for the antiferromagnetic coupling case.

Wu, J.; Carlton, D.; Oelker, E.; Park, J. S.; Jin, E.; Arenholz, E.; Scholl, A.; Hwang, C.; Bokor, J.; Qiu, Z Q

2010-07-16T23:59:59.000Z

375

Gas Dynamics in the LINER Galaxy NGC 5005: Episodic Fueling of a Nuclear Disk  

E-Print Network (OSTI)

We report high-resolution CO(1-0) observations in the central 6 kpc of the LINER galaxy NGC 5005 with the Owens Valley Radio Observatory millimeter array. Molecular gas is distributed in three components - a ring at a radius of about 3 kpc, a strong central condensation, and a stream to the northwest of the nucleus but inside the 3 kpc ring. The central condensation is a disk of about 1 kpc radius with a molecular gas mass of 2 x 10^9 M_sun. The stream between the 3 kpc ring and the nuclear disk lies on a straight dust lane seen in the optical. If this material moves in the plane of the galaxy, it has a velocity offset by up to ~ 150 km/s from galactic rotation. We suggest that an optically inconspicuous stellar bar lying within the 3 kpc ring can explain the observed gas dynamics. This bar is expected to connect the nuclear disk and the ring along the position angle of the northwest stream. A position-velocity cut in this direction reveals features which match the characteristic motions of gas in a barred potential. Our model indicates that gas in the northwest stream is on an x_1 orbit at the bar's leading edge; it is falling into the nucleus with a large noncircular velocity, and will eventually contribute about 2 x 10^8 M_sun to the nuclear disk. If most of this material merges with the disk on its first passage of pericenter, the gas accretion rate during the collision will be 50 M_sun/yr. We associate the nuclear disk with an inner 2:1 Lindblad resonance, and the 3 kpc ring with an inner 4:1 Lindblad resonance. The high rate of bar-driven inflow and the irregular appearance of the northwest stream suggest that a major fueling event is in progress in NGC 5005. Such episodic (rather than continuous) gas supply can regulate the triggering of starburst and accretion activity in galactic nuclei. (abridged)

Kazushi Sakamoto; Andrew J. Baker; Nick Z. Scoville

1999-10-01T23:59:59.000Z

376

A Debris Disk around the Central Star of the Helix Nebula?  

E-Print Network (OSTI)

Excess emission from a point-like source coincident with the central star of the Helix Nebula is detected with Spitzer at 8, 24, and 70 um. At 24 um, the central source is superposed on an extended diffuse emission region. While the [OIV] 25.89 um line contributes to the diffuse emission, a 10-35 um spectrum of the central source shows a strong thermal continuum. The excess emission from the star most likely originates from a dust disk with blackbody temperatures of 90--130 K. Assuming a simple optically thin debris disk model, the dust is distributed in a ring between ~35 and ~150 AU from the central star, possibly arising from collisions of Kuiper-Belt-like Objects or the break-up of comets from an Oort-like cloud that have survived from the post-main-sequence evolution of the central star.

Kate Y. L. Su; Y. -H. Chu; G. H. Rieke; P. J. Huggins; R. Gruendl; R. Napiwotzki; T. Rauch; W. B. Latter; K. Volk

2007-02-11T23:59:59.000Z

377

Excess Infrared Radiation from a Massive DAZ White Dwarf: GD362 - a Debris Disk?  

E-Print Network (OSTI)

We report the discovery of excess K-band radiation from a massive DAZ white dwarf star, GD362. Combining infrared photometric and 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 debris disk. This would be only the second such system known, discovered 18 years after G29-38, the only single white dwarf currently known to be orbited by circumstellar dust. Both of these systems favor a model with accretion from a surrounding debris disk to explain the metal abundances observed in DAZ white dwarfs. Nevertheless, observations of more DAZs in the mid-infrared are required to test if this model can explain all DAZs.

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

2005-09-07T23:59:59.000Z

378

A Free Energy Landscape for Cage Breaking of Three Hard Disks  

E-Print Network (OSTI)

We investigate cage breaking in dense hard disk systems using a model of three Brownian disks confined within a circular corral. This system has a six-dimensional configuration space, but can be equivalently thought to explore a symmetric one-dimensional free energy landscape containing two energy minima separated by an energy barrier. The exact free energy landscape can be calculated as a function of system size. Results of simulations show the average time between cage breaking events follows an Arrhenius scaling when the energy barrier is large. We also discuss some of the consequences of using a one-dimensional representation to understand dynamics in a multi-dimensional space, such as diffusion acquiring spatial dependence and discontinuities in spatial derivatives of free energy.

Gary L. Hunter; Eric R. Weeks

2011-12-21T23:59:59.000Z

379

HOW DO MOST PLANETS FORM?-CONSTRAINTS ON DISK INSTABILITY FROM DIRECT IMAGING  

Science Conference Proceedings (OSTI)

Core accretion and disk instability have traditionally been regarded as the two competing possible paths of planet formation. In recent years, evidence has accumulated in favor of core accretion as the dominant mode, at least for close-in planets. However, it might be hypothesized that a significant population of wide planets formed by disk instabilities could exist at large separations, forming an invisible majority. In previous work, we addressed this issue through a direct imaging survey of B2-A0-type stars and concluded that rates and find that the conclusions hold even if the companions move substantially after formation. Hence, core accretion remains the likely dominant formation mechanism for the total planet population, for every type of star from M-type through B-type.

Janson, Markus [Department of Astrophysics, Princeton University, Peyton Hall, 4 lvy Lane, Princeton, NJ 08544 (United States); Bonavita, Mariangela [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George St, Toronto, ON M5S 3H8 (Canada); Klahr, Hubert [Max Planck Institute for Astronomy, Konigstuhl 17, Heidelberg 69117 (Germany); Lafreniere, David, E-mail: janson@astro.princeton.edu [Department of Physics, University of Montreal, C.P. 6128, Succursale Centre-Ville, Montreal, QC H3C 3J7 (Canada)

2012-01-20T23:59:59.000Z

380

Twistors, Holomorphic Disks, and Riemann Surfaces with Boundary, e-print math.DG/0508038  

E-Print Network (OSTI)

Moduli spaces of holomorphic disks in a complex manifold Z, with boundaries constrained to lie in a maximal totally real submanifold P, have recently been found to underlie a number of geometrically rich twistor correspondences. The purpose of this paper is to develop a general Fredholm regularity criterion for holomorphic curves-withboundary (?,??) ? (Z,P), and then show how this applies, in particular, to various moduli problems of twistor-theoretic interest. 1

Claude Lebrun

2005-01-01T23:59:59.000Z

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381

The Thermal Regulation of Gravitational Instabilities in Protoplanetary Disks II. Extended Simulations with Varied Cooling Rates  

E-Print Network (OSTI)

In order to investigate mass transport and planet formation by gravitational instabilities (GIs), we have extended our 3-D hydrodynamic simulations of protoplanetary disks from a previous paper. Our goal is to determine the asymptotic behavior of GIs and how it is affected by different constant cooling times. Initially, Rdisk = 40 AU, Mdisk = 0.07 Mo, M* = 0.5 Mo, and Qmin = 1.8. Sustained cooling, with tcool = 2 orps (outer rotation periods, 1 orp ~ 250 yrs), drives the disk to instability in ~ 4 orps. This calculation is followed for 23.5 orps. After 12 orps, the disk settles into a quasi-steady state with sustained nonlinear instabilities, an average Q = 1.44 over the outer disk, a well-defined power-law Sigma(r), and a roughly steady Mdot ~ 5(-7) Mo/yr. The transport is driven by global low-order spiral modes. We restart the calculation at 11.2 orps with tcool = 1 and 1/4 orp. The latter case is also run at high azimuthal resolution. We find that shorter cooling times lead to increased Mdots, denser and thinner spiral structures, and more violent dynamic behavior. The asymptotic total internal energy and the azimuthally averaged Q(r) are insensitive to tcool. Fragmentation occurs only in the high-resolution tcool = 1/4 orp case; however, none of the fragments survive for even a quarter of an orbit. Ring-like density enhancements appear and grow near the boundary between GI active and inactive regions. We discuss the possible implications of these rings for gas giant planet formation.

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

2004-07-01T23:59:59.000Z

382

The Scattered Disk as the source of the Jupiter Family comets  

E-Print Network (OSTI)

The short period Jupiter family comets (JFCs) are thought to originate in the Kuiper Belt; specifically, a dynamical subclass of the Kuiper Belt known as the `scattered disk' is argued to be the dominant source of JFCs. However, the best estimates from observational surveys indicate that this source may fall short by more than two orders of magnitude the estimates obtained from theoretical models of the dynamical evolution of Kuiper belt objects into JFCs. We re-examine the scattered disk as a source of the JFCs and make a rigorous estimate of the discrepancy. We find that the uncertainties in the dynamical models combined with a change in the size distribution function of the scattered disk at faint magnitudes (small sizes) beyond the current observational limit offer a possible but problematic resolution to the discrepancy. We discuss several other possibilities: that the present population of JFCs is a large fluctuation above their long term average, that larger scattered disk objects tidally break-up into multiple fragments during close planetary encounters as their orbits evolve from the trans-Neptune zone to near Jupiter, or that there are alternative source populations that contribute significantly to the JFCs. Well-characterized observational investigations of the Centaurs, objects that are transitioning between the trans-Neptune Kuiper belt region and the inner solar system, can test the predictions of the non-steady state and the tidal break-up hypotheses. The classical and resonant classes of the Kuiper belt are worth re-consideration as significant additional or alternate sources of the JFCs.

Kathryn Volk; Renu Malhotra

2008-02-26T23:59:59.000Z

383

SPITZER 24 {mu}m SURVEY FOR DUST DISKS AROUND HOT WHITE DWARFS  

Science Conference Proceedings (OSTI)

Two types of dust disks around white dwarfs (WDs) have been reported: small dust disks around cool metal-rich WDs consisting of tidally disrupted asteroids and a large dust disk around the hot central WD of the Helix planetary nebula (PN) possibly produced by collisions among Kuiper-Belt-like objects. To search for more dust disks of the latter type, we have conducted a Spitzer MIPS 24 {mu}m survey of 71 hot WDs or pre-WDs, among which 35 are central stars of PNe (CSPNs). Nine of these evolved stars are detected and their 24 {mu}m flux densities are at least two orders of magnitude higher than their expected photospheric emission. Considering the bias against the detection of distant objects, the 24 {mu}m detection rate for the sample is {approx}>15%. It is striking that seven, or {approx}20%, of the WD and pre-WDs in known PNe exhibit 24 {mu}m excesses, while two, or 5%-6%, of the WDs not in PNe show 24 {mu}m excesses and they have the lowest 24 {mu}m flux densities. We have obtained follow-up Spitzer Infrared Spectrograph spectra for five objects. Four show clear continuum emission at 24 {mu}m, and one is overwhelmed by a bright neighboring star but still shows a hint of continuum emission. In the cases of WD 0950+139 and CSPN K 1-22, a late-type companion is present, making it difficult to determine whether the excess 24 {mu}m emission is associated with the WD or its red companion. High-resolution images in the mid-infrared are needed to establish unambiguously the stars responsible for the 24 {mu}m excesses.

Chu, You-Hua; Bilikova, Jana; Gruendl, Robert A. [Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Su, Kate Y. L. [Stewart Observatory, University of Arizona, Tucson, AZ 85721 (United States); De Marco, Orsola [Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109 (Australia); Guerrero, Martin A. [Instituto de Astrofisica de Andalucia, CSIC, E-18008 Granada (Spain); Updike, Adria C. [CRESST and the Observational Cosmology Laboratory, NASA/GSFC, Greenbelt, MD 20771 (United States); Volk, Kevin [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Rauch, Thomas, E-mail: yhchu@illinois.edu [Institut fuer Astronomie und Astrophysik Tuebingen (IAAT), Abteilung Astronomie, D-72076 Tuebingen (Germany)

2011-09-15T23:59:59.000Z

384

Manganese trends in a sample of thin and thick disk stars. The origin of Mn  

E-Print Network (OSTI)

CONTEXT: Manganese is an iron-peak element and although the nucleosynthesis path that leads to its formation is fairly well understood, it remains unclear which objects, SN II and/or SN Ia, that contribute the majority of Mn to the interstellar medium. It also remains unclear to which extent the supernovae Mn yields depend on the metallicity of the progenitor star or not. AIMS: By using a well studied and well defined sample of 95 dwarf stars we aim at further constraining the formation site(s) of Mn. METHODS: We derive Mn abundances through spectral synthesis of four Mn I lines at 539.4, 549.2, 601.3, and 601.6 nm. Stellar parameters and data for oxygen are taken from Bensby et al. (2003, 2004, 2005). RESULTS: When comparing our Mn abundances with O abundances for the same stars we find that the abundance trends in the stars with kinematics of the thick disk can be explained by metallicity dependent yields from SN II. We go on and combine our data for dwarf stars in the disks with data for dwarf and giant stars in the metal-poor thick disk and halo from the literature. We find that dwarf and giant stars show the same trends, which indicates that neither non-LTE nor evolutionary effects are a major concern for Mn. Furthermore, the [Mn/O] vs [O/H] trend in the halo is flat. CONCLUSIONS: We conclude that the simplest interpretation of our data is that Mn is most likely produced in SN II and that the Mn yields for such SNae must be metallicity dependent. Contribution from SN Ia in the metal-rich thin disk can not, however, be excluded.

S. Feltzing; M. Fohlman; T. Bensby

2007-03-19T23:59:59.000Z

385

CONVERGENCE STUDIES OF MASS TRANSPORT IN DISKS WITH GRAVITATIONAL INSTABILITIES. I. THE CONSTANT COOLING TIME CASE  

Science Conference Proceedings (OSTI)

We conduct a convergence study of a protostellar disk, subject to a constant global cooling time and susceptible to gravitational instabilities (GIs), at a time when heating and cooling are roughly balanced. Our goal is to determine the gravitational torques produced by GIs, the level to which transport can be represented by a simple {alpha}-disk formulation, and to examine fragmentation criteria. Four simulations are conducted, identical except for the number of azimuthal computational grid points used. A Fourier decomposition of non-axisymmetric density structures in cos (m{phi}), sin (m{phi}) is performed to evaluate the amplitudes A{sub m} of these structures. The A{sub m} , gravitational torques, and the effective Shakura and Sunyaev {alpha} arising from gravitational stresses are determined for each resolution. We find nonzero A{sub m} for all m-values and that A{sub m} summed over all m is essentially independent of resolution. Because the number of measurable m-values is limited to half the number of azimuthal grid points, higher-resolution simulations have a larger fraction of their total amplitude in higher-order structures. These structures act more locally than lower-order structures. Therefore, as the resolution increases the total gravitational stress decreases as well, leading higher-resolution simulations to experience weaker average gravitational torques than lower-resolution simulations. The effective {alpha} also depends upon the magnitude of the stresses, thus {alpha}{sub eff} also decreases with increasing resolution. Our converged {alpha}{sub eff} is consistent with predictions from an analytic local theory for thin disks by Gammie, but only over many dynamic times when averaged over a substantial volume of the disk.

Michael, Scott; Steiman-Cameron, Thomas Y.; Durisen, Richard H. [Astronomy Department, Indiana University, Bloomington, IN 47405 (United States); Boley, Aaron C., E-mail: scamicha@astro.indiana.edu, E-mail: tomsc@astro.indiana.edu, E-mail: durisen@astro.indiana.edu, E-mail: aaron.boley@gmail.com [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)

2012-02-10T23:59:59.000Z

386

Gravitational Runaway and Turbulence Driving in Star-Gas Galactic Disks  

E-Print Network (OSTI)

Galactic disks consist of both stars and gas. The gas is more dynamically responsive than the stars, and strongly nonlinear structures and velocities can develop in the ISM even while stellar surface density perturbations remain fractionally small. We use 2D numerical simulations to explore formation of bound clouds and turbulence generation in the gas of two-component galactic disks. We represent the stars with collisionless particles and follow their orbits using a PM method, and treat the gas as an isothermal, unmagnetized fluid. The two components interact through a combined gravity. Using stellar parameters typical of mid-disk conditions, we find that models with gaseous Toomre parameter Q_g gas-only models, indicating that the destabilizing effect of live stars is offsets the reduced self-gravity of thick disks. This result is also consistent with empirical studies showing that star formation is suppressed when Q_g > 1-2. The bound gaseous clouds that form have mass 6x10^7 Msun each; these represent superclouds that would subsequently fragment into GMCs. Self-gravity and sheared rotation also interact to drive turbulence in the gas when Q_g > Q_c. This turbulence is anisotropic, with more power in sheared than compressive motions. The gaseous velocity dispersion is ~ 0.6 times the thermal speed when Q_g ~ Q_c. This suggests that gravity is important in driving ISM turbulence in many spiral galaxies, since the low efficiency of star formation naturally leads to a state of marginal instability.

Woong-Tae Kim; Eve C. Ostriker

2007-01-26T23:59:59.000Z

387

Identification of the Spawning, Rearing, and Migratory Requirements of Fall Chinook Salmon in the Columbia River Basin, 1991 Annual Progress Report.  

DOE Green Energy (OSTI)

This document is the 1991 annual progress report for selected studies of fall chinook salmon Oncorhynchus tshawytscha conducted by the US Fish and Wildlife Service. The decline in abundance of fall chinook salmon in the Snake River basin has become a growing concern. In April 1992, Snake River fall chinook salmon were listed as ``threatened`` under the Endangered Species Act. Effective recovery efforts for fall chinook salmon can not 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.

1993-07-01T23:59:59.000Z

388

Occultation of the T Tauri Star RW Aurigae A by its Tidally Disrupted Disk  

E-Print Network (OSTI)

RW Aur A is a classical T Tauri star, believed to have undergone a reconfiguration of its circumstellar environment as a consequence of a recent fly-by of its stellar companion, RW Aur B. This interaction stripped away part of the circumstellar disk of RW Aur A, leaving a tidally disrupted arm and a short truncated circumstellar disk. We present photometric observations of the RW Aur system from the Kilodegree Extremely Little Telescope (KELT) survey showing a long and deep dimming that occurred from September 2010 until March 2011. The dimming has a depth of ~2 magnitudes, a duration of ~180 days and was confirmed by archival observations from American Association of Variable Star Observers (AAVSO). We suggest that this event is the result of a portion of the tidally disrupted disk occulting RW Aur A, specifically a fragment of the tidally disrupted arm. The calculated transverse linear velocity of the occulter is in excellent agreement with the measured relative radial velocity of the tidally disrupted arm....

Rodriguez, Joseph E; Stassun, Keivan G; Siverd, Robert J; Cargile, Phillip; Beatty, Thomas G; Gaudi, B Scott

2013-01-01T23:59:59.000Z

389

FREE-FREE EMISSION AND RADIO RECOMBINATION LINES FROM PHOTOEVAPORATING DISKS  

SciTech Connect

Recent infrared observations have demonstrated that photoevaporation driven by high-energy photons from the central star contributes to the dispersal of protoplanetary disks. Here, we show that photoevaporative winds should produce a detectable free-free continuum emission given the range of stellar ionizing photons and X-ray luminosities inferred for young Sun-like stars. We point out that Very Large Array observations of the nearby disk around TW Hya might have already detected this emission at centimeter wavelengths and calculate the wind electron density and mass flow rate. We also estimate the intensities of H radio recombination lines tracing the wind and discuss which ones could be detected with current instrumentation. The detection and profiles of these recombination lines would unambiguously prove our inference of free-free emission from photoevaporating disks like TW Hya. In addition, radio/millimeter data can help constraining wind parameters such as temperature and electron density that are fundamental in measuring mass flow rates.

Pascucci, I. [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Gorti, U.; Hollenbach, D., E-mail: pascucci@lpl.arizona.edu [SETI Institute, 189 Bernardo Ave., Mountain View, CA 94043 (United States)

2012-06-01T23:59:59.000Z

390

PHOTOELECTRIC CROSS-SECTIONS OF GAS AND DUST IN PROTOPLANETARY DISKS  

SciTech Connect

We provide simple polynomial fits to the X-ray photoelectric cross-sections (0.03 keV < E < 10 keV) for mixtures of gas and dust found in protoplanetary disks. Using the solar elemental abundances of Asplund et al., we treat the gas and dust components separately, facilitating the further exploration of evolutionary processes such as grain settling and gain growth. We find that blanketing due to advanced grain growth (a{sub max} > 1 {mu}m) can reduce the X-ray opacity of dust appreciably at E{sub X} {approx} 1 keV, coincident with the peak of typical T Tauri X-ray spectra. However, the reduction of dust opacity by dust settling, which is known to occur in protoplanetary disks, is probably a more significant effect. The absorption of 1-10 keV X-rays is dominated by gas opacity once the dust abundance has been reduced to about 1% of its diffuse interstellar value. The gas disk establishes a floor to the opacity at which point X-ray transport becomes insensitive to further dust evolution. Our choice of fitting function follows that of Morrison and McCammon, providing a degree of backward compatibility.

Bethell, T. J.; Bergin, Edwin A., E-mail: tbethell@umich.edu [Astronomy Department, University of Michigan, Ann Arbor, MI 48109 (United States)

2011-10-10T23:59:59.000Z

391

Probing the Magnetic Field at Sub-Parsec Radii in the Accretion Disk of NGC 4258  

E-Print Network (OSTI)

We present an analysis of polarimetric observations at 22 GHz of the water vapor masers in NGC 4258 obtained with the VLA and the GBT. We do not detect any circular polarization in the spectrum indicative of Zeeman-induced splitting of the maser lines of water, a non-paramagnetic molecule. We have improved the 1-sigma upper limit estimate on the toroidal component of the magnetic field in the circumnuclear disk of NGC 4258 at a radius of 0.2 pc from 300 mG to 90 mG. We have developed a new method for the analysis of spectra with blended features and derive a 1-sigma upper limit of 30 mG on the radial component of the magnetic field at a radius of 0.14 pc. Assuming thermal and magnetic pressure balance, we estimate an upper limit on the mass accretion rate of ~10^(-3.7) M_sun/yr for a total magnetic field of less than 130 mG. We discuss the ramifications of our results on current maser models proposed to explain the observed maser emission structure and the consequences for current accretion theories. We find from our magnetic field limits that the thin-disk model and the jet-disk model are better candidates for accounting for the extremely low-luminosity nature of NGC 4258, than models that include advection-dominated accretion flows.

Maryam Modjaz; James M. Moran; Paul T. Kondratko; Lincoln J. Greenhill

2005-02-11T23:59:59.000Z

392

RESOLVED SUBMILLIMETER OBSERVATIONS OF THE HR 8799 AND HD 107146 DEBRIS DISKS  

Science Conference Proceedings (OSTI)

We present 880 {mu}m Submillimeter Array observations of the debris disks around the young solar analog HD 107146 and the multiple-planet host star HR 8799, at an angular resolution of 3'' and 6'', respectively. We spatially resolve the inner edge of the disk around HR 8799 for the first time. While the data are not sensitive enough (with rms noise of 1 mJy) to constrain the system geometry, we demonstrate that a model by Su et al. based on the spectral energy distribution (SED) with an inner radius of 150 AU predicts the spatially resolved data well. Furthermore, by modeling simultaneously the SED and visibilities, we demonstrate that the dust is distributed in a broad (of order 100 AU) annulus rather than a narrow ring. We also model the observed SED and visibilities for the HD 107146 debris disk and generate a model of the dust emission that extends in a broad band between 50 and 170 AU from the star. We perform an a posteriori comparison with existing 1.3 mm CARMA observations and demonstrate that a smooth, axisymmetric model reproduces all of the available millimeter-wavelength data well.

Hughes, A. Meredith [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Wilner, David J.; Andrews, Sean M.; Murray-Clay, Ruth A.; Qi Chunhua [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Williams, Jonathan P. [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States); Su, Kate Y. L., E-mail: mhughes@astro.berkeley.edu [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

2011-10-10T23:59:59.000Z

393

Resolved Submillimeter Observations of the HR 8799 and HD 107146 Debris Disks  

E-Print Network (OSTI)

We present 880 um Submillimeter Array observations of the debris disks around the young solar analogue HD 107146 and the multiple-planet host star HR 8799, at an angular resolution of 3" and 6", respectively. We spatially resolve the inner edge of the disk around HR 8799 for the first time. While the data are not sensitive enough (with rms noise of 1 mJy) to constrain the system geometry, we demonstrate that a model by Su et al. (2009) based on the spectral energy distribution (SED) with an inner radius of 150 AU predicts well the spatially resolved data. Furthermore, by modeling simultaneously the SED and visibilities, we demonstrate that the dust is distributed in a broad (of order 100 AU) annulus rather than a narrow ring. We also model the observed SED and visibilities for the HD 107146 debris disk and generate a model of the dust emission that extends in a broad band between 50 and 170 AU from the star. We perform an a posteriori comparison with existing 1.3 mm CARMA observations and demonstrate that a s...

Hughes, A Meredith; Andrews, Sean M; Williams, Jonathan P; Su, Kate Y L; Murray-Clay, Ruth A; Qi, Chunhua

2011-01-01T23:59:59.000Z

394

An X-ray Reprocessing Model of Disk Thermal Emission in Type 1 Seyfert Galaxies  

E-Print Network (OSTI)

Using a geometry consisting of a hot central Comptonizing plasma surrounded by a thin accretion disk, we model the optical through hard X-ray spectral energy distributions of the type 1 Seyfert galaxies NGC 3516 and NGC 7469. As in the model proposed by Poutanen, Krolik, & Ryde for the X-ray binary Cygnus X-1 and later applied to Seyfert galaxies by Zdziarski, Lubi\\'nski, & Smith, feedback between the radiation reprocessed by the disk and the thermal Comptonization emission from the hot central plasma plays a pivotal role in determining the X-ray spectrum, and as we show, the optical and ultraviolet spectra as well. Seemingly uncorrelated optical/UV and X-ray light curves, similar to those which have been observed from these objects can be explained by variations in the size, shape, and temperature of the Comptonizing plasma. Furthermore, by positing a disk mass accretion rate which satisfies a condition for global energy balance between the thermal Comptonization luminosity and the power available fr...

Chiang, J

2002-01-01T23:59:59.000Z

395

An X-ray Reprocessing Model of Disk Thermal Emission in Type 1 Seyfert Galaxies  

E-Print Network (OSTI)

Using a geometry consisting of a hot central Comptonizing plasma surrounded by a thin accretion disk, we model the optical through hard X-ray spectral energy distributions of the type 1 Seyfert galaxies NGC 3516 and NGC 7469. As in the model proposed by Poutanen, Krolik, & Ryde for the X-ray binary Cygnus X-1 and later applied to Seyfert galaxies by Zdziarski, Lubi\\'nski, & Smith, feedback between the radiation reprocessed by the disk and the thermal Comptonization emission from the hot central plasma plays a pivotal role in determining the X-ray spectrum, and as we show, the optical and ultraviolet spectra as well. Seemingly uncorrelated optical/UV and X-ray light curves, similar to those which have been observed from these objects can be explained by variations in the size, shape, and temperature of the Comptonizing plasma. Furthermore, by positing a disk mass accretion rate which satisfies a condition for global energy balance between the thermal Comptonization luminosity and the power available from accretion, one can predict the spectral properties of the hard X-ray continuum above $\\sim 50$ keV in type 1 Seyfert galaxies. Forthcoming measurements of the hard X-ray continuum by more sensitive hard X-ray and soft $\\gamma$-ray telescopes, in conjunction with simultaneous optical, UV, and soft X-ray monitoring, will allow the mass accretion rates to be directly constrained for these sources in the context of this model.

James Chiang

2002-02-12T23:59:59.000Z

396

Optimization of disk generator performance for base-load power plant systems applications  

SciTech Connect

Disk generators for use in base-load MHD power plants are examined for both open-cycle and closed-cycle operating modes. The OCD cases are compared with PSPEC results for a linear channel; enthalpy extractions up to 23% with 71% isentropic efficiency are achievable with generator inlet conditions similar to those used in PSPEC, thus confirming that the disk configuration is a viable alternative for base-load power generation. The evaluation of closed-cycle disks includes use of a simplified cycle model. High system efficiencies over a wide range of power levels are obtained for effective Hall coefficients in the range 2.3 to 4.9. Cases with higher turbulence (implying ..beta../sub eff/ less than or equal to 2.4) yield high system efficiencies at power levels of 100 to 500 MW/sub e/. All these CCD cases compare favorably with linear channels reported in the GE ECAS study, yielding higher isentropic efficiences for a given enthalpy extraction. Power densities in the range 70 to 170 MW/m/sup 3/ appear feasible, leading to very compact generator configurations.

Teare, J.D.; Loubsky, W.J.; Lytle, J.K.; Louis, J.F.

1980-01-01T23:59:59.000Z

397

X-ray Light Curves and Accretion Disk Structure of EX Hydrae  

E-Print Network (OSTI)

We present X-ray light curves for the cataclysmic variable EX Hydrae obtained with the Chandra High Energy Transmission Grating Spectrometer and the Extreme Ultraviolet Explorer Deep Survey photometer. We confirm earlier results on the shape and amplitude of the binary light curve and discuss a new feature: the phase of the minimum in the binary light curve, associated with absorption by the bulge on the accretion disk, increases with wavelength. We discuss several scenarios that could account for this trend and conclude that, most likely, the ionization state of the bulge gas is not constant, but rather decreases with binary phase. We also conclude that photoionization of the bulge by radiation originating from the white dwarf is not the main source of ionization, but that it is heated by shocks originating from the interaction between the inflowing material from the companion and the accretion disk. The findings in this paper provide a strong test for accretion disk models in close binary systems.

R. Hoogerwerf; N. S. Brickhouse; C. W. Mauche

2005-04-19T23:59:59.000Z

398

An Iterative Method for the Construction of Equilibrium N-Body Models for Stellar Disks  

E-Print Network (OSTI)

One widely used technique for the construction of equilibrium models of stellar disks is based on the Jeans equations and the moments of velocity distribution functions derived using these equations. Stellar disks constructed using this technique are shown to be "not entirely" in equilibrium. Our attempt to abandon the epicyclic approximation and the approximation of infinite isothermal layers, which are commonly adopted in this technique, failed to improve the situation substantially. We conclude that the main drawback of techniques based on the Jeans equations is that the system of equations employed is not closed, and therefore requires adopting an essentially ad hoc additional closure condition. A new iterative approach to constructing equilibrium N-body models with a given density distribution is proposed. The main idea behind this approach is that a model is first constructed using some approximation method, and is then allowed to adjust to an equilibrium state with the specified density and the required parameters of the velocity distribution remaining fixed in the process. This iterative approach was used to construct isotropic, spherically symmetric models and models of stellar disks embedded in an external potential. The numerical models constructed prove to be close to equilibrium. It is shown that the commonly adopted assumption that the profile of the radial velocity dispersion is exponential may be wrong. The technique proposed can be applied to a wide range of problems involving the construction of models of stellar systems with various geometries.

S. A. Rodionov; N. Ya. Sotnikova

2006-11-06T23:59:59.000Z

399

Evaluation of 1991-1992 Brood Overwinter-Reared Coho Released from Net Pens in Youngs Bay, Oregon : Final Completion Report Youngs Bay Terminal Fishery Project.  

DOE Green Energy (OSTI)

Funding from Bonneville Power Administration was provided to the Oregon Department of Fish and Wildlife and the Clatsop County Economic Development Council`s Fisheries Project to identify and develop terminal fishing opportunities. The 1991 and 1992 brood fingerling coho from Oregon Department of Fish and Wildlife hatcheries were successfully reared during the winter period to smolt stage in Youngs Bay utilizing floating net pens. Based on coded-wire-tag recoveries during 1991--93 from 2-week net-pen acclimation releases, total accountability of coho adults averaged 40,540 fish, with the Youngs Bay commercial harvest accounting for 39%. With reduced ocean harvest impacts during 1994 and 1995, 92% of 51,640 coho in 1994 and 68% of 23,599 coho in 1995 (based on coded-wire-tag recoveries) were accounted for in the Youngs Bay commercial fishery for combined 2-week and overwinter acclimation net-pen releases. Overwinter net-pen acclimation coho accounted for 35,063 and 15,775 coho adults in 1994 and 1995 with 93% and 68% accountable in the Youngs Bay commercial harvest. Based on coded-wire-tag recoveries, less than 1% of the adults resulting from releases at Youngs Bay net pens strayed to hatcheries, while none were recovered on spawning ground surveys during 1991--95. The highest survival rates were observed for 1991 and 1992 brood overwinter coho released in early May. Time of release, not rearing strategy, appears to be the determining factor affecting survival in Youngs Bay.

Hirose, Paul S.

1997-01-01T23:59:59.000Z

400

THE EFFECT OF CORONAL RADIATION ON A RESIDUAL INNER DISK IN THE LOW/HARD SPECTRAL STATE OF BLACK HOLE X-RAY BINARY SYSTEMS  

Science Conference Proceedings (OSTI)

Thermal conduction between a cool accretion disk and a hot inner corona can result in either evaporation of the disk or condensation of the hot corona. At low mass accretion rates, evaporation dominates and can completely remove the inner disk. At higher mass accretion rates, condensation becomes more efficient in the very inner regions, so that part of the mass accretes via a weak (initially formed) inner disk which is separated from the outer disk by a fully evaporated region at mid radii. At still higher mass accretion rates, condensation dominates everywhere, so there is a continuous cool disk extending to the innermost stable circular orbit. We extend these calculations by including the effect of irradiation by the hot corona on the disk structure. The flux which is not reflected is reprocessed in the disk, adding to the intrinsic thermal emission from gravitational energy release. This increases the seed photons for Compton cooling of the hot corona, enhancing condensation of the hot flow, and reinforcing the residual inner disk rather than evaporating it. Our calculations confirm that a residual inner disk can coexist with a hard, coronally dominated spectrum over the range of 0.006< m-dot <0.016 (for {alpha} = 0.2). This provides an explanation for the weak thermal component seen recently in the low/hard state of black hole X-ray binary systems.

Liu, B. F. [National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, P.O. Box 110, Kunming 650011 (China); Done, C. [Department of Physics, University of Durham, South Road, Durham, DH1 3LE (United Kingdom); Taam, Ronald E., E-mail: bfliu@ynao.ac.cn, E-mail: r-taam@northwestern.edu, E-mail: bfliu@nao.cas.cn [Department of Physics and Astronomy, Northwestern University, 2131 Tech Drive, Evanston, IL 60208 (United States)

2011-01-01T23:59:59.000Z

Note: This page contains sample records for the topic "disk brakes rear" from the National Library of EnergyBeta (NLEBeta).
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401

SUSTAINING STAR FORMATION RATES IN SPIRAL GALAXIES: SUPERNOVA-DRIVEN TURBULENT ACCRETION DISK MODELS APPLIED TO THINGS GALAXIES  

Science Conference Proceedings (OSTI)

Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M{sub sun}) {approx}gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.

Vollmer, Bernd [CDS, Observatoire astronomique, UMR 7550, 11 rue de l'universite, 67000 Strasbourg (France); Leroy, Adam K., E-mail: bvollmer@astro.u-strasbg.fr [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)

2011-01-15T23:59:59.000Z

402

EVOLUTION OF SNOW LINE IN OPTICALLY THICK PROTOPLANETARY DISKS: EFFECTS OF WATER ICE OPACITY AND DUST GRAIN SIZE  

SciTech Connect

Evolution of a snow line in an optically thick protoplanetary disk is investigated with numerical simulations. The ice-condensing region in the disk is obtained by calculating the temperature and the density with the 1+1D approach. The snow line migrates as the mass accretion rate ( M-dot ) in the disk decreases with time. Calculations are carried out from an early phase with high disk accretion rates ( M-dot {approx}10{sup -7} M{sub sun} yr{sup -1}) to a later phase with low disk accretion rates ( M-dot {approx}10{sup -12} M{sub sun} yr{sup -1}) using the same numerical method. It is found that the snow line moves inward for M-dot {approx}>10{sup -10} M{sub sun} yr{sup -1}, while it gradually moves outward in the later evolution phase with M-dot {approx}<10{sup -10} M{sub sun} yr{sup -1}. In addition to the silicate opacity, the ice opacity is taken into consideration. In the inward migration phase, the additional ice opacity increases the distance of the snow line from the central star by a factor of 1.3 for dust grains {approx}< 10 {mu}m in size and of 1.6 for {approx}> 100 {mu}m. It is inevitable that the snow line comes inside Earth's orbit in the course of the disk evolution if the viscosity parameter {alpha} is in the range 0.001-0.1, the dust-to-gas mass ratio is higher than a tenth of the solar abundance value, and the dust grains are smaller than 1 mm. The formation of water-devoid planetesimals in the terrestrial planet region seems to be difficult throughout the disk evolution, which imposes a new challenge to planet formation theory.

Oka, Akinori; Nakamoto, Taishi; Ida, Shigeru, E-mail: akinorioka1@gmail.com, E-mail: nakamoto@geo.titech.ac.jp [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo (Japan)

2011-09-10T23:59:59.000Z

403

An extended dust disk in a spiral galaxy; An occulting galaxy pair in ANGST  

E-Print Network (OSTI)

We present an analysis of an occulting galaxy pair, serendipitously discovered in ACS Nearby Galaxy Survey Treasury (ANGST) observations of NGC 253 taken with Hubble Space Telescope's Advanced Camera for Survey in F475W, F606W$ and F814W (SDSS-g, broad V and I). The foreground disk system (at z < 0.06) shows a dusty disk much more extended than the starlight, with spiral lanes seen in extinction out to 1.5 R\\_25, approximately six half-light radii. This pair is the first where extinction can be mapped reliably out to this distance from the center. The spiral arms of the extended dust disk show typical extinction values of A\\_F475W ~ 0.25, A\\_F606W ~ 0.25, and A\\_F814W ~ 0.15. The extinction law inferred from these measures is similar to the local Milky Way one, and we show that the smoothing effects of sampling at limited spatial resolution (<57 pc, in these data) flattens the observed function through mixing of regions with different extinction. This galaxy illustrates the diversity of dust distributions in spirals, and the limitations of adopting a single dust model for optically similar galaxies. The ideal geometry of this pair of overlapping galaxies and the high sampling of HST data make this dataset ideal to analyze this pair with three separate approaches to overlapping galaxies: (A) a combined fit, rotating copies of both galaxies, (B) a simple flip of the background image and (C) an estimate of the original fluxes for the individual galaxies based on reconstructions of their proper isophotes. We conclude that in the case of high quality data such as these, isophotal models are to be preferred.

B. W. Holwerda; W. C. Keel; B. Williams; J. J. Dalcanton; R. S. de Jong

2008-10-15T23:59:59.000Z

404

CHEMICAL COMPOSITIONS OF THIN-DISK, HIGH-METALLICITY RED HORIZONTAL-BRANCH FIELD STARS  

Science Conference Proceedings (OSTI)

We present a detailed abundance analysis and atmospheric parameters of 76 stars from a survey to identify field Galactic red horizontal-branch (RHB) stars. High-resolution echelle spectra (R {approx_equal} 60,000, S/N {>=} 100) were obtained with the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The target stars were selected only by color and parallax information. Overall metallicities and relative abundances of proton-capture elements (C, N, O, Li), {alpha}-elements (Ca and Si), and neutron-capture elements (Eu and La) were determined by either equivalent width or synthetic spectrum analyses. We used CN features at the {lambda}{lambda}7995-8040 region in order to determine the {sup 12}C/{sup 13}C ratios of our targets. Investigation of the evolutionary stages, using spectroscopic T{sub eff} and log g values along with derived {sup 12}C/{sup 13}C ratios, revealed the presence of 18 probable RHB stars in our sample. We also derived kinematics of the stars with available distance information. Taking into account both the kinematics and probable evolutionary stages, we conclude that our sample contains 5 thick-disk and 13 thin-disk RHB stars. Up until now, RHB stars have been considered as members of the thick disk, and were expected to have large space velocities and sub-solar metallicities. However, our sample is dominated by low-velocity solar-metallicity RHB stars; their existence cannot be easily explained with standard stellar evolution.

Afsar, M. [Department of Astronomy and Space Sciences, Ege University, 35100 Bornova, Izmir (Turkey); Sneden, C.; For, B.-Q., E-mail: melike.afsar@ege.edu.tr, E-mail: afsar@astro.as.utexas.edu, E-mail: chris@astro.as.utexas.edu, E-mail: biqing@astro.as.utexas.edu, E-mail: biqing.for@uwa.edu.au [Department of Astronomy and McDonald Observatory, University of Texas, Austin, TX 78712 (United States)

2012-07-15T23:59:59.000Z

405

EVIDENCE FOR A CLUMPY, ROTATING GAS DISK IN A SUBMILLIMETER GALAXY AT z = 4  

SciTech Connect

We present Karl G. Jansky Very Large Array observations of the CO(2-1) emission in the z = 4.05 submillimeter galaxy (SMG) GN20. These high-resolution data allow us to image the molecular gas at 1.3 kpc resolution just 1.6 Gyr after the big bang. The data reveal a clumpy, extended gas reservoir, 14 {+-} 4 kpc in diameter, in unprecedented detail. A dynamical analysis shows that the data are consistent with a rotating disk of total dynamical mass 5.4 {+-} 2.4 Multiplication-Sign 10{sup 11} M {sub Sun }. We use this dynamical mass estimate to constrain the CO-to-H{sub 2} mass conversion factor ({alpha}{sub CO}), finding {alpha}{sub CO} = 1.1 {+-} 0.6 M {sub Sun }(K km s{sup -1} pc{sup 2}){sup -1}. We identify five distinct molecular gas clumps in the disk of GN20 with masses a few percent of the total gas mass, brightness temperatures of 16-31K, and surface densities of >3200-4500 Multiplication-Sign ({alpha}{sub CO}/0.8) M {sub Sun} pc{sup -2}. Virial mass estimates indicate they could be self-gravitating, and we constrain their CO-to-H{sub 2} mass conversion factor to be <0.2-0.7 M {sub Sun }(K km s{sup -1} pc{sup 2}){sup -1}. A multiwavelength comparison demonstrates that the molecular gas is concentrated in a region of the galaxy that is heavily obscured in the rest-frame UV/optical. We investigate the spatially resolved gas excitation and find that the CO(6-5)/CO(2-1) ratio is constant with radius, consistent with star formation occurring over a large portion of the disk. We discuss the implications of our results in the context of different fueling scenarios for SMGs.

Hodge, J. A.; Walter, F. [Max-Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); Carilli, C. L. [National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801-0387 (United States); De Blok, W. J. G. [ASTRON, P.O. Box 2, 7990 AA Dwingeloo (Netherlands); Riechers, D. [Department of Astronomy, California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Daddi, E. [CEA, Laboratoire AIM-CNRS-Universite Paris Diderot, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France); Lentati, L., E-mail: hodge@mpia.de [Astrophysics Group, Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2012-11-20T23:59:59.000Z

406

Detection of steam in the circumstellar disk around a massive Young Stellar Object  

E-Print Network (OSTI)

We report on the observation of hot water vapor (steam) in the inner AU of a young massive star located in the star-forming region IRAS 08576-4334. The water lines are detected in a medium resolution (R=10,000) K-band spectrum taken by the infrared spectrometer ISAAC mounted on the VLT-ANTU. The water vapor is at a mean temperature of 1565+/-510 K, cooler than the hot CO found in the same object, which is at 1660K and the column density is N(H2O)=(2.5 +/- 0.4)x1E18 cm-2. The profile of both H2O and CO lines is best reproduced by the emission from a Keplerian disk. To interpret the data, we also investigate the formation of molecules and especially CO and water vapor in the inner hot and dense part of disks around young high mass stars using a pseudo time-dependent gas-phase chemical model. Molecules are rapidly photodissociated but this destruction is compensated by an efficient formation due to fast neutral-neutral reactions. The ability of CO molecules to self-shield significantly enhances its abundance. Water molecules are sufficiently abundant to be detectable. The observed H2O/CO ratio is reproduced by gas at 1600K and an enhanced UV field over gas density ratio I_UV/nH=1E(-4)- 1E(-6). The simulations support the presence of CO and H2O molecules in the inner disks around young massive stars despite the strong UV radiation and show that the OH radical plays an essential role in hot gas chemistry.

W. -F. Thi; A. Bik

2005-03-24T23:59:59.000Z

407

Formation of Nuclear Disks and Supermassive Black Hole Binaries in Multi-Scale Hydrodynamical Galaxy Mergers  

E-Print Network (OSTI)

(Abridged) We review the results of the first multi-scale, hydrodynamical simulations of mergers between galaxies with central supermassive black holes (SMBHs) to investigate the formation of SMBH binaries in galactic nuclei. We demonstrate that strong gas inflows produce nuclear disks at the centers of merger remnants whose properties depend sensitively on the details of gas thermodynamics. In numerical simulations with parsec-scale spatial resolution in the gas component and an effective equation of state appropriate for a starburst galaxy, we show that a SMBH binary forms very rapidly, less than a million years after the merger of the two galaxies. Binary formation is significantly suppressed in the presence of a strong heating source such as radiative feedback by the accreting SMBHs. We also present preliminary results of numerical simulations with ultra-high spatial resolution of 0.1 pc in the gas component. These simulations resolve the internal structure of the resulting nuclear disk down to parsec scales and demonstrate the formation of a central massive object (~ 10^8 Mo) by efficient angular momentum transport. This is the first time that a radial gas inflow is shown to extend to parsec scales as a result of the dynamics and hydrodynamics involved in a galaxy merger, and has important implications for the fueling of SMBHs. Due to the rapid formation of the central clump, the density of the nuclear disk decreases significantly in its outer region, reducing dramatically the effect of dynamical friction and leading to the stalling of the two SMBHs at a separation of ~1 pc. We discuss how the orbital decay of the black holes might continue in a more realistic model which incorporates star formation and the multi-phase nature of the ISM.

Lucio Mayer; Stelios Kazantzidis; Andres Escala

2008-07-22T23:59:59.000Z

408

Disk12  

NLE Websites -- All DOE Office Websites (Extended Search)

2 2 Area Class Performer Project ID/Report Number Project Title/Report Number Link Introduction Forward / Introduction Read Me - Introduction to Reservoir Depositional Class Program A-Introduction/Read Me.doc Contact at U.S. DOE DOE-NETL Contacts A-Introduction/Contacts March 2008 Class DVD.doc History Summary History of Reservoir Depositional Class Program A-Introduction/Brief History Class Program.doc Hydrocarbon Geoscience Research Strategy DOE-FE-0186 P April 1990 B-Background/Hydrocarbon Geoscience Research Strategy DOE-FE-0186 P April 1990.pdf Background Oil Research Program Implementation Plan B-Background/DOE-FE-0188P-ImplemPlan_April1990.pdf Research Needs to Maximize Economic Producibility of the Domestic Resource B-Background/NIPER 527-DE92001001.pdf

409

Disk44  

NLE Websites -- All DOE Office Websites (Extended Search)

4 4 Area Performer Project ID Project Title Report Number Report Title Link A - Introduction: 'Read Me' File A-Introduction/Read Me EOR version 2.0.pdf DOE-NETL Contacts A-Introduction/Contacts March 2009 EOR DVD.pdf REPORT: DOE's Enhanced Oil Recovery Program -An Archive of Important Results, March 2009 A-Introduction/History File EOR Program Version 2.0_20090320.doc Table of Contents Sort File EOR-2.0 20090311_SORT.xls Process Diagram: Carbon Dioxide Flooding A-Introduction/colcarbon.pdf Process Diagram: Chemical Flooding (Alkaline) A-Introduction/alkaline.PDF Process Diagram: Chemical Flooding (Micellar-Polymer) A-Introduction/micellar-polymer.PDF Process Diagram: Chemical Flooding (Polymer) A-Introduction/polymer.PDF Process Diagram: Chemical Recovery A-Introduction/chem_recovery.PDF

410

Disk22  

NLE Websites -- All DOE Office Websites (Extended Search)

2 2 Area Performer Project ID Project Title Report Number Report Title First Author Link A - Introduction: A 'Read Me' file A-Introduction/Read Me CO2.doc A DOE-NETL Contacts A-Introduction/Contacts for 2008 CO2 DVD.doc A History of EOR Program and Program Evolution A-Introduction/Overview of DOEs CO2 Program History.doc A Process Diagram, Carbon Dioxide Flooding A-Introduction/colcarbon.pdf A Process Diagram, Cyclic Carbon Dioxide Stimulation A-Introduction/colcyclic.pdf A Process Diagram, In Situ Combustion A-Introduction/colinsitu_comb.pdf A Process Diagram, Nitrogen-CO2 Flooding A-Introduction/colnco2.pdf A Process Diagram, Nitrogen Flooding A-Introduction/colnf.pdf A Process Diagram, Miscible Recovery A-Introduction/colmr.pdf A The Past and Future of CO2 EOR Flooding Melzer A-Introduction/Past CO2 History melzer.pdf

411

Disk23  

NLE Websites -- All DOE Office Websites (Extended Search)

3 3 Area Class Performer Project ID Project Title Report Number Report Title First Author Link A - Introduction: A 'Read Me' file Olsen A-Introduction/Read Me.doc A DOE-NETL Contacts Olsen A-Introduction/Contacts for 2008 Env DVD.doc A Introduction and History of Environmental Program and Program Evolution Schatzinger A-Introduction/Brief History Env Program.doc A All Environmental Projects by Performer (as sortable excel spreadsheet) Koons A-Introduction/ALL Env Projects by Performer-050908.xls A Timeline of the Environmental Program from 1991-2008 spreadsheet Olsen A-Introduction/Petroleum Environmental Solutions Timeline 1991 to 2008.xls A All Environmental Projects by Category (as sortable excel spreadsheet) Koons A-Introduction/ALL Env Projects by Category-050508.xls

412

Disk17  

NLE Websites -- All DOE Office Websites (Extended Search)

B APS Technology Inc. DE-FC26-04NT15501 Novel High-Speed Drilling Motor for Oil Exploration & Production Project Fact Sheet B - MicroholeNT15501 Fact Sheet 2005.pdf B...

413

Disk37  

NLE Websites -- All DOE Office Websites (Extended Search)

Petroleum Refinery Process Design, Jicarilla Apache Reservation, New Mexico (JAECO Oil Processing Program) Feasibility Study for a Petroleum Refinery for The Jicarilla...

414

Disk41  

NLE Websites -- All DOE Office Websites (Extended Search)

Technology Center In-House R&D DOEMETC-86-2020 Study of Gas Migration from Naval Oil Shale Reserve No. 3 to the Rulison Field-Research Report; December 1985 B - Reservoir...

415

Characterizing Inflow Conditions Across the Rotor Disk of a Utility-Scale Wind Turbine (Poster)  

DOE Green Energy (OSTI)

Multi-megawatt utility-scale wind turbines operate in a turbulent, thermally-driven atmosphere where wind speed and air temperature vary with height. Turbines convert the wind's momentum into electrical power, and so changes in the atmosphere across the rotor disk influence the power produced by the turbine. To characterize the inflow into utility scale turbines at the National Wind Technology Center (NWTC) near Boulder, Colorado, NREL recently built two 135-meter inflow monitoring towers. This poster introduces the towers and the measurements that are made, showing some of the data obtained in the first few months of operation in 2011.