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Articles 181 - 200 of 200

Full-Text Articles in Physics

On Black Hole Horizon Fluctuations, Kirill Tuchin Jan 1999

On Black Hole Horizon Fluctuations, Kirill Tuchin

Kirill Tuchin

A study of the high angular momentum particles ‘atmosphere’ near the Schwarzschild black hole horizon suggested that strong gravitational interactions occur at invariant distance of the order of 3√M [2]. We present a generalization of this result to the Kerr-Newman black hole case. It is shown that the larger charge and angular momentum black hole bears, the larger invariant distance at which strong gravitational interactions occur becomes. This invariant distance is of order 3√r+2(r+ − r−). This implies that the Planckian structure of the Hawking radiation of extreme black holes is completely broken.

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Burnett Description For Plane Poiseuille Flow, Alejandro Garcia, F. Uribe Jan 1999

Burnett Description For Plane Poiseuille Flow, Alejandro Garcia, F. Uribe

Alejandro Garcia

Two recent works have shown that at small Knudsen number ~K! the pressure and temperature profiles in plane Poiseuille flow exhibit a different qualitative behavior from the profiles obtained by the Navier-Stokes equations. Tij and Santos [J. Stat. Phys. 76, 1399 (1994)] used the Bhatnagar-Gross-Kook model to show that the temperature profile is bimodal and the pressure profile is nonconstant. Malek-Mansour, Baras, and Garcia [Physica A 240, 255 (1997)] qualitatively confirmed these predictions in computer experiments using the direct simulation Monte Carlo method (DSMC). In this paper we compare the DSMC measurements of hydrodynamic variables and non-equilibrium fluxes with numerical …

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Cell Size Dependence Of Transport Coefficients In Stochastic Particle Algorithms, Alejandro Garcia, F. Alexander, B. Alder Jan 1998

Cell Size Dependence Of Transport Coefficients In Stochastic Particle Algorithms, Alejandro Garcia, F. Alexander, B. Alder

Alejandro Garcia

Using the Green–Kubo theory, the dependence of the viscosity and thermal conductivity on cell size is obtained explicitly for stochastic particle methods such as direct simulation Monte Carlo (DSMC) and its generalization, the consistent Boltzmann algorithm (CBA). These analytical results confirm empirical observations that significant errors occur when the cell dimensions are larger than a mean free path.

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Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy Jan 1997

Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy

Alejandro Garcia

The direct simulation Monte Carlo (DSMC) method is used to solve the three-dimensional nano-scale gas film lubrication problem between a gas bearing slider and a rotating disk, and this solution is compared to the numerical solution of the compressible Reynolds equations with the slip flow correction based on the linearized Boltzmann equation as presented by Fukui and Kaneko [molecular gas film lubrication (MGL) method] [ASME J. Tribol. 110, 253 (1988)]. In the DSMC method, hundreds of thousands of simulated particles are used and their three velocity components and three spatial coordinates are calculated and recorded by using a hard-sphere collision …

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Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras Jan 1997

Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras

Alejandro Garcia

No abstract provided.

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A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour Jan 1996

A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour

Alejandro Garcia

Presents a train model that shows the long-range spatial correlations of fluctuations in nonequilibrium fluid systems. Illustration of model through analysis of flat-car trains running on parallel tracks; Simulation of train model in computers; Theoretical analysis for fluctuations in the train model; Relationship between train model and the fluctuating hydrodynamic theory of fluids.

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Trajectory Mapping And Applications To Data From The Upper Atmosphere Research Satellite, Gary A. Morris, Mark R. Schoeberl, Lynn C. Sparling, Paul A. Newman, Leslie R. Lait, Lee Elson, Joe Waters, Robert A. Suttie, Aidan Roche, Jack Kumer, James M. Russell Iii Aug 1995

Trajectory Mapping And Applications To Data From The Upper Atmosphere Research Satellite, Gary A. Morris, Mark R. Schoeberl, Lynn C. Sparling, Paul A. Newman, Leslie R. Lait, Lee Elson, Joe Waters, Robert A. Suttie, Aidan Roche, Jack Kumer, James M. Russell Iii

Gary A. Morris

The problem of creating synoptic maps from asynoptically gathered trace gas data has prompted the development of a number of schemes. Most notable among these schemes are the Kalman filter, the Salby-Fourier technique, and constituent reconstruction. This paper explores a new technique called "trajectory mapping." Trajectory mapping creates synoptic maps from asynoptically gathered data by advecting measurements backward or forward in time using analyzed wind fields. A significant portion of this work is devoted to an analysis of errors in synoptic trajectory maps associated with the calculation of individual parcel trajectories. In particular, we have considered (1) calculational errors; (2) …

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Comment On 'Simulation Of A Two-Dimensional Rayleigh-Bénard System Using The Direct Simulation Monte Carlo Method, Alejandro Garcia, F. Baras, M. Malek Mansour Jan 1995

Comment On 'Simulation Of A Two-Dimensional Rayleigh-Bénard System Using The Direct Simulation Monte Carlo Method, Alejandro Garcia, F. Baras, M. Malek Mansour

Alejandro Garcia

No abstract provided.

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A Consistent Boltzmann Algorithm, Alejandro Garcia, F. Alexander, B. Alder Jan 1995

A Consistent Boltzmann Algorithm, Alejandro Garcia, F. Alexander, B. Alder

Alejandro Garcia

The direct simulation Monte Carlo method for the Boltzmann equation is modified by an additional displacement in the advection process and an enhanced collision rate in order to obtain the exact hard sphere equation of state at all densities. This leads to consistent thermodynamic and transport properties in the low density (Boltzmann) regime. At higher densities transport properties are comparable to the predictions of the Enskog model. The algorithm is faster than molecular dynamics at low and moderate densities and readily run on a parallel architecture

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Electron Energy Loss In Oxygen Plasmas, G. A. Victor, John C. Raymond, Jane L. Fox Nov 1994

Electron Energy Loss In Oxygen Plasmas, G. A. Victor, John C. Raymond, Jane L. Fox

Jane L. Fox

The results of calculations of the energy deposition of energetic electrons in oxygen plasmas are given. In a pure oxygen plasma even with large fractional ionization, much of the electron energy results in the production of additional ionization and excited electronic states. Results are given for separate calculations using theoretical and experimental cross sections for the important O I excitations of 1S and 1D because the theoretical and experimental data are not in agreement. These results are useful for understanding the spectra of oxygen-rich supernova remnants.

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Direct Simulation Monte Carlo For Thin Film Bearings, Alejandro Garcia, B. Alder, F. J. Alexander Jan 1994

Direct Simulation Monte Carlo For Thin Film Bearings, Alejandro Garcia, B. Alder, F. J. Alexander

Alejandro Garcia

The direct simulation Monte Carlo (DSMC) scheme is used to study the gas flow under a read/write head positioned nanometers above a moving disk drive platter (the slider bearing problem). In most cases, impressive agreement is found between the particle-based simulation and numerical solutions of the continuum hydrodynamic Reynolds equation which has been corrected for slip. However, at very high platter speeds the gas is far from equilibrium, and the load capacity for the slider bearing cannot be accurately computed from the hydrodynamic pressure.

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Microscopic Simulation Of Dilute Gases With Adjustable Transport Coefficients, Alejandro Garcia, F. Baras, M. Malek Mansour Jan 1994

Microscopic Simulation Of Dilute Gases With Adjustable Transport Coefficients, Alejandro Garcia, F. Baras, M. Malek Mansour

Alejandro Garcia

The Bird algorithm is a computationally efficient method for simulating dilute gas flows. However, due to the relatively large transport coefficients at low densities, high Rayleigh or Reynolds numbers are difficult to achieve by this technique. We present a modified version of the Bird algorithm in which the relaxation processes are enhanced and the transport coefficients reduced, while preserving the correct equilibrium and nonequilibrium fluid properties. The present algorithm is found to be two to three orders of magnitude faster than molecular dynamics for simulating complex hydrodynamical flows.

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Quantam Wave Turbulence, Alejandro Garcia, M. Haeri, S. Putterman, P. Roberts Jan 1993

Quantam Wave Turbulence, Alejandro Garcia, M. Haeri, S. Putterman, P. Roberts

Alejandro Garcia

The nonlinear quantum kinetic equation for the interaction of sound waves is solved via analytic and numerical techniques. In the classical regime energy cascades to higher frequency (ω) according to the steady-state power law ω-3/2. In the quantum limit, the system prefers a reverse cascade of energy which follows the power law ω-6. Above a critical flux, a new type of spectrum appears which is neither self-similar nor close to equilibrium. This state of nonlinear quantum wave turbulence represents a flow of energy directly from the classical source to the quantum degrees of freedom.

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Multi-Ball Collisions, Terry L. Smith, Jay S. Huebner Jan 1992

Multi-Ball Collisions, Terry L. Smith, Jay S. Huebner

Terry L. Smith

Explanation to use the "double-ball" demonstration as a model for the supernova core bounce.

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Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon Jan 1992

Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon

Alejandro Garcia

We study the phenomenon of slip length using molecular dynamics and direct simulation Monte Carlo simulations of a dilute gas. Our work extends the range of Knudsen numbers that have been previously studied. In a recent paper, Bhattacharya and Lie [Phys. Rev. 43, 761 (1991)] suggest a logarithmic dependence of slip length on Knudsen number. By a simple redefinition of the mean free path, we obtain good agreement between simulation results and Maxwell theory for slip length. The anomalies seen by Bhattacharya and Lie appear to be due to their definition of the mean free path.

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Multi-Ball Collisions, Terry L. Smith, Jay S. Huebner Dec 1991

Multi-Ball Collisions, Terry L. Smith, Jay S. Huebner

Jay S Huebner

Explanation to use the "double-ball" demonstration as a model for the supernova core bounce.

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Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck Jan 1991

Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck

Alejandro Garcia

A reactiodffusion system of polymers undergoing interchange reactions is studied. The equation that describes the dynamics of the system is similar to the Boltzmann equation for a gas of hard spheres. We consider a one-dimensionsl system in which the average length and the concentrations at the boundaries are fixed. The resulting steady states are obtained analytically and with numerical integration of equations obtained by using a local equilibrium approximation. Monte Carlo simulations of experimentally realizable conditions were performed and compared. The results reveal a nonlinear distribution of molecular concentration and mass. The entropy of the polymer distributions is calculated as …

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Fluctuating Hydrodynamics In A Dilute Gas, Alejandro Garcia, G. Lie, E. Clementi Jan 1987

Fluctuating Hydrodynamics In A Dilute Gas, Alejandro Garcia, G. Lie, E. Clementi

Alejandro Garcia

Hydrodynamic fluctuations in a dilute gas subjected to a constant heat flux are studied by both a computer simulation and the Landau-Lifshitz formalism. The latter explicitly incorporates the boundary conditions of the finite system, thus permitting quantitative comparison with the former. Good agreement is demonstrated.

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Hydrodynamic Fluctuations In A Fluid Under Constant Shear, Alejandro Garcia, M. Malek Mansour, G. Lie, E. Clementi, M. Mareschal Jan 1987

Hydrodynamic Fluctuations In A Fluid Under Constant Shear, Alejandro Garcia, M. Malek Mansour, G. Lie, E. Clementi, M. Mareschal

Alejandro Garcia

No abstract provided.

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Nonequilibrium Fluctuations Studied By A Rarefied Gas Simulation, Alejandro Garcia Jan 1986

Nonequilibrium Fluctuations Studied By A Rarefied Gas Simulation, Alejandro Garcia

Alejandro Garcia

A dilute gas under a constant heat flux is studied with use of a Monte Carlo simulation based on the Boltzmann equation. Results for several spatial correlation functions of equal-time fluctuations are reported and compared qualitatively with previous fluctuating hydrodynamics calculations for liquids.

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