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Physical Sciences and Mathematics Commons™
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- Refereed Publications (63)
- Galaxies: evolution (34)
- Publications (30)
- Galaxies: kinematics and dynamics (29)
- Galaxies: formation (21)
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- Galaxies: dwarf (16)
- Galaxies: elliptical and lenticular (16)
- Galaxies: star clusters: general (16)
- CD (15)
- Galaxies: stellar content (13)
- Galaxies: structure (11)
- Galaxies: abundances (8)
- Galaxies: haloes (7)
- Articles (6)
- Galaxies: fundamental parameters (6)
- Quantum (6)
- Dark matter (5)
- Galaxies: halos (5)
- Galaxies: interactions (5)
- Fluctuations (4)
- Galaxies: clusters: general (4)
- Galaxies: photometry (4)
- Gas (4)
- Transport (4)
- Dilute (3)
- Dynamical (3)
- Flow (3)
- Fluid (3)
- Galaxies: clusters: individual (Coma) (3)
- Galaxies: individual: NGC 1023 (3)
Articles 181 - 205 of 205
Full-Text Articles in Physical Sciences and Mathematics
Dynamics Of Stars And Globular Clusters In M87, Aaron J. Romanowsky, C. S. Kochanek
Dynamics Of Stars And Globular Clusters In M87, Aaron J. Romanowsky, C. S. Kochanek
Faculty Publications
We examine the dynamics of the stars and globular clusters in the nearby giant elliptical galaxy M87 and constrain the mass distribution, using all the available data over a large range of radii, including higher order moments of the stellar line-of-sight velocity distributions and the discrete velocities of over 200 globular clusters. We introduce an extension of spherical orbit modeling methods that makes full use of all the information in the data and provides very robust constraints on the mass models. We conclusively rule out a constant mass-to-light ratio model and infer that the radial density profile of the galaxy's …
Molecular Simulations Of Sound Wave Propagation In Simple Gases, Alejandro Garcia, N. Hadjiconstantinou
Molecular Simulations Of Sound Wave Propagation In Simple Gases, Alejandro Garcia, N. Hadjiconstantinou
Faculty Publications
Molecular simulations of sound waves propagating in a dilute hard sphere gas have been performed using the direct simulation Monte Carlo method. A wide range of frequencies is investigated, including very high frequencies for which the period is much shorter than the mean collision time. The simulation results are compared to experimental data and approximate solutions of the Boltzmann equation. It is shown that free molecular flow is important at distances smaller than one mean free path from the excitation point.
Erratum: "Cell Size Dependence Of Transport Coefficients In Stochastic Particle Algorithms", Alejandro Garcia, F. Alexander, B. Alder
Erratum: "Cell Size Dependence Of Transport Coefficients In Stochastic Particle Algorithms", Alejandro Garcia, F. Alexander, B. Alder
Faculty Publications
No abstract provided.
Time Step Truncation Error In Direct Simulation Monte Carlo, Alejandro Garcia, W. Wagner
Time Step Truncation Error In Direct Simulation Monte Carlo, Alejandro Garcia, W. Wagner
Faculty Publications
No abstract provided.
Burnett Description For Plane Poiseuille Flow, Alejandro Garcia, F. Uribe
Burnett Description For Plane Poiseuille Flow, Alejandro Garcia, F. Uribe
Faculty Publications
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 …
Constraints On H0 From The Central Velocity Dispersions Of Lens Galaxies, Aaron J. Romanowsky, C. S. Kochanek
Constraints On H0 From The Central Velocity Dispersions Of Lens Galaxies, Aaron J. Romanowsky, C. S. Kochanek
Faculty Publications
We employ Schwarzschild's method of the orbit modeling to constrain the mass profiles of the central lens galaxies in Q0957+561 and PG 1115+080. We combine the measured, central projected stellar velocity dispersions of these galaxies with the self-similar radial profiles of the rms velocity and of the Gauss-Hermite moment h4 observed in nearby galaxies for 0 lesssim R lesssim 2Reff. For Q0957+561, we find a 16% uncertainty in the galaxy mass and formal 2 σ limits on the Hubble constant of H0=61$\mathstrut{^{+13}_{-15}}$ km s-1 Mpc-1. For PG 1115+080, we find that none of the viable lens models can be ruled …
Cell Size Dependence Of Transport Coefficients In Stochastic Particle Algorithms, Alejandro Garcia, F. Alexander, B. Alder
Cell Size Dependence Of Transport Coefficients In Stochastic Particle Algorithms, Alejandro Garcia, F. Alexander, B. Alder
Faculty Publications
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.
Twisting Of X-Ray Isophotes In Triaxial Galaxies, Aaron J. Romanowsky, C. S. Kochanek
Twisting Of X-Ray Isophotes In Triaxial Galaxies, Aaron J. Romanowsky, C. S. Kochanek
Faculty Publications
We investigate X-ray isophote twists created by triaxiality differences between the luminous stellar distributions and the dark halos in elliptical galaxies. For a typically oblate luminous galaxy embedded in a more prolate halo formed by dissipationless collapse, the triaxiality difference of ΔT simeq 0.7 leads to typical isophote twists of langΔψXrang simeq 16° ± 19° at 3 effective stellar radii. In a model that includes baryonic dissipation, the effect is smaller, with ΔT simeq 0.3 and langΔψXrang simeq 5° ± 8°. Thus, accurate measurements of X-ray isophote twists may be able to set constraints on the interactions between baryons and …
Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras
Anomalous Flow Profile Due To The Curvature Effect On Slip Length, Alejandro Garcia, K. Tibbs, F. Baras
Faculty Publications
No abstract provided.
Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy
Three-Dimensional Direct Simulation Monte Carlo Method For Slider Air Bearings, Alejandro Garcia, W. Huang, D. B. Bogy
Faculty Publications
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 …
Structural And Dynamical Uncertainties In Modelling Axisymmetric Elliptical Galaxies, Aaron J. Romanowsky, C. S. Kochanek
Structural And Dynamical Uncertainties In Modelling Axisymmetric Elliptical Galaxies, Aaron J. Romanowsky, C. S. Kochanek
Faculty Publications
Quantitative dynamical models of galaxies require deprojection of the observed surface brightness to determine the luminosity density of the galaxy. Existing deprojection methods for axisymmetric galaxies assume that a unique deprojection exists for any given inclination, even though the projected density is known to be degenerate to the addition of ‘konus densities’ that are invisible in projection. We develop a deprojection method based on linear regularization that can explore the range of luminosity densities that are statistically consistent with an observed surface brightness distribution. The luminosity density is poorly constrained at modest inclinations (i ≿ 30°), even in the limit …
A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour
A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour
Faculty Publications
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.
Comment On 'Simulation Of A Two-Dimensional Rayleigh-Bénard System Using The Direct Simulation Monte Carlo Method, Alejandro Garcia, F. Baras, M. Malek Mansour
Comment On 'Simulation Of A Two-Dimensional Rayleigh-Bénard System Using The Direct Simulation Monte Carlo Method, Alejandro Garcia, F. Baras, M. Malek Mansour
Faculty Publications
No abstract provided.
A Consistent Boltzmann Algorithm, Alejandro Garcia, F. Alexander, B. Alder
A Consistent Boltzmann Algorithm, Alejandro Garcia, F. Alexander, B. Alder
Faculty Publications
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
Direct Simulation Monte Carlo For Thin Film Bearings, Alejandro Garcia, B. Alder, F. J. Alexander
Direct Simulation Monte Carlo For Thin Film Bearings, Alejandro Garcia, B. Alder, F. J. Alexander
Faculty Publications
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.
Microscopic Simulation Of Dilute Gases With Adjustable Transport Coefficients, Alejandro Garcia, F. Baras, M. Malek Mansour
Microscopic Simulation Of Dilute Gases With Adjustable Transport Coefficients, Alejandro Garcia, F. Baras, M. Malek Mansour
Faculty Publications
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.
Quantam Wave Turbulence, Alejandro Garcia, M. Haeri, S. Putterman, P. Roberts
Quantam Wave Turbulence, Alejandro Garcia, M. Haeri, S. Putterman, P. Roberts
Faculty Publications
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.
Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon
Slip Length In A Dilute Gas, Alejandro Garcia, D. Morris, L. Hannon
Faculty Publications
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.
Stable Isotope Analysis Using Tunable Diode Laser Spectroscopy, Todd B. Sauke, J. F. Becker, M. Loewenstein
Stable Isotope Analysis Using Tunable Diode Laser Spectroscopy, Todd B. Sauke, J. F. Becker, M. Loewenstein
Faculty Publications
Measurements of ratios of stable isotopes are used in such diverse fields as petroleum prospecting, medical diagnostics, and planetary exploration. The narrow emission linewidth available from tunable diode lasers permits high-resolution infrared absorption measurements of closely spaced isotopic rovibrational lines. Our dual beam spectrometer uses the sweep integration technique in a spectral region where adjacent spectral lines are of approximately equal absorbance at the expected isotopic abundances. The experimental results reported here indicate that isotopic ratios of carbon in carbon dioxide can be measured to an accuracy of better than 0.4%. This laser spectroscopic spectrometric technique offers an alternative to …
Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck
Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck
Faculty Publications
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 …
Determination Of Rate Distributions From Kinetic Experiments, Todd B. Sauke, P. J. Steinback, K. Chu, H. Frauenfelder, J. B. Johnson, D. C. Lamb, G. U. Nienhaus, R. D. Young
Determination Of Rate Distributions From Kinetic Experiments, Todd B. Sauke, P. J. Steinback, K. Chu, H. Frauenfelder, J. B. Johnson, D. C. Lamb, G. U. Nienhaus, R. D. Young
Faculty Publications
Rate processes in proteins are often not adequately described by simple exponential kinetics. Instead of modeling the kinetics in the time domain, it can be advantageous to perform a numerical inversion leading to a rate distribution function f(lambda). The features observed in f(lambda) (number, positions, and shapes of peaks) can then be interpreted. We discuss different numerical techniques for obtaining rate distribution functions, with special emphasis on the maximum entropy method. Examples are given for the application of these techniques to flash photolysis data of heme proteins.
Inhomogeneous Broadening In Spectral Bands Of Carbonmonoxymyoglobin: The Connection Between Spectral And Functional Heterogeneity, Todd B. Sauke, P. Ormos, A. Ansari, D. Braunstein, B. R. Cowen, H. Fraunfelder, M. K. Hong, I. E. T. Iben, P. J. Steinbach, R. D. Young
Inhomogeneous Broadening In Spectral Bands Of Carbonmonoxymyoglobin: The Connection Between Spectral And Functional Heterogeneity, Todd B. Sauke, P. Ormos, A. Ansari, D. Braunstein, B. R. Cowen, H. Fraunfelder, M. K. Hong, I. E. T. Iben, P. J. Steinbach, R. D. Young
Faculty Publications
The rebinding kinetics of CO to myoglobin after flash photolysis is nonexponential in time below approximately 180 K; the kinetics is governed by a distribution of enthalpic barriers. This distribution results from inhomogeneities in the protein conformation, referred to as conformational substates. Hole-burning experiments on the Soret and IR CO-stretch bands test the assumption that an inhomogeneous distribution of conformational substates results in inhomogeneously broadened spectra. CO was slowly photolyzed at different wavelengths in the Soret band at 10 K. Both the Soret band and the CO-stretch band A1, centered at 1,945 cm-1, shift during photolysis, demonstrating that different wavelengths …
Fluctuating Hydrodynamics In A Dilute Gas, Alejandro Garcia, G. Lie, E. Clementi
Fluctuating Hydrodynamics In A Dilute Gas, Alejandro Garcia, G. Lie, E. Clementi
Faculty Publications
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.
Hydrodynamic Fluctuations In A Fluid Under Constant Shear, Alejandro Garcia, M. Malek Mansour, G. Lie, E. Clementi, M. Mareschal
Hydrodynamic Fluctuations In A Fluid Under Constant Shear, Alejandro Garcia, M. Malek Mansour, G. Lie, E. Clementi, M. Mareschal
Faculty Publications
No abstract provided.
Nonequilibrium Fluctuations Studied By A Rarefied Gas Simulation, Alejandro Garcia
Nonequilibrium Fluctuations Studied By A Rarefied Gas Simulation, Alejandro Garcia
Faculty Publications
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.