Biomedical subjects

James F Lutsko

Publications and source records attributed to James F Lutsko.

11 recordsLinked to original sources

PubMed2006

Hydrodynamics of an endothermic gas with application to bubble cavitation.

The hydrodynamics for a gas of hard spheres which sometimes experience inelastic collisions resulting in the loss of a fixed, velocity-independent, amount of energy Delta is investigated with the goal of understanding the coupling between hydrodynamics and endothermic chemistry. The homogeneous cooling state of a uniform system and the modified Navier-Stokes equations are discussed and explicit expressions given for the pressure, cooling rates, and all transport coefficients for D dimensions. The Navier-Stokes equations are solved numerically for the case of a two-dimensional gas subject to a circular piston so as to illustrate the effects of the energy loss on the structure of shocks found in cavitating bubbles. It is found that the maximal temperature achieved is a sensitive function of Delta with a minimum occurring near the physically important value of Delta approximately 12,000 K approximately 1 eV.

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PubMed2006

Properties of non-fcc hard-sphere solids predicted by density functional theory.

The free energies of the fcc, bcc, hcp, and simple cubic phases for hard spheres are calculated as a function of density using the fundamental measure theory models of Rosenfeld [Phys. Rev. E 55, 4245 (1997)], Tarazona [Phys. Rev. Lett. 84, 694 (2001)], and Roth [J. Phys.: Condens. Matter 14, 12063 (2002)] in the Gaussian approximation. For the fcc phase, the present work confirms the vanishing of the Lindemann parameter (i.e., vanishing of the width of the Gaussians) near close packing for all three models and the results for the hcp phase are nearly identical. For the bcc phase and for packing fractions above eta approximately 0.56 , all three theories show multiple solid structures differing in the widths of the Gaussians. In all three cases, one of these structures shows the expected vanishing of the Lindemann parameter at close packing, but this physical structure is only thermodynamically favored over the unphysical structures in the Tarazona theory and even then, some unphysical behavior persists at lower densities. The simple cubic phase is stabilized in the model of Rosenfeld for a range of densities and in the Tarazona model only very near close packing.

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PubMed2006

Ginzburg-Landau theory of the liquid-solid interface and nucleation for hard spheres.

The Ginzburg-Landau free energy functional for hard spheres is constructed using the fundamental measure theory approach to density functional theory as a starting point. The functional is used to study the liquid-fcc solid planer interface and the properties of small solid clusters nucleating within a liquid. The surface tension for planer interfaces agrees well with simulation and it is found that the properties of the solid clusters are consistent with classical nucleation theory.

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PubMed2006

Chapman-Enskog expansion about nonequilibrium states with application to the sheared granular fluid.

The Chapman-Enskog method of solution of kinetic equations, such as the Boltzmann equation, is based on an expansion in gradients of the deviations of the hydrodynamic fields from a uniform reference state (e.g., local equilibrium). This paper presents an extension of the method so as to allow for expansions about arbitrary, far-from-equilibrium reference states. The primary result is a set of hydrodynamic equations for studying variations from the arbitrary reference state which, unlike the usual Navier-Stokes hydrodynamics, does not restrict the reference state in any way. The method is illustrated by application to a sheared granular gas which cannot be studied using the usual Navier-Stokes hydrodynamics.

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PubMed2006

Theoretical evidence for a dense fluid precursor to crystallization.

We present classical density functional theory calculations of the free-energy landscape for fluids below their triple point as a function of density and crystallinity. We find that, both for a model globular protein and for a simple atomic fluid modeled with a Lennard-Jones interaction, it is free-energetically easier to crystallize by passing through a metastable dense fluid in accord with the Ostwald rule of stages but in contrast to the alternative of ordering and densifying at once as assumed in the classical picture of crystallization.

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PubMed2005

Transport properties of dense dissipative hard-sphere fluids for arbitrary energy loss models.

The revised Enskog approximation for a fluid of hard spheres which lose energy upon collision is discussed for the case that the energy is lost from the normal component of the velocity at collision but is otherwise arbitrary. Granular fluids with a velocity-dependent coefficient of restitution are an important special case covered by this model. A normal solution to the Enskog equation is developed using the Chapman-Enskog expansion. The lowest order solution describes the general homogeneous cooling state and a generating function formalism is introduced for the determination of the distribution function. The first order solution, evaluated in the lowest Sonine approximation, provides estimates for the transport coefficients for the Navier-Stokes hydrodynamic description. All calculations are performed in an arbitrary number of dimensions.

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PubMed2005

The effect of the range of interaction on the phase diagram of a globular protein.

Thermodynamic perturbation theory is applied to the model of globular proteins studied by ten Wolde and Frenkel [P. R. ten Wolde and D. Frenkel Science 77, 1975 (1997)] using computer simulation. It is found that the reported phase diagrams are accurately reproduced. The calculations show how the phase diagram can be tuned as a function of the length scale of the potential.

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PubMed2004

Rheology of dense polydisperse granular fluids under shear.

The solution of the Enskog equation for the one-body velocity distribution of a moderately dense arbitrary mixture of inelastic hard spheres undergoing planar shear flow is described. A generalization of the Grad moment method, implemented by means of a novel generating function technique, is used so as to avoid any assumptions concerning the size of the shear rate. The result is illustrated by using it to calculate the pressure, normal stresses, and shear viscosity of a model polydisperse granular fluid in which grain size, mass, and coefficient of restitution vary among the grains. The results are compared to a numerical solution of the Enskog equation as well as molecular-dynamics simulations. Most bulk properties are well described by the Enskog theory and it is shown that the generalized moment method is more accurate than the simple (Grad) moment method. However, the description of the distribution of temperatures in the mixture predicted by Enskog theory does not compare well to simulation, even at relatively modest densities.

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PubMed2004

Kinetic theory and hydrodynamics of dense, reacting fluids far from equilibrium.

The kinetic theory for a fluid of hard spheres which undergo endothermic and/or exothermic reactions with mass transfer is developed. The exact balance equations for concentration, density, velocity, and temperature are derived. The Enskog approximation is discussed and used as the basis for the derivation, via the Chapman-Enskog procedure, of the Navier-Stokes reaction equations under various assumptions about the speed of the chemical reactions. It is shown that the phenomenological description consisting of a reaction-diffusion equation with a convective coupling to the Navier-Stokes equations is of limited applicability.

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PubMed2002

Atomic-scale structure of hard-core fluids under shear flow.

The effect of velocity correlations on the equal-time density autocorrelation function, e.g., the pair distribution function (PDF), of a hard-sphere fluid undergoing shear flow is investigated. The PDF at contact is calculated within the Enskog approximation and is shown to be in good agreement with molecular dynamics simulations for shear rates below the shear-induced ordering transition. These calculations are used to construct a nonequilibrium generalized mean-spherical approximation for the PDF at finite separations, which is also found to agree well with the simulation data.

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PubMed2002

Long-ranged correlations in sheared fluids.

The presence of long-ranged correlations in a fluid undergoing uniform shear flow is investigated. An exact relation between the density autocorrelation function and the density-momentum correlation function implies that the former must decay more rapidly than 1/r, in contrast to predictions of simple mode-coupling theory. Analytic and numerical evaluation of a nonperturbative mode-coupling model confirms a crossover from 1/r behavior at "small" r to a stronger asymptotic power-law decay. The characteristic length scale is l approximately sqrt[lambda(0)/a], where lambda(0) is the sound damping constant and a is the shear rate.

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