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## Full-Text Articles in Physics

Approximate Equations Of State In Two-Temperature Plasma Mixtures, John D. Ramshaw, Andrew W. Cook

#### Approximate Equations Of State In Two-Temperature Plasma Mixtures, John D. Ramshaw, Andrew W. Cook

*Physics Faculty Publications and Presentations*

Approximate thermodynamic state relations for multicomponent atomic and molecular gas mixtures are often constructed by artificially partitioning the mixture into its constituent materials and requiring the separated materials to be in temperature and pressure equilibrium. Iterative numerical algorithms have been employed to enforce this equilibration and compute the resulting approximate state relations in single-temperature mixtures. In partially ionized gas mixtures, there is both theoretical and empirical evidence that equilibrating the chemical potentials, number densities, or partial pressures of the free electrons is likely to produce more accurate results than equilibrating the total pressures. Moreover, in many situations of practical interest ...

Simple Approximation For Thermal Diffusion In Ionized Gas Mixtures, John D. Ramshaw

#### Simple Approximation For Thermal Diffusion In Ionized Gas Mixtures, John D. Ramshaw

*Physics Faculty Publications and Presentations*

A simple approximation for thermal diffusion in gas mixtures was recently proposed [1]. This approximation was based upon relations valid for rigid spheres. It is therefore appropriate for molecules with steep repulsive potentials, but not for ionized species interacting via the Coulomb potential. Here we formulate an analogous approximation for ionized species and free electrons. The resulting thermal diffusion coefficients differ in sign from those for hard molecules.

Numerical Simulation Of Nonequilibrium Effects In An Argon Plasma Jet, C. H. Chang, John D. Ramshaw

#### Numerical Simulation Of Nonequilibrium Effects In An Argon Plasma Jet, C. H. Chang, John D. Ramshaw

*Physics Faculty Publications and Presentations*

Departures from thermal (translational), ionization, and excitation equilibrium in an axisymmetric argon plasma jet have been studied by two?dimensional numerical simulations. Electrons, ions, and excited and ground states of neutral atoms are represented as separate chemical species in the mixture. Transitions between excited states, as well as ionization/recombination reactions due to both collisional and radiative processes, are treated as separate chemical reactions. Resonance radiation transport is represented using Holstein escape factors to simulate both the optically thin and optically thick limits. The optically thin calculation showed significant underpopulation of excited species in the upstream part of the jet ...

Self-Consistent Effective Binary Diffusion In Multicomponent Gas Mixtures, John D. Ramshaw

#### Self-Consistent Effective Binary Diffusion In Multicomponent Gas Mixtures, John D. Ramshaw

*Physics Faculty Publications and Presentations*

The correct treatment of diffusion in multicomponent gas mixtures requires solution of a linear system of equations for the diffusive mass fluxes relative to the mass-averaged velocity of the mixture. Effective binary diffusion approximations are often used to avoid solving this system. These approximations are generally internally inconsistent in the sense that the approximate diffusion fluxes do not properly sum to zero. The origin of this inconsistency is identified, and a general procedure for removing it is presented. This procedure applies equally to concentration, forced, pressure, and thermal diffusion, either separately or in combination. It is used to obtain a ...

Dielectric Saturation In Dipolar Fluids. I. The Single-Molecule Distribution Function, John D. Ramshaw

#### Dielectric Saturation In Dipolar Fluids. I. The Single-Molecule Distribution Function, John D. Ramshaw

*Physics Faculty Publications and Presentations*

The functional-derivative formalism is used to investigate the form of the equilibrium single-molecule distribution function n(1) in a finite fluid system of rigid polar molecules subjected to a strong external electric field that varies slowly with position. The investigation is based on the assumption that the long-range asymptotic behavior of the direct correlation function is independent of the external field, and is hence the same as in the unperturbed fluid. This assumption implies that n(1) has the form of a single-molecule Boltzmann factor in which the interaction energy is that of a deformable quasidipole with the local Lorentz ...

Debye–Hückel Theory For Particles Of Arbitrary Electrical Structure, John D. Ramshaw

#### Debye–Hückel Theory For Particles Of Arbitrary Electrical Structure, John D. Ramshaw

*Physics Faculty Publications and Presentations*

Classical linearized Debye–Hückel theory is formulated for a finite fluid system, of arbitrary shape, composed of rigid particles with arbitrary internal electrical structure. The multipole description is eschewed in favor of the more basic description of a particle in terms of its charge density function. This function is left arbitrary, so the particles may be charged or neutral, polar or nonpolar, etc. The theory implies that the direct correlation function *c*(12)=−*v*(12)/*k* *T*, where *v*(12) is the Coulomb interaction energy between the charge densities of particles 1 and 2. In the case of uncharged polar ...

New Method For Generating Density Expansions, John D. Ramshaw

#### New Method For Generating Density Expansions, John D. Ramshaw

*Physics Faculty Publications and Presentations*

The calculus of finite differences is used to develop a new method for expressing the thermodynamic limit of a reasonably arbitrary statistical?mechanical average as a power series in the number density ?. The method is simple, straightforward, and purely analytic: it involves no intermediate expansion in powers of the activity and it avoids the use of graph theory. Moreover, the method is developed independently of the prescription for computing the statistical average, a fact which lends to the results an especially wide range of applicability. In particular, these results may be used in classical or quantum statistical mechanics, for intermolecular ...