37 research outputs found
High Pressure Thermoelasticity of Body-centered Cubic Tantalum
We have investigated the thermoelasticity of body-centered cubic (bcc)
tantalum from first principles by using the linearized augmented plane wave
(LAPW) and mixed--basis pseudopotential methods for pressures up to 400 GPa and
temperatures up to 10000 K. Electronic excitation contributions to the free
energy were included from the band structures, and phonon contributions were
included using the particle-in-a-cell (PIC) model. The computed elastic
constants agree well with available ultrasonic and diamond anvil cell data at
low pressures, and shock data at high pressures. The shear modulus and
the anisotropy change behavior with increasing pressure around 150 GPa because
of an electronic topological transition. We find that the main contribution of
temperature to the elastic constants is from the thermal expansivity. The PIC
model in conjunction with fast self-consistent techniques is shown to be a
tractable approach to studying thermoelasticity.Comment: To be appear in Physical Review
First- and second-order phase transitions in a driven lattice gas with nearest-neighbor exclusion
A lattice gas with infinite repulsion between particles separated by
lattice spacing, and nearest-neighbor hopping dynamics, is subject to a drive
favoring movement along one axis of the square lattice. The equilibrium (zero
drive) transition to a phase with sublattice ordering, known to be continuous,
shifts to lower density, and becomes discontinuous for large bias. In the
ordered nonequilibrium steady state, both the particle and order-parameter
densities are nonuniform, with a large fraction of the particles occupying a
jammed strip oriented along the drive. The relaxation exhibits features
reminiscent of models of granular and glassy materials.Comment: 8 pages, 5 figures; results due to bad random number generator
corrected; significantly revised conclusion
Coupled Clouds and Chemistry of the Giant Planets— A Case for Multiprobes
In seeking to understand the formation of the giant planets and the origin of their atmospheres, the heavy element abundance in well-mixed atmosphere is key. However, clouds come in the way. Thus, composition and condensation are intimately intertwined with the mystery of planetary formation and atmospheric origin. Clouds also provide important clues to dynamical processes in the atmosphere. In this chapter we discuss the thermochemical processes that determine the composition, structure, and characteristics of the Jovian clouds. We also discuss the significance of clouds in the big picture of the formation of giant planets and their atmospheres. We recommend multiprobes at all four giant planets in order to break new ground.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43766/1/11214_2005_Article_1951.pd
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A high-density, high-temperature mixture model
This paper describes a model designed for multicomponent systems. The model is useful for high temperature and high pressures. (WRF
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New approach to multiphase equilibria: application to high-pressure physics problems
A multiphase, multicomponent equation-of-state (EOS) model based on first principles of statistical mechanics is described. The model has been used to study fluid-fluid phase separations in binary (H/sub 2/-He, Ar-Ne, Xe-He, and N/sub 2/-H/sub 2/O) and ternary or more complex systems involving species with C, H, N, and O atoms. Results of these calculations and a brief description of a new theory which can simultaneously describe both solid and fluid EOS properties are given. 26 refs., 4 figs
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Three phase carbon EOS model with electronic excitation
A simple and rapid way for computing EOS data of multiphase solids with a liquid phase is described with emphasis on carbon. The method uses a scaling model for the liquid phase and includes a provision for electronic effects. The free energy minimum determines the stable phase
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