Publications

Results 51–71 of 71

Search results

Jump to search filters

Adaptive tabulation for verified equations of state

AIP Conference Proceedings

Carpenter, John H.

A new adaptive tabulation scheme for multi-phase equations of state (EOS) is described. Adaptation allows verification that a table represents an EOS model to some desired accuracy at a much lower computational cost than standard tables. Computational efficiency is provided through the use of a quad-tree representation. Using both rectangular and triangular interpolation regions results in accurate descriptions of phase boundaries. The new format is demonstrated on a representative multi-phase EOS model. © 2012 American Institute of Physics.

More Details
TYPE Conference YEAR 2012
OSTIScopus

High fidelity equation of state for xenon : integrating experiments and first principles simulations in developing a wide-range equation of state model for a fifth-row element

Magyar, Rudolph J.; Root, Seth R.; Carpenter, John H.; Mattsson, Thomas M.

The noble gas xenon is a particularly interesting element. At standard pressure xenon is an fcc solid which melts at 161 K and then boils at 165 K, thus displaying a rather narrow liquid range on the phase diagram. On the other hand, under pressure the melting point is significantly higher: 3000 K at 30 GPa. Under shock compression, electronic excitations become important at 40 GPa. Finally, xenon forms stable molecules with fluorine (XeF{sub 2}) suggesting that the electronic structure is significantly more complex than expected for a noble gas. With these reasons in mind, we studied the xenon Hugoniot using DFT/QMD and validated the simulations with multi-Mbar shock compression experiments. The results show that existing equation of state models lack fidelity and so we developed a wide-range free-energy based equation of state using experimental data and results from first-principles simulations.

More Details
TYPE Conference YEAR 2010
OSTI

As symmetric spreading in highly advective, disordered environments

Proposed for publication in Physical Review Letters.

Carpenter, John H.

Spreading of bacteria in a highly advective, disordered environment is examined. Predictions of super-diffusive spreading for a simplified reaction-diffusion equation are tested. Concentration profiles display anomalous growth and super-diffusive spreading. A perturbation analysis yields a crossover time between diffusive and super-diffusive behavior. The time's dependence on the convection velocity and disorder is tested. Like the simplified equation, the full linear reaction-diffusion equation displays super-diffusive spreading perpendicular to the convection. However, for mean positive growth rates the full nonlinear reaction-diffusion equation produces symmetric spreading with a Fisher wavefront, whereas net negative growth rates cause an asymmetry, with a slower wavefront velocity perpendicular to the convection.

More Details
TYPE Journal Article YEAR 2005
OSTI
Results 51–71 of 71
Results 51–71 of 71