We report on the completion of the first version of a new-generation simulation code, FLASH. The FLASH code solves the fully compressible, reactive hydrodynamic equations and allows for the use of adaptive mesh refinement. It also contains state-of-the-art modules for the equations of state and thermonuclear reaction networks. The FLASH code was developed to study the problems of nuclear flashes on the surfaces of neutron stars and white dwarfs, as well as in the interior of white dwarfs. We expect, however, that the FLASH code will be useful for solving a wide variety of other problems. This first version of the code has been subjected to a large variety of test cases and is currently being used for production simulations of X-ray bursts, Rayleigh-Taylor and Richtmyer-Meshkov instabilities, and thermonuclear flame fronts. The FLASH code is portable and already runs on a wide variety of massively parallel machines, including some of the largest machines now extant.

https://iopscience.iop.org/article/10.1086/317361/pdf

Flash: An adaptive mesh hydrodynamics code for modeling astrophysical thermonuclear flashes

FLASH: Adaptive Mesh Hydrodynamics Code for Modeling Astrophysical Thermonuclear Flashes

The processes that lead to charging of dust grains in a plasma are briefly reviewed. Whereas for single grains the results have been long known, the reduction of the average charge on a grain by 'Debye screening' has only recently been discovered. This reduction can be important in the Jovian ring and in the rings of Uranus. The emerging field of gravitoelectrodynamics which deals with the motion of charged grains in a planetary magnetosphere is then reviewed. Important mechanisms for distributing grains in radial distance are due to stochastic fluctuations of the grain charge and a systematic variation due to motion through plasma gradients. The electrostatic levitation model for the formation of spokes is discussed, and it is shown that the radial transport of dust contained in the spokes may be responsible for the rich radial structure in Saturn's rings. Finally, collective effects in dusty plasmas are discussed which affect various waves, such as density waves in planetary rings and low-frequency plasma waves. The possibility of charged grains forming a Coulomb lattice is briefly described.

Dusty plasmas in the solar system

Neutron Stars 1: Equation of State and Structure

Complex (dusty) plasmas: current status, open issues, perspectives

An update on the test ban

It is well known that an activity expansion of the grand canonical partition function works well for attractive interactions, but poorly for repulsive interactions, such as occur between atoms and molecules. The virial expansion of the canonical partition function shows just the opposite behavior. This poses a problem for applications that involve both types of interactions, such as occur in the outer layers of low-mass stars. We show that it is possible to obtain expansions for repulsive systems that convert the poorly performing Mayer activity expansion into a series of rational polynomials that converge uniformly to the virial expansion. In the current work we limit our discussion to the second virial approximation. In contrast to the Mayer activity expansion, the activity expansion presented herein converges for both attractive and repulsive systems.

/pdf/improved-convergence-for-two-component-activity-expansions-kanr275zsn.pdf

Improved convergence for two-component activity expansions.

We present a fit formula for the excess internal energy of the one-component plasma in the fluid phase that was obtained from the analytic solution of the mean spherical approximation for charged hard spheres in a uniform neutralizing background by utilizing a new relation for the effective packing fraction. Our results are in much better agreement to recent Monte Carlo data for strong coupling, Γ ≥ 1, than previous results from similar calculations, and extend down to the Debye limit, Γ 0.

Interpolated Mean Spherical Approach to the Energy Equation of State of the Classical One-Component Plasma Fluid

Dr Hugh E. Dewitt contemplates the nuclear arms race from within an American weapons laboratory.

Using a Green's function approach a low density equation of state is derived for quantum plasmas up to the order (e2n)5/2.

H. E. DeWitt

Papers

An update on the test ban

Improved convergence for two-component activity expansions.

Interpolated Mean Spherical Approach to the Energy Equation of State of the Classical One-Component Plasma Fluid

Dr Hugh E. Dewitt contemplates the nuclear arms race from within an American weapons laboratory.

Equation of state for weakly nonideal plasmas