The acceleration of charged particles at astrophysical collisionless shock waves is one of the best studied processes for the energization of particles to ultrarelativistic energies, required by multifrequency observations in a variety of astrophysical situations. In this paper we discuss some work aimed at describing one of the main progresses made in the theory of shock acceleration, namely t...

In many circumstances the perfect fluid conservation equations can be directly integrated to give a Geometric-Thermodynamic equation: typically that the lapse N is the reciprocal of the enthalphy h, (N = 1/h). This result is aesthetically appealing as it depends only on the fluid conservation equations and does not depend on specific field equations such as Einstein’s. Here the form of the Geom...

Maxwell's investigations into the stability of Saturn's rings provide one of the earliest analyses of the dynamics of astrophysical discs. Current research in planetary rings extends Maxwell's kinetic theory to treat dense granular gases of particles undergoing moderately frequent inelastic collisions. Rather than disrupting the rings, local instabilities may be responsible for generating their...

The fundamental physics of magnetic reconnection in laboratory and space plasmas is reviewed by discussing results from theory, numerical simulations, observations from space satellites, and recent results from laboratory plasma experiments. After a brief review of the well-known early work, representative recent experimental and theoretical works are discussed and the essence of significant mo...

Planetary ring systems are rich astrophysical environments that offer some of the most visually stunning solutions to Newton’s Laws in the solar system. Since the discovery of the Saturnian rings in 1610 by Galileo, planetary rings have been a frequent object of study by both physicists and astronomers. In the past thirty years enhanced earth based equipment and the scientific probes Pioneer-11...

Exploratory simulation involves the combination of computational steering and visualization at interactive speeds.This presents a number of challenges for large scientific data sets, such as those from astrophysics. A computational model is required such that steering the simulation while in progress is both physically valid and scientifically useful. Effective and appropriate visualization and...

This paper presents a validation test of the flux-limited diffusion (FLD) approximation for radiation hydrodynamics in the intermediate optical depth regime. We use an implementation of FLD in the ZEUS-2D astrophysical fluid dynamics code and the results of a set of laser-driven radiative shock experiments. One-dimensional simulations are performed to explore grid spacing and time step converge...

Maxwell’s investigations into the stability of Saturn’s rings provide one of the earliest analyses of the dynamics of astrophysical discs. Current research in planetary rings extends Maxwell’s kinetic theory to treat dense granular gases of particles undergoing moderately frequent inelastic collisions. Rather than disrupting the rings, local instabilities may be responsible for generating their...

This paper deals with the problem of hydrodynamic shear turbulence in non-magnetized Keplerian disks. Several papers have appeared recently on the subject, on possible linear instabilities which may be due to the presence of a stable stratification, or caused by deviations from cylindrical rotation. Here we wish to draw attention to another route to hydrodynamic turbulence, which seems to be li...