The stability of accretion shocks in magnetic white dwarfs is investigated. Shock oscillations are simulated numerically, and in the simulations bremsstrahlung and cyclotron cooling are considered in an explicit form. We have found that for shocks with magnetic fields lower than 10 MG, shock oscillations can be sustained; while for magnetic fields greater than 20 MG, the oscillations are suppressed.

When using a formulation of smooth particle hydrodynamics (SPH) which conserves momentum exactly the motion of the particles is observed to be unstable to negative stress. It is also found that under normal circumstances a lattice of SPH particles is potentially unstable to transverse waves. This paper is a summary of a detailed report (Morris 1994) investigating the nature of these and other instabilities in depth. Approaches which may be used to eliminate these instabilities are suggested. It is found that the stability properties of SPH in general improve as higher-order spline interpolants, approximating a Gaussian, are used as kernels.

A simple model for estimating the intrinsic flow direction and speed in the parsec-scale jets associated with extragalactic radio sources is presented. In this model, radio source brightness asymmetries are attributed to the apparent amplification caused when a relativistic jet of radiating material is somewhat aligned with the observers line of sight. The knots of emission commonly seen in parsec-scale radio jets are interpreted as shocks in the relativistic fluid.