Table of contents

The review specializes to the modelling of plasmas in a particular type of fusion experiment, namely the tokamak. Simulation is taken to imply the use of a model which involves variation in at least two coordinate directions and is nonlinear, the nonlinearity invariably being of the advective type. Developments in the period 1976-1992 are covered under five main headings, with particle methods constituting the first. The remaining four concern the solution via mesh-based methods of (1) the Fokker-Planck equation, (2) drift-wave problems, (3) edge models and (4) time-dependent magnetohydrodynamic problems. Care is taken to outline the capabilities of the currently available software. Progress in the. Design of numerical algorithms for the mesh-based simulations is found to have been incremental rather than revolutionary. In particle simulation, gyrokinetic schemes and the ' delta f' method have been found to give dramatic gains in some circumstances. Many of the newer results obtained withstand comparison with experimental observation, although it has not always proved possible to reach the extreme conditions found in tokamaks, especially when three-dimensional effects are important.

Lepton-flavour violation is an important topic in particle physics, nowadays. The standard model, which describes jointly the electromagnetic and weak interactions, strictly conserves lepton flavour. On the other hand, most extensions of the standard model violate lepton-flavour conservation at some level. The article starts with definitions and gives a brief account of the standard model and its possible extensions. The experimental situation is reviewed in connection with the various theoretical predictions. The role of lepton-flavour violation in the search for physics beyond the standard model is emphasized.

Several mechanisms can extend the equilibrium domain of a liquid phase into the solid region of the normal phase diagram. The causes of premelting, which include surface melting, interface curvature and substrate disorder, occur in all types of substances, including H₂O. In the case of H₂O, premelting can have important environmental consequences, among which are the heaving of frozen ground, breakdown of rock and concrete, sintering of snow, flow of glaciers, scavenging of atmospheric trace gases by snow and ice, and the electrification of thunderclouds. The article reviews the basic mechanisms of premelting and discusses their roles in the environmental phenomena. The principal results of numerous studies are reviewed, and trends in current research are outlined.