Two-photon physics, i.e. photon-photon collisions in electron-positron colliders, a relatively new field in elementary particle physics, has become very popular in the last 20 years. Many experiments have been performed in this field, and the theoretical implications (in particular in quantum chromodynamics) have been studied in much detail. Nine international workshops devoted to two-photon physics have taken place between 1973 and 1992.This meeting was particularly timely, since a new generation of electron-positron colliders is presently being built or planned. These colliders will involve a large spectrum of beam energies, but their common characteristics should be a high particle flux (luminosity). This should allow for measuring many new phenomena as well as for studying known processes with much higher precision than before. Particularly promising is the prospect of building a dedicated high-energy photon collider; this should become possible using a laser technique allowing for the “conversion” of a linear electron beam into a photon beam.Over 60 physicists (both experimentalists and theorists), mainly from European countries (France, Britain, Italy, Germany, Russia, as well as Sweden and Switzerland), discussed these new possibilities at the above meeting. Over 30 talks were presented and many extended debates took place.

This volume contains the proceedings of a five-day NATO Advanced Research Workshop "On Three Levels, the mathematical physics of micro-, meso-, and macro phenomena," conducted from July 19 to 23 in Leuven, Belgium. The main purpose of the workshop was to bring together and to confront where relevant, classical and quantum approaches in the rigorous study of the relation between the various levels of physical description. The reader will find here discussions on a variety of topics involving a broad range of scales. For the micro-level, contributions are presented on models of reaction-diffusion pro cesses, quantum groups and quantum spin systems. The reports on quantum disorder, the quantum Hall effect, semi-classical approaches of wave mechanics and the random Schrodinger equation can be situated on the meso-level. Discussions on macroscopic quantum effects and large scale fluctuations are dealing with the macroscopic level of description. These three levels are however not independent and emphasis is put on relating these scales of description. This is especially the case for the contributions on kinetic and hydrodynamicallimits, the discussions on large deviations and the strong and weak coupling limits. The advisory board was composed of J.L. Lebowitz, J.T. Lewis and E.H. Lieb. The organizing committee was formed by Ph.A. Martin, G.L. Sewell, E.R. Speer and A.

The proceedings of the NATO Advanced Study Institute on title], held in Rhodes, Greece, June-July 1992, comprise invited and contributed papers that focus on recent experimental, theoretical, and computational developments in the study of phase alloy transformations. The coverage is in three parts: