Table of contents

(Invited talk at the 20th International Cosmic Ray Conference, Moscow, 2–15 August 1987) The basic topics discussed here are the primary cosmic rays near the earth, cosmic rays in the universe, the origin of cosmic rays, a galactic model with a halo, and some prospects for future research.

This review covers the current theoretical concepts and experimental methods employed in studying the two-dimensional electron density of states in a magnetic field. The authors discuss the different factors that determine the energy distribution of the density of states in real systems. They demonstrate the importance of the screening of random external potential fluctuations by two-dimensional electrons and particularly the oscillatory dependence of screening on electron concentration. When considering the various theoretical approaches and experimental methods, the authors analyze their conditions of applicability and the self-consistency of obtained results. They demonstrate that it is possible to evaluate experimentally the random potential amplitude and range from the oscillations in Landau level broadening.

A plasma formed by the action on a gas of monochromatic radiation whose frequency corresponds to the energy of a resonance transition in the atom is studied. The elementary methods of creating and studying a plasma of this type are analyzed. The kinetics of formation of a photoresonance plasma is studied, including collision processes with participation of excited atoms leading to formation of molecular ions and highly excited atoms, processes of stepwise ionization and triple recombination, and radiative processes. A photoresonance plasma is characterized by a high electron density with a relatively low electron temperature; for this reason the condition of ideality is more easily violated in a plasma of this type. Some ways of utilizing a photoresonance plasma are presented.

This article gives a portrait of a pioneer of Soviet physics, who played a large role in building up theoretical physics in the USSR. At the beginning of this century V. R. Bursian carried out research on the physics of currents in gases and in a vacuum, on dispersion and gyration, on the electron theory of matter, and on the kinetics of chain reactions. Electrophysical methods for geological exploration were first developed by him.

Examples of crystallization of glasses and of the condensation of excitons to form an electron-hole liquid in germanium are used to study the kinetics of nucleation of a new phase. There are considerable advantages in tackling such model systems rather than other systems undergoing a first-order phase transition. Attention is drawn to two different nucleation regimes: transient and quasisteady-state. Special consideration is given to nucleation in an open system from which nuclei of the new phase may be removed rapidly as a result of diffusion or drift to absorbing walls. In such cases very strong supersaturation may be reached and the threshold of the appearance of a new phase may be independent of temperature.