Table of contents

Experimental and theoretical work on ionizing shock waves in a fully ionized plasma is reviewed for the case in which a magnetic field is imposed parallel to the plane of the shock front. The boundary conditions for ionizing shocks are discussed. It is shown that the additional boundary conditions required for ionizing shock waves follow from the ionizational stability of the gas ahead of the shock front. The front structure of ionizing shocks is analyzed qualitatively: some calculated results are also reported. Experimental results on magnetic structures are discussed. The physical mechanisms which shape the shock front in a plasma are examined. Some results calculated for the front structure in a plasma are reported.

This article describes in detail the method of the renormalization group and outlines the possibilities of using it for the analysis of high-energy asymptotics in the framework of quantum field theory. The renormalization group formalism is constructed for an arbitrary scheme of renormalization. The exposition is based on the concepts of effective charge and effective mass. Principal attention is given to the problem of deriving reliable information about the ultraviolet properties of quantized-field models on the basis of perturbation theory calculations. A summary of the results of such calculations for a wide variety of models is given.

The situation is found in a number of rare-earth compounds in which the narrow f level lies near the Fermi level, and configurations of the rare-earth ions differing in the number of f electrons (different valency) have close-lying energies. In this situation many properties of the corresponding substances, both thermodynamic (heat capacity, magnetic susceptibility, compressibility) and kinetic (optical properties, electric conductivity, etc.) are anomalous. Isostructural electronic phase transitions occur in these systems upon changing the external conditions. These are often simultaneously dielectric-metal and magnetic-nonmagnetic transitions. A phase having a narrow resonance level near E_F has been termed an intermediate-valence (IV) phase. This article reviews generally the problem of intermediate valency. The fundamental experimental facts are summarized. The conditions for appearance and the qualitative picture of IV states are discussed. A table is given of the currently know IV substances. The fundamental theoretical approaches to describing their properties and the electronic phase transitions in these systems are treated. The connection is established with other problems (the problem of dielectric-metal transitions, the Kondo effect, etc.). Major attention is paid to the fundamental unsolved problems.

Modern electron theory of metals abounds in geometric terminology and, by using geometric ideas, provides clear descriptions of many complicated phenomena. Some problems in the theory of normal metals that can be interpreted geometrically are examined in this paper in a language accessible to many physicists. Particular attention is devoted to those phenomena and properties that are connected with qualitative (topological) changes in geometric figures such as Fermi surfaces, plane sections though such surfaces, "belts" on the Fermi surface, and so on. Graphical illustrations of these ideas are provided.

In 1936, L. I. Mandel'shtam, together with M. A. Leontovich, extended the concept of Kneser-type relaxation to liquid media, and at the same time introduced the notion of microscopically inhomogeneous acoustical media and of another type of relaxation appearing in such media ("nonlocal relaxation"). These ideas were used (first at the suggestion of L. I. Mandel'shtam) for studying the acoustical behavior of such media as suspensions, emulsions, polycrystals, liquids with gaseous bubbles, etc. At the present time the same picture is used for constructing a theory of the sound propagation in pure high-viscosity liquids (the behavior of which does not fit into the scheme of Kneser-type relaxations) and for clarifying their structure. It has been established that the existing experimental material concerning the propagation of different types of waves in a number of high-viscosity liquids agrees well with the notion of a high-viscosity liquid represented by a microscopically inhomogeneous medium with structure: a disordered liquid with ordered regions ("clusters"). The assumed applicability of the picture of a microscopically inhomogeneous medium to high-viscosity liquids and nonlocal relaxation is likewise supported by observed changes in the values of a number of parameters for such liquids as a result of distillation and the gradual return of these parameters to their initial values.

Recent studies devoted to the problem of constructing a free-electron laser are reviewed. Possible approaches to description of the physical processes on which free-electron lasers are based are discussed briefly, and means of increasing the efficiency of laser arrangements are considered.