Table of contents

Experimental investigations in gravitation and relativity theory are reviewed. The state of experiments that test the equivalence principle, the basis of the relativistic theory of gravitation, is discussed. The latest results of measurements of the classical effects of general relativity in the solar system are given and promising programs of similar experiments in the near future are analyzed. The new possibilities for testing gravitational theories provided by the discovery of the binary pulsar are described. Finally, the problem of searching for bursts of gravitational radiation using terrestrial Weber type antennas is discussed.

A description is given of the current state of the theory of intermolecular interactions. This includes a general physical picture of these interactions and an analysis of the relative contributions of different types of interaction (electrostatic, resonance, induction, dispersion, relativistic, magnetostatic, and exchange). The leading features of each contribution are discussed. A review is also given of methods available for calculating the potential specific for each range of distances between the interacting systems. Particular attention is devoted to an analysis of approximations used in different theoretical calculations.

A review is given of investigations of pulsed high-pressure volume discharges excited by fast-electron beams. The following topics are discussed: classification of discharges; methods for calculating the current-voltage characteristics; analysis of the optimal ways of depositing energy in the gas in the volume stage of the discharge; discharge instability mechanisms and the corresponding experimental observations; applications of discharges. The results are given of calculations of the electric field in the cathode and anode regions, and also in the discharge column in the case of a spatially inhomogeneous ionication of the gap. It is shown that a stable volume flow of the current in molecular gases in which the specific deposited energy is 0.1–1 J/cm³ may be attained in a nonself-sustaining discharge and in a discharge with ionization multiplication. In both cases a spark channel appears in two stages: formation of sparkinitiating centers in the form of plasma regions with a higher density near the electrodes is followed by growth of the spark channel from such initiating centers. In some cases the spark channel growth can be described by the available mathematical models. Discharges in mixtures of rare gases with halogencontaining compounds, when electrons are lost mainly by capture by complex molecules, are considered separately. Applications of volume discharges in laser pumping, switching of pulsed currents, plasma chemistry, etc., are described.

The article reviews the current state of the study of the dielectric properties of a medium in the x-ray and γ-ray frequency regions. Particular attention is devoted to the systematic introduction of the dielectric permittivity tensor in the x-ray region, starting from the most fundamental property of crystals–spatial periodicity. The properties of the permittivity tensor are treated both in terms of the phenomenological theory and on the basis of specific microscopic models. The review includes theoretical and experimental investigations of the contributions of the electronic and nuclear subsystems to the permittivity of crystals. The polarizability of the electron subsystem is considered in the strong-coupling approximation and in terms of the Bloch formalism. Considerable space is devoted to discussion of the permittivity near isolated low-lying nuclear transitions in the presence of hyperfme interactions, where its properties are substantially more complicated and more interesting than those of the permittivity of the electron subsystem. A review is given of the principal phenomena of the polarization optics of Mossbauer radiation. The review analyzes the symmetry properties of the x-ray permittivity and establishes a number of useful relations regarding generalized symmetry operations.

On the basis of forecasts of extraction of fossil fuels during the next fifty years an analysis is made of the accumulation in the Earth's atmosphere of carbon dioxide released in industrial processes. The effect of such changes on the Earth's climate and on harvests is discussed.