Table of contents

The article reviews the present status of the microscopic theory of non-transition-metal lattice vibrations. A regular scheme is described, which makes it possible to analyze in detail the role of the electrons in the formation of the phonon spectrum of metals. It is based on a consistent utilization of a small parameter V_K/∊_F, corresponding to the effective weakness of the interaction between the conduction electron and the ion core (V_K is the Fourier component of this interaction with a momentum transfer equal to one of the reciprocal-lattice vectors). Expansion of the electron-ion energy of the system in terms of this parameter yields, besides the pair interactions that are traditional for metals, also automatically the effective three-particle etc. unpaired inter-ion forces. It is shown that the unpaired forces play an important and sometimes decisive role in a number of questions, such as lattice stability, compressibility, the Cauchy relations for the elastic moduli, and singularities in the phonon spectrum. The theoretical analysis is illustrated by calculations of the static and dynamic properties of metals, and' by comparison with experiment, using Na, Mg, Al, and β-Sn as examples.

Interest in fluids with strong magnetic properties has developed in recent years in connection with technical applications. Artificially created magnetic fluids are suspensions of very fine (~10^–6 cm) particles of ferromagnetic material in ordinary (as a rule nonconducting) liquids. This review briefly describes the methods of preparation and considers the stability problems of magnetic colloids. It deals principally with their physical and hydrodynamic properties. It summarizes the results of theoretical and experimental investigations of the effect of a magnetic field on the equilibrium conditions and on the character of the motion of the suspensions. A considerable part of the article is devoted to an analysis of critical phenomena—instability of the free surface of the liquid in an external field and thermoconvective instability. The mechanisms of relaxation of the magnetization of a suspension are discussed; the most important of these are rotational Brownian motion of the particles and the Néel fluctuation mechanism, which leads to the superparamagnetism of subdomain particles of a ferromagnetic material. Important differences are noted between the hydrodynamics of suspensions of superparamagnetic and of ferromagnetic particles. In the latter case it is necessary to take account of rotation of the particles themselves, which greatly complicates the picture of the interaction of hydrodynamic and magnetic phenomena. Consideration is given to various effects caused by internal rotation: anisotropy of the viscosity and of the magnetic susceptibility, entrainment of the suspension by a rotating field, and dependence of the kinetic coefficients on the field intensity.

The review is devoted to an investigation of the behavior of vortex filaments in hard superconductors. The analysis is carried out in the region of weak magnetic fields, where linear electrodynamics is applicable. This permits a simple physical interpretation of both the properties of isolated vortices and of interactions of vortices with one another and with the surface of the superconductor. A number of examples of the influence of the superconductor outer boundary on the vortex structure are analyzed. It follows from these examples that the vortex lattice is stable relative to a transverse transport current even in an ideally homogeneous sample. Estimates are presented of the maximum transport current at which the vortex structure still remains stable. The role played by the internal surfaces in a superconductor is also illustrated with the interaction of a vortex with a cylindrical cavity or with an interface between two different superconductors as an example.

A review is presented of the observational data on detection of cosmic γ rays. The importance of observations in γ astronomy in solution of a number of basic problems of cosmic-ray physics, astrophysics, and cosmology (for example, the origin and sources of cosmic rays) is emphasized. Observations of isotropic diffuse and galactic components of γ radiation are presented and analyzed. Methods are discussed for searching for discrete sources of cosmic γ rays, and results are presented on detection of γ-ray fluxes from the sun, the Crab nebula, pulsar NP 0532, Cyg X-3, and other discrete sources. The results of the observations definitely indicate a variability of the discrete γ-ray sources. In conclusion a short review is given of new methods of γ-astronomy observations.

Improper ferroelectrics are considered in the review from a unified point of view on the basis of the phenomenological Landau theory of phase transitions. In such ferroelectrics, in contrast to the ordinary ones, the order parameter of the phase transition is not the polarization but another physical quantitiy whose transformation properties are different from those of the polarization. Spontaneous polarization arises in the phase transition as a secondary effect. Therefore, the dielectric anomalies in the improper ferroelectrics are significantly different from the dielectric anomalies in the ordinary ferroelectrics. In particular, the temperature dependence of the permittivity does not obey the Curie-Weiss law, an electric field does not suppress the phase transition, etc. The dielectric anomalies are derived by analyzing a definite form of the thermodynamic potential with a two-component order parameter. Such an analysis turns out to be sufficient for the discussion of the available experimental data. The domain structure of the improper ferroelectrics also possesses specific properties: In particular, there exist domains which do not differ in their polarizations. Since the loss of stability in an improper ferroelectric phase transition occurs not with respect to polarization, the soft mode in the nonpolar phase is inactive in the infrared spectrum. Other distinctive features of the phonon spectrum in the phase-transition region are also considered. The experimental data on improper ferroelectrics are discussed. For the rare-earth molybdates, the theory is in quantitative agreeement with experiment. In certain other improper ferroelectrics the phase transitions are of first order and nowhere near to being of second order. The quantitative description of such transitions requires additional experimental data and further development of the theory.

The existence of two sounds of different natures in the superfluid liquid is one of the best known and most thoroughly investigated properties of helium. An enormous mass of experimental and theoretical material on wave processes in helium has accumulated during the years that have passed since the discovery of second sound. Interest in these problems has especially increased in the last decade, first, because of the discovery of third and fourth sound (oscillations that propagate when the normal component of the liquid is clamped), and second, because of the possibility of investigating ultrashort sound waves by neutron and photon scattering. In this article the fundamental theoretical concepts and experimental results concerning the propagation of sound waves of the several types in superfluid liquid (in He⁴ and He³-He⁴ solutions) are reviewed. Much attention is given to quantitative, as well as qualitative, comparison of the experimental results with theory. The bibliography has been made as complete as possible. The following topics are not discussed, although they touch directly upon the subject under review: the propagation of sound near the lambda point, the passage of waves across liquid-liquid and liquid-vapor interfaces, and the propagation of large-amplitude sound waves.

A review is given of the current state of studies of the confinement and stabilization of hot plasma using high-frequency magnetic fields in the megahertz region. The principles upon which such studies are based are summarized. A theoretical analysis is reported of a plasma confinement system using "traveling-wave" high-frequency fields and of the results of experiments performed with systems of this kind. Another section is devoted to dynamic plasma stabilization systems, the fundamentals of the theory of the dynamic stabilization of the Z pinch, and the results of experiments performed in this field. Experimental data are compared with the basic assumptions of the theory and certain general conclusions are reported with regard to further developments and possibilities in this subject.

This review examines the renormalizability of various theories of vector fields. A discussion is given of how renormalizable theories in which the mass of a vector field arises from spontaneous symmetry breaking are used to construct models of the weak, electromagnetic, and strong interactions. Certain specific schemes and the experimental bounds on the parameters of these schemes are analyzed.