Table of contents

A review is given of the principles and prospects of directed channeling of neutral particles and photons in perfect crystals and in crystals containing microchannels of arbitrarily small width. It is shown that, in all cases (including a homogeneous lattice), the channeling of x rays and γ rays is accompanied by the modulation of the transverse structure of the wave and by a change in the longitudinal attenuation coefficient. The nontrivial special case of Mössbauer radiation channeling is investigated. A detailed discussion is given of the channeling of neutrons in crystals due to the 'optical' Fermi interaction with lattice nuclei, and the magnetic dipole-dipole and coherent Schwinger interactions in magnetic and nonmagnetic crystals. The effects of spin waves, elastic waves, and domain walls on channeling are examined. A discussion is presented of the possibility of channeling of neutral atoms with internal electromagnetic resonances by the induced-dispersive ordering interaction that takes place when the resonance frequency is equal to a harmonic of the bounce frequency associated with longitudinal motion in the periodic lattice. Experiments on neutron and γ-ray channeling are analyzed.

This review article is devoted to results of theoretical and experimental investigations of properties of nanometer metal particles. First, the modern theory of equilibrium structures and shapes of small particles is presented. The next Section deals with the thermodynamics of small particles. It reflects the present state of the theory of surface forces for small particles, including crystalline ones. Validity conditions are pointed out for the standard approach, and an alternative approach is described which is adequate for particles surrounded by their saturated vapor. In it the Laplace pressure is not a real physical force, but a formal quantity that describes the size dependence of the chemical potential. Specific features are described of melting and interphase fluctuations in small particles. In describing the electron properties of the particles emphasis is laid on the smoothed level density and the size dependence of the Fermi energy. Some effects caused by this dependence are presented, in particular the mutual charging of particles of different sizes which manifests itself in an anomalously strong attraction between particles and so on. Magnetic properties of small particles are also described including macroscopic quantum tunneling of magnetization.

Theoretical and experimental studies characterizing the status of the science of thermophoresis in gases at small Knudsen numbers (relative to the dimensions of the object) are analyzed. The known modifications of the theory of thermophoresis amount to an approximation linear in the Knudsen number, while the zero-order approximation corresponds to the result of Epstein. Analysis of the experimental data on thermophoresis of aerosols of high heat conductivity shows that, among all the experiments described in the literature, not one satisfies the requirements that allow one to perform a correct comparison with the theory. Also the results of experiments with aerosols (objects) of low heat conductivity are unsatisfactory. An original method of studying thermophoresis in gases is proposed.

A series of laboratory exercises in nonlinear wave physics assigned to students of the Physics Department of the Moscow State University in the laboratory of the Acoustics Section is described. The series consists of three assignments: 1) experimental investigation of nonlinear waves in dissipative media; 2) Investigation of nonlinear phenomena in acoustic beams by mathematical simulation using personal computers, and 3) Experimental investigation of wave propagation in a medium with dispersion (capillary waves on the surface of a liquid). As a result of carrying out these assignments, the students become familiar with the characteristic features of the behavior of nonlinear waves and the modern methods of describing and studying them.