R e v i e w s

Acoustics and molecular physics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 5

This paper is a review of the studies of high-power acoustic beams, the results of their practical use and prospects for the future. A simplified self-consistent system of equations is presented to describe the behavior of an acoustic beam in liquid, with consideration for the excitation of the entropy and vortex modes and their reverse effect on the acoustic field. Experiments on thermal self-focusing of both quasi-harmonic and discontinuous waves are described, and the self-focusing of sawtooth waves is computed in a geometrical acoustics approximation. The possibility of inertialess self-focusing of sound in a medium with cubic nonlinearity is discussed. The state of the art of extracorporeal lithotripsy - a rapidly developing field at the junction of medicine and nonlinear acoustics is reviewed, and methods for calculating the focusing of high-pow acoustic pulses are described.

Show AbstractR e g u l a r p a p e r s

Theoretical and mathematical physics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 19

The asymmetry of the angular distribution of the radiant power of relativistic electrons in a synchrotron is interpreted based on the proposed model of anharmonic betatron oscillations of electrons. The Krylov-Bogolyubov method is used in the analysis. The computer calculation results agree with experimental data.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 1. P. 23

The problem of suppression of the charmonium $J/\Psi$ production in collisions of heavy ions has been investigated. The charmonium disintegration processes in the hadron gas, $\pi +J/\Psi \to \pi +c+\bar{c}$ and $\rho +J/\Psi\to D+D$ have been considered. The results obtained suggest that the contribution of the charmonium disintegration in collisions with gas hadrons and the contribution of the quark-gluon plasma production to the charmonium $J/\Psi$ birth suppression are effects of the same order of magnitude.

Show AbstractRadiophysics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 28

The effect of the electron drift velocity on the saturation current of a spherical probe has been determined for a diffusion regime, when it is necessary to take into account the electron sink effect. It is shown that for sufficiently large electric fields $Е$, $еЕа\ge kТ_е$ ($a$ is the probe radius and $Т_е$ is the electron temperature) the actual saturation current may notably exceed its value calculated for the case of zero drift velocity.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 1. P. 32

The nonlinear dynamics of a resonance four-wave interaction of two waveguide modes with the first and second harmonics of a charge density wave in a relativistic electron beam has been investigated. It is shown that in the case of relativistic beams there exists an unstable regime in which the second density harmonic is not excited. This phenomenon can be used to produce modulated beams with desired properties.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 1. P. 37

A new approach to wave scattering problems in randomly inhomogeneous media is described. This approach is called the modified traveling wave method and is used for solving the problem of radiation propagation across a one-dimensional layer with random inhomogeneities. It is shown that for this problem the modified traveling wave method generalizes the results of previous studies and helps specify the limits of applicability of the approximations used earlier.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 1991. **46**. N 1. P. 42

The amplitude and phase nonreciprocity is calculated for the interaction of oncoming light beams of finite transverse dimensions with a traveling ultrasonic wave. The ranges of the parameter values are determined for which consideration for the light beam width is essential.

Show AbstractAcoustics and molecular physics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 45

It is shown that in a solid truncated wedge whose local thickness depends quadratically on its height, along with the earlier predicted countable set of antisymmetric acoustic modes localized near the apex, there can also exist a single symmetric acoustic mode. This mode is localized in the vicinity of the wedge apex, and its characteristics are close to those of Rayleigh's surface acoustic mode. The phase velocity and the field structure of the mode are calculated. The lowest-frequency boundary for the region of its existence is determined.

Show AbstractGeophysics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 50

Polarization effects at nonuniform pressures in chemically homogeneous isothermal substances have been theoretically studied on the basis of the Thomas-Fermi-Dirac model. Estimates have been obtained for the Earth's electric and magnetic fields induced by gravitational compression and rotation.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 1. P. 56

Processes of energy exchange in a gravitational suspension flow have been experimentally studied. An equation for the transfer of the potential energy of solid particles has been derived. The anisotropy of pulsatory motions in the flow has been observed, and the possibility of turbulence production upon breakage of structures with an unstable stratification has been shown. Some peculiarities of flow motion in the regime of negative turbulent viscosity are discussed.

Show AbstractAstronomy

Moscow University Physics Bulletin 1991. **46**. N 1. P. 59

Possible reasons for the appearance of two maxima in the time variation of the intensity of $\gamma$ radiation with $E_{\gamma}$ = 2.22 MeV during the solar particle event of June 7, 1980 have been analyzed. It was concluded that these maxima were caused by the anisotropy of the neutron scattering by hydrogen and by the inhomogeneity of the solar atmosphere density in the subphotospheric area during the particle event.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 62

The effects of various surface factors on the semiconductor-metal phase transition in $VO_2$ films were experimentally studied. It has been shown that adsorption of donor $Н_2О$ and $NH_3$ molecules lowers the phase transition critical temperature $Т_с$, adsorption of acceptor $O_2$ molecules exerts no effect on $Т_c$, while adsorption of oxygen ions increases $Т_с$. UV irradiation causes degradation of the semiconductor-metal phase transition. The effect of phase transition photosensitization has been discovered. The experimental data obtained and the data of other researchers on the effects of external factors on the phase transition have been analyzed in terms of the phonon anharmonism model developed by the authors.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 1. P. 74

The molecular dynamics method has been used to study the characteristics of the effect discovered earlier which consists in that an atom emitted from a surface loses energy not only to overcome the forces attracting it to the surface, but also, to a considerable degree, for the recoil of the surrounding atoms. It is shown that analytical models of sputtering do not provide a correct picture of the total energy consumption in sputtering of atoms from the surface, which leads to wrong formulas for the distribution function of sputtered atoms with respect to the kinetic energy and the polar angle.

Show AbstractB r i e f r e p o r t s

Theoretical and mathematical physics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 80

An asymptotic procedure is described for an approximate solution of integro-differential equations in the dynamic viscoelasticity theory for media with relatively rapidly varying properties. The technique proposed is intended for calculating oscillatory and wave processes.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 1. P. 83

The rate of electron transfer from dimer to monomer of bacteriochlorophyll in the reaction center of $\textit{Rhodopseudomonas Viridis}$ has been estimated in terms of the Fermi golden rule. An activationless electron transfer machanism has been considered.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 1. P. 86

The paper deals with mode states of a quantized electromagnetic field which are nearest to classical simultaneous eigenstates of the photon birth and annihilation operators. It is shown that such states are distinct from coherent states but transform into the latter in the limiting cases of weak and strong fields.

Show AbstractRadiophysics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 89

A solution of relativistic kinetic Vlasov-Maxwell equations is obtained and studied within the cubic field approximation for upper hybrid waves propagating perpendicularly to an external magnetic field.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 1991. **46**. N 1. P. 92

Transformation of spatial fluctuations of the field of a completely nonpolarized light wave at the initial stage of beam collapse has been studied and the critical self-focusing power has been computed. It is shown that as radiation propagates in an isotropic medium, the degree of polarization increases, while the spatial coherence decreases.

Show AbstractGeophysics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 95

The results are given of a numerical simulation of a highly anisotropic Phillips' model for a developed disturbance of the sea surface. A conclusion is made on the applicability of the single-harmonic approximation to the calculation of some disturbance characteristics.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1991. **46**. N 1. P. 98

A difference has been found in the kinetics of photoconductivity variation during illumination for undoped a-Si:H films preliminarily annealed or illuminated at elevated temperatures. Several mechanisms have been suggested for photoinduced formation of dangling bonds in the films after their pretreatment under different conditions.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 1. P. 102

The effect of the adsorption of water vapors on the current-voltage characteristics and the frequency dispersion of the capacitance of an a-Si:H Schottky barrier has been studied. It is suggested that the orientational polarizability of water molecules decreases the height of the barrier and, besides, surface hydration affects the distribution of the density of localized electron states due to the saturation of broken silicon bonds with hydroxyl groups.

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