Faculty of Physics
M.V.Lomonosov Moscow State University
Theoretical and mathematical physics

On a relaxation of normal velocity in a crystal

M.Yu. Kovalevskii, V.A. Krasnikov

Moscow University Physics Bulletin 1990. 45. N 4. P. 5

Based on two fundamental ideas of N.N. Bogolyubov, namely the concept of quasi-means and the method of reduced description, the effect of crystal lattice on the dynamics of a superfluid is taken into account within the framework of microscopic description. The coefficient of deceleration of normal velocity is expressed in terms of the correlation function. Equations of motion are derived for densities of additive integrals of motion and superfluid momentum. The positive definiteness of entropy production is proved.

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On some a priori estimates for the solution to the nonlinear diffusion problem

A.V. Schepetilov

Moscow University Physics Bulletin 1990. 45. N 4. P. 10

In this paper, under consideration is a boundary value problem for a quasilinear parabolic equation describing the cementation process in the hardening of a steel specimen. Its solution is compared with the solution to an analogous linear problem. It is shown that by selecting a diffusion coefficient and boundary and initial conditions in the linear case it is possible to obtain a two-sided estimate for the solution to the nonlinear problem using the solution to the linear problem.

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Fermions in the Aharonov-Bohm field: scattering and spin effects

D.V. Gal'tsov, S.A. Voropaev

Moscow University Physics Bulletin 1990. 45. N 4. P. 14

Particular features of scattering of relativistic particles with spin 1/2 in the Aharonov-Bohm gauge field are considered. For this purpose use is made of the model of a solenoid of radius $a$ with subsequent passage to the limit for $a\to 0$, the magnetic flux being conserved. It is shown that the electromagnetic potential affects the initial spin state of the particle.

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On the ground state of two-dimensional electron gas in a quantizing magnetic field

V.R. Khalilov

Moscow University Physics Bulletin 1990. 45. N 4. P. 18

It is shown that the Fermi energy of two-dimensional electron gas in a magnetic field is quantized. Approximate formulas are obtained for the electron ground state energy in weak and strong magnetic fields with consideration for the interaction of electrons at zero temperature. It follows from the results obtained that,depending on the relationship between the problem parameters (electron density, magnetic field intensity, and orbital angular momentum of relative motion), there can occur phase transitions in the electron system. A simple formula is derived, which relates the Landau level occupancy in a strong magnetic field to the orbital angular momentum of the electron pair.

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Mass generation at finite temperature and density in the Gross-Neveu model

A.S. Vshivtsev, V.Ch. Zhukovskii, B.V. Magnitskii

Moscow University Physics Bulletin 1990. 45. N 4. P. 23

The paper examines the effect of finite values of the temperature and chemical potential on mass generation in the Gross-Nevue model. Relations between the mass, chemical potential, and the temperature are found for the fermion gas under consideration.

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Quarkonium dissociation in quark-gluon plasma

R.N. Faustov, I.G. Vasilevskaya

Moscow University Physics Bulletin 1990. 45. N 4. P. 26

Suppression of birth of $J/\Psi$ charmonium in collisions of heavy ions was observed in several experiments. This phenomenon can be a consequence of formation of quark-gluon plasma, charmonium-hadron collisions, and nuclear absorption effects. Therefore, of interest is the dissociation of quarkonium in quark-gluon plasma. In this communication, calculations are carried out for the processes $J/\Psi+g \to c+\bar{c}$ and $\Upsilon + g \to b+\bar{b}$ at various temperatures.

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Determination of wave dispersion in open periodic structures by the probing source method

V.I. Kanavets, A.I. Slepkov, A.V. Fyodorov

Moscow University Physics Bulletin 1990. 45. N 4. P. 31

A method is presented for the theoretical determination of wave dispersion in open periodic structures which does not require solving the dispertion equation. This method can be applied to physical processes in systems typical of relativistic SHF electronics.

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The envelope distribution function and noise immunity in reception of multy-path signals

L.N. Arefyeva, Yu.V. Berezin

Moscow University Physics Bulletin 1990. 45. N 4. P. 35

A general formula is derived for the envelope distribution function $W(A)$ superposition of $N$ coherent fields. The results are used to solve the problem of noise immunity in the reception of data transmitted over an ionospheric channel.

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Processing the probe current-voltage characteristics with consideration for the electron drain to the probe

L.M. Volkova, A.M. Devyatov, M.A. Mal'kov, V.S. Nikolaev

Moscow University Physics Bulletin 1990. 45. N 4. P. 39

It is shown that in conducting probe measurements in He discharge plasma, the drain parameter can be assumed energy independent and equal to $\delta=\delta (kT_e)$ to a good accuracy. When the measurements are carried out in discharge plasma in Ramsauer gases Ar, Kr and Xe, the neglect of the drain parameter energy dependence leads to an error of about 50-70% in the determination of both the mean energy of electrons and their concentration.

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Optics and spectroscopy

Numerical analysis of energy migration in a model of a photosynthetic unit

A.A. Demidov, E.A. Chernyavskaya

Moscow University Physics Bulletin 1990. 45. N 4. P. 45

This paper considers a model problem of the dependence of the efficiency of energy transfer between various forms of Chlorophyll a in a photosynthetic unit on the number of the forms without taking into account spatial heterogeneity in the distribution of these forms within the photosynthetic unit or spatial orientation of Chlorophyll a molecules.

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The monochromatically pumped double-wave solid-state laser

Moscow University Physics Bulletin 1990. 45. N 4. P. 50

The characteristics of a $YAG:Nd^{3+}$ double-wave solid-state laser with monochromatic pumping were studied. Highly stable double-wave lasing was obtained at wavelengths $\lambda_1$ = 1.064 $\mu$m and $\lambda_2$ = 1.318 $\mu$m when a nonlinear-loss element was introduced into the cavity. It was shown that the intensity of generated waves can be controlled by changing the temperature of the active element.

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On a possible mechanism of spectrum detection in molecular computers

A.S. Mikhailov, I.Yu. Poteryaiko

Moscow University Physics Bulletin 1990. 45. N 4. P. 54

A possible mechanism of detecting spectra in molecular computers is suggested. The mechanism is based on particle tunneling along the molecular chain in which the potential profile depends on the spectrum of incident radiation. The tunneling factor is calculated for the elementary potential profile with a finite number of barriers and gaps between them.

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Study of the structure of heterogeneous dye associates in binary solvents

L.V. Levshin, A.M. Saletskii

Moscow University Physics Bulletin 1990. 45. N 4. P. 58

The luminescence spectrum characteristics of solutions of rhodamine dyes with methylene blue in binary solvents have been studied. It is shown that processes of their heterogeneous association depend on the size and composition of the solvation shells of the dye molecules. A mechanism is suggested which explains loss of the fluorescence ability by heterogeneous associates of the dyes studied.

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Acoustics and molecular physics

Wide-band ultrasonic spectroscopy of colloidal media on the basis thermooptical acoustic generator

A.A. Karabutov, M.P. Matrosov, N.B. Podymova, V.A. Pyzh

Moscow University Physics Bulletin 1990. 45. N 4. P. 63

A scheme of wide-band acoustic spectrometer is proposed for investigating the dynamic properties of condensed media. To produce acoustic pluses use is made of an optoacoustic generator with thermooptical sound excitation. The frequency dependence of acoustic absorption in water suspensions of bentonite clays in the 1-14 MHz range has been obtained and the relaxation parameters of these suspensions have been calculated.

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Solid state physics

Magnetization of neodymium-yttrium garnet ferrites

K.P. Belov, N.V. Volkova, L.A. Skipetrova

Moscow University Physics Bulletin 1990. 45. N 4. P. 69

Magnetization of five single crystals of the $Nd_xY_{3-x}Fe_5O_{12}$ ($x$ = 0.0, 0.5, 0.95, 1.39, and 1.72) system was studied in the temperature range from 4.2 К to the Curie temperature. The measurement results suggest that at the helium temperature the [110], [111] and [100] crystallographic directions are the easy, intermediate, and the hard magnetization directions, respectively. The argeement of the experementally found magnetization values with those calculated by the Neel theory is found to be fairly good on the assumption that an uncollinear magnetic structure is formed in these compounds at temperatures below 77 K.

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Theoretical and mathematical physics

Gauge model for the fifth force

G.A. Sardanashvily, E.G. Timoshenko

Moscow University Physics Bulletin 1990. 45. N 4. P. 73

In this paper the Lagrangian and the gauge model equations are constructed for the fifth fundamental interaction and the related corrections to the Newtonian potential are calculated.

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Adsorption of charged particles on a metal surface in the method of two-particle density functionals

A.M. Gadzhiev, O.S. Erkovich, V.V. Komarov, A.M. Popova

Moscow University Physics Bulletin 1990. 45. N 4. P. 76

The properties of an inhomogeneous electron gas near a metal surface were considered. A numerical analysis of the work function and the adsorption energy of hydrogen ions and atoms on the W, Ir, and Pd surfaces was carried out. The calculations were made by the method in which the system energy is a functional of the two-particle density function, and this enables one to take into account the exchange-correlation phenonema.

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Atomic and nuclear physics

Photodetachment of heluim-like hydrogen ion

S.M. Burkov$^1$, N.A. Letyaev$^2$, S.I. Strakhova$^2$

Moscow University Physics Bulletin 1990. 45. N 4. P. 79

By using the $R$-matrix formation, cross-sections of the negative hydrogen ion photodetachment and parameters of the photoelectron angular distribution anisotropy have been calculated. The calculations have been performed in the close-coupling approximation of six states. Comparison has been made with the experimental and theoretical data obtained by other authors.

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Optics and spectroscopy

Quantum fluctuation and squeezed states in a nonlinear resonator

A.V. Belinskiy

Moscow University Physics Bulletin 1990. 45. N 4. P. 83

A quantum solution of the problem of field evolution in a nonlinear resonator with random $Q$ factor is proposed. The inconsistency of relevant semiclassical theories has been demonstrated using the example of phase self-modulation or a paramagnetic gain which occurs in the resonator. In particular, the squeezing efficiency predicted by semiclassical theories proves to be overestimated and the regimes recommended to attain it do not prove to be optimal.

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Numerical study of polarization hysteresis in a double-path optical system with nonlinear medium and rotating mirror

V.A. Bulokhova, A.A. Golubkov, Ya.M. Zhileikin, V.A. Makarov

Moscow University Physics Bulletin 1990. 45. N 4. P. 87

The stability of stationary states of the field in a polarization reflector has been studied. The existence of polarization bistability and effects of hysteresis in the reflector has been shown.

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Astronomy

Groups of minor planets in the case of third-order commensurability

E.L. Vinnikov

Moscow University Physics Bulletin 1990. 45. N 4. P. 90

Groups of resonance asteroids of the third order have been identified and the most numerous group corresponding to the 5:2 commensurability has been described statistically.

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Estimation of the depth of isostatic compensation on Venus

R.V. Gabbasov

Moscow University Physics Bulletin 1990. 45. N 4. P. 93

The average global depth of the isostatic compensation on Venus has been evaluated by the transfer function method on the basis of data on the expansion of the gravitational field and relief of Venus in spherical functions up to the 18th order and power.

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Solid state physics

$Ar^+$ ion implantation-induced production in the dielectric layer of $Ge-GeO_2$ structures

P.K. Kashkarov, A.V. Kolesnikov, A.V. Petrov, I.G. Stroyanova

Moscow University Physics Bulletin 1990. 45. N 4. P. 96

$Ar^+$ ion implantation into a $GeO_2$ film on a Ge surface has been found to induce the generation of hole traps in the ion retardation layer and electron traps in the $GeO_2$ layer at the boundary with Ge, this being manifested by an increased instability of the surface charge under illustration.

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Laser stimulation of nonstationary SHF absorption in a semiconductor

A.N. Bachurin, A.V. Kozar', S.A. Krupenko

Moscow University Physics Bulletin 1990. 45. N 4. P. 99

Considered was the interaction of continuous SHF radiation in the 8-mm wavelength range with laser radiation in the near IR range in a layer of pure crystalline silicon which filled completely the cross-section of a rectangular waveguide. An experimental method is proposed for studying photocarrier diffusion processes and determining charge carrier lifetimes.

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On photoelectric properties of ultrapure silicon

V.A. Morozova, O.G. Koshelev, V.V. Ostroborodova

Moscow University Physics Bulletin 1990. 45. N 4. P. 102

Photoconductivity spectra of ultrapure silicon at 80 К exhibit transitions in which longitudinal acoustic phonons and excitons take part. It is shown that effective trapping centers with a concentration of about $5\times10^{11}$ cm$^{-3}$ change the effective lifetime of charge carriers at 80 К by 3 to 4 orders of magnitude.

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Simulation of the electric structure of amorphous Ni-P systems

V.S. Stepanyuk, B.L. Grigorenko, A.A. Katsnel'son, A. Sas, O.V. Farberovich

Moscow University Physics Bulletin 1990. 45. N 4. P. 106

An attempt was made to trace the variation of the electric structure of a Ni-P system with increasing concentration of P. The effect of the changes at the first and second coordination shells on the electronic structure of the system under study was demonstrated.

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The influence of adsorption-desorption processes on the switching effect in $VO_2$ films

S.Yu. Vinichenko, N.L. Levshin, S.Yu. Poroikov

Moscow University Physics Bulletin 1990. 45. N 4. P. 109

The influence of adsorption of donor and acceptor molecules on the switching effect was studied in vanadium dioxide films. The switching voltage was found to increase with adsorption of donor molecules and to decrease as a result of UV irradiation.

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