R e g u l a r p a p e r s

Moscow University Physics Bulletin 1981. **36**. N 2. P. 1

The paper is concerned with the angular dependence of the imaginary part of the optical potential for even-even nuclei in the low-energy region with allowance for excitation of lower collective states of the target nucleus. It is shown that the principal contribution to Im Vopt is made by the low collective states 2$^{+}$ and 3${-}$ of the target, which completely exhaust the entire imaginary part of the optical potential in the low-energy region. According to calculations, the contribution to Im Vopt, due to formation of the compound nucleus is small.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 8

This paper examines the wave-beam state in an infinite electron plasma at the stage when the particles are captured by the wave and undergo phase mixing. The state of the beam is described by nonlinear selfcongruent equations, the plasma remains a linear, dispersing medium. Estimates are obtained, characterizing the redistribution of the energy of the initial beam at single-mode generation of the longitudinal field by a low-density relativistic electron beam. The maximum generation efficiency amounts to 10% and is attained for nonrelativistic beams at(n$_{0}$/n$_{p}$)$^{1/3}$ ≅0,5, where n$_{0,p}$ are the beam and plasma densities. The u p и, p heating effectiveness at this stage is estimated. A comparison withresults of numerical experiments is performed.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 13

The paper examines a spatial-polarization filter (SPF)employed for supression of two-beam, partially scattered interference. The operation of the filter is based on the assumption that two interference beams have different polarizations and incidence angles. Two versions of operation of such a filter are analyzed for the caser of supression of a two-rbeam concentrated interference in receiving a partially scattered two-beam signal in the presence of additive noise. Analytic expressions, controlling the possible gain in the signal/noise ratio when using this filter are obtained.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 17

The effect of an electrostatic field on the translational motion of dislocations attendant to ultrasonic vibration is investigated. Moving dislocations were produced in an KC1 crystal by indentation and were detected by repeated etching. It follows from the experiments that the combined effect of the electrical and acoustic fields is not equivalent to the effect due to separate application of these fields. Upon combined application of both fields the number of moving dislocations and the mean length of rim rays in the dislocation rosettes is greater than upon application of only the ultrasonic field. Analysis of results shows that the electrical field increases path length and number of the moved dislocations, but has little effect on the starting stresses of translational motion of dislocations.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 23

The temperature dependence of magnetization in the generalized model of a ferromagnetic metal, including the direct interaction between ferromagnetic d -electrons and d-f type exchange, is investigated. It is shown that, at sufficiently low temperature, significantly lower than the Curie temperature T$_{c}$, the temperature dependence of magnetization for a subsystem of localized electrons deviates from Bloch's "T$^{3/2}$"

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 27

Conditions under which one should expect the inception of a smooth random field in a disordered (amorphous or alloyed crystalline) semiconductor are examined. It is shown that such a field may arise in not too well prepared specimens.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 31

The generation of a difference harmonic attending the vertical propagation in the atmosphere of two acoustic waves of close frequency is considered. Pumping of energy from the difference to the primary harmonic is possible at a certain distance from the source. The energy of the difference harmonic, after formation of a discontinuity in the primary radiat ion, tends to some constant value, determined by the ratio of the difference and fundamental frequencies. It is found that nonlinear effects manifest themselves in acoustic waves only at Mach numbers higher than some constant quantity, which depends on the values of the Knudsen number for the atmosphere.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 38

An expression for the shock profile of a spectral line with allowance for nonelastic processes is obtained within the framework of the kinetic approach. The width and shift operator, corresponding to Stark broadening is governed by the behavior of the spectral density of low-frequency field fluctuations. Due to incorporation of the medium's polarization, the resultant expression does not contain a divergence corresponding to large impact parameters.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 44

The paper examines a graphical method for determining domains of stability with respect to a free parameter of systems described by the characteristic equations φ$_{n}$(p)+ ψK$_{m}$(p)=0. Unlike frequency methods, it employs simpler graphs on the real plane (ω $^{2}$, K). The method is advantageous for investigating the stability of higher-order and multicontour systems. Features of the application of the method to certain particular cases are examined. The results are illustrated by numerical examples. In the case of higher-order systems it is advantageous to perform the calculations by computer.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 51

Nonlinear automatic control systems, obeying the Popov criterion of unconditional stability of the equilibrium position in sector [0,k] are discussed. The root loci technique is used for obtaining conditions, in general form, at which this sector is at maximum and equal to the Gurvits sector of corresponding linear systems. Systems with class [3,m] and [4,m] linear parts are investigated.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 58

The existence of an analytic solution of Einstein's equations, which contains a maximum number of physically arbitrary functions, in which scale factor R of the co-moving space passes through a regular minimum, corresponding to the finite density, is shown. Cases of an ideal and a viscous medium upon complete specification of the law of viscosity are considered separately. The nature of the distortion of the comoving space, variation in the volume and density of the ideal and viscous fluids are examined near the regular minimum of R.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 64

The problem of the density of states of deep fluctuation levels in a semiconduct or doped by fine donors and acceptors is considered with allowance for Debye screening. The dependence is found of the leading term of the logarithm of the density of states and of the electron localization radius 1/α on ionization energy E, for different values of parameter δ = N$_d$r$_{0}^{4}$/a$_{B}$, where N$_d$ is the donor population, r$_{0}$ is the screening radius, and a$_{B}$ is the Bohr radius of an isolated doping-material atom. It is clarified that the form of the distribution of doping-material electrons in an optimal fluctuation, the potential energy of an electron in an optimal well, and consequently, also the density of states of deep fluctuation levels are highly dependent on the screening radius r$_{0}$.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 69

X-Ray diffraction analysis of mono- and polycrystals and electron microscopy are employed for investigating the structural mechanism and kinetics of precipitation of ω and α phases and ZrMo$_{2}$, Zr$_{3}$Al, and ZrV$_{2}$, intermetallic compounds from а β solid solution. It is found that an ordered ω$_{2}$ phase is precipitated from an ordered body centered cubic of the β solid solution in the Zr-Mo-Al alloy.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 77

Delocalizations of the A and С excitations of a mercury-like ion in the "bismuth" center of BaS-Bi phosphors at 80°K is investigated by considering the characteristics of a photostimulates scintillation. It is found that excitations in the A band are not accompanied by delocalization of impurity-electron excitations, whereas excitation in the С band is accompanied by delocalization involving "memorization" of the ionization location upon election breakoff.

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

Moscow University Physics Bulletin 1981. **36**. N 2. P. 88

A method for calculating the directivity pattern of the far field of an emitter from the measurement of the pressure and its normal derivative in the near field of the emitter when the condition of free space is not satisfied, i.e., when the boundaries of a homogeneous acoustic domain affect the field produced by the emitter, is suggested.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 81

The need for performing the experiment described herein is justified. The correlation between the transmission spectrum of an aqueous solution at λ = 810 nm and the readings of the neutron monitor (correlation coefficient of 0.63) is found, which may serve as an indication of the relationship between phenomena occuring in the outer space and the structure of aqueous solutions.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 85

The results of experimental studies of two-dimensional angular spectra of orthogonal projections of the vector of a partially scattered field, reflected from the F$_{2}$ ionosphere layer upon vertical sounding are presented. It is found that the center of the angular spectrum deviates from the undisturbed direction, the scattering of the wave along and across the terrestial magnetic field is anisometric, and also the degree of the scattering of orthogonal projections of the field differs.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 91

The spectral distribution and the intensity of induced three-photon scattering near the 5$^2$S$_{1/2}$—5$^2$P$_{1/2,3/2}$ resonance transitions of the rubidium atom upon excitation of a narrow (0.2cm$^{-1}$) frequency-tuned pumping line with intensities up to 30 MW/cm$^2$. The forced three-photon scattering was observed in the form of a wide asymmetric line. A much slower intensity falloff was always observed from the edge of the line, removed from resonance ω$_{0}$ frequency of the atomic transition. The highest-energy pulse due to induced three-photon scattering was attained upon long-wave divergence between pumping frequency ω$_{L}$ and the resonance frequency, i.e., ω$_{0}$-ω$_{L}$~1-4cm $_{-1}$. The dependence of the shift of the maximum of the line of induced three-photon scattering on ω$_{0}$-ω$_{L}$. It is shown that the location of the maximum and the intensity distribution of the induced three-photon scattering line are in satisfactory agreement with theoretical estimates, making allowance for the shift of atomic levels as a result of Stark's dynamic effect.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 95

Adsorption of hydrogen atoms on a real surface of a germanium monocrystal vacuumed at 700°K results in a significant rise in the monotonic component of the surface recombination rate at virtually unchanged capture of. charge carriers onto fast surface states. The quasicontinuous spectrum of recombination nuclei is independent of the spectrum of fast states.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 99

It was found in investigating of the structural states in austenitic Fe alloys with 19% Ni and 10% Ru; 27% Ni and 2% Ru, and in an 34.4% Ni with FCC lattices that particles of a solid Fe-Ru solution in NiO form in the course of electrical polishing. No such particles were observed in a Fe alloy with 20% Ni, which has an α phase structure with a BCC lattice. The formation of the(Fe, Ru, Ni)0 particles is attributed to penetration of oxygen atoms into the austenite lattice.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 102

Moscow University Physics Bulletin 1981. **36**. N 2. P. 105

The diagonalization technique is employed for calculating the excitation energies and the widths of self-ionization $^1$Р$_{1}^{(-)}$ and $^3$Р$_{1}^{(-)}$ states of Fe$^{24+}$ ions, converging to the n = 2 threshold of the residual ion. The calculations were performed with allowance for the spin-orbital interaction, and also in the LS coupling approximation. It is seen by comparing our results with calculations which included Breit's complete operator that in calculating the widths of self ionization levels of helium-like iron ions in the intermediate coupling approximation one can restrict himself to only the single-particle operator of the spinorbital interaction. Here allowance for configuration mixing with respect to the principal quantum number results in only insignificant changes in the excitation energies and width of the self-ionization levels under study.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 108

An algebraic classifcation of electromagnetic fields based on investigating characteristic λ matrices for field tensor F$_{μν}$ is considered. A Petrov-Penrouse type diagram for electromagnetic fields is constructed. An analogy between certain exact solutions for the gravitational and electromagnetic fields is examined.

Show AbstractMoscow University Physics Bulletin 1981. **36**. N 2. P. 112