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

Theoretical and mathematical physics

Moscow University Physics Bulletin 1991. **46**. N 2. P. 4

An exact solution is obtained for electromagnetic waves in a cosmological model of a G$\stackrel{..}{o}$del type universe. It is shown that the character of propagation and the spectrum of electromagnetic waves depend on the rotation only and are independent of the space-time causal structure.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 7

Modern variational-difference methods of calculating dielectric waveguides, in particular lightguides, are reviewed. Consideration is given to the main problems that arise when the method of finite elements and the method of finite differences in the variational formulation are used to study the propagation of electromagnetic waves in straight dielectric waveguides homogeneous along the guiding axis, having a complex shape of the cross section and a complicated profile of permittivity. The paper describes various types of variational formulation, various ways of bounding the region and taking into account the behavior of the field at infinity, as well as methods of reducing the initial problem to the algebraic problem of eigenvalues and calculating eigenvalues and eigenvectors. Special attention is paid to the elimination of physically meaningless spurious solutions, the so called "ghosts".

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 14

In this paper it is proved that in the case of a continuous and absolutely integrable kernel of Whitham's equation, an initially piecewise-smooth (sharpened) perturbation remains piecewise smooth during the whole time of existence of a solution to Cauchy's problem.

Show AbstractAtomic and nuclear physics

Moscow University Physics Bulletin 1991. **46**. N 2. P. 19

A weak (below 400 Oe) low-gradient magnetic field was observed to deflect a small number of evaporated Fe atoms from their initial path by an angle exceeding 90° at distances of about 50 mm. This finding can be explained by the presence of an uncompensated magnetic charge on these atoms.

Show AbstractRadiophysics

Moscow University Physics Bulletin 1991. **46**. N 2. P. 22

A new type of three-mirror telescopic resonator has been developed on the basis of mathematical modeling of electron beam interaction with electromagnetic field in a quasioptical gyrotron. The distribution of the RF field in the resonator enables an optirnum beam-field energy exchange. Up to 90% of the transverse beam energy is transferred to the electromagnetic field.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 28

The mechanism of heating of a molecular gas in a free-localizing RF discharge in a focused beam was investigated. The experiments were made in nitrogen and air at pressures from 1 to 100 Torr. It has been shown that at high values of the reduced electric field strength, one of the principal mechanisms that bring about gas heating in a free-localizing RF discharge is the quenching of long-living electron-excited states of nitrogen molecules.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 32

Thermal noise in a gravitational antenna with a piezoelectric transducer has been studied theoretically. The noise parameters of the piezoelectric transducer have been computed using the fluctuation dissipation theorem and standard techniques for describing noise in linear four-pole networks. The geometrical dimensions of the piezoelectric plate necessary to ensure low intensity of the excess noise for a reactive impedance of the source have been determined.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 36

An electron traveling along a bare dielectric waveguide at a velocity close to the wave phase velocity can be used to control photons in the waveguide. Two possibilities are discussed: a change in photon polarization and re-emission of a photon from one waveguide into the other. The analysis takes into account the radiation friction of an electron.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 1991. **46**. N 2. P. 41

The influence of various nonlinear effects on fluorescence saturation in photosynthesizing organisms has been studied. Approximate analytical formulas for the population of molecular excited states and the saturation factor are obtained using a photosynthetic unit model. The S-S annihilation phenomenon is shown to make the largest contribution to fluorescence saturation.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 46

A solid-state ring laser with an autopumping wave is considered. Part of the radiation is extracted from the laser resonator and is fed into the active medium by means of a moving mirror. It is shown that in this case the autopumping wave can be used to obtain a frequency bias in the ring laser.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 51

It is established that there exists a general similarity between the "focused" pulse (the pulse that has passed through the "time" lens) and "unfocused" pulse which propagate in a linear medium with second-order dispersion. The well-known coincidence of the pulse shape in the distant zone and in the focus is a particular manifestation of this rule.

Show AbstractGeophysics

Moscow University Physics Bulletin 1991. **46**. N 2. P. 60

A nonlinear generation of harmonics due to nonlinearity in a long wave propaiating in shallow water has been considered. The Boussinesq equations taking into account friction against the bottom are solved by the asymptotic averaging method. A set of reduced equations was obtained for the amplitudes of nonlinearly interacting harmonics in a long wave depending on the distance from the coast. The set was solved by the Runge-Kutta method, and the results compared with the data of the specially designed laboratory experiment. The agreement of the calculated and observed amplitudes of the harmonics and of the fundamental wave is good. The conclusion is drawn that friction against the bottom plays an important role in the norilinear dynamics of long waves.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 65

The results of experimental determination of the critical Rayleigh number characterizing the onset of the turbulent free convection regime are presented. It is demonstrated that for the developed free convection regime, in the uppermost layer of water that is cooling from the surface, the Rayleigh number is 1105. This is consistent with the theoretical value for an interfacial layer with one boundary fixed and the other free.

Show AbstractAstronomy

Moscow University Physics Bulletin 1991. **46**. N 2. P. 68

Proceeding from the theory of perturbations, the effect of disk bends and radial flows on the dynamo in a thin disk has been considered. Taking the Galaxy and the spiral galaxies M51 and M81 as an example, it has been established that the role of both factors is not great. The weak influence of the radial flows is explained by the character of their dependence on the radius. The role of the disk bends mainly reduces to an effective change of the rotation curve.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1991. **46**. N 2. P. 74

The introduction of activating $Yb^{3+}$ and $Еr^{3+}$ ions belonging to the right-hand subgroup of the lanthanide series is shown to affect the mechanisms of structure formation in the $BaY_2F_8$ and $LiYF_4$ fluoride matrices. For the optical applications, it is essential that these crystals exhibit two types of microtwin structures corresponding to two types of polymorphic transformation. Another important finding is the appearance in $Еr^{3+}$-doped crystals of active centers responsible for the formation of a structure essentially different from that of the $Yb^{3+}$ activated matrix.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 79

Magnetic and electrical properties of solid solutions of the $Cu_xMn_{1-x}Cr_2S_4$ system have been studied for $x$ = 0; 0.1; 0.2. It has been found that the magnetic moment of these compounds measured at 4.2 K increases with $x$ and corresponds to a valence distribution $\vec{Cu_x^{2+}}\vec{Mn_{1-x}^{2+}}Cr_2^{3+}S_4^{2-}$. The introduction of copper in the ferrimagnetic semiconductor $MnCr_2S_4$ leads to a significant increase in the Curie temperature (above 300 K) and retention of the semiconductor type conductivity. Thus, we have discovered new nondegenerate semiconductors with magnetic ordering temperatures above the room temperature, which is an important factor for their practical application. It is suggested that the growth of $Т_с$ is due to the existence of a strong s-d exchange interaction in compositions with $x$ = 0.1 and 0.2. The magnitude of this interaction is estimated at $AS\approx 0,4$ eV.

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

Theoretical and mathematical physics

Moscow University Physics Bulletin 1991. **46**. N 2. P. 83

The thermodynamic potential of a nonrelativistic gas of electrons (which possess an anomalous magnetic moment) in crossed, uniform electric and magnetic fields has been constructed. The results obtained are used to explain the features of the normal quantum Hall effect in two-dimensional systems.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 87

The feasibility of controlling the amplitude, duration and frequency of two-component optical solitions formed in two-mode fiber light guides, has been studied analytically and numerically.

Show AbstractAtomic and nuclear physics

Moscow University Physics Bulletin 1991. **46**. N 2. P. 90

It is shown that the use of SU(4) and SU(6) groups in analysis of neutral axialvector pp-transitions substantially changes the relation between the singlet and nonsinglet parts of the Ellis-Jaffe rule of sums and partly helps in solving the problem of "spin crisis".

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 1991. **46**. N 2. P. 93

It is reported that explosive self-compression of pulses can be obtained in systems with a nonlinear response of higher orders.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 2. P. 95

Fluorescence spectroscopy with numerical resolution of spectral curves by the Alentsev method has been used to study the interaction of hematoporphyrin with a lipid bilayer of liposomes. The effects of temperature, ionic strength of the solution, and incubation time have been investigated.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1991. **46**. N 2. P. 98

An anomalous temperature dependence of the thermal conductivity of the triglycine selenate crystal has been observed in the region of phase transition. The results are interpreted on the assumption ·of scattering of acoustic phonons by disordered elementary dipoles of the crystal lattice.

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