R e v i e w s

Theoretical and mathematical physics

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

Physical problems involving nonlinear nonlocal equations (NNE) have been reviewed. The topics discussed included (i) local and global existence in time of solutions to nonlinear nonlocal equations, (ii) breaking of solutions in a finite time interval, (iii) estimation of the time of existence of solutions, (iv) smoothing of discontinuous initial perturbations with time, and (v) construction of generalized solutions.

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

Theoretical and mathematical physics

Moscow University Physics Bulletin 1990. **45**. N 5. P. 18

The field and temperature corrections to the photon polarization operator in an external magnetic field have been studied for different limiting values of photon momentum, magnetic field strength, and temperature. Consideration is given to the deformation of the Debye charge screening sphere jin a magnetic field.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 22

The chiral color model predicts the existence of axigluons, a color octet of massive axial-vector gauge bosons. In this connection of interest is the toponium decomposition into axigluons and gluons. In this paper the following types of toponium decay are considered: $\theta \to Ag$, $\theta \to AAg$, and $\theta \to ggg \to AAg$. The decay widths of toponium $S$ states are calculated for various possible values of the axigluon mass.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 29

In quasi-nonperturbing measurements of wave energy, dissipation due to wave interaction in a Kerr medium is shown to restrict the error of determining the number $N$ of quanta to a value of $\sqrt{Nq}$ ($q$ is the absorption coefficient). Self-action of the wave and its dissipation determine the optimum power of the probing wave and the interaction length.

Show AbstractRadiophysics

Moscow University Physics Bulletin 1990. **45**. N 5. P. 34

A method is worked out for analyzing a self-consistent interaction on of a linear electron beam with fields in a multimode periodic waveguide used in relativistic microwave electronics. Investigation of a finite length system showed that at the waveguide surface there is an eddy field corresponding to the surface wave. The electron beam generates entrained fields with a maximum strength in the beam region. Scattering of the surface wave field and the electron beam field by the system inhomogeneities results in the production of a high-power circumaxial radiation.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 40

An electron traveling along a bare dielectric waveguide at a velocity near the phase velocity acquires a transverse momentum proportional to the photon energy. It is proposed that this momenjtum be measured. The effect is analyzed with consideration for the waveguide dispersion, radiation friction and the spurious Cerenkov radiation. Use should be made of a corrugated-wall waveguide to eliminate the Cerenkov emission and to derive the required frequency dependence of the phase velocity.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 1990. **45**. N 5. P. 46

The effect of the structural organization on the energy migration efficiency in a light-collecting antenna (LCA) has been studied by numerical modeling. It is concluded that for an ordered mutual arrangement of Chlorophyll a molecules in an LCA, the rate of energy migration along the photosynthetic unit antenna can markedly exceed that for a random arrangement of the pigment molecules.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 50

A theoretical and numerical analysis of the basic optical and structural properties of thin-layer (the total optical thickness below the quarter-wave) antireflecting structures with a three-layer period has shown that these structures can exert anti-reflecting effects simultaneously in two media with different refractive indexes. Simple analytical relations have been obtained which allow synthesis of such multilayer structures in order to solve various problems of applied optics.

Show AbstractAcoustics and molecular physics

Moscow University Physics Bulletin 1990. **45**. N 5. P. 54

The nonlinear evolution of two-dimensional flows with flow lines represented by angle-modulated circles has been considered for an ideal fluid. To solve the problem, an approximate Burgers equation has Ьеец derived for the flow function and analogies with wave problems of nonlinear acbustics have been used.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 59

Methods of studying the ground reflectivity in the low-frequency range with the help of combined receiving devices are discussed. The value of the acoustic bottom reflectivity obtained by forming unidirectional characteristics of the receiving system is compared with that measured by the interference technique. It is noted that the measurement error can be decreased by a simultaneous use of data on the pressure field sections and the vertical component of the oscillatory velocity field.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1990. **45**. N 5. P. 68

Dissipative properties of CdS single crystals during ultrasonic treatment were investigated using the method of two-component piezoelectric oscillator. The experiments were conducted at frequeancies of the order of 100 kHz, with relative deformation amplitudes up to $5 \times 10^{~4}$. Exposure to ultrasound is shown to produce changes in the dissipative properties, strength characteristics, and the dislocation structure of CdS crystals.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 72

The effect of uniaxial compression along the binary and bisector axes (up to deformations of -0.2%) on the current-voltage characteristics, the dynamics of breakdown development, and the lifetime of nonequilibrium charge carriers was experimentally studied for multivalleу n- and p-type $Bi_{1-x}Sb_x$ semiconductor alloys (0.10 $\leq x \leq$ 0.167) at a temperature of 4.2 K. As a whole, the results can be qualitatively explained on the basis of the available data on compression-induced variation of the energy spectra of these materials.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 76

It has been shown that intrasublattice frustration in a system with two increases equivalent sublattices substantially increase the temperature of transition to a nonergodic state and strengthens the de Almeida-Thouless magnetic field. The dependence of the Edwards-Anderson parameters on the frustration degree has been obtained. The intrasublattice frustration has been found to suppress the sublattice susceptibility.

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

Theoretical and mathematical physics

Moscow University Physics Bulletin 1990. **45**. N 5. P. 81

The paper is devoted to studying qualitative and quantitative aspects of the flotation effect on dispersion characteristics of waves generated by an instantaneous point source on a liquid surface.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 84

A self-adjoint extension of Dirac's Hamiltonian is constructed for fermion motion in the Aharonov-Bohm gauge Held. The problem of bound states is considered and expressions for particle energy levels are obtained.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 87

New harmonic coordinates for Schwarzschild's geometry are found and the corresponding metric is investigated. In contrast to the case of application of Fock's harmonic coordinates, in the new coordinates, particles falling into a black hole attain the event horizon at a finite value of time parameter.

Show AbstractRadiophysics

Moscow University Physics Bulletin 1990. **45**. N 5. P. 90

The paper is devoted to specification of the limits of applicability of the geometrical approach (the quasi-classical WKB method) in describing statistical characteristics of electromagnetic radiation propagating in a planar-layered randomly inhomogeneous medium. It is shown that the geometrical optics method is the limiting case of the modified traveling wave method. Based on the comparison of solutions obtained by these methods for the one-dimensional problem, conditions determining the range of applicability of the geometrical optics approximation are derived.

Show AbstractAstronomy

Moscow University Physics Bulletin 1990. **45**. N 5. P. 93

A certain modification of the algorithm of star observations with the photographic zenith tube makes it possible to use a CCD-matrix in the focal plane. The proposed algorithm minimizes the requirements to the equipment employed for the star image processing and data input into the computer.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1990. **45**. N 5. P. 96

The temperature dependence of the saturation magnetization of amorphous foils of the $Fe_{78}Si_{9}B_{11}C_{2}$ alloy heated up to 900° С was studied. The magnetic phase transition in the amorphous phase was shown to fail due to crystallization of the $\alpha –Fe$, $(Fe, Si)_2(B, С)$, $\gamma – Fe$, and $(Fe, B, C)_3Si$ phases which began at 450°С.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 99

The method of molecular dynamics is used to study the structure of the $Ni_{75}P_{25}$ alloy as dependent on the preparation process. The structure is shown to have "thermal hysteresis". The possibility of predicting structural relaxation is discussed in therms of molecular-dynamic modeling.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 102

The effect of substitutional impurities on the temperature of metal-semiconductor phase transition was theoretically studied with consideration for diagonal and off-diagonal matrix elements of the perturbation operator. The results were compared with experiment data.

Show AbstractMoscow University Physics Bulletin 1990. **45**. N 5. P. 105

A complex of methods was used to study the following properties of undoped a-Si:H specimens: absorption (by the dc photocurrent technique), concentration of dangling bond (DB) type defects (by the EPR technique), and temperature dependence of dark and photoconductivity. To explain the results obtained, a model was proposed which allows, in addition to the growth of DB defect concentration, also for the growth of concentration of shallow centers with energies near the valence band in the a-Si:H mobility gap.

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