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

Theoretical and mathematical physics

Moscow University Physics Bulletin 1991. **46**. N 3. P. 5

It is shown that in the state of thermodynamic equilibrium of a two-component mixture of gases the mean kinetic energies of different kinds of molecules are unequal. Binary (nonmultiplicative) two-temperature distribution functions corresponding to the state of thermodynamic equilibrium have been found. In the general case, the equilibrium temperatures of mixture components turned out to depend on molecular masses and concentrations. The transition to a one-component gas leads to the commonly known results.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 3. P. 10

The quantization of the Weinberg-Salam model has been carried out in the neighborhood of classical solutions to the field equations describing an electrically charged vector (W-boson) field interacting with a neutral scalar field (the Higgs field) in the presence of a superstrong magnetic field, in which the nonlinear effects are taken into account nonperturbatively. The energy spectrum of quantum particles (normal modes of the vector and scalar fields) in the "vacuum" and "kink" sectors has been found. It is shown that the discrete symmetry of the model broken in the two-dimensional approximation is not restored if the instanton contribution to the tunneling effect is taken into account in the quasi-classical approximation.

Show AbstractAtomic and nuclear physics

Moscow University Physics Bulletin 1991. **46**. N 3. P. 17

Mathematical modeling of the process of detection of nuclei by a specially designed spectrometer is described and the main errors of the method are examined. The modeling yielded a dependence of the energy range in which the instrument is capable of separating the nuclei by mass $A$ on their charge $Z$. It is shown that the resolution of the spectrometer can be improved if about half of the nuclei detected are excluded from consideration. The results obtained are compared with accelerator experiment data.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 3. P. 24

The effects of nonexact description of the bremsstrahlung spectrum on the reconstruction of photonuclear reaction cross sections by the methods of mathematical simulation and measurement reduction are analyzed. It is shown that, within the attainable accuracies of photonuclear experiments, the inclusion of the influence of a realistic distribution of the atomic charge and of the contribution of terms of the order of $m_e$ to the amplitude of the bremsstrahlung formation process does not lead to considerable differences in reconstructed cross sections of photonuclear reactions.

Show AbstractRadiophysics

Moscow University Physics Bulletin 1991. **46**. N 3. P. 32

Concentration of negative ions in the positive column of the low-pressure hydrogen plasma was calculated. The main processes of formation and loss of negative ions were taken into account in the calculations. The effective coefficient of diffusion of $H^-$ ions in hydrogen was determined. The upper limit of the $H^-$ ion concentration was estimated experimentally.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 3. P. 37

The temperature, the electron energy distribution function (EEDF), and the concentrations of electrons and iodine ions (positive and negative) were determined for a mixture of helium with iodine vapors by treatment of the current voltage characteristics of a single cylindrical probe and by the method of the probe current second derivative. The results obtained from solving balance equations are in fair agreement with the measurement data.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 3. P. 42

Broad possibilities are demonstrated for the investigation of ergodicity of stationary random processes using characteristic functions. A stochastic interference signal model is considered that is stationary for any number of constituent modes. Its ergodicity relative to the characteristic function, probability density, and moments is proved for the number of modes $m$ = 1, 2. The question of practical application of the results for a finite averaging time is discussed.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 3. P. 48

An approximate theory of propagation of a Gaussian-Hermitian bounded wave beam obliquely incident on an arbitrary plane-conserving electrodynamic structure was constructed using the Rayleigh formalism in the paraxial approximation. The transmission coefficient of the structure is represented as a rapidly converging quadratic Hermitian form comprising the relevant plane-wave factors and their spatial derivatives. The form obtained is convenient for both a numerical study of reflection, absorption, and propagation of bounded wave beams in various media and for analytic calculations and estimations.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 1991. **46**. N 3. P. 53

A general method is proposed for obtaining strong compression of pulses with any form of dependence of the wave number $k(\omega )$ on the frequency $\omega$. Compression of a super-Gaussian pulse in a medium with n-th order dispersion is discussed in detail.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 3. P. 61

The feasibility has been shown of diagnostics of vibrational-level populations in the active medium of a coupled-mode $СО_2$-gasdynamic laser using the energy characteristics of pulsed operation in a Q-switched regime. The expressions have been derived for the determination of the initial population difference of lasing levels from the data measured. Experiments were performed on the $03^10—10^00$ ($\lambda$ = 18.4 μm) and $04^20—03^30$ ($\lambda$ = 17.2 μm) transitions in a $СO_2 —Аr$ gas mixture. An advantage of the method consists in that the use of the $Q$-switched regime allows one to exclude the interaction of vibrational transitions during lasing.

Show AbstractAcoustics and molecular physics

Moscow University Physics Bulletin 1991. **46**. N 3. P. 65

Localized nonpropagating perturbations of the surface which have a soliton shape and arise from vertical oscillations of a cell with a liquid, have been studied theoretically and experimentally. It has been found that both light and dark nonpropagating solitons can be produced depending on the liquid depth, i. e., on the sign of cubic nonlinearity of the medium.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1991. **46**. N 3. P. 69

The theory of the thermo emf of amorphous ferromagnetic materials has been extended to the case of $d$-like current carriers. The thermo emf of Fe-Ni-Si-B and Fe-Co-Cr-Si-B alloys has been measured in a wide temperature range. An extremum in the thermo emf vs temperature curve characteristic of amorphous ferromagnetic materials becomes more pronounced after crystallization. This feature is due to the prevailing contribution of inelastic scattering during crystallization.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 3. P. 74

The effect of fluctuating one-ion anisotropy on the temperature of transition from a paramagnetic state to a spin glass state is discussed within the framework of the two-sublattice model with the infinite interaction radius. It is shown that the proposed theory makes it possible to explain the available experimental data for some substituted ferrimagnetic spin glasses.

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

Theoretical and mathematical physics

Moscow University Physics Bulletin 1991. **46**. N 3. P. 82

A model of a nematic liquid crystal which takes into account orientational fluctuations and short-range correlations of molecules has been studied based on Bogolyubov's variational principle in a pseudoharmonic approximation. The temperature dependences of the mean-square orientational displacement of molecules and the order parameter have been obtained.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 3. P. 86

A formula for the total cross section is obtained which makes it possible to take into account third-order corrections with respect to $\alpha_s$ without calculating loop diagrams and integrating over the region of small momentum values.

Show AbstractMoscow University Physics Bulletin 1991. **46**. N 3. P. 90

The authors consider a class of nonlinear measurement interpretation problems which reduce to calculation of a known function from a nonexactly set argument. A method for solving interpretation problems is offered which helps simplify computation process considerably and approximate well the solution of an exact problem.

Show AbstractAtomic and nuclear physics

Moscow University Physics Bulletin 1991. **46**. N 3. P. 94

Electron impact excitation cross sections a{ all levels of the fine structure of the $3p^53d$ electron configuration of the Ar atom were calculated. The calculations were made in the distorted wave approximation with consideration for the exchange amplitude. The results are compared with the available experimental data.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 1991. **46**. N 3. P. 97

The method of probability matrices taking into account the modern data on the structure of light-harvesting complexes of the photosystem II in higher plants has been used to calculate the fluorescence kinetics for two models with different structures of chlorophyll-protein complexes. In both models, the open and closed type reaction centers are described by single-exponent fluorescence decay curves. The fiuorescence lifetime of a closed center is 1.5 to 2.8 times that of an open one.

Show AbstractAcoustics and molecular physics

Moscow University Physics Bulletin 1991. **46**. N 3. P. 101

An approximate method is proposed for calculating the shape and the directivity pattern of a linear antenna placed in an undercurrent, as well as the dispersion of the directivity pattern due to the statistical scatter of the flow velocity. Methods for optimum selection of antenna parameters to improve its stability to flow effects are discussed.

Show AbstractGeophysics

Moscow University Physics Bulletin 1991. **46**. N 3. P. 106

A transducer for laboratory measurement of submillimeter waves on water surface is described.

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