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

Theoretical and mathematical physics

Moscow University Physics Bulletin 1998. **53**. N 3. P. 1

A theoretical model of a vibrational Coulomb resonance excitation of diatomic molecules sliding at velocities of $10^5$-$10^7$ cm/s over crystal surfaces is suggested. The surface field is represented by the sum of periodic potentials with frequencies proportional to the initial molecule velocities. As an example, the probability of vibrational excitation of the CO and NO molecules is calculated at the level of first-order nonstationary perturbation theory.

Show AbstractMoscow University Physics Bulletin 1998. **53**. N 3. P. 6

A mathematical model of the hearing organ's cochlea is considered as an operator transforming the time signal into the space-time form, and its effective rank is examined.

Show AbstractMoscow University Physics Bulletin 1998. **53**. N 3. P. 12

A singular solution to the two-dimensional dissipative Helmholtz equation in a strip under zero boundary conditions on the walls is considered. The solution, which is constructed by the reflection method, is represented as a series where one term is a fundamental solution to the Helmholtz equation on the plane and the other terms are smooth solutions to the Helmholtz equation in a strip. It is shown that the series formed by smooth solutions is an infinitely differentiable function. Based on the constructed singular solution, the potentials of the single and double layers and the angular potential in a strip are constructed. It is proved that the properties of the strip potentials are determined by the behavior of the well-studied potentials constructed based on the fundamental solution to the Helmholtz equation.

Show AbstractMoscow University Physics Bulletin 1998. **53**. N 3. P. 17

On the basis of Finslerian Hamiltonian function, the real scalar field is considered. It is shown that the use of the special-relativistic Finslerian metric function leads to positivity of field energy. The Finslerian extension of the Pauli-J"ordan function is proposed to derive the required commutators and the relationship between the amplitudes $u^\pm(\textbf{k})$ and $u^\pm(k)$.

Show AbstractRadiophysics

Moscow University Physics Bulletin 1998. **53**. N 3. P. 22

Effect of the SHF-field transversal inhomogeneity on the electron interaction with radiation in a maser with a plane slow-wave structure and a band-like beam in the case of anomalous Doppler effect has been studied. Amplification conditions as a function of a guiding magnetic field have been also studied.

Show AbstractMoscow University Physics Bulletin 1998. **53**. N 3. P. 28

The nonlinear dynamics of electromagnetic wave scattering by a dense monoenergetic electron beam, premodulated in density, is studied. Analytical formulas for the amplitudes of interacting waves and the characteristic evolution time of the processes are obtained. It is found that increasing the beam modulation depth greatly reduces the instability decay time. The wave saturation amplitudes are almost independent of the modulation depth.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 1998. **53**. N 3. P. 33

The fluorescent properties of luciferin-substrate and an analog of the light emitter in the bioluminescent system of fireflies have been studied depending on luciferin microenvironment and structure. For the phenolate form of luciferin, which is a fluorophore analog, a linear dependence between the position of its fluorescence spectrum maximum and the solvent orientational polarizability is observed. The microenvironment of the bioluminescent reaction substrate is shown to be nonhydrophobic.

Show AbstractMoscow University Physics Bulletin 1998. **53**. N 3. P. 39

The propagation and scattering of light in model biological tissues containing moving particles are studied by numerical Monte Carlo simulation using the detected signal time resolution.

Show AbstractAcoustics and molecular physics

Moscow University Physics Bulletin 1998. **53**. N 3. P. 46

Temperature dependences of permittivity and sound velocity and damping near the second-order transition in crystals subjected to nonuniform uniaxial pressure are calculated. The presence of pressure gradients causes broadening of the temperature range within which physical property anomalies are observed. The most substantial changes in the sound damping occur when the pressure gradient is normal to the wave vector of acoustic wave.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1998. **53**. N 3. P. 51

The M$\stackrel{..}{o}$ssbauer spectra of synthetic mackinawites and tochilinites were recorded. The observed differences in isomeric and quadrupole shift values for the $^{57}$Fe components in the spectra of mackinawite and tochilinite sulfide layers were analyzed. The structure of tochilinite was found to contain equal numbers of conjugate FeS and (Fe, Mg)(OH)$_2$ layers with Mg$^{2+}$ ions present only in brucite layers, largely in one of two observed nonequivalent sites.

Show AbstractMoscow University Physics Bulletin 1998. **53**. N 3. P. 57

The influence of ultrasound on the dissipative properties of low-resistance CdS crystals is experimentally studied. It is shown that the main contribution to internal friction in lowresistance samples is made by dislocation mechanisms of ultrasound absorption. The changes that occur in the "dislocation-pinning points" system under the influence of ultrasound are analyzed at various deformation amplitudes.

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

Theoretical and mathematical physics

Moscow University Physics Bulletin 1998. **53**. N 3. P. 66

The problem of a round plate equilibriwn under a constant concentrated force applied at the plate center has been solved. The plate consists of a homogeneous isotropic base and a fairly inhomogeneous (in particular, multilayer) coating much thinner than the base. The concentrated force magnitude is such that the plate sag and the coating thickness are of the same order. The sag is determined by the asymptotic method. The calculation results can be applied in approximate determination of elastic characteristics of thin coatings.

Show AbstractMoscow University Physics Bulletin 1998. **53**. N 3. P. 63

The eigenvalues of the Sturm-Liouville problems for the Bessel equation with boundary conditions of the third kind have been calculated by the differential-parametric method.

Show AbstractAtomic and nuclear physics

Moscow University Physics Bulletin 1998. **53**. N 3. P. 69

By computer simulation, the efficiency of a new unconventional scheme of bremsstrahlung generation has been studied. The scheme is based on the electron beam's repeated transmission through a thin target. This is achieved by using a special focusing magnetic field that returns the scattered electrons back to the target. In the scheme, an almost triple increase of the radiation yield energy and a decrease of the angular divergence of bremsstrahlung photons have been observed.

Show AbstractMoscow University Physics Bulletin 1998. **53**. N 3. P. 73

The operation of a high-current free-electron laser oscillator in the mode of a collective electromagnetic wave excitation is discussed. The starting conditions for launching the device are evaluated. The feasibility of implementing the collective oscillator mode in modern electron accelerators is demonstrated.

Show AbstractMoscow University Physics Bulletin 1998. **53**. N 3. P. 76

The influence of different photodisintegration channels on the time evolution of isotopes in the $^{90}$Sr transmutation chain is investigated. Channels with relatively low (under 15%) contributions into the total cross section are shown to strongly affect the time evolution of isotopes.

Show AbstractAcoustics and molecular physics

Moscow University Physics Bulletin 1998. **53**. N 3. P. 79

Density fluctuations near a blunted body streamlined by a supersonic turbulent flow were experimentally investigated by the laser schlieren-technique. The turbulence was generated by a grid placed in the low-pressure chamber of a shock tube (with cell size of $2\times2$ mm). The test gas was air. The Mach number values of the incident shock wave were 2.2-3.4 and the initial pressure was 3-30 torr. The density-fluctuation structure function and correlation coefficient and also the turbulence scale were determined.

Show AbstractSolid state physics

Moscow University Physics Bulletin 1998. **53**. N 3. P. 82

Hydrogen-induced changes in the structure of thin palladium films deposited under Penning discharge conditions were studied. The dependence of integrated intensity and integrated width of X-ray reflections on the storage time was nonmonotone at the initial stage of degassing. It was revealed that degassing of the structure with a larger number of defects occurred at a lower rate.

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