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

Theoretical and mathematical physics

Moscow University Physics Bulletin 2004. **59**. N 6. P. 1

The relation between the error of the data obtained as a result of a stochastic computer experiment and the quality of their smooth approximation is investigated. It is suggested that reliability should be used as a measure of closeness of agreement (approximation accuracy). The description of the electron energy liberation density function computed by the Monte Carlo simulation technique as a sum of two three-dimensional Gaussian functions is considered as an example. The computation results of reliability as a function of the modeling parameters are presented.

Show AbstractMoscow University Physics Bulletin 2004. **59**. N 6. P. 6

Normal waves in a hollow coaxial cylindrical waveguide fi with Shchukin— Leontovich conditions on the boundary are considered.

Show AbstractMoscow University Physics Bulletin 2004. **59**. N 6. P. 12

Gravitational field of a global monopole in the Randall-Sundrum model of universe with an extra infinite dimension is studied. It is shown that, in contrast to gravitational field of its 4-dimensional analog, the Newtonian potential placed on the brane of the monopole is not vanishing and behaves as $r^{-1}$ at small distances and as $\ln$$(2kr)/r^2$ at large distances.

Show AbstractMoscow University Physics Bulletin 2004. **59**. N 6. P. 17

Exact solutions to the Dirac equation in a strong electric field of point charge $Z|e|$ and an external Coulomb scalar field have been found. It is shown that, in the presence of a scalar field, the range of parameter values at which the corresponding Hamilton operator is Hermitian is substantially wider than in the absence of such a field. This makes it possible to correctly study the problem of the stability of quantum-electrodynamic vacuum with respect to the formation of electron—positron pairs in these fields.

Show AbstractAtomic and nuclear physics

Moscow University Physics Bulletin 2004. **59**. N 6. P. 22

To study the possibility of obtaining an optimal-monoenergetic representation of the cross section of a photonuclear reaction if one knows the experimental reaction yield measured with the help of a $\gamma$-bremsstrahlung beam the reduction method is used. The specially introduced generalized parameters of the cross sections of the reactions $^{34}$S$(\gamma,sn)$ and $^{52}$Cr$(\gamma,n)^{51}$Cr obtained earlier are studied as functions of actually attained energy resolutions. It is found that the optimal-monoenergetic representations of the reaction cross sections attained at resolutions amounting to 0.25 and 0.20 MeV, respectively, differ substantially from those obtained in both experiments.

Show AbstractMoscow University Physics Bulletin 2004. **59**. N 6. P. 31

The possibility of accumulation of the 178Hf isotope in an isomeric state in a sample of natural Hf isotope mixture exposed to a 7-bremsstrahlung beam is considered.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 2004. **59**. N 6. P. 37

Based on the principle of duality, we arrive at a nontrivial modification of the Hamiltonian of an $N$-level atomic system, which gives rise to such effects as the generation of the higher optical harmonics, supercontinuum, and stabilization of the ionization of atoms.

Show AbstractSolid state physics

Moscow University Physics Bulletin 2004. **59**. N 6. P. 45

Coupled oscillations of electron and nuclear systems in an easy-plane antiferromagnet in strong magnetic fields are considered. Based on the Bogolyubov <$\!u$-$v\!$> transformation a spectrum of these oscillations and a new $\eps_{2\bf k}$ mode of collective oscillations in an antiferromagnet have been found. A dynamic shift of a nuclear magnetic resonance frequency associated with this mode has been determined.

Show AbstractMoscow University Physics Bulletin 2004. **59**. N 6. P. 49

Using the electrical compensation method in the photon energy range 1.1— 1.6 eV, spectral relations of the photocurrent of silicon photoelectric transducers irradiated with protons of 1.6 MeV average energy have been measured. It has been shown that with a high accuracy (1—2%) the measured spectra correspond to spectra calculated taking into account inhomogeneity of a proton-generated defect layer. The calculation technique used helps determine the thickness of a defective layer, the average minority-carrier lifetime in this layer and also obtain information on the nature of defect distribution there.

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

Theoretical and mathematical physics

Moscow University Physics Bulletin 2004. **59**. N 6. P. 55

The conditions allowing for the ferromagnetic state of an SU(2) gauge field model to exist are considered. It is shown that tachionic modes can condense into a spatially homogeneous state if the spatial extent of the chromomagnetic field is short enough. A phase transition between this state and the superconducting state is considered.

Show AbstractOptics and spectroscopy

Moscow University Physics Bulletin 2004. **59**. N 6. P. 61

A set of programs for modeling the effect of anisoplanatism on the operation of an adaptive optical phase-conjugation system in conditions of inhomogeneous atmospheric turbulence is described. The space-apart reference and observation objects are considered to be point entities. The turbulent atmosphere is modeled by means of random movable phase screens of specified statistics. The software developed makes it possible to calculate the instantaneous and averaged phase errors in correction for various angular separations of the sources and over a wide range of the adaptive system parameters and atmospheric inhomogeneities.

Show AbstractRadiophysics

Moscow University Physics Bulletin 2004. **59**. N 6. P. 64

To calculate the dissociation rate constants of molecules of atmospheric gases within a broad temperature range, a new method of calculating the level dissociation cross sections that is based on the ill-posed inverse problem solution is used.

Show AbstractGeophysics

Moscow University Physics Bulletin 2004. **59**. N 6. P. 68

Specific features of the ionospheric structure over Western Europe observed during a period of strong heliogeophysical disturbances in the fall, 2003, are considered. A region of enhanced ionization in the nighttime ionosphere on 30/31 October is imaged by four-dimensional tomography based on high-orbiting satellite data. Motion of the spot of enhanced ionization approximately along geomagnetic latitude is traced. Radio tomographic results are compared with the data from a series of digisondes.

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