On the Molecular-Kinetic Theory of the Collective Motion in Liquids

Starting from the molecular-kinetic approach the upper and lower time limits of validity of VLASOV equation, governing the “collisionless” collective motions in liquids are found. The importance of the relaxation of liquid structure in collective motions is shown. The linear response of a liquid is evaluated, and the conditions of strong and weak damping of collective modes are found.     

Determination of first ionization potentials from spectra of electronic energy loss in the vapor of polyatomic organic compounds

It is shown that an analysis of energy loss spectra of electrons scattered at θ=90° in the vapor of polyatomic organic molecules allows determination of the first ionization potentials. Thus, for pyrene, perylene, and POPOP molecules they are 7.7, 7.2, and 8.7 eV, respectively. It is found that the first ionization potentials measured depend considerably on the thermal distribution of the free molecules. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 351–355, May–June, 1999.     

Automating computations in the virtual Tokamak software system

We describe the concept, functional capabilities, graphic user interface (GUI), and operating technique of a specialized system for distributing the computational burden encountered in solving typical problems of controlled thermonuclear fusion. The system is employed in the Virtual Tokamak simulation modeling complex to automate the distribution of computing on a network of computers, making it possible to dramatically improve the productivity of a researcher??s work. The system is useful in various applications that require massive multivariate calculations using one or more application codes, and for supporting websites that provide computing services using locally stored science-intensive application software.     

Nonlocality in PT-symmetric waveguide arrays with gain and loss

We demonstrate that light propagation in waveguide arrays that include PT-symmetric structures can exhibit strongly nonlocal sensitivity to topology of the array at fixed other parameters. We consider an array composed of lossless waveguides, that includes a pair of PT-symmetric waveguides with balanced gain and loss, and reveal that PT-symmetry breaking thresholds are different for planar and circular array configurations. These results demonstrate that PT-symmetric structures can offer new regimes for optical beam shaping compared to conservative structures.     

Method for reconstructing the gamma-ray arrival direction in the converter + calorimeter system

When designing devices of modern gamma astronomy, one of the most important problems is achieving the maximum possible angular resolution. This study is devoted to the method for reconstructing the arrival direction of primary gamma-rays with energies E _γ > 10 GeV in the GAMMA-400 satellite experiment. By the example of the GAMMA-400 gamma telescope, the possibility of improving the angular resolution of gamma telescopes incorporating a “converter + calorimeter” system is shown. The dependence of the angular resolution on the step of silicon strips used to determine the coordinates of incident particles in the converter and calorimeter and the distance between the converter and calorimeter is analyzed.     

Formation of fluorescence bands of polyatomic organic molecules in the gaseous phase upon excitation by electrons

Information on paths in absorption and deactivation of energy gained by molecules in their excitation by electron impact to low-lying singlet states has been obtained from an analysis of changes in the fluorescence spectra of these molecules. It is shown that there is a significant difference in the formation of fluorescence spectra when free molecules are excited by optical radiation and by electrons. It contrast to optical excitation, the interaction of an electron with a molecule is nonselective in character. All electronic states have a chance to be excited, which results in ensembles of emitting molecules with a different store of vibrational energy, and these ensembles each contribute to the fluorescence spectrum. Deceased. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 216–223, March–April, 1998.     

Optical and magneto-optical spectroscopy of thin composite GaAs-MnAs layers

Ellipsometric and magneto-optical investigations of MnAs layers and GaAs-MnAs composites obtained by laser deposition have been performed in the energy range 1.0–4.5 eV. The spectra of the equatorial Kerr effect (EKE) and the refractive and absorption indices have been studied. Diagonal and off-diagonal components of the dielectric tensor have been calculated. It is established that the shape of the EKE spectra of MnAs layers depends on the crystallographic orientation of these layers. Features near 1.9, 3, and 4 eV are distinguished in the energy dependences of the interband density of states of the layers; these features correspond to the energies of interband d-p transitions, obtained from calculations of the MnAs band structure.     

On the Number of Generating Pairs for the Groups L 2 and Sz(22k+1)

For the simple groups G of the title, we find the maximal number n such that the direct product of n copies of G is generated by two elements.     

Ferromagnetism in epitaxial germanium and silicon layers supersaturated with managanese and iron impurities

The possibility of laser synthesis of diluted magnetic semiconductors based on germanium and silicon doped with manganese or iron up to 10–15 at % has been shown. According to data on the electronic levels of 3d atoms in semiconductors, Mn and Fe impurities are most preferable for realizing ferromagnetism in Ge and Si through the Ruderman-Kittel-Kasuya-Yosida mechanism. Epitaxial Ge and Si layers 50–110 nm in thickness were grown on gallium arsenide or sapphire single crystal substrates heated to 200–480°C. The content of a 3d impurity has been measured by x-ray spectroscopy. The ferromagnetism of layers and high magnetic and acceptor activities of Mn in Ge, as well as of Mn and Fe in Si, are manifested in the observation of the Kerr effect, anomalous Hall effect, high hole conductivity, and anisotropic ferromagnetic resonance at 77–500 K. According to the ferromagnetic resonance data, the Curie point of Ge:Mn and Si:Mn on a GaAs substrate and of Si:Fe on an Al₂O₃ substrate is no lower than 420, 500, and 77 K, respectively.