Angular distribution studies on the two-photon ionization of hydrogen-like ions: Relativistic description

The angular distribution of the emitted electrons, following the two-photon ionization of the hydrogen-like ions, is studied within the framework of second order perturbation theory and the Dirac equation. Using a density matrix approach, we have investigated the effects which arise from the polarization of the incoming light as well as from the higher multipoles in the expansion of the electron--photon interaction. For medium- and high-Z ions, in particular, the non-dipole contributions give rise to a significant change in the angular distribution of the emitted electrons, if compared with the electric-dipole approximation. This includes a strong forward emission while, in dipole approxmation, the electron emission always occurs symmetric with respect to the plane which is perpendicular to the photon beam. Detailed computations for the dependence of the photoelectron angular distributions on the polarization of the incident light are carried out for the ionization of H, Xe$^{53+}$, and U$^{91+}$ (hydrogen-like) ions.Comment: 16 pages, 4 figures, published in J Phys

Investigation of the stability of the electron source with a multi-aperture plasma emitter generating a large cross-section electron beam

An experiment was performed to investigate the electric strength of the high-voltage acceleration gap of an electron source with a multi-aperture plasma emitter generating a beam of large cross section (750•150 mm{2}) extracted into the atmosphere through a thin metal foil. It has been shown that the use of a mask in the plasma emitter which partitions the overall emission region to produce a plurality of small-cross-section beamlets, so that the extracted beam is a superposition of beamlets formed by individual emission units whose plasma boundary is stabilized by a fine metal grid, increases the electric strength of the high-voltage acceleration gap. This is of critical importance in cases where the electron source is operated in a repetitive pulse mode at high average power of the beam. In addition, an increase in the electric strength of the acceleration gap is promoted by that the modernized cathode assemblies of the plasma emitter are arranged normal to the axis along which electrons are extracted into the acceleration gap

Modernization of cathode assemblies of electron sources based on low pressure arc discharge

The paper presents modified cathode assemblies, including their main characteristics, for plasma electron sources based on a constricted low-pressure arc initiated by a discharge in crossed electric and magnetic fields. One of the modified cathode assemblies allows the electrode system of the auxiliary discharge to operate at a pressure of≈0.3 Pa, as against ≈ 10 Pa before the modification, provides a larger diameter constriction of the pulsed (up to [tau]=250 [mu]s) arc, and thus extends the range of operating currents for the plasma-cathode discharge system up to I[d]=300 A. The other modified assembly operates at widely varying discharge currents I[d]=5-100 A, provides lesser amounts of cathode microdroplets at the discharge electrodes, and allows the arc to operate at comparatively low voltages. The use of cathode assemblies adapted for specific discharge systems extends the capabilities of plasma- emitter electron sources as well as the range of their applications in scientific and technological fields

Evolution of the Velocity Ellipsoids in the Thin Disk of the Galaxy and the Radial Migration of Stars

Data from the revised Geneva--Copenhagen catalog are used to study the influence of radial migration of stars on the age dependences of parameters of the velocity ellipsoids for nearby stars in the thin disk of the Galaxy, assuming that the mean radii of the stellar orbits remain constant. It is demonstrated that precisely the radial migration of stars, together with the negative metallicity gradient in the thin disk,are responsible for the observed negative correlation between the metallicities and angular momenta of nearby stars, while the angular momenta of stars that were born at the same Galactocentric distances do not depend on either age or metallicity. (abridged)Comment: Astronomy Reports, Vol. 86 No. 9, P.1117-1126 (2009

A review of species of the genus Mocyta (Coleoptera, Staphylinidae) in Ukraine

A review of the genus Mocyta Mulsant & Rey, 1874, which is represented in Ukraine; a description of the main morphological features and diagnostic features is made, data on ecological features, seasonal activity of adults, the distribution of representatives of the genus in Ukraine and the world and the keys to identify the species are presented. The information on the distribution of species of the genus Mocyta in the territory of Ukraine has been clarified and significantly supplemented by new findings. The results can be used to address a number of theoretical issues of faunistics, zoogeography, and ecology, as well as in compiling the inventory of the fauna of the Ukrainian Carpathians, for comparative faunal research, in the analysis of species distribution, in biogeographic constructions, studies of faunogenesis, ecological monitoring and prediction of consequences of the influence of human activities on natural ecosystems of the region. The genus Mocyta is a widespread genus, which in terms of the combination of morphological and biological features belongs to the tribe Athetini Casey, 1910 of the subfamily Aleocharinae Fleming, 1821 of the family Staphylinidae Latreille, 1802. There are 26 known species in the fauna of Palearctic, 5 of which (Mocyta clientula, M. fungi fungi, M. fussi, M. orbata, M. orphana) are represented in the fauna of Ukraine. However, it is likely that there are two more species (M. amplicollis and M. negligens), identified for the surrounding areas, for which characteristics and comparative diagnoses have also been provided. This paper is a continuation of the initiated series of reviews of genera and species of the tribe Athetini of the fauna of Ukraine. Taking into account the wide geographical distribution and significant individual variability in size, colour and shape of the spermatheca of representatives of the genus, the identification of the latter presents some significant difficulties

Lithium-induced phase transitions in lead-free Bi0. 5Na0. 5TiO3 based ceramics

Lithium-substituted 0.95[0.94(Bi0.5Na(0.5–x)Lix)TiO3–0.06BaTiO3]–0.05CaTiO3 materials include the polar rhombohedral R3c and the weakly polar tetragonal P4bm phases. On increasing lithium content, the (R3c/P4bm) phase ratio decreased, while the rhombohedral and tetragonal lattice distortions remained the same. The temperature corresponding to the shoulder in the dielectric permittivity shows no clear shift with respect to lithium substitution because of the rhombohedral distortion remaining constant. Electrical poling produced an increase of the rhombohedral phase fraction together with a rise of the rhombohedral and tetragonal distortion. This confirmed the occurrence of a phase transition from the weakly polar to the polar phase during electrical poling. Four peaks found in the current–electric field (I–E) loops are related to reversible electric field induced transitions. By studying the temperature dependence of the current peaks in the I–E loops, it was found that the minimum temperature where these electric field induced transitions take place decreases with increasing lithium substitution

Generation of low-temperature plasma by low-pressure arcs for synthesis of nitride coatings

Experiments were performed to study gas, metal, and mixed metal-gas plasmas. The plasmas were generated with the use of an arc evaporator and a gas-plasma source with a hot filament and hollow cathode that were operated independently or simultaneously. It has been revealed that the arc current of gas-plasma source affects the parameters of the metal-gas plasma and the element concentrations in the coatings. It has been demonstrated that the characteristics of the nitride coatings produced by plasma-assisted vacuum-arc deposition can be controlled by varying the parameters of the arc in the gas-plasma source

Modernization of electron accelerator with a large cross section beam for radiation effects on materials

The results of the work on the creation of an automated wide-aperture electron accelerator with a grid plasma cathode based on the low-pressure arc discharge and outputting of a large section beam (750X150 mm) in the atmosphere through a outlet foil window. The distinctive feature of such electron accelerator is a weak correlation of beam parameters, as well as a high current beam extraction efficiency to air, reaching ≈ (80 -: 90)% of the current in the accelerating gap at an accelerating voltage of 200 kV, beam current amplitude in the atmosphere up to 30A, frequency and pulse duration up to 50 s-1 and 100 mus, respectively. The electron source provides a stable continuous operation for tens of hours in a repetitively pulsed modes at the maximum average beam power in the atmosphere is ≈ 5 kW. Examples of applications of such accelerator in the radiation-stimulated technology are given, showing the prospects of its using in scientific and technological purposes