Tunneling-assisted impact ionization fronts in semiconductors

We propose a novel type of ionization front in layered semiconductor structures. The propagation is due to the interplay of band-to-band tunneling and impact ionization. Our numerical simulations show that the front can be triggered when an extremely sharp voltage ramp ($\sim 10 {\rm kV/ns}$) is applied in reverse direction to a Si $p^+-n-n^+-$structure that is connected in series with an external load. The triggering occurs after a delay of 0.7 to 0.8 ns. The maximal electrical field at the front edge exceeds $10^6 {\rm V/cm}$. The front velocity $v_f$ is 40 times faster than the saturated drift velocity $v_s$. The front passes through the $n-$base with a thickness of $100 {\mu m}$ within approximately 30 ps, filling it with dense electron-hole plasma. This passage is accompanied by a voltage drop from 8 kV to dozens of volts. In this way a voltage pulse with a ramp up to $500 {\rm kV/ns}$ can be applied to the load. The possibility to form a kilovolt pulse with such a voltage rise rate sets new frontiers in pulse power electronics.Comment: 12 pages, 6 figure

Electronic structure, magnetic and optical properties of intermetallic compounds R2Fe17 (R=Pr,Gd)

In this paper we report comprehensive experimental and theoretical investigation of magnetic and electronic properties of the intermetallic compounds Pr2Fe17 and Gd2Fe17. For the first time electronic structure of these two systems was probed by optical measurements in the spectral range of 0.22-15 micrometers. On top of that charge carriers parameters (plasma frequency and relaxation frequency) and optical conductivity s(w) were determined. Self-consistent spin-resolved bandstructure calculations within the conventional LSDA+U method were performed. Theoretical interpetation of the experimental s(w) dispersions indicates transitions between 3d and 4p states of Fe ions to be the biggest ones. Qualitatively the line shape of the theoretical optical conductivity coincides well with our experimental data. Calculated by LSDA+U method magnetic moments per formula unit are found to be in good agreement with observed experimental values of saturation magnetization.Comment: 16 pages, 5 figures, 1 tabl

Resistive state of superconducting structures with fractal clusters of a normal phase

The effect of morphologic factors on magnetic flux dynamics and critical currents in percolative superconducting structures is considered. The superconductor contains the fractal clusters of a normal phase, which act as pinning centers. The properties of these clusters are analyzed in the general case of gamma-distribution of their areas. The statistical characteristics of the normal phase clusters are studied, the critical current distribution is derived, and the dependencies of the main statistical parameters on the fractal dimension are found. The effect of fractal clusters of a normal phase on the electric field induced by the motion of the magnetic flux after the vortices have been broken away from pinning centers is considered. The voltage-current characteristics of fractal superconducting structures in a resistive state for an arbitrary fractal dimension are obtained. It is found that the fractality of the boundaries of normal phase clusters intensifies magnetic flux trapping and thereby increases the current-carrying capability of the superconductor.Comment: 15 pages with 8 figures, revtex3, alternative e-mail of author is [email protected]

Повышение энергоэффективности гидроаккумулирующих электростанций

Possible ways to improve the energy efficiency of hydroelectric generating sets of pumped-storage power plants (PSPPs) are studied. The Kiev PSPP is used as an example to show how its generating sets can be upgraded. It is concluded based on studies conducted that synchronous motor-generators should be replaced with asynchronized motor-generators. The feasibility of changing over the turbine to variable-speed operation is shown.Рассмотрены возможные пути повышения энергоэффективности гидроагрегатов гидроаккумулирующих электростанций. На примере Киевской ГАЭС показаны способы модернизации её энергоблоков и на основании проведённых исследований сделаны выводы о целесообразности замены синхронных генераторов-двигателей асинхронизированными генераторами-двигателями. Показана целесообразность перевода гидротурбины в режим работы с переменной частотой вращения

Ultrasound-assisted explosive welding: some aspects of formation of joints

This paper presents the results of the effect of ultrasound on structure and properties of explosion welded materials. It is shown that the ultrasound-assisted explosive welding can significantly extend the weldability of aluminum-copper pairs.В работе представлены результаты исследования влияния воздействия ультразвука в процессе сварки взрывом на структуру и свойства получаемых соединений. Показано, что сварка взрывом с воздействием ультразвука позволяет существенно расширить область свариваемости пары алюминий-медь.Работа выполнена в рамках базовой части государственного задания № 2015/16 проект 118

Measurement of the Pion Form Factor in the Energy Range 1.04-1.38 GeV with the CMD-2 Detector

The cross section for the process $e^+e^-\to\pi^+\pi^-$ is measured in the c.m. energy range 1.04-1.38 GeV from 995 000 selected collinear events including 860000 $e^+e^-$ events, 82000 $\mu^+\mu^-$ events, and 33000 $\pi^+\pi^-$ events. The systematic and statistical errors of measuring the pion form factor are equal to 1.2-4.2 and 5-13%, respectively.Comment: 5 pages, 2 figure

Towards the solution of the CP/CAC_{P}/C_{A} anomaly in shell-model calculations of muon capture

Recently many authors have performed shell-model calculations of nuclear matrix elements determining the rates of the ordinary muon capture in light nuclei. These calculations have employed well-tested effective interactions in large scale shell-model studies. For one of the nuclei of interest, namely $^{28}$Si, there exists recent experimental data which can be used to deduce the value of the ratio $C_{P}/C_{A}$ by using the calculated matrix elements. Surprisingly enough, all the abovementioned shell-model results suggest a very small value ($\simeq 0$) for $C_{P}/C_{A}$, quite far from the PCAC prediction and recent data on muon capture in hydrogen. We show that this rather disturbing anomaly is solved by employing effective transition operators. This finding is also very important in studies of the scalar coupling of the weak charged current of leptons and hadrons.Comment: Revtex, 6 pages, 2 figs include

Constraints for hypothetical interactions from a recent demonstration of the Casimir force and some possible improvements

The Casimir force is calculated in the configuration of a spherical lens and a disc of finite radius covered by $Cu$ and $Au$ thin layers which was used in a recent experiment. The correction to the Casimir force due to finiteness of the disc radius is shown to be negligible. Also the corrections are discussed due to the finite conductivity, large-scale and short-scale deviations from the perfect shape of the bounding surfaces and the temperature correction. They were found to be essential when confronting the theoretical results with experimental data. Both Yukawa-type and power-law hypothetical forces are computed which may act in the configuration under consideration due to the exchange of light and/or massless elementary particles between the atoms of the lens and the disc. New constraints on the constants of these forces are determined which follow from the fact that they were not observed within the limits of experimental errors. For Yukawa-type forces the new constraints are up to 30 times stronger than the best ones known up today. A possible improvement of experimental parameters is proposed which gives the possibility to strengthen constraints on Yukawa-type interactions up to $10^4$ times and on power-law interactions up to several hundred times.Comment: 15 pages, 3 figures, subm. to Phys. Rev.

Comparison of superconductivity in Sr_2RuO_4 and copper oxides

To compare the superconductivity in strongly correlated electron systems with the antiferromagnetic fluctuations in the copper oxides and with the ferromagnetic fluctuations in Sr_2RuO_4 a t-J-I model is proposed. The antiferromagnetic coupling J results in the superconducting state of d_{x^2-y^2} symmetry and the ferromagnetic coupling constant I results in the spin-triplet p-type state. The difference in the gap anisotropies provides the large difference in T_c values, for the typical values of the coupling constants: T_c of order of 1K for the ruthenate and T_c of order of 100K for the cuprates.Comment: 4 pages, RevTEX, 3 figs. Submitted to Phys. Rev. Let

Основные аспекты деятельности Европейской сети судебно-экспертных учреждений на современном этапе

The article provides an outline of key events involving the European Network of Forensic Science Institutes. A key aspect of ENFSI activities is participation in the implementation of the European Union Council plan to create an integrated European Forensic Science Area 2020. This work is based on the EU system of direct grants, usually issued for a two-year period. A number of batch themed grants is discussed. The results of the Board, Standing Committee and Working Group activities, as well as scientifc projects coordinated by the ENFSI are presented. The interaction of ENFSI with external partners, primarily with members of the International Forensic Strategic Alliance uniting all major expert networks is briefly analyzed.Дан обзор основных мероприятий Европейской сети судебно-экспертных учреждений (ENFSI) последнего времени. Ключевым аспектом деятельности ассоциации является участие в работе по претворению в жизнь Плана Совета Европы по созданию единого европейского судебно-экспертного пространства – 2020. Указанная работа ENFSI строится на основе системы целевых грантов Европейского Союза, выдаваемых, как правило, на два года. Рассмотрен ряд пакетных тематических грантов. Представлены результаты деятельности президиума, постоянных комитетов и рабочих групп, а также научные работы, в которых ENFSI является координатором. Кратко анализируется взаимодействие ENFSI с внешними партнерами, прежде всего с участниками Международного судебно-экспертного стратегического альянса, который объединяет все крупные экспертные сети