On the Strength of Spin-Isospin Transitions in A=28 Nuclei

The relations between the strengths of spin-isospin transition operators extracted from direct nuclear reactions, magnetic scattering of electrons and processes of semi-leptonic weak interactions are discussed.Comment: LaTeX, 8 pages, 1Postscript with figur

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

New constraints for non-Newtonian gravity in nanometer range from the improved precision measurement of the Casimir force

We obtain constraints on non-Newtonian gravity following from the improved precision measurement of the Casimir force by means of atomic force microscope. The hypothetical force is calculated in experimental configuration (a sphere above a disk both covered by two metallic layers). The strengthenings of constraints up to 4 times comparing the previous experiment and up to 560 times comparing the Casimir force measurements between dielectrics are obtained in the interaction range 5.9 nm$\leq\lambda\leq 115$nm. Recent speculations about the presence of some unexplained attractive force in the considered experiment are shown to be unjustified.Comment: 5 pages, 1 figur

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

Toward An Empirical Theory of Pulsar Emission. VII. On the Spectral Behavior of Conal Beam Radii and Emission Heights

In this paper we return to the old problem of conal component-pair widths and profile dimensions. Observationally, we consider a set of 10 pulsars with prominent conal component pairs, for which well measured profiles exist over the largest frequency range now possible. Apart from some tendency to narrow at high frequency, the conal components exhibit almost constant widths. We use all three profile measures, the component separation as well as the outside half-power and 10% widths, to determine conal beam radii, which are the focus of our subsequent analysis. These radii at different frequencies are well fitted by a relationship introduced by Thorsett (1991), but the resulting parameters are highly correlated. Three different types of behavior are found: one group of stars exhibits a continuous variation of beam radius which can be extrapolated down to the stellar surface along the ``last open field lines''; a second group exhibits beam radii which asymptotically approach a minimum high frequency value that is 3--5 times larger; and a third set shows almost no spectral change in beam radius at all. The first two behaviors are associated with outer-cone component pairs; whereas the constant separation appears to reflect inner-cone emission.Comment: 21 pages, 11 figures, accepted for publication in Astrophysical Journal, uses aaste

Quality standards for distance learning in higher education: a comparative analysis of Canadian and Russian practices

The aim of the investigation is to perform comparative analysis of the quality assessment and policies of quality assurance in postsecondary education in Canada and Russian Federation. Methods. The theoretical methods involve comparative analysis and synthesis, induction and deduction, extrapolation and modelling. Results. Russia and Canada have different policies on quality assurance in the distance learning and are at different stages of implementation of distance learning into postsecondary curricula. The Canadian system of postsecondary education is regulated not by the State but by professional societies, licensing organisations, and experts. Canadian postsecondary institutions have efficient systems of quality assurance, quality standards and accreditation. Blended learning is widely used in Canadian medical schools and is mandatory for continuous professional development. In Russia, the system of quality assurance for distance learning is regulated by the State. At present, Russia has developed policies on distance learning but unified quality standards in this field are absent. Blended learning is used in the medical schools but its implementation has just begun as continuous professional development. Scientific novelty. For the first time, the results of comparative analysis of the policies on quality assurance in distance learning in Russia and Canada are described. Practical significance. This research has showed the needs of the development of the system of quality standards and the policy on quality assurance of distance learning in the Russia postsecondary educationЦель статьи – сравнительный анализ стандартов качества дистанционного образования в высшей школе в Канаде и России. Методы исследования – теоретические: компаративный, анализ и синтез, индукция и дедукция, экстраполяция и моделирование. Результаты. Установлено, что в России и Канаде существуют разные модели оценки качества и экспертизы дистанционного образования, которые находятся на разных этапах внедрения в образовательный процесс дистанционного образования (ДО). В канадской высшей школе нормативное регулирование ДО осуществляется с участием негосударственных структур (независимых экспертов, профессионального сообщества); эффективно функционирует система стандартизации качества в этой области; есть система аккредитации электронных ресурсов; разработаны руководства для пользователей. На территории Канады широкое распространение получила смешанная форма обучения (hybrid method, blended method). Примером тому служит подготовка специалистов в области медицины, где дополнительное профессиональное образование стало невозможным без дистанционных технологий. В отличие от канадской, российская система оценки качества строго иерархизирована и полностью осуществляется государством. Отечественная высшая школа прошла этап создания нормативной базы ДО, определения понятий «цифровой педагогики», но критерии качества дистанционного образования в правовых документах отсутствуют. Общей чертой использования ДО в обеих странах является наличие смешанного обучения, однако в наших вузах дистанционные технологии постдипломного образования только начинают внедряться, а для канадских коллег они уже стали нормой, а зачастую и обязательной составляющей продолжения образования и повышения квалификации (как, например, в медицинской сфере). Научная новизна. Впервые представлены результаты компаративного анализа нормативной базы и практики оценивания результатов обучения в высшей школе с использованием дистанционных технологий в РФ и Канаде. Практическая значимость данного материала заключается в выявлении актуальных потребностей отечественной системы образования по стандартизации качества дистанционного обучения: в российской высшей школе назрела необходимость создания процедуры аттестации качества электронных образовательных ресурсов, и это касается всей системы непрерывного профессионального образовани

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

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.

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

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