Do the precise measurements of the Casimir force agree with the expectations?

An upper limit on the Casimir force is found using the dielectric functions of perfect crystalline materials which depend only on well defined material constants. The force measured with the atomic force microscope is larger than this limit at small separations between bodies and the discrepancy is significant. The simplest modification of the experiment is proposed allowing to make its results more reliable and answer the question if the discrepancy has any relation with the existence of a new force.Comment: 9 pages, LaTeX, 2 Postscript figure

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

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

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]

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

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

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

Magnetothermopower and Magnetoresistivity of RuSr2Gd1-xLaxCu2O8 (x=0, 0.1)

We report measurements of magnetothermopower and magnetoresistivity as a function of temperature on RuSr2Gd1-xLaxCu2O8 (x = 0, 0.1). The normal-state thermopower shows a dramatic decrease after applying a magnetic field of 5 T, whereas the resistivity shows only a small change after applying the same field. Our results suggest that RuO2 layers are conducting and the magnetic field induced decrease of the overall thermopower is caused by the decrease of partial thermopower decrease associated with the spin entropy decrease of the carriers in the RuO2 layers.Comment: 21 pages, 6 figure

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.

Disorder Induced Ferromagnetism in Restricted Geometries

We study the influence of on-site disorder on the magnetic properties of the ground state of the infinite $U$ Hubbard model. We find that for one dimensional systems disorder has no influence, while for two dimensional systems disorder enhances the spin polarization of the system. The tendency of disorder to enhance magnetism in the ground state may be relevant to recent experimental observations of spin polarized ground states in quantum dots and small metallic grains.Comment: 4 pages, 4 figure