Coherent lidars based on intracavity heterodyning of echo signals

The development and technical realization of the method of laser sounding of the atmosphere based on the effects of mixing of reference and external fields of scattering inside a laser cavity are presented. An approximate theory of the method was developed on the basis of the investigations using the model of a three-mirror laser. The nonlinear effect of a wideband laser on frequency-dependent external influences of the atmosphere was investigated. The field measurements of gaseous composition of the atmosphere were performed on the basis of a given method of coherent reception using a tunable CO2 laser

Electrical control of optical orientation of neutral and negatively charged excitons in n-type semiconductor quantum well

We report a giant electric field induced increase of spin orientation of excitons in n-type GaAs/AlGaAs quantum well. It correlates strongly with the formation of negatively charged excitons (trions) in the photoluminescence spectra. Under resonant excitation of neutral heavy-hole excitons, the polarization of excitons and trions increases dramatically with electrical injection of electrons within the narrow exciton-trion bias transition in the PL spectra, implying a polarization sensitivity of 200 % per Volt. This effect results from a very efficient trapping of neutral excitons by the quantum well interfacial fluctuations (so-called "natural" quantum dots) containing resident electrons.Comment: 18 pages, 4 figure

Quantum Oscillations of Elastic Moduli and Softening of Phonon Modes in Metals

In this paper we present a theoretical analysis of the effect of magnetostriction on quantum oscillations of elastic constants in metals under strong magnetic fields. It is shown that at low temperatures a significant softening of some acoustic modes could occur near peaks of quantum oscillations of the electron density of states (DOS) at the Fermi surface (FS). This effect is caused by a magnetic instability of a special kind, and it can give rise to a lattice instability. We also show that the most favorable conditions for this instability to be revealed occur in metals whose Fermi surfaces include nearly cylindrical segments.Comment: 5 pages, 1 figur

Transfer of 0-order coherence matrix along spin-1/2 chain

In this work, we study transfer of coherence matrices along spin-1/2 chains of various length. Unlike higher order coherence matrices, 0-order coherence matrix can be perfectly transferred if its elements are properly fixed. In certain cases, to provide the perfect transfer, an extended receiver together with optimized its unitary transformation has to be included into the protocol. In this work, the asymptotic perfectly transferable 0-order coherence matrix for an infinitely long chain is considered and deviation of a perfectly transferred state from this asymptotic state is studied as a function of the chain length for various sizes of the extended receiver. The problem of arbitrary parameter transfer via the nondiagonal elements of the 0-order coherence matrix is also considered and optimized using the unitary transformation of the extended receiver.Comment: 32 pages, 5 figure

Non-Markovian large amplitude motion and nuclear fission

The general problem of dissipation in macroscopic large-amplitude collective motion and its relation to energy diffusion of intrinsic degrees of freedom of a nucleus is studied. By applying the cranking approach to the nuclear many body system, a set of coupled dynamical equations for the collective classical variables and the quantum mechanical occupancies of the intrinsic nuclear states is derived. Different dynamical regimes of the intrinsic nuclear motion and its consequences on time properties of collective dissipation are discussed. The approach is applied to the descant of the nucleus from the fission barrier.Comment: 9 pages and 3 figure

The experience of positioning the university at the educational services market

The relevance of the problem under study is based on the necessity to find the most productive method of positioning a higher educational organization at the educational services market within the conditions of transfer from the centrally planned economy to a market economy and changing of the thinking format of the young generation. The purpose of the article is to develop a set of marketing actions for positioning a higher educational organization at the educational services market and its assessment. The lead method of studying this problem is modeling which provides the possibility to consider the problem as a process of results-oriented and well-informed managing of the process of development of a university as an educational system. The article contains a set of marketing actions aimed at positioning the university at the educational services market using the organization’s own internal resources and consisting of the interconnected components, such as motivational-target, content-processing and resultassessing; their specific features are described and the algorithm of implementing this set is developed. The developed and assessed system is intended for promotion of the university as a brand at the educational services market, for strengthening and reinforcing its competitive positions and increasing the university’s attractiveness for future students. The materials of the article can be useful for education specialists oriented towards marketing of educational services, for teachers who deliver a course of lectures in disciplines related to pedagogical marketing or marketing of educational services. © 2016 Dorozhkin et al

Эффективность многопоточных вычислений в системах компьютерного моделирования литейных процессов

The utilization of computer simulation software for casting process simulation is becoming essential in the advancement of casting technology in aviation and other high-tech engineering fields. With the increase in the number of computational cores in modern CPUs, the use of multi-threaded computations is becoming increasingly relevant. In this study, the efficiency of multi-threaded computations in modeling casting processes was evaluated using finite element method casting simulation software ProCast and PoligonSoft, which utilize parallel computing architectures with distributed (DMP) and shared (SMP) memory, respectively. Computations were performed on Intel and AMD-based computers, varying the number of computational threads from 4 to 32. The calculation efficiency was evaluated by measuring the calculation speed increase in the filling and solidification of GP25 castings made of ML10 alloy, as well as the complex task of filling and solidification modeling nickel superalloy casing castings with radiation heat transfer simulation. The results indicate that the minimum computation time in ProCast software is observed when using 16 computational threads. This pattern holds true for both computing systems (Intel and AMD processors), and increasing the number of threads beyond this point does not make a practical difference. The performance decrease in this scenario can be attributed to the low-performance energy-efficient cores in systems based on Intel processors or the decrease in core frequency and full loading of physical cores in systems based on AMD processors. Multi-threading the modeling task in PoligonSoft software is less efficient than in ProCast, which is a result of the shared-memory architecture used in PoligonSoft. Despite the significant difference in parallel efficiency, the task of GP25 casting solidification in both PoligonSoft and ProCast is solved in a time close enough to be considered sufficient.Применение систем компьютерного моделирования литейных процессов (СКМ ЛП) становится обязательным при разработке литейной технологии в авиации и других наукоемких областях техники. В связи с увеличением числа расчетных ядер в современных процессорах актуальным становится осуществление многопоточных вычислений. В работе оценивалась эффективность многопоточных вычислений при моделировании литейных процессов с помощью конечно-элементных СКМ ЛП «ProCast» и «ПолигонСофт», использующих архитектуры параллельных расчетов с распределенной (DMP) и общей (SMP) памятью соответственно. Для вычислений применяли компьютеры на базе платформ от компаний «Intel» и «AMD». Число расчетных потоков варьировали от 4 до 32. Эффективность оценивали по приросту скорости расчета заполнения и затвердевания отливки «ГП25» из сплава МЛ10, а также решения сложной задачи моделирования заполнения и затвердевания корпусных отливок из никелевого жаропрочного сплава с учетом радиационного теплообмена. Показано, что минимальное время расчета в СКМ ЛП «ProCast» наблюдается при использовании 16 вычислительных потоков. Причем это характерно для обеих вычислительных систем (на процессорах «Intel» и «AMD»), и увеличение числа потоков выше этого предела не имеет практического смысла. Снижение производительности в данном случае может быть связано с наличием малопроизводительных энергоэффективных ядер в случае применения системы на процессоре «Intel», а также полной загрузки физических ядер и уменьшением частоты ядер для системы на процессоре от «AMD». Распараллеливание задачи моделирования в СКМ ЛП «ПолигонСофт» менее эффективно, чем в СКМ ЛП «ProCast», вследствие реализации архитектуры с общей памятью. В то же время, несмотря на значительную разницу в эффективности распараллеливания, задача затвердевания отливки «ГП25» в СКМ ЛП «ПолигонСофт» и «ProCast» решается за достаточно близкое время

Anisotropic Magnetoconductance in Quench-Condensed Ultrathin Beryllium Films

Near the superconductor-insulator (S-I) transition, quench-condensed ultrathin Be films show a large magnetoconductance which is highly anisotropic in the direction of the applied field. Film conductance can drop as much as seven orders of magnitude in a weak perpendicular field (< 1 T), but is insensitive to a parallel field in the same field range. We believe that this negative magnetoconductance is due to the field de-phasing of the superconducting pair wavefunction. This idea enables us to extract the finite superconducting phase coherence length in nearly superconducting films. Our data indicate that this local phase coherence persists even in highly insulating films in the vicinity of the S-I transition.Comment: 4 pages, 4 figure RevTex, Typos Correcte