Generation of coherent terahertz pulses in Ruby at room temperature

We have shown that a coherently driven solid state medium can potentially produce strong controllable short pulses of THz radiation. The high efficiency of the technique is based on excitation of maximal THz coherence by applying resonant optical pulses to the medium. The excited coherence in the medium is connected to macroscopic polarization coupled to THz radiation. We have performed detailed simulations by solving the coupled density matrix and Maxwell equations. By using a simple $V$-type energy scheme for ruby, we have demonstrated that the energy of generated THz pulses ranges from hundreds of pico-Joules to nano-Joules at room temperature and micro-Joules at liquid helium temperature, with pulse durations from picoseconds to tens of nanoseconds. We have also suggested a coherent ruby source that lases on two optical wavelengths and simultaneously generates THz radiation. We discussed also possibilities of extension of the technique to different solid-state materials

Flip dynamics in octagonal rhombus tiling sets

We investigate the properties of classical single flip dynamics in sets of two-dimensional random rhombus tilings. Single flips are local moves involving 3 tiles which sample the tiling sets {\em via} Monte Carlo Markov chains. We determine the ergodic times of these dynamical systems (at infinite temperature): they grow with the system size $N_T$ like $Cst. N_T^2 \ln N_T$; these dynamics are rapidly mixing. We use an inherent symmetry of tiling sets and a powerful tool from probability theory, the coupling technique. We also point out the interesting occurrence of Gumbel distributions.Comment: 5 Revtex pages, 4 figures; definitive versio

ПРЕОБРАЗОВАТЕЛЬНО-РАСПРЕДЕЛИТЕЛЬНОЕ УСТРОЙСТВО ДЛЯ ТЯГОВЫХ ПОДСТАНЦИЙ

Intense development of power semiconductor units allows designing powerful arcless disconnection devices which could make a single set along with conversion units of traction substations. The authors suggest a promising design of conversion and distribution 3,3 kV unit for DC power traction substations, that has some technical and economic advantages. The circuit is realized with the help of controlled 12 pulse rectifier, built without cathode groups of cells in the second bridges of rectifiers. Three-phase switches of feeders are assembled on thyristors, and the cathodes there-of are electrically interconnected and create the terminals of direct current. The main elements of the unit are described and the algorithm of its operation is studied. Using the MATLAB software, the authors have created mathematical model of traction substation and simulated disconnection of a short-circuit at one of the feeders of overhead catenary, while considering a traction load at the other feeder. To make better demonstration of the model, the results of simulation are shown as an oscilloscope pattern, where the process of disconnection is divided into several stages.Предложена перспективная схема преобразовательно-распределительного устройства 3,3 кВ для тяговых подстанций постоянного тока, обладающая существенными технико-экономическими преимуществами. Схема выполнена с использованием управляемого 12-пульсового выпрямителя, построенного без катодных групп вентилей во вторых мостах выпрямителей. Трехфазные выключатели фидеров собраны на тиристорах, у которых катоды электрически соединены между собой и образуют выводы постоянного тока. Приведено описание основных элементов устройства, а также рассмотрен алгоритм его работы. С помощью программы MATLAB создана математическая модель тяговой подстанции и выполнено моделирование отключения короткого замыкания на одном из фидеров контактной сети. При этом на другом фидере учитывалась тяговая нагрузка. Для наглядности результаты моделирования приведены в виде осциллограммы, на которой весь процесс отключения разделен на несколько этапов.

Generalized quasiperiodic Rauzy tilings

We present a geometrical description of new canonical $d$-dimensional codimension one quasiperiodic tilings based on generalized Fibonacci sequences. These tilings are made up of rhombi in 2d and rhombohedra in 3d as the usual Penrose and icosahedral tilings. Thanks to a natural indexing of the sites according to their local environment, we easily write down, for any approximant, the sites coordinates, the connectivity matrix and we compute the structure factor.Comment: 11 pages, 3 EPS figures, final version with minor change

Classification of one-dimensional quasilattices into mutual local-derivability classes

One-dimensional quasilattices are classified into mutual local-derivability (MLD) classes on the basis of geometrical and number-theoretical considerations. Most quasilattices are ternary, and there exist an infinite number of MLD classes. Every MLD class has a finite number of quasilattices with inflation symmetries. We can choose one of them as the representative of the MLD class, and other members are given as decorations of the representative. Several MLD classes of particular importance are listed. The symmetry-preserving decorations rules are investigated extensively.Comment: 42 pages, latex, 5 eps figures, Published in JPS

Rules for Computing Symmetry, Density and Stoichiometry in a Quasi-Unit-Cell Model of Quasicrystals

The quasi-unit cell picture describes the atomic structure of quasicrystals in terms of a single, repeating cluster which overlaps neighbors according to specific overlap rules. In this paper, we discuss the precise relationship between a general atomic decoration in the quasi-unit cell picture atomic decorations in the Penrose tiling and in related tiling pictures. Using these relations, we obtain a simple, practical method for determining the density, stoichiometry and symmetry of a quasicrystal based on the atomic decoration of the quasi-unit cell taking proper account of the sharing of atoms between clusters.Comment: 14 pages, 8 figure

ПОЗДНЕГОЛОЦЕНОВОЕ ОСАДКОНАКОПЛЕНИЕ В АКТИВНЫХ ГЕОЛОГИЧЕСКИХ СТРУКТУРАХ ЧУКОТСКОГО МОРЯ

The article presents the detailed analysis results considering bottom sediments from the Chukchi Sea. Two core samples, b16 and НС–8 were taken from the northern Herald Canyon 150 km northeast from NE Wrangel Island. Core b16 has been studied in more detail. According to the 210Pb measurements, the recent sedimentation rate amounts to 0.9 mm/y–1 at the sampling point. In the bottom layer of the core sample, the minimum concentrations of biogenic components (SiO2bio, Corg, Ntot, and Br) and the increased concentrations of cold-water diatom species Thalassiosira antarctica may result from low biological productivity during the Maunder Minimum. A correlation with recent global warming (11–22 years) is shown by the increased concentrations of SiO2bio, Corg, Ntot, and Br and the decreased values of magnetic susceptibility and X-ray density in the top layer (1–2 cm) of the same core sample. The results of our geochemical and diatom analysis support the available literature data and confirm that the Late Holocene sedimentation in the Chukchi Sea takes place in the zone wherein the water transits from the Pacific to the Arctic Ocean.Представлены результаты комплексного исследования вещественного состава донных осадков, вскрытых двумя кернами в северной части каньона Геральд Чукотского моря. Одна из полученных колонок была выбрана для более детального исследования. Скорость современного осадконакопления в точке отбора этого керна, измеренная по 210Pb, составляет 0.9 мм/год. Минимальные концентрации биогенных компонентов (SiO2биог., Сорг., Nобщ., Br) и увеличение содержаний холодноводного вида диатомей Thalassiosira antarctica в нижнем слое колонки, вероятно, объясняются низкой биологической продуктивностью во время минимума Маундера. Повышенные концентрации SiO2биог, Сорг, Nобщ, Br, пониженные значения магнитной восприимчивости и рентгеновской плотности в самом верхнем интервале разреза (до 1–2 см) соответствуют последним 11–22 годам глобального потепления климата. Результаты геохимического и диатомового анализов подтверждают имеющиеся в литературе данные о том, что позднеголоценовая седиментация в Чукотском море происходит в зоне транзита тихоокеанских вод в Северный Ледовитый океан

Secondary crystalline phases identification in Cu2ZnSnSe4 thin films: contributions from Raman scattering and photoluminescence

In this work, we present the Raman peak positions of the quaternary pure selenide compound Cu2ZnSnSe4 (CZTSe) and related secondary phases that were grown and studied under the same conditions. A vast discussion about the position of the X-ray diffraction (XRD) reflections of these compounds is presented. It is known that by using XRD only, CZTSe can be identified but nothing can be said about the presence of some secondary phases. Thin films of CZTSe, Cu2SnSe3, ZnSe, SnSe, SnSe2, MoSe2 and a-Se were grown, which allowed their investigation by Raman spectroscopy (RS). Here we present all the Raman spectra of these phases and discuss the similarities with the spectra of CZTSe. The effective analysis depth for the common back-scattering geometry commonly used in RS measurements, as well as the laser penetration depth for photoluminescence (PL) were estimated for different wavelength values. The observed asymmetric PL band on a CZTSe film is compatible with the presence of CZTSe single-phase and is discussed in the scope of the fluctuating potentials’ model. The estimated bandgap energy is close to the values obtained from absorption measurements. In general, the phase identification of CZTSe benefits from the contributions of RS and PL along with the XRD discussion.info:eu-repo/semantics/publishedVersio