High-frequency oscillations in low-dimensional conductors and semiconductor superlattices induced by current in stack direction

A narrow energy band of the electronic spectrum in some direction in low-dimensional crystals may lead to a negative differential conductance and N-shaped I-V curve that results in an instability of the uniform stationary state. A well-known stable solution for such a system is a state with electric field domain. We have found a uniform stable solution in the region of negative differential conductance. This solution describes uniform high-frequency voltage oscillations. Frequency of the oscillation is determined by antenna properties of the system. The results are applicable also to semiconductor superlattices.Comment: 8 pages, 3 figure

Electron Bloch Oscillations and Electromagnetic Transparency of Semiconductor Superlattices in Multi-Frequency Electric Fields

We examine phenomenon of electromagnetic transparency in semiconductor superlattices (having various miniband dispersion laws) in the presence of multi-frequency periodic and non-periodic electric fields. Effects of induced transparency and spontaneous generation of static fields are discussed. We paid a special attention on a self-induced electromagnetic transparency and its correlation to dynamic electron localization. Processes and mechanisms of the transparency formation, collapse, and stabilization in the presence of external fields are studied. In particular, we present the numerical results of the time evolution of the superlattice current in an external biharmonic field showing main channels of transparency collapse and its partial stabilization in the case of low electron density superlattices

Учебный комплекс для изучения русского языка как иностранного (РКИ) "В добрый путь!" и компьютерный тренажер по РКИ

A description of the nationally oriented training complex for learning Russian as a foreign language "V Dobryi Put’!" for German speakers which includes a textbook, an audio-supplement, a video-film and a test system is given. The computer-based training system, designed for this complex ensures effective teaching foreign students Russian phonetics, vocabulary, grammar, speech etiquette, and also facilitates the formation of the necessary communication skills.Приводится описание национально-ориентированного учебного комплекса по РКИ для немецкоговорящих "В добрый путь!", который включает учебник, аудиоприложение, видеофильм и систему тестов. Разработанный для данного комплекса компьютерный тренажер обеспечивает эффективное обучение иностранных учащихся русской фонетике, лексике, грамматике, речевому этикету, а также облегчает формирование необходимых коммуникативных навыков

Fractional and unquantized dc voltage generation in THz-driven semiconductor superlattices

We consider the spontaneous creation of a dc voltage across a strongly coupled semiconductor superlattice subjected to THz radiation. We show that the dc voltage may be approximately proportional either to an integer or to a half- integer multiple of the frequency of the applied ac field, depending on the ratio of the characteristic scattering rates of conducting electrons. For the case of an ac field frequency less than the characteristic scattering rates, we demonstrate the generation of an unquantized dc voltage.Comment: 6 pages, 3 figures, RevTEX, EPSF. Revised version v3: corrected typo

Межкультурная коммуникация и преподавание русского языка иностранным студентам на летних языковых курсах

Introduction: the article considers the content and methods of teaching Russian as a foreign language at language summer courses with due account to (as a form of study-abroad training) the motives of intercultural communication. The specifics of teaching Russian to international students in the cultural field of Ukraine is revealed. The timeliness of the study is determined by constantly increasing academic mobility of students and the need for the development of modern educational technologies. The main purpose of the article is to present an integrated approach to Russian as a foreign language teaching at language summer courses, when cultural needs of the trainees and the motives of intercultural communication are considered. Materials and Methods: teaching methodology draws on specific methods of teaching Russian as a foreign language and models of intercultural competence development. Educational materials for practical teaching of the Russian language are presented; qualitative and quantitative methods to research intercultural communication motives (written questionnaires and interviews on key topics) are used. Results: through working with the learners of language courses – students of Austrian universities – the data on the learners’ motivation factors, the most relevant topics for intercultural dialogue, some important aspects of Russian grammar, and also the data on the most popular knowledge about Ukraine are obtained and carefully analysed. The analysis of the obtained data, carried out by the authors of the study, allowed to optimise the content of the educational process and to incre ase its effectiveness. Discussion and Conclusions: teaching Russian to foreigners, showing a keen interest in the cultural values of Ukraine, suggests a parallel formation of intercultural competence based on understanding the local cultural realities. The presented approach to RFL teaching within the framework of the language summer courses provides not only a strong uptake of linguistic material by international students and considerable improvements in their level of proficiency in the Russian language, but also a significant enhancement of the intercultural competence of the trainees on the basis of a variety of teaching techniques and active intercultural communication of international students with native Russian language speakers when working in tandem. The practical significance of the study is determined by the fact that the proposed approach to Russian as a foreign language teaching may find wide applicatio n in the training of foreigners at language summer courses; research perspectives are determined by the continuous development of this form of education and the increased importance of intercultural compete nce in the practice of cultural interaction.Введение: в статье рассматриваются содержание и методика обучения русскому языку как иностранному на летних языковых курсах, отражающих мотивы межкультурной коммуникации. Раскрыта специфика преподавания русского языка студентам-иностранцам в культурном поле Украины. Актуальность исследования определяется возрастающей академической мобильностью студентов и необходимостью разработки современных образовательных технологий для их обучения. Цель статьи – представить комплексный подход в преподавании русского языка как иностранного на летних языковых курсах, при котором учитываются культурные запросы обучаемых и мотивы межкультурной коммуникации. Материалы и методы: методологическим обоснованием настоящего исследования являются частная методика преподавания русского языка как иностранного и модели развития межкультурной компетенции. Представлены учебные материалы для практического преподавания русского языка; использованы качественные и количественные методы исследования мотивов межкультурной коммуникации (письменные опросы и устные интервью по ключевым темам). Результаты исследования: в процессе работы со слушателями языковых курсов – студентами австрийских университетов – получены и изучены данные о факторах мотивации учащихся, наиболее значимые для них темы межкультурного диалога, важные аспекты русской грамматики, а также данные о наиболее востребованных знаниях об Украине. Анализ полученных данных, проведенный авторами исследования, позволил оптимизировать содержание учебного процесса и повысить его эффективность. Обсуждение и заключения: обучение русскому языку иностранцев предполагает параллельное формирование их межкультурной компетенции на основе понимания местных культурных реалий. Представленный подход к преподаванию русского языка как иностранного в рамках программы летних языковых курсов обеспечивает не только прочное усвоение языкового материала студентами-иностранцами и существенное улучшение их уровня владения русским языком, но и значительное повышение межкультурной компетенции обучаемых на основе применения разнообразных обучающих технологий и активной межкультурной коммуникации иностранных студентов с носителями русского языка при работе в тандеме. Практическое значение исследования определяется тем, что предлагаемый подход может найти широкое применение при обучении иностранцев на летних языковых курсах; перспективы исследования обусловлены непрерывным развитием данной формы обучения и повышением значимости межкультурной компетенции в практике культурного взаимодействия

Theoretical backgrounds of nonlinear THz spectroscopy of semiconductor superlattices

We consider terahertz absorption and gain in a single miniband of semiconductor superlattice subject to a bichromatic electric field in the most general case of commensurate frequencies of the probe and pump fields. Using an exact solution of Boltzmann transport equation, we show that in the small-signal limit the formulas for absorption always contain two distinct terms related to the parametric and incoherent interactions of miniband electrons with the alternating pump field. It provides a theoretical background for a control of THz gain without switching to the negative differential conductivity state. For pedagogical reasons we present derivations of formulas in detail.Comment: 14 page

Solution of the problem of catastrophic relaxation of homogeneous spin precession in superfluid 3^3He-B

The quantitative analysis of the "catastrophic relaxation" of the coherent spin precession in $^3$He-B is presented. This phenomenon has been observed below the temperature about 0.5 T$_c$ as an abrupt shortening of the induction signal decay. It is explained in terms of the decay instability of homogeneous transverse NMR mode into spin waves of the longitudinal NMR. Recently the cross interaction amplitude between the two modes has been calculated by Sourovtsev and Fomin \cite{SF} for the so-called Brinkman-Smith configuration, i.e. for the orientation of the orbital momentum of Cooper pairs along the magnetic field, ${\bf L}\parallel {\bf H}$. In their treatment, the interaction is caused by the anisotropy of the speed of the spin waves. We found that in the more general case of the non-parallel orientation of ${\bf L}$ corresponding to the typical conditions of experiment, the spin-orbital interaction provides the additional interaction between the modes. By analyzing experimental data we are able to distinguish which contribution is dominating in different regimes.Comment: 6 pages, 1 figure, submited to JETP letter