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

Theoretical analysis of resonance states in 4H^{4}H, 4He^{4}He and 4Li^{4}Li above three-cluster threshold

The resonance states of $^{4}H$, $^{4}He$ and $^{4}Li$, embedded in the three-cluster $d+N+N$ continuum, are investigated within a three-cluster model. The model treats the Pauli principle exactly and incorporates the Faddeev components for proper description of the boundary conditions for the two- and three-body continua. The hyperspherical harmonics are used to distinguish and numerate channels of the three-cluster continuum. It is shown that the effective barrier, created by three-cluster configuration $d+N+N$, is strong enough to accommodate two resonance states.Comment: 20 page, 4 figure

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

Презентація іменників singularia та pluralia tantum у курсі російської мови як іноземної

This article considers singularia and pluralia tantum nouns; despite the absence of this topic in programs on teaching Russian as a foreign language (RFL), it must be acknowledged that singularia tantum nouns constitute a significant layer of vocabulary and are quite commonly used, and pluralia tantum nouns are closely linked to cultural discourse and cannot be painlessly excluded from lexical system of the Russian language. Although this phenomenon has been thoroughly studied in classical editions of Russian grammar, problems of category of number and in particular singularia and pluralia tantum nouns are still widely discussed by modern linguists (as is noted, complex subjects can be designated both as forms of singular and forms of plural, therefore the three groups of nouns can be found: pluralia tantum (a single object indicated by plural: ворота), a full-numbered paradigm (one object is indicated by singular: ракушка), and nouns with a paradigm fluctuation (one object is indicated by both singular and plural: дверь / двери); there is a dramatic rise in the use of plural forms of many abstract nouns (риск, продажа) forming a crucial change in the development trend of Russian abstract noun number paradigms). We assume that in RFL teaching, it is important to follow the principles of step by step presentation of theoretical information on this topic (common singularia and pluralia tantum nouns, their grammatical properties, derivative characteristics; proper singularia and pluralia tantum nouns; synonymy, antonymy, and homonymy of singularia and pluralia tantum nouns; occasionalisms, etc.) to help students reach a higher level of Russian language proficiency.У статті розглянуто іменники singularia та pluralia tantum. Не зважаючи на відсутність цієї теми у програмах викладання російської мови як іноземної (далі – РЯІ), треба визнати, що іменники singularia tantum становлять значний прошарок лексики та є доволі вживаними, а іменники pluralia tantum тісно пов’язані з культурологічним дискурсом і не можуть бути безболісно виключені з лексичної системи російської мови. Хоча цей феномен досить ретельно вивчався в класичних виданнях російської граматики, проблеми категорії числа та іменників singularia tantum та pluralia tantum зокрема продовжують широко обговорюватися сучасними лінгвістами. Наприклад, ідеться про те, що складні речі позначають як формами однини, так і формами множини, тому вирізняють три групи іменників: pluralia tantum (окремий предмет, позначений множиною: ворота); ті, що мають повну парадигму (один об’єкт позначається одниною: ракушка), та іменники з коливанням парадигми (один об’єкт позначається як одниною, так і множиною: дверь/двери). Зазначають, що відбувається різке зростання використання множинних форм багатьох абстрактних іменників (риск, продажа), що надзвичайно змінює тенденції розвитку парадигм числа абстрактних іменників у російській мові). Ми виходимо з того, що у викладанні РЯІ важливо дотримуватися принципів покрокової презентації теоретичної інформації за темою: загальні іменники singularia та pluralia tantum, їхні граматичні властивості, дериваційні характеристики; власні іменники singularia та pluralia tantum; синонімія, антонімія й омонімія іменників singularia та pluralia tantum; оказіоналізми тощо», що допомагає студентам підвищити рівень володіння російською мовою

On the nature of the solar-wind-Mars interaction

Plasma measurements near Mars on the U.S.S.R. Mars-2, -3, and -5 spacecraft are considered. The data are compared with simultaneous magnetic measurements. Strong evidence is obtained in favor of a direct interaction and mass exchange between the solar wind plasma and the gaseous envelope of Mars

GRAVITY’S ROLE IN ACCELERATED RUNNING - A COMPARISON OF AN EXPERIENCED POSE® AND HEEL-TOE RUNNER

The purpose of this study was to determine gravity’s role in accelerated running using an experienced male Pose® and heel-toe runner as a comparison. A two-step accelerated run found that maximum horizontal acceleration of the centre of mass (COM) occurred before maximum horizontal ground reaction force (GRF). Maximum horizontal and angular acceleration of the arms and trunk occurred at or before maximum horizontal acceleration of the COM. At maximum horizontal GRF both participants’ stance feet were vertically accelerated. It is suggested that acceleration of the COM occurs via a gravitational torque with GRF being the consequence of, not the cause of these movements. Therefore, practitioners might find this novel perspective helpful when applied to accelerated running

Training system for future specialists: quality control

The development ofinnovative strategy of engineers and skilled workers training quality control in educational professional organizations on the principles of social partnershi