Direct current driven by ac electric field in quantum wells

It is shown that the excitation of charge carriers by ac electric field with zero average driving leads to a direct electric current in quantum well structures. The current emerges for both linear and circular polarization of the ac electric field and depends on the field polarization and frequency. We present a micoscopic model and an analytical theory of such a nonlinear electron transport in quantum wells with structure inversion asymmetry. In such systems, dc current is induced by ac electric field which has both the in-plane and out-of-plane components. The ac field polarized in the interface plane gives rise to a direct current if the quantum well is subjected to an in-plane static magnetic field.Comment: 6 pages, 3 figure

Ultrastructure of meristem and root cap of pea seedlings under spaceflight conditions

Data of electron microscopic analysis of meristem and root cap of pea seedlings grown aboard the Salyut-6 orbital research station in the Oazis apparatus and in the laboratory are presented. The main morphological and anatomical characteristics of the test and control plants are shown to be similar. At the same time, some differences are found in the structural and functional organization of the experimental cells as compared to the controls. They concern first of all the plastic apparatus, mitochondria and Golgi apparatus. It is assumed that cell function for certain periods of weightlessness on the whole ensures execution of the cytodifferentiation programs genetically determined on the Earth. Biochemical and physiological processes vary rather markedly due to lack of initially rigorous determination

Effect of metal cations on the microstructure of sol-gel-synthesized silica

The effect of small doping additions (ten metal cations) on the structural characteristics of the solgel- synthesized silicas was evaluated by the SAXS method. Doping with cobalt, cerium, and silver cations led to separation of metal compounds as single phases. All the tested cations affected the radius of gyration and the fractal dimension of the resultant silica

Concepts of intellectual sphere in Russian, English and French

On the basis of the study of proverbs and sayings in Russian, English and French the concepts “intellect” and “stupidity” are compared. The authors show how life of people is reflected in the language, and prove that words reflect cultural concepts.На основе исследования народных пословиц и поговорок в русском, английском и французском языках сравниваются концепты «ум» и «глупость». Авторы статьи показывают, как жизнь народа отражается в его языке, а слова транслируют культурные концепты

Photodecolourization of congo red dye in presence of Ni3+ layered double hydroxide

Layered double hydroxide containing Ni3+ (Mg/AlNi-LDH) was successfully synthesized by co-precipitation in an oxidizing media. The resulted product was characterized using X-ray diffraction, wavelength dispersive X-ray fluorescence spectrometry. The activity of Mg/AlNi-LDH in the process of photodegradation of Congo red dye using UV light irradiation was evaluated. The initial rate of photodegradation of the dye in the presence of LDH is 1.6 times higher than that of UV irradiated solution. The kinetic data obtained for photodegradation process can be adequately described by pseudo-first-order kinetic model. The presence of Mg/AlNi - LDH leads to increased photodegradation yield compared to destruction only by UV irradiatio

Electron scattering in quantum wells subjected to an in-plane magnetic field

It is shown that the electron scattering by static defects, acoustic or optical phonons in quantum wells subjected to an in-plane magnetic field is asymmetric. The probability of scattering contains terms which are proportional to both the electron wave vector and the magnetic field components. The terms under study are caused by the lack of an inversion center in quantum wells due to structure or bulk inversion asymmetry although they are of pure diamagnetic origin. Such a magnetic field induced asymmetry of scattering can be responsible for a number of phenomena. In particular, the asymmetry of inelastic electron-phonon interaction leads to an electric current flow if only the electron gas is driven out of thermal equilibrium with the crystal lattice.Comment: 5 pages, 1 figur

Children’s books as a sourse of bringing up positive traits of character

On the basis of English and German versions of the fairytale plot of “Snow White and Seven Dwarfs” main traits of character of positive personages are described (diligence, trustfulness, helplessness, readiness to help).На примере английского и немецкого вариантов сказочного сюжета «Белоснежка и семь гномов» анализируются основные черты положительных сказочных героев (трудолюбие, доверчивость, беззащитность, готовность придти на помощь)

On Lidar Sounding of the Atmosphere to Estimate Static and Dynamic Characteristics of Aerosol Inhomogeneities

1. A possible application of intensity fluctuations of a pulse light signal reflected by atmospheric aerosols is analyzed by the correlation method to evaluate static (medium sizes, shape) and dynamic (speed and direction of movement, lifetime) characteristics of aerosol inhomogeneities. The aerosol inhomogeneities are assumed to be expanded, pressed, disintegrated and originated constantly in accordance with random laws, the set of inhomogeneities as a whole traveling together with air masses and having predominant movement in wind direction. It is shown that the characteristics of aerosol inhomogeneities considered can be expressed by the coefficients of the correlation function expansion of the reflected signal fluctuation intensity in Tailor series. 2/ Correlation systems for evaluating static and dynamic characteristics of driving objects can be divided into two types according to the kind and quantity of used information: the systems with coordinates of the information removal "points" to be fixed in space, and the systems with a parallel simultaneous information removal at discrete moments of time. The systems for determination of wind direction considered in are the examples of the first type system. However, the operating information removal for two points is insufficient to estimate completely static and dynamic characteristics of inhomogenities, their quantity ought to be increased up to three of them for two-dimensional problem and up to four of them for three-dimensional problem as it is usually done in the ionospheric studies. The second type systems are used for the investigation of a medium shape and speed of the clouds according to photographs made from satellites. These systems are also used for solution of navigation problems. The use of optical quantum generators with a scanning beam is seen to increase greatly the working information removal in comparison with the first type systems. Nevertheless, scanning rate is not sufficient sometimes in order to consider a general picture of aerosol inhomogeneities to be stationary. In this connection the use of the systems of second type treatment becomes a matter of essential difficulty. 3. Aerosol inhomogeneities simulation has been carried out on the basis of the digital computer experiments with the aim of estimating static and dynamic characteristics of inhomogeneities by an optical beam in the atmosphere at different scanning procedures. The dependence of determination accuracy of these characteristics on the type of chosen laws of aerosol particle distribution in the atmosphere, the parameters of inhomogeneities geometry, their speed and the law of scanning have been obtained

El impacto de procesos demográficos en la formación del estudiantado en Ucrania

It has been founded that the main threats to the economic security of Ukrainian universities and the system of higher education as a whole are the lack of student body, which has been caused by negative migration and demographic processes, as well as the nonconformance of the higher education system to the needs of economy. These processes are factors that led to a decrease in the level of economic security of universities.Se ha constatado que las amenazas principales a la seguridad económica de las universidades ucranianas y al sistema de enseñanza superior en general son la falta del estudiantado. Ha sido causado por la migración negativa y procesos demográficos, así como la disconformidad entre del sistema de enseñanza superior y las necesidades de la economía. Estos procesos son factores que llevaron a una disminución en el nivel de seguridad económica de las universidades