Ring-shaped spatial pattern of exciton luminescence formed due to the hot carrier transport in a locally photoexcited electron-hole bilayer

A consistent explanation of the formation of a ring-shaped pattern of exciton luminescence in GaAs/AlGaAs double quantum wells is suggested. The pattern consists of two concentric rings around the laser excitation spot. It is shown that the luminescence rings appear due to the in-layer transport of hot charge carriers at high photoexcitation intensity. Interestingly, one of two causes of this transport might involve self-organized criticality (SOC) that would be the first case of the SOC observation in semiconductor physics. We test this cause in a many-body numerical model by performing extensive molecular dynamics simulations. The results show good agreement with experiments. Moreover, the simulations have enabled us to identify the particular kinetic processes underlying the formation of each of these two luminescence rings.Comment: 14 pages, 16 figures. Final versio

Эколого-геохимические исследования постпромышленных площадок г. Минска

In the article the results of studying the sites of industrial enterprises, which have stopped their activities fully or partially in Minsk, are discussed. It is shown that in most cases the re-development of industrial sites with a change of their functional purpose is carried out after 10 years or more. Based on the results of preliminary investigation of a number of the former industrial sites, it was established that such sites continue to be sources of pollutants after the completion of enterprises activity. The enrichment of technogenic substrates carried out from industrial sites by surface runoff (sediments near storm collectors and in topographic lows) with heavy metals is shown. The average content of cadmium in sediments is 2,6 (maximum – 3,9), lead – 3,1 (14), copper – 2,5 (2,2), zinc – 1,7 (2,8), nickel – 3,3 (8,0), chromium – 3,4 (6,6) times higher than in soils. The established standards for lead were exceeded in 63 % of cases, for cadmium – in 77 %, for zinc and copper – in 100 % of cases. The maximum permissible concentration was exceeded 5 times for at least one indicator in almost half of the samples (44 %). The dependence of heavy metals accumulation on the specialization of previously carried out industrial activities is shown. The need for improvement of scientific and methodological approaches to studying of contaminated and potentially contaminated post-industrial areas in connection with their planned re-profiling for urban planning purposes is discussed.Обсуждаются результаты изучения территорий промышленных предприятий в г. Минске, которые прекратили свою деятельность полностью или частично. Показано, что в большинстве случаев освоение промплощадок с изменением их функционального назначения осуществляется спустя 10 лет и более; в ряде случаев перепрофилирование касается только производственных корпусов. По результатам рекогносцировочного обследования ряда объектов установлено, что такие предприятия после прекращения функционирования продолжают оставаться источниками распространения загрязняющих веществ. Показано обогащение тяжелыми металлами техногенных субстратов, вынесенных с промышленных площадок поверхностным стоком и сформированных в виде наносов у ливневых коллекторов и в понижениях рельефа. По сравнению с почвами превышение среднего содержания в них кадмия составляет 2,6 раза (максимальное – 3,9), свинца – 3,1 (14), меди – 2,5 (2,2), цинка – 1,7 (2,8), никеля – 3,3 (8,0), хрома – 3,4 (6,6) раза. Установленные нормативы по свинцу превышены в 63 % случаев, по кадмию – 77 %, по цинку и меди – в 100 % случаев. Почти в половине проб (44 %) зафиксировано 5-кратное превышение ПДК хотя бы по одному показателю. Показана зависимость накопления тяжелых металлов от специализации ранее осуществлявшейся производственной деятельности. Обсуждается необходимость совершенствования научно-методических подходов к изучению загрязненных и потенциально загрязненных постпромышленных территорий в связи с планируемым их перепрофилированием для градостроительных целей

Electron-Hole Distribution and Exciton Condensed Phase Formation in Semiconductor Quantum Wells

We study the development of ring luminescence of indirect excitons at macroscopical distances from the central excitation spot in quantum well structures. The Landau model for exciton condensation generalized for particles with finite lifetimes in conditions of inhomogeneous excitation is proposed. The transition between the fragmented and continuous rings and the temperature dependence of the effects are considered. The irradiation of the system by two spatially separated laser spots is simulated as well

Ordered Dissipative Structures in Exciton Systems in Semiconductor Quantum Wells

A phenomenological theory of exciton condensation in conditions of inhomogeneous excitation is proposed. The theory is applied to the study of the development of an exciton luminescence ring and the ring fragmentation at macroscopical distances from the central excitation spot in coupled quantum wells. The transition between the fragmented and the continuous ring is considered. With assumption of a defect in the structure, a possibility of a localized island of the condensed phase in a fixed position is shown. Exciton density distribution is also analyzed in the case of two spatially separated spots of the laser excitation

Effect of interaction between electronic excitations on luminescence from fast charged particle’s track’s region

The paper studies the effect of the interaction between the electronic excitations (excitons) on the light emission yield of the high energy charged particle in the dielectric medium. It is assumed that after being created in the track, the excitons diffuse from its core. Exciton annihilation and the non-radiative part of its lifetime contribute to the losses that manifest themselves as the decrease of the luminescence intensity. The dependence of the losses on the direction of propagation of the high energy charged particle with respect to the crystal axes for crystals with the exciton diffusion anisotropy is calculated. Dynamic interaction between excitons leads to the changes of their motion, affects the inter-exciton distance, and, hence, causes losses due to annihilation. The estimates of the losses are made depending on the interaction: an increase for the exciton attraction, a decrease for the repulsion. The possibility of the exciton condensation in the track region in the inorganic semiconductors is evaluated

Russian-Speaking Diaspora In Finland As A Public Diplomacy Tool

The article deals with complex studies of  the  Finnish case particularly migrants’ inclusion analysis into local cultural and political environments (as conditions to cultural and political environment stability) as well as public diplomacy impact evaluation of an important «soft power»  tool where migrants role is rather high. Authors scrutinize migrants’   interaction with  the  environment,   outline cause-and-effect   links of  this interaction, and unveil external factors that influence the respondents’ political behavior. The research  method is based upon interviews,  which result  in respondents’ typology development, political information channels were defined, and the influence of education and social inclusion upon political communication  was characterized. This method helps to perceive migrants’ integration policy at example of Finland, the fourth most attractive country  in the world in accordance  with the Migrant  Integration  Policy  Index.  Finnish experience could be highly useful for Russia in terms of both national migration policy development.   The resulting characteristics  of migrants’ political communication  might be of high interest in terms of migration policy regulation and understanding the issue of migration quotas, help to predict structural changes in society, also to provide the basis for making decisions on the effective use of public diplomacy tools