Electron transport and optical properties of shallow GaAs/InGaAs/GaAs quantum wells with a thin central AlAs barrier

Shallow GaAs/InGaAs/GaAs quantum well structures with and without a three monolayer thick AlAs central barrier have been investigated for different well widths and Si doping levels. The transport parameters are determined by resistivity measurements in the temperature range 4-300 K and magnetotransport in magnetic fields up to 12 T. The (subband) carrier concentrations and mobilities are extracted from the Hall data and Shubnikov-de Haas oscillations. We find that the transport parameters are strongly affected by the insertion of the AlAs central barrier. Photoluminescence spectra, measured at 77 K, show an increase of the transition energies upon insertion of the barrier. The transport and optical data are analyzed with help of self-consistent calculations of the subband structure and envelope wave functions. Insertion of the AlAs central barrier changes the spatial distribution of the electron wave functions and leads to the formation of hybrid states, i.e. states which extend over the InGaAs and the delta-doped layer quantum wells.Comment: 14 pages, pdf fil

A programme of additional training for participation in the competition worldskills international jewelry

The article presents a comparative analysis of The WorldSkills specification standards for jewelry and professional competencies of the Federal state educational standard of secondary vocational education in the field of "arts and crafts"Проводится сравнительный анализ стандартов спецификации WorldSkills по ювелирному делу и профессиональных компетенций, обозначенных в Федеральном государственном образовательном стандарте среднего профессионального образования в сфере декоративно-прикладного искусства и народных промысло

Categories and methods of civilizational approach in modern philosophical and historical discourse

The diverse contradictions of the modern world, social and international conflicts, the growing trends of both globalization and national isolation, the rapid development of communication technologies against the background of growing gap between poverty and wealth of the countries and within them are evidence of another crisis in the system of international relations, of the entire world order. The growth of entropy has once again raised the question of the lack of a holistic and systematic understanding of the processes of socio-historical development, and actualizes the need to analyze theories that consider the development of large socio-cultural communities. In this regard, it is important to study socio-philosophical and philosophical-historical theories and views, united in a civilizational approach. The dominance of the formational approach in Soviet historical science ended in the late 1980s. And in 1995 the Russian Academy of Sciences recognized that civilizational theory can serve as one of the conceptual principles for analyzing and describing the historical process in textbooks for schools and universities. The object of our article is the essence of the civilizational philosophical and historical concept. The subject is the discourse, in the space of which there is developed a methodology, and are analyzed the categories of the civilizational approach to history. We apply general theoretical research methods: analysis, synthesis, comparison, interpretation. It is shown that within the framework of the theory under consideration methodological differences are significant, so several theoretical varieties are identified and the key categories of the civilizational concept in them are interpreted differently

Features of modern electronic trading in international financial markets

The subject of research is the Internet trading in the American and European financial markets for individuals from the Russian Federation. The relevance of the topic is due to the huge influx of Russian private investors into the global financial market over the past few years, caused by the simplification of the process of opening brokerage accounts, automation of taxation, the possibility of trading via web terminals, as well as significantly changed conditions of online trading in 2022. The whole work is the development of a report on investing in the financial markets of the United States of America and the European Union for citizens of the Russian Federation. The study was conducted using the methods of systematization, grouping and comparison, with their help, analysis and generalization of the results obtained were carried out, conclusions were drawn. It has been established that in the current geopolitical situation and the restrictive measures taken by many multinational banks and companies, private investors of Russian origin have risks of freezing their own assets on brokerage accounts, which can be reduced by opening a brokerage account in companies registered in the territory of countries friendly to the Russian Federation. The article suggests two least risky options for investing in securities of issuers from Europe and USA

Experimental and Theoretical Design Methodology of Hemispherical Shells under Extreme Static Loading

We present mathematical dependences describing the research results for metal half-sperical shells subjected to static loading by external pressure. We studied the behavior and conditions of static buckling of empty, styrofoam- filled and geometrically imperfect shells. Regression equations in the form of incomplete cubic polinomials are derived. In planes of governing parameters we plot isolines, analysis of which makes it possible to draw qualitative and quantitative conclusions on the externally pressurized shell behavior.Представлены математические зависимости, описывающие результаты исследований металлических полусферических оболочек при статическом нагружении внешним давлением. При этом исследовались поведение и условия потери устойчивости как пустотелых, так и заполненных пенопластом оболочек с геометрическими несовершенствами. Получены уравнения регрессии в виде неполных кубических полиномов. В плоскостях определяющих параметров построены изолинии, анализ которых позволяет сделать качественные и количественные выводы о поведении оболочек в условиях нагружения внешним давлением.Представлено математичні залежності, що описують результати досліджень металевих напівсферичних оболонок при статичному навантаженні зовнішнім тиском. При цьому досліджувалися поведінка й умови втрати стійкості як пустотілих, так і заповнених пенопластом оболонок із геометричною недосконалістю. Отримано рівняння регресії у вигляді неповних кубічних поліномів. У плоскостях визначальних параметрів побудовано ізолінії, аналіз яких дозволяє зробити якісні і кількісні висновки щодо поведінки оболонок в умовах навантаження зовнішнім тиском

Electronic Structure of a Hydrogenic Acceptor Impurity in Semiconductor Nano-structures

The electronic structure and binding energy of a hydrogenic acceptor impurity in 2, 1, and 0-dimensional semiconductor nano-structures (i.e. quantum well (QW), quantum well wire (QWW), and quantum dot (QD)) are studied in the framework of effective-mass envelope-function theory. The results show that (1) the energy levels monotonically decrease as the quantum confinement sizes increase; (2) the impurity energy levels decrease more slowly for QWWs and QDs as their sizes increase than for QWs; (3) the changes of the acceptor binding energies are very complex as the quantum confinement size increases; (4) the binding energies monotonically decrease as the acceptor moves away from the nano-structures’ center; (5) as the symmetry decreases, the degeneracy is lifted, and the first binding energy level in the QD splits into two branches. Our calculated results are useful for the application of semiconductor nano-structures in electronic and photoelectric devices

ELECTRICAL CONDUCTIVITY OF TUNGSTEN PHOSPHATE GLASSES

Glasses of different compositions xWO3–(100-x)P2O5 (х = 70, 75, 80, 82 mol. %) have been obtained and investigated. Measurements have been made on electrical conductivity by various electrochemical methods. The maximum value of conductivity in this system at room temperature is 6,7·10-7 S/cm for the composition 82WO3–18P2O5.В данной работе получены и исследованы стёкла системы xWO3–(100-x)P2O5 (при х = 70, 75, 80, 82 мол. %). Изучены их проводящие свойства разными электрохимическими методами. Показано, что состав 82WO3–18P2O5 имеет наибольшую электропроводность при комнатной температуре, которая составляет 6,7·10-7 См/см

INFLUENCE OF SiO2 ON THERMAL PROPERTIES OF TUNGSTEN-PHOSPHATE GLASSES

In this work, the thermal properties of 70WO3–хSiO2–(100 – x)P2O5 glasses at х = 0, 10, 15 mol. % were studied by the DSC. The amorphous state of the obtained samples was monitored using XRD. It was found that the SiO2 addition increases the tendency of tungsten-phosphate glasses to crystallize.В работе исследованы термические свойства стекол 70WO3– хSiO2–(100 – x)P2O5 при х = 0, 10, 15 мол. % методом дифференциальной сканирующей калориметрии (ДСК). Аморфное состояние полученных образцов контролировали с помощью рентгенофлуоресцентного анализа (РФА). Установлено, что введение оксида кремния увеличивает склонность вольфрамофосфатных стекол к кристаллизации

Morphological changes of the gastric mucosa in patients with duodenogasric reflux: relationship with acidity and helicobacter pylori

Purpose: to reveal the peculiarities of the duodenogastric reflux (DGR) impact on acidity and morphological features of the gastric mucosa in patients with "primary" reflux gastritis, as well as in cases of reflux gastritis in combination with H. pylori. Methods: 66 patients with chronic reflux gastritis were examined, 15 people formed a control group. All patients had gastric endoscopy with determination of the gastric acidity and concentration of bile acids. Biopsy material for histological examination was obtained from 55 patients, in 12 cases of suspected intestinal metaplasia additional histochemical (PAS and alcian blue) and immunohistochemical (cytokeratin 20, Villin, carcinoembriogenic antigen, MUC2, CD45) assays were performed. Results: the level of acidity in patients with DGR was higher (pH = 3.55 ± 2.3) compared to the control group (pH = 6.85 ± 1.34). Cases of DGR differed from the control group regarding the mononuclear infiltration (p=0,001), foveolar hyperplasia (p=0,001) in both antral and fundic parts of the stomach, mucosal edema (p=0,022) and atrophy (p=0,02) at the level of the antrum, and intestinal metaplasia (p=0,022) at the level of the body. In the presence of H. pylori infection, in addition to the abovementioned signs, infiltration by cells of acute inflammation (p = 0.005) was detected, which indicates an increase in the damaging effect of H. pylori infection in DGR. Conclusion: DGR may lead to "oxidation" of gastric contents. The effect of DGR leads to intestinal metaplasia of the body and atrophy of the antral part of stomach, chronic inflammation and foveolar hyperplasia. The presence of H. pylori boosts the morphological changes in the gastric mucosa caused by DGR.Цель: выявить характер воздействия дуоденогастрального рефлюкса (ДГР) на морфологические показатели слизистой оболочки желудка при «первичном» рефлюкс-гастрите, в том числе, в сочетании с H.pylori, исследовать связь ДГР с уровнем кислотности. Материалы и методы: обследовано 66 пациентов с рефлюкс-гастритом, 15 человек составили группу контроля. Всем пациентам проведена эзофагогастродуоденоскопия с определением кислотности и концентрации желчных кислот в желудочном содержимом. 55 пациентам проведено гистологическое обследование биопсийного материала слизистой оболочки желудка, при наличии признаков кишечной метаплазии 12 пациентам проведено дополнительное гистохимическое (окраска Шифф-йодной кислотой и альциановым синим) и иммуногистохимическое (определение экспрессии цитокератина 20, виллина, MUC2, ракового эмбрионального антигена, CD45) исследование. результаты: Уровень кислотности у пациентов с ДГР был выше (рН=3,55±2,3) по сравнению с группой контроля (рН=6,85±1,34). Из морфологических признаков при дГр значимо отличались от группы контроля мононуклеарная инфильтрация (р=0,001), фовеолярная гиперплазия (р=0,001) в обоих отделах желудка, отек (р=0,022) и атрофия (р=0,02) антрального отдела, кишечная метаплазия (р=0,022) на уровне тела желудка. При наличии инфекции H. pylori, помимо уже выявленных признаков, выявляется инфильтрация клетками острого воспаления (р=0,005), что свидетельствует об усилении повреждающего действия инфекции H. pylori при ДГР. Выводы: Воздействие ДГР приводит к «окислению» желудочного содержимого. Воздействие ДГР приводит к кишечной метаплазии тела и атрофии антрального отдела желудка на фоне хронического воспаления и фовеолярной гиперплазии. Присутствие H. pylori усиливает вызванные ДГР морфологические изменения слизистой оболочки желудка