Spin relaxation of localized electrons in n-type semiconductors

The mechanisms that determine spin relaxation times of localized electrons in impurity bands of n-type semiconductors are considered theoretically and compared with available experimental data. The relaxation time of the non-equilibrium angular momentum is shown to be limited either by hyperfine interaction, or by spin-orbit interaction in course of exchange-induced spin diffusion. The energy relaxation time in the spin system is governed by phonon-assisted hops within pairs of donors with an optimal distance of about 4 Bohr radii. The spin correlation time of the donor-bound electron is determined either by exchange interaction with other localized electrons, or by spin-flip scattering of free conduction-band electrons. A possibility of optical cooling of the spin system of localized electrons is discussed.Comment: Submitted to the special issue "Optical Orientation", Semiconductor Science and Technolog

Spin relaxation in low-dimensional systems

We review some of the newest findings on the spin dynamics of carriers and excitons in GaAs/GaAlAs quantum wells. In intrinsic wells, where the optical properties are dominated by excitonic effects, we show that exciton-exciton interaction produces a breaking of the spin degeneracy in two-dimensional semiconductors. In doped wells, the two spin components of an optically created two-dimensional electron gas are well described by Fermi-Dirac distributions with a common temperature but different chemical potentials. The rate of the spin depolarization of the electron gas is found to be independent of the mean electron kinetic energy but accelerated by thermal spreading of the carriers.Comment: 1 PDF file, 13 eps figures, Proceedings of the 1998 International Workshop on Nanophysics and Electronics (NPE-98)- Lecce (Italy

МОНИТОРИНГ ИЗМЕНЕНИЙ НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ ГЕОСРЕДЫ В РАЙОНЕ ПЕТРОПАВЛОВСКОГО ГЕОДИНАМИЧЕСКОГО ПОЛИГОНА ПО ДАННЫМ КОМПЛЕКСНЫХ СКВАЖИННЫХ И GPS-ИЗМЕРЕНИЙ НА АКТИВНОЙ ФАЗЕ ПОДГОТОВКИ ЖУПАНОВСКОГО ЗЕМЛЕТРЯСЕНИЯ (30.01.2016; Mw=7.2)

The paper presents the results of comparative analysis of the data regarding the multi-instrumental borehole monitoring data of changes in the geoenvironment stress-strain state and GPS data obtained in the time vicinity of the close strong Zhupanovsky earthquake. The purpose this study was to assess the feasibility of using GPS measurements on routine basis for effective monitoring of strong Kamchatka earthquakes in the area of Petropavlovsk-Kamchatsky. The Zhupanovsky earthquake active phase was chosen as a "test" time interval for comparing GPS and borehole monitoring data. This earthquake has been the strongest seismic event since 2000 in terms of the ratio of the earthquake focus length to the hypocentral distance. The time series borehole electromagnetic and geoacoustic data were compared with the dilatation series reflecting the relative changes in the area of a triangle composed of Kamchatka GPS observation network located in the Petropavlovsk geodynamic testing site. The analysis indicates a high degree of consistency in these time series. GPS data obtained during the active phase of the earthquake preparation is agree with the results of mathematical modeling expected values of volumetric strain on the daylight surface on the eve of the earthquake. A joint analysis of borehole and GPS data made it possible to specify the time limits for the stages of change in the stress-strain state of geoenvironment and to resolve ambiguity of interpretation of the electromagnetic and geoacoustic borehole measurement results at the final stage of preparing the Zhupanovsky earthquake.Приводятся результаты сравнительного анализа данных комплексного скважинного мониторинга изменений напряженно-деформированного состояния геосреды и данных GPS-измерений, полученных во временной окрестности сильного близкого Жупановского землетрясения. Целью исследований являлась оценка целесообразности привлечения на постоянной основе данных GPS-измерений для повышения эффективности системы мониторинга процессов подготовки сильных камчатских землетрясений, функционирующей в районе г. Петропавловска-Камчатского. В качестве «тестового» временного интервала для сравнения данных GPS-измерений с результатами комплексного скважинного мониторинга был выбран интервал активной фазы подготовки Жупановского землетрясения – самого сильного с 2000 г. сейсмического события по величине отношения длины очага землетрясения к гипоцентральному расстоянию. В ходе анализа временные ряды данных скважинных электромагнитных и геоакустических измерений в районе Петропавловского геодинамического полигона сравнивались с рядом дилатации, данные которого отражают относительные изменения площади треугольника, составленного из пунктов Камчатской сети GPS-измерений, расположенных в том же районе. Результаты анализа свидетельствуют о высокой степени согласованности указанных временных рядов. Значимость исходных данных GPS-измерений, полученных на интервале активной фазы подготовки землетрясения, подтверждается их совпадением с оценками ожидаемых величин объемных деформаций на дневной поверхности накануне момента землетрясения, полученными по результатам математического моделирования. Совместный анализ данных скважинных и GPS-измерений позволил уточнить временные границы стадий изменений напряженно-деформированного состояния геосреды, а также устранить неоднозначность в интерпретации результатов электромагнитных и геоакустических скважинных измерений на заключительных стадиях подготовки Жупановского землетрясения

SPONTANEOUS DISSECTION OF CORONARY ARTERY AS A CAUSE OF ACUTE MYOCARDIAL INFARCTION

Spontaneous dissection of coronary arteries (SDCA) is a rare cause factor for acute myocardial infarction. The data provided is modern on the prevalence of SDCA, its predisposing factors as the data on diagnostics and treatment of SDCA. The case described of the myocardial infarction due to SDCA in 34-year old male

Clinical effectiveness of bilateral recanalization of chronic coronary artery occlusion

Aim. To assess the short- and long-term angiographic and clinical effectiveness of endovascular bilateral recanalization of chronic coronary artery occlusion (CCAO), compared to conservative therapeutic strategy. Material and methods. The study included 56 patients with coronary heart disease and CCAO. Angina Functional Class (FC) was assessed clinically and in electrocardiography tests. Local and global myocardial contractility was assessed using echocardiography. Group I (n=36) included CCAO patients who underwent an attempt of bilateral percutaneous coronary angioplasty; Group II (n=20) included CCAO patients who were treated conservatively. Clinical effectiveness of the treatment was assessed at 12 months. Results. At baseline, 16 and 20 Group I patients had FC III and II, respectively. Out of 36 attempts of bilateral recanalization, 27 were successful, based on the angiography results. All these 27 cases were also clinically successful in the short term, and 20 in the long term. Global myocardial contractility increased from 54±3% to 56,9±4% (p=0,03). In Group II, 10 and 10 patients had baseline FC III and II, respectively. The long-term stabilisation of clinical status was observed in 15 patients, with the mean levels of left ventricular ejection fraction of 53,9±2,4% (p=0,9). Observed complications of coronary angioplasty did not result in clinically significant ischemic and haemorrhagic events, while the clinical improvement was substantially more pronounced, compared to Group II. Conclusion. Bilateral CCAO recanalization is a technically demanding procedure, requiring an extensive surgical expertise and experience, and linked to a higher risk of complications. However, it could be used when the antegrade access is impossible; the anaesthesiological risk of coronary artery bypass graft surgery is high; and the patient refuses the cardiac surgery intervention