Short-term dynamics of river water turbidity

An overview of the recently collected datasets of highly discrete water turbidity measurements has allowed for the first hydrological and geographical analysis of short-term fluctuations in water turbidity and the composition of suspended sediments. The novel methodology has been developed to estimate a value of TI, which is the ratio of the difference between the maximum and minimum turbidity for a short period of time (ΔTi) (1 hour with the measurement frequency of 20 minutes) and the total turbidity difference for the water regime phase under study (ΔT HE ). Higher TI values correspond to a greater contribution of diurnal (20-minute) turbidity fluctuations to the seasonal variability of sediment yield. Rivers have been grouped according to the value of water turbidity fluctuations within one hour (20-minute): glacier-fed rivers (the Tarfala, the Dzhankuat) (TI amounts to 0.17-0.22); volcanic rivers (0.22–0.25) and lowland rivers (the Selenga, the Western Dvina) (0.09

Elucidating suspended sediment dynamics in a glacierized catchment after an exceptional erosion event: The Djankuat catchment, Caucasus Mountains, Russia

Suspended sediment yields from glacierized catchments are often among the highest in the world, and their sediment dynamics can be highly variable. This study was undertaken in the 9.1 km2 glacierized catchment of the Djankuat River located in the Russian part of the Northern Caucasus. The outlet of the study catchment is a hydrological gauging station located at an altitude of 2635 m a.m.s.l. (‘N43◦12′31.71′′, E42◦44′05.93′′). The catchment includes a temperate valley glacier (area = 2.42 km2) and three smaller hanging glaciers, several moraine deposits, rock walls, and a large and expanding proglacial area. The main goal of our study was to assess the impact of an exceptional erosion event on 1st July 2015 (with an annual exceedance probability of less than 0.1%) on suspended sediment yields and the relative contributions of various sediment sources The work combined direct suspended sediment discharge measurements at the gauging station during five ablation seasons (2015–2019) with geomorphic mapping techniques based on detailed field observations and sediment source fingerprinting. Results show that mean annual suspended sediment yields reached 1118 t km− 2 year− 1 which is one of the highest measured estimates for any of the glacierized mountain rivers globally. About half of the annual suspended sediment flux was exported during a limited number (1–12% of the annual events) of extreme hydrological events. The sediments mobilized by bank and riverbed erosion within the new lower reach of a tributary channel which appeared after the breakthrough of a lateral moraine became the primary sediment source. It contributed over 50% of the suspended sediment on days with extreme rainfall. Contributions to the suspended sediment load from the glacier source were event-dependent and were only dominant (c. 60–70%) in the upper reaches of the proglacial area (first 800 m). The proglacial part of the study catchment with buried ice was the main sediment source (79%) during non-rain days

Ідентифікація теплового процесу в асинхронному двигуні

Scientific novelty: A methodology for determining losses in an asynchronous motor using a synthesized mathematical model is proposed, taking into account the influence of changes in the quality of electricity on the processes of heating and heat exchange in it. Practical significance: The obtained results indicate the adequacy of the proposed thermal model of an asynchronous motor operating in a network with low-quality electricity. Taking into account the fact that for many types of engines in the reference literature, there are no necessary data on the coefficients of heat transfer and heat capacity, and only the thermal time constants for certain types of engines are given, the value of the specified parameters of the model can be obtained on the basis of the methodology presented in the work. A single-mass thermal model can be useful for analyzing the thermal processes occurring in an induction motor and for improving the efficiency of the motor. In particular, it can help determine the optimal operating temperature of the motor, as well as calculate the necessary cooling system to ensure stable operation of the motor under conditions of variable load and temperature conditions.Наукова новизна: Запропоновано методологію визначення втрат в асинхронному двигуні за допомогою синтезованої математичної моделі з урахуванням впливу зміни якісних показників електроенергії на процеси нагріву та теплообміну в ньому. Практичне значення: Отримані результати свідчать про адекватність запропонованої теплової моделі асинхронного двигуна, що працює в мережі з неякісною електроенергією. Враховуючи те, що для багатьох типів двигунів у довідковій літературі відсутні необхідні дані щодо коефіцієнтів тепловіддачі і теплоємності, а наводяться лише теплові сталі часу для окремих типів двигунів, значення вказаних параметрів моделі може бути отримана на основі методології, представленої в роботі. Одномасова теплова модель може бути корисною для аналізу теплових процесів, що відбуваються в асинхронному двигуні, та для покращення ефективності роботи двигуна. Зокрема, вона може допомогти визначити оптимальну температуру роботи двигуна, а також розрахувати необхідну систему охолодження для забезпечення стабільної роботи двигуна в умовах змінної навантаженості та температурного режиму

A TOOLBOX FOR SEDIMENT BUDGET RESEARCH IN SMALL CATCHMENTS

© 2017, Lomonosov Moscow State University. All rights reserved. Sediment monitoring and assessment remain one of the most challenging tasks in fluvial geomorphology and water quality studies. As a response to various environmental and human disturbance effects, the main sources and pathways of the sediments transported within catchments, especially most pristine small one, may change. The paper discusses state-of-the-art in the sediment budget research for small catchments. We identified nine independent approaches in the sediment transport assessment and applied them in 11 catchments across Eurasia in the framework of an FP-7 Marie Curie-International Research Staff Exchange Scheme in 2012-2016. These methods were classified as: i) Field-based methods (In-situ monitoring of sediment transport;-Soil morphological methods and dating techniques; Sediment source fingerprinting; Sediment-water discharge relationships), ii) GIS and remote sensing approaches (Riverbed monitoring based on remote sensing/historical maps; parametrization of the channel sediment connectivity; Sediment transport remote sensing modeling), and iii) Numerical approaches (Soil erosion modeling and gully erosion (stochastic and empirical models); channel hydrodynamic modeling). We present the background theory and application examples of all selected methods. Linking fieldbased methods and datasets with numerical approaches, process measurements as well as monitoring can provide enhanced insights into sediment transfer and related water quality impacts. Adopting such integrated and multi-scale approaches in a sediment budget framework might contribute to improved understanding of hydrological and geomorphological responses

A toolbox for sediment budget research in small catchments

© 2017, Lomonosov Moscow State University. All rights reserved. Sediment monitoring and assessment remain one of the most challenging tasks in fluvial geomorphology and water quality studies. As a response to various environmental and human disturbance effects, the main sources and pathways of the sediments transported within catchments, especially most pristine small one, may change. The paper discusses state-of-the-art in the sediment budget research for small catchments. We identified nine independent approaches in the sediment transport assessment and applied them in 11 catchments across Eurasia in the framework of an FP-7 Marie Curie-International Research Staff Exchange Scheme in 2012-2016. These methods were classified as: i) Field-based methods (In-situ monitoring of sediment transport;-Soil morphological methods and dating techniques; Sediment source fingerprinting; Sediment-water discharge relationships), ii) GIS and remote sensing approaches (Riverbed monitoring based on remote sensing/historical maps; parametrization of the channel sediment connectivity; Sediment transport remote sensing modeling), and iii) Numerical approaches (Soil erosion modeling and gully erosion (stochastic and empirical models); channel hydrodynamic modeling). We present the background theory and application examples of all selected methods. Linking fieldbased methods and datasets with numerical approaches, process measurements as well as monitoring can provide enhanced insights into sediment transfer and related water quality impacts. Adopting such integrated and multi-scale approaches in a sediment budget framework might contribute to improved understanding of hydrological and geomorphological responses

МАШИННО-ТРАНСФОРМАТОРНИЙ АГРЕГАТ ДЛЯ ВІТРОЕНЕРГЕТИЧНИХ УСТАНОВОК

Background. Electric generators of wind turbines must meet the following requirements: they must be multi-pole; to have a minimum size and weight; to be non-contact, but controlled; to ensure the maximum possible output voltage when working on the power supply system. Multipole and contactless are relatively simply realized in the synchronous generator with permanent magnet excitation and synchronous inductor generator with electromagnetic excitation; moreover the first one has a disadvantage that there is no possibility to control the output voltage, and the second one has a low magnetic leakage coefficient with the appropriate consequences. Purpose. To compare machine dimensions and weight of the transformer unit with induction generators and is an opportunity to prove their application for systems with low RMS-growth rotation. Methodology. A new design of the electric inductor machine called in technical literature as machine-transformer unit (MTU) is presented. A ratio for estimated capacity determination of such units is obtained. Results. In a specific example it is shown that estimated power of MTU may exceed the same one for traditional synchronous machines at the same dimensions. The MTU design allows placement of stator coil at some distance from the rotating parts of the machine, namely, in a closed container filled with insulating liquid. This will increase capacity by means of more efficient cooling of coil, as well as to increase the output voltage of the MTU as a generator to a level of 35 kV or more. The recommendations on the certain parameters selection of the MTU stator winding are presented. The formulas for copper cost calculating on the MTU field winding and synchronous salient-pole generator are developed. In a specific example it is shown that such costs in synchronous generator exceed 2.5 times the similar ones in the MTU.В работе предложена новая конструкция индукторной электрической машины, которая в технической литературе называется – машинно-трансформаторный агрегат (МТА). Для такого агрегата получено соотношение для определения расчетной мощности. На конкретном примере показано, что при одинаковых габаритах расчетная мощность МТА может превышать таковую для обычных синхронных машин. Конструкция МТА позволяет разместить катушки обмотки статора на некотором расстоянии от подвижных элементов машины, а именно, в закрытой емкости, заполненной электроизоляционной жидкостью. Это позволит увеличить мощность за счет более эффективного охлаждения обмотки, а также повысить выходное напряжение МТА как генератора до уровня 35 кВ и более.В роботі запропонована нова конструкція індукторної електричної машини, яка в технічній літературі називається – машинно-трансформаторним агрегатом (МТА). Для такого агрегату отримано співвідношення для визначення розрахункової потужності. На конкретному прикладі показано, що при однакових габаритах розрахункова потужність МТА може перевищувати таку для звичайних синхронних машин. Конструкція МТА дозволяє розмістити котушки обмотки статора на деякій відстані від рухомих елементів машини, а саме, у закритій ємності, заповненій електроізоляційною рідиною. Це дасть змогу збільшити потужність за рахунок більш ефективного охолодження обмотки, а також підвищити вихідну напругу МТА як генератора до рівня 35 кВ і більше

ТЕНДЕНЦИИ РАЗВИТИЯ ЭПИТАКСИАЛЬНОЙ ТЕХНОЛОГИИ НИТРИДНЫХ СОЕДИНЕНИЙ

The main trends in the development of technology for nitride heterostructures element base of microwave−technology and power electronics, as well as light−emitting diodes have been reviewed. It has been noted that most modern technological focus is the development of nitride heterostructures on silicon substrates. The basic problems of nitride compounds on silicon substrate and the ways of their solution have been discussed. Some results of GaN/Si heterostructures technology development in «Elma−Malachit» JSC have been presented. The AlGaN/GaN/Si heterostructures have been grown by MOCVD. We show that early process stages such as Si−surface treatment and Al pre−deposition are of great importance for the growth of crack−free structures with good structural and surface quality. Meanwhile the surface curvature of the grown structures is influenced mainly by the composition of multilayered transition region between the AlN nucleation layer and the GaN layer. Transistors fabricated on AlGaN/GaN structures grown on Si substrates under optimized conditions demonstrated rather good static characteristics: Id,max = 800 mA/mm, Ubr > 120 V, gm = = 170 mS/mm. For the further technology development experimental and technological work should be arranged in close coordination with analytical prediction and calculation of properties of the grown material with mathematical modeling methods. This approach will help enhance the efficiency of technology development and deepen scientific views on the processes responsible for the formation of properties of heterostructures. Рассмотрены основные тенденции в развитии технологии гетероструктур нитридных соединений для элементной базы СВЧ−техники и силовой электроники, а также светоизлучающих диодов. Отмечено, что важнейшим современным технологическим направлением является разработка гетероструктур нитридных соединений на подложках кремния. Рассмотрены основные проблемы гетероэпитаксии нитридных соединений на подложке кремния и пути их решения. Представлены некоторые результаты разработок технологии гетероструктур нитридных соединений на подложках кремния в ЗАО «Элма−Малахит». Гетерострукуры AlGaN/GaN/Si выращены МОС−гидридным методом. Показано, что предэпитаксиальная обработка подложек кремния и начальная стадия процесса выращивания, включающая предварительное покрытие поверхности Si алюминием при подаче в реактор потока ТМА, играют большую роль в формировании гетероструктур, свободных от трещин и с хорошей морфологией. В то же время установлено, что форма поверхности гетероструктур определяется главным образом композицией переходной области между зародышевым слоем AlN и слоем GaN. Транзисторы, изготовленные на основе выращенных гетероструктур AlGaN/GaN/Si, продемонстрировали приемлемые статические характеристики: максимальная плотность тока составила 800 мА/мм, пробивное напряжение — более 120 В, крутизна — 170 мСм/мм. Показано, что для дальнейшего развития гетероструктур нитридных соединений на подложках кремния экспериментально−технологическую работу необходимо организовать в тесном взаимодействии с аналитическим прогнозированием и расчетами свойств выращиваемого материала методами математического моделирования. Такой подход поможет повысить результативность разработок технологии и углубит научные представления в отношении процессов, ответственных за формирование свойств гетероструктур.

Infrared absorption cross sections, and oscillator strengths of interstitial and substitutional double donors in silicon

Infrared absorption cross sections and corresponding oscillator strengths of several intracenter transitions of double donors in silicon, interstitial magnesium (Mg; group IIA) and substitutional chalcogens (Ch = S; Se; group VI), were determined for impurity densities in the ranges 1 × e14–1.6e15 atoms/cm3 for Mg and 2e13–2e16 atoms/cm3 for chalcogens. The concentrations of electrically active atomic and diatomic donor centers were derived from the Hall effect measurements. The experimental integrated cross sections were obtained from low-temperature impurity absorption spectra. The oscillator strengths of related donor transitions were derived and compared with those for shallow single donors in silicon, both determined experimentally and predicted theoretically. The transitions of oscillator strengths of double donors follow the decreasing trend with decreasing radius of donor ground states and increasing an impurity binding energy