Proceedings of the National Academy of Sciences of Belarus, Physical-Technical Series / Известия Национальной академии наук Беларуси. Серия физико-технических наук
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Структура и оптические свойства покрытий алмазоподобного углерода
Get PDFUsing a hybrid method of cathodic arc (PVD) and chemical (CVD) deposition from the gas phase, a new type of coatings containing high amount of sp3 bonds of carbon, capable of absorbing effectively light has been developed.This thin film material is a promised one for optical devices operating in open space environment as antireflective coating for photoreceiver bodies. The hybrid method permits to obtain effective light absorbing coatings having excellent mechanical and tribological properties and is able to sustain temperature cycling in a range from plus 150 to minus 100 oC. The optical characteristics of DLC coatings were studied depending on the content of sp2bound content. The combined physical and chemical deposition of DLC coatings allows to achieve a sufficiently high light absorption (a~10 5 cm–1) and low reflection with a relatively small coating thickness about 1 mm. It has been established that the antireflective properties of such coatings depend on the conditions for their preparation, first of all on hydrocarbon gas pressure С использованием гибридного метода катоднодугового (PVD) и химического (CVD) осаждения из газовой фазы разработан новый тип покрытий с большим содержанием sp2химически связанных атомов углерода, способных эффективно поглощать видимое оптическое излучение.Аморфный тонкопленочный углеродный материал является перспективным для нанесения поглощающих антибликовых покрытий на корпусные детали фотоприемников оптического излучения, работающих в открытом космосе. Гибридный метод позволяет получать сильнопоглощающие покрытия, обладающие также высокими механическими и трибологическими свойствами и способные выдерживать термоциклирование от + 150 до – 100 °С.Проведено исследование оптических характеристик АПУ покрытий в зависимости от содержания sp2связанных атомов углерода. Полученный комбинированным способом физического и химического осаждения АПУ в виде тонких слоев позволяет достичь достаточно высокого поглощения и низкого отражения при сравнительно малой толщине покрытия (a ~ 105 см–1). Установлено, что антибликовые свойства таких покрытий зависят от условий его получения, и прежде всего – от давления газа углеводородов
ВЛИЯНИЕ ДИНАМИЧЕСКОЙ НАГРУЖЕННОСТИ НА ДОЛГОВЕЧНОСТЬ ЗУБЧАТОЙ ПЕРЕДАЧИ ТРАНСМИССИИ ТЯЖЕЛОНАГРУЖЕННЫХ ПРОХОДЧЕСКИХ МАШИН
Get PDFThe article proposes a new method of calculation of the indicators of the durability of the gear transmission of heavy-loaded roadheading machines, allowing a more accurate assessment of the dynamic loading of the teeth. Within the framework of this technique, the elastic moment amplification factors determined by the amplitude-frequency characteristic of transmission are used instead of the specific circumferential dynamic force in the calculation of the maximum operating voltages. The maximum stresses in the bending of teeth and the probability of failure-free operation of the technical system are determined. A spur transmission used in the drive of the Executive body of roadheader is considered as an example of application of the proposed design technique. The comparison of calculated estimations of gear transmission reliability obtained on the basis of the standard method and using amplitude-frequency characteristics is carried out. In the considered design example durability of transfer for a step cycle of loading is more than 2 times higher in comparison with a continuous cycle of loading. It is shown that using a standard calculated coefficient that takes into account dynamic load, the calculated estimations of the durability of the transmission are significantly overestimated. At the same time, the error of the standard method will depend on the frequency range at which the transmission operates, and this error is most significant when the transmission operates near its own frequencies
Аналитический расчет температуры в процессе сушки тонких капиллярно-пористых плоских материалов
Get PDFIn the paper, the authors analyzed the solution of the differential equation of non-stationary heat conduction for an unbounded plate during the heat exchange of plate surfaces with the surrounding medium according to Newton’s law at a constant temperature of the medium. To use the results of solving the equations in the drying of thin flat materials, the dependence of the heat transfer coefficients on temperature and moisture content was studied. As a result of studying and analyzing a number of literature sources, the regularities of the change in the heat transfer coefficients during drying are established with high reliability. Studies of drying of thin wet plates of white and red clays with known heat transfer coefficients have shown that for small values of the heat transfer criterion of the Bio and small temperature gradients over the section of a thin material, application of the results of solutions of the heat transfer equations gives completely satisfactory agreement between the calculated and experimental values of the temperatures and the duration of drying. It is established that for small Bio numbers, the main factor is the external heat and mass transfer of the surface of the material with the surrounding medium and the rate of drying depends little on internal mass transfer. It is shown that the use of numerical methods for solving differential equations is possible with varying degrees of approximation only for accurate and reliable dependences of heat and mass transfer coefficients on moisture content and temperature. For a number of materials with known heat transfer coefficients, the use of analytical methods in calculations is of considerable interest and brings the theory closer to the practice of drying.Приведен анализ решения дифференциальных уравнений нестационарной теплопроводности для неограниченной пластины при теплообмене ее поверхностей с окружающей средой по закону Ньютона при постоянной температуре среды. Для использования результатов решений уравнений в процессах сушки тонких плоских материалов проведено исследование зависимости коэффициентов переноса от температуры и влагосодержания. В результате изучения и анализа ряда литературных источников с высокой достоверностью установлены закономерности изменения коэффициентов теплопереноса в процессе сушки. Исследования сушки тонких влажных пластин из белых и красных глин с известными коэффициентами переноса показали, что при малых значениях теплообменного критерия Био и малых градиентах температур по сечению тонкого материала использование результатов решений уравнений теплопереноса дает вполне удовлетворительное совпадение расчетных и экспериментальных значений температур и длительности сушки. Установлено, что при малых числах Био главным фактором является внешний тепломассообмен поверхности материала с окружающей средой и скорость сушки слабо зависит от внутреннего массопереноса. Показано, что использование численных методов решения дифференциальных уравнений возможно с разной степенью приближенности только при точных и достоверных зависимостях коэффициентов переноса от влагосодержания и температуры. Для ряда материалов с известными коэффициентами переноса использование в расчетах аналитических методов представляет значительный интерес и сближает теорию с практикой сушки
СОВМЕСТНОЕ ОПИСАНИЕ СИГНАЛОВ, ЛИНЕЙНЫХ ЗВЕНЬЕВ И РЕАКЦИЙ СИСТЕМ ТЕЛЕКОММУНИКАЦИЙ И РАДИОЭЛЕКТРОНИКИ
Get PDFMathematical modeling is a basic tool for design and development of modern telecommunications and radioelectronics systems. It is realized on two fundamentally different levels: schematic circuit and block diagram simulation. At the initial stages of design and development of system (i.e. research scientific work, specification of requirements, initial outlay and technical project) simulation on the block diagram level is applied. Its results define the structure and basic parameters of the quality of created facilities. It has been established, that commonly applied software of block diagram simulation has essential flaws, which are resulted from a scarce mathematical description of signals and links. The research described in the article is aimed at working out the mathematical description of signals, linear links and responses. This description will contribute to creating the enhanced library of mathematical models of signals and linear links, as well as automated procedures of formation, transformation and calculation of time-and-frequency characteristics of signals, links and responses.We suggest a mathematical description of signals, linear links and responses on the basis of specifically shaped operator fractional-rational function. It embodies and epitomizes all types of signals, linear links and responses used in modeling and provides needed transformation and creation of the enhanced library of mathematical models of signals and linear links. Subsequently, it allows creation of mathematical algorithms of normalization, reactance transformation and multiplication of models of minimum-phase and nonminimum-phase linear links, as well as generalized models of signals, linear links and responses in frequency- and time-domains. These generalized models make a basis of single mathematical algorithms and automated procedures of calculation frequency- and time-characteristics of signals, links and responses.
ПРОГНОЗИРОВАНИЕ ОСНОВНЫХ ХАРАКТЕРИСТИК ГРАФИКА ПРОДОЛЖИТЕЛ
Get PDFA methodology of forecasting the main characteristics of load duration curves is described: the coefficient of unevenness, the load factor and the magnitude of power consumption. The characteristics are necessary for predicting of the electrical load duration curves over long time periods. Based on extensive statistical information on the hourly loads of the Belarusian energy system for the period from 1997 to 2014, historical trends of characteristics change were found. Each edge scenario was formed by combining the main characteristics of the load duration curve. Scenario approach and the previously developed method of operative restoration of the curves of the duration of the electrical load on the basis of its main characteristics make it possible to obtain possible boundary forms of these curves for a number of future years. A feature of the approach of the proposed methodology is that such characteristics as the amount of power consumption, as well as the shape of the curves of the duration of electric load are predicted in a certain ranges. The width of the ranges is justified by the analysis of the retrospective information and can be adjusted taking into account the newly received information. The proposed approach can be used in optimization programs of energy system planning. The obtained numerical results can be used to optimize the structure of the Belarusian energy system
ФИЗИКО-ХИМИЧЕСКИЕ СВОЙСТВА УЛЬТРАДИСПЕРСНЫХ ПОРОШКОВ КРЕМНИЯ
Get PDFExperimental investigations of ultradispersed silicon powder produced by mechanical grinding are conducted. The process of scaling powders using mechanochemical grinding was studied. It was found that the dimension of crystallites of the silicon powder determines their physical and chemical properties. Finely divided powders of silicon with a particle size ≤10 nm easily decompose water at room temperature into hydrogen and oxygen, they are easily oxidized by air oxygen and actively interact with hydroxides and acids with the release of significant amount of heat. The rate of saturation of micro- and ultradispersed powders with hydrogen at a constant rate of flow in the flow system depends on the temperature of the hydrogen hydrogenation process. It was found that the hydride formed at a low temperature (≤573 K) is in an equilibrium state when it is being hydrogenated in a flow reactor. The treated powder passes into a metastable state with the termination of the thermal action after hydrogenation. Hydrogen, entering the volume of micro- and ultradispersed silicon powder in the temperature range 373–723 K due to the diffusion process, can react not only with silicon atoms to form hydrides of the SiH2 type, but also with hydrides of less active radicals of the type of Si2H4, Si2H6. The hydrogenation process has two distinct stages. It is shown that the temperature of the transition between the stages is determined by the dispersion of micro- and ultradispersed silicon powders and by the structure of hydrides on the particle surface. As a result, it is established that the optimum temperature of hydrogenation should be taken at a temperature of 623 K, at which the maximum mobility of silicon atoms is reached during the formation of hydride. Sharp decrease in the hydrogen content is observed at a temperature above 723 K for the Si2H4 (SiH2)
ВЛИЯНИЕ ОБЩЕЙ ГАЗОВОЙ КРИОТЕРАПИИ НА ТЕПЛОВОЕ СОСТОЯНИЕ ЧЕЛОВЕКА
Get PDFThe therapeutic effect of the whole body gas cryotherapy (WBGC) procedure is achieved when the average temperature of the human’s (patient’s) skin surface during the procedure is in a certain temperature range, and the rate of reduction of this temperature exceeds a certain threshold value. The paper presents the results of a theoretical analysis of the patient’s thermal state at the stage of the therapeutic effect of WBGC. The analysis was based on the results of the numerical simulation of temperature distribution in different parts of patients (mеn) of different body constitution (height, cm × mass, kg) 160 × 60, 175 × 75, 190 × 90. Particular attention was paid to the relationship between the amount of heat flow removed from the skin surface and the rate of cooling of the skin of a patient. The results of numerical modeling are presented graphically and are summarized as the ratio between the dimensionless average temperature of the skin at the treatment stage of the WBGC procedure and the time of the patient’s stay in the procedural chamber, referred to the time of the beginning of this stage. With regard to WBGC within the temperatures range of –160 to –110 °C the following regularities were found: 1) approximate constancy (descripancy less than 1 %) at the stage of therapeutic modality of the coefficient of heat transfer from the skin surface to the gas medium in the treatment chamber; 2) the exponential dependence of the value of cutaneous blood flow rate (blood perfusion) on the mean temperature of cooled cutaneous coverings; 3) linear dependence of the logarithm of the ratio of the rate of skin temperature reduction to the value of heat flux density removed by convection and radiation on the logarithm time
РАЗРАБОТКА ПРОГНОЗИРУЕМОЙ ТРЕХМЕРНОЙ МОДЕЛИ ЛИЦА ПАЦИЕНТА ПОСЛЕ ЛЕЧЕНИЯ ЗУБОЧЕЛЮСТНЫХ АНОМАЛИЙ
Get PDFThe methods of prediction of location of patient’s soft tissues after the treatment of dentoalveolar anomalies are considered. The base forms of teeth mesh models for modelling patient’s dental systems before and also after the medical treatment and patient’s three-dimensional model from his two photos are used as the input data. The relations are established between the base form of the teeth and three-dimensional model. These relations make it possible to modify the form of teeth with smooth modifications of soft tissues on the patient’s head. The prediction position of soft tissues is based on the position of the skeletal profile. A method for constructing the position of patient’s skeletal profile has been developed. It takes into account individual geometric parameters. The algorithm uses the technique of orthodontists to establish a series of geometric relations between the patient’s teeth. An experimental study was conducted by means of visual and numerical evaluation. The mean square deviation between soft tissues of the patient’s face and the predictable position of soft tissues of the patient’s face hadn’t prevail 10 %.
МЕТОДИКА СТРУКТУРНО-ПАРАМЕТРИЧЕСКОГО СИНТЕЗА КОМБИНИРОВАННОГО ГЕНЕРАТОРА ВОЗВРАТНО-ПОСТУПАТЕЛЬНОГО ТИПА ДЛЯ ЭНЕРГОУСТАНОВОК РОБОТОТЕХНИЧЕСКИХ КОМПЛЕКСОВ НА БАЗЕ СВОБОДНОПОРШНЕВОГО ДВИГАТЕЛЯ
Get PDFСистема энергоснабжения современных робототехнических комплексов требует разработки электромеханических преобразователей энергии с высокими энергетическими и минимальными массогабаритными показателями. В связи с этим в качестве перспективной энергоустановки рассматривается свободнопоршневой двигатель с электрическим генератором.Интерес к исследованию энергоустановок на базе свободнопоршневых двигателей обусловлен рядом преимуществ в сравнении с классическими двигателями внутреннего сгорания с кривошипно-шатунным механизмом: относительной простотой конструкции; на 40 % меньшим количеством элементов, что в 2,5–3 раза увеличивает габаритную мощность, удельную массу и металлоемкость свободнопоршневого двигателя; сниженным на 30 % расходом топлива. Также важное конструктивное преимущество энергоустановок на базе свободнопоршневых двигателей – это сравнительно легкое их модульное исполнение. В разрабатываемых энергоустановках на базе свободнопоршневых двигателей зарубежных стран (США, Россия, Германия, Китай, Великобритания, Япония, Швеция, Израиль и др.) в качестве электрической машины переменного тока чаще всего применяются возвратно-поступательные электрические генераторы с поперечным приращением магнитного потока. Основным недостатком такого типа генераторов являются отсутствие согласования электрической и механической подсистем энергоустановки в крайних точках рабочего цикла, что ограничивает эффективность использования свободнопоршневого двигателя и снижает надежность энергоустановки.Для решения этой проблемы было предложено использовать электромеханический преобразователь энергии с поперечным и продольным приращением магнитного потока (комбинированный генератор). Однако в настоящее время отсутствует научно обоснованная методика синтеза такого типа генератора. С целью решения этой задачи была разработана методика структурно-параметрического синтеза комбинированного генератора возвратно-поступательного типа для энергоустановки на базе свободнопоршневого двигателя, основанная на использовании удельной массы комбинированного генератора в качестве целевой функции, что позволяет синтезировать электрическую машину возвратно-поступательного типа с заданным КПД и минимальной удельной массой
