3,585 research outputs found
Microstructure-induced giant elastic nonlinearity of threshold origin: Mechanism and experimental demonstration
No full textMicrostructure-induced giant elastic nonlinearity of threshold origin: Mechanism and experimental demonstration V. Yu. Zaitsev, A. Dyskin, E. Pasternak and L. Matveev EPL, 86 (2009) 44005 Please visit the new website www.epljournal.org Europhysics Letters (EPL) has a new online home at www.epljournal.org Take a look for the latest journal news and information on: • reading the latest articles, free! • receiving free e-mail alerts • submitting your work to EP
Thermoacoustic Instabilities in the Rijke Tube: Experiments and Modeling
Get PDFThermoacoustic instability can appear in thermal devices when unsteady heat release is coupled with pressure perturbations. This effect results in excitation of eigen acoustic modes of the system. These instabilities are important in various technical applications, for instance, in rocket motors and thermoacoustic engines.
A Rijke tube, representing a resonator with a mean flow and a concentrated heat source, is a convenient system for studying the fundamental physics of thermoacoustic instabilities. At certain values of the main system parameters, a loud sound is generated through a process similar to that in real-world devices prone to thermoacoustic instability. Rijke devices have been extensively employed for research purposes. The current work is intended to overcome the serious deficiencies of previous investigations with regard to estimating experimental errors and the influence of parameter variation on the results. Also, part of the objective here is to account for temperature field non-uniformity and to interpret nonlinear phenomena. The major goals of this study are to deliver accurate experimental results for the transition to instability and the scope and nature of the excited regimes, and to develop a theory that explains and predicts the effects observed.
An electrically heated, horizontally oriented, Rijke tube is used for the experimental study of transition to instability. The stability boundary is quantified as a function of major system parameters with measured uncertainties for the data collected. Hysteresis in the stability boundary is observed for certain operating regimes of the Rijke tube.
An innovative theory is developed for modeling the Rijke oscillations. First, linear theory, incorporating thermal analysis that accurately determines the properties of the modes responsible for the transition to instability, is used to predict the stability boundary. Then, a nonlinear extension of the theory is derived by introducing a hypothesis for a special form of the nonlinear heat transfer function. This nonlinear modeling is shown to predict the hysteresis phenomenon and the limit cycles observed during the tests.
A new, reduced-order modeling approach for combustion instabilities in systems with vortex shedding is derived using the developed analytical framework. A hypothesis for the vortex detachment criterion is introduced, and a kicked oscillator model is applied to produce nonlinear results characteristic for unstable combustion systems.
The experimental system and the mathematical model, developed in this work for the Rijke tube, are recommended for preliminary design and analysis of real-world thermal devices, where thermoacoustic instability is a concern.</p
The use of plastic waste as carbon raw materials to obtain TiC-based powders
No full textPlastic pollution is one of the most pressing environmental problems, and a huge amount of effort and money is directed towards solving it. The existing processing methods are ineffective. The main component of all plastic materials (C H ) is carbon. High-purity fine titanium carbide was obtained using plastic waste (polyethylene terephthalate – C H O ) as a carbon raw material. Combustion processes, phase composition and structure of the obtained materials were studied. A probable mechanism for the formation of titanium carbide during the combustion of the (Ti + C H O ) mixture was proposed. During the synthesis, polyethylene terephthalate decomposes into carbon, hydrogen and oxygen. Carbon and oxygen react with titanium and form titanium oxycarbide. Titanium oxycarbide is saturated with carbon to form titanium carbide and carbon dioxide. The remaining hydrogen and carbon dioxide are released from the synthesis products, which leads to self-purification of the synthesis products. The obtained results will create the basis for the development of a fundamentally new, cost-effective technology for recycling plastic waste into carbides and carbide-containing materials. x y 10 8 4 10 8
Medical informatics in occupational and environmental health of Russia: needs of reforms
No full textТрадиция классики в скульптуре Ленинграда-Петербурга. Коллекция скульптуры Русского музея
Get PDFThe author traces the development of classical principles in Russian sculpture from the period of A. T. Matveev to his disciples who finished their creative activity in the 1990s. Matveev school of sculpture was based on the traditions of classicism and became a unique artistic phenomenon in the history of Soviet sculpture. It was a result of pedagogical activities of the outstanding Russian sculptor Alexander Matveev, whose oeuvre is inseparably linked to the principles of classical sculpture. Classicality as a stylistic category of Matveev’s work was noted by his contemporaries. One of the critics defined the peculiarity of the first graduates of Matveev’s school in the 1920s and 1930s as a “classicizing sculptural style” in Soviet sculpture. The images of young characters of the new Soviet epoch dressed in modern clothes invariably revealed classical ideals still retaining high artistic level. However, the politics of ideological pressure and “class approach” even in the sphere of studying and preserving sculptural traditions controlled and held the natural creative process back. Later on, until the 1960s, Matveev’s creative system was forced to oppose official culture:it was a subject to groundless criticism. The works were accused of “formalism” and non-compliance with “standards” of Soviet sculpture. The 1960s–1990s were the heyday of Matveev school. The whole galaxy of sculptors had emerged. They enjoyed their individual peculiarities, though retained Matveev’s typical way of sculptural vision and creative rethinking of classical heritage. It encouraged the artists of the Matveev circle in their quests for modern sculptural forms. The Russian Museum owns a collection of sculptural works made by several generations of artists — Alexander Matveev’s followers — shown at the Alexander Matveev and His School exhibition in 2005.В статье впервые прослеживается развитие классических принципов в русской скульптуре от А. Т. Матвеева к его ученикам, заканчивавшим свою творческую активность в 1990-е гг. Уникальное художественное явление в истории скульптуры советского периода — «матвеевская школа пластики», ставшая хранителем классических традиций, — явилось результатом педагогической деятельности русского скульптора А. Т. Матвеева, творчество которого наиболее органично связано с принципами классического ваяния. Классичность как стилистическая категория скульптуры Матвеева отмечалась его современниками. Особенность художников первых выпусков мастерской Матвеева 1920–1930-х гг. была определена одним из критиков как «классицизирующий стиль ваяния» в советской скульптуре. В изображениях молодых героев советской действительности, одетых в современную одежду, неизменно «просвечивал» идеал классики, сохранялась высокая планка искусства. Однако политика идеологического давления, «классового подхода» даже в области изучения и наследования пластических традиций ограничивала и останавливала естественный творческий процесс. В дальнейшем, вплоть до 1960-х гг. матвеевская творческая система находилась в вынужденном противостоянии официальной культуре, подвергалась необоснованной критике. Произведения обвинялись в «формализме», несоответствии «нормативам» советской скульптуры. В 1960–1990-е гг. «матвеевская школа» переживала настоящий расцвет. Появилась целая плеяда скульпторов, каждый из которых отличался своеобразием, но при этом все сохраняли унаследованный от Матвеева способ пластического видения и творческого переосмысления классического наследия. Именно это позволило художникам круга Матвеева быть новаторами в поисках современной скульптурной формы. В Русском музее сосредоточена коллекция станковой скульптуры нескольких поколений художников-«матвеевцев», экспонировавшаяся на выставке «Александр Матвеев и его школа» в 2005 г
Mid-infrared LEDs versus thermal emitters in IR dynamic scene simulation devices
No full textIn a radical departure from conventional thermal emitter-based dynamic IR scene simulation devices, we have tested
InAsSbP/InAs LEDs grown by liquid phase epitaxy and tuned at several peak-emitting wavelengths inside the mid-IR
band. Light uniformity, radiation apparent temperature (Ta), thermal resistance, and self heating details were
characterized at T=300 K in the microscale by calibrated infrared cameras in the 3-5 mm (light pattern) and 8-12 μm
(heat pattern) bands. We show that LEDs are capable of simulating very hot (Ta ³740 K) targets as well as cold objects
and low observable with respect to a particular background. We resume that cost effective LEDs enable a platform for
photonic scene projection devices able to compete with thermal microemitter MEMS technology in testing and
stimulating very high-speed infrared sensors used for military and commercial applications. Proposals on how to further
increase LEDs performance are given
Features of International and Regional Pharmacovigilance Systems
No full textIntroduction. Ensuring the safety of medicines is the basis for the existence and functioning of any pharmacovigilance system as a type of activity aimed at obtaining and processing information about the undesirable consequences of the use of medicines. The objective of the paper is to identify the features of functioning of international and regional pharmacovigilance systems on the basis of the study conducted. Materials and Methods. To achieve the objective set, the authors have conducted a literature search and performed systemic analysis of the available publications and information presented on the websites of regulatory authorities in different countries. Comparative methods of analysis of the existing pharmacovigilance systems by the types of their organization and functioning in individual countries have been used with further analysis of the indicators of adverse drug reactions reporting. Results. The performed analysis of the peculiarities of functioning of pharmacovigilance systems has made it possible to identify several types of collecting information on adverse drug reactions (the centralized, decentralized, and mixed types), as well as to determine their strengths and weaknesses. It has been revealed that the maximum indicator of the average number of received spontaneous reports of adverse drug reactions per 1 million people a year was registered in countries practicing the centralized type of pharmacovigilance organization. Lower rates have been observed in countries using the decentralized or mixed pharmacovigilance systems. Discussion and Conclusion. The revealed features of the described approaches seem to be important for further improvement of the organization of work of the state system for monitoring the safety of medicines in the Russian Federation and the CIS countries. The use of the centralized type of organization of the pharmacovigilance system promotes active involvement of all actors involved in circulation of medicines, as well as helps to achieve a higher level of expert skills in assessing adverse drug reactions reporting, which contributes to the qualitative analysis of the information received and the timely adoption of regulatory decisions in order to improve safety of patients
КООРДИНАТНЫЕ МОДЕЛИ ТРАЕКТОРИЙ ПУТИ
Get PDFThe author describes theoretical fundamentals, used to proceed with mathematical treatment of the results of measurements of parameters of technical conditions of the rail track. The calculations use different variants of assessment. The first one considers comparable data of two cycles of control. The second one proceeds with superposed, monitoring-based analysis of the indices received out of several measuring cycles with predetermined time intervals and dynamics (mobility) of the points of geodesic network.Особенности теоретических оснований при решении задачи математической обработки результатов измерений параметров технического состояния железнодорожного пути. В расчет берутся отличные друг от друга варианты оценивания: в одном случае с учетом сопоставимых данных двух контрольных циклов, во втором – при совмещении в анализе с помощью мониторинговых средств показателей нескольких циклов измерений, имеющих определенные временные интервалы и свою динамику (подвижность) пунктов геодезической сети.
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