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Search Results: 1 - 10 of 474 matches for " Valeri Vlassov "
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Evaluation of Inherent Uncertainties of the Homogeneous Effective Thermal Conductivity Approach in Modeling of Printed Circuit Boards for Space Applications  [PDF]
Rafael Lopes Costa, Valeri Vlassov
Journal of Electronics Cooling and Thermal Control (JECTC) , 2013, DOI: 10.4236/jectc.2013.31005

Electronic components are normally assembled to printed circuit boards (PCBs). Such components generate heat in operation which must be conducted away efficiently from the small mounting areas to frames where the PCB is fixed. The temperature of the component depends on heat dissipation rate, technology and parameters of mounting, component placement and finally effective thermal conductivity (keff) of the board. The temperature of some components may reach significant magnitudes over 100°C while the PCB frame is kept at near-ambient temperature. The reliability of electronic components is directly related to operating temperature; so the thermal project should be able to provide a correct temperature prediction of all PCB components under the hottest operational condition. In space applications, the main way to spread and reject heat of electronic equipment is by thermal conduction once there is no air available to apply convection-based cooling techniques. The PCB keff is an important parameter for the electronics thermal analysis when the PCB is modeled as a simplified homogeneous board with a unique thermal conductivity. In this paper, an intrinsic uncertainty of such approach is firstly reveled and its magnitude is evaluated for a real space use PCB. The simulation uses SINDA/FLUINT Thermal Desktop and aims to determine the keff of the PCB by comparison between a detailed multi-layered anisotropic model and an

New concept of space radiator with variable emittance
Vlassov, Valeri V;Sousa, Fabiano Luis de;Cuco, Ana Paula C;Silva Neto, Ant?nio J;
Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2010, DOI: 10.1590/S1678-58782010000400001
Abstract: a new concept of space radiator of variable emittance for satellite thermal control is presented. the radiator is composed of two stages which exchange heat through radiation between finned surfaces covered with variable emittance coatings, whose emissivity is increased with temperature. under cold conditions the radiative heat coupling between the stages is minimal, preventing the equipment subcooling, while in hot conditions the heat exchange is increased. a steady-state mathematical model was developed and numerically coupled to an optimization algorithm, and a design optimization procedure was performed. two optimization criteria were employed: minimization of the radiator mass and the power consumption of heater under cold conditions. the generalized extremal optimization algorithm was used as the optimization tool. the design was then modeled in detail using the sinda/fluint package considering orbital conditions of the equars satellite. the performance of the radiator concept proposed here was also compared to a conventional design, for the same operational conditions. it is envisioned that the utilization of such radiators in micro-satellites will lead to considerable electric power savings for safe heaters and may contribute to a longer satellite life. in the design trade-off, the cost for this saving is additional radiator mass and volume.
含能材料 , 1993,
Mini-ribozymes and freezing environment: a new scenario for the early RNA world
A. V. Vlassov
Biogeosciences Discussions , 2005,
Abstract: The RNA World hypothesis states that the present-day life, which is based on DNA genomes and protein enzymes, was preceded by a simpler life form based primarily on RNA. During this era, the genetic information resided in the sequence of RNA molecules and the phenotype derived from the catalytic properties of RNA. Though it is a widely accepted scenario, a number of problems remain unsolved. One of the biggest questions is how complex RNAs could evolve, survive and replicate under typically assumed ''warm and wet'' conditions, taking into account that the RNA phosphodiester backbone is chemically unstable under these conditions. We suggest that prebiotic conditions associated with freezing could have been of key importance in the early RNA World, and discuss the role of primitive catalytic RNA in the evolution of RNA size and complexity.
Biomedical journals and databases in Russia and Russian language in the former Soviet Union and beyond
Vasiliy V Vlassov, Kirill D Danishevskiy
Emerging Themes in Epidemiology , 2008, DOI: 10.1186/1742-7622-5-15
Abstract: The current state of biomedical journals and databases in Russian language is rooted in the history of the USSR and Russia in 20th century. As with many other aspects of life in the Soviet Union, professional and research training was severely hampered during nearly 70 years of communist rule[1,2]. Some of the major issues impeding biomedical science were the change in style of professional training and the isolation of research groups from the rest of the world.In earlier Russian history – the 17th century – the educational system was biased towards specialized professional training in applied fields [3]. European style universities in what is now the former Soviet Union came into being in the 19th century [4]. This was followed by a system of educational reforms implemented by the Soviet government in 1930s which increased the number of technical and medical schools, or "institutes," and separated them from the universities [5]. New institutes discontinued teaching research methods and usually did not carry out any research themselves [3]. All research funding was channeled into a separate branch of "research institutes," thus further isolating centers of higher education from research [6].In the most glorious days of Russian science, the late 19th – early 20th century, the Russian university educational system was tightly interconnected with that of its European counterparts. It was common for graduates of Russian universities to undertake visiting fellowships and nearly all famous Russian scientists had international experience.In the1920s, the door was closed from the Soviet side, nearly 30 years before the "official" drop of the "Iron Curtain" [5]. A rigid hierarchy controlling the thoughts and impeding exchange with "ideological opponents" was introduced in both higher education and research, with only a few exceptions. One of exceptions – the Moscow State University, was created under a special category in the USSR national budget, consuming almost 50% of al
Double Categories in Mathematical Physics
S. S. Moskaliuk,A. T. Vlassov
Mathematics , 2008,
Abstract: Expansion of the categorical point of view on many areas of the mathematics and mathematical physics will cause to deeper understanding of genuine features of these problems. New applications of categorical methods are connected with new additional structures on categories. One of such structures, the double category, is considered in this article. The double category structure is defined as generalization of the bicategory structure. It is shown that double categories exist in the topological and ordinary quantum field theories, and for dynamical systems with inputs and outputs. Morphisms of all these double categories are not maps of sets.
Autonomy and heteronomy in the Kahua ritual; A short meditation on Huaulu society
V. Valeri
Bijdragen tot de Taal-, Land- en Volkenkunde , 1990,
Study of the Four-Rod RFQ Using the Normal Mode Theory of Transmission Lines
Valeri Kapin
Physics , 1999,
Abstract: The normal mode theory of the transmission lines is applied to the studies of the Four-Rod RFQ. This resonator consists of four quadrupole electrodes and stems. It can be simulated by the four-conductor shielded transmission line, which is loaded by sets of coaxial transmission lines corresponding to the support stems. The ideal case of the indefinite periodic Four-Rod RFQ is considered. Formulas for resonance frequency, the voltage distribution along the electrodes and the shunt impedance are obtained.
Black Hole Entropy
Valeri Frolov
Physics , 1994,
Abstract: In the talk different definitions of the black hole entropy are discussed and compared. It is shown that the Bekenstein-Hawking entropy $S^{BH}$ (defined by the response of the free energy of a system containing a black hole on the change of the temperature) differs from the statistical- mechanical entropy $S^{SM}=-\mbox{Tr}(\hat{\rho}\ln \hat{\rho})$ (defined by counting internal degrees of freedom of a black hole). A simple explanation of the universality of the Bekenstein-Hawking entropy (i.e. its independence of the number and properties of the fields which might contribute to $S^{SM}$) is given.
The Weinberg Propagators
Valeri Dvoeglazov
Physics , 1994,
Abstract: An analog of the $j=1/2$ Feynman-Dyson propagator is presented in the framework of the $j=1$ Weinberg's theory. The basis for this construction is the concept of the Weinberg field as a system of four field functions differing by parity and by dual transformations.
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