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1.
L. P. Podenok L. I. Sharakhovskii V. D. Shimanovich O. I. Yas’ko 《Journal of Engineering Physics and Thermophysics》1997,70(1):95-99
The influence of heat transfer processes in arc discharges on the development of thermal instability is considered. A substantial
dependence of the process of destabilization on the plasma properties is shown by the example of argon and helium arcs.
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 1, pp. 93–98, January–February, 1997. 相似文献
2.
In this paper, the imbricated cells multilevel converters are studied and modeled from a control viewpoint. These converters make use of several switches connected in a series, which allows using switches with reduced voltage ratings; these low voltage switches have lower conduction losses and can switch at higher frequency. In addition to this feature common to all converters using series connected switches, the control signals of multilevel converters can be phase shifted to increase the apparent switching frequency and improve the dynamic performances of the whole converter. It is shown that a multilevel inverter leg, composed of p pairs of switches and p-1 capacitors, forms a multivariable nonlinear system that cannot be properly modeled by standard methods such as state-space averaging. The transient behavior of this system depends on the current harmonics and their phase shift with the different control signals. A specific model is detailed, studied, and used to illustrate the properties of these converters. In particular, the natural balancing of the voltage across the switches is demonstrated and the time constants involved in this process are determined 相似文献
3.
We study some specific features of phase formation and gas saturation in the course of chemical and thermal treatment of VT1-0, OT4, and VT14 titanium alloys in carbon-nitrogen-containing (graphite and nitrogen under atmospheric pressure) and nitrogen-containing (molecular nitrogen under atmospheric pressure) media. Saturation was carried out at 750–1100°C, and the time of isothermal holding was 5 or 20 h. We have shown that, irrespective of the composition of the saturating medium, within the range 750–1000°C, the phase composition of coatings is identical and consists of TiN and Ti2N nitrides. The quantitative proportions between them depend on the temperature and time of treatment. Owing to the specific features of the composition of a carbon-nitrogen-containing medium, the depth of the diffusion sublayer increases, and the stoichiometry of cubic nitride decreases, which leads to an increase in the surface microhardness of nitride coatings. Carbonitride coatings are formed only at high saturation temperature (1100°C). Their maximum hardness is 2.5 GPa higher than that of nitrides formed under similar conditions.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 3, pp. 81–87, May–June, 2004. 相似文献
4.
Daniel Caurant Odile Majérus Edward Fadel Marion Lenoir Christel Gervais Olivier Pinet 《Journal of the American Ceramic Society》2007,90(3):774-783
Crystallization of the poorly durable Na2 MoO4 phase able to incorporate radioactive cesium must be avoided in SiO2 –Al2 O3 –B2 O3 –Na2 O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B2 O3 and MoO3 were added to a SiO2 –Na2 O–CaO glass, and crystallization tendency was studied. Na2 MoO4 crystallization tendency decreased with the increase of B2 O3 concentration whereas the tendency of CaMoO4 to crystallize increased due to preferential charge compensation of BO4 − entities by Na+ ions. 29 Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd3+ ) were shown to enter into CaMoO4 crystals formed in glasses. 相似文献
5.
A study of the synthesized Ge22.5Bi7S70.5 glassy system has been carried out. Differential thermal analysis data indicate the retention in the as-quenched sample of two amorphous phases. Thermal conductivity, , measurements on bulk sample reveal that the main contribution to is due to phonon thermal conductivity. Thermal evaporation of the synthesized ingot gives films with Ge20.7Bi6.8S72.5 as composition. The values of the activation energy and the pre-exponential factor calculated from the direct current electrical conductivity above 53 °C suggest that carrier conduction occurred between extended states in these films. The I–V characteristics in the off-state and the switching phenomenon are investigated. A memory switch with a threshold voltage decreasing with temperature is detected for the studied films. Optical parameters such as absorption coefficient, optical gap and refractive index are also determined. Comparison with binary Ge–S glass reveals that the addition of Bi introduces additional absorbing states at band edges. © 1998 Kluwer Academic Publishers 相似文献
6.
7.
AbstractComposite plates play a very important role in engineering applications, especially in aerospace industry. Thermal buckling of such components is of great importance and must be known to achieve an appropriate design. This paper deals with stacking sequence optimisation of laminated composite plates for maximising the critical buckling temperature using a powerful meta-heuristic algorithm called firefly algorithm (FA) which is based on the flashing behaviour of fireflies. The main objective of present work was to show the ability of FA in optimisation of composite structures. The performance of FA is compared with the results reported in the previous published works using other algorithms which shows the efficiency of FA in stacking sequence optimisation of laminated composite structures. 相似文献
8.
9.
M. Grujicic G. Arakere W. C. Bell H. Marvi H. V. Yalavarthy B. Pandurangan I. Haque G. M. Fadel 《Journal of Materials Engineering and Performance》2010,19(3):301-313
The effect of materials processing- and component manufacturing-induced uncertainties in material properties and component
shape and size on the reliability of component performance is investigated. Specifically, reliability of a suspension system
component from a high-mobility multipurpose wheeled vehicle which typically can fail under low-cycle strain-based fatigue
conditions is analyzed. Toward that end, the most advanced reliability-based design optimization methods available in the
literature were combined with the present understanding of low-cycle fatigue durability and applied to the component in question.
This entailed intricate integration of several computational tools such as multibody vehicle dynamics, finite-element simulations,
and fatigue strain-life assessment/prediction techniques. The results obtained clearly revealed the importance of consideration
of material property uncertainties in attaining vehicle performance of critical structural components in complex systems (e.g.,
a vehicle). 相似文献
10.
Michel W. Barsoum Alexander Elkind Fadel A. Selim 《Journal of the American Ceramic Society》1996,79(4):962-966
Diffusion of molten Bi2 O3 into the grain boundaries of sintered, alumina-doped (0.23 and 0.7 mol%) ZnO pellets resulted in varistors with breakdown voltages in the 3–5 V range and nonlinearity coefficients of 10–24. The varistors were fabricated by spreading a thin layer of Bi2 O3 powder on the surface of ZnO pellets and heating the combination to various temperatures (860–1155°C) and different times. The highest nonlinearity coefficients (20–24) and lowest breakdown voltages (3–5 V) were recorded in samples annealed at 860°C for 35 min. Longer annealing times and/or higher temperatures resulted in progressively higher breakdown voltages. Eventually the devices became insulating, which was attributed to the formation of an insulating Bi2 O3 layer between the grains. Separate wetting experiments have shown that the penetration of Bi2 O3 into ZnO grain boundaries was a strong function of alumina doping —the penetration rate was decreased by a factor of 5–7 as the ZnO was doped with as little as 0.2 mol% alumina. It is this slowing down of the penetration of the ZnO grain boundaries that is believed to be critical in the development of the low breakdown voltages observed. 相似文献