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排序方式: 共有1692条查询结果,搜索用时 31 毫秒
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Pavel Strunz Debashis Mukherji Přemysl Beran Ralph Gilles Lukas Karge Michael Hofmann Markus Hoelzel Joachim Rösler Gergely Farkas 《Metals and Materials International》2018,24(5):934-944
An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect of boron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr2Re3 type) phases were measured at ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diffraction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobalt and to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that the transformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperature did not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm of boron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which binds hcp-stabilizing elements (Cr and Re). Moreover, borides were identified in alloys with high boron content. 相似文献
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The inter-comparative analysis of the deterministic safety potential of innovative molten salt systems with critical and sub-critical cores is presented for both fast and thermal neutron spectra. The analysis includes two aspects: the choice of an initial level of sub-criticality and the study of multiple unprotected transients which have been simulated on the basis of one-point kinetics and two-point thermo-hydraulic schemes considering realistic feedback effects. Our preliminary results show that even small levels of sub-criticality (2–3 dollars) of cores can improve their safety characteristics significantly. 相似文献
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D. G. Pavel’ev N. V. Demarina Yu. I. Koshurinov A. P. Vasil’ev E. S. Semenova A. E. Zhukov V. M. Ustinov 《Semiconductors》2004,38(9):1105-1110
Characteristics of ohmic InGaAs contacts in planar diodes based on semiconductor superlattices with a small-area active region
(1–10 μm2) are studied. The diodes were formed on the basis of short (18 or 30 periods) heavily doped (1018 cm−3) GaAs/AlAs superlattices with a miniband width of 24.4 meV. The reduced resistance of the ohmic contact was equal to 2×10−7 Ω cm2 at room temperature. It is shown that the properties of fabricated planar diodes make it possible to use these diodes later
on in semiconductor devices that operate in the terahertz frequency region in a wide temperature range (4–300 K).
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Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 9, 2004, pp. 1141–1146.
Original Russian Text Copyright ? 2004 by Pavel’ev, Demarina, Koshurinov, Vasil’ev, Semenova, Zhukov, Ustinov. 相似文献
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Monique Pavel 《Annals of Mathematics and Artificial Intelligence》1994,10(1-2):193-204
We present a short and rather informal account concerning a problem we posed in earlier work, recall our conjecture at the time, and report on our answer today. Specifically, our purpose is to draw attention to fiberwise topology as a possible mathematical tool for formalizing multi-colored images and other complex signals met in pattern recognition (P.R.), to provide some information concerning the mathematical background of the fiber topological machinery, and indicate how to use it. For a detailed technical study as well as a tentative hierarchical classification of topological images in growing order of complexity and the corresponding topological processing methods, the readers may consult Pavel [5]. The paper ends by mentioning some artificial intelligence (A.I.) aspects of the fiberwise imagery. 相似文献
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Valentina I. Simagina Pavel A. Storozhenko Olga V. Netskina Oksana V. Komova Galina V. Odegova Yury V. Larichev Arcady V. Ishchenko Anna M. Ozerova 《Catalysis Today》2008,138(3-4):253
Catalytic hydrolysis of NaBH4 and NH3BH3 has been studied. It was shown that the nature of the support and the active component of the catalyst affect the H2 generation rate. Despite similar sizes of rhodium particles formed on the surface of different supports (γ-Al2O3, TiO2, carbon), their reactivity is different. Rh/TiO2 with low rhodium concentration (1 wt.%) is the most active catalyst both in the hydrolysis of NaBH4 and NH3BH3. The obtained results show that the rhodium chloride interaction with titania determines the reactivity of rhodium particles formed under action of NaBH4 medium. TEM, DRS UV–vis and XPS were used to characterize the catalysts. 相似文献
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Johann Vollmann Heinrich Grausgruber Helmut Wagentristl Heinrich Wohleser Pavel Michele 《Journal of the science of food and agriculture》2003,83(15):1581-1586
The presence of protease inhibitors in soybean prohibits the utilisation of the raw beans for food and feed. However, little information is available about environmental influences and the effects of nitrogen and sulphur supply on the antinutritional constituents of soybean. As these factors may influence protease inhibitors, soybean genotypes segregated according to the presence or absence of the Kunitz trypsin inhibitor have been evaluated for trypsin inhibitor activity (TIA) in field trials. TIA was affected significantly by environment (geographical location), fertilisation treatment and genotype. Environmental means of TIA were between 69.5 and 104.8 mg g?1. Nitrogen application, which caused an increase in seed protein content, resulted in a reduction in TIA by about 15% as compared with the control. Remarkably, simultaneous application of nitrogen and sulphur in the form of ammonium sulphate had a similar reductive effect on TIA to that of nitrogen application alone, although soybean protease inhibitors are rich in sulphur amino acids. Significant genetic variation in TIA was found both within the genotype class with the Kunitz inhibitor present as well as within the class lacking this inhibitor. The results suggest that TIA of soybean may be modified considerably by genetic improvement and appropriate agronomic management. Copyright © 2003 Society of Chemical Industry 相似文献
10.
A Olteanu L Grosu N Vlasie T Pavel E Barabas I Baciu 《Canadian Metallurgical Quarterly》1997,34(1-4):25-33
The regulatory mechanisms of the cerebral blood flow have preoccupied the physiology department of Cluj since the end of the 4th decade. These studies continued over the last years. The researches progressed from the studies of regulation by blood pressure changes to the nervous regulation and to the metabolic one. This paper's subject is the renin-angiotensin and adrenalin system influence on the changes of cerebral blood flow during the general hypoxic hypoxia and cephalic ischemia. Experiments were performed in 10 dogs anaesthetised with a mixture of chloralose, urethan and morphine. Hypoxic hypoxia was obtained by breathing a mixture of 11% oxygen in nitrogen, in a closed system and cerebral ischemic hypoxia by partial compression of the carotid arteries, after the ligation of the vertebral and thyroid arteries. The arterial blood pressure and the cerebral and hypothalamic blood flow, measured with the heated thermoelement, were registered. The plasma renin activity was tested radioimmunologically before, at 1.5 min, 5, 10 and 15 min, after the beginning of hypoxia. In ischemic hypoxia the experiment was repeated after venous perfusion with propranolol (0.6 mg/kg/h). The systemic blood pressure increased in both forms of hypoxia. The cortical and hypothalamic blood flow increased with the systemic arterial blood pressure. The hypothalamic blood flow remained stable or diminished a little. Propranolol increased the cerebral blood flow during ischemic hypoxia up to 300%. The i.v. administration of angiotensin (1-5 mg/kg) increased the cortical flow, while the hypothalamic flow remained self-regulated. Plasma renin activity increased more in general hypoxic hypoxia, than in cephalic ischemic hypoxia. After propranolol the increase was higher in this hypoxia. Propranolol produced a major activation of the renin-angiotensin system and of the cortical blood flow in ischemic cephalic hypoxia, the renin-angiotensin system being located in the cerebral structure. As well high doses of angiotensin produced cerebral vasodilatation in small cerebral vessels. This effect was found in our experiments in the cortical blood flow too. Our results indicate a beneficial propranolol effect on cortical circulation in ischemic hypoxia. 相似文献