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排序方式: 共有1580条查询结果,搜索用时 718 毫秒
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The Journal of Supercomputing - 相似文献
23.
A cooling cycle with He II convection driven by self-sustained fountain effect pumps is being investigated. Special attention is drawn to the problem of heat transfer at both ends of the superfilter of this loop. The heat exchanger requirements are derived from theoretical considerations on the degradation of the cooling characteristic effected by non-perfect heat exchangers. A shell and tube type heat exchanger, optimized for the warm end of the filter has been operated in this loop with a thermal load of up to 9 W, with 2.8 g s−1 maximum helium flow rate and with inlet temperatures between 1.8 and 3.4 K. Its performance is well described by computations. A different heat exchanger design with finned Cu walls is suggested for the cold end of the pump. Some considerations on its optimization are given. 相似文献
24.
We report a case of subacute bowel obstruction due to a compression of the rectosigmoid junction by a chronically distended bladder, occurring in a 91-year-old male suffering from a long-standing diabetes mellitus and a prostatic adenoma. Radiographic, water-soluble contrast enema and pelvic CT features are reported. 相似文献
25.
OBJECTIVES: Sensory nerves play an important role in mediating neurogenic inflammation and subsequent tissue healing. A decrease in sensory nerve function with increasing age has been reported to correlate with poor tissue healing. Sympathetic nerves are known to modulate sensory nerve function, and changes in this modulation could also have important implications with ageing. The aims of this study were to examine the effect of different frequency electrical stimulation (ES) on the microvascular responses obtained to sensory nerve activation in young, aged and capsaicin-pretreated rats and modulation of these responses by sympathetic efferents. METHODS: Using laser Doppler flowmetry, vascular responses to antidromic ES of the sciatic nerve were monitored in the base of vacuum-induced blisters in the hind footpad. The non-selective alpha-adrenoceptor antagonist phentolamine (3 mg/kg, i.v.) was administered 20 min prior to ES. RESULTS: At high frequency ES (20V, 2ms, 15Hz for 1 min), the vascular response in old rats was significantly reduced (46 percent decrease, p < 0.05) compared to young control. At low frequency ES (20 V, 2 ms, 5 Hz for 1 min) however, older rats produced similar vascular responses to the young. Capsaicin-pretreated rats showed significantly reduced vascular responses to both high and low frequency ES, regardless of age. Pretreatment with phentolamine significantly increased the microvascular response in young rats at high (87 percent) and low (36 percent) frequency ES. In contrast, phentolamine significantly increased the ES-induced response in old rats at high frequency only (147 percent increase). CONCLUSIONS: The results suggest that the aged sensory nerve responds preferentially to low frequency ES and that sympathetic efferents exert an inhibitory modulatory effect on the vascular response evoked by sensory nerve stimulation. There are age-related changes in sympathetic modulation of sensory nerve-mediated responses which is dependent on stimulation frequency. 相似文献
26.
Anoirel Issa 《Journal in Computer Virology》2012,8(4):141-149
Virtual Machines are important infrastructural tools for malware analysis. They provide safe yet accurate way of evaluating real life behavior and impact of any executable code, thus providing a better understanding of obfuscated or non conventional portions of code within a binary file. Many virtual machines, such as VMware, Qemu, VirtualBox and SandBoxes, are available and are widely adopted by malware researchers and analysts. Moreover, many antivirus scanners have their own implementation of emulators to achieve comparable results by running malicious code within a controlled environment in order to decrypt obfuscated code. Virus writers have always responded to these technologies. Most malware today uses anti-debug techniques to counter analysis and evade antivirus detection. Lately, malware like Zeus/SpyEye and associated families such as Smoaler, Dromedan, Kazy, Yakes, and other malware such as Spyrat or W32.Pilleuz, have deployed techniques to disrupt the use of virtual machines and emulators. These malware families are able to implement different variations of disruption techniques within single samples or within related groups of malware before propagation. This paper will present a study of these anti-emulation and anti-virtual machine techniques. 相似文献
27.
Prof. Dr. S. Darwish Dr. M. W. Khalil Dr. M. A. Abdel Rahim Porf. Dr. I. A. Ammar 《Materialwissenschaft und Werkstofftechnik》1989,20(9):299-308
A study on the value metal character of Zr in 0.1 M solutions of H2SO4, HNO3, and H3PO4 has been performed using the anode potential as the primary variable in galvanostatic, potentiostatic, and capacity measurements. A method of surface pre-treatment, which suppresses both O2 evolution and metal dissolution, has been described. Kinetic parameters of oxide growth have been calculated. The results indicate that:
- (i) the high field approximation is applicable following an exponential law, and
- (ii) the height and activation distance of the energy barrier for ion transport through the oxide phase (Verwey model) are the same three acids.
28.
M. A. A. Issa F. A. A. Amin A. M. Hasstb Z. H. Dughaish 《Journal of Materials Science》1989,24(7):2300-2304
Germanium-silicon alloys doped with phosphorus were prepared in vacuum by rapidly pouring the molten alloy into cooled copper moulds containing the phosphorus dopant. Without any further treatment, the ingots are milled into powder of grain size (L 5 µm) and hot pressed. It is shown that a high degree of homogenization of the alloy constituents can be obtained in the final compacts, thus eliminating the need for zone-levelled starting material. It is also shown that this work is in agreement with the plastic flow model of sintering known as the Mackenzie-Shuttleworth-McClelland model. Electrical measurements indicate that the dopant is effectively and uniformly incorporated into the alloy. 相似文献
29.
F. A. A. Amin A. S. S. Al-Ghaffari M. A. A. Issa A. M. Hassib 《Journal of Materials Science》1992,27(5):1250-1254
The thermoelectric properties of fine-grained alloys prepared by either cold pressing and sintering or hot pressing in the range 5–50 m are compared with single-crystal best-direction values. It is shown that for thep-type alloy, almost the entire thermoelectric properties are recovered, i.e. the figure of merit for the finest grain size is almost the same as the best single-crystal value. The same trend is observed in then-type alloy except that 90% of the single-crystal figure of merit is recovered. These results are discussed in terms of a model which suggests that degradation of favourable thermoelectric properties by powdering the alloys is compensated by (1) decrease of thermal conductivity due to scattering of phonons at grain boundaries for grain sizes that are comparable to the mean free path of phonons; and (2) retention of some of the anisotropic properties of the single crystal in the fine-grained compacts. 相似文献
30.