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991.
992.
根据变电站自动化系统对访问控制的需求,分析了IED设备信息模型和信息交换服务这两种访问控制的操作对象,通过对其粒度的粗细划分及访问策略研究,基于RBAC方法设计一种多粒度的访问控制系统.该系统在逻辑上是集中的,在实现上是分布的,它能够为用户的访问提供集中的控制,对用户的权限进行检查,根据请求生成相应的访问决议,并分散到各个有访问控制需求的IED设备上来执行这些控制决议.通过远程配置的实例分析表明该系统能满足变电站自动化的访问控制需求. 相似文献
993.
针对ATM网络中不同业务的需要,提出了一种采用FIFO机制的易于实现的单队列缓存分配方案,但该方案为了获得较高的链路利用率就需要较大的缓存空间·因此进一步提出了旨在减少信息对缓存的占用的多队列链路速率分配算法,并求解了链路速率的分配规则表达式·理论分析表明,该算法能够在一定程度上克服单队列缓存分配算法对缓存空间的耗费,并保证链路速率的合理分配· 相似文献
994.
给出单调函数在偏序集上的一些性质,并给予证明.同时,将全序集上的单调函数与偏序关系中的单调函数进行了比较. 相似文献
995.
ZheChen Wang XunLei Ding YanPing Ma Hai Cao XiaoNan Wu YanXia Zhao ShengGui He 《科学通报(英文版)》2009,54(16):2814-2821
Density functional theory (DFT) study of reaction between vanadium trioxide cluster cation (VO3^+) and ethylene (C2H4) to yield VO2^+ + CH3CHO (acetaldehyde) and VO2CH2^+ + HCHO (formaldehyde) is carried out. Structures of all reactants, products, intermediates, and transition state in the reaction have been optimized and characterized. The results show unexpected barriers in the reaction due to the existence of a η^2-O2 moiety in the ground state structure of VO3^+. The initial reaction steps combining ethylene adsorption, C=C activation and O-O cleavage are proposed as rate limiting processes. Comparison of reactions of VO3^+ + C2H4 with VO3 + C2H4 and VO2^+ + C2H4 in the previous studies is made in detail. The results of this work may shed light on the understanding of C=C bond cleavage in related heterogeneous catalysis. 相似文献
996.
LaBao Zhang YangYin Zhong Lin Kang Jian Chen ZhengMing Ji WeiWei Xu ChunHai Cao 《科学通报(英文版)》2009,54(12):2150-2153
A superconductor single photon detector based on NbN nanowire was fabricated using electron beam lithography (EBL) and reactive ion etching (RIE) for infrared photon detection. When biased well below its critical current at 4.2 K, NbN nanowire is very sensitive to the incident photons. Typical telecommunication photons with a wavelength of 1550 nm were detected by this detector. Data analysis indicates the repeating rate of the device with 200 nm NbN nanowire may be up to 100 MHz, and the quantum efficiency is about 0,01% when biased at 0.95/c. 相似文献
997.
Validation of full cavitation model in cryogenic fluids 总被引:1,自引:0,他引:1
Numerical simulation of cavitation in cryogenic fluids is important in improving the stable operation of the propulsion system
in liquid-fuel rocket. It also represents a broader class of problems where the fluid is operating close to its critical point
and the thermal effects of cavitation are pronounced. The present article focuses on simulating cryogenic cavitation by implementing
the “full cavitation model”, coupled with energy equation, in conjunction with iterative update of the real fluid properties
at local temperatures. Steady state computations are then conducted on hydrofoil and ogive in liquid nitrogen and hydrogen
respectively, based on which we explore the mechanism of cavitation with thermal effects. Comprehensive comparisons between
the simulation results and experimental data as well as previous computations by other researchers validate the full cavitation
model in cryogenic fluids. The sensitivity of cavity length to cavitation number is also examined.
Supported by the National Natural Science Foundation of China (Grant No. 50706042) 相似文献
998.
The aerodynamic characteristics of butterflies, especially those which can migrate overseas, have received a great deal of attention because they have larger-scale wingspans and lower flapping frequencies than other insects such as drosophilae and bees. The objective of this work is to investi-gate the flow structures over a simplified model of Papilio Ulysses, one kind of migratory butterflies, through hydrogen bubble visualizations, and leading-edge vortices, wing-tip vortices, separation bub-bles and horseshoe vortex wake are observed. Moreover, the variations of these structures with the angle of attack are discussed in detail. A new type of leading-edge vortices which resembles the in- versed Chinese character “八” is observed in the experiment. 相似文献
999.
In order to deal with the limitations during the register transfer level verification, a new functional verification method based on the random testing for the system-level of system-on-chip is proposed. The validity of this method is proven theoretically. Specifically, testcases are generated according to many approaches of randomization. Moreover, the testbench for the system-level verification according to the proposed method is designed by using advanced modeling language. Therefore, under the circumstances that the testbench generates testcases quickly, the hardware/software co-simulation and co-verification can be implemented and the hardware/software partitioning planning can be evaluated easily. The comparison method is put to use in the evaluation approach of the testing validity. The evaluation result indicates that the efficiency of the partition testing is better than that of the random testing only when one or more subdomains are covered over with the area of errors, although the efficiency of the random testing is generally better than that of the partition testing. The experimental result indicates that this method has a good performance in the functional coverage and the cost of testing and can discover the functional errors as soon as possible. 相似文献
1000.
纳米压痕法测量纳米晶金属Cu薄膜力学性能的研究 总被引:1,自引:1,他引:0
采用纳米压痕法测量了不同厚度(180~1000nm)的纳米晶Cu膜的硬度和弹性模量.结果表明,Cu膜硬度与厚度的关系类似于Hall-Petch关系,而弹性模量与厚度无关,其值相比块体粗晶Cu下降了约20%,分析位移-载荷曲线发现晶粒尺寸越大的Cu膜其位移跳跃现象越明显.另外,对于不同厚度的Cu膜其临界剪切应力的范围约在3.02~4.07GPa之间,基本接近粗晶Cu的理论剪切强度,位错塞积依然是其塑性变形的主要机制. 相似文献