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981.
一个既定螺旋桨水动力特性数学模型是运行参数的二元函数,可由三维坐标图来表示.立体图解法就是应用MATLAB,以航速、转速和推力(转矩或功率)为坐标轴分别作出螺旋桨水动力特性、原动机外特性的函数立体图,并进行组合和裁剪,为船-机-桨工况配合特性分析提供可视化平台,立体图解法具有众多突出优点,且扩展应用范围广. 相似文献
982.
A computer-aided method to design a hybrid layout—tree-shape planar flowlines is presented. In newtype flowshop layout, the
common machines shared by several flowlines could be located together in functional sections. The approach combines traditional
cell formation techniques with sequence alignment algorithms. Firstly, a sequence analysis based cell formation procedure
is adopted; then the operation sequences for parts are aligned to maximize machines adjacency in hyperedge representations;
finally a tree-shape planar flowline will be obtained for each part family. With the help of a sample of operation sequences
obtained from industry, this algorithm is illustrated. 相似文献
983.
To solve the resource-constrained multiple project scheduling problem (RCMPSP) more effectively, a method based on timed colored
Petri net (TCPN) was proposed. In this methodology, firstly a novel mapping mechanism between traditional network diagram
such as CPM (critical path method)/PERT (program evaluation and review technique) and TCPN was presented. Then a primary TCPN
(PTCPN) for solving RCMPSP was modeled based on the proposed mapping mechanism. Meanwhile, the object PTCPN was used to simulate
the multiple projects scheduling and to find the approximately optimal value of RCMPSP. Finally, the performance of the proposed
approach for solving RCMPSP was validated by executing a mould manufacturing example. 相似文献
984.
Mobile ad hoc networks are often deployed in environments where the nodes of the networks are unattended and have little or
no physical protection against tampering. The nodes of mobile ad hoc networks are thus susceptible to compromise. The networks
are particularly vulnerable to denial of service (DoS) attacks launched through compromised nodes or intruders. In this paper,
we investigated the effects of flooding attacks in network simulation 2 (NS-2) and measured the packet delivery ratio and
packet delay under different flooding frequencies and different numbers of attack nodes. Simulation results show that with
the increase the flooding frequencies and the numbers of attack nodes, network performance drops. But when the frequency of
flooding attacks is greater than a value, the performance decrease gets smooth. Meanwhile the packet delay firstly increases
and then declines to a value of stability at the end. 相似文献
985.
结合某车型制动踏板支架的逆向设计,介绍了基于曲面特征的建模策略和方法,详细分析了扫掠面和旋转面的重构方法,以及逆向设计建模过程中特征曲线提取的方法与技巧. 相似文献
986.
Run-lian Zhang Xiao-nian Wu Xiao-she Dong 《西安交通大学学报(英文版)》2009,21(1):11-16
To maintain the global consistency of the authorizing is a challenge when the system authorization is changed in grid environments. This paper proposes a policy-based automatically negotiating method to deal with this issue. An effective system framework, which includes the certificate management, the access policy repertory, the negotiator and the automatically negotiating mechanism, is designed and implemented. The experimental results show that automated negotiation can quickly regain the global authorization consistency and only cause a little system overhead increasing. Compared with the manual authorization maintaining, the presented method can reduce the negotiating time significantly, and reduce the meaningless grid jobs because the inconsistent privileges are controlled timely. 相似文献
987.
Protective effect of glutamine pretreatment on ischemia-reperfusion injury of spinal cord in rabbits
Jian Lü 《西安交通大学学报(英文版)》2009,21(4):242-245
Objective To investigate the effect of glutamine (Gln) on the content of reduced glutathione hormone (GSH) and aminoglutaminic acid (Glu) of spinal cord following ischemia-reperfusion injury. Methods Totally 40 healthy adult male rabbits were randomly divided into five groups: sham-operation group (S group), ischemia-reperfusion injury group (I/R group), low-dose glutamine group (L Gln group), median-dose glutamine group (M Gln group) and high-dose glutamine group (H Gln group). After glutamine preconditioning, the model of spinal cord ischemia-reporfasion injury was established according to Zivin's method. The general status of animals was observed and the changes of Jacobs scoring were recorded in each group. Malondialdehydes (MDA), GSH, Glu and superoxide dismutase (SOD) activity in lumbar spinal cord tissues were determined using chemical colorimetry. The neuron number and deviation rate in spinal cord anterior horn were observed histopathologically. Results There was no significant difference between L Gin group and I/R group in behavior scoring, SOD activity, content of MDA and Glu, neuron number and deviation rate of spinal cord (P>0.05); however, there was a significant difference in GSH content of spinal cord (P<0.05). M Gln group and I/R group differed significantly (P<0.05) in behavior scoring, SOD activity, content of MDA, Glu, GSH, neuron number and deviation rate of spinal cord. Between H Gln group and M Gln group, there was no significant difference in behavior scoring, content of MDA and Glu, SOD activity, neuron number and aberration rate in spinal cord (P>0.05), whereas there was a significant difference in SOD activity and Giu content (P<0.05). Conclusion Pretreatment with medium-dose glutamine has a protective effect on spinal cord ischemia-reporfasion injury in rabbits, which may be related to the maintenance of GSH content, increase of SOD activity and reduction of MDA. 相似文献
988.
该文主要用浙江省海塘技术规定中的方法计算了断面复杂的混合式海堤的波浪爬高以及越浪量,并通过计算波浪爬高和越浪量来确定海堤的堤顶高程;结合实际工程中遇到的断面比较复杂的海堤,用不同方法进行计算,并对得出的结果进行分析比较;最后通过模型试验进行验证。结果表明,对于复杂的混合式断面,现行规范规定的波浪爬高的计算方法不够完善,计算得到的结果往往偏大,而对越浪量的计算也有很大的局限性,最好通过断面波浪模型试验来分析验证。 相似文献
989.
由于软土地区的高压缩性,该区域的道路下排水管道受各种因素的影响,出现纵向垂直变位。在接口顶部,由于承受不了拉应力而开裂。排水管内水会渗入地层污染地下水,同时地下水也会带着土粒从裂缝中流入排水管内,并且引发路面坍塌或地下水污染等危害。该文对这些病害结合工程实例情况,提出了治理措施,可供类似工程参考。 相似文献
990.