共查询到19条相似文献，搜索用时 234 毫秒
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LONG Tao HONG Fan WU Chi SUN Ling-fi 《重庆大学学报(英文版)》2007,6(4):249-255
Access control in a grid environment is a challenging issue because the heterogeneous nature and independent administration of geographically dispersed resources in grid require access control to use fine-grained policies. We established a task-and-role-based access-control model for computational grid (CG-TRBAC model), integrating the concepts of role-based access control (RBAC) and task-based access control (TBAC). In this model, condition restrictions are defined and concepts specifically tailored to Workflow Management System are simplified or omitted so that role assignment and security administration fit computational grid better than traditional models; permissions are mutable with the task status and system variables, and can be dynamically controlled. The CG-TRBAC model is proved flexible and extendible. It can implement different control policies. It embodies the security principle of least privilege and executes active dynamic authorization. A task attribute can be extended to satisfy different requirements in a real grid system. 相似文献
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The flooding distance is an important parameter in the design and evaluation of a routing protocol,which is related not only to the delay time in the route discovery,but also to the stability and reliability of the route.In this paper, the average flooding distance (AFD) for a mobile ad hoc network (MANET) in a random graph model was given based on the dynamic source routing (DSR) protocol.The influence of spatial reuse on the AFD was also studied.Compared with that in the model without the spatial reuse,the AFD in the model with the spatial reuse has much smaller value,when the connetivity probability between nodes in the network is small and when the number of reused times is large.This means that the route discovery with the spatial reuse is much more effective. 相似文献
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Mobility and resource-limitedness pose challenging issues to service configuration for quality of service （QoS） management in ubiquitous computing environments. Previous configuration approaches, such as static resource reservation, dynamic resource allocation and single service composition are not valid in the environments. In this study, we present an adaptive service configuration approach. Firstly, we reduce the dynamic configuration process to a control model which aims to achieve the variation of critical QoS on minimal level with less resource cost. Secondly, to deal with different QoS variations, we design two configuration strategies--service chain reconfiguration and QoS parameter adjustment--and implement them based on fuzzy logic control theory. Finally, a configuration algorithm is developed to flexibly employ the two configuration strategies in tune with the error of critical QoS in configuration process. The results of simulation experiments suggest that our approach outperforms existing configuration approaches in both QoS improvement and resource utilization. 相似文献
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HU Jia-bing HE Yi-kang NIAN Heng 《浙江大学学报(A卷英文版)》2007,8(8):1330-1339
This paper presents a unified positive-and negative-sequence dual-dq dynamic model of wind-turbine driven doubly-fed induction generator(DFIG) under unbalanced grid voltage conditions. Strategies for enhanced control and operation of a DFIG-used back-to-back(BTB) PWM voltage source converter(VSC) are proposed. The modified control design for the grid-side converter in the stationary αβ frames diminishes the amplitude of DC-link voltage ripples of twice the grid frequency,and the two proposed control targets for the rotor-side converter are alternatively achieved,which,as a result,improve the fault-ride through(FRT) capability of the DFIG based wind power generation systems during unbalanced network supply. A complete unbalanced control scheme with both grid-and rotor-side converters included is designed. Finally,simulation was carried out on a 1.5 MW wind-turbine driven DFIG system and the validity of the developed unified model and the feasibility of the proposed control strategies are all confirmed by the simulated results. 相似文献
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Workload of each service class varies dynamically in the grid environment,making the static service pool size allocation scheme unable to guarantee the QoS requirement of each service class.In this paper,we link the issue of dynamical service pool size allocation scheme with QoS requirement under the varying workload,and formulate the QoS performance of service requests in the grid environment by queue theory.Combined Lagrangian optimization with a bisearch approach,the problem of optimally allocating service pool size scheme is resolved.Simulation results Show efficiency of the optimal service pool size allocation scheme. 相似文献
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A model of dynamic programming for repairing strategies of concrete structures during a projected service period is proposed,which takes into account the degradation in strength of components and the probability of accidental load.This model takes the safety grade of a structural system as the state variable of repairing strategies,and incorporates economic factors including expected repair cost,property loss due to structure failure,goods and material loss due to structure failure,loss of production interrupt due to structure failure,and inspection cost in decision making.It is found that the optimal repairing strategies are sensitive to the probability of accidental loads as well as the failure costs.The practicality of the model is demonstrated by an example. 相似文献
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More and more enterprises are outsourcing activities that are neither cost efficient if done in-house nor central to their businesses. Most of the studies in outsourcing decision making focus on vendor selection. However, little research has been done about location selection, which is also a critical step in offshore service outsourcing. The purpose of this paper is to offer a new method to deal with the destination selection problem in China. We employed the additive SE-DEA model to overcome the drawbacks of traditional DEA and SE-DEA methods, and calculated the relative efficiency of 20 service outsourcing model cities （excluding Xiamen）. Based on two years of longitudinal study, we made a comparison of the 20 cities. Finally we classified the model cities by combining them with the service outsourcing ability dimension and also gave some selection suggestions and development suggestions for outsourcers＇ outsourcing service and the model cities, respectively. 相似文献
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In civil engineering, the nonlinear dynamic instability of structures occurs at a bifurcation point or a limit point. The instability at a bifurcation point can be analyzed with the theory of nonlinear dynamics, and that at a limit point can be discussed with the theory of elastoplasticity. In this paper, the nonlinear dynamic instability of structures was treated with mathematical and mechanical theories. The research methods for the problems of structural nonlinear dynamic stability were discussed first, and then the criterion of stability or instability of structures, the method to obtain the bifurcation point and the limit point, and the formulae of the directions of the branch solutions at a bifurcation point were elucidated. These methods can be applied to the problems of nonlinear dynamic instability of structures such as reticulated shells, space grid structures, and so on. 相似文献
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On maximum power point tracking control strategy for variable speed constant frequency wind power generation 总被引：1，自引：0，他引：1
WU Guo-qing NI Hong-jun WU Guo-xiang ZHOU Jing-ling Zhu Wei-nan MAO Jing-feng CAO Yang 《重庆大学学报(英文版)》2010,9(1):21-28
Based on the characteristic of AC-excited variable speed constant frequency （VSCF） wind power generation, the vector control technique was applied in a doubly fed induction generator （DFIG）. Maximum wind energy or maximum output power point can be tracked by decoupling control of active power and reactive power. The research result shows that the net power of generation system delivered to grid in maximum wind energy tracking mode is not the most. We presented a novel maximum power point tracking （MPPT） control strategy by analyzing the DFIG mathematic model and power relations which delivered the maximum power to the grid. The maximum power point could be tracked automatically without measuring wind speed in the control strategy and the control was independent of optimal turbine power curve, which had excellent dynamic and static performances and robustness. Simulation and experimental results testify the accuracy and validity of the control strategy. 相似文献
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深入研究了一种融合Web服务、网格和对等计算技术,提出了基于管理域划分的空间信息资源管理系统模型,讨论了空间信息资源的部署与发现和空间信息资源的静态调度和动态调度,通过资源级调度和用户级调度二级调度,支持资源提供者和使用者双方协商服务级协定的实现,详细介绍了异构环境中任务迁移的动态关键路径的静态调度算法.在空间信息资源管理模型的基础上,讨论了单一入口点、单点控制、全局用户管理、全局资源管理和全局任务管理构件的相关实现技术. 相似文献
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李静 《重庆第二师范学院学报》2007,20(6):54-56
网格服务体系结构的出现对网格服务发现提出了挑战,UDDI上基于关键词和简单分类的服务发现机制已经不能很好满足需要.本文在分析现有相关研究的基础上,提出了基于服务质量的网格服务发现机制,引入服务质量相似度的概念,为网格服务发现提供了一种有效可行的方法. 相似文献
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制造网格中资源管理系统研究 总被引：7，自引：0，他引：7
为实现制造业的资源共享和协同工作, 以开放网格服务架构(OGSA)为系统框架, 以GT3(Globus Toolkit 3.0)为开发工具, 提出了制造网格的概念. 然而, 由于制造资源的复杂性、多样性、特殊性和分散性, 制造网格中的资源管理问题明显比其他网格应用项目困难得多. 因此, 开发了制造网格信息服务(MGIS), 该服务通过有效集成检测查询服务(MDS)和各种类型的资源封装模板, 实现了制造资源的远程封装、注册、发现和监控. 同时, MGIS与GRAM(globus resource allocation manager)共同构建了制造网格的资源管理系统, 解决了制约制造网格应用的瓶颈问题. 最后, 给出了该系统的应用框架, 并通过制造网格试验床中的一个具体应用实例说明了其实际应用过程. 相似文献
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在高性能并行分布式网格计算环境下,计算节点具有动态、异构、分布和多管理域特性,这使得网格资源的发现及管理变得比较困难。在对网格调度模型分析的基础上,使用模糊聚类的相关理论提出在任务调度之前对资源进行预处理,依据用户QoS需求权重对机器性能进行聚类,得到和用户QoS需求最匹配的较优资源子集。这样既合理地减少了映射的目标资源,又实现了目标资源子集与用户QoS需求的最优匹配。在一定程度上提高了整个系统的性能,满足了不同用户的特殊需求。 相似文献
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许锑 《咸阳师范学院学报》2007,22(6):58-60
为深入分析开放式网格服务模型的基本原理与机制,遵从面向服务的结构原则,充分利用web service的体系结构及集成技术,通过对OGSA的网格服务模型的探讨,展示了多种技术相融合的发展趋势。web service是一种新兴的以服务为中心的分布式系统技术,OGSA的网格服务模型是一种基于web service技术的开放式组件模型。 相似文献
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针对目前的工作流管理系统存在的问题,本文在传统工作流管理系统和目前流行的Web服务技术的基础上,提出了基于Web服务的工作流体系模型,该模型在传统工作流体系模型的基础上,引入Web服务。Web服务在Internet分布式环境下的动态发布、发现和集成应用的特点,能够很好地解决工作流程缺乏柔性,相互之间无法互操作,不能及时响应变化等缺点,提高了工作流程执行效率和服务质量,大大提高工作流系统的应用范围,促进了工作流管理系统的发展。 相似文献
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空间应用系统要求能够依据业务需求,快速、灵活地集成各种已有和新添的Web服务,实现基于空间知识网格环境的协同工作和应用集成,实现按需服务．提出和设计了支持空间知识服务的语义服务描述模型和基于语义的Web服务协同模型,利用协同模型将分散空间服务组合起来．通过引入动态服务组合和服务匹配、绑定机制,并且和空间知识本体库密切配合,实现资源动态绑定,真正有效地支持空间知识服务的动态组合与协同． 相似文献