A structured P2P network based on the small world phenomenon

In this paper, we propose a new structured P2P overlay network, named SW-Uinta(small-world). In order to reduce the routing latency, we firstly construct the Uinta network in which both physical characteristics of network and data semantic are considered. Furthermore, based on Uinta, a nondeterministic caching strategy is employed to allow for poly-logarithmic search time while having only a constant cache size. Compared with the deterministic caching strategy proposed by previous P2P systems, the nondeterministic caching strategy can reduce communication overhead for maintaining the routing cache table. Cache entries in the cache table of peer nodes can be updated by subsequent queries rather than only by running stabilization periodically. In the following, a novel cache replacement scheme, named the SW cache replacement scheme, is used to improve lookup performance, which has proved to satisfy the small-world principle. So we call this network SW-Uinta(small-world). After that, according to the theoretical analysis, it can be proved that SW-Uinta(small-world) can get O((log ² N)/k) search time with O(k) cache size. Lastly, the performance of SW-Uinta(small-world) is compared with those of other structured P2P networks such as Chord and Uinta. It shows that SW-Uinta(small-world) can achieve improved object lookup performance and reduce maintenance cost.

一种数据块关系指导的缓存替换方法

提出了一种数据块关系指导的缓存替换方法BDP(block correlations directed replacement policy).数据块关系所表示的空间局部性可以用来指导存储系统的缓存替换策略.BDP利用历史访问信息和实时访问信息,预测数据块未来的空间局部性特征,并设计数据块驻留时间的控制策略,减少现有替换算法对空间局部性预测失败带来的失效惩罚.同时给出了BDP的有效缓存模型.模拟结果显示,对大多数实际系统工作负载,BDP的失效率相对LRU算法下降11%～38%,优于现有的考虑空间局部性的替换算法.     

一种基于不放回抽样的图像混沌加密算法

针对现有基于混沌序列的图像加密算法的缺陷,提出一种基于不放回抽样的图像混沌加密算法。该算法采用可变模运算和间接地址映射技术,将混沌序列一对一、高度随机地转换为图像像素地址,实现图像的位置置乱和灰度扰乱加密。对混沌序列的分布无严格要求,使混沌序列的参数和初值可以作为密钥被使用。实验结果表明,与现有同类算法相比,该算法性能优越、运算速度快且易于实现。     

Optimal replacement policy for a two-dissimilar-component cold standby system with different repair actions

In this paper, a cold standby repairable system consisting of two dissimilar components and one repairman is studied. When failures occur, the repair of both component 1 and component 2 are not ‘as good as new’. The consecutive operating times of component 1 after repair constitute a decreasing geometric process, while the repair times of component 1 are independent and identically distributed. For component 2, its failure is rectified by minimal repair, and the repair time is negligible. Component 1 has priority in use when both components are good. The replacement policy N is based on the failure number of component 1. Under policy N, we derive the explicit expression of the long-run average cost rate C(N) as well as the average number of repairs of component 2 before the system replaced. The optimal replacement policy N*, which minimises the long-run average cost rate C(N), is obtained theoretically. If the failure rate r(t) of component 2 is increasing, the existence and uniqueness of the optimal policy N* is also proved. Finally, a numerical example is given to validate the developed theoretical model. Some sensitivity analyses are provided to show the influence of some parameters, such as the costs for replacement and repair, and the parameters of the lifetime and repair time distributions of both components, to the optimal replacement policy N* and corresponding average cost rate C(N*).     

Optimal number of minimal repairs with cumulative repair cost limit for a two-unit system with failure rate interactions

A discrete replacement model is presented that includes a cumulative repair cost limit for a two-unit system with failure rate interactions between the units. We assume a failure in unit 1 causes the failure rate in unit 2 to increase, whereas a failure in unit 2 causes a failure in unit 1, resulting in a total system failure. If unit 1 fails and the cumulative repair cost till to this failure is less than a limit L, then unit 1 is repaired. If there is a failure in unit 1 and the cumulative repair cost exceeds L or the number of failures equals n, the entire system is preventively replaced. The system is also replaced at a total failure, and such replacement cost is higher than the preventive replacement cost. The long-term expected cost per unit time is derived using the expected costs as the optimality criterion. The minimum-cost policy is derived, and existence and uniqueness are proved.     

基于低能耗与高缓存命中并存的缓存替换算法

近年来无线传感器被广泛地利用在各个领域,与之相关的优化节能研究也层出不穷.作为信息共享、分发关键技术的缓存技术节能研究成为了研究热点之一.从缓存替换算法的角度对缓存技术节能进行研究,先对已有的缓存替换算法进行比较分析,在继承二分法思想以及无线传感器网络中缓存替换策略的研究思想的基础上,整合基于低能耗和高缓存命中的两种替换算法,构建出兼顾低能耗和高缓存命中双目标的缓存替换算法.最后通过仿真验证该算法在平均延迟时间、能量消耗以及缓存命中三个方面均有不同程度的提升.     

标准模型下强安全的无证书签密方案

首先指出近期提出的一种无证书签密方案易受到公钥替换攻击,并给出了相关攻击实例。进而提出一种新的无双线性对的无证书签密方案,通过对实体的无证书公钥和托管公钥进行独立的密码学验证,确保了新方案不遭受与现有方案类似的公钥替换攻击。在标准模型下,新方案被证明是安全的,能够实现无证书签密的不可伪造性和机密性。对比分析表明,新方案在确保强安全性的同时具有较好的计算性能。     

无证书签名方案的分析及改进

对一个无证书签名方案进行安全性分析,指出该方案不能抵抗公钥替换攻击和恶意的KGC攻击,即攻击者可以通过替换签名者的公钥来伪造任意消息的签名,恶意的KGC(Key Generation Center)可以获取用户的私钥。分析结果显示该方案不能满足无证书签名方案的安全性要求,同时为了应对这两种攻击,提出了改进的方案。     

存储器替换机制及其实现

提出一种解决PACT01一种结合动态可编程逻辑阵列(DPGA)的处理器的新型体系结制中cache的一致性与同步性问题的算法,并且解决多线程支持的快速上下文切换及快速用户级操作问题。存储器替换机制是解决cache的一致性问题及当cache未命中时从局部或远程存储器到cacbe存储器的数据替换问题的一种硬件实现方法,产生冲突的原因是由于多线程并行的写入／读取的位置相同和读或写的位置相同。文中选择的是相联映射策略,同时也选择了最少最近使用LRU算法,即在cache未命中时替换最少最近使用的参考块,为实现LRU算法设置了与每块相对应的计数器。     

关系数据库缓冲区置换策略的性能评测(英文)

缓冲区是计算机领域一个非常重要的研究主题。现在存在很多缓冲区置换策略,广泛地用于操作系统、文件系统、数据库以及存储系统中。提出了一种性能评测方法来评测关系数据库的缓冲区置换策略。这种方法采用直接测试方式,使用五个性能指标,包括新提出的指标以及由于模拟方法的局限性在以前的研究中很少使用的性能指标,同时利用显著性测试并提出一种联合使用多个显著性测试的方法进行置换策略之间的比较,设计和使用多种工作负载在单用户和多用户情况下有效地评测各种策略。使用这种评测方法,在一个真实的关系数据库环境中,对十三种典型的缓冲区置换策略的性能进行了详细、全面的实验研究,从中可以获得一些有用的结论。