Super-proximity routing in structured peer-to-peer overlay networks

Peer-to-Peer systems are emerging as one of the most popular Intemet applications. Structured Peer-to-Peer overlay networks use identifier based routing algorithms to allow robustness, load balancing, and distributed lookup needed in this environment. However, identifier based routing that is independent of Internet topology tends to be of low efficiency. Aimed at improving the routing efficiency, the super-proximity routing algorithms presented in this paper combine Internet topology and over|ay routing table in choosing the next hop. Experimental results showed that the algorithms greatly improve the efficiency of Peer-to-Peer routing.     

结构化P2P网络中关键字搜索算法

为了解决分布式哈希表(DHT)不支持模糊匹配和查找延迟长等问题,提出使用改进的超立方体互连圈结构建立逻辑的关键字搜索层.对于给定的文档和描述该文档的关键字集合,使用反向文档索引(IDF)技术选择文档的重要关键字,并映射到环标号,将描述文档的关键字集映射到立方体标号,有效地提取了关键字对于文档的重要性信息,并通过构造生成树来实施搜索操作.实验结果表明,与使用超立方体结构作为关键字搜索层的算法相比,该算法在查询关键字较少时,具有更好的性能.     

结构化对等网中平均可用容量的分析

为了描述对等网中的可用容量,引入了平均可用容量的概念,分析了应用层图的特性对于对等网可用容量的影响.网络的平均可用容量被定义为用节点和边的平均空闲容量为参数的严格单调增函数.对一个在均匀流量模型下的网络,发现了决定平均可用容量的参数可以用图的出度与平均距离表示,提出了de Bruijn图是一个使平均可用容量最大化的渐近最优选择.证明了当图的出度大于1时,平均可用容量存在一个不可达的上界.     

一种结构化对等网络中的偏向路由算法

由于路由效率高,贪婪式路由算法成为目前基于DHT的结构化P2P协议的首选路由算法,但贪婪式路由算法仅考虑路由效率而忽视了系统中节点负载平衡问题．文章提出一种适用于无状态结构化P2P协议中的偏向路由算法,与传统的路由算法不同的是,偏向路由算法将根据节点间负载变化和路由效率两个方面来动态选择下一跳节点．实验结果表明：与贪婪...     

结构化P2P中基于蜜罐的蠕虫发现策略研究

为解决结构化P2P网络中蠕虫发现时间长、准确率低的问题,提出了基于蜜罐技术的蠕虫发现策略.通过在P2P节点的文件索引哈希表中设置代表蜜罐节点地址信息的(K,V)对,将P2P蠕虫引入蜜罐中,并通过设置过滤名单提高P2P蠕虫的发现准确率.通过在模拟环境中的实验和对比,证明了该发现策略能够在P2P蠕虫爆发后的第一轮感染过程中将蠕虫引入蜜罐并准确的识别出P2P蠕虫.为结构化对等网络的蠕虫发现提供了新的方法.     

基于DHT的结构化P2P覆盖网络算法分析

目前P2P覆盖网络应用十分广泛,关于覆盖网的研究已成为当前网络技术研究领域的热点.关于覆盖网络相应的路由算法在不断发展和完善,先后提出了集中目录式的算法和分布式查找算法.针对基于DHT的覆盖网络算法进行介绍和分析,并指出该领域的最近研究趋势.     

基于DHT的结构化P2P覆盖网络算法分析

目前P2P覆盖网络应用十分广连,关于覆盖网的研究已成为当前网络技术研究领域的热点。关于覆盖网络相应的路由算法在不断发展和完善,先后提出了集中目录式的算法和分布式查找算法。针对基于DHT的覆盖网络算法进行介绍和分析,并指出该领城的最近研究趋势。     

Non-random segregation of sister chromosomes in Escherichia coli

It has long been known that the 5' to 3' polarity of DNA synthesis results in both a leading and lagging strand at all replication forks. Until now, however, there has been no evidence that leading or lagging strands are spatially organized in any way within a cell. Here we show that chromosome segregation in Escherichia coli is not random but is driven in a manner that results in the leading and lagging strands being addressed to particular cellular destinations. These destinations are consistent with the known patterns of chromosome segregation. Our work demonstrates a new level of organization relating to the replication and segregation of the E. coli chromosome.     

Lack of heterogeneity in antihapten antibodies of a phylogenetically primitive shark

Individual mammals have the capacity to express at least one million distinct antigen binding specificities, implying a high degree of structural heterogeneity in the variable heavy and light chain (VH and VL) portions of the antibody molecules. Studies of higher vertebrate species suggest that this heterogeneity is created both through a sizeable repertoire of germ-line VH and VL genes and through random rearrangements of V and joining genes. Additional somatic mechanisms probably also contribute to the ultimate heterogeneity; one-third of murine plasmacytomas producing lambda 1 immunoglobulin carry a somatically mutated Ig1-V gene. The relative contributions of these various mechanisms to the overall imunoglobulin variability are difficult to evaluate. The production of different antibodies to a defined determinant in different individuals of an inbred mouse strain [for example, (3-iodo-4-hydroxy-5-nitrophenyl) acetyl (NIP) in CBA mice] suggests the involvement of somatic mutations or rearrangement but does not rule out the possibility that each individual CBA mouse expresses only a small random fraction from a large germ-line repertoire of V genes determining different anti-NIP binding sites. The opposite finding, that different individuals produce nearly identical antibodies to a defined determinant, would suggest the presence and expression of a limited number of germ-line genes without somatic alterations. Data presented here suggest that primitive sharks (Heterodontus fransisci) produce such antibodies to the hapten furyloxazolone.