HBA: Distributed Metadata Management for Large Cluster-Based Storage Systems

An efficient and distributed scheme for file mapping or file lookup is critical in decentralizing metadata management within a group of metadata servers. This paper presents a novel technique called Hierarchical Bloom Filter Arrays (HBA) to map filenames to the metadata servers holding their metadata. Two levels of probabilistic arrays, namely, the Bloom filter arrays with different levels of accuracies, are used on each metadata server. One array, with lower accuracy and representing the distribution of the entire metadata, trades accuracy for significantly reduced memory overhead, whereas the other array, with higher accuracy, caches partial distribution information and exploits the temporal locality of file access patterns. Both arrays are replicated to all metadata servers to support fast local lookups. We evaluate HBA through extensive trace-driven simulations and implementation in Linux. Simulation results show our HBA design to be highly effective and efficient in improving the performance and scalability of file systems in clusters with 1,000 to 10,000 nodes (or superclusters) and with the amount of data in the petabyte scale or higher. Our implementation indicates that HBA can reduce the metadata operation time of a single-metadata-server architecture by a factor of up to 43.9 when the system is configured with 16 metadata servers.     

认证测试方法的改进及应用

基于串空间模型的认证测试方法被证明是一种分析认证协议的有效工具,为了使之适用于类型更多、规模更大的安全协议,并提高其在协议的认证性、可达性、机密性、非否认性、会话密钥的新鲜性及主体间的关联度上的分析能力,对原有的认证测试方法进行改进,充分利用消息格式,细化分析步骤,增添相关符号以分析复杂协议的更多安全特性。利用该方法能缩减模型检测自动化工具的搜索范围,在解决空间爆炸问题的同时有效地找到多方协议的具体攻击路径,而且它对安全协议的设计和验证也具有一定的指导作用。     

用于电子商务中的数据挖掘技术研究

本文基于国内外的最新研究成果对数据挖掘技术进行了研究,将这些技术应用到具体的电子商务平台中去,得到了可行性验证,从而为此技术在电子商务领域广泛应用起到了示范作用。     

基于遗传算法的Peer to Peer路由算法R GA*

路由算法是制约PeertoPeer 系统整体性能的关键因素之一。目前大多数路由算法无法保证全局收敛,而链路延迟、费用、网络带宽等现实制约因素往往在选路时被忽略。针对上述问题,提出了基于遗传算法的RGA路由算法。通过适度函数和遗传因子,RGA可以快速地实现全局收敛。同时将链路的延迟、费用、带宽等参数插入到适度函数中, 避免了盲目路由。仿真试验的结果表明,RGA路由算法在大规模PeertoPeer系统中是高效和可扩展的。     

可靠组播拥塞控制

拥塞控制作为可靠组播协议的两个重要研究内容之一,已成为近几年来计算机网络与通讯领域的研究热点。分析了组播拥塞控制机制面临的基本问题,以及近几年针对这些问题提出的几种典型方案,最后指出未来的研究方向。     

模糊聚类神经网络的非对称学习算法

通过仿真和分析表明模糊聚类神经网络原有学习算法FCNN的局限性,如初值敏感性、吸引域不灵活和稳定点不合理等;指出造成上述局限的原因主要在于算法的对称性和权值向量的修正缺乏协同。为此,通过在网络模型中引入层内反馈、在算法中引入加速项,消除了算法的对称性并使权值向量的修正具有一定的协同性;通过改进算法结构,消除了小尺度振荡现象并使算法的稳定点趋于合理。计算机仿真结果表明改进后的非对称学习算法AFC可以有效克服原有算法的不足并具有较高的收敛速度。     

Windows NT请求式拨号网络的优化及实现

请求式拨号网络还存在着冗余很大的网络传输和拨号连接,为减少电信成本,文章尝试对Ｗｉｎｄｏｗｓ ＮＴ请求式拨号网络进行优化。     

多孔淀粉对森林浴香精的吸附及释放性能研究

本文采用多孔淀粉吸附法,制备具有一定缓释性能的香精缓释制剂。使用扫描电子显微镜观察其表面多孔并向内部延伸。150目多孔淀粉的平均饱和吸附率为0.785g/g。热重法测得在150℃之前,随着温度的升高,多孔淀粉缓释制剂失重速率加快,至170℃左右时,香精基本释放完全。紫外分光光度法得出,随着时间的延长,质量相等固体中香精含量c缓慢下降,释放速率也逐渐减小;吸附在多孔淀粉中的香精在初期表面阶段释放符合一级反应动力学,方程为logc=-0.03123t+0.9149(r2=0.96799);微孔阶段释放符合二级反应动力学,方程为1/c=0.0051t+0.1338(r2=0.95915)。     

多元酸改性环氧丙烯酸UV树脂的合成

采用部分多元酸代替丙烯酸对环氧丙烯酸UV树脂进行改性,在一定程度上改善了原树脂的脆性,改性后的树脂具有固化速度快、光泽高、黏度高的特点。讨论了合成时所需的催化剂、多元酸用量等因素对树脂性能的影响。     

A METHOD OF HUMAN BIODYNAMIC MEASUREMENT BASED ON VIRTUAL MARKER TECHNOLOGY AND WAVELET ALGORITHM

A new method is reported for human biodynamic measurement, which includes an improved motion measurement system via virtual marker technology and a wavelet algorithm to extract muscle activities from electromyography signals in vivo. Four channels of electromyography signals and twelve virtual markers motion data were collected when the subject did a standard gait experiment. Then, a wavelet algorithm was used to process raw electromyography signals and to extract muscle activity features. The results demonstrated that the proposed method could shorten the motion measurement experiment time and improve the measurement accuracy. The proposed wavelet algorithm could efficiently extract muscle activity features from electromyography signals. The reported method may be potentially used for the human biodynamic research and clinical biomechanics. Possible further improvements for this method are also discussed.