Performance analysis of IEEE 802.11 DCF networks

This paper presents an analytical saturation throughput model of IEEE 802.11DCF （distributed coordination function） with basic access in ad hoc mode. The model takes into account freezing of the backofftimer when a station senses busy channel. It is shown that taking into account this feature of DCF is important in modeling saturation throughput by yielding more accurate and realistic results than models known from literature. The proposed analytical model also takes into account the effect of transmission errors. All essential features of the proposed analytical approach are illustrated with numerical results. The presen- tation of the model is proceeded by an overview of approaches to IEEE 802.11 network performance evaluation presented in the literature.     

本体模块化:特征、描述与方法

近年来,本体模块化研究受到研究者的普遍关注.本文全面综述了本体模块化研究的最新进展,包括本体模块化特征、形式化描述语言及构建与选取方法.在形式化描述方面,主要研究成果有分布式描述逻辑、ε-连接及基于包的描述逻辑,比较分析了它们的特点和关联,讨论了有待进一步解决的问题.在构建和选取方面,介绍了模块化设计模式、模块化划分与抽取方法的最新研究成果.     

分布式认知及其对学习环境设计的影响

分布式认知理论认为认知分布于个体、群体和人工制品之中。其中,个体和人工制品同样重要,群体和人工制品也同样重要。今天,信息技术的发展日益凸显人工制品的价值。在学习活动中,"学习环境"即为"人工制品";分布式认知对人类认知活动和人工制品的认识即为分析学习环境设计的一种理论框架。它基于"认知分布"的视角对学习环境赋予新的隐喻,给予学习环境设计新的启示。这为学习者的有意义学习创设环境提供了有力的"给养"。     

基于VPN的校园数字资源分布式共享应用研究

北京工业职业技术学院信息工程系已初步引入VPN技术,用以解决校外用户访问校园内部资源的难题,本文在此情况的基础上,对VPN在数字资源使用中面临的问题及其分布式共享的应用方式进行了研究,并结合实际的一些应用,阐述了VPN在校园数字资源分布式共享应用中的可行性,同时对应用过程中可能遇到的问题进行了探讨.     

叙词表、分类法与分布式本体

本文分析叙词表、分类法与分布式本体概念的内涵与外延及各自的属性，探讨了三者相互关系，在此基础上提出了建立基于叙词表、分类法与分布式本体模型的设想。这种分布式本体是在语义和知识层次上描述信息系统的概念模型建模工具。通过对这种分布式本体的机理与实现方法的分析与总结得出结论：基于叙词表、分类法构建的分布式本体是在分布异构的网络环境下探索知识发现、知识组织、知识检索、知识服务的有效途径，是智能网络服务的必然归宿。     

分布式计算中的中间件研究

首先阐述了中间件的重要性及其概念，然后介绍了三种主流中间件技术，并对这三种中间件技术做了比较和分析，最后探讨了下一代中间件技术。     

Using query logs to establish vocabularies in distributed information retrieval

Users of search engines express their needs as queries, typically consisting of a small number of terms. The resulting search engine query logs are valuable resources that can be used to predict how people interact with the search system. In this paper, we introduce two novel applications of query logs, in the context of distributed information retrieval. First, we use query log terms to guide sampling from uncooperative distributed collections. We show that while our sampling strategy is at least as efficient as current methods, it consistently performs better. Second, we propose and evaluate a pruning strategy that uses query log information to eliminate terms. Our experiments show that our proposed pruning method maintains the accuracy achieved by complete indexes, while decreasing the index size by up to 60%. While such pruning may not always be desirable in practice, it provides a useful benchmark against which other pruning strategies can be measured.     

分布式计算机联锁系统安全信息传输网络研究

以分布式车站信号计算机联锁控制系统为研究背景，根据分布式计算机联锁控制系统苛求相关数据安全、可靠传输的技术需求，设计了一种基于光纤的安全信息传输局域网，并给出了光纤局域网各节点的硬件及软件的设计方案，最后，以单模光纤为传输介质采用GAN通信构建了分布式双环冗余控制网络。     

Emergent innovation systems and the delivery of clinical services: The case of intra-ocular lenses

This paper is an exploration of the dynamics of technical change in medicine. We argue that innovation in medicine is a process that is distributed across time, space and epistemic and institutional domains; that it entails the entrepreneurial effort of creative individuals as well as the emergence of correlated understanding among heterogeneous agents whose rules of interaction are contingently instituted in socio-economic systems along unfolding scientific and technological trajectories. We illustrate our arguments through an in-depth analysis of a major ophthalmologic innovation - the intra-ocular lens - that has literally transformed the treatment of cataract in the developed world and has the potential to do so in many developing countries. We investigate the advancement of clinical knowledge about the disease, the development of effective technological capabilities and the co-evolution of the supply capacity and demand of a micro-innovation system emerged along a specific sequence of interrelated problems, and associated solutions, which engaged scientists, technicians, practitioners, regulators and patients alike over a period of around three decades.