Nd2-xCexCuO4-δ晶体的生长及性质

为了从电子型超导体的角度探求高温超导体的机理,采用自助熔剂缓冷法成功地生长出了高质量的Nd2-xCexCuO4-δ单晶,并由X射线衍射和扫描电镜证明了晶体是高质量的单晶.用物性测量仪在0～9 T范围内分别测量了磁场平行和垂直样品表面的电阻转变曲线.结果显示,样品零场下零电阻转变温度约为21 K,在80～150 K范围,电阻随温度的变化关系可以用幂指数关系R(T)～T2来描述,但是在低温区表现出N型反常行为.在起始转变温度以下有一个很大的电阻突起峰,且受到磁场的抑制.晶体表现为类重费米子系统性质.样品特征温度为23.1 K.     

切换机制下的宽带码多分址系统接纳控制方法

为了使功率控制系统在接近满负荷运转时能够满足切换呼叫所要求的带宽,以增加整体呼叫接纳概率,提出了基于切换降级的接纳控制方法.切换呼叫和新呼叫共享系统信道,当系统无空闲信道时,新呼叫被阻塞而切换呼叫则可进行降级处理.仿真结果证明:加入降级机制的方法可增加切换用户数,也提高了系统在线用户量,降低了呼叫阻塞概率.     

Trust calculation and delivery control in trust-based access control

Trust management system has been a promising approach to solve the access control problems in open multi-domain environments. However, the calculation of trust and the delivery of the trust are not addressed effectively in the existing trust management systems. To address the problems, this paper proposes a scheme of trust calculation and delivery control. Compared with the other schemes, it is simpler and more flexible, and also easier to be implemented.     

Exploration of energy conservation MAC protocol of WSNs for ubiquitous environment

According to analyze the facade phenomenon of wire-less sensor networks（WSNs）,this paper proposes a feasible method to state clearly and improve the power control efficiency of wire-less sensor networks（WSNs）. One of the crucial problems for WSNs is the design of medium access control （MAC） protocol. Our method want to adjust the activities of the MAC protocols control to achieve the enery conservation when the wireless communication module of sensor nodes is running, which is the major consumer of energy consumed by sensors energy. The energy efficiency of MAC protocol makes a strong impact on the network performance. To some extent,our research work describes and analyze the sources of energy consumption in MAC layer and simultaneously present an optimal method for the design of MAC protocol. Then we discusses some factors impacting on the performance of MAC protocol and metrics of performance evaluation. Eventually, the coming research direction is summarized.     

General attribute based RBAC model for web services

Growing numbers of users and many access policies that involve many different resource attributes in service-oriented environments cause various problems in protecting resource. This paper analyzes the relationships of resource attributes to user attributes based on access policies for Web services, and proposes a general attribute based role-based access control（GARBAC） model. The model introduces the notions of single attribute expression, composite attribute expression, and composition permission, defines a set of elements and relations among its elements and makes a set of rules, assigns roles to user by inputing user＇s attributes values. The model is a general access control model, can support more granularity resource information and rich access control policies, also can be used to wider application for services. The paper also describes how to use the GARBAC model in Web services environments.     

基于关联规则的Web使用挖掘系统

通过分析Web日志记录来发现用户访问行为等,进而识别电子商务中的潜在客户,提高网络信息服务的质量,优化站点结构以及得到对于个性化系统有用的信息.提出一个Web使用挖掘系统的设计方案,包括系统的体系结构、功能结构及每个功能点的详细设计.为Web使用系统开发人员提供有价值的参考信息.     

高校机构知识库建设的影响因素分析

随着国际开放存取运动的兴起和机构知识库建设的展开,我国高校也开始逐步建设自己的机构知识库。在对机构知识库分析的基础上,探讨了其在我国高校信息资源建设中的作用,并通过其中关键因素的分析,讨论了高校机构知识库建设的可行性。     

基于LMDS的小区宽带无线接入网方案设计

针对目前应用于住宅小区中的几种宽带接入技术的不足及为了解决因接入网宽带不足而出现的网络"瓶颈"问题,介绍了近年来受到国内外电信业务经营者普遍重视的一种新兴的宽带无线接入技术--LMDS.对基于LMDS技术的住宅小区宽带无线接入网络进行了设计.该系统可用频带宽,支持话音、数据、图象等双项通信业务,无须架设线路,具有建设速度快、初期投资小、系统扩展性好、受环境制约小、又能满足住宅用户对快速业务的需求.可以预见,LMDS将逐渐成为用于高速多媒体应用的最佳网络接入方案.     

总线LAN状态概率与状态转移概率

对于ＣＳＭＡ／ＣＤ方式和终端设置单缓冲器的总线ＬＡＮ,进行状态分析与系统建模,给出平稳状态下的一种简便计算方法,获得时间离散系统各种基本状态的概率和不同状态相互转移的概率．     

M进制混合DS-SFH CDMA信号在多径随机衰落信道中的性能分析

研究了随机Ｍ进制正交码混合ＤＳＳＦＨ扩频码分多址信号经过多径随机衰落信道,在非相干ＲＡＫＥ接收机中采用等增益组合分集接收时系统的性能．给出了差错概率表示式,并且给出了差错概率的近似计算方法．和以往分析方法不同的是,在计算中只需知道多径衰落功率的一阶、二阶矩,而不需要知道确切的衰落分布．讨论了分集数、Ｍ值、多径衰落、多用户干扰等对系统性能的影响,并进行了数值计算与分析．