代理证券的有效度研究

在完美的市场假设下，经典的资本资产定价模型证明了，证券期望收益率R与β因子存在精确线性关系．而现实中，代理证券的有效边界与市场的有效边界是不一致的．在不引入无风险资产的条件下，本文根据证券组合协方差矩阵的正定性质和证券组合风险函数的凸性，证明了代理证券的有效度与代理证券包含的证券数目存在正向的比例关系．     

基于MIH的增强PMIPv6域间切换方法

针对现有PMIPv6域间切换出现时延较大的问题,基于PMIPv6域内切换和域间切换以及介质独立切换的特性提出一种基于IEEE 802.21 MIH标准的增强型PMIPv6域间切换方法。方法通过L2的方法提前告知移动节点切换目标网络的方法代替L3的网络扫描将切换决策和执行时间点提前，增强网络的无缝切换，性能分析结果表明该增强技术能够减少整个网络时延和丢包率，改善了网络性能。     

伊朗中部伊斯法罕地区土地利用对石灰性土壤磁性质和重金属的空间分布的影响

Anthropogenic activities have caused the accumulation of heavy metals in the soil environment. Pollution of the soils significantly reduces environmental quality and affects human health. In many recent studies, magnetic susceptibility measurements have been used for pollution monitoring. The objective of this research was to determine the spatial variability of magnetic properties and selected heavy metals and the effects of land use on their variability in the surface soils of the Isfahan region, Central Iran. A total of 158 composite surface (0-5 cm) samples of calcareous soils were collected from an area of about 700 km2, located along a cross-border transect from Isfahan City to a steel plant, covering urban, industrial, agricultural and uncultivated land uses. Concentrations of copper (Cu), zinc (Zn), lead (Pb), manganese (Mn), iron (Fe), nickel (Ni), chromium (Cr), and cobalt (Co) and magnetic parameters, magnetic susceptibility at low frequency (χlf), natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM), and isothermal remanent magnetization at the field of 100 mT (IRM100mT) and the backfield of 100 mT (IRM-100mT), were measured in all the soil samples. Results showed that magnetic susceptibility in the urban and industrial land topsoils (0--5 cm) samples was significantly higher than that in the agricultural and uncultivated land soils in the study area. Concentrations of Cu, Zn, Pb, Mn, and Fe were positively correlated with magnetic properties (χlf, IRM100mT, SIRM, IRM-100mT, and NRM), which could be attributed to their inputs from traffic emissions and industrial activities at the study sites. Ni and Cr concentrations showed significant negative correlations with magnetic properties. No significant correlation was found between Co concentration and magnetic parameters. The Tomlinson pollution load index (PLI) showed significant correlation with the magnetic properties (χlf, IRM100mT, SIRM, IRM-100mT, and NRM). The spatial distribution of the selected heavy metals and χlf in the study area suggested that activities at the urban and industrial land sites caused greater pollution as compared to that at the study sites of other land uses. The concentrations of Cu and Zn seemed to have been affected by anthropogenic sources, whereas Ni, Cr, and Co were mainly controlled by natural sources in the study area. Moreover, the concentrations of soil Pb and Fe in the study area could be affected by both lithologic and anthropogenic sources. The magnetic parameters appeared to be a proxy measure for the degree of heavy metal contamination and could be a potential method for the detection and mapping of contaminated soils.     

混沌加密技术与数字图书馆版权保护

混沌加密技术作为一种新型加密技术,已广泛应用于诸多领域.本文介绍了混沌技术的起源、定义、特点及发展,并对混沌加密技术在数字图书馆版权保护中的应用进行了探讨.     

信息安全的核心--加密算法的研究

本文讨论了有关信息安全的核心问题好加密算法。首先,介绍美国ＮＩＳＴ公布的１５个ＡＥＳ候选算法,由此可见国际分组密友发展的潮流和趋势。其次,我们重点讨论其中的一个候选算法即ＣＡＳＴ－２５６算法。     

TWS网络计费系统

TWS网络计费系统是在笔者动手搭建的WINDOWS NT平台上,结合MICROSOFT中的 S(INTERNET INFORMATION SERVER),采用CLIENT/SERVER双层结构模式开发出来的.逻辑上分为客户和后端服务器两个部分,客户部分安装于客户端,可实现客户网费实时查询和留言等功能;后端服务器内建二个管理员帐号,可用来进行日常维护(如增加、删除管理员;查看用户信息等)和特殊处理(如月终处理和关闭、启用违例用户等).整套系统可用于使用代理服务器的任何局域网或广域网上.     

An algorithm of image processing based on discrete wavelet transform compression and chaotic scrambling

An algorithm was proposed in view of the combination of image compression and encryption. We got the approximate part and three detail parts after transforming the image with discrete wavelet transform (DWT), and compressed the image by modifying the detail parts by a given threshold value based on human visual systems. And then, we encrypted the image by scrambling the approximate part because this part held mostly of the energy. Last, a compressed and encrypted image can be achieved after DWT. Simulation result shows a good effect on the combination of compression and encryption.     

基于J2EE的农机社会化服务系统安全问题研究

研究了基于J2EE的Spring框架的MVC架构下农机社会化服务系统的实现,及在J2EE模型下,该应用系统存在的各种安全问题,如身份认证、访问控制、数据传输安全及J2EE部分组件安全问题等。针对这些安全问题,结合J2EE安全机制,提出了SSL安全代理服务器、基于EJB方法的访问控制、使用单点登录方法等相应的解决措施。     

流媒体加密技术研究

从传统密码技术入手，在结合流式样体的特征基础上对其加密／解密机制进行了深入的研究，分析加密方法满足漉媒体实时性应考虑的因素。推导出只有实现了“解密速度〉[数据包长／（该帧的指定解码时间一该帧最后散据包的到达时间）]”的加密算法才能够满足MPEG-1数据漉实时加密的要求．目的是将传统的密码技术与新兴的漉媒体技术相结合，实现多媒体散据的实时加密保护。     

降雪量加密观测资料在短时临近预报中的运用

利用降雪量加密观测资料,运用外推法,有效地提高了暴雪预警信号的发布时效;同时为暴雪预警信号的质量考核提供重要依据。本文还利用降雪量加密观测资料,结合暴雪预警信号的发布指标,分析、归纳出启动、解除降雪量加密观测指标。结合天趋势即可发布暴雪红色预警;反之,即可解除暴雪红色预警。