A model for evaluation and administration of security inobject-oriented databases

The integration of object-oriented programming concepts with databases is one of the most significant advances in the evolution of database systems. Many aspects of such a combination have been studied, but there are few models to provide security for this richly structured information. We develop an authorization model for object-oriented databases. This model consists of a set of policies, a structure for authorization rules, and algorithms to evaluate access requests against the authorization rules. User access policies are based on the concept of inherited authorization applied along the class structure hierarchy. We propose also a set of administrative policies that allow the control of user access and its decentralization. Finally, we study the effect of class structuring changes on authorization     

环境保护地理信息系统的设计

本文主要介绍基于计算机网络的通用型环境保护地理信息系统的功能和实现方法。     

Acetylcholinesterase enhances neurite growth and synapse development through alternative contributions of its hydrolytic capacity, core protein, and variable C termini

Accumulated indirect evidence suggests nerve growth-promoting activities for acetylcholinesterase (AChE). To determine unequivocally whether such activities exist, whether they are related to the capacities of this enzyme to hydrolyze acetylcholine and enhance synapse development, and whether they are associated with alternative splicing variants of AChEmRNA, we used four recombinant human AChEDNA vectors. When Xenopus laevis embryos were injected with a vector expressing the synapse-characteristic human AChE-E6, which contains the exon 6-encoded C terminus, cultured spinal neurons expressing this enzyme grew threefold faster than co-cultured control neurons. Similar enhancement occurred in neurons expressing an insertion-inactivated human AChE-E6-IN protein, containing the same C terminus, and displaying indistinguishable immunochemical and electrophoretic migration properties from AChE-E6, but incapable of hydrolyzing acetylcholine. In contrast, the nonsynaptic secretory human AChE-I4, which contains the pseudointron 4-derived C terminus, did not affect neurite growth. Moreover, no growth promotion occurred in neurons expressing the catalytically active C-terminally truncated human AChE-E4, demonstrating a dominant role for the E6-derived C terminus in neurite extension. Also, AChE-E6 was the only active enzyme variant to be associated with Xenopus membranes. However, postsynaptic length measurements demonstrated that both AChE-E6 and AChE-E4 enhanced the development of neuromuscular junctions in vivo, unlike the catalytically inert AChE-E6-IN and the nonsynaptic AChE-I4. These findings demonstrate an evolutionarily conserved synaptogenic activity for AChE that depends on its hydrolytic capacity but not on its membrane association. Moreover, this synaptogenic effect differs from the growth-promoting activity of AChE, which is unrelated to its hydrolytic capacity yet depends on its exon 6-mediated membrane association.     

广东省伴生放射性矿资源利用过程辐射水平调查

为加强伴生放射性矿物资源开发利过程中放射性环境管理 ,防治放射性污染 ,对广东省几个大型伴生矿(包括稀土矿、钽铌矿和铅锌矿 )资源利用 (开采、冶炼、加工 )过程中天然放射性核素的污染现状进行了调查。调查结果表明 :稀土矿中独居石 ,天然放射性核素含量最高 ,2 3 8U、2 3 2 Th、2 2 6Ra的含量分别为 3.5 1× 1 0 4、1 .74× 1 0 5、4 .8×1 0 4Bq/kg,其冶炼废渣中核素的含量分别为 5 .1 0× 1 0 5、6 .38× 1 0 6、1 .5 2× 1 0 6Bq/kg。稀土选冶厂周围陆地环境 γ射线的空气吸收剂量率比一般地区的高。     

连续小波变换在多元函数空问中的应用

使用连续小波变换讨论了某些偏微分方程和相应的积分方程之间的关系．使用连续小波变换能够将这些偏微分方程变换成相应的积分方程，这些偏微分方程与相应的积分方程不仅在弱收敛意义下是等价的，而且在范数收敛意义下也是等价的．     

准噶尔盆地侏罗系储集层的基本特征及其主控因素分析

从描述储集层基本特征、分析储集层性质的主控因素、建立储集层成因模式和评价、预测储集层性质这 4个层次 ,研究准噶尔盆地重点勘探目标区的侏罗系储集层。系统总结侏罗系储集层岩石学特征 ,认为成岩压实作用强弱是控制储集层性质的关键因素 ;指出相对优质储集层均为剩余原生粒间孔隙型储集层 ,溶蚀作用对渗透率贡献小 ;非煤系储集层的孔隙保存条件明显比煤系储集层好 ,这是三工河组、头屯河组和吐谷鲁群的物性普遍优于八道湾组和西山窑组的原因。在确定储集层性质的控制因素和控制机理基础上 ,建立了煤系和非煤系两大类储集层的成因 演化模型。在上述研究的基础上 ,分地区、分层位评价了储集层 ,并预测了不同渗透率储集层的深度界线及相对优质储集层的平面分布。图 6参 10     

无线Internet接入技术及其发展现状

无线Internet接入是无线通信技术Internet结合的产物，本首先介绍了在线Internet接入的优势，然后详细列举了目前主要的无线Internet接入技术，并给出了应用特点。最后讨论了无线Internet接入的发展现状和存在的主要问题。     

大亚湾核电站18个月换料对流体系统的影响分析和论证

分析了大亚湾核电站18个月换料对流体系统可能产生的影响，根据改进后的燃料管理策略以及相关参数变化，遵照系统设计准则的要求。对14个流体系统的容量和能力进行了计算和论证。论证结果表明，大亚湾核电站现有系统基本满足18个月换料的需求     

On the interaction impedance of the coupled cavity structure

The formula and program for calculating the total and negative first harmonic interaction impedance from the data of “large perturbation measurement” are given. This program is a part of the programs for CCTWT design.     

基于一种特定混沌映射的跳频序列

使用一种简单的分段线性映射构造混沌跳频序列。用于跳频通信中取代传统的伪随机序列（PN序列），分析了此混沌序列的周期性。平衡性，汉明相关特性和线性间隔，最后给出了混沌序列的神经网络实现。仿真和实验结果表明，此序列具有较好的统计特性。应用于跳频多址通信中，可获得较好的抗干扰。抗截获能力。