Primitive recursive selection functions for existential assertions over abstract algebras

We generalize to abstract many-sorted algebras the classical proof-theoretic result due to Parsons, Mints and Takeuti that an assertion (where P is ), provable in Peano arithmetic with induction, has a primitive recursive selection function. This involves a corresponding generalization to such algebras of the notion of primitive recursiveness. The main difficulty encountered in carrying out this generalization turns out to be the fact that equality over these algebras may not be computable, and hence atomic formulas in their signatures may not be decidable. The solution given here is to develop an appropriate concept of realizability of existential assertions over such algebras, generalized to realizability of sequents of existential assertions. In this way, the results can be seen to hold for classical proof systems.This investigation may give some insight into the relationship between specifiability and computability for data types such as the reals, where the atomic formulas, i.e., equations between terms of type real, are not computable.     

Web应用中的攻击防御技术的研究与实现

该文介绍了SQL注入式攻击、XSS跨站脚本攻击、会话劫持3种网络攻击手段的原理,并在此基础上重点论述了如何防范这些攻击的方法。     

s-HITSc: an improved model and algorithm for topic distillation on the Web

Topic distillation on the Web, namely, finding quality information sources related to a given query topic with hyperlink analysis, has been shown to be useful in Web IR. Based on the analysis of three deficiencies of classical topic distillation algorithm HITS, this paper presents an improved model and algorithm named s-HITSc. Given a query topic, the improved algorithm can model a neighborhood graph at site granularity, compute the relevance weights of the nodes to the topic with content analysis, and apply weighted I/O operations in its iterative hyperlink analysis. Theoretical analysis and experimental results show that s-HITSc can control topic drift and identify more reasonable and meaningful authority and hub sites on a given topic.

Web文本特征选择算法的研究

以向量空间模型作为Web文本的表示方法,结合Web文本的结构特征对向量空间模型中的特征选择算法进行了分析并加以改进。在改进的算法中,体现出了特征词在Web文档结构中的位置信息;引入了信息论中熵的概念,用词的熵函数对权值进行调整,从而更加准确地选取有效的特征词。实验验证了改进算法的可行性和有效性。     

湿法磷酸生产中合金材料的合理选用

根据材质的价位与寿命以及磷酸生产厂家使用情况的统计 ,并结合我厂使用的结果 ,应合理分类与合理选用合金材料。萃取槽搅拌桨、料浆泵过流部件选用Cr30。滤洗液泵、磷酸泵、轴流泵等过流部件选用CD - 4MCu。而 941在常温下耐各种浓度的硫酸 ,并具有较好的焊接性能 ,故硫酸泵过流部件用材选择 941。     

GPS-RTK技术在石油天然气井位测量中的应用

定位技术是GPS测量技术发展的一个新突破。基于GPS-RTK测量技术的基本原理和优点,GPS-RTK技术在石油天然气井位测量领域得以应用。井位测量包括初测和复测。测量精度取决于钻井目的。井位测量时应注意以下几点:①基准站应设在井位控制点上;②流动站和基准站之间不宜超过20km,二者之间不能有影响数据传输的障碍物;③GPS卫星高度角不宜小于15°;④GPS接收机100m之内无强大的电磁波辐射源。综合应用表明,GPS-RTK技术在油田井位测量中有布网方便、测量迅速、精度高等优点,不仅能满足井位测量工作的需要,而且适用于公路、铁路、长输管道、输电线路、干渠等线路工程测量,具有广泛的应用前景。     

苯加氢装置管道系统的材料选择

介绍了苯加氢装置管道系统的材料选择和注意事项。     

塑料模具材料选用原则及应用

对塑料模具材料的选用原则和新型模具材料进行了简要的介绍，在此基础上，以成型手机外壳塑料模具为例，对其关键零部件的选材应用进行了主要说明。     

基于QoS的网格服务选择优化机制

在网格服务发现和选择过程中，如何根据请求方（用户）对服务质量的需求，以及网格QoS的动态变化选择网格服务是一个重要问题。该文基于请求方（用户）对不同网格服务QoS赋予的权重不同以及容忍度不同，提出了网格服务选择算法，从而使得请求方（用户）获得的网格服务的性价比最高。