In recent years, the repeat-pass GBSAR (ground based synthetic aperture radar) system has demonstrated its capacity to acquire deformation. Nevertheless, in a variety of applications, it needs to measure the deformation with the precision up to 0.1 mm, which could not be reached by utilizing the traditional PS (permanent scatterer) algorithm in most cases. Generally, one of the main reasons could be summarized into the phase error caused by the rail determination error, because the precision of rail determination might degrade during long working hours. However, the traditional PS algorithm could not compensate for the phase error caused by the rail determination error. In order to solve the problems, we modify the conventional PS algorithm. Firstly, we deduced the transformation relationship between the rail determination error and its corresponding interferometric phase error. Then, the phase errors caused by the atmosphere and the rail determination error were jointly compensated. The experimental data, which were obtained in Fangshan District in Beijing (China), were used to test and verify the performance of the new algorithm. After the comparison between the results processed by the new algorithm and those processed by the traditional algorithm, the proposed method demonstrated its ability to obtain high-precision deformation. 相似文献
DoS攻击是威胁IPv4网络安全的重要问题之一.随着IPv6的发展,相关安全问题也逐步体现并影响IPv6网络的正常运行.该文指出利用IPv6和隧道主机的多地址性,攻击者可获得大量合法IPv6地址,通过伪装成多个虚拟主机实施对目标设备的DoS攻击.这种攻击具有大量的可用地址范围,且受控于同一真实主机,通过不断使用新地址和多地址间配合,可避开以IP为单位的传统检测与防御策略,并可有效放大攻击节点数目或减少实际攻击节点数量.为此提出了基于地址特征分类的防御框架(defense framework based on addresses classification,DFAC).通过分类不同地址特征,构造特征子集,在特征子集基础上实施对虚拟主机攻击的检测和防御,解决虚拟主机引发的放大问题.原型系统实验结果表明,DFAC有效地降低了上述DoS攻击对系统负载的影响. 相似文献
This paper presents the recent process in a long-term research project,called National Knowledge Infrastructure(or NKI).Initiated in the early 2000,the project aims to develop a multi-domain shareable knowledge base for knowledge-intensive applications.To develop NKI,we have used domain-specific ontologies as a solid basis,and have built more than 600 ontologies.Using these ontologies and our knowledge acquisition methods,we have extracted about 1.1 millions of domain assertions.For users to access our NKI knowledge,we have developed a uniform multi-modal human-knowledge interface.We have also implemented a knowledge application programming interface for various applications to share the NKI knowledge. 相似文献
To prevent the same known vulnerabilities from affecting different firmware, searching known vulnerabilities in binary firmware across different architectures is crucial. Because the accuracy of existing cross-architecture vulnerability search methods is not high, we propose a staged approach based on support vector machine (SVM) and attributed control flow graph (ACFG) at the function level to improve the accuracy using prior knowledge. Furthermore, for efficiency, we utilize the k-nearest neighbor (kNN) algorithm to prune and SVM to refine in the function prefilter stage. Although the accuracy of the proposed method using kNN-SVM approach is slightly lower than the accuracy of the method using only SVM, its efficiency is significantly enhanced. We have implemented our approach CVSkSA to search several vulnerabilities in real-world firmware images. The experimental results show that the accuracy of the proposed method using kNN-SVM approach is close to the accuracy of the method using only SVM in most cases, while the former is approximately four times faster than the latter.