角调谐飞秒同步泵浦KTP红外光参量振荡器

用平均输出功率为１．１Ｗ，脉宽为９０ｆｓ的商用再生锁模Ｔｉ：Ｓａｐｐｈｉｒｅ激光器作为泵浦源，用ＫＴＰ作为非线性光学介质，制成一台同步泵浦飞秒光学参量振荡器。其输出调谐范围为１．０４μｍ至１．２６μｍ，平均输出功率在１００ｍｗ左右，脉宽仅约１００ｆｓ。     

基于空间分布描述符的SIFT误匹配校正方法

针对SIFT（scale invariant feature transform）特征描述符因仅利用特征点的局部邻域信息而对散落在图像内相似结构中的点极易发生误匹配的现象,提出了一种基于空间分布描述符的SIFT误匹配校正方法。该方法首先利用SIFT算法进行匹配;然后对于匹配结果中的特征点,再利用图像轮廓像素点对该点的空间分布信息进行重新描述,以形成一种独特性更高的空间分布描述符;最后运用此种描述符,对匹配结果中存在的“一对多”和“一对一”的错误匹配形式,分别采取两种不同的匹配策略进行校正。以真实图像进行的实验结果表明,该方法与RANSAC（随机抽样一致性)算法相比,其在不损失正确匹配的前提下,能够真正提高正确匹配率。     

A novel three-tiered visualization approach for firewall rule validation

Firewall is one of the most critical elements of the current Internet, which can protect the entire network against attacks and threats. While configuring the firewalls, rule configuration has to conform to, or say be consistent with, the demands of the network security policies such that the network security would not be flawed. For the security consistency, firewall rule editing, ordering, and distribution must be done very carefully on each of the cooperative firewalls, especially in a large-scale and multifirewall-equipped network. Nevertheless, a network operator is prone to incorrectly configure the firewalls because there are typically thousands or hundreds of filtering/admission rules (i.e., rules in the Access Control List file, or ACL for short), which could be set up in a firewall; not mentioning these rules among firewalls affect mutually and can make the matter worse. Under this situation, the network operator would hardly know his/her misconfiguration until the network functions beyond the expectation. For this reason, our work is to build a visualized validation system for facilitating the check of security consistency between the rule configuration of firewalls and the demands of network security policies. To do so, the developed validation system utilizes a three-tiered visualization hierarchy along with different compound viewpoints to provide users with a complete picture of firewalls and relationships among them for error debugging and anomaly removal. In addition, in this paper, we also enumerate the source of security inconsistency while setting ACLs and make use of it as a basis of the design of our visualization model. Currently, part of the firewall configuration of our campus network has been used as our system's input to demonstrate our system's implementation.     

Efficient algorithm for mismatching point elimination with interzone limited pre-testing

The elimination of mismatching point is a key step in image mosaic. To speed up the mismatching point elimination in image matching, an efficient algorithm for mismatching point elimination is presented. Based on the RANSAC(random sample consensus) algorithm, the algorithm aims at the feature of the image sequence. First, the match points are sorted, divided into three parts and piecewise picked randomly to estimate the transforming matrix. Second, the matrix is cursorily checked with a novel interzone limited pre-test model, a further check is executed on the matrix that passes the pre-testing to get inliers. Finally, the least-square method is used to the inliers to get the real matrix. Experimental results suggest that the proposed algorithm is of lower complexity, higher accuracy and stableness especially in cruel conditions, which meets the demand of image sequence mosaic well.     

非均质焊接接头裂纹尖端场的HRR主导性与J积分断裂判据

采用反射式贴片云纹干涉法对焊接接头裂纹尖端位移场了测量,并考察了非均质焊接接头中的ＨＲＲ主导有效性与Ｊ积分断裂判据的应用可行性,结果表明,至少对于本文所研究的情形而言,无论是Ａ５３７钢采用ＬＢ５２ＮＳ焊条施焊的高匹配接头,还是９％Ｎｉ钢,采用ＯＫ６９．４５焊条施焊的低匹配接头,横向位移场中ＨＲＲ主导失效,而纵向位移场中ｌｇｖ－ｌｇｒ的线性关系不同于焊缝或母绪的１／（ｎ＋１）。因此,在非均质焊接接头     

HgCdTe／CdZnTe晶格失配与X光衍射貌相的关系研究

文章采用富Te水平推舟液相外延工艺在CdZnTe衬底上生长了HgCdTe外延薄膜。研究了外延薄膜／衬底晶格失配度、X光衍射貌相、红外焦平面器件探测率三者之间的关系。对于HgCdTe外延层的X光衍射貌相我们将其大致分为五类，分别是Crosshatch貌相、混合貌相、均匀背景貌相、Mosaic貌相以及由衬底质量问题引起的沟壑状貌相，采用Crosshatch貌相和混合貌相材料所制备的红外焦平面器件，平均来说其探测率(D*)较高。X射线双轴衍射的实验结果表明，当外延层与衬底的晶格失配度为～0.03％时，外延层会呈现明显的Crosshatch貌相；而当失配度减小时，会逐渐呈现出混合貌相、均匀背景貌相、直至失配度为负值时呈现Mosaic貌相。因此，对于特定截止波长的HgCdTe焦平面器件，可以通过控制HgCdTe／CdZnTe之间的失配，生长出符合我们要求的貌相的碲镉汞外延材料，从而来提高焦平面器件的性能。     

基于兴趣分组和物理拓扑的P2P网络模型

随着P2P网络规模和用户量的增加,P2P环境下的信忠量也随之飞速增长,给用户在搜索、定位和获取信息资源上都带来了巨大的困难.以全分布式非结构化拓扑结构为基础,采用Gnutella协议,提出了一种全新的P2P网络优化模型——NIP2P.NIP2P是将兴趣分组和物理位置相结合的P2P模型,可以提高搜索效率,缩短搜索路径,减...     

Assessment of conservative load transfer for fluid–solid interface with non‐matching meshes

We present a detailed comparative study of three conservative schemes used to transfer interface loads in fluid–solid interaction simulations involving non‐matching meshes. The three load transfer schemes investigated are the node‐projection scheme, the quadrature‐projection scheme and the common‐refinement based scheme. The accuracy associated with these schemes is assessed with the aid of 2‐D fluid–solid interaction problems of increasing complexity. This includes a static load transfer and three transient problems, namely, elastic piston, superseismic shock and flexible inhibitor involving large deformations. We show how the load transfer schemes may affect the accuracy of the solutions along the fluid–solid interface and in the fluid and solid domains. We introduce a grid mismatching function which correlates well with the errors of the traditional load transfer schemes. We also compare the computational costs of these load transfer schemes. Copyright © 2005 John Wiley & Sons, Ltd.     

同向泵浦拉曼放大器中泵浦-信号间四波混频研究

研究了同向泵浦分布式拉曼放大器(DRA)中泵浦-信号间的四波混频(FWM)效应.基于分段求和法,导出了不同零色散波长光纤组成的前向泵浦DRA中FWM功率的计算公式.考虑受激拉曼放大的情况下,数值模拟了DRA中FWM引起的信道串扰随光纤传输距离的演变,以及FWM与光纤零色散波长之间的关系.理论分析了色散补偿光纤(DCF)对FWM串扰的抑制效应.计算结果表明,在采用非零色散位移光纤(NZDSF)作为传输介质的DRA中,泵浦-信号间存在着较强的FWM效应,严重影响了密集波分复用(DWDM)系统的传输性能.引入适量DCF,不仅能降低DRA中FWM引起的信道串扰,还可有效消除色散导致的波形失真.     

应用于HVDC系统的高频模块化直流变压器匹配移相控制策略

高频模块化直流变压器(HMDCT)是构建直流电网的核心设备。HMDCT在传统移相(TPS)控制下的高频交流不匹配工作状态会带来较大的高频电流应力与回流功率,降低了HMDCT的传输效率,因此解决该技术瓶颈成为进一步促进HMDCT在直流电网中应用的关键。鉴于此,提出了一种基于桥臂子模块动态投切技术的HMDCT交流链匹配移相(MPS)控制策略。由分析及实验结果可知,当采用交流链MPS控制策略时,不论HMDCT两端的直流电压变比如何,HMDCT的交流链电压均能够保持在匹配工作状态;且在传输功率相同时,相比于TPS控制,交流链MPS控制具有更小的回流功率及更高的效率。通过样机实验对理论分析的正确性与有效性进行了验证。