基于防水墙系统的信息安全与保密解决方案

一、引言防火墙、IDS、内外网隔离以及其它针对外部网络的访问控制系统,可有效防范来自网络外部的进攻,但对于企业内部的信息保密问题,却一直没有好的防范方法:内部人员可以轻松地将计算机中的机密信息通过网络、存储介质和打印等方式泄露出去,一旦这些敏感信息、重要数据、设计图纸等流失到敌对势力、竞争对手手中,将给国家、企、事业单位造成重大损失。特别是军工行业、政府机关、承担国家敏感课题的科研部门,涉及到更多的国家机密,对于涉密信息采取严密的防护措施更是显得尤为必要。目前,国家制定了很多相关规章制度,明确规定,这些企事…     

An empirical study on user access to entertainment streaming media

I. Introduction Streaming media has been widely used over the Internet in recent years. However, the growing use in streaming media, which generally has large size, can have a significant impact on the user perceived latency and network congestion. A popular approach to reduce the response time and backbone bandwidth consumption is to deploy proxy caches at the edge of the Internet. Due to the large size and different popularity for different part of the streaming video, it is not practical …     

Feasibility study of the application of voltage contrast to printed circuit board

Voltage contrast (VC) has been a powerful tool for the failure analysis of integrated circuits and multichip module. As the packing density of printed circuit board (PCB) is increasing, conventional failure analysis methods to detect open or short circuit in PCBs are no longer adequate, and voltage contrast method could be a method for this purpose. However, unlike the cases of integrated circuits and multichip module, there are many areas in PCB that will produce serious charging effect when examine under the scanning electron microscope. One of the areas is the presence of solder mask on PCB.This work examines the feasibility of using voltage contrast for PCB failure analysis. Specially designed PCB is used for experimentation, and it is found that positive bias on one track and zero bias on another copper track provide a better image contrast as compared to negative and zero biases on the tracks. Also, the variation of the image contrast with different spacing between inter copper tracks has studied. It is found that the variation depends on the presence of solder mask and its location. The variation can be very different for negative bias case as compared to the positive bias case.Finite element analysis is also performed to explain the experimental observations. All the observations can be well explained by the charging effect of the solder masks. The charging effect of solder mask is indeed very significant in affecting the image contrast, and it could reduce the contrast to almost zero in some cases.     

高压直流输电系统开路试验原理分析与工程建议

开路试验是高压直流输电工程投运前必做的一项基本试验。该实验中触发角与直流电压的关系具有特殊性。从换流阀电路模型入手,详细分析了在不带线路工况下换流阀的导通情况,推导出理想情况下直流电压与触发角的关系,并给出了理想电压公式的适用条件。使用三沪I回直流输电工程一次模型,在EMTDC中进行了不带线路和带线路工况下的开路试验,并对试验结果进行了详细的分析。分析和实验结果表明:带线路工况下,直流电压在触发角小于60o后到达额定值是正常的。开路试验保护中设置电压判据是不合理的,可只采用电流原理判据作为试验是否成功的依据。     

Effect of CuO Addition on Microwave Dielectric Properties of 0.80Sm(Mg0.5Ti0.5)O3-0.20Ca0.8Sr0.2TiO3 Ceramics

The effects of CuO addition on phase composition, microstructure, sintering behavior, and microwave dielectric properties of 0.80Sm(Mg_0.5Ti_0.5)O₃-0.20 Ca_0.8Sr_0.2TiO₃(8SMT-2CST) ceramics prepared by a conventional solid-state ceramic route have been studied. CuO addition shows no obvious influence on the phase of the 8SMT-2CST ceramics and all the samples exhibit pure perovskite structure. Appropriate CuO addition can effectively promote sintering and grain growth, and consequently improve the dielectric properties of the ceramics. The sintering temperature of the ceramics decreases by 50°C by adding 1.00 wt.%CuO. Superior microwave dielectric properties with a ε _r of 29.8, Q × f of 85,500 GHz, and τ _f of 2.4 ppm/°C are obtained for 1.00 wt.%CuO doped 8SMT-2CST ceramics sintered at 1500°C, which shows dense and uniform microstructure as well as well-developed grain growth.     

An innovative channel management strategy for highly reliable handoff in cellular networks

In this paper, we have resolved the problem of forced call termination that occurs when mobile traffic is concentrated on a hot‐spot cell in cellular networks. Enhanced Channel Management Scheme (ECMS) is an innovative way to increase the flexibility of channel usage over non‐uniform traffic distribution. ECMS exploits mobile hosts initiated or active in overlapping areas between cells. The scheme consists of three phases to monitor the status of channels on each base station and to make a channel reservation using the availability list maintained for the candidate‐MH selection. When the traffic load in a cell is intolerably high, ECMS invokes the load‐balancing procedure to distribute its traffic to adjacent cells. The reserved channels are used to support the safe and fast handoff. From the simulation, we observed that ECMS outperformed other compatible channel assignment schemes such as directed handoff schemes in blocking probability and channel utilization. Copyright © 2002 John Wiley & Sons, Ltd.     

Facilitation of Gene Transfection and Cell Adhesion by Gelatin‐Functionalized PCL Film Surfaces

Efficient local gene transfection on a tissue scaffold is of crucial importance in facilitating tissue repair and regeneration. In this work, the gelatin‐functionalized polycaprolactone (PCL) film surfaces are prepared via surface‐initiated atom transfer radical polymerization of glycidyl methacrylate. The resultant covalent attachment of gelatin could enhance the cell‐adhesion and local gene transfection properties. The gelatin‐functionalized PCL film surfaces exhibit excellent cell‐adhesion ability to both adherent and suspension cells. The attached adherent cells demonstrate the characteristic elongated morphologies with good spreading capability, while the attached suspension cells can maintain the original status of the round morphologies without spreading. More importantly, the gelatin coupled on the PCL surface could be used to absorb the cationic vector/plasmid deoxyribonucleic acid (pDNA) complexes via electrostatic interaction. The local gene transfection property on the immobilized cells is dependent on both the density of the immobilized cells and the loading types of pDNA complexes. The transfection efficiency of different assemble methods of pDNA complex was compared. With the pre‐ and post‐loading sandwich‐like gene transfection, the gelatin‐functionalized PCL film surface can substantially enhance the transfection properties to different cell lines. The present study is very useful to spatially control local gene delivery within PCL‐based tissue scaffolds.     

Theory of terminated monopole

The theory of a terminated folded monopole was previously studied by Josephson. The equivalent circuit used by that author was incorrect for a folded monopole when its arms are of different diameters. By using the decomposition scheme suggested by Uda and Mushiake we have solved the problem correctly. The circuit parameters involved in the theory are discussed in detail to supplement the work of Uda and Mushiake.     

Micro FET pressure sensor manufactured using CMOS-MEMS technique

The fabrication of a micro field effect transistor (FET) pressure sensor using the commercial 0.35 μm complementary metal oxide semiconductor (CMOS) process and a post-process has been investigated. The pressure sensor is composed of 16 sensing cells in parallel, and each sensing cell includes a suspended membrane and an NMOS. The suspended membrane is the movable gate of the NMOS. The pressure sensor needs a post-process to obtain the suspended membrane after the CMOS process. The post-process employs etchants to etch the sacrificial layers to release the suspended membrane, and then a low-pressure chemical vapor deposition (LPCVD) parylene is used to seal the etching holes in the pressure sensor. The pressure sensor produces a change in current when applying a pressure to the sensing cells. Experimental results show that the pressure sensor has a sensitivity of 0.022 μA/kPa in the pressure range of 0–500 kPa.