电线/电缆绝缘电阻测试方法比较

绝缘电阻是电线／电缆产品的重要指标之一。电线／电缆各芯间的绝缘电阻是否正常在某种程度上反映了电线／电缆产品是否工作正常。由于各种电线／电缆工作的环境不同,绝缘电阻阻值也不相同,因而对绝缘电阻测试方法的选择也应不同。给出了当前绝缘电阻测试的几种方法,分析了各种测试方法的原理和优缺点,比较了各种方法的优缺点及适用范围,最后得出了各种方法比较的一览表：     

晶粒尺寸对氧化锌非线性电阻片中温度和热应力的影响

微观温度分布不均匀将降低氧化锌(ZnO)非线性电阻片的冲击能量吸收能力. 采用二维Voronoi网络(Voronoi diagram)模型, 从微观角度分析了氧化锌非线性电阻片中的电流、温度和热应力的分布. 结果表明: 在击穿区(中电场区), 流经电阻片的电流集中于少数晶粒连结而成的通道, 导致电阻片吸收冲击能量时内部能量吸收不均匀, 引起局部高温和很大的热应力, 造成电阻片发生穿孔或破裂损坏. 另外讨论了晶粒尺寸对氧化锌非线性电阻片内部温度和热应力的影响.     

纳米Ta基阻挡层薄膜及其扩散体系电阻特性研究

采用直流磁控溅射方法在p型（100）Si衬底上制备了3类Ta基纳米阻挡层薄膜及其对应的Cu／barrier／Si复合膜,并对薄膜样品进行了卤钨灯快速热退火（RTA）．用四探针电阻测试仪（FPP）,AFM,SEM-EDS,Alpha—step IQ台阶仪和XRD等分析测试方法对样品快速热退火前后的电阻特性和形貌结构进行了分析表征．实验结果表明,热处理过程中,凝聚、氧化和稳态效应同时出现,方块电阻的增大和下降趋势并存;而高温退火后Cu和Si发生互扩散形成的高阻相Cu3Si与更粗糙的表面形貌引起更强烈的电子散射导致了复合膜系方块电阻的急剧增加．     

最少变量数边界元提取三维VLSI互连电感与电阻

为得到高频复杂结构三维互连电感与电阻需求解电磁场涡流问题. 提出一种三维涡流计算模型, 在导体与无限大自由空间中利用矢量磁位表示其中的电磁场, 得到间接边界积分方程, 并利用边界元离散化技术进行求解. 这种方法避免对导体体积区域进行离散; 作为一种间接边界元方法, 它具有最少的变量数; 由于不对导体中的电流方向进行限制, 可以计算互相垂直导体之间的互电感和互电阻. 数值计算结果利用2-D解析解进行了验证; 计算了互相垂直导体在不同频率和间距下的互电感和互电阻.     

非晶态合金晶化过程的高精度电阻监测研究

发展了一种高精度四线交流电阻测试设备，原位监测Ｎｉ８０Ｐ２０，ＦｅＺｒ２和Ｆｅ８６Ｂ１４非晶合金的晶化动力学过程。结果表明这种方法可以发现非晶合金早期晶化过程，测试出的晶化温度范围明显宽于ＤＳＣ方法，能够更加灵敏地反映晶化过程的信息，这种方法还能够临别共晶型和多形型晶化中的形核和长大过程，而对于初晶型晶化过程电阻测试亦反映了初晶相的形核信息。     

基于二维Chirp-Z变换的前视FMCW雷达成像新方法

机载前视成像作为一种全新的成像雷达工作模式,与调频连续波技术的结合有着诸多的优势.本文以"一发多收"系统为研究对象,根据其成像几何模型给出了基于调频连续波的前视雷达回波信号表达式,利用双基等效单基原理,将回波信号等效为"自发自收"系统时的情况,同时分析了载机在发射信号和接收信号过程中连续运动带来的影响–产生多普勒频移,以及对其近似补偿方法.在此基础上,本文提出了一种针对调频连续波前视雷达成像的基于二维Chirp-Z变换变标的成像算法,给出了算法的完整推导过程和各补偿因子的表达式,整个算法只包含Fourier变换和复乘操作,不涉及插值,易于工程实现.最后仿真数据处理结果验证了本文分析的正确性和算法的有效性.     

自环流网络潮流跟踪算法

运用级数理论给出环流网络潮流跟踪算法. 计算中, 将网络环流等效为一个节点, 从而得到原网络的简化网络. 基于此, 运用图论求出发电机节点到负荷节点的有向路, 进而得到原环流网络的无穷多条有向路. 运用比例分摊原则、级数理论和网络节点间有向路便可得到发电机对负荷的功率分配. 给出了网络自环流系数的定义及其性质. 利用自环流系数的性质, 证明了算法的收敛性定理: 基于比例分摊原则的自环流网络潮流跟踪算法总是收敛的. 同时, 证明了算法的有效性定理: 基于比例分摊原则, 用有向路算法对无损的环流网络进行潮流跟踪时, 任意节点上发电机对所有负荷的贡献总额等于发电机的出力. 并用IEEE14节点系统和国内考核题型Ⅱ证实了该方法.     

基于DWT和DCT数字图像鲁棒水印算法

基于离散小波变换和离散余弦变换,利用混沌系统的优良特性,提出一种新的变换域水印算法.水印嵌入时,首先将宿主图像进行小波变换后选取中频区域,再进行DCT变换,根据水印图像大小进行分块嵌入水印算法在保证不可见性的前提下,最大程度的保证了水印算法的鲁棒性.仿真实验表明,算法在多种攻击下表现出良好的鲁棒性,具有一定的实用意义.     

W-Ti纳米晶薄膜扩散阻挡层的热稳定性研究

采用直流磁控溅射方法在p型(100)Si基体上制备了不同相结构的W-Ti纳米晶薄膜阻挡层及其对应的Cu/W-Ti/Si复合膜, 并对薄膜样品进行了退火热处理. 用四探针电阻测试仪(FPP), XRD, AFM, XPS, FESEM, HRTEM等分析测试方法对不同相结构的薄膜样品退火前后的电阻特性和形貌进行了分析表征. 实验结果表明, 退火温度低于 700℃时, 薄膜基本上保持稳定; 随着退火温度的增加, Cu与Ti反应生成CuTi₃, 同时Si与Cu发生互扩散形成高阻相Cu₃Si, 导致了表面粗糙度增加使方块电阻急剧增加. 同时提出了Cu布线用W-Ti纳米晶薄膜扩散阻挡层退火过程中的失效机理.     

基于DWT-CT的遥感影像数字水印方案

提出一种基于DCT和DWT的遥感影像数字水印方案。首先对水印图像进行Arnold置乱预处理,以破坏像素之间的空间相关性,增强算法鲁棒性;鉴于小波变换良好的局部性和时频分析特性以及多分辨率分析特性,而离散余弦变换具有较好的聚能效应,算法将载体遥感影像进行DWT变换,并选取其子带图像HLl进行DCT变换;最后自适应的将数字水印嵌入所选子块的DC系数上。实验证明本文算法有效提高了水印的不可见性,对JEPG压缩、滤波和叠加噪声等攻击具有较好的鲁棒性。     

基于AODV节能路由协议的改进

在AODV路由算法的基础上,提出一种节能路由算法MEE( Maximum Energy-efficient) -AODV.该算法通过改进AODV的请求(RREQ)分组获得整个网络的平均电池剩余能量,并且综合考虑跳数和节点剩余能量,以达到节能的目的.仿真表明,该算法在节能方面效果明显,延长了网络生存时间,有效提高了网络的性能.     

Selection for resistance to azadirachtin in the green peach aphid,Myzus persicae

Two lines ofMyzus persicae of the same origin were treated repeatedlywith pure azadirachtin (aza), or a refined neem seed extract (NSE), at the equivalent concentration of aza. After 40 generations, the aza-selected line had developed 9-fold resistance to aza compared to a non-selected control line, whereas the NSE-selected line did not. These results suggest that a blend of active constitutents in a botanical insecticide such as neem might diffuse the selection process, mitigating the development of resistance compared to that expected with a single active ingredient.     

Apoptosis and aging: increased resistance to apoptosis enhances the aging process

Apoptosis is a vital component in the evolutionarily conserved host defense system. Apoptosis is the guardian of tissue integrity by removing unfit and injured cells without evoking inflammation. However, apoptosis seems to be a double-edged sword since during low-level chronic stress, such as in aging, increased resistance to apoptosis can lead to the survival of functionally deficient, post-mitotic cells with damaged housekeeping functions. Senescent cells are remarkably resistant to apoptosis, and several studies indicate that host defense mechanisms can enhance anti-apoptotic signaling, which subsequently induces a senescent, pro-inflammatory phenotype during the aging process. At the molecular level, age-related resistance to apoptosis involves (1) functional deficiency in p53 network, (2) increased activity in the NF-κB-IAP/JNK axis, and (3) changes in molecular chaperones, microRNAs, and epigenetic regulation. We will discuss the molecular basis of age-related resistance to apoptosis and emphasize that increased resistance could enhance the aging process.     

基于耗散率最小的“盘点”脉管网络构形优化

以有限温差传热和流动阻力引起的最小耗散率和耗散数为优化目标,在圆盘总面积和脉管网络总体积给定的条件下,对圆盘区域内一级、二级和三级脉管网络进行构形优化,得到耗散率和耗散数最小的各级脉管网络最优构形.结果表明当参数B1?10??时,在相同无量纲质量流率M*(1?M*?102)下,耗散率最小和熵产率最小的一级脉管网络最优构形有明显区别.对于二级脉管网络,当无量纲质量流率在1?M*?102范围内时,传热耗散和流动耗散大小相当,此时脉管网络最优构形随质量流率变化显著.在相同脉管网络总体积和圆盘半径条件下,相同无量纲质量流率时,一级、二级和三级脉管网络最小耗散数性能几乎相同;当无量纲泵功率*5?10(?1,2,3)?i W i时,随着脉管级数的增大,脉管网络最小耗散数减小,此时增加脉管网络的复杂度有利于提高脉管网络的性能.此外,还以复合耗散率为优化目标对脉管性能进行优化.优化结果可从传热优化角度为脉管系统设计提供参考.     

The Curie's Lab and its Women (1906–1934) Le laboratoire Curie et ses Femmes (1906–1934)

When Bouvet discovered the relationship between the binary arithmetic of Leibniz and the hexagrams of the I ching—in reality only a purely formal correspondence—he sent to Leibniz a woodcut diagram of the Fu-Hsi arrangement, which provides the key to the analogy. This diagram, in a re-drawn version, was first published by Gorai Kinzō in a study of Leibniz's interpretation of the I ching and Confucianism which has been influential in providing, indirectly, the principal source for the accounts of Wilhelm and Needham. Yet this pioneering study of Leibniz's interpretation of the hexagrams is virtually unknown. Even the account of Needham, who saved it from complete obscurity, contains one or two inaccuracies about it and these are repeated by Zacher in his otherwise excellent monograph on Leibniz's binary arithmetic.     

The bacterial LexA transcriptional repressor

Bacteria respond to DNA damage by mounting a coordinated cellular response, governed by the RecA and LexA proteins. In Escherichia coli, RecA stimulates cleavage of the LexA repressor, inducing more than 40 genes that comprise the SOS global regulatory network. The SOS response is widespread among bacteria and exhibits considerable variation in its composition and regulation. In some well-characterised pathogens, induction of the SOS response modulates the evolution and dissemination of drug resistance, as well as synthesis, secretion and dissemination of the virulence. In this review, we discuss the structure of LexA protein, particularly with respect to distinct conformations that enable repression of SOS genes via specific DNA binding or repressor cleavage during the response to DNA damage. These may provide new starting points in the battle against the emergence of bacterial pathogens and the spread of drug resistance among them.     

An overview of cancer multidrug resistance: a still unsolved problem

Although various mechanisms involved in anticancer multidrug resistance (MDR) can be identified, it remains a major problem in oncology. Beyond that, the introduction of new “targeted” drugs have not solved the problem. On the contrary, it has been demonstrated that the “classical” MDR-associated mechanisms are similar or identical to those causing resistance to these novel agents. These mechanisms include the enhanced activity of drug pumps, i.e. ABC or alternative transporters; modulation of cellular death pathways; alteration and repair of target molecules; and various less common mechanisms. Together they build a complex network of cellular pathways and molecular mechanisms mediating an individual MDR phenotype. Although the application of new high throughput “-omics” technologies have identified multiple new gene-/protein expression signatures or factors associated with drug resistance, so far none of these findings has been useful for creating improved diagnostic assays, for prediction of individual therapy response, or for development of updated chemosensitizers. Received 05 March 2008; received after revision 21 May 2008; accepted 23 May 2008     

用于中医证候规范研究的模糊神经网络分析模型

为建立一种用于中医证候规范化研究的新模型——基于动态Kohonen网络的模糊神经网络,在分析中医证候规范化研究方法与存在的问题的基础上,采用基于动态Kohonen网络的模糊推理方法,给出了模型的学习算法和新的研究方法,并将该模型应用于中医证候规范化研究,通过Iris数据和临床数据检验,验证了模型的正确性和方法的有效性。     

基于Windows CE的车载监控系统软件设计与实现

本文采用面向对象的程序设计思想设计并实现了铁路大型捣固车的监控系统软件。该系统软件主要对捣固车上的重要电气参数和作业状态信息进行处理、显示、传输。本文对该系统软件各个功能模块分别说明,给出了相应的流程图,并详细说明了作业质量算法。