粗集理论及其在旋转机械故障诊断中的应用 (二)旋转机械故障诊断知识库的形成

旋转机械故障诊断知识库形成的主要环节是信号的采集和信号的分析、整理 ;在所有的机械故障信号中 ,振动诊断技术是故障诊断的常用手段 ,对振动信号实现连续、在线诊断的最重要的数学工具是快速傅里叶变换(FFT)和小波理论。通过对实验的观察 ,建立转子故障特征向量和故障类型之间对应关系的数据库 ,为基于粗集理论故障诊断的决策表的形成提供了原始的知识库     

基于粗糙集的自适应网络入侵检测方法

在分析入侵检测方法的基础上,将粗糙集理论引入入侵检测方法,提出一种改进的基于粗糙集的自适应网络入侵检测方法。通过对入侵数据权值离散化预处理,属性知识约简,规则提取与过滤,提高网络入侵数据的检测率。与基于BP-神经网络的方法,基于专家系统的(ES)的方法,以及普通的基础粗糙集的入侵检测方法进行实验对比,通过实验数据,证明该方法的有效性。     

一种应对APT攻击的安全架构:异常发现

威胁是一种对特定系统、组织及其资产造成破坏的潜在因素,反映的是攻击实施者依照其任务需求对被攻击对象长期持续地施以各种形式攻击的过程.面对高级可持续威胁(advanced persistent threat,APT),在其造成严重经济损失之前,现有的安全架构无法协助防御者及时发现威胁的存在.在深入剖析威胁的外延和内涵的基础上,详细探讨了威胁防御模型.提出了一种应对APT攻击的安全防御理论架构:异常发现,以立足解决威胁发现的难题.异常发现作为防御策略和防护部署工作的前提,通过实时多维地发现环境中存在的异常、解读未知威胁、分析攻击实施者的目的,为制定具有针对性的应对策略提供必要的信息.设计并提出了基于异常发现的安全体系技术架构:"慧眼",通过高、低位协同监测的技术,从APT攻击的源头、途径和终端3个层面监测和发现.     

Cure kinetics of T700/BMI prepreg used for advanced thermoset composite

A new isothermally based, cure kinetic model for the prepreg was presented using an industrially supplied prepreg rather than pure resin. The matrix resin was bismaleimide (BMI) resins, and the reinforcement was carbon fiber T700–12S. The BMI prepreg was measured from 170 to 220°C by isothermal DSC. The isothermal cure reaction heat increases with the increment of cure temperature. The DSC data were analyzed by the proposed nth‐order reaction model. An increase in reaction rate was observed at higher temperature in both neat and prepreg. After reaching the peak value, the reaction rate dropped off faster in prepreg, resulting in a lower average value of the ultimate heat of reaction. It was suggested the presence of carbon fiber had an effect on the cure kinetics as a heat sink. The carbon fibers imposed restrictions on the molecular mobility of the reactive species and did not change the cure mechanism. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2238–2241, 2005     

支持并行化快速实验部署的网络创新实验平台

清华大学网络创新实验(TUNIE)平台为新型网络体系结构的验证和测试提供了有力的工具。在TUNIE平台运行过程中,过长的实验部署耗时会降低整个TUNIE平台的运行效率。对实验部署过程进行分析和测量,发现实验部署的冗长耗时主要由集中式镜像池和串行的实验部署流程引起。为此,提出一种并行化的快速实验部署方案。利用分布式镜像池减少非本地节点的镜像拷贝时间,采用并行化实验部署提高时间维度上的资源利用率。仿真和实际应用结果证明,相比于串行部署方案,该方案可以减少40%~89%的部署耗时,有效提高了实验部署的速度。     

二氧化钛固载杂多酸催化剂的制备及其光催化性能研究

采用浸渍法以TiO2为载体制备了固载型杂多酸光催化剂--H3PW12O40/TiO2,H8SiW12O42/TiO2,H7PMo12O42/TiO2.通过Hammett指示剂与紫外光谱相结合的方法测定固体杂多酸催化剂的酸度,分别考察杂多酸种类、浸渍时间、浸渍浓度、烧结方式、烧结温度对催化剂酸度的影响,并对所制备的催化剂进行了红外光谱和光催化活性测试.结果表明,杂多酸固载到TiO2的表面,得到了催化活性较TiO2更强的复合杂多酸光催化剂,其对酸性大红3R的降解率从纯TiO2的79%提高到91%.以磷钨酸水溶液浸渍TiO2,浸渍浓度为0.10 mol·L-1 ,浸渍时间为28 h,烘干温度为120℃,微波炉焙烧功率为650 W,烧结时间为40 min制得的催化剂活性最高.在HPA-TiO2光催化系统中,杂多酸显著加速电子从TiO2表面到O2分子的传递,改变了TiO2光催化反应历程,从而提高光催化效率.     

真空蒸馏法从铟中脱除Cd、Tl的研究

介绍真空蒸馏法取代传统试剂法从铟中脱除镉和铊。通过实验研究了采用真空蒸馏的方法从铟中脱除铊的最佳工艺条件。实验表明,控制蒸馏温度950℃,恒温时间40m in,即可使残余物中铊的含量为0.0006%,铟的挥发率2.14%。     

Inspection of Remanent Polarization in the Ferroelectric Ceramic PZT 95/5 Through Pyroelectric Effect

Shock-induced depoling of the ferroelectric (FE) ceramic PZT 95/5 is utilized in a number of pulsed power devices. Nondestructive testing of remanent polarization of PZT 95/5 is developed by pyroelectric effect in this paper. Approximately linear relation between the change of polarization during low- to high-temperature rhombohedral FE phase and the remanent polarization was found through pyroelectricity of a single piece of PZT 95/5 ceramics. The change of polarization of a prototype for shock-driven pulsed power during the FE_HT↔FE_LT phase transformation was also investigated through directly measuring the pyroelectric current. Results indicate that pyroelectric effect caused by the reversible FE_HT–FE_LT phase transition could be used as a non-destructive inspection for the remanent polarization of a prototype about shock-driven pulsed power supply.     

Effects of melt‐extension and annealing on row‐nucleated lamellar crystalline structure of HDPE films

The row‐nucleated lamellar crystalline structure of high‐density polyethylene (HDPE) films was prepared by applying elongation stress to HDPE melt during T‐die cast film extrusion and subsequently annealing the extruded films. This unusual crystalline structure was analyzed in terms of lamellar crystalline orientation, long‐period lamellar spacing, crystallite size, and degree of crystallinity. The contribution of melt‐extension represented by draw‐down‐ratio (DDR) to the overall orientation was found to be most noticeable than other processing variables. Meanwhile, the long‐period lamellar spacing, the crystallite size, and the degree of crystallinity were influenced predominantly by the annealing temperature. Finally, the processing (melt extension and annealing temperature) – structure (lamellar crystalline structure) – property (hard elasticity) relationship of HDPE films was investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3326–3333, 2007