Effect of ultrasound on wettability between aramid fibers and epoxy resin

Good wetting of reinforced fiber by resin was a main factor in the improvement of the interface adhesion of their composites. Ultrasound with a frequency of 20 kHz was used to improve the wettability between aramid fibers and epoxy resin during the winding process of the composites. The effects of ultrasound on the viscosity and surface tension of epoxy resin and on the surface characteristics of aramid fibers were investigated. The wettability of aramid fibers and treated epoxy resin under different conditions and of aramid fibers and epoxy resin under ultrasonic online treatment were compared. The results indicated that the main action of ultrasound was to force epoxy resin to impregnate aramid fibers, in addition to the influence of ultrasound on the properties of epoxy resin and aramid fibers. The results of microdebond testing showed that the interfacial shear strength (IFSS) of aramid/epoxy composites could be 26% higher than that of untreated composites because of the improved wettability between aramid fibers and epoxy resin subjected to ultrasonic online treatment. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

纳米级无机粒子对聚乙烯的增强与增韧

对μｍ级ＣａＣＯ３、ＴｉＯ２和ｎｍ级ＳｉＣ／Ｓｉ３Ｎ４粒子填充ＬＤＰＥ的性能进行了研究。实验证明，μｍ级粒子对ＬＤＰＥ虽无明显的增强增韧作用，但也未使基体的机械性能大幅度下降。ｎｍ级ＳｉＣ／Ｓｉ３Ｎ４对ＬＤＰＥ有较大的增强增韧作用，在５％质量分数时冲击强度出现最大值，缺口冲击强度达５５．７ｋＪ／ｍ２为纯ＬＤＰＥ的２０３％；伸长率到６２５％时仍未断裂，为纯ＬＤＰＥ的５００％，但熔体流动速率急剧下降，仅为纯ＬＤＰＥ的２６％，当含量在３％和１５％质量分数时，熔体流动速率分别为纯ＬＤＰＥ的３３７％和１５１％。     

A surrogate-based optimization method with RBF neural network enhanced by linear interpolation and hybrid infill strategy

In engineering, it is computationally prohibitive to directly employ costly models in optimization. Therefore, surrogate-based optimization is developed to replace the accurate models with cheap surrogates during optimization for efficiency. The two key issues of surrogate-based optimization are how to improve the surrogate accuracy by making the most of the available training samples, and how to sequentially augment the training set with certain infill strategy so as to gradually improve the surrogate accuracy and guarantee the convergence to the real global optimum of the accurate model. To address these two issues, a radial basis function neural network (RBFNN) based optimization method is proposed in this paper. First, a linear interpolation (LI) based RBFNN modelling method, LI-RBFNN, is developed, which can enhance the RBFNN accuracy by enforcing the gradient match between the surrogate and the trend observed from the training samples. Second, a hybrid infill strategy is proposed, which uses the surrogate prediction error based surrogate lower bound as the optimization objective to locate the promising region and meanwhile employs a linear interpolation-based sequential sampling approach to improve the surrogate accuracy globally. Finally, extensive tests are investigated and the effectiveness and efficiency of the proposed methods are demonstrated.     

基于遗忘曲线的协同过滤研究

随着信息技术和互联网技术的发展,推荐系统成为解决信息过载的重要方式。而协同过滤因为其算法简单,又能够处理复杂的问题并产生比较良好的效果而被人们广泛应用,也成为了推荐系统中最成功的技术。然而用户的兴趣是时刻变化的,且对于新用户系统无法预测用户的偏好。因此为了解决这一问题,对艾宾浩斯遗忘曲线和推荐算法进行了研究,发现由于人的兴趣是不断变化的,而这种变化是自然遗忘的过程,也就符合遗忘曲线,所以用遗忘函数模拟人的兴趣变化。由于时间对评分的起着很重要的作用,在使用相似度算法时加入了时间因子,对用户的原始评分进行衰减,以此来反应用户的兴趣变化。然后为此算法设计了两组实验来验证算法的有效性。通过两组实验的结果证明,总体上来讲,基于遗忘曲线的相似度的计算方法比传统的算法要好一些。     

Preparation and characterization of a series of polyamides with long alkylene segments: Nylons 12 20, 10 20,s 20,6 20, 4 20 and 2 20

Summary A series of nylons with long alkylene segments between amide groups were newly prepared by step-heating melt-polycondensation of 1,lS-octadecanedicarboxylic acid with various diamines. The prepared polyamides were characterized carefully. The results show that many properties of the prepared nylons change regularly with the length of methylene segments in diamines. In addition, nylon 2 20 has a relatively low molecular weight and much different melting and thermal decomposition behaviors in comparison with other nylons. Received: 21 June 2OO2/Revised version: 18 September 2002/ Accepted: 18 September 2002 Correspondence to Deyue Yan E-mail: dyyan@mail.sjtu.edu.cn Tel: 0086-21-54742863 Fax: 0086-21-54741297     

TD-LTE与TD-SCDMA切换判决机制的探究与仿真

不同网络之间的切换问题是网络间互操作的重要组成部分,尤其是当前备受关注的TD-LTE与TD-SCDMA的切换问题。该文在对常规切换机制剖析的基础上,通过详尽的理论分析,根据现有切换机制的不足,提出了新的切换判决算法机制。新机制中结合了多属性切换判决中的层次分析算法和二维函数收益法,考虑了移动用户的业务喜好,并使用Matlab搭建了网络模型着重针对数据业务进行仿真,根据不同的网络收益值来实现切换的选择,验证了数据业务切换判决算法的有效性。     

喷码机平台WinCE5.0系统的BSP开发

基于以S3C2440A处理器为核心的喷码机硬件开发平台,研究了嵌入式WinCE5.0操作系统板级支持包BSP的开发。分析了喷码机平台的硬件组成和BSP的框架结构,利用源代码重用的思想,完成了Bootloader、OAL、驱动程序、配置文件的开发工作并在BINFS文件系统的基础上实现Multi-bin成功将内核分块。实践表明该BSP在喷码机台上运行稳定,可靠性高,能有效提升系统的开机速度,并使平台拥有了运行大型喷印软件的能力。     

“微课”在高职《计算机应用基础》课程中的应用

随着现代化教学手段的不断发展,＂微课＂作为一种新的教学模式,在《计算机应用基础》课堂中的应用也越来越广泛。由于＂微课＂的特点与现代社会的发展节奏以及学生的认知特点等契合程度比较高,所以＂微课＂在高校教学中受到了广泛的欢迎。在本文中,我们试图通过对＂微课＂在高职《计算机应用基础》课程中的应用进行分析,以充分发掘＂微课＂在《高职计算机应用基础》课程教学中的优势作用。     

省级网站安全监控平台建设的几点建议

针对网站日益增多的安全问题,提出在监管方面重要的技术手段--省级网站安全监控平台,并针对平台实现功能、平台建设、运维等方面提出几点建议.