A reanalysis method for local modification and the application in large-scale problems

A novel reanalysis method, named independent coefficients (IC) method is suggested in this study. This method is proposed to reanalyze structures with local modification which leads to a low-rank change in the stiffness matrix. IC method requires only initial solution as input, and can determine the independent coefficients for each degree of freedoms (DOFs) influenced by structural modifications. Since any extra operations such as decomposition of the initial stiffness matrix is not involved in computation procedure, the IC is a “cheap” algorithm and can be an alternative choice for reanalysis. In order to verify the performance of IC method, several large scale numerical examples are tested. The results demonstrate that the IC method has high accuracy as well as efficiency when the modification is local. The cases involving beyond 1,500,000 DOFs and 3,000,000 DOFs show that IC method has low demands on computer storage, and large scale problems can be easily reanalyzed by this method.     

Solute diffusion through degradable semicrystalline polyethylene glycol/poly(l-lactide) copolymers

Summary The diffusion of C.I. direct orange 34(MW=299) and benzoic acid(MW=122) through degraded semicrystalline polyethylene glycol(PEG)/poly(L-lactide)(PLLA) block copolymers with various PEG contents and PEG segment lengths at 37°C was studied by UV-visible spectroscopy, differential scanning calorimetry(DSC), wide angle X-ray diffractometer (WAXS) and scanning electron microscopy(SEM). The influences of the PEG contents, PEG segment lengths and hydrolytic degradation of PEG/PLLA copolymers on the solute diffusion coefficient and mode for transport were investigated. It is concluded that the diffusion rate increases with the increase of PEG contents and PEG segment lengths in PEG/PLLA copolymers. This is understandable that the increase of PEG content and PEG segment length both make the degree of crystallinity decrease. The steady state of mass flux could not be reached at the diffusion times up to 1000 h, because the copolymers underwent hydrolysis reaction during this period. Furthermore, it is understood that the characteristic time of diffusion as defined by the square of film thickness at an instant of time over the diffusion coefficient of solute through polymer decreases with the increasing diffusion time.     

微波烧结Al2O3-TiC复合材料的研究

以纳米级TiC、Al2 O3 为原料 ,用微波烧结制备Al2 O3 -TiC复合材料 ,并与常规烧结比较。分析了两种烧结方法对制备试样的力学性能的影响 ,并探讨了添加剂对Al2 O3 -TiC复合材料烧结性能的影响     

抗冲聚丙烯结构与性能研究

对部分国内外抗冲聚丙烯(PP)产品进行了微观形态和结构分析，研究其对材料宏观力学性能的影响。实验结果表明：抗冲PP是一个含有PP均聚物、丙烯与乙烯-丙烯两嵌段共聚物、乙丙橡胶(EPR)、聚乙烯均聚物等的多相体系。EPR的分子序列结构对聚合物抗冲击性能起主要作用。在序列结构中，丙烯、乙烯单体在分子链上的位置交换越频繁，抗冲击性能越得到提高。丙烯序列平均长度的增大对抗冲击性能有一定的削弱作用。     

Using silica nanoparticles as curing reagents for epoxy resins to form epoxy–silica nanocomposites

Nanoscale colloidal silica showed high reactivity toward curing epoxy resins to form epoxy–silica nanocomposites under mild conditions. Adding a certain amount (5000 ppm) of magnesium chloride lowered the activation energy of the reaction from 71 to 46 kJ/mol. Less and more magnesium chloride both exhibited counter action on lowering the activation energy of the curing reaction. Tin chloride dihydrate and zinc acetylacetonate hydrate were also added into the curing compositions, however, showing no significant effect on promoting the curing reaction. Through this curing reaction, epoxy–silica nanocomposites containing high silica contents up to 70 wt % were obtained. Therefore, this reaction provided a novel and convenient route in preparation of epoxy–silica nanocomposites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1237–1245, 2005     

磨加工及残余应力对氮化硅陶瓷强度的影响

利用X-射线衍射方法测量了经不同磨削的氮化硅陶瓷表面残余应力及其对抗弯强度的影响。结果表明，磨削工艺所引入的残余应力是拉应力，对陶瓷抗弯强度有显著降低。     

网络边布局技术研究综述

网络边布局技术是网络可视化研究的重要内容,良好的边布局能够有效地展示网络的整体结构并从中揭示出某些隐含的信息模式.为了全面地总结和分析现有网络边布局技术,首先归纳了网络边布局的主要任务,回顾了指导网络边布局的美学标准.然后将网络边布局技术归纳为3类:边路由技术、边融合技术和边集束技术,分别阐述了各类技术中典型布局方法的主要原理和特征,并重点对边集束技术进行了分类分析.最后总结了目前研究中还存在的一些问题,展望了网络边布局技术的发展前景和面临的挑战,以期为相关领域的研究者提供有益参考.     

甲缩醛空气氧化制甲醛催化剂的研制和工艺条件探讨

考察了铁钼催化剂对甲缩醛空气氧化制甲醛的催化性能。制备了多种不同钼铁比和第三、第四组分的催化剂,进行了活性评价和筛选,探讨了适宜的工艺条件范围。对于所选定的催化剂(钼铁比为1.82～1.88;铬铁比为0.1～0.38)在适宜的工艺条件(甲缩醛进料浓度4.5～5.5％;甲缩醛和氧气进料比1:2.0±0.2;空速12000～22000h~(-1);热点温度370～390℃)下,甲醛收率可达85％左右。     

通信用片式介质陶瓷双工器的设计与制作

介绍了通信用介质陶瓷双工器的设计方法和制作过程。该双工器是由接收滤波器和发射滤波器组成的。每种滤波器是由一块高介电常数、高Q值和接近零温度系数的介质陶瓷块制成的。这个陶瓷块上包含两个四分之一波长同轴谐振腔、输入及输出电极和耦合装置,并且输入及输出电极在陶瓷块的同一侧面上,因此滤波器具有体积小巧,结构稳定和安装方便的特点。采用介电常数为90的陶瓷材料制作了中心频率分别为903MHz和927MHz的接收和发射滤波器,经网络分析仪测试,各项技术指标满足设计要求。     

Water uptake of epoxy coatings modified with γ-APS silane monomer

Epoxy resin was modified by a silane monomer, γ-aminopropyltrimethoxy silane (γ-APS), and was used as the protective coatings for LY12 aluminum alloys. The aim of the modification is to reduce the water uptake of polymeric coatings. The water absorption of coatings was measured by coating capacitance method in 3.5 wt.% NaCl aqueous solution. The result indicates that water uptake of epoxy coatings modified with 1.0 wt.% γ-APS decreases compared with pure epoxy coatings, whereas larger amounts of sliane result in the deterioration in performance against water permeation, due to the excessive consumption of epoxide group in epoxy resin by amino-group in silane agent, thus reduce the cross-linking of epxoy coating as a result of presence of excessive curing agent (polyamide). T_g of silane-modified coatings increases slightly after immersion, extremely contrasting with that of pure epoxy coating, which was observed to decrease significantly after water permeation. The formation of Si–O–Si structure resulting from the hydrolysis and condensation of silane components during the immersion in aqueous media may be a reasonable explanation for the abnormal change in T_g of silane-modified coatings. In addition, all silane-modified coatings display better protection performance, which is characterized by higher charge transfer resistances (R_ct) and lower double layer capacitance (C_dl) at substrate/electrolyte interface.