Electromechanical behavior of hybrid carbon/glass fiber composites with tension and bending

To understand the smart (i.e., good memory) characteristics of hybrid composites of carbon fibers (CFs) and glass fibers (GFs) with epoxy resin as a matrix, the changes in the electrical resistance of composites with tension and on bending were investigated. The electrical resistance behavior of composites under tension changed with the composition of the CF/GF, as well as with the applied strain. The fractional electrical resistance increased slowly with increasing strain within a relatively low strain region. However, with further loading it increased stepwise with the strain according to the fracture of the CF layers. The strain sensitivity of the samples increased with increasing CF weight percentage, and the samples incorporating more than 40 wt % CF showed a strain sensitivity higher than 1.54 for a single CF. The changes in the fractional electrical resistance with bending were not so dominant as those with tension. This difference was attributed to the action of two cancelling effects, which are the increasing and decreasing fractional electrical resistance due to tension and compression with bending, respectively. On recovery from a large applied bending, the fractional electrical resistance decreased slowly with unloading because of the increase of contacts between the fibers that resulted from the reorganization of ruptured CFs during the recovery. Even the composites incorporating a relatively small CF content showed an irreversible electrical resistance with both tension and bending. However, the strain sensitivity being larger with tension than with bending is ascribed to the difference in their mechanical behaviors. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2447–2453, 2002     

POE在塑料增韧改性中的应用进展

聚烯烃弹性体(POE)综合性能优异,广泛应用于通用塑料和工程塑料的增韧和抗低温改性中。与传统增韧改性剂相比,POE和功能化的POE在较低含量下就能实现材料的脆—韧转变。综述了POE和功能化SPOE对通用塑料和工程塑料改性的研究概况和应用发展。     

Effect of Additives on the Electromechanical Properties of Pb(Zr,Ti)O3–Pb(Y2/3W1/3)O3 Ceramics

Dielectric and piezoelectric properties of 0.02Pb(Y_2/3W_1/3)O₃ 0.98Pb(Zr0.52Ti0.48)O3 ceramics doped with additives (Nb₂O₅, La₂O₃, MnO₂, and Fe₂O₃) were investigated. The grain sizes of these ceramics decreased with increasing amounts of additives. For additions of MnO₂ and Fe₂O₃, dielectric losses decreased, while for Nb₂O₅ and La₂O₃, these values increased. The maximum values of the mechanical quality factor Q_m were found to be 956 and 975 for additions of 0.9 wt% Fe₂O₃ and 0.7 wt% MnO₂, respectively, but donor dopants (Nb₂O₅ and La₂O₃) did not change the values of Q_m . On the other hand, the piezoelectric constant d₃₃ and the electromechanical coupling factor k_p decreased with additions of MnO₂ and Fe₂O₃, but improved with additions of Nb₂O₅ and La₂O₃.     

Effects of chemical additives on high-field electromechanical properties of PMN–PT–BT ceramics

A chemical additive method using sol–gel reactions was used to modify the composition and resultant properties of a commercially available 0.96(0.91Pb(Mg_1/3Nb_2/3)O₃–0.09PbTiO₃)–0.04 BaTiO₃ (PMN–PT–BT) ceramic. Without an additional ball-mixing process, several combinations of minor additives such as Fe, Ba, Sr, Zn, and Ti were incorporated by the chemical method. Weak- and high-field characteristics including dielectric properties, induced strain and polarization, and associated hystereses were evaluated for the samples sintered at 1200 °C for 4 h. All properties were found to depend on the chemical additives and temperature. Especially, the temperature dependence of high-field characteristics revealed different behavior from that reported for conventionally prepared samples. For example, the samples containing 0.5 wt.% SrO, 0.5 wt.% ZnO, and 0.5 wt.% TiO₂ did not exhibit a transition to piezoelectric behavior at the temperature expected from the dielectric measurements. Overall, the coating process has been successfully used to modify, and in some cases, enhance the high-field characteristics of PMN-based ceramics for electromechanical uses.     

分布式开放存取期刊爬虫的设计与实现

开放存取（open access,OA）期刊属于网络深层资源且分散在互联网中,传统的搜索引擎不能对其建立索引,不能满足用户获取OA期刊资源的需求,从而造成了开放资源的浪费。针对如何集中采集万维网上分散的开放存取期刊资源的问题,提出了一个面向OA期刊的分布式主题爬虫架构。该架构采用主从分布式设计,提出了基于用户预定义规则的OA期刊页面学术信息提取方法,由一个主控中心节点控制多个可动态增减的爬行节点,采用基于Chrome浏览器的插件机制来实现分布式爬行节点的可扩展性和部署的灵活性。     

Interfacial adhesion reaction of polyethylene and starch blends using maleated polyethylene reactive compatibilizer

The interfacial reaction of the polyethylene (PE)/starch blend system containing the reactive compatibilizer maleated polyethylene (m‐PE) was directly characterized by Fourier transform infrared (FTIR) spectroscopy. A significant amount of anhydride groups on m‐PE existed as hydrolyzed forms, resulting in a large amount of carboxyl groups. Using a vacuum‐heating‐cell designed in the laboratory, the carboxyl groups were successfully transformed into the dehydrolyzed state (i.e., anhydride group). This result enabled the direct spectroscopic observation of chemical reaction occurring at the interface. For the PE/starch blend system containing m‐PE, the chemical reaction at the interface was verified by the evolution of ester and carboxyl groups in the FTIR spectra. The effect of the reactive compatibilizer on the interfacial morphology was also examined by scanning electron micrography (SEM). Enhanced interfacial adhesion was clearly observed for the blend system containing reactive compatibilizer. Tensile strengths of blend systems containing m‐PE also increased noticeably compared with the corresponding system without compatibilizer. A similar observation was made for the breaking elongation data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 767–776, 2002     

Solution copolymerization of methyl methacrylate and alkyl methacrylates in a continuous stirred tank reactor(CSTR)

Continuous solution copolymerization of methyl methacrylate with ethyl methacrylate or n-butyl methacrylate was carried out in a continuous stirred tank reactor. Solvent and initiator used were toluene and benzoyl peroxide, respectively. Reaction volume was 1.2 litters, residence time 3 hours and polymerization temperature 80°C. The copolymerization conversions were analyzed by UV spectrophotometry and confirmed by measuring the solid weights of copolymers obtained after evaporating solvent. The copolymerization of methyl methacrylate and alkyl methacrylates followed the second order kinetics. The simulated conversions and copolymerization rates were compared with the experimental results. The average time to reach dynamic steady-state was three and half times of the residence time.     

2500m^3高炉基础自动化系统构成

介绍新钢2×2500m^3高炉基础自动化系统各个子系统的构成,以及环形网络的构成及配置方法。     

无线局域网安全保密管控技术研究

随着网络的发展和无线Wi Fi业务的应用不断普及,无线局域网安全保密性能得到了广泛的重视。本文对无线局域网的安全体系进行分析,研究无线局域网安全保密管控方案,通过性能测试证明本文所设计的无线局域网安全保密管控方案的可行性。     

浅析数字内容的版权保护与建议

数字技术的迅速发展和广泛应用,互联网、电信移动网络等新兴传输方式和手机、机顶盒、电脑等多媒体终端极大地拓展了数字内容的传输范围。数字内容版权保护的问题日益突出,本文从立法和技术角度阐释了数字内容的版权保护,并提出了数字内容版权保护的建议。