The influence of branch length on the deformation and microstructure of polyethylene

The length and number of side chain branches have a profound influence on the microstructure and physical properties of polyethylene (PE). For a series of linear PE copolymers: environmental stress cracking resistance (ESCR), melting points, creep resistance and modulus, and equilibrium spherulite size were all found to increase with increasing branch length (methyl to hexyl) at a given density and molecular weight. It is proposed that (at a fixed molecular weight) branch length and branch concentration determine spherulite size and, consequently, spherulitic boundary areas, in which the dry crazing/voiding occurs during the incubation period of environmental stress cracking (ESC). At a fixed density, decreased spherulite size contributes to greater spherulite boundary slip and increased creep at low (less than 2 MPa) stresses.     

α-Tocopherol alteration of soybean antiherbivory toTrichoplusia ni larvae

The antioxidant vitamin E, -tocopherol, was tested as a candidate elicitor of alterable antiherbivory in soybean plants against cabbage looper larvae. Although a nonspecific antioxidant, vitamin E proved elicitory to the involved sulfhydryl-dependent receptor-energy transducer protein in soybean plasma membrane. Effects of -tocopherol were dependent on dosage, time, and space in the plant. The observed elicited effects were all decreases in herbivory. The best negative phytochemical correlate of looper feeding was the percentage of increased total HPLC peak area of extractables from elicited as compared to nonelicited leaves. Some specific compounds, e.g., glyceollins, were quantitatively major components of the total profile of secondary metabolites.     

Rheology of cementitious paste with silica fume or limestone

The rheological behaviour of cementitious pastes where cement has increasingly been replaced by densified silica fume (SF), untreated SF or limestone has been studied. The effect of SF on the flow resistance, taken as the area under the flow curve, was found to depend on the dispersing ability of the plasticizer as illustrated by pastes with naphtalene sulphonate-formaldehyde condensate (SNF) and polyether grafted polyacrylate (PA).The gel strengths increased with increasing SF replacement of cement independently of plasticizer type. The cementitious gel strength was, however, depending on the type of SF since pastes with densified SF developed lower gel strengths than pastes with untreated SF. This phenomenon was attributed to agglomerates in the densified SF which remained unbroken by the mixing and measurement sequence.Both flow resistance and gel strength decreased with increasing limestone replacement. Thus, silica fume may have an advantage over limestone filler as stabilizing agent for self-compacting concrete preventing segregation upon standing and reduced form pressure due to a more rapid gel formation.     

Effect of puerarin on the P13K pathway for glucose transportation and insulin signal transduction in adipocytes

To explore the effect of puerarin on insulin receptor (IR), insulin receptor substrate-1 (IRS-1) and protein expression of protein kinase B(PKB) in the P13K pathway of the glucose consumption, transportation and insulin signal transduction in 3T3-L1 adipocytes with insulin resistance. The insulin resistance 3T3-L1 adipocytes model was established by free fatty acid induction. The model cells were managed with puerarin in different concentrations. Glucose consumption was detected with glucose oxidase method, glucose transportation rate was determined by 2-deoxy-3H glucose ingesting method, and the IR, IRS-1 and PKB expression were determined by Western blot. Glucose consumption and transportation were significantly decreased in the model adipocytes, but increased after treated with puerarin (P<0.01). Moreover, the level of tyrosine phosphorylation of IR subunit β was higher in the puerarin treated groups, and that of IRS-1 was higher in the group treated with low dose puerarin than that in the model group. The 3T3-L1 adipocytes of insulin resistance model could be induced by free fatty acid successfully, puerarin could promote the glucose utilization in them to alleviate the insulin resistance, which may be related with the action in advancing the tyrosine phosphorylation of IR and IRS-1.     

Expression of green fluoscrescent protein gene in Sclerotinia sclerotiorum

Protoplasts of the pathogenic plant fungus,Sclerotinia sclerotiorum,were transformed using the pPGF plasmid,which contains green fluorescent protein gene,under the control of Aspergillus nidulans regulatory sequences. The pPGF plasmid was introduced by PEG/CaCl2 treatment. Positive transformants were harvested with hygromycin B (HYG) resistance as selective marker,and then were observed with green fluorescence phenomena in response to blue light,which suggested that GFP gene was cloned into genome DNA of S. sclerotiorum. The transformants were verified mitotically stable by Southern blotting analysis and passage culturing. This study is developed as an initial step for further research into infection mechanisms of S. sclerotiorum to plants and interactions with bio-control fungus.     

英屿沟Ⅱ号天桥的设计

为推广预应力混凝土箱梁结构在桥梁方面的应用研究,结合英屿沟Ⅱ号天桥实例,介绍了该组合结构在桥梁方面具体应用的设计思路,介绍了英屿沟Ⅱ号天桥波形钢腹板PC组合箱梁桥主梁结构、预应力体系、波形钢腹板、连接件、防腐、施工流程等的设计,为波形钢腹板PC组合箱梁结构应用于桥梁工程提供了设计经验.     

定向MWNTs/PMMA的原位聚合制备及耐磨损性

采用原位聚合方法制备了定向碳纳米管/聚甲基丙烯酸甲酯复合材料,并且研究了该复合物的耐磨损性.对定向碳纳米管及其复合物进行了傅立叶红外吸收光谱分析、扫描电镜及光学显微镜观察.采用砝码质量法评价了复合物的耐磨损性.分析结果表明,混酸处理后定向碳纳米管附带了-OH、-COOH基等极性基团.混酸处理后定向碳纳米管束状结构被破坏,定向碳纳米管可以单管形态分散于基体中,碳纳米管表面包覆着PMMA.砝码质量法耐磨损性测试结果表明,定向碳纳米管的加入可提高PMMA复合物的耐磨损性和耐划痕性,当定向碳纳米管用量为0.7%时,复合物的耐磨损性能提升了54%.     

基于PSO的负反馈电路参数自适应优化及仿真分析

采用粒子群优化算法,以电压增益、共模抑制比、输入电阻平方根的三者乘积对输出电阻的比作为适应度函数,对差分 共射两级直接耦合电压串联负反馈放大电路中的电阻做自适应优化。结果显示,只要对电路交流指标加以约束,适应度函数值总会减小。当分别对增大电压增益和减小输出电阻进行限制后,电压增益总是尽量小,输出电阻总是尽量大,以使适应度函数在给定约束下取得最大。经EWB软件对优化参数仿真,结果满足线性放大要求。同时说明了可以调整适应度函数形式,找到最佳电路参数,以满足工程上对放大器指标的不同需求。     

世界溶液丁苯橡胶的主要技术进展

评述了溶液丁苯橡胶的技术现状和主要技术进展。介绍了新型锡锂引发剂和用其制备的溶液丁苯橡胶的性能特点，特别是其突出的滚动阻力特性和在不损失湿牵引性下的优异耐磨性。分析了世界，特别是美国、欧洲和日本的溶液丁苯橡胶的需求现状及发展趋势。     

On the oxidation kinetics and mechanisms of various SiC-coated carbon-carbon composites

SiC coatings on the surface of C-C were produced by either silicone resin impregnation/ pyrolysis or reaction sintering. Cycles of resin impregnation/pyrolysis produced an SiC coating, on the walls of fine open pores, which was effective in reducing the oxidation rate of C-C and in shifting the transition temperature to a higher value. Unless it is pre-coated with a pyrocarbon layer before sintering, plain reaction sintered SiC has oxidation behaviors similar to those of the above-mentioned SiC. The dense pyrocarbon film deposition on the surface of C-C could form a better SiC film than others. The carbon film homogenized the surface of C-C and a dense SiC film was established. The oxidation of the coated C-C can be modelled by a set of “oxidation resistors” in series and/or in parallel, with each resistor corresponding to an oxidation element. The controlling mechanism can be resolved from the activation energy. A combined resistant layer, consisting of resin impregnation, pyrocarbon film and reaction sintering SiC, showed the best oxidation resistance of any single-layer coated C-C composite.