Interpretation of quasi-elastic light scattering data for flexible chains: model dependence

The autocorrelation functions and corresponding relaxation times obtained from the forward depolarized quasi-elastic light scattering experiment are exhibited for two quite similar models of flexible polymer chains in solution. A very small change in the chain dynamics is found to be sufficient to change the relaxation time from a relatively short time independent of chain length, with an autocorrelation function suggestive of an unweighted sum of contributions from all the relaxation times in the spectrum of chain motion, to a long time with an autocorrelation function identical with that for the end-to-end vector, strongly dependent upon chain length and dominated by the longest relaxation time in the spectrum. These results raise the question whether widely-used models in which information about short-range chain structure and motion is deliberately omitted can be expected to be appropriate for the interpretation of depolarized scattering experiments.     

Viscosity of ionomer gels

We study the viscosity behaviour of metal sulphonate- (or metal carboxylate-) containing ionomers in solution with non-polar solvents; at relatively low polymer concentration these ionomer solutions show an unusually large thickening behaviour, due to the association of the metallic groups. By regarding the ionomer system as a polymer solution with transient crosslinks, an expression is derived from the viscosity of the sulphonated polymer in terms of the viscosity of the corresponding non-sulphonated polymer and the average number of crosslinks associated with any chain.     

Change of the amorphous state by heat treatment below the glass transition temperature

This study was undertaken to elucidate the state of a polymer in the amorphous state through a change of motion of the molecular chain caused by heat treatment below the glass transition temperature. From dielectric measurements of amorphous poly(ethylene terephthalate) heat-treated below T_g, it was found that the average relaxation time, the distribution of relaxation time and the dielectric strength increase with increase of heat treatment. From these results, it was concluded that the amorphous state becomes more random by heat treatment.     

我国低松弛预应力钢丝钢绞线发展现状和展望

对我国低松弛预应力钢丝、钢绞线的发展及市场现状进行了综述，并对目前我国开发、生产与市场销售的严峻形势作了分析，提醒要上这一项目的厂家要慎重对待。     

利用核磁共振技术研究谷物在储藏过程中的变化

利用核磁共振技术CPMG序列测定自旋．自旋弛豫时问Tz及其相应的质子密度A21、A22检测17种谷物在室温下的储藏过程中核磁共振驰豫参数的变化规律。研究结果表明,随着储藏时间的延长,弛豫时间对应的质子密度呈现下降的趋势,储藏到3～4个月,出现明显的下降;不同谷物在磁共振上的表现明显不同,可以将17种谷物划分为三类,即耐储藏谷物、较耐储藏谷物和不耐储藏谷物。该项技术快速、无损和对样品没有要求,研究结果可以为食品实际工业生产提供一定的理论指导。     

奥氏体不锈压缩螺旋弹簧抗应力松弛性能研究

研究了１Ｃｒ１８Ｎｉ９奥氏体不锈钢丝压缩螺旋弹簧去应力退火、热强压及电强压处理对其组织及应力松弛性能的影响规律，测定了弹簧在不同温度下的应力松弛动力学曲线，用微机回归了这些曲线的动力学方程，并预测了工作１０年后弹簧的负荷损失率。最佳去应力退火工艺为４００～４３０℃、４５ｍｉｎ；最佳热强压处理工艺为２００℃、３１４Ｎ、３ｈ。对弹簧应力松弛动力学、热力学及机理进行了讨论。     

竹浆纤维力学性能的模拟分析

 应用固体力学模型分析比较了竹浆纤维和粘胶纤维的流变性能 ,指出了竹浆纤维的松弛 (或延迟 )时间普遍比粘胶纤维的长 ,发生流变较慢 ,松弛蠕变好于粘胶纤维     

Proton spin–spin relaxation time of peel and flesh of navel orange varieties exposed to freezing temperature

Proton spin–spin relaxation times (T₂) of peel (albedo and flavedo) and juice sacs (flesh segments) of navel oranges were measured at 10 MHz using a Bruker Minispec PC 110 NMR spectrometer. The oranges were subjected to chilling (5 °C) and freezing (−7 °C) temperatures for 20 h and warmed to room temperature before peeling for T₂ measurements. The exposure to chilling or freezing temperature did not affect the T₂ values of peel, but freezing caused an appreciable decrease (∼15%) in the T₂ values of flesh segments of the varieties of navel oranges studied. When the peel was exposed to −20 °C, the T₂ showed a drastic reduction suggesting that the peel did not freeze at −7 °C. The possible cause of reduction in the T₂ values when exposed to freezing temperature may be damage to the juice sac membrane and leakage of juice out of the sac. The difference in the T₂ values between juice sacs of freeze-affected and normal oranges can potentially be used for detection of freeze-damaged fruits. Copyright © 2005 Society of Chemical Industry     

压力容器缠绕用扁钢丝生产工艺探讨

简要介绍压力容器机架缠绕用扁钢丝目前常用的生产工艺,分析对比3种生产工艺的优缺点及产品性能,并将该类钢丝生产工艺同国外比较。提出该类钢丝的最佳生产工艺是最终采用油淬火回火热处理,使钢丝具有较低的松弛值。     

基于协同优化算法的流速仪检定系统设计

提出了一种小型轻便的流速仪检定系统的设计方案,并运用改进的多学科协同优化方法求解各学科设计变量的最优解;首先介绍了算法思想及改进措施,并根据系统设计要求建立了各学科的设计变量、目标函数和约束条件;其次,运用遗传算法求解各学科设计变量的最优解,并根据优化结果完善了系统的设计方案,同时运用计算机仿真等方法验证了优化结果的可行性;结果表明,优化后的检定系统满足流体力学效应、匀速运动时间、系统重量等设计要求,同时证明了协同优化算法解决多学科设计优化问题的有效性。