Chern and Pontryagin Numbers in Perfect Symmetries of Spheres

The paper presents a procedure for constructing smooth actions of finite perfect groups on spheres with fixed point sets having certain prescribed properties (Theorem A); in particular, having any prescribed configuration of Chern and Pontryagin numbers (Corollary C). The main ingredients used are equivariant thickening and equivariant surgery.     

The flow of a variable viscosity fluid between parallel plates with shear heating

A model for the flow of a fluid through a channel with parallel plates is investigated. The channel is narrow, so that the lubrication approximation may be applied. The channel walls are maintained at a constant temperature. Shear heating effects are included and the fluid viscosity decreases exponentially with temperature. When the flow is driven solely by shear stress or imposed velocity at the top, analytical progress is possible. When pressure gradient also drives the flow the problem is solved numerically.     

Rheological behaviour and shear thickening exhibited by aqueous CTAB micellar solutions

In this experimental work we carefully investigate the rheological behaviour and in particular the shear thickening exhibited by aqueous micellar solutions of CTAB with NaSal as added counterion. We are particularly interested in the evolution of the critical shear rate (at which shear thickening occurs) versus C _D , the surfactant concentration. We show that , at fixed salt concentration C _S , increases with C _D following a power law evolution with a positive exponent of + 5.8. On the other hand we show that if the ratio C _D / C _S is fixed, decreases with C _D with a negative exponent of -2.0. Nevertheless investigations of the zero shear viscosity indicate that in all situations (implying variation of the surfactant concentration C _D , or the salt concentration C _S or the temperature) is a decreasing function of the length of the micelles. All these evolutions are compatible with a gelation mechanism which could possibly be associated with entanglement effects of large interacting flowing structures. Received: 3 March 1998 / Revised: 16 June 1998 / Accepted: 3 July 1998     

剪切流动对共混物相行为影响的研究进展

介绍了国外８０年代以来开展的剪切流动对聚合物共混物相容性影响的研究概况，并着重介绍了采用最新的二维小角激光散射流变仪和光学显微流变仪对共混物体系在剪切应力作用下相行为的研究结果，反映了该前沿领域的最新进展。     

疏水缔合型增稠剂聚(丙烯酰胺-丙烯酸高级酯)的合成及增稠性能研究

采用沉淀聚合法合成了聚（丙烯酰胺－丙烯酸十四酯），聚（丙烯酰胺－丙烯酸十六酯）和聚（丙烯酰胺－丙烯酸十八酯），重点讨论了共聚物中疏水基团数量及疏水基团链长对增稠性能的影响。采用凯达尔定氮法和动态热分析（DMTA）测定了共聚物的组成及玻璃化温度。     

Shear and NMR experiments of materials with flow behaviour depending on the deformation history

Oxide ceramic masses react to simple shearing with hardening (peptisation: increase in the shear stress with the shear deformation). In the present study the correlation between the increase in the shear stress and the porosity, agglomeration processes and the type of flow are analysed. For this purpose oxide ceramic masses are tested in a shear device especially developed for pastes and analysed by rheometric experiments, NMR methods and particle size analysis. The results support the hypothesis that structural changes (hardening, increase in the mean porosity) of the material during the peptisation mainly depend on the magnitude and not on the kind of the energy input and thus of the type of flow. The fraction of bound (more generally, the immobilised) water increases with the shear displacement. Also crushing of primary particles could be observed. Both the crushing of solid particles causing an increased solid surface and the formation of a three-dimensional gel structure are microscopic effects capable of resulting in the binding or retaining water. On a macroscopic scale these phenomena cause hardening. Magnetic resonance imaging visualises flow-induced agglomerates, which form owing to the shear flow and increase the porosity averaged over the whole sample. After the shear experiment rolls of paste can be seen which indicate that the general assumption of a plane shear flow in the shear device is not warrantable. Received: 19 July 2001 Accepted: 25 October 2001     

高抗冲聚苯乙烯的增韧机理

概述了以高抗冲聚苯乙烯（ＨＩＰＳ）为中心的有关橡胶增韧机理的理论，并且总结了界面，性能、粒子尺寸、粒 距及缠结密度等因素对橡胶／高分子共混体系性能的影响。     

Comparison of a pump-around, a diffusion-driven, and a shear-driven system for the hybridization of mouse lung and testis total RNA on microarrays

In the present study, we demonstrate the benefits of a shear-driven rotating microchamber system for the enhancement of microarray hybridizations, by comparing the system with two commonly used hybridization techniques: purely diffusion-driven hybridization under coverslip and hybridization using a fully automated hybridization station, in which the sample is pumped in an oscillating manner. Starting from the same amount of DNA for the three different methods, a series of hybridization experiments using mouse lung and testis DNA is presented to demonstrate these benefits. The gain observed using the rotating microchamber is large: both in terms of analysis speed (up to tenfold increase) and in final spot intensity (up to sixfold increase). The gain is due to the combined effect of the hybridization chamber miniaturization (leading to a sample concentration increase if comparing iso-mass conditions) and the transport enhancement originating from the rotational shear-driven flow induced by the rotation of the chamber bottom wall.     

Influence of operational parameters on retention of ultra-high molecular weight polystyrenes in thermal field-flow fractionation

Summary The influence of various parameters (concentration of the injected polymer solution, flow rate, temperature gradient, relaxation conditions) on the retention and shape of the fractogram of ultra-high molecular weight polystyrenes in thermal field-flow fractionation was investigated. Under the operating conditions adopted, reproducible oscillations in the peak shape are observed for molecular weights larger than a few millions, especially at relatively high polymer concentration. They are attributed to some hydrodynamic instabilities. The retention of ultra-high molecular weight polystyrenes at high flow rate is strongly dependent on the initial relaxation period. All of the investigated operational variables have a complex effect on the resulting shape of the fractogram. Consequently, the confirmation of the shear-induced focusing of macromolecules across the channel thickness requires further study. Experiments on reinjection of fractions collected after an initial high speed pass through the separation system leads to the conclusion that shear degradation of the ultra-high molecular weight polymers did not occur under the investigated experimental conditions even at the highest flow rates.     

橡胶中简单剪切与纯剪切的关系

研究了简单剪切与纯剪切的关系，得出了：（１）简单剪切可看成纯剪切加转动，转动角θ有；（２）若简单剪切椭圆的长轴与坐标轴Ｘ的夹角为φ，相应的纯剪椭圆长袖与坐标轴ｙ的夹角为β０，则φ＝β０；（３）橡胶在双向拉伸时剪应变γ的一般表达式为，对简单剪切而言即为