Development of poly(vinyl chloride)/montmorillonite nanocomposites using chelating agents

Different chelating agents such as poly(ethylene glycol), propylene glycol monooctadecanoate and palm oil were used for modification of the surface-treated montmorillonite (MMT). The work also included the development of a technique for mixing chelating agents with MMTs using different methods and different proportions of MMT/chelating agent/ethanol. Evaluation of the result of mixing was performed by thermogravimetric analysis, X-ray diffraction and high-resolution scanning electron microscopy (HR-SEM). The results showed that the chelating agents used were intercalated in MMT, increasing the interlayer spacing. The OMMT was used in the manufacture of composites with rigid PVC using a microcompounder. The master batch concept turned out to be promising in terms of dispersion and delamination of clay, as observed in HR-SEM photographs. However, despite good dispersion and exfoliation of MMT, poor compatibility between clay platelets and PVC matrix remains to be solved to enable full exploitation of its engineering potential. Despite this drawback, good thermal stability and mechanical properties have already been achieved.     

Thermo-cleavable polymers: Materials with enhanced photochemical stability

Photochemical stability of three thermo-cleavable polymers was investigated as thin films under atmospheric conditions. A significant increase in lifetime was observed once the side-chain was cleaved emphasizing the detrimental effect of solubilizing groups on the photochemical stability of conjugated polymers. In addition to their ease of processing, thermo-cleavable polymers thus also offer a greater intrinsic stability under illumination.     

芴2,7位取代的9,9’-二芳基螺芴类化合物的合成及性能

设计并合成了一系列以三苯胺为核,芴衍生物为外围基团的有机蓝光小分子,该合成通过Suzuki反应在9-芳基芴的2位和(或)7位引入相同或不同取代基作为模块,并利用Friedel-Crafts反应将4-甲基三苯胺与这一系列模块结合.用NMR,MS和元素分析进行结构表征.荧光测试结果表明该类化合物溶液的荧光发射波长范围在442～466 nm之间,属蓝光发射.电化学测试显示该类材料的HOMO能级位于-5.15～-5.19 eV之间.差示扫描量热仪与热重分析得出化合物的玻璃化转变温度在166℃以上,热分解温度高于398℃,表明该类材料具有良好的热稳定性.     

A simple proof of the linear instability of rotating liquid drops

We give a simplified proof of the linear instability of equilibrium figures of rotating liquid based on energy estimates.      

Stability of solitary waves for the Ostrovsky equation

Considered herein is the Ostrovsky equation which is widely used to describe the effect of rotation on the surface and internal solitary waves in shallow water or the capillary waves in a plasma. It is shown that the solitary-wave solutions are orbitally stable for certain wave speeds.

     

高岭石—金—硫系列的化学键与稳定性研究

用密度泛函离散变分计算方法（ＤＦＴ－ＤＶＭ），研究了高岭石、高岭石－金和高岭石－金－硫系列，讨论了结构，化学键与稳定性之间的关系。选用了不含金及金或金－硫原子团位于不同方位的多个模型。计算结果表明，金位于层状高岭石侧面的模型比金位于上、下面更为稳定，在金位于层状高岭石侧面的情况下，金靠近铝的模型比金靠近铝空位更为稳定，高岭石－金－硫体系中的金－硫原子团比高岭石－金体系中的更容易被高岭石吸附。模型间     

On two models in the three-dimensional theory of stability of composites

A comparative analysis is made of the infinite-fiber and finite-fiber models in the three-dimensional theory of stability of composites. The results analyzed have been obtained using the three-dimensional linearized theory of stability of deformable bodies. A historical sketch is given of the theory of stability for and approaches used in the mechanics of laminated and fibrous composite materials Translated from Prikladnaya Mekhanika, Vol. 44, No. 8, pp. 3–31, August 2008.     

三维电阻抗成像的体积元方法的数值模拟和分析

电阻抗成像是一类椭圆方程反问题,本文在三维区域上对其进行数值模拟和分析.对于椭圆方程Neumann边值正问题,本文提出了四面体单元上的一类对称体积元格式,并证明了格式的半正定性及解的存在性;引入单元形状矩阵的概念,简化了系数矩阵的计算;提出了对电阻率进行拼接逼近的方法来降低反问题求解规模,使之与正问题的求解规模相匹配;导出了误差泛函的Jacobi矩阵的计算公式,利用体积元格式的对称性和特殊的电流基向量,将每次迭代中需要求解的正问题的个数降到最低.一系列数值实验的结果验证了数学模型的可靠性和算法的可行性.本文所提出的这些方法,已成功应用于三维电阻抗成像的实际数值模拟.     

Assessment of regularized delta functions and feedback forcing schemes for an immersed boundary method

We present an improved immersed boundary method for simulating incompressible viscous flow around an arbitrarily moving body on a fixed computational grid. To achieve a large Courant–Friedrichs–Lewy number and to transfer quantities between Eulerian and Lagrangian domains effectively, we combined the feedback forcing scheme of the virtual boundary method with Peskin's regularized delta function approach. Stability analysis of the proposed method was carried out for various types of regularized delta functions. The stability regime of the 4‐point regularized delta function was much wider than that of the 2‐point delta function. An optimum regime of the feedback forcing is suggested on the basis of the analysis of stability limits and feedback forcing gains. The proposed method was implemented in a finite‐difference and fractional‐step context. The proposed method was tested on several flow problems, including the flow past a stationary cylinder, inline oscillation of a cylinder in a quiescent fluid, and transverse oscillation of a circular cylinder in a free‐stream. The findings were in excellent agreement with previous numerical and experimental results. Copyright © 2008 John Wiley & Sons, Ltd.