Determination of the Failure Stresses for Fluid-filled Microcapsules that Rupture Near the Elastic Regime

The encapsulation of liquids within an external wall or shell is an important technology often utilized in the production of many commercial products. The mechanical characterization of such microcapsules is paramount in order to fully understand their performance in their target environment. Some microcapsules, with wall materials such as inorganic based compounds, rupture at small deformations, commonly near the elastic regime. The study herein presents a general methodology that enables calculation of the failure stresses leading to the elastic-like rupture of microcapsules under parallel compression testing. Two scenarios of failure, brittle and ductile, were considered. Analyses of the critical stresses present within the microcapsule wall during different degrees of fractional deformation were obtained using finite element modelling, resulting in similar values for both the brittle and ductile scenarios. The correlations presented were used to determine the failure stresses of tetraethoxyorthosilane-methyltrimethoxysilane (TEOS-MTMS) microcapsules with a model core oil, which are 11?C14?±?10?MPa. The data were further analyzed using Weibull distributions.     

[UIII{N(SiMe2tBu)2}3]: A Structurally Authenticated Trigonal Planar Actinide Complex

We report the synthesis and characterization of the uranium(III) triamide complex [U^III(N**)₃] [ 1 , N**=N(SiMe₂tBu)₂^?]. Surprisingly, complex 1 exhibits a trigonal planar geometry in the solid state, which is unprecedented for three‐coordinate actinide complexes that have exclusively adopted trigonal pyramidal geometries to date. The characterization data for [U^III(N**)₃] were compared with the prototypical trigonal pyramidal uranium(III) triamide complex [U^III(N“)₃] (N”=N(SiMe₃)₂^?), and taken together with theoretical calculations it was concluded that pyramidalization results in net stabilization for [U^III(N“)₃], but this can be overcome with very sterically demanding ligands, such as N**. The planarity of 1 leads to favorable magnetic dynamics, which may be considered in the future design of U^III single‐molecule magnets.     

Molecular dynamics in a miscible polyester blend

The dynamic mechanical and dielectric spectra of a miscible polyester and polycarbonate blend are investigated with emphasis on the latter technique. It was found that relaxation spectra for the blends from both techniques are broader than those of the constituent homopolymers. This is ascribed to greater intermolecular coupling and concentration fluctuations within the blends. The composition at which the greatest coupling occurs is dependent on the relaxation technique used and is skewed towards the component which shows the highest degree of intermolecular coupling. A number of parameters, such as relaxation time of the polymer molecules in the blend and relaxation strength, are compared as a function of reduced temperature (experimental temperature scaled by the glass transition temperature). Whereas blend behavior is generally intermediate between that of the homopolymers, it appears as though mobility of compositions with low polyester content have a greater relaxation time and possess a higher activation energy when compared to a simple, weighted average of the corresponding homopolymer values. © 1996 John Wiley & Sons, Inc.     

二烯丙基二甲基氯化铵—丙烯酰胺反相乳液聚合的动力学特征研究

采用油酸失水山梨醇酯（ＳＰＡＮ）－壬基酚聚氧化乙烯醚（ＯＰ）复合乳化剂与Ｋ２Ｓ２Ｏ８－Ｎａ２ＳＯ３氧化还原引发剂，进行二烯丙基二甲基氯化铵－丙烯酰胺反相乳液共聚合，测得单体的竞聚率为γＤＡＤＭＡＣ＝０．１４±０．１１，γＡＭ＝５．０５±０．６６；在单体浓度为２５─４５％，引发剂浓度０．０６—０．１％，乳化剂浓度为５—９％，聚合温度３０３Ｋ条件下，得到了共聚反应动力学方程：Ｒｐ＝ｋ［Ｍ］０．６８［Ｉ］１．３１［Ｅ］０．７３，文中对上述结果做了解释．     

不确定信息处理及在归纳学习中的应用

信息的不确定性是由于模糊性、随机性、不完全性、不精确性等因素造成的,不确定性信息在现实世界中广泛存在.关于这方面的研究主要集中在模糊性这种不确定性上.我们课题组在此领域的研究已经持续20余年,概括起来讲,早期的研究兴趣在于模糊(非可加)测度与积分的理论建立,主要研究了传统的可加测度与积分理论到非可加情况的推广;尔后的兴趣转向为如何用数值方法确定非可加测度;近期的研究兴趣在于从已有数据中获取模糊控制规则以及具有模糊表示的归纳学习问题.近10年的研究曾得到了多项基金项目资助,出版专著3部,发表学术论文100余篇,30余篇被SCI收录,20余篇被EI收录,省级以上奖励3项.以下是我们近期研究工作的一个总结,主要包括模糊决策树归纳;基于模糊信息的决策表简化;产生模糊规则的扩张矩阵算法;模糊归纳学习在其他领域中的应用;基于示例学习的模糊控制等.     

Negative thermal expansion in ZrW2O8: mechanisms, rigid unit modes, and neutron total scattering

The local structure of the low-temperature ordered phase of the negative thermal expansion (NTE) material has been investigated by reverse Monte Carlo (RMC) modeling of neutron total scattering data. We obtain, for the first time, quantitative measurements of the extent to which the and polyhedra move as rigid units, and we show that these values are consistent with the predictions of rigid unit mode theory. We suggest that rigid unit modes are associated with the NTE. Our results do not support a recent interpretation of x-ray-absorption fine structure spectroscopy data in terms of a larger rigid structural component involving the Zr-O-W linkage.     

Phonons from powder diffraction: a quantitative model-independent evaluation

We describe a model-independent approach for the extraction of detailed lattice dynamics information from neutron powder diffraction data, based on a statistical analysis of atomistic configurations generated using reverse Monte Carlo structural refinement. Phonon dispersion curves for MgO extracted in this way are shown to reproduce many of the important features found in those determined independently using neutron triple-axis spectroscopy. By means of molecular dynamics simulations, we quantify the extent to which the diffraction data are sensitive to lattice dynamics in this system.     

Stereochemistry and mechanism of the conversion of 5-aminolaevulinic acid into porphobilinogen catalysed by porphobilinogen synthase

(3R)- and (3S)-Deuteriated forms of 5-aminolaevulinic acid have been synthesized and the (3R)-form shows a significantly larger isotope effect when incubated with porphobilinogen synthase from bovine liver and from Bacillus subtilis; based on this and on available crystal structures, a modified mechanism for the enzymic reaction is proposed.