The Roles of Composition and Mesostructure of Cobalt-Based Spinel Catalysts in Oxygen Evolution Reactions

By using the crystalline precursor decomposition approach and direct co-precipitation the composition and mesostructure of cobalt-based spinels can be controlled. A systematic substitution of cobalt with redox-active iron and redox-inactive magnesium and aluminum in a cobalt spinel with anisotropic particle morphology with a preferred 111 surface termination is presented, resulting in a substitution series including Co₃O₄, MgCo₂O₄, Co₂FeO₄, Co₂AlO₄ and CoFe₂O₄. The role of redox pairs in the spinels is investigated in chemical water oxidation by using ceric ammonium nitrate (CAN test), electrochemical oxygen evolution reaction (OER) and H₂O₂ decomposition. Studying the effect of dominant surface termination, isotropic Co₃O₄ and CoFe₂O₄ catalysts with more or less spherical particles are compared to their anisotropic analogues. For CAN-test and OER, Co³⁺ plays the major role for high activity. In H₂O₂ decomposition, Co²⁺ reveals itself to be of major importance. Redox active cations in the structure enhance the catalytic activity in all reactions. A benefit of a predominant 111 surface termination depends on the cobalt oxidation state in the as-prepared catalysts and the investigated reaction.     

Quantitative decomposition of resonance-assisted hydrogen bond energy in β-diketones into resonance and hydrogen bonding (π- and σ-) components using molecular tailoring and function-based approaches

Using the molecular tailoring and function-based approaches allows one to divide the energy of the O─H⋯O═C resonance-assisted hydrogen bond in a series of the β-diketones into resonance and hydrogen bonding components. The magnitude of the resonance component is assessed as about 6 kcal mol⁻¹. This value increases by ca. 1 kcal mol⁻¹ on going from the weak to strong resonance-assisted hydrogen bonding. The magnitude of the hydrogen bonding component varies in the wide range from 2 to 20 kcal mol⁻¹ depending on the structure of the β-diketone in question.     

Nonlinear free vibrations of porous composite microplates incorporating various microstructural-dependent strain gradient tensors

The main objective of the present numerical analysis is to predict the nonlinear frequency ratios associated with the nonlinear free vibration response of porous composite plates at microscale in the presence of different microstructural gradient tensors. To achieve this end, by taking cubic-type elements into account, isogeometric models of porous composite microplates are obtained with and without a central cutout and relevant to various porosity patterns of distribution along the plate thickness. The established unconventional models have the capability to capture the effects of various unconventional gradient tensors continuity on the basis of a refined shear deformable plate formulation. For the simply supported microsized uniform porous functionally graded material (U-PFGM) plate having the oscillation amplitude equal to the plate thickness, it is revealed that the rotation gradient tensor causes to reduce the frequency ratio about 0.73%, the dilatation gradient tensor causes to reduce it about 1.93%, and the deviatoric stretch gradient tensor leads to a decrease of it about 5.19%. On the other hand, for the clamped microsized U-PFGM plate having the oscillation amplitude equal to the plate thickness, these percentages are equal to 0.62%, 1.64%, and 4.40%, respectively. Accordingly, it is found that by changing the boundary conditions from clamped to simply supported, the effect of microsize on the reduction of frequency ratio decreases a bit.

     

Novel filled polymer composites prepared from in situ polymerization via a colloidal approach: II. Blends of kaolin/Nylon-6 in situ composites with conventional Nylon-6 and -66

A novel in situ composite comprised of kaolin clay fillers and polyamide 6 (Nylon-6) was synthesized via a colloidal approach by suspending kaolin particles in aqueous caprolactam and then polymerizing the caprolactam under elevated temperature and pressure. This in situ polymerization technique enables the deposition of nylon molecules directly onto the filler surface. It offers a much larger contact surface area for the nylon molecules to interact with the filler particles and enhances filler/matrix interaction through polymer miscibility. The kaolin particles were shown to be uniformly dispersed in Nylon-6 matrix without appreciable agglomeration. In the highly clay-loaded composites such as the 50/50 kaolin/Nylon-6 in situ composite, the deposited nylon molecules probably form a coated layer on the filler particles. This kind of nylon coated fillers may be applied as a reinforcing entity to commercial Nylon-6 or −;66 by improving particle dispersion and melt processability. The 50/50 kaolin/Nylon-6 in situ composites have been used as a masterbatch for blending with commercial Nylon-6 and Nylon-66 to take advantage of their good properties and to reduce cost. Rheology and mechanical properties of the masterbatch/nylon composites have been investigated in comparison with those of the conventional melt-mixed composites. The improvement of rheological and mechanical properties of the in situ composites has been discussed in relation to the composite structure. © 1996 John Wiley & Sons, Inc.     

振荡Robin混合边值齐次化问题

该文研究了振荡Robin混合边值齐次化问题解的收敛率.该工作的困难之处在于Robin边值上出现的振荡因子以及边界交叉项的处理.该文利用对偶方法巧妙得对振荡积分进行了估计.文中建立了解的H1和L2收敛率,所得结果明显地依赖于维数.该文可以视为将对偶方法和光滑算子,延拓到处理振荡Robin混合边值问题的情形.     

烯丙基硅烷的一步法合成研究

采用一步合成方式,将3-溴丙烯与金属镁在以甲苯和供电子溶剂(乙醚或THF)构成的混合溶剂中进行反应,继而与四氯化硅反应,成功合成了四烯丙基硅烷,其产率在乙醚与3-溴丙烯的摩尔比为4(V甲苯/V乙醚=1·1)时达到极值,超过了91%。研究同时发现,选择THF代替乙醚时,同样在THF与3-溴丙烯的摩尔比为4(V甲苯/VTHF=1·7)时产率达到极值(63·12%)。本过程可提高产率,降低成本,是一条好的生产四烯丙基硅烷的路线。     

汇率变动对进出口影响的实证分析

本文研究了汇率变动对中国进出口的影响,在间接标价法下对论文中所用到的汇率贬值改善国际收支的三个必要条件给出了结论和证明(弹性法);在经济理论及经验研究的基础上,建立了论文中所需要的所有模型并且根据模型对相关经济问题利用现代计量经济学方法进行了实证研究.通过实证研究我们得到的结论是:我国满足汇率贬值改善国际收支的必要条件;出口增加有助于GDP的增长,进口增加对GDP的影响是反向的且随着进口增加这种影响逐渐减弱最终趋于零.     

CONTINUUM TOPOLOGY OPTIMIZATION FOR MONOLITHIC COMPLIANT MECHANISMS OF MICRO-ACTUATORS

A multi-objective scheme for structural topology optimization of distributed compliant mechanisms of micro-actuators in MEMS condition is presented in this work, in which mechanical flexibility and structural stiffness are both considered as objective functions. The compliant micro-mechanism developed in this way can not only provide sufficient output work but also have sufficient rigidity to resist reaction forces and maintain its shape when holding the work-piece. A density filtering approach is also proposed to eliminate numerical instabilities such as checkerboards, mesh-dependency and one-node connected hinges occurring in resulting mechanisms. SIMP is used as the interpolation scheme to indicate the dependence of material modulus on element-regularized densities. The sequential convex programming method, such as the method of moving asymptotes (MMA), is used to solve the optimization problem. The validation of the presented methodologies is demonstrated by a typical numerical example.     

位移约束集成化处理的连续体结构拓扑优化

为解决多工况下多位移约束的连续体结构拓扑优化问题,引入了K-S函数对位移约束进行集成化处理.在建立优化模型时,基于莫尔定理按ICM方法导出约束点位移与设计变量之间的近似显函数关系,然后采用Lagrange乘子法进行求解.给出三个算例对该方法进行验证,并与ESO法、BESO法、MD法以及均匀化方法的结果进行比较.结果表明:该方法计算效率较高,并且能够计算出更合理的结构拓扑.