Trends in the electronic structure of extended gold compounds: implications for use of gold in heterogeneous catalysis

First-principles electronic structure calculations are presented on a variety of Au compounds and species--encompassing a wide range of formal oxidation states, coordination geometries, and chemical environments--in order to understand the potentially systematic behavior in the nature and energetics of d states that are implicated in catalytic activity. In particular, we monitor the position of the d-band center, which has been suggested to signal catalytic activity for reactions such as CO oxidation. We find a surprising absence of any kind of correlation between the formal oxidation state of Au and the position of the d-band center. Instead, we find that the center of the d band displays a nearly linear dependence on the degree of its filling, and this is a general relationship for Au irrespective of the chemistry or geometry of the particular Au compound. Across the compounds examined we find that even small calculated changes in the d-band filling result in a relatively large effect on the position of the d-band center. The results presented here have some important implications for the question of the catalytic activity of Au and indicate that the formal oxidation state is not a determining factor.     

离子液体-水双相体系悬浮聚合法制备对苯二酚分子印迹聚合物微球

通过在[Bmim]PF6离子液体-水双相体系中,以对苯二酚为模板分子,甲基丙烯酸为功能单体,二甲基丙烯酸乙二醇脂为交联剂,采用悬浮聚合法制备得到对苯二酚印迹聚合物微球(MIMs-IL),并通过FTIR等测试技术对MIMs-IL进行了表征。对不同离子液体进行了选择,[Bmim]PF6介质中制备的MIMs-IL的识别性能最好。与从氯仿介质中制备的印迹聚合物微球(MIMs-Or)相比较,MIMs-IL的产率为70.8%,明显高于MIMs-Or的48.7%。采用静态吸附法考察其印迹识别能力的结果表明,MIMs-IL对水中的对苯二酚的识别能力大大强于MIMs-Or。对MIMs-IL识别吸附的热力学和动力学研究结果表明,12h时MIMs-IL及其非印迹聚合物微球(nMIMs-IL)均达到各自饱和吸附量,对于0.50g/L对苯二酚水溶液,MIMs-IL的饱和吸附量是nMIMs-IL的2.67倍。     

Synthesis and activity of a new series of (Z)-3-phenyl-2-benzoylpropenoic acid derivatives as aldose reductase inhibitors

During the course of studies directed towards the discovery of novel aldose reductase inhibitors for the treatment of diabetic complications, we synthesized a series of new (Z)-3-phenyl-2-benzoylpropenoic acid derivatives and tested their in vitro inhibitory activities on rat lens aldose reductase. Of these compounds, (Z)-3-(3,4-dihydroxyphenyl)-2-(4-methylbenzoyl)propenoicacid (3k) was identified as the most potent inhibitor, with an IC50 of 0.49 microM. The theoretical binding mode of 3k was obtained by simulation of its docking into the active site of the human aldose reductase crystal structure.     

温度、pH值和氯离子对X80钢钝化膜内点缺陷扩散系数的影响

借助于Mott-Schottky和点缺陷模型(PDM)研究了溶液温度、pH值以及氯离子对X80管线钢在模拟土壤环境中所形成钝化膜内点缺陷扩散系数D₀的影响. 结果表明: 随着溶液温度的升高、溶液pH值的降低以及氯离子浓度的增大, 钝化膜内的施主密度呈现增大的趋势. 依据点缺陷模型可以得到钝化膜内点缺陷(假设点缺陷为氧空位或铁离子间隙)的扩散系数D₀达到10^－16～10^－17 cm²•S^－1, 且D₀随着溶液温度的升高、溶液pH值的降低及氯离子浓度的增加而增大.     

Microwave Absorbing Materials： Solutions for Real Functions under Ideal Conditions of Microwave Absorption

We present general equations for metal-substrate single-layer microwave absorbing materials. The optimum electromagnetic parameters and matching thicknesses for electric-loss, magnetic-loss, and electromagnetic-loss materials are given, and possible solutions for the equations and the corresponding theoretic curves are discussed as well. The results may be helpful for designing high-performance microwave absorbing materials.     

A new algorithm for workspace analysis for robot manipulators

Summary A new algorithm to determine the workspace of a robot manipulator is presented in this paper. The method is based on the concept of dividing the robot structure into a regional structure and an orientational structure and is much more efficient than many methods currently available. Another advantage is that the method is expedient to plot the contours of the workspace of a robot manipulator on an arbitrarily defined plane or determine the extreme points along a general direction. The problem of determining subspaces of different joint configurations is also addressed and a method to compute them is proposed. Since for an ordinary industrial robot the regional structure is usually solvable to the first three joint variables, the method proposed is efficient computationally. The applicability of the method is demonstrated by some numeric examples.

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Sommario Nel lavoro viene presentato un nuovo algoritmo per determinare il campo di lavoro di un manipolatore robotico. Il metodo utilizza il concetto di dividere la struttura del manipolatore ad una struttura regionale ed una struttura orientamentale ed è molto più efficace di molti metodi esistenti. Un altro vantaggio del metodo è che esso è conveniente per disegnare i contorni del campo di lavoro su un piano specificato arbitrariamente oppure per determinare i punti estremi lungo una direzione generale. Nel lavoro è studiato anche il problema di determinare i sottospazi di configurazioni diverse dei giunti e viene presentato un metodo per calcolarli. Siccome per un robot industriale la struttura regionale è normalmente risolubile per le prime tre variabili dei giunti, il metodo presentato è molto efficace computazionalmente. L'applicabilità del metodo è dimostrata da qualche esempio numerico.

     

二维格子神经元网络的振动共振和非线性振动共振

本文采用数值模拟的方法, 在通过电突触耦合或化学突触耦合的二维格子神经元网络中, 研究了FitzHugh-Nagumo神经元受到双频信号输入时神经元网络对低频信号的响应特性. 结果表明:当固定受到双频输入信号的神经元在体系中所占的比例且FitzHugh-Nagumo神经元参数处于可激发区域时双频信号中的高频部分可诱导出动作电位产生, 而且随着高频输入信号强度的增加, 神经元网络对低频输入信号响应先增大后减小, 出现了极大值, 即发生了振动共振现象. 另外本文还研究了神经元网络对低频输入信号的二次谐波的响应, 同样发现了非线性振动共振现象, 并且体系对低频信号的响应随着其频率ω 的增加也产生共振现象, 即发生了双共振现象. 上述共振现象在以电突触耦合的二维格子神经元网络中和以化学突触耦合的二维格子神经元网络中都可以观察到. 当固定双频输入信号中高频输入信号强度时, 随着受到双频输入信号的神经元在体系中所占比例的变化, 电突触耦合的二维格子神经元网络对低频输入信号的响应与化学突触耦合的二维格子神经元网络对低频输入信号的响应相比有很大的不同.     

A note on algebraic independence criterion for Laurent series in positive characteristic

Periodica Mathematica Hungarica - We study the algebraic independence of Laurent series in positive characteristic which can be fast approximated by rational functions. This can be seen as a...     

Synthesis and Crystal Structure of Palladium(Ⅱ) Complex with 2,2''-Bipyridine-3,3''-dicarboxylic Acid

The title complex Pd(H2BDA)Cl2(2DMSO (C16H14Cl2N2O6PdS2, H2BDA = 2,2'- bipyridine-3,3'-dicarboxylic acid) has been synthesized and characterized by IR spectra, elemental analysis and 1H NMR spectra. Its structure was determined by single-crystal X-ray diffraction analysis. The complex crystallizes in the monoclinic system, space group P21/c with a = 1.3604(6), b = 1.2606(6), c = 1.3521(6) nm, β = 103.677(7)°, V = 2.2530(17) nm3, Mr = 571.75, Z = 4, Dc = 1.686 g/cm3, μ = 1.280 mm-1, F(000) = 1136, R = 0.0405 and wR = 0.0908. The complex presents a planar quadrangle arrangement and is assembled via hydrogen bonds.     

Dynamic Tensile Behavior and Fracture Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Nanowhiskers

Dynamic tensile properties of glass-fiber polymer composites embedded with ZnO nanowhiskers are investigated by a split Hopkinson tensile bar. The stress-strain curves, ultimate strength, failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by the macroscopic and microscopic observation of fractured specimens. The strain rate effect on the mechanical behavior is discussed and a constitutive model is derived by simulating the experimental data. The experimental results show that the materials have an obvious non-linear constitutive relation and strain rate strengthening effect. The composites with ZnO nanowhiskers under dynamic loading have various failure modes and better mechanical properties.