Impact of the Spatial Organization of Bifunctional Metal–Zeolite Catalysts on the Hydroisomerization of Light Alkanes

Improving product selectivity by controlling the spatial organization of functional sites at the nanoscale is a critical challenge in bifunctional catalysis. We present a series of composite bifunctional catalysts consisting of one-dimensional zeolites (ZSM-22 and mordenite) and a γ-alumina binder, with platinum particles controllably deposited either on the alumina binder or inside the zeolite crystals. The hydroisomerization of n-heptane demonstrates that the catalysts with platinum particles on the binder, which separates platinum and acid sites at the nanoscale, leads to a higher yield of desired isomers than catalysts with platinum particles inside the zeolite crystals. Platinum particles within the zeolite crystals impose pronounced diffusion limitations on reaction intermediates, which leads to secondary cracking reactions, especially for catalysts with narrow micropores or large zeolite crystals. These findings extend the understanding of the “intimacy criterion” for the rational design of bifunctional catalysts for the conversion of low-molecular-weight reactants.     

在常规故障和临界人为错误条件下具有易损坏储备部件可修复系统的解的特征值

讨论了一个由两个部件和一个储备部件,并且具有临界人为错误(human error rates)和常规故障(commor-error rates)的随机数学模型,研究了其预解式的表达式及本征值的数目问题,且得出一个本征值对应一个本征元的结论,并给出证明.     

函数列的黎曼积分极限定理的应用

利用函数列的极限理论方法,研究函数列积分极限中积分和极限可交换次序的问题.对一致收敛的可积函数列给出积分的极限定理,对一致有界局部一致收敛函数列给出积分控制收敛定理,通过大量实例表明该理论的意义所在.     

不连续Reissner矩形板的自由振动

用分区加权残值法研究Ressner矩形板在几何形状,边界条件等有突变时的自由振动问题,将研究对象按照结构几何形状和边界条件的具体情况划分为若干子域,在每个子域内用不同的试函数代入该域的内的控制方程到内部残值,并代入板的边界条件和各子域的协调条件得到边界残值和连续性残值,然后用最小二乘法消除残值,得到特征方程,文中讨论了该方法的收敛性和计算精度,求解了开孔矩形板的固有频率,并与已有结果进行了比较,结果表明：？该方法收敛性好,精度较高,适用范围广。     

不同消化方法对测定酸枣叶中部分金属元素含量的比较研究

使用常规湿法和干法消化方法对酸枣叶进行预处理,用火焰原子吸收法测定了其中的Ｃｕ、Ｆｅ、Ｚｎ、Ｍｎ、Ｓｒ、Ｃａ、Ｍｇ等七种金属元素的含量。结果表明,不同消化方法对某些元素产生的影响不同,损失度也有所差别,为样品预处理方法的选择提供了参考数据,也为进一步研究酸枣叶中金属元素的存在形态打下了基础。     

基于动态财务分析的地质灾害保险定价

将经济学中的动态财务分析(DFA)模型应用于地质灾害保险定价中,对离散的灾害事件、经济损失等进行建模分析,计算出纯保费.实证分析以湖南省邵阳市为例,结果表明该模型实用性强、操作简单,计算出来的保费率具有一定的参考价值.     

Finite- N effects for ideal polymer chains near a flat impenetrable wall

This paper addresses the statistical mechanics of ideal polymer chains next to a hard wall. The principal quantity of interest, from which all monomer densities can be calculated, is the partition function, G _N(z) , for a chain of N discrete monomers with one end fixed a distance z from the wall. It is well accepted that in the limit of infinite N , G _N(z) satisfies the diffusion equation with the Dirichlet boundary condition, G _N(0) = 0 , unless the wall possesses a sufficient attraction, in which case the Robin boundary condition, G _N(0) = - G _N ^′(0) , applies with a positive coefficient, . Here we investigate the leading N ^-1/2 correction, G _N(z) . Prior to the adsorption threshold, G _N(z) is found to involve two distinct parts: a Gaussian correction (for z aN ^1/2 with a model-dependent amplitude, A , and a proximal-layer correction (for z a described by a model-dependent function, B(z) .     

Structural characterization of a seven-coordinated organotin(IV) complex: Tris(dimethyl sulphoxide)nitratodiphenyltin(IV) nitrate

A seven-coordinated organotin(IV) compound has been obtained and its IR spectroscopic properties and X-ray crystal structure are reported. Crystals are monoclinic (p2₁/c) with unit-cell dimensions: a 16.017(9), b 10.365(5), c 15.994(8) Å, β 96.1(1)°, Z = 4. The structure has been determined from diffractometer data (Cu-K_a radiation) by conventional Patterson and Fourier techniques and refined by block-diagonal least-squares procedure to an R value of 0.093 for 4298 independent reflections. The structure consists of monomeric seven-coordinated cations [Sn(C₆H₅)₂NO₃{(CH₃)₂SO}₃] and NO₃- anions. Coordination around tin is pentagonal bipyramidaI with the bidentate nitrate group and the three dimethyl sulphoxide molecules in the equatorial positions and the two phenyl rings at the apices. Literature on seven-coordinated tin(IV) compounds and nitratotin(IV) complexes is quoted and discussed.