基于催化应用调控氧化铈纳米材料的形貌

催化剂的设计、合成和结构调控是获得优异性能的关键.传统的策略主要是尽量减小催化剂颗粒尺寸以增加活性中心的数目,即尺寸效应.近年来,材料科学的快速发展使得在纳米尺度上调变催化剂的尺寸和形貌成为可能,特别是通过形貌调控可暴露更多的高活性晶面,大幅度提高催化性能,即纳米催化中的形貌效应.因此,调节催化剂的尺寸与形貌可以单独或协同优化材料的性能.氧化铈作为催化剂的重要组分与结构、电子促进剂被广泛应用于多相催化剂体系.本文总结了近期氧化铈材料形貌可控合成的进展,包括主要的合成策略和表征方法; 进而分析了氧化铈和金-氧化铈催化材料的形貌效应,指出金-氧化铈之间独特的相互作用与载体形貌密切相关; 阐述了氧化铈纳米材料因暴露晶面的差异而获得不同催化性能的化学机制.     

关于任意非负随机序列随机和的一类随机偏差定理

本文引入任意随机变量序列随机极限对数似然比概念,作为任意相依随机序列联合分布与其边缘乘积分布“不相似”性的一种度量,利用构造新的密度函数方法来建立几乎处处收敛的上鞅,在适当的条件下,给出了任意受控随机序列的一类随机偏差定理.     

ZnO双晶纳米梳

以纯锌粉作为原料，用气相输运法在650℃合成了ZnO双晶纳米梳结构，并用高分辨透射电镜 及选区电子衍射等方法对其微观结构进行了研究.结果表明双晶纳米梳两侧的齿针呈一定角 度以孪晶方式对称生长，其孪晶面为(1 1-3)，两侧齿针都垂直于孪晶界，其直径均匀分布 在50—100nm，每一侧梳背和齿针的生长方向均分别为〈0 1-1 0〉和〈0 0 0 1〉.由于孪晶 造成了晶体取向的变化，基于镜像对称的特征，ZnO双晶纳米梳两侧梳背的外缘可以均为Zn 终结的(0 0 0 1)面，因此都可以发生自催化作用并形成分支结构，这种纳米结构的生长过 程与王中林等人提出的极性生长机理相符合. 关键词： 氧化锌 纳米梳 双晶 极性生长     

R~2上带奇异性的非线性多重调和方程的正整解

该文以 Schauder- Tychonoff不动点定理为工具 ,建立了一类平面上带奇异性的非线性多重调和方程的正的径向对称整体解的存在性定理 ,并给出了解的有关性质 ,所得的结果丰富和发展文 [1 - 4]的结果     

A Note on Reducing the Number of Variables in Integer Programming Problems

A necessary and sufficient condition for identification of dominatedcolumns, which correspond to one type of redundant integer variables,in the matrix of a general Integer Programming problem, isderived. The given condition extends our recent work on eliminatingdominated integer variables in Knapsack problems, and revises arecently published procedure for reducing the number of variables ingeneral Integer Programming problems given in the literature. Areport on computational experiments for one class of large scaleKnapsack problems, illustrating the function of this approach, isincluded.     

氢吸附金刚石（001）表面的第一性原理研究

采用第一性原理方法研究氢吸附的金刚石（001）表面，计算了氢吸附金刚石表面构型.通过分析吸附前后空间电荷分布的变化，发现吸附H原子的金刚石（001）表面电荷向H原子转移，即表明氢吸附的金刚石表面带负电.分析了这种现象的微观机制，以及它对金刚石表面电学性质的影响. 关键词： 第一性原理计算 金刚石（001）面 表面吸附 电荷密度分布     

Designing p‐Type Semiconductor–Metal Hybrid Structures for Improved Photocatalysis

A practical strategy is proposed to facilitate the migration of holes in semiconductor (the low rate of which limits photocatalytic efficiency) by taking advantage of the Schottky barrier between p‐type semiconductor and metal. A high work function is found to serve as an important selection rule for building such desirable Schottky junction between semiconductor surface facets and metal. The intrinsic charge spatial distribution has to be taken into account when selecting the facets, as it results in accumulation of photoexcited electrons and holes on certain semiconductor facets. Importantly, the facets have a high work function, the same characteristic required for the formation of Schottky junction in a p‐type semiconductor–metal hybrid structure. As a result, the semiconductor crystals in the hybrid design may be better enclosed by single facets with high work function, so as to synergize the two effects: Schottky barrier versus charge spatial separation.     

Facet‐Dependent Effect of Well‐Defined CeO2 Nanocrystals on the Adsorption and Dephosphorylation of Phosphorylated Molecules

CeO₂ nanocrystals (CN) with different morphologies (i.e., cube, octahedron, and rod) are prepared and the facet‐dependent effect of these CeO₂ nanocrystals on the adsorption and dephosphorylation of phosphorylated molecules is investigated for the first time using the model p‐nitrophenyl disodium orthophorphate (p‐NPP). Due to their different surface atomic configurations, the {111} and {110} facets have much higher adsorption capacity and kinetic catalytic activities than {100} facets. All the CeO₂ nanocrystals can intensely promote the dephosphorylation reaction owing to the strong interaction between Ce cations and phosphoryl oxygens resulting in the cleavage of phosphoester bonds. As was expected, the above facet‐dependent effect can be verified by the practical application results of the CeO₂ nanocrystals on the capture and dephosphorylation of phosphopeptides. Thus, surface engineering could be a useful and feasible strategy for not only fundamentally understanding the interaction between crystal facets and molecules but also effectively developing high‐performance functional materials.     

The characteristic finite element alternating direction method with moving meshes for nonlinear convection‐dominated diffusion problems

In modern numerical simulation of prospecting and exploiting oil‐gas resources and in environmental science, it is necessary to consider numerical method of nonlinear convection‐dominated diffusion problems. This thesis, starting from actual conditions such as the three‐dimensional characteristics of large‐scale science‐engineering computation, puts forward a kind of characteristic finite element alternating direction method with moving meshes. Some techniques, such as calculus of variations, operator‐splitting, generalized L² projection, energy method, negative norm estimate, the theory of prior estimates and techniques, are adopted. Optimal order estimates in L² norm are derived to determine the errors in the approximate solution. Thus the important theoretical problem has been solved. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005     

Polarity and the complexity of the shooting experiment

We exhibit a polar relationship between two measures that have been proposed to evaluate the importance of TSP facets, the Kuhn–Gomory shooting experiment size and the probability of integrality in an augmented LP relaxation. The polarity establishes the complexity of performing the shooting experiment. We illustrate the resulting relationship on the Chinese postman and minimum spanning set problems.