分子轨道波函数相对论效应的高分辨电子动量谱学观测

利用新研制的能量分辨为0.5 eV 的高分辨(e, 2e)谱仪测量了CF3I分子在9—15 eV能区的束缚能谱.新谱仪能较好地分辨该分子碘孤对轨道的自旋轨道劈裂组分5e3/2和5e1/2,并得到了它们各自的电子动量分布以及分支比随动量的变化关系.实验结果清楚地显示了5e3/2和5e1/2态波函数的相对论效应.这是第一个分子轨道波函数相对论效应的直接实验观测.     

Electron energy state spin-splitting in 3D cylindrical semiconductor quantum dots

In this article we study the impact of the spin-orbit interaction on the electron quantum confinement for narrow gap semiconductor quantum dots. The model formulation includes: (1) the effective one-band Hamiltonian approximation; (2) the position- and energy-dependent quasi-particle effective mass approximation; (3) the finite hard wall confinement potential; and (4) the spin-dependent Ben Daniel-Duke boundary conditions. The Hartree-Fock approximation is also utilized for evaluating the characteristics of a two-electron quantum dot system. In our calculation, we describe the spin-orbit interaction which comes from both the spin-dependent boundary conditions and the Rashba term (for two-electron quantum dot system). It can significantly modify the electron energy spectrum for InAs semiconductor quantum dots built in the GaAs matrix. The energy state spin-splitting is strongly dependent on the dot size and reaches an experimentally measurable magnitude for relatively small dots. In addition, we have found the Coulomb interaction and the spin-splitting are suppressed in quantum dots with small height. Received 15 May 2001 / Received in final form 14 May 2002 Published online 13 August 2002     

自支撑电极材料的制备及其电解水性能实验设计

介绍了创新型新能源实验“自支撑电极材料的制备及其电解水性能实验设计”的开设,阐述了由科研成果到开设实验教学的基本设计思路,详细说明了自支撑非铂催化电极的制备方法、结构表征及其在全解水中的应用,并总结分析了该实验课程实践后的经验与反思。教学实践表明：学生对新能源实验表现出了高度的兴趣;实验的开展在培养学生独立调研、实验和写作能力的基础上,更增强了其创新思维和逆向思维的能力。     

First-principles study of two-dimensional van der Waals heterostructure based on ZnO and Mg(OH)2: A potential photocatalyst for water splitting

In this study, the structural, electronic and optical properties of the two-dimensional heterostructure based on ZnO and Mg(OH)₂ are investigated by first-principle calculations. The ZnO/Mg(OH)₂ heterostructure, formed by van der Waals (vdW) interaction, possesses a type-II band structure, which can separate the photogenerated electron–holes constantly. The heterostructure has decent band edge positions for the redox reaction to decompose the water at pH 0 and 7. As for the interfacial properties of the heterostructure, the trend of band bending of the ZnO and Mg(OH)₂ layers in the heterostructure is addressed, which will result a built-in electric field. Besides, the charge-density difference and potential drop across the interface of the ZnO/Mg(OH)₂ vdW heterostructure are also calculated. Finally, the heterostructure is demonstrated that it not only has excellent ability to capture the light near the visible spectrum region, but also can improve the optical performance for the monolayered ZnO and Mg(OH)₂.     

Co3O4@Cu-Based Conductive Metal–Organic Framework Core–Shell Nanowire Electrocatalysts Enable Efficient Low-Overall-Potential Water Splitting

In the work reported herein, the electrocatalytic properties of Co₃O₄ in hydrogen and oxygen evolution reactions have been significantly enhanced by coating a shell layer of a copper-based metal–organic framework on Co₃O₄ porous nanowire arrays and using the products as high-performance bifunctional electrocatalysts for overall water splitting. The coating of the copper-based metal–organic framework resulted in the hybridization of the copper-embedded protective carbon shell layer with Co₃O₄ to create a strong Cu−O−Co bonding interaction for efficient hydrogen adsorption. The hybridization also led to electronically induced oxygen defects and nitrogen doping to effectively enhance the electrical conductivity of Co₃O₄. The optimal as-prepared core–shell hybrid material displayed excellent overall-water-splitting catalytic activity that required overall voltages of 1.45 and 1.57 V to reach onset and a current density of 10 mA cm⁻², respectively. This is the first report to highlight the relevance of hybridizing MOF-based co-catalysts to boost the electrocatalytic performance of nonprecious transition-metal oxides.     

Iron‐Based Molecular Water Oxidation Catalysts: Abundant,Cheap, and Promising

An efficient and robust water oxidation catalyst based on abundant and cheap materials is the key to converting solar energy into fuels through artificial photosynthesis for the future of humans. The development of molecular water oxidation catalysts (MWOCs) is a smart way to achieve promising catalytic activity, thanks to the clear structures and catalytic mechanisms of molecular catalysts. Efficient MWOCs based on noble‐metal complexes, for example, ruthenium and iridium, have been well developed over the last 30 years; however, the development of earth‐abundant metal‐based MWOCs is very limited and still challenging. Herein, the promising prospect of iron‐based MWOCs is highlighted, with a comprehensive summary of previously reported studies and future research focus in this area.     

Polynomial coefficients. Application to spin–spin splitting by N equivalent nuclei of spin I > 1/2

The NMR intensity pattern of a nucleus split by N identical nuclei of spin 1/2 is given by the binomial coefficients. These are conveniently obtained from Pascal's triangle, equivalent to the chemist's branching diagram. Much less well‐known is the pattern from splitting by N identical nuclei of spin I > 1/2. This was originally presented in terms of multinomial coefficients, but polynomial coefficients are more convenient. These describe the number of ways that N objects can be distributed to 2I + 1 numbered boxes. They arise in the polynomial expansion and are conveniently obtained from generalizations of Pascal's triangle. Examples and predictions are given.     

迎风通量差分分裂法对边界层特性的数值模拟

迎风通量差分分裂法作为一种高效率的数值方法,已被广泛地用于模拟各种复杂流场,但用这类方法模拟有边界层存在的超音速粘性流场时,必须保证通量差分分裂为守恒的;否则,将在边界层内引入一个可观的虚假人工扩散项和压力梯度项,歪曲了边界层特性。本文就这个问题进行理论和数值的研究。     

铁道车辆用新型减振材料的摩擦磨损行为研究

对铁道车辆摩擦减振系统所用斜楔和磨耗板新型材料进行了磨损试验研究,并分析了其摩擦磨损行为.结果表明,T10与ADI球铁、奥贝灰铸铁和高分子材料配副的耐磨性均优于45#钢与ADI球铁配副,磨耗板材料的相对耐磨性均优于斜楔,T10与高分子材料配副具有最佳的摩擦磨损性能.     

An operator splitting algorithm for the three-dimensional advection–diffusion equation

Operator splitting algorithms are frequently used for solving the advection–diffusion equation, especially to deal with advection dominated transport problems. In this paper an operator splitting algorithm for the three-dimensional advection–diffusion equation is presented. The algorithm represents a second-order-accurate adaptation of the Holly and Preissmann scheme for three-dimensional problems. The governing equation is split into an advection equation and a diffusion equation, and they are solved by a backward method of characteristics and a finite element method, respectively. The Hermite interpolation function is used for interpolation of concentration in the advection step. The spatial gradients of concentration in the Hermite interpolation are obtained by solving equations for concentration gradients in the advection step. To make the composite algorithm efficient, only three equations for first-order concentration derivatives are solved in the diffusion step of computation. The higher-order spatial concentration gradients, necessary to advance the solution in a computational cycle, are obtained by numerical differentiations based on the available information. The simulation characteristics and accuracy of the proposed algorithm are demonstrated by several advection dominated transport problems. © 1998 John Wiley & Sons, Ltd.