The density functional theory study CO oxidation catalyzed by subnanometer AlAg n (n = 1–3) clusters

The efficiency of AlAg _n (n = 1–3) alloy clusters toward CO oxidation is demonstrated from first-principles theory. It is found that these subnanometer species transform into reaction complexes which catalyze CO oxidation through the Langmuir–Hinshelwood path. It is shown that mixing two different metals (Al and Ag) can have beneficial effects on the catalytic activity and the alloyed AlAg₃ cluster is proposed as the best effective nanocatalysts.     

怎样做好静电演示实验

静电学是电学教学的开始，许多电学的基本概念需要从这里建立：由于静电学的内容比较抽象，很需要我们做一些直观的演示。但是，有些实验，有时却不能很好地演示出来，例如玻璃棒不能很好地带电，起电机不能起电，仪器上保持不住所带的电荷等等，产生这些现象的原因主要是由于静电实验有一个共同的特点，就是“高电压，微电荷”。     

复杂系统可靠性分析中的若干统计问题与进展

概述作者近十年来在复杂系统可靠性分析方法研究方面所做的部分研究工作,其中包括:复杂系统可靠性综合评估方法研究;复杂系统贮存可靠性综合评估方法研究;复杂系统可靠性综合验证方法研究;复杂数据类型下的数据填充算法等内容     

Research on improving the transverse resolution of binary optical element by digital-division-mask technique

We present the digital-division-mask technique for the first time to solve the problem of decline in transverse resolution, which is caused by using digital micro-mirror device (DMD) to make binary optical elements (BOEs). One high-frequency gray-tone mask can be divided into several low-frequency masks by fixed or variable low-frequency period sampling. And the superimposed lithography effect of these low-frequency masks in the spatial or temporal domain is the same as that of the original high-frequency gray-tone mask. The paper firstly analyzes the digital-division-mask technique in theory and describes the feasibility and advantages. Then taking the diffractive surface fabrication of refractive-diffractive hybrid lens as an example, we conclude that the digital-division-mask technique improves the edge sharpness of lithography pattern, and enhances the diffractive efficiency of BOEs by experiment.     

Notable third-order optical nonlinearities of a Keplerate-type polyoxometalate in solution and in thin films of PMMA

The third-order nonlinear optical properties of a Keplerate-type polyoxometalate (NH₄)₁₈[(Bu₄N]₂₄[Mo₁₃₂O₃₇₂(H₂O)₇₂(CH₃COO)₃₀]?ca.7NH₄CH₃COO?ca.173H₂O (denoted Bu₄N-{Mo₁₃₂}) in solution and in films of poly(methylmethacrylate) (denoted PMMA) matrix have been studied by the Z-scan method at 532 nm with a pulse duration of 20 ps. Experimental results show that both the solution and the solid films of Bu₄N-{Mo₁₃₂} have nonlinear self-defocusing effects and notable nonlinear reverse saturable absorption. Embedding Bu₄N-{Mo₁₃₂} as inclusion into PMMA host significantly improves the nonlinear absorption coefficient β, while it reduces the nonlinear refractive coefficient as a result of the higher concentration of Bu₄N-{Mo₁₃₂} in PMMA matrix than in solution. The magnitude of β for solid-state Bu₄N-{Mo₁₃₂} in films increases with the increasing amount of incorporated Bu₄N-{Mo₁₃₂}, while the third-order nonlinear refractive index n ₂ decreases. Experimental results prove the high stability of Bu₄N-{Mo₁₃₂} in PMMA films in inorganic acidic and basic solutions. These studies indicate that Bu₄N-{Mo₁₃₂} in thin solid films of PMMA are potential candidates for fabricating nonlinear optical devices.     

荧光光度法测定对二苯胺偶氮苯磺酸(TPOO)-β-环糊精与氨苄青霉索的包合比和包合常数

探讨TPOO-β-环糊精对氨苄青霉素的包合机理,用荧光光度法测定得出TPOO-β-环糊精与氨苄青霉素按照1∶进行包合,包合常数为3. 02×102L/mol.基于TPOO-β-环糊精与氨苄青霉素进行包合表现出的荧光增强的特性,建立了水溶液中测定氨苄青霉素的荧光光度法,该法具有简便、灵敏、快捷等优点.     

A POSTERIORI ERROR ESTIMATE FOR BOUNDARY CONTROL PROBLEMS GOVERNED BY THE PARABOLIC PARTIAL DIFFERENTIAL EQUATIONS

In this paper, we discuss the a posteriori error estimate of the finite element approximation for the boundary control problems governed by the parabolic partial differential equations. Three different a posteriori error estimators are provided for the parabolic boundary control problems with the observations of the distributed state, the boundary state and the final state. It is proven that these estimators are reliable bounds of the finite element approximation errors, which can be used as the indicators of the mesh refinement in adaptive finite element methods.     

VARIATIONAL DISCRETIZATION FOR OPTIMAL CONTROL GOVERNED BY CONVECTION DOMINATED DIFFUSION EQUATIONS

In this paper, we study variational discretization for the constrained optimal control problem governed by convection dominated diffusion equations, where the state equation is approximated by the edge stabilization Galerkin method. A priori error estimates are derived for the state, the adjoint state and the control. Moreover, residual type a posteriori error estimates in the L^2-norm are obtained. Finally, two numerical experiments are presented to illustrate the theoretical results.     

Label-free and sequence-specific DNA detection down to a picomolar level with carbon nanotubes as support for probe DNA

This study describes a simple and label-free electrochemical impedance spectroscopic (EIS) method for sequence-specific detection of DNA by using single-walled carbon nanotubes (SWNTs) as the support for probe DNA. SWNTs are confined onto gold electrodes with mixed self-assembly monolayers of thioethanol and cysteamine. Single-stranded DNA (ssDNA) probe is anchored onto the SWNT support through covalent binding between carboxyl groups at the nanotubes and amino groups at 5′ ends of ssDNA. Hybridization of target DNA with the anchored probe DNA greatly increases the interfacial electron-transfer resistance (R_et) at the double-stranded DNA (dsDNA)-modified electrodes for the redox couple of Fe(CN)₆^3−/4−, which could be used for label-free and sequence-specific DNA detection. EIS results demonstrate that the utilization of SWNTs as the support for probe DNA substantially increases the surface loading of probe DNA onto electrode surface and thus remarkably lowers the detection limit for target DNA. Under the conditions employed here, R_et is linear with the concentration of target DNA within a concentration range from 1 to 10 pM with a detection limit down to 0.8 pM (S/N = 3). This study may offer a novel and label-free electrochemical approach to sensitive sequence-specific DNA detection.