Model studies of the chemisorption of hydrogen and oxygen on nickel surfaces

Atomic chemisorption of hydrogen and oxygen on the Ni(100) surface has been studied using an Effective Core Potential (ECP) approach described in a previous paper. Clusters of up to 50 nickel atoms have been used to model the surface. The computed chemisorption energies are 62 kcal/mol (exp. 63 kcal/mol) for hydrogen and 106 kcal/mol (exp. 115–130 kcal/mol) for oxygen. Correlating the adsorbate and the cluster-adsorbate bonds is extremely important for obtaining accceptable results, particularly for oxygen. Reasonable convergence of chemisorption energies is obtained with 40–50 cluster atoms for both hydrogen and oxygen. For hydrogen the addition of a third cluster layer stabilizes the results considerably. Both hydrogen and oxygen are adsorbed at (or close to) the four-fold hollow site. The calculated barriers for surface migration are also in good agreement with the experimental estimates. The calculated equilibrium heights above the surface are on the other hand too high compared with experiments. This disagreement is believed to be due to core-valence correlation effects, which are not incorporated in the present ECP. The cluster convergence for the height above the surface is much slower than for the chemisorption energy.     

Doubly excited3Se,3De and3Ge states of two-electron atomic systems

Summary Time-dependent perturbation theory has been applied to calculate the doubly excited triplet statesNsns:³S^e,Npnp:³D^e andNdnd:³G^e (N=2, 3, 4,n=N+1, ... ,5) for He, Li⁺, Be²⁺ and B³⁺. A time-dependent harmonic perturbation causes simulataneous excitation of both the electrons with a change of spin state. The doubly excited energy levels have been identified as the poles of an appropriately constructed linearized variational functional with respect to the driving frequency. In addition to the transition energies, effective quantum numbers of these doubly excited states have been calculated and analytic representations of their wave functions are obtained. These are utilized to estimate the Coulomb repulsion term for these states which checks the consistency of the wave functions. These wave functions may also be used for calculating other physical properties of the systems.     

Heterogeneous ECE Processes at Channel Electrodes: Analytical Solution for all Reaction Rate Constants and Different Diffusion Coefficients

An analytical solution is developed for heterogeneous ECE processes occurring at channel electrode surface for both laminar and turbulent flow. The solution explicitly links the behavior of ECE processes and the parameters. A simple expression of the effective number of electrons transferred, covering all the reaction rate constants and different diffusion coefficients of the reactant A and the intermediate product B, is obtained. Excellent agreement with previous numerical and analytical results is shown . Parametric studies illustrate the effects of diffusion coefficients, hydrodynamic factors and reaction rate constants on the effective number of electrons transferred and the currents.     

Comparison of the effective core potential and model potential methods in studies of electron correlation energy in molecules: Dihalides and halogen hydrides

Summary The effective core potential and model potential methods were used in post-SCF calculations on HC1, HBr, Cl₂, and Br₂ in order to gain insight into the effect of insufficient representation of inner nodes in the valence orbitals of the approximate methods. The results show that while the correlation energy may be slightly overestimated (by 1–7%), both the electric moment functions and the quantities depending on energy differences are consistently similar for the methods studied and close to the results from all-electron calculations.Dedicated to Prof. Klaus Ruedenberg     

Challenges in validating the sterilisation dose for processed human amniotic membranes

Most of the tissue banks in the Asia Pacific region have been using ionising radiation at 25 kGy to sterilise human tissues for save clinical usage. Under tissue banking quality system, any dose employed for sterilisation has to be validated and the validation exercise has to be a part of quality document. Tissue grafts, unlike medical items, are not produced in large number per each processing batch and tissues relatively have a different microbial population. A Code of Practice established by the International Atomic Energy Agency (IAEA) in 2004 offers several validation methods using smaller number of samples compared to ISO 11137 (1995), which is meant for medical products. The methods emphasise on bioburden determination, followed by sterility test on samples after they were exposed to verification dose for attaining of sterility assurance level (SAL) of 10⁻¹. This paper describes our experience in using the IAEA Code of Practice in conducting the validation exercise for substantiating 25 kGy as sterilisation dose for both air-dried amnion and those preserved in 99% glycerol.     

Anab initio investigation of Cu2Se and Cu4Se2

Summary Experimentally known copper selenium clusters show extraordinary geometrical features, especially short Cu-Cu distances. We report the first theoretical investigation of Cu₂Se and Cu₄Se₂. Various quantum chemical methods (SCF, MP2, CPF, CCSD, CCSD(T), LDF) are applied to determine the importance of dynamic electron correlation. We find that inclusion of correlation does not essentially change the electronic structure of the clusters but has a strong influence on geometries. To reduce the computational effort we apply effective core potentials (ECPs) in combination with small, but carefully optimized basis sets. The applicability of simple modellings of correlation energies for approximate inclusion of correlation effects in SCF geometry optimizations is tested.     

双模随机晶体场对混合自旋1/2和自旋1纳米管上相变的影响

本文利用有效场理论研究了自旋1/2和自旋1混合Blume-Capel模型在具有双模随机晶体场的圆柱形Ising纳米管上的磁化和相变. 通过数值计算,我们得到了随温度和随机晶体场参数变化的相图和磁化强度. 结果表明: (1) 改变晶体场的概率和比例,双模随机晶体场可以描述不同掺杂原子对自旋的作用;(2) 对于一定的概率值、负或正的晶体场和晶体场的比例值都存在临界点;(3) 系统显示多种相变温度,一阶相变和二阶相变.     

低压离子色谱法测定土壤中速效钾

通常对土壤中速效钾的测定方法所用仪器昂贵。而低压离子色谱分析仪结构简单,操作简便,速度快,灵敏度高,价格低[1]。本文通过试验,确立了低压离子色谱法测定土壤速效钾的最佳条件,对实际样品的测定结果与推荐值呈显著相关性。1　实验部分土壤经风干、研磨,过100目土壤筛,测定其水份系数[2],贮存于密闭玻璃瓶内备用。准确称取2 0000g土样于50ml烧杯内,加20ml提取剂(0 05mol/LHCl+0 0125mol/LH2SO4),摇匀,25℃提取25分钟,离心分离。连接色谱仪、记录仪、蠕动泵(图1)。自制2J 3低压离子色谱仪,量程10×10μs,蠕动泵流速10刻度,记录仪量…     

THE THEORETICAL STUDY OF ADSORPTION OF METAL IONS ON CHITOSAN

1. INTRODUCTION Chitin, the most abundant natural amino polysaccharide and estimated to be produced annually almost as much as cellulose, is well known to consist of 2-acetamido-2-deoxy-β-D- glucose through α, β(1→4) linkage. Chitin is the major source of surface pollution in coastalareas. Chitosan is the N-deacetylated derivative of chitin and their structures are shown in Fig. 1. Fig. 1 Structures of Chitin and Chitosan Because of the excellent properties such as biocompatibility…     

Economics of food irradiation

The number of products being radiation processed worldwide is constantly increasing and today includes such diverse items as medical disposables, fruits and vegetables, spices, meats, seafoods and waste products. This range of products to be processed has resulted in a wide range of irradiator designs and capital and operating cost requirements.This paper discusses the economics of low dose food irradiation applications and the effects of various parameters on unit processing costs. It provides a model for calculating specific unit processing costs by correlating known capital costs with annual operating costs and annual throughputs. It is intended to provide the reader with a general knowledge of how unit processing costs are derived.