Finite-element methods for singularly perturbed high-order elliptic two-point boundary value problems. II: convection-diffusion-type problems

e-mail address: stynes{at}bureau.ucc.ie We consider singularly perturbed high-order elliptic two-pointboundary value problems of convection-diffusion type. Undersuitable hypotheses, the coercivity of the associated bilinearform is proved and a representation result for the solutionsof such problems is given. A family of Galerkin finite-elementmethods based on piecewise polynomial test/trial functions ona Shishkin mesh is constructed and proved to be convergent,uniformly in the perturbation parameter, in energy and Wnorms. Numerical results are presentedfor a second-order problem and fourth-order problems.     

Finite-element methods for singularly perturbed high-order elliptic two-point boundary value problems. I: reaction-diffusion-type problems

We consider singularly perturbed high-order elliptic two-pointboundary value problems of reaction-diffusion type. It is shownthat, on an equidistant mesh, polynomial schemes cannot achievea high order of convergence that is uniform in the perturbationparameter. Piecewise polynomial Galerkin finite-element methodsare then constructed on a Shishkin mesh. Almost optimal convergenceresults, which are uniform in the perturbation parameter, areobtained in various norms. Numerical results are presented fora fourth-order problem. e-mail address: stynes{at}bureau.ucc.ie.     

SPECIES DIFFERENCES IN RESPONSE TO PHOTOHEMOLYTIC AGENTS

Species differences in red blood cell susceptibility to the photohemolytic agents chlorpromazine, menadione and tetracycline were examined in mouse, rat, dog, and human blood. Menadione and tetracycline (25 microM) hemolyzed mouse but not dog, rat, or human red blood cells (RBC) when irradiated with UV light but not in the dark. Chlorpromazine (25 microM) produced a photohemolytic response in all four species with mouse and rat RBC lysing fastest followed by human then dog cells. Investigations into the nature of these species differences suggested that the size of mouse RBC may contribute to its high sensitivity to photohemolytic agents. An investigation of the effect of UV light on key antioxidant enzymes revealed species differences in enzyme inactivation. These data suggest that mouse RBC may be particularly vulnerable to phototoxic agents, especially those compounds which produce active oxygen species and, therefore, may prove more useful than human RBC as a model for predicting phototoxic potential of some chemical entities.     

C2H221分子转动角动量定向分布(Orientation)及其碰撞弛豫和转移

利用圆偏振激光受激Raman抽运,以 C₂H₂分子为样品选择性地制备了它的电子基态单一转动态(X¹Σ⁺_g,ν″₂＝1,J″的角动量定向布居(orientation)．并从圆偏振紫外激光诱导的A¹A_u(ν′₃＝1)←X¹Σ⁺_g(ν″₂＝1)的荧光（谱）,直接测定了 C₂H₂(X¹Σ^＋_g,ν″₂＝1,J″＝4,7,8,…,13）的角动量定向布居值．从时间分辨的荧光信号谱测定了角动量定向布居的碰撞弛豫速率常数,同时还研究了由各初始激励的转动态向其他邻近转动态碰撞诱导的角动量定向布居转移． 关键词：     

基于原位和RNT技术的铜锌合金摩擦磨损性能

采用基于原位全息显微技术和放射性核素技术的摩擦磨损试验装置,在润滑条件下对Cu Zn36/100Cr6配对摩擦体系中Cu Zn36的磨损行为进行了研究.利用装置中的全息显微镜对Cu Zn36磨痕表面微观形貌和粗糙度进行原位分析,利用放射性核素磨损量测量系统精确测量Cu Zn36的实时磨损量;利用扫描电镜对Cu Zn36及100Cr6钢球磨面进行观察和分析,利用X射线光电子能谱分析仪对Cu Zn36磨痕表层的元素化合态进行定量分析.结果表明:在试验法向载荷为1.9~3.0 MPa范围内时,Cu Zn36表现出良好耐磨性,原因是Cu Zn36在试验过程中形成了具有高硬度和自润滑性的Zn O强化层,主要磨损方式为疲劳磨损.在较差磨合试验过程中,磨痕表面耐磨层一直处于"形成-破坏-再形成-再破坏"的动态过程,主要磨损方式为磨粒磨损和黏着磨损.     

Optical Aspartame Biosensor Based on Bienzyme Immobilisation on Egg Shell Membrane

Aspartame is a widely used artificial sweetener in many low calorie foods and beverages. Determination of its concentration in foodstuff is important as aspartame is a relatively expensive material. A novel optical biosensor for the determination of aspartame in beverage based on a bienzyme system is presented. An aspartame biosensor was fabricated employing a bienzyme system composed of chymotrypsin and alcohol oxidase immobilised onto a egg shell membrane and an oxygen-sensitive optode membrane as the transducer. The detection schemes involve the enzymatic reactions of aspartame leading to the depletion of oxygen level of the medium with concomitant enhancement of the fluorescence intensity of the oxygen-sensitive membrane.     

Alkali and alkaline earth metal compounds: core—valence basis sets and importance of subvalence correlation

Core-valence basis sets for the alkali and alkaline earth metals Li, Be, Na, Mg, K, and Ca are proposed. The basis sets are validated by calculating spectroscopic constants of a variety of diatomic molecules involving these elements. Neglect of (3s, 3p) correlation in K and Ca compounds will lead to erratic results at best, and chemically nonsensical ones if chalcogens or halogens are present. The addition of low-exponent p functions to the K and Ca basis sets is essential for the smooth convergence of molecular properties. Inclusion of inner-shell correlation is important for accurate spectroscopic constants and binding energies of all the compounds. In basis set extrapolation/convergence calculations, the explicit inclusion of alkali and alkaline earth metal subvalence correlation at all steps is essential for K and Ca, strongly recommended for Na, and optional for Li and Mg, while in Be compounds an additive treatment in a separate ‘core correlation’ step is probably sufficient. Consideration of (ls) inner-shell correlation energy in first-row elements requires the inclusion of (2s, 2p) ‘deep core’ correlation energy in K and Ca for consistency. The latter requires special CCVnZ ‘deep core correlation’ basis sets. For compounds involving Ca bound to electronegative elements, additional d functions in the basis set are strongly recommended. For optimal basis set convergence in such cases, we suggest the sequence CV(D + 3d)Z, CV(T + 2d)Z, CV(Q + d)Z, and CV5Z on calcium.     

Parallelized sampling of the Gibbs ensemble

An expression for the probability distribution of NVT-like sub-ensembles constituting the Gibbs ensemble is derived. Knowledge of this distribution makes it possible to carry out the simulation without the explicit exchange of real particles between the simulation boxes and to evaluate directly any Gibbs ensemble average from a series of independent simultaneous simulations (Monte Carlo or molecular dynamics) performed on a set of NVT-likt sub-ensembles with the fixed distribution of particles. An implementation of the method, which is tailored mainly for complex systems, is exemplified for the square-well fluid, and its efficiency and results are compared with those obtained from the conventional Gibbs ensemble simulations.     

Effect of surface modification on the pore condensation of fluids: experimental results and density functional theory

The physisorption and pore condensation of a polar fluid (CHF₃) in a series of MCM-41 type mesoporous silica materials with native and chemically modified pore walls has been studied over the temperature range 168–293 K, corresponding to reduced temperatures T/T_c in the range 0.56-0.98, where T_c is the critical temperature of the fluid. Chemical modification of the pore walls by attachment of Si(CH₃)₃ groups causes a shift in pore condensation to higher relative pressures p/p0. This effect is most pronounced for materials with narrow pores (2.9 nm) at low temperatures. In the theoretical part of the work density functional theory based on a simple cubic lattice model of the confined fluid has been used to analyse the combined effect of a reduced pore width and weaker fluid-wall interaction caused by the surface coating. For realistic values of the model parameters it is found that the effect of the lower pore width is outweighed by the opposing effect of the lower fluid-wall interactions. The weaker temperature dependence of the pore existence curve observed experimentally for the surface modified materials can be traced back to a crossover from a two-step to a single-step process of pore filling predicted by the model.