G-, F-, and ∊-Matrices for XY4Z Molecules of C4V Symmetry

XY₄ Z molecules or ions with a square-pyramid structure (C_4v) are relatively rare. This explains the infrequency of investigations of their vibrational spectra, with analysis in normal coordinates and computation of the mean-square amplitudes of vibration.     

Application of a fractional steps method for the numerical solution of the two-dimensional modeling of the Lake Mariut

A fractional steps technique for the numerical solution of the shallow water equations is applied to study the water velocity in Lake Mariut, its concentration and the distribution of the temperature along it. Lake Mariut is considering the most productive natural systems in Egypt. The current configuration of this lake is changing rapidly, due to people’s activities and natural processes. Most of its water supply comes from polluted agricultural drains. Several problems affect the conservation of the Lake Mariut, mainly pollution, land reclamation, intensive aquatic vegetation, over fishing and coastal erosion. The shallow water equations for this lake are discretized on a fixed grid and time stepped with the fractional steps method, where the Riemann invariants of the equations are interpolated at each time step along the characteristics of the equations using a cubic spline interpolation. The method is efficient and simple, since it evolves the equations without the iterative steps involved in the multi-dimensional interpolation problem. The absence of iterative steps in the present technique makes it very suitable for the problems in which small time steps and grid sizes are required and the simplicity of the method makes it very suitable for parallel computer. Therefore, the method provides numerical algorithms which are more efficient than other classical schemes.     

Construction of the reaction networks for heterogeneous catalytic reactions: Fischer—Tropsch synthesis and related reactions

The key approaches to the generation of reaction networks for the synthesis of products from CO and H₂ are considered. The selection rules for the elementary steps on the surface of heterogeneous catalysts are formulated. Data on the surface compounds and steps related to reactions of CO and H₂ are analyzed and a set of transforms (models of elementary steps) for generation of the reaction network are selected. Eight variants of generation of reaction networks for the formation of C1 products with different sets of transforms (12 to 31) were tested in computer experiments, and eight reaction networks comprising 34 substances and 132 to 1647 elementary steps were obtained. The pathways to CO₂, CH₄, and CH₃OH and pairs of compounds CH₄, CO₂ and CH₄, HCOOH obtained from the reaction network (220 elementary steps) are compared with the published schemes.     

Comparison of dynamically coated SE-54, SP-2250 and carbowax 20M wall-coated open tubular (WCOT) glass capillary columns,prepared after surface pretreatment with Superox™-4 or with BaCO3

A new surface pretreatment for the preparation of wall-coated open tubular (WCOT) glass capillary columns has been evaluated. This technique involves the application of a non-extractable layer of Superox?-4, a 4,000,000 MW polyethylene glycol, to the glass surface as a pretreatment and deactivation agent. Unlike other polyethylene glycols, Superox-4 is stable at high temperatures (> 300°C) in the absence of oxygen, coats smoothly onto a bare glass surface and resists droplet formation. WCOT columns (SE-54, Carbowax 20M, and SP-2250) prepared using this technique are compared to columns prepared using a modified Grob [2,3] BaCO₃ procedure. The Superox-4 pretreated columns were equal or superior in quality to the BaCO₃ pretreated columns, based on the appearance of an activity standard and the effective theoretical plates (N_eff) per meter. Chromatograms showing practical application of the WCOT columns prepared using both methods is given.     

基于TestStand的检波功率放大器测试软件的开发应用

针对传统检波功率放大器测试设备测试效率低、操作繁琐、易误操作的缺点,设计了基于TestStand的检波功率放大器自动测试软件。该软件充分利用TestStand多线程并行高速执行的特点,实现了多套产品的同时自动测试;通过设计自定义测试项,并且将测试流程和测试项的设计分离,增强了软件的复用性和维护性;实际应用证明,该软件提高了测试效率,降低了测试成本,促进了自动测试设备领域的新发展。     

分步加压法测量薄壁空心玻璃微球的耐压能力

 根据空心玻璃微球（HGM）耐内、外压能力与玻璃强度及形状因子的关系,用压力负荷分步增加的方法分别实验测量了直径为350μm～550μm、壁厚＜1.1μm的3种配方HGM的耐内、外压能力及HGM玻璃的杨氏模量和拉伸强度,并由强度测定值给出了不同直径与壁厚HGM的耐内、外压能力的计算式,分析了测量误差,提出了改进方案。     

New approach to the numerical solution of forward-backward equations

This paper is concerned with the approximate solution of functional differential equations having the form: x′(t) = αx(t) + βx(t - 1) + γx(t + 1). We search for a solution x, defined for t ∈ [−1, k], k ∈ ℕ, which takes given values on intervals [−1, 0] and (k-1, k]. We introduce and analyse some new computational methods for the solution of this problem. Numerical results are presented and compared with the results obtained by other methods.      

Low energy ion scattering by atomic steps on the single crystal surface

The energy, angular distributions and trajectories of particles scattered on surfaces of Ni(100) and Cu(100), with both ideal and damaged, and semi-infinite and isolated atomic steps, have been calculated. It has been shown that from the correlation between the experimental and calculated energy distributions of the scattered particles, one may determine the spatial extension of the isolated atomic steps and the distance between them on the single crystal surface damaged by ion bombardment. The energy and angular distributions of ions dechanneled from semi-infinite steps on the GaP(100) surface have been presented. It has been shown that the dechanneling ions form the characteristic peaks in the angular and energy distributions of the scattered particles.     

The upwind finite difference fractional steps methods for two‐phase compressible flow in porous media

The upwind finite difference fractional steps methods are put forward for the two‐phase compressible displacement problem. Some techniques, such as calculus of variations, multiplicative commutation rule of difference operators, decomposition of high‐order difference operators, and prior estimates, are adopted. Optimal order estimates in L² norm are derived to determine the error in the approximate solution. This method has already been applied to the numerical simulation of seawater intrusion and migration‐accumulation of oil resources. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 67–88, 2003     

Fiske steps in surface intrinsic Josephson junctions of Bi2Sr2CaCu2O8+δ single crystals

Current－voltage characteristics of the surface intrinsic Josephson junctions under a magnetic field parallel to CuO_2 planes have been studied experimentally. Fiske steps in such a junction have been observed. The Swihart velocity for the junction is found to be 7.2×10^5m/s, which corresponds to the velocity mode of a single junction.