Hydrate dissociation conditions for gas mixtures containing carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons using SAFT

A new method, a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate dissociation conditions for binary gas mixtures with carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons in the presence of aqueous solutions. The statistical associating fluid theory (SAFT) equation of state is employed to characterize the vapor and liquid phases and the statistical model of van der Waals and Platteeuw for the hydrate phase. The predictions of the proposed model were found to be in satisfactory to excellent agreement with the experimental data.

Controllable negative and positive group delay in transmission through a single quantum well at finite magnetic fields

We investigate the controllable negative and positive group delay in transmission through a single quantum well at the finite longitudinal magnetic fields. It is shown that the magneto-coupling effect between the longitudinal motion component and the transverse Landau orbits plays an important role in the group delay. The group delay depends not only on the width of potential well and the incident energy, but also on the magnetic-field strengthen and the Landau quantum number. The results show that the group delay can be changed from positive to negative by the modulation of the magnetic field. These interesting phenomena may lead to the tunable quantum mechanical delay line. (c) 2007 Elsevier B.V. All rights reserved.

有限元子域法分析土石混合介质的饱和导水率

在黄土高原水蚀风蚀交错地区,碎石的存在影响着土壤的水力学特性,因此研究土石混合介质的渗流运动对该地区的植被恢复建设具有重要的指导意义。虽然用有限元法分析地下水渗流的工作很多,但对土石混合介质而言,由于有限元法的解题规模迅速增加,其研究甚少。本模型采用子域法矩形单元,假定土石体中石块含量增加不影响土的孔隙率且石块不透水分析了土石混合介质中的渗流过程。结果表明,影响土石混合介质饱和导水率的主要因素是土石介质的含石率;石块的大小基本不影响混合介质饱和导水率;石块分布方式增加水流路径时,会影响混合介质饱和导水率。这一数值分析结论与土石体渗流问题的部分理论结果和试验结果吻合良好。本模型子域法计算效率高,结果较准确,可用于较大规模的土石混合介质渗流分析,还可推广用于土石混合介质的三维分析和多级子域法有限元技术以获得更大规模的解题效果。

Analysis of Si/GaAs Bonding Stresses with the Finite Element Method

In conjunction with ANSYS, we use the finite element method to analyze the bonding stresses of Si/GaAs. We also apply a numerical model to investigate a contour map and the distribution of normal stress,shearing stress,and peeling stress,taking into full consideration the thermal expansion coefficient as a function of temperature. Novel bonding structures are proposed for reducing the effect of thermal stress as compared with conventional structures. Calculations show the validity of this new structure.

Elastic Strain Field Distribution of a Self-Organized Growth Lensed-Shaped Quantum Dot by Finite Element Method

The stress and strain fields in self-organized growth coherent quantum dots (QD) structures are investigated in detail by two-dimension and three-dimension finite element analyses for lensed-shaped QDs. The nonobjective isolate quantum dot system is used. The calculated results can be directly used to evaluate the conductive band and valence band confinement potential and strain introduced by the effective mass of the charge carriers in strain QD.

Stress analysis of silica-based arrayed waveguide grating by a finite element method

The stress distribution in silica optical waveguides on silicon is calculated by using finite element method (FEM). The waveguides are mainly subjected to compressive stress along the x direction and the z direction, and it is accumulated near the interfaces between the core and cladding layers. The shift of central wavelength of silica arrayed waveguide grating (AWG) on silicon-substrate with the designed wavelength and the polarization dependence are caused by the stress in the silica waveguides.