Analysis of super compact finite difference method and application to simulation of vortex–shock interaction

Turbulence and aeroacoustic noise high‐order accurate schemes are required, and preferred, for solving complex flow fields with multi‐scale structures. In this paper a super compact finite difference method (SCFDM) is presented, the accuracy is analysed and the method is compared with a sixth‐order traditional and compact finite difference approximation. The comparison shows that the sixth‐order accurate super compact method has higher resolving efficiency. The sixth‐order super compact method, with a three‐stage Runge–Kutta method for approximation of the compressible Navier–Stokes equations, is used to solve the complex flow structures induced by vortex–shock interactions. The basic nature of the near‐field sound generated by interaction is studied. Copyright © 2001 John Wiley & Sons, Ltd.     

Analysis of generation of terahertz radiation by nonlinear mixing of laser frequencies in GaAs crystal

Generation of terahertz (THz) radiation by nonlinear mixing of laser frequencies in GaAs crystal is considered for the case of free and guided propagation of THz waves. In the first case the strong diffraction of the THz radiation leads to the deviation from the known square-law growth of the generator power with increasing crystal length, In the second case the spatial divergence of the exciting laser beam results in the appearance of a maximum in the generated power dependence on the radius of the nonlinear waveguide. According to estimations, the optimal radius of the laser beam is 18 μm for the waveguide length of 6 mm and the maximal generated THz power is ～27 W at the laser beam power of 10 kW.     

First demonstration of a temporal coherence analysis through a parametric interferometer

We analyze the temporal coherence of an optical infrared radiation in the visible domain by using a Mach-Zehnder interferometer and a wavelength conversion stage in each arm. We exploit a sum frequency generation process in bulk PPLN crystal to convert the infrared radiation at 1.55 μm into 0.63 μm before the interferometric mixing. The applicability of the Wiener-Kintchine theorem through up-conversion processes is here demonstrated by direct comparisons among visible and infrared measurements.     

The First Homochiral Diamond-Like Coordination Polymer Containing Cubane Cluster （Cu4I4） as Connecting Node and Cinchonine as Donor-Acceptor （or Push-Pull Electronic Effect） Building Block

The reaction of CuI with cinchonine （an organic donor-acceptor chromophore） afforded a homochiral 3D diamondoid network [Cu4I4（cinchonine）2]n （1） containing a cubane cluster （Cu4I4） as a connecting node. This is the first homochiral coordination polymer with diamondoid nets containing a cluster as a connecting note. Its thermal stability and solid state optical properties such as fluorescence, circular dichroism and second-harmonic generation response were also reported.     

Equivalence-free exhaustive generation of matroid representations

In this paper we present an algorithm for the problem of exhaustive equivalence-free generation of 3-connected matroids which are represented by a matrix over some finite (partial) field, and which contain a given minor. The nature of this problem is exponential, and it appears to be much harder than, say, isomorph-free generation of graphs. Still, our algorithm is very suitable for practical use, and it has been successfully implemented in our matroid computing package MACEK [http://www.mcs.vuw.ac.nz/research/macek, 2001-05].     

Thermal effects observable during quasi-phasematched second harmonic generation in periodically poled crystal fibres

The impact of transient and steady-state thermal effects on the conversion efficiency of quasi-phasematched second harmonic generation in periodically poled LiNbO₃ fibres is discussed. The response time and wavelength variation of the quasi-phasematching condition depend on the thermal conductivity of the fibre, its enclosure and the thermal coefficient of the crystal’s refractive index.     

Deactivation of Pd particles supported on Nb2O5/Cu3Au(1 0 0): SFG and TPD studies from UHV to 100 mbar

Structural changes that occur on Pd-Nb₂O₅/Cu₃Au(1 0 0) model catalysts upon thermal annealing were followed by sum frequency generation (SFG) and temperature-programmed desorption (TPD) using CO as probe molecule. SFG experiments were performed both under ultrahigh vacuum and mbar pressure. Heating the catalyst to temperatures above 300 K lead to an irreversible 50% decrease in the CO adsorption capacity and modified the remaining adsorption sites. Alterations of the phase between resonant and non-resonant SFG signals upon annealing indicate a change in the electronic structure of the surface, which excludes Pd sintering or migration of Nb₂O₅ over Pd particles to cause the observed effect and rather suggests the formation of “mixed Pd-NbO_x” sites. The same changes in surface properties also occur during CO hydrogenation at 1 bar and high temperature, pointing to an involvement of “mixed Pd-NbO_x” sites in catalytic reactions.     

An algebraic boundary orthogonalization procedure for structured grids

An algebraic procedure for grid orthogonalization has been developed. It is often difficult to include both grid clustering and orthogonalization in a grid generation method. Often the degree and extent of orthogonality are hard to control when orthogonalization is included in a complicated grid generation method. Fortunately, grid orthogonalization can be performed independently of grid generation. The orthogonalization method developed is simple and includes invertibility control. Copyright © 2000 John Wiley & Sons, Ltd.     

自适应坐标变换方法

提出求解流体力学Euler方程的自适应坐标变换方法,它们保持网格夹角近似不变、保持物质界面为Lagrange描述,且使得网格速度与流体速度的差在最小二乘意义下达到极小.所提出的新坐标系能自适应于流体流场的若干重要特性.     

二次谐波产生中入射啁啾脉冲对相位的影响

讨论了基波为叔率啁啾脉冲的二次谐波产生过程，结果表明选取合适的啁啾参量可以提高二次谐波的光强，但同时会使其波形和相位发生变化，三次相位的畸变主要取决于入射的基波啁啾脉冲，而与相位匹配的失谐量关系不大。