基于非结构四边形网格的WENO格式

基于非结构四边形网格发展求解双曲守恒律的三阶加权基本无振荡（WENO）格式.针对任意非结构四边形网格选取重构模板,并给出基于线性多项式的三阶线性重构.但对于一般的非结构四边形网格,会出现非常大的线性权和负权,使得非线性重构的WENO格式对光滑问题也不稳定.本文给出一个处理非常大的线性权的优化重构方法,对优化后得到的负线性权采用分裂方法进行处理.对于非线性权,提出一种考虑局部网格和物理量间断的新光滑度量因子.采用优化重构方法和新的非线性权,当前的三阶WENO格式在质量很差的网格上也具有很好的稳定性.理论的三阶精度在数值精度测试算例中得到验证,同时一范数和无穷范数的误差绝对值不依赖于网格质量;具有强间断的数值结果证明了当前格式的有效性.     

Global vector-field reconstruction of nonlinear dynamical systems from a time series with SVD method and validation with Lyapunov exponents

A method for the global vector-field reconstruction of nonlinear dynamical systems from a time series is studied in this paper. It employs a complete set of polynomials and singular value decomposition (SVD) to estimate a standard function which is certtral to the algorithm. Lyapunov exponents and dimension, calculated from the differential equations of a standard system, are used for the validation of the reconstruction. The algorithm is proven to be practical by applying it to a Roessler system.     

Fast measurement of rocking curve of reflection high-energy electron diffraction by using quasi-1D convergent beam

In order to investigate dynamic change in surface structure, we tried to measure the rocking curve of reflection high-energy electron diffraction (RHEED) by using a quasi-1D convergent beam method, which means a superposition of a hundred RHEED patterns at different glancing angles on one image. After we have checked the experimental accuracy, it is confirmed that the measurement time is shortened to 0.3 s by using this method. We also show an application of this method to a real time observation of surface segregation of B atoms while a highly B-doped Si is annealed.     

Measuring the Au(1 1 1) surface state at the solid–liquid interface

We present the first direct observation of an occupied noble metal surface state at the metal/liquid interface. The Au(1 1 1) Shockley-like surface state was measured by scanning tunneling spectroscopy (STS) at the Au(1 1 1)/n-tetradecane interface. These results show that the surface state of gold survives in a liquid environment, and can be probed by STS. More generally it indicates that STS can be used to study electronic properties of surfaces at the solid/liquid interface, and that spectra can be directly compared to measurements and calculations of a surface’s electronic structure in ultra-high vacuum.     

基于局部梯度特征的红外微扫描成像技术研究

从空间邻近度和像素相似性角度出发,提出了微扫描和基于梯度特征加权插值技术相结合的方法.该方法利用320×240凝视型红外焦平面探测器,在DSP+FPGA硬件平台上得以实现.实验证明：与经典微扫描技术相比,它既能提高图像空间分辨率,抑制噪音,又能较好地增强红外图像的边缘.     

一种基于偏振解析的三维表面重建方法

提出用解析反射光偏振图像来重建透明物体表面形状的原理及实现方法。从物体表面反射的光具有一定的偏振特性,偏振特性的不同反映了物体的形状和反射特性的不同,这两者之间存在一种必然的联系。通过分析物体表面反射光的偏振分布,可以得到物体的表面形状。依据菲涅耳反射公式,推导出偏振度与物体表面法线间的函数关系,据此构建相应算法,对由CCD照相机拍得的被测物体的偏振灰度图像进行处理,重建出被测物体的表面形状。实验结果证明提出的方法是实用且有效的。     

3D reconstruction of nanocrystalline particles from a single projection

This paper describes an approach to retrieve the three-dimensional atomic structure of a nanocrystalline particle from the reconstructed electron exit wave function in a single projection direction. The method employs wave propagation to determine the local exit surface of each atomic column together with its mass. The exit wave in between colums is used as internal calibration so as to remove the background noise and improve the precision to the level of single atom sensitivity. The validity of the approach is tested with exit wave functions of a gold wedge reconstructed from simulated images containing different levels of noise.     

反射式高能电子衍射实时监控的分子束外延生长GaAs晶体衬底温度校准及表面相变的研究

以反射式高能电子衍射(RHEED)作为实时监测工具,根据GaAs(100)表面重构相与衬底温度、As₄等效束流压强之间的关系,对分子束外延(MBE)系统中衬底测温系统进行了校准,这种方法也适用于其他的MBE系统.为生长高质量的外延薄膜材料、研究InGaAs表面粗糙化及相变等过程提供了实验依据. 关键词： 分子束外延 反射式高能电子衍射 表面重构 温度校准     

基于三次样条插值的图像多尺度方向边缘重构

为了检测小结构的轮廓以及大目标的边缘,将多尺度边缘检测与小波变换有机地结合起来,利用小波分析方法来研究信号的多尺度边缘特征。针对图像信号的多尺度边缘检测和重构问题,利用二进小波变换的多尺度分析特性,定义了图像在水平和垂直方向的多尺度边缘。同时,利用三次样条插值算法,提出了一种由二进小波变换在水平和垂直方向的极值重构图像信号的算法。实验结果显示多尺度重建方法与著名的交替投影算法相比,算法复杂度低,图像重建速度提高了20倍,而且重建图像质量较好,其峰值信噪比提高了1 dB以上。     

Ag/Si(111)-(7X7) Heteroepitaxy—STM Experiment and KMC Simulations

Heteroepitaxial growth of Ag on Si(111)-(7X7) surface at various conditions was experimentally studied by scanning tunneling microscopy. A growth model based on experiments was used for kinetic Monte Carlo (KMC) simulations. The simulations of nucleation and island growth at low coverage and fitting experimental data provided basic growth parameters. Further growth—formation of a discontinuous transition film (wetting layer)—was implemented into the basic model. The suggested growth mechanism was successfully tested using the KMC simulations. The choice of experiments, the role of minimizing processes and parameters in the model, and efficiency of the used approach is demonstrated and discussed.