Focussing and defocussing of ballistic phonons in diamond and Nb3Sn

The ballistic propagation of phonons in diamond and Nb₃Sn at 40 and at 4.2 K is examined. The nature of variation of the phonon magnification factor has been analysed both in the wave vector as well as group velocity spaces. Using the Polar Schmidt-net with Pole at (π/2,π/2), the mappings of phonon focussing and defocussing are made. It is shown that the mapping for theFTA mode for Nb₃Sn exhibits islands acting as impenetrable barriers for phonon propagation.     

X-ray mapping of freeze-dried cryosections from biological cells

Elemental mapping of freeze-dried cryosections from biological cells was done using the energy window mode and the quantitative mode. Quantitative mapping requires long measuring times and high electron exposure resulting in inhomogeneous shrinkage and distortion of the cryosection. Collection of X-ray spectra for quantitative analysis of intracellular structures and compartments combined with energy window mapping was found to be sufficiently fast and reliable to reveal inhomogeneities of the element distribution in cells. However, this method is suitable only for mapping elements without overlapping peaks in the X-ray spectrum.     

A finite element method for the two‐dimensional extended Boussinesq equations

A new numerical method for Nwogu's (ASCE Journal of Waterway, Port, Coastal and Ocean Engineering 1993; 119 :618)two‐dimensional extended Boussinesq equations is presented using a linear triangular finite element spatial discretization coupled with a sophisticated adaptive time integration package. The authors have previously presented a finite element method for the one‐dimensional form of these equations (M. Walkley and M. Berzins (International Journal for Numerical Methods in Fluids 1999; 29 (2):143)) and this paper describes the extension of these ideas to the two‐dimensional equations and the application of the method to complex geometries using unstructured triangular grids. Computational results are presented for two standard test problems and a realistic harbour model. Copyright © 2002 John Wiley & Sons, Ltd.     

Simulated annealing for constrained global optimization

Hide-and-Seek is a powerful yet simple and easily implemented continuous simulated annealing algorithm for finding the maximum of a continuous function over an arbitrary closed, bounded and full-dimensional body. The function may be nondifferentiable and the feasible region may be nonconvex or even disconnected. The algorithm begins with any feasible interior point. In each iteration it generates a candidate successor point by generating a uniformly distributed point along a direction chosen at random from the current iteration point. In contrast to the discrete case, a single step of this algorithm may generateany point in the feasible region as a candidate point. The candidate point is then accepted as the next iteration point according to the Metropolis criterion parametrized by anadaptive cooling schedule. Again in contrast to discrete simulated annealing, the sequence of iteration points converges in probability to a global optimum regardless of how rapidly the temperatures converge to zero. Empirical comparisons with other algorithms suggest competitive performance by Hide-and-Seek.This material is based on work supported by a NATO Collaborative Research Grant, no. 0119/89.     

Micro‐Raman mapping on polished cross sections: a tool to define the penetration depth of conservation treatment on cultural heritage

Nowadays, in order to preserve the surfaces of works of art, several organic and inorganic substances are used. To evaluate the penetration depth and the distribution of these substances inside the materials, it is essential to define the effectiveness of a conservative treatment. Owing to the ambiguous results obtained with the current analytical techniques, the achievement of this aim is critical. This study shows how micro‐Raman mapping on polished cross section is an effective tool capable of investigating the inner portions of the materials. A set of painted plasters has been treated with ammonium oxalate solutions, an inorganic substance widely used for conservation works of carbonatic materials. The micro‐Raman mapping of the lines of the newly formed calcium oxalate allowed correlation of the penetration depth and the distribution of the product inside the specimens with different conditions of treatment. Moreover, a good agreement between micro‐Raman spectroscopy and microscopic techniques has been obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

机车多普勒测速雷达波束方向校正方法

安装在机车上的多普勒测量雷达,其天线波束方向与地面的实际夹角和理想值之间存在一定的偏差,并且随着机车长时间的振动,夹角也会改变。这给机车速度的测量和行驶距离的推算造成了不可忽视的误差。本文利用双天线多普勒雷达来校正波束偏向引起的误差,提出了平均值方法和角度自适应校正方法。铁路实测数据实验表明这两种方法均不同程度地提高了测量精度,并已在青藏线上的新型机车上验证了性能更好的角度自适应校正方法。     

基于自适应窗和形状自适应小波变换的SAR图像相干斑抑制

结合SAR图像空域的先验知识和小波域系数的特性,提出了一种新的SAR图像相干斑抑制算法.使用最近提出的局部多项式近似-置信区间交叉(local polynomial approximation-intersection of confidence intervals(LPA-ICI))构造自适应窗,寻找到与SAR图像中每个像素点相对应的同质区域,在每个同质区域内利用本文给出的快速形状自适应小波变换进行硬阈值收缩抑斑,最后根据本文提出的稀疏加权方法融合多个估计样本获得最终抑斑图像.实验结果表明本文提出的算法有着很好的抑斑性能,尤其是在去除重构图像中的"振铃"效应以及有效保留原始SAR图像中的点目标方面性能更突出.     

基于卷积小波包变换的自适应多用户检测

为提高DS-CDMA多用户系统检测的效率,提出了基于卷积小波包变换的自适应算法。理论分析和仿真结果表明,该算法收敛速度快,且计算量增加较少,是一种高效的自适应检测算法。     

多模型自适应控制的模型切换算法研究

针对非线性时变系统在自适应控制过程中瞬态响应差的问题,提出了一种基于多模型自适应控制的模型切换算法.首先,在多模型框架下,通过在模型切换中使Lyapunov函数产生最大的负跳变而选择辨识模型,同时重置参数;其次,通过Lyapunov方法分析了整个系统的闭环稳定性;最后,通过一个仿真实验,表明该算法可以有效地提高系统的瞬态响应性能.