A fictitious domain decomposition method for the solution of partially axisymmetric acoustic scattering problems. Part 2: Neumann boundary conditions

We present a fictitious domain decomposition method for the fast solution of acoustic scattering problems characterized by a partially axisymmetric sound‐hard scatterer. We apply this method to the solution of a mock‐up submarine problem, and highlight its computational advantages and intrinsic parallelism. A key component of our method is an original idea for addressing a Neumann boundary condition in the general framework of a fictitious domain method. This idea is applicable to many other linear partial differential equations besides the Helmholtz equation. Copyright © 2003 John Wiley & Sons, Ltd.     

连续小波变换VLSI实现综述

小波变换是信号处理、图像压缩和模式识别等诸多领域中一个非常有效的数学分析工具。然而，实时小波变换计算量大，需要专用硬件来实现。连续小波变换的VLSI实现在处理速度、功耗及适用频率范围方面部具有较明显的优势，且实现方法灵活。本文对近年来有关该领域的研究情况作了综合评述，讨论了其中存在的问题，并指出了今后的若干发展方向，特别是瞬时缩展电路技术是实现低电压低功耗小波变换芯片的重要途经之一。     

结构-波浪-海床耦合系统中大圆筒结构的波压力响应

以沉入式大圆筒结构为对象，通过设计随机波浪水槽实验，测取了在单筒和连续筒两种结构型式、两种沉入深度和两种波谱输入下结构表面的动波压力分布。波面高度以及波压力历程均在领域进行分析。通过计算结构表面沿高程和沿环向的波压力谱及波压力传递函数，将单筒实测结果与基于线性绕射理论的解析解进行了比较，同时也详细对比了两种结构型式下的实测结果。文中汇报了在研究中获得的新发现及进行的相应分析，特别是在结构——波浪——海床动力相互作用下对波压力响应机理以及针对连续筒的研究，可为工程应用提供有价值的参考。     

一种空间自适应小波门限去噪算法

提出了一种空间自适应小波门限去噪算法,该算法在小波域对含噪小波系数做两次自适应去噪,两次自适应门限分别基于最大似然(ML)方差估计和最大后验概率(MAP)方差估计.仿真结果表明,该算法与其它自适应门限去噪算法相比,去噪后的图象具有更高的峰值信噪比(PSNR).     

A frequency domain approach to fault detection in sampled-data systems

This paper deals with fault detection problems in sampled-data (SD) systems. A tool is first introduced for the analysis of intersample behavior of SD systems in the frequency domain from the viewpoint of fault detection and isolation. Based on it, a direct design approach of fault detection systems for SD systems is proposed, and further the problem of full decoupling from unknown disturbances is studied.     

Synthesis and characterization of poly(siloxane-urethane)s

A series of polyurethane block copolymers based on hydroxy-terminated polydimethylsiloxane and poly(propylene glycol) soft segments of molecular weights 1818 and 2000, respectively, were synthesized. The hard segments consisted of 4,4′-diphenylnethane diisocyanate and 1,4-butanediol as the chain extender. Samples with different molar ratios were prepared. We tried to synthesize polydimethylsiloxane-based polyurethanes (PDMS-PU) containing a hard block as major fraction and a soft block as minor fraction for preparing toughened rigid systems. After a study of the pure polydimethylsiloxane-based polyurethane and poly(propylene glycol)-based polyurethane (PPG-PU), (mixed polyol)-based block copolymers and blends of PDMS-PU and PPG-PU were synthesized, and characterized by means of differential scanning calorimetry, tensile testing and scanning electron microscopy. In (mixed polyol)-based copolymers and lower hard-segment content blends, macro-phase separation occurred, but blends with higher hard-segment contents showed significant reduction in amounts of phase separation.     

高聚物共混物及嵌段共聚物熔体的流变性（Ⅰ）共混物熔体的流动特性

综述了高聚物二元共混物及嵌段共聚物熔体的静态流变性，分析了不同共混体系的流动曲线，总结了共混物的流动特性及规律     

解析小波及在振动分析中的应用

本文在希尔伯特变换和小波定义的基础上,提出解析小波及解析小波变换,分析了它的一个重要性质即对信号可实现正交滤波、提取包络。最后给出了小波在轴承振动共振解调应用的实例。     

自身相位噪声测量的分析

本文分析一种不需要参考（标准）信号源的相位噪声测量系统，该系统在被测通道里插入窄带晶体滤波器滤除被测信号的大部分噪声，作为参考信号再与被测信号进行比较，实现了信号源自身相位噪声的测量．本文还介绍一种自动相位噪声谱测量装置     

Wavelet packet based channel equalization

Recently, considerable amount of attention is being given to the field of wavelets and wavelet packets. It has found numerous applications in signal representation, image compression and applied mathematics. In this paper, we present a channel equalization method based on wavelet packets. The proposed equalizer structure is based on the fact that for sufficiently narrowband sequences, a non-ideal channel can be modelled as an attenuation and delay. If the data sequence is used to modulate a set of narrowband wavelet packets, then no equalization is required at the receiver end. The equalization problem reduces to that of determining the delay introduced by the channel for each of the wavelet packets. A minimum square variance algorithm for adaptively choosing the delay has been proposed. This algorithm has been shown to perform as desired analytically in a simple delay channel case. Simulations have been used to study its performance in the non-ideal channel’s case and the results corroborate theoretical predictions.