Rocky coast processes: with special reference to the recession of soft rock cliffs

Substantial progress in research on the recession of coastal cliffs composed of soft materials has been made in recent years and data with higher accuracy have been accumulated. This paper provides the state of the art review in the recession studies and highlights two new findings obtained from the reanalysis of existing data. The review topics are: episodic and localized nature of cliff recession; the development of cliffline; the relationship between cliff height and recession rate; mechanisms of cliff toe erosion by waves; a fundamental equation for wave-induced toe erosion; factors controlling toe erosion; and slope instabilities and mass movements. The findings are presented on (1) the temporal change in cliffline recession mode and (2) the effect of beach sediment at the cliff base on the cliff erosion.     

继电保护中多路模拟量采集系统的设计

介绍了一种基于高性能浮点DSP芯片TMS320C32、CPLD芯片XC95288和A/D采样芯片AD976组成的多路采集系统的工作原理以及设计方法。通过对第一路施加特殊的电压量,在CCS开发环境下读取采样缓冲区的值,并利用Matlab对采样数据进行了全波傅氏变换。此外,该系统已在继电保护中得到广泛应用,实践表明,该系统能较好地解决多路模拟量的采集,并确保了采样数据的安全可靠性。     

双频抽运提高SBS相位共轭保真度

相位共轭保真度是相位共轭镜技术用于强激光系统中的一个重要指标。采用四波混频加强SBS的方法 ,其相干拍频驱动声子场 ,能提高SBS相位共轭保真度。对于双频单池结构 ,使用列阵相机测量激光束能量远场角分布 ,在SBS转换效率最佳时 ,对相干驱动SBS相位共轭保真度进行了实验研究     

基于开关电流技术的连续小波变换的实现方法

开关电流技术是一种新的模拟抽样数据处理技术。开关电流电路具有一般电路不具有的优点，与标准数字CMOS工艺兼容。连续小波变换是分析非平稳信号的有力工具，在信号处理上有广泛的应用。本文提出用开关电流技术实现连续小波变换的方法，并用Matlab仿真证明了其理论可行性。     

反铁磁晶体的红外频率特性

研究了红外频段非线性s偏振表面波在反铁磁晶体和电介质交界面上的频率特性，求出了非线性色散方程，揭示了非线性s偏振表面波存在一个临界频率，低于这个频率，非线性s偏振表面波的频率范围，发现功率不再是决定导波频率范围的唯一因素，两种材料的介电常数比在这里起了至关重要的作用。     

MIM隧道发光结的负阻现象

本文介绍了薄膜隧道发光结的基本结构、发光机理，阐述了其Ｉ－Ｖ特性中的负阻现象。简单介绍了ＭＩＭ结构负阻的几种解释，根据热像仪照片和低温测试结果分析，再结合Ｄｅａｒｍａｌｅｙ导电模型，我们提出了ＭＩＭ负阻的物理模型，理论与实验符合较好，最后分析了负阻现象的应用前景。     

Approximation of bandlimited functions

Many signals encountered in science and engineering are approximated well by bandlimited functions. We provide suitable error bounds for the approximation of bandlimited functions by linear combinations of certain special functions—the prolate spheroidal wave functions of order 0. The coefficients in the approximating linear combinations are given explicitly via appropriate quadrature formulae.     

宽带无源光网络(BPON)关键技术的发展与研究

宽带无源光网络（BPON）是实现宽带、多业务接入的理想物理平台，本文介绍了BPON网络的发展，重点讨论了将ATM技术和PON技术相结合的APON系统及其升级系统SuperPON的基本结构和关键技术，对最近兴起的将以太技术和PON技术相结合的EPON系统的基本概念和工作原理也进行了阐述，并对未来BPON技术的发展进行了展望。     

Effective magnetic properties of a composite material with circular conductive elements

Effective magnetic properties of a composite meta-material consisting of periodically arranged circular conductive elements are studied theoretically. A general expression for the effective bulk permeability is obtained with mutual effects and lattice ordering being taken into account. The resonance frequency of the permeability is found to be strongly dependent on the size and shape of the unit cell. Frequency dispersion of the permeability is studied with special attention paid to the frequency range, where negative values of the permeability are possible. Corresponding recommendations for optimisation of the meta-materials with negative permeability are made. The results are confirmed by numerical simulations of the finite structure behaviour in an external magnetic field. Received 19 April 2002 Published online 31 July 2002     

Comparisons between model equations for long waves

Summary Considered here are model equations for weakly nonlinear and dispersive long waves, which feature general forms of dispersion and pure power nonlinearity. Two variants of such equations are introduced, one of Korteweg-de Vries type and one of regularized long-wave type. It is proven that solutions of the pure initial-value problem for these two types of model equations are the same, to within the order of accuracy attributable to either, on the long time scale during which nonlinear and dispersive effects may accumulate to make an order-one relative difference to the wave profiles.This research was supported in part by the National Science Foundation. A considerable portion of the project was completed while the first author was resident at the Institute for Mathematics and Its Applications, University of Minnesota.