Evaluation of Cracks in Elastic Media using Surface Signals

This paper provides a theoretical study of quantitatively identifying cracks in plane elastic media from surface signals induced by a piezoelectric actuator. The surface signals are used as the boundary condition of the problem to generate a reverse wave field, which represents the scattered waves from the cracks. An imaging technique is then used to determine the sizes, shapes and positions of existing cracks based on the determined scattered waves. Numerical examples are provided to show the feasibility of using surface signals to characterize embedded cracks.     

The Eigenvalue Problem for the 2D Laplacian in ℋ-Matrix Arithmetic and Application to the Heat and Wave Equation

A class of matrices (-matrices) has recently been introduced by Hackbusch for approximating large and fully populated matrices arising from FEM and BEM applications. These matrices are data-sparse and allow approximate matrix operations of almost linear complexity. In the present paper, we choose a special class of -matrices that provides a good approximation to the inverse of the discrete 2D Laplacian. For these 2D -matrices we study the blockwise recursive schemes for block triangular linear systems of equations and the Cholesky and LDL^T factorization in an approximate arithmetic of almost linear complexity. Using the LDL^T factorization we compute eigenpairs of the discrete 2D Laplacian in -matrix arithmetic by means of a so-called simultaneous iteration for computing invariant subspaces of non-Hermitian matrices due to Stewart. We apply the -matrix techniques to approximate the solutions of the high-frequency 2D wave equation for smooth initial data and the 2D heat equation for arbitrary initial data by spectral decomposition of the discrete 2D Laplacian in, up to logarithmic factors, optimal complexity.     

井间地震勘探的误区及出路

井间地震勘探的目的是获得主频和分辨率都很高的地下记录。然而,目前的井间地震勘探陷进了一个误区,即井间地震勘探的大部分射线都落在临界角以外的区域。本文通过对一些实例的分析,确信井间地震勘探的射线入射角小于或大于临界角是成功或失败的标志。文中采用弹性波波动方程正演模型论证,当地层水平时,在井下激发,地震波场在左、右两侧很快超过了临界角,形成极为复杂的波场紊乱区(笔者称之为“牛角尖”)。在这个区域内,射线理论已经不再适用,初至也无法准确拾取,造成了井间成像的极大困难。据此,文中明确指出了今后发展井间地震勘探工作的出路在于将射线的入射角控制在临界角以内并保证震源有足够的能量。     

乐甫波传感器及其应用进展

乐甫波是声表面波的一种,它是在沉积于基片表面的薄层声波导中传播的波。介绍了乐甫波器件的构成和制造工艺,乐甫波传感器传感原理和常用的结构形式,论述了乐甫波传感器当前的研究情况。     

TE013 Mode High Temperature Superconductor Millimeter Resonator

This paper describes a TE₀₁₃ mode dielectric resonator at 36.098 GHz. The dielectric resonator was formed by sandwiching a cylindrical piece of polished dielectric (sapphire) rod between two GdBa₂Cu₃O_7–x (GBCO) High Temperature Superconductor (HTS) thin films. The resonator was tested as a two-port device at a temperature of 77 K. A 62700 unload quality factor Q ₀ was obtained. The surface resistance (Rs) of the HTS film had been determined as 9.4 m at 77 K and 36 GHz.     

有效倍频行为中相位匹配条件的适用范围

任何一种理论都有它的适用范围,相位匹配条件亦不例外,因此我们可以问是否存在一个判据,它告诉我们什么时候可以“相位匹配地”讨论有效倍频现象以及什么时候必须“非相位匹配地”讨论。本文基于晶体的离散原子结构状态讨论了有效倍频行为中先前Franken和Ward所描述的相位匹配条件的适用范围,粗略地说,每当所有有关的光波波长都比晶格中原子间距大得多时,“相位匹配地”讨论就足够了,也即是足够精确了。     

FFT解调的短波跳频系统自适应实时信道估值

在分析伪错线性外推算法置信度的基础上,结合短波FH／DQPSK系统FFT的解调技术,提出了一种适用于短波瑞利衰落信道BER设计的自适应线性外推算法,并进行了数值模拟,其结果表明：该算法能够准确地反映信道的实际比特误码特性,并绝对误差Δmax=0.018,且该算法监测范围较伪错线性外推算法监测的范围更宽,基本上能覆盖该信道的实际比特误码范围（10^-1-10^-4)。最后提供了该算法可行的硬件实现方案。     

基于双单片机的正弦信号源设计

采用直接数字频率合成（DDS）芯片AD9850，设计了基于双单片机AT89S52的正弦信号源电路。该信号源能输出频率可调正弦信号、模拟幅度调制（AM）信号、二进制PSK信号和二进制ASK信号。     

基于MSC1211单片机的RFID接收系统设计

为了满足现有和新兴RFID标准的要求，设计了一种以MSC1211单片机为控制核心的高频RFID接收系统。介绍了MSC1211单片机的特点与性能，阐述了RFID接收系统基带电路的工作原理，叙述了接收器的程序设计方法并给出了程序流程图。     

基于混合基函数分解的宽带连续谱信号分析

分析宽带信号时,对信号进行某种变换,准确而有效地分析信号是问题关键所在.提出了基于混合基函数的信号分解方法,通过引入过完备的分解基函数为成份复杂信号主要分量的提取创造有力条件,使得信号分解方法具备不同的分解特性,特别是结构性分解原则能够有效地提高结构紧密分量的分辨能力.选取过完备小波包基函数逼近连续谱主要分量,用余弦基函数逼近线谱主要分量,利用基追踪(BP)算法有效地提取了低频连续谱分量.通过对基函数的通带通性进行分析,选取合适的小波或小波包基函数.实验证实该方法通过引入稀疏性分解,仅使用少数小波包基函数就能够准确重构连续谱主要分量的时域信号形式.