任意相位差条纹信号细分方法的研究

为消除传统细分方法中由于两路条纹信号不正交引入的细分误差，提出了一种可对任意相位差条纹信号直接细分的新方法。根据两路条纹信号的极性和幅值大小，把一个信号周期分成8个区段。高速采集两路条纹信号，通过判断信号采样点所处的区段是否跳变对信号幅值交点进行动态跟踪。对不足一个周期的条纹移动，当测量出起点与终点的幅值，计算出其所在的区段及位置后，结合两路信号的交点，可实现对任意相位差条纹信号的细分。实验结果表明，该方法突破了传统细分方法必须信号正交的限制，可对任意相位差信号进行准确地细分，降低了条纹测量中器件安装与调试的难度，具有更强的环境适应性和抗干扰能力。     

用人字形光栅检验校正光束准直性

分析人字形光栅副莫尔条纹的特点，研究了一种用莫尔偏折术检校光束准直性的改进方法，利用双场莫尔条纹方向平行性进行判定，此法使用方便且精度可提高一倍以上。     

Computer Simulation of a 3-D Sensing System with Structured Illumination

A computer simulation system of three-dimensional sensing with structured illumination is presented. It includes the generation of deformed fringe patterns from 3-D shapes and the reconstruction of 3-D shapes, conversely. Some experimental results of the deformed fringe pattern and the reconstructed object shapes are presented. We have also discussed the effect of some major system parameters on the measurement results and considered how to correct these parameters according to the measurement result of the standard plane. Using this simulation system, the major system parameters: environmental conditions, measurement accuracy and algorithm evaluation of the 3-D shape measurement system based on PMP, FTP, SPM, etc., can be researched. © 1997 Elsevier Science Ltd. All rights reserved.     

基于非线性预测效果的癫痫脑电信号的特征提取方法

在非线性时间序列预测研究的基础上,提出了基于非线性预测效果的癫痫脑电信号特征提取方法,从脑电信号中自动检测出癫痫脑电信号.采用基于可预测性的选取嵌入维数的方法确定脑电信号序列的嵌入维数,进行相空间重构.实验结果表明:基于非线性预测效果的特征提取方法提取的特征能明显地区分癫痫脑电信号与正常脑电信号,该非线性特征提取方法适合小数据量的情况且对噪声的稳定性好.     

A new method of non-contact gauge block calibration using a fringe-counting technique: I. Theoretical basis

A new non-contact interference method for gauge block or length bar calibration is presented. A central interference fringe of polychromatic light is used for the determination of the end surface position of the measured artefact. Distances referring to these positions are measured using a fringe-counting technique, with a wavelength-stabilized laser interferometer. Absolute and comparative measurement methods are proposed. A new technique for central interference fringe detection and identification is discussed.     

Shear Induced Crystallization,a Relaxation Phenomenon in Polymer Melts: A Re‐Collection

Thread‐like nuclei for the crystallization of polymers which are formed at high deformation rates in a temperature range close to the equilibrium melting point appear to be practically stable at temperatures where spherulites are melting. However, the fact that the great majority of experiments on flow induced crystallization have been carried out at temperatures below the melting temperature of the spherulites leads to the conclusion that the precursors for elongated structures, as formed under those conditions, are practically stable from the moment of their creation. In other words: their relaxation times are much longer than any deformation time applied. As a consequence, deformation times as independent parameters lose their importance in these experiments. Long lasting deformations under low stresses can yield the same precursors as short term deformations under high loads. Apparently the only condition is that the applied specific work is the same.     

迈克耳孙干涉仪条纹计数器的研制

设计了电路简单、可自动识别条纹移动方向的迈克耳孙干涉仪条纹计数器。该计数器仅用9个常见的分立元件即实现了对光信号的采集、放大、滤波、整形的功能,并有效地去除了计数过程中的干扰因素。输出信号经条纹移动方向识别电路后,送入可逆计数器能自动进行相应的加计数或减计数并显示。     

基于1–10GHz空地链路信号的雨强监测方法可行性研究

空地链路上的微波信号受降雨影响, 会产生功率衰减和去极化效应. 基于这些物理特性, 本文提出利用1–10 GHz空地链路信号的降雨干扰项获取雨强的方法, 并开展了相关理论研究. 根据空地链路信号与雨滴复杂的相互作用, 研究了空地链路信号频率为1–10 GHz时, 雨强 (rain rate, R) 对衰减 (attenuation, A) 和交叉极化分辨率 (cross-polarization discrimination, XPD)的影响, 分别建立了A-R和XPD-R关系模型. 通过数值模拟, 分别分析了利用上述两个关系模型估测雨强的可行性, 并系统研究了不同频率、极化方式和仰角条件下的适用性. 研究结果表明, 对于水平极化或圆极化, 且频率较高的空地链路信号, 利用A-R关系反演强降雨具有理论上的可行性; 对于不同频率和极化方式的信号, XPD-R关系模型都可以用于反演雨强, 并且对于1–50 mm·h^-1范围内的雨强, XPD较为敏感; 不同仰角条件下, A-R和XPD-R 模型都适用. 在4–10 GHz时, 本文的XPD-R模型和国际电信联盟ITU-R中XPD预测模型的结果非常接近. 所得出的结论对于下一步开展相关的验证实验, 拓展卫星系统的气象应用, 实时估测降雨强度, 实现全球降雨观测具有重要的参考价值. 关键词： 空地链路信号 雨强 衰减特性 交叉极化分辨率(XPD)     

Optimal transmission of “television type” gaussian signals through a noiseless feedback channel

Using the methods and results of the theory of conditionally Gaussian filtering of stochastic processes and fields, an optimal scheme of “television type” signal transmission through a noiseless feedback channel is constructed under the usual power conditions, the signals being evolutionary Gaussian fields θ={θ_t(x)),tε[0,T),xεDεRⁿ . Explicit representations for optimal coding and decoding functionals, which are optimal in the sense of a special square criterion, and the expression for the error of signal reproduction are given.     

Intensity analysis methods for transient signals

Conventionally, the Fourier transform is applied for sound intensity analysis of stationary signals, but this method can be applied for analyzing non-stationary transient signals. Instead of the Fourier transform analysis, instantaneous spectrum analysis methods such as the Wigner-Ville distribution and the wavelet transform are proposed. By using the mathematical example as a transient signal, advantages and disadvantages of these methods including the short-time Fourier transform are compared. From calculation results, it is considered that the STFT method is the most suitable for the accurate measurement of sound intensity levels, but the WT method is also recommended from its higher resolution of transient signals.