Reversed and Anomalous Doppler Effects in Photonic Crystals and other Time-dependent Periodic Media

We predict that reversed and anomalous non-relativistic Doppler shifts can be observed under some circumstances when light reflects from a shock wave front propagating through a photonic crystal, or material with a periodic modulation of the dielectric. This theoretical prediction is generalizable and applies to wave-like excitations in a variety of periodic media. An experimental observation of this effect has recently been made (Seddon, N. and Bearpark, T. Science, 302 (2003) 1537) and we provide a brief discussion of this experiment.     

Sonochemical Activation of Al/Ni Hydrogenation Catalyst

This paper proposes a sonochemical approach to the nanostructuring of Al/Ni catalyst with high content of accessible Ni centers and a high reusability. The surface and bulk composition as well as pore size distribution of this catalyst are controlled synergistically by adjusting the ultrasound intensity in aqueous solution. Sonochemical activation of Al/Ni alloy leads to formation of mesoporous Al/Ni metallic based frameworks with surface area up to 125 m² g^?1, and regular distribution of nickel active center in the porous matrix. One of the opportunities of porous Al/Ni catalyst is that due to a time‐resolved controllable formation of protective oxide layer it can be stored and handled under air in comparison to traditional Raney catalysts which need inert conditions. The Al/Ni catalyst is characterized by scanning electron microscopy (SEM), electron diffraction spectroscopy (EDS), X‐ray photoelectron spectroscopy (XPS), confocal scanning fluorescence microscopy (CSFM), solid‐state NMR experiments, and powder X‐ray diffraction analysis (PXRD). The catalytic activity was investigated for the hydrogenation of acetophenone.     

激光双截面转速波动法监测转轴动态扭矩

基于激光多普勒效应和转动动力学原理,提出一种直接监测转轴动态扭矩的新方法,并建立了数学模型。通过构造光学测试系统使4束高相干激光投射到转轴轴段两截面上4点,具有多普勒频移的反射光在光电探测器上发生混频,光电流频差正比于角速度。测得相邻时刻两截面的瞬时转速,得到轴段转速波动值及两端面相对转速波动值,进而实现转轴动态扭矩的直接监测。实验验证了该方法的可行性。与传统方法相比,该方法实时性强,具有较宽的动态范围,对动态扭矩的识别值提高了5%~10%,反映了转轴扭矩波动的动态特性。     

WCDMA系统中基于多普勒频移估计的信道估计方法

Rake接收机是CDMA系统抗多径的有效手段，信道估计对其性能有很大的影响。传统方法是利用连续多个时隙的导频段估计出的信道参数，再对估计值进行平均。这种固定平均的方法不适合3G系统信道变化范围大的环境。本文提出了直接利用每个导频段的信道参数的包络来估计最大多普勒频移，再运用指数平滑法来调整各被估计时隙的权值的信道估计方法。仿真结果表明，该方法能准确有效地估计出信道参数，改善系统性能。     

深空测距中可变带宽超窄带锁相环设计

采用超窄带锁相环是深空测距中提高微弱信号检测能力的有效手段,传统的模拟锁相环带宽范围有限且可靠性、稳定性差,数字锁相环则没有上述限制。介绍了一种数字超窄带锁相环的基本原理和环路结构,对其性能进行理论分析和计算机仿真。针对深空测距中存在的多普勒频偏,提出了数字锁相环变带宽的门限设定方法,完成了数字锁相环的FPGA设计与实现。     

基于中频模板信号的脉冲压缩性能分析

由雷达发射、接收系统导致的信号幅度、相位失真以及由目标径向速度导致的目标多普勒频率是影响脉冲压缩性能的三个主要因素。本文从理论上分析了这三个因素影响脉冲压缩性能的算法原理,通过仿真验证了它们的实际影响效果,对仿真中的情况进行解释说明,对相应指标要求进行了分析,并对在影响脉冲压缩性能的因素存在下的信号处理方法提出了实际的建议。     

基于形状插值的B超图像三维表面重建

B超图像由于受其成像机理的限制,其成像质量较差,无法采用与CT(计算机断层扫描)、MRI(磁共振成像)类似的三维重建方法。针对B超图像的缺点,采用基于形状的插值方法将其转换为等分辨率体数据。此外,对插值算法进行了适当改进,使重建的速度和效果得到明显改善。最后,分别采用移动立方体(marching cubes)算法、连接轮廓线、光线投射(ray casting)算法对B超图像进行三维重建。结果表明,移动立方体算法在重建的真实性和快速性方面都得到了更满意的效果。     

Performances comparison of pulse-pair and 2-step prediction algorithms for the doppler spectrum estimation

In this work we use real data provided by terminal pulse Doppler radar (WSR-88D) echoes to estimate the windshear hazards disastrous for the aircraft takeoffs and landings. Briefly two different methods are used to estimate the received Doppler moments. The second central moment which is the variance of the wind speed is called width or shear. A first method is in the time domain and also called pulse-pair, while the second is in the frequency domain. The main aim of this study is a performances comparison of results provided by the two mentioned methods and assumes that the power spectrums of the received signals are approached with the Gaussian shape.     

高铁规划要点及测试情况分析

从理论分析、实地测试2个方面同时入手,针对郑西高铁测试过程中发现的问题提出了解决思路和实施方案,并给出了高铁规划中的一些技术要点.     

一种高动态短突发信号伪码快速捕获方法

根据实际的应用背景,针对高动态的突发短帧信号的特性,研究其信号快速捕获问题,提出了一种适应高动态环境,捕获时间短的捕获方法。该方法采用一种频率分割的方案,将大的多普勒频偏分割为若干小频率段,每个频率段并行处理,采用等待式的数字相关处理办法,各自完成相关积累和视频积累,并经过自适应门限判决,输出同步信号检测脉冲,完成伪码的快速捕获。