基于Colley-Tukey算法对GPS捕获过程的优化

根据GPS捕获过程中相关运算的计算速度要求,针对常用的频域FFT算法速度快但规定采样点的点数N必须为2的整数幂的缺点,分析了如何利用Colley-Tukey算法对部分可分解的N值的相关运算进行优化,从而在时域算法保证精确度,同时又在速度上接近FFT算法.最后在Matlab环境下对算法进行了验证.     

信息安全中的数字水印技术

随着信息网络的日新月异,信息的合法使用和保护成为当前重要的热门话题.文中针对日益引起人们关注的数字水印技术,详细讨论了信息隐藏中数字水印技术的概念、基本特征、通用模型等.总结概括了这种技术的发展以及研究状况,在此基础上,提出进一步发展和研究的方向.     

Q开关Nd:YAG激光脱毛效果的动物实验研究

为探讨激光脱毛的效果及碳霜在激光脱毛中的作用,采用外涂碳霜与NdYAG激光照射,对豚鼠进行脱毛效果的观察,发现外涂碳霜对组织病理改变和毛发再生均无影响.实验结果表明,Q开关NdYAG激光脱毛是一种安全有效的治疗方法,脱毛效果与照射剂量有关,高于阈值3～4倍剂量的激光照射脱毛效果较好.     

Minimal realization for lifted periodic filters

Practical applications in signals and systems often deal with lifted models of periodic digital filters, to which well-known methods and computing software for linear time-invariant (LTI) systems can be applied in the analysis and synthesis of periodic filters. When the design of a periodic filter is based on the lifted model, the resultant filter is usually in the lifted LTI form and needs to be further converted into the periodic form for implementational and computational purposes. In this paper, we present a computational procedure for obtaining a minimal realization of periodic digital filters from the fifted model.This work was supported by the Australian Research Council.     

Image quality assessment by visual gradient similarity

A full-reference image quality assessment (IQA) model by multiscale visual gradient similarity (VGS) is presented. The VGS model adopts a three-stage approach: First, global contrast registration for each scale is applied. Then, pointwise comparison is given by multiplying the similarity of gradient direction with the similarity of gradient magnitude. Third, intrascale pooling is applied, followed by interscale pooling. Several properties of human visual systems on image gradient have been explored and incorporated into the VGS model. It has been found that Stevens' power law is also suitable for gradient magnitude. Other factors such as quality uniformity, visual detection threshold of gradient, and visual frequency sensitivity also affect subjective image quality. The optimal values of two parameters of VGS are trained with existing IQA databases, and good performance of VGS has been verified by cross validation. Experimental results show that VGS is competitive with state-of-the-art metrics in terms of prediction precision, reliability, simplicity, and low computational cost.     

选区激光熔化成型悬垂结构的计算机辅助工艺参数优化

为了提高选区激光熔化(SLM)成型悬垂结构的质量,从调节成型方向和能量输入入手研究悬垂结构的计算机辅助工艺参数优化。以减小零件模型整体难成型悬垂面的面积为目标,以零件模型非成型方向的两个旋转角度为优化变量,建立成型方向的优化模型,并基于遗传算法实现优化模型参数的求解。通过遍历零件模型中的所有三角面片,建立倾斜角静态查找表,并在成型时查表实现能量输入的实时调节。实验结果表明,经成型方向优化,零件模型难成型悬垂面的面积从555.12mm2减小为16.211mm2,所需支撑数量明显减少;成型后所得零件无明显悬垂物和翘曲变形,成型质量明显改善。     

基于干涉仪动态相移的光纤激光器跳模检测方法

针对已有方法在单频光纤激光器跳模检测中存在的不足,提出一种基于非平衡光纤Michelson干涉仪动态相移的跳模检测方法。使用干涉仪将激光器跳模时的光频突变转换为相位工作点的突变,并通过同步监测相位工作点的正余弦函数两路信号来跟踪与判断它的动态相移,成功实现了对超窄线宽掺铒光纤环形激光器偶发的随机跳模以及由开机瞬态热效应触发的连续多次跳模的测量与分析。结果表明,该方法检测灵敏度高,跳模判据实时直观,并能测量跳模前后可能发生的频漂,为评价单频光纤激光器的模式稳定能提供有效的测试手段。     

基于复合式抛物面聚光器的LED反光杯建模研究

针对复合式抛物面聚光器(CPC)无法在TracePro软件中直接建模的不足,结合TracePro软件特点,对CPC关键参数进行了分析,通过数学模型对参数之间的几何关系进行了推导,得出了计算公式,实现了CPC在TracePro中的建模。将CPC设计成反光杯应用于LED灯具中,可方便地进行光学模拟和分析,进而有效地缩短产品开发周期和开发成本。为CPC设计提供了数学依据,通过建模验证了该方法的可行性,有效提高了设计效率。结果表明,用通过该方法设计出的CPC做成的LED反光杯,可以极大地提高灯具的发光效率。为其在照明领域的发展应用提供了更好的使用价值和前景。     

Weighted 3D GS Algorithm for Image-Qquality Improvement of Multi-Plane Holographic Display

Theoretically,three-dimensional(3D) GS algorithm can realize 3D displays;however,correlation of the output image is restricted because of the interaction among multiple planes,thus failing to meet the image-quality requirements in practical applications.We introduce the weight factors and propose the weighted 3D GS algorithm,which can realize selective control of the correlation of multi-plane display based on the traditional 3D GS algorithm.Improvement in image quality is accomplished by the selection of appropriate weight factors.     

激光相干偏振光束合成技术的研究进展

激光相干偏振光束合成是近几年光束合成领域的热点。综述了国内外关于相干偏振光束合成的研究方案,对几种典型的方案进行了分析和评价。研究表明,基于主振荡功率放大(MOPA)结构的相干偏振光束合成方案有同时获得大功率、高光束质量的可行性,并且易于扩展。