高性能SAR成像程序的并行粒度选择技术

高性能并行仿真程序必须采用针对性的并行优化技术以获得高效的性能加速。而根据程序特性,确定适合的并行粒度是设计并行优化技术的基础。因此,以典型合成孔径雷达(SAR)成像程序--距离-多普勒(RD)程序为代表,研究了高性能SAR成像程序的并行粒度选择技术,重点针对并行粒度的基本准则和RD算法的并行粒度选择方法进行了研究。实验结果证明,经过并行粒度优化选择的SAR成像程序能够获得显著的性能提升,并且具有良好的可扩展性。     

实值离散ＧＡＢＯＲ变换及其最优双正交分析窗函数特性

Ｇabor变换在信号、图像处理中是一非常有用的工具。本文首先回顾了作者曾提出的实值离散Gabor变换方法,然后着重讨论了在已知综合窗函数的条件下,双正交分析窗函数的最优解特性,指出在许多情况下,这些最优解（如最小范数解与最优正交解）都是相同的,并讨论了采用奇异值分解（SVD）理论求解双正交分析窗函烽的方法。文末还给出了计算机求解实例。     

基于测量的接纳控制研究

与传统的接纳控制算法相比,基于测量的纳控制有诸多优点,首先它无需知识应用的流量模型,其次它能动态适应网络的负载变化,提高网络资源的利用率。文中分析了基于测量的接纳控制的基本思想,并在此基础上提出和实现了一种自适应的接纳控制算法（Adaptive Measurement-Based Admission Control,AMBAC).作者通过实验对该算法进行了验证,发现在系统资源利用率（或接纳能力）接近的情况下,与传统的（固定时间窗口的）,MBAC相比,AMBAC能达到更低的平均分组丢失率。     

基于线段与线段求交的矩形窗口裁剪算法

我们首先对线段是否完全可见进行判定 ,然后对被裁剪线段与矩形窗口四边所在的线段是否相交进行判定并求交。若交点存在则用替换法替换相应的点 ,最后连接被替换后的点得到被裁剪后的线段 ;若交点不存在则线段完全不可见 ,线段将被完全裁剪掉。     

加窗傅里叶变换在谐波分析中的应用

针对稳定状态下的电能质量信号,采用一种组合余弦窗的汉宁窗,将该窗函数与快速傅里叶变换相结合进行电能质量中的谐波分析,并利用Matlab7.0进行仿真验证,发现将窗函数与快速傅里叶变换相结合,在很大程度上能减少谐波泄漏,有效减弱谐波之间的干扰,有利于测量到较为精确的电能信号的幅值和相位.     

Exact and heuristic algorithms for the aerial refueling parallel machine scheduling problem with due date-to-deadline window and ready times

The Aerial Refueling Scheduling Problem (ARSP) can be defined as determining the refueling completion times for fighter aircrafts (jobs) on multiple tankers (machines) to minimize the total weighted tardiness. ARSP can be modeled as a parallel machine scheduling with ready times and due date-to-deadline window to minimize total weighted tardiness. ARSP assumes that the jobs have different ready times and a due date-to-deadline window between refueling due date and a deadline to return without refueling. In this paper, we first formulate the ARSP as a mixed integer programming model. The objective function is a piece-wise tardiness cost that takes into account due date-to-deadline windows and job priorities. Since ARSP is NP-hard, two heuristics are proposed to obtain solutions in reasonable computation times, namely (1) modified ATC rule (MATC), (2) a simulated annealing method (SA). The proposed heuristic algorithms are tested in terms of solution quality and CPU time through computational experiments with data randomly generated to represent aerial refueling operations of an in-theater air operation. Solutions provided by both algorithms were compared to optimal solutions for problems with up to 12 jobs and to each other for larger problems with up to 60 jobs. The results show that, MATC is more likely to outperform SA especially when the problem size increases, although it has significantly worse performance than SA in terms of deviation from optimal solution for small size problems. Moreover CPU time performance of MATC is significantly better than SA in both cases.     

Performance analysis of fast GPS signal acquisition based on PMF and Window FFT

Combining the advantages of partial matched filter(PMF) and fast Fourier transform(FFT),an improved fast acquisition method for GPS C/A code is proposed.According to PMF-FFT acquisition architecture,the greater the number of PMF will bring out the more slowly amplitude decreasing of the amplitude-frequency response,the smaller scale of the corresponding PMF,and the larger computation of the FFT.In order to compensate the frequency spectrum attenuation caused by spectrum leakage and fence effect,adding window function to PMF-FFT is presented.Through comparing the influences to the acquisition performance based on rectangular,Hamming,Blackman and Rife-Vincent(Ⅲ) window functions,an improved Rife-Vincent Ⅲ windowing algorithm is recommended for the fast acquisition based on PMF-FFT.     

基于温度植被干旱指数的黄河源区土壤表层含水量反演

为了对黄河源区的土壤表层含水量进行反演与时空分析,利用黄河源区2006年第65—321天MODIS温度和植被指数产品数据,计算了温度植被干旱指数(TVDI),构建了不同像元尺度窗口的LST/NDVI斜率与实测表层土壤相对含水量之间的线性关系,比较了不同尺度像元窗口的拟合效果。分析结果表明:9×9像元窗口的拟合效果(回归系数R2为0.65)优于其他像元窗口尺度;季节尺度的拟合精度(回归系数R2为0.76)优于长时间序列的拟合精度;夏季模拟值与实测值的均方根误差为0.09,模拟精度满足实验要求,可用于黄河源区短时间序列的土壤表层含水量反演。     

基于Nuttall窗插值FFT的电力谐波虚拟测量仪

为了提高虚拟仪器测量电力系统谐波的精度,研究了加窗FFT插值算法的原理,对比分析了几种重要的窗函数的频谱特性,提出了将Nuttall窗插值FFT算法引入LabVIEW平台的方案,给出了算法的具体程序,并进行了仿真和实验验证.结果表明,基于Nuttall窗插值FFT的电力谐波虚拟测量仪精度高,实现方便,开发周期短,能快速地在普通PC机上完成高精度的谐波分析.     

凯瑟窗改进谐波法测电力电容器介质损耗因数

针对基于快速傅里叶变换(FFT)的传统谐波分析法测电力电容器介质损耗因数(tanδ)时会由于非同步采样和非整周期截断造成频谱泄露和栏栅效应的问题,依据凯瑟(Kaiser)窗函数主瓣和旁瓣衰减比例自由选择的特性,采用基于凯瑟窗的相位校正的改进谐波算法测量电力电容器介质损耗因数.在电网基波频率变化、介损角真值发生变化以及白噪声干扰等3种条件下,仿真分析该算法和基于Hanning窗、Blackman窗的插值算法的测量误差,并通过实验进行验证.结果表明,该算法与Hanning窗和Blackman窗插值算法相比能更有效地克服基波频率波动及白噪声等对电力电容器tanδ测量的影响.基于Kaiser窗函数的改进谐波算法抑制频谱泄漏效果好,准确度高,满足电力电容器介质损耗因数tanδ在线监测的要求.