基于矩阵式变换器的异步电机直接转矩控制策略

研究一种基于矩阵式变换器的异步电机控制策略,分析了异步电机的直接转矩控制方法和矩阵式变换器的空间矢量调制,给出了在直接转矩控制方案中,矩阵式变换器矢量电压的选择.这一控制策略同时实现了矩阵式变换器的空间矢量调制和异步电机的直接转矩控制.利用MATLAB仿真平台实现了该控制策略,仿真结果表明:采用这一控制策略的调速系统具有良好的静、动态性能,并且保持了单位功率因素.     

Makinson一个公开问题的注记

公式集的essential原子在逻辑中扮演了重要角色,如在SAT问题中可以去掉非essemial原子,从而加快搜索解的速度.将essential原子引入到赋值集是近年的一个研究热点,2005年Makinson提出一个关于essential原子的公开问题.现解决了这个公开问题,即证明了结论:任何原子都不是赋值集V的essential原子当且仅当等价的赋值都属于V或者都不属于V.     

基于改进独立分量分析的高光谱数据分类研究

高光谱数据波段数目多,光谱信息量大,采用传统的分类方法无法取得较好的精确分类效果.针对上述问题,结合独立分量分析(ICA)和概率神经网络(PNN)在高光谱数据特征提取及分类中的优势,提出了一种改进的独立分量分析与概率神经网络相结合的高光谱数据分类方法,首先采用改进的独立分昔分析对高光谱数据进行降维,然后采用概率神经网络对提取的独立分量进行分类.通过仿真实验结果表明,方法可以在获得较高分类精度的同时大大节省分类的时间.     

一种用于辅助导航的快速图像匹配方法

为了提高辅助导航中多传感器图像匹配的精确性和实时性,首先提取图像的边缘特征,并用3-4距离变换(3-4DT)方法对边缘二值图像进行变换,以变换后的边缘距离图像为匹配特征;针对传统Hausdorff距离的局限性提出了一种融合点集重合数的Hausdorff距离,并以之为相似性度量;搜索策略根据人眼视觉系统的机制采用一种由远到近的分层匹配方法,同时使用一种改进的实数编码遗传算法来加快底层图像匹配的速度。实验结果为平均匹配时间为1283m s,平均误差值为1.036,表明匹配方法能满足导航要求。     

基于方向导数的多光谱图像快速融合新算法

针对提升小波变换的特点,研究图像融合规则,提出了一种新的基于方向导数的多分辨多光谱图像快速融合算法。首先,利用提升小波变换得到待融合源图像的多分辨分析;然后以小波域方向导数为判据,在图像的多分辨分析的相应各级上进行融合,得到融合图像的多分辨分析;最后,利用提升小波反变换重构融合图像。使用多光谱图像对算法进行验证并与方向对比度算法进行对比,结果表明,融合图像完好的融合了源图像的信息,且算法运算时间短。     

基于XMPP协议的服务器集群研究

描述了在实现基于XMPP协议的即时通信系统服务器集群时遇到的关键性问题,从安全、性能和通用性方面提出了解决方案,重点介绍了服务器间的寻址和路由机制、服务期间通信的安全机制、故障转移机制。     

Toward a free-space parallel optoelectronic computer: a 300-MHz optoelectronic counter using holographic interconnects

We built and tested one of the key components of a free-space holographically interconnected stored-program optoelectronic computer: a counter. The counter is constructed with 1-ns-latency optoelectronic NOR gates and is interconnected with holographic optical elements. Two synchronization methods were also demonstrated: the gate-and-strobe method and the time-of-flight method. These counters represent prototypical optoelectronic finite-state controllers. They were developed to demonstrate the feasibility of providing optoelectronic controllers for optoelectronic processors.     

Partial correction for turbulent distortions in telescopes

To provide complete compensation for turbulent distortions in the visible range at aperture dimensions typical for modern telescopes (6-10 m), one needs to develop adaptive systems with hundreds of control channels. More simple adaptive systems that provide complete compensation in the infrared range can give an essential advantage in angular resolution in the visible range too. In this case the image brightness characterized by the Strehl ratio remains much less than that in the diffraction-limited case, i.e., the system provides only partial compensation. We present the results of numerical calculations of the partially corrected point-spread function and discuss possible approaches to composing the adaptive system configuration.     

Improving the contrast of topographical AFM images by a simple averaging filter

New image-processing methods were applied to atomic force microscopy images in order to visualize small details on the surface of virus particles and living cells. Polynomial line flattening and plane fitting of topographical images were performed as first step of the image processing. In a second step, a sliding window approach was used for low-pass filtering and data smoothing. The size of the filtering window was adjusted to the size of the small details of interest. Subtraction of the smoothed data from the original data resulted in images with enhanced contrast. Topographical features which are usually not visible can be easily discerned in the processed images. The method developed in this study rendered possible the detection of small patterns on viral particles as well as thin cytoskeleton fibers of living cells. It is shown that the sliding window approach gives better results than Fourier-filtering. Our method can be generally applied to increase the contrast of topographical images, especially when small features are to be highlighted on relatively high objects.     

基于多传感器信息融合城市车辆导航定位

针对全球定位系统信号易受城市复杂的环境干扰,接收不可靠、航位推算只能进行短时间高精度导航、地图匹配仅可在拐弯处才能提供与地图精度相当的修正信息、城区车辆导航存在“盲区”问题,研制了采用蓝牙技术的新型路标传感器,研究了基于自适应联合卡尔曼滤波算法的多传感器信息融合技术。大量的试验研究表明：采用该信息融合技术后,城区车辆导航定位精度达到10m以内,符合高精度导航定位要求。