Modeling and experimental investigation for electrolytic corrosion prevention in high frequency micro EDM using deionized water

The characteristics of the prevention of electrolytic corrosion during micro electrical discharge machining (EDM) using deionized water and high frequency bipolar pulse were investigated. Electrolytic corrosion during micro EDM using deionized water was analyzed using an equivalent electrical circuit based on the electrical double layer theory. Based on the analysis and experimental verification, a narrow positive pulse duration should be provided to the workpiece to prevent corrosion. A negative voltage with zero average applied voltage (V_{avg, app}) is also essential for this purpose. If V_{avg, app} is positive or negative, electrolytic corrosion occurs on the workpiece or tool, respectively. Micro holes and 3D structures without corrosion were successfully fabricated using a high frequency bipolar pulse with a pulse duration of 0.2?μs and a period of 1?μs, as well as V_{avg, app}?=?0?V.     

针对大规模无线多跳网络的鱼眼机会路由协议

考虑到无线网络中广播特性、丢包特性、节点移动等对网络性能的影响,提出一种针对大规模无线多跳网络的鱼眼机会路由协议。在机会路由的基础上加入鱼眼技术,减少链路状态更新信息。在鱼眼路由表中加入链路传输概率,得到转发列表,并且简化机会路由协议的报文头结构,从而实现高效的数据传输。NS2仿真结果表明,该协议能降低网络端到端延时,提高网络吞吐量。     

基于图像识别的井下机车轨道检测方法

针对传统图像识别算法耗时大、对复杂环境识别效果差等缺点,提出一种针对煤矿井下环境的轨道检测方法。根据井下光线亮度不均匀的特点,设计井下复杂环境下的灰度拉伸与边缘提取算法,提高轨道检测的有效性。给出基于优先级的轨道内侧边缘搜索算法。后帧图像在基于前帧图像检测结果建立的感兴趣区中进行轨道检测,可降低计算量,提高实时性。现场实验结果证明,该方法能有效检测出机车轨道,且相比传统方法耗时明显减小。     

Building of road boundary map based on laser radar

A method for road boundary detection and tracking using laser ladar with respect to a vehicle’s local coordinates is proposed.It can be applied to different types of road conditions,such as roads with or without curbs,having relatively rough road surface and with obstacles on road surface.In the method,some line segments are extracted after a series of preprocessing on range data.The extracted line segments are combined and further selected.They are then united to match the road models and generate the road boundary points which are tracked by Kalman filter.Then the obtained road boundary points are transformed to build a precise vector map by least squares fitting algorithm.These fitted line segments represent road boundary vectors.The vector map is precise enough to provide ample road information such as the orientation of road,the road width and the passable road region.Finally,extensive experiments conducted in urban and semi-urban environment demonstrate the robustness,effectiveness and viability of the proposed method.     

基于DSP的正弦逆变电源设计

介绍了一种采用DSP控制的正弦逆变电源设计方案,描述了系统的硬件工作原理,介绍了高频变压器参数算法、SPWM波形的产生原理、系统控制算法和功率元器件选型。提出了一种通过无功容量计算LCL滤波器的方法,通过实验证明了其可行性。最后总结了设计时的注意事项。     

基于主成分分析的密度聚类算法

密度聚类算法可以描述任意形状的聚类,可以有效地处理异常数据,适合处理大数据集,但不适用于高维数据集的聚类,因此提出了基于主成分分析的密度聚类算法,将DBSCAN算法应用于PCA的k个主成分张成的子空间,解决了DBSCAN算法用于高维数据集的问题.运用气象数据进行实验,结果表明：主成分个数k值的选择严重影响聚类效果,故提出k的基本选择方法,正确选择k值情况下,该算法具有较好的聚类效果.     

水电厂电阻测温的抗干扰探讨

电阻测温的干扰一直困扰着水电厂的安全运行。文中从电阻温度检测器测温原理入手,研究了水电厂电阻测温的干扰源,并提出了对应的抗干扰措施,提高水电厂电阻测温抗干扰水平。     

侧向进水口立轴旋涡数值模拟

为了研究侧向进水口立轴旋涡的运动特性,以RNG模型为基础,引入VOF方法捕捉自由液面的变化,对立轴旋涡的形态及其运动轨迹进行了三维数值模拟,并对旋涡水面线和三维速度分布进行了分析。结果表明,侧向进水口前的旋涡是非对称的,其涡轴是一条空间曲线,旋涡下部在进水口的抽吸拉伸作用下发生扭曲。旋涡运动可分为三部分,第一部分水面线呈漏斗状,与对称旋涡类似,第二部分旋涡运动逐渐从竖向转为横向,第三部分为横向运动。在旋涡的上半部,轴向速度随着水深的增加而增大,当旋涡逐渐由竖向转为横向运动时,轴向速度逐渐减小直至为零。最大切向速度发生在淹没深度的52%处。     

On Kalman filtering over fading wireless channels with controlled transmission powers

We study stochastic stability of centralized Kalman filtering for linear time-varying systems equipped with wireless sensors. Transmission is over fading channels where variable channel gains are counteracted by power control to alleviate the effects of packet drops. We establish sufficient conditions for the expected value of the Kalman filter covariance matrix to be exponentially bounded in norm. The conditions obtained are then used to formulate stabilizing power control policies which minimize the total sensor power budget. In deriving the optimal power control laws, both statistical channel information and full channel information are considered. The effect of system instability on the power budget is also investigated for both these cases.     

Self-clocking principle for congestion control in the Internet

The self-clocking principle (SCP) of Transmission Control Protocol (TCP) had been analyzed for a network implementing a per-flow buffering scheme. The ideal SCP is yet unknown for the Internet which implements a first-in–first-out buffering scheme. This paper derives an ideal SCP for the Internet by formulating the traffic transmission control as a typical control problem and then solving it by a control-theoretic approach. The ideal SCP reveals the defect of the SCP being deployed in the Internet that it is insufficient to avoid congestion by adjusting the packet effective window based on records of the outstanding packets of a single source; instead outstanding packets from other sources also have to be counted. The ideal SCP also reveals the difficulties of developing and implementing an effective self-clocking scheme for congestion control in the Internet.