Sparking at cathode tools during electrochemical machining in flow-through cells

The current density used in electrochemical machining can be increased only up to a certain value, above which the formation of electric sparks on the cathode (tool) is observed, whereby the latter is damaged and the anode surface becomes rough. The present work is devoted to the measurement of this critical density for small metal cathodes placed on the wall of a flow-through channel for Reynolds numbers from 1265 up to 5902 and static pressures ranging from 0.1 up to 1.0 MPa. The results are correlated by criterion equations which gave values of critical (sparking) cathodic current density,j _s, with an average error of 7.1 % for laminar flow and 4.1 % for turbulent flow. The equations can be used for the calculation of the sparking current density for industrial flow-through cells for electrochemical machining.     

Photocatalytic degradation rate of oxalic acid on the semiconductive layer of n-TiO2 particles in the batch mode plate reactor Part I: Mass transfer limits

Organic compounds dissolved in water can be decomposed on a layer of n-TiO2 particles irradiated by u.v. light, which generates holes and electrons in the TiO2 material. Dissolved oxygen was used as electron scavenger and holes reacted with water to give OH radicals. The rate of degradation of the dissolved organic compounds by OH radicals is limited by the transfer of either oxygen or of theorganic compounds to the surface of n-TiO2 particles. The consequence of these limits is that, in the batch mode reactor with recirculation of the liquid, the dependence of the concentration of an organic compound on time has either a linear or an exponential form. Experiments with decomposition of oxalic acid in aqueous solutions using a plate reactor (60 cm × 120 cm) confirmed the analysis. Equations for evaluation of the mass transfer coefficient of the dissolved species to the surface of the plate reactor with a moving liquid fil m were developed for the case of the thickness of the Nernst diffusion layer being thinner than the thickness of the liquid. The experimentally obtained decomposition rate of oxalic acid was about 60 to 80% of the theoretical decomposition rate limited by oxygen flux through the film of a moving liquid. The present theory neglects the diffusion of oxygen into the porous layer of n-TiO2.     

Theory of porous electrodes—XI. The positive plate of the lead-acid battery

Partial differential equations describing the transport of mass and electricity in the pores of the positive electrode of a lead acid battery were derived. The theory is based on exact transport equations and on the assumption that the solid porous matrix has a metallic conductivity. Volume changes in both phases are taken into account. Numerical solutions obtained on a computer are presented for the case where the influence of electrolyte between the electrodes can be neglected. The solutions depend on the product of electrode thickness times current density, and on the initial porosity.     

图像FAST角点检测算法的FPGA实现与系统集成

基于Vivado HLS工具封装了包括FAST算法和AXI接口的FPGA硬件IP,并将该IP集成到工业摄像机的嵌入式系统中,工作摄像机中FAST算法的最终处理结果传输给视觉检测设备主机。利用相同图像的FAST角点检测算法对FPGA算法电路和OpenCV算法程序进行对比实验,完成相同功能的情况下前者的处理速度比后者快约60倍,该功能在工业摄像机中使数据带宽最多减小9%,显示出本文的工作可提高工业视觉检测设备的检测效率和性能。相关技术可应用于其他图像处理算法,也可推广到二维传感器阵列数据的处理。     

现代汉语分词系统通用接口设计与实现

现代汉语文本自动分词是中文信息处理的重要基石,为此提供一个通用的分词接口是非常重要的。本文提出了通用分词接口的目标,论述了它的原理和设计方案。该系统已经初步实现。     

基于“固结词串”实例的中文分词研究

近几年的中文分词研究中,基于条件随机场(CRF)模型的中文分词方法得到了广泛的关注。但是这种分词方法在处理歧义切分方面存在一定的问题。CRF虽然可以消除大部分原有的分词歧义,却会带来更多新的错误切分。该文尝试找到一种简单的、基于“固结词串”实例的机器学习方法解决分词歧义问题。实验结果表明,该方法可以简单有效的解决原有的分词歧义问题,并且不会产生更多新的歧义切分。     

应用二叉树剪枝识别韵律短语边界

句子的韵律短语识别是语音合成的重要研究内容。本文提出了应用统计语言模型生成的二叉树,结合最大熵方法识别待合成汉语句子的语音停顿点。文中给出了二叉树相关的模型训练和生成算法;二叉树与语音停顿点之间的关系;在最大熵方法中应用二叉树剪枝识别句子的韵律短语。实验结果表明,在搜索算法中,利用二叉树进行剪枝,可以很大程度上提高语音停顿预测的正确率和召回率,基于试验数据的f-Score提高了近35%。     

基于互连网的术语定义获取系统

文中介绍了一个实验性的基于互联网的术语定义获取系统,可以方便、迅速的从互连网上查找术语的定义以及与定义有关的内容,给用户迅速获得新生术语以及新技术词汇的定义方面的知识提供方便。系统采用一组术语定义的语言学模式,以多线程方式高效下载网页,并从中匹配符合术语定义模式的文本段落,再经一定后续处理,形成返回给用户的结果。系统中使用的语言学模式是在一定量的科技期刊语料库中获取的。试验结果表明系统的运行效率高,结果的准确度比较令人满意。     

真空合成TiB_2工艺研究

本文就TiB_2的真空合成工艺进行初步探讨。采用XRD分析技术对在不同温度下的试样进行相结构组成分析;由气相色谱法测定粉末的C和O_2等杂质;通过电子探针对粉末进行扫描形貌(SEM)观察。实验表明:原料配碳(C_m)和合成温度(T)是影响粉末质量的关键因素。