Influence of the Workpiece Stiffness on the Electromagnetic Sheet Metal Forming Process into Dies

Electromagnetic sheet metal forming is a high speed forming process using pulsed magnetic fields to form metals with high electrical conductivity such as aluminum. Thereby, workpiece velocities of more than 300 m/s are achievable, which can cause difficulties when forming into a die. The kinetic energy, which is related to the workpiece velocity, must be dissipated in a short time slot when the workpiece hits the die; otherwise undesired effects, for example rebound can occur. One possibility to handle this shortcoming is to locally increase the stiffness of the workpiece. A modal analysis is carried out in order to determine the stiffness of specific regions of the workpiece so that an estimation concerning the feasibility of the desired geometry is possible in advance without doing cost and time consuming experiments. Thereby, the desired geometry of the workpiece will be fractionized in significant sectors. This approach has to define the internal force variables acting on the cutting edge, which are required to constrain the numerical model. Finally, a method will be developed with the objective of calculating the stiffness of each sector. The numerical results will be verified by experiments. This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati, OH, October 15-19, 2006.     

Enhanced Oxygen Diffusion Along Internal Oxide–Metal Matrix Interfaces in Ni–Al Alloys During Internal Oxidation

A study of the internal oxidation of dilute Ni–Al alloys in an NiO/Ni Rhines pack was performed at 800, 1000, and 1100°C. Considerable deviations from the classical internal oxidation model have been observed. The rate of internal oxidation depends not only on the concentration of the alloying element but also on its nature, which contributes to determining the size, shape, orientation and distribution of the internal oxide precipitates. For instance, the precipitates in the Ni–Al alloys are continuous rods, arranged in a cone-shaped configuration that extends from the surface to the internal oxide front. The observed depths of internal oxidation for the various concentrations of aluminum are discussed and related to the morphologies of the internal oxide precipitates. The apparent N^(s) _oD_o values determined from internal oxide penetrations increase with increasing solute content in the alloy. It is postulated that diffusivity of oxygen is enhanced along the internal oxide–metal matrix interface compared with that in the metal matrix.     

Gas Source Molecular Beam Epitaxy Growth of Si_(1-x)Ge_x/Si Alloys

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Al、V微合金高强度船板的研究

采用Gleeble-1500热模拟试验机测试了2种微合金钢(Al、Al V)经1150℃加热、20％压缩变形条件下的显微组织状态，结果表明，Al、V复合强化的试验钢以2℃／s速度冷却时，钢中出现针状铁素体。冷却速度为5℃／s时出现贝氏体，而Al强化钢中出现针状铁素体的冷速要达到5℃／s，因此建议生产含V钢时冷速控制在1～5℃／s。     

一起变压器油气在线监测装置报警故障的分析及处理

鉴于一起220 k V变压器油气在线监测装置的报警故障,对变压器油的色谱数据进行了分析,对2号主变压器进行吊罩检查,结果表明:故障因变压器梯级绝缘垫块结构设计存在缺陷,在运行中逐步造成垫块松动、脱落所致,并提出了处理措施。     

Using static suffix array in dynamic application: Case of text compression by longest first substitution

Over the last decade, enhanced suffix arrays (ESA) have replaced suffix trees in many applications. Algorithms based on ESAs require less space, while allowing the same time efficiency as those based on suffix trees. However, this is only true when a suffix structure is used as a static index. Suffix trees can be updated faster than suffix arrays, which is a clear advantage in applications that require dynamic indexing. We show that for some dynamic applications a suffix array and the derived LCP-interval tree can be used in such a way that the actual index updates are not necessary. We demonstrate this in the case of grammar text compression with longest first substitution and provide the source code. The proposed algorithm has O(N²)$O(N^2)$ worst case time complexity but runs in O(N)$O(N)$ time in practice.     

改进的软件错误报告自动分类算法

软件错误报告的自动分类能够节省大量人力和时间,然而用户提交的错误报告主观性较强,对错误报告的描述较随意,造成自动分类的效率低下。为此,基于传统的词频-逆向文件频率( TF-IDF )算法,结合文档内词条频度与词条在同类别及不同类别文档中的分布情况,提出2种特征降维的改进算法,降维后再对词条进行权值处理,进一步提高特征降维的效果。实验结果表明,应用该算法得到的错误报告自动分类在精确率、召回率、F1值和准确度等指标上比现有算法都有明显提高。     

基于大规模MIMO网络的低复杂度块对角化算法

在多用户MIMO系统下行链路中,块对角化（Block diagonalization, BD）预编 码算法的和速率性能要优于匹配滤波算法（Matched filter, MF）和迫零算法（Zero forc i ng, ZF）。然而,传统的BD算法利用矩阵分解来构造除当前用户的其他所有用户信道的零空 间,需要O(N2)浮点运算次数（Float point operations, FLOPs）。当 基站的天线数N趋向于大规模时,BD算法计算复杂度巨大。本文 提出一种基于投影子方法构造其他用户合成信道的零空间的BD算法,该算法仅需O( N)FLOPs。仿真表明：同传统的BD算法相比,本文所提出的低复杂度BD算法显著地降低 了实现复杂度,而和速率性能损失微小,仍然优于MF和ZF,并且当N趋 向于大规模时,它的和速率性能趋向于传统的BD算法和SVD算法。