Fabrication of SiC particle reinforced composite on aluminium surface by friction stir processing

Abstract

A feasibility investigation has been carried out of the formation of surface composite by uniformly distributing SiC particles 1˙25 µm in size into a surface layer of an A 1050-H24 Al plate through friction stir processing (FSP). The SiC particle was filled into a groove cut on the Al plate, covered by an Al sheet 2 mm thick, and a rotating tool was penetrated from the cover sheet so that the probe tip reached a depth beyond the groove bottom. The effects of process parameters (rotation speed and travelling speed) and applying multiple passes on the distribution of SiC particle in the nugget zone were investigated. The effects of groove size and its position relative to the tool probe were also investigated. Applying multiple passes had a great effect on the homogeneity of the SiC particle distribution. At rotation speeds of 2000–3000 rev min^?1, the SiC particles tended to cluster in some places in the nugget zone. By decreasing the rotation speed to 1000–1500 rev min^?1, the SiC particle was distributed in almost all the nugget zone area when the groove was 2–3 mm wide and 1˙5 mm deep. On the other hand, the stirring action of FSP was insufficient to distribute homogenously the SiC particles when the groove size was increased to 3×2 mm. By shifting the groove position towards the advancing side of the tool probe, the distribution of the SiC particles in the nugget zone became better. The defect free nugget zone with homogenously distributed SiC particles was obtained in a sample produced by FSP at rotation speeds of 1500 rev min^?1 for the first pass and 1250 rev min^?1 for the second and third passes. Microhardness of the nugget zone was increased to a level as high as 55 HV when the groove size was 3×1˙5 mm. The effect of the rotation speed on the particles dispersion was discussed with particular reference to the vertical material flow in the nugget zone.     

一种NOMA系统中的反馈深度神经网络检测算法

在上行非正交多址(Non-orthogonal Multiple Access, NOMA)系统中,针对传统基于串行干扰消除(Successive Interference Cancellation, SIC)检测存在同个时频块内用户间干扰的问题,提出了一种新型的NOMA检测算法。通过将SIC检测的反馈消除结构和深度神经网络结合起来,设计出了一种新型的反馈深度神经网络(Feedback Deep Neural Network, FDNN)结构。FDNN模型分为两个模块,检测模块通过深度神经网络实现非线性检测,反馈模块通过权重矩阵重构信号并消除用户干扰。通过重复检测和反馈过程,FDNN依次检测出各个用户的符号,并达到了良好的性能。仿真结果表明FDNN检测算法相较于SIC检测具有更低的误符号率和误比特率,并验证了其具有更良好的抗用户间干扰的性能。     

Analysis of the Linear GSIC Multiuser Detector Using a Matrix Iterative Approach

In this work, we use a new approach that relies on the theory of matrix iterative analysis to study the convergence behavior of the linear group-wise successive interference cancellation (GSIC) detector. Particularly, we show that the linear GSIC detector is in fact a realization of a modified block successive over-relaxation (BSOR) iterative method where the relaxation factor is a matrix instead of scalar. Consequently, to study the convergence behavior of the GSIC detector, we propose two new corollaries that extend the famous work of Kahan (Varga, Matrix iterative analysis, 2000) to the case where the relaxation factor is a matrix instead of a scalar. Using the two new corollaries we develop two new conditions of convergence for the linear GSIC detector. Simulation results are in excellent agreement with theory.

改进的增加时间分集的OFDM系统

在现有文献的基础上提出了一种改进的增加时间分集的OFDM系统,在原来的系统中增加了空时编码。在接收端,采用一种低复杂度的MMSE信道均衡算法使得系统的空间分集和时间分集得以有效地利用。仿真结果表明,这种结构可以提高系统在高速移动信道环境下的误码率性能和稳定性。     

Ultrasonic brazing of high fraction volume of SiC particulate reinforced aluminium matrix composites

Abstract

The ultrasonic brazing of 55 vol.-%SiC_p/A356 composites in air has been investigated. When the ultrasonic vibration is applied for 0·5 s, the oxide layer is still continuous at most places between the filler metal and the composites. As the ultrasonic action time increases, the oxide film sufficiently disappears in the bond region, resulting in the complete wetting of Zn–Al alloy with the composites and the significant mass transfer between the SiC/A356 and the Zn–Al alloy is observed. As the dissolving of the composites on the surface, the SiC particles in the base materials get into the bond metals in which reinforcements are distributed uniformly. The shear strength of bonds increases with the ultrasonic acting time.     

改进Turbo-BLAST检测算法及其仿真

Turbo-BLAST系统基于MMSE的迭代软干扰消除检测技术可有效克服由于V-BLAST的应用带来的多流干扰,但是在迭代检测译码过程中存在错误传播,并且收敛性较差,尤其在接收天线远小于发射天线时。而MAP迭代检测算法的性能接近最优,但复杂度随发射天线和调制阶数呈指数增长。所以本文把这两种算法相结合,提出改进的SIC-MAP/MMSE检测算法。仿真结果表明,在相同频谱利用率的条件下,这种新检测算法在性能和收敛性上明显优于MMSE的迭代软干扰消除(SIC-MMSE)检测技术。     

Turbo均衡在移动通信中的研究

为消除符号间的干扰,Douillard．et．a1提出了turbo均衡这种迭代均衡和解码的方法。在Prokis’B信道下,对Turbo均衡的性能进行仿真,采用基于MMSE的线性均衡(MMSE—LE)和判决反馈均衡(MMSE—DFE)算法,以及appMMSE—LE／SIC算法,通过性能仿真,对不同算法、不同的迭代次数对系统性能的影响进行比较。结果表明:appMMSE—LE／SIC算法在复杂性几乎没有增加的情况下,性能提高了很多。     

硅碳素处理含锰地下水的试验研究

对硅碳素（ANJ．SIC）和锰砂去除锰的效果进行试验研究。试验表明：ANJ．SIC有较好的除锰效果,当原水含锰量为2．06～2．34mg／L,流速范围在5．2—16．11m／h变化时,去除率在100％～94％,相同情况下锰砂的去除率在43％～32％。流速发生变化时,ANJ．SIC维持的出水达标时间发生变化,流速越大,ANJ．SIC达到吸附饱和的时间越短。ANJ．SIC各层对锰的去除率随时间变化单调下降,并呈下降减缓的趋势。去除率没有集中在某一部分的现象,各层均有一定的去除能力。     

Fast Converging Adaptive MMSE Multiuser Detector for DS-CDMA System

A fast converging adaptive minimum-mean-squared-error (MMSE) multiuser detector is proposed for direct-sequence code-division multiple-access (DS-CDMA) systems with severe near-far problem where the convergence rate of adaptive MMSE detectors for distinct users can be very different. It is shown that by successively cancelling the interference signals of strong power users, the convergence rate of the proposed detectors for weak power users can be significantly increased, which helps to reduce the length of training sequence for tracking. It is also shown that the order of cancellation and several important parameters required for interference cancellation can be determined from the convergence behavior of the proposed detector. Numerical results are presented to show that the proposed detector offers improved performance in various DS-CDMA environments.Zhiwei Mao received the B.Sc. degrees from Beijing University of Posts and Telecommunications (BUPT), Beijing, China in 1996 and 1999, respectively. Since 2000, she had been a Research Assistant and graduate student in the Department of Electrical and Coumputer Engineering, University of Victoria, Victoria, BC, Canada. She received the Ph.D. degree in electrical engineering in 2003. Currently, she is an Assistant Professor at Lakehead University, Thunder Bay, Ontario, Canada.Her research interests include wireless communications, multiuser detection, digital communications and digital singal processing.Vijay K. Bhargava received the B.Sc., M.Sc., and Ph.D. degree from Queens University, Kingston, ON, Canada in 1970, 1972 and 1974 respectively.Currently, he is a Professor and Head of the Department of Electrical and Computer Engineering at the University of British Columbia, Vancouver, Canada. Previously he was with the Univeristy of Victoria (1984–2003) and with Concordia University in Montréal (1976–1984). He is a co-author of the book Digital Communications by Satellite (New York: Wiley, 1981), co-editor of Reed-Solomon Codes and Their Applications (New York: IEEE, 1994) and co-editor of Communications, Information and Network Security (Boston: Kluwer, 2002). His research interest are in wireless communications.Dr. Bhargava is a Fellow of the B.C. Advanced Systems Institute, Engineering Institute of Canada (EIC), the IEEE, the Canadian Academy of Engineering and the Royal Society of Canada. He is a recipient of the IEEE Centennial Medal (1984), IEEE Canadas McNaughton Gold Medal (1995), the IEEE Haraden Pratt Award (1999), the IEEE Third Millennium Medal (2000), IEEE Graduate Teaching Award (2002), and the Eadie Medal of the Royal Society of Canada (2004).Dr. Bhargava is very active in the IEEE and was nominated by the IEEE Board of Director for the Office of IEEE President-Elect. Currently he serves on the Board of Communications Society. He is an Editor for the IEEE Transactions on Wireless Communications. He is a Past President of the IEEE Information Theory Society.