Projected gradient descent based on soft thresholding in matrix completion

Matrix completion is the extension of compressed sensing. In compressed sensing, we solve the underdetermined equations using sparsity prior of the unknown signals. However, in matrix com- pletion, we solve the underdetermined equations based on sparsity prior in singular values set of the unknown matrix, which also calls low-rank prior of the unknown matrix. This paper firstly introduces basic concept of matrix completion, analyses the matrix suitably used in matrix completion, and shows that such matrix should satisfy two conditions： low rank and incoherence property. Then the paper provides three reconstruction algorithms commonly used in matrix completion： singular value thresholding algorithm, singular value projection, and atomic decomposition for minimum rank ap- proximation, puts forward their shortcoming to know the rank of original matrix. The Projected Gradient Descent based on Soft Thresholding （STPGD）, proposed in this paper predicts the rank of unknown matrix using soft thresholding, and iteratives based on projected gradient descent, thus it could estimate the rank of unknown matrix exactly with low computational complexity, this is verified by numerical experiments. We also analyze the convergence and computational complexity of the STPGD algorithm, point out this algorithm is guaranteed to converge, and analyse the number of it- erations needed to reach reconstruction error. Compared the computational complexity of the STPGD algorithm to other algorithms, we draw the conclusion that the STPGD algorithm not only reduces the computational complexity, but also improves the precision of the reconstruction solution.     

基于多层快速多极子和有限元混合求解的飞行器天线布局设计

设计一种微带天线,以该天线为基础进行飞行器天线布局设计,并考虑遮挡的判断问题。模型仿真采用多层快速多极子和有限元的方法混合求解,设置混合场积分方法提高收敛性,解决了电大尺寸模型复杂电磁场的计算问题,兼顾运算速度和精度,得出并分析飞行器上3天线、4天线、5天线以不同方式布局的远场方向图仿真结果,并提出一种方向图评估法则,对飞行器天线布局有一定参考意义。     

图像恢复的小波域加速Landweber迭代阈值方法

该文利用对忠诚项的二次逼近方法,提出了一种小波域加速Landweber迭代阈值算法。该算法的每次迭代是对前两次迭代结果的线性组合做阈值处理。与标准的迭代阈值算法相比,该方法收敛速度更快。由于参数的可选择性,新算法更有灵活性。数值实验表明新算法能够有效地提高恢复图像的质量,是一种行之有效的图像恢复方法。     

多电平变换器SVPWH策略

论文针对多电平变换器的特点,介绍了基于两电平SVPWM、60°坐标系、虚空间矢量、神经网络以及虚坐标系等多种多电平变换器SVPWM的算法,分析这些算法的优缺点。     

基于新型距离度量的以卷积码为分量码的MLC／PDL性能

该文着重研究了一种新的距离度量在以卷积码为分量码、MQAM调制的MLC/PDL系统中的应用。在Rayleigg衰落信道下通过计算机仿真,验证了此度量的有效性,并得到在此度量下设计多级码的准则。     

用基函数神经网络实现多阈值图象分割

本文介绍了一种用基函数神经网络实现多阈值图象分割的新方法。它从函数逼近的角度研究基于灰度直方图的多阈值分割问题，提出了一种模糊反向传播学习算法，采用该算法的高斯基函数网络能够准确检测直方图中包含的子区域和它们的分布函数，而且速度很快。实验表明本文的方法在实际图象分割中是有效的。     

A fast iterative scheme for multilevel thresholding methods

The previously published optimal thresholding techniques based on some objective functions are very efficient in the bi-level thresholding case, but they are impractical when extended to multilevel thresholding. The reason for this is their computational complexity which grows exponentially with the number of thresholds. In this paper, an iterative scheme is proposed to render these optimal thresholding techniques more practical. The proposed algorithm starts with a bi-level thresholding, then uses the initial results to obtain higher-order thresholds. This algorithm is iterative and the convergence is proved. We also introduce some useful programming techniques to make the computation more efficient. The proposed algorithm can therefore determine the number of thresholds automatically as well as save a significant amount of computing time.     

Personal Trusted Devices for Web Services: Revisiting Multilevel Security

In this paper we revisit the concept of mandatory access control and investigate its potential with personal digital assistants (PDA). Only if applications are clearly separated and Trojans cannot leak personal information can these PDAs become personal trusted devices. Limited processing power and memory can be overcome by using Web services instead of full-fledged applications – a trend also in non-mobile computing. Web services, however, introduce additional security risks, some of them specific for mobile users. We propose an identification scheme that can be effectively used to protect privacy and show how this system builds upon a light-weight version of mandatory access control.     

Toward Meaningful Connectivity: Using Multilevel Communication Research to Reframe Digital Inequality

Digital inequality, or unequal access to the Internet and technologies that connect to it, has preoccupied communication scholars since the Internet's introduction into popular culture. The relationships between digital and broader social inequalities suggest that meaningful digital connectivity—that is, having the technical skills necessary to engage technology and mobilize information resources to address everyday needs—can empower socially disenfranchised individuals, families, and communities to address challenges related to those disparities. In this essay, we overview the arc of communication research on technology engagement and its consequences. On this foundation, we argue why multilevel research that accounts for individual‐, family‐, and community‐level influences on meaningful digital connectivity is the best path forward for research on digital inequality.