Rotational invariance of two-level group codes over dihedral and dicyclic groups

Phase-rotational invariance properties for two-level constructed, (using a binary code and a code over a residue class integer ring as component codes) Euclidean space codes (signal sets) in two and four dimensions are discussed. The label codes are group codes over dihedral and dicyclic groups respectively. A set of necessary and sufficient conditions on the component codes is obtained for the resulting signal sets to be rotationally invariant to several phase angles.     

多电平PWM控制技术发展

多电平PWM控制技术一直是多电平变换器研究的核心内容之一。基于传统两电平PWM技术研究的经验，经过近十几年的发展，多电平PWM控制技术已形成了儿类不同的实现方法，同时新的控制方法还在涌现。与两电平相比，多电平PWM方法需要面对一些新出现的问题，并拓展PWM控制的内涵，进而形成新的PWM控制思路。按照目前的发展情况，多电平PWM控制方法一般有多电平载波PWM方法、多电平空间矢量PWM方法，以及其他优化的PWM方法。本文对已有多电平PWM控制技术进行了归纳和分析，最后指出多电平空间矢量法和载波调制法在一定条件下具有内在的一敛性。     

全寿命周期企业信息系统评价模型研究

针对企业信息系统评价的特点提出了全寿命周期评价体系,对系统实施的计划阶段、项目阶段、提升阶段分别依据其评价的侧重点与内容建立多层次的评价指标,并采用层次灰色评价法建立了全寿命周期企业信息系统评价模型,最后通过实例分析说明了全寿命周期信息系统评价模型的科学性和适用性。     

A new five-level inverter with reduced leakage current for photovoltaic system applications

A general growth is being seen in the use of renewable energy resources, and photovoltaic cells are becoming increasingly popular for converting green renewable solar energy into electricity. Since the voltage produced by photovoltaic cells is DC, an inverter is required to connect them to the grid with or without transformers. Transformerless inverters are often used for their low cost and low power loss, and light weight. However, these inverters suffer from leakage current in the system, a challenge that needs to be addressed. In this paper, a topology with two alternative connection models is presented to stabilize the common mode voltage and reduce the leakage current. The output voltage characteristic of the proposed inverter is five-level, which reduces the harmonic distortion in the output current compared to the two- and three-level inverters. The operation modes and output of the proposed topology are described and analyzed. The structures of the proposed inverter are simulated in MATLAB/Simulink and are compared with some well-known structures. Results show that the proposed structure with both connection models effectively reduces leakage current and improves grid current THD.     

一种基于多值RRAM的快速逻辑电路

针对移动物联网设备,提出一种基于多值RRAM的快速逻辑电路,以实现非易失性存储与快速逻辑运算。利用RRAM多值存储特性,采用Crossbar结构,实现了简单快速的译码器与高存储密度查找表,使逻辑电路具有较快的运算速度和较小的面积。基于该结构实现了4位、8位和16位的乘法器,其外围电路采用SMIC 65 nm CMOS工艺实现,而其核心多值RRAM则采用Verilog-A 模型模拟。仿真结果表明,与传统CMOS逻辑电路相比,基于多值RRAM的16位乘法器的速度提高了35.7%,面积减少了14%。     

Cuckoo search algorithm and wind driven optimization based study of satellite image segmentation for multilevel thresholding using Kapur’s entropy

The objective of image segmentation is to extract meaningful objects. A meaningful segmentation selects the proper threshold values to optimize a criterion using entropy. The conventional multilevel thresholding methods are efficient for bi-level thresholding. However, they are computationally expensive when extended to multilevel thresholding since they exhaustively search the optimal thresholds to optimize the objective functions. To overcome this problem, two successful swarm-intelligence-based global optimization algorithms, cuckoo search (CS) algorithm and wind driven optimization (WDO) for multilevel thresholding using Kapur’s entropy has been employed. For this purpose, best solution as fitness function is achieved through CS and WDO algorithm using Kapur’s entropy for optimal multilevel thresholding. A new approach of CS and WDO algorithm is used for selection of optimal threshold value. This algorithm is used to obtain the best solution or best fitness value from the initial random threshold values, and to evaluate the quality of a solution, correlation function is used. Experimental results have been examined on standard set of satellite images using various numbers of thresholds. The results based on Kapur’s entropy reveal that CS, ELR-CS and WDO method can be accurately and efficiently used in multilevel thresholding problem.     

A coarse-to-fine framework to efficiently thwart plagiarism

This paper presents a systematic framework using multilevel matching approach for plagiarism detection (PD). A multilevel structure, i.e. document-paragraph-sentence, is used to represent each document. In document and paragraph level, we use traditional dimensionality reduction technique to project high dimensional histograms into latent semantic space. The Earth Mover’s Distance (EMD), instead of exhaustive matching, is employed to retrieve relevant documents, which enables us to markedly shrink the searching domain. Two PD algorithms are designed and implemented to efficiently flag the suspected plagiarized document sources. We conduct extensive experimental verifications including document retrieval, PD, the study of the effects of parameters, and the empirical study of the system response. The results corroborate that the proposed approach is accurate and computationally efficient for performing PD.     

Analysis of the thermal elastohydrodynamic lubrication of a finite line contact

A complete numerical solution for the thermal elastohydrodynamic lubrication (EHL) problem of a finite line contact between an infinite plane and an axially profiled cylindrical roller is obtained. The pressure profile and the film shape in the middle part of the roller are very different from those at the ends. However, the finite line contact results in the middle part of the roller are nearly the same as those of the corresponding infinite line contact. It is revealed that, in a finite line contact, the maximum pressure, the highest film temperature and the minimum film thickness all occur at the end regions of the roller. A comparison is made between isothermal and thermal solutions of a finite line contact. In addition, variations in the minimum film thickness, the maximum pressure and the highest temperature with the dimensionless velocity parameter, the slide/roll ratio and the radius of the end profiles of the roller are discussed.     

An efficient method for multilevel color image thresholding using cuckoo search algorithm based on minimum cross entropy

Among various thresholding methods, minimum cross entropy is implemented for its effectiveness and simplicity. Although it is efficient and gives excellent result in case of bi-level thresholding, but its evaluation becomes computationally costly when extended to perform multilevel thresholding owing to the exhaustive search performed for the optimum threshold values. Therefore, in this paper, an efficient multilevel thresholding technique based on cuckoo search algorithm is adopted to render multilevel minimum cross entropy more practical and reduce the complexity. Experiments have been conducted over different color images including natural and satellite images exhibiting low resolution, complex backgrounds and poor illumination. The feasibility and efficiency of proposed approach is investigated through an extensive comparison with multilevel minimum cross entropy based methods that are optimized using artificial bee colony, bacterial foraging optimization, differential evolution, and wind driven optimization. In addition, the proposed approach is compared with thresholding techniques depending on between-class variance (Otsu) method and Tsalli’s entropy function. Experimental results based on qualitative results and different fidelity parameters depicts that the proposed approach selects optimum threshold values more efficiently and accurately as compared to other compared techniques and produces high quality of the segmented images.