一种基于新型查表方法的统一计算设备架构并行计算全息算法

为解决点源法计算全息速度较慢的问题,提出了一种新的查表算法,命名为三角函数查表法(T-LUT算法)。该算法是基于点源法基本的数学公式,通过一系列数学近似与恒等变换,生成了一种纯相位查找表,该查找表具有三维特性,并具有生成速度快、精度高、占用内存少等特点,克服了点源法重复计算相位的缺点。同时采用统一计算设备架构(CUDA)并行计算在图形处理器(GPU)上加以实现,并进行了三次并行优化。在算法的验证与对比实验中,采用单显卡(GPU显卡)实现T-LUT算法,在不牺牲全息图再现像质量的前提下,成功地将点源法计算全息的速度大幅度提升。实验发现在不同的物空间采样点数量的情况下,速度相对于点源法GPU运算提升30倍至近千倍不等。     

基于BP神经网络的人脸识别系统研究

本文设计了一种基于BP神经网络的人脸识别系统,并对其进行了性能分析.该系统首先利用离散小波变换获取包含人脸图像大部分原始信息的低频分量,对图像数据进行降维;再由PCA算法对人脸图像进行主成分特征提取,进一步降低图像数据的处理量;最后使用经过训练后的BP神经网络对待测人脸进行分类识别.详细介绍了离散小波变换、PCA特征提取以及BP神经网络分类设计.通过系统仿真实验与分析发现:人脸特征的提取是该系统的关键;同时,由于人脸灰度信息的统计特征与有监督训练BP神经网络分类器,使该系统只在固定类别,并且光照均匀的人脸识别应用场景中具有较高的识别准确率.因此,很难在复杂环境中应用.     

由背面工艺导致的3.3-kV NPT-IGBT阳极注入效率降低效应的实验研究

The anode injection efficiency reduction of 3.3-kV-class non-punch-through insulated-gate bipolar transistors (NPT-IGBTs) due to backside processes is experimentally studied through comparing the forward blocking capabilities of the experiments and the theoretical breakdown model in this paper. Wafer lifetimes are measured by a μ-PCD method, and well designed NPT-IGBTs with a final wafer thickness of 500 μm are fabricated. The test results show higher breakdown voltages than the theoretical breakdown model in which anode injection efficiency reduction is not considered. This indicates that anode injection efficiency reduction must be considered in the breakdown model. Furthermore, the parameters related to anode injection efficiency reduction are estimated according to the experimental data.     

可信网络的发展及其面对的技术挑战

随着信息网络的基础性、全局性作用日益增强,传统的网络理论与技术,尤其是网络安全,已经不能满足网络发展的需要,提供系统的安全可信的服务已经成为网络研究的新趋势。本文认为可信网络应该是网络和用户的行为及其结果总是可预期与可管理的。网络可信主要包括服务提供者的可信、网络信息传输的可信性和终端用户的可信等3个方面的内容。从网络与用户行为的可信模型、可信网络的体系结构、服务的可生存性、网络的可管理性4个方面进行研究,以便为解决可信网络面临的科学问题提供思路。     

Mechanochemical Dimerization of Aldoximes to Furoxans

Solvent-free mechanical milling is a new, environmentally friendly and cost-effective technology that is now widely used in the field of organic synthesis. The mechanochemical solvent-free synthesis of furoxans from aldoximes was achieved through dimerization of the in situ generated nitrile oxides in the presence of sodium chloride, Oxone and a base. A variety of furoxans was obtained with up to a 92% yield. The present protocol has the advantages of high reaction efficiency and mild reaction conditions.     

Beam dynamics studies on BEPC-Ⅱstorage rings at the commissioning stage

During the 1st and 2nd stages of the commissioning of the upgrade project of the Beijing Electron Positron Collider(BEPC Ⅱ),which started on Nov.12,2006 and Oct.24,2007,respectively,we got the luminosity one tenth of its design value,provided beams to synchrotron radiation users for about 4 months,and studied beam dynamics as well.In this paper,some beam dynamics studies on the storage rings and their preliminary results are given.     

MEMIS: A Mobile-Supported English-Medium Instruction System

Education is one of the most important elements in our lives, as it provides a direct gain in knowledge. Thus, in order to provide better academic achievement, more and more instructors are adapting collaborative learning to their classes. However, two major problems lurk behind collaborative learning. First, it is difficult to apply collaborative learning because students tend to engage passively with traditional lectures. As a result, interactive technologies such as clickers have been applied to increase interactive learning and raise the rate of interaction. Nevertheless, these interactive technologies still have some limitations, such as limited mobility, high costs, setup issues, technical difficulties, and little support of higher-order thinking skills. Second, recently there has been an increasing number of EMI (English as Medium of Instruction) courses added to university course offerings in countries where English is not the first language. The goal of these courses is to support university internationalization and address the global status of English. However, it is even harder to achieve in-class interaction in large EMI lecture courses. In addition, some studies argue that EMI courses might affect the overall learning of course content because of students’ poor lecture comprehension and passive engagement in class.In order to address the limitations of interactive technologies, encourage more collaborative learning, facilitate greater in-class interaction in large lecture courses, and resolve students’ poor lecture comprehension in EMI courses, the author introduces MEMIS (Mobile-Supported English-Medium Instruction System), which includes both a T&S (Teachers & Students) mobile app and an EMI pedagogical method. The author first provides detailed implementation and all the features of the T&S mobile app, which improves students’ perceptions of classroom participation and in-class interaction. Then the author explains how she develops her EMI pedagogy such that it utilizes the features of the T&S mobile app to: 1) increase students’ overall learning in her EMI course, 2) develop students’ construction of knowledge and higher-order thinking, and 3) achieve all six cognitive processes from Bloom’s revised taxonomy. The author adapts a quasi-experimental design, statistically analyzes the effectiveness of both exam scores and final grades between a control group and an experimental group, and then asks students to evaluate their experiences and provide feedback about MEMIS. Based on both statistical results and students’ overall feedback, the author confirms that MEMIS is an effective approach that improves lecture comprehension, encourages more class engagement, promotes collaborative learning, and achieves better learning outcomes.     

General gap-utilizing strategy for non-persistent traffic in wireless networks

We focus on a general strategy which exploits nonpersistent traffic gaps to reduce data delay/loss caused by some communication-breaking actions, e.g. handover and neighbor scanning. Those actions usually interrupt transmission or take up transferring chances for a period time, hence incur QoS downgrades. Our study discusses the details on how to choose the optimal gaps for them in order to minimize the bad impact, which provides a potential guidance for protocol and system design.     

Base-induced photorearrangements from 3-styrylfurans to 2-methylnaphthalenes

Irradiation of 3-(4-substituted styryl)furans in basic media yielded a series of 7-substituted-2-methylnaphthalenes, including methoxy, isopropyl, ethyl, methyl, fluoro, and cyano substituents. This base-induced photorearrangement involves cis-trans photoisomerization, 6e photocyclization, base-induced elimination, and a Norrish Type I photoreaction and is a novel method to synthesize unsymmetrical 2,7-disubstituted naphthalenes.     

Wavelets with differential relation

Divergence-free wavelets are successfully applied to numerical solutions of Navier-Stokes equation and to analysis of incompressible flows. They closely depend on a pair of one-dimensional wavelets with some differential relations. In this paper, we point out some restrictions of those wavelets and study scaling functions with the differential relation; Wavelets and their duals are discussed; In addition to the differential relation, we are particularly interested in a class of examples with the interpolatory property; It turns out there is a connection between our examples and Micchelli’s work.