Rate-equation-based circuit model of high-speed semiconductor lasers

Based oil rare equations of semiconductor laser, a symbolically-defined model for optical transmission system performance evaluation and network characterization in both time- and frequency domains is presented. The steady-state and small-signal characteristics, such as current-photon density curve, current-voltage curve, and input impedance, call be predicted from this model. Two important dynamic characteristics, second-order harmonic distortion and two-tone third-order intermodulation products, are evaluated under different driving conditions. Experiments show that the simulated results agree well with the published data. (c) 2007 Wiley Periodicals, Inc.

集群网络评测模型的新探索

传统集群网络(cluster area network,简称cLAN)的评测模型主要考虑了延迟、带宽、路由、拥塞、网络拓扑结构等因素.但这些因素是否足以描述实际应用程序在集群上的通信行为,或者对其在集群系统上的性能给出一个很好的预测呢?当对NAS Parallel Benchmark(2.4版本)在集群系统深腾1800(DeepComp 1800)上进行大量测试时发现,集群网络的通信性能可以被一种特殊的通信模式(LU模式)所严重影响.更深入的研究表明,这个影响LU模式的因素是独立于前面所述的如延迟、带宽、路由、拥塞、网络拓扑结构等因素的.因此有必要对集群网络的评测模型重新进行审视,并增加一个新的性能评测因子以反映这个新发现的现象.从研究结果来看,这个重新审视也将对集群系统上的并行算法设计以及实际大规模科学计算的应用程序性能的优化提供一些新的思路.

国产万亿次机群系统NPB性能测试分析

对3个国产万亿次机群系统进行了NPB性能测试分析,重点研究大规模并行处理时(处理器数目达到上千个)的性能特点和趋势.分析了不同的处理器、互连网络等系统配置对NPB性能的影响,发现NPB的8个程序在3个万亿次机器上的性能特点和表现并不一致,表明国产高性能机群在设计上正在逐渐走出同质化的趋势,向多样化发展.进一步分析表明,目前NPB程序的可扩展性可以达到几百个处理器,但尚不能达到上千个处理器,NPB程序能发挥出的系统峰值的百分比仍然徘徊在10%左右,机群系统的并行可扩展性和应用程序对机器运算潜能的利用还需要进一步提高.对于处理器数目达到上千个的万亿次机群系统来说,对集合通信和细粒度通信能力的支持亟需提高.

两种线程池的实现和性能评价

线程池被广泛地应用在中间件如Web应用服务器、事务监控器等的实现中。实现线程池的方法主要有半同步/半异步(Half-Sync/Half-Asyn)模式和领导者/跟随者(Leader/Follower)模式。实现了这两种线程池,从理论上分析了它们的性能,并进行了性能实验。实验数据表明Leader/Follower模式具有较高的性能优势。

基于ISO/IEC 9126标准的软件质量评价系统

中国计算机学会

基于模糊评价方法的软件质量评价研究

针对软件质量评价研究中的度量问题建立了基于ISO/IEC 9126标准的软件质量指标体系模型,结合质量评价方法研究中的常见问题,运用指标体系模型和模糊数学方法对软件质量评价标准进行模糊化处理,以度量数据为基础,根据软件质量子特性和指标之间的关系,采用模糊综合评价方法评价子特性质量和特性质量,通过建立软件质量评价模型,有效地解决了软件质量的多指标评价问题,可用于指导用户进行软件过程改进.

Approximate analytical optical transfer function for a wavefront-coded imaging system with two-dimensional rectangularly separable phase masks

Wavefront coding can be used to extend the depth of field of incoherent imaging systems and is a powerful system-level technique. In order to assess the performance of a wavefront-coded imaging system, defocused optical transfer function (OTF) is the metric frequently used. Unfortunately, to the best of our knowledge, among all types of phase masks, it is usually difficult to obtain the analytical OTF except the cubic one. Although numerical computation seems good enough for performance evaluation, the approximate analytical OTF is still indispensable because it can reflect the relationship between mask parameters and system frequency response in a clearer way. Thus, a method is proposed to derive the approximate analytical OTF for two-dimensional rectangularly separable phase masks. The analytical results are well consistent with the direct numerical computations, but the proposed method can be accepted only from engineering point of view and needs rigorous proof in future. (c) 2010 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3485759]

Fabrication of a miniature twin-fuel-cell on silicon wafer

The fabrication and performance evaluation of a miniature twin-fuel-cell on silicon wafers are presented in this paper. The miniature twin-fuel-cell was fabricated in series using two membrane-electrode-assemblies sandwiched between two silicon substrates in which electric current, reactant, and product flow. The novel structure of the miniature twin-fuel-cell is that the electricity interconnect from the cathode of one cell to the anode of another cell is made on the same plane. The interconnect was fabricated by sputtering a layer of copper over a layer of gold on the top of the silicon wafer. Silicon dioxide was deposited on the silicon wafer adjacent to the copper layer to prevent short-circuiting between the twin cells. The feed holes and channels in the silicon wafers were prepared by anisotropic silicon etching from the back and front of the wafer with silicon dioxide acting as intrinsic etch-stop layer. Operating on dry H-2/O-2 at 25 degreesC and atmospheric pressure, the measured peak power density was 190.4 mW/cm(2) at 270 mA/cm(2) for the miniature twin-fuel-cell using a Nafion 112 membrane. Based on the polarization curves of the twin-fuel-cell and the two single cells, the interconnect resistance between the twin cells was calculated to be in the range from 0.0113 Omega (at 10 mA/cm(2)) to 0.0150 Omega (at 300 mA/cm(2)), which is relatively low. (C) 2003 Elsevier Science Ltd. All rights reserved.

An Electro-osmotic Fuel Pump for Dircet Methanol Fuel Cells

This work reports on the design and performance evaluation of a miniature direct methanol fuel cell(DMFC)integrated with an electro_osmotic(EO)pump for methanol delivery.Electro-osmotic pumps require minimal parasitic power while boasting no moving parts and simple fuel cell integration.Here ,aneletro-osmotic pump is realized from a commercially available porous glass frit.We characterize a custom-fabricated DMFC with a free convection cathode and coupled to an extennal electro-osmotic pump operated at applied potentials of 4.0,7.0,and 10V.Maximum gross power density of our free convection DMFC(operated at 50°)is 55 mW/cm2 using 4.0 mol/L concentration methanol solution supplied by the EO pump.Experimental results show that electro-osmotic pumps can deliver 2.0,4.0 and 8.0mol/L methanol/water mixtures to DMFCs while utilizing ~5.0% of the fuel cell power.Furthermore ,we discuss pertinent design considerations when using electro-osmotic pumps with DMFCs and areas of further study.

Microspheres and microcapsules, a survey of manufacturing techniques: Part III: Solvent evaporation

A methodological survey of microsphere formation and microencapsulation techniques based on solvent extraction/evaporation techniques is presented. Thus, basic features of solvent extraction and solvent evaporation processes, including droplet formation, droplet/particle stabilization, and solvent removal, are outlined. Preparation of a wide range of microspherical and microcapsular products based on biodegradable polyesters, polysaccharides, and nonbiodegradable polymers are discussed. Dependence of microcapsule characteristics on manufacturing parameters, as well as performance evaluation of microspherical and microcapsular products, are also briefly covered.

Anodic Stripping Voltammetry at Bismuth-Coated and Uncoated Carbon Microdisk Electrodes:Application to Trace Metals Analysis in Flood Samples

This article reports on the performance of a bismuth-coated carbon microdisk electrode (BiFμE) for the determination of trace heavy metals by anodic stripping voltammetry (ASV). The BiFμE was prepared by electrodeposition of a metallic bismuth film onto the microdisk, by applying an in-situ electroplating procedure. To test the performance of the BiFμE, ASV measurements were performed on synthetic solutions containing Cd2+, Pb2+, and Cu2+ as target ions. The results indicated that cadmium and lead gave well-defined ASV peaks with no interference, and their quantitative determination could be carried out straightforwardly. In particular, linear calibration curves over the range 5.0 x 10-8-1.0 x 10-6M for both ions, and detection limits of 7.8 and 2.9 nM, for cadmium and lead, respectively, after applying a 60 sec preconcentration step, were obtained. The reproducibility was also satisfactory, the relative standard deviation (RSD) being within 2.5% for both ions. Copper, instead, gave an ASV response that. in most experimental conditions, overlapped with that of bismuth. This circumstance made the determination of copper at the BiFμE difficult. Since the latter element could be detected reliably at the uncoated carbon microdisk electrode (CμE), both BiFμE and CμE were employed, respectively, for the determination of lead and copper ions in drinking water, wine, and tomato sauce.

Image Ratio Features for Facial Expression Recognition Application

Video-based facial expression recognition is a challenging problem in computer vision and human-computer interaction. To target this problem, texture features have been extracted and widely used, because they can capture image intensity changes raised by skin deformation. However, existing texture features encounter problems with albedo and lighting variations. To solve both problems, we propose a new texture feature called image ratio features. Compared with previously proposed texture features, e. g., high gradient component features, image ratio features are more robust to albedo and lighting variations. In addition, to further improve facial expression recognition accuracy based on image ratio features, we combine image ratio features with facial animation parameters (FAPs), which describe the geometric motions of facial feature points. The performance evaluation is based on the Carnegie Mellon University Cohn-Kanade database, our own database, and the Japanese Female Facial Expression database. Experimental results show that the proposed image ratio feature is more robust to albedo and lighting variations, and the combination of image ratio features and FAPs outperforms each feature alone. In addition, we study asymmetric facial expressions based on our own facial expression database and demonstrate the superior performance of our combined expression recognition system.

Petri网理论在柔性制造系统(FMS)性能分析中的应用

本文用 Petri 网的一个子类——时间事件图对流水车间型和作业车间型的柔性制造系统(FMS)建模并进行理论分析,给出了可行排序的判定条件及系统中托盘数量配置与系统生产率的关系,对系统的主要性能指标,如生产周期、工件驻留时间、在制品库存等给出了定量描述.这些结果为系统的设计和运行提供了理论依据.

复杂离散制造过程建模与性能评价方法研究

离散制造系统是制造业中最为复杂的制造系统之一，其生产特点表现在：生产方式的异步、并行；生产柔性强；调度复杂性高等方面。要实现对复杂离散制造系统的控制，首先必须对其建模。随着制造系统自动化程度提高，规模的增大，组成因素的复杂化，性能评价问题变得日益复杂并越来越受到人们的重视。提供直观的模型描述方法、有效的数学理论工具和模型分析方法及分析软件，是制造系统性能评价迫切需要解决的问题。为此本文进行了以下工作： 首先，提出了一种支持性能评价的制造过程模型框架。该框架体现了车间生产闭环控制机制，全面描述了车间制造过程相关组成要素之间的关系，可用于指导制造过程的建模和基于性能评价的优化控制。模型框架核心部分是生产过程模型、过程控制模型和过程性能模型，这三部分构成了制造过程模型。该过程模型在工厂模型的支持下，由事件模型驱动，受策略模型约束，通过一些过程准则和方法进行测量和监视，对性能相关数据进行统计、分析和评估，反映在性能指标上。 第二，确定了离散车间性能评价指标体系。该指标体系建立了不同性能指标与不同层次、不同类型的制造过程以及不同性能评价主体之间的关联，为选择评价方法奠定了基础。该指标体系按照车间目标将性能指标分为三大类，即时间、质量、成本；每一类细化为三个层次，分别是基本性能指标、扩展性能指标和综合性能指标。 第三，基于随机Petri网建立了具有随机机器故障的制造过程性能模型。该模型包含两个基本的状态转换环，将正常状态和异常情况分别描述；基于故障的随机特征，设置了服从泊松分布的故障发生模块；根据不同的故障发现模式，衍生出若干状态转换环，清晰地将故障发生、发现分离；还考虑了中断作业的处理，使模型更接近实际系统动态行为特征。另外，本文设计了考虑成本信息的作业优先级调度规则，并基于随机高级Petri网（SHLPN）应用到混流装配线动态调度问题中；针对流水线上存在的一类共享资源—维修工人，建立了考虑系统状态的维修排序规则SHLPN模型。通过数学分析和仿真方法结合实现了对以上制造过程模型的性能评价，验证了模型的有效性。 第四，针对性能评价的需求和Petri网在制造过程成本分析方面存在的不足，提出了一种适合制造过程成本分析的价格时间Petri网，并给出了相应的状态空间化简方法。通过对装配生产线多目标工人指派问题的求解，验证了模型和方法的有效性。 最后，根据管理控制过程和生产过程的特点以及它们之间的关系，提出了基于进程代数与Petri网的分层生产控制方法。采用Petri网和进程代数相结合的方法将物流和信息流集成在一个模型中，Petri网描述基于状态的与生产过程有关的过程流，进程代数描述计划、调度等与控制有关的推理过程，构成了两层分布式的车间生产控制结构。 综上可见，本文提出的制造过程建模、性能评价和控制方法，可以支持复杂离散制造系统的分析和综合；基于过程模型实现了复杂离散制造系统的生产过程模拟和性能分析；能够发现影响系统性能的瓶颈环节；为制造过程的改进和制造系统性能的提高提供了依据；进而实现了制造系统自主闭环自适应的优化控制。本文的研究工作具有重要的理论意义和实际应用价值。