24 resultados para communication performance evaluation
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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.
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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.
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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.
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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.
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IEEE, IEEE Comp Soc, Tech Council Software Engn
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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.
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通过噪音对令牌运行过程的作用 ,本文分析了在噪音环境下 FF Fieldbus的性能变化 .本文首先建立了令牌运行过程的自动机模型 ,然后利用此模型分析了噪音对令牌运行方式的影响 .根据噪音的影响 ,本文推导出令牌运行时间和令牌平均运行时间 .最后利用解析表达式分析出噪音分布对 FF Fieldbus性能的影响 .
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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.
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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。