基于多物理场模拟的低水甲烷燃料固体氧化物燃料电池的抗积碳阳极设计（英文）

本文采用与实验I-V曲线高度吻合的多物理场全耦合数值模型来模拟低水甲烷燃料SOFC的运行过程.基于抗积碳电流密度实验数据推导出的动力学积碳活性判据,利用多场耦合数值模型系统研究了电池工作参数和阳极扩散阻碍层厚度对阳极积碳倾向的影响.仿真模拟揭示了燃料利用率、电流密度、扩散阻碍层厚度和电池工作电压的相互关系.结果表明,在阳极添加400 um厚的扩散阻碍层是实现SOFC高功率密度和不积碳运行的最优设计.这种阳极结构设计对实现高效率低成本的SOFC技术具有重要意义.     

甲烷固体氧化物燃料电池多物理场模拟及积碳分析

建立了相关实验电池多物理场模型,该模型包括了电化学反应的电化学势平衡方程、甲烷水汽重整的通用速率方程和描述阳极复杂组分气体输运的菲克定律形式尘气模型. 该理论模型的电流～电压 曲线与实验数据很好地吻合,验证了理论模型的有效性. 理论分析发现,低水汽含量甲烷重整反应中水汽的反应级数为1. 理论模型的数值仿真计算还给出多个物理量的详细信息. 据此对碳沉积机制进行深入分析,清楚地描述了工作电流对抑制焦炭生成的机制. 分析比较了积碳活性的两个表达式,发现它们都可以正确地定性反映积碳活性变化趋势,但定量数值并不确切;阳极扩散层降低积碳临界电流的机制也获得了解释. 值得指出的是,虽然积碳活性模型只是定性正确,但分析表明积碳临界电流的降低却可以通过积碳活性模型进行定量解释.     

平板式阳极支撑SOFC多场耦合数值模拟

建立了平板式固体氧化物燃料电池多场耦合数学模型,利用商业CFD软件FLUENT对包括阳极和阴极多孔介质、致密固体氧化物电解质、燃料流道、氧化剂流道、电流收集双极板、外壳的单电池三维整体计算区域进行了数值模拟,得到了流场、温度场、组分浓度场、电流密度场、Nernst电动势、活化过电势和欧姆过电势等重要物理量的详细分布,并分析了影响电池性能的主要因素。模拟结果与SOFC研制单位提供的实验数据基本符合。     

直接甲醇燃料电池气、液相流动数值模拟

本文建立了直接甲醇燃料电池(DMFC)的二维两相模型,并重点研究阳极的两相流动和质量传递.模型考虑甲醇串流现象,定量计算了在不同电流密度下甲醇串流量的大小及其对电池工作性能的影响;模型中提出求解气、液单相流速的方法,并分别研究气、液流速对物质传递和电池性能的影响.定量分析发现:由甲醇串流产生的寄生电势导致实际开路电压值远低于理论值;在大电流密度下扩散层和催化层内的气相体积分数非常大,阻碍了液相燃料向催化层扩散,成为制约电池性能的关键因素;扩散层和催化层内存在气、液两相的反向流动,且气、液相速度分别有利于排出生成气体并推动液体燃料到达催化层;减小多孔介质的扩散率将削弱对流,恶化电池性能.     

平板式固体氧化物燃料电池多物理场耦合建模

固体氧化物燃料电池(Solid oxide fuel cell,SOFC)在高温下工作,影响电池性能和结构完整性的因素众多,如何能够综合考虑这些因素并准确地预测和优化电池结构与工作性能是亟待解决的问题。使用COMSOL软件建立了单个平板式固体氧化物燃料电池多场耦合有限元三维模型,考虑电化学反应、物质浓度、流体流动、传热和固体力学多物理因素共同作用下,探明了电池在工作阶段的气体摩尔分数、电流密度、温度和热应力的分布规律。结果表明,氢气和氧气的摩尔分数随着气体流动的方向逐渐降低;在电池空气入口处,电解质电流密度较大;电池温度分布不均匀并产生了较大的热应力。本文建立的SOFC多场耦合模型可为后续SOFC的研究提供分析方法和理论支持。     

质子交换膜燃料电池及其发电系统模拟

本文通过质子交换膜燃料电池单电池子模型、布气管子模型、流场子模型相互耦合,对电池堆传热传质过程加以数值模拟,得到单电池及电池堆的流场、温场、当地电流密度分布、过电位分布;给定平均电流密度下单电池及电池堆输出电压等参数;并比较了平均电流密度、布气管尺寸对电池输出电压、堆内反应物分配的影响;在此基础上,对整个ＰＥＭＦＣ发电系统进行流程模拟和参数分析,得到平均电流密度、重整器Ｓ／Ｃ等主要参数对系统性能影响．     

被动式直接甲醇燃料电池阳极混合对流模拟

本文根据被动式微小型直接甲醇燃料电池的运行特性,建立了其阳极膜电极二维、非等温、稳态数学模型。模拟结果表明:阳极膜电极内部温度的分布是不均匀的,最高温度出现在阳极催化层,且质子交换膜的温度要高于阳极气体扩散层。由于被动式直接甲醇燃料电池燃料的供给与消耗所引起的强制对流的存在,使得混合对流温度场和速度矢量场与自然对流情况下的不尽相同,利用模型对此进行了数值分析。     

双钨极耦合电弧数值模拟

基于流体力学方程组和麦克斯韦方程组, 在合理的边界条件下, 建立了双钨极耦合电弧三维准静态数学模型. 通过对方程组的迭代求解, 获得了不同钨极间距和电弧长度下耦合电弧的温度场、流场、电弧压力和电流密度分布等重要结果, 与已有的实验研究符合良好. 模拟结果表明: 与相同条件下的钨极惰性气体保护焊电弧相比, 双钨极耦合电弧的最高温度和最大等离子流速较低, 阳极表面电弧压力和电流密度峰值明显减小; 钨极间距和弧长对耦合电弧的温度场、流场、电流密度和电弧压力等都具有显著的影响, 且耦合电弧阳极的电弧压力和电流密度分布不能用高斯近似进行描述. 关键词： 耦合电弧 三维模型 数值模拟     

�ŷ�ɢ�绡��������λ�ε�������״ЧӦ

采用简化阴极的一维边界层模型,将同轴磁旋转电弧等离子体发生器的阴极与弧柱耦合求解,使用FLUENT软件,数值模拟了不同锥角阴极的形状对磁分散电弧等离子体、阴极弧根和阳极弧根位形的影响.结果表明:阴极弧根具有扩散特征,其电流密度为107A·m-2量级;阴极形状的改变引起阴极弧根位形和电流密度分布变化,从而影响等离子体参数分布;随着阴极锥角的增大,阴极弧根从阴极前端移动到阴极侧面,等离子体区域向下游偏移,等离子体轴向厚度减小.     

PEMFC气体扩散层内各向异性传递过程数值模拟

质子交换膜燃料电池(PEMFC)气体扩散层(GDL)具有各向异性属性,常规数值模拟对GDL采取均匀模型,忽略了各向异性传递过程对PEMFC性能的影响。本文发展了一个三维非等温单相模型,在GDL平面内和GDL厚度方向采用不同的传递系数,模拟了各向异性传递系数对PEMFC整体和局部性能的影响。在本文计算条件下,GDL各向异性和均匀模型模拟得到的电池极化曲线几乎完全相同,但电池电流密度分布和温度分布等局部特性存在很大差异。该结果进一步证明了不能单独用极化曲线来验证电池数学模型的正确性。     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.     

Real-time restoration of rotational blurred image using gradient-loading

The key to the restoration of rotational motion blurred image is how to restore the image under a low cost and to correct the irreversibility of the degradation function matrix.Based on the special qualities of degradation function matrix and precise deduction in space-domain, we present a new approach using gradient-loading for restoration of rotational blurred image.By easily adding a gradient operator, the irreversibility of the original matrix is corrected and can be applied for inverse filtering then.Gradientloading is the optimized approach which combines the advantages of both the approaches using constrained least square filtering and traditional diagonal-loading.Compared with the approach using least square filtering, its peak signal-to-noise ratio (PSNR) is improved from 3.18 to 6.46dB, while the computing time is reduced to 1/2-1/3.Experimental results demonstrate the effectiveness, noise-resistibility, robustness, and low complexity of this approach, which make it more suitable for real-time environment.     

All-Optical Logic Device Using Bent Nonlinear Tapered Y-Junction Waveguide Structure

We propose an all-optical logic device made of a bent tapered Y-junction waveguide with a Kerr-type nonlinear interface. It could provide an AND gate, OR gate, and exclusive-OR (XOR) gate. We could obtain different transmission results by adjusting the bending angle. The numerical simulation results show that the device functions as AND, OR, and XOR gates.     

Real-time, continuous-wave terahertz imaging by a pyroelectric camera

Real-time, continuous-wave terahertz (THz) imaging is demonstrated. A 1.89-THz optically-pumped farinfrared laser is used as the illumination source, and a 124 × 124 element room-temperature pyroelectric camera is adopted as the detector. With this setup, THz images through various wrapping materials are shown. The results show that this imaging system has the potential applications in real-time mail and security inspection.