Numerical investigation of flow field configuration and contact resistance for PEM fuel cell performance

A steady-state three-dimensional non-isothermal computational fluid dynamics (CFD) model of a proton exchange membrane fuel cell is presented. Conservation of mass, momentum, species, energy, and charge, as well as electrochemical kinetics are considered. In this model, the effect of interfacial contact resistance is also included. The numerical solution is based on a finite-volume method. In this study the effects of flow channel dimensions on the cell performance are investigated. Simulation results indicate that increasing the channel width will improve the limiting current density. However, it is observed that an optimum shoulder size of the flow channels exists for which the cell performance is the highest. Polarization curves are obtained for different operating conditions which, in general, compare favorably with the corresponding experimental data. Such a CFD model can be used as a tool in the development and optimization of PEM fuel cells.     

Structural motion of water-resisting key strata lying on overburden

Water-preserved mining is one of the important parts of the 'Green Mining' technological system. The purpose of wa-ter-preserved mining is to prevent water from bursting out in coal mines and thus to protect water resources. The principle of wa-ter-resisting key strata (WKS) is proposed to establish a model capable of guiding and developing water-preserved mining technol-ogy. The experimental model of the WKS is constructed following requirements of the Data Image Correlative Method (DICM).Five experimental schemes are designed according to different combined patterns of the WKS. The water-resisting performance of the WKS is analyzed from observation of structural stability. All of them provide referential value for water-preserved mining.     

磁粉探伤用环形试件的几何尺寸

根据磁偶极子链近似理论对Betz环的分析结果，推导出下列关系：（m-1）／mlnm=2（h-a）／Dln（D／D-2h）（其中m=D／d，D-环外径，d-环内径，a-小孔半径，h-小孔埋藏深度），从而得悉：D、d、a、h中只有3个是独立的。由上式的数值计算证明：英国的BS6072-1981标准试件设计合理，而日本的儿SG0565-1982中B型对比试件的内径过小，无法达到环的使用目的，给出了改进后的合理内径尺寸。     

三维流固耦合瞬态温度场有限元程序

本文提出了流固耦合温度场的有限元法,并用于湿式离合器摩擦片的温度场计算。其主要优点是将流体和摩擦片作为一个整件来求解它们的温度场。另外,由于利用具有特殊加权函数的Petrov-Galerkin法进行有限元离散,使能量方程能进行迭代解。     

The multidimensional structure of perfectionism in clinically distressed and college student samples.

Confirmatory factor analysis was used to evaluate 2 multidimensional measures of perfectionism (R. 0 Frost, P. Marten, C. Lahart, & R. Rosenblate, 1990; P. L. Hewitt & G. L. Flett, 1991). On a first-order level, support was found for Hewitt and Flett's (1991) original 3-factor conceptualization of perfectionism, although only for an empirically derived 15-item subset. Support was also obtained for 5 of the 6 dimensions proposed by R. O. Frost et al. (1990), but the model only displayed good fit when a refined scale containing 22 of the original 35 items was used. A second-order analysis found evidence for 2 higher-order factors of adaptive and maladaptive perfectionism. Perfectionism dimensions correlated in expected directions with personality domains, symptom distress, and academic achievement. The brief measures of perfectionism also retained the construct-related validity displayed by the full-item versions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

塑炼1,2-聚丁二烯的无扰尺寸

利用测得(?)和[η]数据,由Stockmayer-Fixman-Burchard、Stockmayer-Kurata-Roig和Inagaki-Suzuki-Kurata方程外推,估算了塑炼过程中不同1,2-链节含量的1,2-聚丁二烯(1,2-PB)的无扰尺寸变化规律。1,2-链节含量分别为40％和87.2％时,随薄通次数的增加,无扰尺寸降低;但前者薄通50次后变化很小,后者薄通100次后仍有波动。1,2-链节含量为87.2％的1,2-PB,薄通后放置30d,其无扰尺寸随薄通次数的增加而降低的程度,均大于当日测定的结果。     

Fractal Dimensions of Simulated and Real Fat Crystal Networks in 3D Space

The microstructure of fat crystal networks is closely related to rheological properties of fat products, and thus is of particular interest to food scientists. The fractal dimensions of fat crystal networks calculated by microscopy methods such as box-counting, D _b, particle-counting, D _f, and mass fractal dimension, D _m, have been extensively employed to quantify the microstructure of fats. This work revealed the microstructural basis of D _b, D _f, and D _m in 3D space through both computer simulation and experiments on the high melting fraction of milk fat crystal networks. Similar to our previous simulation study on the fractal dimensions of fat crystal networks in 2D space, D _b is sensitive to crystal size, area fraction, and not sensitive to distribution orderliness of crystals, which is the percentage of evenly distributed fat crystals within the simulated fat crystal networks. D _f and D _m were not affected by any of the microstructural factors studied in the simulation.     

低于(n-1)维的两个子空间的交空间求法

本文阐述了在ｎ维空间Ｅｎ（ｎ≥４）中求作均低于（ｎ－１）维的两个子空间的交空间的一般方法．     

曲线轨道空间振动响应特性研究

曲线轨道空间振动存在平面内振动、平面外弯扭耦合振动,通过建立曲线轨道空间振动频域解析模型,对曲线轨道动力响应特性进行研究。将曲线轨道视为圆形结构的一部分,利用圆形结构周期性的特性,在一个基本元之内求解曲线轨道的动力响应。通过引入移动谐振荷载作用下轨梁动力响应的频域数学模态,得出曲线轨道轨梁频域响应的级数表达。在频域内采用数学模态叠加法表示曲线轨梁的纵向、横向、垂向及扭转振动,进而求解得到基本元内轨梁的频域动力响应。经计算表明,文中提出的频域解析模型能够得到精确的曲线轨道频域响应。通过分析速度、半径、超高等因素,得到以下结论：准静态激励下单个移动轴荷载对曲线轨梁的垂向、横向及扭转振动的影响范围在作用点两侧±5m左右;轴荷载移动速度对曲线轨梁横向位移、扭转变形具有显著的影响,随着速度的增加,曲线轨道由过超高状态逐渐过渡到理想超高状态,最终进入欠超高状态,轨梁横向位移、扭转变形方向发生改变,响应幅值先减小后增加;半径、超高和速度对曲线轨梁垂向位移、横向位移及扭转变形影响较大;随着半径的增加,速度对位移响应的影响程度降低;准静态移动轴荷载列作用下曲线轨梁垂向、横向及扭转频域响应主要集中在40Hz以内的频段;横向振动、扭转振动频谱分布范围较宽。     

Preservation of protein fluorescence in embedded human dendritic cells for targeted 3D light and electron microscopy

In this study, we present a correlative microscopy workflow to combine detailed 3D fluorescence light microscopy data with ultrastructural information gained by 3D focused ion beam assisted scanning electron microscopy. The workflow is based on an optimized high pressure freezing/freeze substitution protocol that preserves good ultrastructural detail along with retaining the fluorescence signal in the resin embedded specimens. Consequently, cellular structures of interest can readily be identified and imaged by state of the art 3D confocal fluorescence microscopy and are precisely referenced with respect to an imprinted coordinate system on the surface of the resin block. This allows precise guidance of the focused ion beam assisted scanning electron microscopy and limits the volume to be imaged to the structure of interest. This, in turn, minimizes the total acquisition time necessary to conduct the time consuming ultrastructural scanning electron microscope imaging while eliminating the risk to miss parts of the target structure. We illustrate the value of this workflow for targeting virus compartments, which are formed in HIV‐pulsed mature human dendritic cells.