Design,fabrication and performance analysis of a 200 W PEM fuel cell short stack

A PEM fuel cell short stack of 200 W capacity, with an active area of 100 cm² has been designed and fabricated in-house. The status of unit cell performance was 0.55 W cm⁻². Based on the unit cell technology, a short stack has been developed. The proper design of uniform flow distribution, cooling plate and compressed end plate were important to achieve the best performance of the short stack. The performance of four cells stack was analyzed in static and dynamic modes. In the static mode of polarization curve, the stack has peak power density of 0.55 W cm⁻² (220 W) at 0.5 V per cell, when the voltage was scanning from low to high voltage (1.5–3.5 V), and resulted in minimum water flooding inside the stack. In this study a series of dynamic loadings were tested to simulate the vehicle acceleration. The fuel cell performances respond to dynamic loading influenced by the hydrogen/air stoichiometric, back pressure, and dynamic-loading time. It was needed high hydrogen stoichiometric and back pressure to maintain high dynamic performance. In the long-time stable power testing, the stack was difficult to maintain at high performance, due to the water flooding at high output power. An adjusting cathode back-pressure method for purging water was proposed to prevent the water flooding at flow channels and maintain the stable output power at 170 W (0.42 W cm⁻²).     

The role of water in the device performance of n-type PTCDI-C8 organic field-effect transistors with solution-based gelatin dielectric

Gelatin is a natural protein, which works well as the gate dielectric for N,N-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C₈) organic field-effect transistors (OFETs). An aqueous solution process was applied to form the gelatin gate dielectric on poly(ethylene terephthalate) (PET) by spin-coating and subsequent casting. The field-effect mobility in the saturation regime (μ_FE,sat) and the threshold voltage (V_T) values of a typical 40 nm PTCDI-C₈ OFET are (0.22 cm² V⁻¹ s⁻¹, 55 V) in vacuum and (0.74 cm² V⁻¹ s⁻¹, 2.6 V) in air ambient. The maximum voltage shift in hysteresis is also reduced from 10 V to 2 V when the operation environment for PTCDI-C₈ OFETs is changed from vacuum to air ambient. Nevertheless, a slight reduction of electron mobility was found when the device was stressed in the air ambient. The change in the device performance has been attributed to the charged ions generation owing to water absorption in gelatin in air ambient.     

Master Diagnostic Curve for Dispersion Coefficient of Soils

A master diagnostic curve (MDC) method is proposed for identifying the dispersion coefficient from observed breakthrough curve in soil–column experiments. The method uses matching of diagnostically plotted points to the MDC. Accurate identification of the dispersion coefficient is possible with a parallel shift of only one axis. Another advantage of the method is that the MDC is an invariant curve and once prepared, can be used for different data sets characterized by high Péclet number. The new method is simple, does not require large computations as in conventional least-squares approach, and yields a quick and accurate estimate of the dispersion coefficient. The new method does not require an initial guess for the dispersion coefficient. It can also yield a value of the dispersion coefficient from a single observed concentration. Although subjectivity is involved in matching, there is a transparent visual realization of the reliability of the estimated dispersion coefficient, and the points with substantial errors. The new method has several advantages over the least-squares approach and is suited for an advanced study on the subject. An estimate of the dispersion coefficient obtained using the new method is as good as obtained using a good optimization method.     

CS3000系统在特种溶剂油厂的应用

介绍了CS3000系统控制站技术性能和组态内容,通过复杂控制回路组态过程和技术的详细分析,总结了特种溶剂油厂在DCS软件组态方面的特点,以及在软件组态和调试工作中的体会,加深了DCS现场应用的理解和认识,有助于提高DCS的整体应用水平和效率。     

辐照过程中间隙环形成的Fokker—Planck方程解

空洞和间隙环的形成,是辐照过程中材料微观结构演变的基本问题。本文给出了间隙环形成的Fokker-Planck方程解。该解表征了辐照过程中不同尺寸的间隙环随时间形成的主要特征。对于316不锈钢,计算值与实验值一致。该方法能快速,精确地算出高剂量下的大尺寸间隙环浓度。     

Model reference adaptive control with unknown relative degree

This work presents an indirect, model reference adaptive control for minimum phase linear systems of arbitrary relative degree. Global stability of the closed-loop system is proved in spite of bounded disturbances and asympotic tracking is achieved in the ideal case.     

T300/LD2热循环时产生滞后环原因及改善方法探讨

T300/LD2复合材料在热循环时产生滞后环并留下很大的残留应变。本文对T300/LD2试样在热循环时产生滞后环和残留应变的原因进行分析和探讨。实验结果表明,基体在热循环时大量的塑性变形是产生滞后环和残留应变的主要原因,并通过在界面预设不同应力和缩短热循环温度区间来研究界面应力状态和热循环温度区间跟热循环时滞后环和残留应变之间的关系。提出了改善残留应变和滞后的方法(1)尽量减少复合材料的使用环境中的温度变化,(2)根据材料的使用环境,经过各种预处理使复合材料在工作时基体处于弹性变形状态,(3)提高基体的屈服强度。     

Practical strain extensometry for biaxial cruciform specimens—Part 1

Of a number of methods for testing materials under biaxial stress conditions, the cruciform specimen with tension/compression loading of the arms allows exploration of the whole in-plane failure envelope. This paper highlights the problems arising in the measuring, monitoring and control of strains in cruciform specimens subject to static and cyclic biaxial loading. Three extensometers are described which have been used respectively for testing high strain fatigue in steels, fatigue crack propagation in steels and fatigue and fracture of a glass reinforced polyester composite. Each extensometer uses a full bridge resistance strain gauge circuit; two are based on bending of a beam and the third on deformation of a thin ring. Examples are shown of stress/strain loops for equibiaxial and shear conditions from fatigue tests on a steel and g.r.p.     

HYSTERESIS IN STABLE RIVULET FLOWS

Detailed, theoretical analysis of the structure of water rivulets on inclined stainless steel plates is presented. Experimental results clearly demonstrate the variability of the width and height of a rivulet as a result of changing liquid flowrates within the flowing rivulet. Predicted results generated using the Laplace equation for curved interfaces combined with the Navier-Stokes equation characterize the flowing rivulet by establishing the expected, the maximum and the minimum dimensions of a flowing rivulet. The predictions also show that a simplified film model describing rivulet flow, which is often used as an approximation to the full rivulet model presented here, is inadequate.     

New Approach to Designing Multilayer Feedforward Neural Network Architecture for Modeling Nonlinear Restoring Forces. I: Formulation

This paper addresses the modeling problem of nonlinear and hysteretic dynamic behaviors through a constructive modeling approach which exploits existing mathematical concepts in artificial neural network modeling. In contrast with many neural network applications, which often result in large and complex “black-box” models, here, the writers strive to produce phenomenologically accurate model behavior starting with network architecture of manageable/small sizes. This affords the potential of creating relationships between model parameter values and observed phenomenological behaviors. Here a linear sum of basis functions is used in modeling nonlinear hysteretic restoring forces. In particular, nonlinear sigmoidal activation functions are chosen as the core building block for their robustness in approximating arbitrary functions. The appropriateness and effectiveness of this set of basis function in modeling a wide variety of nonlinear dynamic behaviors observed in structural mechanics are depicted from an algebraic and geometric perspective.