纤维共晶生长界面前沿三维扩散场解析

修正Ｊａｃｋｓｏｎ和Ｈｕｎｔ关于在垂直生长方向截面上溶质扩散各向同性假设，求解三维Ｌａｐｏｌａｃｅ方程，获得纤维共晶生长界面前沿三维稳态扩散场，并证明Ｊａｃｋｓｏｎ和Ｈｕｎｔ的二维模型是实际生长的二维简化和一阶近似，并用丁二腈（ＳＣＮ）一梓脑（ＣＡＭ）纤维共晶系统计算生长界面前沿溶质分布。     

一种碳－碳复合材料长寿命防氧化涂层的失效机制

用液相法联合ＣＶＤ法和硅化法制备了一种碳－碳复合材料复合梯度涂层，在此基础上对这种涂层在氧化过程中的失效机制进行了研究．结果表明：氧化层与液相层界面反应生成的气相产物是涂层失效的根本原因界面上气泡的不均匀形核、长大和破裂导致涂层表面出现孔洞．孔洞处气泡优先形核、长大和破裂并发展成为缺陷而使涂层失效     

碳/碳复合材料MoSi2/SiC涂层在动态氧化环境下的性能研究

为了考察MoSi₂/SiC防氧化涂层体系在动态氧化环境下的防护能力,对碳/碳复合材料MoSi₂/SiC涂层试样在1100~1500℃下进行了高温燃气高质流冲刷环境下的氧化试验。结果表明,在1100~1500℃的燃气动态环境下,具有稳定的氧化失重速率,氧化失重曲线近似呈直线关系,氧化失重和氧化失重速率均随着氧化温度的升高而降低,表现出该涂层抗高质流冲刷和氧化的能力随温度的升高而提高,在该温度区间内,随着温度的升高,具有更优异的抗氧化和抗高质流冲刷的能力。     

Combined shape and sizing optimization of truss structures

 In this paper, an evolutionary optimization method is presented for weight minimum problem of a 3-dimensional truss structure in terms of nodal coordinates and element cross-sectional areas. The structure is subject to stress, local buckling and displacement constraints. Two types of design variables with different natures are optimized separately: (1) a fully stressed design (FSD) and scaling techniques are applied to sizing variables and (2) the evolutionary node shift method is applied to shape variables. Alternating procedure is utilized to couple the two types of variables and to combine the results. The optimum solution is achieved gradually from the initial configuration design. Two typical truss structures are examined to illustrate the validity of the method. Received: 22 October 2001 / Accepted: 04 June 2002 This research work is supported by the National Natural Science Foundation of China under the guarantees no. 10072050 and 10172072, respectively.     

Performance of miniaturized direct methanol fuel cell (DMFC) devices using micropump for fuel delivery

A fuel cell is a device that can convert chemical energy into electricity directly. Among various types of fuel cells, both polymer electrolyte membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) can work at low temperature (<80 °C). Therefore, they can be used to supply power for commercial portable electronics such as laptop computers, digital cameras, PDAs and cell phones. The focus of this paper is to investigate the performance of a miniaturized DMFC device using a micropump to deliver fuel. The core of this micropump is a piezoelectric ring-type bending actuator and the associated nozzle/diffuser for directing fuel flow. Based on the experimental measurements, it is found that the performance of the fuel cell can be significantly improved if enough fuel flow is induced by the micropump at anode. Three factors may contribute to the performance enhancement including replenishment of methanol, decrease of diffusion resistance and removal of carbon dioxide. In comparison with conventional mini pumps, the size of the piezoelectric micropump is much smaller and the energy consumption is much lower. Thus, it is very viable and effective to use a piezoelectric valveless micropump for fuel delivery in miniaturized DMFC power systems.     

A parameters design approach to improve product quality and equipment performance in hot rolling

This study presents the application of parameters design to improve both the product quality and the equipment performance in a hot sheet rolling plant. Three empirical models were developed to predict and explain the relationship between variation in some process parameters and the type and range of product defects together with equipment disorders observed. The investigation is based on the analysis of the results of a set of designed experiments.The most critical process parameters were set at specified values and the effect of the change in these parameters, on rolled sheets quality and rolling equipment performance is evaluated. The three process parameters considered are the reduction ratio (Rd), the slab temperature (T_s), and the exit strip speed (Sp). The quality characteristics considered are: profile and flatness of rolled sheets and distance between chatter marks, the performance indicators considered are: rolling force, vibration measurements, and the rolling mill wear rate.Through optimization of process parameters, it was possible to reduce chattering. Consequently, chatter marks and roll wear were greatly reduced. Product flatness and profile were improved. Plant down time and production scrap was considerably reduced. This investigation proved that it is possible to improve both product quality and equipment performance in the hot rolling plant through the parameters design approach.     

Improved durability of Si/B/N/C random inorganic networks

The inherent high temperature durability as well as the hardness of random inorganic networks composed of Si, B, N and C, can be raised through the incorporation of rigid structural elements (e.g. borazine rings) as well as through an increase of the carbon content. This has been shown by comparison of the high temperature durabilities and micromechanical properties of newly synthesized Si/B/N/C ceramics derived from different acyclic and cyclic single source precursors. Crosslinking of these specially designed monomers with methylamine provides highly homogeneous preceramic polymers, in which the predetermined structural features of the molecular precursors are embedded. Subsequent pyrolysis and calcination up to 1500 °C converts the polymers into all-inorganic amorphous silicon boron carbonitrides. Depending on the constitution of the precursors, the as-obtained materials exhibit a combination of a high carbon content together with borazine rings embedded into the covalent network. Comparing the high temperature stability, hardness and stiffness of the synthesized ceramics, the best performance is achieved when carbon rich borazine derivatives are employed as single source precursors. Thus, the high temperature durability can be raised up to at least 2000 °C, and, at the same time, the microhardness and elastic modulus is maximized up to 14.5 and 127 GPa, respectively. The new materials have been characterized by IR spectroscopy, elemental analysis, XRD, SEM, DTA/TG, and by nanoindentation.     

ER流体特性及其研究现状

本文简要介绍了ER流体现象及其力学和电学性能,给出了描述ER流体行为的一般理论,提出了ER流体应用中目前存在的主要问题。