二维C/SiC复合材料连接的显微结构与性能

采用Ni基连接剂作为中间层在1300℃、真空条件下对二维纺织C/SiC复合材料用液相渗透法进行了加压连接，所旋压力为20MPa，连接保温时间分别为15，30，45，60min。用扫描电镜SEM及能谱分析了连接情况，结果表明所采用Ni基连接剂与C/SiC复合材料有较好的润湿性，Ni基连接剂熔融后可进入复合材料的孔隙。接头三点弯曲强度可达60MPa。     

Maximum stiffness design of laminated composite plates via a constrained global optimization approach

The optimal lamination arrangements of laminated composite plates with maximum stiffness subject to side constraints are investigated via a constrained multi-start global optimization approach. In the optimal design process, the deformation analysis of laminated composite plates is accomplished by utilizing a shear deformable laminated composite finite element and the optimal design problem, which has been converted into an unconstrained minimization problem via the general augmented Lagrangian method, is solved by utilizing the proposed unconstrained multi-start global optimization technique to determine the optimal fiber angles and layer group thicknesses of the laminated composite plates for attaining maximum stiffness and simultaneously satisfying the imposed side constraints. The feasibility of the proposed constrained multi-start global optimization algorithm is validated by means of a simple but representative example and its applications are demonstrated by means of a number of examples on the maximum stiffness design of symmetrically laminated composite plates. The effects of length-to-thickness ratio, aspect ratio, and number of layer groups upon the optimum fiber angles and layer group thicknesses of the plates are investigated.     

攀钢烧结机漏风调查及降低漏风率研究

调查了攀钢１号，２号烧结机密封设备的磨损变形情况；系统测定了２号烧结机中修前后各部位的漏风情况；分析了风率高的原因，提出了降低漏风率的主要措施。在１号，３号烧结机头尾风箱安装重锤式密封装置及篦塞加工方法后，漏风率均降低了５．４４％。     

Using handhelds in a Jigsaw cooperative learning environment

Abstract This paper reports our implementation of a handheld wireless environment to support Jigsaw cooperative learning activities in a college setting. A quasi-experimental research design was conducted to investigate the effects of using handhelds, as well as issues associated with the use of handheld technology. Two intact classes of fourth-year students from a five-year junior nursing college participated in the experiment. Our findings showed that handheld tools enhanced both students' attitudes and performance in learning, and promoted better interactions among students and instructors. We also found that the handheld technology was not sophisticated enough to support cooperative learning goals without full support from a technology specialist.     

On the aerodynamic forces of a plunging airfoil

The generation of aerodynamic forces by a plunging NACA0012 airfoil at a Reynolds number of 20,000 was studied for a range of non-dimensional plunge frequenciesk and amplitudesh using a 2D unsteady compressible Navier-Stokes solver, an unsteady panel method (UPM) and Garrick’s analysis. Calculations using these two methods indicate that the forces collapse reasonably well withkh (or equivalents the Strouhal number), but are only weak functions ofk. In contrast results from the NS code indicate that the forces are dependent on bothk andkh independently, with large variations at low frequencies. The frequency dependence was found to be a result of vortex shedding from the leading edge of the airfoil, and appears to result from two factors. Firstly at high plunge frequenciesk, the leading edge vortex does not have sufficient time to grow, whereas at lowk the vortex can become a sizeable fraction of the airfoil chord before separating. Secondly once the vortex separates, it is convected downstream over the surface of the airfoil. Due to the low pressure in the vortex core, thrust is maintained while the vortex is upstream of the airfoil maximum thickness point (where the airfoil surface is tilted upstream and the vortex low pressure creates an upstream suction force). Once past this point, the airfoil surface is tilted downstream and the vortex contributes to drag rather than thrust. At high plunge frequencies the vortex cannot be convected far downstream before the motion cycle creates another leading edge vortex on the opposite side of the airfoil, so the impact is lessened. At lowk however the vortex travels far downstream over the airfoil surface, causing drag for a larger portion of the flapping cycle, and therefore lower propulsive efficiency. These results have strong implications on how the thrust and the propulsive efficiency can be maximised by controlling the relative amplitudes and phases of combined pitching and plunging motions of an airfoil.     

A systematic method of adaptive joint design considering different assembly sequence in sheet metal product

In sheet metal assembly, not only the component variations and tool errors, but also the component structure (joint type) and assembly process (assembly sequence) affect the final dimensional quality. In this paper, a systematic method for adaptive joint design considering different assembly sequence is proposed to meet the in-process dimensional adjustability of KCs (key characteristics). First, the adaptive characteristic of the sheet metal joint is depicted. Then, the mathematical model in order for concurrently optimizing both joint type and different assembly sequence is presented. How to evaluate the combination of joint type and assembly sequence is carried out according to two conditions: (1) for single KC, and (2) for multiple KCs. The KC confliction is considered to ensure the important KCs. Genetic algorithm is used to resolve the optimization of joint design. An example is chosen to demonstrate our method finally, and various joint designs are acquired according to different assembly sequences by this means. The proposed methods make it possible for us to improve the dimensional quality of product in the design stage.     

Preparation and Characterization of Superconducting B1-Type Mo1-xNbxN Thin Films

Solid-solution thin films, Mo_1−xNb_xN, with B1 (NaCl) structure have been deposited on substrates at 450°C by reactive sputtering of composite targets with Mo and Nb metals in an equimolar Ar and N₂ gas mixture. The lattice parameter of the solid solution increased linearly with an increase of Nb content, x . The superconducting transition temperature, T _c, of the Mo-rich films ( x ≦ 0.12) was around 6 K, which was lower than that expected from theoretical prediction. The residual resistivity ratio, r =ρ(300 K)/ρ(20 K), of the films varied with x , and a minimum value of r was observed in the vicinity of x = 0.5.     

稀土改性镍催化剂对CO2甲烷化反应的影响

以稀土为助剂 ,金属镍为活性组份 ,研究了不同稀土对镍催化剂的改性作用 ,同时用活性比表面、H2 -TPD、CO2 - TPD及 XPS等方法对催化剂进行了表征。结果表明 ,稀土对镍催化剂的 CO2 甲烷化活性有明显的促进作用 ,其中以稀土 Sm的改善效果最好 ;海泡石和 Sm既能增大镍催化剂的活性比表面积 ,又能提高 H2 和 CO2 的吸附量 ,同时降低反应的活化能 ,增大镍上的电子云密度。     

USB信息认证器的设计

给出了一种PC使用的USB信息认证外围设备。它使用USB接口,可为电子商务、电子政务提供高强度信息安全保障它基于抗篡改的硬件设计。通过USB接口与计算机相连接,可提供数据完整性、数字签名和数字认证等安全功能。