First step of anodization influences the final nanopore arrangement in anodized alumina

Anodic porous alumina is a well-known template material for nanofabrication. To obtain highly ordered nanoporous array, sophisticated and expensive methods are applied. On the other hand there is two-step self organized anodization, which is much cheaper, but obtained alumina arrangement is not ideal. In our paper, influence of the first step of anodization on the final AAO structure arrangement is studied in details. Anodizations were carried out in 0.3 M oxalic acid at 35 °C at various potentials and durations of the first step of anodization. Second step of the anodization was constant for all the experiments and was 15 min long. Oxide layer thickness formed during the first step of the anodization was 50, 100, 150 and 200 μm and after oxide removal, remaining concaves were serving as a mask for further growth during second step of the anodization. The longer first step of anodization, the higher regularity ratio and circularity, and lower percentage of defects in the nanoporous array. Anodic porous alumina was formed at four various potentials: 30, 40, 50, 60 V. The best arrangement of nanopores was found for samples anodized at 40 V. Maximum of regularity ratio was corresponding to the minimum of defect content in the AAO array. Long enough first step of two-step self-organized anodization in 0.3 M oxalic acid can provide high-ordered nanoporous template for fabrication of various nanomaterials with new, unique properties.     

不同碱金属氢氧化物对纤维素羧甲基化的影响

以不同碱金属氢氧化物(NaOH,KOH)为碱化剂,利用淤浆法合成CMC,对纤维素的碱化及羧甲基化进行了研究。结果表明,NaOH质量分数为25%,纤维素达到最大的润胀,KOH质量分数在20%~35%,纤维素的润胀率出现平台区;同一质量分数下,纤维素在NaOH溶液中的润胀率和吸附碱量都比在KOH中高;CMC的取代度随NaOH用量的增加急剧增加,而随KOH量的增加较为缓慢;取代度相近时,羧甲基纤维素钾的耐酸性和耐盐性比羧甲基纤维素钠差。     

A thermodynamic framework for the modeling of crystallizable shape memory polymers

Shape memory polymers are a relatively new class of materials that have the ability to retain a temporary shape, which can be reset to the original shape with the use of a suitable trigger, typically an increase in temperature. The temporary shapes can be very complex and the deformations involved large. These materials are finding use in a large variety of important applications; hence the need to model their behavior. In this paper, we develop constitutive equations to model the thermo-mechanical behavior of crystallizable shape memory polymers. Crystallizable shape memory polymers are called crystallizable because the temporary shape is fixed by a crystalline phase, while return to the original shape is due to the transition of this crystalline phase. The modeling is carried out using a framework that was developed recently for studying crystallization in polymers and is based on the theory of multiple natural configurations. In this paper we formulate constitutive equations for the original amorphous phase and the semi-crystalline phase that is formed after the onset of crystallization. In addition we model the transition of the crystalline phase to capture the return of the polymer to its original shape. These models for shape memory effects in polymers have been developed within a full thermodynamic framework, extending our previous work in which the models were developed within a mechanical setting [G. Barot, I.J. Rao, Constitutive modeling of the mechanics associated with crystallizable shape memory polymers, ZAMP 57 (4) (2006) 652-681]. The model is applied to the problem of inflation and extension of a hollow cylinder. The results are consistent with what has been observed in experiments.     

一类大尺寸印制板安装孔位的自动排布方法研究

螺栓紧固型印制板在雷达领域应用广泛.对于大尺寸的螺栓紧固型印制板,为了结构可靠及性能稳定,设计时需要在上面排布大量的安装孔,而印制线在结构上的规律性较弱,从而导致安装孔的布置成为一项繁琐的工作.为了减轻设计师的负担,有效提高工作效率,针对一类大尺寸印制板,根据印制线主要由水平线段和竖直线段组成的特点,设计了一套可以自动地为印制板排布安装孔位的算法.将此算法应用于3个具体的工程实例,发现在适当的参数下,算法排布的安装孔与原印制板有较高的相似度,且满足印制板设计要求,表明该算法具有一定的工程意义.     

FE analysis of geometry effects of an artificial bird striking an aeroengine fan blade

Bird strike resistance of aeroengines is a strict certification requirement. Apart from costly experimental bird strike tests, explicit numerical modeling techniques have been employed. However, due to the complicated bird geometry, artificial bird models are still not well defined and it is a perennial problem selecting an appropriate representative artificial bird geometry for the simulations. To examine the relative effects of the artificial bird geometry, explicit 3-D finite element analyses are conducted herein using the commercial code LS-DYNA. As a validation test, we first studied the nonlinear transient dynamic response of an artificial bird striking a rigid flat target. Following the validation, we studied the impact behavior of an artificial bird impinging a flexible aeroengine fan blade. The study focused on the three most-frequently used configurations in the literature: namely, hemispherical-ended cylinder, straight-ended cylinder, and ellipsoid, at various length-to-diameter aspect ratios. The results show that the initial contact area between the bird and target in the early phase of the impact event would have a significant effect on the peak impact force. The aspect ratio of the bird striking both rigid panel and flexible fan blade was found to have little influence on the normalized impact force and impulse.     

多间低温冷库的温度集中监测系统

分析多间低温冷库温度集中监测系统的设计方案、硬件系统和软件系统。该温度集中监测系统采用PC机与数据采集控制器进行通讯,对组态软件进行二次开发,实时采集监测温度。运行试验表明,该系统具有性能稳定可靠、安装简单、监测精度高等特点,具备温度的实时动画显示、趋势曲线、数据库查询、报表输出打印等功能。     

应用OpenGL建立机器人可视化仿真系统

通过对机器人系统的位置、速度和加速度的分析,在VC的开发环境下构建了一个基于OpenGL的机器人可视化仿真系统,在此基础上进行运动学和动力学仿真实验。     

3－TRS型关联机器人的几何特性分析

本文根据３－ＴＲＳ型机器人的结构特点，分析了它的工作空间，灵活性，奇异位形等几何特性。     

基于组态软件的空压机集群监控系统

以组态软件为基础，通过计算机实现对多台空气压缩机进行集中监控。介绍了系统的设计思想、技术要点和运行方式。系统主要功能有：远程读取压缩机的状态、运行参数和报警信息、显示运行参数的曲线图、远程控制压缩机的开机和关机以及参数设定。可以记录压缩机运行过程中参数变化历程并进行历史数据的图形绘制显示。     

PLC和组态软件在除尘控制系统中的应用

介绍西门子S7-200 PLC和WinCC组态软件在除尘控制系统中的应用。通过分析除尘系统的特点，给出了相应的控制策略及算法，设计了相关的程序模块。利用WinCC组态模拟现场画面，操作界面简单明了，方便易用。实际应用表明由S7-200PLC和WinCC组态软件构成的控制系统具有成本低廉、经济实用、可靠性高等特点，同时节约了设备投资。