Interaction between Electrical Arc and Nd: YAG Laser Radiation

This paper describes the stabilization and guidance of plasma plumes through the interaction with low power laser radiation. The stabilization and guidance have been found to be governed by several physical effects. One effect is the localized rise of electrical conductivity. As the laser provides a channel of increased conductivity an alignment and a stabilisation of the electrical arc can be obtained. This feature can be exploited to achieve more efficient and flexible plasma processes. Investigations on plasma guidance with respect to different laser wavelengths and interaction modes will be presented by means of example in welding and EDM.     

Layered Laser Vaporization of PMMA Manufacturing 3D Mould Cavities

This paper deals with an innovative technique concerning CO₂ laser machining in order to create 3D cavities to be used as moulds for the casting of polymer resins, vaporizing PMMA layer by layer.The removal of a single layer is achieved using multiple overlapping straight grooves. The groove profile (depth and width) has been predicted by theoretical models which investigate the influence of cutting sequence, number of passes, laser beam scanning speed and radiant flux.The removal depth varies proportionally with the number of layers, while the surface roughness, influenced by the grooves spacing and the orientation of the scanning direction between successive layers, cannot be decreased under a minimum value.     

液封Pr和Sc对开口矩形液池热-溶质毛细对流的影响

在基于提拉法制备晶体材料的背景下,采用格子玻尔兹曼方法对具有自由表面的双层矩形液池内热-溶质毛细对流进行数值模拟.通过频谱分析确定双层热-溶质毛细对流的流动类型,在自由表面雷诺数Re2、界面雷诺数Re1、下熔体层普朗特数Pr1和施密特数Sc1分别为600、300、1.0和100的条件下,研究了液封层普朗特数和施密特数对熔体层热-溶质毛细对流的影响.通过双层热-溶质毛细对流和单层系统的对比表明,液封对下层毛细对流可以起到很好的抑制作用.在液封Sc2=100、Pr2=0.4~10.0条件下,毛细对流都是双频准周期型.随着Pr2的增加,第一基频和第二基频都减小,系统稳定性增加;在Pr2=1.0、Sc2=20~100条件下,随着Sc2的增大,系统的振荡频率增大,对流将从周期模型再次转变为准周期型,稳定性降低.     

Impact of PTFE distribution across the GDL on the water droplet removal from a PEM fuel cell electrode containing binder

By progress of the new generation of electrical powertrains and reducing of the fossil fuel resources, vehicle industry becomes more interested in utilizing proton exchange membrane (PEM) fuel cells. However, practical utilization of them is faced with some challenges including liquid water accumulation in the porous electrodes. The common belief for mitigating this issue is the treatment of electrodes' gas diffusion layers (such as carbon papers consisting of carbon fibers and binder for binding fibers) with a highly hydrophobic material such as poly-tetra-fluoro-ethylene (PTFE). In the current investigation, 3D stochastic reconstructions and 3D lattice Boltzmann simulations are employed to discover the impact of PTFE distribution as well as the role of binder content on the removal process of a water droplet from a PEM fuel cell electrode for the first time. Nine different simulations with three dissimilar PTFE distributions and three dissimilar binder contents are implemented. The results demonstrate that the PTFE distribution and the existence of binder can greatly affect the removal efficiency of water droplet from gas diffusion layer. Unexpectedly, for higher binder contents, the uniform distribution of PTFE is less effective. Besides, for a specific PTFE distribution adding binder can effectively hinder the removal process of droplet.     

EXAMINATION OF THE LBM IN SIMULATION OF MICROCHANNEL FLOW IN TRANSITIONAL REGIME

The gas flows in micro-electro-mechanical systems possess relatively large Knudsen number and usually belong to the slip flow and transitional flow regimes. Recently the lattice Boltzmann method (LBM) was proposed by Nie et al. in Journal of Statistical Physics, vol. 107, pp. 279–289, in 2002 to simulate the microchannel and microcavity flows in the transitional flow regime. The present article intends to test the feasibility of doing so. The results of using the lattice Boltzmann method and the direct simulation Monte Carlo method show good agreement between them for small Kn (Kn = 0.0194), poor agreement for Kn = 0.194, and large deviation for Kn = 0.388 in simulating microchannel flows. This suggests that the present version of the lattice Boltzmann method is not feasible to simulate the transitional channel flow.     

基于格子Boltzmann的喷印OLED散点墨滴沉积仿真分析

为解决喷印OLED发光层制备中基板污点、涂布不均等问题引起的Mura缺陷,建立基于BGK-LBM（单松弛格子Boltzmann方法）的三维数值模型,对喷印OLED像素槽附近墨滴落点偏差引起的散点沉积缺陷进行仿真分析。先研究不同墨滴尺寸以不同撞击速度撞击不同接触角平板后的最大铺展半径,再以最大铺展半径为参考研究不同润湿性梯度下的像素槽外墨滴的铺展回流。结果表明：对于微米级直径的OLED喷印墨滴,尺寸越大、墨滴撞击速度越大、像素坑内接触角越小其最大铺展半径越大;而针对存在落点偏差的散点,当最大铺展半径大于或等于散点的落点偏差时,将在足够的像素槽基板内外接触角差值引起的润湿性梯度牵引下重新进入像素槽内;撞击速度还影响其回缩阶段的回缩速度,撞击速度越小回缩越慢,因而墨滴会存在受到润湿性梯度的影响而被牵引向润湿度高的一侧;只有当像素槽内外接触角造成的润湿性梯度足够时,在撞击铺展后边缘进入像素槽边界处的墨滴才能被牵引重新流入像素槽内,散点沉积缺陷即得到抑制。本文提出的最大铺展半径可以用来拓宽像素槽外墨滴的有效落点范围,作为喷印OLED制备中打印精度控制的参考,用于指导生产。     

2-氨基-5-氟吡啶的合成

2-氨基-5-氟吡啶是合成肽脱甲酰基酶抑制剂LBM415的重要中间体.以2-氨基吡啶为原料,经过混酸硝化,氨基乙酰化保护,硝基还原,重氮化及席曼反应引入氟原子以及水解脱乙酰基等步骤合成2-氨基-5-氟吡啶.该路线简化了实验操作,避免了文献报道的在原料2-氯-5-氨基吡啶的合成、中间产物的分离和最终产品的纯化过程中出现的收率低以及纯度不高的问题.各步反应比较适宜的工艺条件(反应温度,反应时间,摩尔收率)分别为,硝化反应:45℃,2 h,41%;氨基保护:回流,1 h,96.3%;硝基还原:回流,1 h,90%;重氮化:-5～0℃,2 h,81.4%;席曼反应:130℃,0.5 h,乙酰基水解:回流,2.5 h,两步反应总收率为51.6%.产物熔点与文献报道一致,并通过1H-NMR和IR确认了2-氨基-5-氟吡啶的结构.     

Warm Laser Shock Peening: New developments and process optimization

Laser Shock Peening is a well-known technology able to enhance the fatigue life of mechanical components. Surface residual stress is induced by means of the recoil pressure of an ablated coating in a confining medium interacting with a high power density laser.Warm Laser Shock Peening is obtained by laser peening a pre-warmed workpiece surface: combining the thermal effect of the pre-heated surface and the mechanical phenomenon of the recoil shock pressure, the dynamic aging of the surface microstructure is obtained. Precipitates surrounded by dense dislocation together with residual stress considerable increase the mechanical properties of the workpiece.     

基于格子Boltzmann方法的一维Burgers方程的数值模拟

基于格子Boltzmann方法(LBM)的一维Burgers方程的数值解法,已有2-bit和4-bit模型。文中通过选择合适的离散速度模型构造出恰当的平衡态分布函数; 然后, 利用单松弛的格子Bhatnagar-Gross-Krook模型、Chapman-Enskog展开和多尺度技术, 提出了用于求解一维Burgers方程的3-bit的格子Boltzmann模型,即D1Q3模型,并进行了数值实验。实验结果表明,该方法的数值解与解析解吻合的程度很好,且误差比现有文献中的误差更小,从而验证了格子Boltzamnn模型的有效性。     

异构平台下格子Boltzmann方法实现及性能分析

对CPU+GPU异构平台下的多种并行编程模式进行了研究,并针对格子Boltzmann方法实现了CUDA,MPI+CUDA,MPI+OpenMP+CUDA多级并行算法。结果表明,算法具有较好的加速性能;提出的根据计算量比例参数调节CPU和GPU之间负载均衡的方法,对于在异构平台上实现多级并行处理及资源的有效利用具有一定的参考和应用价值。