结合电子设计竞赛的“电力电子技术”课程教学改革实践

电子设计竞赛是提高学生动手能力、加强创新设计能力、增进团队合作等能力的有效手段,同时也能促进高校相关课程的改革。\"电力电子技术\"课程涉及电子技术、控制技术和电力技术,主要内容包括电力电子器件、整流电路、逆变电路、直流-直流变换、交流-交流变频、PWM控制技术及软开关等,课程实践性和工程性都很强。根据\"电力电子技术\"课程特点及存在的问题,提出相应的课程教学改革思路并加以实践,包括将\"电力电子技术\"课程与电子设计竞赛结合,把电赛题目带进课堂,通过案例式教学讲授知识点,积极动员学生参与电子设计竞赛,积累好的作品反馈于课程教学等。结果表明:结合电子设计竞赛的\"电力电子技术\"课程选课学生数有明显提升,参与电子设计竞赛的学生人数和获奖比例有一定提高

Preparation and Characterization of TiO_2 Nanotubes Array by Anodic Oxidation in Anionic Modified Glycerol-Based Electrolyte

本文采用电化学阳极氧化法以含氟的甘油和水混合溶液为电解液在纯钛表面制备了一层排列规整的TIO2纳米管阵列,研究了电解液中额外添加3种2价阴离子、不同的电解时间及不同的添加物浓度等因素对所获得的TIO2纳米管阵列形貌的影响。结果表明,在改性电解液中制备的TIO2纳米管阵列的长度均超过了未改性的电解液中制备的,并随着氧化时间的增长,纳米管管口直径增大,管壁变薄;同时添加的(nH4)2TIf6浓度在0.025~0.1 MOl.l-1范围内均可获得管长更长且形貌较好的TIO2纳米管阵列。High-order TiO2 nanotube arrays on titanium foils were prepared in glycerol-based electrolyte containing fluorine and water by electrochemical anodic oxidation in this work.The influence of different dianion additives,different oxidation duration and concentration of electrolyte additives on the effect of the morphology of TiO2 nanotube arrays were investigated.Results showed that the length of TiO2 nanotube arrays in the modified electrolyte were longer than the samples in the unmodified electrolyte.And with the growth of oxidation duration,the diameter of the nanotubes increased,the wall were thinner;moreover better and longer TiO2 nanotube arrays can be prepared in the glycerol-based electrolyte with the range of the concentration of(NH4)2TiF6.国家自然科学基金(No.30970887;30600149); 卫生部科学研究基金(No.WKJ2008-02-037); 福建省杰青项目(No.2011J06019); 教育部重点项目(No.209061); 福建省纳米材料重点实验室科学基金(No.NM10-03)资助项

Bending modes and transition criteria for a flexible fiber in viscous flows

The present paper follows our previous work in which a coupling approach of smoothed particle hydrodynamics (SPH) and element bending group (EBG) was developed for modeling the interaction of viscous incompressible flows with flexible fibers. It was also shown that a flexible object may experience drag reduction because of its reconfiguration due to fluid force on it. However, the reconfiguration of deformable bodies does not always result in drag reduction as different deformation patterns can result in different drag scales. In the present work, we studied the bending modes of a flexible fiber in viscous flows using the presented SPH and EBG coupling approach. The flexible fiber is immersed in a fluid and is tethered at its center point, while the two ends of the fiber are free to move. We showed that the fiber undergoes four different bending modes: stable U-shape, slight swing, violent flapping, and stable closure modes. We found there is a transition criterion for the flexible fiber from slight swing, suddenly to violent flapping. We defined a bending number to characterize the bending dynamics of the interaction of flexible fiber with viscous fluid and revealed that this bending number is relevant to the non-dimensional fiber length. We also identified the critical bending number from slight swing mode to violent flapping mode

血小板膜糖蛋白Ⅱb/Ⅲa受体拮抗剂RGDS对血小板释放反应的影响

【目的】观察血小板膜糖蛋白Ⅱb/Ⅲa（GPⅡb/Ⅲa）拮抗剂——四肽Arg-Gly-Asp-Ser（RGDS）对血小板聚集和CD62p表达的作用,探讨RGDS对血小板聚集和释放反应的影响。【方法】检测二磷酸腺苷（ADP;终浓度5μmol/L,下同）诱导血小板聚集的最大聚集率（rPA,max）、静息血小板和ADP诱导的血小板CD62p表达,检测不同浓度RGDS对ADP诱导的rPA,max的抑制率和血小板CD62p表达的抑制率,进行回归分析。【结果】5种浓度（50、100、200、400、800μmol/L）的RGDS对rPA,max均有显著抑制作用。正常人静息血小板CD62p表达率为（3.5±0.6）%;ADP激动的血小板CD62p表达率为（65.6±13.8）%,两组比较有显著性差异（P〈0.01）;50、100μmol/L的RGDS对血小板CD62p表达无抑制作用;当RGDS浓度≥200μmol/L时（200、400、800μmol/L）,其可抑制血小板CD62p的表达;RGDS对rPA,max的抑制作用和其对血小板CD62p表达的抑制作用相关。【结论】RGDS浓度〈200μmol／L时，对ADP诱导的血小板释放反应无影响；RGDS浓度≥200μmol/L时，可抑制ADP诱导的血小板释放反应；与RGDS显著的抗聚集效应相比，其对血小板释放反应的影响比较小：RGDS抑制血小板释放反应的作用与其抗血小板聚集有关

中小企业存货管理存在的问题及对策分析

中国经济迅速发展，想要跟上社会经济发展的脚步，中小企业对存货管理的要求要随之提升到更高的层面。存货管理直接影响着企业资金运作水平和效率，中小企业加强对存货管理的重视程度是企业生存和发展的必要前提。论文描述了存货管理对中小企业自身发展的重要性，并提出了主要问题，最后提出相应的对策建议。</jats:p

波流环境下拦油栅失效问题的SPH数值模拟研究

波流环境下拦油栅失效问题的SPH数值模拟研

波流环境下海洋溢油拦截的SPH数值模拟研究

通过对SPH方法进行适当修正,对波流环境下拦油栅的运动与溢油拦截进行了数值模拟。所得到的SPH计算结果能够有效重现多种拦油栅失效模式。进一步的研究表明,除了自身的形状、尺寸和姿态角等因素外,拦油栅的拦油效果还受到多种因素的影响,包括漏油的密度和黏性、油量、水流和风浪等环境因素。通过分析对应

van der Waals液滴的光滑粒子法模拟

微液滴广泛存在于微纳米流动及生物与化学工程领域,研究其形成,变形,破碎与融合的过程与机理具有重要的科学与工程意义。本文应用光滑粒子法(SPH)分析和研究了van derWaals(vdW)流体微液滴动力学问题,包括液滴的形成,振荡,以及碰撞与融合的过程。研究表明,使用传统核函数的的光滑粒子法存在应力不稳定性,在微液滴动力学问题的数值模拟过程中产生粒子聚集现象。本文通过深入分析SPH方法应力不稳定性产生的原因,提出了一种二阶导数非负的核函数,有效消除了应力不稳定现象,能够准确模拟液滴的形成,振荡,以及碰撞与融合的过程

光滑粒子动力学sph方法应力不稳定性的一种改进方案

Smoothed particle hydrodynamics (SPH) is a Lagrangian meshfree particle method. It has special advantages in modeling large deformation and free surface flow, and has been widely applied to different problems in engineering and science. However, the classical SPH suffers from stress instability which resticts its further development and applications. The fundamental reason of stress instability is that the stress state and the kernel do not match each other. For frequently used bell-shaped kernel function, in tensile state the attraction between particles increases as particle spacing decreases, thereby leading to tensile instability. In a compressible state, the repulsive force between particles increases, and then decreases as particle spacing decreases, thereby leading to compressible instability. In this paper is presented an approach to removing stress instability in SPH by proposing a new kernel function and a modified SPH discrete form. In the modified SPH, the force between particles is always repulsive and it increases as particle spacing decreases. Two numerical examples are given to test the proposed approachs, and the obtained numerical results clearly demonstrate that the new approach can eliminate stress instability effectively