电机驱动微装配在双光子制备微结构中的应用

对微结构的制作、微装配系统进行了研究. 采用飞秒激光双光子聚合微加工技术制作有底座、精细的三维立体“拱形”微结构, 其高250μm、长300μm、厚50μm. 将此微结构与实验室自主搭建的二维微装配平台相结合, 利用自主编程的人机交互界面驱动步进电机, 远程操控微装配设备; 将荧光闪烁陶瓷粉末装配到微结构中, 对装配后的微结构进行荧光光谱表征发现, 纯荧光粉末和微结构中的荧光粉末的发射光谱在测量误差范围内基本一致, 表明荧光粉末的光学性质未发生改变. 利用该装置可以将各类微纳米级材料和微结构进行装配, 形成含有不同材料的微结构系统.     

Change in motor cortex activation for muscle release by motor learning

For central nervous system disorders'' rehabilitation, it is important to accurately understand motor control and implement an appropriate motor learning process to induce neuroplastic changes. The neurophysiological studies have revealed that neural control mechanisms are crucial during both the onset of muscular activities and muscle release after contraction. When performing various movements during daily activities, muscle relaxation control enables precise force output and timing control. Moreover, surround inhibition is a functional mechanism in the motor system. Surround inhibition of the motor system may be involved in the selective execution of desired movements. This review demonstrates cortical excitability resulting from motor learning, movement control mechanisms including muscle relaxation and the suppression of nontarget muscle groups, and the voluntary drive''s importance that is required for movement.     

Spontaneous translation of nanodroplet over a heterogeneous surface due to thermal cycles: role of solid–liquid interfacial fluctuations

ABSTRACT

We study the molecular-scale features of the solid surface that result in the spontaneous motion of a nanodroplet due to the periodic variation of temperature. We first employ a thermodynamic model to predict the variation of solid–fluid interfacial properties that can result in the above motion. The model identifies a composite (surface couple) made of two surfaces that are characterised by a large difference between the entropic parts of the solid–liquid interfacial free energies. In order to understand the molecular-scale features of the two surfaces that may form a surface couple, we performed grand canonical Monte Carlo simulations of Lennard Jones fluid and crystalline surfaces made of Lennard Jones-like atoms. We then used the cumulant expansions of the perturbation formulas to divide the interfacial entropy into two parts: The one that is directly affected by the solid–fluid attraction (direct part), and the other (indirect part) that is indirectly affected by the solid–fluid attraction via the alteration of interfacial fluctuations. Our results indicate that two surfaces form a surface couple if the differences between their chemical natures lead to large differences in the indirect part of the interfacial entropy, while the direct part remains relatively unaffected.     

An Improved Composite Multiscale Fuzzy Entropy for Feature Extraction of MI-EEG

Motor Imagery Electroencephalography (MI-EEG) has shown good prospects in neurorehabilitation, and the entropy-based nonlinear dynamic methods have been successfully applied to feature extraction of MI-EEG. Especially based on Multiscale Fuzzy Entropy (MFE), the fuzzy entropies of the τ coarse-grained sequences in τ scale are calculated and averaged to develop the Composite MFE (CMFE) with more feature information. However, the coarse-grained process fails to match the nonstationary characteristic of MI-EEG by a mean filtering algorithm. In this paper, CMFE is improved by assigning the different weight factors to the different sample points in the coarse-grained process, i.e., using the weighted mean filters instead of the original mean filters, which is conductive to signal filtering and feature extraction, and the resulting personalized Weighted CMFE (WCMFE) is more suitable to represent the nonstationary MI-EEG for different subjects. All the WCMFEs of multi-channel MI-EEG are fused in serial to construct the feature vector, which is evaluated by a back-propagation neural network. Based on a public dataset, extensive experiments are conducted, yielding a relatively higher classification accuracy by WCMFE, and the statistical significance is examined by two-sample t-test. The results suggest that WCMFE is superior to the other entropy-based and traditional feature extraction methods.     

Effective synthesis of novel O-acetylated compounds over ZrO2-Al2O3 solid acid

The solid acids such as ZrO₂, Al₂O₃ and ZrO₂-Al₂O₃ containing different ZrO₂ loadings (10–80 mol%) were prepared by solution combustion method (SCM) and characterized for their total surface acidity by NH₃-TPD/n-butylamine back titration method and crystallinity by powder X-ray diffraction (PXRD) technique. These solid acids were evaluated for their catalytic activity in the synthesis of novel O-acetylated products from substituted phenols, pyridine alcohols and aryl alcohols with acetic anhydride (AA) as an acetylating agent. The reaction conditions were optimized by varying the catalyst, molar ratio of the reactants, reaction temperature and amount of the catalyst. All the solid acids used in this study exhibited good catalytic activity in the reaction. In particular, ZrO₂-Al₂O₃ containing 80 mol% of ZrO₂ was found to be highly active in the acetylation reaction with high yield of acetylated products. Triangular correlation between the surface acidity, crystallinity and catalytic activity of solid acids was observed. These solid acids were found to be reactivable and reusable.     

一种创新型感应电机调速系统的设计与实现

鉴于传统电力电子相关课程实验既无法直观了解电路内部构造,也不能有效提升实际动手能力的情况,设计了一种基于实验室环境的开放式创新型感应电机变频调速系统,改造了主电路和控制电路的电源,在适应实验室用电环境的同时,能实现主电路低压可测量和提升学生实验的安全性;并设计了采样电路和保护电路,能加深学生对电路的了解,增强实际动手能力.经实验验证,该系统能完成多段速运动控制、模拟量与数字量给定调速等相关实验.     

由定子电流信号分析陀螺电机滚珠轴承故障诊断与分类（英文）

在陀螺电机中,轴承故障是最普遍的失效形式。针对陀螺电机球轴承中各组成部分出现故障难以区分,而更换整套轴承又造成巨大浪费的问题,提出了一种基于电流信号分析的陀螺电机轴承故障分类方法。该方法通过采集定子电流信号,并应用数学分析工具,提取出定子电流的特征信号。通过使用顺序递推法排除了冗余和无效特征,然后用最佳的特征信号建立特征空间。通过使用隐马尔科夫模型,对轴承的典型故障(外环故障、内环故障、球故障和保持架故障)进行了准确的分类。该方法的有效性在一台具有不同轴承故障的直流无刷陀螺电机上得到验证,实验结果显示分类的正确率达到97.1%。     

基于电磁力近似算法的驱动电机NVH快速仿真方法

电动汽车驱动电机产生的电磁噪声是汽车NVH关注的重点问题,对其进行全转速段多工况NVH仿真通常需要耗费大量时间和计算资源。该文通过有限单元分析揭示了电机气隙电磁力随转速变化的规律,并根据这一规律提出了基于外特性曲线的电磁力时间缩放及插值的近似算法。文章采用电磁力到结构网格的映射算法对结构振动有限元模型进行激励力加载,使用声场有限元方法计算电机的辐射噪声,最终实现了车用驱动电机的电磁振动及噪声的快速仿真。使用该方法对车用电机进行全转速段振动噪声仿真,可大大压缩多工况电磁场有限元分析所需的计算时间,提升仿真效率。     

无溶剂热处理固相转化法简易制备沸石咪唑酯骨架材料

设计开发了一种无需溶剂，通过热处理固相转化制备沸石咪唑酯骨架材料（ZIFs）的简易方法.该方法无需溶剂及其它预处理，只需将金属源与有机配体固相混合后于低温（200℃）热处理即可实现多孔晶体材料的制备.所合成材料H-ZIF-67为具有方纳石拓扑结构的纳米晶体，与传统方式合成的ZIFs材料一致.粉末X射线衍射（PXRD）分析结果表明产物的晶体结构与标准ZIFs谱图一致.通过扫描电子显微镜（SEM）、透射电子显微镜（TEM）、N₂吸附-脱附分析、热重分析（TGA）和傅里叶变换红外光谱（FTIR）等手段对合成的材料进行了表征，发现H-ZIF-67材料具有与ZIFs材料类似的特性.该方法经济、高效，摒弃了传统方法合成ZIFs材料周期长、处理过程复杂的弊端，为ZIFs材料的量产提供了新思路.     

Application of acoustic methods for a non-destructive evaluation of the elastic properties of several typologies of materials

In solid phase materials, differently from what happens in the fluid phase, elastic waves propagate both through longitudinal and transverse waves. From the speed of propagation of longitudinal and transverse waves, it is possible to evaluate important elastic properties of the solids under study, namely the Young’s modulus, the Poisson’s coefficient, the bulk modulus and the shear modulus. This work suggests an accurate method for measuring wave propagation speeds in homogeneous and non-homogeneous materials with the purpose to evaluate their mechanical properties and the associated uncertainty.First of all, to assess the performance of the proposed methodology, based on the “pulse-echo” technique, in terms of accuracy and precision, measurements of wave propagation speeds have been carried out, in atmospheric conditions, in well-known homogeneous and isotropic materials, such as copper, aluminum, stainless steel and also polymethyl methacrylate (Plexiglas®), Teflon® and optical glass BK7. These results were compared with the values reported in literature (if present), showing how published speed of sound data are very disperse and not so reliable owing to the lack of a precise uncertainty evaluation and of the temperature value associated to the measurement. Then, the same experimental apparatus was used for measuring speed of sound as a function of temperature (from 274.15 to 313.15 K) for 304 stainless steel and oxygen free copper, showing a good accuracy of the results also for temperature conditions far from ambient. Finally, the same procedure was applied to a non-homogeneous solid, obtaining some very preliminary results in typical mediterranean building material, as Carrara marble.