Si原子在Si(001)表面及其台阶附近扩散的分子动力学模拟

采用Stillinger-Weber势,利用分子动力学方法模拟了Si原子在Si(001)表面和该表面单层台阶附近扩散的动力学过程。(1)给出单个Si原子在Si(001)表面垂直于二聚体排方向扩散的扩散路径和扩散机制。Si原子在Si(001)表面垂直于二聚体排方向扩散能够减弱Si原子在Si(001)表面扩散的各向异性。(2)模拟不仅给出与以往文献中原子从SA台阶下台面扩散到上台面相同的扩散路径而且还给出原子从成键的SB台阶上台面扩散到下台面的一种新的扩散机制:增原子通过与表面原子之间的交换。从而解释实验上观察到的Si(001)表面双层原子台阶形成的机制。无论是单个Si原子在Si(001)表面垂直于二聚体排方向扩散还是在Si(001)表面的单层台阶附近扩散,增原子和表面原子之间的交换机制都起着重要的作用。     

花岗石磨抛表面粗糙度及光泽度与分形维数关系的研究

阐述了花岗石表面轮廓的特点,提出对原始轮廓曲线进行高斯滤波,然后进行粗糙度及分形计算的方法:并对花岗石表面光泽度和粗糙度、分形维数之间的关系进行了研究.通过分析认为高斯滤波适合花岗石表面轮廓的粗糙度及分形研究,计算方法可靠、简捷.     

全反射时的表面波特性

本文讨论了全反射时的表面现象,从表面波的透入深度、相速、波长以及能流等方面论述了表面皮的特性;从而说明表面波虽亦是进入光疏介质中的波场,但跟进入光疏介质中的折射波有着完全不同的性质。最后得到的结论是只有当入射角大于临界角时才有表面波存在,但在入射角等于临界角时,在光疏介质界面上所存在的波场并非表面波。     

硅氧烷表面活性剂在化妆品中的应用

介绍了硅氧烷表面活性剂的结构，种类和性能，及硅氧烷表面活性剂和其改性产品在化妆品中的使用。     

The effect of shoe type on gait in forefoot strike runners during a 50-km run

PurposeTo observe the relative change in foot-strike pattern, pressure characteristics, surface electromyography (sEMG) recordings, and stride characteristics in forefoot strike runners wearing both minimalist and traditional shoes during a 50-km run.MethodsFour experienced minimalist runners were enrolled in this study. Each runner ran a 50-km simulated run in both minimalist shoes and traditional shoes. Pressure data, sEMG recordings, and limited 3D motion capture data were collected during the initial 0.8 km and final 0.8 km for each trial.ResultsThree runners in the traditional shoe type condition and one runner in the minimalist shoe type condition demonstrated a more posterior initial contact area (midfoot strike (MFS) pattern) after the 50-km run, which was supported by increased activity of the tibialis anterior in the pre-contact phase (as per root mean square (RMS) values). In addition, in both pre- and post-run conditions, there were increased peak pressures in the minimalist shoe type, specifically in the medial forefoot. Muscle fatigue as defined by a decreased median frequency observed in isometric, constant force contractions did not correspond with our hypothesis in relation to the observed foot strike change pattern. Finally, step rate increased and step length decreased after the 50-km run in both shoe type conditions.ConclusionMore runners adopted a more posterior initial contact area after the 50-km run in the traditional shoe type than in the minimalist shoe type. The runners who adopted a more posterior initial contact area were more closely associated with an increased median frequency of the medial gastrocnemius, which suggests there may be a change in motor unit recruitment pattern during long-distance, sustained velocity running. The increased peak pressures observed in the medial forefoot in the minimalist shoe type may predispose to metatarsal stress fractures in the setting of improper training.     

Characterization of surface EMG signals using improved approximate entropy

An improved approximate entropy （ApEn） is presented and applied to characterize surface electromyography （sEMG） signals. In most previous experiments using nonlinear dynamic analysis, this certain processing was often confronted with the problem of insufficient data points and noisy circumstances, which led to unsatisfactory results. Compared with fractal dimension as well as the standard ApEn, the improved ApEn can extract information underlying sEMG signals more efficiently and accurately. The method introduced here can also be applied to other medium-sized and noisy physiological signals.