辐射带电粒子在电磁场中的运动方程

带电粒子和电磁场相互作用时,带电粒子激发电磁场的同时电磁场又对粒子有反作用,要求解带电粒子与电磁场系统的动力学问题,必须把两者之间的相互作用同时考虑,才能得出完整的粒子运动方程以及电磁场.在经典电动力学的基础上,讨论了辐射阻尼力影响下非相对论性带电粒子在复合场中的运动,导出了辐射带电粒子的完整地运动方程,模拟了带电粒子对外辐射的电磁能量.     

Lower leg and foot contributions to turnout in female pre-professional dancers: A 3D kinematic analysis

Turnout is a central element of classical ballet which involves sustained external rotation of the lower limbs during dance movements. Lower leg and foot compensation mechanisms which are often used to increase turnout have been attributed to the high incidence of lower limb injury in dancers. Evaluation of dancers’ leg posture is needed to provide insight into the lower limb kinematic strategies used to achieve turnout. The primary purpose of this study was to use 3D kinematic analyses to determine the lower leg and foot compensations that are incorporated by female university dancers to accentuate their turnout. Active and passive external tibiofemoral rotation (TFR) was also measured. A moderate-strong negative relationship was observed between hip external rotation (HER) and foot abduction in the three first position conditions. A moderate negative relationship was found between passive TFR and foot abduction in all first position conditions. Our findings suggest dancers are more likely to pronate, than rotate the knee to compensate for limited HER. Dancers with a limited capacity to pronate may force additional rotation via the knee. Ongoing research would benefit from more in-depth analyses of the foot/ankle complex using a multi-segment foot model.     

略论梁启超历史进化论及其动力因

梁启超认为历史是“进化”的，它具有进步性和曲折性，呈无极限之螺旋状而非直线上升。历史“进化”之动力因多种多样，其中最主要的是“革”和“力”。梁的历史进化论，激励着当时中国人救亡保种的斗争活动，具有重要的时代意义。     

机械结构对两轮移动足球机器人运动精度影响研究

以自行设计的两轮移动足球机器人的机械结构为对象,从理想情况和实际情况分别进行机器人小车的运动学分析与建模,进行比较并得出结论。分析了驱动轮半径对运动学模型的影响。最后从机械结构的设计上讨论了对小车运动精度的影响,并提出相关改进措施。     

A fast motion estimation algorithm for mobile communications

The limitation of processing power, battery life and memory capacity of portable terminals requires reducing encoding complexity in mobile communications. Motion estimation (ME) is the most computationally intensive module in a typical video codec, which determines not only the encoder's performance but also the reconstructed video quality. In this paper, a fast ME algorithm for H.264/AVC baseline profile coding is proposed based on the analysis of motion vector field and error surface, and the statistical distributions of different type macroblocks (MBs). Simulation results showed that: in comparison with MVFAST, the proposed algorithm can decrease the computational load over 7.2% with no requirement of expanding memory capacity while maintaining the same video quality as MVFAST. Furthermore, its simplicity makes it easy to be implemented on hardware.     

The effect of different foot and hand set-up positions on backstroke start performance

Foot and hand set-up position effects were analysed on backstroke start performance. Ten swimmers randomly completed 27 starts grouped in trials (n = 3) of each variation, changing foot (totally immersed, partially and totally emerged) and hand (lowest, highest horizontal and vertical) positioning. Fifteen cameras recorded kinematics, and four force plates collected hands and feet kinetics. Standardised mean difference and 95% confidence intervals were used. Variations with feet immersed have shown lower vertical centre of mass (CM) set-up position (0.16 m), vertical impulse exerted at the hands, horizontal and vertical impulse exerted at the feet (0.28, 0.41, 0.16 N/BW.s, respectively) than feet emerged with hands horizontal and vertically positioned. Most variations with feet partially emerged exhibited higher and lesser vertical impulse exerted at hands than feet immersed and emerged (e.g. vertical handgrip, 0.13, 0.15 N/BW.s, respectively). Variation with feet emerged and hands on the lowest horizontal handgrip depicted shorter horizontal (0.23, 0.26 m) and vertical CM positioning at flight (0.16, 0.15 m) than the highest horizontal and vertical handgrip, respectively. Start variations have not affected 15-m time. Variations with feet partially or totally emerged depicted advantages, but focusing on the entry and underwater biomechanics is relevant for a shorter start time.     

女性情感和心理视像下的欲望简史——对《无穷动》的一种深度解读

影片《无穷动》展现了“禁欲”和“纵欲”两种时代氛围中,“欲望”的实现路径和表述模式发生的重大变化。“欲望”在影片中成为一种人性催化剂和显影剂,通过对“欲望”、“深描”以及对“欲望表达模式”的辨析,揭示了中国现代化转型期间特有的身份政治和性别政治的交汇和斗争,这种交汇和斗争极具革命意义和颠覆价值。     

基于虚拟仪器的电主轴性能测试平台的研制

电主轴是数控机床三大高新技术之一,作为数控机床核心功能部件,其国产化对我国数控机床发展有着十分重要的意义。本文介绍了电主轴主要性能参数指标,并设计基于虚拟仪器的电主轴性能测试平台,应用于生产过程中的质量控制。     

Adaptive robust approximate constraint-following control for mechanical systems

We formulate control problems of mechanical systems as constraint following. The system contains uncertainty which is (possibly fast) time-varying. It is unknown but bounded. The bound is, however, unknown. The objective is to design control which renders approximate constraint following. Adaptive laws are constructed. The controls are then based on the adaptive parameters. We are able to demonstrate guaranteed system performance, regardless of the uncertainty.