Determinants of the half-turn with the ball in sub-elite youth soccer players

We explored the biomechanics of the 180° change-of-direction with the ball (half-turn) in soccer. We aimed at identifying movement strategies which enhance the players’ half-turning performance, by characterising technique kinematics and understanding the structure of biomechanical and anthropometrics variables. Ten Under-13 sub-elite male players were recorded with an optoelectronic motion analyser while performing a 5-m straight dribbling followed by a half-turn with the sole. Joints kinematics differences between faster and slower trials were found in support-side hip rotation, driving-side hip adduction, trunk flexion and rotation, and arms abduction. To unveil the data-set structure, a principal component (PC) analysis and a stepwise linear discriminant analysis were performed using 30 biomechanical parameters and four anthropometric variables for each trial. Seven retained PCs explained 79% of the overall variability, featuring combinations of original variables that help in understanding the factors facilitating fast half-turns: keeping short steps, minimising lateral and forward body movements, and centre-of-mass lowering, even with ample lower limbs ranges of motion (RoM); abducting the upper limbs while limiting trunk flexion and pelvic inclination RoM. Balance and task-constrained exercises may be proposed to improve this technique. Moreover, a quantitative knowledge of the movement structure could give coaches objective insights to better instruct young players.     

刚体定点运动的有限转角不是轴矢量

传统结论仍然正确：刚体定点运动的有限转角不是轴矢量．     

水稻插秧机后插式分插机构研究

本文用计算机对水稻插秧机后插式分插机构进行了分析研究。通过秧针端点运动轨迹上的6个特定点，分析了后插式分插机构的运动学和动力学。经理论分析和田间试验表明，后插式分插机构的结构参数选择是合理的，插秧性能是优良的。     

纳苏彝语的空间位移

动态空间主要指语言表达中焦点（F）的空间位移,常用位移动词、词缀、连动结构等表示。纳苏彝语的空间位移主要有表达人体空间、动物体空间,以及无生命物体的不同位移形式。纳苏彝语的不同位移,一是通过动词前加方向前缀构成,表示相对于说话者或地势来说行为所表示的是空间进行的方向。其次是连动结构表示位移,即在行为动词或位移动词后加方向动词“来”或“去”表示位移,表达空间位移的向心和离心。     

用Pro/Engineer实现平面机构的虚拟运动

在《机械设计基础》课程中，平面机构由于其运动相对比较复杂，学生很难想象、掌握其运动过程。本介绍了利用Pro/Engineer提供的Mechaism功能实现平面机构虚拟运动的方法和过程，并给出了三个具体的图例。     

分数布朗运动环境中混合期权的保险精算定价

利用保险精算方法,在假设标的资产价格服从几何分数布朗运动的情况下,推导出了混合期权的定价公式,并且假设股票预期收益率、波动率和无风险利率均为时间的函数,推导了参数依赖于时间的混合期权的定价公式.     

Comparative study between fully tethered and free swimming at different paces of swimming in front crawl

Tethered swimming is a method often used to measure or enhance the physical and technical resources of swimmers. Although it is highlighted that the technique used in tethered swimming is probably different from that used in free conditions, there are few comparative studies on this subject. The current study aims to compare fully tethered and free swimming based on kinematic hand parameters (orientation, velocity and acceleration of the hand, sweepback and angle of attack), which are known to act directly on the generation of propulsive forces. The results show that there are significant differences during the stretch and catch phases but less during the insweep and upsweep phases. Tethered swimming makes it possible to estimate the propelling forces generated by the hand in free swimming at distance and middle-distance paces, but overestimates it at sprint pace. However, in view of the modifications of the kinematic parameters, it should not be used under repeated conditions of use, such as for the development of swimmers’ capacity.     

X5032立式铣床主传动系统正交齿轮参数化实体建模及动态仿真

通过分析X5032立式铣床主传动系统,利用VC＋＋6.0作为SolidWorks的开发工具对直齿圆锥齿轮进行参数化建模,并且对零件进行虚拟装配和传动系统的动态仿真,结合Animator插件对正交轴圆锥齿轮的传动过程进行实时录制,实现动态仿真,为立式铣床的传动系统中正交齿轮的受力分析及其他的力学性能分析奠定了理论基础.     

简谐振动初位相的确定

为解决简谐振动三个特征量中较难确定的初位相,分别运用分析法、图线分析法、旋转矢量法、分析旋转矢量法等方法进行了讨论,并介绍了一些方便、快捷的确定初位相的方法.     

艺术体操项目计算机辅助动作编排及演示系统研究

针对我国艺术体操项目中集体项目的编排水平落后于欧洲强队的现状，探索了计算机技术在编排方面的辅助作用，特别是实现了一个应用计算机虚拟现实技术开发艺术体操集体项目的编排(演示)系统，它由二维平面辅助设计系统、三维动作演示系统、三维器械演示系统组成，该系统使得艺术体操集体项目的编排过程具有可视化和可编辑性，编排结果具有可重用性。使用该系统不仅可以缩短编排周期，而且还可以拓展教练员的编排空间。