Development and Validation of a Method for Determining Tridimensional Angular Displacements with Special Applications to Ice Hockey Motions

Abstract

Tridimensional angular displacements of the skates were determined with a single cinecamera used in conjunction with two orthogonal rods attached to the rear part of the skater's boots. The method was based on the commutative law with the imposed restrictions that two of the angles were small in relation to the other one, and that a sequence of angular displacements was defined. This approach required the sole determinations of the planar coordinates of the three points delimiting the orthogonal rods. An experimental setup was designed to validate the method: the criterion angles were approximated with less than 2 degrees of error. Subsequently, the method was applied to a practical situation: the two-legged stop in ice hockey. The combination of this tridimensional method with instrumented strain gauge skates for the measurement of forces provides a new and powerful tool for performing kinetic analyses in tridimensional skating activities.     

Tennis

The study investigated differences in the one‐ (SH) and two‐handed (DH) backhands when hit flat, across‐court (AC) and down‐the‐line (DL), and with heavy topspin DL (TDL). The ability to disguise each of these backhands when hitting the above strokes was also assessed. Eighteen college‐level male tennis players, identified as having a high performance topspin SH (n = 6) or DH (n = 12) backhand drive, participated in the study. Players were required to hit three AC, DL and TDL backhands from the baseline with their preferred technique, while being filmed with two high‐speed video cameras operating at 200 Hz. The highest horizontal velocity backhand for each stroke was analysed. Results indicated that the sequential coordination of five body segments (hips, shoulder, upper arm, forearm, and hand/racquet rotations) was required for the execution of the SH stroke. The same number of segments were generally coordinated in the DH stroke (hips, shoulders, and varying degrees of upper arm and forearm rotations followed by hand/racquet movement). Mature players produced comparable racquet horizontal velocities 0.005 s prior to impact using either the SH or DH backhand technique. The SH backhand was characterised by a more rotated shoulder alignment than the DH stroke (SH: 119.1°; DH: 83.4°) at the completion of the backswing. At impact the ball was impacted further in front (SH: 0.59 m; DH: 0.40 m) and a similar distance to the side of the body (SH: 0.75 m; DH: 0.70 m). Players using the DH backhand technique delayed the horizontal acceleration of the racquet towards the ball (SH: 0.13 s; DH: 0.08 s prior to impact) and thus were capable of displaying a similar hitting motion closer to impact than players with a SH technique.     

具二维核共振条件多点边值问题解的存在性

利用Mawhin的重合度理论得到一类二阶非线性微分方程多点边值问题在二维核共振条件下解的存在性.     

C语言指针探讨

结合实例从五个方面对C语言指针进行分析和探讨:阐述C语言指针的概念和正确使用指针变量,区分指针变量和指针的指向变量的含义和用法;通过判断变量与运算符*,[]和()的结合顺序来确定变量的数据类型及指向变量或成员变量的类型;指出指针与数组的关系,通过指针来访问数组元素和采用下标法数组元素的等价关系;作为函数参数的指针变量,可以改变所指向的主调函数变量的值;指针可以实现动态存储分配,用来实现对链表的创建、插入和删除等操作。     

新旧动能转换背景下红色文化资源的开发利用——以“沂蒙精神”为例

新旧动能转换是新时代背景下第一、第二和第三产业协同融合发展的重大举措,红色文化资源作为重要生产要素,需通过“新科技”“新模式”“新资源”“新服务”等新动能的转换,实现自身政治价值、文化价值和经济价值更大更广范围的开发利用。“沂蒙精神”文化资源是红色文化资源的典型代表,该资源的开发,需结合其资源禀赋,包括自身特点、价值、类型等,通过加快数字转型、变革思维模式、完善人才战略、重构服务体系等路径,实现新旧动能的转换,完成开发利用的升级。     

非单调压缩随机算子方程组的解及其连续性

本文给出一类具有分段压缩性质的含参量随机算子方程组的解的存在性、唯一性定理,并在此基础上,讨论了其解关于参数的连续依赖性。     

社会资本和农民工城市创业——以电视剧《都市外乡人》女主角为个案

社会资本是一种无形资本,它是农民工创业的必要资源.本文尝试以社会资本为起点,以《都市外乡人》女主角为个案,考察了农民工创业过程中,社会资本的存在形式和构建,并应用边燕杰的"企业社会资本"的概念,来探讨女主角作为企业经营者,她的社会交往对于企业发展的意义.     

实对称行列式表示的二次型的特征值与标准形

设n阶实对称矩阵B的特征值为λ1，λ2，…，λn，则二次型|X 0^B X^T|的特征值为λi'=-Πk=1,k≠i n λk，使B对角化的正交变换X^T=PY^T可使它简化为|Y 0^C Y^Y|,其中C=diag(λ1,λ2,…，λn).     

武术中旋风脚的力学分析及教学

针对目前体育教学中武术是一个老师不愿教、而且不好教的问题 ,对旋风脚进行力学分析 ,探讨了教学途径、方法及要注意的问题 ,从本质上阐明旋风脚这个技术动作的发力原理 ,对于武术教学实践具有一定的指导意义     

基于三角模的模糊粗糙集与模糊关系之间的联系

研究了论域上模糊关系与（φ，T）一粗糙集上的近似算子之间的联系：给出了满足一定条件的（φ，T）一粗糙集与特殊模糊关系之间的等价条件；定义了上可定义模糊集合。并证明了它是完备的分配格。同时对其结构进行了刻画．