A review of tennis racket performance parameters

The application of advanced engineering to tennis racket design has influenced the nature of the sport. As a result, the International Tennis Federation has established rules to limit performance, with the aim of protecting the nature of the game. This paper illustrates how changes to the racket affect the player-racket system. The review integrates engineering and biomechanical issues related to tennis racket performance, covering the biomechanical characteristics of tennis strokes, tennis racket performance, the effect of racket parameters on ball rebound and biomechanical interactions. Racket properties influence the rebound of the ball. Ball rebound speed increases with frame stiffness and as string tension decreases. Reducing inter-string contacting forces increases rebound topspin. Historical trends and predictive modelling indicate swingweights of around 0.030–0.035 kg/m² are best for high ball speed and accuracy. To fully understand the effect of their design changes, engineers should use impact conditions in their experiments, or models, which reflect those of actual tennis strokes. Sports engineers, therefore, benefit from working closely with biomechanists to ensure realistic impact conditions.     

Synchronized lower limb kinematics with pelvis orientation achieves the non-rotational shot

A non-rotational (NR) shot is now a well-known scoring move in soccer. To execute the NR shot, it is necessary to deprive the ball of any rotational forces during the impact phase. To execute the NR shot, it is natural that the force vector acting from the foot would pass through the ball’s center of gravity; however, the coordinated motion of the lower limb joint’s angular displacement and the pelvis is still unclear. The aim of this study is to estimate the coordinated leg and pelvis motion during the NR shot as compared to that during instep kicking. Four right-leg dominant college league players were asked to perform a NR shot and an instep kick a total of 10 times each. Hip, knee, and ankle joint angular displacements in the sagittal plane and pelvis yaw and roll rotational motions during both types of kicks were calculated with 14 IR reflective markers using a 3D real-time motion analysis system with a 250-Hz sampling. The Euclidean distances of the joint space of the NR shot and the instep kick were also calculated to detect similarities in the coordinated motion of the lower limb. The results showed that the lower limb joint motions in the sagittal plane were not different; however, the pelvis roll and yaw motions were apparently different, and these phenomena could simulate a pendulum motion with changes in both the vertical and horizontal displacements. These results suggest that the coordinated motion of the lower limb joint’s angular displacement shows high similarity between the NR shot and the instep kick, and the pelvis roll and yaw synchronized orientation is essential for achieving the NR shot.     

Elite wheelchair rugby: a quantitative analysis of chair configuration in Australia

Limited recommendations of wheelchair configurations for court sports have been identified in the published literature. To accommodate the wide range of impairments in wheelchair rugby, players are given a point score that reflects their impairment. Players have regularly been grouped as high-, mid-, or low-point players in research, with high-point players having greater levels of muscle function compared with other classifications. This research documented the wheelchair configurations of elite Australian wheelchair rugby players across classification groups. Significant differences (p < 0.05) were found for increased seat height and decreased seat depth for high-point players compared with low- and mid-point groups, respectively. Low-point players displayed reduced wheelchair mass compared with high- and mid-point players, as well as increased frame length. Camber angles showed no significant differences across the classification groups. The incorporation of anthropometric measures, such as the elbow angle at the top dead center, was also investigated. While elbow angle showed no significant differences, seat height-to-total arm length ratio was higher for high-point players. Participants also completed surveys detailing their perception of the effect of altering wheelchair configurations. It is suggested that wheelchair configurations should consider an individual’s anthropometrics, impairment, training history, and court role to promote optimal performance, with predictive modeling having the potential to reduce the associated time and cost.     

Direct skeletal attachment prosthesis for the amputee athlete: the unknown potential

Lower limb amputees often experience complications with the use of conventional socket-type prostheses, which further reduce their already compromised ability to perform the activities of daily living, or to participate in sporting activities. During the last two decades, a new technology of direct skeletal attachment (osseointegration) of prosthesis to the femoral residuum has been developed. The aim of this research was to assess the implant design, surgery protocols, and functional testing of this new technology on the first 100 patients using the Integral Leg Prosthesis procedure. This new knowledge can guide future engineering developments of osseointegration within the sporting arena. Between 1999 and 2013, direct skeletal implantation was performed on 112 amputees, from two centres in Germany and Australia. From the experience of the surgical team, modifications were made to the implant design. This re-engineering of the implant has reduced the surgical revisions due to infection from 29 % with the early implant design down to 7 %. The functional testing of the 34 Australian cases were assessed pre- and 12 months post-implant with significant improvements of one complete K-scale; the Q-TFA measures increased (50.9–86.7), whilst the Timed Up and Go decreased significantly (12.43 s ± 3.89 to 8.03 s ± 2.80), and the 6 min walk increased (304.0–383.9 m). From these findings, osseointegration technology is realistically the way of the future for amputee athletes. Further refinement of the implant design and sports-specific functional testing are required to define the potential of this technology.     

论刑事诉讼中的“举证责任”——我国与英美法系国家“举证责任”理论之比较

由于诉讼模式和历史习惯的差异,各国法学家关于"举证责任"的观点大相径庭。通过从实体和程序两个方面对我国和英美法系国家的"举证责任"的理论进行比较,力图对我国"举证责任"的理论和立法技术起到借鉴作用。     

略论国际恐怖主义

国际恐怖主义是世界上国家、民族、阶级、宗教问题等各种尖锐矛盾绚反映，是世界范围内南北经济、政治发展不平衡生成的毒瘤。目前，国际社会越来越重视反恐斗争中国际合作问题，并采取了一系列打击恐怖活动的措施。     

乙烯式卤代烃亲核取代历程讨论

乙烯式卤代烃难发生亲核取代反应,反应历程研究受到限制.在双键碳中引入超离去基,反应顺利进行,且立体构型发生反转,证明该反应为SN2历程.     

当前沿海开放城市的社区教育构架研究

本文以社会主义市场经济的发展和近年来经济建设的巨大成就为背景,立足于沿海社区教育发展现实,着眼于近期和将来一段时间社区教育发展趋势,对未来社区教育系统构架和学制系统进行研究,力图揭示未来社区教育构架模型。     

浅谈计算机辅助数学教学的优越性

随着计算机在校园的广泛应用,计算机辅助教学已经受到社会各界的普遍关注,本文从六个方面阐述了计算机辅助数学教学的优越性.     

加强和改进大学生思想政治教育要把握规律性

2004年8月,中共中央、国务院发出了《关于进一步加强和改进大学生思想政治教育的意见》。2005年2月,中宣部和教育部提出《关于进一步加强和改进高等学校思想政治理论课的意见》。这是新世纪新阶段,我国政治生活中的一件大事。认真学习领会、贯彻落实这两个文件的精神和要求,使大学生思想政治教育得到进一步加强和改进,是高校教师面临的一项重要任务。我们要认识和把握大学生思想政治教育的规律,从实际出发,认真完成党和人民交给我们的这项任务。一、提高对加强和改进大学生思想政治教育意义的认识邓小平说:思想政治工作是我们的优势,什么时…