Comparison of biomechanical characteristics between male and female elite fast bowlers

This study investigated ball release speed and performance kinematics between elite male and female cricket fast bowlers. Fifty-five kinematic parameters were collected for 20 male and 20 female elite fast bowlers. Group means were analysed statistically using an independent samples approach to identify differences. Significant differences were found between: ball release speed; run-up speed; the kinematics at back foot contact (BFC), front foot contact (FFC), and ball release (BR); and the timings between these key instants. These results indicate that the female bowlers generated less whole body linear momentum during the run-up than the males. The male bowlers also utilised a technique between BFC and FFC which more efficiently maintained linear momentum compared to the females. As a consequence of this difference in linear momentum at FFC, the females typically adopted a technique more akin to throwing where ball release speed was contributed to by both the whole body angular momentum and the large rotator muscles used to rotate the pelvis and torso segments about the longitudinal axis. This knowledge is likely to be useful in the coaching of female fast bowlers although future studies are required to understand the effects of anthropometric and strength constraints on fast bowling performance.     

基于缸内压力重构的船舶柴油机燃烧起终点识别

为对船舶柴油机缸内燃烧过程进行快速诊断,提出一种船舶柴油机燃烧起终点识别的新方法。该方法通过构建韦伯燃烧模型模拟缸内压力曲线,然后建立缸内燃烧和散热模型。根据计算出的燃烧放热率、缸内温度和缸内压力升高率,分析其燃烧起点,并通过缸内压力变异分析研究燃烧终点。结果表明:与实测压力相比,用韦伯燃烧模型得到的压力在燃烧相和膨胀相上呈现出较好的相似性,可替代实测压力对其波动进行修正,且计算时间短。船舶柴油机瞬时燃烧放热率、缸内温度、缸内压力升高率均能提供燃烧起点特征信息;在燃烧终点缸内压力变异系数有突变现象;瞬时传热对燃烧起点无直接影响。两种传热模型均表明船舶柴油机样机缸内燃烧的速燃期和缓燃期均由两个阶段组成。     

影响大强度负荷后血乳酸清除速率的因素

为揭示大强度负荷后放松活动强度、运动员运动水平和机能水平与血乳酸清除速率之间的关系,选择２２名游泳运动员进行实验。结果表明：放松活动强度影响血乳酸清除速率,血乳酸下降曲线存在“拐点”现象,其位置与运动员个体训练水平,机体血乳酸清除能力有关;运动员运动等级水平高、ＩＬＡＴ指数小则血乳酸清除能力强。     

我国优秀女子铁饼运动员最后用力阶段身体重心运动节奏特征分析

采用文献资料法、三维录像解析法以及数理统计等研究方法,以2007年全国田径锦标赛女子铁饼前8名的投掷技术为研究对象,对我国优秀女子铁饼运动员在掷铁饼最后用力阶段身体重心的时间、空间以及速度节奏进行了定量分析.同时采用Person相关分析对我国优秀女子铁饼运动员最后用力阶段身体重心的时间、空间以及速度的变化与投掷成绩进行了检验,提出了我国优秀女子铁饼运动员最后用力阶段身体重心节奏变化的量化指标.     

掷标枪最后用力左侧支撑的作用

从生物力学角度对掷标枪左侧支撑动作进行了全面分析 ,论证了左侧支撑是掷标枪技术中的重要技术环节。     

关于古代希腊、罗马解放奴隶现象的思考

奴隶解放是奴隶制社会的一个重要现象。从军事、政治、经济、奴隶主个人情感及娱乐等方面探讨了奴隶制国家和奴隶主个人解放奴隶的原因。     

对我国优秀女子标枪运动员最后用力阶段右肩与右髋速度特征的三维运动学分析

运用三维运动学分析方法对参加第 13届亚运会的我国 6名优秀女子标枪运动员的最后用力阶段的技术动作进行解析 ,结果表明 :最后用力阶段右髋动作加快与制动的时机不甚理想 ,躯干相关肌群有过早收缩发力的现象 ,从而影响右肩速度的变化 ;发现右肩速度超过右髋速度的时机也不理想 ,右肩与右髋的动量传递效果与右脚的拖拉制动动作连接不紧 ,以至减小了最后用力的效果     

热力循环及总能系统学科发展战略

热力循环与总能系统是本世纪能源与环境科学的主要议题之一,也是在国家中长期科技规划中位于优先位置的需要关注的重点。本文分析了该学科的地位和作用,指出了领域学科交叉的发展特点,提出了学科发展方向:能的梯级利用与热力循环创新、能量释放的新机理、中低温能源转换利用与正逆耦合循环、多能源综合互补系统、控制污染排放的新途径。本文提出的热力循环与总能系统发展战略旨在开辟节约能源、能源与环境协调发展的新方向。     

Scaling the cricket pitch to fit junior players

ABSTRACT

Studies in several sports have shown the benefits of adapting the playing environment to fit junior players. Frequently the changes are pragmatic choices based on space constraints or existing line markings, or the result of simple scaling based on stature. In this study, a method of scaling the cricket pitch length is presented which is based on the age-specific size and performance of the bowlers and batters. The objective was a pitch length which enabled young bowlers to bowl good length deliveries while releasing the ball at a more downward angle, similar to elite bowlers. The steeper release angle has the benefit of reducing the sensitivity of the ball flight distance to the variability of ball release. Based on data from county standard under-10 and under-11 players a pitch length of 16.22 yards (14.83 m) was calculated, 19% shorter than previously recommended for under-11s in England. A shorter pitch also increases the temporal challenge for batters, encouraging a wider variety of shots and improved anticipation skills. Pitch lengths scaled in this way to fit the players’ abilities as they develop will enable a more consistent ball release by bowlers and more consistent temporal demand for batters.     

张力索网结构零应力态与预应力态计算方法

研究目的：减小张力索网结构所求实际预应力与预期预应力之间的差异,并更完善地描述结构力学行为。创新要点：提出张力索网结构全过程分析概念,并用10个状态描述了其物理或分析的状态,以及15个过程揭示了状态间内在的逻辑关系和力学分析理论;在应力释放分析中,采用逆分析法提出了一种用于求解合理零应力状态的迭代计算方法;在预应力成形分析中,为获取预应力状态建立了另一种迭代计算方法。研究方法：应力释放分析主要包括四个步骤：构件无应力长度及伸长量计算,最小范数最小二乘法,数值迭代方法,和执行程序（图4）;预应力成形分析在能量方程的基础上提出了控制方程的显式表达式,并为避免初始刚度矩阵的奇异问题而采用了合理自应力模态（图5）。重要结论：比较本文提出的计算方法与动力松弛法得到的零应力态,发现结果吻合良好,证明计算过程收敛性良好且结果准确。在预应力成形分析中,采用本文迭代方法可以有效消除所求实际预应力与预期预应力之间的差异。此外,提出的所有计算方法都符合模块化流程,具有广泛适用性。