The role of pelvis-thorax coupling in controlling within-golf club swing speed

Pelvis-thorax coordination has been recognised to be associated with swing speed. Increasing angular separation between the pelvis and thorax has been thought to initiate the stretch shortening cycle and lead to increased clubhead speed. The purpose of this study was to determine whether pelvis-thorax coupling played a significant role in regulating clubhead speed, in a group of low-handicap golfers (mean handicap = 4.1). Sixteen participants played shots to target distances determined based on their typical 5- and 6-iron shot distances. Half the difference between median 5- and 6-iron distance for each participant was used to create three swing effort conditions: “minus”, “norm”, and “plus”. Ten shots were played under each swing effort condition using both the 5-iron and 6-iron, resulting in six shot categories and 60 shots per participant. No significant differences were found for X-factor for club or swing effort. X-factor stretch showed significant differences for club and swing effort. Continuous relative phase (CRP) results mainly showed evidence of the stretch shortening cycle in the downswing and that it was more pronounced late in the downswing as swing effort increased. Substantial inter-individual CRP variability demonstrated the need for individual analyses when investigating coordination in the golf swing.     

相对论效应对含碘复合物非键作用的影响研究

本文通过几个简单含碘复合物的相对论密度泛函计算,考察了相对论效应对碘键作用的影响。最后结果表明相对论效应对碘键作用影响较小,一般计算时可以忽略,采用pbeO／6—311G^＊或pvDZ、pvTZ基组可以很好地描述含碘复合物,而选择好的相关能方法则是成功计算相对论效应的关键。     

Influence of birth quarter on the rate of physical activities and sports participation

Abstract

The purpose of this study was to assess the potential influence of birth quarter on the frequency of physical activity and participation in specific activities during adulthood. We used data from one national and one provincial survey, the 2005 Canadian Community Health Survey and the 1998 Quebec Social and Health Survey (Enquête sociale et de santé du Québec) respectively. We analysed the distribution of participants at each level of practice of a given leisure activity and work-related physical activity. In the Canadian Community Health Survey, a relative age effect was found for participation in soccer in the 25- to 60-year-old population. However, for volleyball, a significant relative age effect was also observed but with over-representation of the last quarters of the year for the whole population and for men aged 12–60 years. In the Quebec Social and Health Survey, significant differences in the frequency of distribution without a relative age effect were revealed for participation in women's ice hockey, work-related physical activity level, and stage of change for physical activity. Overall, the data indicate that the systematic relative age effect reported in other studies for some competitive sports, such as ice hockey and soccer, is not as prevalent in leisure physical activities during adulthood. This may reflect lower competitive selection and attrition in population physical activity compared with competitive sports in younger athletes.     

A behavioural dynamic model of the relative age effect

Abstract

The relationship between date of birth and success in a variety of sports, including hockey, is well established. This phenomenon is known as the relative age effect (RAE). We model the RAE in Canadian youth hockey as a positive feedback loop where an initial age advantage is reinforced through additional training and playing opportunities based on perceived skill superiority. The same causal mechanism leads to a higher quit rate for relatively younger players. Our model effectively replicates the birth month distribution of Canadian National Hockey League players (R² = 86.79%) when driven by Canadian birth distributions. We use this model to evaluate three policies that aim to lessen the RAE. All of the policies reduce the RAE with a significant delay. The most effective policy is a combination of providing additional support to age disadvantaged children and rotating the cut-off date for youth leagues between January 1st and July 1st annually. In equilibrium, this approach leads to a 96% reduction in the RAE compared to the base case.     

用Excel内置函数管理学生成绩——献给一线的中小学教师

2011年至2012年,我校连续两年承担了黔南州小学紧缺学科教师培训工作,我系承担了信息技术学科的培训任务。在培训中,了解到老师们在Excel函数应用这一块是一空白,尤其是用Excel内置函数管理学生的考试成绩。作为一名小学教师,如果你想使你的工作轻松一点,那么,这是一篇值得你认真学习Excel常用函数的文章。     

A practical iterative two-view metric reconstruction with uncalibrated cameras

This paper presents a practical iterative algorithm for two-view metric reconstruction without any prior knowledge about the scene and motion in a nonsingular geometry configuration. The principal point is assumed to locate at the image center with zero skew and the same aspect ratio, and the interior parameters are fixed, so the self-calibration becomes focal-length cali- bration. Existing focal length calibration methods are direct solutions of a quadric composed of fundamental matrix, which are sensitive to noise. A quaternion-based linear iterative Least-Square Method is proposed in this paper, and one-dimensional searching for optimal focal length in a constrained region instead of solving optimization problems with inequality constraints is applied to simplify the computation complexity, then unique rotational matrix and translate vector are recovered. Experiments with simulation data and real images are given to verify the algorithm.     

经典力学的剖析与发展

论证了惯性质量，引力质量，惯性参照系，惯性力的不合理必，确定了物质质量的概念，统一了惯性参数照系和非惯性参照系，否定了力的绝对性，引出了加速相对性原理和力相对性原理，提出了相对力，相对加速度，相对参照系和绝对力，绝对加速度，绝对参照系的新概念，建立起初步绝对相对论力学。     

相对价格视角下中国国内市场整合水平测度?

基于相对价格的视角,研究了1992－2011年间中国国内市场整合水平及其发展趋势,结果显示：这一时期中国国内市场整合水平是逐渐提高的,但市场整合进程并非一帆风顺。虽然各省区在此期间市场整合走势与全国走势基本相同,但不同省区的市场整合进程存在差异,特别是京津沪三个市的市场整合水平偏低。     

用Mathematica计算氢原子光谱的相对强度

光谱强度是量度光谱的重要宏观物理量,研究氢原子光谱相对强度的分布可以加深对量子跃迁几率的认识。计算氢原子光谱的相对强度分布时由M athem atica软件给出处理矩阵元和特殊函数等复杂计算问题的编程,简洁地得到莱曼系和巴尔末系前三条谱线相对强度之比,计算结果与理论和实验结果相符合,展现了M athem atica软件在计算量子力学问题方面的精确性和高效性。