动力学数学模型下弧圈球运行轨迹的研究

通过建立乒乓球的动力数学模型,对弧圈球在每一种情况下的运动规律及运行轨迹变化曲线进行分析。结果显示：影响弧圈球运行轨迹的主要因素有乒乓球运动方向、运动速度、旋转速率、加速度及Magnus力,其中乒乓球运动方向和Magnus力的变化是改变乒乓球速度变化的重要因素;在运行过程中,球向的不断变化使弧圈球的速度及加速度也不断改变;而影响乒乓球运行轨迹的直接因素是旋转速率,且弧圈球第一弧线和第二弧线在不同旋转速率下存在着明显的区别。     

Differences in strength and speed demands between 4v4 and 8v8 small-sided football games

ABSTRACT

The aims of this study were (i) to characterise the acceleration demands of two different formats of small-sided game (SSG), i.e., 4v4 + goalkeepers (4v4 + GK) and 8v8 + goalkeepers (8v8 + GK); (ii) to analyse the correlation between performance in power-based tests and acceleration-based physical loading during the two different SSG formats and (iii) to analyse the neuromuscular-induced fatigue. Eighteen adult male footballers participated in the study (20.7 ± 1.0 years, 178 ± 5 cm and 71.4 ± 2.1 kg). Baseline measurements were obtained from countermovement jumps, 15 s repeated jumps and 5 and 15 m sprints. A total of 36 min was analysed for each SSG (4v4 + GK: two sets of 3 × 6 min, and 8v8 + GK: 2 × 18 min). Heart rate, blood lactate, perceived exertion and movement pattern (GPS) were analysed. Distances covered by very-high-intensity activities and very-high-speed running were lower in 4v4 + GK than in 8v8 + GK (effect sizes (ES) = ?0.69 ± 0.67 and ?1.04 ± 0.67, respectively; very likely), while accelerations and decelerations were higher in 4v4 + GK than in 8v8 + GK (ES = 1.13–1.52; almost certainly). Blood lactate concentrations were higher (ES = 1.40 ± 0.58; almost certainly) and players perceived themselves to be more tired (ES = 0.80–2.31; almost certainly) after 4v4 + GK than after 8v8 + GK. Sprint ability in 5 and 15 m tests decreased (ES = 0.87 ± 0.58 and 0.89 ± 0.58, respectively; almost certainly) only after 4v4 + GK. This SSG format appeared more demanding in relation to repetitions and fatigue development of muscle power-based actions than 8v8 + GK. It may therefore be logical to use the former type of SSG to target development of power-related football actions.     

狭义相对论中各变换式的重新推导及合理性分析

鉴于狭义相对论的不自恰性,对整个理论体系存在的两处失误进行了修正,使之在符合现有实验的基础上,与经典理论达到融合。首先指出导出洛仑兹时空变换式的原始数学模型存在缺陷,对其修正后,重新推导出了新的洛仑兹时空变换式。其次对力的定义进行了严格分析,据此导出两惯性系间的力变换式,简洁明了。对比新旧变换式(推论),阐述了旧变换式存在的不合理之处和新变换式的合理性。     

拓展训练对提高体育集体项目运动员团队精神的研究

对拓展训练和体育集体项目运动员团队精神的现状进行了分析研究.通过对问卷调查结果的统计处理与逻辑分析,证明了拓展训练对提高体育集体项目运动员团队精神的显著效果,为探询一种新颖、有效的心理训练手段提供参考.     

中国双向FDI协调发展的减排效应研究

本文将IFDI与OFDI作为一个系统,测度其耦合协调水平,作为双向FDI协调发展的指标。在Copeland-Taylor的分析框架下创新性地引入双向FDI协调发展,分析了双向FDI协调发展对碳排放的影响机制。基于2004—2016年中国碳排放数据,采用动态空间面板模型和系统广义矩估计方法,并结合中介效应模型,从时间和空间的二维视角,揭示双向FDI协调发展对碳排放的影响及效应。结果表明：中国碳排放具有空间上的显著关联和时间上的路径依赖,区域协同、长期治理是实现碳减排的关键;传导机制检验表明：中国双向FDI协调发展对碳排放具有显著的抑制效应,且规模效应为正,结构效应与技术效应为负,结构效应与技术效应的主导地位是双向FDI协调发展表现出减排效应的根本原因。     

睡美人文献识别方法分析与改进构想

[目的/意义] 睡美人文献是指那些发表初期遭遇长时间的冷遇,随后突然引起广泛关注的文献。这些文献往往蕴含着重大科学发现,对其进行识别研究具有重大意义。通过对现有识别方法的梳理和分析,提出识别睡美人文献方法的改进思路和做法。[方法/过程] 明确以高被引文献作为睡美人文献识别研究的对象,选取文献年被引频次累积变化趋势作为研究切入点,提出累积被引速度和累积被引加速度两个指标,明确自引的处理方法。[结果/结论] 提出睡美人文献识别方法的改进思路与实证路线,在一定程度上优化了识别方法,同时为睡美人文献预测方法的研究提供一定的基础。     

试论高校体育教学中拓展训练的实施

体育教学中的拓展训练在高校中是一种创新的教学方式,是体育课程体系改革的结果,拓展训练把多学科和体育很好的结合在一起,这种教学方式突破了传统的教育形势,扩大了体育课程的空间,使体育课程的多样化功能得以实现。本文主要分析了高校体育教学中进行拓展训练的原因及重要意义、几点对策。     

拓展训练对提高体育集体项目运动员团队凝聚力的研究

通过文献及理论分析,认为拓展训练可提高体育集体项目运动员团队的凝聚力,建议针对体育集体项目运动团队的不同特点选择性的开展拓展训练。     

对高校引入新生“认知性”拓展训练的效果分析

本文主要采用文献资料法和问卷调查法对我校在新生军训期间引入“拓展训练”进行试验研究,了解该训练对普通高校新生大学生活的影响。结果显示,这三天的拓展训练对他们适应大学生活有着积极作用。建议普通高校引入“拓展性”拓展训练,根据实际情况可以将这种训练纳入日常的课程当中。     

Determination of the centre of mass kinematics in alpine skiing using differential global navigation satellite systems

In the sport of alpine skiing, knowledge about the centre of mass (CoM) kinematics (i.e. position, velocity and acceleration) is essential to better understand both performance and injury. This study proposes a global navigation satellite system (GNSS)-based method to measure CoM kinematics without restriction of capture volume and with reasonable set-up and processing requirements. It combines the GNSS antenna position, terrain data and the accelerations acting on the skier in order to approximate the CoM location, velocity and acceleration. The validity of the method was assessed against a reference system (video-based 3D kinematics) over 12 turn cycles on a giant slalom skiing course. The mean (± s) position, velocity and acceleration differences between the CoM obtained from the GNSS and the reference system were 9 ± 12 cm, 0.08 ± 0.19 m · s^-1 and 0.22 ± 1.28 m · s^-2, respectively. The velocity and acceleration differences obtained were smaller than typical differences between the measures of several skiers on the same course observed in the literature, while the position differences were slightly larger than its discriminative meaningful change. The proposed method can therefore be interpreted to be technically valid and adequate for a variety of biomechanical research questions in the field of alpine skiing with certain limitations regarding position.