基于虚拟地球的电离层电子密度时空多维可视化方法     

郭长顺  范湘涛  谭剑  詹勤  亢叙杰 《中国科学院大学学报》2019,36(6):817-824

针对多维多时相电离层电子密度数据在Web环境中传输困难而无法满足实时可视化需求以及传统面绘制方法无法反映原始数据场全貌的问题,从电离层电子密度源数据处理出发,使用视频压缩编码方法,实现时间序列数据的高效传输;借助WebGL可编程渲染管道,提出基于GPU加速的电离层电子密度光线投射体绘制方法,并采用自适应步长采样和早期光线终止法,提高可视化质量与体绘制效率;最后,基于开源虚拟地球平台Cesium,实现电离层电子密度的多层动态交互式可视化,验证所提方法的可行性和有效性,为电离层电子密度的科学可视化和辅助研究提供技术支持。  相似文献   

Comparison of step-by-step kinematics of resisted,assisted and unloaded 20-m sprint runs     

Roland van den Tillaar  Paul Gamble 《Sports biomechanics / International Society of Biomechanics in Sports》2019,18(5):539-552

This investigation examined step-by-step kinematics of sprint running acceleration. Using a randomised counterbalanced approach, 37 female team handball players (age 17.8 ± 1.6 years, body mass 69.6 ± 9.1 kg, height 1.74 ± 0.06 m) performed resisted, assisted and unloaded 20-m sprints within a single session. 20-m sprint times and step velocity, as well as step length, step frequency, contact and flight times of each step were evaluated for each condition with a laser gun and an infrared mat. Almost all measured parameters were altered for each step under the resisted and assisted sprint conditions (η² ≥ 0.28). The exception was step frequency, which did not differ between assisted and normal sprints. Contact time, flight time and step frequency at almost each step were different between ‘fast’ vs. ‘slow’ sub-groups (η² ≥ 0.22). Nevertheless overall both groups responded similarly to the respective sprint conditions. No significant differences in step length were observed between groups for the respective condition. It is possible that continued exposure to assisted sprinting might allow the female team-sports players studied to adapt their coordination to the ‘over-speed’ condition and increase step frequency. It is notable that step-by-step kinematics in these sprints were easy to obtain using relatively inexpensive equipment with possibilities of direct feedback.  相似文献   

加速度传感仪在射击射箭运动训练中的应用          下载免费PDF全文

米卫国 《体育科研》2010,31(1):77-79

采用加速度传感仪来分析射击射箭项目的专项技术特点,通过相关部位的加速变化曲线来反映专项技术动作的稳定性及时相等特征,方法新颖,具有良好的可行性。实践说明,进一步提高加速度传感仪的精度、适宜频率、教据侍输方式及校准方法等将是方法本身在射击射箭项目中深入应用的发展方向。  相似文献   

排球正面扣球两种挥臂动作分析   总被引：1，自引：0，他引：1  

龚雅丽  黄尔联 《体育科学》1992,(6)

对国内外女子排球名将的两种扣球挥臂动作进行了统计分析,明确了两种挥臂动作的特点、效能和作用的异同。对中国女排两种典型挥臂动作进行了摄影与解析。分析认为两种扣球方式均为优秀的扣球动作,可在不同条件下,发挥其独特的效能。故训练时应根据运动员的各自条件,因人而异地施训。  相似文献   

对一个角动量守恒问题的质疑     

王红梅  刘辉兰  李海彦 《宜春学院学报》2007,29(2):72-73

通过对一个角动量守恒问题错误解法的分析,指出错误产生的主要原因,然后分别用两种方法给出该题的解法.  相似文献   

对投掷项目最后用力躯干三维运动特征的研究   总被引：6，自引：0，他引：6  

郑亚平  周玉斌  章柳云 《北京体育大学学报》2001,24(2):274-276

最后用力动作在投掷技术中的重要作用众所周知 ,它是有机体在多种合力作用下完成的。以往在对投掷技术的分析基本是限于平面的研究 ,利用生物力学进行三维的分析研究甚少。通过在这方面对投掷诸项最后用力躯干动作的运动进行研究 ,并进行对比分析 ,阐述了最后用力躯干绕额状轴、纵轴和矢状轴三维运动的形式与特征 ,对改进投掷技术教学效果、完善技术动作概念有一定的指导意义。  相似文献   

Speed kills,speed thrills: constraining and enabling accelerations in academic work-life     

Filip Vostal 《Globalisation, Societies & Education》2015,13(3):295-314

Intensification, speed of change and faster pace of life have recently emerged as significant issues in studies analysing the current academic climate. This article takes up the ‘social acceleration thesis’ as a conceptual resource for capturing the relationship between the individual experience of time and the changing structure and operations of contemporary academia. Using qualitative data from the UK, it analyses the texture and implications of the accelerating pace of academic work-life. It argues that such pace is both resented, as well as strategically managed by academics. In this way, the analysis opens up more agentic approach to the overall dynamisation in academic work-life and argues that it is possible to conceive acceleration as practical and even thrilling. Against the background of such an approach, the article concludes by stating that acceleration in academic work-life is an ambivalent experience and by questioning recent propositions under the label of slow academia.  相似文献   

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

Matthias Gilgien  Jörg Spörri  Julien Chardonnens  Josef Kröll  Philippe Limpach  Erich Müller 《Journal of sports sciences》2015,33(9):960-969

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.  相似文献   

Effects of unsteady conditions on propulsion generated by the hand’s motion in swimming: a systematic review     

Lara Elena Gomes  Jefferson Fagundes Loss 《Journal of sports sciences》2015,33(16):1641-1648

The understanding of swimming propulsion is a key factor in the improvement of performance in this sport. Propulsive forces have been quantified under steady conditions since the 1970s, but actual swimming involves unsteady conditions. Thus, the purpose of the present article was to review the effects of unsteady conditions on swimming propulsion based on studies that have compared steady and unsteady conditions while exploring their methods, their limitations and their results, as well as encouraging new studies based on the findings of this systematic review. A multiple database search was performed, and only those studies that met all eligibility criteria were included. Six studies that compared steady and unsteady conditions using physical experiments or numerical simulations were selected. The selected studies verified the effects of one or more factors that characterise a condition as unsteady on the propulsive forces. Consequently, much research is necessary to understand the effect of each individual variable that characterises a condition as unsteady on swimming propulsion, as well as the effects of these variables as a whole on swimming propulsion.  相似文献   

混凝土环境中BFRP筋耐久性能试验研究(英文)     

朱莹  吴刚  董志强  汪昕  吴智深 《东南大学学报》2014,(3):323-329

针对玄武岩纤维增强树脂基复合筋(BFRP)在混凝土环境中的耐碱性能进行了加速腐蚀试验研究.腐蚀试验环境包括3种,分别为自来水、盐水及室内空气环境,将包裹有混凝土保护层的BFPR筋试件分别放置在上述3种环境中,试验同时采用碱溶液直接浸泡BFRP筋作为对比,对直接碱溶液浸泡环境与混凝土包裹环境之间的加速系数进行了研究.试验采用60℃的高温进行加速.试验结果表明:自来水和盐水浸泡对于包裹有混凝土的BFRP筋试件没有明显差异.分析认为,与混凝土内部高碱性的孔隙溶液接触是BFRP筋退化的主要原因,当经受高温和高湿环境共同作用时,混凝土环境中BFRP筋的退化将明显加速;BFRP筋的退化速率在初期较快,随着龄期的增长,退化速率降低.基于试验数据分析表明,对于所采用的BFRP筋,60℃饱和吸湿混凝土环境下,BFRP筋2.18 a的退化程度与60℃碱溶液直接浸泡环境下1 a的退化程度相当.  相似文献