Effects of forward trunk lean on hamstring muscle kinematics during sprinting

This study aimed to investigate the effects of forward trunk lean on hamstring muscle kinematics during sprinting. Eight male sprinters performed maximal-effort sprints in two trunk positions: forward lean and upright. A three-dimensional musculoskeletal model was used to compute the musculotendon lengths and velocity of the biceps femoris long head, semitendinosus, and semimembranosus muscles during the sprinting gait cycle. The musculotendon lengths of all the three hamstring muscles at foot strike and toe-off were significantly greater during the forward trunk lean sprint than during the upright trunk sprint. In addition, a positive peak musculotendon lengthening velocity was observed in the biceps femoris long head and semimembranosus muscles during the late stance phase, and musculotendon lengths at that instant were significantly greater during the forward trunk lean sprint than during the upright trunk sprint. The present study provides significant evidence that a potential for hamstring muscle strain injury involving forward trunk lean sprinting would exist during the stance phase. The results also indicate that the biceps femoris long head and semimembranosus muscles are stretched during forward trunk lean sprinting while contracting eccentrically in the late stance phase; thus, the elongation load on these muscles could be increased.     

功能动作模式下短跑训练实证研究

功能动作训练用于短跑中,在于优化短跑运动员的技术动作,预防运动损伤,提高核心力量和核心稳定性。文章运用文献资料法、实验法、数理统计法等研究方法,对西北师范大学体育教育专业田径专选组学生短跑技术进行了研究。结果表明：（1）经过为期三个月的教学实验,实验组和对照组的步幅、步频、100米成绩与实验前相比都有明显的提高（p<0.05）。且实验组高于对照组。（2）功能动作训练能有效的提高短跑运动员的核心力量和核心稳定性。     

Largest Silurian Vertebrate Discovered from Yunnan,China

<正>An apparent absence of Silurian fishes more than half-a-metre in length has been viewed as evidence that gnathostomes(jawed vertebrates)were restricted in size and diversity prior to the Devonian.A team led by Professor ZHU Min,Institute of Vertebrate Paleontology and Paleoanthropology(IVPP)of the Chinese Academy of Sciences has unearthed a bony fi sh with an estimated length of about 1 meter from the Silurian Kuanti Formation in Yunnan Province of southwestern China,revealing that pre-Devonian gnathostomes could attain comparatively large sizes.The study published on June 12 in the journal of Scientifi c Reports adds     

三种途径获取至关重要的“弧微分”

第一种途径是自创的,仅按极限的定义并结合使用两点间的距离公式和拉格朗日中值定理就可获得弧微分计算公式;第二种途径是经典的,需要用到定积分定义、变上限函数等等;第三种途径是高职高专教材编写者常用的,它需要先默认弦长与弧长之比的极限为1;为了按顺序编写教材,第一种途径最宜。     

Reliabilities of leg and vertical stiffness during treadmill running

The aim of this study was to determine the intra-participant variabilities (i.e. intra-day and inter-day reliabilities) in leg and vertical stiffness, as well as related kinematic parameters, during treadmill running using the sine-wave method. Twenty-two healthy men ran on a treadmill at 4.44 m/s, and the flight and contact times were measured with a high-speed video camera. Three 30-s running bouts with 2-min inter-bout rests were performed to examine the intra-day reliability, and single 30-s running bouts on three separate days with 24- to 48-h inter-bout intervals were performed to examine the inter-day reliability. The reliability statistics included repeated-measure analyses of variance, average inter-trial correlations, intra-class correlation coefficients (ICCs), Cronbach's α reliability coefficient, and the coefficient of variation. Both leg and vertical stiffness produced high ICCs within 0.972 and 0.982, respectively, and between 0.922 and 0.873 days, respectively. High values were also observed for all of the reliability coefficients. Similar results were found regarding contact time, flight time, step length, and step rate. It was concluded that the measurements of leg and vertical stiffness, as well as related kinematic parameters, obtained using the sine-wave method during treadmill running at 4.44 m/s, were highly reliable, both within and across days.     

理想第二类超导体的临界场

借助Ｇｉｎｚｂｕｒｇ－Ｌａｕｄａｕ理论，阐述了理想第二类超导体处于混合态的临界场，并得出下临界场Ｈｃ１与穿透深度λ、相干长度ξ有关，上临界场Ｈｃ２与参量α有关的结论。     

步长步频及其派生指标在短跑训练实践中的运用

恰当地运用步长、步频及其派生指标对不同的个体进行合理、科学的比较,是对运动员的速度能力作出客观、准确的判断和进行有针对的、卓有成效的速度训练的前提和保证。本文结合运动训练实例,对不同指标的运用差别进行了分析,并提出了应注意的问题。     

泰国留学生三组普通话辅音的实验研究

以两名汉语普通话水平为初、中级的泰国留学生作为研究对象,以声学实验为手段,通过对比分析泰国学生普通话三组塞擦音、擦音与中国发音人之间的差异,寻找泰国学生二语习得过程中语音方面的偏误和障碍,最后针对这些偏误和障碍提出教学对策。经过实验分析发现,泰国留学生在汉语普通话的音节时长、声母时长方面与中国发音人存在差异;另外,泰国学生在发这三组音时,舌位均较前。     

孔隙分布不均匀性对渗透率影响的MRTLBM法研究

孔隙率与渗透率是多孔介质非常重要的属性参数,采用MRT LBM研究孔隙率损失与渗透率损失相关性以及同孔隙率异构孔隙对渗透率特性的影响。结果表明：当存在使孔隙率均匀变小的沉积、沉降或结焦等因素时,渗透率损失率是孔隙率损失率的2倍左右;同孔隙率异构多孔体中,渗透率有巨大差异;同孔隙率异构多孔体中最大孔喉最小孔喉比越大渗透率越小;同孔隙率多孔体中迂曲度越大渗透率越小。     

论文被引的文本因素分析：多学科视角

文献长度、参考文献数量是否影响论文被引频次,不同学科有不同的检验结果。网络环境下,题名字数、关键词个数是否对论文被引具有显著影响,尚未见文献报道。通过对来自6个学科的455篇论文被引的文本因素进行分析,发现：①关键词个数对文献被引存在明显的影响;②参考文献数量对英文语种文献的被引确实存在显著影响,但对中文语种文献被引的影响却不能通过显著性检验;③多学科背景下,文献篇幅长短及题名字数多少对文献被引没有显著影响;④存在“中国学者所发表的英文论文,篇幅越长越有可能不被引用”的现象。