世界优秀男子乒乓球运动员特长技术分析

采用文献资料等方法,对世界优秀男子乒乓球运动员特长技术进行研究,旨在提升我国乒乓球项目特长技术创新与发展。结果表明：世界优秀男子乒乓球运动员特长技术主要有8项,分别为,瓦尔德内尔横拍直握式发球技术和晃接技术、科贝尔反手侧拧技术、金泽洙步法技术、蒋澎龙加力推挡技术、格林卡反手横向拉球技术、马琳加转摆短技术和正手前冲弧圈球技术、朱世赫削中反攻技术、王皓直板横打技术。     

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.     

Anticipatory postural adjustments during cutting manoeuvres in football and their consequences for knee injury risk

Abstract

Anticipatory postural adjustments (APAs), i.e. preparatory positioning of the head, the trunk and the foot, are essential to initiate cutting manoeuvres during football games. The aim of the present study was to determine how APA strategies during cutting manoeuvres are influenced by a reduction of the time available to prepare the movement.

Thirteen football players performed different cutting tasks, with directions of cutting either known prior to the task or indicated by a light signal occurring 850, 600 or 500 ms before ground contact.

With less time available to prepare the cutting manoeuvre, the head was less orientated towards the cutting direction (P = 0.033) and the trunk was even more rotated in the opposite direction (P = 0.002), while the foot placement was not significantly influenced. Moreover, the induced higher lateral trunk flexion correlated with the increased knee abduction moment (r = 0.41; P = 0.009).

Increasing lateral trunk flexion is the main strategy used to successfully perform a cutting manoeuvre when less time is available to prepare the movement. However, higher lateral trunk flexion was associated with an increased knee abduction moment and therefore an increased knee injury risk. Reducing lateral trunk flexion during cutting manoeuvres should be part of training programs seeking the optimisation of APAs.     

乒乓球运动员应加强快速、准确、灵活的步法训练

论述了乒乓球运动员在短时间内,根据来球方向、速度、落点以及旋转等快速作出判断时步法移动的重要意义,并提出一些训练措施。     

台阶无氧功率实验方法新探

应用身高百分比对每步跨台阶垂直高度进行标定的方法，对２１名运动员和４３名学生的台阶无氧功率实验进行了方法学研究。结果证明，以不同每步跨台阶垂直高度所测得的个体无氧功率有明显差异；认为个体最大台阶无氧功率与个体最佳用力幅度有密切关系，后者可以反映受试的训练水平和技术水平，对选材和机能评定有参考价值。     

对纵箱支撑跳越教学步骤的实验研究

根据人类跳越障碍的自然活动能力，设计了一套纵箱支撑跳越教学步骤，经实验证明，此教学步骤可有效地预防教学中学生不良心理、生理状态的产生     

基于四阶累积量的CSPRIT算法

分析了基于二阶统计的CSPRIT算法在空间相关高斯噪声环境中存在的问题，提出将四阶累积量与CSPRIT算法相结合，处理一维二元相移键控信号（BPSK）和多元幅移键控信号（MASK），实现信号到达角（DOA）的估计和波束形成器的构造。与基于二阶统计的CSPRIT算法相比，基于四阶累积量的改进算法能够有效抑制空间相关的高斯噪声，提高信号估计精度。计算机仿真验证了该算法的有效性。     

A novel controller design and evaluation for networked control systems with time-variant delays

A new delayed state-variable model for networked control systems is presented, upon which a linear quadratic regulator (LQR) is designed. A method of delays-estimation online is also given. A fuzzy logic with LQR controller is addressed for the difficulty on implementation of LQR in networked control systems (NCSs) with time-variant delays. Simulation results prove that the novel controller can make the system stable and robustly preserve the performance in terms of time-variant delays.     

Estimation of 2-D ARMA model parameters by using equivalent AR approach

In this paper, the problem of estimating the parameters of a two-dimensional autoregressive moving-average (2-D ARMA) model driven by an unobservable input noise is addressed. In order to solve this problem, the relation between the parameters of a 2-D ARMA model and their 2-D equivalent autoregressive (EAR) model parameters is investigated. Based on this relation, a new algorithm is proposed for determining the 2-D ARMA model parameters from the coefficients of the 2-D EAR model. This algorithm is a three-step approach. In the first step, the parameters of the 2-D EAR model that is approximately equivalent to the 2-D ARMA model are estimated by applying 2-D modified Yule-Walker (MYW) equation to the process under consideration. Then, the moving-average parameters of the 2-D ARMA model are obtained solving the linear equation set constituted by using the EAR coefficients acquired in the first step. Finally, the autoregressive parameters of the 2-D ARMA model are found by exploiting the values obtained in first and second steps. The performance of the proposed algorithm is compared with other 2-D ARMA parameter and spectral estimation algorithms available in the technical literature by means of three different criteria. As a result of this comparison, it is shown that the parameters and the corresponding power spectrums estimated by using the proposed algorithm are converged to the original parameters and the original power spectrums, respectively.     

巴斯卡分布NB(r,p)中参数r的估计

巴斯卡分布NB（r,p)是重要的离散型分布之一，当r已知时，巴斯卡分布NB（r,p)中未知参数p(p∈（0，1））的估计是众所周知的。本文分别在p已知和未知的条件下，研究了参数r(r∈（1，2，…}）的估计，并得到了它们的渐近性质。