Perception of kinematic characteristics of tennis strokes for anticipating stroke type and direction

The purpose of this study was to determine the sources of visual information used by highly skilled tennis players in anticipating their opponent's shots. In Experiment 1, motion analysis of the strokes showed that the relative motion between the racquet and forearm was different between the ground strokes and lobs, but there were no reliable kinematic differences when shot direction was varied. In Experiment 2, 12 skilled tennis players observed the opponent hitting strokes in a normal video or in a point-light display with different segments occluded. Players' anticipation accuracy was not degraded by the use of the point-light display. Occluding the racquet and forearm significantly reduced the participant's ability to determine the type of stroke produced.     

Teachers' perspectives on the challenges of teaching physical education in urban schools: the student emotional filter

The purpose of this study was to analyze how the challenges of urban schools influence physical education teachers' emotional understanding and connections with their students and the implications on their teaching. Sixty-one elementary physical educators from an urban school district in the midwestern U.S. were interviewed multiple times (N = 136) over 3 years using interpretive methodology. Teachers reported five unique challenges that significantly shaped their thinking about students and their careers, along with strategies they used to overcome or manage those challenges. The challenges were: (a) insufficient instructional resources, (b) implementing culturally relevant pedagogy, (c) dealing with community violence, (d) integrating more games in curricula, and (e) teaching in a culture of basketball. Implications centered on the guilt-inducing nature of urban teaching, developing an informed and realistic vision of urban physical education, and the role of teacher preparation and professional development.     

Physical and metabolic demands of training and match-play in the elite football player

In soccer, the players perform intermittent work. Despite the players performing low-intensity activities for more than 70% of the game, heart rate and body temperature measurements suggest that the average oxygen uptake for elite soccer players is around 70% of maximum (VO(2max). This may be partly explained by the 150 - 250 brief intense actions a top-class player performs during a game, which also indicates that the rates of creatine phosphate (CP) utilization and glycolysis are frequently high during a game. Muscle glycogen is probably the most important substrate for energy production, and fatigue towards the end of a game may be related to depletion of glycogen in some muscle fibres. Blood free-fatty acids (FFAs) increase progressively during a game, partly compensating for the progressive lowering of muscle glycogen. Fatigue also occurs temporarily during matches, but it is still unclear what causes the reduced ability to perform maximally. There are major individual differences in the physical demands of players during a game related to physical capacity and tactical role in the team. These differences should be taken into account when planning the training and nutritional strategies of top-class players, who require a significant energy intake during a week.     

逃不掉的逃兵

这是我不训练的第一个暑假，它比想象中轻松，又比想象中难熬。二十四个小时的空调，二十四个小时的昏昏欲睡。想到曾经的队友们在此刻的展光笼罩下热身，在此刻的骄阳下冲刺，在此刻的塑胶跑道上压腿。再看到现在的自己吃着冰淇淋，拿着遥控器慢悠悠地调台。就觉得自己像逃离一线、回家投亲、享受资产阶级生活的逃兵。     

关于理科教育的一种理论根据

关于理科教育的任何一种合理的理论根据必须包括教育目的、学科和一种学习的模型。 教育目的 关于学校应达到的目的,曾是许多论文的主题,但它们中间存在着争论和分歧。对这些争论本文将不涉及,但有一个是例外;这个例外就是美国教育政策委员会1961年报告书中扼要陈述的,即认为教育的中心目的是教学生思维。这一任务在该委员会的“美国教育的中心目的”论文中详细地阐述如下:     

Failure to obtain value enhancement by within-trial contrast in simultaneous and successive discriminations

The present research tested the generality of the “work ethic“ effect described by Clement, Feltus, Kaiser, and Zentall (2000). In Experiment 1, we trained 10 pigeons on a pair of either simultaneous or successive discriminations. One discrimination followed a high-effort requirement (20 pecks to the center key) and the other followed a low-effort requirement (1 peck). Contrary to Clement et al.’s results, we found that preferences between the S⁺ and S⁻ stimuli in transfer tests depended on the event that initiated the trial: Pigeons preferred the stimulus from the baseline discrimination whose initiating event was most dissimilar from that preceding the test trial. Preferences were similar but less extreme in the successive condition. In Experiment 2, we investigated whether test preferences depended on the amount of training. A total of 12 pigeons were trained on a pair of simultaneous discriminations, except that test sessions were scheduled after every three baseline sessions. Preferences increased across test sessions but were similar to those in Experiment 1. Together with Vasconcelos, Urcuioli, and Lionello-DeNolf (2007a), our study represents a second failure to replicate Clement et al.’s work ethic effect. The finding that preference depends on the event that initiates the test trial suggests that choice probes may not provide unambiguous assessments of stimulus value.     

Modeling water and carbon fluxes above summer maize field in North China Plain with back-propagation neural networks

INTRODUCTION Dynamics of carbon and water vapor fluxesexchange between the atmosphere and the ecosystembiosphere, depend on complex and non-liner interplayamong physiological, ecological, biochemical andedaphic factors and meteorological conditions (Jarvis,1995; Leuning et al., 1995). There are many studiesquantifying the fluxes across different time and spacescales as well as assessing the environment con-straints on them by some kinds of biophysical orempirical models whose resul…     

英国《化学习题精选》(一)

《化学习题精选》是英国中学化学教师为学生提供复习和提高作业质量而编的。它的特点有:1.围绕题目编成一系列短小的问题。这些问题系按照英国现用的教材结构编写的;由浅入深,由易到难,逐步引导学生的学习兴趣;可在课内外用作讨论或练习之用。2.作者将各小题划分为三种类型:(1)知识性(以K表示),理解性(以C表示)及综合性(以H表示)。每小题都注明评分标准,用以了解学生的知识水平和分析问题、解决问题的能力。本书共有一百题,我们根据我国中学化学教学大纲的内容选译部分习题,供教师们参考、选用。选译习题中也略有超我国教材水平的,可作因材施教之用。习题的后面,附有用数字回答问题的答案。     

Deafness, language skills, and rehearsal: a model for the development of a memory strategy

We review a series of studies that evaluate the role of developing language skills as a prerequisite to spontaneous rehearsal use in deaf populations. We propose a theoretical model that summarizes the contribution of language skills by highlighting the interrelations among age, language proficiency, and automatized language skills. In an initial test of the model, an index of deaf children's language experience was found to be an almost complete mediator of strategy use. Increasing language proficiency, therefore, was implicated as a critical variable in predicting children's spontaneous rehearsal use, minimizing any direct contribution from age per se. In a more direct assessment of the link between general language proficiency and rehearsal use, pragmatic language skills (as measured by the Language Proficiency Profile: LPP-I) were found to be a nearly complete mediator of rehearsal use, with the remaining contributions of age and language experience being nonsignificant. Language proficiency, therefore, was identified as a strong and necessary prerequisite for rehearsal to be used spontaneously as a memory strategy. The additional hypothesis that the automatization of these general language skills, measured by a rapid automatized naming task (RAN), contributes to spontaneous rehearsal was also evaluated. Automatized language emerged as a partial mediator of the language proficiency → rehearsal use relation but additional language-processing variables were implicated. We discuss these findings as they relate to issues around the nature of language proficiency and the identification of those automatized language skills involved in rehearsal.