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1.
The aim of this study was to assess the effect of the hand’s acceleration on the propulsive forces and the relative contribution of the drag and lift on their resultant force in the separate phases of the front crawl underwater arm stroke. Ten female swimmers swam one trial of all-out 25-m front crawl. The underwater motion of each swimmer’s right hand was recorded using four camcorders and four periscope systems. Anatomical landmarks were digitised, and the propulsive forces generated by the swimmer’s hand were estimated from the kinematic data in conjunction with hydrodynamic coefficients. When the hand’s acceleration was taken into account, the magnitude of the propulsive forces was greater, with the exception of the mean drag force during the final part of the underwater arm stroke. The mean drag force was greater than the mean lift force in the middle part, while the mean lift force was greater than the mean drag force in the final part of the underwater arm stroke. Thus, swimmers should accelerate their hands from the beginning of their backward motion, press the water with large pitch angles during the middle part and sweep with small pitch angles during the final part of their underwater arm stroke.  相似文献   
2.
This study investigated whether the associations between parental distress with conduct problems (CPs) and prosocial behaviors (PBs) are moderated by children's skin conductance (SC) and heart rate (HR) reactivity to fear. Participants were 147 Greek-Cypriot children (Mage = 7.30, 44.2% girls), selected from a larger screening sample (data were collected from 2015 to 2018). Longitudinal associations suggested that children with high HR reactivity to fear were more likely to display PB, whereas those with low SC reactivity were more likely to engage in CP behaviors. In contrast, interaction effects suggested that children high on SC reactivity to fear were more susceptible to the effects of parental distress, as indicated by their higher vulnerability to engage in CP (cross-sectionally) behaviors and their lower scores on PB (cross-sectionally and longitudinally).  相似文献   
3.
We investigated the linear kinematics and the change in energy of the barbell and the angular kinematics of the trunk and leg during the snatch technique of 12 elite male Greek weightlifters under competitive conditions after the new weight classification. Two S-VHS cameras operating at 60 Hz were used to record the lifts. The spatial coordinates of selected points were calculated using the direct linear transformation procedure; after digital filtering of the raw data, the angular displacements and angular velocities were calculated for the hip, knee and ankle joints. The following variables were also calculated for the barbell: vertical and horizontal displacement, vertical linear velocity and acceleration, external mechanical work and power output. The results revealed that all weightlifters flexed their knees during the transition phase, independently of their weight category. This indicates that the athletes use the elastic energy produced during the stretch–shortening cycle to enhance their performance. In nine athletes, we found that the barbell trajectory did not cross a vertical reference line that passed through the initial position of the barbell. The vertical linear velocity of the barbell was increased continuously from the beginning of the movement until the second maximum extension of the knee joint, with no notable dip being observed. Regarding the change in energy of the barbell, we found that the mechanical work for the vertical displacement of the barbell in the first pull was significantly greater than the mechanical work in the second pull. In contrast, the estimated average mechanical power output of the athletes during the vertical displacement of the barbell was significantly greater in the second pull than in the first pull. We conclude that the major elements of the snatch technique of elite Greek weightlifters have not been aff ected by the new weight classification.  相似文献   
4.
The aim of this study was to determine what visual information expert soccer players encode when they are asked to make a decision. We used a repetition-priming paradigm to test the hypothesis that experts encode a soccer pattern's structure independently of the players' physical characteristics (i.e., posture and morphology). The participants were given either realistic (digital photos) or abstract (three-dimensional schematic representations) soccer game patterns. The results showed that the experts benefited from priming effects regardless of how abstract the stimuli were. This suggests that an abstract representation of a realistic pattern (i.e., one that does not include visual information related to the players' physical characteristics) is sufficient to activate experts' specific knowledge during decision making. These results seem to show that expert soccer players encode and store abstract representations of visual patterns in memory.  相似文献   
5.
The aim of this study was to investigate the relative influence of step length (SL) and step frequency (SF) on step velocity (SV) during the approach run of high-level long jumpers and to quantify the asymmetry of these step characteristics. Spatiotemporal data of the approach run were collected during national competition from 10 long jumpers (age 26.2 ± 4.1 years, height 1.84 ± 0.06 m, mass 72.77 ± 3.23 kg, personal best performance 7.96 ± 0.30 m). Analyses were conducted for total approach, early approach and late approach. For the total approach 4/10 athletes were SF reliant and 6/10 athletes favoured neither characteristic. At the early approach, 3/10 athletes were SF reliant and 7/10 athletes favoured neither. During late approach 2/10 athletes demonstrated SL reliance, 7/10 athletes were SF reliant and 1/10 athletes favoured neither. Four athletes displayed significant asymmetry for SL and three for SF. However, no athletes demonstrated significant asymmetry for SV indicating that the asymmetrical demands of take-off do not have a marked influence on step characteristic asymmetry, probably due to the constraints of the event. Consideration should be given to the potentially conflicting demands between limbs for individual athletes.  相似文献   
6.
The aim of this study was to determine what visual information expert soccer players encode when they are asked to make a decision. We used a repetition-priming paradigm to test the hypothesis that experts encode a soccer pattern's structure independently of the players' physical characteristics (i.e., posture and morphology). The participants were given either realistic (digital photos) or abstract (three-dimensional schematic representations) soccer game patterns. The results showed that the experts benefited from priming effects regardless of how abstract the stimuli were. This suggests that an abstract representation of a realistic pattern (i.e., one that does not include visual information related to the players'physical characteristics) is sufficient to activate experts'specific knowledge during decision making. These results seem to show that expert soccer players encode and store abstract representations of visual patterns in memory.  相似文献   
7.
In the present study, we develop and deploy a conceptual framework of “scaffolding” in groupwork learning, through the analysis of the pursuit of a learning goal over time. The analysis follows individuals’ different experiences of an interaction as well as collective experiences, considering individual attainment as a result of a bi-directional contextualized conversation and action. We detect, describe and evaluate two (2) types of interaction that can be characterized as “scaffolding process”: the first concerns “Scaffolding individual thinking” and the second “Scaffolding collective thinking”. The latter, apart from presenting the educational advantages of collective thinking through peer discussion (D) and curriculum-focused evaluation context of Teacher Initiation – Student Response – Teacher Follow up (IRF), also presents the advantage of ‘spiral’ verbal exchanges in which the teacher “tunes in” to the students’ present state of ability or understanding (spiral IDRF).  相似文献   
8.
In this paper, we explore the process of becoming a teacher educator in the pedagogical use of digital tools in mathematics teaching. The study took place in the context of an in-service program during the trainees’ engagement in their practicum fieldwork activities including the process observation–reflection–design–implementation–reflection. We explored the features of this context that facilitated the trainees’ transition from the level of trainee educator to the level of teacher educator as well as the nature of the trainees’ documentation work for teachers. The results showed that observation of other teacher educators’ teaching in conjunction with reflection during the program’s respective sessions facilitated the trainees’ transition to the professional level. The identified operational invariants underlying the trainees’ designs concerned the focus of their observation in teacher education classrooms, the importance they attributed to the constraints and opportunities provided by the wider educational context and epistemological issues regarding the teaching and learning of mathematics with technology. The analysis of trainees’ designs revealed three kinds of documents (“explanatory,” “instructive” and “facilitative”) and corresponding roles of trainees during the implementation. These documents targeted different aspects of TPACK depending on the trainees’ conceptualizations of teachers’ roles either “as students” or “of students.”  相似文献   
9.
We investigated the linear kinematics and the change in energy of the barbell and the angular kinematics of the trunk and leg during the snatch technique of 12 elite male Greek weightlifters under competitive conditions after the new weight classification. Two S-VHS cameras operating at 60 Hz were used to record the lifts. The spatial coordinates of selected points were calculated using the direct linear transformation procedure; after digital filtering of the raw data, the angular displacements and angular velocities were calculated for the hip, knee and ankle joints. The following variables were also calculated for the barbell: vertical and horizontal displacement, vertical linear velocity and acceleration, external mechanical work and power output. The results revealed that all weightlifters flexed their knees during the transition phase, independently of their weight category. This indicates that the athletes use the elastic energy produced during the stretch-shortening cycle to enhance their performance. In nine athletes, we found that the barbell trajectory did not cross a vertical reference line that passed through the initial position of the barbell. The vertical linear velocity of the barbell was increased continuously from the beginning of the movement until the second maximum extension of the knee joint, with no notable dip being observed. Regarding the change in energy of the barbell, we found that the mechanical work for the vertical displacement of the barbell in the first pull was significantly greater than the mechanical work in the second pull. In contrast, the estimated average mechanical power output of the athletes during the vertical displacement of the barbell was significantly greater in the second pull than in the first pull. We conclude that the major elements of the snatch technique of elite Greek weightlifters have not been affected by the new weight classification.  相似文献   
10.
This study analyses the discourse among the teacher and the students, members of three (3) small groups, who learn in the environment of a stand-alone computer. Two educational environments are examined: the first one, a “virtual laboratory” (Virtual scale-DELYS) and the second one, a computer modeling environment (ModelsCreator). The ‘Virtual Scale’ environment provides users with curriculum focused feedback and in that sense it can be categorized as directive. The ModelsCreator environment provides users merely with a representation of their own conception of curriculum concepts, so it can be categorized as an open-ended environment. The goal of this research is to exemplify the way the two educational software environments support (a) the development of collective thinking in peer— and teacher-led discussion and (b) students’ autonomy. The software tools of the “Virtual scale” along with the resources provided for the problem solving created an educational framework of hypothesis testing. This framework did not limit the students’ contributions by directing them to give short answers. Moreover, it supported the students’ initiatives by providing tools, representations and procedures that offered educationally meaningful feedback. Based on the above results, we discuss a new educationally important structure of software mediation and describe the way the two software activities resourced collective thinking and students’ initiatives. Finally, for each type of software environment, we propose certain hypotheses for future research regarding the support of collaborative problem solving.  相似文献   
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