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1.
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. 相似文献
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Comparing the pre- and post-impact ball and racquet kinematics of elite tennis players' first and second serves: a preliminary study 总被引：1，自引：0，他引：1
Chow JW Carlton LG Lim YT Chae WS Shim JH Kuenster AF Kokubun K 《Journal of sports sciences》2003,21(7):529-537
The aim of this study was to compare the pre- and post-impact three-dimensional kinematics of the ball and racquet during first and second serves performed by elite tennis players. Data were collected from four male and four female right-handed professional players during competition using two high-speed cameras (200 Hz). For each player, one first serve and one second serve from the 'deuce' or right service court that landed within the specified target area were analysed. To test for significant differences between the first and second serves, Wilcoxon tests (P < or = 0.05) were performed on selected parameters. The results indicate that the ball travelled forward and to the left during the flight phase of the toss in all but one trial. The average pre-impact ball forward location for the first serve was significantly more in front and had a higher associated forward ball velocity than the corresponding values for the second serve. On average, the decrease in post-impact ball speed from the first to the second serve was 24.1%. No significant differences between the first and second serves were found in the pre-impact racquet head speed and orientation, which was represented as a unit vector perpendicular to the racquet face. The major adjustments made by the players when going from the first to second serve were a decrease in pre-impact ball forward location (P < or = 0.01) and an increase in the pre-impact racquet vertical and lateral velocities (both P < or = 0.05). This implies that the players tossed the ball closer to the body and imparted topspin and sidespin on the ball by changing the racquet vertical and lateral velocities when going from the first to the second serve. 相似文献
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This paper presents a mathematical model for laser-induced rapid electro-kinetic patterning (REP) to elucidate the mechanism for concentrating particles in a microchannel non-destructively and non-invasively. COMSOL®(v4.2a) multiphysics software was used to examine the effect of a variety of parameters on the focusing performance of the REP. A mathematical model of the REP was developed based on the AC electrothermal flow (ACET) equations, the dielectrophoresis (DEP) equation, the energy balance equation, the Navier-Stokes equation, and the concentration-distribution equation. The medium was assumed to be a diluted solute, and different electric potentials and laser illumination were applied to the desired place. Gold (Au) electrodes were used at the top and bottom of a microchannel. For model validation, the simulation results were compared with the experimental data. The results revealed the formation of a toroidal microvortex via the ACET effect, which was generated due to laser illumination and joule-heating in the area of interest. In addition, under some conditions, such as the frequency of AC, the DEP velocity, and the particle size, the ACET force enhances and compresses resulting in the concentration of particles. The conditions of the DEP velocity and the ACET velocity are presented in detail with a comparison of the experimental results. 相似文献
4.
Electric field-driven separation and purification techniques, such as isoelectric focusing (IEF) and isotachophoresis, generate heat in the system that can affect the performance of the separation process. In this study, a new mathematical model is presented for IEF that considers the temperature rise due to Joule heating. We used the model to study focusing phenomena and separation performance in a microchannel. A finite volume-based numerical technique is developed to study temperature-dependent IEF. Numerical simulation for narrow range IEF (6 < pH < 10) is performed in a straight microchannel for 100 ampholytes and two model proteins: staphylococcal nuclease and pancreatic ribonuclease. Separation results of the two proteins are obtained with and without considering the temperature rise due to Joule heating in the system for a nominal electric field of 100 V/cm. For the no Joule heating case, constant properties are used, while for the Joule heating case, temperature-dependent titration curves and thermo-physical properties are used. Our numerical results show that the temperature change due to Joule heating has a significant impact on the final focusing points of proteins, which can lower the separation performance considerably. In the absence of advection and any active cooling mechanism, the temperature increase is the highest at the mid-section of a microchannel. We also found that the maximum temperature in the system is a strong function of the ΔpK? value of the carrier ampholytes. Simulation results are also obtained for different values of applied electric fields in order to find the optimum working range considering the simulation time and buffer temperature. Moreover, the model is extended to study IEF in a straight microchip where pH is formed by supplying H+ and OH−, and the thermal analysis shows that the heat generation is negligible in ion supplied IEF. 相似文献
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Education and Information Technologies - Virtual reality (VR) technology is playing a crucial role in the changing paradigm of education. In many cases, however, VR technology is not being taught... 相似文献
7.
Quality in Inclusive Preschool Classrooms 总被引：1，自引：1，他引：0
Linda L. Hestenes Deborah J. Cassidy Jonghee Shim Archana V. Hegde 《Early education and development》2013,24(4):519-540
Research Findings: Quality of care for preschool children in inclusive and noninclusive classrooms was examined in two studies. In Study 1, comparisons across a large sample of classrooms (N = 1, 313) showed that inclusive classrooms were higher than noninclusive classrooms in global quality as well as on two dimensions of quality (Activities/Materials and Language/Interactions). In Study 2, a more diverse sample of 44 classrooms (20 inclusive and 24 noninclusive) did not reveal differences on the global measures of quality but did show a difference on a measure of teacher–child interactions. Teachers in inclusive classrooms had higher quality and more appropriate interactions with all children than did teachers from noninclusive classrooms. Ratings of perceived severity of children's disabilities were not related to any of the measures of classroom quality in either study. Practice or Policy: Both studies suggest that including children with disabilities in regular preschool classrooms does not result in lower quality programs or in less adequate teacher–child interactions, particularly for children with mild to moderate disabilities. Results illustrate the importance of continued education for early childhood professionals on high-quality teacher–child interactions. Faculty in personnel preparation programs as well as policymakers need to continue to promote high-quality interactions between teachers and children. 相似文献
8.
The current study examined how teachers’ perfectionism (personal standards [PS] and concern over mistakes [COM]) relates to their achievement goals for teaching, instructional practices (creation of mastery vs. performance classroom goal structures), job satisfaction, and flow experience during teaching. The data were collected from teachers (N = 143; mean age = 43.5; 70% female; 100% European American) practicing in the Midwestern U.S. Path analyses indicated that teachers’ high personal standards predicted endorsement of mastery goals for teaching, creation of mastery goal structure emphasizing personal progress and learning, high job satisfaction, and frequent flow experience during teaching. On the contrary, teachers’ high concern over mistakes predicted endorsement of performance-approach and -avoidance goals, creation of classroom performance goal structure emphasizing competition among students, low job satisfaction, and infrequent flow experience during teaching. A significant interaction between PS and COM was found for fluency (subscale of flow) experience, indicating that PS can buffer the harmful effects of COM. Therefore, the study evidenced the benefits of PS and the drawbacks of COM. 相似文献
9.
Stuart JH Biddle CK John Wang Nikos LD Chatzisarantis 《Journal of sports sciences》2013,31(12):973-989
Three studies are reported of children and youth aged 11–19 years (n?=?3478) examining the nature of beliefs about athletic ability. Drawing on related research in academic, moral and stereotyping domains, development of a psychometric instrument assessing athletic ability beliefs is detailed. Support was found for a multidimensional hierarchical structure that is invariant across age and gender. Confirmatory factor analysis revealed a structure comprising two higher-order factors of entity and incremental beliefs underpinned by beliefs that athletic ability is stable and a gift (entity), and is open to improvement and can be developed through learning (incremental). Incremental beliefs, indirectly through a task goal orientation, and entity beliefs directly, predicted self-reported amotivation towards physical education and sport. On the other hand, enjoyment of physical activity in youth was predicted directly by task orientation and incremental beliefs. Predictions concerning the moderating role of perceived competence were not supported. Our findings highlight the importance of ability beliefs and goals in understanding the determinants of physical activity in children and youth. 相似文献
10.
Guided by the intergroup contact hypothesis and intergroup contact theory, the authors examined US Americans' (N=403) communication experiences and relational solidarity with their most frequent Japanese contact and associations with their attitudes toward Japanese as a cultural group. Structure Equation Modeling (SEM) results showed that both communication frequency and quality had an indirect effect through relational solidarity on affective, behavioral, and cognitive attitudes, demonstrating the critical mediating role of relational solidarity. Results also revealed that communication quality was positively and directly associated with the attitudinal measures. Implications of the findings are discussed with respect to prior literature on relational communication in intergroup and intercultural contexts. 相似文献