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101.
Keith?KoenigEmail author Nan?Davis?Mitchell Thomas?E.?Hannigan J.?Keith?Clutter 《Sports Engineering》2004,7(2):105-117
The speed at which a player can swing a bat is central to the games of baseball and softball, determining, to a large extent,
the hit speed of the ball. Experimental and analytical studies of bat swing speed were conducted with particular emphasis
on the influence of bat moment of inertia on swing speed. Two distinct sets of experiments measured the swing speed of colege
baseball and fast-pitch softball players using weighted rods and modified bats. The swing targets included flexible targets,
balls on a tee and machine pitched balls. Internal mass alterations provided a range of inertial properties. The average measured
speeds, from 22 to 31 m s−1, are consistent with previous studies. Bat speed approximately correlates with the moment of inertia of the bat about a vertical
axis of rotation through the batter's body, the speed generally decreasing as this moment of inertia increases. The analytical
model assumes pure rotation of the batter/bat system about a vertical axis through the batter's body. Aerodynamic drag of
the batter's arms and the bat is included in the model. The independent variable is bat moment of inertia about the rotation
axis. There is reasonable agreement between the model and the measured speeds. Detailed differences between the two suggest
the importance of additional degrees of freedom in determining swing speed. 相似文献
102.
Rowe DA McDonald SM Mahar MT Raedeke TD 《Research quarterly for exercise and sport》2005,76(4):407-415
A multitrait-multimethod (MTMM) matrix was used to evaluate validity evidence for a digital image manipulation (DIM) body image measurement technique in young women. One hundred one young women completed the DIM procedure and the Thompson and Gray (1995) Contour Drawing Rating Scale to measure self-ideal discrepancy and size perception accuracy components of body image. Seven-day test-retest reliability was acceptable (R = .81-.95). Convergent validity for self-ideal discrepancy was higher (r = .74) than the corresponding heterotrait, monomethod coefficients (r = .46, r = .23) and heterotrait-heteromethod coefficients (r = .18, r = .12). However, the convergent validity coefficient for size perception accuracy was r = .12. The pattern of correlations in the MTMM matrix met the criteria of Campbell and Fiske (1959) for validity of these procedures to measure self-ideal discrepancy but not size perception accuracy. The DIM procedure addresses some of the criticisms associated with figure-rating scales, such as unrepresentativeness of the figures, scale coarseness, and restriction of range in responses. DIM, therefore, represents a realistic, valid alternative to figure-rating scales for measuring self-ideal discrepancy. 相似文献
103.
A Murray TC Aitchison G Ross K Sutherland I Watt D McLean 《Journal of sports sciences》2013,31(9):927-935
The aim of this study was to compare sprint performance over 10 and 20?m when participants ran while towing resistances, weighing between 0 and 30% of body mass. The sample of 33 participants consisted of male rugby and soccer players (age 21.1?±?1.8 years, body mass 83.6?±?13.1?kg, height 1.82?±?0.1?m; mean?±?s). Each participant performed two sets of seven sprints over 20?m using a Latin rectangular design. The times were recorded at 10 and 20?m using electronic speed gates. The sprints of 13 players were video-recorded to allow calculation of stride length and frequency. For both sprints, a quadratic relationship was observed between sprint time and resistance as sprint time increased from 2.94?s to 3.80?s from 0 to 30% resistance. This relationship was statistically significant but considered not to be meaningful for performance because, over the range of resistances used in this study, the quadratic model was never more than 1% (in terms of sprint time) from the linear model. As resistance increased, the stride length shortened, with mean values of 1.63?±?0.13?m at 0% body mass and 1.33?±?0.13?m at 30% of body mass. There was no significant change in stride frequency with increasing resistance. The results show that in general there is an increase in sprint time with an increase in resistance. No particular resistance in the range tested (0?–?30%) can be recommended for practice. 相似文献
104.
SCHOOL RACIAL CLIMATE AND THE ACADEMIC ACHIEVEMENT OF AFRICAN AMERICAN HIGH SCHOOL STUDENTS: THE MEDIATING ROLE OF SCHOOL ENGAGEMENT 下载免费PDF全文
Charity Brown Griffin Shauna M. Cooper Isha W. Metzger Alexandrea R. Golden C. Nicole White 《Psychology in the schools》2017,54(7):673-688
This investigation utilized an integrative model of development for ethnic minority children and a process model of engagement to explore whether three dimensions of school engagement (behavioral, emotional, and cognitive) mediated relationships between school racial climate, academic performance, and educational aspirations. A total of 139 African American students were recruited from a high school in the southeastern United States. Findings revealed an indirect association between perceptions of racial fairness and academic achievement indicators through behavioral and cognitive engagement. Behavioral and cognitive engagement also mediated relationships between youths’ perceived peer discrimination and academic achievement indicators. No significant indirect associations between teacher discrimination and academic achievement through school engagement dimensions were found. Study limitations, future directions, and implications are discussed. 相似文献
105.
Thomas Kwan-choi Tse 《British Journal of Religious Education》2017,39(3):257-268
Plans by the Hong Kong Government to introduce moral and national education (MNE) as a compulsory subject in primary and secondary schools in 2010 encountered strong opposition. The controversy over the plans has lasted for two years, with the government and its supporters claiming that the subject will help to instil a stronger sense of national identity in children and critics deriding it as biased and constituting a form of brainwashing. The subject is also seen as posing troubles or a considerable threat to local Christian schools because most of them have had their own religious education programmes for years. Most Christian school-sponsoring bodies and parachurch organisations oppose the subject’s introduction, urging the government to scrap its curricular guidelines, and many say they will boycott its implementation. To bring the issues surrounding MNE into sharper focus, this article traces the development of Christian education in Hong Kong and analyses how local Christian communities perceive and have responded to the official proposal. Three prominent themes commonly emphasised in the Christian discourse are plural identities, conditional patriotism and universal values. These themes could shed light on wider theoretical discussion about the positive roles of religion and religious education for citizenship education. 相似文献
106.
Sasha Nikolic Thomas F. Suesse Timothy J. McCarthy Thomas L. Goldfinch 《European Journal of Engineering Education》2017,42(6):1277-1295
Minimal research papers have investigated the use of student evaluations on the laboratory, a learning medium usually run by teaching assistants with little control of the content, delivery and equipment. Finding the right mix of teaching assistants for the laboratory can be an onerous task due to the many skills required including theoretical and practical know-how, troubleshooting, safety and class management. Using larger classes with multiple teaching assistants, a team-based teaching (TBT) format may be advantageous. A rigorous three-year study across twenty-five courses over repetitive laboratory classes is analysed using a multi-level statistical model considering students, laboratory classes and courses. The study is used to investigate the effectiveness of the TBT format, and quantify the influence each demonstrator has on the laboratory experience. The study found that TBT is effective and the lead demonstrator most influential, influencing up to 55% of the laboratory experience evaluation. 相似文献
107.
The present study explored the relationship between the intelligence of young adults and their performance on the Test of Variables of Attention (TOVA). The study also examined whether significant differences existed between adults with and without attention-deficit/ hyperactivity disorder (ADHD) on TOVA errors of omission, errors of commission, mean correct response time, and variability, as well as on performance on the freedom from distractibility (FD) factor on the Wechsler Adult Intelligence Scale-Revised (WAIS-R). Seventy-nine adults participated in the study, including 17 with ADHD and 62 college students without ADHD. Pearson product-moment correlations indicated that none of the correlations between Full Scale IQ (FSIQ) and TOVA variables were significant. Analysis of variance results revealed that adults with ADHD made more errors of omission on the TOVA than did controls. Between-group differences were not found on the remaining dependent variables. 相似文献
108.
109.
OBJECTIVE: Previous research has indicated that women who experience childhood physical abuse or childhood sexual abuse are at increased risk for posttraumatic stress disorder (PTSD) and adult victimization. Recently, peritraumatic dissociation (PD) has been suggested as another possible risk factor for PTSD and adult victimization. The purpose of the present study was to investigate the effects of childhood physical and sexual abuse and PD on PTSD and adult victimization. METHOD: A sample of 467 female college students completed questionnaires about childhood and adult sexual and physical abuse experiences, PD, and PTSD symptoms. RESULTS: The combined sexual and physical abuse (CA) and sexual abuse only (SA) groups reported significantly higher numbers of PTSD symptoms than the physical abuse only (PA) and no abuse (NA) groups. The CA and PA groups reported significantly more adult sexual and physical victimization than the SA and NA groups. Across all four groups, higher levels of PD were associated with higher levels of PTSD and adult sexual and physical victimization. CONCLUSIONS: The results of the current study suggest that different types of childhood abuse may lead to different adult problems. The results also indicated that PD may have a broad effect on PTSD development and adult victimization. 相似文献
110.
The first large-scale, nationwide academic achievement testing program using Stanford Achievement Test (Stanford) for deaf and hard-of-hearing children in the United States started in 1969. Over the past three decades, the Stanford has served as a benchmark in the field of deaf education for assessing student academic achievement. However, the validity and reliability of using the Stanford for this special student population still require extensive scrutiny. Recent shifts in educational policy environment, which require that schools enable all children to achieve proficiency through accountability testing, warrants a close examination of the adequacy and relevance of the current large-scale testing of deaf and hard-of-hearing students. This study has three objectives: (a) it will summarize the historical data over the last three decades to indicate trends in academic achievement for this special population, (b) it will analyze the current federal laws and regulations related to educational testing and special education, thereby identifying gaps between policy and practice in the field, especially identifying the limitations of current testing programs in assessing what deaf and hard-of-hearing students know, and (c) it will offer some insights and suggestions for future testing programs for deaf and hard-of-hearing students. 相似文献