Tennis forehand kinematics change as post-impact ball speed is altered     

Seeley MK  Funk MD  Denning WM  Hager RL  Hopkins JT 《Sports biomechanics / International Society of Biomechanics in Sports》2011,10(4):415-426

Peak joint angles and joint angular velocities were evaluated for varying speed forehands in an attempt to better understand what kinematic variables are most closely related to increases in post-impact ball velocity above 50% of maximal effort. High-speed video was used to measure three-dimensional motion for 12 highly skilled tennis players who performed forehands at three different post-impact ball speeds: fast (42.7 +/- 3.8 m/s), medium (32.1 +/- 2.9 m/s), and slow (21.4 +/- 2.0 m/s). Several dominant-side peak joint angles (prior to ball impact) increased as post-impact ball speed increased from slow to fast: wrist extension (16%), trunk rotation (28%), hip flexion (38%), knee flexion (27%), and dorsiflexion (5%). Between the aforementioned peak joint angles and ball impact, dominant-side peak angular velocities increased as ball speed increased from slow to fast: peak wrist flexion (118%), elbow flexion (176%), trunk rotation (99%), hip extension (143%), knee extension (56%), and plantarflexion (87%). Most kinematic variables changed as forehand ball speed changed; however, some variables changed more than others, indicating that range of motion and angular velocity for some joints may be more closely related to post-impact ball speed than for other joints.  相似文献   

友善员工更富于创造力     

Cheyenne Hopkins 《海外英语》2003,(11):17

It may seem more professional to stay impersonal(非个人的)at work, but in fact friendlier employees are more productive.A comparison of the American work ethic(道德规范)toapproaches in other countries shows that keeping an emotional distance may not be the most effective way to get the job done.  相似文献   

Are Virtual Labs as Effective as Hands-on Labs for Undergraduate Physics? A Comparative Study at Two Major Universities     

Marjorie Darrah  Roxann Humbert  Jeanne Finstein  Marllin Simon  John Hopkins 《Journal of Science Education and Technology》2014,23(6):803-814

Most physics professors would agree that the lab experiences students have in introductory physics are central to the learning of the concepts in the course. It is also true that these physics labs require time and money for upkeep, not to mention the hours spent setting up and taking down labs. Virtual physics lab experiences can provide an alternative or supplement to these traditional hands-on labs. However, physics professors may be very hesitant to give up the hands-on labs, which have been such a central part of their courses, for a more cost and time-saving virtual alternative. Thus, it is important to investigate how the learning from these virtual experiences compares to that acquired through a hands-on experience. This study evaluated a comprehensive set of virtual labs for introductory level college physics courses and compared them to a hands-on physics lab experience. Each of the virtual labs contains everything a student needs to conduct a physics laboratory experiment, including: objectives, background theory, 3D simulation, brief video, data collection tools, pre- and postlab questions, and postlab quiz. This research was conducted with 224 students from two large universities and investigated the learning that occurred with students using the virtual labs either in a lab setting or as a supplement to hands-on labs versus a control group of students using the traditional hands-on labs only. Findings from both university settings showed the virtual labs to be as effective as the traditional hands-on physics labs.  相似文献   

The Accuracy of Dixon’s Formula for Obtaining Critical F-Values     

James R. Morrow JR.  Kenneth D. Hopkins 《Journal of Experimental Education》2013,81(2):113-115

The F-distribution approximation suggested by Dixon was investigated at various combinations of alpha and degrees of freedom. Tabled values were compared with values computed utilizing the suggested formula. The results indicate that while the formula is not useful in all cases, the adequacy of the approximation generally increases as alpha, v₁, and v₂ increase. It is suggested that the approximation may be utilized when certain restrictions regarding alpha, v1, and v2 are met.  相似文献   

Scaling Up Innovative Technology-Based Mathematics     

Deborah Tatar  Jeremy Roschelle  Jennifer Knudsen  Nicole Shechtman  Jim Kaput  Bill Hopkins 《学习科学杂志》2013,22(2):248-286

We report on the initial attempts at evaluating at scale a particular technological/curricular innovation that enables more students to develop deeper knowledge. The methods, issues, and findings of the current pilot experiment speak not only to the success of SimCalc MathWorlds, the focus of our research program, but also to the evaluation at scale of a broad class of representationally innovative technologies and to the merit of long-term investment in design-based research. In particular, we present conditions and findings from a completed pilot experiment involving 21 seventh-grade mathematics teachers from Texas. Pilot outcomes suggest that (a) innovative representational technologies can have an important impact on student learning, (b) considerable impact can be found across a wide range of teachers and conditions, and (c) these gains can be detected even in the absence of other desirable conditions. In particular, detection of student gains does not, in our case, depend on having a long-term context of learning, long-term teacher professional development, or a shift to learner-centered constructivist pedagogy. The full experiment will replicate and extend our experimental design with a wider range of teachers and schools, model the factors that contribute to classroom success with such technology, and explore what happens as research support fades away.  相似文献   

The path of least resistance: a voice‐relational analysis of disabled students’ experiences of discrimination in English universities     

Laurence Hopkins 《International Journal of Inclusive Education》2013,17(7):711-727

Recent legislation means that it is now illegal to treat a student, for reasons relating to a disability, less favourably than a non‐disabled student unless this is justified to maintain academic standards. However, recent research has identified numerous barriers faced by students with disabilities when they attempt to access the higher education curriculum. This study uses a methodology combining life‐story approaches with a voice‐relational analysis and aims to explore in more detail these barriers by listening to first person accounts from university students with a disability. The students’ narratives suggest that disabled students have to work considerably harder than non‐disabled students to overcome a wide range of physical, attitudinal, social, cultural and political barriers. Students appear to take the path of least resistance by choosing routes where the barriers are least great and it is argued that in this way they are being discriminated against. The research shows that voice‐relational methodology is excellent at producing a thorough account of the phenomenological world of these students without neglecting a materialist and cultural analysis of their environment. These insider perspectives are then used to suggest possible improvements to policy and practice in higher education.  相似文献   

The relationship between quality of the present level of academic achievement and functional performance statement and student learning     

Matthew K. Burns  Erica S. Lembke  McKinzie D. Duesenberg-Marshall  Stephanie Hopkins  Stacy Hirt  Monica E. Romero  Elizabeth Thomas  Jo Ann Steinbauer  Amber Del Gaiso  Scott Crooks 《Journal of Research in Special Educational Needs》2023,23(4):365-374

The present level of academic achievement and functional performance (PLAAFP) is an essential component of the individualised educational program (IEP) process because it identifies student strengths and areas for growth. However, there is minimal research that examines components of an IEP and student outcomes. The current study examined the relationship between PLAAFP quality and student achievement, and between training and ongoing professional development and quality of the PLAAFP. The data were obtained from 211 special education teachers in one state. Results suggested that ongoing professional development predicted the quality of the PLAAFP statement, accounted for a large amount of the variance (r² = 0.14) in the PLAAFP quality score, and was a stronger predictor than participating in a single training. Additionally, PLAAFP quality predicted winter achievement scores beyond the school district, fall achievement scores and teacher variables, and accounted for significant and moderate amount of unique variance for reading (r² = 0.05) and math (r² = 0.07). Implications for research and practice are included.  相似文献   

Seasonal training and performance of competitive swimmers     

Andrew M. Stewart  William G. Hopkins 《Journal of sports sciences》2013,31(11):873-884

To determine the relationship between prescribed training and seasonal-best swimming performance, we surveyed 24 swim coaches and 185 of their age-group and open-class swimmers specializing in sprint (50 and 100 m) and middle-distance (200 and 400 m) events in a summer and winter season. We expressed effects on training as either multiples of swimmers' standard deviations (effect size, ES) or as correlations ( r ). Coaches prescribed higher mileage and longer repetitions of lower intensity to middle-distance swimmers than to sprinters (ES = 0.4-1.5); as competitions approached, repetition intensity and duration of rest intervals increased (ES = 0.5-0.9), whereas session and repetition distances decreased (ES = 0.4-1.3). The 95% likely ranges of the true values for these effects were about - 0.3. Weekly mileage swum at an easy or moderate pace remained at almost 60% of the total throughout both seasons. Interval training reduced gradually from 40% of total distance in the build-up to 30% at the end of tapering. Older swimmers had shorter rests and swam more miles ( r = 0.5-0.8). After partialling out the effects of age on performance ( r = 0.7-0.8), better performance was significantly associated only with greater weekly mileage ( r = 0.5-0.8) and shorter duration of rest intervals ( r = 0.6-0.7) in middle-distance swimmers. Weconclude that periodization of training and differences in training between sprint and middle-distance events were broadly in accord with principles of specificity. Strong effects of specificity on performance were not apparent, but weak effects might have been detected with a larger sample.  相似文献   

The effect of recovery strategies on physical performance and cumulative fatigue in competitive basketball     

Paul G. Montgomery  David B. Pyne  Will G. Hopkins  Jason C. Dorman  Katherine Cook  Clare L. Minahan 《Journal of sports sciences》2013,31(11):1135-1145

Abstract

To evaluate the effectiveness of recovery strategies on physical performance during a 3-day tournament style basketball competition, 29 male players (mean age 19.1 years, s = 2.1; height 1.84 m, s = 0.34; body mass 88.5 kg, s = 14.7) were assigned to one of three treatment groups: carbohydrate + stretching (7.7 g · kg ^?1 · day ^?1, s = 1.7; ‘n = 9), cold water immersion (11°C, 5 × 1; n = 10) or full leg compression garments (18 mmHg, ～18 h; n = 10). Effects of the recovery strategies on pre–post tournament performance tests were expressed as the mean change (% ± standard deviation of the change score). Changes and differences were standardized for accumulated game time, assessed against the smallest worthwhile change for each test, and reported qualitatively. Accumulated fatigue was evident over the tournament with small to moderate impairments in performance tests. Sprint and agility performance decreased by 0.7% (s = 1.3) and 2.0% (s = 1.9) respectively. Vertical jump decreased substantially after the first day for all treatments, and remained suppressed post-tournament. Cold water immersion was substantially better in maintaining 20-m acceleration with only a 0.5% (s = 1.4) reduction in 20-m time after 3 days compared with a 3.2% (s = 1.6) reduction for compression. Cold water immersion (?1.4%, s = 1.7) and compression (?1.5%, s = 1.7) showed similar substantial benefits in maintaining line-drill performance over the tournament, whereas carbohydrate + stretching elicited a 0.4% (s = 1.8) reduction. Sit-and-reach flexibility decreased for all groups, although cold water immersion resulted in the smallest reduction in flexibility. Basketball tournament play elicited small to moderate impairments in physical test performance. In conclusion, cold water immersion appears to promote better restoration of physical performance measures than carbohydrate + stretching routines and compression garments.  相似文献   

大学生感觉寻求人格特质与网络成瘾     

郭莲荣  梅松丽  张明 《教育科学》2009,25(3)

目的:调查大学生网络使用情况、感觉寻求特点及其与网络成癌的关系.方法:采用基本信息问卷、网络使用情况问卷、网络成瘾问卷、感觉寻求问卷对651名大学生进行调查.结果表明:(1)网络成瘾总分不具有性别、年龄、年级、专业、家庭类型、父母学历、网龄的差异性;(2)网络成瘾总分具有上网地点、生源、网络功能使用、网络使用目的的差异性;(3)网络成瘾总分与周上网时间、周上网次数、每次上网时间具有高相关;(4)网络成瘾总分与去抑制分量表得分与感觉寻求总分相关显著.结论:网络成瘾与网络使用情况、感觉寻求特点具有一定的关系.  相似文献