Bat speed,trajectory, and timing for collegiate baseball batters hitting a stationary ball

The aims of this study were to examine whether batters hit stationary balls at the time of peak speed of the bat head and whether the impact occurs at the lowest point of the bat trajectory. Eight university baseball players hit three balls, each hung with a string; each ball was made of a different material and was different in weight. Bat movement was captured by four 240-Hz infrared cameras and analysed three-dimensionally. Time for peak speed of the bat head varied according to the conditions. When stationary balls of standard weight were used, the bat head was at maximum speed at impact with the ball; then, it decelerated drastically owing to the impact. In contrast, maximum speed was obtained after impact when lightweight stationary balls were used. The time–speed profile of the bat head before impact in the lightweight ball condition was identical with that in the standard weight ball condition. Regardless of conditions, the timing of the lowest point of the bat head was nearly identical for each batter and most participants hit the stationary balls at about the lowest point of the bat trajectory     

Modelling the flight of a soccer ball in a direct free kick

This study involved a theoretical and an experimental investigation of the direct free kick in soccer. Our aim was to develop a mathematical model of the ball's flight incorporating aerodynamic lift and drag forces to explore this important 'set-play'. Trajectories derived from the model have been compared with those obtained from detailed video analysis of experimental kicks. Representative values for the drag and lift coefficients have been obtained, together with the implied orientation of the ball's spin axis in flight. The drag coefficient varied from 0.25 to 0.30 and the lift coefficient from 0.23 to 0.29. These values, used with a simple model of a defensive wall, have enabled free kicks to be simulated under realistic conditions, typical of match-play. The results reveal how carefully attackers must engineer the dynamics of a successful kick. For a central free kick some 18.3 m (20 yards) from goal with a conventional wall, and initial speed of 25 m·s^?1, the ball's initial elevation must be constrained between 16.5° and 17.5° and the ball kicked with almost perfect sidespin.     

Promoting Psychological Growth in a High School Class

This article describes a curriculum and presents the research results of a primary prevention model which was designed to promote the personal growth of high school students and was unlike most high school remedial counseling models. The intervention served as an operational translation of cognitive-development theory. Using a practicum-seminar format, students learned and practiced the basic counseling skills of active listening-empathic responding. The development of role taking was seen as the essential variable in the promotion of personal growth and development.     

人力资本产权残缺与员工激励效率损失

产权的一个最主要功能是给主体以激励。完整的人力资本产权能够给人力资本载体以激励,使其最大限度地提高人力资本的使月效率．而人力资本产权的残缺将会带来激励的困难．当前我国大多数企业存在着人力资本产权残缺的问题,即企业对员工人力资本的所有权、使用权以及处置权的不恰当分配和使用使得其收益权无法实现,最终导致员工激励效率损失,减少人力资本有效供给量,造成企业绩效的降低．     

SCRAMBLING CONTENT IN ACHIEVEMENT TESTING: AN APPLICATION OF MULTIPLE MATRIX SAMPLING IN EXPERIMENTAL DESIGN

This study was designed to research the question of scrambling item content in the construction of achievement tests, so that very general implications could be drawn for both examinee and item populations. To achieve this generality, the methodology of multiple matrix sampling was combined with a simple two group experimental design: a random group of 8th graders responded to mathematics, science, social studies, reading, and language arts achievement items organized in a scrambled (random) test format, while another random group responded to the same items organized in a fixed (segregated by subject matter) test format. The results indicated that scrambling cognitive test items has minimal or no effect on mean examinee test performance or on any of the other parameters included in the analysis.     

Personal variables affecting the perspectives of head‐teachers and teachers towards teacher participation in school decision‐making

The article reviews research which has taken place relating to the influence of certain biographical factors on head‐teacher and teacher perspectives on who should take decisions within schools. The particular biographical factors which are considered are status, sex, age, length of experience and school size. Each is examined independently and shown to have some influence though existing research does not always agree on the type or extent of this influence. The article concludes by stating that whatever this influence might be, it is only one small aspect of the complex decision‐making process.     

A Profile of Lousy Supervision: Experienced Counselors' Perspectives

The authors used data from interviews with experienced counselors to examine ineffective supervision practices. The data yielded 6 overarching principles (e.g., unbalanced, intolerant of differences, untrained/immature) that permeated 3 general spheres of lousy supervision (e.g., technical/cognitive).