A three-dimensional analysis of the contributions of upper limb joint movements to horizontal racket head velocity at ball impact during tennis serving

In this study, we examined the relationship between upper limb joint movements and horizontal racket head velocity to clarify joint movements for developing racket head speed during tennis serving. Sixty-six male tennis players were videotaped at 200 Hz using two high-speed video cameras while hitting high-speed serves. The contributions of each joint rotation to horizontal racket velocity were calculated using vector cross-products between the angular velocity vectors of each joint movement and relative position vectors from each joint to the racket head. Major contributors to horizontal racket head velocity at ball impact were shoulder internal rotation (41.1%) and wrist palmar flexion (31.7%). The contribution of internal rotation showed a significant positive correlation with horizontal racket head velocity at impact (r = 0.490, P < 0.001), while the contribution of palmar flexion showed a significant negative correlation (r = - 0.431, P < 0.001). The joint movement producing the difference in horizontal racket head velocity between fast and slow servers was shoulder internal rotation, and angular velocity of shoulder internal rotation must be developed to produce a high racket speed.     

What causes the similarities and differences among the social sciences in different cultures? Focusing on Japan and the West

As the title suggest, this article attempts to account for variations in the approach to the social sciences between Japan and the West. Ito identifies and provides examples for two categories of research that are peculiar to Japan: (1) A tradition of academic interest in long‐term longitudinal social surveys; and (2) Theories that are based on words and concepts that are unique to the Japanese language and experience. He also covers the special focus that Disaster Communication research has had in the country.

The second half of the paper deals with the great deal of similarities in approach to research between the West and Japan by looking at the significance and impact of key developments in the histories of the two cultures.     

具有有限检查次数的库存系统最优点检策略

首先导出了点检时间序列相对应的期望成本 .由于使具有有限点检次数库存系统期望成本降低到最小的最优点检时间序列的数值计算比较困难 ,本文给出了计算一般最优点检时间序列的算法和Weibull分布情况下的计算步骤实例 .据此计算出最优点检策略的数值结果 .与周期点检策略相比 ,本文策略有效地降低了成本 .     

Factors affecting achievement in a satellite‐delivered Japanese language program

Abstract

This article reviews previous research and reports on a study relating to six factors relevant to achievement in learning a new language: motivation, language learning styles, language learning strategies, gender, course level, and previous experience in learning a foreign language. Although motivation, learning styles, gender, and learning strategy use were all found to be influential, motivation was the single most important predictor of success. The authors suggest that awareness and understanding of the influence and interaction of student characteristics on achievement will allow instructors to provide optimal learning opportunities for all students.     

Neurodevelopmental Correlates of Theory of Mind in Preschool Children

Baseline electroencephalogram (EEG) data were collected from twenty-nine 4-year-old children who also completed batteries of representational theory-of-mind (RTM) tasks and executive functioning (EF) tasks. Neural sources of children's EEG alpha (6–9 Hz) were estimated and analyzed to determine whether individual differences in regional EEG alpha activity predicted children's RTM performance, while statistically controlling for children's age and EF skills. Results showed that individual differences in EEG alpha activity localized to the dorsal medial prefrontal cortex (dMPFC) and the right temporal–parietal juncture (rTPJ) were positively associated with children's RTM performance. These findings suggest that the maturation of dMPFC and rTPJ is a critical constituent of preschoolers' explicit theory-of-mind development.     

The optimal object posture that minimizes contact forces in grasping

Because of the ill-posedness of grasping, one feasible method must be selected from possible strategies. Among many factors, this paper focuses on the posture of an object: which object direction is best when it is grasped. Then, the object is assumed to be held with three points where the contact forces can be generated in any directions. To evaluate the object posture, the norm of contact force vector consisting of the normal and tangential forces is selected. Consequently, the contact force becomes minimal when the center of mass of the grasped object and the centroid of the triangle composed by three contact points are aligned in the gravitational direction.