Describing the plastic deformation of aluminium softball bats

Hollow aluminium bats were introduced over 30 years ago to provide improved durability over wooden bats. Since their introduction, however, interest in hollow bats has focused almost exclusively around their hitting performance. The aim of this study was to take advantage of the progress that has been made in predicting bat performance using finite elements and apply it to describe bat durability. Accordingly, the plastic deformation from a ball impact of a single-wall aluminum bat was numerically modelled. The bat deformation from the finite-element analysis was then compared with experiment using a high-speed bat test machine. The ball was modelled as an isotropic, homogeneous, viscoelastic sphere. The viscoelastic parameters of the ball model were found from instrumented, high-speed, rigid-wall ball impacts. The rigid-wall ball impacts were modelled numerically and showed good agreement with the experimentally obtained response. The strain response of the combined bat-ball model was verified with a strain-gauged bat at intermediate ball impact speeds in the elastic range. The strain response of the bat-ball model exhibited positive correlation with the experimental measurements. High-speed bat-ball impacts were performed experimentally and simulated numerically at increasing impact speeds which induced correspondingly increased dent sizes in the bat. The plastic deformation from the numerical model found good agreement with experiment provided the aluminium work hardening and strain rate effects were appropriately described. The inclusion of strain rate effects was shown to have a significant effect on the bat deformations produced in the finite-element simulations. They also helped explain the existence of high bat stresses found in many performance models.     

Analysis of non-urban end users' MEDLINE training.

The University of Oklahoma Health Sciences Center (OUHSC) Library mailed a MEDLINE End User Practice Survey Form to 310 health professionals who had attended MEDLINE seminars supported by a two-year NLM grant. The survey sought to determine how many respondents had obtained NLM codes, reasons for not obtaining a code, searching time done since the seminar, differences in the use of information since taking the seminar, factors helpful in successful searching, and factors contributing to frustrations. The most prevalent reasons for not obtaining a code were lack of a microcomputer and modem, infrequent use of MEDLINE, cost, lack of time, complications, and ability to obtain free searches.     

The influence of live- vs. video-model presentation on the early acquisition of a new complex coordination

Background: Demonstration is a widely used method in sports teaching and coaching, based on the assumption that it is more beneficial than verbal instructions or trial-and-error methods for skill acquisition. Although in teaching/coaching situations, the demonstration is usually carried out in front of the learners, in a research context, it is most often presented via a video. However, a direct comparison between these two types of model has rarely been undertaken in a motor context.

Purpose: In this study, we aimed to compare the effectiveness of the observation of a live and a videomodel for the early acquisition of a complex judo movement.

Research Design: Participants observed either a live or a videomodel executing the task. After observation, they practised for three minutes taking five trials and then performed it for analysis. This procedure was repeated three times. The form and technique of each participant's execution were evaluated using a technical score.

Main results: The results indicated a significant improvement in the task execution by the end of the practice session. However, this improvement occurred only for the video-model group between the second and third blocks of practice.

Conclusions: The video demonstration seems more effective than the live one for the early acquisition of a completely new complex coordination. This may be due to the simplification of the visual information in the former condition because of its two-dimensionality. This simplification may allow the observer to identify the more key elements that would guide him/her for the subsequent performance of the task.     

Prenatal Caloric Intake and the Development of Academic Achievement Among U.S. Children From Ages 5 to 14

Few studies have examined the relation between maternal caloric intake during pregnancy and growth in child academic achievement while controlling for important confounding influences. Using data from the National Longitudinal Survey of Youth, the current study examined the effects of reduced prenatal caloric intake on growth in scores on the Peabody Individual Achievement Test from ages 5 to 14. While models controlling for within‐family covariates showed that prenatal caloric intake was associated with lower reading and mathematical achievement at age 5, models controlling for between‐family covariates (such as maternal IQ) and unobserved familial confounders revealed only a statistically significant association between siblings differentially exposed to prenatal caloric intake and mathematical achievement at age 5.