Comparison of a finite element model of a tennis racket to experimental data

Modern tennis rackets are manufactured from composite materials with high stiffness-to-weight ratios. In this paper, a finite element (FE) model was constructed to simulate an impact of a tennis ball on a freely suspended racket. The FE model was in good agreement with experimental data collected in a laboratory. The model showed racket stiffness to have no influence on the rebound characteristics of the ball, when simulating oblique spinning impacts at the geometric stringbed centre. The rebound velocity and topspin of the ball increased with the resultant impact velocity. It is likely that the maximum speed at which a player can swing a racket will increase as the moment of inertia (swingweight) decreases. Therefore, a player has the capacity to hit the ball faster, and with more topspin, when using a racket with a low swingweight.     

Hydrostatic Weighing during Different Stages of the Menstrual Cycle

Abstract

This study compared the physiological responses (oxygen consumption and energy expenditure) of Nordic Walking to regular walking under field-testing conditions. Eleven women (M age = 27.1 years, SD = 6.4) and 11 men (M age = 33.8 years, SD = 9.0) walked 1,600 m with and without walking poles on a level, 200-m track. For women, Nordic Walking resulted in increased oxygen consumption (M = 14.9 ml·kg¹·min^?1 , SD = 3.2 vs. M = 17.9 ml·kg¹·min^?1 , SD = 3.5; p < .001), caloric expenditure (M = 4.6 kcal·min^?1 , SD = 1.2 vs. M = 5.4 kcal·min^?1 , SD = 1.2; p < .001), and heart rate (M = 113.7 bpm, SD = 12.0 vs. M = 118.7 bpm, SD = 14.8; p < .05) compared to regular walking. For men, Nordic Walking resulted in increased oxygen consumption (M = 12.8 ml·kg¹·min^?1 , SD = 1.8 vs. M = 15.5, SD = 3.4 ml·kg¹·min^?1; p < .01), caloric expenditure (M = 5.7 kcal·min^?1 , SD = 1.3 vs. M = 6.9 kcal·min^?1 , SD = 1.8; p < .001), and heart rate (M = 101.6 bpm, SD = 12.0 bpm vs. M = 109.8 bpm, SD = 14.7; p < .01) compared to regular walking. Nordic Walking, examined in the field, results in a significant increase in oxygen use and caloric expenditure compared to regular walking, without significantly increasing perceived exertion.     

Effects of an intervention programme with teachers on the development of positive behaviours in Spanish physical education classes

Background: The physical education (PE) context has been emphasised as an ideal environment for developing positive behaviours among students. Under the Positive Youth Development paradigm, various initiatives have been conducted with the aim of promoting personal and social responsibility among adolescents. Self-Determination Theory has been widely used to analyse students’ motivational processes during PE classes.

Purpose: This study aimed to measure the effects of a multidisciplinary intervention with teachers on the development of positive behaviours in PE classes.

Participants: Twenty PE teachers participated in the study (M_age?=?35 years; SD?=?2.32) along with 777 of their students (M_age?=?12.81 years; SD?=?.93). The teachers (male?=?16; female?=?4) were between the ages of 29 and 48 years (M?=?35.2 years; SD?=?2.32). The students who participated in this study (male?=?377; female?=?400) were divided into 52 classes and were between the ages of 12 and 16 years (M?=?12.81; SD?=?.93).

Research design: A quasi-experimental design was used that consisted of a control group and three groups in which an intervention was developed. In the control group, the teachers did not receive any type of intervention; in the second group, the teachers received a training programme to develop strategies for supporting basic psychological needs and promoting positive behaviours; in the third group, the teachers received a didactic unit to promote positive behaviours; and in the last group the teachers received a combination of the two previous interventions.

Data analysis: A repeated-measures ANCOVA (analysis of covariance) was used for every dependent variable included in the study to analyse the effect of Group?×?Time interaction, including Gender and Grade Level as covariates. The fixed effects caused by Intercept, Group, Time, and the Group?×?Time interaction were calculated using compound symmetry as the type of covariance and restricted maximum likelihood as the estimation method.

Findings: By examining the differences between pre-test and post-test, it was determined that in comparison with the students in the control group, the students from the three experimental groups had generally improved scores on the variables related to positive behaviours, such as perceptions of the teacher's support, as well as the development of the targeted behaviours.

Conclusions: These results provide information about the efficacy of an intervention programme with teachers that consists of strategies for developing positive behaviour and support for basic psychological needs to promote the development of positive student behaviour.     

A perpetual motion machine: The preserved digital scholarly record

• Digital preservation will never be a solved problem: it needs constant reinvention, and is going to become harder over time.
• Scholarship is changing and this is affecting what needs to be preserved and what preservation means to the future of knowledge discovery.
• The diversification of outputs means that knowledge exists in a network of contextual metadata, data, software, standards and publications—requiring multilateral management of this complex knowledge graph.
• Preservation demands new skills, technologies and resources from librarians, publishers, funders and institutions—and more joined-up thinking about archiving.