The planarity of the stickface motion in the field hockey hit

The field hockey hit is an important but poorly understood stroke. In this study, we investigated the planarity of the stickface motion during the downswing to better characterize the kinematics and to assess the suitability of planar pendulum models for simulating the hit. Thirteen experienced female field hockey players were filmed executing hits with a single approach step, and the kinematics of the centre of the stickface were measured. A method was developed for identifying how far back from impact the stickface motion was planar. Orthogonal regression was used to fit least-squares planes to the stickface path during sections of the downswing of varying length, with each section ending at impact. A section was considered planar if the root mean square residual between the stickface path and the fitted plane was less than 0.25% of the distance travelled by the stickface during that period. On average, the stickface motion was planar for the last 83 ± 12% of its downswing path, with the length of the planar section ranging from 1.85 m to 2.70 m. The suitability of a planar model for the stickface motion was supported, but further investigation of the stick and arm kinematics is warranted.     

A faster running speed is associated with a greater body weight loss in 100-km ultra-marathoners

In 219 recreational male runners, we investigated changes in body mass, total body water, haematocrit, plasma sodium concentration ([Na(+)]), and urine specific gravity as well as fluid intake during a 100-km ultra-marathon. The athletes lost 1.9 kg (s = 1.4) of body mass, equal to 2.5% (s = 1.8) of body mass (P < 0.001), 0.7 kg (s = 1.0) of predicted skeletal muscle mass (P < 0.001), 0.2 kg (s = 1.3) of predicted fat mass (P < 0.05), and 0.9 L (s = 1.6) of predicted total body water (P < 0.001). Haematocrit decreased (P < 0.001), urine specific gravity (P < 0.001), plasma volume (P < 0.05), and plasma [Na(+)] (P < 0.05) all increased. Change in body mass was related to running speed (r = -0.16, P < 0.05), change in plasma volume was associated with change in plasma [Na(+)] (r = -0.28, P < 0.0001), and change in body mass was related to both change in plasma [Na(+)] (r = -0.36) and change in plasma volume (r = 0.31) (P < 0.0001). The athletes consumed 0.65 L (s = 0.27) fluid per hour. Fluid intake was related to both running speed (r = 0.42, P < 0.0001) and change in body mass (r = 0.23, P = 0.0006), but not post-race plasma [Na(+)] or change in plasma [Na(+)] (P > 0.05). In conclusion, faster runners lost more body mass, runners lost more body mass when they drank less fluid, and faster runners drank more fluid than slower runners.     

Creatine kinase activity weakly correlates to volume completed following upper body resistance exercise

In the current study, we examined the relationship between serum creatine kinase (CK) activity following upper body resistance exercise with a 1- or 3-min rest between sets. Twenty men performed two sessions, each consisting of four sets with a 10-repetition maximum load. The results demonstrated significantly greater volume for the 3-min condition (M = 4156 kg, SD = 867, for 3 min; vs. M = 3503 kg SD = 759, for 1 min; p < .001), with no significant differences in delta CK activity between conditions (p = .574). Nevertheless, there was a weak correlation between the delta CK activity and total volume of exercise completed (r = .55 with a 1-min rest, and r = .45 with a 3-min rest). Therefore, the volume following upper body resistance exercise correlates weakly with serum CK levels, irrespective of rest interval length between sets.     

Robust block second order sliding mode control for a quadrotor

This paper presents the design of a controller based on the block control technique combined with the super twisting control algorithm for trajectory tracking of a quadrotor helicopter. A first order exact differentiator is used in order to estimate the virtual control inputs, which simplifies the control law design. In addition, the wind parameter resulting from the aerodynamic forces is also estimated in order to ensure robustness against these unmatched perturbations. The stability and finite time convergence of the exact differentiator have been recently proved by means of Lyapunov functions, and therefore the stability analysis of the proposed controller has been carried out along the same lines. The performance and effectiveness of the proposed controller are tested in a simulation study taking into account external disturbances.     

Parents and sex education—looking beyond ‘the birds and the bees’

The social and political climate of sex education over the last two decades has dramatically changed, with parents now being encouraged to work in partnership with professionals. This paper seeks to further the argument that involving parents in their child's sex education does matter and can have an impact on their child's future sexual health. It discusses the reality of parents' roles and skills in providing sex education within the family. In particular, the discussion explores myths parents associate with sex education, involving fathers in provision, siblings as peer educators, health professionals' attitudes towards involving parents, and school partnerships. The author calls for professionals to involve parents alongside other sources of sex education in health and educational strategies to address sexual health issues and improve sex education. Otherwise future generations of children will experience a closed cultural attitude towards sexual matters and we will not achieve lower teenage pregnancy rates or view sex education positively.     

Towards an American Jewish Education

My function is to analyze a survey of adult Jewish education and to present briefly some of my own views on the subject. The survey was planned and conducted under the direction of the National Advisory Council on Adult Jewish Education of the American Association for Jewish Education. The Advisory Council includes the directors or representatives of a number of important religious and lay national Jewish agencies which sponsor adult Jewish education. The responses to the questionnaires were analyzed and the Survey Report was written by Rabbi Samuel I. Cohen.     

The Jewish Educational System—A Plea for Organic Unity

This article analyzes the career commitments and retention patterns among graduates of the DeLeT program (Day School Leadership Through Teaching) who were prepared for day-school teaching at Brandeis University and Hebrew Union College-Jewish Institute of Religion. Employing t-tests to analyze survey responses, we identify factors that shape and support teachers' career commitments to Jewish day schools. Our findings suggest that those who stay in Jewish day school teaching are likely to do so because of more commitment to the Jewish community, greater perception of effective teacher preparation experience, and better school support in comparison to those who leave teaching in this setting. These findings are consistent with a multi-layered understanding of teachers' lives and career commitments, which is illustrated in the interaction between person, program, and setting.