The application of biomechanics to penalty corner drag-flick training: a case of Study

The penalty corner is one of the most important game situations in field hockey with one third of all goals resulting from this tactical situation. The aim of this study was to develop and apply a training method, based on previous studies, to improve the drag- flick skill on a young top-class field hockey player. A young top-class player exercised three times per week using specific drills over a four week period. A VICON optoelectronic system (Oxford Metrics, Oxford, UK) was employed to capture twenty drag-flicks, with six cameras sampling at 250 Hz, prior and after the training period. In order to analyze pre- and post-test differences a dependent t-test was carried out. Angular velocities and the kinematic sequence were similar to previous studies. The player improved (albeit not significantly) the angular velocity of the stick. The player increased front foot to the ball at T1 (p < 0.01) and the drag-flick distances. The range of motion from the front leg decreased from T1 to T6 after the training period (p < 0.01). The specific training sessions conducted with the player improved some features of this particular skill. This article shows how technical knowledge can help with the design of training programs and whether some drills are more effective than others.

Injury incidence in a Spanish sub-elite professional football team: A prospective study during four consecutive seasons

The aim of this study was to investigate the injury incidence and injury characteristics of a Spanish sub-elite professional football team during four consecutive seasons. A team was followed prospectively from the season 2003-2004 to 2006-2007 and individual player exposure and time loss injuries were recorded during all club training sessions and matches. A total of 313 time-loss injuries were recorded. The mean injury incidence was 10.9 injuries/1000 hours (5.2 injuries/1000 training hours and 44.1 injuries/1000 match hours). The injury incidence during competitive matches was higher (p < 0.001) than in friendly matches (55.8 vs. 22.6 injuries/1000 hours). The incidence of major injuries (>28 days absence) was 0.4 injuries/1000 hours. The thigh was the most commonly (35%) injured region and caused 29% of all competitive match absence. Muscle injuries in the four main groups of the lower limbs (hamstrings, adductors, quadriceps and calf muscles) caused 43% of competitive match unavailability. The results of this study show that the risk to sustain a major injury in the course of the season was low for sub-elite footballers in comparison to elite players. Thigh strains were the first cause of absence in competition due to injury.

Percolation in soils at Different Bulk Densities: Porosity, Connectivity and Grey Threshold.

To improve percolation modelling on soils the geometrical properties of the pore space must be understood; this includes porosity, particle and pore size distribution and connectivity of the pores. A study was conducted with a soil at different bulk densities based on 3D grey images acquired by X-ray computed tomography. The objective was to analyze the effect in percolation of aspects of pore network geometry and discuss the influence of the grey threshold applied to the images. A model based on random walk algorithms was applied to the images, combining five bulk densities with up to six threshold values per density. This allowed for a dynamical perspective of soil structure in relation to water transport through the inclusion of percolation speed in the analyses. To evaluate separately connectivity and isolate the effect of the grey threshold, a critical value of 35% of porosity was selected for every density. This value was the smallest at which total-percolation walks appeared for the all images of the same porosity and may represent a situation of percolation comparable among bulks densities. This criterion avoided an arbitrary decision in grey thresholds. Besides, a random matrix simulation at 35% of porosity with real images was used to test the existence of pore connectivity as a consequence of a non-random soil structure.

Kinematical Comparison of the 200 m Backstroke Turns between National and Regional Level Swimmers

biomecanica de la natación

Towards efficient processing of RDF Data Streams

In the last years, there has been an increase in the amount of real-time data generated. Sensors attached to things are transforming how we interact with our environment. Extracting meaningful information from these streams of data is essential for some application areas and requires processing systems that scale to varying conditions in data sources, complex queries, and system failures. This paper describes ongoing research on the development of a scalable RDF streaming engine.

Thermal control of SUNRISE, a balloon-borne solar telescope

SUNRISE is a balloon-borne solar telescope flown with a long-duration balloon by NASA's Columbia Scientific Balloon Facility team from Esrange (Swedish Space Corporation), on 8 June 2009. SUNRISE has been a challenging mission from the thermal point of view because of its size and power dissipation. Thus, a dedicated thermal analysis has been carried out to find a solution that allows all the devices to be kept within their appropriate temperature ranges, without exceeding the allowable temperature gradients, critical for optical devices. In this article, the thermal design of SUNRISE is described. A geometrical mathematical model and a thermal mathematical model of the whole system have been set up for the different load cases in order to obtain the temperature distribution and gradients in the system. Some trade-offs have been necessary to fulfil all the thermal requirements. The thermal hardware used to achieve it is described. Finally, the temperatures obtained with the models have been compared with flight data.

Assessment of species diversity and state of "Stipa tenacissima" steppes

North African steppes are subjected to extreme degradation resulting in the reduction of their surface, genetic erosion of resources, and decrease in biodiversity. "Stipa tenacissima" steppes, which constitute one of the most representative vegetation types in the driest areas of the Mediterranean basin, are continuously degrading. With the aim of contributing to a better knowledge of the floristic composition and diagnosing the state of degradation of these steppes, we conducted a phytoecological analysis of 10 "S. tenacissima" sites in Tunisia. Floristic inventory compiled a systematic list of 46 vascular plant species belonging to 43 genera and 26 families. Species richness ranged from 4 to 18 species per 900 m2. Total vegetation cover was moderate and fluctuated between 22.8% and 49.9%. Our results revealed also a decreasing trend in species richness with increasing elevation (ρ = –0.585). Indeed, species richness was negatively correlated with slope (ρ = –0.19) and positively correlated with sand content (ρ = 0.262). Biological types were dominated by chamaephytes; this chamaephytization is due to the phenomenon of aridization and overgrazing. Moreover, the low species cover and the appearance of nonpalatable species highlighted the vulnerability of these steppes to degradation.