87,298 research outputs found
A pilot study to compare footwork techniques used in Table Tennis
No full textA pilot study to compare footwork techniques used in Table Tennis
Ivan Malagoli Lanzoni, Roberto Lobietti, Franco Merni
Faculty of Exercise and Sport Science, University of Bologna, Italy
INTRODUCTION
Footwork and steps (one step, side to side, slide step, turn step, cross step, and combinations of these steps) are fundamental in table tennis. Players should use the best technique for guarantying the shortest time to arrive in the right position, that gives the possibility to play the best shot. This study aims to define the different footwork techniques used by table tennis players. To compare different footwork techniques for giving useful suggestions to coaches and implementing better training for players, from a technical and physical point of view.
METHODS
1. Analysis of male players 4 matches from the 2006 Italian Championships and 4 matches from 2006 World Team Table Tennis Championships (videos recorded from television).
2. To record the 5 different types of steps defined and the 16 types of shots (drive and back) was used a 16 x 5 table. To carry out this analysis it has always been taken into account the last step before the shot or before the attempt to hit the ball.
3. The analysis of the frequencies of the different types of steps were performed and percentages calculated.
4. The non-parametric Chi Square test were performed to identify significant differences (α=0.01) in the use of footwork techniques by the 8 players considered.
RESULTS
The results allow a qualitative description of the various step movements.
The most frequent step is the one step with a frequency of 33.5%; the second one is the chassè with a frequency of 20,8%; they are followed by the Stroke without step 16.3%; the Turn step15.4 %; the Crossover 8.8% and the Slide step 5.3%. Chi Square analysis, by comparing the use of different types of steps by the players at low level, shows significant differences between them (χ2 (15) = 50.09, p<0.01) as between found for the highest level in a previous study (χ2 (15) = 40.63, p<0.01). A comparison with data relative to the highest level confirmed inter individual (χ2 (35) = 222.62, p<0.01).
and inter groups differences (χ2 (5) = 61.24, p<0.01).
DISCUSSION
Analysis of the matches suggests inter individual differences in the characteristics of the steps movements. The “one step” is especially used to hit the ball in the forehand and backhand push to return the service.
Further studies on a larger number of matches, will permit a better understanding in the use of footwork techniques.
REFERENCES
Lames M. (2006), Modelling the interaction in game sport – relative phase and moving correlations. JSSM 5, pp. 556-560
Lobietti,R., Merni F. (2006), Blocking footwork techniques used by male and female volleyball players are different, JHMS, 51 (5), pp. 307-320
Malagoli Lanzoni I., Lobietti R., Merni F. (2007), Footwork techniques used in table tennis: a qualitative analysis, Proceedings book of The 10th Anniversary ITTF Sport Science Congress, 18-20 maggio 2007, Zagreb, Croatia. ISBN 978-953-6378-69-2.
Tepper G. (2003), ITTF Level 1 Coaching manual, www.ittf.co
Morphodynamic Modeling of Alluvial Rivers and Floodplains
No full textThis article gives and overview of the large spectrum of models based on first principles (mass and momentum conservation) developed in the field of fluvial morphodynamics. After describing the main morphological features of alluvial rivers and their floodplains, the chapter gives a general classification of the modeling approaches available in literature. Next, it delineates the morphodynamic problem and briefly summarizes the procedures used to solve the governing equations, depending on the spatial and temporal scales resolved. The problem of the closures arising from depth-averaging is then discussed. The various models are grouped with reference to the morphological features to be simulated. The dynamics of small-scale and large-scale bedforms in single-thread straight rivers and the modeling of braided, anastomosing and meandering rivers are then considered. Finally, the simulation of the coupled river-floodplain evolution is tackled. The chapter ends with a delineation of the modeling perspectives
Advancing contact between a rigid pin and a FGM circular beam with clearance
No full textThe progressive and frictionless contact problem between a rigid circular pin and a circular beam with a uniform cross-section made of elastic functionally graded material (FGM) is investigated under clearance-fit conditions. The stress and displacement fields in the FGM circular beam are taken from the general solution for plane elastic problems involving FGMs in polar coordinates, analogous to Mitchell’s solution for homogeneous isotropic materials. The frictionless contact conditions yield a set of dual series equations similar to those obtained for a homogeneous and isotropic elastic circular beam, then reduced to a linear system of infinite equations, which is solved by truncation. By assuming discrete values of the contact angle, the corresponding stress and displacement fields within the lug are derived and, in turn, the resultant load acting on the rigid pin is assessed. The new analytical results are then validated against finite element predictions and a satisfactory agreement is observed for typical geometries and various material grading parameters. The present findings can assist mechanical engineers in optimally designing innovative pinned connections and improving their load-bearing capacity by exploiting the advantages of FGMs
Shear deformable beams in contact with an elastic half-plane
No full textThe present work deals with the contact problem of a Timoshenko beam bonded to an elastic semi-infinite substrate under different loading conditions. The analysis allows investigating the effects induced by shear compliance of the beam, the stress intensity factors ad the beam edges as well as the singular nature of the interfacial stresses
Mechanical application of orius laevigatus nymphs for the control of Frankliniella occidentalis in greenhouse crops
No full textThe development of improved technology for use of beneficial organisms in greenhouse crops includes mechanical application methods to that can reduce labour costs compared to manual application while preserving the quality of the applied natural ene-mies. A pneumatic distribution system, verified as effective in previous study with mites (Phytoseiulus persimilis Athias-Henriot and Amblyseius swirskii Athias-Henriot), was tested for application of the predatory bug Orius laevigatus (Fieber). Laboratory and field tests were used to assess the efficiency of mechanical distribution of nymphs of O. laevigatus. The efficiency of mechanical distribution was evaluated comparing the biological parameters of the predator (survival, fecundity, fecundity rate and lon-gevity) dispensed mechanically with to those following manual distribution. Nymphal survival immediately after and 10 days after the dispensing was calculated as proportion of nymphs reaching adulthood. We found that mechanical applications caused a reduction of predator survival in comparison to manual sprinkling of 21% and 36% immediately after and 10 days after the dis-pensing, respectively. The causes of the reduced survival from mechanical application were attributed to the combined effect of the extraction system and the velocity of airflow that transports the predator. Moreover, the biological parameters of adult females that survived mechanical distribution as nymphs, showed no significant differences compared to the same following manual dis-tribution. In the greenhouse test, the mechanically released nymphs of O. laevigatus were as effective as those manually released in controlling Frankliniella occidentalis (Pergande) in a cucumber crop. Consistently, the yield and quality of cucumber fruits did not show differences in the mechanical vs. manual application. Mechanical application time was significantly lower compared to manual application, determining a 5.5 higher effective work capacity compared to traditional manual distribution
Double lap shear test on steel fabric reinforced cementitious matrix (SFRCM)
No full textThe present work deals with the experimental characterization of the mechanical behaviour of a galvanized steel fabric reinforced cementitious matrix (SFRCM).The present work deals with the experimental characterization of the mechanical bond behaviour of a galvanized steel fabric reinforced cementitious matrix (SFRCM) laminated on concrete support. The specimens, made of two low strength concrete blocks connected with a galvanized steel fabric embedded in a geo-polymeric mortar layers, have been tested according to double lap test (DLT) set-up. Six different groups of specimens have been tested varying both the lamination length and the steel fabric density. In order to reproduce the load-slip or bond-slip curves, a tri-linear bond slip model together with its parameters identification has been proposed. For some specimens, the slip profile and the slip distribution has been analysed and split into the substrate laminate slip and inner laminate layers slip. This distinction has been used as a measure of the fabric-matrix compatibility. In addition, the effect induced by the rigid blocks rotation occurred during the DLT has been argued. The DIC optical system monitoring has been used to asses both the force-slip distribution and the crack opening displacement (COD)
Probing the link between dynamics and stellar evolution: Blue Straggler Stars in Globular clusters
No full textIn this contribution we review the main observational properties of Blue Straggler Stars (BSS) in Galactic Globular Clusters. A flower of results on the BSS frequency, radial distribution, and chemical composition are presented and discussed
La Comunità internazionale in Dante: il Monarchia
No full textTra il 1310 e il 1313, in coincidenza della discesa di Enrico VII in Italia, Dante scrive il Monarchia. L’opera auspica l’istituzione di una Monarchia universale al fine di ristabilire la pace, la giustizia e la libertà degli individui in uno scenario politico in tumulto. Diversi critici hanno sostenuto che il Monarchia, lungi dal rappresentare una mera utopia ideologica, esporrebbe una vera e propria teoria dello Stato e/o della Comunità internazionale. Il presente contributo è volto a fornire un’analisi sulla teoria della Comunità internazionale in Dante. Esso si divide in tre parti: la prima descrive brevemente il contenuto del Monarchia. La seconda illustra la fortuna dell’opera e l’altalenante influenza che la stessa ha avuto sugli autori di diritto internazionale successivi. La terza ricostruisce, elabora e attualizza la teoria della Comunità internazionale in Dante sotto forma di ‘Monarchia istituzionale’ e di ‘Monarchia normativa’. L’obiettivo è dimostrare come, dopo oltre sette secoli, il monarchia costituisca ancora fonte di riflessione e di spunti sul problema del modello di governance globale e sui compiti precipui del diritto internazionale contemporaneo
Land-based sources of marine pollution and dumping at sea
No full textIt is now generally accepted that a rule of customary international law, as also reflected in Article 194(1) of the United Nations Convention on the Law of the Sea (UNCLOS), provides an obligation for States to take, in accordance with their capabilities, ‘all measures (...) that are necessary to prevent, reduce and control pollution of the marine environment from any source’. Indeed, the causes and anthropogenic factors giving rise to marine pollution are varied. However, its main sources can be broadly classified in two categories: land-based sources, which account for approximately 80 per cent of marine pollution, and dumping at sea, which accounts for a further 10 per cent. The present contribution aims to provide an overview of the international regulation, both global and regional, on these two sources of marine pollution
- …
