Footwork technique used in elite table tennis matches

Notational and Match analysis are very well-recognized methods to collect information about the most common technical-tactical performance indicators in table tennis: footwork and stroke types. The aim of this study was to compare footwork distributions in men (M) and women (W) elite table tennis competitions. Nine men’s and nine women’s matches were analyzed. All players were in the top 120 (M) and 111 (W) positions of the ITTF world ranking. An expert coach analyzed game video recordings in slow motion with the software Kinovea and collected data about the footwork types used by the players during the games. The results showed differences between M and W: M prefer to use one step (35.6%, W: 21.9%), W prefer to hit the ball without performing any step (W: 40.2%, M: 20.4%), the chassé is equally used (M: 19.7%, W: 21.7%), and the crossover is mainly used by M (11.1%, W: 3.7%). The pivot is mainly used by M (9.9%, W: 7.8%), and W prefer the slide (4.9%, M: 3.2%). In conclusion, this study can be useful for physical trainers, performance analysts, and coaches, to design specific footwork training sessions for M and W elite table tennis players

Serve analyses of elite European table tennis matches

The purpose of this study was to analyze the serve activities of elite European table tennis players. Twenty matches (78 games, 1466 points) of semifinal and final German League and Europe TOP 16 in men’s (in the top 30 of ETTU Rank list) were analyzed. Differences in serving activities (type, stroke type, outcome and placement) were analyzed according results outcome of match, game, point, phase of the game and type of games. Results showed that forehand short serve prevailed (76.9%) instead other types of serve, mostly placed in the middle of the table on the opponent’s backhand side. Percentage of point won directly with serve was 11.6%, points won with 3rd stroke - 22.4% and points won with 5th stroke after serve (10.9%). Lost points after serve mostly were after 3rd stroke (25.0%) and after 5th stroke (22.4%) and serve errors were noted in 1.5% of all analyzed points. In the 3rd phase of the game serve points were won mostly with 3rd and 5th stroke instead previous phases of the game. Results of Pearson’s chi-squared test showed an association between match outcomes and serve type and outcome, serve type and outcome considering phase of the game and different type of games with serve type, outcome and placing zones

Generalized Berreman's model of the elastic surface free energy of a nematic liquid crystal on a sawtoothed substrate

In this paper we present a generalization of Berreman's model for the elastic contribution to the surface free-energy density of a nematic liquid crystal in presence of a sawtooth substrate which favours homeotropic anchoring, as a function of the wavenumber of the surface structure $q$, the tilt angle $\alpha$ and the surface anchoring strength $w$. In addition to the previously reported non-analytic contribution proportional to $q\ln q$, due to the nucleation of disclination lines at the wedge bottoms and apexes of the substrate, the next-to-leading contribution is proportional to $q$ for a given substrate roughness, in agreement with Berreman's predictions. We characterise this term, finding that it has two contributions: the deviations of the nematic director field with respect to the corresponding to the isolated disclination lines, and their associated core free energies. Comparison with the results obtained from the Landau-de Gennes model shows that our model is quite accurate in the limit $wL>1$, when strong anchoring conditions are effectively achieved.Comment: 13 pages, 9 figures; revised version submitted to Phys. Rev.

A Meshless Solution to the Vibration Problem of Cylindrical Shell Panels

The Meshless Analog Equation Method (MAEM) is a purely mesh-free method for solving partial differential equations (PDEs). In the present study, the method is applied to the dynamic analysis of cylindrical shell structures. Based on the principle of the analog equation, MAEM converts the three governing partial differential equations in terms of displacements into three uncoupled substitute equations, two of 2nd order (Poisson's) and one of 4th order (biharmonic), with fictitious sources. The fictitious sources are represented by series of Radial Basis Functions (RBFs) of multiquadric (MQ) type, and the substitute equations are integrated. The integration allows the representation of the displacements by new RBFs, which approximate the displacements accurately and also their derivatives involved in the governing equations. By inserting the approximate solution in the governing differential equations and taking into account the boundary and initial conditions and collocating at a predefined set of mesh-free nodal points, we obtain a system of ordinary differential equations of motion. The solution of the system gives the unknown time-dependent series coefficients and the solution to the original problem. Several shell panels are analyzed using the method, and the numerical results demonstrate its efficiency and accuracy

Numerical solution for diffusion equations with distributed order in time using a Chebyshev collocation method

In this work we present a new numerical method for the solution of the distributed order time fractional diffusion equation. The method is based on the approximation of the solution by a double Chebyshev truncated series, and the subsequent collocation of the resulting discretised system of equations at suitable collocation points. An error analysis is provided and a comparison with other methods used in the solution of this type of equation is also performed

Revisiting Some Developments of Boundary Elements for Thick Plates in Brazil

This work reviews the developments of Boundary Element Method formulations to solve several types of plate bending problems, including non-linear bending. The formulation is developed and solved using the standard BEM procedure, and different integration approaches were discussed and tested. Object oriented implementation issues are commented. Results were obtained for linear and non-linear elastic bending as well as buckling of selected cases of thick plates, including cases of step variation in thickness under large displacements regime