Bubble collapse near porous plates

A gas or vapour bubble near a solid boundary collapses towards the boundary due to the asymmetry induced by the nearby boundary. High surface pressure and shear stress from this collapse can damage, or clean, the surface. A porous boundary, such as a filter, would act similarly to a solid boundary but with reduced asymmetry and thus reduced effect. Prior research has measured the cleaning effect of bubbles on filters using ultrasonic cleaning, but it is not known how the bubble dynamics are fundamentally affected by the porosity of the surface. We address this question experimentally by investigating how the standoff distance, porosity, pore size, and pore shape affect two collapse properties: bubble displacement and bubble rebound size. We show that these properties depend primarily on the standoff distance and porosity of the boundary and extend a previously developed numerical model that approximates this behaviour. Using the numerical model in combination with experimental data, we show that bubble displacement and bubble rebound size each collapse onto respective single curves

Bioimpedance real-time charazterization of neointimal tissue inside stents

It is hereby presented a new approach to monitor restenosis in arteries fitted with a stent during an angioplasty. The growth of neointimal tissue is followed up by measuring its bioimpedance with Electrical Impedance Spectroscopy (EIS). Besides, a mathematical model is derived to analytically describe the neointima’s histological composition from its bioimpedance. The model is validated by finite-element analysis (FEA) with COMSOL Multiphysics®. Satisfactory correlation between the analytical model and the FEA simulation is achieved for most of the characterization range, detecting some deviations introduced by the thin "double layer" that separates the neointima and the blood. It is shown how to apply conformal transformations to obtain bioimpedance models for stack-layered tissues over coplanar electrodes. Particularly, this is applied to characterize the neointima in real-time. This technique is either suitable as a main mechanism of restenosis follow-up or it can be combined with proposed blood-pressure-measuring intelligent stents to auto-calibrate the sensibility loss caused by the adherence of the tissue on the micro-electro-mechanical sensors (MEMS).Ministerio de Economía, Industria y Competitividad (Spain): projects TEC2013-46242-C3-1-PMinisterio de Economía, Industria y Competitividad (Spain): projects TEC2013-46242-C3-2-

Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors

Bubbles are known to influence energy and mass transfer in gas evolving electrodes. However, we lack a detailed understanding on the intricate dependencies between bubble evolution processes and electrochemical phenomena. This review discusses our current knowledge on the effects of bubbles on electrochemical systems with the aim to identify opportunities and motivate future research in this area. We first provide a base background on the physics of bubble evolution as it relates to electrochemical processes. Then we outline how bubbles affect energy efficiency of electrode processes, detailing the bubble-induced impacts on activation, ohmic and concentration overpotentials. Lastly, we describe different strategies to mitigate losses and how to exploit bubbles to enhance electrochemical reactions.Comment: Joule(2020

Sequencing Effects of Neuromuscular Training on Physical Fitness in Youth Elite Tennis Players

[EN] The aim of the present study was to analyze the effects of a 5-week neuromuscular training (NMT) implemented before or after a tennis session in pre-pubertal players on selected components of physical fitness. Sixteen elite and well-trained tennis players with a mean age of 12.9 ± 0.4 years participated in this study, and were assigned to either a training group performing NMT before tennis specific training (BT; n=8) or a group that conducted NMT after tennis specific training (AT; n=8). Pre and post-tests included: speed (5,10 and 20 m); modified 5-0-5 agility test; countermovement jump (CMJ); overhead medicine ball throw (MBT); and serve velocity (SV). Results showed that the BT group achieved positive effects from pre- to post-test measures in speed (d = 0.52, 0.32 and 1.08 for 5, 10 and 20 m respectively) 5-0-5 (d = 0.22), CMJ (d = 0.29), MBT (d = 0.51) and SV (d = 0.32), while trivial (10 m, 20 m, CMJ, SV, MBT) or negative effects (d = -0.19 and -0.24 for 5 m and 5- 0-5 respectively), while trivial or negative effects were reported for the AT group. The inclusion of a NMT session before the regular tennis training led to positive effects from pre- to post-test measures in performance-related variables (i.e., jump, sprint, change of direction capacity, as well as upper body power), while conducting the same exercise sessions after the regular tennis training was not accompanied by the same improvements

In-Season Effect of a Combined Repeated Sprint and Explosive Strength Training Program on Elite Junior Tennis Players

The aim of this study was to analyze the effects of a combined explosive strength and repeated sprint-training program (two times per week) on performance (sprint, jumping ability and repeated sprint ability) in young elite tennis players during a competitive period. Eight competitive internationally ranked male junior tennis players participated in an 8 week training intervention. After training, except for percentage of decrement in the repeated sprint test (p = 0.72) and maximal aerobic performance (p = 1.0), all performance variables (i.e., sprint, countermovement jump, repeated sprint ability) were significantly improved (p < 0.05; Effect sizes ranging from 0.56 to 1.12). Although one can expect grater effects of explosive strength or repeated sprint training programs alone than a combined program, the results obtained here show that the inclusion of a combined explosive strength and repeated sprint training program seems to be an effective training tool to improve neuromuscular performance (i.e., changes in jumping ability and single sprint) as well as repeated sprint ability in high-level tennis players. In-Season Effect of a Combined Repeated Sprint and Explosive Strength Training Program on Elite Junior Tennis Players (PDF Download Available). Available from: https://www.researchgate.net/publication/269115556_In-Season_Effect_of_a_Combined_Repeated_Sprint_and_Explosive_Strength_Training_Program_on_Elite_Junior_Tennis_Players [accessed Jul 24, 2017]

Acute and Time-Course Effects of Traditional and Dynamic Warm-Up Routines in Young Elite Junior Tennis Players

Despite the large number of studies that have examined the acute effects of different warm up modalities (WU) on physical performance, none of them have documented the time course of potential performance recovery in tennis players. The aim of this study was twofold: (a) to analyze and compare the acute effects of two different WU modalities (traditional WU [TWU] and dynamic WU [DWU]) on physical performance (i.e., CMJ, sprint, serve speed and accuracy) in elite junior players, as well as (b) to monitor the time course of any WU-induced changes after 30 and 60 min of simulated match-play. Twelve junior elite players completed both WUs modalities (TWU and DWU) in a counterbalanced order on separate days. In each experimental session, counter movement jump (CMJ), 20-m sprint, tennis serve speed and accuracy tests were performed before (immediately after TWU or DWU) during (30 min) and after 60 min of a simulated match play. Measures were compared via four factorial (WU intervention and time) repeated measures ANOVAs. There were main effects of WU (TWU and DWU) throughout the time for all the variables analysed. The results indicate that DWU routine led to significantly faster 20 m sprint times and higher CMJs as well as faster and more accurate tennis serves at both post warm-up and 30 min match-play testing moments in comparison with the scores reported by the TWU routine (p 75-99%). No significant intergroup differences were found at 60-min match-play testing moment in any variable (except for the 20 m sprint). Therefore, the findings of this study recommend for optimal performance in these elite tennis players, DWU routines should be performed prior to formal training and competition rather than TWU routines.SIThe authors have no support or funding to report

Preseason training: the effects of a 17-day high-intensity shock microcycle in elite tennis players

Preseasons in tennis are normally reduced to 5 to 7 weeks duration, and coaches should use an integrated approach to conditioning and skill-based work. The aim of the present study was to investigate the effects of adding a high-intensity training (HIT) shock microcycle to the normal training content in several physical performance indicators in the preseason training of high-level male tennis players. Over 17 days, 12 male tennis players performed 13 HIT sessions in addition to their usual training. Physical performance tests (30:15 intermittent fitness test [VIFT], 20 m sprint, countermovement jump [CMJ], repeated sprint ability [RSA]) were conducted before (pre-test) and 5 days after the intervention (post-test). After the shock microcycle, results showed a significant increase in the VIFT (p < 0.001; Large ES) and a significant decrease in the mean RSA time (RSAm) (p = 0.002; Small ES), while there were no significant changes in the other parameters analysed (e.g., 20 m, CMJ, best RSA time [RSAb]; percentage of decrement in the RSA [%Dec]). Moreover, the training load (TL) during tennis sessions was significantly higher (p < 0.01; Large ES) than the TL during the integrated sessions, except during the first training session. A 17-day shock microcycle (i.e., 13 HIT sessions) in addition to the regular tennis training significantly improved parameters that can impact physical performance in tennis. Moreover, additional sessions, including running exercises based on the 30:15ITF and on-court specific exercises, were characterised by significantly lower TL than tennis-training sessions

Within-Session Sequence of the Tennis Serve Training in Youth Elite Players

[EN] The influence of muscular fatigue on tennis serve performance within regular training sessions is unclear. Therefore, the aim of the present study was to examine the within-session sequence of the tennis serve in youth tennis. Twenty-five young male (14.9 ± 0.9 years) and fe- male (14.5 ± 0.9 years) players participated in this within-subject crossover study, and they were randomly but sex-matched assigned to different training sequences (serve exercise before tennis training (BTS) or after tennis training (ATS)). Pre- and post-tests included serve velocity performance and accuracy, shoulder strength, and range-of-motion (ROM) performance (internal/external rota- tion). Results showed that after one week of serve training conducted following the ATS sequence, significant decreases were found in serve performance (e.g., speed and accuracy), with standardized differences ranging from d = 0.29 to 1.13, as well as the shoulder function (strength [d = 0.20 to 1.0] and ROM [d = 0.17 to 0.31]) in both female and male players, compared to the BTS sequence. Based on the present findings, it appears more effective to implement serve training before the regular tennis training in youth players. If applied after training, excessive levels of fatigue may cause shoulder imbalances that could be related to an increased injury risk.SIThe authors are grateful to all the athletes who took part in this study