Dynamics and control of the shape and size of a sitting drop-like meniscus, occurring in single-crystal growth     

Agneta M. Balint  Stefan Balint 《Journal of The Franklin Institute》2010,347(1):30-52

This paper concerns the following topics: dependence of shape and size of a static meniscus sitting like a drop on the controllable part of pressure difference across the free surface; stability of static menisci; procedure for creation of a stable static meniscus, appropriate for the growth of a rod with constant radius; temperature gradients and crystallization front displacement; equation for crystal dimension change rate; evolution of crystal radius and of the level of crystallization front; and control of cross-section during growth. This kind of problems appears in semiconductor single-crystal rod growth from a melt by edge-defined film-fed growth (EFG) technique. The novel case where the upper radius of the meniscus is larger than the shaper radius and the meniscus is sitting like a drop is analyzed. For some of the topics numerical illustrations are given. The obtained results can be useful in experiment planning and technology design of single-crystal rod growth by the EFG method. With this aim this study was undertaken.  相似文献   

The influence of physical exercise on the relation between the phase of cardiac cycle and shooting accuracy in biathlon     

Germano Gallicchio  Thomas Finkenzeller  Gerold Sattlecker  Stefan Lindinger 《European Journal of Sport Science》2019,19(5):567-575

This study examined the influence of physical exercise on the relation between shooting accuracy and the phase of the cardiac cycle in which the shot is fired. Thirteen experienced biathletes (8 females, mean age 17 years) fired from the standing position at rest and right after a submaximal exercise on a bicycle ergometer. Shooting accuracy and the timing of each shot relative to the R-waves of the electrocardiogram (ECG) were recorded. Best shots (with greatest accuracy) and worst shots (with lowest accuracy) were fired prevalently in different phases of the cardiac cycle. In the rest condition, best shots were fired less frequently from 200 to 300?ms and more frequently from 500 to 600?ms after the R-wave, compared to worst shots. In the exercise condition, best shots were fired less frequently from 100 to 200?ms after the R-wave and from 20% to 30% of the R-R interval, compared to worst shots. These findings support the hypothesis that shooting accuracy is influenced by the cardiac cycle phase due to the ballistocardiac recoil generated at each heartbeat. To achieve best results athletes could be trained (e.g. through biofeedback) to fire within a specific phase of the cardiac cycle.  相似文献   

Forward acceleration of the centre of mass during ski skating calculated from force and motion capture data     

Caroline Göpfert  Mikko V. Pohjola  Vesa Linnamo  Olli Ohtonen  Walter Rapp  Stefan J. Lindinger 《Sports Engineering》2017,20(2):141-153

The purpose of this paper was to present and evaluate a methodology to determine the contribution of bilateral leg and pole thrusts to forward acceleration of the centre of mass (COM) of cross-country skiers from multi-dimensional ground reaction forces and motion capture data. Nine highly skilled cross-country (XC) skiers performed leg skating and V2-alternate skating (V2A) under constant environmental conditions on snow, while ground reaction forces measured from ski bindings and poles and 3D motion with high-speed cameras were captured. COM acceleration determined from 3D motion analyses served as a reference and was compared to the results of the proposed methodology. The obtained values did not differ during the leg skating push-off, and force–time curves showed high similarity, with similarity coefficients (SC) >0.90 in the push-off and gliding phases. In V2A, leg and pole thrusts were shown to contribute 35.1 and 65.9% to the acceleration of the body, respectively. COM acceleration derived from ground reaction forces alone without considering the COM position overestimated the acceleration compared to data from motion analyses, with a mean difference of 17% (P < 0.05) during leg push-off, although the shapes of force–time curves were similar (SC = 0.93). The proposed methodology was shown to be appropriate for determining the acceleration of XC skiers during leg skating push-off from multi-dimensional ground reaction forces and the COM position. It was demonstrated that both the COM position and ground reaction forces are needed to find the source of acceleration.  相似文献   

Cycling power output produced during flat and mountain stages in the Giro d'Italia: a case study     

Vogt S  Schumacher YO  Blum A  Roecker K  Dickhuth HH  Schmid A  Heinrich L 《Journal of sports sciences》2007,25(12):1299-1305

Until recently, the physiological demands of cycling competitions were mostly reflected by the measurement of heart rate and the indirect estimation of exercise intensity. The purpose of this case study was to illustrate the varying power output of a professional cyclist during flat and mountain stages of a Grand Tour (Giro d'Italia). Nine stage recordings of a cyclist of the 2005 Giro d'Italia were monitored using a mobile power measurement device (SRM Trainingssystem, Julich, Germany), which recorded direct power output and heart rate. Stages were categorized into flat (n = 5) and mountain stages (n = 4). Data were processed electronically, and the overall mean power in flat and mountain stages and maximal mean power for various durations were calculated. Mean power output was 132 W +/- 26 (2.0 W x kg(-1) +/- 0.4) for the flat and 235 W +/- 10 (3.5 W x kg(-1) +/- 0.1) for the mountain stages. Mountain stages showed higher maximal mean power (367 W) for longer durations (1800 s) than flat stages (239 W). Flat stages are characterized by a large variability of power output with short bursts of high power and long periods with reduced intensity of exercise, whereas mountain stages mostly require submaximal, constant power output over longer periods.  相似文献   

Beyond linearity: Using IRT-scaled level models to describe the relation between prior proportional reasoning skills and fraction learning outcomes     

Constanze Schadl  Stefan Ufer 《Child development》2023,94(6):1642-1658

Previous research on the role of prior skills like proportional reasoning skills for the development of mathematical concepts offers conclusions such as “more (prior skills) is better (for later learning).” Insights, which prior skill level goes along with which level of learning outcomes, may advance the understanding of the development of mathematical concepts. An exploratory approach is presented based on level models to describe the relation between symbolic proportional reasoning skills and fraction outcomes beyond linearity. Analyses draw on samples of German fourth to sixth graders from a scaling (2017, N = 325, 54.8% female) and longitudinal study (2018/2019, N = 436, 42.7% female). Particularly mastering natural and internal rational ratios in proportional reasoning seems relevant for successful fraction learning.  相似文献