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Thesis (M.A.)--Western Michigan University, 2003. / Includes bibliographical references (leaves 43-46). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Thesis (M.A.)--Western Michigan University, 2003. / Includes bibliographical references (leaves 43-46).

The men's steeplechase event requires participants to jump over thirty-five 0.914-meter-tall obstacles, 4 rigid barriers and 1 fixed barrier followed by a 3.66-meter-long water pit per lap, over a 3000-meter distance. This study investigated the effect of increasing running velocity, through a range of 5.33 m/s to 6.66 m/s, on takeoff and landing ground reaction forces, for males during steeplechase hurdling using a force plate embedded under a track surface. Subjects completed 1 trial within each of 6 different pace ranges in a random order, once with a hurdle following the force plate to measure the takeoff ground reaction forces and a second time with the hurdle prior to the force plate to measure the landing ground reaction forces. Within a repeated measures linear mixed model during takeoff, peak vertical force (r2 = 0.1968, p < 0.01) and horizontal propulsive impulse (r2 = 0.0287, p = 0.02) were positively correlated with increasing velocity, and ground time (r2 = 0.1904, p < 0.01) was negatively correlated with increasing velocity. Within a repeated measures linear mixed model during landing, vertical impact force loading rate (r2 = 0.0099, p < 0.01) was positively correlated with increasing velocity and ground time (r2 = 0.2889, p < 0.01), vertical impulse (r2 = 0.1704, p = 0.02), and horizontal braking impulse (r2 = 0.0004, p = 0.05) were negatively correlated with increasing velocity. As male steeplechasers prepared to hurdle at increasing speeds, they produced a greater peak vertical force on the takeoff step while decreasing the ground time during takeoff, and increasing the horizontal propulsive impulse to carry themselves beyond the hurdle. While landing from the hurdle at increasing speeds, the athlete decreased the amount of time spent on the landing stance and the vertical impulse, and increased the magnitude of horizontal braking impulse and vertical loading rate. The relationships of these variables: takeoff peak vertical force, takeoff ground time, takeoff horizontal impulse, landing ground time, and landing vertical loading rate to increasing velocity were all comparable to overground running responses. The data differed from running by not indicating any change in hurdling takeoff horizontal braking impulse; however, the horizontal braking impulse did increase on hurdling landing. It was expected to decrease on hurdling landing due to the foot landing more underneath the center of mass after hurdling compared to running. The decrease in landing vertical impulse as speed increased also differed from normal running steps. We suggest that further research include kinematic measures to better understand the relationship between these variables as hurdling velocity increases.

Thesis (M.S.)--Brigham Young University. Dept. of Exercise Sciences, 2008. / Includes bibliographical references.

Les phénomènes interfaciaux impliqués dans les écoulements polyphasiques existent dans de nombreux procédés industriels. Des gouttes et des bulles sont des éléments typiques pour comprendre les phénomènes interfaciaux. Ainsi, cette thèse étudie les gouttes (bulles) impliquées dans la manipulation d’une interface, y compris la rupture de l'interface, le mouvement d’une goutte sur une surface superhydrophobe et le contact sur un support solide à l’aide d’un système d'acquisition pour des signaux électriques. Dans la première partie, une caméra rapide est utilisée pour étudier la dynamique de pincement des fluides homogènes et des ferrrofluides hétérogènes à travers des systèmes confinés et non-confinés liquide-liquide ou liquide-gaz. L'effet de compétition entre les différentes forces telles que la poussée d’Archimède, la force magnétique, la gravité et la tension interfaciale sur la rupture finale d’un fluide interne dans un environnement fluide externe est démontré et quantifié. La deuxième partie est consacrée à la manipulation d’une goutte aqueuse à l’aide d’une interface superhydrophobe sous deux angles distincts : saut d’obstacle de la goutte sur une surface solide revêtue d’une couche superhydrophobe ; déshabillement d’une goutte enveloppée de particules superhydrophobes dite "marbre liquide" sur un film huileux. Le comportement dynamique du saut d’obstacle et du déshabillement des gouttes est quantifié et comparé dans des conditions opératoires très différentes telles que la viscosité, la tension interfaciale, la géométrie d’obstacle, etc. La troisième partie est dévolue au contact d’une goutte sur un support solide: contact initial, étalement, et pincement final des fluides tant newtoniens que non newtoniens, grâce à une méthodologie combinant la caméra rapide et un système d'acquisition ultra-rapide d’un signal électrique / The interfacial phenomena in multiphase flows widely exist in numerous industrial processes. Drops and bubbles are typical models to investigate these interfacial phenomena. Thus this thesis investigates the drop (bubble) involved interface manipulation, including the breakup of interface, drop’s motion on superhydrophobic surface and Dripping-on-Substrate with an acquisition system of electric signals. In the first part, the pinch-off dynamics of homogenous fluids and heterogeneous ferrrofluids, unconfined liquid-liquid (liquid-gas) or confined liquid-liquid systems was investigated by a high-speed camera. The effect of buoyancy, magnetic force, gravity and interface tension between internal and external fluids on the final pinch-off was demonstrated and quantified. The second part focuses on the drop manipulation on superhydrophobic interface through two distinct approaches: superhydrophobic coating on a substrate and superhydrophobic particles enveloping a liquid drop to form “liquid marble”. The hurdling behavior of liquid drops on superhydrophobic obstacles and undressing dynamics of liquid marbles on oil films were discussed and the slope motion of liquid drops and liquid marbles were then compared. The third part concentrates on the Dripping-on- Substrate behavior: initial contact and spreading on a solid surface, final pinch-off of Newtonian fluids and filament thinning of non-Newtonian fluids, through a methodology combining the high-speed camera and ultra-high-speed acquisition device of an electric signal