Search

Research was conducted to examine the impact of the intermediate buffer layer on the structural and optical characteristics of gallium nitride (GaN) films grown on the oxygen and zinc surfaces of zinc oxide substrates. These properties were analyzed using techniques such as photoluminescence, atomic force microscopy, x-ray double diffraction, transmission electron microscopy and reflectivity. Differences in thermal expansion coefficients indicate that the GaN epilayers were grown with compressive strain.

The microstructural characteristics and surface resistance of epitaxial films of YBa2Cu3O(7-delta) on magnesium oxide are investigated. The films, which were grown by pulsed laser deposition, vary in thickness from 800 nm. to 1,900 nm. According to measurements and observations, the films which had only one epitaxial orientation relationship (OR) had lower values of surface resistance. Moreover, evidence that critical current density decreases with increasing thickness is gathered from the match between the local density of films containing threading dislocations.

In men's artistic gymnastics the backward giant circle on the high bar is used to produce the angular momentum that the gymnast needs for executing somersaulting dismounts. Dismounts in which the gymnast performs two somersaults in the layout (straight body) position require the greatest angular momentum. However, it appears there are two distinct techniques that elite gymnasts use when performing backward giant circles prior to a double layout somersault dismount. The “traditional” technique has been superseded by the “scooped” technique which is now used by the majority of elite gymnasts. To determine whether the scooped technique is better at producing angular momentum, a simulation model was used to optimize the angular momentum about the mass center at release. The model was evaluated using data obtained from a force/video analysis of accelerated giant circles. The model was able to estimate the reaction forces measured by strain gauges on the bar to within 9% of the peak forces, and the body rotation angle to within 1% of total rotation. During the optimizations, the joint angle time histories of the model were manipulated in order to maximize the angular momentum about the model's mass center at release. Two optima were found which were characteristic of the two backward giant circle techniques used by elite gymnasts. The traditional technique produced more angular momentum than the scooped technique, although both were capable of producing sufficient angular momentum for a double layout somersault dismount. This suggests that the preference of elite gymnasts for the scooped technique must be based on factors other than the production of angular momentum. [ABSTRACT FROM AUTHOR]

An angle-driven computer simulation model of aerial movement was used to determine the maximum amount of twist that can be produced in a forward 1½ somersault dive from a three-metre springboard using various aerial twisting techniques. The segmental inertia parameters of an elite springboard diver were used in the simulations and lower bounds were placed on the durations of arm and hip angle changes based on recorded performances of twisting somersaults. A limiting dive was identified as that producing the largest possible whole number of twists. Simulations of the limiting dives were found using simulated annealing optimisation to produce the required amounts of somersault, tilt and twist after a flight time of 1.5 s. Additional optimisations were then run to seek solutions with the arms less adducted during the twisting phase. It was found that the upper limits ranged from two to five twists with arm abduction ranges lying between 6° and 17°. Similar results were obtained when the inertia parameters of two other springboard divers were used. [ABSTRACT FROM AUTHOR]