Thesis (M.Sc.)--Boston University, Henry M. Goldman School of Graduate Dentistry, 1977 (Dental Public Health). / Includes bibliographical references: (leaves 6,13).

Sous l’effet des sollicitations mécaniques répétées induites par les passages des trains, on observe l’apparition de fissures de fatigue de contact dans les rails. Une fois amorcées, celles-ci peuvent se propager et mener à la rupture du rail. Dans un contexte d’intensification du trafic, l’optimisation de la politique de maintenance devient stratégique pour les entreprises du transport ferroviaire. Dans ce contexte, un modèle 3D éléments finis du contact roue/rail en courbe a été développé pour reproduire les mécanismes d’amorçage des fissures "Head Check". Ce modèle permet de simuler la sollicitation répétée du contact roue/rail. Cette modélisation a permis d’analyser l’influence de la plasticité sur la distribution de la pression de contact et sur les champs mécaniques résiduels au sein du rail au cours du chargement cyclique. Il ainsi est montré que l’actualisation du contact au cours des chargements répétés est du premier ordre. Les résultats ont permis d’identifier des zones potentielles d’amorçage de fissures de Head Check correspondant à des points matériels sur lesquels la déformation plastique s’accumule de manière considérable. En effet, on observe une correspondance entre ces orientations « accommodées » de la déformation plastique principale et l’orientation des micro-fissures amorcées sur la surface des rails ayant cumulé un faible tonnage (0-10 MGT). Ceci conforte le fait que la méthode proposée est un outil prometteur pour la simulation 3D de la fatigue du contact roue-rail. / As a result of repeated loading induced by train passages, rails are subjected to rolling contact fatigue cracks. Once initiated, cracks could propagate and lead to rail failure. In a context of increased traffic, maintenance policy optimization becomes strategic for railway companies. Thus to define an enhanced planning of maintenance, a better understanding of rail fatigue damage mechanisms is crucial. Under the circumstances, a 3D wheel-rail rolling contact finite element model has been developed in order to reproduce « Head Check » cracks initiation mechanisms. This model allows sequential repeated wheel-rail rolling contact loading. Thus this calculation procedure is used to analyze the influence of plasticity on contact pressure distribution and consequently on residual mechanical fields in the rail during cyclic loading. It is shown that contact conditions evolution during repeated loading must be considered in the first order. The results allowed the identification of potential Head Check cracks initiation zones that correspond to material points on which plastic deformation accumulates significantly. Indeed, there is a correspondence between the « accommodated » principal plastic strain directions and orientation of micro-cracks initiated on rails surface subjected to low cumulative tonnage (0-10MGT). This reinforces the fact that our proposed method is a promising tool for 3D wheel-rail rolling contact fatigue simulation.

No description available.

No description available.

The sternocleidomastoid (SCM) and upper trapezius (UT) muscles are the primary dynamic stabilizers of the head and neck and likely attenuate head acceleration with direct and indirect impacts. Increasing the strength of the SCM and UT through cervical resistance training has been recommended to prevent concussions in football players. The purpose of this study was to examine the effects of an eight-week isoinertial cervical resistance training program on SCM and UT muscle activity (EMG) and kinematic responses of the head and neck during a standard football tackle in college-aged males. Sixteen college-aged males (21.6 ± 2.8 y, 94.6 ± 13.3 kg) with previous high school football or rugby playing experience completed an eight-week isoinertial cervical resistance training program consisting of three sets of 10 repetitions of neck extension, flexion, right and left lateral flexion at 60-80% of 10 repetition maximum two to three times a week. Isometric cervical strength, neck girth, EMG, and kinematic responses of the head and neck during a standard football tackle were measured before and after training. All kinematic data were gathered using a three-dimensional motion capturing system. Training resulted in 7 and 10% increases in isometric cervical extension and left lateral flexion strength, respectively, but no changes were seen in isometric flexion or right lateral flexion strength or neck girth. Additionally, training had no influence on the EMG responses of the SCM or UT, peak linear (7.23 vs. 7.59 g, p = 0.115; pre- vs. post-training) or angular (431.96 vs. 452.37 rad/s2, p = 0.864) head accelerations during the standard football tackle. The UT demonstrated approximately 40% higher absolute EMG activity than the SCM during tackling both before and after training. Under the current experimental conditions, despite modest increases in isometric cervical extension and left lateral flexion strength, the eight-week isoinertial cervical resistance training program failed to augment dynamic stabilization of the head and neck during a standard football tackle in college-aged males. Future research should examine the effects of both slow speed load-intensive and high speed low-to-moderate load intensity isoinertial training as well as plyometric training in decreasing head acceleration during football tackling for injury prevention purposes.

This project aims to design and construct a 3D CAD model of a humanoid robot head; this means the mechanisms that simulate the motions of the neck, the eyes and the eyelids. The project was developed in collaboration with Cognition and Interaction Laboratory at the University of Skövde. From the literature review, it was found that most of the humanoid robots at the market are able to perform neck movements. The problem is that the neck motions today are not smooth as human neck and the movements of face details, such as the eyes and the mouth, are less developed. Only robots created for interaction research between human and robots allows for face expressions. However, the rest of the bodies of such robots are not as well developed as the face. The conclusion is that there is no humanoid robot that presents a full expression face and a well-developed body. This project presents new mechanical concepts for how to provide smooth humanoid neck motions as well as how to show expressions of the robots face. Three parts of the humanoid heads: the neck, the eyes and the eyelids were investigated. By examining different mechanical concepts used today two types of mechanisms were found: parallel and serial. In the neck the serial mechanism was chosen because the motion obtained is smoother. The eyes and the eyelids were designed with a serial mechanism due to the limitations of the space in the head. The three parts were built in to a 3D CAD program in order to test the entire head mechanism. This results in a head mechanism that enables smooth motion of the neck and provides enough degrees of freedom to simulate feelings due to eye expressions.

Dissertation (Ph.D.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for the Doctor of Philosophy in Foundations of Education, Research and Measurement." Bibliography: leaves 114-127.

Thesis (EdD)--Open University.

Thesis (Ph. D.)--University of Kansas, 1973. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 424-437).

Proefschrift--Leyden. / Curriculum vitae. "Dit proefschrift verschijnt met obereenkomstige paginering in de Archives néerlandaises de zoologie, tome XII, 1e livraison." eContent provider-neutral record in process. Description based on print version record. Bibliography: p. 109-111.