Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

La synthèse du graphène reste une étape problématique mais la technique par dépôt de vapeur chimique sur les métaux a beaucoup progressé ces trois dernières années, c'est-à-dire depuis que l'on sait qu'il est possible de retirer sans le dénaturer le graphène de son support métallique. Cette étape de transfert appelle à l'étude de la force d'interaction qui a lieu entre graphène et métal. L'influence de cette liaison graphène-métal sur la structure électronique a déjà été largement étudiée et nous proposons plutôt ici de nous pencher sur la dispersion des phonons. Celle du graphène isolé est d'ailleurs remarquable pour les deux grandes anomalies de Kohn (KA) qu'elle présente sur sa branche de plus haute fréquence aux points de haute symétrie Gamma et K. La pente de la dispersion autour de ces KA est une mesure directe du couplage électron-phonon (EPC) entre ces modes de phonons et les électrons des points de Dirac. Nous avons montré que cet EPC, qui a par exemple beaucoup d'influence sur la mobilité électronique ou sur le processus de résonnance Raman, est fortement altéré suite à l'interaction avec certains substrats métalliques. Lors de notre étude ab initio du graphène sur nickel(111), nous avons en effet observé une disaparition complète des anomalies de Kohn. Ceci est dû à la forte hybridation entre les bandes pi du graphène et les bandes d du nickel. La spéctroscopie Raman et la diffraction électronique à basse énergie sont des moyens efficaces et courants pour caractériser le graphène sur les substrats métalliques. Nos résultats montrent comment tirer de ces mesures davantage d'informations concernant le caractère physisorbé ou chimisorbé du graphène sur le métal. / The fabrication of high quality large-area graphene films is one of the biggest problem. Recently, the synthesis by chemical vapor deposition of hydrocarbons over a metallic substrate have shown promising results. To manage as well as possible the transfer process of the graphene layer in an insulator, it is important to know the interaction strength between the graphene layer and the metallic substrate. We propose in this paper to calculate the phonon dispersion of an adsorbed graphene. The phonon dispersion of graphene is known to display two strong Kohn Anomalies (kinks) in the highest optical branch (HOB) at the high-symmetry points Gamma and K. The phonon slope around the Kohn anomalies is related to the electron-phonon-coupling (EPC) with the graphene pi bands. We show that this EPC, which has strong impact, for example, on Raman scattering and electron transport, can be strongly modified due to interaction with a metallic substrate. For graphene grown on a Ni(111) surface, our ab initio calculations show a total suppression of the Kohn anomaly ; the HOB around Gamma and K becomes completely flat. This is due to the strong hybridization of the graphene pi-bands with the nickel d-bands that lifts the linear crossing of the pi bands at K. Raman spectroscopy and low-energy electron diffraction are quick and reliable methods to characterize graphene on metallic substrates. Our results show how to obtain additional information, by means of vibrational and photoemission spectroscopy, on the chemisorption or physisorption of graphene layers on metal surfaces.

Congenital anomalies (CAs) are the leading cause of infant mortality and one of the leading causes of death for young children in developed countries. As significant improvements have been seen world-wide in controlling childhood infectious disease and issues related to poor nutrition, CAs are now making a proportionally bigger impact on the health of the worlds children. In addition to the impact of CA status on the individual child and ones family, prevalence of CAs has a significant impact on the population, as children with birth defects can cost the system a great deal of money in the provision of specialized health and education services.<p>When conducting surveillance of five selected CAs between 1990 and 1999, Saskatchewan Health found significant regional differences in the prevalence of these CAs. The purpose of this study is to ascertain whether or not there is a regional difference in all types of CAs, to assess whether or not any regional disparities also exist in the use of health care services by children with and without CAs and to determine what factors influence childrens use of health care services in the study population.<p>This study follows a birth cohort of 17,414 children (9169 cases and 8245 controls) born between January 1, 1994 to December 31, 1998 until their 5th birthday, death or emigration out of Saskatchewan. Through graphical analysis, it was revealed that while an overall regional difference does not exist in the prevalence of CAs in Saskatchewan, there are regional differences in the prevalence of 13 of the 22 specific categories of conditions studied. One-way ANOVAs showed that children with CAs have higher numbers of physician visits (p<0.001) and hospitalizations (p<0.001), and longer lengths of stay in hospital (p<0.001) than children without CAs. Regional differences were found for all outcome variables for the total population, and for children with and without CAs. The outcome with the most substantial differences between children with and without CAs was length of stay, which may indicate differential access to outpatient services throughout the province. Finally, using Andersons theoretical framework of factors that influence the use of health care services (need characteristics, predisposing characteristics and enabling characteristics) three negative binomial models were built to examine childrens use of health care services using variables from each category. <p>This study found significant regional differences for all outcome measures studied, and found that region of residence was a significant predictor of childrens use of health care services even after accounting for a variety of other maternal and child factors.

Congenital anomalies (CAs) are the leading cause of infant mortality and one of the leading causes of death for young children in developed countries. As significant improvements have been seen world-wide in controlling childhood infectious disease and issues related to poor nutrition, CAs are now making a proportionally bigger impact on the health of the worlds children. In addition to the impact of CA status on the individual child and ones family, prevalence of CAs has a significant impact on the population, as children with birth defects can cost the system a great deal of money in the provision of specialized health and education services.<p>When conducting surveillance of five selected CAs between 1990 and 1999, Saskatchewan Health found significant regional differences in the prevalence of these CAs. The purpose of this study is to ascertain whether or not there is a regional difference in all types of CAs, to assess whether or not any regional disparities also exist in the use of health care services by children with and without CAs and to determine what factors influence childrens use of health care services in the study population.<p>This study follows a birth cohort of 17,414 children (9169 cases and 8245 controls) born between January 1, 1994 to December 31, 1998 until their 5th birthday, death or emigration out of Saskatchewan. Through graphical analysis, it was revealed that while an overall regional difference does not exist in the prevalence of CAs in Saskatchewan, there are regional differences in the prevalence of 13 of the 22 specific categories of conditions studied. One-way ANOVAs showed that children with CAs have higher numbers of physician visits (p<0.001) and hospitalizations (p<0.001), and longer lengths of stay in hospital (p<0.001) than children without CAs. Regional differences were found for all outcome variables for the total population, and for children with and without CAs. The outcome with the most substantial differences between children with and without CAs was length of stay, which may indicate differential access to outpatient services throughout the province. Finally, using Andersons theoretical framework of factors that influence the use of health care services (need characteristics, predisposing characteristics and enabling characteristics) three negative binomial models were built to examine childrens use of health care services using variables from each category. <p>This study found significant regional differences for all outcome measures studied, and found that region of residence was a significant predictor of childrens use of health care services even after accounting for a variety of other maternal and child factors.

Thesis (Ph. D.)--University of Hong Kong, 1989.

In Chapter 1, I investigate whether returns of strategies based on asset pricing anomalies exhibit time series persistence which can be attributed to flow-induced trading by mutual funds. I find persistence for thirteen characteristics, which is statistically significant for five including size, corporate investment, and bankruptcy likelihood. The persistence is not explained by individual stock momentum and is not limited to certain calendar months. The return predictability can be used to construct new trading strategies, which on average earn 4.5% annually. A price pressure measure of mutual fund flow-driven trading explains a substantial part of the strategy performance persistence. In Chapter 2, we propose a new approach for estimating expected returns on individual stocks from firm characteristics. We treat expected returns as latent variables and develop a procedure that filters them out using the characteristics as signals and imposing restrictions implied by a one factor asset pricing model. The estimates of expected returns obtained by applying our method to thirteen asset pricing anomalies generate a wide cross-sectional dispersion of realized returns. Our results provide evidence of strong commonality in the anomalies. The use of portfolios based on the filtered expectations as test assets increases the power of asset pricing tests. In Chapter 3, we examine the sensitivity of fourteen asset pricing anomalies to extreme observations using robust regression methods. We find that although all anomalies except size are strong and robust for stocks with presumably low returns, most of them are sensitive to individual influential observations for stocks with presumably high returns. For some anomalies, extreme observations distort regression results for all stocks and even portfolio returns. When the impact of such observations is mitigated, eight anomalies become positively related to expected returns for stocks with low characteristics meaning that these anomalies have an inverted J-shaped form. Chapter 4 concludes by summarizing the main contributions of three chapters and their implications. / text

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

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Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal