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yes / The accurate prediction of the dilution and motion of the produced denser water (e.g. discharge of concentrated brine generated during solution mining and desalination) is of importance for environmental protection. Boundary conditions and ambient stratification can significantly affect the dilution and motion of gravity currents. In this study, a multiphase model is applied to simulate the gravity current descending a slope into a linearly stratified ambient. The k- turbulence model is used to better simulate the near bed motion. The mathematical model, initial and boundary conditions and the details of the numerical scheme are described. The time-dependent evolution of the gravity current, the flow thickness and the velocity and density field are simulated for a range of flow parameters. Simulations show that the Kelvin–Helmholtz billows are generated at the top of trailing fluid by the interfacial velocity shear. The K-H type instability becomes weaker with the slope distance from the source due to the decrease of the interfacial velocity shear along slope. The ambient stratification restricts and decreases the current head velocity as it descends slope, which differs from the situation in homogenous ambient while the head velocity remains an approximately steady state. Motion of the descending flow into the stratified ambient has two stages: initial acceleration and deceleration at later stage based on the balance of inertial, buoyancy and friction forces. When the descending current approaches the initial neutral position at later stage, it separates from the slope and spreads horizontally into environment. The simulated results, such as vertical velocity and density profiles and front positions, agree well with the measurements, indicating that the mathematical model can be successfully applied to simulate the effect of the boundary condition and ambient stratification on the dilution and propagation of gravity currents. / UK EPSRC

Cyanobacteria are a naturally occurring component of reservoir aquatic ecosystems. Given that some species possess the ability to control their depth within the water column, they have a competitive advantage over other species of photosynthetic organisms. This leads to the potential for cyanobacteria blooms, and because of taste and odor problems, as well as possible toxin production associated with certain species of cyanobacteria, these organisms can cause major problems in drinking water production. The Western Virginia Water Authority installed a solar-powered circulator in Falling Creek Reservoir, located in Bedford County, Virginia, in an attempt to limit the growth of these organisms through limiting light exposure by circulating them deeper within the reservoir. Experiments were performed during the summer of 2008 to quantify the effect of the circulator on the reservoir. Temperature, dissolved oxygen, water velocity, and photosynthetic yield were monitored before and during operation of the unit. The overall effect of the mixer was limited to the first 10 m immediately adjacent to the unit during the afternoon. The effect was stronger during the morning when the difference in density between the intake water and the surface of the reservoir was smaller, allowing the water to travel up to 80 m away from the unit. Although the circulator was only intended to mix and possibly deepen the epilimnion, the entire reservoir became mixed about two weeks after the circulator was put into operation. The reservoir is quite shallow, leading to a weak stratification that is easily disrupted by the operation of the circulator. / Master of Science

Yes / Consanguineous marriage is a controversial topic in many Western societies, with attention mainly focused on the health of immigrant communities from Asia and Africa. In the UK consanguinity is especially prevalent in the Pakistani community which now numbers over 1.1 million. Less attention has been paid to the influence of hereditary population stratification within Pakistani communities. In particular, biraderi (literally brotherhood) membership which denotes male lineages that largely govern marriage partner choice and hence the transmission of disease genes. The various roles played by biraderi and their relationship to other socio-occupational and kinship terms, such as caste, quom and zat, are often overlooked in health-based studies. The interchangeable use of these different kinship terms without rigorous definition can create identity uncertainty and hinders inter-study comparisons. Where feasible, standardization of terminology would be both desirable and beneficial, with biraderi the preferred default term to identify specific social and genetic relationships within the Pakistani diaspora.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Social Stratification is an enduring influence in contemporary societies which shapes many outcomes over the lifecourse. Social Stratification is also a key mechanism by which social inequalities are transmitted from one generation to the next. This thesis presents a set of inter-related case studies which explore social stratification in contemporary Britain. This thesis focuses on the analysis of an appropriate set of large scale social survey datasets, which contain detailed micro-level data. The thesis begins with a detailed review of one area of social survey research practice which has been neglected, namely the measurement and operationalisation of ‘key variables’. Three case studies are then presented which undertake original analyses using five different large-scale social survey resources. Throughout this thesis detailed consideration of the operationalisation of variables is made and a range of statistical modelling approaches are employed to address middle range theories regarding the processes of social stratification. Case study one focuses on cognitive inequalities in the early years of childhood. This case study builds on research which has indicated that social stratification impacts on the cognitive performance of young children. This chapter makes the original contribution of charting the extent of social inequalities on childhood cognitive abilities between three British birth cohorts. There are clear patterns of social inequality within each cohort. Between the cohorts there is also evidence that the association between socio-economic advantage and childhood cognitive capability have remained largely stable over the post-war period, in spite of the raft of policy measures that have been floated to tackle social inequality. Case study two investigates the recent sociological idea that there is a ‘middle’ group of young people who are absent in sociological inquiries. This chapter sets out to explore the existence of a ‘middle’ group based on their socio-economic characteristics. This case study focuses on school GCSE examination performance, and finds that performance is highly stratified by parental occupational positions. The analysis provided no persuasive evidence of the existence of a ‘middle’, mediocre or ordinary group of young people. The analytical benefits of studying the full attainment spectrum are emphasised, over a priori categorisation. Case study three combines the analysis of intra-generational and inter-generational status attainment perspectives by studying the influences of social origins, educational attainment and cognitive abilities across the occupational lifecourse. This case study tests theoretical ideas regarding the importance of these three areas of influence over time. This case study therefore presents a detailed picture of social stratification processes. The results highlight that much more variation in occupational positions is observed between individuals, rather than across an individual’s lifecourse. The influence of social origins, educational attainment and cognitive ability on occupational positions appear to decrease across an individual’s occupational lifecourse. A brief afterword that showcases a sensitivity analysis is presented at the end of the thesis. This brief exposition is provided to illustrate the potential benefit of undertaking sensitivity analyses when developing research which operationalises key variables in social stratification. It is argued that such an activity is beneficial and informative and should routinely be undertaken within sociological analyses of social surveys. The thesis concludes with a brief reflection on large-scale survey research and statistical modelling and comments on potential areas for future research.

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

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

Cette thèse est consacrée à l’étude de la turbulence homogène stratifiée instable, un écoulement idéalisé décrivant l’évolution de la turbulence au sein d’une zone de mélange de type Rayleigh-Taylor. Cette approche se concentre sur l’évolution des quantités fluctuantes ;l’influence de l’écoulement moyen est prise en compte au travers d’un gradient moyen de densité. Un modèle spectral est utilisé pour étudier cette turbulence, conjointement à des simulations numériques directes. En comparaison avec ces simulations, l’étape de validation du modèle met en lumière le rôle des termes de stratification sur la dynamique du transfert d’énergie. Une première étude montre l’établissement, dans l’état autosemblable, de lois d’échelles ainsi que l’influence de la distribution initiale d’énergie sur l’état asymptotique et sur l’anisotropie de l’écoulement. Dans une seconde étude, la rétroaction de la turbulence sur le gradient moyen est introduite, dans un premier temps, afin de rapprocher la dynamique autosemblable de la turbulence homogène stratifiée instable de celle observée en turbulence Rayleigh-Taylor. Dans un second temps, l’influence d’un renversement de la stratification sur la dynamique du mélange est étudiée au travers d’un profil d’accélération variable. / This thesis is dedicated to the study of unstably stratified homogeneous turbulence.This flow is an idealized framework introduced to investigate the turbulence developing at the centerline of a Rayleigh-Taylor mixing zone. This approach focuses on turbulent quantities, when the mean flow acts on the turbulent field through a mean density gradient.A spectral model and direct numerical simulations are used to study this turbulent flow.The validation step reveals the role of stratification terms on the energy transfer dynamic.Then, a first study shows the emergence of scaling laws in the self-similar state, together with the large scale energy distribution impact on the asymptotic state and on the flow anisotropy. In a second study, the turbulent retroaction on the mean density gradient is introduced in order to bring unstably stratified homogeneous turbulence closer to theRayleigh-Taylor turbulence dynamics. This step leads to investigate the consequences of a stratification inversion on the mixing dynamics through a variable acceleration profile.

Nous étudions la stratification de Newton des variétés de Shimura de type PEL aux places de bonne réduction. Nous considérons la strate basique de certaines variétés de Shimura simples de type PEL modulo une place de bonne réduction. Sous des hypothèses simplificatrices nous prouvons une relation entre la cohomologie l-adique de ce strate basique et la cohomologie de la variété de Shimura complexe. En particulier, nous obtenons des formules explicites pour le nombre de points dans la strate basique sur des corps finis, en termes de représentations automorphes. Nous obtenons les résultats à l'aide de la formule des traces et de la troncature de la formule de Kottwitz pour le nombre de points sur une variété de Shimura sur un corps fini. Nous montrons, en utilisant la formule des traces, que n'importe quelle strate de Newton d'une variété de Shimura de type PEL de type (A) est non vide en une place de bonne réduction. Ce résultat a déjà été établi par Viehmann-Wedhorn; nous donnons une nouvelle preuve de ce théorème. Considérons la strate basique des variétés de Shimura associées à certains groupes unitaires dans les cas où cette strate est une variété finie. Alors, nous démontrons un résultat d' équidistribution pour les opérateurs de Hecke agissant sur cette strate. Nous relions le taux de convergence avec celui de la conjecture de Ramanujan. Dans nos formules ne figurent que des représentations automorphes cuspidales sur Gl_n pour lesquelles cette conjecture est connue, et nous obtenons donc des estimations très bonnes sur la vitesse de convergence. En collaboration avec Erez Lapid nous calculons le module de Jacquet d'une représentation en échelle pour tout sous-groupe parabolique standard du groupe général linéaire sur un corps local non-archimédien. / We study the Newton stratification of Shimura varieties of PEL type, at the places of good reduction. We consider the basic stratum of certain simple Shimura varieties of PEL type at a place of good reduction. Under simplifying hypotheses we prove a relation between the l-adic cohomology of this basic stratum and the cohomology of the complex Shimura variety. In particular we obtain explicit formulas for the number of points in the basic stratum over finite fields, in terms of automorphic representations. We obtain our results using the trace formula and truncation of the formula of Kottwitz for the number of points on a Shimura variety over a finite field. We prove, using the trace formula that any Newton stratum of a Shimura variety of PEL-type of type (A) is non-empty at a prime of good reduction. This result is already established by Viehmann-Wedhorn; we give a new proof of this theorem. We consider the basic stratum of Shimura varieties associated to certain unitary groups in cases where this stratum is a finite variety. Then, we prove an equidistribution result for Hecke operators acting on the basic stratum. We relate the rate of convergence to the bounds from the Ramanujan conjecture of certain particular cuspidal automorphic representations on Gl_n. The Ramanujan conjecture turns out to be known for these automorphic representations, and therefore we obtain very sharp estimates on the rate of convergence. We prove that any connected reductive group G over a non-Archimedean local field has a cuspidal representation. Together with Erez Lapid we compute the Jacquet module of a Ladder representation at any standard parabolic subgroup of the general linear group over a non-Archimedean local field.