Granular materials are in abundance in nature and are estimated to constitute over 75% of all raw materials passing through the industry. Granular or particulate solids are thus of considerable interest to many industrial sectors and research communities, where many unsolved challenges still remain. This thesis investigates the micro- and macro-phenomena in densely packed particulate systems by means of the Discrete Element Method (DEM), which is a numerical tool for analysing the internal complexities of granular material as the mechanical interactions are considered at the grain scale. It presents an alternative approach to phenomenological continuum approaches when studying localisation problems and finite deformation problems in granular materials. In order to develop a comprehensive theoretical understanding of particulate matter and to form a sound base to improve industrial processes, it is desirable to study the mechanical behaviour of granular solids subject to a variety of loading conditions. In this thesis, three loading actions were explored in detail, which are biaxial compression, rigid object penetration and progressive formation of granular piles. The roles of particle shape and contact friction in each of these loading scenarios were investigated. The resulting packing structures were compared and studied to provide a micromechanical insight into the development of contact force network which governs the collective response. The interparticle contact forces and displacements were then used to evaluate the equivalent continuum stress and strain components thus providing the link between micro- and macroscopic descriptions. The information collected from the evolution of strong contact network illustrates the underlying mechanism of force transmission and propagation. DEM simulations presented in this thesis demonstrate strong capability in predicting the bulk behaviour as well as capturing local phenomenon occurring in the system. The research first simulates a testing environment of biaxial compression in DEM, in which the phenomenon of strain localisation was investigated, with special attention given to the interpretation of underlying failure mechanism. Several key micromechanical quantities of interest were extracted to understand the bifurcation instability, such as force chains, contact orientation, particle rotation and void ratio. In the simulation of progressive formation of granular piles, a counterintuitive pressure profile with a significant pressure dip under the apex was predicted for three models under certain conditions. Both particle shape and preparation history were shown to be important in the resulting pressure distribution. During the rigid body penetration into a granular sample, the contact forces were used to evaluate the equivalent continuum stress components. Significant stress concentration was developed around the punch base which further led to successive collapse and reformation of force chains. Taking the advantage of micromechanical analysis at particle scale, two distinct bearing failure mechanisms were identified as the penetration proceeded. To further quantify the nature of strain mobilisation leading to failure, Particle Image Velocimetry (PIV) was employed to measure the deformation over small strain interval in association with shear band propagation in the biaxial test and deformation pattern in the footing test. The captured images from DEM simulation and laboratory experiments were evaluated through PIV correlation. This optical measuring technique is able to yield a significant improvement in the accuracy and spatial resolution of the displacement field over highly strained and localised regions. Finally, a series of equivalent DEM simulations were also conducted and compared with the physical footing experiments, with the objective of evaluating the capability of DEM in producing satisfactory predictions.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

L'ACTH stimule son récepteur au niveau du cortex surrénalien afin d'enclencher la synthèse et la sécrétion de cortisol chez l'humain.L'hypothèse du projet propose qu'il existe une régulation moléculaire de MC2R (melanocortin-2 receptor) qui permet les [i.e. aux] cellules corticosurrénaliennes de s'adapter aux variations physiologiques d'ACTH. Mon projet de doctorat a consisté à utiliser MC2R et MRAP (MC2R accessory protein) recombinés dans les cellules embryonnaires de rein humain (HEK) 293/FRT (Flp recombinase target). J'ai développé ce modèle entièrement humain afin de contourner les problèmes d'expression fonctionnelle de MC2R (avant 2005) dans le but d'approfondir nos connaissances sur la régulation fonctionnelle de MC2R. Les objectifs spécifiques étaient de : 1) Déterminer le rôle des isoformes MRAP1 dans l'expression fonctionnelle de MC2R. 2) Déterminer les différences entre MRAPs. 3) Analyser l'internalisation et le recyclage de MC2R. 4) Déterminer la contribution des 9 serines (S) et thréonines (T) intracellulaires de MC2R dans sa régulation fonctionnelle. 5) Déterminer si la phosphorylation des MAPKs (mitogen-activated protein kinases) induite par l?ACTH est liée au processus d'internalisation de MC2R. Premièrement, MC2R est exprimé à la membrane plasmique des cellules 293/FRT mais de manière non-fonctionnelle. La co-expression de l'une ou l'autre des isoformes MRAP1 (MRAP[alpha] ou MRAP[béta]) humaines augmente l'expression membranaire de MC2R. MRAP[alpha] n'induit pas autant l'expression membranaire de MC2R que MRAP[béta], ce qui se répercute sur la capacité de liaison de l?ACTH et aussi sur les réponses maximales d'AMPc. Par contre, MRAP[alpha] permet une plus grande affinité pour l?ACTH que MRAP[béta], ce qui se traduit par une plus grande sensibilité des cellules à l?ACTH (section 3.1). Deuxièmement, MC2R est N-glycosylé sur ses deux sites de N-glycosylation, mais cette dernière n'est pas requise pour sa fonctionnalité (article non-présenté). Troisièmement, le système ACTH/MC2R/MRAP1/MRAP2 du poisson zèbre a été caractérisé (article non-présenté) et s'est soldé par l'observation que zfMRAP1 procure 10 fois plus de sensibilité à l?ACTH que MRAP[alpha]. Quatrièmement, chaque domaine C-terminal semble servir au triage des protéines MRAP1 au niveau de l'appareil de Golgi car MRAP[alpha] (pré-Golgi), MRAP[béta] (post-Golgi) et leur version tronquée, MRAPdCT (au Golgi), sont préférentiellement localisées dans différents compartiments cellulaires. Les MRAP1s et les MRAP2 modulent l'expression de MC2R. En retour, MC2R augmente l'expression et le ciblage membranaire des MRAP1s (section 3.2). Cinquièmement, l'internalisation de MC2R est clathrine-, dynamine- et arrestine-dépendente. Le recyclage et la resensibilisation de MC2R permet à l?ACTH d'entretenir une production d'AMPc soutenue. Les isoformes MRAP1 internalisent avec MC2R dans des endosomes positifs pour Rab4, Rab5 et Rab11 (section 3.3). Sixièmement, plusieurs S/T sont susceptibles d'être impliquées dans la désensibilisation, l'internalisation et dans la régulation de l'expression membranaire de MC2R. Le résidu T143, cible potentielle de la protéine kinase C (PKC), est critique à l'expression membranaire de MC2R (section 3.3). Finalement, l'activation des voies MAPK n'est pas liée à l'interaction MC2R-arrestine durant l'internalisation (article non-présenté).

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

This thesis provides a critical review of the Transition movement, a grassroots response to peak oil and climate change, co-founded by this author. It focuses on two key aspects of the Transition approach, resilience and economic relocalisation, with the aim of analysing whether and how they can be implemented in a locality based on the Transition approach, and assessing what socio-economic and community-related structures would be necessary to implement such a process. The focus of the research is Totnes, Devon, which because of its status as the UK’s first Transition initiative and the longer history of various initiatives to promote local resilience, offers a valuable case study of attempts to practically implement resilience and localisation. A variety of research methods were employed, including surveys, focus groups, oral history and in-depth interviews, as well less conventional public participation methods such as Open Space and World Café. The first major finding was that Transition Town Totnes (TTT) has become a significant organisation in the town, with a high level of popular support. It was also found that the obstacles to resilience and relocalisation lie not, as was hypothesised, in a lack of skills or an absence of community cohesion, but in issues of governance and the need for increased social entrepreneurship. It was found that what researchers call the ‘Value Action Gap’ (i.e. the gap between people’s declared sympathies and intentions and their actions) exists in Totnes as much as anywhere else, but that some of TTT’s projects, such as ‘Transition Together’, are working imaginatively to overcome this and to reduce emissions. From this evidence is it concluded that Transition’s approach towards relocalisation and reducing carbon emissions can be argued to be effective in, generating engagement and initiating new enterprises. Like other ‘green’ initiatives, it struggles to engage those from more disadvantaged backgrounds, but some of its initiatives are showing promise for overcoming this. Its primary contribution is in suggesting a redefining of resilience, not as a state of preparedness for disaster, but as a desired characteristic of a sustainable society. A more resilient community, it is argued, would be one more in control of its food and energy production, as well as being one that enables inward financial investment. It also argues that the government focus on ‘localism’, the devolving of political power to the local level, ought to be expanded to include ‘localisation’, the strengthening of local production to meet local needs, a shift which would financially benefit local communities. It argues that the key challenge for Transition initiatives such as TTT is going to be scaling up from being ‘niche’ organisations to become economically viable organisations with a broad appeal and engagement, and also articulates the need for ‘Resilience Indicators’ which would allow communities to measure the degree to which their levels of resilience are increasing.

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

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

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