Tese de Mestrado Integrado. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto. 2011

Tese de Mestrado Integrado. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto. 2011

Tese de Programa Doutoral. Sistemas Sustentáveis de Energia. Universidade do Porto. Faculdade de Engenharia. 2011

<div>Let <i>K₀</i>(Var<i>_k</i>) be the Grothendieck group of varieties over a field <i>k</i>. We construct an exact category, denoted Add(Var_<i>k</i>)_<i>S</i>, such that there is a surjection <i>K₀</i>(Var<i>k</i>)→<i>K₀</i>(Add(Var<i>_k</i>)_<i>S</i>).If we consider only zero dimensional varieties, then this surjection is an isomorphism. Like <i>K₀</i>(Var<i>_k</i>), the group K_<i>0</i>(Add(Var_<i>k</i>)<i>_S</i>) is also generated by isomorphism classes of varieties,and we construct motivic measures on <i>K₀</i>(Add(Var<i>_k</i>)<i>_S</i>) including the Euler characteristic if <i>k</i>=<i>C</i>, and point counting measures and the zeta function if <i>k</i> is finite.<br></div>

Depuis 1949, date à laquelle Bloembergen en introduisit le concept, la diffusion de spin nucléaire suscite un vif intérêt en résonance magnétique. La diffusion de spin, qui peut être définie comme le transfert de polarisation de spin induit par l’interaction dipolaire, est un mécanisme omniprésent dans les solides. Les mesures expérimentales de ce phénomène contiennent des informations sur la structure du système étudié. La diffusion de spin est cependant un problème quantique à N corps, ce qui rend sa description ab initio relativement difficile. L’objectif principal de cette thèse est d’obtenir une description quantitative et ab initio de la diffusion de spin, en modélisant de manière adéquate la dynamique à N corps sous-jacente. Tout d’abord, nous exploitons une approche existante, reposant sur l’utilisation d’une équation maître pour les polarisations, dans le cas de la diffusion de spin entre carbones permise par les protons (PDSD). Ensuite, nous introduisons une méthode permettant de simuler l’évolution temporelle d’un ensemble d’observables pour un système de spins nucléaires fortement couplés, en utilisant les corrélations de petit ordre dans l’espace de Liouville (LCL). Le modèle LCL fournit une description précise du transfert de polarisation pour les systèmes polycristallins soumis à la rotation à l’angle magique. Après avoir décrit le modèle, nous analysons plus en détail la réduction de l’espace de Liouville pour les solides, afin d’identifier les conditions dans lesquelles l’approximation LCL est valide. Enfin, nous effectuons des simulations de la diffusion de spin entre pro- tons (PSD) et entre carbones (PDSD), à partir de la structure des cristaux étudiés et sans aucun paramètre libre, et nous constatons pour des solides organiques polycristallins que leur accord avec les mesures expérimentales est excellent. / Since its introduction by Bloembergen in 1949, nuclear spin diffusion has been a topic of significant interest in magnetic resonance. Spin diffusion, which can be defined as the transfer of spin polarisation induced by the dipolar interaction, is a ubiquitous transport mechanism in solids. Experimental observations of spin diffusion contain structural information. However, the many-body nature of the problem makes it difficult to describe from first principles. The central goal of this thesis is to obtain a quantitative description of the spin diffusion phenomenon from first-principles, through the development of suitable models of the underlying many-body dynamics. To that end we first consider an extension of an existing approach that relies on a master equation to describe the polarisations, for the case of proton-driven carbon-13 spin diffusion (PDSD). Second, a novel approach is introduced for the simulation of the time evolution of selected observables for large strongly coupled nuclear spin systems, using low-order correlations in Liouville space (LCL). Following the introduction of this new simulation method, Liouville-space reduction in solids is analysed in more detail, in order to identify the conditions under which the LCL approximation is valid. Finally, using the LCL model, simulations of proton spin diffusion (PSD) and PDSD are performed, directly from crystal geometry and with no adjustable parameters, and are found to be in excellent agreement with experimental measurements for polycrystalline organic solids.

Yaksagana

No description available.

Background: To describe the scoring methodology and MRI assessments used to evaluate the cross-sectional features observed in cases and controls, to define change over time for different MRI features, and to report the extent of changes over a 24-month period in the Foundation for National Institutes of Health Osteoarthritis Biomarkers Consortium study nested within the larger Osteoarthritis Initiative (OAI) Study. Methods: We conducted a nested case-control study. Cases (n = 406) were knees having both radiographic and pain progression. Controls (n = 194) were knee osteoarthritis subjects who did not meet the case definition. Groups were matched for Kellgren-Lawrence grade and body mass index. MRIs were acquired using 3 T MRI systems and assessed using the semi-quantitative MOAKS system. MRIs were read at baseline and 24 months for cartilage damage, bone marrow lesions (BML), osteophytes, meniscal damage and extrusion, and Hoffa- and effusion-synovitis. We provide the definition and distribution of change in these biomarkers over time. Results: Seventy-three percent of the cases had subregions with BML worsening (vs. 66 % in controls) (p = 0.102). Little change in osteophytes was seen over 24 months. Twenty-eight percent of cases and 10 % of controls had worsening in meniscal scores in at least one subregion (p < 0.001). Seventy-three percent of cases and 53 % of controls had at least one area with worsening in cartilage surface area (p < 0.001). More cases experienced worsening in Hoffa- and effusion synovitis than controls (17 % vs. 6 % (p < 0.001); 41 % vs. 18 % (p < 0.001), respectively). Conclusions: A wide range of MRI-detected structural pathologies was present in the FNIH cohort. More severe changes, especially for BMLs, cartilage and meniscal damage, were detected primarily among the case group suggesting that early changes in multiple structural domains are associated with radiographic worsening and symptomatic progression.

Th. licence--Droit--Toulouse, 1868-04-27.

Th. licence--Droit--Paris, 1866-08-28.