Dissertations / Theses on the topic 'Gradient Variable'

Due to the advent of varied types of masonry systems a comprehensive failure mechanism of masonry essential for the understanding of its behaviour is impossible to be determined from experimental testing. As masonry is predominantly used in wall structures a biaxial stress state dominates its failure mechanism. Biaxial testing will therefore be necessary for each type of masonry, which is expensive and time consuming. A computational method would be advantageous; however masonry is complex to model which requires advanced computational modelling methods. This thesis has formulated a damage mechanics inspired modelling method and has shown that the method effectively determines the failure mechanisms and deformation characteristics of masonry under biaxial states of loading.

Ce travail apporte une contribution a la caracterisation des couches minces par ellipsomerie spectroscopique a angle variable. Nous presentons les differentes modifications apportees a l'ellipsometre d'origine et decrivons les procedures d'etalonnage utilisees. La reduction des erreurs systematiques et aleatoires est egalement traitee. Une etude originale a ete menee sur les derivees partielles des angles ellipsometriques psi et delta par rapport aux differents parametres de l'echantillon (epaisseurs, indices, angle d'incidence). Celle-ci nous a conduit a introduire le concept de sensibilite integrale relative (sir) qui s'est avere tres utile pour localiser les zones angulaires les plus interessantes et pour comparer entre elles les sensibilites de la mesure ellipsometrique aux divers parametres de l'echantillon. L'interet de mesures spectroscopiques a plusieurs angles d'incidence est discute. Deux applications principales ont ete traitees dans ce memoire: la premiere concerne la mesure des indices de semi-conducteurs ii-vi a grands gaps. L'etude realisee porte sur des substrats massifs de cdmnte et sur des couches epitaxiees de cdmgte. Une loi d'indice permettant de decrire le comportement de la fonction dielectrique du cdmgte sur l'ensemble du domaine spectral est proposee. Dans la zone transparente, deux lois de sellmeier donnant les indices du cdmnte et du cdmgte pour toute concentration de manganese ou de magnesium, ont ete etablies. La seconde porte sur la caracterisation de couches a gradient d'indice. Une methode permettant d'analyser des couches de profil d'indice a priori quelconque est proposee. Elle a ete validee sur des couches inhomogenes de gaalas et d'oxy-nitrure de silicium. L'ellipsometrie s'est revelee etre une technique bien adaptee a ce type de caracterisation puisque des profils polynomiaux du quatrieme degre ont pu etre mis en evidence sur des couches d'oxy-nitrure de silicium a fort gradient d'indice

Controls on denudation in the eastern Bolivian Andes are evaluated by synthesis of new and existing denudation estimates from basin-morphometry, stream - powered fluvial incision, landslide mapping, sediment flux, erosion surfaces, thermochronology, foreland basin sediment volumes, and structural restorations. Centered at 17.5 °S, the northeastern Bolivian Andes exhibit high relief, a wet climate, and a narrow fold- thrust belt. In contrast, the southeastern Bolivian Andes have low relief, a semi-arid climate, and a wide fold-thrust belt. Basin -morphometry indicates a northward increase in relief and relative denudation. Stream-power along river profiles shows greater average incision rates in the north by a factor of 2 to 4. In the south, profile knickpoints with high incision rates are controlled by fold-thrust belt structures such as the surface expressions of basement megathrusts, faults, folds, and lithologic boundaries. Landslide and sediment-flux data are controlled by climate, elevation, basin morphology, and size and show a similar trend; short -term denudation-rate averages are greater in the north (1- 9 mm/yr) than the south (0.3-0.4 mm/yr). Long-term denudation-rate estimates including fission track, basin fill, erosion surfaces, and structural restorations also exhibit greater values in the north (0.2-0.8 mm/yr) compared to the south (0.04-0.3 mm/yr). Controls on long-term denudation rates include relief, orographic and global atmospheric circulation patterns of precipitation, climate change, glaciation, and fold-thrust belt geometry and kinematics. The denudation synthesis supports two conclusions: 1) denudation rates have increased towards the present 2) an along-strike disparity in denudation (greater in the north) has existed since at least the Miocene and has increased towards the present. Denudation rates and controls suggest that Bolivian mountain morphology is controlled by both its orientation at mid-latitude, and the feedbacks between uplift, kinematics, orographic effects on precipitation, glaciation, and the increased erosion that accompanies orogenesis.

Le développement de lasers solides de puissance-moyenne élevée doit faire face à des problèmes très spécifiques. La gestion de la thermique et de l'amplification de l'émission spontanée (ASE) pour de larges amplificateurs lasers deviennent des points clés lorsque l'augmentation de l'énergie de vient conséquente. Lucia est une chaîne laser de forte puissance moyenne qui repose sur le concept du miroir actif avec un cristal ou une céramique d'Yb:YAG comme milieu à gain. Comme pour d'autres systèmes lasers comparables, la distribution des ions actifs du milieu à gain est homogène en volume. Un profil variable du taux de dopage présente des avantages significatifs en termes de gain et par conséquent ouvre le chemin à une minimisation efficace des effets délétères de l'ASE et de l'échauffement. Cette thèse concerne la fabrication de tels milieux à gain. La méthode de croissance cristalline Bagdasarov, grâce à plusieurs de ses particularités, a permis d'obtenir plusieurs cristaux d'Yb:YAG avec profils de dopage variables contrôlés jusqu'à des valeurs de gradient de 3 at%/cm. Les résultats expérimentaux sont en bon accord avec les modèles mathématiques. Des simulations complémentaires de la température et du profil de gain montre que même avec des gradients plus faibles, les performances énergétiques des amplificateurs Lucia peuvent être améliorées jusqu'à 30%. Il est aussi alors possible d'utiliser des milieux à gain plus fins ce qui a pour conséquence positive une meilleure extraction de la chaleur. De larges cristaux d'Yb:YAG de 90 mm de diamètre ont été produits.

Made available in DSpace on 2017-07-10T18:13:17Z (GMT). No. of bitstreams: 1 Thales Serrano Silva.pdf: 828664 bytes, checksum: e2d48b84a411318cdf1e6bae706172fe (MD5) Previous issue date: 2014-04-25<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>With the growth of the aquaculture even small mortality rates take big losses, so this study was goal to evaluate possible causes of death in fish at industrial scale in transportation. So eight abiotic variables of water quality were examined: water temperature, dissolved oxygen, ammonia, nitrate, nitrite, pH, conductivity and turbidity, as well transportation time and density and gradient difference of the variables from the catch to the end transport. For this ten samplings between setembro/2013 and fevereiro/2014 were performed in western Paraná. The water sampling were performed at three different times during the transport process, because it was necessary to subdivide them for obtain the difference in gradient of environmental variables and identify which is the most critical step of the process. To characterize the quality of water, the abiotic variables were summarized using Principal Component Analysis (PCA). The combined variation of variables was summarized in an index called variation in environmental gradient (&#916;G). Further, to verify which variables were associated with mortality, the Probit model was used in the linear regressions. Both analyzes were evaluated at a significance level of five percent. APC in three main axes, which indicated high concentrations of nitrite for time pond, in loading the variables analyzed were satisfactory and unloading time had water with high levels of nitrate, electrical conductivity and ammonia. In linear regressions nitrite was significant for mortality in pond time, water temperature and electrical conductivity for loading and ammonia and dissolved oxygen for unloading time. Abrupt changes in gradient of the variables did not cause fish mortality and nitrogenous waste found in large concentrations at the end of the transport interfered in fish mortality. With that suggest that fish are subjected to stress before the transport process due to bad quality of water pond.<br>Com o crescimento da aquicultura até mesmo pequenas taxas de mortalidade assumem grandes prejuízos, logo, este estudo teve o objetivo de avaliar possíveis causas de óbitos em peixes no transporte em escala industrial. Assim, foram examinadas oito variáveis abióticas de qualidade de água: temperatura da água, oxigênio dissolvido, amônia, nitrato, nitrito, pH, condutividade elétrica e turbidez, além de tempo e densidade de transporte e diferença de gradiente das variáveis desde a captura até o final do transporte. Para isto foram realizadas dez amostragens entre setembro/2013 e fevereiro/2014, na região oeste do Paraná. As coletas de água foram realizadas em três momentos diferentes durante o processo de transporte, pois foi necessário subdividi-las para obter a diferença de gradiente das variáveis ambientais assim como identificar qual a etapa mais crítica do processo. Para caracterizar a qualidade da água, as variáveis abióticas foram sumarizadas através de Análise de Componentes Principais (ACP). A amplitude conjunta das variáveis foi sumarizada num índice denominado variação no gradiente ambiental (&#8710;G). Na sequência, para verificar quais variáveis estiveram associadas às mortalidades, foi utilizado o modelo Probito nas regressões lineares. Ambas as análises foram avaliadas ao nível de significância de cinco por cento. Na APC foram retidos três eixos principais, os quais indicaram altas concentrações de nitrito para o tempo viveiro, no momento carregamento as variáveis analisadas apresentaram-se satisfatórias e o momento descarregamento apresentou água com elevados índices de nitrato, condutividade elétrica e amônia. Nas regressões lineares o nitrito mostrou-se significante para mortalidade no tempo viveiro, temperatura da água e condutividade elétrica para o carregamento e oxigênio dissolvido e amônia no momento descarregamento. Mudanças abruptas de gradiente das variáveis não ocasionaram mortalidade dos peixes e os resíduos nitrogenados encontrados em grandes concentrações ao final do transporte interferem na mortalidade dos peixes. Com isso pode-se sugerir que os peixes estão submetidos à estresse antes do processo de transporte devido má qualidade da água no momento viveiro.

In a reinforcement learning task an agent must learn a policy for performing actions so as to perform well in a given environment. Policy gradient methods consider a parameterized class of policies, and using a policy from the class, and a trajectory through the environment taken by the agent using this policy, estimate the performance of the policy with respect to the parameters. Policy gradient methods avoid some of the problems of value function methods, such as policy degradation, where inaccuracy in the value function leads to the choice of a poor policy. However, the estimates produced by policy gradient methods can have high variance.¶ In Part I of this thesis we study the estimation variance of policy gradient algorithms, in particular, when augmenting the estimate with a baseline, a common method for reducing estimation variance, and when using actor-critic methods. A baseline adjusts the reward signal supplied by the environment, and can be used to reduce the variance of a policy gradient estimate without adding any bias. We find the baseline that minimizes the variance. We also consider the class of constant baselines, and find the constant baseline that minimizes the variance. We compare this to the common technique of adjusting the rewards by an estimate of the performance measure. Actor-critic methods usually attempt to learn a value function accurate enough to be used in a gradient estimate without adding much bias. In this thesis we propose that in learning the value function we should also consider the variance. We show how considering the variance of the gradient estimate when learning a value function can be beneficial, and we introduce a new optimization criterion for selecting a value function.¶ In Part II of this thesis we consider online versions of policy gradient algorithms, where we update our policy for selecting actions at each step in time, and study the convergence of the these online algorithms. For such online gradient-based algorithms, convergence results aim to show that the gradient of the performance measure approaches zero. Such a result has been shown for an algorithm which is based on observing trajectories between visits to a special state of the environment. However, the algorithm is not suitable in a partially observable setting, where we are unable to access the full state of the environment, and its variance depends on the time between visits to the special state, which may be large even when only few samples are needed to estimate the gradient. To date, convergence results for algorithms that do not rely on a special state are weaker. We show that, for a certain algorithm that does not rely on a special state, the gradient of the performance measure approaches zero. We show that this continues to hold when using certain baseline algorithms suggested by the results of Part I.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008.<br>This thesis examines the role of agricultural activity in the process of invasion of west coast renosterveld fragments by annual alien grass species. This highly endangered vegetation type has less than 5% remaining, it is vital to understand the mechanisms allowing invasion of annual alien grasses in order to effectively prevent the loss of the many rare and endemic species found in west coast renosterveld. This study was divided into three major components. Firstly the distribution of indigenous and alien plant species in relation to fence lines, separating active agricultural fields from untransformed vegetation, was described. Regression analysis was used to test for relationships between distances from agricultural fields and soil physical and chemical characteristics in natural vegetation. Cover by annual alien invasive grasses in untransformed vegetation decreased significantly with distance away from agricultural land. Secondly alien and indigenous grass seed banks were sampled along the transects, at the same sites, in order to establish whether the seed banks correlated with above ground cover. Results varied among sites and seed banks were correlated with the vegetation cover at only one site. It appears that there are a multitude of factors determining the distribution of annual alien grass cover. Thirdly a greenhouse experiment established the role that nitrogen plays in the success of the alien grass Avena fatua. This species was grown in competition with three indigenous species, an annual forb (Dimorphotheca pluvialis), a geophyte (Oxalis purpurea) and an indigenous perennial grass (Tribolium uniolae) at three levels of soil nitrogen. The geophyte was largely unaffected, while growth of the annual and indigenous perennial grasses was negatively affected by competition with A. fatua. Nitrogen did not seem to affect competitive interactions. Management of these renosterveld patches, in order to conserve them effectively, will require a multi-faceted approach, including prevention of further invasion and removal of invasive grasses already present.

Submitted by Jaqueline Silva (jtas29@gmail.com) on 2016-09-12T20:46:48Z No. of bitstreams: 2 Dissertação - Abssan Matuzinhos de Moura - 2016.pdf: 1317960 bytes, checksum: d406a9bf2b4d0bbca0ad6e3b52da498d (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)<br>Approved for entry into archive by Jaqueline Silva (jtas29@gmail.com) on 2016-09-12T20:47:11Z (GMT) No. of bitstreams: 2 Dissertação - Abssan Matuzinhos de Moura - 2016.pdf: 1317960 bytes, checksum: d406a9bf2b4d0bbca0ad6e3b52da498d (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)<br>Made available in DSpace on 2016-09-12T20:47:11Z (GMT). No. of bitstreams: 2 Dissertação - Abssan Matuzinhos de Moura - 2016.pdf: 1317960 bytes, checksum: d406a9bf2b4d0bbca0ad6e3b52da498d (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-04-29<br>The gradient method is a classical optimization methods to minimize a function. This method deserves special mention for its simplicity and easy understanding. This work is based on the study of the gradient method with step size given by the variant Barzilai- Borwein. Our goal is to present the convergence of the method with this variant. First we will study the two-dimensional case, for strictly convex quadratic functions. In this case, besides obtaining the convergence of the method, we see that such convergence occurs with R-superlinear rate. In the final part of the work, we will study the method with the variant Barzilai-Borwein not necessarily quadratic functions, concluding that the method converges.<br>O Método Gradiente é um dos métodos clássicos de otimização para minimizar uma função. Esse método merece um destaque especial pela sua simplicidade e fácil compreensão. Este trabalho se baseia no estudo do Método Gradiente com tamanho do passo dado pela variante de Barzilai-Borwein. Nosso objetivo é apresentar a convergência do método com esta variante. Primeiro faremos o estudo no caso bidimensional, para funções quadráticas estritamente convexas. Neste caso, além de obtermos a convergência do método, veremos que tal convergência ocorre com taxa R-superlinear. Na parte final do trabalho, faremos o estudo do método com a variante de Barzilai-Borwein para funções não necessariamente quadráticas, concluindo que o método converge.

This study proposes novel optimization methodologies for the optimization of problems that reveal non-physical step discontinuities. More specifically, it is proposed to use gradient-only techniques that do not use any zeroth order information at all for step discontinuous problems. A step discontinuous problem of note is the shape optimization problem in the presence of remeshing strategies, since changes in mesh topologies may - and normally do - introduce non-physical step discontinuities. These discontinuities may in turn manifest themselves as non-physical local minima in which optimization algorithms may become trapped. Conventional optimization approaches for step discontinuous problems include evolutionary strategies, and design of experiment (DoE) techniques. These conventional approaches typically rely on the exclusive use of zeroth order information to overcome the discontinuities, but are characterized by two important shortcomings: Firstly, the computational demands of zero order methods may be very high, since many function values are in general required. Secondly, the use of zero order information only does not necessarily guarantee that the algorithms will not terminate in highly unfit local minima. In contrast, the methodologies proposed herein use only first order information, rather than only zeroth order information. The motivation for this approach is that associated gradient information in the presence of remeshing remains accurately and uniquely computable, notwithstanding the presence of discontinuities. From a computational effort point of view, a gradient-only approach is of course comparable to conventional gradient based techniques. In addition, the step discontinuities do not manifest themselves as local minima.<br>Thesis (PhD)--University of Pretoria, 2011.<br>Mechanical and Aeronautical Engineering<br>unrestricted

Il s'agit d'etudier l'influence d'une variation rapide de l'epaisseur d'une plaque composite verre-epoxy soumise a un chargement de flexion pure. Le profil de la zone a epaisseur variable est defini par deux parametres geometriques que nous faisons evoluer pour etudier leur influence. Un modele numerique par elements finis a deux echelles a ete developpe. La premiere est macroscopique et concerne la majeure partie a epaisseur constante. Elle permet de calculer le comportement global de l'eprouvette. La deuxieme est mesoscopique et represente les domaines a epaisseur variable. Elle permet le calcul de l'etat local de concentration de contraintes. Une loi de transition est introduite au niveau des frontieres entre les deux zones a echelle de modelisation differente. Pour valider ce modele et etudier les types de rupture, une campagne experimentale a ete menee. Elle a consiste a caracteriser le composite et a solliciter en flexion pure des eprouvettes composites presentant la forme adoptee lors de la modelisation. Elles sont fabriquees par le procede rtm. La sollicitation de flexion pure est assuree grace a un banc d'essais entierement concu au sein du laboratoire et adapte aux structures flexibles. Une bonne correlation entre les resultats numeriques et experimentaux a ete observee

Currently, the transplantation of islets of Langerhans is a viable means to maintain control of blood sugar levels and reduce the risk of hypoglycemia in defined populations with brittle type I diabetes mellitus or those requiring pancreatectomy. However, the process of islet isolation is highly variable and not all isolations result in islet numbers or quality suitable for transplantation. This thesis aimed to improve transplantation success through optimization and standardization of the isolation process and to identify pretransplant variables associated with early islet engraftment. A previously disregarded enzyme activity, tryptic-like activity (TLA), has been identified to influence pancreas digestion efficiency and islet isolation success in both the preclinical and clinical situations. For human pancreases, islet isolation success rates improved from 0% in the lowest TLA group to over 50% in the highest TLA groups without affecting islet quality. These findings should help standardize evaluation of enzymes for clinical islet isolation. A closed, automated, pump-made gradient system was compared to the open, manual method for islet separation. No differences were observed in expected gradient volumes, islet yields or total purities between the two methods. The pump-made gradient system successfully removed manual influences on density gradient production while fulfilling regulatory requirements for closed system processing. Islet quantification was evaluated with computer-assisted digital imaging analysis (DIA) and a semi-closed assessment system. By using the DIA system method, which measures islet purity and pellet volume instead of manual counting methods, variation in islet counts and purity reduced by almost half. By using a transplant outcome measurement of C-peptide adjusted by blood glucose and creatinine, we identified four pretransplant factors that affect early transplant outcome. Of the four factors, one was related to the organ transport time, one to function of the islets, and two to the transplanted tissue volume. When these four factors were put into a predictive model, it accounted for about 40% of the transplant outcome. The work contained in this thesis identifies and optimizes a number of critical elements related to islet isolation and transplantation protocols.

Le Cefeidi Classiche sono gli indicatori primari di distanza piu' utilizzati. Relazioni ben definite intercorrono tra il loro periodo e la loro luminosita', sia nella banda ottica che in quella del vicino infrarosso. Grazie a queste relazioni e' possibile determinare le loro distanze con grade accuratezza. Inoltre sono i migliori traccianti di stelle di massa intermedia. Infatti, poiche' sono distribuite lungo tutto il disco Galattico, possono essere adottate per tracciare i gradienti radiali di abbondanza di ferro e elementi pesanti. Negli ultimi anni sono stati fatti molti progressi verso la comprensione e caratterizzazione dell'influenza che la composizione chimica potrebbe avere sulla relazione Periodo-Luminosita' (PL) delle Cefeidi, ma tale problema rimane ancora irrisolto. Inoltre, nonostante l'esistenza di un gradiente di abbondanza Galattico sia oggi largamente accettata, il suo preciso valore e' ancora da definire. Con lo scopo di comprendere meglio questi punti fondamentali, abbiamo rivolto la nostra attenzione su due obiettivi principali: i) valutare l'influenza della metallicita' sulla PL nelle bande V e K. ii) dare una stima accurata del gradiente di abbondanza Galattico tra 5 e 17 kpc, utilizzando misure omogenee di composizione chimica per un campione che comprende 270 Cefeidi situate lungo il disco e delle quali abbiamo ottenuto una buona stima delle distanze. Per valutare l'effetto che la metallicita' ha sulla PL, abbiamo messo in relazione, per le bande V e K, i residui dalla PL standard di Freedman et al. (2001) e Persson et al. (2004), rispettivamente, all'abbondanza di ferro ([Fe/H]). A tale scopo, abbiamo usato misure dirette del ferro per 68 Cefeidi Galattiche e Magellaniche ricavate dall'analisi di spettri ad alta risoluzione e alto rapporto segnale rumore (S/N) ottenuti con strumenti e telescopi ESO (FEROS@1.5m e UVES@VLT). In questo studio, abbiamo trovato una metallicita' media circa solare (sigma = 0.10) per il campione Galattico (32 stelle), -0.33 dex (sigma = 0.13) per quello della grande Nube di Magellano (LMC, 22 stelle) e -0.75 dex (sigma = 0.08) per la Piccola Nube di Magellano (SMC, 14 stelle). Il numero delle nostre misure di abbondanza per le Cefeidi Magellaniche risulta essere piu' del doppio di quello totale studiato fino ad ora ad alta risoluzione. I nostri risultati mostrano che la metallicita' influisce sulla PL delle Cefeidi e questa constatazione non dipende dal modulo di distanza adottato per LMC. Risultati basati sulla distanza canonica di LMC (DM_LMC = 18.5) indicano un ben definito effetto nella banda visuale V e un effetto piu' lieve in quella nel vicino infrarosso K. In dettaglio, abbiamo visto che i due bin di metallicita', quello povero di metalli e quello ricco, nella banda visuale, si trovano rispettivamente a ~ 2 sigma e a ~ 9 sigma, rispetto all'ipotesi di indipendenza e i due bins hanno una differenza di 3 sigma. Nella banda infrarossa, il bin povero di metalli si trova entro 1 sigma consistente con zero mentre quello ricco di metalli differisce dall'ipotesi di indipendenza di ~ 4 sigma. Inoltre, i due bins differiscono tra loro ~ 2 sigma. Questi risultati suggeriscono che la PL delle Cefeidi non puo' essere considerata Universale. Per indagare il gradiente di abbondanza Galattico, abbiamo fornito due nuove calibrazioni, una empirica e una teorica, di due indici di metallicita' basati sulla fotometria di Walraven. I migliori risultati sono stati ottenuti con le relazioni teoriche tra la metallicita' e gli Indici di Colore (MIC). Queste sono basate su un insieme omogeneo di tracce evolutive solar-scaled per stelle di massa intermedia e su previsioni pulsazionali riguardanti la topologia della striscia di instabilita'. Lo scatter intrinseco delle relazioni e' ~ 0.1 dex. Usando le relazioni calibrate, abbiamo ottenuto metallicita' fotometriche per l'intero campione di Walraven (122 stelle). Di queste, 51 disponevano di misure accurate di abbondanza di ferro in letteratura, per le rimanenti 71 abbiamo fornito noi una nuova stima. Abbiamo, inoltre, aggiunto le 4 per cui avevamo stimato le distanze con il metodo del Baade-Wesselink. Per aumentare ulteriormente il numero dei traccianti, abbiamo incluso anche 116 Cefeidi dal set di dati di Andrievsky et al. (2002b), 63 da quello di Lemasle et al. (2007), 6 dal campione di Szila'di et al. (2007) e 10 da quello di Romaniello et al. (2008). In questo modo siamo riusciti ad ottenere un campione di 270 stelle. Il risultato ottenuto facendo un fit lineare dell'intero dataset, indica che il gradiente di abbondanza Galattico presenta una pendenza di -0.048 +- 0.004 dex/kpc, in ottimo accordo con le stime piu' recenti. In ogni modo, la variazione dell'abbondanza di ferro lungo il disco, sembra essere meglio descritta da una distribuzione bimodale con una pendenza maggiore verso il bulge e un appiattimento del gradiente in direzione del disco piu' esterno con una discontinuita' attorno Rg ~ 10 kpc. Dall'analisi dei nostri dati non sembra emergere nessuna discontinuita' ma abbiamo trovato che le Cefeidi presentano un aumento dello spread in contenuto di ferro e che questo spread possa dipendere dalla longitudine Galattocentrica. Il verificarsi di uno spread in metallicita' in funzione della longitudine Galactocentrica indica che il gradiente radiale dovrebbe essere utilizzato con cautela nel porre dei limiti per l'evoluzione chimica in tutto il disco. Infine, con questi risultati, abbiamo deciso di fare un fit esponenziale del gradiente ottenendo uno scarto quadratico medio di 0.129 dex.<br>Classical Cepheids are the most popular primary distance indicator. They obey to well defined optical and near-infrared (NIR) Period-Luminosity (PL) relations and their distances can be estimated with an accuracy of a few percent. They also are, the best tracers of intermediate-mass stars. In particular, since they are distributed across the Galactic disk they can be adopted to trace the iron and heavy element radial gradients. In the past few years, significant progress has been made to understand and characterize the influence that chemical composition may have on the Cepheids Period-Luminosity relation but this issue is still unsettled. Although the existence of the Galactic abundance gradient is now widely accepted, its value still need to be established. To better understand these fundamental points, we focused our attenction on two main topics: i) the influence of the stellar iron content on the PL relation in the V and in the K band. ii) the behavior of the Galactic iron gradient between 5 and 17 kpc, using homogeneous iron abundances for 270 Galactic Cepheids located across the disk together with accurate distance determinations. To asses the effect of the metallicity on the PL relation, we have related the V and the K-band residuals from the standard PL relations of Freedman et al. (2001) and Persson et al. (2004), respectively, to iron abundance ([Fe/H]). We used iron measurements for 68 Galactic and Magellanic Cepheids based on high resolution and high signal-to-noise ratio (S/N) spectra collected with FEROS@1.5m and UVES@VLT (ESO, Telescopes). We have found a mean [Fe/H] ~ solar (sigma = 0.10) for our Galactic sample (32 stars), -0.33 dex (sigma = 0.13) for the Large Magellanic Cloud (LMC, 22 stars) and -0.75 dex (sigma = 0.08) for the Small Magellanic Cloud (SMC, 14 stars). Our abundance measurements of the Magellanic Cepheids double the number of stars studied up to now at high resolution. Our results show that the metallicity affects the Cepheid PL relation and this finding does not depend on the adopted LMC distance modulus. Results based on the canonical LMC distance (DM_LMC = 18.5) indicate a well defined effect in the V and a mild effect in the K-band PL relations. In particular, the metal-poor and the metal-rich bins are, in the visual band, at ~ 2 sigma and ~ 9 sigma, respectively, from the null hypothesis and the two bins differ at 3 sigma level. In the infrared band, the metal-poor bin is within 1 sigma consistent with zero while the metal-rich bin differs from the null hypothesis by ~ 4 sigma. Moreover, the magnitude residuals in the two metallicity bins differ by ~ 2 sigma. These findings support the evidence that the Cepheid PL relation is not Universal. To investigate the Galactic abundance gradient, we provided new calibrations of two photometric metallicity indices based on Walraven photometry. The best results have been obtained by the theoretical Metallicity-Index Color (MIC) relations. They rely on a homogeneous set of scaled-solar evolutionary tracks for intermediate-mass stars and on pulsation predictions concerning the topology of the instability strip. The intrinsic accuracy of the MIC relations are ~ 0.1 dex. Using the calibrated relations we have estimated photometric metallicities for the entire Walraven sample (122 Cepheids). Among them, 51 had accurate iron abundaces available in litterature and 71 are new estimates. We added four metal-rich Cepheids for which we collected high resolution spectra and for which we derived accurate distances based on the Baade-Wesselink technique. Moreover, to improve the number of tracers, we have also included 116 Cepheids from Andrievsky et al. (2002), 63 from Lemasle et al. (2007), 6 from Szila'di et al. (2007) and 10 from Romaniello et al. (2008) to end up with 270 Galactic Cepheids. Our result, over the entire data set, indicates that the iron gradient in the Galactic disk presents a slope of -0.048 +- 0.004 dex/kpc which is in very good agreement with the most recent literature values. However, the hypothesis of a linear gradient is still widely debated. Several investigations suggest a bimodal distribution with a steeper slope toward the bulge and a flattening of the gradient toward the outer disk with a discontinuity at Rg ~ 10 kpc. Our data do not support the discontinuity hypothesis but we have found that Cepheids present an increase in the spread in iron abundance and that it may depend on the Galactocentric longitude. The occurrence of this spread indicates that linear radial gradients should be cautiously treated to constrain the chemical evolution of the Galactic disk. Finally, with these results in hands, we decided to fit the Galactic abundance gradient with an exponential distribution, finding a good fit (rms=0.129 dex).

Climate change is expected to have a profound impact on freshwater fish communities, especially at higher latitudes. In this study I investigated potential effects of climate change on the niche structure of Eurasian perch (Perca fluviatilis) by looking at their diet across a latitudinal gradient and at varying light climate. Dietary niche width of Eurasian perch did not differ significantly between boreal and temperate latitudes. Additionally, no significant difference in the prevalence of specialist individuals was found along the latitudinal gradient and water transparency levels. Habitat was the main factor that significantly affected niche width and level of specialization with both being significantly higher in the littoral habitat. Taken together my results suggest that climate change might indirectly affect niche patterns by altering fish densities through changes in productivity resulting in niche and specialization variation among habitats.

En el presente Trabajo de Título se ha revisado la información bibliográfica existente y se ha estudiado la existencia del flujo no lineal en el Sistema Tuyajto, ubicado en la II Región de Antofagasta, aproximadamente 70 km. al sureste del poblado de Socaire. Esta cuenca presenta en algunas zonas valores de gradientes hidráulicos muy superiores a lo acostumbrado en flujos subterráneos, razón por la cual se pone en discusión la existencia del flujo laminar lineal. De esta manera, se pretende establecer las consideraciones especiales sobre el tratamiento habitual de evaluación de disponibilidad de recursos subterráneos. El estudio del comportamiento de los flujos en medios porosos ha sido estudiado por un gran número de investigadores, entre ellos Darcy, quien estableció empíricamente una relación lineal entre la velocidad del fluido y el gradiente de energía. En medios en los que en que se presentan altos gradientes hidráulicos, la ley de resistencia es proporcional a una combinación de la velocidad del flujo y el cuadrado de ésta, ya que se suman las fuerzas de inercia a los trabajos realizados por las fuerzas viscosas. Este fenómeno, ha sido motivo de muchos experimentos e investigaciones teóricas, centrándose en dos aspectos principales: establecer un límite superior a la ley de Darcy y proveer adecuadas relaciones para la ley de flujo. En este aspecto, los estudios realizados por Forchheimer, Ward, y Pérez Franco han sentado las bases conceptuales para poder definir de manera correcta el comportamiento del flujo y los parámetros propios que lo caracterizan. De esta forma, basándose en las investigaciones mencionadas y mediante el análisis de pruebas de bombeo, se determinó los parámetros intrínsecos del acuífero, asociados a los trabajos viscosos por medio de la metodología clásica, y los asociados a los trabajos inerciales mediante una viable metodología no convencional. De esta manera, fue posible establecer los límites de flujo de Darcy, y así identificar las zonas con flujo no lineal en el sistema. Luego, se concluye que el flujo no lineal puede aparecer en acuíferos de alta como baja conductividad, siempre qu la relación entre la conductividad hidráulica turbulenta y de Darcy sea pequeña. Finalmente, la evaluación de la recarga aportante en el traspaso de cuencas, resultó menor al utilizar la metodología no lineal, en comparación con el enfoque clásico de Darcy. De esta manera, cuando no se conocen las propiedades del acuífero, se recomienda partir de la suposición de que el flujo es no lineal.

Cette thèse porte sur la modélisation de l’écoulement et du transport en milieu poreux ;nous effectuons des simulations numériques et démontrons des résultats de convergence d’algorithmes.Au Chapitre 1, nous appliquons des méthodes de volumes finis pour la simulation d’écoulements à densité variable en milieu poreux ; il vient à résoudre une équation de convection diffusion parabolique pour la concentration couplée à une équation elliptique en pression.Nous nous appuyons sur la méthode des volumes finis standard pour le calcul des solutions de deux problèmes spécifiques : une interface en rotation entre eau salée et eau douce et le problème de Henry. Nous appliquons ensuite la méthode de volumes finis généralisés SUSHI pour la simulation des mêmes problèmes ainsi que celle d’un problème de bassin salé en dimension trois d’espace. Nous nous appuyons sur des maillages adaptatifs, basés sur des éléments de volume carrés ou cubiques.Au Chapitre 2, nous nous appuyons de nouveau sur la méthode de volumes finis généralisés SUSHI pour la discrétisation de l’équation de Richards, une équation elliptique parabolique pour le calcul d’écoulements en milieu poreux. Le terme de diffusion peut être anisotrope et hétérogène. Cette classe de méthodes localement conservatrices s’applique àune grande variété de mailles polyédriques non structurées qui peuvent ne pas se raccorder.La discrétisation en temps est totalement implicite. Nous obtenons un résultat de convergence basé sur des estimations a priori et sur l’application du théorème de compacité de Fréchet-Kolmogorov. Nous présentons aussi des tests numériques.Au Chapitre 3, nous discrétisons le problème de Signorini par un schéma de type gradient,qui s’écrit à l’aide d’une formulation variationnelle discrète et est basé sur des approximations indépendantes des fonctions et des gradients. On montre l’existence et l’unicité de la solution discrète ainsi que sa convergence vers la solution faible du problème continu. Nous présentons ensuite un schéma numérique basé sur la méthode SUSHI.Au Chapitre 4, nous appliquons un schéma semi-implicite en temps combiné avec la méthode SUSHI pour la résolution numérique d’un problème d’écoulements à densité variable ;il s’agit de résoudre des équations paraboliques de convection-diffusion pour la densité de soluté et le transport de la température ainsi que pour la pression. Nous simulons l’avance d’un front d’eau douce assez chaude et le transport de chaleur dans un aquifère captif qui est initialement chargé d’eau froide salée. Nous utilisons des maillages adaptatifs, basés sur des éléments de volume carrés<br>This thesis bears on the modelling of groundwater flow and transport in porous media; we perform numerical simulations by means of finite volume methods and prove convergence results. In Chapter 1, we first apply a semi-implicit standard finite volume method and then the generalized finite volume method SUSHI for the numerical simulation of density driven flows in porous media; we solve a nonlinear convection-diffusion parabolic equation for the concentration coupled with an elliptic equation for the pressure. We apply the standard finite volume method to compute the solutions of a problem involving a rotating interface between salt and fresh water and of Henry's problem. We then apply the SUSHI scheme to the same problems as well as to a three dimensional saltpool problem. We use adaptive meshes, based upon square volume elements in space dimension two and cubic volume elements in space dimension three. In Chapter 2, we apply the generalized finite volume method SUSHI to the discretization of Richards equation, an elliptic-parabolic equation modeling groundwater flow, where the diffusion term can be anisotropic and heterogeneous. This class of locally conservative methods can be applied to a wide range of unstructured possibly non-matching polyhedral meshes in arbitrary space dimension. As is needed for Richards equation, the time discretization is fully implicit. We obtain a convergence result based upon a priori estimates and the application of the Fréchet-Kolmogorov compactness theorem. We implement the scheme and present numerical tests. In Chapter 3, we study a gradient scheme for the Signorini problem. Gradient schemes are nonconforming methods written in discrete variational formulation which are based on independent approximations of the functions and the gradients. We prove the existence and uniqueness of the discrete solution as well as its convergence to the weak solution of the Signorini problem. Finally we introduce a numerical scheme based upon the SUSHI discretization and present numerical results. In Chapter 4, we apply a semi-implicit scheme in time together with a generalized finite volume method for the numerical solution of density driven flows in porous media; it comes to solve nonlinear convection-diffusion parabolic equations for the solute and temperature transport as well as for the pressure. We compute the solutions for a specific problem which describes the advance of a warm fresh water front coupled to heat transfer in a confined aquifer which is initially charged with cold salt water. We use adaptive meshes, based upon square volume elements in space dimension two

Des observations expérimentales montrent que les modélisations locales ne suffisent pas pour décrire le comportement de matériaux sollicités par de forts gradients des champs mécaniques, qui résultent, par exemple, de la localisation des déformations. On propose ici une démarche constructive qui étend les lois locales de type standard généralisé pour rendre compte des effets de gradients. Elle se fonde, d'une part, sur une méthode d'homogénéisation pour construire une loi à gradients de variables internes à l'échelle du point matériel, et d'autre part, sur une formulation de cette loi à l'échelle de la structure, où les variables sont dorénavant les champs de variables internes. Cette formulation variationnelle du comportement offre un cadre adéquat pour examiner des questions telles que l'existence de solutions au problème d'évolution, le choix des espaces fonctionnels pour les variables internes ou encore le lien entre modèles locaux et modèles à gradients. Par ailleurs, après discrétisation temporelle, la loi de comportement s'exprime comme la minimisation d'une énergie, problème d'optimisation qui est résolu ici au moyen d'un algorithme de lagrangien augmenté. Ce choix permet de confiner les fortes non linéarités – dont le caractère non différentiable de l'énergie – au niveau des points d'intégration, ce qui autorise une introduction aisée de ces développements dans un code de calcul préexistant, le Code_Aster® en l'occurrence. Trois applications permettent alors de mettre en lumière les potentialités de la démarche. Tout d'abord, un modèle élastique fragile illustre son caractère constructif et opérationnel, depuis la construction du modèle jusqu'aux simulations numériques. Ensuite, l'insertion dans ce cadre variationnel des modèles de plasticité à gradients, abondamment employés dans la littérature, démontre le degré de généralité de la formulation. Enfin, son application à la loi de Rousselier pour modéliser un mécanisme de rupture ductile des aciers permet d'examiner l'interaction entre grandes déformations plastiques, d'une part, et comportement non local, d'autre part.

Presentation d'une procedure d'optimisation en variables mixtes pour la conception de procedes et l'identification de modeles de genie chimique. Developpement d'un algorithme de programmation mixte base sur un principe de decomposition, de projection et de relaxation permettant le traitement des problemes non lineaires a variables non necessairement separables. Presentation d'une procedure de decomposition de superstructure permettant de denombrer l'ensemble de toutes les variables discretes et continues du probleme. Illustration par deux exemples d'application: conception optimale d'un procede comportant un ensemble de reacteurs-separateurs et identification d'un modele de representation d'une operation de traitement d'effluents aqueux

The vast majority of rivers in the developed world are affected by human alteration, which in turn negatively affects the species that rely on these highly diverse and species rich areas to survive. Homogenization of previously heterogenic areas due to a change in water discharge and the substrate availability in the rivers is often regarded as the main reason for the loss of species richness in rivers and the riparian zone. Because of this, there are a lot of restoration projects which main goal is to increase heterogeneity. The goal of this thesis is to compare hydrology and geomorphology variables between four types of reaches with high flow velocity (rapids in free-flowing reaches, rapids with regulated flow, impounded reaches and reaches in outlet channels below hydropower plants). In this thesis I wanted to find out how changes in geomorphology and hydrology affect fish species richness, riparian vegetation richness and aquatic vascular plants species richness. The result show that both fish species richness and riparian vegetation species richness are negatively affected by the changes in geomorphology and hydrology. There was no significant difference for aquatic vascular plants when comparing the regulation types. The most altered reach type, outlet channels, had significantly fewer fish species compared to the less altered reach type, impounded reaches. Outlet channels also had less riparian vegetation cover compared to all other regulation types, and fewer riparian vegetation species compared to both free-flowing reaches and impounded reaches. In conclusion, hydropower plants and timber floating have both negatively impacted the riverine ecosystem, and in turn caused a decrease in species richness for fish and riparian plants. The reaches studied in this thesis will continue to be altered and the species richness and species composition will change from an ecosystem that relied on the natural flow regime to an ecosystem more used to the flow regime created by the hydropower plants.

Made available in DSpace on 2014-06-11T19:25:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-06Bitstream added on 2014-06-13T20:27:37Z : No. of bitstreams: 1 simalmoreira_l_me_guara.pdf: 2039741 bytes, checksum: 40e1e56a7f2c21c69823f17d854f8994 (MD5)<br>Universidade Estadual Paulista (UNESP)<br>A atitude de um satélite artificial representa sua orientação no espaço, de modo que através da atitude pode-se conhecer a orientação espacial do satélite pela relação entre dois sistemas de coordenadas, um dels fixo no corpo do setélite e o outro associado com umsistema de referência inercial. Apesar da atitude ser bem representada por vários conjuntos de variáveis, todos estes apresentam limitações em sua utilização. Focaliza-se neste trabalho um conjunto de variáveis canônicas não singulares, aplicáveis ao movimento racional de satélites artificiais. Estas variáveis são úteis para o caso em que o vetor momento angular de rotação coincide com o maior momento principal de inércia do satélite. As equações dinâmicas do movimento rotacional são deduzidas pelo formalismo hamiltoniano e então integradas para análise do movimento rotacional livre de torques externos. Soluções analíticas aproximadas são obtidas e comparadas com as soluções gerais, representadas em funções elípticas, e com soluções numéricas. A Hamiltoniana média associada ao Torque de Gradiente de Gravidade é também incluida e as equações diferenciais do movimento pertubado são deduzidas em termos das variáveis não singulares. A integração analítica e numérica destas equações permite uma análise qualitativa e quantitativa das variáveis não singulares utilizadas para o movimento rotacional, quando se considera a pertubação provocada pelo Torque da Gradiente de Gravidade. Ao mesmo tempo esta análise aponta para limitações de intervalos de tempo em que algumas soluções devem ser utilizadas. Aplicações são realizadas para satélites com características similares as dos Satélites Brasileirs de Coleta de Dados (SCD1 e SCD2).<br>The attitude of an artificial satellite represents its orientation in the space, in way that through the attitude can be known the spatial orientation of the satellite for the relation between two systems of coordinates, one of them fixed in the satellite and other associate with an Inertial Referencce System. Many sets of variables are used to represent the satellite attitude, but some of them present limitations in its use. A set of non-singular canonical variables, applicable to the rotational motion of artificial satellites, is focused in this work. Thse variables are useful for the case where the rotational angular momentum vector coincides with the biggest principal moment of inertia of the satellite. The dynamic equations of the rotational motion are deduced by the Hamiltonian formalism and then they are integrated for the analysis of the torque-free rotational motion. Approximated analytical solutions are gotten and compared with the general solutions and numerical solutions. The associated mean Hamiltonian to the Gravity Gradient Torque also enclosed and the differential equations of the motion are deduced for the non-singular variables. The analytical and numeical integration of these equations allow a qualitative and quantitative analysis of these non-singular variables, when the disturbance of the Gravity Gradiente Torque is considered. At the same time this analysis point to limitations of time intervals where some solutions must be used. Applications are done for the satellite with similar characteristics of the Brzilian Satellites of Collection of Data (SCD1 and SCD2).

Made available in DSpace on 2016-12-12T20:12:33Z (GMT). No. of bitstreams: 1 PGEF15MA045.pdf: 2685012 bytes, checksum: 4acd01767b6cb362dbdc068d1ce9cf23 (MD5) Previous issue date: 2015-04-29<br>Riparian Forests is importante ecological systems for vital maintenence of the landscape of its rivers. This study aimed to characterize the physicochemical properties of forest soils and verifying the relationship with the structure the floristic composition and diversity of the riparian forest of the Pelotas River along na altitudinal gradiente. There were installed four plots with dimensions of 30 x 30 m, divided into nine sub-plots of 10 x 10 m in each of three áreas of study, so called: one área (28° 30 58 W) 1700 meters; Area 2 (28°19 58 S 0 49°40 27 W) 0- 1200 meters; Area 3 (28° 28 39,65 S - 50° 04 03,73 W) 850 meters. All individuals presente in plots with 5 &#706;_ cm DAP they were identified. Species were classified in: ecological groups, dispersion strategy. For the analysis physicalchemical properties of the soil, we used principal componente analysis (PCA). The existence of floristic-structural diferences between the three áreas studied was verified by a Multivariate Analysis of Variance permutation (PERMANOVA). It was the influence of the physicochemical properties of soil on vegetation by linear adjustments of environmental variables by ordering produced by analysis of Multidimensional Nonmetric Scalling (NMDS), and those siginificant variables (p&#706;0.001) pltted as vectors. Trough the phytosociological descriptors measured the forest structure. The diversity was assessed using the diversity index of Shannon-Wiener (H ), Pielou evennes (J ). there was the phytogeographic features: endemic species or non-endemic to the Atlantic Rainforest. 77 species, gathered in 33 families and 52 genera were identified. Myrtaceae (16), Solanaceae (five) and Lauraceae (four) were the richest families. As regardsthe ecological group: Pionners 20%; Secondary 62%; Climax 18%. As the dispersion syndrome: Zoochoric 82%; Anemochoric 13%; Autochorous 5%; showed a high heterogeneity of soil conditions: higher altitude had more acidic and less fertile soils; places with lower altitudes showed less acidic and more fertile soils. The NMDS showed that the tree componente showed variation related to changes in the soil environment and the altitude separating the floristic composition into two distinct groups. The Shannon-Wiener diversity and evenness were: área (H / j ): 1 (1.28 to 0.42); 2 (2.40 to 0.68); 3 (3.28 to 0.83). The diameter distribution showed fotrm of inverted J . Among the endemic species of the Atlantic Forest, the highlights: Crinodendron brasiliensis Reitz & LB Sm beig located strictly in santa catarina Area 1 and Luchea divaricata Mart. & Zucc. Being located only in Area 3, but with wide distribution in he Atlantic Forest. We concluded a high edaphic heterogeneity along the altitudinal gradiente, directly influencing the floristic composition of riparian forest, causing a high floristic substitution between study áreas, significantly increasing the fiversity and the tree structure of Riparian Forest of Rio Pelotas of local higher altitude to the lower altitude<br>As Florestas Ciliares constituem sistemas ecológicos importantes para a manutenção dos rios. Objetivou-se caracterizar a composição florística, estrutura e a diversidade da Floresta Ciliar do Rio Pelotas ao longo de um gradiente altitudinal e relacioná-las com as propriedades físicas e químicas de solos florestais. Foram instaladas quatro parcelas com dimensões de 30 x 30 m, subdivididas em nove subparcelas de 10 x 10 m, em cada uma das três áreas de estudo, assim denominadas: Área 1 (280 8&#8223;18&#8223;&#8223; S 490 30&#8223;58&#8223;&#8223; O) - 1700 metros; Área 2 (28019&#8223; 58&#8223;&#8223; S 49040&#8223; 27&#8223;&#8223; O) - 1200 metros; Área 3 (280 28&#8223;39,65 S 500 04&#8223;03,73 O) - 850 metros. Todos os indivíduos, presentes nas parcelas, com &#8805; cinco cm de DAP foram levantados. Classificaram-se as espécies em: grupos ecológicos e estratégia de dispersão. Para a análise das propriedades físicas e químicas dos solos, utilizou-se Análise de Componentes Principais (PCA). A existência de diferenças florísticas-estruturais entre as três áreas estudadas foi verificada por meio de uma Análise de Variância Multivariada Permutacional (PERMANOVA). Verificou-se a influência das propriedades físicas e químicas dos solos sobre a vegetação por meio de ajustes lineares das variáveis ambientais pela ordenação produzida pela análise de Escalonamento Multidimensional Não-Métrico (NMDS), sendo aquelas variáveis significativas (p < 0,001) plotadas na forma de vetores. Através dos descritores fitossociológicos mediu-se a estrutura da floresta. A diversidade foi avaliada utilizando-se o índice diversidade de Shannon-Wiener (H&#8223;), equabilidade de Pielou (J&#8223;). Observou-se às características fitogeográficas: Espécies endêmicas ou não endêmicas da Mata Atântica. Foram identificadas 77 espécies, reunidas em 33 famílias e 52 gêneros. Myrtaceae (16), Solanaceae (cinco) e Lauraceae (quatro) foram às famílias de maior riqueza. Quanto ao grupo ecológico: Pioneiras 20%; Secundarias 62%; Climácicas 18%. Quanto à Síndrome de dispersão: Zoocorica 82%; Anemocorica 13%; Autocorica 5%;. A PCA indicou uma elevada heterogeneidade das condições edáficas: local com maior altitude apresentou solos mais ácidos e menos férteis; os locais com menores altitudes apresentaram solos menos ácidos e mais férteis. A NMDS mostrou que o componente arbóreo apresentou variações associadas à variação do ambiente edáfico e a altitude separando a composição florística em dois grupos distintos. A diversidade Shannon-Wiener e equabilidade Pielou foram: Área (H&#8223; / J&#8223;): 1 (1,28 - 0,42); 2 (2,40 - 0,68); 3 (3,28 - 0,83). A distribuição diamétrica mostrou forma de J invertido. Dentre as espécies endêmicas da Mata Atlântica, se destacaram: Crinodendron brasiliense Reitz & LB Sm localizando-se restritamente em Santa Catarina Área 1 e Luehea divaricata Mart. & Zucc. localizando-se apenas na Área 3, porém com ampla distribuição na Mata Atlântica. Concluí-se uma elevada heterogeneidade edáfica ao longo do gradiente altitudinal, influenciando diretamente na composição florística de floresta ciliar, ocorrendo uma elevada substituição florística entre as áreas de estudo, aumentando significativamente a diversidade e a estrutura arbórea de Floresta Ciliar do Rio Pelotas dos locais de maior altitude para os de menor altitude

A thesis submitted to the College of Dental Medicine of Nova Southeastern University of the degree of Master of Science in Dentistry. Objectives: The purpose of this study was to evaluate clinical outcomes based on the American Board of Orthodontics Objective Grading System (ABO-OGS) in a 30-month postgraduate orthodontic residency and to determine what factors affected these treatment outcomes. Methods: Consecutively debonded cases from July 1, 2010 to June 30, 2011 treated by residents in the Orthodontics Department at Nova Southeastern University were graded using the ABO-OGS. The age and sex of the patient, the treatment time, the missed appointments and the number of providers were documented. Discrepancy indices were calculated for each patient. These variables were assessed and their associations with the obtained treatment outcome scores were evaluated. Results: The average OGS score of the debonded cases was 33.87. There was no significant correlation between total OGS score and the demographic or explanatory variables. There were significant correlations found between the discrepancy index (DI) and the treatment time, the number of providers, but not the OGS. Significant correlations were also identified between treatment time and the number of failed appointments and the number of providers. Extraction cases were shown to have a significantly longer treatment time. Out of the eight objective measurements of the OGS, occlusal contacts, marginal ridges, buccolingual inclination and alignment/rotations scored the highest points in our evaluation with an average of 7.81, 6.37, 5.04, and 5.01 respectively. Conclusions: This study indicated the Nova Southeastern University Orthodontic Department average OGS score is about 6 points higher than the ABO clinical exam passing score. The initial complexity of a case was not a pre-determined factor for the final treatment results. This study identified several aspects of treatment outcomes that need improvement including, occlusal contacts, marginal ridges, correcting buccolingual inclination and improving the alignment.

L'objectif de cette étude, réalisée en collaboration avec l'Agence d'Essais Ferroviaire (AEF) de la SNCF, est de proposer une méthode de calcul de durée de vie sous chargements complexes (chargements multiaxiaux d'amplitude variable) en fatigue à grande durée de vie. La première partie du document présente une analyse critique de différentes méthodes de la littérature dans ce domaine. La seconde partie du document présente la base de données expérimentales établie en vue de l'identification et de l'évaluation de la méthode proposée. Cette base de données est constituée d'essais sur éprouvettes lisses sous une large gamme de sollicitations à complexité croissante (les essais vont de la traction d'amplitude constante à des essais de flexion-torsion hors phase d'amplitude variable) mais également sur roue de TGV à échelle 1 (essais réalisés à l'AEF, sous chargements d'amplitude variable inspirés d'enregistrements en service). La suite du document présente une nouvelle méthode de calcul de durée de vie sous chargements multiaxiaux d'amplitude variable. En conservant une base énergétique et la notion de seuil de "non endommagement" définies au cours des précédents travaux menés au LAMEFIP, cette proposition prend en compte l'effet, sur la durée de vie, de la répartition spatiale des contraintes dans la pièce. Basée sur une définition incrémentale du travail de déformation fourni au matériau, cette proposition s'affranchit de toute méthode de comptage de cycle et est apte à prévoir la durée de vie d'une structure soumise à une sollicitation quelconque d'amplitude variable. Les prévisions de cette méthode sont confrontées à des résultats de différents essais de la littérature, notamment obtenus sur des éprouvettes entaillées, et aux résultats expérimentaux de l'étude. Enfin la méthode proposée est appliquée à un cas industriel : la prévision de la tenue en fatigue de la toile d'une roue de train à grande vitesse sous chargements d'amplitude constante ou par blocs. Les prévisions de la méthode, appliquée en post-processeur des résultats de calculs éléments finis sur la roue, sont en bon accord avec les résultats d'essais.

Gliomas are a common type of brain tumour and for the treatment of a patient it is important to determine the tumour’s grade of malignancy. This is done today by a biopsy, a histopathological analysis of the tumourous tissue, that is classified by the World Health Organization on a malignancy scale from I to IV. Recent studies have shown that the local image variance (LIV) and the intratumoural susceptibility signal (ITSS) in susceptibility-weighted MR images correlate to the tumour grade. This thesis project aims to develop a software program as aid for the radiologists when grading a glioma. The software should by image analysis be able to separate the gliomas into low grade (I-II) and high grade (III-IV). The result is a graphical user interface written in Python 3.4.3. The user chooses an image, draws a region of interest and starts the analysis. The analyses implemented in the program are LIV and ITSS mentioned above, and the code can be extended to contain other types of analyses as research progresses. To validate the image analysis, 16 patients with glioma grades confirmed by biopsy are included in the study. Their susceptibility-weighted MR images were analysed with respect to LIV and ITSS, and the outcome of those image analyses was tested versus the known grades of the patients. No statistically significant difference could be seen between the high and the low grade group, in the case of LIV. This was probably due to hemorrhage and calcification, characteristic for some tumours and interpreted as blood vessels. Concerning ITSS a statistically significant difference could be seen between the high and the low grade group (p &lt; 0.02). The sensitivity and specificity was 80% and 100% respec- tively. Among these 16 gliomas, 11 were astrocytic tumours and between low and high grade astrocytomas a statistically significant difference was shown. The degree of LIV was significantly different between the two groups (p &lt; 0.03) and the sensitivity and specificity were 86% and 100% respectively. The degree of ITSS was significantly different between the two groups (p &lt; 0.04) and the sensitivity and specificity were 86% and 100% respectively. Spearman correlation showed a correlation between LIV and tumour grade (for all gliomas r = 0.53 and p &lt; 0.04, for astrocytomas r = 0.84 and p &lt; 0.01). A correlation was also found between ITSS and tumour grade (for all gliomas r = 0.69 and p &lt; 0.01, for astrocytomas r = 0.63 and p &lt; 0.04). The results indicate that SWI is useful for distinguishing between high and low grade astrocytoma with 1.5T imaging within this cohort. It also seems possible to distinguish between high and low grade glioma with ITSS.

Ce mémoire est une synthèse de plusieurs études à l'intersection des systèmes dynamiques dans l'analyse statistique de séquences, de l'analyse d'algorithmes dans des arbres aléatoires et des processus stochastiques discrets. Les résultats établis ont des applications dans des domaines variés allant des séquences biologiques aux modèles de régression linéaire, processus de branchement, en passant par la statistique fonctionnelle et les estimations d'indicateurs de risque appliqués à l'assurance. Tous les résultats établis utilisent d'une façon ou d'une autre le caractère récursif de la structure étudiée, en faisant apparaître des invariants comme des martingales. Elles sont au coeur de ce mémoire, utilisées comme outils dans les preuves ou comme objets d'étude.

Multimetric ecological condition assessment has become an important biodiversity management tool. This study was the first to examine the reliability of these ecological surrogates across variable environments, and the implications for surrogate efficacy. It was demonstrated that through strategic application and design of the multimetric ecological condition index, the effects of environmental gradients and disturbance regimes can be mitigated, and that ecological condition assessment may serve as a scientifically rigorous approach for conservation planning.

L'urbanisation croissante de ces dernières décennies nécessite une connaissance approfondie de la dynamique de la biodiversité en milieu urbain afin d’aider à la mise en place de politiques de développement urbain favorisant le maintien de cette biodiversité. Ce travail de doctorat a évalué l'homogénéisation taxonomique et la composition fonctionnelle des communautés de flore spontanée le long d’un gradient d’urbanisation en prenant comme unité d’étude le jardin privatif, ainsi que la structure génétique d’une espèce de plante, Parietaria judaica.L'homogénéisation taxonomique varie le long du gradient d’urbanisation. Les jardins privatifs des centres villes étudiés seraient moins riches, mais favoriseraient la diversité taxonomique au regard de la composition spécifique des communautés de par leurs expositions, aménagements et pratiques. L'étude des traits des communautés met en évidence des variations de la composition fonctionnelle le long du gradient d’urbanisation. Les zones de forte densité de bâti filtrent des traits, notamment liés à la dispersion et à la persistance des espèces. L'endozoochorie pourrait permettre le franchissement des bâtis qui entourent les jardins.Enfin, l’absence de structure génétique de Parietaria judaica à l’échelle locale des villes suggère des échanges génétiques quelle que soit la densité de bâti, tandis qu’une structure génétique marquée est observée à l’échelle régionale, entre les trois sites.Le jardin privatif qui à l’instar des autres habitats du milieu urbain, présentent des communautés végétales qui peuvent participer aux dynamiques de la végétation urbaine<br>Increasing urbanization in recent decades requires a thorough understanding of the dynamics of urban biodiversity to aid in the establishing of urban development policies to promote the biodiversity. This doctoral work evaluated the taxonomic homogenization and functional composition of spontaneous flora communities along a gradient of urbanization taking as the unit of study the private garden, and the genetic structure of a plant species, Parietaria judaica.Taxonomic homogenization varies along the urbanization gradient. The private gardens of the centers studied cities are less rich but would enhance taxonomic diversity in terms of species composition of communities through their exposure, planning and practices.The study of traits communities highlights changes in the functional composition along the urbanization gradient. High built-up density areas filter traits, in particular linked to the dispersion and persistence of species. The endozoochorie could allow the crossing of built around the gardens.Finally, the lack of genetic structure of Parietaria judaica at local scale suggests genetic exchange regardless of the built-up density, while a significant genetic structure was observed at the regional level between the three sites.The private gardens, which like the other green patchs in urban areas, have plant communities that can participate in the dynamics of urban vegetation

In this thesis, we develop numerical methods for solving five nonstandard optimal control problems. The main idea of each method is to reformulate the optimal control problem as, or approximate it by, a nonlinear programming problem. The decision variables in this nonlinear programming problem influence its cost function (and constraints, if it has any) implicitly through the dynamic system. Hence, deriving the gradient of the cost and the constraint functions is a difficult task. A major focus of this thesis is on developing methods for computing these gradients. These methods can then be used in conjunction with a gradient-based optimization technique to solve the optimal control problem efficiently.The first optimal control problem that we consider has nonlinear inequality constraints that depend on the state at two or more discrete time points. These time points are decision variables that, together with a control function, should be chosen in an optimal manner. To tackle this problem, we first approximate the control by a piecewise constant function whose values and switching times (the times at which it changes value) are decision variables. We then apply a novel time-scaling transformation that maps the switching times to fixed points in a new time horizon. This yields an approximate dynamic optimization problem with a finite number of decision variables. We develop a new algorithm, which involves integrating an auxiliary dynamic system forward in time, for computing the gradient of the cost and constraints in this approximate problem.The second optimal control problem that we consider has nonlinear continuous inequality constraints. These constraints restrict both the state and the control at every point in the time horizon. As with the first problem, we approximate the control by a piecewise constant function and then transform the time variable. This yields an approximate semi-infinite programming problem, which can be solved using a penalty function algorithm. A solution of this problem immediately furnishes a suboptimal control for the original optimal control problem. By repeatedly increasing the number of parameters used in the approximation, we can generate a sequence of suboptimal controls. Our main result shows that the cost of these suboptimal controls converges to the minimum cost.The third optimal control problem that we consider is an applied problem from electrical engineering. Its aim is to determine an optimal operating scheme for a switchedcapacitor DC-DC power converter—an electronic device that transforms one DC voltage into another by periodically switching between several circuit topologies. Specifically, the optimal control problem is to choose the times at which the topology switches occur so that the output voltage ripple is minimized and the load regulation is maximized. This problem is governed by a switched system with linear subsystems (each subsystem models one of the power converter’s topologies). Moreover, its cost function is non-smooth. By introducing an auxiliary dynamic system and transforming the time variable (so that the topology switching times become fixed), we derive an equivalent semi-infinite programming problem. This semi-infinite programming problem, like the one that approximates the continuously-constrained optimal control problem, can be solved using a penalty function algorithm.The fourth optimal control problem that we consider involves a general switched system, which includes the model of a switched-capacitor DC-DC power converter as a special case. This switched system evolves by switching between several subsystems of nonlinear ordinary differential equations. Furthermore, each subsystem switch is accompanied by an instantaneous change in the state. These instantaneous changes—so-called state jumps—are influenced by control variables that, together with the subsystem switching times, should be selected in an optimal manner. As with the previous optimal control problems, we tackle this problem by transforming the time variable to obtain an equivalent problem in which the switching times are fixed. However, the functions governing the state jumps in this new problem are discontinuous. To overcome this difficulty, we introduce an approximate problem whose state jumps are governed by smooth functions. This approximate problem can be solved using a nonlinear programming algorithm. We prove an important convergence result that links the approximate problem’s solution with the original problem’s solution.The final optimal control problem that we consider is a parameter identification problem. The aim of this problem is to use given experimental data to identify unknown state-delays in a nonlinear delay-differential system. More precisely, the optimal control problem involves choosing the state-delays to minimize a cost function measuring the discrepancy between predicted and observed system output. We show that the gradient of this cost function can be computed by solving an auxiliary delay-differential system. On the basis of this result, the optimal control problem can be formulated—and hence solved—as a standard nonlinear programming problem.

Orientador: Maria Cecília F. P. S. Zanardi<br>Banca: Rodolpho Vilhena de Moraes<br>Banca: Sandro da Silva Fernandes<br>Resumo: A atitude de um satélite artificial representa sua orientação no espaço, de modo que através da atitude pode-se conhecer a orientação espacial do satélite pela relação entre dois sistemas de coordenadas, um dels fixo no corpo do setélite e o outro associado com umsistema de referência inercial. Apesar da atitude ser bem representada por vários conjuntos de variáveis, todos estes apresentam limitações em sua utilização. Focaliza-se neste trabalho um conjunto de variáveis canônicas não singulares, aplicáveis ao movimento racional de satélites artificiais. Estas variáveis são úteis para o caso em que o vetor momento angular de rotação coincide com o maior momento principal de inércia do satélite. As equações dinâmicas do movimento rotacional são deduzidas pelo formalismo hamiltoniano e então integradas para análise do movimento rotacional livre de torques externos. Soluções analíticas aproximadas são obtidas e comparadas com as soluções gerais, representadas em funções elípticas, e com soluções numéricas. A Hamiltoniana média associada ao Torque de Gradiente de Gravidade é também incluida e as equações diferenciais do movimento pertubado são deduzidas em termos das variáveis não singulares. A integração analítica e numérica destas equações permite uma análise qualitativa e quantitativa das variáveis não singulares utilizadas para o movimento rotacional, quando se considera a pertubação provocada pelo Torque da Gradiente de Gravidade. Ao mesmo tempo esta análise aponta para limitações de intervalos de tempo em que algumas soluções devem ser utilizadas. Aplicações são realizadas para satélites com características similares as dos Satélites Brasileirs de Coleta de Dados (SCD1 e SCD2).<br>Abstract: The attitude of an artificial satellite represents its orientation in the space, in way that through the attitude can be known the spatial orientation of the satellite for the relation between two systems of coordinates, one of them fixed in the satellite and other associate with an Inertial Referencce System. Many sets of variables are used to represent the satellite attitude, but some of them present limitations in its use. A set of non-singular canonical variables, applicable to the rotational motion of artificial satellites, is focused in this work. Thse variables are useful for the case where the rotational angular momentum vector coincides with the biggest principal moment of inertia of the satellite. The dynamic equations of the rotational motion are deduced by the Hamiltonian formalism and then they are integrated for the analysis of the torque-free rotational motion. Approximated analytical solutions are gotten and compared with the general solutions and numerical solutions. The associated mean Hamiltonian to the Gravity Gradient Torque also enclosed and the differential equations of the motion are deduced for the non-singular variables. The analytical and numeical integration of these equations allow a qualitative and quantitative analysis of these non-singular variables, when the disturbance of the Gravity Gradiente Torque is considered. At the same time this analysis point to limitations of time intervals where some solutions must be used. Applications are done for the satellite with similar characteristics of the Brzilian Satellites of Collection of Data (SCD1 and SCD2).<br>Mestre

Out-of-autoclave manufacturing processes for composite materials are increasing in importance for aerospace and automotive industries. Vacuum Infusion processes are leading the push to move out of the autoclave. An understanding of the various process parameters associated with resin infusion is necessary to produce quality product. Variance in compaction, resin, and vacuum pressures are studied, concentrating on developing a compaction pressure profile as it relates to fiber volume fraction. The purpose of this research is twofold: (1) to show and quantify the existence of a resin pressure gradient in compression testing using rigid tooling, and (2) to use measured test data to validate and improve resin flow simulation models. One-dimensional compression tests revealed a pressure gradient across the diameter of the compression tool. The pressure gradient follows trends consistent with Darcy's Law. Compression tests revealed fabric hysteresis during compaction as shown in previous studies. Fiber compaction pressure was found to not be directly equal to compressive forces of the Instron when resin is present in the system. The relationship between Instron, resin and compaction pressures is defined. The compression study was used to validate previously developed flow simulation models. Resin pressures are critical to developing an accurate two-dimensional radial flow simulation for low permeability fabrics. It is feasible to determine final fiber volume fraction at a given compaction pressure.

La tesis se inscribe en un doble ámbito científico formado por la Estadística y la Pedagogía. El objetivo de la tesis es la investigación de modelos estadísticos y estrategias de análisis que puedan ser de utilidad en el seguimiento de sistemas de evaluación complejos. Su motivación se encuentra en la necesidad de analizar las Pruebas de Aptitud para el Acceso a la Universidad (PAAU), que regulan el acceso a la universidad en España, desde la perspectiva de la ciencia estadística. La validez y fiabilidad de los exámenes COU (Curso de Orientación Universitaria) y PAAU han merecido una atención especial a lo largo de la investigación. Asimismo, se analizan con detenimiento las principales fuentes de variación de dichas notas: las diferencias entre centros de secundaria y el proceso de corrección de las pruebas PAAU.<br/>En la Introducción, una vez resumidas las características del sistema de evaluación de las pruebas PAAU y discutido el papel de la estadística en el tratamiento de datos en educación, se establecen los objetivos concretos de la tesis, a la luz de las necesidades existentes y de los trabajos de investigación realizados hasta el momento.<br/>El Capítulo 1 ilustra las diferencias entre los exámenes COU y las pruebas PAAU. Se aborda el estudio de la asociación entre ambas puntuaciones. La modelización de la variación de la nota PAAU individual por medio de modelos de regresión coeficientes aleatorios permite evidenciar (y medir) las diferencias entre centros de secundaria en cuanto a los estándares utilizados en COU. Este primer capítulo contiene una detallada introducción a los modelos de coeficientes aleatorios, también llamados modelos de nivel múltiple, que posteriormente se aplicaran en los capítulos 2 y 4, en la versión de modelos multivariantes de componentes de la varianza. El segundo capitulo, en un enfoque que complementa el anterior, se centra en el estudio de las medias (de COU y de PAAU) de cada centro, en la estructura de covarianza entre ambas. Como resultado relevante cabe citar la aplicación a la selección de la combinación más eficiente. <br/>El Capítulo 3 se ha dedicado enteramente a la calidad del sistema de corrección de los exámenes PAAU. La modelización presentada ha permitido evaluar el impacto de los correctores en términos de la varianza debida a las diferencias en el grado de severidad y a la varianza generada por la inconsistencia. Para la obtención de los datos se ha requerido del diseño de experimentos. Dichos experimentos, que han evidenciado una serie de puntos débiles del sistema, deberían ser realizados de manera sistemática cada año en una estrategia de mejora de la calidad del proceso. <br/>El Capítulo 4 estudia la covarianza del conjunto de notas PAAU tanto a nivel estudiante como a nivel centro, ofreciendo nuevos elementos de reflexión para la validez de dichas pruebas. <br/>El Capítulo 5 resume la aplicación de varias propuestas de la tesis a la primera convocatoria de las pruebas PAAU-LOGSE. <br/>El Capítulo 6 incluye las conclusiones de la tesis así como una serie de propuestas de seguimiento y mejora de la calidad global del sistema.

Thesis (Ph.D.)--Case Western Reserve University, 2004<br>Title from PDF (viewed on 01 October 2009) Department of Mechanical Engineering Includes abstract Includes bibliographical references Available online via the OhioLINK ETD Center

This doctoral thesis proposes a new algorithm for the reconstruction of impedance images in monitored objects. The algorithm eliminates the spatial resolution problems present in existing reconstruction methods, and, with respect to the monitored objects, it exploits both the partial knowledge of configuration and the material composition. The discussed novel method is designed to recognize certain significant fields of interest, such as material defects or blood clots and tumors in biological images. The actual reconstruction process comprises two phases; while the former stage is focused on industry-related images, with the aim to detect defects in conductive materials, the latter one concentrates on biomedical applications. The thesis also presents a description of the numerical model used to test the algorithm. The testing procedure was centred on the resulting impedivity value, influence of the regularization parameter, initial value of the numerical model impedivity, and effect exerted by noise on the voltage electrodes upon the overall reconstruction results. Another issue analyzed herein is the possibility of reconstructing impedance images from components of the magnetic flux density measured outside the investigated object. The given magnetic field is generated by a current passing through the object. The created algorithm for the reconstruction of impedance images is modeled on the proposed algorithm for EIT-based reconstruction of impedance images from voltage. The algoritm was tested for stability, influence of the regularization parameter, and initial conductivity. From the general perspective, the thesis describes the methodology for both magnetic field measurement via NMR and processing of the obtained data.

La distance entre deux lois est étudiée lorsque les probabilités sont définies sur un espace de Banach séparable. Nous montrons que cette distance est atteinte par une fonction, dite associée, lorsque l'une des lois est diffuse l'autre discrète. Une condition nécessaire et suffisante pour reconnaitre le caractère associé est donnée par la cyclique monotonie. De plus un algorithme est donné pour obtenir de manière effective la fonction associée. Lorsque nous sommes dans un Hilbert séparable ces résultats sont étendus en utilisant des techniques de sous-gradients et d'analyse convexe

Lagoas costeiras são ecossistemas cruciais para conservação da biodiversidade local e global. O sistema do rio Tramandaí (SRT) apresenta uma série de lagoas costeiras rasas conectadas por canais naturais, e uma saída, via estuário de Tramandaí, para o oceano. Esse sistema é dividido em dois subsistemas, ao norte e ao sul do estuário, resultado de padrões hidrodinâmicos e da influência do vento e que definem características ambientais distintas a esses subsistemas. Um gradiente decrescente, de norte a sul, no estado trófico dessas lagoas já foi verificado. No presente estudo é testada hipótese de variabilidade espacial (lagoas e subsistemas) e temporal (estações do ano) na magnitude de variáveis abióticas e de descritores ecológicos das assembleias de peixes (composição, riqueza, diversidade, dominância) do SRT. Também é avaliada a relação entre variáveis abióticas e descritores das assembleias nesses subsistemas. É comparada a seletividade de captura de um amostrador ativo (rede de arrasto de praia) e de um amostrador passivo (redes de emalhe). Amostragens foram conduzidas de novembro de 2008 a abril de 2010 com rede de arrasto de praia e redes de emalhe, na zona litoral das lagoas Itapeva, Quadros e Malvas no subsistema norte, e nas lagoas Fortaleza, Rondinha e Barros no subsistema sul. Entre abril de 2009 e março de 2010, amostras de água foram coletadas e dez variáveis foram mensuradas em laboratório. Análises de ordenação (NMDS) mostraram clara diferença de composição, abundância numérica (CPUEn) e em biomassa (CPUEb) de espécies entre amostradores. A análises de ANOSIM e SIMPER mostraram baixa similaridade desses parâmetros entre amostradores. Houve diferença no tamanho dos peixes coletados com redes de arrasto e emalhe. Turbidez e DBO5 tiveram médias superiores no subsistema norte, enquanto que condutividade, salinidade, dureza, sólidos totais dissolvidos e transparência de Secchi no subsistema sul. Temporalmente foram verificadas diferenças de temperatura, pH, salinidade, turbidez, dureza, sólidos totais dissolvidos, oxigênio dissolvido, sólidos suspensos e profundidade, mas somente os dados de pH, condutividade, turbidez e DBO5 mostraram interação entre os fatores espaço e tempo. As assembleias das margens rasas da zona litoral foram dominadas por dez espécies, resultando em alta similaridade de composição, CPUEn e CPUEb entre os subsistemas. A riqueza de espécies variou espacial e temporalmente. Diversidade e equitabilidade espacialmente, e CPUEn e CPUEb temporalmente. As assembleias das regiões pelágicas da zona litoral foram dominadas por sete espécies, com dominância numérica das espécies L. anus e A. aff. fasciatus no subsistema norte. A NMDS mostrou similaridades maiores de composição, CPUEn e CPUEb entre amostras de um mesmo subsistema, no entanto, a ANOSIM não apresentou resultados significativos para rejeição das hipóteses nulas. CPUE n e b, diversidade e equitabilidade variaram espacialmente, enquanto a riqueza, temporalmente. A análise de correlação canônica (CCA) mostrou que temperatura, DBO5, sólidos suspensos e dureza responderam por 46% da variabilidade dos dados de abundância numérica das espécies. Os resultados sugerem que amostradores ativos e passivos reproduzem diferentes imagens da assembleia por eles amostrada, indicando que o delineamento amostral para estudos com peixes nesses ecossistemas deve contemplar tais diferenças. As diferenças ambientais dos subsistemas refletem em diferenças na qualidade da água e os resultados obtidos confirmam os pressupostos do gradiente trófico. A estrutura das assembleias de peixes foi mais variável em resposta as condições ambientais em escala espacial, enquanto que temporalmente, houve maior coerência na variabilidade dos dados. As relações das espécies com as variáveis ambientais são discutidas com base no comportamento alimentar e/ou reprodutivo das mesmas e na qualidade do habitat. Tais resultados podem ser úteis como subsídio a elaboração de estudos de manejo costeiro do SRT, sobretudo com relação aos recursos pesqueiros, e na proposição de modelos de estrutura das assembleias de peixes de lagoas costeiras subtropicais.<br>Coastal lakes ecosystems are crucial for conserving biodiversity both locally and globally. The river Tramandaí system (SRT) comprises a series of shallow coastal lagoons, connected by natural channels, and has an output via Tramandaí estuary into the ocean. This system is divided into two subsystems, north and south of the Tramandaí estuary, as result of hydrodynamic patterns, influence of wind and environmental characteristics that define the subsystems. A trophic gradient decreasing from north to south in those lagoons was identified. In this study is tested the hypothesis of spatial (lagoons and subsystems) and temporal (seasons) variabilities in the amplitude of abiotic variables and descriptors of the fish assemblages (species composition, richness, diversity, dominance) in the SRT. It also assessed the relationship between abiotic variables and descriptors of the fish assemblages in these subsystems. Is compared the selectivity of the active fishing (beach seining) and passive (gill netting) fishing. Sampling was conducted from November 2008 to April 2010 with beach seine and gill nets in the littoral zone of lakes Itapeva, Quadros and Malvas in north subsystem, and Fortaleza, Rondinha and Barros lakes, in south subsystem. Between April 2009 and March 2010 water samples were collected and ten variables were measured in the laboratory. Analyses of ordination (NMDS) showed clear differences in composition, numerical abundance (CPUEn) and biomass (CPUEb) of species between samplers. The analysis of similarity (ANOSIM and SIMPER) showed low similarity of these parameters between nets. There was a difference in the size of the fish caught with beach seine and gill nets. Turbidity and BOD5 averages were higher in the northern subsystem, while the conductivity, salinity, hardness, total dissolved solids and Secchi transparency in the south subsystem. Temporally were observed differences in temperature, pH, salinity, turbidity, hardness, total dissolved solids, dissolved oxygen, suspended solids and depth, but only the data for pH, conductivity, turbidity, BOD5 showed interaction between the factors space and time. The assemblages of the shallow margins of the coastal zone were dominated by ten species resulting in high similarity of composition, CPUEn and CPUEb between subsystems. Species richness varied spatially and temporally, while diversity and evenness only spatially and CPUEn and CPUEb only temporally. The assemblages of the pelagic regions of the coastal zone were dominated by seven species with numerical dominance of L. anus and A. aff. fasciatus in north subsystem. The NMDS showed greatest similarity in composition, CPUEn and CPUEb between samples of the same subsystem, the ANOSIM however, showed no significant results for rejection of the null hypothesis. CPUE n and b, diversity and equitability varied between lakes and subsystems, while the richness between seasons. The canonical correlation analysis (CCA) showed that four variables (temperature, BOD, suspended solids and hardness) account for 46% of data variability of species abundance. Samples of the north subsystem were directly influenced by temperature, BOD and suspended solids while the south subsystem by the hardness. The results suggest that active and passive samplers reproduce different images of the assemblage sampled and indicate that the sampling design for studies of these ecosystems should include such differences. The environmental differences in subsystems reflect in water quality differences and the results confirm the assumptions of a trophic gradient decreasing from north to south in the SRT. The structure of the fish assemblages was more variable in response to environmental conditions in spatial scale between subsystems, while there was greater consistency in the temporal variability of the data. The relationships between the species and environmental variables are discussed based on the feeding behavior and / or reproduction of the same and by habitat quality. These results may be useful as an aid to preparing studies of coastal management of SRT, especially with respect to fisheries, and in proposing models of the structure of the fish assemblages of subtropical coastal lagoons.

Les travaux présentés dans cette thèse sont divisés en quatre parties. La première est consacrée à la présentation du modèle de reconstruction tomographique. Dans la deuxième partie, nous traitons une approche variationnelle qui consiste en un problème de minimisation non-différentiable avec une contrainte non convexe, d'intérieur vide pour les topologies usuelles. L'étude numérique de l'approche précédente est faite dans la troisième partie. Elle est basée sur le système d'optimalité, la méthode d'Uzawa et une méthode de gradient à pas optimal pour écrire un schéma numérique. Dans la quatrième partie, nous nous intéressons à l'approche par lignes de niveaux pour résoudre des problèmes de propagation de fronts. Cette méthode fait apparaître des équations de type Hamilton-Jacobi du second ordre avec un terme non-local. Nous prouvons l'existence et l'unicité d'une solution de viscosité pour ces équations dans deux cas: celui des fronts compacts et celui des fronts non compacts<br>The thesis at hand is composed of four parts. The first of which is devoted to present our model of tomographic reconstruction. The second part treats a non-differentiable variational problem with a non-convex constraint the interior of which is empty for usual topologies. A numerical study of the above approach is elaborated in the third part. A numerical scheme is derived based upon our optimal system, the method of Uzawa and a gradient descent method. In the last part, we use a level-set approach to solve the front propagation problem. A second order Hamilton-Jacobi type equation with a non-local term comes into play. We prove the existence and uniqueness of a viscosity solution in both compact and non-compact fronts cases