<p>This thesis reports the results of a twofold study on the recently proposed phenomenon of &lsquo / stellar pulsations&rsquo / in young brown dwarfs by the seminal study of Palla and Baraffe (2005) (PB05, thereafter). The PB05 study presents results of a non-adiabatic linear stability analysis showing that young brown dwarfs should become pulsationally unstable during the deuterium burning phase of their evolution.</p>

Two separate problems are to be investigated in this thesis. The first problem is the propagation of waves through a short rod (or slug) of viscoelastic material. The second problem is the study of impact of a short viscoelastic rod (or slug) on a stationary semi-infinite viscoelastic. rod. The viscoelastic materials are modelled as standard linear solids which involve 3 material parameters and the motion is treated. as one-dimensional. For the first study, a viscoelastic slug is placed between two semi-infinite elastic rods and a wave initiated in the first rod is transmitted through the slug into the second rod. The objective is to relate the transmitted signal to the material parameters of the slug. We solve the governing system of partial differential equations using the Laplace transform and we examine the propagating velocity discontinuity using discontinuity analysis and the limit theorem of the Laplace transform. We then approximate the solution of the propagating disturbance using the regular perturbation method. We invert the Laplace transformed solution numerically to obtain the transmitted signal for several viscosity time constants and ratios of acoustic impedances. We compare the results obtained using the above techniques. In the second problem, we first model the impact and solve the governing system of partial differential equations in the Laplace transform domain. Then we examine the propagating stress and velocity discontinuities using discontinuity analysis. We approximate the solutions of the propagating stress and velocity using the regular and multiple scales perturbation methods. In this problem, we first consider the slug is elastic and the rod is viscoelastic. Secondly, we consider the slug is viscoelastic and the rod is elastic and thirdly, we consider both materials are viscoelastic. Numerically we invert the Laplace transformed solutions for the interface stress and interface velocity for several viscosity time constants and ratios of acoustic impedances to determine whether the slug and the rod part company or remain in contact. Then we compare the results obtained using the discontinuity analysis, regular and multiple scales perturbation methods.

Saxitoxins were extracted from a bloom of toxic Anabaena circinalis and used to spike treated water from Hope Valley Reservoir (HVTW) and Milli-Q water. The waters were treated with ozone using the batch method and saxitoxin levels were measured in the samples using HPLC. The results for oxidation of saxitoxins in Milli-Q water versus HVTW show that despite the presence of natural organic matter(NOM) and the production of vastly different ozone residuals, there was a similar removal of all saxitoxins in both waters. The results show that high concentrations of saxitoxins were present in solution after ozonation with doses and contact times typically used in water treatment. Relating the toxin destruction to ozone residual showed that even with a residual ozone concentration of 0.8 mg/L after 10 minutes contact in HVTW, over 60% of the initial saxitoxin content was still present in the samples. The presence of an ozone residual in the water could not be related to saxitoxin destruction and it appeared that saxitoxin removal occurred more rapidly when ozone was consumed rather than stabilised in solution. The results indicate that the mechanism for toxin removal is probably based on the reaction with a hydroxyl radical species as the oxidant rather than molecular ozone. The results obtained during these experiments indicate that ozone is not an effective oxidant for this class of compound. A range of ozone doses were applied to two different treated reservoir waters that had been spiked with microcystins LA (mLA) and LR (mLR). At the ozone dose where a residual was first measured in the sample after 5 minutes exposure time, no microcystins were detected by HPLC in either water. The removal of mLA and mLR was identical in all samples. The absence of mLA and mLR by HPLC was supported by a loss of toxicity using a highly sensitive and specific bioassay (PP2A) and by in vivo studies in mice. In both waters microcystins were removed with an ozone dose typical of that used in drinking water treatment. The results indicate that conventional ozone treatment was effective in removing hepatotoxicity at microcystin levels greater than those likely to be found in drinking water. Two waters were sampled from reservoirs in South Australia. One was collected directly from Happy Valley Reservoir (HVRW) and the other from Myponga Reservoir after treatment but before chlorination (MFCW). They were spiked with mLA and mLR and chlorinated to measure toxin removal and chlorine consumption using the CT concept. In MFCW at pH 7 there was a better removal of both mLA and mLR than in HVRW at pH 8.1. There was also a lesser effect from water temperature upon toxin removal in MFCW. Microcystin LA was less easily removed than mLR at both temperatures in both waters. For HVRW, at the higher pH, this required an initial dose of 7 mg/L of chlorine which corresponded to a CT of around 70 min.mg/L. If the water temperature was reduced to 6??C then under these conditions there would still be 40% of the initial concentration of mLA and mLR present in this water. At this temperature a final chlorine residual of 3.5 mg/L after 30 minutes, requiring a chlorine dose of 8mg/L and corresponding to a CT of about 95 min.mg/L, was required to reduce microcystin levels below the WHO guidelines. This implies that in colder climates the application of chlorine for microcystin removal may require elevated chlorine doses and CT values. Arrhenius activation energies were calculated for mLA and mLR in both waters, revealing different Ea values for both toxins. Due to the complexity of the reactions and the possible effects of pH in solution, this system was considered too complicated to be described by the Arrhenius equation. NOM was collected from Myponga Reservoir in South Australia using magnetic ion exchange (MIEX??) resin. The collected NOM was desorbed and separated into fractions of different molecular weight and character using ultrafiltration and mixed resin ion exchange. At approximately 5 mg/L dissolved organic carbon (DOC) the measured apparent second order rate constant (kapp) for mLA and mLR removal was fairly similar in both the high molecular weight fraction (designated F3), and the intermediate high molecular weight fraction (designated F2). The low molecular weight fraction (designated EN) had slightly higher kapp values as would be expected due to the less reactive nature of the NOM in this fraction. This meant more chlorine was available to react with microcystins in this fraction. Fractions F3 and F2 produced similar kapp values to those from the parent water source following treatment, indicating the similar reactivity of these NOM fractions at comparable DOC levels. Increasing the DOC concentration in the F2 fraction increased kapp for both mLA and mLR due to the additional chlorine needed to react with the additional NOM present. The results showed that pH, temperature and DOC concentration have a higher impact upon chlorination rates, and the efficiency of toxin removal, than NOM character alone. In general it is assumed that chlorine will be more effective at removing toxins in water with a low SUVA and low specific colour as these indicate less 'reactive' NOM in the water. The results of this study show that toxin removal was more effective in the EN fraction as indicated by the higher kapp. This fraction also had the lowest SUVA and lowest specific colour which supports the generally held view in water treatment. Relating the toxin removal to chlorine residual in these reconstituted fractionated NOM samples, indicated that a residual of around 1.5 mg/L after 30 minutes contact was generally adequate to remove all toxins in water with a DOC level of around 5 mg/L. This is consistent with the results obtained in real waters, where at 20??C a chlorine residual of 2 mg/L was found to be sufficient for removal of both mLA and mLR.

Les états de charmonium fournissent une source de connaissances pertinente pour déterminer les paramètres fondamentaux du Modèle Standard. Un aspect important de la compréhension et des tests de la QCD est de faire des prédictions précises du spectre des hadrons et de les tester par rapport à des données expérimentales de haute qualité. Notre cadre théorique est Lattice QCD, qui est considéré comme le seul moyen connu de traiter le lagrangien QCD complet de manière non perturbative et bien adaptée au calcul numérique. En utilisant l'action Wilson-Clover avec N_f = 2 saveurs dynamiques, nous étudierons les deux mésons charmonium eta_c et J/\psi. Nous allons également étudier certaines propriétés de leur première excitation radiale eta_c (2S) et \psi(2S). / Charmonium states provide a relevant source of knowledge for determining fundamental parameters of the Standard Model. An important aspect of understanding Quantum ChromoDynamics (QCD) is to make precise predictions of the hadron spectrum and to test them against high-quality experimental data. Our theoretical framework is Lattice QCD, which is considered to be the only known way to treat the full QCD Lagrangian non perturbatively from first principles, in a manner well suited to numerical computation. By using the Wilson-Clover action with N_f = 2 dynamical flavors, we will study the two charmonium mesons eta_c and J/\psi. We will also investigate some properties of their first radial excitations eta_c(2S) and psi(2S).

This thesis explores ideas from transport theory and optimal control to develop novel Monte Carlo methods to perform efficient statistical computation. The first project considers the problem of constructing a transport map between two given probability measures. In the Bayesian formalism, this approach is natural when one introduces a curve of probability measures connecting the prior to posterior by tempering the likelihood function. The main idea is to move samples from the prior using an ordinary differential equation (ODE), constructed by solving the Liouville partial differential equation (PDE) which governs the time evolution of measures along the curve. In this work, we first study the regularity solutions of Liouville equation should satisfy to guarantee validity of this construction. We place an emphasis on understanding these issues as it explains the difficulties associated with solutions that have been previously reported. After ensuring that the flow transport problem is well-defined, we give a constructive solution. However, this result is only formal as the representation is given in terms of integrals which are intractable. For computational tractability, we proposed a novel approximation of the PDE which yields an ODE whose drift depends on the full conditional distributions of the intermediate distributions. Even when the ODE is time-discretized and the full conditional distributions are approximated numerically, the resulting distribution of mapped samples can be evaluated and used as a proposal within Markov chain Monte Carlo and sequential Monte Carlo (SMC) schemes. We then illustrate experimentally that the resulting algorithm can outperform state-of-the-art SMC methods at a fixed computational complexity. The second project aims to exploit ideas from optimal control to design more efficient SMC methods. The key idea is to control the proposal distribution induced by a time-discretized Langevin dynamics so as to minimize the Kullback-Leibler divergence of the extended target distribution from the proposal. The optimal value functions of the resulting optimal control problem can then be approximated using algorithms developed in the approximate dynamic programming (ADP) literature. We introduce a novel iterative scheme to perform ADP, provide a theoretical analysis of the proposed algorithm and demonstrate that the latter can provide significant gains over state-of-the-art methods at a fixed computational complexity.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-08-07T20:04:03Z No. of bitstreams: 1 TUILLY DE FÁTIMA MACEDO FURTADO GUERRA – DISSERTAÇÃO (PPGECA) 2016.pdf: 2570702 bytes, checksum: dc3123f0ac79b6573767e39e1c19c4c4 (MD5) / Made available in DSpace on 2018-08-07T20:04:03Z (GMT). No. of bitstreams: 1 TUILLY DE FÁTIMA MACEDO FURTADO GUERRA – DISSERTAÇÃO (PPGECA) 2016.pdf: 2570702 bytes, checksum: dc3123f0ac79b6573767e39e1c19c4c4 (MD5) Previous issue date: 2017-03-17 / Capes / O processo Anammox essencialmente é a desnitrificação autotrófica na qual nitrogênio amoniacal é oxidado por nitrito para nitrogênio molecular. O nitrito pode ser produzido em águas residuárias pela oxidação da amônia pelas Nitrosomonas. Todavia, tem-se que evitar que as bactérias do gênero Nitrobacter se desenvolvam para evitar a oxidação do nitrito para nitrato. O processo Anammox se aplica particularmente em águas ricas em amônia e pobres em material orgânico, como por exemplo, efluentes de digestores anaeróbios. Na prática tem sido aplicado com sucesso para efluentes de digestores de lodo aquecidos a 37 °C, mas a aplicação à temperatura ambiente na Europa (5 a 15 °C) não tem sido eficiente, pela dificuldade de eliminação da etapa de nitratação. Na presente pesquisa, procurou-se estabelecer se a nitrificação parcial é factível para a faixa de temperatura de esgotos no Brasil, para uma possível aplicação do processo Anammox visando à remoção de nitrogênio dos efluentes de reatores UASB. Para tanto, foram determinadas as constantes cinéticas da nitritação e nitratação em um sistema de lodo ativado entre a faixa de temperaturas de 12,7°C a 31 °C e as constantes de meia saturação do oxigênio dissolvido. A respirometria foi a ferramenta utilizada para determinar as taxas de nitritação e de nitratação e estimar as outras constantes cinéticas relevantes, sendo mostrado pelos resultados que esta é uma ferramenta útil na determinação das constantes cinéticas. Os valores encontrados das constantes cinéticas de crescimento das nitritadoras e nitratadoras em função da temperatura mostraram uma tendência de prevalecimento da nitritação sobre a nitratação em toda a faixa avaliada. Através da determinação da idade lodo mínima para a nitritação e nitratação pode-se estimar que operando um sistema de lodo ativado a temperatura ambiente adotando uma idade de lodo de 4 dias é possível promover a nitrificação parcial. / The Anammox process is essentially autotrophic denitrification in which ammoniacal nitrogen is oxidized by nitrite to molecular nitrogen. Nitrite can be produced in wastewater by the oxidation of ammonia by Nitrosomonas. However, it has to be avoided that bacteria of the genus Nitrobacter develop to avoid the oxidation of nitrite to nitrate. The Anammox process is applied particularly in ammonium rich waters and poor in organic material, such as effluent from anaerobic digesters. In practice it has been successfully applied to effluent from sludge digesters heated to 37 ° C, but application at room temperature in Europe (5 to 15 ° C) has not been efficient due to the difficulty of eliminating the nitration step. In the present research, it was tried to establish if the partial nitrification is feasible for the range of sewage temperature in Brazil, for a possible application of the Anammox process aiming at the removal of nitrogen from UASB reactor effluents. For this, the kinetic constants of nitriding and nitration were determined in an activated sludge system between the temperature range of 12.7 ° C to 31 ° C and the half-saturation constants of the dissolved oxygen. The respirometry was the tool used to determine nitration and nitration rates and to estimate the other relevant kinetic constants, and it is shown by the results that this is a useful tool in the determination of kinetic constants. The values of the kinetic constants of the nitriding and nitrating agents as a function of temperature showed a tendency of nitriding over nitration over the entire range. By determining the age minimum sludge for nitriding and nitration it can be estimated that operating a sludge activated system at room temperature adopting a sludge age of 4 days can promote partial nitrification.

La maitrise de la qualité des produits carnés transformés (conservés, marinés, cuits, salés, digérés...) nécessite une meilleure compréhension des mécanismes responsables des phénomènes oxydatifs et des lois cinétiques qui les régissent. Au cours des processus oxydatifs, la phase d’initiation des oxydations est capitale. Cette phase se caractérise par la vitesse à laquelle l’oxygène et le peroxyde d’hydrogène réagissent avec le fer dont la viande est plus ou moins riche selon l’espèce. Les radicaux libres, principalement superoxyde (O2°-) et hydroxyle (OH°) conduisent à l’oxydation des lipides et des protéines de la viande. Ce travail s’appuie en alternance sur des expérimentations avec un milieu modèle bien contrôlé et des sondes spécifiques permettant de caractériser la production radicalaire, et sur des simulations de calculs avec un modèle stœchio-cinétique basé sur un ensemble de réactions élémentaires et de réactions bilans permettant d’évaluer l’incidence i) de chacun des paramètres du système réactionnel (constante réactionnelle k, énergie d’activation Ea, réactivité du fer P) ii) de la concentration en réactants (Fer, H2O2, chlorure et antioxydants iii) des conditions environnementales (température, pH et force ionique) sur les cinétiques de production des radicaux libres. Les résultats expérimentaux montrent : (1) un effet synergique des oxydants et de la température sur les oxydations (2) une incidence importante des contres ions et du pH sur les complexes du fer et les niveaux d’oxydation (3) un important effet de la nature des oxydants et des antioxydants sur l'oxydation. Les constantes de vitesse controversées et les énergies d'activation de certaines réactions ainsi que les coefficients de réactivité du fer ont été ajustés localement un par un. Les prédictions du modèle stoechio-cinétique reproduisent des tendances expérimentales, exceptés pour des concentrations élevées en réactants, pour des températures extrêmes et certains antioxydants. Une optimisation globale des valeurs des k, des Ea et de la réactivité du fer pourrait améliorer les résultats prédictifs. / Control of meat quality during meat processes (storage, cooking, curing, digestion) requires a better understanding of the mechanisms responsible of the oxidative phenomena and of the kinetic laws that govern them. The initiation stage of oxidation is crucial and characterized by the rate of reaction of oxygen and hydrogen peroxide with iron; this latter compound is more or less rich depending on muscles, animals and species. Superoxide radical (O2°- ) and hydroxyl radical (OH°) are produced and initiate the cascade of reactions implicated in protein and lipid oxidations. To investigate the impact of the physicochemical parameters on the free radicals production our trials were carried out with a mimetic model of meat using two specific probes (nitroblue tetrazolium and terephthalate) and a stoichio-kinetic mathematical model composed of interactive chemical reactions. This approach enables to measure many production kinetics of O2°- and OH° and to assess unknown kinetic parameters (rate constant and activation energy and iron reactivity) by comparison of calculations to measurements. The experimental results show: (1) a synergistic effect of oxidants and temperature on oxidations (2) a significant effect of counter ions and pH on iron complexes and oxidation levels (3) a significant effect of oxidants and antioxidants on oxidation. Controversial rate constants and activation energies of some reactions as well as iron reactivity coefficients were adjusted. The predictions of the stoechio-kinetic model reproduce experimental trends except for high reactants concentrations, for extreme temperatures and for some antioxidants. A global optimization of k, Ea and iron reactivities values could improve predictive results.

The Lyons group denoted by Ly is a Sporadic Simple Group of order 51765179004000000 = 28 37 56 7 11 31 37 67. It(Ly) has a trivial Schur Multiplier and a trivial Outer Automorphism Group. Its maximal subgroups are G2(5) of order 5859000000 and index 8835156, 3 McL:2 of order 5388768000 and index 9606125, 53 L3(5) of order 46500000 and index 1113229656, 2 A11 of order 29916800 and index 1296826875, 51+4 + :4S6 of order 9000000 and index 5751686556, 35:(2 M11) of order 3849120 and index 13448575000, 32+4:2 A5 D8 of order 699840 and index 73967162500, 67:22 of order 1474 and index 35118846000000 and 37:18 of order 666 and index 77725494000000. Its existence was suggested by Richard Lyons. Lyons characterized its order as the unique possible order of any nite simple group where the centralizer of some involution is isomorphic to the nontrivial central extension of the alternating group of degree 11 by the cyclic group of order 2. Sims proved the existence of this group and its uniqueness using permutations and machine calculations. In this dissertation, we compute the (p; q; t)-generations of the Lyons group for dis- tinct primes p, q and t which divide the order of Ly such that p < q < t. For computations, we made use of the Computer Algebra System GAP / Mathematical Sciences / M.Sc. (Mathematics)

L’objectif de cette thèse est d’étudier les interactions entre polyélectrolytes (PE) de charges opposées par analyse frontale continue en électrophorèse capillaire (FACCE) et par titration calorimétrique isotherme (ITC), en fonction de la force ionique du milieu et des paramètres physico-chimiques relatifs aux deux partenaires (taux de charge chimique, masse molaire, ramification). Un copolymère statistique d’acrylamide et de 2-acrylamido-2-méthyl-propane sulfonate (PAMAMPS) de taux de charge variant entre 15% et 100% a été synthétisé et caractérisé pour cette étude. En tant que polycation modèle, la poly(L-lysine) a été retenue, sous sa forme linéaire (PLL) ou ramifiée / hyperbranchée (DGL). Des mesures par turbidimétrie ont permis d’étudier la stabilité des complexes de polyélectrolytes (PEC) en fonction de la force ionique du milieu. La détermination de la stœchiométrie des PEC par 1H-RMN a permis d’établir une règle générale pour prédire les stœchiométries de charge des PEC. Les paramètres thermodynamiques d’interactions (constantes et stœchiométries d’interaction, contribution entropique et enthalpique) ont été déterminés, par le tracé systématique des isothermes d’adsorption, en considérant le modèle d’interactions des sites indépendants de même énergie. Une dépendance linéaire entre le logarithme des constantes d’interactions et le logarithme de la force ionique a été observée. Cette dépendance en force ionique confirme le caractère entropique des interactions entre PE de charges opposées. Elle permet aussi de quantifier le nombre de contre-ions relargués lors de la formation du PEC. Cette quantité de contre-ions libérés a pu être comparée à la quantité totale de contre-ions condensés. Cette modélisation permet, en outre, de prédire les constantes d’interaction pour des taux de charge intermédiaires et à différentes forces ioniques. / The aim of this thesis is to study the interactions between oppositely charged polyelectrolytes (PE) by frontal analysis continuous capillary electrophoresis (FACCE) and isothermal titration calorimetry (ITC) as a function of the ionic strength of the medium and the physico-chemical properties related to the two partners (chemical charge density, molar mass, ramification). Statistical copolymers of acrylamide and 2-acrylamido-2-methyl-propane sulfonate (PAMAMPS) with chemical charge densities varying between 15% and 100% were synthesized and characterized for this study. Poly(L-lysine) under their linear (PLL) or ramified/hyperbranched (DGL) forms were used as model polycations. Turbidity measurements allowed the study of the stability of the polyelectrolyte complexes (PEC) as a function of the ionic strength of the medium. PEC charge stoichiometries were measured by 1H-NMR, and a general predictive rule that estimates the PEC charge stoichiometry was enounced. The thermodynamic binding parameters (binding constant, stoichiometry, enthalpic and entropic contributions) were determined, by systematically plotting the isotherms of adsorption, and using the model of independent and identical interacting sites. A linear dependence between the logarithm of the binding constants and the logarithm of the ionic strength was observed. This linear dependence confirmed the entropic character of the interactions between oppositely charged PE and allowed quantifying the number of released counter-ions that were compared to the total number of condensed counter-ions. Furthermore, this modelling allowed predicting the binding constants for intermediate chemical charge densities and at different ionic strengths.

Este trabalho apresenta duas técnicas de ensaios não-destrutivos por ultra-som realizados em um tanque com água para determinar as constantes elásticas de materiais compostos de fibra de vidro/epóxi. A primeira técnica é a transmissão direta utilizando um par de transdutores. A segunda é a técnica de pulso-eco, utilizando um único transdutor. A água do tanque atua como um acoplante para transferir a energia mecânica do transdutor para a amostra. Como o transdutor não fica em contato direto com a amostra, pode-se garantir um acoplamento constante. O sistema de medição dota de um dispositivo que permite medir a velocidade da onda elástica sob diferentes ângulos de incidência, através da rotação manual da amostra. Devido ao fenômeno de conversão de modos com incidência oblíqua na interface amostra-água, ensaios por ultra-som em tanques com água fornecem as informações necessárias para o cálculo das constantes elásticas em amostras de materiais anisotrópicos, numa dada direção, a partir das medições das velocidades longitudinal e de cisalhamento. Numa dada direção de propagação em um meio anisotrópico, existem três ondas elásticas distintas: uma longitudinal e duas de cisalhamento. Se as constantes elásticas do material são conhecidas, é possível obter as três velocidades em uma dada direção bastando resolver a equação de Christoffel. Invertendo a equação de Christoffel, obtém-se as constantes elásticas a partir das velocidades medidas em uma dada direção. Os experimentos são realizados com amostras de fibra de vidro/epóxi unidirecionais e bidirecionais, utilizando transdutores com freqüências de 0,5 MHz, 1 MHz e 2,25 MHz. Os resultados experimentais obtidos utilizando ambas as técnicas são comparados com um modelo denominado “Regra das Misturas” e com resultados da literatura. / In this work, two ultrasonic non destructive techniques were implemented in a water tank and used to determine the elastic constants of glass-epoxy composites samples. The first is the through-transmission technique implemented with a pair of ultrasonic transducers. The second is the back-reflection technique that uses a single transducer in pulse-eco mode. The water acts as a couplant and transfers the mechanical energy from the transducer to the sample. As the transducer is not in direct contact with the sample, we can guarantee a good coupling with the immersion technique. With the system device, it is possible to measure the velocities of the elastic waves in different angles by manually rotating the sample. Due to wave mode conversion phenomenon at the sample-water interface with oblique incidence, ultrasonic immersion testing provides information to calculate the elastic constants of the specimen by measuring longitudinal and shear wave speeds. There are three different modes of waves, one longitudinal and two shear waves, for any given direction of propagation in an anisotropic medium. If the elastic constants of a medium are known, it is possible to obtain the three wave speeds in particular propagations directions by solving the Christoffel equation. Inverting the Christoffel equation, it is possible to obtain the elastic constants from the measured wave speed in several specific directions of the anisotropic material. Measurements were carried out on unidirectional and bidirectional glass-epoxy composite samples, using transducers with central frequency of 0.5 MHz, 1 MHz, and 2.25 MHz. The experimental results obtained with both techniques are compared with a model denominated “Rule of Mixture” estimation and with the literature.