Thesis (M.E.-Res.)--University of Wollongong, 2008. / Typescript. Includes bibliographical references: leaf 163-172.

Thesis (M.Sc.(Meteorology))--University of Pretoria, 2008. / Summary in English. Includes bibliographical references.

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A fotodegradação de pesticidas, como os derivados de carbamatos orgânicos, possui um papel importante do ponto de vista ambiental, pois estes são extensivamente utilizados e comumente encontrados como contaminantes da água e do solo. O Rearranjo Foto-Fries (PFR) - a conversão fotoquímica de aril ésteres para orto- e para-hidroxifenonas - desempenha um importante papel na fotodegradação de drogas e pesticidas carbamatos, além de ser um passo chave para a síntese de um grande número de compostos e polímeros funcionais. Embora exista um grande número de estudos experimentais a respeito desse rearranjo, alguns pontos dessa reação ainda estão sob debate. O objetivo deste trabalho é estudar o processo de fotodissociação em carbamatos aromáticos e derivados e, particularmente, fornecer uma visão geral do mecanismo do Rearranjo Foto-Fries, utilizando metodologias computacionais. Entre essas metodologias estão TDDFT, cálculos multiconfiguracionais e Surface Hopping. A superfície de energia potencial para o PFR foi estudada no vácuo gasosa e utilizando solvatação implícita e explícita. Nessa última, a distribuição do solvente foi obtida por simulações de Monte Carlo. Um modelo envolvendo três estados é proposto para o PFR, baseado em cálculos CASSCF(14,12)/CASPT2(14,12). Este modelo fornece uma visão global de todos os passos envolvidos na reação, da fotodissociação até a tautomerização final. O papel do solvente ainda não foi esclarecido, pois a sua adição (implícita ou explícita) não alterou significativamente o comportamento do caminho dissociativo. / The photodegradation of pesticides, such as carbamate derivatives, has an environmentally important role, since they are extensively used and commonly found as contaminants in water and soils. The Photo-Fries rearrangement (PFR) - a photochemical conversion of aryl esters to ortho- and para-hydroxyphenones - plays an important role in the photodegradation of drugs and carbamate pesticides, besides being a key step in the synthesis of a large number of compounds and functional polymers. Although there is a large number of experimental studies about the mechanism of PFR, some points of this reaction are still under debate. The goal of this work is to study the photodissociation process in aromatic carbamates and derivatives and, particularly, is to provide a comprehensive picture of PFR, based on computational methods. Several methodologies were used, such as TDDFT, multiconfigurational methods and Trajectory Surface Hopping simulations. Comprehensive explorations of the potential energy surfaces were done in the gas phase and with implicit and explicit solvent, whose distribution was obtained from sequential Monte Carlo sampling. A three-state model for the Photo-Fries Rearrangement is proposed based on CASSCF(14,12)/CASPT2(14,12) calculations. It provides a comprehensive mechanistic picture of all steps of the reaction, from the photoabsorption to the final tautomerization. The role of the solvent is still not understood since the addition of solvent (implicit or explicit) do not change the dissociative pathway significantly.

De nos jours, l'incomplétude du modèle standard des particules est largement reconnue. L'une de ses failles les plus évidentes est le manque d'explication de l'énorme excédent de matière par rapport à l'antimatière dans l'univers, que l'on appelle l'asymétrie baryonique de l'univers. De nouvelles violations de CP (conjugaison de charge et parité spatiale) absentes dans le modèle standard sont supposées être responsables de cette asymétrie. Une telle violation pourrait être observée dans la matière ordinaire à travers un ensemble d'interactions violant les symétries de parité et de renversement du temps (impaires pour P,T) dont les prépondérantes sont les interactions du moment dipolaire électrique de l'électron (eEDM), électron-nucléon scalaire-pseudoscalaire (enSPS) et du moment quadripolaire magnétique nucléaire (nMQM). Ainsi, une preuve expérimentale d'une constante d'interaction impaire pour P,T serait une preuve de cette nouvelle physique au-delà du modèle standard. Le calcul des paramètres moléculaires correspondants est réalisé en utilisant une approche d'interaction de configurations relativiste à quatre composantes dans des molécules diatomiques polaires contenant un actinide, qui sont des systèmes particulièrement appropriés pour les expèriences eEDM, tels que ThO qui a permis d'assigner à l'eEDM la borne supérieure la plus contraignante et ThF+ qui sera utilisé dans une expérience à venir. Ces résultats sont d'une importance cruciale dans l'interprétation des mesures puisque les constantes fondamentales ne peuvent être évaluées que si l'on associe les mesures de décalages énergétiques et les paramètres moléculaires théoriques. / Nowadays, the incompleteness of the Standard Model of particles is largely acknowledged. One of its most obvious shortcomings is the lack of explanation for the huge surplus of matter over antimatter in the universe, the so-called Baryon Asymmetry of the Universe. New CP (Charge conjugation and spatial Parity) violations absent in the SM are assumed to be responsible for this asymmetry. Such a violation could be observed in ordinary matter through a set of interactions violating both parity and time-reversal symmetries (P,T-odd), among which the preponderant ones are the electron Electric Dipole Moment (eEDM), the electron-nucleon scalar-pseudoscalar (enSPS) and the nuclear magnetic quadrupole moment (nMQM) interactions. Hence, an experimental evidence of a non-zero P,T-odd interaction constant would be a probe of this New Physics beyond the Standard Model. The calculation of the corresponding molecular parameters is performed by making use of an elaborate four-component relativistic configuration interaction approach in polar diatomic molecules containing an actinide, that are particularly adequate systems for eEDM experiments, such as ThO that allowed for assigning the most constraining upper bound on the eEDM and ThF+ that will be used in a forthcoming experiment. Those results will be of crucial importance in the interpretation of the measurements since the fundamental constants can only be evaluated if one combines both experimental energy shift measurements and theoretical molecular parameters.

The observational approach to cosmology is the endeavour to reconstruct the geometry of the Universe using only data that is theoretically verifiable within the causal boundaries of a cosmological observer. Using this approach, it was shown in [36] that given ideal cosmological observations, the only essential assumption necessary to determine the geometry of the Universe is a theory of gravity. Assuming General Relativity, the full set of Einstein field equations (EFEs) can be used to reconstruct the geometry of the Universe using direct observations on the past null cone (PNC) as initial conditions. Observationally and theoretically this is a very ambitious task and therefore, current developments have been restricted to spherically symmetric dust models while only relaxing the usual assumption of homogeneity in the radial direction. These restricted models are important for the development of theoretical foundations and also useful as verification models since they avoid the circularity of verifying what has already been assumed. The work presented in this thesis is the development of such a model where numerical relativity (NR) is used to simulate the observable universe. Similar to the work of Ellis and co-workers [36], a reference frame based on the PNC is used. The reference frame used here, however, is based on that of the characteristic formalism of NR, which has developed for calculating the propagation of gravitational waves. This provides a formalism that is well established in NR, making the use of existing algorithms possible. The Bondi-Sachs coordinates of the characteristic formalism is, however, not suitable for calculations beyond the observer apparent horizon (AH) since the diameter distance used as a radial coordinate becomes multi-valued when the cosmological PNC reconverges in the history of a universe, smaller in the past. With this taken into consideration, the Bondi-Sachs characteristic formalism is implemented for cosmology and the problem approaching the AH is investigated. Further developments address the limitations approaching the AH by introducing a metric based on the Bondi-Sachs metric where the radial coordinate is replaced with an affine parameter. The model is derived with a cosmological constant Λ incorporated into the EFEs where Λ is taken as a parameter of the theory of gravity rather than as a matter source term. Similar to the conventional characteristic formalism, this model consists of a system of differential equations for numerically evolving the EFEs as a characteristic initial value problem (CIVP). A numerical code implemented for the method has been found to be second order convergent. This code enables simulations of different models given identical data on the initial null cone and provides a method to investigate their physical consistency within the causally connected region of our current PNC. These developments closely follow existing 3D schemes developed for gravitational wave simulations, which should make it natural to extend the affine CIVP beyond spherical symmetric simulations. The developments presented in this thesis is an extended version of two papers published earlier.

Les alliages de zirconium sont utilisés comme matériaux de gainage des combustibles nucléaires dans les réacteurs à eau pressurisée. Ces gaines sont utilisées dans un milieu extrêmement radiatif et corrosif, elles peuvent dans certains cas être le siège de fortes variations de température et doivent répondre à des sollicitations mécaniques importantes, que ce soit en conditions de service ou accidentelles. Dans un tel contexte, il est intéressant de pouvoir prédire les transformations de phases ayant lieu au sein de la gaine en fonction des variations de température et de composition chimique, la précipitation de phases fragiles induites par la présence des éléments d’alliages, mais aussi de tester de nouvelles compositions d’alliages afin de l’optimiser.La méthode la plus adaptée pour la modélisation thermodynamique de systèmes multiconstitués est la méthode Calphad (CALculation of PHAse Diagrams). Il s’agit d’une méthode semi-empirique, consistant à modéliser les enthalpies libres des différentes phases constitutives d’un système par ajustement de certains paramètres, dans le but de reproduire les données expérimentales.Ce mémoire détaille la construction d’une base de données thermodynamiques du système quinaire Cr-Fe-Nb-Sn-Zr selon la méthode Calphad. L’originalité de notre démarche est liée à l’utilisation des calculs DFT de manière systématique et massive. Il s’agit en particulier de calculer par DFT les enthalpies de formation de tous les end-members des phases intermétalliques constitutives du système quinaire. De plus, des calculs sur des mailles « quasi aléatoires » (SQS) sont également effectués de manière systématique afin de déterminer les enthalpies de mélange des solutions solides binaires en structure fcc, bcc et hcp. En outre, une étape importante de ce travail consiste à compléter les données expérimentales de la littérature par de nouvelles mesures sur des systèmes choisis. En particulier, nous nous sommes employés à décrire quelques équilibres de phases des systèmes ternaires Cr-Nb-Sn, Cr-Fe-Sn, Cr-Sn-Zr et Fe-Nb-Sn qui n’avaient jamais été déterminés expérimentalement. Nous avons ensuite utilisé ces calculs et ces nouvelles données expérimentales en complément de données de la littérature comme données d’entrée pour la modélisation thermodynamique des vingt sous-systèmes binaires et ternaires du système quinaire considéré. Enfin, le pouvoir prédictif de notre base de données a pu être vérifié en confrontant ces prédictions à des données expérimentales relatives à des alliages quinaires industriels ou à de nouveaux concepts de gaines / Currently, zirconium alloys are used as fuel cladding materials in PWR (Pressurized Water Reactors). The claddings stand in a very corrosive and radiative environnement, and can be submitted to temperature variations. In addition, the claddings will be subjected to mechanical stresses in reactor or accidental conditions. Thus, it appears useful to have a better understanding of phase transformations occurring in these alloys, as a function of temperature and chemical composition variations, but also to forecast the precipitation of fragile phases induced by the addition of alloying elements. At last, the ability to test new alloy compositions may allow to optimize it.The most suitable method for the thermodynamic modeling of multicomponent systems is the Calphad method (CALculation of PHAse Diagrams). The Calphad method is a widely used technique of semi-empirical modelling of phase diagrams. It consists in the description of the Gibbs energies of the different phases by fitting parameters allowing to describe the experimental data.This report details the design of a thermodynamic database considering the five following elements Zr, Cr, Fe, Nb, and Sn. The originality of this database lies in a systematic use of DFT calculations. Indeed, DFT calculations are performed to predict the formation enthalpy of the intermetallic phases appearing in these systems. Moreover, the SQS method (Special Quasirandom Structure) is used to predict the mixing enthalpy of the fcc, bcc and hcp binary solid solutions. Besides, experimental investigations are an important step of this thesis. Since no experimental data were available for the Cr-Fe-Sn, Cr-Nb-Sn, Cr-Sn-Zr and Fe-Nb-Sn ternary systems, new experimental data are provided, within this study, on the isothermal sections of these systems at different temperatures. All these calculated data in addition to the experimental data and the data from literature are used as input data for the Calphad modelling of the twenty binary and ternary systems which are then combined in the new database. A last part is dedicated to comparisons between predictions obtained with our new database and experimental results on industrial quinary alloys and a new concept of claddings

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