Dissertations / Theses on the topic 'Fundamental constants'

The purpose of this study was to investigate the fundamental characteristics of a chelating surfactant in terms of solution behaviour, chelation of divalent metal ions, and interaction in mixtures with different foaming agents and divalent metal ion, as well as examining its prospects in some practical applications. Chelating surfactants are functional molecules, with both surface active and chelating properties, which are water soluble and therefore suitable for chelation in many aqueous environments. The dual functionality offers the possibility to recover the chelating surfactant as well as the metals. The DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant 4-C12-DTPA (2-dodecyldiethylenetriaminepentaacetic acid) was synthesized at Mid Sweden University. In the absence of metal ions, all eight donor atoms in the headgroup of 4-C12-DTPA are titrating and the headgroup charge can be tuned from +3 to -5 by altering the pH. The solution properties, studied by surface tension measurements and NMR diffusometry, were consequently found strongly pH dependent. pH measurements of chelating surfactant solutions as a function of concentration was used to extract information regarding the interaction between surfactants in the aggregation process. Small differences in the conditional stability constants (log K) between coordination complexes of DTPA and 4-C12-DTPA, determined by competition measurements utilizing electrospray ionization mass spectrometry (ESI-MS), indicated that the hydrocarbon tail only affected the chelating ability of the headgroup to a limited extent. This was further confirmed in hydrogen peroxide bleaching of thermomechanical pulp (TMP) treated with 4-C12-DTPA. Interaction parameters for mixed systems of 4-C12-DTPA and different foaming agents were calculated following the approach of Rubingh’s regular solution theory. The mixtures were also examined with addition of divalent metal ions in equimolar ratio to the chelating surfactant. Strong correlation was found between the interaction parameter and the phase transfer efficiency of Ni2+ ions during flotations. Furthermore, a significant difference in log K between different metal complexes with 4-C12-DTPA enabled selective recovery of the metal ion with the highest log K. The findings in this study contribute to the understanding of the fundamental characteristics of chelating surfactants, which can be further utilized in practical applications.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior<br>No primeiro capÃtulo da dissertaÃÃo, à apresentada uma breve introduÃÃo do trabalho. Em seguida, no segundo capÃtulo, sÃo demonstradas noÃÃes e propriedades de espaÃos vetoriais topolÃgicos. Dando seguimento ao presente estudo, no terceiro capÃtulo, efetua-se a abordagem da teoria das distribuiÃÃes, onde se proporciona, como exemplo a distribuiÃÃo delta de Dirac, na qual, por conseguinte, sÃo definidas ainda operaÃÃes com distribuiÃÃes, entre elas a convoluÃÃo de uma distribuiÃÃo com uma funÃÃo teste, e por fim, ainda no mesmo capitulo à feito uma anÃlise das distribuiÃÃes com suporte compacto. No capÃtulo quatro, por sua vez, explana-se a transformada de Fourier e suas propriedades, bem como, propriedades de funÃÃes que pertencem ao espaÃo de Schwartz e ainda, à feito um estudo das distribuiÃÃes temperadas. Finalmente, no quinto e Ãltimo capÃtulo à demonstrado o teorema de Malgrange-Ehrenpreis, que à a temÃtica principal do trabalho elaborado, o qual afirma que todo operador diferencial com coeficientes constantes tem uma soluÃÃo fundamental. Destarte, à implementado um estudo de alguns exemplos afins ao teorema.<br>In the first chapter of the dissertation, is a brief introduction. Then in the second chapter, are shown notions and properties of topological vector spaces. Following the present study, the third chapter, is effected the approach to the theory of distributions, which provides, as an example the Dirac delta distribution, in which, therefore, are dened further distribution operations, including the convolution of a distribution with a test function, and finally, still in same chapter an analysis is made of distributions with compact support. In chapter four, in turn, explains to the Fourier transform and its properties, as well as properties of functions belonging to Schwartz space and also a study is made of tempered distributions. Finally, the fifth and final chapter is shown the Malgrange-Ehrenpreis theorem, which is the main theme of the work done,which states that any differential operator with constant coecients has a fundamental solution. Thus, it implemented a study of some examples related to the theorem.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>In this thesis we present a proof of the Malgrange-Ehrenpreis theorem, which states that every operator with constant coefficients non identically zero has a fundamental solution.<br>Nessa dissertação apresentamos uma demonstração do Teorema de Malgrange-Ehrenpreis, que afirma que todo operador de coeficientes constantes não identicamente nulo tem uma solução fundamental.

Many physical theories beyond the Standard Model predict time variations of basic physics parameters. Direct measurement of the time variations of these parameters is very difficult or impossible to achieve. By contrast, measurements of fundamental constants are relatively easy to achieve, both in the laboratory and by astronomical spectra of atoms and molecules in the early universe. In this work, measurements of the proton to electron mass ratio mu and the fine structure constant alpha are combined to place mildly model-dependent limits on the fractional variation of the quantum chromodynamic scale and the sum of the fractional variations of the Higgs vacuum expectation value (VEV) and the Yukawa couplings on time-scales of more than half the age of the universe. The addition of another model parameter allows the fractional variation of the Higgs VEV and the Yukawa couplings to be computed separately. Limits on their variation are found at the level of less than 5 x 10(-5) over the past 7 Gyr. A model-dependent relation between the expected fractional variation of a relative to mu tightens the limits to 10(-7) over the same time span. Limits on the present day rate of change of the constants and parameters are then calculated using slow roll quintessence. A primary result of this work is that studies of the dimensionless fundamental constants such as a and mu, whose values depend on the values of the physics parameters, are excellent monitors of the limits on the time variation of these parameters.

Made available in DSpace on 2014-07-29T16:02:18Z (GMT). No. of bitstreams: 1 Dissertacao Lidiane Mayumi Hieda.pdf: 465165 bytes, checksum: a5ce3ff47770899f6a4edcca3e40ed69 (MD5) Previous issue date: 2011-05-13<br>This work was based on papers On Compact Minimal Surfaces with non-negative Gaussian Curvature in a Space of Constant Curvature: I and Minimal Surfaces with Constant Curvature in 4-dimensional Space Forms, by Katsuei Kenmotsu, consisting in the classification of minimal surfaces with constant Gaussian curvature K in a 4-dimensional space form without any global assumption. We will show that an isometric minimal immersion x: M2(K) &#8594; M4(c), where c is sectional curvature, is either totally geodesic, or locally Clifford Torus, or locally a Veronese surface. As a corollary, we have that there is not isometric minimal immersions with constant negative Gaussian curvature into unit sphere S4(1) even locally.<br>Este trabalho foi baseado nos artigos On CompactMinimal Surfaces with non-negative Gaussian Curvature in a Space of Constant Curvature: I e Minimal Surfaces with Constant Curvature in 4-dimensional Space Forms de Katsuei Kenmotsu que consistem em classificar superfícies mínimas com curvatura Gaussiana constante K nas formas espaciais 4-dimensionais, sem alguma hipótese global. Mostraremos que uma imersão isométrica mínima x : M2(K) &#8594; M4(c), onde c é a curvatura seccional, ou é totalmente geodésica, ou localmente um Toro de Clifford, ou localmente uma superfície de Veronese. Como corolário, temos que não existe uma imersão isométrica mínima com curvatura Gaussiana constante negativa numa esfera unitária S4(1) mesmo que localmente.

Este trabalho apresenta o procedimento que desenvolvemos e empregamos para determinar os valores a serem adotados para as energias de um conjunto de raios gama comumente utilizados como padrões de calibração, bem como sua respectiva matriz de covariância, esta obtida pela primeira vez. A matriz de covariância entre as energias destes padrões revelou muitos casos de correlações com valores absolutos maiores que 0,8, correlações estas que precisam ser corretamente consideradas para não comprometer a qualidade das análises efetuadas com o uso daquelas energias. No procedimento desenvolvido foi considerada a relação entre as energias dos raios gama (em múltiplos de eV) e as constantes fundamentais das quais dependem: h, e, c e o parâmetro de rede do Silício (aSi), o que possibilitou atualizar os resultados para as constantes fundamentais recomendadas de 2002. Uma metodologia para a inclusão de novos resultados experimentais ao conjunto de padrões de modo a preservar sua auto-consistência também foi desenvolvida neste trabalho. Este método considera adequadamente as covariâncias e atualiza todo o conjunto de padrões para incorporar as novas informações experimentais em uma única etapa. Por fim, utilizamos as metodologias de análise desenvolvidas e o conjunto de padrões aqui recomendados para analisar dados de medidas dos raios gama do decaimento do 233U e, assim, estudar a adequação de três diferentes modelos de estrutura nuclear para o 229Th, bem como as energias de excitação dos estados nucleares. A energia do primeiro estado excitado do 229Th, um estado metaestável de energia inferior a 10 eV, foi determinada com base naqueles diferentes modelos.<br>This work presents the procedure which we have developed and employed to determine the values to be adopted for the energies of a set of gamma-rays in common use as calibration standards, publishing for the fist time their respective covariance matrix. Several correlations with absolute values exceeding 0.8 were found, revealing the necessity of considering correctly the covariance matrix in any analysis to be done with the use of these standards in order not to interfere with the quality of the analysis. The procedure here presented considers correctly the relation between the gamma-ray energies (given in eV) and the fundamental constants h, e, c, and the lattice parameter (aSi), allowing the updating of the set with respect to the 2002 recommended values for those constants. A methodology for the inclusion of new experimental results in the set of standards, in a way which preserve its selfconsistency, was also developed in this work. In this method the updating of the whole set of standards is performed in a single step, while considering adequately the covariances. Finally, the standard set recommended here and the methodology developed in this work were employed to analyze data of gamma-rays measurement which follow the 233U decay and therewith to decide about the adequacy of three different nuclear structure models for 229Th and the excitation energy of its nuclear states. The energy of the first excited state of 229Th, a meta-stable state of less than 10 eV, was determined taking into account those different models.

Dissertação (mestrado)—Universidade de Brasília, Instituto de Química, Programa de Pós-Graduação em Química, 2013.<br>Submitted by Albânia Cézar de Melo (albania@bce.unb.br) on 2013-08-02T13:30:30Z No. of bitstreams: 1 2013_DanielFranciscoScalabriniMachado.pdf: 5725103 bytes, checksum: 8f6bf029a5f00c5912c1e6d191541f74 (MD5)<br>Approved for entry into archive by Guimaraes Jacqueline(jacqueline.guimaraes@bce.unb.br) on 2013-08-02T15:37:46Z (GMT) No. of bitstreams: 1 2013_DanielFranciscoScalabriniMachado.pdf: 5725103 bytes, checksum: 8f6bf029a5f00c5912c1e6d191541f74 (MD5)<br>Made available in DSpace on 2013-08-02T15:37:47Z (GMT). No. of bitstreams: 1 2013_DanielFranciscoScalabriniMachado.pdf: 5725103 bytes, checksum: 8f6bf029a5f00c5912c1e6d191541f74 (MD5)<br>O objetivo principal deste trabalho foi o cálculo das energias e constantes espectroscópicas rovibracionais do sistema molecular Cl2 incluindo correções relativísticas no cálculo das energias eletrônicas ab initio obtidas em um trabalho de Luiz G. de Macedo e Wibe A. de Jong. Neste trabalho além do estado fundamental, foram realizados cálculos de 20 estados excitados deste sistema diatômico. As funções de Rydberg e Bond Order generalizadas de grau 10 foram utilizadas como formas analíticas para ajustar as curvas de energia potencial geradas a partir das energias eletrônicas. Com estas formas analíticas as energias rovibracionais e as constantes espectroscópicas foram obtidas através de duas abordagens distintas. A primeira combina as energias obtidas via solução da Equação de Schrödinger Nuclear com uma equação espectroscópica. Na segunda aplica-se o método de Dunham. As constantes espectroscópicas obtidas estão em excelente acordo com os dados experimentais e teóricos disponíveis para alguns estados eletrônicos. ______________________________________________________________________________ ABSTRACT<br>The main goal of this work was the calculation of the rovibrational energies and spectroscopic constants of the Cl2 molecular system including relativistic corrections within the calculation of the ab initio electronic energies performed in a previous work by Luiz G. de Macedo and Wibe A. de Jong. In this work, besides the ground state, 20 excited states of this diatomic system were also included. Rydberg as well as generalized Bond Order functions were used as analytical forms to fit the potential energy curves generated from the electronic energies. With the analytical forms in hand, rovibrational energies and spectroscopic constants were obtained using two different approaches. The first one combines the solutions of the Nuclear Schrödinger Equation with a spectroscopic equation. The second applies the Dunham method. The calculated spectroscopic constants are in excellent agreement with available experimental and theoretical data for some electronic states.

O objetivo do presente estudo, de cunho teórico-analítico, configura-se como uma tentativa de compreensão da forma pela qual se estabeleceram, no Brasil, as identidades profissionais das professoras de primeiras letras e das coordenadoras pedagógicas, mutuamente referidas, e o mal-estar decorrente das modalidades pelas quais se instituíram, com as reformas educacionais, suas competências desejáveis mediante diferentes descrições das respectivas funções. Na busca de entender teoricamente como se produzem essas identidades nas estruturas hierárquicas das instituições escolares, os aportes teóricos de Foucault forneceram ferramentas úteis para problematizar os saberes vigentes e compreender como certos saberes são desqualificados nas relações de poder. A compreensão de Foucault acerca da relação entre saber e poder, principalmente, possibilita outras leituras dos discursos pedagógicos, acumulados e veiculados como verdades, que permeiam a construção das identidades dessas profissionais. A análise sociológica de Bauman, por sua vez, ajuda a elucidar o presente em que estamos imersos, que ele chama de modernidade \"leve\" e \"líquida\" e, assim, torna possível entender as redistribuições e realocações dos poderes e os novos padrões de dependência na instituição escolar, apesar de o discurso pedagógico dominante aparentemente convocar \"autodeterminação\" e \"liberdade\" como características centrais da constituição dessas identidades em estudo. A presente investigação busca, dessa forma, primeiramente elucidar no Brasil o percurso histórico da profissão de professora das primeiras letras e assim compreender como se configuraram as estruturas hierárquicas, isto é, a \"função supervisora\" nas reformas educacionais das décadas de 20 e 30, caracterizada pela inspiração empresarial na administração escolar e pela instituição da figura do especialista em novos métodos de ensino. É realizada a seguir a análise de quatro volumes da coleção O Coordenador pedagógico, organizada por Vera Nigro de Souza Placco e Laurinda Ramalho de Almeida, publicada a partir de 1998, escolhida pelo elevado número de edições, o que demonstra sua aprovação pelo público. A coleção possibilita o acesso a alguns dos principais discursos que norteiam a constituição da identidade desses profissionais. Os artigos aí presentes são resultados, na sua maioria, de dissertações de teses e de pesquisas de avaliação de projetos implementados na rede pública ou particular. Como conclusão, observa-se que os discursos educacionais em geral enfatizam a constituição de profissionais \"autônomos\", \"críticos\" e \"reflexivos\". Imersos nesse discurso homogeneizante e sofisticado nas suas propostas de auto-exame, no entanto, tanto professores como coordenadores paradoxalmente vão limitando as possibilidades de pensar e de constituir suas identidades. Uma possível ação questionadora seria a de duvidar desse lugar idealizado nas descrições da função dos coordenadores pedagógicos, que definem missões impossíveis, lugar em que, na maioria das vezes, são vistos como detentores de uma consciência crítica embasada nos conhecimentos da ciência, e capazes de constituir professores \"autônomos\" e \"reflexivos\". Duvidar, assim, dessa relação, quando ela se estabelece pela necessidade da tutela desse especialista, a fim de buscar outras formas de relação que permitam de fato que as professoras das primeiras letras possam se desenvolver enquanto profissionais.<br>This study aims at attempting to comprehend the way the professional identities of primary school teachers and pedagogic coordinators has been established in Brazil and the subsequent ill-feeling originated by the educational restructuring of their competencies in the light of their new roles. The search for the understanding of how these identities are constructed in the hierarchical structure of schools can be backed up by Foucault-based theories that provide useful tools for analyzing the present kinds of knowledge, at the same time that it helps understand how they can be disqualified before unequal encounters. Foucault\'s understanding of the relationship between power and knowledge makes it possible to envisage different interpretations of the pedagogical discourse which has been established and passed on as truths that permeate the make-up of the identity of a teaching professional. Bauman\'s sociological approach, in turn, helps to elucidate the present scenario where we are, which he named \"light\" and \"liquid\" modernity. Such suggested approach makes it possible to understand the redistributions and allocations of the powers and the new patterns of dependence at the educational institution, despite the fact that the dominant pedagogical discourse seems to capitalize on \"self-determination\" and \"freedom\" as central characteristics in the construction of the identities under investigation. Thus, the present study seeks to elucidate, from a historical perspective, the path of the primary school teacher as a means to shed some light on how the hierarchical relations came to be, namely that of the \"supervisor\" in the educational restructuring of the 20\'s and 30?\'s. The referred restructuring seems to have been highly influenced by the entrepreneurial spirit present in school administration trends and by the institution of a specialist in the new teaching methods. Four volumes of the series O Coordenador Pedagógico (the Pedagogic Coordinatior) published as of 1998 and organized by Vera Nigro de Souza Placco and Laurinda Ramalho de Almeida are chosen and analyzed due to the significant number of editions, which seems to be indicative of its approval by the target audience. This collection makes it possible to have access to some of the main discourse samples that guide the identity construction of the professionals of the area. Most of the articles therein result from theses, dissertations and research on the evaluation of projects implemented in private and public educational institutions. As a conclusion, it is possible to observe that the educational discourse, in general, emphasizes the construction of \"autonomous\", \"critical\" and \"reflexive\" professionals. Given the homogenous and sophisticated nature of such discourse, filled with self-analysis proposals, both teachers and coordinators limit their possibilities of thinking and constructing their identities. One possible approach to this paradox would be to dispute the idealization of the role of the pedagogical coordinator that defines impossible missions and appears to be the bearer of a critical conscience that, based on scientific background, is capable of educating teachers to be \"autonomous\" and \"reflexive\". This way, disputing this relation may bring in new possibilities of relationships and approaches to allow the primary school teachers to develop as professionals.

Cette thèse est consacrée à l'étude de la géométrie des variétés de Fano complexes en utilisant les propriétés des sous-faisceaux du fibré tangent et la géométrie du diviseur fondamental. Les résultats principaux compris dans ce texte sont : (i) Une généralisation de la conjecture de Hartshorne: une variété lisse projective est isomorphe à un espace projectif si et seulement si son fibré tangent contient un sous-faisceau ample.(ii) Stabilité du fibré tangent des variétés de Fano lisses de nombre de Picard un : à l'aide de théorèmes d'annulation sur les espaces hermitiens symétriques irréductibles de type compact M, nous montrons que pour presque toute intersection complète générale dans M, le fibré tangent est stable. La même méthode nous permet de donner une réponse sur la stabilité de la restriction du fibré tangent de l'intersection complète à une hypersurface générale.(iii) Non-annulation effective pour des variétés de Fano et ses applications : nous étudions la positivité de la seconde classe de Chern des variétés de Fano lisses de nombre de Picard un. Ceci nous permet de montrer un théorème de non-annulation pour les variétés de Fano lisses de dimension n et d'indice n-3. Comme application, nous étudions la géométrie anticanonique des variétés de Fano et nous calculons les constantes de Seshadri des diviseurs anticanoniques des variétés de Fano d'indice grand.(iv) Diviseurs fondamentaux des variétés de Moishezon lisses de dimension trois et de nombre de Picard un : nous montrons l'existence d'un diviseur lisse dans le système fondamental dans certain cas particulier<br>This thesis is devoted to the study of complex Fano varieties via the properties of subsheaves of the tangent bundle and the geometry of the fundamental divisor. The main results contained in this text are:(i) A generalization of Hartshorne's conjecture: a projective manifold is isomorphic to a projective space if and only if its tangent bundle contains an ample subsheaf.(ii) Stability of tangent bundles of Fano manifolds with Picard number one: by proving vanishing theorems on the irreducible Hermitian symmetric spaces of compact type M, we establish that the tangent bundles of almost all general complete intersections in M are stable. Moreover, the same method also gives an answer to the problem of stability of the restriction of the tangent bundle of a complete intersection on a general hypersurface.(iii) Effective non-vanishing for Fano varieties and its applications: we study the positivity of the second Chern class of Fano manifolds with Picard number one, this permits us to prove a non-vanishing result for n-dimensional Fano manifolds with index n-3. As an application, we study the anticanonical geometry of Fano varieties and calculate the Seshadri constants of anticanonical divisors of Fano manifolds with large index.(iv) Fundamental divisors of smooth Moishezon threefolds with Picard number one: we prove the existence of a smooth divisor in the fundamental linear system in some special cases

Cette thèse a pour objectif l’amélioration de l’exactitude du gravimètre atomique du LNE-SYRTE. Ce gravimètre utilise des techniques d’interférométrie atomique pour déterminer l’accélération de la pesanteur g subie par des atomes de Rubidium 87 en chute libre. Il constitue la référence métrologique nationale pour la mesure de g et ses biais doivent donc être évalués avec la meilleure incertitude.Au début de cette thèse, le budget d’incertitude total était de 4.3µGal,dominé par l’incertitude de 4.0µGal associée au biais lié aux aberrations du front d’onde des lasers Raman utilisés pour réaliser les séparatrices lumineuses de l’interféromètre. Pour améliorer l’évaluation de cet effet, nous avons implémenté une source d’atomes ultra froids et mesuré g dans une large gamme de températures. Le développement d’un modèle de l’expérience accompagné par une simulation de l’impact des fronts d’ondes sur la mesure nous a permis d’évaluer pour la première fois ce biais, avec une incertitude record de 1.3µGal, soit trois fois meilleure que précédemment.Le gravimètre participe au projet de balance de Kibble du LNE qui visait à mesurer la constante de Planck par la pesée du kg et dans lequel une mesure exacte de g est nécessaire.Nous avons ainsi contribué à la révolution qu’a connue le système international d’unités, avec la décision de réviser le SI en fixant la valeur numérique de la constante de Planck et en modifiant la définition du kg, entrée en vigueur le 20 Mai 2019<br>This thesis aims to improve the accuracy of the Cold Atom Gravimeter from LNESYRTE.This gravimeter employs atom interferometry techniques to measure the local gravityacceleration g of free falling Rubidium 87 cold atoms. This gravimeter is the national metrologicalreference meaning that all its biases must be evaluated with the lowest uncertainties. At the beginningof this thesis, the total accuracy budget of 4.3μGal was dominated by the uncertainty onthe wavefront aberration bias which accounted for 4.0μGal. In order to improve the evaluation ofthis effect, we implemented an ultra-cold atom source, with which we performed g measurementsover a wide range of temperatures. The developpment of a complete model of the experiment anda simulation of the impact of the wavefronts on the g measurements allowed us to gain insightson the evaluation of this bias which uncertainty was thus improved by a factor three and is now1.3μGal. Finally the gravimeter participated in the Kibble balance project which goal was tolink the Planck constant to the kg unit. This project needed the determination and transfer ofthe absolute g value. We contributed to the revolution of the International System of Units : thePlanck constant is now fixed and the definition of the kg is modified. This new definition is noweffective since 20 May 2019

Today, the main research field for the automotive industry is to find solutions for active safety. In order to perceive the surrounding environment, tracking nearby traffic objects plays an important role. Validation of the tracking performance is often done in staged traffic scenarios, where additional sensors, mounted on the vehicles, are used to obtain their true positions and velocities. The difficulty of evaluating the tracking performance complicates its development. An alternative approach studied in this thesis, is to record sequences and use non-causal algorithms, such as smoothing, instead of filtering to estimate the true target states. With this method, validation data for online, causal, target tracking algorithms can be obtained for all traffic scenarios without the need of extra sensors. We investigate how non-causal algorithms affects the target tracking performance using multiple sensors and dynamic models of different complexity. This is done to evaluate real-time methods against estimates obtained from non-causal filtering. Two different measurement units, a monocular camera and a LIDAR sensor, and two dynamic models are evaluated and compared using both causal and non-causal methods. The system is tested in two single object scenarios where ground truth is available and in three multi object scenarios without ground truth. Results from the two single object scenarios shows that tracking using only a monocular camera performs poorly since it is unable to measure the distance to objects. Here, a complementary LIDAR sensor improves the tracking performance significantly. The dynamic models are shown to have a small impact on the tracking performance, while the non-causal application gives a distinct improvement when tracking objects at large distances. Since the sequence can be reversed, the non-causal estimates are propagated from more certain states when the target is closer to the ego vehicle. For multiple object tracking, we find that correct associations between measurements and tracks are crucial for improving the tracking performance with non-causal algorithms.

Interest in the variation of fundamental constants has recently been stimulated by claims that the fine structure constant, α, was smaller in the past. Physicists are investigating whether α is currently varying using a number of methods including atomic clock experiments and quasar absorption spectra. To date atomic clock experiments have not reached the same level of precision as the quasar results but the precision to which transition frequencies are being measured is increasing dramatically and very soon atomic clock experiments based on Earth will be able to rival or surpass the quasar results. In order to relate the change in transition frequencies to a variation of α accurate calculations of relativistic effects in atoms and their dependence upon α are needed. Other effects, such as the small shift of transition frequencies due to blackbody radiation also need to be accounted for. In this thesis we perform accurate calculations of the dependence of transition frequencies in two-valence-electron atoms and ions on a variation of α. The relativistic Hartree-Fock method is used with many-body perturbation theory and configuration interaction methods to calculate transition frequencies. We also consider transitions with an enhanced sensitivity to α variation. In particular, narrow lines that correspond to atomic transitions between close lying, long-lived atomic states of different configurations. The small transition frequency, coupled with differences in the electron structure ensures a strong enhancement of the relative frequency change compared to a possible change in α . We also show that using the modified form of the Dirac Hamiltonian, as suggested by Bekenstein, does not affect the analysis of the quasar data pertaining to a measurement of α variation, nor does it affect atomic clock experiments. Finally we have performed calculations of the size of the frequency shift induced by a static electric field on the clock transition frequencies of the hyperfine splitting in Y b+, Rb, Cs, Ba+, and Hg+. The calculations are used to find the frequency shifts due to blackbody radiation which are needed for accurate frequency measurements and improvements of the limits on variation of α. Our result for Cs [??v/=E2 = -2:26(2) x 10-10Hz/(V/m)2] is in good agreement with early measurements and ab initio calculations. We present arguments against recent claims that the actual value might be smaller. The difference (~ 10%) is due to the continuum spectrum in the sum over intermediate states.

The consistency of fundamental constants is assumed in the Standard Model. However, new physics theories allow them to be dynamical. Different tests can be made at various epochs of the universe. In particular, current bounds at the time of emission of the Cosmic Microwave Background (CMB) permit variations up to 1% of their present values. A change of this order can produce an accumulation of tritium which would later decay and modify the ionization history of the Universe by up to O(0.1%). This Tritium Decay Scenario (TDS) can modify the CMB to an observable level and thus provides a new probe of Varying Fundamental Constants (VFC). We analyze the WMAP 7-year and SPT data with respect to the TDS and find no evidence for VFC. The data disfavors a portion of the parameter space at 95% Confidence Level (CL). We forecast the sensitivity of Planck to the TDS and find that a larger range of parameters can be excluded at 3σ CL.<br>Graduate

El Modelo Estándar y la Relatividad General son las teorías que explican, con gran éxito, los fenómenos físicos a bajas energías. Las ecuaciones de dichas teorías involucran ciertos parámetros que tienen la particularidad de permanecer invariantes en el espacio-tiempo. Son las llamadas constantes fundamentales. Desde la hipótesis de Dirac en 1937, según la cual, las constantes fundamentales son simples funciones de la edad del Universo; la variación temporal y espacial de dichas constantes ha sido objeto de numerosos trabajos de investigación. El interés teórico en este tema proviene del hecho de que varias de las teorías que intentan unificar las cuatro interacciones fundamentales de la Física tienen diferentes predicciones para la variación de estos parámetros. Los datos observacionales y experimentales cumplen un rol muy importante ya que nos permiten testear la validez de estas teorías al establecer límites sobre la variación de las constantes fundamentales. La investigación experimental comprende desde mediciones en laboratorio hasta datos de origen cosmológico. La mayoría de los resultados obtenidos son consistentes con una variación nula de las constantes fundamentales. En los últimos años, Webb y colaboradores propusieron el denominado método de los muchos multipletes para analizar observaciones de quásares de alto corrimiento al rojo, obteniendo como resultado una variación no nula de la constante de estructura fina α. Para poder explicar los datos obtenidos propusieron una variación espacial de α de tipo dipolar. De ser cierta esta variación, debería tener consecuencias en las luminosidades medidas de las Supernovas Tipo Ia (SNIa). Esto se debe a que la luminosidad máxima alcanzada en la explosión depende de α a través de la opacidad de la atmósfera en expansión y de la energía liberada. La importancia de las SNIa radica en que pueden ser utilizadas como candelas estándar debido a su notable homogeneidad. En este trabajo se utilizan las distancias luminosas de Supernovas tipo Ia (SNIa) con el fin de testear el modelo fenomenológico dipolar propuesto por Webb y colaboradores. Para ello, se realiza un análisis estadístico con el objetivo de contrastar los valores observacionales de las distancias luminosas con las predicciones teóricas del modelo dipolar. Éstas se calculan introduciendo una modificación debida a la posible variación de α. Por otro lado, se utilizan estos mismos datos para realizar un análisis estadístico obteniendo nuevos parámetros para el modelo dipolar, verificando luego su consistencia con aquellos obtenidos a partir de las observaciones de quásares. Los resultados indican que los datos de SNIa actuales no permiten distinguir entre un modelo con variación de espacial de α de tipo dipolar y el Modelo Estándar donde α no varía. También se concluye la inconsistencia entre los parámetros de dipolo obtenidos a partir de las observaciones de SNIa con los que se obtuvieron a partir de las observaciones de quásares. Por último, se realiza una primera estimación para una posible variación espacial de tipo dipolar, tanto de la velocidad de la luz c como de β = h*c, con h la constante de Planck reducida; añadiendo además en estos casos la dependencia de la masa de Chandrasekhar con dichas constantes.<br>The large-number hypothesis conjectures that fundamental constants may vary. Accordingly, the space-time variation of fundamental constants has been an active subject of research for decades. Recently, using data obtained with large telescopes a phenomenological model in which the fine structure constant might vary spatially has been proposed. In this work, we test whether this hypothetical spatial variation of , which follows a dipole law, is compatible with the data of distant thermonuclear type Ia supernovae. Unlike previous works, in our calculations we consider not only the variation of the luminosity distance when a varying is adopted, but we also take into account the variation of the peak luminosity of Type Ia supernovae resulting from a variation of . We find that there is no significant difference between the several phenomenological models studied here and the standard one, in which does not vary spatially. We conclude that the present set of data of Type Ia supernovae is not able to distinguish the standard model from the dipole models, and thus cannot be used to discard nor to confirm the proposed spatial variation of . Also, we carry out a first estimation of the possible spatial variation of speed of light c and = ¯hc, where ¯h is the reduced Planck constant.

O setor dos transportes representa uma forma de ligação entre estados. Este satisfaz as necessidades globais ao permitir a movimentação de pessoas e bens. Sendo essencial para o desenvolvimento económico, encontra-se muitas vezes associado ao comércio mundial, representando uma ferramenta essencial e estratégica para a evolução das nações. Contudo, os custos de transporte são variáveis com poder influenciador sobre valor das mercadorias transacionadas. Sendo este um risco constante, torna-se importante gerir corretamente a sua variação e saber agir com base nos acontecimentos. Focando a variação do preço dos combustíveis e o sector de transporte de mercadorias a atuar em Portugal, procurou-se saber se as empresas em causa possuem um modelo de gestão de riscos e se têm mecanismos de defesa face às oscilações do preço do petróleo e seus derivados. Com o objetivo de compreender como são geridas as empresas de transportes de mercadorias a operar em Portugal, foi elaborado um questionário que permitiu recolher informação necessária para apurar conclusões relevantes. Com as empresas da amostra classificadas de micro a grandes empresas, sediadas em Portugal continental e nas ilhas, um dos focos do estudo foi transmitir informação credível e fundamentada. No questionário são abordados assuntos como a existência, ou não, de um modelo de gestão de riscos, qual a expectativa de evolução dos riscos do negócio e quais são as ferramentas usadas na atenuação dos riscos face à variação do preço dos combustíveis. Os resultados revelam que a maioria das empresas possui mecanismos de defesa face às oscilações do preço do petróleo, todavia resta saber se estas estão a retirar o máximo proveito dos procedimentos usados ou se, por outro lado, estes não estão a ser usados da forma correta.