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Gamma-ray bursts (GRBs) are one of the phenomena that still puzzle the astrophysi- cists. Due to their extreme luminosities, they are visible in cosmological distances. They could provide a tool for understanding the early Universe. This thesis focuses on the estimation of the total energy released by the GRBs, their luminosities and how these quantities depend on the redshift. For a sample of 28 long GRBs with known redshifts, a dependence of their total energies and luminosities on the redshift is found. The thesis further studied if this dependence is either an observational bias or a real astrophysical phenomenon. Firstly, proper use of k-correction revealed that it has lit- tle effect on the redshift dependence of these quantities. Secondly, a new approach has been proposed to investigate the redshift dependence of the luminosity function. Thirdly, selection effect has been found, when investigating the sample of bursts with known redshifts, implying a caution when combining data from different sources. All these efforts show that the observational bias can still explain the redshift dependence.

Le Large Area Telescope à bord du satellite Fermi, lancé le 11 juin 2008, est un télescope spatial observant l'univers des hautes énergies. L'instrument couvre l'intervalle en énergie de 20MeV à 300GeV avec une sensibilité nettement améliorée et la capacité de localiser des sources ponctuelles. Il détecte les photons ? par leur conversion en paire électron- positron, et mesure leur direction et leur énergie grâce à un trajectographe et un calorimètre. Cette thèse présente les courbes de lumières et les mesures spectrales résolues en phase des pulsars radio et gamma détectés par le LAT. La mesure des paramètres spectraux (flux, indice spectral, et énergie de coupure) dépend des fonctions de réponse de l'instrument (IRFs). Une méthode développée pour la validation en orbite de la surface efficace est présentée en utilisant le pulsar de Vela. Les efficacités des coupures entre les données du LAT et les données simulées sont comparées à chaque niveau de la rejection du fond. Les résultats de cette analyse sont propagés vers les IRFs pour évaluer les systématiques des mesures spectrales. La dernière partie de cette thèse présente les découvertes de nouveaux pulsars ? individuels tels que PSR J0205+6449, J2229+6114, et J1048-5832 à partir des données du LAT et des éphémérides radio et X. Des analyses temporelles et spectrales sont investies dans le but de contraindre les modèles d'émission gamma. Finalement, nous discutons les propriétés d'une large population de pulsars gamma détectés par le LAT, incluant les pulsars normaux et les pulsars milliseconde. / The Large Area Telescope (LAT) on Fermi, launched on 2008 June 11, is a space telescope to explore the high energy ?-ray universe. The instrument covers the energy range from 20MeV to 300GeV with greatly improved sensitivity and ability to localize ?-ray point sources. It detects ?-rays through conversion to electron-positron pairs and measurement of their direction in a tracker and their energy in a calorimeter. This thesis presents the ?-ray light curves and the phase-resolved spectral measurements of radio-loud gamma-ray pulsars detected by the LAT. The measurement of pulsar spectral parameters (i.e. integrated flux, spectral index, and energy cut-off) depends on the instrument response functions (IRFs). A method developed for the on-orbit validation of the effective area is presented using the Vela pulsar. The cut efficiencies between the real data and the simulated data are compared at each stage of the background rejection. The results are then propagated to the IRFs, allowing the systematic uncertainties of the spectral parameters to be estimated. The last part of this thesis presents the discoveries, using both the LAT observations and the radio and X ephemeredes, of new individual ?-ray pulsars such as PSR J0205+6449, and the Vela-like pulsars J2229+6114 and J1048-5832. Timing and spectral analysis are investigated in order to constrain the ?-ray emission model. In addition, we discuss the properties of a large population of ?-ray pulsars detected by the LAT, including normal pulsars, and millisecond pulsars.

Neste trabalho investigamos o tunelamento ressonante em estruturas de dupla barreira GaAs/(AlGa)As que foram fabricadas em mesas quadradas de tamanho lateral mesoscópico e macroscópico (&#8764 10&#956m &#215 10&#956m). Uma camada tipo &#948 com diferentes concentrações de Silício foi incorporada no centro do poço quântico. As características I(V) mostram algumas estruturas em posição de voltagem abaixo do pico de ressonância principal que são atribuídas a estados relacionados a impurezas. Tais estados localizados estão presentes no poço quântico com energias de ligação bem maiores do que um doador de Silício isolado. Estes estados de maior energia de ligação são atribuídos a pares de doadores distribuídos aleatoriamente. Em alguns dispositivos onde estados relacionados a impurezas podem ser identificados isoladamente na característica I(V), um efeito destacável pode ser observado. Um pica na característica I(V) aparece nas mais baixas temperaturas medidas (abaixo de 1K) quando o nível de Fermi no emissor se alinha com o estado localizado relacionado a impureza. Tal pico e atribuído a interação Coulombiana entre o elétron no sitio localizado e os elétrons no gás bidimensional (emissor). / We have investigated resonant tunneling in GaAs/(AlGa)As double barrier structures which have been fabricated into square mesoscopic and macroscopic size mesas (&#8764 10&#956m &#215 10&#956m) A &#948 layer with different concentrations of Silicon donors was incorporated at the centre of the quantum well. The I(V) characteristics show some features below the threshold for the main resonance that are due to impurity related state. Such localized states are found to be related to the presence of donor impurities in the vicinity of the quantum well with binding energies much higher than the single isolated hydrogen donor. These higher binding energy states are identified as being due to random pairs of shallow donors. In some devices where an isolated impurity related state can be identified in the 1(V characteristics a remarkable effect is observed. A peak appears at low temperatures (below 1K) in the 1(V) characteristics when the emitter Fermi level matches the localized state. Such feature is attributed to the Coulomb interaction between the electron on the localized site and the electrons in the Fermi sea of the 2DEG.

Investigaremos algumas propriedades dinâmicas e de transporte para um conjunto de partículas clássicas não interagentes em diversos sistemas físicos. Os sistemas descritos aqui, em sua maioria, apresentam estrutura mista no espaço de fase no sentido de que curvas invariantes do tipo spanning, mares de caos e ilhas periódicas estão presentes. A descrição de cada sistema será feita utilizando mapeamentos discretos não lineares. Detalharemos a forma de obter os mapeamentos assim como discutiremos algumas de suas propriedades dinâmicas. Expoentes de Lyapunov serão utilizados para caracterizar a região de caos nos sistemas. Hipóteses de escala são usadas para provar que certos observáveis, por exemplo a energia média ao longo de mares de caos, são invariantes de escala. Consideraremos também que quando uma partícula, ou de forma equivalente um conjunto delas atinge uma determinada altura no espaço de fases, ela pode escapar. Ao estudar o escape de partículas, vemos que o histograma do número de partículas que atingem uma certa altura (ou energia) h no espaço de fases em uma dada iterada n, ao qual observamos ser invariante de escala, cresce rapidamente até atingir um máximo e então tende à zero para n grande. Quando a altura h varia proporcionalmente a posição da primeira curva invariante spanning, podemos confirmar uma invariância de escala do histograma de frequências. O mesmo ocorre para a probabilidade de sobrevivência da partícula à dinâmica. Neste contexto, abordaremos os seguintes problemas: (1) Um guia de ondas senoidalmente corrugado; (2) Uma família de mapas Hamiltonianos bidimensionais que recupera diversos modelos; (3) Partículas confinadas em uma caixa com potenciais infinitos nas bordas e contendo em seu interior um poço de potencial dependente periodicamente do tempo; (4) Analisaremos um bilhar ovóide com dependência temporal introduzida através de giro, onde para certas condições observamos que este não apresenta um aparente crescimento ilimitado de energia (aceleração de Fermi), desta forma sendo um possível contra-exemplo da conjectura LRA. Esta tese é um resumo de 8 artigos que foram publicados em revistas internacionais. / We investigate some dynamical and transport properties for a set of non-interacting classical particles. The systems here described, for the most part, present mixed structure in the phase space in the sense that invariant spanning curves, chaotic seas and periodic islands are present. The dynamics of each model is described by using non-linear mappings. We show all the details to construct the mappings and discuss some of their dynamical properties including fixed points stability among others. Lyapunov exponents will be obtained to characterize the chaotic dynamics observed in the phase space. Moreover some scaling hypotheses are used to prove that certain observables, including the average energy, are scaling invariant. We consider also that when a particle or an ensemble of them reach a certain portion of the phase space, they can escape. When studying the escape, we see that the histogram for the number of particles that reach certain height (or energy) h in the phase space for the iteration n, for which we observe to be scaling invariant, grows quickly until reaching a maximum and then goes towards zero for large enough n. When changing the height h proportionally to the position of the first invariant spanning curve, we can confirm the scaling invariance. The same happens for the survival probability for a particle in the chaotic dynamics. In this way, we will discuss the following problems: (1) A corrugated waveguide; (2) A family of two-dimensional Hamiltonian mappings which can reproduce different scaling exponents; (3) Particles confined to bounce in the interior of a time-dependent potential well; (4) We will analyse a rotating oval billiard, where for certain conditions we observed that this system does not present the unbounded energy growth (Fermi acceleration), in this way it is a possible counterexample of the LRA conjecture. This thesis is as summary of eight papers already published.

Thesis advisor: Kevin S. Bedell / Landau Fermi-liquid theory was first introduced by L. D. Landau in the effort of understanding the normal state of Fermi systems, where the application of the concept of elementary excitations to the Fermi systems has proved very fruitful in clarifying the physics of strongly correlated quantum systems at low temperatures. In this thesis, I use Landau Fermi-liquid theory to study the transport phenomena of two different correlated quantum liquids: the strongly interacting ultracold Fermi gases and the ferromagnet/normal metal (F/N) junctions. The detailed work is presented in chapter II and chapter III of this thesis, respectively. Chapter I holds the introductory part and the background knowledge of this thesis. In chapter II, I study the transport properties of a Fermi gas with strong attractive interactions close to the unitary limit. In particular, I compute the transport lifetimes of the Fermi gas due to superfluid fluctuations above the BCS transition temperature Tc. To calculate the transport lifetimes I need the scattering amplitudes. The scattering amplitudes are dominated by the superfluid fluctuations at temperatures just above Tc. The normal scattering amplitudes are calculated from the Landau parameters. These Landau parameters are obtained from the local version of the induced interaction model for computing Landau parameters. I also calculate the leading order finite temperature corrections to the various transport lifetimes. A calculation of the spin diffusion coefficient is presented in comparison to the experimental findings. Upon choosing a proper value of F0a, I am able to present a good match between the theoretical result and the experimental measurement, which indicates the presence of the superfluid fluctuations near Tc. Calculations of the viscosity, the viscosity/entropy ratio and the thermal conductivity are also shown in support of the appearance of the superfluid fluctuations. In chapter III, I study the spin transport in the low temperature regime (often referred to as the precession-dominated regime) between a ferromagnetic Fermi liquid (FFL) and a normal metal metallic Fermi liquid (NFL), also known as the (F/N) junction, which is considered as one of the most basic spintronic devices. In particular, I explore the propagation of spin waves and transport of magnetization through the interface of the F/N junction where nonequilibrium spin polarization is created on the normal metal side of the junction by electrical spin injection. I calculate the probable spin wave modes in the precession-dominated regime on both sides of the junction especially on the NFL side where the system is out of equilibrium. Proper boundary conditions at the interface are introduced to establish the transport of the spin properties through the F/N junction. A possible transmission conduction electron spin resonance (CESR) experiment is suggested on the F/N junction to see if the predicted spin wave modes could indeed propagate through the junction. Potential applications based on this novel spin transport feature of the F/N junction are proposed in the end. / Thesis (PhD) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Neste trabalho usamos a teoria de Thomas-Fermi para estudar as propriedades eletrônicas de semicondutores planarmente dopados, ou delta-dopados, com densidade de dopantes de moderada a alta. O principal objetivo do trabalho é a verificação de que esta teoria apresenta muito bons resultados com os do método auto-consistente na aproximação de Hartree quando aplicada a este tipo de problema. Verificamos que muitas situações físicas relacionadas a semicondutores delta-dopados podem ser descritas de uma maneira simples e com muito bons resultados. Estudamos o problema de um poço isolado e o problema da super-rede, comparando os resultados de Thomas-Fermi e Hartree. / In this work we have used the Thomas-Fermi theory to study the electronic properties of planar doped semiconductors, or delta-doping, with a moderate to high density of dopants. The main aim of this work is to verify that this theory gives very good results when compared with the self-consistent method in the Hartree aproximation. We have checked that many physical situations related to delta-doping can be described in a simple manner and also with very good results. We have studied the single delta problem and the superlattice problem and we have compared the Thomas-Fermi´s and Hartree´s results.

Le manuscrit présente des expériences réalisées avec des gaz quantiques de Chrome, un élément présentant un large spin électronique S=3 et des interactions dipolaires non négligeables. Nous avons produit un nouveau gaz quantique, une mer de Fermi avec l'isotope ⁵³Cr, en optimisant la co-évaporation avec l'isotope bosonique, contenant jusqu’à 1000 atomes a T=TF= 0.66± 0.08. Nous avons obtenu de nouveaux résultats sur la thermodynamique d'un condensat de Bose Einstein (CBE) avec degré de liberté de spin. En refroidissant rapidement un gaz thermique multi-composante, nous observons que la dynamique de condensation est affectée par les collisions d'échange de spin. Nous démontrons aussi un nouveau mécanisme de refroidissement, utilisant le degré de liberté de spin, lorsque le CBE est produit dans le niveau de spin de plus basse énergie. Les interactions dipolaires peuplent thermiquement les états de spin excités à bas champ magnétique, et une purification du CBE est obtenue en retirant sélectivement ces atomes. Enfin nous présentons des expériences de dynamique de spin. Dans une première expérience, cette dynamique est obtenue en utilisant un double puits avec des états de spin opposés. Ceci a permis une première mesure d'une des longueurs de diffusion du ⁵²Cr: ɑo = 13.5 ±¹⁵ ₁₀ aB. Nous présentons également des résultats préliminaires dans un piége harmonique et dans un réseau3D. La dynamique de spin est produite par rotation du spin des atomes. La comparaison avecla théorie nous permet de mettre en évidences l'apparition de corrélations quantiques. / This thesis presents experimental results performed with Quantum gases of Chromium atoms. The specificity of Chromium resides in its large electronic spin S=3 and non negligible dipole-dipole interaction (DDI) between atoms. We produced a new quantum gas, a Fermi sea of the ⁵³Cr isotope. Optimization of the co-evaporation with the ⁵²Cr bosonic isotope leads to 10³ atoms at T=TF= 0.66± 0.08. We obtained new results on thermodynamics of a spinor Bose gas. By "shock cooling" a thermal multi-spin component gas, we find that the dynamics of the BEC is affected by spin changing collisions. We also demonstrate a new cooling mechanism based on the spin degrees of freedom when the Bose Einstein condensate (BEC) is in the lowest energy spin state. Dipolar interactions thermally populate spin excited states at low magnetic field. Purication of the BEC is obtained by selectively removing these thermal atoms. Finally, we present spin dynamics experiments. spin following preparation of atoms in a double well trap in opposite stretch spin states allow to measure the last unknown scattering length of ⁵²Cr: ɑo = 13.5 ±¹⁵ ₁₀ ɑB (with ɑB the Bohr radius). We then present preliminary results performed in a 3D lattice and in the bulk, where spin excitation is performed by a spin rotation. We investigate for different experimental congurations which of a theory with or without quantum correlations ts best our data.

Investigaremos algumas propriedades dinâmicas e de transporte para um conjunto de partículas clássicas não interagentes em diversos sistemas físicos. Os sistemas descritos aqui, em sua maioria, apresentam estrutura mista no espaço de fase no sentido de que curvas invariantes do tipo spanning, mares de caos e ilhas periódicas estão presentes. A descrição de cada sistema será feita utilizando mapeamentos discretos não lineares. Detalharemos a forma de obter os mapeamentos assim como discutiremos algumas de suas propriedades dinâmicas. Expoentes de Lyapunov serão utilizados para caracterizar a região de caos nos sistemas. Hipóteses de escala são usadas para provar que certos observáveis, por exemplo a energia média ao longo de mares de caos, são invariantes de escala. Consideraremos também que quando uma partícula, ou de forma equivalente um conjunto delas atinge uma determinada altura no espaço de fases, ela pode escapar. Ao estudar o escape de partículas, vemos que o histograma do número de partículas que atingem uma certa altura (ou energia) h no espaço de fases em uma dada iterada n, ao qual observamos ser invariante de escala, cresce rapidamente até atingir um máximo e então tende à zero para n grande. Quando a altura h varia proporcionalmente a posição da primeira curva invariante spanning, podemos confirmar uma invariância de escala do histograma de frequências. O mesmo ocorre para a probabilidade de sobrevivência da partícula à dinâmica. Neste contexto, abordaremos os seguintes problemas: (1) Um guia de ondas senoidalmente corrugado; (2) Uma família de mapas Hamiltonianos bidimensionais que recupera diversos modelos; (3) Partículas confinadas em uma caixa com potenciais infinitos nas bordas e contendo em seu interior um poço de potencial dependente periodicamente do tempo; (4) Analisaremos um bilhar ovóide com dependência temporal introduzida através de giro, onde para certas condições observamos que este não apresenta um aparente crescimento ilimitado de energia (aceleração de Fermi), desta forma sendo um possível contra-exemplo da conjectura LRA. Esta tese é um resumo de 8 artigos que foram publicados em revistas internacionais. / We investigate some dynamical and transport properties for a set of non-interacting classical particles. The systems here described, for the most part, present mixed structure in the phase space in the sense that invariant spanning curves, chaotic seas and periodic islands are present. The dynamics of each model is described by using non-linear mappings. We show all the details to construct the mappings and discuss some of their dynamical properties including fixed points stability among others. Lyapunov exponents will be obtained to characterize the chaotic dynamics observed in the phase space. Moreover some scaling hypotheses are used to prove that certain observables, including the average energy, are scaling invariant. We consider also that when a particle or an ensemble of them reach a certain portion of the phase space, they can escape. When studying the escape, we see that the histogram for the number of particles that reach certain height (or energy) h in the phase space for the iteration n, for which we observe to be scaling invariant, grows quickly until reaching a maximum and then goes towards zero for large enough n. When changing the height h proportionally to the position of the first invariant spanning curve, we can confirm the scaling invariance. The same happens for the survival probability for a particle in the chaotic dynamics. In this way, we will discuss the following problems: (1) A corrugated waveguide; (2) A family of two-dimensional Hamiltonian mappings which can reproduce different scaling exponents; (3) Particles confined to bounce in the interior of a time-dependent potential well; (4) We will analyse a rotating oval billiard, where for certain conditions we observed that this system does not present the unbounded energy growth (Fermi acceleration), in this way it is a possible counterexample of the LRA conjecture. This thesis is as summary of eight papers already published.

In dieser Doktorarbeit wurde die elektronische Struktur von konventionellen und unkonventionellen Supraleitern untersucht. Das Ziel dieser Arbeit war es, die dHvA Parameter zu berechnen und mit experimentellen Daten zu vergleichen. Mit Hilfe des Bandstrukturprogrammes FPLO, welches auf der DFT basiert, untersuchten wir Diboride (MgB$_2$ und TaB$_2$) und schwere Fermionenverbindungen (CeMIn$_5$ und PuMGa$_5$, M=Co, Rh, und Ir) innerhalb der LSD-Näherung. / In this thesis theoretical study of the electronic structure of conventional and unconventional superconductor compounds was carried out. The goal was to calculate the dHvA parameters in comparison with available experimental data. By means of FPLO band structure code based on DFT within LSDA we investigated diborides (MgB$_2$ and TaB$_2$) and heavy fermion compounds (CeMIn$_5$ and PuMGa$_5$, M=Co, Rh, and Ir).