No description available.

Advances in nanofabrication have bolstered the development of new optical devices with potential uses ranging from conventional optoelectronics, such as lasers and solar cells, to novel devices, like single photon or entangled photon sources. Quantum encryption of optical communications, in particular, requires devices that couple efficiently to an optical fiber and emit, on demand, indistinguishable photons. With these goals in mind, ultrafast spectroscopy is used to study the electron dynamics in epitaxially grown InAs/GaAs quantum dots (QDs). Quantifying the behavior of these systems is critical to the development of more efficient devices. Studies of two newly developed InGaAs QD structures, quantum dot clusters (QDCs) and QDs embedded in photonic wires, are presented herein. GaAs photonic wires with diameters in the range of 200 to 250 nm support only the fundamental HE11 guided mode. To fully quantify these new systems, the emission dynamics of QDs contained within wires in a large range of diameters are studied. Time correlated single photon counting measurements of the ground state exciton lifetimes are in very good agreement with predicted theoretical values for the spontaneous emission rates. For diameters smaller than 200 nm, QD emission into the HE11 mode is strongly inhibited and non-radiative processes dominate the decay rate. The best small diameter wires exhibit inhibition factors as high as 16, on par with the current state of the art for photonic crystals. The QDCs are the product of a hybrid growth technique that combines droplet heteroepitaxy with standard Stranski-Krastanov growth to create many different geometries of QDs. The work presented in this dissertation concentrates specifically on hexa-QDCs consisting of six InAs QDs around a GaAs nanomound. The first ever spectral and temporal properties of QDs within individual hexa-QDCs are presented. The QDs exhibit narrow exciton resonances with good temperature stability, indicating that excitons are well confined within individual QDs. A distinct biexponential decay is observed even at the single QD level. This behavior suggests that non-radiative decay mechanisms and exciton occupation of dark states play a significant role in the recombination dynamics in the QDCs. / text

No description available.

L’étude des propriétés plasmoniques est un champ de recherche actuellement très actif. En particulier, la possibilité de manipuler la lumière à des échelles sub-longueur d’ondes rend ce domaine très attractif. Récemment, plusieurs études ont montré que les plasmons collectifs dans des méta-matériaux bi-dimensionnels constitués de nanoparticules métalliques se comportaient de manière similaire aux électrons dans les cristaux et partageaient certaines de leurs propriétés. Dans ce manuscrit, nous présentons une théorie unifiée permettant de décrire les propriétés de tels modes plasmoniques dans des réseaux ordonnés de géométrie arbitraires constitués de nanoparticules métalliques couplées en champ proche. En particulier, nous évaluons les taux de décroissance de ces modes ainsi que leurs décalages en fréquence afin de prédire leur observabilité expérimentale. / The study of plasmonic properties is one of the fields of research currently very active. In particular, the ability to manipulate light at subwavelength scales makes this subject very appealing. Recently, several studies have shown that collective plasmons in two-dimensional meta-materials based on metallic nanoparticles behave similarly to electrons in crystals and share some of their properties. In this manuscript, we present a unified theory for describing the properties of such modes in regular arrays of arbitrary geometries constituted by near-field coupled spherical nanoparticles. In particular, we have evaluated the linewidths of these modes as well as their frequency shifts in order to discussed their experimental observabilities.

Este trabalho é dedicado ao estudo de propriedades teóricas dos operadores integrais positivos em \'L POT. 2\' (X; u), quando X é um espaço topológico localmente compacto ou primeiro enumerável e u é uma medida estritamente positiva. Damos ênfase à análise de propriedades espectrais relacionadas com extensões do Teorema de Mercer e ao estudo dos espaços de Hilbert de reprodução relacionados. Como aplicação, estudamos o decaimento dos autovalores destes operadores, em um contexto especial. Finalizamos o trabalho com a análise de propriedades de suavidade das funções do espaço de Hilbert de reprodução, quando X é um subconjunto do espaço euclidiano usual e u é a medida de Lebesgue usual de X / In this work we study theoretical properties of positive integral operators on \'L POT. 2\'(X; u), in the case when X is a topological space, either locally compact or first countable, and u is a strictly positive measure. The analysis is directed to spectral properties of the operator which are related to some extensions of Mercer\'s Theorem and to the study of the reproducing kernel Hilbert spaces involved. As applications, we deduce decay rates for the eigenvalues of the operators in a special but relevant case. We also consider smoothness properties for functions in the reproducing kernel Hilbert spaces when X is a subset of the Euclidean space and u is the Lebesgue measure of the space

Neste trabalho obtemos taxas de decaimento para autovalores e valores singulares de operadores integrais gerados por núcleos de quadrado integrável sobre a esfera unitária em \'R POT. m+1\', m 2, sob hipóteses sobre ambos, certas derivadas do núcleo e o operador integral gerado por tais derivadas. Este tipo de problema é comum na literatura, mas as hipóteses geralmente são definidas via diferenciação usual em \'R POT m+1\'. Aqui, as hipóteses são todas definidas via derivada de Laplace-Beltrami, um conceito genuinamente esférico investigado primeiramente por W. Rudin no começo dos anos 50. As taxas de decaimento apresentadas são ótimas e dependem da dimensão m e da ordem de diferenciabilidade usada para definir as condições de suavidade / In this work we obtain decay rates for singular values and eigenvalues of integral operators generated by square integrable kernels on the unit sphere in \'R m+1\', m 2, under assumptions on both, certain derivatives of the kernel and the integral operators generated by such derivatives. This type of problem is common in the literature but the assumptions are usually defined via standard differentiation in \'R POT. m+1\'. Here, the assumptions are all defined via the Laplace-Beltrami derivative, a concept first investigated by W. Rudin in the early fifties and genuinely spherical in nature. The rates we present are optimal and depend on both, the differentiability order used to define the smoothness conditions and the dimension m

Neste trabalho obtemos taxas de decaimento para autovalores e valores singulares de operadores integrais gerados por núcleos de quadrado integrável sobre a esfera unitária em \'R POT. m+1\', m 2, sob hipóteses sobre ambos, certas derivadas do núcleo e o operador integral gerado por tais derivadas. Este tipo de problema é comum na literatura, mas as hipóteses geralmente são definidas via diferenciação usual em \'R POT m+1\'. Aqui, as hipóteses são todas definidas via derivada de Laplace-Beltrami, um conceito genuinamente esférico investigado primeiramente por W. Rudin no começo dos anos 50. As taxas de decaimento apresentadas são ótimas e dependem da dimensão m e da ordem de diferenciabilidade usada para definir as condições de suavidade / In this work we obtain decay rates for singular values and eigenvalues of integral operators generated by square integrable kernels on the unit sphere in \'R m+1\', m 2, under assumptions on both, certain derivatives of the kernel and the integral operators generated by such derivatives. This type of problem is common in the literature but the assumptions are usually defined via standard differentiation in \'R POT. m+1\'. Here, the assumptions are all defined via the Laplace-Beltrami derivative, a concept first investigated by W. Rudin in the early fifties and genuinely spherical in nature. The rates we present are optimal and depend on both, the differentiability order used to define the smoothness conditions and the dimension m

Este trabalho é dedicado ao estudo de propriedades teóricas dos operadores integrais positivos em \'L POT. 2\' (X; u), quando X é um espaço topológico localmente compacto ou primeiro enumerável e u é uma medida estritamente positiva. Damos ênfase à análise de propriedades espectrais relacionadas com extensões do Teorema de Mercer e ao estudo dos espaços de Hilbert de reprodução relacionados. Como aplicação, estudamos o decaimento dos autovalores destes operadores, em um contexto especial. Finalizamos o trabalho com a análise de propriedades de suavidade das funções do espaço de Hilbert de reprodução, quando X é um subconjunto do espaço euclidiano usual e u é a medida de Lebesgue usual de X / In this work we study theoretical properties of positive integral operators on \'L POT. 2\'(X; u), in the case when X is a topological space, either locally compact or first countable, and u is a strictly positive measure. The analysis is directed to spectral properties of the operator which are related to some extensions of Mercer\'s Theorem and to the study of the reproducing kernel Hilbert spaces involved. As applications, we deduce decay rates for the eigenvalues of the operators in a special but relevant case. We also consider smoothness properties for functions in the reproducing kernel Hilbert spaces when X is a subset of the Euclidean space and u is the Lebesgue measure of the space

The first aim of this thesis is to perform relativistic calculation of atomic and ionic polarizabilities and two-photon decay rates. Hydrogenic systems are treated by the Lagrange-mesh method. The extension to alkali-like systems is realized by means of a semiempirical-core-potential approach combined with the Lagrange-mesh method. The studied systems are partitioned into frozen-core electrons and an active valence electron. The core orbitals are defined by a Dirac-Hartree-Fock (DHF) calculation using the GRASP2K package. The valence electron is described by a Dirac-like Hamiltonian involving a core-polarization potential to simulate the core-valence electron correlation. Polarizabilities appear in a large number of fields and applications, namely in cold atoms physics, metrology and chemical physics. Two-photon transitions are part of a priori highly unlikely processes and are therefore called forbidden radiative processes. Experimental situations report decays from metastable excited states through these channels. Long lifetimes were measured for highly charged Be-like ions in recent storage-ring experiments, but their interpretation is problematic. The study of the competition between forbidden (one-photon beyond the dipole approximation, or multi-photon) and unexpected (hyperfine-induced or induced by external magnetic fields) radiative processes is all obviously relevant. The second aim of this thesis is to perform relativistic ab initio calculations of electronic isotope-shift (IS) factors by using the multiconfiguration DHF (MCDHF) method implemented in the RIS3/GRASP2K and RATIP program packages. Using the MCDHF method, two different approaches are adopted for the computation of electronic IS factors for a set of transitions between low-lying levels of neutral systems. The first one is based on the estimate of the expectation values of the one- and two-body nuclear recoil Hamiltonian for a given isotope, including relativistic corrections derived by Shabaev, combined with the calculation of the total electron densities at the origin. In the second approach, the relevant electronic factors are extracted from the calculated transition shifts for given triads of isotopes. These electronic quantities together with observed ISs between different pairs of isotopes provide the changes in mean-square charge radii of the atomic nuclei. Within this computational approach for the estimation of the mass- and field-shift factors, different models for electron correlation are explored in a systematic way to determine a reliable computational strategy, and to estimate theoretical error bars of the IS factors. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Au cours d’une réponse immunitaire primaire, les lymphocytes T CD8 mémoires émergent à partir d'un environnement de forte activation immunitaire. Les cellules régulatrices T CD4 FoxP3+ (LTregs) jouent un rôle clé de suppression de la réponse immunitaire. Nous montrons que les LTregs sont nécessaires pour la génération d’une réponse mémoire T CD8 fonctionnelle. En absence de LTregs lors du priming, les LT CD8 mémoires générées prolifèrent faiblement et ne parviennent pas à se différencier après une réactivation antigénique en effecteurs cytotoxiques secondaires fonctionnelles. Nous suggérons que les LTregs agissent tôt, lors de la phase d'expansion des LT CD8, en réduisant l’exposition des précurseurs mémoires T CD8 à l'interleukine-2. Ce nouveau rôle crucial des LTregs a des implications pour le développement optimal de vaccin.Chez les patients sous traitement antirétroviral efficace et prolongée (ART), le VIH peut persister dans un petit pool de cellules T CD4 mémoires quiescentes de longue durée de vie infectées par du virus latent intégré. Ce réservoir latent comprend différentes sous-populations mémoires. Nos résultats suggèrent une contraction progressive de la taille du réservoir latent autour d'un noyau formé de sous-populations T CD4 mémoires moins différenciées (centrales mémoires TCM et souches mémoires TSCM). Ce processus très lent semble dépendre de la taille initiale et du taux de décroissance qui diffère entre les sous-populations mémoires infectées de manière latente. Nos résultats suggèrent également une extrême stabilité du sous-réservoir TSCM, dont la taille est directement liée à l'exposition cumulée au virus plasmatique avant le début du traitement ART, soulignant l'importance d'une initiation précoce du traitement antirétroviral efficace. La présence de cette dynamique intrinsèque dans le réservoir latent peut avoir des implications pour la conception de stratégies optimales de purge thérapeutique contre le VIH. / During the primary immune response, CD8 memory emerges from an environment of strong immune activation. The FoxP3 regulatory CD4 T-cell subset (Treg) is known as a key suppressive component of the immune system. We report that Tregs are required for the generation of functional CD8 memory. In the absence of Tregs during priming, the resulting memory cells proliferate poorly and fail to differentiate into functional cytotoxic secondary effectors following antigen reactivation. We find that the Tregs act early, during the expansion phase of primary CD8 effectors, by fine tuning interleukin-2 exposure of CD8 memory precursors. This crucial new role of Tregs has implications for optimal vaccine development. In patients who are receiving prolonged antiretroviral treatment (ART), HIV can persist within a small pool of long-lived resting memory CD4 T cells infected with integrated latent virus. This latent reservoir involves distinct memory subsets. We provide results that suggest a progressive reduction of the size of the blood latent reservoir around a core of less-differentiated memory subsets (central memory and stem cell-like memory).This process appears to be driven by the differences in initial sizes and decay rates between latently infected memory subsets. Our results also suggest an extreme stability of the TSCM sub-reservoir, the size of which is directly related to cumulative plasma virus exposure before the onset of ART, stressing the importance of early initiation of effective ART. The presence of these intrinsic dynamics within the latent reservoir may have implications for the design of optimal HIV therapeutic purging strategies.