Le comportement d’un fluide confiné dans un milieu poreux peu perméable (micro- and méso-pores) a été étudié en ce qui concerne ses propriétés de diffusion de masse, de conductivité thermique et de thermodiffusion. Pour ce faire des simulations de dynamique moléculaire hors équilibre ont été réalisées sur des mélanges binaires modèles placés dans des conditions thermodynamiques diverses, confinés dans des milieux poreux de géométrie lamellaire de différentes natures (lisse ou atomique, plus ou moins adsorbant) en utilisant l’ensemble __//_ et l’ensemble grand canonique. Les résultats ont montré que les effets du milieu poreux sur les propriétés de transport sont d’autant plus marqués que lataille de pore est petite, que l’adsorption est forte et que la température est basse. Les résultats ont permis d’évaluer quantitativement ces effets. Il a aussi été montré que la rugosité des murs a un impact très important sur le coefficient de diffusion de masse et non négligeable sur celui de thermodiffusion. / The aim of this work was to study how a fluid confined in a low permeability porous medium (micro- and meso-porous) behaves concerning its properties of mass diffusion, thermal conductivity and thermal diffusion. For this purpose, non-equilibrium molecular dynamics simulations have been performed on simple binary mixtures placed in various thermodynamic conditions, confined in a porous medium of lamellar geometry of different types (structure-less or atomistic, more or less adsorbent) in __//_ and grand canonical ensembles. The results show that the effects of porous medium on transport properties are more pronounced when the pore size is small, the adsorption is strong and the temperature is low. The results allowed to evaluate these effects quantitatively. In addition, it has been found that the wall roughness has a major impact on the mass diffusion coefficient and a non negligible one on the thermal diffusion coefficient.

Single self-assembled semiconductor quantum dots (QDs) are able to emit single-photons and entangled-photons pairs. They are therefore considered as potential candidate building blocks for quantum information processing (QIP) and communication. To exploit them fully, the ability to precisely control their optical properties is needed due to several reasons. For example, the stochastic nature of their growth ends up with only little probability of finding any two or more QDs emitting indistinguishable photons. These are required for two-photon quantum interference (partial Bell-state measurement), which lies at the heart of linear optics QIP. Also, most of the as-grown QDs do not fulfil the symmetries required for generation of entangled-photon pairs. Additionally, tuning is required to establish completely new systems, for example, 87Rb atomic-vapors based hybrid semiconductoratomic (HSA) interface or QDs with significant heavy-hole (HH)-light-hole (LH) mixings. The former paves a way towards quantum memories and the latter makes the optical control of hole spins much easier required for spin- based QIP. This work focuses on the optical properties of a new type of QDs optimized for HSA experiments and their broadband tuning using strain. It was created by integrating the membranes, containing QDs, onto relaxor-ferroelectric actuators and was quantified with a spatial resolution of ~1 µm by combining measurements of the µ-photoluminescence of the regions surrounding the QDs and dedicated modeling. The emission of a neutral exciton confined in a QD usually consists of two fine-structure-split lines which are linearly polarized along orthogonal directions. In our QDs we tune the emission energies as large as ~23meV and the fine-structure-splitting by more than 90 µeV. For the first time, we demonstrate that strain is able to tune the angle between the polarization direction of these two lines up to 40° due to increased strain-induced HH-LH mixings up to ~55%. Compared to other quantum emitters, QDs can be easily integrated into optoelectronic devices, which enable, for example, the generation of non-classical light under electrical injection. A novel method to create sub-micrometer sized current-channels to efficiently feed charge carriers into single QDs is presented in this thesis. It is based on focused-laserbeam assisted thermal diffusion of manganese interstitial ions from the top GaMnAs layer into the underlying layer of resonant tunneling diode structures. The combination of the two methods investigated in this thesis may lead to new QDbased devices, where direct laser writing is employed to preselect QDs by creating localized current-channels and strain is used to fine tune their optical properties to match the demanding requirements imposed by QIP concepts.

Single self-assembled semiconductor quantum dots (QDs) are able to emit single-photons and entangled-photons pairs. They are therefore considered as potential candidate building blocks for quantum information processing (QIP) and communication. To exploit them fully, the ability to precisely control their optical properties is needed due to several reasons. For example, the stochastic nature of their growth ends up with only little probability of finding any two or more QDs emitting indistinguishable photons. These are required for two-photon quantum interference (partial Bell-state measurement), which lies at the heart of linear optics QIP. Also, most of the as-grown QDs do not fulfil the symmetries required for generation of entangled-photon pairs. Additionally, tuning is required to establish completely new systems, for example, 87Rb atomic-vapors based hybrid semiconductoratomic (HSA) interface or QDs with significant heavy-hole (HH)-light-hole (LH) mixings. The former paves a way towards quantum memories and the latter makes the optical control of hole spins much easier required for spin- based QIP. This work focuses on the optical properties of a new type of QDs optimized for HSA experiments and their broadband tuning using strain. It was created by integrating the membranes, containing QDs, onto relaxor-ferroelectric actuators and was quantified with a spatial resolution of ~1 µm by combining measurements of the µ-photoluminescence of the regions surrounding the QDs and dedicated modeling. The emission of a neutral exciton confined in a QD usually consists of two fine-structure-split lines which are linearly polarized along orthogonal directions. In our QDs we tune the emission energies as large as ~23meV and the fine-structure-splitting by more than 90 µeV. For the first time, we demonstrate that strain is able to tune the angle between the polarization direction of these two lines up to 40° due to increased strain-induced HH-LH mixings up to ~55%. Compared to other quantum emitters, QDs can be easily integrated into optoelectronic devices, which enable, for example, the generation of non-classical light under electrical injection. A novel method to create sub-micrometer sized current-channels to efficiently feed charge carriers into single QDs is presented in this thesis. It is based on focused-laserbeam assisted thermal diffusion of manganese interstitial ions from the top GaMnAs layer into the underlying layer of resonant tunneling diode structures. The combination of the two methods investigated in this thesis may lead to new QDbased devices, where direct laser writing is employed to preselect QDs by creating localized current-channels and strain is used to fine tune their optical properties to match the demanding requirements imposed by QIP concepts.

<p> The existence of significant and consistent fractionation of sulfur isotopes in natural coexisting sulfide mineral pairs is demonstrated. Such fractionations are shown to depend exclusively on the mineralogy of the assemblage and temperature of equilibration, consistent with a process of fractionation during equilibrium exchange of sulfur isotopes between the sulfide phases . The fractionation of sulfur isotopes between galena, sphalerite and pyrite has been determined experimentally over the temperature range 300-725°C . The fractionation for each mineral pair is shown to vary as T^(-2) so that three isotope geothermometer s have been calibrated. Experi mental results are applied to natural sulfide assemblages to determine the temperature of equilibration and extent to which isotopic equilibriurn has b een attained. </p> / Thesis / Doctor of Philosophy (PhD)

Ces travaux de thèse visent à étudier les transferts couplés de chaleur, de masse et d’air au sein des matériaux poreux. Sur le volet de la modélisation, il s’agit de prédire le comportement hygrothermique de ces matériaux, à l’aide d’un modèle macroscopique, qui intègre à la fois l’effet du phénomène de thermodiffusion et celui de la pression totale de l’air s’exerçant sur les parois du bâtiment. Ce modèle, dont les paramètres d’entrée sont évalués expérimentalement, utilise des moteurs de transfert continus, d’où la possibilité de traiter des problèmes de transferts dans les matériaux multicouches. Il présente aussi l’avantage d’admettre, dans certaines configurations, des solutions analytiques d’où la possibilité d’entreprendre des comparaisons avec des solutions numériques. De plus, une justification formelle des équations de bilan de ce modèle a été abordée, moyennant l’utilisation d’une approche à changement d’échelle « micro-macro ». Il s’agit d’affiner la modélisation des transferts hydriques du comportement macroscopique, en utilisant des informations issues de la microstructure. Le passage de l’échelle microscopique à l’échelle macroscopique a été réalisé à l’aide de la méthode d’homogénéisation par prise de moyenne. Une des difficultés de l’utilisation de ce modèle réside dans l’identification des nombreux paramètres caractérisant les propriétés hygrothermiques des matériaux. Une partie du travail a été consacrée à l’évaluation des principales propriétés intrinsèques des matériaux moyennant l’élaboration de différents prototypes expérimentaux au laboratoire. Par ailleurs, une approche expérimentale dédiée à l’évaluation du processus de la thermodiffusion dans les matériaux poreux a été entreprise. Pour cela, une expérimentation relative à la détermination de l’effet du gradient de température et de la dynamique du processus d’échange d’eau à l’intérieur des parois a été mise en place au laboratoire. L’utilisation de la plateforme expérimentale MegaCup du Technical University of Denmark a permis de collecter des données relatives à la sensibilité de l’effet de la thermodiffusion sur les transferts couplés de chaleur, d’air et d’humidité. Une comparaison des résultats expérimentaux et numériques a ensuite été effectuée. Peu d’écarts ont été relevés. Aussi, une investigation expérimentale portant sur la contribution des infiltrations massiques sur les transferts hydriques dans les matériaux de construction a été réalisée. Moyennant le développement d’un banc d’essai, une caractérisation expérimentale du coefficient d’infiltration d’humidité a été entreprise. Ce dernier est utilisé comme paramètre d’entrée des modèles de simulation numérique. / The purpose of this thesis is to study coupled heat air and moisture transfer in porous building materials. Concerning the modeling part, the interest is to predict the hygrothermal behavior, with a macroscopic model, that incorporates simultaneously the effect of thermodiffusion phenomenon and that of total pressure on the building walls. The input parameters are evaluated experimentally using continuous driving potentials, where the ability to deal with problems of transfer in multilayer materials. In some configurations, it presents the advantage to undertake analytical solution that can be confronted with numerical solutions. Furthermore, a formal justification of balance equations of the developed model was addressed through the use of ascaling approach. Then, the modeling of macroscopic moisture transfer behavior, by implementing information from the microstructure can be refined. The transition of the microscopic to macroscopic scale was performed using the mean field homogenization. One of the difficulties with the use of this model lies in the identification of many parameters characterizing the hygrothermal properties of materials. Therefore, a part of the present work was devoted to the evaluation of the main properties of materials through the development of various experimental prototypes in the laboratory. More over, an experimental approach dedicated to the evaluation of the thermodiffusion process in porous materials has been undertaken. In this way, an experimentation concerning the determination of the temperature gradient and dynamics of water exchange process inside walls has been established. Furthermore, the use of the experimental platform MegaCup at theTechnical University of Denmark has collected data on the sensitivity of the thermodiffusion effect. Subsequently, a comparison of the experimental and the numerical results was performed. Few differences were observed. Otherwise, an experimental investigation on the contribution of the mass infiltration of water transfers in building materials was performed. A characterization of the moisture infiltration coefficient was performed through the development of the experimental test. This coefficient was used as an input parameter in the simulation models.

Diese Arbeit stützt sich auf die theoretische und experimentelle Untersuchung der Thermodiffusion im Magnetfeld. Bei magnetischen Flüssigkeiten als kolloidalen Suspensionen versteht man unter der Thermodiffusion einen durch einen Temperaturgradienten angestoßenen unidirektionalen Partikeltransport, der zur Separation des Fluids führt. Beschrieben wird die Thermodiffusion theoretisch über das Konzentrationsprofil der Partikel in Abhängigkeit von Zeit und Ort in einer Fluidschicht. Die Experimente detektieren die Separation des Fluids über die Konzentrationsdifferenz zwischen zwei Fluidkammern. Die Bestimmung des Soret-Koeffizienten erfolgt über einen Datenfit zwischen experimentellen und theoretischen Daten. Für das kerosinbasierte Ferrofluid EMG905 wurden zwei Effekte festgestellt. Bei kleinen Magnetfeldstärken wandern die Partikel zum kalten Rand der Schicht (ST>0), bei steigenden Feldstärken kehrt sich diese Richtung um (ST<0). Die Ergebnisse der Untersuchungen zur Thermodiffusion gehen dann in eine lineare Stabilitätsanalyse einer Ferrofluidschicht bei anliegendem Temperaturgradienten und Magnetfeld ein. Dabei wird festgestellt, dass die kritische Rayleigh-Zahl als charakteristische Größe zum Einsetzen von Konvektion von dem Soret-Koeffizienten abhängt. Ist letzterer positiv, wird das Einsetzen von Konvektion begünstigt, ist er wiederum negativ, so kann Konvektion vollständig unterdrückt werden.

Diese Arbeit stützt sich auf die theoretische und experimentelle Untersuchung der Thermodiffusion im Magnetfeld. Bei magnetischen Flüssigkeiten als kolloidalen Suspensionen versteht man unter der Thermodiffusion einen durch einen Temperaturgradienten angestoßenen unidirektionalen Partikeltransport, der zur Separation des Fluids führt. Beschrieben wird die Thermodiffusion theoretisch über das Konzentrationsprofil der Partikel in Abhängigkeit von Zeit und Ort in einer Fluidschicht. Die Experimente detektieren die Separation des Fluids über die Konzentrationsdifferenz zwischen zwei Fluidkammern. Die Bestimmung des Soret-Koeffizienten erfolgt über einen Datenfit zwischen experimentellen und theoretischen Daten. Für das kerosinbasierte Ferrofluid EMG905 wurden zwei Effekte festgestellt. Bei kleinen Magnetfeldstärken wandern die Partikel zum kalten Rand der Schicht (ST>0), bei steigenden Feldstärken kehrt sich diese Richtung um (ST<0). Die Ergebnisse der Untersuchungen zur Thermodiffusion gehen dann in eine lineare Stabilitätsanalyse einer Ferrofluidschicht bei anliegendem Temperaturgradienten und Magnetfeld ein. Dabei wird festgestellt, dass die kritische Rayleigh-Zahl als charakteristische Größe zum Einsetzen von Konvektion von dem Soret-Koeffizienten abhängt. Ist letzterer positiv, wird das Einsetzen von Konvektion begünstigt, ist er wiederum negativ, so kann Konvektion vollständig unterdrückt werden.