Cette étude porte sur la mesure de la température à l’échelle microscopique par voie optique dans la gamme UV-visible par comptage de photons à l’aide d’un PMT refroidi. À partir des avantages et des inconvénients de chaque technique existante, la première partie permet de comprendre les orientations de nos travaux. Le Second Chapitre montre et insiste sur l’intérêt de travailler aux courtes longueurs d’onde (limite de diffraction, précision sur la mesure...), d’utiliser la méthode multi-spectrale pour s’affranchir de paramètres inconnus (e.g. l’émissivité) en choisissant judicieusement les longueurs d’onde de travail, ainsi que les lois statistiques classiques pour mesurer le flux photonique sachant son émission aléatoire. Le Chapitre Trois présente le banc de mesure (microscope optique, système de mesure du flux photonique...) et une attention toute particulière est portée sur la conception des éléments chauffants servant à l’étalonnage. Le Quatrième Chapitre présente les résultats en températures obtenues à l’aide des lois statistiques. Ils valident le bon fonctionnement du dispositif, la mise au point de la zone microscopique, et l’intérêt de bien modéliser les filtres monochromatiques. Enfin, des améliorations sur la précision de la mesure (réseau de diffraction, analyseur multi-canal) et pour mesurer des températures plus faibles (LIF, méthode corrélation temporelle) sont présentées dans le Cinquième Chapitre / The aim of this study is to measure microscale temperature by optical way in the UV-visible range by photons counting using a cooled PMT. From the existing techniques advantages and disadvantages, this first part allows to understand the choices of this study. The second part shows and underlines the interest in working in short wavelengths (diffraction limit, measurement accuracy), in using the multi-spectral method to get rid of unknown parameters (e.g. emissivity) by choosing judicious working wavelengths, as well as the statistic laws to measure the photonic flux knowing its random emission. The third chapter presents the optical bench (optical microscope, photonic flux measurement facility…). A particularly attention is given to the design of the heated elements, which allow to calibrate the facility. The fourth part exposes the temperature results obtained through statistic laws. They validate the well-running of the facility, the microscopic area focusing, and the interest to model correctly the filters. Finally, measurement accuracy improvements (diffraction grating, multi-channel analyzer) and lower temperature measurement techniques (LIF, time-correlated method) are presented in the fifth part

No description available.

Les travaux réalisés dans le cadre de cette thèse de doctorat caractérisent de manière cohérente la physique des plasmas d'argon à la pression atmosphérique en présence d'espèces réactives. Ces travaux sont motivés par les lacunes manifestes de la compréhension des plasmas froids à la pression atmosphérique, celles-ci étant en grande partie dues au nombre restreint de techniques de diagnostic permettant de les caractériser. Dans ce contexte, des diagnostics optiques permettant l'obtention des propriétés fondamentales (température du gaz et des électrons, densité d'états excités) sont d'abord développés et validés tant pour les plasmas microonde que pour les décharges à barrière diélectriques d'argon à la pression atmosphérique. En particulier, une méthode couplant des mesures d'émission optique des transitions 2p-1s de l'argon à un modèle collisionnel-radiatif décrivant la population des niveaux émetteurs 2p permettant d'obtenir la température des électrons est présentée, de même qu'un moyen d'obtenir la température du gaz à l'aide de mesures d'élargissement spectral de raies et la densité d'états métastables de l'argon à l'aide de mesures de spectroscopie d'absorption par diode laser accordable en longueur d'onde. Par la suite, ces diagnostics optiques sont employés pour étudier l'influence de l'ajout de gaz diatomiques dans un plasma microonde, mettant en évidence l'efficacité avec laquelle ils en viennent à dominer la cinétique de la décharge en absorbant la majorité de la puissance fournie au plasma. Une comparaison entre le bilan de puissance des électrons qu'ils permettent de calculer à celui d'un diagnostic électrique est également effectué dans le cas d'une décharge à barrière diélectrique d'argon en présence de précurseurs d'anhydrides. Finalement, les propriétés fondamentales de deux conffgurations de jets de plasmas s'écoulant dans l'air ambiant, l'une radiofréquence, l'autre microonde, sont également examinées. Dans le premier cas, les effets de l'air ambiant sur ces propriétés sont mis de l'avant, alors que dans le second cas, la position d'injection du précurseur organosilicié HMDSO dans le jet de plasma est évaluée pour le dépôt de revêtements fonctionnels sur des substrats de verre. Ces derniers travaux révèlent l'obtention d'un revêtement antibuée dans des conditions opératoires spécifiques, un résultat fort prometteur pour l'industrie du verre. / The research done in this Ph.D. thesis consistently characterizes the physics of argon plasmas at atmospheric pressure in the presence of reactive species. This work is motivated by the obvious deficiencies in the understanding of cold plasmas at atmospheric pressure, which are largely due to the limited number of diagnostic techniques used to characterize them. In this context, optical diagnostics allowing the obtaining of fundamental properties (gas and electron temperature, number density of excited species) are first developed and validated in a microwave argon plasma as well as in a dielectric barrier discharge in argon at atmospheric pressure. In particular, a method coupling optical emission measurements of argon 2p-1s transitions to collisional-radiative modelling of the emitting 2p levels is presented in order to get the electron temperature, as well as a means to obtain the gas temperature by the spectral broadening of emission lines and the number density of argon metastable states from tunable laser diode absorption spectroscopy measurements. Subsequently, these optical diagnostics are used to study the influence adding diatomic gases in microwave argon plasmas, highlighting the efficiency with which they start dominating the discharge kinetics by absorbing most of the supplied power. A comparison between the electron power balance calculated from such optical diagnostics to that obtained from electrical diagnostics is also made in the case of an argon-based dielectric barrier discharge with anhydride precursors. Finally, the fundamental properties of two plasmas jet configurations (one radiofrequency, the other microwave) expanding in ambient air are also examined. In the first case, the effects of ambient air on these properties are featured, while in the second case, the injection position of the organosilicon precursor HMDSO in the plasma jet is studied for the deposition of functionnal coatings on glass substrates. The latter reveals the obtaining of an antifog coating under specific operating conditions, a very promising result for the glass industry.

Forests can be considered as one of the most important Earth's ecosystems not only because of oxygen production and carbon sequestration via photosynthesis, but also as a source of many natural resources (such as wood) and as a habitat of many specific plants and animals. Monitoring of forest health status is thus crucial activity for keeping all production and ecosystem functions of forests. The main aim of the thesis is development of an alternative approach for forest health status based on airborne hyperspectral data (HyMap) analysis supported by field sampling. The proposed approach tries to use similar vegetation parameters which are used in case of the current methods of forest health status assessment based on field inspections. It is believed that importance of such new methods will significantly increase in the time when the planned satellite hyperspectral missions (e.g. EnMap) will move into operational phase. The developed forest health monitoring approach is practically demonstrated on mature Norway spruce (Picea abies L. Karst) forests of the Sokolov lignite basin which were affected by long-term coal mining and heavy industry and therefore high variability of forest health status was assumed in this case. Two leaf level radiative transfer models were used for simulating spectral...

Der Strahlungstransport stellt eine von drei Arten des Wärmetransports zwischen Gebieten unterschiedlicher Temperatur dar. Eine der einfachsten Formen bildet der Strahlungstransport im Vakuum, ein Vorgang, der im kosmischen Umfeld, beispielsweise bei der Energieübertragung von einem Stern auf seine Planeten, beobachtbar ist. Hierbei ist es hinreichend, sich auf die Betrachtung von Oberflächen zu beschränken. Strahlungstransport kann jedoch auch in semitransparenten Medien, wie biologischem Gewebe oder Glas, beobachtet werden. Das Medium, in dem der Strahlungstransport erfolgt, wirkt sich durch Vorgänge wie Absorption, Emission, Reflexion oder Streuung auf den Strahlungstransport aus. Für die Modellierung des Strahlungstransports in einem solchen Umfeld können verschiedene Modelle, darunter das Strahlenmodell, genutzt werden. Dieses Modell beschreibt den Wärmetransport anhand einer skalaren Größe, die Strahlungsintensität genannt wird. Betrachtet wird die Strahlungsintensität in diesem Modell entlang eines Strahls in eine vorgegebene Richtung. Die mathematische Darstellung des Strahlenmodells des Strahlungstransports in partizipierenden Medien führt auf eine richtungsabhängige Integro-Differentialgleichung. Ist die Richtungsabhängigkeit nicht von Interesse, so kann der Übergang zu einer winkelintegrierten Form erfolgen. Dieser Übergang führt schließlich auf ein System schwach singulärer fredholmscher Integralgleichungen zweiter Art. Dieses charakterisiert nun nicht mehr die erwähnte Strahlungsintensität, sondern beschreibt die sogenannte Einstrahlung sowie den Strahlungsfluss. Das System singulärer Integralgleichungen kann mittels eines Galerkin-Ansatzes numerisch gelöst werden. Geht man von einer hinreichenden Glattheit des Randes aus, kann die Kompaktheit des Operators der Integralgleichungen gezeigt werden. Dies wiederum erlaubt Rückschlüsse auf die Existenz und Eindeutigkeit einer Lösung. Ein Augenmerk bei der Ermittlung der Galerkin-Näherung ist auf die Bestimmung der singulären Integrale der Galerkin-Diskretisierung zu richten. Für die Bestimmung multidimensionaler, singulärer Integrale stellt die Arbeit das Verfahren der hierarchischen Integration vor. Basierend auf einer Zerlegung des Integrationsgebietes, erfolgt die Beschreibung singulärer Integrale durch ein Gleichungssystem, dessen rechte Seite nur von regulären Integralen abhängig ist. Können diese regulären Integrale sowie die Lösung des Gleichungssystems exakt bestimmt werden, so sind auch die singulären Integrale exakt bestimmt. Bei einer numerischen Bestimmung der regulären Integrale ist die Fehlerordnung ausschlaggebend für den Fehler der singulären Integrale. Als Integrationsgebiete werden Hyperwürfel beliebiger Dimension sowie Simplizes bis einschließlich Dimension 3 als Integrationsgebiete betrachtet. Als Voraussetzungen an den Kern des Doppelintegrals sind nur die Eigenschaften der Translationsinvarianz sowie der Homogenität zu richten. Kann ein nicht translationsinvarianter oder nicht homogener Kern eines Integrals in Summanden zerlegt werden, die selbst translationsinvariant und homogen sind, ist auch die Bestimmung solcher Integrale möglich. Darüber hinaus stellt die Arbeit Verbindungen zu dem Begriff des Hadamard partie finie her. Auf diese Weise lässt sich das Verfahren der hierarchischen Integration für beliebige Dimensionen und beliebige Singularitätsordnungen anwenden. Die Strahlungstransportgleichung ist im Allgemeinen mittels eines Galerkin-Ansatzes lösbar, führt jedoch auf eine voll besetzte Systemmatrix. Numerische Beispiele beleuchten daher Methoden der Matrixkompression mittels hierarchischer Matrizen sowie der direkten Erzeugung schwach besetzter Matrizen über regulären Gittern und Gittern mit hängenden Knoten und skizziert Ansätze zur Parallelisierung auf entsprechenden Computersystemen.

[pt] Estudamos duas classes de equações diferenciais parciais, nomeadamente: uma equação de transferência radiativa e uma equação do calor duplamente não-linear. O primeiro modelo envolve uma equação não-local, na presença de um operador de espalhamento. Estuda-se a boa colocação do problema no semi-plano, no regime peaked. Prova-se um lema de averaging, que produz regularidade interior para o problema, além de regularização fracionária para as derivadas temporais da solução. O segundo conjunto de resultados da tese trata de uma equação de Trudinger com graus de não-linearidade distintos. Aproxima-se este problema pela p-equação do calor e importa-se regularidade da última para a primeira. Como consequência, mostra-se um resultado de regularidade melhorada no contexto não homogêneo. / [en] We consider two classes of partial differential equations. Namely: the radiative transfer equation and a doubly nonlinear model. The former concerns a nonlocal problema, driven by a scattering operator. We study the well-posedness of solutions in the peaked regime, for the half-space. A new averaging lemma yields interior regularity for the solutions and improved fractional regularization for the time derivatives. The second model we examine is a Trudinger equation with distinct nonlinearities degrees. Inspired by ideas launched by L. Caffarelli, we resort to approximation methods and prove improved regularity results for the solutions. The strategy is to relate our equation with p-caloric functions.

Do changes in how cross-equatorial energy transport is partitioned between the ocean and atmosphere impact the hemispheric climate response to forcing? To find out, we alter the cross-equatorial ocean heat transport in a state-of-the-art GCM and ascertain how changes in energy transport and its partitioning impact hemispheric climate and precipitation sensitivity following abrupt CO2-doubling. We further evaluate the applicability our results in CMIP6-class ESMs, where AMOC facilitates the northward cross-equatorial ocean heat transport. In our experiments, changes in ocean cross-equatorial energy transport trigger compensating changes in atmospheric energy transport through changes in the Hadley cells and a shift in the Intertropical Convergence Zone. However, the climate sensitivity in each hemisphere is linearly related to the ocean heat transport convergence, not atmospheric energy transport convergence, due to the impact of ocean heating on evaporation and atmospheric specific humidity. Similarly, we also find that ocean heat transport convergence controls the hemispheric precipitation sensitivity through the impact of ocean heating on surface evaporation. This relationship is also evident in CMIP6 models, where we find differences in hemispheric precipitation sensitivity to be related to the Atlantic Meridional Overturning Circulation (AMOC). Changes in the AMOC control hemispheric differences in upper ocean heat content, which then affect how the hydrologic cycle responds to CO2 forcing in each hemisphere. These results suggest that ocean dynamics impact the hemispheric climate response to CO2 forcing, particularly how much regional precipitation changes with warming. / Graduate

Grasslands are one of the most important ecosystems on Earth, covering approximately one-third of the Earth’s surface. Grassland biodiversity is important as many services provided by such ecosystems are crucial for the human economy and well-being. Given the importance of grasslands ecosystems, in recent years research has been carried out on the potential to monitor them with novel remote sensing techniques. Improved detectors technology and novel sensors providing fine-scale hyperspectral imagery have been enabling new methods to monitor plant traits (PTs) and biodiversity. The aims of the work were to study different approaches to monitor key grassland PTs such as Leaf Area Index (LAI) and biodiversity-related traits. The thesis consists of 3 parts: 1) Evaluating the performance of remote sensing methods to estimate LAI in grassland ecosystems, 2) Estimating plant biodiversity by using the optical diversity approach in grassland ecosystems, and 3) Investigating the relationship between PTs variability with alpha and beta diversity for the applicability of the optical diversity approach in a subalpine grassland of the Italian Alps To evaluate the performance of remote sensing methods to estimate LAI, temporal and spatial observations of hyperspectral reflectance and LAI were analyzed at a grassland site in Monte Bondone, Italy (IT-MBo). In 2018, ground temporal observations of hyperspectral reflectance and LAI were carried out at a grassland site in Neustift, Austria (AT-NEU). To estimate biodiversity, in 2018 and 2019 a floristics survey was conducted to determine species composition and hyperspectral data were acquired at two grassland sites: IT-MBo and University of Padova’s Experimental Farm, Legnaro, Padua, Italy (IT-PD) respectively. Furthermore, in 2018, biochemistry analysis of the biomass samples collected from the grassland site IT-MBo was carried out to determine the foliar biochemical PTs variability. The results of the thesis demonstrated that the grassland spectral response across different spectral regions (Visible: VIS, red-edge: RE, Near-infrared: NIR) showed to be both site-specific and scale-dependent. In the first part of the thesis, the performance of spectral vegetation indices (SVIs) based on visible, red-edge (RE), and NIR bands alongside SVIs solely based or NIR-shoulder bands (wavelengths 750 - 900 nm) was evaluated. A strong correlation (R2 > 0.8) was observed between grassland LAI and both RE and NIR-shoulder SVIs on a temporal basis, but not on a spatial basis. Using the PROSAIL Radiative Transfer Model (RTM), it was demonstrated that grassland structural heterogeneity strongly affects the ability to retrieve LAI, with high uncertainties due to structural and biochemical PTs co-variation. In the second part, the applicability of the spectral variability hypothesis (SVH) was questioned and highlighted the challenges to use high-resolution hyperspectral images to estimate biodiversity in complex grassland ecosystems. It was reported that the relationship between biodiversity (Shannon, Richness, Simpson, and Evenness) and optical diversity metrics (Coefficient of variation (CV) and Standard deviation (SD)) is not consistent across plant communities. The results of the second part suggested that biodiversity in terms of species richness could be estimated by optical diversity metrics with an R2 = 0.4 at the IT-PD site where the grassland plots were artificially established and are showing a lower structure and complexity from the natural grassland plant communities. On the other hand, in the natural ecosystems at IT-MBo, it was more difficult to estimate biodiversity indices, probably due to structural and biochemical PTs co-variation. The effects of canopy non-vegetative elements (flowers and dead material), shadow pixels, and overexposed pixels on the relationship between optical diversity metrics and biodiversity indices were highlighted. In the third part, we examined the relationship between PTs variability (at both local and community scales, measured by standard deviation and by the Euclidean distances of the biochemical and biophysical PTs respectively) and taxonomic diversity (both α-diversity and β-diversity, measured by Shannon’s index and by Jaccard dissimilarity index of the species, families, and functional groups percent cover respectively) in Monte Bondone, Trentino province, Italy. The results of the study showed that the PTs variability metrics at alpha scale were not correlated with α-diversity. However, the results at the community scale (β-diversity) showed that some of the investigated biochemical and biophysical PTs variations metrics were associated with β-diversity. The SVH approach was also tested to estimate β-diversity and we found that spectral diversity calculated by spectral angular mapper (SAM) showed to be a better proxy of biodiversity in the same ecosystem where the spectral diversity failed to estimate alpha diversity, this leading to the conclusion that the link between functional and species diversity may be an indicator of the applicability of optical sampling methods to estimate biodiversity. The findings of the thesis highlighted that grassland structural heterogeneity strongly affects the ability to retrieve both LAI and biodiversity, with high uncertainties due to structural and biochemical PTs co-variation at complex grassland ecosystems. In this context, the uncertainties of satellite-based products (e.g., LAI) in monitoring grassland canopies characterized by either spatially or temporally varying structure need to be carefully taken into account. The results of the study highlighted that the poor performance of optical diversity proxies in estimating biodiversity in structurally heterogeneous grasslands might be due to the complex relationships between functional diversity and biodiversity, rather than the impossibility to detect functional diversity with spectral proxies.

In dieser Arbeit untersuchen wir kollektive Strahlungseffekte in Nanofaser-gekoppelten atomaren Ensembles, die sich über Tausende von optischen Wellenlängen erstrecken. Wir koppeln bis zu 1000 Atome optisch an die geführten Moden einer optischen Nanofaser, die langreichweitige Dipol-Dipol Wechselwirkungen zwischen den Atomen vermittelt. Wir realisieren eine unidirektionale Kopplung und damit ein kaskadiertes Quantensystem, in dem die Dynamik jedes Atoms ausschließlich durch die Dynamik der vorgelagerten Atome bestimmt wird. Wir regen die Atome mit nanofasergeführten optischen Pulsen kohärent an, was uns ermöglicht, den gesamten Parameterbereich von schwacher Anregung bis hin zur voll-ständigen Inversion zu erforschen. Wir stellen fest, dass die kohärente Vorwärtsstreuung, die für die Superradianz im Regime der schwachen Anregung verantwortlich ist, auch nahe voller Inversion eine wichtige Rolle für die Dynamik spielt. Wir beobachten superradiante Puls-Dynamik, die in unserem System trotz des makroskopischen Abstands zwischen den Atomen und einer asymmetrischen Kopplung auftritt. Wir stellen fest, dass die emittierte Spitzenleistung noch schneller mit der Anzahl der Atome skaliert als im Fall der idealen Dicke Superradianz, was auf eine kollektiv erhöhte Sammeleffizienz der nanofasergeführten Mode zurückzuführen ist. Die Analyse der Kohärenz-Eigenschaften des superradianten Pulses erlaubt es uns, zwei Regime der Puls-Dynamik zu identifizieren. Wir entwickeln ein kaskadiertes Wechselwirkungsmodell und zeigen, dass es die kollektive Dynamik unseres Systems über den gesamten in dieser Arbeit untersuchten Parameterbereich akkurat beschreibt. Schließlich untersuchen wir die getriebene Dynamik eines Nanofaser-gekoppelten Ensembles von Drei-Niveau-Atomen. Wir treiben Zwei-Photonen-Rabi-Oszillationen zwischen den beiden Grundzuständen eines $\Lambda$-Systems und beobachten die damit verbundene oszillatorische Raman-Verstärkung und -Absorption. / In this thesis, we study collective radiative effects in nanofiber-coupled atomic ensembles that extend over thousands of optical wavelengths. We optically couple up to 1000 atoms to the guided modes of an optical nanofiber, which mediates long-range dipole-dipole interactions between the atoms. We engineer the coupling to be unidirectional, realizing a cascaded quantum system in which the dynamics of each atom is solely determined by the dynamics of upstream atoms. We coherently excite the atoms using nanofiber-guided optical pulses, allowing us to explore the entire parameter regime from weak excitation to full inversion. We find that coherent forward scattering, which is responsible for superradiance in the weak excitation regime, plays an important role for the dynamics even close to full inversion. We observe superradiant burst dynamics, which occurs in our system despite the macroscopic separation between the atoms and an asymmetric coupling. We find that the peak-emitted power scales even faster with the number of atoms than in the case of ideal Dicke superradiance due to a collectively enhanced channeling efficiency into the nanofiber-guided mode. By analyzing the coherence properties of the superradiant burst, we directly identify two regimes of burst dynamics. In the second regime, there is no initial coherence, and the superradiant burst is seeded by vacuum fluctuations. We introduce a cascaded interaction model and find that it accurately describes the collective dynamics of our system over the entire parameter regime explored in this thesis. Finally, we study the driven dynamics of a nanofiber-coupled ensemble of three-level atoms. We drive two-photon Rabi oscillations between the two ground states of a $\Lambda$ system and observe the associated oscillatory Raman gain and absorption.

Combustion with a high surface area continuous solid immersed within the flame, referred to as combustion in porous media, is an innovative approach to combustion as the solid within the flame acts as an internal regenerator distributing heat from the combustion byproducts to the upstream reactants. By including the solid structure, radiative energy extraction becomes viable, while the solid enables a vast extension of flammability limits compared to conventional flames, while offering dramatically reduced emissions of NOx and CO, and dramatically increased burning velocities. Efforts documented within are used for the development of a streamlined set of design principles, and characterization of the flame's behavior when operating under such conditions, to aid in the development of future combustors for lean burn applications in open flow systems. Principles described herein were developed from a combination of experimental work and reactor network modeling using CHEMKIN-PRO. Experimental work consisted of a parametric analysis of operating conditions pertaining to reactant flow, combustion chamber geometric considerations and the viability of liquid fuel applications. Experimental behavior observed, when utilizing gaseous fuels, was then used to validate model outputs through comparing thermal outputs of both systems. Specific details pertaining to a streamlined chemical mechanism to be used in simulations, included within the appendix, and characterization of surface area of the porous solid are also discussed. Beyond modeling the experimental system, considerations are also undertaken to examine the applicability of exhaust gas recirculation and staged combustion as a means of controlling the thermal and environmental output of porous combustion systems. This work was supported by ACS PRF "51768-ND10 and NSF IIP 1343454.