MSc (Mathematics) / Department of Mathematics and Applied Mathematics / The unsteady hydromagnetic chemically reacting mixed convection MHD ow over a permeable stretching sheet embedded in a porous medium with thermal radiation and heat source/sink is investigated numerically. The original partial di erential equations are converted into ordinary di erential equations by using similarity transformation. The governing non-linear partial di erential equations of Momentum, Energy, and Concentration are considered in this study. The e ects of various physical parameters on the velocity, temperature, and species concentration have been discussed. The parameters include the Prandtl number (Pr), Magnetic parameter (M), the Schmidt number (Sc), Unsteady parameter (A), buoyancy forces ratio parameter (N), Chemical reaction (K), Radiation parameter (Nr), Eckert number (Ec), local heat source/sink parameter (Q) and buoyancy parameter due to temperature ( ). The coe cient of Skin friction and Heat transfer are investigated. The coupled non-linear partial di erential equations governing the ow eld have been solved numerically using the Spectral Relaxation Method (SRM). The results that are obtained in this study are then presented in tabular forms and on graphs and the observations are discussed. / NRF

Detta examensarbete har utförts med begäran från Trafikförvaltningen. Arbetets huvudmål är att undersöka om det är möjligt att använda värmestrålning direkt mot ytan av strömskenan för att hindra isbildning på en kortare tid då absorptiviteten är som bäst. / This dissertation has been written with the request from Trafikvörvaltningen. The study's main goal is to investigate whether it is possible to use heat radiation against the surface of the third rail to prevent ice creation during the best efficient of absorptivity.

Dunkle Materie bindet etwa 24 % der gesamten Energie im Universum. Bis heute ist jedoch dessen Ursprung nicht bekannt. Untersuchungen von Galaxien und kosmologischen Messungen deuten auf Dunkle Materie hin. Ein Kandidat für Dunkle Materie ist das sogenannte Weakly Interactive Massive Particle (WIMP), welches nur der Schwerkraft und der schwachen Wechselwirkung unterliegt. Eines dieser supersymmetrischen Teilchen ist das Neutralino. Das Ziel dieser Arbeit ist es, nach Dunkler Materie in dieser Form zu suchen. Aufgrund seiner Nähe sowie der hohen Dichte an Dunkler Materie bietet das Zentrum unserer Galaxie besondere Möglichkeiten zur Suche nach diesen Teilchen. Es wird vermutet, dass Neutralinos miteinander wechselwirken, dabei in Teilchen des Standard Modells zerfallen und so Photonen mit hohen Energien entstehen. Die Suche nach hochenergetischen Gammastrahlen in der Nähe des Galaktischen Zentrums kann folglich das Rätsel der Dunklen Materie lösen. Das Gammastrahlenobservatorium VERITAS hat das Galaktische Zentrum für etwa 108 Stunden beobachtet. Diese Daten wurden mittels einer unbinned Likelihood-Analyse auf die Existenz von Dunkler Materie untersucht. Da VERITAS das Galaktische Zentrum bei geringer Elevation beobachtet, können nur Gammastrahlen in einem Energiebereich zwischen 4 und 70 TeV detektiert werden. Die Analysemethode modelliert sowohl die räumliche Verteilung der Dunklen Materie als auch das Gammastrahlenspektrum. Der Beitrag der Gammastrahlen, welcher nicht von Dunkler Materie erzeugt wird, ist mittels einer punktförmigen Quelle modelliert. Zum Schluss wird der Untergrund mit realen Daten außerhalb des Galaktischen Zentrums abgeschätzt. Im Energiebereich zwischen 4 und 100 TeV wurden keine Signale der Dunklen Materie gefunden. Obere Grenzwerte für den Wechselwirkungsquerschnitt der WIMPs ergeben ⟨σv⟩ < (6.6 − 7.6) × 10−25 cm^3 oberhalb von 70 TeV in einem 95-prozentigen Erwartungsintervall. / Dark matter accounts for 24% of the universe’s energy, but the form in which it is stored is currently unknown. Understanding what form this matter takes is one of the major unsolved mysteries of modern physics. Much evidence exists for dark matter in the measurements of galaxies, dwarf galaxies, galaxy clusters, and cosmological measurements. One theory posits dark matter is a new undiscovered particle that only interacts via gravity and the weak force, called a weakly interacting massive particle (WIMP). One WIMP candidate is a supersymmetric particle called a neutralino. The objective of this thesis is to search for these dark matter particles, and attempt to measure their mass and cross section. Dark matter particles appear to concentrate in most galaxy-scale gravitational wells. One region of space that is both nearby and assumed to have a high density of dark matter is the center of our own galaxy. The neutralino is expected to annihilate into Standard Model particles, which may decay into photons. Therefore, a search for gamma rays near the Galactic Center may uncover the presence of dark matter. 108 hours of VERITAS gamma-ray observations of the Galactic Center are used in an unbinned likelihood analysis to search for dark matter. The Galactic Center’s low elevation results in VERITAS observing gamma rays in the 4–70 TeV energy range. The analysis used in this thesis consists of modeling the halo of dark matter at the Galactic Center, as well as the spectrum of gamma rays produced when two WIMPs annihilate. A point source is added to model the non-dark-matter gamma-ray emission detected from the Galactic Center. Background models are constructed from data of separate off-Galactic-Center observations. No dark matter signal is found in the 4–100 TeV mass range. Upper limits on the WIMP’s velocity-averaged cross section have been calculated, which above 70 TeV result in new limits of ⟨σv⟩ < (6.6 − 7.6) × 10−25 cm3 at the 95% confidence level.

<p>Similar to thermodynamic phase transitions in matter, readily apparent changes in optical response arise in the transition from isotropic to anisotropic optical phases. Treating the anisotropy of the dielectric permittivity as a control parameter, which changes continuously from zero to a nonzero finite value at the transition, in this work we describe the resulting effect on light propagation. </p> <p><br></p> <p>We begin by investigating a simple case of the manifestations of such optical transition in lossy media. In the presence of loss, isotropic materials do not support Brewster phenomenon, however, if one changes the anisotropy continuously, the exact zero in the reflection at the Brewster incidence angle is recovered. Next, in the case of uniaxial anisotropy, we uncover dramatic changes in far-field thermal radiation induced by the transitions between metal, dielectric, and hyperbolic optical regimes that can be observed in the same material. We demonstrate that continuous evolution between different ''phases'' in the electromagnetic response imprints a characteristic signature in the far-field thermal emission. Finally, we show that the evolution of the optical anisotropy from uniaxial to biaxial symmetry brings qualitatively new optical modes which are different from the conventional propagating and evanescent fields. These emergent ''ghost'' waves offer a unique way to control mode interactions in optical systems. Our work uncovers the connection between the macroscopic properties of the optical materials and the transitions between different regimes of the electromagnetic response in these media. At last, we propose a range of potential applications of the resulting phenomena, from perfect absorption in lossy media to thermal radiation and optical sensing.</p>

Les techniques de camouflage, mimétisme ou invisibilité ont récemment connu une forte émergence, qui se poursuit aujourd’hui avec l’apparition des méta-surfaces. C’est dans ce contexte que ce travail de doctorat a été réalisé, notamment avec un premier objectif d’étendre ces outils et concepts aux problèmes inverses du domaine de la diffusion de la chaleur. La suite du travail a concerné le rayonnement thermique, les méta-surfaces et les transformations de champ. Après avoir étendu les techniques de mimétisme au domaine de la conduction, nous avons résolu le problème inverse associé, qui consiste à camoufler des objets imposés en forme ou conductivité. Ce premier travail a permis de mettre en évidence les classes de transformation qui laissent invariantes les paramètres physiques, conférant ainsi plus de pragmatisme au domaine du mimétisme. Nous avons ensuite considéré le cas du rayonnement thermique, et démontré pour la première fois que les illusions par rayonnement étaient envisageables, en appui sur l’invariance du théorème de fluctuation/dissipation. Dans une deuxième étape, nous avons mis au point une nouvelle méthode pour calculer le rayonnement thermique par des objets de forme arbitraire, mettant en jeu des méta-surfaces inhomogènes, anisotropes, chirales et non locales. Nous montrons également comment tirer profit des méta-surfaces pour remplacer les capes volumiques tout en conservant la fonction de camouflage. Cette technique est particulièrement prometteuse pour les applications, même si elle reste intrinsèquement liée à l’éclairement. Des techniques similaires sont développées pour que soit facilité l’utilisation de transformations discontinues de l’espace. / Mimetism, camouflage or invisibility have motivated numerous efforts in the last decade, which are now extended with metasurfaces. This PhD work fits this international context and was first focused on inverse problems in heat conduction before we address thermal radiation and metasurfaces, field transformation. After we generalize the mimetism techniques to heat diffusion, we solved the associated inverse problem which consists of the camouflage of given objects, that is, objects with shape or conductivity that are before hand chosen. The results allowed us to emphasize the class of transformations which hold the physical parameters, hence giving more pragmatism to the field of mimetism. Then we addressed the case of thermal radiation and proved for the first time that mimetism effects could also be controlled in this field, on the basis of the fluctuation/dissipation theorem. In a second step, we built an original technique able to predict the thermal radiation from objects of arbitrary shapes. This technique involves inhomogeneous, anisotropic, chiral and nonlocal metasurfaces. We also show how to take more benefits of metasurfaces in order to replace the bulk mimetism cloaks. We believe this technique to give again more push forward to the field, though the mimetism efficiency now relies on the illumination conditions. Similar techniques are further developed to allow a practical use of discontinuous space transformations. Eventually, field transformation is introduced to complete all these results.

Das Gebiet der bodengebundenen Gamma-Astronomie bietet Zugang zu Photonen im TeV-Energiebereich und hat sich in den letzten Jahrzehnten vor allem durch den Erfolg der abbildenden atmosphärischen Cherenkov-Technik profiliert. In dieser Arbeit werden zwei dieser Cherenkov-Teleskop-Systeme, VERITAS und das zukünftige CTA, mit Hilfe von Monte-Carlo-Simulationen in Hinblick auf deren Sensitivität auf hochenergetische Gammastrahlung (E > 50 GeV) untersucht. Besonderes Augenmerk wird hierbei auf die Beobachtungsmöglichkeit mit CTA unter Mondlicht gelegt. Es wird gezeigt, dass dadurch eine Beobachtungszeitverlängerung um etwa 30% ohne signifikante Sensitivitätsverluste erreicht werden kann, was besonders wichtig für zeitlich variable Quellen ist. Eine dieser variablen Quellklassen sind aktive Galaxienkerne, welche zur Zeit etwa ein Drittel der bekannten hochenergetischen Gammastrahlungsquellen repräsentieren. Die meisten davon sind Blazare, deren Emission durch nicht-thermische Strahlung aus gebündelten Strömen von Materie und Energie (sogenannten Jets) dominiert wird. Diese Jets breiten sich mit annähernd Lichtgeschwindigkeit aus und sind in Sichtlinie des Betrachters ausgerichtet. Der Blazar B2 1215+30 wurde zwischen 2008 und 2012 mit VERITAS fast 100 Stunden beobachtet. Die Datenanalyse, welche in dieser Arbeit präsentiert wird, weist die Quelle mit einer Signifikanz von neun sigma nach und offenbart Langzeitvariabilität mit einem hellen Flusszustand im Jahr 2011. Multi-Wellenlängen-Daten werden verwendet um die spektrale Energieverteilung von B2 1215+30 zu konstruieren, welche gut mit einem leptonischen Ein-Zonen-Modell beschrieben werden kann. Das verwendete Modell wird im Detail vorgestellt und mögliche Einschränkungen an den Modellparameterraum untersucht. Die Ergebnisse der Modellierung von B2 1215+30 werden diskutiert und in Zusammenhang mit anderen bekannten hochenergetischen Gammastrahlen-Blazaren gesetzt. / Ground-based gamma-ray astronomy, which provides access to photons in the TeV energy range, has been a rapidly developing discipline over the past decades. In this thesis, the performance of the current- and next-generation imaging atmospheric Cherenkov telescopes VERITAS and CTA is evaluated using Monte Carlo simulations. Special emphasis is given to the possible extension of the duty cycle of CTA. It is shown that an increase of about 30% in observation time can be achieved through operation under partial moonlight without significant losses in performance. The increased observation time is especially important when studying astronomical objects which are variable at very high energies (VHE; E>50 GeV), such as active galactic nuclei (AGN), as this allows the extension of monitoring or multi-wavelength campaigns on these occasionally flaring sources. AGN represent to date about one third of the population of known VHE gamma-ray sources. Most of them are blazars, whose emission is dominated by non-thermal radiation of relativistic jets closely aligned to the line of sight of the observer. The blazar B2 1215+30 has been observed by VERITAS for nearly 100 hours between 2008 and 2012. The data analysis presented in this thesis yields a detection significance of 9.0 sigma and shows long-term variability with a relatively bright flux state in 2011. Multi-wavelength data are used to construct the spectral energy distribution of B2 1215+30 which is well described by a one-zone leptonic model. The model is presented in detail and possible constraints are investigated. The results of the modeling are discussed and put in context with other VHE-detected blazars.

L'objectif de cette thèse est la modélisation du rayonnement thermique directionnel des surfaces et de la correction angulaire sur la LST par des méthodes empiriques et physiques ainsi que l'analyse de validation sur le terrain. L'émissivité directionnelle des surfaces naturelles a été obtenue à partir du produit émissivité MODIS et est ensuite utilisée dans l'algorithme de split-window de correction angulaire sur la LST. Les modèles de paramétrage de l'émissivité directionnelle et du rayonnement thermique ont été développés. En ce qui concerne les pixels non iso-thermiques, la méthode de jour-TISI a été proposée pour obtenir l'émissivité directionnelle et la température effective à partir de données multi-angulaires infrarouges médian et thermique. Cela a été validé à l'aide de données aéroportée. Le modèle de noyaux Kernel BRDF a été vérifié dans le domaine de l'infrarouge thermique et son extension a servi à la normalisation angulaire de la LST. Un nouveau modèle, FovMod, qui concerne l'empreinte du capteur au sol, a été développé pour simuler la température de brillance directionnelle de couvert végétal en rang. Basé sur le résultat de la simulation de FovMod, une empreinte optimale pour la validation de champ de vue a été obtenue. Cette thèse a étudié systématiquement le rayonnement thermique directionnel et les corrections angulaires sur la température de surface et ses résultats amélioreront la précision sur la température et émissivité à partir de données de télédétection. Ils fourniront également des indices pour la conception de capteurs infrarouges thermiques multi-angulaires aéro/spatio portés et également pour la mesure au sol des paramètres de surface. / The aim of this thesis is the modeling of surface directional thermal radiation and angular correction on the LST by using empirical and physical methods as well as the analysis of field validation. The work has conducted to some conclusions. The directional emissivity of natural surfaces was obtained from MODIS emissivity product and then used in the split-window algorithm for angular correction on LST. The parameterization models of directional emissivity and thermal radiation were developed. As for the non-isothermal pixels, the daytime-TISI method was proposed to retrieve directional emissivity and effective temperature from multi-angular middle and thermal infrared data. This was validated using an airborne dataset. The kernel-driven BRDF model was checked in the thermal infrared domain and its extension was used to make angular normalization on the LST. A new model, namely FovMod that concerns on the footprint of ground sensor, was developed to simulate directional brightness temperature of row crop canopy. Based on simulation result of the FovMod, an optimal footprintfor field validation of LST was obtained. This thesis has systematically investigated the topic of directional thermal radiation and angular correction on surface temperature and its findings will improve the retrieval accuracy of temperature and emissivity from remotely sensed data and will also provide suggestion for the future design of airborne or spaceborne multi-angular thermal infrared sensors and also for the ground measurement of surface parameters.

Les transferts thermiques par rayonnement dans des mousses sont modélisés à partir de la morphologie du matériau et des propriétés de sa phase solide. Dans ce travail de thèse, une attention particulière est portée sur les modèles radiatifs de Monte Carlo. Les différentes approches d’homogénéisation telles que « Homogeneous Phase » (HPA) and « Multi Phase » (MPA) sont discutées et comparées. Des développements novateurs sont proposés pour améliorer la précision des résultats. Nos avancées permettent de générer numériquement trois types de mousses périodiques couvrant un large domaine de matériaux cellulaires: mousse à pores fermés à haute porosité, mousse à cellules ouvertes à basse et haute porosité. Pour ces dernières, des comparaisons morphologiques avec des données expérimentales tomographiques, montrent des résultats satisfaisants et tendent à valider nos modèles de génération. Des mousses dont la phase solide est opaque ont tout d’abord été étudiées. Nos simulations ont permis de trouver de nouvelles lois analytiques précises permettant d’estimer les propriétés radiatives de ces matériaux à partir de données morphologiques. Ensuite, nous avons considéré des mousses, dont la phase solide est semi transparente. La modélisation du transfert radiatif au sein de ces milieux cellulaires est plus complexe. Les méthodes de modélisation des propriétés radiatives de la littérature, HPA et MPA, sont testées. Des simulations de Monte carlo directes dans les matériaux ont permis de mettre en exergue les limites de ces modèles. Des modèles novateurs ont été proposés afin d’ améliorer la précision des simulations. Ils sont basés sur une méthode hybride directe-inverse et une modification de l’équation de transfert radiatif classique. Ces nouveaux modèles (HPA+ et MPA+) ont été testés sur un ensemble varié de morphologies générées numériquement. Les modèles améliorés sont systématiquement plus précis que les modèles existants / Cellular media such as plastic, ceramic and metal foams present specific characteristics that make them interesting for a number of applications related to thermal engineering. Their ability to minimize natural convection makes them ideal candidates for insulation applications, while the high specific surface and permeability to fluid of open cell foams makes them interesting heat transfer enhancers. In addition, their permeability to light makes them an ideal candidate for thermal radiation based applications, such as porous burners or solar energy collectors. In many of these application, thermal radiation heat transfer can have a significant influence on the heat transfer process. Both accurate radiation models and accurate morphological models of the structure of the foam are required. This work provides an original contribution on both these accounts. A discussion of the literature on numerical methods for radiation heat transfer in cellular media is presented, with focus on Monte Carlo methods. Homogeneous Phase (HPA) and Multi Phase (MPA) methods are discussed. Further efforts are required to accurately model and digitally replicate of foam morphologies. Our goal is to digitally generate three commonly occurring types of foam structures, covering a large range of real materials: high-porosity open cell foams, high-porosity closed cell foams, low-porosity open-cell structures. For high-porosity open cell foams, the automated parametric digital generation technique was validated against a dataset consisting of raw morphological data obtained by tomographic analysis. The generation capabilities were then applied to parametrically investigate the influence of morphological parameters on the radiative properties (namely, the extinction coefficient) of an opaque open-cell foam. Highly accurate analytical relationships were subsequently deduced and validated by comparison with results obtained from tomography samples. Modeling radiation in foams with a semi-transparent solid phase is substantially more complex. A Direct Monte-Carlo Homogenization reference technique is proposed, that allows to simulate radiation within arbitrary cavities and calculate macroscopic radiative quantities based on a Representative Elementary Volume (REV) of cellular material. The technique is validated against full scale Monte Carlo simulations. Improvements of the existing Homogeneous Phase and Multi Phase approach are proposed, through extensive use of inverse methods and the addition of one equation to take into account specific phenomena taking place in the semi-transparent solid phase. The resulting Improved Homogenized Approaches are extensively tested by comparing them with Direct Monte Carlo Homogenization simulations and existing homogenized models, on a varied set of morphologies making full use of the previously developed digital generation techniques. The improved models consistently outperform existing homogenized models.

Les phonons polaritons de surface (SPhPs) sont des ondes électromagnétiques de surface évanescentes générées par le couplage phonon-photon et se propageant le long d’une interface entre un milieu polaire (tel que SiO2 et SiC) et un diélectrique. Dans ce mémoire, nous nous intéressons à de possibles applications des SPhPs pour améliorer les performances thermiques des nanosystèmes, en focalisant leur énergie thermique avec des micro- et nanostructures, en réduisant leurs angles de diffraction à travers des ouvertures sub-longueur d’onde, et en démontrant leur émission thermique cohérente large-bande. Nous avons aussi effectué des mesures par microscopie spectrophotométrique infrarouge de micro-objets et démontré l’excitation thermique de modes de grandes longueurs de propagation dans un large domaine spectral. Nos résultats sont obtenus sur des bases à la fois théoriques, de simulations numériques et expérimentales. Ces travaux sont pertinents dans les domaines liés au transfert thermique, à l’optique infrarouge, au rayonnement thermique de champ proche, à la microscopie infrarouge, et à la polaritonique. / Surface phonon-polaritons (SPhPs) are evanescent electromagnetic surface waves generated by the phononphoton coupling and that propagate along the interface of a polar medium (such as SiO2 and SiC) and a dielectric one. In this work, we investigate possible applications of SPhPs for enhancing the thermal performance of micro- and nanoscale devices, focusing of thermal energy with micro-structures, decreasing the diffraction angles of infrared radiation on subwavelength apertures, and demonstrating broadband coherent thermal emission. We also perform infrared spectroscopy microscopy measurements of microscale objects and demonstrate long-range thermally excited surface modes in a broad frequency range. The results presented in this thesis can have possible applications in fields related to heat transfer, infrared optics, near-field thermal radiation, infrared microscopy, and polaritonics.

Processos de fragmentação são ferramentas fundamentais no estudo de íons por espectrometria de massas, pois permitem a obtenção de informação sobre a estrutura e termoquímica destes íons . Desenvolvemos uma técnica de dissociação de íons baseada na ativação destes através da absorção multifotônica sequencial de radiação infravermelha de um filamento incandescente. Nesta técnica, íons aprisionados na cela de um espectrômetro de massas por transformada de Fourier são submetidos a radiação do filamento por intervalos de tempo relativamente longos (da ordem de segundos), e passam por um processo de multíplos eventos de absorção e emissão de radiação, até a energia interna dos íons atingir um nível suficiente para a fragmentação. A partir deste modelo para o processo foram implementados métodos computacionais que permitem a simulação da dissociação. A realização destas simulações exige o conhecimento do espectro vibracional do íon, que normalmente tem que ser obtido por algum método teórico de cálculo, como foi feito neste trabalho paro o caso de alguns dos íons estudados. O método de dissociação unimolecular induzida por absorção de radiação infravermelha foi aplicado na determinação das energias de ativação e de dissociação dos íons moleculares de acetofenona, p-cimeno e cumeno. Este método também mostrou-se capaz de diferenciar diferentes estruturas isomericas, e foi com esta finalidade aplicado no estudo da isomerização ceto-enol do íon molecular de acetofenona. Demonstrou-se também a capacidade do método dissociar os íons moleculares de n-butilbenzeno e brometo de alila. / Fragmentation processes are fundamental tools for the mass spectrometric study of ions because they provide information on structure and termochemistry of these ions. We have developed a dissociation technique that is based on the multiphoton activation of trapped ions by infrared radiation emitted by an incandescent filament. In this technique, ions trapped in the cell of a Fourier Transform mass spectrometer are exposed to the filament radiation for long time periods (seconds), and a process of multiple absorption and emition events occurs, until the internal energy of the ions is high enough for fragmentation. Computational methods have been implemented from this model allowing for simulation of the dissociation process. For this simulation the ion vibrational spectra, that normally must be obtained from theoretical calculations, is also required, as has been done in this work for some of the studied ions. The method of unimolecular dissociation induced by infrared radiation was applied to the determination of activation and dissociation energies of the molecular ions of acetophenone, p-cymene and cumene. This method also proved to be capable in the differentiation of isomeric structures, and was so applied in the study for the keto-enol isomerization of the acetophenone molecular ion. It was also shown that the method can dissociate the molecular ions of n-butylbenzene an allyl bromide.