La conduction thermique devient moins efficace à mesure que la taille des struc-tures diminuent en desous du micron, car la diffusion de surface des phononsdevient prédominante et limite plus efficacement les phonons que la diffusionphonon-phonon Umklapp. Des études récentes ont indiqué que les phonon po-laritons de surface (SPhPs), qui sont les ondes électromagnétiques évanescentesgénérées par l’hybridation des phonons optiques et des photons et se propageantà la surface d’une surface diélectrique polaire, pourraient servir de nouveauxvecteurs de chaleur pour améliorer les performances thermiques dans des dis-positifs micro- et nano-métriques. Nous étudions l’état des SPhPs existantdans un film submicronique diélectrique dans une large gamme de fréquences.Le calcul de la conductivité thermique des SPhPs basé sur l’équation de trans-port de Boltzmann (BTE) montre que le flux de chaleur transporté par lesSPhPs est supérieur à celui des phonons. Nous effectuons également une mesurede réflectance thermique dans le domaine temporel (TDTR) de films submi-croniques deSiNet démontrons que la conductivité thermique due aux SPhPsà haute température augmente lorsque l’épaisseur du film dimine. Les résultatsprésentés dans cette thèse ont des applications potentielles dans le domaine dutransfert de chaleur, de la gestion thermique, du rayonnement en champ proche et de la polaritoniques. / Thermal conduction becomes less efficient as structures scale down into submicron sizes since phonon-boundary scattering becomes predominant and impede phonons more efficiently than Umklapp scattering. Recent studies indicated that the surface phonon polaritons (SPhPs), which are the evanescent electromagnetic waves generated by the hybridation of the optical phonons and the photons and propagating at the surface of a polar dielectric material surface, potentially serve as novel heat carriers to enhance the thermal performance in micro- and nanoscale devices. We study the condition of SPhPs existing in a dielectric submicron film with a broad frequency range. The calculaton of SPhPs thermal conductivity based on Boltzmann transport equation (BTE) demonstrates that the heat flux carried by SPhPs exceeds the one carried by phonons. We also conduct a time-domain-thermal-reflectance (TDTR) measurement of $SiN$ submicron films and demonstrate that the thermal conductivity due to the SPhPs at high temperatures increases by decreasing the film thickness. The results presented in this thesis have potential applications in the field of heat transfer, thermal management, near-field radiation and polaritonics.

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[pt] Os sistemas eletromagnéticos de telemetria através de formações geológicas têm sido cada vez mais estudados na última década devido às importantes aplicações de engenharia para a indústria de exploração de óleo e gás. Várias técnicas computacionais puramente numéricas têm sido utilizadas para modelar esses cenários. No entanto, elas exigem um tratamento ardiloso para às bruscas mudanças na condutividade elétrica presente nas formações geológicas. Além disso, o custo computacional necessário para o processo de discretização é muito grande, e as instabilidades em baixas frequências se tornam críticas para problemas em que largas escalas estão envolvidas. Esta pesquisa apresenta uma formulação semianalítica para analisar a propagação dos campos eletromagnéticos em um meio estratificado, dissipativo, e com anisotropia biaxial. A solução proposta emprega uma nova abordagem no domínio espectral onde uma integral baseada na transformada de Hankel é apresentada para modelar a propagação de ondas devido a fontes de corrente do tipo anel com simetria azimutal. O método proposto é empregado para a análise de cenários geofísicos análogos aos do Pré-Sal brasileiro, onde rochas carbonáticas de alta condutividade são predominantes. Além disso, o efeito das formações do pré e pós-sal nos campos eletromagnéticos e sua interação com o tubo metálico que reveste o poço de petróleo é então computado para ambientes isotrópicos e anisotrópicos. É apresentada uma série de resultados de validação que mostram que a técnica proposta é numericamente estável, robusta e computacionalmente eficiente para modelar vários problemas representativos de telemetria sem fio em poços de petróleo. / [en] Electromagnetic telemetry systems through complex geological formations have been increasingly investigated in the last decade due to important engineering applications for the oil and gas industry exploration. Many brute-force computational electromagnetic techniques have been used for modeling this scenario. However, they require a tricky treatment of the large conductivity contrasts present in the soil formations. Also, high-cost computational resources are required for the discretization process and the low-frequency instabilities become critical for such large-scale problems. This research presents a semi-analytic formulation for analyzing the electromagnetic field propagation in a biaxially anisotropic and lossy stratified media. The proposed solution employs a novel spectral domain approach where a Hankel-based integral transform is introduced for modeling wave propagation due to azimuthally symmetric current loop sources. The proposed method is employed for analyzing geophysical scenarios analogous to those of the Brazilian Pre-Salt, where high conductivity carbonate rocks are prevalent. Also, the effect of the pre and post-salt formations on the electromagnetic fields and its interaction with the metallic casing of an oil well is then computed for both isotropic and anisotropic environments. It is presented a series of validation results which show that the proposed technique is numerically stable, robust and computationally efficient for modeling several representative problems of wireless oil well telemetry.

Submitted Ph.D. thesis is concerning the application and interpretation of seismic surface waves in a broad range of frequencies and scales. Using surface waves as a supplement to the methods dealing with body waves seems to be worth the effort. Surface wave interpretation can be used to obtain new information about the studied medium and simultaneously it can overcome, in some cases, the limitations of other seismic techniques. Moreover, surface waves are usually present on measured records and hence for its usage it is not necessary to modify the standard measuring procedures. One of the results of this thesis is an original algorithm for dispersive waveform calculation. The program works in an arbitrary range of frequencies and scales. The input parameter for the calculation is the dispersion curve. In this point the algorithm differs from all other approaches used so far. Algorithm is based on a summation of frequency components with shifts corresponding to the velocity dispersion and distance. The resulting waveform only contains an individual dispersive wave of the selected mode, thus being particularly suitable for testing of methodologies for dispersive wave analysis. The algorithm was implemented into the program DISECA. Furthermore, a new procedure was designed to calculate the dispersion...

This thesis develops a one-dimensional version of a new data driven model of turbulence that uses the KL expansion to provide a spectral solution of the turbulent flow field based on analysis of Particle Image Velocimetry (PIV) turbulent data. The analysis derives a 2nd order random field over the whole flow domain that gives better turbulence properties in areas of non-uniform flow and where flow separates than the present models that are based on the Navier-Stokes Equations. These latter models need assumptions to decrease the number of calculations to enable them to run on present day computers or super-computers. These assumptions reduce the accuracy of these models. The improved flow field is gained at the expense of the model not being generic. Therefore the new data driven model can only be used for the flow situation of the data as the analysis shows that the kernel of the turbulent flow field of undular hydraulic jump could not be related to the surface waves, a key feature of the jump. The kernel developed has two parts, called the outer and inner parts. A comparison shows that the ratio of outer kernel to inner kernel primarily reflects the ratio of turbulent production to turbulent dissipation. The outer part, with a larger correlation length, reflects the larger structures of the flow that contain most of the turbulent energy production. The inner part reflects the smaller structures that contain most turbulent energy dissipation. The new data driven model can use a kernel with changing variance and/or regression coefficient over the domain, necessitating the use of both numerical and analytical methods. The model allows the use of a two-part regression coefficient kernel, the solution being the addition of the result from each part of the kernel. This research highlighted the need to assess the size of the structures calculated by the models based on the Navier-Stokes equations to validate these models. At present most studies use mean velocities and the turbulent fluctuations to validate a models performance. As the new data driven model gives better turbulence properties, it could be used in complicated flow situations, such as a rock groyne to give better assessment of the forces and pressures in the water flow resulting from turbulence fluctuations for the design of such structures. Further development to make the model usable includes; solving the numerical problem associated with the double kernel, reducing the number of modes required, obtaining a solution for the kernel of two-dimensional and three-dimensional flows, including the change in correlation length with time as presently the model gives instant realisations of the flow field and finally including third and fourth order statistics to improve the data driven model velocity field from having Gaussian distribution properties. As the third and fourth order statistics are Reynolds Number dependent this will enable the model to be applied to PIV data from physical scale models. In summary, this new data driven model is complementary to models based on the Navier-Stokes equations by providing better results in complicated design situations. Further research to develop the new model is viewed as an important step forward in the analysis of river control structures such as rock groynes that are prevalent on New Zealand Rivers protecting large cities.

En la realización de este trabajo se obtendrán las expresiones analíticas que permiten describir las propiedades acústicas de una red de elementos dispersivos en el interior de una guía de ondas, permitiendo así, obtener en el límite de homogenización los parámetros efectivos que caracterizan al metamaterial y la verificación experimental de las propiedades acústicas del metamaterial. Matemáticamente este problema se tratará con la teoría de la dispersión múltiple, ya que las geometrías a tratar en este trabajo van a ser cilíndricas y dicha teoría se ha demostrado ser la mas efectiva para esos casos y usando la técnica de ¿mode matching ¿para la resolución general del problema de la dispersión de campo acústico en el interior de una guía de ondas. / Graciá Salgado, R. (2014). Diseño y caracterización de metamateriales acústicos basados en guías de onda [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/38759 / TESIS

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal. / L'objectif de cette thèse est de mieux comprendre les phénomènes physiques et chimiques se produisant dans un plasma de haute densité conçu pour la gravure sous­micrométrique de couches minces. Le plasma est produit dans le chlore par une onde électromagnétique de surface et peut être confiné par un champ magnétique statique uniforme. La flexibilité du réacteur en termes de conditions opératoires rend possible une étude paramétrique de l'influence du confinement magnétique sur les caractéristiques du plasma. Pour cela, nous avons examiné les propriétés du plasma au moyen de plusieurs méthodes de diagnostics comme les sondes électrostatiques, le photodétachement des ions négatifs par Jaser, la propagation d'ondes acoustiques ioniques et la spectroscopie d'émission optique. Dans un premier temps, nous nous sommes intéressés à l'influence des conditions opératoires sur les propriétés spatiales du plasma, en ce qui a trait aux caractéristiques électriques (électrons, ions positifs et négatifs) et chimiques (neutres réactifs). Dans un deuxième temps, nous avons examiné l'impact du rapport d'aspect du réacteur (i.e. rapport de la longueur du réacteur sur son rayon) tant sur les caractéristiques électriques que chimiques du plasma. Parallèlement à ces études expérimentales, nous avons développé un modèle fluide bidimensionnel, résolvant de manière auto cohérente les deux premiers moments de l'équation de Boltzmann et l'équation de Poisson. En utilisant une approche semi-implicite, nous avons pu conserver un temps de calcul assez faible et ainsi utiliser ce modèle pour l'étude d'un plasma de diffusion dans un gaz électropositif. Nous avons ainsi pu estimer la valeur du coefficient de diffusion perpendiculaire dans le cas d'un gaz électropositif soumis à un champ magnétique axial uniforme. Les résultats obtenus sont qualitativement en bon accord avec le coefficient de diffusion proposé par Liebermann et Lichtenberg. / The aim of this thesis is to achieve a better understanding of physical and chemical phenomena occurring in a high-density plasma designed for sub-micron etching of thin films. The plasma is produced in chlorine by means of an electromagnetic surface wave and it can be confined by a uniform static magnetic field. The flexibility offered by the reactor in terms of operating conditions makes possible a parametric study of the influence of the magnetic confinement on the plasma characteristics. Thus, we have examined the plasma properties by means of several diagnostics techniques, including electrostatic probes, laser photodetachment of negative ions, ion acoustic wave propagation and optical emission spectroscopy. First, we investigated the influence of the operating conditions on the spatial properties of the plasma; this includes electric characteristics ( electrons, positive and negative ions) as well as chemical characteristics (reactive neutrals). Second, we studied the impact of the reactor aspect ratio (i.e. reactor length/radius ratio) on both electrical and chemical characteristics. Together with these experimental studies, we have developed a bidimensionnal fluid model, by solving selfconsistently the first two moments of Bolzmann equation and Poisson's equation. Using a semi-implicit scheme, it was possible to maintain a short computation time and to use this model to investigate a diffusion plasma in an electropositive gas. We were thus able to estimate the value of the diffusion coefficient in the direction perpendicular to the magnetic field. The results thus obtained are in good qualitative agreement with the diffusion coefficient proposed by Liebermann and Lichtenberg.

Tout d'abord, des ondes de surface, solutions de problèmes aux limites hyperboliques non linéaires, sont étudiées : on construit une solution BKW sous forme de développement infini en puissance de epsilon. On le justifie rigoureusement, en construisant une solution exacte, qui admet ce développement asymptotique. On montre que la solution n'est pas nécessairement purement localisée sur la frontière, même lorsque le terme source l'est ; l'exemple d'un cas particulier de l'élasticité est traité. Ensuite, on étudie la réflexion d'ondes non linéaires discontinues, pour des problèmes aux limites hyperboliques, faiblement bien posés, ni fortement stables, ni fortement instables. On étudie comment les singularités d'une solution striée sont réfléchies lorsque la solution atteint la frontière. On prouve des estimations striées et en normes infinies. On montre qu'une discontinuité du gradient de la solution à travers un hyperplan peut être réfléchie en une discontinuité de la solution elle-même. / We first study surface waves, solutions of hyperbolic nonlinear boundary value problems. We construct BKW solutions in the weakly nonlinear regime with infinite expansion in powers of ε. We rigorously justify this expansion,constructing exact solutions, which admit the asymptotic expansions. We also show that the solution is not necessarily localized at the order O(ε∞) in the interior, even if the data are ; a particular case of elasticity is studied: we prove that fast oscillatory elastic surface waves can produce non trivial internal non oscillatory displacements.Afterwards, we study the reflection of non linear discontinuous waves, for weakly well-posed hyperbolic boundary value problems, satisfying the (WR) condition, which has been introduced in [1, 12], that is in a case where the IBVP is neither strongly stable, nor strongly unstable. We study how the singularities of a striated solution are reflected when the solution hits the boundary. We prove striated estimates and L∞ estimates and observe the loss of one derivative: we show that a discontinuityof the gradient of the solution across an hyperplane can be reflected in a discontinuity across an hyperplane of the solution itself.