Ground penetrating radar (GPR) is widely used to identify locations of sinkholes in covered karst terrain in Florida. Some sinkholes serve as hydraulic conduits between the surficial and underlying aquifers. Their role is critical in determining the surficial aquifer response to pumping in deeper aquifers. Improved methods for discriminating between hydraulically active sinkholes and plugged sinkholes could help regional water management. In the covered karst of west-central Florida a clay-rich weathering horizon forms over the limestone. The clay-rich layer is in turn overlain by surficial sands. Ground penetrating radar profiles typically show a strong reflector from the top of clay-rich horizon as well as internal layering within sands. Active sinkholes are expected to have sandy conduits that broach the clay layer, and perhaps layering in the overlying sand indicative of ongoing subsidence. Three dimensional simulations of GPR profiles over sinkhole with and without conduits were run with the finite-difference time-domain (FDTD) program GPRMAX. Results from the synthetic surveys were then processed with standard techniques, including migration. The modeling confirms that conduits appear in GPR records primarily as gaps in the return from the clay layer. The modeling also shows that non-traditional survey geometries (varying antenna spacing and orientation) are unlikely to recover more information than traditional proximal transmitter-receiver separation. Also examined are GPR profiles and 3D grids over a set of active and inactive sinkholes in Tampa, Florida. Results from these surveys showed decent structural recovery of a small sinkhole similar in structure to that of the modeled ones. Indications of active subsidence and possible conduit structure were apparent from this data. Finally, the dense surveys served as a benchmark to compare interpretations taken with the same surveys at lower spatial resolutions and profiles with 2D-only processing methods in order to understand errors in analysis and interpretation that are possible from 2D surveys. Two-dimensional surveys, 2D processed and migrated, showed some similarity to the 3D results previously mentioned but contained more complexities and artifacts, which led to poorer interpretation ability.

L'une des approches pour améliorer les performances des cellules solaires organiques, sans augmenter l'épaisseur de la couche photoactive, consiste à incorporer des nanoparticules (NPs) métalliques dans cette couche ou à proximité pour bénéficier de la diffusion de la lumière incidente ou de résonances de plasmons de surface localisés. Cependant, ces NPs métalliques peuvent engendrer des recombinaisons des porteurs de charges électriques, créer des court-circuits ou favoriser l'extinction des excitons au contact du métal. Une solution est alors de protéger ces NPs métalliques par un revêtement diélectrique (coquille ou couche fine). L'objectif de cette thèse est d'étudier l'influence de nanostructures de type cœur–coquille (métal-diélectrique) sur les performances optiques et photoélectriques de cellules solaires organiques, à l'aide de modélisations numériques et de réalisations expérimentales. Dans un premier temps, une étude numérique prédictive, basée sur une modélisation par méthode FDTD, nous a permis d'analyser l'influence de paramètres architecturaux et opto-géométriques sur les propriétés optiques de cellules solaires plasmoniques. Par la suite, nous avons synthétisé et caractérisé des nanosphères (NSs) avec un cœur métallique en argent ou en or recouverts d'une fine coquille de silice. L'incorporation de NSs Ag@SiO2 synthétisées (voie humide) ou de NPs Ag/SiO2 déposées par évaporation (voie sèche) dans des cellules solaires à architecture inverse ont permis d'augmenter le photocourant de 12% ou de 18% respectivement par rapport à la cellule de référence (sans NSs). / One of the approaches to improve the organic solar cells performance without increasing the thickness of the photoactive layer is to incorporate metallic nanoparticles (NPs) in this layer or in its proximity to have benefited from light scattering or localized surface plasmon resonance effects. However, these NPs can generate charge carriers recombination, short circuits or exciton quenching due to the contact with the metal. A solution is then to coat these MNPs with a dielectric (thin shell or layer) to protect them. The objective of this thesis is to study the influence of metal­dielectric core­shell nanostructures on the optical and photoelectric performances of organic solar cells, by using numerical modeling and experiments. First, a predictive numerical analysis by FDTD modeling allowed us to optimize the influence of architectural and optogeometric parameters on optical properties of plasmonic organic solar cells. Silver or gold core nanospheres (NSs) coated with a thin silica shell were synthesized and characterized. Finally, the integration of chemically synthesized Ag@SiO 2 NSs (wet process) or Ag/SiO 2 NPs deposited by evaporation (dry process) in inverted organic solar cells has increased the photocurrent by 12% or 18%, respectively, compared to the reference cell(without NSs).

The main topic of this diploma thesis is the modeling of nonlinear effects in ultrasonic fields. The work deals with application of finite difference method (FDTD) on the Westervelt equation and the subsequent creation of the model of ultrasonic fields in MATLAB. This thesis also includes theoretical analysis of ultra-acoustic and technical aspects of diagnostic ultrasonography. In addition, this document includes verification of theoretical assumptions by using created model.