Structure-aware image denoising, super-resolution, and enhancement methods

Denoising, super-resolution and structure enhancement are classical image processing applications. The motive behind their existence is to aid our visual analysis of raw digital images. Despite tremendous progress in these fields, certain difficult problems are still open to research. For example, denoising and super-resolution techniques which possess all the following properties, are very scarce: They must preserve critical structures like corners, should be robust to the type of noise distribution, avoid undesirable artefacts, and also be fast. The area of structure enhancement also has an unresolved issue: Very little efforts have been put into designing models that can tackle anisotropic deformations in the image acquisition process. In this thesis, we design novel methods in the form of partial differential equations, patch-based approaches and variational models to overcome the aforementioned obstacles. In most cases, our methods outperform the existing approaches in both quality and speed, despite being applicable to a broader range of practical situations.Entrauschen, Superresolution und Strukturverbesserung sind klassische Anwendungen der Bildverarbeitung. Ihre Existenz bedingt sich in dem Bestreben, die visuelle Begutachtung digitaler Bildrohdaten zu unterstützen. Trotz erheblicher Fortschritte in diesen Feldern bedürfen bestimmte schwierige Probleme noch weiterer Forschung. So sind beispielsweise Entrauschungsund Superresolutionsverfahren, welche alle der folgenden Eingenschaften besitzen, sehr selten: die Erhaltung wichtiger Strukturen wie Ecken, Robustheit bezüglich der Rauschverteilung, Vermeidung unerwünschter Artefakte und niedrige Laufzeit. Auch im Gebiet der Strukturverbesserung liegt ein ungelöstes Problem vor: Bisher wurde nur sehr wenig Forschungsaufwand in die Entwicklung von Modellen investieret, welche anisotrope Deformationen in bildgebenden Verfahren bewältigen können. In dieser Arbeit entwerfen wir neue Methoden in Form von partiellen Differentialgleichungen, patch-basierten Ansätzen und Variationsmodellen um die oben erwähnten Hindernisse zu überwinden. In den meisten Fällen übertreffen unsere Methoden nicht nur qualitativ die bisher verwendeten Ansätze, sondern lösen die gestellten Aufgaben auch schneller. Zudem decken wir mit unseren Modellen einen breiteren Bereich praktischer Fragestellungen ab

Methodology for Shot-Peening Induced Intragranular Residual Stress Prediction

Résumé Le grenaillage est un traitement mécanique des surfaces qui consiste à projeter des billes à très haute vitesse à la surface d’une pièce. Ce traitement est utilisé depuis plus d’une soixantaine d’année dans l’industrie pour améliorer la durée de vie en fatigue des matériaux par l’introduction de contraintes résiduelles de compression et de gradients de duretés en sous surface. Le procédé a longtemps été simplement considéré comme bénéfique sans réelle quantification des bénéfices apportés sur la durée de vie en fatigue et les évolutions de microstructures. En effet, modéliser le procédé a longtemps été un verrou car cela implique de simuler un grand nombre d’impacts, de reproduire avec précision la cinétique des billes et de prendre en compte un certain nombre de non-linéarités dues au contact et aux déformations plastiques. Cependant les avancées de ces dix dernières années ont permis le développement de modèles pouvant prédire avec précision le profil moyen de contraintes résiduelles en profondeur ainsi que les gradients d’écrouissage résultants. Peu d’études ont cependant tenté de prédire les contraintes résiduelles et l’écrouissage induits à l’échelle d’un grain. Les variations intragranulaires des contraintes ont pourtant une influence sur la durée de vie à grand nombre de cycle d’un matériau. Par ailleurs l’écrouissage local constitue une donnée cruciale pour certains modèles de prédiction de durée de vie en fatigue. Les verrous principaux à lever pour effectuer de telles prédictions sont l’identification précise de modèles de plasticité cristalline à l’échelle de la surface et dans les conditions du procédé, ainsi que le développement de méthodes expérimentales de validation des modèles développés. L’objectif de cette thèse est de développer une méthodologie pour la prédiction des contraintes résiduelles et de l’écrouissage intragranulaire à l’aide de modèles de plasticité cristalline par éléments finis et de validations expérimentales. Des essais d’indentation sphérique sur des monocristaux de cuivre sont présentés afin d’estimer le champ de contrainte induit en sous surface expérimentalement et numériquement. Les résultats révèlent que l’anisotropie de la plasticité cristalline peut induire des contraintes résiduelles de tension en sous surface. La comparaison des champs numériques et expérimentaux confirme aussi la possibilité de comparer des champs de contraintes estimés par EBSD à haute résolution à ceux prédits par des modèles de plasticité cristalline de façon suffisament quantitative pour permettre la validation de modèle. Les évolutions microstructurales induites par le grenaillage d’un coin sont ensuite étudiées par des estimations EBSD de densités de dislocations géométriquement nécessaires à l’aide de nouvelles méthodes d’indexation alternatives. Les différences d’écrouissage relevées démontrent l’importance de modéliser le procédé à l’échelle du grain. Une méthodologie pour l’identification de loi de plasticité cristalline à haute vitesse basée sur des essais de microcompression est détaillée. Une attention particulière à été portée sur le caractère bien posé du problème d’identification, à l’aide d’indice d’identifiabilités. Un canon a grenailler capable de projeter des billes isolées avec une large gamme de vitesse et une haute précision a été développé pour valider le modèle. Un code a été implémenté pour estimer la trajectoire de la bille en trois dimensions avec une précision de 200 μm pour servir d’entré aux modèles éléments finis. La validation du modèle précédent est effectuée par comparaison du déplacement de la bille, de la topologie de l’empreinte d’impact et du champ de désorientation sous l’empreinte estimés expérimentalement et numériquement. Enfin la possibilité d’utiliser le déplacement de la bille et le champ de contraintes résiduelles induit par un impact est explorée par une étude d’identifiabilité détaillée. Ces travaux offrent de nouveaux outils et méthodologies pour l’identification de paramètres et la validation de modèles à l’échelle du grain et à haute vitesse. ---------- Abstract Shot peening is a mechanical surface treatment which consist in projecting several spherical particles onto a material’s surface. The process have been widely used in the industry over more than sixty years to enhance material’s fatigue properties by introduction of subsurface compressive stresses and hardening gradients. It has been long used as a ’nice to have’ without any quantification of its benefits as its modeling involved a large number of impacts, complex shot kinematics and non linearities induced by contact and plastic deformations. Nonetheless, advances over the past twenty years provided models that successfully reproduced experimentally measured average residual stress profiles and hardening gradients. However, only few attempts to predict the residual stress and hardening variations at the grain scale have yet been reported. Intragranular stress variations could influence a structure high cycle fatigue behaviour and local hardening could be a crucial input for fatigue life predictions models. The main barriers to achieve such predictions are mainly the difficulty to identify accurate crystal plasticity models in the process conditions as well as defining relevant validation procedures to assess the ability of the models to predict residual stress variations. The objective of this thesis is to develop a methodology for shot peening induced intragranular residual stress and hardening prediction using crystal plasticity finite element simulations and experimental validations. Indentation on single crystal copper are first presented to assess the residual stress variations in a single grain under the indent both experimentally and numerically. The results reveal that crystal plasticity anisotropy could induce subsurface tensile residual stresses under a spherical contact. It also demonstrates that experimental residual stress fields estimated by high angular resolution electron backscattered diffraction could be quantitatively compared to finite element models. This finding makes it a relevant tool for constitutive behaviour validation. The microstructural evolutions induced by shot peening of a corner are investigated using electron backscatter diffraction geometrically necessary dislocation estimations with recently developed alternative indexation methods. The differences in hardening gradient close to the corner compared with a reference shot peened material evidences that accurately predict microstructural evolutions induced by the process at the grain scale is necessary to predict the induced hardening distribution. These works provides new evidences of the relevance of modeling the process at the crystal scale. A methodology for identification of crystal plasticity parameters at high strain rates using micropillar compression is then detailed. Particular attention is paid to the identification problem well-posedness using identifiability indicators provided by the literature. A shotpeening canon that can propel single shot over a wide velocity range with high aiming precision is developed. An in-house code that can estimate the shot trajectory within 200 μm is implemented to provide input for finite element analyses. The setup is used for validation of the previously identified model by comparison of the shot displacement impact dent topography and in-depth crystal misorientation field. Finally, the possibility to use the shot displacement curve and residual stress field under the dent produced by the setup is investigated through a detailed identifiability analyses. These works provide new tools and methodologies for crystal plasticity parameters identification and validation at the grain scale and at high strain rates

Experimental studies on the formation of pyrite and marcasite and the mechanisms of arsenic incorporation

Iron disulfide (FeS2) has two polymorphs, pyrite and marcasite. Pyrite is the most abundant sulfide in the Earth's crust. Both minerals can host economic amount of gold and environmentally hazardous arsenic and are found to coexist in hydrothermal mineralization. With time, thermodynamically metastable marcasite can transform to pyrite. However, the kinetics of the marcasite to pyrite transformation, and the mechanisms of arsenic incorporation during growth of pyrite are not well-constrained. This thesis presents experimental results and discussions on: (i) the formation of pyrite and marcasite under dry and hydrothermal conditions (Chapter 2 and 3), and (ii) incorporation of arsenic into pyrite during the growth of pyrite on pyrite seeds (Chapter 4). In Chapter 2, the transformation from marcasite to pyrite was studied by in situ synchrotron powder X-ray diffraction (PXRD) at 520 °C and 540 °C, and ex situ anneal/quench experiments at 400 °C, 462 °C, and 520 °C. It was found that the mechanism and kinetics of this transformation depend not only on temperature, but also on particle size, the presence of water vapor, and the presence of pyrite inclusions in marcasite. Under dry conditions, the transformation is limited by surface nucleation and occurs via epitaxial nucleation of pyrite on marcasite, with {100}pyrite//{101}marcasite and {001}pyrite//{010}marcasite. In contrast, in the presence of water vapor, there is little crystallographic orientation relationship between the two phases; the transformation is limited by surface nucleation, but modification of the surface properties by water vapor results in a different nucleation mechanism, and consequently different kinetics. Kinetic analysis estimates a half-life of 1.5 Ma at 300 °C for the transformation under dry conditions with pyrite-free marcasite grains (<38 μm), but this estimation should be used with extreme caution due to the complexity of the process. From synchrotron X-ray fluorescence elemental mapping, trace elements (As and Pb) play an insignificant role in the transformation. However, the presence of a fluid phase changes the behavior of Pb. Under dry conditions randomly oriented particles of galena formed in pyrite, while under water vapor conditions arrays of nano-to-microparticles of galena precipitated in pores. This chapter highlights that although the natural occurrence of marcasite can indicate low temperature environments, precise estimation of temperature should not be made without considering the influences from various reaction parameters. In Chapter 3, combined in-situ synchrotron PXRD and ex situ experiments were conducted under hydrothermal conditions at 190 °C and 210 °C and pH 1, aiming to study the controls on the precipitation of pyrite and marcasite from supersaturated hydrothermal solutions and the kinetics of hydrothermal transformation from marcasite to pyrite. In situ PXRD experiments show the important role of saturation index on the precipitation of pyrite and marcasite; at 190 °C, hydrothermal fluids rich in ΣS(-II) (0.9 mM) favors the precipitation of nanocrystalline pyrite (23 nm) due to high saturation index, while S(-II)-free fluids produce a mixture of marcasite and pyrite nanocrystals (21-46 nm) due to low saturation index. Fluid/rock ratio (70 and 120 g/g at 210 °C) can affect saturation index of the fluids, resulting in complex nucleation and crystal growth dynamics such as the evolution of crystallite size, phase abundance, and pyrite/marcasite ratio. Ex situ experiments show the rapid transformation from marcasite to pyrite at 210 °C; around 83% marcasite is transformed to pyrite in just 3 weeks, compared to 4.3 million years or 6.3 trillion years at 210 °C based on extrapolation using the kinetic models reported in early studies under dry conditions. These results suggest that saturation index influences the dynamics of precipitation under hydrothermal conditions and controls the phase selection between pyrite and marcasite, and that marcasite may not survive over geological time in low temperature environments in the presence of acidic hydrothermal fluids. In Chapter 4, the formation of zoned arsenian pyrite was studied by growing pyrite on pyrite seeds in O2-free, As-enriched fluids at 200 °C and pH 7. The distribution and concentrations of As in pyrite, as well as the morphology of the zoning are influenced by sulfur source; i.e., native sulfur or Na2S2O3·5H2O. For experiments with native sulfur, up to four concentric alternate zones of As-rich (first zone on pyrite seed) and As-free pyrite grow on pyrite seeds. For experiments with Na2S2O3·5H2O, an aggregate of concentrically zoned pyrite microparticles (~1 µm) precipitate on the surface of pyrite seeds. Based on EMPA, the maximum concentration of As is 4.3 wt. %. However, the TEM-EDS analyses reveal ≤5.8 wt. % of As. HRTEM and selected area electron diffraction (SAED) pattern combined with EBSD analyses document epitaxial growth of As-pyrite on pyrite seed in the presence of native sulfur, but aggregation of randomly oriented aggregates of pyrite microparticles in the presence of thiosulfate. High-angle annular dark-field scanning TEM (HAADF-STEM), HRTEM observations, and EDS mapping show a sharp boundary and trails of pores between the pyrite seed and the product and between the growth zones. In the presence of native sulfur, the thickness of the As-pyrite growth zones is ~ 50 nm, while the subsequently formed growth zones of “barren” pyrite are ~5000 nm thick. X-ray absorption near edge structure (XANES) analyses reveal that speciation of As in pyrite depends on the S-source: (i) anionic As(-I) substitutes for S in pyrite as As2 pair when native S is used, and (ii) cationic As(II)/As(III) substitutes for Fe when thiosulfate is used. Our experiments show that the incorporation of As into pyrite and the formation and morphology of pyrite growth zones are controlled by the source of sulfur in hydrothermal fluids. This thesis highlights the factors that control the mechanisms of the formation and transformation of pyrite and marcasite and the dependence of As incorporation into arsenian pyrite structure as a function of S and As source in the presence of pyrite seeds. These outcomes should benefit our understanding of the formation and alteration of Carlin-type, epithermal, volcanic-hosted massive sulfide (VMS), and orogenic Au deposits

Evaporation and dissolution of droplets in ternary systems

The evaporation and dissolution of droplets in multi-component systems are omnipresent in nature, science, and many advanced technologies. However, these droplets have much less been studied than droplets consisting of a pure liquid only. The two-way interactions between the fluid properties and hydrodynamics make the dynamical behavior of the droplet complicated. In this thesis, we give our contributions to this field by studying the evaporation and dissolution of Ouzo droplets. Ouzo is an anise-flavored aperitif, primarily consisting of water, ethanol and a small amount of anise oil. The Ouzo droplet may be seen as a model system for any ternary mixture of liquids with different volatilities and mutual solubilities. In Part I, we explored the evaporating and dissolving processes of “ouzo” (water, ethanol, and anise oil) droplets on surfaces. Through a series of studies, we revealed microdroplet nucleation processes triggered by the evaporation or dissolution of the droplets in ternary systems and consequently induced dynamical behaviors of the droplets. In Part II, we performed exploratory research on the application of the evaporating multicomponent droplets. Inspired by the interesting phenomenon observed in Part I, we proposed a method for evaporation-driven particles assembly. Through this method, the evaporating colloid ouzo droplets acquire a “self-lubrication” ability, which improves the supraparticle fabrication technique. In the last Part III, our attention focused on the nucleated nanodroplets on the surface induced by the “ouzo effect.” We used the solvent exchange method to form the surface nanodroplets in a narrow channel with controlled flow conditions. A comprehensive three-dimensional (3D) spherical cap fitting procedure was developed for the accurate extraction of the morphologic characteristics of complete or truncated spherical caps from atomic force microscopy (AFM) images

Polymer Processing and Surfaces

This book focuses on fundamental and applied research on polymer processing and its effect on the final surface as the optimization of polymer surface properties results in the unique applicability of these over other materials. The development and testing of the next generation of polymeric and composite materials is of particular interest. Special attention is given to polymer surface modification, external stimuli-responsive surfaces, coatings, adhesion, polymer and composites fatigue analysis, evaluation of the surface quality and microhardness, processing parameter optimization, characterization techniques, among others

Surfaces and interfaces in thin-film and conventional li-ion batteries

El capítulo 4 está sujeto a confidencialidad por el autor. 194 p.En esta tesis doctoral titulada "Surfaces and Interfaces in Thin-Film and Conventional Li-ion Batteries" se presentan los resultados del trabajo experimental realizado en relación a materiales del estado del arte en baterías íon-litio. En particular, en una primera parte se describen los resultados obtenidos al estudiar la superficie de electrodos formados por el material Titanato de Litio (Li4Ti5O12, LTO). En esta primera parte el estudio se centra en la evolución de las fases presentes en la superficie del electrodo a lo largo del ciclado electroquímico. En una segunda parte, continuando con los electrodos basados en el material LTO, se estudia el efecto de capas protectoras depositadas en electrodos convencionales mediante la técnica de sputtering. En esta parte se describe el efecto positivo que dichas capas protectoras tienes en el comportamiento electroquímico de los electrodos, al mismo tiempo que se estudia el origen de dicha mejora. Finalmente, en un último capítulo se describe la deposición, caracterización y optimización de electrodos de capa fina del material LiMn1.5Ni0.5O4. Además de una caracterización composicional, morfológica, estructural y electroquímica de los electrodos, se dedica especial atención a las intercaras, tanto la del colector de corriente-electrodo como la del electrodo-electrolito sólido

Super-Flexible Sensors and Advanced 3D Morphing Actuators based on Elastic Instability

Super-flexible devices based on soft materials have the potential to sustain large mechanical deformations, enabling advanced applications such as flexible electronics, soft robots, artificial skin, and biomedical transducers. Subject to a large compression, materials may undergo different types of elastic instabilities such as wrinkles, creases, and folds. Despite recent growing interests in turning this usually unwanted phenomenon into useful engineering applications (e.g. tactile sensing), this topic remains relatively under-researched. Therefore, this thesis focuses on developing the control mechanisms of elastic instabilities, and their applications in sensing and actuation systems. Elastic instabilities induced strain-gated logic sensing technology is developed by research into micro structured metal-elastomer tri-layer system. The test structures are designed to study the deformation behaviour and to exploit the large strain sensing mechanism. The stepwise electrical signals are achieved (from ~1010 to ~120 Ω at first switching stage and then to ~50 Ω at second switching stage) that survived much higher than usual compressive strains of up to 60%. On the other hand, elastic instabilities induced topo-optical sensing strategy is created by patterning microstructure arrays within the tri-layer system. Two unwanted phenomena (creases/folds and oxygen quenching effect) are turned into a responsive and programmable 'fold to glitter' function through micro engineering, which can light up areas of an object or material by creating microscopic creases/folds within its surface. The signal-Noise-Ratio (SNR) contrast in optical pattern generation is improved by 6 folds due to the oxygen quenching effect. The numerical analysis by ABAQUS provides the fundamental theory on the mechanism of generating targeted folding through simulating the in-plane and out-of-plane strain energy localization. Different luminescent optical patterns are demonstrated under in-plane uniaxial or equi-biaxial compression. Apart from the surface deformation, the bulk deformation of heterogeneous layered structures of soft functional hydrogel is also developed to generate the controllable and reconfigurable 3D morphing device. The initial configurations with various shapes (“S”, “W” and “C”) are demonstrated due to the swelling ratio mismatch. The developed sensing and actuation technologies provide opportunities for future applications in flexible electronics, tuneable optics, soft robotics and bio-medical systems