Master of Science / Department of Agronomy / Jay M. Ham / The potential environmental impact of animal feeding operations on air quality has created the need for accurate air emissions measurements. Of particular concern are ammonia emissions from cattle feedlots, operations that contribute a large portion of the agricultural ammonia emissions inventory. Micrometeorological methods are ideal for emissions measurements from large, open-source areas like feedlot pens; however, theoretical assumptions about the boundary layer must be made, which may not hold true above the heterogeneous, fetch-limited surface of the feedlot. Thus, the first objective of this work was to characterize the surface boundary layer of an open-air cattle feedlot and provide insight into how micrometeorological techniques might be applied to these non-ideal sites. Eddy covariance was used to measure fluxes of momentum, heat, water, and carbon dioxide from a commercial cattle feedlot in central Kansas. Data supported the use of eddy covariance and similar methods (i.e., relaxed eddy accumulation) for flux measurements from both cattle and pen surfaces. The modeled cumulative source area contributing to eddy covariance measurements at a 6 m sample height was dominated by just a few pens near the tower, making the characteristics of those pens especially important when interpreting results. The second objective was to develop a system for measuring ammonia fluxes from feedlots. A new type of relaxed eddy accumulation system was designed, fabricated, and tested that used honeycomb denuders to independently sample ammonia in up-moving and down-moving eddies. Field testing of the relaxed eddy accumulation system at a feedlot near Manhattan, KS showed fluxes of ammonia ranged between 60 and 130 μg m-2 s-1 during the summer of 2007. Even in the high ammonia environment (e.g., 300-600 μg m-3), the honeycomb denuders had enough capacity for the 4-hour sampling duration and could be used to measure other chemical species that the denuders could be configured to capture. Results provide a foundation for emissions measurements of ammonia and other gases at cattle feedlots and help address some of the challenges that micrometeorologists face with any non-ideal source area.

L’objectif de cette thèse est d’étudier expérimentalement les deformations de microcapsules dans un écoulement confiné. Les microcapsules sont composées d’albumine du sérum humain avec des concentrations de 5 à 20 [g/100mL]. Leur taille varie de 50 à 1000 [μm]. Les capsules sont injectées dans des écoulements de Poiseuille produits dans des canaux microfluidiques présentant deux sections différentes : circulaire ou carrée.La mesure des caractéristiques géométriques de microcapsules déformées couplée à des simulations numériques mène à la détermination du module de cisaillement surfacique. Cette caractéristique mécanique augmente fortement tant avec la taille qu’avec la concentration en protéine de la capsule, et plus précisément avec le produit de ces deux paramètres.Le fluide est ensemencé avec des microparticules pour mesurer l’écoulement induit par une capsule dans un capillaire cylindrique par la méthode de la vélocimétrie par suivi de particules. Les zones de recirculation et de perturbation sont alors déduites et comparées avec la simulation numérique d’un objet rigide dans un capillaire et présentant le profil donné par les expériences. Finalement un système original de visualisation optique est consacré à l’observation simultanée de la vue de côté et de la vue de face des capsules pour obtenir sa forme entière. Ceux-ci révèlent l’existence des plis tout autour de la membrane des capsules. Le seuil de formation et l’évolution de ces plis sont étudiés en fonction de la vitesse, de la taille et du confinement, dans des canaux de section circulaire ou carrée. / The objective of this thesis is to study experimentally microcapsule deformations in confined flows. The microcapsules are made of cross-linked proteins, the human serum albumin (HSA) with concentrations from 5 to 20 [g/100mL]. Their size vary from 50 to 1000 [μm]. Capsules are injected in Poiseuille flows generated within microfluidics channels with two different cross sections geometries : circular or square.The measurement of geometrical characteristics of deformed microcapsules coupled with numerical simulations leads to the determination of the surface shear modulus. This mechanical characteristic increases strongly with both the size and the protein concentration of the capsule, and more precisely with the product of these two parameters.The flow is seeded with microparticles to measure the induced flow of a capsule in a cylindrical capillary by particle tracking velocimetry. The recirculation and perturbation zones are then deduced and compared with numerical simulation of a rigid body flowing in a capillary. Finally an original system of optical visualization is dedicated to the simultaneous observation of the side and the front view of the capsules to get its whole shape. These reveal radial wrinkles all around capsules membrane. The formation threshold and the evolution of these wrinkles are studied as function of the capsule velocity and size and the confinement within capillaries with circular or square cross–section.

L’objectif de ce travail est d’améliorer la compréhension des phénomènes de Corrosion Sous Contrainte (CSC) susceptibles d’être rencontrés sur les fils d’armures des conduites flexibles, faits d’aciers ferrito-perlitiques. Dans l’annulaire des conduites flexibles, l’environnement chimique des aciers est constitué d’une « eau de mer » confinée et saturée en CO2. Celui-ci favorise la formation d’une couche protectrice de sidérite qui semble avoir un effet déterminant sur la vitesse de corrosion de l’acier. Les conditions de service entrainant des fluctuations de l’environnement ou des contraintes appliquées s’ajoutant à des contraintes résiduelles peuvent provoquer la rupture des conditions d’équilibre entre l’acier et son environnement protecteur, et amorcer ainsi la CSC.Les paramètres microstructuraux et mécaniques qui gouvernent l’amorçage et la propagation de fissures par CSC dans les aciers ferrito-perlitiques dans un milieu confiné simulé sont identifiés au moyen d’essais de traction lente menés sous différents potentiels électrochimiques sur des éprouvettes lisses et micro-entaillées. La phase d’amorçage met en jeu des effets de synergie entre la localisation de la plasticité et la dissolution de l’acier. Cependant, des effets de l’hydrogène doivent être pris en compte dans la propagation des fissures. L’hydrogène, au travers d’interactions hydrogène/plasticité, entraine l’avancée des fissures. Il a été également démontré que l’emploi de microstructures particulières peut favoriser ou retarder les effets de l’hydrogène sans pour autant affecter la limite d’élasticité de la même manière. / In confined solutions containing dissolved CO2, ferrito-pearlitic steels can suffer Stress Corrosion Cracking (SCC). We could find such situations in the annulus of flexible pipes. In these conditions, a protective corrosion product, the siderite FeCO3, is formed on the steel surface decreasing the corrosion rate. In service, environment fluctuation (such as pH, potential…) and/or an addition of applied stress can disturb the balance between the steel and this protective film, causing the fracture of the latter and leading to SCC.The objective is to understand the mechanism of SCC in such environments and to identify the parameters controlling the initiation and the propagation of cracks. Slow strain rate tensile tests in confined solution are carried out on smooth and notched specimens to study crack initiation and propagation. Crack initiation is controlled by synergistic effects between localized plasticity and the dissolution processes. However, hydrogen effects must be considered to explain crack propagation. Through hydrogen/plasticity interactions, hydrogen ingress leads to crack propagation. It is also demonstrated that the design and use of specific microstructures may promote or delay hydrogen effects, without affecting the yield strength in the same manner. Finally, the influence of a torsional pre-strain on the susceptibility to Environmentally-Assisted Cracking of a cold-worked ferrito-pearlitic steel is studied.

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Orientador: Alex Antonelli / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-29T05:01:21Z (GMT). No. of bitstreams: 1 CajahuaringaMacollunco_OscarSamuel_D.pdf: 15985103 bytes, checksum: f54d17d6335170c62196c9e329f257d9 (MD5) Previous issue date: 2015 / Resumo: Apesar de serem substâncias muito diferentes, silício e gálio, na fase líquida, compartilham muitas anomalias nas suas propriedades termodinâmicas. Evidências teóricas e experimentais sugerem que esses líquidos podem sofrer a chamada transição de fase líquido-líquido (LLPT). Especula-se que este tipo de transição é acompanhada por uma transição dinâmica entre um líquido frágil e um líquido forte, com base nas hipóteses de que o surgimento de um "dip" na função auto-intermediária de espalhamento logo após o regime balístico e o aparecimento do excesso de modos vibracionais em baixas frequências após a LLPT estariam relacionados com o comportamento de líquidos fortes. Foi realizado um estudo da dinâmica desses sistemas através das funções de correlação nas vizinhanças da LLPT usando simulações clássicas. Observamos apenas no caso do silício o aparecimento do "dip" na função auto-intermediária de espalhamento. A densidade de estados vibracionais reduzida de ambos os líquidos apresenta picos em baixas frequências, sugerindo que ambos os líquidos seriam fortes. Desta forma, nos dois casos estudados, as duas hipóteses não são conclusivas. Visando um melhor entendimento, determinamos a viscosidade de cisalhamento de ambos os líquidos em um amplo intervalo de temperatura. A apresentação desses resultados no chamado gráfico de Angell, indica que, em ambos os casos, a LLPT é acompanhada de uma transição de um líquido frágil para um líquido menos frágil, o que não dá suporte às especulações de uma transição frágil-forte. Além de investigar a LLPT em gálio "bulk", foi também estudado o gálio líquido confinado em nanofendas, ou seja, um sistema quase-bidimensional. Foi observada a transição de fase de primeira ordem entre um líquido isotrópico e um líquido ordenado. Por meio de uma série de análises estruturais, tanto de ordem translacional quanto orientacional, conseguimos identificar o líquido ordenado como a fase hexática, que é prevista ocorrer em sistemas bidimensionais segundo a teoria de Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY). Como a LLPT em gálio bulk foi identificada em simulações de dinâmica clássica, realizamos um estudo visando obter evidência da LLPT em simulações de primeiros princípios, que são em princípio mais realísticas. Utilizando o chamado método-Z, que permite estimar a temperatura de fusão, determinamos que o regime super-resfriado do gálio líquido descrito por cálculos de primeiros princípios ocorre em temperaturas abaixo de 400 K. Partindo de um líquido em equilíbrio em 500 K, realizamos simulações a pressão constante igual a zero em que o líquido foi resfriado para 260 K em um intervalo de 145 ps. Não foi observada uma mudança abrupta no volume durante o resfriamento. A fim de melhorar a amostragem em nossas simulações de primeiros princípios, realizamos um estudo de dinâmica molecular a volume constante com troca de réplicas. Foram usadas um total de 10 réplicas entre 400 K e 260 K, em simulações com a duração de 100 ps. Neste caso, a pressão decresceu monotonicamente com a temperatura, o que é característico de líquidos simples que não sofrem LLPT. Cabe ressaltar que nas simulações clássicas que identificaram a LLPT em gálio, a taxa de resfriamento foi muito mais lenta, da ordem de nano-segundos, que seria inexequível para simulações de primeiros princípios / Abstract: Despite of being very different substances, silicon and gallium, in their liquid phase, share several anomalous thermodynamic properties. Theoretical and experimental evidence suggest that these liquids can undergo the so-called liquid-liquid phase transition (LLPT). There has been speculated that this transition is accompanied by a dynamic transition form a fragile liquid to a strong liquid, based on the hypothesis that the development of a dip in the self-intermediate scattering function, just after the ballistic regime, and the appearance of excess low frequency vibrational modes just after the LLPT would be related to the behavior of strong liquids. It was performed a study of the dynamics of these systems through the correlation functions in the vicinity of the LLPT using classical simulations. We observed the development of a dip in the self-intermediate scattering function only in the case o silicon. The reduced density of vibrational states of both liquids exhibits peaks in low frequencies, suggesting both liquids to be strong. Therefore, for the two cases we studied, the two hypotheses are not conclusive. In order to achieve a better understanding, we determined the shear viscosity of both liquids for a wide range of temperatures. By plotting the data in the so-called Angell plot one can see that, in both cases, the LLPT is accompanied by a transition of a fragile liquid to a less fragile liquid, which does not give support to the speculations of a fragile-to-strong transition. Aside from investigating the LLPT in bulk gallium, it was also studied liquid gallium confined in nanoslits. i.e., a quasi two-dimensional system. It was observed a first-order transition between an isotropic liquid and an ordered liquid. Through a series of structural analyses, both translational and orientational, we were able to identify the ordered liquid as the hexatic phase, which is predict to occur in two-dimensional systems according to the Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) theory. Since the LLPT in gallium has been found in classical molecular dynamics simulations, we performed a study aimed to obtain evidence of the LLPT in first-principles simulations, which are, in principle, more realistic. Using the so-called Z-method, which allows one to estimate the melting temperature, we determined the supercooled regime of liquid gallium, described by first-principles, to occur below 400 K. Starting from an equilibrated liquid at 500 K, we performed simulations at zero pressure in which the liquid was cooled down to 260 K in an interval of 145 ps. No abrupt change in the volume was observed as the liquid was cooled. In order to improve sampling in our first-principles simulations, we performed a study using constant volume molecular dynamics with replica exchange. Ten replicas were used between 400 K and 260 K, in simulations 100 ps long. In this case, pressure decreased monotonically with temperature, which is the behavior of simple liquids, which do not exhibit the LLPT. It should be emphasized that in the classical simulations that identified the LLPT in gallium, the cooling rates were much slower, of the order of nanoseconds, which would be unfeasible for first-principles simulations / Doutorado / Física / Doutor em Ciências / 1000949 / CAPES

Le débat sur l'origine du comportement anormal de l'eau (H2O), que peut être dû, au niveau moléculaire, à sa capacité à former des réseaux de liaisons hydrogène, est encore ouvert. Les anomalies de le H2O sont fortement accentuées dans la région surfondue du diagramme de phase (PD). Beaucoup de simulations numérique ont expliqué cet comportement en suggérant l'existence d'une transition de phase liquide-liquide (LLPT) entre deux phases de densité différente: Low Density Liquid et High Density Liquid, séparées par une ligne de coexistence terminant sur un point critique (CP) (hypothèse de le 2°point critique). Malheureusement, ce CP, s'il existe, réside dans le No man's land, une région du PD difficile à explorer expérimentalement à cause de la cristallisation spontanée. Confiner H2O dans des géométries nanométrique peut abaisser la température de congélation, en ouvrant la possibilité d'entrer dans le No man's land et d'enquêter sur l'existence de LLPT. Nous avons étudié H2O confiné dans une matrice mésoporeuse (MCM-41), en mettant l'accent sur l'existence d'un minimum de densité (DM) à 210 K, qui devrait être directement lié au second CP supposé. Nos expériences ont exploité la spectroscopie infrarouge, la diffusion de neutrons à petit angle et la diffraction de neutrons sur une large gamme de Q. L'interprétation de nos résultats a conduit à conclure que dans le centre du pore de MCM-41 se forme une hétérophase solide, à une température proche a quelle prétendu par d'autres auteurs pour le DM. Donc l'approche expérimentale commune est faux et ce qui a été précédemment interprété comme un signe de DM à 210 K est en réalité dû au début d'un événement de cristallisation. / Le débat sur l'origine du comportement anormal de l'eau (H2O), qui peut être dû, au niveau moléculaire, à sa capacité à former des réseaux de liaisons hydrogène, est encore ouvert. Les anomalies du H2O sont fortement accentuées dans la région surfondue du diagramme de phase (PD). Beaucoup de simulations numérique ont expliqué cet comportement en suggérant l'existence d'une transition de phase liquide-liquide (LLPT) entre deux phases de densité différente: Low Density Liquid et High Density Liquid, séparées par une ligne de coexistence terminant sur un point critique (CP) (hypothèse de le 2°point critique). Malheureusement, ce CP, s'il existe, réside dans le No man's land, une région du PD difficile à explorer expérimentalement à cause de la cristallisation spontanée. Confiner H2O dans des géométries nanométrique peut abaisser la température de congélation, en ouvrant la possibilité d'entrer dans le No man's land et d'enquêter sur l'existence de LLPT. Nous avons étudié H2O confiné dans une matrice mésoporeuse (MCM-41), en mettant l'accent sur l'existence d'un minimum de densité (DM) à 210 K, qui devrait être directement lié au second CP supposé. Nos expériences ont exploité la spectroscopie infrarouge, la diffusion de neutrons à petit angle et la diffraction de neutrons sur une large gamme de Q. L'interprétation de nos résultats a conduit à conclure que dans le centre du pore de MCM-41 se forme une hétérophase solide, à une température proche a quelle prétendu par d'autres auteurs pour le DM. Donc l'approche expérimentale commune est faux et ce qui a été précédemment interprété comme un signe de DM à 210 K est en réalité dû au début d'un événement de cristallisation.

InGaN based light emitting devices operating in the blue and near UV spectral regions are commercialized and used in many applications. InGaN heterostructures experience compositional inhomogeneity and thus potential fluctuations, such that regions of higher indium composition are formed and correspond to lower potentials. The indium rich regions form localization centers that save carriers from non-radiative recombination at dislocations, thus despite the large defect density, their quantum efficiency are surprisingly large. However, the conventional c-plane InGaN QWs suffer from high internal piezoelectric and spontaneous fields. These fields are detrimental for the performance of such structures as they lead to the quantum confined stark effect causing red-shift of the emission as well as reducing the electrons and holes wavefunctions overlap, thereby reducing the radiative recombination rate. However, growth of InGaN QWs on semipolar and nonpolar planes greatly reduced the polarization fields. Semipolar and nonpolar QWs experience an outstanding property which is polarized luminescence, opening a new frontier for applications for InGaN emitting devices. While nonpolar QWs have larger degree of polarized emission than semipolar QWs, semipolar QWs can emit in longer wavelengths due to their higher indium uptake. In this thesis, semipolar 20¯21 and nonpolar m-plane InGaN/GaN QWs were investigated. Photoluminescence, spectral and polarization dynamics were all studied in order to form a whole picture of the carrier dynamics in the QWs. Time resolved photoluminescence measurements were conducted for following carriers distribution between extended and localized states. Both the semipolar and nonpolar samples showed efficient luminescence through short radiative recombination times, as well as carrier localization in lower potential sites after thermal activation of excitons. Carrier localization was found to be benign as it didn’t degrade the performance of the samples or decrease the polarization ratio of their emission. However, the structures showed modest potential variations with the absence of deep localization centers or quantum dots. High polarization ratios were measured for both samples, which is well-known for nonpolar QWs. The high polarization ratio for the semipolar sample is of great importance, thus semipolar 20¯21 QWs should be considered for longer wavelength emitters with highly polarized spontaneous emission.

Les réservoirs de type "tight oil" et "shale gaz" ont une partie importante de leur volume poreux occupée par des micropores (< 2nm) et des mesopores (entre 2 et 50 nm). Ce type d'environnement crée de fortes forces d’interaction dans le fluide confiné avec les parois du pores et entre ses propres molécules, ce qui change fortement la thermodynamique du fluide. Un travail important doit donc être effectué sur le développement de méthodes de mise à l'échelle de la distribution de pore pour effectuer des simulations réservoir à grande échelle. Premièrement, des simulations moléculaires sont effectuées sur des fluides confinés afin d'obtenir des propriétés thermodynamiques de référence à l'équilibre liquide/vapeur pour différentes tailles de pore. Ensuite, une comparaison des données de simulation moléculaire avec les résultats issus des équation d'état utilisées dans la littérature a permis de mettre en valeur la méthode de flash avec pression capillaire et changement du point critique comme la meilleure méthode existante pour décrire la physique du fluide confiné. Des simulations fines d'écoulement matrice/fracture ont donc été effectuées pour différentes tailles de pore. Des modèles de mise à l'échelle en maillage grossier ont été ensuite construits à partir du même cas synthétique et les résultats ont été comparés avec ceux des simulations de référence en maillage fin. Un nouveau modèle de triple porosité considérant fracture, petit pores et grand pores avec une approche MINC a donné des résultats très proches du maillage fin. Finalement un réservoir stimulé hydrauliquement à grande échelle a été simulé pour différentes distributions de pores avec le modèle développé. / Tight oil and shale gas reservoirs have a significant part of their pore volume occupied by micro (below 2nm) and mesopores (between 2 and 50nm). This kind of environment creates strong interaction forces in the confined fluid with pore walls as well as between its own molecules and then changes dramatically the fluid phase behavior. An important work has therefore to be done on developing upscaling methodology of the pore size distribution for large scale reservoir simulations. Firstly, molecular simulations are performed on different confined fluids in order to get reference thermodynamic properties at liquid/vapor equilibrium for different pore sizes. Then, the comparison with commonly used modified equation of state (EOS) in the literature highlighted the model of flash with capillary pressure and critical temperature and pressure shift as the best one to match reference molecular simulation results. Afterwards fine grid matrix/fracture simulations have been built and performed for different pore size distributions. Then, coarse grid upscaling models have then been performed on the same synthetic case and compared to the reference fine grid results. A new triple porosity model considering fracture, small pores and large pores with MINC (Multiple Interacting Continua) approach, has shown very good match with the reference fine grid results. Finally a large scale stimulated reservoir volume with different pore size distribution inside the matrix has been built using the upscaling method developed here.

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