In cardiac biomechanics, there is an apparent knowledge gap in 3D cardiac elastin structure and its biomechanical roles. In this study, we fill this knowledge gap via novel biomedical imaging and bioengineering means. In Aim 1, we created an overall mapping of 3D microstructures of the epicardial elastin fibers on porcine left ventricles (LV) using a laser scanning confocal microscope. We demonstrated the location- and depth-dependencies of the epicardial elastin network. Histological staining was also applied to reveal the patterns of endocardial and interstitial elastin fibers, as well as elastin fibers associated with the Purkinje fibers. In Aim 2, a novel algorithm was developed to better reconstruct the elastin fiber network and extract topological fiber metrics. We created a “fiberness” mask via fiber segmentation and fiber skeletonization to obtain the one-voxel-thick centerline skeleton and remove spurious fiber branches, thus generating topological and geometrical descriptors and bringing the study of cardiac elastin to a new level. In Aim 3, we successfully developed a semi-quantitative approach to characterize the residual stress in the epicardial layer by calculating the total angular change due to curling. Our novel curling angle characterization clearly reveals the existence of residual stress as well as the direction (circumferential vs. longitudinal) and location-dependency of the residual stress. In Aim 4, for the first time we estimated the regional residual stress of the epicardial layer on the intact LV via a four-step methodology: (i) quantify regional residual strains by comparing in situ and stressree marker dimensions; (ii) obtain regional tension-stretch/stress-stretch curves along the circumferential and longitudinal directions; (iii) adjust the biaxial curves to the 0g load reference; (iv) estimate the circumferential and longitudinal residual stresses via residual strains. This method accurately estimates the residual stress in the epicardial layer in various LV anatomical locations. We found that the location-dependency of circumferential and longitudinal residual stresses correlates with the curvature of heart surfaces. Our studies show that the epicardial layer, with its rich elastin content, might function as a balloon that wraps around the heart, and the residual stress sets up a boundary condition that assists with LV contraction.

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A specialty class of alloys known as tungsten heavy alloys (WHAs) possess extremely desirable qualities for adoption in nuclear fusion reactors. Their high temperature stability, improvement in fracture toughness over other brittle candidates, and promising performance in initial experimental trials have demonstrated their utility, and recent advancements have been made in understanding and applying these multiphase materials systems. To that end, Pacific Northwest National Laboratory in collaboration with Virginia Tech have sought to understand and tailor the structure and properties of these materials to optimize them for service in fusion reactor interiors; thereby improving the robustness, efficiency, and longevity of structural materials selected for service in an extremely hostile environment. In this analysis of material viability, a multiscale investigation of the connections between structure-property relationships in these multiphase composite microstructures has been undertaken, employing advanced characterization techniques to bridge the macro, micro, and nanoscales for the purpose of generating a framework for the understanding of the ductile phase toughening effect in these systems. This analysis has yielded evidence suggesting the effectiveness of WHA microstructures in the simultaneous expression of high strength and toughness owes to the intimately bonded nature of the boundary which exists between the dissimilar phases in these bi-phase microstructures. Analytical techniques have been employed to provide added dimensionality to traditional materials characterization techniques, providing the first three-dimensional microstructure reconstructions exhibiting the effects of thermomechanical processing on these dual-phase microstructures, and the first time-resolved approach to the observation of WHA deformation through in-situ uniaxial tension testing. The contributions of purposefully introduced microstructural anisotropy and its contribution to texturing and boundary conformations is discussed, and an emphasis has been placed on the study of the interface between the dissimilar phases and its role in the overall expression of ductile phase toughening. In short, this collective work utilizes multiscale and multidimensional characterization techniques in the in-depth analysis and discussion of WHA systems to connect their structure to the properties which make them excellent candidates for fusion reactor systems. / Doctor of Philosophy / In the ongoing effort to realize nuclear fusion for commercial energy generation, there are numerous hurdles which must be overcome. A primary issue in the creation of these reactors is the implementation of materials which interface with the superheated plasma in the reactor interior, called plasma facing materials and components (PFMCs). These PFMCs must be able to withstand environmental conditions which will melt, irradiate, embrittle, and fracture a majority of common structural materials. Therefore these materials must exhibit unparalleled robustness in the form of high thermal and irradiation resistance. One class of alloys which is currently being considered for this purpose is tungsten heavy alloys (WHAs). These materials have exhibited excellent viability in early-stage experimental trials, and have necessarily become the subject of extended examination as PFMC candidates. In a joint collaboration between Pacific Northwest National Laboratory and Virginia Tech, these materials have been subjected to rigorous experimental testing and analysis to determine what underlying physics are responsible for their excellent properties. Advanced analytical techniques have been applied to observe the connections which exist between the atomic structure of boundaries and have been connected to the expression of observable properties on the macroscale. This work has provided the first available data on the full three-dimensional approach to the study of WHAs as well as the first dynamic observation of how the materials deform, leading to the conclusion that the two-phase composite-like structure of these alloys owe their combination of strength and ductility to the strong bond which exists between the two phases. This information on how material structure influences properties can be used to improve alloy design and produce even more effective WHA materials going forward.

A numerical model was developed to evaluate the performance of detailed solid oxide fuel cell (SOFC) anode microstructures obtained from experimental reconstruction techniques or generated from synthetic computational techniques. The model is also capable of identifying the linear triple phase boundary (TPB) reaction sites and evaluating the effective transport within the detailed structures, allowing a comparison between the structural properties and performance to be conducted. To simulate the cell performance, a novel numerical coupling technique was developed in OpenFOAM and validated. The computational grid type and mesh properties were also evaluated to establish appropriate mesh resolutions to employ when studying the performance. The performance of a baseline synthetic electrode structure was evaluated using the model and under the applied conditions it was observed that the ionic potential had the largest influence over the performance. The model was used in conjunction with a computational synthetic electrode manufacturing algorithm to conduct a numerical powder to power parametric study investigating the effects of the manufacturing properties on the performance. An improvement in the overall performance was observed in structures which maximized the number of reaction sites and had well established transport networks in the ion phase. From the manufacturing parameters studied a performance increase was observed in structures with low porosity and ionic solid volume fractions near the percolation threshold, and when the anodes were manufactured from small monosized particles or binary mixtures comprising of smaller oxygen ion conductive particles. Insight into the anode thickness was also provided and it was observed that the current distribution within the anode was a function of the applied overpotential and an increase in the overpotential resulted in the majority of the current production to increase and shift closer to the electrode-electrolyte interface. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-10-01 09:41:47.617

Les pathologies cardiovasculaires restent un des problèmes majeurs de santé publique qui justifie les recherches menées pour améliorer notre compréhension de la fonction cardiaque. Celles-ci nécessitent une bonne connaissance de la microarcInstitut de Technologie de Harbin - Chineecture myocardique afin de mieux comprendre les relations entre les fonctions mécanique, hémodynamique et les changements structuraux induits par les maladies cardiaques. Pour ce faire il est nécessaire d’accéder à une connaissance précise de l’arrangement spatial des composants du tissu. Cependant, notre compréhension de l’arcInstitut de Technologie de Harbin - Chineecture du coeur est limitée par le manque de description 3D de l’organisation des structures à l’échelle microscopique. Nous proposons d’explorer la structure 3D du tissu cardiaque en utilisant l’imagerie X synchrotron par contraste de phase disponible à l’ESRF. Pour la première fois, 9 échantillons de tissu de la paroi du ventricule gauche (VG) humain sont imagés à la résolution isotrope de 3,5 μm et analysés. Cette thèse est centrée sur la description 3D d’un des constituants principal du tissu: la matrice extracellulaire (MEC). La MEC inclue: l’endomysium qui entoure et sépare les myocytes et les capillaires de façon individuelle, le perimysium qui entoure et sépare des groupes de myocytes et l’épimysium qui enveloppe le muscle cardiaque dans son ensemble. Chaque échantillon reconstruit fait environ 30 Gb, ce qui représente une quantité importante de données à traiter et à visualiser. Pour ce faire, nous avons développé un algorithme automatique de traitement d’image pour binariser chaque échantillon et isoler la MEC. Ensuite, nous avons extrait des parametres statistiques relatifs à la microarcInstitut de Technologie de Harbin - Chineecture de l’ECM, principalement l’épaisseur des plans de clivage (PC) et les distances inter-PC. Les résultats montrent que l’arrangement local des PC diffère selon l’emplacement au sein du VG (postérieur, antérieur, septal) et de leur distance à l’apex (plus complexe). L’épaisseur des PC extraite de tous les échantillons va approximativement de 24 μm à 59 μm et la distance inter-PC de 70 μm à 280 μm avec une variation locale significative de la déviation standard. Ce sont de nouveaux marqueurs quantitatifs de la MEC du tissu cardiaque humain qui sont d’un intérêt majeur pour une meilleure compréhension de la fonction cardiaque. / Cardiovascular diseases remain one of the most serious health problems, motivating research to deepen our understanding of the myocardial function. To succeed, there is a need to get detailed information about the spatial arrangement of the cardiac tissue components. Currently, our understanding of the cardiac microarcInstitut de Technologie de Harbin - Chineecture is limited by the lack of 3D descriptions of the cardiac tissue at the microscopic scale. This thesis investigates the 3D cardiac tissue microstructure using X-Ray µ-CT phase contrast imaging available at the ESRF. For the first time, 9 human cardiac left ventricle (LV) wall samples are imaged at an isotropic resolution (3.5 µm) and analysed. We focus on the description of the cardiac extracellular matrix (CEM) that is one of the main components of the tissue. The CEM includes: the endomysium that surrounds and separates individual myocytes and capillaries, the perimysium that surrounds groups of myocytes and the epimysium that surrounds the entire heart muscle. Each reconstructed sample is about 30 Gb which represents a large amount of data to process and display. To succeed, we developed an automatic image processing algorithm to binarise each sample by selecting the CEM. We extract statistical features of the ECM, mainly the thickness of the cleavage planes (CP) and the inter-CP distances. The results show that the local 3D arrangement of the CP differs according to their location in the LV (posterior, anterior, septal) and their distance from the apex (more complex). The thickness of the CP extracted from all the samples roughly ranges from 24 µm to 59 µm and the inter-CP distances from 70 µm to 280 µm with significant local variations of the standard deviation. Those new quantitative markers of the ECM of the human cardiac are of main interest for a better understanding of the heart function.

Ce travail porte sur la compréhension de l’impact de la microstructure sur les performances des Cellules à Oxyde Solide (SOC), avec une illustration sur l’électrode à oxygène en LSCF-CGO. Une approche couplant de la modélisation géométrique et électrochimique a été adoptée pour cet effet. Le modèle des champs aléatoires plurigaussiens et un autre basé sur des empilements de sphères ont été développés et adaptés pour les microstructures des SOCs. Ces modèles 3D de géométrie stochastique ont été ensuite validés sur différentes électrodes reconstruites par nano-holotomographie aux rayons X au synchrotron ou par tomographie avec un microscope électronique à balayage couplé à une sonde ionique focalisée. Ensuite, des corrélations semi-analytiques ont été proposées et validées sur une large base de microstructures synthétiques. Ces relations permettent de relier les paramètres ‘primaires’ de l’électrode (la composition, la porosité et les diamètres des phases) aux paramètres qui pilotent les réactions électrochimiques (la densité de points triples, les surfaces spécifiques interphases) et sont particulièrement pertinents pour les équipes de mise-en-forme des électrodes qui ont plus de contrôle sur ce premier ensemble de paramètres. Concernant la partie portant sur l’électrochimie, des tests sur une cellule symétrique en LSCF-CGO ont permis de valider un modèle déjà développé au sein du laboratoire, et qui permet de simuler la réponse électrochimique d’une électrode à oxygène à partir des données thermodynamiques et de microstructure. Finalement, le couplage des deux modèles validés a permis d’étudier l’impact de la composition des électrodes, leur porosité ou encore taille des grains sur leurs performances. Ces résultats pourront guider les équipes de mise-en-forme des électrodes vers des électrodes plus optimisées. / This work aims at better understanding the impact of Solid Oxide Cells (SOC) microstructure on their performance, with an illustration on an LSCF-CGO electrode. A coupled 3D stochastic geometrical and electrochemical modeling approach has been adopted. In this frame, a plurigaussian random field model and an in-house sphere packing algorithm have been adapted to simulate the microstructure of SOCs. The geometrical models have been validated on different electrodes reconstructed by synchrotron X-ray nano-holotomography or focused ion-beam tomography. Afterwards, semi-analytical microstructural correlations have been proposed and validated on a large dataset of representative synthetic microstructures. These relationships allow establishing the link between the electrode ‘basic’ parameters (composition, porosity and grain size), to the ‘key’ electrochemical parameters (Triple Phase Boundary length density and Specific surface areas), and are particularly useful for cell manufacturers who can easily control the first set of parameters. Concerning the electrochemical part, a reference symmetrical cell made of LSCF-CGO has been tested in a three-electrode setup. This enabled the validation of an oxygen electrode model that links the electrode morphological parameters to its polarization resistance, taking into account the thermodynamic data. Finally, the coupling of the validated models has enabled the investigation of the impact of electrode composition, porosity and grain size on the cell electrochemical performance, and thus providing useful insights to cell manufacturers.

<div>In contrast to traditional steel and aluminum, short fiber reinforced polymer composites (SFRCs) provide promising alternatives in material selection for automotive and aerospace applications due to their potential to decrease weight while maintaining excellent mechanical properties. However, uncertainties about the influence of complex microstructures and defects on mechanical response have prevented widespread adoption of material models for</div><div>SFRCs. In order to build confidence in models’ predictions requires deepened insight into the heterogenous damage mechanisms. Therefore, this research takes a micro-mechanics standpoint of assessing the damage behavior of SFRCs, particularly micro-void nucleation at the fiber tips, by passing information of microstructural attributes within neighborhoods of incipient damage and non-damage sites, into a framework that establishes correlations between the microstructural information and damage. To achieve this, in-situ x-ray tomography of the gauge sections of two cylindrical injection molded dog-bone specimens, composed of E-glass fibers in a polypropylene matrix, was conducted while the specimens were monotonically loaded until failure. This was followed by (i) the development of microstructural characterization frameworks for segmenting fiber and porosity features in 3D images, (ii) the development of a digital volume correlation informed damage detection framework that confines search spaces of potential damage sites, and (iii) the use of a Gaussian process classification framework to explore the dependency of micro-void nucleation on neighboring microstructural defects by ranking each of their contributions. Specifically, the analysis considered microstructural metrics related to the closest fiber, the closest pore, and the local stiffness, and the results demonstrated that less stiff resin rich areas were more relevant for micro-void nucleation than clustered fiber tips, T-intersections of fibers, or varying porosity volumes. This analysis provides a ranking of microstructural metrics that induce microvoid nucleation, which can be helpful for modelers to validate their predictions on proclivity of damage initiation in the presence of wide distributions of microstructural features and</div><div>manufacturing defects. </div>

The dissertation deals with the image processing in digital holographic microscopy and X-ray computed tomography. The focus of the work lies in the proposal of data processing techniques to meet the needs of the biological experiments. Transmitted light holographic microscopy is particularly used for quantitative phase imaging of transparent microscopic objects such as living cells. The phase images are affected by the phase aberrations that make the analysis particularly difficult. Here, we present a novel algorithm for dynamical processing of living cells phase images in a time-lapse sequence. The algorithm compensates for the deformation of a phase image using weighted least squares surface fitting. Moreover, it identifies and segments the individual cells in the phase image. This property of the algorithm is important for real-time cell quantitative phase imaging and instantaneous control of the course of the experiment. The efficiency of the propounded algorithm is demonstrated on images of rat fibrosarcoma cells using an off-axis holographic microscope. High resolution X-ray computed tomography is increasingly used technique for the study of the small rodent bones micro-structure. In this part of the work, the trabecular and cortical bone morphology is assessed in the distal half of rat femur. We developed new method for mapping the cortical position and dimensions from a central longitudinal axis with one degree angular resolution. This method was used to examine differences between experimental groups. The bone position in tomographic slices is aligned before the mapping using the propound standardization procedure. The activity of remodelling process of the long bone is studied on the system of cortical canals.