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Over half a century ago, the paper entitled “Absence of Diffusion in Certain Random Lattices” was published by P. Anderson and described a metal-to-insulator transition phenomenon where electron diffusion does not occur in disordered semiconductors. This phenomenon is now commonly referred to as “Anderson localization” (AL). Since the AL detailed in Anderson’s paper arose from the wave nature of electrons, similar behavior should be observed in other wave systems, more specifically in optics. Given the utility of optical fibers, extensive theoretical treatment has been conducted on transverse Anderson localization (TAL, disorder in x- and y-directions, with the z-direction remaining invariant) in such systems. Only recently has it been experimentally observed, paving the way for studies into the influence of fiber material on linear and nonlinear TAL. This Dissertation represents the first materials study of doped silicate transverse Anderson localizing optical fibers (TALOFs) and their corresponding passive and active optical properties. More specifically, Chapter I reviews microstructured and multicore optical fiber, and methods of their fabrication, in order to develop an understanding of the impact of the core microstructure on waveguide properties. Then, an overview of TALOFs is developed to provide insights into the different materials and fabrication methods used to develop the few TALOFs reported to date. The former fiber systems are well studied; therefore, this research Dissertation will be focused on the novel effects and material influences on the latter (Anderson) systems. Chapter II begins the development of these novel fibers through in situ phase separation in optical fibers drawn using the molten core method (MCM). Limitations in the resulting fibers were studied, and adaptations to the fabrication method were made to elongate the already formed microphases through development and subsequent use of a two-tier MCM. Chapter III introduces an alternative fiber fabrication technique, namely the stack-and-draw method, specifically adapted to utilize MCM-derived precursor fibers in the stack. The resulting fibers are characterized to understand the effects of processing on the core microstructure, and ultimately to understand how the core microstructure leads to TAL. Chapters IV and V investigate the material properties and potential applications of the TALOFs that resulted from the fabrication technique developed in Chapter III. Specifically, Chapter IV investigates both Yb3+ and Er3+ doped TALOFs for solid-state lasing and amplification respectively. The resulting experimental observations and present limitations of these fibers for active applications are discussed. In Chapter V, the first nonlinear optical TALOFs are explored. Even though the higher refractive index phases possessed an estimated nonlinear refractive index (n2) similar to silica, small modal effective areas were demonstrated due to the strong localization in certain regions of these TALOFs. As a result, nonlinear optical frequency shifts were demonstrated for the first time in a TALOF, attributed to Raman and four-wave mixing (FWM), concomitantly. While not decisive into the underlying nature of TAL in the presence of optical nonlinearities, this suggests that the two are not mutually exclusive. Finally, Chapter VI summarizes the findings of this Dissertation, discusses the challenges with further fiber development in these TALOFs, and provides examples for future efforts in improving both the fibers themselves, and ultimately the understanding of these fibers.

As fibre-reinforced cementitious composites (FRCC) are multi-scale materials, their structural performance depends on the micro-scale properties of the fibre-matrix bond. However, the development and utilisation of FRCC are restricted due to the limited knowledge of the micro-scale phenomena that influence the bond between the fibres and the cementitious matrix and its response to loading. The focus of this research was the definition of the properties of the fibre surface and the cement paste surrounding it, which affect the formation and performance of the fibre-matrix bond. The examination involved analysing the effect of the surface roughness of steel fibres on the microstructure of the interfacial transition zone (ITZ) and the degradation of the fibre-matrix bond under repeated loading. The micro-scale properties were explored by employing a different approach to applying the existing experimental techniques to the FRCC. The utilisation of scanning electron microscopy (SEM) and phase-contrast micro-computed tomography (µCT) enabled the identification of the changes in the distributions of calcium hydroxide, calcium silicate hydrate, pores and unhydrated cement grains within the ITZ. The application of phase-contrast µCT allowed access to the three-dimensional microstructure of the cement paste around the fibre. The importance of the surface roughness of steel fibres for the packing of cementitious grains was examined by estimating the average height and wavelength of surface irregularities using an SEM image analysis and directly measuring the parameters using an atomic force microscope and stylus profilometer. The effect of the fibre surface roughness on its wettability was evaluated through contact angle goniometry. The decrease in the mobility of the water along the fibres that was observed with an increase in fibre surface roughness facilitated the reduction in the porosity near these fibres, which was confirmed using SEM. The resulting mechanical response of the bond between the cement paste and fibres with different types of surface roughness was examined under direct tension cycles with gradually increasing amplitudes. The outcomes of the fibre pull-out tests indicated that the detected micro-scale changes in the properties of the fibres and the cement paste surrounding them influenced the maximum capacity of the fibre-matrix bond and its deterioration. The development of the residual slip was identified from the beginning of loading with the three stages of evolution: deceleration, steady stage and acceleration. This study points out that the properties of the fibre surface and the cement paste surrounding it clearly affect the performance of the fibre-matrix bond by introducing novel insights about the fibre-matrix interaction that advance the development and modelling of FRCC. [ABSTRACT FROM AUTHOR]

In this paper, a novel approach is utilized to investigate the deformation mechanisms at the microstructural level in 3D printed alloys. The complex in-situ heat treatments during 3D printing leaves a unique and complicated microstructure in the as-built 3D printed metals, particularly alloys. The microstructure is made of a hierarchical stacking of some interconnected geometrical shapes, namely meltpools, grains, and cells. These are connected to each other by boundaries that might have different element compositions, and consequently, material properties, compared to the interior region of each geometrical unit. Deformation mechanisms in this microstructure are still highly unexplored, mainly because of the challenges on the way of performing experiments at the micrometer length scale. In this work, we establish an image processing framework that directly converts the SEM images taken from the microstructure of 3D printed 316L stainless steel alloys into CAD models. The model of the complicated microstructure is then scaled up, and the scaled model is 3D printed using polymeric materials. For 3D printing these samples, two polymers with contrasting mechanical properties are used. Distribution of these two polymers mimics the arrangement of soft and stiff regions in the microstructure of 3D printed alloys. These representative samples are subjected to mechanical loads and digital image correlation is utilized to investigate the deformation mechanisms, particularly the delocalization of stress concentration and also the crack propagation, at the microstructural level of 3D printed metals. Besides experiments, computational modeling using finite element method is also performed to study the same deformation mechanisms at the microstructure of 3D printed 316L stainless steel. Our results show that the hierarchical arrangement of stiff and soft phases in 3D printed alloys delocalizes the stress concentration and has the potential to make microstructures with significantly improved damage tolerance capabilities.

This dissertation describes experimental investigations of deposited atomic clusters and of films of metal particles produced by cluster deposition on graphite. It consists of three chapters presenting a review of the addressed subjects, the experimental techniques, and a summary of the results. The main body of results is described in full in afourth chapter as research papers. A systematic study of the impact of metal cluster trimers on highly oriented pyrolitic graphite (HOPG) is investigated. The creation of defects at the surface of graphite is found to be independento f the masso f the atoms in the two typeso f clusters considered The electron energy loss spectroscopy (EELS) of collective electronic excitations (plasmons) in a film of silver particles is presented A weak positive dispersion of the plasmon mode is measured and exhibits a higher ftequency of the mode with parallel momentum close to zero than in Ag surfaces. The adsorption of cinnamaldehydeis examined on nanostructured palladium surfaces. The EELS spectrum of cinnamaldehyde adsorbed on palladium is presented, as well as that of condensed layers of cinnamaldehyde on HOPG. Findings of this thesis involve different physical and chemical properties of the cluster surface system with a view in using cluster deposition for practical applications such as the investigation of model catalysts.

Statistical models of price volatility most commonly use low-frequency (daily, weekly, or monthly) returns. However, despite their availability, two types of financial data have not been extensively studied: high-frequency data where sampling periods are on the order of seconds; and open, close, high, and low (OCHL) data which incorporate intraperiod extremes.The first part of this dissertation focuses on the development of a filtering-based method for the estimation of volatility in high-frequency returns, which contrasts currently popular averaging-based approaches. The second part of this dissertation develops a foundational and novel method for likelihood-based estimation for bivariate OCHL, an approach unfeasible until now.In Chapter 2, we formulate a discrete-time Bayesian stochastic volatility model for high-frequency stock-market data that directly accounts for microstructure noise, and outline a Markov chain Monte Carlo algorithm for parameter estimation. The methods described in this paper are designed to be coherent across all sampling timescales, with the goal of estimating the latent log-volatility signal from data collected at arbitrarily short sampling periods. In keeping with this goal, we carefully develop a method for eliciting priors. The empirical results derived from both simulated and real data show that directly accounting for microstructure noise in a state-space formulation allows for well-calibrated estimates of the log-volatility process driving prices.In Chapter 3, we present and motivate the bivariate OCHL problem, enumerate the fundamental limitations of some common out-of-the-box approaches, and present a semidiscrete Galerkin numerical solver for computing the likelihood of the observed data. In addition, we prove the consistency of maximum likelihood estimates under the approximate density given by the solver.Chapter 4 develops a closed-form, analytic solution to the OCHL likelihood problem in parameter ranges where the Galerkin solver requires near-infinite compute time and memory to produce numerically accurate results. A matching solution is also proposed to interpolate between parameter regions where neither the Galerkin nor analytic solutions are applicable. Thus, we present a method for producing likelihoods based on OCHL data over all model parameter ranges, which is a key requirement in statistical estimation algorithms. We use numerical experiments in both Chapters 3 and 4 to show the validity of our methods and demonstrate the increase in statistical power in estimating price volatility and correlation when using bivariate OCHL data.

This dissertation is divided into three chapters, where each is an independent paper intended to be submitted as a refereed journal article. The main thrust of the research project overarching all three papers is to develop a high fidelity, geometrically explicit approach to finite element modeling fatigue at the microstructural length scale. Each paper is a study within this thrust, and the following is a sweeping overview of each study. More detailed abstracts for each paper are given at the beginning of each chapter. The paper in the first chapter is the fourth in a series of papers focused on implementing, calibrating, and validating criteria for simulating microstructurally small fatigue crack (MSFC) evolution, with high strain conditions in aluminum alloy (AA)7075-T651 as the proof-test application. MSFC evolution is divided into three stages: incubation, nucleation, and propagation. The specific focus of this paper is on the last stage, MSFC propagation, which is microstructure-governed fatigue crack growth through grains and/or along grain boundaries. Three simulated field metrics, crack tip displacement, crack-induced plastic slip localization, and maximum tangential stress ahead of the crack, previously investigated for prediction of nucleation, are investigated in this paper to determine their dependence on microstructural heterogeneities after nucleation. A total of 21 simulations are performed on a simplified baseline model of an AA7075-T651 microstructural region containing an MSFC. All three metrics are determined to be significantly dependent on the local microstructure immediately subsequent to nucleation. The particle spawning the crack and the orientation(s) of the grain(s) immediately surrounding the nucleated MSFC most influence the MSFC metrics. The paper in the second chapter focuses on the implementation of a computational framework that accurately and probabilistically models fatigue crack propagation at the microstructural scale, once again with high strain conditions in AA7075-T651 as the proof-test application. Toolsets are presented that generate and discretize statistically accurate microstructure geometry models and explicitly simulate the evolution of microstructurally small fatigue cracks. The concept is demonstrated through two model simulations and feasibility of the approach is critically evaluated. The paper in the third chapter is the fifth in the same series of papers described above for the first chapter. The focus of this paper is again on the last MSFC evolution stage, MSFC propagation. High resolution, micro-scale images of three propagating MSFC's are analyzed to determine dependencies of MSFC propagation on microstructural heterogeneities. Additionally, the three MSFC metrics studied in the first chapter - maximum tangential stresses, plastic slip localization, and crack displacements local to the crack front - are simulated in a finite element model that replicates an observed MSFC and the surrounding microstructure. The detailed observations and simulation reveal that MSFC propagation in AA7075T651 is highly dependent on the local microstructure, and MSFC behavior due to these dependencies can be predicted by the computed field metrics.

The history of steel dates back to the 17th century and has been instrumental in the betterment of every aspect of our lives ever since, from the pin that holds the paper together to the automobile that takes us to our destination steel touch everyone every day. Pathbreaking improvements in manufacturing techniques, access to advanced machinery and understanding of factors like heat treatment and corrosion resistance have aided in the advancement in the properties of steel in the last few years. This thesis report will attempt to elaborate upon the specific influence of composition, microstructure, and secondary processing techniques on both the static (uni-axial tensile) and dynamic (impact) properties of the four high strength steels AerMet®100, PremoMetTM290, 300M and TenaxTM 310. The steels were manufactured and marketed for commercial use by CARPENTER TECHNOLOGY, Inc (Reading, PA, USA). The specific heat treatment given to the candidate steels determines its microstructure and resultant mechanical properties spanning both static and dynamic. Test specimens of the steels were precision machined and conformed to standards specified and prescribed by the American Society for Testing Materials (ASTM) for both tensile tests and Charpy V-Notch impact tests. Based on similarity of the secondary processing technique the candidate specialty steels were divided into two groups: (i) AerMet®100 and PremoMetTM290, (ii) 300M and TenaxTM310. The impact toughness response and resultant fracture behavior of the steels were studied at different temperatures ranging from -180°C to +170°C. Tensile tests were performed at room temperature and the final fracture behavior of the candidate steel was established at both the macroscopic and fine microscopic levels. The intrinsic microscopic mechanisms governing the impact toughness, quasi static deformation and final fracture behavior of each of the chosen high strength steels will be elaborated upon in light of the conjoint and mutually interactive influences of composition, intrinsic microstructural effects, and nature of loading.

Valuation of corporate debt has been an extremely important, albeit imprecise task in asset pricing. Both structural models and reduced form models have had limited success in explaining the corporate yield spreads observed in actual markets. Taking advantage of a unique corporate bond dataset from the National Association of Securities Dealers, this dissertation investigates whether informed trading takes place in the high-yield corporate bond market, and its implications for corporate bond pricing. Differing from previous studies, I find that current corporate bond returns have explanatory power for future stock price changes. This implies that the corporate bond market serve important roles in disseminating new information. Based on this finding, this dissertation also demonstrates that in addition to liquidity, the amount of information based trading plays an important role in determining yield spreads of risky corporate bonds, which is consistent with the hypothesis that investors require higher return to compensate them for bearing the risks of trading with more informed traders. In line with a strand of recent literature on the implications of market microstructure for asset pricing, this paper suggests that corporate bond yields might embed an information risk premium that is ignored by existing bond pricing models.

Microstructure of blended pastes of lime and cement were studied in this paper. An increment of complexity of the microstructure was found when pastes increase their percentage in cement. Microstructural characteristics as porosity, morphology of the pores, pore size distribution and surface fractal dimension were evaluated in the different pastes studying the modification with the variation of composition. The capillary water absorption is also evaluated obtaining higher capillary coefficients values for the pastes with higher amounts of lime. The increase of complexity of the microstructure, due to the cement in the pastes, leads to slight deviations of the parallel tube model.