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Pages
 Title
 Model building incorporating discrimination between rival mathematical models in heat transfer
 Creator
 Van Fossen, Gerald James, 1942
 Date
 1973
 Collection
 Electronic Theses & Dissertations
 Title
 Constitutive modeling of the thermal response of rubberlike materials
 Creator
 Wang, Yuhui
 Date
 2006
 Collection
 Electronic Theses & Dissertations
 Title
 Structure and evolutionary dynamics in fitness landscapes
 Creator
 Pakanati, Anuraag R.
 Date
 2015
 Collection
 Electronic Theses & Dissertations
 Description

Evolution can be conceptualized as an optimization algorithm that allows populations to search through genotypes for those that produce high fitness solutions. This search process is commonly depicted as exploring a “fitness landscape”, which combines similarity relationships among genotypes with the concept of a genotypefitness map. As populations adapt to their fitness landscape, they accumulate information about the fitness landscape in which they live. A greater understanding of...
Show moreEvolution can be conceptualized as an optimization algorithm that allows populations to search through genotypes for those that produce high fitness solutions. This search process is commonly depicted as exploring a “fitness landscape”, which combines similarity relationships among genotypes with the concept of a genotypefitness map. As populations adapt to their fitness landscape, they accumulate information about the fitness landscape in which they live. A greater understanding of evolution on fitness landscapes will help elucidate fundamental evolutionary processes. I examine methods of estimating information acquisition in evolving populations and find that these techniques have largely ignored the effects of common descent. Since information is estimated by measuring conserved genomic regions across a population, common descent can create a severe bias by increasing similarities among unselected regions. I introduce a correction method to compensate for the effects of common descent on genomic information and empirically demonstrate its efficacy.Next, I explore three instantiations of NK, Avida, and RNA fitness landscapes to better understand structural properties such as the distribution of peaks and the size of basins of attraction. I find that the fitness of peaks is correlated with the fitness of peaks within their neighborhood, and that the size of peaks' basins of attraction tends to be proportional to the heights of the peaks. Finally, I visualize local dynamics and perform a detailed comparison between the space of what evolutionary trajectories are technically possible from a single starting point and the results of actual evolving populations.
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 Title
 On minimization of some nonsmooth convex functionals arising in micromagnetics
 Creator
 Gao, Hongli
 Date
 2015
 Collection
 Electronic Theses & Dissertations
 Description

This thesis is motivated by studying the properties of ferromagnetic materials usingthe LandauLifshitz theory of micromagnetics. In this theory the state of a ferromagneticmaterial is described by the magnetization vector m in terms of a total micromagnetic energythat consists of several competing subenergies: exchange energy, anisotropy energy, externalinteraction energy and magnetostatic energy. For large ferromagnetic materials and undersome limiting regimes of the model, the exchange...
Show moreThis thesis is motivated by studying the properties of ferromagnetic materials usingthe LandauLifshitz theory of micromagnetics. In this theory the state of a ferromagneticmaterial is described by the magnetization vector m in terms of a total micromagnetic energythat consists of several competing subenergies: exchange energy, anisotropy energy, externalinteraction energy and magnetostatic energy. For large ferromagnetic materials and undersome limiting regimes of the model, the exchange energy can be negligible and the totalenergy becomes a reduced model. Our investigations focus on the study of such a reducedmodel of LandauLifshitz theory.The primary focus of the thesis includes two parts: the minimization (static) study andthe evolution (dynamic) study. We investigate a new method for the existence of minimizersof the reduced micromagnetic energy based on a duality method. In this method, the reducedmicromagnetic energy is closely related to a convex functional (the dual functional) on thecurlfree vector functions. Our minimization and dynamics studies are based on the studyof the minimization and gradient ow of this dual functional. Much of the thesis is focusedon the minimization problem of two special cases: soft case and uniaxial case on the annulusdomain; in particular, in the soft case, for some range of the parameter, the energy minimizersof the original micromagnetic energy are constructed through the EulerLagrange equationof the dual functional using the characteristics method for a reduced Eikonal type equation.The second direction of our study of this thesis is an attempt to obtain certain reasonabledynamic process for the evolution of m, where the asymptotic behavior of the gradient owof the reduced energy functional is investigated.
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 Title
 Multiscale modeling of polymer nanocomposites
 Creator
 Sheidaei, Azadeh
 Date
 2015
 Collection
 Electronic Theses & Dissertations
 Description

In recent years, polymer nanocomposites (PNCs) have increasingly gained more attention due to their improved mechanical, barrier, thermal, optical, electrical and biodegradable properties in comparison with the conventional microcomposites or pristine polymer. With a modest addition of nanoparticles (usually less than 5wt. %), PNCs offer a wide range of improvements in moduli, strength, heat resistance, biodegradability, as well as decrease in gas permeability and flammability. Although...
Show moreIn recent years, polymer nanocomposites (PNCs) have increasingly gained more attention due to their improved mechanical, barrier, thermal, optical, electrical and biodegradable properties in comparison with the conventional microcomposites or pristine polymer. With a modest addition of nanoparticles (usually less than 5wt. %), PNCs offer a wide range of improvements in moduli, strength, heat resistance, biodegradability, as well as decrease in gas permeability and flammability. Although PNCs offer enormous opportunities to design novel material systems, development of an effective numerical modeling approach to predict their properties based on their complex multiphase and multiscale structure is still at an early stage. Developing a computational framework to predict the mechanical properties of PNC is the focus of this dissertation. A computational framework has been developed to predict mechanical properties of polymer nanocomposites. In chapter 1, a microstructure inspired material model has been developed based on statistical technique and this technique has been used to reconstruct the microstructure of Halloysite nanotube (HNT) polypropylene composite. This technique also has been used to reconstruct exfoliated Graphene nanoplatelet (xGnP) polymer composite. The model was able to successfully predict the material behavior obtained from experiment. Chapter 2 is the summary of the experimental work to support the numerical work. First, different processing techniques to make the polymer nanocomposites have been reviewed. Among them, melt extrusion followed by injection molding was used to manufacture high density polyethylene (HDPE) – xGnP nanocomposties. Scanning electron microscopy (SEM) also was performed to determine particle size and distribution and to examine fracture surfaces. Particle size was measured from these images and has been used for calculating the probability density function for GNPs in chapter 1. A series of nanoindentation tests have been conducted to reveal the spatial variation of the superstructure developed along and across the flow direction of injectionmolded HDPE/GNP.The uniaxial tensile test and shear test have been conducted on HDPE and xGnP/HDPE specimens. The stressstrain curves for HDPE obtained from these experiments have been used in chapter 5 to calibrate the modified Gurson–Tvergaard–Needleman to capture the damage progression in HDPE. In chapter 3, the 3D microstructure model developed in chapter 1 was incorporated in a damage modeling problem in nanocomposite where damage initiation has been modeled using cohesivezone model. There is a significant difference between the properties of inclusion and the host polymer in polymer nanocomposite, which leads to the damage evolution during deformation due to a huge stress concentration between nanofiller and polymer. The finite element model of progressive debonding in nanoreinforced composite has been proposed based on the cohesivezone model of the interface. In order to model cohesivezone, a cohesive zone traction displacement relation is needed. This curve may be obtained either through a fiber pullout experiment or by simulating the test using molecular dynamics. In the case of nanofillers, conducting fiber pullout test is very difficult and result is often not reproducible. In chapter 4, molecular dynamics simulation of polymer nanocomposite has been performed. One of the goals was to extract the loaddisplacement curves of graphene/HDPE pullout test and obtain cohesive zone parameters in chapter 3. Finally, in chapter 5, a damage model of HDPE/GNP nanocomposite has been developed based on matrix cracking and fiber debonding. This 3D microstructure model was incorporated in a damage modeling problem in nanocomposite where damage initiation and damage progression have been modeled using cohesivezone and modified GursonTvergaardNeedleman (GTN) material models.
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 Title
 Modeling galactic chemical evolution in cosmological simulations
 Creator
 Peruta, Carolyn Cynthia
 Date
 2013
 Collection
 Electronic Theses & Dissertations
 Description

The most fundamental challenges to models of galactic chemical evolution (GCE) are uncertainties in the basic inputs, including the properties of the stellar initial mass function (IMF), stellar nucleosynthetic yields, and the rate of return of mass and energy to the interstellar and intergalactic medium by Type Ia and II supernovae and stellar winds. In this dissertation, we provide a critical examination of widely available stellar nucleosynthetic yield data, with an eye toward modeling GCE...
Show moreThe most fundamental challenges to models of galactic chemical evolution (GCE) are uncertainties in the basic inputs, including the properties of the stellar initial mass function (IMF), stellar nucleosynthetic yields, and the rate of return of mass and energy to the interstellar and intergalactic medium by Type Ia and II supernovae and stellar winds. In this dissertation, we provide a critical examination of widely available stellar nucleosynthetic yield data, with an eye toward modeling GCE in the broad scope of cosmological hydrodynamical simulations. We examine the implications of uncertain inputs for the Galactic stellar IMF, and nucleosynthetic yields from stellarevolution calculations, on our ability to ask detailed questions regarding the observed Galactic chemicalabundance patterns. We find a marked need for stellar feedback data from stars of initial mass 8 to 12 M_{sun} and above 40 M_{sun}, and for initial stellar metallicities above and below solar, Z_{sun}=0.02. We find the largest discrepancies amongst nucleosynthetic yield calculations are due to various groups' treatment of hot bottom burning, formation of the 13C pocket in asymptotic giantbranch (AGB) stars, and details of mass loss, rotation, and convection in all stars. Our model of GCE is used to postprocess simulations to explore in greater detail the nucleosynthetic evolution of the stellar populations and interstellar/intergalactic medium, and to compare directly to the chemical abundances of the Milky Way stellar halo and dwarf spheroidal galaxy stellar populations.
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 Title
 Optimal design problems in thinfilm and diffractive optics
 Creator
 Wang, Yuliang
 Date
 2013
 Collection
 Electronic Theses & Dissertations
 Description

Optical components built from thinfilm layered structures are technologically very important. Applications include but are not limited to energy conversion and conservation, data transmission and conversion, space technology, imaging and so on. In practice these structures are defined by various parameters such as the refractiveindex profile, the layer thickness and the period. The problem to find the combination of parameters which yield the spectral response closest to a given target...
Show moreOptical components built from thinfilm layered structures are technologically very important. Applications include but are not limited to energy conversion and conservation, data transmission and conversion, space technology, imaging and so on. In practice these structures are defined by various parameters such as the refractiveindex profile, the layer thickness and the period. The problem to find the combination of parameters which yield the spectral response closest to a given target function is referred to as optimal design. This dissertation considers several topics in the mathematical modeling and optimal design of these structures through numerical optimization. A key step in numerical optimization is to define an objective function the measures the discrepancy between the target performance and that of the current solution. Our first topic is the impact of the objective function, its metric in particular, on the optimal solution and its performance. This is done by numerical experiments with different types of antireflection coatings using twomaterial multilayers. The results confirm existing statements and provide a few new findings, e.g. some specific metrics can yield particularly better solutions than others. Rugates are optical coatings presenting continuous refractiveindex profiles. They have received much attention recently due to technological advances and their potential better optical performance and environmental properties. The Fourier transform method is a widely used technique for the design of rugates. However, it is based on approximate expressions with strict assumptions and has many practical limitations. Our second topic is the optimal design of rugates through numerical optimization of objective functions with penalty terms. We found solutions with similar performance and novel solutions by using different metrics in the penalty term. Existing methods used only local basis functions such as piecewise constant or linear functions for the discretization of the refractiveindex profile. Our third topic is the use global basis functions such as sinusoidal functions in the discretization. A simple transformation is used to overcome the difficulty of bound constraints and the result is very promising. Both multilayer and rugate coatings can be obtained using this method. Diffraction gratings are thinfilm structures whose optical properties vary periodically along one or two directions. Our final topic is the optimal design of such structures in the broadband case. The objective functions and their gradient are obtained by solving variational problems and their adjoints with finite element method. Interesting phenomena are observed in the numerical experiments. Limitations and future work in this direction are pointed out.
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 Title
 Mathematical modeling and simulation of mechanoelectrical transducers and nanofluidic channels
 Creator
 Park, Jin Kyoung
 Date
 2014
 Collection
 Electronic Theses & Dissertations
 Description

Remarkable advances in nanotechnology and computational approaches enable researchers to investigate physical and biological phenomena in an atomic or molecular scale. Smallerscale approaches are important to study the transport of ions and/or molecules through ion channels in living organisms as well as exquisitely fabricated nanofluidic channels. Both subjects have similar physical properties and hence they have common mathematical interests and challenges in modeling and simulating the...
Show moreRemarkable advances in nanotechnology and computational approaches enable researchers to investigate physical and biological phenomena in an atomic or molecular scale. Smallerscale approaches are important to study the transport of ions and/or molecules through ion channels in living organisms as well as exquisitely fabricated nanofluidic channels. Both subjects have similar physical properties and hence they have common mathematical interests and challenges in modeling and simulating the transport phenomena. In this work, we first propose and validate a molecular level prototype for mechanoelectrical transducer (MET) channel in mammalian hair cells.Next, we design three ionic diffusive nanofluidic channels with different types of atomic surface charge distribution, and explore the current properties of each channel. We construct the molecular level prototype which consists of a charged blocker, a realistic ion channel and its surrounding membrane. The Gramicidin A channel is employed to demonstrate the realistic channel structure, and the blocker is a positively charged atom of radius $1.5$\AA\, which is placed at the mouth region of the channel. Relocating this blocker along one direction just outside the channel mouth imitates the opening and closing behavior of the MET channel. In our atomic scale design for an ionic diffusive nanofluidic channel, the atomic surface charge distribution is easy to modify by varying quantities and signs of atomic charges which are equally placed slightly above the channel surface. Our proposed nanofluidic systems constitutes a geometrically welldefined cylindrical channel and two reservoirs of KCl solution. For both the mammalian MET channel and the ion diffusive nanofluidic channel, we employ a wellestablished ion channel continuum theory, PoissonNernstPlanck theory, for three dimensional numerical simulations. In particular, for the nanoscaled channel descriptions, the generalized PNP equations are derived by using a variational formulation and by incorporating nonelectrostatic interactions. We utilize several useful mathematical algorithms, such as Dirichlet to Neumann mapping and the matched interface and boundary method, in order to validate the proposed models with charge singularities and complex geometry. Moreover, the secondorder accuracy of the proposed numerical methods are confirmed with our nanofluidic system affected by a single atomic charge and eight atomic charges, and further study the channels with a unipolar charge distribution of negative ions and a bipolar charge distribution. Finally, we analyze electrostatic potential and ion conductance through each channel model under the influence of diverse physical conditions, including external applied voltage, bulk ion concentration and atomic charge. Our MET channel prototype shows an outstanding agreement with experimental observation of rat cochlear outer hair cells in terms of open probability. This result also suggests that the tip link, a connector between adjacent stereocilia, gates the MET channel. Similarly, numerical findings, such as ion selectivity, ion depletion and accumulation, and potential wells, of our proposed ion diffusive realistic nanochannels are in remarkable accordance with those from experimental measurements and numerical simulations in the literature. In addition, simulation results support the controllability of the current within a nanofluidic channel.
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 Title
 Fast solver for large scale eddy current nondestructive evaluation problems
 Creator
 Lei, Naiguang
 Date
 2014
 Collection
 Electronic Theses & Dissertations
 Description

Eddy current testing plays a very important role in nondestructive evaluations of conducting test samples. Based on Faraday's law, an alternating magnetic field source generates induced currents, called eddy currents, in an electrically conducting test specimen. The eddy currents generate induced magnetic fields that oppose the direction of the inducing magnetic field in accordance with Lenz's law. In the presence of discontinuities in material property or defects in the test specimen, the...
Show moreEddy current testing plays a very important role in nondestructive evaluations of conducting test samples. Based on Faraday's law, an alternating magnetic field source generates induced currents, called eddy currents, in an electrically conducting test specimen. The eddy currents generate induced magnetic fields that oppose the direction of the inducing magnetic field in accordance with Lenz's law. In the presence of discontinuities in material property or defects in the test specimen, the induced eddy current paths are perturbed and the associated magnetic fields can be detected by coils or magnetic field sensors, such as Hall elements or magnetoresistance sensors. Due to the complexity of the test specimen and the inspection environments, the availability of theoretical simulation models is extremely valuable for studying the basic field/flaw interactions in order to obtain a fuller understanding of nondestructive testing phenomena.Theoretical models of the forward problem are also useful for training and validation of automated defect detection systems. Theoretical models generate defect signatures that are expensive to replicate experimentally. In general, modelling methods can be classified into two categories: analytical and numerical. Although analytical approaches offer closed form solution, it is generally not possible to obtain largely due to the complex sample and defect geometries, especially in threedimensional space. Numerical modelling has become popular with advances in computer technology and computational methods. However, due to the huge time consumption in the case of large scale problems, accelerations/fast solvers are needed to enhance numerical models.This dissertation describes a numerical simulation model for eddy current problems using finite element analysis. Validation of the accuracy of this model is demonstrated via comparison with experimental measurements of steam generator tube wall defects. These simulations generating twodimension raster scan data typically takes one to two days on a dedicated eightcore PC. A novel direct integral solver for eddy current problems and GPUbased implementation is also investigated in this research to reduce the computational time.
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 Title
 Near duplicate image search
 Creator
 Li, Fengjie
 Date
 2014
 Collection
 Electronic Theses & Dissertations
 Description

Information retrieval addresses the fundamental problem of how to identify the objects from database that satisfies the information needs of users. Facing the information overload, the major challenge in search algorithm design is to ensure that useful information can be found both accurately and efficiently from large databases.To address this challenge, different indexing and retrieval methods had been proposed for different types of data, namely sparse data (e.g. documents), dense data (e...
Show moreInformation retrieval addresses the fundamental problem of how to identify the objects from database that satisfies the information needs of users. Facing the information overload, the major challenge in search algorithm design is to ensure that useful information can be found both accurately and efficiently from large databases.To address this challenge, different indexing and retrieval methods had been proposed for different types of data, namely sparse data (e.g. documents), dense data (e.g. dense feature vectors) and bagoffeatures (e.g. local feature represented images). For sparse data, inverted index and document retrieval models had been proved to be very effective for large scale retrieval problems. For dense data and bagoffeature data, however, there are still some open problems. For example, Locality Sensitive Hashing, a stateoftheart method for searching high dimensional vectors, often fails to make a good tradeoff between precision and recall. Namely, it tends to achieve high preci sion but with low recall or vice versa. The bagofwords model, a popular approach for searching objects represented bagoffeatures, has a limited performance because of the information loss during the quantization procedure.Since the general problem of searching objects represented in dense vectors and bagoffeatures may be too challenging, in this dissertation, we focus on nearly duplicate search, in which the matched objects is almost identical to the query. By effectively exploring the statistical proper ties of near duplicities, we will be able to design more effective indexing schemes and search algorithms. Thus, the focus of this dissertation is to design new indexing methods and retrieval algorithms, for near duplicate search in large scale databases, that accurately capture the data simi larity and delivers more accurate and efficient search. Below, we summarize the main contributions of this dissertation:Our first contribution is a new algorithm for searching near duplicate bagoffeatures data. The proposed algorithm, named random seeding quantization, is more efficient in generating bagof words representations for near duplicate images. The new scheme is motivated by approximating the optimal partial matching between bagoffeatures, and thus produces a bagofwords representation capturing the true similarities of the data, leading to more accurate and efficient retrieval of bagoffeatures data.Our second contribution, termed Random Projection Filtering, is a search algorithm designed for efficient near duplicate vector search. By explicitly exploiting the statistical properties of near duplicity, the algorithm projects high dimensional vectors into lower dimensional space and filter out irrelevant items. Our effective filtering procedure makes RPF more accurate and efficient to identify nearly duplicate objects in databases.Our third contribution is to develop and evaluate a new randomized range search algorithm for near duplicate vectors in high dimensional spaces, termed as Random Projection Search. Different from RPF, the algorithm presented in this chapter is suitable for a wider range of applications be cause it does not require the sparsity constrains for high search accuracy. The key idea is to project both the data points and the query point into an one dimensional space by a random projection, and perform one dimensional range search to find the subset of data points that are within the range of a given query using binary search. We prove the theoretical guarantee for the proposed algorithm and evaluate its empirical performance on a dataset of 1.1 billion image features.
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 Title
 Circulation and exchange in the Saginaw BayLake Huron system : observations and numerical modeling
 Creator
 Nguyen, Tuan Duc
 Date
 2014
 Collection
 Electronic Theses & Dissertations
 Description

Knowledge of lake circulation is essential for addressing many issues ranging from water quality to human and ecosystem health. Lake Huron, the third largest of the Great Lakes by volume, has been significantly affected by natural and anthropogenic activities. Since Lake Huron is a connecting waterway between the upper and lower Great Lakes, understanding Lake Huron circulation and thermal structure is also important for questions involving the lower lakes. In this study, we use a three...
Show moreKnowledge of lake circulation is essential for addressing many issues ranging from water quality to human and ecosystem health. Lake Huron, the third largest of the Great Lakes by volume, has been significantly affected by natural and anthropogenic activities. Since Lake Huron is a connecting waterway between the upper and lower Great Lakes, understanding Lake Huron circulation and thermal structure is also important for questions involving the lower lakes. In this study, we use a threedimensional, unstructured grid hydrodynamic model to examine circulation, thermal structure, ice cover extent, and exchange in the Saginaw Bay  Lake Huron system during summer months for 3 consecutive years (20092011) and winter months for 2 years (2010 and 2013). The model was tested against ADCP observations of currents, data from a Lagrangian drifter experiment in the Saginaw Bay, observations of temperature from thermistor chains, and temperature data from the National Data Buoy Center stations. Mean circulation was predominantly cyclonic in the main basin of Lake Huron with current speeds in the surface layer being highest in August in summer and in January in winter. Circulation in the Saginaw Bay was characterized by the presence of an anticyclonic gyre at the mouth of the outer bay and two recirculating cells within the inner bay for both seasons. The ice cover data extracted from Moderate Resolution Imaging Spectroradiometer (MODIS) with relatively high spatial resolution and from the Great Lakes Ice Atlas were used to test against results obtained from an ice model. The results show that the ice model was able to simulate lake circulation and ice cover extent in winter season reasonably well. The percent coverage of ice reached a maximum of 38.3% and 38.7% in midFebruary in 2010 and beginning of March in 2013 respectively. New estimates are provided for the mean flushing times (computed as the volume of the bay divided by the rate of inflow) and residence times (computed as efolding flushing times treating the bay as a continuously stirred tank reactor) for Saginaw Bay for summer and winter seasons. The average flushing time (over the three months of summer and for all three years) was 23.0 days for the inner bay and 9.9 days for the entire bay. The corresponding values for the winter season are 43.2 days and 15.6 days respectively. The mean efolding flushing time was 62 days for summer and 64.7 days for winter for the inner bay and 115 days for the summer and 114.2 days for the winter conditions for the entire bay. Empirical relations between the mean residence time and river discharge were proposed. To characterize the behavior of river plumes in the inner Saginaw Bay, the absolute diffusivity values in the alongshore and crossshore directions were calculated using data from GPSenabled Lagrangian drifters and simulation results based on particle transport models.
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 Title
 Credit markets, financial crises, and the macroeconomy
 Creator
 Hyun, Junghwan
 Date
 2014
 Collection
 Electronic Theses & Dissertations
 Description

This study consists of three chapters, each of which is an individual paper. The first chapter investigates how the dynamic process of reallocation of credit across firms behaves before and after financial crises. Applying the methodology proposed by Davis and Haltiwanger (1992) for measuring job reallocation, we construct measures of credit reallocation across Korean firms in the 19812012 period. The credit boom preceding the 1997 financialcrisis featured a modest intensity of credit...
Show moreThis study consists of three chapters, each of which is an individual paper. The first chapter investigates how the dynamic process of reallocation of credit across firms behaves before and after financial crises. Applying the methodology proposed by Davis and Haltiwanger (1992) for measuring job reallocation, we construct measures of credit reallocation across Korean firms in the 19812012 period. The credit boom preceding the 1997 financialcrisis featured a modest intensity of credit reallocation. By contrast,after the crisis and the associated reforms, credit reallocationsignificantly intensified and started to comove with the business cycle, while credit growth slowed down (deleveraging). The higher dynamism of the credit sector in reallocating liquidity cannot be explained by “flight to quality” episodes but reflectsa structural change in the credit reallocation process that has persisted since the end of the crisis. The intensification of credit reallocation appears to have been associated with enhanced allocative efficiency.The second chapter explores the evolution of credit reallocation across Korean nonfinancial firms for the period 19812012. I employ a dynamic latent factor model that decomposes regional credit reallocation rates into national, regionspecific and idiosyncratic components. I find that the common factor explaining common movement across 16 regional credit flows increased after the 1997 financial crisis. The common factor comoves withnational excess reallocation. It is positively and strongly correlated with national excess reallocation, while it is negatively correlated withnational net credit growth. It exhibits mild countercyclicality. I examine what extent the volatility of credit reallocation was driven bynational, regionspecific and idiosyncratic components. This study uncovers evidence that the national factor accounts for a sizable fraction of regional reallocation rates of total credit and loans, while it plays only a minor role in explaining the fluctuation in regional reallocation rates of bonds.The last chapter explores the relationship between religion and bank performance. The study uses data on credit unions in Korea for the period 2000 to 2007 to investigate the effects of religion on bank performance. The empirical results show that credit unions based on religious institutions not only suffer less from troubled loans but they also enjoy higher profits relative to ordinary ones. I find that the religious credit unions' unique features, such as non random potential clientele, rich soft information and reputational incentive to repay, are likely to be what enables them to outperform.
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 Title
 Multiscale modeling and estimation of Poisson processes with applications to emission computed tomography
 Creator
 Timmermann, Klaus Edmond
 Date
 2000
 Collection
 Electronic Theses & Dissertations
 Title
 Surface matching and chemical scoring to detect unrelated proteins binding similar small molecules
 Creator
 Van Voorst, Jeffrey Ryan
 Date
 2011
 Collection
 Electronic Theses & Dissertations
 Description

SURFACE MATCHING AND CHEMICAL SCORING TO DETECT UNRELATED PROTEINS BINDING SIMILAR SMALL MOLECULESByJeffrey Ryan Van VoorstHow can one deduce if two clefts or pockets in different protein structures bind the same small molecule if there is no significant sequence or structural similarity between the proteins? Human pattern recognition, based on extensive structural biology or ligand design experience, is the best choice when the number of sites is small. However, to be able to scale to the...
Show moreSURFACE MATCHING AND CHEMICAL SCORING TO DETECT UNRELATED PROTEINS BINDING SIMILAR SMALL MOLECULESByJeffrey Ryan Van VoorstHow can one deduce if two clefts or pockets in different protein structures bind the same small molecule if there is no significant sequence or structural similarity between the proteins? Human pattern recognition, based on extensive structural biology or ligand design experience, is the best choice when the number of sites is small. However, to be able to scale to the thousands of structures in structural databases requires implementing that experience as computational method. The primary advantage of such a computational tool is to be able to focus human expertise on a much smaller set of enriched binding sites.Although a number of tools have been developed for this purpose by many groups [61, 51, 86, 88, 91], to our knowledge, a basic hypothesis remains untested: two proteins that bind the same small molecule have binding sites with similar chemical and shape features, even when the proteins do not share significant sequence or structural similarity. A computational method to compare protein small molecule binding sites based on surface and chemical complementarity is proposed and implemented as a software package named SimSite3D. This method is protein structure based, does not rely on explicit protein sequence or main chain similarities, and does not require the alignment of atomic centers. It has been engineered to provide a detailed search of one fragment site versus a dataset of about 13,000 full ligand sites in 2&ndash4 hours (on one processor core).Several contributions are presented in this dissertation. First, several examples are presented where SimSite3D is able to find significant matches between binding sites that have similar ligand fragments bound but are unrelated in sequence or structure. Second, including the complementarity of binding site molecular surfaces helps to distinguish between sites that share a similar chemical motif, but do not necessarily bind the same molecule. Third, a number of clear examples are provided to illustrate the challenges in comparing binding sites which should be addressed in order for a binding site comparison method to gain widespread acceptance similar to that enjoyed by BLAST[3, 4]. Finally, an optimization method for addressing protein (and small molecule) flexibility in the context of binding site comparisons is presented, prototyped, and tested.Throughout the work, computational models were chosen to strike a delicate balance between achieving sufficient accuracy of alignments, discriminating between accurate and poor alignments, and discriminating between similar and dissimilar sites. Each of these criteria is important. Due to the nature of the binding site comparison problem, each criterion presents a separate challenge and may require compromises to balance performance to achieve acceptable performance in all three categories.At the present, the problem of addressing flexibility when comparing binding site surfaces has not been presented or published by any other research group. In fact, the problem of modeling flexibility to determine correspondences between binding sites is an untouched problem of great importance. Therefore, the final goal of this dissertation is to prototype and evaluate a method that uses inverse kinematics and gradient based optimization to optimize a given objective function subject to allowed protein motions encoded as stereochemical constraints. In particular, we seek to simultaneously maximize the surface and chemical complementarity of two closely aligned sites subject to directed changes in side chain dihedral angles.
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 Title
 Discrete choice models of hunting and fishing in Michigan
 Creator
 Knoche, Scott
 Date
 2014
 Collection
 Electronic Theses & Dissertations
 Description

In this dissertation I employ multiple discrete choice modeling methods and data collection approaches to make both methodological and empirical contributions which focus on a variety of managementrelevant programs and policies. In dissertation chapter 1, I examine the potential for researchers to estimate recreation demand models using widely available secondary data on recreation site choice that lacks some income and trip details. I find that substituting zipcode median income for...
Show moreIn this dissertation I employ multiple discrete choice modeling methods and data collection approaches to make both methodological and empirical contributions which focus on a variety of managementrelevant programs and policies. In dissertation chapter 1, I examine the potential for researchers to estimate recreation demand models using widely available secondary data on recreation site choice that lacks some income and trip details. I find that substituting zipcode median income for individualreported income, and constructing estimates of trips based on days spent hunting and the distance of the hunting site from the individual's residence, generate welfare estimates that are similar to results using individualreported information on income and trips. This research indicates potential for utilizing a wide range of previously ignored recreation site choice data for recreation demand modeling purposes. Dissertation chapters 2 and 3 are supported by the procedure developed in dissertation chapter 1. Dissertation chapter 2 estimates a discrete choice model of ruffed grouse hunting in Michigan with the objective of estimating both the economic benefits of all publicly accessible hunting land in Michigan for ruffed grouse hunters and the potential changes to ruffed grouse hunter economic benefits as a result of a proposal to ban the use of firearms in approximately 67,000 acres of national forest wilderness area. Economic benefits of publicly accessible hunting land for ruffed grouse hunters in Michigan was estimated to be about $30 million in 2008, with economic benefits of the 67,000 acres of national forest wilderness area to ruffed grouse hunters estimated at about $45,000. Dissertation chapter 3 estimates the economic benefits of the USDA Conservation Reserve Program for pheasant hunters in Michigan by linking a previously developed spatially explicit, landscape based model of pheasant sightings to a discrete choice model of pheasant hunter site choice. Chapter 3 also estimates the potential economic benefits generated through the initiation of a multiagency and stakeholder pheasant habitat restoration plan. Results show that economic benefits for pheasant hunters depend critically on restoration site selection. Dissertation chapter 4 uses a choice experiment survey of Michigan trout anglers to examine the willingness of anglers to make tradeoffs between changes in driving distance to a fishing site and changes in attributes available at fishing sites. On average, trout anglers prefer higher catch rates, shorter travel distances to a fishing site, and are highly averse to strict fishing regulations such as catchandrelease only and artificial flies only regulations. However, there is evidence of preference heterogeneity within the trout angler population for these regulations, with some anglers preferring (all else equal) to fish in areas with these restrictions. This distribution of angler preferences is used to examine the proportion of anglers who can be made better off when strict regulations induce catchrelated quality improvements at a fishing site.
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 Title
 Study of a class of LandauLifshitz equations of ferromagnetism without exchange energy
 Creator
 Deng, Wei
 Date
 2012
 Collection
 Electronic Theses & Dissertations
 Description

LandauLifshitz equations of ferromagnetism, which are based on several competing energy contributions, are important mathematical models for the evolution of magnetization field $\m$ of a ferromagnetic material. Many problems, such as existence, stability, regularity, asymptotic behavior, thinfilm limit and numerical computation, have been well studied for the LandauLifshitz equations that include the socalled exchange energy. However, these problems turn out to be quite challenging for...
Show moreLandauLifshitz equations of ferromagnetism, which are based on several competing energy contributions, are important mathematical models for the evolution of magnetization field $\m$ of a ferromagnetic material. Many problems, such as existence, stability, regularity, asymptotic behavior, thinfilm limit and numerical computation, have been well studied for the LandauLifshitz equations that include the socalled exchange energy. However, these problems turn out to be quite challenging for equations without the exchange energy. The main reason is that when the exchange energy is included, one automatically has the magnetization vector $\m\in L^\infty((0,\infty);H^1(\Omega))$ from energy estimates, which gives some compactness and stability that are needed for using the standard methods; however, in the cases without the exchange energy, one only has $\m\in L^\infty((0,\infty);L^\infty(\Omega))$, which is too rough to get the needed compactness and stability. In this thesis, we investigate some problems for models of reduced LandauLifshitz equations with noexchange energy.In Chapter 1, we introduce the LandauLifshitz theory of ferromagnetism and summarize the main results of the thesis. The readers can check out the main results quickly in this chapter and then go to the corresponding chapters for details of proof, more discussions and further references.In Chapter 2, we study the {\em quasistationary limit} of a simple LandauLifshitzMaxwell system with the permittivity parameter $\epsilon$ approaching zero and, using this quasistationary limit, establish the existence of global weak solutions to the reduced LandauLifshitz equations with initial value $\m_0\in L^\infty(\Omega).$In Chapter 3, we establish a local $L^2$stability theorem for the global weak solutions in finite time. The key in the proof of stability theorem is that we split the nonlocal term $H_\m$ into two parts: one is bounded in $L^\infty(\Omega)$ and the other bounded in $L^2(\Omega)$. Using this stability theorem, we also provide another proof for the existence of global weak solutions for a full expression of the noexchange energy with applied field $\a(x)\in L^\infty(\Omega)$.In Chapter 4, we prove a higher time regularity for the regular solutions, using mainly induction method, together with several interpolation results. In this chapter, we also study the weak $\omega$limit sets for the socalled {\em softcase} and study the asymptotic behaviors for the special case when $\Omega$ is ellipsoid and initial values $\m_0$ are constant.In Chapter 5, we investigate a different model called the fractional LandauLifshitz equations and establish the existence of global weak solutions with initial value $\m_0\in H^\alpha(\Omega)$, where $0<\alpha<1$. In this new model, in contrast to the case when only the nonlocal term $H_\m$ is included, we have some compactness in $H^\alpha(\Omega)$, which enables us to apply the Galerkin method to establish the existence of global weak solution.
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 Title
 Changing hearts and minds : imagined intergroup contact's effect on warmth and competence stereotypes
 Creator
 O'Connor, Rachel C.
 Date
 2015
 Collection
 Electronic Theses & Dissertations
 Description

Imagined intergroup contact was introduced as an easy and efficient method of improving the quality of intergroup interactions allowing better prejudice reduction. It has proven effective at improving many intergroup outcomes, however some previous research points to limitations of the method and suggest that perhaps imagined intergroup contact is more effective at reducing certain types of prejudice than others. The Stereotype Content Model posits distinct types of prejudice directed at...
Show moreImagined intergroup contact was introduced as an easy and efficient method of improving the quality of intergroup interactions allowing better prejudice reduction. It has proven effective at improving many intergroup outcomes, however some previous research points to limitations of the method and suggest that perhaps imagined intergroup contact is more effective at reducing certain types of prejudice than others. The Stereotype Content Model posits distinct types of prejudice directed at different social groups based on perceptions of the group members’ warmth and competence. In the current study, I sought to investigate whether imagined intergroup contact works equally well for groups that experience different types of prejudice based on their differences on the dimensions of warmth and competence. Additionally, I examined the duration of the effects of intergroup contact by comparing outcomes both immediately after and one week later. Results indicated that imagined intergroup contact was not successful at creating more positive stereotype perceptions for any groups, regardless of their previous standing on warmth and competence. Unsurprisingly, patterns for intergroup emotions and behavioral tendencies predicated on these stereotype differences were not observed either. However, select behavioral tendencies were higher following imagined interactions with some social groups, indicating that part of intergroup contact’s influence on behavior is independent of its influence on stereotypes and emotions. Furthermore, many intergroup outcomes deteriorated over the period of a week, especially in the control condition. Results are discussed in terms of their implications for the theories of both imagined intergroup contact and the Stereotype Content Model.
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 Title
 The continuoustime principalagent problem with moral hazard and recursive preferences
 Creator
 Sinha, Sumit Kumar
 Date
 2011
 Collection
 Electronic Theses & Dissertations
 Description

"The thesis deals with the three problems that belong to the intersection between stochastic analysis and financial economics. The problems are: 1. Continuoustime PrincipalAgent Problem with moral hazard under recursive preferences. 2. General maximization principle with application to problems that arise in financial economics. 3. A Functional version of Ito formula."P. 1.
 Title
 Modeling and simulations of evaporating spray, turbulent flow, and combustion in internal combustion engines
 Creator
 Srivastava, Shalabh
 Date
 2015
 Collection
 Electronic Theses & Dissertations
 Description

A multicomponent droplet evaporation model, which discretizes the onedimensional mass and temperature profiles inside a droplet with a finite volume method and treats the liquid phase as thermodynamically real, has been developed and implemented into a largeeddy simulation (LES) code for evaporating and reacting spray simulations. Single drop evaporation results obtained by the variable property multicomponent model are shown to match with the constant property model in the limiting...
Show moreA multicomponent droplet evaporation model, which discretizes the onedimensional mass and temperature profiles inside a droplet with a finite volume method and treats the liquid phase as thermodynamically real, has been developed and implemented into a largeeddy simulation (LES) code for evaporating and reacting spray simulations. Single drop evaporation results obtained by the variable property multicomponent model are shown to match with the constant property model in the limiting conditions. The LES code with the multicomponent model is used along with the KelvinHelmholtz  RayleighTaylor (KHRT) droplet breakup model to simulate realistic fuel sprays in a closed vessel and is found to reasonably well predict the experimentally observed nonlinear behavior of spray penetration lengths with changing ambient conditions for nhexadecane and 4 different multicomponent surrogate diesel fuels with 28 components. The effects of various modeling assumptions and gas and liquid parameters on the drop and spray evolution and evaporation are investigated in details.A previously studied single piston Rapid Compression Machine (RCM), extended to a twinpiston RCM, is simulated by LES for different stroke ratios of the two pistons, as a precursor to the study of opposed piston twostroke engines. Opposed piston engines, which have recently generated interest due to their high power density and fuel economy, are mechanically simpler compared to conventional fourstroke engines but involve highly unsteady, turbulent and cyclevariant flows. LES of turbulent spray combustion in a generic single cylinder, opposedpiston, twostroke engine configuration has been conducted with the twophase filtered mass density function (FMDF) model, which is an EulerianLagrangianLagrangian subgridscale probability density function (PDF) model for LES of twophase turbulent reacting flows. The effects of various geometric parameters, operating conditions and spray parameters on the flow evolution, turbulence, spray and combustion in the engine are studied. The cycletocycle variations in the flow variables like swirl and tumble are found to be significant while those in thermodynamic variables like temperature are negligible. The hybrid LES/FMDF methodology has been applied to simulate nonreacting turbulent spray for singlecomponent and multicomponent fuels and the consistency of the method has been established. The effects of spray parameters like nozzle hole diameter, injection pressure and injected fuel temperature on the spray penetration length are found to qualitatively follow experimental trends. Combustion simulations of ndodecane fuel sprays are carried out for the opposed piston engine with a global kinetics mechanism and the consistency of the LES and FMDF components is demonstrated.
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 Title
 Efficient and secure system design in wireless communications
 Creator
 Song, Tianlong
 Date
 2016
 Collection
 Electronic Theses & Dissertations
 Description

Efficient and secure information transmission lies in the core part of wireless system design and networking. Comparing with its wired counterpart, in wireless communications, the total available spectrum has to be shared by different services. Moreover, wireless transmission is more vulnerable to unauthorized detection, eavesdropping and hostile jamming due to the lack of a protective physical boundary.Today, the two most representative highly efficient communication systems are CDMA (used...
Show moreEfficient and secure information transmission lies in the core part of wireless system design and networking. Comparing with its wired counterpart, in wireless communications, the total available spectrum has to be shared by different services. Moreover, wireless transmission is more vulnerable to unauthorized detection, eavesdropping and hostile jamming due to the lack of a protective physical boundary.Today, the two most representative highly efficient communication systems are CDMA (used in 3G) and OFDM (used in 4G), and OFDM is regarded as the most efficient system. This dissertation will focus on two topics: (1) Explore more spectrally efficient system design based on the 4G OFDM scheme; (2) Investigate robust wireless system design and conduct capacity analysis under different jamming scenarios. The main results are outlined as follows.First, we develop two spectrally efficient OFDMbased multicarrier transmission schemes: one with messagedriven idle subcarriers (MCMDIS), and the other with messagedriven strengthened subcarriers (MCMDSS). The basic idea in MCMDIS is to carry part of the information, named carrier bits, through idle subcarrier selection while transmitting the ordinary bits regularly on all the other subcarriers. When the number of subcarriers is much larger than the adopted constellation size, higher spectral and power efficiency can be achieved comparing with OFDM. In MCMDSS, the idle subcarriers are replaced by strengthened ones, which, unlike idle ones, can carry both carrier bits and ordinary bits. Therefore, MCMDSS achieves even higher spectral efficiency than MCMDIS.Second, we consider jammingresistant OFDM system design under fullband disguised jamming, where the jamming symbols are taken from the same constellation as the information symbols over each subcarrier. It is shown that due to the symmetricity between the authorized signal and jamming, the BER of the traditional OFDM system is lower bounded by a modulation specific constant. We develop an optimal precoding scheme, which minimizes the BER of OFDM systems under fullband disguised jamming. It is shown that the most efficient way to combat fullband disguised jamming is to concentrate the total available power and distribute it uniformly over a particular number of subcarriers instead of the entire spectrum. The precoding scheme is further randomized to reinforce the system jamming resistance.Third, we consider jamming mitigation for CDMA systems under disguised jamming, where the jammer generates a fake signal using the same spreading code, constellation and pulse shaping filter as that of the authorized signal. Again, due to the symmetricity between the authorized signal and jamming, the receiver cannot really distinguish the authorized signal from jamming, leading to complete communication failure. In this research, instead of using conventional scrambling codes, we apply advanced encryption standard (AES) to generate the securityenhanced scrambling codes. Theoretical analysis shows that: the capacity of conventional CDMA systems without secure scrambling under disguised jamming is actually zero, while the capacity can be significantly increased by secure scrambling.Finally, we consider a game between a powerlimited authorized user and a powerlimited jammer, who operate independently over the same spectrum consisting of multiple bands. The strategic decisionmaking is modeled as a twoparty zerosum game, where the payoff function is the capacity that can be achieved by the authorized user in presence of the jammer. We first investigate the game under AWGN channels. It is found that: either for the authorized user to maximize its capacity, or for the jammer to minimize the capacity of the authorized user, the best strategy is to distribute the power uniformly over all the available spectrum. Then, we consider fading channels. We characterize the dynamic relationship between the optimal signal power allocation and the optimal jamming power allocation, and propose an efficient twostep water pouring algorithm to calculate them.
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