Browsing by Subject "Heterogeneity"
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Item Adverse Selection and Advantageous Selection in Insurance Markets(2014-08-08) Wu, XiThis dissertation consists of three essays about adverse selection and advantageous selection in life insurance and health insurance markets. Firstly, I confirm the advantageous selection in voluntary private health insurance markets in Europe and detect the sources of such advantageous selection by using data from Survey of Health, Ageing and Retirement in Europe (SHARE). Specifically, I find, on the extensive margin, individuals with symptom are less likely to own VPHI than those without any symptom; on the intensive margin, the more the number of symptoms the individual has, the less likely she has VPHI. Same conclusion can be obtained when using a subjective measure of health. The sources of this advantageous selection include asset, education, longevity expectations, as well as cognitive ability. Conditional on these factors, individuals whose health is worse are more likely to purchase VPHI. Secondly, I identify the adverse selection problem in life insurance markets in the presence of both adverse and advantageous private information. Conventional theory for private information of adverse selection predicts a positive correlation between insurance coverage and ex post risk. However, Cawley and Philipson (1999) reported a neutral or even negative correlation between mortality risk and insurance coverage in the life insurance market. A recent growing literature has shown that such puzzle could be attributed to the multiple dimensions of private information coexisting in the market. Specifically, I provide evidence of the existence of private information both on mortality risk and on life insurance preferences. I show that these two dimensions of private information have an offsetting effect on the relationship between subsequent mortality and life insurance purchases, which makes the identification of the private information on mortality risk difficult under the traditional setting. Instead, I apply the mixture density model and successfully detect a positive correlation between individual mortality and insurance coverage. Moreover, I examine the mortality risk related to each of the two main types of life insurance contracts ? term and whole life insurance. Our two-period model shows that, given an individual, the relative income, rather than the risk, dominates the choice between whole and term life insurance policies, indicating that a systematic risk difference between these two pools should not be observed. Moreover, when the income of these two periods are the same, whole life insurance policies, the one with more capability of avoiding reclassification risk, would be always favored if the individual is risk averse. Empirical results support the conclusions made in the theoretical model. This paper also, empirically confirms the partial lock-in of consumers embodied in the more front-loading contract as proposed by Hendel and Lizzeri (2003). Specifically, I find as a more front-loaded contract, whole life insurance policy is associated with a lower lapsation rate and thus retains a healthier pool after 65 years old.Item Bayesian estimation of finite mixture roughness model(2016-12) Serigos, Pedro A. (Pedro Antonio); Prozzi, Jorge Alberto; Zhang, Zhanmin; Gilbert, Robert B; Müller, Peter; Mikhail, MagdyHighway infrastructure systems provide a crucial service to society and constitute a major asset with a significant maintenance and rehabilitation cost, highway pavements comprising a major component of the total cost. The increasing need for greater capital investment, in the face of ever-decreasing federal funding to maintain highway infrastructure, highlights the importance of developing and implementing effective methods for managing pavement assets. A key for the success of pavement management is to accurately predict the future condition of the pavements in the network. This dissertation proposes a mixture of regression models to capture the systematic differences in pavement performance not explained by variables typically available in pavement management systems. This approach assumes that the heterogeneous pavement performance, which results from the combined effect of the several unobserved factors and interactions, is manifested through a finite number of latent groups. The estimation of the proposed model allows for defining the parameters of the group-specific models while clustering the observations into the latent groups. The insights provided by the model-based clustering of performance data can also be incorporated into the design of maintenance and rehabilitation strategies, as clustering of sections according to their deterioration rate allows for identifying pavements in the network with structural deficiencies and tailoring actions in response. The gain in model fit, along with the insights provided by the proposed methodology for the unsupervised model-based clustering of pavement performance was demonstrated using experimental data. In addition, the proposed mixture model was applied to develop a Bayesian pavement roughness model specified with variables from an existing pavement management system, plus climatic and preventive maintenance variables, and estimated using nationwide field data from the Long-Term Pavement Performance program. Lastly, the developed roughness mixture model was calibrated for Texas pavement conditions by combining both the nationwide data and data extracted from the processing and merging of various Texas Department of Transportation databases. The proposed methodology produces accurate predictions of the progression of roughness as well as robust estimates of the factor effects driving the deterioration of pavements, which, ultimately, lead to a more efficient management of highway assets.Item Bayesian hierarchical modelling of pavement performance(2015-05) Serigos, Pedro Antonio, M.S. in Statistics; Müller, Peter, 1963 August 9-; Prozzi, Jorge AA challenge currently faced by local, state and federal transportation agencies is the constantly increasing traffic demand, combined with a less increasing availability of funds for the maintenance of the highway infrastructure. A key factor for the success of a pavement management system is that it contains accurate and reliable pavement performance models. Inadequate prediction of the highway infrastructure future condition can lead to an inappropriately estimated budget or misallocation of funds. This study had the main objectives of quantifying the uncertainty of pavement performance model parameters and proposing a hierarchical model specification in order to account for heterogeneity across different subpopulations of pavements. The uncertainty of each pavement performance parameter was quantified by estimating their marginal posterior distribution using both a non-hierarchical and a hierarchical specification of the model. The posterior distribution of each model parameter was sampled using a combination of the Gibbs and Metropolis-Hastings techniques. The hierarchical model was specified in order to capture the different damaging effect that environmental factors and traffic characteristics have on pavements between the subpopulations with thinner and thicker hot-mix asphalt layer. The results from the study showed a significant dispersion of the pavement performance parameters. In addition, accounting for the heterogeneous effect between subpopulations resulted in a significant improvement of the fitting of the model as opposed to assuming complete pooling across pavement sections.Item Depositional systems and sequence stratigraphy of the M1 sandstone in Tarapoa, Ecuador(2014-12) Ye, Yu; Steel, R. J.; Olariu, CornelCampanian M1 Sandstone is one of the major prospective sandstone units in the Tarapoa field in Oriente Basin, Ecuador. The M1 Sandstone is always markedly sharp based, averages 25 m in thickness, shows upward increasing marine bioturbation and generally fines upward from coarse to very fine grained sandstone. In cores, the sandstones at base are amalgamated coarse to fine grained with prominent cross stratification (dm thick), sometimes clearly bi-directional and contains mud drapes. These suggest strong tidal or fluvial-tidal currents in estuary channels or delta distributary channels. The finer grained intervals in the middle are brackish-water intensely bioturbated and dominated by mud drapes, wavy and flaser bedding suggestive of intertidal flats. Associated overlying coals and coaly shales suggest supratidal conditions. The sandstones at top are cross stratified and contain mud drapes. These again suggest strong tidal or fluvial-tidal currents in estuary channels or delta distributary channels. The stacking pattern of facies in M1 Sandstone reveals the evolution of the M1 depositional system, as well as the sequence stratigraphy of M1 sandstone. The evolution includes four stages of deposition which indicates an initial sea level rise, a subsequent sea level fall, and another sea level rise. Lateral sand-mud heterogeneity exists in the study area, forming “shale barriers”, i.e. elongate shale-rich zones that are lateral barriers to hydrocarbon migration. They are interpreted to be abandoned tidal channels filled with muddy tidal flat deposits during the sea level fall. An alternative hypothesis was established to explain the stacking pattern of facies in M1 Sandstone. A tide-dominated delta with poor fluvial input experienced intense tidal erosion and produced a sharp base at the base of M1 Sandstone. Then subtidal sand bars, intertidal flats, and supratidal sediments were deposited in sequence during a continuous regression. The core and well logs in an extension of the study area in the northwest is interpreted as more distal open shelf deposits, beyond the mouth of the Tarapoa estuary system, where transgressive tidal shelf ridges were coeval with the Tarapoa estuary system. This interpretation allows us to predict the environment between the two areas as a transition zone between tide-dominated estuary and open shelf.Item Development of peridynamics-based hydraulic fracturing model for fracture growth in heterogeneous reservoirs(2016-05) Ouchi, Hisanao; Sharma, Mukul M.; Olson, Jon E.; Foster, John T.; Espinoza, Nicolas; Kallivokas, Loukas F.Oil and gas reservoirs are heterogeneous at different length scales. At the micro-scale mechanical property differences exist due to mineral grains of different composition and the distribution of organic material. At the centimeter or core scale, micro-cracks, sedimentary bedding planes, natural fractures, planes of weakness and faults exist. At the meter or log scale, larger scale bedding planes, fractures and faults are evident in most sedimentary rocks. All these heterogeneities contribute to the complexity in fracture geometry. However, very little research has been conducted on evaluating the effect of these heterogeneities on fracture propagation, primarily due to the absence of a numerical framework capable of incorporating such heterogeneities in fracture growth models. In this dissertation we developed a novel method for simulating hydraulic fractures in heterogeneous reservoirs based on peridynamics and then utilized it to elucidate the complicated fracture propagation mechanisms in naturally fractured, heterogeneous reservoirs. Peridynamics is a recently developed continuum mechanics theory specially developed to account for discontinuities such as fractures. Its integral formulation minimizes the impact of spatial derivatives in the stress balance equation making it particularly suitable for handling discontinuities in the domain. No fluid flow formulation existed in the peridynamics framework since this theory had not been applied to fluid driven fracturing processes. In this dissertation, a new peridynamics fluid flow formulation for flow in a porous medium and inside a fracture was derived as a first step in the development of a peridynamics-based hydraulic fracturing model. In the subsequent section, a new peridynamics-based hydraulic fracturing model was developed by modifying the existing peridynamics formulation of solid mechanics and coupling it with the newly derived peridynamic fluid flow formulation. Finally, new shear failure criteria were introduced into the model for simulating interactions between hydraulic fractures (HF) and natural fractures (NF). This model can simulate non-planar, multiple fracture growth in arbitrarily heterogeneous reservoirs by solving fracture propagation, deformation, fracturing fluid pressure, and pore pressure simultaneously. The validity of the model was shown through comparing model results with analytical solutions (1-D consolidation problem, the KGD model, the PKN model, and the Sneddon solution) and experiments. The 2-D and 3-D interactions behavior between a HF and a NF were investigated by using the newly developed peridynamics-based hydraulic fracturing model. The 2-D parametric study for the interaction between a HF and a NF revealed that, in addition to the well-known parameters (the principal stress difference, the approach angle, the fracture toughness of the rock, the fracture toughness of the natural fracture, and the shear failure criteria of the natural fracture), poroelastic effects also have a large influence on the interaction between a HF and a NF if leak-off is high. The 3-D interaction study elucidated that the height of the NF, the position of the NF, and the opening resistance of the NF have a huge impact on the three-dimensional interaction behavior between a HF and a NF. The effects of different types of vertical heterogeneity on fracture propagation were systematically investigated by using domains of different length scales. This research clearly showed the mechanisms and the controlling factors of characteristic fracture propagation behaviors (“turning”, “kinking”, and “branching”) near the layer interface. In layered systems, the mechanical property contrast between layers, the dip angle and the stress contrast all play an important role in controlling the fracture trajectory. Each of these effects was investigated in detail. The effect of micro-scale heterogeneity (due to varying mineral composition) on fracture geometry was studied next. It was shown that even at the micro-scale, fracture geometry can be quite complex and is determined by the geometry and distribution of mineral grains and their mechanical properties.Item Dissecting the heterogeneity of prostate cancer cells(2013-08) Liu, Xin, active 2013; Jolly, Christopher A.; Tang, Dean G.Prostate cancer (PCa) is heterogeneous containing phenotypically diverse cells. It is unclear whether these phenotypically different PCa cells are functionally distinct and possess divergent tumorigenic potential. Androgen signaling plays important roles in differentiation and survival of malignant PCa cells, and prostate specific antigen (PSA) as one of the androgen signaling target genes is used as a biomarker of AR signaling to assess tumor progression and evaluate therapeutic efficiency in clinic. Here we present evidence for discordant AR and PSA expression resulting in AR⁺/PSA⁺, AR⁺/PSA⁻, AR⁻/PSA⁻, and AR⁻/PSA⁺ PCa cells in human tumors. We also show that prostate tumor PSA mRNA levels inversely correlate with poor clinical outcomes and patient survival. By employing a lentiviral reporter system, we have fractionated bulk PCa cells into PSA⁺ and PSA⁻[superscript '/lo'] cell populations, with the former being AR⁺/PSA⁺ and the latter containing both AR⁺/PSA⁻ and AR⁻/PSA⁻ cells. The PSA⁺ and PSA⁻[superscript '/lo'] PCa cells demonstrate distinct molecular, cellular, and tumor-propagating properties. PSA⁻[superscript '/lo'] PCa cells are quiescent and refractory to stresses including androgen deprivation, exhibit high clonogenic potential, and possess long-term tumor-propagating capacity. They preferentially express stem cell genes and can undergo asymmetric cell division to generate PSA⁺ cells. Of great clinical interest, PSA⁻[superscript '/lo'] PCa cells can initiate robust tumor development and resist androgen ablation in castrated hosts, and they harbor highly tumorigenic castration resistant PCa cells. In contrast, PSA⁺ PCa cells possess more limited tumor-propagating capacity, undergo symmetric division, and are sensitive to castration. Systemic androgen levels dynamically regulate the relative abundance of PSA⁺/PSA⁻[superscript '/lo'] PCa cells in the tumors, which in turn impact the kinetics of tumor growth. Further studies reveal that the PSA⁻[superscript '/lo'] PCa cell population harbors several overlapping but nonidentical tumorigenic subsets including ALDH⁺, CD44⁺, and [alpha]2[beta]1⁺ cells and ALDH⁺CD44⁺[alpha]2[beta]1⁺ can further enrich castration resistant PCa cells. These observations together suggest that heterogeneous PCa cells are organized as a tumorigenic hierarchy. Our results have important implications in understanding how different subpopulations of PCa cells manifest differential responses to current androgen deprivation therapy (ADT).Item Effect of cation symmetry on probe rotational diffusion in ionic liquids studied by fluorescence recovery after photobleaching(2013-08) Udugama-Arachchilage, Rakhitha W.; Quitevis, Edward L.; Myles, Charles W.The glass transition (Tg) is an interesting but challenging problem. Although this phenomenon has been studied for over half a century, Tg is still not well understood especially at the molecular level. One important feature which seems to be missing in the current understanding is its inherent heterogeneous dynamics. Ionic liquids are used in this study because of their fascinating physicochemical properties and they have been extensively studied in last two decades. The ability to change their structure to obtain a desired property for a specific application and the possibility of making millions of ionic liquids are very important characteristics in ILs. Understanding of the structure and dynamics of ILs and their mixtures with common solvents is necessary for their use in variety of applications and in their improvements. The dynamics of imidazolium-based ionic liquids were investigated near Tg. Ionic liquids are unique in terms of their structure and dynamics. Imidazolium-based ionic liquids are known for their structural hetereogeneity through the formation polar and nonpolar domains in the liquid state and their dynamical heterogeneity in the liquid and glassy state. Symmetric effect of cations in imidazolium-based ionic liquids was investigated. These studies showed that the dynamic heterogeneity cannot be necessarily explained by the structural heterogeneity near Tg.Item Feasibility of isotropic inversion in orthorhombic media : the Barrett unconventional model(2016-05) Yanke, Andrew James; Spikes, Kyle; Sen, Mrinal K; Fomel, Sergey BGeophysicists often relegate shale reservoirs as having higher symmetries (e.g., transversely isotropic (TI) or isotropic) than what reality demonstrates. Routine application of TI (or even isotropic) algorithms to orthorhombic media neglects the associated errors because we never know the true model in practice. This thesis evaluates the viability of isotropic post-stack and pre-stack seismic inversion to orthorhombic media using the SEAM Barrett Unconventional Model, the most realistic depositional model to date. The Barrett Model contains buried topography, simulated stratigraphy, and designated reservoir zones with orthorhombic anisotropy. I inverted the Barrett data volume for isotropic elastic property cubes, which I compared to the model volume in each symmetry-plane of an orthorhombic medium. If the stacked seismic data contained only the near offsets, post-stack inversion resolved acoustic impedances that closely matched the true model both within and outside of the reservoir zones at all well locations. Anisotropy most affected the far offsets, so muting them predictably enhanced the post-stack inversion. I maintained all offsets for pre-stack inversion, but a parabolic radon filter eliminated nonhyperbolic behavior (rather than nonhyperbolic moveout analysis) at far offsets. The pre-stack impedance attributes adequately described the vertical heterogeneity of the true model at a cross-validation well, but the inverted values increasingly relied on the initial model with depth. The inverted density estimates experienced notable oscillations relative to the initial model, particularly where steep contrasts in elastic properties occurred. Mismatch of the inverted elastic properties at the well locations can be attributed to noise, thin layering effects, band limitation, steep contrasts in elastic properties, AVO behavior stacked into the data, an inaccurate starting model, and the effects of anisotropy. The most significant sources of error include small-scale reflectivity and comprehensive filtering of nonhyperbolic phenomena. Away from the well locations, the isotropic inversion gave no visual indication of reservoir geobodies, but it sufficiently described the elastic property variations near reservoir mid-sections. Moreover, I showed that the inverted elastic properties differ from their orthorhombic models by no more than 35%. The greatest misfits occurred near reservoir contacts and geobody locations. The computed impedance models in each symmetry-plane have distinctive differences, but isotropic inversion dismisses these variations entirely. I conclude that isotropic inversion should not be a surrogate for orthorhombic methods in data preconditioning and quantitative reservoir characterization.Item Heterogeneity of polymers: diluents nanoconfined in rubber networks and mechanical hole burning spectroscopy(Texas Tech University, 2008-12) Qin, Qian; McKenna, Gregory B.; Quitevis, Edward L.; Vaughn, Mark W.; Khare, RajeshHeterogeneity at micrometer or nanometer scale is of great importance and has drawn considerable attention in recent years. Many physical properties of materials, such as dynamic relaxation, diffusion or transport phenomenon can be affected and explained by the heterogeneous nature. The present dissertation focuses on the heterogeneity of polymers and consists of two parts of projects. The first part of dissertation studies the nanoscale heterogeneity and structure in rubber networks. Thermoporosimetry is applied to characterize the network heterogeneity, which extends the Gibbs-Thomson model concerning the relationship between the melting point depression and the crystal size and requires the quantitative agreement between the Flory-Huggins theory and the melting points of the diluents in the uncrosslinked rubber. This dissertation presents the first systematic investigation on the validity of the Flory-Huggins theory in terms of melting point depression of diluents mixing with polymers. The correct use of thermoporosimetry to obtain the nanoheterogeneity of rubber networks and its calibration by controlled porous glasses are discussed and addressed. The second part of dissertation focuses on the characterization of dynamic heterogeneity of polymers by means of a novel rheological method called Mechanical Spectral Hole Burning (MSHB). The MSHB on a triblock copolymer in the vicinity of its order-disorder transition is investigated. By successfully distinguishing the heterogeneity from homogeneity as well as different heterogeneity degrees, MSHB promises to be a potentially powerful tool to probe dynamic heterogeneity for polymeric materials. Additionally, the MSHB is further investigated on a series of polystyrene/ diethyl phthalate solutions. The effect of different types of heterogeneity such as entanglement length, entanglement density and chain end density is explored and different types of dynamics are examined by the MSHB. The results are consistent with a heterogeneous dynamics over the time scales from close to Rouse regime into the rubbery plateau regime and for the rubbery plateau-to-terminal flow transition regime. Terminal relaxation dynamics, on the other hand, is found to be homogeneous for the PS/diethyl phthalate solutions investigated.Item Improving the accuracy and realism of Bayesian phylogenetic analyses(2009-08) Brown, Jeremy Matthew; Hillis, David M., 1958-Central to the study of Life is knowledge both about the underlying relationships among living things and the processes that have molded them into their diverse forms. Phylogenetics provides a powerful toolkit for investigating both aspects. Bayesian phylogenetics has gained much popularity, due to its readily interpretable notion of probability. However, the posterior probability of a phylogeny, as well as any dependent biological inferences, is conditioned on the assumed model of evolution and its priors, necessitating care in model formulation. In Chapter 1, I outline the Bayesian perspective of phylogenetic inference and provide my view on its most outstanding questions. I then present results from three studies that aim to (i) improve the accuracy of Bayesian phylogenetic inference and (ii) assess when the model assumed in a Bayesian analysis is insufficient to produce an accurate phylogenetic estimate. As phylogenetic data sets increase in size, they must also accommodate a greater diversity of underlying evolutionary processes. Partitioned models represent one way of accounting for this heterogeneity. In Chapter 2, I describe a simulation study to investigate whether support for partitioning of empirical data sets represents a real signal of heterogeneity or whether it is merely a statistical artifact. The results suggest that empirical data are extremely heterogeneous. The incorporation of heterogeneity into inferential models is important for accurate phylogenetic inference. Bayesian phylogenetic estimates of branch lengths are often wildly unreasonable. However, branch lengths are important input for many other analyses. In Chapter 3, I study the occurrence of this phenomenon, identify the data sets most likely to be affected, demonstrate the causes of the bias, and suggest several solutions to avoid inaccurate inferences. Phylogeneticists rarely assess absolute fit between an assumed model of evolution and the data being analyzed. While an approach to assessing fit in a Bayesian framework has been proposed, it sometimes performs quite poorly in predicting a model’s phylogenetic utility. In Chapter 4, I propose and evaluate new test statistics for assessing phylogenetic model adequacy, which directly evaluate a model’s phylogenetic performance.Item Investigation of the effects of buoyancy and heterogeneity on the performance of surfactant floods(2014-12) Tavassoli, Shayan; Pope, G. A.; Sepehrnoori, Kamy, 1951-The primary objectives of this research were to understand the potential for gravity-stable surfactant floods for enhanced oil recovery without the need for mobility control agents and to optimize the performance of such floods. Surfactants are added to injected water to mobilize the residual oil and increase the oil production. Surfactants reduce the interfacial tension (IFT) between oil and water. This reduction in IFT reduces the capillary pressure and thus the residual oil saturation, which then results in an increase in the water relative permeability. The mobility of the surfactant solution is then greater than the mobility of the oil bank it is displacing. This unfavorable mobility ratio can lead to hydrodynamic instabilities (fingering). The presence of these instabilities results in low reservoir sweep efficiency. Fingering can be prevented by increasing the viscosity of the surfactant solution or by using gravity to stabilize the displacement below a critical velocity. The former can be accomplished by using mobility control agents such as polymer or foam. The latter is called gravity-stable surfactant flooding, which is the subject of this study. Gravity-stable surfactant flooding is an attractive alternative to surfactant polymer flooding under certain favorable reservoir conditions. However, a gravity-stable flood requires a low velocity less than the critical velocity. Classical stability theory predicts the critical velocity needed to stabilize a miscible flood by gravity forces. This theory was tested for surfactant floods with ultralow interfacial tension and found to over-estimate the critical velocity compared to both laboratory displacement experiments and fine-grid simulations. Predictions using classical stability theory for miscible floods were not accurate because this theory did not take into account the specific physics of surfactant flooding. Stability criteria for gravity-stable surfactant flooding were developed and validated by comparison with both experiments and fine-grid numerical simulations. The effects of vertical permeability, oil viscosity and heterogeneity were investigated. Reasonable values of critical velocity require a high vertical permeability without any continuous barriers to vertical flow in the reservoir. This capability to predict when and under what reservoir conditions a gravity-stable surfactant flood can be performed at a reasonable velocity is highly significant. Numerical simulations were also used to show how gravity-stable surfactant flooding can be optimized to increase critical velocity, which shortens the project life and improves the economics of the process. The critical velocity for a stable surfactant flood is a function of the microemulsion viscosity and it turns out there is an optimum value that can be used to significantly increase the velocity and maintain stability. For example, the salinity gradient can be optimized to gradually decrease the microemulsion viscosity. Another alternative is to inject a polymer drive following the surfactant solution, but using polymer complicates the process and adds to its cost without significant benefit in most gravity-stable surfactant floods. A systematic approach was introduced to make decisions on using polymer in applications based on stability criteria and cost. Also, the effect of an aquifer on gravity-stable surfactant floods was investigated as part of a field-scale study and strategies were developed to minimize its effect on the process. This study has provided new insights into the design of an optimized gravity-stable surfactant flood. The results of the numerical simulations show the potential for high oil recovery from gravity-stable surfactant floods using horizontal wells. Application of gravity-stable surfactant floods reduces the cost and complexity of the process. The widespread use of horizontal wells has greatly increased the attractiveness and potential for conducting surfactant floods in a gravity-stable mode. This research has provided the necessary criteria and tools needed to determine when gravity-stable surfactant flooding is an attractive alternative to conventional surfactant-polymer flooding.Item Modeling Biogeochemistry and Flow within Heterogeneous Formations in Variably-Saturated Media(2012-10-19) Arora, BhavnaThis dissertation focuses on understanding the complex interactions between hydrological and geochemical processes, and specifically how these interactions are affected by subsurface heterogeneity across scales. Heterogeneity in the form of macropores and fractures provide preferential flowpaths and affect contaminant transport. Biogeochemical processes are also strongly affected by such heterogeneities. Any lithological layering or interface (e.g. plume fringe, wetland-aquifer boundary, etc.) increases biogeochemical activity around that interface. Hydrologic conditions, rainfall events, drainage patterns, and pH variations are also dominant controls on redox processes and thereby affect contaminant distribution and migration. An inherent limitation of modeling fate and transport of contaminants in the subsurface is that the interactions among biogeochemical processes are complex and non-linear. Therefore, this research investigates the effect of hydrological variations and physical heterogeneity on coupled biogeochemical processes across column and landfill scales. Structural heterogeneity in the form of macropore distributions (no macropore, single macropore, and multiple macropores) in experimental soil columns is investigated to accurately model preferential flow and tracer transport. This research is crucial to agricultural systems where soil and crop management practices modify soil structure and alter macropore densities. The comparison between deterministic and stochastic approaches for simulating preferential flow improved the characterization of interface parameters of the dual permeability model, and outlined the need for efficient sampling algorithms or additional datasets to yield unique (equifinal) soil hydraulic parameters. To evaluate the effect of heterogeneity on redox processes, repacked soil columns with homogeneous and heterogeneous (layered) profiles from soil cores collected at the Norman Landfill site, Oklahoma, USA were employed. Results indicate that heterogeneity in the form of textural layering is paramount in controlling redox processes in the layered column. To evaluate the effect of hydrologic conditions on redox processes, temporal data at the Norman landfill site was used. Results indicate that seasonal hydrologic variations exert dominant control over redox-sensitive concentrations. An integrated MCMC algorithm was devised to upscale linked biogeochemical processes from the column to the field scale. Results indicate that heterogeneity and hydrologic processes are paramount in controlling effective redox concentrations at the Norman landfill site.Item Modeling of recovery process characterization using magnetic nanoparticles(2013-12) Rahmani, Amir Reza; Bryant, Steven L.; Huh, ChunStable dispersions of magnetic nanoparticles that are already in use in biomedicine as image-enhancing agents, also have potential use in subsurface applications. Surface-coated nanoparticles are capable of flowing through micron-size pores across long distances in a reservoir with modest retention in rock. Tracing these contrast agents using the current electromagnetic tomography technology could potentially help track the flood-front in waterflood and EOR processes and characterize the reservoir. The electromagnetic (EM) tomography used in the petroleum industry today is based on the difference between the electrical conductivity of reservoir fluids as well as other subsurface entities. The magnetic nanoparticles that are considered in this study, however, change the magnetic permeability of the flooded region, which is a novel application of the existing EM tomography technology. As the first fundamental step, the magnetic permeability change in rock due to injecting magnetic nanoparticles is quantified as a function of particle and reservoir properties. Subsequently, a new formulation is devised to compute the sensitivity of magnetic measurements to magnetic permeability perturbations. The results are then compared with the sensitivity to conductivity perturbations to identify the application space of magnetic contrast agents. Using numerical simulations, the progress of magnetic nanoparticle bank is monitored in the reservoir through time-lapse magnetic tomography measurements that are expected. Initially, simple models for displacement of injection banks are assumed and the level of complexity is gradually increased to incorporate the realities of fluid flow in the reservoir. The fluid-flow behavior of the nanoparticles is dynamically integrated with time-lapse magnetic response. Since the nanoparticles could help illuminate the flow paths, they could be used to indirectly measure reservoir heterogeneities. Therefore, numerous case studies are demonstrated where reservoir heterogeneity could potentially be inferred. Finally, fundamental pore-scale models are developed as a first step towards the multiple fluid phases extension of the EM tomography application. Using magnetic nanoparticles to improve electromagnetic tomography provides several strategic advantages. One key advantage is that the magnetic nanoparticles provide high resolution measurements at very low frequencies where the conductivity contrast is hardly detectable and casing effect is manageable. In addition, the sensitivity of magnetic measurements at the early stages of the flood is significantly improved with magnetic nanoparticles. Moreover, the vertical resolution of magnetic measurements is significantly enhanced with magnetic nanoparticles present in the vicinity of source or receiver. The fact that the progress of the magnetic slug can be detected at very early stages of the flood, that the traveling slug’s vertical boundaries can be identified at low frequencies, that the reservoir heterogeneities could potentially be characterized, and that the magnetic nanoparticles can be sensed much before the actual arrival of the slug at the observer well, provides significant value of using magnetic contrast agents for reservoir illumination.Item Modeling steam assisted gravity drainage in heterogeneous reservoirs using different upscaling techniques(2014-05) Kumar, Dhananjay; Srinivasan, SanjayThis thesis presents different methods that improve the ability to relate the flow properties of heterogeneous reservoirs to equivalent anisotropic flow properties in order to predict the performance of the Steam Assisted Gravity Drainage (SAGD) process. Process simulation using full scale heterogeneous reservoirs are inefficient and so the need arises to develop equivalent anisotropic reservoirs that can capture the effect of reservoir heterogeneity. Since SAGD is highly governed by permeability in the reservoir, effective permeability values were determined using different upscaling techniques. First, a flow-based upscaling technique was employed and a semi-analytical model, derived by Azom and Srinivasan, was used to determine the accuracy of the upscaling. The results indicated inadequacy of flow-based upscaling schemes to derive effective direction permeabilities consistent with the unique flow geometry during the SAGD process. Subsequently, statistical upscaling was employed using full 3D models to determine relationships between the heterogeneity variables: k[subscript italic v]⁄k[subscript italic h] , correlation length and shale proportion. An iterative procedure coupled with an optimization algorithm was deployed to determine optimal k[subscript italic v] and k[subscript italic k] values. Further regression analysis was performed to explore the relationship between the variables of shale heterogeneity in a reservoir and the corresponding effective properties. It was observed that increased correlation lengths and shale proportions both decrease the dimensionless flow rates at given dimensionless times and that the semi-analytical model was more accurate for cases that contained lower shale proportions. Upscaled heterogeneous values inputted into the semi-analytical model resulted in underestimation of oil flow rate due to the inability to fully account for the impact of reservoir barriers and the configuration of flow streamlines during the SAGD process. Statistical upscaling using geometric averaging as the initial guess was used as the basis for developing a relationship between correlation length, shale proportion and k[subscript italic v]⁄k[subscript italic h]. The initial regression models did not accurately predict the anisotropic ratio because of insufficient data points along the regression surface. Subsequently a non-linear regression model that was 2nd order in both length and shale proportion was calibrated by executing more cases with varying levels of heterogeneity and the regression model revealed excellent matches to heterogeneous models for the prediction cases.Item Populating a Linked Data Entity Name System(2016-05) Kejriwal, Mayank; Miranker, Daniel P.; Ghosh, Joydeep; Price, Eric; Miikkulainen, Risto; Mooney, RaymondResource Description Framework (RDF) is a graph-based data model used to publish data as a Web of Linked Data. RDF is an emergent foundation for large-scale data integration, the problem of providing a unified view over multiple data sources. An Entity Name System (ENS) is a thesaurus for entities, and is a crucial component in a data integration architecture. Populating a Linked Data ENS is equivalent to solving an Artificial Intelligence problem called instance matching, which concerns identifying pairs of entities referring to the same underlying entity. This dissertation presents an instance matcher with four properties, namely automation, heterogeneity, scalability and domain independence. Automation is addressed by employing inexpensive but well-performing heuristics to automatically generate a training set, which is employed by other machine learning algorithms in the pipeline. Data-driven alignment algorithms are adapted to deal with structural heterogeneity in RDF graphs. Domain independence is established by actively avoiding prior assumptions about input domains, and through evaluations on ten RDF test cases. The full system is scaled by implementing it on cloud infrastructure using MapReduce algorithms.Item Scale-up of reactive processes in heterogeneous media(2014-12) Singh, Harpreet, active 21st century; Srinivasan, SanjayPhysical and chemical heterogeneities cause the porous media transport parameters to vary with scale, and between these two types of heterogeneities geological heterogeneity is considered to be the most important source of scale-dependence of transport parameters. Subsurface processes associated with chemical alterations result in changing reservoir properties with interlinked spatial and temporal scale, and there is uncertainty in the evolution of those properties and the chemical processes. This dissertation provides a framework and procedures to quantify the spatiotemporal scaling characteristics of reservoir attributes and transport processes in heterogeneous media accounting for chemical alterations in the reservoir. Conventional flow scaling groups were used to assess their applicability in scaling of recovery and Mixing Zone Length (MZL) in presence of chemical reactivity and permeability heterogeneity through numerical simulations of CO₂ injection. It was found out that these scaling groups are not adequate enough to capture the scaling of recovery and transport parameters in the combined presence of chemical reactivity and physical heterogeneity. In this illustrative example, MZL was investigated as a function of spatial scale, temporal scale, multi-scale heterogeneity, and chemical reactivity; key conclusions are that 1) the scaling characteristics of MZL distinctly differ for low permeability and high permeability media, 2) heterogeneous media with spatial arrangements of both high and low permeability regions exhibit scaling characteristics of both high and low permeability media, 3) reactions affect scaling characteristics of MZL in heterogeneous media, 4) a simple rescaling can combine various MZL curves by merging them into a single MZL curve irrespective of the correlation length of heterogeneity, and 5) estimates of MZL (and consequently predictions of oil recovery) will fluctuate corresponding to displacements in a permeable medium whose lateral length is smaller than the correlation length of geological formation. We illustrate and extend the procedure of estimating Representative Elementary Volume (REV) to include temporal scale by coupling it with spatial scale. The current practice is to perform spatial averaging of attributes and account for residual variability by calibration and history matching. This results in poor predictions of future reservoir performance. The proposed semi-analytical technique to scale-up in both space and time provides guidance for selection of spatial and temporal discretizations that takes into account the uncertainties due to sub-processes. Finally, a probabilistic particle tracking (PT) approach is proposed to scale-up flow and transport of diffusion-reaction (DR) processes while addressing multi-scale and multi-physics nature of DR mechanisms and also maintaining consistent reservoir heterogeneity at different levels of scales. This multi-scale modeling uses a hierarchical approach which is based on passing the macroscopic subsurface heterogeneity down to the finer scales and then returning more accurate reactive flow response. This PT method can quantify the impact of reservoir heterogeneity and its uncertainties on statistical properties such as reaction surface area and MZL, at various scales.Item Talking politics : political opinion expression and avoidance across conservative, liberal, and heterogeneous groups(2016-05) Peacock, Cynthia Clemons; Stroud, Natalie Jomini; Jarvis, Sharon E; Dailey, Rene; Donovan, Erin; McCombs, MaxwellDiscussion among the public about politics and public affairs is a hallmark of deliberative democracy. Specifically, sharing information, expressing opinions, and learning about the perspectives of others defines a deliberative system. People oftentimes find expressing their political opinions difficult, unpleasant, and even threatening. Yet when people refrain from expressing their ideas and opinions, those points of view remain absent from the public sphere. The implications of avoiding the expression of political opinions are considered detrimental by those who think that society is better when people communicate their positions and understand the perspectives of others. This dissertation centers on the occurrence—and avoidance—of political opinion expression, or the act of openly stating one’s political opinion. I employed quantitative, thematic, and content analyses to investigate data from The Electronic Dialogue Project in Campaign 2000 (ED2K) and an original survey, to explore how often and in what contexts people avoid expressing their opinions during political conversations, the ways in which diverse opinions and opinion expression avoidance take place in conservative, liberal, and heterogeneous networks, the motivations for avoiding the expression of political opinions, and the strategies employed in avoidance. Among other findings, I provide evidence that challenges some commonly held assumptions about political talk. Results indicate that even within one conversation, people both expressed and avoided expressing their opinions about politics. Within political discussions overall, whether discussion members were in disagreement with one another did not influence their likelihood of directly expressing their opinions. Ideologically heterogeneous groups did not emerge as bastions of diverse opinions. Finally, I used a thematic analysis and drew from interpersonal communication, mass communication, political science, and social psychology, to uncover the motivations and strategies involved in people’s decisions to avoid expressing political opinions. Political talk is perhaps the most accessible form of political engagement and helps people to understand themselves, each other, and the world around us. This dissertation examined the occurrence of and contexts surrounding political opinion expression and avoidance, and the existence of disagreement and diversity in political discussions.Item The antecedents and outcomes of preschool programs for children in America(2016-05) Ansari, Arya; Gershoff, Elizabeth T.; Crosnoe, Robert; Benner, Aprile; Kim, Su Yeong; Callahan, RebeccaThere has been an increased interest in the early childhood years as a point of intervention and, specifically, on preschool programs, which hold great promise in preparing children for school. Despite the extensive body of literature on preschool education, there remain a number of key issues that need to be addressed to move the early childhood field forward. This dissertation addresses three of these areas that require continued attention. First, we need to know why Latino children from U.S.- and foreign-born households are under-enrolled in preschool education (Aim 1). The second area that we need to know more about is the potential long-term benefits of large-scale preschool programs (Aim 2). Finally, the third area where more information is needed is on the different sources of heterogeneity in the benefits of preschool for children (Aim 3). Thus, the aims of this dissertation were to address these gaps in the knowledge-base by using data from the Early Childhood Longitudinal Study Birth (ECLS-B) and Kindergarten (ECLS-K 1998) Cohorts. The first set of findings reveals that there are important differences that exist within the Latino population (culture, household resources, parents’ beliefs about school readiness, and child elicitation) with respect to preschool selection. These differences indicate that, in order to boost the preschool enrollment of Latino children from U.S.- and foreign-born households, policymakers may need to focus on targeting a specific set of barriers. Findings from Aim 2 underscore the potential long-term benefits of preschool education. Specifically, despite evidence for partial convergence of test scores, children who attended preschool at age four consistently outperformed their classmates who attended informal care in areas of academic achievement through the end of middle school. Although all children benefited from preschool participation, analyses from Aim 3 of this dissertation revealed that there was evidence for systematic heterogeneity, with findings supporting developmental theories on cumulative advantage and diverging destinies. Taken together, the results from this dissertation add to the existing evidence base on preschool education by highlighting new means of engaging families in the preschool market and underscoring both how and why preschool programs have long-term benefits for children.Item The glass transition in confined and heterogeneous systems(Texas Tech University, 2008-08) Zheng, Wei; Simon, Sindee L.; Quitevis, Edward L.; Weeks, Brandon L.; McKenna, Gregory B.The glass transition (Tg) is an interesting but challenging problem. Although this phenomenon has been studied for over half a century, Tg is still not well understood especially at the molecular level. One important feature which seems to be missing in the current understanding is its inherent heterogeneous dynamics. The aim of this work is to study the Tg behavior under various conditions such as for material freeze-dried from dilute solutions, confined in nanopores, and blended with other components, and to examine the relation between the dynamic heterogeneity and the observed Tg behavior. Freeze-dried materials from dilute solutions show different Tg behavior from the bulk; however, the origin of the difference remains unclear. In this work, the residual solvent effect on the calorimetric Tg of freeze-dried polystyrene is investigated. A linear correlation is found between the Tg depression and the residual solvent concentration, in agreement with data in the literature, indicating that the Tg depression observed for polymers freeze dried from dilute solution is due to residual solvent. Confinement at the nanoscale is also found to affect the glass transition behavior. Two hydrogen-bonded liquids, glycerol and propylene glychol, confined in silanized and unsilanized nanopores are studied to elucidate the confinement effects on Tg. Upon confinement, these two materials show similar behavior except that an additional Tg is observed for propylene glycol. We find that the confinement effects strongly depend on the competition between size effects and surface effects. Recently, a self-concentration model was proposed to predict the segmental dynamics of misicible polymer blends. To test this model, in this work, the dynamic properties of athermal blends of poly(á-methyl styrene) with its oligomer is examined. The effective Tgs of the components determined from the calorimetric transition can be described by the self-concentration model. However, the self-concentration value obtained is much lower than the theoretical prediction, indicating weak chain connectivity effects in the athermal mixture. Moreover, compared to the pure materials, the blends exhibit considerably broadened transitions and depressed enthalpy overshoots, presumably resulting from their broader relaxation time distribution. In addition to studies dealing with confined or heterogeneous systems, calorimetric measurements of Tg and the limiting fictive temperature, Tf', as a function of cooling and heating rates are performed for a polystyrene to examine the relationship between the Tg and Tf' and to examine the conversion dependence of the apparent activation energy.