Quaternary magnetic studies have provided the conceptual framework to bridge magnetic studies into ancient systems. In cases where environmental materials have been subjected to diagenetic alteration two questions come to mind: 1) What part of the magnetic signal is preserved in the rocks; and 2) can the preserved signal be used to infer/identify magnetic patterns that are characteristic of the depositional, post-depositional, and/or diagenetic environment. Analyses of multi-parameter magnetic experiments conducted on upper Mississippian and lower Pennsylvanian continental successions reveal that distinct depositional, pedogenic, and diagenetic magnetic patterns can be separated and identified. Evidence for a primary depositional signal in several of the upper Mississippian lithofacies is identified by a detrital remanence component attributed to source-area-derived magnetite/titanomagnetite. Red and gray vertisols preserve a Mississippian pedogenic signal characterized by magnetic enrichment, depletion, and amalgamation patterns that are associated with the removal and transport of Fe-rich clays as well as vertical mixing by shrink-swell mechanisms. These well-developed vertisols are interpreted to reflect significant hiatuses in sedimentation associated with prolonged exposure on interfluve/floodplain surfaces that may correlative with incised valleys (lowstand surface of erosion). Similarly, in lower Pennsylvanian quartz arenite facies, early siderite cementation zones as well as conglomerate lags with distinctive magnetic characteristics are thought to reflect periods of prolonged exposure and to define unconformities within compound valley fills. / Master of Science

The first part of this dissertation investigates the possibility of an output cut by a firm as a result of an increase in demand in industries with constrained capacities. We are specially interested in the crude oil industry, although the paper has implications beyond that market. Two simple closely related models are developed. In both models a firm cuts the output at some point solely because of an increase in demand. We use this fact to explain the sharp decline of the crude oil prices in 1986. There are price and quantity hysteresis in the second model. The price hysteresis has two implications. First, the price path when the demand increases might be different from the price path when the demand decreases. This in turn implies that a temporary shock in the demand for (or supply of) crude oil can cause permanent changes in the price. We claim that the temporary changes in the supply of crude oil in 1973 resulted in the price hysteresis phenomenon described in the second model in such a way that it kept the prices high even after the return of the producers to the market. The second part investigates the relationship between the taste for public expenditure and the size and distribution of social groups in a society. Societies with ethnic heterogeneity spend less on redistribution and welfare programs and impose lower tax rates relative to homogeneous societies. We construct a theoretical model to explain these facts. There are two social groups in the model: a minority group and a majority group. When members of one group feel empathy for each other but not for members of the other group, then taxes, and redistribution depend upon the size and distribution of those groups. At first, the equilibrium tax rate and redistribution decrease as the size of the minority group increases from zero, then eventually, the relationship between them becomes positive. / Ph. D.

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Climate warming has been extensively documented over the last few decades, with northern environments experiencing greater increases in temperature than lower and mid-latitudes. Impacts of climate warming include: an increase in the rain to snow ratio, changes in precipitation magnitude and timing, increased soil warming, permafrost thaw, latitudinal and altitudinal expansion of tree-line, proliferation of tall shrubs into tundra, intensification of the freshwater cycle, and changes to stream volume and water quality. However, forecasting how these changes will affect northern, high latitude environments is difficult due to a lack of process-based research across scales. Wolf Creek Research Basin (WCRB) in Southern Yukon is a well-established mesoscale alpine catchment comprised of three ecozones and has hydrometric and meteorological records spanning 25 years. In this thesis, extensive field campaigns generated hydrochemical, stable isotope, and high-frequency in-situ datasets that were analyzed in conjunction with historical data from WCRB to refine and advance existing conceptual models. These distinct datasets were collected within a nested experimental design to more precisely describe relationships between catchment conditions, ecohydrological processes and stream water quantity and quality beginning at the headwater scale and with scaling to the outlet of WCRB. Optical data was combined with dissolved organic carbon (DOC) concentrations to assess source areas and in-stream dissolved organic matter (DOM) quality across landscape units. Headwater DOC concentrations and fluxes from 2015-2016 were compared to the previous decade to assess changing export. In situ sensors that record chromophoric DOM (CDOM) at high frequency were paired with discharge and conductivity measurements to assess concentration-discharge relationships at event, seasonal and annual scales. Conceptual models of conductivity and major ion transport were confirmed while high-frequency CDOM-Q insights refined our understanding of DOC movement. As vegetation community composition and characteristics change, it is expected that components of the water balance will be altered at both the canopy level and within the critical zone. Compartmentalization of water within the critical zone is increasingly important to provide insights into how water cycles within catchments. Dual isotope and lc-excess approaches showed that bulk and xylem water were significantly different from the LMWL and stream water isotopes of δ2H and δ18O. Meanwhile, an increasingly enriched xylem water isotope signal overlapped with bulk soil water values as the growing season continued, which suggests the opportunistic use of available mobile soil water. / Dissertation / Doctor of Philosophy (PhD) / Climate warming has been extensively documented over the last few decades, with northern environments experiencing greater increases in temperature than lower and mid-latitudes. Impacts of climate warming include: an increase in the rain to snow ratio, changes in precipitation magnitude and timing, increased soil warming, permafrost thaw, latitudinal and altitudinal expansion of trees and shrubs becoming taller and moving to new areas. Climate change has the capacity to then affect the cycling of water leading to differences in how much water is present in streams and possibly leading to decreasing in water quality. Models and other tools are used to forecast these changes but benchmarking outcomes is difficult because northern environments are less well studied than other, more accessible locations. New types of information, including water quality, isotope and optical datasets, were used to explore previous understanding of how processes interact in space and time.

We examine the relaxed minimization problem for ferromagnetic bodies using the nonlocal exchange energy model. We show that the model possesses a wide range of phenomena including hysteresis, hysteresis subloops, Barkhausen effect, and demagnetization. The results are in three parts. First, we examine analytically the problem of a unit sphere of ferromagnetic material. We show that when the exchange energy is zero we duplicate De Simone's model which has a wide range of measure-valued minimizers. As the exchange energy grows our model stabilizes at the saturated solutions of the Stoner-Wohlfarth model. Here, the measure-valued minimizers are eliminated. Next, we examine numerically the problem of a body composed of several unit spheres of ferromagnetic material. We show that a constrained problem that focuses on the resultant field energy produces results similar to the unconstrained problem with considerable savings in time and resources. Finally, we examine numerically the constrained problem on a moderately large body. It is shown that the constrained problem contains all the hysteresis phenomena mentioned above. / Ph. D.

In recent years, the ferroelectric oxides belonging to the family of layered perovskite, e.g., SrBi₂(Ta₁₋_xNb_x)₂O₉ (or SBTN), were identified as promising candidates for nonvolatile memory applications. SrBi₂Ta₂O₉ (or SBT) thin films were found to exhibit no fatigue up to 10¹² switching cycles, very good retention properties and low leakage current densities on Pt electrodes. However, high temperature processing, ie. 750 - 800°C, is needed for SBT to exhibit ferroelectric properties. Moreover, the fundamental properties of SBTN have not been fully characterized. In this research, SBTN solid solutions were studied from two aspects: the technical aspect and scientific aspect. From the technical point of view, low temperature processing of SBTN ferroelectric thin films was developed. In this part of study, SBTN thin films were made by metalorganic decomposition method (MOD) and were deposited on Pt-electrodes. The structure development study by a non-destructive optical method, spectroscopic ellipsometry, was proposed to determine nucleation and grain growth temperatures. The information on structure development can be obtained by observing how the refractive indices and film thicknesses change as functions of annealing temperature. The results of structure development study for SBT thin films suggest that the ferroelectric properties are controlled by grain growth process rather than nucleation process. The critical factor for ferroelectric properties was to have grain size exceeding a critical value, i.e., 0.1 µm. Applying this concept, low temperature processing can be achieved by growing larger grains at lower temperature. The processing temperature of SBTN thin films was reduced by 50 - 100°C by adding excess Bi or increasing Nb/Ta ratio. The optimum excess Bi content in SBT was 30 - 50%; within this range, limited solid solution of Bi₂O₃ and SBT was formed. From the scientific aspect of view, optical properties and ionic transport phenomena of SBTN bulk ceramics were investigated for the first time. The reason of using bulk ceramics is to exclude the difficulties associated with thin film technology, e.g., grain size effect and electrode-ferroelectric interface effect. These bulk property studies provide fundamental understanding of SBTN materials and provide a guideline for process development in device applications. The optical dispersion functions of bulk SBTN were obtained by using various angle spectroscopic ellipsometry with a surface layer correction. The values of refractive indices were found to vary with composition, which are possibly associated with crystallographic orientation. Using the Lorentz Oscillator model, the approximate energy band gaps of SBTN solid solutions were estimated to be about 5 eV. The ionic transport phenomena of SBT and SrBi₂Nb₂O₉ (or SBN) were investigated by using impedance spectroscopy. This technique allows to separate the effect of ion transport in grain, grain boundary and electrode-ferroelectric interface. In this study, the fatigue model of bismuth layered oxides was discussed through ionic conductivity and interface absorption effect. One conducting species, oxygen vacancies with positive charges, was assumed in the model. High ionic conductivities of SBT and SBN (~ 10¯⁷ S/cm) comparing to Pb(Zr₁₋_xTi_x)O₃ (~ 10¯¹¹-10¯¹⁰ S/cm) suggests high defect concentration and high charge mobility in bismuth layered oxide materials. As a result, the most possible model to explain high resistance to fatigue of SBT/SBN was the easy recovery of oxygen vacancies from the entrapment at electrode-ferroelectric interfaces. / Ph. D.

Energy is lost when a rope transfers from a slack state to a taut state. This transfer is called a snap load and can be very violent. It is proposed to use synthetic fiber ropes as a type of passive control device in new or existing structures to mitigate seismic response. Experimental static and snap load (dynamic) tests were conducted on various synthetic fiber ropes. An eleven-foot-tall drop tower was built in the Virginia Tech Structures and Materials Laboratory in order to conduct these tests. Force and acceleration of the drop plate, which slides vertically within the drop tower, were measured with respect to time for all dynamic tests. Acceleration data was integrated using the trapezoidal or midpoint rule to obtain velocity and displacement values. Plots were made for each test in order to give a better representation of the results. These plots include representations of force and acceleration vs. time, force vs. absolute displacement, force vs. velocity, and force, acceleration, velocity, and displacement vs. time (during the initial taut phase only). Test results show that energy was dissipated in all of the dynamic drop tests, which was expected. Also, the displacement of each rope did not return to zero at the same time that the force returned to zero after the initial snap load. This proves that the ropes undergo some permanent elongation under load. The stiffness of each rope increased with continuous testing. As more tests are conducted on each rope, the strands are pulled tighter into the braided configuration, which causes the rope to become stiffer. / Master of Science