A laboratory test program was conducted to investigate the effects of temperature, solution strength, and applied stress over increasing conditioning durations on cation exchange processes in sodium bentonite (Na-B) geosynthetic clay liners (GCLs). The test program was intended to determine if the variables of temperature, solution strength, and applied stress had beneficial or detrimental effects on the engineering behavior of Na-B GCLs in municipal solid waste (MSW) landfills and laboratory testing applications. Needlepunched-reinforced, double non-woven Na-B GCL specimens were conditioned in fluids of increasing ionic strength (DI water, 2 mM CaCl2, 50 mM CaCl2, and 200 mM CaCl2 representing control, pore water, mild MSW leachate, and harsh MSW leachate, respectively), temperatures of 5 degrees C, 20 degrees C, 40 degrees C, and 60 degrees C, and overburden stresses (30 kPa and 500 kPa representing stresses experienced by cover and bottom liner systems, respectively) which are all representative of geoenvironmental conditions observed in MSW landfill barrier systems. Cation exchange in the bentonite component of all conditioned Na-B GCL specimens was quantified by measuring the bound cation (BC) complexes and cation exchange capacities (CEC) of the specimens using inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis and by conducting index tests to determine the dimensional characteristics, swell index, and gravimetric moisture content of the specimens. For zero stress conditions, periodic measurements of electrical conductivity, total dissolved solids, sodium and calcium cation concentration, and temperature of the conditioning fluids were recorded to supplement bound cation complex data. For applied stress conditions, electrical conductivity, total dissolved solids, and temperature of the conditioning fluid were recorded. For zero stress conditions, 152 mm x 152 mm Na-B GCL specimens were conditioned in all conditioning fluids and temperatures over increasing time durations ranging from 4 hours to 32 days. For applied stress conditions, 60-mm-diameter Na-B GCL specimens were conditioned in 50 mM CaCl2 conditioning fluid at all temperatures for 4 to 16 days under the applied overburden stresses of 30 kPa and 500 kPa. Temperature, solution strength, and applied stress were all observed to affect cation exchange in the bentonite component of Na-B GCLs. Cation exchange processes were observed to increase with increasing temperature, increasing solution strength, and decreasing applied overburden stress. The majority of cation exchange processes were observed to occur within 8 to 10 days for specimens conditioned under zero stress. Cation exchange processes were observed to have a higher sensitivity to changes in solution strength (up to 625% increase in the change of Na+ BC from DI water to 200 mM CaCl2) compared to changes in temperature (up to 52% increase in the change of Na+ BC from 5 degrees C to 60 degrees C) in zero stress conditions. Changes in the bound cations of the Na-B GCL specimens over time were not reflected in the periodic electrical conductivity measurements taken of the high strength conditioning fluids. The results of this study can be used for quality assurance evaluations of in-service GCLs using thresholds developed for index properties. From the numerical thresholds determined in this study, hydrated Na-B GCL specimens sampled from the field conditioned under zero stress that exhibit swell indices greater than or equal to approximately 70% of the swell index reported by the manufacturer and gravimetric moisture contents of greater than or equal to approximately 200% will likely exhibit adequate hydraulic barrier performance. Hydrated Na-B GCL specimens sampled from the field conditioned under zero stress that exhibit swell indices of less than or equal to approximately 20% of the swell index reported by the manufacturer and gravimetric moisture contents of less than or equal to approximately 100% will likely exhibit inadequate hydraulic barrier performance. The Na-B GCL component of cover liner systems may be susceptible to high rates of cation exchange due to experiencing low overburden stress and elevated temperatures compared to typical earth temperatures. The Na-B GCL component of bottom liner systems may exhibit low rates of cation exchange due to experiencing high overburden stress and cooler temperatures.

Interstellar plasma — interstellar clouds in particular — play an important role in determining the structure and evolution of galaxies. Understanding the time evolution of such plasmas requires knowledge of the chemical processes that drive their dynamics. Two processes are studied in this dissertation: radiative electron attachment (REA) via dipole-bound states (DBSs) and dissociative recombination (DR). Of the several hundred molecules detected in the interstellar medium, only eight anions have been detected: CN-, C3N-, C5N-, C7N-, C4H-, C6H-, C8H-, and C10H-. Their production mechanism is not well known; REA was suggested as a possible formation pathway, but previous theoretical studies have found that REA rate coefficients were too low to explain the formation of CN-, C3N-, and C5N-. It was later suggested that including DBSs — an electron weakly bound at a large distance to the large dipole moment of a neutral molecule — could appreciably enhance the REA rate coefficients. The first portion of this study is dedicated to investigating the role of the large dipole moment of rotating C3N using an accurate \it ab initio approach with electronic and rotational resolution. DBS wavefunctions of C3N- are calculated and used to obtain REA cross sections that produce even smaller rate coefficients, suggesting that C3N- is efficiently formed by a different process. The second part of this study investigates DR in the difficult case of molecules with low-lying eletronic resonances, although these are not necessary for the approach. An approach to treat both direct and indirect mechanisms of DR in a diatomic ion with electronic, vibrational, and rotational resolution using R-matrix scattering calculations, frame transformation theory, and multichannel quantum defect theory is presented and applied to the CH+ and CF+ molecular ions at low collision energies. The calculated CH+ cross sections agree well with recent rotationally state-resolved experimental results and overall better than previous theoretical results. The calculated CF+ cross sections agree well with experimental results, although these do not have rotational resolution, and overall better than previous theoretical results at low energies. Additionally, the method can study rovibronic (de-)excitation — a process in competition with DR. These are calculated and compared to previous theoretical calculations for CH+, which which our results agree well with the exception of dipole-driven rotational excitation cross sections. This discrepancy is tentatively attibuted to negelcting the contribution of higher partial waves in the description of the incident electron, which will be incorporated in future studies.

In this licentiate thesis, we study the action of Hecke operators on Drinfeld cusp forms via the theory of crystals over function fields. The thesis contains one preliminary chapter, in which we recall some basic theory of Drinfeld modules and Drinfeld modular forms, as well as the Eichler-Shimura theory developed by Böckle. The core of the thesis consists of Chapter II, in which we prove a Lefschetz trace formula for crystals over stacks and deduce a Ramanujan bound for Drinfeld modular forms, and Chapter III, in which we compute traces and slopes of Hecke operators. We formulate several questions and conjectures based on our data. We also include an appendix in which we discuss the relationship between traces of an operator in positive characteristic and its eigenvalues.

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