Methane hydrates are naturally-occurring ice-like substances found in permafrost and in ocean sediments along continental shelves. These compounds are often the source of cold seeps—plumes which vent methane into aquatic environments, and may subsequently release the potent greenhouse gas into the atmosphere. Methane hydrates and methane gas seeps are of particular interest both for their potential as an energy source and for their possible contribution to climate change. In an effort to improve location of hydrates through the use of seismic surveys and echo-sounding technology, this work aims to describe the low-frequency (10 Hz to 10 kHz) acoustic behavior of methane gas bubbles and methane hydrates in water under simulated ocean-floor conditions of low temperatures and high pressures. Products of the experiments and analysis presented in this thesis include (a) passive acoustic techniques for measurement of gas flux from underwater seeps, (b) a modified form of Wood's model of low-frequency sound propagation through a bubbly liquid containing real gas, and (c) low-frequency measurements of bulk moduli and dissociation pressures of four natural samples of methane hydrates. Experimental procedures and results are presented, along with analytical and numerical models which support the findings. / text

Studies in this dissertation were conducted to explore the roles of organic cation transporters (OCTs) in the disposition of N-butylpyridinium Chloride (NBuPy-Cl) and structurally related ILs. Following a single i.v. dose to rats, the blood concentration of NBuPy-Cl and 1-butyl-1-methylpyrrolidinium chloride (BmPy-Cl) decreased in a biphasic manner with a clearance of 3.3 and 7 ml/min, respectively. More than 84% of dosed compounds were excreted in the urine. Depending on the vehicle, the dermal absorption of BmPy-Cl and NBuPy-Cl (5 mg/kg, 125 μg/cm²) was 10-35% at 96 h. Following a single oral (50 mg/kg) administration to rats, the maximum blood concentrations of both ILs were reached in less than 90 min in rats. Most of the orally dosed NBuPy-Cl (62-68 %) was excreted in the urine in 72 h. However, more of the dosed BmPy-Cl was eliminated in the feces Its oral bioavailability was only 47%. The elimination differences between BmPy-Cl and NBuPy-Cl were not altered by the size (0.5, 5, or 50 mg/kg) or frequency (1 or 5 administrations) of oral doses. In all urine and blood samples, only parent compounds were detected. Co-administration of NBuPy-Cl and inulin intravenously to rats revealed that the clearance of NBuPy-Cl exceeded the rat glomerular filtration rate, suggesting a renal secretion processing. The in vitro transport studies demonstrated that NBuPy-Cl, BmPy-Cl and 1-butyl-3-methylimidazolium chloride are substrates (Kt, 9~277 μM), as well as inhibitors (IC₅₀: 0.2~7.5 μM), of rOCT1/2 and hOCT2. Their inhibitory effects increased dramatically with increasing the alkyl chain length. The IC₅₀ values were 0.1, 3.8, 14 and 671 μM (hexyl-, butyl-, ethyl-pyridinium and pyridinium chloride) for rOCT2 mediated metformin transport. Similar structurally related inhibitory kinetics were observed for rOCT1 and hOCT2. In vivo co-administration of NBuPy-Cl prolonged the plasma half-life and reduced renal clearance of the diabetic drug, metformin. In summary, BmPy-Cl and NBuPy-Cl are partially absorbed from gastrointestinal tract. The present in blood is eliminated rapidly in the urine as parent, by renal filtration and OCT-mediated secretion. ILs also compete with other substrates of OCTs and have the potential to alter their pharmacokinetic profiles.

Quantum magnetic materials provide pathways to exotic spin-disordered phases. We study two broad classes of quantum spin systems and their ground states. The first class is that of spin-dimer systems, which form valence-bond-solid states. In such systems, competition between interactions among the dimers can lead to interesting magnetization behaviour. We explain the magnetization of Ba3Cr2O8 as a Bose-Einstein condensate of spin-carrying excitations. Furthermore, we investigate possible dimerized and nearby magnetically ordered states in the Shastry-Sutherland compound (CuCl)LaNb2O7. The second class of spin systems feature geometric frustration, which may stabilize spin-liquid states without any order or particular dimerization. We argue the proximity of the face-centred-cubic double perovskite La2LiMoO6 to such a phase, to explain its lack of long-range order. We argue for the coexistence of such a state, along with spiral magnetic order, to explain the anomalous thermodynamic measurements in the spin-density-wave phase of powder samples of Volborthite, a distorted kagome-lattice spin system. Finally, we study spin liquid phases that have spin correlations consistent with those found from inelastic neutron scattering of the disordered kagome-lattice material Herbertsmithite. We predict electron spin resonance absorption lineshapes associated with these phases.

Quantum magnetic materials provide pathways to exotic spin-disordered phases. We study two broad classes of quantum spin systems and their ground states. The first class is that of spin-dimer systems, which form valence-bond-solid states. In such systems, competition between interactions among the dimers can lead to interesting magnetization behaviour. We explain the magnetization of Ba3Cr2O8 as a Bose-Einstein condensate of spin-carrying excitations. Furthermore, we investigate possible dimerized and nearby magnetically ordered states in the Shastry-Sutherland compound (CuCl)LaNb2O7. The second class of spin systems feature geometric frustration, which may stabilize spin-liquid states without any order or particular dimerization. We argue the proximity of the face-centred-cubic double perovskite La2LiMoO6 to such a phase, to explain its lack of long-range order. We argue for the coexistence of such a state, along with spiral magnetic order, to explain the anomalous thermodynamic measurements in the spin-density-wave phase of powder samples of Volborthite, a distorted kagome-lattice spin system. Finally, we study spin liquid phases that have spin correlations consistent with those found from inelastic neutron scattering of the disordered kagome-lattice material Herbertsmithite. We predict electron spin resonance absorption lineshapes associated with these phases.

The behavior of sp-valent solids and liquids under compression is a field of intense re- search. At high pressure, they often undergo phase transitions to new structures with novel properties such as superconductivity, high-energy density, and superhardness. Furthermore, knowledge of these materials is essential for understanding the structure and evolution of planets. Molecular systems such as nitrogen and carbon dioxide are particularly interesting as energetic materials: their strong molecular bonds break under compression spawning transformations to exotic polymeric phases. We have used first-principles theory and molecular dynamics to make predictions for the properties of dense nitrogen, carbon dioxide, magnesium silicate, and magnesium oxide. For nitrogen, we provide evidence for a rare first-order liquid-liquid phase transition; only the second such transition seen in an elemental fluid. New finite-temperature structure search techniques have been developed and applied to predict a thermodynamically stable polymeric metal phase of solid nitrogen. Regarding carbon dioxide, we have computed its high-pressure liquid phase diagram over a broad pressure-temperature range, revealing rich structural diversity. We have also designed new free energy methods to explore the stability of free CO2 under deep mantle conditions. Lastly, first-principles molecular dynamics and finite-temperature free energy methods were used to predict a high-pressure phase separation transition in liquid MgSiO3 and also characterize the high-pressure phase diagram of MgO, including its melting curve.

Relative densities and heat capacity ratios have been measured for selected aqueous systems. These measurements have been used to calculate apparent molar volumes and heat capacities. Densities of aqueous sodium bromide have been measured from 374 to 522 K and 10.00 to 30.00 MPa using a recently developed high temperature and pressure vibrating tube densimeter. These data have been used to test the utility of an automated high temperature and pressure densimetric data analysis program. Apparent molar volumes and heat capacities of several aqueous rare earth sulphate systems at 298.15 K and 0.10 MPa have been reported, and discussed in terms of ionic contributions. Single ion partial molar volumes and heat capacities for aqueous trivalent rare earth species have been estimated in a review of apparent molar data from the literature and through the use of semi-empirical Debye-Huckel equation. These singles ion properties have subsequently been used to estimate the single ion properties of the monosulphate and disulphate rare earth complex species. Rigorous relaxation calculations are presented in a discussion of apparent molar heat capacities, where relaxation contributions are shown to be negative. Apparent molar volumes and densities for aqueous L-histidine, L-phenylalanine, L-tyrosine, L-tryptophan, and L-dopa have been used to estimate reported partial molar properties have been added to several reported properites for other amino acids and peptides to construct an additivity scheme that utilises the revised Helgeson, Kirkham, and Flowers (HKF) equations of state for neutral organic species. A volumetric study of aqueous glycine, L-serine, and glyclylglycine has been conducted at temperatures from 298 K to 423 K and pressures from 0.10 to 30.00 MPa. These data have been used to evaluate HKF coefficients in a discussion of peptide stability at elevated temperatures and pressures. / xvii, 220 leaves : ill. ; 28 cm.

The purpose of clarification in the sugar industry is to remove soluble, insoluble and colloidal matter from cane juice. Efficient clarification is required to produce high quality sugar and to prevent entrainment of solids in downstream equipment. The objective of this study is to produce a Computational Fluid Dynamics (CFD) model of the Magra Ultrasep clarifier. This was accomplished by: • Modelling the hydrodynamics of a laboratory scale clarifier In the Fluent CFD program. • Incorporating the flocculation process into the CFD model. • Performing experiments on a pilot scale clarifier to obtain parameter values for the flocculation model. The hydrodynamic model of the clarifier showed the presence of a recirculation zone above the baffle plate. Particle injections using Fluent's discrete phase modelling option determined that particles within the size range of IOOj..Lm to 4mm would circulate in this region, forming the bed of floc particles required for the Magra Ultrasep to work efficiently. The flocculation process in Fluent was represented using three different solid phases of different particle sizes. Small and medium sized particles were allowed to combine to form larger particles by changing the volume fractions according to three rate equations. A fibre glass laboratory scale model was set up at Maidstone Sugar Mill and fed the same sugar cane juice that enters the Rapi-Dorr clarifiers. The experimental results were then fed into a simplified flocculation model in MATLAB. An overall rate constant (k) of 5kg.m-3.s-) for the flocculation kinetic equation satisfied the experimental result. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.

Ionic liquids (ILs) are liquid organic salts at room temperature which are composed of only ions (cations and anions). Ionic liquids are regarded as “novel solvents” and have been gaining attention as alternatives to volatile molecular organic solvents. Ionic liquids have outstanding properties, such as negligible vapor pressure (no or limited evaporation or volatilization), low melting point, thermal stability, and ionic conductivity. They can be used in efficient and clean energy production and storage. The synthesis of the low-cost and performance-effective ionic liquids using inexpensive raw materials is presented and characterized. Characterization was done using Thermogravimetric Analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Differential Thermometry (DSC-TGA). Cost effective ionic liquids were synthesized and characterized and then compared to commercially available ionic liquids. Results for newly synthesized ionic liquids suggest that these cost effective ionic liquids were electroconductive and thermally stable when compared to the raw materials used for synthesis of ionic liquids. The thermal stability of these ionic liquids was less, however, when compared to the regular higher cost ionic liquids. FTIR characterization also provided secondary evidence on expected functional groups of newly synthesized ionic liquids. Viscosity of the syntehsized ionic liquids was higher when comapred to the commercially avaialable ionic liquids.

A prototype sensor array was developed for use with laboratory automation to permit closed-loop control of liquid-levels in a multiwell microplate geometry. A simple electrical model for non-contact capacitance-based fluid sensors was extended to describe a fluid-level dependency. The new model shows that a charge-transfer based capacitance transducer employing a liquid-specific calibration can be used to obtain an output signal that varies linearly with the liquid-level when fringe-field effects are negligible. The calibration also compensates for liquid-to-liquid conductivity and permittivity differences. / The sensor was tested using sodium chloride (NaCl) and ethanol solutions to simulate the range of conductivity and permittivity typical in biological and chemical research. Measured capacitance was a second-order function of liquid volume due to fringe-field effects and was compensated for by adding a hardware-based calibration. Liquid-volume measurement error averaged 0.2% of the 120mul fill volume with a standard deviation of 0.6% (< mul). The maximum absolute error for all liquids was 2.7% (3mul).

Tetrachloroethene (PCE) is a major groundwater contaminant that often persists as dense, nonaqueous phase liquids (DNAPLs) in subsurface environments. Dissolved-phase PCE plumes emanate from DNAPL source zones, which act as continuous sources of contamination for decades. Removal of DNAPL source zones is crucial to achieve lasting remedy of contaminated aquifers. This research explored the contributions of the microbial reductive dechlorination process (i.e., anaerobic bioremediation) to PCE-DNAPL source zone remediation, either in isolation or as a polishing step for the removal of residual DNAPL remaining after application of surfactant enhanced aquifer remediation (SEAR), an emerging physical-chemical source zone treatment. Specific objectives of this research were to: (1) evaluate the ability of microorganisms to dechlorinate in the presence of PCE-DNAPL and at high dissolved-phase PCE concentrations expected near/in DNAPL source zones, (2) assess the distribution and activity of key dechlorinating populations during bioenhanced PCE-DNAPL dissolution in continuous-flow column experiments, (3) determine the influence of Tween 80, a biodegradable surfactant commonly used in SEAR, on the microbial reductive dechlorination process, (4) design and optimize quantitative real-time PCR (qPCR) protocols to detect and enumerate key dechlorinating populations (e.g., Geobacter lovleyi, Sulfurospirillum multivorans), and (5) explore the effects of oxygen on Dehalococcoides viability and biomarker quantification. This research demonstrated that microbial dechlorinating activity within DNAPL source zones promotes bioenhanced dissolution although many dechlorinating isolates cannot tolerate saturated PCE concentrations. Application of newly designed qPCR protocols established a direct link between dissolution enhancement and the distribution of relevant dechlorinating populations in the vicinity of PCE-DNAPL. The limited and reversible impact of Tween 80 on key dechlorinators supported the feasibility of a treatment train approach of SEAR followed by microbial reductive dechlorination to remediate PCE-DNAPL source zones. Finally, experiments with oxygen-exposed, Dehalococcoides-containing cultures suggested limitations of using Dehalococcoides DNA and RNA biomarkers for monitoring bioremediation at field sites. These findings advance the scientific understanding of the microbial reductive dechlorination process and are relevant to environmental remediation practitioners. The advantages and current shortcomings of PCE-DNAPL source zone bioremediation, as well as recommendations for future research, are discussed.