Phosphofructokinase from Escherichia coli (EcPFK) is allosterically regulated by MgADP and phosphoenolpyruvate (PEP), which act to activate or inhibit, respectively, by changing the substrate (Fru-6-P) affinity of the enzyme. Both ligands bind to the same allosteric site in EcPFK. Therefore, the questions we want to address are how these two molecules regulate EcPFK and how the allosteric signal is propagated throughout the enzyme. EcPFK has 28 potential site-site interactions. These interactions in turn derive from multiple copies of 6 potentially unique homotropic interactions and 4 potentially unique heterotropic interactions. Making hybrid tetramer of EcPFK is used to isolate a single heterotropic interaction. To improve the yield of the 1:3 hybrid, the in vivo hybrid formation method was developed. Four heterotropic interactions were isolated by this manner and re-evaluated. The same kinetics characteristics were obtained for each 1:3 hybrid from both the in vivo and in vitro method. To address the question of how the allosteric signal is transmitted throughout EcPFK, we identified residues (G184, Asp59 and S157) that are important for the allosteric regulation for both PEP inhibition and MgADP activation. The impact of each mutation on individual interaction is unique and also suggests that the structural basis for PEP inhibition is different from that for MgADP activation. Most importantly, since the sum of each heterotropic interaction with a modification in only one subunit is equal to the total heterotropic interaction with a modification in all four subunits, this result indicates that the heterotropic allosteric signal transmission is realized in a single subunit. The 23Ã heterotropic interaction, which contributes the most to the PEP inhibition, was chosen to study the dynamic properties. Fluorescence was used to study the dynamic perturbations of the 23Ã interaction upon ligand binding. Taking advantage of the hybrid formation strategy and the tryptophan-shift mutagenesis method, a tryptophan residue can be placed at different individual locations throughout the native subunit containing the 23Ã heterotropic interaction. The steady-state anisotropy and lifetime measurement at each tryptophan position indicate that the 23Ã allosteric interaction involves the perturbation of side-chain dynamics both near and quite far away from the respective ligand binding sites.

Introduction: Claims that foot orthoses can resolve low-back pain are common in the marketing of these devices. The claims are based on the notion that wearing the orthoses will limit excess pronation at the subtalar joint thus reducing excessive internal tibial and femoral rotations. Excess leg rotations increase the anterior tilt of the pelvis and subsequently the degree of lumbar lordosis. Since lumbar lordosis has been suggested as a cause of low-back pain, it is speculated that foot orthoses could be used to treat and prevent pain to the low-back by reducing the forward curvature of the spine. This mechanical link between foot function and the low-back has not been investigated by experimental studies. Purpose: The purpose of this thesis was to investigate whether increased internal rotation of the femur induced an anterior tilt of the pelvis thus increasing the degree of lumbar lordosis and if external rotation induced a posterior pelvic tilt thus decreasing the degree of lumbar lordosis. Methods: In order to internally and externally rotate the femur, participants placed their feet in 18 different foot positions. Seven of these positions ranged from 15 degrees of foot eversion to 15 degrees of foot inversion and 11 positions ranged from 40 degrees of external foot rotation to 40 degrees of internal foot rotation. Six cameras surrounded the motion capture area and angles of pelvic tilt and lumbar lordosis were calculated. Results: Foot eversion and inversion did not have a statistically significant effect on pelvic tilt and lumbar lordosis. In-toeing had a statistically significant linear relationship with anterior pelvic tilt (R2=0.35, F1,131=69.79, p=0.00). Internally and externally rotating the feet had no effect on lumbar lordosis (R2=0.001, F1,153=0.09, p=0.77). Conclusion: Internally rotating the legs caused the pelvis to tilt anteriorly but only at extreme ranges of motion, much greater than what would normally be seen during gait. At which point, lumbar angles remained unaffected. This study does not dispute the effectiveness of foot orthoses to treat low-back pain but the results do not support the mechanical link proposed as the mechanism by which they work.

Chalcopyrite (CuFeS2) is the most abundant of the copper sulfides and also one of the most refractory for leaching. Several processing routes have been proposed to overcome drawbacks associated with environmental problems related to copper extraction from this mineral. Atmospheric leaching in acidic ferric sulfate is regarded as being particularly attractive over other hydrometallurgical systems. However, the challenge has been to overcome the problem of slow extraction rates due to passivity encountered at high solution potentials in this system. This highlights the need to investigate better operating conditions to optimize copper extraction and prevent the problem of passivation, and to develop suitable modeling tools to assess and diagnose leaching performance. In this work, a dissolution rate expression for chalcopyrite leaching in acidic ferric sulfate media is proposed accounting for effects in the active and passive regions under potentials from 415 to 550 mV (Ag/AgCl). A model of chemical speciation in the bulk solution elucidates the idea of passivation caused by precipitation of ferric species and their consequent adsorption onto the chalcopyrite surface. Electrochemical studies on massive samples of chalcopyrite involving characterization and modeling of the anodic and cathodic half-cell reactions of chalcopyrite leaching together with mixed potential considerations lead to the development of the mathematical expression for dissolution rate. The mathematical model was calibrated with electrochemical parameters and results are in good agreement with real leaching data from batch tests for solution potential regions where passivity is not observed. On the other hand, the passive region was modeled by means of adjusting parameters related to adsorption energies of the passivating species. Results of the model for this region deviate from real data as potential becomes higher probably due to diffusion resistance through a layer composed of ferric complexes.

The main hypothesis of this thesis was that the regulation of oxygen uptake (VO2) kinetics at the onset of exercise in trained young men is linked to cardiovascular adaptations. Two studies were conducted to investigate the interrelationships between oxygen (O2) transport and O2 utilization in accelerating VO2 kinetics at the onset of exercise. In the first study, simultaneous kinetics of VO2 and cardiac output (Q) were studied during the transition to heavy and moderate cycling exercise (Chapter 2). The acceleration of VO2 kinetics during the heavy exercise that followed prior moderate or heavy exercise was enabled by the rapid increase in Q; whereas, the acceleration of VO2 kinetics during moderate exercise that followed a heavy warm-up was associated with small changes in Q kinetics. The objective of the second study was to determine, in a model of forearm exercise, if the elevation of forearm blood flow (FBF) prior to the onset of exercise by prior circulatory occlusion would accelerate FBF and muscle oxygen uptake (VO2mus)kinetics during subsequent exercise as demonstrated previously for prior exercise (Chapter 3). Prolonged ischemia (15 min occlusion) followed by 3 min recovery reduced FBF and impaired VO2mus kinetics during subsequent heavy hand-grip exercise. However, prior heavy exercise confirmed the previous findings and resulted in a faster FBF and VO2mus kinetics. There was a high positive correlation between the time course of change in FBF and VO2mus at the onset heavy exercise. In a follow up of the second study, to investigate a possible mechanism for the slower adaptation of VO2mus following ischemia, the prior occlusion condition was repeated after ingesting a high dose of ibuprofen. Prostaglandin inhibition by ibuprofen augmented the FBF response during reactive hyperaemia and restored FBF during the heavy exercise that followed 15 min of circulatory occlusion to the control level. These two studies provide evidence that O2 delivery plays a dominant role in accelerating VO2 kinetics at the onset of heavy exercise in trained young men. The findings exposed differences in the mechanisms regulating pulmonary VO2 and VO2mus with prior exercise resulting in higher Q and FBF, but no changes in O2 extraction to yield the faster increase in pulmonary VO2 and VO2 at the onset of subsequent heavy exercise. In contrast, prior occlusion slightly retarded the increase in FBF and significantly reduced O2 extraction thus delaying VO2 kinetics. The precise mechanisms impairing VO2mus kinetics at the onset of heavy forearm hand-grip exercise that starts after a brief recovery from prolonged occlusion are still unknown, but this impairment may be partially due to a vasoconstrictor effect restricting blood flow during the adaptation to exercise and redistribution of the blood to the periphery. In a third study, the influence of muscle activity on the VO2 slow component during heavy exercise and O2 cost during moderate exercise that followed a heavy warm-up were examined (Chapter 4). The heavy exercise VO2 slow component was attenuated in a graded fashion by prior moderate and heavy warm-ups, and the principal components analysis showed a moderate but significant correlation between the changes in the integrated electromyographic activity and the VO2 slow component amplitude. The higher O2 cost of moderate exercise following a heavy warm-up was associated with higher mean power frequency. Changes in VO2 slow component and increased O2 cost during moderate exercise after prior heavy warm-up appear to be related to some changes in surface electromyographic activity which may provide some evidence for increased muscle fibres recruitment.

No description available.

This thesis seeks to investigate the adsorption capabilities of activated carbon and carbon nanotubes. The adsorption of methanol on both of these substances was tested for their application in a solar based refrigeration cycle. Research on carbon nanotubes and their growth has been carried out for applications in the semiconductor industry. Enough focus has not been given to the use of nanotubes for refrigeration purposes. Adsorption refrigerators have been designed with the energy source being solar energy. Various adsorbent/adsorbate pairs have been tested in literature. The present work focuses on carbon nanotubes because theoretically, nanotubes should be able to adsorb better than activated carbon due to their high surface to volume ratios and hence a higher number of adsorption sites available for methanol to adsorb. The amount of adsorption of methanol on nanotubes depends on whether the end caps of the nanotubes are open or closed and also on the hydrophilic nature of the nanotubes. Nanotubes with ends closed are supposed to adsorb less than the nanotubes with their ends opened. The ends of carbon nanotubes can be blocked because of iron and other impurities. In this project, nanotubes are annealed under high vacuum to open the end caps. The hydrophobic nature of the nanotubes is corrected by treating them with concentrated nitric acid. The hydrophobic nature of the nanotubes is corrected by treating them with concentrated nitric acid. The acid treated nanotubes are used to obtain adsorption data at different temperatures. The adsorption of methanol on activated carbon, pristine and treated carbon nanotubes is measured at different temperatures. Electron microscopy is used to validate that annealing the nanotubes at high temperature under vacuum opens the end caps of the nanotubes. Finally, a matrix of nanotubes and carbon powder is prepared with different concentrations. The mixture is tested for adsorption of methanol. It is observed that the carbon nanotubes, pristine or treated, do not perform better than activated carbon. However, performance seems to increase when mixtures of activated carbon and carbon nanotubes are used as adsorbent. Also, it is found that mixtures containing annealed nanotubes perform better than mixtures with pristine nanotubes. Kinetics of the adsorption process is calculated for the different adsorbents used, which is used to explain the increase in the amount of methanol adsorbed for the activated carbon-carbon nanotube mixture.

In this research we illustrate how particle-particle and particle-substrate interactions affect structure in interfacial colloidal systems. A number of tools are used to quantify characteristics of deposited structures. These results help understand the effects of colloidal system interactions and deposition kinetics on the degree of ordering in interfacial colloidal structures. The first set of experiments involve 2.34 ?m silica colloids interacting with silica substrates in 0mM, 5mM, 10mM, and 100mM NaCl solutions. Only the 100mM NaCl solution resulted in rapid deposition driven by van der Waals attraction, while residual electrostatic repulsion produced levitation at lower ionic strengths. This allowed direct observation of the effects of varying magnitudes of attractive interactions on interfacial colloidal structures. Rapid deposition of positively charged 1?m latex colloids on negatively charged silica substrates driven by Coulombic and van der Waals attraction produced surface structures similar to those obtained with only van der Waals attraction. Experiments on 2.34 ?m silica colloids interacting with silica substrates in 10mM NaCl/pH 5.5 and 10mM NaCl/pH 10 conditions resulted in slower deposition rates. It was also found that slower deposition rates produced more compact structures displaying a higher degree of order. Another set of experiments was aimed at understanding interactions and structures formed in systems of polymerically levitated particles. Total internal reflection microscopy (TIRM) experiments revealed the influence of underlying substrate chemistry on interaction profiles in these systems. Basic experiments were also performed on the effects of varying amounts of specific ions on the dispersion stability in these systems. At conditions producing instability in polymeric systems, a similar degree of order was observed in comparison to experiments involving rapid deposition via salt addition in electrostatically stabilized systems. The results of this research clearly indicate that particle-particle and particle-substrate interactions are critical in determining structure formation by deposition. While the principal focus of this research is to study structures formed in various kinetic regimes, it also provides a basis for future studies aimed at tuning attractive interactions to produce equilibrium colloidal crystals on substrates.

Sedimentary basins can contain close to 20% by volume pore fluids that are commonly classified as brines. These fluids can become undersaturated with respect to calcite as a result of processes such as migration, dispersive mixing, or anthropogenic injection of CO2. This study measured calcite solubility and dissolution rates in geologically relevant Na-Ca-Mg-Cl synthetic brines (35 to 200 g L-1 TDS). In brines < 50 g L-1 TDS, the EQPITZER calculated calcium carbonate ion activity product (IAP) at steady-state was in reasonable agreement (±10%) with the thermodynamic solubility constant for calcite (Kc). However, the IAP systematically exceeded Kc in more concentrated brines. The deviation was strongly correlated with calcium concentration and also was observed in magnesium-free solutions. This is interpreted as an uncertainty in the carbonate ion activity coefficient, and minor adjustment in stoichiometric association constants (K*M2+CO30) for the CaCO30 or MgCo30 ion pairs would correct for the error. The dissolution rate dependency on brine composition, pCO2 (0.1 to 1 bar), and temperature (25.0 to 82.5 °C) was modeled using the empirical rate equation ()nkR&#8486;&#8722;=1 where R is the rate, k and n are empirical fitting terms, and &#8486; the degree of disequilibrium with respect to calcite. When &#8486; was defined relative to an apparent kinetic solubility, n could be assumed first-order over the range of &#8486; investigated (&#8486; = 0.2 to 1.0). Rates increased with increasing pCO2 as did the sensitivity to brine concentration. At 0.1 bar, rates were nearly independent of concentration (k = 13.0 ±2.0 x 10-3 moles m-1 hr-1). However, at higher CO2 partial pressures rates became composition dependent and the rate constant, k, was shown to be a function of temperature, pCO2, ionic strength, and calcium and magnesium activity. The rate constant (k) can be estimated from a multiple regression (MR) model of the form k = B0 + B1(T) + B2(pCo2) + B4(aCa2+) + B5(aMg2+). A relatively high activation energy (Ea = 20 kJ mol-1) was measured, along with a stirring rate independence suggesting the dissolution is dominated by surface controlled processes at saturation states &#8486; > 0.2 in these calcium-rich brines. These findings offer important implications to reaction-transport models in carbonate-bearing saline reservoirs.

Acrylamide is considered a carcinogen in animals and a possible carcinogen in humans. It has been found in starch rich foods cooked at high temperatures. Vacuum frying (10 Torr) was studied as a possible alternative to reduce acrylamide formation in potato chips. Seven potato cultivars were analyzed to determine their influence on acrylamide formation during traditional and vacuum frying. The White Rose cultivar produced the highest level of acrylamide during both traditional and vacuum frying. Vacuum frying (10 Torr, 118oC, 8 min) produced chips with lower acrylamide content than those produced under traditional frying (165oC, 4 min) for all cultivars. The cultivar Atlantic was used to determine the kinetics of acrylamide formation during traditional and vacuum frying at different temperatures because it is a good chipping cultivar and it was the most abundant in the lab. Acrylamide accumulation under vacuum frying was modeled using first-order kinetics, and during traditional frying it was modeled using the logistic kinetic model. The behavior of the kinetics of acrylamide content in potato chips fried under the two processes was different mainly due to the different temperatures used. During traditional frying, higher temperatures areused (150oC to 180oC) and acrylamide after some time is produced but also starts degrading, producing a constant level of acrylamide content at longer times. During vacuum frying (10 Torr), acrylamide increased exponentially (but at lower levels) for all frying times. The effect of potato components was studied by infusing leached potato slices with predetermined amounts of glucose and asparagine. Increasing glucose and asparagine content in the slices increased the acrylamide content in the potato chips. Color could not be used as an indication of acrylamide content, since potato chips with similar color had very different acrylamide concentrations.

Produced water, a byproduct of oil and gas production, includes almost 98% of all waste generated by oil and gas exploration and their production activities. This oil contaminated waste water has a great impact on our environment and is considered to be a high-cost liability. The Department of Energy’s Oil and Gas Environmental Program is concerned with the development of new and affordable technology to clean this produced water. Organically modified clays are proposed as a good option for removal of oil from produced water. Organoclay, incorporated into a treatment process shows promise of being a cost effective method of treatment to remove crude oil from brine either as a final treatment prior to brine disposal at sea or as a precursor to desalination. Organoclay also pre-polishes the waste water before further treatment. This research studies the efficacy of using organoclay to remove oil by measuring its adsorption capacity to remove the oil from a SAE 30 (Golden West Superior) motor oil-water emulsion. A kinetic model was developed to examine the time dependent behavior of the oil adsorbing characteristics of the organoclay and to investigate how closely the experimentally obtained data matches the kinetic model. It was found that organoclay is effective in removing various percentages of oil depending on the concentrations of a SAE 30 (Golden West Superior) motor oil-water emulsion. Moreover, it was found that the experimental data closely follow the kinetic behavior of the organoclay as shown by the kinetic model. Since this research is specific to a particular type of oil, SAE 30, further research is required for verifying the adsorption capacity of organoclay in other types of oils. Moreover, it is also recommended that the adsorption capacity of the organoclay, together with conventional adsorbent such as GAC (Granular Activated Carbon), be investigated to determine if there is any further improvement in the adsorption capacity. Lastly, a detailed investigation using the actual produced water from the oil field should be conducted to determine the efficacy of the organoclay system in removing oil from water produced in the field.