Thesis (Ph. D.)--University of Wisconsin--Madison, 1950. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1948. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 34-35).

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Doctor of Philosophy. Johannesburg, March, 2018 / Reduction behavior of South African Mamatwan manganese ore using methane-argon- hydrogen gas mixture was investigated experimentally in the temperature range of 1050ºC to 1250ºC. The effect of changing gas mixture composition, time and temperature was studied using a vertical tube furnace. After each test, three representative samples were prepared; one was analyzed by chemical analysis to obtain metallization results as a function of each reducing condition for each time interval over the total reduction period of two hours. Second sample was analyzed by X-ray diffraction to determine the progress of phase changes; the third sample was mounted, polished and submitted for SEM-EDAX in order to examine the morphology of the ore and its changes in the course of reduction. It was seen that CH4 was an effective reductant as it cracked, supplying the reaction site with hydrogen gas and very fine solid carbon. The excess carbon from cracking of methane ensures regeneration of reductants CO and H2 from reaction product gases of CO2 and H2O ensuring low partial pressure of oxygen at the reaction site. Hydrogen gas may also be involved in the reduction of iron oxide components of the ore. Moreover, depending upon temperature and CH4/H2 ratio in the gas phase the activity of carbon in the system reaches values much higher than unity, shifting the reduction reaction by carbon to lower temperatures. It was observed that bulk of the metallization occurred in the first thirty to forty minutes and the metallization reached some kind of a reduction maximum at 73% metallization. The Mn/Fe ratios in the resulting alloy were higher than those in ordinary carbothermic solid-state reduction, indicating the simultaneous reduction of Fe and Mn at these low reducing temperatures due to a low oxygen potential set up by the methane bearing gas mixtures. It was seen that metallization of Mamatwan ore proceed in two stages. First, reduction of the higher oxides to MnO and metallic iron. Second, reduction of any remaining oxides and MnO to mixed carbide of iron and manganese. During first stage values of effective CO-CO2 diffusivities generated by the model were found to lie in the range from 1.45 *10-6 cm2sec-1 to 8.43*10-6 cm2sec-1 at 1100ºC. Apparent activation energy for first stage calculated in the temperature range of 1050ºC to 1250ºC varied from 1.47 kJ/mol to 24.72 kJ/mol indicating possibility of diffusional control. For the second stage the experimental curves could be duplicated with the mathematical model reasonably well with a maximum difference between the experimental and predicted values being about 5 percent. Rate of metallization values during the second stage (Ms) changed between 1.83*10-8 mol.sec-1.cm-2 and 8.55*10-8 mol.sec-1.cm-2. Specific rate constant values (ks) for the second stage, varied from 5.53*10-6 cm/sec to 3.16*10-5 cm/sec which are much smaller than specific rate constant for the first stage of reduction (kf), which varied from 1.64*10-4 cm/sec to 1.15*10-4 cm/sec, as the rate of second stage of the reduction is much slower than the rate of the first stage. X ray analysis revealed that manganese ore was reduced primarily to carbide Mn7C3 at lower temperature range of the experiments, but at 1200ºC the dominant reaction product was Mn5C2 in both mixtures of methane-argon and methane-hydrogen. The S.E.M images revealed that the product metallic phase occurred all throughout the surface, with globular formation in case of reduction where hydrogen was the carrier gas. / MT 2018

No description available.

Manganese (Mn) is considered important for normal growth and reproduction. Because Mn can cross the blood brain barrier and accumulate in the hypothalamus, and because it has been suggested that infants and children are potentially more sensitive to Mn than adults, we wanted to determine the effects of Mn exposure on puberty-related hormones and the onset of puberty, and discern the site and mechanism of Mn action. We demonstrated that the central administration of manganese chloride (MnCl2) stimulated luteinizing hormone (LH) release in prepubertal rats. Incubation of medial basal hypothalamus (MBH) in vitro showed this effect was due to a Mn-induced stimulation of luteinizing hormone releasing hormone (LHRH). Further demonstration that this is a hypothalamic site of action was shown by in vivo blockade of LHRH receptors and the lack of a direct pituitary action of Mn to stimulate LH release in vitro. Chronic supplementation of low dose of MnCl2 caused elevated serum levels of LH, follicle stimulating hormone (FSH) and estradiol or testosterone. Importantly, Mn supplementation advanced the timing of puberty in both sexes. We investigated the mechanism by which Mn induces LHRH/LH release from the hypothalamus. Blocking the NMDA receptor, IGF1 receptor, or inhibiting nitric oxide synthase in vivo was ineffective in altering Mn-induced LH release. Dose-response, pharmacological blockade and nitrite assessments indicated that the lowest doses of Mn used stimulated LHRH release, but did not induce nitric oxide (NO) production, while only the highest dose of Mn stimulated NO. Conversely, a dose-dependent inhibition of Mn-induced LHRH release was observed in the presence of ODQ, a specific blocker of soluble guanylyl cyclase. Furthermore, Mn stimulated the release of cyclic GMP (cGMP) and LHRH from the same MBH, and a protein kinase G (PKG) inhibitor, KT5823, blocked Mn-induced LHRH release. Collectively, these data demonstrate that Mn can stimulate specific puberty-related hormones both acutely and chronically, and furthermore, suggest that low levels of Mn facilitate the normal onset of puberty. The principal action of Mn within the hypothalamus is to facilitate the activation of guanylyl cyclase, which subsequently stimulates the cGMP/PKG pathway resulting in the stimulation of prepubertal LHRH secretion.

Manganese (Mn) is considered important for normal growth and reproduction. Because Mn can cross the blood brain barrier and accumulate in the hypothalamus, and because it has been suggested that infants and children are potentially more sensitive to Mn than adults, we wanted to determine the effects of Mn exposure on puberty-related hormones and the onset of puberty, and discern the site and mechanism of Mn action. We demonstrated that the central administration of manganese chloride (MnCl2) stimulated luteinizing hormone (LH) release in prepubertal rats. Incubation of medial basal hypothalamus (MBH) in vitro showed this effect was due to a Mn-induced stimulation of luteinizing hormone releasing hormone (LHRH). Further demonstration that this is a hypothalamic site of action was shown by in vivo blockade of LHRH receptors and the lack of a direct pituitary action of Mn to stimulate LH release in vitro. Chronic supplementation of low dose of MnCl2 caused elevated serum levels of LH, follicle stimulating hormone (FSH) and estradiol or testosterone. Importantly, Mn supplementation advanced the timing of puberty in both sexes. We investigated the mechanism by which Mn induces LHRH/LH release from the hypothalamus. Blocking the NMDA receptor, IGF1 receptor, or inhibiting nitric oxide synthase in vivo was ineffective in altering Mn-induced LH release. Dose-response, pharmacological blockade and nitrite assessments indicated that the lowest doses of Mn used stimulated LHRH release, but did not induce nitric oxide (NO) production, while only the highest dose of Mn stimulated NO. Conversely, a dose-dependent inhibition of Mn-induced LHRH release was observed in the presence of ODQ, a specific blocker of soluble guanylyl cyclase. Furthermore, Mn stimulated the release of cyclic GMP (cGMP) and LHRH from the same MBH, and a protein kinase G (PKG) inhibitor, KT5823, blocked Mn-induced LHRH release. Collectively, these data demonstrate that Mn can stimulate specific puberty-related hormones both acutely and chronically, and furthermore, suggest that low levels of Mn facilitate the normal onset of puberty. The principal action of Mn within the hypothalamus is to facilitate the activation of guanylyl cyclase, which subsequently stimulates the cGMP/PKG pathway resulting in the stimulation of prepubertal LHRH secretion.

No description available.

No description available.

No description available.

Otoliths are calcified structures located in the inner ear of teleost fish. They are formed by the crystallisation of calcium carbonate in the form of aragonite onto a protein matrix. Otoliths grow continuously during the lifespan of the fish by the deposition of concentric layers of aragonite and protein. During the formation of otoliths, trace elements are potentially incorporated into the otolith either by substitution for Ca or through co-precipitation with other carbonates. Since it has been suggested that otolith composition is reflective of the external environment (i.e. food and/or water) otoliths have been used as a temporal record to address many fisheries questions. Generally, toxicological studies focus on soft tissues (e.g. liver, kidneys, muscle) to determine metal exposure in fish. However, interpretation of the metal concentrations can be challenging due to the labile nature of metals in these tissues. A more recent approach to investigate temporal trends of metal exposure involves the use of otoliths. Otoliths are metabolically inert so that, once metals are incorporated they are not subject to remobilization. Red Lake, located in the Canadian Shield in Northwestern Ontario is recognized as a popular fishing area. However, over the last decade lake trout have experienced a drastic decline, with concurrent increase in the age distribution. One hypothesis for the recruitment failure has focused on the metals present in the water as a result of past mining activities. A retrospective analysis of the elemental signatures in the lake trout otoliths was performed to determine whether trace element concentrations have changed in Red Lake over the past three decades. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to determine trace elements in otoliths recovered from lake trout from 1960 to 2008. Mn was incorporated into the otoliths and there was a suggestion that concentrations peaked between 1980 and 1989 in Red Lake. Concentrations of Mn in lake trout otoliths ranged from 0 mg/g to 10.1 mg/g. Potential contributors to the elevated concentrations could have been associated to the local geology. In addition to geology further uncertainties concerning the water and diet to otolith relationships could also contributed to the Mn concentrations. Augmented diets failed to increase metal concentrations in otoliths. Further research is required to further investigate the relationship between Mn in the environment and the incorporation into the otolith.