No description available.

Please read the abstract in the section 00front of this document / Thesis (PhD(Water Resource Management))--University of Pretoria, 2008. / Microbiology and Plant Pathology / PhD / unrestricted

Investigations into the reduction of high concentration aqueous copper sulfate solutions with hydrogen, carbon monoxide and mixtures of these gases were conducted. The effect of increasing the copper sulfate concentration was to enhance the rate of reduction in both the hydrogen and carbon monoxide systems. The rate of reduction was increased by increasing pressure, temperature, and the concentration of ammonium sulfate buffer. Under mixtures of hydrogen and carbon monoxide the rate of reduction was intermediate between the rate under pure hydrogen and pure carbon monoxide. Based on the reaction mechanisms and rate equations developed by previous investigators a mathematical model of the reduction processes under hydrogen and carbon monoxide was developed. By fitting the model to the experimental results, rate constants for the high concentration reduction were determined. The use of carbon monoxide, with or without hydrogen, was found to reduce or minimize the plastering problem associated with the hydrogen reduction of copper. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

For some years the crops of two of the plots on one of the fields of the experiment station farm had been very poor. These two plots had been received ammonium sulfate as a source of nitrogen for a long period of years and it seemed evident that the poor yield might be due to the continued use of this salt. In order to determine whether or not this was the case, the following investigations were undertaken.

Black liquor recovery boilers experience significant fire-side fouling problems due to the deposition of entrained particulate matter. Increased understanding of the mechanisms by which particles deposit on these surfaces will lead to more effective management of the resultant problems. There is some evidence which suggests that the sub-micron fraction of this particulate matter deposits by thermophoresis. In an effort to determine conclusively if this is the case, a facility (the Multifuel Combustor at Sandia National Laboratories) was used which could generate and deposit fly ash under conditions that mimic those found in full scale recovery boilers, and dynamically monitor deposit growth rates. Experiments where both the deposit thickness and surface temperature were monitored in situ resulted in linear deposit growth rates despite highly non-linear surface temperature increases. This rules out thermophoresis as the dominant deposition mechanism since it is dependent on the changing thermal driving force. The morphology of the windward side deposit indicates an inertially-dependent mechanism is at work in spite of the size of the particles, which are considerably smaller than what would be commonly considered inertially impacting particles. Leeward side deposits also grow linearly, indicating that thermophoresis, although possibly contributing to deposition, is not the rate-controlling mechanism. Deposition efficiencies fell in the range of 5-15%. The morphology of the sub-micron deposits is highly structured and dendritic in appearance, with over 90% voidage. The particles form long strings or filaments which grow in parallel, indicating that the particles have a high sticking efficiency and do not roll or settle subsequent to impacting. There is minimal contact between adjacent filaments. Recently published research confirms the presence of particles in the 1-50 micron range in recovery boilers. Deposition experiments were performed on this size range as well. Termed Intermediate-size, these particles deposit many times more efficiently, and produce linear deposit growth rates just as the sub-micron particles. They also deposited in clusters of filaments which grew rapidly upward and slowly outward until the adjacent clusters merged. However in this size range the clusters tended to branch out more rapidly than the sub-micron deposits. Deposition efficiencies fell in the range of 40-65%. / Graduation date: 1999

The sulphation and sulphate decomposition occurring during the oxidation of nickel concentrates were studied by thermal analysis. Samples of industrial nickel concentrates were heated in inert gas to temperatures between 400°C and 850°C and oxidized isothermally in air or in a 4%O2-96%N2 mixture. During isothermal oxidation of the concentrates, SO2 evolved from the roasting reactions led to partial formation of metal sulphates. Following the oxidation and sulphation of the sample, the decomposition of the formed sulphates was studied. This was completed either by heating the sulphated sample to 950°C to thermally decompose the sulphates, or by lowering the partial pressure of oxygen while holding the sample at the isothermal oxidation temperature. The sulphation of the sample was found to follow the parabolic rate law, implying diffusion as the rate controlling-step. The thermal decomposition of the sulphates occurred at a near constant rate, implying zero-order kinetics.

The sulphation and sulphate decomposition occurring during the oxidation of nickel concentrates were studied by thermal analysis. Samples of industrial nickel concentrates were heated in inert gas to temperatures between 400°C and 850°C and oxidized isothermally in air or in a 4%O2-96%N2 mixture. During isothermal oxidation of the concentrates, SO2 evolved from the roasting reactions led to partial formation of metal sulphates. Following the oxidation and sulphation of the sample, the decomposition of the formed sulphates was studied. This was completed either by heating the sulphated sample to 950°C to thermally decompose the sulphates, or by lowering the partial pressure of oxygen while holding the sample at the isothermal oxidation temperature. The sulphation of the sample was found to follow the parabolic rate law, implying diffusion as the rate controlling-step. The thermal decomposition of the sulphates occurred at a near constant rate, implying zero-order kinetics.

The mechanisms of plant response to nutrient limitation and utilisation are of great interest for agricultural purposes. Phosphate is a non-renewable resource and is one of the most important nutrients required for plant growth. Recently a new family of plant protein kinases, composed of 10 members, were discovered because of their involvement in stresses and their responses to the hormone abscisic acid (ABA). In Arabidopsis, all of these SnRK2 protein kinases have been shown to be activated by drought or hyperosmostic stress, with the exception of SnRK2.9. Five members are also activated by ABA treatment. Recently SnRK2.8 was linked to metabolic processes by being down regulated in low nutrient level conditions. In the present study, SnRK2.9 was investigated and shown to play a role in metabolic pathways, but in an opposite manner. Contrarily to SnRK2.8, transcripts level of SnRK2.9 is induced in response to phosphate, nitrogen, and sulphur deprivation. Interestingly, opposite to most phosphate-starvation inducible genes, sucrose decreases SnRK2.9's transcripts level. Transgenic plants that overexpress SnRK2.9 do not appear to be affected in terms of growth. On the other hand, overexpressing antisense SnRK2.9 or mutated snrk2.9 at residue Asp-123 by conversion to Glu (D123E), showed reduced plant growth. This phenotype was more pronounced in the absence of phosphate. A T-DNA knockout line for SnRK2.9 showed a 45% decrease in root and shoot biomass compared to wild-type Arabidopsis when grown under phosphate deprivation. Similar trends were observed when the Arabidopsis gene was introduced in Medicago sativa (alfalfa) under the control of the CaMV 35S promoter. Overexpressing D123E Atsnrk2.9 had a serious inhibitory effect on growth and the plants were no longer responsive to changes in phosphate levels. In Arabidopsis, the D123E snrk2.9 overexpressors had a 66% reduction in total seed yield when grown under +Pi conditions and a 33% reduction under -Pi conditions. These Arabidopsis transgenic lines do not share similar traits to the known phosphate metabolic mutants Pho1, Pho2, and Siz1. SnRK2.9 appears to play a key role in biomass and seed production. / Thesis (Ph.D, Biology) -- Queen's University, 2007-09-26 12:35:00.626

No description available.

Abstract will not load on to DSpace