The isotopic fractionation of sulphur in the plant metabolism of sulphate by chlorella was investigated; and for this purpose an apparatus was devised for growing chlorella under sterile conditions. A green alga from the shores of Lake Erie, and mustard plants from the field were also investigated. No isotopic fractionation was found in the plant metabolism of sulphate either in the laboratory or in nature. A new method for the reduction of sulphate to hydrogen sulphide was also developed. / Thesis / Master of Science (MS)

This thesis describes an experiment in the ultraviolet absorption of hydrocarbons.

This dissertation includes two accounts of rigorous modeling of petroleum refinery modeling using rigorous reaction and fractionation units. The models consider various process phenomena and have been extensively used during a course of a six-month study to understand and predict behavior. This work also includes extensive guides to allow users to develop similar models using commercial software tools. (1) Predictive Modeling of Large-Scale Integrated Refinery Reaction and Fractionation Systems from Plant Data: Fluid Catalytic Cracking (FCC) Process with Planning Applications: This work presents the methodology to develop, validate and apply a predictive model for an integrated fluid catalytic cracking (FCC) process. We demonstrate the methodology by using data from a commercial FCC plant in the Asia Pacific with a feed capacity of 800,000 tons per year. Our model accounts for the complex cracking kinetics in the riser-regenerator and associated gas plant phenomena. We implement the methodology with Microsoft Excel spreadsheets and a commercial software tool, Aspen HYSYS/Petroleum Refining from Aspen Technology, Inc. The methodology is equally applicable to other commercial software tools. This model gives accurate predictions of key product yields and properties given feed qualities and operating conditions. This work differentiates itself from previous work in this area through the following contributions: (1) detailed models of the entire FCC plant, including the overhead gas compressor, main fractionator, primary and sponge oil absorber, primary stripper and debutanizer columns; (2) process to infer molecular composition required for the kinetic model using routinely collected bulk properties of feedstock; (3) predictions of key liquid product properties not published alongside previous related work (density, D-86 distillation curve and flash point); (4) case studies showing industrially useful applications of the model; and (5) application of the model with an existing LP-based planning tool. (2) Predictive Modeling of Large-Scale Integrated Refinery Reaction and Fractionation Systems from Plant Data: Continuous Catalyst Regeneration (CCR) Reforming Process: This work presents a model for the rating and optimization of an integrated catalytic reforming process with UOP-style continuous catalyst regeneration (CCR). We validate this model using plant data from a commercial CCR reforming process handling a feed capacity of 1.4 million tons per year in the Asia Pacific. The model relies on routinely monitored data such ASTM distillation curves, paraffin-napthene- aromatic (PNA) analysis and operating conditions. We account for dehydrogenation, dehydrocyclization, isomerization and hydrocracking reactions that typically occur with petroleum feedstock. In addition, this work accounts for the coke deposited on the catalyst and product recontacting sections. This work differentiates itself from the reported studies in the literature through the following contributions: (1) detailed kinetic model that accounts for coke generation and catalyst deactivation; (2) complete implementation of a recontactor and primary product fractionation; (3) feed lumping from limited feed information; (4) detailed procedure for kinetic model calibration; (5) industrially relevant case studies that highlight the effects of changes in key process variables; and (6) application of the model to refinery-wide production planning. / Ph. D.

The purpose of this thesis was to experimentally investigate the influence of increasing sulfide concentrations on the 34S isotope enrichment in sulfate during dissimilatory sulfate reduction (DSR). Two independent batch culture experiments with different maximum sulfide concentrations of up to 20 mM in the first and up to 40 mM in the second experiment were conducted using the marine sulfate reducer Desulfobacter latus. A comparison of the results from both experiments revealed a distinct offset towards more positive δ34S(SO42-) values in the 'high-sulfide' experiment, compared to the 'low-sulfide' experiment. While a Rayleigh type fractionation model was able to match the slopes - i.e., enrichment factors - of both experiments, it failed to reproduce the proper y-axis intercept in the 'high-sulfide' experiment. I therefore propose a new fractionation model that allows for a backward flow of ambient H2S into the bacterial cell and a subsequent enzymatically mediated oxidation of H2S to sulfate. The new backward flow increases with elevated H2S concentrations and is described as a first order rate constant. Unlike a Rayleigh type fractionation model, my model explains the slope and y-intercept of both experiments with a single parameter set. The new model with H2S-reflux further suggests that it can be used to determine growth kinetic parameters like the half-saturation constant through δ34S measurements. These findings support the hypothesis of microbially mediated, bi-directional S-fluxes between oxidized and reduced sulfur species. Because the S-transport during DSR appears to be bi-directional, great care must be taken when evaluating culture experiments with a Rayleigh type fractionation model, owing to the fact that an evident S-backward flow violates the prerequisites for applying the Rayleigh model. A variable S-backward flow results in variable enrichment factors which increased from -11 (no H2S) to ≈-17 ‰ (40 mM of H2S) in my experiments. I show for the first time the significance of a bi-directional H2S transport across the cell membrane during DSR and its consequences for the 34S-isotope fractionation in sulfate.

The purpose of this thesis was to experimentally investigate the influence of increasing sulfide concentrations on the 34S isotope enrichment in sulfate during dissimilatory sulfate reduction (DSR). Two independent batch culture experiments with different maximum sulfide concentrations of up to 20 mM in the first and up to 40 mM in the second experiment were conducted using the marine sulfate reducer Desulfobacter latus. A comparison of the results from both experiments revealed a distinct offset towards more positive δ34S(SO42-) values in the 'high-sulfide' experiment, compared to the 'low-sulfide' experiment. While a Rayleigh type fractionation model was able to match the slopes - i.e., enrichment factors - of both experiments, it failed to reproduce the proper y-axis intercept in the 'high-sulfide' experiment. I therefore propose a new fractionation model that allows for a backward flow of ambient H2S into the bacterial cell and a subsequent enzymatically mediated oxidation of H2S to sulfate. The new backward flow increases with elevated H2S concentrations and is described as a first order rate constant. Unlike a Rayleigh type fractionation model, my model explains the slope and y-intercept of both experiments with a single parameter set. The new model with H2S-reflux further suggests that it can be used to determine growth kinetic parameters like the half-saturation constant through δ34S measurements. These findings support the hypothesis of microbially mediated, bi-directional S-fluxes between oxidized and reduced sulfur species. Because the S-transport during DSR appears to be bi-directional, great care must be taken when evaluating culture experiments with a Rayleigh type fractionation model, owing to the fact that an evident S-backward flow violates the prerequisites for applying the Rayleigh model. A variable S-backward flow results in variable enrichment factors which increased from -11 (no H2S) to ≈-17 ‰ (40 mM of H2S) in my experiments. I show for the first time the significance of a bi-directional H2S transport across the cell membrane during DSR and its consequences for the 34S-isotope fractionation in sulfate.

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2009 / Polypropylene is an extremely versatile material and has a broad spectrum of applications due to the variations in properties which are possible with this material. The variations in the properties of the material are governed by the microstructure of the chains constituting the polymer. The microstructure varies according to the production methods, i.e. the polymerisation conditions. Varying the manner in which the polymer is produced therefore changes the properties of the material allowing the polymers’ use for different applications. The most important factor affecting the way in which the polymers are produced is the nature of the active sites on the catalyst. Changing the chemical environment of the active sites changes the way in which the polymerisation is controlled and greatly affects the types of chains produced and thus polymer properties. The study examines the structure-property relationships of polyolefins with specific focus on the polypropylene homopolymer. The temperature rising elution fractionation (TREF) technique is used extensively in order to isolate specific fractions of the polymer. The importance of specific TREF fractions is investigated via a two pronged investigative methodology. On the one hand specific TREF fractions are removed from a sample, allowing the analysis of the properties of the material without that specific fraction, thereby revealing the influence which the fraction in question has on the properties. The other branch of the study investigates the chemical modification of the active sites of a Ziegler-Natta catalyst so as to be able to modify the properties of the polymer in the reactor, in a similar manner to physically removing fractions. The techniques are related and it was discovered that the amount of the fractions of the polymer, found to be important using the one technique, also turned out to be important using the other method. Initial method development work utilised a polypropylene-1-pentene copolymer since the molecular heterogeneity of this material is such that large differences are observed upon removal of fractions. The technique was then applied to a Ziegler-Natta catalysed polypropylene homopolymer. Each TREF fraction is successively removed and the residual material analysed. Specific TREF fractions were found to play a significant role in determining the polymer properties since there was a drastic reduction in properties upon removal of these fractions. The polymerisation of propylene was also performed at a variety of conditions in order to investigate different ways in which the catalyst system could be modified. Specific reaction conditions were chosen for in-depth analysis and structure-property correlation. The chemical modification of the active sites was accomplished via the introduction of an external Lewis base (electron donor) to the polymerisation system, and also by varying the external donor/catalyst ratio used. Two different external donors were used during the study namely Diphenyl-dimethoxysilane (DPDMS) and methyl-phenyl-dimethoxysilane (MPDMS). It is observed that there are definite links between the amounts of specific fractions present in the polymer and the polymer properties, as observed via both the physical removal of fractions and the chemical modification of active sites.

Background In the treatment of head and neck cancers (HNCs), radiotherapy (RT) has the advantage of organ preservation compared to surgery. However, treatment toxicities associated with RT can affect important functions for everyday life, both in the acute and late stage. RT to macroscopic tumour in HNC is commonly combined with elective RT to cervical lymph nodes at risk of microscopic involvement. The resulting risk reduction of the elective treatment based on dose-volume parameters is sparsely evaluated. So is the relationship between the elective treatment and treatment toxicity. The present thesis addresses these aspects. A strategy aimed at improving the outcome of RT is accelerated fractionation (AF). AF strives to shorten total treatment time to minimise proliferation of the tumour tissue during the RT period. We have investigated the impact of AF on both disease control and toxicity. Methods In the ARTSCAN study, 750 patients with localised HNC were randomised between AF (68 Gy in 4.5 weeks) and conventional fractionation (CF) (68 Gy in 7 weeks). The elective treatment volume was prescribed 46 Gy with CF in both treatment arms. The thesis is based on four individual papers, investigating the issues above in the whole study population or in sub-populations. Results No difference in disease control or late toxicity between CF and AF was observed at five years. However, there was an increased acute toxicity with AF. Weight loss was associated with treatment volume, independent of tumour stage. The elective treatment volume was found to be an independent risk factor for late aspiration, as well as mean dose to the pharyngeal constrictor muscles, neck dissection, and age at randomisation. There was a significant risk reduction for node relapses in volumes treated to an elective dose. Only a relapse in volumes treated to >60 Gy affected the survival. Conclusion The present thesis questions the benefit of AF in definitive RT as well as extensive elective treatment of the cervical nodes.

Application of phosphorus fertilizer can lead to changes in soil test P and increase both labile and non-labile phosphorus pools. Sequential fractionation showed that the labile (H2O-P and NaHCO3-P) fractions significantly (P < 0.05) increased with the addition of phosphorus fertilizer across all sites. Significant increase was observed in the non-labile (NaOH-P, HCl-P and Residual-P) fractions during the accumulation phase. During the depletion phase, when no further P was added, the accumulated P in the labile P fractions declined but not to the original level. The rates of P application, soil properties, soil test P methods used and time effect all had significant effects on soil test P changes in the extraction experiment. Mehlich-3 extracted the greatest amount of P from the two depths and Olsen-P was intermediate while the smallest amount was extracted with water. The pattern of the rate of change in extractable P with P addition for the 0 – 7.5 cm depth was not site dependent as the results obtained at the different sites were similar. / October 2016

: In freshwater systems phosphorus (P) is the limiting element in the cause of eutrophication. In many Swedish lakes, causes of eutrophication have been attributed to more of internal loading than external since the external loading has been fairly well managed. Internal loading is linked to the mobility of sediment P, which are known to be Bioavailable P (BAP). Sediments from Lake Hällerstadsjön in Sweden was studied to know the BAP concentration and its possible release into the water column under reduced conditions. Sediments were sampled at two different depths, 0-5 cm and 5-10cm. BAP was determined by a phosphorus fractionation scheme. Sediments were incubated under oxic and anoxic conditions in the laboratory to evaluate sediment P release. Spatial variation in the distribution of P forms across the lake was also studied, in order to examine possible local patterns, particularly along a transect from the main inlet to the outlet. Fractionation analyses showed a trend of; Residual-P &gt; NaOH-P &gt; HCl-P &gt; BD-P &gt; Loosely bound P. The fractions constituting the BAP was higher at the 0-5 cm sediment depth than 5-10 cm. Sediment P flux was recorded for anoxic but not oxic sediment. BAP correlated significantly with sediment P flux (P= 0.01). Spatially, the P distribution varied both at depths and along a latitudinal transect, from the main inlet to the outlet.  Dredging of the surface sediments with high BAP content would possibly be an effective means of preventing eutrophication of the lake.

Student Number : 9201769X - M Med research report - School of Clinical Medicine - Faculty of Health Sciences / A PROSPECTIVE RANDOMIZED TRIAL OF TWO FRACTIONATION REGIMENS OF RADIATION THERAPY IN THE MANAGEMENT OF AIDSASSOCIATED KAPOSI SARCOMA OBJECTIVE: To compare a standard fractionation scheme with a hypofractionated scheme in the treatment of AIDS-associated Kaposi sarcoma with the aim of showing noninferiority of the shorter schedule. PATIENTS AND METHODS: HIV positive patients with histologically proven Kaposi sarcoma presenting consecutively to Radiation Oncology at Johannesburg Hospital were randomized between January 2003 and May 2004 to receive a standard regimen of 24 Gy in 12 fractions (ARM A) or the study regimen of 20 Gy in 5 fractions (ARM B). The radiation technique used was individualized for each site in accordance with departmental practice. Follow-up assessment was done at monthly intervals. Treatment response and toxicity were recorded at each follow-up visit. RESULTS: A total of 60 patients were recruited, of which 41 were male and 19 were female. The median age was 36 years (range: 23 – 55 years). Thirteen patients died prior to receiving treatment. The remaining 47 patients were treated to 65 sites, of which 35 sites received 24 Gy in 12 fractions (ARM A) and 30 sites received 20 Gy in 5 fractions (ARM B). The main indications for treatment were pain (n=71), oedema (n=44), functional impairment (n=35), cosmesis (n=14) and bleeding (n=4). At the time of reporting 28 patients were alive and 32 patients have died. The overall survival of the whole group was 37% at 1 year. A complete response was recorded at 28 sites, a partial response at 19 sites and stable disease at 3 sites. The mean time to maximum objective response was 3 months (range: 1 – 14 months). The response rates were equal in the 2 treatment arms (p=0.73). Local control was equal in the 2 treatment arms with a median local recurrence free survival of 150 days for ARM A and 455 days for ARM B (p=0.11, log rank test). Acute skin toxicity occurred at 27 sites. Moist desquamation developed at 7 sites while necrosis developed at 2 sites. Acute skin toxicity was equal in the 2 treatment arms (p=0.77). Acute mucosal toxicity occurred at 2 sites. Late skin reactions developed at 21 sites, of which necrosis or ulceration occurred at 5 sites. Chronic skin reactions were equivalent in the 2 treatment arms (p=0.24). Post radiation oedema developed at 5 sites. CONCLUSION: In our experience, 20 Gy in 5 fractions gave similar results to 24 Gy in 12 fractions in terms of treatment response, local recurrence free survival and toxicity in this small group of patients.