The separation of platinum and gold from an industrial feed solution
- Authors: Louw, Talana
- Date: 2008
- Subjects: Platinum -- Separation , Gold , Separation -- Technology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10400 , http://hdl.handle.net/10948/731 , Platinum -- Separation , Gold , Separation -- Technology
- Description: In this thesis, the aim was to develop resins which are platinum and gold specific to be utilized for the early removal of these metals from the industrial feed. Efforts were therefore directed towards the synthesis of silica based resins with active centra which were designed for platinum and gold specificity respectively. The large chlorometallate ions in the feed stream were characterized in terms of physical parameters relevant to phase distribution namely distortability (RD), charge density, softness (σ) etc. Matching cations for each of the types were investigated. In order to attempt the design of platinum specific resins different structural amines were used to aminate the silicone precursor and subsequently to fix these onto the silica framework. Two different solvents i.e. alcohol and dmf were used for this process, resulting in two sets of resins with different properties. For gold specific resins, various polyethers were attached to a different type of silicone precursor, which was attached to the silica framework. The design was based on previous experience with these ions with reference to their behaviour towards different types of cations. The platinum species PtCl6 2- and PtCl4 2-, the gold species AuCl4 -, as well as the most important contaminants in the feed stream were typified bearing in mind size, charge, charge density and distortability. Different types of cationic centra having differences in charge density, stereochemical crowding and extent of hydrophobicity were synthesized and tested both as solvent extractants (where possible) and silica based resins. The results indicated that partly screened secondary ammonium cationic resin species, which could be regarded as “intermediate”, proved to be satisfactory both in their high percentage extraction for PtCl4 2- and rejection of contaminants like chlororhodates, chloroiridates(III) and FeCl4 -. It was, however, necessary to work at a redox potential where iridium(IV) in the form of IrCl6 2- is absent. Various 2-aminoalkane resins were prepared with variation in the length of alkane group and synthesized in the two different solvents. The latter resulted in two sets of resins with different compactness also having significantly different properties with reference to platinum specificity, HCl effect and stripping potential. The 2- aminobutane and 2-aminoheptane resins both proved to be very satisfactory platinum specific resins with respect to selectivity, platinum capacity and stripping potential. The various physical parameters could be utilized to accommodate the chemical behaviour. To obtain gold specific resins, experiments were performed with resins having oxygen-donor atoms which can readily be protonated to form onium type cations for example amides and ether oxygen atoms. In the case of the latter, various polyethers with a different number of ether groups (polyether groups linked by ethylene and propylene groups) and variations of hydrophobicity (by substitution) have also been studied. Linked to the polyether groups were alkane and aryl groups. Those having 8 to 10 ether groups and aromatic tail ends proved to be moderately successful in terms of gold capacity and sharp breakthrough curves of their columns, however, platinum could not be very effectively rejected.
- Full Text:
- Date Issued: 2008
- Authors: Louw, Talana
- Date: 2008
- Subjects: Platinum -- Separation , Gold , Separation -- Technology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10400 , http://hdl.handle.net/10948/731 , Platinum -- Separation , Gold , Separation -- Technology
- Description: In this thesis, the aim was to develop resins which are platinum and gold specific to be utilized for the early removal of these metals from the industrial feed. Efforts were therefore directed towards the synthesis of silica based resins with active centra which were designed for platinum and gold specificity respectively. The large chlorometallate ions in the feed stream were characterized in terms of physical parameters relevant to phase distribution namely distortability (RD), charge density, softness (σ) etc. Matching cations for each of the types were investigated. In order to attempt the design of platinum specific resins different structural amines were used to aminate the silicone precursor and subsequently to fix these onto the silica framework. Two different solvents i.e. alcohol and dmf were used for this process, resulting in two sets of resins with different properties. For gold specific resins, various polyethers were attached to a different type of silicone precursor, which was attached to the silica framework. The design was based on previous experience with these ions with reference to their behaviour towards different types of cations. The platinum species PtCl6 2- and PtCl4 2-, the gold species AuCl4 -, as well as the most important contaminants in the feed stream were typified bearing in mind size, charge, charge density and distortability. Different types of cationic centra having differences in charge density, stereochemical crowding and extent of hydrophobicity were synthesized and tested both as solvent extractants (where possible) and silica based resins. The results indicated that partly screened secondary ammonium cationic resin species, which could be regarded as “intermediate”, proved to be satisfactory both in their high percentage extraction for PtCl4 2- and rejection of contaminants like chlororhodates, chloroiridates(III) and FeCl4 -. It was, however, necessary to work at a redox potential where iridium(IV) in the form of IrCl6 2- is absent. Various 2-aminoalkane resins were prepared with variation in the length of alkane group and synthesized in the two different solvents. The latter resulted in two sets of resins with different compactness also having significantly different properties with reference to platinum specificity, HCl effect and stripping potential. The 2- aminobutane and 2-aminoheptane resins both proved to be very satisfactory platinum specific resins with respect to selectivity, platinum capacity and stripping potential. The various physical parameters could be utilized to accommodate the chemical behaviour. To obtain gold specific resins, experiments were performed with resins having oxygen-donor atoms which can readily be protonated to form onium type cations for example amides and ether oxygen atoms. In the case of the latter, various polyethers with a different number of ether groups (polyether groups linked by ethylene and propylene groups) and variations of hydrophobicity (by substitution) have also been studied. Linked to the polyether groups were alkane and aryl groups. Those having 8 to 10 ether groups and aromatic tail ends proved to be moderately successful in terms of gold capacity and sharp breakthrough curves of their columns, however, platinum could not be very effectively rejected.
- Full Text:
- Date Issued: 2008
The influence of site characteristics on growth and wood properties of Pinus radiata and Pinus elliottii in the Southern and Eastern Cape forestry regions of South Africa
- Authors: Sigcau, Chulumanco
- Date: 2023-04
- Subjects: Forests and forestry -- Environmental aspects , Pine – Growth -- South Africa , Pinus radiata
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61234 , vital:69828
- Description: The intensive nature of plantation forestry in South Africa requires efficiency and financial viability in production systems, amidst a complex growing environment subjected to changing macro-climatic patterns. The success of plantation forestry operations depends, amongst others, on our understanding of tree growth and wood formation patterns in response to variable growing conditions in both space and time. This study was conducted on the two most commonly used species in the southern and Eastern Cape forestry regions, i.e., Pinus radiata and P. elliottii. The region is regarded as highly suitable for plantation forestry in terms of climatic conditions, but soil characteristics pose several challenges due to nutritional disorders and poor drainage. The study focused on investigating the influence of both soil and climatic conditions on the growth and Wood Density properties of the two species, and to establish functional relationships where possible. The two species showed comparable growth rates at the reference age of 13 years on the range of sites sampled in the study area. An analysis of variance showed greater differences in Site Index between than within sample plots, pointing towards the possible influence of site on growth variation. Correlations between climatic variables and the growth of both species were generally weak and contradictory. Possible reasons for this phenomenon are discussed. It is proposed that the general favourable climatic profile of the region and hydromorphic nature of soils reduce the chances of significant correlations between variables influencing moisture availability and tree growth. The analysis of correlations between soil parameters and tree growth revealed some influence of soil organic C and Na on the growth of P. elliottii. This is discussed in terms of our understanding of the influence of soil parent material and soil ecology. The absence of any correlations between soil chemical parameters and the growth of P. radiata was conspicuous. This is in contradiction with earlier studies on the species in the region and can possibly be explained in terms of the site-specific fertilizing policy of the industry, as well as the less diverse range of sites sampled than in the past, which can mask or reduce nutrient limitations for tree growth. However, P. radiata did show a high level of sensitivity towards effective soil depth. Site-quality prediction models are proposed for the two species, but with variable application value due to the limited options of significant control variables that can be considered for inclusion in the models. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Science and Management, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Sigcau, Chulumanco
- Date: 2023-04
- Subjects: Forests and forestry -- Environmental aspects , Pine – Growth -- South Africa , Pinus radiata
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61234 , vital:69828
- Description: The intensive nature of plantation forestry in South Africa requires efficiency and financial viability in production systems, amidst a complex growing environment subjected to changing macro-climatic patterns. The success of plantation forestry operations depends, amongst others, on our understanding of tree growth and wood formation patterns in response to variable growing conditions in both space and time. This study was conducted on the two most commonly used species in the southern and Eastern Cape forestry regions, i.e., Pinus radiata and P. elliottii. The region is regarded as highly suitable for plantation forestry in terms of climatic conditions, but soil characteristics pose several challenges due to nutritional disorders and poor drainage. The study focused on investigating the influence of both soil and climatic conditions on the growth and Wood Density properties of the two species, and to establish functional relationships where possible. The two species showed comparable growth rates at the reference age of 13 years on the range of sites sampled in the study area. An analysis of variance showed greater differences in Site Index between than within sample plots, pointing towards the possible influence of site on growth variation. Correlations between climatic variables and the growth of both species were generally weak and contradictory. Possible reasons for this phenomenon are discussed. It is proposed that the general favourable climatic profile of the region and hydromorphic nature of soils reduce the chances of significant correlations between variables influencing moisture availability and tree growth. The analysis of correlations between soil parameters and tree growth revealed some influence of soil organic C and Na on the growth of P. elliottii. This is discussed in terms of our understanding of the influence of soil parent material and soil ecology. The absence of any correlations between soil chemical parameters and the growth of P. radiata was conspicuous. This is in contradiction with earlier studies on the species in the region and can possibly be explained in terms of the site-specific fertilizing policy of the industry, as well as the less diverse range of sites sampled than in the past, which can mask or reduce nutrient limitations for tree growth. However, P. radiata did show a high level of sensitivity towards effective soil depth. Site-quality prediction models are proposed for the two species, but with variable application value due to the limited options of significant control variables that can be considered for inclusion in the models. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Science and Management, 2023
- Full Text:
- Date Issued: 2023-04
Optimizing herbicide-use for the killing of eucalypt stumps
- Authors: Mavhungu, Tshilidzi
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53857 , vital:46023
- Description: The South Africa (SA) forest industry relies on plantations of exotic forestry trees (Pinus, Acacia and Eucalyptus) to fulfil its timber requirements. With 52.0% of the afforested land in South Africa planted to various eucalypts and their hybrid combinations. Of the total area planted to eucalypts in SA, 75 000 ha is re-established annually by means of silvicultural regimes and operations matched to site productivity, desired end-product and method of regeneration. Unlike other commercially grown tree species, eucalypt species have the ability to coppice after felling. Coppicing is a common form of regeneration in South African forestry as it allows the plantation owner the option of a second timber rotation without replanting. However, if any factors affecting coppicing are compromised, and the site is to be replanted, then it is important to kill the stumps before replanting as rapid initial growth of the coppice shoots will require earlier control than that associated with normal weeding operations. Over time, various methods of woody plant control have been proposed and tested, with most of these making use of herbicides as opposed to the repeated manual removal of coppice regrowth. Globally, most industries subscribe to standards associated with sustainable production (economic, environmental and social) against which they are measured. Within SA, 80% of the forests are certified though either the Forest Stewardship Council (FSC) or International Standards Organisation (ISO) which recommend the identification and avoidance of ‘highly hazardous’ chemicals; the promotion of ‘non-chemical’ methods for pest management as an element of an integrated pest and vegetation management strategy; and the appropriate use of chemicals that are used. To test the current recommendations for killing eucalypt stumps to include other species, the potential of reducing herbicides used, and the influence of time after application on the survival of eucalypt stumps, two trials were initiated at Entabeni plantation (Venda, Limpopo) and one at Wilgeboom plantation (Bushbuckridge, Mpumalanga) between 2018 and 2020. Extending eucalypt cut-stump control practices: Most of the trial work on killing of eucalypts in SA has been conducted on Eucalyptus grandis, Eucalyptus camaldulensis or Eucalyptus macarthurii, with all grown on shorter pulpwood rotations. To extend current recommendation to include Eucalyptus cloeziana (grown on a longer rotation for poles), a trial was established in 2018 at Entabeni plantation (Limpopo Province) to quantify the interaction between Application method (basal-frill; cut-surface; foliar) and Herbicide (no herbicide applied; Roundup; Garlon; Roundup + Garlon) for the killing of 12 year-old stumps following harvesting. Assessments were carried out at 1, 3 and 6 months following application and included Stump survival, Stump quarter with coppice and Coppice heath. Relative to the control plots (100% survival), all herbicides tested were equally effective, 70–90% of the stumps killed. This study confirms previous research regarding the killing of eucalypt stumps. Roundup, Garlon or a combination of two, when applied according to label recommendations to a stump as a basal-frill or cut-surface application (within 30 minutes of felling) resulted in 70-90% of the stumps killed. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Mavhungu, Tshilidzi
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/53857 , vital:46023
- Description: The South Africa (SA) forest industry relies on plantations of exotic forestry trees (Pinus, Acacia and Eucalyptus) to fulfil its timber requirements. With 52.0% of the afforested land in South Africa planted to various eucalypts and their hybrid combinations. Of the total area planted to eucalypts in SA, 75 000 ha is re-established annually by means of silvicultural regimes and operations matched to site productivity, desired end-product and method of regeneration. Unlike other commercially grown tree species, eucalypt species have the ability to coppice after felling. Coppicing is a common form of regeneration in South African forestry as it allows the plantation owner the option of a second timber rotation without replanting. However, if any factors affecting coppicing are compromised, and the site is to be replanted, then it is important to kill the stumps before replanting as rapid initial growth of the coppice shoots will require earlier control than that associated with normal weeding operations. Over time, various methods of woody plant control have been proposed and tested, with most of these making use of herbicides as opposed to the repeated manual removal of coppice regrowth. Globally, most industries subscribe to standards associated with sustainable production (economic, environmental and social) against which they are measured. Within SA, 80% of the forests are certified though either the Forest Stewardship Council (FSC) or International Standards Organisation (ISO) which recommend the identification and avoidance of ‘highly hazardous’ chemicals; the promotion of ‘non-chemical’ methods for pest management as an element of an integrated pest and vegetation management strategy; and the appropriate use of chemicals that are used. To test the current recommendations for killing eucalypt stumps to include other species, the potential of reducing herbicides used, and the influence of time after application on the survival of eucalypt stumps, two trials were initiated at Entabeni plantation (Venda, Limpopo) and one at Wilgeboom plantation (Bushbuckridge, Mpumalanga) between 2018 and 2020. Extending eucalypt cut-stump control practices: Most of the trial work on killing of eucalypts in SA has been conducted on Eucalyptus grandis, Eucalyptus camaldulensis or Eucalyptus macarthurii, with all grown on shorter pulpwood rotations. To extend current recommendation to include Eucalyptus cloeziana (grown on a longer rotation for poles), a trial was established in 2018 at Entabeni plantation (Limpopo Province) to quantify the interaction between Application method (basal-frill; cut-surface; foliar) and Herbicide (no herbicide applied; Roundup; Garlon; Roundup + Garlon) for the killing of 12 year-old stumps following harvesting. Assessments were carried out at 1, 3 and 6 months following application and included Stump survival, Stump quarter with coppice and Coppice heath. Relative to the control plots (100% survival), all herbicides tested were equally effective, 70–90% of the stumps killed. This study confirms previous research regarding the killing of eucalypt stumps. Roundup, Garlon or a combination of two, when applied according to label recommendations to a stump as a basal-frill or cut-surface application (within 30 minutes of felling) resulted in 70-90% of the stumps killed. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2021
- Full Text:
- Date Issued: 2021-12
Design of metal ion-selective reagents for recovery of precious metals
- Authors: Moleko-Boyce, Pulleng
- Date: 2019
- Subjects: Bioinorganic chemistry , Metal complexes Speciation (Chemistry)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/42510 , vital:36664
- Description: The study is divided into two sections; namely, (1) the design of rhodium(III) specific chelating ligands (tridentate bis-benzimidazole derivatives), and (2) the development of iridium(IV)-specific quaternary diammonium cations with electron donating and electron withdrawing groups. Bis-benzimidazole chelating ligands used were bis((1H-benzimidazol-2-yl)methyl)amine (NNN1), bis((1H-benzimidazol-2-yl)ethyl)amine (NNN2), bis((1H-benzimidazol-2-yl)methyl)sulfide (NSN1) and bis((1H-benzimidazol-2-yl)ethyl)sulfide (NSN2). Quaternary diammonium cations used were tetramethylbenzyl-1,10-diammonium chloride (QuatDMDAMeBnz), tetrabenzyl-1,10-diammonium chloride (QuatDMDABnz), tetratrifluoromethylbenzyl-1,10-diammonium chloride (QuatDMDACF3Bnz) and tetranitrobenzyl-1,10-diammonium chloride (QuatDMDANO2Bnz). For both studies, polyvinylbenzylchloride (PVBC) nanofibers were used as support material. The PVBC nanofibers which were functionalised with bis-benzimidazole derivatives and quaternary diammonium cations, respectively, were investigated for the selectivity for Rh(III) over Ir(III), Pt(II), Pd(II) and Ni(II), and for separation of Ir(IV) from Rh(III), respectively. The sorbent materials were characterised by FTIR, SEM, BET surface area, TGA, EDS and elemental analysis, and the results showed that the functionalization of the sorbent materials was successful.The efficiency of bis-benzimidazole derivatives and quaternary diammonium cations, respectively, were investigated in a column study under dynamic flow adsorption conditions. The adsorption kinetics and isotherms were investigated under batch conditions and fitted on pseudo-first-order and pseudo-second-order model, and Freundlich and Langmuir isotherm, respectively. It was observed that the bis-benzimidazole derivatives showed uptake of [RhCl3(H2O)3], and the loading capacities were observed in the following order; NSN1 (181.06 mg/g) > NSN2 (148.55 mg/g) > NNN1 (131.88 mg/g) > NNN2 (75.87 mg/g). The bis-benzimidazole derivatives preference for metal ions was further investigated with a multi-element solution containing Rh(III), Ir(III), Pt(II), Pd(II) and Ni(II). The bis-benzimidazole derivatives showed the following order of loading capacity: NSN1 (47.28 mg/g) > NSN2 (23.89 mg/g) > NNN1 (17.47 mg/g) > NNN2 (14.91 mg/g) for Rh(III); NSN2 (10.64 mg/g) > NNN2 (6.84 mg/g) > NSN1 (5.74 mg/g) > NNN1 (5.02 mg/g) for Ir(III); NNN2 (33.96 mg/g) > NSN1 (30.95 mg/g) > NSN2 (19.95 mg/g) > NNN1 (14.92 mg/g) for Pt(II); NNN1 (47.94 mg/g) > NNN2 (28.90 mg/g) > NSN1 (16.22 mg/g) > NSN2 (15.83 mg/g) for Pd(II). Bis-benzimidazole derivatives showed no uptake of nickel(II) under these conditions. It was observed the ligand-selectivity order for Rh(III) was similar in both single-element and multi-element studies. This order showed that the bis-benzimidazoles containing a sulfur atom showed a high preference for rhodium(III) compared to Pt(II) which had a high preference for NNN2 as well as Pd(II) which had a high preference for NNN1. Ir(III) generally had a lower preference for the ligands presumably due to its higher kinetic inertness compared with Rh(III). Column sorption of [IrCl6]2- and [RhCl5(H2O)]2- on nanofibers functionalized with diammonium cations was carried out and the loading capacities of [IrCl6]2- were obtained. [RhCl5(H2O)]2- was not adsorbed by the sorbent materials while [IrCl6]2- was loaded onto the column. The loading capacities of [IrCl6]2- with the quaternary diammonium sorbent materials increased in the order of F-QuatDMDAMeBnz (60.29 mg/g) < F-QuatDMDABnz (67.61 mg/g) < F-QuatDMDACF3Bnz (107.59 mg/g) < F-QuatDMDANO2Bnz (140.47 mg/g). The loading capacity for Ir(IV) with quaternary diammonium cationic nanofibers increased with an increase in the electron-withdrawing nature of the quaternizing group. The charge delocalizing ability of the nitrobenzyl group resulted in the best interaction of the diammonium cation with [IrCl6]2-. Batch equilibrium studies were carried out to assess the efficiency of bis-benzimidazole chelating derivatives as adsorbents using a multi-metal solution (Rh(III), Ir(III), Pt(II), Pd(II) and Ni(II)) in 0.5 M HCl. The efficiency of the quaternary diammonium cations was tested using a binary metal solution (Ir(IV) and Rh(III)) in 6 M HCl. The isothermal batch adsorption studies of a multi-metal solution with bis-benzimidazoles derivatives fitted the Langmuir isotherm model which confirmed monolayer adsorption onto a homogeneous surface. The Langmuir isotherm parameter (qe (mg/g)), using functionalized nanofibers, showed the order of NNN2 (128.21 mg/g) > NSN1 (99.01 mg/g) > NSN2 (91.74 mg/g) > NNN1 (84.03 mg/g) for Pt(II); NNN1 (66.23 mg/g) > NNN2 (5.89 mg/g) > NSN1 (1.40 mg/g) > NSN2 (0.59 mg/g) for Pd(II); NSN2 (10.64 mg/g) > NNN2 (6.84 mg/g) > NSN1 (5.74 mg/g) > NNN1 (5.02 mg/g) for Ir(III); NSN1 (140.85 mg/g) > NSN2 (109.89 mg/g) > NNN1 (104.17 mg/g) > NNN2 (91.74 mg/g) for Rh(III). The pseudo-first-order kinetics model was found to be the best fit to describe the adsorption kinetics of all metal ions onto all the sorbent materials. K1 (min-1) value in pseudo-first-order kinetics showed the same order of adsorption as observed in the Langmuir isotherms. The isothermal batch adsorption studies of [IrCl6]2- and [RhCl5(H2O)]2- with quaternary diammonium cations fitted the Freundlich isotherm model and confirmed to be effective for multiple-layered adsorption onto a heterogeneous surface. The Freundlich isotherm parameter (kf (mg/g)) using functionalized quaternary diammonium cationic nanofibers increased in the order of F-QuatDMDANO2Bnz (794.33 mg/g) > F-QuatDMDACF3Bnz (185.35 mg/g) > F-QuatDMDABnz (156.32 mg/g) > F-QuatDMDAMeBnz (112.46 mg/g) for Ir(IV) uptake. F-QuatDMDANO2Bnz resin showed the highest adsorption than that of F-QuatDMDAMeBnz, F-QuatDMDABnz and F-QuatDMDACF3Bnz and this order is similar to what was observed in column studies. The quaternary diammonium cations were shown to have the highest adsorption capacity for Ir(IV) compared with Rh(III). The adsorption of Rh(III) was also observed to increase in the order of F-QuatDMDANO2Bnz (177.83 mg/g) > F-QuatDMDACF3Bnz (40.37 mg/g) > F-QuatDMDABnz (36.98 mg/g) > F-QuatDMDAMeBnz (12.71 mg/g). The pseudo-second-order kinetic model was found to be the best fit to describe the adsorption kinetics of both metal ions onto all the sorbent materials. K2 (g.mg-1min-1) value in pseudo-second-order kinetics showed the same order of adsorption as observed in the Freundlich isotherms. The adsorption studies showed adsorption takes place via chemisorption process. This thesis presents PGMs and iridium-specific materials that could be applied in solutions of secondary PGMs sources containing rhodium, platinum and palladium with bis-benzimidazoles as well as in feed solutions from ore processing with diammonium cations for iridium recovery.
- Full Text:
- Date Issued: 2019
- Authors: Moleko-Boyce, Pulleng
- Date: 2019
- Subjects: Bioinorganic chemistry , Metal complexes Speciation (Chemistry)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/42510 , vital:36664
- Description: The study is divided into two sections; namely, (1) the design of rhodium(III) specific chelating ligands (tridentate bis-benzimidazole derivatives), and (2) the development of iridium(IV)-specific quaternary diammonium cations with electron donating and electron withdrawing groups. Bis-benzimidazole chelating ligands used were bis((1H-benzimidazol-2-yl)methyl)amine (NNN1), bis((1H-benzimidazol-2-yl)ethyl)amine (NNN2), bis((1H-benzimidazol-2-yl)methyl)sulfide (NSN1) and bis((1H-benzimidazol-2-yl)ethyl)sulfide (NSN2). Quaternary diammonium cations used were tetramethylbenzyl-1,10-diammonium chloride (QuatDMDAMeBnz), tetrabenzyl-1,10-diammonium chloride (QuatDMDABnz), tetratrifluoromethylbenzyl-1,10-diammonium chloride (QuatDMDACF3Bnz) and tetranitrobenzyl-1,10-diammonium chloride (QuatDMDANO2Bnz). For both studies, polyvinylbenzylchloride (PVBC) nanofibers were used as support material. The PVBC nanofibers which were functionalised with bis-benzimidazole derivatives and quaternary diammonium cations, respectively, were investigated for the selectivity for Rh(III) over Ir(III), Pt(II), Pd(II) and Ni(II), and for separation of Ir(IV) from Rh(III), respectively. The sorbent materials were characterised by FTIR, SEM, BET surface area, TGA, EDS and elemental analysis, and the results showed that the functionalization of the sorbent materials was successful.The efficiency of bis-benzimidazole derivatives and quaternary diammonium cations, respectively, were investigated in a column study under dynamic flow adsorption conditions. The adsorption kinetics and isotherms were investigated under batch conditions and fitted on pseudo-first-order and pseudo-second-order model, and Freundlich and Langmuir isotherm, respectively. It was observed that the bis-benzimidazole derivatives showed uptake of [RhCl3(H2O)3], and the loading capacities were observed in the following order; NSN1 (181.06 mg/g) > NSN2 (148.55 mg/g) > NNN1 (131.88 mg/g) > NNN2 (75.87 mg/g). The bis-benzimidazole derivatives preference for metal ions was further investigated with a multi-element solution containing Rh(III), Ir(III), Pt(II), Pd(II) and Ni(II). The bis-benzimidazole derivatives showed the following order of loading capacity: NSN1 (47.28 mg/g) > NSN2 (23.89 mg/g) > NNN1 (17.47 mg/g) > NNN2 (14.91 mg/g) for Rh(III); NSN2 (10.64 mg/g) > NNN2 (6.84 mg/g) > NSN1 (5.74 mg/g) > NNN1 (5.02 mg/g) for Ir(III); NNN2 (33.96 mg/g) > NSN1 (30.95 mg/g) > NSN2 (19.95 mg/g) > NNN1 (14.92 mg/g) for Pt(II); NNN1 (47.94 mg/g) > NNN2 (28.90 mg/g) > NSN1 (16.22 mg/g) > NSN2 (15.83 mg/g) for Pd(II). Bis-benzimidazole derivatives showed no uptake of nickel(II) under these conditions. It was observed the ligand-selectivity order for Rh(III) was similar in both single-element and multi-element studies. This order showed that the bis-benzimidazoles containing a sulfur atom showed a high preference for rhodium(III) compared to Pt(II) which had a high preference for NNN2 as well as Pd(II) which had a high preference for NNN1. Ir(III) generally had a lower preference for the ligands presumably due to its higher kinetic inertness compared with Rh(III). Column sorption of [IrCl6]2- and [RhCl5(H2O)]2- on nanofibers functionalized with diammonium cations was carried out and the loading capacities of [IrCl6]2- were obtained. [RhCl5(H2O)]2- was not adsorbed by the sorbent materials while [IrCl6]2- was loaded onto the column. The loading capacities of [IrCl6]2- with the quaternary diammonium sorbent materials increased in the order of F-QuatDMDAMeBnz (60.29 mg/g) < F-QuatDMDABnz (67.61 mg/g) < F-QuatDMDACF3Bnz (107.59 mg/g) < F-QuatDMDANO2Bnz (140.47 mg/g). The loading capacity for Ir(IV) with quaternary diammonium cationic nanofibers increased with an increase in the electron-withdrawing nature of the quaternizing group. The charge delocalizing ability of the nitrobenzyl group resulted in the best interaction of the diammonium cation with [IrCl6]2-. Batch equilibrium studies were carried out to assess the efficiency of bis-benzimidazole chelating derivatives as adsorbents using a multi-metal solution (Rh(III), Ir(III), Pt(II), Pd(II) and Ni(II)) in 0.5 M HCl. The efficiency of the quaternary diammonium cations was tested using a binary metal solution (Ir(IV) and Rh(III)) in 6 M HCl. The isothermal batch adsorption studies of a multi-metal solution with bis-benzimidazoles derivatives fitted the Langmuir isotherm model which confirmed monolayer adsorption onto a homogeneous surface. The Langmuir isotherm parameter (qe (mg/g)), using functionalized nanofibers, showed the order of NNN2 (128.21 mg/g) > NSN1 (99.01 mg/g) > NSN2 (91.74 mg/g) > NNN1 (84.03 mg/g) for Pt(II); NNN1 (66.23 mg/g) > NNN2 (5.89 mg/g) > NSN1 (1.40 mg/g) > NSN2 (0.59 mg/g) for Pd(II); NSN2 (10.64 mg/g) > NNN2 (6.84 mg/g) > NSN1 (5.74 mg/g) > NNN1 (5.02 mg/g) for Ir(III); NSN1 (140.85 mg/g) > NSN2 (109.89 mg/g) > NNN1 (104.17 mg/g) > NNN2 (91.74 mg/g) for Rh(III). The pseudo-first-order kinetics model was found to be the best fit to describe the adsorption kinetics of all metal ions onto all the sorbent materials. K1 (min-1) value in pseudo-first-order kinetics showed the same order of adsorption as observed in the Langmuir isotherms. The isothermal batch adsorption studies of [IrCl6]2- and [RhCl5(H2O)]2- with quaternary diammonium cations fitted the Freundlich isotherm model and confirmed to be effective for multiple-layered adsorption onto a heterogeneous surface. The Freundlich isotherm parameter (kf (mg/g)) using functionalized quaternary diammonium cationic nanofibers increased in the order of F-QuatDMDANO2Bnz (794.33 mg/g) > F-QuatDMDACF3Bnz (185.35 mg/g) > F-QuatDMDABnz (156.32 mg/g) > F-QuatDMDAMeBnz (112.46 mg/g) for Ir(IV) uptake. F-QuatDMDANO2Bnz resin showed the highest adsorption than that of F-QuatDMDAMeBnz, F-QuatDMDABnz and F-QuatDMDACF3Bnz and this order is similar to what was observed in column studies. The quaternary diammonium cations were shown to have the highest adsorption capacity for Ir(IV) compared with Rh(III). The adsorption of Rh(III) was also observed to increase in the order of F-QuatDMDANO2Bnz (177.83 mg/g) > F-QuatDMDACF3Bnz (40.37 mg/g) > F-QuatDMDABnz (36.98 mg/g) > F-QuatDMDAMeBnz (12.71 mg/g). The pseudo-second-order kinetic model was found to be the best fit to describe the adsorption kinetics of both metal ions onto all the sorbent materials. K2 (g.mg-1min-1) value in pseudo-second-order kinetics showed the same order of adsorption as observed in the Freundlich isotherms. The adsorption studies showed adsorption takes place via chemisorption process. This thesis presents PGMs and iridium-specific materials that could be applied in solutions of secondary PGMs sources containing rhodium, platinum and palladium with bis-benzimidazoles as well as in feed solutions from ore processing with diammonium cations for iridium recovery.
- Full Text:
- Date Issued: 2019
Flash floods prediction in South African urban areas: Jukskei river catchment as case study
- Authors: Mawasha, Tshepo Sylvester
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Geographic information systems
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/52059 , vital:43429
- Description: This study explored the change relation of multi-temporal land-use/land-cover (LULC) conditions in order to determine how they contribute to change in surface runoff volumes and peak discharge, in an effort to predict flash flooding within the Jukskei River catchment. The research is divided into three main parts: (1) LULC change modeling, (2) rainfall-runoff modeling, and (3) flash floods prediction. Three multi-temporal satellite images of Landsat-5 MMS (1987), Landsat-5 TM (2001) and Landsat-8 OLI (2015) were used for LULC modeling. The analysis of the LULC model revealed that there is a continuous increment in built-up area, from 37.7% to 56.2%, in the expense of other LULC classes for the 28-years preceding this study (i.e., 1987 to 2015). Rainfall-runoff model output results revealed that, for these 28 years, there has been an increase in surface runoff due to change in LULC by 21.5%, 32.9% and 45.5% for 1987, 2001 and 2015, respectively. Due to an increase in surface runoff volume and impervious surface over time, the analysis of HEC-RAS/GeoRAS showed that floodplain extent, flood depth, flood velocity, depth-velocity and the level of damage increases especially in low elevation areas and areas at closed proximity to the Jukskei River. Thus, the building structures and infrastructures are at risk of being affected by flash floods during the rainy season. The findings of this study are expected to be used as basic data for the identification of causative factors of flash floods, areas that generate high surface runoff volume, and the prediction of flash floods within the catchment in future. The flood damage maps developed in this study will be useful to policy-makers and the relevant authorities, as well as to local residents, in finding suitable measures for residential development along the floodplain while reducing flood risk in the study area. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2021
- Full Text: false
- Date Issued: 2021-04
- Authors: Mawasha, Tshepo Sylvester
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Geographic information systems
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/52059 , vital:43429
- Description: This study explored the change relation of multi-temporal land-use/land-cover (LULC) conditions in order to determine how they contribute to change in surface runoff volumes and peak discharge, in an effort to predict flash flooding within the Jukskei River catchment. The research is divided into three main parts: (1) LULC change modeling, (2) rainfall-runoff modeling, and (3) flash floods prediction. Three multi-temporal satellite images of Landsat-5 MMS (1987), Landsat-5 TM (2001) and Landsat-8 OLI (2015) were used for LULC modeling. The analysis of the LULC model revealed that there is a continuous increment in built-up area, from 37.7% to 56.2%, in the expense of other LULC classes for the 28-years preceding this study (i.e., 1987 to 2015). Rainfall-runoff model output results revealed that, for these 28 years, there has been an increase in surface runoff due to change in LULC by 21.5%, 32.9% and 45.5% for 1987, 2001 and 2015, respectively. Due to an increase in surface runoff volume and impervious surface over time, the analysis of HEC-RAS/GeoRAS showed that floodplain extent, flood depth, flood velocity, depth-velocity and the level of damage increases especially in low elevation areas and areas at closed proximity to the Jukskei River. Thus, the building structures and infrastructures are at risk of being affected by flash floods during the rainy season. The findings of this study are expected to be used as basic data for the identification of causative factors of flash floods, areas that generate high surface runoff volume, and the prediction of flash floods within the catchment in future. The flood damage maps developed in this study will be useful to policy-makers and the relevant authorities, as well as to local residents, in finding suitable measures for residential development along the floodplain while reducing flood risk in the study area. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2021
- Full Text: false
- Date Issued: 2021-04
The medicinal plant Sutherlandia Frutescens regulates gene expression to reverse insulin resistace in rats
- Authors: Fortuin, Melissa
- Date: 2013
- Subjects: Insulin resistance , Medicinal plants , Genetic regulation , Insulin resistance -- Animal models
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10349 , http://hdl.handle.net/10948/d1020823
- Description: Obesity can lead to Type 2 Diabetes, both conditions increase in association with physical inactivity and high-energy diets, resulting in elevated blood glucose, decreased insulin sensitivity and increased insulin resistance. Sutherlandia frutescens (S.frutescens), an anti-diabetic plant, reverses and prevents insulin resistance in a rat model and human cell culture model. Gene expression analysis in hepatocyte cultures, identified genes down regulated in insulin resistance and up regulated by S.frutescens. These included genes encoding vesicle transporter proteins, hypothesised to be linked to hepatic lipid accumulation and lipid droplet formation during insulin resistance. The aim of this study was to investigate critical genes involved in lipid droplet formation, vesicle assembly and transport in high fat diet (HFD)-induced insulin resistant rat liver tissue during the development of insulin resistance and the reversal of these changes by S.frutescens. Rats were fed a low fat diet (LFD) or HFD supplemented with S.frutescens for 2, 4 and 8 weeks. Rats fed a HFD for 12 weeks developed insulin resistance, confirmed by plasma glucose and insulin levels (compared to normal controls). Groups of these rats were gavaged with S. frutescens (50mg/kg BW), Metformin (13mg/kg BW) or water for a further 4 weeks and starved for 12 hours, anaesthetized and blood removed by heart puncture. Liver was stored in RNA-Later™ for qRT-PCR and snap-frozen in liquid nitrogen for western blotting and confocal microscopy analysis. Changes in expression of vesicle transporter genes VAMP3 and NSF were analysed by qRT-PCR and changes in the protein expression by western blotting analysis. Proteins were localised within the liver by confocal immunohistochemistry using ZEN lite™ software. Statistical analysis was performed using One-Way ANOVA and unpaired t-test. mRNA gene expression of vesicle transport components VAMP3, NSF and SNAP25 showed relatively moderate changes with considerable individual variation within control or experimental groups. Uncorrelated changes in mRNA and protein products were found and may be due to differential regulation by siRNA. Proteins also showed altered staining patterns in high fat diet rats that reverted towards normal on S. frutescens treatment, potentially reflecting functional changes associated with transport of lipid-filled vesicles.
- Full Text:
- Date Issued: 2013
- Authors: Fortuin, Melissa
- Date: 2013
- Subjects: Insulin resistance , Medicinal plants , Genetic regulation , Insulin resistance -- Animal models
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10349 , http://hdl.handle.net/10948/d1020823
- Description: Obesity can lead to Type 2 Diabetes, both conditions increase in association with physical inactivity and high-energy diets, resulting in elevated blood glucose, decreased insulin sensitivity and increased insulin resistance. Sutherlandia frutescens (S.frutescens), an anti-diabetic plant, reverses and prevents insulin resistance in a rat model and human cell culture model. Gene expression analysis in hepatocyte cultures, identified genes down regulated in insulin resistance and up regulated by S.frutescens. These included genes encoding vesicle transporter proteins, hypothesised to be linked to hepatic lipid accumulation and lipid droplet formation during insulin resistance. The aim of this study was to investigate critical genes involved in lipid droplet formation, vesicle assembly and transport in high fat diet (HFD)-induced insulin resistant rat liver tissue during the development of insulin resistance and the reversal of these changes by S.frutescens. Rats were fed a low fat diet (LFD) or HFD supplemented with S.frutescens for 2, 4 and 8 weeks. Rats fed a HFD for 12 weeks developed insulin resistance, confirmed by plasma glucose and insulin levels (compared to normal controls). Groups of these rats were gavaged with S. frutescens (50mg/kg BW), Metformin (13mg/kg BW) or water for a further 4 weeks and starved for 12 hours, anaesthetized and blood removed by heart puncture. Liver was stored in RNA-Later™ for qRT-PCR and snap-frozen in liquid nitrogen for western blotting and confocal microscopy analysis. Changes in expression of vesicle transporter genes VAMP3 and NSF were analysed by qRT-PCR and changes in the protein expression by western blotting analysis. Proteins were localised within the liver by confocal immunohistochemistry using ZEN lite™ software. Statistical analysis was performed using One-Way ANOVA and unpaired t-test. mRNA gene expression of vesicle transport components VAMP3, NSF and SNAP25 showed relatively moderate changes with considerable individual variation within control or experimental groups. Uncorrelated changes in mRNA and protein products were found and may be due to differential regulation by siRNA. Proteins also showed altered staining patterns in high fat diet rats that reverted towards normal on S. frutescens treatment, potentially reflecting functional changes associated with transport of lipid-filled vesicles.
- Full Text:
- Date Issued: 2013
Development of a small production platform for citronellal processing
- Mafu, Lubabalo Rowan, Zeelie, Ben
- Authors: Mafu, Lubabalo Rowan , Zeelie, Ben
- Date: 2016
- Subjects: Organic compounds -- Synthesis , Plasticizers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/8488 , vital:26370
- Description: The aim of the project was to develop a small production platform for citronellal processing. The objective of the study was to develop a single continuous flow reactor system for the synthesis of novel derivatives of citronellal and isopulegol. The first step was to develop a continuous flow reactor system for the isopulegol synthesis. The stainless steel tubular fixed-bed reactor equipped with a reaction column (I.D: 9.53 mm and length: 120 mm) was used for the study. The reactor column was packed with H-ZMS-5 zeolite extrusion catalyst. The solvent-free cyclisation reaction of citronellal was investigated and at optimum conditions, 100% of citronellal conversion and almost 100% selectivity towards isopulegol was achieved. A good catalytic performance was observed from the H-ZSM-5 catalyst and proved to be stable for a prolonged reaction time. The second reaction step was to develop a continuous flow reactor system for the synthesis of isopulegyl-ether derivatives. A UniQsis FlowSyn reactor system equipped with a stainless steel reactor column was used for the study. The reactor column was packed with amberlyst-15 dry catalyst. Wherein, n-propanol was employed as a model etherifying agent and as a reaction solvent. At optimum reaction condition, only 30% selectivity of isopulegyl propoxy-ether was achieved. The reaction was found to depend highly on temperature and residence time. The increase of these parameters was found to increase the side reactions and reduced the selectivity of the desired product. Other heterogeneous catalysts such as H-beta zeolite, aluminium pillared clay, Aluminium oxide and H-ZSM-5 were also evaluated in the reaction. Among these catalysts, a catalytic activity was observed with H-beta zeolite (19%) and aluminium pillared clay (5%). Based on these results, none of the evaluated catalysts provided the desired selectivity (greater than 70%) towards the isopulegyl propoxy-ether, therefore the process was not investigated further. In light of this, the isopulegol etherification synthetic route was terminated. Consequently, another analogue of citronellal was used as an alternative intermediate in place of isopulegol, namely para-menthane-3,8-diol (PMD). The initial studies for the synthesis of the novel PMD di-esters from isopulegol were performed in the batch-scale reactor. In a solvent-free reaction, acetic anhydride was initially used as a model acetylating agent. The reaction was performed using polymer-bound scandium triflate (PS-Sc(OTf)3) catalyst. The effect of reaction parameters such as temperature, molar ratio, and reaction time were studied towards the PMD conversion and di-esters selectivity. At optimum reaction conditions, PMD conversion of 70% and di-acetate selectivity of 67% were observed. The reaction was found to follow the zeroth-order kinetics with respect to PMD conversion and obeyed the Arrhenius equation. Other types of di-ester derivatives were synthesized from PMD by varying the carbon chain length of the acetylating agent. The prepared compounds were separated from the product mixtures by vacuum distillation, purified on a column chromatography and characterised by FT-IR, GC-MS, and 1H-NMR, 13C-NMR. The developed methodology was optimised in flow by using an ArrheniumOne microwave-assisted continuous-flow fixed-bed reactor system. A detailed experimental design was used to carry-out the reactions. The reaction parameters such as temperature and flow-rate were studied towards the PMD conversion and di-ester selectivity. From the experimental design analysis, the di-ester selectivity was found to depend highly on the residence time (flow-rate) and significantly on temperature. The PMD conversion and di-ester selectivity were found to increase with decrease in the flow-rate. The conversion and selectivity achieved in the continuous flow process were significantly higher than the achieved in the batch-scale process with respect to the residence time.
- Full Text:
- Date Issued: 2016
- Authors: Mafu, Lubabalo Rowan , Zeelie, Ben
- Date: 2016
- Subjects: Organic compounds -- Synthesis , Plasticizers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/8488 , vital:26370
- Description: The aim of the project was to develop a small production platform for citronellal processing. The objective of the study was to develop a single continuous flow reactor system for the synthesis of novel derivatives of citronellal and isopulegol. The first step was to develop a continuous flow reactor system for the isopulegol synthesis. The stainless steel tubular fixed-bed reactor equipped with a reaction column (I.D: 9.53 mm and length: 120 mm) was used for the study. The reactor column was packed with H-ZMS-5 zeolite extrusion catalyst. The solvent-free cyclisation reaction of citronellal was investigated and at optimum conditions, 100% of citronellal conversion and almost 100% selectivity towards isopulegol was achieved. A good catalytic performance was observed from the H-ZSM-5 catalyst and proved to be stable for a prolonged reaction time. The second reaction step was to develop a continuous flow reactor system for the synthesis of isopulegyl-ether derivatives. A UniQsis FlowSyn reactor system equipped with a stainless steel reactor column was used for the study. The reactor column was packed with amberlyst-15 dry catalyst. Wherein, n-propanol was employed as a model etherifying agent and as a reaction solvent. At optimum reaction condition, only 30% selectivity of isopulegyl propoxy-ether was achieved. The reaction was found to depend highly on temperature and residence time. The increase of these parameters was found to increase the side reactions and reduced the selectivity of the desired product. Other heterogeneous catalysts such as H-beta zeolite, aluminium pillared clay, Aluminium oxide and H-ZSM-5 were also evaluated in the reaction. Among these catalysts, a catalytic activity was observed with H-beta zeolite (19%) and aluminium pillared clay (5%). Based on these results, none of the evaluated catalysts provided the desired selectivity (greater than 70%) towards the isopulegyl propoxy-ether, therefore the process was not investigated further. In light of this, the isopulegol etherification synthetic route was terminated. Consequently, another analogue of citronellal was used as an alternative intermediate in place of isopulegol, namely para-menthane-3,8-diol (PMD). The initial studies for the synthesis of the novel PMD di-esters from isopulegol were performed in the batch-scale reactor. In a solvent-free reaction, acetic anhydride was initially used as a model acetylating agent. The reaction was performed using polymer-bound scandium triflate (PS-Sc(OTf)3) catalyst. The effect of reaction parameters such as temperature, molar ratio, and reaction time were studied towards the PMD conversion and di-esters selectivity. At optimum reaction conditions, PMD conversion of 70% and di-acetate selectivity of 67% were observed. The reaction was found to follow the zeroth-order kinetics with respect to PMD conversion and obeyed the Arrhenius equation. Other types of di-ester derivatives were synthesized from PMD by varying the carbon chain length of the acetylating agent. The prepared compounds were separated from the product mixtures by vacuum distillation, purified on a column chromatography and characterised by FT-IR, GC-MS, and 1H-NMR, 13C-NMR. The developed methodology was optimised in flow by using an ArrheniumOne microwave-assisted continuous-flow fixed-bed reactor system. A detailed experimental design was used to carry-out the reactions. The reaction parameters such as temperature and flow-rate were studied towards the PMD conversion and di-ester selectivity. From the experimental design analysis, the di-ester selectivity was found to depend highly on the residence time (flow-rate) and significantly on temperature. The PMD conversion and di-ester selectivity were found to increase with decrease in the flow-rate. The conversion and selectivity achieved in the continuous flow process were significantly higher than the achieved in the batch-scale process with respect to the residence time.
- Full Text:
- Date Issued: 2016
Tribocorrosion properties of friction stir welded and laser welded titanium alloy
- Authors: Davoren, Brandon Hilton
- Date: 2017
- Subjects: Chemistry, Technical -- Research Materials -- Mechanical properties , Aluminum alloys
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/33250 , vital:32605
- Description: Titanium alloy Ti6Al4V has extensive uses in aerospace, dentistry and the biomedical industry. When used in these applications there is often a need to weld two or more pieces of titanium alloy together. This can be done by either friction stir weld or laser weld methods. These welded regions are often exposed to corrosive environments in addition to factors such as induced additional mechanical wear. Thus to accurately report on the viability of the material in a specific application, the corrosion, wear and their synergistic effects need to be studied. Friction stir welding, which is a well-suited method for joining plates of Ti6Al4V, creates regions in the material that are affected differently. These regions can be described as the parent material, advancing side, retreating side and the weld zone. The tribological properties of the different friction stir weld regions were analysed in air using different loads, frequencies, experimental duration and surrounding environments. When the applied load was increased some of the weld regions showed an increase in the specific wear rate. For example, the weld zone region showed a decrease when compared to the parent material. In this tribology study the effect of the counter material was evaluated. E52100, Si3N4, SS 316 and alumina counter materials were used in the test procedure which was conducted in air on the weld regions. The parent material was found to have the highest average specific wear rates with the four counter materials when compared to the weld zone samples. The regions affected by the friction stir weld process all showed, on average, lower specific wear rates than the parent material. For the various tested samples, the coefficient of friction and material compatibility that was found to be the most stable, was the alumina ball. Owing to this as well as its chemical stability, alumina was determined to be the best material for further tribocorrosion studies. The friction stir welded samples, that were cut from a cross section of a friction stir weld plate, were analyzed in 3.5% NaCl and dilute Harrison’s solution respectively. The effect of wear on the electrochemical properties was studied under open circuit voltage (OCV) and fixed 0.2 V and 0.4 V applied potential conditions respectively. The effect of wear on the corrosion properties was studied using potentiodynamic polarization. From analyzing the friction stir weld regions in both a wear and wear-free environment, the synergistic properties, namely the effect of wear on corrosion and the effect of corrosion on wear, were able to be calculated. The first electrochemical study was performed under OCV conditions. In the presence of applied wear, the open circuit potential of the friction stir weld samples, in both 3.5% NaCl and dilute Harrison’s solution, was found to decrease from the initial stabilized value. Of interest was the rate at which the OCV recovered. It was found to follow a second order repassivation growth model which was explained in terms of an initial film growth stage, followed by a film thickening stage that results in a new OCV. The second synergized electrochemical-wear study was under fixed 0.2 V and 0.4 V applied potential conditions. In both solutions, 3.5% NaCl and dilute Harrison’s solution, a large increase in the current was observed during the applied wear experiment. The samples submerged in 3.5% NaCl were found to have higher average currents during the wear experiment than those in dilute Harrison’s solution. The rapid decrease in the current, after the applied wear ceased, was found to also follow the second order repassivation model. The electrochemical-wear synergism was done by using potentiodynamic polarization tests. The friction stir weld regions as well as the laser samples were analysed in a wear as well as a wear-free environment in order to determine the effect that wear had on the corrosion properties. In both 3.5% NaCl and dilute Harrison’s solution the corrosion rates were found to increase by 100-fold when the wear was present. The effect of the wear process on corrosion could also be described by synergistic factor, where values close to 1 would imply that applied wear had little effect on the corrosion properties and vice versa. The synergistic factors showed that the corrosion rate was greatly affected by the presence of wear with corrosion synergistic factors of 20 and upward for the friction stir welded samples. The results showed that the weld zone region had a lower corrosion rate than the parent material. This implied that the main weld zone was shown to have the least effect of wear on corrosion and would therefore show the lowest likelihood of failure due to corrosion when compared to the parent material. The wear synergistic factor was found to be between 1 and 1.6 for the friction stir weld regions. This implied that the wear rates of the friction stir welded samples were slightly affected by the presence of a corrosive environment and that the wear properties of the laser welded samples were enhanced by the presence of a corrosive environment. Similar studies performed on laser welded samples showed unusually different results due to the small nature of the laser weld region, with inconclusive results when compared to the friction stir welded samples.
- Full Text:
- Date Issued: 2017
- Authors: Davoren, Brandon Hilton
- Date: 2017
- Subjects: Chemistry, Technical -- Research Materials -- Mechanical properties , Aluminum alloys
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/33250 , vital:32605
- Description: Titanium alloy Ti6Al4V has extensive uses in aerospace, dentistry and the biomedical industry. When used in these applications there is often a need to weld two or more pieces of titanium alloy together. This can be done by either friction stir weld or laser weld methods. These welded regions are often exposed to corrosive environments in addition to factors such as induced additional mechanical wear. Thus to accurately report on the viability of the material in a specific application, the corrosion, wear and their synergistic effects need to be studied. Friction stir welding, which is a well-suited method for joining plates of Ti6Al4V, creates regions in the material that are affected differently. These regions can be described as the parent material, advancing side, retreating side and the weld zone. The tribological properties of the different friction stir weld regions were analysed in air using different loads, frequencies, experimental duration and surrounding environments. When the applied load was increased some of the weld regions showed an increase in the specific wear rate. For example, the weld zone region showed a decrease when compared to the parent material. In this tribology study the effect of the counter material was evaluated. E52100, Si3N4, SS 316 and alumina counter materials were used in the test procedure which was conducted in air on the weld regions. The parent material was found to have the highest average specific wear rates with the four counter materials when compared to the weld zone samples. The regions affected by the friction stir weld process all showed, on average, lower specific wear rates than the parent material. For the various tested samples, the coefficient of friction and material compatibility that was found to be the most stable, was the alumina ball. Owing to this as well as its chemical stability, alumina was determined to be the best material for further tribocorrosion studies. The friction stir welded samples, that were cut from a cross section of a friction stir weld plate, were analyzed in 3.5% NaCl and dilute Harrison’s solution respectively. The effect of wear on the electrochemical properties was studied under open circuit voltage (OCV) and fixed 0.2 V and 0.4 V applied potential conditions respectively. The effect of wear on the corrosion properties was studied using potentiodynamic polarization. From analyzing the friction stir weld regions in both a wear and wear-free environment, the synergistic properties, namely the effect of wear on corrosion and the effect of corrosion on wear, were able to be calculated. The first electrochemical study was performed under OCV conditions. In the presence of applied wear, the open circuit potential of the friction stir weld samples, in both 3.5% NaCl and dilute Harrison’s solution, was found to decrease from the initial stabilized value. Of interest was the rate at which the OCV recovered. It was found to follow a second order repassivation growth model which was explained in terms of an initial film growth stage, followed by a film thickening stage that results in a new OCV. The second synergized electrochemical-wear study was under fixed 0.2 V and 0.4 V applied potential conditions. In both solutions, 3.5% NaCl and dilute Harrison’s solution, a large increase in the current was observed during the applied wear experiment. The samples submerged in 3.5% NaCl were found to have higher average currents during the wear experiment than those in dilute Harrison’s solution. The rapid decrease in the current, after the applied wear ceased, was found to also follow the second order repassivation model. The electrochemical-wear synergism was done by using potentiodynamic polarization tests. The friction stir weld regions as well as the laser samples were analysed in a wear as well as a wear-free environment in order to determine the effect that wear had on the corrosion properties. In both 3.5% NaCl and dilute Harrison’s solution the corrosion rates were found to increase by 100-fold when the wear was present. The effect of the wear process on corrosion could also be described by synergistic factor, where values close to 1 would imply that applied wear had little effect on the corrosion properties and vice versa. The synergistic factors showed that the corrosion rate was greatly affected by the presence of wear with corrosion synergistic factors of 20 and upward for the friction stir welded samples. The results showed that the weld zone region had a lower corrosion rate than the parent material. This implied that the main weld zone was shown to have the least effect of wear on corrosion and would therefore show the lowest likelihood of failure due to corrosion when compared to the parent material. The wear synergistic factor was found to be between 1 and 1.6 for the friction stir weld regions. This implied that the wear rates of the friction stir welded samples were slightly affected by the presence of a corrosive environment and that the wear properties of the laser welded samples were enhanced by the presence of a corrosive environment. Similar studies performed on laser welded samples showed unusually different results due to the small nature of the laser weld region, with inconclusive results when compared to the friction stir welded samples.
- Full Text:
- Date Issued: 2017
Identification and classification of micro-estuaries using selected abiotic and biotic characteristics along the Eastern Cape coast, South Africa
- Authors: Naidoo, Lyndle Sherae
- Date: 2017
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11920 , vital:27007
- Description: Many of the larger estuaries along the South African coastline are highly degraded due to human impacts, highlighting the need to conserve pristine systems. There are approximately 100 micro-estuaries along our coastline which have not yet been identified or classified and hence their ecological functioning is unknown. The aim of this study was to identify and classify micro-estuaries along the Eastern Cape coast. Specific objectives of the study were to: 1) map the distribution of estuarine habitats in a selection of micro-estuaries and assess changes over time; 2) measure the physico-chemical characteristics of the micro-estuaries in the field; 3) investigate the distribution of vegetation, identify macrophyte species and habitat integrity and classify the micro-estuaries sampled using abiotic and botanical characteristics. A total of 30 systems were identified of which 10 were selected for sampling which took place seasonally (2015-2016). A relationship between open water surface area and short term rainfall was only evident in Cunge, Sandy Bottom and Ichabana. In the field it was observed that after heavy rainfall, open water surface area increased and mouth breaching occurred. Salinity was the only water column characteristic that showed differences; salinity increased in response to over wash events. Sand was dominant in all systems and there were no differences in sediment characteristics. A total of 8 macroalgal species, 16 estuarine macrophyte species, six freshwater species and 72 riparian plant species were found. Seed bank reserves were low in all systems despite them being vegetated. Only abiotic characteristics were used for classification using Principle Components Analysis since there were no botanical differences between systems. Micro-estuaries were larger (> 0.03 ha), had a higher salinity (oligohaline, mesohaline and polyhaline conditions) and a constant water body. Micro-outlets were smaller (< 0.03 ha), had a lower salinity (oligohaline conditions were most common) and showed periods of drying. Five micro-estuaries (Shelbertsstroom, Kwesani, Cunge, Mtwendwe and Mtendwe) and five micro-outlets (Stromatolite, Sandy Bottom, Ichabana, Palm Tree and Black Rock) were classified. This study has shown that the micro-estuaries along the Eastern Cape coast are pristine (i.e. intact riparian zone and catchment), untouched and highly dynamic systems (i.e. great variation in water surface area and mouth condition) highlighting their need for protection.
- Full Text:
- Date Issued: 2017
- Authors: Naidoo, Lyndle Sherae
- Date: 2017
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11920 , vital:27007
- Description: Many of the larger estuaries along the South African coastline are highly degraded due to human impacts, highlighting the need to conserve pristine systems. There are approximately 100 micro-estuaries along our coastline which have not yet been identified or classified and hence their ecological functioning is unknown. The aim of this study was to identify and classify micro-estuaries along the Eastern Cape coast. Specific objectives of the study were to: 1) map the distribution of estuarine habitats in a selection of micro-estuaries and assess changes over time; 2) measure the physico-chemical characteristics of the micro-estuaries in the field; 3) investigate the distribution of vegetation, identify macrophyte species and habitat integrity and classify the micro-estuaries sampled using abiotic and botanical characteristics. A total of 30 systems were identified of which 10 were selected for sampling which took place seasonally (2015-2016). A relationship between open water surface area and short term rainfall was only evident in Cunge, Sandy Bottom and Ichabana. In the field it was observed that after heavy rainfall, open water surface area increased and mouth breaching occurred. Salinity was the only water column characteristic that showed differences; salinity increased in response to over wash events. Sand was dominant in all systems and there were no differences in sediment characteristics. A total of 8 macroalgal species, 16 estuarine macrophyte species, six freshwater species and 72 riparian plant species were found. Seed bank reserves were low in all systems despite them being vegetated. Only abiotic characteristics were used for classification using Principle Components Analysis since there were no botanical differences between systems. Micro-estuaries were larger (> 0.03 ha), had a higher salinity (oligohaline, mesohaline and polyhaline conditions) and a constant water body. Micro-outlets were smaller (< 0.03 ha), had a lower salinity (oligohaline conditions were most common) and showed periods of drying. Five micro-estuaries (Shelbertsstroom, Kwesani, Cunge, Mtwendwe and Mtendwe) and five micro-outlets (Stromatolite, Sandy Bottom, Ichabana, Palm Tree and Black Rock) were classified. This study has shown that the micro-estuaries along the Eastern Cape coast are pristine (i.e. intact riparian zone and catchment), untouched and highly dynamic systems (i.e. great variation in water surface area and mouth condition) highlighting their need for protection.
- Full Text:
- Date Issued: 2017
Assessment of indigenous forest degradation and deforestation along the wild coast, near Port St John’s, Eastern Cape Province, South Africa
- Katende, Lukyamuzi Lucky Fulgentius
- Authors: Katende, Lukyamuzi Lucky Fulgentius
- Date: 2018
- Subjects: Deforestation -- South Africa -- Eastern Cape , Forest degradation -- South Africa -- Eastern Cape Forest management -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/30649 , vital:31006
- Description: Indigenous forests along the Wild Coast of the Eastern Cape Province have experienced both degradation and deforestation over the past decades. In early 2000, steps were taken to rehabilitate some of the degraded areas. Nevertheless, there is no monitoring mechanism in place, so little is known about the extent of degradation and impact of the rehabilitation efforts. The present study assesses the extent to which deforestation and degradation of the indigenous forests have occurred, and evaluates rehabilitation efforts in the study area around Port Saint John’s. Forest degradation was defined as the decrease in forest cover density while deforestation was defined as an increase in the trend of light forests and/ or a decrease in dense forests. The details for this study were obtained from multi – temporal remotely sensed data for a period between 1982 and 2013 (31 years). Multi-temporal Landsat satellite imagery for 1982, 1986, 1989, 2002, 2009 and 2013 was acquired and analysed. On the basis of prior knowledge of the area, the supervised classification approach was used. The Maximum likelihood supervised classification technique was used to extract information from satellite data. The classified images were filtered using a majority filtering procedure to reduce noise. Google Earth (Astrium) ancillary images were used to refine the classification based on expert rules. The derived changes in the degraded and rehabilitated areas were further validated through field visits. The overall image classification accuracy generated from Landsat image data ranged from 80% to 90%. It was noted that the area of dense forest almost doubled between 1986 and 1989, coinciding with a 59% decrease in the light forest. Subsequently, dense forests increased by 14,820 ha while light forests decreased by 16,690 ha between 1989 and 2002. The subsequent reduction in light forest coverage is explained by the establishment of the Participatory Forest Management (PFMA) approach by Department of Water Affairs and Forestry (DWAF) which reversed the degradation trend. However, specific degradation hotspots were identified, particularly where new settlements have been established. The emergence of the non-vegetated area increased gradually from 7% in 1986 to 23.4% in 2013. Notably, dense forest was observed to have experienced higher rates of forest degradation and deforestation than the light forest. The highest number patches were 4 recorded between 2002 and 1998, followed by between 2010 and 2013 and lastly 1986. Based on spatial connectedness of patches, the year 1986 had the highest landscape connectedness of forest vegetation (CONAT = 35.3) followed by 2002 and 1996 while the year 2010 and 2013 had the lowest landscape contiguity. Over the study period, the distribution of patches clearly shows that forest degradation and deforestation rates were lower in the years 1986, 1998 and tremendously increased in the later period of between 2010 and 2013. However, as a result of rehabilitation efforts, dense forest was seen to steadily gain more land than light forest. Finer details of degradation trends could not be easily picked from the images used in the study, given their spatial resolution limitations. That notwithstanding, the trends identified are good for overview decisions. The study has also established that de-agraianisation, forest restoration and rehabilitation greatly contributed to increased forest cover. Therefore, with more use of GIS by forest managers, and imagery of the high resolution being readily available, forests will in future be easily monitored using remote sensing.
- Full Text:
- Date Issued: 2018
- Authors: Katende, Lukyamuzi Lucky Fulgentius
- Date: 2018
- Subjects: Deforestation -- South Africa -- Eastern Cape , Forest degradation -- South Africa -- Eastern Cape Forest management -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/30649 , vital:31006
- Description: Indigenous forests along the Wild Coast of the Eastern Cape Province have experienced both degradation and deforestation over the past decades. In early 2000, steps were taken to rehabilitate some of the degraded areas. Nevertheless, there is no monitoring mechanism in place, so little is known about the extent of degradation and impact of the rehabilitation efforts. The present study assesses the extent to which deforestation and degradation of the indigenous forests have occurred, and evaluates rehabilitation efforts in the study area around Port Saint John’s. Forest degradation was defined as the decrease in forest cover density while deforestation was defined as an increase in the trend of light forests and/ or a decrease in dense forests. The details for this study were obtained from multi – temporal remotely sensed data for a period between 1982 and 2013 (31 years). Multi-temporal Landsat satellite imagery for 1982, 1986, 1989, 2002, 2009 and 2013 was acquired and analysed. On the basis of prior knowledge of the area, the supervised classification approach was used. The Maximum likelihood supervised classification technique was used to extract information from satellite data. The classified images were filtered using a majority filtering procedure to reduce noise. Google Earth (Astrium) ancillary images were used to refine the classification based on expert rules. The derived changes in the degraded and rehabilitated areas were further validated through field visits. The overall image classification accuracy generated from Landsat image data ranged from 80% to 90%. It was noted that the area of dense forest almost doubled between 1986 and 1989, coinciding with a 59% decrease in the light forest. Subsequently, dense forests increased by 14,820 ha while light forests decreased by 16,690 ha between 1989 and 2002. The subsequent reduction in light forest coverage is explained by the establishment of the Participatory Forest Management (PFMA) approach by Department of Water Affairs and Forestry (DWAF) which reversed the degradation trend. However, specific degradation hotspots were identified, particularly where new settlements have been established. The emergence of the non-vegetated area increased gradually from 7% in 1986 to 23.4% in 2013. Notably, dense forest was observed to have experienced higher rates of forest degradation and deforestation than the light forest. The highest number patches were 4 recorded between 2002 and 1998, followed by between 2010 and 2013 and lastly 1986. Based on spatial connectedness of patches, the year 1986 had the highest landscape connectedness of forest vegetation (CONAT = 35.3) followed by 2002 and 1996 while the year 2010 and 2013 had the lowest landscape contiguity. Over the study period, the distribution of patches clearly shows that forest degradation and deforestation rates were lower in the years 1986, 1998 and tremendously increased in the later period of between 2010 and 2013. However, as a result of rehabilitation efforts, dense forest was seen to steadily gain more land than light forest. Finer details of degradation trends could not be easily picked from the images used in the study, given their spatial resolution limitations. That notwithstanding, the trends identified are good for overview decisions. The study has also established that de-agraianisation, forest restoration and rehabilitation greatly contributed to increased forest cover. Therefore, with more use of GIS by forest managers, and imagery of the high resolution being readily available, forests will in future be easily monitored using remote sensing.
- Full Text:
- Date Issued: 2018
Towards measuring corporate sustainability in the Nelson Mandela Bay automotive manufacturing sector
- Authors: Adams, Abulele
- Date: 2015
- Subjects: Sustainability -- South Africa -- Port Elizabeth Sustainable development -- South Africa -- Port Elizabeth
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/18465 , vital:28648
- Description: This study explored the methods available for measuring corporate sustainability and created an instrument to measure corporate sustainability in the Nelson Mandela Bay (NMB) automotive manufacturing sector. The instrument was created based on three components of sustainability which are environment, society and economy. The study went a step further and added a fourth dimension, current trends to design a measuring instrument. The instrument was then applied on participating companies and further refined to improve it. A total of 16 multi-dimensional indicators to measure corporate sustainability were created and applied to 12 companies in the automotive manufacturing sector. The indicators were used to create a composite corporate sustainability index which can be used to compare the corporate sustainability performance of companies. These indicators were created based on theoretical research and fist hand experience observing the automotive manufacturing sector in the NMB. The indicators were applied to companies as a pilot to test whether they are feasible. Following this, the indicators were refined, improved and applied to more companies to measure corporate sustainability performance. The results of the study were the measuring instrument created, the creation of a composite index as well as the application of the instrument on 12 companies to determine whether the instrument was refined enough to detect differences in the corporate sustainability performance of companies. The results are discussed and further recommendations are made for improvements in the creation and application of the instrument to measure corporate sustainability in the NMB automotive manufacturing sector.
- Full Text:
- Date Issued: 2015
Towards measuring corporate sustainability in the Nelson Mandela Bay automotive manufacturing sector
- Authors: Adams, Abulele
- Date: 2015
- Subjects: Sustainability -- South Africa -- Port Elizabeth Sustainable development -- South Africa -- Port Elizabeth
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/18465 , vital:28648
- Description: This study explored the methods available for measuring corporate sustainability and created an instrument to measure corporate sustainability in the Nelson Mandela Bay (NMB) automotive manufacturing sector. The instrument was created based on three components of sustainability which are environment, society and economy. The study went a step further and added a fourth dimension, current trends to design a measuring instrument. The instrument was then applied on participating companies and further refined to improve it. A total of 16 multi-dimensional indicators to measure corporate sustainability were created and applied to 12 companies in the automotive manufacturing sector. The indicators were used to create a composite corporate sustainability index which can be used to compare the corporate sustainability performance of companies. These indicators were created based on theoretical research and fist hand experience observing the automotive manufacturing sector in the NMB. The indicators were applied to companies as a pilot to test whether they are feasible. Following this, the indicators were refined, improved and applied to more companies to measure corporate sustainability performance. The results of the study were the measuring instrument created, the creation of a composite index as well as the application of the instrument on 12 companies to determine whether the instrument was refined enough to detect differences in the corporate sustainability performance of companies. The results are discussed and further recommendations are made for improvements in the creation and application of the instrument to measure corporate sustainability in the NMB automotive manufacturing sector.
- Full Text:
- Date Issued: 2015
Assessing the statistical methodologies of business research in the South African context
- Authors: Ndou, Aifheli Amos
- Date: 2011
- Subjects: Statistics -- South Africa , Commercial statistics -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:8631 , http://hdl.handle.net/10948/1484 , Statistics -- South Africa , Commercial statistics -- South Africa
- Description: The aim of the study is to establish an acceptable classification scheme for the statistical methods used in business research. The approach compares the statistical component of the research and evaluates how it has changed over time and across different journals. If, as expected, the statistical expertise has changed, the change would be identified with the view to recommending curriculum changes for Statistics Departments of South African tertiary institutions.
- Full Text:
- Date Issued: 2011
- Authors: Ndou, Aifheli Amos
- Date: 2011
- Subjects: Statistics -- South Africa , Commercial statistics -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:8631 , http://hdl.handle.net/10948/1484 , Statistics -- South Africa , Commercial statistics -- South Africa
- Description: The aim of the study is to establish an acceptable classification scheme for the statistical methods used in business research. The approach compares the statistical component of the research and evaluates how it has changed over time and across different journals. If, as expected, the statistical expertise has changed, the change would be identified with the view to recommending curriculum changes for Statistics Departments of South African tertiary institutions.
- Full Text:
- Date Issued: 2011
Assessing growth response patterns of microalgae to varying environmental conditions using sediments from ephemeral wetlands
- Authors: Mazwane, Sixolile
- Date: 2018
- Subjects: Microalgae -- South Africa , Wetland conservation -- South Africa Landscape ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22398 , vital:29966
- Description: Ephemeral wetlands serve as habitats for different fauna and flora. Microalgae make up a bulk of primary production in newly inundated wetlands and have a big influence on the aquatic community structure. As ephemeral wetlands have cyclical drying and wetting phases, algal species found in these habitats have evolved adaptations (i.e. dormancy and cysts) to survive during dry periods and become productive upon inundation. Algae have been used as ecological indicators in many aquatic ecosystems including wetlands, particularly associated with water quality and with varying inundation states. Whilst temperature and water level have been shown to affect microalgal biomass independently, this study aims to assess the effects of these two factors simultaneously on microalgal biomass, species diversity and community changes. The aim of the study was to investigate microalgal dynamics using two ephemeral wetlands in the Nelson Mandela Bay Municipality. The growth response patterns of microalgal communities to varying temperatures and inundation levels through experiments using dry temporary wetland sediments was also assessed. Dry sediments were collected from two depression wetlands with different sediment characteristics (1592 and Elephant Wallow (EW)). The study consisted of replicated treatments with three different surface area: volume ratios (SA:V) (Low surface area: volume (LSAV), Medium (MSAV) and High (HSAV)), inundated with distilled water. The microcosms were placed inside a Conviron environmental growth chamber and illuminated at between 106 to 138 μmol.m-2s-1, with a 12:12 light-dark cycle at constant temperatures of 12 °C (mean winter) and 22 °C (mean summer). Physicochemical data were recorded, and biological samples were collected every 4 days over a 28-day inundation period. In the field, Electrical conductivity (EC) and pH showed a gradual increase over the inundation period. The systems were well oxygenated (6-10 mg L-1). Overall, phytoplankton biomass in the field was ~10 μg L-1 whereas benthic biomass (MPB) was significantly higher 10 – 300 mg L-1. Within the experiments, the phytoplankton biomass showed a pattern while MPB biomass increased gradually for both experiments. There were no significant (p>0.05) differences between the 1592 and EW phytoplankton biomass. However, the MPB biomass showed significant (p<0.05) differences between the two sediments (EW high, 1592 low) and the experiments, respectively. In the winter experiment, the 1592 sediment had high phytoplankton biomass compared to EW, the reverse was observed for the MPB biomass. In summer experiment, similar results were observed in terms of phytoplankton biomass. For the MPBs, 1592 had greater biomass for all treatments compared to EW. The phytoplankton community for both field samples and experiments was dominated by chlorophytes (>50 %), followed by cyanophytes and euglenophytes (with cryptophytes in summer experiment) for both field and experiments. The MPB community was dominated by bacillariophytes (55 %) and chlorophytes (25 %) in the 1592 sediments and this was also the case with EW sediments bacillariophytes (70 %), although cyanophytes (15 %) made up the remainder of the MPB community. The 1592 sediments supported higher diatom abundances under the HSAV compared to the same treatment from the EW wetland suggesting that possibly grain size or texture might be responsible. In contrast, sediments from EW under LSAV conditions showed higher diatom cell numbers possibly indicating that increased water depth has the propensity to support greater diatom assemblages compared with the same water level for sediments from 1592. The results indicate that microalgae community is influenced by sediment type more than it is by water level. From this study it was also established that microalgae were able to reemerge from their dormancy state upon inundation and that tank experiments were successful in simulating natural ephemeral wetland conditions. The findings from this study will add to the available baseline data on microalgal dynamics in the ephemeral wetlands in South Africa, especially in semi-arid areas. This information can be valuable in enhancing our understanding regarding the role of microalgae in ephemeral wetlands in order to conserve them.
- Full Text:
- Date Issued: 2018
- Authors: Mazwane, Sixolile
- Date: 2018
- Subjects: Microalgae -- South Africa , Wetland conservation -- South Africa Landscape ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22398 , vital:29966
- Description: Ephemeral wetlands serve as habitats for different fauna and flora. Microalgae make up a bulk of primary production in newly inundated wetlands and have a big influence on the aquatic community structure. As ephemeral wetlands have cyclical drying and wetting phases, algal species found in these habitats have evolved adaptations (i.e. dormancy and cysts) to survive during dry periods and become productive upon inundation. Algae have been used as ecological indicators in many aquatic ecosystems including wetlands, particularly associated with water quality and with varying inundation states. Whilst temperature and water level have been shown to affect microalgal biomass independently, this study aims to assess the effects of these two factors simultaneously on microalgal biomass, species diversity and community changes. The aim of the study was to investigate microalgal dynamics using two ephemeral wetlands in the Nelson Mandela Bay Municipality. The growth response patterns of microalgal communities to varying temperatures and inundation levels through experiments using dry temporary wetland sediments was also assessed. Dry sediments were collected from two depression wetlands with different sediment characteristics (1592 and Elephant Wallow (EW)). The study consisted of replicated treatments with three different surface area: volume ratios (SA:V) (Low surface area: volume (LSAV), Medium (MSAV) and High (HSAV)), inundated with distilled water. The microcosms were placed inside a Conviron environmental growth chamber and illuminated at between 106 to 138 μmol.m-2s-1, with a 12:12 light-dark cycle at constant temperatures of 12 °C (mean winter) and 22 °C (mean summer). Physicochemical data were recorded, and biological samples were collected every 4 days over a 28-day inundation period. In the field, Electrical conductivity (EC) and pH showed a gradual increase over the inundation period. The systems were well oxygenated (6-10 mg L-1). Overall, phytoplankton biomass in the field was ~10 μg L-1 whereas benthic biomass (MPB) was significantly higher 10 – 300 mg L-1. Within the experiments, the phytoplankton biomass showed a pattern while MPB biomass increased gradually for both experiments. There were no significant (p>0.05) differences between the 1592 and EW phytoplankton biomass. However, the MPB biomass showed significant (p<0.05) differences between the two sediments (EW high, 1592 low) and the experiments, respectively. In the winter experiment, the 1592 sediment had high phytoplankton biomass compared to EW, the reverse was observed for the MPB biomass. In summer experiment, similar results were observed in terms of phytoplankton biomass. For the MPBs, 1592 had greater biomass for all treatments compared to EW. The phytoplankton community for both field samples and experiments was dominated by chlorophytes (>50 %), followed by cyanophytes and euglenophytes (with cryptophytes in summer experiment) for both field and experiments. The MPB community was dominated by bacillariophytes (55 %) and chlorophytes (25 %) in the 1592 sediments and this was also the case with EW sediments bacillariophytes (70 %), although cyanophytes (15 %) made up the remainder of the MPB community. The 1592 sediments supported higher diatom abundances under the HSAV compared to the same treatment from the EW wetland suggesting that possibly grain size or texture might be responsible. In contrast, sediments from EW under LSAV conditions showed higher diatom cell numbers possibly indicating that increased water depth has the propensity to support greater diatom assemblages compared with the same water level for sediments from 1592. The results indicate that microalgae community is influenced by sediment type more than it is by water level. From this study it was also established that microalgae were able to reemerge from their dormancy state upon inundation and that tank experiments were successful in simulating natural ephemeral wetland conditions. The findings from this study will add to the available baseline data on microalgal dynamics in the ephemeral wetlands in South Africa, especially in semi-arid areas. This information can be valuable in enhancing our understanding regarding the role of microalgae in ephemeral wetlands in order to conserve them.
- Full Text:
- Date Issued: 2018
A multiscale remote sensing assessment of subtropical indigenous forests along the wild coast, South Africa
- Authors: Blessing, Sithole Vhusomuzi
- Date: 2015
- Subjects: Forests and forestry -- South Africa -- Remote sensing , Forest conservation , Remote sensing , Geographic information systems
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10677 , http://hdl.handle.net/10948/d1021169
- Description: The subtropical forests located along South Africa’s Wild Coast region, declared as one of the biodiversity hotspots, provide benefits to the local and national economy. However, there is evidence of increased pressure exerted on the forests by growing population and reduced income from activities not related to forest products. The ability of remote sensing to quantify subtropical forest changes over time, perform species discrimination (using field spectroscopy) and integrating field spectral and multispectral data were all assessed in this study. Investigations were conducted at pixel, leaf and sub-pixel levels. Both per-pixel and sub-pixel classification methods were used for improved forest characterisation. Using SPOT 6 imagery for 2013, the study determined the best classification algorithm for mapping sub-tropical forest and other land cover types to be the maximum likelihood classifier. Maximum likelihood outperformed minimum distance, spectral angle mapper and spectral information divergence algorithms, based on overall accuracy and Kappa coefficient values. Forest change analysis was made based on spectral measurements made at top of the atmosphere (TOC) level. When applied to the 2005 and 2009 SPOT 5 images, subtropical forest changes between 2005-2009 and 2009-2013 were quantified. A temporal analysis of forest cover trends in the periods 2005-2009 and 2009-2013 identified a decreasing trend of -3648.42 and -946.98 ha respectively, which translated to 7.81 percent and 2.20 percent decrease. Although there is evidence of a trend towards decreased rates of forest loss, more conservation efforts are required to protect the Wild Coast ecosystem. Using field spectral measurements data, the hierarchical method (comprising One-way ANOVA with Bonferroni correction, Classification and Regression Trees (CART) and Jeffries Matusita method) successfully selected optimal wavelengths for species discrimination at leaf level. Only 17 out of 2150 wavelengths were identified, thereby reducing the complexities related to data dimensionality. The optimal 17 wavelength bands were noted in the visible (438, 442, 512 and 695 nm), near infrared (724, 729, 750, 758, 856, 936, 1179, 1507 and 1673 nm) and mid-infrared (2220, 2465, 2469 and 2482 nm) portions of the electromagnetic spectrum. The Jeffries-Matusita (JM) distance method confirmed the separability of the selected wavelength bands. Using these 17 wavelengths, linear discriminant analysis (LDA) classified subtropical species at leaf level more accurately than partial least squares discriminant analysis (PLSDA) and random forest (RF). In addition, the study integrated field-collected canopy spectral and multispectral data to discriminate proportions of semi-deciduous and evergreen subtropical forests at sub-pixel level. By using the 2013 land cover (using MLC) to mask non-forested portions before sub-pixel classification (using MTMF), the proportional maps were a product of two classifiers. The proportional maps show higher proportions of evergreen forests along the coast while semi-deciduous subtropical forest species were mainly on inland parts of the Wild Coast. These maps had high accuracy, thereby proving the ability of an integration of field spectral and multispectral data in mapping semi-deciduous and evergreen forest species. Overall, the study has demonstrated the importance of the MLC and LDA and served to integrate field spectral and multispectral data in subtropical forest characterisation at both leaf and top-of-atmosphere levels. The success of both the MLC and LDA further highlighted how essential parametric classifiers are in remote sensing forestry applications. Main subtropical characteristics highlighted in this study were species discrimination at leaf level, quantifying forest change at pixel level and discriminating semi-deciduous and evergreen forests at sub-pixel level.
- Full Text:
- Date Issued: 2015
- Authors: Blessing, Sithole Vhusomuzi
- Date: 2015
- Subjects: Forests and forestry -- South Africa -- Remote sensing , Forest conservation , Remote sensing , Geographic information systems
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10677 , http://hdl.handle.net/10948/d1021169
- Description: The subtropical forests located along South Africa’s Wild Coast region, declared as one of the biodiversity hotspots, provide benefits to the local and national economy. However, there is evidence of increased pressure exerted on the forests by growing population and reduced income from activities not related to forest products. The ability of remote sensing to quantify subtropical forest changes over time, perform species discrimination (using field spectroscopy) and integrating field spectral and multispectral data were all assessed in this study. Investigations were conducted at pixel, leaf and sub-pixel levels. Both per-pixel and sub-pixel classification methods were used for improved forest characterisation. Using SPOT 6 imagery for 2013, the study determined the best classification algorithm for mapping sub-tropical forest and other land cover types to be the maximum likelihood classifier. Maximum likelihood outperformed minimum distance, spectral angle mapper and spectral information divergence algorithms, based on overall accuracy and Kappa coefficient values. Forest change analysis was made based on spectral measurements made at top of the atmosphere (TOC) level. When applied to the 2005 and 2009 SPOT 5 images, subtropical forest changes between 2005-2009 and 2009-2013 were quantified. A temporal analysis of forest cover trends in the periods 2005-2009 and 2009-2013 identified a decreasing trend of -3648.42 and -946.98 ha respectively, which translated to 7.81 percent and 2.20 percent decrease. Although there is evidence of a trend towards decreased rates of forest loss, more conservation efforts are required to protect the Wild Coast ecosystem. Using field spectral measurements data, the hierarchical method (comprising One-way ANOVA with Bonferroni correction, Classification and Regression Trees (CART) and Jeffries Matusita method) successfully selected optimal wavelengths for species discrimination at leaf level. Only 17 out of 2150 wavelengths were identified, thereby reducing the complexities related to data dimensionality. The optimal 17 wavelength bands were noted in the visible (438, 442, 512 and 695 nm), near infrared (724, 729, 750, 758, 856, 936, 1179, 1507 and 1673 nm) and mid-infrared (2220, 2465, 2469 and 2482 nm) portions of the electromagnetic spectrum. The Jeffries-Matusita (JM) distance method confirmed the separability of the selected wavelength bands. Using these 17 wavelengths, linear discriminant analysis (LDA) classified subtropical species at leaf level more accurately than partial least squares discriminant analysis (PLSDA) and random forest (RF). In addition, the study integrated field-collected canopy spectral and multispectral data to discriminate proportions of semi-deciduous and evergreen subtropical forests at sub-pixel level. By using the 2013 land cover (using MLC) to mask non-forested portions before sub-pixel classification (using MTMF), the proportional maps were a product of two classifiers. The proportional maps show higher proportions of evergreen forests along the coast while semi-deciduous subtropical forest species were mainly on inland parts of the Wild Coast. These maps had high accuracy, thereby proving the ability of an integration of field spectral and multispectral data in mapping semi-deciduous and evergreen forest species. Overall, the study has demonstrated the importance of the MLC and LDA and served to integrate field spectral and multispectral data in subtropical forest characterisation at both leaf and top-of-atmosphere levels. The success of both the MLC and LDA further highlighted how essential parametric classifiers are in remote sensing forestry applications. Main subtropical characteristics highlighted in this study were species discrimination at leaf level, quantifying forest change at pixel level and discriminating semi-deciduous and evergreen forests at sub-pixel level.
- Full Text:
- Date Issued: 2015
Incidence of bacterial infections and colonisation in patients admitted to a tuberculosis hospital
- Authors: Annear, Dale John
- Date: 2018
- Subjects: Medical microbiology , Microbiology Bacteriology Tuberculosis -- Hospitals -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21482 , vital:29526
- Description: Patients with drug resistant tuberculosis (TB) are treated with multiple antibiotics including moxifloxacin, linezolid, and meropenem, which puts them at greater risk for colonisation by multi-drug resistant (MDR) bacteria. The objectives of this study were to: (i) assess the antimicrobial prescribing patterns practiced within the hospital by retrospective patient file review; (ii) determine the spectrum of bacterial colonisation in TB patients upon admission and during hospitalisation; (iii) identify bacterial isolates and evaluate antimicrobial susceptibility profiles; (iv) detect antimicrobial resistance genes in the bacterial isolates by PCR and DNA sequencing; and (v) investigate genetic relatedness of Klebsiella pneumoniae isolates using Multi Locus Sequence Typing. Nasal, groin and rectal swabs [for the detection of extended spectrum beta lactamases (EBSLs), carbapenem-resistant Enterobacteriaceae (CRE), vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA)] were analysed from a cohort of patients (n=37) admitted either from the community (n = 28) or from other healthcare facilities (n=9) to a TB hospital. Swab samples were collected at admission and at four week intervals thereafter during hospitalization. Identification and antimicrobial susceptibility testing of bacterial isolates (n=62) were determined at the National Health Laboratory Services (NHLS) by the VITEK-MS and Vitek 2 systems respectively. Additional antimicrobial susceptibility testing was conducted by Sensititre Gram Negative Xtra (GNFX2) MIC plates. PCR and DNA sequencing were used for detection of resistance genes. Patients (n=13/37; 35%) were colonized by MDR bacteria (ESBLs [n=11], MRSA [n=2]) on admission. Colonization rates were lower in patients admitted from the community (9/28; 32%) compared to those transferred from other healthcare facilities (4/9; 44%). All admitted patients who did not exhibit colonization at baseline and who were resident within the hospital for longer than 4 weeks (17/37; 46% of total patients) became colonised by an ESBL-producing Enterobacteriaceae species. No patients acquired MRSA during hospitalisation. Among ESBL Enterobacteriaceae, Escherichia coli (41/62; 66%) and K. pneumoniae [14/62; 23%]) predominated. Nineteen percent (7/37) of patients demised during their hospitalization. Both the Vitek system and Sensititre Gram Negative Xtra (GNFX2) MIC plates susceptibilities were similar for most antimicrobials, however there were discrepancies for tigecycline susceptibility profiles. A high number of isolates exhibited resistance to aminoglycosides and fluoroquinolones. Genes encoding for ESBLs (CTX-M-14, CTX-M-15, SHV-28, OXA-1, and OXY-2-9) were detected among ESBL Enterobacteriaceae. Two Enterobacteriaceae isolates with reduced carbapenem susceptibility did not contain carbapenemase-encoding genes. MLST revealed unique sequence types and genetic diversity among the K. pneumoniae isolates from hospitalised patients. However, the source and colonization routes of these isolates could not be determined, which requires further investigation. This study provides insight into the spectrum of bacterial pathogen colonisation in hospitalised TB patients and suggests a review of infection control programs and practices at the TB hospital.
- Full Text:
- Date Issued: 2018
- Authors: Annear, Dale John
- Date: 2018
- Subjects: Medical microbiology , Microbiology Bacteriology Tuberculosis -- Hospitals -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21482 , vital:29526
- Description: Patients with drug resistant tuberculosis (TB) are treated with multiple antibiotics including moxifloxacin, linezolid, and meropenem, which puts them at greater risk for colonisation by multi-drug resistant (MDR) bacteria. The objectives of this study were to: (i) assess the antimicrobial prescribing patterns practiced within the hospital by retrospective patient file review; (ii) determine the spectrum of bacterial colonisation in TB patients upon admission and during hospitalisation; (iii) identify bacterial isolates and evaluate antimicrobial susceptibility profiles; (iv) detect antimicrobial resistance genes in the bacterial isolates by PCR and DNA sequencing; and (v) investigate genetic relatedness of Klebsiella pneumoniae isolates using Multi Locus Sequence Typing. Nasal, groin and rectal swabs [for the detection of extended spectrum beta lactamases (EBSLs), carbapenem-resistant Enterobacteriaceae (CRE), vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA)] were analysed from a cohort of patients (n=37) admitted either from the community (n = 28) or from other healthcare facilities (n=9) to a TB hospital. Swab samples were collected at admission and at four week intervals thereafter during hospitalization. Identification and antimicrobial susceptibility testing of bacterial isolates (n=62) were determined at the National Health Laboratory Services (NHLS) by the VITEK-MS and Vitek 2 systems respectively. Additional antimicrobial susceptibility testing was conducted by Sensititre Gram Negative Xtra (GNFX2) MIC plates. PCR and DNA sequencing were used for detection of resistance genes. Patients (n=13/37; 35%) were colonized by MDR bacteria (ESBLs [n=11], MRSA [n=2]) on admission. Colonization rates were lower in patients admitted from the community (9/28; 32%) compared to those transferred from other healthcare facilities (4/9; 44%). All admitted patients who did not exhibit colonization at baseline and who were resident within the hospital for longer than 4 weeks (17/37; 46% of total patients) became colonised by an ESBL-producing Enterobacteriaceae species. No patients acquired MRSA during hospitalisation. Among ESBL Enterobacteriaceae, Escherichia coli (41/62; 66%) and K. pneumoniae [14/62; 23%]) predominated. Nineteen percent (7/37) of patients demised during their hospitalization. Both the Vitek system and Sensititre Gram Negative Xtra (GNFX2) MIC plates susceptibilities were similar for most antimicrobials, however there were discrepancies for tigecycline susceptibility profiles. A high number of isolates exhibited resistance to aminoglycosides and fluoroquinolones. Genes encoding for ESBLs (CTX-M-14, CTX-M-15, SHV-28, OXA-1, and OXY-2-9) were detected among ESBL Enterobacteriaceae. Two Enterobacteriaceae isolates with reduced carbapenem susceptibility did not contain carbapenemase-encoding genes. MLST revealed unique sequence types and genetic diversity among the K. pneumoniae isolates from hospitalised patients. However, the source and colonization routes of these isolates could not be determined, which requires further investigation. This study provides insight into the spectrum of bacterial pathogen colonisation in hospitalised TB patients and suggests a review of infection control programs and practices at the TB hospital.
- Full Text:
- Date Issued: 2018
Passive acoustic monitoring of coastal dolphins (Sousa plumbea and Tursiops aduncus) in Plettenberg Bay: temporal patterns and group dynamics
- Authors: Hlati, Kuhle
- Date: 2018
- Subjects: Marine mammals -- Effect of noise on -- Research , Oceanography Aquatic ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/30050 , vital:30813
- Description: In this study, passive acoustic monitoring (PAM) was used to investigate the diel patterns of occurrence and activities of coastal dolphins (Sousa plumbea and Tursiops aduncus) in Plettenberg Bay, during April 2015 - July 2017. Automatic detectors were used to extract dolphin whistles and echolocation clicks from the acoustic recordings. The vocalizations were extracted without identifying the dolphin species due to insufficient visual observation data collected concurrent with the acoustic recordings to conclusively discriminate the two species. The correct detection performance and false alarm rate of the detectors for each acoustic recorder were evaluated and automatic detection protocols were developed. For a recorder that was initially deployed in the study (DSG recorder), the detectors achieved 64 - 80% true detection rates with false alarm rates of 10 - 22%. A more modern recorder (MicroMARS recorder) which replaced this one had a lower signal-to-noise ratio (SNR) and could sample at a higher frequency, the detectors achieved greater than 80% true detection rates and less than 5% false alarm rates. It was evident that SNR and sampling rate influenced the detection performance of the detectors. When acoustic recordings were compared to visual observations which were conducted concurrently with some of the recordings, it was apparent that acoustic recorders performed nearly twice as well as land-based observers in terms of overall detection of dolphin groups. Group size and behaviour affected acoustic detection rates of dolphins; large groups that were visually detected and which were foraging at the time, were more likely to be acoustically detected than small groups or single animals or groups associated travelling at the time. The detection rates of echolocation clicks and whistles showed a diel pattern of occurrence of coastal dolphins in Plettenberg Bay with a higher nighttime than daytime occurrence. The detection rates were higher from midday to midnight with a peak during dusk. The high activity of dolphins in the late afternoon and evening reported in this study was also supported by visual data (afternoons) in the area and acoustic studies in other regions. Comparison of acoustic detection rates and visual data from this study with past observations suggest that the occurrence patterns of T. aduncus in the bay appear to have changed; such a change may be influenced by changes in prey behaviour or distribution, or other factors. The significally higher detection rates of echolocation clicks than whistles and dominant foraging behaviour based on visual data suggest that Robberg may be an important feeding ground for the coastal dolphins that are frequenting Plettenberg Bay. The current study builds on a growing body of literature demonstrating that PAM and automatic detectors are powerful and effective tools for monitoring cetacean species. However, there are several factors that limit the detection of vocalization such as direction of the sound source, distance from hydrophone, sound propagation conditions, low SNR and acoustic masking. Regardless of these limitations, results from PAM showed diel patterns of occurrence of the coastal dolphins in the bay which could have not been achieved from visual monitoring, in particular the high nighttime occurrence patterns. PAM holds potential to be largely utilized in South Africa for dolphin and other cetacean studies. Further research and monitoring using PAM could potentially assist to better understand the drivers of the dolphin occurrence and activity patterns in the bay.
- Full Text:
- Date Issued: 2018
- Authors: Hlati, Kuhle
- Date: 2018
- Subjects: Marine mammals -- Effect of noise on -- Research , Oceanography Aquatic ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/30050 , vital:30813
- Description: In this study, passive acoustic monitoring (PAM) was used to investigate the diel patterns of occurrence and activities of coastal dolphins (Sousa plumbea and Tursiops aduncus) in Plettenberg Bay, during April 2015 - July 2017. Automatic detectors were used to extract dolphin whistles and echolocation clicks from the acoustic recordings. The vocalizations were extracted without identifying the dolphin species due to insufficient visual observation data collected concurrent with the acoustic recordings to conclusively discriminate the two species. The correct detection performance and false alarm rate of the detectors for each acoustic recorder were evaluated and automatic detection protocols were developed. For a recorder that was initially deployed in the study (DSG recorder), the detectors achieved 64 - 80% true detection rates with false alarm rates of 10 - 22%. A more modern recorder (MicroMARS recorder) which replaced this one had a lower signal-to-noise ratio (SNR) and could sample at a higher frequency, the detectors achieved greater than 80% true detection rates and less than 5% false alarm rates. It was evident that SNR and sampling rate influenced the detection performance of the detectors. When acoustic recordings were compared to visual observations which were conducted concurrently with some of the recordings, it was apparent that acoustic recorders performed nearly twice as well as land-based observers in terms of overall detection of dolphin groups. Group size and behaviour affected acoustic detection rates of dolphins; large groups that were visually detected and which were foraging at the time, were more likely to be acoustically detected than small groups or single animals or groups associated travelling at the time. The detection rates of echolocation clicks and whistles showed a diel pattern of occurrence of coastal dolphins in Plettenberg Bay with a higher nighttime than daytime occurrence. The detection rates were higher from midday to midnight with a peak during dusk. The high activity of dolphins in the late afternoon and evening reported in this study was also supported by visual data (afternoons) in the area and acoustic studies in other regions. Comparison of acoustic detection rates and visual data from this study with past observations suggest that the occurrence patterns of T. aduncus in the bay appear to have changed; such a change may be influenced by changes in prey behaviour or distribution, or other factors. The significally higher detection rates of echolocation clicks than whistles and dominant foraging behaviour based on visual data suggest that Robberg may be an important feeding ground for the coastal dolphins that are frequenting Plettenberg Bay. The current study builds on a growing body of literature demonstrating that PAM and automatic detectors are powerful and effective tools for monitoring cetacean species. However, there are several factors that limit the detection of vocalization such as direction of the sound source, distance from hydrophone, sound propagation conditions, low SNR and acoustic masking. Regardless of these limitations, results from PAM showed diel patterns of occurrence of the coastal dolphins in the bay which could have not been achieved from visual monitoring, in particular the high nighttime occurrence patterns. PAM holds potential to be largely utilized in South Africa for dolphin and other cetacean studies. Further research and monitoring using PAM could potentially assist to better understand the drivers of the dolphin occurrence and activity patterns in the bay.
- Full Text:
- Date Issued: 2018
The synthesis, empirical and theoretical studies of various (N→B) diarylborinate esters
- Authors: Manana, Pholani Sakhile
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/53869 , vital:46027
- Description: A series of core-functionalized borinic acids was synthesized from Grignard reagents and tributylborate and reacted with ethanolamine, amino acids, 2-pyridylmethanol as well as 2-(ethyl amino ethanol). Among the borinic acids synthesized were the ones bearing: para-(2, 15, 16, 22, 27)-methyl, (3, 20, 25)-chloro, (4, 23, 26)-fluoro, (5)-methoxy; meta-(7, 17)-methyl, (9)-fluoro; ortho-(6)-methyl, (8)-chloro, (10, 18, 19)-methoxy substituents on their respective aromatic systems. All compounds obtained by condensation of the borinic acids with the aforementioned nitrogen-containing substrates were characterized structurally by means of diffraction studies based on single crystals and found to constitute chelate esters/amides featuring covalent B-O and dative N→B bonds. The chelate compounds researched in this study could be classified into four families and represent the compounds: ethanol amine: (1) 2,2-diphenyl-1,3,2-oxazaborolidines, (2) 2,2-bis(p-tolyl)-1,3,2-oxazaborolidines, (3) 2,2-bis(p-chlorophenyl)-1,3,2-oxazaborolidines, (4) 2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines, (5) 2,2-bis(p-methoxyphenyl)-1,3,2-oxazaborolidines, (6) 2,2-bis(o-tolyl)-1,3,2-oxazaborolidines, (7) 2,2-bis(m-tolyl)-1,3,2-oxazaborolidines, (8) 2,2-bis(o-chlorophenyl)-1,3,2-oxazaborolidines, (9) 2,2-bis(m-fluorophenyl)-1,3,2-oxazaborolidines, (10) 2,2-bis(o-methoxyphenyl)-1,3,2-oxazaborolidines. α-amino acids : (14) 4-methyl-2,2-diphenyl-1,3,2-oxazaborolidin-5-ones, (15) 2,2-bis(p-tolyl)-1,3,2-oxazaborolidin-5-ones, (16) 4-methyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidin-5-ones, (17) 4-isopropyl-2,2-bis(m-tolyl)-1,3,2-oxazaborolidin-5-ones, (18) 4-methyl-2,2-bis(o-methoxyphenyl)-1,3,2- oxazaborolidin-5-ones, (19) 4-acetamidyl-2,2-bis(o-methoxyphenyl)-1,3,2- oxazaborolidin-5-ones, (20) 4-phenylethane-2,2-bis(p-chlorophenyl)-1,3,2 oxazaborolidin-5-ones. 2-pyridylmethanol: (21) 1,3-hydroxypyridyl-2,2-diphenyl 1,3,2-oxazaborolidines, (22) 1,3-hydroxypyridyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidines, (23) 1,3-hydroxypyridyl-2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines 2-(ethyl amino ethanol): (24) 3-ethyl-2,2-diphenyl-1,3,2-oxazaborolidines, (25) 3-ethyl-2,2-bis(p-chlorophenyl)-1,3,2-oxazaborolidines, (26) 3-ethyl-2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines, (27) 3-ethyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidines. Apart from structural studies in the solid state, the compounds were also characterized by means of multinuclear NMR spectroscopy (1H, 11B, 13C) as well as UV/vis and FTIR. The typical 11B resonances were found in the range of (4-10 ppm). A series of characteristic metrical parameters for the compounds in the solid state as well as typical NMR shifts for the chelate target molecules was established that allowed for the determination of the coordination induced shift. The carbon atom bonded to the oxygen atom shifted upfield, while the carbon atom bonded to the nitrogen atom shifted downfield. Factors mentioned in the literature that has an influence on the hydrolytic stability on the heterocyclic borinate motif have been taken into consideration and verified for the systems researched in this study. The substitution at the nitrogen atom with one ethyl group caused the greatest increases in the N→B bond length (27) 1.714 Å, due to the increase in the nitrogen Lewis basicity, making it the least hydrolytically stable, these include compounds (24-26). Furthermore, DFT calculations were performed by employing Becke’s three parameter hybrid exchange functional with Lee–Yang–Parr functional (B3LYP) method using the Gaussian 16 program package (Rev. B01) employing the basis set 6-311++G(d,p), to corroborate and correlate the experimental findings, which gave a general R-squared value of 0.9978 for calculated vs experimental 13C chemical shifts. Thermal properties are recorded for select compounds, indicating the ΔH and the melting points. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Manana, Pholani Sakhile
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/53869 , vital:46027
- Description: A series of core-functionalized borinic acids was synthesized from Grignard reagents and tributylborate and reacted with ethanolamine, amino acids, 2-pyridylmethanol as well as 2-(ethyl amino ethanol). Among the borinic acids synthesized were the ones bearing: para-(2, 15, 16, 22, 27)-methyl, (3, 20, 25)-chloro, (4, 23, 26)-fluoro, (5)-methoxy; meta-(7, 17)-methyl, (9)-fluoro; ortho-(6)-methyl, (8)-chloro, (10, 18, 19)-methoxy substituents on their respective aromatic systems. All compounds obtained by condensation of the borinic acids with the aforementioned nitrogen-containing substrates were characterized structurally by means of diffraction studies based on single crystals and found to constitute chelate esters/amides featuring covalent B-O and dative N→B bonds. The chelate compounds researched in this study could be classified into four families and represent the compounds: ethanol amine: (1) 2,2-diphenyl-1,3,2-oxazaborolidines, (2) 2,2-bis(p-tolyl)-1,3,2-oxazaborolidines, (3) 2,2-bis(p-chlorophenyl)-1,3,2-oxazaborolidines, (4) 2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines, (5) 2,2-bis(p-methoxyphenyl)-1,3,2-oxazaborolidines, (6) 2,2-bis(o-tolyl)-1,3,2-oxazaborolidines, (7) 2,2-bis(m-tolyl)-1,3,2-oxazaborolidines, (8) 2,2-bis(o-chlorophenyl)-1,3,2-oxazaborolidines, (9) 2,2-bis(m-fluorophenyl)-1,3,2-oxazaborolidines, (10) 2,2-bis(o-methoxyphenyl)-1,3,2-oxazaborolidines. α-amino acids : (14) 4-methyl-2,2-diphenyl-1,3,2-oxazaborolidin-5-ones, (15) 2,2-bis(p-tolyl)-1,3,2-oxazaborolidin-5-ones, (16) 4-methyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidin-5-ones, (17) 4-isopropyl-2,2-bis(m-tolyl)-1,3,2-oxazaborolidin-5-ones, (18) 4-methyl-2,2-bis(o-methoxyphenyl)-1,3,2- oxazaborolidin-5-ones, (19) 4-acetamidyl-2,2-bis(o-methoxyphenyl)-1,3,2- oxazaborolidin-5-ones, (20) 4-phenylethane-2,2-bis(p-chlorophenyl)-1,3,2 oxazaborolidin-5-ones. 2-pyridylmethanol: (21) 1,3-hydroxypyridyl-2,2-diphenyl 1,3,2-oxazaborolidines, (22) 1,3-hydroxypyridyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidines, (23) 1,3-hydroxypyridyl-2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines 2-(ethyl amino ethanol): (24) 3-ethyl-2,2-diphenyl-1,3,2-oxazaborolidines, (25) 3-ethyl-2,2-bis(p-chlorophenyl)-1,3,2-oxazaborolidines, (26) 3-ethyl-2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines, (27) 3-ethyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidines. Apart from structural studies in the solid state, the compounds were also characterized by means of multinuclear NMR spectroscopy (1H, 11B, 13C) as well as UV/vis and FTIR. The typical 11B resonances were found in the range of (4-10 ppm). A series of characteristic metrical parameters for the compounds in the solid state as well as typical NMR shifts for the chelate target molecules was established that allowed for the determination of the coordination induced shift. The carbon atom bonded to the oxygen atom shifted upfield, while the carbon atom bonded to the nitrogen atom shifted downfield. Factors mentioned in the literature that has an influence on the hydrolytic stability on the heterocyclic borinate motif have been taken into consideration and verified for the systems researched in this study. The substitution at the nitrogen atom with one ethyl group caused the greatest increases in the N→B bond length (27) 1.714 Å, due to the increase in the nitrogen Lewis basicity, making it the least hydrolytically stable, these include compounds (24-26). Furthermore, DFT calculations were performed by employing Becke’s three parameter hybrid exchange functional with Lee–Yang–Parr functional (B3LYP) method using the Gaussian 16 program package (Rev. B01) employing the basis set 6-311++G(d,p), to corroborate and correlate the experimental findings, which gave a general R-squared value of 0.9978 for calculated vs experimental 13C chemical shifts. Thermal properties are recorded for select compounds, indicating the ΔH and the melting points. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text:
- Date Issued: 2021-12
Impact of fracking fluid on Karoo plants based on field and greenhouse experiments
- Authors: Liddell, Duncan Carlyle
- Date: 2020
- Subjects: Plants -- South Africa -- Little Karoo , Desert ecology -- South Africa Great Karoo (South Africa)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49125 , vital:41603
- Description: Fracking fluid has been indicated to be detrimental to vegetation. In forest vegetation the fracking fluid caused ground vegetation to be extensively damaged with high mortality rates and trees showing premature leaf loss following application. A study by Martin (2017) investigated these effects on Karoo vegetation in a greenhouse and found it to increase stress and reduced the growth with some life forms being identified as sensitive. The current study followed on the work of Martin testing additional species in the same greenhouse and applying different treatments of fracking fluid to Karoo vegetation in their habitat. The plants were monitored by measuring their height, photosynthetic efficiency (stress), biomass allocation and the temperature of the sites. The greenhouse plants had increased growth associated with repeated fracking fluid treatments while having variable stress levels with different treatments of the fracking fluid. The farm had mixed results being generally more stressed due to the treatments, the repeated fracking fluid treatments showed greater growth. The farm vegetation was more sensitive due to prolonged drought which is suspected to play a large role in the different response to fracking fluid between the two sites. The several hypotheses based on the finding of Martin (2017) were not supported by the data in this study. However, the application of fracking fluid did affect the tree species as they were found to be sensitive, while the other plant species was generally stressed after the applications. The greenhouse study cannot accurately represent the effects of fracking fluid on the farm vegetation, due to the large difference in the environment thus, more field studies would need to be conducted to determine the effects of fracking fluid.
- Full Text:
- Date Issued: 2020
- Authors: Liddell, Duncan Carlyle
- Date: 2020
- Subjects: Plants -- South Africa -- Little Karoo , Desert ecology -- South Africa Great Karoo (South Africa)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49125 , vital:41603
- Description: Fracking fluid has been indicated to be detrimental to vegetation. In forest vegetation the fracking fluid caused ground vegetation to be extensively damaged with high mortality rates and trees showing premature leaf loss following application. A study by Martin (2017) investigated these effects on Karoo vegetation in a greenhouse and found it to increase stress and reduced the growth with some life forms being identified as sensitive. The current study followed on the work of Martin testing additional species in the same greenhouse and applying different treatments of fracking fluid to Karoo vegetation in their habitat. The plants were monitored by measuring their height, photosynthetic efficiency (stress), biomass allocation and the temperature of the sites. The greenhouse plants had increased growth associated with repeated fracking fluid treatments while having variable stress levels with different treatments of the fracking fluid. The farm had mixed results being generally more stressed due to the treatments, the repeated fracking fluid treatments showed greater growth. The farm vegetation was more sensitive due to prolonged drought which is suspected to play a large role in the different response to fracking fluid between the two sites. The several hypotheses based on the finding of Martin (2017) were not supported by the data in this study. However, the application of fracking fluid did affect the tree species as they were found to be sensitive, while the other plant species was generally stressed after the applications. The greenhouse study cannot accurately represent the effects of fracking fluid on the farm vegetation, due to the large difference in the environment thus, more field studies would need to be conducted to determine the effects of fracking fluid.
- Full Text:
- Date Issued: 2020
Continuous flow synthesis of a key intermediate towards the antidiabetic drug repaglinide
- Authors: Williams, Arushan
- Date: 2023-04
- Subjects: Diabetes -- Miscellanea -- South Africa , Diabetes –Treatment
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61064 , vital:69715
- Description: Across the world, diabetes is one of the leading causes of deaths attributed to noncommunicable diseases (NCDs). In Africa, a huge proportion of African countries’ annual healthcare budgets are consumed by diabetes (7 %) with many already experiencing healthcare budget deficits. The prevalence of diabetes is rapidly growing and threatens the economic productivity and livelihood of many families within the region. The world leaders have invested heavily in reducing the pandemic by focusing on increasing the availability of affordable essential medicines in developing countries. The majority of diabetes cases are due to type 2 diabetes (90 %) and may be treated using oral hypoglycaemic drugs (OHDs). Repaglinide (REP) is a non-sulfonylurea insulin secretagogue (meglitinide) with greater HbA1c reduction than metformin in newly onset type 2 diabetic patients, however due to the high price of REP outside Asia, cheaper and less effective OHDs are prescribed to patients. Many of the reported synthetic routes towards REP utilize a key intermediate, 2-(3-ethoxy-4- iethoxycarbonyl)phenyl)acetic acid. The key intermediate contributes significantly to the price of REP as many of the intermediate’s synthetic routes suffer from long reaction times, low yields and industrial complex approaches. Therefore, this has prompted us to investigate an efficient process towards the synthesis of 2-(3-ethoxy-4-(ethoxycarbonyl)phenyl)acetic acid using multiple continuous flow systems. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Williams, Arushan
- Date: 2023-04
- Subjects: Diabetes -- Miscellanea -- South Africa , Diabetes –Treatment
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61064 , vital:69715
- Description: Across the world, diabetes is one of the leading causes of deaths attributed to noncommunicable diseases (NCDs). In Africa, a huge proportion of African countries’ annual healthcare budgets are consumed by diabetes (7 %) with many already experiencing healthcare budget deficits. The prevalence of diabetes is rapidly growing and threatens the economic productivity and livelihood of many families within the region. The world leaders have invested heavily in reducing the pandemic by focusing on increasing the availability of affordable essential medicines in developing countries. The majority of diabetes cases are due to type 2 diabetes (90 %) and may be treated using oral hypoglycaemic drugs (OHDs). Repaglinide (REP) is a non-sulfonylurea insulin secretagogue (meglitinide) with greater HbA1c reduction than metformin in newly onset type 2 diabetic patients, however due to the high price of REP outside Asia, cheaper and less effective OHDs are prescribed to patients. Many of the reported synthetic routes towards REP utilize a key intermediate, 2-(3-ethoxy-4- iethoxycarbonyl)phenyl)acetic acid. The key intermediate contributes significantly to the price of REP as many of the intermediate’s synthetic routes suffer from long reaction times, low yields and industrial complex approaches. Therefore, this has prompted us to investigate an efficient process towards the synthesis of 2-(3-ethoxy-4-(ethoxycarbonyl)phenyl)acetic acid using multiple continuous flow systems. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-04
The photodecomposition of different polymorphic forms of 1,4-dihydropyridine channel blockers
- Authors: Francis, Farzaana
- Date: 2011
- Subjects: Photodegradation , Nifedipine , Nimodipine , Dihydropyridine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10378 , http://hdl.handle.net/10948/1496 , Photodegradation , Nifedipine , Nimodipine , Dihydropyridine
- Description: 1,4-Dihydropyridines (DHPs) are a classification of compounds used as calcium channel blockers in the treatment of various conditions. These compounds readily undergo photodegradation. The degradants produced have no pharmaceutical activity and render the drugs ineffective. DHPs also exhibit polymorphism. Nifedipine and Nimodipine are two such drugs. This study aimed to monitor the photodegradation of these two drugs and to establish the effect of particle size, polymorphism and β-Cyclodextrin (β-CD) on the rate of photodegradation. Different polymorphs (namely the amorphous and stable crystalline polymorphs) of the two drugs were prepared for use in the study. Mixtures of each drug with β-CD were also prepared for photostability studies. The mixtures were prepared in a 1:1 molar ratio. The rate of photodegradation was studied with a 500 W metal halide lamp in accordance to ICH guidelines. The study employed samples on a small scale where degradation was analysed with High Performance Liquid Chromatography, and also samples on a larger scale where degradation was monitored with Powder X-ray Diffraction. The two sets of results of observing the degradation process by two analytical techniques where compared in terms of their quantification methods. The extent of photodegradation was suitably modelled and fitted using the Avrami-Erofeyev kinetic equation. Smaller particle size showed increased photodegradation for Nimodipine; the effect was insignificant for Nifedipine however. For both drugs it was found that the amorphous polymorph underwent faster photodegradation. The study showed that β-CD caused an increase in photodegradation for both drugs under these experimental conditions.
- Full Text:
- Date Issued: 2011
- Authors: Francis, Farzaana
- Date: 2011
- Subjects: Photodegradation , Nifedipine , Nimodipine , Dihydropyridine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10378 , http://hdl.handle.net/10948/1496 , Photodegradation , Nifedipine , Nimodipine , Dihydropyridine
- Description: 1,4-Dihydropyridines (DHPs) are a classification of compounds used as calcium channel blockers in the treatment of various conditions. These compounds readily undergo photodegradation. The degradants produced have no pharmaceutical activity and render the drugs ineffective. DHPs also exhibit polymorphism. Nifedipine and Nimodipine are two such drugs. This study aimed to monitor the photodegradation of these two drugs and to establish the effect of particle size, polymorphism and β-Cyclodextrin (β-CD) on the rate of photodegradation. Different polymorphs (namely the amorphous and stable crystalline polymorphs) of the two drugs were prepared for use in the study. Mixtures of each drug with β-CD were also prepared for photostability studies. The mixtures were prepared in a 1:1 molar ratio. The rate of photodegradation was studied with a 500 W metal halide lamp in accordance to ICH guidelines. The study employed samples on a small scale where degradation was analysed with High Performance Liquid Chromatography, and also samples on a larger scale where degradation was monitored with Powder X-ray Diffraction. The two sets of results of observing the degradation process by two analytical techniques where compared in terms of their quantification methods. The extent of photodegradation was suitably modelled and fitted using the Avrami-Erofeyev kinetic equation. Smaller particle size showed increased photodegradation for Nimodipine; the effect was insignificant for Nifedipine however. For both drugs it was found that the amorphous polymorph underwent faster photodegradation. The study showed that β-CD caused an increase in photodegradation for both drugs under these experimental conditions.
- Full Text:
- Date Issued: 2011