Ecological assessment and biogeography of coastal vegetation and flora in southern Mozambique
- Authors: Massingue, Alice Obed
- Date: 2019
- Subjects: Coastal plants -- Mozambique , Coastal plants Marine biodiversity -- Mozambique Coastal biodiversity -- Mozambique
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/40988 , vital:36280
- Description: This study considered aspects of the vegetation of the coastal zone of southern Mozambique, an area with a rich biodiversity. The vegetation and flora were assessed in their current state including the associated anthropogenic pressures. The environmental conditions that determined the distribution of the vegetation were evaluated. A hierarchical classification, description and ecological interpretation of the vegetation and flora of the coastal zone in southern Mozambique are presented. Analysis was based on 242 sample quadrats that were distributed in a stratified manner throughout the study area. The vegetation could be grouped into six distinct types of vegetation: Dune Forest, Coastal Forest, Coastal Grassland, Coastal Miombo, Coastal Savanna and Coastal Woodland. Species diversity was high for the all the vegetation types, particularly in the woody elements. A total of 673 species in 410 genera was recorded. They represented 104 families with Fabaceae and Rubiaceae being the most common. Of these, 6.6% were endemic or near-endemic to the coastal zone of southern Mozambique with Coastal Forest being the habitat with the greatest endemism. All soils from different vegetation types had poor agricultural potential. Soil properties were the strongest defining environmental feature separating the vegetation types: e.g. pH was high in Dune Forest compared to the others. Results from Maxent modelling suggest that the distribution of endemic species is influenced by a combination of climatic and non-climatic variables. Soil type, temperature annual range and precipitation of the driest month were the most important predictor variables. Overlaying the potential distributions of the seven selected species indicated two areas of abundance of endemic species – these should be given attention for conservation. Endemic species are not well protected in southern Mozambique – their sampled and potential habitats are largely outside protected areas. Hence, additional reserves should be created to improve their protection. Most endemic and near-endemics species were found in the south, from Ponta de Ouro (Matutuine, south of Maputo Province) to Manhica district (north of the Maputo Province) forming part of the Maputaland Centre of Endemism. A second concentration of endemism was found in the Inhambane Province, specifically the Inhassoro and Vilanculos districts. This is proposed to be an Important Plants Area (IPA). Because most endemics and near-endemics are found in the Coastal Forest, their main threat is harvesting for charcoal production, although none of the endemic species are specifically targeted for charcoal production. In Inhambane they are also threatened by the tourism industry, agriculture and settlements. The impact of the habitat destruction on endemic species is expected to cause severe declines in the near future. The tourism industry and harvesting of trees for charcoal production and over-frequent fires are the main drivers of vegetation loss in this region. Shifting agriculture, harvesting for firewood and construction materials, cattle grazing (at a minor scale) are also impacts, but these were only observed in a small area of Maputo Province. Although the study was done in coastal zone of southern Mozambique, effective management of whole coastal zone of the country will be required to maintain a functioning and diverse ecosystem. Priorities for management are to ensure that forests are protected, in particular, Dune Forest. Actions are required to minimise degradation of coastal vegetation. Further research on Coastal Forest restoration should be planned, as field observations in this study confirm that forest in the coastal zone of southern Mozambique has resilience.
- Full Text:
- Date Issued: 2019
- Authors: Massingue, Alice Obed
- Date: 2019
- Subjects: Coastal plants -- Mozambique , Coastal plants Marine biodiversity -- Mozambique Coastal biodiversity -- Mozambique
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/40988 , vital:36280
- Description: This study considered aspects of the vegetation of the coastal zone of southern Mozambique, an area with a rich biodiversity. The vegetation and flora were assessed in their current state including the associated anthropogenic pressures. The environmental conditions that determined the distribution of the vegetation were evaluated. A hierarchical classification, description and ecological interpretation of the vegetation and flora of the coastal zone in southern Mozambique are presented. Analysis was based on 242 sample quadrats that were distributed in a stratified manner throughout the study area. The vegetation could be grouped into six distinct types of vegetation: Dune Forest, Coastal Forest, Coastal Grassland, Coastal Miombo, Coastal Savanna and Coastal Woodland. Species diversity was high for the all the vegetation types, particularly in the woody elements. A total of 673 species in 410 genera was recorded. They represented 104 families with Fabaceae and Rubiaceae being the most common. Of these, 6.6% were endemic or near-endemic to the coastal zone of southern Mozambique with Coastal Forest being the habitat with the greatest endemism. All soils from different vegetation types had poor agricultural potential. Soil properties were the strongest defining environmental feature separating the vegetation types: e.g. pH was high in Dune Forest compared to the others. Results from Maxent modelling suggest that the distribution of endemic species is influenced by a combination of climatic and non-climatic variables. Soil type, temperature annual range and precipitation of the driest month were the most important predictor variables. Overlaying the potential distributions of the seven selected species indicated two areas of abundance of endemic species – these should be given attention for conservation. Endemic species are not well protected in southern Mozambique – their sampled and potential habitats are largely outside protected areas. Hence, additional reserves should be created to improve their protection. Most endemic and near-endemics species were found in the south, from Ponta de Ouro (Matutuine, south of Maputo Province) to Manhica district (north of the Maputo Province) forming part of the Maputaland Centre of Endemism. A second concentration of endemism was found in the Inhambane Province, specifically the Inhassoro and Vilanculos districts. This is proposed to be an Important Plants Area (IPA). Because most endemics and near-endemics are found in the Coastal Forest, their main threat is harvesting for charcoal production, although none of the endemic species are specifically targeted for charcoal production. In Inhambane they are also threatened by the tourism industry, agriculture and settlements. The impact of the habitat destruction on endemic species is expected to cause severe declines in the near future. The tourism industry and harvesting of trees for charcoal production and over-frequent fires are the main drivers of vegetation loss in this region. Shifting agriculture, harvesting for firewood and construction materials, cattle grazing (at a minor scale) are also impacts, but these were only observed in a small area of Maputo Province. Although the study was done in coastal zone of southern Mozambique, effective management of whole coastal zone of the country will be required to maintain a functioning and diverse ecosystem. Priorities for management are to ensure that forests are protected, in particular, Dune Forest. Actions are required to minimise degradation of coastal vegetation. Further research on Coastal Forest restoration should be planned, as field observations in this study confirm that forest in the coastal zone of southern Mozambique has resilience.
- Full Text:
- Date Issued: 2019
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
A comparative study of artificial neural networks and physics models as simulators in evolutionary robotics
- Pretorius, Christiaan Johannes
- Authors: Pretorius, Christiaan Johannes
- Date: 2019
- Subjects: Neural networks (Computer science)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/30789 , vital:31131
- Description: The Evolutionary Robotics (ER) process is a technique that applies evolutionary optimization algorithms to the task of automatically developing, or evolving, robotic control programs. These control programs, or simply controllers, are evolved in order to allow a robot to perform a required task. During the ER process, use is often made of robotic simulators to evaluate the performance of candidate controllers that are produced in the course of the controller evolution process. Such simulators accelerate and otherwise simplify the controller evolution process, as opposed to the more arduous process of evaluating controllers in the real world without use of simulation. To date, the vast majority of simulators that have been applied in ER are physics- based models which are constructed by taking into account the underlying physics governing the operation of the robotic system in question. An alternative approach to simulator implementation in ER is the usage of Artificial Neural Networks (ANNs) as simulators in the ER process. Such simulators are referred to as Simulator Neural Networks (SNNs). Previous studies have indicated that SNNs can successfully be used as an alter- native to physics-based simulators in the ER process on various robotic platforms. At the commencement of the current study it was not, however, known how this relatively new method of simulation would compare to traditional physics-based simulation approaches in ER. The study presented in this thesis thus endeavoured to quantitatively compare SNNs and physics-based models as simulators in the ER process. In order to con- duct this comparative study, both SNNs and physics simulators were constructed for the modelling of three different robotic platforms: a differentially-steered robot, a wheeled inverted pendulum robot and a hexapod robot. Each of these two types of simulation was then used in simulation-based evolution processes to evolve con- trollers for each robotic platform. During these controller evolution processes, the SNNs and physics models were compared in terms of their accuracy in making pre- dictions of robotic behaviour, their computational efficiency in arriving at these predictions, the human effort required to construct each simulator and, most im- portantly, the real-world performance of controllers evolved by making use of each simulator. The results obtained in this study illustrated experimentally that SNNs were, in the majority of cases, able to make more accurate predictions than the physics- based models and these SNNs were arguably simpler to construct than the physics simulators. Additionally, SNNs were also shown to be a computationally efficient alternative to physics-based simulators in ER and, again in the majority of cases, these SNNs were able to produce controllers which outperformed those evolved in the physics-based simulators, when these controllers were uploaded to the real-world robots. The results of this thesis thus suggest that SNNs are a viable alternative to more commonly-used physics simulators in ER and further investigation of the potential of this simulation technique appears warranted.
- Full Text:
- Date Issued: 2019
- Authors: Pretorius, Christiaan Johannes
- Date: 2019
- Subjects: Neural networks (Computer science)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/30789 , vital:31131
- Description: The Evolutionary Robotics (ER) process is a technique that applies evolutionary optimization algorithms to the task of automatically developing, or evolving, robotic control programs. These control programs, or simply controllers, are evolved in order to allow a robot to perform a required task. During the ER process, use is often made of robotic simulators to evaluate the performance of candidate controllers that are produced in the course of the controller evolution process. Such simulators accelerate and otherwise simplify the controller evolution process, as opposed to the more arduous process of evaluating controllers in the real world without use of simulation. To date, the vast majority of simulators that have been applied in ER are physics- based models which are constructed by taking into account the underlying physics governing the operation of the robotic system in question. An alternative approach to simulator implementation in ER is the usage of Artificial Neural Networks (ANNs) as simulators in the ER process. Such simulators are referred to as Simulator Neural Networks (SNNs). Previous studies have indicated that SNNs can successfully be used as an alter- native to physics-based simulators in the ER process on various robotic platforms. At the commencement of the current study it was not, however, known how this relatively new method of simulation would compare to traditional physics-based simulation approaches in ER. The study presented in this thesis thus endeavoured to quantitatively compare SNNs and physics-based models as simulators in the ER process. In order to con- duct this comparative study, both SNNs and physics simulators were constructed for the modelling of three different robotic platforms: a differentially-steered robot, a wheeled inverted pendulum robot and a hexapod robot. Each of these two types of simulation was then used in simulation-based evolution processes to evolve con- trollers for each robotic platform. During these controller evolution processes, the SNNs and physics models were compared in terms of their accuracy in making pre- dictions of robotic behaviour, their computational efficiency in arriving at these predictions, the human effort required to construct each simulator and, most im- portantly, the real-world performance of controllers evolved by making use of each simulator. The results obtained in this study illustrated experimentally that SNNs were, in the majority of cases, able to make more accurate predictions than the physics- based models and these SNNs were arguably simpler to construct than the physics simulators. Additionally, SNNs were also shown to be a computationally efficient alternative to physics-based simulators in ER and, again in the majority of cases, these SNNs were able to produce controllers which outperformed those evolved in the physics-based simulators, when these controllers were uploaded to the real-world robots. The results of this thesis thus suggest that SNNs are a viable alternative to more commonly-used physics simulators in ER and further investigation of the potential of this simulation technique appears warranted.
- Full Text:
- Date Issued: 2019
A Model for Crime Management in Smart Cities
- Authors: Westraadt, Lindsay
- Date: 2019
- Subjects: Smart cities , Computer networks -- security measures
- Language: English
- Type: Thesis , Doctoral , PHD
- Identifier: http://hdl.handle.net/10948/45635 , vital:38922
- Description: The main research problem addressed in this study is that South African cities are not effectively integrating and utilising available, and rapidly emerging smart city data sources for planning and management. To this end, it was proposed that a predictive model, that assimilates data from traditionally isolated management silos, could be developed for prediction and simulation at the system-of-systems level. As proof of concept, the study focused on only one aspect of smart cities, namely crime management. Subsequently, the main objective of this study was to develop and evaluate a predictive model for crime management in smart cities that effectively integrated data from traditionally isolated management silos. The Design Science Research process was followed to develop and evaluate a prototype model. The practical contributions of this study was the development of a prototype model for integrated decision-making in smart cities, and the associated guidelines for the implementation of the developed modelling approach within the South African IDP context. Theoretically, this work contributed towards the development of a modelling paradigm for effective integrated decision-making in smart cities. This work also contributed towards developing strategic-level predictive policing tools aimed at proactively meeting community needs, and contributed to the body of knowledge regarding complex systems modelling.
- Full Text:
- Date Issued: 2019
- Authors: Westraadt, Lindsay
- Date: 2019
- Subjects: Smart cities , Computer networks -- security measures
- Language: English
- Type: Thesis , Doctoral , PHD
- Identifier: http://hdl.handle.net/10948/45635 , vital:38922
- Description: The main research problem addressed in this study is that South African cities are not effectively integrating and utilising available, and rapidly emerging smart city data sources for planning and management. To this end, it was proposed that a predictive model, that assimilates data from traditionally isolated management silos, could be developed for prediction and simulation at the system-of-systems level. As proof of concept, the study focused on only one aspect of smart cities, namely crime management. Subsequently, the main objective of this study was to develop and evaluate a predictive model for crime management in smart cities that effectively integrated data from traditionally isolated management silos. The Design Science Research process was followed to develop and evaluate a prototype model. The practical contributions of this study was the development of a prototype model for integrated decision-making in smart cities, and the associated guidelines for the implementation of the developed modelling approach within the South African IDP context. Theoretically, this work contributed towards the development of a modelling paradigm for effective integrated decision-making in smart cities. This work also contributed towards developing strategic-level predictive policing tools aimed at proactively meeting community needs, and contributed to the body of knowledge regarding complex systems modelling.
- Full Text:
- Date Issued: 2019
Early Jurassic dolerites of the Karoo Large Igneous Province ( KLIP): an analysis of their age and emplacement history from sea level to the Drakensberg Mountains in the Eastern Cape , South Africa Submitted
- Authors: Muedi, Thomas Tshifhiwa
- Date: 2019
- Subjects: Geological time , Geochemistry Geology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/41908 , vital:36608
- Description: South Africa hosts one of the largest Large Igneous Provinces (LIPs that is likely linked to the early separation of East and West Gondwana. However, despite many studies, the relationship between dolerites and volcanic basalts of this LIP (also known as the Karoo Large Igneous Province or KLIP) remains unsolved, because of poorly linked age dates (timing), geochemistry and emplacement mechanisms. This problem is in part because different unreliable dating techniques with large margin of errors have been applied This study aims to address these issues by performing new geo chemical and high resolution geochronological analyses on a number of dolerites (sills and dykes), volcanic s also referred to in the literature as the Drakensberg flood basalts) and samples from drill cores and field outcrops. This project is focused on dolerites in the Eastern Cape Province and provides results from field mapping of dolerites (sills and dykes) from the sea level to an elevation of circa 1350 metres above sea level (MASL) and their link to the volcanic in the Eastern Cape Province. The dolerite dykes observed trends from metres to hundreds of kilometres and cut across volcanic, which have similar geochemistry. The intrusive dolerites collected from the field and from d rill core samples were likely emplaced by magma infiltration through pre-existing sub vertical brittle fractures and fissures and then emplaced horizontally as sills circa 183 Ma Detailed fracture mapping across host rock to the dolerite was carried out to test if they acted as possible pathways for magmatic emplacements. The dolerite dykes and fractures mapped in the host sedimentary rocks have a dominant NW direction, especially towards volcanic basalts. The project provides tests based on the geochemical relationships of the dolerites and basalts from sixty-six (66) cores and field outcrop samples. The results confirm that the chemical analyses from the volcanic basalts an d dolerites are closely related and reveal that most samples are Ocean Island Basalt OIB), but some also reveal subduction related processes. This is consistent with models that suggest subduction along south west Gondwana may have influenced plumemagmatism derived from the lower mantle that initiated break up of this supercontinent e.g de Wit and Stern 1981 Storey et al , 1992 ; Torsvik et al., 2006 and Burke et al., 2008)
- Full Text:
- Date Issued: 2019
- Authors: Muedi, Thomas Tshifhiwa
- Date: 2019
- Subjects: Geological time , Geochemistry Geology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/41908 , vital:36608
- Description: South Africa hosts one of the largest Large Igneous Provinces (LIPs that is likely linked to the early separation of East and West Gondwana. However, despite many studies, the relationship between dolerites and volcanic basalts of this LIP (also known as the Karoo Large Igneous Province or KLIP) remains unsolved, because of poorly linked age dates (timing), geochemistry and emplacement mechanisms. This problem is in part because different unreliable dating techniques with large margin of errors have been applied This study aims to address these issues by performing new geo chemical and high resolution geochronological analyses on a number of dolerites (sills and dykes), volcanic s also referred to in the literature as the Drakensberg flood basalts) and samples from drill cores and field outcrops. This project is focused on dolerites in the Eastern Cape Province and provides results from field mapping of dolerites (sills and dykes) from the sea level to an elevation of circa 1350 metres above sea level (MASL) and their link to the volcanic in the Eastern Cape Province. The dolerite dykes observed trends from metres to hundreds of kilometres and cut across volcanic, which have similar geochemistry. The intrusive dolerites collected from the field and from d rill core samples were likely emplaced by magma infiltration through pre-existing sub vertical brittle fractures and fissures and then emplaced horizontally as sills circa 183 Ma Detailed fracture mapping across host rock to the dolerite was carried out to test if they acted as possible pathways for magmatic emplacements. The dolerite dykes and fractures mapped in the host sedimentary rocks have a dominant NW direction, especially towards volcanic basalts. The project provides tests based on the geochemical relationships of the dolerites and basalts from sixty-six (66) cores and field outcrop samples. The results confirm that the chemical analyses from the volcanic basalts an d dolerites are closely related and reveal that most samples are Ocean Island Basalt OIB), but some also reveal subduction related processes. This is consistent with models that suggest subduction along south west Gondwana may have influenced plumemagmatism derived from the lower mantle that initiated break up of this supercontinent e.g de Wit and Stern 1981 Storey et al , 1992 ; Torsvik et al., 2006 and Burke et al., 2008)
- Full Text:
- Date Issued: 2019
The social sustainability of low-cost housing: the role of social capital and sense of place
- Authors: Williams-Bruinders, Leizel
- Date: 2019
- Subjects: Housing -- South Africa , City planning -- South Africa Cities and towns -- Research Urban geography
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/44390 , vital:37161
- Description: In the past twenty years we have seen the South African government deliver the largest number of houses in the world (NDHS, 2011). However, this great effort does not appeal to the principles that policies have set out in terms of equality. Along with the delivery of this high level of state funded housing, many of the RDP dwellers feel as though they have been marginalised and forced out of the area of opportunity, namely, the CBD and the northern suburbs (Huchzermeyer, 2003). Many researchers believe that the South African housing delivery pattern resembles that of apartheid segregationist planning, which exacerbated the social inequalities in the country (Huchzermeyer, 2003; Donaldson, 2001; Harrison et al., 2003). To gain an in-depth understanding of the lived experiences of residents of a low-cost housing settlement, an interpretative phenomenological analysis was undertaken. The emergent themes emanating from the research study revealed that social problems were pertinent factors to the lack of formulation of community social cohesion. Without this aspect, community building will be hampered, and thus cohesive neighbourhoods will be lacking. To this end, social innovation is proposed as a solution to the Zanemvula development. The issue of social development needs to placed back on the housing agenda, as is stated in the latest Housing Act.
- Full Text:
- Date Issued: 2019
- Authors: Williams-Bruinders, Leizel
- Date: 2019
- Subjects: Housing -- South Africa , City planning -- South Africa Cities and towns -- Research Urban geography
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/44390 , vital:37161
- Description: In the past twenty years we have seen the South African government deliver the largest number of houses in the world (NDHS, 2011). However, this great effort does not appeal to the principles that policies have set out in terms of equality. Along with the delivery of this high level of state funded housing, many of the RDP dwellers feel as though they have been marginalised and forced out of the area of opportunity, namely, the CBD and the northern suburbs (Huchzermeyer, 2003). Many researchers believe that the South African housing delivery pattern resembles that of apartheid segregationist planning, which exacerbated the social inequalities in the country (Huchzermeyer, 2003; Donaldson, 2001; Harrison et al., 2003). To gain an in-depth understanding of the lived experiences of residents of a low-cost housing settlement, an interpretative phenomenological analysis was undertaken. The emergent themes emanating from the research study revealed that social problems were pertinent factors to the lack of formulation of community social cohesion. Without this aspect, community building will be hampered, and thus cohesive neighbourhoods will be lacking. To this end, social innovation is proposed as a solution to the Zanemvula development. The issue of social development needs to placed back on the housing agenda, as is stated in the latest Housing Act.
- Full Text:
- Date Issued: 2019
Cheetah Acinonyx jubatus behaviour and resource use in response to other African large carnivores
- Authors: Cornhill, Kristina
- Date: 2019
- Subjects: Cheetahs -- Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/44735 , vital:38169
- Description: Competition occurs between species for shared resources. Subordinate species employ resource selection to shift their resource use away from that of dominant species in order to avoid the negative consequences of competition. Only in Africa is the post-Pleistocene large carnivore guild intact, consisting of lions Panthera leo, spotted hyaenas Crocuta crocuta, leopards Panthera pardus, cheetahs Acinonyx jubatus, and African wild dogs Lycaon pictus. Therefore, only in Africa can we explore how large carnivores co-exist with one another in a diverse community. Cheetahs are a subordinate member of the large carnivore guild due to their small stature and solitary nature. However, we still do not fully understand how competition shapes cheetah behaviour and resource use. I used cheetahs as a model subordinate predator to determine the behavioural responses and resource selection of cheetah in response to assumed competition from other large carnivores. I experimentally explored the behavioural response of cheetah to large carnivore scent sources (scats) and their presence at cheetah scent-marking sites to test for avoidance of such cues. Moreover, using unplanned experiments based on the resource use of cheetahs in the absence and then presence of lions (assessing space and time use by cheetah) and African wild dogs (assessing prey use by both species), I evaluated resource selection by cheetahs as a way to reduce competition with these large carnivores. In addition, I measured spatial and temporal partitioning between cheetahs and all four large carnivores at camera trap sites. Finally, I assessed whether cheetahs responded to competitors using a long term proactive response or a short term reactive response. I found that all four of the other large carnivores in the guild shaped cheetahs resource use, however, all did so on different axes in accordance with the niche complementarity hypothesis. Lions and spotted hyenas were avoided through time, African wild dogs through space and prey use, and lions and leopards on the spatiotemporal axis. Moreover, I show that cheetahs utilize a reactive response to competition that allows them to avoid risk while still obtaining necessary resources.
- Full Text:
- Date Issued: 2019
- Authors: Cornhill, Kristina
- Date: 2019
- Subjects: Cheetahs -- Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/44735 , vital:38169
- Description: Competition occurs between species for shared resources. Subordinate species employ resource selection to shift their resource use away from that of dominant species in order to avoid the negative consequences of competition. Only in Africa is the post-Pleistocene large carnivore guild intact, consisting of lions Panthera leo, spotted hyaenas Crocuta crocuta, leopards Panthera pardus, cheetahs Acinonyx jubatus, and African wild dogs Lycaon pictus. Therefore, only in Africa can we explore how large carnivores co-exist with one another in a diverse community. Cheetahs are a subordinate member of the large carnivore guild due to their small stature and solitary nature. However, we still do not fully understand how competition shapes cheetah behaviour and resource use. I used cheetahs as a model subordinate predator to determine the behavioural responses and resource selection of cheetah in response to assumed competition from other large carnivores. I experimentally explored the behavioural response of cheetah to large carnivore scent sources (scats) and their presence at cheetah scent-marking sites to test for avoidance of such cues. Moreover, using unplanned experiments based on the resource use of cheetahs in the absence and then presence of lions (assessing space and time use by cheetah) and African wild dogs (assessing prey use by both species), I evaluated resource selection by cheetahs as a way to reduce competition with these large carnivores. In addition, I measured spatial and temporal partitioning between cheetahs and all four large carnivores at camera trap sites. Finally, I assessed whether cheetahs responded to competitors using a long term proactive response or a short term reactive response. I found that all four of the other large carnivores in the guild shaped cheetahs resource use, however, all did so on different axes in accordance with the niche complementarity hypothesis. Lions and spotted hyenas were avoided through time, African wild dogs through space and prey use, and lions and leopards on the spatiotemporal axis. Moreover, I show that cheetahs utilize a reactive response to competition that allows them to avoid risk while still obtaining necessary resources.
- Full Text:
- Date Issued: 2019
β-N-Methylamino-L-Alanine is a developmental neurotoxin
- Authors: Scott, Laura Louise
- Date: 2019
- Subjects: Neurotoxic agents , Nervous system -- Diseases
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43633 , vital:36949
- Description: β-N-methylamino-L-alanine (BMAA) has been implicated in the development of the neurodegenerative diseases Amyotrophic Lateral Sclerosis/Parkinsonism Dementia Complex (ALS/PDC), Amyotrophic Lateral Sclerosis (ALS) and Alzheimer’s Disease (AD), but to date no animal model has adequately substantiated this link at environmentally relevant or even exaggerated BMAA exposure levels. The resulting controversy over a possible role for BMAA in neurodegenerative diseases was further hampered by a lack of evidence for mechanistic explanation for the disease pathology associated with these diseases However, the different responses to BMAA that have been observed in neonatal compared to adult rats, together with the findings of epidemiological studies that exposure to environmental factors in utero or in the early stages of life may be important for the development of ALS several years later, suggested that age of exposure might be the determining factor of BMAA neurotoxicity. This study therefore specifically addresses the developmental nature of BMAA as a neurotoxin, and investigates the pathology and progressive nature of that pathology after exposure to the toxin at the most susceptible age. This study demonstrated the importance of BMAA exposure age over total BMAA dose by showing that the administration of a single neonatal dose of BMAA to rodents on postnatal day (PND) 3, 4 and 5, and not prenatally or on PND 6, 7 and 10, caused behavioural, locomotor, emotional and long-term cognitive deficits, clinical symptoms of neurodegeneration as well as pathological hallmarks of AD, PD and ALS in the central nervous system. Furthermore, the observed behavioural deficits and distribution of neuronal loss and proteinopathies in the rodent central nervous system following exposure to BMAA on PND 3, 4 and 5 (corresponding to the developing age of an infant during the third trimester of pregnancy) is consistent with that typically associated with the disruption of normal dopamine and/or serotonin signaling in the brain and the consequent alteration in normal hippocampal and striatal neurogenesis that is modulated, in part, by dopamine. The pattern of spread and rate of propagation of pathology in this neonatal rat BMAA model provided further evidence that BMAA potentially exerts its effect by acting on neurotransmitter signaling. The observed late onset of typical ALS symptoms and pathology suggest that in this BMAA model AD and/or PD related symptoms develop first, followed by the start of ALS symptoms only after the AD and/or PD neuropathological deficits have severely progressed. This study also demonstrated that BMAA exposure at different doses and at different developmental ages resulted in the development of different combinations of either AD and/or PD and/or ALS pathology and/or symptoms in rats, and it is therefore feasible that in humans the age and/or frequency of exposure as well as the BMAA dose might similarly be a major determinant of the variant of AD, PD and/or ALS that might develop in adulthood. Based on the low BMAA dose that was able to cause AD and/or PD-like neuropathological abnormalities in rats in this study, it is feasible that a pregnant human could over the course of her pregnancy, and specifically during the third trimester of pregnancy, consume sufficient BMAA to result in her unborn child developing AD and/or PD and/or ALS up to 30-50 years later. This neonatal BMAA model is the only non-transgenic rodent model that reproduces the behavioural deficits, neuropathology and clinical symptoms that are typically associated with AD, PD and ALS in humans and that, more importantly, mimics the delayed onset of disease symptoms and typical slow progression of these neurodegenerative diseases with age. It now seems very likely that BMAA is a developmental neurotoxin that, as a result of perinatal, but probably prenatal exposure, causes or contributes significantly to the development of neurodegenerative diseases in humans.
- Full Text:
- Date Issued: 2019
- Authors: Scott, Laura Louise
- Date: 2019
- Subjects: Neurotoxic agents , Nervous system -- Diseases
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43633 , vital:36949
- Description: β-N-methylamino-L-alanine (BMAA) has been implicated in the development of the neurodegenerative diseases Amyotrophic Lateral Sclerosis/Parkinsonism Dementia Complex (ALS/PDC), Amyotrophic Lateral Sclerosis (ALS) and Alzheimer’s Disease (AD), but to date no animal model has adequately substantiated this link at environmentally relevant or even exaggerated BMAA exposure levels. The resulting controversy over a possible role for BMAA in neurodegenerative diseases was further hampered by a lack of evidence for mechanistic explanation for the disease pathology associated with these diseases However, the different responses to BMAA that have been observed in neonatal compared to adult rats, together with the findings of epidemiological studies that exposure to environmental factors in utero or in the early stages of life may be important for the development of ALS several years later, suggested that age of exposure might be the determining factor of BMAA neurotoxicity. This study therefore specifically addresses the developmental nature of BMAA as a neurotoxin, and investigates the pathology and progressive nature of that pathology after exposure to the toxin at the most susceptible age. This study demonstrated the importance of BMAA exposure age over total BMAA dose by showing that the administration of a single neonatal dose of BMAA to rodents on postnatal day (PND) 3, 4 and 5, and not prenatally or on PND 6, 7 and 10, caused behavioural, locomotor, emotional and long-term cognitive deficits, clinical symptoms of neurodegeneration as well as pathological hallmarks of AD, PD and ALS in the central nervous system. Furthermore, the observed behavioural deficits and distribution of neuronal loss and proteinopathies in the rodent central nervous system following exposure to BMAA on PND 3, 4 and 5 (corresponding to the developing age of an infant during the third trimester of pregnancy) is consistent with that typically associated with the disruption of normal dopamine and/or serotonin signaling in the brain and the consequent alteration in normal hippocampal and striatal neurogenesis that is modulated, in part, by dopamine. The pattern of spread and rate of propagation of pathology in this neonatal rat BMAA model provided further evidence that BMAA potentially exerts its effect by acting on neurotransmitter signaling. The observed late onset of typical ALS symptoms and pathology suggest that in this BMAA model AD and/or PD related symptoms develop first, followed by the start of ALS symptoms only after the AD and/or PD neuropathological deficits have severely progressed. This study also demonstrated that BMAA exposure at different doses and at different developmental ages resulted in the development of different combinations of either AD and/or PD and/or ALS pathology and/or symptoms in rats, and it is therefore feasible that in humans the age and/or frequency of exposure as well as the BMAA dose might similarly be a major determinant of the variant of AD, PD and/or ALS that might develop in adulthood. Based on the low BMAA dose that was able to cause AD and/or PD-like neuropathological abnormalities in rats in this study, it is feasible that a pregnant human could over the course of her pregnancy, and specifically during the third trimester of pregnancy, consume sufficient BMAA to result in her unborn child developing AD and/or PD and/or ALS up to 30-50 years later. This neonatal BMAA model is the only non-transgenic rodent model that reproduces the behavioural deficits, neuropathology and clinical symptoms that are typically associated with AD, PD and ALS in humans and that, more importantly, mimics the delayed onset of disease symptoms and typical slow progression of these neurodegenerative diseases with age. It now seems very likely that BMAA is a developmental neurotoxin that, as a result of perinatal, but probably prenatal exposure, causes or contributes significantly to the development of neurodegenerative diseases in humans.
- Full Text:
- Date Issued: 2019
Behavioural flexibility in an endangered seabird during current changes
- Authors: Traisnel, Gwendoline
- Date: 2019
- Subjects: Penguins -- South Africa , Penguins -- Behavior Sea birds -- Behavior Sea birds -- Ecology
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43800 , vital:37048
- Description: Penguins spend a large part of their life cycle at sea and are amongst the most threatened seabirds as they suffer high mortality and have low reproductive success. Across the world, many populations are currently declining despite the constant development of conservation actions. The lack of information at the individual level reduces the understanding of individual variability and its potential role in the population dynamics of these vulnerable species. For example, long-lived species are characterised by substantial individual heterogeneity in their contribution to the overall population dynamic that should be understood when considering the implemention of conservation policies. This thesis explored some of the primary mechanisms behind inter-individual differences in behaviour and breeding success in the endangered African penguin Spheniscus demersus. On Bird island (Algoa Bay), nest defence behaviours were investigated on adults brooding chicks 1-3 weeks-old and chicks were measured at regular intervals (every 5 days) to assess their growth rate, a proxy for breeding success in this species. All adults were sexed and implanted with a passive integrated transponder which was used for individual identification. In this species, males are usually larger than females and have a higher survival rates both as juveniles and as adults. A subsample of them was equipped with tracking devices (GPSs and Time Depth Recorders), sometimes over consecutive foraging trips and across years. Finally, mate and nest fidelity were investigated to understand the drivers and consequences of this trait in that population. Breeding success was linked to nest defence behaviours, with bolder birds generally showing lower breeding success. This relation could not, however, be explained by differences in foraging strategies. Males were generally bolder than females when defending the nests, but their foraging behaviour did not vary with their personality. They generally had lower foraging effort than females. By contrast, bolder females performed more sinuous path, more wiggles and travelled larger vertical distances than shyer ones. Overall, females were more flexible than males over consecutive trips, suggesting that they probably adjust their behaviours to the offspring needs in this species. However, no sex difference in behavioural flexibility between sexes was visible across years, indicating that environmental variability may equally impact females and males’ behaviour over such time-scale. Generally, consistency was time-scale dependent as penguins increased their foraging flexibility across years, potentially adjusting to the variability of the environment. Interestingly, foraging consistency over consecutive trips increased during years of poor environmental conditions, and individuals with consistent foraging strategies were more successful than more flexible individuals when resources were extremely scarce. Finally, while nest and mate fidelity were high in this species, individuals that changed nest/partners, improved their breeding outcome. Particularly, after low breeding success females were more likely to change nest site and thereby partner to possibly improve their fitness. The potential biased adult sex ratio towards males in this population may facilitate changes in females which may have more partners available to re-mate than males. The present thesis reveals the existence of individual differences in behaviour and breeding success which relate to personality in penguins. These findings highlight the importance to integrate individual variability to predict future population dynamics in the context of global changes to understand the resilience and vulnerability of the species.
- Full Text:
- Date Issued: 2019
- Authors: Traisnel, Gwendoline
- Date: 2019
- Subjects: Penguins -- South Africa , Penguins -- Behavior Sea birds -- Behavior Sea birds -- Ecology
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43800 , vital:37048
- Description: Penguins spend a large part of their life cycle at sea and are amongst the most threatened seabirds as they suffer high mortality and have low reproductive success. Across the world, many populations are currently declining despite the constant development of conservation actions. The lack of information at the individual level reduces the understanding of individual variability and its potential role in the population dynamics of these vulnerable species. For example, long-lived species are characterised by substantial individual heterogeneity in their contribution to the overall population dynamic that should be understood when considering the implemention of conservation policies. This thesis explored some of the primary mechanisms behind inter-individual differences in behaviour and breeding success in the endangered African penguin Spheniscus demersus. On Bird island (Algoa Bay), nest defence behaviours were investigated on adults brooding chicks 1-3 weeks-old and chicks were measured at regular intervals (every 5 days) to assess their growth rate, a proxy for breeding success in this species. All adults were sexed and implanted with a passive integrated transponder which was used for individual identification. In this species, males are usually larger than females and have a higher survival rates both as juveniles and as adults. A subsample of them was equipped with tracking devices (GPSs and Time Depth Recorders), sometimes over consecutive foraging trips and across years. Finally, mate and nest fidelity were investigated to understand the drivers and consequences of this trait in that population. Breeding success was linked to nest defence behaviours, with bolder birds generally showing lower breeding success. This relation could not, however, be explained by differences in foraging strategies. Males were generally bolder than females when defending the nests, but their foraging behaviour did not vary with their personality. They generally had lower foraging effort than females. By contrast, bolder females performed more sinuous path, more wiggles and travelled larger vertical distances than shyer ones. Overall, females were more flexible than males over consecutive trips, suggesting that they probably adjust their behaviours to the offspring needs in this species. However, no sex difference in behavioural flexibility between sexes was visible across years, indicating that environmental variability may equally impact females and males’ behaviour over such time-scale. Generally, consistency was time-scale dependent as penguins increased their foraging flexibility across years, potentially adjusting to the variability of the environment. Interestingly, foraging consistency over consecutive trips increased during years of poor environmental conditions, and individuals with consistent foraging strategies were more successful than more flexible individuals when resources were extremely scarce. Finally, while nest and mate fidelity were high in this species, individuals that changed nest/partners, improved their breeding outcome. Particularly, after low breeding success females were more likely to change nest site and thereby partner to possibly improve their fitness. The potential biased adult sex ratio towards males in this population may facilitate changes in females which may have more partners available to re-mate than males. The present thesis reveals the existence of individual differences in behaviour and breeding success which relate to personality in penguins. These findings highlight the importance to integrate individual variability to predict future population dynamics in the context of global changes to understand the resilience and vulnerability of the species.
- Full Text:
- Date Issued: 2019
An assessment of the social ecological system of Mabira forest and environs: implications for vulnerability to climate variability
- Authors: Jjagwe, Aisha
- Date: 2019
- Subjects: Climate hazards
- Language: English
- Type: Thesis , Doctoral , Degree
- Identifier: http://hdl.handle.net/10948/44726 , vital:38163
- Description: Tropical forests are attracting attention in climate change debates considering the fundamental role they play as carbon sinks. Mabira Central Forest Reserve (CFR) found in the Lake Victoria basin region and of significance in achieving the Sustainable Development Goals. It has however undergone drastic degradation since the 1970s and its social economic ecological and environmental functions are at risk. The present study assessed the Social Ecological System (SES) of Mabira CFR and environs as well as the implications for vulnerability to climate variability. It focused on; i) assessment of the spatial temporal changes of Mabira CFR; to which Landsat images of 1975, 1986, 2000 and 2015 were used in combination with ground truthing for a successful classification of land use/cover types. ii) Determine the implications of land use/cover types and forest management options for above ground biomass (AGB) and soil organic carbon (SOC); here Velle, (1995) allometric equation was adopted for the AGB while the Walkley and Black (1934) was used to determine soil organic carbon iii) Determine the implications of land use cover change for livelihood and vulnerability to climate change impacts; to this the Social Ecological systems framework by Ostrom (2009) was adopted to understand the vulnerability implications for land use cover change (LUCC) and Climate variability in a forest based community. The study reveals that heavy deforestation and degradation continue to pose threats to Mabira CFR and environs. Major drivers of LUCC are: population expansion, loss of soil fertility, poor agricultural practices, establishment of roadside markets, industrialization and unclear forestry boundary. Findings indicate that although forest comprised the biggest coverage between 1975 and 2000, it has faced massive reduction between 2000 and 2015. Major forest conversions have been to subsistence farming (5.94%). The implications of LUCC are reflected in; the exposure of soils to degradation as seen from deforestation; soil erosion; carbon sequestration and climate variability constraining livelihoods. AGB and carbon was found highest in the strict nature reserve where on average the parameters noted above were found to be bigger. The recreation buffer had less carbon compared to the strict nature reserve; however the production zone, which had scattered trees with smaller parameters, registered the lowest average total AGB and carbon. Results indicate a perfectly strong relationship between the AGB and carbon variables. Results also indicate that approximately 6,771092.344 tonnes are sunk in the strict nature reserve. SOC analyzed based on the soil carbon percentage content. In terms of soil depth, the 0-10cm and 10-20cm soil layers had relatively similar variations of least square means for carbon than at 20-30cm soil layer. The highest SOC was observed in the soil surface of 0-10 cm depth, with the highest mean of 2.78 % across all the management zones. The amount of soil organic matter also varied with land use /cover types. Study findings reveal that LUCC and land management have a direct influence on soil organic carbon accumulation. Results indicate that LUCC implications for AGB and SOC as well as climate variability lead to livelihood vulnerability. Climate hazards experienced have affected SES, temperature variation range between 1oC -2oC. These variations are likely to increase vulnerability. This study recommends mapping of LUCC to identify priority areas for intervention. Priority should be given to reducing deforestation and restore degraded areas. Future research should focus on building adaptive capacity for forest based communities to mitigate climate change, improving forest tenure as a strategy for climate change impacts, integrating climate change into forest policy reviews.
- Full Text:
- Date Issued: 2019
- Authors: Jjagwe, Aisha
- Date: 2019
- Subjects: Climate hazards
- Language: English
- Type: Thesis , Doctoral , Degree
- Identifier: http://hdl.handle.net/10948/44726 , vital:38163
- Description: Tropical forests are attracting attention in climate change debates considering the fundamental role they play as carbon sinks. Mabira Central Forest Reserve (CFR) found in the Lake Victoria basin region and of significance in achieving the Sustainable Development Goals. It has however undergone drastic degradation since the 1970s and its social economic ecological and environmental functions are at risk. The present study assessed the Social Ecological System (SES) of Mabira CFR and environs as well as the implications for vulnerability to climate variability. It focused on; i) assessment of the spatial temporal changes of Mabira CFR; to which Landsat images of 1975, 1986, 2000 and 2015 were used in combination with ground truthing for a successful classification of land use/cover types. ii) Determine the implications of land use/cover types and forest management options for above ground biomass (AGB) and soil organic carbon (SOC); here Velle, (1995) allometric equation was adopted for the AGB while the Walkley and Black (1934) was used to determine soil organic carbon iii) Determine the implications of land use cover change for livelihood and vulnerability to climate change impacts; to this the Social Ecological systems framework by Ostrom (2009) was adopted to understand the vulnerability implications for land use cover change (LUCC) and Climate variability in a forest based community. The study reveals that heavy deforestation and degradation continue to pose threats to Mabira CFR and environs. Major drivers of LUCC are: population expansion, loss of soil fertility, poor agricultural practices, establishment of roadside markets, industrialization and unclear forestry boundary. Findings indicate that although forest comprised the biggest coverage between 1975 and 2000, it has faced massive reduction between 2000 and 2015. Major forest conversions have been to subsistence farming (5.94%). The implications of LUCC are reflected in; the exposure of soils to degradation as seen from deforestation; soil erosion; carbon sequestration and climate variability constraining livelihoods. AGB and carbon was found highest in the strict nature reserve where on average the parameters noted above were found to be bigger. The recreation buffer had less carbon compared to the strict nature reserve; however the production zone, which had scattered trees with smaller parameters, registered the lowest average total AGB and carbon. Results indicate a perfectly strong relationship between the AGB and carbon variables. Results also indicate that approximately 6,771092.344 tonnes are sunk in the strict nature reserve. SOC analyzed based on the soil carbon percentage content. In terms of soil depth, the 0-10cm and 10-20cm soil layers had relatively similar variations of least square means for carbon than at 20-30cm soil layer. The highest SOC was observed in the soil surface of 0-10 cm depth, with the highest mean of 2.78 % across all the management zones. The amount of soil organic matter also varied with land use /cover types. Study findings reveal that LUCC and land management have a direct influence on soil organic carbon accumulation. Results indicate that LUCC implications for AGB and SOC as well as climate variability lead to livelihood vulnerability. Climate hazards experienced have affected SES, temperature variation range between 1oC -2oC. These variations are likely to increase vulnerability. This study recommends mapping of LUCC to identify priority areas for intervention. Priority should be given to reducing deforestation and restore degraded areas. Future research should focus on building adaptive capacity for forest based communities to mitigate climate change, improving forest tenure as a strategy for climate change impacts, integrating climate change into forest policy reviews.
- Full Text:
- Date Issued: 2019
Microalgae as indicators of environmental change in the St Lucia estuarine system
- Authors: Nunes, Monique
- Date: 2019
- Subjects: Microalgae -- South Africa -- St Lucia estuarine
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/31165 , vital:31333
- Description: The St Lucia system represents 56% of the estuarine habitat area in South Africa. This dynamic estuarine lake responds to a complex interaction of climatic and anthropogenic drivers. There has been a long history of human interventions and the extended drought (2002-2012) led to major changes. In 1952, the inlet shared between the estuarine system and the Mfolozi River was artificially separated, which significantly reduced freshwater inflow. The systems were separated because of the silt load from the expanding agricultural activities in the Mfolozi River catchment. The drought prompted a critical review of re-establishing the historic connection, and in July 2012, the beach spillway was excavated marking the start of restoring connectivity. Increased rainfall coupled with the partial re-connection with the agriculturally-impacted Mfolozi River shifted the St Lucia estuarine system to a new wet phase. This study investigated the microalgal dynamics of the estuarine system as it transitioned to this new wet phase. Results showed that the phytoplankton and microphytobenthos (MPB) biomass was low (< 5 ug l-1 and < 60 mg m-2 respectively) throughout the system due to nutrient and light availability, water residence time and sediment type. The increased freshwater inflow from the Mfolozi River was limited to the Narrows and available nutrients promoted the growth of cyanobacteria and dinophytes in the water column. Of interest was the presence of the potentially harmful algal species Prorocentrum minimum. A weekly study investigated the relationship between freshwater inflow, phytoplankton succession and the introduction and persistence of harmful microalgal species in the lower reaches. The increased freshwater inflow received from the Mfolozi River has led to a system in a constant state of flux. The changes in salinity, light availability and water residence time, shifted the phytoplankton functional group structure to one where chlorophytes and euglenoids were dominant. The persistence of the nutrient tolerant euglenoids highlighted the influence of the nutrient-enriched freshwater inflow on the phytoplankton functional groups. However, the relative abundance of all functional groups remained low due to the rapid change in environmental conditions. The next step was to test the use of an artificial substrate as a monitoring method to detect nutrient induced change. Findings from the 28-day study showed that epilithic diatom communities growing on glass slides were good indicators of nutrient enrichment. The epilithic algal biomass increased significantly from 1.5 mg m-2 (Day 14) to 6 mg m-2 (Day 21), following peak river inflow. In contrast, the phytoplankton and MPB showed no discernible increase in biomass. Epilithic diatom community diversity, richness and evenness scores declined due to the increasing relative abundance of a single nutrient tolerant species, Cocconeis placentula var. euglypta. The use of diatoms as indicators of change depends on the accuracy of identification to species level. This can be a slow process requiring a high level of taxonomic expertise. Considering that molecular phylogenetic methods are readily used to produce a reliable taxonomic list, the suitability of DNA metabarcoding for diatom monitoring in the St Lucia Estuary was tested. Comparisons between the molecular and morphological method indicated that the diatom taxonomic composition was similar at 9 to 27% for genus level and 2 to 9% at species level. The low taxonomic similarity was related to the large number of unclassified DNA representative sequences included in the molecular inventory due to the incomplete DNA library database. However, the available operational taxonomic units (OTUs) from the molecular method did provide an effective alternative to determine the relevant community diversity estimates required for the application of the South African Estuarine Health Index (EHI). This research has highlighted the dynamic nature of the St Lucia estuarine system and the effectiveness of the microalgal communities to differentiate between the cyclical climatic phases and anthropogenic stressors such as nutrient enrichment.
- Full Text:
- Date Issued: 2019
- Authors: Nunes, Monique
- Date: 2019
- Subjects: Microalgae -- South Africa -- St Lucia estuarine
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/31165 , vital:31333
- Description: The St Lucia system represents 56% of the estuarine habitat area in South Africa. This dynamic estuarine lake responds to a complex interaction of climatic and anthropogenic drivers. There has been a long history of human interventions and the extended drought (2002-2012) led to major changes. In 1952, the inlet shared between the estuarine system and the Mfolozi River was artificially separated, which significantly reduced freshwater inflow. The systems were separated because of the silt load from the expanding agricultural activities in the Mfolozi River catchment. The drought prompted a critical review of re-establishing the historic connection, and in July 2012, the beach spillway was excavated marking the start of restoring connectivity. Increased rainfall coupled with the partial re-connection with the agriculturally-impacted Mfolozi River shifted the St Lucia estuarine system to a new wet phase. This study investigated the microalgal dynamics of the estuarine system as it transitioned to this new wet phase. Results showed that the phytoplankton and microphytobenthos (MPB) biomass was low (< 5 ug l-1 and < 60 mg m-2 respectively) throughout the system due to nutrient and light availability, water residence time and sediment type. The increased freshwater inflow from the Mfolozi River was limited to the Narrows and available nutrients promoted the growth of cyanobacteria and dinophytes in the water column. Of interest was the presence of the potentially harmful algal species Prorocentrum minimum. A weekly study investigated the relationship between freshwater inflow, phytoplankton succession and the introduction and persistence of harmful microalgal species in the lower reaches. The increased freshwater inflow received from the Mfolozi River has led to a system in a constant state of flux. The changes in salinity, light availability and water residence time, shifted the phytoplankton functional group structure to one where chlorophytes and euglenoids were dominant. The persistence of the nutrient tolerant euglenoids highlighted the influence of the nutrient-enriched freshwater inflow on the phytoplankton functional groups. However, the relative abundance of all functional groups remained low due to the rapid change in environmental conditions. The next step was to test the use of an artificial substrate as a monitoring method to detect nutrient induced change. Findings from the 28-day study showed that epilithic diatom communities growing on glass slides were good indicators of nutrient enrichment. The epilithic algal biomass increased significantly from 1.5 mg m-2 (Day 14) to 6 mg m-2 (Day 21), following peak river inflow. In contrast, the phytoplankton and MPB showed no discernible increase in biomass. Epilithic diatom community diversity, richness and evenness scores declined due to the increasing relative abundance of a single nutrient tolerant species, Cocconeis placentula var. euglypta. The use of diatoms as indicators of change depends on the accuracy of identification to species level. This can be a slow process requiring a high level of taxonomic expertise. Considering that molecular phylogenetic methods are readily used to produce a reliable taxonomic list, the suitability of DNA metabarcoding for diatom monitoring in the St Lucia Estuary was tested. Comparisons between the molecular and morphological method indicated that the diatom taxonomic composition was similar at 9 to 27% for genus level and 2 to 9% at species level. The low taxonomic similarity was related to the large number of unclassified DNA representative sequences included in the molecular inventory due to the incomplete DNA library database. However, the available operational taxonomic units (OTUs) from the molecular method did provide an effective alternative to determine the relevant community diversity estimates required for the application of the South African Estuarine Health Index (EHI). This research has highlighted the dynamic nature of the St Lucia estuarine system and the effectiveness of the microalgal communities to differentiate between the cyclical climatic phases and anthropogenic stressors such as nutrient enrichment.
- Full Text:
- Date Issued: 2019
A framework to measure human behaviour whilst reading
- Salehzadeh, Seyed Amirsaleh, Greyling, Jean
- Authors: Salehzadeh, Seyed Amirsaleh , Greyling, Jean
- Date: 2019
- Subjects: Computational intelligence , Machine learning Artificial intelligence Neural networks (Computer science)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43578 , vital:36921
- Description: The brain is the most complex object in the known universe that gives a sense of being to humans and characterises human behaviour. Building models of brain functions is perhaps the most fascinating scientific challenge in the 21st century. Reading is a significant cognitive process in the human brain that plays a critical role in the vital process of learning and in performing some daily activities. The study of human behaviour during reading has been an area of interest for researchers in different fields of science. This thesis is based upon providing a novel framework, called ARSAT (Assisting Researchers in the Selection of Appropriate Technologies), that measures the behaviour of humans when reading text. The ARSAT framework aims at assisting researchers in the selection and application of appropriate technologies to measure the behaviour of a person who is reading text. The ARSAT framework will assist to researchers who investigate the reading process and find it difficult to select appropriate theories, metrics, data collection methods and data analytics techniques. The ARSAT framework enhances the ability of its users to select appropriate metrics indicating the effective factors on the characterisation of different aspects of human behaviour during the reading process. As will be shown in this research study, human behaviour is characterised by a complicated interplay of action, cognition and emotion. The ARSAT framework also facilitates selecting appropriate sensory technologies that can be used to monitor and collect data for the metrics. Moreover, this research study will introduce BehaveNet, a novel Deep Learning modelling approach, which can be used for training Deep Learning models of human behaviour from the sensory data collected. In this thesis, a comprehensive literature study is presented that was conducted to acquire adequate knowledge for designing the ARSAT framework. In order to identify the contributing factors that affect the reading process, an overview of some existing theories of the reading process is provided. Furthermore, a number of sensory technologies and techniques that can be applied to monitoring the changes in the metrics indicating the factors are also demonstrated. Only, the technologies that are commercially available on the market are recommended by the ARSAT framework. A variety of Machine Learning techniques were also investigated when designing the BehaveNet. The BehaveNet takes advantage of the complementarity of Convolutional Neural Networks, Long Short-Term Memory networks and Deep Neural Networks. The design of a Human Behaviour Monitoring System (HBMS), by utilising the ARSAT framework for recognising three attention-seeking activities of humans, is also presented in this research study. Reading printed text, as well as speaking out loudly and watching a programme on TV were proposed as activities that a person unintentionally may shift his/her attention from reading into distractions. Between sensory devices recommended by the ARSAT framework, the Muse headband which is an Electroencephalography (EEG) and head motion-sensing wearable device, was selected to track the forehead EEG and a person’s head movements. The EEG and 3-axes accelerometer data were recorded from eight participants when they read printed text, as well as the time they performed two other activities. An imbalanced dataset consisting over 1.2 million rows of noisy data was created and used to build a model of the activities (60% training and 20% validating data) and evaluating the model (20% of the data). The efficiency of the framework is demonstrated by comparing the performance of the models built by utilising the BehaveNet, with the models built by utilising a number of competing Deep Learning models for raw EEG and accelerometer data, that have attained state-of-the-art performance. The classification results are evaluated by some metrics including the classification accuracy, F1 score, confusion matrix, Receiver Operating Characteristic curve, and Area under Curve (AUC) score. By considering the results, the BehaveNet contributed to the body of knowledge as an approach for measuring human behaviour by using sensory devices. In comparison with the performance of the other models, the models built by utilising the BehaveNet, attained better performance when classifying data of two EEG channels (Accuracy = 95%; AUC=0.99; F1 = 0.95), data of a single EEG channel (Accuracy = 85%; AUC=0.96; F1 = 0.83), accelerometer data (Accuracy = 81%; AUC = 0.9; F1 = 0.76) and all of the data in the dataset (Accuracy = 97%; AUC = 0.99; F1 = 0.96). The dataset and the source code of this project are also published on the Internet to help the science community. The Muse headband is also shown to be an economical and standard wearable device that can be successfully used in behavioural research.
- Full Text:
- Date Issued: 2019
- Authors: Salehzadeh, Seyed Amirsaleh , Greyling, Jean
- Date: 2019
- Subjects: Computational intelligence , Machine learning Artificial intelligence Neural networks (Computer science)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43578 , vital:36921
- Description: The brain is the most complex object in the known universe that gives a sense of being to humans and characterises human behaviour. Building models of brain functions is perhaps the most fascinating scientific challenge in the 21st century. Reading is a significant cognitive process in the human brain that plays a critical role in the vital process of learning and in performing some daily activities. The study of human behaviour during reading has been an area of interest for researchers in different fields of science. This thesis is based upon providing a novel framework, called ARSAT (Assisting Researchers in the Selection of Appropriate Technologies), that measures the behaviour of humans when reading text. The ARSAT framework aims at assisting researchers in the selection and application of appropriate technologies to measure the behaviour of a person who is reading text. The ARSAT framework will assist to researchers who investigate the reading process and find it difficult to select appropriate theories, metrics, data collection methods and data analytics techniques. The ARSAT framework enhances the ability of its users to select appropriate metrics indicating the effective factors on the characterisation of different aspects of human behaviour during the reading process. As will be shown in this research study, human behaviour is characterised by a complicated interplay of action, cognition and emotion. The ARSAT framework also facilitates selecting appropriate sensory technologies that can be used to monitor and collect data for the metrics. Moreover, this research study will introduce BehaveNet, a novel Deep Learning modelling approach, which can be used for training Deep Learning models of human behaviour from the sensory data collected. In this thesis, a comprehensive literature study is presented that was conducted to acquire adequate knowledge for designing the ARSAT framework. In order to identify the contributing factors that affect the reading process, an overview of some existing theories of the reading process is provided. Furthermore, a number of sensory technologies and techniques that can be applied to monitoring the changes in the metrics indicating the factors are also demonstrated. Only, the technologies that are commercially available on the market are recommended by the ARSAT framework. A variety of Machine Learning techniques were also investigated when designing the BehaveNet. The BehaveNet takes advantage of the complementarity of Convolutional Neural Networks, Long Short-Term Memory networks and Deep Neural Networks. The design of a Human Behaviour Monitoring System (HBMS), by utilising the ARSAT framework for recognising three attention-seeking activities of humans, is also presented in this research study. Reading printed text, as well as speaking out loudly and watching a programme on TV were proposed as activities that a person unintentionally may shift his/her attention from reading into distractions. Between sensory devices recommended by the ARSAT framework, the Muse headband which is an Electroencephalography (EEG) and head motion-sensing wearable device, was selected to track the forehead EEG and a person’s head movements. The EEG and 3-axes accelerometer data were recorded from eight participants when they read printed text, as well as the time they performed two other activities. An imbalanced dataset consisting over 1.2 million rows of noisy data was created and used to build a model of the activities (60% training and 20% validating data) and evaluating the model (20% of the data). The efficiency of the framework is demonstrated by comparing the performance of the models built by utilising the BehaveNet, with the models built by utilising a number of competing Deep Learning models for raw EEG and accelerometer data, that have attained state-of-the-art performance. The classification results are evaluated by some metrics including the classification accuracy, F1 score, confusion matrix, Receiver Operating Characteristic curve, and Area under Curve (AUC) score. By considering the results, the BehaveNet contributed to the body of knowledge as an approach for measuring human behaviour by using sensory devices. In comparison with the performance of the other models, the models built by utilising the BehaveNet, attained better performance when classifying data of two EEG channels (Accuracy = 95%; AUC=0.99; F1 = 0.95), data of a single EEG channel (Accuracy = 85%; AUC=0.96; F1 = 0.83), accelerometer data (Accuracy = 81%; AUC = 0.9; F1 = 0.76) and all of the data in the dataset (Accuracy = 97%; AUC = 0.99; F1 = 0.96). The dataset and the source code of this project are also published on the Internet to help the science community. The Muse headband is also shown to be an economical and standard wearable device that can be successfully used in behavioural research.
- Full Text:
- Date Issued: 2019
Microstructural evolution of welded creep aged 12% cr martensitic stainless steel
- Authors: Marx, Genevéve
- Date: 2019
- Subjects: Stainless steel -- Welding
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30766 , vital:31128
- Description: Tempered martensite ferritic (TMF) steels with 9-12% Cr additions are used extensively for high-pressure steam pipes in coal-fired power plants. They operate at temperatures above 500ºC and are consequently susceptible to creep damage. Due to economic reasons, welding must be performed on service exposed materials when a component needs to be replaced. Fusion welding results in the formation of different microstructural regions within the weldment. The primary failure mechanism of TMF steel welded components is Type IV cracking that results from accelerated void formation in the fine-grained heat affected zone (FGHAZ) during creep. Short-term creep-tests performed across weldments made on new and service exposed steels have shown that the weldment consistently fails in the FGHAZ of the service exposed material. This observation has not yet been fully explained since not much is known about the microstructural evolution of creep aged material during welding. Thus, further investigation on the microstructure of welded creep aged material is warranted. The main aim of this thesis was to investigate the microstructural evolution when welding upon creep aged 9-12% Cr martensitic steels using advanced electron microscopy techniques. X20CrMoV12-1 (12% Cr) in the virgin and long-term service-exposed state were investigated. GleebleTM weld simulation of the FGHAZ was performed on the materials. Detailed microstructural investigations were conducted on the parent and simulated FGHAZ materials to analyse the voids, dislocation density, micro-grains, and precipitates (M23C6, MX, Laves, Z-phase) in the materials. Light Microscopy (LM) and Scanning Electron Microscopy (SEM) was used to examine the voids. Twin-jet electropolished specimens were prepared for precipitate, micro-grain and substructure analyses using Transmission Kikuchi Diffraction (TKD) combined with Energy Dispersive Spectrometry (EDS), Concentric Backscatter (CBS) imaging, Energy-Filtered Transmission Electron Microscopy (EFTEM), and Annular Dark-Field Scanning Transmission Electron Microscopy (ADF-STEM) combined with EDS. The precipitates were extracted from the iron matrix using Bulk Replication and further investigated using EFTEM and STEM-EDS.
- Full Text:
- Date Issued: 2019
- Authors: Marx, Genevéve
- Date: 2019
- Subjects: Stainless steel -- Welding
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30766 , vital:31128
- Description: Tempered martensite ferritic (TMF) steels with 9-12% Cr additions are used extensively for high-pressure steam pipes in coal-fired power plants. They operate at temperatures above 500ºC and are consequently susceptible to creep damage. Due to economic reasons, welding must be performed on service exposed materials when a component needs to be replaced. Fusion welding results in the formation of different microstructural regions within the weldment. The primary failure mechanism of TMF steel welded components is Type IV cracking that results from accelerated void formation in the fine-grained heat affected zone (FGHAZ) during creep. Short-term creep-tests performed across weldments made on new and service exposed steels have shown that the weldment consistently fails in the FGHAZ of the service exposed material. This observation has not yet been fully explained since not much is known about the microstructural evolution of creep aged material during welding. Thus, further investigation on the microstructure of welded creep aged material is warranted. The main aim of this thesis was to investigate the microstructural evolution when welding upon creep aged 9-12% Cr martensitic steels using advanced electron microscopy techniques. X20CrMoV12-1 (12% Cr) in the virgin and long-term service-exposed state were investigated. GleebleTM weld simulation of the FGHAZ was performed on the materials. Detailed microstructural investigations were conducted on the parent and simulated FGHAZ materials to analyse the voids, dislocation density, micro-grains, and precipitates (M23C6, MX, Laves, Z-phase) in the materials. Light Microscopy (LM) and Scanning Electron Microscopy (SEM) was used to examine the voids. Twin-jet electropolished specimens were prepared for precipitate, micro-grain and substructure analyses using Transmission Kikuchi Diffraction (TKD) combined with Energy Dispersive Spectrometry (EDS), Concentric Backscatter (CBS) imaging, Energy-Filtered Transmission Electron Microscopy (EFTEM), and Annular Dark-Field Scanning Transmission Electron Microscopy (ADF-STEM) combined with EDS. The precipitates were extracted from the iron matrix using Bulk Replication and further investigated using EFTEM and STEM-EDS.
- Full Text:
- Date Issued: 2019
An investigation of plant conservation strategies employed in Makhanda, South Africa: an educational exploration
- Authors: Cimi, Pumlani Viwe
- Date: 2019
- Subjects: Plant conservation , Rare plants Biodiversity conservation
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/37979 , vital:34276
- Description: The school curriculum in South Africa gives educators the freedom to design and organise learning experiences according to their local circumstances and availability of resources. In that context, this study advocates conservation education through use of plants on school grounds and visits to local herbaria and botanical gardens as part of the school curriculum. Trees growing on street verges in town suburbs are also a resource that could be using for teaching. School learners from three schools representing different areas of Makhanda (Grahamstown) participated in plant-related activities and were surveyed to determine their prior knowledge about plants and plant conservation. Learners answered a series of questions in writing using a funnel sequence and the inverted funnel sequence in questionnaire design. This motivated respondents to co-operate and fully complete a questionnaire. In addition, the non-participant observation technique was used to capture behavioural reactions to the activities in order to supplement the data generated through questionnaires and interviews. This proved to be a purposeful, systematic and a selective way of watching and listening to an interaction phenomenon as it takes place. Interviews and questionnaires revealed that most Makhanda residents (especially in rural and township areas) use traditional medicine and medicinal plants to treat many diseases. They also use plants for cultural activities. Traditional remedies are practised among the rural and township communities because of ease of availability, convenience, and also due to social, psychological and cultural reasons. Medicinal plants have been increasingly recognized for their role not only for health care, but also for improving the economic status. Community members and street vendors were also questioned using semi-structured interviews. Open-ended questions were used successfully to assess the person’s knowledge, attitudes, opinions, beliefs and feelings. This type of interview ensures that a specific question does not lose its purpose. These interviews were used to determine how community members see, interpret and relate to nature. In the interviews, I also assessed the real needs of the local communities because there is a tendency to think that our power, knowledge and resources can give us the right to predict what communities really need without actually asking them. When our imposed initiatives fail, we often accuse these communities of a lack of interest in our issue of interest. Documents on plants and their uses kept in the Selmar Schönland Herbarium were compared with the information given by community members and street vendors. Xhosa plant names and ethnobotanical information given by the community members and street vendors was used to augment existing information on plant use. A further aim of this study was to investigate the potential use of plant resources provided by the street trees and gardens for education. Makhanda streets were sampled and, of the 1 435 plants that were countered from 17 streets, only 15 indigenous species were represented, while 20 alien species were recorded. These trees can be used for lessons on both alien and indigenous plants. Notable differences in tree density and species richness were evident across suburbs with the highest density and richness found in the more affluent suburbs and poor representation of trees in the township. This will affect learner perceptions and viewpoints. The results from the analysed data revealed that use of the school grounds, botanical gardens, the local herbarium and town streets are effective in plant conservation education in schools and communities. These types of resources could be used for environmental education for future generations in South Africa and all over the world.
- Full Text:
- Date Issued: 2019
- Authors: Cimi, Pumlani Viwe
- Date: 2019
- Subjects: Plant conservation , Rare plants Biodiversity conservation
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/37979 , vital:34276
- Description: The school curriculum in South Africa gives educators the freedom to design and organise learning experiences according to their local circumstances and availability of resources. In that context, this study advocates conservation education through use of plants on school grounds and visits to local herbaria and botanical gardens as part of the school curriculum. Trees growing on street verges in town suburbs are also a resource that could be using for teaching. School learners from three schools representing different areas of Makhanda (Grahamstown) participated in plant-related activities and were surveyed to determine their prior knowledge about plants and plant conservation. Learners answered a series of questions in writing using a funnel sequence and the inverted funnel sequence in questionnaire design. This motivated respondents to co-operate and fully complete a questionnaire. In addition, the non-participant observation technique was used to capture behavioural reactions to the activities in order to supplement the data generated through questionnaires and interviews. This proved to be a purposeful, systematic and a selective way of watching and listening to an interaction phenomenon as it takes place. Interviews and questionnaires revealed that most Makhanda residents (especially in rural and township areas) use traditional medicine and medicinal plants to treat many diseases. They also use plants for cultural activities. Traditional remedies are practised among the rural and township communities because of ease of availability, convenience, and also due to social, psychological and cultural reasons. Medicinal plants have been increasingly recognized for their role not only for health care, but also for improving the economic status. Community members and street vendors were also questioned using semi-structured interviews. Open-ended questions were used successfully to assess the person’s knowledge, attitudes, opinions, beliefs and feelings. This type of interview ensures that a specific question does not lose its purpose. These interviews were used to determine how community members see, interpret and relate to nature. In the interviews, I also assessed the real needs of the local communities because there is a tendency to think that our power, knowledge and resources can give us the right to predict what communities really need without actually asking them. When our imposed initiatives fail, we often accuse these communities of a lack of interest in our issue of interest. Documents on plants and their uses kept in the Selmar Schönland Herbarium were compared with the information given by community members and street vendors. Xhosa plant names and ethnobotanical information given by the community members and street vendors was used to augment existing information on plant use. A further aim of this study was to investigate the potential use of plant resources provided by the street trees and gardens for education. Makhanda streets were sampled and, of the 1 435 plants that were countered from 17 streets, only 15 indigenous species were represented, while 20 alien species were recorded. These trees can be used for lessons on both alien and indigenous plants. Notable differences in tree density and species richness were evident across suburbs with the highest density and richness found in the more affluent suburbs and poor representation of trees in the township. This will affect learner perceptions and viewpoints. The results from the analysed data revealed that use of the school grounds, botanical gardens, the local herbarium and town streets are effective in plant conservation education in schools and communities. These types of resources could be used for environmental education for future generations in South Africa and all over the world.
- Full Text:
- Date Issued: 2019
An evaluation and comparison of the plasticiser effects of p -Menthane-3,8-diol-citronellal acetal plasticiser with triethyl citrate and bis(2-ethylhexyl) terephthalate on ethylcellulose films.
- Authors: Marx, Johannes Scheepers
- Date: 2019
- Subjects: Plasticisers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/44629 , vital:38164
- Description: In recent years, much attention has been focused on research to replace petroleumbased commodity plastics, in a cost-effective manner, with biodegradable materials offering competitive mechanical properties. The use of natural and/or biodegradable plasticisers, with low toxicity and good compatibility with several plastics, resins, rubber and elastomers in substitution of conventional plasticisers, such as phthalates and other synthetic plasticisers attract the market along with the increasing worldwide trend towards the use of bio-polymers. The main research objective entailed the behaviour of the novel bio-plasticiser PMDcitronellal acetal (PMD-CA) and its comparison with other commercial bio-plasticiser, triethyl citrate (TEC) and a non-phthalate plasticiser bis(2-ethylhexyl) terephthalate (DOTP), on ethylcellulose (EC) films to evaluate whether it would be feasible to replace them with PMD-CA. The films were produced by a casting technique and were characterised by mechanical properties, thermoanalysis, Scanning Electron Microscopy, disintegration and Fourier-Transform Infrared (FT-IR) spectroscopy. The addition of any of the three plasticisers to EC film increased the flexibility of the films. The plasticisers PMD-CA and DOTP added to EC formed tougher films as compared to EC films containing TEC shown by the high % elongation at break, strain and displacement. Statistically, it was proved that PMD-CA and DOTP had a more significant effect on % elongation of EC films than TEC, postulated to be due to their similar molecular size and structure. Thermoanalytical studies conducted revealed that the thermal degradation process of EC films proceeded in three basic stages, namely dehydration, depolymerisation and pyrolytic decomposition. Thermoanalytical analysis showed that unplasticised EC films had a higher glass transition value compared to the films containing any of the plasticisers and that PMD-CA and DOTP are more effective plasticisers compared to TEC due to their lower glass transition temperatures. The presence of plasticisers in the polymer matrix did change the surface morphology of polymer films. The addition of hydroxypropyl methylcellulose (HPMC) to EC PMD-CA and EC DOTP films caused more significant globule-like bubbles which were not uniform in size on the surface of these films. Observations were made that the type of plasticiser coating with or without pore former influenced the disintegration properties of films. HPMC, as pore former, played a significant role in the drug release system matrix. EC PMD-CA and EC DOTP polymeric films controlled the disintegration of the films in the acidic and weakly acidic medium. EC and EC TEC films had less significant control on the disintegration rate of the acidic and weakly acidic disintegration media. FT-IR characterisation of the films revealed comparable peaks observed in all the polymer-plasticiser combinations and therefore it was concluded that chemical interactions did not exist between the polymers and plasticisers. Added excipients (plasticisers and pore formers) were found to be compatible with EC films. It was concluded within the scope of this research that EC films plasticised with PMDCA, DOTP or TEC outperformed film properties of those compared to unplasticised EC film. The plasticising properties of the novel bio-plasticiser PMD-CA are similar compared to DOTP, and superior to triethyl citrate and could therefore be considered as an effective bioplasticiser for enteric coating formulations in the pharmaceutical industry.
- Full Text:
- Date Issued: 2019
- Authors: Marx, Johannes Scheepers
- Date: 2019
- Subjects: Plasticisers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/44629 , vital:38164
- Description: In recent years, much attention has been focused on research to replace petroleumbased commodity plastics, in a cost-effective manner, with biodegradable materials offering competitive mechanical properties. The use of natural and/or biodegradable plasticisers, with low toxicity and good compatibility with several plastics, resins, rubber and elastomers in substitution of conventional plasticisers, such as phthalates and other synthetic plasticisers attract the market along with the increasing worldwide trend towards the use of bio-polymers. The main research objective entailed the behaviour of the novel bio-plasticiser PMDcitronellal acetal (PMD-CA) and its comparison with other commercial bio-plasticiser, triethyl citrate (TEC) and a non-phthalate plasticiser bis(2-ethylhexyl) terephthalate (DOTP), on ethylcellulose (EC) films to evaluate whether it would be feasible to replace them with PMD-CA. The films were produced by a casting technique and were characterised by mechanical properties, thermoanalysis, Scanning Electron Microscopy, disintegration and Fourier-Transform Infrared (FT-IR) spectroscopy. The addition of any of the three plasticisers to EC film increased the flexibility of the films. The plasticisers PMD-CA and DOTP added to EC formed tougher films as compared to EC films containing TEC shown by the high % elongation at break, strain and displacement. Statistically, it was proved that PMD-CA and DOTP had a more significant effect on % elongation of EC films than TEC, postulated to be due to their similar molecular size and structure. Thermoanalytical studies conducted revealed that the thermal degradation process of EC films proceeded in three basic stages, namely dehydration, depolymerisation and pyrolytic decomposition. Thermoanalytical analysis showed that unplasticised EC films had a higher glass transition value compared to the films containing any of the plasticisers and that PMD-CA and DOTP are more effective plasticisers compared to TEC due to their lower glass transition temperatures. The presence of plasticisers in the polymer matrix did change the surface morphology of polymer films. The addition of hydroxypropyl methylcellulose (HPMC) to EC PMD-CA and EC DOTP films caused more significant globule-like bubbles which were not uniform in size on the surface of these films. Observations were made that the type of plasticiser coating with or without pore former influenced the disintegration properties of films. HPMC, as pore former, played a significant role in the drug release system matrix. EC PMD-CA and EC DOTP polymeric films controlled the disintegration of the films in the acidic and weakly acidic medium. EC and EC TEC films had less significant control on the disintegration rate of the acidic and weakly acidic disintegration media. FT-IR characterisation of the films revealed comparable peaks observed in all the polymer-plasticiser combinations and therefore it was concluded that chemical interactions did not exist between the polymers and plasticisers. Added excipients (plasticisers and pore formers) were found to be compatible with EC films. It was concluded within the scope of this research that EC films plasticised with PMDCA, DOTP or TEC outperformed film properties of those compared to unplasticised EC film. The plasticising properties of the novel bio-plasticiser PMD-CA are similar compared to DOTP, and superior to triethyl citrate and could therefore be considered as an effective bioplasticiser for enteric coating formulations in the pharmaceutical industry.
- Full Text:
- Date Issued: 2019
Development of spunlaced nonwoven filters from PAN, PPS and PI fibres for industrial use
- Authors: Maduna, Lebo
- Date: 2019
- Subjects: Textile fibers -- Mechanical properties , Nonwoven fabrics --Technological innovations Textile fibers, Synthetic -- Mechanical properties
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32610 , vital:32266
- Description: The aim of this work was to produce filter fabrics suitable for high temperature and other conditions encountered in coal power plants using the spunlacing manufacturing technique. Polyacrylonitrile (PAN), polyphenylene sulfide (PPS) and polyimide (PI) fibres being combined suitable for this purpose, each at three aerial density of (440, 500 and 560 g/m2) and each at three water jet pressures of (60, 80 and 90 bars) were produced. The effect of changing these on the fabric air permeability, tensile strength and filtration properties were investigated and optimized. For this purpose, the Box-Behnken experimental design (BBD) was considered the best and therefore used. The PPS/PI fabrics were found to consistently have the highest air permeability, tensile strength and filtration performance, followed by the PPS fabrics and the PAN fabrics. As could be expected, an increase in area weight and water jet pressure generally resulted in a decrease in air permeability irrespective of the fabric types, this being due to the increased number of fibres and therefore greater fibre surface area and entanglement respectively. For fabric tensile strength, the effects of varying fabric area weight and water jet pressure were not so straight forward. For cross direction (CD) an increase in water jet pressure resulted in an increase tensile strength whereas in the machine direction (MD) there was a decrease when the water jet pressure was increased. The filtration efficiency and dust holding capacity of the fabrics were found to be around 96% and 211g/m2, respectively, with the exception of the PPS (500 g/m2 80 bar) fabrics. Increasing the amount of dust being fed to the fabric during each loading cycle, it caused an increase in pressure drop, as the fabrics became increasingly clogged forming a cake layer.
- Full Text:
- Date Issued: 2019
- Authors: Maduna, Lebo
- Date: 2019
- Subjects: Textile fibers -- Mechanical properties , Nonwoven fabrics --Technological innovations Textile fibers, Synthetic -- Mechanical properties
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32610 , vital:32266
- Description: The aim of this work was to produce filter fabrics suitable for high temperature and other conditions encountered in coal power plants using the spunlacing manufacturing technique. Polyacrylonitrile (PAN), polyphenylene sulfide (PPS) and polyimide (PI) fibres being combined suitable for this purpose, each at three aerial density of (440, 500 and 560 g/m2) and each at three water jet pressures of (60, 80 and 90 bars) were produced. The effect of changing these on the fabric air permeability, tensile strength and filtration properties were investigated and optimized. For this purpose, the Box-Behnken experimental design (BBD) was considered the best and therefore used. The PPS/PI fabrics were found to consistently have the highest air permeability, tensile strength and filtration performance, followed by the PPS fabrics and the PAN fabrics. As could be expected, an increase in area weight and water jet pressure generally resulted in a decrease in air permeability irrespective of the fabric types, this being due to the increased number of fibres and therefore greater fibre surface area and entanglement respectively. For fabric tensile strength, the effects of varying fabric area weight and water jet pressure were not so straight forward. For cross direction (CD) an increase in water jet pressure resulted in an increase tensile strength whereas in the machine direction (MD) there was a decrease when the water jet pressure was increased. The filtration efficiency and dust holding capacity of the fabrics were found to be around 96% and 211g/m2, respectively, with the exception of the PPS (500 g/m2 80 bar) fabrics. Increasing the amount of dust being fed to the fabric during each loading cycle, it caused an increase in pressure drop, as the fabrics became increasingly clogged forming a cake layer.
- Full Text:
- Date Issued: 2019
Development of titanium dioxide for photo-electrochemical hydrogen production
- Authors: Mbulanga, Crispin Munyelele
- Date: 2019
- Subjects: Titanium dioxide , Nanostructured materials Water chemistry Environmental chemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/40735 , vital:36231
- Description: TiO2 is an attractive material for photo electrochemical hydrogen production and in this work the synthesis of this compound by hydrothermal, gel-calcination and one-step templating methods is investigated. Rutile-phase TiO2 rods, which are known to offer direct electrical pathways for photo generated electrons when using TiO2 as a photo anode in a photo-electrochemical hydrogen cell, were prepared on both F:SnO2 (FTO) coated glass and Ti foil substrates. Anatase-phase TiO2 tubes and mixed rutile-anatase-phase TiO2 nanostructured films were developed on FTO-coated glass substrates. Rutile-phase TiO2 rod-like structures, were synthesized hydrothermally at 150 oC for different times (6 – 20 hours) on FTO-coated glass substrate, in an aqueous solution of hydrochloric acid and titanium butoxide. The rod-like structures were found to comprise bundles of crystalline prismatic TiO2 nanorods, each approximately 4 nm in width. Each bundle was tetragonal in shape and highly oriented with respect to the substrate surface. The average diameter of the bundles varied depending on the growth time, and reached a mean diameter of ~175 nm after 20 hours of growth. In terms of Raman scattering, these bundles of nanorods acted as single entities, appearing to act as “larger” crystals to the lattice phonons. Hence, phonon confinement effects could not be observed, because the translational symmetry is preserved at the boundaries between individual rods. Moreover, as the preferential perpendicular orientation of the bundles improved with growth time, an unusual increase in the room and low (77K) temperature Eg/A1g Raman band intensity ratios was observed. The low temperature Raman peak position and peak width data was interpreted as supporting the hypothesis that the bundles of nanorods acting as single entities from the point of view of the lattice phonons. The phonon symmetries and frequencies (in cm-1) of these bundles of rutile-phase TiO2 were found to be consistent with rutile-phase TiO2 phonon symmetries and frequencies. Rutile-phase TiO2 rod-like structures were prepared on Ti foil following a two-step gel-calcination method, which involves a gel-deposition process in 5 M NaOH solution at 76 oC for 24 hours to produce a Na- (and Ti-) based layer of gelatinous material, followed by calcination at 600 oC or 800 oC for 1 hour. It is shown that the use of an alkali-based solution such as NaOH and KOH during gel-deposition, leads to the formation of faceted nanorods of rutile-phase TiO2 upon calcination at high temperature. When a solution that does not contain any alkali element, such as H2O2, was used, the material formed upon calcination at 800 oC were clustered nanoparticles, rather than nanorods. From the experiments it was deduced that the high temperature calcination step converted the Na(or K)-based amorphous gel (formed on the Ti surface during a 24-h soak in NaOH (KOH) solution) into faceted Na-titanate rods, which converted into nanorods of rutile-phase TiO2 when Na(or K) evaporates in the form of an oxide. Anatase-phase TiO2 tube-like structures were produced by a one-step templating solution approach, on FTO-coated glass substrate. ZnO nanorod templates were prepared by chemical bath deposition on FTO-coated glass substrate, and then treated in an aqueous mixture of ammonium hexafluorotitanate and boric acid. To study the effect of the template morphology and deposition processes on the formation of anatase TiO2 tubes, different times (10 – 60 minutes) and concentrations of the precursors are used. Calcination at 550 oC converted the Ti-based material developed on the ZnO rods into TiO2 nanostructures. A 10 minute deposition yielded tubes with dimensions resembling those of the ZnO template. However, the tube walls still contained Zn traces. Based on experimental observations, it was concluded that the production of titanium hydroxide complexes on ZnO surfaces takes place through two competing processes: the development of a Ti-based material and partial dissolution of ZnO along the c-axis. Calcination at 550 oC in air finally yielded anatase TiO2. Mixed rutile-anatase-phase TiO2 nanostructured films on FTO-coated glass substrate were prepared by decorating bundles of crystalline prismatic TiO2 nanorods (prepared hydrothermally) with anatase-phase TiO2 particles, using the same precursors mentioned above. The effect of reaction time and precursor concentrations were investigated. It was found that the precursor concentration ratio and reaction time played key roles in controlling the decoration process. Optimal ratios and decoration times were established based on the density of anatase-phase TiO2 decorating particles on the surface of bundles of rutile-phase TiO2 nanorods. The optical properties of rutile-phase TiO2 rods were investigated. The thickness of the TiO2 layer was calculated from reflectance fringes, and agreed well with the length of rods observed using SEM. The room temperature absorption edge of Eg=2.90 eV extracted from the transmittance spectrum correlated with typical values reported for TiO2. The room temperature absorption edge of the conductive layer of F:SnO2 (Eg=3.56 eV) could also be extracted from the transmittance spectrum. Finally, the absorption of white light by rutile-phase TiO2 rods was confirmed to be enhanced by annealing the rods in either hydrogen or nitrogen at 600 oC. Defects (possibly oxygen vacancies) or disorder in the near surface layers of TiO2 induced during the reduction experiments, created new electronic states in the band gap, as reported in literature.
- Full Text:
- Date Issued: 2019
- Authors: Mbulanga, Crispin Munyelele
- Date: 2019
- Subjects: Titanium dioxide , Nanostructured materials Water chemistry Environmental chemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/40735 , vital:36231
- Description: TiO2 is an attractive material for photo electrochemical hydrogen production and in this work the synthesis of this compound by hydrothermal, gel-calcination and one-step templating methods is investigated. Rutile-phase TiO2 rods, which are known to offer direct electrical pathways for photo generated electrons when using TiO2 as a photo anode in a photo-electrochemical hydrogen cell, were prepared on both F:SnO2 (FTO) coated glass and Ti foil substrates. Anatase-phase TiO2 tubes and mixed rutile-anatase-phase TiO2 nanostructured films were developed on FTO-coated glass substrates. Rutile-phase TiO2 rod-like structures, were synthesized hydrothermally at 150 oC for different times (6 – 20 hours) on FTO-coated glass substrate, in an aqueous solution of hydrochloric acid and titanium butoxide. The rod-like structures were found to comprise bundles of crystalline prismatic TiO2 nanorods, each approximately 4 nm in width. Each bundle was tetragonal in shape and highly oriented with respect to the substrate surface. The average diameter of the bundles varied depending on the growth time, and reached a mean diameter of ~175 nm after 20 hours of growth. In terms of Raman scattering, these bundles of nanorods acted as single entities, appearing to act as “larger” crystals to the lattice phonons. Hence, phonon confinement effects could not be observed, because the translational symmetry is preserved at the boundaries between individual rods. Moreover, as the preferential perpendicular orientation of the bundles improved with growth time, an unusual increase in the room and low (77K) temperature Eg/A1g Raman band intensity ratios was observed. The low temperature Raman peak position and peak width data was interpreted as supporting the hypothesis that the bundles of nanorods acting as single entities from the point of view of the lattice phonons. The phonon symmetries and frequencies (in cm-1) of these bundles of rutile-phase TiO2 were found to be consistent with rutile-phase TiO2 phonon symmetries and frequencies. Rutile-phase TiO2 rod-like structures were prepared on Ti foil following a two-step gel-calcination method, which involves a gel-deposition process in 5 M NaOH solution at 76 oC for 24 hours to produce a Na- (and Ti-) based layer of gelatinous material, followed by calcination at 600 oC or 800 oC for 1 hour. It is shown that the use of an alkali-based solution such as NaOH and KOH during gel-deposition, leads to the formation of faceted nanorods of rutile-phase TiO2 upon calcination at high temperature. When a solution that does not contain any alkali element, such as H2O2, was used, the material formed upon calcination at 800 oC were clustered nanoparticles, rather than nanorods. From the experiments it was deduced that the high temperature calcination step converted the Na(or K)-based amorphous gel (formed on the Ti surface during a 24-h soak in NaOH (KOH) solution) into faceted Na-titanate rods, which converted into nanorods of rutile-phase TiO2 when Na(or K) evaporates in the form of an oxide. Anatase-phase TiO2 tube-like structures were produced by a one-step templating solution approach, on FTO-coated glass substrate. ZnO nanorod templates were prepared by chemical bath deposition on FTO-coated glass substrate, and then treated in an aqueous mixture of ammonium hexafluorotitanate and boric acid. To study the effect of the template morphology and deposition processes on the formation of anatase TiO2 tubes, different times (10 – 60 minutes) and concentrations of the precursors are used. Calcination at 550 oC converted the Ti-based material developed on the ZnO rods into TiO2 nanostructures. A 10 minute deposition yielded tubes with dimensions resembling those of the ZnO template. However, the tube walls still contained Zn traces. Based on experimental observations, it was concluded that the production of titanium hydroxide complexes on ZnO surfaces takes place through two competing processes: the development of a Ti-based material and partial dissolution of ZnO along the c-axis. Calcination at 550 oC in air finally yielded anatase TiO2. Mixed rutile-anatase-phase TiO2 nanostructured films on FTO-coated glass substrate were prepared by decorating bundles of crystalline prismatic TiO2 nanorods (prepared hydrothermally) with anatase-phase TiO2 particles, using the same precursors mentioned above. The effect of reaction time and precursor concentrations were investigated. It was found that the precursor concentration ratio and reaction time played key roles in controlling the decoration process. Optimal ratios and decoration times were established based on the density of anatase-phase TiO2 decorating particles on the surface of bundles of rutile-phase TiO2 nanorods. The optical properties of rutile-phase TiO2 rods were investigated. The thickness of the TiO2 layer was calculated from reflectance fringes, and agreed well with the length of rods observed using SEM. The room temperature absorption edge of Eg=2.90 eV extracted from the transmittance spectrum correlated with typical values reported for TiO2. The room temperature absorption edge of the conductive layer of F:SnO2 (Eg=3.56 eV) could also be extracted from the transmittance spectrum. Finally, the absorption of white light by rutile-phase TiO2 rods was confirmed to be enhanced by annealing the rods in either hydrogen or nitrogen at 600 oC. Defects (possibly oxygen vacancies) or disorder in the near surface layers of TiO2 induced during the reduction experiments, created new electronic states in the band gap, as reported in literature.
- Full Text:
- Date Issued: 2019
A multi-factor model for range estimation in electric vehicles
- Authors: Smuts, Martin Bradley
- Date: 2019
- Subjects: Electric vehicles , Hybrid electric vehicles Energy consumption Machine learning Information technology -- Management
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43589 , vital:36926
- Description: Electric vehicles (EVs) are well-known for their challenges related to trip planning and energy consumption estimation. Range anxiety is currently a barrier to the adoption of EVs. One of the issues influencing range anxiety is the inaccuracy of the remaining driving range (RDR) estimate in on-board displays. RDR displays are important as they can help drivers with trip planning. The RDR is a parameter that changes under environmental and behavioural conditions. Several factors (for example, weather, and traffic) can influence the energy consumption of an EV that are not considered during the RDR estimation in traditional on-board computers or third-party applications, such as navigation or mapping applications. The need for accurate RDR estimation is growing, since this can reduce the range anxiety of drivers. One way of overcoming range anxiety is to provide trip planning applications that provide accurate estimations of the RDR, based on various factors, and which adapt to the users’ driving behaviour. Existing models used for estimating the RDR are often simplified, and do not consider all the factors that can influence it. Collecting data for each factor also presents several challenges. Powerful computing resources are required to collect, transform, and analyse the disparate datasets that are required for each factor. The aim of this research was to design a Multi-factor Model for range estimation in EVs. Five main factors that influence the energy consumption of EVs were identified from literature, namely, Route and Terrain, Driving Behaviour, Weather and Environment, Vehicle Modelling, and Battery Modelling. These factors were used throughout this research to guide the data collection and analysis processes. A Multi-factor Model was proposed based on four main components that collect, process, analyse, and visualise data from available data sources to produce estimates relating to trip planning. A proof-of-concept RDR system was developed and evaluated in field experiments, to demonstrate that the Multi-factor Model addresses the main aim of this research. The experiments were performed to collect data for each of the five factors, and to analyse their impact on energy consumption. Several machine learning techniques were used, and evaluated, for accuracy in estimating the energy consumption, from which the RDR can be derived, for a specified trip. A case study was conducted with an electric mobility programme (uYilo) in Port Elizabeth, South Africa (SA). The case study was used to investigate whether the available resources at uYilo were sufficient to provide data for each of the five factors. Several challenges were noted during the data collection. These were shortages of software applications, a lack of quality data, technical interoperability and data access between the data collection instruments and systems. Data access was a problem in some cases, since proprietary systems restrict access to external developers. The theoretical contribution of this research is a list of factors that influence RDR and a classification of machine learning techniques that can be used to estimate the RDR. The practical contributions of this research include a database of EV trips, proof-of-concept RDR estimation system, and a deployed machine learning model that can be accessed by researchers and EV practitioners. Four research papers were published and presented at local and international conferences. In addition, one conference paper was published in an accredited journal: NextComp 2017 (Appendix C), Conference Paper, Pointe aux Piments (Mauritius); SATNAC 2017 (Appendix F), Conference Paper, Barcelona (Spain); GITMA 2018 (Appendix B), Conference Paper, Mexico City (Mexico); SATNAC 2018 (Appendix G), Conference Paper, George (South Africa), and IFIP World Computer Congress 2018 (Appendix E), Journal Article.
- Full Text:
- Date Issued: 2019
- Authors: Smuts, Martin Bradley
- Date: 2019
- Subjects: Electric vehicles , Hybrid electric vehicles Energy consumption Machine learning Information technology -- Management
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43589 , vital:36926
- Description: Electric vehicles (EVs) are well-known for their challenges related to trip planning and energy consumption estimation. Range anxiety is currently a barrier to the adoption of EVs. One of the issues influencing range anxiety is the inaccuracy of the remaining driving range (RDR) estimate in on-board displays. RDR displays are important as they can help drivers with trip planning. The RDR is a parameter that changes under environmental and behavioural conditions. Several factors (for example, weather, and traffic) can influence the energy consumption of an EV that are not considered during the RDR estimation in traditional on-board computers or third-party applications, such as navigation or mapping applications. The need for accurate RDR estimation is growing, since this can reduce the range anxiety of drivers. One way of overcoming range anxiety is to provide trip planning applications that provide accurate estimations of the RDR, based on various factors, and which adapt to the users’ driving behaviour. Existing models used for estimating the RDR are often simplified, and do not consider all the factors that can influence it. Collecting data for each factor also presents several challenges. Powerful computing resources are required to collect, transform, and analyse the disparate datasets that are required for each factor. The aim of this research was to design a Multi-factor Model for range estimation in EVs. Five main factors that influence the energy consumption of EVs were identified from literature, namely, Route and Terrain, Driving Behaviour, Weather and Environment, Vehicle Modelling, and Battery Modelling. These factors were used throughout this research to guide the data collection and analysis processes. A Multi-factor Model was proposed based on four main components that collect, process, analyse, and visualise data from available data sources to produce estimates relating to trip planning. A proof-of-concept RDR system was developed and evaluated in field experiments, to demonstrate that the Multi-factor Model addresses the main aim of this research. The experiments were performed to collect data for each of the five factors, and to analyse their impact on energy consumption. Several machine learning techniques were used, and evaluated, for accuracy in estimating the energy consumption, from which the RDR can be derived, for a specified trip. A case study was conducted with an electric mobility programme (uYilo) in Port Elizabeth, South Africa (SA). The case study was used to investigate whether the available resources at uYilo were sufficient to provide data for each of the five factors. Several challenges were noted during the data collection. These were shortages of software applications, a lack of quality data, technical interoperability and data access between the data collection instruments and systems. Data access was a problem in some cases, since proprietary systems restrict access to external developers. The theoretical contribution of this research is a list of factors that influence RDR and a classification of machine learning techniques that can be used to estimate the RDR. The practical contributions of this research include a database of EV trips, proof-of-concept RDR estimation system, and a deployed machine learning model that can be accessed by researchers and EV practitioners. Four research papers were published and presented at local and international conferences. In addition, one conference paper was published in an accredited journal: NextComp 2017 (Appendix C), Conference Paper, Pointe aux Piments (Mauritius); SATNAC 2017 (Appendix F), Conference Paper, Barcelona (Spain); GITMA 2018 (Appendix B), Conference Paper, Mexico City (Mexico); SATNAC 2018 (Appendix G), Conference Paper, George (South Africa), and IFIP World Computer Congress 2018 (Appendix E), Journal Article.
- Full Text:
- Date Issued: 2019
A gatherer’s paradise? early humans and plant foraging on the Cape south coast, South Africa
- Authors: Botha, Maria Susan
- Date: 2019
- Subjects: Plant remains (Archaeology) -- South Africa , Plant physiology Plant ecology Botany -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/37139 , vital:34124
- Description: Humans were driven to refugia during the cold and dry glacial Marine Isotope Stage 6 (MIS6) (~195–125 ka); only a few places, including the Cape south coast, show archaeological evidence of continuous human occupation. It has been hypothesised that the Cape south coast provided the requisite shelter to ensure human’s earliest survival because it provided all the right ingredients. The shores offer abundant shellfish, the land a diverse array of plants, and the climate was ameliorated due to the proximity of the then exposed Palaeo-Agulhas Plain to the warm Agulhas current. The aim of this study is to determine whether the indigenous flora of this region could have provided a sufficient edible resource for early humans. Residents of the Cape south coast have genetic ancestry linking them to the Khoe-San, the original inhabitants of the area, and still have an extensive knowledge of the local edible plants. With their help, I set out to determine a) whether humans have been utilising the same plant species over time, b) what the foraging potential of the edible plants in the region is and c) how resilient these plants are to human foraging. If we know whether the plant species known and used today were the same as those that were utilised by past humans, we can then use the contemporary knowledge to make predictions about past utilisation. To answer this question, I collated two databases: archaeological (all plant species found in archaeological sites [dating 0 to 80,000 BP]) and contemporary (all plant species in the modern-day ethnographic literature [last 400 years]) that occur within the Greater Cape Floristic Region(GCFR). I found a significant number of plant species shared between the two databases, which suggests that at least some plant species have been used by humans over a long period of time. To determine the indigenous plant foraging potential of the region, I foraged for food in the Cape south coast (451 bouts) monthly over a two-year period with the help of local inhabitants. The findings show that edible plant resources are distributed patchily and focusing on specific vegetation types would greatly enhance chances of harvesting 2,000 kcal per day, which is considered the daily calorific requirements for a typical hunter-gatherer. I then sought to understand how resilient these plants [(with an emphasis on plants with an underground storage organ (USO)] would be to human foraging. To do this, I set out plots and harvested all edible foods for three consecutive years with the help of foragers. Results indicate that there was a significant reduction in edible weight only in the third year of consecutive harvesting. In conclusion, using various approaches, this study investigates the plant food potential of the Cape south coast from the perspective of early human consumers. The findings suggest that knowledge regarding useful plants dates back to at least 80,000 BP. Food resources are patchily distributed across the main vegetation types found within the Cape south coast and occur in hotspots, i.e. concentrated areas hosting high densities of edible plant foods, surrounded by areas with very low plant food densities. Foragers could have harvested their daily calorific quota more easily if they focused their harvesting efforts in specific vegetation types found in the Cape south coast. Furthermore, many USOs circumvent climatic fluctuations, herbivory or both by staggering their emergence over multiple years, which implies they have some resilience to human foraging.
- Full Text:
- Date Issued: 2019
- Authors: Botha, Maria Susan
- Date: 2019
- Subjects: Plant remains (Archaeology) -- South Africa , Plant physiology Plant ecology Botany -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/37139 , vital:34124
- Description: Humans were driven to refugia during the cold and dry glacial Marine Isotope Stage 6 (MIS6) (~195–125 ka); only a few places, including the Cape south coast, show archaeological evidence of continuous human occupation. It has been hypothesised that the Cape south coast provided the requisite shelter to ensure human’s earliest survival because it provided all the right ingredients. The shores offer abundant shellfish, the land a diverse array of plants, and the climate was ameliorated due to the proximity of the then exposed Palaeo-Agulhas Plain to the warm Agulhas current. The aim of this study is to determine whether the indigenous flora of this region could have provided a sufficient edible resource for early humans. Residents of the Cape south coast have genetic ancestry linking them to the Khoe-San, the original inhabitants of the area, and still have an extensive knowledge of the local edible plants. With their help, I set out to determine a) whether humans have been utilising the same plant species over time, b) what the foraging potential of the edible plants in the region is and c) how resilient these plants are to human foraging. If we know whether the plant species known and used today were the same as those that were utilised by past humans, we can then use the contemporary knowledge to make predictions about past utilisation. To answer this question, I collated two databases: archaeological (all plant species found in archaeological sites [dating 0 to 80,000 BP]) and contemporary (all plant species in the modern-day ethnographic literature [last 400 years]) that occur within the Greater Cape Floristic Region(GCFR). I found a significant number of plant species shared between the two databases, which suggests that at least some plant species have been used by humans over a long period of time. To determine the indigenous plant foraging potential of the region, I foraged for food in the Cape south coast (451 bouts) monthly over a two-year period with the help of local inhabitants. The findings show that edible plant resources are distributed patchily and focusing on specific vegetation types would greatly enhance chances of harvesting 2,000 kcal per day, which is considered the daily calorific requirements for a typical hunter-gatherer. I then sought to understand how resilient these plants [(with an emphasis on plants with an underground storage organ (USO)] would be to human foraging. To do this, I set out plots and harvested all edible foods for three consecutive years with the help of foragers. Results indicate that there was a significant reduction in edible weight only in the third year of consecutive harvesting. In conclusion, using various approaches, this study investigates the plant food potential of the Cape south coast from the perspective of early human consumers. The findings suggest that knowledge regarding useful plants dates back to at least 80,000 BP. Food resources are patchily distributed across the main vegetation types found within the Cape south coast and occur in hotspots, i.e. concentrated areas hosting high densities of edible plant foods, surrounded by areas with very low plant food densities. Foragers could have harvested their daily calorific quota more easily if they focused their harvesting efforts in specific vegetation types found in the Cape south coast. Furthermore, many USOs circumvent climatic fluctuations, herbivory or both by staggering their emergence over multiple years, which implies they have some resilience to human foraging.
- Full Text:
- Date Issued: 2019
The synthesis and assessment of thioxanthone- and xanthone- derived compounds as hosts for application in host-guest chemistry
- Authors: Greyling, Lizé
- Date: 2019
- Subjects: Chemistry, Organic , Biochemistry
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/42525 , vital:36665
- Description: In this work, the host capabilities of two structurally related compounds, N,N’-bis(9-phenyl-9- thioxanthenyl)ethylenediamine (H1) and N,N’-bis(9-phenyl-9-xanthenyl)ethylenediamine (H2) were compared in the presence of a wide variety of guest species. Additionally, the selectivity displayed by these host compounds were examined when exposed to mixtures of guests in order to ascertain whether it would be feasible to employ them in alternative separation strategies for the purification of industrially relevant chemicals. H1 and H2 were synthesized by reacting thioxanthone and xanthone with phenylmagnesium bromide. The resultant alcohol was then treated with perchloric acid and, finally, two of these molecules were effectively linked by utilizing ethylenediamine to afford the two host compounds. Initially, H1 and H2 were investigated for their inclusion abilities by recrystallizing each from a number of potential isomeric and non-isomeric guest compounds such as the xylenes and ethylbenzene, methylanisoles and anisole, methylpyridines and pyridine, methylcyclohexanones and cyclohexanone, heterocyclic five- and six- membered ring compounds, alkylsubstituted benzenes, anilines, and dihaloalkanes. H1 displayed excellent inclusion ability when presented with the above-mentioned compounds, and a 1:1 H:G ratio was consistently preferred in each case. H2 also proved to be successful in this regard but did not include the methylcyclohexanones and cyclohexanone nor the heterocyclic five-membered ring solvents. Furthermore, varying host:guest ratios were observed for the complexes formed with H2. Mixed competition experiments were carried out in the presence of either isomeric or related but non-isomeric guest species. When H1 and H2 were independently recrystallized from mixtures of the former, selectivity orders correlated for both hosts, but it was observed that H2 exhibited an enhanced selectivity for the preferred guests in each case, compared with H1. Interestingly, in mixtures of the latter, host behaviours were distinctly opposing (with the exception of the dihaloalkanes). H1, and even more so H2, demonstrated very high selectivities for p-xylene, aniline and N,Ndimethylaniline from the xylene and aniline guest series, respectively, where selectivities were found to be ~90% or higher for host recrystallization experiments from respective mixtures of these guests. Single crystal X-ray diffraction, Hirshfeld surface and thermal analyses were employed in order to elucidate the reasons for any selectivity observations. The inclusion of these guests was, in most cases, found to be as a result of interactions between host and guest species, which included π∙∙∙π stacking, C‒H∙∙∙π, hydrogen bonding and various other short contact types. Guest compounds were accommodated in either cavities or channels and this was dependent on the nature of the guest. The host molecule conformations showed H1 to adopt a bent tricyclic fused ring system with the N atoms of the linker in a synclinal arrangement, while in complexes with H2, the fused ring system was near-planar and the N atoms adopted an antiperiplanar geometry. These key differences resulted in a very ordered host‒host packing for H2 as a direct result of the more planar O-containing ring and linear linker; for H1, on the other hand, the buckled S-containing ring and gauche-orientated N atoms resulted in a less ordered packing, which ultimately related to the differences in the behaviour of the two host species. Hirshfeld surface analyses, in general, did not provide much information to explain the host selectivities, with the exception of complexes containing the five-membered ring guest heterocyclics. Thermal analyses were completed on all suitable host-guest complexes and, in most cases but not all, the onset and peak temperatures (terms Ton and Tp, respectively) were related to the thermal stability of the complexes, which were used to rationalize the selectivities of these host compounds.
- Full Text:
- Date Issued: 2019
- Authors: Greyling, Lizé
- Date: 2019
- Subjects: Chemistry, Organic , Biochemistry
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/42525 , vital:36665
- Description: In this work, the host capabilities of two structurally related compounds, N,N’-bis(9-phenyl-9- thioxanthenyl)ethylenediamine (H1) and N,N’-bis(9-phenyl-9-xanthenyl)ethylenediamine (H2) were compared in the presence of a wide variety of guest species. Additionally, the selectivity displayed by these host compounds were examined when exposed to mixtures of guests in order to ascertain whether it would be feasible to employ them in alternative separation strategies for the purification of industrially relevant chemicals. H1 and H2 were synthesized by reacting thioxanthone and xanthone with phenylmagnesium bromide. The resultant alcohol was then treated with perchloric acid and, finally, two of these molecules were effectively linked by utilizing ethylenediamine to afford the two host compounds. Initially, H1 and H2 were investigated for their inclusion abilities by recrystallizing each from a number of potential isomeric and non-isomeric guest compounds such as the xylenes and ethylbenzene, methylanisoles and anisole, methylpyridines and pyridine, methylcyclohexanones and cyclohexanone, heterocyclic five- and six- membered ring compounds, alkylsubstituted benzenes, anilines, and dihaloalkanes. H1 displayed excellent inclusion ability when presented with the above-mentioned compounds, and a 1:1 H:G ratio was consistently preferred in each case. H2 also proved to be successful in this regard but did not include the methylcyclohexanones and cyclohexanone nor the heterocyclic five-membered ring solvents. Furthermore, varying host:guest ratios were observed for the complexes formed with H2. Mixed competition experiments were carried out in the presence of either isomeric or related but non-isomeric guest species. When H1 and H2 were independently recrystallized from mixtures of the former, selectivity orders correlated for both hosts, but it was observed that H2 exhibited an enhanced selectivity for the preferred guests in each case, compared with H1. Interestingly, in mixtures of the latter, host behaviours were distinctly opposing (with the exception of the dihaloalkanes). H1, and even more so H2, demonstrated very high selectivities for p-xylene, aniline and N,Ndimethylaniline from the xylene and aniline guest series, respectively, where selectivities were found to be ~90% or higher for host recrystallization experiments from respective mixtures of these guests. Single crystal X-ray diffraction, Hirshfeld surface and thermal analyses were employed in order to elucidate the reasons for any selectivity observations. The inclusion of these guests was, in most cases, found to be as a result of interactions between host and guest species, which included π∙∙∙π stacking, C‒H∙∙∙π, hydrogen bonding and various other short contact types. Guest compounds were accommodated in either cavities or channels and this was dependent on the nature of the guest. The host molecule conformations showed H1 to adopt a bent tricyclic fused ring system with the N atoms of the linker in a synclinal arrangement, while in complexes with H2, the fused ring system was near-planar and the N atoms adopted an antiperiplanar geometry. These key differences resulted in a very ordered host‒host packing for H2 as a direct result of the more planar O-containing ring and linear linker; for H1, on the other hand, the buckled S-containing ring and gauche-orientated N atoms resulted in a less ordered packing, which ultimately related to the differences in the behaviour of the two host species. Hirshfeld surface analyses, in general, did not provide much information to explain the host selectivities, with the exception of complexes containing the five-membered ring guest heterocyclics. Thermal analyses were completed on all suitable host-guest complexes and, in most cases but not all, the onset and peak temperatures (terms Ton and Tp, respectively) were related to the thermal stability of the complexes, which were used to rationalize the selectivities of these host compounds.
- Full Text:
- Date Issued: 2019