An investigation into the readiness of open source software to build a Telco Cloud for virtualising network functions
- Authors: Chindeka, Tapiwa C
- Date: 2020
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/124320 , vital:35593
- Description: Cloud computing offers new mechanisms that change the way networks can be created and managed. The increased demand for multimedia and Internet of Things (IoT) services using the Internet Protocol is also fueling the need to look more into a networking approach that is less reliant on physical hardware components and allows new networks and network components to be created on-demand. Network Function Virtualisation (NFV) is a networking paradigm that decouples network functions from the hardware on which they run on. This offers new approaches to telecommunication providers who are looking to new ways of improving Quality of Service (QoS) in cost effective ways. Cloud technologies have given way to more specialised cloud environments such as the telco cloud. The telco cloud is a cloud environment where telecommunication services are hosted utilising NFV techniques. As the use of telecommunication standards moves towards 5G, network services will be provided in a virtualised manner in order to keep up with the demand. Open source software is a driver for innovation as it is has a collaborative culture to support it. This research investigates the readiness of open source tools to build a telco cloud that supports functions such as autoscaling and fault tolerance. Currently available open source software was explored for the different aspects involved in building a cloud from the ground up. The ETSI NFV MANO framework is also discussed as it is a widely used guiding standard for implementing NFV. Guided by the ETSI NFV MANO framework, open source software was used in an experiment to build a resilient cloud environment in which a virtualised IP Multimedia Subsystem (vIMS) network was deployed. Through this experimentation, it is evident that open source tools are mature enough to build the cloud environment and its ETSI NFV MANO compliant orchestration. However, features such as autoscaling and fault tolerance are still fairly immature and experimental.
- Full Text:
- Date Issued: 2020
- Authors: Chindeka, Tapiwa C
- Date: 2020
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/124320 , vital:35593
- Description: Cloud computing offers new mechanisms that change the way networks can be created and managed. The increased demand for multimedia and Internet of Things (IoT) services using the Internet Protocol is also fueling the need to look more into a networking approach that is less reliant on physical hardware components and allows new networks and network components to be created on-demand. Network Function Virtualisation (NFV) is a networking paradigm that decouples network functions from the hardware on which they run on. This offers new approaches to telecommunication providers who are looking to new ways of improving Quality of Service (QoS) in cost effective ways. Cloud technologies have given way to more specialised cloud environments such as the telco cloud. The telco cloud is a cloud environment where telecommunication services are hosted utilising NFV techniques. As the use of telecommunication standards moves towards 5G, network services will be provided in a virtualised manner in order to keep up with the demand. Open source software is a driver for innovation as it is has a collaborative culture to support it. This research investigates the readiness of open source tools to build a telco cloud that supports functions such as autoscaling and fault tolerance. Currently available open source software was explored for the different aspects involved in building a cloud from the ground up. The ETSI NFV MANO framework is also discussed as it is a widely used guiding standard for implementing NFV. Guided by the ETSI NFV MANO framework, open source software was used in an experiment to build a resilient cloud environment in which a virtualised IP Multimedia Subsystem (vIMS) network was deployed. Through this experimentation, it is evident that open source tools are mature enough to build the cloud environment and its ETSI NFV MANO compliant orchestration. However, features such as autoscaling and fault tolerance are still fairly immature and experimental.
- Full Text:
- Date Issued: 2020
An investigation of the morphological and electrochemical properties of anode titanate materials used in li-ion batteries
- Authors: Gelant, Charmaine
- Date: 2020
- Subjects: Electrodes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48346 , vital:40851
- Description: The chemistry involved in the synthesis of lithium titanium oxide (Li4Ti5O12) for lithium ion battery applications is critical for understanding and optimizing the most cost-efficient manufacturing route. This study investigates the sol-gel synthesis technique of Li4Ti5O12 using triethanolamine (TEOA) as complexing agent by means of in-situ Powder X-ray Diffraction (PXRD). The influence of doping with various metals such as Al3+, Mg2+ , Co3+ and Ni2+ that were made as precursors was considered for comparison purposes due to literature showing improved electrochemical performance using the molecular formula of Li4Ti4.95M0.05O12. The in-situ PXRD technique was used to identify the phase changes that occurred in the thermal synthesis process from the sol-gel precursors to the final crystalline oxides. The materials’ decomposition mechanisms were characterized by thermal gravimetric analysis (TGA) as the precursors were gradually heated to obtain the final oxides. BET surface area analysis and scanning electron microscopy (SEM) were used in order to obtain a morphological understanding of the materials during the synthetic route at specific temperature regions. The in-situ studies have shown that the precursor materials are amorphous at room temperature to about 550 °C, after which the spinel and anatase formed, with relatively small crystallites and a large surface area. The study also showed that a crystalline intermediate phase formed at around 150-200 °C, which then disappeared above 250 °C and was speculated to be a titanium acid (H2Ti2O5.H2O). Upon further heating above 250 °C, the anatase phase converted to the high temperature stable TiO2 phase, rutile, also with an increased formation of the expected LTO spinel phase around 850 °C. Keeping the material at 850 °C, isothermally, did show further conversion of the rutile into the desired spinel phase Li4Ti5O12 (LTO) with an increase in the crystallite size and a decrease in surface area. SEM analysis of the material at 850 °C did show some extensive sintering of the particles with some samples indicating the presence of an additional β-Li2TiO3 phase that formed at the high temperatures. Upon cooling, the βLi2TiO3 phase showed a distinctive powder diffraction pattern besides the typical spinel II LTO phase. The study showed that in comparison to the oxide formed at 850 °C, a mixed phase material of the spinel LTO, anatase and rutile could be achieved at temperatures close to 650 °C with very small crystallites and a relatively large surface area that showed desirable electrochemical properties. Suitable Li-ion coin cells were built with the undoped spinel and doped materials that were isothermally made at 650 °C and 850 °C, whereby their electrochemical properties were tested in the form of cell capacity, electrochemical impedance spectroscopy (EIS) and differential capacity (dQ/dV) studies. The cells made with the materials at 850 °C provided reasonable capacity where the dQ/dV plots did show a single step redox reaction at around 1.5V vs Li/Li+ . These were compared to cells made with commercially available LTO and highlighted the importance of high surface area and small particle size of the active material in order to achieve acceptable electrochemical performances. The cells with the materials made at 650 °C showed to have good capacity upon the first discharge with a number of irreversible phase transitions that were subsequently not observed upon recharging. The dQ/dV graphs showed that the phase transitions were unique to the mixed phase composition of the material made at low temperatures and the cells made with the doped spinel materials were on average better performing than the undoped LTO material. Subsequent grinding steps of the active material made at 850 °C improved the capacity performance of the cells but were still lower when compared to the commercially available material. Hence, significantly longer grinding and processing time would be required to achieve battery active materials that are acceptable for commercial use. This study highlights the importance of understanding the phase transitions that occur during the synthesis route of making battery active material, where doping with different elements and using lower temperatures during synthesis could lead to electroactive materials that do not require additional excessive processing steps such as grinding.
- Full Text:
- Date Issued: 2020
- Authors: Gelant, Charmaine
- Date: 2020
- Subjects: Electrodes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48346 , vital:40851
- Description: The chemistry involved in the synthesis of lithium titanium oxide (Li4Ti5O12) for lithium ion battery applications is critical for understanding and optimizing the most cost-efficient manufacturing route. This study investigates the sol-gel synthesis technique of Li4Ti5O12 using triethanolamine (TEOA) as complexing agent by means of in-situ Powder X-ray Diffraction (PXRD). The influence of doping with various metals such as Al3+, Mg2+ , Co3+ and Ni2+ that were made as precursors was considered for comparison purposes due to literature showing improved electrochemical performance using the molecular formula of Li4Ti4.95M0.05O12. The in-situ PXRD technique was used to identify the phase changes that occurred in the thermal synthesis process from the sol-gel precursors to the final crystalline oxides. The materials’ decomposition mechanisms were characterized by thermal gravimetric analysis (TGA) as the precursors were gradually heated to obtain the final oxides. BET surface area analysis and scanning electron microscopy (SEM) were used in order to obtain a morphological understanding of the materials during the synthetic route at specific temperature regions. The in-situ studies have shown that the precursor materials are amorphous at room temperature to about 550 °C, after which the spinel and anatase formed, with relatively small crystallites and a large surface area. The study also showed that a crystalline intermediate phase formed at around 150-200 °C, which then disappeared above 250 °C and was speculated to be a titanium acid (H2Ti2O5.H2O). Upon further heating above 250 °C, the anatase phase converted to the high temperature stable TiO2 phase, rutile, also with an increased formation of the expected LTO spinel phase around 850 °C. Keeping the material at 850 °C, isothermally, did show further conversion of the rutile into the desired spinel phase Li4Ti5O12 (LTO) with an increase in the crystallite size and a decrease in surface area. SEM analysis of the material at 850 °C did show some extensive sintering of the particles with some samples indicating the presence of an additional β-Li2TiO3 phase that formed at the high temperatures. Upon cooling, the βLi2TiO3 phase showed a distinctive powder diffraction pattern besides the typical spinel II LTO phase. The study showed that in comparison to the oxide formed at 850 °C, a mixed phase material of the spinel LTO, anatase and rutile could be achieved at temperatures close to 650 °C with very small crystallites and a relatively large surface area that showed desirable electrochemical properties. Suitable Li-ion coin cells were built with the undoped spinel and doped materials that were isothermally made at 650 °C and 850 °C, whereby their electrochemical properties were tested in the form of cell capacity, electrochemical impedance spectroscopy (EIS) and differential capacity (dQ/dV) studies. The cells made with the materials at 850 °C provided reasonable capacity where the dQ/dV plots did show a single step redox reaction at around 1.5V vs Li/Li+ . These were compared to cells made with commercially available LTO and highlighted the importance of high surface area and small particle size of the active material in order to achieve acceptable electrochemical performances. The cells with the materials made at 650 °C showed to have good capacity upon the first discharge with a number of irreversible phase transitions that were subsequently not observed upon recharging. The dQ/dV graphs showed that the phase transitions were unique to the mixed phase composition of the material made at low temperatures and the cells made with the doped spinel materials were on average better performing than the undoped LTO material. Subsequent grinding steps of the active material made at 850 °C improved the capacity performance of the cells but were still lower when compared to the commercially available material. Hence, significantly longer grinding and processing time would be required to achieve battery active materials that are acceptable for commercial use. This study highlights the importance of understanding the phase transitions that occur during the synthesis route of making battery active material, where doping with different elements and using lower temperatures during synthesis could lead to electroactive materials that do not require additional excessive processing steps such as grinding.
- Full Text:
- Date Issued: 2020
Analysis of bacterial Mur amide ligase enzymes for the identification of inhibitory compounds by in silico methods
- Chamboko, Chiratidzo Respina
- Authors: Chamboko, Chiratidzo Respina
- Date: 2020
- Subjects: Mur amide ligases , Ligases , Ligand binding (Biochemistry) , Antibacterial agents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/163430 , vital:41036
- Description: An increased emergence of resistant pathogenic bacterial strains over the years has resulted in many people dying of untreatable infections. This has become one of the most critical global public health problems, as resistant strains are complicating treatment of infectious diseases, increasing human morbidity, mortality, and health care costs. A very limited amount of effective antibiotics is currently available, but the development of novel classes of antibacterial agents is becoming a priority. Mur amide ligases are enzymes that have been identified as potentially good targets for antibiotics, as they are uniquely found in bacteria. They are responsible for the formation of peptide bonds in a growing peptidoglycan structure for bacterial cell walls. The current work presented here focused on characterizing these Mur amide ligase enzymes and obtaining inhibitory compounds that could potentially be of use in drug discovery of antibacterial agents. To do this, multiple sequence alignment, motif analysis and phylogenetic tree constructions were carried out, followed by docking studies and molecular dynamic simulations. Prior to docking, homology modelling of missing residues in the MurF structure (PDB 1GG4) was performed. Characterization results revealed the Mur amide ligase enzymes contained defined conservation in limited regions, that ultimately mapped towards the central domain responsible for ATP binding (presence of a conserved GKT motif). Further analysis of results further unraveled the unique patterns observed within each group of the family of enzymes. As a result of these findings, docking studies were carried out on each Mur amide ligase structure. At most, two ligands were identified to be sufficiently inhibiting each Mur amide ligase. The ligands obtained were SANC00574 and SANC00575 for MurC, SANC00290 and SANC00438 for MurD, SANC00290 and SANC00525 for MurE and SANC00290 and SANC00434 for MurF. The two best ligands identified for each enzyme had docked in the active site of their respective proteins, passed Lipinski’s rule of five and had substantially low binding energies. Molecular dynamic simulations were then performed to analyze the behavior of the proteins and protein-ligand complexes, to confirm the lead compounds as good inhibitors of the Mur amide ligases. In the case of MurC, MurD and MurE complexes, the identified ligands clearly impacted the behavior of the protein, as the ligand bound proteins became more compact and stable, while flexibility decreased. There was however an opposite effect on MurF complexes, that resulted in identified inhibitors being discarded. As a potential next step, in vivo and in vitro experiments can be performed with identified ligands from this research, to further support the information presented.
- Full Text:
- Date Issued: 2020
- Authors: Chamboko, Chiratidzo Respina
- Date: 2020
- Subjects: Mur amide ligases , Ligases , Ligand binding (Biochemistry) , Antibacterial agents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/163430 , vital:41036
- Description: An increased emergence of resistant pathogenic bacterial strains over the years has resulted in many people dying of untreatable infections. This has become one of the most critical global public health problems, as resistant strains are complicating treatment of infectious diseases, increasing human morbidity, mortality, and health care costs. A very limited amount of effective antibiotics is currently available, but the development of novel classes of antibacterial agents is becoming a priority. Mur amide ligases are enzymes that have been identified as potentially good targets for antibiotics, as they are uniquely found in bacteria. They are responsible for the formation of peptide bonds in a growing peptidoglycan structure for bacterial cell walls. The current work presented here focused on characterizing these Mur amide ligase enzymes and obtaining inhibitory compounds that could potentially be of use in drug discovery of antibacterial agents. To do this, multiple sequence alignment, motif analysis and phylogenetic tree constructions were carried out, followed by docking studies and molecular dynamic simulations. Prior to docking, homology modelling of missing residues in the MurF structure (PDB 1GG4) was performed. Characterization results revealed the Mur amide ligase enzymes contained defined conservation in limited regions, that ultimately mapped towards the central domain responsible for ATP binding (presence of a conserved GKT motif). Further analysis of results further unraveled the unique patterns observed within each group of the family of enzymes. As a result of these findings, docking studies were carried out on each Mur amide ligase structure. At most, two ligands were identified to be sufficiently inhibiting each Mur amide ligase. The ligands obtained were SANC00574 and SANC00575 for MurC, SANC00290 and SANC00438 for MurD, SANC00290 and SANC00525 for MurE and SANC00290 and SANC00434 for MurF. The two best ligands identified for each enzyme had docked in the active site of their respective proteins, passed Lipinski’s rule of five and had substantially low binding energies. Molecular dynamic simulations were then performed to analyze the behavior of the proteins and protein-ligand complexes, to confirm the lead compounds as good inhibitors of the Mur amide ligases. In the case of MurC, MurD and MurE complexes, the identified ligands clearly impacted the behavior of the protein, as the ligand bound proteins became more compact and stable, while flexibility decreased. There was however an opposite effect on MurF complexes, that resulted in identified inhibitors being discarded. As a potential next step, in vivo and in vitro experiments can be performed with identified ligands from this research, to further support the information presented.
- Full Text:
- Date Issued: 2020
Analysis of bacterial Mur amide ligase enzymes for the identification of inhibitory compounds by in silico methods
- Chamboko, Chiratidzo Respina
- Authors: Chamboko, Chiratidzo Respina
- Date: 2020
- Subjects: Pathogenic microorganisms -- Analysis , Drug resistance in microorganisms , Microorganisms -- Effect of drugs on , Antibiotics -- Effectiveness , Pathogenic bacteria , Drug tolerance , Enzymes -- Analysis , Peptide antibiotics
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/161911 , vital:40690
- Description: An increased emergence of resistant pathogenic bacterial strains over the years has resulted in many people dying of untreatable infections. This has become one of the most critical global public health problems, as resistant strains are complicating treatment of infectious diseases, increasing human morbidity, mortality, and health care costs. A very limited amount of effective antibiotics is currently available, but the development of novel classes of antibacterial agents is becoming a priority. Mur amide ligases are enzymes that have been identified as potentially good targets for antibiotics, as they are uniquely found in bacteria. They are responsible for the formation of peptide bonds in a growing peptidoglycan structure for bacterial cell walls. The current work presented here focused on characterizing these Mur amide ligase enzymes and obtaining inhibitory compounds that could potentially be of use in drug discovery of antibacterial agents. To do this, multiple sequence alignment, motif analysis and phylogenetic tree constructions were carried out, followed by docking studies and molecular dynamic simulations. Prior to docking, homology modelling of missing residues in the MurF structure (PDB 1GG4) was performed. Characterization results revealed the Mur amide ligase enzymes contained defined conservation in limited regions, that ultimately mapped towards the central domain responsible for ATP binding (presence of a conserved GKT motif). Further analysis of results further unraveled the unique patterns observed within each group of the family of enzymes. As a result of these findings, docking studies were carried out on each Mur amide ligase structure. At most, two ligands were identified to be sufficiently inhibiting each Mur amide ligase. The ligands obtained were SANC00574 and SANC00575 for MurC, SANC00290 and SANC00438 for MurD, SANC00290 and SANC00525 for MurE and SANC00290 and SANC00434 for MurF. The two best ligands identified for each enzyme had docked in the active site of their respective proteins, passed Lipinski’s rule of five and had substantially low binding energies. Molecular dynamic simulations were then performed to analyze the behavior of the proteins and protein-ligand complexes, to confirm the lead compounds as good inhibitors of the Mur amide ligases. In the case of MurC, MurD and MurE complexes, the identified ligands clearly impacted the behavior of the protein, as the ligand bound proteins became more compact and stable, while flexibility decreased. There was however an opposite effect on MurF complexes, that resulted in identified inhibitors being discarded. As a potential next step, in vivo and in vitro experiments can be performed with identified ligands from this research, to further support the information presented.
- Full Text:
- Date Issued: 2020
- Authors: Chamboko, Chiratidzo Respina
- Date: 2020
- Subjects: Pathogenic microorganisms -- Analysis , Drug resistance in microorganisms , Microorganisms -- Effect of drugs on , Antibiotics -- Effectiveness , Pathogenic bacteria , Drug tolerance , Enzymes -- Analysis , Peptide antibiotics
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/161911 , vital:40690
- Description: An increased emergence of resistant pathogenic bacterial strains over the years has resulted in many people dying of untreatable infections. This has become one of the most critical global public health problems, as resistant strains are complicating treatment of infectious diseases, increasing human morbidity, mortality, and health care costs. A very limited amount of effective antibiotics is currently available, but the development of novel classes of antibacterial agents is becoming a priority. Mur amide ligases are enzymes that have been identified as potentially good targets for antibiotics, as they are uniquely found in bacteria. They are responsible for the formation of peptide bonds in a growing peptidoglycan structure for bacterial cell walls. The current work presented here focused on characterizing these Mur amide ligase enzymes and obtaining inhibitory compounds that could potentially be of use in drug discovery of antibacterial agents. To do this, multiple sequence alignment, motif analysis and phylogenetic tree constructions were carried out, followed by docking studies and molecular dynamic simulations. Prior to docking, homology modelling of missing residues in the MurF structure (PDB 1GG4) was performed. Characterization results revealed the Mur amide ligase enzymes contained defined conservation in limited regions, that ultimately mapped towards the central domain responsible for ATP binding (presence of a conserved GKT motif). Further analysis of results further unraveled the unique patterns observed within each group of the family of enzymes. As a result of these findings, docking studies were carried out on each Mur amide ligase structure. At most, two ligands were identified to be sufficiently inhibiting each Mur amide ligase. The ligands obtained were SANC00574 and SANC00575 for MurC, SANC00290 and SANC00438 for MurD, SANC00290 and SANC00525 for MurE and SANC00290 and SANC00434 for MurF. The two best ligands identified for each enzyme had docked in the active site of their respective proteins, passed Lipinski’s rule of five and had substantially low binding energies. Molecular dynamic simulations were then performed to analyze the behavior of the proteins and protein-ligand complexes, to confirm the lead compounds as good inhibitors of the Mur amide ligases. In the case of MurC, MurD and MurE complexes, the identified ligands clearly impacted the behavior of the protein, as the ligand bound proteins became more compact and stable, while flexibility decreased. There was however an opposite effect on MurF complexes, that resulted in identified inhibitors being discarded. As a potential next step, in vivo and in vitro experiments can be performed with identified ligands from this research, to further support the information presented.
- Full Text:
- Date Issued: 2020
Analysis of maximum power point tracking data for obtaining photovoltaic parameters
- Authors: Chitura, Anesu Godfrey
- Date: 2020
- Subjects: Photovoltaic power system
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/18576 , vital:42610
- Description: As a standard, photovoltaic (PV) modules are rated by the use of standard test conditions (STC). Such details entail current and voltage (I-V) measurements for modules under an irradiance of 1000 W/m2 an air mass ration of 1.5 global spectrum and 25˚C cell temperature. Outdoor weather conditions continuously vary with time and from one location to the other. This further offset the expected operational power outputs as outdoor conditions are generally characterized by high cell temperatures. The technology one uses will also complicate the power output prediction since different module technologies respond to these outdoor conditions differently. I-V tracers are able to measure the full I-V curve of the module thus can give the operational PV parameters at any given time. However, these tracers are sold at exorbitant prices and they require skilled personnel in order to operate them. Most if not all tracers require isolation of the module under test thereby disrupting the power production function of the module._________________________________________________________________________________________________________________________________________ In this study a method to obtain photovoltaic (PV) parameters using the maximum power point tracking (MPPT) data is presented and tested under natural outdoor conditions. The method features a customized data acquisition system (DAS) designed for the measurement and storage of meteorological and MPPT data. The DAS is capable of extracting parameters from any combination of modules with an open circuit voltage 〖(V〗_oc) less than or equal to 120 Volts and a short circuit current 〖(I〗_sc) of 100 Amps. The system used is capable of extracting MPPT data using a reliable, improved storage and a programmable data logger. In order to match the sampling operational speeds of internal charge controller switches a computer interfaced Peripheral Component Interconnect (PCI) card was also used. Data collection and characterization of the MPPT data was done in such a way that the power generation process remained uninterrupted throughout the whole process. The regression nonlinear least squares method was used to fit MPPT crests and obtain the knee part of the I-V curve. This was then extrapolated to obtain the full I-V curve, which then produces the operational PV parameters. The resultant parameters from the characterization process were logged and accessible at any time. The end result was a method that can be incorporated within a charge controller for quick, hands-free PV parameter extraction, using only the MPPT scanned data.
- Full Text:
- Date Issued: 2020
- Authors: Chitura, Anesu Godfrey
- Date: 2020
- Subjects: Photovoltaic power system
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/18576 , vital:42610
- Description: As a standard, photovoltaic (PV) modules are rated by the use of standard test conditions (STC). Such details entail current and voltage (I-V) measurements for modules under an irradiance of 1000 W/m2 an air mass ration of 1.5 global spectrum and 25˚C cell temperature. Outdoor weather conditions continuously vary with time and from one location to the other. This further offset the expected operational power outputs as outdoor conditions are generally characterized by high cell temperatures. The technology one uses will also complicate the power output prediction since different module technologies respond to these outdoor conditions differently. I-V tracers are able to measure the full I-V curve of the module thus can give the operational PV parameters at any given time. However, these tracers are sold at exorbitant prices and they require skilled personnel in order to operate them. Most if not all tracers require isolation of the module under test thereby disrupting the power production function of the module._________________________________________________________________________________________________________________________________________ In this study a method to obtain photovoltaic (PV) parameters using the maximum power point tracking (MPPT) data is presented and tested under natural outdoor conditions. The method features a customized data acquisition system (DAS) designed for the measurement and storage of meteorological and MPPT data. The DAS is capable of extracting parameters from any combination of modules with an open circuit voltage 〖(V〗_oc) less than or equal to 120 Volts and a short circuit current 〖(I〗_sc) of 100 Amps. The system used is capable of extracting MPPT data using a reliable, improved storage and a programmable data logger. In order to match the sampling operational speeds of internal charge controller switches a computer interfaced Peripheral Component Interconnect (PCI) card was also used. Data collection and characterization of the MPPT data was done in such a way that the power generation process remained uninterrupted throughout the whole process. The regression nonlinear least squares method was used to fit MPPT crests and obtain the knee part of the I-V curve. This was then extrapolated to obtain the full I-V curve, which then produces the operational PV parameters. The resultant parameters from the characterization process were logged and accessible at any time. The end result was a method that can be incorporated within a charge controller for quick, hands-free PV parameter extraction, using only the MPPT scanned data.
- Full Text:
- Date Issued: 2020
Analysis of the effectiveness of Tulbaghia Violacea extracts as devulcanizing agents for synthetic CIS-1,4-polyisoprene vulcanizates
- Authors: Gxakuma, Lutho
- Date: 2020
- Subjects: Plant extracts , Plant products -- South Africa Medicinal plants -- South Africa Plants -- Analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49093 , vital:41600
- Description: Tulbaghia violacea is an indigenous plant commonly known as wild garlic, wilde knoffel in Afrikaans, isihaqa in Zulu or itswele lomlambo in Xhosa. Its leaves and bulbs are widely used as herbal remedies for various ailments and its medicinal uses include fever and colds, asthma, tuberculosis and stomach problems. Like all other members of the Alliacea family, Tulbaghia violacea produces a distinctive garlic-like odour when its leaves or rhizomes are damaged, resulting in the release of cysteine-derived sulphur compounds which include the oil-soluble organo-sulphur compounds and water-soluble cysteine derivatives. Chemically synthesized sulphur containing compounds have been reported to be effective devulcanizing agents and many industries prefer to perform devulcanization using them. Most commonly applied devulcanizing agents include disulphides, thiophenols and their zinc salts, and mercaptans which are mixed with the rubber scrap powder under specific reaction conditions. In this study, instead of performing devulcanization by using industrial synthesized sulphur containing compounds, the effectiveness of the extracts of organo-sulphur containing compounds from Tulbaghia violacea are evaluated as potential devulcanizing agents for synthetic cis-1,4-polyisoprene vulcanizates. This is a new, cheap and greener practice of rubber devulcanization. Diallyl disulphide, which is one of the organo-sulphur containing compounds present in Tulbaghia violacea, is the devulcanizing agent of interest to this study. The organo-sulphur containing compounds were extracted from the bulbs, roots and leaves of the plant using the soxhlet and ultrasonic bath extraction method. The solvent system used in the soxhlet extraction method was 2% of 2-propanol in n-hexane whereas in ultrasonic bath extraction method the solvent system used was 100% ethanol. An essential oil extract was obtained from the plant organs. The yield of the essential oil extracts obtained using the soxhlet extraction method was higher compared to the yield of the essential oil extracts obtained using the ultrasonic bath extraction method. According to the Fourier-Transform Infrared spectroscopy, the organo-sulphur containing compounds were present in the essential oil extracts of the plant. The essential oil extracts that were extracted using the soxhlet extraction method were chosen for further analysis. It was found out that the allyl sulphide and diallyl disulphide have the same retention time from the High Performance Liquid Chromatography (using a normal phase column). The Differential Scanning Calorimeter indicated that the allyl sulphide was not present in the essential oil extracts whereas the diallyl disulphide was present in the essential oil extract of the roots and leaves. The High Performance Liquid Chromatography was used to quantify the presence of the diallyl disulphide in the essential oil extract of roots and leaves. The quantity of diallyl disulphide was 23% in the dry mass of the essential oil extract of roots. In the essential oil extract of leaves the diallyl disulphide was very low concentrated and the High Performance Liquid Chromatography was less sensitive to detect it. According to the Thermogravimetric Analyser, it was found that the essential oil extracts begin to degrade at 120 °C and experience a multistage degradation. The softening temperature of the essential oil extracts was 60 °C from the Simultaneous Differential Scanning Calorimeter-Thermogravimetric Analyser. Conventional vulcanization of synthetic cis-1,4-polyisoprene was prepared with the vulcanization ingredients of zinc oxide, sulphur, stearic acid and N-tert-butyl-2-benzothiazole sulphenamide. The vulcanized synthetic cis-1,4-polyisoprene produced, under the heating temperature of 160 °C, was mixed with the essential oil extracts using the internal mixer at 60 °C and the two-roll mill. The overall torque, tan delta and the total crosslink density were the properties of interest of synthetic cis-1,4-polyisoprene vulcanizate in this study. The devulcanization temperature for the treated synthetic cis-1,4-polyisoprene vulcanizate with the essential oil extracts was optimized using the Dynamic Moving Die Rheometer and Dynamic Rubber Process Analyser. The amount of essential oil extracts at which they are effective devulcanizing agents for synthetic cis-1,4-polyisoprene vulcanizate was also optimized. During optimization a change on the latter mentioned properties of synthetic cis-1,4-polyisoprene vulcanizate was observed, indicating that the essential oil extracts have an effect as potential devulcanizing agents. The essential oil extracts increased the tan delta and reduced the overall torque, and total crosslink density of synthetic cis-1,4-polyisoprene vulcanizate as expected from devulcanizing agents. 200 °C was a preferable devulcanization temperature whereas essential oil extracts were effective as devulcanizing agent at 1.4%. However, the essential oil extracts influenced the overall torque and tan delta of synthetic cis-1,4-polyisoprene vulcanizate during the mixing process in the internal mixer at 60 °C, which was before heating at 200 °C. The essential oil extracts had a higher influence on the overall torque of synthetic cis-1,4-polyisoprene vulcanizate under heating at 200 °C whereas at 60 °C, during the mixing process, they had a higher influence on the tan delta of synthetic cis-1,4-polyisoprene vulcanizate. The essential oil extract of leaves had a higher influence on the overall torque whereas the essential oil extract of bulbs had a higher influence on the tan delta of synthetic cis-1,4-polyisoprene vulcanizate at 200 °C. The essential oil extract of roots shown a greater influence on the overall torque and tan delta of synthetic cis-1,4-polyisoprene vulcanizate at 60 °C during the mixing process. The effect of the essential oil extracts on the reversing heat capacity of synthetic cis-1,4-polyisoprene vulcanizate was also investigated using the Modulated Differential Scanning Calorimetry method. The essential oil extract of bulbs and roots influenced the reversing heat capacity of synthetic cis-1,4-polyisoprene vulcanizate by reducing it whereas the essential oil extract of leaves caused a temperature shift of the reversing heat capacity curve from the Modulated Differential Scanning Calorimeter thermogram of synthetic cis-1,4-polyisoprene vulcanizate. Therefore, the results indicated that the essential oil extracts of Tulbaghia violacea have an effect as an alternative potential devulcanizing agents for conventional vulcanized synthetic cis-1,4-polyisoprene whether the diallyl disulphide compound is present or not in them.
- Full Text:
- Date Issued: 2020
- Authors: Gxakuma, Lutho
- Date: 2020
- Subjects: Plant extracts , Plant products -- South Africa Medicinal plants -- South Africa Plants -- Analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49093 , vital:41600
- Description: Tulbaghia violacea is an indigenous plant commonly known as wild garlic, wilde knoffel in Afrikaans, isihaqa in Zulu or itswele lomlambo in Xhosa. Its leaves and bulbs are widely used as herbal remedies for various ailments and its medicinal uses include fever and colds, asthma, tuberculosis and stomach problems. Like all other members of the Alliacea family, Tulbaghia violacea produces a distinctive garlic-like odour when its leaves or rhizomes are damaged, resulting in the release of cysteine-derived sulphur compounds which include the oil-soluble organo-sulphur compounds and water-soluble cysteine derivatives. Chemically synthesized sulphur containing compounds have been reported to be effective devulcanizing agents and many industries prefer to perform devulcanization using them. Most commonly applied devulcanizing agents include disulphides, thiophenols and their zinc salts, and mercaptans which are mixed with the rubber scrap powder under specific reaction conditions. In this study, instead of performing devulcanization by using industrial synthesized sulphur containing compounds, the effectiveness of the extracts of organo-sulphur containing compounds from Tulbaghia violacea are evaluated as potential devulcanizing agents for synthetic cis-1,4-polyisoprene vulcanizates. This is a new, cheap and greener practice of rubber devulcanization. Diallyl disulphide, which is one of the organo-sulphur containing compounds present in Tulbaghia violacea, is the devulcanizing agent of interest to this study. The organo-sulphur containing compounds were extracted from the bulbs, roots and leaves of the plant using the soxhlet and ultrasonic bath extraction method. The solvent system used in the soxhlet extraction method was 2% of 2-propanol in n-hexane whereas in ultrasonic bath extraction method the solvent system used was 100% ethanol. An essential oil extract was obtained from the plant organs. The yield of the essential oil extracts obtained using the soxhlet extraction method was higher compared to the yield of the essential oil extracts obtained using the ultrasonic bath extraction method. According to the Fourier-Transform Infrared spectroscopy, the organo-sulphur containing compounds were present in the essential oil extracts of the plant. The essential oil extracts that were extracted using the soxhlet extraction method were chosen for further analysis. It was found out that the allyl sulphide and diallyl disulphide have the same retention time from the High Performance Liquid Chromatography (using a normal phase column). The Differential Scanning Calorimeter indicated that the allyl sulphide was not present in the essential oil extracts whereas the diallyl disulphide was present in the essential oil extract of the roots and leaves. The High Performance Liquid Chromatography was used to quantify the presence of the diallyl disulphide in the essential oil extract of roots and leaves. The quantity of diallyl disulphide was 23% in the dry mass of the essential oil extract of roots. In the essential oil extract of leaves the diallyl disulphide was very low concentrated and the High Performance Liquid Chromatography was less sensitive to detect it. According to the Thermogravimetric Analyser, it was found that the essential oil extracts begin to degrade at 120 °C and experience a multistage degradation. The softening temperature of the essential oil extracts was 60 °C from the Simultaneous Differential Scanning Calorimeter-Thermogravimetric Analyser. Conventional vulcanization of synthetic cis-1,4-polyisoprene was prepared with the vulcanization ingredients of zinc oxide, sulphur, stearic acid and N-tert-butyl-2-benzothiazole sulphenamide. The vulcanized synthetic cis-1,4-polyisoprene produced, under the heating temperature of 160 °C, was mixed with the essential oil extracts using the internal mixer at 60 °C and the two-roll mill. The overall torque, tan delta and the total crosslink density were the properties of interest of synthetic cis-1,4-polyisoprene vulcanizate in this study. The devulcanization temperature for the treated synthetic cis-1,4-polyisoprene vulcanizate with the essential oil extracts was optimized using the Dynamic Moving Die Rheometer and Dynamic Rubber Process Analyser. The amount of essential oil extracts at which they are effective devulcanizing agents for synthetic cis-1,4-polyisoprene vulcanizate was also optimized. During optimization a change on the latter mentioned properties of synthetic cis-1,4-polyisoprene vulcanizate was observed, indicating that the essential oil extracts have an effect as potential devulcanizing agents. The essential oil extracts increased the tan delta and reduced the overall torque, and total crosslink density of synthetic cis-1,4-polyisoprene vulcanizate as expected from devulcanizing agents. 200 °C was a preferable devulcanization temperature whereas essential oil extracts were effective as devulcanizing agent at 1.4%. However, the essential oil extracts influenced the overall torque and tan delta of synthetic cis-1,4-polyisoprene vulcanizate during the mixing process in the internal mixer at 60 °C, which was before heating at 200 °C. The essential oil extracts had a higher influence on the overall torque of synthetic cis-1,4-polyisoprene vulcanizate under heating at 200 °C whereas at 60 °C, during the mixing process, they had a higher influence on the tan delta of synthetic cis-1,4-polyisoprene vulcanizate. The essential oil extract of leaves had a higher influence on the overall torque whereas the essential oil extract of bulbs had a higher influence on the tan delta of synthetic cis-1,4-polyisoprene vulcanizate at 200 °C. The essential oil extract of roots shown a greater influence on the overall torque and tan delta of synthetic cis-1,4-polyisoprene vulcanizate at 60 °C during the mixing process. The effect of the essential oil extracts on the reversing heat capacity of synthetic cis-1,4-polyisoprene vulcanizate was also investigated using the Modulated Differential Scanning Calorimetry method. The essential oil extract of bulbs and roots influenced the reversing heat capacity of synthetic cis-1,4-polyisoprene vulcanizate by reducing it whereas the essential oil extract of leaves caused a temperature shift of the reversing heat capacity curve from the Modulated Differential Scanning Calorimeter thermogram of synthetic cis-1,4-polyisoprene vulcanizate. Therefore, the results indicated that the essential oil extracts of Tulbaghia violacea have an effect as an alternative potential devulcanizing agents for conventional vulcanized synthetic cis-1,4-polyisoprene whether the diallyl disulphide compound is present or not in them.
- Full Text:
- Date Issued: 2020
Analysis of the regulation of HSP90α expression upon differentiation of C2C12 cells
- Authors: Holm, Nathan Christopher
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/163318 , vital:41028
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Biochemistry and Microbiology, 2020.
- Full Text:
- Date Issued: 2020
- Authors: Holm, Nathan Christopher
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/163318 , vital:41028
- Description: Thesis (MSc)--Rhodes University, Faculty of Science, Biochemistry and Microbiology, 2020.
- Full Text:
- Date Issued: 2020
Applying high-resolution remote sensing to quantify baboon damage at a sub-compartment level in pine stands in the Mpumalanga escarpment region of South Africa
- Authors: Ferreira, Regardt
- Date: 2020
- Subjects: Environmental sciences -- Remote sensing , Geographic information systems Remote sensing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49082 , vital:41599
- Description: Managing risk in intensively managed monoculture plantation forests is an essential task to ensure sustainable yield and a continuous flow of forest products. However, since risks can be either biotic or abiotic, not all of them have a predictable pattern of spread, which can cause severe losses if management does not have the chance to implement mitigation action. Monitoring the change in forest health is vital as this provides the opportunity for preventative management and quantifies the amount of damage that management has to deal with. To provide this window of opportunity for appropriate action, constant monitoring is required. Until recently, forest health was measured through field surveys which provided adequate data. This procedure, however, is time consuming. Remote sensing has become very popular as a monitoring tool, due to its ability to provide assessment data in a fraction of the time. In this study, baboon damage in plantations along the Mpumalanga escarpment area of South Africa was monitored using remote sensing methods. While there are many methods of forest health monitoring using remote sensing, some approaches are less suitable as they either monitor damage caused at a plantation level, use lower spatial resolution (>10m) datasets or map damage using one available time period. The purpose of this study was first to establish the impact of baboon damage through time, using Sentinel-2 satellite imagery with all vegetation indices available, and the Extreme Gradient Boosting (XGboost) algorithm. The second part focused on analysing the damage at a tree level using PlanetScope imagery using a deep Learning approach. Overall, the study found that the use of Sentinel-2 data and PlanetScope data could accurately distinguish between the varying severity of baboon damage, achieving an accuracy of 95% and 82%. The processing time of the deep learning Artificial Neural Network (ANN) was greatly affected by the number of hidden layers and neurons used. Implementation of techniques used in this study has the potential to improve the accuracy of forest health monitoring in compartment forestry in South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Ferreira, Regardt
- Date: 2020
- Subjects: Environmental sciences -- Remote sensing , Geographic information systems Remote sensing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49082 , vital:41599
- Description: Managing risk in intensively managed monoculture plantation forests is an essential task to ensure sustainable yield and a continuous flow of forest products. However, since risks can be either biotic or abiotic, not all of them have a predictable pattern of spread, which can cause severe losses if management does not have the chance to implement mitigation action. Monitoring the change in forest health is vital as this provides the opportunity for preventative management and quantifies the amount of damage that management has to deal with. To provide this window of opportunity for appropriate action, constant monitoring is required. Until recently, forest health was measured through field surveys which provided adequate data. This procedure, however, is time consuming. Remote sensing has become very popular as a monitoring tool, due to its ability to provide assessment data in a fraction of the time. In this study, baboon damage in plantations along the Mpumalanga escarpment area of South Africa was monitored using remote sensing methods. While there are many methods of forest health monitoring using remote sensing, some approaches are less suitable as they either monitor damage caused at a plantation level, use lower spatial resolution (>10m) datasets or map damage using one available time period. The purpose of this study was first to establish the impact of baboon damage through time, using Sentinel-2 satellite imagery with all vegetation indices available, and the Extreme Gradient Boosting (XGboost) algorithm. The second part focused on analysing the damage at a tree level using PlanetScope imagery using a deep Learning approach. Overall, the study found that the use of Sentinel-2 data and PlanetScope data could accurately distinguish between the varying severity of baboon damage, achieving an accuracy of 95% and 82%. The processing time of the deep learning Artificial Neural Network (ANN) was greatly affected by the number of hidden layers and neurons used. Implementation of techniques used in this study has the potential to improve the accuracy of forest health monitoring in compartment forestry in South Africa.
- Full Text:
- Date Issued: 2020
Assessing community structure and trophic interrelationships in three differently impacted headwater streams in the AmatholeWinterberg freshwater ecoregion, South Africa
- Authors: Matomela, Nonjabulo Happy
- Date: 2020
- Subjects: Stream ecology -- South Africa -- Eastern Cape , Freshwater animals -- Ecology -- South Africa -- Eastern Cape , Kat River (South Africa) -- , Lushington River (South Africa) , Elands River (South Africa) , Eyre River (South Africa) , Food chains (Ecology) -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Land use -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/147653 , vital:38658
- Description: Afromontane regions represent some of the highly threatened ecosystems on the planet as they harbour endemic and often relic freshwater fauna. These ecologically sensitive ecosystems have been altered by multiple impacts, including invasion by non-native fishes, replacement of diverse indigenous vegetation with monoculture plantations, agricultural and mining activities, hydrological modifications, and degradation of instream habitats, with potential detrimental effects on aquatic community structures and food web dynamics. The aim of the present study was to compare spatio-temporal patterns of macroinvertebrate and fish communities as well as food web dynamics in three differently impacted headwater tributaries of the Kat River in the Amathole-Winterberg freshwater ecoregion in the Eastern Cape Province of South Africa. The upper Kat River catchment was the ideal model for purposes of the present study as it contains streams with varying degrees of human impact. The streams considered in the present study were (i) the Eyre River which was considered to closely represent near-natural conditions as it is the least impacted stream in this catchment, with the riparian zone dominated by relatively intact and diverse native woody vegetation, (ii) the Elands River whose catchment has been altered by agricultural activities, and (iii) the Lushington River, whose riparian zone has been heavily invaded by black wattle. The three headwater streams were generally distinguished based on the physical-chemical variables. The Elands River was characterised by high conductivity and total dissolved solids (TDS). In addition, the Elands River was more alkaline and relatively warmer than the other two rivers. This suggested the negative influence of agriculture activities on the water quality in the Elands River. In general, the Lushington and Eyre rivers had comparable physical and chemical variables. However, the Lushington River was generally characterised by low streamflow, likely as a consequent of black wattle which is known for altering hydrological regimes of streams .The Eyre River and Lushington River were comparable in terms of macroinvertebrate richness and diversity, whereas the Elands River was characterised by low macroinvertebrate diversity and richness. Redundancy analysis indicated that the macroinvertebrate communities were mostly influenced by seasonality, with land-use accounting for a small but significant difference in community composition. In comparison, the generalised linear mixed-effects models (GLMMs) showed that chubbyhead barb abundance was significantly influenced by land-use patterns. Evaluation of food web dynamics using stable isotope analysis revealed that the food web structure in the three rivers differed substantially as a result of land-use. Specifically, the Eyre River was characterised by less variation in stable isotope values of basal food sources and consequently, the consumer groups had a narrow isotopic breadth. In contrast, the Elands River was characterised by a wide variation in basal food sources and therefore, a wider isotopic breadth for consumers. The Lushington River was spatially variable in terms of basal sources and isotopic breadth for consumers. The study concluded that food webs and trophic interrelationships were a more informative indicator of land-use than community structure was in evaluating the impact of land-use patterns on aquatic communities. In addition, future studies should seek to investigate food webs interrelationships in addition to community structure to infer a more conclusive river assessment.
- Full Text:
- Date Issued: 2020
- Authors: Matomela, Nonjabulo Happy
- Date: 2020
- Subjects: Stream ecology -- South Africa -- Eastern Cape , Freshwater animals -- Ecology -- South Africa -- Eastern Cape , Kat River (South Africa) -- , Lushington River (South Africa) , Elands River (South Africa) , Eyre River (South Africa) , Food chains (Ecology) -- South Africa -- Eastern Cape , Water quality -- South Africa -- Eastern Cape , Land use -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/147653 , vital:38658
- Description: Afromontane regions represent some of the highly threatened ecosystems on the planet as they harbour endemic and often relic freshwater fauna. These ecologically sensitive ecosystems have been altered by multiple impacts, including invasion by non-native fishes, replacement of diverse indigenous vegetation with monoculture plantations, agricultural and mining activities, hydrological modifications, and degradation of instream habitats, with potential detrimental effects on aquatic community structures and food web dynamics. The aim of the present study was to compare spatio-temporal patterns of macroinvertebrate and fish communities as well as food web dynamics in three differently impacted headwater tributaries of the Kat River in the Amathole-Winterberg freshwater ecoregion in the Eastern Cape Province of South Africa. The upper Kat River catchment was the ideal model for purposes of the present study as it contains streams with varying degrees of human impact. The streams considered in the present study were (i) the Eyre River which was considered to closely represent near-natural conditions as it is the least impacted stream in this catchment, with the riparian zone dominated by relatively intact and diverse native woody vegetation, (ii) the Elands River whose catchment has been altered by agricultural activities, and (iii) the Lushington River, whose riparian zone has been heavily invaded by black wattle. The three headwater streams were generally distinguished based on the physical-chemical variables. The Elands River was characterised by high conductivity and total dissolved solids (TDS). In addition, the Elands River was more alkaline and relatively warmer than the other two rivers. This suggested the negative influence of agriculture activities on the water quality in the Elands River. In general, the Lushington and Eyre rivers had comparable physical and chemical variables. However, the Lushington River was generally characterised by low streamflow, likely as a consequent of black wattle which is known for altering hydrological regimes of streams .The Eyre River and Lushington River were comparable in terms of macroinvertebrate richness and diversity, whereas the Elands River was characterised by low macroinvertebrate diversity and richness. Redundancy analysis indicated that the macroinvertebrate communities were mostly influenced by seasonality, with land-use accounting for a small but significant difference in community composition. In comparison, the generalised linear mixed-effects models (GLMMs) showed that chubbyhead barb abundance was significantly influenced by land-use patterns. Evaluation of food web dynamics using stable isotope analysis revealed that the food web structure in the three rivers differed substantially as a result of land-use. Specifically, the Eyre River was characterised by less variation in stable isotope values of basal food sources and consequently, the consumer groups had a narrow isotopic breadth. In contrast, the Elands River was characterised by a wide variation in basal food sources and therefore, a wider isotopic breadth for consumers. The Lushington River was spatially variable in terms of basal sources and isotopic breadth for consumers. The study concluded that food webs and trophic interrelationships were a more informative indicator of land-use than community structure was in evaluating the impact of land-use patterns on aquatic communities. In addition, future studies should seek to investigate food webs interrelationships in addition to community structure to infer a more conclusive river assessment.
- Full Text:
- Date Issued: 2020
Assessing invasive alien aquatic plant species, phytoremediation effects using biological indicators in the Swartkops River system
- Authors: Tshithukhe, Getrude
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa -- Eastern Cape , Alien plants -- Biological control -- South Africa -- Eastern Cape , Phytoremediation -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167665 , vital:41501
- Description: Pollution effluents in freshwater ecosystems are becoming increasingly ubiquitous as a result of cumulative anthropogenic activities, such as wastewater treatments works, and industrial, agricultural and mining activities. These activities are more noticeable in urban river atchments where there is greater human population densities and industrial developments. The ecological effects of anthropogenic activities on freshwater ecosystems include: excessive deposition of contaminants such as nutrients, pharmaceuticals, microplastics and other chemicals, which change physicochemical properties, causing a decline in aquatic biodiversity. These effects, impact negatively on the resilience of freshwater, making the systems vulnerable to invasion by alien aquatic plants. Ultimately, the loss of local biodiversity associated with the invasive alien aquatic plants (IAAP) results in a loss of some ecosystem goods and services. The Swartkops River system, Eastern Cape Province, drains most of the neighbouring formal and informal settlements, agricultural lands and industries, and hence is exposed to water pollution from human activities along the river catchment. Various water quality assessments are needed to evaluate the extent of pollutants and their impacts on the river ecosystem. Phytoremediation is one approach employed internationally for removing harmful nutrients and chemicals in freshwater ecosystems. Most studies measure the success of phytoremediation through measuring the reduction of contaminants in water or soil chemistry in mesocosm settings, which may not take into account all the important environmental factors that exist in the field. The present study assesses the phytoremediation potential of Pontederia (Eichhornia) crassipes and Salvinia molesta by evaluating water and sediment chemistry, periphyton and aquatic macroinvertebrate community recovery along seven field sites (excluding IAAP species mats sites) located upstream and downstream IAAP species mats on the Swartkops River between April and September 2018. Water and sediment samples were collected once monthly on ten seven field sites, including the IAAP species mat sites. Periphyton and aquatic macroinvertebrates were collected on seven sites, excluding the IAAP mat sites. Pontederia crassipes and S. molesta infestation in Swartkops River showed positive phytoremediation results and improved some water and sediment chemistry in the downstream treatments as compared to upstream treatments. Although there were some fluctuations with some variables, important water and sediment chemistry were reduced downstream. By contrast, biological assessment results did not show any response to the presence of IAAP species and phytoremediation. Periphyton and aquatic macroinvertebrates diversity and community assemblages were more influenced by water quality. Although IAAP species did provide improvement in water and sediments chemistry, multiple effluent point and non-point sources in Swartkops outpaced phytoremediation. Taxa evenness and relative taxa abundance showed significant differences between the upstream and downstream sites, however taxa richness and Shannon’s diversity showed no significant differences, indicating no relative recovery in biodiversity for either periphyton or aquatic macroinvertebrates. Similarly, the upstream and downstream sites showed similar periphyton and aquatic macroinvertebrates assemblages structure, all dominated by pollution tolerant taxa, thus indicating no functional diversity improvement down river; because of improvement in water chemistry downstream sites, it was expected that periphyton and aquatic macroinvertebrates assemblage structure would also improve at these downstream sites.It is possible that the phytoremediation process is outpaced by effluent discharges, given the multiple sources and distance between upstream and downstream mat sites. The study showed phytoremediation potential but the results were not indicated by biological indicators. A replica study conducted on a moderately disturbed river system is recommended to measure the success and recovery of biological indicators and assemblage composition following IAAP species phytoremediation; a moderately disturbed river compared to a largely disturbed river will broaden findings and look at differences for a wider application of phytoremediation.
- Full Text:
- Date Issued: 2020
- Authors: Tshithukhe, Getrude
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa -- Eastern Cape , Alien plants -- Biological control -- South Africa -- Eastern Cape , Phytoremediation -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167665 , vital:41501
- Description: Pollution effluents in freshwater ecosystems are becoming increasingly ubiquitous as a result of cumulative anthropogenic activities, such as wastewater treatments works, and industrial, agricultural and mining activities. These activities are more noticeable in urban river atchments where there is greater human population densities and industrial developments. The ecological effects of anthropogenic activities on freshwater ecosystems include: excessive deposition of contaminants such as nutrients, pharmaceuticals, microplastics and other chemicals, which change physicochemical properties, causing a decline in aquatic biodiversity. These effects, impact negatively on the resilience of freshwater, making the systems vulnerable to invasion by alien aquatic plants. Ultimately, the loss of local biodiversity associated with the invasive alien aquatic plants (IAAP) results in a loss of some ecosystem goods and services. The Swartkops River system, Eastern Cape Province, drains most of the neighbouring formal and informal settlements, agricultural lands and industries, and hence is exposed to water pollution from human activities along the river catchment. Various water quality assessments are needed to evaluate the extent of pollutants and their impacts on the river ecosystem. Phytoremediation is one approach employed internationally for removing harmful nutrients and chemicals in freshwater ecosystems. Most studies measure the success of phytoremediation through measuring the reduction of contaminants in water or soil chemistry in mesocosm settings, which may not take into account all the important environmental factors that exist in the field. The present study assesses the phytoremediation potential of Pontederia (Eichhornia) crassipes and Salvinia molesta by evaluating water and sediment chemistry, periphyton and aquatic macroinvertebrate community recovery along seven field sites (excluding IAAP species mats sites) located upstream and downstream IAAP species mats on the Swartkops River between April and September 2018. Water and sediment samples were collected once monthly on ten seven field sites, including the IAAP species mat sites. Periphyton and aquatic macroinvertebrates were collected on seven sites, excluding the IAAP mat sites. Pontederia crassipes and S. molesta infestation in Swartkops River showed positive phytoremediation results and improved some water and sediment chemistry in the downstream treatments as compared to upstream treatments. Although there were some fluctuations with some variables, important water and sediment chemistry were reduced downstream. By contrast, biological assessment results did not show any response to the presence of IAAP species and phytoremediation. Periphyton and aquatic macroinvertebrates diversity and community assemblages were more influenced by water quality. Although IAAP species did provide improvement in water and sediments chemistry, multiple effluent point and non-point sources in Swartkops outpaced phytoremediation. Taxa evenness and relative taxa abundance showed significant differences between the upstream and downstream sites, however taxa richness and Shannon’s diversity showed no significant differences, indicating no relative recovery in biodiversity for either periphyton or aquatic macroinvertebrates. Similarly, the upstream and downstream sites showed similar periphyton and aquatic macroinvertebrates assemblages structure, all dominated by pollution tolerant taxa, thus indicating no functional diversity improvement down river; because of improvement in water chemistry downstream sites, it was expected that periphyton and aquatic macroinvertebrates assemblage structure would also improve at these downstream sites.It is possible that the phytoremediation process is outpaced by effluent discharges, given the multiple sources and distance between upstream and downstream mat sites. The study showed phytoremediation potential but the results were not indicated by biological indicators. A replica study conducted on a moderately disturbed river system is recommended to measure the success and recovery of biological indicators and assemblage composition following IAAP species phytoremediation; a moderately disturbed river compared to a largely disturbed river will broaden findings and look at differences for a wider application of phytoremediation.
- Full Text:
- Date Issued: 2020
Assessing the Social Sustainability of Wind Energy in the Karoo
- Authors: Hechter, J P
- Date: 2020
- Subjects: Wind power -- South Africa -- Karoo
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48378 , vital:40854
- Description: Background: In an ecologically conscious world, the need for sustainable development and the need to produce alternative energy is at the forefront of discussions. South Africa has been witnessing to a surge in wind energy developments in recent years. Although, environmental impacts often enjoy more emphasis, social impacts are equally important. Recently social sustainability was seen as an integral part of sustainable development for the future and can no longer be ignored. Wind energy is pathway towards sustainable development but can have detrimental impacts on social sustainability. On the one hand wind energy is said to impact culture, sense of places and cause unrest in a community, however, on the other hand it is said to be socially sustainable to the point where wind energy is incorporated into local culture and not to mention the employment opportunities it can create. This is particularly important for vulnerable communities found in the Karoo, where unemployment is very high. Purpose/ Aim: The aim of this study was to assess the social sustainability of a wind energy project in the Karoo by constructing a theoretical assessment model designed to produce appropriate and specific social indicators. Methodology: A literature review was undertaken to gain insights into the social sustainability of wind energy which also served as the theoretical backbone for the model and assessment parameters. The assessment model produced 10 indicators which was used as interview schedule with key stakeholders in the study area. A total of 31 qualitative interviews were conducted and produced a good data set. Findings: The results from this study show that here was no significant negative impact reported with regards to social sustainability. The wind developer is committed to the community based on the various social initiative funded by it. Although a definite positive impact and improvement in terms of social sustainability is evident in the area, there is still a long way to go as many outcomes set by the wind developer is yet to achieved.
- Full Text:
- Date Issued: 2020
- Authors: Hechter, J P
- Date: 2020
- Subjects: Wind power -- South Africa -- Karoo
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48378 , vital:40854
- Description: Background: In an ecologically conscious world, the need for sustainable development and the need to produce alternative energy is at the forefront of discussions. South Africa has been witnessing to a surge in wind energy developments in recent years. Although, environmental impacts often enjoy more emphasis, social impacts are equally important. Recently social sustainability was seen as an integral part of sustainable development for the future and can no longer be ignored. Wind energy is pathway towards sustainable development but can have detrimental impacts on social sustainability. On the one hand wind energy is said to impact culture, sense of places and cause unrest in a community, however, on the other hand it is said to be socially sustainable to the point where wind energy is incorporated into local culture and not to mention the employment opportunities it can create. This is particularly important for vulnerable communities found in the Karoo, where unemployment is very high. Purpose/ Aim: The aim of this study was to assess the social sustainability of a wind energy project in the Karoo by constructing a theoretical assessment model designed to produce appropriate and specific social indicators. Methodology: A literature review was undertaken to gain insights into the social sustainability of wind energy which also served as the theoretical backbone for the model and assessment parameters. The assessment model produced 10 indicators which was used as interview schedule with key stakeholders in the study area. A total of 31 qualitative interviews were conducted and produced a good data set. Findings: The results from this study show that here was no significant negative impact reported with regards to social sustainability. The wind developer is committed to the community based on the various social initiative funded by it. Although a definite positive impact and improvement in terms of social sustainability is evident in the area, there is still a long way to go as many outcomes set by the wind developer is yet to achieved.
- Full Text:
- Date Issued: 2020
Associations between family history of diseases of lifestyle, lifestyle behaviour and anthropometric nutritional status of pre-school children in ECD centres in the Nelson Mandela Bay Municipality
- Authors: Wilson, Teresa Margaret
- Date: 2020
- Subjects: Nutrition--Evaluation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46344 , vital:39602
- Description: Introduction: Childhood overweight and obesity is an escalating global health issue. In Africa, overweight and obesity prevalence in children has nearly doubled since 2000(World Health Organisation, 2018).TheSANHANES-1 study (2013) identified that overweight and obesity in were most prevalent in urban informal areas of South Africa, with approximately a quarter of the children classified as overweight or obese (Shisana et al., 2013).In the Nelson Mandela Bay Municipality(NMBM), a double burden of disease was identified in the lower socio-economic population (Phekana et al., 2016). This study and others recommended further study into the contributing factors and behaviours which play a role in the development of overweight and obesity in children. These include household dietary intake, family history of lifestyle diseases, as well as the children’s and parental physical activity and sedentary time (Zhang et al.,2016).Aim: The aim of the study was to determine the associations between family history of diseases of lifestyle, lifestyle behaviour and anthropometric nutritional status of pre-school children in NMBM to describe underlying causes of childhood overweight and obesity.Methods: A cross-sectional design, using a quantitative approach, was used for this study(Ethics approval: H18-HEA-DIET-004). The study population included adult parents and/or caregivers of children from urban areas of Nelson Mandela Bay Municipality attending crèches and schools in these areas, in the age group from birth to 96 months (8 years). Randomised cluster sampling of crèches and schools from an existing database of anthropometrical data of children attending these crèches and schools in the area was done and a final sample of n=155obtained. With the assistance of a trained fieldworker, respondents completed a questionnaire detailing the family history of lifestyle diseases, physical activity levels and sedentary screen time behaviours, and a graphical adjusted version of a household dietary diversity questionnaire. Data about children’s activity levels in the preschool/creche environment was collected by the fieldworker by assessing the ECD centres’daily activity schedules. The anthropometric data of the children of the respondents was accessed from an existing database of these measurements. The data was described using means and standard deviations. Inferential statistics determined any existing associations between these underlying influences of childhood obesity.Results: Only 2% (n=3) of the children were underweight and 12% (n=9) were at risk of becoming underweight as classified by WAZ. HAZ scores identified26% (n=40) of the children at risk of becoming stunted, and 6% (n=9) of the children were already stunted. WHZ classified5% (n=8)of the children as overweight and 5% (n=8)as obese. A further 22% (n=34) of the children were at risk of becoming overweight.BMI/age classificationidentified25% (n=38) of the children as overweight and a further 12% (n=19) as obese. Out of the sample, 12%(n=17) of mothers and 8% (n=7) of fathers were categorised as overweight-to-obese according to the SA specific waist circumference(WC)cut-offs. Out of the children, 15% (n=22) have at least one parent who was overweight-to-obese. Traditional WC categories were classified48% (n=67) of the mothers as overweight-to-obese and at high risk for metabolic syndrome. Of all the lifestyle diseases, hypertension was the most prevalent with 29% (n=41) of households having at least one parent with hypertension. Parental physical activity was grossly overestimated, and the results found to be invalid. The Diet Variety and Frequency score resulted in a mean of 65.00 (n=154, SD=27.37) out of a possible 100 for the households in this sample, and junk food was consumed on three to four occasions per day in 32% (n=49) of households. There were no significant associations found between the parents’ variables and underweight children. Statistically small to medium effect associations were found between parental weight (both SA specific and traditional categories) and overweight children (classified by WHZ and BMI/age). Conclusions and recommendations: The prevalence of overweight and obesity among children in the NMBM was high. The only possible underlying cause of childhood overweight and obesity in pre-school children in the NMBM that could be determined by this study was parents’ weight classified by WC. However, it must be reiterated that due to the cross-sectional nature of the study, an association does not immediately mean causation, and the results are not adequate to rule out other underlying factors influencing childhood obesity. It is recommended that the results of the study are used to incentivise the final implementation of all the intervention targets laid out in the Strategic Plan for the Prevention and Control of Obesity in South Africa 2015-2020 in NMB, and for the development of the future obesity strategy after 2020. The results have shown the necessity for future health interventions to be targeted at the family as a unit.
- Full Text:
- Date Issued: 2020
- Authors: Wilson, Teresa Margaret
- Date: 2020
- Subjects: Nutrition--Evaluation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46344 , vital:39602
- Description: Introduction: Childhood overweight and obesity is an escalating global health issue. In Africa, overweight and obesity prevalence in children has nearly doubled since 2000(World Health Organisation, 2018).TheSANHANES-1 study (2013) identified that overweight and obesity in were most prevalent in urban informal areas of South Africa, with approximately a quarter of the children classified as overweight or obese (Shisana et al., 2013).In the Nelson Mandela Bay Municipality(NMBM), a double burden of disease was identified in the lower socio-economic population (Phekana et al., 2016). This study and others recommended further study into the contributing factors and behaviours which play a role in the development of overweight and obesity in children. These include household dietary intake, family history of lifestyle diseases, as well as the children’s and parental physical activity and sedentary time (Zhang et al.,2016).Aim: The aim of the study was to determine the associations between family history of diseases of lifestyle, lifestyle behaviour and anthropometric nutritional status of pre-school children in NMBM to describe underlying causes of childhood overweight and obesity.Methods: A cross-sectional design, using a quantitative approach, was used for this study(Ethics approval: H18-HEA-DIET-004). The study population included adult parents and/or caregivers of children from urban areas of Nelson Mandela Bay Municipality attending crèches and schools in these areas, in the age group from birth to 96 months (8 years). Randomised cluster sampling of crèches and schools from an existing database of anthropometrical data of children attending these crèches and schools in the area was done and a final sample of n=155obtained. With the assistance of a trained fieldworker, respondents completed a questionnaire detailing the family history of lifestyle diseases, physical activity levels and sedentary screen time behaviours, and a graphical adjusted version of a household dietary diversity questionnaire. Data about children’s activity levels in the preschool/creche environment was collected by the fieldworker by assessing the ECD centres’daily activity schedules. The anthropometric data of the children of the respondents was accessed from an existing database of these measurements. The data was described using means and standard deviations. Inferential statistics determined any existing associations between these underlying influences of childhood obesity.Results: Only 2% (n=3) of the children were underweight and 12% (n=9) were at risk of becoming underweight as classified by WAZ. HAZ scores identified26% (n=40) of the children at risk of becoming stunted, and 6% (n=9) of the children were already stunted. WHZ classified5% (n=8)of the children as overweight and 5% (n=8)as obese. A further 22% (n=34) of the children were at risk of becoming overweight.BMI/age classificationidentified25% (n=38) of the children as overweight and a further 12% (n=19) as obese. Out of the sample, 12%(n=17) of mothers and 8% (n=7) of fathers were categorised as overweight-to-obese according to the SA specific waist circumference(WC)cut-offs. Out of the children, 15% (n=22) have at least one parent who was overweight-to-obese. Traditional WC categories were classified48% (n=67) of the mothers as overweight-to-obese and at high risk for metabolic syndrome. Of all the lifestyle diseases, hypertension was the most prevalent with 29% (n=41) of households having at least one parent with hypertension. Parental physical activity was grossly overestimated, and the results found to be invalid. The Diet Variety and Frequency score resulted in a mean of 65.00 (n=154, SD=27.37) out of a possible 100 for the households in this sample, and junk food was consumed on three to four occasions per day in 32% (n=49) of households. There were no significant associations found between the parents’ variables and underweight children. Statistically small to medium effect associations were found between parental weight (both SA specific and traditional categories) and overweight children (classified by WHZ and BMI/age). Conclusions and recommendations: The prevalence of overweight and obesity among children in the NMBM was high. The only possible underlying cause of childhood overweight and obesity in pre-school children in the NMBM that could be determined by this study was parents’ weight classified by WC. However, it must be reiterated that due to the cross-sectional nature of the study, an association does not immediately mean causation, and the results are not adequate to rule out other underlying factors influencing childhood obesity. It is recommended that the results of the study are used to incentivise the final implementation of all the intervention targets laid out in the Strategic Plan for the Prevention and Control of Obesity in South Africa 2015-2020 in NMB, and for the development of the future obesity strategy after 2020. The results have shown the necessity for future health interventions to be targeted at the family as a unit.
- Full Text:
- Date Issued: 2020
Azadipyrromethenes for applications in photodynamic antimicrobial chemotherapy, photodynamic therapy and optical limiting
- Authors: Dubazana, Nadine
- Date: 2020
- Subjects: Dyes and dyeing -- Chemistry , Photochemotherapy , Cancer -- Photochemotherapy , Anti-infective agents , Staphylococcus aureus , Nonlinear optics , Azadipyrromethenes , BODIPY
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166150 , vital:41333
- Description: Azadipyrromethenes, azaBODIPYs and zinc azadipyrromethene complexes were prepared and characterised to examine the effect on their photophysical properties of incorporating phenyl groups at the 1,3,5,7-positions with electron-donating and withdrawing groups at the para-positions. To enhance their ability to generate singlet oxygen, appropriate structural modifications were made through the addition of a Zn(II) ion or halogenation at the 2,6 positions. In vitro photodynamic therapy (PDT) studies targeting MCF-7 human breast cancer cells were carried out. To evaluate and understand the effectiveness of the dyes as photosensitisers, cellular uptake, phototoxicity and the half-maximal inhibitory concentration (IC50) values were analysed. Photodynamic antimicrobial chemotherapy (PACT) studies were also carried out to study the effectiveness of the dyes against Staphylococcus aureus (S. aureus). Dyes with donor-π-acceptor (D-π-A) properties were synthesised and tested against the second harmonic of the Nd:YAG laser in optical limiting (OL) studies. The second-order hyperpolarisability, third-order susceptibility and nonlinear absorption coefficient values were determined. The results suggest that 1,3,5,7-azaBODIPY dyes may be less suitable for use in this context than analogous D-π-A 3,5-distyrylBODIPY dyes. Molecular modelling was carried out to identify the structure-property relationships of the synthesised dyes by analysing trends in the energies of the frontier molecular orbitals (MOs) and spectroscopic properties.
- Full Text:
- Date Issued: 2020
- Authors: Dubazana, Nadine
- Date: 2020
- Subjects: Dyes and dyeing -- Chemistry , Photochemotherapy , Cancer -- Photochemotherapy , Anti-infective agents , Staphylococcus aureus , Nonlinear optics , Azadipyrromethenes , BODIPY
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166150 , vital:41333
- Description: Azadipyrromethenes, azaBODIPYs and zinc azadipyrromethene complexes were prepared and characterised to examine the effect on their photophysical properties of incorporating phenyl groups at the 1,3,5,7-positions with electron-donating and withdrawing groups at the para-positions. To enhance their ability to generate singlet oxygen, appropriate structural modifications were made through the addition of a Zn(II) ion or halogenation at the 2,6 positions. In vitro photodynamic therapy (PDT) studies targeting MCF-7 human breast cancer cells were carried out. To evaluate and understand the effectiveness of the dyes as photosensitisers, cellular uptake, phototoxicity and the half-maximal inhibitory concentration (IC50) values were analysed. Photodynamic antimicrobial chemotherapy (PACT) studies were also carried out to study the effectiveness of the dyes against Staphylococcus aureus (S. aureus). Dyes with donor-π-acceptor (D-π-A) properties were synthesised and tested against the second harmonic of the Nd:YAG laser in optical limiting (OL) studies. The second-order hyperpolarisability, third-order susceptibility and nonlinear absorption coefficient values were determined. The results suggest that 1,3,5,7-azaBODIPY dyes may be less suitable for use in this context than analogous D-π-A 3,5-distyrylBODIPY dyes. Molecular modelling was carried out to identify the structure-property relationships of the synthesised dyes by analysing trends in the energies of the frontier molecular orbitals (MOs) and spectroscopic properties.
- Full Text:
- Date Issued: 2020
Bayesian accelerated life tests for the Weibull distribution under non-informative priors
- Authors: Mostert, Philip
- Date: 2020
- Subjects: Accelerated life testing -- Statistical methods , Accelerated life testing -- Mathematical models , Failure time data analysis , Bayesian statistical decision theory , Monte Carlo method , Weibull distribution
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/172181 , vital:42173
- Description: In a competitive world where products are designed to last for long periods of time, obtaining time-to-failure data is both difficult and costly. Hence for products with high reliability, accelerated life testing is required to obtain relevant life-data quickly. This is done by placing the products under higher-than-use stress levels, thereby causing the products to fail prematurely. Part of the analysis of accelerated life-data requires a life distribution that describes the lifetime of a product at a given stress level and a life-stress relationship – which is some function that describes the way in which the life distribution changes across different stress levels. In this thesis it is assumed that the underlying life distribution is the wellknown Weibull distribution, with shape parameter constant over all stress levels and scale parameter as a log-linear function of stress. The primary objective of this thesis is to obtain estimates from Bayesian analysis, and this thesis considers five types of non-informative prior distributions: Jeffreys’ prior, reference priors, maximal data information prior, uniform prior and probability matching priors. Since the associated posterior distribution under all the derived non-informative priors are of an unknown form, the propriety of the posterior distributions is assessed to ensure admissible results. For comparison purposes, estimates obtained via the method of maximum likelihood are also considered. Finding these estimates requires solving non-linear equations, hence the Newton-Raphson algorithm is used to obtain estimates. A simulation study based on the time-to-failure of accelerated data is conducted to compare results between maximum likelihood and Bayesian estimates. As a result of the Bayesian posterior distributions being analytically intractable, two methods to obtain Bayesian estimates are considered: Markov chain Monte Carlo methods and Lindley’s approximation technique. In the simulation study the posterior means and the root mean squared error values of the estimates under the symmetric squared error loss function and the two asymmetric loss functions: the LINEX loss function and general entropy loss function, are considered. Furthermore the coverage rates for the Bayesian Markov chain Monte Carlo and maximum likelihood estimates are found, and are compared by their average interval lengths. A case study using a dataset based on accelerated time-to-failure of an insulating fluid is considered. The fit of these data for the Weibull distribution is studied and is compared to that of other popular life distributions. A full simulation study is conducted to illustrate convergence of the proper posterior distributions. Both maximum likelihood and Bayesian estimates are found for these data. The deviance information criterion is used to compare Bayesian estimates between the prior distributions. The case study is concluded by finding reliability estimates of the data at use-stress levels.
- Full Text:
- Date Issued: 2020
- Authors: Mostert, Philip
- Date: 2020
- Subjects: Accelerated life testing -- Statistical methods , Accelerated life testing -- Mathematical models , Failure time data analysis , Bayesian statistical decision theory , Monte Carlo method , Weibull distribution
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/172181 , vital:42173
- Description: In a competitive world where products are designed to last for long periods of time, obtaining time-to-failure data is both difficult and costly. Hence for products with high reliability, accelerated life testing is required to obtain relevant life-data quickly. This is done by placing the products under higher-than-use stress levels, thereby causing the products to fail prematurely. Part of the analysis of accelerated life-data requires a life distribution that describes the lifetime of a product at a given stress level and a life-stress relationship – which is some function that describes the way in which the life distribution changes across different stress levels. In this thesis it is assumed that the underlying life distribution is the wellknown Weibull distribution, with shape parameter constant over all stress levels and scale parameter as a log-linear function of stress. The primary objective of this thesis is to obtain estimates from Bayesian analysis, and this thesis considers five types of non-informative prior distributions: Jeffreys’ prior, reference priors, maximal data information prior, uniform prior and probability matching priors. Since the associated posterior distribution under all the derived non-informative priors are of an unknown form, the propriety of the posterior distributions is assessed to ensure admissible results. For comparison purposes, estimates obtained via the method of maximum likelihood are also considered. Finding these estimates requires solving non-linear equations, hence the Newton-Raphson algorithm is used to obtain estimates. A simulation study based on the time-to-failure of accelerated data is conducted to compare results between maximum likelihood and Bayesian estimates. As a result of the Bayesian posterior distributions being analytically intractable, two methods to obtain Bayesian estimates are considered: Markov chain Monte Carlo methods and Lindley’s approximation technique. In the simulation study the posterior means and the root mean squared error values of the estimates under the symmetric squared error loss function and the two asymmetric loss functions: the LINEX loss function and general entropy loss function, are considered. Furthermore the coverage rates for the Bayesian Markov chain Monte Carlo and maximum likelihood estimates are found, and are compared by their average interval lengths. A case study using a dataset based on accelerated time-to-failure of an insulating fluid is considered. The fit of these data for the Weibull distribution is studied and is compared to that of other popular life distributions. A full simulation study is conducted to illustrate convergence of the proper posterior distributions. Both maximum likelihood and Bayesian estimates are found for these data. The deviance information criterion is used to compare Bayesian estimates between the prior distributions. The case study is concluded by finding reliability estimates of the data at use-stress levels.
- Full Text:
- Date Issued: 2020
Biology, stock assessment and angler attitudes towards the introduction of slot size limits for a recreationally important species Sparodon durbanensis (Sparidae) in South Africa
- Authors: Hewett, Kyle
- Date: 2020
- Subjects: Sparidae -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48389 , vital:40855
- Description: Sparodon durbanensis (white musselcracker) is an endemic fish species in the Family Sparidae found in shallow (< 20 m) coastal waters from the Western Cape to KwaZulu-Natal. It is large-growing, late-maturing, long-lived and is a popular target species in the South African marine shore-based line and spear fisheries. Management regulations for the species have remained the same for over two decades despite anecdotal information of population declines. However, since the last life history-information for S. durbanensis was collected in the late 1980s, there is a paucity of contemporary information needed to inform wise management. The aim of this study was to collect contemporary socio-ecological information on the species and its fishery in order to better inform the management of the species. In order to do this, the growth-rate of historical and contemporary samples of Sparodon durbanensis was compared, a length-based stock assessment was performed and the knowledge and attitudes of anglers towards the introduction of improved regulations were investigated. The growth-rate was compared using otolith width as a proxy for fish growth. It was found that the growth-rate had remained relatively stable between 1963 and 2010, suggesting that S. durbanensis may be resilient to the increasing levels of environmental variability observed throughout its range and that the historical growth parameters determined for this species may remain applicable for contemporary stock assessment. The batch fecundity was determined for 50 mm size classes and used to estimate the percentage cumulative population batch fecundity using historical 803 mm FL (904 mm TL) and contemporary 776 mm FL (874 mm TL) length structure, respectively. Based on these observations a suitable harvest slot limit of 600-850 mm TL was suggested. A Length-Based Spawning Potential Ratio (SPR) model was used to provide the first formal stock assessment for S. durbanensis. The input parameters of M/k=1.44, L∞=1021 mm FL, L50=350 mm FL and L95=800 mm FL and length composition data comprising of 134 lengths obtained from a collection of competitive angling catches, estimated a SPR of 41%, which is above the 40% target reference point. A total of 126 online and face– to-face, replica questionnaires were completed by spearfishermen and recreational shore anglers. Responses indicated that anglers that target S. durbanensis are generally a specialized group who are knowledgeable about the biology and ecology of the species and are passionate about the conservation of the species. Participants indicated that Marine Protected Areas are likely the most effective regulation in the current suite of regulations used to manage the fishery and suggested that poor law enforcement was the major factor inhibiting the efficacy of fishery regulations. New proposed regulations, such as a harvest slot limit (and particularly the one between 600-850 mm TL) for S. durbanensis, was well supported, however participants suggested that non-compliance was a concern. Although, the SPR remained above the 40% target reference point, further declines in the stock status should be prevented through the implementation of a 600-850 mm TL harvest slot limit. Based on the findings of this study, this limit should provide protection against both growth and recruitment overfishing by providing protection to sexually immature, fast growing fish and to large adults that contribute the greatest proportion to population replenishment.
- Full Text:
- Date Issued: 2020
- Authors: Hewett, Kyle
- Date: 2020
- Subjects: Sparidae -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48389 , vital:40855
- Description: Sparodon durbanensis (white musselcracker) is an endemic fish species in the Family Sparidae found in shallow (< 20 m) coastal waters from the Western Cape to KwaZulu-Natal. It is large-growing, late-maturing, long-lived and is a popular target species in the South African marine shore-based line and spear fisheries. Management regulations for the species have remained the same for over two decades despite anecdotal information of population declines. However, since the last life history-information for S. durbanensis was collected in the late 1980s, there is a paucity of contemporary information needed to inform wise management. The aim of this study was to collect contemporary socio-ecological information on the species and its fishery in order to better inform the management of the species. In order to do this, the growth-rate of historical and contemporary samples of Sparodon durbanensis was compared, a length-based stock assessment was performed and the knowledge and attitudes of anglers towards the introduction of improved regulations were investigated. The growth-rate was compared using otolith width as a proxy for fish growth. It was found that the growth-rate had remained relatively stable between 1963 and 2010, suggesting that S. durbanensis may be resilient to the increasing levels of environmental variability observed throughout its range and that the historical growth parameters determined for this species may remain applicable for contemporary stock assessment. The batch fecundity was determined for 50 mm size classes and used to estimate the percentage cumulative population batch fecundity using historical 803 mm FL (904 mm TL) and contemporary 776 mm FL (874 mm TL) length structure, respectively. Based on these observations a suitable harvest slot limit of 600-850 mm TL was suggested. A Length-Based Spawning Potential Ratio (SPR) model was used to provide the first formal stock assessment for S. durbanensis. The input parameters of M/k=1.44, L∞=1021 mm FL, L50=350 mm FL and L95=800 mm FL and length composition data comprising of 134 lengths obtained from a collection of competitive angling catches, estimated a SPR of 41%, which is above the 40% target reference point. A total of 126 online and face– to-face, replica questionnaires were completed by spearfishermen and recreational shore anglers. Responses indicated that anglers that target S. durbanensis are generally a specialized group who are knowledgeable about the biology and ecology of the species and are passionate about the conservation of the species. Participants indicated that Marine Protected Areas are likely the most effective regulation in the current suite of regulations used to manage the fishery and suggested that poor law enforcement was the major factor inhibiting the efficacy of fishery regulations. New proposed regulations, such as a harvest slot limit (and particularly the one between 600-850 mm TL) for S. durbanensis, was well supported, however participants suggested that non-compliance was a concern. Although, the SPR remained above the 40% target reference point, further declines in the stock status should be prevented through the implementation of a 600-850 mm TL harvest slot limit. Based on the findings of this study, this limit should provide protection against both growth and recruitment overfishing by providing protection to sexually immature, fast growing fish and to large adults that contribute the greatest proportion to population replenishment.
- Full Text:
- Date Issued: 2020
BODIPY dyes for application in the photo-oxidation of pollutants, photodynamic antimicrobial chemotherapy, and nonlinear optics
- Authors: Kelechi, Lebechi Augustus
- Date: 2020
- Subjects: Dyes and dyeing -- Chemistry , Fluorescent probes , Fluorescence spectroscopy
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/140298 , vital:37859
- Description: The synthesis and structural characterization of a series of BODIPY dyes to analyze both the effects of halogenations at the 2,6-positions and the introduction of styryl groups at the 3,5-positions. The photophysical properties of these dyes were investigated to determine their suitability as singlet oxygen-generating photosensitiser dyes for application in photocatalytic degradation of azo dyes and in photodynamic antimicrobial chemotherapy (PACT). Upon halogenation, the dyes showed high to moderate singlet oxygen quantum yields. The potential utility of electrospun polystyrene (PS) nanofibres embedded with halogenated BODIPY dyes for the photocatalytic degradation of Orange G and Methyl Orange from textile industry effluents were investigated. A comparison of the singlet oxygen quantum yield of the BODIPY dyes in solution and when embedded in the PS nanofibres support demonstrates that its photosensitiser properties are maintained in the nanofibre mats. The photocatalytic degradation properties of the PS nanofibres for Orange G and Methyl Orange were determined by using a 530 nm and 660 nm light-emitting diodes. The rate of photodegradation increases with both the Orange G and Methyl Orange concentrations and follows pseudo-first-order kinetics. The PACT activities of brominated BODIPYs on Escherichia coli and Staphylococcus aureus were investigated. Log reduction values of over 9 were obtained during the photoinactivation of Staphylococcus aureus. To be able to red-shift the main spectral band of the BODIPY dyes into the therapeutic window, styryl groups were introduced at the 3,5-positions through a modified Knoevenagel condensation reaction. Because the red-shifted spectral band lies above 532 nm, the second harmonic of the Nd:YAG laser, there is very minute absorption at this wavelength. One of the novel brominated BODIPY dyes was investigated for its potential utility as optical limiting materials in nonlinear optics (NLO), and the dyes demonstrated typical nonlinear absorption behaviour characterised by reverse saturable absorption (RSA) in Z-scan measurements. Excellent optical limiting parameters were obtained for third-order susceptibility and hyperpolarisability.
- Full Text:
- Date Issued: 2020
- Authors: Kelechi, Lebechi Augustus
- Date: 2020
- Subjects: Dyes and dyeing -- Chemistry , Fluorescent probes , Fluorescence spectroscopy
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/140298 , vital:37859
- Description: The synthesis and structural characterization of a series of BODIPY dyes to analyze both the effects of halogenations at the 2,6-positions and the introduction of styryl groups at the 3,5-positions. The photophysical properties of these dyes were investigated to determine their suitability as singlet oxygen-generating photosensitiser dyes for application in photocatalytic degradation of azo dyes and in photodynamic antimicrobial chemotherapy (PACT). Upon halogenation, the dyes showed high to moderate singlet oxygen quantum yields. The potential utility of electrospun polystyrene (PS) nanofibres embedded with halogenated BODIPY dyes for the photocatalytic degradation of Orange G and Methyl Orange from textile industry effluents were investigated. A comparison of the singlet oxygen quantum yield of the BODIPY dyes in solution and when embedded in the PS nanofibres support demonstrates that its photosensitiser properties are maintained in the nanofibre mats. The photocatalytic degradation properties of the PS nanofibres for Orange G and Methyl Orange were determined by using a 530 nm and 660 nm light-emitting diodes. The rate of photodegradation increases with both the Orange G and Methyl Orange concentrations and follows pseudo-first-order kinetics. The PACT activities of brominated BODIPYs on Escherichia coli and Staphylococcus aureus were investigated. Log reduction values of over 9 were obtained during the photoinactivation of Staphylococcus aureus. To be able to red-shift the main spectral band of the BODIPY dyes into the therapeutic window, styryl groups were introduced at the 3,5-positions through a modified Knoevenagel condensation reaction. Because the red-shifted spectral band lies above 532 nm, the second harmonic of the Nd:YAG laser, there is very minute absorption at this wavelength. One of the novel brominated BODIPY dyes was investigated for its potential utility as optical limiting materials in nonlinear optics (NLO), and the dyes demonstrated typical nonlinear absorption behaviour characterised by reverse saturable absorption (RSA) in Z-scan measurements. Excellent optical limiting parameters were obtained for third-order susceptibility and hyperpolarisability.
- Full Text:
- Date Issued: 2020
Building a flexible and inexpensive multi-layer switch for software-defined networks
- Authors: Magwenzi, Tinashe
- Date: 2020
- Subjects: Software-defined networking (Computer network technology) , Telecommunication -- Switching systems , OpenFlow (Computer network protocol) , Local area networks (Computer networks)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/142841 , vital:38122
- Description: Software-Defined Networking (SDN) is a paradigm which enables the realisation of programmable network through the separation of the control logic from the forwarding functions. This separation is a departure from the traditional architecture. Much of the work done in SDN enabled devices has concentrated on higher end, high speed networks (10s GBit/s 100s GBit/s), rather than the relatively low bandwidth links (10s MBit/s to a few GBit/s) which are seen, for example, in South Africa. As SDN is increasingly becoming more accepted, due to its advantages over the traditional networks, it has been adopted for industrial purposes such as networking in data centres and network providers. The demand for programmable networks is increasing but is limited by the ability of providers to upgrade their infrastructure. In addition, as access to the Internet has become less expensive, the use of Internet is increasing in academic institutions, NGOs, and small to medium enterprises. This thesis details a means of building and managing a small scale Software-Defined Network using commodity hardware and open source tools. Core to the SDN Network illustrated in this thesis is the prototype of a multi-layer SDN switch. The proposed device is targeted to serve lower bandwidth communication (in relation to commercially produced high speed SDN-enabled devices). The performance of the prototype multilayer switch had shown to achieve: data-rates of up to 99.998%, average latencies that are under 40µs during forwarding/switching and under 100µs during routing while using packet sizes between 64 bytes and 1518 bytes, and a jitter of less than 15µs during all tests. This research explores in detail the design, development, and management of a multi-layer switch and its placement and integration in small scale SDN network. This includes testing of Layer 2 forwarding and Layer 3 routing, OpenFlow compliance testing, the management of the switch using created SDN applications, and real life network functionality such as forwarding, routing and VLAN networking to demonstrate its real world applicability.
- Full Text:
- Date Issued: 2020
- Authors: Magwenzi, Tinashe
- Date: 2020
- Subjects: Software-defined networking (Computer network technology) , Telecommunication -- Switching systems , OpenFlow (Computer network protocol) , Local area networks (Computer networks)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/142841 , vital:38122
- Description: Software-Defined Networking (SDN) is a paradigm which enables the realisation of programmable network through the separation of the control logic from the forwarding functions. This separation is a departure from the traditional architecture. Much of the work done in SDN enabled devices has concentrated on higher end, high speed networks (10s GBit/s 100s GBit/s), rather than the relatively low bandwidth links (10s MBit/s to a few GBit/s) which are seen, for example, in South Africa. As SDN is increasingly becoming more accepted, due to its advantages over the traditional networks, it has been adopted for industrial purposes such as networking in data centres and network providers. The demand for programmable networks is increasing but is limited by the ability of providers to upgrade their infrastructure. In addition, as access to the Internet has become less expensive, the use of Internet is increasing in academic institutions, NGOs, and small to medium enterprises. This thesis details a means of building and managing a small scale Software-Defined Network using commodity hardware and open source tools. Core to the SDN Network illustrated in this thesis is the prototype of a multi-layer SDN switch. The proposed device is targeted to serve lower bandwidth communication (in relation to commercially produced high speed SDN-enabled devices). The performance of the prototype multilayer switch had shown to achieve: data-rates of up to 99.998%, average latencies that are under 40µs during forwarding/switching and under 100µs during routing while using packet sizes between 64 bytes and 1518 bytes, and a jitter of less than 15µs during all tests. This research explores in detail the design, development, and management of a multi-layer switch and its placement and integration in small scale SDN network. This includes testing of Layer 2 forwarding and Layer 3 routing, OpenFlow compliance testing, the management of the switch using created SDN applications, and real life network functionality such as forwarding, routing and VLAN networking to demonstrate its real world applicability.
- Full Text:
- Date Issued: 2020
Change of perspectives and behaviour regarding lifestyle, with emphasis on dietary habits, in a rural community
- Authors: Barnard, Mariska
- Date: 2020
- Subjects: Food habits
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46384 , vital:39565
- Description: Background: The steady increase in deaths due to non-communicable diseases (NCDs) in South Africa is raising concern, as 63% of all deaths worldwide are attributed to NCDs and these diseases cause 36 million deaths each year, with 80 % of incidences occurring in low-and middle-income countries. In rural communities where income is increasing, the prevalence of NCDs are increasing as well. Due to the lack of NCD prevention and treatment in rural communities, it is expected that, if health promotion strategies are not implemented and socio-economic development in South Africa continues, there will soon be an uncontrollable NCD epidemic. It has been found that dietary risks affected people’s healthirrespective of their age, gender or residential sociodemographic development and that dietary improvement might prevent one in every five deaths worldwide.Aim:The aim of this study was to determine the factors that influence the perceptions and behaviour in a rural community with a low socio-economic status regarding dietary habits and to use the knowledge to formulate an effective dietary modification strategy.Designand methodology:For this study,action research with a quantitative and qualitative component was followed.The quantitative component focuses on measureable aspects, and the qualitative component focuses on meaning. Data was collected following the standard operating procedure for anthropometry, blood pressure and blood glucose. Further methods used were questionnaires, 24-hour dietary recalls and focus group discussions. Data were analysed using Microsoft Excel, FoodFinder3 and other calculations.Sample and setting:A convenience sample (n = 16) wasused and this study was undertaken on request of the non-governmental organization, Karoo Angels and included all participants who earn an income and who do not work for themselves, that were willing to participate and living in Rietbron and Vondeling, in the Sarah BaartmanDistrict in the Eastern Cape. Results:Weight changes took place, both the crafters in the mild thinness category gained weight, one gained 3.9 kg and the other 0.5 kg. The three crafters in the normal category did not have to gain or lose weight, but all three ofthem gained an average of 3.6 kg. For the group who had to lose weight, no statistically significant weight change took place from before the intervention (76.08 ±17.67 kg) to after the intervention (75.81 ± 17.81 kg, t(10) = 0.692, p = 0.505). The maximum weight lost ivwas 3.1 kg and the maximum weight gained was 3.2 kg. Changes took place regarding BMI, waist circumference, waist-to-hip ratio and neck circumference. Some positively changed their BMI status.After the implementation of the intervention, there was a slight decrease in frequency of alcohol consumption, but smoking and physical activity remained mostly the same. Hypertension was the most prevalent NCD and is linked to smoking and alcohol consumption which is prevalent in this study. Fruit and vegetable consumption is low, and a slight increase in consumption was evident. A maximum dietary diversityscore of seven and minimum of two, where the mean was 3.81was found. The crafters’ diet did not meet the DASH diet recommendation,the mean energy distribution is of all macronutrients differ with ±4% and none of the participants’ mean micronutrients intake met the recommendations of the DASH diet or RDA. Factors that prevent them from reaching their goals included low income, low availability of fruit, vegetables and transport and no storage for food.Conclusion:It is important to consider the individuals’ living conditions, resources, knowledge, motivation and social group. The environment and resources available have a significant impact on the lifestyle of the individuals. Directing efforts of behaviour change to increase dietary diversity as the main objective, might be a more efficient way to change behaviour.Recommendations:Future studies should consider doing this study over a longer time period. The involvement of a psychologist would also be beneficial to assist the process of behaviour change.
- Full Text:
- Date Issued: 2020
- Authors: Barnard, Mariska
- Date: 2020
- Subjects: Food habits
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/46384 , vital:39565
- Description: Background: The steady increase in deaths due to non-communicable diseases (NCDs) in South Africa is raising concern, as 63% of all deaths worldwide are attributed to NCDs and these diseases cause 36 million deaths each year, with 80 % of incidences occurring in low-and middle-income countries. In rural communities where income is increasing, the prevalence of NCDs are increasing as well. Due to the lack of NCD prevention and treatment in rural communities, it is expected that, if health promotion strategies are not implemented and socio-economic development in South Africa continues, there will soon be an uncontrollable NCD epidemic. It has been found that dietary risks affected people’s healthirrespective of their age, gender or residential sociodemographic development and that dietary improvement might prevent one in every five deaths worldwide.Aim:The aim of this study was to determine the factors that influence the perceptions and behaviour in a rural community with a low socio-economic status regarding dietary habits and to use the knowledge to formulate an effective dietary modification strategy.Designand methodology:For this study,action research with a quantitative and qualitative component was followed.The quantitative component focuses on measureable aspects, and the qualitative component focuses on meaning. Data was collected following the standard operating procedure for anthropometry, blood pressure and blood glucose. Further methods used were questionnaires, 24-hour dietary recalls and focus group discussions. Data were analysed using Microsoft Excel, FoodFinder3 and other calculations.Sample and setting:A convenience sample (n = 16) wasused and this study was undertaken on request of the non-governmental organization, Karoo Angels and included all participants who earn an income and who do not work for themselves, that were willing to participate and living in Rietbron and Vondeling, in the Sarah BaartmanDistrict in the Eastern Cape. Results:Weight changes took place, both the crafters in the mild thinness category gained weight, one gained 3.9 kg and the other 0.5 kg. The three crafters in the normal category did not have to gain or lose weight, but all three ofthem gained an average of 3.6 kg. For the group who had to lose weight, no statistically significant weight change took place from before the intervention (76.08 ±17.67 kg) to after the intervention (75.81 ± 17.81 kg, t(10) = 0.692, p = 0.505). The maximum weight lost ivwas 3.1 kg and the maximum weight gained was 3.2 kg. Changes took place regarding BMI, waist circumference, waist-to-hip ratio and neck circumference. Some positively changed their BMI status.After the implementation of the intervention, there was a slight decrease in frequency of alcohol consumption, but smoking and physical activity remained mostly the same. Hypertension was the most prevalent NCD and is linked to smoking and alcohol consumption which is prevalent in this study. Fruit and vegetable consumption is low, and a slight increase in consumption was evident. A maximum dietary diversityscore of seven and minimum of two, where the mean was 3.81was found. The crafters’ diet did not meet the DASH diet recommendation,the mean energy distribution is of all macronutrients differ with ±4% and none of the participants’ mean micronutrients intake met the recommendations of the DASH diet or RDA. Factors that prevent them from reaching their goals included low income, low availability of fruit, vegetables and transport and no storage for food.Conclusion:It is important to consider the individuals’ living conditions, resources, knowledge, motivation and social group. The environment and resources available have a significant impact on the lifestyle of the individuals. Directing efforts of behaviour change to increase dietary diversity as the main objective, might be a more efficient way to change behaviour.Recommendations:Future studies should consider doing this study over a longer time period. The involvement of a psychologist would also be beneficial to assist the process of behaviour change.
- Full Text:
- Date Issued: 2020
Coherent detection of data and timing signals over optical fiber for telescope networks
- Authors: Nfanyana, Ketshabile
- Date: 2020
- Subjects: Fiber optics , Very large array telescopes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49226 , vital:41612
- Description: Telescope networks are increasingly being developed with networks such as the SKA telescope demanding the use of high-end technology to be incorporated. These networks require accurate clock signals to be transported to antennas as well as massive data to be transported from individual parabolic array antennas to a central computer for data analysis. To achieve this, optical fiber technology forms the backbone of these networks, proving high speed transmission and required bandwidth. For a distributed telescope network, coherent detection technology serves as the ideal optical fiber technology candidate for transport of information to a correlator. Use of this technology constitutes too many benefits. Sensitivity of the system is improved, and advanced modulation formats can be employed thereby improving spectral efficiency. Furthermore, coherent detection allows for digital signal processing algorithms to be employed for equalization of transmission impairments such as chromatic dispersion (CD), polarization mode dispersion (PMD), phase noise and nonlinear effects in the electrical domain. CD equalization is performed in the time or frequency domain using digital filters which suppress the fibers dispersion effectively. PMD equalization is usually performed in the time domain through the use of adaptive filters which employ algorithms such as least mean squares (LMS) and constant modulus algorithm (CMA). These algorithms further equalize residual CD. In mitigation of phase noise (carrier phase recovery), feed-forward and feedback carrier phase algorithms are used. Fiber nonlinearities and other impairments are compensated using the digital backpropagation algorithm which solves for the Manakov equation and nonlinear Schrödinger equation (NLSE). Distribution of stable clock signals to individual antennas is an important aspect of telescope networks. Clock signals are used to drive the digitizers and time stamping of received antenna information. These clock signals can be distributed using coherent detection technology by phase modulating the clock so as to provide inherent phase modulation robustness to noise through the fiber. In this thesis, we present coherent detection of non-return-to-zero pseudorandom binary sequence (PRBS-7) using binary phase shift keying (BPSK) through 26.6 km non-zero dispersion shifted fiber (NZDSF) at 10 Gbps. Digital signal processing for equalization of CD and PMD was performed offline using MATLAB software. For residual CD and PMD equalization, the LMS algorithm was used. The performance of the system, bit error rate (BER), was compared with that of an intensity modulated on-off keying (OOK) signal at the same bit rate. Basing on receiver sensitivity performance of OOK at 10-9 bit error rate, BPSK achieved superior performance with receiver sensitivity improvements of 18.37 dB and 13.89 dB attained for back-to-back and transmission over fiber, respectively. Phase modulation transmission of a 4 GHz clock signal was also conducted. Frequency instability, Allan variance and phase noise, of phase modulated clock was compared with that of intensity modulated clock. Moreover, we present an all optical clock generation scheme using frequency heterodyning technique. Allan variance values in the range of 10-10 were attained. The frequency instability of this clock generation scheme was quantified using the spectrum analyzer method. Furthermore, an all-photonic technique for data latency tracking of 5G networks over optical fiber is presented. The technique is spectrally efficient and is able to track latency down to the nano second timescale.
- Full Text:
- Date Issued: 2020
- Authors: Nfanyana, Ketshabile
- Date: 2020
- Subjects: Fiber optics , Very large array telescopes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49226 , vital:41612
- Description: Telescope networks are increasingly being developed with networks such as the SKA telescope demanding the use of high-end technology to be incorporated. These networks require accurate clock signals to be transported to antennas as well as massive data to be transported from individual parabolic array antennas to a central computer for data analysis. To achieve this, optical fiber technology forms the backbone of these networks, proving high speed transmission and required bandwidth. For a distributed telescope network, coherent detection technology serves as the ideal optical fiber technology candidate for transport of information to a correlator. Use of this technology constitutes too many benefits. Sensitivity of the system is improved, and advanced modulation formats can be employed thereby improving spectral efficiency. Furthermore, coherent detection allows for digital signal processing algorithms to be employed for equalization of transmission impairments such as chromatic dispersion (CD), polarization mode dispersion (PMD), phase noise and nonlinear effects in the electrical domain. CD equalization is performed in the time or frequency domain using digital filters which suppress the fibers dispersion effectively. PMD equalization is usually performed in the time domain through the use of adaptive filters which employ algorithms such as least mean squares (LMS) and constant modulus algorithm (CMA). These algorithms further equalize residual CD. In mitigation of phase noise (carrier phase recovery), feed-forward and feedback carrier phase algorithms are used. Fiber nonlinearities and other impairments are compensated using the digital backpropagation algorithm which solves for the Manakov equation and nonlinear Schrödinger equation (NLSE). Distribution of stable clock signals to individual antennas is an important aspect of telescope networks. Clock signals are used to drive the digitizers and time stamping of received antenna information. These clock signals can be distributed using coherent detection technology by phase modulating the clock so as to provide inherent phase modulation robustness to noise through the fiber. In this thesis, we present coherent detection of non-return-to-zero pseudorandom binary sequence (PRBS-7) using binary phase shift keying (BPSK) through 26.6 km non-zero dispersion shifted fiber (NZDSF) at 10 Gbps. Digital signal processing for equalization of CD and PMD was performed offline using MATLAB software. For residual CD and PMD equalization, the LMS algorithm was used. The performance of the system, bit error rate (BER), was compared with that of an intensity modulated on-off keying (OOK) signal at the same bit rate. Basing on receiver sensitivity performance of OOK at 10-9 bit error rate, BPSK achieved superior performance with receiver sensitivity improvements of 18.37 dB and 13.89 dB attained for back-to-back and transmission over fiber, respectively. Phase modulation transmission of a 4 GHz clock signal was also conducted. Frequency instability, Allan variance and phase noise, of phase modulated clock was compared with that of intensity modulated clock. Moreover, we present an all optical clock generation scheme using frequency heterodyning technique. Allan variance values in the range of 10-10 were attained. The frequency instability of this clock generation scheme was quantified using the spectrum analyzer method. Furthermore, an all-photonic technique for data latency tracking of 5G networks over optical fiber is presented. The technique is spectrally efficient and is able to track latency down to the nano second timescale.
- Full Text:
- Date Issued: 2020
Combination ecosystem green engineering and early life history processes to enhance the intertidal biodiversity in the Port of East London
- Authors: Mafanya, Sandisiwer
- Date: 2020
- Subjects: Biotic communities -- South Africa -- East London , Perna -- Ecology --South Africa -- South Africa-- East London , Mexilhao mussel -- Ecology -- South Africa -- East London , Habitat (Ecology) -- Modification -- South Africa -- East London , Benthic animals -- Effect of habitat modification on -- South Africa -- East London , Harbors -- Environmental aspects -- South Africa -- East London
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166376 , vital:41357
- Description: Marine coastal ecosystems are highly impacted by anthropogenic activities, including the development of, and practices within, harbours and/or ports. Artificial structures associated with harbours have a different chemical composition, texture and orientation than that of the natural benthic habitats they have replaced, and are therefore not generally favourable for the settlement and occurrence of indigenous species. Attempts are being made to identify what structures and materials can be used to aid in the rehabilitation of native species within harbours. The aim of this study was to investigate the effects of utilising environmentally-friendly artificial structures (tiles) with varying complexity (crevices and ridges with different depths) with ecological engineers (the indigenous bivalve Perna perna), on the associated benthic biodiversity within an international port in South Africa (Port of East London). The objectives of the study were to test the effects of artificial habitat complexity and the presence of bivalves on 1) the growth, mortality and biomass of a selected model species of ecosystem engineer (P. perna), and 2) the associated intertidal biodiversity. Tiles seeded with bivalves (P. perna) were deployed at two sites in the Port of East London and monitored monthly over a period of 12 months (November 2016-October 2017) to assess survival, growth and associated biodiversity. Environmental variables were also measured every month. The results of the three-way repeated measures ANOVAs indicated that tile treatment (especially high complexity of 2.5 and 5 cm) had an effect on the diversity of mobile species, length, height and biomass of the bivalves used as model ecosystem engineer, indicating the potentials for protection from wave dislodgement and refuge provision. Treatment (especially flat tiles) also had an effect on sessile/sedentary species diversity, indicating the greater proportion of space provided by these non-complex tiles. In addition, month had an effect on the mortality, height and biomass of the bivalves. Mortality was highest in October 2017, while the growth in height and biomass of P. perna were largest in January and October 2017 respectively. The use of artificial tiles also had a positive effect on the survival, growth, and biomass of bivalves (especially the length, weight and dry weight in 2.5 cm and 5 cm complexity). Additionally, this research investigated patterns of settlement and recruitment of the local bivalve population (P. perna) in the Port of East London and adjacent natural coastline to understand the early life history temporal and spatial dynamics of this model ecosystem engineer species. Settlement and recruitment were assessed every month by deploying and replacing artificial collectors for a total period of 19 months (November 2016-May 2018). The results of the two-way ANOVAs indicated that month and site (port vs natural) had an effect on settlement and recruitment of bivalves. Settlement and recruitment of bivalves were highest in July 2017 (port) and March 2018 (natural rocky shore). This study has highlighted that the use of artificial concrete tiles with increased complexity, as well as the investigation of the early stages of mussel populations could be important to consider in a framework of rehabilitation of urban coastal environments such as the Port of East London. Ecological engineering (in terms of increased complexity and heterogeneity) has indeed the potentials to be incorporated in South African programmes aiming at improving natural biodiversity in coastal urban environments. Nonetheless, the spatio-temporal variability of early driver of mussel populations (settlement and recruitment) is also an important feature to be closely monitored if biodiversity in South African coastal armouring is to be enhanced effectively and in the long term.
- Full Text:
- Date Issued: 2020
- Authors: Mafanya, Sandisiwer
- Date: 2020
- Subjects: Biotic communities -- South Africa -- East London , Perna -- Ecology --South Africa -- South Africa-- East London , Mexilhao mussel -- Ecology -- South Africa -- East London , Habitat (Ecology) -- Modification -- South Africa -- East London , Benthic animals -- Effect of habitat modification on -- South Africa -- East London , Harbors -- Environmental aspects -- South Africa -- East London
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/166376 , vital:41357
- Description: Marine coastal ecosystems are highly impacted by anthropogenic activities, including the development of, and practices within, harbours and/or ports. Artificial structures associated with harbours have a different chemical composition, texture and orientation than that of the natural benthic habitats they have replaced, and are therefore not generally favourable for the settlement and occurrence of indigenous species. Attempts are being made to identify what structures and materials can be used to aid in the rehabilitation of native species within harbours. The aim of this study was to investigate the effects of utilising environmentally-friendly artificial structures (tiles) with varying complexity (crevices and ridges with different depths) with ecological engineers (the indigenous bivalve Perna perna), on the associated benthic biodiversity within an international port in South Africa (Port of East London). The objectives of the study were to test the effects of artificial habitat complexity and the presence of bivalves on 1) the growth, mortality and biomass of a selected model species of ecosystem engineer (P. perna), and 2) the associated intertidal biodiversity. Tiles seeded with bivalves (P. perna) were deployed at two sites in the Port of East London and monitored monthly over a period of 12 months (November 2016-October 2017) to assess survival, growth and associated biodiversity. Environmental variables were also measured every month. The results of the three-way repeated measures ANOVAs indicated that tile treatment (especially high complexity of 2.5 and 5 cm) had an effect on the diversity of mobile species, length, height and biomass of the bivalves used as model ecosystem engineer, indicating the potentials for protection from wave dislodgement and refuge provision. Treatment (especially flat tiles) also had an effect on sessile/sedentary species diversity, indicating the greater proportion of space provided by these non-complex tiles. In addition, month had an effect on the mortality, height and biomass of the bivalves. Mortality was highest in October 2017, while the growth in height and biomass of P. perna were largest in January and October 2017 respectively. The use of artificial tiles also had a positive effect on the survival, growth, and biomass of bivalves (especially the length, weight and dry weight in 2.5 cm and 5 cm complexity). Additionally, this research investigated patterns of settlement and recruitment of the local bivalve population (P. perna) in the Port of East London and adjacent natural coastline to understand the early life history temporal and spatial dynamics of this model ecosystem engineer species. Settlement and recruitment were assessed every month by deploying and replacing artificial collectors for a total period of 19 months (November 2016-May 2018). The results of the two-way ANOVAs indicated that month and site (port vs natural) had an effect on settlement and recruitment of bivalves. Settlement and recruitment of bivalves were highest in July 2017 (port) and March 2018 (natural rocky shore). This study has highlighted that the use of artificial concrete tiles with increased complexity, as well as the investigation of the early stages of mussel populations could be important to consider in a framework of rehabilitation of urban coastal environments such as the Port of East London. Ecological engineering (in terms of increased complexity and heterogeneity) has indeed the potentials to be incorporated in South African programmes aiming at improving natural biodiversity in coastal urban environments. Nonetheless, the spatio-temporal variability of early driver of mussel populations (settlement and recruitment) is also an important feature to be closely monitored if biodiversity in South African coastal armouring is to be enhanced effectively and in the long term.
- Full Text:
- Date Issued: 2020