The horizontal application of the environmental right to Juristic persons at sea
- Authors: Maseka, Ntemesha Mwila
- Date: 2024-04
- Subjects: Environmental law--South Africa , Marine Living Resources Act , Marine environment
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/66098 , vital:74350
- Description: Due to its vast resources, the ocean has been designated the new “economic frontier”. States are focusing on unlocking this potential to boost economic growth, employment and innovation. Because of their substantial resources, corporations are key actors in driving the development of the ocean economy. Although corporations undeniably contribute significantly to realising the ocean economy’s potential, their main activities—including offshore oil and gas exploration and production and fishing—pose great threats to marine ecosystems. This harm to the marine environment may also threaten and adversely impact many people’s lives, health, well-being, livelihood, culture and traditions. In the South African context, this reality is notably seen through Operation Phakisa. This government initiative aims to unlock the economic potential of the ocean economy to expedite the implementation of solutions to poverty, unemployment and inequality. This race to utilise the oceans and its resources brings to the fore the interaction between the right to have the environment protected and socio-economic development anticipated in section 24 of the South African Constitution. The South African Constitution through section 8(2) acknowledges that non-State actors such as corporations can abuse human rights in horizontal relationships. However, unlike the State, non-State actors are only bound in certain circumstances. Therefore, this thesis examines whether and, if so, to what extent section 24 of the Constitution binds juristic persons at sea. This thesis examines the direct application of international norms to non-State actors to determine how international human rights law addresses non-State actors' conduct that impairs an individual’s guaranteed rights. It was determined that international human rights law has an indirect horizontal effect. This means that in cases where a non-State actor impairs an individual’s human rights, international law permits the victim to hold the State responsible for the violation rather than the non-State actor who was the perpetrator. For a non-State actor to incur direct obligations to uphold certain human rights, the State must create these obligations in its domestic law. The thesis explored how the South African Bill of Rights imposes direct human rights obligations on non-State actors in a horizontal dispute. It was found that whether an entrenched right binds a non-State actor depends on a multi-factor enquiry confirmed by the Constitutional Court. Based on that enquiry, it concluded that the environmental right is capable of and suitable for horizontal application. Furthermore, non-State actors can bear positive and negative constitutional human rights obligations arising from the environmental right. A failure to comply with these obligations would violate this constitutional right. The most significant findings of this thesis pertain to the applicability of South Africa’s human rights law framework at sea. This is because the legal regime applicable at sea differs from that on land. The United Nations Convention on the Law of the Sea assigns jurisdiction to States in the different maritime zones for different purposes. To elucidate South Africa's rights and obligations as delineated in the LOSC, the thesis focused on two examples: the exploitation of marine living resources and the prospection, exploration, and exploitation of marine non-living resources. Subsequently, the extent to which South Africa has taken measures in its domestic law to implement those rights and duties was assessed. In addition, this approach was appropriate because questions concerning the horizontal application of the South African Bill of Rights necessitate contextual analysis and cannot be answered a priori and in the abstract. Using the multi-factor enquiry, the study showed that, in principle, section 24 of the Constitution might bind juristic persons within South Africa’s territorial jurisdiction, exclusive economic zone jurisdiction, continental shelf jurisdiction and under South Africa’s personal jurisdiction. Furthermore, juristic persons who control vessels registered in South Africa or control a vessel entitled to be registered in South Africa but has departed to a place outside South Africa without being registered might also be constitutionally bound based on flag State jurisdiction. The sole means of preventing South Africa from exercising its authority this way requires severing the jurisdictional connection between South Africa and the juristic person. It was recommended that in ocean-related matters, the connecting factor between South Africa and the juristic person must be considered as an additional factor in the enquiry to determine whether a particular right binds that juristic person. Additionally, since the scope of corresponding rights-holders are “everyone”, even people outside South Africa present in places where the juristic person who is the corresponding duty- bearer operates or where their conduct is felt can hold these actors accountable for their constitutional human rights obligations. , Thesis (LLD) -- Faculty of Law, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Maseka, Ntemesha Mwila
- Date: 2024-04
- Subjects: Environmental law--South Africa , Marine Living Resources Act , Marine environment
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/66098 , vital:74350
- Description: Due to its vast resources, the ocean has been designated the new “economic frontier”. States are focusing on unlocking this potential to boost economic growth, employment and innovation. Because of their substantial resources, corporations are key actors in driving the development of the ocean economy. Although corporations undeniably contribute significantly to realising the ocean economy’s potential, their main activities—including offshore oil and gas exploration and production and fishing—pose great threats to marine ecosystems. This harm to the marine environment may also threaten and adversely impact many people’s lives, health, well-being, livelihood, culture and traditions. In the South African context, this reality is notably seen through Operation Phakisa. This government initiative aims to unlock the economic potential of the ocean economy to expedite the implementation of solutions to poverty, unemployment and inequality. This race to utilise the oceans and its resources brings to the fore the interaction between the right to have the environment protected and socio-economic development anticipated in section 24 of the South African Constitution. The South African Constitution through section 8(2) acknowledges that non-State actors such as corporations can abuse human rights in horizontal relationships. However, unlike the State, non-State actors are only bound in certain circumstances. Therefore, this thesis examines whether and, if so, to what extent section 24 of the Constitution binds juristic persons at sea. This thesis examines the direct application of international norms to non-State actors to determine how international human rights law addresses non-State actors' conduct that impairs an individual’s guaranteed rights. It was determined that international human rights law has an indirect horizontal effect. This means that in cases where a non-State actor impairs an individual’s human rights, international law permits the victim to hold the State responsible for the violation rather than the non-State actor who was the perpetrator. For a non-State actor to incur direct obligations to uphold certain human rights, the State must create these obligations in its domestic law. The thesis explored how the South African Bill of Rights imposes direct human rights obligations on non-State actors in a horizontal dispute. It was found that whether an entrenched right binds a non-State actor depends on a multi-factor enquiry confirmed by the Constitutional Court. Based on that enquiry, it concluded that the environmental right is capable of and suitable for horizontal application. Furthermore, non-State actors can bear positive and negative constitutional human rights obligations arising from the environmental right. A failure to comply with these obligations would violate this constitutional right. The most significant findings of this thesis pertain to the applicability of South Africa’s human rights law framework at sea. This is because the legal regime applicable at sea differs from that on land. The United Nations Convention on the Law of the Sea assigns jurisdiction to States in the different maritime zones for different purposes. To elucidate South Africa's rights and obligations as delineated in the LOSC, the thesis focused on two examples: the exploitation of marine living resources and the prospection, exploration, and exploitation of marine non-living resources. Subsequently, the extent to which South Africa has taken measures in its domestic law to implement those rights and duties was assessed. In addition, this approach was appropriate because questions concerning the horizontal application of the South African Bill of Rights necessitate contextual analysis and cannot be answered a priori and in the abstract. Using the multi-factor enquiry, the study showed that, in principle, section 24 of the Constitution might bind juristic persons within South Africa’s territorial jurisdiction, exclusive economic zone jurisdiction, continental shelf jurisdiction and under South Africa’s personal jurisdiction. Furthermore, juristic persons who control vessels registered in South Africa or control a vessel entitled to be registered in South Africa but has departed to a place outside South Africa without being registered might also be constitutionally bound based on flag State jurisdiction. The sole means of preventing South Africa from exercising its authority this way requires severing the jurisdictional connection between South Africa and the juristic person. It was recommended that in ocean-related matters, the connecting factor between South Africa and the juristic person must be considered as an additional factor in the enquiry to determine whether a particular right binds that juristic person. Additionally, since the scope of corresponding rights-holders are “everyone”, even people outside South Africa present in places where the juristic person who is the corresponding duty- bearer operates or where their conduct is felt can hold these actors accountable for their constitutional human rights obligations. , Thesis (LLD) -- Faculty of Law, 2024
- Full Text:
- Date Issued: 2024-04
Effects of annealing on the structural and optical properties of nanostructured TiO2
- Talla, Assane, Urgessa, Zelalem
- Authors: Talla, Assane , Urgessa, Zelalem
- Date: 2023-12
- Subjects: Titanium dioxide , Nanostructured materials , Nanotubes
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62655 , vital:72907
- Description: In this thesis, the structural, morphological and optical properties of titanium dioxide (TiO2) are investigated. Titanium dioxide (TiO2) nanotubes are prepared by anodic oxidation of titanium foil. The as-anodised samples are thermally annealed at various temperatures in nitrogen, air, oxygen and vacuum. The purpose is to study how the annealing conditions affect the properties of the nanostructures, including the anatase to rutile phase transformation. In all annealing atmospheres, except in vacuum, the dominant phase is found to be anatase when annealing is performed up to 600 oC. Above 700 oC the rutile phase becomes dominant. The anatase phase is stable above 600 oC in vacuum and does not evolve significantly up to 900 oC. The morphologies of the tubes tend to deteriorate with increased annealing temperature, in nitrogen, air and oxygen atmospheres, due to sintering effects. However, the integrity of the nanotubes is maintained up to 900 oC in vacuum. The photoluminescence (PL) spectra suggest mainly the presence of oxygen vacancies and self-trapped excitons, with respective emission bands around 2.5 eV and 2.3 eV. The results show that both the annealing temperature and atmosphere strongly influence the crystalline and optical properties of the TiO2 nanotubes. In addition, the phase transformation from anatase to rutile for samples annealed in an oxygen-rich environment is investigated in detail. Complementary structural information obtained from transmission electron microscopy and Raman analysis for oxygen-annealed samples reveals that the nucleation of the rutile phase starts from the titanium substrate and then propagates along the tubes. The results provide suitable annealing conditions to control the phase content and morphology of anodic TiO2 nanotubes. The PL characteristics of bulk crystalline anatase TiO2, namely virgin and hydrogen-annealed at 600 oC for 1 h, are studied. The low temperature PL spectra at 5.5 K shows near band edge (NBE) emissions with two dominant lines ascribed to shallow donor bound exciton and possibly free to bound recombination. The two main transitions are assisted by optical phononmodes. Temperature-dependent PL measurements performed on these anatase crystals reveal that the donor bound exciton is stable below 90 K. Hydrogen trapped in oxygen vacancies is proposed to be the shallow donor. In addition, two activation processes are involved for the thermal quenching of donor bound excitons. The total activation energy is found to correlate well with the localisation energy of the bound exciton. Site-selective PL spectra obtained from anodic TiO2 tubes reveals that the luminescence of the nanostructures depends on the morphology. The result shows unusual near-band edge emission (NBE) for these structures, which is rarely observed in indirect band gap TiO2. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Talla, Assane , Urgessa, Zelalem
- Date: 2023-12
- Subjects: Titanium dioxide , Nanostructured materials , Nanotubes
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62655 , vital:72907
- Description: In this thesis, the structural, morphological and optical properties of titanium dioxide (TiO2) are investigated. Titanium dioxide (TiO2) nanotubes are prepared by anodic oxidation of titanium foil. The as-anodised samples are thermally annealed at various temperatures in nitrogen, air, oxygen and vacuum. The purpose is to study how the annealing conditions affect the properties of the nanostructures, including the anatase to rutile phase transformation. In all annealing atmospheres, except in vacuum, the dominant phase is found to be anatase when annealing is performed up to 600 oC. Above 700 oC the rutile phase becomes dominant. The anatase phase is stable above 600 oC in vacuum and does not evolve significantly up to 900 oC. The morphologies of the tubes tend to deteriorate with increased annealing temperature, in nitrogen, air and oxygen atmospheres, due to sintering effects. However, the integrity of the nanotubes is maintained up to 900 oC in vacuum. The photoluminescence (PL) spectra suggest mainly the presence of oxygen vacancies and self-trapped excitons, with respective emission bands around 2.5 eV and 2.3 eV. The results show that both the annealing temperature and atmosphere strongly influence the crystalline and optical properties of the TiO2 nanotubes. In addition, the phase transformation from anatase to rutile for samples annealed in an oxygen-rich environment is investigated in detail. Complementary structural information obtained from transmission electron microscopy and Raman analysis for oxygen-annealed samples reveals that the nucleation of the rutile phase starts from the titanium substrate and then propagates along the tubes. The results provide suitable annealing conditions to control the phase content and morphology of anodic TiO2 nanotubes. The PL characteristics of bulk crystalline anatase TiO2, namely virgin and hydrogen-annealed at 600 oC for 1 h, are studied. The low temperature PL spectra at 5.5 K shows near band edge (NBE) emissions with two dominant lines ascribed to shallow donor bound exciton and possibly free to bound recombination. The two main transitions are assisted by optical phononmodes. Temperature-dependent PL measurements performed on these anatase crystals reveal that the donor bound exciton is stable below 90 K. Hydrogen trapped in oxygen vacancies is proposed to be the shallow donor. In addition, two activation processes are involved for the thermal quenching of donor bound excitons. The total activation energy is found to correlate well with the localisation energy of the bound exciton. Site-selective PL spectra obtained from anodic TiO2 tubes reveals that the luminescence of the nanostructures depends on the morphology. The result shows unusual near-band edge emission (NBE) for these structures, which is rarely observed in indirect band gap TiO2. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
Effects of fire on architecture and composition of canopy shrubs in subtropical dune thicket of the southeastern Cape Floristic Region
- Strydom, Tiaan, Grobler, Adriaan
- Authors: Strydom, Tiaan , Grobler, Adriaan
- Date: 2023-12
- Subjects: Plant ecology -- Research , Plant communities -- South Africa , Browsing (Animal behavior)
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62632 , vital:72899
- Description: Disturbance, such as fire and megaherbivory, is a pervasive phenomenon globally and has different effects on the flora and vegetation of different ecosystems. The Cape Floristic Region (CFR) of South Africa includes the distinctive Subtropical Thicket biome, which occurs as interrupted blocks that are not exposed to fire, but also as mosaics with the fire-prone vegetation of the Fynbos biome, especially on coastal dunes where thicket species are exposed to fire. Subtropical Dune Thicket (hereafter thicket) thus co-occurs with Fynbos, capable of supporting intense fires that can lead to thicket shrub defoliation and mortality. Thicket also experiences disturbance from meso- and megaherbivores that causes defoliation and mortality of shrubs. The aim of this study was to investigate the resilience of thicket shrub species to varying disturbance levels from fire and browsing to understand what drives thicket persistence in a fire-prone landscape. Firstly, I established the architectural traits of thicket species in long unburnt and post-fire contexts and investigated the relationships between these traits and the survival, resprouting ability and persistence of thicket shrubs. In mature thicket, I identified three distinct architectural guilds, namely hedge formers, lateral spreaders, and vertical growers. In post-fire thicket I identified three resprouting architectures, namely weak resprouters, moderate resprouters and strong resprouters. There was no strong relationship between the unburnt and post-fire resprouting architectures. Secondly, I compared thicket species and architectural composition in patches of landscape that experience different levels of fire exposure to assess the potential effect of fire frequency on determining thicket structure. I recognised three thicket vegetation units, each with a distinct structure and each corresponding to the level of fire exposure in the landscape. The first unit, forest-thicket, is exposed to low levels of fire frequency (> 100 years) and harbours forest species, many of which were vertical growers. The second unit, thicket, is exposed to moderate levels of fire frequency (50-100 years) and is dominated by lateral spreaders. The last unit, fynbos-thicket, is exposed to high levels of fire frequency (10-50 years) and here hedge-forming shrubs dominate the canopy cover. Forest-thicket and fynbos-thicket had a diverse set of shrub species with many being restricted to their respective vegetation type, whereas thicket had a lower diversity with no unique shrub species. , Thesis (DPhil) -- Faculty of Science, School of Natural Resource Management, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Strydom, Tiaan , Grobler, Adriaan
- Date: 2023-12
- Subjects: Plant ecology -- Research , Plant communities -- South Africa , Browsing (Animal behavior)
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62632 , vital:72899
- Description: Disturbance, such as fire and megaherbivory, is a pervasive phenomenon globally and has different effects on the flora and vegetation of different ecosystems. The Cape Floristic Region (CFR) of South Africa includes the distinctive Subtropical Thicket biome, which occurs as interrupted blocks that are not exposed to fire, but also as mosaics with the fire-prone vegetation of the Fynbos biome, especially on coastal dunes where thicket species are exposed to fire. Subtropical Dune Thicket (hereafter thicket) thus co-occurs with Fynbos, capable of supporting intense fires that can lead to thicket shrub defoliation and mortality. Thicket also experiences disturbance from meso- and megaherbivores that causes defoliation and mortality of shrubs. The aim of this study was to investigate the resilience of thicket shrub species to varying disturbance levels from fire and browsing to understand what drives thicket persistence in a fire-prone landscape. Firstly, I established the architectural traits of thicket species in long unburnt and post-fire contexts and investigated the relationships between these traits and the survival, resprouting ability and persistence of thicket shrubs. In mature thicket, I identified three distinct architectural guilds, namely hedge formers, lateral spreaders, and vertical growers. In post-fire thicket I identified three resprouting architectures, namely weak resprouters, moderate resprouters and strong resprouters. There was no strong relationship between the unburnt and post-fire resprouting architectures. Secondly, I compared thicket species and architectural composition in patches of landscape that experience different levels of fire exposure to assess the potential effect of fire frequency on determining thicket structure. I recognised three thicket vegetation units, each with a distinct structure and each corresponding to the level of fire exposure in the landscape. The first unit, forest-thicket, is exposed to low levels of fire frequency (> 100 years) and harbours forest species, many of which were vertical growers. The second unit, thicket, is exposed to moderate levels of fire frequency (50-100 years) and is dominated by lateral spreaders. The last unit, fynbos-thicket, is exposed to high levels of fire frequency (10-50 years) and here hedge-forming shrubs dominate the canopy cover. Forest-thicket and fynbos-thicket had a diverse set of shrub species with many being restricted to their respective vegetation type, whereas thicket had a lower diversity with no unique shrub species. , Thesis (DPhil) -- Faculty of Science, School of Natural Resource Management, 2023
- Full Text:
- Date Issued: 2023-12
Establishment of a high-content neurodegenerative disease model screening platform
- Authors: Swanepoel, Bresler
- Date: 2023-12
- Subjects: Molecular neurobiology , Nervous system -- Diseases , Nervous system -- Degeneration
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62644 , vital:72906
- Description: The identification of viable therapeutic targets and new treatments for central nervous system disorders, especially neurodegenerative diseases, remain major challenges in the field of drug discovery. Over the past few years there has been a steady decline in the turnaround time of current screening processes to yield viable drugs. Therefore, an increasing need exists for better technologies, protocols, and the screening of larger libraries. High-throughput screening provides the best solution to this problem and has become a key part in the drug discovery and development process. Likewise, high-content analysis has gained popularity over the past few years and is suitable for high-throughput screening. The aim of this study was to establish a comprehensive in vitro neuroprotective screening platform incorporating high throughput screening, using Parkinson’s disease as the neurodegenerative disease of interest. To evaluate the success of this platform, the neuroprotective potential of two mushrooms (Hericium erinaceus and Phlebopus sudanicus), two plants (Lippia javanica and Myrothamnus flabellifolia) and two seaweeds (Eucheuma denticulatum and Kappaphycus alvarezii) were investigated. Aqueous and ethanolic extracts of the selected natural products were evaluated across 21 parameters associated with four hallmarks of neurodegeneration: acquiring senescence, acquiring cell death, neuroinflammation and altered metabolism/cell survival. Based on the effects of these selected natural products on the 21 parameters, their potential mechanisms of action were elucidated. In addition to this, the natural products were scored under each of these therapeutic targets in an attempt to identify the most suitable animal models for future studies. The scoring system indicated that animal models investigating anti-senescence ability would be more suited for extracts of H. erinaceus, P. sudanicus and E. denticulatum whereas studies investigating the prevention of cell death would be more suited for extracts of E. denticulatum, L. javanica and K. alvarezii. Likewise, models based on neuroinflammation would be best suited for extracts of H. erinaceus, E. denticulatum and L. javanica while studies examining altered metabolism/cell survival would be best suited to extracts of H. erinaceus, E. denticulatum, K. alvarezii and M. flabellifolia. Considering the pleiotropic nature of the selected natural products, models that can combine these therapeutic targets could be of great interest. 6-OHDA proved to be capable of inducing favourable effects, in all the parameters investigated, with regard to a neurodegenerative state. However, it is known to have some disadvantages when it comes to pathological features such as the lack of the ability to induce Lewy body formation. Choosing the correct inducer remains a daunting task and no model, whether cell-based or animal-based, exists yet in which all the features of neurodegenerative diseases have been successfully replicated. The limitations of the current models, however, does not mean that they do not produce valuable insights. This is especially true if the mechanism of action for a specific compound or natural product is unknown. Animal models are still indispensable for the validation and interpretation of the results obtained from cell models with particular importance to toxicity. Therefore, this study assessed the best studied extract with the highest overall score for its toxicity using a zebrafish larvae-based model. Assessment of the toxicity of H. erinaceus revealed that both aqueous and ethanolic extracts resulted in death at the highest concentrations. This was supported by the results obtained in the in vitro cytotoxicity screening. In conclusion, this highlighted the importance of using physiologically relevant concentrations and supported the translational value of the current cell-based screening model to animal models and possibly humans. The findings of the present study suggest that a scoring system, which categorizes the different activities of selected natural products into distinct groups, can be a useful tool to improve the translatability of in vitro results to animal models. Furthermore, the current study arguably provides the most comprehensive neuroprotective screening platform in existence. Future research can look at expanding the platform through incorporation of additional parameters based on other hallmarks of neurodegeneration, not covered in this study, including protein folding and aggregation, altered epigenetics and the examination of other neuronal markers such as the involvement of astrocytes, oligodendrocytes, and microglia. In addition to this, future research can make use of more sophisticated cell models such as differentiated, human induced pluripotent stem cells and three-dimensional cultures. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Swanepoel, Bresler
- Date: 2023-12
- Subjects: Molecular neurobiology , Nervous system -- Diseases , Nervous system -- Degeneration
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62644 , vital:72906
- Description: The identification of viable therapeutic targets and new treatments for central nervous system disorders, especially neurodegenerative diseases, remain major challenges in the field of drug discovery. Over the past few years there has been a steady decline in the turnaround time of current screening processes to yield viable drugs. Therefore, an increasing need exists for better technologies, protocols, and the screening of larger libraries. High-throughput screening provides the best solution to this problem and has become a key part in the drug discovery and development process. Likewise, high-content analysis has gained popularity over the past few years and is suitable for high-throughput screening. The aim of this study was to establish a comprehensive in vitro neuroprotective screening platform incorporating high throughput screening, using Parkinson’s disease as the neurodegenerative disease of interest. To evaluate the success of this platform, the neuroprotective potential of two mushrooms (Hericium erinaceus and Phlebopus sudanicus), two plants (Lippia javanica and Myrothamnus flabellifolia) and two seaweeds (Eucheuma denticulatum and Kappaphycus alvarezii) were investigated. Aqueous and ethanolic extracts of the selected natural products were evaluated across 21 parameters associated with four hallmarks of neurodegeneration: acquiring senescence, acquiring cell death, neuroinflammation and altered metabolism/cell survival. Based on the effects of these selected natural products on the 21 parameters, their potential mechanisms of action were elucidated. In addition to this, the natural products were scored under each of these therapeutic targets in an attempt to identify the most suitable animal models for future studies. The scoring system indicated that animal models investigating anti-senescence ability would be more suited for extracts of H. erinaceus, P. sudanicus and E. denticulatum whereas studies investigating the prevention of cell death would be more suited for extracts of E. denticulatum, L. javanica and K. alvarezii. Likewise, models based on neuroinflammation would be best suited for extracts of H. erinaceus, E. denticulatum and L. javanica while studies examining altered metabolism/cell survival would be best suited to extracts of H. erinaceus, E. denticulatum, K. alvarezii and M. flabellifolia. Considering the pleiotropic nature of the selected natural products, models that can combine these therapeutic targets could be of great interest. 6-OHDA proved to be capable of inducing favourable effects, in all the parameters investigated, with regard to a neurodegenerative state. However, it is known to have some disadvantages when it comes to pathological features such as the lack of the ability to induce Lewy body formation. Choosing the correct inducer remains a daunting task and no model, whether cell-based or animal-based, exists yet in which all the features of neurodegenerative diseases have been successfully replicated. The limitations of the current models, however, does not mean that they do not produce valuable insights. This is especially true if the mechanism of action for a specific compound or natural product is unknown. Animal models are still indispensable for the validation and interpretation of the results obtained from cell models with particular importance to toxicity. Therefore, this study assessed the best studied extract with the highest overall score for its toxicity using a zebrafish larvae-based model. Assessment of the toxicity of H. erinaceus revealed that both aqueous and ethanolic extracts resulted in death at the highest concentrations. This was supported by the results obtained in the in vitro cytotoxicity screening. In conclusion, this highlighted the importance of using physiologically relevant concentrations and supported the translational value of the current cell-based screening model to animal models and possibly humans. The findings of the present study suggest that a scoring system, which categorizes the different activities of selected natural products into distinct groups, can be a useful tool to improve the translatability of in vitro results to animal models. Furthermore, the current study arguably provides the most comprehensive neuroprotective screening platform in existence. Future research can look at expanding the platform through incorporation of additional parameters based on other hallmarks of neurodegeneration, not covered in this study, including protein folding and aggregation, altered epigenetics and the examination of other neuronal markers such as the involvement of astrocytes, oligodendrocytes, and microglia. In addition to this, future research can make use of more sophisticated cell models such as differentiated, human induced pluripotent stem cells and three-dimensional cultures. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
Finite difference methods for Burgers-Huxley equation and biofilm formation
- Authors: Tijani, Yusuf Olatunji
- Date: 2023-12
- Subjects: Burgers equation , Terrestrial heat flow , Applied mathematics
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62732 , vital:72934
- Description: In this thesis, we constructed some versions of finite difference scheme for the Burgers-Huxley equation and for a set of partial differential equations (PDEs) arising in biofilm formation. The Burgers-Huxley equation serves as a fundamental model that describes the interaction between reaction mechanisms, convection effects, and diffusion transport. It has applications in the study of wave mechanics, population dynamics, physiology, fluid mechanics to list but a few. The study of biofilm formation is becoming increasingly important due to micro-organisms (i.e. bacteria) forming a protected mode from the host defense mechanism which may result in alteration in the host gene transcription and growth rate. Applications can be found useful in the treatment of bacterial infections, contamination of foods and water quality. We designed two nonstandard finite difference and two exponential finite difference schemes for the Burgers-Huxley equation. Numerical experiments with six cases and in three different regimes were studied. We show that the nonstandard scheme preserves the properties of the continuous equation which include positivity and boundedness. The stability region of the explicit exponential scheme was obtained and we outlined the algorithm for the implicit exponential scheme. The performance of the four schemes are compared in regard to absolute error, relative error, L1 and L∞ norms. For a singularly perturbed Burgers-Huxley equation, a novel nonstandard finite difference technique is constructed. It is demonstrated numerically that the NSFD scheme outperforms the classical scheme by comparing maximum pointwise errors and rate of convergence. We then solved the 2D Burgers-Huxley equation using four novel nonstandard finite difference schemes (NSFD1, NSFD2, NSFD3 and NSFD4). The numerical profiles from NSFD1 and NSFD2 exhibit some deviation from the exact profile. Our quest for a better performing scheme led to the modification of NSFD1 using the remainder effect technique. NSFD4 was designed by employing the time splitting approach. All the schemes preserve the properties of the continuous model (positivity and boundedness). The performance of all the schemes are analysed. We construct three nonstandard finite difference schemes for the equations modelling biomass equation and coupled substrate-biomass system of equations respectively. We checked the accuracy of our scheme by the conservation of physical properties (positivity, boundedness, biofilm formation and annihilation) since an analytical solution is not available. We show the instability, lack of conservation of physical properties by the classical scheme. Our proposed scheme shows good performance when compared with other results in the literature. The results here give more insight into the benefits of the nonstandard finite difference approximations. , Thesis (DPhil) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics , 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Tijani, Yusuf Olatunji
- Date: 2023-12
- Subjects: Burgers equation , Terrestrial heat flow , Applied mathematics
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62732 , vital:72934
- Description: In this thesis, we constructed some versions of finite difference scheme for the Burgers-Huxley equation and for a set of partial differential equations (PDEs) arising in biofilm formation. The Burgers-Huxley equation serves as a fundamental model that describes the interaction between reaction mechanisms, convection effects, and diffusion transport. It has applications in the study of wave mechanics, population dynamics, physiology, fluid mechanics to list but a few. The study of biofilm formation is becoming increasingly important due to micro-organisms (i.e. bacteria) forming a protected mode from the host defense mechanism which may result in alteration in the host gene transcription and growth rate. Applications can be found useful in the treatment of bacterial infections, contamination of foods and water quality. We designed two nonstandard finite difference and two exponential finite difference schemes for the Burgers-Huxley equation. Numerical experiments with six cases and in three different regimes were studied. We show that the nonstandard scheme preserves the properties of the continuous equation which include positivity and boundedness. The stability region of the explicit exponential scheme was obtained and we outlined the algorithm for the implicit exponential scheme. The performance of the four schemes are compared in regard to absolute error, relative error, L1 and L∞ norms. For a singularly perturbed Burgers-Huxley equation, a novel nonstandard finite difference technique is constructed. It is demonstrated numerically that the NSFD scheme outperforms the classical scheme by comparing maximum pointwise errors and rate of convergence. We then solved the 2D Burgers-Huxley equation using four novel nonstandard finite difference schemes (NSFD1, NSFD2, NSFD3 and NSFD4). The numerical profiles from NSFD1 and NSFD2 exhibit some deviation from the exact profile. Our quest for a better performing scheme led to the modification of NSFD1 using the remainder effect technique. NSFD4 was designed by employing the time splitting approach. All the schemes preserve the properties of the continuous model (positivity and boundedness). The performance of all the schemes are analysed. We construct three nonstandard finite difference schemes for the equations modelling biomass equation and coupled substrate-biomass system of equations respectively. We checked the accuracy of our scheme by the conservation of physical properties (positivity, boundedness, biofilm formation and annihilation) since an analytical solution is not available. We show the instability, lack of conservation of physical properties by the classical scheme. Our proposed scheme shows good performance when compared with other results in the literature. The results here give more insight into the benefits of the nonstandard finite difference approximations. , Thesis (DPhil) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics , 2023
- Full Text:
- Date Issued: 2023-12
The use of a novel chemical system towards improving waste tyre pyrolysis and the quality of waste tyre pyrolysis products
- Tsipa, Phuti Cedric, Iwarere, Samuel
- Authors: Tsipa, Phuti Cedric , Iwarere, Samuel
- Date: 2023-12
- Subjects: Tires -- Recycling , Rubber chemicals , Rubber, Reclaimed
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62666 , vital:72912
- Description: Pyrolysis process is one of the most efficient methods in the waste tyre recycling sector at this moment, hence the attention it is receiving. However, this process has some limitations, with the main one being that it is non-conventional and typically energy intensive. In addition, its resultant products have been reported to have significantly poorer properties relative to their virgin counterparts, making it difficult to incorporate them in the mainstream of raw materials. For instance, waste tyre pyrolysis oil typically has poor fuel properties, high sulfur content, high amount of polycyclic aromatic hydrocarbons (PAHs) and strong unpleasant odour; on the other hand, the quality of the recovered carbon black is dependent on the feedstock and the pyrolysis process conditions. Hence the need for further research and development to make the process effective and improve the quality of resultant products. The aim of this research project was to study the impact of pre-pyrolysis treatment of tyre crumbs and post-pyrolysis treatment of the oil using a novel chemical system on the quality/composition of the resultant products. In addition, the study compared the impact of pre- and post-pyrolysis treatments on the optimum pyrolysis time and temperature (energy). The equipment employed in this study included a vertical fixed bed pyrolysis pilot reactor (modified to suit the reaction/experiment) as well as characterization techniques such as fourier transform infrared (FTIR), elemental analysis (carbon, hydrogen, nitrogen and sulfur – CHNS analysis), gas chromatography coupled to mass spectrometer (GCMS), gas chromatography coupled to flame photometric detector (GCFPD), thermo-gravimetric and derivative analysis (TG/DTG isothermal analysis, and proximate analysis) and scanning electron microscope (SEM). The highlight of the findings is that chemically pre-treating tyre crumbs with a mixture of protonic acid and organic solvent before pyrolysis significantly lowered the temperature required to pyrolyze them, from around 400-500 ℃ to 100-115 ℃. This meant that by using the chemical treatment on waste tyres a lot of energy can be saved. In addition, the sulfur content in the oil fraction was reduced from a total of 1.7 wt% to a total of about 0.2 wt%. This also showed that the contaminants in oil were significantly reduced. The oil was condensed into three (3) collectors for fractionation; in collector 2 was about 54 % of the total oil with sulfur content of about 0.015 wt%. The PAHs amounts were also lowered, as literature indicated that PAHs are mostly formed at around 600-700 ℃. It was also found that the oil produced from post-pyrolysis treatment of oil has a petroleum-like smell, whereas the pre-pyrolysis treated oil has a tyre-like pungent odour. Furthermore, the post-pyrolysis treated oil contains higher contents of alkanes and benzene, toluene, xylene (BTX). Findings of this study have a profound potential impact on the waste tyre recycling industry; for example, reduced production energy cost due to lowered temperature required for pyrolysis, improved quality of the products such as lowered sulfur and PAHs content as well as improved quality of the residual char and odour. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Tsipa, Phuti Cedric , Iwarere, Samuel
- Date: 2023-12
- Subjects: Tires -- Recycling , Rubber chemicals , Rubber, Reclaimed
- Language: English
- Type: Doctorial theses , text
- Identifier: http://hdl.handle.net/10948/62666 , vital:72912
- Description: Pyrolysis process is one of the most efficient methods in the waste tyre recycling sector at this moment, hence the attention it is receiving. However, this process has some limitations, with the main one being that it is non-conventional and typically energy intensive. In addition, its resultant products have been reported to have significantly poorer properties relative to their virgin counterparts, making it difficult to incorporate them in the mainstream of raw materials. For instance, waste tyre pyrolysis oil typically has poor fuel properties, high sulfur content, high amount of polycyclic aromatic hydrocarbons (PAHs) and strong unpleasant odour; on the other hand, the quality of the recovered carbon black is dependent on the feedstock and the pyrolysis process conditions. Hence the need for further research and development to make the process effective and improve the quality of resultant products. The aim of this research project was to study the impact of pre-pyrolysis treatment of tyre crumbs and post-pyrolysis treatment of the oil using a novel chemical system on the quality/composition of the resultant products. In addition, the study compared the impact of pre- and post-pyrolysis treatments on the optimum pyrolysis time and temperature (energy). The equipment employed in this study included a vertical fixed bed pyrolysis pilot reactor (modified to suit the reaction/experiment) as well as characterization techniques such as fourier transform infrared (FTIR), elemental analysis (carbon, hydrogen, nitrogen and sulfur – CHNS analysis), gas chromatography coupled to mass spectrometer (GCMS), gas chromatography coupled to flame photometric detector (GCFPD), thermo-gravimetric and derivative analysis (TG/DTG isothermal analysis, and proximate analysis) and scanning electron microscope (SEM). The highlight of the findings is that chemically pre-treating tyre crumbs with a mixture of protonic acid and organic solvent before pyrolysis significantly lowered the temperature required to pyrolyze them, from around 400-500 ℃ to 100-115 ℃. This meant that by using the chemical treatment on waste tyres a lot of energy can be saved. In addition, the sulfur content in the oil fraction was reduced from a total of 1.7 wt% to a total of about 0.2 wt%. This also showed that the contaminants in oil were significantly reduced. The oil was condensed into three (3) collectors for fractionation; in collector 2 was about 54 % of the total oil with sulfur content of about 0.015 wt%. The PAHs amounts were also lowered, as literature indicated that PAHs are mostly formed at around 600-700 ℃. It was also found that the oil produced from post-pyrolysis treatment of oil has a petroleum-like smell, whereas the pre-pyrolysis treated oil has a tyre-like pungent odour. Furthermore, the post-pyrolysis treated oil contains higher contents of alkanes and benzene, toluene, xylene (BTX). Findings of this study have a profound potential impact on the waste tyre recycling industry; for example, reduced production energy cost due to lowered temperature required for pyrolysis, improved quality of the products such as lowered sulfur and PAHs content as well as improved quality of the residual char and odour. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
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