A comparative polarimetric study of the 43 GHz and 86 GHz SiO masers toward the supergiant star VY CMa
- Authors: Richter, Laura
- Date: 2012
- Subjects: Masers Supergiant stars Polarization (Light) Very long baseline interferometry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5454 , http://hdl.handle.net/10962/d1005239
- Description: The aim of this thesis is to perform observational tests of SiO maser polarisation and excitation models, using component-level comparisons of multiple SiO maser transitions in the 43 GHz and 86 GHz bands at milliarcsecond resolution. These observations reqwre very long baseline interferometric imaging with very accurate polarimetric calibration. The supergiant star VY CMa was chosen as the object of this study due to its high SiO maser luminosity, many detected SiO maser lines, and intrinsic scientific interest. Two epochs of full-polarisation VLBA observations of VY CMa were performed. The Epoch 2 observations were reduced using several new data reduction methods developed as part of this work, and designed specifically to improve the accuracy of circular polarisation calibration of spectral-line VLBI observations at millimetre wavelengths. The accuracy is estimated to be better than 1% using these methods. The Epoch 2 images show a concentration of v= l and v=2 J= 1-0 SiO masers to the east and northeast of the assumed stellar position. The v=l J=2-1 masers were more evenly distributed around the star, with a notable lack of emission in the northeast. There is appreciable spatial overlap between these three lines. The nature of the overlap is generally consistent with the predictions of hydrodynamical circumstellar SiO maser simulations. Where the v=l J = 1-0 and J =2-1 features overlap, the v=l J = 2-1 emission is usually considerably weaker. This is not predicted by current hydrodynamical models, but can be explained in the context of collisional pumping in a low density environment. Six observational tests of weak-splitting maser polarisation models were performed, including intercomparisons of linear polarisation in the v=l J=1-0 and J=2-1lines, linear polarisation versus saturation level, linear polarisation versus distance from the star, circular polarisation in the v= l J = 1-0 and J=2-1 lines, circular versus linear polarisation and modeling of ~ 900 electric-vector position angle rotations. The polarisation model tests generally do not support non-Zeeman circular polarisation mechanisms. For the linear polarisation tests, the results are more consistent with models that predict similar linear polarisation across transitions. The scientific importance of these tests is described in detail and avenues for future work are described.
- Full Text:
- Authors: Richter, Laura
- Date: 2012
- Subjects: Masers Supergiant stars Polarization (Light) Very long baseline interferometry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5454 , http://hdl.handle.net/10962/d1005239
- Description: The aim of this thesis is to perform observational tests of SiO maser polarisation and excitation models, using component-level comparisons of multiple SiO maser transitions in the 43 GHz and 86 GHz bands at milliarcsecond resolution. These observations reqwre very long baseline interferometric imaging with very accurate polarimetric calibration. The supergiant star VY CMa was chosen as the object of this study due to its high SiO maser luminosity, many detected SiO maser lines, and intrinsic scientific interest. Two epochs of full-polarisation VLBA observations of VY CMa were performed. The Epoch 2 observations were reduced using several new data reduction methods developed as part of this work, and designed specifically to improve the accuracy of circular polarisation calibration of spectral-line VLBI observations at millimetre wavelengths. The accuracy is estimated to be better than 1% using these methods. The Epoch 2 images show a concentration of v= l and v=2 J= 1-0 SiO masers to the east and northeast of the assumed stellar position. The v=l J=2-1 masers were more evenly distributed around the star, with a notable lack of emission in the northeast. There is appreciable spatial overlap between these three lines. The nature of the overlap is generally consistent with the predictions of hydrodynamical circumstellar SiO maser simulations. Where the v=l J = 1-0 and J =2-1 features overlap, the v=l J = 2-1 emission is usually considerably weaker. This is not predicted by current hydrodynamical models, but can be explained in the context of collisional pumping in a low density environment. Six observational tests of weak-splitting maser polarisation models were performed, including intercomparisons of linear polarisation in the v=l J=1-0 and J=2-1lines, linear polarisation versus saturation level, linear polarisation versus distance from the star, circular polarisation in the v= l J = 1-0 and J=2-1 lines, circular versus linear polarisation and modeling of ~ 900 electric-vector position angle rotations. The polarisation model tests generally do not support non-Zeeman circular polarisation mechanisms. For the linear polarisation tests, the results are more consistent with models that predict similar linear polarisation across transitions. The scientific importance of these tests is described in detail and avenues for future work are described.
- Full Text:
A critical realist exploration of the implementation of a new curriculum in Swaziland
- Authors: Pereira, Liphie
- Date: 2012
- Subjects: Critical realism Education -- Philosophy Critical pedagogy -- Swaziland Curriculum change -- Swaziland Education -- Swaziland Education and state -- Swaziland Education -- Aims and objectives -- Swaziland Critical discourse analysis International General Certificate of Secondary Education
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1484 , http://hdl.handle.net/10962/d1003365
- Description: This study offers an in-depth exploration of the conditions from which the implementation of a curriculum called the International General Certificate of Secondary Education (IGCSE), later localised into Swaziland General Certificate of Secondary Education (SGCSE), emerged and the constraining and enabling conditions for the implementation of the new I/SGCSE curriculum. It derives its theoretical foundation from Roy Bhaskar’s critical realism and Margaret Archer’s concept of analytical separability. The study therefore offers explanations about the curriculum change and its implementation that are based on how structural, cultural, and agential mechanisms operating at a deeper level of reality (the intransitive layer of reality or the domain of the real) and existing independently of what we see, know or believe of them (the transitive layer of reality or domains of the actual and empirical) interacted to condition the emergence of I/SGCSE and the way it is implemented. I conduct a critical discourse analysis of relevant literature, I/SGCSE documents and interview data in order to identify those mechanisms that were cultural and also those that were structural and agential. Bernstein’s concepts of classification and framing are used to analyse observation data in order to explore the influence of these mechanisms on the teaching practices of the teachers who took part in the study. Analysis of the data suggests that the change from General Certificate of Education Ordinary Level (GCE O-level) to I/SGCSE was conditioned by inconsistencies between the cultural and structural mechanisms of the Swazi context. Many of the cultural elements of the Swazi context such as the discourses of good citizens, of competitive advantage, and of quality education draw from global discourses which view relations between people from a postmodernist position and therefore support weakly classified and framed pedagogic practices. In contrast, the discourse of morality and many of the structural elements of the Swazi context, such as the pre2006 education system and the Tinkhundla government system, all view reality from a modernist position, therefore supporting strong relations of power and control. The cultural system therefore exerted more influence in conditioning the change from the strongly classified and framed GCE O-level curriculum to the weakly classified and framed I/SGCSE curriculum. Furthermore, the analysis of interview and observation data suggests that inconsistencies between the global discourses and the discourses and structures that teachers confront in their day-to-day lives, together with the decisions teachers made in response to structural constraints, created constraining conditions for the change from GCE O-level to I/SGCSE. The study adds to knowledge on curriculum change and implementation through insights into the enabling and constraining effects of mechanisms operating at a deeper level of reality on curriculum-change decisions and on the ability of teachers to implement curriculum changes. The focus on the deeper level of reality may therefore contribute towards emancipatory knowledge which could be used not only by the Ministry of Education and Training and teachers in Swaziland but also elsewhere to inform future planning, decision making, and practice in relation to curriculum change and implementation.
- Full Text:
- Authors: Pereira, Liphie
- Date: 2012
- Subjects: Critical realism Education -- Philosophy Critical pedagogy -- Swaziland Curriculum change -- Swaziland Education -- Swaziland Education and state -- Swaziland Education -- Aims and objectives -- Swaziland Critical discourse analysis International General Certificate of Secondary Education
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1484 , http://hdl.handle.net/10962/d1003365
- Description: This study offers an in-depth exploration of the conditions from which the implementation of a curriculum called the International General Certificate of Secondary Education (IGCSE), later localised into Swaziland General Certificate of Secondary Education (SGCSE), emerged and the constraining and enabling conditions for the implementation of the new I/SGCSE curriculum. It derives its theoretical foundation from Roy Bhaskar’s critical realism and Margaret Archer’s concept of analytical separability. The study therefore offers explanations about the curriculum change and its implementation that are based on how structural, cultural, and agential mechanisms operating at a deeper level of reality (the intransitive layer of reality or the domain of the real) and existing independently of what we see, know or believe of them (the transitive layer of reality or domains of the actual and empirical) interacted to condition the emergence of I/SGCSE and the way it is implemented. I conduct a critical discourse analysis of relevant literature, I/SGCSE documents and interview data in order to identify those mechanisms that were cultural and also those that were structural and agential. Bernstein’s concepts of classification and framing are used to analyse observation data in order to explore the influence of these mechanisms on the teaching practices of the teachers who took part in the study. Analysis of the data suggests that the change from General Certificate of Education Ordinary Level (GCE O-level) to I/SGCSE was conditioned by inconsistencies between the cultural and structural mechanisms of the Swazi context. Many of the cultural elements of the Swazi context such as the discourses of good citizens, of competitive advantage, and of quality education draw from global discourses which view relations between people from a postmodernist position and therefore support weakly classified and framed pedagogic practices. In contrast, the discourse of morality and many of the structural elements of the Swazi context, such as the pre2006 education system and the Tinkhundla government system, all view reality from a modernist position, therefore supporting strong relations of power and control. The cultural system therefore exerted more influence in conditioning the change from the strongly classified and framed GCE O-level curriculum to the weakly classified and framed I/SGCSE curriculum. Furthermore, the analysis of interview and observation data suggests that inconsistencies between the global discourses and the discourses and structures that teachers confront in their day-to-day lives, together with the decisions teachers made in response to structural constraints, created constraining conditions for the change from GCE O-level to I/SGCSE. The study adds to knowledge on curriculum change and implementation through insights into the enabling and constraining effects of mechanisms operating at a deeper level of reality on curriculum-change decisions and on the ability of teachers to implement curriculum changes. The focus on the deeper level of reality may therefore contribute towards emancipatory knowledge which could be used not only by the Ministry of Education and Training and teachers in Swaziland but also elsewhere to inform future planning, decision making, and practice in relation to curriculum change and implementation.
- Full Text:
A structural and functional specification of a SCIM for service interaction management and personalisation in the IMS
- Authors: Tsietsi, Mosiuoa Jeremia
- Date: 2012
- Subjects: Internet Protocol multimedia subsystem , Internet Protocol multimedia subsystem -- Specifications , Long-Term Evolution (Telecommunications) , European Telecommunications Standards Institute , Wireless communication systems , Multimedia communications
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4606 , http://hdl.handle.net/10962/d1004864 , Internet Protocol multimedia subsystem , Internet Protocol multimedia subsystem -- Specifications , Long-Term Evolution (Telecommunications) , European Telecommunications Standards Institute , Wireless communication systems , Multimedia communications
- Description: The Internet Protocol Multimedia Subsystem (IMS) is a component of the 3G mobile network that has been specified by standards development organisations such as the 3GPP (3rd Generation Partnership Project) and ETSI (European Telecommunication Standards Institute). IMS seeks to guarantee that the telecommunication network of the future provides subscribers with seamless access to services across disparate networks. In order to achieve this, it defines a service architecture that hosts application servers that provide subscribers with value added services. Typically, an application server bundles all the functionality it needs to execute the services it delivers, however this view is currently being challenged. It is now thought that services should be synthesised from simple building blocks called service capabilities. This decomposition would facilitate the re-use of service capabilities across multiple services and would support the creation of new services that could not have originally been conceived. The shift from monolithic services to those built from service capabilities poses a challenge to the current service model in IMS. To accommodate this, the 3GPP has defined an entity known as a service capability interaction manager (SCIM) that would be responsible for managing the interactions between service capabilities in order to realise complex services. Some of these interactions could potentially lead to undesirable results, which the SCIM must work to avoid. As an added requirement, it is believed that the network should allow policies to be applied to network services which the SCIM should be responsible for enforcing. At the time of writing, the functional and structural architecture of the SCIM has not yet been standardised. This thesis explores the current serv ice architecture of the IMS in detail. Proposals that address the structure and functions of the SCIM are carefully compared and contrasted. This investigation leads to the presentation of key aspects of the SCIM, and provides solutions that explain how it should interact with service capabilities, manage undesirable interactions and factor user and network operator policies into its execution model. A modified design of the IMS service layer that embeds the SCIM is subsequently presented and described. The design uses existing IMS protocols and requires no change in the behaviour of the standard IMS entities. In order to develop a testbed for experimental verification of the design, the identification of suitable software platforms was required. This thesis presents some of the most popular platforms currently used by developers such as the Open IMS Core and OpenSER, as well as an open source, Java-based, multimedia communication platform called Mobicents. As a precursor to the development of the SCIM, a converged multimedia service is presented that describes how a video streaming application that is leveraged by a web portal was implemented for an IMS testbed using Mobicents components. The Mobicents SIP Servlets container was subsequently used to model an initial prototype of the SCIM, using a mUlti-component telephony service to illustrate the proposed service execution model. The design focuses on SIP-based services only, but should also work for other types of IMS application servers as well.
- Full Text:
- Authors: Tsietsi, Mosiuoa Jeremia
- Date: 2012
- Subjects: Internet Protocol multimedia subsystem , Internet Protocol multimedia subsystem -- Specifications , Long-Term Evolution (Telecommunications) , European Telecommunications Standards Institute , Wireless communication systems , Multimedia communications
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4606 , http://hdl.handle.net/10962/d1004864 , Internet Protocol multimedia subsystem , Internet Protocol multimedia subsystem -- Specifications , Long-Term Evolution (Telecommunications) , European Telecommunications Standards Institute , Wireless communication systems , Multimedia communications
- Description: The Internet Protocol Multimedia Subsystem (IMS) is a component of the 3G mobile network that has been specified by standards development organisations such as the 3GPP (3rd Generation Partnership Project) and ETSI (European Telecommunication Standards Institute). IMS seeks to guarantee that the telecommunication network of the future provides subscribers with seamless access to services across disparate networks. In order to achieve this, it defines a service architecture that hosts application servers that provide subscribers with value added services. Typically, an application server bundles all the functionality it needs to execute the services it delivers, however this view is currently being challenged. It is now thought that services should be synthesised from simple building blocks called service capabilities. This decomposition would facilitate the re-use of service capabilities across multiple services and would support the creation of new services that could not have originally been conceived. The shift from monolithic services to those built from service capabilities poses a challenge to the current service model in IMS. To accommodate this, the 3GPP has defined an entity known as a service capability interaction manager (SCIM) that would be responsible for managing the interactions between service capabilities in order to realise complex services. Some of these interactions could potentially lead to undesirable results, which the SCIM must work to avoid. As an added requirement, it is believed that the network should allow policies to be applied to network services which the SCIM should be responsible for enforcing. At the time of writing, the functional and structural architecture of the SCIM has not yet been standardised. This thesis explores the current serv ice architecture of the IMS in detail. Proposals that address the structure and functions of the SCIM are carefully compared and contrasted. This investigation leads to the presentation of key aspects of the SCIM, and provides solutions that explain how it should interact with service capabilities, manage undesirable interactions and factor user and network operator policies into its execution model. A modified design of the IMS service layer that embeds the SCIM is subsequently presented and described. The design uses existing IMS protocols and requires no change in the behaviour of the standard IMS entities. In order to develop a testbed for experimental verification of the design, the identification of suitable software platforms was required. This thesis presents some of the most popular platforms currently used by developers such as the Open IMS Core and OpenSER, as well as an open source, Java-based, multimedia communication platform called Mobicents. As a precursor to the development of the SCIM, a converged multimedia service is presented that describes how a video streaming application that is leveraged by a web portal was implemented for an IMS testbed using Mobicents components. The Mobicents SIP Servlets container was subsequently used to model an initial prototype of the SCIM, using a mUlti-component telephony service to illustrate the proposed service execution model. The design focuses on SIP-based services only, but should also work for other types of IMS application servers as well.
- Full Text:
A systematic revision of selected genera of afrotropical curtonotidae (Diptera: schizophora: ephydroidea) : a phylogenetic approach
- Authors: Kirk-Spriggs, Ashley H
- Date: 2012
- Subjects: Curtonotidae -- Research Diptera -- Research Flies -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5627 , http://hdl.handle.net/10962/d1004747
- Description: The first comprehensive phylogeny of the family Curtonotidae is presented based on molecular markers and morphology. This enabled assessment of evolutionary relatedness, species radiation and zoogeography. A revised classification of the world fauna of the family, based on the results of this study is outlined. Nomenclatural acts flowing from these analyses include: the recognition three new Afrotropical species of Axinota van der Wulp; four new species of a new genus, Tigrisomyia Kirk-Spriggs; and nineteen new species of Curtonotum (six Madagascan and thirteen African). Ten informal species-groups of Curtonotum are recognised. Identification keys are provided for the Afrotropical species of these genera and errors in previous interpretations and designation of type specimens are resolved. Species distributions are mapped and interpreted and discussion is made of the historical biogeographical significance of these distributions.
- Full Text:
- Authors: Kirk-Spriggs, Ashley H
- Date: 2012
- Subjects: Curtonotidae -- Research Diptera -- Research Flies -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5627 , http://hdl.handle.net/10962/d1004747
- Description: The first comprehensive phylogeny of the family Curtonotidae is presented based on molecular markers and morphology. This enabled assessment of evolutionary relatedness, species radiation and zoogeography. A revised classification of the world fauna of the family, based on the results of this study is outlined. Nomenclatural acts flowing from these analyses include: the recognition three new Afrotropical species of Axinota van der Wulp; four new species of a new genus, Tigrisomyia Kirk-Spriggs; and nineteen new species of Curtonotum (six Madagascan and thirteen African). Ten informal species-groups of Curtonotum are recognised. Identification keys are provided for the Afrotropical species of these genera and errors in previous interpretations and designation of type specimens are resolved. Species distributions are mapped and interpreted and discussion is made of the historical biogeographical significance of these distributions.
- Full Text:
An analysis of ionospheric response to geomagnetic disturbances over South Africa and Antarctica
- Authors: Ngwira, Chigomezyo Mudala
- Date: 2012
- Subjects: Geomagnetism -- South Africa , Geomagnetism -- Antarctica , Ionospheric storms -- South Africa , Ionospheric storms -- Antarctica
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5534 , http://hdl.handle.net/10962/d1012957
- Description: The ionosphere is of practical importance for satellite-based communication and navigation systems due to its variable refractive nature which affects the propagation of trans-ionospheric radio signals. This thesis reports on the first attempt to investigate the mechanisms responsible for the generation of positive ionospheric storm effects over mid-latitude South Africa. The storm response on 15 May 2005 was associated with equatorward neutral winds and the passage of travelling ionospheric disturbances (TIDs). The two TIDs reported in this thesis propagated with average velocities of ∼438 m/s and ∼515 m/s respectively. The velocity of the first TID (i.e. 438 m/s) is consistent with the velocities calculated in other studies for the same storm event. In a second case study, the positive storm enhancement on both 25 and 27 July 2004 lasted for more than 7 hours, and were classified as long-duration positive ionospheric storm effects. It has been suggested that the long-duration positive storm effects could have been caused by large-scale thermospheric wind circulation and enhanced equatorward neutral winds. These processes were in turn most likely to have been driven by enhanced and sustained energy input in the high-latitude ionosphere due to Joule heating and particle energy injection. This is evident by the prolonged high-level geomagnetic activity on both 25 and 27 July. This thesis also reports on the phase scintillation investigation at the South African Antarctic polar research station during solar minimum conditions. The multi-instrument approach that was used shows that the scintillation events were associated with auroral electron precipitation and that substorms play an essential role in the production of scintillation in the high latitudes. Furthermore, the investigation reveals that external energy injection into the ionosphere is necessary for the development of high-latitude irregularities which produce scintillation. Finally, this thesis highlights inadequate data resources as one of the major shortcomings to be addressed in order to fully understand and distinguish between the various ionospheric storm drivers over the Southern Africa mid-latitude region. The results presented in this thesis on the ionospheric response during geomagnetic storms provide essential information to direct further investigation aimed at developing this emerging field of study in South Africa.
- Full Text:
- Authors: Ngwira, Chigomezyo Mudala
- Date: 2012
- Subjects: Geomagnetism -- South Africa , Geomagnetism -- Antarctica , Ionospheric storms -- South Africa , Ionospheric storms -- Antarctica
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5534 , http://hdl.handle.net/10962/d1012957
- Description: The ionosphere is of practical importance for satellite-based communication and navigation systems due to its variable refractive nature which affects the propagation of trans-ionospheric radio signals. This thesis reports on the first attempt to investigate the mechanisms responsible for the generation of positive ionospheric storm effects over mid-latitude South Africa. The storm response on 15 May 2005 was associated with equatorward neutral winds and the passage of travelling ionospheric disturbances (TIDs). The two TIDs reported in this thesis propagated with average velocities of ∼438 m/s and ∼515 m/s respectively. The velocity of the first TID (i.e. 438 m/s) is consistent with the velocities calculated in other studies for the same storm event. In a second case study, the positive storm enhancement on both 25 and 27 July 2004 lasted for more than 7 hours, and were classified as long-duration positive ionospheric storm effects. It has been suggested that the long-duration positive storm effects could have been caused by large-scale thermospheric wind circulation and enhanced equatorward neutral winds. These processes were in turn most likely to have been driven by enhanced and sustained energy input in the high-latitude ionosphere due to Joule heating and particle energy injection. This is evident by the prolonged high-level geomagnetic activity on both 25 and 27 July. This thesis also reports on the phase scintillation investigation at the South African Antarctic polar research station during solar minimum conditions. The multi-instrument approach that was used shows that the scintillation events were associated with auroral electron precipitation and that substorms play an essential role in the production of scintillation in the high latitudes. Furthermore, the investigation reveals that external energy injection into the ionosphere is necessary for the development of high-latitude irregularities which produce scintillation. Finally, this thesis highlights inadequate data resources as one of the major shortcomings to be addressed in order to fully understand and distinguish between the various ionospheric storm drivers over the Southern Africa mid-latitude region. The results presented in this thesis on the ionospheric response during geomagnetic storms provide essential information to direct further investigation aimed at developing this emerging field of study in South Africa.
- Full Text:
An investigation into the antidiabetic and catalytic properties of oxovanadium(IV) complexes
- Authors: Walmsley, Ryan Steven
- Date: 2012
- Subjects: Hypoglycemic agents Ligands (Biochemistry) Complex compounds Potentiometry Proton transfer reactions Stability Imidazoles Vanadium catalysts
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4320 , http://hdl.handle.net/10962/d1004978
- Description: In part 1 of this thesis, the antidiabetic activity of a series of novel oxovanadium(IV) complexes was investigated. A range of bidentate N,O-donor ligands, which partially mimic naturally occurring bioligands, were prepared and reacted with the vanadyl ion to form the corresponding bis-coordinated complexes. Initially, 2-(2ˊ-hydroxyphenyl)-1R-imidazoline (where R = H, ethyl and ethanol) ligands were prepared. The aqueous pH-metric chemical speciation was investigated using glass electrode potentiometry which allowed for the determination of protonation and stability constants of the ligands and complexes, respectively. The species distribution diagrams generated from this information gave an indication of how the complexes might behave across the broad pH range experienced in the digestive and circulatory systems. This information was used to create an improved 2nd generation of ligands that were constructed by combining the imidazole and carboxylic acid functionalities. These corresponding bis[(imidazolyl)carboxylato]-oxovanadium(IV) complexes displayed a broader pH-metric stability. Both sets of complexes improved glucose uptake and reduced coagulation in vitro. In part 2 of this thesis, a range of homogeneous and heterogeneous oxovanadium(IV) catalysts were prepared. Firstly, Merrifield beads were functionalized with ligands from Part 1 and then reacted with vanadyl sulfate to afford the corresponding heterogeneous catalysts. These displayed promising catalytic activity for the peroxide facilitated oxidation of thioanisole, styrene and ethylbenzene as well as the oxidative bromination of phenol red. Smaller imidazole-containing beads with higher surface areas than the Merrifield beads were prepared by suspension polymerization. These beads similarly demonstrated excellent catalytic activity for the oxidation of thioanisole and were highly recyclable. In attempt to increase the exposed catalytic surface area, while retaining the ease of separation achieved in the before mentioned systems, micron to nano sized electrospun fibers containing coordinating ligands were fabricated. The corresponding oxovanadium(IV) functionalized fibers were applied to the oxidation of thioanisole using a continuous flow system. The flexible and porous nature of the fiber mats was well suited to this approach. After optimization of the reactant flow rate and catalyst amount, near quantitative (> 99%) oxidation was achieved for an extended period. In addition, leaching of vanadium was mitigated by modification of the attached ligand or polymer material.
- Full Text:
- Authors: Walmsley, Ryan Steven
- Date: 2012
- Subjects: Hypoglycemic agents Ligands (Biochemistry) Complex compounds Potentiometry Proton transfer reactions Stability Imidazoles Vanadium catalysts
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4320 , http://hdl.handle.net/10962/d1004978
- Description: In part 1 of this thesis, the antidiabetic activity of a series of novel oxovanadium(IV) complexes was investigated. A range of bidentate N,O-donor ligands, which partially mimic naturally occurring bioligands, were prepared and reacted with the vanadyl ion to form the corresponding bis-coordinated complexes. Initially, 2-(2ˊ-hydroxyphenyl)-1R-imidazoline (where R = H, ethyl and ethanol) ligands were prepared. The aqueous pH-metric chemical speciation was investigated using glass electrode potentiometry which allowed for the determination of protonation and stability constants of the ligands and complexes, respectively. The species distribution diagrams generated from this information gave an indication of how the complexes might behave across the broad pH range experienced in the digestive and circulatory systems. This information was used to create an improved 2nd generation of ligands that were constructed by combining the imidazole and carboxylic acid functionalities. These corresponding bis[(imidazolyl)carboxylato]-oxovanadium(IV) complexes displayed a broader pH-metric stability. Both sets of complexes improved glucose uptake and reduced coagulation in vitro. In part 2 of this thesis, a range of homogeneous and heterogeneous oxovanadium(IV) catalysts were prepared. Firstly, Merrifield beads were functionalized with ligands from Part 1 and then reacted with vanadyl sulfate to afford the corresponding heterogeneous catalysts. These displayed promising catalytic activity for the peroxide facilitated oxidation of thioanisole, styrene and ethylbenzene as well as the oxidative bromination of phenol red. Smaller imidazole-containing beads with higher surface areas than the Merrifield beads were prepared by suspension polymerization. These beads similarly demonstrated excellent catalytic activity for the oxidation of thioanisole and were highly recyclable. In attempt to increase the exposed catalytic surface area, while retaining the ease of separation achieved in the before mentioned systems, micron to nano sized electrospun fibers containing coordinating ligands were fabricated. The corresponding oxovanadium(IV) functionalized fibers were applied to the oxidation of thioanisole using a continuous flow system. The flexible and porous nature of the fiber mats was well suited to this approach. After optimization of the reactant flow rate and catalyst amount, near quantitative (> 99%) oxidation was achieved for an extended period. In addition, leaching of vanadium was mitigated by modification of the attached ligand or polymer material.
- Full Text:
An investigation into the control of audio streaming across networks having diverse quality of service mechanisms
- Authors: Foulkes, Philip James
- Date: 2012
- Subjects: Streaming audio -- Testing Data transmission systems -- Testing Computer networks -- Management Computer networks -- Evaluation Computer network protocols -- Standards
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4607 , http://hdl.handle.net/10962/d1004865
- Description: The transmission of realtime audio data across digital networks is subject to strict quality of service requirements. These networks need to be able to guarantee network resources (e.g., bandwidth), ensure timely and deterministic data delivery, and provide time synchronisation mechanisms to ensure successful transmission of this data. Two open standards-based networking technologies, namely IEEE 1394 and the recently standardised Ethernet AVB, provide distinct methods for achieving these goals. Audio devices that are compatible with IEEE 1394 networks exist, and audio devices that are compatible with Ethernet AVB networks are starting to come onto the market. There is a need for mechanisms to provide compatibility between the audio devices that reside on these disparate networks such that existing IEEE 1394 audio devices are able to communicate with Ethernet AVB audio devices, and vice versa. The audio devices that reside on these networks may be remotely controlled by a diverse set of incompatible command and control protocols. It is desirable to have a common network-neutral method of control over the various parameters of the devices that reside on these networks. As part of this study, two Ethernet AVB systems were developed. One system acts as an Ethernet AVB audio endpoint device and another system acts as an audio gateway between IEEE 1394 and Ethernet AVB networks. These systems, along with existing IEEE 1394 audio devices, were used to demonstrate the ability to transfer audio data between the networking technologies. Each of the devices is remotely controllable via a network neutral command and control protocol, XFN. The IEEE 1394 and Ethernet AVB devices are used to demonstrate the use of the XFN protocol to allow for network neutral connection management to take place between IEEE 1394 and Ethernet AVB networks. User control over these diverse devices is achieved via the use of a graphical patchbay application, which aims to provide a consistent user interface to a diverse range of devices.
- Full Text:
- Authors: Foulkes, Philip James
- Date: 2012
- Subjects: Streaming audio -- Testing Data transmission systems -- Testing Computer networks -- Management Computer networks -- Evaluation Computer network protocols -- Standards
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4607 , http://hdl.handle.net/10962/d1004865
- Description: The transmission of realtime audio data across digital networks is subject to strict quality of service requirements. These networks need to be able to guarantee network resources (e.g., bandwidth), ensure timely and deterministic data delivery, and provide time synchronisation mechanisms to ensure successful transmission of this data. Two open standards-based networking technologies, namely IEEE 1394 and the recently standardised Ethernet AVB, provide distinct methods for achieving these goals. Audio devices that are compatible with IEEE 1394 networks exist, and audio devices that are compatible with Ethernet AVB networks are starting to come onto the market. There is a need for mechanisms to provide compatibility between the audio devices that reside on these disparate networks such that existing IEEE 1394 audio devices are able to communicate with Ethernet AVB audio devices, and vice versa. The audio devices that reside on these networks may be remotely controlled by a diverse set of incompatible command and control protocols. It is desirable to have a common network-neutral method of control over the various parameters of the devices that reside on these networks. As part of this study, two Ethernet AVB systems were developed. One system acts as an Ethernet AVB audio endpoint device and another system acts as an audio gateway between IEEE 1394 and Ethernet AVB networks. These systems, along with existing IEEE 1394 audio devices, were used to demonstrate the ability to transfer audio data between the networking technologies. Each of the devices is remotely controllable via a network neutral command and control protocol, XFN. The IEEE 1394 and Ethernet AVB devices are used to demonstrate the use of the XFN protocol to allow for network neutral connection management to take place between IEEE 1394 and Ethernet AVB networks. User control over these diverse devices is achieved via the use of a graphical patchbay application, which aims to provide a consistent user interface to a diverse range of devices.
- Full Text:
An investigation into the impact of fairtrade in South Africa
- Authors: Jari, Bridget
- Date: 2012
- Subjects: Competition, Unfair -- Research -- South Africa Price maintenance -- Research -- South Africa Fair trade associations -- South Africa Sustainable development -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1006 , http://hdl.handle.net/10962/d1002741
- Description: World international trade is moving towards more free trade, through globalization and trade liberalization. These moves are guided by trade theories which state that on an aggregated level, nations involved in free trade should benefit, and further that free trade is fair. However, in practice, contradictory views have been raised, stating that free trade may not necessarily be benefiting all participants equally. Rather, other nations, especially developing nations, have become worse-off after opening up their markets for free trade. On the other hand, many developed nations have benefited substantially from free trade. Among other factors, the difference in benefits is believed to have been influenced by the types of commodities being traded (where developing nations mainly trade in primary goods and developed nations in anufactured goods) and unequal power relations (some nations for example, the EU and the US, still adopt protectionism in their agricultural sector). In order to address market imbalances resulting from free trade, Fairtrade has arisen. Fairtrade aims to improve international trading conditions in order to benefit small-scale farmers and farm workers in the developing nations. The Fairtrade organization further claims that its principles are in line with sustainable development. However, Fairtrade suffers a credibility gap because there is a lack of independent research to support their claims. To date in South Africa, there is little research examining the claims of the Fairtrade organization. In order to contribute to the Fairtrade discussion in South Africa, this study has investigated the validity of Fairtrade‘s claims that it contributes towards sustainable development. The study utilised primary data, which was collected from ten commercial farms and two small-scale farmer cooperatives located in the Eastern Cape and Western Cape provinces that are/were Fairtrade certified. The main reason for including commercial farmers and small-scale farmer cooperatives in the study was for comparing relative impacts in the two Fairtrade structures. The data was then analysed using a sustainable livelihoods framework, which was developed in the study. The study focussed on investigating the impact of Fairtrade tools, which are minimum prices, premiums, pre-financing and support for long-term relationships, on its intended beneficiaries. Minimum prices offered to producers cover production costs and are above market prices, and Fairtrade premiums are to be invested in developmental projects. Therefore, examining the influence of Fairtrade tools on individuals and communities provides an overview of how Fairtrade influences development. The results of the study show that sampled Fairtrade beneficiaries in South Africa have witnessed substantial positive changes as a result of Fairtrade. The Fairtrade initiative has managed to empower small-scale producers and farm workers, as well as leverage development opportunities for their wider communities. It has supported organizational development in the supply chain, facilitated investment in community development projects and in business-related training. Producers, both commercial and small-scale producers, managed to access a market that offers stable prices, and have gained from minimum prices. Furthermore, small-scale farmers have been allowed an opportunity to expand their business into export markets, and enjoyed an increase in incomes. Fairtrade benefits further trickle down to non-Fairtrade community members, in the form of employment creation and community development. Despite positive effects, Fairtrade producers faced challenges, including high Fairtrade administration costs and a small market for Fairtrade commodities. The study concludes that in the face of challenges, Fairtrade brings economic, social and environmental benefits, but as compared to economic and social development, the impact on environmental development is rather limited. Even though that is the case, Fairtrade offers valuable development opportunities to producers in South Africa.
- Full Text:
- Authors: Jari, Bridget
- Date: 2012
- Subjects: Competition, Unfair -- Research -- South Africa Price maintenance -- Research -- South Africa Fair trade associations -- South Africa Sustainable development -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1006 , http://hdl.handle.net/10962/d1002741
- Description: World international trade is moving towards more free trade, through globalization and trade liberalization. These moves are guided by trade theories which state that on an aggregated level, nations involved in free trade should benefit, and further that free trade is fair. However, in practice, contradictory views have been raised, stating that free trade may not necessarily be benefiting all participants equally. Rather, other nations, especially developing nations, have become worse-off after opening up their markets for free trade. On the other hand, many developed nations have benefited substantially from free trade. Among other factors, the difference in benefits is believed to have been influenced by the types of commodities being traded (where developing nations mainly trade in primary goods and developed nations in anufactured goods) and unequal power relations (some nations for example, the EU and the US, still adopt protectionism in their agricultural sector). In order to address market imbalances resulting from free trade, Fairtrade has arisen. Fairtrade aims to improve international trading conditions in order to benefit small-scale farmers and farm workers in the developing nations. The Fairtrade organization further claims that its principles are in line with sustainable development. However, Fairtrade suffers a credibility gap because there is a lack of independent research to support their claims. To date in South Africa, there is little research examining the claims of the Fairtrade organization. In order to contribute to the Fairtrade discussion in South Africa, this study has investigated the validity of Fairtrade‘s claims that it contributes towards sustainable development. The study utilised primary data, which was collected from ten commercial farms and two small-scale farmer cooperatives located in the Eastern Cape and Western Cape provinces that are/were Fairtrade certified. The main reason for including commercial farmers and small-scale farmer cooperatives in the study was for comparing relative impacts in the two Fairtrade structures. The data was then analysed using a sustainable livelihoods framework, which was developed in the study. The study focussed on investigating the impact of Fairtrade tools, which are minimum prices, premiums, pre-financing and support for long-term relationships, on its intended beneficiaries. Minimum prices offered to producers cover production costs and are above market prices, and Fairtrade premiums are to be invested in developmental projects. Therefore, examining the influence of Fairtrade tools on individuals and communities provides an overview of how Fairtrade influences development. The results of the study show that sampled Fairtrade beneficiaries in South Africa have witnessed substantial positive changes as a result of Fairtrade. The Fairtrade initiative has managed to empower small-scale producers and farm workers, as well as leverage development opportunities for their wider communities. It has supported organizational development in the supply chain, facilitated investment in community development projects and in business-related training. Producers, both commercial and small-scale producers, managed to access a market that offers stable prices, and have gained from minimum prices. Furthermore, small-scale farmers have been allowed an opportunity to expand their business into export markets, and enjoyed an increase in incomes. Fairtrade benefits further trickle down to non-Fairtrade community members, in the form of employment creation and community development. Despite positive effects, Fairtrade producers faced challenges, including high Fairtrade administration costs and a small market for Fairtrade commodities. The study concludes that in the face of challenges, Fairtrade brings economic, social and environmental benefits, but as compared to economic and social development, the impact on environmental development is rather limited. Even though that is the case, Fairtrade offers valuable development opportunities to producers in South Africa.
- Full Text:
Assessing the effect of a laundry detergent ingredient (LAS) on organisms of a rural South African river
- Authors: Gordon, Andrew K
- Date: 2012
- Subjects: Detergent pollution of rivers, lakes, etc. -- Research -- South Africa -- Eastern Cape Water -- Pollution -- Research -- South Africa -- Eastern Cape Stream health -- Research -- South Africa -- Eastern Cape Stream ecology -- Research -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6042 , http://hdl.handle.net/10962/d1006201
- Description: Powdered laundry detergents are consumed in high volumes worldwide. Post use, they are directed toward water resources via wastewater treatment works or, as is the situation in many rural areas of South Africa, they enter the environment directly as a result of laundry washing activity undertaken alongside surface waters. Within wastewater treatment works, the main ingredient in powdered laundry detergents, the narcotic toxin linear alkylbenzene sulfonate (LAS), is mostly removed, rendering the waste stream a negligible risk to the aquatic biota of receiving waters. In contrast, the biological and ecological impacts of direct LAS input to the aquatic environment, as a consequence of near-stream laundry washing, are yet to be fully realised. Consequently, this thesis posed two research questions: 1) 'What are the LAS concentrations in a small rural South African river'? and 2) 'Is the in-stream biological community negatively affected at these concentrations?' The chosen study area, the community of Balfour in the Eastern Cape Province, is like many rural areas of South Africa where inadequate provision of piped water to homesteads necessitates laundry washing alongside the nearby Balfour River. The first research question was addressed in two ways: by predicting LAS concentrations in Balfour River water by assessing detergent consumption and laundry washing behaviour of residents living alongside the river; and measuring actual in- stream LAS concentrations on different days of the week and during different seasons. Results indicated that LAS concentrations were highly variable temporally and spatially. High peak concentrations of LAS occurred infrequently and were limited to the immediate vicinity of near-stream laundry washing activity with the highest measured concentration being 342 μg.L ⁻¹ and the average 21 μg.L ⁻¹ over the sampling period. The second research question was addressed by integrating the chemical evidence, determined from the first research question, with the biological evidence of stress responses measured in macroinvertebrates collected downstream of near-stream laundry washing activity on the Balfour River. Predicted and measured LAS exposure concentrations from the Balfour River were compared to a water quality guideline for LAS (304 μg.L ⁻¹), specifically derived in this thesis. Biological stress responses were measured at different levels of organisation: two sub-cellular responses (lipid peroxidation and cholinesterase activity); three measures of macroinvertebrate tolerance to water quality impairment; five measures of community composition; three measures of community richness; and a surrogate measure of ecosystem function (functional feeding groups). Weight-of-evidence methodology was utilised to assess, integrate and interpret the chemical and biological evidence, and at its conclusion, determined no effect on the in-stream biological community of the Balfour River downstream of laundry washing activity.
- Full Text:
- Authors: Gordon, Andrew K
- Date: 2012
- Subjects: Detergent pollution of rivers, lakes, etc. -- Research -- South Africa -- Eastern Cape Water -- Pollution -- Research -- South Africa -- Eastern Cape Stream health -- Research -- South Africa -- Eastern Cape Stream ecology -- Research -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6042 , http://hdl.handle.net/10962/d1006201
- Description: Powdered laundry detergents are consumed in high volumes worldwide. Post use, they are directed toward water resources via wastewater treatment works or, as is the situation in many rural areas of South Africa, they enter the environment directly as a result of laundry washing activity undertaken alongside surface waters. Within wastewater treatment works, the main ingredient in powdered laundry detergents, the narcotic toxin linear alkylbenzene sulfonate (LAS), is mostly removed, rendering the waste stream a negligible risk to the aquatic biota of receiving waters. In contrast, the biological and ecological impacts of direct LAS input to the aquatic environment, as a consequence of near-stream laundry washing, are yet to be fully realised. Consequently, this thesis posed two research questions: 1) 'What are the LAS concentrations in a small rural South African river'? and 2) 'Is the in-stream biological community negatively affected at these concentrations?' The chosen study area, the community of Balfour in the Eastern Cape Province, is like many rural areas of South Africa where inadequate provision of piped water to homesteads necessitates laundry washing alongside the nearby Balfour River. The first research question was addressed in two ways: by predicting LAS concentrations in Balfour River water by assessing detergent consumption and laundry washing behaviour of residents living alongside the river; and measuring actual in- stream LAS concentrations on different days of the week and during different seasons. Results indicated that LAS concentrations were highly variable temporally and spatially. High peak concentrations of LAS occurred infrequently and were limited to the immediate vicinity of near-stream laundry washing activity with the highest measured concentration being 342 μg.L ⁻¹ and the average 21 μg.L ⁻¹ over the sampling period. The second research question was addressed by integrating the chemical evidence, determined from the first research question, with the biological evidence of stress responses measured in macroinvertebrates collected downstream of near-stream laundry washing activity on the Balfour River. Predicted and measured LAS exposure concentrations from the Balfour River were compared to a water quality guideline for LAS (304 μg.L ⁻¹), specifically derived in this thesis. Biological stress responses were measured at different levels of organisation: two sub-cellular responses (lipid peroxidation and cholinesterase activity); three measures of macroinvertebrate tolerance to water quality impairment; five measures of community composition; three measures of community richness; and a surrogate measure of ecosystem function (functional feeding groups). Weight-of-evidence methodology was utilised to assess, integrate and interpret the chemical and biological evidence, and at its conclusion, determined no effect on the in-stream biological community of the Balfour River downstream of laundry washing activity.
- Full Text:
Assessing the impacts of invasive non-native African sharptooth catfish Clarias Gariepinus
- Authors: Kadye, Wilbert Takawira
- Date: 2012
- Subjects: Catfishes -- South Africa -- Eastern Cape Biological invasions -- South Africa -- Great Fish River Biological invasions -- South Africa -- Sundays River Clarias gariepinus Freshwater ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5227 , http://hdl.handle.net/10962/d1005070
- Description: Invasive species are of particular concern as they have the potential to alter community structure and food web relationships within their invaded habitats. African sharptooth catfish Clarias gariepinus, a generalist predator, was introduced through an inter-basin water transfer scheme into the Great Fish and Sundays Rivers, Eastern Cape, South Africa, where it threatens the native riverine biota. This thesis assessed its impact from a trophic perspective. Patterns in catfish distribution and abundance revealed an upstream to downstream gradient that was associated with spatial distribution of most species within the mainstream, and a mainstream to tributary gradient that was associated with the spatial distribution of native minnows. The catfish was predicted to occur widely within the mainstem habitats and to decrease progressively along the mainstrem to tributary gradient with the physico-chemical environment being a good proxy for predicting both its occurrence and abundance. The results suggest the catfish proliferated within mainstem habitats where invasion resistance was possibly reduced due to alteration of flow. Population dynamics and size structuring of two native cyprinid minnows Pseudobarbus afer and Barbus anoplus, threatened by catfish, were examined within uninvaded headwater streams in relation to their proximate physical habitats. Their habitats were characterised by seasonal variation in physico-chemical conditions and a spatial variation in substrata compositions. No evidence of differences was found between seasons for density and capture probability for either species. The population size and density for P. afer was found to increase with increasing proportion of boulders. In comparison, B. anoplus population size and probability of capture increased with increasing proportion of bedrock and bank vegetation, respectively. Size structuring was explained predominantly by seasonality and habitat variables for P. afer and B. anoplus, respectively. Stable isotope ratios of carbon and nitrogen were used to compare the spatial variation in both the community-wide and catfish-specific niches and to estimate catfish prey sources from different habitats within the invaded systems. Aquatic community and catfish niches were statistically different among localities, suggesting that each locality had a distinct community-wide trophic structure. Dispersion metrics indicated no evidence of differences in the clustering among individuals, but provided evidence of differences in path trajectories for the comparisons of catfish populations that suggested dietary plasticity within different localities. Dietary studies revealed both ontogenetic shift and omnivory that suggested that catfish may exhibit less pronounced top-down effects within its invaded habitats. Manipulative experiments were used to test the response of benthic macroinvertebrates within two rivers that were differentially impacted by catfish as a presstype disturbance. Macroinvertebrates were non-responsive to catfish presence within a system where catfish had previously been established. In contrast, excluding catfish in this system indicated a response that suggested the importance of refuge within invaded habitats and the possible recovery pattern of certain macroinvertebrate taxa. By comparison, introduction of catfish within previously uninvaded localities provided evidence of direct catfish impact through elimination of conspicuous taxa. Acoustic telemetry was used to investigate catfish movement patterns within an invaded lentic habitat and provided evidence that habitat utilisation was non-random. The shallow and structured river mouth habitat, which was most utilised, was probably the most ideal for its breeding and feeding. This inferred potential overlap with native species and suggested the risk of predation and competitive interference. Catfish also exhibited both nocturnal and diurnal activity patterns that were probably related to feeding.
- Full Text:
- Authors: Kadye, Wilbert Takawira
- Date: 2012
- Subjects: Catfishes -- South Africa -- Eastern Cape Biological invasions -- South Africa -- Great Fish River Biological invasions -- South Africa -- Sundays River Clarias gariepinus Freshwater ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5227 , http://hdl.handle.net/10962/d1005070
- Description: Invasive species are of particular concern as they have the potential to alter community structure and food web relationships within their invaded habitats. African sharptooth catfish Clarias gariepinus, a generalist predator, was introduced through an inter-basin water transfer scheme into the Great Fish and Sundays Rivers, Eastern Cape, South Africa, where it threatens the native riverine biota. This thesis assessed its impact from a trophic perspective. Patterns in catfish distribution and abundance revealed an upstream to downstream gradient that was associated with spatial distribution of most species within the mainstream, and a mainstream to tributary gradient that was associated with the spatial distribution of native minnows. The catfish was predicted to occur widely within the mainstem habitats and to decrease progressively along the mainstrem to tributary gradient with the physico-chemical environment being a good proxy for predicting both its occurrence and abundance. The results suggest the catfish proliferated within mainstem habitats where invasion resistance was possibly reduced due to alteration of flow. Population dynamics and size structuring of two native cyprinid minnows Pseudobarbus afer and Barbus anoplus, threatened by catfish, were examined within uninvaded headwater streams in relation to their proximate physical habitats. Their habitats were characterised by seasonal variation in physico-chemical conditions and a spatial variation in substrata compositions. No evidence of differences was found between seasons for density and capture probability for either species. The population size and density for P. afer was found to increase with increasing proportion of boulders. In comparison, B. anoplus population size and probability of capture increased with increasing proportion of bedrock and bank vegetation, respectively. Size structuring was explained predominantly by seasonality and habitat variables for P. afer and B. anoplus, respectively. Stable isotope ratios of carbon and nitrogen were used to compare the spatial variation in both the community-wide and catfish-specific niches and to estimate catfish prey sources from different habitats within the invaded systems. Aquatic community and catfish niches were statistically different among localities, suggesting that each locality had a distinct community-wide trophic structure. Dispersion metrics indicated no evidence of differences in the clustering among individuals, but provided evidence of differences in path trajectories for the comparisons of catfish populations that suggested dietary plasticity within different localities. Dietary studies revealed both ontogenetic shift and omnivory that suggested that catfish may exhibit less pronounced top-down effects within its invaded habitats. Manipulative experiments were used to test the response of benthic macroinvertebrates within two rivers that were differentially impacted by catfish as a presstype disturbance. Macroinvertebrates were non-responsive to catfish presence within a system where catfish had previously been established. In contrast, excluding catfish in this system indicated a response that suggested the importance of refuge within invaded habitats and the possible recovery pattern of certain macroinvertebrate taxa. By comparison, introduction of catfish within previously uninvaded localities provided evidence of direct catfish impact through elimination of conspicuous taxa. Acoustic telemetry was used to investigate catfish movement patterns within an invaded lentic habitat and provided evidence that habitat utilisation was non-random. The shallow and structured river mouth habitat, which was most utilised, was probably the most ideal for its breeding and feeding. This inferred potential overlap with native species and suggested the risk of predation and competitive interference. Catfish also exhibited both nocturnal and diurnal activity patterns that were probably related to feeding.
- Full Text:
Bayliss-Hillman adducts as scaffolds for the construction of novel compounds with medicinal potential
- Authors: Idahosa, Kenudi Christiana
- Date: 2012
- Subjects: Antimalarials -- Research Malaria -- Chemotherapy -- Research AIDS (Disease) -- Treatment -- Research AIDS (Disease) -- Chemotherapy -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4410 , http://hdl.handle.net/10962/d1006763
- Description: This project has focused on exploring the application of Baylis-Hillman (BH) {a.k.a. Morita-Baylis-Hillman (MBH)} scaffolds in the construction of various compounds with medicinal potential. A series of 2-nitrobenzaldehydes has been treated under BH conditions, with two different activated alkenes, viz., (MVK) and methyl acrylate, using (DABCO) or (3-HQ) as catalyst. While most of the BH reactions were carried out at room temperature, some reactions were conducted using microwave irradiation. The resulting BH adducts have been subjected to dehydration, conjugate addition and allylic substitution to obtain appropriate intermediates, which have been used in turn, to synthesize possible lead compounds, viz., cinnamate esters as HIV-1 integrase inhibitors, 3-(aminomethyl)quinolines and quinolones as anti-malarials and cinnamate ester-AZT conjugates as dual-action HIV-1 integrase-reverse transcriptase (IN-RT) inhibitors. Conjugate addition reactions of methyl acrylate-derived BH β-hydroxy esters with the amines, piperidine, propargylamine and 2-amino-5-(diethylamino)pentane, has afforded a range of products as diastereomeric mixtures in moderate to excellent yields. Catalytic hydrogenation of the aminomethy β-hydroxy esters derivatives, using a palladium-oncarbon (Pd-C) catalyst, has afforded the corresponding, novel 3-aminomethyl-2- quinolone derivatives in moderate yields. Effective allylic substitution reactions of the MVK-derived BH β-hydroxy ketones (via a conjugate addition-elimination pathway) using in situ-generated HCl has afforded the corresponding α-chloromethyl derivatives, which have been reacted with various amines, including piperidine, piperazine, propargylamine and 2-amino-5-(diethylamino)pentane, to yield α-aminomethyl derivatives. Catalytic hydrogenation of selected α-aminomethyl derivatives, using a Pd-C catalyst, has afforded the corresponding, novel 3- (aminomethyl)-2-methylquinoline derivatives in low to moderate yields. A bioassay, conducted on a 6-hydroxy-2-methyl-3-[(piperidin-1-yl)methyl]quinoline isolated early in the study indicated anti-malarial activity and prompted further efforts in the synthesis of analogous compounds. Reaction of the methyl acrylate-derived BH adducts with POCl3 has provided access to α-(chloromethyl)cinnamate ester derivatives, which have been aminated to afford α- (aminomethyl)cinnamate ester derivatives as potential HIV-1 integrase inhibitors. The α- (propargylaminomethyl)cinnamates were used, in turn, as substrates for the “click chemistry” reaction with 3'-azido-3'-deoxythymidine (AZT– an azide and an established reverse transcriptase HIV-1 inhibitor) to afford cinnamate ester-AZT conjugates as potential dual-action HIV-1 integrase-reverse transcriptase (IN-RT) inhibitors. Computer modelling and docking studies of a cinnamate ester-AZT conjugate into the HIV-1 integrase and reverse transcriptase active-sites revealed potential hydrogen-bonding interactions with amino acid residues within the receptor cavities. The isolated products have been appropriately characterized using IR, 1- and 2-D NMR and HRMS techniques, while elucidation of the stereochemistry of the double bond in the BH-derived halomethyl derivatives has been assigned on the basis of NOE, computer modelling and X-ray crystallographic data.
- Full Text:
- Authors: Idahosa, Kenudi Christiana
- Date: 2012
- Subjects: Antimalarials -- Research Malaria -- Chemotherapy -- Research AIDS (Disease) -- Treatment -- Research AIDS (Disease) -- Chemotherapy -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4410 , http://hdl.handle.net/10962/d1006763
- Description: This project has focused on exploring the application of Baylis-Hillman (BH) {a.k.a. Morita-Baylis-Hillman (MBH)} scaffolds in the construction of various compounds with medicinal potential. A series of 2-nitrobenzaldehydes has been treated under BH conditions, with two different activated alkenes, viz., (MVK) and methyl acrylate, using (DABCO) or (3-HQ) as catalyst. While most of the BH reactions were carried out at room temperature, some reactions were conducted using microwave irradiation. The resulting BH adducts have been subjected to dehydration, conjugate addition and allylic substitution to obtain appropriate intermediates, which have been used in turn, to synthesize possible lead compounds, viz., cinnamate esters as HIV-1 integrase inhibitors, 3-(aminomethyl)quinolines and quinolones as anti-malarials and cinnamate ester-AZT conjugates as dual-action HIV-1 integrase-reverse transcriptase (IN-RT) inhibitors. Conjugate addition reactions of methyl acrylate-derived BH β-hydroxy esters with the amines, piperidine, propargylamine and 2-amino-5-(diethylamino)pentane, has afforded a range of products as diastereomeric mixtures in moderate to excellent yields. Catalytic hydrogenation of the aminomethy β-hydroxy esters derivatives, using a palladium-oncarbon (Pd-C) catalyst, has afforded the corresponding, novel 3-aminomethyl-2- quinolone derivatives in moderate yields. Effective allylic substitution reactions of the MVK-derived BH β-hydroxy ketones (via a conjugate addition-elimination pathway) using in situ-generated HCl has afforded the corresponding α-chloromethyl derivatives, which have been reacted with various amines, including piperidine, piperazine, propargylamine and 2-amino-5-(diethylamino)pentane, to yield α-aminomethyl derivatives. Catalytic hydrogenation of selected α-aminomethyl derivatives, using a Pd-C catalyst, has afforded the corresponding, novel 3- (aminomethyl)-2-methylquinoline derivatives in low to moderate yields. A bioassay, conducted on a 6-hydroxy-2-methyl-3-[(piperidin-1-yl)methyl]quinoline isolated early in the study indicated anti-malarial activity and prompted further efforts in the synthesis of analogous compounds. Reaction of the methyl acrylate-derived BH adducts with POCl3 has provided access to α-(chloromethyl)cinnamate ester derivatives, which have been aminated to afford α- (aminomethyl)cinnamate ester derivatives as potential HIV-1 integrase inhibitors. The α- (propargylaminomethyl)cinnamates were used, in turn, as substrates for the “click chemistry” reaction with 3'-azido-3'-deoxythymidine (AZT– an azide and an established reverse transcriptase HIV-1 inhibitor) to afford cinnamate ester-AZT conjugates as potential dual-action HIV-1 integrase-reverse transcriptase (IN-RT) inhibitors. Computer modelling and docking studies of a cinnamate ester-AZT conjugate into the HIV-1 integrase and reverse transcriptase active-sites revealed potential hydrogen-bonding interactions with amino acid residues within the receptor cavities. The isolated products have been appropriately characterized using IR, 1- and 2-D NMR and HRMS techniques, while elucidation of the stereochemistry of the double bond in the BH-derived halomethyl derivatives has been assigned on the basis of NOE, computer modelling and X-ray crystallographic data.
- Full Text:
Biological synthesis of metallic nanoparticles and their interactions with various biomedical targets
- Authors: Sennuga, Afolake Temitope
- Date: 2012
- Subjects: Nanoparticles Biosynthesis Nanotechnology Biomineralization Morphology Ceruloplasmin Ribonucleases Adenosine triphosphatase Acetylcholinesterase Platinum Gold Silver
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4009 , http://hdl.handle.net/10962/d1004069
- Description: The synthesis of nanostructured materials, especially metallic nanoparticles, has accrued utmost interest over the past decade owing to their unique properties that make them applicable in different fields of science and technology. The limitation to the use of these nanoparticles is the paucity of an effective method of synthesis that will produce homogeneous size and shape nanoparticles as well as particles with limited or no toxicity to the human health and the environment. The biological method of nanoparticle synthesis is a relatively simple, cheap and environmentally friendly method than the conventional chemical method of synthesis and thus gains an upper hand. The biomineralization of nanoparticles in protein cages is one of such biological approaches used in the generation of nanoparticles. This method of synthesis apart from being a safer method in the production of nanoparticles is also able to control particle morphology. In this study, a comparative biological synthesis, characterization and biomedical effects of metallic nanoparticles of platinum, gold and silver were investigated. Metallic nanoparticles were biologically synthesized using cage-like (apoferritin), barrel-like (GroEL) and non-caged (ribonuclease) proteins. Nanoparticles generated were characterized using common techniques such as UV-visible spectroscopy, scanning and transmission electron microscopy, inductively coupled optical emission spectroscopy, Fourier transform infra-red spectroscopy and energy dispersion analysis of X-rays (EDAX). Nanoparticles synthesised biologically using apoferritin, GroEL and RNase with exhibited similar chemical and physical properties as thoses nanoparticles generated chemically. In addition, the metallic nanoparticles fabricated within the cage-like and barrel-like cavities of apoferritin and GroEL respectively, resulted in nanoparticles with relatively uniform morphology as opposed to those obtained with the non-caged ribonuclease. The enzymatic (ferroxidase) activity of apoferritin was found to be greatly enhanced with platinum (9-fold), gold (7-fold) and silver (54-fold) nanoparticles. The ATPase activity of GroEL was inhibited by silver nanoparticles (64%), was moderately activated by gold nanoparticles (47%) and considerably enhanced by platinum nanoparticles (85%). The hydrolytic activity of RNase was however, lowered by these metallic nanoparticles (90% in Ag nanoparticles) and to a higher degree with platinum (95%) and gold nanoparticles (~100%). The effect of synthesized nanoparticles on the respective enzyme activities of these proteins was also investigated and the potential neurotoxic property of these particles was also determined by an in vitro interaction with acetylcholinesterase. Protein encapsulated nanoparticles with apoferrtin and GroEL showed a decreased inhibition of acetylcholinesterase (<50%) compared with nanoparticles attached to ribonuclease (>50%). Thus, it can be concluded that the cavities of apoferitin and GroEL acted as nanobiofactories for the synthesis and confinement of the size and shape of nanoparticles. Furthermore, the interior of these proteins provided a shielding effect for these nanoparticles and thus reduced/prevented their possible neurotoxic effect and confirmed safety in their method of production and application. The findings from this study would prove beneficial in the application of these nanoparticles as a potential drug/drug delivery vehicle for the prevention, treatment/management of diseases associated with these enzymes/proteins.
- Full Text:
- Authors: Sennuga, Afolake Temitope
- Date: 2012
- Subjects: Nanoparticles Biosynthesis Nanotechnology Biomineralization Morphology Ceruloplasmin Ribonucleases Adenosine triphosphatase Acetylcholinesterase Platinum Gold Silver
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4009 , http://hdl.handle.net/10962/d1004069
- Description: The synthesis of nanostructured materials, especially metallic nanoparticles, has accrued utmost interest over the past decade owing to their unique properties that make them applicable in different fields of science and technology. The limitation to the use of these nanoparticles is the paucity of an effective method of synthesis that will produce homogeneous size and shape nanoparticles as well as particles with limited or no toxicity to the human health and the environment. The biological method of nanoparticle synthesis is a relatively simple, cheap and environmentally friendly method than the conventional chemical method of synthesis and thus gains an upper hand. The biomineralization of nanoparticles in protein cages is one of such biological approaches used in the generation of nanoparticles. This method of synthesis apart from being a safer method in the production of nanoparticles is also able to control particle morphology. In this study, a comparative biological synthesis, characterization and biomedical effects of metallic nanoparticles of platinum, gold and silver were investigated. Metallic nanoparticles were biologically synthesized using cage-like (apoferritin), barrel-like (GroEL) and non-caged (ribonuclease) proteins. Nanoparticles generated were characterized using common techniques such as UV-visible spectroscopy, scanning and transmission electron microscopy, inductively coupled optical emission spectroscopy, Fourier transform infra-red spectroscopy and energy dispersion analysis of X-rays (EDAX). Nanoparticles synthesised biologically using apoferritin, GroEL and RNase with exhibited similar chemical and physical properties as thoses nanoparticles generated chemically. In addition, the metallic nanoparticles fabricated within the cage-like and barrel-like cavities of apoferritin and GroEL respectively, resulted in nanoparticles with relatively uniform morphology as opposed to those obtained with the non-caged ribonuclease. The enzymatic (ferroxidase) activity of apoferritin was found to be greatly enhanced with platinum (9-fold), gold (7-fold) and silver (54-fold) nanoparticles. The ATPase activity of GroEL was inhibited by silver nanoparticles (64%), was moderately activated by gold nanoparticles (47%) and considerably enhanced by platinum nanoparticles (85%). The hydrolytic activity of RNase was however, lowered by these metallic nanoparticles (90% in Ag nanoparticles) and to a higher degree with platinum (95%) and gold nanoparticles (~100%). The effect of synthesized nanoparticles on the respective enzyme activities of these proteins was also investigated and the potential neurotoxic property of these particles was also determined by an in vitro interaction with acetylcholinesterase. Protein encapsulated nanoparticles with apoferrtin and GroEL showed a decreased inhibition of acetylcholinesterase (<50%) compared with nanoparticles attached to ribonuclease (>50%). Thus, it can be concluded that the cavities of apoferitin and GroEL acted as nanobiofactories for the synthesis and confinement of the size and shape of nanoparticles. Furthermore, the interior of these proteins provided a shielding effect for these nanoparticles and thus reduced/prevented their possible neurotoxic effect and confirmed safety in their method of production and application. The findings from this study would prove beneficial in the application of these nanoparticles as a potential drug/drug delivery vehicle for the prevention, treatment/management of diseases associated with these enzymes/proteins.
- Full Text:
Comparative biogeography and ecology of freshwater fishes in the Breede and associated river systems, South Africa
- Authors: Chakona, Albert
- Date: 2012
- Subjects: Freshwater fishes -- South Africa -- Breede River , Freshwater fishes -- South Africa -- Geographical distribution , Freshwater fishes -- Ecology , Feshwater fishes -- Genetics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5372 , http://hdl.handle.net/10962/d1015694
- Description: Distribution patterns and levels of genetic diversity in extant taxa are a product of complex palaeogeographic processes and climatic oscillations as well as the species’ intrinsic ecological adaptations. The Cape Floristic Region of South Africa presents a unique system for studying the processes that promote species diversification and distribution patterns. This region has a high degree of endemism of both terrestrial and aquatic biota and is clearly isolated from neighbouring areas by the Cape Fold Mountains and the Great Escarpment. The objective of this study was to firstly examine the ecology of freshwater fishes belonging to the genera Galaxias, Pseudobarbus and Sandelia in the south-western CFR. This was followed by an assessment of the genetic diversity of these taxa. Unique lineages were identified and their distribution was mapped. The work aimed to explore the role of the region’s complex palaeogeographic and climatic history as well as the role of the species’ ecological adaptations in driving lineage diversification and shaping contemporary distribution patterns. The four main components of the study can be summarised as follows: 1. Habitat associations of three widely distributed lineages of Galaxias zebratus Pseudobarbus burchelli and Sandelia capensis were evaluated at multiple localities in minimally disturbed mountain tributaries of the Breede, Duiwenhoks and Goukou River systems. The lineages have distinct habitat associations which were related to differences in their morphological traits. The slender-bodied Galaxias ‘nebula’ and the fusiform-shaped Pseudobarbus ‘Breede’ are capable of exploiting upper reaches with faster water velocity. By contrast, the laterally compressed Sandelia ‘eastern’ is restricted to lower reaches, making this lineage more susceptible to a wide array of impacts. 2. A recently discovered lineage of Galaxias zebratus, (Galaxias ‘nebula’), was found to be capable of tolerating emersion for a prolonged period of time. This is the first time that such capabilities have been documented in an African galaxiid. These adaptations have implications for the interpretation of Galaxias ‘nebula’s wide distribution range. 3. The phylogeography of Galaxias ‘nebula’ across its entire distribution range was investigated using two mitochondrial genes (cytochrome c oxidase subunit I (COI) and cytochrome b (cyt b)). This lineage has a complex evolutionary history that was influenced by both intrinsic and extrinsic factors. Rare events such as episodic drainage connections during Pleistocene and Holocene pluvial periods, possibly augmented by river confluences during periods of lower sea-levels and river capture events seem to be the most credible explanation for the extensive contemporary distribution and the relatively shallow genetic divergence between different river systems. 4. Mitochondrial cyt b sequences were used (i) to assess genetic diversity in G. zebratus, P. burchelli and S. capensis from the south-western CFR and (ii) to determine the roles of intrinsic ecological adaptations and extrinsic landscape and climatic changes in promoting genetic diversification and shaping present day distribution patterns of lineages in the three taxa. Marine incursions during periods of major sea-level transgressions are proposed to have isolated populations in upland refugia, thereby driving allopatric divergence in these species. Subsequent connections of rivers during wetter periods and lower sea-levels are proposed to have facilitated post-speciation dispersal of lineages to attain present day distribution patterns. While detailed morphological studies and further genetic analysis are needed to substantiate the taxonomic status of the newly discovered lineages of Galaxias zebratus, Pseudobarbus burchelli and Sandelia capensis, results of the present study indicate that the south-western CFR represents a previously unrecognised centre of freshwater fish diversity and microendemism in the broader Cape Floristic Region. Accurate identification of lineages and comprehensive mapping of their distribution is a fundamental pre-requisite for ecological studies, assessing conservation status and implementation of appropriate conservation measures.
- Full Text:
- Authors: Chakona, Albert
- Date: 2012
- Subjects: Freshwater fishes -- South Africa -- Breede River , Freshwater fishes -- South Africa -- Geographical distribution , Freshwater fishes -- Ecology , Feshwater fishes -- Genetics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5372 , http://hdl.handle.net/10962/d1015694
- Description: Distribution patterns and levels of genetic diversity in extant taxa are a product of complex palaeogeographic processes and climatic oscillations as well as the species’ intrinsic ecological adaptations. The Cape Floristic Region of South Africa presents a unique system for studying the processes that promote species diversification and distribution patterns. This region has a high degree of endemism of both terrestrial and aquatic biota and is clearly isolated from neighbouring areas by the Cape Fold Mountains and the Great Escarpment. The objective of this study was to firstly examine the ecology of freshwater fishes belonging to the genera Galaxias, Pseudobarbus and Sandelia in the south-western CFR. This was followed by an assessment of the genetic diversity of these taxa. Unique lineages were identified and their distribution was mapped. The work aimed to explore the role of the region’s complex palaeogeographic and climatic history as well as the role of the species’ ecological adaptations in driving lineage diversification and shaping contemporary distribution patterns. The four main components of the study can be summarised as follows: 1. Habitat associations of three widely distributed lineages of Galaxias zebratus Pseudobarbus burchelli and Sandelia capensis were evaluated at multiple localities in minimally disturbed mountain tributaries of the Breede, Duiwenhoks and Goukou River systems. The lineages have distinct habitat associations which were related to differences in their morphological traits. The slender-bodied Galaxias ‘nebula’ and the fusiform-shaped Pseudobarbus ‘Breede’ are capable of exploiting upper reaches with faster water velocity. By contrast, the laterally compressed Sandelia ‘eastern’ is restricted to lower reaches, making this lineage more susceptible to a wide array of impacts. 2. A recently discovered lineage of Galaxias zebratus, (Galaxias ‘nebula’), was found to be capable of tolerating emersion for a prolonged period of time. This is the first time that such capabilities have been documented in an African galaxiid. These adaptations have implications for the interpretation of Galaxias ‘nebula’s wide distribution range. 3. The phylogeography of Galaxias ‘nebula’ across its entire distribution range was investigated using two mitochondrial genes (cytochrome c oxidase subunit I (COI) and cytochrome b (cyt b)). This lineage has a complex evolutionary history that was influenced by both intrinsic and extrinsic factors. Rare events such as episodic drainage connections during Pleistocene and Holocene pluvial periods, possibly augmented by river confluences during periods of lower sea-levels and river capture events seem to be the most credible explanation for the extensive contemporary distribution and the relatively shallow genetic divergence between different river systems. 4. Mitochondrial cyt b sequences were used (i) to assess genetic diversity in G. zebratus, P. burchelli and S. capensis from the south-western CFR and (ii) to determine the roles of intrinsic ecological adaptations and extrinsic landscape and climatic changes in promoting genetic diversification and shaping present day distribution patterns of lineages in the three taxa. Marine incursions during periods of major sea-level transgressions are proposed to have isolated populations in upland refugia, thereby driving allopatric divergence in these species. Subsequent connections of rivers during wetter periods and lower sea-levels are proposed to have facilitated post-speciation dispersal of lineages to attain present day distribution patterns. While detailed morphological studies and further genetic analysis are needed to substantiate the taxonomic status of the newly discovered lineages of Galaxias zebratus, Pseudobarbus burchelli and Sandelia capensis, results of the present study indicate that the south-western CFR represents a previously unrecognised centre of freshwater fish diversity and microendemism in the broader Cape Floristic Region. Accurate identification of lineages and comprehensive mapping of their distribution is a fundamental pre-requisite for ecological studies, assessing conservation status and implementation of appropriate conservation measures.
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Conveniencing the family in agri-based processing enterprise : a grounded theory study of strategic leaders' cultural assumptions and strategising activities
- Authors: Kanyangale, Macdonald Isaac
- Date: 2012
- Subjects: Small business -- Malawi -- Management Agriculture -- Malawi -- Business management Agriculture -- Economic aspects -- Malawi Grounded theory -- Study and teaching
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1181 , http://hdl.handle.net/10962/d1002798
- Description: As leaders of small and medium enterprises (SMEs), strategic leaders are responsible for strategising, the approach to which is influenced by their cultural paradigm. The effects of this strategising are manifested in the day-to-day activities of these leaders. This study aims to build an understanding of the shared cultural assumptions of strategic leaders in agri-based processing SMEs and how these assumptions affect the strategising activities that are adopted when addressing critical incidents related to the internal integration and external adaptation of the SME. Using Strauss and Corbin‟s (1990) grounded theory method, this study develops a theory titled Conveniencing the Family in Business, which is induced from critical incidents. A sample of critical incidents was gathered from 44 qualitative interviews conducted with strategic leaders of various agri-based processing SMEs operating in Malawi. This study found that strategic leaders display persistent and stable pragmatic business survival mind sets, but dynamic cultural assumptions about relationships with organisation members. The cultural influence of these assumptions is manifested in two distinctive and alternative processes making up the theory of conveniencing the family in business. These are the humanising and commodifying of relationships with organisation members, and they are evident in hostile and friendly business environments, respectively. Humanising of relationships with all members of the organisation builds and capitalises on inclusive, organisation-wide social capital that secures the future of the business. On the other hand, commodifying of relationships with non-family organisation members weakens collective support, which becomes mainly dependent on family and friendship ties. Thus, commodifying of relationships serves to perpetuate the close integration of business activity and family requirements to ultimately convenience the family in business, and represents the desired modus operandi of strategic leaders. As strategic leaders of SMEs have not yet conceptualised this, providing them with the conceptual theory developed here may be helpful towards a consistent re-orientation of the internal organisational support in a way that does not exclude but rather harnesses the wider solidarity of organisation members. The process explained by this theory is iterative, dynamic and distinguishes patterns of relationships amongst organisation members, which either enhances or compromises their collective support for the leaders and the enterprise. This by implication affects the performance of the enterprise. The results of this study are discussed from the perspective of social exchange and social capital theory, thereby contributing to the understanding of the strategising activities of strategic leaders, as well as the processes of building or destroying social capital in this type of enterprise.
- Full Text:
- Authors: Kanyangale, Macdonald Isaac
- Date: 2012
- Subjects: Small business -- Malawi -- Management Agriculture -- Malawi -- Business management Agriculture -- Economic aspects -- Malawi Grounded theory -- Study and teaching
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1181 , http://hdl.handle.net/10962/d1002798
- Description: As leaders of small and medium enterprises (SMEs), strategic leaders are responsible for strategising, the approach to which is influenced by their cultural paradigm. The effects of this strategising are manifested in the day-to-day activities of these leaders. This study aims to build an understanding of the shared cultural assumptions of strategic leaders in agri-based processing SMEs and how these assumptions affect the strategising activities that are adopted when addressing critical incidents related to the internal integration and external adaptation of the SME. Using Strauss and Corbin‟s (1990) grounded theory method, this study develops a theory titled Conveniencing the Family in Business, which is induced from critical incidents. A sample of critical incidents was gathered from 44 qualitative interviews conducted with strategic leaders of various agri-based processing SMEs operating in Malawi. This study found that strategic leaders display persistent and stable pragmatic business survival mind sets, but dynamic cultural assumptions about relationships with organisation members. The cultural influence of these assumptions is manifested in two distinctive and alternative processes making up the theory of conveniencing the family in business. These are the humanising and commodifying of relationships with organisation members, and they are evident in hostile and friendly business environments, respectively. Humanising of relationships with all members of the organisation builds and capitalises on inclusive, organisation-wide social capital that secures the future of the business. On the other hand, commodifying of relationships with non-family organisation members weakens collective support, which becomes mainly dependent on family and friendship ties. Thus, commodifying of relationships serves to perpetuate the close integration of business activity and family requirements to ultimately convenience the family in business, and represents the desired modus operandi of strategic leaders. As strategic leaders of SMEs have not yet conceptualised this, providing them with the conceptual theory developed here may be helpful towards a consistent re-orientation of the internal organisational support in a way that does not exclude but rather harnesses the wider solidarity of organisation members. The process explained by this theory is iterative, dynamic and distinguishes patterns of relationships amongst organisation members, which either enhances or compromises their collective support for the leaders and the enterprise. This by implication affects the performance of the enterprise. The results of this study are discussed from the perspective of social exchange and social capital theory, thereby contributing to the understanding of the strategising activities of strategic leaders, as well as the processes of building or destroying social capital in this type of enterprise.
- Full Text:
Curriculum reform in Lesotho: exploring the interface between environmental education and geography in selected schools
- Authors: Raselimo, Mohaeka Gabriel
- Date: 2012
- Subjects: Curriculum planning -- Lesotho Curriculum change -- Lesotho Educational evaluation -- Lesotho Environmental education -- Study and teaching (Secondary) -- Lesotho Geography -- Study and teaching (Secondary) -- Lesotho Agenda 21 (Program)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1488 , http://hdl.handle.net/10962/d1003369
- Description: This study sought to explore the interface between environmental education (EE) and school geography with a view to understanding a process of curriculum reform in the context of Lesotho. The research was based on the curriculum reform process that was initiated by a Danish donor-funded project, known as the Lesotho Environmental Education Support Project (LEESP), which operated from 2001 to 2004. Driven by a sustainable development imperative, the project was intended to assist Lesotho in the implementation of local action for Agenda 21 by introducing environmental education into the formal education system. Deviating slightly from much published research on geographical and environmental education, which focuses on how geography contributes to environmental education, this study explored how the latter has shaped the former in terms of content and pedagogy. Using the lens of critical curriculum theory, I sought to understand the political nature of the curriculum and of curriculum change, focusing on the LEESP curriculum policy development, dissemination and implementation at classroom level. The study employed Bernstein's concepts of classification and framing to illuminate issues of power and control between discourses, and between teachers and learners. Operating within an interpretive qualitative research orientation, the study used a case study method focusing on five secondary/high schools in Lesotho. The data was generated through document analysis, interviews and classroom observations. The study examined the assumptions, values and ideologies underpinning environmental education curriculum intentions as reflected in LEESP documents. It also investigated the social process of conceptualising and disseminating environmental education to understand the challenges faced as education practitioners made sense of environmental education innovations in the specific contexts of Lesotho, and how these could possibly influence what happens at the classroom level. The analysis of the LEESP documents revealed that while there are many areas of synergy between the LEESP environmental education policy guidelines and the national education ideals in Lesotho, achievement of the transformational visions of action competence, which was the overarching concept in the reform process, would require major structural changes. The study also highlights issues of participation, contestations, tensions and contradictions associated with the conceptualisation and dissemination of environmental education. At implementation level, there is a disjuncture between environmental education policy intentions and practice. Geography teachers in the research schools generally understood the existence of environmental education in their schools in terms of environmental management. The findings also revealed that while there is generally a strong environmental dimension in geography content, as reflected in both curriculum materials and classroom practice, the subject still retains its disciplinary boundaries and makes little use of knowledge from other subjects or the everyday knowledge of the learners. Finally, it emerged that while the geography teachers in their rhetoric espoused learner-centred methods, in practice they generally employed traditional teacher-centred and book-centred methods. The study concludes that a lack of change in school geography in Lesotho, of the sort envisaged in LEESP, may be attributed to contextual and structural factors such as an overemphasis on examinations, and certain perceptions on the part of teachers and learners embedded in the history and culture of their society. A model of teacher professional development capable of supporting curriculum change is therefore proposed.
- Full Text:
- Authors: Raselimo, Mohaeka Gabriel
- Date: 2012
- Subjects: Curriculum planning -- Lesotho Curriculum change -- Lesotho Educational evaluation -- Lesotho Environmental education -- Study and teaching (Secondary) -- Lesotho Geography -- Study and teaching (Secondary) -- Lesotho Agenda 21 (Program)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1488 , http://hdl.handle.net/10962/d1003369
- Description: This study sought to explore the interface between environmental education (EE) and school geography with a view to understanding a process of curriculum reform in the context of Lesotho. The research was based on the curriculum reform process that was initiated by a Danish donor-funded project, known as the Lesotho Environmental Education Support Project (LEESP), which operated from 2001 to 2004. Driven by a sustainable development imperative, the project was intended to assist Lesotho in the implementation of local action for Agenda 21 by introducing environmental education into the formal education system. Deviating slightly from much published research on geographical and environmental education, which focuses on how geography contributes to environmental education, this study explored how the latter has shaped the former in terms of content and pedagogy. Using the lens of critical curriculum theory, I sought to understand the political nature of the curriculum and of curriculum change, focusing on the LEESP curriculum policy development, dissemination and implementation at classroom level. The study employed Bernstein's concepts of classification and framing to illuminate issues of power and control between discourses, and between teachers and learners. Operating within an interpretive qualitative research orientation, the study used a case study method focusing on five secondary/high schools in Lesotho. The data was generated through document analysis, interviews and classroom observations. The study examined the assumptions, values and ideologies underpinning environmental education curriculum intentions as reflected in LEESP documents. It also investigated the social process of conceptualising and disseminating environmental education to understand the challenges faced as education practitioners made sense of environmental education innovations in the specific contexts of Lesotho, and how these could possibly influence what happens at the classroom level. The analysis of the LEESP documents revealed that while there are many areas of synergy between the LEESP environmental education policy guidelines and the national education ideals in Lesotho, achievement of the transformational visions of action competence, which was the overarching concept in the reform process, would require major structural changes. The study also highlights issues of participation, contestations, tensions and contradictions associated with the conceptualisation and dissemination of environmental education. At implementation level, there is a disjuncture between environmental education policy intentions and practice. Geography teachers in the research schools generally understood the existence of environmental education in their schools in terms of environmental management. The findings also revealed that while there is generally a strong environmental dimension in geography content, as reflected in both curriculum materials and classroom practice, the subject still retains its disciplinary boundaries and makes little use of knowledge from other subjects or the everyday knowledge of the learners. Finally, it emerged that while the geography teachers in their rhetoric espoused learner-centred methods, in practice they generally employed traditional teacher-centred and book-centred methods. The study concludes that a lack of change in school geography in Lesotho, of the sort envisaged in LEESP, may be attributed to contextual and structural factors such as an overemphasis on examinations, and certain perceptions on the part of teachers and learners embedded in the history and culture of their society. A model of teacher professional development capable of supporting curriculum change is therefore proposed.
- Full Text:
Deciding and doing what's right for people and planet : an investigation of the ethics-oriented learning of novice environmental educators
- Authors: Olvitt, Lausanne Laura
- Date: 2012
- Subjects: Environmental education Environmental ethics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1913 , http://hdl.handle.net/10962/d1007238
- Description: This study probes the ethics-oriented reflexive deliberations of three novice environmental education practitioners in South Africa. Two of the cases examined work in a local government context, and the third in an environmental non-governmental organisation context. All three practitioners are studying a one-year professional development course in environmental education. The research asks how their ethical deliberations ‘come to be what they are’, at the interface of their workplace and course-based learning processes. Working within a relational, social realist ontology, the study takes a sociocultural-historical approach to learning, development and social change. Cultural-historical activity theory (CHAT) provides theoretical tools and a descriptive language to approach the rich, qualitative data derived from workplace and course observations, extensive interviews, and document review. Critical discourse analysis was used as a secondary analytical tool to probe ethical and environmental discourses that were found to be influential in the course and workplace activity systems. Data from the three case studies was analysed in stages. In the first stage, CHAT provided a theoretical perspective and language of description to analyse the interacting activity systems in which each learner-practitioner’s ethics-oriented reflexive deliberations occurred. This provided a platform for the second stage of analysis which was framed by Margaret Archer’s (1995) social realist theory of morphogenesis/ morphostasis, followed by a summative retroductive analysis, to give an account of the interplay of historically-emergent social and cultural structures and individual reflexivity in relation to the ethical dimensions of environmental education practice. The study traces how ethics-oriented reflexive deliberations occur at the untidy, unpredictable intersection of workplace, course and personal contexts, and are strongest when they are situated in authentic contexts that resonate with learner-practitioners’ ‘ultimate concerns’ (after Archer, 2003; 2007). In this study, the learner-practitioners’ ‘ultimate concerns’ included family, personal well-being, social justice, cultural identity and religious commitments. The scope and depth of learner-practitioners’ social-ecological knowledge was also identified as a key factor influencing ethics-oriented reflexive deliberations, although the mediation of such knowledge can be hindered by language and conceptual ii barriers, amongst others. The study also noted how ethical positions circulating in the workplace, course and personal contexts were diverse, uneven and dynamic. Some ethical positions were found to be more explicitly differentiated than others, either resonating with or being overlooked by the learner-practitioners as they deliberated the ethical dimensions of their environmental education practice. In situations where there was limited depth, conceptual clarity and/ or confidence to engage directly with ethical concerns, there was a tendency towards (inadvertent) ethical relativism. Insights derived from the study suggest that these factors have limiting effects on the ethics-oriented reflexive deliberations of novice environmental educators. These insights point to the need for ethical deliberations to be re-personalised in context and underpinned by depth knowledge. A relational and pragmatic approach to environmental ethics (that recognises the validity of judgemental rationality – which can be fallible – and which seeks out practical adequacy) is put forward as appropriate and potentially generative in environmental education and training processes. This would need to be supported by careful attention to the influence of environmental discourses and practices in shaping ethical deliberations, and may also be helpful in developing a much-needed accessible, everyday language of ethical engagement. This study’s contribution to new knowledge in the field of environmental education is through its account of ethics-oriented reflexive deliberations emerging (in the Archerian morphogenetic sense) in complex, indeterminate ways at the interface of sociocultural and social-ecological contexts. The ethics-oriented reflexive deliberations of novice environmental educators occur in relation to their ‘ultimate concerns’ and are advanced or hindered by the historically-emergent practices, discourses and material realities of their workplace, personal and educational contexts. These insights require that the complex interplay of intersecting contexts and concerns that shape ethics-oriented reflexive deliberations be acknowledged and carefully mediated in both workplace-based and coursebased professional development processes.
- Full Text:
- Authors: Olvitt, Lausanne Laura
- Date: 2012
- Subjects: Environmental education Environmental ethics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1913 , http://hdl.handle.net/10962/d1007238
- Description: This study probes the ethics-oriented reflexive deliberations of three novice environmental education practitioners in South Africa. Two of the cases examined work in a local government context, and the third in an environmental non-governmental organisation context. All three practitioners are studying a one-year professional development course in environmental education. The research asks how their ethical deliberations ‘come to be what they are’, at the interface of their workplace and course-based learning processes. Working within a relational, social realist ontology, the study takes a sociocultural-historical approach to learning, development and social change. Cultural-historical activity theory (CHAT) provides theoretical tools and a descriptive language to approach the rich, qualitative data derived from workplace and course observations, extensive interviews, and document review. Critical discourse analysis was used as a secondary analytical tool to probe ethical and environmental discourses that were found to be influential in the course and workplace activity systems. Data from the three case studies was analysed in stages. In the first stage, CHAT provided a theoretical perspective and language of description to analyse the interacting activity systems in which each learner-practitioner’s ethics-oriented reflexive deliberations occurred. This provided a platform for the second stage of analysis which was framed by Margaret Archer’s (1995) social realist theory of morphogenesis/ morphostasis, followed by a summative retroductive analysis, to give an account of the interplay of historically-emergent social and cultural structures and individual reflexivity in relation to the ethical dimensions of environmental education practice. The study traces how ethics-oriented reflexive deliberations occur at the untidy, unpredictable intersection of workplace, course and personal contexts, and are strongest when they are situated in authentic contexts that resonate with learner-practitioners’ ‘ultimate concerns’ (after Archer, 2003; 2007). In this study, the learner-practitioners’ ‘ultimate concerns’ included family, personal well-being, social justice, cultural identity and religious commitments. The scope and depth of learner-practitioners’ social-ecological knowledge was also identified as a key factor influencing ethics-oriented reflexive deliberations, although the mediation of such knowledge can be hindered by language and conceptual ii barriers, amongst others. The study also noted how ethical positions circulating in the workplace, course and personal contexts were diverse, uneven and dynamic. Some ethical positions were found to be more explicitly differentiated than others, either resonating with or being overlooked by the learner-practitioners as they deliberated the ethical dimensions of their environmental education practice. In situations where there was limited depth, conceptual clarity and/ or confidence to engage directly with ethical concerns, there was a tendency towards (inadvertent) ethical relativism. Insights derived from the study suggest that these factors have limiting effects on the ethics-oriented reflexive deliberations of novice environmental educators. These insights point to the need for ethical deliberations to be re-personalised in context and underpinned by depth knowledge. A relational and pragmatic approach to environmental ethics (that recognises the validity of judgemental rationality – which can be fallible – and which seeks out practical adequacy) is put forward as appropriate and potentially generative in environmental education and training processes. This would need to be supported by careful attention to the influence of environmental discourses and practices in shaping ethical deliberations, and may also be helpful in developing a much-needed accessible, everyday language of ethical engagement. This study’s contribution to new knowledge in the field of environmental education is through its account of ethics-oriented reflexive deliberations emerging (in the Archerian morphogenetic sense) in complex, indeterminate ways at the interface of sociocultural and social-ecological contexts. The ethics-oriented reflexive deliberations of novice environmental educators occur in relation to their ‘ultimate concerns’ and are advanced or hindered by the historically-emergent practices, discourses and material realities of their workplace, personal and educational contexts. These insights require that the complex interplay of intersecting contexts and concerns that shape ethics-oriented reflexive deliberations be acknowledged and carefully mediated in both workplace-based and coursebased professional development processes.
- Full Text:
Development of a hydraulic sub-model as part of a desktop environmental flow assessment method
- Authors: Desai, Ahmed Yacoob
- Date: 2012
- Subjects: Hydrologic models -- Research -- South Africa Hydraulic engineering -- South Africa Rivers -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6041 , http://hdl.handle.net/10962/d1006200
- Description: Countries around the world have been developing ecological policies to protect their water resources and minimise the impacts of development on their river systems. The concept of ‘minimum flows’ was initially established as a solution but it did not provide sufficient protection as all elements of a flow regime were found to be important for the protection of the river ecosystem. “Environmental flows” were developed to determine these flow regimes to maintain a river in some defined ecological condition. Rapid, initial estimates of the quantity component of environmental flows may be determined using the Desktop Reserve Model in South Africa. However, the Desktop Reserve Model is dependent upon the characteristics of the reference natural hydrology used. The advancements in hydraulic and ecological relationships from the past decade have prompted the development of a Revised Desktop Reserve Model (RDRM) that would incorporate these relationships. The research in this thesis presents the development of the hydraulic sub-model for the RDRM. The hydraulic sub-model was designed to produce a realistic representation of the hydraulic conditions using hydraulic parameters/characteristics from readily available information for any part of South Africa. Hydraulic data from past EWR studies were used to estimate the hydraulic parameters. These estimated hydraulic parameters were used to develop hydraulic estimation relationships and these relationships were developed based on a combination of regression and rule-based procedures. The estimation relationships were incorporated into the hydraulic sub-model of the integrated RDRM and assessments of the hydraulic outputs and EWR results were undertaken to assess the ‘applicability’ of the hydraulic sub-model. The hydraulic sub-model was assessed to be at a stage where it can satisfactorily be incorporated in the RDRM and that it is adequately robust in many situations. Recommendations for future work include the refinement of estimation of the channel forming discharge or the use of spatial imagery to check the maximum channel width estimation. It is also proposed that a future version of the hydraulic sub-model could include flow regime change impacts on channel geomorphology and sedimentology so that flow management scenarios can be more effectively assessed.
- Full Text:
- Authors: Desai, Ahmed Yacoob
- Date: 2012
- Subjects: Hydrologic models -- Research -- South Africa Hydraulic engineering -- South Africa Rivers -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6041 , http://hdl.handle.net/10962/d1006200
- Description: Countries around the world have been developing ecological policies to protect their water resources and minimise the impacts of development on their river systems. The concept of ‘minimum flows’ was initially established as a solution but it did not provide sufficient protection as all elements of a flow regime were found to be important for the protection of the river ecosystem. “Environmental flows” were developed to determine these flow regimes to maintain a river in some defined ecological condition. Rapid, initial estimates of the quantity component of environmental flows may be determined using the Desktop Reserve Model in South Africa. However, the Desktop Reserve Model is dependent upon the characteristics of the reference natural hydrology used. The advancements in hydraulic and ecological relationships from the past decade have prompted the development of a Revised Desktop Reserve Model (RDRM) that would incorporate these relationships. The research in this thesis presents the development of the hydraulic sub-model for the RDRM. The hydraulic sub-model was designed to produce a realistic representation of the hydraulic conditions using hydraulic parameters/characteristics from readily available information for any part of South Africa. Hydraulic data from past EWR studies were used to estimate the hydraulic parameters. These estimated hydraulic parameters were used to develop hydraulic estimation relationships and these relationships were developed based on a combination of regression and rule-based procedures. The estimation relationships were incorporated into the hydraulic sub-model of the integrated RDRM and assessments of the hydraulic outputs and EWR results were undertaken to assess the ‘applicability’ of the hydraulic sub-model. The hydraulic sub-model was assessed to be at a stage where it can satisfactorily be incorporated in the RDRM and that it is adequately robust in many situations. Recommendations for future work include the refinement of estimation of the channel forming discharge or the use of spatial imagery to check the maximum channel width estimation. It is also proposed that a future version of the hydraulic sub-model could include flow regime change impacts on channel geomorphology and sedimentology so that flow management scenarios can be more effectively assessed.
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Development of molecularly imprinted polymer based solid phase extraction sorbents for the selective cleanup of food and pharmaceutical residue samples
- Authors: Batlokwa, Bareki Shima
- Date: 2012
- Subjects: Sorbents -- Research Nanofibers -- Research Aflatoxins -- Research Electrospinning -- Research Extraction (Chemistry) -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4309 , http://hdl.handle.net/10962/d1004967
- Description: This thesis presents the development of chlorophyll, cholic acid, aflatoxin B1 molecularly imprinted polymer (MIP) particles and cholic acid MIP nanofibers for application as selective solid phase extraction (SPE) sorbents. The particles were prepared by bulk polymerization and the nanofibers by a novel approach combining molecular imprinting and electrospinning technology. The AFB1 MIP particles were compared with an aflatoxin specific immunoextraction sorbent in cleaning-up and pre-concentrating aflatoxins from nut extracts. They both recorded high extraction efficiencies (EEs) of > 97 % in selectively extracting the aflatoxins (AFB1, AFB2, AFG1 and AFG2). High reproducibility marked by the low %RSDs of < 1% and low LODs of ≤ 0.02 ng/g were calculated in all cases. The LODs were within the monitoring requirements of the European Commission. The results were validated with a peanut butter certified reference material. The chlorophyll MIP on the other hand selectively removed chlorophyll that would otherwise interfere during pesticide residue analysis (PRA) from > 0.6 to <0.09 Au in green plants extracts. The extracted chlorophyll was removed to far below the level of ≥ 0.399 Au that is usually associated with interference during PRA. Furthermore, the MIP demonstrated better selectivity by removing only chlorophyll (> 99%) in the presence of planar pesticides than the currently employed graphitized carbon black (GCB) that removed both the chlorophyll (> 88%) and planar pesticides (> 89%). For the interfering cholic acid during drug residue analysis, cholic acid MIP electrospun nanofibers demonstrated to be more sensitive and possessing higher loading capacity than the MIP particles. 100% cholic acid was removed by the nanofibers from standard solutions relative to 80% by the particles. This showed that the nanofibers have better performance than the micro particles and as such have potential to replace the particle based SPE sorbents that are currently in use. All the templates were optimally removed from the prepared MIPs by employing a novel pressurized hot water extraction template removal method that was used for the first time in this thesis. The method employed only water, an environmentally friendly solvent to remove templates to ≥ 99.6% with template residual bleeding of ≤ 0.02%.
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- Authors: Batlokwa, Bareki Shima
- Date: 2012
- Subjects: Sorbents -- Research Nanofibers -- Research Aflatoxins -- Research Electrospinning -- Research Extraction (Chemistry) -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4309 , http://hdl.handle.net/10962/d1004967
- Description: This thesis presents the development of chlorophyll, cholic acid, aflatoxin B1 molecularly imprinted polymer (MIP) particles and cholic acid MIP nanofibers for application as selective solid phase extraction (SPE) sorbents. The particles were prepared by bulk polymerization and the nanofibers by a novel approach combining molecular imprinting and electrospinning technology. The AFB1 MIP particles were compared with an aflatoxin specific immunoextraction sorbent in cleaning-up and pre-concentrating aflatoxins from nut extracts. They both recorded high extraction efficiencies (EEs) of > 97 % in selectively extracting the aflatoxins (AFB1, AFB2, AFG1 and AFG2). High reproducibility marked by the low %RSDs of < 1% and low LODs of ≤ 0.02 ng/g were calculated in all cases. The LODs were within the monitoring requirements of the European Commission. The results were validated with a peanut butter certified reference material. The chlorophyll MIP on the other hand selectively removed chlorophyll that would otherwise interfere during pesticide residue analysis (PRA) from > 0.6 to <0.09 Au in green plants extracts. The extracted chlorophyll was removed to far below the level of ≥ 0.399 Au that is usually associated with interference during PRA. Furthermore, the MIP demonstrated better selectivity by removing only chlorophyll (> 99%) in the presence of planar pesticides than the currently employed graphitized carbon black (GCB) that removed both the chlorophyll (> 88%) and planar pesticides (> 89%). For the interfering cholic acid during drug residue analysis, cholic acid MIP electrospun nanofibers demonstrated to be more sensitive and possessing higher loading capacity than the MIP particles. 100% cholic acid was removed by the nanofibers from standard solutions relative to 80% by the particles. This showed that the nanofibers have better performance than the micro particles and as such have potential to replace the particle based SPE sorbents that are currently in use. All the templates were optimally removed from the prepared MIPs by employing a novel pressurized hot water extraction template removal method that was used for the first time in this thesis. The method employed only water, an environmentally friendly solvent to remove templates to ≥ 99.6% with template residual bleeding of ≤ 0.02%.
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Electrochemical sensing and immunosensing using metallophthalocyanines and biomolecular modified surfaces
- Authors: Mashazi, Philani Nkosinathi
- Date: 2012
- Subjects: Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Measles -- Measurement
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5580 , http://hdl.handle.net/10962/d1018248
- Description: The synthesis of cobalt and manganese phthalocyanine complexes bearing eight hexylthio and four amino substituents was carried out. The formation of thin films of these complexes using different modification methods was also studied. Hexylthio functionalized metallophthalocyanine complexes were immobilized onto gold electrode surfaces using the self-assembly techniques. Surface modifications using cobalt and manganese tetraamino phthalocyanine as polymers, monolayers (onto electrografted surfaces) and as carbon nanotube – metallophthalocyanine conjugates was also carried out. The new method of modifying gold electrodes with metal tetraamino phthalocyanine complexes was investigated. The modified electrode surfaces were studied for their electrocatalytic properties and as potential electrochemical sensors for the detection of hydrogen peroxide (H₂O₂). The limits of detection for the H₂O₂ were of the orders of ~10⁻⁷ M for all the modified electrodes. The modified electrodes gave very good analytical parameters; such as good sensitivity, linearity at studied concentration range and well-defined analytical peaks with increased current densities. The modification methods were reproducible, highly conducting thin films were formed and the modified electrodes were very stable. The design of electrochemical immunosensors for the detection of measles-specific antibodies was also carried out. The modified surface with measles-antigen as sensing element was accomplished using covalent immobilization for an intimate connection of the measles-antigen as a sensing layer onto an electrode surface. Two methods of detecting measles-specific antibodies were investigated and these methods were based on electrochemical impedance, i.e. label-free detection, and voltammetric method using horse-radish peroxidase (HRP) labeled antibody as a reporter. The detection of measles-specific antibodies was accomplished using both these methods. The potential applications of the designed immunosensor were evaluated in real samples (human and newborn calf serum) and the electrodes could detect the antibodies in the complex sample matrix with ease.
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- Authors: Mashazi, Philani Nkosinathi
- Date: 2012
- Subjects: Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Measles -- Measurement
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5580 , http://hdl.handle.net/10962/d1018248
- Description: The synthesis of cobalt and manganese phthalocyanine complexes bearing eight hexylthio and four amino substituents was carried out. The formation of thin films of these complexes using different modification methods was also studied. Hexylthio functionalized metallophthalocyanine complexes were immobilized onto gold electrode surfaces using the self-assembly techniques. Surface modifications using cobalt and manganese tetraamino phthalocyanine as polymers, monolayers (onto electrografted surfaces) and as carbon nanotube – metallophthalocyanine conjugates was also carried out. The new method of modifying gold electrodes with metal tetraamino phthalocyanine complexes was investigated. The modified electrode surfaces were studied for their electrocatalytic properties and as potential electrochemical sensors for the detection of hydrogen peroxide (H₂O₂). The limits of detection for the H₂O₂ were of the orders of ~10⁻⁷ M for all the modified electrodes. The modified electrodes gave very good analytical parameters; such as good sensitivity, linearity at studied concentration range and well-defined analytical peaks with increased current densities. The modification methods were reproducible, highly conducting thin films were formed and the modified electrodes were very stable. The design of electrochemical immunosensors for the detection of measles-specific antibodies was also carried out. The modified surface with measles-antigen as sensing element was accomplished using covalent immobilization for an intimate connection of the measles-antigen as a sensing layer onto an electrode surface. Two methods of detecting measles-specific antibodies were investigated and these methods were based on electrochemical impedance, i.e. label-free detection, and voltammetric method using horse-radish peroxidase (HRP) labeled antibody as a reporter. The detection of measles-specific antibodies was accomplished using both these methods. The potential applications of the designed immunosensor were evaluated in real samples (human and newborn calf serum) and the electrodes could detect the antibodies in the complex sample matrix with ease.
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Electrochemistry and photophysicochemical studies of titanium, tantalum and vanadium phthalocyanines in the presence of nanomaterials
- Authors: Chauke, Vongani Portia
- Date: 2012
- Subjects: Phthalocyanines -- Synthesis Electrochemistry Titanium Tantalum Vanadium
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4313 , http://hdl.handle.net/10962/d1004971
- Description: The syntheses of tetra- and octa-substituted phthalocyanine complexes of titanium (IV) oxide vanadium (IV) oxide and tantalum (V) hydroxide and their electrochemical characterisation are presented in this work. The structures and purity of these complexes were confirmed by NMR, infrared and mass spectroscopies and elemental analysis. They show good solubility in most common solvents especially non-viscous solvents such as dichloromethane and chloroform. The cyclic voltammograms (CV) showed reversible to quasi reversible behavior for all the reduction couples and the oxidation peaks were irreversible. Spectroelectrochemistry of the complexes confirmed metal and ring redox processes for TaPc and TiPc derivatives and ring based processes only for VPc complexes. The synthesis of gold nanoparticles and their conjugation with the new phthalocyanines was carried out. Similarly, single walled carbon nanotubes were conjugated to selected tantalum complexes and the characterization of all the nanomaterials and their conjugates using different techniques that include TEM, XRD and AFM is also presented in this work. The photophysical and photochemical properties and photocatalytic oxidation of cyclohexene properties of the newly synthesised in the presence of gold nanoparticles were investigated. The compounds were stable, well within the stability range for phthalocyanines. The singlet oxygen quantum yield values increased drastically in the presence of gold nanoparticles. The photocatalytic products obtained from the reaction were cyclohexene oxide, 2-cyclohexen-1-ol, 2-cyclohexene-1-one and 1,4-cyclohexanediol. The percentage conversion values, yields and selectivity values improved significantly in the presence of AuNPs. Singlet oxygen was determined to be the main agent involved in the photocatalytic oxidation of cyclohexene. The electrocatalytic oxidation of bisphenol A and p-nitrophenol was carried out using nickel tetraamino phthalocyanine and all the newly synthesised metallophthalocyanine in the presence of gold nanoparticles and single walled carbon nanotubes. The charge transfer behaviour of AuNPs was enhanced in the presence of TaPc, TiPc and VPc complexes. The presence of single walled carbon nanotubes further improved electron transfer and minimised electrode passivation.
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- Authors: Chauke, Vongani Portia
- Date: 2012
- Subjects: Phthalocyanines -- Synthesis Electrochemistry Titanium Tantalum Vanadium
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4313 , http://hdl.handle.net/10962/d1004971
- Description: The syntheses of tetra- and octa-substituted phthalocyanine complexes of titanium (IV) oxide vanadium (IV) oxide and tantalum (V) hydroxide and their electrochemical characterisation are presented in this work. The structures and purity of these complexes were confirmed by NMR, infrared and mass spectroscopies and elemental analysis. They show good solubility in most common solvents especially non-viscous solvents such as dichloromethane and chloroform. The cyclic voltammograms (CV) showed reversible to quasi reversible behavior for all the reduction couples and the oxidation peaks were irreversible. Spectroelectrochemistry of the complexes confirmed metal and ring redox processes for TaPc and TiPc derivatives and ring based processes only for VPc complexes. The synthesis of gold nanoparticles and their conjugation with the new phthalocyanines was carried out. Similarly, single walled carbon nanotubes were conjugated to selected tantalum complexes and the characterization of all the nanomaterials and their conjugates using different techniques that include TEM, XRD and AFM is also presented in this work. The photophysical and photochemical properties and photocatalytic oxidation of cyclohexene properties of the newly synthesised in the presence of gold nanoparticles were investigated. The compounds were stable, well within the stability range for phthalocyanines. The singlet oxygen quantum yield values increased drastically in the presence of gold nanoparticles. The photocatalytic products obtained from the reaction were cyclohexene oxide, 2-cyclohexen-1-ol, 2-cyclohexene-1-one and 1,4-cyclohexanediol. The percentage conversion values, yields and selectivity values improved significantly in the presence of AuNPs. Singlet oxygen was determined to be the main agent involved in the photocatalytic oxidation of cyclohexene. The electrocatalytic oxidation of bisphenol A and p-nitrophenol was carried out using nickel tetraamino phthalocyanine and all the newly synthesised metallophthalocyanine in the presence of gold nanoparticles and single walled carbon nanotubes. The charge transfer behaviour of AuNPs was enhanced in the presence of TaPc, TiPc and VPc complexes. The presence of single walled carbon nanotubes further improved electron transfer and minimised electrode passivation.
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