A comparison of the vulcanisation of Polyisoprene by a range of Thiuram Diulfides
- Authors: Van Rooyen, Jason Leigh
- Date: 2007
- Subjects: Vulcanization , Vulcanization accelerators
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10399 , http://hdl.handle.net/10948/733 , Vulcanization , Vulcanization accelerators
- Description: This study was initiated in an attempt to investigate dithiocarbamic acid accelerated sulfur vulcanisation. This was, however, found impossible due to the innate instability of dithiocarbamic acids. The focus of the study was then shifted toward thiuram disulfide accelerated sulfur vulcanisation, with emphasis being placed on a rate comparison. Three groups of accelerators were investigated, namely the aromatic, linear aliphatic and cyclic aliphatic thiuram disulfide adducts. The analysis methods that were employed were conventional rubber (cis-1,4-polyisoprene) techniques coupled to model (squalene) compound investigations. The data that was collected consisted of rheometrical torque vs. time data in the rubber system while the data obtained in the model compound study consisted of sulfur and accelerator concentration data as determined by means of high performance liquid chromatography (HPLC). The aromatic accelerators were synthesised in our labs by means of an addition reaction between the aromatic amine and CS2 in basic medium and subsequent oxidation with K3Fe(CN)6, all in a 1:1 molar ratio. The reaction yield was low due to the instability of the dithiocarbamate intermediates and a sluggish oxidation reaction. In the rate constant determination a first order mathematical approach was used for the rubber system as crosslinking is considered to roughly obey first order kinetics. The model compound data was also found to more accurately fit the first order rate law, with an initial slopes method also being applied to the system to determine secondary rate constants and relative rates for the system. The determination of vulcanisation rate constants in the cis-1,4-polyisoprene system was a success, while the rate data determined by means of the squalene model was more related to the rate of accelerator and sulfur consumption as opposed to the rate of crosslinking as is the case with the rubber rate data. The sulfur first order rate data mirrored the rate data derived from the rubber system more closely than the corresponding accelerator rate data, the relative rate data determined by means of initial slopes method, proved that the homolytic cleavage of thiuram disulfides and the subsequent formation of accelerator polysulfides were not limiting steps. This is seen in the similar relative rate data derived from both the raw sulfur and accelerator data in systems that exhibit vastly different vulcanisation rates. Squalene was deemed a suitable model for the cis-1,4-polyisoprene system, although one should consider the extent of charring and solution effects in the individual systems to account for possible incongruities that may be observed between the rubber and simulated system. The lack of agreement between the rubber and model compound rate constant data lies in the fact that the rate of crosslinking is not simplistically related to the rate at which accelerator and sulfur is consumed, this being especially true for the rate at which the accelerator is consumed. Thus the discussion over the acceleratory rates in the various accelerator systems was limited to observations made in the rubber system, with the model compound data was used exclusively to elucidate mechanistic processes. It was discovered that the groups of accelerators examined, namely linear, cyclic and aromatic thiuram disulfide adducts, produced vastly varied rate data. The aromatic thiuram disulfide adducts had only a slight acceleratory effect on the rate of vulcanisation as compared to the unaccelerated sulfur system. The morpholine adduct had a moderately larger rate of acceleration followed by tetramethyl and tetrethylthiuram disulfide, with N’N-dicyclopentamethylenethiuram disulfide having the fastest rate of acceleration.
- Full Text:
- Date Issued: 2007
- Authors: Van Rooyen, Jason Leigh
- Date: 2007
- Subjects: Vulcanization , Vulcanization accelerators
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10399 , http://hdl.handle.net/10948/733 , Vulcanization , Vulcanization accelerators
- Description: This study was initiated in an attempt to investigate dithiocarbamic acid accelerated sulfur vulcanisation. This was, however, found impossible due to the innate instability of dithiocarbamic acids. The focus of the study was then shifted toward thiuram disulfide accelerated sulfur vulcanisation, with emphasis being placed on a rate comparison. Three groups of accelerators were investigated, namely the aromatic, linear aliphatic and cyclic aliphatic thiuram disulfide adducts. The analysis methods that were employed were conventional rubber (cis-1,4-polyisoprene) techniques coupled to model (squalene) compound investigations. The data that was collected consisted of rheometrical torque vs. time data in the rubber system while the data obtained in the model compound study consisted of sulfur and accelerator concentration data as determined by means of high performance liquid chromatography (HPLC). The aromatic accelerators were synthesised in our labs by means of an addition reaction between the aromatic amine and CS2 in basic medium and subsequent oxidation with K3Fe(CN)6, all in a 1:1 molar ratio. The reaction yield was low due to the instability of the dithiocarbamate intermediates and a sluggish oxidation reaction. In the rate constant determination a first order mathematical approach was used for the rubber system as crosslinking is considered to roughly obey first order kinetics. The model compound data was also found to more accurately fit the first order rate law, with an initial slopes method also being applied to the system to determine secondary rate constants and relative rates for the system. The determination of vulcanisation rate constants in the cis-1,4-polyisoprene system was a success, while the rate data determined by means of the squalene model was more related to the rate of accelerator and sulfur consumption as opposed to the rate of crosslinking as is the case with the rubber rate data. The sulfur first order rate data mirrored the rate data derived from the rubber system more closely than the corresponding accelerator rate data, the relative rate data determined by means of initial slopes method, proved that the homolytic cleavage of thiuram disulfides and the subsequent formation of accelerator polysulfides were not limiting steps. This is seen in the similar relative rate data derived from both the raw sulfur and accelerator data in systems that exhibit vastly different vulcanisation rates. Squalene was deemed a suitable model for the cis-1,4-polyisoprene system, although one should consider the extent of charring and solution effects in the individual systems to account for possible incongruities that may be observed between the rubber and simulated system. The lack of agreement between the rubber and model compound rate constant data lies in the fact that the rate of crosslinking is not simplistically related to the rate at which accelerator and sulfur is consumed, this being especially true for the rate at which the accelerator is consumed. Thus the discussion over the acceleratory rates in the various accelerator systems was limited to observations made in the rubber system, with the model compound data was used exclusively to elucidate mechanistic processes. It was discovered that the groups of accelerators examined, namely linear, cyclic and aromatic thiuram disulfide adducts, produced vastly varied rate data. The aromatic thiuram disulfide adducts had only a slight acceleratory effect on the rate of vulcanisation as compared to the unaccelerated sulfur system. The morpholine adduct had a moderately larger rate of acceleration followed by tetramethyl and tetrethylthiuram disulfide, with N’N-dicyclopentamethylenethiuram disulfide having the fastest rate of acceleration.
- Full Text:
- Date Issued: 2007
A model for adaptive multimodal mobile notification
- Authors: Brander, William
- Date: 2007
- Subjects: Mobile computing , Context-aware computing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10473 , http://hdl.handle.net/10948/699 , Mobile computing , Context-aware computing
- Description: Information is useless unless it is used whilst still applicable. Having a system that notifies the user of important messages using the most appropriate medium and device will benefit users that rely on time critical information. There are several existing systems and models for mobile notification as well as for adaptive mobile notification using context awareness. Current models and systems are typically designed for a specific set of mobile devices, modes and services. Communication however, can take place in many different modes, across many different devices and may originate from many different sources. The aim of this research was to develop a model for adaptive mobile notification using context awareness. An extensive literature study was performed into existing models for adaptive mobile notification systems using context awareness. The literature study identified several potential models but no way to evaluate and compare the models. A set of requirements to evaluate these models was developed and the models were evaluated against these criteria. The model satisfying the most requirements was adapted so as to satisfy the remaining criteria. The proposed model is extensible in terms of the modes, devices and notification sources supported. The proposed model determines the importance of a message, the appropriate device and mode (or modes) of communication based on the user‘s context, and alerts the user of the message using these modes. A prototype was developed as a proof-of-concept of the proposed model and evaluated by conducting an extensive field study. The field study highlighted the fact that most users did not choose the most suitable mode for the context during their initial subscription to the service. The field study also showed that more research needs to be done on an appropriate filtering mechanism for notifications. Users found that the notifications became intrusive and less useful the longer they used them.
- Full Text:
- Date Issued: 2007
- Authors: Brander, William
- Date: 2007
- Subjects: Mobile computing , Context-aware computing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10473 , http://hdl.handle.net/10948/699 , Mobile computing , Context-aware computing
- Description: Information is useless unless it is used whilst still applicable. Having a system that notifies the user of important messages using the most appropriate medium and device will benefit users that rely on time critical information. There are several existing systems and models for mobile notification as well as for adaptive mobile notification using context awareness. Current models and systems are typically designed for a specific set of mobile devices, modes and services. Communication however, can take place in many different modes, across many different devices and may originate from many different sources. The aim of this research was to develop a model for adaptive mobile notification using context awareness. An extensive literature study was performed into existing models for adaptive mobile notification systems using context awareness. The literature study identified several potential models but no way to evaluate and compare the models. A set of requirements to evaluate these models was developed and the models were evaluated against these criteria. The model satisfying the most requirements was adapted so as to satisfy the remaining criteria. The proposed model is extensible in terms of the modes, devices and notification sources supported. The proposed model determines the importance of a message, the appropriate device and mode (or modes) of communication based on the user‘s context, and alerts the user of the message using these modes. A prototype was developed as a proof-of-concept of the proposed model and evaluated by conducting an extensive field study. The field study highlighted the fact that most users did not choose the most suitable mode for the context during their initial subscription to the service. The field study also showed that more research needs to be done on an appropriate filtering mechanism for notifications. Users found that the notifications became intrusive and less useful the longer they used them.
- Full Text:
- Date Issued: 2007
An assessment of habitat suitability of the proposed Tyefu community game reserve in Ngqushwa (fomerly Peddie) district, Eastern Cape
- Authors: Mamfengu, Phozisa Faith
- Date: 2007
- Subjects: Game farms -- South Africa -- Eastern Cape -- Management , Habitat (Ecology) , Eastern Cape (South Africa) -- Social conditions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10653 , http://hdl.handle.net/10948/736 , Game farms -- South Africa -- Eastern Cape -- Management , Habitat (Ecology) , Eastern Cape (South Africa) -- Social conditions
- Description: Land use forms such as cultivation and livestock farming have become less productive and unsustainable in the Tyefu communal villages of Ngqushwa (Formerly Peddie) district, Eastern Cape, South Africa. This is manifest in abandoned and severely degraded cultivation fields as well as transformed vegetation, making it difficult to earn a land based livelihood. Against the backdrop of severe land degradation and poverty levels in these communal villages, game farming has been recommended as an ecologically, economically and socially sustainable form of land use. Tyefu Community Reserve is a project, recommended by the Subtropical Thicket Ecosystem Project (STEP) backed by the Department of Environment Affairs and Tourism (DEAT), for hunting and venison selling. The proposed area has been fenced and animals to be stocked in the reserve have been requested on a loan basis. Such an undertaking requires an understanding of the abundance and condition of vegetation, terrain parameters, and an assessment of potential wildlife species, as well as the carrying capacity of the recommended reserve as a habitat. With the aid of orthophoto maps, Subtropical Thicket Ecosystem Planning (STEP) shapefiles, ASTER satellite imagery and a High Resolution Digital Camera Image, vegetation types were mapped and their condition was assessed. A Digital Elevation Model (DEM) of the area was used to extract terrain parameters such as slope and aspect. The carrying capacity of the proposed reserve was determined using a model originally developed by Boshoff et al. (2001) for estimating potential wildlife and abundance. The proposed reserve is predominantly covered by dense thicket as compared to the adjacent Tyefu communal villages where thicket has been severely degraded. The prominent topographic characteristics such as slope reveal an escarpment ringing the proposed reserve with gentle slopes towards the centre. Slope direction has also influenced the distribution of vegetation in the proposed reserve, as the moist south facing slopes tend to have a greater proportion of dense thicket as opposed to the warm north facing slopes. Vegetation types and topography of the reserve can provide suitable habitat to a variety of wildlife species and are likely to influence the distribution of mammals in the proposed reserve. The carrying capacity model developed has been useful in determining potential species that can be supported by the reserve, and estimating their abundance. Given the small size of the proposed community reserve (about 1800ha), it has been recommended that it should be stretched to link up with the existing Great Fish River Game Complex. It will then fit within the framework as envisaged by STEP (2004), in the form of Fish River Biodiversity Initiative, a conservation corridor bordering the Great Fish River.
- Full Text:
- Date Issued: 2007
- Authors: Mamfengu, Phozisa Faith
- Date: 2007
- Subjects: Game farms -- South Africa -- Eastern Cape -- Management , Habitat (Ecology) , Eastern Cape (South Africa) -- Social conditions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10653 , http://hdl.handle.net/10948/736 , Game farms -- South Africa -- Eastern Cape -- Management , Habitat (Ecology) , Eastern Cape (South Africa) -- Social conditions
- Description: Land use forms such as cultivation and livestock farming have become less productive and unsustainable in the Tyefu communal villages of Ngqushwa (Formerly Peddie) district, Eastern Cape, South Africa. This is manifest in abandoned and severely degraded cultivation fields as well as transformed vegetation, making it difficult to earn a land based livelihood. Against the backdrop of severe land degradation and poverty levels in these communal villages, game farming has been recommended as an ecologically, economically and socially sustainable form of land use. Tyefu Community Reserve is a project, recommended by the Subtropical Thicket Ecosystem Project (STEP) backed by the Department of Environment Affairs and Tourism (DEAT), for hunting and venison selling. The proposed area has been fenced and animals to be stocked in the reserve have been requested on a loan basis. Such an undertaking requires an understanding of the abundance and condition of vegetation, terrain parameters, and an assessment of potential wildlife species, as well as the carrying capacity of the recommended reserve as a habitat. With the aid of orthophoto maps, Subtropical Thicket Ecosystem Planning (STEP) shapefiles, ASTER satellite imagery and a High Resolution Digital Camera Image, vegetation types were mapped and their condition was assessed. A Digital Elevation Model (DEM) of the area was used to extract terrain parameters such as slope and aspect. The carrying capacity of the proposed reserve was determined using a model originally developed by Boshoff et al. (2001) for estimating potential wildlife and abundance. The proposed reserve is predominantly covered by dense thicket as compared to the adjacent Tyefu communal villages where thicket has been severely degraded. The prominent topographic characteristics such as slope reveal an escarpment ringing the proposed reserve with gentle slopes towards the centre. Slope direction has also influenced the distribution of vegetation in the proposed reserve, as the moist south facing slopes tend to have a greater proportion of dense thicket as opposed to the warm north facing slopes. Vegetation types and topography of the reserve can provide suitable habitat to a variety of wildlife species and are likely to influence the distribution of mammals in the proposed reserve. The carrying capacity model developed has been useful in determining potential species that can be supported by the reserve, and estimating their abundance. Given the small size of the proposed community reserve (about 1800ha), it has been recommended that it should be stretched to link up with the existing Great Fish River Game Complex. It will then fit within the framework as envisaged by STEP (2004), in the form of Fish River Biodiversity Initiative, a conservation corridor bordering the Great Fish River.
- Full Text:
- Date Issued: 2007
An intelligent user interface model for contact centre operations
- Authors: Singh, Akash
- Date: 2007
- Subjects: User interfaces (Computer systems) , Human-computer interaction , Mobile computing , Customer services -- Management , Call centers -- Customer services
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10475 , http://hdl.handle.net/10948/d1011399 , User interfaces (Computer systems) , Human-computer interaction , Mobile computing , Customer services -- Management , Call centers -- Customer services
- Description: Contact Centres (CCs) are at the forefront of interaction between an organisation and its customers. Currently, 17 percent of all inbound calls are not resolved on the first call by the first agent attending to that call. This is due to the inability of the contact centre agents (CCAs) to diagnose customer queries and find adequate solutions in an effective and efficient manner. The aim of this research is to develop an intelligent user interface (IUI) model to support and improve CC operations. A literature review of existing IUI architectures, modelbased design and existing CC software together with a field study of CCs has resulted in the design of an IUI model for CCs. The proposed IUI model is described in terms of its architecture, component-level design and interface design. An IUI prototype has been developed as a proof of concept of the proposed IUI model. The IUI prototype was evaluated in order to determine to what extent it supports problem identification and query resolution. User testing, incorporating the use of eye tracking and a post-test questionnaire, was used in order to determine the usability and usefulness of the prototype. The results of this evaluation show that the users were highly satisfied with the task support and query resolution assistance provided by the IUI prototype. This research resulted in the design of an IUI model for the domain of CCs. This model can be used to assist the development of CC applications incorporating IUIs. Use of the proposed IUI model is expected to support and enhance the effectiveness and efficiency of CC operations. Further research is needed to conduct a longitudinal study to determine the impact of IUIs in the CC domain.
- Full Text:
- Date Issued: 2007
- Authors: Singh, Akash
- Date: 2007
- Subjects: User interfaces (Computer systems) , Human-computer interaction , Mobile computing , Customer services -- Management , Call centers -- Customer services
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10475 , http://hdl.handle.net/10948/d1011399 , User interfaces (Computer systems) , Human-computer interaction , Mobile computing , Customer services -- Management , Call centers -- Customer services
- Description: Contact Centres (CCs) are at the forefront of interaction between an organisation and its customers. Currently, 17 percent of all inbound calls are not resolved on the first call by the first agent attending to that call. This is due to the inability of the contact centre agents (CCAs) to diagnose customer queries and find adequate solutions in an effective and efficient manner. The aim of this research is to develop an intelligent user interface (IUI) model to support and improve CC operations. A literature review of existing IUI architectures, modelbased design and existing CC software together with a field study of CCs has resulted in the design of an IUI model for CCs. The proposed IUI model is described in terms of its architecture, component-level design and interface design. An IUI prototype has been developed as a proof of concept of the proposed IUI model. The IUI prototype was evaluated in order to determine to what extent it supports problem identification and query resolution. User testing, incorporating the use of eye tracking and a post-test questionnaire, was used in order to determine the usability and usefulness of the prototype. The results of this evaluation show that the users were highly satisfied with the task support and query resolution assistance provided by the IUI prototype. This research resulted in the design of an IUI model for the domain of CCs. This model can be used to assist the development of CC applications incorporating IUIs. Use of the proposed IUI model is expected to support and enhance the effectiveness and efficiency of CC operations. Further research is needed to conduct a longitudinal study to determine the impact of IUIs in the CC domain.
- Full Text:
- Date Issued: 2007
An investigation into the introduction of process analytical technology, using near infrared analysis, to selected pharmaceutical processes
- Authors: Naicker, Krishnaveni
- Date: 2007
- Subjects: Near infrared spectroscopy , Pharmaceutical chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10153 , http://hdl.handle.net/10948/577 , http://hdl.handle.net/10948/d1011710 , Near infrared spectroscopy , Pharmaceutical chemistry
- Description: Introduction: Process analytical technologies are systems for the analysis and control of manufacturing processes to assure acceptable end-product quality. This is achieved by timely measurements of critical parameters and performance attributes of raw material and in-process material and processes. The introduction of process analytical technology using near infrared analysis was investigated in three areas, namely incoming raw material analysis, blend uniformity analysis and moisture determination in the fluid bed dryer. Methodology: Incoming raw material identification - The FOSS XDS rapid content analyzer was used for the development of a NIR method for the identification and material qualification of starch maize and lactose monohydrate. Blend uniformity analysis – The SP15 Laboratory Blender fitted with near infrared probe was utilized for the study. Two types of blend experiments were designed to monitor the distribution of magnesium stearate (lubricant) in the blend, namely, a powder blend utilizing lactose monohydrate and a granule blend utilizing Ridaq® granule. Software methods were developed to monitor the standard deviation of the absorbance at the wavelengths that were specific for lactose monohydrate, Ridaq® granule and magnesium stearate. To confirm the prediction of end-point using near infrared, results were verified using an atomic absorption method for magnesium stearate. The blends were sampled at the selected time intervals corresponding to three states of the blend, namely, before end-point, at end-point and after end-point using a sampling plan. An additional six blends were conducted for the granule blend and sampled when the standard deviation had reached a value below 3 x 10-6 at the magnesium stearate wavelength at four consecutive data points (standard deviation value extrapolated from blends carried out to predetermined time intervals). Moisture determination in the fluid bed dryer – Moisture values for two products (Product A and Product B) were retrospectively collected from past production batches. A process capability study was conducted on the moisture values to determine if the current process was in a state of control. Results and Discussion: Incoming raw material identification – The algorithms used for the spectral library were able to distinguish between the raw materials selected. The spectral library positively identified the starch maize and lactose monohydrate samples that were not present in the library. The negative challenge with pregelatinised starch and tablettose demonstrated that the spectral library was able to differentiate between closely related compounds. Blend uniformity analysis – Blends sampled at the predetermined time intervals demonstrated a homogeneous state when the standard deviation of the absorbance was low and a non-homogeneous state when the standard deviation of the absorbance was high, thus near infrared prediction on the state of the blend was confirmed by the standard analytical methods. The series of Ridaq® granule and magnesium stearate blends sampled when the standard deviation was below 3 x 10-6 were homogeneous with the exception of one blend that was marginally out of specification. Blend durations were significantly lower than the standard blend durations used in the facility and ranged from 112 to 198 seconds. Moisture determination in the fluid bed dryer – From the process capability study of the two products it was noted that Product A is stable but can still be optimized while Product B is at a desirable state. The statistical evaluation of the moisture values for Product A and Product B demonstrated that the use of the product temperature to monitor the moisture gave consistent results. The current process is stable and capable of producing repeatable results although near infrared provides a means for continuously monitoring the product moisture and allows one to take action to prevent over-drying or under-drying. Conclusion: From the investigations conducted, it can be seen that there is definitely a niche for process analytical technology at this pharmaceutical company. The implementation is a gradual process of change, which may take time, probably several years (Heinze & Hansen 2005).
- Full Text:
- Date Issued: 2007
- Authors: Naicker, Krishnaveni
- Date: 2007
- Subjects: Near infrared spectroscopy , Pharmaceutical chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10153 , http://hdl.handle.net/10948/577 , http://hdl.handle.net/10948/d1011710 , Near infrared spectroscopy , Pharmaceutical chemistry
- Description: Introduction: Process analytical technologies are systems for the analysis and control of manufacturing processes to assure acceptable end-product quality. This is achieved by timely measurements of critical parameters and performance attributes of raw material and in-process material and processes. The introduction of process analytical technology using near infrared analysis was investigated in three areas, namely incoming raw material analysis, blend uniformity analysis and moisture determination in the fluid bed dryer. Methodology: Incoming raw material identification - The FOSS XDS rapid content analyzer was used for the development of a NIR method for the identification and material qualification of starch maize and lactose monohydrate. Blend uniformity analysis – The SP15 Laboratory Blender fitted with near infrared probe was utilized for the study. Two types of blend experiments were designed to monitor the distribution of magnesium stearate (lubricant) in the blend, namely, a powder blend utilizing lactose monohydrate and a granule blend utilizing Ridaq® granule. Software methods were developed to monitor the standard deviation of the absorbance at the wavelengths that were specific for lactose monohydrate, Ridaq® granule and magnesium stearate. To confirm the prediction of end-point using near infrared, results were verified using an atomic absorption method for magnesium stearate. The blends were sampled at the selected time intervals corresponding to three states of the blend, namely, before end-point, at end-point and after end-point using a sampling plan. An additional six blends were conducted for the granule blend and sampled when the standard deviation had reached a value below 3 x 10-6 at the magnesium stearate wavelength at four consecutive data points (standard deviation value extrapolated from blends carried out to predetermined time intervals). Moisture determination in the fluid bed dryer – Moisture values for two products (Product A and Product B) were retrospectively collected from past production batches. A process capability study was conducted on the moisture values to determine if the current process was in a state of control. Results and Discussion: Incoming raw material identification – The algorithms used for the spectral library were able to distinguish between the raw materials selected. The spectral library positively identified the starch maize and lactose monohydrate samples that were not present in the library. The negative challenge with pregelatinised starch and tablettose demonstrated that the spectral library was able to differentiate between closely related compounds. Blend uniformity analysis – Blends sampled at the predetermined time intervals demonstrated a homogeneous state when the standard deviation of the absorbance was low and a non-homogeneous state when the standard deviation of the absorbance was high, thus near infrared prediction on the state of the blend was confirmed by the standard analytical methods. The series of Ridaq® granule and magnesium stearate blends sampled when the standard deviation was below 3 x 10-6 were homogeneous with the exception of one blend that was marginally out of specification. Blend durations were significantly lower than the standard blend durations used in the facility and ranged from 112 to 198 seconds. Moisture determination in the fluid bed dryer – From the process capability study of the two products it was noted that Product A is stable but can still be optimized while Product B is at a desirable state. The statistical evaluation of the moisture values for Product A and Product B demonstrated that the use of the product temperature to monitor the moisture gave consistent results. The current process is stable and capable of producing repeatable results although near infrared provides a means for continuously monitoring the product moisture and allows one to take action to prevent over-drying or under-drying. Conclusion: From the investigations conducted, it can be seen that there is definitely a niche for process analytical technology at this pharmaceutical company. The implementation is a gradual process of change, which may take time, probably several years (Heinze & Hansen 2005).
- Full Text:
- Date Issued: 2007
An investigation into the learnability of object-oriented case tools for computing education
- Authors: Scholtz, Brenda Mary
- Date: 2007
- Subjects: Computer science -- Study and teaching , Object-oriented programming (Computer science) , ACSES (Computer system)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10476 , http://hdl.handle.net/10948/694 , Computer science -- Study and teaching , Object-oriented programming (Computer science) , ACSES (Computer system)
- Description: The use of Computer Aided Software Engineering (CASE) tools for teaching object-oriented systems analysis and design (OOSAD) has many potential benefits, but there are also several problems associated with the usage of these tools. A large portion of these problems relate to the usability and learnability of these tools. Learnability is one of the most important attributes of usability and refers to the capability of the system to enable the user to learn its application. The main research question that this study aims to address is “How can the learnability of OO CASE tools for computing education in South Africa be evaluated?”. In order to answer this question several frameworks for evaluating CASE tool usability and learnability were investigated. One of these frameworks, as proposed by Senapathi, was selected as being the most appropriate for evaluating CASE tool learnability for computing education. This framework maintains that the learnability of a CASE tool is dependent on context of use factors such as the tool used, as well as user characteristics such as gender. The primary aim of this research was thus to validate Senapathi's framework for CASE tool learnability in a South African context. A secondary aim of the research was to extend the implementation of the framework in order to enable the comparison of two CASE tools and to support the inclusion of other user characteristics. An experiment was performed at the Nelson Mandela Metropolitan University (NMMU) in 2006. The participants recruited for this experiment were second year computing students at NMMU. During this experiment, the learnability of two OO CASE tools, namely IBM's Rational Software Modeller and Microsoft's Visio, was evaluated and compared. The quantitative and qualitative results supported Senapathi's results and showed that her framework could be used to evaluate CASE tool learnability and could be adapted to evaluate two CASE tools. The results also showed that the majority of the participants rated the learnability of Microsoft Visio higher for both tasks and that the main reasons participants preferred Visio was due to its simplicity, familiarity and recoverability.
- Full Text:
- Date Issued: 2007
- Authors: Scholtz, Brenda Mary
- Date: 2007
- Subjects: Computer science -- Study and teaching , Object-oriented programming (Computer science) , ACSES (Computer system)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10476 , http://hdl.handle.net/10948/694 , Computer science -- Study and teaching , Object-oriented programming (Computer science) , ACSES (Computer system)
- Description: The use of Computer Aided Software Engineering (CASE) tools for teaching object-oriented systems analysis and design (OOSAD) has many potential benefits, but there are also several problems associated with the usage of these tools. A large portion of these problems relate to the usability and learnability of these tools. Learnability is one of the most important attributes of usability and refers to the capability of the system to enable the user to learn its application. The main research question that this study aims to address is “How can the learnability of OO CASE tools for computing education in South Africa be evaluated?”. In order to answer this question several frameworks for evaluating CASE tool usability and learnability were investigated. One of these frameworks, as proposed by Senapathi, was selected as being the most appropriate for evaluating CASE tool learnability for computing education. This framework maintains that the learnability of a CASE tool is dependent on context of use factors such as the tool used, as well as user characteristics such as gender. The primary aim of this research was thus to validate Senapathi's framework for CASE tool learnability in a South African context. A secondary aim of the research was to extend the implementation of the framework in order to enable the comparison of two CASE tools and to support the inclusion of other user characteristics. An experiment was performed at the Nelson Mandela Metropolitan University (NMMU) in 2006. The participants recruited for this experiment were second year computing students at NMMU. During this experiment, the learnability of two OO CASE tools, namely IBM's Rational Software Modeller and Microsoft's Visio, was evaluated and compared. The quantitative and qualitative results supported Senapathi's results and showed that her framework could be used to evaluate CASE tool learnability and could be adapted to evaluate two CASE tools. The results also showed that the majority of the participants rated the learnability of Microsoft Visio higher for both tasks and that the main reasons participants preferred Visio was due to its simplicity, familiarity and recoverability.
- Full Text:
- Date Issued: 2007
Assessing program code through static structural similarity
- Authors: Naude, Kevin Alexander
- Date: 2007
- Subjects: Computer networks -- Security measures , Internet -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10478 , http://hdl.handle.net/10948/578 , Computer networks -- Security measures , Internet -- Security measures
- Description: Learning to write software requires much practice and frequent assessment. Consequently, the use of computers to assist in the assessment of computer programs has been important in supporting large classes at universities. The main approaches to the problem are dynamic analysis (testing student programs for expected output) and static analysis (direct analysis of the program code). The former is very sensitive to all kinds of errors in student programs, while the latter has traditionally only been used to assess quality, and not correctness. This research focusses on the application of static analysis, particularly structural similarity, to marking student programs. Existing traditional measures of similarity are limiting in that they are usually only effective on tree structures. In this regard they do not easily support dependencies in program code. Contemporary measures of structural similarity, such as similarity flooding, usually rely on an internal normalisation of scores. The effect is that the scores only have relative meaning, and cannot be interpreted in isolation, ie. they are not meaningful for assessment. The SimRank measure is shown to have the same problem, but not because of normalisation. The problem with the SimRank measure arises from the fact that its scores depend on all possible mappings between the children of vertices being compared. The main contribution of this research is a novel graph similarity measure, the Weighted Assignment Similarity measure. It is related to SimRank, but derives propagation scores from only the locally optimal mapping between child vertices. The resulting similarity scores may be regarded as the percentage of mutual coverage between graphs. The measure is proven to converge for all directed acyclic graphs, and an efficient implementation is outlined for this case. Attributes on graph vertices and edges are often used to capture domain specific information which is not structural in nature. It has been suggested that these should influence the similarity propagation, but no clear method for doing this has been reported. The second important contribution of this research is a general method for incorporating these local attribute similarities into the larger similarity propagation method. An example of attributes in program graphs are identifier names. The choice of identifiers in programs is arbitrary as they are purely symbolic. A problem facing any comparison between programs is that they are unlikely to use the same set of identifiers. This problem indicates that a mapping between the identifier sets is required. The third contribution of this research is a method for applying the structural similarity measure in a two step process to find an optimal identifier mapping. This approach is both novel and valuable as it cleverly reuses the similarity measure as an existing resource. In general, programming assignments allow a large variety of solutions. Assessing student programs through structural similarity is only feasible if the diversity in the solution space can be addressed. This study narrows program diversity through a set of semantic preserving program transformations that convert programs into a normal form. The application of the Weighted Assignment Similarity measure to marking student programs is investigated, and strong correlations are found with the human marker. It is shown that the most accurate assessment requires that programs not only be compared with a set of good solutions, but rather a mixed set of programs of varying levels of correctness. This research represents the first documented successful application of structural similarity to the marking of student programs.
- Full Text:
- Date Issued: 2007
- Authors: Naude, Kevin Alexander
- Date: 2007
- Subjects: Computer networks -- Security measures , Internet -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10478 , http://hdl.handle.net/10948/578 , Computer networks -- Security measures , Internet -- Security measures
- Description: Learning to write software requires much practice and frequent assessment. Consequently, the use of computers to assist in the assessment of computer programs has been important in supporting large classes at universities. The main approaches to the problem are dynamic analysis (testing student programs for expected output) and static analysis (direct analysis of the program code). The former is very sensitive to all kinds of errors in student programs, while the latter has traditionally only been used to assess quality, and not correctness. This research focusses on the application of static analysis, particularly structural similarity, to marking student programs. Existing traditional measures of similarity are limiting in that they are usually only effective on tree structures. In this regard they do not easily support dependencies in program code. Contemporary measures of structural similarity, such as similarity flooding, usually rely on an internal normalisation of scores. The effect is that the scores only have relative meaning, and cannot be interpreted in isolation, ie. they are not meaningful for assessment. The SimRank measure is shown to have the same problem, but not because of normalisation. The problem with the SimRank measure arises from the fact that its scores depend on all possible mappings between the children of vertices being compared. The main contribution of this research is a novel graph similarity measure, the Weighted Assignment Similarity measure. It is related to SimRank, but derives propagation scores from only the locally optimal mapping between child vertices. The resulting similarity scores may be regarded as the percentage of mutual coverage between graphs. The measure is proven to converge for all directed acyclic graphs, and an efficient implementation is outlined for this case. Attributes on graph vertices and edges are often used to capture domain specific information which is not structural in nature. It has been suggested that these should influence the similarity propagation, but no clear method for doing this has been reported. The second important contribution of this research is a general method for incorporating these local attribute similarities into the larger similarity propagation method. An example of attributes in program graphs are identifier names. The choice of identifiers in programs is arbitrary as they are purely symbolic. A problem facing any comparison between programs is that they are unlikely to use the same set of identifiers. This problem indicates that a mapping between the identifier sets is required. The third contribution of this research is a method for applying the structural similarity measure in a two step process to find an optimal identifier mapping. This approach is both novel and valuable as it cleverly reuses the similarity measure as an existing resource. In general, programming assignments allow a large variety of solutions. Assessing student programs through structural similarity is only feasible if the diversity in the solution space can be addressed. This study narrows program diversity through a set of semantic preserving program transformations that convert programs into a normal form. The application of the Weighted Assignment Similarity measure to marking student programs is investigated, and strong correlations are found with the human marker. It is shown that the most accurate assessment requires that programs not only be compared with a set of good solutions, but rather a mixed set of programs of varying levels of correctness. This research represents the first documented successful application of structural similarity to the marking of student programs.
- Full Text:
- Date Issued: 2007
Characterisation of InAs-based epilayers by FTIR spectroscopy
- Authors: Baisitse, Tshepiso Revonia
- Date: 2007
- Subjects: Fourier transform infrared spectroscopy , Gallium arsenide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10534 , http://hdl.handle.net/10948/474 , Fourier transform infrared spectroscopy , Gallium arsenide semiconductors
- Description: This study focuses on the characterization of InAs and InAs1-xSbx epitaxial layers by infrared reflectance and transmittance spectroscopy and Hall measurements. Reflectance measurements were performed in order to obtain the dielectric parameters and to extract from these information about the electrical properties (mobility and carrier concentration) of this important III-V material system. The transmittance measurements were used to determine the bandgap of InAsSb. Infrared reflectivity and transmittance measurements were performed in the wavelength range 200 – 2000 cm-1 on InAs and InAsSb layers grown on three types of substrates. A classical two oscillator model that takes into account both the free carriers and the lattice, was used to analyse the reflectance data using the BMDP® computer curve fitting software. The dielectric parameters and the electrical properties (carrier concentration and mobility) were extracted from the simulations. Due to the low free carrier concentration in the epitaxial structures, the plasma resonance frequency (ωp) values obtained from the simulations of reflectance spectra measured above 200 cm-1, were in the order of 20-30 cm-1. These low values were confirmed by direct measurements of ωp in reflectance spectra obtained in the range 15-200 cm-1. The simulated carrier concentration and mobility values determined optically were compared to the values determined by Hall measurements at room temperature and previously reported values by other researchers. The simulated values obtained were in reasonable agreement with the Hall values. The simulated and measured carrier concentrations obtained for InAs layers were significantly higher than the intrinsic carrier concentration for InAs at room temperature, indicating notable concentrations of donors resulting from the growth process.
- Full Text:
- Date Issued: 2007
- Authors: Baisitse, Tshepiso Revonia
- Date: 2007
- Subjects: Fourier transform infrared spectroscopy , Gallium arsenide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10534 , http://hdl.handle.net/10948/474 , Fourier transform infrared spectroscopy , Gallium arsenide semiconductors
- Description: This study focuses on the characterization of InAs and InAs1-xSbx epitaxial layers by infrared reflectance and transmittance spectroscopy and Hall measurements. Reflectance measurements were performed in order to obtain the dielectric parameters and to extract from these information about the electrical properties (mobility and carrier concentration) of this important III-V material system. The transmittance measurements were used to determine the bandgap of InAsSb. Infrared reflectivity and transmittance measurements were performed in the wavelength range 200 – 2000 cm-1 on InAs and InAsSb layers grown on three types of substrates. A classical two oscillator model that takes into account both the free carriers and the lattice, was used to analyse the reflectance data using the BMDP® computer curve fitting software. The dielectric parameters and the electrical properties (carrier concentration and mobility) were extracted from the simulations. Due to the low free carrier concentration in the epitaxial structures, the plasma resonance frequency (ωp) values obtained from the simulations of reflectance spectra measured above 200 cm-1, were in the order of 20-30 cm-1. These low values were confirmed by direct measurements of ωp in reflectance spectra obtained in the range 15-200 cm-1. The simulated carrier concentration and mobility values determined optically were compared to the values determined by Hall measurements at room temperature and previously reported values by other researchers. The simulated values obtained were in reasonable agreement with the Hall values. The simulated and measured carrier concentrations obtained for InAs layers were significantly higher than the intrinsic carrier concentration for InAs at room temperature, indicating notable concentrations of donors resulting from the growth process.
- Full Text:
- Date Issued: 2007
Consistent testing for lag length in cointegrated relationships
- Authors: Liu, Limin
- Date: 2007
- Subjects: Cointegration -- South Africa , Econometrics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10575 , http://hdl.handle.net/10948/547 , http://hdl.handle.net/10948/d1011715 , Cointegration -- South Africa , Econometrics
- Description: In the past few decades the theory of cointegration has been widely used in the empirical analysis of economic data. The reason is that, it captures the economic notion of a long-run economic relation. One of the problems experienced when applying cointegrated techniques to econometric modelling is the determination of lag lengths for the modelled variables. Applied studies have resulted in contradictory choices for lag length selection. This study reviews and compares some of the well-known information criteria using simulation techniques for bivariate models.
- Full Text:
- Date Issued: 2007
- Authors: Liu, Limin
- Date: 2007
- Subjects: Cointegration -- South Africa , Econometrics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10575 , http://hdl.handle.net/10948/547 , http://hdl.handle.net/10948/d1011715 , Cointegration -- South Africa , Econometrics
- Description: In the past few decades the theory of cointegration has been widely used in the empirical analysis of economic data. The reason is that, it captures the economic notion of a long-run economic relation. One of the problems experienced when applying cointegrated techniques to econometric modelling is the determination of lag lengths for the modelled variables. Applied studies have resulted in contradictory choices for lag length selection. This study reviews and compares some of the well-known information criteria using simulation techniques for bivariate models.
- Full Text:
- Date Issued: 2007
Cytokine properties of CD23 on human Eosinophilic cells
- Authors: Ferreira, Lauren
- Date: 2007
- Subjects: Cytokines , CD23 antigen , Eosinophil
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10333 , http://hdl.handle.net/10948/503 , http://hdl.handle.net/10948/d1012001 , Cytokines , CD23 antigen , Eosinophil
- Description: CD23, the low affinity IgE receptor, is expressed by various cell types and has numerous functions depending on the form of the protein, its interaction with various ligands and the type of cell involved. CD23 is pivotal in the regulation of IgE, with the soluble form involved in up-regulation, while the membrane bound form is involved in the down-regulation. It is clear why it is believed to be a central molecule in allergic responses, and a therapeutic target for the treatment of allergic disease. In this study a recombinant form of the entire extracellular domain of the protein, exCD23, was produced by PCR cloning and expressed in E. coli. His•Tag™s were introduced onto the C-terminus and N-terminus, respectively, in order to simplify the purification procedure. After renaturation and purification, the recombinant exCD23 bound IgE, indicating its activity. From the IgE binding studies it was established that the position of the tag did not influence the binding. GST•Tagged™ exCD23 was also produced in an attempt to increase the solubility of the recombinant protein, but this proved unsuccessful. Butyrate differentiated EoL-1 cells were treated with the Nterminal His•Tagged™ exCD23, and the protein appeared to suppress the secretion of the constitutively expressed cytokines, especially IL-8 and IFN- , when compared to untreated cells. In addition, treatment of the EoL-1 cells with exCD23 had a significant proliferative effect, but could not induce differentiation of this cell line into mature eosinophilic-like cells.
- Full Text:
- Date Issued: 2007
- Authors: Ferreira, Lauren
- Date: 2007
- Subjects: Cytokines , CD23 antigen , Eosinophil
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10333 , http://hdl.handle.net/10948/503 , http://hdl.handle.net/10948/d1012001 , Cytokines , CD23 antigen , Eosinophil
- Description: CD23, the low affinity IgE receptor, is expressed by various cell types and has numerous functions depending on the form of the protein, its interaction with various ligands and the type of cell involved. CD23 is pivotal in the regulation of IgE, with the soluble form involved in up-regulation, while the membrane bound form is involved in the down-regulation. It is clear why it is believed to be a central molecule in allergic responses, and a therapeutic target for the treatment of allergic disease. In this study a recombinant form of the entire extracellular domain of the protein, exCD23, was produced by PCR cloning and expressed in E. coli. His•Tag™s were introduced onto the C-terminus and N-terminus, respectively, in order to simplify the purification procedure. After renaturation and purification, the recombinant exCD23 bound IgE, indicating its activity. From the IgE binding studies it was established that the position of the tag did not influence the binding. GST•Tagged™ exCD23 was also produced in an attempt to increase the solubility of the recombinant protein, but this proved unsuccessful. Butyrate differentiated EoL-1 cells were treated with the Nterminal His•Tagged™ exCD23, and the protein appeared to suppress the secretion of the constitutively expressed cytokines, especially IL-8 and IFN- , when compared to untreated cells. In addition, treatment of the EoL-1 cells with exCD23 had a significant proliferative effect, but could not induce differentiation of this cell line into mature eosinophilic-like cells.
- Full Text:
- Date Issued: 2007
Depressive disorders and chronic comorbid disease states: a pharmacoepidemiological evaluation
- Authors: Kritiotis, Lia Costas
- Date: 2007
- Subjects: Depression, Mental , Child psychopathology , Adolescent psychopathology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10151 , http://hdl.handle.net/10948/653 , Depression, Mental , Child psychopathology , Adolescent psychopathology
- Description: The treatment of Depressive Disorders in patients with chronic comorbid disease states warrants careful consideration of the risk-benefit ratio pertaining to the pharmacokinetic and pharmacodynamic characteristics of the antidepressant being considered, against the physiological susceptibilities of the patient; potential drug-drug interactions and depressive symptoms. The primary aim of this study was to investigate the relationship between Depressive Disorders and the most frequently diagnosed chronic comorbid disease states in a depressed South African study population; and to comment on the appropriateness of antidepressants prescribed to these patients. This retrospective drug utilisation study consisted of two parts: the first part focused on the prevalence of the most frequently diagnosed chronic comorbidities in a depressed South African population (N = 21 171). The three most prevalent chronic comorbid disease states were Hypertension (52.87 percent), Lipid Disorders (20.40 percent) and Arthritis (16.70 percent). The second part of the study included an assessment of the antidepressants prescribed to depressed patients in 2004 (N = 6 150). Emphasis was placed on the suitability of antidepressants selected for depressed adult patients (18 years of age and older) with comorbid Hypertension, Lipid Disorders or Arthritis. SSRIs were prescribed most frequently to the depressed patients during 2004 (59.67 percent). SSRIs are the suggested first-line treatments for depressed patients with multiple chronic comorbid disease states. However, of the SSRIs, fluoxetine has the least favourable pharmacokinetic profile and was found to be the antidepressant prescribed most often. Amitriptyline, which was the TCA prescribed most frequently, produces the greatest degree of anticholinergic, sedative and hypotensive effects, relative to other agents in the same antidepressant class. Thus, it is not recommended as a first-line antidepressant, especially in depressed patients with comorbidities. This study identifies potential areas of intervention regarding antidepressant prescribing in depressed individuals with chronic comorbid disease states and offers recommendations to promote the selection of optimal, individualised drug treatment strategies for these patients.
- Full Text:
- Date Issued: 2007
- Authors: Kritiotis, Lia Costas
- Date: 2007
- Subjects: Depression, Mental , Child psychopathology , Adolescent psychopathology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10151 , http://hdl.handle.net/10948/653 , Depression, Mental , Child psychopathology , Adolescent psychopathology
- Description: The treatment of Depressive Disorders in patients with chronic comorbid disease states warrants careful consideration of the risk-benefit ratio pertaining to the pharmacokinetic and pharmacodynamic characteristics of the antidepressant being considered, against the physiological susceptibilities of the patient; potential drug-drug interactions and depressive symptoms. The primary aim of this study was to investigate the relationship between Depressive Disorders and the most frequently diagnosed chronic comorbid disease states in a depressed South African study population; and to comment on the appropriateness of antidepressants prescribed to these patients. This retrospective drug utilisation study consisted of two parts: the first part focused on the prevalence of the most frequently diagnosed chronic comorbidities in a depressed South African population (N = 21 171). The three most prevalent chronic comorbid disease states were Hypertension (52.87 percent), Lipid Disorders (20.40 percent) and Arthritis (16.70 percent). The second part of the study included an assessment of the antidepressants prescribed to depressed patients in 2004 (N = 6 150). Emphasis was placed on the suitability of antidepressants selected for depressed adult patients (18 years of age and older) with comorbid Hypertension, Lipid Disorders or Arthritis. SSRIs were prescribed most frequently to the depressed patients during 2004 (59.67 percent). SSRIs are the suggested first-line treatments for depressed patients with multiple chronic comorbid disease states. However, of the SSRIs, fluoxetine has the least favourable pharmacokinetic profile and was found to be the antidepressant prescribed most often. Amitriptyline, which was the TCA prescribed most frequently, produces the greatest degree of anticholinergic, sedative and hypotensive effects, relative to other agents in the same antidepressant class. Thus, it is not recommended as a first-line antidepressant, especially in depressed patients with comorbidities. This study identifies potential areas of intervention regarding antidepressant prescribing in depressed individuals with chronic comorbid disease states and offers recommendations to promote the selection of optimal, individualised drug treatment strategies for these patients.
- Full Text:
- Date Issued: 2007
Development of an antiretroviral solid dosage form using multivariate analysis
- Authors: Nqabeni, Luxolo
- Date: 2007
- Subjects: Analysis of variance , Experimental design , Multivariate analysis , Antiretroviral agents -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10145 , http://hdl.handle.net/10948/705 , Analysis of variance , Experimental design , Multivariate analysis , Antiretroviral agents -- South Africa
- Description: The aim of pharmaceutical development is to design a quality product and the manufacturing process to deliver the product in a reproducible manner. The development of a new and generic formulation is based on a large number of experiments. Statistics provides many tools for studying the conditions of formulations and processes and enables us to optimize the same while being able to minimize our experimentation. The purpose of this study was to apply experimental design methodology (DOE) and multivariate analysis to the development and optimization of tablet formulations containing 150 mg lamivudine manufactured by direct compression.
- Full Text:
- Date Issued: 2007
- Authors: Nqabeni, Luxolo
- Date: 2007
- Subjects: Analysis of variance , Experimental design , Multivariate analysis , Antiretroviral agents -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10145 , http://hdl.handle.net/10948/705 , Analysis of variance , Experimental design , Multivariate analysis , Antiretroviral agents -- South Africa
- Description: The aim of pharmaceutical development is to design a quality product and the manufacturing process to deliver the product in a reproducible manner. The development of a new and generic formulation is based on a large number of experiments. Statistics provides many tools for studying the conditions of formulations and processes and enables us to optimize the same while being able to minimize our experimentation. The purpose of this study was to apply experimental design methodology (DOE) and multivariate analysis to the development and optimization of tablet formulations containing 150 mg lamivudine manufactured by direct compression.
- Full Text:
- Date Issued: 2007
Elephant feeding behaviour and forage offtake implications in the Addo Elephant National Park
- Authors: Lessing, Joan Susanna
- Date: 2007
- Subjects: Elephants -- South Africa -- Addo Elephant National Park , Elephants -- Behavior , Addo Elephant National Park (South Africa) , Mammals -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10712 , http://hdl.handle.net/10948/542 , http://hdl.handle.net/10948/d1012016 , Elephants -- South Africa -- Addo Elephant National Park , Elephants -- Behavior , Addo Elephant National Park (South Africa) , Mammals -- Behavior
- Description: Elephants, as megaherbivores and keystone species have major impacts, both positive and negative, on ecosystems such as the Subtropical Thicket of the Eastern Cape. The feeding behaviour of elephants was quantified so as to firstly determine the preferred feeding heights of elephants, and secondly to determine if feeding behaviour and impact varies with size and sex. The preferred feeding height was determined with experimental feeding trials. Feeding height, pluck size, foraging rate and the proportion of plant material discarded were used to test for differences between elephants of different sizes and sexes in the Addo Elephant National Park. The influence of plant growth form on sex-specific feeding was also considered. Elephants preferred to feed at the lowest heights. The preferred feeding height was not related to body size. A wide range of feeding heights was recorded including and extending beyond, both the preferred and maximum feeding height of co-existing indigenous browsers. There was no difference in feeding height between the sizes and sexes. In free ranging conditions, all elephants fed at levels above the preferred foraging height when browsing. There was no difference in feeding behaviour between the different sized elephants, or between males and females. Adult elephants however exhibited larger ranges of feeding heights, pluck sizes, foraging rates and intake rates, including the maximum and minimum values. Growth form influenced the feeding of male and female elephants differently. Elephant feeding behaviour appears to limit opportunities for resource partitioning by way of feeding height segregation. Elephants are also capable of dominating the browse resources available to co-existing browsers by removing large amounts of forage at lower heights. The extent of elephant impact seems to be comparable between sizes and sexes, although adults and especially larger males are often able to use foraging opportunities that other elephants can not effectively utilize. Findings suggest that the feeding heights of elephants are determined by forage availability and reflect the diet in terms of browse or grass. The findings can be used, together with browse inventory methods, to determine browse resources available to elephants, and can also be used to develop monitoring tools to assess the impacts of elephants on plants.
- Full Text:
- Date Issued: 2007
- Authors: Lessing, Joan Susanna
- Date: 2007
- Subjects: Elephants -- South Africa -- Addo Elephant National Park , Elephants -- Behavior , Addo Elephant National Park (South Africa) , Mammals -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10712 , http://hdl.handle.net/10948/542 , http://hdl.handle.net/10948/d1012016 , Elephants -- South Africa -- Addo Elephant National Park , Elephants -- Behavior , Addo Elephant National Park (South Africa) , Mammals -- Behavior
- Description: Elephants, as megaherbivores and keystone species have major impacts, both positive and negative, on ecosystems such as the Subtropical Thicket of the Eastern Cape. The feeding behaviour of elephants was quantified so as to firstly determine the preferred feeding heights of elephants, and secondly to determine if feeding behaviour and impact varies with size and sex. The preferred feeding height was determined with experimental feeding trials. Feeding height, pluck size, foraging rate and the proportion of plant material discarded were used to test for differences between elephants of different sizes and sexes in the Addo Elephant National Park. The influence of plant growth form on sex-specific feeding was also considered. Elephants preferred to feed at the lowest heights. The preferred feeding height was not related to body size. A wide range of feeding heights was recorded including and extending beyond, both the preferred and maximum feeding height of co-existing indigenous browsers. There was no difference in feeding height between the sizes and sexes. In free ranging conditions, all elephants fed at levels above the preferred foraging height when browsing. There was no difference in feeding behaviour between the different sized elephants, or between males and females. Adult elephants however exhibited larger ranges of feeding heights, pluck sizes, foraging rates and intake rates, including the maximum and minimum values. Growth form influenced the feeding of male and female elephants differently. Elephant feeding behaviour appears to limit opportunities for resource partitioning by way of feeding height segregation. Elephants are also capable of dominating the browse resources available to co-existing browsers by removing large amounts of forage at lower heights. The extent of elephant impact seems to be comparable between sizes and sexes, although adults and especially larger males are often able to use foraging opportunities that other elephants can not effectively utilize. Findings suggest that the feeding heights of elephants are determined by forage availability and reflect the diet in terms of browse or grass. The findings can be used, together with browse inventory methods, to determine browse resources available to elephants, and can also be used to develop monitoring tools to assess the impacts of elephants on plants.
- Full Text:
- Date Issued: 2007
Endozoochory in the subtropical thicket: comparing effects of species with different digestive systems on seed fate
- Authors: Davis, Shavaughn
- Date: 2007
- Subjects: Seeds -- Dispersal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10714 , http://hdl.handle.net/10948/494 , http://hdl.handle.net/10948/d1012018 , Seeds -- Dispersal
- Description: Endozoochory is an important form of seed dispersal and as such plays a fundamental role in plant population and community ecology. This is especially true in the Subtropical Thicket biome where many plant species are adapted for endozoochory. Endozoochorous seed dispersal is carried out by a wide range of thicket fauna, but changes in the faunal assemblage associated with transformed thicket threatens to disrupt the process of endozoochorous seed dispersal and in turn the regeneration dynamics of thicket plants. Outside of conservation areas, indigenous seed dispersers are often replaced by domestic species, such as goats, which are hypothesized to differ in their seed dispersal efficiencies. The dispersal efficiencies of important thicket seed dispersers that occur in transformed and untransformed thicket were therefore investigated. The influence of gut morphologyphysiology on seed gut passage time, seed mortality and germination in animal species representing different digestive models was measured, as well as the role of black-backed jackal in thicket plant seed dispersal. Black-backed jackal were found to disperse the seeds of few thicket plant species and are therefore not considered important thicket seed dispersers under the climatic conditions prevailing during the study. The average gut passage time of seeds was found to differ significantly between birds and mammals, but not between elephants (hindgut fermentor), goats (ruminant) and pigs (omnivore, foregut fermentor) as was expected considering the differences in their digestive morphology. A significantly shorter gut passage of large seeds compared with small seeds was observed in goats, due to the regurgitation of larger seeds. Seed regurgitation in ruminants may prove to be an important factor contributing to their quality as seed dispersers in transformed thicket. The mortality of seeds was significantly higher in goats than in elephants, probably due to the efficient digestion associated with ruminants. The effect of gut passage on seed germination was not consistent and varied between animal species and across different thicket plant species. It was concluded that seed dispersers that occur in transformed and untransformed thicket differ in their seed dispersal efficiency due, in part, to differences in the nature of their digestive tracts. This has important implications for the process of seed dispersal in thicket, and the rehabilitation of degraded thicket vegetation.
- Full Text:
- Date Issued: 2007
- Authors: Davis, Shavaughn
- Date: 2007
- Subjects: Seeds -- Dispersal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10714 , http://hdl.handle.net/10948/494 , http://hdl.handle.net/10948/d1012018 , Seeds -- Dispersal
- Description: Endozoochory is an important form of seed dispersal and as such plays a fundamental role in plant population and community ecology. This is especially true in the Subtropical Thicket biome where many plant species are adapted for endozoochory. Endozoochorous seed dispersal is carried out by a wide range of thicket fauna, but changes in the faunal assemblage associated with transformed thicket threatens to disrupt the process of endozoochorous seed dispersal and in turn the regeneration dynamics of thicket plants. Outside of conservation areas, indigenous seed dispersers are often replaced by domestic species, such as goats, which are hypothesized to differ in their seed dispersal efficiencies. The dispersal efficiencies of important thicket seed dispersers that occur in transformed and untransformed thicket were therefore investigated. The influence of gut morphologyphysiology on seed gut passage time, seed mortality and germination in animal species representing different digestive models was measured, as well as the role of black-backed jackal in thicket plant seed dispersal. Black-backed jackal were found to disperse the seeds of few thicket plant species and are therefore not considered important thicket seed dispersers under the climatic conditions prevailing during the study. The average gut passage time of seeds was found to differ significantly between birds and mammals, but not between elephants (hindgut fermentor), goats (ruminant) and pigs (omnivore, foregut fermentor) as was expected considering the differences in their digestive morphology. A significantly shorter gut passage of large seeds compared with small seeds was observed in goats, due to the regurgitation of larger seeds. Seed regurgitation in ruminants may prove to be an important factor contributing to their quality as seed dispersers in transformed thicket. The mortality of seeds was significantly higher in goats than in elephants, probably due to the efficient digestion associated with ruminants. The effect of gut passage on seed germination was not consistent and varied between animal species and across different thicket plant species. It was concluded that seed dispersers that occur in transformed and untransformed thicket differ in their seed dispersal efficiency due, in part, to differences in the nature of their digestive tracts. This has important implications for the process of seed dispersal in thicket, and the rehabilitation of degraded thicket vegetation.
- Full Text:
- Date Issued: 2007
Field and laboratory measurements of PMD using interferometric techniques
- Authors: Mankga, Maphuti Comfort
- Date: 2007
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10531 , http://hdl.handle.net/10948/557 , Fiber optics , Polarization (Light)
- Description: In this study, the generalized and traditional interferometric techniques (GINTY and TINTY) are used to investigate some of the important aspects of Polarization Mode Dispersion (PMD) phenomenon in optical fibres. Measurements of PMD and chromatic dispersion (CD) are performed on buried optical fibre cable in the Pretoria Telkom’s metropolitan network. The upgradeability of this network was investigated, and it was observed that just over a half of the fibres are upgradeable to 10 Gb.s-1 transmissions. Long-haul aerial network in the Northern Cape was also tested for upgradeability to 10 Gb.s-1. It was found that 41 percent of the fibres tested are upgradeable to 10 Gb.s-1. Long-term monitoring showed that PMD varies rapidly in aerial fibres and, on the other hand, it is relatively stable in buried cables. Investigations on the accuracy of the techniques showed that polarization scrambling is essential for the reduction of the measurements uncertainties. Furthermore, it was observed that TINTY underestimates the single scan PMD distributions. The study on the effect of the change in mode coupling on various fibre configurations was performed, and fibres showed a reduction in PMD after the introduction of mode coupling. Measurements of PMD conducted in the laboratory on cabled fibre with low PMD showed the floor sensitivity of TINTY. Comparison between GINTY and Jones Matrix Eigeanalysis (JME) PMD measurements methods were performed on an emulator, and the results showed a good agreement in the measured PMD.
- Full Text:
- Date Issued: 2007
- Authors: Mankga, Maphuti Comfort
- Date: 2007
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10531 , http://hdl.handle.net/10948/557 , Fiber optics , Polarization (Light)
- Description: In this study, the generalized and traditional interferometric techniques (GINTY and TINTY) are used to investigate some of the important aspects of Polarization Mode Dispersion (PMD) phenomenon in optical fibres. Measurements of PMD and chromatic dispersion (CD) are performed on buried optical fibre cable in the Pretoria Telkom’s metropolitan network. The upgradeability of this network was investigated, and it was observed that just over a half of the fibres are upgradeable to 10 Gb.s-1 transmissions. Long-haul aerial network in the Northern Cape was also tested for upgradeability to 10 Gb.s-1. It was found that 41 percent of the fibres tested are upgradeable to 10 Gb.s-1. Long-term monitoring showed that PMD varies rapidly in aerial fibres and, on the other hand, it is relatively stable in buried cables. Investigations on the accuracy of the techniques showed that polarization scrambling is essential for the reduction of the measurements uncertainties. Furthermore, it was observed that TINTY underestimates the single scan PMD distributions. The study on the effect of the change in mode coupling on various fibre configurations was performed, and fibres showed a reduction in PMD after the introduction of mode coupling. Measurements of PMD conducted in the laboratory on cabled fibre with low PMD showed the floor sensitivity of TINTY. Comparison between GINTY and Jones Matrix Eigeanalysis (JME) PMD measurements methods were performed on an emulator, and the results showed a good agreement in the measured PMD.
- Full Text:
- Date Issued: 2007
Improving construction planning through 4D planning
- Authors: Allen, Christopher James
- Date: 2007
- Subjects: Construction industry -- Management , Construction industry -- Computer-aided design
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9698 , http://hdl.handle.net/10948/467 , http://hdl.handle.net/10948/d1011923 , Construction industry -- Management , Construction industry -- Computer-aided design
- Description: Construction Planning will increasingly play a more critical role within the realm of the Built Environment. Existing practices used to plan and communicate the construction process to be undertaken are failing to deliver the desired results for construction companies and clients alike. At a time of unprecedented growth in the industry around the world, which is leading to a general skills shortage, especially in management positions, construction planners are increasingly being asked to deal with more responsibility. As with other industries, technological improvement in the tools at their disposal is one way to address the inadequacies of the present situation. Increasingly, three dimensional design packages are being used to generate construction information which can then be used for quantities calculations, automated manufacturing processes and construction simulation. The latter forms the basis for their use in the process of planning, through new technologies being developed as virtual construction tools or 4D planning, the addition of time to the 3D model environment, but using the elements within the model as the basis for the construction programme. The benefit of using the design information to form the basis of the programme is that the interface tasks and logistical activities, as well as location related constraints, can be identified and then communicated to all levels within the construction team through a time based visual image. The purpose of this study is therefore to establish a scientifically analysed alternative method for the creation, review and delivery of construction programmes. In order to achieve the research objectives, three methodologies have been employed. Firstly, the literature review in the fields of planning including existing methodologies and previous research of 4D related techniques has been analysed. An overview of the perceived weaknesses to current practises and proposed solution will be explored and best case scenarios outlined and further investigated. Secondly, the 51 Lime Street project provides an environment in which the proposed 4D planning techniques have been implemented and the benefits of the process can, through observation / participation methodology, be validated. Thirdly, through interview questionnaires, with Lime St contractors and management, and e-mail questionnaires to a broader sample stratum, data on the ability of the tools, the techniques employed on 51 Lime Street and similar projects have been collated and statistically analysed to validate the reliability and relevance for future implementation. The result of the research will provide management teams with a practical alternative to existing planning methodologies. Construction planners will have alternative technique that can further enhance their role within the project team whilst increasing their ability to communicate the team’s vision to a wider audience, making them and the project more efficient and effective in the process. It has been proposed that clients insist on the use of 3D from the commencement of the design process so that this information can be passed downstream through the construction process and onto facilities management. Planners need to be able to communicate their requirements better and the 4D planning models provide both a more inclusive way of planning alongside a better communications medium in the form of moving images. A picture tells a thousand words.
- Full Text:
- Date Issued: 2007
- Authors: Allen, Christopher James
- Date: 2007
- Subjects: Construction industry -- Management , Construction industry -- Computer-aided design
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9698 , http://hdl.handle.net/10948/467 , http://hdl.handle.net/10948/d1011923 , Construction industry -- Management , Construction industry -- Computer-aided design
- Description: Construction Planning will increasingly play a more critical role within the realm of the Built Environment. Existing practices used to plan and communicate the construction process to be undertaken are failing to deliver the desired results for construction companies and clients alike. At a time of unprecedented growth in the industry around the world, which is leading to a general skills shortage, especially in management positions, construction planners are increasingly being asked to deal with more responsibility. As with other industries, technological improvement in the tools at their disposal is one way to address the inadequacies of the present situation. Increasingly, three dimensional design packages are being used to generate construction information which can then be used for quantities calculations, automated manufacturing processes and construction simulation. The latter forms the basis for their use in the process of planning, through new technologies being developed as virtual construction tools or 4D planning, the addition of time to the 3D model environment, but using the elements within the model as the basis for the construction programme. The benefit of using the design information to form the basis of the programme is that the interface tasks and logistical activities, as well as location related constraints, can be identified and then communicated to all levels within the construction team through a time based visual image. The purpose of this study is therefore to establish a scientifically analysed alternative method for the creation, review and delivery of construction programmes. In order to achieve the research objectives, three methodologies have been employed. Firstly, the literature review in the fields of planning including existing methodologies and previous research of 4D related techniques has been analysed. An overview of the perceived weaknesses to current practises and proposed solution will be explored and best case scenarios outlined and further investigated. Secondly, the 51 Lime Street project provides an environment in which the proposed 4D planning techniques have been implemented and the benefits of the process can, through observation / participation methodology, be validated. Thirdly, through interview questionnaires, with Lime St contractors and management, and e-mail questionnaires to a broader sample stratum, data on the ability of the tools, the techniques employed on 51 Lime Street and similar projects have been collated and statistically analysed to validate the reliability and relevance for future implementation. The result of the research will provide management teams with a practical alternative to existing planning methodologies. Construction planners will have alternative technique that can further enhance their role within the project team whilst increasing their ability to communicate the team’s vision to a wider audience, making them and the project more efficient and effective in the process. It has been proposed that clients insist on the use of 3D from the commencement of the design process so that this information can be passed downstream through the construction process and onto facilities management. Planners need to be able to communicate their requirements better and the 4D planning models provide both a more inclusive way of planning alongside a better communications medium in the form of moving images. A picture tells a thousand words.
- Full Text:
- Date Issued: 2007
In vitro testing to investigate the anticoagulant/antithrombotic and antidiabetic biological activity of Leonotis Leonurus
- Authors: Mnonopi, Nandipha Olivia
- Date: 2007
- Subjects: Leonotis leonurus -- Physiological aspects , Medicinal plants -- South Africa , Materia medica, Vegetable -- South Africa , Plant bioactive compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10331 , http://hdl.handle.net/10948/693 , Leonotis leonurus -- Physiological aspects , Medicinal plants -- South Africa , Materia medica, Vegetable -- South Africa , Plant bioactive compounds
- Description: The rising costs of prescription drugs in the maintenance of personal health and wellbeing have increased the interest in medicinal plants. The World Health Organization estimates that 65 percent-80 percent of the world’s population use traditional medicine as their primary form of health care. In this project the focus has been on the use of Leonotis leonurus extracts as a traditional medicine. The major chemical constituent of this plant is marrubiin, which is a diterpenoid labdane lactone formed from a precursor called premarrubiin. Aqueous and acetone extract (AL and OL extract, respectively) of this plant has been found to have an antithrombotic effect, with IC50 values of 3mg/ml and 6mg/ml, respectively. The extracts also have an effect on fibrinolysis, where the lysis time was decreased by more than 50 percent by the organic extract and standard marrubiin. In whole blood ADP-induced platelet aggregation, the organic extract inhibited aggregation by 68 percent at a final concentration of 138μg/ml (equivalent to 7.2μg/ml marrubiin). Marrubiin has also been screened for antithrombotic/anticoagulant activity; no antithrombotic activity has been observed but it increased the rate of fibrinolysis, by decreasing lysis time by 64 percent and also decreasing fibrin formation. From these findings it can be concluded that marrubiin has a fibrinolytic effect and antiplatelet aggregation effect. In the diabetic studies, in hyperglycemic condition, the OL (10μg/ml) extract and standard marrubiin significantly increased insulin secretion by 200 percent (2-fold) and 400 percent (4-fold), respectively, with respect to the control. The OL extract and standard marrubiin stimulated the release of insulin, the stimulatory index was significantly increased by 450 percent (4.5-fold) and 500 percent (5-fold), respectively, with respect to the control. In the apoptotic studies, in the normoglycemic and hyperglycemic conditions, the OL extract decreased the occurrence of apoptosis, in a dose-dependent manner, with the lower concentrations inducing apoptosis significantly higher than the relevant controls. Standard marrubiin did not have an effect on apoptosis in hyperglycemic condition, but it decreased the occurrence of apoptosis by 200 percent (2-fold) under normoglycemic conditions. The OL extract increased proliferation by 148 percent (1.48- fold) and 155 percent (1.55-fold) in normoglycemic and hyperglycemic conditions, respectively. The same effect was observed for standard marrubiin, where, proliferation was increased by 180 percent (1.8-fold) and 200 percent (2.0-fold) in normoglycemic and hyperglycemic conditions, respectively. RT-PCR displayed that standard marrubiin inhibited the expression of insulin by 50 percent under normoglycemic conditions.
- Full Text:
- Date Issued: 2007
- Authors: Mnonopi, Nandipha Olivia
- Date: 2007
- Subjects: Leonotis leonurus -- Physiological aspects , Medicinal plants -- South Africa , Materia medica, Vegetable -- South Africa , Plant bioactive compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10331 , http://hdl.handle.net/10948/693 , Leonotis leonurus -- Physiological aspects , Medicinal plants -- South Africa , Materia medica, Vegetable -- South Africa , Plant bioactive compounds
- Description: The rising costs of prescription drugs in the maintenance of personal health and wellbeing have increased the interest in medicinal plants. The World Health Organization estimates that 65 percent-80 percent of the world’s population use traditional medicine as their primary form of health care. In this project the focus has been on the use of Leonotis leonurus extracts as a traditional medicine. The major chemical constituent of this plant is marrubiin, which is a diterpenoid labdane lactone formed from a precursor called premarrubiin. Aqueous and acetone extract (AL and OL extract, respectively) of this plant has been found to have an antithrombotic effect, with IC50 values of 3mg/ml and 6mg/ml, respectively. The extracts also have an effect on fibrinolysis, where the lysis time was decreased by more than 50 percent by the organic extract and standard marrubiin. In whole blood ADP-induced platelet aggregation, the organic extract inhibited aggregation by 68 percent at a final concentration of 138μg/ml (equivalent to 7.2μg/ml marrubiin). Marrubiin has also been screened for antithrombotic/anticoagulant activity; no antithrombotic activity has been observed but it increased the rate of fibrinolysis, by decreasing lysis time by 64 percent and also decreasing fibrin formation. From these findings it can be concluded that marrubiin has a fibrinolytic effect and antiplatelet aggregation effect. In the diabetic studies, in hyperglycemic condition, the OL (10μg/ml) extract and standard marrubiin significantly increased insulin secretion by 200 percent (2-fold) and 400 percent (4-fold), respectively, with respect to the control. The OL extract and standard marrubiin stimulated the release of insulin, the stimulatory index was significantly increased by 450 percent (4.5-fold) and 500 percent (5-fold), respectively, with respect to the control. In the apoptotic studies, in the normoglycemic and hyperglycemic conditions, the OL extract decreased the occurrence of apoptosis, in a dose-dependent manner, with the lower concentrations inducing apoptosis significantly higher than the relevant controls. Standard marrubiin did not have an effect on apoptosis in hyperglycemic condition, but it decreased the occurrence of apoptosis by 200 percent (2-fold) under normoglycemic conditions. The OL extract increased proliferation by 148 percent (1.48- fold) and 155 percent (1.55-fold) in normoglycemic and hyperglycemic conditions, respectively. The same effect was observed for standard marrubiin, where, proliferation was increased by 180 percent (1.8-fold) and 200 percent (2.0-fold) in normoglycemic and hyperglycemic conditions, respectively. RT-PCR displayed that standard marrubiin inhibited the expression of insulin by 50 percent under normoglycemic conditions.
- Full Text:
- Date Issued: 2007
Isolation of bioactive metabolites with activity against HIV-1 target proteins from extracts of Sutherlandia frutescens and Lobostemon trigonus
- Authors: Dambuza, Ntokozo Shirley
- Date: 2007
- Subjects: Medicinal plants -- Africa, Southern , HIV infections -- Alternative treatment -- Africa, Southern , Plant bioactive compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10335 , http://hdl.handle.net/10948/492 , http://hdl.handle.net/10948/d1012003 , Medicinal plants -- Africa, Southern , HIV infections -- Alternative treatment -- Africa, Southern , Plant bioactive compounds
- Description: Acquired Immunodeficiency Syndrome (AIDS) is a human disease caused by the human immunodeficiency virus type 1 (HIV-1) and it is one of the biggest social, economic and health challenges in the world. The Joint United Nations Programme on HIV/AIDS (UNAIDS) and World Health Organization (WHO) estimated that between 33.4 to 46.0 million people around the world were living with HIV/AIDS in December 2005 and the highest estimates are in the Sub-Saharan Africa (around 25 million). In more developed countries a combined antiretroviral therapy called highly active antiretroviral therapy (HAART) is used, which results in reduced progression to AIDS in most patients. Despite the beneficial effects of HAART, significant side effects are experienced by treated patients. In addition, most infected people live in countries where the treatment is very expensive or, in many cases, not available at all. These people therefore rely on medicinal plants for health care. In this study, aqueous extracts from Sutherlandia frutescens and Lobostemon trigonus were screened for potential anti-HIV activities in a series of in vitro enzymatic assays, including reverse transcriptase, HIV-1 protease and glycohydrolases. Two extracts of Sutherlandia leaves (SFL-1 and SFL-2) were prepared that inhibited HIV reverse transcriptase and a Lobostemon leaf extract (LTL) was shown to also inhibit this enzyme. All extracts were assayed at 1.25mg/ml. Tannin content was determined for all active extracts using a tannic acid assay. SFL-1 and SFL-2 were found to contain about 6 percent and 7 percent tannins, respectively, and LTL contained 31% tannins by weight. Tannins were removed using polyamide columns and three fractions were collected for each. The extracts were also fractionated with Sephadex G-25, Amberlite IR 120 and Dowex 1-X8 as size exclusion, cation exchange and anion exchange, respectively. Extracts were also fractionated by preparative thin layer chromatography where two compounds were separated from S. frutescens extract with high activity against reverse transcriptase while showing insignificant inhibition towards other enzymes tested. SFL-BFW-10 and SFL-WEF-7 inhibited reverse transcriptase by almost 100 percent and the IC50 values calculated for these compounds were 0.34 and 0.23mg/ml, respectively. Cytotoxicity of these compounds was evaluated on Chang liver cells and peripheral blood mononuclear cells (PBMCs). None of these compounds showed any significant inhibition of cell proliferation. The purity of these compounds could not be confirmed because there was insufficient material to use in the techniques required to show purity and identification. Therefore, TLC was used to determine the nature of these compounds. SFL-BFW-10 was identified as an organic acid and SFL-WEF-7 was identified as flavonoid.
- Full Text:
- Date Issued: 2007
- Authors: Dambuza, Ntokozo Shirley
- Date: 2007
- Subjects: Medicinal plants -- Africa, Southern , HIV infections -- Alternative treatment -- Africa, Southern , Plant bioactive compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10335 , http://hdl.handle.net/10948/492 , http://hdl.handle.net/10948/d1012003 , Medicinal plants -- Africa, Southern , HIV infections -- Alternative treatment -- Africa, Southern , Plant bioactive compounds
- Description: Acquired Immunodeficiency Syndrome (AIDS) is a human disease caused by the human immunodeficiency virus type 1 (HIV-1) and it is one of the biggest social, economic and health challenges in the world. The Joint United Nations Programme on HIV/AIDS (UNAIDS) and World Health Organization (WHO) estimated that between 33.4 to 46.0 million people around the world were living with HIV/AIDS in December 2005 and the highest estimates are in the Sub-Saharan Africa (around 25 million). In more developed countries a combined antiretroviral therapy called highly active antiretroviral therapy (HAART) is used, which results in reduced progression to AIDS in most patients. Despite the beneficial effects of HAART, significant side effects are experienced by treated patients. In addition, most infected people live in countries where the treatment is very expensive or, in many cases, not available at all. These people therefore rely on medicinal plants for health care. In this study, aqueous extracts from Sutherlandia frutescens and Lobostemon trigonus were screened for potential anti-HIV activities in a series of in vitro enzymatic assays, including reverse transcriptase, HIV-1 protease and glycohydrolases. Two extracts of Sutherlandia leaves (SFL-1 and SFL-2) were prepared that inhibited HIV reverse transcriptase and a Lobostemon leaf extract (LTL) was shown to also inhibit this enzyme. All extracts were assayed at 1.25mg/ml. Tannin content was determined for all active extracts using a tannic acid assay. SFL-1 and SFL-2 were found to contain about 6 percent and 7 percent tannins, respectively, and LTL contained 31% tannins by weight. Tannins were removed using polyamide columns and three fractions were collected for each. The extracts were also fractionated with Sephadex G-25, Amberlite IR 120 and Dowex 1-X8 as size exclusion, cation exchange and anion exchange, respectively. Extracts were also fractionated by preparative thin layer chromatography where two compounds were separated from S. frutescens extract with high activity against reverse transcriptase while showing insignificant inhibition towards other enzymes tested. SFL-BFW-10 and SFL-WEF-7 inhibited reverse transcriptase by almost 100 percent and the IC50 values calculated for these compounds were 0.34 and 0.23mg/ml, respectively. Cytotoxicity of these compounds was evaluated on Chang liver cells and peripheral blood mononuclear cells (PBMCs). None of these compounds showed any significant inhibition of cell proliferation. The purity of these compounds could not be confirmed because there was insufficient material to use in the techniques required to show purity and identification. Therefore, TLC was used to determine the nature of these compounds. SFL-BFW-10 was identified as an organic acid and SFL-WEF-7 was identified as flavonoid.
- Full Text:
- Date Issued: 2007
MOCVD growth and electrical characterisation of InAs thin films
- Authors: Shamba, Precious
- Date: 2007
- Subjects: Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10527 , http://hdl.handle.net/10948/706 , Metal organic chemical vapor deposition
- Description: In this work, a systematic study relating the surface morphologies, electrical and structural properties of both doped and undoped InAs and InAsSb epitaxial films grown by metalorganic chemical vapour deposition (MOCVD) was undertaken. A comparative study using TBAs and AsH3 as the group V source in the growth of InAs revealed a considerable improvement, primarily in the electrical properties of InAs grown using TBAs with no significant difference in the surface morphology. InAs layers grown using TBAs, exhibited superior 77 K mobilities of up to 46 000 cm2/Vs, exceeding the best MOCVD data to date. The feasibility of tetraethyl tin (TESn) as an n-type dopant in InAs was to our knowledge investigated for the first time. The incorporation efficiency of this dopant was extensively studied as a function of substrate temperature, V/III ratio, substrate orientation and TESn flow rate. Results from this study show that the doping efficiency is temperature dependent and is not influenced by a variation of the V/III ratio or substrate orientation. Furthermore, Sn doping concentrations could be controlled over 2 orders of magnitude ranging between 2.7 x 1017 and 4.7 x 1019 cm-3 with 77 K mobilities ranging from 12 000 to 1300 cm2/Vs. The electrical properties of zinc doped InAs employing dimethyl zinc (DMZn) as the ptype dopant, were studied as a function of V/III ratio and substrate orientation. The effect of a variation of these parameters on the structural properties and surface morphology of InAs is also reported. The substrate orientation appears to have no influence on the Zn incorporation. An increase in Zn incorporation resulted in a deterioration of both the surface morphology and structural quality of the InAs layers. The incorporation efficiency of DMZn in InAsSb was studied as a function of growth temperature, V/III ratio and DMZn flow rate. A higher Zn incorporation was observed in InAsSb epitaxial layers grown at a lower temperature and V/III ratio as opposed to the layers grown at a higher temperature and V/III ratio. This study also revealed that the use of DMZn caused a dopant memory effect. A two-layer model proposed by Nedoluha and Koch (1952) was used to simulate the Hall measurements of Zn doped InAs and InAsSb in order to correct the shortcomings of conventional Hall measurements in determining the electrical properties exhibited by these materials.
- Full Text:
- Date Issued: 2007
- Authors: Shamba, Precious
- Date: 2007
- Subjects: Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10527 , http://hdl.handle.net/10948/706 , Metal organic chemical vapor deposition
- Description: In this work, a systematic study relating the surface morphologies, electrical and structural properties of both doped and undoped InAs and InAsSb epitaxial films grown by metalorganic chemical vapour deposition (MOCVD) was undertaken. A comparative study using TBAs and AsH3 as the group V source in the growth of InAs revealed a considerable improvement, primarily in the electrical properties of InAs grown using TBAs with no significant difference in the surface morphology. InAs layers grown using TBAs, exhibited superior 77 K mobilities of up to 46 000 cm2/Vs, exceeding the best MOCVD data to date. The feasibility of tetraethyl tin (TESn) as an n-type dopant in InAs was to our knowledge investigated for the first time. The incorporation efficiency of this dopant was extensively studied as a function of substrate temperature, V/III ratio, substrate orientation and TESn flow rate. Results from this study show that the doping efficiency is temperature dependent and is not influenced by a variation of the V/III ratio or substrate orientation. Furthermore, Sn doping concentrations could be controlled over 2 orders of magnitude ranging between 2.7 x 1017 and 4.7 x 1019 cm-3 with 77 K mobilities ranging from 12 000 to 1300 cm2/Vs. The electrical properties of zinc doped InAs employing dimethyl zinc (DMZn) as the ptype dopant, were studied as a function of V/III ratio and substrate orientation. The effect of a variation of these parameters on the structural properties and surface morphology of InAs is also reported. The substrate orientation appears to have no influence on the Zn incorporation. An increase in Zn incorporation resulted in a deterioration of both the surface morphology and structural quality of the InAs layers. The incorporation efficiency of DMZn in InAsSb was studied as a function of growth temperature, V/III ratio and DMZn flow rate. A higher Zn incorporation was observed in InAsSb epitaxial layers grown at a lower temperature and V/III ratio as opposed to the layers grown at a higher temperature and V/III ratio. This study also revealed that the use of DMZn caused a dopant memory effect. A two-layer model proposed by Nedoluha and Koch (1952) was used to simulate the Hall measurements of Zn doped InAs and InAsSb in order to correct the shortcomings of conventional Hall measurements in determining the electrical properties exhibited by these materials.
- Full Text:
- Date Issued: 2007
Multi-income level investment in golf estates
- Authors: Ngubeni, Steven Piet
- Date: 2007
- Subjects: Real estate development , Sustainable development -- South Africa , Housing development -- South Africa , Planned communities
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9694 , http://hdl.handle.net/10948/771 , Real estate development , Sustainable development -- South Africa , Housing development -- South Africa , Planned communities
- Description: The government of South African has stated its intentions to enforce a policy which will compel developers of upmarket residential properties to set aside 20 percent of their upmarket residential developments to accommodate affordable housing. The developers on the other hand, have expressed concerns about this approach. The principal aim of this study and of the research was to investigate the desirability of the concept of multi-income-level investment approach to the development of golf estates. A phenomenological strand of qualitative research method was used in the research. The following formed the focal point of the research: • An investigation into the perceptions of the stakeholders, especially the buyers of up-market properties, about mixed-income-level investments in golf estates. • The potential effect of the implementation of including affordable housing in the development of golf estates • An investigation of the perceived effect on the profitability of investments by the inclusion of affordable housing in golf estate properties. • The extent of the contribution of including affordable housing in golf estate developments to the reduction of the current backlog
- Full Text:
- Date Issued: 2007
- Authors: Ngubeni, Steven Piet
- Date: 2007
- Subjects: Real estate development , Sustainable development -- South Africa , Housing development -- South Africa , Planned communities
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9694 , http://hdl.handle.net/10948/771 , Real estate development , Sustainable development -- South Africa , Housing development -- South Africa , Planned communities
- Description: The government of South African has stated its intentions to enforce a policy which will compel developers of upmarket residential properties to set aside 20 percent of their upmarket residential developments to accommodate affordable housing. The developers on the other hand, have expressed concerns about this approach. The principal aim of this study and of the research was to investigate the desirability of the concept of multi-income-level investment approach to the development of golf estates. A phenomenological strand of qualitative research method was used in the research. The following formed the focal point of the research: • An investigation into the perceptions of the stakeholders, especially the buyers of up-market properties, about mixed-income-level investments in golf estates. • The potential effect of the implementation of including affordable housing in the development of golf estates • An investigation of the perceived effect on the profitability of investments by the inclusion of affordable housing in golf estate properties. • The extent of the contribution of including affordable housing in golf estate developments to the reduction of the current backlog
- Full Text:
- Date Issued: 2007