Social media reviews to investigate restaurant dinning experiences
- Authors: Van Achterbergh, Leon
- Subjects: Hospitality industry -- Social aspects , Restaurants -- Social aspects , Social media -- Economic aspects , Consumers -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9349 , http://hdl.handle.net/10948/d1021126
- Description: Restaurateurs often assume that customers' online reviews of their dining experiences are a reflection of their dining preferences. This study finds this assumption not to be true. Online written reviews do not explain diners’ preferred dining experiences. In this study post-experience reactions captured in reviews are shown to be contextually different to established dining preferences. Results show online reviews to be most important in facilitating customer dining expectations, but not influencing customers’ preferences in dining experiences. Evidence gathered during the secondary research shows that in general, social media has become the great marketing equaliser in commerce. In the dining industry, restaurants cannot solely rely on traditional media in the initial attraction and retention of dining customers. Continuous interaction between the business and customers is increasingly necessary for restaurateurs to remain competitive and in-touch with customers’ needs. This study concentrates its research area on the post-experience evaluation phase as found on review websites, like TripAdvisor. TripAdvisor has especially become a popular means to perpetuate word-of-mouth opinions of dining experiences among prospective customers. Research shows clear evidence of the importance of other's online opinions in the consumer decision-making process. The main variables of the study, namely customer experiences, restaurant dining and social media, are theoretically explored within the disciplines of service management and customer behaviour. These theories have laid a sound foundation for the subsequent research methods followed. The main purpose of the study was using social media reviews from TripAdvisor to investigate dining experiences in the restaurant industry. The outcomes desired were: firstly to advise the restaurant industry about superior customer practices, secondly emphasising the importance for industry of social media use in the dining experience, and thirdly rendering clarification on the experience perceptions of customers about factors that might lead to ‘delight’ and ‘frustration’. This research centralises the constructs of delight and frustration factors, which are typically extremely emotional dining experiences for the customer, that have the common element of surprise. Methodologically, the research required two phases: firstly, the qualitative analysis of online user-generated content by content analysis. The global sample consisted of seven international cities, which included the best, worst and average-rated TripAdvisor restaurant reviews. The content analysis produced the theoretical base for the dining perception variables used in the empirical survey. In the second phase of the study, the global surveys administered resulted in measuring the general public’s perceptions of the delight and frustration factors of dining experiences. Subsequently, the research process required various quantitative data analyses to reach substantial results with inferences. The results and interpreted findings achieved were twofold: Firstly, from the content analysis: customers regard service quality as relatively unimportant in relation to the holistic dining experience. Customers regarded food and beverage quality as crucial in the dining experience. Value for money increasingly becomes an issue as customers become more frustrated, more so than when the dining was generally experienced as pleasant. Secondly, from the empirical data: mood and aesthetics are essential, especially when diners chose between their favourite restaurants. Further results show managing the service basics for restaurants is essential; this included welcoming, professional, attentive and friendly service. Service consistency has also proven to be imperative in customers’ perceptions. Results further show that different nationalities could perceive food quality and service reliability differently. In addition, men and women could perceive food quality, mood and aesthetics, and value for money differently. This study recommends various findings to the restaurant industry: most importantly that the post-experience reviews are contextually different to customers’ dining preferences. The factor determining the reputation of a restaurant is food quality and not so much service quality. Value for money should be associated with a specific service or product feature for it to be of meaningful consequence to the restaurateur.
- Full Text:
- Authors: Van Achterbergh, Leon
- Subjects: Hospitality industry -- Social aspects , Restaurants -- Social aspects , Social media -- Economic aspects , Consumers -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9349 , http://hdl.handle.net/10948/d1021126
- Description: Restaurateurs often assume that customers' online reviews of their dining experiences are a reflection of their dining preferences. This study finds this assumption not to be true. Online written reviews do not explain diners’ preferred dining experiences. In this study post-experience reactions captured in reviews are shown to be contextually different to established dining preferences. Results show online reviews to be most important in facilitating customer dining expectations, but not influencing customers’ preferences in dining experiences. Evidence gathered during the secondary research shows that in general, social media has become the great marketing equaliser in commerce. In the dining industry, restaurants cannot solely rely on traditional media in the initial attraction and retention of dining customers. Continuous interaction between the business and customers is increasingly necessary for restaurateurs to remain competitive and in-touch with customers’ needs. This study concentrates its research area on the post-experience evaluation phase as found on review websites, like TripAdvisor. TripAdvisor has especially become a popular means to perpetuate word-of-mouth opinions of dining experiences among prospective customers. Research shows clear evidence of the importance of other's online opinions in the consumer decision-making process. The main variables of the study, namely customer experiences, restaurant dining and social media, are theoretically explored within the disciplines of service management and customer behaviour. These theories have laid a sound foundation for the subsequent research methods followed. The main purpose of the study was using social media reviews from TripAdvisor to investigate dining experiences in the restaurant industry. The outcomes desired were: firstly to advise the restaurant industry about superior customer practices, secondly emphasising the importance for industry of social media use in the dining experience, and thirdly rendering clarification on the experience perceptions of customers about factors that might lead to ‘delight’ and ‘frustration’. This research centralises the constructs of delight and frustration factors, which are typically extremely emotional dining experiences for the customer, that have the common element of surprise. Methodologically, the research required two phases: firstly, the qualitative analysis of online user-generated content by content analysis. The global sample consisted of seven international cities, which included the best, worst and average-rated TripAdvisor restaurant reviews. The content analysis produced the theoretical base for the dining perception variables used in the empirical survey. In the second phase of the study, the global surveys administered resulted in measuring the general public’s perceptions of the delight and frustration factors of dining experiences. Subsequently, the research process required various quantitative data analyses to reach substantial results with inferences. The results and interpreted findings achieved were twofold: Firstly, from the content analysis: customers regard service quality as relatively unimportant in relation to the holistic dining experience. Customers regarded food and beverage quality as crucial in the dining experience. Value for money increasingly becomes an issue as customers become more frustrated, more so than when the dining was generally experienced as pleasant. Secondly, from the empirical data: mood and aesthetics are essential, especially when diners chose between their favourite restaurants. Further results show managing the service basics for restaurants is essential; this included welcoming, professional, attentive and friendly service. Service consistency has also proven to be imperative in customers’ perceptions. Results further show that different nationalities could perceive food quality and service reliability differently. In addition, men and women could perceive food quality, mood and aesthetics, and value for money differently. This study recommends various findings to the restaurant industry: most importantly that the post-experience reviews are contextually different to customers’ dining preferences. The factor determining the reputation of a restaurant is food quality and not so much service quality. Value for money should be associated with a specific service or product feature for it to be of meaningful consequence to the restaurateur.
- Full Text:
Resource Allocation Framework in Fog Computing for the Internet of Things Environments
- Authors: Vambe, William Tichaona
- Date: 2020
- Subjects: Internet of things Cloud computing
- Language: English
- Type: Thesis , Doctoral , PhD (Computer Science)
- Identifier: http://hdl.handle.net/10353/18498 , vital:42575
- Description: Fog computing plays a pivotal role in the Internet of Things (IoT) ecosystem because of its ability to support delay-sensitive tasks, bringing resources from cloud servers closer to the “ground” and support IoT devices that are resource-constrained. Although fog computing offers some benefits such as quick response to requests, geo-distributed data processing and data processing in the proximity of the IoT devices, the exponential increase of IoT devices and large volumes of data being generated has led to a new set of challenges. One such problem is the allocation of resources to IoT tasks to match their computational needs and quality of service (QoS) requirements, whilst meeting both task deadlines and user expectations. Most proposed solutions in existing works suggest task offloading mechanisms where IoT devices would offload their tasks randomly to the fog layer or cloud layer. This helps in minimizing the communication delay; however, most tasks would end up missing their deadlines as many delays are experienced during offloading. This study proposes and introduces a Resource Allocation Scheduler (RAS) at the IoT-Fog gateway, whose goal is to decide where and when a task is to be offloaded, either to the fog layer, or the cloud layer based on their priority needs, computational needs and QoS requirements. The aim directly places work within the communication networks domain, in the transport layer of the Open Systems Interconnection (OSI) model. As such, this study follows the four phases of the top-down approach because of its reusability characteristics. To validate and test the efficiency and effectiveness of the RAS, the fog framework was implemented and evaluated in a simulated smart home setup. The essential metrics that were used to check if round-trip time was minimized are the queuing time, offloading time and throughput for QoS. The results showed that the RAS helps to reduce the round-trip time, increases throughput and leads to improved QoS. Furthermore, the approach addressed the starvation problem, a phenomenon that tends to affect low priority tasks. Most importantly, the results provides evidence that if resource allocation and assignment are appropriately done, round-trip time can be reduced and QoS can be improved in fog computing. The significant contribution of this research is the novel framework which minimizes round-trip time, addresses the starvation problem and improves QoS. Moreover, a literature reviewed paper which was regarded by reviewers as the first, as far as QoS in fog computing is concerned was produced.
- Full Text:
- Date Issued: 2020
- Authors: Vambe, William Tichaona
- Date: 2020
- Subjects: Internet of things Cloud computing
- Language: English
- Type: Thesis , Doctoral , PhD (Computer Science)
- Identifier: http://hdl.handle.net/10353/18498 , vital:42575
- Description: Fog computing plays a pivotal role in the Internet of Things (IoT) ecosystem because of its ability to support delay-sensitive tasks, bringing resources from cloud servers closer to the “ground” and support IoT devices that are resource-constrained. Although fog computing offers some benefits such as quick response to requests, geo-distributed data processing and data processing in the proximity of the IoT devices, the exponential increase of IoT devices and large volumes of data being generated has led to a new set of challenges. One such problem is the allocation of resources to IoT tasks to match their computational needs and quality of service (QoS) requirements, whilst meeting both task deadlines and user expectations. Most proposed solutions in existing works suggest task offloading mechanisms where IoT devices would offload their tasks randomly to the fog layer or cloud layer. This helps in minimizing the communication delay; however, most tasks would end up missing their deadlines as many delays are experienced during offloading. This study proposes and introduces a Resource Allocation Scheduler (RAS) at the IoT-Fog gateway, whose goal is to decide where and when a task is to be offloaded, either to the fog layer, or the cloud layer based on their priority needs, computational needs and QoS requirements. The aim directly places work within the communication networks domain, in the transport layer of the Open Systems Interconnection (OSI) model. As such, this study follows the four phases of the top-down approach because of its reusability characteristics. To validate and test the efficiency and effectiveness of the RAS, the fog framework was implemented and evaluated in a simulated smart home setup. The essential metrics that were used to check if round-trip time was minimized are the queuing time, offloading time and throughput for QoS. The results showed that the RAS helps to reduce the round-trip time, increases throughput and leads to improved QoS. Furthermore, the approach addressed the starvation problem, a phenomenon that tends to affect low priority tasks. Most importantly, the results provides evidence that if resource allocation and assignment are appropriately done, round-trip time can be reduced and QoS can be improved in fog computing. The significant contribution of this research is the novel framework which minimizes round-trip time, addresses the starvation problem and improves QoS. Moreover, a literature reviewed paper which was regarded by reviewers as the first, as far as QoS in fog computing is concerned was produced.
- Full Text:
- Date Issued: 2020
Customer relationship management in small to medium tourism enterprises (SMTEs) in the Eastern Cape Province
- Authors: Vallabh, Dinesh
- Date: 2014
- Subjects: Customer relations -- Management , Small business -- South Africa -- Eastern Cape , Tourism -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9322 , http://hdl.handle.net/10948/d1020797
- Description: The role of entrepreneurship in small to medium tourism enterprises is well recognised and acknowledged as a significant contributor to economic development and employment opportunities. Worldwide, small to medium tourism enterprises play a dominant role in the tourism industry. These businesses are often vulnerable to external economic forces and find it increasingly difficult to transform their strategic and operational management to face the challenges placed upon them. This study focuses on small to medium tourism enterprises in the Eastern Cape Province, which is economically the poorest province of South Africa. To ensure the growth and sustainability of small to medium tourism enterprises, owners need to make efficient and effective business decisions regarding the challenges their businesses face. The study examines the factors impacting customer relationship management in the context of small to medium tourism enterprises in the Eastern Cape. Customer relationship management, that is, building relationships with customers, has become of pivotal importance to many organisations as businesses strive to be competitive and profitable. While large organisations practice customer relationship management to enable them to better target profitable customers, improve customer services, enhance customer retention and ultimately improve business performance, small businesses often need assistance in understanding and effecting this complex relationship. The factors that could impact customer relationship management in the organisations are the focus of this study. Three major factors were identified, namely, strategic, operational, and organisational factors. The study furthermore examined the extent to which these factors are present in the tourism and hospitality sector of the Eastern Cape and investigated the relationships between these factors. Quantitative research was deemed appropriate for this study. Systematic random sampling was employed to select a sample of 332 respondent organisations from the 2012 database of the Eastern Cape Parks and Tourism Agency consisting of formally registered small to medium tourism enterprises. A total of 310 usable questionnaires were finally obtained. Both descriptive and inferential statistics were used in the study. Descriptive statistics were computed to reflect the organisations‟ and respondent managers‟ general characteristics and to summarise their measurement scores. Using inferential statistics, the study further investigated relationships between customer relationship management factors, as well as demographic factors. Data were subjected to exploratory factor analysis and both the validity (refer to section 2.10.1) and reliability (refer to section 2.10.2) of the research instrument was assessed. The relationships between customer relationship management variables were also investigated (refer to section 2.11.4). The research results support an overall significant association between customer relationship management readiness and business strategy, customer strategy, touch points and competencies, skills and technology. Relationships were also explored among customer relationship management factors and demographic characteristics. Significant results were found between perceived business performance and the gender of managers, family businesses and gross annual turnover. The most salient contributions of this research can be summarised as follows. The overview of the importance of tourism and the role of small to medium enterprises in the tourism and hospitality industry of the Eastern Cape will benefit researchers and potential owners who have an interest in this sector. The study contributes to an improved understanding of the factors that should precede customer relationship management. The study established a profile of the small to medium tourism enterprises in the Eastern Cape which can serve as a basis for future research. A measuring instrument for assessing respondents‟ views on the existence of the strategic, operational and organisational factors in their organisations was developed. This instrument showed good internal validity and reliability and can serve as a basis for the same purpose in contexts other than the tourism and hospitality sector. This research has made a contribution toward a largely under-researched area concerning customer relationship management in small to medium enterprises. Recommendations for managers and consideration of future research included the following. Managers need to have a strategic vision and a strong customer-centric focus. Through understanding customers and their needs, offerings can be tailored to maximize the overall value of customers, thereby, improving business performance. Through efficient operational processes in place, enhanced customer service levels can be attained in the organisations. Managers need to effectively manage customer information through data warehousing and technology. Top management commitment is a crucial element for ensuring improved customer services. Managers need to train staff with respect to customer services, thus enhancing CRM. Future researchers can conduct a longitudinal study and investigate the same factors which could impact customer relationship management. A verification of the usefulness of the measuring instrument in examining the determinants of customer relationship management and the level of development regarding other small businesses is suggested. It is recommended that this study be replicated abroad in an effort to verify to what extent the determinants of customer relationship management are evident in small businesses of other countries.
- Full Text:
- Date Issued: 2014
- Authors: Vallabh, Dinesh
- Date: 2014
- Subjects: Customer relations -- Management , Small business -- South Africa -- Eastern Cape , Tourism -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9322 , http://hdl.handle.net/10948/d1020797
- Description: The role of entrepreneurship in small to medium tourism enterprises is well recognised and acknowledged as a significant contributor to economic development and employment opportunities. Worldwide, small to medium tourism enterprises play a dominant role in the tourism industry. These businesses are often vulnerable to external economic forces and find it increasingly difficult to transform their strategic and operational management to face the challenges placed upon them. This study focuses on small to medium tourism enterprises in the Eastern Cape Province, which is economically the poorest province of South Africa. To ensure the growth and sustainability of small to medium tourism enterprises, owners need to make efficient and effective business decisions regarding the challenges their businesses face. The study examines the factors impacting customer relationship management in the context of small to medium tourism enterprises in the Eastern Cape. Customer relationship management, that is, building relationships with customers, has become of pivotal importance to many organisations as businesses strive to be competitive and profitable. While large organisations practice customer relationship management to enable them to better target profitable customers, improve customer services, enhance customer retention and ultimately improve business performance, small businesses often need assistance in understanding and effecting this complex relationship. The factors that could impact customer relationship management in the organisations are the focus of this study. Three major factors were identified, namely, strategic, operational, and organisational factors. The study furthermore examined the extent to which these factors are present in the tourism and hospitality sector of the Eastern Cape and investigated the relationships between these factors. Quantitative research was deemed appropriate for this study. Systematic random sampling was employed to select a sample of 332 respondent organisations from the 2012 database of the Eastern Cape Parks and Tourism Agency consisting of formally registered small to medium tourism enterprises. A total of 310 usable questionnaires were finally obtained. Both descriptive and inferential statistics were used in the study. Descriptive statistics were computed to reflect the organisations‟ and respondent managers‟ general characteristics and to summarise their measurement scores. Using inferential statistics, the study further investigated relationships between customer relationship management factors, as well as demographic factors. Data were subjected to exploratory factor analysis and both the validity (refer to section 2.10.1) and reliability (refer to section 2.10.2) of the research instrument was assessed. The relationships between customer relationship management variables were also investigated (refer to section 2.11.4). The research results support an overall significant association between customer relationship management readiness and business strategy, customer strategy, touch points and competencies, skills and technology. Relationships were also explored among customer relationship management factors and demographic characteristics. Significant results were found between perceived business performance and the gender of managers, family businesses and gross annual turnover. The most salient contributions of this research can be summarised as follows. The overview of the importance of tourism and the role of small to medium enterprises in the tourism and hospitality industry of the Eastern Cape will benefit researchers and potential owners who have an interest in this sector. The study contributes to an improved understanding of the factors that should precede customer relationship management. The study established a profile of the small to medium tourism enterprises in the Eastern Cape which can serve as a basis for future research. A measuring instrument for assessing respondents‟ views on the existence of the strategic, operational and organisational factors in their organisations was developed. This instrument showed good internal validity and reliability and can serve as a basis for the same purpose in contexts other than the tourism and hospitality sector. This research has made a contribution toward a largely under-researched area concerning customer relationship management in small to medium enterprises. Recommendations for managers and consideration of future research included the following. Managers need to have a strategic vision and a strong customer-centric focus. Through understanding customers and their needs, offerings can be tailored to maximize the overall value of customers, thereby, improving business performance. Through efficient operational processes in place, enhanced customer service levels can be attained in the organisations. Managers need to effectively manage customer information through data warehousing and technology. Top management commitment is a crucial element for ensuring improved customer services. Managers need to train staff with respect to customer services, thus enhancing CRM. Future researchers can conduct a longitudinal study and investigate the same factors which could impact customer relationship management. A verification of the usefulness of the measuring instrument in examining the determinants of customer relationship management and the level of development regarding other small businesses is suggested. It is recommended that this study be replicated abroad in an effort to verify to what extent the determinants of customer relationship management are evident in small businesses of other countries.
- Full Text:
- Date Issued: 2014
Rainfall variability in Southern Africa, its influences on streamflow variations and its relationships with climatic variations
- Authors: Valimba, Patrick
- Date: 2005
- Subjects: Rain and rainfall -- Africa, Southern Climatic changes -- Africa, Southern Streamflow -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6030 , http://hdl.handle.net/10962/d1006159
- Description: Hydrological variability involving rainfall and streamflows in southern Africa have been often studied separately or have used cumulative rainfall and streamflow indices. The main objective of this study was to investigate spatio-temporal variations of rainfall, their influences on streamflows and their relationships with climatic variations with emphasis on indices that characterise the hydrological extremes, floods and droughts. It was found that 60-70% of the time when it rains, daily rainfalls are below their long-term averages and daily amounts below 10 mm are the most frequent in southern Africa. Spatially, climatologies of rainfall sub-divided the southern African subcontinent into the dry western/southwestern part and the “humid” eastern and northern part. The daily amounts below 20 mm contribute significantly to annual rainfall amounts in the dry part while all types of daily rainfall exceeding 1 mm have comparable contributions in the humid part. The climatologies indicated the highest likelihood of experiencing intense daily events during the core of the wet seasons with the highest frequencies in central Mozambique and the southern highlands of Tanzania. Interannual variations of rainfall indicated that significant changes had occurred between the late-1940s and early-1980s, particularly in the 1970s. The changes in rainfall were more evident in the number of daily rainfall events than in rainfall amounts, led generally to increasing early summer and decreased late summer rainfall. It was also found that intra-seasonal dry day sequences were an important parameter in the definition of a rainy season’s onset and end in southern Africa apart from rainfall amounts. Interannual variations of the rainy season characteristics (onset, end, duration) followed the variations of rainfall amounts and number of events. The duration of the rainy season was affected by the onset (Tanzania), onset or end (tropical southern Africa - southwestern highlands of Tanzania, Zambia, northern Zimbabwe and central Mozambique) and end (the remaing part of southern Africa). Flow duration curves (FDCs) identified three types of rivers (ephemeral, seasonal and perennial) in southern Africa with ephemeral rivers found mainly in the dry western part of the region. Seasonal streamflow patterns followed those of rainfall while interannual streamflow variations indicated significant changes of mean flows with little evidences of high and low flow regime changes except in Namibia and some parts of northern Zimbabwe. It was, however, not possible to provide strong links between the identified changes in streamflows and those in rainfall. Regarding the influences of climate variability on hydrological variability in southern Africa, rainfall variations in southern Africa were found to be influenced strongly by ENSO and SST in the tropical Indian ocean and moderately by SST in the south Madagascar basin. The influence of ENSO was consistent for all types of daily rainfall and peaks for the light and moderate (< 20 mm) events in the southern part and for the intense events in the northern part. SST in the tropical Indian ocean influence the light and moderate events while SST close to the region influence the heavy events. However, the relationships experienced significant changes in the mid-1950s and in the 1970s. The former changes led to improved associations while the latter deteriorated or reversed the relationships. The influences of climatic variables on streamflows and rainy season characteristics were inferred from the rainfall-streamflow and rainfall-climatic variables relationships.
- Full Text:
- Date Issued: 2005
- Authors: Valimba, Patrick
- Date: 2005
- Subjects: Rain and rainfall -- Africa, Southern Climatic changes -- Africa, Southern Streamflow -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6030 , http://hdl.handle.net/10962/d1006159
- Description: Hydrological variability involving rainfall and streamflows in southern Africa have been often studied separately or have used cumulative rainfall and streamflow indices. The main objective of this study was to investigate spatio-temporal variations of rainfall, their influences on streamflows and their relationships with climatic variations with emphasis on indices that characterise the hydrological extremes, floods and droughts. It was found that 60-70% of the time when it rains, daily rainfalls are below their long-term averages and daily amounts below 10 mm are the most frequent in southern Africa. Spatially, climatologies of rainfall sub-divided the southern African subcontinent into the dry western/southwestern part and the “humid” eastern and northern part. The daily amounts below 20 mm contribute significantly to annual rainfall amounts in the dry part while all types of daily rainfall exceeding 1 mm have comparable contributions in the humid part. The climatologies indicated the highest likelihood of experiencing intense daily events during the core of the wet seasons with the highest frequencies in central Mozambique and the southern highlands of Tanzania. Interannual variations of rainfall indicated that significant changes had occurred between the late-1940s and early-1980s, particularly in the 1970s. The changes in rainfall were more evident in the number of daily rainfall events than in rainfall amounts, led generally to increasing early summer and decreased late summer rainfall. It was also found that intra-seasonal dry day sequences were an important parameter in the definition of a rainy season’s onset and end in southern Africa apart from rainfall amounts. Interannual variations of the rainy season characteristics (onset, end, duration) followed the variations of rainfall amounts and number of events. The duration of the rainy season was affected by the onset (Tanzania), onset or end (tropical southern Africa - southwestern highlands of Tanzania, Zambia, northern Zimbabwe and central Mozambique) and end (the remaing part of southern Africa). Flow duration curves (FDCs) identified three types of rivers (ephemeral, seasonal and perennial) in southern Africa with ephemeral rivers found mainly in the dry western part of the region. Seasonal streamflow patterns followed those of rainfall while interannual streamflow variations indicated significant changes of mean flows with little evidences of high and low flow regime changes except in Namibia and some parts of northern Zimbabwe. It was, however, not possible to provide strong links between the identified changes in streamflows and those in rainfall. Regarding the influences of climate variability on hydrological variability in southern Africa, rainfall variations in southern Africa were found to be influenced strongly by ENSO and SST in the tropical Indian ocean and moderately by SST in the south Madagascar basin. The influence of ENSO was consistent for all types of daily rainfall and peaks for the light and moderate (< 20 mm) events in the southern part and for the intense events in the northern part. SST in the tropical Indian ocean influence the light and moderate events while SST close to the region influence the heavy events. However, the relationships experienced significant changes in the mid-1950s and in the 1970s. The former changes led to improved associations while the latter deteriorated or reversed the relationships. The influences of climatic variables on streamflows and rainy season characteristics were inferred from the rainfall-streamflow and rainfall-climatic variables relationships.
- Full Text:
- Date Issued: 2005
An exploration of the prior conceptual understanding of measurement of first year national certificate (vocational) Engineering students
- Authors: Vale, Pamela
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/8033 , vital:21337
- Description: Measurement is acknowledged to be a critical component in mathematics education and is particularly important for vocational Engineering students, for whom this is a key skill required in the workplace. The goal of this research was to explore the existing measurement conceptualisations of vocational Engineering students at the outset of their course, as evident in their engagement with mediated measurement tasks. The focus on students’ prior knowledge in measurement, was for the value that this awareness holds in understanding the learning needs of the students. Students participated in five measurement tasks. Four took the form of dynamically assessed task-based interviews, and the fifth was a written test assessing what they had learned during their Mathematics classes. Domains of measurement that were assessed in these tasks included length, area, surface area, volume and flow rate. The interviewer took the role of mediator and students were assessed according to the number of moments of mediation and the degree of mediation required to successfully complete the task. Students’ responsiveness to this mediation provided insight as to their conceptualisations of the measurements relevant to the task. This research was exploratory in nature and adopted an open and flexible approach to the data analysis. Critical incidents were identified and coded according to the mediation offered and the actions of the students during the measuring activity. This allowed patterns to emerge that revealed stable and emerging conceptualisations that related to embodied and symbolic aspects of measurement. Evidence was found that for many of these students the link between the embodied and symbolic aspects of the concept was broken. This insight allowed suggestions to be formulated about how better to facilitate these students’ learning of measurement.
- Full Text:
- Date Issued: 2017
- Authors: Vale, Pamela
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/8033 , vital:21337
- Description: Measurement is acknowledged to be a critical component in mathematics education and is particularly important for vocational Engineering students, for whom this is a key skill required in the workplace. The goal of this research was to explore the existing measurement conceptualisations of vocational Engineering students at the outset of their course, as evident in their engagement with mediated measurement tasks. The focus on students’ prior knowledge in measurement, was for the value that this awareness holds in understanding the learning needs of the students. Students participated in five measurement tasks. Four took the form of dynamically assessed task-based interviews, and the fifth was a written test assessing what they had learned during their Mathematics classes. Domains of measurement that were assessed in these tasks included length, area, surface area, volume and flow rate. The interviewer took the role of mediator and students were assessed according to the number of moments of mediation and the degree of mediation required to successfully complete the task. Students’ responsiveness to this mediation provided insight as to their conceptualisations of the measurements relevant to the task. This research was exploratory in nature and adopted an open and flexible approach to the data analysis. Critical incidents were identified and coded according to the mediation offered and the actions of the students during the measuring activity. This allowed patterns to emerge that revealed stable and emerging conceptualisations that related to embodied and symbolic aspects of measurement. Evidence was found that for many of these students the link between the embodied and symbolic aspects of the concept was broken. This insight allowed suggestions to be formulated about how better to facilitate these students’ learning of measurement.
- Full Text:
- Date Issued: 2017
Hop as an anti-cancer drug target
- Vaaltyn, Michaelone Chantelle
- Authors: Vaaltyn, Michaelone Chantelle
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/164704 , vital:41156 , doi:10.21504/10962/164704
- Description: Thesis (PhD)--Rhodes University, Biochemistry and Microbiology, 2020
- Full Text:
- Date Issued: 2020
- Authors: Vaaltyn, Michaelone Chantelle
- Date: 2020
- Subjects: Uncatalogued
- Language: English
- Type: thesis , text , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/164704 , vital:41156 , doi:10.21504/10962/164704
- Description: Thesis (PhD)--Rhodes University, Biochemistry and Microbiology, 2020
- Full Text:
- Date Issued: 2020
Aspects of the nutritional physiology and dietary requirements of juvenile and adult sharptooth catfish, Clarias Gariepinus (Pisces : clariidae)
- Authors: Uys, Wynand
- Date: 1990
- Subjects: Clariidae Catfishes Catfishes -- Nutrition-requirements Clarias
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5225 , http://hdl.handle.net/10962/d1005068
- Description: Past and current research on the biology and culture of the sharptooth catfish (Clarias gariepinus) has stimulated the development of its commercial production. At the inception of this project in 1985, it was decided that the development of an optimal dry feed was the most important step in developing a more complete culture technology for the species. The objectives of the project were, therefore, to investigate aspects of the nutritional physiology and dietary requirements of the species to provide the necessary information for the formulation of optimum economical feeds. A review of the natural feeding biology of the species provided valuable information with regard to its food preferences. From this information, and by estimating the nutritional composition of its preferred natural diet, it could be concluded that the animal requires a relatively high dietary protein content. This conclusion was substantiated by studies of the functional morphology of the digestive system (gross and fine structure). The characteristics of the digestive system and external anatomy were found to be typical of an opportunistic, omnivorous predator. The ontogenetic development of the digestive system is relatively fast, and enables the utilization of a variety of diets efficiently from an early stage. Since the ability of an animal to digest a given substance is predominantly dependent on the presence of appropriate enzymes the quantification and characterization of C. gariepinus digestive enzyme activities were investigated on an experimental basis. This work revealed that the animal has relatively high levels of digestive enzyme activities, and that its proteolytic enzyme activities correspond with those of other carnivorous fishes, while its starch digesting abilities correspond with those of specialized herbivores. Also, the high levels of lysozyme and alkaline phosphatase indicate an adaptation to detritivory, making this fish a truly opportunistic omnivore. Evidence was found to suggest that sharptooth catfish are able to re-absorb secreted digestive enzymes in the posterior section of its intestinal tract. It was shown that digestive enzyme activities were induced by food intake, and that no inherent rhythmicity in digestive activities seemed to occur. The development of digestive enzyme systems in the early life history of this animal was found to be also extremely rapid (complete within 10-16 days after hatching). It was also shown that artificial dry feed stimulates higher levels of digestive enzyme activities in larvae and juveniles than natural food. Although increased cellulase activity was found in larvae and juveniles that were fed on live zooplankton, the relative contribution of exogenous prey enzymes to protein digestion could not be ascertained. Specific nutritional requirements were investigated by means of feeding trials. The results of these trials confirmed the above indications regarding the dietary requirements of sharptooth catfish. It was concluded that for optimal growth and production performance, this animal requires a dietary protein content of 40-42%, a dietary lipid content of 10-12% and that diets should contain 14-16 kJ/g digestible energy. The optimum protein-to-energy ratio was found to be 26-29mg protein per kJ of digestible energy. Dietary requirements are evidently the same for juveniles and adults, except that younger fish require higher relative feeding levels. Finally, practical feed formulations were evaluated in terms of their economic feasibility. The results of these trials are presented along with recommendations on the formulation of commercial feeds for C. gariepinus. A computer program with which to implement least cost feed formulation by means of linear programming is provided.
- Full Text:
- Date Issued: 1990
- Authors: Uys, Wynand
- Date: 1990
- Subjects: Clariidae Catfishes Catfishes -- Nutrition-requirements Clarias
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5225 , http://hdl.handle.net/10962/d1005068
- Description: Past and current research on the biology and culture of the sharptooth catfish (Clarias gariepinus) has stimulated the development of its commercial production. At the inception of this project in 1985, it was decided that the development of an optimal dry feed was the most important step in developing a more complete culture technology for the species. The objectives of the project were, therefore, to investigate aspects of the nutritional physiology and dietary requirements of the species to provide the necessary information for the formulation of optimum economical feeds. A review of the natural feeding biology of the species provided valuable information with regard to its food preferences. From this information, and by estimating the nutritional composition of its preferred natural diet, it could be concluded that the animal requires a relatively high dietary protein content. This conclusion was substantiated by studies of the functional morphology of the digestive system (gross and fine structure). The characteristics of the digestive system and external anatomy were found to be typical of an opportunistic, omnivorous predator. The ontogenetic development of the digestive system is relatively fast, and enables the utilization of a variety of diets efficiently from an early stage. Since the ability of an animal to digest a given substance is predominantly dependent on the presence of appropriate enzymes the quantification and characterization of C. gariepinus digestive enzyme activities were investigated on an experimental basis. This work revealed that the animal has relatively high levels of digestive enzyme activities, and that its proteolytic enzyme activities correspond with those of other carnivorous fishes, while its starch digesting abilities correspond with those of specialized herbivores. Also, the high levels of lysozyme and alkaline phosphatase indicate an adaptation to detritivory, making this fish a truly opportunistic omnivore. Evidence was found to suggest that sharptooth catfish are able to re-absorb secreted digestive enzymes in the posterior section of its intestinal tract. It was shown that digestive enzyme activities were induced by food intake, and that no inherent rhythmicity in digestive activities seemed to occur. The development of digestive enzyme systems in the early life history of this animal was found to be also extremely rapid (complete within 10-16 days after hatching). It was also shown that artificial dry feed stimulates higher levels of digestive enzyme activities in larvae and juveniles than natural food. Although increased cellulase activity was found in larvae and juveniles that were fed on live zooplankton, the relative contribution of exogenous prey enzymes to protein digestion could not be ascertained. Specific nutritional requirements were investigated by means of feeding trials. The results of these trials confirmed the above indications regarding the dietary requirements of sharptooth catfish. It was concluded that for optimal growth and production performance, this animal requires a dietary protein content of 40-42%, a dietary lipid content of 10-12% and that diets should contain 14-16 kJ/g digestible energy. The optimum protein-to-energy ratio was found to be 26-29mg protein per kJ of digestible energy. Dietary requirements are evidently the same for juveniles and adults, except that younger fish require higher relative feeding levels. Finally, practical feed formulations were evaluated in terms of their economic feasibility. The results of these trials are presented along with recommendations on the formulation of commercial feeds for C. gariepinus. A computer program with which to implement least cost feed formulation by means of linear programming is provided.
- Full Text:
- Date Issued: 1990
The invertebrates of temporary rivers in the Eastern Cape, South Africa
- Authors: Uys, Amanda Cloete
- Date: 1998
- Subjects: Rivers -- South Africa -- Eastern Cape Stream ecology -- South Africa -- Eastern Cape Freshwater invertebrates -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5628 , http://hdl.handle.net/10962/d1004908
- Description: Temporary rivers in dryland regions are subject to highly variable and unpredictable rainfall and flow, and are considered unstable systems relative to perennial rivers of temperate zones. Little is known of the ecology of South Africa's temporary rivers, despite their abundance. The research presented focusses on the aquatic invertebrates inhabiting intermittently-flowing rivers in the 'arid corridor' of the Eastern Cape, South Africa. The major aims of the work were: to investigate which invertebrates inhabit these rivers, how the fauna is affected by environmental variability at various spatial and temporal scales, whether or not a characteristic fauna can be associated with these rivers or the hydrological phases which characterise them, and to establish to what extent faunal overlap occurs between different temporary rivers and between natural and modified temporary and perennial rivers. Research results indicate that the fauna of the Eastern Cape temporary rivers shows little structure at the scales of investigation, and that communities are generally non-equilibrial in character. The major forces shaping the biota are considered to be physical rather than biological, and the most important of these are: present and antecedent hydrological conditions and their duration; time of year; and biotope character, extent and heterogeneity. Three groups of fauna were identified as inhabitants of the temporary rivers: 'residents', 'facultative taxa' and 'opportunist colonists'. Taxa were tentatively allocated to these groups. Faunal resemblance was fairly high in Eastern Cape temporary rivers at the level of family, but not at more detailed taxonomic levels. A comparison between faunas of temporary and perennial rivers in different regions of South Africa illustrated the influence of geographical location on diversity. Within regions, however, there was no indication that perennial rivers were more diverse than intermittent rivers. The relatively high diversities in temporary rivers in this study are attributed at least in part to the heterogeneity in surface water conditions over time. A conceptual framework envisioning a continuum between perennial and temporary rivers is proposed as a basis for ongoing research into these rivers. A supporting terminology for the range of river flow types in South Africa is presented.
- Full Text:
- Date Issued: 1998
- Authors: Uys, Amanda Cloete
- Date: 1998
- Subjects: Rivers -- South Africa -- Eastern Cape Stream ecology -- South Africa -- Eastern Cape Freshwater invertebrates -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5628 , http://hdl.handle.net/10962/d1004908
- Description: Temporary rivers in dryland regions are subject to highly variable and unpredictable rainfall and flow, and are considered unstable systems relative to perennial rivers of temperate zones. Little is known of the ecology of South Africa's temporary rivers, despite their abundance. The research presented focusses on the aquatic invertebrates inhabiting intermittently-flowing rivers in the 'arid corridor' of the Eastern Cape, South Africa. The major aims of the work were: to investigate which invertebrates inhabit these rivers, how the fauna is affected by environmental variability at various spatial and temporal scales, whether or not a characteristic fauna can be associated with these rivers or the hydrological phases which characterise them, and to establish to what extent faunal overlap occurs between different temporary rivers and between natural and modified temporary and perennial rivers. Research results indicate that the fauna of the Eastern Cape temporary rivers shows little structure at the scales of investigation, and that communities are generally non-equilibrial in character. The major forces shaping the biota are considered to be physical rather than biological, and the most important of these are: present and antecedent hydrological conditions and their duration; time of year; and biotope character, extent and heterogeneity. Three groups of fauna were identified as inhabitants of the temporary rivers: 'residents', 'facultative taxa' and 'opportunist colonists'. Taxa were tentatively allocated to these groups. Faunal resemblance was fairly high in Eastern Cape temporary rivers at the level of family, but not at more detailed taxonomic levels. A comparison between faunas of temporary and perennial rivers in different regions of South Africa illustrated the influence of geographical location on diversity. Within regions, however, there was no indication that perennial rivers were more diverse than intermittent rivers. The relatively high diversities in temporary rivers in this study are attributed at least in part to the heterogeneity in surface water conditions over time. A conceptual framework envisioning a continuum between perennial and temporary rivers is proposed as a basis for ongoing research into these rivers. A supporting terminology for the range of river flow types in South Africa is presented.
- Full Text:
- Date Issued: 1998
Aspects of the biology, thermal physiology and nutritional ecology of Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae), a specialist herbivore introduced into South Africa for the biological control of Chromolaena odorata (L.) King and Robinson (Asteraceae)
- Authors: Uyi, Osariyekemwen
- Date: 2015
- Subjects: Chromolaena odorata , Chromolaena odorata -- Biological control -- South Africa , Arctiidae
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5936 , http://hdl.handle.net/10962/d1017916
- Description: Chromolaena odorata (L.) King and Robinson (Asteraceae) is an invasive weedy shrub native to the Americas that has proven to be a significant economic and ecological burden to many tropical and sub-tropical regions of the world where it impacts negatively on agriculture, biodiversity and livelihoods. A distinct biotype of C. odorata was first recognised as naturalized in KwaZulu-Natal (KZN) province, South Africa, in the 1940s and has since spread to other climatically suitable provinces. Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae) was released in KZN, South Africa, as a biological control agent against the weed between 2001 and 2009. Although the moth did establish at one out of some 30 release sites, its population level is generally low in the field. This thesis attempts to unravel the reasons for the poor performance of P. insulata in South Africa.Studies of life history traits of P. insulata in the laboratory indicated that the moth possess good biological attributes such as low mortality, high fecundity, egg hatchability and high female mating success. Overall, adult female moths eclosed before their male counterparts suggesting the presence of protogyny. Beyond the contribution of this study to our understanding of the life history traits of erebid moths, it hypothesized that the absence of protandry might have contributed to the low population levels of the moth in the field. To determine if a degree of agent-host plant incompatibility is culpable for the poor performance of P. insulata, insect performance metrics were compared on two distinct C. odorata plants (one from Florida and another from South Africa) in laboratory experiments. Pareuchaetes insulata performance metrics were similar on both plant forms; there were no significant differences in total leaf area consumed, egg and larval development, immature survival rates, feeding index (FI), host suitability index (HSI), growth index (GI), and fecundity between the Floridian and southern African C. odorata plants. In sum, there was no evidence to demonstrate that differences in plant forms in C. odorata are culpable for the poor performance of P. insulata in South Africa.The effects of temperature on the developmental and reproductive life history traits, locomotion performance and thermal tolerance range of P. insulata were studied in order to elucidate the possible role of temperature on the poor performance of the moth. The results showed that at temperatures below 25 °C, mortality increased and development time was prolonged. Fecundity and egg hatchability were negatively affected at a constant temperature of 15 °C. Results futher showed that third instar larvae were unable to initiate movement at 6 °C and locomotor abilities were significantly reduced at 11 °C. In sum, it is hypothesized that both direct and indirect negative impacts of low temperature may partly explain the poor performance of P. insulata in South Africa. Theeffects of seasonal and spatial variations in the leaf characteristics of C. odorata on the performance of P. insulata were investigated. Foliar nitrogen and magnesium concentrations were higher in shaded plants during winter due to low temperatures. Leaves of C. odorata plants growing in the shaded habitat (relative to full sun) and leaves of plants during autumn (relative to winter) were more nutritionally balanced and suitable for herbivore performance. Consequently, P. insulata developed faster, had heavier pupal mass and increased fecundity when reared on shaded leaves (relative to full sun) or when reared on autumn leaves compared to leaves growing in winter. This study demonstrates that low winter temperatures can indirectly affect insect herbivore performance by changing the phytochemistry of host plant and hypothesized that excess nitrogen and possibly magnesium may have detrimental effects on the insect herbivore performance.A cross-feeding experiment was conducted to determine P. insulata response to a change in the diet of offspring due to a shift in plant quality in shaded versus full sun habitats. The results showed that a ‘negative switch’ in herbivore diet (i.e. when progeny from parents reared on shaded leaves were fed on full sun leaves) resulted in high (40%) mortality, prolonged development time and reduced fecundity. Thus full sun foliage is an inferior diet for P. insulata offspring. In laboratory experiments, foliar nitrogen was positively correlated with the performance of P. insulata. From this study, it is demonstrably evident that the poor performance of P. insulata on C. odorata in South Africa is caused by multiple factors such as low temperatures as well as spatio-temporal variations in the leaf characteristic of C. odorata leaves. This study shows the complexity of determining the causes of low populations and apparent low impact of biological control agents and herbivorous insects generally, in the field. The implications of this research to the biological control programme against C. odorata and the direction of future research for the control of C. odorata are discussed.
- Full Text:
- Date Issued: 2015
- Authors: Uyi, Osariyekemwen
- Date: 2015
- Subjects: Chromolaena odorata , Chromolaena odorata -- Biological control -- South Africa , Arctiidae
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5936 , http://hdl.handle.net/10962/d1017916
- Description: Chromolaena odorata (L.) King and Robinson (Asteraceae) is an invasive weedy shrub native to the Americas that has proven to be a significant economic and ecological burden to many tropical and sub-tropical regions of the world where it impacts negatively on agriculture, biodiversity and livelihoods. A distinct biotype of C. odorata was first recognised as naturalized in KwaZulu-Natal (KZN) province, South Africa, in the 1940s and has since spread to other climatically suitable provinces. Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae) was released in KZN, South Africa, as a biological control agent against the weed between 2001 and 2009. Although the moth did establish at one out of some 30 release sites, its population level is generally low in the field. This thesis attempts to unravel the reasons for the poor performance of P. insulata in South Africa.Studies of life history traits of P. insulata in the laboratory indicated that the moth possess good biological attributes such as low mortality, high fecundity, egg hatchability and high female mating success. Overall, adult female moths eclosed before their male counterparts suggesting the presence of protogyny. Beyond the contribution of this study to our understanding of the life history traits of erebid moths, it hypothesized that the absence of protandry might have contributed to the low population levels of the moth in the field. To determine if a degree of agent-host plant incompatibility is culpable for the poor performance of P. insulata, insect performance metrics were compared on two distinct C. odorata plants (one from Florida and another from South Africa) in laboratory experiments. Pareuchaetes insulata performance metrics were similar on both plant forms; there were no significant differences in total leaf area consumed, egg and larval development, immature survival rates, feeding index (FI), host suitability index (HSI), growth index (GI), and fecundity between the Floridian and southern African C. odorata plants. In sum, there was no evidence to demonstrate that differences in plant forms in C. odorata are culpable for the poor performance of P. insulata in South Africa.The effects of temperature on the developmental and reproductive life history traits, locomotion performance and thermal tolerance range of P. insulata were studied in order to elucidate the possible role of temperature on the poor performance of the moth. The results showed that at temperatures below 25 °C, mortality increased and development time was prolonged. Fecundity and egg hatchability were negatively affected at a constant temperature of 15 °C. Results futher showed that third instar larvae were unable to initiate movement at 6 °C and locomotor abilities were significantly reduced at 11 °C. In sum, it is hypothesized that both direct and indirect negative impacts of low temperature may partly explain the poor performance of P. insulata in South Africa. Theeffects of seasonal and spatial variations in the leaf characteristics of C. odorata on the performance of P. insulata were investigated. Foliar nitrogen and magnesium concentrations were higher in shaded plants during winter due to low temperatures. Leaves of C. odorata plants growing in the shaded habitat (relative to full sun) and leaves of plants during autumn (relative to winter) were more nutritionally balanced and suitable for herbivore performance. Consequently, P. insulata developed faster, had heavier pupal mass and increased fecundity when reared on shaded leaves (relative to full sun) or when reared on autumn leaves compared to leaves growing in winter. This study demonstrates that low winter temperatures can indirectly affect insect herbivore performance by changing the phytochemistry of host plant and hypothesized that excess nitrogen and possibly magnesium may have detrimental effects on the insect herbivore performance.A cross-feeding experiment was conducted to determine P. insulata response to a change in the diet of offspring due to a shift in plant quality in shaded versus full sun habitats. The results showed that a ‘negative switch’ in herbivore diet (i.e. when progeny from parents reared on shaded leaves were fed on full sun leaves) resulted in high (40%) mortality, prolonged development time and reduced fecundity. Thus full sun foliage is an inferior diet for P. insulata offspring. In laboratory experiments, foliar nitrogen was positively correlated with the performance of P. insulata. From this study, it is demonstrably evident that the poor performance of P. insulata on C. odorata in South Africa is caused by multiple factors such as low temperatures as well as spatio-temporal variations in the leaf characteristic of C. odorata leaves. This study shows the complexity of determining the causes of low populations and apparent low impact of biological control agents and herbivorous insects generally, in the field. The implications of this research to the biological control programme against C. odorata and the direction of future research for the control of C. odorata are discussed.
- Full Text:
- Date Issued: 2015
Modelling storm-time TEC changes using linear and non-linear techniques
- Authors: Uwamahoro, Jean Claude
- Date: 2019
- Subjects: Magnetic storms , Astronomy -- Computer programs , Imaging systems in astronomy , Ionospheric storms , Electrons -- Measurement , Magnetosphere -- Observations
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/92908 , vital:30762
- Description: Statistical models based on empirical orthogonal functions (EOF) analysis and non-linear regression analysis (NLRA) were developed for the purpose of estimating the ionospheric total electron content (TEC) during geomagnetic storms. The well-known least squares method (LSM) and Metropolis-Hastings algorithm (MHA) were used as optimization techniques to determine the unknown coefficients of the developed analytical expressions. Artificial Neural Networks (ANNs), the International Reference Ionosphere (IRI) model, and the Multi-Instrument Data Analysis System (MIDAS) tomographic inversion algorithm were also applied to storm-time TEC modelling/reconstruction for various latitudes of the African sector and surrounding areas. This work presents some of the first statistical modeling of the mid-latitude and low-latitude ionosphere during geomagnetic storms that includes solar, geomagnetic and neutral wind drivers.Development and validation of the empirical models were based on storm-time TEC data derived from the global positioning system (GPS) measurements over ground receivers within Africa and surrounding areas. The storm criterion applied was Dst 6 −50 nT and/or Kp > 4. The performance evaluation of MIDAS compared with ANNs to reconstruct storm-time TEC over the African low- and mid-latitude regions showed that MIDAS and ANNs provide comparable results. Their respective mean absolute error (MAE) values were 4.81 and 4.18 TECU. The ANN model was, however, found to perform 24.37 % better than MIDAS at estimating storm-time TEC for low latitudes, while MIDAS is 13.44 % more accurate than ANN for the mid-latitudes. When their performances are compared with the IRI model, both MIDAS and ANN model were found to provide more accurate storm-time TEC reconstructions for the African low- and mid-latitude regions. A comparative study of the performances of EOF, NLRA, ANN, and IRI models to estimate TEC during geomagnetic storm conditions over various latitudes showed that the ANN model is about 10 %, 26 %, and 58 % more accurate than EOF, NLRA, and IRI models, respectively, while EOF was found to perform 15 %, and 44 % better than NLRA and IRI, respectively. It was further found that the NLRA model is 25 % more accurate than the IRI model. We have also investigated for the first time, the role of meridional neutral winds (from the Horizontal Wind Model) to storm-time TEC modelling in the low latitude, northern and southern hemisphere mid-latitude regions of the African sector, based on ANN models. Statistics have shown that the inclusion of the meridional wind velocity in TEC modelling during geomagnetic storms leads to percentage improvements of about 5 % for the low latitude, 10 % and 5 % for the northern and southern hemisphere mid-latitude regions, respectively. High-latitude storm-induced winds and the inter-hemispheric blows of the meridional winds from summer to winter hemisphere have been suggested to be associated with these improvements.
- Full Text:
- Date Issued: 2019
- Authors: Uwamahoro, Jean Claude
- Date: 2019
- Subjects: Magnetic storms , Astronomy -- Computer programs , Imaging systems in astronomy , Ionospheric storms , Electrons -- Measurement , Magnetosphere -- Observations
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/92908 , vital:30762
- Description: Statistical models based on empirical orthogonal functions (EOF) analysis and non-linear regression analysis (NLRA) were developed for the purpose of estimating the ionospheric total electron content (TEC) during geomagnetic storms. The well-known least squares method (LSM) and Metropolis-Hastings algorithm (MHA) were used as optimization techniques to determine the unknown coefficients of the developed analytical expressions. Artificial Neural Networks (ANNs), the International Reference Ionosphere (IRI) model, and the Multi-Instrument Data Analysis System (MIDAS) tomographic inversion algorithm were also applied to storm-time TEC modelling/reconstruction for various latitudes of the African sector and surrounding areas. This work presents some of the first statistical modeling of the mid-latitude and low-latitude ionosphere during geomagnetic storms that includes solar, geomagnetic and neutral wind drivers.Development and validation of the empirical models were based on storm-time TEC data derived from the global positioning system (GPS) measurements over ground receivers within Africa and surrounding areas. The storm criterion applied was Dst 6 −50 nT and/or Kp > 4. The performance evaluation of MIDAS compared with ANNs to reconstruct storm-time TEC over the African low- and mid-latitude regions showed that MIDAS and ANNs provide comparable results. Their respective mean absolute error (MAE) values were 4.81 and 4.18 TECU. The ANN model was, however, found to perform 24.37 % better than MIDAS at estimating storm-time TEC for low latitudes, while MIDAS is 13.44 % more accurate than ANN for the mid-latitudes. When their performances are compared with the IRI model, both MIDAS and ANN model were found to provide more accurate storm-time TEC reconstructions for the African low- and mid-latitude regions. A comparative study of the performances of EOF, NLRA, ANN, and IRI models to estimate TEC during geomagnetic storm conditions over various latitudes showed that the ANN model is about 10 %, 26 %, and 58 % more accurate than EOF, NLRA, and IRI models, respectively, while EOF was found to perform 15 %, and 44 % better than NLRA and IRI, respectively. It was further found that the NLRA model is 25 % more accurate than the IRI model. We have also investigated for the first time, the role of meridional neutral winds (from the Horizontal Wind Model) to storm-time TEC modelling in the low latitude, northern and southern hemisphere mid-latitude regions of the African sector, based on ANN models. Statistics have shown that the inclusion of the meridional wind velocity in TEC modelling during geomagnetic storms leads to percentage improvements of about 5 % for the low latitude, 10 % and 5 % for the northern and southern hemisphere mid-latitude regions, respectively. High-latitude storm-induced winds and the inter-hemispheric blows of the meridional winds from summer to winter hemisphere have been suggested to be associated with these improvements.
- Full Text:
- Date Issued: 2019
An analysis of sources and predictability of geomagnetic storms
- Authors: Uwamahoro, Jean
- Date: 2011
- Subjects: Ionospheric storms Solar flares Interplanetary magnetic fields Magnetospheric substorms Coronal mass ejections Space environment Neural networks (Computer science)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5451 , http://hdl.handle.net/10962/d1005236
- Description: Solar transient eruptions are the main cause of interplanetary-magnetospheric disturbances leading to the phenomena known as geomagnetic storms. Eruptive solar events such as coronal mass ejections (CMEs) are currently considered the main cause of geomagnetic storms (GMS). GMS are strong perturbations of the Earth’s magnetic field that can affect space-borne and ground-based technological systems. The solar-terrestrial impact on modern technological systems is commonly known as Space Weather. Part of the research study described in this thesis was to investigate and establish a relationship between GMS (periods with Dst ≤ −50 nT) and their associated solar and interplanetary (IP) properties during solar cycle (SC) 23. Solar and IP geoeffective properties associated with or without CMEs were investigated and used to qualitatively characterise both intense and moderate storms. The results of this analysis specifically provide an estimate of the main sources of GMS during an average 11-year solar activity period. This study indicates that during SC 23, the majority of intense GMS (83%) were associated with CMEs, while the non-associated CME storms were dominant among moderate storms. GMS phenomena are the result of a complex and non-linear chaotic system involving the Sun, the IP medium, the magnetosphere and ionosphere, which make the prediction of these phenomena challenging. This thesis also explored the predictability of both the occurrence and strength of GMS. Due to their nonlinear driving mechanisms, the prediction of GMS was attempted by the use of neural network (NN) techniques, known for their non-linear modelling capabilities. To predict the occurrence of storms, a combination of solar and IP parameters were used as inputs in the NN model that proved to predict the occurrence of GMS with a probability of 87%. Using the solar wind (SW) and IP magnetic field (IMF) parameters, a separate NN-based model was developed to predict the storm-time strength as measured by the global Dst and ap geomagnetic indices, as well as by the locally measured K-index. The performance of the models was tested on data sets which were not part of the NN training process. The results obtained indicate that NN models provide a reliable alternative method for empirically predicting the occurrence and strength of GMS on the basis of solar and IP parameters. The demonstrated ability to predict the geoeffectiveness of solar and IP transient events is a key step in the goal towards improving space weather modelling and prediction.
- Full Text:
- Date Issued: 2011
- Authors: Uwamahoro, Jean
- Date: 2011
- Subjects: Ionospheric storms Solar flares Interplanetary magnetic fields Magnetospheric substorms Coronal mass ejections Space environment Neural networks (Computer science)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5451 , http://hdl.handle.net/10962/d1005236
- Description: Solar transient eruptions are the main cause of interplanetary-magnetospheric disturbances leading to the phenomena known as geomagnetic storms. Eruptive solar events such as coronal mass ejections (CMEs) are currently considered the main cause of geomagnetic storms (GMS). GMS are strong perturbations of the Earth’s magnetic field that can affect space-borne and ground-based technological systems. The solar-terrestrial impact on modern technological systems is commonly known as Space Weather. Part of the research study described in this thesis was to investigate and establish a relationship between GMS (periods with Dst ≤ −50 nT) and their associated solar and interplanetary (IP) properties during solar cycle (SC) 23. Solar and IP geoeffective properties associated with or without CMEs were investigated and used to qualitatively characterise both intense and moderate storms. The results of this analysis specifically provide an estimate of the main sources of GMS during an average 11-year solar activity period. This study indicates that during SC 23, the majority of intense GMS (83%) were associated with CMEs, while the non-associated CME storms were dominant among moderate storms. GMS phenomena are the result of a complex and non-linear chaotic system involving the Sun, the IP medium, the magnetosphere and ionosphere, which make the prediction of these phenomena challenging. This thesis also explored the predictability of both the occurrence and strength of GMS. Due to their nonlinear driving mechanisms, the prediction of GMS was attempted by the use of neural network (NN) techniques, known for their non-linear modelling capabilities. To predict the occurrence of storms, a combination of solar and IP parameters were used as inputs in the NN model that proved to predict the occurrence of GMS with a probability of 87%. Using the solar wind (SW) and IP magnetic field (IMF) parameters, a separate NN-based model was developed to predict the storm-time strength as measured by the global Dst and ap geomagnetic indices, as well as by the locally measured K-index. The performance of the models was tested on data sets which were not part of the NN training process. The results obtained indicate that NN models provide a reliable alternative method for empirically predicting the occurrence and strength of GMS on the basis of solar and IP parameters. The demonstrated ability to predict the geoeffectiveness of solar and IP transient events is a key step in the goal towards improving space weather modelling and prediction.
- Full Text:
- Date Issued: 2011
Oral narratives as intertexts in selected Nigerian films
- Authors: Usman, Joshua
- Date: 2019
- Subjects: Folk literature -- Nigeria , Oral tradition -- Nigeria Motion pictures -- Nigeria
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43721 , vital:37038
- Description: This research into the interface between orality and Nigerian film builds on previous scholarly works in the field (Ladebo (1992), Onabajo and M’Bayo (2009), Omolola (2013), Ezeigbo (2013), Mgbemere (2015) and Onzuike (2016)). Evident from these studies is the prevalence of recurring patterns of oral narratives in Nigerian film. The aim of this study is to consider the following research questions: Do film producers/directors adopt the use of oral narratives in Nigerian film texts? How do oral narratives translate into films? What is the rate of recurrence of oral narratives in Nigerian films? Do oral narratives aesthetically influence the quality of Nigerian films? For the purpose of this study a selection of nine Nigerian films (three each from the Yoruba, Hausa and Igbo groups). These films are analysed as primary texts to show the occurrence of elements of orature and oral narratives. Underpinning such analysis is the theory of intertextuality as coined by the French linguist Julia Kristeva. Kristeva sees the text as “intertextuality […] within the text of society and history” (Kristeva, 1980: 37). This approach is augmented by the views of Greenblatt on New Historicism, which implies literature should be studied and interpreted within the context of the history of the author and cultural/social context. The nine films under discussion are considered within their cultural/social context.
- Full Text:
- Date Issued: 2019
- Authors: Usman, Joshua
- Date: 2019
- Subjects: Folk literature -- Nigeria , Oral tradition -- Nigeria Motion pictures -- Nigeria
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/43721 , vital:37038
- Description: This research into the interface between orality and Nigerian film builds on previous scholarly works in the field (Ladebo (1992), Onabajo and M’Bayo (2009), Omolola (2013), Ezeigbo (2013), Mgbemere (2015) and Onzuike (2016)). Evident from these studies is the prevalence of recurring patterns of oral narratives in Nigerian film. The aim of this study is to consider the following research questions: Do film producers/directors adopt the use of oral narratives in Nigerian film texts? How do oral narratives translate into films? What is the rate of recurrence of oral narratives in Nigerian films? Do oral narratives aesthetically influence the quality of Nigerian films? For the purpose of this study a selection of nine Nigerian films (three each from the Yoruba, Hausa and Igbo groups). These films are analysed as primary texts to show the occurrence of elements of orature and oral narratives. Underpinning such analysis is the theory of intertextuality as coined by the French linguist Julia Kristeva. Kristeva sees the text as “intertextuality […] within the text of society and history” (Kristeva, 1980: 37). This approach is augmented by the views of Greenblatt on New Historicism, which implies literature should be studied and interpreted within the context of the history of the author and cultural/social context. The nine films under discussion are considered within their cultural/social context.
- Full Text:
- Date Issued: 2019
A participatory communication approach of rural cattle project: a case study of Nguni cattle project in the Eastern Cape, South Africa
- Authors: Usadolo, Sam Erevbenagie
- Date: 2011
- Subjects: Communication in community development -- South Africa , Nguni cattle -- South Africa , Participatory rural appraisal
- Language: English
- Type: Thesis , Doctoral , PhD (Com)
- Identifier: vital:11370 , http://hdl.handle.net/10353/d1015407 , Communication in community development -- South Africa , Nguni cattle -- South Africa , Participatory rural appraisal
- Description: project. It did this by reviewing relevant literature in development communication. The review done showed that literature is replete with arguments critical of the dominant paradigm due to its top-down nature of communication. Scholars critical of dominant paradigm argue that participatory communication should be given a prominent role to ensure that stakeholders work in concert to realise the stated objectives of their development project. The study highlighted many contentious issues surrounding the nature and practices of participatory communication. It pointed out that the issues have played themselves out in literature in the form of different typologies of participatory practices, which were dealt with extensively in this study. The discussion of participatory communication in literature is also mindful of different models of communication and the space they occupy in participatory communication practices. In this study, there was a discussion of transactional communication models as depicted by Nair and White (1993:52) and Steinberg (1997:19). Both scholars emphasise that participatory communication will not achieve its stated purpose without mutual agreement of the parties in communication. They equally stress the recognition of the possible effects of some contextual factors which may have bearing on the prevailing nature of communication. A review of different communication tools used by participatory development communicator was given in the study. These different communication tools were discussed in view of how these tools can be used to advance participatory practice in a development project, especially with reference to the project examined in this study. Using qualitative research method, different and appropriate interview methods such as semi-structured, focus group and post-survey interviews were used to collect data from the respondents in this study. The analysis and discussion of the data revealed that different challenges on the ground could affect participatory communication practices in a development project. With regard to the project examined in this study, the analysis showed that there is a weak stakeholder relationship, especially stakeholders identified in this study as field officers. The study highlighted that stakeholders such as the agricultural extension officers and animal health technicians are not very active in the implementation process of the project. Some of the reasons pointed out is the fact that the secondary stakeholder such as the Provincial Department of Agricultural (PDoA) to which these field officers belong is not playing active role in ensuring that they complement the efforts of other field officers such as the IDC representatives. The second reason is the fact that the participatory focus of the project was not properly communicated to the beneficiaries. This also transpired in their inability to reflect participatory practice in their relationship with the beneficiaries and other stakeholders of the project. Other challenges, among others, as pointed out in the analysis showed that participatory communication practice requires expert personnel to be successful. In the case of the project examined, apart from the fact that there is shortage of manpower to handle the challenges mentioned in the study, there is no communication expert among the few active personnel in the field. The findings of this study showed that there was no clear role and identification of responsibilities let alone coordination of all actors involved in the project. Through the selected case study, this study has not only provided avenue to explore both theoretically and practically participatory communication, but has added to participatory communication discourse that there is no easy answer to challenges field officers encounter in practice. This is the reason the different participatory practices characterising nature of the project this study has investigated was given.
- Full Text:
- Date Issued: 2011
- Authors: Usadolo, Sam Erevbenagie
- Date: 2011
- Subjects: Communication in community development -- South Africa , Nguni cattle -- South Africa , Participatory rural appraisal
- Language: English
- Type: Thesis , Doctoral , PhD (Com)
- Identifier: vital:11370 , http://hdl.handle.net/10353/d1015407 , Communication in community development -- South Africa , Nguni cattle -- South Africa , Participatory rural appraisal
- Description: project. It did this by reviewing relevant literature in development communication. The review done showed that literature is replete with arguments critical of the dominant paradigm due to its top-down nature of communication. Scholars critical of dominant paradigm argue that participatory communication should be given a prominent role to ensure that stakeholders work in concert to realise the stated objectives of their development project. The study highlighted many contentious issues surrounding the nature and practices of participatory communication. It pointed out that the issues have played themselves out in literature in the form of different typologies of participatory practices, which were dealt with extensively in this study. The discussion of participatory communication in literature is also mindful of different models of communication and the space they occupy in participatory communication practices. In this study, there was a discussion of transactional communication models as depicted by Nair and White (1993:52) and Steinberg (1997:19). Both scholars emphasise that participatory communication will not achieve its stated purpose without mutual agreement of the parties in communication. They equally stress the recognition of the possible effects of some contextual factors which may have bearing on the prevailing nature of communication. A review of different communication tools used by participatory development communicator was given in the study. These different communication tools were discussed in view of how these tools can be used to advance participatory practice in a development project, especially with reference to the project examined in this study. Using qualitative research method, different and appropriate interview methods such as semi-structured, focus group and post-survey interviews were used to collect data from the respondents in this study. The analysis and discussion of the data revealed that different challenges on the ground could affect participatory communication practices in a development project. With regard to the project examined in this study, the analysis showed that there is a weak stakeholder relationship, especially stakeholders identified in this study as field officers. The study highlighted that stakeholders such as the agricultural extension officers and animal health technicians are not very active in the implementation process of the project. Some of the reasons pointed out is the fact that the secondary stakeholder such as the Provincial Department of Agricultural (PDoA) to which these field officers belong is not playing active role in ensuring that they complement the efforts of other field officers such as the IDC representatives. The second reason is the fact that the participatory focus of the project was not properly communicated to the beneficiaries. This also transpired in their inability to reflect participatory practice in their relationship with the beneficiaries and other stakeholders of the project. Other challenges, among others, as pointed out in the analysis showed that participatory communication practice requires expert personnel to be successful. In the case of the project examined, apart from the fact that there is shortage of manpower to handle the challenges mentioned in the study, there is no communication expert among the few active personnel in the field. The findings of this study showed that there was no clear role and identification of responsibilities let alone coordination of all actors involved in the project. Through the selected case study, this study has not only provided avenue to explore both theoretically and practically participatory communication, but has added to participatory communication discourse that there is no easy answer to challenges field officers encounter in practice. This is the reason the different participatory practices characterising nature of the project this study has investigated was given.
- Full Text:
- Date Issued: 2011
Justice through language : a critical analysis of the use of foreign African interpreters in South African courtrooms
- Authors: Usadolo, Sam Erevbenagie
- Date: 2010
- Subjects: Translators
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:8363 , http://hdl.handle.net/10948/1503 , Translators
- Description: This study represents an analysis of the use of foreign African interpreters in South African courtrooms in the context of the necessity of court interpreting as a vehicle through which accused persons can express themselves in defence of their rights, which may have been violated. As a background to the study, due consideration is given to the history of interpreting, followed by some theoretical perspectives of interpreting, where the differences between translation and interpreting are explained. The discussion of some of the theoretical issues of interpreting also focuses on the notion of equivalence, and the divergent views of scholars regarding this notion, which range from formal equivalence (a source-language oriented approach), through dynamic equivalence (in terms of which translation/interpreting must be in agreement with the form and cultural expectations of the receptor language community) to skopos theory (functional in approach and target text oriented). In discussing the role of the court interpreter, the role boundaries with regard to his/her professional relationship with other participants in the courtroom are highlighted. A related topic, namely that of quality in interpreting, is investigated in relation to quality control by professional associations in different countries, who act as regulatory authorities in this regard. A review of court interpreting in South Africa and selected countries in Africa and the EU, such as Nigeria, Benin, Kenya, Zimbabwe, Namibia, Mozambique and Portugal reveals that efforts to develop court interpreting in some Africa and EU countries are either non-existent or at an incipient stage of development. While South Africa, compared to other countries in Africa, is making progress, she is far behind EU countries such as the UK, France and Spain –all of which possess accreditation systems, professional associations and registers of court interpreters. An analysis of the data collected on foreign African court interpreters shows that, although they work in the same courtrooms as their South African counterparts on a daily basis, they are treated differently in terms of employment procedures, training, remuneration, and such like. The study points out that some factors such as (a) the lack of adequate crosscultural awareness and (b) of a balanced proficiency in their language pair, as well as (c) and the existence of divergent dialects in those languages may pose a challenge to foreign African court interpreters in interpreting cross-border languages and in performing sight translations. The study further reveals that foreign African court interpreters are in serious breach of the professional code of conduct, as exemplified by instances of conflict of interest and partiality in their practices. As regards the management of court interpreters, the findings indicate a general laxity on the side of management, as a result of which there is a lack, inter alia, of an appropriate evaluation or monitoring strategy aimed at detecting such cases of conflict of interest and partiality.
- Full Text:
- Date Issued: 2010
- Authors: Usadolo, Sam Erevbenagie
- Date: 2010
- Subjects: Translators
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:8363 , http://hdl.handle.net/10948/1503 , Translators
- Description: This study represents an analysis of the use of foreign African interpreters in South African courtrooms in the context of the necessity of court interpreting as a vehicle through which accused persons can express themselves in defence of their rights, which may have been violated. As a background to the study, due consideration is given to the history of interpreting, followed by some theoretical perspectives of interpreting, where the differences between translation and interpreting are explained. The discussion of some of the theoretical issues of interpreting also focuses on the notion of equivalence, and the divergent views of scholars regarding this notion, which range from formal equivalence (a source-language oriented approach), through dynamic equivalence (in terms of which translation/interpreting must be in agreement with the form and cultural expectations of the receptor language community) to skopos theory (functional in approach and target text oriented). In discussing the role of the court interpreter, the role boundaries with regard to his/her professional relationship with other participants in the courtroom are highlighted. A related topic, namely that of quality in interpreting, is investigated in relation to quality control by professional associations in different countries, who act as regulatory authorities in this regard. A review of court interpreting in South Africa and selected countries in Africa and the EU, such as Nigeria, Benin, Kenya, Zimbabwe, Namibia, Mozambique and Portugal reveals that efforts to develop court interpreting in some Africa and EU countries are either non-existent or at an incipient stage of development. While South Africa, compared to other countries in Africa, is making progress, she is far behind EU countries such as the UK, France and Spain –all of which possess accreditation systems, professional associations and registers of court interpreters. An analysis of the data collected on foreign African court interpreters shows that, although they work in the same courtrooms as their South African counterparts on a daily basis, they are treated differently in terms of employment procedures, training, remuneration, and such like. The study points out that some factors such as (a) the lack of adequate crosscultural awareness and (b) of a balanced proficiency in their language pair, as well as (c) and the existence of divergent dialects in those languages may pose a challenge to foreign African court interpreters in interpreting cross-border languages and in performing sight translations. The study further reveals that foreign African court interpreters are in serious breach of the professional code of conduct, as exemplified by instances of conflict of interest and partiality in their practices. As regards the management of court interpreters, the findings indicate a general laxity on the side of management, as a result of which there is a lack, inter alia, of an appropriate evaluation or monitoring strategy aimed at detecting such cases of conflict of interest and partiality.
- Full Text:
- Date Issued: 2010
Growth and characterization of ZnO nanorods using chemical bath deposition
- Authors: Urgessa, Zelalem Nigussa
- Date: 2012
- Subjects: Zinc oxide , Photoluminescence , Semiconductor nanocrystals , Semiconductors -- Materials , Chemical reactions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10559 , http://hdl.handle.net/10948/d1021124 , http://hdl.handle.net/10948/d1021119
- Description: Semiconductor devices are commonplace in every household. One application of semiconductors in particular, namely solid state lighting technology, is destined for a bright future. To this end, ZnO nanostructures have gained substantial interest in the research community, in part because of its requisite large direct band gap. Furthermore, the stability of the exciton (binding energy 60 meV) in this material, can lead to lasing action based on exciton recombination and possibly exciton interaction, even above room temperature. Therefore, it is very important to realize controllable growth of ZnO nanostructures and investigate their properties. The main motivation for this thesis is not only to successfully realize the controllable growth of ZnO nanorods, but also to investigate the structure, optical and electrical properties in detail by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy (steady state and time resolved) and X-ray diffraction (XRD). Furthermore, strong rectification in the ZnO/p-Si heterojunction is demonstrated. Nanorods have been successfully synthesized on silicon by a two-step process, involving the pre-coating of the substrate by a seed layer, followed by the chemical bath deposition of the nanorods. ZnO seed layers with particle sizes of about 5 nm are achieved by the thermal decomposition of zinc acetate dihydrate dissolved in ethanol. The effects of the seed layer density on the distribution, alignment and uniformity of subsequently grown nanorods were studied. The aspect ratio, orientation and distribution of nanorods are shown to be well controlled through adjusting the density of the ZnO nanoparticles pre-coated onto the substrates. It is shown that the seed layer is a prerequisite for the growth of well aligned ZnO nanorods on lattice mismatched Si substrate. The influence of various nanorod growth parameters on the morphology, optical and electrical properties of the nanorods were also systematically studied. These include the oxygen to zinc molar ratio, the pH of the growth solution, the concentration of the reactants, the growth temperature and growth time, different hydroxide precursors and the addition of surface passivating agents to the growth solution. By controlling these xii parameters different architectures of nanostructures, like spherical particles, well aligned nanorods, nanoflowers and thin films of different thicknesses are demonstrated. A possible growth mechanism for ZnO nanostructures in solution is proposed. XRD indicated that all the as-grown nanostructures produced above 45 C crystallize in the wurtzite structure and post growth annealing does not significantly enhance the crystalline quality of the material. In material grown at lower temperature, traces of zinc hydroxide were observed. The optical quality of the nanostructures was investigated using both steady-state PL and time-resolved (TR) PL from 4 K to room temperature. In the case of as-grown samples, both UV and defect related emissions have been observed for all nanostructures. The effect of post-growth annealing on the optical quality of the nanostructures was carefully examined. The effect of annealing in different atmospheres was also investigated. Regardless of the annealing environment annealing at a temperature as low as 300 C enhances the UV emission and suppresses defect related deep level emission. However, annealing above 500 C is required to out-diffuse hydrogen, the presence of which is deduced from the I4 line in the low temperature PL spectra of ZnO. TRPL was utilized to investigate lifetime decay profiles of nanorods upon different post growth treatments. The bound exciton lifetime strongly depends on the post-growth annealing temperature: the PL decay time is much faster for as grown rods, confirming the domination of surface assisted recombination. In general, the PL analysis showed that the PL of nanorods have the same characteristics as that of bulk ZnO, except for the stronger contribution from surface related bound excitons in the former case. Surface adsorbed impurities causing depletion and band bending in the near surface region is implied from both time resolved and steady state PL. Finally, although strong rectification in the ZnO/p-Si heterojunction is illustrated, no electroluminescence has been achieved. This is explained in terms of the band offset between ZnO and Si and interfacial states. Different schemes are proposed to improve the performance of ZnO/Si heterojunction light emitting devices.
- Full Text:
- Date Issued: 2012
- Authors: Urgessa, Zelalem Nigussa
- Date: 2012
- Subjects: Zinc oxide , Photoluminescence , Semiconductor nanocrystals , Semiconductors -- Materials , Chemical reactions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10559 , http://hdl.handle.net/10948/d1021124 , http://hdl.handle.net/10948/d1021119
- Description: Semiconductor devices are commonplace in every household. One application of semiconductors in particular, namely solid state lighting technology, is destined for a bright future. To this end, ZnO nanostructures have gained substantial interest in the research community, in part because of its requisite large direct band gap. Furthermore, the stability of the exciton (binding energy 60 meV) in this material, can lead to lasing action based on exciton recombination and possibly exciton interaction, even above room temperature. Therefore, it is very important to realize controllable growth of ZnO nanostructures and investigate their properties. The main motivation for this thesis is not only to successfully realize the controllable growth of ZnO nanorods, but also to investigate the structure, optical and electrical properties in detail by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy (steady state and time resolved) and X-ray diffraction (XRD). Furthermore, strong rectification in the ZnO/p-Si heterojunction is demonstrated. Nanorods have been successfully synthesized on silicon by a two-step process, involving the pre-coating of the substrate by a seed layer, followed by the chemical bath deposition of the nanorods. ZnO seed layers with particle sizes of about 5 nm are achieved by the thermal decomposition of zinc acetate dihydrate dissolved in ethanol. The effects of the seed layer density on the distribution, alignment and uniformity of subsequently grown nanorods were studied. The aspect ratio, orientation and distribution of nanorods are shown to be well controlled through adjusting the density of the ZnO nanoparticles pre-coated onto the substrates. It is shown that the seed layer is a prerequisite for the growth of well aligned ZnO nanorods on lattice mismatched Si substrate. The influence of various nanorod growth parameters on the morphology, optical and electrical properties of the nanorods were also systematically studied. These include the oxygen to zinc molar ratio, the pH of the growth solution, the concentration of the reactants, the growth temperature and growth time, different hydroxide precursors and the addition of surface passivating agents to the growth solution. By controlling these xii parameters different architectures of nanostructures, like spherical particles, well aligned nanorods, nanoflowers and thin films of different thicknesses are demonstrated. A possible growth mechanism for ZnO nanostructures in solution is proposed. XRD indicated that all the as-grown nanostructures produced above 45 C crystallize in the wurtzite structure and post growth annealing does not significantly enhance the crystalline quality of the material. In material grown at lower temperature, traces of zinc hydroxide were observed. The optical quality of the nanostructures was investigated using both steady-state PL and time-resolved (TR) PL from 4 K to room temperature. In the case of as-grown samples, both UV and defect related emissions have been observed for all nanostructures. The effect of post-growth annealing on the optical quality of the nanostructures was carefully examined. The effect of annealing in different atmospheres was also investigated. Regardless of the annealing environment annealing at a temperature as low as 300 C enhances the UV emission and suppresses defect related deep level emission. However, annealing above 500 C is required to out-diffuse hydrogen, the presence of which is deduced from the I4 line in the low temperature PL spectra of ZnO. TRPL was utilized to investigate lifetime decay profiles of nanorods upon different post growth treatments. The bound exciton lifetime strongly depends on the post-growth annealing temperature: the PL decay time is much faster for as grown rods, confirming the domination of surface assisted recombination. In general, the PL analysis showed that the PL of nanorods have the same characteristics as that of bulk ZnO, except for the stronger contribution from surface related bound excitons in the former case. Surface adsorbed impurities causing depletion and band bending in the near surface region is implied from both time resolved and steady state PL. Finally, although strong rectification in the ZnO/p-Si heterojunction is illustrated, no electroluminescence has been achieved. This is explained in terms of the band offset between ZnO and Si and interfacial states. Different schemes are proposed to improve the performance of ZnO/Si heterojunction light emitting devices.
- Full Text:
- Date Issued: 2012
Colour vision of the citrus psylla Trioza erytreae (Del Guercio) (Homoptera: Psyllidae) in relation to alightment colour preferences
- Authors: Urban, Alan Joseph
- Date: 1977
- Subjects: Trioza , Homoptera , Jumping plant-lice , Color vision
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5885 , http://hdl.handle.net/10962/d1013286
- Description: The colour vision of adult citrus psylla, Trioza erytreae, was investigated in the laboratory using the behavioural parameters: alightment and walking. Light green flushing leaves (under which the nymphs develop) were significantly preferred, visually, to dark green mature leaves for alightment. Diffuse reflectance spectroscopy showed (when expressed in the parameters of human colour vision) that flush has a very slightly longer dominant wavelength, and roughly double the reflectance and purity. Alightrnent frequency correlated almost equally well with "purity" (as noted by Moericke, 1952 et seq., in "yellow-sensitive" aphids) as with the aphidological colour parameter "long/short ratio" developed by Kennedy et al. (1961). Elucidation of the mechanism underlying the citrus psylla's alightment colour preference was initially attempted with a printed spectrum and several paint series of measured spectral characteristics. It was clear that T.erytreae belongs to the "yellow-sensitive" group of Homoptera, but it was impossible to distinguish which pararneter(s) of colour the psyllids were responding to. Phototactic (walking) response to the individual parameters of colour was therefore measured using a monochromator. The phototactic action spectrum (against wavelength) was tri-modal, with peaks in the yellow-green (YG), blue (B), and ultra= violet (UV). Rate of phototaxis was not influenced by bandwidth (roughly equivalent to purity), but was proportional to intensity (roughly equivalent to reflectance). To investigate the influence of the above three wavelength regions on alightment, use was made of a very simple flight chamber incorporating a target of coloured light. Yellow-green and UV light both independently stimulated alightment . Their effect was additive. Different thresholds indicated distinct YG and UV receptor systems. Blue light alone did not stimulate alightment, and was strongly alightment-inhibitory in combination both with YG and with UV light. On the basis of the above physiological/behavioural findings, a new alightment formula was drawn up for describing the hamopteran's apparent manner of alightment determining integration of surface reflectance. The flush preference and alightment distributions on the series of artificial surfaces were found to correlate slightly more accurately, on average, as well as more consistently, with the new formula than with previously-available colour parameters. These findings are placed in perspective to the literature, and their possible economic relevance is discussed.
- Full Text:
- Date Issued: 1977
- Authors: Urban, Alan Joseph
- Date: 1977
- Subjects: Trioza , Homoptera , Jumping plant-lice , Color vision
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5885 , http://hdl.handle.net/10962/d1013286
- Description: The colour vision of adult citrus psylla, Trioza erytreae, was investigated in the laboratory using the behavioural parameters: alightment and walking. Light green flushing leaves (under which the nymphs develop) were significantly preferred, visually, to dark green mature leaves for alightment. Diffuse reflectance spectroscopy showed (when expressed in the parameters of human colour vision) that flush has a very slightly longer dominant wavelength, and roughly double the reflectance and purity. Alightrnent frequency correlated almost equally well with "purity" (as noted by Moericke, 1952 et seq., in "yellow-sensitive" aphids) as with the aphidological colour parameter "long/short ratio" developed by Kennedy et al. (1961). Elucidation of the mechanism underlying the citrus psylla's alightment colour preference was initially attempted with a printed spectrum and several paint series of measured spectral characteristics. It was clear that T.erytreae belongs to the "yellow-sensitive" group of Homoptera, but it was impossible to distinguish which pararneter(s) of colour the psyllids were responding to. Phototactic (walking) response to the individual parameters of colour was therefore measured using a monochromator. The phototactic action spectrum (against wavelength) was tri-modal, with peaks in the yellow-green (YG), blue (B), and ultra= violet (UV). Rate of phototaxis was not influenced by bandwidth (roughly equivalent to purity), but was proportional to intensity (roughly equivalent to reflectance). To investigate the influence of the above three wavelength regions on alightment, use was made of a very simple flight chamber incorporating a target of coloured light. Yellow-green and UV light both independently stimulated alightment . Their effect was additive. Different thresholds indicated distinct YG and UV receptor systems. Blue light alone did not stimulate alightment, and was strongly alightment-inhibitory in combination both with YG and with UV light. On the basis of the above physiological/behavioural findings, a new alightment formula was drawn up for describing the hamopteran's apparent manner of alightment determining integration of surface reflectance. The flush preference and alightment distributions on the series of artificial surfaces were found to correlate slightly more accurately, on average, as well as more consistently, with the new formula than with previously-available colour parameters. These findings are placed in perspective to the literature, and their possible economic relevance is discussed.
- Full Text:
- Date Issued: 1977
Laccase production by selected bacteria species isolated from some aquatic and terrestrial milieu of the Eastern Cape : applications in wastewater treatment
- Authors: Unuofin, John Onolame
- Date: 2018
- Subjects: Laccase Sewage -- Purification -- Biological treatment Water -- Purification
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/9626 , vital:34810
- Description: Aromatic pollutants are a diverse group of chemicals which are continuously produced from industrialization, urbanization and sophistication in technological advancement. Pristine water source polluted by these chemicls makes the water unsafe for human consumption, and as well disrupts the trophic structure of the aquatic milieu. Physico-chemical treatment techniques employed so far have been accompanied by major drawbacks which have overriden the relative successes recorded, hence, greener, simpler and more efficient methods of pollutant transformation is imperative. The prospect of enzymatic treatment of pollutants has gradually been receiving growing attention in contemporary times due to the their environmental friendliness and production economic feasiblity. Laccase, a multicopper oxidase has heightened its appeal towards environmental and biotechnological applications due to its broad substrate specificity and its requirement of atmospheric molecular oxygen as a cosubstrate and the discharge of water as the byproduct. Hence, this present study was designed to evaluate the biotechnological potentials of laccases produced by some bacteria species from some aquatic biomes of the Eastern Cape Province, South Africa. The laccase-producing bacteria were isolated from selected environmental samples by selective enrichment using selective aromatic compounds as sole carbon source and subsequently, laccase-screening phenolic substrates. The laccase-producing bacteria were identified by molecular techniques as proteobacteria belonging to the following genera: Achromobacter, Bordetella, Citrobacter, Pseudomonas and Stenotrophomonas. Optimisation of laccase production in a submerged fermentation was by traditional and statistical methods, where four isolates (Hb9c; Achromobacter xylosoxidans HWN16, Hb16c; Bordetella bronchisepta HSO16, Berl11b2; Stenotrophomonas maltophilia BIJ16, Ie1c; Citrobacter freundii LLJ16) were evaluated for the fermentative production of laccase from lignocellulosic agroindustrial residues. Predictions from statistical optimisation showed that weakly acidic conditions (pH 5) and low agitation speed (100 rpm) were required for maximum laccase production from mandarin peelings (0.5 g/200 mL) and NaNO3 (0.25 g/200 mL) in Hb9c, maize stover (0.50 g/200 mL) and NaNO3 (0.050 g/200mL) in Berl11b2 while a lower agitation speed (50 rpm) was required for maximum laccase output from 2.0 g/200 mL maize stover and 0.050 g/200 mL KNO3 in Ie1c. However, 2.50 g/200 mL wheat bran, 0.050 g/200 mL yeast extract and 50 rpm agitiation under acidic conditions (pH3) yielded maximum laccase titres in Hb16c. Further characterisation of Hb9c and Ie1c laccase secretions portrayed their polyextremotolerant capacities. They were active at a broad range of tempertaure (0-90 degreesC); with optima at 70°C (Hb9c) and 60°C (Ie1c), pH (3-11); with optima at pH 6 (Ie1c) and pH 8 (Hb9c), respectively, and were equally thermo- and pH-stable. Their activities were either improved or left unabated by high concentrations of cations, detergents, and chloride. In addition, catalytic activities of Hb9c and Ie1c laccase secretions increased when they were preincubated with 2 – 20 percent of fluoride, a potent inhibitor. Consequently, a molecular perspective depicted the isolates to have multiple homologous laccase encoding genes. The enzymes were successfully immobilised on solid supports comprising gelatin and Na-alginate with a recovery of cca. 85 percent residual activity after 8 cycles of oprertional stability experiments. The immobilised laccases were remarkable in the decolourisation of synthetic dyes, albeit, free forms also elicited satisfactory performances. Ultimately, the application of free laccases in denim bleaching, individually or with a blend of a mediator, ABTS, showed that denim colours could be bleached without the need for chemical bleaching agents. The results obtained suggest the bacteria laccases produced from lignocellulosic wastes may serve as potent degraders of phenolic pollutants in water and, may also contribute to the bioeconomy and promote greener techniques for industrial applications.
- Full Text:
- Date Issued: 2018
- Authors: Unuofin, John Onolame
- Date: 2018
- Subjects: Laccase Sewage -- Purification -- Biological treatment Water -- Purification
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/9626 , vital:34810
- Description: Aromatic pollutants are a diverse group of chemicals which are continuously produced from industrialization, urbanization and sophistication in technological advancement. Pristine water source polluted by these chemicls makes the water unsafe for human consumption, and as well disrupts the trophic structure of the aquatic milieu. Physico-chemical treatment techniques employed so far have been accompanied by major drawbacks which have overriden the relative successes recorded, hence, greener, simpler and more efficient methods of pollutant transformation is imperative. The prospect of enzymatic treatment of pollutants has gradually been receiving growing attention in contemporary times due to the their environmental friendliness and production economic feasiblity. Laccase, a multicopper oxidase has heightened its appeal towards environmental and biotechnological applications due to its broad substrate specificity and its requirement of atmospheric molecular oxygen as a cosubstrate and the discharge of water as the byproduct. Hence, this present study was designed to evaluate the biotechnological potentials of laccases produced by some bacteria species from some aquatic biomes of the Eastern Cape Province, South Africa. The laccase-producing bacteria were isolated from selected environmental samples by selective enrichment using selective aromatic compounds as sole carbon source and subsequently, laccase-screening phenolic substrates. The laccase-producing bacteria were identified by molecular techniques as proteobacteria belonging to the following genera: Achromobacter, Bordetella, Citrobacter, Pseudomonas and Stenotrophomonas. Optimisation of laccase production in a submerged fermentation was by traditional and statistical methods, where four isolates (Hb9c; Achromobacter xylosoxidans HWN16, Hb16c; Bordetella bronchisepta HSO16, Berl11b2; Stenotrophomonas maltophilia BIJ16, Ie1c; Citrobacter freundii LLJ16) were evaluated for the fermentative production of laccase from lignocellulosic agroindustrial residues. Predictions from statistical optimisation showed that weakly acidic conditions (pH 5) and low agitation speed (100 rpm) were required for maximum laccase production from mandarin peelings (0.5 g/200 mL) and NaNO3 (0.25 g/200 mL) in Hb9c, maize stover (0.50 g/200 mL) and NaNO3 (0.050 g/200mL) in Berl11b2 while a lower agitation speed (50 rpm) was required for maximum laccase output from 2.0 g/200 mL maize stover and 0.050 g/200 mL KNO3 in Ie1c. However, 2.50 g/200 mL wheat bran, 0.050 g/200 mL yeast extract and 50 rpm agitiation under acidic conditions (pH3) yielded maximum laccase titres in Hb16c. Further characterisation of Hb9c and Ie1c laccase secretions portrayed their polyextremotolerant capacities. They were active at a broad range of tempertaure (0-90 degreesC); with optima at 70°C (Hb9c) and 60°C (Ie1c), pH (3-11); with optima at pH 6 (Ie1c) and pH 8 (Hb9c), respectively, and were equally thermo- and pH-stable. Their activities were either improved or left unabated by high concentrations of cations, detergents, and chloride. In addition, catalytic activities of Hb9c and Ie1c laccase secretions increased when they were preincubated with 2 – 20 percent of fluoride, a potent inhibitor. Consequently, a molecular perspective depicted the isolates to have multiple homologous laccase encoding genes. The enzymes were successfully immobilised on solid supports comprising gelatin and Na-alginate with a recovery of cca. 85 percent residual activity after 8 cycles of oprertional stability experiments. The immobilised laccases were remarkable in the decolourisation of synthetic dyes, albeit, free forms also elicited satisfactory performances. Ultimately, the application of free laccases in denim bleaching, individually or with a blend of a mediator, ABTS, showed that denim colours could be bleached without the need for chemical bleaching agents. The results obtained suggest the bacteria laccases produced from lignocellulosic wastes may serve as potent degraders of phenolic pollutants in water and, may also contribute to the bioeconomy and promote greener techniques for industrial applications.
- Full Text:
- Date Issued: 2018
Pharmacological investigations of Kedrostis africana (L.) Cogn. and Vernonia mespilifolia Less. used in folk medicine in the Eastern Cape, South Africa
- Authors: Unuofin, Jeremiah Oshiomame
- Date: 2017
- Subjects: Medicinal plants -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/9231 , vital:34307
- Description: The prevalence of obesity and its co-morbidity is increasing in South Africa. High calorie diet, sedentary lifestyle and the cultural belief that being fat or obese signifies beauty, wellness and wealth are major causative factors. This study was undertaken to scientifically validate two major medicinal plants used traditionally in the Raymond Mhlaba Municipality for the mespilifolia Less. were used singly and in combination. According to ethnobotanical studies,these two plants are regarded as wild plants and are only used for medicinal purposes. There has been a dearth of scientific reports on the two plants and to the best of our knowledge, this study is the first to investigate the nutritional, antioxidant, antimicrobial, safety and anti-obesity potentials of the two plants and their combination. This study revealed that both plants are rich in nutrients. K. africana had greater ash (16.28 percent), crude fat (1.12 percent), Ca (2505 mg/100g), Mg (485 mg/100g) and Fe (89.95 mg/100g) while V. mespilifolia showed higher crude fibre (29.24 percent), crude protein (10.75 percent), P (400 mg/100g), Na (570 mg/100g), Cu (1.55 mg/100g) and Mn (4.70 mg/100g). K. africana and V. mespilifolia both contributed 223.37 Kcal/kg and 237.37 Kcal/kg of energy respectively. The polyphenolic evaluation of the acetone, aqueous and ethanol extracts of the plants revealed that the acetone extract of the combination of both plants had higher total phenol (144.59 mgGAE/g) and flavonoid (803.93 mgQE/g) contents, the ethanol extract of the combined plant also had the highest tannin contents (1.25 mgTAE/g), while the acetone extracts of K. Africana had the highest proanthocyanidin content (585 mgCE/g). The antioxidant assays revealed that the ethanol extract for V. mespilifolia had higher scavenging potentials of ABTS, DPPH and vinitric oxide radicals while the aqueous extract of the combination of both had higher scavenging potential for hydrogen peroxide radicals. Evaluation of antimicrobial potential of the extracts using the minimial inhibitory concentration (MIC) assay against 6 bacteria (Actinomyces odontolyticus, Lactobacillus sakei, Staphylococcus aureus, Enterobacter cloacae, Pseudomonas aeruginosa and Bacteriodes thetaiotomicron) and 4 fungi (Candida albicans, Microsporium gypsum, Penicillium chrysogenum and Trichophyton tonsurans) revealed that the plants possess antimicrobial activity. The MIC of the extracts against the tested bacterial strains ranged from 2.5 mg/mL to 5 mg/mL acetone and ethanol extracts of V. mespilifolia and the combined plants as well as the ethanol extracts of K. africana. However, no activity was observed for the acetone extract of K. africana and aqueous extracts of V. mespilifolia and the combination of both plants. Only three fungal strains (Candida albicans, Microsporium gypsum and Penicillium chrysogenum) were susceptible to the organic extracts with an MIC 0.3125 mg/mL to 5 mg/mL while the aqueous extracts showed no activity against all the fungal strains. None of the plant extracts showed any activity against Trichophyton tonsurans. The brine shrimp toxicity test revealed that all the three extracts of V. mespilifolia, aqueous and ethanol extracts of K. africana and aqueous and acetone extracts of the combination of both plants were toxic in relative to Meyer’s index and other indices of toxicity. The cytotoxic effect of the aqueous and ethanol extracts of V. mespilifolia, K. africana and their combination were also evaluated using HeLa cells. From this study, all the extracts tested had IC50 values were greater than 20 μg/mL which connotes that they are not toxic. According to the American National Cancer Institute, crude plant extracts are considered cytotoxic in an in vitro assay when concentrations 20 μg/mL and below produce 50% inhibition of tumor cells, after an exposure time of 48 hours. In vivo acute evaluation of single oral administration of 2000 and 5000/kg body weight did not produce mortality or significant behavioral changes during 14 days observation. In addition, the sub-acute administration of the aqueous extract at 200, 400 and 600 mg/kg/bwt/ day over a period of 28 days revealed no mortality or morbidity. The weekly body and organ weight of the rats were not significantly different from those of the controls and extract treated rats. The aqueous extracts at all doses did not show any significant (p > 0.05) effect on biomarkers of liver and renal damage. Haematological evaluation revealed that oral administration of aqueous extracts of K. africana, V. mespilifolia and the combination of both plants did not induce anaemia or leucocytosis in the animals. Furthermore, histopathological evaluation of the internal organs revealed no detectable inflammation at the the doses administered over a period of 28 days. These results demonstrated that the aqueous extracts of K. africana, V. mespilifolia and the combination of both plants was potentially safe for consumption orally even in chronic administration. Enzyme based in-vitro antiobesity evaluation of the aqueous and ethanolic extracts of K. africana, V. mespilifolia and their combination revealed that the ethanol extracts of both plants and their combination exhibited moderate inhibitory activities against α-amylase, α- glucosidase and pancreatic lipase. However, the standards used for the various inhibition assays exhibited much higher inhibitory actions when compared to any of the extracts. This suggests that the mechanism by which these two plants and their combination exert anti-obesity effects are probably not by inhibition of key enzymes of carbohydrate and fat metabolism.
- Full Text:
- Date Issued: 2017
- Authors: Unuofin, Jeremiah Oshiomame
- Date: 2017
- Subjects: Medicinal plants -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/9231 , vital:34307
- Description: The prevalence of obesity and its co-morbidity is increasing in South Africa. High calorie diet, sedentary lifestyle and the cultural belief that being fat or obese signifies beauty, wellness and wealth are major causative factors. This study was undertaken to scientifically validate two major medicinal plants used traditionally in the Raymond Mhlaba Municipality for the mespilifolia Less. were used singly and in combination. According to ethnobotanical studies,these two plants are regarded as wild plants and are only used for medicinal purposes. There has been a dearth of scientific reports on the two plants and to the best of our knowledge, this study is the first to investigate the nutritional, antioxidant, antimicrobial, safety and anti-obesity potentials of the two plants and their combination. This study revealed that both plants are rich in nutrients. K. africana had greater ash (16.28 percent), crude fat (1.12 percent), Ca (2505 mg/100g), Mg (485 mg/100g) and Fe (89.95 mg/100g) while V. mespilifolia showed higher crude fibre (29.24 percent), crude protein (10.75 percent), P (400 mg/100g), Na (570 mg/100g), Cu (1.55 mg/100g) and Mn (4.70 mg/100g). K. africana and V. mespilifolia both contributed 223.37 Kcal/kg and 237.37 Kcal/kg of energy respectively. The polyphenolic evaluation of the acetone, aqueous and ethanol extracts of the plants revealed that the acetone extract of the combination of both plants had higher total phenol (144.59 mgGAE/g) and flavonoid (803.93 mgQE/g) contents, the ethanol extract of the combined plant also had the highest tannin contents (1.25 mgTAE/g), while the acetone extracts of K. Africana had the highest proanthocyanidin content (585 mgCE/g). The antioxidant assays revealed that the ethanol extract for V. mespilifolia had higher scavenging potentials of ABTS, DPPH and vinitric oxide radicals while the aqueous extract of the combination of both had higher scavenging potential for hydrogen peroxide radicals. Evaluation of antimicrobial potential of the extracts using the minimial inhibitory concentration (MIC) assay against 6 bacteria (Actinomyces odontolyticus, Lactobacillus sakei, Staphylococcus aureus, Enterobacter cloacae, Pseudomonas aeruginosa and Bacteriodes thetaiotomicron) and 4 fungi (Candida albicans, Microsporium gypsum, Penicillium chrysogenum and Trichophyton tonsurans) revealed that the plants possess antimicrobial activity. The MIC of the extracts against the tested bacterial strains ranged from 2.5 mg/mL to 5 mg/mL acetone and ethanol extracts of V. mespilifolia and the combined plants as well as the ethanol extracts of K. africana. However, no activity was observed for the acetone extract of K. africana and aqueous extracts of V. mespilifolia and the combination of both plants. Only three fungal strains (Candida albicans, Microsporium gypsum and Penicillium chrysogenum) were susceptible to the organic extracts with an MIC 0.3125 mg/mL to 5 mg/mL while the aqueous extracts showed no activity against all the fungal strains. None of the plant extracts showed any activity against Trichophyton tonsurans. The brine shrimp toxicity test revealed that all the three extracts of V. mespilifolia, aqueous and ethanol extracts of K. africana and aqueous and acetone extracts of the combination of both plants were toxic in relative to Meyer’s index and other indices of toxicity. The cytotoxic effect of the aqueous and ethanol extracts of V. mespilifolia, K. africana and their combination were also evaluated using HeLa cells. From this study, all the extracts tested had IC50 values were greater than 20 μg/mL which connotes that they are not toxic. According to the American National Cancer Institute, crude plant extracts are considered cytotoxic in an in vitro assay when concentrations 20 μg/mL and below produce 50% inhibition of tumor cells, after an exposure time of 48 hours. In vivo acute evaluation of single oral administration of 2000 and 5000/kg body weight did not produce mortality or significant behavioral changes during 14 days observation. In addition, the sub-acute administration of the aqueous extract at 200, 400 and 600 mg/kg/bwt/ day over a period of 28 days revealed no mortality or morbidity. The weekly body and organ weight of the rats were not significantly different from those of the controls and extract treated rats. The aqueous extracts at all doses did not show any significant (p > 0.05) effect on biomarkers of liver and renal damage. Haematological evaluation revealed that oral administration of aqueous extracts of K. africana, V. mespilifolia and the combination of both plants did not induce anaemia or leucocytosis in the animals. Furthermore, histopathological evaluation of the internal organs revealed no detectable inflammation at the the doses administered over a period of 28 days. These results demonstrated that the aqueous extracts of K. africana, V. mespilifolia and the combination of both plants was potentially safe for consumption orally even in chronic administration. Enzyme based in-vitro antiobesity evaluation of the aqueous and ethanolic extracts of K. africana, V. mespilifolia and their combination revealed that the ethanol extracts of both plants and their combination exhibited moderate inhibitory activities against α-amylase, α- glucosidase and pancreatic lipase. However, the standards used for the various inhibition assays exhibited much higher inhibitory actions when compared to any of the extracts. This suggests that the mechanism by which these two plants and their combination exert anti-obesity effects are probably not by inhibition of key enzymes of carbohydrate and fat metabolism.
- Full Text:
- Date Issued: 2017
Optimization of the vermidegradation of cow dung – waste paper mixtures
- Authors: Unuofin, Frank Oshioname
- Date: 2014
- Subjects: Biodegradation , Vermicomposting , Waste paper , Earthworm culture , Phosphatic fertilizers
- Language: English
- Type: Thesis , Doctoral , PhD (Soil Science)
- Identifier: vital:11966 , http://hdl.handle.net/10353/d1021276 , Biodegradation , Vermicomposting , Waste paper , Earthworm culture , Phosphatic fertilizers
- Description: Vermicomposting is an eco-friendly waste management strategy. Its successful performance necessitate that key functioning parameters like earthworm stocking density, nutrient enrichment be established for each target waste/waste mixture. One main target waste mixture in South Africa, and in the University of Fort Hare in particular is waste paper mixed with cow dung and rock phosphate (RP) for phosphorus (P) enrichment. This study was carried out to address the following specific objectives, to determine (i) the effect of Eisenia fetida stocking density on the bioconversion of cow dung waste paper mixtures enriched with rock phosphate, (ii) an optimum application rate of low grade South African Rock Phosphate and time required for efficient vermicomposting of cow dung-waste paper mixtures, and (iii) to determine if the phosphorus in RP is responsible for improved biodegradation during the vermicomposting of cow dung-waste paper mixtures. Results of this study revealed that bioconversion of cow dung waste paper mixtures enriched with RP was highly dependent on E. fetida stocking density and time. The stocking density of 12.5 g-worms kg-1 feedstock of the mixtures resulted in highest earthworm growth rate and humification of the waste mixture as reflected by a C: N ratio of < 12, polymerization index (PI) or humic acid/fulvic acid ratio of > 1.9, and a humification index of >13 for the cow dung waste paper mixtures. A germination test carried out also revealed that the resultant vermicompost had no inhibitory effect on the germination of tomato, carrot, and radish. Extractable P increased with stocking density up to 22.5 g-worm kg-1 feedstock, suggesting that for maximum P release from RP enriched wastes, a high stocking density should be considered. Informed by an earlier study which demonstrated that RP improved vermidegration, a follow up study was done to determine the optimum amount of rock phosphate necessary for efficient vermidegradation of cow dung waste paper mixtures while ensuring a phosphorus rich vermicompost. The results showed that addition of RP at rates ≤ 1% P as RP efficiently enhanced the bioconversion of cow dung waste paper mixtures as reflected by low C: N ratio, high polymerization index (PI), HI and HR used as maturity indicators for matured compost. Final vermicompost products obtained at minimum amounts of RP application rates resulted highly humified vermicompost with finer morphological structure, with no inhibitory effect on the germination of tomato, carrot, and radish similar to the ones obtained at higher RP rates. The findings suggest that 1%P as RP application rate is optimum for efficient vermidegradation of cow dung waste paper mixtures. Since P or Ca happen to be the most prevalent elements in most rock phosphate used for compost enrichment, a study was carried out to determine if P or Ca in RP is predominantly responsible for the improved biodegradation of cow-dung waste paper mixture observed during vermicomposting. Phosphorus sources in form of triple superphosphate (TSP), phosphoric acid (PHA) and Ca in form of calcium chloride (CaCl2) salt were compared with rock phosphate. The results from the study indicated that TSP, a water soluble P source, resulted in greater and faster degradation of the waste mixtures than RP while the Ca source had the least effect. With TSP incorporation the compost maturity C: N ratio of 12 was reached within 28 days while RP, PHA and CaCl2 needed 42, 56 and more than 56 days, respectively. The results indicated that P was largely responsible for the enhanced bioconversion of the waste mixtures. This appeared linked to the effect of P to stimulate microbial growth as reflected by higher microbial biomass carbon levels where water soluble P sources were applied. The C: N ratios of the final vermicomposts at day 56 were 10, 11.5, 13, 14, and 23 for TSP, RP,PHA, Control (No P added) and CaCl2 treatments, respectively. Although TSP gave superior superior performance, RP may still be the preferred additive in the vermicomposting of cow dung waste paper mixtures as it is cheaper and produces mature compost in a shorter period of 8 weeks. Generally, the results of this study have shown that the vemidegradation of cow dung waste paper mixtures can be optimized through adoption of an E. fetida stocking density of 12.5g- worm kg-1 and an RP incorporation rate of 1% P as RP. However, higher rates of RPincorporation may be adopted where final vermicomposts with higher P fertilizer value are desired. Phosphorus appears to be the RP constituent responsible for its ability to enhance the vermidegradation of cow dung waste paper mixtures. Future studies should explore the effectiveness of other P-bearing minerals for their effectiveness in enhancing vemidegradation.
- Full Text:
- Date Issued: 2014
- Authors: Unuofin, Frank Oshioname
- Date: 2014
- Subjects: Biodegradation , Vermicomposting , Waste paper , Earthworm culture , Phosphatic fertilizers
- Language: English
- Type: Thesis , Doctoral , PhD (Soil Science)
- Identifier: vital:11966 , http://hdl.handle.net/10353/d1021276 , Biodegradation , Vermicomposting , Waste paper , Earthworm culture , Phosphatic fertilizers
- Description: Vermicomposting is an eco-friendly waste management strategy. Its successful performance necessitate that key functioning parameters like earthworm stocking density, nutrient enrichment be established for each target waste/waste mixture. One main target waste mixture in South Africa, and in the University of Fort Hare in particular is waste paper mixed with cow dung and rock phosphate (RP) for phosphorus (P) enrichment. This study was carried out to address the following specific objectives, to determine (i) the effect of Eisenia fetida stocking density on the bioconversion of cow dung waste paper mixtures enriched with rock phosphate, (ii) an optimum application rate of low grade South African Rock Phosphate and time required for efficient vermicomposting of cow dung-waste paper mixtures, and (iii) to determine if the phosphorus in RP is responsible for improved biodegradation during the vermicomposting of cow dung-waste paper mixtures. Results of this study revealed that bioconversion of cow dung waste paper mixtures enriched with RP was highly dependent on E. fetida stocking density and time. The stocking density of 12.5 g-worms kg-1 feedstock of the mixtures resulted in highest earthworm growth rate and humification of the waste mixture as reflected by a C: N ratio of < 12, polymerization index (PI) or humic acid/fulvic acid ratio of > 1.9, and a humification index of >13 for the cow dung waste paper mixtures. A germination test carried out also revealed that the resultant vermicompost had no inhibitory effect on the germination of tomato, carrot, and radish. Extractable P increased with stocking density up to 22.5 g-worm kg-1 feedstock, suggesting that for maximum P release from RP enriched wastes, a high stocking density should be considered. Informed by an earlier study which demonstrated that RP improved vermidegration, a follow up study was done to determine the optimum amount of rock phosphate necessary for efficient vermidegradation of cow dung waste paper mixtures while ensuring a phosphorus rich vermicompost. The results showed that addition of RP at rates ≤ 1% P as RP efficiently enhanced the bioconversion of cow dung waste paper mixtures as reflected by low C: N ratio, high polymerization index (PI), HI and HR used as maturity indicators for matured compost. Final vermicompost products obtained at minimum amounts of RP application rates resulted highly humified vermicompost with finer morphological structure, with no inhibitory effect on the germination of tomato, carrot, and radish similar to the ones obtained at higher RP rates. The findings suggest that 1%P as RP application rate is optimum for efficient vermidegradation of cow dung waste paper mixtures. Since P or Ca happen to be the most prevalent elements in most rock phosphate used for compost enrichment, a study was carried out to determine if P or Ca in RP is predominantly responsible for the improved biodegradation of cow-dung waste paper mixture observed during vermicomposting. Phosphorus sources in form of triple superphosphate (TSP), phosphoric acid (PHA) and Ca in form of calcium chloride (CaCl2) salt were compared with rock phosphate. The results from the study indicated that TSP, a water soluble P source, resulted in greater and faster degradation of the waste mixtures than RP while the Ca source had the least effect. With TSP incorporation the compost maturity C: N ratio of 12 was reached within 28 days while RP, PHA and CaCl2 needed 42, 56 and more than 56 days, respectively. The results indicated that P was largely responsible for the enhanced bioconversion of the waste mixtures. This appeared linked to the effect of P to stimulate microbial growth as reflected by higher microbial biomass carbon levels where water soluble P sources were applied. The C: N ratios of the final vermicomposts at day 56 were 10, 11.5, 13, 14, and 23 for TSP, RP,PHA, Control (No P added) and CaCl2 treatments, respectively. Although TSP gave superior superior performance, RP may still be the preferred additive in the vermicomposting of cow dung waste paper mixtures as it is cheaper and produces mature compost in a shorter period of 8 weeks. Generally, the results of this study have shown that the vemidegradation of cow dung waste paper mixtures can be optimized through adoption of an E. fetida stocking density of 12.5g- worm kg-1 and an RP incorporation rate of 1% P as RP. However, higher rates of RPincorporation may be adopted where final vermicomposts with higher P fertilizer value are desired. Phosphorus appears to be the RP constituent responsible for its ability to enhance the vermidegradation of cow dung waste paper mixtures. Future studies should explore the effectiveness of other P-bearing minerals for their effectiveness in enhancing vemidegradation.
- Full Text:
- Date Issued: 2014
Synthesis and exploration of resorcinol derivatives as Plasmodium falciparum Hsp90 inhibitors
- Authors: Umumararungu, Théoneste
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/717 , vital:19984
- Description: In this research project, we have synthesized a series of nine dimethyl ether resorcinol analogues of NMS-E973 (L-1) 38, a potent Hsp90 inhibitor. These analogues were chosen because they share the same pharmacophore with NMS-E973 (L-1) 38 and were thus expected to have a similar biological activity. Moreover, it is generally easier to synthesize the dimethyl ether resorcinol analogues of NMS-E973 (L-1) 38 as compared to their demethylated counterparts. Since other Hsp90 inhibitors such as geldanamycin 19 have demonstrated anti-plasmodial activity, we also expected our compounds to be Hsp90 inhibitors and to possess anti-plasmodial activity. However, our compounds were tested for growth inhibitory activity of Plasmodium falciparum and not for P. falciparum Hsp90 (PfHSP90) inhibitory activity. The synthesis involved a series of steps that led to the formation of the ester compound TU-011 (L-7) 43 that was then used as a precursor for different NMS-E973 (L-1) 38 analogues. The choice of analogues to be synthesized was dictated by binding affinity predictions obtained from molecular docking. The chosen synthetic analogues were active against chloroquine-sensitive Plasmodium falciparum (3D7 strain) in a Plasmodium lactate dehydrogenase assay and they were not generally cytotoxic to human cervical adenocarcinoma cell line HeLa. The most active of our compounds was TU-018 (L-103) 50 with an IC50 value of approximately 1.830 µM as compared to the standard, chloroquine, with an IC50 value of 0.01062 µM. Some of the compounds showed mild cytotoxicity towards HeLa cells with IC50 values higher than 25 µM as compared to the standard apoptosis inducer drug, emetine that had an IC50 value of 0.09948 µM. These results highlight the fact that the synthesized analogues are novel relatively non-toxic anti-plasmodial agents.
- Full Text:
- Date Issued: 2016
- Authors: Umumararungu, Théoneste
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/717 , vital:19984
- Description: In this research project, we have synthesized a series of nine dimethyl ether resorcinol analogues of NMS-E973 (L-1) 38, a potent Hsp90 inhibitor. These analogues were chosen because they share the same pharmacophore with NMS-E973 (L-1) 38 and were thus expected to have a similar biological activity. Moreover, it is generally easier to synthesize the dimethyl ether resorcinol analogues of NMS-E973 (L-1) 38 as compared to their demethylated counterparts. Since other Hsp90 inhibitors such as geldanamycin 19 have demonstrated anti-plasmodial activity, we also expected our compounds to be Hsp90 inhibitors and to possess anti-plasmodial activity. However, our compounds were tested for growth inhibitory activity of Plasmodium falciparum and not for P. falciparum Hsp90 (PfHSP90) inhibitory activity. The synthesis involved a series of steps that led to the formation of the ester compound TU-011 (L-7) 43 that was then used as a precursor for different NMS-E973 (L-1) 38 analogues. The choice of analogues to be synthesized was dictated by binding affinity predictions obtained from molecular docking. The chosen synthetic analogues were active against chloroquine-sensitive Plasmodium falciparum (3D7 strain) in a Plasmodium lactate dehydrogenase assay and they were not generally cytotoxic to human cervical adenocarcinoma cell line HeLa. The most active of our compounds was TU-018 (L-103) 50 with an IC50 value of approximately 1.830 µM as compared to the standard, chloroquine, with an IC50 value of 0.01062 µM. Some of the compounds showed mild cytotoxicity towards HeLa cells with IC50 values higher than 25 µM as compared to the standard apoptosis inducer drug, emetine that had an IC50 value of 0.09948 µM. These results highlight the fact that the synthesized analogues are novel relatively non-toxic anti-plasmodial agents.
- Full Text:
- Date Issued: 2016