Curcumin analogues as ligands for Re (I) and (V)
- Authors: Schmitt, Bonell
- Date: 2012
- Subjects: Rhenium , Ligands , Chemistry, Inorganic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10443 , http://hdl.handle.net/10948/d1020975
- Description: Coordination properties of 4-bromo-N-(diethylcarbamothioyl)benzamide (Hbeb) and 4-bromo-N-(diphenylcarbamothioyl)benzamide (Hbpb) with oxorhenium(V) and rhenium(I) are reported and discussed. Transition metal complexes of these ligands were studied due to the wide range of applications of thiourea derivatives in biological fields. N-[Di(alkyl/aryl)carbamothioyl]benzamide derivatives readily coordinate to metal ions as O,S-donors and the catalytic property of the complexes can be altered by these ligands, due to steric and electronic properties provided by various substituents. The coordination possibilities of curcumin with rhenium(V) are discussed, as well as the difficulties encountered. Analogues of curcumin have been made, which also contains a seven-spacer unit between the phenyl rings, which would be more reactive and more effective in bonding to rhenium and which have greater or a similar biological activity to curcumin. This was done by assessing the coordination properties of 1,5-bis(salicylidene)thiocarbohydrazide (H4salt) and 2,4-bis(vanilidene)thiocarbohydrazide (H4vant) with oxorhenium(V) and rhenium(I) starting materials. Two rhenium(V) complex salts of the core [ReX(PPh3)2]4+ (X = Br, I), containing a coordinated imido nitrogen, are reported. One is a ‘2+1’ complex, coordinating bi- and monodentately, with the other a similar ‘3+0’ complex containing a tridentate imido-coordinated Schiff base. Selected compounds were tested against oesophageal cancer cell lines in order to evaluate and compare their effectiveness in eliminating or reducing the cancer cells in the test medium during biological testing.
- Full Text:
- Date Issued: 2012
- Authors: Schmitt, Bonell
- Date: 2012
- Subjects: Rhenium , Ligands , Chemistry, Inorganic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10443 , http://hdl.handle.net/10948/d1020975
- Description: Coordination properties of 4-bromo-N-(diethylcarbamothioyl)benzamide (Hbeb) and 4-bromo-N-(diphenylcarbamothioyl)benzamide (Hbpb) with oxorhenium(V) and rhenium(I) are reported and discussed. Transition metal complexes of these ligands were studied due to the wide range of applications of thiourea derivatives in biological fields. N-[Di(alkyl/aryl)carbamothioyl]benzamide derivatives readily coordinate to metal ions as O,S-donors and the catalytic property of the complexes can be altered by these ligands, due to steric and electronic properties provided by various substituents. The coordination possibilities of curcumin with rhenium(V) are discussed, as well as the difficulties encountered. Analogues of curcumin have been made, which also contains a seven-spacer unit between the phenyl rings, which would be more reactive and more effective in bonding to rhenium and which have greater or a similar biological activity to curcumin. This was done by assessing the coordination properties of 1,5-bis(salicylidene)thiocarbohydrazide (H4salt) and 2,4-bis(vanilidene)thiocarbohydrazide (H4vant) with oxorhenium(V) and rhenium(I) starting materials. Two rhenium(V) complex salts of the core [ReX(PPh3)2]4+ (X = Br, I), containing a coordinated imido nitrogen, are reported. One is a ‘2+1’ complex, coordinating bi- and monodentately, with the other a similar ‘3+0’ complex containing a tridentate imido-coordinated Schiff base. Selected compounds were tested against oesophageal cancer cell lines in order to evaluate and compare their effectiveness in eliminating or reducing the cancer cells in the test medium during biological testing.
- Full Text:
- Date Issued: 2012
Factors influencing first-year students’ career decisions to pursue an IT career
- Authors: Twani, Malibongwe
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/54135 , vital:46306
- Description: The process of deciding on a career is a dauntingand life-changing decision,which all scholarshave had to make. Various factors influence a first-year student’s career choice decision and selected field of study. Career decision-making,as a field of study, has been extensivelyresearched,globally. The research studies focusingon IT career choicesof studentshave indicated that scholars choosing careers in Information Technology (IT) are influenced by factors such as salaries, knowledge of career opportunities, the reputation of IT-related fields in society and by parents, teachers and role models. Recent research indicates that exposure to new technologies and programming concepts at the school level can influence a scholar’s IT career choice. Theories relating to career choice have focused on the characteristics of individuals and their environment. Career choice models have identified factors that influenced a student’s career choice.In South Africahowever,there have been limited studies investigating the factors influencing students’ career decisions in choosing careers in Computer Science (CS), Information Systems (IS) and Information Technology (IT)using mixed-methods.This study aims to investigate the factors that influence first-year students’ decisionsin choosing an IT career at the Nelson Mandela University.The research study pursueda pragmatisticapproach,using a mixed-methods approach. In investigating theories andfactors that influence students’ decisionsin choosing IT careers,the study used systematic literature reviews. The decision-making theories and factorsin theliterature review facilitated the creation of the conceptual framework for IT career decision making. A questionnaire was developed and distributed amongst ITand Non-ITfirst-year studentsin 2021. Fourhundredand eightparticipants completed the survey. The data obtained from the survey were statistically analysed, includingdescriptive analysis andExploratory Factor Analysis(EFA). Additionally, inferential statistics were used namely; Correlations, t-test, Confirmatory Factor Analysis(CFA)and Structural Equation Modelling(SEM). The study results wereinterpreted andcompared with iiiotherrelevantstudies. Recommendations were madeto address the factorsthat influencefirst-year students’ IT career decisions.The study highlighted that high academic confidence and personal attributes amongststudents,whowereinvolved at an early age in programming and using computers,chose IT as a career. The study showed significant statistical differences betweenIT and Non-IT groups in perceptions about the IT industry and identifying job title descriptions.Additionally, a significant statistical difference between languages and genders was identified in understanding careers. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Twani, Malibongwe
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/54135 , vital:46306
- Description: The process of deciding on a career is a dauntingand life-changing decision,which all scholarshave had to make. Various factors influence a first-year student’s career choice decision and selected field of study. Career decision-making,as a field of study, has been extensivelyresearched,globally. The research studies focusingon IT career choicesof studentshave indicated that scholars choosing careers in Information Technology (IT) are influenced by factors such as salaries, knowledge of career opportunities, the reputation of IT-related fields in society and by parents, teachers and role models. Recent research indicates that exposure to new technologies and programming concepts at the school level can influence a scholar’s IT career choice. Theories relating to career choice have focused on the characteristics of individuals and their environment. Career choice models have identified factors that influenced a student’s career choice.In South Africahowever,there have been limited studies investigating the factors influencing students’ career decisions in choosing careers in Computer Science (CS), Information Systems (IS) and Information Technology (IT)using mixed-methods.This study aims to investigate the factors that influence first-year students’ decisionsin choosing an IT career at the Nelson Mandela University.The research study pursueda pragmatisticapproach,using a mixed-methods approach. In investigating theories andfactors that influence students’ decisionsin choosing IT careers,the study used systematic literature reviews. The decision-making theories and factorsin theliterature review facilitated the creation of the conceptual framework for IT career decision making. A questionnaire was developed and distributed amongst ITand Non-ITfirst-year studentsin 2021. Fourhundredand eightparticipants completed the survey. The data obtained from the survey were statistically analysed, includingdescriptive analysis andExploratory Factor Analysis(EFA). Additionally, inferential statistics were used namely; Correlations, t-test, Confirmatory Factor Analysis(CFA)and Structural Equation Modelling(SEM). The study results wereinterpreted andcompared with iiiotherrelevantstudies. Recommendations were madeto address the factorsthat influencefirst-year students’ IT career decisions.The study highlighted that high academic confidence and personal attributes amongststudents,whowereinvolved at an early age in programming and using computers,chose IT as a career. The study showed significant statistical differences betweenIT and Non-IT groups in perceptions about the IT industry and identifying job title descriptions.Additionally, a significant statistical difference between languages and genders was identified in understanding careers. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text:
- Date Issued: 2021-12
Assessment of the microalgal community structure and biomass in surface waterbodies of the Eastern Cape Karoo region earmarked for shale gas exploration
- Authors: Roussouw, Natasha Kimberlee
- Date: 2018
- Subjects: Fresh water -- Eastern Cape , Water-supply -- South Africa -- Eastern Cape Water-supply, Rural -- South Africa -- Eastern Cape Constructed wetlands Watershed management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/35234 , vital:33655
- Description: The Eastern Cape Karoo region of South Africa typically displays low rainfall and high temperatures, which is particularly concerning considering the shale gas exploration/extraction project proposed recently. Almost 90% of the fracking fluid consists of water and with the Karoo region already classified as a water-stressed region, the increased demand for freshwater for fracking could put further pressure on water resources of the region. By understanding the ecological functioning of the lower trophic levels, likely implications for higher trophic levels can be determined, and ultimately, recommendations for mitigation actions can be made. Here, observations aimed at understanding the dynamics of lower trophic levels are presented, that is, the microalgal biomass and assemblage composition within three characteristic surface waterbodies of the region. In addition, the work focuses on the smaller, more dynamic temporary wetland systems typical of this water-scarce region, with the aim of understanding the significance of single species macrophyte cover in relation to the lower trophic levels. Thirty-three waterbodies were sampled (natural depressions = 13, dams = 9, rivers = 11) during November 2014 (austral spring) and April 2015 (austral autumn). Waterbody physico-chemistry, hydro-morphometry, habitat cover and surrounding land-use, as well as microalgal biomass and assemblage composition within each waterbody type were measured. Thirteen natural depression wetlands were sampled during October 2015, December 2015 and March 2016. Once again, waterbody physico-chemistry, microalgal biomass and assemblage composition were measured. However, in addition, Schoenoplectus decipiens macrophyte cover and microalgal (diatom) species composition were also determined. In general, no significant differences in microalgal biomass between the three main waterbody types of the Eastern Cape Karoo region were found; however, the different waterbody types each displayed distinct microalgal assemblage compositions. Also, Schoenoplectus decipiens cover had negligible effects on microalgal biomass and assemblages in the temporary wetlands investigated here. These results suggest that the generalist nature of species occupying these systems allows them to adapt to the ever-changing conditions typical of this region. Ongoing monitoring initiatives considering impending hydraulic fracturing activities should include a comprehensive species-level diversity census, which could further inform management of any impacts associated with this potential disturbance.
- Full Text:
- Date Issued: 2018
- Authors: Roussouw, Natasha Kimberlee
- Date: 2018
- Subjects: Fresh water -- Eastern Cape , Water-supply -- South Africa -- Eastern Cape Water-supply, Rural -- South Africa -- Eastern Cape Constructed wetlands Watershed management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/35234 , vital:33655
- Description: The Eastern Cape Karoo region of South Africa typically displays low rainfall and high temperatures, which is particularly concerning considering the shale gas exploration/extraction project proposed recently. Almost 90% of the fracking fluid consists of water and with the Karoo region already classified as a water-stressed region, the increased demand for freshwater for fracking could put further pressure on water resources of the region. By understanding the ecological functioning of the lower trophic levels, likely implications for higher trophic levels can be determined, and ultimately, recommendations for mitigation actions can be made. Here, observations aimed at understanding the dynamics of lower trophic levels are presented, that is, the microalgal biomass and assemblage composition within three characteristic surface waterbodies of the region. In addition, the work focuses on the smaller, more dynamic temporary wetland systems typical of this water-scarce region, with the aim of understanding the significance of single species macrophyte cover in relation to the lower trophic levels. Thirty-three waterbodies were sampled (natural depressions = 13, dams = 9, rivers = 11) during November 2014 (austral spring) and April 2015 (austral autumn). Waterbody physico-chemistry, hydro-morphometry, habitat cover and surrounding land-use, as well as microalgal biomass and assemblage composition within each waterbody type were measured. Thirteen natural depression wetlands were sampled during October 2015, December 2015 and March 2016. Once again, waterbody physico-chemistry, microalgal biomass and assemblage composition were measured. However, in addition, Schoenoplectus decipiens macrophyte cover and microalgal (diatom) species composition were also determined. In general, no significant differences in microalgal biomass between the three main waterbody types of the Eastern Cape Karoo region were found; however, the different waterbody types each displayed distinct microalgal assemblage compositions. Also, Schoenoplectus decipiens cover had negligible effects on microalgal biomass and assemblages in the temporary wetlands investigated here. These results suggest that the generalist nature of species occupying these systems allows them to adapt to the ever-changing conditions typical of this region. Ongoing monitoring initiatives considering impending hydraulic fracturing activities should include a comprehensive species-level diversity census, which could further inform management of any impacts associated with this potential disturbance.
- Full Text:
- Date Issued: 2018
The diversity and distribution patterns of intertidal fish in the Agulhas bioregion
- Authors: Roux, Maryanne
- Date: 2013
- Subjects: Intertidal fishes , Marine fishes -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10723 , http://hdl.handle.net/10948/d1019712
- Description: This study aimed to expand the existing knowledge on the diversity and distribution patterns of intertidal fishes in the Sardinia Bay MPA and adjacent open access areas. It focussed particularly on in intertidal fish communities along the Agulhas Bioregion coast which has been understudied, especially in recent years. Typical resident species belonging to the family Clinidae were the most abundant, conforming to previous studies. Species from the family Gobiidae were the second most abundant in this study but this family was not previously recorded as being abundant. Transient species were unimportant in the current study which is in contrast to previous studies in the region and suggests a change in species composition. Certain transient species utilised intertidal rockpools as part of their nursery areas in the Eastern Cape, as has previously been found around Algoa Bay. A decrease in species richness from east to west was recorded in this study which has been noted by previous authors and the diversity and distribution patterns of the intertidal fish in the current study conformed to patterns found previously. The position of the biogeographic boundary between the Agulhas and Natal Bioregions could not be confirmed but Wavecrest (along the Transkei coastline) appeared to be part of a transition zone rather than a fixed break. More sampling around this area is recommended to determine the location and understand the dynamic nature of this boundary. The fish species were found to be vertically distributed across the shore with most of the resident species being more abundant across the low shore while the transient species were more abundant in the middle to low shore pools. This vertical distribution has been found at many sites around the world. The volume of the pools proved to be the primary controlling factor while the effect of temperature on vertical distribution could not be demonstrated. The benefits of the Sardinia Bay Marine Protected Area on this unexploited community of fishes could not be demonstrated but the long term benefit of protection has yet to be shown. Results from this study suggest that despite the correspondence with general biogeographic trends, the intertidal fish community has changed in composition (at least in terms of transient species) during the last 30 years and the cause for these changes may in part be reduced recruitment from exploited linefish.
- Full Text:
- Date Issued: 2013
- Authors: Roux, Maryanne
- Date: 2013
- Subjects: Intertidal fishes , Marine fishes -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10723 , http://hdl.handle.net/10948/d1019712
- Description: This study aimed to expand the existing knowledge on the diversity and distribution patterns of intertidal fishes in the Sardinia Bay MPA and adjacent open access areas. It focussed particularly on in intertidal fish communities along the Agulhas Bioregion coast which has been understudied, especially in recent years. Typical resident species belonging to the family Clinidae were the most abundant, conforming to previous studies. Species from the family Gobiidae were the second most abundant in this study but this family was not previously recorded as being abundant. Transient species were unimportant in the current study which is in contrast to previous studies in the region and suggests a change in species composition. Certain transient species utilised intertidal rockpools as part of their nursery areas in the Eastern Cape, as has previously been found around Algoa Bay. A decrease in species richness from east to west was recorded in this study which has been noted by previous authors and the diversity and distribution patterns of the intertidal fish in the current study conformed to patterns found previously. The position of the biogeographic boundary between the Agulhas and Natal Bioregions could not be confirmed but Wavecrest (along the Transkei coastline) appeared to be part of a transition zone rather than a fixed break. More sampling around this area is recommended to determine the location and understand the dynamic nature of this boundary. The fish species were found to be vertically distributed across the shore with most of the resident species being more abundant across the low shore while the transient species were more abundant in the middle to low shore pools. This vertical distribution has been found at many sites around the world. The volume of the pools proved to be the primary controlling factor while the effect of temperature on vertical distribution could not be demonstrated. The benefits of the Sardinia Bay Marine Protected Area on this unexploited community of fishes could not be demonstrated but the long term benefit of protection has yet to be shown. Results from this study suggest that despite the correspondence with general biogeographic trends, the intertidal fish community has changed in composition (at least in terms of transient species) during the last 30 years and the cause for these changes may in part be reduced recruitment from exploited linefish.
- Full Text:
- Date Issued: 2013
Using an intelligent self-service solution to support telecommunication service provisioning
- Authors: Barlow, Sherwin Riaan
- Date: 2012
- Subjects: Telecommunication systems -- Management , Electronic commerce -- Computer programs , Web applications
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10484 , http://hdl.handle.net/10948/d1013417
- Description: The increasing competition between telecommunication service providers (TSPs) and the large amounts of human resource costs incurred to provision telecommunication services to small, medium and micro enterprises (SMMEs), highlight the need for effective self-service provisioning methods to reduce costs. Existing service provisioning methods do not effectively support SMMEs in the service provisioning process. The current methods used are manual and Web-based. The manual service provisioning method is labour and time-intensive. TSPs are being forced to cut human resource costs as the profit margins for provisioning services are narrow due to competition. The current web-based systems do not allow SMMEs to effectively purchase services as they provide long textual lists to consult and limited information about services. The objective of this research was to develop an intelligent web-based self-service system to support SMMEs in telecommunication service provisioning, using a Design Science Research methodology. A constraint-based, knowledge-based recommender system was selected as the most appropriate intelligent system to support telecommunication service provisioning. A prototype called SelPro was developed as a solution to address the shortcomings of the current ineffective service provisioning methods available for SMMEs. SelPro incorporates an interactive wizard-style user interface with dynamic recommendations to support novice users as well as an expert interface which provides less user support. An expert review and a user study were conducted to determine if SelPro was usable, useful and effective. SelPro was perceived as being usable for SMMEs wishing to purchase telecommunication services. Expert participants were satisfied with the usability of SelPro and perceived it as being useful, easy to use and easy to learn. SelPro was considered effective because of the high task success ratings provided by the participants using the two interfaces. The research determined that intelligent web-based self-service provisioning can be used to effectively support SMMEs in telecommunication service provisioning. General design recommendations for similar systems were proposed and future work will involve using intelligent systems to support large enterprises in telecommunication service provisioning.
- Full Text:
- Date Issued: 2012
- Authors: Barlow, Sherwin Riaan
- Date: 2012
- Subjects: Telecommunication systems -- Management , Electronic commerce -- Computer programs , Web applications
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10484 , http://hdl.handle.net/10948/d1013417
- Description: The increasing competition between telecommunication service providers (TSPs) and the large amounts of human resource costs incurred to provision telecommunication services to small, medium and micro enterprises (SMMEs), highlight the need for effective self-service provisioning methods to reduce costs. Existing service provisioning methods do not effectively support SMMEs in the service provisioning process. The current methods used are manual and Web-based. The manual service provisioning method is labour and time-intensive. TSPs are being forced to cut human resource costs as the profit margins for provisioning services are narrow due to competition. The current web-based systems do not allow SMMEs to effectively purchase services as they provide long textual lists to consult and limited information about services. The objective of this research was to develop an intelligent web-based self-service system to support SMMEs in telecommunication service provisioning, using a Design Science Research methodology. A constraint-based, knowledge-based recommender system was selected as the most appropriate intelligent system to support telecommunication service provisioning. A prototype called SelPro was developed as a solution to address the shortcomings of the current ineffective service provisioning methods available for SMMEs. SelPro incorporates an interactive wizard-style user interface with dynamic recommendations to support novice users as well as an expert interface which provides less user support. An expert review and a user study were conducted to determine if SelPro was usable, useful and effective. SelPro was perceived as being usable for SMMEs wishing to purchase telecommunication services. Expert participants were satisfied with the usability of SelPro and perceived it as being useful, easy to use and easy to learn. SelPro was considered effective because of the high task success ratings provided by the participants using the two interfaces. The research determined that intelligent web-based self-service provisioning can be used to effectively support SMMEs in telecommunication service provisioning. General design recommendations for similar systems were proposed and future work will involve using intelligent systems to support large enterprises in telecommunication service provisioning.
- Full Text:
- Date Issued: 2012
Peri-urban agriculture and population growth : the case of Asmara, Eritrea
- Authors: Fessahaie, Tesfamichael
- Date: 2012
- Subjects: Urban agriculture -- Eritrea -- Asmara , Cities and towns -- Eritrea -- Asmara -- Growth
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10668 , http://hdl.handle.net/10948/d109790
- Description: The aim of this thesis is to provide a differentiated view of peri-urban agriculture in the context of urban population growth in Asmara, Eritrea. Peri-urban agriculture is viewed as a distinct type of broader urban agriculture, and in this case is not as subsistence-orientated as other branches of it. Urban population growth is comprised of three elements, namely, natural population increase, rural-urban migration and outward movement of people to the urban periphery linked to urban expansion. Each receives extensive treatment. Asmara is the capital city of Eritrea and using Weeks (2004:473) phrase can be termed as a “primate city”. As such, it exerts a major influence on the political, economic and cultural life of the country, but has never been subjected to this type of research. The analytical framework that is adopted is that of urban population growth. In order to operationalize it, theoretical insights into each of its three branches were applied. For example, the informalisation of the economy in developing cities was used to explain the operation of peri-urban agriculture in the context of natural population growth. An adaption of the original Harris-Todaro Model by Fields (2004) was used for the migrants, and the Mosaic Model by Bryant and Johnson (1992) for those facing urban encroachment. Primary data were collected in the field by the author with the help of research assistants. This was supplemented by secondary data which involved reports commissioned by the Ministry of Agriculture and the Ministry of Public Works. Focus Group discussions were also held to supplement the data with information, views and insights that do not emerge in one-to-one interviews. This thesis demonstrates that those respondents operating within the context of natural population growth make a viable living from peri-urban agriculture, but that they also recognise that there are considerable challenges to be faced. Three sub-groups of farmers are identified. Of these, poultry farmers are the most vulnerable because of the high costs of the inputs, the uncertainty associated with avian „flu and an undeveloped distribution network. The vegetable producers, on the other hand, have a sophisticated marketing network, but low levels of education, high household numbers and an impending shortage of land and water. The agriculturalists that have migrated to Asmara seem to have created sustainable occupations for themselves over a number of years. However, 75 percent of them felt that migration to Asmara was not worthwhile. This negative view is explained in terms of the struggle it has taken to maintain such a living and the growing shortage of land. This set of farmers achieves lower production levels than its city-reared counterparts, carries considerable expenses and has to hire its land. The farmers who have had to cope with urban encroachment fall into two classes. The first has chosen to remain in peri-urban agriculture despite feeling the pressure to scale down activities and thus have a lower income. The majority of this group are dairy farmers who have to trade off increasing costs of cattle feed against shrinking grazing land. They are unwilling to take the initiative to solve their land problems, but look to the authorities to do so. The second class of respondents in this category have abandoned their agricultural holdings. The majority of these agriculturalists are poultry farmers living in the Eastern side of the city. A shortage of agricultural land, high population densities and high costs of inputs make poultry farming difficult. This thesis, therefore, presents a multifaceted view of peri-urban agriculture. While each set of farmers has to cope with its own particular circumstances, there is a common factor. This is the tension between preserving agricultural land on the urban fringe and the need to expand the city to accommodate its inhabitants.
- Full Text:
- Date Issued: 2012
- Authors: Fessahaie, Tesfamichael
- Date: 2012
- Subjects: Urban agriculture -- Eritrea -- Asmara , Cities and towns -- Eritrea -- Asmara -- Growth
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10668 , http://hdl.handle.net/10948/d109790
- Description: The aim of this thesis is to provide a differentiated view of peri-urban agriculture in the context of urban population growth in Asmara, Eritrea. Peri-urban agriculture is viewed as a distinct type of broader urban agriculture, and in this case is not as subsistence-orientated as other branches of it. Urban population growth is comprised of three elements, namely, natural population increase, rural-urban migration and outward movement of people to the urban periphery linked to urban expansion. Each receives extensive treatment. Asmara is the capital city of Eritrea and using Weeks (2004:473) phrase can be termed as a “primate city”. As such, it exerts a major influence on the political, economic and cultural life of the country, but has never been subjected to this type of research. The analytical framework that is adopted is that of urban population growth. In order to operationalize it, theoretical insights into each of its three branches were applied. For example, the informalisation of the economy in developing cities was used to explain the operation of peri-urban agriculture in the context of natural population growth. An adaption of the original Harris-Todaro Model by Fields (2004) was used for the migrants, and the Mosaic Model by Bryant and Johnson (1992) for those facing urban encroachment. Primary data were collected in the field by the author with the help of research assistants. This was supplemented by secondary data which involved reports commissioned by the Ministry of Agriculture and the Ministry of Public Works. Focus Group discussions were also held to supplement the data with information, views and insights that do not emerge in one-to-one interviews. This thesis demonstrates that those respondents operating within the context of natural population growth make a viable living from peri-urban agriculture, but that they also recognise that there are considerable challenges to be faced. Three sub-groups of farmers are identified. Of these, poultry farmers are the most vulnerable because of the high costs of the inputs, the uncertainty associated with avian „flu and an undeveloped distribution network. The vegetable producers, on the other hand, have a sophisticated marketing network, but low levels of education, high household numbers and an impending shortage of land and water. The agriculturalists that have migrated to Asmara seem to have created sustainable occupations for themselves over a number of years. However, 75 percent of them felt that migration to Asmara was not worthwhile. This negative view is explained in terms of the struggle it has taken to maintain such a living and the growing shortage of land. This set of farmers achieves lower production levels than its city-reared counterparts, carries considerable expenses and has to hire its land. The farmers who have had to cope with urban encroachment fall into two classes. The first has chosen to remain in peri-urban agriculture despite feeling the pressure to scale down activities and thus have a lower income. The majority of this group are dairy farmers who have to trade off increasing costs of cattle feed against shrinking grazing land. They are unwilling to take the initiative to solve their land problems, but look to the authorities to do so. The second class of respondents in this category have abandoned their agricultural holdings. The majority of these agriculturalists are poultry farmers living in the Eastern side of the city. A shortage of agricultural land, high population densities and high costs of inputs make poultry farming difficult. This thesis, therefore, presents a multifaceted view of peri-urban agriculture. While each set of farmers has to cope with its own particular circumstances, there is a common factor. This is the tension between preserving agricultural land on the urban fringe and the need to expand the city to accommodate its inhabitants.
- Full Text:
- Date Issued: 2012
In silico and in vitro screening of marrubiin and marrubiin derivatives for antidiabetic activity on PTP1ß, C2C12 myocytes, chang liver hepatocytes and 3T3-L1 adipocytes
- Authors: Nicholas, Rudi Berto
- Date: 2013
- Subjects: Hypoglycemic agents , Diabetes -- Treatment -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10347 , http://hdl.handle.net/10948/d1020638
- Description: Diabetes mellitus (DM) is a life changing disease which affects a large portion of the population and the economy through high medical costs and loss of productivity. Marrubiin (MAR), a diterpenoid isolated from Leonotis leonurus, a plant indigenous to Southern Africa, is used by traditional healers to alleviate DM symptoms. This study aims to screen the inhibitory potential of MAR and MAR derivatives on PTP1β and glucose uptake properties of Chang liver, C2C12 and 3T3-L1 cells. Marrubiin and 19 of its derivatives were tested to determine the inhibition constants for PTP1β. A Ki of 21 μM and 0.047 μM was detected for oleanolic acid in silico and in vitro, respectively. All other diterpene derivatives did not display substantial levels of inhibition of PTP1β. Treatment of Chang liver cells with the various MAR derivatives (10 μM) did not significantly increase glucose uptake beyond metformin, a known antidiabetic drug. The various treatments showed a protective/proliferative effect on the C2C12 muscle cells with two MAR treatments (DC16 and DC18) significantly increasing glucose uptake as compared to metformin in C2C12 muscle cells. It was noted that DC17, DC18 and MAR significantly increased glucose uptake in 3T3-L1 adipocytes, relative to the control. Contrary to cytotoxicity studies with Chang liver and C2C12 muscle cells, adipocytes displayed no cytotoxicity to treatments while a significant increase in cell viability was seen for DC9 and DC15. To unravel the mechanism of action, Western blotting analysis was completed and an increased expression of PTP1β was observed for treatments with DC17 and DC6 was seen in adipocytes, while DC18 and metformin decreased expression significantly. This correlated with a significant decrease of Ser 612 phosphorylation of insulin receptor substrate (IRS1) for DC17. Real time qPCR of IRS1 and GLUT4 highlighted that DC17 and MAR were able to significantly increase expression of IRS1 and GLUT4, respectively. The results show that MAR and the selected derivatives (DC6, DC17, DC18) have been found to increase glucose uptake in peripheral tissue types with IRS1, GLUT4 and PTP1β being associated with the mechanism of action. However, a complete understanding of the mechanisms is yet to be established.
- Full Text:
- Date Issued: 2013
- Authors: Nicholas, Rudi Berto
- Date: 2013
- Subjects: Hypoglycemic agents , Diabetes -- Treatment -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10347 , http://hdl.handle.net/10948/d1020638
- Description: Diabetes mellitus (DM) is a life changing disease which affects a large portion of the population and the economy through high medical costs and loss of productivity. Marrubiin (MAR), a diterpenoid isolated from Leonotis leonurus, a plant indigenous to Southern Africa, is used by traditional healers to alleviate DM symptoms. This study aims to screen the inhibitory potential of MAR and MAR derivatives on PTP1β and glucose uptake properties of Chang liver, C2C12 and 3T3-L1 cells. Marrubiin and 19 of its derivatives were tested to determine the inhibition constants for PTP1β. A Ki of 21 μM and 0.047 μM was detected for oleanolic acid in silico and in vitro, respectively. All other diterpene derivatives did not display substantial levels of inhibition of PTP1β. Treatment of Chang liver cells with the various MAR derivatives (10 μM) did not significantly increase glucose uptake beyond metformin, a known antidiabetic drug. The various treatments showed a protective/proliferative effect on the C2C12 muscle cells with two MAR treatments (DC16 and DC18) significantly increasing glucose uptake as compared to metformin in C2C12 muscle cells. It was noted that DC17, DC18 and MAR significantly increased glucose uptake in 3T3-L1 adipocytes, relative to the control. Contrary to cytotoxicity studies with Chang liver and C2C12 muscle cells, adipocytes displayed no cytotoxicity to treatments while a significant increase in cell viability was seen for DC9 and DC15. To unravel the mechanism of action, Western blotting analysis was completed and an increased expression of PTP1β was observed for treatments with DC17 and DC6 was seen in adipocytes, while DC18 and metformin decreased expression significantly. This correlated with a significant decrease of Ser 612 phosphorylation of insulin receptor substrate (IRS1) for DC17. Real time qPCR of IRS1 and GLUT4 highlighted that DC17 and MAR were able to significantly increase expression of IRS1 and GLUT4, respectively. The results show that MAR and the selected derivatives (DC6, DC17, DC18) have been found to increase glucose uptake in peripheral tissue types with IRS1, GLUT4 and PTP1β being associated with the mechanism of action. However, a complete understanding of the mechanisms is yet to be established.
- Full Text:
- Date Issued: 2013
Water, salt and nutrient budgets of the Swartkops and Sundays river estuaries using the loicz biogeochemical budgeting protocol
- Authors: Potgieter, Matthys Johannes
- Date: 2008
- Subjects: Estuarine oceanography , Groundwater flow -- South Africa -- Swartkops River Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10705 , http://hdl.handle.net/10948/903 , Estuarine oceanography , Groundwater flow -- South Africa -- Swartkops River Estuary
- Description: The Swartkops River and Sundays River Estuaries are different in terms of morphology and the level of human impact. Budget models of DIP and DIN were constructed for each estuary at different riverine flow rates, using the Land-Ocean Interactions in the Coastal Zone (LOICZ) protocol. Nutrient dynamics in the estuaries were investigated using nutrient data and the results of the models. The Swartkops River Estuary acted as a sink of DIP and DIN, while being net heterotrophic. The Sundays River Estuary acted as a source of DIP and DIN, while being net autotrophic. Both systems were net denitrifying. The Swartkops River Estuary shows greater anthropogenic impacts in terms of nutrient loads than the Sundays River Estuary. A shift in nutrient concentration trends and system properties occurred between conditions of low and high riverine flow rates. The Swartkops River and Sundays River Estuaries were shown to be ‘outwellers’ of DIN and DIP, while having an important influence on the ratio of DIN:DIP exported to the adjacent ocean. Comparisons with other estuaries suggested that riverine flow into estuaries in the Eastern Cape region may display natural DIN:DIP ratios which are lower than the global average for “pristine” systems. Such ratios would be decreased further by increased water extraction for human activities.
- Full Text:
- Date Issued: 2008
- Authors: Potgieter, Matthys Johannes
- Date: 2008
- Subjects: Estuarine oceanography , Groundwater flow -- South Africa -- Swartkops River Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10705 , http://hdl.handle.net/10948/903 , Estuarine oceanography , Groundwater flow -- South Africa -- Swartkops River Estuary
- Description: The Swartkops River and Sundays River Estuaries are different in terms of morphology and the level of human impact. Budget models of DIP and DIN were constructed for each estuary at different riverine flow rates, using the Land-Ocean Interactions in the Coastal Zone (LOICZ) protocol. Nutrient dynamics in the estuaries were investigated using nutrient data and the results of the models. The Swartkops River Estuary acted as a sink of DIP and DIN, while being net heterotrophic. The Sundays River Estuary acted as a source of DIP and DIN, while being net autotrophic. Both systems were net denitrifying. The Swartkops River Estuary shows greater anthropogenic impacts in terms of nutrient loads than the Sundays River Estuary. A shift in nutrient concentration trends and system properties occurred between conditions of low and high riverine flow rates. The Swartkops River and Sundays River Estuaries were shown to be ‘outwellers’ of DIN and DIP, while having an important influence on the ratio of DIN:DIP exported to the adjacent ocean. Comparisons with other estuaries suggested that riverine flow into estuaries in the Eastern Cape region may display natural DIN:DIP ratios which are lower than the global average for “pristine” systems. Such ratios would be decreased further by increased water extraction for human activities.
- Full Text:
- Date Issued: 2008
Correlation of photovoltaics plant performance metrics
- Authors: Vumbugwa, Monphias
- Date: 2018
- Subjects: Photovoltaic cells , Perfomance -- Evaluation , Thin films
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/45657 , vital:38924
- Description: The generation of electrical energy using Photovoltaic (PV) technology has increased globally with the decrease in the cost of PV systems and the rise in electrical power demand. In South Africa, the support by the government in implementing the Renewable Energy Independent Power Producer Procurement Programme (REIPPPP) has seen a growth in PV system deployment and investment in roof and ground mounted, stand alone and grid connected PV plants. This rapid growth shows that the PV industry is becoming highly competitive as there is a shift to low carbon emissions and it is anticipated to be the most affordable source of electricity. Hence, there is need to develop maintenance and fault diagnosis expertise and capabilities in the PV industry, which can in turn improve the dependability, productiveness and lifespan of PV systems. Solar PV modules directly receive and convert solar irradiance into electricity and may not generate the expected optimum energy due to abnormalities which arise when they are exposed to harsh unfavorable environmental conditions in the field. Thermal Infrared (TIR) imaging is widely used as a fault diagnosis tool in operating PV modules and mostly in large PV power plants. Therefore, there is need to research the interpretation of the observed thermal signatures and the impact that the anomalies have on electrical output of the system so as to improve the PV maintenance systems. This research focuses on identifying performance limiting defects using an Infra-Red (I-R) camera, mounted on an Unmanned Aerial Vehicle (UAV), to understand the effect of thermal signatures on current-voltage (I-V) characteristics of PV module strings. Aerial TIR imaging using a UAV can rapidly identify abnormalities in operational PV modules strings as hotspots. Any deviation of the string I-V curve, from the expected, indicates a problem with one or more PV modules in the string. However, locating the faulty module involves measuring I-V parameters of the individual modules in a string, which is not feasible in large PV power plants. Therefore, there is a need to estimate the power loss associated with the thermal signatures in PV module strings. Visual inspection may help in identifying the exact cause of some hotspots, while other hotspots need special characterization techniques, such as Electroluminescence (EL) and UV Fluorescence (UV-F), which can indicate if a solar cell is cracked or has weak busbars or contact finger connections.
- Full Text:
- Date Issued: 2018
- Authors: Vumbugwa, Monphias
- Date: 2018
- Subjects: Photovoltaic cells , Perfomance -- Evaluation , Thin films
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/45657 , vital:38924
- Description: The generation of electrical energy using Photovoltaic (PV) technology has increased globally with the decrease in the cost of PV systems and the rise in electrical power demand. In South Africa, the support by the government in implementing the Renewable Energy Independent Power Producer Procurement Programme (REIPPPP) has seen a growth in PV system deployment and investment in roof and ground mounted, stand alone and grid connected PV plants. This rapid growth shows that the PV industry is becoming highly competitive as there is a shift to low carbon emissions and it is anticipated to be the most affordable source of electricity. Hence, there is need to develop maintenance and fault diagnosis expertise and capabilities in the PV industry, which can in turn improve the dependability, productiveness and lifespan of PV systems. Solar PV modules directly receive and convert solar irradiance into electricity and may not generate the expected optimum energy due to abnormalities which arise when they are exposed to harsh unfavorable environmental conditions in the field. Thermal Infrared (TIR) imaging is widely used as a fault diagnosis tool in operating PV modules and mostly in large PV power plants. Therefore, there is need to research the interpretation of the observed thermal signatures and the impact that the anomalies have on electrical output of the system so as to improve the PV maintenance systems. This research focuses on identifying performance limiting defects using an Infra-Red (I-R) camera, mounted on an Unmanned Aerial Vehicle (UAV), to understand the effect of thermal signatures on current-voltage (I-V) characteristics of PV module strings. Aerial TIR imaging using a UAV can rapidly identify abnormalities in operational PV modules strings as hotspots. Any deviation of the string I-V curve, from the expected, indicates a problem with one or more PV modules in the string. However, locating the faulty module involves measuring I-V parameters of the individual modules in a string, which is not feasible in large PV power plants. Therefore, there is a need to estimate the power loss associated with the thermal signatures in PV module strings. Visual inspection may help in identifying the exact cause of some hotspots, while other hotspots need special characterization techniques, such as Electroluminescence (EL) and UV Fluorescence (UV-F), which can indicate if a solar cell is cracked or has weak busbars or contact finger connections.
- Full Text:
- Date Issued: 2018
Cape gannets in contrasting environments: ehaviour, demographics and indicators of environmental change
- Authors: Ryklief, Rabiah
- Date: 2017
- Subjects: Endemic birds -- South Africa Marine pollution -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21167 , vital:29452
- Description: Marine communities represent biological networks, where physical and chemical changes in the marine environment can influence the physiology and behaviour of marine organisms. Stochastic marine conditions can alter key biological interactions and thus, influence the mechanisms that underpin population demography and phenotypic plasticity. Marine top predators, such as seabirds, are often controlled by bottom-up processes and their ability to cope with variable ocean conditions lies in their physiological and behavioural response to such perturbations. Seabirds are central-place foragers during the breeding season making them particularly vulnerable to environmental fluctuations as they face constrains associated with reproductive effort in addition to self-maintenance. The Cape gannet Morus capensis is a medium-sized pelagic seabird that is endemic to southern Africa. The Cape gannet has experienced considerable change in population distribution and abundance over the past 50 years. These changes have been linked to a combination of fishing pressure and climate-mediated regime shifts of their preferred prey, i.e. sardine Sardinops sagax and anchovy ngraulis encrasicolus. Historically, Malgas Island was the largest Cape gannet colony in South Africa. However, it is now in a state of population decline, despite its occurrence within one of the most productive upwelling systems in the world, the Benguela Current. At present, Bird Island is the largest Cape gannet colony and has recently stabilised, despite regular immigration of gannets from the west coast. Furthermore, Bird Island lies within the Agulhas bioregion and is subject to low levels of productivity from the nutrient-poor Agulhas current. Malgas and Bird islands are the two most populous of the six extant Cape gannet colonies. Birds at these colonies provided a natural experiment due to the contrasting population trajectories and environmental conditions at their colonies. The foraging ecology and behaviour of Cape gannets were studied during the breeding season to assess the mechanistic links connecting climate and fisheries to population demography. Cape gannets displayed considerable inter-annual variation in foraging effort and distribution across a five-year period. This highlights the importance of long-term datasets to contextualise the degree of natural variation within a species, as well as considerations for conservation management. For the first time, oceanographic variables such as sea surface temperature and chlorophyll-a, indices that reflect marine productivity, were used to predict Cape gannet foraging distribution. Furthermore, Cape gannets at Bird Island had an energy budget deficit in a year when foraging effort was much higher in comparison to what was observed at Malgas Island. This in turn was linked to the first identification of nutritional stress in a Sulid species. Reasons for this include a combination of higher intra-specific competition in conjunction with a lower energetic content of referential prey species at Bird Island. Foraging effort showed more variability at Malgas Island in comparison to Bird Island, likely due to Malgas Island gannets often taking two short foraging trips a day, whereas Bird Island gannets often spent the night at sea. Some degree of phenotypic plasticity was evidenced by substantial variations across breeding seasons and ocean basins in foraging effort and behaviour.
- Full Text:
- Date Issued: 2017
- Authors: Ryklief, Rabiah
- Date: 2017
- Subjects: Endemic birds -- South Africa Marine pollution -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21167 , vital:29452
- Description: Marine communities represent biological networks, where physical and chemical changes in the marine environment can influence the physiology and behaviour of marine organisms. Stochastic marine conditions can alter key biological interactions and thus, influence the mechanisms that underpin population demography and phenotypic plasticity. Marine top predators, such as seabirds, are often controlled by bottom-up processes and their ability to cope with variable ocean conditions lies in their physiological and behavioural response to such perturbations. Seabirds are central-place foragers during the breeding season making them particularly vulnerable to environmental fluctuations as they face constrains associated with reproductive effort in addition to self-maintenance. The Cape gannet Morus capensis is a medium-sized pelagic seabird that is endemic to southern Africa. The Cape gannet has experienced considerable change in population distribution and abundance over the past 50 years. These changes have been linked to a combination of fishing pressure and climate-mediated regime shifts of their preferred prey, i.e. sardine Sardinops sagax and anchovy ngraulis encrasicolus. Historically, Malgas Island was the largest Cape gannet colony in South Africa. However, it is now in a state of population decline, despite its occurrence within one of the most productive upwelling systems in the world, the Benguela Current. At present, Bird Island is the largest Cape gannet colony and has recently stabilised, despite regular immigration of gannets from the west coast. Furthermore, Bird Island lies within the Agulhas bioregion and is subject to low levels of productivity from the nutrient-poor Agulhas current. Malgas and Bird islands are the two most populous of the six extant Cape gannet colonies. Birds at these colonies provided a natural experiment due to the contrasting population trajectories and environmental conditions at their colonies. The foraging ecology and behaviour of Cape gannets were studied during the breeding season to assess the mechanistic links connecting climate and fisheries to population demography. Cape gannets displayed considerable inter-annual variation in foraging effort and distribution across a five-year period. This highlights the importance of long-term datasets to contextualise the degree of natural variation within a species, as well as considerations for conservation management. For the first time, oceanographic variables such as sea surface temperature and chlorophyll-a, indices that reflect marine productivity, were used to predict Cape gannet foraging distribution. Furthermore, Cape gannets at Bird Island had an energy budget deficit in a year when foraging effort was much higher in comparison to what was observed at Malgas Island. This in turn was linked to the first identification of nutritional stress in a Sulid species. Reasons for this include a combination of higher intra-specific competition in conjunction with a lower energetic content of referential prey species at Bird Island. Foraging effort showed more variability at Malgas Island in comparison to Bird Island, likely due to Malgas Island gannets often taking two short foraging trips a day, whereas Bird Island gannets often spent the night at sea. Some degree of phenotypic plasticity was evidenced by substantial variations across breeding seasons and ocean basins in foraging effort and behaviour.
- Full Text:
- Date Issued: 2017
Aspects of the ecology and biology of Gilchristella aestuarius (G & T) (Pisces: Clupeidae) in the Swartkops estuary, Port Elizabeth
- Talbot, Marie Marcel Jean-Francois
- Authors: Talbot, Marie Marcel Jean-Francois
- Date: 1982-12
- Subjects: Fishes -- Ecology -- South Africa -- Swartkops River Estuary , Swartkops River Estuary (South Africa)
- Language: English
- Type: Master's theses , Manuscripct
- Identifier: http://hdl.handle.net/10948/52352 , vital:43613
- Description: The Department of Zoology at the University of Port Elizabeth has an ongoing programme on the Swartkops estuary with the eventual aim of drawing up the energy pathways of the system. Marais (1976) has investigated the nutritional ecology of the grunter Pommadasys cormersoni while Melville-Smith (1978) and Melville-Smith and Baird (1981) reported on the ecology of larval fish. Winter (1979) studied the ecological parameters of fish populations, but this work was not a detailed account of each population. Wooldridge (1979) studied components of the 3 zooplankton community in some detail. It became evident that there was a significant lack of understanding of the ecological relationships between plankton and piscivorous fish, which was crucial to the elucidation of the interactions and trophodynamics of the Swartkops estuarine system. Since G. aestuarius is an important link in the energy pathway from the plankton to the nekton, and in terms of numbers dominates the seine net catches made in the estuary (Winter, 1979), this study was motivated. The aim was to investigate the important biological parameters of the estuarine round herring population namely the population structure, distribution and abundance, individual growth rate from field data, the food and feeding habits, reproduction and respiration, all of which are essential for the understanding of the dynamics of a species. These parameters were later converted into energy terms and the construction of an energy budget was attempted. , Thesis (MSc) -- Faculty of Science, 1982
- Full Text:
- Date Issued: 1982-12
- Authors: Talbot, Marie Marcel Jean-Francois
- Date: 1982-12
- Subjects: Fishes -- Ecology -- South Africa -- Swartkops River Estuary , Swartkops River Estuary (South Africa)
- Language: English
- Type: Master's theses , Manuscripct
- Identifier: http://hdl.handle.net/10948/52352 , vital:43613
- Description: The Department of Zoology at the University of Port Elizabeth has an ongoing programme on the Swartkops estuary with the eventual aim of drawing up the energy pathways of the system. Marais (1976) has investigated the nutritional ecology of the grunter Pommadasys cormersoni while Melville-Smith (1978) and Melville-Smith and Baird (1981) reported on the ecology of larval fish. Winter (1979) studied the ecological parameters of fish populations, but this work was not a detailed account of each population. Wooldridge (1979) studied components of the 3 zooplankton community in some detail. It became evident that there was a significant lack of understanding of the ecological relationships between plankton and piscivorous fish, which was crucial to the elucidation of the interactions and trophodynamics of the Swartkops estuarine system. Since G. aestuarius is an important link in the energy pathway from the plankton to the nekton, and in terms of numbers dominates the seine net catches made in the estuary (Winter, 1979), this study was motivated. The aim was to investigate the important biological parameters of the estuarine round herring population namely the population structure, distribution and abundance, individual growth rate from field data, the food and feeding habits, reproduction and respiration, all of which are essential for the understanding of the dynamics of a species. These parameters were later converted into energy terms and the construction of an energy budget was attempted. , Thesis (MSc) -- Faculty of Science, 1982
- Full Text:
- Date Issued: 1982-12
Characterization of chromatic dispersion in single mode fibre
- Authors: Wassin, Shukree
- Date: 2014
- Subjects: Fiber optics Electromagnetic waves , Electromagnetic waves -- Transmission
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47807 , vital:40379
- Description: In this dissertation, an investigation of chromatic dispersion is presented. The Pulse delay and phase Shift chromatic dispersion characterization techniques were used for conducting the measurements. The experiments were performed in a modern optical fibre research laboratory and chromatic dispersion measurements were carried out on several lengths of G.652 and G.655 single mode fibres. The pulse delay characterization technique measures the time of flight between two modulated optical signals whilst propagating along the fibre under test. During phase shift experiments, the group delay is obtained by measuring the relative phase difference as a function of wavelength, between adjacent sinusoidal light signals. The pulse delay and phase shift characterization techniques illustrated excellent agreement in the measured! chromatic Dispersion coefficients along the G.652 standard single mode! fibre as well as the G.655 positive and negative non-zero dispersion shifted fibre. It was found that the measurement accuracy improved as the fibre length increased. A periodic shift between the modulated optical signals, propagating along the fibre was experimentally observed. It is to be remarked that the longer wavelength signals propagated faster along the G.655 positive non-zero dispersion shifted fibre in comparison to its transmission within the G.655 negative non-zero dispersion shifted fibre. Furthermore, it was found that the sinusoidal signal shifted towards the left along the G.655 negative NZDSF fibre whilst the shift occurred towards the right along the G.655 positive NZDSF fibre. Generally, the shift arising along the G.655 fibres was found to be smaller than the shift seen throughout the G.652 fibres. Towards the end of this study, a chromatic dispersion compensation system was designed and tested. Once characterization of the compensation link was completed, it was experimentally illustrated that the chromatic dispersion across the system was successfully reduced. Finally, a sum of squares of error statistical test showed that the phase shift technique is more accurate in comparison to the pulse delay method. This result was found to be in good agreement with published work found in literature.
- Full Text:
- Date Issued: 2014
- Authors: Wassin, Shukree
- Date: 2014
- Subjects: Fiber optics Electromagnetic waves , Electromagnetic waves -- Transmission
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47807 , vital:40379
- Description: In this dissertation, an investigation of chromatic dispersion is presented. The Pulse delay and phase Shift chromatic dispersion characterization techniques were used for conducting the measurements. The experiments were performed in a modern optical fibre research laboratory and chromatic dispersion measurements were carried out on several lengths of G.652 and G.655 single mode fibres. The pulse delay characterization technique measures the time of flight between two modulated optical signals whilst propagating along the fibre under test. During phase shift experiments, the group delay is obtained by measuring the relative phase difference as a function of wavelength, between adjacent sinusoidal light signals. The pulse delay and phase shift characterization techniques illustrated excellent agreement in the measured! chromatic Dispersion coefficients along the G.652 standard single mode! fibre as well as the G.655 positive and negative non-zero dispersion shifted fibre. It was found that the measurement accuracy improved as the fibre length increased. A periodic shift between the modulated optical signals, propagating along the fibre was experimentally observed. It is to be remarked that the longer wavelength signals propagated faster along the G.655 positive non-zero dispersion shifted fibre in comparison to its transmission within the G.655 negative non-zero dispersion shifted fibre. Furthermore, it was found that the sinusoidal signal shifted towards the left along the G.655 negative NZDSF fibre whilst the shift occurred towards the right along the G.655 positive NZDSF fibre. Generally, the shift arising along the G.655 fibres was found to be smaller than the shift seen throughout the G.652 fibres. Towards the end of this study, a chromatic dispersion compensation system was designed and tested. Once characterization of the compensation link was completed, it was experimentally illustrated that the chromatic dispersion across the system was successfully reduced. Finally, a sum of squares of error statistical test showed that the phase shift technique is more accurate in comparison to the pulse delay method. This result was found to be in good agreement with published work found in literature.
- Full Text:
- Date Issued: 2014
The feeding ecology and habitat selection of small antelopes in the Overberg Renosterveld, Western Cape
- Authors: Jansen van Vuuren, Amauréé
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Fynbos ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/52014 , vital:43436
- Description: Human impacts have altered natural ecosystems which required species to become resilient in order to survive the anthropogenic landscape. The study area is located in the highly fragmented Overberg area in the Western Cape of South Africa. The high degree of fragmentation of the area is as a result of the nutrient rich soils and favourable topography which makes the area highly suitable for agricultural practices. The agriculture practiced in the area is mainly grain crops and livestock farming and the remaining patches of natural vegetation consist of Fynbos and Renosterveld vegetation. The patches of Fynbos and Renosterveld vegetation acts as movement corridors to allow species movement through the anthropogenic landscape. The anthropogenic landscape requires species to be resilient and to adapt to a novel habitat which poses new threats as well as new resources. The aim of the study is to investigate the effect of landscape transformation, resulting from agricultural practices, on the feeding and behavioural dynamics of five small specialist browser species in a fragmented lowland Fynbos and Renosterveld system. The objectives were to determine the forage preferences of each of the five specialist browser species and to determine which site-specific characteristics, drive the seasonal habitat use of the five specialist browser species. The five specialist browser species were bushbuck (Tragelaphus sylvaticus), Cape grysbok (Rhaphicerus melanotis), common duiker (Sylvicapra grimmia), grey rhebok (Pelea capreolus) and steenbok (Rhaphicerus campestris). To determine the dietary selection of the five specialist browser species we collected dung samples and performed a histological analysis on the dung samples. To determine the habitat use of the five specialist browser species we used an occupancy analysis framework on camera trap data collected on each of the species. Some species appeared more dependent on the food resources from the anthropogenic landscape and spent more time in the crops but required close by cover of natural vegetation. Others appeared more dependent on the remaining pockets of natural vegetation for food resources and spent more time in the natural vegetation. These species would occasionally move into the crops to utilise the food resources. Both the anthropogenic as well as the natural landscape contributed to the diets of all of the species. These species have been resilient to changes in the landscape and appear to be benefiting from the resources presented in the novel landscape. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2021
- Full Text: false
- Date Issued: 2021-04
- Authors: Jansen van Vuuren, Amauréé
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Fynbos ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/52014 , vital:43436
- Description: Human impacts have altered natural ecosystems which required species to become resilient in order to survive the anthropogenic landscape. The study area is located in the highly fragmented Overberg area in the Western Cape of South Africa. The high degree of fragmentation of the area is as a result of the nutrient rich soils and favourable topography which makes the area highly suitable for agricultural practices. The agriculture practiced in the area is mainly grain crops and livestock farming and the remaining patches of natural vegetation consist of Fynbos and Renosterveld vegetation. The patches of Fynbos and Renosterveld vegetation acts as movement corridors to allow species movement through the anthropogenic landscape. The anthropogenic landscape requires species to be resilient and to adapt to a novel habitat which poses new threats as well as new resources. The aim of the study is to investigate the effect of landscape transformation, resulting from agricultural practices, on the feeding and behavioural dynamics of five small specialist browser species in a fragmented lowland Fynbos and Renosterveld system. The objectives were to determine the forage preferences of each of the five specialist browser species and to determine which site-specific characteristics, drive the seasonal habitat use of the five specialist browser species. The five specialist browser species were bushbuck (Tragelaphus sylvaticus), Cape grysbok (Rhaphicerus melanotis), common duiker (Sylvicapra grimmia), grey rhebok (Pelea capreolus) and steenbok (Rhaphicerus campestris). To determine the dietary selection of the five specialist browser species we collected dung samples and performed a histological analysis on the dung samples. To determine the habitat use of the five specialist browser species we used an occupancy analysis framework on camera trap data collected on each of the species. Some species appeared more dependent on the food resources from the anthropogenic landscape and spent more time in the crops but required close by cover of natural vegetation. Others appeared more dependent on the remaining pockets of natural vegetation for food resources and spent more time in the natural vegetation. These species would occasionally move into the crops to utilise the food resources. Both the anthropogenic as well as the natural landscape contributed to the diets of all of the species. These species have been resilient to changes in the landscape and appear to be benefiting from the resources presented in the novel landscape. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2021
- Full Text: false
- Date Issued: 2021-04
Relationship between temparament and linear body parameters of beef cattle under communal grazing system
- Authors: Nekhofhe, Avhasei Justice
- Date: 2002
- Subjects: Cattle , Grazing
- Language: English
- Type: Thesis , Masters , MTech (Agricultural Management)
- Identifier: vital:10965 , http://hdl.handle.net/10948/113 , Cattle , Grazing
- Description: Introduction : Indigenous cattle are mostly reared where the traditional farming is practiced including Northern Region of South Africa. The majority of farmers own Nguni type of cattle although other breeds are found in the region. They perform well under harsh conditions and they seem to produce better under intensive management. However, communal farmers are becoming aware and interested in indigenous breeds especially Nguni cattle type because of their adaptability. Beef cattle production and research require constant movement and handling of livestock (Erf et al., 1992 & Grandin, 1993). Dipping, castration, branding, ear-tagging and counting is commonly practiced as beef cattle management norms hence dehorning are partly practiced as some of the animals had horns which were disturbing them to pass through crushpens and as a result they increased bruising to other animals. At Matatani and Muledzhi areas animals including calves are packed in the crushpens, counted, weighed and temperament traits were also measured on the scale and this is done in order to document the information for this research and future use. Temperament is a behavioural response of animals as handled by man. It is important to be measured in beef cattle farmers under communal grazing conditions as it reduces farmer’s profit and it makes the stock man’s work unpleasant. Therefore, it is also needs to be improved for the improvement of beef cattle schemes. Management system of communal farmers was not conducive to better quality meat due to horns in some animals which ultimately cause bruising in other animals. However, exotic bulls were bought at random for the improvement of other breed types found in these two areas. The focus of this study is almost in Nguni cattle type managed under communal grazing system. Lastly, the purpose of this study is to determine behavioral response of beef cattle under communal management system at their dipping tanks.
- Full Text:
- Date Issued: 2002
- Authors: Nekhofhe, Avhasei Justice
- Date: 2002
- Subjects: Cattle , Grazing
- Language: English
- Type: Thesis , Masters , MTech (Agricultural Management)
- Identifier: vital:10965 , http://hdl.handle.net/10948/113 , Cattle , Grazing
- Description: Introduction : Indigenous cattle are mostly reared where the traditional farming is practiced including Northern Region of South Africa. The majority of farmers own Nguni type of cattle although other breeds are found in the region. They perform well under harsh conditions and they seem to produce better under intensive management. However, communal farmers are becoming aware and interested in indigenous breeds especially Nguni cattle type because of their adaptability. Beef cattle production and research require constant movement and handling of livestock (Erf et al., 1992 & Grandin, 1993). Dipping, castration, branding, ear-tagging and counting is commonly practiced as beef cattle management norms hence dehorning are partly practiced as some of the animals had horns which were disturbing them to pass through crushpens and as a result they increased bruising to other animals. At Matatani and Muledzhi areas animals including calves are packed in the crushpens, counted, weighed and temperament traits were also measured on the scale and this is done in order to document the information for this research and future use. Temperament is a behavioural response of animals as handled by man. It is important to be measured in beef cattle farmers under communal grazing conditions as it reduces farmer’s profit and it makes the stock man’s work unpleasant. Therefore, it is also needs to be improved for the improvement of beef cattle schemes. Management system of communal farmers was not conducive to better quality meat due to horns in some animals which ultimately cause bruising in other animals. However, exotic bulls were bought at random for the improvement of other breed types found in these two areas. The focus of this study is almost in Nguni cattle type managed under communal grazing system. Lastly, the purpose of this study is to determine behavioral response of beef cattle under communal management system at their dipping tanks.
- Full Text:
- Date Issued: 2002
The effect of laundering on the physical and thermal properties of phase change textile materials
- Authors: Scheepers, Ricardo
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Textile chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/52038 , vital:43443
- Description: Phase change materials (PCMs) have been incorporated into clothing and textiles to provide added value in terms of thermoregulation and thus added comfort to the wearer in extreme weather conditions and sporting activities. Since clothing is laundered many times during the service life of the textile, the effects of simulated domestic laundering on the physical and thermal properties of a non-woven textile which contains PCMs were investigated. The thermal properties, such as the thermal degradation, melting, evaporation and crystallisation were measured by the TGA and DSC analytical techniques. The physical properties, such as the microcapsule size distribution, and the microcapsule morphologies of the PCM microcapsules, were measured by the SEM and Raman analytical techniques. The main objectives of this study were to determine the effect of repeated laundering at different wash temperatures on the mass loss, enthalpy, and physical changes in PCM. Thermal degradation as determined by TGA thermograms was found to be higher at a wash temperature of 60°C relative to that of a wash temperature at 30°C, the mass loss being 4.6% more at 60°C than at 30°C. This was asserted to physical changes such as size and shape of the PCM microcapsules as evident in SEM images. The SEM images showed broken and collapsed PCM microcapsules in the web and around the fibre, indicating evaporation of the thermoregulating content of the PCM. It was found that the heat capacity of the sample washed at 60°C was much lower than that of the unwashed sample, the difference being approximately 50% in terms of the latent heat capacity as determined by DSC thermograms. This implies that the latent heat effectiveness of the PCM has decreased significantly. The physical properties of the PCM such as the intermolecular interaction, the intensity and width of peaks, polarisation, degree of crystallinity and the orientation changed as illustrated in the Raman analysis. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text: false
- Date Issued: 2021-04
- Authors: Scheepers, Ricardo
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Textile chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/52038 , vital:43443
- Description: Phase change materials (PCMs) have been incorporated into clothing and textiles to provide added value in terms of thermoregulation and thus added comfort to the wearer in extreme weather conditions and sporting activities. Since clothing is laundered many times during the service life of the textile, the effects of simulated domestic laundering on the physical and thermal properties of a non-woven textile which contains PCMs were investigated. The thermal properties, such as the thermal degradation, melting, evaporation and crystallisation were measured by the TGA and DSC analytical techniques. The physical properties, such as the microcapsule size distribution, and the microcapsule morphologies of the PCM microcapsules, were measured by the SEM and Raman analytical techniques. The main objectives of this study were to determine the effect of repeated laundering at different wash temperatures on the mass loss, enthalpy, and physical changes in PCM. Thermal degradation as determined by TGA thermograms was found to be higher at a wash temperature of 60°C relative to that of a wash temperature at 30°C, the mass loss being 4.6% more at 60°C than at 30°C. This was asserted to physical changes such as size and shape of the PCM microcapsules as evident in SEM images. The SEM images showed broken and collapsed PCM microcapsules in the web and around the fibre, indicating evaporation of the thermoregulating content of the PCM. It was found that the heat capacity of the sample washed at 60°C was much lower than that of the unwashed sample, the difference being approximately 50% in terms of the latent heat capacity as determined by DSC thermograms. This implies that the latent heat effectiveness of the PCM has decreased significantly. The physical properties of the PCM such as the intermolecular interaction, the intensity and width of peaks, polarisation, degree of crystallinity and the orientation changed as illustrated in the Raman analysis. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text: false
- Date Issued: 2021-04
Investigation of the potential separation of isomers and related compounds using host compound (2R,3R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol
- Authors: Pohl, Pieter Lourens
- Date: 2018
- Subjects: Chemistry, Organic , Clathrate compounds Thermal analysis
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23131 , vital:30432
- Description: In this study, we investigated the potential of a host compound, (2R,3R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT), for use in the separation of isomers and related compounds using host-guest chemistry. The title molecule, DMT, is composed of a butane chain bearing hydroxyl moieties on the terminal carbons and methoxy moieties on the two internal, chiral carbon atoms. In addition, there are two phenyl rings on each of the terminal carbons. The synthesis of DMT was carried out by subjecting the diester of naturally-occurring optically active tartaric acid to a Grignard reaction employing phenylmagnesium bromide. Subsequent methylation of the secondary hydroxy groups with dimethyl sulfate afforded DMT. The resulting host molecule was investigated for its inclusion abilities by crystallizing with a number of potential aromatic, aliphatic and alicyclic guests such as toluene, aniline, nitrobenzene, anisole, cyclohexane, ethyl acetate and ethanol. Host:guest ratios were determined by means of 1H-NMR spectroscopy. Of the hosts investigated, DMT favoured a host:guest ratio of 2:1 for all included guests investigated. It complexed with most non-polycyclic aromatic guests as well as cyclohexane, cyclohexene and cyclohexanone. It was not able to include short chain or branched alcohols such as methanol, ethanol or 2-propanol, or other hetero-aliphatic or hetero- cyclic compounds such as diethyl ether, acetonitrile, morpholine or dioxane. Competition inclusion experiments were performed in which DMT was crystallized from equimolar and non-equimolar binary, ternary and quaternary mixtures of appropriate guests. The mother liquor mixtures and resultant crystals were subjected to GC-MS analysis in order to determine whether DMT showed discriminatory behaviour towards the guests from a mixture. It was observed that DMT was able to differentiate between related compounds, for example, the host preferred to include N,N-dimethylaniline compared with N-methylaniline and aniline. The host also discriminated against isomers, for example, p-xylene was preferentially included over o-xylene and m-xylene, while o-cresol was included in preference to p-cresol and m-cresol. Single crystal X-ray analysis was used to investigate the host–guest interactions responsible for guest inclusion, as well as to discern reasons for the host’s selective behaviour. X-ray data for the inclusion complexes indicated that each complex was isostructural, crystallizing in the monoclinic C2 crystal system. A pair of 1,3- and 2,4- intramolecular hydrogen bonds, as well as intramolecular non-classic hydrogen bonds between adjacent ortho-aromatic hydrogens and hydroxy moieties was a significant stabilizing factor for the geometry of the host. Guests were held within discrete cavities in the crystal lattice, and experienced only π–π stacking, CH–π interactions and other short contacts. Thermal analyses were used to determine the relative thermal stabilities of the complexes, and these data compared to the selectivity preference of DMT, obtained from the competition experiments, in order to assess the reasons for any discriminatory behaviour. Finally, Hirshfeld surface analysis data was used to determine if the thermal stability of the complexes was related to the number and type of interactions between host and guest.
- Full Text:
- Date Issued: 2018
- Authors: Pohl, Pieter Lourens
- Date: 2018
- Subjects: Chemistry, Organic , Clathrate compounds Thermal analysis
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23131 , vital:30432
- Description: In this study, we investigated the potential of a host compound, (2R,3R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT), for use in the separation of isomers and related compounds using host-guest chemistry. The title molecule, DMT, is composed of a butane chain bearing hydroxyl moieties on the terminal carbons and methoxy moieties on the two internal, chiral carbon atoms. In addition, there are two phenyl rings on each of the terminal carbons. The synthesis of DMT was carried out by subjecting the diester of naturally-occurring optically active tartaric acid to a Grignard reaction employing phenylmagnesium bromide. Subsequent methylation of the secondary hydroxy groups with dimethyl sulfate afforded DMT. The resulting host molecule was investigated for its inclusion abilities by crystallizing with a number of potential aromatic, aliphatic and alicyclic guests such as toluene, aniline, nitrobenzene, anisole, cyclohexane, ethyl acetate and ethanol. Host:guest ratios were determined by means of 1H-NMR spectroscopy. Of the hosts investigated, DMT favoured a host:guest ratio of 2:1 for all included guests investigated. It complexed with most non-polycyclic aromatic guests as well as cyclohexane, cyclohexene and cyclohexanone. It was not able to include short chain or branched alcohols such as methanol, ethanol or 2-propanol, or other hetero-aliphatic or hetero- cyclic compounds such as diethyl ether, acetonitrile, morpholine or dioxane. Competition inclusion experiments were performed in which DMT was crystallized from equimolar and non-equimolar binary, ternary and quaternary mixtures of appropriate guests. The mother liquor mixtures and resultant crystals were subjected to GC-MS analysis in order to determine whether DMT showed discriminatory behaviour towards the guests from a mixture. It was observed that DMT was able to differentiate between related compounds, for example, the host preferred to include N,N-dimethylaniline compared with N-methylaniline and aniline. The host also discriminated against isomers, for example, p-xylene was preferentially included over o-xylene and m-xylene, while o-cresol was included in preference to p-cresol and m-cresol. Single crystal X-ray analysis was used to investigate the host–guest interactions responsible for guest inclusion, as well as to discern reasons for the host’s selective behaviour. X-ray data for the inclusion complexes indicated that each complex was isostructural, crystallizing in the monoclinic C2 crystal system. A pair of 1,3- and 2,4- intramolecular hydrogen bonds, as well as intramolecular non-classic hydrogen bonds between adjacent ortho-aromatic hydrogens and hydroxy moieties was a significant stabilizing factor for the geometry of the host. Guests were held within discrete cavities in the crystal lattice, and experienced only π–π stacking, CH–π interactions and other short contacts. Thermal analyses were used to determine the relative thermal stabilities of the complexes, and these data compared to the selectivity preference of DMT, obtained from the competition experiments, in order to assess the reasons for any discriminatory behaviour. Finally, Hirshfeld surface analysis data was used to determine if the thermal stability of the complexes was related to the number and type of interactions between host and guest.
- Full Text:
- Date Issued: 2018
Investigating the role of UAVs and convolutional neural networks in the identification of invasive plant species in the Albany Thicket
- Authors: Wesson, Frank Cameron
- Date: 2023-04
- Subjects: Drone aircraft -- Control systems , Drone -- South Africa , Albany Thicket -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61097 , vital:69755
- Description: The study aimed to determine whether plant species could be classified by using high resolution aerial imagery and a convolutional neural network (CNN). The full capabilities of a CNN were examined including testing whether the platform could be used for land cover and the evaluation of land change over time. A drone or unmanned aerial vehicle (UAV) was used to collect the aerial data of the study area, and 45 subplots were used for the image analysis. The CNN was coded and operated in RStudio, and digitised data from the input imagery were used as training and validation data by the programme to learn features. Four classifications were performed using various quantities of input data to access the performance of the neural network. In addition, tests were performed to understand whether the CNN could be used as a land cover and land change detection tool. Accuracy assessments were done on the results to test reliability and accuracy. The best-performing classification achieved an average user and producer accuracy of above 90%, while the overall accuracy was 93%, and the kappa coefficient score was 0.86. The CNN was also able to predict the land coverage area of Opuntia to be within 4% of the ground truthing data area. A change in land cover over time was detected by the programme after the manual clearing of the invasive plant had been undertaken. This research has determined that the use of a CNN in remote sensing is a very powerful tool for supervised image classifications and that it can be used for monitoring land cover by accurately estimating the spatial distribution of plant species and by monitoring the species' growth or decline over time. A CNN could also be used as a tool for landowners to prove that they are making efforts to clear invasive species from their land. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Wesson, Frank Cameron
- Date: 2023-04
- Subjects: Drone aircraft -- Control systems , Drone -- South Africa , Albany Thicket -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61097 , vital:69755
- Description: The study aimed to determine whether plant species could be classified by using high resolution aerial imagery and a convolutional neural network (CNN). The full capabilities of a CNN were examined including testing whether the platform could be used for land cover and the evaluation of land change over time. A drone or unmanned aerial vehicle (UAV) was used to collect the aerial data of the study area, and 45 subplots were used for the image analysis. The CNN was coded and operated in RStudio, and digitised data from the input imagery were used as training and validation data by the programme to learn features. Four classifications were performed using various quantities of input data to access the performance of the neural network. In addition, tests were performed to understand whether the CNN could be used as a land cover and land change detection tool. Accuracy assessments were done on the results to test reliability and accuracy. The best-performing classification achieved an average user and producer accuracy of above 90%, while the overall accuracy was 93%, and the kappa coefficient score was 0.86. The CNN was also able to predict the land coverage area of Opuntia to be within 4% of the ground truthing data area. A change in land cover over time was detected by the programme after the manual clearing of the invasive plant had been undertaken. This research has determined that the use of a CNN in remote sensing is a very powerful tool for supervised image classifications and that it can be used for monitoring land cover by accurately estimating the spatial distribution of plant species and by monitoring the species' growth or decline over time. A CNN could also be used as a tool for landowners to prove that they are making efforts to clear invasive species from their land. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
The coordination chemistry of Rhenium(V) with multidentate no-donor ligands
- Authors: Abrahams, Abubak'r
- Date: 2009
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10370 , http://hdl.handle.net/10948/912 , Rhenium , Ligands
- Description: The neutral distorted octahedral complexes [ReOCl(L)] {H2L = N,N-bis(2- hydroxybenzyl)-2-(2-aminoethyl)dimethylamine (H2had), N,N-bis(2-hydroxybenzyl) aminomethylpyridine (H2hap); N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)pyridine (H2hae)} were prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H2L in ethanol. The X-ray structure determinations of [ReOCl(had)] and [ReOCl(hap)] were performed, and in both complexes the chloride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen. Treatment of trans-[ReO2(py)4]I with two equivalents and one equivalent each of H2had in acetone afforded the iodide salts of the oxypyridinium-ammonium zwitterions N1-(2-hydroxybenzyl)-N2,N2- dimethyl-N1-((2-oxypyridinium)-1-methyl)ethane-1,2-diamine [Hhpd]+ and N2,N2- dimethyl-N1-bis((2-oxypyridinium)-1-methyl)ethane-1,2-diamine [dod]+ respectively. In [Hhpd]I, one of the 2-hydroxyphenyl groups of H2had is substituted by an oxypyridinium group, and in [dod]I, both 2-hydroxyphenyl groups are converted. The X-ray crystal structure determination of the starting material H2had, [Hhpd]I and [dod]I reveals trigonal pyramidal geometries around the central amino nitrogen. The complex salt [ReO(bsa)]PF6 (H2bsa=bis(N-methylsalicylicylideneiminopropyl) amine) was prepared from the reaction of cis-[ReO2I(PPh3)2] with H2bsa in toluene. The dianionic pentadentate ligand bsa is coordinated to the ReO3+ moiety via one secondary amino and two imino nitrogens, and two anionic phenolate oxygens. The complex was characterized by spectroscopy and analytical data, and the structure has been determined by single-crystal X-ray diffraction analysis. The complex exhibits a distorted octahedral geometry around the central rhenium(V) ion, with the basal plane being defined by a phenolate oxygen, two imino nitrogens and the secondary amino. ix A. Abrahams Nelson Mandela Metropolitan University The reaction of a two-fold molar excess of the potentially NN-donor ligand 2,2’- dipyridylamine (dpa) with trans-[ReO(OEt)Cl2(PPh3)2] in ethanol led to the isolation of [ReOCl2(OEt)(dpa)]. The X-ray crystal structure shows that the NN-chelated dpa is coordinated in the equatorial plane cis to the oxo and ethoxo groups, which are in trans positions relative to each other. The treatment of trans- [ReOCl3(PPh3)2] with a tenfold molar excess of dpa in ethanol at the refluxing temperature yielded the trans-dioxo complex [ReO2(dpa)2]Cl, but with a twofold molar excess only (μ-O)[{ReOCl2(dpa)}2] was isolated. Repeating the latter reaction with (n-Bu4N)[ReOCl4] as starting material in ethanol at room temperature a dark green product, also with the formulation (μ-O)[{ReOCl2(dpa)}2], was isolated. The reaction of equimolar quantities of bis(pyridin-2-yl)methyl)amine (HBPA) with (n-Bu4N)[ReOCl4] in acetone at room temperature led to the isolation of the sixcoordinate rhenium(V) complex [ReOCl(H2O)(BPA)]Cl. IR, NMR and X-ray crystallographic results indicate that BPA is coordinated as a tridentate uninegative chelate, with deprotonation of the amine nitrogen. The water molecule is coordinated trans to the oxo group, with the Re=O and Re-OH2 bond distances equal to 1.663(9) and 2.21(1) Å respectively. Complexes of the general formula [ReOX2{(C5H4N)CH(O)CH2(C5H4N)}] (X = Cl, I) were prepared by the reactions of trans-[ReOCl3(PPh3)2] and trans- [ReOI2(OEt)(PPh3)2] with cis-1,2-di-(2-pyridyl)ethylene (DPE) in ethanol and benzene in air. Experimental evidence shows that the coordinated DPE ligand has undergone addition of water at the ethylenic carbons, and that the (C5H4N)CH(O)CH2(C5H4N) moiety acts as a uninegative tridentate NON-donor ligand. The X-ray crystal structures of both complexes show a distorted octahedral geometry around the rhenium(V) centre. The treatment of trans-[ReOCl3(PPh3)2] with H2dbd in a 2:1 molar ratio in acetonitrile led to the isolation of the ligand-bridged dimer (μ-dbd)[ReOCl2(PPh3)]2. The X-ray crystal structure of the complex reveals a dinuclear structure in which two rhenium(V) ions are bridged by the dbd ligand. Each rhenium ion is in a x A. Abrahams Nelson Mandela Metropolitan University distorted octahedral geometry. The basal plane is defined by a phosphorus atom of the PPh3 group, two chlorides cis to each other, and a pyridyl nitrogen atom of dbd. The oxo group and alcoholate oxygen of dbd lie in trans axial positions. The complexes cis-[ReOX2(msa)(PPh3)] (X = Cl, Br, I) were prepared from trans- [ReOCl3(PPh3)2], trans-[ReOBr3(PPh3)2] or trans-[ReOI2(OEt)(PPh3)2] with 2-(1- iminoethyl)phenol (Hmsa) in acetonitrile. An X-ray crystallographic study shows that the bonding distances and angles in the comlexes are nearly identical, and that the two halides in each complex are coordinated cis to each other in the equatorial plane cis to the oxo group. The oxo-bridged dinuclear rhenium(V) complex [(μ-O){ReOCl(amp)}2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] and 6-amino-3-methyl-1-phenyl- 4-azahept-2-ene-1-one (Hamp) in acetone. The characterization of the complex by elemental analysis, infrared and 1H NMR spectroscopy and X-ray crystallography shows that amp is coordinated as a monoanionic NNO-donor chelate as an amino-amido ketone. However, the reaction of the similar ligand 7- amino-4,7-dimethyl-5-aza-3-octen-2-one (Hada) with [Re(CO)5Br] produced the product fac-[Re(CO)3Br(Hada)], with Hada coordinated as a neutral NN-donor amino-imino-ketone.
- Full Text:
- Date Issued: 2009
- Authors: Abrahams, Abubak'r
- Date: 2009
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10370 , http://hdl.handle.net/10948/912 , Rhenium , Ligands
- Description: The neutral distorted octahedral complexes [ReOCl(L)] {H2L = N,N-bis(2- hydroxybenzyl)-2-(2-aminoethyl)dimethylamine (H2had), N,N-bis(2-hydroxybenzyl) aminomethylpyridine (H2hap); N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)pyridine (H2hae)} were prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H2L in ethanol. The X-ray structure determinations of [ReOCl(had)] and [ReOCl(hap)] were performed, and in both complexes the chloride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen. Treatment of trans-[ReO2(py)4]I with two equivalents and one equivalent each of H2had in acetone afforded the iodide salts of the oxypyridinium-ammonium zwitterions N1-(2-hydroxybenzyl)-N2,N2- dimethyl-N1-((2-oxypyridinium)-1-methyl)ethane-1,2-diamine [Hhpd]+ and N2,N2- dimethyl-N1-bis((2-oxypyridinium)-1-methyl)ethane-1,2-diamine [dod]+ respectively. In [Hhpd]I, one of the 2-hydroxyphenyl groups of H2had is substituted by an oxypyridinium group, and in [dod]I, both 2-hydroxyphenyl groups are converted. The X-ray crystal structure determination of the starting material H2had, [Hhpd]I and [dod]I reveals trigonal pyramidal geometries around the central amino nitrogen. The complex salt [ReO(bsa)]PF6 (H2bsa=bis(N-methylsalicylicylideneiminopropyl) amine) was prepared from the reaction of cis-[ReO2I(PPh3)2] with H2bsa in toluene. The dianionic pentadentate ligand bsa is coordinated to the ReO3+ moiety via one secondary amino and two imino nitrogens, and two anionic phenolate oxygens. The complex was characterized by spectroscopy and analytical data, and the structure has been determined by single-crystal X-ray diffraction analysis. The complex exhibits a distorted octahedral geometry around the central rhenium(V) ion, with the basal plane being defined by a phenolate oxygen, two imino nitrogens and the secondary amino. ix A. Abrahams Nelson Mandela Metropolitan University The reaction of a two-fold molar excess of the potentially NN-donor ligand 2,2’- dipyridylamine (dpa) with trans-[ReO(OEt)Cl2(PPh3)2] in ethanol led to the isolation of [ReOCl2(OEt)(dpa)]. The X-ray crystal structure shows that the NN-chelated dpa is coordinated in the equatorial plane cis to the oxo and ethoxo groups, which are in trans positions relative to each other. The treatment of trans- [ReOCl3(PPh3)2] with a tenfold molar excess of dpa in ethanol at the refluxing temperature yielded the trans-dioxo complex [ReO2(dpa)2]Cl, but with a twofold molar excess only (μ-O)[{ReOCl2(dpa)}2] was isolated. Repeating the latter reaction with (n-Bu4N)[ReOCl4] as starting material in ethanol at room temperature a dark green product, also with the formulation (μ-O)[{ReOCl2(dpa)}2], was isolated. The reaction of equimolar quantities of bis(pyridin-2-yl)methyl)amine (HBPA) with (n-Bu4N)[ReOCl4] in acetone at room temperature led to the isolation of the sixcoordinate rhenium(V) complex [ReOCl(H2O)(BPA)]Cl. IR, NMR and X-ray crystallographic results indicate that BPA is coordinated as a tridentate uninegative chelate, with deprotonation of the amine nitrogen. The water molecule is coordinated trans to the oxo group, with the Re=O and Re-OH2 bond distances equal to 1.663(9) and 2.21(1) Å respectively. Complexes of the general formula [ReOX2{(C5H4N)CH(O)CH2(C5H4N)}] (X = Cl, I) were prepared by the reactions of trans-[ReOCl3(PPh3)2] and trans- [ReOI2(OEt)(PPh3)2] with cis-1,2-di-(2-pyridyl)ethylene (DPE) in ethanol and benzene in air. Experimental evidence shows that the coordinated DPE ligand has undergone addition of water at the ethylenic carbons, and that the (C5H4N)CH(O)CH2(C5H4N) moiety acts as a uninegative tridentate NON-donor ligand. The X-ray crystal structures of both complexes show a distorted octahedral geometry around the rhenium(V) centre. The treatment of trans-[ReOCl3(PPh3)2] with H2dbd in a 2:1 molar ratio in acetonitrile led to the isolation of the ligand-bridged dimer (μ-dbd)[ReOCl2(PPh3)]2. The X-ray crystal structure of the complex reveals a dinuclear structure in which two rhenium(V) ions are bridged by the dbd ligand. Each rhenium ion is in a x A. Abrahams Nelson Mandela Metropolitan University distorted octahedral geometry. The basal plane is defined by a phosphorus atom of the PPh3 group, two chlorides cis to each other, and a pyridyl nitrogen atom of dbd. The oxo group and alcoholate oxygen of dbd lie in trans axial positions. The complexes cis-[ReOX2(msa)(PPh3)] (X = Cl, Br, I) were prepared from trans- [ReOCl3(PPh3)2], trans-[ReOBr3(PPh3)2] or trans-[ReOI2(OEt)(PPh3)2] with 2-(1- iminoethyl)phenol (Hmsa) in acetonitrile. An X-ray crystallographic study shows that the bonding distances and angles in the comlexes are nearly identical, and that the two halides in each complex are coordinated cis to each other in the equatorial plane cis to the oxo group. The oxo-bridged dinuclear rhenium(V) complex [(μ-O){ReOCl(amp)}2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] and 6-amino-3-methyl-1-phenyl- 4-azahept-2-ene-1-one (Hamp) in acetone. The characterization of the complex by elemental analysis, infrared and 1H NMR spectroscopy and X-ray crystallography shows that amp is coordinated as a monoanionic NNO-donor chelate as an amino-amido ketone. However, the reaction of the similar ligand 7- amino-4,7-dimethyl-5-aza-3-octen-2-one (Hada) with [Re(CO)5Br] produced the product fac-[Re(CO)3Br(Hada)], with Hada coordinated as a neutral NN-donor amino-imino-ketone.
- Full Text:
- Date Issued: 2009
Sandy beach morphodynamics and macrobenthic communities in temperate, subtropical and tropical regions : a macroecological approach
- Authors: Soares, Alexandre Goulart
- Date: 2003
- Subjects: Seashore ecology , Intertidal ecology , Benthos
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11077 , http://hdl.handle.net/10948/293 , Seashore ecology , Intertidal ecology , Benthos
- Description: A comprehensive study involving 52 microtidal beaches spanning from reflective to dissipative states and located in tropical, subtropical and temperate regions in the Atlantic, Pacific and Indian oceans was carried out to unravel the relative roles of latitude and beach morphodynamics in determining beach macrobenthic species richness, abundance, biomass and mean individual body sizes. Since beach slope is one of the most important factors controlling beach fauna, a model based on beach geometry was applied to the sub-aerial beach deposit to understand the role of physical factors in predicting equilibrium beach slopes. Additionally, it was tested if the occurrence of beach types is related to latitude, and how physical factors change with morphodynamics and latitude. The beach morphometric model makes three assumptions: 1) that the cross-section of a beach deposit is equivalent to a right-angled triangle, 2) that the physical hydrodynamic factors (wave height and spring tide amplitude) and the beach deposit characteristics (sand grain size, beach slope and width) are interchangeable with their geometric counterparts producing an equation to explain beach geometry, and 3) that the predicted beach slope is in equilibrium with the hydrodynamic and sedimentological forces. The equation for predicting beach slope was derived and then tested against field data collected over 52 beaches. The predicted slopes were not significantly different from the observed slopes of the studied natural beaches. However some estimated slopes were different than observed ones. Possible sources of deviation between calculated and observed slopes may be the systematic sampling errors associated with field data. Alternatively, observed slopes could be the result of past hydrodynamic conditions, explaining the differences with the slopes calculated by the beach morphometric model, which assumes a state of equilibrium between beach slope and hydrodynamic conditions. A higher correlation of beach faunal structure with observed slopes rather than with present hydrodynamic conditions could then be indicative of faunal responses to previous hydrodynamic conditions in the same way was the observed slopes. The beach morphometric model could therefore be also useful in predicting faunal responses to changing hydrodynamic conditions. Since the model does not consider wave period, it is concluded that further tests should be done using laboratory and time-series field data and incorporating the role of wave period and beach permeability to ascertain its predictive value. Tropical regions had significantly more beaches in a reflective state than temperate and subtropical regions. Some tropical beaches were fronted by coral reefs, which not only provided coarse carbonate particles, but also additionally dissipated the low wave energy present in these climatic areas. Only one dissipative beach with high energy was found in the tropics, in southeast Madagascar. Temperate and subtropical regions, on the other hand, were dominated by dissipative beaches with medium to fine sands. Open oceanic reflective beaches were non-existent in the subtropics and rare in temperate regions, only occurring in estuaries, enclosed bays or on islands facing the continent. Intermediate beaches were more common in the subtropics but also occurred frequently in the other two regions, having higher energy in temperate regions. Reflective beaches had significantly steeper slopes, coarser sands, smaller waves and shorter swash lengths when compared to dissipative beaches. Additionally, reflective beaches were narrower, had deeper water tables and in consequence shorter saturation zones. Wave periods and surfzone widths were on average larger on dissipative than on reflective beaches. The frequency of occurrence of beach types is therefore related to the climatic signature of each latitude. Mid latitudes would be predicted to have more dissipative beaches with large and long waves because of their proximity to the storm generating belt around 50-60° S - these beaches will have a predominantly finer sands because of the input by rivers in rainy areas. Lower latitudes will have more reflective beaches due to a modal low energy wave climate and also because of the presence of inshore and offshore biotic structures such as coral reefs that dissipate even more the energy from the waves. Tropical and subtropical regions had larger marine species pools than temperate regions. After controlling for biogeographical differences in total species pool, dissipative beaches were on average significantly richer than intermediate and reflective beaches. Crustaceans were also more diverse on dissipative beaches, this difference being not significant for either molluscs or polychaetes. Significant relationships were found between total beach species richness (with or without terrestrial species), crustacean and mollusc species richness with beach morphodynamics as represented by the Dean’s index. Indices incorporating the role of tide, such as BSI, were less important in predicting species richness on the microtidal beaches studied here. Several other physical factors were also significantly correlated with species richness, the most important being the Beach Deposit Index, i.e. BDI, a composite index of beach slope and grain size. The highest correlation was between BDI and relative species richness, i.e. local beach species richness / regional species richness. Total regional marine species richness was higher in Madagascar and North Brazil (tropical beaches) than in Southeast Brazil (subtropical), or the West Coast of South Africa and South-Central Chile (temperate beaches). Not only was the pool of species capable of colonizing beaches richer in tropical and subtropical regions, but also local diversity of each morphodynamic beach type was higher among tropical beaches than their temperate counterparts. Although the results of this study agree with the predictions of the swash exclusion hypotheses, several reflective and intermediate beaches had higher species richness than predicted before and this seems to be linked to the presence of finer sediments and a less turbulent flow for larvae to settle. It is concluded that beach species richness is not necessarily controlled by one major morphodynamic parameter; this control is complex and probably involves multiple interacting biotic (biological interactions) and abiotic (e.g. grain size, wave height, beach slope and width, water table) factors. Species richness seems to be controlled on two different scales: on an evolutionary one where tropical and subtropical regions have higher regional and local diversity due to higher speciation rates; and on an ecological scale, where fine grained sand beaches have their carrying capacity enhanced by higher larval settlement rates and survival of recruits towards adulthood. On average dissipative beaches had higher total densities and macrofaunal abundances than reflective ones. Crustaceans, terrestrial species and cirolanid isopods such as Excirolana spp. were also more abundant on dissipative beaches. The difference was not significant for molluscs and polychaetes. Significant relationships were found between total abundance, crustacean species richness and beach morphodynamics as represented by the Dean’s index. Again, BSI was less important than individual physical factors in determining faunal abundance on the studied microtidal beaches. Several other physical factors were also significantly correlated with abundance, the most important being the Beach Deposit Index (BDI). The highest correlation was between BDI and total macrofaunal abundance. Factors related to surf zone processes, and possibly productivity, were highly correlated with total community, crustaceans, Excirolana spp. and terrestrial species abundances. The abundances of polychaetes and molluscs were better correlated with factors related to the beach deposit (BDI, slope, grain size and water table depth). Significant differences were observed between latitudinal regions for the average beach and also for each beach type. In general temperate beaches harboured larger community densities and abundances, and also crustacean, Excirolana spp. and terrestrial abundances. Mollusc and polychaete abundances were larger on subtropical and tropical beaches. The control of abundance on a sandy beach is complex and involves multifactorial processes at evolutionary and ecological scales. At evolutionary scales animals seem to attain higher abundances in the region where they first evolved, e.g. amphipods and isopods in temperate regions. At ecological scales they attain higher abundances where productivity is higher (total macrofaunal, crustaceans, Excirolana spp., terrestrial spp.) or where the settlement environment is more benign (molluscs and polychaetes). Dissipative beaches supported larger average and total community biomass than reflective beaches. Crustaceans, terrestrial species and cirolanid isopods such as Excirolana spp. also had larger biomass on dissipative beaches. The difference was not significant for molluscs and polychaetes. Significant relationships were found between the biomass of community and taxonomic groups with beach morphodynamics as represented by the Dean’s morphodynamic index. On the microtidal beaches studied here, BSI was less important than other morphodynamic indices and single physical factors in determining faunal biomass and mean individual body size. Surf zone characteristics such as wave height, period and surf zone width had the highest correlations with community, crustacean.
- Full Text:
- Date Issued: 2003
- Authors: Soares, Alexandre Goulart
- Date: 2003
- Subjects: Seashore ecology , Intertidal ecology , Benthos
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11077 , http://hdl.handle.net/10948/293 , Seashore ecology , Intertidal ecology , Benthos
- Description: A comprehensive study involving 52 microtidal beaches spanning from reflective to dissipative states and located in tropical, subtropical and temperate regions in the Atlantic, Pacific and Indian oceans was carried out to unravel the relative roles of latitude and beach morphodynamics in determining beach macrobenthic species richness, abundance, biomass and mean individual body sizes. Since beach slope is one of the most important factors controlling beach fauna, a model based on beach geometry was applied to the sub-aerial beach deposit to understand the role of physical factors in predicting equilibrium beach slopes. Additionally, it was tested if the occurrence of beach types is related to latitude, and how physical factors change with morphodynamics and latitude. The beach morphometric model makes three assumptions: 1) that the cross-section of a beach deposit is equivalent to a right-angled triangle, 2) that the physical hydrodynamic factors (wave height and spring tide amplitude) and the beach deposit characteristics (sand grain size, beach slope and width) are interchangeable with their geometric counterparts producing an equation to explain beach geometry, and 3) that the predicted beach slope is in equilibrium with the hydrodynamic and sedimentological forces. The equation for predicting beach slope was derived and then tested against field data collected over 52 beaches. The predicted slopes were not significantly different from the observed slopes of the studied natural beaches. However some estimated slopes were different than observed ones. Possible sources of deviation between calculated and observed slopes may be the systematic sampling errors associated with field data. Alternatively, observed slopes could be the result of past hydrodynamic conditions, explaining the differences with the slopes calculated by the beach morphometric model, which assumes a state of equilibrium between beach slope and hydrodynamic conditions. A higher correlation of beach faunal structure with observed slopes rather than with present hydrodynamic conditions could then be indicative of faunal responses to previous hydrodynamic conditions in the same way was the observed slopes. The beach morphometric model could therefore be also useful in predicting faunal responses to changing hydrodynamic conditions. Since the model does not consider wave period, it is concluded that further tests should be done using laboratory and time-series field data and incorporating the role of wave period and beach permeability to ascertain its predictive value. Tropical regions had significantly more beaches in a reflective state than temperate and subtropical regions. Some tropical beaches were fronted by coral reefs, which not only provided coarse carbonate particles, but also additionally dissipated the low wave energy present in these climatic areas. Only one dissipative beach with high energy was found in the tropics, in southeast Madagascar. Temperate and subtropical regions, on the other hand, were dominated by dissipative beaches with medium to fine sands. Open oceanic reflective beaches were non-existent in the subtropics and rare in temperate regions, only occurring in estuaries, enclosed bays or on islands facing the continent. Intermediate beaches were more common in the subtropics but also occurred frequently in the other two regions, having higher energy in temperate regions. Reflective beaches had significantly steeper slopes, coarser sands, smaller waves and shorter swash lengths when compared to dissipative beaches. Additionally, reflective beaches were narrower, had deeper water tables and in consequence shorter saturation zones. Wave periods and surfzone widths were on average larger on dissipative than on reflective beaches. The frequency of occurrence of beach types is therefore related to the climatic signature of each latitude. Mid latitudes would be predicted to have more dissipative beaches with large and long waves because of their proximity to the storm generating belt around 50-60° S - these beaches will have a predominantly finer sands because of the input by rivers in rainy areas. Lower latitudes will have more reflective beaches due to a modal low energy wave climate and also because of the presence of inshore and offshore biotic structures such as coral reefs that dissipate even more the energy from the waves. Tropical and subtropical regions had larger marine species pools than temperate regions. After controlling for biogeographical differences in total species pool, dissipative beaches were on average significantly richer than intermediate and reflective beaches. Crustaceans were also more diverse on dissipative beaches, this difference being not significant for either molluscs or polychaetes. Significant relationships were found between total beach species richness (with or without terrestrial species), crustacean and mollusc species richness with beach morphodynamics as represented by the Dean’s index. Indices incorporating the role of tide, such as BSI, were less important in predicting species richness on the microtidal beaches studied here. Several other physical factors were also significantly correlated with species richness, the most important being the Beach Deposit Index, i.e. BDI, a composite index of beach slope and grain size. The highest correlation was between BDI and relative species richness, i.e. local beach species richness / regional species richness. Total regional marine species richness was higher in Madagascar and North Brazil (tropical beaches) than in Southeast Brazil (subtropical), or the West Coast of South Africa and South-Central Chile (temperate beaches). Not only was the pool of species capable of colonizing beaches richer in tropical and subtropical regions, but also local diversity of each morphodynamic beach type was higher among tropical beaches than their temperate counterparts. Although the results of this study agree with the predictions of the swash exclusion hypotheses, several reflective and intermediate beaches had higher species richness than predicted before and this seems to be linked to the presence of finer sediments and a less turbulent flow for larvae to settle. It is concluded that beach species richness is not necessarily controlled by one major morphodynamic parameter; this control is complex and probably involves multiple interacting biotic (biological interactions) and abiotic (e.g. grain size, wave height, beach slope and width, water table) factors. Species richness seems to be controlled on two different scales: on an evolutionary one where tropical and subtropical regions have higher regional and local diversity due to higher speciation rates; and on an ecological scale, where fine grained sand beaches have their carrying capacity enhanced by higher larval settlement rates and survival of recruits towards adulthood. On average dissipative beaches had higher total densities and macrofaunal abundances than reflective ones. Crustaceans, terrestrial species and cirolanid isopods such as Excirolana spp. were also more abundant on dissipative beaches. The difference was not significant for molluscs and polychaetes. Significant relationships were found between total abundance, crustacean species richness and beach morphodynamics as represented by the Dean’s index. Again, BSI was less important than individual physical factors in determining faunal abundance on the studied microtidal beaches. Several other physical factors were also significantly correlated with abundance, the most important being the Beach Deposit Index (BDI). The highest correlation was between BDI and total macrofaunal abundance. Factors related to surf zone processes, and possibly productivity, were highly correlated with total community, crustaceans, Excirolana spp. and terrestrial species abundances. The abundances of polychaetes and molluscs were better correlated with factors related to the beach deposit (BDI, slope, grain size and water table depth). Significant differences were observed between latitudinal regions for the average beach and also for each beach type. In general temperate beaches harboured larger community densities and abundances, and also crustacean, Excirolana spp. and terrestrial abundances. Mollusc and polychaete abundances were larger on subtropical and tropical beaches. The control of abundance on a sandy beach is complex and involves multifactorial processes at evolutionary and ecological scales. At evolutionary scales animals seem to attain higher abundances in the region where they first evolved, e.g. amphipods and isopods in temperate regions. At ecological scales they attain higher abundances where productivity is higher (total macrofaunal, crustaceans, Excirolana spp., terrestrial spp.) or where the settlement environment is more benign (molluscs and polychaetes). Dissipative beaches supported larger average and total community biomass than reflective beaches. Crustaceans, terrestrial species and cirolanid isopods such as Excirolana spp. also had larger biomass on dissipative beaches. The difference was not significant for molluscs and polychaetes. Significant relationships were found between the biomass of community and taxonomic groups with beach morphodynamics as represented by the Dean’s morphodynamic index. On the microtidal beaches studied here, BSI was less important than other morphodynamic indices and single physical factors in determining faunal biomass and mean individual body size. Surf zone characteristics such as wave height, period and surf zone width had the highest correlations with community, crustacean.
- Full Text:
- Date Issued: 2003
A study of the reintegration of female former child soldiers in Gulu District, northern Uganda
- Authors: Bertelsen, Anna
- Date: 2014
- Subjects: Women soldiers -- Uganda -- Gulu District , Child soldiers -- Uganda -- Gulu District , Patriarchy -- Uganda -- Gulu District
- Language: English
- Type: Thesis , Masters , MPhil
- Identifier: vital:8324 , http://hdl.handle.net/10948/d1020192
- Description: This research explores the perceptions and experiences of female former child soldiers in regard to their reintegration within the community of Gulu District, northern Uganda. In many societies women are generally excluded due to prevailing patriarchal hegemonies, with northern Uganda being no exception. Moreover, former child soldiers are commonly marginalized and discriminated against because members of communities commonly believe that they should be punished for the perceived atrocities that they allegedly committed during times of conflict, rather than be reintegrated into society. In this regard female former child soldiers can be identified as a particularly vulnerable and marginalized group. Therefore, it can be suggested that although the distinction between traditional gender roles has been eroded during times of armed conflict, there is still widespread evidence that women are largely overlooked and disregarded in the process of peace building. In order to explore the perceptions and experiences of former female child soldiers, a qualitative case study method was utilized based on in-depth face to face interviews with women from Gulu District, northern Uganda. The findings of this study indicate that, even though these women went through considerable hardships, all of them displayed a strong sense of resilience. Many of them had taken on the role as active change agents in their own lives and provided an array of suggestions on how their situation could be improved. The major themes constructed from the study include: challenges facing returnees; facilitating factors for returnees and suggestions on improved reintegration. Based on these findings a number of recommendations emerged. The recommendations are presented in order to assist organizations and other stakeholders involved in reintegration of child soldiers in northern Uganda and elsewhere in the world. Apart from providing information to the existing body of research, future areas of proposed research are also outlined.
- Full Text:
- Date Issued: 2014
- Authors: Bertelsen, Anna
- Date: 2014
- Subjects: Women soldiers -- Uganda -- Gulu District , Child soldiers -- Uganda -- Gulu District , Patriarchy -- Uganda -- Gulu District
- Language: English
- Type: Thesis , Masters , MPhil
- Identifier: vital:8324 , http://hdl.handle.net/10948/d1020192
- Description: This research explores the perceptions and experiences of female former child soldiers in regard to their reintegration within the community of Gulu District, northern Uganda. In many societies women are generally excluded due to prevailing patriarchal hegemonies, with northern Uganda being no exception. Moreover, former child soldiers are commonly marginalized and discriminated against because members of communities commonly believe that they should be punished for the perceived atrocities that they allegedly committed during times of conflict, rather than be reintegrated into society. In this regard female former child soldiers can be identified as a particularly vulnerable and marginalized group. Therefore, it can be suggested that although the distinction between traditional gender roles has been eroded during times of armed conflict, there is still widespread evidence that women are largely overlooked and disregarded in the process of peace building. In order to explore the perceptions and experiences of former female child soldiers, a qualitative case study method was utilized based on in-depth face to face interviews with women from Gulu District, northern Uganda. The findings of this study indicate that, even though these women went through considerable hardships, all of them displayed a strong sense of resilience. Many of them had taken on the role as active change agents in their own lives and provided an array of suggestions on how their situation could be improved. The major themes constructed from the study include: challenges facing returnees; facilitating factors for returnees and suggestions on improved reintegration. Based on these findings a number of recommendations emerged. The recommendations are presented in order to assist organizations and other stakeholders involved in reintegration of child soldiers in northern Uganda and elsewhere in the world. Apart from providing information to the existing body of research, future areas of proposed research are also outlined.
- Full Text:
- Date Issued: 2014