Deposition of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shells around CdSeTe alloyed core quantum dots: effects on optical properties
- Adegoke, Oluwasesan, Nyokong, Tebello, Forbes, Patricia B C
- Authors: Adegoke, Oluwasesan , Nyokong, Tebello , Forbes, Patricia B C
- Date: 2015
- Language: English
- Type: Article
- Identifier: vital:7289 , http://hdl.handle.net/10962/d1020342
- Description: In this work, we synthesized water-soluble L-cysteine-capped alloyed CdSeTe core quantum dots (QDs) and investigated the structural and optical properties of deposition of each of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shell layers. Photophysical results showed that the overcoating of a CdS shell around the alloyed CdSeTe core [quantum yield (QY) = 8.4%] resulted in effective confinement of the radiative exciton with an improved QY value of 93.5%. Subsequent deposition of a ZnSe shell around the CdSeTe/CdS surface decreased the QY value to 24.7%, but an increase in the QY value of up to 49.5% was observed when a ZnS shell was overcoated around the CdSeTe/CdS/ZnSe surface. QDs with shell layers showed improved stability relative to the core. Data obtained from time-resolved fluorescence measurements provided useful insight into variations in the photophysical properties of the QDs upon the formation of each shell layer. Our study suggests that the formation of CdSeTe/CdS core/shell QDs meets the requirements of quality QDs in terms of high photoluminescence QY and stability, hence further deposition of additional shells are not necessary in improving the optical properties of the core/shell QDs. Copyright © 2015 John Wiley & Sons, Ltd. , Original publication is available at http://dx.doi.org/10.1002/bio.3013
- Full Text: false
- Date Issued: 2015
- Authors: Adegoke, Oluwasesan , Nyokong, Tebello , Forbes, Patricia B C
- Date: 2015
- Language: English
- Type: Article
- Identifier: vital:7289 , http://hdl.handle.net/10962/d1020342
- Description: In this work, we synthesized water-soluble L-cysteine-capped alloyed CdSeTe core quantum dots (QDs) and investigated the structural and optical properties of deposition of each of CdS, CdS/ZnSe and CdS/ZnSe/ZnS shell layers. Photophysical results showed that the overcoating of a CdS shell around the alloyed CdSeTe core [quantum yield (QY) = 8.4%] resulted in effective confinement of the radiative exciton with an improved QY value of 93.5%. Subsequent deposition of a ZnSe shell around the CdSeTe/CdS surface decreased the QY value to 24.7%, but an increase in the QY value of up to 49.5% was observed when a ZnS shell was overcoated around the CdSeTe/CdS/ZnSe surface. QDs with shell layers showed improved stability relative to the core. Data obtained from time-resolved fluorescence measurements provided useful insight into variations in the photophysical properties of the QDs upon the formation of each shell layer. Our study suggests that the formation of CdSeTe/CdS core/shell QDs meets the requirements of quality QDs in terms of high photoluminescence QY and stability, hence further deposition of additional shells are not necessary in improving the optical properties of the core/shell QDs. Copyright © 2015 John Wiley & Sons, Ltd. , Original publication is available at http://dx.doi.org/10.1002/bio.3013
- Full Text: false
- Date Issued: 2015
Histological validation of gonadal macroscopic staging criteria for Labeo cylindricus (Pisces: Cyprinidae)
- Booth, Anthony J, Weyl, Olaf L F
- Authors: Booth, Anthony J , Weyl, Olaf L F
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124593 , vital:35634 , https://doi.org/10.1080/15627020.2000.11657094
- Description: Histological examination of gametogenesis revealed that the current staging criteria used to assess gonadal recrudescence of the redeye labeo, Labeo cylindricus, were adequate. Gametogenesis was qualitatively similar to that of freshwater teleosts with a clearly defined seasonal reproductive cycle. L. cylindricus undergoes seasonal gross morphological and cytological gonadal changes with previtellogenesis dominating during the winter, vitellogenic development during spring and summer culminating in large-scale spawning at the end of summer. Post-spawning mass atresia of oocytes was evident in autumn. The histological data presented support macroscopical evidence that L. cylindricus is a synchronous iteroparous spawner, reproducing over a short period each year throughout its life-span.
- Full Text:
- Date Issued: 2010
- Authors: Booth, Anthony J , Weyl, Olaf L F
- Date: 2010
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124593 , vital:35634 , https://doi.org/10.1080/15627020.2000.11657094
- Description: Histological examination of gametogenesis revealed that the current staging criteria used to assess gonadal recrudescence of the redeye labeo, Labeo cylindricus, were adequate. Gametogenesis was qualitatively similar to that of freshwater teleosts with a clearly defined seasonal reproductive cycle. L. cylindricus undergoes seasonal gross morphological and cytological gonadal changes with previtellogenesis dominating during the winter, vitellogenic development during spring and summer culminating in large-scale spawning at the end of summer. Post-spawning mass atresia of oocytes was evident in autumn. The histological data presented support macroscopical evidence that L. cylindricus is a synchronous iteroparous spawner, reproducing over a short period each year throughout its life-span.
- Full Text:
- Date Issued: 2010
Structure and agency in the age of climate change
- Authors: Cherry, Janet
- Subjects: South Africa -- Economic conditions , South Africa -- Social conditions , f-sa
- Language: English
- Type: text , Lectures
- Identifier: http://hdl.handle.net/10948/21033 , vital:29429
- Description: What I will present here is based on my grappling over the past three decades with one of the central problems of social science – the relationship between social structure and human agency. This is not a new problem for social scientists; from Karl Marx, who understood that human beings make history, but not in circumstances of their choosing; to the French structuralists who conceived the term ‘relative autonomy’ and ‘overdetermination’; to Anthony Giddens’ ‘structuration theory’ and other contemporary sociologists. What is new are the changing physical circumstances of the world in which we live, which mean that human society can no longer afford to analyse ourselves and our social, political and economic systems independently of the natural world.
- Full Text:
- Authors: Cherry, Janet
- Subjects: South Africa -- Economic conditions , South Africa -- Social conditions , f-sa
- Language: English
- Type: text , Lectures
- Identifier: http://hdl.handle.net/10948/21033 , vital:29429
- Description: What I will present here is based on my grappling over the past three decades with one of the central problems of social science – the relationship between social structure and human agency. This is not a new problem for social scientists; from Karl Marx, who understood that human beings make history, but not in circumstances of their choosing; to the French structuralists who conceived the term ‘relative autonomy’ and ‘overdetermination’; to Anthony Giddens’ ‘structuration theory’ and other contemporary sociologists. What is new are the changing physical circumstances of the world in which we live, which mean that human society can no longer afford to analyse ourselves and our social, political and economic systems independently of the natural world.
- Full Text:
'Meaningful engagement’: Towards a language rights paradigm for effective language policy implementation
- Docrat, Zakeerah, Kaschula, Russell H
- Authors: Docrat, Zakeerah , Kaschula, Russell H
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/174812 , vital:42512 , https://doi.org/10.1080/02572117.2015.1056455
- Description: This article aims to develop the concept of ‘meaningful engagement’ in terms of the contemporary language policy implementation framework in South Africa. By exploring the current language policies, implementation and the current lack of effectiveness, the authors offer a new implementation focus drawn from the legal concept of ‘meaningful engagement’. ‘Meaningful engagement’ is a concept within the socio-economic rights sphere. This article expands and advances the concept within a language policy framework. Against the enabling legislative environment created by the Use of Official Languages Act 12 of 2012 and the overarching Constitutional framework which embeds the rights of all official languages, ‘meaningful engagement’ is developed and applied to selected language policies and practices.
- Full Text:
- Date Issued: 2015
- Authors: Docrat, Zakeerah , Kaschula, Russell H
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/174812 , vital:42512 , https://doi.org/10.1080/02572117.2015.1056455
- Description: This article aims to develop the concept of ‘meaningful engagement’ in terms of the contemporary language policy implementation framework in South Africa. By exploring the current language policies, implementation and the current lack of effectiveness, the authors offer a new implementation focus drawn from the legal concept of ‘meaningful engagement’. ‘Meaningful engagement’ is a concept within the socio-economic rights sphere. This article expands and advances the concept within a language policy framework. Against the enabling legislative environment created by the Use of Official Languages Act 12 of 2012 and the overarching Constitutional framework which embeds the rights of all official languages, ‘meaningful engagement’ is developed and applied to selected language policies and practices.
- Full Text:
- Date Issued: 2015
Being a Born Free: the misunderstandings and missed opportunities facing young South Africans
- Authors: Malila, Vanessa
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/158680 , vital:40220 , https://hdl.handle.net/10520/EJC175765
- Description: Young South Africans are often referred to as the Born Frees - a term which sometimes means people born after 1994, sometimes people born after 1990, or young people who came of age politically after 1994. I've come to really dislike the term Born Frees and particularly the way it is used by the media and the politicians. By calling young people Born Frees, society is using apartheid as a reference point to identify a post-apartheid generation. This reference point (the transition to a 'free' society) unfortunately does not resonate with many of the young people that I've encountered in my research and many feel insulted by the implications of this term, which does not apply to them in any way. Should South African society really be using the transition from apartheid to define its young people and how does it relate to the lives of real young people in South Africa today? Are they really Born Free, free from what, free to do what, free individuals or free as a collective? I will look at some of the stereotypes being used in the mainstream media of Born Frees, and then look at the reaction to this term by some real young South Africans.
- Full Text:
- Date Issued: 2015
- Authors: Malila, Vanessa
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/158680 , vital:40220 , https://hdl.handle.net/10520/EJC175765
- Description: Young South Africans are often referred to as the Born Frees - a term which sometimes means people born after 1994, sometimes people born after 1990, or young people who came of age politically after 1994. I've come to really dislike the term Born Frees and particularly the way it is used by the media and the politicians. By calling young people Born Frees, society is using apartheid as a reference point to identify a post-apartheid generation. This reference point (the transition to a 'free' society) unfortunately does not resonate with many of the young people that I've encountered in my research and many feel insulted by the implications of this term, which does not apply to them in any way. Should South African society really be using the transition from apartheid to define its young people and how does it relate to the lives of real young people in South Africa today? Are they really Born Free, free from what, free to do what, free individuals or free as a collective? I will look at some of the stereotypes being used in the mainstream media of Born Frees, and then look at the reaction to this term by some real young South Africans.
- Full Text:
- Date Issued: 2015
Synthesis and photophysical properties of nanocomposites of aluminum tetrasulfonated phthalocyanine covalently linked to glutathione capped CdTe/CdS/ZnS quantum dots
- Oluwole, David O, Britton, Jonathan, Mashazi, Philani N, Nyokong, Tebello
- Authors: Oluwole, David O , Britton, Jonathan , Mashazi, Philani N , Nyokong, Tebello
- Date: 2015
- Language: English
- Type: text , Article
- Identifier: vital:7276 , http://hdl.handle.net/10962/d1020291 , http://dx.doi.org/10.1016/j.synthmet.2015.04.015
- Description: Aluminum tetrasulfonated phthalocyanine (ClAlTSPc) was covalently linked with different sizes of glutathione capped CdTe/CdS/ZnS quantum dots (QDs). The photophysical and Förster resonance energy transfer (FRET) properties of the nanoconjugates were investigated. The CdTe/CdS/ZnS(6.3) nanocomposite showed the highest enhancement in its photophysical properties while (CdTe/CdS/ZnS(3.2) nanocomposite showed the least. Highest FRET efficiency was observed in the linked CdTe/CdS/ZnS(6.3) nanocomposites at 93%. Hence, the combination of CdTe/CdS/ZnS with ClAlTSPc exhibited excellent photophysical properties. , Original publication is available at http://dx.doi.org/10.1016/j.synthmet.2015.04.015
- Full Text: false
- Date Issued: 2015
- Authors: Oluwole, David O , Britton, Jonathan , Mashazi, Philani N , Nyokong, Tebello
- Date: 2015
- Language: English
- Type: text , Article
- Identifier: vital:7276 , http://hdl.handle.net/10962/d1020291 , http://dx.doi.org/10.1016/j.synthmet.2015.04.015
- Description: Aluminum tetrasulfonated phthalocyanine (ClAlTSPc) was covalently linked with different sizes of glutathione capped CdTe/CdS/ZnS quantum dots (QDs). The photophysical and Förster resonance energy transfer (FRET) properties of the nanoconjugates were investigated. The CdTe/CdS/ZnS(6.3) nanocomposite showed the highest enhancement in its photophysical properties while (CdTe/CdS/ZnS(3.2) nanocomposite showed the least. Highest FRET efficiency was observed in the linked CdTe/CdS/ZnS(6.3) nanocomposites at 93%. Hence, the combination of CdTe/CdS/ZnS with ClAlTSPc exhibited excellent photophysical properties. , Original publication is available at http://dx.doi.org/10.1016/j.synthmet.2015.04.015
- Full Text: false
- Date Issued: 2015
Anton and Vale van der Merwe: reinterpreting Afro-Oriental studio ceramics traditions in South Africa
- Authors: Steele, John
- Date: 2015
- Language: English
- Type: text , Article
- Identifier: http://hdl.handle.net/11260/968 , vital:30077
- Description: Growing awareness of ancient Chinese Song and Yuan ceramics, amongst other Oriental traditions, by people with western connections such as Bernard Leach and Michael Cardew, in conjunction with influences from Japanese associates such as Soyetsu Yanagi, Kenkichi Tomimoto, and Shoji Hamada, (De Waal 1997, Harrod 2012, Kikuchi 1977, Leach 1976) has had many consequences. It spread a consciousness idealizing self-sufficient pottery studios where potters were in touch with all aspects of creating utilityware, largely from local materials for local use. Out of this emerged an Anglo-Oriental studio ceramic philosophy of form and practice, associated mainly with hand-made high temperature reduction fired ceramics. These ideas spread to South Africa in the late 1950s, and by the early 1960s local studios were being established along these lines. This studio ceramics movement grew exponentially in South Africa, initiating a phase of Afro-Oriental ceramics that remains a powerful way of life and visual arts influence. This paper seeks to explore aspects of Afro- Oriental studio ceramics in South Africa, with particular reference to the Leach/Hamada/Cardew to Rabinowitz, and Van der Merwe lineage.
- Full Text:
- Date Issued: 2015
- Authors: Steele, John
- Date: 2015
- Language: English
- Type: text , Article
- Identifier: http://hdl.handle.net/11260/968 , vital:30077
- Description: Growing awareness of ancient Chinese Song and Yuan ceramics, amongst other Oriental traditions, by people with western connections such as Bernard Leach and Michael Cardew, in conjunction with influences from Japanese associates such as Soyetsu Yanagi, Kenkichi Tomimoto, and Shoji Hamada, (De Waal 1997, Harrod 2012, Kikuchi 1977, Leach 1976) has had many consequences. It spread a consciousness idealizing self-sufficient pottery studios where potters were in touch with all aspects of creating utilityware, largely from local materials for local use. Out of this emerged an Anglo-Oriental studio ceramic philosophy of form and practice, associated mainly with hand-made high temperature reduction fired ceramics. These ideas spread to South Africa in the late 1950s, and by the early 1960s local studios were being established along these lines. This studio ceramics movement grew exponentially in South Africa, initiating a phase of Afro-Oriental ceramics that remains a powerful way of life and visual arts influence. This paper seeks to explore aspects of Afro- Oriental studio ceramics in South Africa, with particular reference to the Leach/Hamada/Cardew to Rabinowitz, and Van der Merwe lineage.
- Full Text:
- Date Issued: 2015
Fish predation regimes modify benthic diatom community structures: experimental evidence from an in situ mesocosm study
- Wasserman, Ryan J, Vink, Tim J F, Dalu, Tatenda, Froneman, P William
- Authors: Wasserman, Ryan J , Vink, Tim J F , Dalu, Tatenda , Froneman, P William
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68052 , vital:29190 , https://doi.org/10.1111/aec.12255
- Description: Publisher version , Diatoms are important primary producers in shallow water environments. Few studies have assessed the importance of biological interactions in structuring these communities. In the present study, benthic diatom community structure in relation to manipulated food webs was assessed using in situ mesocosms, whereby predator-free environments and environments comprising two different fish species were assessed. Zooplankton abundance, settled algal biomass and the diatom community were monitored over a 12‐day period across each of the three trophic scenarios. Differences among treatments over time were observed in zooplankton abundances, particularly copepods. Similarly, the benthic diatom community structure changed significantly over time across the three trophic treatments. However, no differences in total algal biomass were found among treatments. This was likely the result of non‐diatom phytoplankton contributions. We propose that the benthic diatom community structure within the mesocosms was influenced by trophic cascades and potentially through direct consumption by the fish. The study highlights that not only are organisms at the base of the food web affected by predators at the top of the food web, but that predator identity is potentially an important consideration for predator–prey interaction outcomes with consequences for multiple trophic levels.
- Full Text: false
- Date Issued: 2015
- Authors: Wasserman, Ryan J , Vink, Tim J F , Dalu, Tatenda , Froneman, P William
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68052 , vital:29190 , https://doi.org/10.1111/aec.12255
- Description: Publisher version , Diatoms are important primary producers in shallow water environments. Few studies have assessed the importance of biological interactions in structuring these communities. In the present study, benthic diatom community structure in relation to manipulated food webs was assessed using in situ mesocosms, whereby predator-free environments and environments comprising two different fish species were assessed. Zooplankton abundance, settled algal biomass and the diatom community were monitored over a 12‐day period across each of the three trophic scenarios. Differences among treatments over time were observed in zooplankton abundances, particularly copepods. Similarly, the benthic diatom community structure changed significantly over time across the three trophic treatments. However, no differences in total algal biomass were found among treatments. This was likely the result of non‐diatom phytoplankton contributions. We propose that the benthic diatom community structure within the mesocosms was influenced by trophic cascades and potentially through direct consumption by the fish. The study highlights that not only are organisms at the base of the food web affected by predators at the top of the food web, but that predator identity is potentially an important consideration for predator–prey interaction outcomes with consequences for multiple trophic levels.
- Full Text: false
- Date Issued: 2015
Brown hyena habitat selection varies among sites in a semi-arid region of southern Africa
- Welch, Rebecca J, Tambling, Craig J, Bissett, Charlene, Gaylard, Angela, Müller, Konrad, Slater, Kerry, Strauss, W Maartin, Parker, Daniel M
- Authors: Welch, Rebecca J , Tambling, Craig J , Bissett, Charlene , Gaylard, Angela , Müller, Konrad , Slater, Kerry , Strauss, W Maartin , Parker, Daniel M
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123277 , vital:35423 , https://doi.10.1093/jmammal/gyv189
- Description: In the last 50 years, the human impact on ecosystems has been greater than during any other time period in human history (Millennium Ecosystem Assessment 2003). Large carnivores face anthropogenic threats worldwide, specifically persecution, habitat degradation, and habitat fragmentation (Everatt et al. 2014; Groom et al. 2014; Ripple et al. 2014; Wolfe et al. 2015). Because large carnivores often occupy high trophic levels, their presence influences species at lower levels through trophic cascades (Ripple et al. 2014). Natural experiments, taking advantage of large carnivore management, have shown that large predators provide fundamental ecosystem and economic services that help maintain healthy and diverse ecosystems (Ripple et al. 2014). Additionally, carnivores play an important role in other ecosystem processes, for example, scavenging carnivores may provide regulatory services, such as waste removal, nutrient cycling, and disease regulation. Such services add stability to ecosystems and ensure energy flow through multiple trophic levels (DeVault et al. 2003; Wilson and Wolkovich 2011).
- Full Text:
- Date Issued: 2015
- Authors: Welch, Rebecca J , Tambling, Craig J , Bissett, Charlene , Gaylard, Angela , Müller, Konrad , Slater, Kerry , Strauss, W Maartin , Parker, Daniel M
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123277 , vital:35423 , https://doi.10.1093/jmammal/gyv189
- Description: In the last 50 years, the human impact on ecosystems has been greater than during any other time period in human history (Millennium Ecosystem Assessment 2003). Large carnivores face anthropogenic threats worldwide, specifically persecution, habitat degradation, and habitat fragmentation (Everatt et al. 2014; Groom et al. 2014; Ripple et al. 2014; Wolfe et al. 2015). Because large carnivores often occupy high trophic levels, their presence influences species at lower levels through trophic cascades (Ripple et al. 2014). Natural experiments, taking advantage of large carnivore management, have shown that large predators provide fundamental ecosystem and economic services that help maintain healthy and diverse ecosystems (Ripple et al. 2014). Additionally, carnivores play an important role in other ecosystem processes, for example, scavenging carnivores may provide regulatory services, such as waste removal, nutrient cycling, and disease regulation. Such services add stability to ecosystems and ensure energy flow through multiple trophic levels (DeVault et al. 2003; Wilson and Wolkovich 2011).
- Full Text:
- Date Issued: 2015
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