Temperature dependence of persistent luminescence in CaAl2O4: Eu2+, Nd3+ related to beta irradiation and optical excitation
- Kalita, Jitumani M, Chithambo, Makaiko L
- Authors: Kalita, Jitumani M , Chithambo, Makaiko L
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/105158 , vital:32470 , https://doi.org/10.1016/j.jlumin.2018.10.062
- Description: Mechanisms responsible for the emission of persistent luminescence in CaAl2O4:Eu2+,Nd3+ are typically studied following excitation by ultraviolet or visible light. In contrast, we have studied the persistent luminescence from this material after beta irradiation and optical excitation. These studies have been carried out at 25 °C as well as at various temperatures up to 100 °C. A thermoluminescence (TL) glow curve measured at 1 °C/s following beta irradiation showed a glow peak at 63 °C. On the other hand, a glow curve measured after 15 s of optical excitation by polychromatic white light shows a peak at 102 °C. The partial heating procedure reveals that each of the TL peaks consist of several overlapping components. The TL in each case was analysed for kinetic parameters. The initial rise analysis carried out on the rising edge of the overlapping components shows that the activation energy of the component peaks corresponding to beta irradiation is consistent at (0.59 ± 0.01) eV. In comparison, activation energies corresponding to optical excitation increases with the partial heating temperature from (0.71 ± 0.01) eV to (0.76 ± 0.01) eV. The activation energy of (0.59 ± 0.01) eV is ascribed to an oxygen vacancy whereas the range of activation energies between (0.71 ± 0.01) eV and (0.76 ± 0.01) eV is ascribed to the 4 f levels of the Nd dopant.
- Full Text: false
- Authors: Kalita, Jitumani M , Chithambo, Makaiko L
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/105158 , vital:32470 , https://doi.org/10.1016/j.jlumin.2018.10.062
- Description: Mechanisms responsible for the emission of persistent luminescence in CaAl2O4:Eu2+,Nd3+ are typically studied following excitation by ultraviolet or visible light. In contrast, we have studied the persistent luminescence from this material after beta irradiation and optical excitation. These studies have been carried out at 25 °C as well as at various temperatures up to 100 °C. A thermoluminescence (TL) glow curve measured at 1 °C/s following beta irradiation showed a glow peak at 63 °C. On the other hand, a glow curve measured after 15 s of optical excitation by polychromatic white light shows a peak at 102 °C. The partial heating procedure reveals that each of the TL peaks consist of several overlapping components. The TL in each case was analysed for kinetic parameters. The initial rise analysis carried out on the rising edge of the overlapping components shows that the activation energy of the component peaks corresponding to beta irradiation is consistent at (0.59 ± 0.01) eV. In comparison, activation energies corresponding to optical excitation increases with the partial heating temperature from (0.71 ± 0.01) eV to (0.76 ± 0.01) eV. The activation energy of (0.59 ± 0.01) eV is ascribed to an oxygen vacancy whereas the range of activation energies between (0.71 ± 0.01) eV and (0.76 ± 0.01) eV is ascribed to the 4 f levels of the Nd dopant.
- Full Text: false
The elephant in the ‘room’: determinants of songbird assemblages in the Thicket Biome, South Africa
- Authors: Parker, Daniel M
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/105134 , vital:32468 , https://doi.org/10.1080/01584197.2018.1562847
- Description: When vegetation structure is altered, songbird communities may be affected. Despite speculation that African Elephant (Loxodonta africana) browsing impacts bird communities, existing data are limited. I sampled the bird communities of the Albany Thicket Biome at 10 sites in the Eastern Cape, South Africa, half with elephants and half without. Songbird community parameters were best predicted by how long elephants had been present, elephant density and the percentage cover of thicket vegetation. The sites where elephants had been present for longer had more bird species and increased songbird density and diversity. However, bird density also increased with increasing thicket vegetation cover and this is a phenomenon unlikely to be compatible with long-term elephant presence. There was an almost equal split between the number of bird species that appeared to be negatively affected by changes in habitat structure (47%) and those which benefited (53%). Smaller birds were generally more abundant as vegetation structural integrity increased and larger birds were more abundant when vegetation structural integrity declined. The browsing of elephants could be viewed as facilitative for songbirds in the short term. However, this effect may not persist in the long term because all elephant populations (notorious tree-fellers) in the Eastern Cape are found in fenced areas where natural migration is not possible. More broadly, my data provide important insight into how avian communities respond to habitat transformation at the local and regional scales.
- Full Text: false
- Authors: Parker, Daniel M
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/105134 , vital:32468 , https://doi.org/10.1080/01584197.2018.1562847
- Description: When vegetation structure is altered, songbird communities may be affected. Despite speculation that African Elephant (Loxodonta africana) browsing impacts bird communities, existing data are limited. I sampled the bird communities of the Albany Thicket Biome at 10 sites in the Eastern Cape, South Africa, half with elephants and half without. Songbird community parameters were best predicted by how long elephants had been present, elephant density and the percentage cover of thicket vegetation. The sites where elephants had been present for longer had more bird species and increased songbird density and diversity. However, bird density also increased with increasing thicket vegetation cover and this is a phenomenon unlikely to be compatible with long-term elephant presence. There was an almost equal split between the number of bird species that appeared to be negatively affected by changes in habitat structure (47%) and those which benefited (53%). Smaller birds were generally more abundant as vegetation structural integrity increased and larger birds were more abundant when vegetation structural integrity declined. The browsing of elephants could be viewed as facilitative for songbirds in the short term. However, this effect may not persist in the long term because all elephant populations (notorious tree-fellers) in the Eastern Cape are found in fenced areas where natural migration is not possible. More broadly, my data provide important insight into how avian communities respond to habitat transformation at the local and regional scales.
- Full Text: false
‘In defence of chick-lit’: refashioning feminine subjectivities in Ugandan and South African contemporary women’s writing
- Authors: Spencer, Lynda G
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/138736 , vital:37669 , DOI: 10.1177/1464700119831544
- Description: Ugandan and South African contemporary women’s narratives reflect on the rapid pace of change in the social lives of women in two countries that are contending with the aftermath of conflict and violence. This article will interrogate how contemporary women writers such as Goretti Kyomuhendo (Whispers from Vera), Zukiswa Wanner (The Madams and Behind Every Successful Man) and Cynthia Jele (Happiness is a Four-Letter Word) are embracing chick-lit as a form of writing, while simultaneously short-circuiting this genre to create an experimental form that allows them to reflect on the realities of women and engage with the contradictions, complexities and ambiguities of contemporary feminine subjectivities.
- Full Text: false
- Authors: Spencer, Lynda G
- Date: 2019
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/138736 , vital:37669 , DOI: 10.1177/1464700119831544
- Description: Ugandan and South African contemporary women’s narratives reflect on the rapid pace of change in the social lives of women in two countries that are contending with the aftermath of conflict and violence. This article will interrogate how contemporary women writers such as Goretti Kyomuhendo (Whispers from Vera), Zukiswa Wanner (The Madams and Behind Every Successful Man) and Cynthia Jele (Happiness is a Four-Letter Word) are embracing chick-lit as a form of writing, while simultaneously short-circuiting this genre to create an experimental form that allows them to reflect on the realities of women and engage with the contradictions, complexities and ambiguities of contemporary feminine subjectivities.
- Full Text: false
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