Time-resolved luminescence from quartz: an overview of contemporary developments and applications
- Authors: Chithambo, Makaiko L , Pagonis, Vasilis , Ankjærgaard, Christina
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124743 , vital:35658 , https://doi.org/10.1016/j.physb.2015.10.014
- Description: Time-resolved optical stimulation of luminescence has become established as a key method for measurement of optically stimulated luminescence from quartz, feldspar and α-Al2O3:C, all materials of interest in dosimetry. The aim of time-resolved optical stimulation is to separate in time the stimulation and emission of luminescence. The luminescence is stimulated from a sample using a brief light pulse and the emission monitored during stimulation in the presence of scattered stimulating light or after pulsing, over photomultiplier noise only. Although the use of the method in retrospective dosimetry has been somewhat limited, the technique has been successfully applied to study mechanisms in the processes leading up to luminescence emission. The main means for this has been the temperature dependence of the luminescence intensity as well as the luminescence lifetimes determined from time-resolved luminescence spectra. In this paper we review some key developments in theory and applications to quartz including methods of evaluating lifetimes, techniques of evaluating kinetic parameters using both the dependence of luminescence intensity and lifetime on measurement temperature, and of lifetimes on annealing temperature. We then provide an overview of some notable applications such as separation of quartz signals from a quartz–feldspar admixture and the utility of the dynamic throughput, a measure of luminescence measured as a function of the pulse width. The paper concludes with some suggestions of areas where further exploration would advance understanding of dynamics of luminescence in quartz and help address some outstanding problems in its application.
- Full Text: false
- Date Issued: 2016
Trophic interactions in an austral temperate ephemeral pond inferred using stable isotope analysis
- Authors: Dalu, Tatenda , Weyl, Olaf L F , Froneman, P William , Wasserman, Ryan J
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/68022 , vital:29185 , https://doi.org/10.1007/s10750-015-2533-5
- Description: Publisher version , Ephemeral ponds are vulnerable aquatic habitats which are difficult to protect given their dynamic nature and sensitivity to degradation during dry periods. Little information is available on these habitats in austral regions, with almost no information on food-web structure and complexity. The study aimed to assess trophic interactions among dominant organisms in an ephemeral pond food web, and investigate the importance of autochthonous and allochthonous carbon, using 13C and 15N isotopes. Results of the investigation suggest that the food web comprised four trophic levels, with the top predators being Notonectids (Notonecta sp.) and diving beetles (Cybister tripunctatus (Olivier)). Intermediary trophic levels comprised zooplankton (daphniids and copepodids), macroinvertebrates (e.g. micronectids and molluscs) and tadpoles. Generalist feeders dominated the higher trophic levels (>3) with specialists comprising the lower trophic levels (≤3). The consumers preferred autochthonous fine particulate organic matter, epiphyton and submerged macrophyte organic matter sources over allochthonous sources. Autochthonous organic matter was transferred to the food web via zooplankton and select macroinvertebrates including Micronecta sp. and Physa sp. The food-web structure within the pond appeared to reflect the secondary stage of trophic structural complexity in the evolution of ephemeral ponds over the course of their hydro-period.
- Full Text: false
- Date Issued: 2016
Vertebrate Biostratigraphy of the Witteberg Group and the Devonian-Carboniferous boundary in South Africa
- Authors: Gess, Robert W
- Date: 2016
- Language: English
- Type: text , boook chapter
- Identifier: http://hdl.handle.net/10962/73987 , vital:30248 , https://doi.org/10.1007/978-3-319-40859-0_13
- Description: Witteberg Group rocks are Late Devonian to Early Carboniferous in age. Comparison with Laurasian sea-level curves has correlated the earliest Carboniferous Tournasian transgression, with the argillaceous Kweekvlei Formation, overlying the arenaceous Witpoort Formation. The Devonian/Carboniferous boundary is globally characterised by a Mass Extinction which extinguished the entire grade of placoderm fish and radically reduced sarcopterygian and acanthodian diversity, preluding an Early Carboniferous radiation of actinopterygians. Analysis of Cape Supergroup biostratigraphy reveals that a fauna preservationally dominated by placoderms, sharks, and gyracanthid acanthodians may be traced from the Upper Bokkeveld Group through the Wagondrift Formation (Witteberg Group) to the Witpoort Formation, wherein it displays an increased diversity of placoderms, as well as sarcopterygians. Overlying strata contain no placoderms or sarcopterygians, but present are some relict sharks and acanthodians, and an increasing abundance of actinopterygians. This congruence confirms sea-level curve based age estimates of the Witteberg Group and the position of the Devonian/Carboniferous boundary.
- Full Text: false
- Date Issued: 2016
Water footprint assessment of citrus production in South Africa: A case study of the Lower Sundays River Valley
- Authors: Munro, Samantha A , Fraser, Gavin C G , Snowball, Jeanette D , Pahlow, Markus
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69240 , vital:29463 , https://doi.org/10.1016/j.jclepro.2016.06.142
- Description: Water footprint assessment is a developing method that is being increasingly applied to quantify water use, prioritise reductions, assess sustainability and provide information to achieve sustainable, efficient, and equitable water use. The objectives of this paper were to conduct a water footprint assessment of primary citrus production within the Lower Sundays River Valley in South Africa using local, high-resolution data and to examine indicators (water scarcity, pollution, efficiency, productivity and access) to determine the sustainability of blue, green and grey water footprints of a wet, dry and average year. Lemons were found to have the lowest blue and combined green-blue water footprint per ton of production across all climatic years, followed by soft citrus, valencias and navels. Valencias had the lowest, and navels the highest grey WF (relating to inorganic nitrogen). Lemons, despite their high crop water and fertiliser requirements, were regarded more economically efficient in comparison to valencias, soft citrus and navels, in that they provided higher net income and more employment hours per m3 of water in comparison to other citrus crops. In an average season, lemons generated approximately 39% more income per m3 of water than navels, despite navels being the dominant cultivar. Blue water consumption for citrus in the catchment was calculated to be 58.7 Mm3 for an average season and 89.2 Mm3 for a dry season. Due to an inter-basin transfer scheme, no physical water scarcity occurred, and both environmental and basic human needs are met. Water pollution levels related to nitrogen however, exceeded the assimilative capacity of the run-off in dry years. The area also experiences institutional and infrastructural scarcity and 14% of the population do not have access to piped water. Stakeholders and governments may use the results of water footprint assessments to determine the status of river basins, make evaluations for future water usage and the potential impacts of expanding agriculture and different management strategies. Including environmental and socio-economic indicators will also improve the integrity of water footprint assessments.
- Full Text: false
- Date Issued: 2016
Ways of belonging: meanings of “Nature” among Xhosa-speaking township residents in South Africa
- Authors: Cocks, Michelle L , Alexander, Jamie K , Mogano, Lydia , Vetter, Susan M
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/66021 , vital:28877 , https://doi.org/10.2993/0278-0771-36.4.820
- Description: publisher version , The concept of biocultural diversity, originally used to describe indigenous people and their ways of using and managing natural resources, has more recently been applied within the urban context to understand the variability of interactions between humans and nature. Significant progress has been made internationally in acknowledging the need to preserve and maintain green spaces in urban environments. Current efforts to address the need for greening urban areas in South Africa primarily focus on the establishment and maintenance of botanical gardens and parks as well as various green belts within the urban landscape. South Africa's urban areas are overwhelmingly shaped by the historical segregation of space and stark disparities in wealth. The distribution, quality, and extent of urban green spaces reflect this. Many township dwellers do not have access to these amenities and their interactions with nature are thus usually constrained to access to municipal commonages. This article explores how areas of natural vegetation in municipal commonages on the outskirts of urban centers in South Africa continue to offer places of cultural, spiritual, and restorative importance to Xhosa-speaking township dwellers. A case study from Grahamstown, an urban center in the Eastern Cape with a population of around 80,000, illustrates how ability to access and move through such places contributes to people's well-being, identity formation, and shared heritage. A case is made for adopting a biocultural diversity approach to spatial planning and urban development within the South African context.
- Full Text: false
- Date Issued: 2016
What lies beneath: exploring the deeper purposes of feedback on student writing through considering disciplinary knowledge and knowers
- Authors: Van Heerden, Martina , Clarence, Sherran , Bharuthram, Sharita
- Date: 2016
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/59856 , vital:27669 , https://doi.org/10.1080/02602938.2016.1212985
- Description: Feedback plays an integral role in students’ learning and development, as it is often the only personal communication that students have with tutors or lecturers about their own work. Yet, in spite of its integral role in student learning, there is disagreement between how students and tutors or lecturers perceive the pedagogic purpose of feedback. Central to this disagreement is the role that feedback has to play in ensuring that students produce the ‘right’ kinds of knowledge, and become the ‘right’ kinds of knowers within their disciplines. This paper argues that, in order to find common ground between students and tutors or lecturers on what feedback is for, and how to both give and use it effectively, we need to conceptualise disciplinary knowledge and knowers anew. We offer, as a useful starting point, the Specialisation dimension of Legitimation Code Theory as both practical theory and methodological tool for exploring knowledge and knowers in English Studies and Law as two illustrative cases. The paper concludes that this analysis offers lecturers and tutors a fresh understanding of the disciplinary knowledge and knower structures they work within and, relatedly, a clearer view of the work their feedback needs to do within these.
- Full Text: false
- Date Issued: 2016
Playing broken telephone with student feedback: the possibilities and issues of transformation within a South African case of a collegial rationality model of evaluation
- Authors: Belluigi, Dina Z
- Date: 2013
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/66943 , vital:29003 , https://doi.org/10.1016/B978-1-84334-655-5.50001-5
- Description: publisher version , Drawing on the case of a small South African university which espouses a social justice approach to transformation, this chapter considers the possibilities and challenges created for student feedback within an institutional context that gives the individual lecturer a large degree of autonomy in evaluation. The chapter looks at some of the dominant perceptions of student feedback in addition to how it is collected and utilised, by referring to the institution’s policies and guideline documents; institutional research conducted with course coordinators; responses elicited from 40 lecturers on the issues outlined in this chapter; the author’s own reflections as a staff developer in the institution; and specific examples of good practice from lecturers situated within social science disciplines. The emerging concerns which structured this discussion are: the impact of student feedback on improving quality; enabling student voice; increasing student ownership; and the educational value of evaluation processes.
- Full Text: false
- Date Issued: 2013