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Welcome to ResearchSpace, the institutional repository of the CSIR. ResearchSpace is an open access electronic archive collecting, preserving and distributing scholarly digital materials created by the CSIR.

Recent Submissions

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Establishing in vitro screening protocols based on phenotypic plasticity of Amaranthus dubius and Galinsoga parviflora seeds for drought, salinity, and heat tolerance

(2024) Areington, CA; O’Kennedy, Martha M; Sershen

The vulnerability of commercial crops under a changing climate has led scientists to consider wild crop species as alternative food sources. The aim of this study was to identify plastic physiological and morphological traits that could be used to in vitro screen Amaranthus dubius and Galinsoga parviflora seeds for drought, salinity, and heat tolerance. To establish the lethal dose/temperature, 50% (LD/T50), for each stress, seeds for both were subjected to various mannitol and NaCl stresses and a range of temperatures. Percentage seedling emergence was selected as the initial indicator of tolerance and used to establish the LD/T50 for in vitro screening for both species. Seeds of both were then screened at the LD/T50 concentrations/temperatures established, and seedlings that emerged after 21 days were measured for leaf area, root (RL), shoot length (SL), chlorophyll content (Chl), fresh, dry mass, and leaf number. Data for these were used to quantify plasticity in terms of Valladares’s phenotypic plasticity index. For A. dubius, three (viz. RL, SL, and Chl) showed some plasticity (≥0.53) and tolerance across all three stressors. For G. parviflora all traits except SL showed some plasticity (≥0.58) and tolerance across all three stressors. Both species had high phenotypic plasticity across all three stressors, which suggests that wild leafy vegetables may possess the ability to tolerate climate change-associated stressors and should be considered for future breeding programs.

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Theoretical analysis of on-axis obstructed Laguerre-Gauss beams

(2024) Mabena, Chemist A

Advances in the generation of structured light beams have led to their increased adoption in various applications such as laser-based material processing, optical microscopy, and optical communication. However, the reliability of these beams, particularly Laguerre-Gauss beams, further hinges on their resilience against damage caused by obstructions. In this work, the self-reconstruction of Laguerre-Gauss beams upon on-axis obstruction is analyzed by modeling the obstructed beam in terms of two orthogonal components–one component representing the attenuated beam and another representing the perturbation by the obstruction. Due to the orthogonality of the two components, the perturbation term is reminiscent of harmonic distortion in signal processing. This approach provides a simple method to quantify the damage via the modal cross-talk generated by the obstruction. To this end, closed-form expressions are derived to calculate the modal spectrum and the total damage caused by the obstruction. The results show that amplitude-obstructed Laguerre-Gauss beams self-reconstruct in the central region. The reduced intensity of the outer rings is shown to be due to the attenuated component being out of phase with the perturbation component. In the case of an on-axis obstruction with phase perturbation, the beam suffers more damage in certain parameter windows and may become reshaped. The results of this work provide a tool that could inform design methods and strategies in applications of structured light.

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Insights on who funds climate change adaptation research in South Africa

(2025-02) Mantlana, Khanyisa B; Nondlazi, Basanda X; Naidoo, Sasha; Ramoelo, A

Background: This article examines the funding landscape of climate change adaptation research in South Africa to understand the origin, distribution, and thematic prioritization of funding for climate change research in South Africa. Methods: The article used specific search terms to query peer-reviewed publications in the Web of Science and Scopus databases (1985 to 2023). Results: Environmental Science emerged as the most dominant research area during this period, while Agriculture appeared in the top four positions among research areas in climate change adaptation research in South Africa in both databases. The largest number of publications on climate change adaptation research in South Africa is generated through domestic funding, followed by the United States, the United Kingdom, and Germany. The National Research Foundation (NRF) had the highest number of publications. The analysis revealed a strong paucity of funding relationship between South Africa and other African countries in the field of climate change adaptation research. Conclusions: Knowledge of these trends can inform policy decisions on funding of climate change adaptation in South Africa and strategic partnerships between South Africa and the rest of the world.

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From species to pixels: Monitoring rangeland quality & productivity by leveraging the NDVI-RCI relationship

(2025-01) Nondlazi, Basanda X; Cho, Moses A; Mantlana, Khanyisa B; Ramoelo, A

Grasslands are highly vulnerable to climate and changes in grazing management, yet little is known about the national rangeland response to long-term (>18 years) grazing management that may confound climate effects. This study assessed the correlation between Normalized Difference Vegetation Index (NDVI), i.e., productivity and Rangeland Condition Index (RCI) i.e., quality and predicted historical grazing management (26 years) using Ecological Index Method (EIM) analysis of 72 relevés in the Highland Sourveld (HSV). Relationships between 150 NDVI and 72 RCI samples showed a rate of 0.125 change in NDVI for every 12.5% change in RCI. In 1983, the HSV’s rangeland carrying capacity (RCC) ranged from 2.0 - 2.2 ha/AU/yr (land required to support one mature bovine for 1 year), with an NDVI of 0.43, like the benchmark. site. By 2009, the RCC decreased to 3.2 ha/AU/yr, with NDVI <0.30. Selective overgrazing, reduced RCC by increasing Increaser II species and reducing Decreaser species presence. Findings suggest combining NDVI and RCI is more effective than using either alone. Integrating remote sensing with traditional ecological data (Ecological Remote Sensing - eRS) improves our understanding of rangeland vulnarability, thus, ideal for permanent monitoring of public rangelands in South Africa.

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Radar detectability of light aircraft micro‐Doppler modulation

(2024-10) Berndt, Robert J; Gaffar, MYA; Nel, Willem AJ; O’Hagan, DW

The critical role of specifying micro-Doppler mode performance in the modelling and development of modern radar systems is investigated. The authors focus on the detection of micro-Doppler modulation from light aircraft, analysing data from eight helicopters and nine propeller aircraft. With the growing need for accurate target classification in radar technology, incorporating micro-Doppler detection metrics into radar performance specifications has become increasingly important. This research offers a novel approach to measuring the detectability of micro-Doppler modulation relative to returns from the main fuselage. The investigation covers the impacts of various preprocessing techniques, polarisation, and aspect angle on detection capabilities. Findings reveal that, on average, micro-Doppler modulation from propellers is detectable at distances between 50% and 100% of the range at which the fuselage is detected. For helicopters, this range decreases to between 30% and 80%. Additionally, the study introduces empirically derived statistical models designed to predict micro-Doppler detection ranges in relation to fuselage returns, enhancing the predictability and specificity of radar system performance. This novel contribution presents a basis for improving radar system specifications, leading ultimately to more predictable and reliable light aircraft classification.