Research Publications/Outputs

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130000-year-old fossil elephant found near Durban, South-Africa: preliminary-report
(Bureau Scientific Publications, 1993-04) Ramsay, PJ; Smith, AM; Lee-Thorp, JC; Vogel, JC; Tyldsley, M; Kidwell, W
A modern African elephant tusk was discovered within a late Pleistocene aeolianite at Reunion Rocks, south of Durban. Ionium dating indicates that the tusk is older than 112 kyr BP with stratigraphic control suggesting a date at ca. 130 kyr BP. Preliminary carbon stable-isotopic analyses indicate that the elephant was a grass-grazer. Strontium isotopic analyses indicate a marine signature: this implies that the tusk suffered marine diagenesis or that the elephant accumulated a marine strontium isotope signature by living along the coastline.
1910–2010: How infrastructure grew our nation
(South African Institution of Civil Engineering, 2010-10) Wall, K
One hundred years ago this year, South Africa was established by an Act of Union. That Act gave us the shape and the texture that defined us as a nation. And it is wonderful that, despite all the exclusions and discriminations since May 1910, we have survived intact as a state and still live within those same, unchanged borders. While articles in the daily press earlier this year discussed political and governance aspects of how far we have travelled as a nation over the last 100 years, the author in this article reflects on infrastructure development and service delivery over the last century. Engineering infrastructure has indeed revolutionised the way we live, work, study, play, dispose of wastes, travel and communicate. Aircraft and the motor car, with improved roads, have revolutionised inter-city travel; the Internet (and Wiki) have revolutionised how learners prepare assignments; computers (and software) have revolutionised data sorting and analysis; aerial photography and satellite imagery have revolutionised map-making – the list could go on.
20-year LiDAR observations of stratospheric sudden warming over a mid-latitude site, Observatoire de Haute Provence (44°N, 6°E): Case study and statistical characteristics
(Copernicus Publications, 2007-11) Charyulu, DV; Sivakumar, V; Bencherif, H; Kirgis, G; Hauchecorne, A; Rao, DN
The present study delineates the characteristics of Stratospheric Sudden Warming (SSW) events observed over the Observatoire de Haute Provence (OHP: 44°N, 6°E). The study uses 20 years of Rayleigh LiDAR temperature measurements for the 1982-2001 period, which corresponds to 2629 daily temperature profiles. The characteristics of warming events are presented in terms of type of warming (major and minor), magnitude of warming, height of occurrence, day and period of occurrence with emphasis on wave propagation and isentropic transport conditions. The major and minor warming events are classified with respect to temperature increase and reversal in the zonal wind direction in the polar region using National Centre for Environmental Prediction (NCEP) reanalysis data. SSWs occur with a mean frequency of 2.15 events per winter season. The percentages of occurrence of major and minor warming events are found to be ~23 % and ~77 %, respectively. The observed major and minor SSW is associated with descent of stratopause layer by -6 to 6 km range. The height of occurrences of major SSW are distributed between 38 km and 54 km with magnitude in the 12.2-35.7 K temperature range, while the minor SSW appear in 42-54 km range, closer to the usual stratopause layer (~47 km) and with a slightly larger range of temperature magnitude (10.2-32.8 K). The observed major and minor events are examined in connection with Quasi-Biennial Oscillation (QBO) phases and presented.
2014 Election forecast - a post-election analysis
(Operations Research Society of South Africa (ORSSA), 2017-06) Ittmann, HW; Holloway, Jennifer P; Dudeni-Tlhone, Nontembeko
General elections are held every five years in South Africa. During the 12 to 24 hour period after the close of the voting booths, the expected final results are of huge interest to the electorate and politicians. In the past, the Council for Scientific and Industrial Research (CSIR) has developed an election forecasting model in order to provide the media and political analysts with forecasts of the final results during this period of peak interest. In formulating this model, which forecasts the election results as the results from voting districts (VDs) become available, some assumptions had to be made. In particular, assumptions were made about the clustering of previous voting patterns as well as the order in which VD results are released. This election forecasting model had been used successfully for a number of elections in the past and in these previous elections, with around 5% {10% of the results available, the predictions produced by the model were very close to the final outcome, particularly for the ANC, being the largest party. For the 2014 national election, however, the predictions, with close to 50% of the voting district results known (equivalent to an estimated 40% of the total votes), were still not accurate and varied by more than 1% for both the ANC and the EFF. This paper outlines a post-election analysis to determine the reasons for these discrepancies and how they relate directly to the model assumptions. The aim is to highlight how practical realities can affect the assumptions and consequently their impact on the forecasted results. Reference is made to previous election forecasts and the 2014 post-election analysis is presented.
The 2020 WMO symposium on climatological, meteorological and environmental factors in the COVID-19 pandemic: A special issue from symposium presentations
(2021-06) Sweijd, Neville; Zaitchik, BF
The COVID-19 pandemic has become one of the great historical events of the modern era, presenting a generational challenge to the world. Questions about the role of weather on SARS-CoV-2 transmission led to the gathering of scientists at an online event, the “International Virtual Symposium on Climatological, Meteorological and Environmental factors in the COVID-19 pandemic,” convened on 4–6 August 2020 under the auspices of the World Meteorological Organization. This collection of papers arise from the Symposium.
2D numerical model for heat transfer on a laser deposited high entropy alloy baseplate using Comsol Multiphysics
(2021-12) Dada, A; Popoola, P; Mathe, Ntombizodwa R; Adeosun, S; Aramide, O
In an optimization study, cracks were observed in the microstructures of laser-deposited HEAs on a steel baseplate from residual stresses, thus, the optimization of crack-free microstructures was achieved by the optimization of the laser parameters by baseplate preheating attributed to the lowering of the thermal gradients of the deposition process. This study reports the finite element analysis on the temperature distribution by the moving laser modelled to achieve process optimization with the necessary boundary conditions. Simulation has been reported as a facilitating tool in predicting the behaviour of materials during process optimization. Comsol Multiphysics 4.4, was used to create a 2D transient heat transfer time-dependent model to simulate the temperature distribution and the laser heating of the A301 steel baseplate surface and determine the effect of temperature on the optimization process of the alloys. Gaussian profiles were used as the heat source distributed per time. The results are presented in terms of thermal fields and Gaussian temperature profiles. Which show the temperature distribution that occurred in the steel baseplate during fabrication and the high cooling rate of the laser additive manufacturing technique restricted thermal stresses, improving adhesion and facilitating the optimization process.
3-D breast anthropometry of plus-sized women in South Africa
(Taylor & Francis, 2011-09) Pandarum, R; Winnie, Y; Hunter, Lawrance
Exploratory retail studies in South Africa indicate that plus-sized women experience problems and dissatisfaction with poorly fitting bras. The lack of 3-D anthropometric studies for the plus-size women's bra market initiated this research. 3-D body torso measurements were collected from a convenience sample of 176 plus-sized women in South Africa. 3-D breast measurements extracted from the TC(2) NX12-3-D body scanner 'breast module' software were compared with traditional tape measurements. Regression equations show that the two methods of measurement were highly correlated although, on average, the bra cup size determining factor 'bust minus underbust' obtained from the 3-D method is approximately 11% smaller than that of the manual method. It was concluded that the total bust volume correlated with the quadrant volume (r = 0.81), cup length, bust length and bust prominence, should be selected as the overall measure of bust size and not the traditional bust girth and the underbust measurement. Statement of Relevance: This study contributes new data and adds to the knowledge base of anthropometry and consumer ergonomics on bra fit and support, published in this, the Ergonomics Journal, by Chen et al. (2010) on bra fit and White et al. (2009) on breast support during overground running.
3-substituted anilines as scaffolds for the construction of glutamine synthetase and DXP-reductoisomerase inhibitors
(Taylor & Francis, 2009-01) Mutorwa, M; Salisu, S; Blatch, GL; Kenyon, C; Kaye, PT
Access to a series of truncated ATP analogs, as potential anti-tuberculosis agents, has been explored via alkylation and acylation of 3-aminophenol, whereas chloroacetylation, using chloroacetyl chloride, and subsequent Arbuzov phosphonation of a series of 3-substituted anilines have afforded a series of phosphonate derivatives as potential antimalarial agents.
330 mJ single-frequency Ho:YLF slab amplifier
(Optical Society of America, 2013-04) Strauss, Hencharl J; Preussler, D; Esser, MJD; Koen, W; Jacobs, Cobus; Collett, OJP; Bollig, C
We report on a double-pass Ho:YLF slab amplifier which delivered 350 ns long single-frequency pulses of up to 330 mJ at 2064 nm, with a maximum M(sup2) of 1.5 at 50 Hz. It was end pumped with a diode-pumped Tm:YLF slab laser and seeded with up to 50 mJ of single-frequency pulses.
3D edge detection seismic attributes used to map potential conduits for water and methane in deep gold mines in the Witwatersrand basin, South Africa
(Society of Exploration Geophysicists, 2012-09) Manzi, MSD; Durrheim, RJ; Hein, KAA; King, N
Inrushes of ground water and the ignition of flammable gases pose risks to workers in deep South African gold mines. Large volumes of water may be stored in solution cavities in dolomitic rocks that overlie the Black Reef (BLR) Formation, while there are several possible sources for methane, namely, coal seams, kerogen found in some gold ore bodies, or methane introduced by igneous intrusions. Potential conduits that may transport water and methane to underground workings were mapped using 3D reflection seismic data. Edge detection attributes successfully identified many faults, some with displacements as small as 10 m. Faults that displace the Ventersdorp Contact Reef (VCR) and the BLR horizons were of special interest, as known occurrences of fissure water and methane in underground workings show a good correlation with faults that were imaged on the VCR and BLR horizons. Because there are uncertainties in determining the linkage of faults with aquifers and methane sources, it is considered prudent to assume that all structures that displace the VCR and BLR horizons are potential conduits.
3D evaluation of fine-scale normalised DSMs in urban settings
(2020-09) Breytenbach, Andre
Humankind often needs to accurately model, identify and spatially quantify aboveground phenomena on the Earth’s surface for informed decision-making. Height data derived from digital elevation models (DEMs) is often used to achieve this. This study conducted a deterministic assessment of three normalised digital surface models (nDSMs) of different spatial resolutions, namely 2m, 4m and 12m, derived from VHR digital stereo aerial photography, tri-stereo Pléiades imagery and Tandem-X InSAR data, respectively. Covering a predominantly built-up area within a city landscape, the nDSMs were vertically and volumetrically compared to assess their quality and fit-for-use. In each case a consistent systematic evaluation was accomplished against a lidar derived reference surface at matching spatial resolutions (co-registered) using a semi-automated GIS routine. The relative height and volumetric errors were statistically analysed and described, including those computed individually over nine urban land cover/land use (LCLU) classes and several selected large buildings. Higher vertical accuracies were reported across single storey structures and areas with no to little or short vegetation, as apposed to substantially lower accuracies obtained over multi-levelled buildings and tall (dense) woody vegetation. Here significant underestimations of volumes exacerbated by lower spatial resolutions were also observed across each nDSM. Conversely, notable volume overestimations were found over predominantly grass-covered areas in especially the finer-scaled nDSMs. VHR elevation data is recommended to model and quantify aboveground elements spatially in 3D (e.g. buildings, earthworks and woody vegetation) in urban landscapes, but a sensitivity test beforehand remains critical to ensure more reliable outcomes for users and stakeholders alike.
5G: the convergence of wireless communications
(Springerlink, 2015-03) Chavez-Santiago, R; Szydelko, M; Kliks, A; Foukalas, F; Haddad, Y; Nolan, KE; Kelly, MY; Masonta, Moshe T; Balasingham, I
As the rollout of 4G mobile communication networks takes place, representatives of industry and academia have started to look into the technological developments toward the next generation (5G). Several research projects involving key international mobile network operators, infrastructure manufacturers, and academic institutions, have been launched recently to set the technological foundations of 5G. However, the architecture of future 5G systems, their performance, and mobile services to be provided have not been clearly defined. In this paper, we put forth the vision for 5G as the convergence of evolved versions of current cellular networks with other complementary radio access technologies. Therefore, 5G may not be a single radio access interface but rather a ”network of networks”. Evidently, the seamless integration of a variety of air interfaces, protocols, and frequency bands, requires paradigm shifts in the way networks cooperate and complement each other to deliver data rates of several Gigabits per second with end-to-end latency of a few milliseconds. We provide an overview of the key radio technologies that will play a key role in the realization of this vision for the next generation of mobile communication networks. We also introduce some of the research challenges that need to be addressed.
A 6-bit, 500-MS/s current-steering DAC in SiGe BiCMOS technology and considerations for SFDR performance
(Elsevier, 2015-04) Reddy, Reeshen; Sinha, S
This paper presents a six-bit current-steering digital-to-analogue converter (DAC), which optimises the spurious free dynamic range (SFDR) performance of high-speed binary weighted architectures by lowering current switch distortion and reducing the clock feedthrough effect. A novel current source cell is implemented that comprises heterojunction bipolar transistor current switches, negative-channel metal-oxide semiconductor (NMOS) cascode and NMOS current source to overcome distortion by specifically enhancing the SFDR for high-speed DACs. The DAC is implemented using silicon¿germanium (SiGe) BiCMOS 130 nm technology and achieves a better than 21.96 dBc SFDR across the Nyquist band for a sampling rate of 500 MS/s with a core size of 0.1 mm2 and dissipates just 4 mW compared to other BiCMOS DACs that achieve similar SFDR performance with higher output voltages, resulting in a much larger power dissipation.
99mTc-MDP as an imaging tool to evaluate the in vivo biodistribution of solid lipid nanoparticles
(Elsevier, 2018-11) Mandiwana, Vusani; Kalombo, Lonji; Grobler, A; Zeevaart, JR
The aim of this study was to establish the in vivo uptake and tissue distribution of (sup)99mTc-MDP-encapsulated Solid Lipid Nanoparticles (SLNs) post administration. Radioactive (sup)99mTc-MDP encapsulated into SLNs was administered to rats to trace their biodistribution through imaging and ex vivo studies. As expected IV injected (sup)99mTc-MDP exhibited predominant visual bone uptake and a high localisation of particles in the kidneys (3.87%ID/g) followed by bone (2.66%ID/g). IV administered 99mTc-MDP encapsulated by SLN showed similar uptake than (sup)99mTc-MDP. Orally administrated (sup)99mTc-MDP showed no uptake in any organs except the GI-tract while orally administered (sup)99mTc-MDP-SLN showed distinct transfer of (sup)99mTc-MDP from the GI tract with measurable levels in the kidneys and bone.
A novel biogenic silicon-based anode material for lithium-ion batteries: A review
(2024-08) Seroka, Ntalane S; Luo, Hongze; Khotseng, L
Silicon possesses a 10-fold specific capacity compared to commonly used carbon-based anodes. The volume instability, among other impediments for practical use of silicon anodes, leads to the rapid decay of the capacity because of poor cyclability. Urgent mechanisms are required to improve lithium-ion storage during cycling and prevent volume variation in the silicon structure. Biogenic silicon derived from sugarcane bagasse can be used in nanoelectronic devices. Over the years, electrode materials have been an essential part of battery components. Moreover, electrode materials are favourable for highly portable nanoelectronics, hybrid as well as pure electric vehicles, etc. Furthermore, the biogenic silicon chosen for this study was based on natural abundance, environmental friendliness, and affordability. However, most silicon anodes are hindered by unstable volume expansion, variation in solid electrolyte interface films, and poor electrical conductivity. The focus is on silicon anodes, recent developments, and the potential of biogenic silicon from sugarcane waste, exploring its physicochemical properties to meet the requirements of a suitable anode material.
A review of machine learning techniques for optical wireless communication in intelligent transport systems
(2024-11) Sefako, T; Yang, F; Song, J; Balmahoon, Reevana; Cheng, L
Intelligent Transport Systems (ITS) are crucial for safety, efficiency, and reduced congestion in transportation. They require efficient, secure, high-speed communication. Radio Frequency (RF) technologies like Fifth Generation (5G), Beyond 5G (B5G), and Sixth Generation (6G) are promising, but spectrum scarcity mandates coexistence with Optical Wireless Communication (OWC) networks, which offer high data rates and security, forming a strong foundation for hybrid RF/OWC applications in ITS. In this paper, we delve into the application of Machine Learning (ML) to enhance data communications within OWC systems in ITS. We commence by conducting an in-depth examination of the data communication prerequisites and the associated challenges within the ITS domain. Subsequently, we elucidate the compelling rationale behind the convergence of heterogeneous RF technologies with OWC for data communications in ITS scenarios. Our investigation then pivots towards elucidating the indispensable role played by ML in optimizing data communications via OWC within ITS. To provide a comprehensive perspective, we systematically evaluate and compare a spectrum of ML methodologies employed in OWC ITS data communications. As a culmination of our study, we proffer a set of valuable recommendations and illuminate promising avenues for future research endeavors that warrant further exploration within this critical intersection of ML, OWC, and ITS data communications.
A review of metal pollution in a transformed, urban South African Estuary
(2024-12) Ndhlovu, A; Adams, JB; Nel, M; Newman, Brent K; Rishworth, GM; Human, LRD
Metal pollutants enter coastal water bodies from agricultural, industrial, and domestic wastewater activities amongst other sources. These pollutants are often transported through the food chain to higher trophic levels including organisms such as fish. Ultimately, they may pass to humans that consume contaminated seafoods. As such, it is imperative to understand how metals in estuarine systems are transported across trophic levels. Baseline data on metal concentrations are of crucial importance to evaluate changes over time and amongst areas to inform management and conservation strategies. In this assessment, we compile and discuss a database of metal concentrations recorded in various environmental media in the Swartkops River estuary, as a baseline against which future comparisons can be made. The Swartkops Estuary is subjected to considerable anthropogenic pressure that has led to a deterioration in water quality. We also provide a conceptual model to understand the flow of metals in the estuary. We furthermore identify lines of future research that will address gaps and uncertainties in the existing data and provide recommendations for remediation. Studies on metal concentrations in the water column of the estuary are limited. Studies on metals in sediment suggest that the estuary is not significantly metal contaminated. While studies revealed that plants do accumulate metals and fauna studies show differences in metal concentrations in the tissue of invertebrates and fish. It is difficult to conclude if these fauna are accumulating metals in their tissue compared to historically and if concentrations reflect uptake as a consequence of exposure to metal contaminated water, sediment and food.
A review on thermally induced phase separation technology in the fabrication of microporous polymer membrane devices for sustained-repellent delivery: Crystallization and morphological studies
(2024-08) Tewo, RK; Mapossa, AB; Ray, Suprakas S; Mhike, W; Sundararaj, U
This article reports recent advances in thermally induced phase separation technology in fabricating microporous scaffold polymeric membranes as devices suitable for the controlled release of insect repellent. The key aspects, such as the crystallization behavior and morphological study of the polymeric membrane-based repellent, were reported and discussed. Studies demonstrated that trapping of such repellents into microporous polymeric materials can be achieved by spinodal decomposition of the polymer/liquid repellent system. Usually, solubility is enhanced at elevated temperatures. Rapid cooling of such solution below the UCST leads to the formation of cocontinuous phase structures by decomposition. The polymer then forms an open-cell structure with the repellent trapped inside. Approaches to forming such an open-cell polymer structure containing mosquito repellent were successfully performed and confirmed with the SEM and POM techniques. It showed the structure of a polymer and liquid repellent prepared by spinodal decomposition, providing proof that thermally induced spinodal decomposition is a route to trap liquid mosquito repellent into a microporous polymer matrix. Additionally, the effects of polymer type, repellent nature, cooling conditions, and fillers on the morphology and performance of TIPS membranes are also discussed. Finally, challenges in developing microporous polymeric membrane-based repellent using TIPS technology are addressed.
A two-tailed pricing scheme for optimal EV charging scheduling using multiobjective reinforcement learning
(2024-03) Adetunji, KE; Hofsajer, IW; Abu-Mahfouz, Adnan MI; Cheng, L
Electric vehicles (EVs) are crucial to the reduction of carbon emissions. However, their charging poses a threat to power system networks. Hence, EV charging control strategies are developed to curb this challenge, using charging prices to incentivize EV drivers to choose EV charging stations (EVCS) favourable to the grid's stability. The challenge of this strategy is the likelihood of EV drivers accepting EVCS suggestions. To increase the probability of accepting EVCS suggestions, we introduce a two-tailed incentive pricing (TTIP) scheme in an EV charging coordination model, where incentives are offered as charging prices and parking time. We formalized the EV charging problem as a multiobjective Markov decision process and proposed a deep deterministic policy gradient (DDPG) to solve it. To tackle the challenge of continuous action space that leads to the dimensionality curse, the proposed DDPG models the action space using a metaheuristic-based technique. The proposed scheme implements a multiple reward system to generate Pareto optimal solutions and a decision-making technique to choose the compromise reward. Using real-world electricity prices and the IEEE 33-bus distribution network, numerical simulations show that our proposed TTIP scheme yields an average of 18% improvement in grid stability than the sustainable policy following, random, and price-greedy algorithms. It also improves the EV charging profit margins by an average of 28%.
a-MnO2 nanorod/onion-like carbon composite cathode material for aqueous zinc-ion battery
(Elsevier, 2019-05) Palaniyandy, Nithyadharseni; Kebede, Mesfin A; Raju, Kumar; Ozoemena, KI; Le Roux, Lukas; Mathe, Mahlanyane K; Jayaprakasam, R
Onion-like carbon (OLC) integrated a-MnO2 nanorods (a-MnO2/OLC) composite has been studied as a viable cathode material for potential development of high-performance zinc-ion batteries (ZIBs). XRD results revealed the tetragonal phase of the a-MnO2 materials, and the FE-SEM and HR-TEM images show nano-sized rod-shaped morphology with an average diameter of 30 nm. The BET surface area of the a-MnO2/OLC composite was almost 6 times (247.22 m2/g) higher than that of the pristine (42.48 m2/g) material and the thermogravimetric investigation was exposed 50% of MnO2 and 50% OLC is presented in the composite. The electrochemical performance of the cells was evaluated by galvanostatic cycling (GC), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using 1 M ZnSO4 plus 0.1 M MnSO4 additive as electrolyte and Zn foil as the anode. Cycling results indicate that a-MnO2/OLC composite exhibits a stable and high reversible capacity of 168 mAh g-1 (93% capacity retention) compared to the a-MnO2 material with a capacity of 104 mAh g-1 (81% capacity retention) after 100 cycles.

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