Research Articles

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    On the Triggering Mechanisms of Upward Lightning
    (Nature Research, 2019-12) Schumann, C.; Saba, M; Warner, T.; Ferro, M.; Helsdon Jr, J.H.; Thomas, R.; Orville, R.E.
    Upward lightning studies took place in Rapid City, South Dakota, USA and S. Paulo, Brazil during the summer thunderstorm seasons from 2011 to 2016. One of the main objectives of these campaigns was to evaluate and characterize the triggering of upward positive leaders from tall objects due to preceding nearby flash activity. 110 upward flashes were observed with a combination of high- and standard-speed video and digital still cameras, electric field meters, fast electric-field antenna systems, and for two seasons, a Lightning Mapping Array. These data were analyzed, along with correlated lightning location system data, to determine the triggering flash type responsible for the initiation of upward leaders from towers. In this paper, we describe the various processes during flash activity that can trigger upward leaders from tall objects in the USA and in Brazil. We conclude that the most effective triggering component is the propagation of the in-cloud negative leader during the continuing current that follows a positive return stroke.
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    Review of channel estimation for candidate waveforms of next generation networks.
    (MDPI, 2019-09) Ijiga, O.E.; Ogundile, O.O.; Familua, A.D.; Versfeld, D.J.J.
    The advancement in wireless communication applications encourages the use of effective and efficient channel estimation (CE) techniques because of the varying behaviour of the Rayleigh fading channel. In most cases, the emphasis of most proposed CE schemes is to improve the CE performance and complexity for ensuring quality signal reception and improved system throughput. Candidate waveforms whose designs are based on filter bank multi-carrier (FBMC) modulation techniques such as filter bank orthogonal frequency division multiplexing based on offset quadrature amplitude modulation (OFDM-OQAM), universal filtered multicarrier (UFMC) and generalised frequency division multiplexing based on offset quadrature amplitude modulation (GFDM-OQAM) are no exception to the use of these proposed CE techniques in the literature. These schemes are considered as potential waveform candidates for the physical/media access control layer of the emerging fifth generation (5G) networks. Therefore, pinpoint CE techniques represent an important requirement for these waveforms to attain their full potentials. In this regard, this paper reviews the concept of CE as applicable to these waveforms as well as other waveform candidates under consideration in the emerging 5G networks. Since the design of the majority of the waveform candidates is filter based, a review of the general filter design considerations is presented in this paper. Secondly, we review general CE techniques for candidate waveforms of next generation networks and classify some of the studied CE techniques. In particular, we classify the CE schemes used in filter bank OFDM-OQAM and GFDM-OQAM based transceivers and present a performance comparison of some of these CE schemes. Besides, the paper reviews the performances of two linear CE schemes and three adaptive based CE schemes for two FBMC based waveform candidates assuming near perfect reconstruction (NPR) and non-perfect reconstruction (Non-PR) filter designs over slow and fast frequency selective Rayleigh fading channels. The results obtained are documented through computer simulations, where the performances of the studied CE schemes in terms of the normalised mean square error (NMSE) are analysed. Lastly, we summarise the findings of this work and suggest possible research directions in order to improve the potentials of the studied candidate waveforms over Rayleigh fading channels.
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    Analysis of Bounded Distance Decoding for Reed Solomon Codes.
    (South African Institute of Electrical Engineers., 2018-09) Babalola, O.P.; Versfeld, D.J.J.
    Bounded distance decoding of Reed-Solomon codes involves finding a unique codeword if there is at least one codeword within the given distance. A corrupted message having errors that is less than or equal to half the minimum distance corresponds to a unique codeword and therefore, the probability of decoding error is one for a minimum distance decoder. However, increasing the decoding radius to be slightly higher than half of the minimum distance may result in multiple codewords within the Hamming sphere. In this study, we computed the probability of having unique codewords for (7, k) RS codes when the decoding radius is increased from the error correcting capability t to t+1. Simulation results show a significant effect of the code rates on the probability of having unique codewords. It also shows that the probability of having unique codeword for low rate codes is close to one.
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    Flexor tendon injuries of the hand: Chris Hani Baragwanath academic hospital patient demographics
    (2017) Bismilla, Shaaheen
    The hand is an intricate and important body appendage which plays a vital role in our activities of daily living. Flexor tendon injuries to the hand make up a large amount of patients seen at hospitals all over the world. Hand injuries are quite common and contribute to approximately 28% of injuries to the human body. A prospective study was conducted, with patients who had sustained flexor tendon hand injuries. The patients who presented to Chris Hani Baragwanath Academic Hospital from 02 March 2015 to 29 July 2015 were included in the study. The aim of this study was to document and identify the causes (mechanism of injury) and demographic details of patients presenting with flexor tendon injuries at Chris Hani Baragwanath Academic Hospital hands unit. There were 96 patients in the study, with 80 being right hand dominant and 16 being left hand dominant. Zones II and zones III were the most common flexor zones affected (27 each). There was also a significant amount of zone V injuries (23). Zone IV was the least common zone affected (5). The results also showed that the most common injury to flexor tendons of the hands occurred in young adult males, the majority of whom were unemployed. This disproves our hypothesis, as it was hypothesised that most injuries would occur in the work place. This study was undertaken in an attempt to reduce the incidence and frequency of hand injuries in our community, by assessing the common causes and patient particulars of flexor tendon injuries. This information can now be used to teach awareness which now can be used in the work place.
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    Thermal excitation of gadolinium-based contrast agents using spin resonance.
    (Public Library of Science, 2016-06) Dinger, S.C.; Fridjhon, P.; Rubin, D.M.
    Theoretical and experimental investigations into the thermal excitation of liquid paramagnetic contrast agents using the spin resonance relaxation mechanism are presented. The electronic spin-lattice relaxation time ole of gadolinium-based contrast agents, which is estimated at 0.1 ns, is ten orders of magnitude faster than the relaxation time of protons in water. The shorter relaxation time is found to significantly increase the rate of thermal energy deposition. To the authors knowledge this is the first study of gadolinium based contrast agents in a liquid state used as thermal agents. Analysis shows that when ô1e and other experimental parameters are optimally selected, a maximum theoretical heating rate of 29.4 °C.s.1 could be achieved which would suffice for clinical thermal ablation of neoplasms. The experimental results show a statistically significant thermal response for two out of the four contrast agents tested. The results are compared to the simulated estimates via analysis of a detailed model of the system. While these experimentally determined temperature rises are small and thus of no clinical utility, their presence supports the theoretical analysis and strongly suggests that the chemical structure of the selected compounds plays an important role in this mechanism of heat deposition. There exists an opportunity for the development of alternative gadolinium-based compounds with an order of magnitude longer τ1e in a diluted form to be used as an efficient hyperthermia agent for clinical use.