College of Agriculture, Engineering and Science

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1-D particle-in-cell simulations of plasmas with kappa velocity distributions.
(2013) Abdul, Reginald Francis.; Mace, Richard Lester.
The main aim of this project was the development of a particle-in-cell (PIC) plasma simulation code. While particle-in-cell simulations are not new, they have largely focused on using an initial Maxwellian particle loading. The new feature the code implemented for this project is the use of kappa distributions as an initial loading. This specialises the code for the investigation of waves and instabilities in space plasmas having kappa-type velocity distributions. The kappa distribution has been found to provide a better fit to space plasma particle velocity distributions than the Maxwellian in a wide variety of situations. In particular, it possesses a power law tail which is a frequent feature of charged particle velocity distributions in space plasmas. Traditionally, the treatment of such out-of-equilibrium velocity distributions has been via a summation over several Maxwellians with different temperatures and average number densities. Instead, the approach used in this work is guided by recent advances in non-extensive statistical mechanics, which provide a rigorous underpinning for the existence of kappa distributions. As case studies, the simulation code was used to investigate the ion-acoustic instability as well as electrostatic Bernstein waves in both Maxwellian and kappa plasmas. Results were compared to kinetic theory and the differences in the Maxwellian and kappa plasma behaviours are discussed. To analyse the instabilities various diagnostics were used, including Fourier analysis of the wave fields to determine the dispersion relation, and particle binning to determine the particle velocity distributions. Both the Maxwellian and kappa particle loading algorithms were found to agree well with the theoretical velocity distributions and the dispersion relations were found to agree with kinetic theory for both kappa and Maxwellian plasmas. The code was developed in the C programming language using an incremental approach that enabled careful testing after each new level of sophistication was added. A version of the code was parallelised using Message Passing Interface (MPI) to take advantage of the distributed supercomputing environment provided by the CHPC.
2,4,6-Trichloro-1,3,5-triazine as a triorthogonal chemoselective linker.
(2019) Rotimi, Sheyi Ebenezer.; Albericio, Fernando.; Garcia de la Torre, Beatriz.
Abstract available in PDF.
2-generations of the sporadic simple groups.
(1997) Ganief, Moegamad Shahiem.; Moori, Jamshid.
A group G is said to be 2-generated if G = (x, y), for some non-trivial elements x, y E G. In this thesis we investigate three special types of 2-generations of the sporadic simple groups. A group G is a (l, rn, n )-generated group if G is a quotient group of the triangle group T(l, rn, n) = (x, y, zlx1 = ym = zn = xyz = la). Given divisors l, rn, n of the order of a sporadic simple group G, we ask the question: Is G a (l, rn, n)-generated group? Since we are dealing with simple groups, we may assume that III +l/rn + l/n < 1. Until recently interest in this type of generation had been limited to the role it played in genus actions of finite groups. The problem of determining the genus of a finite simple group is tantamount to maximizing the expression III +l/rn +Iln for which the group is (l,rn,n)-generated. Secondly, we investigate the nX-complementary generations of the finite simple groups. A finite group G is said to be nX-complementary generated if, given an arbitrary non-trivial element x E G, there exists an element y E nX such that G = (x, y). Our interest in this type of generation is motivated by a conjecture (Brenner-Guralnick-Wiegold [18]) that every finite simple group can be generated by an arbitrary non-trivial element together with another suitable element. It was recently proved by Woldar [181] that every sporadic simple group G is pAcomplementary generated, where p is the largest prime divisor of IGI. In an attempt to further the theory of X-complementary generations of the finite simple groups, we pose the following problem. Which conjugacy classes nX of the sporadic simple groups are nX-complementary generated conjugacy classes. In this thesis we provide a complete solution to this problem for the sporadic simple groups HS, McL, C03, Co2 , Jt , J2 , J3 , J4 and Fi 22 · We partially answer the question on (l, rn, n)-generation for the said sporadic groups. A finite non-abelian group G is said to have spread r iffor every set {Xl, X2, ' , "xr } of r non-trivial distinct elements, thpre is an element y E G such that G = (Xi, y), for all i. Our interest in this type of 2-generation comes from a problem by BrennerWiegold [19] to find all finite non-abelian groups with spread 1, but not spread 2. Every sporadic simple group has spread 1 (Woldar [181]) and we show that every sporadic simple group has spread 2.
2D3V electromagnetic particle-in-cell simulations of plasmas having kappa velocity distributions.
(2018) Abdul, Reginald Francis.; Mace, Richard Lester.
It is now well established that the kappa distribution is a more appropriate kinetic model for space plasmas than the Maxwellian distribution. In particular it possesses a power-law tail, frequently observed in space plasmas. The research presented in this thesis outlines the development of a two-dimensional electromagnetic particle-in-cell (PIC) simulation code, designed to run on general purpose graphics processing units (GPGPUs), and presents results from simulations of waves and instabilities obtained using it. While PIC simulations are not new, the majority have focussed on the old paradigm of initial particle loadings with a Maxwellian velocity distribution, or one of its variants. Distinguishing this research from previous PIC simulations is the use of the kappa distribution for the initial particle loading. To achieve this, a fast and e cient algorithm for generating multi-dimensional kappa distributed deviates was developed. The code is rst applied to the study of waves in an electron-ion plasma, in a stable equilibrium con guration with a constant background magnetic eld. Both species are modelled by isotropic (a) kappa and (b) Maxwellian velocity distributions. In each case, spectral analysis of the eld uctuations is performed, allowing mode identi cation. For parallel propagation, the maximum uctuation intensities follow the dispersion relations for the L and R modes, respectively, while those at perpendicular propagation follow the dispersion relations for the X, O and electromagnetic electron and ion Bernstein waves. The variation of wave intensity for the oblique angles is also investigated. For the kappa case, this yields new and important information presently unavailable by analysis alone. The e ects of the kappa distribution on wave intensity, as well as its e ect on the dispersion relations of the modes is discussed in detail. The second application is to the simulation of the electron temperature anisotropy driven whistler instability in an electron-ion plasma, where the electron species is modelled by the (a) bi-kappa and (b) bi-Maxwellian velocity distribution. For parallel propagation, the maximum eld uctuation intensities agree well with the dispersion relation for the whistler instability in a kappa plasma. While most of the wave intensity is in the parallel whistler mode, the oblique modes also contribute signi cantly to the overall uctuation spectrum, but their intensities vary with angle of propagation relative to the magnetic eld. The dependence of the growth rate on the index e of the electron kappa distribution is discussed in detail and compared with the well known Maxwellian results. Saturation of the instability via pitch angle scattering, reducing the electron temperature anisotropy, is observed.
3D modelling segmentation, quantification and visualisation of cardiovascular magnetic resonance images.
(2014) Brijmohan, Yarish.; Mneney, Stanley Henry.; Rae, William Ian Duncombe.
Progress in technology in the field of magnetic resonance imaging (MRI) has provided medical experts with a tool to visualise the heart during the cardiac cycle. The heart contains four chambers namely the left and right ventricles and the left and right atria. Each chamber plays an important role in the circulation of blood throughout the body. Imbalances in the circulatory system can lead to several cardiovascular diseases. In routine clinical medical practice MRIs are produced in large quantities on a daily basis to assist in clinical diagnosis. In practice, the interpretation of these images is generally performed visually by medical experts due to the minimal number of automatic tools and software for extracting quantitative measures. Segmentation refers to the process of detecting regions within an image and associating these regions with known objects. For cardiac MRI, segmentation of the heart distinguishes between different ventricles and atriums. If the segmentation of the left ventricle and right ventricle exists, doctors will be interested in quantifying the thickness of the ventricle walls, the movement of each ventricle, blood volumes, blood flow-rates, etc. Several cardiac MRI segmentation algorithms have been developed over the past 20 years. However, much attention of these segmentation methods was afforded to the left ventricle and its functionality due to its approximately cylindrical shape. Analysis of the right ventricle also plays an important role in heart disease assessment and coupled with left ventricle analysis, will produce a more intuitive and robust diagnostic tool. Unfortunately, the crescent like shape of the right ventricle makes its mathematical modelling difficult. Another issue associated with segmenting cardiac MRI is that the quality of images can be severely degraded by artefactual signals and image noise emanating from equipment errors, patient errors and image processing errors. The presence of these artefacts attribute to additional difficulty for segmentation algorithms and many of the currently available segmentation methods cannot account for all of the abovementioned categories. A further downfall of current segmentation algorithms is that there is no readily available standard methodology to compare the accuracy of these approaches, as each author has provided results on different cardiac MRI datasets and segmentation done by human readers (expert segmentation) is subjective. This thesis addresses the issues of accuracy comparison by providing a framework of mathematical, statistical and clinical accuracy measures. The use of publically available cardiac MRI datasets in which expert segmentation is performed is analysed. The framework allows the author of a new segmentation algorithm to choose a subset of the measures to test their algorithm. A clinical measure is proposed in this thesis which does not require expert segmentation on the cardiac MRI dataset, where the stroke volumes of the left and right ventricle are compared to each other. This thesis proposes a new three dimensional cardiac MRI segmentation algorithm that is able to segment both the left and right ventricles. This approach provides a robust technique that improves on the use of the difference of Gaussians (DoG) image filter. The main focus was to find and extract the region of interest that contains the ventricles and remove all the unwanted information so that the DoG parameters are created from intensity profiles of this localised region. Two methods are proposed to achieve this localisation, depending on the type of cardiac MRI dataset that is present. The first method is used if the cardiac MRI dataset contains images from a single MRI view. Local and global motion maps are created per MRI slice using pixel intensities from images at all time points though the cardiac cycle. The segmentation results show a slight drop in evaluation metrics on the state of the art algorithms for the left ventricle and a significant improvement over the state of the art algorithms for the right ventricle using the publically available cardiac MRI datasets. The algorithm is also robust enough to withstand the influence of image noise and simulated patient movement. The second approach to find the region of interest is used if there are MRIs from three views present in the cardiac MRI dataset. The novel method projects ventricle segmentation in the three dimensional space from two cardiac MRI views to provide an automatic ventricle localisation in the third MRI view. This method utilises an iterative approach with convergence criteria to provide final ventricle segmentation in all three MRI views. The results show increase in segmentation accuracy per iteration and a small stroke volumetric error measurement on final segmentation. Finally, proposed in this thesis is a triangular surface mesh reconstruction algorithm to create the visualisation of both the left and right ventricles. The segmentation of the ventricles are extracted from the MRI per slice and combined to form a three dimensional point set. The use of segmentation from the three orthogonal MRI views further improves the visualisation. From the three dimensional point set, the surface mesh is constructed using Delaunay triangulation, convex hulls and alpha hulls. The volume of the ventricles are calculated by performing a high resolution voxelisation of the ventricle mesh and thereafter several quantification measures are computed. The volume methodology is compared to the commonly used Simpsons method and the results illustrate that the proposed method is superior.
A 40,000-year record of vegetation and fire history from the Tate Vondo region, Northeastern Southpansberg, South Africa.
(2014) Baboolal, Deeva Lata.; Finch, Jemma M.
Records from the Quaternary period are used to confirm possible inferred climatic changes, reveal the responses of species to these changes, and serve as an archive against which modern environmental dynamics can be assessed. Fueled by a need to understand current climatic changes, the call for palaeoclimatic research in the southern African subregion has become more compelling. In southern Africa, such research has been largely restricted to springs and swamps as the subregion lacks natural lakes, with some exception of a few coastal lakes such as Lake Sibaya and Lake Eteza. Due to the arid and semi-arid landscapes which prevail in southern Africa, there is a paucity of suitable sedimentary deposits in the region. The highly organic peat deposit of Mutale Wetland, situated in the Tate Vondo region of the northeastern Soutpansberg presents an ideal opportunity for conducting palaeoenvironmental research. The Mutale Wetland contains relatively old sediments dating back to >30,000 cal years BP, placing this record within the late Quaternary period. Palaeoenvironmental techniques including radiocarbon, pollen and charcoal analyses were applied to produce a palaeoenvironmental reconstruction for Tate Vondo. A 302 cm sedimentary core was extracted from the Mutale Wetland. Detailed analyses show that prior to ca. 34,000 cal yr BP, conditions were fairly warm and dry. This is inferred from a dominance of open grassland vegetation. An expansion of Podocarpus forests together with an increase in fynbos elements suggest a shift to cool, subhumid conditions during the LGM. Cooler conditions persisted until ca. 12,000 cal yr BP. Thereafter, a climatic amelioration was experienced. The appearance of low charcoal concentrations throughout the late Pleistocene suggests that fire was infrequent. Between ca. 4000 – 1500 cal yr BP, conditions became warmer and drier, inferred from the development of arid savanna vegetation. The sharp increase in charcoal after ca. 4000 cal yr BP, broadly coinciding with the arrival of the first agriculturalists in the area, has implications for the history of human occupation in the Soutpansberg rather than shifts in climate. The succession from savanna to fynbos vegetation together with expanded forests implies a return to cool and moist conditions from ca. 1500 – 400 cal yr BP. Arid savanna persists from ca. 400 to the present, implying warmer and drier conditions towards the present day. Furthermore, from ca. 400 cal yr BP, the pollen and charcoal record indicate that the majority of recent changes in vegetation have been driven by anthropogenic activity. This record has contributed to an improved understanding of late Quaternary changes in climate, vegetation history and human impact in the northeastern Soutpansberg.
57 Fe Mössbauer studies of 57 Mn* implanted III-V semiconductors InP and InAs.
(2011) Dlamini, Wendy Bonakele.; Naidoo, D.; Bharuth-Ram, Krishanlal.
III-V compound semiconductors such as Gallium Arsenide, Indium Phosphide as well as Indium Arsenide have recently demonstrated the capability of applications in high speed semiconductor devices compared to those made from Silicon. As a result, III-V compound semiconductors have drawn attention of material researchers, in particular in understanding the effects that may occur during manufacturing of these devices. Optical and electrical properties of a device may alter when a foreign atom is introduced during the manufacturing of the device. However, the foreign atom may also lead to the formation of lattice disorder (defects). A convenient way of introducing impurity atoms into a substrate and tailoring their functionality for particular applications is by ion implantation. Mössbauer spectroscopy is a useful technique usually utilized for understanding site location of the impurity atoms in a lattice and the formation of defect complexes. The focus of this dissertation is the study of lattice location of ion implanted ⁵⁷Mn/⁵⁷Fe ions in the III-V semiconductors InP, n-type InAs and p type InAs, and the annealing of implantation induced lattice damage in these samples. ⁵⁷Fe Mössbauer spectroscopy studies have been conducted on III-V semiconductors InP, n-type InAs and p-type InAs with the 57Fe Mössbauer state being populated following the implantation of radioactive ⁵⁷Mn⁺ ions which has the advantage that extremely low fluence implantations are sufficient to give data with good statistics. The ⁵⁷Mn⁺ ions were accelerated to 60 keV at the ISOLDE/CERN facility and implanted with fluences of up to 2x10¹² ions/cm² into single crystal samples which were held at 300 –700 K in an implantation chamber. βdecay of the Mn⁺ imparts an average recoil energy of 40 keV to the daughter ⁵⁷*Fe which are then re-distributed onto interstitial and/or substitutional sites, or trapped in defect complexes and damage sites. The Mössbauer spectra were collected with a light-weight parallel plate avalanche counter, with ⁵⁷Fe enriched stainless steel electrodes, mounted on a conventional drive unit outside the implantation chamber. The spectra were analyzed with the Mössbauer fitting code VINDA which allowed for simultaneous fits of the set of spectra for each sample collected at different temperatures. Acceptable fits to the Mössbauer spectra of the InP, n-type InAs and p-type InAs samples required three components: an asymmetric doublet attributed to Fe atoms in implantation induced damaged environments, a single line assigned to Fe on substitutional In sites, and a weak symmetric doublet assigned to impurity-vacancy complexes. In InP there is already an appreciable substitutional Fe (Feѕ) fraction on implantation at room temperature; while in the InAs samples FeS only becomes significant above 400 K. In all samples, the asymmetric doublet dominates the spectra below 400 K. Implantation damage, however, anneals quite rapidly and at high temperatures (above 400 K), the single line due to Feѕ dominates the spectra while the Fe-defect complex dissociates at 500 K. The implantation induced damage is observed to anneal fast in the arsenide samples compared to the phosphide sample. The slow annealing of the damage in InP was supported by the higher Debye temperature (290 K) extracted from the temperature dependence of the site population for the damage site in InP compared with InAs (194 K and 200 K for n-type and p-type, respectively). Variations in the isomer shift and quadrupole splitting for the damage site in InP at high temperatures (above 400 K) suggest structural changes in the neighborhood of the ⁵⁷Fe probe. Furthermore, the isomer shifts of the spectral components were consistent with near trivalent state and fully trivalent state i.e., Fe³⁺ with d⁵ electron configuration for Fe ions in the damage site and at the substitutional (In) site, respectively. The impurity Fe atoms associated with vacancies are identified to be in the Fe²⁺ state with a d⁶ electron configuration.
A critical analysis of current approaches to SMME development and support within the eThekwini Municipal Area.
(2009) Chetty, Anneline.; Bob, Urmilla.
Small, Medium and Micro Enterprises (SMMEs) are considered to be the engines of growth of any economy. In the light of recent economic events and the recession that is surging rapidly across the globe, more and more attention is being focused on SMME development and support. Whilst there are a number of organisations (both public and private) which provide support to SMMEs within the eThekwini Municipality Area (EMA), the overall impacts of these initiatives on SMME growth and development is minimal and there is a dearth of studies that critically examine business support services for SMMEs which the public and private sectors provided. One of the major reasons for this minimal impact is the lack of communication and coordination between various service providers which often results in fragmentation and duplication of services. This study analyses the support measures offered to SMMEs not only from the perspective of the SMMEs themselves but also examines the perspectives of service providers from both the public and private sectors. This study is also placed within a multi-disciplinary conceptual framework which includes the political economy approach, neoliberalism, the public-private-sector debate and empowerment theories with specific reference to the South African context. This study is unique in that it analyses SMME development and support within the EMA from various perspectives within a single study. The objectives of this study were to investigate the awareness and experiences of SMMEs with regards to their support and development and also to critically examine the attitudes and perceptions of service providers (both public and private) towards SMME development and support. In addition, this study sought to assess the capacity of both the private and public sectors to provide effective support and development to SMMEs. An additional objective of this study was to determine the value placed on support measures by determining SMMEs’ willingness to pay for services provided, but more importantly to determine the attitudes of the public and private sectors towards the payment for services offered. Both qualitative and quantitative methods were adopted. In terms of the latter, quantitative surveys were conducted with 250 SMMEs who attended various fairs and conferences held across the EMA. Semi-structured interviews (qualitative approach) were conducted with representatives from the private and public sectors that provide support or services to the SMMEs in the EMA. In this regard, 53 representatives from the public sector and 50 from the private sector were interviewed. The analysis was undertaken thematically and, where relevant, findings pertaining to the different stakeholders interviewed were compared and discussed. Some of the key findings indicate that SMME respondents were more aware of local government and the services they provide than any other tier of government. Furthermore, SMME respondents within the study did not fully grasp the concept of Business Development Services (BDS) and the associated benefits for their business. SMMEs rely heavily on government to provide services free of charge. The main finding is that private sector service providers are better qualified, positioned and trained to provide BDS than the public sector whose main roles should be that of regulator, facilitator and promoter. Whilst government has been a strong proponent of SMME development and support since 1994, this study presents a strong case for the increased role of the private sector. In addition, this study also motivates that local government through their Municipalities can play a significant role in SMME development and support in partnership with the private sector.
A critical assessment of the Namibian protected area management effectiveness tracking tool.
(2010) Mulonga, Samison Nzehengwa.; Dent, Mark Clifford.
Protected Areas (PAs) are one of the most effective mechanisms for biodiversity conservation. They are found in almost every country and have been adopted by the international community through various conventions and agreements. However setting aside areas as protected areas does not automatically qualify them to be effectively managed. Research around the world has shown that some PAs are not well managed due to different reasons in different parts of the world. Therefore it is important to determine management effectiveness of PAs to ascertain whether they are managed according to the objectives for which they were created. The Management Effectiveness Tracking Tool (METT) is one of the tools developed to evaluate management effectiveness of PAs around the world. The tool has been implemented in a number of countries including Namibia where it has been modified into the Namibia Management Effectiveness Tracking Tool (NAMETT) through the United Nations Development Programme and Global Environment Facility’s Strengthening the Protected Areas Network (SPAN) project. However the effectiveness of this tool in providing necessary information about PA management effectiveness was not ascertained before implementation. The Namibian PA management authorities on the other hand need a tool for determining management effectiveness of PAs for management decision-making and as part of their obligations through international conventions which they signed. The aim of this research study was to analyse and assess the NAMETT as a management effectiveness tool for PAs in Namibia, by looking at the strength and weakness of the tool. This will inform whether its worthwhile adopting the tool as a standard management effectiveness evaluation tool for Namibia’s PAs. To accomplish this NAMETT assessment data obtained from the two NAMETT assessments undertaken by SPAN project was analysed. Furthermore different qualitative techniques were used including a semi-structured questionnaire as part of a case study approach. A comprehensive literature review was undertaken in the process and links to students undertaking similar research projects and professionals in the PA management industry were established and complemented the research data. Data obtained from NAMETT assessment undertaken by SPAN project appear to provide a picture of the different levels of management effectiveness in Namibia’s PAs suggesting the tool could be adopted for management effectiveness of Namibia’s PAs. Research data and information gathered shows that at the moment there is no management effectiveness tracking tool in Namibia. PA management authorities lack the necessary management effectiveness information for decision making. Currently only reports, the Incident Book Monitoring System (IBMS) and park inspections are the only sources of information for PA management authorities in Namibia. These tools are inadequate as they do not provide information at a strategic level which can help show trends and weakness and strength in PA management. Therefore a METT tool based on the World Commission on Protected Area’s Framework of which Namibia is a signatory is warranted. The NAMETT provides good information but lacks a link or section that should highlight the health of the ecosystem or provide information on biodiversity. Furthermore the tool has shortfalls in terms of implementation training and guidelines to assist implementers. Despite this, stakeholders who participated in the research project indicated that the tool should be adopted as the standard management effectiveness tool for PAs in Namibia. This however should come with alignment of the tool to local conditions and development of implementation guidelines as well as linkage to other form of PA management tools such as game counts and the IBMS. There is lack of robust management system for PAs in Namibia which will consolidate implementation of NAMETT. Such a system should involve planning, implementation, reporting and adaptive management. Therefore if NAMETT is to be adopted there is a need for such a system to be in place to enable data and information from the different tools to be able to complement each other for informed decision making about PA management.
A framework for modelling the interactions between biochemical reactions and inorganic ionic reactions in aqueous systems.
(2022) Brouckaert, Christopher John.; Lokhat, David.
Bio‐processes interact with the aqueous environment in which they take place. Integrated bio‐process and three‐phase (aqueous–gas–solid) multiple strong and weak acid/base system models are being developed for a range of wastewater treatment applications, including anaerobic digestion, biological sulphate reduction, autotrophic denitrification, biological desulphurization and plant‐wide wastewater treatment systems. In order to model, measure and control such integrated systems, a thorough understanding of the interaction between the bio‐processes and aqueous‐phase multiple strong and weak acid/bases is required. This thesis is based on a series of five papers that were published in Water SA during 2021 and 2022. Chapter 2 (Part 1 of the series) sets out a conceptual framework and a methodology for deriving bioprocess stoichiometric equations. It also introduces the relationship between alkalinity changes in bioprocesses and the underlying reaction stoichiometry, which is a key theme of the series. Chapter 3 (part 2 of the series) presents the stoichiometric equations of the major biological processes and shows how their structure can be analysed to provide insight into how bioprocesses interact with the aqueous environment. Such insight is essential for confident, effective and reliable use of model development protocols and algorithms. Where aqueous ionic chemistry is combined with biological chemistry in a bioprocess model, it is advantageous to deal with the very fast ionic reactions in an equilibrium sub‐model. Chapter 4 (part 5 of the series) presents details of how of such an equilibrium speciation sub‐model can be implemented, based on well‐known open‐source aqueous chemistry models. Specific characteristics of the speciation calculations which can be exploited to reduce the computational burden are highlighted. The approach is illustrated using the ionic equilibrium sub‐model of a plant‐wide wastewater treatment model as an example. Provided that the correct measurements are made that can quantify the material content of the bioprocess products (outputs), the material content of the bioprocess reactants (inputs) can be determined from the bioprocess products via stoichiometry. The links between the modelling and measurement frameworks, which use summary measures such as chemical oxygen demand (COD) and alkalinity, are described in parts 3 and 4 of the series, which are included as appendices to the thesis. An additional paper, presenting case study on modelling an auto‐thermal aerobic bio‐reactor, is included as a third appendix, as it demonstrates the application of some of the principles developed in the series of papers.
A framework to improve irrigation design and operating strategies in the South African sugarcane industry.
(2009) Jumman, Ashiel.; Senzanje, Aidan.; Lecler, Neil Louis.
The purpose of this study was to develop a framework to assess irrigation design and operating strategies. This objective was achieved successfully and the framework was applied to formulate guidelines to increase farm profitability whilst using scarce resources, such as water and electricity, effectively. The study was targeted at sugarcane irrigated with semi-permanent irrigation systems. “ZIMsched 2.0”, a water balance and crop yield prediction model and the “Irriecon V2” economic assessment model were available at the start of the study. The missing link, however, was a relatively cost effective and efficient method to design and cost irrigation hardware alternatives. Irrigation hardware impacts on both the agronomic and economic performance of systems, for example, through different peak design capacities and associated operating limitations. Thus, a novel, spreadsheet-based irrigation design tool, with an automated costing component, was developed to complete the framework. The framework was used to investigate the costs and benefits of potential design and operating solutions to a selection of irrigation issues, including: over-irrigation on shallow soils, the opportunity to shift electricity use out of expensive peak periods and, the opportunity to demonstrate the benefits of deficit irrigation strategies. For shallow soils, the increase in system hardware costs, needed to better match water application to soils, increased margins due to more effective water use. Innovative deficit designs and operating strategies allowed for reductions in water and electricity costs. The reduced costs, however, did not always offset yield penalties and revenue loss resulting from water stress. The financial benefits of deficit irrigation strategies were shown when water savings were used to convert dry land cane into irrigated cane. This highlighted the differences between the direct and opportunity costs of water. Finally, a field work component, relating to the precise monitoring of irrigation strategies and corresponding crop responses was included in this study. Systems which enabled soil water potential and stalk extension to be monitored remotely via the internet were considered useful for the successful implementation of an optimum irrigation strategy. The easily accessible data allows for effective decision making and more importantly, reassures famers of the current state of their crop.
A laboratory and glasshouse investigation on the effect of liming with fly ash and processed stainless steel slag on two contrasting South African soils.
(2008) Ndoro, Esina Tambudzayi.; Hughes, Jeffrey Colin.
Soil acidity is a major land degradation problem that limits crop production globally. The high cost of traditional liming materials (calcitic limestone, dolomite etc.) and the vast areas of land that require liming have led to the exploratory utilisation of alkaline industrial by- products such as fly ash and stainless steel slag. The liming potential and effects of liming with fly ash (from the Duvha power station) and processed stainless steel slag (Calmasil) on two acid soils were investigated in this study. The quality of fly ash and Calmasil as liming materials and their potential impacts on the soil quality and plant growth were investigated. The effects of liming with these materials on soil pH, EC, extractable Al, Mn, base cations and trace elements were investigated in an incubation experiment. A glasshouse trial was conducted to assess the effects of these materials on the growth of an acid intolerant crop, perennial rye grass. The incubation and glasshouse study were of a factorial design with two acid soils (the Avalon and Inanda soils), three materials (fly ash, Calmasil and lime); and five application rates of 0, 50, 100, 200 and 400% of the recommended optimum liming rate (OLR) for the growth of perennial rye grass. Characterization of fly ash showed that the major elements (>5%) present (Si > Al > Fe) are not comparable to lime (Ca > Si > Mg) and that it has a low liming potential (calcium carbonate equivalence (CCE) of 9.6%) in comparison to lime. The chemical composition of Calmasil is comparable to lime with Ca > Si > Mg as the major elements and it has a very high liming potential (CCE = 97%). The incubation experiment showed that adding fly ash and Calmasil increased the pH of both soils. However, at the optimum liming rate (100% OLR), only the treatment with Calmasil in the Avalon soil attained pH levels within the desired pH range. Extractable Al and Mn decreased with addition of fly ash and Calmasil to levels comparable to lime in the incubated soils. Addition of fly ash and Calmasil also increased the extractable base cations of both soils. The yield-response of perennial rye grass to treatments in both soils was in the following order: fly ash > Calmasil > lime. Application of fly ash at > 200% OLR in the Avalon soil caused injury of ryegrass. Application of fly ash and Calmasil at lower rates has great agronomic potential in ameliorating soil acidity.
A review of the engineering properties of concrete with paper mill waste ash — towards sustainable rigid pavement construction.
(Silicon) Pillay, Deveshan L.; Oladimeji B., Olalusi; Mostafa, Mohamed M.H.
The drastic surge in urbanisation and construction-related activities is increasing the demand for cement and aggregates, especially for concrete production. Concrete is utilised for a wide variety of structural applications, including rigid pavements construction, due to its superior strength and durability performance. However, the production of cement and concrete increases carbon footprint; and the source of natural aggregates depletes. Hence, there is an increased demand for pavement designs that incorporate sustainable materials and maintain a consistent level of service. In rigid pavements construction, this can be achieved with the integration of alternate binder systems, such as paper mill ash (PMA). This paper presents a systematic review of the engineering properties of PMA as a partial cement replacement material for sustainable concrete production. The review is focused on the influence of PMA on the engineering properties of concrete. The main advantages and limitation of using PMA were highlighted and discussed. Grey areas for possible research exploit were also identified. Based on the superior tensile (2.68 – 3.98 MPa) and flexural (4.04 – 5.01 MPa) strength results documented in the various works of literature reviewed, it can be concluded that PMA is a feasible alternative binder material for rigid pavement applications. This, coupled with its negligible CO2e emission value, indicate that PMA is beneficial to the sustainability and serviceability states of rigid pavements. The viewpoint of this review will be useful for researchers for their future studies and guide stakeholders in the construction industry to have more understanding of PMA concrete.
A review of the fluvial geomorphology monitoring of the receiving streams of the Mooi-Mgeni [River] Transfer Scheme Phase 1.
(2009) Hunter, Alistair Malcolm Scott.; Kotze, Donovan Charles.; Dent, Mark Clifford.; Archer, Lynette Deborah.
The Mgeni River is the major water resource for the eThekwini Metropolitan and Msunduzi Municipalities. At the end of 2002, the Mooi-Mgeni Transfer Scheme Phase 1, which transfers water from the Mooi River into the Mgeni catchment to augment the water supply to this region, was completed. The interbasin transfer of water resulted in the loss of habitat, erosion of the stream channel and transformation of the riparian zone in the receiving streams. Stream regulation resulting in an altered flow regime is considered the greatest threat to a riverine environment. An Environmental Management Plan (EMP), incorporating fluvial geomorphological monitoring procedures, was implemented to monitor the impact of the transfer on the receiving streams, the Mpofana and Lions Rivers, and to determine the rate and magnitude of erosion. A comparison of the geomorphological monitoring procedure of the EMP with best practice geomorphological monitoring derived from a review of the national and international stream geomorphological literature was conducted in this study. In addition, the implementation of the EMP geomorphological monitoring procedures was described and onsite observations of physical impacts on the receiving streams were completed. The geomorphological monitoring of the EMP included the use of erosion pins, survey of stream cross-sections and fixed-point photography. Photographs and data were collected from February 2003 to June 2006. The comparison of these monitoring methods against stream assessment best practices revealed the strengths and weaknesses of the geomorphological monitoring implemented in the receiving streams. Several key weaknesses were revealed. Firstly, an inadequate number of stream cross sections was included in the monitoring procedures. Secondly, although the erosion pins indicated some general trends in the erosion of the stream channel, they did not give a true impression of the rate and magnitude of change in slope and channel width of the stream, and the location of the erosion pins sites did not take into account the actual direction of flow during transfer as erosion pin sites were selected during low flow conditions. In addition, it was difficult to determine whether the erosion pins had been lost due to erosion or to turbulence. The results were difficult to assess and did not show whether the erosion was localised at the pins or the section of bank or stream profile. Thirdly, analysis of platform changes in the stream channel (e.g. through a comparison of aerial photograph sets) was lacking and no attempt was made to integrate the results from the different methods. Overall, the study concluded that the geomorphological monitoring of the EMP was limited, and it did not highlight the rate and magnitude of erosion in the receiving streams. Based on the findings of this study, recommendations are provided for geomorphological monitoring of the receiving streams of the Mooi Mgeni Transfer Scheme.
A semi-empirical formulation for determination of rain attenuation on terrestrial radio links.
(2010) Odedina, Modupe Olubunmi.; Afullo, Thomas Joachim Odhiambo.
Advances in today’s fast growing communication systems have resulted in congestion in the lower frequency bands and the need for higher capacity broadband services. This has made it inevitable for service providers to migrate to higher frequency bands so as to accommodate the ever increasing demands on radio communication systems. However, the reliability of such systems at these frequency bands tend to be severely degraded due to some natural atmospheric phenomena of which rain is the dominant factor. This is not to say that other factors have become unimportant; however, if attenuation by rain is so severe that a radio link is unavailable for use, then other factors become secondary. Therefore, it is paramount to establish a model capable of predicting the behaviour of these systems in the presence of rain. This study employs a semi-empirical approach for the formulation of rain attenuation models using the knowledge of rain rate, raindrop size distribution, and a signal level measurement recorded at 19.5 GHz on a horizontally polarized terrestrial radio link. The semi-empirical approach was developed by considering the scattering effect of an electromagnetic wave propagating through a medium containing raindrops. The complex forward scattering amplitudes for the raindrops are determined for all raindrop sizes at different frequencies, utilizing the Mie scattering theory on spherical dielectric raindrops. From these scattering amplitudes, the extinction cross-sections for the spherical raindrops are calculated. Applying the power-law regression to the real part of the calculated extinction cross-section, power-law coefficients are determined at different frequencies. The power-law model generated from the extinction crosssection is integrated over different raindrop-size distribution models to formulate theoretical rain attenuation models. The developed rain attenuation models are used with 0.01 R rain rate statistics determined for four locations in different rain climatic zones in South Africa to calculate the specific rain attenuation. From a horizontally polarized 6.73 km terrestrial line-of-sight link in Durban, South Africa,experimental rain attenuation measurements were recorded at 19.5 GHz. These rain attenuation measurements are compared with the results obtained from the developed attenuation models with the same propagation parameters to establish the most appropriate attenuation models that describe the behaviour of radio link performance in the presence of rain. For the purpose of validating the results, it is compared with the ITU-R rain attenuation model. This study also considers the characteristics and variations associated with rain attenuation for terrestrial communication systems. This is achieved by utilizing the ITU-R power-law rain attenuation model on 5-year rain rate data obtained from the four different climatic rain zones in South Africa to estimate the cumulative distributions of rain attenuation. From the raindrop size and 1-minute rain rate measurement recorded in Durban with a distrometer over six months, rain events over the six months are classified into drizzle, widespread, shower and thunderstorm rain types and the mean rain rate statistics determined for each class of rain. Drop-size distribution for all the rain types is estimated. This research has shown a statistical analysis of rain fade data and proposed an empirical rain attenuation model for South Africa localities. This work has also drawn out theoretical rain attenuation prediction models based on the assumption that the shapes of raindrops are spherical. The results predicted from these theoretical attenuation models have shown that it is not the raindrop shapes that determine the attenuation due to rain, but the raindrop size distribution and the rain rate content in the drops. This thesis also provides a good interpretation of cumulative rain attenuation distribution on seasonal and monthly basis. From these distributions, appropriate figures of fade margin are derived for various percentages of link availability in South Africa.
A simulation study of cane transport system improvements in the Sezela Mill area.
(2009) Giles, R. C.; Bezuidenhout, Carel Nicolaas.
The South African sugar industry is of significant local and international importance and covers an area in excess of 450 000 hectares. This area yields approximately 21 million tons of sugarcane per annum which is transported almost exclusively by road, from farms to the sugar mills. The industry is under increasing economic pressures to improve its productivity and competitiveness and sugarcane transport in the sugarcane supply chain has been identified as one area where large improvements and associated cost reductions can be made. This is mainly due to the excess in number of vehicles in the inbound transport system, the high relative cost of transport compared to other production costs in producing sugarcane, and the high fixed costs associated with truck fleet operations. A simulation case study of the transport system was completed in 2005 in the Sezela Mill area in which approximately 2.2 million tons of sugarcane is transported per annum over an average distance of 29 km by approximately 120 independently managed vehicles owned by a wide range of hauliers and individual growers. This amounts to an estimated cost of R58 million per annum. This study investigated the potential savings that could occur as a result of a central fleet control system with integrated vehicle scheduling. A scheduling software package named ASICAM, which resulted in significant savings in the timber industry (Weintraub et al, 1996), was applied within the Sezela region. Results suggested that the number of trucks in the fleet could theoretically be reduced by at least 50%, providing that a central office controls vehicle movements and that all hauliers serve all growers in an equitable fashion. In addition, investigations towards decreasing loading times, decreasing offloading times, changing vehicle speeds and increasing payloads by reducing trailer tare mass showed further reductions in the number of trucks required.
A study of bruchid resistance and its inheritance in Malawian dry bean germplasm.
(2007) Kananji, Geoffrey Acrey Duncan.; Melis, Robertus Johannes Maria.; Derera, John.; Laing, Mark Delmege.
Dry bean (Phaseolus vulgaris L.) is economically and nutritionally an important legume, not only in Malawi, but in many parts of Africa and Latin America. Unfortunately, two bruchid species (Acanthoscelides obtectus Say, and Zabrotes subfasciatus Boheman) are known to cause extensive damage in storage, reducing the economic importance, food value and planting value of the crop. The aim of this study was to: i) ascertain farmers’ perceptions of the importance of bruchids as storage pests, and to identify their preferred varietal traits in dry beans; ii) screen Malawian dry bean landraces for effective and adaptable sources of resistance to the two bruchid species; iii) determine the gene action and inheritance of bruchid resistance. Farmers’ perceptions on the importance of the two bruchid species to beans both in the field and in storage were established using a participatory rural appraisal (PRA) in three extension planning areas (EPAs) in Lilongwe agricultural development division (ADD). Results confirmed that the two bruchid species are important storage pests, causing serious storage losses among smallholder farmers. In the absence of any control measures, farmers indicated that more than 50% of their stored beans could be lost to bruchids. Indigenous bruchid control measures are not very effective, making it necessary to search for other control methods. It was also clear from the PRA results that breeders need to consider both agronomic and culinary traits in bean cultivar development. This would enhance uptake of newly developed varieties. To address the problem of bruchid damage experienced by smallholder farmers, a total of 135 dry bean genotypes, comprising 77 landraces and 58 improved varieties (obtained from collaborating partners) were tested under laboratory infestation (nochoice test methods) and field infestation (free-choice test methods). The objective of this study was to identify effective sources of resistance to the two bruchid species. Results of the study showed that there was a wide variation among the genotypes for resistance to the two bruchid species. Overall results showed that 88% of the genotypes ranged from susceptible to highly susceptible to Z. subfasciatus and only 12% of the genotypes were moderately resistant to resistant. Genotype screening for resistance to A. obtectus showed that only 12.5% were resistant, whereas 87.5% were moderately to highly susceptible. All of the improved genotypes were 100% susceptible to A. obtectus in storage. One landrace, KK35, consistently showed a high level of resistance to both bruchids under laboratory infestation, with results similar to the resistant checks (SMARC 2 and SMARC 4), while another landrace, KK90, displayed stable resistance under both laboratory and field infestation. However, performance of most genotypes was not consistent with field and laboratory screenings, suggesting that mechanisms of bruchid resistance in the field are different from that in the laboratory and field screening should always be used to validate laboratory screening. Resistance in the field was not influenced by morphological traits. The seed coat played a significant role in conferring resistance to both bruchid species in the laboratory, whereas arcelin did not play any significant role in conferring resistance in the landraces. The inheritance of resistance to A. obtectus was studied in a 6 x 6 complete diallel mating design, involving crosses of selected Malawian dry bean landraces. The F1 crosses, their reciprocals, and six parents were infested with seven F1 generation (1 to 3 d old) insects of A. obtectus in a laboratory, no-choice test. There were significant differences among genotypes for general combining ability (GCA) and specific combining ability (SCA). However, SCA accounted for 81% of the sum of squares for the crosses, indicating predominance of the non-additive gene action contributing to bruchid resistance. A chi-square test for a single gene model showed that 5 of the 13 F2 populations fitted the 1:2:1 segregation ratio of resistant, intermediate and susceptible classes, respectively indicating partial dominance. The eight F2 populations did not conform to the two gene model of 1:4:6:4:1 segregation ratio of resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible classes, respectively. Average degree of dominance was in the partial dominance range in five F3 populations, but in general resistance was controlled by over-dominance gene action in the F2 populations. The additive-dominance model was adequate to explain the variation among genotypes indicating that epistatic effects were not important in controlling the bruchid resistance. The frequency distribution of the 13 F3 populations for resistance to A. obtectus provided evidence for transgressive segregation, suggesting that resistance is conditioned by more than one gene. Reciprocal differences were not significant in the F2 generation seed; but were significant in four crosses in the F3 generation seed for adult bruchid emergence, suggesting that maternal effects or cytoplasmic gene effects also played a role in the inheritance of resistance to the common bean weevil. Through this study, important sources of bruchid resistance in dry bean have been identified in Malawian landraces (KK35, KK90 and KK73). These resistant sources will be used in a breeding programme to develop bruchid resistant bean cultivars, as well as improve resistance in susceptible commercial bean cultivars currently grown by farmers in Malawi.
A study of rain attenuation on terrestrial paths at millimetric wavelengths in South Africa.
(2006) Olubunmi, Fashuyi Modupe.; Afullo, Thomas Joachim Odhiambo.
Rain affects the design of any communication system that relies on the propagation of electromagnetic waves. Above a certain threshold of frequency, the attenuation due to rain becomes one of the most important limits to the performance of terrestrial line-of-sight (LOS) microwave links. Rain attenuation which is the dominant fading mechanism at these frequencies is based on nature which can vary from location-to-Iocation and from year-to year. In this dissertation, the ITU-R global prediction techniques for predicting the cumulative distribution of rain attenuation on terrestrial links are studied using a five-year rain rate data for twelve different geographical locations in the Republic of South Africa. The specific attenuation rR (dB/km) for both horizontal and vertical polarization is determined. The path attenuation (dB) exceeded for 0.01% of the time is estimated using the available existing models for the twelve different geographical locations on a I-minute integration time rain rate at 0.01% exceedance of the time averaged over a period of 5 years. A comparison study is done on these available rain attenuation mode'ls; The ITU-R model, Crane Global model, and the Moupfouma models at different frequencies and propagation path lengths based on the actual I-minute integration time rain rate exceeded at 0.01% of the time averaged over a period of 5 years for each geographical locations. Finally, from the actual signal attenuation measurements recorded in Durban over a period of 1 year at 19.5 GHz and a propagation path length of 6.73 km, a logarithmic attenuation model and power attenuation model is proposed for Durban, South Africa. Recommendation for future work is given in the concluding chapter for future improvement on this study. Radio communication designers will find the results obtain in the report useful.
A study on the atmospheric and environmental impacts of aerosol, cloud and precipitation interaction.
(2022) Yakubu, Abdulaziz Tunde.; Chetty, Naven.
Understanding the mechanisms and processes of aerosol-cloud-precipitation interactions (ACPI) is essential in the determination of the specific role of aerosols in modulating extreme weather events and climate change in the long run. Atmospheric aerosols are mainly of various types and are emitted from differing sources. Considering they commonly exist in the heterogeneous forms in most environments, they significantly influence the incoming solar energy and the general perturbation of the clouds depending on their constituents. Thus, a systemic identification and characterisation of these particles are essential for proper representation in climate models. To better understand the process of climate change, this research explores the climate diversity of South Africa to examine aerosol sources and types concerning the atmospheric aerosol suspension over the region and their role in clouds and precipitation formation. The study further provided answers to the cause of extreme precipitation events, including drought and occasional flooding experienced over the region. Also, an insightful explanation of the process of ACPI is provided in the context of climate change. Furthermore, the research found that the effective radiative forcing (RF) over South Africa as monitored in Cape Town and Pretoria is negative (i.e., cooling effect) and provided an analysis of the cause. Similarly, the validation of some satellite datasets from MISR (Multiangle Imaging Spectroradiometer) and MODIS (Moderate Resolution Imaging Spectroradiometer) instruments against AERONET (Aerosol Robotic Network) is conducted over the region. Although a significant level of agreement is observed for the two instruments, intense improvements are needed, especially regarding measurements over water surfaces. Finally, the study demonstrated the proficiency of effective rainfall prediction from satellite instrument cloud datasets using machine learning algorithms.
A systems-thinking based evaluation of predator conflict management on selected South African farms.
(2008) Snow, Timothy V.
The backbone of this study was a systems thinking based analysis of the management and control of predators as practiced in South Africa since the advent of Europeans in 1652. The first bounties were introduced for a variety of animal species in 1656. Many species became labeled as vermin and were persecuted, often with the intention of eradication. A variety of controls have been applied, of which many have not kept pace with contemporary thinking or technology, and which by simply killing predators fail to address the crux of the issue of predator – livestock conflict. Many of the methods used cannot be applied to specifically remove an individual damage-causing animal. Considerable collateral ecological damage is inflicted by the killing of animals regarded as innocent bystanders. The objective of the analysis was to highlight the futility of temporary solutions which fail to resolve the conflict in the long term. These quick fixes frequently perpetuate an ecological imbalance which exacerbates the predator – livestock conflict. The analysis used raw data from a questionnaire survey conducted by the Poison Working Group of the Endangered Wildlife Trust (EWT-PWG) (2003). The EWT-PWG intended to assess pesticide abuse as toxicant for predators by farmers, and to identify all control methods used. The data forthcoming was Cartesian in nature and a fixed snap-shot in time. This study sought to identify the root cause of the conflict by applying systems thinking which added the dimension of cause and effect interrogation. The study categorised and described predator conflict management methods as lethal or preventative, and assessed each category in archetypal terms from a systems thinking perspective. It also sought to identify leverage points, or small changes which have profound effects, to stimulate a change in approach to humanpredator conflict management. In order to assess and illustrate the positive change brought about by application of preventative methods, a small group of farmers who had initiated changes in their predator conflict management over the five years subsequent to the EWTPWG survey were selected from the original group for reassessment. Through evaluation of predator conflict management methods from a systems thinking perspective, and by probing learning processes, the shortcomings or failure of inappropriate management responses to conflict situations were shown to exacerbate conflicts. Contrarily, it was illustrated that application of systems thinking and a process of addressing the root cause of conflict issues in predator conflict management, was a longer term solution. The study illustrated that application of long term proactive prevention and conflict avoidance principles, can offer long term solutions for predator conflict managers.

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