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Browsing Journal Articles by browse.metadata.cluster "National Integrated Cyber InfraStructure"
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Item Computational development and validation of a representative MDI-BDO–based polyurethane hard segment model(2021-01) Karunarathna, B; Jayakody, RS; Karunanayake, L; Govender, Krishna KSegmented polyurethanes show extraordinary physicochemical properties, mainly owing to the nature and the chemistry of the hard segment domains. There are yet many inexplicable physiochemical properties of MDI-BDO–based hard polyurethane segments such as the geometry, cis–trans isomerism, electronic structure, chemical reactivity, the inter-hard-segment interactions, and the photo-response. In the present study, it was attempted to develop and validate a model system that would facilitate further research on the structural and chemical properties of the MDI-BDO hard segments. It was found that the trans isomer of urethane bond is more stable than the cis isomer, and it is argued here that thermal transformation from trans to cis not possible due to the high rotational energy barrier. The differences between the calculated IR spectra of the cis and trans isomers are proposed as a powerful differentiation tool. The calculated Fukui indices show that cis and trans isomers are different in their chemical reactivity. The findings of the present study suggest intermolecular and intramolecular pi-stacking and highly plausible two significant types of hydrogen bond types between hard segments. In the present study, a model system for MDI-BDO hard segment was developed and successfully validated via computational experiments. Further calculations done with the new model provided an indispensable understanding of the structure, cis–trans isomerism, reactivity, and intermolecular interactions of the MDI-BDO hard segments. The proposed model can be further improved in the future by incorporating suitable soft segments. In summary, the model system developed and validated in the present study has provided new opportunities to understand and further study the structural and chemical features of the hard segments of the MDI-BDO–based polyurethane.Item Description of a network attack ontology presented formally(Springer, 2021-06) Van Heerden, Renier P; Leenen, L; Irwin, B; Misra, S; Tyagi, AKThe identification of network attacks in real-time is becoming increasingly important. Most Artificial Intelligence (AI) applications use machine learning to do the classification of attack types but the advantage of an ontological approach is that automated reasoning is the underpinning theory rather than automated learning. Automated reasoners allow automated classification and this powerful feature is the basis for the developing of an early warning system for active network attacks. In this paper, the authors describe how to employ Semantic Technologies by building an ontology to identify network attack types in order to support the automated classification of current network attacks by recognising relevant properties which are then mapped to relevant attack scenarios depicted in the ontology. The ontology engineering guidelines provided by Noy and McGuinness (2001) were used to build the ontology. The classes and relationships of the ontology are described formally and implemented in Protégé, an ontology editor. A core class in the ontology is the Attack Scenario class that represents different types of network attacks, for example, a Denial of Service attack. The ontology is evaluated by showing two examples of real attacks that correctly classified by the presented ontology. The presented ontology is to be expanded in future work. The aim of this paper is not to present a complete network attack ontology, but rather to present a proof of the concept of how to formally describe such an ontology, with the view to providing a baseline for future development of details. Row examples are explored to demonstrate how specific instances of attacks are classified using the ontology.Item A DFT study of two-dimensional CdS/TiS2 on isotropic chalcogenide AgSbTe2 thermoelectric material: Electronic charge transfer and optical properties(2022-08) Kiarii, EM; Govender, Krishna K; Mamo, MA; Govender, PPCalculations of AgSbTe2 thermoelectric material and 2d CdS/TiS2 and their heterostructures were carried out using Density Functional Theory in Cambridge Serial Total Energy Package code as implemented in Material Studio 2018 software. The work function, thermal transport, electronic and optical properties were calculated. The results revealed that the heterostructures are possible to be achieved with improved properties. The electronic and thermal transport properties were likened with the description of equations derived from Boltzmann transport theory and Mott expressed in the maximum achievable Figure merit. Orbital contributions from the electron movement show valence and conduction band atomic shells.Item Isoniazid-loaded orodispersible strips: Methodical design, optimization and in vitro-in silico characterization(2021-08) Adeleke, Oluwatoyin A; Tsai, P; Karry, KM; Monama, Nkwe O; Michniak-Kohn, BBDrug treatment remains the most effective global approach to managing and preventing tuberculosis. This work focuses on formulating and evaluating an optimized polyvinyl alcohol-polyethylene glycol based orodispersible strip containing isoniazid, a first-line anti-tubercular agent. A solvent casting method guided through a Taguchi experimental design was employed in the fabrication, optimization and characterization of the orodispersible strip. The optimized strip was physically amalgamated with a monolayer, uniformly distributed surface geometry. It was 159.2 ± 3.0 µm thick, weighed 36.9 ± 0.3 mg, had an isoniazid load of 99.5 ± 0.8%w/w, disintegration and dissolution times of 17.6 ± 0.9 s and 5.5 ± 0.1 min respectively. In vitro crystallinity, thermal measurements and in silico thermodynamic predictions confirmed the strip's intrinsic miscibility, thermodynamic stability and amorphous nature. A Korsmeyer-Peppas (r = 0.99; n > 1 = 1.07) fitted kinetics typified by an initial burst release of 49.4 ± 1.9% at 4 min and a total of 99.8 ± 3.3% at 30 min was noted. Ex vivo isoniazid permeation through porcine buccal mucosa was bi-phasic and characterized by a 50.4 ± 3.8% surge and 95.6 ± 2.9% at 5 and 120 min respectively. The strip was physicomechanically robust, environmentally stable and non-cytotoxic.Item Model inter-comparison for short-range forecasts over the southern African domain(2021-09) Mulovhedzi, PT; Rambuwani, GT; Bopape, MJ; Maisha, R; Monama, Nkwe ONumerical weather prediction (NWP) models have been increasing in skill and their capability to simulate weather systems and provide valuable information at convective scales has improved in recent years. Much effort has been put into developing NWP models across the globe. Representation of physical processes is one of the critical issues in NWP, and it differs from one model to another. We investigated the performance of three regional NWP models used by the South African Weather Service over southern Africa, to identify the model that produces the best deterministic forecasts for the study domain. The three models – Unified Model (UM), Consortium for Small-scale Modelling (COSMO) and Weather Research and Forecasting (WRF) – were run at a horizontal grid spacing of about 4.4 km. Model forecasts for precipitation, 2-m temperature, and wind speed were verified against different observations. Snow was evaluated against reported snow records. Both the temporal and spatial verification of the model forecasts showed that the three models are comparable, with slight variations. Temperature and wind speed forecasts were similar for the three different models. Accumulated precipitation was mostly similar, except where WRF captured small rainfall amounts from a coastal low, while it over-estimated rainfall over the ocean. The UM showed a bubble-like shape towards the tropics, while COSMO cut-off part of the rainfall band that extended from the tropics to the sub-tropics. The COSMO and WRF models simulated a larger spatial coverage of precipitation than UM and snow-report records.Item Quantum mechanistic studies of the oxidation of ethylene by rhenium oxo complexes(2021-08) Fosu, EA; Obuah, C; Hamenu, L; Aniagyei, A; Ainooson, MK; Govender, Krishna KTransition-metal-mediated oxygen transfer reactions are of importance in both industry and academia; thus, a series of rhenium oxo complexes of the type ReO3L (L=O-, Cl-, F-, OH-, Br-, I-) and their effects as oxidation catalysts on ethylene have been studied. The activation and reaction energies for the addition pathways involving multiple spin states (singlet and triplet) have been computed. In all cases, structures on the singlet potential energy surfaces showed higher stability compared to their counterparts on the triplet potential energy surfaces (PESs). Frontier Molecular Orbital calculations show electrons flow from the HOMO of ethylene to the LUMO of rhenium for all complexes studied except ReO4- where the reverse case occurs. In the reaction between ReO3L (L=O-, Cl-, F-, OH-, Br-, and I-) and ethylene, the concerted [3+2] addition pathway on the singlet PES leading to the formation of dioxylate intermediate is favored over the [2+2] addition pathway leading to the formation of a metallaoxetane intermediate and subsequent rearrangement to the dioxylate. The activation and the reaction energies for the formation of the dioxylate on the singlet PES for the ligands studied followed the order O->OH-I->F->Br->Cl- and O->OH->F->I->Br->Cl-, respectively. Furthermore, the activation and the reaction energies for the formation of the metallaoxetane intermediate increase in the order O->OH->I->Br->Cl->F- and O-> Br->I->Cl->OH->F-, respectively. The subsequent rearrangement of the metallaoxetane intermediate to the dioxylate is only feasible in the case of ReO4-. Of all the complexes studied, the best dioxylating catalyst is ReO3Cl (singlet surface) and the best epoxidation catalyst is ReO3F (singlet surface).Item A systems thinking approach to value-added services adoption in national research and education networks(2021-09) Pillay, Kasandra; Erasmus, Louwrence D; Pretorius, JCThe growing importance of advanced or value-added services (services over and above basic connectivity services) in national research and education networks (NRENs) is well understood in the research and education community. These services are made available to further distinguish and enhance national research and education networks’ offerings from that of commercial internet service providers. Systems thinking allows a ‘bigger view’ of a situation to be analyzed. This paper presents a model that was developed, refined and validated using design science research methods and a systems thinking approach. The model is a causal diagram developed to enable the visualization of how factors in the NREN services adoption context are interrelated. The model was refined and validated with international NREN experts. As a result of the evaluation stage, a shared mental model and understanding of the NREN’s advanced services delivery ecosystem was developed. The model can be used as a communication and decision-making tool to facilitate services adoption from NRENs to their research and education communities.Item Utilisation of a virtual honeynet to proactively secure the South African National Research and Education Network against cyberattacks(2024-07) Meyer, Heloise; Barbour, Graham D; McDonald, Andre M; Badenhorst, Danielle P; Gertenbach, Wian PSouth Africa is witnessing a significant increase in cyberattacks. Although such an increase in cyberattacks can be attributed to various factors, poor investment in cybersecurity technology and lack of awareness are causing South Africa to be a target of interest. While cyberattacks are targeting various sectors, it is the cyberattacks impacting critical infrastructure that are a growing concern. The South African National Research and Education Network (SA NREN) is a high-speed network dedicated to science, research, education and innovation traffic. With the growth of the SA NREN and the continuous increase in cyberattacks affecting South African institutions, proactive steps are required to secure and protect the SA NREN. This responsibility lies with the SA NREN Cybersecurity Incident Response Team (CSIRT), which was established in 2016 to offer protection against cyberattacks. While various proactive measures are currently in place to monitor the SA NREN, the CSIRT continues to explore alternative cost-effective solutions to secure the NREN. This paper investigates the benefits of utilising a novel low-interaction secure shell (SSH) honeynet, referred to as the Virtual Honeynet, to monitor and proactively secure the SA NREN. The Virtual Honeynet uses virtual containers to reduce resource requirements and improve performance. The investigation involved the experimental deployment of the Virtual Honeynet on the SA NREN over a twelve-day period and the evaluation of the captured data. The evaluation conducted focused on extracting behavioural and geographical intelligence from the raw data to guide the deployment of cyber measures to secure the SA NREN. The results presented in this paper confirm the value the Virtual Honeynet offers to the SA NREN as a technology to proactively secure the network.