Browsing by Author "Nieuwoudt, I."

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    A multiobjective approach towards weapon assignment in a ground-based air defence environment
    (Operations Research Society of South Africa, 2013) Lotter, D. P.; Nieuwoudt, I.; Van Vuuren, J. H.
    A typical ground-based air defence (GBAD) environment comprises defended assets on the ground which require protection from enemy aircraft entering the defended airspace. Protection against these aircraft is afforded by means of pre-deployed ground-based weapon systems that are assigned to engage these enemy aircraft according to some pre-specified criterion or set of criteria. The conditions under which human operators have to propose assignments of weapon systems to engage these aircraft are severely stressful since time is a critical factor and there is no room for error. Some progress has already been made with respect to the design of computerised threat evaluation and weapon assignment (TEWA) decision support systems (DSSs) within the context of a GBAD system. However, the weapon assignment (WA) component within such a TEWA DSS is typically based on a single criterion (objective). The aim in this paper is to model the WA problem as a multiobjective decision problem. A list of relevant factors (related to objectives) is identified by means of feedback received from a WA questionnaire which was completed by a number of military experts. For illustrative purposes, two objectives, namely the cost of assigning weapon systems for engagement and the accumulated survival probabilities of observed threats as a result of these engagements, were isolated from these factors in order to derive a bi-objective WA model. This model is solved in the context of a simulated, but realistic, GBAD environment by means of an existing multiobjective solution technique called the Nondominated Sorting Genetic Algorithm II.
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    On the(d)–chromatic number of a complete balanced multipartite graph
    (Operations Research Society of South Africa, 2007) Burger, A. P.; Nieuwoudt, I.; Van Vuuren, J. H.
    In this paper we solve (approximately) the problem of finding the minimum number of colours with which the vertices of a complete, balanced, multipartite graph G may be coloured such that the maximum degrees of all colour class induced subgraphs are at most some specified integer d 2 N. The minimum number of colours in such a colouring is referred to as the (d)–chromatic number of G. The problem of finding the (d)–chromatic number of a complete, balanced, multipartite graph has its roots in an open graph theoretic characterisation problem and has applications conforming to the generic scenario where users of a system are in conflict if they require access to some shared resource. These conflicts are represented by edges in a so–called resource access graph, where vertices represent the users. An efficient resource access schedule is an assignment of the users to a minimum number of groups (modelled by means of colour classes) where some threshold d of conflict may be tolerated in each group. If different colours are associated with different time periods in the schedule, then the minimum number of groupings in an optimal resource access schedule for the above set of users is given by the (d)–chromatic number of the resource access graph. A complete balanced multipartite resource access graph represents a situation of maximum conflict between members of different user groups of the system, but where no conflict occurs between members of the same user group (perhaps due to an allocation of diverse duties to the group members).
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    Tonsillar hypertrophy and prolapse in a child – is epiglottitis a predisposing factor for sudden unexpected death?
    (BMC (part of Springer Nature), 2020-01-20) Nieuwoudt, I.; Goussard, P.; Verster, J.; Dempers, J.
    Background: Tonsillitis, with associated tonsillar hypertrophy, is a common disease of childhood, yet it is rarely associated with sudden death due to airway obstruction. Lethal complications involving the inflamed tonsils include haemorrhage, retropharyngeal abscess and disseminated sepsis. Case presentation: We report on a case of sudden and unexpected death in an 8-year-old female who was diagnosed with and treated for tonsillitis. The child was diagnosed with acute tonsillitis 2 days prior to her collapse and was placed on a course of oral antibiotics. There were no signs of upper or lower airway obstruction. She was found to be unresponsive by her caregiver and gasping for air in her bed in the early hours of the second morning after the start of treatment. Autopsy showed massive and symmetrically enlarged palatine tonsils. The tonsils filled the pharynx almost completely. The epiglottis and laryngeal mucosa at the base of the epiglottis in the vicinity of the aryepiglottic membrane and the superior aspect of the larynx displayed red-purple discoloration, with mucosal swelling and edema. Histological examination of the palatine tonsils revealed prominent lymphoid hyperplasia, but no evidence of acute inflammation. Conclusion: Palatine tonsillar hypertrophy in infants is a common feature of both viral and bacterial tonsillitis and has been postulated as a possible risk factor for Sudden and Unexplained Death in Infancy (SUDI), based on the theory of mechanical impediment of breathing by narrowing of the upper airway. The rounded shape of the tonsils may facilitate some airflow past the enlarged structures and hence protect against asphyxial death when the enlarged tonsils fill the laryngo-pharynx. Epiglottal and proximal laryngeal edema may play a more significant role in asphyxial unexpected deaths in cases of tonsillitis with tonsillar hypertrophy than previously suspected. This focusses the importance of careful examination of the epiglottis and proximal laryngeal mucosa, as part of a thorough examination of the laryngo-pharynx in cases of sudden death associated with tonsillar hypertrophy.