Browsing by Author "Van Vuuren, Jan H."

Now showing 1 - 7 of 7
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    A concept demonstrator for self-organising demand-driven inventory management in pharmaceutical supply chains
    (South African Institute for Industrial Engineering, 2018) Du Plessis, Marno; Van Vuuren, Jan H.; Van Eeden, Joubert
    ENGLISH ABSTRACT: Perennial stock-outs of essential medicines are commonplace in the pharmaceutical supply chains of developing countries. Stock-outs are mainly attributed to a general lack of collective information sharing in pharmaceutical supply chains. In this paper, a computerised agent-based simulation model concept demonstrator is proposed and demonstrated hypothetically as part of a larger drive to establish the value of leveraging information sharing in pharmaceutical supply chains with a view to enhance decision-making. The objective of this paper is to outline the prerequisite research inputs, design requirements and hypothetical implementation of the aforementioned demonstrator. The work reported on in this paper remains a work in progress.
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    A decision support tool for quantifying the risk profile of south Africa’s pharmaceutical supply distribution network
    (South African Institute for Industrial Engineering, 2018-10) Nolting, Christian Wolfgang; Grobbelaar, Sara S.; Van Vuuren, Jan H.
    ENGLISH ABSTRACT: South Africa is facing a serious burden of disease, which is exacerbated by a dysfunctional public health care system. Blind, general estimates are often made in respect of crucial pharmaceutical inventory variables. This results in slow-moving pharmaceutical drugs being overstocked and fast-moving drugs being understocked at outlets and distribution centres. Consequently, large wastages are incurred in terms of drugs being discarded in bulk after passing their expiration date. As a result, patients are deprived of essential medicines due to enduring stock-outs. This paper aims to present the conceptual design of a decision support tool, which aids decision makers in determining pharmaceutical inventory variables that align with key objectives and keep the best interest of patients in mind.
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    Die effek van veelvuldige lynverwydering op die onafhanklikheidsgetal van ’n asikliese grafiek
    (AOSIS, 2018) Van Vuuren, Jan H.
    ENGLISH ABSTRACT: A subset X ⊆ V of the vertex set V of a graph G = (V,E) is an independent set in G if no two vertices of V are adjacent in G. The cardinality of a largest independent set in G is called the independence number of G and is denoted by α(G). A non-empty graph G is p-stable if p is the largest number of arbitrary edges that can be removed from G without changing the independence number of the resulting graph, and q-critical if q is the smallest number of arbitrary edges that have be removed from G in order necessarily to change the independence number of the resulting graph. The classes of p-stable and q-critical forests (acyclic graphs) of order n are characterised in this paper for all permissible values of p, q and n.
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    Enumerasie van self-ortogonale Latynse vierkante met simmetriese ortogonale maats
    (LitNet Academic, 2012-04) Burger, Alewyn P.; Kidd, Martin P.; Van Vuuren, Jan H.
    OPSOMMING: vierkante met simmetriese, ortogonale maats (SOLVSOMs), ’n probleem wat nog nie in die literatuur oor kombinatoriese ontwerpe aangespreek is nie. In die besonder bepaal ons die getal (ry, kolom)-paratoopklasse van SOLVSOMs van orde n ≤ 10 deur inligting in bestaande, uitputtende databasisse van self-ortogonale Latynse vierkante en simmetriese Latynse vierkante met behulp van ’n boomsoektog met terugkering (Eng: backtracking) te kombineer. Ons bepaal ook die getal verskillende SOLVSOMs, SOLVSOMs in standaardvorm en transponentisomorfismeklasse van SOLVSOMs van ordes n ≤ 10 deur gebruikmaking van standaard tegnieke uit abstrakte algebra. In die proses beantwoord ons ’n 34 jaar-oue oop bestaansvraag oor SOLVSOMs van orde 10 deur aan te toon dat geen so ’n ontwerp bestaan nie. Aangesien ’n SOLVSOM van orde n in standaardvorm ekwivalent is aan ’n spelskedule vir ’n gadevermydende gemengde-dubbels rondomtalie-tennistoernooi vir n getroude pare, dui hierdie resultaat daarop dat geen so ’n toernooi vir 10 getroude pare geskeduleer kan word nie.
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    Seeking optimality in fruit pulping schedules : a case study
    (Operations Research Society of South Africa, 2000) Huddlestone, Grant E.; Van Vuuren, Jan H.
    The process of scheduling fruit pulping for the production of fruit juices is of great importance in the beverage industry. Decisions have to be made regarding available processing time, the disposal of fruit that will not be pulped before stock loss due to spoilage, the fulfilment of customer demand and an optimal financial position. Sheduling depends on the capacity of the work force, pulping machine limitations and delivery deadlines. However, the situation is often encountered where the plant manager has to decide which fruit batches (usually from stock piles of overwhelming proportions during the harvesting season) are to be pulped in order to minimize losses due to fruit deterioration. Such decisions are usually done manually, based on intuition and experience. A mathematical model is presented here which constructs a pulping strategy while minimising cascading financial losses associated with fruit grade drops within the stock pile. It is shown in particular that a minimisation of fruit losses is not a good criterion for optimality, and that substantial financial gains may be accomplished when minimising financial losses in stead of fruit losses, which is currently standard practice at most fruit pulping plants.
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    Simulation modelling as a decision support in developing a sterile insect-inherited sterility release strategy for Eldana saccharina (Lepidoptera: Pyralidae)
    (Florida Entomological Society, 2016) Potgieter, Linke; Van Vuuren, Jan H.; Conlong, Des E.
    ENGLISH SUMMARY : A user-friendly simulation tool for determining the impact of the sterile insect technique/inherited sterility technique (SIT/IS) on populations of the African sugarcane stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae) is described in this paper. The simulation tool is based on a spatio-temporal model. The design of the simulation tool is such that it is applicable for use in a number of pest/crop and pest control scenarios. It uses 4 interacting subsystems (pest species population dynamics, crop dynamics, environmental dynamics and economics) within a specified spatial domain. Furthermore, the spatial domain describes the layout of the agricultural crop (position, size, shape, crop age and variety of the different fields contained within the crop area). The pest species population subsystem describes E. saccharina population dynamics (but is designed to also include population dynamics of other pest species) under the influence of the IS technique. The E. saccharina module developed utilizes mean-field and spatio-temporal models, and includes dynamics of all E. saccharina life stages under the influence of the control measure. Only temperature and damage caused by E. saccharina are currently included as variables in the sugarcane dynamics subsystem. This subsystem estimates stalk length as a function of time and temperature, and sucrose percentage as a function of damage caused by E. saccharina boring. Interaction between E. saccharina population growth and sugarcane growth is described by a decreasing s-shaped density-dependent mortality function—the older the cane, the higher the carrying capacity (more food resources) and corresponding infestation and damage levels. The only environmental factor considered as an independent variable in the environmental dynamics subsystem is temperature. Possible extensions to this subsystem are discussed. The economics subsystem developed includes the estimation of the recoverable value, percentage, expected revenue and the cost of control. No other farm expenditures are taken into account. As such only profit or loss expected from applying the IS technique is estimated. The profit or loss is defined as the increase in revenue expected less the cost of applying a pest control measure. An example of using the simulation tool is presented in the context of a real field scenario of a simulated SIT/IS program against E. saccharina at a pilot site near the Eston area of KwaZulu-Natal, South Africa.
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    Walk modelling when designing small bus transit networks
    (Southern African Institute for Industrial Engineering, 2021) Husselmann, Gunther; Van Vuuren, Jan H.; Andersen, Simen Johann
    ENGLISH ABSTRACT: Models for the design of public bus transit networks are usually based on the historically observed origin-demand travel patterns of potential passengers. The option of a passenger choosing to walk is, however, not usually incorporated into the design models for such networks. We argue that the absence of this model feature might lead to significant sub-optimality, especially in the design of small public bus transit networks. A novel approach to including this feature in the bus frequency setting aspect of public bus transit network design models is demonstrated in this paper, in which passenger transit modal choices are modelled on the basis of an existing optimal strategy transit assignment model. The newly proposed bi-objective route design and frequency setting models are applied to a realistic case study involving the establishment of a public bus transit system for students on a university campus; and this model implementation is used to gain insight into passenger route choice behaviour, based on individual preferences between walking or using buses. It is shown in the context of this case study that including the option of a passenger walking in the design models for public bus transit networks can affect the efficacy of the final network, especially if the network is small.