Thesis (MSc (Mathematics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In this thesis, we consider the multi-constraints QoS routing problem in IP networks. Namely, we consider the problem of minimizing the path delays on IP networks. We use genetic algorithms to perform the optimization, some penalty function methods and the simulated annealing method for handling the problems constraints. Our aim is to compare the performance of di erent penalty function methods and the simulated annealing method. The penalty function methods under consideration include penalty methods with non-stationary as well as stationary penalty coe cients. The basis for doing the comparisons are the maximum link and path delays, the maximum and average path length, and the CPU time. We used four virtual networks as test examples. We found that, generally, the performances of the simulated annealing method, the dynamic and co-evolutionary penalty function methods are better than the performances of the adaptive, annealing and the static penalty function methods. Dynamic coe cients seem to have a slight edge over stationary coe cients. Simulated annealing turned out to be the slowest of the approaches investigated. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek hoe om die multi-beperking QoS (\quality of service") roeteringsprobleem vir IP netwerke op te los. Meer spesi ek, die doel is om die netwerkpadvertragings te minimeer. Genetiese algoritmes word gebruik om die probleem deur middel van optimering op te los, en die multi-beperkings word hanteer met behulp van boetefunksies. Daar word ook gekyk na die tempersimulasie benadering (\simulated annealing"). Die doel van die tesis is om die boetefunksies en tempersimulasie te vergelyk. Beide konstante en nie-konstante boetefunksies word ondersoek en nuwe konstante boetefunksies word geformuleer deur die nie-konstante boeteko e si ente vas te pen. Al hierdie metodes word gemeet deur te kyk na die maksimum skakel- en padvertraging, die maksimum en gemiddelde padlengte, en die verwerkingstyd. Vier virtuele netwerke word gebruik as 'n toetsraamwerk. Die uiteindelike gevolgtrekking is dat die verskillende boetefunksies rofweg dieselfde antwoorde produseer. Nie-konstante ko e si ente presteer ietwat beter as konstante ko e si ente. Die tempersimulasie was aan die einde van die dag, die stadigste benadering waarna gekyk is.

Thesis (MSc (Mathematics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: One of the early results that we encounter in Analysis is that every metric space admits a completion, that is a complete metric space in which it can be densely embedded. We present in this work a new construction which appears to be more general and yet has nice properties. These spaces subsequently called hyperconvex spaces allow one to extend nonexpansive mappings, that is mappings that do not increase distances, disregarding the properties of the spaces in which they are defined. In particular, theorems of Hahn-Banach type can be deduced for normed spaces and some subsidiary results such as fixed point theorems can be observed. Our main purpose is to look at the structures of this new type of “completion”. We will see in particular that the class of hyperconvex spaces is as large as that of complete metric spaces. / AFRIKAANSE OPSOMMING: Een van die eerste resultate wat in die Analise teegekom word is dat enige metriese ruimte ’n vervollediging het, oftewel dat daar ’n volledige metriese ruimte bestaan waarin die betrokke metriese ruimte dig bevat word. In hierdie werkstuk beskryf ons sogenaamde hiperkonvekse ruimtes. Dit gee ’n konstruksie wat blyk om meer algemeen te wees, maar steeds gunstige eienskappe het. Hiermee kan nie-uitbreidende, oftewel afbeeldings wat nie afstande rek nie, uitgebrei word sodanig dat die eienskappe van die ruimte waarop dit gedefinieer is nie ’n rol speel nie. In die besonder kan stellings van die Hahn- Banach-tipe afgelei word vir genormeerde ruimtes en sekere addisionele ressultate ondere vastepuntstellings kan bewys word. Ons hoofdoel is om hiperkonvekse ruimtes te ondersoek. In die besonder toon ons aan dat die klas van alle hiperkonvekse ruimtes net so groot soos die klas van alle metriese ruimtes is.

Thesis (MSc (Mathematics))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Within lattice theory, an interesting question asked is whether a given abstract lattice may be represented concretely as subsets of a closure system on a topological space. This is true for boolean algebras, bounded distributive lattices and arbitrary bounded lattices. In particular, there are a multitude of ways to represent bounded lattices. We present some of these ideas, as well as an analysis of the differences between them. We further investigate the attempts that were made to extend the above representations to lattices endowed with operators, in particular the work done on bounded distributive lattices with operators. We then make a new contribution by extending this work to arbitrary bounded lattices with operators. We also show that the so-called sufficiency operator has a relational representation in the bounded lattice case. / AFRIKAANSE OPSOMMING: Binne die raamwerk van tralie teorie word die vraag soms gevra of ’n gegewe tralie konkreet veteenwoordig kan word as subversamelings van ’n afsluitingssisteem op ’n topologiese ruimte. Die voorgenoemde is waar vir, onder andere, boolse algebras, begrensde distributiewe tralies en algemene begrensde tralies. Daar is veral vir begrensde tralies menigte maniere om hul te verteenwoordig. Ons bied sommige van hierdie idees voor, asook ’n analiese van die verskille daarin teenwoordig. Verder ondersoek ons ook sommige van die maniere waarop tralies tesame met operatore verteenwoordig kan word. Ons sal spesiale aandag gee aan distributiewe tralies met operatore, soos gedoen in, met die idee om die voorgenoemde uit te brei na algemene begrensde tralies met operatore. Ons toon dan verder aan dat die sogenoemde voldoende operator ook ’n relasionele verteenwoordiging het in die begrensde tralie geval.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Barrier options are options whose payoff depends on whether or not the underlying asset price hits a certain level - the barrier - during the life of the option. Closed-form solutions for the prices of these path-dependent options are available in the Black-Scholes framework. It is well{known, however, that the Black-Scholes model does not price even the so-called vanilla options correctly. There are a number of popular asset price models based on exponential Lévy dynamics which are all able to capture the volatility smile, i.e. reproduce market-observed prices of vanilla options. This thesis investigates the potential model risk associated with the pricing of barrier options in several exponential Lévy models. First, the Variance Gamma, Normal Inverse Gaussian and CGMY models are calibrated to market-observed vanilla option prices. Barrier option prices are then evaluated in these models using Monte Carlo methods. The prices obtained are then compared to each other, as well as the Black-Scholes prices. It is observed that the different exponential Lévy models yield barrier option prices which are quite close to each other, though quite different from the Black-Scholes prices. This suggests that the associated model risk is low. / AFRIKAANSE OPSOMMING: Versperring opsies is opsies met 'n afbetaling wat afhanklik is daarvan of die onderliggende bateprys 'n bepaalde vlak - die versperring - bereik gedurende die lewe van die opsie, of nie. Formules vir die pryse van sulke opsies is beskikbaar binne die Black-Scholes raamwerk. Dit is egter welbekend dat die Black-Scholes model nie in staat is om selfs die sogenaamde vanilla opsies se pryse korrek te bepaal nie. Daar bestaan 'n aantal populêre bateprysmodelle gebaseer op eksponensiële Lévy-dinamika, wat almal in staat is om die mark-waarneembare vanilla opsie pryse te herproduseer. Hierdie tesis ondersoek die potensiële modelrisiko geassosieer met die prysbepaling van versperring opsies in verskeie eksponseniële Lévy-modelle. Eers word die Variance Gamma{, Normal Inverse Gaussian- en CGMY-modelle gekalibreer op mark-waarneembare vanilla opsiepryse. Die pryse van versperring opsies in hierdie modelle word dan bepaal deur middel van Monte Carlo metodes. Hierdie pryse word dan met mekaar vergelyk, asook met die Black-Scholespryse. Dit word waargeneem dat die versperring opsiepryse in die verskillende eksponensiële Lévymodelle redelik na aan mekaar is, maar redelik verskil van die Black-Scholespryse. Dit suggereer dat die geassosieerde modelrisiko laag is.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: It is well known that the ring of integers Z and the ring of polynomials A = Fr[T] over a finite field Fr have many properties in common. It is due to these properties that almost all the famous (multiplicative) number theoretic results over Z have analogues over A. In this thesis, we are devoted to utilising this analogy together with the theory of Carlitz modules. We do this to survey and compare the analogues of cyclotomic polynomials, the size of their coefficients and cyclotomic extensions over the rational function field k = Fr(T). / AFRIKAANSE OPSOMMING: Dit is bekend dat Z, die ring van heelgetalle en A = Fr[T], die ring van polinome oor ’n eindige liggaam baie eienskappe in gemeen het. Dit is as gevolg van hierdie eienskappe dat feitlik al die bekende multiplikative resultate wat vir Z geld, analoë in A het. In hierdie tesis, fokus ons op die gebruik van hierdie analogie saam met die teorie van die Carlitz module. Ons doen dit om ’n oorsig oor die analoë van die siklotomiese polinome, hul koëffisiënte, en siklotomiese uitbreidings oor die rasionele funksie veld k = Fr(T).

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Biofilms are aggregations of bacteria that can thrive wherever there is a watersurface or water-interface. Sometimes they can be beneficial; for example, biofilms are used in water and waste-water treatment. The filter used to remove contaminants acts as a scaffold for microbial attachment and growth. However, biofilms could have bad effects, especially on a persons health. They can cause chronic diseases and serious infections. The importance of biofilms in industrial and medical settings, is the main reason of the mathematical studies performed up to now, concerning biofilms. Biofilms have been mathematical modelling targets over the last 30 years. The complex structure and growth of biofilms make them difficult to study. Biofilm formation is a multi-stage process and occurs in even the most unlikely of environmental conditions. Models of biofilms vary from the discrete to the continuous; accounting for one-species to multi-species and from one-scale to multi-scale models. A model may even have both discrete and continuous parts. The implication of these differences is that the tools used to model biofilms differ; we present and review some of these models. The aim in this thesis is to model the early initiation of biofilm formation. This stage involves bacterial movement towards a surface and the attachment to the boundary which seeds a biofilm. We use a diffusion equation to describe a bacterial random walk and appropriate boundary conditions to model surface attachment. An analytical solution is obtained which gives the bacterial density as a function of position and time. The model is also analysed for stability. Independent of this model, we also give a reaction diffusion equation for the distribution of sensing molecules, accounting for production by the bacteria and natural degradation. The last model we present is of Keller-Segel type, which couples the dynamics of bacterial movement to that of the sensing molecules. In this case, bacteria perform a biased random walk towards the sensing molecules. The most important part of this chapter is the derivation of the boundary conditions. The adhesion of bacteria to a surface is presented by zero-Dirichlet boundary conditions, while the equation describing sensing molecules at the interface needed particular conditions to be set. Bacteria at the boundary also produce sensing molecules, which may then diffuse and degrade. In order to obtain an equation that includes all these features we assumed that mass is conserved. We conclude with a numerical simulation. / AFRIKAANSE OPSOMMING: Biofilms is die samedromming van bakterieë wat kan floreer waar daar ’n wateroppervlakte of watertussenvlak is. Soms kan hulle voordelig wees, soos byvoorbeeld, biofilms word gebruik in water en afvalwater behandeling. Die filter wat gebruik word om smetstowwe te verwyder, dien as ’n steier vir mikrobiese verbinding en groei. Biofilms kan ook egter slegte gevolge he, veral op ’n persoon se gesondheid. Hulle kan slepende siektes en ernstige infeksies veroorsaak. Die belangrikheid van biofilms in industriële en mediese omgewings, is die hoof rede vir die wiskundige studies wat tot dusver uitgevoer is met betrekking tot biofilms. Biofilms is oor die afgelope 30 jaar al ’n teiken vir wiskundige modellering. Die komplekse struktuur en groei van biofilms maak dit moeilik om hul te bestudeer. Biofilm formasie is ’n multi-fase proses, en gebeur selfs in die mees onwaarskynlikste omgewings. Modelle wat biofilms beskryf wissel van die diskreet tot die kontinu, inkorporeer een of meer spesies, en strek van eentot multi-skaal modelle. ’n Model kan ook oor beide diskreet en kontinue komponente besit. Dit beteken dat die tegnieke wat gebruik word om biofilms te modelleer ook verskil. In hierdie proefskrif verskaf ons ’n oorsig van sommige van hierdie modelle. Die doel in hierdie proefskrif is om die vroeë aanvang van biofilm ontwikkeling te modeleer. Hierdie fase behels ’n bakteriële beweging na ’n oppervlak toe en die aanvanklike aanhegsel wat sal ontkiem in ’n biofilm. Ons gebruik ’n diffusievergelyking om ’n bakteriële kanslopie te beskryf, met geskikte randvoorwaardes. ’n Analities oplossing is verkry wat die bakteriële bevolkingsdigtheid beskryf as ’n funksie van tyd en posisie. Die model is ook onleed om te toets vir stabiliteit. Onafhanklik van die model, gee ons ook ’n reaksiediffusievergelyking vir die beweging van waarnemings-molekules, wat insluit produksie deur die bakterieë en natuurlike afbreking. Die laaste model wat ten toon gestel word is ’n Keller-Segel tipe model, wat die bakteriese en waarnemings-molekule dinamika koppel. In hierdie geval, neem die bakterieë ’n sydige kanslopie agter die waarnemings molekules aan. Die belangrikste deel van hierdie hoofstuk is die afleiding van die randvoorwaardes. Die klewerigheid van die bakterieë tot die oppervlak word vvorgestel deur nul-Dirichlet randvoorwaardes, terwyl die vergelyking wat waarnemingsmolekule gedrag by die koppelvlak beskryf bepaalde voorwaardes nodig het. Bakterieë op die grensvlak produseer ook waarnemings-molekules wat diffundeer en afbreek. Om te verseker dat al hierdie eienskappe omvat is in ’n vergelyking is die aanname gemaak dat massa behoud bly. Ter afsluiting is numeriese simulasie van die model gedoen.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Substance abuse is an imminent danger on the health of both substance users and nonusers. In general, abuse of psychoactive substances is associated with high risk behaviour, mortality and morbidity. The drug use cycle involves inextricably intertwined variants such as production, trading and usage of both licit and illicit addictive substances. The dynamics of substance use involve initiation, addiction, rehabilitation/treatment and quitting/ recovery. In response to supply and abuse of monster drugs, control strategies such as law enforcement and rehabilitation have been stepped up to reduce access to drugs by targeting drug kingpins and harm reduction respectively. In this thesis, we model the factors affecting the prevalence of substance abuse, the effect of drug lords on the prevalence of substance abuse, and the impact of substance abuse on the prevalence of HIV/AIDS. We formulate mathematical models based on systems of autonomous differential equations describing the dynamics of the sub- populations involved in the drug using cycle. We examine the effects of amelioration, rehabilitation/treatment and re- initiation on the prevalence of substance abuse. Our results suggest that, recruitment into rehabilitation and amelioration in the presence of quitting for light users reduce the prevalence of substance abuse; re-initiation and amelioration without quitting for light users increase the prevalence of substance abuse. Our assessment of the impact of drug lords and the effect of law enforcement on drug epidemics shows that, the presence of drug lords seriously constraints the efforts to reduce substance abuse since they increase access to drugs. However, law enforcement if stepped up in response to the population of drug lords, greatly reduces the prevalence of substance abuse. Given the associated influence of drugs on high risky behaviour, as a cofactor for sexually transmitted infections, we assess the influence of substance abuse on the prevalence of Human Immunodeficiency Virus (HIV). Our results show that dissemination of information regarding HIV and drug use reduces HIV prevalence whereas, there is faster spread of the epidemic and high prevalence with increased sexual contact. / AFRIKAANSE OPSOMMING: Dwelmmisbruik is ’n dreigende gevaar vir die gesondheid van beide dwelm gebruikers en nie-gebruikers. In die algemeen, word die misbruik van psigoaktiewe dwelms verbind met hoë risiko gedrag, mortaliteit en morbiditeit. Die dwelmgebruikskringloop behels onlosmaaklik vervlegde variante soos vervaardiging, handel en gebruik van beide wettige en onwettige verslawende middels. Die dinamika van dwelms behels aanvang, verslawing, rehabilitasie/ behandeling en staking/herstel. In reaksie op die misbruik en verskaffing van monster dwelms, is beheer strategieë soos wetstoepassing en rehabilitasie verskerp, om die toegang tot dwelms te verminder, deur onderskeidelik te fokus op dwelmspilfigure en skadebeperking. Die belangrikste doel van hierdie verhandeling is om die faktore te modelleer wat die voorkoms van dwelmmisbruik beïnvloed, die uitwerking van dwelmbase op die voorkoms van dwelmmisbruik, en die trefkrag van dwelmmisbruik op die voorkoms van MIV / VIGS. Ons formuleer wiskundige modelle gegrond op stelsels van outonome differensiaalvergelykings, wat die dinamika beskryf van die sub-bevolkinge wat in die dwelmgebruikskringloop betrokke is. Ons ondersoek die effekte van verbetering, rehabilitasie/behandeling en heraanvang op die voorkoms van dwelmmisbruik. Ons resultate dui dat, werwing tot rehabilitasie en verbetering in die teenwoordigheid van stakende tydelike verbruikers, die voorkoms van dwelmmisbruik verminder; heraanvang en verbetering sonder dat tydelike verbruikers staak, verhoog die voorkoms van dwelmmisbruik. Ons raming van die invloed van dwelmbase en die uitwerking van wetstoepassing op dwelm-epidemies toon dat, die teenwoordigheid van dwelmbase belemmer grotendeels die pogings om dwelmmisbruik te verminder, aangesien hulle toegang tot dwelms verhoog. Nietemin, as die wetstoepassing verskerp word in reaksie op die dwelmbaasbevolking, word die voorkoms van dwelmmisbruik aansienlik verminder. Gegewe die gepaardgaande invloed van dwelms op hoë risiko gedrag as ’n kofaktor vir seksueel oordraagbare infeksies, beraam ons die invloed van dwelmmisbruik op die voorkoms van die Menslike Immunogebreksvirus (MIV). Ons resultate toon dat inligtingverspreiding rakende MIV en dwelmgebruik, MIV-voorkoms verlaag, terwyl daar ’n vinniger verspreiding van die epidemie en hoë voorkoms is, met verhoogde seksuele kontak.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: We consider the utility portfolio optimization problem of an investor whose activities are influenced by an exogenous financial risk (like bad weather or energy shortage) in an incomplete financial market. We work with a fairly general non-Markovian model, allowing stochastic correlations between the underlying assets. This important problem in finance and insurance is tackled by means of backward stochastic differential equations (BSDEs), which have been shown to be powerful tools in stochastic control. To lay stress on the importance and the omnipresence of BSDEs in stochastic control, we present three methods to transform the control problem into a BSDEs. Namely, the martingale optimality principle introduced by Davis, the martingale representation and a method based on Itô-Ventzell’s formula. These approaches enable us to work with portfolio constraints described by closed, not necessarily convex sets and to get around the classical duality theory of convex analysis. The solution of the optimization problem can then be simply read from the solution of the BSDE. An interesting feature of each of the different approaches is that the generator of the BSDE characterizing the control problem has a quadratic growth and depends on the form of the set of constraints. We review some recent advances on the theory of quadratic BSDEs and its applications. There is no general existence result for multidimensional quadratic BSDEs. In the one-dimensional case, existence and uniqueness strongly depend on the form of the terminal condition. Other topics of investigation are measure solutions of BSDEs, notably measure solutions of BSDE with jumps and numerical approximations. We extend the equivalence result of Ankirchner et al. (2009) between existence of classical solutions and existence of measure solutions to the case of BSDEs driven by a Poisson process with a bounded terminal condition. We obtain a numerical scheme to approximate measure solutions. In fact, the existing self-contained construction of measure solutions gives rise to a numerical scheme for some classes of Lipschitz BSDEs. Two numerical schemes for quadratic BSDEs introduced in Imkeller et al. (2010) and based, respectively, on the Cole-Hopf transformation and the truncation procedure are implemented and the results are compared. Keywords: BSDE, quadratic growth, measure solutions, martingale theory, numerical scheme, indifference pricing and hedging, non-tradable underlying, defaultable claim, utility maximization. / AFRIKAANSE OPSOMMING: Ons beskou die nuts portefeulje optimalisering probleem van ’n belegger wat se aktiwiteite beïnvloed word deur ’n eksterne finansiele risiko (soos onweer of ’n energie tekort) in ’n onvolledige finansiële mark. Ons werk met ’n redelik algemene nie-Markoviaanse model, wat stogastiese korrelasies tussen die onderliggende bates toelaat. Hierdie belangrike probleem in finansies en versekering is aangepak deur middel van terugwaartse stogastiese differensiaalvergelykings (TSDEs), wat blyk om ’n onderskeidende metode in stogastiese beheer te wees. Om klem te lê op die belangrikheid en alomteenwoordigheid van TSDEs in stogastiese beheer, bespreek ons drie metodes om die beheer probleem te transformeer na ’n TSDE. Naamlik, die martingale optimaliteits beginsel van Davis, die martingale voorstelling en ’n metode wat gebaseer is op ’n formule van Itô-Ventzell. Hierdie benaderings stel ons in staat om te werk met portefeulje beperkinge wat beskryf word deur geslote, nie noodwendig konvekse versamelings, en die klassieke dualiteit teorie van konvekse analise te oorkom. Die oplossing van die optimaliserings probleem kan dan bloot afgelees word van die oplossing van die TSDE. ’n Interessante kenmerk van elkeen van die verskillende benaderings is dat die voortbringer van die TSDE wat die beheer probleem beshryf, kwadratiese groei en afhanglik is van die vorm van die versameling beperkings. Ons herlei ’n paar onlangse vooruitgange in die teorie van kwadratiese TSDEs en gepaartgaande toepassings. Daar is geen algemene bestaanstelling vir multidimensionele kwadratiese TSDEs nie. In die een-dimensionele geval is bestaan ââen uniekheid sterk afhanklik van die vorm van die terminale voorwaardes. Ander ondersoek onderwerpe is maatoplossings van TSDEs, veral maatoplossings van TSDEs met spronge en numeriese benaderings. Ons brei uit op die ekwivalensie resultate van Ankirchner et al. (2009) tussen die bestaan van klassieke oplossings en die bestaan van maatoplossings vir die geval van TSDEs wat gedryf word deur ’n Poisson proses met begrensde terminale voorwaardes. Ons verkry ’n numeriese skema om oplossings te benader. Trouens, die bestaande self-vervatte konstruksie van maatoplossings gee aanleiding tot ’n numeriese skema vir sekere klasse van Lipschitz TSDEs. Twee numeriese skemas vir kwadratiese TSDEs, bekendgestel in Imkeller et al. (2010), en gebaseer is, onderskeidelik, op die Cole-Hopf transformasie en die afknot proses is geïmplementeer en die resultate word vergelyk.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: For solid tumours to grow and metastise, they need to pass through two distinct stages: the avascular growth phase in which the tumour remains in a limited diffusion size and the vascular growth phase where the invasion may take place. In order to accomplish the transition from the former to the latter growth phase, a solid tumour may secrete a substance known as tumour angiogenesis factor (TAF) into the surrounding tissues to stimulate its own blood vessels. Once the tumour has its own blood supply, it can invade other parts of the body destroying healthy tissues organs by secreting the matrix degrading enzymes (MDE). During the invasion, the adhesion both cell-cell and cell-matrix play an extremely important role. In this work, we review some mathematical models dealing with various stages of development of solid tumours and the resulting reaction diffusion equations are solved using the Crank-Nicolson finite differences scheme. We also present a system of reaction-diffusion-taxis partial differential equations, with nonlocal (integral) terms describing the interactions between cancer cells and the host tissue. We then investigate the local and global existence of the solution of the previous model using the semigroup method and Sobolev embeddings. / AFRIKAANSE OPSOMMING: Daar is twee afsonderlike fases nodig vir soliede kanker gewasse om te groei en kwaadaardig te word: die avaskulêre groeifase waarin die gewas tot ’n sekere diffusie grootte beperk word en die vaskulêre groei fase waar die indringing plaasvind. Ten einde die oorgang tussen die twee fases te bewerkstellig, skei die soliede gewas ân stof in die omliggende weefsel af wat bekend staan as âtumor angiogenese factorâ (TAF). Dit stimuleer die vorming van die gewas se eie bloedvate. Wanneer die gewas sy eie bloedtoevoer het, kan dit ander dele van die liggaam indring en gesonde orgaanweefsel vernietig deur die afskeiding van die âmatrix degrading enzymesâ (MDE). Gedurende hierdie proses speel die sel-sel en sel-matriks interaksies ân belangrike rol. In hierdie werk het ons ân paar wiskundige modelle vergelyk wat die verskillende stadiums van die ontwikkeling van soliede gewasse beskryf. Die gevolglike diffusiereaksie vergelykings is opgelos deur gebruik te maak van die âCrank-Nicolson finite differences schemeâ. Ons bied ook ’n stelsel van âreaction-diffusion-taxisâ, met nie-lokale (integrale) terme wat die interaksies tussen kankerselle en die gasheerweefsel beskryf. Ons stel dan ondersoek in na die lokale en globale bestaan van die oplossing van die vorige model, met behulp van die semi-groep metode en die Sobolev ingebeddings.

Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: While research and population surveys in HIV/AIDS are well established in developed countries, Sub-Saharan Africa is still experiencing scarce HIV/AIDS information. Hence it depends on results obtained from models. Due to this dependence, it is important to understand the strengths and limitations of these models very well. In this study, a simple mathematical model is formulated and then extended to incorporate various features such as stages of HIV development, time delay in AIDS death occurrence, and risk groups. The analysis is neither purely mathematical nor does it concentrate on data but it is rather an exploratory approach, in which both mathematical methods and numerical simulations are used. It was found that the presence of stages leads to higher prevalence levels in a short term with an implication that the primary stage is the driver of the disease. Furthermore, it was found that time delay changed the mortality curves considerably, but it had less effect on the proportion of infectives. It was also shown that the characteristic behaviour of curves valid for most epidemics, namely that there is an initial increase, then a peak, and then a decrease occurs as a function of time, is possible in HIV only if low risk groups are present. It is concluded that reasonable or quality predictions from mathematical models are expected to require the inclusion of stages, risk groups, time delay, and other related properties with reasonable parameter values. / AFRIKAANSE OPSOMMING: Terwyl navorsing en bevolkingsopnames oor MIV/VIGS in ontwikkelde lande goed gevestig is, is daar in Afrika suid van die Sahara slegs beperkte inligting oor MIV/VIGS beskikbaar. Derhalwe moet daar van modelle gebruik gemaak word. Dit is weens hierdie feit noodsaaklik om die moontlikhede en beperkings van modelle goed te verstaan. In hierdie werk word ´n eenvoudige model voorgelˆe en dit word dan uitgebrei deur insluiting van aspekte soos stadiums van MIV outwikkeling, tydvertraging by VIGS-sterftes en risikogroepe in bevolkings. Die analise is beklemtoon nie die wiskundage vorme nie en ook nie die data nie. Dit is eerder ´n verkennende studie waarin beide wiskundige metodes en numeriese simula˙sie behandel word. Daar is bevind dat insluiting van stadiums op korttermyn tot ho¨er voorkoms vlakke aanleiding gee. Die gevolgtrekking is dat die primˆere stadium die siekte dryf. Verder is gevind dat die insluiting van tydvestraging wel die kurwe van sterfbegevalle sterk be¨ınvloed, maar dit het min invloed op die verhouding van aangestekte persone. Daar word getoon dat die kenmerkende gedrag van die meeste epidemi¨e, naamlik `n aanvanklike styging, `n piek en dan `n afname, in die geval van VIGS slegs voorkom as die bevolking dele bevat met lae risiko. Die algehele gevolgtrekking word gemaak dat vir goeie vooruitskattings met sinvolle parameters, op grond van wiskundige modelle, die insluiting van stadiums, risikogroepe en vertragings benodig word.