Science PhD degrees awarded in March 2011
PhD grade toegeken in Maart 2011
AMER, Ismael (Polimeerwetenskap)
Molecular weight effects on crystallization of polypropylene.
The use of fractionation techniques for semicrystalline polymers like polypropylene is quite common. It is generally accepted that the fractionation by crystallizability of polypropylene is dependent only on the degree of isotacticity of the polymer. Crystallization phenomena was dependent on both molecular weight and isotacticity, and that the effect differed of molecular weight from crystallization in the bulk to that in solution. This finding significantly affects the way that results of fractionation experiments should be interpreted, as these results are often used to relate structure and properties of these polymers.
Promotor: Prof AJ van Reenen
AKHURST, Timothy John (Biochemie)
Symbolic control analysis of cellular systems.
Metabolic Control Analysis (MCA) provides a powerful quantitative framework for analysing control and regulation in cellular systems. Using algebraic computation, a general implementation of the symbolic matrix inversion of MCA was presented requiring only the system stoichiometry and any allosteric interactions as input. The algebraic expressions generated allow an in-depth analysis of the control distribution within a system and of the parameters which exhibit the greatest effect on this distribution. By quantifying the control patterns or “routes of regulation”, perturbations and their propagation were investigated through a cellular system by which regulatory pathways are favoured under changing conditions.
Promotor: Prof JM Rohwer
Medepromotor: Prof J-HS Hofmeyr
BAZELET, Corinna S (Entomologie)
Grasshopper bioindicators of effective large-scale ecological networks.
With so much pressure on the environment, sustainable ways forward for wood production the need to be found. The requirements for timber products must be coupled with the sustainable setting aside of land to maintain ecological processes and to conserve biodiversity. This can be done by creating large networks of natural land among blocks of plantation trees. To do this effectively a yardstick is required to indicate that our design and management decisions are the right ones. This study found that grasshoppers are excellent indicators of good conservation, and have now been developed into a practical management tool for modern forestry.
Promotor: Prof M.J. Samways
DE VILLIERS, David (Fisika)
Characterisation of heavy mineral sands and soils by radiometry and its use in mineral beneficiation and agriculture.
Radioactivity is well known and well understood, but its usefulness in industrial applications to optimise processes or increase economic viability is not yet fully utilised by many industries. Focuses on the application of radiometry was applied in heavy mineral separation and vineyard soil classification. Compared to current quality control measures, novel results were obtained that show that radiometry can make a major contribution in monitoring, relatively cheaply, the product quality in a heavy mineral separation plant.
Promotor: Dr JA Stander
Medepromotor: Prof A Roozendaal
EYÉGHÉ-BICKONG, Hans André (Biochemie)
Role of surfactin from Bacillus subtilis in protection against antimicrobial peptides produced by selected Bacillus species.
Cohabiting soil bacteria elicit resistance mechanisms which generally entails neutralization or antagonism of a competitor’s antibiotics. Bacillus subtilis, producing the peptide surfactin, is able to cohabitate with bacteria producing the lytic antibiotic peptides, gramicidin S and the tyrocidines. Surfactin acts antagonistically towards the activity of these antibiotic peptides, by inducing protective biofilms in B subtilis and forming inactive complexes with the antibiotic peptides. This may explain the ability of B. subtilis to cohabitate with bacteria producing the lytic peptides. The loss of antimicrobial activity of soil containing surfactin producers may lead to the survival of plant pathogens detrimental to agriculture.
Promotor: Prof M Rautenbach
FOURIE, Frana (Dierkunde)
Evaluating earthworm responses on various organisational levels for use in a species sensitivity model for ecological risk assessment in soils.
Sensitiwiteit vir toksiese stowwe verskil tussen spesies van grondorganismes. Spesiesensitiwiteits indekse word, tydens ekologiese risikobepaling, as maatstaf gebruik om te bepaal of bepaalde gifstowwe in die grond nadelig sal wees vir ‘n kritiese persentasie van aanwesige spesies. Tydens hierdie studie is die moontlike gebruik van suborganismiese biomerkertoetse, as meer sensitiewe maatstawwe van sensitiwiteit, in teenstelling tot lewensloop eienskappe en mortaliteit, ondersoek. Vyf erdwurmspesies, waaronder uitheemse sowel as endemiese, was aan ‘n fungisied, koperoksichloried, wat algemeen in wingerde gespuit word, blootgestel. Die bevinding is gemaak dat die biomerkertoetse, wat meer sensitief is vir lae konsentrasies van toksikante, wel bruikbaar is in spesiesensitiwiteitsmodelle.
Promotor: Prof SA Reinecke
Medepromotor: Prof AJ Reinecke
GEETS, Sjirk (Ekologie)
Assembly and disassembly of bird pollination communities at the Cape of Africa.
The question of how pollination structures plant and bird communities at the Cape of Africa was addressed. Bird-plant pollination mutualisms were an important ecological factor structuring Proteaceae and nectar-feeding bird communities, suggesting an important role for community wide pollination mutualisms. These mutualistic communities are disassembled through the anthropogenic impacts of beekeeping, roads, habitat fragmentation, fire frequencies and invasive alien plants. By linking pollination and plant demography, the future of plant population could be predicted and illustrate that the disassembly of bird pollination communities only becomes important for plant persistence once the mutualism has almost entirely broken down.
Promotor: Dr A Pauw
HARBRON, Jannetta (Fisiologiese Wetenskappe)
The association between genotype and BMI, health and lifestyle indicators as well as weight loss outcomes in overweight/obese Caucasian adults.
Seven polymorphisms were investigated in overweight/obese Causasian adults. GNB3 C825T was associated with triglyceride and glucose levels and metabolic syndrome. Mutant allele carriers of FTO rs 1421085/rs17817449 had poorer eating behaviours and higher intake of high-fat foods. Mutant allele carriers of FTO rs 17817449 and ADRB2 Arg16Gly and subjects with both the mutant alleles of INSIG2 rs 7566605 and ADRB2 Arg16Gly lost less weight on a six month weigh loss program. Improved eating behaviour in wild-type homozygotes of FTO rs1421085 was associated with better weight loss. The FTO results add novel insights into a growing body of evidence that this gene plays a role in obesity management.
Promotor: Prof M Senekal
Medepromotor: Prof M Zaahl
HLALELE, Lebohang (Polimeerwetenskap)
Kinetic and mechanistiv features of nitroxide-mediated (co)polymerization.
Polymers play an essential role in modern life. They are used for increasingly sophisticated applications. The consequence is that accurate control over the structure of the polymers is of utmost importance in this project. New techniques were used to obtain detailed information regarding the polymerization processes of styrene, n-butyl acrylate (BA) and their copolymerization. Specifically, Nitroxide Mediated Polymerization (NMP) was used, where a variety of in situ NMR techniques were utilized. Remarkable discoveries in his work included the independence of polymerization rate on the initiator concentration in the homopolymerization of BA. Several previously unknown rate parameters were measured.
Promotor: Prof L Klumperman
JOOSTE, Anna Elizabeth Catharina (Genetika)
Identification and molecular characterization of three genetic variants of grapevine leafroll-associated virus 3 (GLRaV-3) from South African vineyards and their spread in local vineyards.
Leafroll disease is one of the most destructive diseases of grapevines worldwide, and is spreading rapidly in South African vineyards. The ampelovirus, Grapevine leafroll-assoociated virus 3 is considered the primary cause of this disease. Whole-genome sequencing of three genetic variants of this virus that were identified in local vineyards and revealed significant variantion in the 5’ untranslated region of the genome. The significance of this finding still needs to be resolved. Multi-season surveys showed that variant group II occurs predominantly in the vineyard studied and that the spread of variants within disease clusters did not follow expected patterns. The understanding of the genetic diversity of GLRaV-3 in local vineyards has been advanced, allowing the development of diagnostics and effective management programmes for the disease.
Promotor: Prof JT Burger
Medepromotor: Dr DE Goszczynski
KEYSTER, Marshall (Plantbiotegnologie)
Nitric oxide-mediated signalling in legumes and its role in maize responses to salt stress.
Signalling roles were investigated of nitric oxide (NO) in regulating root nodule development and root nodule functioning, extending it to regulation of plant responses to salt stress. It was established that NO is required for nodule development and functioning and also shows that NO enhances plant salt tolerance when applied exogenously. The findings have far-reaching impact on future biotechnological approaches for enhancing legume crop productivity.
Promotor: Dr. N. N. Ludidi
KRIEL, Johannes Nicolaas (Fisika)
A duality construction for interacting quantum hall systems.
The fractional quantum Hall effect presents a prime example of a strongly interacting quantum many body system where standard perturbative approaches fail. Yet, a dual description in terms of weakly interacting composite fermions has been applied very successfully to describe this system. The microscopic underpinning of this dual picture is after 30 years still an outstanding problem. This problem is addressed in a rigorous mathematical setting. Within this framework simple analytic expressions for the gaps are derived for the first time. These agree within a few percent with the values obtained from extensive numerical calculations.
Promotor: Prof FG Scholtz
Medepromotor: Prof HB Geyer
KRUGER, Maria Jacoba (Fisiologiese Wetenskappe)
Immune and satellite cells: important role players in muscle recovery after injury.
Physiological effects of both acute and chronic oral consumption of grape seed extract were investigated in an in vivo model of skeletal muscle injury. Results indicated that faster recovery was facilitated by grape seed-derived procyanidolic oligomers (PCO’s) via increased activation and recruitment of muscle satellite cells into the injured tissue to facilitate healing, as well as by modulation of the inflammatory response to injury. Subsequent cell culture-based assays further elucidated PCO’s effects on inflammation: firstly, neutrophil migration into the injured tissue was inhibited and secondly, data suggest an earlier switch in tissue macrophage phenotype to achieve an anti-inflammatory micro-environment.
Promotor: Dr C Smith
Medepromotor: Prof KH Myburgh
MALGAS-ENUS, Rehana (Chemie)
The preparation and characterization of multinuclear catalysts based on novel dendrimers: Application in the oligomerization and polymerization of unsaturated hydrocarbons.
The development of new synthetic protocols to produce a series of nickel complexes based on novel dendritic ligands was described. The evaluation of these complexes as catalysts in the oligomerization and polymerization of unsaturated hydrocarbons is also reported. The work provides significant insight into the behaviour of multinuclear catalysts and represents one of the few examples where dendritic catalysts are employed in selective oligomerization of alkenes. This is significant in that it provides us with a means of producing highly sought-after feedstocks for the chemical industry in a more controlled fashion.
Promotor: Prof SF Mapolie
MALHERBE, Sulette (Wynbiotegnologie)
Investigation of the impact of commercial malolactic fermentation starter cultures on red wine aroma compounds, sensory properties and consumer preference.
Appelmelksuurgisting is ’n belangrike suurstabiliserende stap in rooiwynbereiding.’n Onbekende aspek, naamlik die impak van appelmelksuurkulture op die aroma en mondgevoel van wyn, was ondersoek. Die bydrae van vier kommersiële appelmelksuurkulture tot sensoriese en chemiese eienskappe van eksperimentele wyne, is bestudeer. ’n Chemies-analitiese platform is geskep vir intensiewe karakterisering van kwaliteitsbepalende wyngeurkomponente. Sensoriese evaluerings het kultuurspesifieke vegetatiewe en vrugtige karakters in die wyne aangetoon, terwyl verbruikerstudies die intrinsieke faktore wat verbruikervoorkeure vir bepaalde wynstyle beinvloed, uitgelig het. ’n Baie waardevolle bydrae tot toekomstige sensoriese en verbruikerstudies op wyn, asook tot appelmelksuurgistingnavorsing is gemaak.
Promotor: Dr HH Nieuwoudt
Medepromotors: Prof M du Toit en Dr AGJ Tredoux
NOACH-PIENAAR, Lee-Ann (Soologie)
The effects of genotype and/or environment on the phenotypic expressions of mandibular gland signals in honeybees (Apis mellifera).
Unique characteristics, associated with reproductive dominance, enabled the establishment of Apis mellifera capensis workers as social parasites in colonies of A. mellifera. scutellata. Their production of queen like mandibular gland pheromones is a potential proximate factor in their success. The pheromone communication dilemma was addressed by investigating whether the phenotypic expression of mandibular gland signals in honeybee workers are under genetic and/or environmental influences. Mandibular gland pheromone production, linked to reproductive potential in honeybee workers, was determined by a combination of environmental and genetic factors. Adopting this integrated ecological, behavioural, and genetic approach contributed to a better understanding of socially regulated mechanisms underlying colony functioning and the disruption thereof. Promotor: Prof TC Wossler
RAAD, Darian Nicholas (Operasionele Navorsing)
Multi-objective optimisation of water distribution systems design using metaheuristics.
The problem of designing a water distribution system was considered under the competing objectives of cost minimization and reliability maximization, whilst satisfying hydraulic requirements. Numerous state-of-the-art multi-objective metaheuristics were investigated towards design optimization, including existing and novel algorithms. A systematic analysis using renowned benchmarks revealed that a hyperheuristic paradigm is superior to traditional methods for the design of large systems. The first rigorous scientific analysis of three popular reliability surrogate measures was conducted, evaluating designs on the basis of robustness under uncertain demands and pipe failures. The Network resilience measure was identified as the most practical reliability indicator for real-world water systems design.
Promotor: Prof JH van Vuuren
Medepromotor: Dr A Sinske
RETIEF, Liezel ((Chemie)
Analysis of vegetable oils, seeds and beans by TGA and NMR Spectroscopy.
New and rapid methods was developed for the determination of major fatty acid components in locally produced vegetable oils, including olive, marula nuts, apricot kernel, avocado pear and macadamia nut vegetable oils using quantitative 13C and 31P Nuclear Magnetic Resonance spectroscopy. Several edible oil-containing seeds and beans, including sesame, sunflower, poppy, and pumpkin seeds, as well as soy, mung, black and kidney beans were investigated by means of Thermo-gravimetric Analysis as well as solid-state 13C NMR spectroscopy, resulting in a new semi-quantitative method for the rapid estimation of the oil, protein and carbohydrate content of these seeds and beans. This technique can replace traditional time-consuming analytical methods for the determination of the major nutritional components of seeds and beans.
Promotor: Prof KR Koch
ROBERTSON, Steven (Biochemie)
Receptor concentration affects glucocorticoid action.
Glucocorticoid-receptor levels vary between tissues and individuals and are altered by physiological and pharmacological effectors. The implications of differences in glucocorticoid-receptor concentration were investigated and it was shown that positive cooperative ligand-binding and increased ligand-binding affinity occured at high levels of glucocorticoid-receptor and that this was linked to increased ligand-independent dimerization of the glucocorticoid-receptor. The downstream consequences of this behaviour include modulation of glucocorticoid-receptor nuclear localization, shifts in the potency and bio-character of transrepression and transactivation and ligand-independent transactivation of genes. These findings suggest an important mechanism of action through which the glucocorticoid-receptor is primed to respond to sub-saturating glucocorticoid concentrations and may explain the inter-individual as well as tissue specific responses to glucocorticoid treatment.
Promotor: Prof A Louw
Medepromotor: Prof JP Hapgood
STYGER, Gustav (Wyn Biotegnologie)
Elucidating the metabolic pathways responsible for higher alcohol production in Saccharomyces cerevisiae.
Yeast strains are responsible for alcoholic fermentation, but also produce many important aroma and flavour compounds which impact on the quality of wine. Different yeast strains produce different aroma profiles, but the genetic and metabolic regulations responsible for these differences are not understood. A systematic, large scale screening approach to identify genes that impact on the aroma production network. Ten genes were identified and, through genetic analysis, the genes were places within this complex metabolic network. This is the first report describing a direct screening approach for genes involved in secondary metabolism.
Promotor: Prof FF Bauer
SWEED, Muhamed (Polimeerwetenskappe)
Free volume properties of semi-crystalline polymers.
Free volume (or unoccupied space) is a fundamental property of polymer materials responsible for many of the unique properties of these materials. Positrons (anti-electrons) were used to probe the free volume properties of polymers using the positron annihilation lifetime spectroscopy technique. In the case of semi-crystalline polymers, there is the possibility of the formation, localization and subsequent annihilation of the ortho-positronium probe within different areas of the complex morphology. A detailed systematic study was carried out on selected semi-crystalline polymers to correlate the chain structure, morphology and physical properties of these materials. This has lead to a better understanding of the structure–property relationship in commercially important polyolefin materials.
Promotor: Prof PE Mallon
TALJAARD, Susan (Geografie en Omgewingstudie)
An implementation model for integrated coastal management in South Africa –from legislation to practice.
‘n Implementeringsmodel vir Geïntegreerde Kusbestuur (GKB), soos voorsien in die nasionale Kusbeleid en die Geïntegreerde Kusbestuurswet in Suid-Afrika word voorgestel. Die ontwerp kombineer paradigmas van ekosisteem-gebaseerde bestuur en ruimtelike beplanning met tradisionele probleem- of uitkoms-gebaseerde benaderings. Akteursbetrokkenheid, sektorgebaseerde bestuurstelsels, hulpbronvisie, hulpbrondoelwitte en ruimtelike soneringskomponente word binne interafhanklike hulpbron- en akteursiklusse vervat om ondoeltreffende operasionalisering van huidige beleid en wetgewing te ondervang. Netwerke vir wetenskaplike ondersteuning en ’n volhoubare finasiële ondersteuningsmeganisme is sleutelkomponente in die model. Die navorsing lewer twee hoofprodukte: ’n werkbare, wetenskaplik geloofwaardige GKB-impllementeringsmodel: en ’n proses vir die toekomstige verfyning van aanpasbare, land-spesifieke kusbestuursmodelle, insluitend veertien evalueringsmaatstawwe.
Promotor: Prof JH van der Merwe
VAN ZYL, Jacobus Visser (Wiskunde)
On the Latimer-MacDuffee Theorem for polynomials over finite fields.
Latimer & MacDuffee showed that there is a one-to-one correspondence between equivalence classes of matrices with a given minimum polynomial and equivalence classes of ideals of a certain ring. An algorithm were develop to produce a representative in each equivalence class of matrices taken over the ring of polynomials over a finite field. A modified version of the Latimer-MacDuffee theorem was proven which holds for proper equivalence classes of matrices an operation was define that makes the set of equivalence classes of matrices into an Abelian group, the class group.
Promotor: Prof F Breuer
VOUA OTOMO, Patricks (Plant en Dierkunde)
Stress responses of Eisenia andrei and Enchytraeus doerjesi (Oligochaeta) to combined effects of temperature and metal contamination.
The toxic effects of heavy metals on beneficial soil organisms were studied using life-cycle and biomarker parameters. Mixture interaction between cadmium (non-essential metal) and Zinc (essential metal) were investigated and modelled mathematically. A novel finding was the occurrence of a switch between synergism and antagonism, depending on either concentration or ratio between the substances. Experiments were done at different temperatures and showed that with a change in temperature the toxicity of substances and mixtures can change, indicating that changes in ambient temperature resulting from climate change could affect the toxicity of substances in the environment.
Promotor: Prof SA Reinecke
Medepromotor: Prof AJ Reinecke