Research Report for Masters degree Faculty of Health Sciences / Since the early 1980's, global trends in dental caries have indicated that 80% of the caries is present in approximately 20% of the population which suggests a variation in susceptibility to the disease. In Sub-Saharan Africa and in South Africa, caries prevalence has shown a downward trend in preschool and school children. The reasons for this decline are obscure and have not been attributed to dietary habit, oral hygiene, the use of fluoride dentrifices or to any public health prevention program. Furthermore, the numbers of mutans streptococci, a group of pathogens associated with dental caries, have remained similar in children with and without caries. This implies that good dental health is possible in the presence of high prevalence of mutans streptococci, but raises speculation that the decrease in dental caries, may be caused by a change in virulence of these strains. It is also unclear if these bacterial strains are acquired through inter-familial transmission or genetically altered by influences from the oral environment. This thesis reports the first studies of gene expression and bacterial virulence in relation to traditional African-foods using clinical isolates from South African children. To establish the source of transmission, the phenotype and genotype of mutans streptococci strains from 31, five-year-old black, and coloured, children and their mothers living in Gauteng were characterized. The children were examined for caries, and plaque and salivary samples collected from both the children and their mothers. Samples were selectively cultured for mutans streptococci, biochemically differentiated and the genetic diversity of these isolates determined by PCR-RFLP of the gtfB and gtfI glucosyltransferase virulence genes. Phenotyping showed that Streptococcus mutans were 90% (155/172) prevalent, but the detection of Streptococcus sobrinus was low and comprised 10% (17/172) of the remaining vii isolates. Twenty-six percent of S. mutans clinical isolates (41/155) did not metabolise melibiose and the gtfA gene encoding for the uptake of this sugar was absent in 26 of the 41 melibiose-negative strains. GtfB gene polymorphisms in S. mutans clinical isolates from the two ethnic populations and from caries-free and caries-active 5-year-old children were similar (Principal Components Analysis). However high genetic diversity was observed in S. mutans isolates, with 23 different gtfB amplitypes shown by PCR-RFLP analysis. Sixteen different gtfI amplitypes were indicated in S. sobrinus clinical strains. The percentage match between gtfB amplitypes (HaeIII enzyme digests) in the children and their mothers ranged from 3% to 9% in caries-free children and caries-active children, respectively. Identical gtfB amplitypes from melibiose-negative phenotypes were shared by four mothers and their children only. To determine the growth and virulence response of the variant mutans streptococci genotypes, six laboratory reference strains (NCTC) and five, clinical isolates were challenged to traditional African staple foods and food combinations. The bacteria were exposed in batch culture for 16 hours to maize, samp, brown bread, maize+milk+sugar, maize+gravy, samp+beans, brown bread+margarine+peanut butter, 3% sucrose and a synthetic complex medium, BHI+3% sucrose. Results showed that growth was slow in maize (5.6 h) and samp (5.7 h) indicated by the long doubling time and the low number of generations (g = 4.2; g = 3.6). Sufficient lactic and acetic acid was produced to drop the pH to below 5.7, the ‘critical’ level for enamel demineralisation during the fermentation of brown bread (5.37), bread+margarine+peanut butter (5.51) and 3% sucrose (5.32). Water-insoluble extracellular polysaccharides produced was significantly lower (P<0.05) in samp and maize and viii maize+milk+sugar, with most residual glucose found in BHI + 3% sucrose (1.61±0.52 mg/mL) and maize+gravy (0.51±0.61 mg/mL). Mean concentrations of extracellular protein ranged from a low of 0.015±0.007 mg/mL in samp+beans to a high of 0.29±0.16 mg/mL in BHI + 3% sucrose. The inherent pH of individual foods closest to neutral was: milk (7.0) beans (6.07), samp (6.20), maize (6.82) and peanut butter (6.90). However, beans (5.7×10 G3 [H%]), milk (5.1 ×10G3 [H ]) and peanut butter (4.0×10 [H ]) showed more efficient buffering, which in combination % G3 % with other food components, raised the inherent buffering capacity of the food. These mixed foods required a larger quantity of acid to be produced by bacterial metabolism to lower the pH to 5.7. A preliminary study on the effect of single foods on S. mutans gtfB gene expression showed that mRNA gtfB transcripts were mostly inhibited in clinical isolates, but not in reference strains. The gtfI gene of all S. sobrinus test strains was expressed in 3% sucrose and BHI+3% sucrose, but the response differed in the remaining foods.The statistically significant association shown between mutans streptococci phenotype, gtf gene expression and the food challenge (P<0.0001), verifies that expressed phenotypic characteristics is dependent on gene expression. The results presented in this thesis show that a high diversity of gtf genes exists in mutans streptococci clinical isolates from South African black African, and coloured, 5-year-old children and their mothers. However, no specific genotype was unique either to dental status or ethnic population, with children acquiring genotypes from other points of contact besidesthe mother. Furthermore, the growth and virulence response (acidogenesis, water-insoluble ECP) of S. mutans and S. sobrinus genotypes and reference strains are subject to the dietary nutrients available. The inherent buffering capacity of maize, samp, maize+milk+sugar, maize+gravy and samp+beans, coupled to a low sucrose content, make these foods non-caries promoting, but the ability of test bacteria to remain viable on these nutrients, indicate that the mutans streptococci have a natural adaptive ability to assimilate other nutrients as a source of carbon when sucrose is limited. The control of gtfB and gtfI gene expression by traditional African foods suggests that virulence of the mutans streptococci are influenced more by the dietary environment than by genotype. Also, the difference in virulence properties between clinical and laboratory reference strains indicate an attenuation in virulence of wild-type strains.

This thesis examines how designs based on a conjunction between craft and digital techniques may offer new possibilities for an architect or designer in contemporary practice. How is it relevant that what initially appear to be two distinct approaches to designing and making can be introduced to each other and coalesce to form a constructive attitude of mutually borrowed logic? The thesis champions the crafting of innovative design and the incorporation of digitally derived procedures that allow for globally efficient dissemination and malleability. Such procedures have occupied the practice of architecture and design for some time, giving rise to the current sobriquet of a 'post-digital age'. I propose that at this point in time we can usefully speculate on the relationship between physical making and computer-based production. Too often the stylistic overtures popularly attached to the terms 'digital' and 'craft' narrow our perception of what each term may encompass and how they are likely to manifest. Traditionally, digitally derived design practice is attributed the efficiency of a mathematically precise mode of operation - an oscillation between zeroes and ones that produces a universal logic of smoothly rendered forms. By contrast, 'craft' is often cast into the realm of amateurish making, complete with mistakes, dropped stitches, fingerprints or other traces of human fault that are understood as being charming in the context of handmade human endeavour yet fall short when measured against 'serious' artistic categories that include architecture, design and fine art. This thesis seeks to move beyond such accepted and somewhat polarised positions. First, the thesis offers clearer and more dynamic definitions of the terms 'craft' and 'digital', seeking the ability for each to hold fast to the inherent merits of their particular logic while also finding productive opportunities to integrate with each other. Second, the thesis examines how crafted production can combine with digital tools to offer a useful direction for contemporary design practice. Case studies of contemporary architects' and designers' works are drawn on to illustrate and make observations on the different relationships that the selected practitioners have discovered in their projects, all of which conjoin the conception and manifestation of digital craft. The case studies vary in scale from fabric and furniture production to large-scale installations of significant spatial effect, to entire architectural projects. The range is useful in discussing how the concept of digital craft in architecture can be re ad from various perspectives. This reflects the numerous ways in which digitally created design is used to realise crafted results and is mindful of the fact that architectural processes often follow technological innovation first practiced at more intimate scales such as in industrial design. It is also interesting to compare the idea of the more intimately scaled relationship that craft has traditionally held with architectural practice. Finally, the thesis will speculate upon future developments for the conjunction of digital craft in architecture and design, and will pose several questions for further discussion.

In order to study the electronic and optical properties of complex materials an approach providing a reliable estimate of band gaps in combination with the reasonable description of the ground state is required. In the present study of pure and defective perovskite crystals, the fulfillment of such requirements is clearly demonstrated using a simple hybrid HF/DFT scheme containing an admixture of non-local Fock exchange. In present theoretical investigations, a wide class of perovskite oxides is represented by three, the most attractive (from a scientific point of view) crystals of SrTiO3, BaTiO3, and PbTiO3 in their high symmetry cubic phases. These perovskite crystals present a great technological and fundamental interest due to their numerous applications related to ferroelectricity, non-linear and electro-optics, superconductivity, and catalysis. Although the above-mentioned perovskite-type materials have been intensively investigated theoretically and experimentally at least in the last fifteen years, a proper description of their electronic properties is still an area of active research. In order to make a contribution to the explanation of various electro-optical effects observed in perovskite materials, their ground-state properties have been calculated from first principles and analyzed in the present study.