Biofilms are important in nature and in engineered processes. Because of this, a fundamental understanding of their growth and behaviour is required. This work aimed at monitoring biofilm growth using a biological rotating reactor and the Rotoscope biofilm monitor. Both methods worked on the principle of a rotating circular disc that was semi-submerged in water and the light reflected of the area that was outside of the water. Light reflectance on the disc was taken three times a day and the average recorded as the daily reading. It was noticed that in both systems, growth of biofilms on the discs caused a decrease in the amount of light reflected. A decrease in light reflectance indicated an increase in biofilm thickness. The growth of biofilm was confirmed by scanning electron microscopy analysis. The addition of a biocide caused a slight increase in light reflectance indicating partial biofilm removal. The Rotoscope was very sensitive to changes in biofilm characteristics. Rotoscope met the requirements needed for an on-line, real-time and non-destructive biofilm monitoring system. The aged anolyte was effective in killing both suspended and biofilm bacteria at a concentration of 1:10 irrespective of its age and storage conditions. Exposure of aerobic bacteria to different concentrations of sodium nitrite at different time intervals indicated that sodium nitrite had a limited, or no biocidal effect on these bacteria mostly encountered in biofilms. The ready to use chlorine dioxide was also used as the means of controlling biofilms. MIC for RTU ClO2 was found to be 80ppm, which in certain instances killed all bacteria immediately upon exposure while in other cases an exposure time of 1h was required. It was indicated that at this concentration, biofilms were removed. This was confirmed by scanning electron microscopy analysis. Proteins of suspended bacteria treated with 1:10 and 1:100 anolyte dilutions and the control were extracted and compared using SDS-PAGE. Protein bands of bacteria treated with 1:10 NaCl derived anolyte were fewer and fainter as compared to those from untreated cells. More bands were produced in cells treated with 1:100 NaCl derived anolyte as compared to the untreated cells. Cells treated with the non-halide anolyte, both 1:10 and 1:100 dilutions, produced more bands than in the untreated cells. Anolyte destroyed vital proteins for bacterial survival causing cell death or it caused fragmentation of proteins to small peptides, reducing the number of viable cells. NaNO2 was ineffective as biocide while aged anolyte and RTU liquid ClO2 were effective as biocides. SDS-PAGE indicated that anolyte killed bacteria by affecting their proteins. / Dissertation (MSc)--University of Pretoria, 2008. / Microbiology and Plant Pathology / unrestricted

Radio-Frequency (RF) lesioning, or RF ablation, is a method that uses high frequency currents for thermal coagulation of pathological tissue or signal pathways. The current is delivered from an electrode, which also contains a temperature sensor permitting control of the current at a desired target temperature. In the brain, RF lesioning can e.g. be used for treatment of severe chronic pain and movement disorders such as Parkinson’s disease. This thesis focuses on modelling and simulation with the aim of gaining better understanding and predictability of the lesioning process in the central brain.   The finite element method (FEM), together with experimental comparisons, was used to study the effects of electric and thermal conductivity, blood perfusion (Paper I), and cerebrospinal fluid (CSF) filled cysts (Paper II) on resulting lesion volume and shape in brain tissue. The influence of blood perfusion was modelled as an increase in thermal conductivity in non-coagulated tissue. This model gave smaller simulated lesions with increasing blood perfusion as heat was more efficiently conducted from the rim of the lesion. If the coagulation was not taken into consideration, the lesion became larger with increasing thermal conductivity instead, as the increase in conducted heat was compensated for through an increased power output in order to maintain the target temperature. Simulated lesions corresponded well to experimental in-vivo lesions. The electric conductivity in a homogeneous surrounding had little impact but this was not true for a heterogeneous surrounding. CSF has a much higher electric conductivity than brain tissue, which focused the current to the cyst if the electrode tip was in contact with both a cyst and brain tissue. Heating of CSF could also cause considerable convective flow and as a result a very efficient heat transfer. This affected both simulated and experimental lesion sizes and shapes. As a result both very large and very small lesions could be obtained depending on whether sufficient power was supplied or if the heating was mitigated over a large volume.   Clinical (Paper IV) and experimental (Paper III) measurements were used for investigation of changes in reflected light intensity from undamaged and coagulating brain tissue respectively. Monte Carlo (MC) simulations for light transport were made for comparison (Paper V). For the optical measurements, an RF electrode with adjacent optical fibres was used and this electrode was also modelled for the optical simulations. According to the MC simulations, coagulation should make grey matter lighter and white matter darker, while thalamic light grey should remain approximately the same. Experiments in ex-vivo porcine tissue gave an increase in reflected light intensity from grey matter at approximately 50 °C but the signal was very variable and the isotherm 60 °C gave better agreement between simulated and experimental lesions. No consistent decrease in reflected light intensity could be seen during coagulation of white matter. Clinical measurements were performed during the creation of 21 trajectories for deep brain stimulation electrodes. In agreement with the simulations, reflected light intensity was found to differentiate well between undamaged grey, light grey and white matter.   In conclusion, blood perfusion and CSF in particular may greatly affect the lesioning process and can be important to consider when planning surgery. Reflected light intensity seems unreliable for the detection of coagulation in light grey brain matter such as the thalamus. However, it seems very promising for navigation in the brain and for detection of coagulation in other tissue types such as muscle.

Golf courses can expand hundreds of acres, making scouting for both pests and beneficial insect populations a time-consuming task. Scouting for insects is labor-intensive, potentially damaging, but is an integral part of an integrated pest and pollinator management (IPPM) plan. Virginia golf courses are currently using remote sensing and light reflectance to detect non-insect pests in turfgrass. This thesis aims to develop remote sensing and light reflectance methods to aid in a turfgrass IPPM plan, to document the phenology of ABW weevil (Listronotus maculicollis Kirby, Coleoptera: Curculionidae, ABW), and to catalogue pollinator-friendly out-of-play areas. Light reflectance, the measurement of the amount of light reflected, of plants can be used as a proxy for the health of a plant. The light reflectance of turfgrass affected by ABW stress and plants in the out-of-play areas of golf courses was collected proximally and remotely, using a backpack spectrometer and an unmanned aerial vehicle (UAV), respectively. Mathematical light reflectance indices were applied and compared to insect populations in both areas to determine the correlation. The Normalized Difference Vegetation Index (NDVI), which uses red and near-infrared wavelengths to indicate stress, was found to highlight ABW stressed turfgrass. The Structure Intensive Vegetation Pigment Index (SIPI), which uses red and green wavelengths to highlight flowering plants, was found to highlight potential pollinator- friendly habitats in out-of-play areas. When applied to flights, NDVI could help in the targeted application of insecticides to combat the annual bluegrass weevil, therefore reducing their presence in the environment. The use of SIPI could highlight potential pollinator friendly habitats and therefore assist superintendents in the development of their IPPM plan. / Master of Science in Life Sciences / Scouting, such as completing visual monitoring or taking soil core samples, is an important part in the development of an integrated pest and pollinator management (IPPM) plan for Virginia golf courses; an IPPM plan focuses on control of a pest, while considering the needs of pollinators. The size of golf courses makes scouting for insect pests and beneficial insects a time-consuming task. Golf courses are currently using remote sensing, the use of drones in combination with other technology, to scout for other pests or disease. Light reflectance, the measurement of the amount of light reflected, is often used in combination with remote sensing as a proxy for the health of plants. This thesis developed remote sensing and light reflectance techniques not only to detect a common turfgrass pest, the annual bluegrass weevil (Listronotus maculicollis Kirby, Coleoptera: Curculionidae, ABW), but to also predict the presence of potential pollinator habitats in the out-of-play areas of Virginia golf courses. Instruments such as a spectrometer and a drone were used to collect light reflectance at the ground level and aerially, respectively. Ground data was collected through soap water flushes to detect adult ABW, and visual monitoring of potentially pollinating bees, beetles, butterflies, and flies. The light reflectance and ground data were compared using mathematical indices to determine if there was a relationship between the presence of insects and a particular index. Indices could be applied to drone flights that golf course superintendents are already performing, and they can use this information to highlight potential areas of insect presence. This will help them to take care not to apply insecticides in areas with pollinators or to only apply necessary insecticides where there is likely a presence of ABW. This will reduce the labor, other costs, and the environmental impact of insecticides.