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The dimorphic yeast <i>Candida albicans</i> is capable of growth in a budding yeast form and in a mycelial form. Growing in the yeast form in the digestive and vaginal tracts it normally presents no problems to the host; however, when the dimorphic transition takes place and mycelial growth is initiated, symptoms of candidiasis manifest in the host tissues. This thesis studies the control of the dimorphic response and investigates some of the cellular changes which accompany it. Germ tube formation was induced in a defined amino acids/salts medium. Temperature, pH and culture density were critical factors in stimulating the dimorphic response. Different percentages of term tube formation were recorded for eight different strains of <i>C. albicans</i>. Each strain also acidified the growth medium to a different extent; this was correlated to the extent of filamentation of each strain. Internal pH changes were monitored using the weak and technique and ³¹P nuclear magnetic resonance spectroscopy during bud and germ tube formation. In mycelial cells there was an initial increase in internal pH from 6.8 to around 8.0, followed by a gradual decrease to neutrality at the actual time of germ tube emergence. Cells in the budding form of growth did not exhibit such a marked increase in cytoplasmic alkalinisation. Mutant strains which were unable to produce germ tubes did not show cytoplasmic alkalinisation under conditions which would normally promote mycelial growth. Activation of the plasmamembrane ATPase may account for this increase in internal pH since diethylstilboestrol inhibited cytoplasmic alkalinisation and germ tube formation without affecting cell viability. Weak bases induced artificially, a rise in internal pH which was accompanied by germ tube formation. Potassium ions were found to enter cells as protons were expelled at the initiation of mycelial growth. Lactic acid prevented any rise in internal pH during germ tube formation. It also collapsed the ΔpH of the cells preventing growth by bud or germ tube formation. This may relate to the observation that endogenous <i>Lactobacilli</i> compete with <i>C. albicans</i> in the vagina and may explain why topically applied live yoghurt cultures soothe vaginal candidiasis. Transport of methionine was found not to be significantly different in cells induced to the budding or mycelial form. Transport or arginine and glutamate was induced by growing cells in the presence of these amino acids. The amino acid pool levels changed during the dimorphic process in <i>C. albicans</i>. A rapid increase in the pool level was shown within the first hour of both bud and hyphal growth followed by a gradual decrease. Little or no evidence was found in support of the hypothesis that the formation of hyphae is a response to nutrient starvation.

The purpose of this research program was to measure the efficiency of evacuated tube solar collectors under various operating conditions including: the angle of inclination towards the incident solar radiation, heat transfer fluid flow rate, glazing installation, and number of evacuated tubes. The operating conditions and configurations were chosen to represent realistic or probable installation scenarios and environmental conditions. Furthermore, the research aimed to identify the suitability of evacuated tube solar collectors to each of the scenarios. The scope of the research project was limited to the efficiency of a single tube, and various configurations of a 32-tube panel, not the entire solar domestic hot water or space heating system. Thus, factors such as heat loss in the tubing, solar storage tank, and heat exchanger efficiency were not investigated. The findings indicated that efficiency varied by approximately 5% in general between the different collector configurations.

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Combustion is responsible for providing energy for many applications, especially in propulsion and rocket propellants. Shock tubes provide a controlled, repeatable means of studying combustion characteristics; although, most of these studies require the fuel in a mixture to exist in pure gas-phase. This makes it challenging to test low-vapor-pressure fuels that tend to remain in condensed form. Low-vapor-pressure fuels are commonly used in many combustion applications, making combustion studies of these fuels important. A method to study low-vapor-pressure fuels using a shock tube approach is to inject the fuel into the shock tube as tiny, uniformly-sized aerosol droplets. The sub-micron-sized aerosol droplets remain uniformly suspended in the shock tube prior to running the experiment. An incident shock wave vaporizes the liquid fuel droplets, then the reflected shock wave initiates ignition of the mixture. This study presents the characterization of an aerosol fuel injection method to the shock tube to study the combustion of low-vapor-pressure fuels. An aerosol generator was used to produce repeatable, uniformly-sized fuel droplets, and flow controllers were used to control and measure oxygen and argon dilution gas injected into the shock tube. A technique was developed to ensure consistent and repeatable aerosol fuel production rates over which calibration curves were found. This study presents the ignition delay times for C7H16 (ϕ = 1.0) at a pressure of 2.0 atm for temperatures from 1220 - 1427 K, C7H8 (ϕ = 1.0) at 1.9 atm over a temperature range of 1406 – 1791 K, and C12H26 (ϕ = 0.3) at 3.0 atm for the temperature range of 1293 – 1455 K. The ignition delay times for heptane and toluene were compared to the literature values at the same conditions and were found to be in good agreement. Laser extinction (visible laser at 632nm) was used to verify the presence of aerosol fuel droplets inside the shock tube for dodecane, but showed the heptane aerosol vaporized upon injection into the shock tube. Initial laser absorption (3.39 µm) measurements were also taken. This aerosol technique was found to successfully evaluate combustion effects of low-vapor-pressure fuels; however, was limited by the range of possible fuel concentrations. Further work needs to be performed on the verification of aerosol spatial uniformity and obtaining higher fuel concentrations.