Chytridiomycosis, a disease of amphibians caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), is an ideal system for studying how temperature influences the host-pathogen relationship because both the host and the pathogen are ectothermic. In this dissertation, I employ a three-pronged approach to investigate the relationship between temperature and the prevalence, severity, and outcome of Bd infections in Northern cricket frogs (Acris crepitans) using both laboratory experiments and field studies. In Chapter One, I conducted a Bd exposure study to determine whether constant temperatures affect Bd pathogenesis differently in live hosts than in culture. Exposure frogs were inoculated weekly with 100 million zoospores of a virulent strain of Bd and frogs were incubated at one of six temperatures: 11, 14, 17, 20, 23, or 26°C. Infection prevalence and pathogen load in Bd-exposed frogs were highest at 14°C while survival was lowest at 11˚C. These results demonstrate that Bd pathogenicity peaks at different temperatures in live hosts than Bd growth peaks at in culture. In Chapter Two, I combine a field study that assesses the effect of microhabitat choice, seasonality and latitude on Bd prevalence and severity in wild amphibian populations with a laboratory study that investigates how temperatures that fluctuate during diurnal and nocturnal cycles influence Bd pathogenicity. Across all states, I found that year was the only significant predictor of infection prevalence, but probability of infection was predicted by year, month, and latitude, and pathogen load was predicted by month and body temperature. In my experimental study, I found infection prevalence and pathogen load to be highest, and survival lowest, in the Louisiana winter group (7˚-17˚C). In my third chapter, I used a biophysical model, Niche Mapper, to predict probability of survival and infection prevalence in Northern cricket frogs by modelling host body temperature. I found that the probability of an infected frog surviving thirty days in May was highest in Southern Louisiana and lowest in Northern Michigan. These studies demonstrate that temperature is an important influence on infection outcome in live hosts. / 1 / Julia Madeleine Sonn

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A magneto-optical apparatus has been designed to investigate flux and current distributions in various forms of high-temperature superconductor after the application of external magnetic fields, transport currents, and both in sequence. It is concluded that flux motion depends significantly on the superconductor characteristic flux pinning strength and geometry. The flux profiles at the surface of an isolated thin film strip, and thin films in x-array and shunted-x-array arrangements have been studied in detail. It has been found that the theoretical flux profile, characterised by a logarithmic singularity at its edges and a vertical slope at the flux front, become rounded when the sample thickness is taken into account. Experiment has confirmed that the current density reaches its critical value in the flux-penetrated region while there is a continuous non-zero current density in the central flux-free region. Also magnetic interactions exist between the strips. Band-shaped and dome-shaped flux distributions caused by geometrical barrier at different weak pinning strengths were observed in Bi2Sr2CaCu2O8+x single crystals between 20 K and 70 K. The geometrical barrier also governs the transport current leading to a square-shaped distribution near the crystal edges at 20 K. Cracks and defects in Bi-2223/Ag tapes were visualised without destruction of the tape. The inhomogeneous flux distribution indicated that defects, including cracks, in superconducting filaments limit the current-carrying capacity of the tape. In addition, at 70 K a fraction of the transport current has been found to flow in the silver sheath. An investigation of the influence of the twin planes on vortex motion in a YBa2Cu3O7-d single crystal has shown that after a twin barrier is initially overcome, the twin planes, regardless of their directions, act as an easy-flow channel for vortex penetration at low temperatures as the pinning strength in the twin planes is weaker than that in the untwinned region, whereas, they act as a barrier at high temperatures where the pinning strength in the twin planes is stronger. Furthermore, vortex penetration along the twin planes is a factor of four greater than that for the untwinned region at 25 K.

Wheat production is the largest enterprise within the Australian grain industry, with an annual gross value of production of approximately $4 billion. However high temperature stress (>35°C) and zinc (Zn) deficiency in soils are a frequent occurrence across the Australian wheat belt and represent two of the most important environmental limitations to wheat production and grain quality. The work presented here has shown for the first time that Zn nutrition can provide wheat plants with a level of tolerance to high temperature stress. Field trials, along with controlled environment studies, showed that supplementary Zn nutrition improved photosynthetic activity during a high temperature event, by stabilising chlorophyll initial fluorescence, Fo. Since increases in Fo under heat stress are associated with an increase in lipid fluidity of the thylakoid membranes at high temperature, the results suggested that adequate Zn fertilisation could preserve membrane integrity during heat stress. Electron microscopy confirmed this hypothesis, and showed that adequate Zn nutrition could maintain the integrity of a number of cellular membranes during high temperature, including the tonoplast, chloroplast envelope and the thylakoid membranes. Measurements of canopy temperature depression showed an improvement in the evaporative cooling of the canopy with supplementary Zn nutrition in the Zn inefficient varieties, suggesting better soil water extraction under warm conditions. Supplementary Zn nutrition also increased the kernel weight of plants grown under warm conditions in the field, however this was unrelated to the improvement in photosynthetic ctivity. Nevertheless, results from both controlled environment and field experiments demonstrated that the detrimental effects of low Zn availability and high temperature on the yield of Zn inefficient or thermosensitive wheat varieties will be most damaging when these stresses occur in combination. Analysis of protein composition showed that supplementary Zn fertilisation increased the glutenin:gliadin ratio in the grain. This suggests that Zn fertilisation may improve the bread-making quality of wheat under conditions of Zn deficiency. The results also showed a negative association between grain Zn concentration and the number of days over 35°C during grain filling, which suggests that the negative effects of high temperature stress on grain protein composition will be compounded when plants are grown on soils of low Zn availability. This thesis represents a valuable contribution to the understanding of the relationships between micronutrient supply and environmental stress. Further studies should be undertaken to establish whether the protective effect of Zn on the photosynthetic apparatus will be maintained under consecutive heat stress events, to determine the ways in which Zn ions stabilise and protect bio- membranes under heat stress and to confirm the positive effects of Zn on grain protein composition and baking quality. / Thesis (Ph.D.)--School of Agriculture and Wine, 2004.

In this thesis, the interpretation and reduction of ocean heat flow measurements are discussed on the basis of theoretical models. The instrument effect x heat flow measurements is investigated for the case of long period measurements by studying the heat conduction along the measurement probe for both steady and unsteady state bottom temperatures. This effect is found to be unimportant. Measurement errors due to recent bottom temperature transients are studied and the possible magnitude of such errors is estimated. Moreover, effects of climatic variation on the ocean floor temperature are estimated on the basis of diffusion models. It is shown that climatic variations with periods longer than one thousand years will be unattenuated and will affect the entire ocean floor. The perturbation method is used to study the effects of an irregular topography and a variable thickness of ocean floor sediments on the heat flow. Some special examples are given to provide a comparison between the perturbation solutions and exact solutions of similar problems. The perturbation method is also applied to a buried body with different thermal conductivity from its surroundings and the reliability of the perturbation solution is examined. Heat flow anomalies due to heat transport by magma intruded into crustal layers is studied by solving the heat conduction equation. It is shown that magmatic intrusions can lead to very large surface heat flow anomalies. Finally, the possibility of deriving the ocean floor thermal gradient on the basis of on-ship measurements performed on sediment cores is investigated. The results appear positive. The temperature variations in flowing wells and the temperature variation in a cylindrical sediment core influenced by the movement of water along the axis of the core are also studied. / Graduation date: 1968

In comparison with solar radiation, the energy of geothermal heat flowing through the sea bottom is extremely small; nevertheless, this energy is not insignificant in the circulation of the bottom water. Calculations indicate that in the deep basins of the South Atlantic the water volume transport necessary to remove this heat is at least one-tenth of the total northward flow of Antarctic Bottom Water. Plots of mean values of near bottom salinity and oxygen versus mean potential temperatures help to trace the movement of the bottom water. Geothermal and adiabatic warming associated with downslope flow combine to produce a deep temperature (in situ) minimum in portions of most of the deep basins of the world. Adiabatic or near adiabatic temperature gradients have been measured near the bottom in many of these basins. Evidence of superadiabatic gradients from temperature measurements made with reversing thermometers is inconclusive; however, careful measurements with closely spaced thermometers suggest that such gradients do exist over vertical distances of a few hundred meters in some of the deepest basins. Decreasing potential density with depth, as found in some of the Atlantic Basins in association with sharp temperature and salinity gradients, is not necessarily an indication of unstable equilibrium. This is demonstrated by the results of stability calculations in the manner prescribed by Hesselberg and Sverdrup (1915). / Graduation date: 1968

Graduation date: 1969

Graduation date: 1996

Graduation date: 1993

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 112-118).