The roles of phylogeny and body size in avian heat stress physiology, and how they interact to set the upper limits to heat dissipation capacity, are largely unexplored. Determining thermal end points and maximum capacity for evaporative heat dissipation in species from diverse ecological guilds and evolutionary clades is vital for understanding species-specific vulnerability to future climatic scenarios. I measured evaporative water loss (EWL), resting metabolic rate (RMR) and body temperature (Tb) in three arid-zone passerines and three columbids of varying mass, namely the scaly-feathered weaver (Sporopipes squamifrons, ~11 g, SFW), sociable weaver (Philetairus socius, ~26 g, SW), white-browed sparrow weaver (Plocepasser mahali, ~40 g, WBW), Namaqua dove (Oena capensis, ~37 g, ND), laughing dove (Spilopelia senegalensis, ~89 g, LD) and Cape turtle dove (Streptopelia capicola, ~148 g, CTD) at maximum air temperatures (Ta) of 48–60°C. I found that evaporative water loss increased approximately linearly in all six species above a Ta of ~ 40 °C, which resulted in SFW, SW, WBW, ND, LD and CTD dissipating a maximum of 140, 220, 190, 498, 218 and 231 % of metabolic heat loads at the highest Tas respectively. All six species used facultative hyperthermia at high Tas and were able to regulate Tb up to and just beyond Tb = 45 °C. At the highest Tas experienced, passerines exhibited uncontrolled increases in Tb above 45 °C, resulting in 57, 100 and 100 % of SFW, SW and WBW respectively, reaching thermal limits at Ta = 48, 52 and 54 °C. Very few doves exhibited uncontrolled hyperthermia or reached thermal limits at their highest respective test Tas (Ta = 56, 68 and 60 °C in CTD, LD and ND respectively), suggesting that these birds could potentially survive higher Tas, and that lethal Tb was marginally higher than my conservative estimations. A conventional analysis found significant differences between doves and passerines in the slopes of EWL as well as the magnitude of the change in RMR, EWL and Tb between Ta = 35 and 48 °C. However, once phylogeny was controlled for, these differences were shown to be a result of phylogenetic inertia. Both a conventional analysis and a phylogenetic independent contrast (PIC) found a significant effect of body mass on slope of EWL, change in EWL (PIC only) and change in Tb between Ta = 35 and 48 °C. From the results of this study, I argue that by utilizing high ratios of cutaneous EWL to respiratory EWL, doves generate much less metabolic heat at high Tas than passerines. I suggest that larger passerines are better able to tolerate heat than smaller passerines, whereas the opposite is the case in doves. The lack of data from small doves obscured this finding in the conventional and PIC analyses. Further studies on the upper limits to the avian capacity for evaporative cooling and heat tolerance are critical for larger-scale mechanistic modeling of vulnerability to extreme heat events under current and future climate scenarios. / Dissertation (MSc)--University of Pretoria, 2014. / DST/NRF Centre of Excellence at the Percy FitzPatrick Institute (University of Cape Town) / University of New Mexico / Zoology and Entomology / MSc / Unrestricted

Orientador: Prof. Dr. José Rubens Maiorino / Dissertação (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Energia, 2016. / O presente trabalho desenvolveu um código, intitulado STH-MOX-Th (Simplified Thermal- Hydraulics code-Mixed Oxide Thorium), com o objetivo de calcular os limites térmicos (temperaturas limite do combustível e do revestimento, além do DNBR-"Departure of Nucleate Boiling Ratio"- mínimo) de um reator PWR do tipo vareta para combustíveis de UO2 e óxidos mistos de Urânio-Tório. ((U,Th)O2) utilizando correlações específicas para cada combustível cujo coeficiente de condutividade térmica é uma função dependente da temperatura. Para tal resolução, foi utilizado o método de Runge-kutta de 4ª ordem. O código analisa apenas o canal mais quente do núcleo do reator e, por conta dessa simplificação, possui uma parte hidráulica simples. Além da parte hidráulica, o programa calcula a distribuição axial e radial das temperaturas do refrigerante e vareta, bem como distribuições de entalpia e pressão. Todos esses cálculos foram realizados no início do ciclo do combustível no caso do (U, Th)O2 e para o UO2 e, além disso, o código calcula casos considerando a queima do combustível (meio e final de ciclo) somente para o UO2, uma vez que não foi encontrada nenhuma correlação para o coeficiente de condutividade térmica para o (U,Th)O2 em função da queima. Para validar o programa foram utilizados dados referentes a usina de Angra 2 para a entrada do programa e os resultados comparados com os reportados pelo Relatório Final de Análise de Segurança da Eletronuclear e do reator AP-1000, desenvolvido pela Westinghouse. A grande contribuição do trabalho, é o cálculo dos limites térmicos de um reator utilizando óxidos mistos de urânio e tório no núcleo do reator AP-1000, que é objeto das pesquisas na UFABC. Apesar de não ser original, o trabalho possuí fins didáticos e será extremamente útil no que diz respeito a uma primeira análise dos limites térmicos de um reator nuclear. / The present study developed a code, named STH-MOX-Th (Simplified Thermal-Hydraulics code-Mixed Oxide Thorium), created in order to calculate the thermal limits (limit temperature of the fuel and of the coating, besides the DNBR -"Departure of Nucleate Boiling Ratio"- minimum) of a PWR rod type reactor to UO2 fuel and mixed oxides of Uranium- Thorium. ((U,Th)O2) using specific correlations to each fuel which coefficient of thermal conductivity is a function dependent on temperature. For such a resolution, the method Runge-kutta of 4th order was employed. The code analyses only the hottest channel of the reactor core and, because of this simplification, it has one simple hydraulic part. In addition to the hydraulic part, the program calculates the axial and radial distribution of refrigerant and rod temperatures, as well as the distributions of enthalpy and pressure. All these calculations were done in the beginning of the fuel cycle in the case of (U,Th)O2and, for UO2, the code also calculates cases that consider the fuel burning (beginning, middle and end of the fuel cycle) only for UO2, once it was not found any correlation to the coefficient of thermal conductivity to (U,Th)O2 being dependent on fuel burning.In order to validate the program, data from Angra 2 plant were used to the program input and the results were compared with the ones reported by the Final Report on Security Analysis of Eletronuclear and with the ones of AP-1000 reactor, developed by Westinghouse. As the main contribution, the program made such calculations to the project of the fuel reactor of (U-Th) O2, APTh-1000. Although this study is not original, it has learning purposes and will be extremely useful concerning a very first analysis of the thermal limits of a nuclear reactor.