The previously unknown chemical and physical properties of the ternary rare-earth inter­metallic compounds, RETGe (RE=Sc, Y, La–Lu; T=Ag, Au), are investigated using a variety of experimental techniques. The RETGe are found to crystallise in three basic different crystal structure types (CaIn2-, Fe2P-, and CeCu2-type derivatives).

This work is considered about changes of electric conductivity in lead-free soldered joint's affected by current and thermal stress. The theoretical part describes factors influencing the solder joint electric conductivity and solder joint reliability. The basis of the practical part is the design of the testing method of the soldered joint's electric conductivity. The aim of this part is to measure and observe changes of solder joint electric conductivity after current and thermal stress in various material a procedural combinations.

Humans are modifying animal populations, indirectly accelerating or reducing the geomorphic alterations caused by animals. Species have been monitored and studied with focus on domesticated animals but little research has been undertaken on wild animals. This study analyses the geomorphic impact of elephants on Tembe Elephant Park, so that the changes they cause to the landscape may be quantified. To conduct this research four sites were chosen: an area where elephants had been excluded for twenty-five years, where excluded for five years, where elephants exist at present and where elephants mud wallow. Three of the four study sites were classed as sand forest (twenty-five-years exclusion, five-years exclusion and where elephants exist) and were analysed and compared to determine the similarities and differences in climate, microclimate, vegetation and the soil’s physical and chemical properties. The wallow site was not compared to any other study site, but was observed and mapped to quantify the geomorphic impact of elephants wallowing. When the sand forest sites were compared the climate, vegetation type and soil were found to be similar. Where elephants were present: the vegetation was inconsistent in basil cover, canopy height, structure and class. Soils were more compacted with a low infiltration rate, higher temperature, lower soil moisture, higher pH and a lower electric conductivity and air relative humidity was the highest. Where elephants have been excluded for twenty-five years, the opposite trends arose from the data analysis. The vegetation was consistent in basil cover, canopy height, structure and class, and the soils were less compacted with a high infiltration rate, low temperature, higher soil moisture, lower pH and a higher electric conductivity. The microclimate showed a trend where the air relative humidity was the lowest. At the elephant wallow site data showed that the wallows were in general circular in shape, 52.5m3 of soil was removed per month for the last nine months and the surface area of the wallows increased by 165.5m2 per month for nine months from April to December 2008. All the results from this study show that the elephant activity in Tembe Elephant Park has geomorphic consequences. From the results, it is possible to conclude that the geomorphic impacts of elephants on Tembe Elephant Park are contributing to a nutrient cycle shift in the sand forest biome, as they change aspects of the vegetation, microclimate, soil and landscape, which are the foundation of the cycle. / Dissertation (MA)--University of Pretoria, 2011. / Geography, Geoinformatics and Meteorology / MA / Unrestricted

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 1977 / Vita. / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Materials Science and Engineering

Indiana University-Purdue University Indianapolis (IUPUI) / Proton exchange membrane fuel cells (PEMFC’s) offer an attractive alternative energy resource over traditional fossil fuels. The advantages such as high power density, relatively quick start-up, rapid response to varying loads and low operating temperatures make it a preferred technology option compared to other alternative energy sources. Nafion® by DuPont plays an integral role in the success of PEM fuel cells due to its high proton conductivity and high chemical and thermal stability. This research project aims to study the effect of mechanical and hygro-thermal stresses on the mechanical performance and proton conductivity of the membrane by subjecting it to realistic operating conditions such as those encountered in an automobile. In this thesis, the time-dependent behavior of the membrane has been modeled using a Prony series and the change in the conductivity due to mechanical loading was experimentally measured. The modeling of both electrochemical and mechanical properties can further be used in studying the degradation properties of the membrane and should guide the development of better membrane materials. Visco-elastic stress relaxation theory has been used in modeling the time-dependent behavior of the specimen. The EIS spectrum has been analyzed using a non-linear least squares method and an equivalent circuit method was also used to fit the spectra. This project was conducted in three phases. In the first phase a novel test facility was built to perform the experiments. A conductivity measurement test cell that measured the proton conductivity of a membrane was modeled and manufactured. The second phase included the design of different experiments that helped in modeling the interdependence of electrochemical and mechanical properties of the membrane. In this process, three series of experiments that tested the electrochemical and mechanical properties of the specimen were conducted. The membrane was held at constant strain and the through plane impedance was measured at different times during the test, specifically before and after stretching at ambient and varying environmental conditions. The membrane was also subjected to both mechanical and hygro-thermal loading conditions during the test. In the third phase, time-dependant mathematical model for the changes in the material properties were developed. The experimental apparatus thus tested the mechanical and electrochemical properties of the membrane simultaneously while the specimen was being subjected to constant mechanical and varying hygro-thermal conditions. Since the testing method is a novel procedure, the reliability and repeatability of the experimental facility has been verified before conducting the experiments. The experimental apparatus can further be used to test the membrane at varying strain rates and different hygro-thermal loading conditions in a consistent manner. The model developed can be used to analyze the degradation behavior of membrane and also to build better fabrication methods and membrane materials in future.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The quality of the seeds used in any agricultural cultivation is one of the important factors for the obtaining of a number of ideal plants and high productivity. The evaluation of the physiological potential of the seeds is essential to the quality control programs utilized by producing companies and this evaluation is realized through vigor tests. Cytogenetic studies also provide information about the quality of the seeds, allowing to identify anomalies that compromise the vigor. For the obtainment of precise results in agricultural experiments, the determination of the samples‟ size to be used is one of the main quality components of the experiments. Thereby, the objectives of this study aimed to determine and standardize the methodologies of the mass and individual electric conductivity tests for the physiological quality of the wheat seeds; detect cytogenetic and physiological alterations that occur during the deterioration process of the seeds submitted to the artificial aging and estimate the sample size, in number of seeds, for the average estimation of individual electric conductivity in different times of soaking. Five varieties of wheat seeds were used: Fundacep Horizonte, Fundacep Campo Real, Quartzo, Mirante and Ônix, subdivided into two subgroups of seeds for each variety (high and low vigor) through the methodology of accelerated aging. Each group was evaluated physiologically by the determinations of germination tests and vigor tests. Later on, the seeds were submitted to the tests to be standardized: mass electric conductivity and individual electric conductivity, in nine soaking periods (1, 2, 3, 4, 5, 6, 7, 8, and 24 hours). For the cytogenetic analysis, the seeds from the varieties Fundacep Campo Real and Ônix were used. They were submitted to the accelerated aging process by zero, 24, 48, 72, 96 and 120 hours, at 42ºC and 100% of relative air humidity. Physiological determinations were also effectuated and the cytogenetic analyses were realized through conventional techniques, as chromosome observation and mitotic index. To determine the sample size, an interactive process of resampling was conducted with 1000 resamplings, with restitution, using different sample sizes, starting with one seed and adding a seed to each interaction until the maximum size of 400 seeds. The obtained results reveal that the individual electric conductivity test was effective for the separation of the groups of wheat seeds and the best combination was the utilization of 25 ml of soaking solution and samples of 75 seeds, during the periods of 8 and 24 hours. The individual electric conductivity test was efficient for the vigor determination of the wheat seeds with the possibility of reading with reduced period of one hour of seed soaking. The seed deterioration caused by the accelerated aging has relation with the reduction of the germination potential and the vigor of the wheat seeds from the varieties Campo Real and Ônix; the stress caused by the accelerated aging on the seeds from both varieties leads to a drastic reduction on the mitotic index and the accelerated aging leads to an increase of anomalies frequency, possibly, related to a genotypic effect. The sampling, in number of wheat seeds, to evaluate the individual electric conductivity is of 44 seeds; for groups in which the accelerated aging was not applied, it is 27 seeds; for groups artificially aged, the amplitudes are from 3 to 5 uS. cm-1 seed-1, for soaking time from one to 24 hours. / A qualidade das sementes utilizadas em qualquer cultivo agrícola é um dos fatores importantes para obtenção de um número de plantas ideal e alta produtividade. A avaliação do potencial fisiológico das sementes é essencial aos programas de controle de qualidade empregados por empresas produtoras e, essa avaliação é realizada através de testes de vigor. Estudos citogenéticos também fornecem informações sobre a qualidade das sementes, permitindo identificar anomalias que comprometem o vigor. Para obtenção de resultados precisos em experimentes para qualidade de experimentos. Desse modo, os objetivos desse estudo foram determinar e padronizar metodologias para os testes de condutividade elétrica massal e individual visando a determinação da qualidade fisiológica de sementes de trigo; detectar alterações citogenéticas e fisiológicas que ocorrem durante o processo de deterioração das sementes submetidas ao envelhecimento artificial; e determinar o tamanho de amostra, em número de sementes, para a estimação da média de condutividade elétrica individual em diferentes tempos de embebição. Foram utilizadas cinco cultivares de trigo: Fundacep Horizonte, Fundacep Campo Real, Quartzo, Mirante e Ônix, subdivididas em dois sublotes de sementes para cada cultivar (alto e baixo vigor) através da metodologia do envelhecimento acelerado. Cada lote foi avaliado fisiologicamente pelas determinações do teste de germinação e testes de vigor. Posteriormente, as sementes foram submetidas aos testes a serem padronizados: condutividade elétrica massal e condutividade elétrica individual, por nove períodos de imersão (1, 2, 3, 4, 5, 6, 7, 8 e 24 horas). Para as análises citogenéticas, foram utilizadas sementes das cultivares Fundacep Campo Real e Ônix, submetidas ao processo de envelhecimento acelerado por zero, 24, 48, 72, 96 e 120 horas, à 42ºC e 100% de UR. Determinações fisiológicas também foram efetuadas e as análises citogenéticas foram realizadas através de técnicas convencionais, como observação dos cromossomos e índice mitótico. Para determinar o tamanho de amostra, realizou-se um processo interativo de reamostragem com 1000 reamostragens, com reposição, utilizando diferentes tamanhos de amostras, iniciando com uma semente e acrescentando uma semente em cada interação até o tamanho máximo de 400 sementes. Os resultados obtidos revelaram que o teste de condutividade elétrica individual foi eficiente para a separação dos lotes de sementes de trigo e a melhor combinação foi a utilização de 25mL de solução de embebição e amostras de 75 sementes, nos períodos de 8 e 24 horas e, que o teste de condutividade elétrica individual foi eficiente para a determinação do vigor das sementes de trigo com a possibilidade de leitura com período reduzido de uma hora de embebição das sementes. A deterioração das sementes causada pelo envelhecimento acelerado tem relação com a diminuição do potencial germinativo e de vigor das sementes de trigo das cultivares Campo Real e Ônix; o estresse causado pelo envelhecimento acelerado nas sementes de ambas as cultivares leva a drástica redução no índice mitótico e, o envelhecimento acelerado leva ao aumento da frequência de anomalias cromossômicas, porém com respostas distintas para as cultivares analisadas, possivelmente, vinculado a efeito genotípico. A amostragem, em número de sementes de trigo, para avaliar a condutividade elétrica individual é de 44 sementes; para lotes em que não foram aplicados o envelhecimento acelerado, é de 27 sementes; para lotes envelhecidos artificialmente, para amplitudes de 3 a 5 uS cm-1 semente-1, para tempos de embebição das sementes de uma a 24horas.

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