A stochastic dynamic micromagnetics code using the LLG equation has been developed and applied to study the seed induced magnetic reversal of a cobalt element array. The spin orientation of the seed element is chosen to be antiparallel to the spin orientation of the first element in the array producing a domain wall that is stabilized by the strong crystalline anisotropy and exchange interactions of cobalt. By exposing the element array to an applied magnetic field for a specific time, the domain wall moved along the easy axis and was pinned at a specific position. In this manner, the portions of the element array to be switched could be controlled arbitrarily and information can be stored in the array in terms of the total magnetization of the array. The effects of the magnitude of applied field, the cutting area and the cellsize of the element array were also studied.

Made available in DSpace on 2016-08-10T10:44:16Z (GMT). No. of bitstreams: 1 SILVIA MOREIRA DOS SANTOS.pdf: 6306361 bytes, checksum: e51992308d1bf5bdde4febb0cd7e0277 (MD5) Previous issue date: 2012-03-02 / João Leite Stream consists on an approximate area of 765 km ², in which its main watercourse has a length of 135 km. The chosen study area was the reservoir implanted in João Leite Stream, situated in the upstream of Goiania, along with Balm hill. The sampling points were: P1 (situated in the upstream of Terezópolis reservoir), P2 (reservoir), P3 (situated in the downstream of bus reservoir) and P4 (catchment - SANEAGO). This study aimed at data attainment to evaluate the changes in the reservoir, as well as at correlating the results of hydrobiological and abiotic components through statistical analysis. The variables studied were: climatic (air temperature and precipitation), physicochemical (water temperature, transparency, pH, energy conductivity, turbidity, dissolved oxygen, organic matter, total phosphorus and nitrate) and hydrobiological (chlorophyll a, pheophytin a and phytoplankton density). During the study, the amount of rainfall recorded was 1529 mm. In the reservoir, the temperature varied from 26.3°C to 28.2ºC in the dry season, and from 22.6°C to 26.8°C during the rains, exceeding the amounts recorded for the other locations in the same period. The reservoir lentic waters environment favored the retention of cleaner waters, with low turbidity amounts compared to other sampling locations. The lowest concentrations of DO saturation were observed in P2. The highest concentrations of oxygen were detected in March/2010 at points P1, P2 and P3. The organic matter at all sampling locations was the highest from January/10 to April/10 and the lowest amounts recorded were in January/11 at all locations (0.4 mg / L to 0.5 mg / L). The t test applied to the data, demonstrated the existence of significant differences between the sampling locations, except for the variables in phosphate, organic matter and cyanobacteria that suggested amounts closer to the records of the sampled locations. Mostly, the parameters analyzed were classified among the minimum required by CONAMA 357/2005. Predominantly, it was at the reservoir that occurred the largest temporal and seasonal variations, demonstrating the particular characteristics of the lentic environments in relation to lotic environments. The richness of the total Chlorophyceae exceeded 34%, followed by the Cyanophyceae, with over 18% at all locations, whereas all other classes contributed less than 5% of the total rate of richness. In P2 the richness of the rate recorded was higher when compared with the other locations. During March 2010, it was recorded the first occurrence of flowering, being the dominant species Cylindrospermopsis raciborskii, a cyanobacterium with toxicity showed in other studies. The distance of 10.42 kilometers traveled by the water to the point of catchment may explain the low density of Cylindrospermopsis raciborskii in catchment (P4), in the same period in which flowering was occurring in P2. The rating of P2 regarding the degree of hypertrophy ranged from oligotrophic to mesotrophic using chlorophyll a parameter during the sampling period. / O Ribeirão João Leite apresenta uma área aproximada de 765 km², sendo que o seu curso d água principal tem uma extensão de 135 km. A área de estudo escolhida foi o reservatório implantado neste ribeirão, à montante da cidade de Goiânia, junto ao morro do Bálsamo. Os pontos amostrados foram: P1 (à montante do reservatório em Terezópolis), P2 (reservatório), P3 (à jusante do reservatório) e P4 (captação na SANEAGO). O objetivo foi avaliar as alterações ocorridas no ambiente lótico para lêntico (reservatório), nos período de janeiro de 2010 a janeiro de 2011, assim como correlacionar os resultados hidrobiológicos e componentes abióticos por meio de análises estatísticas. As variáveis estudadas foram: climatológicas (temperatura do ar e precipitação), físico-químicas (temperatura da água, transparência, pH, condutividade elétrica, turbidez, oxigênio dissolvido, matéria orgânica, fosfato e nitrato total) e hidrobiológicas (clorofila a, feofitina a e densidade fitoplanctônica). Durante o estudo, a precipitação total registrada foi de 1529 mm. No reservatório a temperatura variou entre 26,3ºC a 28,2ºC no período de estiagem e 22,6ºC a 26,8°C durante as chuvas, superando os valores registrados para os ambientes lóticos. O ambiente lêntico favoreceu a permanência de águas limpas, claras e baixa turbidez em comparação aos demais pontos amostrados. O teste t demonstrou a existência de diferença significativa entre os pontos de amostragem, a exceção da variável fosfato, matéria orgânica e cianobactérias que sugeriram valores mais próximos entre os registros dos pontos amostrados. Em sua maioria os parâmetros analisados estiveram enquadrados dentro do mínimo exigido pelo CONAMA 357/2005. Predominantemente foi no reservatório que ocorreram as maiores variações temporais e sazonais, demonstrando a característica particular do ambiente lêntico em relação aos ambientes. lóticos. A riqueza total da classe Chlorophyceae superou 34%, seguida pela classe Cyanophyceae, com mais de 18%, em todos os pontos, enquanto que todas as outras classes contribuíram com menos de 5% do total de riqueza de taxa. No P2 a riqueza de taxa registrada foi maior quando comparada com os demais pontos. Durante o mês de março de 2010 foi registrada a primeira ocorrência de floração, sendo a espécie dominante Cylindrospermopsis raciborskii, uma cianobactéria com toxicidade já comprovada em outros estudos. A distância de 10,42 km percorrida pela água até o ponto de captação pode explicar a baixa densidade de Cylindrospermopsis raciborskii na captação (P4), no mesmo período em que estava ocorrendo floração no P2. A classificação do P2 quanto ao grau de trofia variou de oligotrófico a mesotrófico utilizando o parâmetro da clorofila a durante o período amostrado.