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Impactos das atividades antrópicas sobre a comunidade dos macroinvertebrados bentônicos do Rio Cuiabá e Várzea Grande - MT
(Universidade Federal de São Carlos, 2002-08-02) Lima, João Batista; Gessner, Alaíde Aparecida Fonseca; https://lattes.cnpq.br/8465752836529703
The benthonic macroinvertebrates community has been widely used to evaluate the effects of the anthropic activities on the aquatic ecosystems, but in brazil the studies on the taxocenosis of the macroinvertebrates are scarce, particularly for large rivers crossing metropolitan regions and therefore under urban impacts. The distribution of the macroinvertebrates as well the physical and chemical parameters of the water was studied along the Cuiaba River, between the cities Varzea Grande and Cuiaba. It is noteworthy that these two cities throw out domestic sewage and industrial effluents into the river. The study was conducted during the periods of rainy and dry seasons in the years of 1999 and 2000. During this time the closing of the storage dam of Manso River was completed. This river is one of the main affluents of the Cuiabá River, upstream to the studies region. The sampling was made at six sites in both margins using artificial substrates exposed during six weeks. The resultes shoed differences in the taxocenotic structure of the macroinvertebrate community, and in the physical and chemical parameters of the water. These differences were related to the urban impact and to the closing of dam. The left margin in station 1 has been the best distribution standard of benthonic macroinvertebrates in relation of the others places, it was reflected by the indices of diversity. Oligochaeta and Chironomidae larvae were dominants along the river, however Chironomidae was more abundant in dry seasons and Oligochaeta in rainy seasons.
Caracterização de sistemas varistores a base de SnO2-MnO2
(Universidade Federal de São Carlos, 2002-08-02) Orlandi, Marcelo Ornaghi; Leite, Edson Roberto; Longo, Elson; https://lattes.cnpq.br/9848311210578810
This work focussed on the effect of addition of Nb2O5 on the electrical and microestructural properties of SnO2-MnO2 based ceramics. It was also studied the effect of heat-treatments in a oxygen-rich atmosphere in these properties. The parent system was 99,5% SnO2-0,5% MnO2 in molar ratio, a dense system that did not present non-ohmic behavior. The addition of Nb2O5 on this system promoted an increase on the charge carrier number in the SnO2 matrix and, then, varistor properties were observed. Otherwise, the upper doping level, 0.25% mol of Nb2O5 system showed an higher porosity, due to the decrease on the thermal sintering properties, that depleted the varistor characteristic of this system. A detailed study on the electrical properties were performed using impedance spectroscopy and the obtained results showed that Nb2O5 tends to form an electronic trapping level between the valence and the conduction bands, modifying the potential barrier properties formed in the grain boundaries region. In order to explain the obtained results, it was proposed a parallel equivalent circuit model, based on the grain boundaries contributions to electrical properties. Heat-treatments under oxygen-rich atmosphere did not changed the observed electrical properties in the systems, due to the presence of numerous secondary phases (rich in oxygen and manganese), localized in triple points in the grain boundaries. It is pointed the there is a oxygen local enrichment in these phases, not significantly altering the observed macroscopical electrical characteristics in the analyzed systems.