Federal University of Roraima

About: Federal University of Roraima is a based out in . It is known for research contribution in the topics: Population & Thermogravimetry. The organization has 981 authors who have published 1218 publications receiving 7849 citations. The organization is also known as: Federal University of Roraima.

Water use efficiency of cassava plants under competition conditions

Abstract: Objetivou-se com este trabalho avaliar caracteristicas associadas a eficiencia de uso da agua de plantas de mandioca sob competicao ou nao com plantas daninhas. O experimento foi realizado em condicoes de ambiente aberto, sendo as unidades experimentais compostas por vasos de fibra de vidro de 150 dm3preenchidos com Latossolo Vermelho Amarelo, previamente adubado. Os tratamentos consistiram no cultivo de plantas de mandioca isoladas e associadas a tres especies daninhas (Bidens pilosa, Commelina benghalensis e Brachiaria plantaginea). Apos inicio da brotacao das manivas, 15 dias apos o plantio, fez-se o desbaste das plantas daninhas, semeadas no momento do plantio das manivas, deixando-se oito plantas de B. pilosa, quatro de C. benghalensis e quatro de B. plantaginea. Aos 60 dias apos a emergencia (DAE), foram avaliados a condutância estomatica de vapores de agua (Gs), pressao de vapor na câmara subestomatica (Ean), gradiente entre temperatura da folha e do ar (ΔT), taxa de transpiracao (E) e a eficiencia do uso da agua (EUA). A especie B. pilosa demonstrou maior capacidade de afetar o crescimento das plantas de mandioca. B. plantaginea e muito eficiente em utilizar a agua, principalmente por apresentar metabolismo C4 , e se mantem competitiva com a mandioca mesmo sob baixo status hidrico temporario. C. benghalensis, por sua vez, nao e boa competidora por luz e aparentemente nao e causadora primaria do esgotamento da agua no solo. Os efeitos, nesse caso, das plantas daninhas, foram mais associados a competicao. No entanto, eles foram considerados entre moderados a baixos. Isso implica que a competicao estabelecida a nivel experimental foi baixa.

Virulence of Metarhizium anisopliae and Beauveria bassiana to Ctenocephalides felis felis

Abstract: Ctenocephalides felis felis is a flea species that parasitizes dogs and cats. The current study verified the in vitro virulence of the entomopathogenic fungi Metarhizium anisopliae and Beauveria bassiana to eggs and adults of C. felis felis. The fungal isolates were cultivated on rice grains in plastic bags. Conidial suspensions were then prepared by immersing the grains in Tween 80 aqueous solution (0.01%). Eggs and adults of C. felis felis were obtained from a laboratory colony. Experiments were composed of one control and four treatment groups (10(5), 10(6), 10(7), and 10(8) conidia mL(-1)). Both insect pathogens inhibited egg hatchability and caused adult mortality. Among isolates used in this study, M. anisopliae (isolate E9) was the most successful at inhibiting hatching, while B. bassiana (isolate 986) was the most powerful for causing mortality in adults. The results indicate that these entomopathogenic fungi have promising potential for use in controlling both C. felis felis egg and adult stages.

Temperature effects on the occurrence of long interatomic distances in atomic chains formed from stretched gold nanowires.

Abstract: The origin of long interatomic distances in suspended gold atomic chains formed from stretched nanowires remains the object of debate despite the large amount of theoretical and experimental work. Here, we report new atomic resolution electron microscopy observations acquired at room and liquid-nitrogen temperatures and theoretical results from ab initio quantum molecular dynamics on chain formation and stability. These new data are suggestive that the long distances are due to contamination by carbon atoms originating from the decomposition of adsorbed hydrocarbon molecules.

Dinâmica de rizóbios em solo do cerrado de Roraima durante o período de estiagem

Abstract: The biological nitrogen fixation in legumes is performed by a group of bacteria known as rhizobia. The survival of these bacteria in soils is affected by several factors, such as temperature, drought and soil fertility. This study was performed to evaluate the dynamics of rhizobia in the soil after soybean cultivation and during a dry season in the cerrado of Roraima. Three areas were sampled: i) native cerrado as reference; ii) an area previously cultivated with soybean for one season; and iii) another one cultivated for two seasons also with soybean. The soil was sampled at a depth of 0-10 cm in five times (0, 45, 90, 135 and 180 days) during the dry season (September 2006 to March 2007). The rhizobial density in the soil was evaluated by the most probable number method with infection of soybean and cowpea plants. It was observed very low number of soybean nodulating bacteria in the reference area, but a high density, of up to several hundred rhizobia capable to nodulate cowpea was measured in this same area. Cropping of soybean with inoculated seeds increased rhizobial density evaluated by both trapping hosts. In cropped areas, an intense reduction of rhizobium density was observed just after soybean harvest, and this reduction continued until the end of the period of evaluation. It was concluded that soybean cultivation increases the density of rhizobial in the cerrado soil; however, this density is drastically reduced, during the dry season, by 99% at the end of the dry period.

Os lagos do lavrado de Boa Vista - Roraima: fisiografia, físico-química das águas, mineralogia e química dos sedimentos

Abstract: The landscape of northeast portion of the Roraima state is formed by a plain surface, covered by savanna, where many lakes, wetlands and Mauritia flexuosa paths occur. These lakes exhibit several shapes, but the most frequent ones are drop-shape, circular, ellipsoid and twin shapes, being generally related to small water courses (igarapes) like its headwaters. The lacustrine basins are very small and shallow. The water’s level is seasonally controlled, during the drought season several lakes, wetlands and paths dry and stress the grassy ones and the Mauritia flexuosa. The lakes vegetation is compost by dense communities of aquatic macrophytes, mainly for Cyperaceae, which occupies whole lake or distributes in a circular and concentric zone, with a deeper and bubbling center area, indicative of water spring. The lakes don’t present own fine sediments, its substratum’s material is mostly sandy and the grains show no roundness until to low roundness as well as low sphericity. They are essentially constituted of quartz, being less frequent kaolinite. The chemical composition displays high concentrations of SiO2 and low values of Al2O3 and Fe2O3 allowing to correlate them to Boa Vista Formation sediments. The external and internal lacustrine features suggest that occurrence of these lakes in savanna environment are related to near surface groundwater, that during the rainy season intercepts the shallow land surface depressions, in the form of springs forming the lakes and wetlands. The whole landscape of lakes formed by green and open fields represents a singular lake system in the Amazon region which due the accelerate and disordered urban expansion of the Boa Vista city suffers environmental impacts including the extinction of many lakes and alteration of the waters quality through of anthropogenic activities such as clothes laundering and end destination of domestic effluents.