Electrostatics of electron-hole interactions in van der Waals heterostructures

The role of dielectric screening of electron-hole interaction in van der Waals heterostructures is theoretically investigated. A comparison between models available in the literature for describing these interactions is made and the limitations of these approaches are discussed. A simple numerical solution of Poissons equation for a stack of dielectric slabs based on a transfer matrix method is developed, enabling the calculation of the electron-hole interaction potential at very low computational cost and with reasonable accuracy. Using different potential models, direct and indirect exciton binding energies in these systems are calculated within Wannier-Mott theory, and a comparison of theoretical results with recent experiments on excitons in two-dimensional materials is discussed.Comment: 10 pages, 8 figure

Estresse por déficit hídrico em plantas forrageiras.

bitstream/CNPC-2010/23051/1/doc89.pd

Produção e distribuição sazonal de litter em áreas de caatinga sob diferentes manejos.

Resumo: O litter compreende restos vegetais e animais. Sua presença confere proteção ao solo evitando o efeito negativo das enxurradas, mantendo a temperatura e estrutura do solo. Este trabalho objetivou quantificar a produção e distribuição de litter em áreas de caatinga raleada e não manipulada. Três áreas foram utilizadas: raleada para fins pastoris, raleada para fins apícolas e não manipulada. A produção foi obtida a partir do lançamento de molduras e 1,0x0,25m em diferentes épocas do ano de 2012. O litter foi fracionado manualmente em seus componentes e determinados suas proporções da massa total. A área não manipulada apresentou maior produção de litter, 5.714,35 Kg/ha enquanto a área de Caatinga raleada para fins apícolas a menor produção, 3.921,21 Kg/ha. A miscelânea foi a fração do litter que apresentou maior representatividade chegando a responder por 50% de toda a produção. A produção de litter de uma área nativa pode ser semelhante a uma área raleada. A produção tem relação direta com a precipitação. Esta mostrou sazonalidade na produção total, contrariando suas frações que mantiveram-se equilibrados durante todo o ano. [Seasonal production and distribution of litter in different areas under caatinga managements]. Abstract: The litter includes plant and animal remains. Its presence confers protection to the ground avoiding the negative effect of floods, keeping the temperature and soil structure. This study aimed to quantify the production and distribution of litter in areas of thinned caatinga and not manipulated. Three areas were used for grazing purposes thinned, thinned for apiculture and not manipulated. The production was obtained from the launch of frames and 1.0 x0, 25m at different times of the year 2012. The litter was manually fractionated into its components, and certain proportions of their total mass. The area had not manipulated greater production of litter, 5714.35 kg / ha while the area of Caatinga thinned for apiculture lower production, 3921.21 kg / ha. The smorgasbord was the fraction of the litter with the highest representation coming to account for 50% of all production. The production of litter from an area native can be similar to a thinned area. The production is directly related to precipitation. The total production of litter showed seasonality, contradicting its fractions which remained balanced throughout the year

Efeito do processamento térmico na composição química, compostos bioativos e atividade antioxidante de cultivares de feijão-caupi.

This study aimed to determine the effect of cooking on the centesimal compositions, the content of bioactive compounds, and antioxidant activities in beans of the cowpea cultivars. The beans were cooked without soaking (1:5 w/v) in a pressure cooker for 780 seconds..

Uso do orçamento forrageiro em abordagem participativa para produção de caprinos no bioma caatinga.

Resumo: O uso do orçamento forrageiro (OF) com enfoque participativo visa envolver agricultores no processo de construção de técnicas que possam ser facilmente utilizadas para o manejo sustentável dos recursos naturais. O objetivo deste trabalho foi testar OF como instrumento para planejamento do rebanho caprino. A experiência foi conduzida em área individual de 11ha, em assentamento no sertão do Apodi (RN). A área foi composta por cultivo de algodão agroecológico, sistema agrossilvipastoril e pasto nativo. O rebanho foi de vinte animais. OF foi realizado em três etapas: levantamento da produção de massa seca total de forragem disponível, avaliação do efetivo animal e planejamento. As informações do levantamento determinaram o tempo máximo de uso da área para manter as metas de ganho de peso para cabritos e manutenção de peso dos adultos. As práticas agroecológicas aumentaram a oferta de forragem. Houve manutenção do peso das cabras e ganhos de peso nas novilhas. Os cabritos ganharam peso de forma linear. O monitoramento permitiu confirmar que a ferramenta do orçamento forrageiro foi efetiva em auxiliar no planejamento zootécnico do rebanho no semiárido. [Forage budget on participatory approach to goat production in caatinga biome]. Abstract: Forage budget (FB) using participatory approach had been used to include smallholders in technology generation process and improving transfer technology for others. This research was carried out to test FB as a tool to make a planning for goat production system in Brazilian semi arid land. In an individual settlement area about 11 ha was implemented it. There were agroecological cotton system, agrossilvipastoral and native vegetation there. There were 20 animal in the area. FB was implemented in three phases: quantification of forage biomass total and available, herd evaluation and planning. It was determinate a maximum time to keep animal in the land using information from planning that preview as goal keep weight in goats and gain weight in kids. Ecological practices improved amount of forage. There was possible keep weight in goats. Young goats had gained weight. All kids gained weight during experimental period. Monitoring zootechnical aspects were effective to ensure forage budget like a good tool to help smallholders in sustainable planning use natural resources

Reação de clones comerciais de cajueiro anão à antracnose e ao mofo preto.

A expansao da cultura do cajueiro depende, fundamentalmente, da adocao de modernas tecnicas de producao, colheita e utilizacao de seus produtos. Evidentemente, o uso de clones de cajueiro anao representa um consenso generalizado dentro deste novo enfoque empresarial da cultura.bitstream/CNPAT-2010/11951/1/Ct-012.pd

Mineral content, phenolic compounds and bioactive amines of cheese bread enriched with cowpea.

Cheese bread presents great acceptance and market expansion. Due to the lack of standardization in its manufacturing, various ingredients can be added. It was aimed to determine the content of minerals, bioactive compounds and antioxidant activity in cheese bread enriched with biofortified cowpea. Two formulations were prepared, standard cheese bread (without cowpea) and enriched cheese bread. The minerals were analyzed using the plasma emission spectrometry technique with inductive coupling, phenolic compounds and antioxidant activity were determined by spectrophotometry and the amines by High Performance Liquid Chromatography. All analyzes were performed in triplicate and for the comparison of the means between two variables, Student?s t-test was applied and for multiple comparisons, the Tukey test. It was observed that the enriched cheese bread is source of copper, zinc and sodium and presents high content of calcium, phosphorus and magnesium, considering the recommendations for the children?s audience. The concentrations of total phenolics, flavonoids and condensed tannins increased significantly with the introduction of cowpea. It was also observed an significant increase of spermidine, cadaverine and agmatine. The antioxidant activity was statistically higher in enriched cheese bread. It is concluded, therefore, that cheese bread with cowpea contributes to the supply of minerals and bioactive compounds