Magnetization profile for impurities in graphene nanoribbons

The magnetic properties of graphene-related materials and in particular the spin-polarised edge states predicted for pristine graphene nanoribbons (GNRs) with certain edge geometries have received much attention recently due to a range of possible technological applications. However, the magnetic properties of pristine GNRs are not predicted to be particularly robust in the presence of edge disorder. In this work, we examine the magnetic properties of GNRs doped with transition-metal atoms using a combination of mean-field Hubbard and Density Functional Theory techniques. The effect of impurity location on the magnetic moment of such dopants in GNRs is investigated for the two principal GNR edge geometries - armchair and zigzag. Moment profiles are calculated across the width of the ribbon for both substitutional and adsorbed impurities and regular features are observed for zigzag-edged GNRs in particular. Unlike the case of edge-state induced magnetisation, the moments of magnetic impurities embedded in GNRs are found to be particularly stable in the presence of edge disorder. Our results suggest that the magnetic properties of transition-metal doped GNRs are far more robust than those with moments arising intrinsically due to edge geometry.Comment: submitte

Impurity segregation in graphene nanoribbons

The electronic properties of low-dimensional materials can be engineered by doping, but in the case of graphene nanoribbons (GNR) the proximity of two symmetry-breaking edges introduces an additional dependence on the location of an impurity across the width of the ribbon. This introduces energetically favorable locations for impurities, leading to a degree of spatial segregation in the impurity concentration. We develop a simple model to calculate the change in energy of a GNR system with an arbitrary impurity as that impurity is moved across the ribbon and validate its findings by comparison with ab initio calculations. Although our results agree with previous works predicting the dominance of edge disorder in GNR, we argue that the distribution of adsorbed impurities across a ribbon may be controllable by external factors, namely an applied electric field. We propose that this control over impurity segregation may allow manipulation and fine-tuning of the magnetic and transport properties of GNRs.Comment: 5 pages, 4 figures, submitte

Controle biológico da mosca branca Trialeurodes vaporariorum (Homoptera, Aleyrodidae), em casas de vegetação.

Casas de vegetação podem ser consideradas ilhas ecológicas nas quais as condições ambientais diferem muito daquelas encontradas em campo aberto, onde plantas e animais estão expostos as constantes variações abióticas e bióticas do meio. Nesses ambientes o suprimento de energia e alimento é sem limites ao crescimento do vegetal e rápido e exuberante, fornecendo um ótimo habitat para predadores. O efeito de isolamento das pragas dentro de uma casa de vegetação contribui para a não efetividade das medidas de controle e, ainda, para o aumento e manutenção da resistência aos pesticidas devido ao seu uso prolongado.bitstream/item/90508/1/1713-Controle-biologico-da-mosca-branca.pd

Hole-LO phonon interaction in InAs/GaAs quantum dots

We investigate the valence intraband transitions in p-doped self-assembled InAs quantum dots using far-infrared magneto-optical technique with polarized radiation. We show that a purely electronic model is unable to account for the experimental data. We calculate the coupling between the mixed hole LO-phonon states using the Fr\"ohlich Hamiltonian, from which we determine the polaron states as well as the energies and oscillator strengths of the valence intraband transitions. The good agreement between the experiments and calculations provides strong evidence for the existence of hole-polarons and demonstrates that the intraband magneto-optical transitions occur between polaron states

Detecção e identificação molecular de Xanthomonas spp. causadoras da mancha bacteriana do tomateiro.

Neste comunicado são relatados os procedimentos para a identificação molecular das quatro espécies de Xanthomonas associadas à mancha bacteriana do tomateiro.bitstream/item/72192/1/cot-841.pd

The effect of a stellar magnetic variation on the jet velocity

Stellar jets are normally constituted by chains of knots with some periodicity in their spatial distribution, corresponding to a variability of order of several years in the ejection from the protostar/disk system. A widely accepted theory for the presence of knots is related to the generation of internal working surfaces due to variations in the jet ejection velocity. In this paper we study the effect of variations in the inner disk-wind radius on the jet ejection velocity. We show that a small variation in the inner disk-wind radius produce a variation in the jet velocity large enough to generate the observed knots. We also show that the variation in the inner radius may be related to a variation of the stellar magnetic field.Comment: 5 pages, 3 figures, accepted for publication in Ap

Uso de adubos verdes como estratégia para restabelecer a produção agrícola do sítio Hikari, Nova Friburgo, RJ, após evento climático.

Este texto relata como a autora principal, agricultora na comunidade Rio Grande, Nova Friburgo-RJ, em parceria com o Núcleo de Pesquisa e Treinamento para Agricultores (NPTA) da Embrapa na Região Serrana do Rio de Janeiro, estabeleceu estratégia no sentido de restabelecer a produção agrícola de sua propriedade, afetada por deslizamentos e enchentes provocadas pela maior catástrofe climática e geotécnica do país, ocorrida em janeiro de 2011.Trabalho apresentado no 4. Seminário de Agroecologia do Distrito Federal e Entorno, Brasília, DF