Wavepacket scattering on graphene edges in the presence of a (pseudo) magnetic field

The scattering of a Gaussian wavepacket in armchair and zigzag graphene edges is theoretically investigated by numerically solving the time dependent Schr\"odinger equation for the tight-binding model Hamiltonian. Our theory allows to investigate scattering in reciprocal space, and depending on the type of graphene edge we observe scattering within the same valley, or between different valleys. In the presence of an external magnetic field, the well know skipping orbits are observed. However, our results demonstrate that in the case of a pseudo-magnetic field, induced by non-uniform strain, the scattering by an armchair edge results in a non-propagating edge state.Comment: 8 pages, 7 figure

Controle de plantas daninhas na cultura do morangueiro com cobertura do solo.

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All-strain based valley filter in graphene nanoribbons using snake states

A pseudo-magnetic field kink can be realized along a graphene nanoribbon using strain engineering. Electron transport along this kink is governed by snake states that are characterized by a single propagation direction. Those pseudo-magnetic fields point towards opposite directions in the K and K' valleys, leading to valley polarized snake states. In a graphene nanoribbon with armchair edges this effect results in a valley filter that is based only on strain engineering. We discuss how to maximize this valley filtering by adjusting the parameters that define the stress distribution along the graphene ribbon.Comment: 8 pages, 6 figure

Light controlled magnetoresistance and magnetic field controlled photoresistance in CoFe film deposited on BiFeO3

We present a magnetoresistive-photoresistive device based on the interaction of a piezomagnetic CoFe thin film with a photostrictive BiFeO3 substrate that undergoes light-induced strain. The magnitude of the resistance and magnetoresistance in the CoFe film can be controlled by the wavelength of the incident light on the BiFeO3. Moreover, a light-induced decrease in anisotropic magnetoresistance is detected due to an additional magnetoelastic contribution to magnetic anisotropy of the CoFe film. This effect may find applications in photo-sensing systems, wavelength detectors and can possibly open a research development in light-controlled magnetic switching properties for next generation magnetoresistive memory devices.Comment: 5 pages, 4 figures, journal pape

Abundances on the Main Sequence of Omega Centauri

Abundance ratios of carbon, nitrogen and strontium relative to iron, calculated using spectrum synthesis techniques, are given for a sample of main sequence and turnoff stars that belong to the globular cluster omega Centauri. The variations of carbon, nitrogen and/or strontium show several different abundance patterns as a function of [Fe/H]. The source of the enhancements/depletions in carbon, nitrogen and/or strontium may be enrichment from asymptotic giant branch stars of low (1--3 solar masses) and intermediate (3--8 solar masses) mass. Massive rotating stars which produce excess nitrogen without carbon and oxygen overabundances may also play a role. These abundances enable different contributors to be considered and incorporated into the evolutionary picture of omega Cen.Comment: 43 Pages, 13 Figures. Accepted for publication in Ap

Levantamento de fungos causadores de podridões de colmo em milho na região Centro Oeste do Brasil.

As podridões de colmo estão entre as mais importantes doenças da cultura do milho. Vários são os patógenos causadores de podridões de colmo em plantas de milho, incluindo fungos e bactérias. Entre os principais, destacam-se Fusarium verticillioides, Fusarium graminearum, Colletotrichum graminicola, Stenocarpella macrospora, Stenocarpella maydis e Macrophomina phaseolina. O presente trabalho teve como objetivo realizar um levantamento da incidência de fungos causadores de podridões de colmo em milho na região Centro-Oeste do Brasil. Foram realizadas coletas de amostras nos estados de Goiás, Mato Grosso e Mato Grosso do Sul. Durante as coletas das amostras foi possível verificar uma elevada incidência de plantas apresentando sintomas de podridão de colmo em, praticamente, todas as regiões. Dentre os patógenos detectados, as maiores frequências foram verificadas para Fusarium spp. Nigrospora spp. e Stenocarpella spp., com freqüência de 45,7, 38,3 e 29,9%, respectivamente. Coletotrichum graminicola e Rhizoctonia spp. apresentaram frequência de 5,8 e 3,4%. Os demais fungos apresentaram menos de 3% de ocorrência nos isolamentos. Esses resultados demonstram a grande variabilidade de fungos envolvidos com as podridões de colmo na cultura do milho no Centro-Oeste do Brasil. Revelam, também, a elevada ocorrência de fungos do gênero Fusarium spp. e Stenocarpella spp., os quais predominaram nas amostras analisadas no presente trabalho. Os trabalhos de monitoramento da ocorrência de fungos causadores de podridões de colmo são fundamentais para o desenvolvimento e a adoção das melhores estratégias de controle desta doença na cultura do milho.bitstream/item/145936/1/bol-133.pd