Análise da rotação de cultura na área de reforma de canavial.

A partir do problema exposto, o trabalho analisará o processo de rotação de culturas em área de reforma do canavial, enfatizando a capacidade das usinas na coordenação dos processos e recursos, considerando a estrutura de governança e os custos de transação, como fatores importantes para o desenvolvimento da atividade. A análise terá um caráter empírico pelo estudo de caso de três usinas em regiões heterogêneas na produção de cana-de-açúcar, baseando-se na Teoria dos Custos de Transação (TCT) (FIANI, 2002)

Upper bound for the conductivity of nanotube networks

Films composed of nanotube networks have their conductivities regulated by the junction resistances formed between tubes. Conductivity values are enhanced by lower junction resistances but should reach a maximum that is limited by the network morphology. By considering ideal ballistic-like contacts between nanotubes we use the Kubo formalism to calculate the upper bound for the conductivity of such films and show how it depends on the nanotube concentration as well as on their aspect ratio. Highest measured conductivities reported so far are approaching this limiting value, suggesting that further progress lies with nanowires other than nanotubes.Comment: 3 pages, 1 figure. Minor changes. Accepted for publication in Applied Physics Letter

Enhanced Optical Dichroism of Graphene Nanoribbons

The optical conductivity of graphene nanoribbons is analytical and exactly derived. It is shown that the absence of translation invariance along the transverse direction allows considerable intra-band absorption in a narrow frequency window that varies with the ribbon width, and lies in the THz range domain for ribbons 10-100nm wide. In this spectral region the absorption anisotropy can be as high as two orders of magnitude, which renders the medium strongly dichroic, and allows for a very high degree of polarization (up to ~85) with just a single layer of graphene. The effect is resilient to level broadening of the ribbon spectrum potentially induced by disorder. Using a cavity for impedance enhancement, or a stack of few layer nanoribbons, these values can reach almost 100%. This opens a potential prospect of employing graphene ribbon structures as efficient polarizers in the far IR and THz frequencies.Comment: Revised version. 10 pages, 7 figure

Disorder Induced Localized States in Graphene

We consider the electronic structure near vacancies in the half-filled honeycomb lattice. It is shown that vacancies induce the formation of localized states. When particle-hole symmetry is broken, localized states become resonances close to the Fermi level. We also study the problem of a finite density of vacancies, obtaining the electronic density of states, and discussing the issue of electronic localization in these systems. Our results also have relevance for the problem of disorder in d-wave superconductors.Comment: Replaced with published version. 4 pages, 4 figures. Fig. 1 was revise

Aprendizagem e disseminação de conhecimento nos colaboratórios das redes de pesquisa da Embrapa.

O objetivo deste artigo é apresentar e discutir uma proposta de modelo conceitual para a criação de Colaboratórios para as redes de pesquisa da Embrapa. Os Colaboratórios são espaços virtuais de aprendizagem que, estruturados sob uma lógica sócio-interacionista e com ferramentas da web 2.0, tendem a potencializar a construção de novos conhecimentos e aprendizagens entre os cientistas das redes de pesquisa, fomentando também a aprendizagem organizacional.SBIE 2012