H.O. Frota

Spin caloritronics in graphene

Spin caloritronics, the combination of spintronics with thermoelectrics, exploiting both the intrinsic spin of the electron and its associated magnetic moment in addition to its fundamental electronic charge and temperature, is an emerging technology mainly in the development of low-power-consumption technology. In this work, we study the thermoelectric properties of a Rashba dot attached to two single layer/bilayer graphene sheets as leads. The temperature difference on the two graphene leads induces a spin current, which depends on the temperature and chemical potential. We demonstrate that the Rashba dot behaves as a spin filter for selected values of the chemical potential and is able to filter electrons by their spin orientation. The spin thermopower has also been studied where the effects of the chemical potential, temperature, and also the Rashba term have been observed.

Spintronics in a magnetic quantum dot

Spintronics or spin electronics has been a growing area of research based on the active control and manipulation of spin degrees of freedom. In this work, we study the thermoelectric properties of a quantum dot using the Anderson model in presence of the repulsive Coulomb interaction within the mean-field formalism. The temperature difference applied across the dot drives a spin current which depends on the temperature and chemical potential. We demonstrate that the quantum dot in presence of the Coulomb interaction behaves as a spin filter for selected values of the chemical potential and is able to filter electrons by their spin orientation. The spin thermopower has also been studied where the effects of the impurity energy level, temperature and also the Coulomb term have been observed.

Conductance through glycine in a graphene nanogap

We report theoretical analysis of charge transport process through a single glycine molecule utilizing graphene nanogaps. Density functional theory and non-equilibrium Green’s function method are employed to investigate the transport properties of glycine inside the gap. The projected density of states, transmittance, and the current–voltage characteristics are determined with changes in the molecular orientation inside the nanogap of c.a 0.8 nm. The current values demonstrate a high sensitivity on the orientation of the molecule. The conductance of the molecule is also dependent on the voltage.

Módulo complexo de compósitos asfálticos com argila calcinada sob flexão a quatro pontos

RESUMO Na analise mecanicista, o modulo complexo e um parâmetro de fundamental importância para construcao de modelos constitutivos do comportamento do concreto asfaltico. Dentre as opcoes mais modernas para sua obtencao, encontram-se os testes de flexao a quatro pontos, amplamente difundidos na Europa e objeto do presente estudo. Realizou-se esse experimento para obtencao do modulo dinâmico e ângulo de fase, empregando-se condicoes representativas de Manaus (AM) no tocante ao agregado graudo e temperatura, que na superficie dos pavimentos alcanca em torno de 60°C por longas horas do dia. Como material graudo, ante a escassez regional de agregado petreo, utilizou-se o Agregado Sinterizado de Argila Calcinada (ASAC), alternativa promissora diante da abundância de materia prima e viabilidade tecnica e financeira. Como resultado obteve-se pontualmente o modulo dinâmico e ângulo de fase a diversas frequencias e temperaturas. Por fim, consideradas as condicoes locais de temperatura e trafego, o modulo dinâmico apresentou grandes variacoes, indicando queda de ate 93,3% em seu valor, situacao em que o pavimento apresenta-se muito suscetivel a deformacoes permanentes, problema recorrente nos pavimentos asfalticos locais.