Navegando por Autor "Mello, V.D."
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Artigo Effects of graphene on light transmission spectra in Dodecanacci photonic quasicrystals(Elsevier, 2019) Silva, E.F.; Vasconcelos, Manoel Silva de; Costa, C.H.; Anselmo, Dory Hélio Aires de Lima; Mello, V.D.We make a theoretical study of light waves, for both TE and TM polarization with oblique incidence. The light waves propagate on SiO2/TiO2 multilayers, organized by Dodecanacci sequence, where we consider a graphene monolayer at the interfaces between distinct layers. We also calculate numerically the optical transmissivity spectrum, by using the transfer matrix method, for the cases with a graphene sheet and without a graphene sheet at the interfaces. Our results indicate that the whole optical spectrum becomes affected by the presence of graphene in the interfaces. Among these effects, we can highlight the shift of bandgaps to high-frequency regions, the emergence of a graphene induced bandgap at low-frequency regions, and the decreasing of transmittance in the whole frequency range considered here. The self-similarity, which is a property that indicates a fractal spectrum, keeps essentially unchanged when we consider graphene sheets between the layers. Our studies can be applied to electromagnetic filters, where an input gate voltage, applied on the graphene sheets, can control the bandgaps which arise on these structuresArtigo Magnetocaloric effect of thin Dy films(ELSEVIER, 2006) Mello, V.D.; Dantas, Ana L.; Carriço, Artur da SilvaWe report a theoretical study of the magnetocaloric effect (MCE) of Dy thin films, and show that the confinement of spins in the direction perpendicular to the surfaces leads to a considerable enhancement of the MCE. The adiabatic temperature change, 1T , for external field strength change, 1H, of the order of a few kOe, is much larger than what is found in bulk Dy, reaching 1T 1H = 6 K/T for ultra-thin films.