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\bibitem{Zarenia_etal2010} {\textquotedblleft}\textit{Simplified model for the energy levels of quantum rings in single layer and bilayer graphene}{\textquotedblright}. Zarenia M, Pereira JM, Chaves A, Peeters FM, Farias GA, Physical review : B : condensed matter and materials physics \textbf{81}, 045431 (2010).   http://doi.org/10.1103/PhysRevB.81.045431

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