Topological line defects in graphene nanoislands

Resumen del trabajo presentado a la 13th European Conference on Surface Crystallography and Dynamics, celebrada en Donostia-San Sebastián (España) del 19 al 21 de junio de 2017.Understanding grain boundaries in polycrystalline graphene is crucial for the control of both their electronic and mechanical properties. Depending on their topological structure, boundaries can impede transport across grains, or host their own one dimensional metallic states. Concerning mechanical stability, they can either weaken or strengthen the graphene sheet. We here report experimental evidence on some predicted and other new topological defect boundary structures, as found by Scanning Tunnelling Microscopy (STM) in graphene nanoislands grown on Ni(111) by CVD. By using mild annealing temperatures, we obtain multi-domain nanoislands with different types of domain boundaries. High-resolution STM images allow us to characterize both the stacking and orientation of graphene domains and the boundary atomic structure. From a statistical analysis of the rotated domains, we conclude that their abundance is closely related to the boundary energetics, evidencing that the selection of rotational domains is determined by boundary rather than stacking energetics. linear and ring boundaries separating 30º rotated domains are particularly interesting: the linear ones are predicted to be transparent to Dirac electrons, whereas confined resonances have already been observed in quantum dots bound by similar ring boundaries.Peer reviewe

Decision making in fuzzy environment and multicriteria power engineering problems

This paper presents results of research into the use of the Bellman-Zadeh approach to decision making in a fuzzy environment for solving multicriteria power engineering problems. The application of the approach conforms to the principle of guaranteed result and provides constructive lines in computationally effective obtaining harmonious solutions on the basis of solving associated maxmin problems. The presented results are universally applicable and are already being used to solve diverse classes of power engineering problems. It is illustrated by considering problems of power and energy shortage allocation, power system operation, optimization of network configuration in distribution systems, and energetically effective voltage control in distribution systems. (c) 2011 Elsevier Ltd. All rights reserved.National Council for Scientific and Technological Development of Brazil (CNPq)Minas Gerais State Energy Company (CEMIG