Theory of Andreev reflection in a two-orbital model of iron-pnictide superconductors

A recently developed theory for the problem of Andreev reflection between a normal metal (N) and a multiband superconductor (MBS) assumes that the incident wave from the normal metal is coherently transmitted through several bands inside the superconductor. Such splitting of the probability amplitude into several channels is the analogue of a quantum waveguide. Thus, the appropriate matching conditions for the wave function at the N/MBS interface are derived from an extension of quantum waveguide theory. Interference effects between the transmitted waves inside the superconductor manifest themselves in the conductance. We provide results for a FeAs superconductor, in the framework of a recently proposed effective two-band model and two recently proposed gap symmetries: in the sign-reversed s-wave ($\Delta\cos(k_x)\cos(k_y)$) scenario resonant transmission through surface Andreev bound states (ABS) at nonzero energy is found as well as destructive interference effects that produce zeros in the conductance; in the extended s-wave ($\Delta[\cos(k_x)+\cos(k_y)]$) scenario no ABS at finite energy are found.Comment: 4 pages, 5 figure

Múltiplos sacos embrionários em ovários do acesso sexual de Brachiaria brizantha (Poaceae).

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The art of Bosch - a mirror to death and beyond

Who really pays attention to poetry, philosophy, painting or other art form? We rather seek for what is immediately needed or quickly consumable, what doesn't bother nor disturb us. Emotions and cultural products are strongly linked. But the perception of art depends on how it impresses us. Art can confront us with a reality. In a civilization dominated by images, through the media, advertising and virtual worlds, art, like life and death, is rarely valued. We approached on this study, the way in which college students - of both sexes, from courses of management, history and psychology - interpreted the image/painting ‘Paradise: Ascent of the Blessed’, from Hieronymus Bosch, which alludes to death and beyond-death. We analyzed the thoughts, feelings, images and symbols that emerged from their answers, through open questions, after seeing the image/painting. Men revealed security, like they were watching for something they see as controllable and far away from them. Women expressed an active emotional involvement, as well as fear, belief in God and hope in finding a path through the darkness, revealing an intense feeling of proximity before death and immortality. Students of psychology, in particular, revealed a more emotional reaction to the image/death, than the future historians. The conceptions of the first ones are closer to the women's perspectives, while the others resemble those of men. This work invited us to reflect about ourselves, the power of images, death, and on what lies beyond death and life