406 research outputs found
Scale Factor Self-Dual Cosmological Models
We implement a conformal time scale factor duality for
Friedmann-Robertson-Walker cosmological models, which is consistent with the
weak energy condition. The requirement for self-duality determines the
equations of state for a broad class of barotropic fluids. We study the example
of a universe filled with two interacting fluids, presenting an accelerated and
a decelerated period, with manifest UV/IR duality. The associated self-dual
scalar field interaction turns out to coincide with the "radiation-like"
modified Chaplygin gas models. We present an equivalent realization of them as
gauged K\"ahler sigma models (minimally coupled to gravity) with very specific
and interrelated K\"ahler- and super-potentials. Their applications in the
description of hilltop inflation and also as quintessence models for the late
universe are discussed.Comment: v3, improved and extended version to be published in JHEP; new
results added to sect.2; 4 figures; 17pg
Digestibilidade de dietas constantes de feno de capim mandante e milho, suplementadas com farelos de algodão e de mamona desintoxicada.
Foi realizado um estudo comparativo entre os farelos de algodão e de mamona desintoxicada, através de ensaio de digestibilidade com ovinos adultos, como suplementos proteícos de uma dieta básica constante de capim mandante e milho moido (grão)
Graphene formed on SiC under various environments: Comparison of Si-face and C-face
The morphology of graphene on SiC {0001} surfaces formed in various
environments including ultra-high vacuum, 1 atm of argon, and 10^-6 to 10^-4
Torr of disilane is studied by atomic force microscopy, low-energy electron
microscopy, and Raman spectroscopy. The graphene is formed by heating the
surface to 1100 - 1600 C, which causes preferential sublimation of the Si
atoms. The argon atmosphere or the background of disilane decreases the
sublimation rate so that a higher graphitization temperature is required, thus
improving the morphology of the films. For the (0001) surface, large areas of
monolayer-thick graphene are formed in this way, with the size of these areas
depending on the miscut of the sample. Results on the (000-1) surface are more
complex. This surface graphitizes at a lower temperature than for the (0001)
surface and consequently the growth is more three-dimensional. In an atmosphere
of argon the morphology becomes even worse, with the surface displaying
markedly inhomogeneous nucleation, an effect attributed to unintentional
oxidation of the surface during graphitization. Use of a disilane environment
for the (000-1) surface is found to produce improved morphology, with
relatively large areas of monolayer-thick graphene.Comment: 22 pages, 11 figures, Proceedings of STEG-2 Conference; eliminated
Figs. 4 and 7 from version 1, for brevity, and added Refs. 18, 29, 30, 31
together with associated discussio
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