347 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
Maternal pneumococcal nasopharyngeal carriage and risk factors for neonatal carriage after the introduction of pneumococcal conjugate vaccines in The Gambia.
OBJECTIVES: Pneumococcal nasopharyngeal carriage occurs early in life. However, the role of vertical transmission is not well understood. The aims of this study were to describe carriage among mothers and their newborns, and to assess for risk factors for neonatal carriage. METHODS: In a nested retrospective cohort study, we analysed data from the control arm of a randomized controlled trial conducted in The Gambia 2 to 3 years after introduction of pneumococcal conjugate vaccine (PCV) 13. Nasopharyngeal swabs were collected from 374 women and their newborns on the day of delivery, then 3, 6, 14 and 28 days later. Pneumococci were isolated and serotyped using conventional microbiologic methods. RESULTS: Carriage increased from 0.3% (1/373) at birth to 37.2% (139/374) at day 28 (p <0.001) among neonates and from 17.1% (64/374) to 24.3% (91/374) (p 0.015) among women. In both groups, PCV13 vaccine-type (VT) serotypes accounted for approximately one-third of the pneumococcal isolates, with serotype 19A being the most common VT. Maternal carriage (adjusted odds ratio (OR) = 2.82; 95% confidence interval (CI), 1.77-4.80), living with other children in the household (adjusted OR = 4.06; 95% CI, 1.90-8.86) and dry season (OR = 1.98; 95% CI, 1.15-3.43) were risk factors for neonatal carriage. Over half (62.6%) of the neonatal carriage was attributable to living with other children in the same household. CONCLUSIONS: Three years after the introduction of PCV in The Gambia, newborns are still rapidly colonized with pneumococcus, including PCV13 VT. Current strategies for pneumococcal control in Africa do not protect this age group beyond the herd effect
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