4,464 research outputs found
Coasting cosmologies with time dependent cosmological constant
The effect of a time dependent cosmological constant is considered in a
family of scalar tensor theories. Friedmann-Robertson-Walker cosmological
models for vacumm and perfect fluid matter are found. They have a linear
expansion factor, the so called coasting cosmology, the gravitational
"constant" decreace inversely with time; this model satisfy the Dirac
hipotesis. The cosmological "constant" decreace inversely with the square of
time, therefore we can have a very small value for it at present time.Comment: 7 pages, latex file (ijmpal macro), accepted for publication in Int.
Mod. Phys.
General approach for studying first-order phase transitions at low temperatures
By combining different ideas, a general and efficient protocol to deal with
discontinuous phase transitions at low temperatures is proposed. For small
's, it is possible to derive a generic analytic expression for appropriate
order parameters, whose coefficients are obtained from simple simulations. Once
in such regimes simulations by standard algorithms are not reliable, an
enhanced tempering method, the parallel tempering -- accurate for small and
intermediate system sizes with rather low computational cost -- is used.
Finally, from finite size analysis, one can obtain the thermodynamic limit. The
procedure is illustrated for four distinct models, demonstrating its power,
e.g., to locate coexistence lines and the phases density at the coexistence.Comment: 5 page
Human case of West Nile neuroinvasive disease in Portugal, summer 2015
A case of West Nile virus (WNV) infection was reported in the Algarve region, Portugal, in the first week of September 2015. WNV is known to circulate in Portugal, with occasional reports in horses and birds (2004 to 2011) and very sporadically human cases (in 2004 and in 2010). Here we present the clinical and laboratory aspects related to the first human case of West Nile neuroinvasive disease reported in Portugal
Toward a spatial understanding of staple food and nonstaple food production in Brazil
Brazilian agricultural census data at the municipal level are used to develop and map a simple index of staple food versus nonstaple food agriculture for Brazil over time (1996-2006). The results show spatial variation in the direction and degree of the shift toward or away from staple food cropping across Brazil. The index is presented as an important methodological step toward a systematic geographic understanding of crop share changes surrounding food versus fuel and other nonfood crop production. (1996 ?? 2006 ?) Los datos del censo agropecuario brasileno a nivel municipal se utilizan para desarrollar y cartografiar un indice simple de la agricultura de alimentos esenciales versus la de alimentos no esenciales del Brasil durante un tiempo (1996-2006). Los resultados muestran variacion espacial en la direccion y grado del cambio hacia cultivos para alimentacion esencial, o lo contrario, en Brasil. El indice se presenta como un paso metodologico importante hacia un entendimiento geografico sistematico de cambios hacia un tipo de cosecha compartida que privilegia la produccion de alimentos, contra las cosechas para combustibles y otra produccion no alimentaria66224925
Constraining cosmological parameters from N-body simulations with Variational Bayesian Neural Networks
Methods based on Deep Learning have recently been applied on astrophysical
parameter recovery thanks to their ability to capture information from complex
data. One of these methods is the approximate Bayesian Neural Networks (BNNs)
which have demonstrated to yield consistent posterior distribution into the
parameter space, helpful for uncertainty quantification. However, as any modern
neural networks, they tend to produce overly confident uncertainty estimates
and can introduce bias when BNNs are applied to data. In this work, we
implement multiplicative normalizing flows (MNFs), a family of approximate
posteriors for the parameters of BNNs with the purpose of enhancing the
flexibility of the variational posterior distribution, to extract ,
, and from the QUIJOTE simulations. We have compared this method
with respect to the standard BNNs, and the flipout estimator. We found that
MNFs combined with BNNs outperform the other models obtaining predictive
performance with almost one order of magnitude larger that standard BNNs,
extracted with high accuracy (), and precise uncertainty
estimates. The latter implies that MNFs provide more realistic predictive
distribution closer to the true posterior mitigating the bias introduced by the
variational approximation and allowing to work with well-calibrated networks.Comment: 15 pages, 4 figures, 3 tables, submitted. Comments welcom
Improving light harvesting in polymer photodetector devices through nanoindented metal mask films
To enhance light harvesting in organic photovoltaic devices, we propose the incorporation of a metal (aluminum) mask film in the system’s usual layout. We fabricate devices in a sandwich geometry, where the mask (nanoindented with a periodic array of holes of sizes d and spacing s) is added between the transparent electrode and the active layer formed by a blend of the semiconducting polymer P3HT and substituted fullerene. Its function is to promote trapping of the incident light into the device’s cavity (the region corresponding to the active layer). For d, we set a value that allows light diffraction through the holes in the relevant absorption range of the polymer. To optimize the mask structure, we consider a very simple model to determine the s leading to trapped fields that are relatively intense and homogeneous within the device. From measurements of the action spectra, we show that, indeed, such architecture can considerably improve the resulting photocurrent efficiencies—one order of magnitude in the best situation studied.
Emissão de N2O e CH4 em diferentes níveis de palhada remanescente na cultura de cana-de-açúcar na região de Dourados, MS.
Programa boas práticas agropecuárias em bovinos de corte na Região Sul do Brasil: situação atual e perspectivas.
O BPA-Gado de Corte na região Sul; O diagnóstico dos estabelecimentos filiados a APROCCIMA: A posição dos estabelecimentos quanto aos itens obrigatórios do BPA, A posição dos estabelecimentos quanto aos itens altamente recomendáveis, Análise integrada das conformidades.bitstream/item/55755/1/DT87.pdfTambém publicado na versão impressa
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