485 research outputs found
Nonsingular FRW cosmology and nonlinear electrodynamics
The possibility to avoid the cosmic initial singularity as a consequence of
nonlinear effects on the Maxwell eletromagnetic theory is discussed. For a flat
FRW geometry we derive the general nonsingular solution supported by a magnetic
field plus a cosmic fluid and a nonvanishing vacuum energy density. The
nonsingular behavior of solutions with a time-dependent -term are
also examined. As a general result, it is found that the functional dependence
of can uniquely be determined only if the magnetic field remains
constant. All these models are examples of bouncing universes which may exhibit
an inflationary dynamics driven by the nonlinear corrections of the magnetic
field.Comment: 20 pages, 7 figure
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Remote system for detection of low-levels of methane based on photonic crystal fibres and wavelength modulation spectroscopy
In this work we described an optical fibre sensing system for detecting low levels of methane. The properties of hollow-core photonic crystal fibres are explored to have a sensing head with favourable characteristics for gas sensing, particularly in what concerns intrinsic readout sensitivity and gas diffusion time in the sensing structure. The sensor interrogation was performed applying the Wavelength Modulation Spectroscopy technique, and a portable measurement unit was developed with performance suitable for remote detection of low levels of methane. This portable system has the capacity to simultaneously interrogate four remote photonic crystal fibre sensing heads. Copyright © 2009 J. P. Carvalho et al
Bayesian Analysis and Constraints on Kinematic Models from Union SNIa
The kinematic expansion history of the universe is investigated by using the
307 supernovae type Ia from the Union Compilation set. Three simple model
parameterizations for the deceleration parameter (constant, linear and abrupt
transition) and two different models that are explicitly parametrized by the
cosmic jerk parameter (constant and variable) are considered. Likelihood and
Bayesian analyses are employed to find best fit parameters and compare models
among themselves and with the flat CDM model. Analytical expressions
and estimates for the deceleration and cosmic jerk parameters today ( and
) and for the transition redshift () between a past phase of cosmic
deceleration to a current phase of acceleration are given. All models
characterize an accelerated expansion for the universe today and largely
indicate that it was decelerating in the past, having a transition redshift
around 0.5. The cosmic jerk is not strongly constrained by the present
supernovae data. For the most realistic kinematic models the
confidence limits imply the following ranges of values: ,
and , which are compatible with the
CDM predictions, , and .
We find that even very simple kinematic models are equally good to describe the
data compared to the concordance CDM model, and that the current
observations are not powerful enough to discriminate among all of them.Comment: 13 pages. Matches published versio
Diversity and Genetic Relationship of Free-Range Chickens from the Northeast Region of Brazil
In this study, we aimed to evaluate the genetic diversity within and among chicken breeds from the northeast region of Brazil (states of Bahia and Piauí) using microsatellite markers. In addition, we assessed the identity and genetic relationships of chickens from Europe, Africa, and South America, as well as their influence on the formation of the Brazilian breeds. A total of 25 microsatellite markers and a panel containing 886 samples from 20 breeds (including the Brazilian chickens) were used in this study. Different statistical parameters were used to estimate the genetic diversity and relationship among the genetic groups studied. Our study indicates that the Brazilian Creole chickens have high genetic variability. The results show that chickens reared in the states of Bahia and Piauí could have originated from different ancestors. The Brazilian breeds studied have an evolutionary relationship with chickens from Portugal, Nigeria, Chile, and Spain. Our results will contribute directly to the conservation and recognition of Brazilian Creole chicken breeds and provide a solid basis for the demonstration of their genetic identity and genetic conservation of American Creole chicken populations
Constraining the dark energy with galaxy clusters X-ray data
The equation of state characterizing the dark energy component is constrained
by combining Chandra observations of the X-ray luminosity of galaxy clusters
with independent measurements of the baryonic matter density and the latest
measurements of the Hubble parameter as given by the HST key project. By
assuming a spatially flat scenario driven by a "quintessence" component with an
equation of state we place the following limits on the
cosmological parameters and : (i) and (1) if the
equation of state of the dark energy is restricted to the interval (\emph{usual} quintessence) and (ii) and
() if violates the null energy condition and assume values (\emph{extended} quintessence or ``phantom'' energy). These results are in
good agreement with independent studies based on supernovae observations,
large-scale structure and the anisotropies of the cosmic background radiation.Comment: 6 pages, 4 figures, LaTe
Hyperendemicity, heterogeneity and spatial overlap of leprosy and cutaneous leishmaniasis in the southern Amazon region of Brazil
Neglected tropical diseases characterized by skin lesions are highly endemic in the state of Mato Grosso, Brazil. We analyzed the spatial distribution of leprosy and Cutaneous Leishmaniasis (CL) and identified the degree of overlap in their distribution. All new cases of leprosy and CL reported between 2008 and 2017 through the national reporting system were included in the study. Scan statistics together with univariate Global and Local Moran's I were employed to identify clusters and spatial autocorrelation for each disease, with the spatial correlation between leprosy and CL measured by bivariate Global and Local Moran's I. Finally, we evaluated the demographic characteristics of the patients. The number of leprosy (N = 28,204) and CL (N = 24,771) cases in Mato Grosso and the highly smoothed detection coefficients indicated hyperendemicity and spatial distribution heterogeneity. Scan statistics demonstrated overlap of high-risk clusters for leprosy (RR = 2.0; P <0.001) and CL (RR = 4.0; P <0.001) in the North and Northeast mesoregions. Global Moran's I revealed a spatial autocorrelation for leprosy (0.228; P = 0.001) and CL (0.311; P = 0.001) and a correlation between them (0.164; P = 0.001). Both diseases were found to be concentrated in urban areas among men aged 31-60 years, of brown-skinned ethnicity and with a low educational level. Our findings indicate a need for developing integrated and spatially as well as socio-demographically targeted public health policies
Ongoing monkeypox virus outbreak, Portugal, 29 April to 23 May 2022
Up to 27 May 2022, Portugal has detected 96 confirmed
cases of monkeypox. We describe 27 confirmed
cases (median age: 33 years (range: 22–51); all males),
with an earliest symptom onset date of 29 April.
Almost all cases (n = 25) live in the Lisbon and Tagus
Valley health region. Most cases were neither part of
identified transmission chains, nor linked to travel or
had contact with symptomatic persons or with animals,
suggesting the possible previously undetected
spread of monkeypox.info:eu-repo/semantics/publishedVersio
Seroprevalence of Toxoplasma gondii infection among indian people living in Iauareté, São Gabriel da Cachoeira, Amazonas, Brazil
Tolerância de fungos ectomicorrízicos a metais pesados em meio de cultura adicionado de solo contaminado
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