695 research outputs found
Kerr black holes with synchronised Proca hair: lensing, shadows and EHT constraints
We investigate the gravitational lensing by spinning Proca stars and the shadows
and lensing by Kerr black holes (BHs) with synchronised Proca hair, discussing both theoretical
aspects and observational constraints from the Event Horizon Telescope (EHT) M87* and Sgr
A* data. On the theoretical side, this family of BHs interpolates between Kerr-like solutions —
exhibiting a similar optical appearance to that of Kerr BHs — to very non-Kerr like solutions,
exhibiting exotic features such as cuspy shadows, egg-like shadows and ghost shadows. We
interpret these features in terms of the structure of the fundamental photon orbits, for which
different branches exist, containing both stable and unstable orbits, with some of the latter not
being shadow related. On the observational side, we show that current EHT constraints are
compatible with all such BHs that could form from the growth of the superradiant instability
of Kerr BHs. Unexpectedly, given the (roughly) 10% error bars in the EHT data — and in
contrast to their scalar cousin model —, some of the BHs with up to 40% of their energy in
their Proca hair are compatible with the current data. We estimate the necessary resolution
of future observations to better constrain this model.publishe
Decay rate and decoherence control in coupled dissipative cavities
We give a detailed account of the derivation of a master equation for two
coupled cavities in the presence of dissipation. The analytical solution is
presented and physical limits of interest are discussed. Firstly we show that
the decay rate of initial coherent states can be significantly modified if the
two cavities have different decay rates and are weakly coupled through a wire.
Moreover, we show that also decoherence rates can be substantially altered by
manipulation of physical parameters. Conditions for experimental realizations
are discussed.Comment: 19 pages, 1 table, accepted by Physica
Kalb-Ramond excitations in a thick-brane scenario with dilaton
We compute the full spectrum and eigenstates of the Kalb-Ramond field in a
warped non-compact Randall-Sundrum -type five-dimensional spacetime in which
the ordinary four-dimensional braneworld is represented by a sine-Gordon
soliton. This 3-brane solution is fully consistent with both the warped
gravitational field and bulk dilaton configurations. In such a background we
embed a bulk antisymmetric tensor field and obtain, after reduction, an
infinite tower of normalizable Kaluza-Klein massive components along with a
zero-mode. The low lying mass eigenstates of the Kalb-Ramond field may be
related to the axion pseudoscalar. This yields phenomenological implications on
the space of parameters, particularly on the dilaton coupling constant. Both
analytical and numerical results are given.Comment: 10 pages, 13 figures, and 2 tables. Final version to appear in The
European Physical Journal
Observational constraint on generalized Chaplygin gas model
We investigate observational constraints on the generalized Chaplygin gas
(GCG) model as the unification of dark matter and dark energy from the latest
observational data: the Union SNe Ia data, the observational Hubble data, the
SDSS baryon acoustic peak and the five-year WMAP shift parameter. It is
obtained that the best fit values of the GCG model parameters with their
confidence level are ()
, ()
. Furthermore in this model, we can see that the
evolution of equation of state (EOS) for dark energy is similar to quiessence,
and its current best-fit value is with the confidence
level .Comment: 9 pages, 5 figure
Computation of the Power Spectrum in Chaotic Inflation
The phase-integral approximation devised by Fr\"oman and Fr\"oman, is used
for computing cosmological perturbations in the quartic chaotic inflationary
model. The phase-integral formulas for the scalar power spectrum are explicitly
obtained up to fifth order of the phase-integral approximation. As in previous
reports [1-3], we point out that the accuracy of the phase-integral
approximation compares favorably with the numerical results and those obtained
using the slow-roll and uniform approximation methods.Comment: Accepted in JCAP (15 pages, 5 figures). arXiv admin note: substantial
text overlap with arXiv:0904.429
Transfer learning for galaxy morphology from one survey to another
© 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.Deep Learning (DL) algorithms for morphological classification of galaxies have proven very successful, mimicking (or even improving) visual classifications. However, these algorithms rely on large training samples of labelled galaxies (typically thousands of them). A key question for using DL classifications in future Big Data surveys is how much of the knowledge acquired from an existing survey can be exported to a new dataset, i.e. if the features learned by the machines are meaningful for different data. We test the performance of DL models, trained with Sloan Digital Sky Survey (SDSS) data, on Dark Energy survey (DES) using images for a sample of 5000 galaxies with a similar redshift distribution to SDSS. Applying the models directly to DES data provides a reasonable global accuracy ( 90%), but small completeness and purity values. A fast domain adaptation step, consisting in a further training with a small DES sample of galaxies (500-300), is enough for obtaining an accuracy > 95% and a significant improvement in the completeness and purity values. This demonstrates that, once trained with a particular dataset, machines can quickly adapt to new instrument characteristics (e.g., PSF, seeing, depth), reducing by almost one order of magnitude the necessary training sample for morphological classification. Redshift evolution effects or significant depth differences are not taken into account in this study.Peer reviewedFinal Accepted Versio
Seroprevalence of Kaposi Sarcoma–associated Herpesvirus and Other Serologic Markers in the Brazilian Amazon
To determine the presence of Kaposi sarcoma–associated herpesvirus (KSHV) and other serologic markers, we tested serum specimens of 339 Amerindians, 181 rural non-Amerindians, and 1,133 urban blood donors (13 Amerindians) in the Brazilian Amazon. High KSHV seroprevalence in children and inverse association with herpes simplex virus type 2 indicates predominant nonsexual transmission among Amerindians
Improvements chemical processes to obtain Fenitoin
Foram otimizados os processos para obtenção de Fenitoína (5,5-difenil-2,4-imidazolidinadiona), fármaco utilizado no grande mal da epilepsia psicomotora. Os processos poderão ser adaptados para escala piloto visando suprir a demanda do Rio Grande do Sul, que foi de 1.395 kg e 8.690 kg no Brasil, em 1990.Improvements were made with the chemical processes to obtain Fenitoin, a drug used in the psicomotor eplepsia treatment. The processes can be adapted to "pilot plant scale" in order to achieve the demand of fenitoin in Rio Grande do Sul. In 1990 the consumption on fenitoin in Brazil was 8.650 Kg and in Rio Grande do Sul 1.395 Kg
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