2,667 research outputs found
Kernel regression estimates of time delays between gravitationally lensed fluxes
Strongly lensed variable quasars can serve as precise cosmological probes,
provided that time delays between the image fluxes can be accurately measured.
A number of methods have been proposed to address this problem. In this paper,
we explore in detail a new approach based on kernel regression estimates, which
is able to estimate a single time delay given several datasets for the same
quasar. We develop realistic artificial data sets in order to carry out
controlled experiments to test of performance of this new approach. We also
test our method on real data from strongly lensed quasar Q0957+561 and compare
our estimates against existing results.Comment: Updated to match published versio
Physical Properties, Star Formation, and Active Galactic Nucleus Activity in Balmer Break Galaxies at 0 < z < 1
We present a spectroscopic study with the derivation of the physical
properties of 37 Balmer break galaxies, which have the necessary lines to
locate them in star-forming-AGN diagnostic diagrams. These galaxies span a
redshift range from 0.045 to 0.93 and are somewhat less massive than similar
samples of previous works. The studied sample has multiwavelength photometric
data coverage from the ultraviolet to MIR Spitzer bands. We investigate the
connection between star formation and AGN activity via optical, mass-excitation
(MEx) and MIR diagnostic diagrams. Through optical diagrams, 31 (84%)
star-forming galaxies, 2 (5%) composite galaxies and 3 (8%) AGNs were
classified, whereas from the MEx diagram only one galaxy was classified as AGN.
A total of 19 galaxies have photometry available in all the IRAC/Spitzer bands.
Of these, 3 AGN candidates were not classified as AGN in the optical diagrams,
suggesting they are dusty/obscured AGNs, or that nuclear star formation has
diluted their contributions. Furthermore, the relationship between SFR surface
density (\Sigma_{SFR}) and stellar mass surface density per time unit
(\Sigma_{M_{\ast}/\tau}) as a function of redshift was investigated using the
[OII] \lambda3727, 3729, H\alpha \lambda6563 luminosities, which revealed that
both quantities are larger for higher redshift galaxies. We also studied the
SFR and SSFR versus stellar mass and color relations, with the more massive
galaxies having higher SFR values but lower SSFR values than less massive
galaxies. These results are consistent with previous ones showing that, at a
given mass, high-redshift galaxies have on average larger SFR and SSFR values
than low-redshift galaxies. Finally, bluer galaxies have larger SSFR values
than redder galaxies and for a given color the SSFR is larger for higher
redshift galaxies.Comment: preprint version, 36 pages, 17 figures, 3 tables, accepted for
publication in the Astrophysical Journa
Spillover and diffraction sidelobe contamination in a double-shielded experiment for mapping Galactic synchrotron emission
We have analyzed observations from a radioastronomical experiment to survey
the sky at decimetric wavelengths along with feed pattern measurements in order
to account for the level of ground contamination entering the sidelobes. A
major asset of the experiment is the use of a wire mesh fence around the
rim-halo shielded antenna with the purpose of levelling out and reducing this
source of stray radiation for zenith-centered 1-rpm circular scans. We
investigate the shielding performance of the experiment by means of a geometric
diffraction model in order to predict the level of the spillover and
diffraction sidelobes in the direction of the ground. Using 408 MHz and 1465
MHz feed measurements, the model shows how a weakly-diffracting and unshielded
antenna configuration becomes strongly-diffracting and double-shielded as
far-field diffraction effects give way to near-field ones. Due to the
asymmetric response of the feeds, the orientation of their radiation fields
with respect to the secondary must be known a priori before comparing model
predictions with observational data. By adjusting the attenuation coefficient
of the wire mesh the model is able to reproduce the amount of differential
ground pick-up observed during test measurements at 1465 MHz.Comment: 14 pages, 17 eps + 1 gif figures and 4 Tables. Accepted for
publication in A&AS. Fig.7 available at full resolution from
http://www.das.inpe.br/~tello/publications.ht
Analysis of the Thermal Behavior of a Vehicle Cabin Using a Dynamic Thermal Model
This work analyzes the thermal behavior of a vehicle cabin by using a dynamic thermal model, which allows to accurately reproduce the vehicle interior temperature under different external environmental conditions. The thermal model considers heat transfer through the glazed and opaque surfaces of the vehicle using the energy balance method. It considers changes in weather conditions, vehicle geometry, body construction characteristics, types of opaque and glazed surfaces, and existing thermal loads. Experimental tests (with and without solar radiation) were carried out to validate the dynamic thermal model. The model predicts the temperature variations of the air inside the vehicle cabin. The results showed a maximum variation of 1.38 K without solar incidence and 3.78 K with solar radiation.
Keywords: dynamic thermal model, vehicle, heat balance, thermal load.
Resumen
El objetivo principal del presente trabajo fue analizar el comportamiento tĂ©rmico de la cabina de un vehĂculo utilizando un modelo tĂ©rmico dinĂĄmico, que permite reproducir de manera precisa el comportamiento de la temperatura interior del vehĂculo bajo distintas condiciones ambientales externas. El modelo tĂ©rmico considera la transferencia de calor a travĂ©s de las superficies acristaladas y opacas del vehĂculo utilizando el mĂ©todo de balance de energĂa, para lo cual se toman en cuenta los cambios en las condiciones climatolĂłgicas, la geometrĂa del vehĂculo, las caracterĂsticas constructivas de la carrocerĂa, tipos de superficies opacas y acristaladas y las cargas tĂ©rmicas existentes. Se realizaron ensayos experimentales (con y sin radiaciĂłn solar) para validar el modelo tĂ©rmico dinĂĄmico. El modelo permite reproducir las variaciones de la temperatura del aire interior de la cabina del vehĂculo. Los resultados obtenidos muestran una variaciĂłn mĂĄxima de 1.38 K, sin incidencia solar y 3.78 K con radiaciĂłn solar.
Palabras Clave: modelo tĂ©rmico dinĂĄmico, vehĂculo, balance de calor, carga tĂ©rmica
Extended-spectrum beta-lactamases-producing <i>Escherichia coli</i> in common vampire bats <i>Desmodus rotundus</i> and livestock in Peru
Antibiotic resistance mediated by bacterial production of extendedâspectrum betaâlactamase (ESBL) is a global threat to public health. ESBL resistance is most commonly hospitalâacquired; however, infections acquired outside of hospital settings have raised concerns over the role of livestock and wildlife in the zoonotic spread of ESBLâproducing bacteria. Only limited data are available on the circulation of ESBLâproducing bacteria in animals. Here, we report ESBLâproducing Escherichia coli in wild common vampire bats Desmodus rotundus and livestock near Lima, Peru. Molecular analyses revealed that most of this resistance resulted from the expression of blaCTXâMâ15 genes carried by plasmids, which are disseminating worldwide in hospital settings and have also been observed in healthy children of Peru. Multilocus sequence typing showed a diverse pool of E. coli strains carrying this resistance that were not always host speciesâspecific, suggesting sharing of strains between species or infection from a common source. This study shows widespread ESBL resistance in wild and domestic animals, supporting animal communities as a potential source of resistance. Future work is needed to elucidate the role of bats in the dissemination of antibioticâresistant strains of public health importance and to understand the origin of the observed resistance
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