282 research outputs found
On a functional satisfying a weak Palais-Smale condition
In this paper we study a quasilinear elliptic problem whose functional
satisfies a weak version of the well known Palais-Smale condition. An existence
result is proved under general assumptions on the nonlinearities.Comment: 18 page
Spectrum extraction from detector plane images for the medium-resolution spectrometer of the mid-Infrared Instrument on-board the James Webb Space Telescope
The Mid-Infrared Instrument (MIRI) on-board the James Webb Space Telescope (JWST) performs mediumresolution spectroscopy in the 5 to 28.5micron wavelength range. In this paper two algorithms are presented that will be used to extract 1D spectra from the 2D absolutely calibrated detector science frames acquired with the Medium-Resolution Spectrometer (MRS) of MIRI. The first spectral extraction algorithm performs standard aperture photometry on point and extended sources. The second algorithm, applicable only to point sources, uses the instrument point spread function (PSF) and the pixel signal variance as a weighting function, to extract the signal from the detector pixels in an optimized way. This "optimal" extraction is also optimal in the case of faint source observations. The two algorithms are tested on MIRI ground test data and compared. For point sources, the optimal extraction algorithm is found to be more reliable than the aperture extraction algorithm
Wavelength calibration of the JWST-MIRI medium resolution spectrometer
We present the wavelength and spectral resolution characterisation of the
Integral Field Unit (IFU) Medium Resolution Spectrometer for the Mid-InfraRed
Instrument (MIRI), to fly onboard the James Webb Space Telescope in 2014. We
use data collected using the Verification Model of the instrument and develop
an empirical method to calibrate properties such as wavelength range and
resolving power in a portion of the spectrometer's full spectral range (5-28
microns). We test our results against optical models to verify the system
requirements and combine them with a study of the fringing pattern in the
instrument's detector to provide a more accurate calibration. We show that
MIRI's IFU spectrometer will be able to produce spectra with a resolving power
above R=2800 in the wavelength range 6.46-7.70 microns, and that the unresolved
spectral lines are well fitted by a Gaussian profile.Comment: 12 pages, submitted to SPIE Proceedings vol. 7731, Space Telescopes
and Instrumentation 2010: Optical, Infrared, and Millimeter Wav
Disk galaxies with broken luminosity profiles from cosmological simulations
We present SPH cosmological simulations of the formation of three disk
galaxies with a detailed treatment of chemical evolution and cooling. The
resulting galaxies have properties compatible with observations: relatively
high disk-to-total ratios, thin stellar disks and good agreement with the
Tully-Fisher and the luminosity-size relations. They present a break in the
luminosity profile at 3.0 +- 0.5 disk scale lengths, while showing an
exponential mass profile without any apparent breaks, in line with recent
observational results. Since the stellar mass profile is exponential, only
differences in the stellar populations can be the cause of the luminosity
break. Although we find a cutoff for the star formation rate imposed by a
density threshold in our star formation model, it does not coincide with the
luminosity break and is located at 4.3 +- 0.4 disk scale lengths, with star
formation going on between both radii. The color profiles and the age profiles
are "U-shaped", with the minimum for both profiles located approximately at the
break radius. The SFR to stellar mass ratio increases until the break,
explaining the coincidence of the break with the minimum of the age profile.
Beyond the break we find a steep decline in the gas density and, consequently,
a decline in the SFR and redder colors. We show that most stars (64-78%) in the
outer disk originate in the inner disk and afterwards migrate there. Such
stellar migrations are likely the main origin of the U-shaped age profile and,
therefore, of the luminosity break.Comment: 8 pages, 4 figures. Accepted by ApJ
Primera atención psicológica: resultados preliminares de la aplicación de un protocolo innovador en vÃctimas de catástrofes ambientales para la prevención de trastornos de ansiedad
En los últimos años la Argentina ha tenido que enfrentar una serie de eventos
catastróficos (inundaciones, accidentes ferroviarios, incendios, explosiones, etc) que han
dejado diverso grado de secuelas en la salud mental de la población. La atención de las
vÃctimas en los primeros instantes posteriores al evento resulta crucial, no sólo para el
cuidado de la integridad fÃsica, sino también para la prevención de toda una variedad de
trastornos de la ansiedad que afectan la salud mental (estrés postraumático, ataques de
pánico, agorafobias, depresión, etc.). Este último aspecto de la salud ha sido descuidado
por no contar en nuestro paÃs con protocolos de intervención actualizados según los
aportes de las neurociencias.
El protocolo de Primera Atención Psicológica (PAP) provee a los socorristas,
psicólogos, asistentes sociales, bomberos, policÃas, enfermeros, voluntarios, etc. de
herramientas sencillas y eficaces para prevenir estos trastornos de ansiedad. A través de
ellas, se induce a las vÃctimas a que activen diversas regiones de la corteza frontal,
implicada en la toma de decisiones, a fin de inhibir la actividad exacerbada del cerebro
lÃmbico, producto de estrés derivado de la situación vivida, sacando de esta manera a las
vÃctimas del estado catatónico, disminuyendo asà el riesgo de trauma psicológico. A su
vez, el uso de este protocolo permite modificar el estado de histeria que presentan,
algunas vÃctimas, reduciendo su agresividad y desorganización.
La importancia del estudio de situaciones de catástrofes se justifica por los efectos
colaterales que estas producen en la salud de una comunidad, ocasionar provocar
trastornos fÃsicos y psicológicos. Por tal motivo, resulta central la intervención
programada de recursos humanos entrenados en la toma de decisiones y las acciones
eficaces, asà como la sustentabilidad de tales competencias operativas tendientes a
promover la prevención y reducción del riesgo y su articulación con las instituciones
gubernamentales de protección civil.
Desde esta perspectiva, el Instituto Universitario del Ejército (IUE), como parte del
sistema universitario nacional y en el contexto de las acciones de cooperación
académica y cientÃfica que llevan a cabo las universidades nacionales, desarrolla un plan
de trabajo integrado por una serie de proyectos articulados y formación de recursos
humanos en red. Este plan es pertinente con las polÃticas del Ministerio de Defensa en
materia de asistencia a situaciones de emergencias y los proyectos que integran el plan
se enmarcan en las áreas prioritarias definidas por el Ministerio. El IUE, a través de un
acuerdo con la Universidad de Tell Hai (Israel), con el apoyo de la UNTREF, la UNCa
y la UAI, efectuó una capacitación intensiva con representantes de los distintos actores
sociales mencionados con un posterior ejercicio de simulacro de accidente ferroviario
que involucró a más de 200 personas. Todo el ejercicio fue documentado en video. Los
análisis preliminares son el objeto de este trabajo.publishedVersio
Cosmic Evolution of Stellar Disk Truncations: From z~1 to the Local Universe
We have conducted the largest systematic search so far for stellar disk
truncations in disk-like galaxies at intermediate redshift (z<1.1), using the
Great Observatories Origins Deep Survey South (GOODS-S) data from the Hubble
Space Telescope - ACS. Focusing on Type II galaxies (i.e. downbending profiles)
we explore whether the position of the break in the rest-frame B-band radial
surface brightness profile (a direct estimator of the extent of the disk where
most of the massive star formation is taking place), evolves with time. The
number of galaxies under analysis (238 of a total of 505) is an order of
magnitude larger than in previous studies. For the first time, we probe the
evolution of the break radius for a given stellar mass (a parameter well suited
to address evolutionary studies). Our results suggest that, for a given stellar
mass, the radial position of the break has increased with cosmic time by a
factor 1.3+/-0.1 between z~1 and z~0. This is in agreement with a moderate
inside-out growth of the disk galaxies in the last ~8 Gyr. In the same period
of time, the surface brightness level in the rest-frame B-band at which the
break takes place has increased by 3.3+/-0.2 mag/arcsec^2 (a decrease in
brightness by a factor of 20.9+/-4.2). We have explored the distribution of the
scale lengths of the disks in the region inside the break, and how this
parameter relates to the break radius. We also present results of the
statistical analysis of profiles of artificial galaxies, to assess the
reliability of our results.Comment: 22 pages, 14 figures, accepted for publication in ApJ. Figures 1, 3
and 6 have somehow downgraded resolution to match uploading requirement
Radial Distribution of Near-UV Flux in Disc Galaxies in the range 0<z<1
(Abridged) The goal of this paper is to quantify the changes on the SF
distribution within the disc galaxies in the last ~8 Gyr. We use as a proxy for
the SF radial profile the Near-UV surface brightness distributions, allowing
suitably for extinction. We compare the effective radii (R_eff) and
concentration of the flux distribution in the rest-frame Near-UV for a sample
of 270 galaxies in the range 0<z<1. This radial distribution is compared to
that measured in the rest-frame B-band, which traces older stellar populations.
The analysis is performed using deep, high resolution, multi-band images from
GALEX, SDSS, and HST/ACS - GOODS-South. The relation R_eff(NUV)- M* suffers a
moderate change between z~1 and z~0: at a fixed stellar mass of 1E10 M_sun,
galaxies increase their effective radii by a factor 1.18+/-0.06. Median
profiles in NUV show signs of truncation at R~R_eff, and median colour profiles
(NUV-B) show a minimum (a "bluest" point) also around R~1-1.5 R_eff. The
distributions of NUV flux are more compact at z~1 than nowadays, in terms of
the fraction of flux enclosed in a specific radius (in kpc). Our results
indicate that the SF surface density has decreased dramatically in discs since
z~1, and this decline has been more intense in the central parts (<~R_eff) of
the galaxies. In addition, our data suggest that the bulges/pseudo-bulges have
grown in surface brightness with regard to the discs since z~1.Comment: 26 pages, 21 figures, accepted for publication in Astronomy &
Astrophysics on March 21s
Non-radial sign-changing solutions for the Schroedinger-Poisson problem in the semiclassical limit
We study the existence of nonradial sign-changing solutions to the
Schroedinger-Poisson system in dimension N>=3. We construct nonradial
sign-changing multi-peak solutions whose peaks are displaced in suitable
symmetric configurations and collapse to the same point. The proof is based on
the Lyapunov-Schmidt reduction
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