1,145 research outputs found
Einstein-Maxwell-scalar black holes: the hot, the cold and the bald
The phenomenon of spontaneous scalarisation of charged black holes (BHs) has
recently motivated studies of various Einstein-Maxwell-scalar models. Within
these models, different classes of BH solutions are possible, depending on the
non-minimal coupling function , between the scalar field and the
Maxwell invariant. Here we consider the class wherein both the (bald)
electrovacuum Reissner-Nordstr\"om (RN) BH and new scalarised BHs co-exist, and
the former are never unstable against scalar perturbations. In particular we
examine the model, within this subclass, with a quartic coupling function:
. The domain of existence of the scalarised BHs,
for fixed , is composed of two branches. The first branch (cold
scalarised BHs) is continuously connected to the extremal RN BH. The second
branch (hot scalarised BHs) connects to the first one at the minimum value of
the charge to mass ratio and it includes overcharged BHs. We then assess the
perturbative stability of the scalarised solutions, focusing on spherical
perturbations. On the one hand, cold scalarised BHs are shown to be unstable by
explicitly computing growing modes. The instability is quenched at both
endpoints of the first branch. On the other hand, hot scalarised BHs are shown
to be stable by using the S-deformation method. Thus, in the spherical sector
this model possesses two stable BH local ground states (RN and hot scalarised).
We point out that the branch structure of BHs in this model parallels the one
of BHs in five dimensional vacuum gravity, with [Myer-Perry BHs, fat rings,
thin rings] playing the role of [RN, cold scalarised, hot scalarised] BHs.Comment: 12 pages, 6 figure
Evidence for intermediate-age stellar populations in early-type galaxies from K-band spectroscopy
The study of stellar populations in early-type galaxies in different
environments is a powerful tool for constraining their star formation
histories. This study has been traditionally restricted to the optical range,
where dwarfs around the turn-off and stars at the base of the RGB dominate the
integrated light at all ages. The near-infrared spectral range is especially
interesting since in the presence of an intermediate-age population, AGB stars
are the main contributors. In this letter, we measure the near-infrared indices
NaI and D for a sample of 12 early-type galaxies in low density
environments and compare them with the Fornax galaxy sample presented by Silva
et al. (2008). The analysis of these indices in combination with Lick/IDS
indices in the optical range reveals i) the NaI index is a metallicity
indicator as good as C4668 in the optical range, and ii) D is a
tracer of intermediate-age stellar populations. We find that low-mass galaxies
in low density environments show higher NaI and D than those located
in Fornax cluster, which points towards a late stage of star formation for the
galaxies in less dense environments, in agreement with results from other
studies using independent methods.Comment: 7 pages, 3 figures, accepted for publication in ApJ
Combination of DROOL rules and Protégé knowledge bases in the ONTO-H annotation tool
ONTO-H is a semi-automatic collaborative tool for the semantic annotation of documents, built as a Protégé 3.0 tab plug-in. Among its multiple functionalities aimed at easing the document annotation process, ONTO-H uses a rule-based system to create cascading annotations out from a single drag and drop operation from a part of a document into an already existing concept or instance of the domain ontology being used for annotation. It also gives support to the detection of name conflicts and instance duplications in the creation of the annotations. The rule system runs on top of the open source rule engine DROOLS and is connected to the domain ontology used for annotation by means of an ad-hoc programmed Java proxy
On the Environmental Dependence of Cluster Galaxy Assembly Timescale
We present estimates of CN and Mg overabundances with respect to Fe for
early-type galaxies in 8 clusters over a range of richness and morphology.
Spectra were taken from the Sloan Digital Sky Survey (SDSS) DR1, and from WHT
and CAHA observations. Abundances were derived from absorption lines and single
burst population models, by comparing galaxy spectra with appropriately
broadened synthetic model spectra. We detect correlations between [Mg/CN] and
[CN/Fe] and cluster X-ray luminosity. No correlation is observed for [Mg/Fe].
We also see a clear trend with the richness and morphology of the clusters.
This is interpreted given varying formation timescales for CN, Mg and Fe, and a
varying star formation history in early-type galaxies as a function of their
environment: intermediate-mass early-type galaxies in more massive clusters are
assembled on shorter timescales than in less massive clusters, with an upper
limit of ~1 Gyr.Comment: Accepted for publication in ApJ Letter
The cosmic evolution of the spatially-resolved star formation rate and stellar mass of the CALIFA survey
We investigate the cosmic evolution of the absolute and specific star
formation rate (SFR, sSFR) of galaxies as derived from a spatially-resolved
study of the stellar populations in a set of 366 nearby galaxies from the
CALIFA survey. The analysis combines GALEX and SDSS images with the 4000 break,
H_beta, and [MgFe] indices measured from the datacubes, to constrain parametric
models for the SFH, which are then used to study the cosmic evolution of the
star formation rate density (SFRD), the sSFR, the main sequence of star
formation (MSSF), and the stellar mass density (SMD). A delayed-tau model,
provides the best results, in good agreement with those obtained from
cosmological surveys. Our main results from this model are: a) The time since
the onset of the star formation is larger in the inner regions than in the
outer ones, while tau is similar or smaller in the inner than in the outer
regions. b) The sSFR declines rapidly as the Universe evolves, and faster for
early than for late type galaxies, and for the inner than for the outer regions
of galaxies. c) SFRD and SMD agree well with results from cosmological surveys.
At z< 0.5, most star formation takes place in the outer regions of late spiral
galaxies, while at z>2 the inner regions of the progenitors of the current E
and S0 are the major contributors to SFRD. d) The inner regions of galaxies are
the major contributor to SMD at z> 0.5, growing their mass faster than the
outer regions, with a lookback time at 50% SMD of 9 and 6 Gyr for the inner and
outer regions. e) The MSSF follows a power-law at high redshift, with the slope
evolving with time, but always being sub-linear. f) In agreement with galaxy
surveys at different redshifts, the average SFH of CALIFA galaxies indicates
that galaxies grow their mass mainly in a mode that is well represented by a
delayed-tau model, with the peak at z~2 and an e-folding time of 3.9 Gyr.Comment: 23 pages, 16 figures, 6 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
Treatment of slaughterhouse wastewater in a UASB reactor and an anaerobic filter
A study was performed to assess the feasibility of anaerobic treatment of slaughterhouse wastewaters in a UASB (Upflow Anaerobic Sludge Blanket) reactor and in an AF (Anaerobic Filter). Among the different streams generated, the slaughter line showed the highest organic content with an average COD of 8000 mg/l, of which 70% was proteins. The suspended solids content represented between 15 and 30% of the COD. Both reactors had a working volume of 21. They were operated at 37°C. The UASB reactor was run at OLR (Organic Loading Rates) of 1–6.5 kg COD/m3/day. The COD removal was 90% for OLR up to 5 kg COD/m3/day and 60% for an OLR of 6.5 kg COD/m3/day. For similar organic loading rates, the AF showed lower removal efficiencies and lower percentages of methanization. At higher OLR sludge, flotation occurred and consequently the active biomass was washed out from the filter. The results indicated that anaerobic treatment systems are applicable to slaughterhouse wastewaters and that the UASB reactor shows a better performance, giving higher COD removal efficiencies than the AF
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