7,068 research outputs found
Environmental effects on galaxy evolution. II: quantifying the tidal features in NIR-images of the cluster Abell 85
This work is part of a series of papers devoted to investigate the evolution
of cluster galaxies during their infall. In the present article we imaged in
NIR a selected sample of galaxies through- out the massive cluster Abell 85 (z
= 0.055). We obtained (JHK) photometry for 68 objects, reaching 1 mag/arcsec^2
deeper than 2MASS. We use these images to unveil asymmetries in the outskirts
of a sample of bright galaxies and develop a new asymmetry index, alpha_An,
which allows to quantify the degree of disruption by the relative area occupied
by the tidal features on the plane of the sky. We measure the asymmetries for a
subsample of 41 large area objects finding clear asymmetries in ten galaxies,
most of them being in groups and pairs projected at different clustercentric
distances, some of them located beyond R500 . Combining information on the
Hi-gas content of blue galaxies and the distribution of sub-structures across
Abell 85, with the present NIR asymmetry analysis, we obtain a very powerful
tool to confirm that tidal mechanisms are indeed present and are currently
affecting a fraction of galaxies in Abell 85. However, when comparing our deep
NIR images with UV-blue images of two very disrupted (jellyfish) galaxies in
this cluster, we discard the presence of tidal 1 interactions down to our
detection limit. Our results suggest that ram-pressure stripping is at the
origin of such spectacular disruptions. We conclude that across a complex
cluster like Abell 85, environment mechanisms, both gravitational and
hydrodynamical, are playing an active role in driving galaxy evolution.Comment: 30 pages, 13 figures, Accepted for Publication in A
Resonant transmission of light through finite chains of subwavelength holes
In this paper we show that the extraordinary optical transmission phenomenon
found before in 2D hole arrays is already present in a linear chain of
subwavelength holes, which can be considered as the basic geometrical unit
showing this property. In order to study this problem we have developed a new
theoretical framework, able to analyze the optical properties of finite
collections of subwavelength apertures and/or dimples (of any shape and placed
in arbitrary positions) drilled in a metallic film.Comment: Accepted for publication in Phys. Rev. Let
The Borexino Thermal Monitoring & Management System and simulations of the fluid-dynamics of the Borexino detector under asymmetrical, changing boundary conditions
A comprehensive monitoring system for the thermal environment inside the
Borexino neutrino detector was developed and installed in order to reduce
uncertainties in determining temperatures throughout the detector. A
complementary thermal management system limits undesirable thermal couplings
between the environment and Borexino's active sections. This strategy is
bringing improved radioactive background conditions to the region of interest
for the physics signal thanks to reduced fluid mixing induced in the liquid
scintillator. Although fluid-dynamical equilibrium has not yet been fully
reached, and thermal fine-tuning is possible, the system has proven extremely
effective at stabilizing the detector's thermal conditions while offering
precise insights into its mechanisms of internal thermal transport.
Furthermore, a Computational Fluid-Dynamics analysis has been performed, based
on the empirical measurements provided by the thermal monitoring system, and
providing information into present and future thermal trends. A two-dimensional
modeling approach was implemented in order to achieve a proper understanding of
the thermal and fluid-dynamics in Borexino. It was optimized for different
regions and periods of interest, focusing on the most critical effects that
were identified as influencing background concentrations. Literature
experimental case studies were reproduced to benchmark the method and settings,
and a Borexino-specific benchmark was implemented in order to validate the
modeling approach for thermal transport. Finally, fully-convective models were
applied to understand general and specific fluid motions impacting the
detector's Active Volume.Comment: arXiv admin note: substantial text overlap with arXiv:1705.09078,
arXiv:1705.0965
Composition of the Innermost Core Collapse Supernova Ejecta
With presently known input physics and computer simulations in 1D, a
self-consistent treatment of core collapse supernovae does not yet lead to
successful explosions, while 2D models show some promise. Thus, there are
strong indications that the delayed neutrino mechanism works combined with a
multi-D convection treatment for unstable layers. On the other hand there is a
need to provide correct nucleosynthesis abundances for the progressing field of
galactic evolution and observations of low metallicity stars. The innermost
ejecta is directly affected by the explosion mechanism, i.e. most strongly the
yields of Fe-group nuclei for which an induced piston or thermal bomb treatment
will not provide the correct yields because the effect of neutrino interactions
is not included. We apply parameterized variations to the neutrino scattering
cross sections and alternatively, parameterized variations are applied to the
neutrino absorption cross sections on nucleons in the ``gain region''. We find
that both measures lead to similar results, causing explosions and a Ye>0.5 in
the innermost ejected layers, due to the combined effect of a short weak
interaction time scale and a negligible electron degeneracy, unveiling the
proton-neutron mass difference. We include all weak interactions (electron and
positron capture, beta-decay, neutrino and antineutrino capture on nuclei, and
neutrino and antineutrino capture on nucleons) and present first
nucleosynthesis results for these innermost ejected layers to discuss how they
improve predictions for Fe-group nuclei. The proton-rich environment results in
enhanced abundances of 45Sc, 49Ti, and 64Zn as requested by chemical evolution
studies and observations of low metallicity stars as well as appreciable
production of nuclei in the mass range up to A=80.Comment: 13 pages, 8 figures. Final versio
On the fraction of intermediate-mass close binaries that explode as type-Ia supernovae
Type-Ia supernovae (SNe-Ia) are thought to result from a thermonuclear
runaway in white dwarfs (WDs) that approach the Chandrasekhar limit, either
through accretion from a companion or a merger with another WD. I compile
observational estimates of the fraction eta of intermediate-mass stars that
eventually explode as SNe-Ia, supplement them with several new estimates, and
compare them self-consistently. The estimates are based on five different
methods, each utilising some observable related to the SN-Ia rate, combined
with assumptions regarding the IMF: the ratio of SN-Ia to core-collapse rates
in star-forming galaxies; the SN-Ia rate per unit star-formation rate; the
SN-Ia rate per unit stellar mass; the iron to stellar mass ratio in galaxy
clusters; and the abundance ratios in galaxy clusters. The five methods
indicate that a fraction in the range eta~2-40% of all stars with initial
masses of 3-8 M_sun (the generally assumed SN-Ia progenitors) explode as
SNe-Ia. A fraction of eta~15% is consistent with all five methods for a range
of plausible IMFs. Considering also the binarity fraction among such stars, the
mass ratio distribution, the separation distribution, and duplicity (every
binary can produce only one SN-Ia explosion), this implies that nearly every
intermediate mass close binary ends up as a SN-Ia, or possibly more SNe-Ia than
progenitor systems. Theoretically expected fractions are generally one to two
orders of magnitude lower. The problem could be solved: if all the
observational estimates are in error; or with a ``middle-heavy'' IMF; or by
some mechanism that strongly enhances the efficiency of binary evolution toward
SN-Ia explosion; or by a non-binary origin for SNe-Ia.Comment: MNRAS, accepted versio
Electron microprobe analysis of cryolite
Comunicação apresentada em: EMAS 2013 : 13th European
Workshop on Modern Developments and Applications in Microbeam Analysis, Centro de Congressos da AlfĂąndega do Porto, Portugal, 12 to 16 May 2013A sample of cryolite was studied with a JEOL JXA 8500-F electron microprobe under several operating conditions. A TAP crystal was used to analyse Na and Al
and a LDE1 crystal to analyse F. As F and Na are both highly "volatile" elements, special care must be taken during analysis. The measurement order of Na, F
and Al is not irrelevant and optimum conditions may also result in different combinations of accelerating voltage, beam current, beam size or counting times.
Relevant X-ray signals were recorded in order to investigate the behaviour of the Na Ka and F Ka counts with elapsed time. The incident beam current was
also recorded at the same time. In a clear contrast to what has normally been reported in the EPMA analysis of aluminosilicates and silicate glasses, we found
that the Na X-ray counts increase with time. This increment of X-rays intensities for sodium in cryolite depends on the operating conditions and is
accompanied by a strong migration of fluorine from the beam excitation volume, leading to a decrease in F X-ray counting rates. It was also observed that
higher incident beam currents induce higher radiation damage in the mineral. The current instability is consistent with possible electron induced dissociation in
the cryolite structure. An analytical protocol was achieved for 6 kV and 15kV accelerating voltage for the correct EPMA analysis of cryolite
Integrin-mediated transactivation of P2X7R via hemichannel-dependent ATP release stimulates astrocyte migration.
Our previous reports indicate that ligand-induced αVÎČ3 integrin and Syndecan-4 engagement increases focal adhesion formation and migration of astrocytes. Additionally, ligated integrins trigger ATP release through unknown mechanisms, activating P2X7 receptors (P2X7R), and the uptake of Ca(2+) to promote cell adhesion. However, whether the activation of P2X7R and ATP release are required for astrocyte migration and whether αVÎČ3 integrin and Syndecan-4 receptors communicate with P2X7R via ATP remains unknown. Here, cells were stimulated with Thy-1, a reported αVÎČ3 integrin and Syndecan-4 ligand. Results obtained indicate that ATP was released by Thy-1 upon integrin engagement and required the participation of phosphatidylinositol-3-kinase (PI3K), phospholipase-C gamma (PLCÎł) and inositol trisphosphate (IP3) receptors (IP3R). IP3R activation leads to increased intracellular Ca(2+), hemichannel (Connexin-43 and Pannexin-1) opening, and ATP release. Moreover, silencing of the P2X7R or addition of hemichannel blockers precluded Thy-1-induced astrocyte migration. Finally, Thy-1 lacking the integrin-binding site did not stimulate ATP release, whereas Thy-1 mutated in the Syndecan-4-binding domain increased ATP release, albeit to a lesser extent and with delayed kinetics compared to wild-type Thy-1. Thus, hemichannels activated downstream of an αVÎČ3 integrin-PI3K-PLCÎł-IP3R pathway are responsible for Thy-1-induced, hemichannel-mediated and Syndecan-4-modulated ATP release that transactivates P2X7Rs to induce Ca(2+) entry. These findings uncover a hitherto unrecognized role for hemichannels in the regulation of astrocyte migration via P2X7R transactivation induced by integrin-mediated ATP release
Corrigendum to âPhylogeography of the Variable Antshrike (Thamnophilus caerulescens), a South American passerine distributed along multiple environmental gradientsâ [Mol. Phylogenet. Evol. 148 (2020) 106810](S1055790320300828)(10.1016/j.ympev.2020.106810)
© 2020 Elsevier Inc. The authors regret: (a) The information of Table 2 has incorrect values in column 6. The following table has the correct values. (b) Also, there is a minor typo in the section âData accessibilityâ, in the word: âalignmentsareâ. The correct words are: âalignments areâ. The authors would like to apologize for any inconvenience caused
Phylogeography of the Variable Antshrike (Thamnophilus caerulescens), a South American passerine distributed along multiple environmental gradients
© 2020 Elsevier Inc. The Neotropics show a wealth of distributional patterns shared by many co-distributed species. A distinctive pattern is the so-called âcircum-Amazonian distribution,â which is observed in species that do not occur in Amazonia but rather along a belt of forested habitats spanning south and east of Amazonia, the Andean foothills, and often into the Venezuelan Coastal Range and the Tepuis. Although this pattern is widespread across animals and plants, its underlying biogeographic mechanisms remain poorly understood. The Variable Antshrike (Thamnophilus caerulescens) is a sexually dimorphic suboscine passerine that exhibits extreme plumage variation and occurs along the southern portion of the circum-Amazonian belt. We describe broad-scale phylogeographic patterns of T. caerulescens and assess its demographic history using DNA sequences from the mitochondrion and ultraconserved elements (UCEs). We identified three genomic clusters: a) northern Atlantic Forest; b) southeastern Cerrado and central-southern Atlantic Forest, and c) Chaco and Andes. Our results were consistent with Pleistocene divergence followed by gene flow, mainly between the latter two clusters. There were no genetic signatures of rapid population expansions or bottlenecks. The population from the northern Atlantic Forest was the most genetically divergent group within the species. The demographic history of T. caerulescens was probably affected by series of humid and dry periods throughout the Quaternary that generated subtle population expansions and contractions allowing the intermittent connection of habitats along the circum-Amazonian belt. Recognizing the dynamic history of climate-mediated forest expansions, contractions, and connections during the South American Pleistocene is central toward a mechanistic understanding of circum-Amazonian distributions
Observations of SN2011fe with INTEGRAL
SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in
M101 few hours after the explosion. From the early spectra it was immediately
realized that it was a Type Ia supernova thus making this event the brightest
one discovered in the last twenty years. In this paper the observations
performed with the instruments on board of INTEGRAL (SPI, IBIS/ISGRI, JEM-X and
OMC) before and after the maximum of the optical light as well as the
interpretation in terms of the existing models of --ray emission from
such kind of supernovae are reported. All INTEGRAL high-energy have only been
able to provide upper limits to the expected emission due to the decay of
Ni. These bounds allow to reject explosions involving a massive white
dwarf in the sub--Chandrasekhar scenario. On the other hand, the optical light
curve obtained with the OMC camera suggests that the event was produced by a
delayed detonation of a CO white dwarf that produced M of
Ni. In this particular case, INTEGRAL would have only been able to
detect the early --ray emission if the supernova had occurred at a
distance of 2 -3 Mpc, although the brightest event could be visible up to
distances larger by a factor two.Comment: Proceedings of "An INTEGRAL view of the high-energy sky (the first 10
years)" the 9th INTEGRAL Workshop, October 15-19, 2012, Paris, France, in
Proceedings of Science (INTEGRAL 2012), Eds. A. Goldwurm, F. Lebrun and C.
Winkler, http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=176, id number
PoS (INTEGRAL 2012) 103 (2013
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