324 research outputs found
A common origin of magnetism from planets to white dwarfs
This is the final version of the article. Available from the publisher via the DOI in this record.Isolated magnetic white dwarfs have field strengths ranging from kilogauss to gigagauss. However, the origin of the magnetic field has not been hitherto elucidated. Whether these fields are fossil, hence the remnants of original weak magnetic fields amplified during the course of the evolution of their progenitor stars, or are the result of binary interactions, or, finally, they are produced by other internal physical mechanisms during the cooling of the white dwarf itself, remains a mystery. At sufficiently low temperatures, white dwarfs crystallize. Upon solidification, phase separation of its main constituents, 12C and 16O, and of the impurities left by previous evolution occurs. This process leads to the formation of a RayleighâTaylor unstable liquid mantle on top of a solid core. This convective region, as it occurs in solar system planets like the Earth and Jupiter, can produce a dynamo able to yield magnetic fields of strengths of up to 0.1 MG, thus providing a mechanism that could explain magnetism in single white dwarfs.This work has been supported by MINECO grants ESP2013-
47637-P, ESP2015-66134-R (J.I.), and AYA2014-59084-P
(E.G.-B.), by the European Union FEDER funds, by grants
2014SGR1458 (J.I.), 2014SGR0038 (E.G.-B.) of the AGAUR,
and by the CERCS program of the Generalitat de Catalunya
The variation of the gravitational constant inferred from the Hubble diagram of Type Ia supernovae
We consider a cosmological model with a variable gravitational constant, G,
based on a scalar-tensor theory. Using the recent observational data for the
Hubble diagram of type Ia supernovae (SNeIa) we find a phenomenological
expression describing the variation of G. The corresponding variation of the
fine structure constant \alpha within multidimensional theories is also
computed and is shown not to support known constraints on \Delta \alpha /
\alpha.Comment: LaTeX, 12 pages, 3 figs. In the replaced version figures are added
and some errors are correcte
Phenotypic responses to interspecies competition and commensalism in a naturally derived microbial co-culture
The fundamental question of whether different microbial species will co-exist or compete in a given environment depends on context, composition and environmental constraints. Model microbial systems can yield some general principles related to this question. In this study we employed a naturally occurring co-culture composed of heterotrophic bacteria, Halomonas sp. HL-48 and Marinobacter sp. HL- 58, to ask two fundamental scientific questions: 1) how do the phenotypes of two naturally co-existing species respond to partnership as compared to axenic growth? and 2) how do growth and molecular phenotypes of these species change with respect to competitive and commensal interactions? We hypothesized â and confirmed â that co-cultivation under glucose as the sole carbon source would result in competitive interactions. Similarly, when glucose was swapped with xylose, the interactions became commensal because Marinobacter HL-58 was supported by metabolites derived from Halomonas HL- 48. Each species responded to partnership by changing both its growth and molecular phenotype as assayed via batch growth kinetics and global transcriptomics. These phenotypic responses depended on nutrient availability and so the environment ultimately controlled how they responded to each other. This simplified model community revealed that microbial interactions are context-specific and different environmental conditions dictate how interspecies partnerships will unfold
VE-cadherin RGD motifs promote metastasis and constitute a potential therapeutic target in melanoma and breast cancers
13 p.-6 fig.We have investigated the role of vascular-endothelial (VE)-cadherin in melanoma
and breast cancer metastasis. We found that VE-cadherin is expressed in highly
aggressive melanoma and breast cancer cell lines. Remarkably, inactivation of VEcadherin triggered a significant loss of malignant traits (proliferation, adhesion,
invasion and transendothelial migration) in melanoma and breast cancer cells. These
effects, except transendothelial migration, were induced by the VE-cadherin RGD
motifs. Co-immunoprecipitation experiments demonstrated an interaction between
VE-cadherin and α2ÎČ1 integrin, with the RGD motifs found to directly affect ÎČ1
integrin activation. VE-cadherin-mediated integrin signaling occurred through specific
activation of SRC, ERK and JNK, including AKT in melanoma. Knocking down VEcadherin suppressed lung colonization capacity of melanoma or breast cancer cells
inoculated in mice, while pre-incubation with VE-cadherin RGD peptides promoted lung metastasis for both cancer types. Finally, an in silico study revealed the association of high VE-cadherin expression with poor survival in a subset of melanoma patients and breast cancer patients showing low CD34 expression. These findings support a general role for VE-cadherin and other RGD cadherins as critical regulators of lung and liver metastasis in multiple solid tumours. These results pave the way for cadherin-specific RGD targeted therapies to control disseminated metastasis in multiple cancers.BEP was an FPI fellow from Ministry of Economy and Competitiveness (MINECO). This research was supported by grants BIO2012-31023 and BIO2015-66849 from MINECO and PRB2 (IPT13/0001-ISCIII-SGEFI/FEDER) to JIC.Peer reviewe
s-Process Nucleosynthesis in Carbon Stars
We present the first detailed and homogeneous analysis of the s-element
content in Galactic carbon stars of N-type. Abundances of Sr,Y, Zr (low-mass
s-elements, or ls) and of Ba, La, Nd, Sm and Ce (high-mass s-elements, hs) are
derived using the spectral synthesis technique from high-resolution spectra.
The N-stars analyzed are of nearly solar metallicity and show moderate
s-element enhancements, similar to those found in S stars, but smaller than
those found in the only previous similar study (Utsumi 1985), and also smaller
than those found in supergiant post-AGB stars. This is in agreement with the
present understanding of the envelope s-element enrichment in giant stars,
which is increasing along the spectral sequence M-->MS-->S-->SC-->C during the
AGB phase. We compare the observational data with recent -process
nucleosynthesis models for different metallicities and stellar masses. Good
agreement is obtained between low mass AGB star models (M < 3 M_o) and
s-elements observations. In low mass AGB stars, the 13C(alpha, n)16O reaction
is the main source of neutrons for the s-process; a moderate spread, however,
must exist in the abundance of 13C that is burnt in different stars. By
combining information deriving from the detection of Tc, the infrared colours
and the theoretical relations between stellar mass, metallicity and the final
C/O ratio, we conclude that most (or maybe all) of the N-stars studied in this
work are intrinsic, thermally-pulsing AGB stars; their abundances are the
consequence of the operation of third dredge-up and are not to be ascribed to
mass transfer in binary systems.Comment: 31 pages, 10 figures, 6 tables. Accepted in Ap
Magnetic Fields and the Crystallization of White Dwarfs
This is the final version. Available from Astronomical Society of the Pacific via the link in this recordEuroWD16: 20th European White Dwarf Workshop, 25-29 July 2016, Warwick, UKThe evolution of white dwarfs can be described as a cooling process.
When the temperature is low enough, the interior experiences a phase transition and
crystallizes. Crystallization introduces two new sources of energy, latent heat and chemical sedimentation, and induces the formation of a convective mantle around the solid
core. This structure, which is analogous to that of the Earth, could induce the formation
of a magnetic field via dynamo mechanism. In this work we discuss the viability of
such mechanism, and its use as a diagnostic tool of crystallization.MINECOEuropean UnionGeneralitat de Cataluny
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
Observation of SN2011fe with INTEGRAL. I. Pre--maximum phase
SN2011fe was detected by the Palomar Transient Factory on August 24th 2011 in
M101 a few hours after the explosion. From the early optical 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. The distance of the event
offered the rare opportunity to perform a detailed observation with the
instruments on board of INTEGRAL to detect the gamma-ray emission expected from
the decay chains of Ni. The observations were performed in two runs, one
before and around the optical maximum, aimed to detect the early emission from
the decay of Ni and another after this maximum aimed to detect the
emission of Co. The observations performed with the instruments on board
of INTEGRAL (SPI, IBIS/ISGRI, JEMX and OMC) have been analyzed and compared
with the existing models of gamma-ray emission from such kind of supernovae. In
this paper, the analysis of the gamma-ray emission has been restricted to the
first epoch. Both, SPI and IBIS/ISGRI, only provide upper-limits to the
expected emission due to the decay of Ni. These upper-limits on the
gamma-ray flux are of 7.1 10 ph/s/cm for the 158 keV line
and of 2.3 10 ph/s/cm for the 812 keV line. These bounds
allow to reject at the level explosions involving a massive white
dwarf, M in the sub--Chandrasekhar scenario and specifically
all models that would have substantial amounts of radioactive Ni in the
outer layers of the exploding star responsible of the SN2011fe event. The
optical light curve obtained with the OMC camera also suggests that SN2011fe
was the outcome of the explosion, possibly a delayed detonation although other
models are possible, of a CO white dwarf that synthesized M
of Ni. For this specific model.Comment: Accepted for publication in A&A. 10 pages, 10 figure
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