5,247 research outputs found
The radial abundance gradient of oxygen towards the Galactic anticentre
We present deep optical spectroscopy of eight HII regions located in the
anticentre of the Milky Way. The spectra were obtained at the 10.4m GTC and
8.2m VLT. We determined Te([NII]) for all objects and Te([OIII]) for six of
them. We also included in our analysis an additional sample of 13 inner-disc
Galactic Hii regions from the literature that have excellent T_e
determinations. We adopted the same methodology and atomic dataset to determine
the physical conditions and ionic abundances for both samples. We also detected
the CII and OII optical recombination lines in Sh 2-100, which enables
determination of the abundance discrepancy factor for this object. We found
that the slopes of the radial oxygen gradients defined by the HII regions from
R_25 (= 11.5 kpc) to 17 kpc and those within R_25 are similar within the
uncertainties, indicating the absence of flattening in the radial oxygen
gradient in the outer Milky Way. In general, we found that the scatter of the
O/H ratios of Hii regions is not substantially larger than the observational
uncertainties. The largest possible local inhomogeneities of the oxygen
abundances are of the order of 0.1 dex. We also found positive radial gradients
in Te([O III]) and Te([N II]) across the Galactic disc. The shapes of these
temperature gradients are similar and also consistent with the absence of
flattening of the metallicity distribution in the outer Galactic disc.Comment: 20 pages, 11 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Transverse Takahashi Identities and Their Implications for Gauge Independent Dynamical Chiral Symmetry Breaking
In this article, we employ transverse Takahashi identities to impose valuable
non-perturbative constraints on the transverse part of the fermion-photon
vertex in terms of new form factors, the so called functions. We show
that the implementation of these identities is crucial in ensuring the correct
local gauge transformation of the fermion propagator and its multiplicative
renormalizability. Our construction incorporates the correct symmetry
properties of the under charge conjugation operation as well as their
well-known one-loop expansion in the asymptotic configuration of incoming and
outgoing momenta. Furthermore, we make an explicit analysis of various existing
constructions of this vertex against the demands of transverse Takahashi
identities and the previously established key features of quantum
electrodynamics, such as gauge invariance of the critical coupling above which
chiral symmetry is dynamically broken. We construct a simple example in its
quenched version and compute the mass function as we vary the coupling strength
and also calculate the corresponding anomalous dimensions . There is
an excellent fit to the Miransky scalling law and we find rather
naturally in accordance with some earlier results in literature, using
arguments based on Cornwall-Jackiw-Tomboulis effective potential technique.
Moreover, we numerically confirm the gauge invariance of this critical
coupling.Comment: 16 pages, 4 figure
Sufficient conditions for rescaling expansivity
We demonstrate that any k*-expansive vector field on a closed manifold
exhibits rescaling expansiveness. This enhances the principal outcome outlined
in \cite{a}. The verification of this assertion hinges on the introduction and
exploration of the novel concept termed as a "singular-expansive flow," which
will be thoroughly examined.Comment: 17 pages. To appear in Annales de la Facult\'e des Sciences de
Toulous
Superfluid Optomechanics with Phononic Nanostructures
In quantum optomechanics, finding materials and strategies to limit losses
has been crucial to the progress of the field. Recently, superfluid 4He was
proposed as a promising mechanical element for quantum optomechanics. This
quantum fluid shows highly desirable properties (e.g. extremely low acoustic
loss) for a quantum optomechanical system. In current implementations,
superfluid optomechanical systems suffer from external sources of loss, which
spoils the quality factor of resonators. In this work, we propose a new
implementation, exploiting nanofluidic confinement. Our approach, based on
acoustic resonators formed within phononic nanostructures, aims at limiting
radiation losses to preserve the intrinsic properties of superfluid 4He. In
this work, we estimate the optomechanical system parameters. Using recent
theory, we derive the expected quality factors for acoustic resonators in
different thermodynamic conditions. We calculate the sources of loss induced by
the phononic nanostructures with numerical simulations. Our results indicate
the feasibility of the proposed approach in a broad range of parameters, which
opens new prospects for more complex geometries.Comment: 20 pages, 19 figure
On the abundance discrepancy problem in HII regions
The origin of the abundance discrepancy is one of the key problems in the
physics of photoionized nebula. In this work, we analize and discuss data for a
sample of Galactic and extragalactic HII regions where this abundance
discrepancy has been determined. We find that the abundance discrepancy factor
(ADF) is fairly constant and of the order of 2 in all the available sample of
HII regions. This is a rather different behaviour than that observed in
planetary nebulae, where the ADF shows a much wider range of values. We do not
find correlations between the ADF and the O/H, O++/H+ ratios, the ionization
degree, Te(High), Te(Low)/ Te(High), FWHM, and the effective temperature of the
main ionizing stars within the observational uncertainties. These results
indicate that whatever mechanism is producing the abundance discrepancy in HII
regions it does not substantially depend on those nebular parameters. On the
contrary, the ADF seems to be slightly dependent on the excitation energy, a
fact that is consistent with the predictions of the classical temperature
fluctuations paradigm. Finally, we obtain that Te values obtained from OII
recombination lines in HII regions are in agreement with those obtained from
collisionally excited line ratios, a behaviour that is again different from
that observed in planetary nebulae. These similar temperature determinations
are in contradiction with the predictions of the model based on the presence of
chemically inhomogeneous clumps but are consistent with the temperature
fluctuations paradigm. We conclude that all the indications suggest that the
physical mechanism responsible of the abundance discrepancy in HII regions and
planetary nebulae are different.Comment: 14 pages, 8 figures, 9 tables. Accepted for publication in the Ap
Evaluación del Potencial de Manglares y Pastos Marinos como Hábitats Esenciales para Peces Juveniles Arrecifales, en un Área Marina Protegida del Caribe Colombiano
M dwarf stars in the light of (future) exoplanet searches
We present a brief overview of a splinter session on M dwarf stars as planet
hosts that was organized as part of the Cool Stars 17 conference. The session
was devoted to reviewing our current knowledge of M dwarf stars and exoplanets
in order to prepare for current and future exoplanet searches focusing in low
mass stars. We review the observational and theoretical challenges to
characterize M dwarf stars and the importance of accurate fundamental
parameters for the proper characterization of their exoplanets and our
understanding on planet formation.Comment: 4 pages, 1 figure. Summary of the splinter session "M dwarf stars in
the light of (future) exoplanet searches" held at the 17th Cambridge Workshop
on Cool Stars, Stellar Systems, and the Sun, June 28th 2012, Barcelona,
Spain. Submitted for publication in Astronomische Nachrichten - Astronomical
Notes (AN) 334, Issue 1-2, Eds Klaus Strassmeier and Mercedes L\'opez-Morale
MicroRNA Profiling and Bioinformatics Target Analysis in Dorsal Hippocampus of Chronically Stressed Rats: Relevance to Depression Pathophysiology
Indexación: Scopus.1Laboratory of Neuroplasticity and Neurogenetics, Faculty of Chemical and Pharmaceutical Sciences, Department of Biochemistry and Molecular Biology, Universidad de Chile, Santiago, Chile, 2National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Durham, NC, United States, 3Centro de Genómica y Bioinformática, Facultad de Ciencias, Universidad Mayor, Santiago, Chile, 4Millennium Institute for Integrative Biology (iBio), FONDAP Center for Genome Regulation, Departamento de Genética Molecular y Microbiología, Pontificia Universidad Católica de Chile, Santiago, Chile, 5Department of Kinesiology, Faculty of Health Sciences, Universidad Católica del Maule, Talca, Chile, 6Escuela de Química y Farmacia, Facultad de Medicina, Universidad Andres Bello, Santiago, Chile.This study was supported by the following grants: FONDECYT 1120528 (JLF), Fondo Central de Investigación, Universidad de Chile ENL025/16 (JLF), ES090079 (JAC). Research in RG and EV laboratories is funded by Instituto Milenio iBio – Iniciativa Científica Milenio MINECON.Studies conducted in rodents subjected to chronic stress and some observations in humans after psychosocial stress, have allowed to establish a link between stress and the susceptibility to many complex diseases, including mood disorders. The studies in rodents have revealed that chronic exposure to stress negatively affects synaptic plasticity by triggering changes in the production of trophic factors, subunit levels of glutamate ionotropic receptors, neuron morphology, and neurogenesis in the adult hippocampus. These modifications may account for the impairment in learning and memory processes observed in chronically stressed animals. It is plausible then, that stress modifies the interplay between signal transduction cascades and gene expression regulation in the hippocampus, therefore leading to altered neuroplasticity and functioning of neural circuits. Considering that miRNAs play an important role in post-transcriptional-regulation of gene expression and participate in several hippocampus-dependent functions; we evaluated the consequences of chronic stress on the expression of miRNAs in dorsal (anterior) portion of the hippocampus, which participates in memory formation in rodents. Here, we show that male rats exposed to daily restraint stress (2.5 h/day) during 7 and 14 days display a differential profile of miRNA levels in dorsal hippocampus and remarkably, we found that some of these miRNAs belong to the miR-379-410 cluster. We confirmed a rise in miR-92a and miR-485 levels after 14 days of stress by qPCR, an effect that was not mimicked by chronic administration of corticosterone (14 days). Our in silico study identified the top-10 biological functions influenced by miR-92a, nine of which were shared with miR-485: Nervous system development and function, Tissue development, Behavior, Embryonic development, Organ development, Organismal development, Organismal survival, Tissue morphology, and Organ morphology. Furthermore, our in silico study provided a landscape of potential miRNA-92a and miR-485 targets, along with relevant canonical pathways related to axonal guidance signaling and cAMP signaling, which may influence the functioning of several neuroplastic substrates in dorsal hippocampus. Additionally, the combined effect of miR-92a and miR-485 on transcription factors, along with histone-modifying enzymes, may have a functional relevance by producing changes in gene regulatory networks that modify the neuroplastic capacity of the adult dorsal hippocampus under stress. © 2018 Muñoz-Llanos, García-Pérez, Xu, Tejos-Bravo, Vidal, Moyano, Gutiérrez, Aguayo, Pacheco, García-Rojo, Aliaga, Rojas, Cidlowski and Fiedler.https://www.frontiersin.org/articles/10.3389/fnmol.2018.00251/ful
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