7,511 research outputs found
XMM-Newton and Chandra observations of G272.2-3.2. Evidence of stellar ejecta in the central region
We aim to study the spatial distribution of the physical and chemical
properties of the X-ray emitting plasma of the supernova remnant G272.2-3.2, in
order to get important constraints on its ionization stage, on the progenitor
supernova explosion, and the age of the remnant. We report combined XMM-Newton
and Chandra images, median photon energy map, silicon and sulfur equivalent
width maps, and a spatially resolved spectral analysis for a set of regions of
the remnant. Complementary radio and H{\alpha} observations, available in the
literature, are also used to study the multi-wavelength connection of all
detected emissions. The X-ray morphology of the remnant displays an overall
structure with an almost circular appearance, a centrally brightened hard
region, with a peculiar elongated hard structure oriented along the
northwest-southeast direction of the central part. The X-ray spectral study of
the regions shows distinct K{\alpha} emission-line features of metal elements,
confirming the thermal origin of the emission. The X-ray spectra are well
represented by an absorbed VNEI thermal plasma model, which produces elevated
abundances of Si, S, and Fe in the circular central region, typical of ejecta
material. The values of abundances found in the central region of the SNR favor
a Type Ia progenitor for this remnant. The outer region shows abundances below
the solar value, as expected if the emission arises from the shocked ISM. The
relatively low ionization timescales suggests non-equilibrium ionization. We
identify the location of the contact discontinuity. Its distance to the outer
shock is higher than expected for expansion in a uniform media, what suggests
that the remnant spent most of its time in a more dense medium.Comment: 9 pages, 7 figures. Accepted for publication in A&
Propiedades mecánicas de cermets basados en diboruro de titanio
Las propiedades mecánicas de los cermets basados en diboruro de titanio (TiB
2
) dependen críticamente de la composición de
la fase ligante. Se ha comprobado que tanto la tenacidad como la dureza aumentan significativamente si se evita la formación
de boruros secundarios durante la sinterización en fase líquida. Las observaciones fractográficas realizadas en cermets basados en TiB
2
sin boruros secundarios confirman el comportamiento plástico de la fase ligante durante la fractura. La ruta
pulvimetalúrgica aplicada a estos materiales permite la modificación intencionada de la estructura de la fase ligante desde
ferrita a austenita mediante adiciones de aluminio a las mezclas de polvos. Los valores de tenacidad más elevados se han
obtenido para los cermets con matriz austenítica. El análisis mediante difracción de rayos X de la superficie de fractura de
estos materiales confirma que la fase ligante experimenta transformación martensítica durante la fractura, mecanismo de
aumento de tenacidad ya observado en otros sistemas. Esta nueva familia de materiales duros presenta una excelente combinación de dureza y tenacidad, comparable a la obtenida con grados comerciales de carburos cementados (WC-Co).Peer reviewe
High resolution observations of Cen A: Yellow and red supergiants in a region of jet-induced star formation?
We present the analysis of near infrared (NIR), adaptive optics (AO) Subaru
and archived HST imaging data of a region near the northern middle lobe (NML)
of the Centaurus A (Cen A) jet, at a distance of kpc north-east (NE)
from the center of NGC5128. Low-pass filtering of the NIR images reveals strong
-- above the background mean -- signal at the expected position of
the brightest star in the equivalent HST field. Statistical analysis of the NIR
background noise suggests that the probability to observe signal at
the same position, in three independent measurements due to stochastic
background fluctuations alone is negligible () and, therefore,
that this signal should reflect the detection of the NIR counterparts of the
brightest HST star. An extensive photometric analysis of this star yields
, visual-NIR, and NIR colors expected from a yellow supergiant (YSG) with
an estimated age Myr. Furthermore, the second and third
brighter HST stars are, likely, also supergiants in Cen A, with estimated ages
Myr and Myr, respectively. The ages of
these three supergiants are in good agreement with the ages of the young
massive stars that were previously found in the vicinity and are thought to
have formed during the later phases of the jet-HI cloud interaction that
appears to drive the star formation (SF) in the region for the past
Myr.Comment: 11 pages, 6 figures, 2 tables, accepted for publication in Ap
Searching for galactic sources in the Swift GRB catalog
Since the early 1990s Gamma Ray Bursts have been accepted to be of
extra-galactic origin due to the isotropic distribution observed by BATSE and
the redshifts observed via absorption line spectroscopy. Nevertheless, upon
further examination at least one case turned out to be of galactic origin. This
particular event presented a Fast Rise, Exponential Decay (FRED) structure
which leads us to believe that other FRED sources might also be Galactic. This
study was set out to estimate the most probable degree of contamination by
galactic sources that certain samples of FREDs have. In order to quantify the
degree of anisotropy the average dipolar and quadripolar moments of each sample
of GRBs with respect to the galactic plane were calculated. This was then
compared to the probability distribution of simulated samples comprised of a
combination of isotropically generated sources and galactic sources. We observe
that the dipolar and quadripolar moments of the selected subsamples of FREDs
are found more than two standard deviations outside those of random
isotropically generated samples.The most probable degree of contamination by
galactic sources for the FRED GRBs of the Swift catalog detected until February
2011 that do not have a known redshift is about 21 out of 77 sources which is
roughly equal to 27%. Furthermore we observe, that by removing from this sample
those bursts that may have any type of indirect redshift indicator and multiple
peaks gives the most probable contamination increases up to 34% (17 out of 49
sources). It is probable that a high degree of contamination by galactic
sources occurs among the single peak FREDs observed by Swift.Comment: Published to A&A, 4 pages, 5 figures, this arXiv version includes
appended table with all the bursts considered in this stud
Through the magnifying glass: ALMA acute viewing of the intricate nebular architecture of OH231.8+4.2
We present continuum and molecular line emission ALMA observations of OH
231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch
(AGB) star. The high angular resolution (~0.2-0.3 arcsec) and sensitivity of
our ALMA maps provide the most detailed and accurate description of the overall
nebular structure and kinematics of this object to date. We have identified a
number of outflow components previously unknown. Species studied in this work
include 12CO, 13CO, CS, SO, SO2, OCS, SiO, SiS, H3O+, Na37Cl, and CH3OH. The
molecules Na37Cl and CH3OH are first detections in OH 231.8+4.2, with CH3OH
being also a first detection in an AGB star. Our ALMA maps bring to light the
totally unexpected position of the mass-losing AGB star (QX Pup) relative to
the large-scale outflow. QX Pup is enshrouded within a compact (<60 AU) parcel
of dust and gas (clump S) in expansion (V~5-7 km/s) that is displaced by
0.6arcsec to the south of the dense equatorial region (or waist) where the
bipolar lobes join. Our SiO maps disclose a compact bipolar outflow that
emerges from QX Pup's vicinity. This outflow is oriented similarly to the
large-scale nebula but the expansion velocities are about ten times lower (~35
km/s). We deduce short kinematical ages for the SiO outflow, ranging from
~50-80 yr, in regions within ~150 AU, to ~400-500 yr at the lobe tips (~3500
AU). Adjacent to the SiO outflow, we identify a small-scale hourglass-shaped
structure (mini-hourglass) that is probably made of compressed ambient material
formed as the SiO outflow penetrates the dense, central regions of the nebula.
The lobes and the equatorial waist of the mini-hourglass are both radially
expanding with a constant velocity gradient. The mini-waist is characterized by
extremely low velocities, down to ~1 km/s at ~150 AU, which tentatively suggest
the presence of a stable structure. (abridged
Long-distance radiative corrections to the di-pion tau lepton decay
We evaluate the model-dependent piece of O(alpha) long-distance radiative
corrections to tau^- \to \pi^- \pi^0\nu_{\tau} decays by using a meson
dominance model. We find that these corrections to the di-pion invariant mass
spectrum are smaller than in previous calculations based on chiral perturbation
theory. The corresponding correction to the photon inclusive rate is tiny
(-0.15%) but it can be of relevance when new measurements reach better
precision.Comment: 4 pages, 2 figures. An estimate of the shift produced in the
evaluation of the h.v.p. contribution to the muon anomalous magnetic moment
is added. Version to appear in Phys. Rev.
Effects of introgressed 4Nv Aegilops ventricosa chromosome on yield and yield components in bread wheat.
Effects of introgressed 4Nv Aegilops ventricosa chromosome on yield and yield components in bread whea
Association of Motivational Climate With Addictive Behaviors Depending on Type of Sport in University Students: Structural Equation Analysis
This research study aims at contrasting a structural model of the associations between the alcohol consumption, tobacco
dependence, and the problematic use of video games with motivational climate toward sport depending on the category of
sports practiced in a sample of Physical Education university students. The sample consisted of 775 university students from
the Autonomous Community of Andalusia (Spain), aged between 21 and 35 (22.22 ± 3.76) years. The instruments used
were the Perceived Motivational Climate in Sport Questionnaire (PMCSQ-2), the Alcohol Use Disorders Identification Test
(AUDIT), the Fagerström Test for Nicotine Dependence (FTND), and the Questionnaire of Experiences Related to Video
Games (QERV) questionnaires. A path model that fitted properly in the multigroup analysis for both categories of sports was
used, χ2 = 19.843; gl = 8; p = .011; comparative fit index (CFI) = 0.911; normed fit index (NFI) = 0.903; incremental fit
index (IFI) = 0.912; root mean square error approximation (RMSEA) = 0.085. An inverse association was shown between
task climate and tobacco consumption in individual sports, being weaker in collective sports. This association is not significant
for collective sports, but it is for individual sports for ego climate. However, a positive association was found between ego
climate and the use of video games in individual sports, not being significant in the case of collective sports. The importance
of promoting motivational climates oriented toward tasks that are based on the practice of collective sports is established,
because they could act as protective factors against the development of addictive behavior in university students.This
research study has been supported by the Education Innovation
Project PID 16-45, named “Implementation of digital resources in
the classroom for the development of psychosocial and motivational
factors in students of the degree in Primary Education with
the speciality in Physical Education,” funded by the University of
Granada. Education Innovation Project PIBD Advanced 470,
named “Program of teaching intervention in students of the degree
in primary education and early childhood education through the use
of new technologies for the improvement of the psychosocial factors
of the students,” funded by the University of Granada. Project
I+D+I “DISPERSA,” with code number TIN2015-67149-C3-R,
named “Design of Pervasive Games Based on Learning Experiences
Sensitive to Context” funded by the Ministry of Economy and
Competitiveness. Precompetitive Research Projects for Young
Researchers (PPJI_B-05); Self-plan Research of the University of
Granada
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