240 research outputs found
A causal look into the quantum Talbot effect
A well-known phenomenon in both optics and quantum mechanics is the so-called
Talbot effect. This near field interference effect arises when infinitely
periodic diffracting structures or gratings are illuminated by highly coherent
light or particle beams. Typical diffraction patterns known as quantum carpets
are then observed. Here the authors provide an insightful picture of this
nonlocal phenomenon as well as its classical limit in terms of Bohmian
mechanics, also showing the causal reasons and conditions that explain its
appearance. As an illustration, theoretical results obtained from diffraction
of thermal He atoms by both N-slit arrays and weak corrugated surfaces are
analyzed and discussed. Moreover, the authors also explain in terms of what
they call the Talbot-Beeby effect how realistic interaction potentials induce
shifts and distortions in the corresponding quantum carpets.Comment: 12 pages, 6 figure
Evaporation Ages: a New Dating Method for Young Star Clusters
The ages of young star clusters are fundamental clocks to constrain the
formation and evolution of pre-main-sequence stars and their protoplanetary
disks and exoplanets. However, dating methods for very young clusters often
disagree, casting doubts on the accuracy of the derived ages. We propose a new
method to derive the kinematic age of star clusters based on the evaporation
ages of their stars. The method is validated and calibrated using hundreds of
clusters identified in a supernova-driven simulation of the interstellar medium
forming stars for approximately 40 Myr within a 250 pc region. We demonstrate
that the clusters' evaporation-age uncertainty can be as small as about 10% for
clusters with a large enough number of evaporated stars and small but realistic
observational errors. We have obtained evaporation ages for a pilot sample of
10 clusters, finding a good agreement with their published isochronal ages. The
evaporation ages will provide important constraints for modeling the
pre-main-sequence evolution of low-mass stars, as well as to investigate the
star-formation and gas-evaporation history of young clusters. These ages can be
more accurate than isochronal ages for very young clusters, for which
observations and models are more uncertain.Comment: 13 pages, 11 figures, 2 tables, submitted to A&A on Nov 14th, 202
Corona-Australis DANCe I. Revisiting the census of stars with Gaia-DR2 data
Context. Corona-Australis is one of the nearest regions to the Sun with recent and ongoing star formation, but the current picture of its stellar (and substellar) content is not complete yet.
Aims. We take advantage of the second data release of the Gaia space mission to revisit the stellar census and search for additional members of the young stellar association in Corona-Australis.
Methods. We applied a probabilistic method to infer membership probabilities based on a multidimensional astrometric and photometric data set over a field of 128 deg(2) around the dark clouds of the region.
Results. We identify 313 high-probability candidate members to the Corona-Australis association, 262 of which had never been reported as members before. Our sample of members covers the magnitude range between G greater than or similar to 5 mag and G less than or similar to 20 mag, and it reveals the existence of two kinematically and spatially distinct subgroups. There is a distributed "off-cloud" population of stars located in the north of the dark clouds that is twice as numerous as the historically known "on-cloud" population that is concentrated around the densest cores. By comparing the location of the stars in the HR-diagram with evolutionary models, we show that these two populations are younger than 10 Myr. Based on their infrared excess emission, we identify 28 Class II and 215 Class III stars among the sources with available infrared photometry, and we conclude that the frequency of Class II stars (i.e. "disc-bearing" stars) in the on-cloud region is twice as large as compared to the off-cloud population. The distance derived for the Corona-Australis region based on this updated census is d = 149.4(-0.4)(+0.4) pc, which exceeds previous estimates by about 20 pc.
Conclusions. In this paper we provide the most complete census of stars in Corona-Australis available to date that can be confirmed with Gaia data. Furthermore, we report on the discovery of an extended and more evolved population of young stars beyond the region of the dark clouds, which was extensively surveyed in the past
The star formation history of Upper Scorpius and Ophiuchus
We aim to study spatial and kinematic substructures of the region encompassed
by Upper Scorpius and Ophiuchus star-forming regions, determining dynamical
traceback ages and studying the star formation history of the complex. We
identified seven different groups in this region. Four groups (nu Sco, beta
Sco, sigma Sco and delta Sco) are part of Upper Scorpius, two groups (rho Oph
and alpha Sco) are in Ophiuchus, and another group (pi Sco) is a nearby young
population. We found an age gradient from the rho Oph group (the youngest) to
the delta Sco group (<~5 Myr), showing that star formation was a sequential
process for the past 5 Myr. Our traceback analysis shows that Upper Scorpius
and rho Oph groups share a common origin. The closer group of pi Sco is
probably older, and the traceback analysis suggests that this group and the
alpha Sco group have a different origin, likely related to other associations
in the Sco-Cen complex. Our study shows that this region has a complex star
formation history that goes beyond the current formation scenario, likely a
result of stellar feedback from massive stars, supernovae explosions, and
dynamic interactions between stellar groups and the molecular gas. In
particular, we speculate that photo-ionisation from the massive delta Sco star
could have triggered star formation first in the beta Sco group and then in the
nu Sco group. The perturbations of stellar orbits due to stellar feedback and
dynamical interactions could also be responsible for the 1-3 Myr difference
that we found between dynamical traceback ages and isochronal ages.Comment: Accepted for publication in A&
NGC 6705 a young -enhanced Open Cluster from OCCASO data
The stellar [/Fe] abundance is sometimes used as a proxy for stellar
age, following standard chemical evolution models for the Galaxy, as seen by
different observational results. In this work we show that the Open Cluster
NGC6705/M11 has a significant -enhancement [/Fe] dex,
despite its young age (300 Myr), challenging the current paradigm. We use
high resolution (R) high signal-to-noise (70) spectra of 8 Red
Clump stars, acquired within the OCCASO survey. We determine very accurate
chemical abundances of several elements, using an equivalent width
methodology (Si, Ca and Ti), and spectral synthesis fits (Mg and O). We obtain
[Si/Fe]=, [Mg/Fe]=, [O/Fe]=,
[Ca/Fe]= and [Ti/Fe]=. Our results place these
cluster within the group of young [/Fe]-enhanced field stars recently
found by several authors in the literature. The ages of our stars have an
uncertainty of around 50 Myr, much more precise than for field stars. By
integrating the cluster's orbit in several non-axisymmetric Galactic
potentials, we establish the M11's most likely birth radius to lie between
6.8-7.5 kpc from the Galactic center, not far from its current position. With
the robust Open Cluster age scale, our results prove that a moderate
[/Fe]-enhancement is no guarantee for a star to be old, and that not
all -enhanced stars can be explained with an evolved blue straggler
scenario. Based on our orbit calculations, we further argue against a Galactic
bar origin of M11.Comment: 10 pages, 6 figures, accepted in A&
Impact of multimorbidity on disability and quality of life in the Spanish older population
Background
Population aging is closely related to high prevalence of chronic conditions in developed countries. In this context, health care policies aim to increase life span cost-effectively while maintaining quality of life and functional ability. There is still, however, a need for further understanding of how chronic conditions affect these health aspects. The aim of this paper is to assess the individual and combined impact of chronic physical and mental conditions on quality of life and disability in Spain, and secondly to show gender trends.
Methods
Cross-sectional data were collected from the COURAGE study. A total of 3,625 participants over 50 years old from Spain were included. Crude and adjusted multiple linear regressions were conducted to detect associations between individual chronic conditions and disability, and between chronic conditions and quality of life. Separate models were used to assess the influence of the number of diseases on the same variables. Additional analogous regressions were performed for males and females.
Results
All chronic conditions except hypertension were statistically associated with poor results in quality of life and disability. Depression, anxiety and stroke were found to have the greatest impact on outcomes. The number of chronic conditions was associated with substantially lower quality of life [ß for 4+ diseases: -18.10 (-20.95,-15.25)] and greater disability [ß for 4+ diseases: 27.64 (24.99,30.29]. In general, women suffered from higher rates of multimorbidity and poorer results in quality of life and disability.
Conclusions
Chronic conditions impact greatly on quality of life and disability in the older Spanish population, especially when co-occurring diseases are added. Multimorbidity considerations should be a priority in the development of future health policies focused on quality of life and disability. Further studies would benefit from an expanded selection of diseases. Policies should also deal with gender idiosyncrasy in certain cases
The Corona Australis star formation complex is accelerating away from the Galactic plane
We study the kinematics of the recently discovered Corona Australis (CrA)
chain of clusters by examining the 3D space motion of its young stars using
Gaia DR3 and APOGEE-2 data. While we observe linear expansion between the
clusters in the Cartesian XY directions, the expansion along Z exhibits a
curved pattern. To our knowledge, this is the first time such a nonlinear
velocity-position relation has been observed for stellar clusters. We propose a
scenario to explain our findings, in which the observed gradient is caused by
stellar feedback, accelerating the gas away from the Galactic plane. A
traceback analysis confirms that the CrA star formation complex was located
near the central clusters of the Scorpius Centaurus (Sco-Cen) OB association
10-15 Myr ago. It contains massive stars and thus offers a natural source of
feedback. Based on the velocity of the youngest unbound CrA cluster, we
estimate that a median number of about two supernovae would have been
sufficient to inject the present-day kinetic energy of the CrA molecular cloud.
This number agrees with that of recent studies. The head-tail morphology of the
CrA molecular cloud further supports the proposed feedback scenario, in which a
feedback force pushed the primordial cloud from the Galactic north, leading to
the current separation of 100 pc from the center of Sco-Cen. The formation of
spatially and temporally well-defined star formation patterns, such as the CrA
chain of clusters, is likely a common process in massive star-forming regions.Comment: Accepted for publication as a Letter in Astronomy and Astrophysic
The cosmic DANCe of Perseus I: Membership, phase-space structure, mass, and energy distributions
Context. Star-forming regions are excellent benchmarks for testing and
validating theories of star formation and stellar evolution. The Perseus
star-forming region being one of the youngest (<10 Myr), closest (280-320 pc),
and most studied in the literature, is a fundamental benchmark. Aims. We aim to
study the membership, phase-space structure, mass, and energy (kinetic plus
potential) distribution of the Perseus star-forming region using public
catalogues (Gaia, APOGEE, 2MASS, PanSTARRS). Methods. We use Bayesian
methodologies accounting for extinction to identify the Perseus physical groups
in the phase-space, retrieve their candidate members, derive their properties
(age, mass, 3D positions, 3D velocities, and energy), and attempt to
reconstruct their origin. Results. We identify 1052 candidate members in seven
physical groups (one of them new) with ages between 3 and 10 Myr, dynamical
super-virial states, and large fractions of energetically unbound stars. Their
mass distributions are broadly compatible with that of Chabrier for masses >0.1
and do not show hints of over-abundance of low-mass stars in NGC1333
with respect to IC348. These groups' ages, spatial structure, and kinematics
are compatible with at least three generations of stars. Future work is still
needed to clarify if the formation of the youngest was triggered by the oldest.
Conclusions. The exquisite Gaia data complemented with public archives and
mined with comprehensive Bayesian methodologies allow us to identify 31% more
members than in previous studies, discover a new physical group (Gorgophone: 7
Myr, 191 members, and 145 ), and confirm that the spatial, kinematic,
and energy distributions of these groups support the hierarchical
star-formation scenario.Comment: Accepted for publication in Astronomy & Astrophysics, 29 pages, 22
Figures, 8 tables one of them electroni
Vasoactive intestinal peptide in human nasal mucosa
Vasoactive intestinal peptide (VIP), which is present with acetylcholine in parasympathetic nerve fibers, may have important regulatory functions in mucous membranes. The potential roles for VIP in human nasal mucosa were studied using an integrated approach. The VIP content of human nasal mucosa was determined to be 2.84 +/- 0.47 pmol/g wet weight (n = 8) by RIA. VIP-immunoreactive nerve fibers were found to be most concentrated in submucosal glands adjacent to serous and mucous cells. 125I-VIP binding sites were located on submucosal glands, epithelial cells, and arterioles. In short-term explant culture, VIP stimulated lactoferrin release from serous cells but did not stimulate [3H]glucosamine-labeled respiratory glycoconjugate secretion. Methacholine was more potent than VIP, and methacholine stimulated both lactoferrin and respiratory glycoconjugate release. The addition of VIP plus methacholine to explants resulted in additive increases in lactoferrin release. Based upon the autoradiographic distribution of 125I-VIP binding sites and the effects on explants, VIP derived from parasympathetic nerve fibers may function in the regulation of serous cell secretion in human nasal mucosa. VIP may also participate in the regulation of vasomotor tone
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