20,057 research outputs found
Revisited fluorine abundances in the globular cluster M22 (NGC 6656)
Fluorine is a fairly good tracer of formation histories of multiple stellar
populations in globular clusters as already revealed by several studies. Large
variations in fluorine abundance in red giant stars of the globular cluster M22
have been recently reported by two different groups. Futhermore, one of these
studies claims that the abundance of fluorine is anti-correlated with sodium
abundances in this cluster, leading to strong conclusions on the chemical
history of M22. To validate this important finding, we re-examine the F
abundance determinations of some of the previously studied stars. We have thus
reanalysed some high-resolution VLT/CRIRES spectra of RGB stars found in M22 in
order to re-estimate their fluorine abundance from the spectral synthesis of
the HF line at 2.336microns. Unlike what has been previously estimated, we show
that only upper limits or doubtful fluorine abundances with large uncertainties
in M22 RGB stars can be derived. This is probably caused by an incorrect
identification of continuum fluctuations as the HF signature combined with a
wrong correction of the stellar radial velocity. Such continuum fluctuations
could be the consequences of telluric residuals that are still present in the
analysed spectra. Therefore, no definitive conclusions on the chemical
pollution caused by the M22 first stellar generation can presently be drawn
from the fluorine content of this cluster.Comment: A&A, in pres
Fluorine abundances and the puzzle of globular cluster chemical history
The abundance of fluorine in a few Galactic globular clusters is known to
strongly vary from star-to-star. These unexpected chemical properties are an
additional confirmation of the chemical inhomogeneities already found in
several GC, and probably caused by the first generations of stars formed in
these systems. The aim of this article is to complement our understanding of
the F-behaviour in GC stars and to look for new constraints on the formation
histories of their multiple stellar populations. We have collected near-IR
spectra of 15 RGB stars belonging to GC spanning a wide range of metallicity:
47 Tuc, M4, NGC6397 and M30. F, Na and Fe abundances have been estimated by
spectral synthesis. No anticorrelation between F and Na abundances are found
for the most metal-rich cluster of the sample (47 Tuc). In this GC, RGB stars
indeed exhibit rather small differences in [F/Fe] unlike the larger ones found
for the [Na/Fe] ratios. This reveals a rather inhomogeneous stellar system and
a complex chemical evolution history for 47 Tuc . In M4, one star of our study
confirms the previous Na-F distribution reported by another group in 2005. For
the two very metal-poor GC (NGC6397 and M30), only upper limits of F abundances
have been derived. We show that F abundances could be estimated in such
metal-poor GC with current telescopes and spectrographs only if unexpected
F-rich giants are found and/or exceptional observational conditions are met.
The distribution of the F and Na abundances in GC reveal that their RGB members
seem to belong to two well-separated regions. All the RGB stars analysed so far
in the different GC are indeed found to be either F-rich Na-poor or F-poor
Na-rich. Such well-separated bimodal regimes are consistent with the separate
formation episodes suspected in most galactic GC.Comment: Astronomy & Astrophysics, in pres
Infrared spectroscopy of the dwarf starburst galaxy Henize 2-10
Researchers present 1.2 to 2.2 micron spectra of the nucleus of Henize 2 to 10, taken at United Kingdom Infrared Telescope (UKIRT) with the cool grating spectrometer 2 (CGS 2). This galaxy displays strong line emission from interstellar H (+) (1.282 and 2.166 microns) and (Fe (+)) (1.256 and 1.644 microns), in common with other star-forming galaxy nuclei. However, the 1 to 0 S(1) line of molecular hydrogen at 2.122 micron is not detected - the upper limit of 0.15 (3 sigma) for the value of the flux ratio I sub 1-os(1)/I sub Br gamma is much lower than the typical values of 0.4 to 0.9 measured in a sample of 28 non-interacting starburst galaxies. From the Pa beta/Br gamma line ratio researchers derive a total extinction of A sub v approx. 4 mag. The de-reddened H (+) and (Fe (+) line fluxes are used to estimate the total ionizing luminosity and the average supernova rate in the central 150 pc of He 2 to 10. By comparison of these estimates with existing Infrared Astronomy Satellite (IRAS) and radio continuum data, researchers are able to set limits on the range of stellar masses present in this unevolved (less than 10(exp 7) year old) starburst nucleus. Possible reasons for the low H2/H+ line ratios observed in young starburst systems (He 2 to 10, NGC 7714, IIZw40; e.g., Moorwood and Oliva 1988) are briefly discussed
2D-Oide effect
The Oide effect considers the synchrotron radiation in the final focusing
quadrupole and it sets a lower limit on the vertical beam size at the
Interaction Point, particularly relevant for high energy linear colliders. The
theory of the Oide effect was derived considering only the radiation in the
focusing plane of the magnet. This article addresses the theoretical
calculation of the radiation effect on the beam size consider- ing both
focusing and defocusing planes of the quadrupole, refered to as 2D-Oide. The
CLIC 3 TeV final quadrupole (QD0) and beam parameters are used to compare the
theoretical results from the Oide effect and the 2D-Oide effect with particle
tracking in PLACET. The 2D-oide demonstrates to be important as it increases by
17% the contribution to the beam size. Further insight into the aberrations
induced by the synchrotron radiation opens the possibility to partially correct
the 2D-Oide effect with octupole mag
Resistive plate chambers for time-of-flight measurements
The applications of Resistive Plate Chambers (RPCs) have recently been
extended by the development of counters with time resolution below 100 ps sigma
for minimum ionising particles. Applications to HEP experiments have already
taken place and many further applications are under study. In this work we
address the operating principles of such counters along with some present
challenges, with emphasis on counter aging.Comment: Presented at "PSD6 - 6th International Conference on Position
Sensitive Detectors", 9-13 September 2002, Leicester, UK. Submitted to
Nuclear Instruments and Methods
Automated derivation of stellar atmospheric parameters and chemical abundances: the MATISSE algorithm
We present an automated procedure for the derivation of atmospheric
parameters (Teff, log g, [M/H]) and individual chemical abundances from stellar
spectra. The MATrix Inversion for Spectral SythEsis (MATISSE) algorithm
determines a basis, B_\theta(\lambda), allowing to derive a particular stellar
parameter \theta by projection of an observed spectrum. The B_\theta(\lambda)
function is determined from an optimal linear combination of theoretical
spectra and it relates, in a quantitative way, the variations in the spectrum
flux with variations in \theta. An application of this method to the GAIA/RVS
spectral range is described, together with its performances for different types
of stars of various metallicities. Blind tests with synthetic spectra of
randomly selected parameters and observed input spectra are also presented. The
method gives rapid, accurate and stable results and it can be efficiently
applied to the study of stellar populations through the analysis of large
spectral data sets, including moderate to low signal to noise spectra
CFD model-based analysis and experimental assessment of key design parameters for an integrated unglazed metallic thermal collector façade
Active façade systems incorporating solar thermal collectors currently offer very promising energetic solutions. From among the available systems, a simple solution is the unglazed heat collector for potential integration in low-temperature applications. However, when adopting system definitions, the modification of some design parameters and their impact has to be fully understood. In this study, the case of an unglazed collector integrated into a sandwich panel is assessed and a specific analysis is performed for a proper assessment of the influence of key design parameters. Based on that case study of the real built system, a CFD model is developed and validated and a parametric assessment is then performed, by altering the configurations of both the panel and the hydraulic circuit. In this way, the potential of each measure to harness solar energy can be evaluated and each parameter with its different level of impact can be highlighted, to identify those of higher relevance. A characterization of the real solution completes the study, by providing the efficiency curves and the total energy collected during the experimental campaign. The maximum estimate of the efficiency of a 6 m2 façade was within a range between 0.47 and 0.34 and the heat loss factor was between 4.8 and 7.5. The case study exercises reveal the real energy efficiency and solar production patterns. There was also an opportunity to consider significant improvements to increase the output of the active façade. The main conclusions concerned the different criteria that improved the definition of the system and greater comprehension of alternative designs that may be integrated in the underlying concept.The authors are grateful to the Basque Government for fundingthis research through projects IT781-13 and IT1314-19 and to allthose involved in the different stages for their guidance andinvaluable help.The authors would also like to thank all those companies andresearchers participating in the BASSE project for their stronginvolvement during that research. Results from BASSE project haveinspired present research. The BASSE project received funding fromthe European Union, RFCS Program, Research Fund for Coal and Steel project Building Active Steel Skin (BASSE, Grant Agreement noRFSR-CT-2013-00026
Intersection between class and gender and its effect on the quality of employment in Chile
Indexación: Web of Science; Scopus.En este artículo se analiza el efecto de la intersección entre clase y género sobre la calidad
del empleo en Chile. La medida de posición de clase utilizada está basada en la propuesta de
Erik O. Wright y la calidad del empleo en una medida multidimensional, que incluye un índice
de condiciones objetivas de empleo y dos índices de condiciones subjetivas (motivación en
el trabajo y percepción del control sobre el proceso de trabajo). Los resultados demuestran
que la clase y el género determinan diferencias significativas en la calidad objetiva y subjetiva
del empleo. Sin embargo, los datos también indican que el género (particularmente, el
hecho de ser mujer) no actúa necesariamente como “amplificador” de las desigualdades
de clase observadas en el mercado laboral. A partir de esto, al final del artículo se plantean
algunas reflexiones sobre cómo opera la intersección entre clase y género en el mercado
laboral chileno.This study explores the impact of the intersection between class and gender on the quality
of employment in Chile. The method used to measure social class position is based on the
work of Erik O. Wright, while, for the quality of employment, a multidimensional measurement
was used, including one index for objective working conditions and two indices for subjective
ones (motivation on the job and the perception of control over work processes). The results
demonstrate that class and gender give rise to signifcant differences in objective and
subjective job quality. However, the data also indicate that gender (more specifcally, the fact
of being female) does not necessarily amplify the class-based inequalities observed in the
labour market. Drawing on these fndings, a number of thoughts about how the class/gender
intersection operates in the Chilean labour market are shared in the fnal section of this studyhttp://hdl.handle.net/11362/4079
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Relationship between thoracic kyphosis and neural axis abnormalities in patients with adolescent idiopathic scoliosis.
Purpose:Previous studies have suggested an association between increased thoracic kyphosis and neural axis abnormalities in patients with adolescent idiopathic scoliosis (AIS). However, the basis for this finding is unclear, and this association has been mainly noted in retrospective studies on a non-consecutive series of patients. The purpose of this study was to assess the relationship between thoracic kyphosis and neural axis abnormalities in patients with AIS. Methods:We studied a consecutive series of AIS patients treated with spinal fusion. Thoracic kyphosis (T2 to T12) was measured from preoperative lateral radiographs. All patients underwent a spine magnetic resonance imaging (MRI) prior to surgery, and MRI reports were reviewed to determine the presence of neural axis abnormalities. Statistical analyses included descriptive statistics and chi-squared analysis. Results:This study included 210 patients with AIS. There were no significant differences in age or gender between patients with thoracic hypokyphosis (kyphosis < 20°), normal thoracic kyphosis (kyphosis 20° to 40°) and thoracic hyperkyphosis (kyphosis > 40°) (p > 0.05). Neural axis abnormalities were present in 17.9% of patients with thoracic hypokyphosis, 9.8% of patients with normal thoracic kyphosis and 13.6% of patients with thoracic hyperkyphosis (p = 0.60). There were no significant differences in rates of Chiari malformation, syrinx, intra-spinal masses and other central nervous system abnormalities between groups (p > 0.05). Conclusions:Thoracic kyphosis was not associated with neural axis abnormalities in our consecutive series of patients with AIS. Increased thoracic kyphosis may not be a reliable indicator for the presence of neural axis abnormalities in patients with AIS. Level of Evidence:IV
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