1,294 research outputs found
Ba & Eu Abundances in M15 giant stars
To investigate the Ba and Eu abundances for a sample of 63 giant stars in the
globular cluster M15. This is the largest sample of M15 giants stars for which
Ba abundances have been determined and, due to the target selection of the
original research programme, the Ba abundances are complete along the red giant
branch. Stellar parameters were taken from the previous key study and a
microturbulence-surface gravity relation was determined for precise measurement
of the Ba line at 6496.898 Angstroms, which has a high sensitivity to
microturbulence. Element abundances for Ba, La, Eu, Ca, Ni and Fe were
calculated using spectrum synthesis and equivalent widths techniques. A bimodal
distribution in Ba, Eu and La abundances was found within the sample. The low
Ba,Eu,La mode had mean abundances of =-2.41+/-0.16,
=-1.80+/-0.08 and =-2.19+/-0.13 while the high Ba,Eu,La mode
had mean abundances of =-2.00+/-0.16, =-1.65+/-0.13 and
=-1.95+/-0.11. Both modes are indicative of a pollution scenario
dominated by the r-process, hence contributions from explosive nucleosynthesis
of massive stars. There may be evidence of further enhancement by another heavy
element process and of potential anticorrelations in Na-O for both modes
indicating a complex formation and evolution history for M15.Comment: 20 pages, 15 figure
Differential chemical abundance analysis of a 47 Tuc AGB star with respect to Arcturus
This study resolves a discrepancy in the abundance of Zr in the 47 Tucanae
asymptotic giant branch star Lee 2525. This star was observed using the echelle
spectrograph on the 2.3 m telescope at Siding Spring Observatory. The analysis
was undertaken by calibrating Lee 2525 with respect to the standard giant star
Arcturus. This work emphasises the importance of using a standard star with
stellar parameters comparable to the star under analysis rather than a
calibration with respect to the Sun (Koch & McWilliam 2008). Systematic errors
in the analysis process are then minimised due to the similarity in atmospheric
structure between the standard and programme stars. The abundances derived for
Lee 2525 were found to be in general agreement with the Brown & Wallerstein
(1992) values except for Zr. In this study Zr has a similar enhancement
([Zr/Fe] = +0.51 dex) to another light s-process element, Y ([Y/Fe] = +0.53
dex), which reflects current theory regarding the enrichment of s-process
elements by nuclear processes within AGB stars (Busso et al. 2001). This is
contrary to the results of Brown & Wallerstein (1992) where Zr was
under-abundant ([Zr/Fe] = +0.51 dex) and Y was over-abundant ([Y/Fe] = +0.50
dex) with respect to Fe.Comment: 11 pages, 5 figures Accepted for publication in MNRA
The Metabolism and Transplacental Transfer of Oseltamivir in the Ex Vivo Human Model
Oseltamivir phosphate is extensively metabolized in the ex vivo
human placenta model, and the transplacental passage of the metabolite oseltamivir
carboxylate is incomplete. Objective. To evaluate the metabolism and transplacental transfer of oseltamivir (Tamiflu) in the ex vivo human placental model.
Study Design. Perfusion studies were performed in six placentas from term, uncomplicated deliveries. Concentrations of oseltamivir phosphate (OP) that were 5-6 fold, 20–30 fold, and 600–800 fold above the therapeutic peak were tested, as neither OP nor its active metabolite, oseltamivir carboxylate (OC),
could be detected at near-therapeutic concentrations. The transplacental transfer and accumulation of OC were
assessed using the 14C antipyrine reference method.
Results. OP was extensively metabolized to OC. In the 4 placentas with the highest concentration of OP, OC had a mean clearance index of 0.13 ± 0.08, suggesting that transplacental passage occurs at a relatively low rate. Measurable fetal accumulation occurred in the two placentas with the highest initial concentrations.
Conclusions. Oseltamivir phosphate was extensively metabolized in the ex vivo model. Transplacental transfer of the metabolite was incomplete and accumulation was minimal
Prerequisites for Successful Fiscal Reform: Some Preliminary Results
Journal of Public Budgeting, Accounting and Financial Management, Winter 1998.Refereed Journal ArticleThis paper examines whether any relationship exists between
success or failure of policy reform on the one hand, and various
political/economic conditions in place at the time of reform on the other.
Nineteen countries were scored using three financial variables to measure the
degree of success or failure of the reform. The independent variables were
country scores for ten different economic and political conditions. The
independent variables were used to try and predict a priori which of the nineteen
countries would succeed and which would fail. Eighteen of the nineteen
countries were correctly placed into their respective success group. However
only three of the ten conditions appeared important in predicting success: a
visionary leader, a crisis, and a comprehensive program. Other writers have
suggested different sets of predicting variables
Recent progress on the accurate determination of the equation of state of neutron and nuclear matter
The problem of accurately determining the equation of state of nuclear and
neutron matter at density near and beyond saturation is still an open
challenge. In this paper we will review the most recent progress made by means
of Quantum Monte Carlo calculations, which are at present the only ab-inito
method capable to treat a sufficiently large number of particles to give
meaningful estimates depending only on the choice of the nucleon-nucleon
interaction. In particular, we will discuss the introduction of
density-dependent interactions, the study of the temperature dependence of the
equation of state, and the possibility of accurately studying the effect of the
onset of hyperons by developing an accurate hyperon-nucleon and
hyperon-nucleon-nucleon interaction.Comment: 3 figures, 1 table, to appear in the Proceedings of "XIII Convegno di
Cortona su Problemi di Fisica Nucleare Teorica", Cortona (Italy), April 6-8,
201
s- and r-process element abundances in the CMD of 47 Tucanae using the Robert Stobie Spectrograph on SALT
A recent study by Wylie et al 2006 has revealed that s-process element
abundances are enhanced relative to iron in both red giant branch and
asymptotic giant branch stars of 47 Tucanae. A more detailed investigation into
s-process element abundances throughout the colour-magnitude diagram of 47
Tucanae is vital in order to determine whether the observed enhancements are
intrinsic to the cluster. This paper explores this possibility through
observational and theoretical means. The visibility of s- and r-process element
lines in synthetic spectra of giant and dwarf stars throughout the colour
magnitude diagram of 47 Tucanae has been explored. It was determined that a
resolving power of 10 000 was sufficient to observe s-process element abundance
variations in globular cluster giant branch stars. These synthetic results were
compared with the spectra of eleven 47 Tucanae giant branch stars observed
during the performance verification of the Robert Stobie Spectrograph on the
Southern African Large Telescope. Three s-process elements, Zr, Ba, Nd, and one
r-process element, Eu, were investigated. No abundance variations were found
such that [X/Fe] = 0.0 +/- 0.5 dex. It was concluded that this resolving power,
R ~ 5000, was not sufficient to obtain exact abundances but upper limits on the
s-process element abundances could be determined.Comment: 7 pages, 11 figure
The Gaia-ESO Survey: N-body modelling of the Gamma Velorum cluster
The Gaia-ESO Survey has recently unveiled the complex kinematic signature of
the Gamma Velorum cluster: this cluster is composed of two kinematically
distinct populations (hereafter, population A and B), showing two different
velocity dispersions and a relative ~2 km s^-1 radial velocity (RV) shift. In
this paper, we propose that the two populations of the Gamma Velorum cluster
originate from two different sub-clusters, born from the same parent molecular
cloud. We investigate this possibility by means of direct-summation N-body
simulations. Our scenario is able to reproduce not only the RV shift and the
different velocity dispersions, but also the different centroid (~0.5 pc), the
different spatial concentration and the different line-of-sight distance (~5
pc) of the two populations. The observed 1-2 Myr age difference between the two
populations is also naturally explained by our scenario, in which the two
sub-clusters formed in two slightly different star formation episodes. Our
simulations suggest that population B is strongly supervirial, while population
A is close to virial equilibrium. We discuss the implications of our models for
the formation of young star clusters and OB associations in the Milky Way.Comment: 12 pages, 7 figures, 2 tables, Astronomy and Astrophysics, in pres
Renal and Segmental Artery Hemodynamic Response to Mild Hypercapnia
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The AMBRE project: chemical evolution models for the Milky Way thick and thin discs
We study the chemical evolution of the thick and thin discs of the Galaxy by comparing detailed chemical evolution models with recent data from the Archéologie avec Matisse Basée sur les aRchives de l'ESO project. The data suggest that the stars in the thick and thin discs form two distinct sequences with the thick disc stars showing higher [α/Fe] ratios. We adopt two different approaches to model the evolution of thick and thin discs. In particular, we adopt (i) a two-infall approach where the thick disc forms fast and before the thin disc and by means of a fast gas accretion episode, whereas the thin disc forms by means of a second accretion episode on a longer time-scale; (ii) a parallel approach, where the two discs form in parallel but at different rates. By comparing our model results with the observed [Mg/Fe] versus [Fe/H] and the metallicity distribution functions in the two Galactic components, we conclude that the parallel approach can account for a group of α-enhanced metal-rich stars present in the data, whereas the two-infall approach cannot explain these stars unless they are the result of stellar migration. In both approaches, the thick disc has formed on a time-scale of accretion of 0.1 Gyr, whereas the thin disc formed on a time-scale of 7 Gyr in the solar region. In the two-infall approach, a gap in star formation between the thick and thin disc formation of several hundreds of Myr should be present, at variance with the parallel approach where no gap is present
The Gaia-ESO Survey: Tracing interstellar extinction
Large spectroscopic surveys have enabled in the recent years the computation
of three-dimensional interstellar extinction maps thanks to accurate stellar
atmospheric parameters and line-of-sight distances. Such maps are complementary
to 3D maps extracted from photometry, allowing a more thorough study of the
dust properties. Our goal is to use the high-resolution spectroscopic survey
Gaia-ESO in order to obtain with a good distance resolution the interstellar
extinction and its dependency as a function of the environment and the
Galactocentric position. We use the stellar atmospheric parameters of more than
5000 stars, obtained from the Gaia-ESO survey second internal data release, and
combine them with optical (SDSS) and near-infrared (VISTA) photometry as well
as different sets of theoretical stellar isochrones, in order to calculate
line-of-sight extinction and distances. The extinction coefficients are then
compared with the literature to discuss their dependancy on the stellar
parameters and position in the Galaxy. Within the errors of our method, our
work does not show that there is any dependence of the interstellar extinction
coefficient on the atmospheric parameters of the stars. We do not find any
evidence of the variation of E(J-H)/E(J-K) with the angle from the Galactic
centre nor with Galactocentric distance. This suggests that we are dealing with
a uniform extinction law in the SDSS ugriz bands and the near-IR JHKs bands.
Therefore, extinction maps using mean colour-excesses and assuming a constant
extinction coefficient can be used without introducing any systematic errors.Comment: 13 pages, 14 figures, 1 Appendix accepted for publication in
Astronomy&Astrophysic
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