206 research outputs found
The chemical composition of globular clusters in the Local Group
We present detailed abundance measurements for 45 globular clusters (GCs) in
galaxies in (and, in one case, beyond) the Local Group. The measurements are
based on new high-resolution integrated-light spectra of GCs in NGC 185, NGC
205, M31, M33, and NGC 2403, combined with reanalysis of previous observations
of GCs in the Fornax dSph, WLM, NGC 147, NGC 6822, and the Milky Way. The GCs
cover the range -2.8 < [Fe/H] < -0.1 and we determined abundances for Fe, Na,
Mg, Si, Ca, Sc, Ti, Cr, Mn, Ni, Cu, Zn, Zr, Ba, and Eu. Corrections for non
local thermodynamic equilibrium effects are included for Na, Mg, Ca, Ti, Mn,
Fe, Ni, and Ba. For several of the galaxies, our measurements provide the first
quantitative constraints on the detailed composition of their metal-poor
stellar populations. Overall, the GCs in different galaxies exhibit remarkably
uniform abundance patterns of the alpha-, iron-peak, and neutron-capture
elements, with a dispersion of less than 0.1 dex in [alpha/Fe] for the full
sample. There is a hint that GCs in dwarf galaxies are slightly less
alpha-enhanced (by about 0.04 dex on average) than those in larger galaxies.
One GC in M33 (HM33-B) resembles the most metal-rich GCs in the Fornax dSph
(Fornax 4) and NGC 6822 (SC7) by having alpha-element abundances closer to
scaled-solar values, possibly hinting at an accretion origin. We find that the
alpha-element abundances strongly correlate with those of Na, Sc, Ni, and Zn.
Several GCs with [Fe/H]<-1.5 are deficient in Mg compared to other
alpha-elements. We find no GCs with strongly enhanced r-process abundances as
reported for metal-poor stars in some ultra-faint dwarfs and the Magellanic
Clouds. The similarity of the abundance patterns for metal-poor GCs in
different environments points to similar early enrichment histories and only
allow for minor variations in the initial mass function.Comment: 34 pages + 6 appendices. Accepted for publication in Astronomy &
Astrophysic
Observational constraints on the origin of the elements. V. Non-LTE abundance ratios of [Ni/Fe] in Galactic stars and enrichment by sub-Chandrasekhar mass SNe
We constrain the role of different SN Ia channels in the chemical enrichment
of the Galaxy by studying the abundances of nickel in Galactic stars. We
investigate four different SN Ia sub-classes, including the classical
single-degenerate near-Chandrasekhar mass SN Ia, the fainter SN Iax systems
associated with He accretion from the companion, as well as two sub-Ch mass SN
Ia channels. The latter include the double-detonation of a white dwarf
accreting helium-rich matter and violent white dwarf mergers. NLTE models of Fe
and Ni are used in the abundance analysis. In the GCE models, we include new
delay time distributions arising from the different SN Ia channels, as well as
recent yields for core-collapse supernovae and AGB stars. The data-model
comparison is performed using a Markov chain Monte Carlo framework that allows
us to explore the entire parameter space allowed by the diversity of explosion
mechanisms and the Galactic SN Ia rate, taking into account the uncertainties
of the observed data. We show that NLTE effects have a non-negligible impact on
the observed [Ni/Fe] ratios in the Galactic stars. The NLTE corrections to Ni
abundances are not large, but strictly positive, lifting the [Ni/Fe] ratios by
~+0.15 dex at [Fe/H] =-2. We find that that the distributions of [Ni/Fe] in LTE
and in NLTE are very tight, with a scatter of < 0.1 dex at all metallicities,
supporting earlier work. In LTE, most stars have scaled-solar Ni abundances,
[Ni/Fe] = 0, with a slight tendency for sub-solar [Ni/Fe] ratios at lower
[Fe/H]. In NLTE, however, we find a mild anti-correlation between [Ni/Fe] and
metallicity, and a slightly elevated [Ni/Fe] ratios at [Fe/H] < -1.0. The NLTE
data can be explained by the GCE models calculated with a substantial, ~ 75%,
fraction of sub-Ch SN Ia.Comment: accepted for publication in Astronomy & Astrophysics, abridged
version of the abstrac
The Prince and the Pauper: Evidence for the early high-redshift formation of the Galactic -poor disc population
Context. The presence of [/Fe]-[Fe/H] bi-modality in the Milky Way
disc has animated the Galactic archaeology community since more than two
decades. Aims. Our goal is to investigate the chemical, temporal, and
kinematical structure of the Galactic discs using abundances, kinematics, and
ages derived self-consistently with the new Bayesian framework SAPP. Methods.
We employ the public Gaia-ESO spectra, as well as Gaia EDR3 astrometry and
photometry. Stellar parameters and chemical abundances are determined for 13
426 stars using NLTE models of synthetic spectra. Ages are derived for a
sub-sample of 2 898 stars, including subgiants and main-sequence stars. The
sample probes a large range of Galactocentric radii, 3 to 12 kpc, and
extends out of the disc plane to 2 kpc. Results. Our new data confirm the
known bi-modality in the [Fe/H] - [/Fe] space, which is often viewed as
the manifestation of the chemical thin and thick discs. The over-densities
significantly overlap in metallicity, age, and kinematics, and none of these is
a sufficient criterion for distinguishing between the two disc populations.
Different from previous studies, we find that the -poor disc population
has a very extended [Fe/H] distribution and contains 20 old stars
with ages of up to 11 Gyr. Conclusions. Our results suggest that the
Galactic thin disc was in place early, at look-back times corresponding to
redshifts z 2 or more. At ages 9 to 11 Gyr, the two disc
structures shared a period of co-evolution. Our data can be understood within
the clumpy disc formation scenario that does not require a pre-existing thick
disc to initiate a formation of the thin disc. We anticipate that a similar
evolution can be realised in cosmological simulations of galaxy formation.Comment: 14 pages, 10 figures, re-submitted to A&
Acceptance of technology-enhanced learning for a theoretical radiological science course: a randomized controlled trial
<p>Abstract</p> <p>Background</p> <p>Technology-enhanced learning (TEL) gives a view to improved education. However, there is a need to clarify how TEL can be used effectively. The study compared students' attitudes and opinions towards a traditional face-to-face course on theoretical radiological science and a TEL course where students could combine face-to-face lectures and e-learning modules at their best convenience.</p> <p>Methods</p> <p>42 third-year dental students were randomly assigned to the traditional face-to-face group and the TEL group. Both groups completed questionnaires before the beginning and after completion of the course on attitudes and opinions towards a traditional face-to-face lectures and technology-enhanced learning. After completion of the course both groups also filled in the validated German-language TRIL (Trierer Inventar zur Lehrevaluation) questionnaire for the evaluation of courses given at universities.</p> <p>Results</p> <p>Both groups had a positive attitude towards e-learning that did not change over time. The TEL group attended significantly less face-to-face lectures than the traditional group. However, both groups stated that face-to-face lectures were the basis for education in a theoretical radiological science course.</p> <p>The members of the TEL group rated e-mail reminders significantly more important when they filled in the questionnaire on attitudes and opinions towards a traditional face-to-face lectures and technology-enhanced learning for the second time after completion of the course.</p> <p>The members of the technology-enhanced learning group were significantly less confident in passing the exam compared to the members of the traditional group. However, examination results did not differ significantly for traditional and the TEL group.</p> <p>Conclusions</p> <p>It seems that technology-enhanced learning in a theoretical radiological science course has the potential to reduce the need for face-to-face lectures. At the same time examination results are not impaired. However, technology-enhanced learning cannot completely replace traditional face-to-face lectures, because students indicate that they consider traditional teaching as the basis of their education.</p
Post-Infection Immunodeficiency Virus Control by Neutralizing Antibodies
BACKGROUND: Unlike most acute viral infections controlled with the appearance of virus-specific neutralizing antibodies (NAbs), primary HIV infections are not met with such potent and early antibody responses. This brings into question if or how the presence of potent antibodies can contribute to primary HIV control, but protective efficacies of antiviral antibodies in primary HIV infections have remained elusive; and, it has been speculated that even NAb induction could have only a limited suppressive effect on primary HIV replication once infection is established. Here, in an attempt to answer this question, we examined the effect of passive NAb immunization post-infection on primary viral replication in a macaque AIDS model. METHODS AND FINDINGS: The inoculums for passive immunization with simian immunodeficiency virus mac239 (SIVmac239)-specific neutralizing activity were prepared by purifying polyclonal immunoglobulin G from pooled plasma of six SIVmac239-infected rhesus macaques with NAb induction in the chronic phase. Passive immunization of rhesus macaques with the NAbs at day 7 after SIVmac239 challenge resulted in significant reduction of set-point plasma viral loads and preservation of central memory CD4 T lymphocyte counts, despite the limited detection period of the administered NAb responses. Peripheral lymph node dendritic cell (DC)-associated viral RNA loads showed a remarkable peak with the NAb administration, and DCs stimulated in vitro with NAb-preincubated SIV activated virus-specific CD4 T lymphocytes in an Fc-dependent manner, implying antibody-mediated virion uptake by DCs and enhanced T cell priming. CONCLUSIONS: Our results present evidence indicating that potent antibody induction post-infection can result in primary immunodeficiency virus control and suggest direct and indirect contribution of its absence to initial control failure in HIV infections. Although difficulty in achieving requisite neutralizing titers for sterile HIV protection by prophylactic vaccination has been suggested, this study points out a possibility of non-sterile HIV control by prophylactic vaccine-induced, sub-sterile titers of NAbs post-infection, providing a rationale of vaccine-based NAb induction for primary HIV control
PDGF-C Induces Maturation of Blood Vessels in a Model of Glioblastoma and Attenuates the Response to Anti-VEGF Treatment
Recent clinical trials of VEGF inhibitors have shown promise in the treatment of recurrent glioblastomas (GBM). However, the survival benefit is usually short-lived as tumors escape anti-VEGF therapies. Here we tested the hypothesis that Platelet Derived Growth Factor-C (PDGF-C), an isoform of the PDGF family, affects GBM progression independent of VEGF pathway and hinders anti-VEGF therapy.We first showed that PDGF-C is present in human GBMs. Then, we overexpressed or downregulated PDGF-C in a human GBM cell line, U87MG, and grew them in cranial windows in nude mice to assess vessel structure and function using intravital microscopy. PDGF-C overexpressing tumors had smaller vessel diameters and lower vascular permeability compared to the parental or siRNA-transfected tumors. Furthermore, vessels in PDGF-C overexpressing tumors had more extensive coverage with NG2 positive perivascular cells and a thicker collagen IV basement membrane than the controls. Treatment with DC101, an anti-VEGFR-2 antibody, induced decreases in vessel density in the parental tumors, but had no effect on the PDGF-C overexpressing tumors.These results suggest that PDGF-C plays an important role in glioma vessel maturation and stabilization, and that it can attenuate the response to anti-VEGF therapy, potentially contributing to escape from vascular normalization
The GALAH Survey : Non-LTE departure coefficients for large spectroscopic surveys
19 pages, 25 figures, 2 tables, arXiv abstract abridged; accepted for publication in A&AMassive sets of stellar spectroscopic observations are rapidly becoming available and these can be used to determine the chemical composition and evolution of the Galaxy with unprecedented precision. One of the major challenges in this endeavour involves constructing realistic models of stellar spectra with which to reliably determine stellar abundances. At present, large stellar surveys commonly use simplified models that assume that the stellar atmospheres are approximately in local thermodynamic equilibrium (LTE). To test and ultimately relax this assumption, we have performed non-LTE calculations for different elements (H, Li, C, N, O, Na, Mg, Al, Si, K, Ca, Mn, and Ba), using recent model atoms that have physically-motivated descriptions for the inelastic collisions with neutral hydrogen, across a grid of 1D MARCS model atmospheres that spans , , and . We present the grids of departure coefficients that have been implemented into the GALAH DR3 analysis pipeline in order to complement the extant non-LTE grid for iron. We also present a detailed line-by-line re-analysis of stars from GALAH DR3. We found that relaxing LTE can change the abundances by between and for different lines and stars. Taking departures from LTE into account can reduce the dispersion in the versus plane by up to , and it can remove spurious differences between the dwarfs and giants by up to . The resulting abundance slopes can thus be qualitatively different in non-LTE, possibly with important implications for the chemical evolution of our Galaxy.Peer reviewe
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