1,093 research outputs found
Barium abundance in red giants of NGC 6752. Non-local thermodynamic equilibrium and three-dimensional effects
(Abridged) Aims: We study the effects related to departures from non-local
thermodynamic equilibrium (NLTE) and homogeneity in the atmospheres of red
giant stars in Galactic globular cluster NGC 6752, to assess their influence on
the formation of Ba II lines. Methods: One-dimensional (1D) local thermodynamic
equilibrium (LTE) and 1D NLTE barium abundances were derived using classical 1D
ATLAS stellar model atmospheres. The three-dimensional (3D) LTE abundances were
obtained for 8 red giants on the lower RGB, by adjusting their 1D LTE
abundances using 3D-1D abundance corrections, i.e., the differences between the
abundances obtained from the same spectral line using the 3D hydrodynamical
(CO5BOLD) and classical 1D (LHD) stellar model atmospheres. Results: The mean
1D barium-to-iron abundance ratios derived for 20 giants are _{1D
NLTE} = 0.05 \pm0.06 (stat.) \pm0.08 (sys.). The 3D-1D abundance correction
obtained for 8 giants is small (~+0.05 dex), thus leads to only minor
adjustment when applied to the mean 1D NLTE barium-to-iron abundance ratio for
the 20 giants, _{3D+NLTE} = 0.10 \pm0.06(stat.) \pm0.10(sys.). The
intrinsic abundance spread between the individual cluster stars is small and
can be explained in terms of uncertainties in the abundance determinations.
Conclusions: Deviations from LTE play an important role in the formation of
barium lines in the atmospheres of red giants studied here. The role of 3D
hydrodynamical effects should not be dismissed either, even if the obtained
3D-1D abundance corrections are small. This result is a consequence of subtle
fine-tuning of individual contributions from horizontal temperature
fluctuations and differences between the average temperature profiles in the 3D
and 1D model atmospheres: owing to the comparable size and opposite sign, their
contributions nearly cancel each other.Comment: Minor typos corrected. Accepted for publication in A&A (9 pages, 3
figures, 6 tables
The Inositol 5-Phosphatase dOCRL Controls PI(4,5)P2 Homeostasis and Is Necessary for Cytokinesis
SummaryDuring cytokinesis, constriction of an equatorial actomyosin ring physically separates the two daughter cells. At the cleavage furrow, the phosphoinositide PI(4,5)P2 plays an important role by recruiting and regulating essential proteins of the cytokinesis machinery [1]. Accordingly, perturbation of PI(4,5)P2 regulation leads to abortive furrowing and binucleation [2–4]. To determine how PI(4,5)P2 is regulated during cytokinesis, we individually knocked down each of the enzymes controlling the phosphoinositide (PIP) cycle in Drosophila. We show that depletion of the Drosophila ortholog of human oculocerebrorenal syndrome of Lowe 1 (OCRL1), an inositol 5-phosphatase mutated in the X-linked disorder oculocerebrorenal Lowe syndrome, triggers a high rate of cytokinesis failure. In absence of dOCRL, several essential components of the cleavage furrow were found to be incorrectly localized on giant cytoplasmic vacuoles rich in PI(4,5)P2 and in endocytic markers. We demonstrate that dOCRL is associated with endosomes and that it dephosphorylates PI(4,5)P2 on internal membranes to restrict this phosphoinositide at the plasma membrane and thereby regulates cleavage furrow formation and ingression. Identification of dOCRL as essential for cell division may be important to understand the molecular basis of the phenotypic manifestations of Lowe syndrome
Developing reading-writing connections; the impact of explicit instruction of literary devices on the quality of children's narrative writing
The purpose of this collaborative schools-university study was to investigate how the explicit instruction of literary devices during designated literacy sessions could improve the quality of children's narrative writing. A guiding question for the study was: Can children's writing can be enhanced by teachers drawing attention to the literary devices used by professional writers or “mentor authors”? The study was conducted with 18 teachers, working as research partners in nine elementary schools over one school year. The research group explored ways of developing children as reflective authors, able to draft and redraft writing in response to peer and teacher feedback. Daily literacy sessions were complemented by weekly writing workshops where students engaged in authorial activity and experienced writers' perspectives and readers' demands (Harwayne, 1992; May, 2004). Methods for data collection included video recording of peer-peer and teacher-led group discussions and audio recording of teacher-child conferences. Samples of children's narrative writing were collected and a comparison was made between the quality of their independent writing at the beginning and end of the research period. The research group documented the importance of peer-peer and teacher-student discourse in the development of children's metalanguage and awareness of audience. The study suggests that reading, discussing, and evaluating mentor texts can have a positive impact on the quality of children's independent writing
HerMES: Candidate Gravitationally Lensed Galaxies and Lensing Statistics at Submillimeter Wavelengths
We present a list of 13 candidate gravitationally lensed submillimeter
galaxies (SMGs) from 95 square degrees of the Herschel Multi-tiered
Extragalactic Survey, a surface density of 0.14\pm0.04deg^{-2}. The selected
sources have 500um flux densities (S_500) greater than 100mJy. Gravitational
lensing is confirmed by follow-up observations in 9 of the 13 systems (70%),
and the lensing status of the four remaining sources is undetermined. We also
present a supplementary sample of 29 (0.31\pm0.06deg^{-2}) gravitationally
lensed SMG candidates with S_500=80--100mJy, which are expected to contain a
higher fraction of interlopers than the primary candidates. The number counts
of the candidate lensed galaxies are consistent with a simple statistical model
of the lensing rate, which uses a foreground matter distribution, the intrinsic
SMG number counts, and an assumed SMG redshift distribution. The model predicts
that 32--74% of our S_500>100mJy candidates are strongly gravitationally lensed
(mu>2), with the brightest sources being the most robust; this is consistent
with the observational data. Our statistical model also predicts that, on
average, lensed galaxies with S_500=100mJy are magnified by factors of ~9, with
apparently brighter galaxies having progressively higher average magnification,
due to the shape of the intrinsic number counts. 65% of the sources are
expected to have intrinsic 500micron flux densities less than 30mJy. Thus,
samples of strongly gravitationally lensed SMGs, such as those presented here,
probe below the nominal Herschel detection limit at 500 micron. They are good
targets for the detailed study of the physical conditions in distant dusty,
star-forming galaxies, due to the lensing magnification, which can lead to
spatial resolutions of ~0.01" in the source plane.Comment: ApJ in press. 31 pages, 16 figures, 5 tables. This version updated to
match accepted versio
The double sub-giant branch of NGC 6656 (M22): a chemical characterization
We present an abundance analysis of 101 subgiant branch (SGB) stars in the
globular cluster M22. Using low resolution FLAMES/GIRAFFE spectra we have
determined abundances of the neutron-capture strontium and barium and the light
element carbon. With these data we explore relationships between the observed
SGB photometric split in this cluster and two stellar groups characterized by
different contents of iron, slow neutron-capture process (s-process) elements,
and the alpha element calcium, that we previously discovered in M22's red-giant
stars. We show that the SGB stars correlate in chemical composition and
color-magnitude diagram position: the stars with higher metallicity and
relative s-process abundances define a fainter SGB, while stars with lower
metallicity and s-process content reside on a relatively brighter SGB. This
result has implications for the relative ages of the two stellar groups of M22.
In particular, it is inconsistent with a large spread in ages of the two SGBs.
By accounting for the chemical content of the two stellar groups, isochrone
fitting of the double SGB suggests that their ages are not different by more
than 300 Myr.Comment: 21 pages, 12 figures, accepted for publication in A&
The global governance of human cloning: the case of UNESCO
Since Dolly the Sheep was cloned in 1996, the question of whether human reproductive cloning should be banned or pursued has been the subject of international debate. Feelings run strong on both sides. In 2005, the United Nations adopted its Declaration on Human Cloning to try to deal with the issue. The declaration is ambiguously worded, prohibiting “all forms of human cloning inasmuch as they are incompatible with human dignity and the protection of human life”. It received only ambivalent support from UN member states. Given this unsatisfactory outcome, in 2008 UNESCO (the United Nations Educational, Scientific and Cultural Organization) set up a Working Group to investigate the possibility of a legally binding convention to ban human reproductive cloning. The Working Group was made up of members of the International Bioethics Committee, established in 1993 as part of UNESCO’s Bioethics Programme. It found that the lack of clarity in international law is unhelpful for those states yet to formulate national regulations or policies on human cloning. Despite this, member states of UNESCO resisted the idea of a convention for several years. This changed in 2015, but there has been no practical progress on the issue. Drawing on official records and first-hand observations at bioethics meetings, this article examines the human cloning debate at UNESCO from 2008 onwards, thus building on and advancing current scholarship by applying recent ideas on global governance to an empirical case. It concludes that, although human reproductive cloning is a challenging subject, establishing a robust global governance framework in this area may be possible via an alternative deliberative format, based on knowledge sharing and feasibility testing rather than the interest-based bargaining that is common to intergovernmental organizations and involving a wide range of stakeholders. This article is published as part of a collection on global governance
Measurement of the diffractive structure function in deep inelastic scattering at HERA
This paper presents an analysis of the inclusive properties of diffractive
deep inelastic scattering events produced in interactions at HERA. The
events are characterised by a rapidity gap between the outgoing proton system
and the remaining hadronic system. Inclusive distributions are presented and
compared with Monte Carlo models for diffractive processes. The data are
consistent with models where the pomeron structure function has a hard and a
soft contribution. The diffractive structure function is measured as a function
of \xpom, the momentum fraction lost by the proton, of , the momentum
fraction of the struck quark with respect to \xpom, and of . The \xpom
dependence is consistent with the form \xpoma where
in all bins of and
. In the measured range, the diffractive structure function
approximately scales with at fixed . In an Ingelman-Schlein type
model, where commonly used pomeron flux factor normalisations are assumed, it
is found that the quarks within the pomeron do not saturate the momentum sum
rule.Comment: 36 pages, latex, 11 figures appended as uuencoded fil
Measurements of fiducial and differential cross sections for Higgs boson production in the diphoton decay channel at s√=8 TeV with ATLAS
Measurements of fiducial and differential cross sections are presented for Higgs boson production in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The analysis is performed in the H → γγ decay channel using 20.3 fb−1 of data recorded by the ATLAS experiment at the CERN Large Hadron Collider. The signal is extracted using a fit to the diphoton invariant mass spectrum assuming that the width of the resonance is much smaller than the experimental resolution. The signal yields are corrected for the effects of detector inefficiency and resolution. The pp → H → γγ fiducial cross section is measured to be 43.2 ±9.4(stat.) − 2.9 + 3.2 (syst.) ±1.2(lumi)fb for a Higgs boson of mass 125.4GeV decaying to two isolated photons that have transverse momentum greater than 35% and 25% of the diphoton invariant mass and each with absolute pseudorapidity less than 2.37. Four additional fiducial cross sections and two cross-section limits are presented in phase space regions that test the theoretical modelling of different Higgs boson production mechanisms, or are sensitive to physics beyond the Standard Model. Differential cross sections are also presented, as a function of variables related to the diphoton kinematics and the jet activity produced in the Higgs boson events. The observed spectra are statistically limited but broadly in line with the theoretical expectations
Measurement of the production of a W boson in association with a charm quark in pp collisions at √s = 7 TeV with the ATLAS detector
The production of a W boson in association with a single charm quark is studied using 4.6 fb−1 of pp collision data at s√ = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96+0.26−0.30 at Q 2 = 1.9 GeV2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio σ(W + +c¯¯)/σ(W − + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s−s¯¯¯ quark asymmetry
Measurement of χ c1 and χ c2 production with s√ = 7 TeV pp collisions at ATLAS
The prompt and non-prompt production cross-sections for the χ c1 and χ c2 charmonium states are measured in pp collisions at s√ = 7 TeV with the ATLAS detector at the LHC using 4.5 fb−1 of integrated luminosity. The χ c states are reconstructed through the radiative decay χ c → J/ψγ (with J/ψ → μ + μ −) where photons are reconstructed from γ → e + e − conversions. The production rate of the χ c2 state relative to the χ c1 state is measured for prompt and non-prompt χ c as a function of J/ψ transverse momentum. The prompt χ c cross-sections are combined with existing measurements of prompt J/ψ production to derive the fraction of prompt J/ψ produced in feed-down from χ c decays. The fractions of χ c1 and χ c2 produced in b-hadron decays are also measured
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