180 research outputs found
The value of measurement of macular carotenoid pigment optical densities and distributions in age-related macular degeneration and other retinal disorders
AbstractThere is increasing recognition that the optical and antioxidant properties of the xanthophyll carotenoids lutein and zeaxanthin play an important role in maintaining the health and function of the human macula. In this review article, we assess the value of non-invasive quantification of macular pigment levels and distributions to identify individuals potentially at risk for visual disability or catastrophic vision loss from age-related macular degeneration, and we consider the strengths and weaknesses of the diverse measurement methods currently available
Correction to: A novel preference-informed complementary trial (PICT) design for clinical trial research influenced by strong patient preferences (Trials, (2021), 22, 1, (206), 10.1186/s13063-021-05164-1)
Following the publication of the original article [1], we were notified that the Acknowledgements section needs to accommodate additional collaborators. The original article has been corrected
The metallicity profile of M31 from spectroscopy of hundreds of HII regions and PNe
The oxygen abundance gradients among nebular emission line regions in spiral
galaxies have been used as important constraints for models of chemical
evolution. We present the largest ever full-wavelength optical spectroscopic
sample of emission line nebulae in a spiral galaxy (M31). We have collected
spectra of 253 HII regions and 407 planetary nebulae with the Hectospec
multi-fiber spectrograph of the MMT. We measure the line-of-sight extinction
for 199 HII regions and 333 PNe; we derive oxygen abundance directly, based on
the electron temperature, for 51 PNe; and we use strong line methods to
estimate oxygen abundance for 192 HII regions and nitrogen abundance for 52 HII
regions. The relatively shallow oxygen abundance gradient of the more extended
HII regions in our sample is generally in agreement with the result of Zaritsky
et al. (1994), based on only 19 M31 HII regions, but varies with the
strong-line diagnostic employed. Our large sample size demonstrates that there
is significant intrinsic scatter around this abundance gradient, as much as 3
times the systematic uncertainty in the strong line diagnostics. The intrinsic
scatter is similar in the nitrogen abundances, although the gradient is
significantly steeper. On small scales (deprojected distance < 0.5 kpc), HII
regions exhibit local variations in oxygen abundance that are larger than 0.3
dex in 33% of neighboring pairs. We do not identify a significant oxygen
abundance gradient among PNe, but we do find a significant gradient in the [N
II] ratio that varies systematically with surface brightness. Our results
underscore the complex and inhomogeneous nature of the ISM of M31, and our
dataset illustrates systematic effects relevant to future studies of the
metallicity gradients in nearby spiral galaxies.Comment: 22 pages, 14 figures, 5 tables. Accepted for publication in ApJ, full
tables available at
http://www.cfa.harvard.edu/~nsanders/papers/M31/summary.htm
High resolution AMI Large Array imaging of spinning dust sources: spatially correlated 8 micron emission and evidence of a stellar wind in L675
We present 25 arcsecond resolution radio images of five Lynds Dark Nebulae
(L675, L944, L1103, L1111 & L1246) at 16 GHz made with the Arcminute
Microkelvin Imager (AMI) Large Array. These objects were previously observed
with the AMI Small Array to have an excess of emission at microwave frequencies
relative to lower frequency radio data. In L675 we find a flat spectrum compact
radio counterpart to the 850 micron emission seen with SCUBA and suggest that
it is cm-wave emission from a previously unknown deeply embedded young
protostar. In the case of L1246 the cm-wave emission is spatially correlated
with 8 micron emission seen with Spitzer. Since the MIR emission is present
only in Spitzer band 4 we suggest that it arises from a population of PAH
molecules, which also give rise to the cm-wave emission through spinning dust
emission.Comment: accepted MNRA
Séance spécialisée : géodynamique des bassins océaniques et des marges continentales
Une morphologie de fonds sous-marins bathyaux comportant des indurations liées à des dépôts ferro-manganésifères inclus dans des sédiments hémipélagiques peu ou pas cimentés a été découverte sur une ride volcanique tertiaire au large de la Nouvelle-Calédonie (SW Pacifique). Elle semble être en relation avec des circulations hydrothermales au travers de la couverture sédimentaire pendant l'activité volcanique miocène de la ride des Loyauté. (Résumé d'auteur
When Do Stars Go BOOM?
The maximum mass of a star that can produce a white dwarf (WD) is an
important astrophysical quantity. One of the best approaches to establishing
this limit is to search for WDs in young star clusters in which only massive
stars have had time to evolve and where the mass of the progenitor can be
established from the cooling time of the WD together with the age of the
cluster. Searches in young Milky Way clusters have not thus far yielded WD
members more massive than about 1.1, well below the Chandrasekhar
mass of , nor progenitors with masses in excess of about
. However, the hunt for potentially massive WDs that escaped their
cluster environs is yielding interesting candidates. To expand the cluster
sample further, we used HST to survey four young and massive star clusters in
the Magellanic Clouds for bright WDs that could have evolved from stars as
massive as 10. We located five potential WD candidates in the
oldest of the four clusters examined, the first extragalactic single WDs thus
far discovered. As these hot WDs are very faint at optical wavelengths, final
confirmation will likely have to await spectroscopy with 30-metre class
telescopes.Comment: 10 pages, 5 figures, accepted to the Astrophysical Journal Letter
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