18,407 research outputs found
Progression from ocular hypertension to visual field loss in the English hospital eye service
Background There are more than one million National Health Service visits in England and Wales each year for patients with glaucoma or ocular hypertension (OHT). With the ageing population and an increase in optometric testing, the economic burden of glaucoma-related visits is predicted to increase. We examined the conversion rates of OHT to primary open-angle glaucoma (POAG) in England and assessed factors associated with risk of conversion.
Methods Electronic medical records of 45 309 patients from five regionally different glaucoma clinics in England were retrospectively examined. Conversion to POAG from OHT was defined by deterioration in visual field (two consecutive tests classified as stage 1 or worse as per the glaucoma staging system 2). Cox proportional hazards models were used to examine factors (age, sex, treatment status and baseline intraocular pressure (IOP)) associated with conversion.
Results The cumulative risk of conversion to POAG was 17.5% (95% CI 15.4% to 19.6%) at 5 years. Older age (HR 1.35 per decade, 95% CI 1.22 to 1.50, p<0.001) was associated with a higher risk of conversion. IOP-lowering therapy (HR 0.45, 95% CI 0.35 to 0.57, p<0.001) was associated with a lower risk of conversion. Predicted 5-year conversion rates for treated and untreated groups were 14.0% and 26.9%, respectively.
Conclusion Less than one-fifth of OHT patients managed in glaucoma clinics in the UK converted to POAG over a 5-year period, suggesting many patients may require less intensive follow-up. Our study provides real-world evidence for the efficacy of current management (including IOP-lowering treatment) at reducing risk of conversion
Spectroscopic search for binaries among EHB stars in globular clusters
We performed a spectroscopic search for binaries among hot Horizontal Branch
stars in globular clusters. We present final results for a sample of 51 stars
in NGC6752, and preliminary results for the first 15 stars analyzed in M80. The
observed stars are distributed along all the HBs in the range 8000 < Teff <
32000 K, and have been observed during four nights. Radial velocity variations
have been measured with the cross-correlation technique. We carefully analyzed
the statistical and systematic errors associated with the measurements in order
to evaluate the statistical significance of the observed variations. No close
binary system has been detected, neither among cooler stars nor among the
sample of hot EHB stars (18 stars with Teff > 22000 K in NGC6752). The data
corrected for instrumental effects indicate that the radial velocity variations
are always below the 3sigma level of ~15 km/s. These results are in sharp
contrast with those found for field hot subdwarfs, and open new questions about
the formation of EHB stars in globular clusters, and possibly of the field
subdwarfs.Comment: To appear in Baltic Astronomy. Proceedings of the 2nd meeting on Hot
Subdwarf Stars, La Palma, June 2005. 4 pages, 2 figure
The peculiar horizontal branch morphology of the Galactic globular clusters NGC 6388 and NGC 6441: new insights from UV observations
Context. In this paper we present multiband optical and UV Hubble Space Telescope photometry of the two Galactic globular clusters NGC 6388 and NGC 6441.
Aims. We investigate the properties of their anomalous horizontal branches in different photometric planes in order to shed light on the nature of the physical mechanism(s) responsible for the existence of an extended blue tail and of a slope in the horizontal branch, visible in all the color-magnitude diagrams.
Methods. New photometric data have been collected and carefully reduced. Empirical data have been compared with updated stellar models of low-mass, metal-rich, He-burning structures, transformed to the observational plane with appropriate model atmospheres.
Results. We have obtained the first UV color-magnitude diagrams for NGC 6388 and NGC 6441. These diagrams confirm previous results, obtained in optical bands, about the presence of a sizeable stellar population of extremely hot horizontal branch stars. At least in NGC 6388, we find a clear indication that at the hot end of the horizontal branch the distribution of stars forms a hook-like feature, closely resembling those observed in NGC 2808 and Omega Cen. We briefly review the theoretical scenarios that have been suggested for interpreting this observational feature. We also investigate the tilted horizontal branch morphology and provide further evidence that supports early suggestions that this feature cannot be interpreted as an effect of differential reddening. We show that a possible solution of the puzzle is to assume that a small fraction - ranging between 10-20% - of the stellar population in the two clusters is strongly helium-enriched (Y ~ 0.40 in NGC 6388 and Y ~ 0.35 in NGC 6441). The occurrence of a spread in the He abundance between the canonical value (Y ~ 0.26) and the quoted upper limits can significantly help in explaining the "whole" morphology of the horizontal branch and the pulsational properties of the variable stars in the target clusters
Fluctuation Analysis of Human Electroencephalogram
The scaling behaviors of the human electroencephalogram (EEG) time series are
studied using detrended fluctuation analysis. Two scaling regions are found in
nearly every channel for all subjects examined. The scatter plot of the scaling
exponents for all channels (up to 129) reveals the complicated structure of a
subject's brain activity. Moment analyses are performed to extract the gross
features of all the scaling exponents, and another universal scaling behavior
is identified. A one-parameter description is found to characterize the
fluctuation properties of the nonlinear behaviors of the brain dynamics.Comment: 4 pages in RevTeX + 6 figures in ep
Magnetic ordering in GdNi2B2C revisited by resonant x-ray scattering: evidence for the double-q model
Recent theoretical efforts aimed at understanding the nature of
antiferromagnetic ordering in GdNi2B2C predicted double-q ordering. Here we
employ resonant elastic x-ray scattering to test this theory against the
formerly proposed, single-q ordering scenario. Our study reveals a satellite
reflection associated with a mixed-order component propagation wave vector,
viz., (q_a,2q_b,0) with q_b = q_a approx= 0.55 reciprocal lattice units, the
presence of which is incompatible with single-q ordering but is expected from
the double-q model. A (3q_a,0,0) wave vector (i.e., third-order) satellite is
also observed, again in line with the double-q model. The temperature
dependencies of these along with that of a first-order satellite are compared
with calculations based on the double-q model and reasonable qualitative
agreement is found. By examining the azimuthal dependence of first-order
satellite scattering, we show the magnetic order to be, as predicted,
elliptically polarized at base temperature and find the temperature dependence
of the "out of a-b plane" moment component to be in fairly good agreement with
calculation. Our results provide qualitative support for the double-q model and
thus in turn corroborate the explanation for the "magnetoelastic paradox"
offered by this model.Comment: 8 pages, 5 figures. Submitted to Phys. Rev.
Coordinates and 2MASS and OGLE identifications for all stars in Arp's 1965 finding chart for Baade's Window
Aims: We seek to provide 2MASS and OGLE identifications and coordinates for
all stars in the finding chart published by Arp\,(1965). This chart covers the
low extinction area around NGC 6522, also known as Baade's window, at
coordinates (l,b)=(1.02,-3.92).
Methods: A cross correlation, using numerical techniques, was performed
between a scan of the original finding chart from Arp (1965) and 2MASS and
OGLE-II images and stellar coordinates.
Results: We provide coordinates for all stars in Arp's finding chart and
2MASS and OGLE identifications wherever possible. Two identifications in
quadrant II do not appear in the original finding chart.Comment: 30 pages, accepted by A&A as a Research Not
The AMBRE Project: searching for the closest solar siblings
Finding solar siblings, that is, stars that formed in the same cluster as the
Sun, will yield information about the conditions at the Sun's birthplace. We
search for solar sibling candidates in AMBRE, the very large spectra database
of solar vicinity stars. Since the ages and chemical abundances of solar
siblings are very similar to those of the Sun, we carried out a chemistry- and
age-based search for solar sibling candidates. We used high-resolution spectra
to derive precise stellar parameters and chemical abundances of the stars. We
used these spectroscopic parameters together with Gaia DR2 astrometric data to
derive stellar isochronal ages. Gaia data were also used to study the
kinematics of the sibling candidates. From the about 17000 stars that are
characterized within the AMBRE project, we first selected 55 stars whose
metallicities are closest to the solar value (-0.1 < [Fe/H] < 0.1 dex). For
these stars we derived precise chemical abundances of several iron-peak, alpha-
and neutron-capture elements, based on which we selected 12 solar sibling
candidates with average abundances and metallicities between -0.03 to 0.03 dex.
Our further selection left us with 4 candidates with stellar ages that are
compatible with the solar age within observational uncertainties. For the 2 of
the hottest candidates, we derived the carbon isotopic ratios, which are
compatible with the solar value. HD186302 is the most precisely characterized
and probably the most probable candidate of our 4 best candidates. Very precise
chemical characterization and age estimation is necessary to identify solar
siblings. We propose that in addition to typical chemical tagging, the study of
isotopic ratios can give further important information about the relation of
sibling candidates with the Sun. Ideally, asteroseismic age determinations of
the candidates could solve the problem of imprecise isochronal ages.Comment: Accepted for publication in A&
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