2,139 research outputs found
On certain other sets of integers
We show that if A is a subset of {1,...,N} containing no non-trivial
three-term arithmetic progressions then |A|=O(N/ log^{3/4-o(1)} N).Comment: 29 pp. Corrected typos. Added definitions for some non-standard
notation and remarks on lower bound
The GALEX Ultraviolet Atlas of Nearby Galaxies
We present images, integrated photometry, and surface-brightness and color profiles for a total of 1034 nearby galaxies recently observed by the Galaxy Evolution Explorer (GALEX) satellite in its far-ultraviolet (FUV; λ_(eff) = 1516 Å) and near-ultraviolet (NUV; λ_(eff) = 2267 Å) bands. Our catalog of objects is derived primarily from the GALEX Nearby Galaxies Survey (NGS) supplemented by galaxies larger than 1' in diameter serendipitously found in these fields and in other GALEX exposures of similar of greater depth. The sample analyzed here adequately describes the distribution and full range of properties (luminosity, color, star formation rate [SFR]) of galaxies in the local universe. From the surface brightness profiles obtained we have computed asymptotic magnitudes, colors, and luminosities, along with the concentration indices C31 and C42. We have also morphologically classified the UV surface brightness profiles according to their shape. This data set has been complemented with archival optical, near-infrared, and far-infrared fluxes and colors. We find that the integrated (FUV − K) color provides robust discrimination between elliptical and spiral/irregular galaxies and also among spiral galaxies of different subtypes. Elliptical galaxies with brighter K-band luminosities (i.e., more massive) are redder in (NUV − K) color but bluer in (FUV − NUV) (a color sensitive to the presence of a strong UV upturn) than less massive ellipticals. In the case of the spiral/irregular galaxies our analysis shows the presence of a relatively tight correlation between the (FUV − NUV) color (or, equivalently, the slope of the UV spectrum, β) and the total infrared-to-UV ratio. The correlation found between (FUV − NUV) color and K-band luminosity (with lower luminosity objects being bluer than more luminous ones) can be explained as due to an increase in the dust content with galaxy luminosity. The images in this Atlas along with the profiles and integrated properties are publicly available through a dedicated Web page
GALEX Ultraviolet Photometry of Globular Clusters in M31
We present ultraviolet photometry for globular clusters (GCs) in M31 from 15
square deg of imaging using the Galaxy Evolution Explorer (GALEX). We detect
200 and 94 GCs with certainty in the near-ultraviolet (NUV; 1750 - 2750
Angstroms) and far-ultraviolet (FUV; 1350 - 1750 Angstroms) bandpasses,
respectively. Our rate of detection is about 50% in the NUV and 23% in the FUV,
to an approximate limiting V magnitude of 19. Out of six clusters with
[Fe/H]>-1 seen in the NUV, none is detected in the FUV bandpass. Furthermore,
we find no candidate metal-rich clusters with significant FUV flux, because of
the contribution of blue horizontal-branch (HB) stars, such as NGC 6388 and NGC
6441, which are metal-rich Galactic GCs with hot HB stars. We show that our
GALEX photometry follows the general color trends established in previous UV
studies of GCs in M31 and the Galaxy. Comparing our data with Galactic GCs in
the UV and with population synthesis models, we suggest that the age range of
M31 and Galactic halo GCs are similar.Comment: This paper will be published as part of the Galaxy Evolution Explorer
(GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of
papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after
November 22, 200
Identification and validation of clinical predictors for the risk of neurological involvement in children with hand, foot, and mouth disease in Sarawak
Background: Human enterovirus 71 (HEV71) can cause Hand, foot, and mouth disease (HFMD) with neurological
complications, which may rapidly progress to fulminant cardiorespiratory failure, and death. Early recognition of children
at risk is the key to reduce acute mortality and morbidity.
Methods: We examined data collected through a prospective clinical study of HFMD conducted between 2000 and 2006
that included 3 distinct outbreaks of HEV71 to identify risk factors associated with neurological involvement in children
with HFMD.
Results: Total duration of fever ≥ 3 days, peak temperature ≥ 38.5°C and history of lethargy were identified as
independent risk factors for neurological involvement (evident by CSF pleocytosis) in the analysis of 725 children
admitted during the first phase of the study. When they were validated in the second phase of the study, two or more
(≥ 2) risk factors were present in 162 (65%) of 250 children with CSF pleocytosis compared with 56 (30%) of 186 children
with no CSF pleocytosis (OR 4.27, 95% CI2.79–6.56, p < 0.0001). The usefulness of the three risk factors in identifying
children with CSF pleocytosis on hospital admission during the second phase of the study was also tested. Peak
temperature ≥ 38.5°C and history of lethargy had the sensitivity, specificity, positive predictive value (PPV) and negative
predictive value (NPV) of 28%(48/174), 89%(125/140), 76%(48/63) and 50%(125/251), respectively in predicting CSF
pleocytosis in children that were seen within the first 2 days of febrile illness. For those presented on the 3rd or later day
of febrile illness, the sensitivity, specificity, PPV and NPV of ≥ 2 risk factors predictive of CSF pleocytosis were 75%(57/
76), 59%(27/46), 75%(57/76) and 59%(27/46), respectively.
Conclusion: Three readily elicited clinical risk factors were identified to help detect children at risk of neurological
involvement. These risk factors may serve as a guide to clinicians to decide the need for hospitalization and further
investigation, including cerebrospinal fluid examination, and close monitoring for disease progression in children with
HFMD
The Recent Star Formation in NGC 6822: an Ultraviolet Study
We characterize the star formation in the low-metallicity galaxy NGC 6822
over the past few hundred million years, using GALEX far-UV (FUV, 1344-1786 A)
and near-UV (NUV, 1771-2831 A) imaging, and ground-based Ha imaging. From GALEX
FUV image, we define 77 star-forming (SF) regions with area >860 pc^2, and
surface brightness <=26.8 mag(AB)arcsec^-2, within 0.2deg (1.7kpc) of the
center of the galaxy. We estimate the extinction by interstellar dust in each
SF region from resolved photometry of the hot stars it contains: E(B-V) ranges
from the minimum foreground value of 0.22mag up to 0.66+-0.21mag. The
integrated FUV and NUV photometry, compared with stellar population models,
yields ages of the SF complexes up to a few hundred Myr, and masses from 2x10^2
Msun to 1.5x10^6 Msun. The derived ages and masses strongly depend on the
assumed type of interstellar selective extinction, which we find to vary across
the galaxy. The total mass of the FUV-defined SF regions translates into an
average star formation rate (SFR) of 1.4x10^-2 Msun/yr over the past 100 Myr,
and SFR=1.0x10^-2 Msun/yr in the most recent 10 Myr. The latter is in agreement
with the value that we derive from the Ha luminosity, SFR=0.008 Msun/yr. The
SFR in the most recent epoch becomes higher if we add the SFR=0.02 Msun/yr
inferred from far-IR measurements, which trace star formation still embedded in
dust (age <= a few Myr).Comment: Accepted for publication in ApJ, 21 pages, 6 figures, 3 table
The Look-back Time Evolution of Far-Ultraviolet Flux from the Brightest Cluster Elliptical Galaxies at z < 0.2
We present the GALEX UV photometry of the elliptical galaxies in Abell
clusters at moderate redshifts (z < 0.2) for the study of the look-back time
evolution of the UV upturn phenomenon. The brightest elliptical galaxies (M_r <
-22) in 12 remote clusters are compared with the nearby giant elliptical
galaxies of comparable optical luminosity in the Fornax and Virgo clusters. The
sample galaxies presented here appear to be quiescent without signs of massive
star formation or strong nuclear activity, and show smooth, extended profiles
in their UV images indicating that the far-UV (FUV) light is mostly produced by
hot stars in the underlying old stellar population. Compared to their
counterparts in nearby clusters, the FUV flux of cluster giant elliptical
galaxies at moderate redshifts fades rapidly with ~ 2 Gyrs of look-back time,
and the observed pace in FUV - V color evolution agrees reasonably well with
the prediction from the population synthesis models where the dominant FUV
source is hot horizontal-branch stars and their progeny. A similar amount of
color spread (~ 1 mag) in FUV - V exists among the brightest cluster elliptical
galaxies at z ~ 0.1, as observed among the nearby giant elliptical galaxies of
comparable optical luminosity.Comment: Accepted for publication in the Special GALEX ApJ Supplement,
December 200
Probing the Intermediate-Age Globular Clusters in NGC 5128 from Ultraviolet Observations
We explore the age distribution of the globular cluster (GC) system of the
nearby elliptical galaxy NGC 5128 using ultraviolet (UV) photometry from Galaxy
Evolution Explorer (GALEX) observations, with UV - optical colors used as the
age indicator. Most GCs in NGC 5128 follow the general trends of GCs in M31 and
Milky Way in UV - optical color-color diagram, which indicates that the
majority of GCs in NGC 5128 are old similar to the age range of old GCs in M31
and Milky Way. A large fraction of spectroscopically identified
intermediate-age GC (IAGC) candidates with ~ 3-8 Gyr are not detected in the
FUV passband. Considering the nature of intermediate-age populations being
faint in the far-UV (FUV) passband, we suggest that many of the
spectroscopically identified IAGCs may be truly intermediate in age. This is in
contrast to the case of M31 where a large fraction of spectroscopically
suggested IAGCs are detected in FUV and therefore may not be genuine IAGCs but
rather older GCs with developed blue horizontal branch stars. Our UV photometry
strengthens the results previously suggesting the presence of GC and stellar
subpopulation with intermediate age in NGC 5128. The existence of IAGCs
strongly indicates the occurrence of at least one more major star formation
episode after a starburst at high redshift.Comment: 8 pages, 3 figures, accepted for ApJ Lette
Air quality and error quantity: pollution and performance in a high-skilled, quality-focused occupation
We provide the first evidence that short-term exposure to air pollution affects the work performance of a group of highly-skilled, quality-focused employees. We repeatedly observe the decision-making of individual professional baseball umpires, quasi-randomly assigned to varying air quality across time and space. Unique characteristics of this setting combined with high-frequency data disentangle effects of multiple pollutants and identify previously under-explored acute effects. We find a 1 ppm increase in 3-hour CO causes an 11.5% increase in the propensity of umpires to make incorrect calls and a 10 mg/m3 increase in 12-hour PM2.5 causes a 2.6% increase. We control carefully for a variety of potential confounders and results are supported by robustness and falsification checks
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