230 research outputs found
The G Dwarf Problem Exists in Other Galaxies
Stellar population models with abundance distributions determined from the
analytic Simple model of chemical evolution fail to match observations of the
nuclei of bulge-dominated galaxies in three respects. First, the spectral
energy distribution in the mid-ultraviolet range 2000 < lam < 2400 exceeds
observation by ~ 0.6 mag. Most of that excess is due to metal-poor main
sequence stars. Second, the models do not reproduce metal-sensitive optical
absorption features that arise mainly from red giant stars. Third, the strength
of a Ca II index sensitive to hot stars does not jibe with the predicted number
of A-type horizontal branch stars. The number of metal poor stars in galaxies
is at least a factor of two less than predicted by the Simple model, exactly
similar to the ``G Dwarf problem'' in the solar cylinder. Observations at
larger radii in local group galaxies indicate that the paucity of metal poor
stars applies globally, rather than only in the nuclei. Because of the
dominance of metal rich stars, primordial galaxies will have a plentiful dust
supply early in their star formation history, and thus will probably have weak
Lyman-alpha emission, as is apparently observed. We confirm that early-type
galaxies cannot have been formed exclusively from mergers of small all-stellar
subsystems, a result already established by dynamical simulations. The
constraint of peaked abundance distributions will limit future chemical
evolution models. It will also make age estimates for the stellar populations
in early type galaxies and bulges more secure.Comment: 14 pages, LaTeX includes 3 postscript figures. Uses AAS LaTeX v 4.0
and times.sty. Accepted for publication in the Astronomical Journal.
Postscript available at http://shemesh.gsfc.nasa.gov/~dorman/Ben.htm
Ultraviolet Radiation from Evolved Stellar Populations: II. The Ultraviolet Upturn Phenomenon in Elliptical Galaxies
We present an analysis of the far-ultraviolet upturn phenomenon (UVX)
observed in elliptical galaxies and spiral galaxy bulges. Our premise is that
the UV radiation from these systems emanates primarily from extreme horizontal
branch (EHB) stars and their progeny. We re-derive the broad-band UV colors
and for globular clusters and elliptical galaxies from the
available satellite data and investigate color-color and color-line strength
correlations. We also provide the ingredients necessary for constructing models
with arbitrary HB morphologies.Comment: uuencoded compressed postscript file, 60pp. (revisions on pp.
7,8,22,33,37 & 57
Mass Loss In M67 Giants: Evidence From Isochrone Fitting
We present a study of the stellar content of the open cluster M67. We have
computed new evolutionary sequences of stellar models with solar abundance that
cover all phases of evolution from the Zero-Age Main Sequence to the bright end
of the Asymptotic Giant Branch (AGB). We examine the fit between the calculated
and the observed red giant branch (RGB) in particular, and discuss factors that
most influence its quality. The distinct color gap between the RGB and the
clump giants is compared with the temperature gap between the He-burning tracks
and the computed 5 Gyr isochrone. This purely differential approach strongly
indicates that the clump giants have M \lta 0.70\msun\ , implying an amount
of mass loss ( \msun) well in excess of that found in globular
cluster stars. Observational constraints on mass loss processes favor the
interpretation that mass loss in cool low-mass giant stars increases with
metallicity.Comment: 21pp., plain TeX astro-ph/yymmnn
Validation of predicted mRNA splicing mutations using high-throughput transcriptome data
Interpretation of variants present in complete genomes or exomes reveals numerous sequence changes, only a fraction of which are likely to be pathogenic. Mutations have been traditionally inferred from allele frequencies and inheritance patterns in such data. Variants predicted to alter mRNA splicing can be validated by manual inspection of transcriptome sequencing data, however this approach is intractable for large datasets. These abnormal mRNA splicing patterns are characterized by reads demonstrating either exon skipping, cryptic splice site use, and high levels of intron inclusion, or combinations of these properties. We present, Veridical, an in silico method for the automatic validation of DNA sequencing variants that alter mRNA splicing. Veridical performs statistically valid comparisons of the normalized read counts of abnormal RNA species in mutant versus non-mutant tissues. This leverages large numbers of control samples to corroborate the consequences of predicted splicing variants in complete genomes and exomes
Extraction of incarcerated medial epicondyle from the elbow joint using conventional nerve stimulator:a case report
INTRODUCTION: Incarceration of the medial epicondyle is a well-recognised sequelae following closed reduction of the elbow. Manipulation for extraction is not usually successful and hence an incarcerated medial epicondyle is usually an indication for open reduction and fixation. CASE PRESENTATION: We describe a simple technique of closed reduction using a conventional nerve stimulator to extract an incarcerated medial epicondyle in a 13-year-old Caucasian boy. This technique uses contraction of the attached common flexor muscles to indirectly extract the trapped medial epicondyle. CONCLUSIONS: This is a simple technique using a commonly available nerve stimulator and may obviate the need for extensile open reduction for extraction of the incarcerated medial epicondyle. We would recommend this technique where closed reduction methods have failed
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