1,003 research outputs found
The Milky Way's stellar halo - lumpy or triaxial?
We present minimum chi-squared fits of power law and Hernquist density
profiles to F-turnoff stars in eight 2.5 deg wide stripes of SDSS data: five in
the North Galactic Cap and three in the South Galactic cap. Portions of the
stellar Galactic halo that are known to contain large streams of tidal debris
or other lumpy structure, or that may include significant contamination from
the thick disk, are avoided. The data strongly favor a model that is not
symmetric about the Galaxy's axis of rotation. If included as a free parameter,
the best fit to the center of the spheroid is surprisingly approx 3 kpc from
the Galactic center in the direction of the Sun's motion. The model fits favor
a low value of the density of halo stars at the solar position. The alternative
to a non-axisymmetric stellar distribution is that our fits are contaminated by
previously unidentified lumpy substructure.Comment: 10 pages, 10 figs, to appear in proceedings of conference "Physics at
the end of the Galactic Cosmic Ray Spectrum", Journal of Physics: Conf.
series, eds. G. Thomson and P. Sokolsk
Error statistics of hidden Markov model and hidden Boltzmann model results
<p>Abstract</p> <p>Background</p> <p>Hidden Markov models and hidden Boltzmann models are employed in computational biology and a variety of other scientific fields for a variety of analyses of sequential data. Whether the associated algorithms are used to compute an actual probability or, more generally, an odds ratio or some other score, a frequent requirement is that the error statistics of a given score be known. What is the chance that random data would achieve that score or better? What is the chance that a real signal would achieve a given score threshold?</p> <p>Results</p> <p>Here we present a novel general approach to estimating these false positive and true positive rates that is significantly more efficient than are existing general approaches. We validate the technique via an implementation within the HMMER 3.0 package, which scans DNA or protein sequence databases for patterns of interest, using a profile-HMM.</p> <p>Conclusion</p> <p>The new approach is faster than general naïve sampling approaches, and more general than other current approaches. It provides an efficient mechanism by which to estimate error statistics for hidden Markov model and hidden Boltzmann model results.</p
Retrospective Evaluation of Clinical Experience With Intravenous Ascorbic Acid in Patients With Cancer.
BACKGROUND: Intravenous ascorbic acid (IV AA) has been used extensively in cancer patients throughout the United States. Currently, there are limited data on the safety and clinical effects of IV AA. The purpose of this study was to expand the current literature using a retrospective analysis of adverse events and symptomatic changes of IV AA in a large sample of cancer patients.
METHODS: We conducted a retrospective chart review of all patients receiving IV AA for cancer at the Thomas Jefferson University Hospital over a 7-year period. We assessed all reports of adverse events, laboratory findings, and hospital or emergency department admissions. We also reviewed quality-of-life data, including fatigue, nausea, pain, appetite, and mood.
RESULTS: There were 86 patients who received a total of 3034 doses of IV AA ranging from 50 to 150g. In all, 32 patients received only ascorbic acid as part of their cancer management (1197 doses), whereas 54 patients received ascorbic acid in conjunction with chemotherapy (1837 doses). The most common adverse events related to ascorbic acid were temporary nausea and discomfort at the injection site. All events reported in the ascorbic acid alone group were associated with less than 3% of the total number of infusions. Patients, overall, reported improvements in fatigue, pain, and mood while receiving ascorbic acid.
CONCLUSIONS: The results of this retrospective analysis support the growing evidence that IV AA is generally safe and well tolerated in patients with cancer, and may be useful in symptom management and improving quality of life
Tracing Sagittarius Structure with SDSS and SEGUE Imaging and Spectroscopy
We show that the Sagittarius dwarf tidal stream can be traced with very red
K/M-giant stars selected from SDSS photometry. A subset of these stars are
spectroscopically confirmed with SEGUE and SDSS spectra, and the distance scale
of 2MASS and SDSS M giants is calibrated to the RR Lyrae distance scale. The
absolute g band magnitude of the K/M-giant stars at the tip of the giant branch
is M_g=-1.0. The line-of-sight velocities of the M giant and BHB stars that are
spatially coincident with the Sgr dwarf tidal stream are consistent with those
of previous authors, reinforcing the need for new models that can explain all
of the Sgr tidal debris stream observations. We estimate stellar densities
along the tidal tails that can be used to help constrain future models. The
K/M-giant, BHB, and F-turnoff stars in the lower surface brightness tidal
stream that is adjacent to the main leading Sgr dwarf tidal tail have
velocities and metallicities that are similar to those of the stars in the
leading tidal tail. The ratio of K/M giants to BHBs and BHBs to F-turnoff stars
are also similar for both branches of the leading tidal tail. We show that
there is an additional low-metallicity tidal stream near the Sgr trailing tidal
tail.Comment: 19 figures, accepted for publication in ApJ, references update
The Orbit of the Orphan Stream
We use recent SEGUE spectroscopy and SDSS and SEGUE imaging data to measure
the sky position, distance, and radial velocities of stars in the tidal debris
stream that is commonly referred to as the "Orphan Stream." We fit orbital
parameters to the data, and find a prograde orbit with an apogalacticon,
perigalacticon, and eccentricity of 90 kpc, 16.4 kpc and 0.7, respectively.
Neither the dwarf galaxy UMa II nor the Complex A gas cloud have velocities
consistent with a kinematic association with the Orphan Stream. It is possible
that Segue-1 is associated with the Orphan Stream, but no other known Galactic
clusters or dwarf galaxies in the Milky Way lie along its orbit. The detected
portion of the stream ranges from 19 to 47 kpc from the Sun and is an indicator
of the mass interior to these distances. There is a marked increase in the
density of Orphan Stream stars near (l,b)=(253,49) deg., which could indicate
the presence of the progenitor at the edge of the SDSS data. If this is the
progenitor, then the detected portion of the Orphan Stream is a leading tidal
tail. We find blue horizontal branch (BHB) stars and F turnoff stars associated
with the Orphan Stream. The turnoff color is (g-r)_0=0.22. The BHB stars have a
low metallicity of [Fe/H]=-2.1. The orbit is best fit to a halo potential with
a halo plus disk mass of about 2.6x10^11 Solar masses, integrated to 60 kpc
from the Galactic center. Our best fit is found with a logarithmic halo speed
of v_halo=73+/-24 km/s, a disk+bulge mass of M(R< 60 kpc) = 1.3x10^11 Solar
masses, and a halo mass of M(R< 60 kpc) = 1.4x10^11 Solar masses. The Orphan
Stream is projected to extend to 90 kpc from the Galactic center, and
measurements of these distant parts of the stream would be a powerful probe of
the mass of the Milky Way (truncated).Comment: 17 Figures, ApJ accepte
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