277 research outputs found
Galactic structure studies with BATC star counts
We report the first results of star counts carried out with the National
Astronomical Observatories (NAOC) 60/90 cm Schmidt Telescope in 15
intermediate-band filters from 3000 to 10000 {\AA} in the BATC survey. We
analyze a sample of over 1400 main sequence stars (V), which lie
in the field with central coordinates R.A.= and
DEC=47 (J2000). The field of view is 0.95
deg, and the spatial scale was 1\arcsec.67. In our model, the
distribution of stars perpendicular to the plane of the Galaxy is given by two
exponential disks (thin disk plus thick disk) and a de Vaucouleurs halo. Based
on star counts, we derive the scale heights of the thin disk to be
pc and of the thick disk to be pc,
respectively, with a local density of of the thin disk. We find that
the observed counts support an axial ratio of for a de Vaucouleurs
law, implying a more flattened halo.
We also derive the stellar luminosity function (SLF) for the thin disk, and
it partly agrees with the Hipparcos luminosity function.Comment: 17pages,9 figure
Metallicity Estimates for Old Star Clusters in M33
Using the theoretical stellar population synthesis models of BC96, Kong et
al. (2003) showed that some BATC colors and color indices could be used to
disentangle the age and metallicity effect. They found that there is a very
good relation between the flux ratio of L_{8510}/L_{9170} and the metallicity
for stellar populations older than 1 Gyr. In this paper, based on the Kong et
al. results and on the multicolor spectrophotometry of Ma et al. (2001,
2002a,b,c), we estimate the metallicities of 31 old star clusters in the nearby
spiral galaxy M33, 23 of which are ``true'' globular clusters. The results show
that most of these old clusters are metal poor. We also find that the ages and
metal abundance for these old star clusters of M33 do not vary with deprojected
radial position.Comment: Accepted for Publication in A&A, 13 pages, 7 figures (1 figure of
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Age Estimations of M31 Globular Clusters from Their Spectral Energy Distributions
This paper presents accurate spectral energy distributions (SEDs) of 16 M31
globular clusters (GCs) confirmed by spectroscopy and/or high
spatial-resolution imaging, as well as 30 M31 globular cluster candidates
detected by Mochejska et al. Most of these candidates have m_V > 18, deeper
than previous searches, and these candidates have not yet been confirmed to be
globular clusters. The SEDs of these clusters and candidates are obtained as
part of the BATC Multicolor Survey of the Sky, in which the
spectrophotometrically-calibrated CCD images of M31 in 13 intermediate-band
filters from 4000 to 10000 A were observed. These filters are specifically
designed to exclude most of the bright and variable night-sky emission lines
including the OH forest. In comparison to the SEDs of true GCs, we find that
some of the candidate objects are not GCs in M31. SED fits show that
theoretical simple stellar population (SSP) models can fit the true GCs very
well. We estimate the ages of these GCs by comparing with SSP models. We find
that, the M31 clusters range in age from a few ten Myr to a few Gyr old, as
well as old GCs, confirming the conclusion that has been found by Barmby et a,
Williams & Hodge, Beasley et al., Burstein et al. and Puzia et al. in their
investigations of the SEDs of M31 globular clusters.Comment: Accepted for Publication in A&Ap, 13 pages, 6 figure
A "super" star cluster grown old: the most massive star cluster in the Local Group
We independently redetermine the reddening and age of the globular cluster
037-B327 in M31 by comparing independently obtained multicolour photometry with
theoretical stellar population synthesis models. 037-B327 has long been known
to have a very large reddening value, which we confirm to be
E(B-V)=1.360+-0.013, in good agreement with the previous results. We
redetermine its most likely age at 12.4+- 3.2 Gyr.
037-B327 is a prime example of an unusually bright early counterpart to the
ubiquitous ``super'' star clusters presently observed in most high-intensity
star-forming regions in the local Universe. In order to have survived for a
Hubble time, we conclude that its stellar IMF cannot have been top-heavy. Using
this constraint, and a variety of SSP models, we determine a photometric mass
of M_{GC}=(3.0+-0.5)*10^7, somewhat depending on the SSP models used, the
metallicity and age adopted and the IMF representation. This mass, and its
relatively small uncertainties, make this object the most massive star cluster
of any age in the Local Group. Assuming that the photometric mass estimate thus
derived is fairly close to its dynamical mass, we predict that this GC has a
(one-dimensional) velocity dispersion of order (72+-13)km/s. As a surviving
"super" star cluster, this object is of prime importance for theories aimed at
describing massive star cluster evolution.Comment: Accepted for Publication in MNRAS, 8 pages, 4 figure
Study of the occurrence of intra-abdominal hypertension and abdominal compartment syndrome in patients of blunt abdominal trauma and its correlation with the clinical outcome in the above patients
The Eighth Data Release of the Sloan Digital Sky Survey: First Data from SDSS-III
The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with
new instrumentation and new surveys focused on Galactic structure and chemical
evolution, measurements of the baryon oscillation feature in the clustering of
galaxies and the quasar Ly alpha forest, and a radial velocity search for
planets around ~8000 stars. This paper describes the first data release of
SDSS-III (and the eighth counting from the beginning of the SDSS). The release
includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap,
bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a
third of the Celestial Sphere. All the imaging data have been reprocessed with
an improved sky-subtraction algorithm and a final, self-consistent photometric
recalibration and flat-field determination. This release also includes all data
from the second phase of the Sloan Extension for Galactic Understanding and
Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars
at both high and low Galactic latitudes. All the more than half a million
stellar spectra obtained with the SDSS spectrograph have been reprocessed
through an improved stellar parameters pipeline, which has better determination
of metallicity for high metallicity stars.Comment: Astrophysical Journal Supplements, in press (minor updates from
submitted version
Properties of resistant cells generated from lung cancer cell lines treated with EGFR inhibitors
<p>Abstract</p> <p>Background</p> <p>Epidermal growth factor receptor (EGFR) signaling plays an important role in non-small cell lung cancer (NSCLC) and therapeutics targeted against EGFR have been effective in treating a subset of patients bearing somatic EFGR mutations. However, the cancer eventually progresses during treatment with EGFR inhibitors, even in the patients who respond to these drugs initially. Recent studies have identified that the acquisition of resistance in approximately 50% of cases is due to generation of a secondary mutation (T790M) in the EGFR kinase domain. In about 20% of the cases, resistance is associated with the amplification of MET kinase. In the remaining 30-40% of the cases, the mechanism underpinning the therapeutic resistance is unknown.</p> <p>Methods</p> <p>An erlotinib resistant subline (H1650-ER1) was generated upon continuous exposure of NSCLC cell line NCI-H1650 to erlotinib. Cancer stem cell like traits including expression of stem cell markers, enhanced ability to self-renew and differentiate, and increased tumorigenicity <it>in vitro </it>were assessed in erlotinib resistant H1650-ER1 cells.</p> <p>Results</p> <p>The erlotinib resistant subline contained a population of cells with properties similar to cancer stem cells. These cells were found to be less sensitive towards erlotinib treatment as measured by cell proliferation and generation of tumor spheres in the presence of erlotinib.</p> <p>Conclusions</p> <p>Our findings suggest that in cases of NSCLC accompanied by mutant EGFR, treatment targeting inhibition of EGFR kinase activity in differentiated cancer cells may generate a population of cancer cells with stem cell properties.</p
Phononic dispersion in anisotropic pseudo-fractal hyper-lattices
Fractal and pseudo-fractal microstructures have proved promising in increasing the range of detectable frequen-cies for devices used in the realm of electromagnetism. Due to mechanical-electrical duality it is conjectured theymay provideflexible solutions capable of closing/widening bandgaps and increasing tailorability in phononic lat-tices. Pseudo-fractal hyper-lattices have been considered in this work and different aspects of dispersion surfacemorphology and frequency band structure are studied. It has been observed that higher frequencies that can beexcited in the simple square lattice are almost the same as those in the pseudo-fractal structures, however;through introduction of higher levels the pseudo-fractal hyper-lattice presents new features not observable inthe ordinary lattice. By increasing the order of pseudo-fractal structure the number of degrees-of-freedom in-creases and dispersion surfaces morphologies change thus frequency gaps are eliminated. This phenomenoncan be of advantage for acoustic/phononic visibility/detectability e.g. in designing sensors. In the classical analogyto quantum level repulsion surfacesflatten which sufficiently decreases the sound group velocity in the pseudo-fractal structure, and can be used for numerous practical applications
Repeated PTZ Treatment at 25-Day Intervals Leads to a Highly Efficient Accumulation of Doublecortin in the Dorsal Hippocampus of Rats
BACKGROUND: Neurogenesis persists throughout life in the adult mammalian brain. Because neurogenesis can only be assessed in postmortem tissue, its functional significance remains undetermined, and identifying an in vivo correlate of neurogenesis has become an important goal. By studying pentylenetetrazole-induced brain stimulation in a rat model of kindling we accidentally discovered that 25±1 days periodic stimulation of Sprague-Dawley rats led to a highly efficient increase in seizure susceptibility. METHODOLOGY/PRINCIPAL FINDINGS: By EEG, RT-PCR, western blotting and immunohistochemistry, we show that repeated convulsive seizures with a periodicity of 25±1 days led to an enrichment of newly generated neurons, that were BrdU-positive in the dentate gyrus at day 25±1 post-seizure. At the same time, there was a massive increase in the number of neurons expressing the migratory marker, doublecortin, at the boundary between the granule cell layer and the polymorphic layer in the dorsal hippocampus. Some of these migrating neurons were also positive for NeuN, a marker for adult neurons. CONCLUSION/SIGNIFICANCE: Our results suggest that the increased susceptibility to seizure at day 25±1 post-treatment is coincident with a critical time required for newborn neurons to differentiate and integrate into the existing hippocampal network, and outlines the importance of the dorsal hippocampus for seizure-related neurogenesis. This model can be used as an in vivo correlate of neurogenesis to study basic questions related to neurogenesis and to the neurogenic mechanisms that contribute to the development of epilepsy
Galaxy morphological classification in deep-wide surveys via unsupervised machine learning
Accepted versionGalaxy morphology is a fundamental quantity, that is essential not only for the full spectrum of galaxy-evolution studies, but also for a plethora of science in observational cosmology. While a rich literature exists on morphological-classification techniques, the unprecedented data volumes, coupled, in some cases, with the short cadences of forthcoming 'Big-Data' surveys (e.g. from the LSST), present novel challenges for this field. Large data volumes make such datasets intractable for visual inspection (even via massively-distributed platforms like Galaxy Zoo), while short cadences make it difficult to employ techniques like supervised machine-learning, since it may be impractical to repeatedly produce training sets on short timescales. Unsupervised machine learning, which does not require training sets, is ideally suited to the morphological analysis of new and forthcoming surveys. Here, we employ an algorithm that performs clustering of graph representations, in order to group image patches with similar visual properties and objects constructed from those patches, like galaxies. We implement the algorithm on the Hyper-Suprime-Cam Subaru-Strategic-Program Ultra-Deep survey, to autonomously reduce the galaxy population to a small number (160) of 'morphological clusters', populated by galaxies with similar morphologies, which are then benchmarked using visual inspection. The morphological classifications (which we release publicly) exhibit a high level of purity, and reproduce known trends in key galaxy properties as a function of morphological type at zPeer reviewe
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