368 research outputs found
The Effects of Close Companions (and Rotation) on the Magnetic Activity of M Dwarfs
We present a study of close white dwarf and M dwarf (WD+dM) binary systems
and examine the effect that a close companion has on the magnetic field
generation in M dwarfs. We use a base sample of 1602 white dwarf -- main
sequence binaries from Rebassa et al. to develop a set of color cuts in GALEX,
SDSS, UKIDSS, and 2MASS color space to construct a sample of 1756 WD+dM
high-quality pairs from the SDSS DR8 spectroscopic database. We separate the
individual WD and dM from each spectrum using an iterative technique that
compares the WD and dM components to best-fit templates. Using the absolute
height above the Galactic plane as a proxy for age, and the H{\alpha} emission
line as an indicator for magnetic activity, we investigate the age-activity
relation for our sample for spectral types \leqM7. Our results show that
early-type M dwarfs (\leqM4) in close binary systems are more likely to be
active and have longer activity lifetimes compared to their field counterparts.
However, at a spectral type of M5 (just past the onset of full convection in M
dwarfs), the activity fraction and lifetimes of WD+dM binary systems becomes
more comparable to that of the field M dwarfs. One of the implications of
having a close binary companion is presumed to be increased stellar rotation
through disk-disruption, tidal effects, or angular momentum exchange. Thus, we
interpret the similarity in activity behavior between late-type dMs in WD+dM
pairs and late-type field dMs to be due to a decrease in sensitivity in close
binary companions (or stellar rotation), which has implications for the nature
of magnetic activity in fully-convective stars. (Abridged)Comment: 21 pages, 19 figures, emulateapj style, accepted to Astronomical
Journal June 28, 201
Optimized Sparse Matrix Operations for Reverse Mode Automatic Differentiation
Sparse matrix representations are ubiquitous in computational science and
machine learning, leading to significant reductions in compute time, in
comparison to dense representation, for problems that have local connectivity.
The adoption of sparse representation in leading ML frameworks such as PyTorch
is incomplete, however, with support for both automatic differentiation and GPU
acceleration missing. In this work, we present an implementation of a CSR-based
sparse matrix wrapper for PyTorch with CUDA acceleration for basic matrix
operations, as well as automatic differentiability. We also present several
applications of the resulting sparse kernels to optimization problems,
demonstrating ease of implementation and performance measurements versus their
dense counterparts
Comparative Gene Expression Profiling of Benign and Malignant Lesions Reveals Candidate Therapeutic Compounds for Leiomyosarcoma
Leiomyosarcoma (LMS) is a malignant, soft-tissue tumor for which few effective therapies exist. Previously, we showed that there are three molecular subtypes of LMS. Here, we analyzed genes differentially expressed in each of the three LMS subtypes as compared to benign leiomyomas and then used the Connectivity Map (cmap) to calculate enrichment scores for the 1309 cmap drugs in order to identify candidate molecules with the potential to induce a benign, leiomyoma-like phenotype in LMS cells. 11 drugs were selected and tested for their ability to inhibit the growth of three human LMS cell lines. We identified two drugs with in vitro efficacy against LMS, one of which had a strongly negative enrichment score (Cantharidin) and the other of which had a strongly positive enrichment score (MG-132). Given MG-132's strong inhibitory effect on LMS cell viability, we hypothesized that LMS cells may be sensitive to treatment with other proteasome inhibitors and demonstrated that bortezomib, a clinically-approved proteasome inhibitor not included in the original cmap screen, potently inhibited the viability of the LMS cell lines. These findings suggest that systematically linking LMS subtype-specific expression signatures with drug-associated expression profiles represents a promising approach for the identification of new drugs for LMS
Persistent Magnetic Wreaths in a Rapidly Rotating Sun
When our Sun was young it rotated much more rapidly than now. Observations of
young, rapidly rotating stars indicate that many possess substantial magnetic
activity and strong axisymmetric magnetic fields. We conduct simulations of
dynamo action in rapidly rotating suns with the 3-D MHD anelastic spherical
harmonic (ASH) code to explore the complex coupling between rotation,
convection and magnetism. Here we study dynamo action realized in the bulk of
the convection zone for a system rotating at three times the current solar
rotation rate. We find that substantial organized global-scale magnetic fields
are achieved by dynamo action in this system. Striking wreaths of magnetism are
built in the midst of the convection zone, coexisting with the turbulent
convection. This is a surprise, for it has been widely believed that such
magnetic structures should be disrupted by magnetic buoyancy or turbulent
pumping. Thus, many solar dynamo theories have suggested that a tachocline of
penetration and shear at the base of the convection zone is a crucial
ingredient for organized dynamo action, whereas these simulations do not
include such tachoclines. We examine how these persistent magnetic wreaths are
maintained by dynamo processes and explore whether a classical mean-field
-effect explains the regeneration of poloidal field.Comment: 17 pages, 9 figures, 1 appendix, emulateapj format; published version
of sections 3-4, 7 and appendix from arXiv:0906.240
A Design Guide for Open Online Courses
This guide is a comprehensive summary of how we went about creating Citizen Maths, an open online maths course and service.
The guide shares our design principles and the techniques we used to put them into practice.
Our aim is to provide â with the appropriate âtranslationâ â a resource that will be useful to to other teams who are developing online education initiatives
The XMM Cluster Survey: The Dynamical State of XMMXCS J2215.9-1738 at z=1.457
We present new spectroscopic observations of the most distant X-ray selected
galaxy cluster currently known, XMMXCS J2215.9-1738 at z=1.457, obtained with
the DEIMOS instrument at the W. M. Keck Observatory, and the FORS2 instrument
on the ESO Very Large Telescope. Within the cluster virial radius, as estimated
from the cluster X-ray properties, we increase the number of known
spectroscopic cluster members to 17 objects, and calculate the line of sight
velocity dispersion of the cluster to be 580+/-140 km/s. We find mild evidence
that the velocity distribution of galaxies within the virial radius deviates
from a single Gaussian. We show that the properties of J2215.9-1738 are
inconsistent with self-similar evolution of local X-ray scaling relations,
finding that the cluster is underluminous given its X-ray temperature, and that
the intracluster medium contains ~2-3 times the kinetic energy per unit mass of
the cluster galaxies. These results can perhaps be explained if the cluster is
observed in the aftermath of an off-axis merger. Alternatively, heating of the
intracluster medium through supernovae and/or Active Galactic Nuclei activity,
as is required to explain the observed slope of the local X-ray
luminosity-temperature relation, may be responsible.Comment: 13 pages, 6 figures, accepted for publication in Ap
The XMM Cluster Survey: a massive galaxy cluster at z = 1.45
We report the discovery of XMMXCS J2215.9-1738, a massive galaxy cluster at z=1.45, which was found in the XMM Cluster Survey. The cluster candidate was initially identified as an extended X-ray source in archival XMM data. Optical spectroscopy shows that six galaxies within a ~60" diameter region lie at z=1.45+/-0.01. Model fits to the X-ray spectra of the extended emission yield kT=7.4+2.7-1.8 keV (90% confidence); if there is an undetected central X-ray point source, then kT=6.5+2.6-1.8 keV. The bolometric X-ray luminosity is LX=4.4+0.8-0.6C 1044 ergs s-1 over a 2 Mpc radial region. The measured TX, which is the highest for any known cluster at z>1, suggests that this cluster is relatively massive for such a high redshift. The redshift of XMMXCS J2215.9-1738 is the highest currently known for a spectroscopically confirmed cluster of galaxies
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A human lung tumor microenvironment interactome identifies clinically relevant cell-type cross-talk.
BackgroundTumors comprise a complex microenvironment of interacting malignant and stromal cell types. Much of our understanding of the tumor microenvironment comes from in vitro studies isolating the interactions between malignant cells and a single stromal cell type, often along a single pathway.ResultTo develop a deeper understanding of the interactions between cells within human lung tumors, we perform RNA-seq profiling of flow-sorted malignant cells, endothelial cells, immune cells, fibroblasts, and bulk cells from freshly resected human primary non-small-cell lung tumors. We map the cell-specific differential expression of prognostically associated secreted factors and cell surface genes, and computationally reconstruct cross-talk between these cell types to generate a novel resource called the Lung Tumor Microenvironment Interactome (LTMI). Using this resource, we identify and validate a prognostically unfavorable influence of Gremlin-1 production by fibroblasts on proliferation of malignant lung adenocarcinoma cells. We also find a prognostically favorable association between infiltration of mast cells and less aggressive tumor cell behavior.ConclusionThese results illustrate the utility of the LTMI as a resource for generating hypotheses concerning tumor-microenvironment interactions that may have prognostic and therapeutic relevance
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