294 research outputs found
Dispersal of molecular clouds by ionising radiation
The role of feedback from massive stars is believed to be a key element in
the evolution of molecular clouds. We use high-resolution 3D SPH simulations to
explore the dynamical effects of a single O7 star located at the centre of a
molecular cloud with mass 10^4M_sun and radius 6.4pc. The initial internal
structure of the cloud is characterised by its fractal dimension, D=2.0 - 2.8,
and its log-normal density PDF. (i) As regards star formation, in the short
term ionising feedback is positive, in the sense that star formation occurs
much more quickly in gas that is compressed by the high pressure of the ionised
gas. However, in the long term ionising feedback is negative, in the sense that
most of the cloud is dispersed with an outflow rate of up to ~0.01M_sun/yr, on
a timescale comparable with the sound-crossing time for the ionised gas
(~1-2Myr), and triggered star formation is therefore limited to a few percent
of the cloud's mass. (ii) As regards the morphology of the ionisation fronts
(IFs) bounding the HII region and the systematics of outflowing gas, we
distinguish two regimes. For low D<=2.2, the initial cloud is dominated by
large-scale structures, so the neutral gas tends to be swept up into a few
extended coherent shells, and the ionised gas blows out through a few large
holes between these shells; we term these HII regions "shell-dominated".
Conversely, for high D>=2.6, the initial cloud is dominated by small-scale
structures, and these are quickly overrun by the advancing IF, thereby
producing neutral pillars whilst the ionised gas blows out through a large
number of small holes between the pillars; we term these HII regions
"pillar-dominated". (iii) As regards the injection of bulk kinetic energy, by
~1Myr, the expansion of the HII region has delivered a rms velocity of ~6km/s;
this represents less than 0.1% of the total energy radiated by the O7 star.Comment: 13 pages, 8 figures, 2 tables; submitted to MNRA
Dynamical HII Region Evolution in Turbulent Molecular Clouds
We present numerical radiation-hydrodynamic simulations of the evolution of
HII regions formed in an inhomogeneous medium resulting from turbulence
simulations. We find that the filamentary structure of the underlying density
distribution produces a highly irregular shape for the ionized region, in which
the ionization front escapes to large distances in some directions within
80,000 years. In other directions, on the other hand, neutral gas in the form
of dense globules persists within 1 parsec of the central star for the full
duration of our simulation (400,000 years). Divergent photoablation flows from
these globules maintain a root-mean-squared velocity in the ionized gas that is
close to the ionized sound speed. Simulated images in optical emission lines
show morphologies that are in strikingly detailed agreement with those observed
in real HII regions.Comment: Minor changes to sync with accepted version. 7 pages, ApJ in press.
Accompanying video available at
http://ifront.org/wiki/Turbulent_Hii_Regions/Paper
The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectrum at 148 and 218 GHz from the 2008 Southern Survey
We present measurements of the cosmic microwave background (CMB) power
spectrum made by the Atacama Cosmology Telescope at 148 GHz and 218 GHz, as
well as the cross-frequency spectrum between the two channels. Our results
clearly show the second through the seventh acoustic peaks in the CMB power
spectrum. The measurements of these higher-order peaks provide an additional
test of the {\Lambda}CDM cosmological model. At l > 3000, we detect power in
excess of the primary anisotropy spectrum of the CMB. At lower multipoles 500 <
l < 3000, we find evidence for gravitational lensing of the CMB in the power
spectrum at the 2.8{\sigma} level. We also detect a low level of Galactic dust
in our maps, which demonstrates that we can recover known faint, diffuse
signals.Comment: 19 pages, 13 figures. Submitted to ApJ. This paper is a companion to
Hajian et al. (2010) and Dunkley et al. (2010
The Atacama Cosmology Telescope: Data Characterization and Map Making
We present a description of the data reduction and mapmaking pipeline used
for the 2008 observing season of the Atacama Cosmology Telescope (ACT). The
data presented here at 148 GHz represent 12% of the 90 TB collected by ACT from
2007 to 2010. In 2008 we observed for 136 days, producing a total of 1423 hours
of data (11 TB for the 148 GHz band only), with a daily average of 10.5 hours
of observation. From these, 1085 hours were devoted to a 850 deg^2 stripe (11.2
hours by 9.1 deg) centered on a declination of -52.7 deg, while 175 hours were
devoted to a 280 deg^2 stripe (4.5 hours by 4.8 deg) centered at the celestial
equator. We discuss sources of statistical and systematic noise, calibration,
telescope pointing, and data selection. Out of 1260 survey hours and 1024
detectors per array, 816 hours and 593 effective detectors remain after data
selection for this frequency band, yielding a 38% survey efficiency. The total
sensitivity in 2008, determined from the noise level between 5 Hz and 20 Hz in
the time-ordered data stream (TOD), is 32 micro-Kelvin sqrt{s} in CMB units.
Atmospheric brightness fluctuations constitute the main contaminant in the data
and dominate the detector noise covariance at low frequencies in the TOD. The
maps were made by solving the least-squares problem using the Preconditioned
Conjugate Gradient method, incorporating the details of the detector and noise
correlations. Cross-correlation with WMAP sky maps, as well as analysis from
simulations, reveal that our maps are unbiased at multipoles ell > 300. This
paper accompanies the public release of the 148 GHz southern stripe maps from
2008. The techniques described here will be applied to future maps and data
releases.Comment: 20 pages, 18 figures, 6 tables, an ACT Collaboration pape
The Atacama Cosmology Telescope: Cosmology from Galaxy Clusters Detected via the Sunyaev-Zel'dovich Effect
We present constraints on cosmological parameters based on a sample of
Sunyaev-Zel'dovich-selected galaxy clusters detected in a millimeter-wave
survey by the Atacama Cosmology Telescope. The cluster sample used in this
analysis consists of 9 optically-confirmed high-mass clusters comprising the
high-significance end of the total cluster sample identified in 455 square
degrees of sky surveyed during 2008 at 148 GHz. We focus on the most massive
systems to reduce the degeneracy between unknown cluster astrophysics and
cosmology derived from SZ surveys. We describe the scaling relation between
cluster mass and SZ signal with a 4-parameter fit. Marginalizing over the
values of the parameters in this fit with conservative priors gives sigma_8 =
0.851 +/- 0.115 and w = -1.14 +/- 0.35 for a spatially-flat wCDM cosmological
model with WMAP 7-year priors on cosmological parameters. This gives a modest
improvement in statistical uncertainty over WMAP 7-year constraints alone.
Fixing the scaling relation between cluster mass and SZ signal to a fiducial
relation obtained from numerical simulations and calibrated by X-ray
observations, we find sigma_8 = 0.821 +/- 0.044 and w = -1.05 +/- 0.20. These
results are consistent with constraints from WMAP 7 plus baryon acoustic
oscillations plus type Ia supernoava which give sigma_8 = 0.802 +/- 0.038 and w
= -0.98 +/- 0.053. A stacking analysis of the clusters in this sample compared
to clusters simulated assuming the fiducial model also shows good agreement.
These results suggest that, given the sample of clusters used here, both the
astrophysics of massive clusters and the cosmological parameters derived from
them are broadly consistent with current models.Comment: 12 pages, 7 figures. Submitted to Ap
Genetic association study of QT interval highlights role for calcium signaling pathways in myocardial repolarization.
The QT interval, an electrocardiographic measure reflecting myocardial repolarization, is a heritable trait. QT prolongation is a risk factor for ventricular arrhythmias and sudden cardiac death (SCD) and could indicate the presence of the potentially lethal mendelian long-QT syndrome (LQTS). Using a genome-wide association and replication study in up to 100,000 individuals, we identified 35 common variant loci associated with QT interval that collectively explain ∼8-10% of QT-interval variation and highlight the importance of calcium regulation in myocardial repolarization. Rare variant analysis of 6 new QT interval-associated loci in 298 unrelated probands with LQTS identified coding variants not found in controls but of uncertain causality and therefore requiring validation. Several newly identified loci encode proteins that physically interact with other recognized repolarization proteins. Our integration of common variant association, expression and orthogonal protein-protein interaction screens provides new insights into cardiac electrophysiology and identifies new candidate genes for ventricular arrhythmias, LQTS and SCD
Acute myeloid leukemia of donor origin after allogeneic stem cell transplantation from a sibling who harbors germline XPD and XRCC3 homozygous polymorphisms
A 54-year-old woman was diagnosed with infiltrative ductal breast carcinoma. Two years after treatment, the patient developed an acute myeloid leukemia (AML) which harbored del(11q23) in 8% of the blast cells. The patient was submitted for allogeneic stem cell transplantation (aSCT) from her HLA-compatible sister. Ten months after transplantation, she relapsed with an AML with basophilic maturation characterized by CD45low CD33high, CD117+, CD13-/+, HLA Drhigh, CD123high, and CD203c+ blast cells lacking expression of CD7, CD10, CD34, CD15, CD14, CD56, CD36, CD64, and cytoplasmic tryptase. Karyotype analysis showed the emergence of a new clone with t(2;14) and FISH analysis indicated the presence of MLL gene rearrangement consistent with del(11q23). Interestingly, AML blast cell DNA tested with microsatellite markers showed the same pattern as the donor's, suggesting that this AML emerged from donor cells. Additionally, polymorphisms of the XPA, XPD, XRCC1, XRCC3 and RAD51 DNA repair genes revealed three unfavorable alleles with low DNA repair capacity
Genomic, Pathway Network, and Immunologic Features Distinguishing Squamous Carcinomas
This integrated, multiplatform PanCancer Atlas study co-mapped and identified distinguishing
molecular features of squamous cell carcinomas (SCCs) from five sites associated with smokin
Pan-cancer Alterations of the MYC Oncogene and Its Proximal Network across the Cancer Genome Atlas
Although theMYConcogene has been implicated incancer, a systematic assessment of alterations ofMYC, related transcription factors, and co-regulatoryproteins, forming the proximal MYC network (PMN),across human cancers is lacking. Using computa-tional approaches, we define genomic and proteo-mic features associated with MYC and the PMNacross the 33 cancers of The Cancer Genome Atlas.Pan-cancer, 28% of all samples had at least one ofthe MYC paralogs amplified. In contrast, the MYCantagonists MGA and MNT were the most frequentlymutated or deleted members, proposing a roleas tumor suppressors.MYCalterations were mutu-ally exclusive withPIK3CA,PTEN,APC,orBRAFalterations, suggesting that MYC is a distinct onco-genic driver. Expression analysis revealed MYC-associated pathways in tumor subtypes, such asimmune response and growth factor signaling; chro-matin, translation, and DNA replication/repair wereconserved pan-cancer. This analysis reveals insightsinto MYC biology and is a reference for biomarkersand therapeutics for cancers with alterations ofMYC or the PMN
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