2,606 research outputs found
Repressive Interactions Between Transcription Factors Separate Different Embryonic Ectodermal Domains.
The embryonic ectoderm is composed of four domains: neural plate, neural crest, pre-placodal region (PPR) and epidermis. Their formation is initiated during early gastrulation by dorsal-ventral and anterior-posterior gradients of signaling factors that first divide the embryonic ectoderm into neural and non-neural domains. Next, the neural crest and PPR domains arise, eithe
Exome-wide association study of pancreatic cancer risk
We conducted a case-control exome-wide association study to discover germline variants in coding regions that affect risk for pancreatic cancer, combining data from 5 studies. We analyzed exome and genome sequencing data from 437 patients with pancreatic cancer (cases) and 1922 individuals not known to have cancer (controls). In the primary analysis, BRCA2 had the strongest enrichment for rare inactivating variants (17/437 cases vs 3/1922 controls) (P=3.27x10(-6); exome-wide statistical significance threshold P<2.5x10(-6)). Cases had more rare inactivating variants in DNA repair genes than controls, even after excluding 13 genes known to predispose to pancreatic cancer (adjusted odds ratio, 1.35, P=.045). At the suggestive threshold (P<.001), 6 genes were enriched for rare damaging variants (UHMK1, AP1G2, DNTA, CHST6, FGFR3, and EPHA1) and 7 genes had associations with pancreatic cancer risk, based on the sequence-kernel association test. We confirmed variants in BRCA2 as the most common high-penetrant genetic factor associated with pancreatic cancer and we also identified candidate pancreatic cancer genes. Large collaborations and novel approaches are needed to overcome the genetic heterogeneity of pancreatic cancer predisposition
ISO LWS Spectroscopy of M82: A Unified Evolutionary Model
We present the first complete far-infrared spectrum (43 to 197 um) of M82,
the brightest infrared galaxy in the sky, taken with the Long Wavelength
Spectrometer of the Infrared Space Observatory (ISO). We detected seven fine
structure emission lines, [OI] 63 and 145 um, [OIII] 52 and 88 um, [NII] 122
um, [NIII] 57 um and [CII] 158 um, and fit their ratios to a combination
starburst and photo-dissociation region (PDR) model. The best fit is obtained
with HII regions with n = 250 cm^{-3} and an ionization parameter of 10^{-3.5}
and PDRs with n = 10^{3.3} cm^{-3} and a far-ultraviolet flux of G_o =
10^{2.8}. We applied both continuous and instantaneous starburst models, with
our best fit being a 3-5 Myr old instantaneous burst model with a 100 M_o
cut-off. We also detected the ground state rotational line of OH in absorption
at 119.4 um. No excited level OH transitions are apparent, indicating that the
OH is almost entirely in its ground state with a column density ~ 4x10^{14}
cm^{-2}. The spectral energy distribution over the LWS wavelength range is well
fit with a 48 K dust temperature and an optical depth, tau_{Dust} proportional
to lambda^{-1}.Comment: 23 pages, 4 figures, accepted by ApJ, Feb. 1, 199
Cosmology with the Highly Redshifted 21cm Line
In addition to being a probe of Cosmic Dawn and Epoch of Reionization
astrophysics, the 21cm line at is also a powerful way to constrain
cosmology. Its power derives from several unique capabilities. First, the 21cm
line is sensitive to energy injections into the intergalactic medium at high
redshifts. It also increases the number of measurable modes compared to
existing cosmological probes by orders of magnitude. Many of these modes are on
smaller scales than are accessible via the CMB, and moreover have the advantage
of being firmly in the linear regime (making them easy to model theoretically).
Finally, the 21cm line provides access to redshifts prior to the formation of
luminous objects. Together, these features of 21cm cosmology at provide
multiple pathways toward precise cosmological constraints. These include the
"marginalizing out" of astrophysical effects, the utilization of redshift space
distortions, the breaking of CMB degeneracies, the identification of signatures
of relative velocities between baryons and dark matter, and the discovery of
unexpected signs of physics beyond the CDM paradigm at high redshifts.Comment: Science white paper submitted to Decadal 2020 surve
Microwave Spectroscopy of Thermally Excited Quasiparticles in YBa_2Cu_3O_{6.99}
We present here the microwave surface impedance of a high purity crystal of
measured at 5 frequencies between 1 and 75 GHz. This data
set reveals the main features of the conductivity spectrum of the thermally
excited quasiparticles in the superconducting state. Below 20 K there is a
regime of extremely long quasiparticle lifetimes, due to both the collapse of
inelastic scattering below and the very weak impurity scattering in the
high purity -grown crystal used in this study. Above 20 K, the
scattering increases dramatically, initially at least as fast as .Comment: 13 pages with 10 figures. submitted to Phys Rev
The balloon-borne large-aperture submillimeter telescope for polarimetry: BLAST-Pol
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry
(BLAST-Pol) is a suborbital mapping experiment designed to study the role
played by magnetic fields in the star formation process. BLAST-Pol is the
reconstructed BLAST telescope, with the addition of linear polarization
capability. Using a 1.8 m Cassegrain telescope, BLAST-Pol images the sky onto a
focal plane that consists of 280 bolometric detectors in three arrays,
observing simultaneously at 250, 350, and 500 um. The diffraction-limited
optical system provides a resolution of 30'' at 250 um. The polarimeter
consists of photolithographic polarizing grids mounted in front of each
bolometer/detector array. A rotating 4 K achromatic half-wave plate provides
additional polarization modulation. With its unprecedented mapping speed and
resolution, BLAST-Pol will produce three-color polarization maps for a large
number of molecular clouds. The instrument provides a much needed bridge in
spatial coverage between larger-scale, coarse resolution surveys and narrow
field of view, and high resolution observations of substructure within
molecular cloud cores. The first science flight will be from McMurdo Station,
Antarctica in December 2010.Comment: 14 pages, 9 figures Submitted to SPIE Astronomical Telescopes and
Instrumentation Conference 201
Experimentally Engineering the Edge Termination of Graphene Nanoribbons
The edges of graphene nanoribbons (GNRs) have attracted much interest due to
their potentially strong influence on GNR electronic and magnetic properties.
Here we report the ability to engineer the microscopic edge termination of high
quality GNRs via hydrogen plasma etching. Using a combination of
high-resolution scanning tunneling microscopy and first-principles
calculations, we have determined the exact atomic structure of plasma-etched
GNR edges and established the chemical nature of terminating functional groups
for zigzag, armchair and chiral edge orientations. We find that the edges of
hydrogen-plasma-etched GNRs are generally flat, free of structural
reconstructions and are terminated by hydrogen atoms with no rehybridization of
the outermost carbon edge atoms. Both zigzag and chiral edges show the presence
of edge states.Comment: 16+9 pages, 3+4 figure
WARNING: Physics Envy May Be Hazardous To Your Wealth!
The quantitative aspirations of economists and financial analysts have for
many years been based on the belief that it should be possible to build models
of economic systems - and financial markets in particular - that are as
predictive as those in physics. While this perspective has led to a number of
important breakthroughs in economics, "physics envy" has also created a false
sense of mathematical precision in some cases. We speculate on the origins of
physics envy, and then describe an alternate perspective of economic behavior
based on a new taxonomy of uncertainty. We illustrate the relevance of this
taxonomy with two concrete examples: the classical harmonic oscillator with
some new twists that make physics look more like economics, and a quantitative
equity market-neutral strategy. We conclude by offering a new interpretation of
tail events, proposing an "uncertainty checklist" with which our taxonomy can
be implemented, and considering the role that quants played in the current
financial crisis.Comment: v3 adds 2 reference
Transparent Conducting Oxides for Photovoltaics: Manipulation of Fermi Level, Work Function and Energy Band Alignment
Doping limits, band gaps, work functions and energy band alignments of undoped and donor-doped transparent conducting oxides Znâ, InâOâ, and SnOâ as accessed by X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) are summarized and compared. The presented collection provides an extensive data set of technologically relevant electronic properties of photovoltaic transparent electrode materials and illustrates how these relate to the underlying defect chemistry, the dependence of surface dipoles on crystallographic orientation and/or surface termination, and Fermi level pinning
- âŠ