1,188 research outputs found
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Upper tropospheric ozone production from lightning NOx-impacted convection: Smoke ingestion case study from the DC3 campaign
Š2015. American Geophysical Union. All Rights Reserved. As part of the Deep Convective Cloud and Chemistry (DC3) experiment, the National Science Foundation/National Center for Atmospheric Research (NCAR) Gulfstream-V (GV) and NASA DC-8 research aircraft probed the chemical composition of the inflow and outflow of two convective storms (north storm, NS, south storm, SS) originating in the Colorado region on 22 June 2012, a time when the High Park wildfire was active in the area. A wide range of trace species were measured on board both aircraft including biomass burning (BB) tracers hydrogen cyanide (HCN) and acetonitrile (ACN). Acrolein, a much shorter lived tracer for BB, was also quantified on the GV. The data demonstrated that the NS had ingested fresh smoke from the High Park fire and as a consequence had a higher VOC OH reactivity than the SS. The SS lofted aged fire tracers along with other boundary layer ozone precursors and was more impacted by lightning NOx (LNOx) than the NS. The NCAR master mechanism box model was initialized with measurements made in the outflow of the two storms. The NS and SS were predicted to produce 11 and 14ppbv of O3, respectively, downwind of the storm over 2days. Sensitivity tests revealed that the ozone production potential of the SS was highly dependent on LNOx. Normalized excess mixing ratios, ÎX/ÎCO, for HCN and ACN were determined in both the fire plume and the storm outflow and found to be 7.0Âą0.5 and 2.3Âą0.5pptvppbv-1, respectively, and 1.4Âą0.3pptvppbv-1 for acrolein in the outflow only
Dust-free quasars in the early Universe
The most distant quasars known, at redshifts z=6, generally have properties
indistinguishable from those of lower-redshift quasars in the rest-frame
ultraviolet/optical and X-ray bands. This puzzling result suggests that these
distant quasars are evolved objects even though the Universe was only seven per
cent of its current age at these redshifts. Recently one z=6 quasar was shown
not to have any detectable emission from hot dust, but it was unclear whether
that indicated different hot-dust properties at high redshift or if it is
simply an outlier. Here we report the discovery of a second quasar without
hot-dust emission in a sample of 21 z=6 quasars. Such apparently hot-dust-free
quasars have no counterparts at low redshift. Moreover, we demonstrate that the
hot-dust abundance in the 21 quasars builds up in tandem with the growth of the
central black hole, whereas at low redshift it is almost independent of the
black hole mass. Thus z=6 quasars are indeed at an early evolutionary stage,
with rapid mass accretion and dust formation. The two hot-dust-free quasars are
likely to be first-generation quasars born in dust-free environments and are
too young to have formed a detectable amount of hot dust around them.Comment: To be published in Nature on the 18 March 2010
An Optimized Chloroplast DNA Extraction Protocol for Grasses (Poaceae) Proves Suitable for Whole Plastid Genome Sequencing and SNP Detection
peer-reviewedBackground
Obtaining chloroplast genome sequences is important to increase the knowledge about the fundamental biology of plastids, to understand evolutionary and ecological processes in the evolution of plants, to develop biotechnological applications (e.g. plastid engineering) and to improve the efficiency of breeding schemes. Extraction of pure chloroplast DNA is required for efficient sequencing of chloroplast genomes. Unfortunately, most protocols for extracting chloroplast DNA were developed for eudicots and do not produce sufficiently pure yields for a shotgun sequencing approach of whole plastid genomes from the monocot grasses.
Methodology/Principal Findings
We have developed a simple and inexpensive method to obtain chloroplast DNA from grass species by modifying and extending protocols optimized for the use in eudicots. Many protocols for extracting chloroplast DNA require an ultracentrifugation step to efficiently separate chloroplast DNA from nuclear DNA. The developed method uses two more centrifugation steps than previously reported protocols and does not require an ultracentrifuge.
Conclusions/Significance
The described method delivered chloroplast DNA of very high quality from two grass species belonging to highly different taxonomic subfamilies within the grass family (Lolium perenne, Pooideae; MiscanthusĂgiganteus, Panicoideae). The DNA from Lolium perenne was used for whole chloroplast genome sequencing and detection of SNPs. The sequence is publicly available on EMBL/GenBank
f(R) theories
Over the past decade, f(R) theories have been extensively studied as one of
the simplest modifications to General Relativity. In this article we review
various applications of f(R) theories to cosmology and gravity - such as
inflation, dark energy, local gravity constraints, cosmological perturbations,
and spherically symmetric solutions in weak and strong gravitational
backgrounds. We present a number of ways to distinguish those theories from
General Relativity observationally and experimentally. We also discuss the
extension to other modified gravity theories such as Brans-Dicke theory and
Gauss-Bonnet gravity, and address models that can satisfy both cosmological and
local gravity constraints.Comment: 156 pages, 14 figures, Invited review article in Living Reviews in
Relativity, Published version, Comments are welcom
Construction of a Mean Square Error Adaptive Euler--Maruyama Method with Applications in Multilevel Monte Carlo
A formal mean square error expansion (MSE) is derived for Euler--Maruyama
numerical solutions of stochastic differential equations (SDE). The error
expansion is used to construct a pathwise a posteriori adaptive time stepping
Euler--Maruyama method for numerical solutions of SDE, and the resulting method
is incorporated into a multilevel Monte Carlo (MLMC) method for weak
approximations of SDE. This gives an efficient MSE adaptive MLMC method for
handling a number of low-regularity approximation problems. In low-regularity
numerical example problems, the developed adaptive MLMC method is shown to
outperform the uniform time stepping MLMC method by orders of magnitude,
producing output whose error with high probability is bounded by TOL>0 at the
near-optimal MLMC cost rate O(TOL^{-2}log(TOL)^4).Comment: 43 pages, 12 figure
An anti-CD30 single-chain Fv selected by phage display and fused to Pseudomonas exotoxin A (Ki-4(scFv)-ETĂ) is a potent immunotoxin against a Hodgkin-derived cell line
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Self-assembly and anti-amyloid cytotoxicity activity of amyloid beta peptide derivatives
The self-assembly of two derivatives of KLVFF, a fragment Abeta(16-20) of the amyloid beta (Abeta) peptide, is investigated and recovery of viability of neuroblastoma cells exposed to Abeta is observed at sub-stoichiometric peptide concentrations. Fluorescence assays show that NH2-KLVFF-CONH2 undergoes hydrophobic collapse and amyloid formation at the same critical aggregation concentration (cac). In contrast, NH2-K(Boc)LVFF-CONH2 undergoes hydrophobic collapse at a low concentration, followed by amyloid formation at a higher cac. These findings are supported by the beta-sheet features observed by FTIR. Electrospray ionization mass spectrometry indicates that NH2-K(Boc)LVFF-CONH2 forms a significant population of oligomeric species above the cac. Cryo-TEM, used together with SAXS to determine fibril dimensions, shows that the length and degree of twisting of peptide fibrils seem to be influenced by the net peptide charge. Grazing incidence X-ray scattering from thin peptide films shows features of beta-sheet ordering for both peptides, along with evidence for lamellar ordering of NH2-KLVFF-CONH2. This work provides a comprehensive picture of the aggregation properties of these two KLVFF derivatives and show their utility, in unaggregated form, in restoring the viability of neuroblastoma cells against Abeta-induced toxicity
New MR sequences in daily practice: susceptibility weighted imaging. A pictorial essay
Background Susceptibility-weighted imaging (SWI) is a
relatively new magnetic resonance (MR) technique that
exploits the magnetic susceptibility differences of various
tissues, such as blood, iron and calcification, as a new
source of contrast enhancement. This pictorial review is
aimed at illustrating and discussing its main clinical
applications.
Methods SWI is based on high-resolution, threedimensional
(3D), fully velocity-compensated gradientecho
sequences using both magnitude and phase images.
A phase mask obtained from the MR phase images is
multiplied with magnitude images in order to increase the
visualisation of the smaller veins and other sources of
susceptibility effects, which are displayed at best after postprocessing
of the 3D dataset with the minimal intensity
projection (minIP) algorithm.
Results SWI is very useful in detecting cerebral microbleeds
in ageing and occult low-flow vascular malformations,
in characterising brain tumours and degenerative diseases of the brain, and in recognizing calcifications in
various pathological conditions. The phase images are
especially useful in differentiating between paramagnetic
susceptibility effects of blood and diamagnetic effects of
calcium. SWI can also be used to evaluate changes in iron
content in different neurodegenerative disorders.
Conclusion SWI is useful in differentiating and characterising
diverse brain disorders
Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV
The performance of muon reconstruction, identification, and triggering in CMS
has been studied using 40 inverse picobarns of data collected in pp collisions
at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection
criteria covering a wide range of physics analysis needs have been examined.
For all considered selections, the efficiency to reconstruct and identify a
muon with a transverse momentum pT larger than a few GeV is above 95% over the
whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4,
while the probability to misidentify a hadron as a muon is well below 1%. The
efficiency to trigger on single muons with pT above a few GeV is higher than
90% over the full eta range, and typically substantially better. The overall
momentum scale is measured to a precision of 0.2% with muons from Z decays. The
transverse momentum resolution varies from 1% to 6% depending on pseudorapidity
for muons with pT below 100 GeV and, using cosmic rays, it is shown to be
better than 10% in the central region up to pT = 1 TeV. Observed distributions
of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO
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