357 research outputs found
Using Uplug and SiteSeeker to construct a cross language search engine for Scandinavian languages
Proceedings of the 17th Nordic Conference of Computational Linguistics
NODALIDA 2009.
Editors: Kristiina Jokinen and Eckhard Bick.
NEALT Proceedings Series, Vol. 4 (2009), 26-33.
© 2009 The editors and contributors.
Published by
Northern European Association for Language
Technology (NEALT)
http://omilia.uio.no/nealt .
Electronically published at
Tartu University Library (Estonia)
http://hdl.handle.net/10062/9206
Palladium-catalyzed stereoselective domino arylation-acylation:an entry to chiral tetrahydrofluorenone scaffolds
A palladium-catalyzed domino arylation-cyclization of biocatalytically derived cyclic 1,3-dienes is demonstrated. The reaction introduces a high degree of structural complexity in a single step, giving access to tricyclic tetrahydrofluorenones with full regio- and stereoselectivity. The transformation proceeds through a novel acylation-terminated Heck-type sequence, and quantum chemical calculations indicate that C-H activation is involved in the terminating acylation step
Palladium Catalyzed Stereoselective Arylation of Biocatalytically Derived Cyclic 1,3-Dienes:Chirality Transfer via a Heck-Type Mechanism
Microbial arene oxidation of benzoic acid with Ralstonia eutropha B9 provides a chiral highly functionalized cyclohexadiene, suitable for further structural diversification. Subjecting this scaffold to a Pd-catalyzed Heck reaction effects a regio- and stereoselective arylation of the cyclohexadiene ring, with 1,3-chirality transfer of stereogenic information installed in the microbial arene oxidation. Quantum chemical calculations explain the selectivity both by a kinetic preference for the observed arylation position and by reversible carbopalladation in competing positions. Further product transformation allowed the formation of a tricyclic ketone possessing four stereogenic centers. This demonstrates the capability of the method to introduce stereochemical complexity from planar nonchiral benzoic acid in just a few steps
GRB 090417B and its Host Galaxy: A Step Towards an Understanding of Optically-Dark Gamma-Ray Bursts
GRB 090417B was an unusually long burst with a T_90 duration of at least 2130
s and a multi-peaked light curve at energies of 15-150 keV. It was optically
dark and has been associated with a bright star-forming galaxy at a redshift of
0.345 that is broadly similar to the Milky Way. This is one of the few cases
where a host galaxy has been clearly identified for a dark gamma-ray burst and
thus an ideal candidate for studying the origin of dark bursts. We find that
the dark nature of GRB 090417B cannot be explained by high redshift, incomplete
observations, or unusual physics in the production of the afterglow. Assuming
the standard relativistic fireball model for the afterglow we find that the
optical flux is at least 2.5 mag fainter than predicted by the X-ray flux. The
Swift/XRT X -ray data are consistent with the afterglow being obscured by a
dense, localized sheet of dust approximately 30-80 pc from the burst along the
line of sight. Our results suggest that this dust sheet imparts an extinction
of A_V >~ 12 mag, which is sufficient to explain the missing optical flux. GRB
090417B is an example of a gamma-ray burst that is dark due to the localized
dust structure in its host galaxy.Comment: Accepted for publication in Ap
Adverse clinical sequelae after skin branding: a case series
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens
Functionally heterogeneous human satellite cells identified by single cell RNA sequencing.
Although heterogeneity is recognized within the murine satellite cell pool, a comprehensive understanding of distinct subpopulations and their functional relevance in human satellite cells is lacking. We used a combination of single cell RNA sequencing and flow cytometry to identify, distinguish, and physically separate novel subpopulations of human PAX7+ satellite cells (Hu-MuSCs) from normal muscles. We found that, although relatively homogeneous compared to activated satellite cells and committed progenitors, the Hu-MuSC pool contains clusters of transcriptionally distinct cells with consistency across human individuals. New surface marker combinations were enriched in transcriptional subclusters, including a subpopulation of Hu-MuSCs marked by CXCR4/CD29/CD56/CAV1 (CAV1+). In vitro, CAV1+ Hu-MuSCs are morphologically distinct, and characterized by resistance to activation compared to CAV1- Hu-MuSCs. In vivo, CAV1+ Hu-MuSCs demonstrated increased engraftment after transplantation. Our findings provide a comprehensive transcriptional view of normal Hu-MuSCs and describe new heterogeneity, enabling separation of functionally distinct human satellite cell subpopulations
Atomic diffraction from nanostructured optical potentials
We develop a versatile theoretical approach to the study of cold-atom
diffractive scattering from light-field gratings by combining calculations of
the optical near-field, generated by evanescent waves close to the surface of
periodic nanostructured arrays, together with advanced atom wavepacket
propagation on this optical potential.Comment: 8 figures, 10 pages, submitted to Phys. Rev.
Dust and Metal Column Densities in Gamma-Ray Burst Host Galaxies
In this paper we present the results from the analysis of a sample of 28
gamma-ray burst (GRB) afterglow spectral energy distributions, spanning the
X-ray through to near-infrared wavelengths. This is the largest sample of GRB
afterglow spectral energy distributions thus far studied, providing a strong
handle on the optical depth distribution of soft X-ray absorption and
dust-extinction systems in GRB host galaxies. We detect an absorption system
within the GRB host galaxy in 79% of the sample, and an extinction system in
71% of the sample, and find the Small Magellanic Cloud (SMC) extinction law to
provide an acceptable fit to the host galaxy extinction profile for the
majority of cases, consistent with previous findings. The range in the soft
X-ray absorption to dust-extinction ratio, N_{H,X}/Av, in GRB host galaxies
spans almost two orders of magnitude, and the typical ratios are significantly
larger than those of the Magellanic Clouds or Milky Way. Although dust
destruction could be a cause, at least in part, for the large N_{H,X}/Av
ratios, the good fit provided by the SMC extinction law for the majority of our
sample suggests that there is an abundance of small dust grains in the GRB
environment, which we would expect to have been destroyed if dust destruction
were responsible for the large N_{H,X}/Av ratios. Instead, our analysis
suggests that the distribution of N_{H,X}/Av in GRB host galaxies may be mostly
intrinsic to these galaxies, and this is further substantiated by evidence for
a strong negative correlation between N_{H,X}/Av and metallicity for a
subsample of GRB hosts with known metallicity. Furthermore, we find the
N_{H,X}/Av ratio and metallicity for this subsample of GRBs to be comparable to
the relation found in other more metal-rich galaxies.Comment: 23 pages, 10 figures, accepted for publication in MNRA
GRB 120711A: an intense INTEGRAL burst with long-lasting soft gamma-ray emission and a powerful optical flash
A long and intense gamma-ray burst (GRB) was detected by INTEGRAL on July 11
2012 with a duration of ~115s and fluence of 2.8x10^-4 erg cm^-2 in the 20
keV-8 MeV energy range. GRB 120711A was at z~1.405 and produced soft gamma-ray
emission (>20 keV) for at least ~10 ks after the trigger. The GRB was observed
by several ground-based telescopes that detected a powerful optical flash
peaking at an R-band brightness of ~11.5 mag at ~126 s after the trigger. We
present a comprehensive temporal and spectral analysis of the long-lasting soft
gamma-ray emission detected in the 20-200 keV band with INTEGRAL, the Fermi/LAT
post-GRB detection above 100 MeV, the soft X-ray afterglow from XMM-Newton,
Chandra, and Swift and the optical/NIR detections from Watcher, Skynet, GROND,
and REM. We modelled the long-lasting soft gamma-ray emission using the
standard afterglow scenario, which indicates a forward shock origin. The
combination of data extending from the NIR to GeV energies suggest that the
emission is produced by a broken power-law spectrum consistent with synchrotron
radiation. The afterglow is well modelled using a stratified wind-like
environment with a density profile k~1.2, suggesting a massive star progenitor
(i.e. Wolf-Rayet). The analysis of the reverse and forward shock emission
reveals an initial Lorentz factor of ~120-340, a jet half-opening angle of
~2deg-5deg, and a baryon load of ~10^-5-10^-6 Msun consistent with the
expectations of the fireball model when the emission is highly relativistic.
Long-lasting soft gamma-ray emission from other INTEGRAL GRBs with high peak
fluxes, such as GRB 041219A, was not detected, suggesting that a combination of
high Lorentz factor, emission above 100 MeV, and possibly a powerful reverse
shock are required. Similar long-lasting soft gamma-ray emission has recently
been observed from the nearby and extremely bright Fermi/LAT burst GRB 130427A.Comment: 21 pages, 10 figures. Accepted for publication in Astronomy and
Astrophysic
Radiological progression of end colostomy trephine diameter and area
Development of a parastomal hernia is common following abdominoperineal excision
(APE). The true incidence is difficult to assess fully owing to differing lengths of follow-up and techniques used to assess herniation; radiological or clinical. The primary aim of this study was to evaluate colostomy diameter by studying the rate of change of axial and sagittal trephine diameters, trephine area, and the ratio of the trephine over time. A secondary aim was to investigate variation in trephine area and variables affecting parastomal hernia over time
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