20,434 research outputs found
Infrared Dark Cloud Cores in the SCUBA Legacy Catalogue
We present an investigation of candidate Infrared Dark Cloud cores as
identified by Simon et al. (2006) located within the SCUBA Legacy Catalogue.
After applying a uniform noise cut to the Catalogue data we identify 154
Infrared Dark Cloud cores that were detected at 850um and 51 cores that were
not. We derive column densities for each core from their 8um extinction and
find that the IRDCs detected at 850um have higher column densities (a mean of
1.7x10^22 cm-2) compared to those cores not detected at 850um (a mean of
1.0x10^22 cm-2). Combined with sensitivity estimates, we suggest that the cores
not detected at 850um are low mass, low column density and low temperature
cores that are below the sensitivity limit of SCUBA at 850um. For a subsample
of the cores detected at 850um those contained within the MIPSGAL area) we find
that two thirds are associated with 24um sources. Cores not associated with
24um emission are either ``starless'' IRDC cores that perhaps have yet to form
stars, or contain low mass YSOs below the MIPSGAL detection limit. We see that
those ``starless'' IRDC cores and the IRDC cores associated with 24um emission
are drawn from the same column density population and are of similar mass. If
we then assume the cores without 24um embedded sources are at an earlier
evolutionary stage to cores with embedded objects we derive a statistical
lifetime for the quiescent phase of a few 10^3-10^4 years. Finally, we make
conservative predictions for the number of observed IRDCs that will be observed
by the Apex Telescope Galactic Plane Survey (ATLASGAL), the Herschel Infrared
Galactic Plane Survey (Hi-GAL), the JCMT Galactic Plane Survey (JPS) and the
SCUBA-2 ``All Sky'' Survey (SASSy).Comment: 18 pages, 3 tables, 10 figure
Potential for measuring the longitudinal and lateral profile of muons in TeV air showers with IACTs
Muons are copiously produced within hadronic extensive air showers (EAS)
occurring in the Earth's atmosphere, and are used by particle air shower
detectors as a means of identifying the primary cosmic ray which initiated the
EAS. Imaging Atmospheric Cherenkov Telescopes (IACTs), designed for the
detection of gamma-ray initiated EAS for the purposes of Very High Energy (VHE)
gamma-ray astronomy, are subject to a considerable background signal due to
hadronic EAS. Although hadronic EAS are typically rejected for gamma-ray
analysis purposes, single muons produced within such showers generate clearly
identifiable signals in IACTs and muon images are routinely retained and used
for calibration purposes. For IACT arrays operating with a stereoscopic
trigger, when a muon triggers one telescope, other telescopes in IACT arrays
usually detect the associated hadronic EAS. We demonstrate for the first time
the potential of IACT arrays for competitive measurements of the muon content
of air showers, their lateral distribution and longitudinal profile of
production slant heights in the TeV energy range. Such information can provide
useful input to hadronic interaction models.Comment: 15 pages, 11 figures, 2 tables, accepted for publication in
Astroparticle Physic
On-the-fly memory compression for multibody algorithms.
Memory and bandwidth demands challenge developers of particle-based codes that have to scale on new architectures, as the growth of concurrency outperforms improvements in memory access facilities, as the memory per core tends to stagnate, and as communication networks cannot increase bandwidth arbitrary. We propose to analyse each particle of such a code to find out whether a hierarchical data representation storing data with reduced precision caps the memory demands without exceeding given error bounds. For admissible candidates, we perform this compression and thus reduce the pressure on the memory subsystem, lower the total memory footprint and reduce the data to be exchanged via MPI. Notably, our analysis and transformation changes the data compression dynamically, i.e. the choice of data format follows the solution characteristics, and it does not require us to alter the core simulation code
Relaxation of strained silicon on Si0.5Ge0.5 virtual substrates
Strain relaxation has been studied in tensile strained silicon layers grown on Si0.5Ge0.5 virtual substrates, for layers many times the critical thickness, using high resolution x-ray diffraction. Layers up to 30 nm thick were found to relax less than 2% by the glide of preexisting 60° dislocations. Relaxation is limited because many of these dislocations dissociate into extended stacking faults that impede the dislocation glide. For thicker layers, nucleated microtwins were observed, which significantly increased relaxation to 14%. All these tensile strained layers are found to be much more stable than layers with comparable compressive strain
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In vitro and in vivo modification of Neisseria gonorrhoeae lipooligosaccharide epitope structure by sialylation.
After growth of gonococci in the presence of cytidine monophospho-N-acetyl-neuraminic acid (CMP-NANA), their 4.5-kD lipooligosaccharide (LOS) component was increased by approximately 400 daltons, whereas the LOS of strains lacking the 4.5-kD component were unaffected. Expression of mAb-defined epitopes on the 4.5-kD component was decreased on LOS of strains grown in CMP-NANA, and treatment of the LOS with neuraminidase reversed this affect. Gonococci incubated with human PMNs also had decreased expression of the 4.5-kD+ epitopes. A detergent extract of gonococci incorporated radiolabeled NANA in the LOS, suggesting the presence of a sialyltransferase in gonococci. Exogenous sialyltransferases also could use LOS as an acceptor
EDGE: a code to calculate diffusion of cosmic-ray electrons and their gamma-ray emission
The positron excess measured by PAMELA and AMS can only be explained if there
is one or several sources injecting them. Moreover, at the highest energies, it
requires the presence of nearby (hundreds of parsecs) and middle age
(maximum of hundreds of kyr) source. Pulsars, as factories of electrons
and positrons, are one of the proposed candidates to explain the origin of this
excess. To calculate the contribution of these sources to the electron and
positron flux at the Earth, we developed EDGE (Electron Diffusion and Gamma
rays to the Earth), a code to treat diffusion of electrons and compute their
diffusion from a central source with a flexible injection spectrum. We can
derive the source's gamma-ray spectrum, spatial extension, the all-electron
density in space and the electron and positron flux reaching the Earth. We
present in this contribution the fundamentals of the code and study how
different parameters affect the gamma-ray spectrum of a source and the electron
flux measured at the Earth.Comment: Presented at the 35th International Cosmic Ray Conference (ICRC2017),
Bexco, Busan, Kore
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