21,922 research outputs found
A Monte Carlo Template based analysis for Air-Cherenkov Arrays
We present a high-performance event reconstruction algorithm: an Image
Pixel-wise fit for Atmospheric Cherenkov Telescopes (ImPACT). The
reconstruction algorithm is based around the likelihood fitting of camera pixel
amplitudes to an expected image template. A maximum likelihood fit is performed
to find the best-fit shower parameters. A related reconstruction algorithm has
already been shown to provide significant improvements over traditional
reconstruction for both the CAT and H.E.S.S. experiments. We demonstrate a
significant improvement to the template generation step of the procedure, by
the use of a full Monte Carlo air shower simulation in combination with a
ray-tracing optics simulation to more accurately model the expected camera
images. This reconstruction step is combined with an MVA-based background
rejection.
Examples are shown of the performance of the ImPACT analysis on both
simulated and measured (from a strong VHE source) gamma-ray data from the
H.E.S.S. array, demonstrating an improvement in sensitivity of more than a
factor two in observation time over traditional image moments-fitting methods,
with comparable performance to previous likelihood fitting analyses. ImPACT is
a particularly promising approach for future large arrays such as the Cherenkov
Telescope Array (CTA) due to its improved high-energy performance and
suitability for arrays of mixed telescope types.Comment: 13 pages, 10 figure
A Generic Algorithm for IACT Optical Efficiency Calibration using Muons
Muons produced in Extensive Air Showers (EAS) generate ring-like images in
Imaging Atmospheric Cherenkov Telescopes when travelling near parallel to the
optical axis. From geometrical parameters of these images, the absolute amount
of light emitted may be calculated analytically. Comparing the amount of light
recorded in these images to expectation is a well established technique for
telescope optical efficiency calibration. However, this calculation is usually
performed under the assumption of an approximately circular telescope mirror.
The H.E.S.S. experiment entered its second phase in 2012, with the addition of
a fifth telescope with a non-circular 600m mirror. Due to the differing
mirror shape of this telescope to the original four H.E.S.S. telescopes,
adaptations to the standard muon calibration were required. We present a
generalised muon calibration procedure, adaptable to telescopes of differing
shapes and sizes, and demonstrate its performance on the H.E.S.S. II array.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
Effect of pressure on the crystal structure of alpha-glycylglycine to 4.7 GPa; application of Hirshfeld surfaces to analyse contacts on increasing pressure
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
Effect of pressure on the crystal structure of L-serine-I and the crystal structure of L-serine-II at 5.4 GPa
Quantitative measurements of the thermopower of Andreev interferometers
Using a new second derivative technique and thermometers which enable us to
determine the local electron temperature in a mesoscopic metallic sample, we
have obtained quantitative measurements of the low temperature field and
temperature dependent thermopower of Andreev interferometers. As in previous
experiments, the thermopower is found to oscillate as a function of magnetic
field. The temperature dependence of the thermopower is nonmonotonic, with a
minimum at a temperature of K. These results are discussed from the
perspective of Andreev reflection at the normal-metal/superconductor interface.Comment: 6 pages, 4 figure
\u27Texas Maroon’ Bluebonnet
The Texas state flower, the bluebonnet, encompasses all six of the Lupinus species native to Texas. The most widespread and popular bluebonnet, Lupinus texensis Hook., is a winter annual that produces violet-blue [violet-blue group 96A, Royal Horticultural
Society (RHS), 1982] racemes in early to midspring and is predominately self-pollinating.
The Texas Dept. of Transportation uses this species widely for floral displays along roadsides throughout much of the state (Andrews, 1986). Rare white and even rarer pink variants exist in native populations, and a breeding project was initiated in 1985 to develop bluebonnets with novel flower colors for use as bedding plants. ‘Abbott Pink’ was the first seed-propagated cultivar to be developed from this program (Parsons and Davis, 1993). The second cultivar, ‘Barbara Bush’ with novel lavender shade flowers, was developed more recently (Parsons et al., 1994). As with the cultivars previously developed, we used recurrent phenotypic selection to develop ‘Texas Maroon’. This cultivar is intended for use as a bedding plant for maroon flower color
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