147 research outputs found
Development of HPD Clusters for MAGIC-II
MAGIC-II is the second imaging atmospheric Cherenkov telescope of the MAGIC
observatory, which has recently been inaugurated on Canary island of La Palma.
We are currently developing a new camera based on clusters of hybrid photon
detectors (HPD) for the upgrade of MAGIC-II. The photon detectors feature a
GaAsP photocathode and an avalanche diode as electron bombarded anodes with
internal gain, and were supplied by Hamamatsu Photonics K.K. (R9792U-40). The
HPD camera with high quantum efficiency will increase the MAGIC-II sensitivity
and lower the energy threshold. The basic performance of the HPDs has been
measured and a prototype of an HPD cluster has been developed to be mounted on
MAGIC-II. Here we report on the status of the HPD cluster and the project of
eventually using HPD clusters in the central area of the MAGIC-II camera.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200
The major upgrade of the MAGIC telescopes, Part II: A performance study using observations of the Crab Nebula
MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes located in
the Canary island of La Palma, Spain. During summer 2011 and 2012 it underwent
a series of upgrades, involving the exchange of the MAGIC-I camera and its
trigger system, as well as the upgrade of the readout system of both
telescopes. We use observations of the Crab Nebula taken at low and medium
zenith angles to assess the key performance parameters of the MAGIC stereo
system. For low zenith angle observations, the standard trigger threshold of
the MAGIC telescopes is ~50GeV. The integral sensitivity for point-like sources
with Crab Nebula-like spectrum above 220GeV is (0.66+/-0.03)% of Crab Nebula
flux in 50 h of observations. The angular resolution, defined as the sigma of a
2-dimensional Gaussian distribution, at those energies is < 0.07 degree, while
the energy resolution is 16%. We also re-evaluate the effect of the systematic
uncertainty on the data taken with the MAGIC telescopes after the upgrade. We
estimate that the systematic uncertainties can be divided in the following
components: < 15% in energy scale, 11-18% in flux normalization and +/-0.15 for
the energy spectrum power-law slope.Comment: 21 pages, 25 figures, accepted for publication in Astroparticle
Physic
RuralâUrban Migration and Experience of Childhood Abuse in the Young Thai Population
Evidence suggests that certain migrant populations are at increased risk of abusive behaviors. It is unclear whether this may also apply to Thai ruralâurban migrants, who may experience higher levels of psychosocial adversities than the population at large. The study aims to examine the association between migration status and the history of childhood sexual, physical, and emotional abuse among young Thai people in an urban community. A population-based cross-sectional survey was conducted in Northern Bangkok on a representative sample of 1052 young residents, aged 16â25Â years. Data were obtained concerning: 1) exposuresâmigration (defined as an occasion when a young person, born in a more rural area moves for the first time into Greater Bangkok) and age at migration. 2) outcomesâchild abuse experiences were assessed with an anonymous self report adapted from the Conflict Tactics Scales (CTS). There were 8.4%. 16.6% and 56.0% reporting sexual, physical, and emotional abuse, respectively. Forty six percent of adolescents had migrated from rural areas to Bangkok, mostly independently at the age of 15 or after to seek work. Although there were trends towards higher prevalences of the three categories of abuse among early migrants, who moved to Bangkok before the age of 15, being early migrants was independently associated with experiences of physical abuse (OR 1.9 95%CI 1.1â3.2) and emotional abuse (OR 2.0, 95%CI 1.3â3.0) only. Our results suggest that ruralâurban migration at an early age may place children at higher risk of physical and emotional abuse. This may have policy implications for the prevention of childhood abuse particularly among young people on the move
Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy
Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA
Global urban environmental change drives adaptation in white clover.
Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale
Bromination of double-walled carbon nanotubes
Double-walled carbon nanotubes (DWCNTs) synthesized by catalytic chemical vapor deposition (CCVD) have been functionalized by bromine vapor at room temperature. At least two different bromine species were detected in the product using X-ray photoelectron spectroscopy (XPS) and thermal gravimetric analysis. The primary form is negatively charged Br2 molecules exhibiting an intense resonance at âŒ238 cmâ1 in the Raman spectrum. The electron transfer from the nanotubes to the adsorbed molecules is detected from C 1s XPS and near-edge X-ray absorption fine structure spectra. The optical absorption spectra reveal that although the metallic nanotubes are more reactive to Br2, the outer semiconducting nanotubes also readily interact with Br2 adsorbates. The secondary bromine form is attributed to covalent C-Br bonding, and its possible sources are discussed in the light of quantum-chemical calculations. Analysis of the XPS, Raman, and optical absorption spectra of the Br-DWCNTs annealed at 100-170 °
C indicates preservation of a part of bromine molecules in samples that affects the electronic and vibration properties of nanotubes
Global urban environmental change drives adaptation in white clover
Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale
Evolution of the histological and functional structure of ectoderm, chordamesoderm and their derivatives in Anamnia
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