1,746 research outputs found
SST-GATE: A dual mirror telescope for the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) will be the world's first open
observatory for very high energy gamma-rays. Around a hundred telescopes of
different sizes will be used to detect the Cherenkov light that results from
gamma-ray induced air showers in the atmosphere. Amongst them, a large number
of Small Size Telescopes (SST), with a diameter of about 4 m, will assure an
unprecedented coverage of the high energy end of the electromagnetic spectrum
(above ~1TeV to beyond 100 TeV) and will open up a new window on the
non-thermal sky. Several concepts for the SST design are currently being
investigated with the aim of combining a large field of view (~9 degrees) with
a good resolution of the shower images, as well as minimizing costs. These
include a Davies-Cotton configuration with a Geiger-mode avalanche photodiode
(GAPD) based camera, as pioneered by FACT, and a novel and as yet untested
design based on the Schwarzschild-Couder configuration, which uses a secondary
mirror to reduce the plate-scale and to allow for a wide field of view with a
light-weight camera, e.g. using GAPDs or multi-anode photomultipliers. One
objective of the GATE (Gamma-ray Telescope Elements) programme is to build one
of the first Schwarzschild-Couder prototypes and to evaluate its performance.
The construction of the SST-GATE prototype on the campus of the Paris
Observatory in Meudon is under way. We report on the current status of the
project and provide details of the opto-mechanical design of the prototype, the
development of its control software, and simulations of its expected
performance.Comment: In Proceedings of the 33rd International Cosmic Ray Conference
(ICRC2013), Rio de Janeiro (Brazil). All CTA contributions at arXiv:1307.223
GPS water level measurements for Indonesia's Tsunami Early Warning System
On Boxing Day 2004, a severe tsunami was generated by a strong earthquake in Northern Sumatra causing a large number of casualties. At this time, neither an offshore buoy network was in place to measure tsunami waves, nor a system to disseminate tsunami warnings to local governmental entities. Since then, buoys have been developed by Indonesia and Germany, complemented by NOAA's Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys, and have been moored offshore Sumatra and Java. The suite of sensors for offshore tsunami detection in Indonesia has been advanced by adding GPS technology for water level measurements. <br><br> The usage of GPS buoys in tsunami warning systems is a relatively new approach. The concept of the German Indonesian Tsunami Early Warning System (GITEWS) (Rudloff et al., 2009) combines GPS technology and ocean bottom pressure (OBP) measurements. Especially for near-field installations where the seismic noise may deteriorate the OBP data, GPS-derived sea level heights provide additional information. <br><br> The GPS buoy technology is precise enough to detect medium to large tsunamis of amplitudes larger than 10 cm. The analysis presented here suggests that for about 68% of the time, tsunamis larger than 5 cm may be detectable
Corte e carbonização como uma alternativa ao corte e queima: estudos na Amazônia.
Neste capítulo são apresentados vários estudos realizados em Manaus cujo principal objetivo foi verificar o efeito da aplicação de carvão vegetal no manejo do Latossolo Amarelo (xanthic Ferralsol) na terra firme em Manaus - Brasil. Os estudos foram conduzidos na Estação Experimental da Embrapa Amazônia Ocidental no km 30 da Rodovia AM-010. Também é descrito uma forma de manejo indígena da fertilidade do solo pela queima e uso de fontes orgânica
Late Quaternary Tectonics, Incision, and Landscape Evolution of the Calchaquí River Catchment, Eastern Cordillera, NW Argentina
Unraveling the relative impacts of climate, tectonics, and lithology on landscape evolution is complicated by the temporal and spatial scale over which observations are made. We use soil and desert pavement classification, longitudinal river profiles, 10Be-derived catchment mean modern and paleo-erosion rates, and vertical incision rates to test whether, if we restrict our analyses to a spatial scale over which climate is relatively invariant, tectonic and lithologic factors will dominate the late Quaternary landscape evolution of the Calchaquí River Catchment, NW Argentina. We find that the spatial distribution of erosion rates, normalized channel steepness indices, and concavity indices reflect active tectonics and lithologic resistance. Knickpoints are spatially coincident with tectonic and/or lithologic discontinuities, indicating local base-level control by faulting. Catchment mean erosion rates, ranging from 22.5 ± 2.6 to 121.9 ± 13.7 mm/kyr, and paleo-erosion rates, ranging from 56 +43/-19 to 105 +60/-33 mm/kyr, are similar, possibly suggesting that Quaternary climate changes have not had a strong enough influence on erosion rates to be detected using cosmogenic 10Be. However, punctuated abandonment of pediment and strath terraces at 43.6 +15.0/-11.6, 91.2 +54.2/-22.2, and 151 +92.7/-34.1 ka and disparities between vertical incision rates and catchment mean erosion rates could suggest periods of landscape transience, possibly reflecting climate cyclicity. Our results emphasize the role of tectonic uplift and lithologic contrasts in shaping long-term erosion rates and channel morphology at the relatively local scale of the Calchaqui River Catchment, in contrast to regional-scale studies which find precipitation to exert the dominant control
Non-parametric comparison of histogrammed two-dimensional data distributions using the Energy Test
When monitoring complex experiments, comparison is often made between regularly acquired histograms of data and reference histograms which represent the ideal state of the equipment. With the larger HEP experiments now ramping up, there is a need for automation of this task since the volume of comparisons could overwhelm human operators. However, the two-dimensional histogram comparison tools available in ROOT have been noted in the past to exhibit shortcomings. We discuss a newer comparison test for two-dimensional histograms, based on the Energy Test of Aslan and Zech, which provides more conclusive
discrimination between histograms of data coming from different distributions than methods provided in a recent ROOT release.The Science and Technology Facilities Council, U
Nitrogen retention and plant uptake on a highly weathered central Amazonian Ferralsol amended with compost and charcoal.
Inspired by the sustained fertility of anthropogenic Terra Preta soils in the central Amazon Basin, we studied the effect of charcoal as soil amendment
Investigation of A1g phonons in YBa2Cu3O7 by means of LAPW atomic-force calculations
We report first-principles frozen-phonon calculations for the determination
of the force-free geometry and the dynamical matrix of the five Raman-active
A1g modes in YBa2Cu3O7. To establish the shape of the phonon potentials atomic
forces are calculated within the LAPW method. Two different schemes - the local
density approximation (LDA) and a generalized gradient approximation (GGA) -
are employed for the treatment of electronic exchange and correlation effects.
We find that in the case of LDA the resulting phonon frequencies show a
deviation from experimental values of approximately -10%. Invoking GGA the
frequency values are significantly improved and also the eigenvectors are in
very good agreement with experimental findings.Comment: 15 page
Superconducting Magnetization above the Irreversibility Line in Tl2Ba2CuO6
Piezolever torque magnetometry has been used to measure the magnetization of
superconducting Tl2Ba2CuO6. Three crystals with different levels of oxygen
overdoping were investigated in magnetic fields up to 10 Tesla. In all cases,
the magnetization above the irreversibility line was found to depart from the
behaviour M ~ ln(Hc2/H) of a simple London-like vortex liquid. In particular,
for a strongly overdoped (Tc = 15K) crystal, the remnant superconducting order
above the irreversibility line is characterized by a linear diamagnetic
response (M ~ H) that persists well above Tc and also up to the highest field
employed.Comment: RevTeX, 11 pages, 7 encapsulated PostScript figures, submitted to
Physical Review
Oxygen-isotope effect on the in-plane penetration depth in underdoped Y_{1-x}Pr_xBa_2Cu_3O_{7-delta} as revealed by muon-spin rotation
The oxygen-isotope (^16O/^18O) effect (OIE) on the in-plane penetration depth
in underdoped Y_{1-x}Pr_xBa_2Cu_3O_{7-delta} was studied by
muon-spin rotation. A pronounced OIE on was observed
with a relative isotope shift of
=-5(2)% for x =0.3 and -9(2)% for
x=0.4. It arises mainly from the oxygen-mass dependence of the in-plane
effective mass . The OIE exponents of T_{c} and of
exhibit a relation that appears to be generic for
cuprate superconductors.Comment: 4 pages, 4 eps figures, RevTex
Fundamental Properties of the Highly Ionized Plasmas in the Milky Way
The cooling transition temperature gas in the interstellar medium (ISM),
traced by the high ions, Si IV, C IV, N V, and O VI, helps to constrain the
flow of energy from the hot ISM with T >10^6 K to the warm ISM with T< 2x10^4
K. We investigate the properties of this gas along the lines of sight to 38
stars in the Milky Way disk using 1.5-2.7 km/s resolution spectra of Si IV, C
IV, and N V absorption from the Space Telescope Imaging Spectrograph (STIS),
and 15 km/s resolution spectra of O VI absorption from the Far Ultraviolet
Spectroscopic Explorer (FUSE). The absorption by Si IV and C IV exhibits broad
and narrow components while only broad components are seen in N V and O VI. The
narrow components imply gas with T<7x10^4 K and trace two distinct types of
gas. The strong, saturated, and narrow Si IV and C IV components trace the gas
associated with the vicinities of O-type stars and their supershells. The
weaker narrow Si IV and C IV components trace gas in the general ISM that is
photoionized by the EUV radiation from cooling hot gas or has radiatively
cooled in a non-equilibrium manner from the transition temperature phase, but
rarely the warm ionized medium (WIM) probed by Al III. The broad Si IV, C IV, N
V, and O VI components trace collisionally ionized gas that is very likely
undergoing a cooling transition from the hot ISM to the warm ISM. The cooling
process possibly provides the regulation mechanism that produces N(C IV)/N(Si
IV) = 3.9 +/- 1.9. The cooling process also produces absorption lines where the
median and mean values of the line widths increase with the energy required to
create the ion.Comment: Accepted for publication in the ApJ. Only this PDF file contains all
the figures and tables in a single fil
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