2,159 research outputs found
Challenging EGNOS in the Swiss Alps
In view of the operational validation of EGNOS, some early tests are being performed with the EGNOS System Test Bed (ESTB). This prototype has been broadcasting an EGNOS-like signal since early 2000. The performance of ESTB is reduced compared to the full deployed EGNOS, but it gives the opportunity to test EGNOS equipment and gain experience. Eurocontrol, skyguide and the Swiss Federal Institute of Technology in Lausanne (EPFL) are active in data collection and analysis in order to study the signal-in-space performance for the civil aviation users. The objective of this work was to analyse the system’s performance during flight tests in the Swiss Alps where the topography is a challenge for satellite-based navigation systems. Sion regional airport was selected for its location in a valley surrounded by very high mountains. Moreover, the use of EGNOS on regional places is expected to bring significant operational benefits. A new GNSS procedure including both the approach and a special missed-approach with a 89° turn in the valley was designed for these tests. A total of 13 approaches and missed-approaches were flown in November 2002 by a Dornier 128 belonging to the Technical University of Braunschweig (TUBS) and a King Air 100 belonging to SENASA (Sociedad para las Enseñanzas Aeronáuticas Civiles S.A.). Around 8 hours of data were recorded from different receivers on the ground and in the air. This paper shows that the accuracy and integrity obtained during the tests with the EGNOS System Test Bed fulfils the stringent requirements of civil aviation even in a difficult environment. However, some progress still has to be made on the availability and continuity parameters. This will be the case once the real EGNOS will be operational. It also demonstrates that EGNOS-based procedures are feasible and that it could bring important operational benefits to regional places with a limited ground navigation infrastructure
Parsec-scale dust distributions in Seyfert galaxies - Results of the MIDI AGN snapshot survey
The emission of warm dust dominates the mid-infrared spectra of active
galactic nuclei (AGN). Only interferometric observations provide the necessary
angular resolution to resolve the nuclear dust and to study its distribution
and properties. The investigation of dust in AGN cores is hence one of the main
science goals for the MID-infrared Interferometric instrument MIDI at the VLTI.
As the first step, the feasibility of AGN observations was verified and the
most promising sources for detailed studies were identified. This was carried
out in a "snapshot survey" with MIDI using Guaranteed Time Observations. In the
survey, observations were attempted for 13 of the brightest AGN in the
mid-infrared which are visible from Paranal. The results of the three
brightest, best studied sources have been published in separate papers. Here we
present the interferometric observations for the remaining 10, fainter AGN. For
8 of these, interferometric measurements could be carried out. Size estimates
or limits on the spatial extent of the AGN-heated dust were derived from the
interferometric data of 7 AGN. These indicate that the dust distributions are
compact, with sizes on the order of a few parsec. The derived sizes roughly
scale with the square root of the luminosity in the mid-infrared, s ~ sqrt(L),
with no clear distinction between type 1 and type 2 objects. This is in
agreement with a model of nearly optically thick dust structures heated to T ~
300 K. For three sources, the 10 micron feature due to silicates is tentatively
detected either in emission or in absorption. Based on the results for all AGN
studied with MIDI so far, we conclude that in the mid-infrared the differences
between individual galactic nuclei are greater than the generic differences
between type 1 and type 2 objects.Comment: 18 pages, 8 figures, updated to version published in A&A 502, 67-8
Cold Dust in Three Massive Evolved Stars in the LMC
Massive evolved stars can produce large amounts of dust, and far-infrared
(IR) data are essential for determining the contribution of cold dust to the
total dust mass. Using Herschel, we search for cold dust in three very dusty
massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue
Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red
supergiant. We model the spectral energy distributions using radiative transfer
codes and find that these three stars have mass-loss rates up to 10^-3 solar
masses/year, suggesting that high-mass stars are important contributors to the
life-cycle of dust. We found far-IR excesses in two objects, but these excesses
appear to be associated with ISM and star-forming regions. Cold dust (T < 100
K) may thus not be an important contributor to the dust masses of evolved
stars.Comment: accepted to A&A as part of the Herschel first results special issu
Ice chemistry in embedded young stellar objects in the Large Magellanic Cloud
We present spectroscopic observations of a sample of 15 embedded young
stellar objects (YSOs) in the Large Magellanic Cloud (LMC). These observations
were obtained with the Spitzer Infrared Spectrograph (IRS) as part of the
SAGE-Spec Legacy program. We analyze the two prominent ice bands in the IRS
spectral range: the bending mode of CO_2 ice at 15.2 micron and the ice band
between 5 and 7 micron that includes contributions from the bending mode of
water ice at 6 micron amongst other ice species. The 5-7 micron band is
difficult to identify in our LMC sample due to the conspicuous presence of PAH
emission superimposed onto the ice spectra. We identify water ice in the
spectra of two sources; the spectrum of one of those sources also exhibits the
6.8 micron ice feature attributed to ammonium and methanol. We model the CO_2
band in detail, using the combination of laboratory ice profiles available in
the literature. We find that a significant fraction (> 50%) of CO_2 ice is
locked in a water-rich component, consistent with what is observed for Galactic
sources. The majority of the sources in the LMC also require a pure-CO_2
contribution to the ice profile, evidence of thermal processing. There is a
suggestion that CO_2 production might be enhanced in the LMC, but the size of
the available sample precludes firmer conclusions. We place our results in the
context of the star formation environment in the LMC.Comment: Minor corrections to Table 2. Accepted for publication in ApJ, 66
pages, 9 figures (some in color), 4 table
Public Spending Patterns: The Regional Allocation of Public Investment in Greece by Political Period
Emergent complex neural dynamics
A large repertoire of spatiotemporal activity patterns in the brain is the
basis for adaptive behaviour. Understanding the mechanism by which the brain's
hundred billion neurons and hundred trillion synapses manage to produce such a
range of cortical configurations in a flexible manner remains a fundamental
problem in neuroscience. One plausible solution is the involvement of universal
mechanisms of emergent complex phenomena evident in dynamical systems poised
near a critical point of a second-order phase transition. We review recent
theoretical and empirical results supporting the notion that the brain is
naturally poised near criticality, as well as its implications for better
understanding of the brain
The impact of point mutations in the human androgen receptor : classification of mutations on the basis of transcriptional activity
Peer reviewedPublisher PD
Study of Zγ events and limits on anomalous ZZγ and Zγγ couplings in pp̄ collisions at s=1.96TeV
We present a measurement of the Zγ production cross section and limits on anomalous ZZγ and Zγγ couplings for form-factor scales of Λ=750 and 1000 GeV. The measurement is based on 138 (152) candidates in the eeγ (μμγ) final state using 320(290)pb-1 of pp̄ collisions at s=1.96TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are |h10,30Z|<0.23, |h20,40Z|<0.020, |h10,30γ|<0.23, and |h20,40γ|<0.019 for Λ=1000GeV. © 2005 The American Physical Society
A Spitzer Space Telescope far-infrared spectral atlas of compact sources in the Magellanic Clouds. I. The Large Magellanic Cloud
[abridged] We present 52-93 micron spectra obtained with Spitzer in the
MIPS-SED mode, of a representative sample of luminous compact far-IR sources in
the LMC. These include carbon stars, OH/IR AGB stars, post-AGB objects and PNe,
RCrB-type star HV2671, OH/IR red supergiants WOHG064 and IRAS05280-6910, B[e]
stars IRAS04530-6916, R66 and R126, Wolf-Rayet star Brey3a, Luminous Blue
Variable R71, supernova remnant N49, a large number of young stellar objects,
compact HII regions and molecular cores, and a background galaxy (z~0.175). We
use the spectra to constrain the presence and temperature of cold dust and the
excitation conditions and shocks within the neutral and ionized gas, in the
circumstellar environments and interfaces with the surrounding ISM. Evolved
stars, including LBV R71, lack cold dust except in some cases where we argue
that this is swept-up ISM. This leads to an estimate of the duration of the
prolific dust-producing phase ("superwind") of several thousand years for both
RSGs and massive AGB stars, with a similar fractional mass loss experienced
despite the different masses. We tentatively detect line emission from neutral
oxygen in the extreme RSG WOHG064, with implications for the wind driving. In
N49, the shock between the supernova ejecta and ISM is revealed by its strong
[OI] 63-micron emission and possibly water vapour; we estimate that 0.2 Msun of
ISM dust was swept up. Some of the compact HII regions display pronounced
[OIII] 88-micron emission. The efficiency of photo-electric heating in the
interfaces of ionized gas and molecular clouds is estimated at 0.1-0.3%. We
confirm earlier indications of a low nitrogen content in the LMC. Evidence for
solid state emission features is found in both young and evolved object; some
of the YSOs are found to contain crystalline water ice.Comment: Accepted for publication in The Astronomical Journal. This paper
accompanies the Summer 2009 SAGE-Spec release of 48 MIPS-SED spectra, but
uses improved spectrum extraction. (Fig. 2 reduced resolution because of
arXiv limit.
- …