9,774 research outputs found
Spacelab experiment computer study. Volume 2: Study elements and approach
For abstract, see volume 1 N77-13097
Flight control system design factors for applying automated testing techniques
Automated validation of flight-critical embedded systems is being done at ARC Dryden Flight Research Facility. The automated testing techniques are being used to perform closed-loop validation of man-rated flight control systems. The principal design features and operational experiences of the X-29 forward-swept-wing aircraft and F-18 High Alpha Research Vehicle (HARV) automated test systems are discussed. Operationally applying automated testing techniques has accentuated flight control system features that either help or hinder the application of these techniques. The paper also discusses flight control system features which foster the use of automated testing techniques
The Galactic Faraday depth sky revisited
The Galactic Faraday depth sky is a tracer for both the Galactic magnetic
field and the thermal electron distribution. It has been previously
reconstructed from polarimetric measurements of extra-galactic point sources.
Here, we improve on these works by using an updated inference algorithm as well
as by taking into account the free-free emission measure map from the Planck
survey. In the future, the data situation will improve drastically with the
next generation Faraday rotation measurements from SKA and its pathfinders.
Anticipating this, the aim of this paper is to update the map reconstruction
method with the latest development in imaging based on information field
theory. We demonstrate the validity of the new algorithm by applying it to the
Oppermann et al. (2012) data compilation and compare our results to the
previous map.\\ Despite using exactly the previous data set, a number of novel
findings are made: A non-parametric reconstruction of an overall amplitude
field resembles the free-free emission measure map of the Galaxy. Folding this
free-free map into the analysis allows for more detailed predictions. The joint
inference enables us to identify regions with deviations from the assumed
correlations between the free-free and Faraday data, thereby pointing us to
Galactic structures with distinguishably different physics. We e.g. find
evidence for an alignment of the magnetic field within the line of sights along
both directions of the Orion arm.Comment: 16 pages, 15 figure
Estimating extragalactic Faraday rotation
(abridged) Observations of Faraday rotation for extragalactic sources probe
magnetic fields both inside and outside the Milky Way. Building on our earlier
estimate of the Galactic contribution, we set out to estimate the extragalactic
contributions. We discuss the problems involved; in particular, we point out
that taking the difference between the observed values and the Galactic
foreground reconstruction is not a good estimate for the extragalactic
contributions. We point out a degeneracy between the contributions to the
observed values due to extragalactic magnetic fields and observational noise
and comment on the dangers of over-interpreting an estimate without taking into
account its uncertainty information. To overcome these difficulties, we develop
an extended reconstruction algorithm based on the assumption that the
observational uncertainties are accurately described for a subset of the data,
which can overcome the degeneracy with the extragalactic contributions. We
present a probabilistic derivation of the algorithm and demonstrate its
performance using a simulation, yielding a high quality reconstruction of the
Galactic Faraday rotation foreground, a precise estimate of the typical
extragalactic contribution, and a well-defined probabilistic description of the
extragalactic contribution for each data point. We then apply this
reconstruction technique to a catalog of Faraday rotation observations. We vary
our assumptions about the data, showing that the dispersion of extragalactic
contributions to observed Faraday depths is most likely lower than 7 rad/m^2,
in agreement with earlier results, and that the extragalactic contribution to
an individual data point is poorly constrained by the data in most cases.Comment: 20 + 6 pages, 19 figures; minor changes after bug-fix; version
accepted for publication by A&A; results are available at
http://www.mpa-garching.mpg.de/ift/faraday
カイワ ダイアログ アンショウ ニ ジュウジ サセル ガイコクゴ シドウホウ ガ スピーキングジ ノ テイケイ ヒョウゲン ノ シヨウ ト アンキ ガクシュウ ニ オヨボス エイキョウ ニ カンスル キソ ケンキュウ
PDF/A formatsAccess: via World Wide Web東京外国語大学大学院総合国際学研究科博士 (学術) 論文 (2016年4月)Author's thesis (Ph.D)--Tokyo University of Foreign Studies, 2016博甲第214号Bibliography: p. 183-195Summary in English and Japanese東京外国語大学 (Tokyo University of Foreign Studies)博士 (学術
Automatic Detection of Expanding HI Shells Using Artificial Neural Networks
The identification of expanding HI shells is difficult because of their
variable morphological characteristics. The detection of HI bubbles on a global
scale therefore never has been attempted. In this paper, an automatic detector
for expanding HI shells is presented. The detection is based on the more stable
dynamical characteristics of expanding shells and is performed in two stages.
The first one is the recognition of the dynamical signature of an expanding
bubble in the velocity spectra, based on the classification of an artificial
neural network. The pixels associated with these recognized spectra are
identified on each velocity channel. The second stage consists in looking for
concentrations of those pixels that were firstly pointed out, and to decide if
they are potential detections by morphological and 21-cm emission variation
considerations. Two test bubbles are correctly detected and a potentially new
case of shell that is visually very convincing is discovered. About 0.6% of the
surveyed pixels are identified as part of a bubble. These may be false
detections, but still constitute regions of space with high probability of
finding an expanding shell. The subsequent search field is thus significantly
reduced. We intend to conduct in the near future a large scale HI shells
detection over the Perseus Arm using our detector.Comment: 39 pages, 11 figures, accepted by PAS
Hierarchical progressive surveys. Multi-resolution HEALPix data structures for astronomical images, catalogues, and 3-dimensional data cubes
Scientific exploitation of the ever increasing volumes of astronomical data
requires efficient and practical methods for data access, visualisation, and
analysis. Hierarchical sky tessellation techniques enable a multi-resolution
approach to organising data on angular scales from the full sky down to the
individual image pixels. Aims. We aim to show that the Hierarchical progressive
survey (HiPS) scheme for describing astronomical images, source catalogues, and
three-dimensional data cubes is a practical solution to managing large volumes
of heterogeneous data and that it enables a new level of scientific
interoperability across large collections of data of these different data
types. Methods. HiPS uses the HEALPix tessellation of the sphere to define a
hierarchical tile and pixel structure to describe and organise astronomical
data. HiPS is designed to conserve the scientific properties of the data
alongside both visualisation considerations and emphasis on the ease of
implementation. We describe the development of HiPS to manage a large number of
diverse image surveys, as well as the extension of hierarchical image systems
to cube and catalogue data. We demonstrate the interoperability of HiPS and
Multi-Order Coverage (MOC) maps and highlight the HiPS mechanism to provide
links to the original data. Results. Hierarchical progressive surveys have been
generated by various data centres and groups for ~200 data collections
including many wide area sky surveys, and archives of pointed observations.
These can be accessed and visualised in Aladin, Aladin Lite, and other
applications. HiPS provides a basis for further innovations in the use of
hierarchical data structures to facilitate the description and statistical
analysis of large astronomical data sets.Comment: 21 pages, 6 figures. Accepted for publication in Astronomy &
Astrophysic
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