9,893 research outputs found
A fast 2D image reconstruction algorithm from 1D data for the Gaia mission
A fast 2-dimensional image reconstruction method is presented, which takes as
input 1-dimensional data acquired from scans across a central source in
different orientations. The resultant reconstructed images do not show
artefacts due to non-uniform coverage in the orientations of the scans across
the central source, and are successful in avoiding a high background due to
contamination of the flux from the central source across the reconstructed
image. Due to the weighting scheme employed this method is also naturally
robust to hot pixels. This method was developed specifically with Gaia data in
mind, but should be useful in combining data with mismatched resolutions in
different directions.Comment: accepted (18 pages, 13 figures) will appear in Experimental Astronom
Validation of the new Hipparcos reduction
Context.A new reduction of the astrometric data as produced by the Hipparcos
mission has been published, claiming accuracies for nearly all stars brighter
than magnitude Hp = 8 to be better, by up to a factor 4, than in the original
catalogue. Aims.The new Hipparcos astrometric catalogue is checked for the
quality of the data and the consistency of the formal errors as well as the
possible presence of error correlations. The differences with the earlier
publication are explained. Methods. The internal errors are followed through
the reduction process, and the external errors are investigated on the basis of
a comparison with radio observations of a small selection of stars, and the
distribution of negative parallaxes. Error correlation levels are investigated
and the reduction by more than a factor 10 as obtained in the new catalogue is
explained. Results.The formal errors on the parallaxes for the new catalogue
are confirmed. The presence of a small amount of additional noise, though
unlikely, cannot be ruled out. Conclusions. The new reduction of the Hipparcos
astrometric data provides an improvement by a factor 2.2 in the total weight
compared to the catalogue published in 1997, and provides much improved data
for a wide range of studies on stellar luminosities and local galactic
kinematics.Comment: 12 pages, 19 figures, accepted for publication by Astronomy and
Astrophysic
Severe Language Effect in University Rankings: Particularly Germany and France are wronged in citation-based rankings
We applied a set of standard bibliometric indicators to monitor the
scientific state-of-arte of 500 universities worldwide and constructed a
ranking on the basis of these indicators (Leiden Ranking 2010). We find a
dramatic and hitherto largely underestimated language effect in the
bibliometric, citation-based measurement of research performance when comparing
the ranking based on all Web of Science (WoS) covered publications and on only
English WoS covered publications, particularly for Germany and France.Comment: Short communication, 3 pages, 4 figure
The Geometric Calibration of the Planck satellite using point-source observations
The geometric calibration of the Planck satellite is investigated,
specifically those parameters which require the use of the science data for
their extraction. Methods for the recovery of these geometric-calibration
parameters from point source detections in the science data are presented,
together with the accuracies which may be achieved. These methods apply to the
a posteriori evaluation of these parameters using all the mission data, and may
be incorporated into the initial stages of the construction of the Planck final
compact source catalogue. It is found that this process achieves the pointing
requirements, provided that the geometric-calibration parameters vary only
slowly in time. Indeed the errors in the pointing reconstruction due to the
geometric calibration parameters may be seen to approach those due to the star
tracker.Comment: 11 pages, 10 figures, Accepted for publication by MNRA
Optimizing point-source parameters for scanning satellite surveys
We describe a method for deriving the position and flux of point and compact
sources observed by a scanning survey mission. Results from data simulated to
test our method are presented, which demonstrate that at least a 10-fold
improvement is achievable over that of extracting the image parameters,
position and flux, from the equivalent data in the form of pixel maps. Our
method achieves this improvement by analysing the original scan data and
performing a combined, iterative solution for the image parameters. This
approach allows for a full and detailed account of the point-spread function,
or beam profile, of the instrument. Additionally, the positional information
from different frequency channels may be combined to provide the flux-detection
accuracy at each frequency for the same sky position. Ultimately, a final check
and correction of the geometric calibration of the instrument may also be
included. The {\it Planck} mission was used as the basis for our simulations,
but our method will be beneficial for most scanning satellite missions,
especially those with non-circularly symmetric point-spread functions.Comment: 13 pages, 14 figures, 3 tables, accepted for publication by MNRA
SiON integrated optics elliptic couplers for Fizeau-based Optical Coherence Tomography
The use of integrated optics for Optical Coherence Tomography (OCT) can offer significant cost reductions and new applications. We designed, fabricated, and characterized Silicon oxynitride (SiON) elliptic couplers that are used to focus light from a chip into the off-chip environment. Fizeau-based OCT measurements are performed and compared to calculations
Особливості формування етнічного складу селянської верстви Степового Побужжя
In this short paper we sketch a brief introduction to our Krimp algorithm. Moreover, we briefly discuss some of the large body of follow up research. Pointers to the relevant papers are provided in the bibliography
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