240,613 research outputs found
Automated Optical Inspection and Image Analysis of Superconducting Radio-Frequency Cavities
The inner surface of superconducting cavities plays a crucial role to achieve
highest accelerating fields and low losses. For an investigation of this inner
surface of more than 100 cavities within the cavity fabrication for the
European XFEL and the ILC HiGrade Research Project, an optical inspection robot
OBACHT was constructed. To analyze up to 2325 images per cavity, an image
processing and analysis code was developed and new variables to describe the
cavity surface were obtained. The accuracy of this code is up to 97% and the
PPV 99% within the resolution of 15.63 . The optical obtained
surface roughness is in agreement with standard profilometric methods. The
image analysis algorithm identified and quantified vendor specific fabrication
properties as the electron beam welding speed and the different surface
roughness due to the different chemical treatments. In addition, a correlation
of with a significance of between an obtained
surface variable and the maximal accelerating field was found
The Effect of Unresolved Contaminant Stars on the Cross-Matching of Photometric Catalogues
A fundamental process in astrophysics is the matching of two photometric
catalogues. It is crucial that the correct objects be paired, and that their
photometry does not suffer from any spurious additional flux. We compare the
positions of sources in WISE, IPHAS, 2MASS, and APASS with Gaia DR1 astrometric
positions. We find that the separations are described by a combination of a
Gaussian distribution, wider than naively assumed based on their quoted
uncertainties, and a large wing, which some authors ascribe to proper motions.
We show that this is caused by flux contamination from blended stars not
treated separately. We provide linear fits between the quoted Gaussian
uncertainty and the core fit to the separation distributions.
We show that at least one in three of the stars in the faint half of a given
catalogue will suffer from flux contamination above the 1% level when the
density of catalogue objects per PSF area is above approximately 0.005. This
has important implications for the creation of composite catalogues. It is
important for any closest neighbour matches as there will be a given fraction
of matches that are flux contaminated, while some matches will be missed due to
significant astrometric perturbation by faint contaminants. In the case of
probability-based matching, this contamination affects the probability density
function of matches as a function of distance. This effect results in up to 50%
fewer counterparts being returned as matches, assuming Gaussian astrometric
uncertainties for WISE-Gaia matching in crowded Galactic plane regions,
compared with a closest neighbour match.Comment: 10 pages, 6 figures; accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
The Munich Near-Infrared Cluster Survey (MUNICS) -- II. The K-Band Luminosity Function of Field Galaxies to z ~ 1.2
(Abriged) We present a measurement of the evolution of the rest-frame K-band
luminosity function to z ~ 1.2 using a sample of more than 5000 K-selected
galaxies drawn from the MUNICS dataset. Distances and absolute K-band
magnitudes are derived using photometric redshifts from spectral energy
distribution fits to BVRIJK photometry. These are calibrated using >500
spectroscopic redshifts. We obtain redshift estimates having a rms scatter of
0.055 and no mean bias. We use Monte-Carlo simulations to investigate the
influence of the errors in distance associated with photometric redshifts on
our ability to reconstruct the shape of the luminosity function. Finally, we
construct the rest-frame K-band LF in four redshift bins spanning 0.4<z<1.2 and
compare our results to the local luminosity function. We discuss and apply two
different estimators to derive likely values for the evolution of the number
density, Phi*, and characteristic luminosity, M*, with redshift. While the
first estimator relies on the value of the luminosity function binned in
magnitude and redshift, the second estimator uses the individually measured
{M,z} pairs alone. In both cases we obtain a mild decrease in number density by
\~ 25% to z=1 accompanied by brightening of the galaxy population by 0.5 to 0.7
mag. These results are fully consistent with an analogous analysis using only
the spectroscopic MUNICS sample. The total K-band luminosity density is found
to scale as dlog(rho_L)/dz = 0.24. We discuss possible sources of systematic
errors and their influence on our parameter estimates.Comment: Accepted for publication in Ap
A Measurement of Newton's Gravitational Constant
A precision measurement of the gravitational constant has been made using
a beam balance. Special attention has been given to determining the
calibration, the effect of a possible nonlinearity of the balance and the
zero-point variation of the balance. The equipment, the measurements and the
analysis are described in detail. The value obtained for G is 6.674252(109)(54)
10^{-11} m3 kg-1 s-2. The relative statistical and systematic uncertainties of
this result are 16.3 10^{-6} and 8.1 10^{-6}, respectively.Comment: 26 pages, 20 figures, Accepted for publication by Phys. Rev.
Photometric Selection of QSO Candidates From GALEX Sources
We present a catalog of 36,120 QSO candidates from the Galaxy Evolution
Explorer (GALEX) Release Two (GR2) UV catalog and the USNO-A2.0 optical
catalog. The selection criteria are established using known quasars from the
Sloan Digital Sky Survey (SDSS). The SDSS sample is then used to assign
individual probabilities to our GALEX-USNO candidates. The mean probability is
~50%, and would rise to ~65% if better morphological information than that from
USNO were available to eliminate galaxies. The sample is ~40% complete for
i<=19.1. Candidates are cross-identified in 2MASS, FIRST, SDSS, and XMM-Newton
Slewing Survey (XMMSL1), whenever such counterparts exist. The present catalog
covers the 8000 square degrees of GR2 lying above 25 degrees Galactic latitude,
but can be extended to all 24,000 square degress that satisfy this criterion as
new GALEX data become available.Comment: AASTeX v5.2, 31 pages, 9 figures. Accepted for publication in ApJ.
Extended tables available in the online edition of the journa
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