119,052 research outputs found
Principal Component Analysis of Cavity Beam Position Monitor Signals
Model-independent analysis (MIA) methods are generally useful for analysing
complex systems in which relationships between the observables are non-trivial
and noise is present. Principle Component Analysis (PCA) is one of MIA methods
allowing to isolate components in the input data graded to their contribution
to the variability of the data. In this publication we show how the PCA can be
applied to digitised signals obtained from a cavity beam position monitor
(CBPM) system on the example of a 3-cavity test system installed at the
Accelerator Test Facility 2 (ATF2) at KEK in Japan. We demonstrate that the PCA
based method can be used to extract beam position information, and matches
conventional techniques in terms of performance, while requiring considerably
less settings and data for calibration
Calibration and Sensitivity Analysis of a Stereo Vision-Based Driver Assistance System
Az http://intechweb.org/ alatti "Books" fül alatt kell rákeresni a "Stereo Vision" címre és az 1. fejezetre
A reanalysis of the Gaia Data Release 2 photometric sensitivity curves using HST/STIS spectrophotometry
CONTEXT: The second Gaia data release (DR2) took place on April 2018. DR2
included photometry for more than 1.3 10^9 sources in G, BP, and RP. Even
though Gaia DR2 photometry is very precise, there are currently three
alternative definitions of the sensitivity curves that show significative
differences. AIMS: The aim of this paper is to improve the quality of the input
calibration data to produce new compatible definitions of the three bands and
to identify the reasons for the discrepancies between previous definitions.
METHODS: We have searched the HST archive for STIS spectra with G430L+G750L
data obtained with wide apertures and combined them with the CALSPEC library to
produce a high quality SED library of 122 stars with a broad range of colors,
including three very red stars. We have used it to compute new sensitivity
curves for G, BP, and RP using a functional analytical formalism. RESULTS: The
new curves are significantly better than the two previous attempts, REV and
WEI. For G we confirm the existence of a systematic bias in magnitude and
correct a color term present in REV. For BP we confirm the need to define two
magnitude ranges with different sensitivity curves and measure the cut between
them at G = 10.87 with a significant increase in precision. The new curves also
fit the data better than either REV or WEI. For RP we obtain a sensitivity
curve that better fits the STIS spectra and we find that the differences with
previous attempts reside in a systematic effect between ground-based and HST
spectral libraries. Additional evidence from color-color diagrams indicate that
the new sensitivity curve is more accurate. Nevertheless, there is still room
for improvement in the accuracy of the sensitivity curves because of the
current dearth of good-quality red calibrators: adding more to the sample
should be a priority before Gaia data release 3 takes place.Comment: Accepted for publication in A&A, revised version with minor change
CalFUSE v3: A Data-Reduction Pipeline for the Far Ultraviolet Spectroscopic Explorer
Since its launch in 1999, the Far Ultraviolet Spectroscopic Explorer (FUSE)
has made over 4600 observations of some 2500 individual targets. The data are
reduced by the Principal Investigator team at the Johns Hopkins University and
archived at the Multimission Archive at Space Telescope (MAST). The
data-reduction software package, called CalFUSE, has evolved considerably over
the lifetime of the mission. The entire FUSE data set has recently been
reprocessed with CalFUSE v3.2, the latest version of this software. This paper
describes CalFUSE v3.2, the instrument calibrations upon which it is based, and
the format of the resulting calibrated data files.Comment: To appear in PASP; 29 pages, 13 figures, uses aastex, emulateap
The Murchison Widefield Array: Design Overview
The Murchison Widefield Array (MWA) is a dipole-based aperture array
synthesis telescope designed to operate in the 80-300 MHz frequency range. It
is capable of a wide range of science investigations, but is initially focused
on three key science projects. These are detection and characterization of
3-dimensional brightness temperature fluctuations in the 21cm line of neutral
hydrogen during the Epoch of Reionization (EoR) at redshifts from 6 to 10,
solar imaging and remote sensing of the inner heliosphere via propagation
effects on signals from distant background sources,and high-sensitivity
exploration of the variable radio sky. The array design features 8192
dual-polarization broad-band active dipoles, arranged into 512 tiles comprising
16 dipoles each. The tiles are quasi-randomly distributed over an aperture
1.5km in diameter, with a small number of outliers extending to 3km. All
tile-tile baselines are correlated in custom FPGA-based hardware, yielding a
Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point
spread function (PSF) quality. The correlated data are calibrated in real time
using novel position-dependent self-calibration algorithms. The array is
located in the Murchison region of outback Western Australia. This region is
characterized by extremely low population density and a superbly radio-quiet
environment,allowing full exploitation of the instrumental capabilities.Comment: 9 pages, 5 figures, 1 table. Accepted for publication in Proceedings
of the IEE
Good practice guide for calibrating a hydrophone "in situ" with a non-omnidirectional source at 10 kHz (26-34)
The aim of this paper is to provide the basis for the calibration of a hydrophonePeer ReviewedPostprint (published version
The Herschel-SPIRE instrument and its in-flight performance
The Spectral and Photometric Imaging REceiver (SPIRE), is the Herschel Space Observatory`s submillimetre camera and spectrometer. It contains a three-band imaging photometer operating at 250, 350 and 500 μm, and an imaging Fourier-transform spectrometer (FTS) which covers simultaneously its whole operating range of 194–671 μm (447–1550 GHz). The SPIRE detectors are arrays of feedhorn-coupled bolometers cooled to 0.3 K. The photometer has a field of view of 4´× 8´, observed simultaneously in the three spectral bands. Its main operating mode is scan-mapping, whereby the field of view is scanned across the sky to achieve full spatial sampling and to cover large areas if desired. The spectrometer has an approximately circular field of view with a diameter of 2.6´. The spectral resolution can be adjusted between 1.2 and 25 GHz by changing the stroke length of the FTS scan mirror. Its main operating mode involves a fixed telescope pointing with multiple scans of the FTS mirror to acquire spectral data. For extended source measurements, multiple position offsets are implemented by means of an internal beam steering mirror to achieve the desired spatial sampling and by rastering of the telescope pointing to map areas larger than the field of view. The SPIRE instrument consists of a cold focal plane unit located inside the Herschel cryostat and warm electronics units, located on the spacecraft Service Module, for instrument control and data handling. Science data are transmitted to Earth with no on-board data compression, and processed by automatic pipelines to produce calibrated science products. The in-flight performance of the instrument matches or exceeds predictions based on pre-launch testing and modelling: the photometer sensitivity is comparable to or slightly better than estimated pre-launch, and the spectrometer sensitivity is also better by a factor of 1.5–2
The VLA Low-frequency Sky Survey
The Very Large Array (VLA) Low-frequency Sky Survey (VLSS) has imaged 95% of
the 3*pi sr of sky north of declination = -30 degrees at a frequency of 74 MHz
(4 meter wavelength). The resolution is 80" (FWHM) throughout, and the typical
RMS noise level is ~0.1 Jy/beam. The typical point-source detection limit is
0.7 Jy/beam and so far nearly 70,000 sources have been catalogued. This survey
used the 74 MHz system added to the VLA in 1998. It required new imaging
algorithms to remove the large ionospheric distortions at this very low
frequency throughout the entire ~11.9 degree field of view. This paper
describes the observation and data reduction methods used for the VLSS and
presents the survey images and source catalog. All of the calibrated images and
the source catalog are available online (http://lwa.nrl.navy.mil/VLSS) for use
by the astronomical community.Comment: 53 pages, including 3 tables and 15 figures. Has been accepted for
publication in the Astronomical Journa
The Maunakea Spectroscopic Explorer Book 2018
(Abridged) This is the Maunakea Spectroscopic Explorer 2018 book. It is
intended as a concise reference guide to all aspects of the scientific and
technical design of MSE, for the international astronomy and engineering
communities, and related agencies. The current version is a status report of
MSE's science goals and their practical implementation, following the System
Conceptual Design Review, held in January 2018. MSE is a planned 10-m class,
wide-field, optical and near-infrared facility, designed to enable
transformative science, while filling a critical missing gap in the emerging
international network of large-scale astronomical facilities. MSE is completely
dedicated to multi-object spectroscopy of samples of between thousands and
millions of astrophysical objects. It will lead the world in this arena, due to
its unique design capabilities: it will boast a large (11.25 m) aperture and
wide (1.52 sq. degree) field of view; it will have the capabilities to observe
at a wide range of spectral resolutions, from R2500 to R40,000, with massive
multiplexing (4332 spectra per exposure, with all spectral resolutions
available at all times), and an on-target observing efficiency of more than
80%. MSE will unveil the composition and dynamics of the faint Universe and is
designed to excel at precision studies of faint astrophysical phenomena. It
will also provide critical follow-up for multi-wavelength imaging surveys, such
as those of the Large Synoptic Survey Telescope, Gaia, Euclid, the Wide Field
Infrared Survey Telescope, the Square Kilometre Array, and the Next Generation
Very Large Array.Comment: 5 chapters, 160 pages, 107 figure
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