218 research outputs found
Modeling a Slicer Mirror Using Zemax User-Defined Surface
A slicer mirror is a complex surface composed by many tilted and decentered
mirrors sub-surfaces. The major difficulty to model such a complex surface is
the large number of parameters used to define it. The Zemax's
multi-configuration mode is usually used to specify each parameters (tilts,
curvatures, decenters) for each mirror sub-surface which are then considered
independently. Otherwise making use of the User-Defined Surface (UDS-DLL) Zemax
capability, we are able to consider the set of sub-surfaces as a whole surface.
In this paper, we present such a UDS-DLL tool comparing its performance with
those of the classical multi-configuration mode. In particular, we explore the
use of UDS-DLL to investigate the cross-talk due to the diffraction on the
slicer array mirrors which has been a burden task when using
multi-configuration mode.Comment: Submitted to the proceedings of the Durham Integral Field
Spectroscopy Workshop July 4th-8th 200
Divergent Roles for M4 in the Gating of Two Prokaryotic Pentameric Ligand-Gated Ion Channels
Parametric Inversion of Brillouin spectra using L-curve criterion to enhance the accuracy of distributed strain measurement
International audienceTo ensure stability and durability of engineering structure in natural soil, optical fiber sensors have gained interest over last decade. In addition to conventional geophysical sensors, Brillouin spectra based sensor enables to perform distributed strain measurement. Its algorithm performs a strain measurement with a 40cm spatial sampling over several kilometers. The monitoring of engineering installations needs a centimeter spatial sampling and a better strain accuracy. Previous works highlighted that the industrialized algorithm has great limitation for the exploitation of the local information contained into Brillouin spectra. Indeed, based on its asymmetry and broadening, it is possible to estimate local Brillouin frequencies with a better strain accuracy. We propose here to apply a parametric inverse method using L-curve criterion to estimate the strain with a 5cm spatial sampling. To validate this method, a one-to-one scale experiment has been implemented by optical fiber cable at several depths. Comparing the distributed strain provided by the Brillouin based sensor and our algorithm with a reference strain sensor, the proposed algorithm successfully fulfills the combination of a 5cm spatial sampling over kilometers and a high strain accuracy
First experimental results of very high accuracy centroiding measurements for the neat astrometric mission
NEAT is an astrometric mission proposed to ESA with the objectives of
detecting Earth-like exoplanets in the habitable zone of nearby solar-type
stars. NEAT requires the capability to measure stellar centroids at the
precision of 5e-6 pixel. Current state-of-the-art methods for centroid
estimation have reached a precision of about 2e-5 pixel at two times Nyquist
sampling, this was shown at the JPL by the VESTA experiment. A metrology system
was used to calibrate intra and inter pixel quantum efficiency variations in
order to correct pixelation errors. The European part of the NEAT consortium is
building a testbed in vacuum in order to achieve 5e-6 pixel precision for the
centroid estimation. The goal is to provide a proof of concept for the
precision requirement of the NEAT spacecraft. In this paper we present the
metrology and the pseudo stellar sources sub-systems, we present a performance
model and an error budget of the experiment and we report the present status of
the demonstration. Finally we also present our first results: the experiment
had its first light in July 2013 and a first set of data was taken in air. The
analysis of this first set of data showed that we can already measure the pixel
positions with an accuracy of about 1e-4 pixel.Comment: SPIE conference proceeding
A detector interferometric calibration experiment for high precision astrometry
Context: Exoplanet science has made staggering progress in the last two
decades, due to the relentless exploration of new detection methods and
refinement of existing ones. Yet astrometry offers a unique and untapped
potential of discovery of habitable-zone low-mass planets around all the
solar-like stars of the solar neighborhood. To fulfill this goal, astrometry
must be paired with high precision calibration of the detector.
Aims: We present a way to calibrate a detector for high accuracy astrometry.
An experimental testbed combining an astrometric simulator and an
interferometric calibration system is used to validate both the hardware needed
for the calibration and the signal processing methods. The objective is an
accuracy of 5e-6 pixel on the location of a Nyquist sampled polychromatic point
spread function.
Methods: The interferometric calibration system produced modulated Young
fringes on the detector. The Young fringes were parametrized as products of
time and space dependent functions, based on various pixel parameters. The
minimization of func- tion parameters was done iteratively, until convergence
was obtained, revealing the pixel information needed for the calibration of
astrometric measurements.
Results: The calibration system yielded the pixel positions to an accuracy
estimated at 4e-4 pixel. After including the pixel position information, an
astrometric accuracy of 6e-5 pixel was obtained, for a PSF motion over more
than five pixels. In the static mode (small jitter motion of less than 1e-3
pixel), a photon noise limited precision of 3e-5 pixel was reached
USING INTERNATIONAL CLASSIFICATION OF DISEASES NINTH REVISION CODES OVERESTIMATES THE FREQUENCY OF TRUE STROKE
NectarCAM : a camera for the medium size telescopes of the Cherenkov Telescope Array
NectarCAM is a camera proposed for the medium-sized telescopes of the
Cherenkov Telescope Array (CTA) covering the central energy range of ~100 GeV
to ~30 TeV. It has a modular design and is based on the NECTAr chip, at the
heart of which is a GHz sampling Switched Capacitor Array and a 12-bit Analog
to Digital converter. The camera will be equipped with 265 7-photomultiplier
modules, covering a field of view of 8 degrees. Each module includes the
photomultiplier bases, high voltage supply, pre-amplifier, trigger, readout and
Ethernet transceiver. The recorded events last between a few nanoseconds and
tens of nanoseconds. The camera trigger will be flexible so as to minimize the
read-out dead-time of the NECTAr chips. NectarCAM is designed to sustain a data
rate of more than 4 kHz with less than 5\% dead time. The camera concept, the
design and tests of the various subcomponents and results of thermal and
electrical prototypes are presented. The design includes the mechanical
structure, cooling of the electronics, read-out, clock distribution, slow
control, data-acquisition, triggering, monitoring and services.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
3-D deconvolution of hyper-spectral astronomical data
In this paper we present a general forward fitting method for multichannel
image restoration based on regularized chi2. We introduce separable
regularizations that account for the dynamic of the model and take advantage of
the continuities present in the data, leaving only two hyper-parameters to
tune. We illustrate a practical implementation of this method in the context of
host galaxy subtraction for the Nearby SuperNova factory. We show that the
image restoration obtained fulfills the stringent requirements on bias and
photometricity needed by this program. The reconstruction yields sub-percent
integrated residuals in all the synthetic filters considered both on real and
simulated data. Even though our implementation is tied to the SNfactory data,
the method translates to any hyper-spectral data. As such, it is of direct
relevance to several new generation instruments like MUSE. Also, this technique
could be applied to multi-band astronomical imaging for which image
reconstruction is important, for example to increase image resolution for weak
lensing surveys.Comment: 14 pages, 12 figures, 3 tables. Accepted for publication in MNRA
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