374 research outputs found
Static spectropolarimeter concept adapted to space conditions and wide spectrum constraints
The issues related to moving elements in space and instruments working in
broader wavelength ranges lead to a need for robust polarimeters, efficient on
a wide spectral domain, and adapted to space conditions. As part of the UVMag
consortium, created to develop spectropolarimetric UV facilities in space, such
as the Arago mission project, we present an innovative concept of static
spectropolarimetry. We studied a static and polychromatic method for
spectropolarimetry, applicable to stellar physics. Instead of modulating the
polarization information temporally, as usually done in spectropolarimeters,
the modulation is performed in a spatial direction, orthogonal to the spectral
one. Thanks to the proportionality between phase retardance imposed by a
birefringent material and its thickness, birefringent wedges can be used to
create this spatial modulation. The light is then spectrally cross-dispersed,
and a full-Stokes determination of the polarization over the whole spectrum can
be obtained with a single-shot measurement. The use of Magnesium Fluoride
wedges, for example, could lead to a compact, static polarimeter working at
wavelengths from 0.115 mm up to 7 mm. We present the theory and simulations of
this concept, as well as laboratory validation and a practical application to
Arago.Comment: Article accepted for publication in Applied Optics on 20 July 201
Connectomics-based network analyses and structure-symptom relationships in obsessive-compulsive disorder
Etude et caractérisation d'onde de pression générée par une décharge électrique dans l'eau. Application à la fracturation électrique de roches
Dans de nombreuses régions du monde, d immenses réserves gazéifères dites non conventionnelles sont piégées dans des roches faiblement perméables qui ne peuvent pas être exploitées par des méthodes de forage classiques. Bien que très controversée, la seule méthode d exploitation de ces gisements repose actuellement sur la technique de fracturation hydraulique. Pour ces raisons, une collaboration de recherche a débuté en 2007 entre la société TOTAL et le Laboratoire de Génie Electrique de l université de Pau (récemment devenu le laboratoire SIAME), visant à étudier l opportunité d utiliser la fracturation électrique comme solution alternative à la fracturation hydraulique. Cette méthode repose sur un procédé dynamique de fracturation de la roche par application d une onde de pression créée suite à l initiation d un arc électrique dans un liquide. Ce travail, financé par TOTAL dans le cadre d une bourse CIFRE, s inscrit dans la continuité de travaux déjà engagés sur cette thématique et vise particulièrement à approfondir les connaissances concernant le cœur du procédé de fracturation : la décharge électrique dans l eau et la caractérisation de l onde de pression résultante. Dans cette optique, l importance du circuit et des paramètres électriques de l arc a été démontrée en termes d injection de courant et de transfert de puissance. Une formule empirique permettant de prévoir la valeur de la pression dynamique a, par conséquent, été établie. Afin d optimiser le rendement électro-acoustique, une étude spécifique a été menée sur l effet du mode de rupture diélectrique du fluide. Ces travaux ont également permis de proposer des solutions concernant le contrôle de la dynamique de l onde de pression. Enfin, les effets des propriétés thermodynamiques du fluide sur sa rigidité diélectrique, sur la consommation d énergie, ainsi que sur la propagation de l onde de pression ont été analysés afin d établir une série de conclusions permettant d optimiser le procédé.Numerous parts of the world contain huge unconventional gas reserves which are located in low permeability rocks, and consequently, cannot be produced by classical drilling techniques. Besides its numerous detractors, the only currently available method to exploit these reservoirs relies on hydraulic fracturing. For these reasons, a research collaboration was started in 2007 between the Total Company and the Electrical Engineering Laboratory of Pau university (recently renamed SIAME Laboratory). The main goal was to study the potential concerning the use of the electrical fracturing technique as an alternative to hydraulic fracturing. This method is based on a dynamic rock fracturing process through the applying of a pressure wave enhanced by the generation of an electrical arc into a liquid. This work, which is financed by TOTAL through a CIFRE funding, follows the track initiated on this topic and mainly intends to improve the knowledge concerning the critical part of the fracturing process: the electrical discharge in water and the resulting pressure wave characterization. In this purpose, the importance of the circuit and of the arc electrical parameters was demonstrated in terms of current injection and power transfer. An empirical formula used to predict the dynamic pressure value has consequently been established. In order to optimize the electro acoustic efficiency, a specific study was performed on the liquid dielectric breakdown modus. This work allowed us to suggest new solutions concerning the dynamic pressure wave control. Finally, the fluid thermodynamic properties effects on its dielectric strength, on the energy consumption, and on the pressure wave propagation were analyzed in order to draw conclusions for the process optimization.PAU-BU Sciences (644452103) / SudocSudocFranceF
The Mid-Infrared Instrument for the James Webb Space Telescope, V: Predicted Performance of the MIRI Coronagraphs
The imaging channel on the Mid-Infrared Instrument (MIRI) is equipped with
four coronagraphs that provide high contrast imaging capabilities for studying
faint point sources and extended emission that would otherwise be overwhelmed
by a bright point-source in its vicinity. Such bright sources might include
stars that are orbited by exoplanets and circumstellar material, mass-loss
envelopes around post-main-sequence stars, the near-nuclear environments in
active galaxies, and the host galaxies of distant quasars. This paper describes
the coronagraphic observing modes of MIRI, as well as performance estimates
based on measurements of the MIRI flight model during cryo-vacuum testing. A
brief outline of coronagraphic operations is also provided. Finally, simulated
MIRI coronagraphic observations of a few astronomical targets are presented for
illustration
NLRP3 E311K mutation in a large family with Muckle-Wells syndrome - description of a heterogeneous phenotype and response to treatment
The Mid-Infrared Instrument for the James Webb Space Telescope, III: MIRIM, The MIRI Imager
In this article, we describe the MIRI Imager module (MIRIM), which provides
broad-band imaging in the 5 - 27 microns wavelength range for the James Webb
Space Telescope. The imager has a 0"11 pixel scale and a total unobstructed
view of 74"x113". The remainder of its nominal 113"x113" field is occupied by
the coronagraphs and the low resolution spectrometer. We present the instrument
optical and mechanical design. We show that the test data, as measured during
the test campaigns undertaken at CEA-Saclay, at the Rutherford Appleton
Laboratory, and at the NASA Goddard Space Flight Center, indicate that the
instrument complies with its design requirements and goals. We also discuss the
operational requirements (multiple dithers and exposures) needed for optimal
scientific utilization of the MIRIM.Comment: 29 pages, 9 figure
Functional and structural connectivity of the amygdala in obsessive-compulsive disorder
Background: The amygdala is known to be involved in anxiety processing, but its role in the psychopathology of obsessive-compulsive disorder (OCD) is still unclear. Aims: In this MRI study we investigated potential alterations in structural and functional connectivity of the amygdala in 42 adult patients with OCD and 37 healthy subjects. Method: Psychophysiological interaction analysis was used to explore amygdala functional connectivity during a negative affective task. Probabilistic tractography was then employed to study structural connectivity and integrity of underlying white matter fiber tracts. Results: Compared to controls, OCD patients showed a significantly increased functional connectivity of the left amygdala with mostly parieto-occipital regions during task. No structural connectivity differences could be found between the groups. In addition, only patients showed a significant association between functional and structural connectivity of these regions. Moreover, symptom severity was negatively associated with structural integrity of the underlying white matter tracts. Conclusions: Present results emphasize the relevance of the amygdala for OCD and may reflect that neuronal alterations in structural connectivity could be associated with functional connectivity alterations in broader networks. (C) 2016 The Authors. Published by Elsevier Inc
Current results of the PERSEE testbench: the cophasing control and the polychromatic null rate
Stabilizing a nulling interferometer at a nanometric level is the key issue
to obtain deep null depths. The PERSEE breadboard has been designed to study
and optimize the operation of a cophased nulling bench in the most realistic
disturbing environment of a space mission. This presentation focuses on the
current results of the PERSEE bench. In terms of metrology, we cophased at 0.33
nm rms for the piston and 80 mas rms for the tip/tilt (0.14% of the Airy disk).
A Linear Quadratic Gaussian (LQG) control coupled with an unsupervised
vibration identification allows us to maintain that level of correction, even
with characteristic vibrations of nulling interferometry space missions. These
performances, with an accurate design and alignment of the bench, currently
lead to a polychromatic unpolarised null depth of 8.9E-6 stabilized at 3E-7 on
the [1.65-2.45] \mum spectral band (37% bandwidth).Comment: 17 pages, 10 figures, proceedings of the Optics+Photonics SPIE
conference, San Diego, 201
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