83 research outputs found
Influence of different dry milling processes on the properties of an attapulgite clay, contribution of inverse gas chromatography
Attention, cette publication comporte un corrigendum.International audienceThe effect of dry milling processes on the surface properties of an attapulgite clay, also called palygorskite, was investigated by carrying out experiments with different types of grinding devices. Ground products were then characterized by size measurement, scanning electron microscopy, X-ray diffraction, adsorption-desorption of N-2 and inverse gas chromatography at infinite dilution (IGC-ID) as well as finite concentration conditions (IGC-PC). These analyses were performed to evaluate the changes in particle size distribution, morphology, crystallinity and surface properties of attapulgite powder, respectively. Among the tested dry grinding devices, grinding in an air jet mill (Alpine 50 AS) and a vibratory ball mill (Pulverisette 0) led to the most significant particle size reduction. SEM photomicrographs showed that a breakage of the fibrous structure took place during dry grinding. Moreover, long grinding in Pulverisette 0 resulted in the complete destruction of fibre morphology followed by agglomeration. XRD analysis showed that whatever the grinding process, the microstructure of the attapulgite was not affected. IGC confirmed that only grinding in Pulverisette 0 affected the surface properties notably. In this case, the most significant decreases were observed in the dispersive component of the surface energy (164 to 116 mJ/m(2)) and in the specific surface area obtained with the octane probe (114.5 m(2)/g to 62.6 m(2)/g) by IGC-ID and IGC-FC, respectively. At the same time, a modification of the distribution functions of the adsorption energies (DFAE), giving information about surface heterogeneity, was noticed
Spiral inflow feeding the nuclear starburst in M83, observed in H-alpha emission with the GHAFAS Fabry-Perot interferometer
We present observations of the nearby barred starburst galaxy, M83 (NGC5236),
with the new Fabry-Perot interferometer GHAFAS mounted on the 4.2 meter William
Herschel Telescope on La Palma. The unprecedented high resolution observations,
of 16 pc/FWHM, of the H-alpha-emitting gas cover the central two kpc of the
galaxy. The velocity field displays the dominant disk rotation with signatures
of gas inflow from kpc scales down to the nuclear regions. At the inner Inner
Lindblad Resonance radius of the main bar and centerd at the dynamical center
of the main galaxy disk, a nuclear rapidly
rotating disk with scale length of pc has formed. The nuclear
starburst is found in the vicinity as well as inside this nuclear disk, and our
observations confirm that gas spirals in from the outer parts to feed the
nuclear starburst, giving rise to several star formation events at different
epochs, within the central 100 pc radius of M83.Comment: Accepted for publication in ApJ Letters. High-resolution version can
be found at http://www.astro.su.se/~kambiz/DOC/paper-M83.pd
First light of VLT/HiRISE: High-resolution spectroscopy of young giant exoplanets
A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed to leverage the capabilities of existing instruments that offer either high-contrast imaging or high-dispersion spectroscopy by coupling them using optical fibers. In this work, we present the implementation and first on-sky results of the High-Resolution Imaging and Spectroscopy of Exoplanets (HiRISE) instrument at the Very Large Telescope (VLT), which combines the exoplanet imager SPHERE with the recently upgraded high-resolution spectrograph CRIRES using single-mode fibers. The goal of HiRISE is to enable the characterization of known companions in the H band at a spectral resolution on the order of R = λ/âλ = 100 000 in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak value of ~3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to illustrate its potential
First light of VLT/HiRISE: High-resolution spectroscopy of young giant exoplanets
A major endeavor of this decade is the direct characterization of young giant
exoplanets at high spectral resolution to determine the composition of their
atmosphere and infer their formation processes and evolution. Such a goal
represents a major challenge owing to their small angular separation and
luminosity contrast with respect to their parent stars. Instead of designing
and implementing completely new facilities, it has been proposed to leverage
the capabilities of existing instruments that offer either high contrast
imaging or high dispersion spectroscopy, by coupling them using optical fibers.
In this work we present the implementation and first on-sky results of the
HiRISE instrument at the very large telescope (VLT), which combines the
exoplanet imager SPHERE with the recently upgraded high resolution spectrograph
CRIRES using single-mode fibers. The goal of HiRISE is to enable the
characterization of known companions in the band, at a spectral resolution
of the order of , in a few hours of
observing time. We present the main design choices and the technical
implementation of the system, which is constituted of three major parts: the
fiber injection module inside of SPHERE, the fiber bundle around the telescope,
and the fiber extraction module at the entrance of CRIRES. We also detail the
specific calibrations required for HiRISE and the operations of the instrument
for science observations. Finally, we detail the performance of the system in
terms of astrometry, temporal stability, optical aberrations, and transmission,
for which we report a peak value of 3.9% based on sky measurements in
median observing conditions. Finally, we report on the first astrophysical
detection of HiRISE to illustrate its potential.Comment: 17 pages, 15 figures, 3 tables. Submitted to A&A on 19 September 202
Emission of volatile halogenated compounds, speciation and localization of bromine and iodine in the brown algal genome model Ectocarpus siliculosus
This study explores key features of bromine and iodine metabolism in the filamentous brown alga and genomics model Ectocarpus siliculosus. Both elements are accumulated in Ectocarpus, albeit at much lower concentration factors (2-3 orders of magnitude for iodine, and <Â 1 order of magnitude for bromine) than e.g. in the kelp Laminaria digitata. Iodide competitively reduces the accumulation of bromide. Both iodide and bromide are accumulated in the cell wall (apoplast) of Ectocarpus, with minor amounts of bromine also detectable in the cytosol. Ectocarpus emits a range of volatile halogenated compounds, the most prominent of which by far is methyl iodide. Interestingly, biosynthesis of this compound cannot be accounted for by vanadium haloperoxidase since the latter have not been found to catalyze direct halogenation of an unactivated methyl group or hydrocarbon so a methyl halide transferase-type production mechanism is proposed
Prime Focus Spectrograph (PFS) for the Subaru telescope: Ongoing integration and future plans
PFS (Prime Focus Spectrograph), a next generation facility instrument on the 8.2-meter Subaru Telescope, is a very wide-field, massively multiplexed, optical and near-infrared spectrograph. Exploiting the Subaru prime focus, 2394 reconfigurable fibers will be distributed over the 1.3 deg field of view. The spectrograph has been designed with 3 arms of blue, red, and near-infrared cameras to simultaneously observe spectra from 380nm to 1260nm in one exposure at a resolution of ⌠1.6-2.7Ă
. An international collaboration is developing this instrument under the initiative of Kavli IPMU. The project recently started undertaking the commissioning process of a subsystem at the Subaru Telescope side, with the integration and test processes of the other subsystems ongoing in parallel. We are aiming to start engineering night-sky operations in 2019, and observations for scientific use in 2021. This article gives an overview of the instrument, current project status and future paths forward
Ătude de lâoxydation photoinduite dâalcools normaux et ramifiĂ©s chimisorbĂ©s en surface dâune alumine Îł
Lâoxydation photoinduite dâalcools chimisorbĂ©s en surface dâune alumine y est Ă©tudiĂ©e en fonction de diffĂ©rents paramĂštres de la source dâirradiation â longueur dâonde, intensitĂ© â du degrĂ© de branchement et de la longueur de la chaĂźne des alcools chimisorbĂ©s ainsi que de la pression dâoxygĂšne.LâĂ©tude par spectroscopie infrarouge et par microgravimĂ©trie de lâĂ©volution de ces solides sous irradiation prouve que la prĂ©sence dâoxygĂšne est nĂ©cessaire.A des longueurs dâonde supĂ©rieures Ă 300 nm, il est observĂ© la transformation simple de lâalcoolate en cĂ©tone pour les alcools secondaires et en carboxylates superficiels pour les alcools primaires.Une Ă©quation cinĂ©tique du premier ordre par rapport au nombre de photons absorbĂ©s, permet de rendre-compte de la vitesse dâapparition de ces carboxylates superficiels. Un schĂ©ma rĂ©actionnel est proposĂ© dans lequel les alcools chimisorbĂ©s agissent comme des piĂšges des radicaux anions oxygĂ©nĂ©s qui rĂ©sultent de lâinteraction de lâoxygĂšne avec les Ă©lectrons de la bande de conduction.A des longueurs dâonde plus courtes que 300 nm, un processus de dĂ©gradation plus complexe est observĂ© qui est dĂ» certainement Ă la superposition de phĂ©nomĂšnes photocatalytiques et de phĂ©nomĂšnes de photolyse directe. Il en rĂ©sulte pour des temps dâirradiation Ă©levĂ©s, une dĂ©gradation totale des alcools chimisorbĂ©s en dioxyde de carbone et eau
Ătude par chromatographie gazeuse inverse, Ă concentration finie, des propriĂ©tĂ©s de surface d'Ă©chantillons obtenus par traitement thermique de la goethite : distribution des sites d'adsorption des alcanes
La chromatographie Gazeuse Inverse (CGI), à concentration finie, a été utilisée pour évaluer les propriétés de surface d'échantillons d'hématite obtenus par traitement thermique de la goethite. A
partir des isothermes d'adsorption des alcanes, on détermine la courbe de distribution des sites de surface en fonction de l'énergie d'adsorption de molécules sondes. On montre que ces courbes
Ă©voluent en fonction du traitement thermique de la goethite et traduisent une importante modification de surface de l'hĂ©matite formĂ©e aprĂšs un chauffage Ă 500 âC
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