405 research outputs found
Selective conversion of nitroarenes using a carbon nanotube-ruthenium nanohybrid
International audienceRuthenium nanoparticles were assembled on carbon nanotubes and the resulting nanohybrid was used in the hydrazine-mediated catalytic hydrogenation of various nitroarenes, at room temperature. Depending on the solvent, a selective transformation occurred, giving either access to the corresponding aniline or hydroxylamine derivative
Room temperature Suzuki coupling of aryl iodides, bromides, and chlorides using a heterogeneous carbon nanotube-palladium nanohybrid catalyst
International audiencePalladium nanoparticles were immobilized on multi-walled carbon nanotubes by a layer-by-layer approach, resulting in a well-defined assembly. The nanohybrid was found effective in promoting Suzuki cross couplings of various halogenated aromatics, including chlorinated ones, with arylboronic acids under sustainable conditions. The heterogeneous catalyst could also easily be recovered from the reaction mixture and reused with no loss of activity over several cycles
Continuum field description of crack propagation
We develop continuum field model for crack propagation in brittle amorphous
solids. The model is represented by equations for elastic displacements
combined with the order parameter equation which accounts for the dynamics of
defects. This model captures all important phenomenology of crack propagation:
crack initiation, propagation, dynamic fracture instability, sound emission,
crack branching and fragmentation.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett. Additional
information can be obtained from http://gershwin.msd.anl.gov/theor
Submillimetre point sources from the Archeops experiment: Very Cold Clumps in the Galactic Plane
Archeops is a balloon-borne experiment, mainly designed to measure the Cosmic
Microwave Background (CMB) temperature anisotropies at high angular resolution
(~ 12 arcminutes). By-products of the mission are shallow sensitivity maps over
a large fraction of the sky (about 30 %) in the millimetre and submillimetre
range at 143, 217, 353 and 545 GHz. From these maps, we produce a catalog of
bright submillimetre point sources. We present in this paper the processing and
analysis of the Archeops point sources. Redundancy across detectors is the key
factor allowing to sort out glitches from genuine point sources in the 20
independent maps. We look at the properties of the most reliable point sources,
totalling 304. Fluxes range from 1 to 10,000 Jy (at the frequencies covering
143 to 545 GHz). All sources are either planets (2) or of galactic origin.
Longitude range is from 75 to 198 degrees. Some of the sources are associated
with well-known Lynds Nebulae and HII compact regions in the galactic plane. A
large fraction of the sources have an IRAS counterpart. Except for Jupiter,
Saturn, the Crab and Cas A, all sources show a dust-emission-like modified
blackbody emission spectrum. Temperatures cover a range from 7 to 27 K. For the
coldest sources (T<10 K), a steep nu^beta emissivity law is found with a
surprising beta ~ 3 to 4. An inverse relationship between T and beta is
observed. The number density of sources at 353 GHz with flux brighter than 100
Jy is of the order of 1 per degree of Galactic longitude. These sources will
provide a strong check for the calibration of the Planck HFI focal plane
geometry as a complement to planets. These very cold sources observed by
Archeops should be prime targets for mapping observations by the Akari and
Herschel space missions and ground--based observatories.Comment: Version matching the published article (English improved). Published
in Astron. Astrophys, 21 pages, 13 figures, 4 tables Full article (with
complete tables) can be retrieved at
http://www.archeops.org/Archeops_Publicatio
Submillimeter dust emission of the M17 complex measured with PRONAOS
We map a 50' x 30' area in and around the M17 molecular complex with the
French submillimeter balloon-borne telescope PRONAOS, in order to better
understand the thermal emission of cosmic dust and the structure of the
interstellar medium. The PRONAOS-SPM instrument has an angular resolution of
about 3', corresponding to a size of 2 pc at the distance of this complex, and
a high sensitivity up to 0.8 MJy/sr. The observations are made in four wide
submillimeter bands corresponding to effective wavelengths of 200, 260, 360 and
580 um. Using an improved map-making method for PRONAOS data, we map the M17
complex and faint condensations near the dense warm core. We derive maps of
both the dust temperature and the spectral index, which vary over a wide range,
from about 10 K to 100 K for the temperature and from about 1 to 2.5 for the
spectral index. We show that these parameters are anticorrelated, the cold
areas (10-20 K) having a spectral index around 2, whereas the warm areas have a
spectral index between 1 and 1.5. We discuss possible causes of this effect,
and we propose an explanation involving intrinsic variations of the grain
properties. Indeed, to match the observed spectra with two dust components
having a spectral index equal to 2 leads to very large and unlikely amounts of
cold dust. We also give estimates of the column densities and masses of the
studied clumps. Three cold clumps (14-17 K) could be gravitationally unstable.Comment: 16 pages, 4 figures, accepted June 2002 in Astronomy & Astrophysic
XPAD: pixel detector for material sciences
Currently available 2D detectors do not make full use of the high flux and high brilliance of third generation synchrotron sources. The XPAD prototype, using active pixels, has been developed to fulfil the needs of materials science scattering experiments. At the time, its prototype is build of eight modules of eight chips. The threshold calibration of /spl ap/4 10/sup 4/ pixels is discussed. Applications to powder diffraction or SAXS experiments prove that it allows to record high quality data
Submillimeter Emission from Water in the W3 Region
We have mapped the submillimeter emission from the 1(10)-1(01) transition of
ortho-water in the W3 star-forming region. A 5'x5' map of the W3 IRS4 and W3
IRS5 region reveals strong water lines at half the positions in the map. The
relative strength of the Odin lines compared to previous observations by SWAS
suggests that we are seeing water emission from an extended region. Across much
of the map the lines are double-peaked, with an absorption feature at -39 km/s;
however, some positions in the map show a single strong line at -43 km/s. We
interpret the double-peaked lines as arising from optically thick,
self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted
lines originate in emission near W3 IRS4. In this model, the unusual appearance
of the spectral lines across the map results from a coincidental agreement in
velocity between the emission near W3 IRS4 and the blue peak of the more
complex lines near W3 IRS5. The strength of the water lines near W3 IRS4
suggests we may be seeing water emission enhanced in a photon-dominated region.Comment: Accepted to A&A Letters as part of the special Odin issue; 4 page
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