689 research outputs found
L'usage des systĂšmes d'informations Ă©lectroniques en recherche scientifique : le cas de la neurophysiologie.
Nous prĂ©sentons les premiers rĂ©sultats d'une enquĂȘte destinĂ©e Ă mieux connaĂźtre les pratiques de recherche d'information bibliographique et documentaire chez les chercheurs scientifiques. 64 chercheurs et Ă©tudiants doctorants en neurophysiologie ont rĂ©pondu Ă un questionnaire portant sur les mĂ©thodes, les outils, et les objectifs des recherches d'information typiques dans leur activitĂ©. De plus, 11 personnes parmi les rĂ©pondants ont participĂ© Ă un entretien individuel semi structurĂ©. Il en ressort que l'usage d'outils informatisĂ©s de recherche d'information bibliographique (RIB) est dĂ©sormais pratique courante, au dĂ©triment des index et autres sources imprimĂ©es. Les principaux outils utilisĂ©s sont la base de donnĂ©es bibliographiques PubMed et le moteur de recherche Google, avec toutefois de nombreux autres outils plus spĂ©cifiques utilisĂ©s Ă titre complĂ©mentaire. Les rĂ©pondants mentionnent des objectifs trĂšs variĂ©s, comme l'acquisition de connaissances nouvelles, mais aussi la recherche de techniques expĂ©rimentales, la veille documentaire, l'alimentation du dĂ©bat scientifique, ou l'aide Ă l'enseignement. Les difficultĂ©s que rencontrent les experts en neurosciences intĂ©gratives dans l'exploitation des outils informatiques de RIB spĂ©cialisĂ©s semblent surtout liĂ©es Ă l'absence de formation des experts Ă ces outils. Les chercheurs dĂ©finissent l'outil informatique de RIB « idĂ©al » comme fiable et exhaustif, mais aussi rapide et facile Ă utiliser et apprendre . De fait, le facteur temps apparaĂźt dĂ©terminant dans leur choix d'utilisation ou non d'un outil particulier. Cette Ă©tude ouvre la voie Ă des expĂ©riences plus spĂ©cifiques, qui porteront sur les stratĂ©gies cognitives des experts dans ce type de tĂąches
The VIPERS Multi-Lambda Survey. I. UV and NIR Observations, multi-color catalogues and photometric redshifts
We present observations collected in the CFHTLS-VIPERS region in the
ultraviolet (UV) with the GALEX satellite (far and near UV channels) and the
near infrared with the CFHT/WIRCam camera (-band) over an area of 22 and
27 deg, respectively. The depth of the photometry was optimized to measure
the physical properties (e.g., SFR, stellar masses) of all the galaxies in the
VIPERS spectroscopic survey. The large volume explored by VIPERS will enable a
unique investigation of the relationship between the galaxy properties and
their environment (density field and cosmic web) at high redshift (0.5 < z <
1.2). In this paper, we present the observations, the data reductions and the
build-up of the multi-color catalogues. The CFHTLS-T0007 (gri-{\chi}^2) images
are used as reference to detect and measure the -band photometry, while
the T0007 u-selected sources are used as priors to perform the GALEX photometry
based on a dedicated software (EMphot). Our final sample reaches ~25
(at 5{\sigma}) and ~22 (at 3{\sigma}). The large spectroscopic sample
(~51,000 spectroscopic redshifts) allows us to highlight the robustness of our
star/galaxy separation, and the reliability of our photometric redshifts with a
typical accuracy 0.04 and a catastrophic failure rate {\eta} <
2% down to i~23. We present various tests on the band completeness and
photometric redshift accuracy by comparing with existing, overlapping deep
photometric catalogues. Finally, we discuss the BzK sample of passive and
active galaxies at high redshift and the evolution of galaxy morphology in the
(NUV-r) vs (r-K_s) diagram at low redshift (z < 0.25) thanks to the high image
quality of the CFHTLS. The images, catalogues and photometric redshifts for 1.5
million sources (down to 25 or 22) are released and
available at this URL: http://cesam.lam.fr/vipers-mls/Comment: 14 pages, 16 figures. Accepted for publication in A&A. Version to be
publishe
Trunk sway in mildly disabled multiple sclerosis patients with and without balance impairment
Multiple sclerosis (MS) causes a broad range of neurological symptoms. Most common is poor balance control. However, knowledge of deficient balance control in mildly affected MS patients who are complaining of balance impairment but have normal clinical balance tests (CBT) is limited. This knowledge might provide insights into the normal and pathophysiological mechanisms underlying stance and gait. We analysed differences in trunk sway between mildly disabled MS patients with and without subjective balance impairment (SBI), all with normal CBT. The sway was measured for a battery of stance and gait balance tests (static and dynamic posturography) and compared to that of age- and sex-matched healthy subjects. Eight of 21 patients (38%) with an Expanded Disability Status Scale of 1.0-3.0 complained of SBI during daily activities. For standing on both legs with eyes closed on a normal and on a foam surface, patients in the no SBI group showed significant differences in the range of trunk roll (lateral) sway angle and velocity, compared to normal persons. Patients in the SBI group had significantly greater lateral sway than the no SBI group, and sway was also greater than normal in the pitch (anterior-posterior) direction. Sway for one-legged stance on foam was also greater in the SBI group compared to the no SBI and normal groups. We found a specific laterally directed impairment of balance in all patients, consistent with a deficit in proprioceptive processing, which was greater in the SBI group than in the no SBI group. This finding most likely explains the subjective symptoms of imbalance in patients with MS with normal CBT
Observable Signatures of the low-z Circum-Galactic and Inter-Galactic Medium : UV Line Emission in Simulations
We present for the first time predictions for UV line emission of
intergalactic and circumgalactic gas from Adaptive Mesh Resolution (AMR) Large
Scale Structure (LSS) simulations at redshifts 0.3<z<1.2, with specific
emphasis on observability with current and near-future UV instrumentation. In
three transitions of interest (Lya, OVI and CIV) there is a clear bimodality in
the type of objects : the overwhelming majority of flux stems from discrete,
compact sources, while a much larger volume fraction is filled by more tenuous
gas. We characterise both object types with regard to number density, physical
size and shape, brightness, luminosity, velocity structure, mass, temperature,
ionisation state, and metal content. Degrading AMR grids to characteristic
resolutions of available (such as FIREBall) or foreseeable instrumentation,
allows to assess which inferences can be drawn from currently possible
observations, and set foundations to prepare observing strategies for future
missions. In general, the faint emission of the IGM and filamentary structure
remains beyond capabilities of instruments with only short duration exposure
potential (stratospheric balloons), even for optimistic assumptions for Lya,
while the yet fainter metal line transitions for these structures will remain
challenging for long duration exposures (space-based telescopes), mostly due to
low metallicity pushing them more than three orders of magnitudes in brightness
below Lya radiation. For the circum-galactic medium (CGM) the situation is more
promising, and it is foreseeable that in the near future we will not only just
dectect such sources, but the combination of all three lines in addition to
velocity information will yield valuable insight into the physical processes at
hand, illuminating important mechanisms during the formation of galaxies and
their backreaction onto the IGM from whence they formed. (abrigded)Comment: Accepted for publication in MNRAS (2011 November 08, received in
original form 2011 September 14). 27 pages, 19 figures, 3 tables. Some of the
figures have degraded resolution due to file size limitations. For
high-resolution version, please contact the first autho
Slider-Block Friction Model for Landslides: Application to Vaiont and La Clapiere Landslides
Accelerating displacements preceding some catastrophic landslides have been
found empirically to follow a time-to-failure power law, corresponding to a
finite-time singularity of the velocity [{\it Voight},
1988]. Here, we provide a physical basis for this phenomenological law based on
a slider-block model using a state and velocity dependent friction law
established in the laboratory and used to model earthquake friction. This
physical model accounts for and generalizes Voight's observation: depending on
the ratio of two parameters of the rate and state friction law and on the
initial frictional state of the sliding surfaces characterized by a reduced
parameter , four possible regimes are found. Two regimes can account for
an acceleration of the displacement. We use the slider-block friction model to
analyze quantitatively the displacement and velocity data preceding two
landslides, Vaiont and La Clapi\`ere. The Vaiont landslide was the catastrophic
culmination of an accelerated slope velocity. La Clapi\`ere landslide was
characterized by a peak of slope acceleration that followed decades of ongoing
accelerating displacements, succeeded by a restabilizing phase. Our inversion
of the slider-block model on these data sets shows good fits and suggest to
classify the Vaiont (respectively La Clapi\`ere) landslide as belonging to the
velocity weakening unstable (respectively strengthening stable) sliding regime.Comment: shortened by focusing of the frictional model, Latex document with
AGU style file of 14 pages + 11 figures (1 jpeg photo of figure 6 given
separately) + 1 tabl
First Detection of Polarization of the Submillimetre Diffuse Galactic Dust Emission by Archeops
We present the first determination of the Galactic polarized emission at 353
GHz by Archeops. The data were taken during the Arctic night of February 7,
2002 after the balloon--borne instrument was launched by CNES from the Swedish
Esrange base near Kiruna. In addition to the 143 GHz and 217 GHz frequency
bands dedicated to CMB studies, Archeops had one 545 GHz and six 353 GHz
bolometers mounted in three polarization sensitive pairs that were used for
Galactic foreground studies. We present maps of the I, Q, U Stokes parameters
over 17% of the sky and with a 13 arcmin resolution at 353 GHz (850 microns).
They show a significant Galactic large scale polarized emission coherent on the
longitude ranges [100, 120] and [180, 200] deg. with a degree of polarization
at the level of 4-5%, in agreement with expectations from starlight
polarization measurements. Some regions in the Galactic plane (Gem OB1,
Cassiopeia) show an even stronger degree of polarization in the range 10-20%.
Those findings provide strong evidence for a powerful grain alignment mechanism
throughout the interstellar medium and a coherent magnetic field coplanar to
the Galactic plane. This magnetic field pervades even some dense clouds.
Extrapolated to high Galactic latitude, these results indicate that
interstellar dust polarized emission is the major foreground for PLANCK-HFI CMB
polarization measurement.Comment: Submitted to Astron. & Astrophys., 14 pages, 12 Fig., 2 Table
QUBIC: The QU Bolometric Interferometer for Cosmology
One of the major challenges of modern cosmology is the detection of B-mode
polarization anisotropies in the CMB. These originate from tensor fluctuations
of the metric produced during the inflationary phase. Their detection would
therefore constitute a major step towards understanding the primordial
Universe. The expected level of these anisotropies is however so small that it
requires a new generation of instruments with high sensitivity and extremely
good control of systematic effects. We propose the QUBIC instrument based on
the novel concept of bolometric interferometry, bringing together the
sensitivity advantages of bolometric detectors with the systematics effects
advantages of interferometry. Methods: The instrument will directly observe the
sky through an array of entry horns whose signals will be combined together
using an optical combiner. The whole set-up is located inside a cryostat.
Polarization modulation will be achieved using a rotating half-wave plate and
interference fringes will be imaged on two focal planes (separated by a
polarizing grid) tiled with bolometers. We show that QUBIC can be considered as
a synthetic imager, exactly similar to a usual imager but with a synthesized
beam formed by the array of entry horns. Scanning the sky provides an
additional modulation of the signal and improve the sky coverage shape. The
usual techniques of map-making and power spectrum estimation can then be
applied. We show that the sensitivity of such an instrument is comparable with
that of an imager with the same number of horns. We anticipate a low level of
beam-related systematics thanks to the fact that the synthesized beam is
determined by the location of the primary horns. Other systematics should be
under good control thanks to an autocalibration technique, specific to our
concept, that will permit the accurate determination of most of the systematics
parameters.Comment: 12 pages, 10 figures, submitted to Astronomy and Astrophysic
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