259 research outputs found
Estimation du nombre de tortues vertes femelles adultes Chelonia mydas par saison de ponte à Tromelin et Europa (Océan Indien) (1973-1985)
Nouvelle découverte d'empreintes laissées par des dinosaures dans la formation des couches rouges (bassin de Cuzco-Sicuani, Sud du Pérou) : conséquences stratigraphiques et tectoniques
La dĂ©couverte d'empreintes laissĂ©es par le dinosaures vers le sommet de la formation des Couches Rouges permet de prĂ©ciser la stratigraphie du Sud du PĂ©rou. La durĂ©e de la sĂ©dimentation continentale du bassin de Cuzco-Sicuani n'excĂ©derait pas 20 Ma (santonien - palĂ©ocĂšne) et non plus 45 Ma, comme cela Ă©tait jusqu'Ă prĂ©sent admis. Le bassin d'avant-pays de Cuzco-Sicuani est caractĂ©risĂ© par une dĂ©formation synsĂ©dimentaire essentiellement compressive pendant toute la durĂ©e de la sĂ©dimentation des "Couches Rouges". En consĂ©quence, une durĂ©e Ă©quivalente Ă celle de cette sĂ©dimentation peut ĂȘtre retenue pour ces Ă©vĂ©nements tectoniques qui marquent ici le dĂ©but de la surrection de la chaĂźne andine. La phase pĂ©ruvienne, traditionnellement placĂ©e vers 85 Ma, reprĂ©senterait ainsi le dĂ©but de ces Ă©vĂ©nements tectoniques. (RĂ©sumĂ© d'auteur
Production of Low-Carbon Magnetic Steel for the LHC Superconducting Dipole and Quadrupole Magnets
In 1996 CERN negotiated a contract with Cockerill Sambre Ăą ARCELOR Group for the supply of 50Ă 000 tonnes of low-carbon steel for the LHC main magnets: this was the first contract to be placed for the project, and one of the single largest. In 2005 Ăą after nine years of work Ăą the contract is being successfully completed. This paper describes the steel specifically developed, known as MAGNETILù¹, its manufacturing and quality control process, organization of production, logistics and contract follow-up. Extensive statistics have been collected relating to physical, mechanical and technological parameters. Specific attention is dedicated to magnetic measurements (coercivity and permeability) performed at both room and cryogenic temperatures, the equipment used and statistical results. Reference is also made to the resulting precision of the fineblanked laminations used for the magnet yoke. The technology transfer from the particle accelerator domain to industry is ongoing, for example for the screening of high voltage cables buried in the ground
Découverte de restes dinosauriens et mammalien d'ùge crétacé supérieur à la base des couches rouges du synclinal de Bagua (Andes nord-péruviennes) : aspects stratigraphiques, sédimentologiques et paléogéographiques concernant la régression fini-crétacée
Automated diffeomorphic registration of anatomical structures with rigid parts: application to dynamic cervical MRI.
International audienceWe propose an iterative two-step method to compute a diffeomorphic non-rigid transformation between images of anatomical structures with rigid parts, without any user intervention or prior knowledge on the image intensities. First we compute spatially sparse, locally optimal rigid transformations between the two images using a new block matching strategy and an efficient numerical optimiser (BOBYQA). Then we derive a dense, regularised velocity field based on these local transformations using matrix logarithms and M-smoothing. These two steps are iterated until convergence and the final diffeomorphic transformation is defined as the exponential of the accumulated velocity field. We show our algorithm to outperform the state-of-the-art log-domain diffeomorphic demons method on dynamic cervical MRI data
Complex organic molecules in low-mass protostars on Solar System scales -- II. Nitrogen-bearing species
The chemical inventory of planets is determined by the physical and chemical
processes that govern the early phases of star formation. The aim is to
investigate N-bearing complex organic molecules towards two Class 0 protostars
(B1-c and S68N) at millimetre wavelengths with ALMA. Next, the results of the
detected N-bearing species are compared with those of O-bearing species for the
same and other sources. ALMA observations in Band 6 ( 1 mm) and Band 5
( 2 mm) are studied at 0.5" resolution, complemented by Band 3
( 3 mm) data in a 2.5" beam. NH2CHO, C2H5CN, HNCO, HN13CO, DNCO,
CH3CN, CH2DCN, and CHD2CN are identified towards the investigated sources.
Their abundances relative to CH3OH and HNCO are similar for the two sources,
with column densities that are typically an order of magnitude lower than those
of O-bearing species. The largest variations, of an order of magnitude, are
seen for NH2CHO abundance ratios with respect to HNCO and CH3OH and do not
correlate with the protostellar luminosity. In addition, within uncertainties,
the N-bearing species have similar excitation temperatures to those of
O-bearing species ( 100 300 K). The similarity of most abundances
with respect to HNCO, including those of CH2DCN and CHD2CN, hints at a shared
chemical history, especially the high D/H ratio in cold regions prior to star
formation. However, some of the variations in abundances may reflect the
sensitivity of the chemistry to local conditions such as temperature (e.g.
NH2CHO), while others may arise from differences in the emitting areas of the
molecules linked to their different binding energies in the ice. The two
sources discussed here add to the small number of sources with such a detailed
chemical analysis on Solar System scales. Future JWST data will allow a direct
comparison between the ice and gas abundances of N-bearing species.Comment: Accepted to A&A, 41 pages, 37 figure
The composition of the protosolar disk and the formation conditions for comets
Conditions in the protosolar nebula have left their mark in the composition
of cometary volatiles, thought to be some of the most pristine material in the
solar system. Cometary compositions represent the end point of processing that
began in the parent molecular cloud core and continued through the collapse of
that core to form the protosun and the solar nebula, and finally during the
evolution of the solar nebula itself as the cometary bodies were accreting.
Disentangling the effects of the various epochs on the final composition of a
comet is complicated. But comets are not the only source of information about
the solar nebula. Protostellar disks around young stars similar to the protosun
provide a way of investigating the evolution of disks similar to the solar
nebula while they are in the process of evolving to form their own solar
systems. In this way we can learn about the physical and chemical conditions
under which comets formed, and about the types of dynamical processing that
shaped the solar system we see today.
This paper summarizes some recent contributions to our understanding of both
cometary volatiles and the composition, structure and evolution of protostellar
disks.Comment: To appear in Space Science Reviews. The final publication is
available at Springer via http://dx.doi.org/10.1007/s11214-015-0167-
Quantifying the interplay between environmental and social effects on aggregated-fish dynamics
Demonstrating and quantifying the respective roles of social interactions and
external stimuli governing fish dynamics is key to understanding fish spatial
distribution. If seminal studies have contributed to our understanding of fish
spatial organization in schools, little experimental information is available
on fish in their natural environment, where aggregations often occur in the
presence of spatial heterogeneities. Here, we applied novel modeling approaches
coupled to accurate acoustic tracking for studying the dynamics of a group of
gregarious fish in a heterogeneous environment. To this purpose, we
acoustically tracked with submeter resolution the positions of twelve small
pelagic fish (Selar crumenophthalmus) in the presence of an anchored floating
object, constituting a point of attraction for several fish species. We
constructed a field-based model for aggregated-fish dynamics, deriving
effective interactions for both social and external stimuli from experiments.
We tuned the model parameters that best fit the experimental data and
quantified the importance of social interactions in the aggregation, providing
an explanation for the spatial structure of fish aggregations found around
floating objects. Our results can be generalized to other gregarious species
and contexts as long as it is possible to observe the fine-scale movements of a
subset of individuals.Comment: 10 pages, 5 figures and 4 supplementary figure
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