89 research outputs found
Innovations agroécologiques en Martinique : freins et leviers organisationnels, institutionnels, techniques et économiques
Les résultats montrent tout d’abord que la filière de produits dits « biologiques » se structure en deux organisations de producteurs qui se différencient, tant par le mode de certification choisie que par leur niveaux d’insertion dans les dispositifs institutionnels conventionnels. Dans les deux cas néanmoins, un frein important est l’absence de maîtrise d’indicateurs sur les conditions d’évaluation économique et financière des produits biologiques. Par ailleurs, trois freins majeurs sont mis en évidence par l’analyse technico-économique et agronomique des exploitations (i) l’absence de référentiels et d’appui technique adaptés aux conditions locales, (ii) la faiblesse et la dispersion concernant l’approvisionnement et l’accès aux intrants adaptés et enfin (iii) la faible productivité du travail. Une action collective de coordination impliquant les collectivités locales, les organisations de producteurs, les organismes techniques et la recherche est nécessaire
A new experiment for the determination of the 18F(p,alpha) reaction rate at nova temperatures
The 18F(p,alpha) reaction was recognized as one of the most important for
gamma ray astronomy in novae as it governs the early 511 keV emission. However,
its rate remains largely uncertain at nova temperatures. A direct measurement
of the cross section over the full range of nova energies is impossible because
of its vanishing value at low energy and of the short 18F lifetime. Therefore,
in order to better constrain this reaction rate, we have performed an indirect
experiment taking advantage of the availability of a high purity and intense
radioactive 18F beam at the Louvain La Neuve RIB facility. We present here the
first results of the data analysis and discuss the consequences.Comment: Contribution to the Classical Novae Explosions conference, Sitges,
Spain, 20-24 May 2002, 5 pages, 3 figure
The Acceleration and Storage of Radioactive Ions for a Beta-Beam Facility
The term beta-beam has been coined for the production of a pure beam of
electron neutrinos or their antiparticles through the decay of radioactive ions
circulating in a storage ring. This concept requires radioactive ions to be
accelerated to as high Lorentz gamma as 150. The neutrino source itself
consists of a storage ring for this energy range, with long straight sections
in line with the experiment(s). Such a decay ring does not exist at CERN today,
nor does a high-intensity proton source for the production of the radioactive
ions. Nevertheless, the existing CERN accelerator infrastructure could be used
as this would still represent an important saving for a beta-beam facility.Comment: beta-beam working group website at http://cern.ch/beta-bea
D(18F,pa)15N reaction applied to nova gamma-ray emission
The 18F(p,alpha)15O reaction is recognized to be one of the most important
reactions for nova gamma-ray astronomy as it governs the early E <= 511keV
gamma emission. However in the nova temperature regime, its rate remains
largely uncertain due to unknown low-energy resonance strengths. We report here
the measurement of the D(18F,p)19F(alpha)15N one-nucleon transfer reaction,
induced by a 14 MeV 18F radioactive beam impinging on a CD2 target; outgoing
protons and 15N (or alpha-particles) were detected in coincidence in two
silicon strip detectors. A DWBA analysis of the data resulted in new limits to
the contribution of low-energy resonances to the rate of the 18F(p,alpha)15O
reaction.Comment: Rapid Communication to appear in Phys. Rev. C., 4 pages and 4 figure
Indirect study of 19Ne states near the 18F+p threshold
The early E < 511 keV gamma-ray emission from novae depends critically on the
18F(p,a)15O reaction. Unfortunately the reaction rate of the 18F(p,a)15O
reaction is still largely uncertain due to the unknown strengths of low-lying
proton resonances near the 18F+p threshold which play an important role in the
nova temperature regime. We report here our last results concerning the study
of the d(18F,p)19F(alpha)15N transfer reaction. We show in particular that
these two low-lying resonances cannot be neglected. These results are then used
to perform a careful study of the remaining uncertainties associated to the
18F(p,a)15O and 18F(p,g)19Ne reaction rates.Comment: 18 pages, 8 figures. Accepted in Nuclear Physics
The SPIRAL radioactive ion beam facility
This document describes the scientific goals as well as the technical choices of the SPIRAL project (Système de Production d'Ions Radioactifs et d'Accélération en Ligne)
Reduction of repeatability error for analysis of variance-Simultaneous Component Analysis (REP-ASCA): application to NIR spectroscopy on coffee sample
A method to reduce repeatability error in multivariate data for Analysis of variance-Simultaneous Component Analysis (REP-ASCA) has been developed. This method proposes to adapt the acquisition protocol by adding a set containing repeated measures for describing repeatability error. Then, an orthogonal projection is performed in the row-space to reduce the repeatability error of the original dataset. Finally, ASCA is performed on the orthogonalized dataset. This method was evaluated on NIR spectral data of coffee beans. This study shows that the repeatability error due to physical variations between measurements can alter results of the analysis of variance. These effects are predominant in factors analysis and can be seen on spectra as constant or non-constant baselines. By reducing repeatability error with REP-ASCA, baselines are removed and factor analysis provides more information about chemical content of the factors of interest
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