169 research outputs found
Transitions institutionnelles et agricoles dans les périmètres irrigués du pôle Petrolina-Juazeiro (Brésil) : d'une logique sociale vers une logique managériale
Mis en place dans les années 60 dans un objectif de lutte contre l'exode rural et la pauvreté, les périmètres publics irrigués du Nordeste brésilien (pôle de Petrolina-Juazeiro) connaissent depuis 1985 une évolution de leur mode de gestion (transfert aux usagers, désengagement financier de l'Etat) et des systèmes de production (développement d'entreprises agricoles et de l'arboriculture fruitière). Malgré des conditions naturelles et institutionnelles favorables, ces périmètres rencontrent des difficultés de recouvrement des factures d'eau auprès des producteurs. Les comportements des irrigants en matière de paiement des factures d'eau s'expliquent par les conditions dans lesquelles ils ont effectué leur transition vers l'arboriculture fruitière. Les difficultés financières individuelles des petites exploitations familiales, qui peuvent aboutir à l'abandon de l'agriculture irriguée, ont des conséquences collectives: diminution de la maintenance des ouvrages, dégradation du service de l'eau, tensions entre irrigants et gestionnaires. Pour concilier l'objectif social initial des périmètres irrigués avec une logique économique plus libérale, on propose de développer les capacités managériales des agriculteurs, des gestionnaires et de l'environnement des exploitations (crédit, commercialisation). Ceci implique une évolution des démarches de conseil vers l'aide à la gestion stratégique. Plusieurs outils sont proposés en ce sens. (Résumé d'auteur)
Thermal emission from the Earth-sized exoplanet TRAPPIST-1 b using JWST
The TRAPPIST-1 system is remarkable for its seven planets that are similar in
size, mass, density, and stellar heating to the rocky planets Venus, Earth, and
Mars in our own Solar System (Gillon et al. 2017). All TRAPPIST-1 planets have
been observed with the transmission spectroscopy technique using the Hubble or
Spitzer Space Telescopes, but no atmospheric features have been detected or
strongly constrained (Ducrot et al. 2018; de Wit et al. 2018; Zhang et al.
2018; Garcia et al. 2022). TRAPPIST-1 b is the closest planet to the system's M
dwarf star, and it receives 4 times as much irradiation as Earth receives from
the Sun. This relatively large amount of stellar heating suggests that its
thermal emission may be measurable. Here we present photometric secondary
eclipse observations of the Earth-sized TRAPPIST-1 b exoplanet using the F1500W
filter of the MIRI instrument on JWST. We detect the secondary eclipse in each
of five separate observations with 8.7-sigma confidence when all data are
combined. These measurements are most consistent with the re-radiation of the
TRAPPIST-1 star's incident flux from only the dayside hemisphere of the planet.
The most straightforward interpretation is that there is little or no planetary
atmosphere redistributing radiation from the host star and also no detectable
atmospheric absorption from carbon dioxide (CO) or other species.Comment: Submitted to Natur
Cities and their water socio-footprint: a dynamic socio-technical network
International audienceThrough examples of interactions among urban and rural areas we have built the concept of urban water socio-footprint, on the basis of concepts of water and urban footprints. This urban water socio-footprint entails making explicit the socio-technical network which disseminates the impact of urban activities on water system or due to their specific needs towards water system. Animating this footprint with people, their dynamics and migration, their concerns about various places leads to couple the dynamics of water system and land use in the whole urban systems, including built and non built, cultivated and non cultivated areas. This raises the issue of the existence of institutions to take in charger the links which are emerging through these multiple sources of interdependences
Identification of target-specific bioisosteric fragments from ligand-protein crystallographic data
Bioisosteres are functional groups or atoms that are structurally different but that can form similar intermolecular interactions. Potential bioisosteres were identified here from analysing the X-ray crystallographic structures for sets of different ligands complexed with a fixed protein. The protein was used to align the ligands with each other, and then pairs of ligands compared to identify substructural features with high volume overlap that occurred in approximately the same region of geometric space. The resulting pairs of substructural features can suggest potential bioisosteric replacements for use in lead-optimisation studies. Experiments with 12 sets of ligand-protein complexes from the Protein Data Bank demonstrate the effectiveness of the procedure
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