Infrastructure de transport et développement économique : quelles dynamiques d'appropriation par les acteurs productifs

La communication propose une piste de renouvellement de l'analyse du lien entre infrastructures de transport et développement économique. Elle montre la diversité de sensibilité des firmes aux infrastructures, en fonction des modalités de coordination à l'œuvre entre les acteurs. Notre recherche vise à montrer en effet que les investissements en infrastructures auront une influence différenciée selon les modalités de coordination à l'œuvre et les ressorts sur lesquels elles s'appuient. L'influence des politiques d'investissement n'est donc ni homogène, ni uniforme. Nous illustrerons les possibilités d'appropriation du futur Canal Seine - Nord Europe à travers l'exemple des logiques productives des firmes de la filière céréalière.ECONOMIE ; DEVELOPPEMENT ; INFRASTRUCTURE de TRANSPORT

La logistique, un vecteur pour de nouvelles trajectoires d'innovation dans les circuits courts alimentaires de proximité ? Etude de cas de formes de coopérations multi-acteurs et multi-niveaux dans les Hauts-de-France

55ème colloque de l'Association de Science Régionale de Langue Française, Caen, France, 04-/07/2018 - 06/07/2018While the economic, social and environmental sustainability of short food supply chains (SFSC) is challenged, the logistics turns into a central issue and is considered both by academics and public or private actors. Among the possible optimizations, collective solutions arise and imply cooperation. In this communication, we will focus on multi-actors and multi-level cooperation, which suppose producers organized in groups and private economic actors and/or public actors. Then we assume that these forms of cooperation may catalyze innovations, especially logistical ones. Relying on two case studies, we will question the role of the multi-actors and multi-level cooperation in the logistical innovations trajectories of SFSC. We will also interrogate, at a larger scale, their impacts on dynamics of SFSC and the territories beyond the logistical specificity.Alors que la durabilité aussi bien économique et social qu'environnemental des circuits courts alimentaires de proximité (CCAP) est questionnée, la logistique devient un enjeu central abordée autant par la recherche scientifique que par les acteurs publics ou privés. Parmi les optimisations possibles, les solutions collectives émergent et supposent de fait des coopérations. Dans ce cadre, nous nous proposons d'étudier les coopérations multi-acteurs et multi-niveaux, celles impliquant non seulement des producteurs réunis en collectifs mais également des acteurs économiques privés et/ou des acteurs publics. Nous formulons l'hypothèse que ces coopérations sont en mesure de catalyser des innovations, notamment en matière logistique. En nous appuyant sur deux études de cas, il s'agit, dès lors, de questionner le rôle de ces dernières dans les trajectoires d'innovations logistiques pour les CCAP et de s'interroger sur leurs impacts sur les CCAP et les territoires au-delà de la question logistique

Gaia Data Release 2 Mapping the Milky Way disc kinematics

Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources as well as line-of-sight velocities for 7.2 million stars brighter than G(RVS) = 12 mag. Both samples provide a full sky coverage. Aims. To illustrate the potential of Gaia DR2, we provide a first look at the kinematics of the Milky Way disc, within a radius of several kiloparsecs around the Sun. Methods. We benefit for the first time from a sample of 6.4 million F-G-K stars with full 6D phase-space coordinates, precise parallaxes (sigma((omega) over bar)/(omega) over bar Results. Gaia DR2 allows us to draw 3D maps of the Galactocentric median velocities and velocity dispersions with unprecedented accuracy, precision, and spatial resolution. The maps show the complexity and richness of the velocity field of the galactic disc. We observe streaming motions in all the components of the velocities as well as patterns in the velocity dispersions. For example, we confirm the previously reported negative and positive galactocentric radial velocity gradients in the inner and outer disc, respectively. Here, we see them as part of a non-axisymmetric kinematic oscillation, and we map its azimuthal and vertical behaviour. We also witness a new global arrangement of stars in the velocity plane of the solar neighbourhood and in distant regions in which stars are organised in thin substructures with the shape of circular arches that are oriented approximately along the horizontal direction in the U - V plane. Moreover, in distant regions, we see variations in the velocity substructures more clearly than ever before, in particular, variations in the velocity of the Hercules stream. Conclusions. Gaia DR2 provides the largest existing full 6D phase-space coordinates catalogue. It also vastly increases the number of available distances and transverse velocities with respect to Gaia DR1. Gaia DR2 offers a great wealth of information on the Milky Way and reveals clear non-axisymmetric kinematic signatures within the Galactic disc, for instance. It is now up to the astronomical community to explore its full potential.Peer reviewe

Gaia Data Release 2: The celestial reference frame (Gaia-CRF2)

Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars which define akinematically non-rotating reference frame in the optical domain. A subset of them have accurate VLBI positions which allow the axes of thereference frame to be aligned with the ICRF radio frame. Aims. We aim to describe the astrometric and photometric properties of the quasars selected to represent Gaia-CRF2, the celestial reference frame of Gaia DR2, and to compare the optical and radio positions for sources with accurate VLBI positions. Methods. Descriptive statistics are used to characterise the overall properties of the quasar sample. Residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. Positional differences are calculated relative to a prototype version of the forthcoming ICRF3. Results. Gaia-CRF2 is materialised by the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues. The sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range G ' 16 to 21 mag with accurately known optical positions. The median positional uncertainty is 0.12 mas for G < 18 mag and 0.5 mas at G = 20 mag. Large-scale systematics are estimated to be in the range 20 to 30 μas. The accuracy claims are supported by the parallaxes and proper motions of the quasars in Gaia DR2. The optical positions for a subset of 2820 sources in common with the ICRF3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions. Conclusions. Based on less than 40% of the data expected from the nominal Gaia mission, Gaia-CRF2 is the first realisation of a non-rotating global optical reference frame meeting the ICRS prescriptions, i.e. built only on extragalactic sources. In accuracy it matches the current radio frame realised in the ICRF but with a much higher density of sources in all parts of the sky except along the Galactic equator

Gaia Data Release 2 Observations of solar system objects

CONTEXT: The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations. AIMS: We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality. METHODS: To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP). RESULTS: The overall astrometric performance is close to the expectations, with an optimal range of brightness G ∼ 12 − 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G ∼ 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects

Gaia Data Release 3. The Galaxy in your preferred colours: Synthetic photometry from Gaia low-resolution spectra

peer reviewedGaia Data Release 3 provides novel flux-calibrated low-resolution spectrophotometry for ≃220 million sources in the wavelength range 330 nm ≤ λ ≤ 1050 nm (XP spectra). Synthetic photometry directly tied to a flux in physical units can be obtained from these spectra for any passband fully enclosed in this wavelength range. We describe how synthetic photometry can be obtained from XP spectra, illustrating the performance that can be achieved under a range of different conditions - for example passband width and wavelength range - as well as the limits and the problems affecting it. Existing top-quality photometry can be reproduced within a few per cent over a wide range of magnitudes and colour, for wide and medium bands, and with up to millimag accuracy when synthetic photometry is standardised with respect to these external sources. Some examples of potential scientific application are presented, including the detection of multiple populations in globular clusters, the estimation of metallicity extended to the very metal-poor regime, and the classification of white dwarfs. A catalogue providing standardised photometry for ≃2.2 × 108 sources in several wide bands of widely used photometric systems is provided (Gaia Synthetic Photometry Catalogue; GSPC) as well as a catalogue of ≃105 white dwarfs with DA/non-DA classification obtained with a Random Forest algorithm (Gaia Synthetic Photometry Catalogue for White Dwarfs; GSPC-WD)

Les rives de l'Escaut comme espace d'apprentissage du transport fluvial pour les acteurs l'aménagement ? Analyse de deux projets dans le Valenciennois

International audienc

L’apprentissage performant du transport fluvial. Quel accompagnement du projet de canal Seine-Nord Europe ?

Le transport routier, devenu le mode de transport dominant des biens et des personnes, soulève des enjeux sociétaux et environnementaux majeurs. En réponse aux externalités négatives engendrées par celui-ci, l’action publique se renforce en faveur de transports " alternatifs ", notamment ferroviaires et fluviaux. En complément aux lourds investissements consentis pour l’amélioration des réseaux correspondants, telle la réalisation du canal Seine-Nord Europe, la France et l’Europe développent des aides financières à la faveur de ces modes de transport ou imposent des taxes au transport routier. Pour autant, ces politiques fondées sur les coûts du transport n’ont pas encore réussi à inverser la tendance, ce qui suggère que d’autres ressorts du report modal restent à trouver. La thèse propose d’éclairer la question du report modal vers la voie d’eau dans le transport de marchandises. L’approche évolutionniste qui fonde l’analyse conduira à considérer que les choix de transport s’effectuent dans le cadre d’une organisation dont les membres se coordonnent de multiples façons pour atteindre le but commun de livrer la marchandise. Elle conduira à révéler les connaissances qui fondent les organisations logistiques et de transport (OLT) routières et fluviales. L’hypothèse principale est alors que le transfert de la route au fluvial suppose une évolution des connaissances associées aux OLT dans le cadre d’un apprentissage organisationnel. Cet apprentissage doit en outre être associé à une évolution radicale des connaissances, pour que les OLT fluviales soient performantes et pérennes. Une lecture institutionnaliste complète l’analyse en s’intéressant aux modalités de sélection des connaissances qui interviennent dans la construction des paradigmes d’évaluation de la performance des OLT. Elle montre l’influence des interrelations entre les membres des OLT sur les itinéraires d’apprentissages, notamment les relations de confiance et les rapports de force qui se manifestent à l’occasion des transactions, ou à l’occasion de rapports informels. Ainsi, le report modal pérenne vers la voie d’eau dépendra de la capacité des OLT à déployer les conditions d’un apprentissage organisationnel qui favorise cette évolution radicale. L’analyse permet in fine d’envisager comment la puissance publique peut soutenir cet apprentissage performant. L’analyse s’appuie sur des entretiens semi-directifs effectués auprès de différents membres d’OLT choisies d’une part dans la filière de l’agroalimentaire, filière parmi les principales utilisatrices de la voie d’eau, et d’autre part dans d’autres filières pour leur tentative, réussie ou non, de transformation d’OLT routières en OLT fluviales