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A decomposition theorem for projective manifolds with nef anticanonical bundle
No full textLet X be a simply connected projective manifold with nef anticanonical bundle. We prove that X is a product of a rationally connected manifold and a manifold with trivial canonical bundle. As an application we describe the MRC fibration of any projective manifold with nef anticanonical bundle
Des passés déplacés : mémoires des migrations [coord. n° 100 de : Communications]
No full textInternational audienceDepuis les années 1970, émergent, dans de nombreux pays, des initiatives visant à valoriser les mémoires des migrations. Toutes ont pour objectif l’obtention d’une reconnaissance et la pleine acceptation des migrants (immigrés et émigrés) et de leurs descendants par les populations locales. Ce numéro analyse en amont les raisons et les conditions de cet intérêt ainsi que les caractéristiques des initiateurs mais surtout en aval les effets paradoxaux des actions entreprises. Il questionne l’intérêt conféré par les personnes concernées, migrants et descendants, à ces initiatives, ainsi que l’écart entre les mémoires transmises dans l’espace privé et les usages publics du passé. Enfin, il interroge la croyance en les bienfaits de la mise en récit publique et de la patrimonialisation des passés migratoires et leur capacité à agir sur les représentations des migrations
Translation in astrocyte distal processes sets molecular heterogeneity at the gliovascular interface
No full textInternational audienceAstrocytes send out long processes that are terminated by endfeet at the vascular surface and regulate vascular functions as well as homeostasis at the vascular interface. To date, the astroglial mechanisms underlying these functions have been poorly addressed. Here we demonstrate that a subset of messenger RNAs is distributed in astrocyte endfeet. We identified, among this transcriptome, a pool of messenger RNAs bound to ribosomes, the endfeetome, that primarily encodes for secreted and membrane proteins. We detected nascent protein synthesis in astrocyte endfeet. Finally, we determined the presence of smooth and rough endoplasmic reticulum and the Golgi apparatus in astrocyte perivascular processes and endfeet, suggesting for local maturation of membrane and secreted proteins. These results demonstrate for the first time that protein synthesis occurs in astrocyte perivascular distal processes that may sustain their structural and functional polarization at the vascular interface
An Inertial-Aided Homography-Based Visual Servo Control Approach for (Almost) Fully Actuated Autonomous Underwater Vehicles
No full textInternational audienceA nonlinear inertial-aided image-based visual servo control approach for the stabilisation of (almost) fully-actuated autonomous underwater vehicles (AUVs) is proposed. It makes use of the homography matrix between two images of a planar scene as feedback information while the system dynamics are exploited in a cascade manner in control design: an outer-loop control defines a reference setpoint based on the homography matrix and an inner-loop control ensures the stabilisation of the setpoint by assigning the thrust and torque controls. Unlike conventional solutions that only consider the system kinematics, the proposed control scheme is novel in considering the full system dynamics (incorporating all degrees of freedom, nonlinearities and couplings as well as interactions with the surrounding fluid) and in not requiring information of the relative depth and normal vector of the observed scene. Augmented with integral corrections , the proposed controller is robust with respect to model uncertainties and disturbances. The almost global asymptotic stability of the closed-loop system is demonstrated, which is the largest domain of attraction one can achieve by means of continuous feedback control. Simulation results illustrating these properties on a realistic AUV model subjected to a sea current are presented and finally experimental results on a real AUV are reported
Land cover change as a consequence of natural and human impact: SE Baltic Sea region example
No full textInternational audienceMain task of this research is to make suggestions for further research on land cover change and to use land cover change analysis as indicator of micro-climate change in example of Lithuanian Baltic Sea coastal zone.Coastal zones are among those areas that have been subject to intense human pressure due to their natural resources. As a transitional zone, between land and sea, coastal zones hold some of the most valuable and productive habitats on earth. Huge amounts of energy circulate in these zones, which attracts all sort of human interest and activities (Rivis et al, 2016; Schlacher et al., 2014; Bicknell et al., Sperb et al., 2006). A large number of population lives near the coastal zone.Analysis on the land use and land cover change as a consequence on human livelihoods as well as on the environment is a matter of concern for sustainable development and management of natural resources. The Baltic Sea and coast is one of the most vital natural resources of Lithuania. Only a small part of the Baltic Sea coast belongs to Lithuania (~91 km.) and almost half of it belongs to the National park area and Natura 2000 or other prohibited area (State Cadastre of Protected Areas, 2014).Retrospective analysis of land cover dynamics and its driving force has been undertaken using satellite images of Landsat5 TM year 1989, Landsat5 TM year 2000 and Landsat8 TM year 2014 and 2016 with 30 m spatial resolution of Lithuanian Western part. Analysis of building’s geodatabase (year 1997 and 2016) applied on orthophoto of Lithuanian Western part was made in order to identify socio-economic change and its difference’s impact to nowadays land cover change. In detail statistical, mathematical analysis of ongoing processes have been made using national statistical data and in field trips of most areas of interest. Results showed that during research period landscapes in terms of agriculture, urbanization and human behavior had changed the most. Further research will be carried out in terms of micro-climate change evaluation
Détection et Classification Minimax d'Observations Discrètes
No full textNational audienceCet article s'intéresse au calcul d'un test minimax de niveau contraint entre plusieurs hypothèses impliquant des observations discrètes et une fonction de perte arbitraire. Le test minimax de niveau contraint minimise le risque de classification maximum et il garantit simultanément que la probabilité de rejeter l'hypothèse nulle, appelé le niveau du test, est bornée par une valeur donnée. Ce type de test est particulièrement adapté au problème de détection et de classification simultanée. Cet article montre que le test minimax de niveau contraint est la solution d'un problème de programmation linéaire qui calcule le risque maximum de classification et la distribution a priori la plus défavorable. Le test minimax égalise les risques de classification dont les probabilités a priori sont strictement positives. Le test est appliqué au problème de détection et d'estimation ponctuelle discrète qui consiste à détecter puis estimer la valeur d'un paramètre appartenant à un ensemble fini
Constructive Minimax Classification of Discrete Observations with Arbitrary Loss Function
No full textInternational audienceThis paper develops a multihypothesis testing framework for calculating numerically the optimal minimax test with discrete observations and an arbitrary loss function. Discrete observations are common in data processing and make tractable the calculation of the minimax test. Each hypothesis is both associated to a parameter defining the distribution of the observations and to an action which describes the decision to take when the hypothesis is true. The loss function measures the gap between the parameters and the actions. The minimax test minimizes the maximum classification risk. It is the solution of a finite linear programming problem which gives the worst case classification risk and the worst case prior distribution. The minimax test equalizes the classification risks whose prior probabilities are strictly positive. The minimax framework is applied to vector channel decoding which consists in classifying some codewords transmitted on a binary asymmetric channel. The Hamming metric is used to measure the number of differences between the emitted codeword and the decoded one
BRANCHED HOLOMORPHIC CARTAN GEOMETRIES AND CALABI-YAU MANIFOLDS
No full textWe introduce the concept of a branched holomorphic Cartan geometry. It generalizes to higher dimension the definition of branched (flat) complex projective structure on a Riemann surface introduced by Mandelbaum. This new framework is much more flexible than that of the usual holomorphic Cartan geometries. We show that all compact complex projective manifolds admit branched flat holomorphic projective structure. We also give an example of a non-flat branched holomorphic normal projective structure on a compact complex surface. It is known that no compact complex surface admits such a structure with empty branching locus. We prove that non-projective compact simply connected Kähler Calabi-Yau manifolds do not admit branched holomorphic projective structures. The key ingredient of its proof is the following result of independent interest: If E is a holomorphic vector bundle over a compact simply connected Kähler Calabi-Yau manifold, and E admits a holomorphic connection, then E is a trivial holomorphic vector bundle equipped with the trivial connection
Optimization of oriented and parametric cellular structures by the homogenization method
No full textInternational audienceWe present here a topology optimization method based on a homogenization approach to design oriented and parametrized cellular structures. The present work deals with 2-D square cells featuring a rectangular hole, because their structure is close to that of rank-2 sequential laminates, which are optimal for compliance optimization. For several cells, the value and the parametric sensitivities of their effective elastic tensor can easily be computed, by the resolution of a cell problem. The obtained results can be used to build a surrogate model for the homogenized constitutive law. Moreover, we add the local orientation of the cells to our problem. Then, an optimal composite shape is computed thanks to an alternate directions algorithm. The crucial ingredient of the methodology is the extraction of a quasi-periodic and additive manufacturable structure from the previously obtained composite shape, based on the introduction of a space transformation
First constraints on the timing of the Ecuadorian Coastal Cordillera upliftand geodynamic implications
No full textInternational audienceThe Carnegie Ridge subduction beneath the South American plate is currently considered as responsiblefor the acceleration of the northward escape of the North Andean Block, for the opening of the GuayaquilGulf, and for the uplift of the coastal forearc domain of western Ecuador, since at least Late Pleistocene. How-ever, the exact timing and amount of uplift of the coastal forearc domain and its Coastal Cordillera is poorly known.In this study, we provide the first detrital apatite (U-Th-Sm)/He (AHe) and zircon U/Pb ages from thecoastal domain in order to constrain the thermal history of both the Coastal Cordillera and its foreland basin.Our preliminary results indicate that the Middle-Late Miocene Angostura Fm was buried during Late Miocene,recording high enough temperatures to partially reset AHe ages. We show that the basin then records1 km ofuplift associated to erosion and cooling since Early Pliocene (5 Ma)