Les espaces de l'halieutique

L'étang de Thau est un espace lagunaire semi fermé dont les communications avec la mer sont limitées. L'exploitation de la palourde, ressource intrinsèquement peu mobile, est au coeur de l'activité de pêche dans cet étang. Il semble donc, a priori, que les notions d'espace mis en oeuvre par l'exploitation de cette ressource présentent un caractère de proximité et une dimension localisée à l'écosystème "étang de Thau". Dès lors, on pourrait penser que la connaissance écologique de ce milieu - où d'importants programmes scientifiques ont été réalisées -, alliée à la faible mobilité de cette population de bivalves fouisseurs, constituent des conditions favorables à une gestion "efficace" de cet écosystème. Ce sentiment est renforcé par le contexte social dans lequel évoluent les communautés de pêcheurs qui ont derrière elles une longue pratique de la gestion (prud'homies). Or, après une période florissante achevée en 1992, cette pêcherie traverse une crise aiguë. Les professionnels constatent en effect une forte diminution des stocks qui se traduit par (i) une régression des quantités pêchées par jours de travail (PUE) (ii) une diminution des prix (contre toute logique de marché) et (iii) une décroissance du nombre de pêcheurs. Parallèlement on observe une transformation des méthodes de pêche avec la généralisation de la pêche en plongée aux dépens de "l'arselière" technique traditionnelle qui a quasiment disparu. Dans ce contexte, et à la demande de la profesison, un programme pluridisciplinaire (programme Palourde) a été mis en oeuvre afin d'identifier les limites du système actuel puis d'élaborer un nouveau système de gestion. Ce travail a été mené selon une démarche de concertation élargie de l'ensemble des partenaires de l'exploitation (pêcheurs, mareyeurs, gestionnaires) et de façon négociée entre les acteurs... (Résumé d'auteur

La rivière et sa mise en paysage dans les parcs et jardins : étude de cas dans l'Ouest français

L\u27objectif de cet article est d\u27étudier les formes de mobilisation de la ressource en eau (énergétique, esthétique) dans les parcs et jardins. Deux hypothèses seront examinées : les parcs et jardins sont des motifs paysagers pertinents pour observer les trajectoires d\u27usage de la ressource en eau et ses conséquences hydrodynamiques ; l\u27artificialisation des hydrosystèmes n\u27est pas toujours synonyme de dégradation mais peut au contraire être génératrice de diversité paysagère et d\u27ingéniosité hydraulique (Baridon, 2007). Il s\u27agit d\u27aborder ces espaces sous l\u27angle géo-historique enrichi de l\u27histoire de l\u27art des parcs et jardins. Dans un premier temps, nous proposerons une description des sites d\u27étude avant d’analyser les projets et les intentions hydrauliques. Les paysages construits sont ensuite analysés afin de mettre en exergue les transformations des formes et les dynamiques fluviales entre la Renaissance et le XXIe siècle. La recherche se fonde sur deux études de cas choisies dans le bassin versant du Couasnon (265 km²), rivière angevine tributaire de la Loire. La démarche retenue associe : une lecture systémique de la trajectoire des paysages fluviaux où les formes fluviales mises en projet sont abordées comme l\u27expression d\u27une interaction nature/société ; une caractérisation des aménagements hydrauliques du parc dans le contexte de la vallée. L\u27étude s\u27appuie sur l\u27analyse diachronique de séries de cartes et de plans, de photographies et d\u27observations de terrain

Impact of the 26-30 May 2003 solar events on the earth ionosphere and thermosphere.

During the last week of May 2003, the solar active region AR 10365 produced a large number of flares, several of which were accompanied by Coronal Mass Ejections (CME). Specifically on 27 and 28 May three halo CMEs were observed which had a significant impact on geospace. On 29 May, upon their arrival at the L1 point, in front of the Earth's magnetosphere, two interplanetary shocks and two additional solar wind pressure pulses were recorded by the ACE spacecraft. The interplanetary magnetic field data showed the clear signature of a magnetic cloud passing ACE. In the wake of the successive increases in solar wind pressure, the magnetosphere became strongly compressed and the sub-solar magnetopause moved inside five Earth radii. At low altitudes the increased energy input to the magnetosphere was responsible for a substantial enhancement of Region-1 field-aligned currents. The ionospheric Hall currents also intensified and the entire high-latitude current system moved equatorward by about 10°. Several substorms occurred during this period, some of them - but not all - apparently triggered by the solar wind pressure pulses. The storm's most notable consequences on geospace, including space weather effects, were (1) the expansion of the auroral oval, and aurorae seen at mid latitudes, (2) the significant modification of the total electron content in the sunlight high-latitude ionosphere, (3) the perturbation of radio-wave propagation manifested by HF blackouts and increased GPS signal scintillation, and (4) the heating of the thermosphere, causing increased satellite drag. We discuss the reasons why the May 2003 storm is less intense than the October-November 2003 storms, although several indicators reach similar intensities

On twisted Fourier analysis and convergence of Fourier series on discrete groups

We study norm convergence and summability of Fourier series in the setting of reduced twisted group $C^*$-algebras of discrete groups. For amenable groups, F{\o}lner nets give the key to Fej\'er summation. We show that Abel-Poisson summation holds for a large class of groups, including e.g. all Coxeter groups and all Gromov hyperbolic groups. As a tool in our presentation, we introduce notions of polynomial and subexponential H-growth for countable groups w.r.t. proper scale functions, usually chosen as length functions. These coincide with the classical notions of growth in the case of amenable groups.Comment: 35 pages; abridged, revised and update

Isometric group actions on Banach spaces and representations vanishing at infinity

Our main result is that the simple Lie group $G=Sp(n,1)$ acts properly isometrically on $L^p(G)$ if $p>4n+2$. To prove this, we introduce property ({\BP}_0^V), for $V$ be a Banach space: a locally compact group $G$ has property ({\BP}_0^V) if every affine isometric action of $G$ on $V$, such that the linear part is a $C_0$-representation of $G$, either has a fixed point or is metrically proper. We prove that solvable groups, connected Lie groups, and linear algebraic groups over a local field of characteristic zero, have property ({\BP}_0^V). As a consequence for unitary representations, we characterize those groups in the latter classes for which the first cohomology with respect to the left regular representation on $L^2(G)$ is non-zero; and we characterize uniform lattices in those groups for which the first $L^2$-Betti number is non-zero.Comment: 28 page

Breathing Current Domains in Globally Coupled Electrochemical Systems: A Comparison with a Semiconductor Model

Spatio-temporal bifurcations and complex dynamics in globally coupled intrinsically bistable electrochemical systems with an S-shaped current-voltage characteristic under galvanostatic control are studied theoretically on a one-dimensional domain. The results are compared with the dynamics and the bifurcation scenarios occurring in a closely related model which describes pattern formation in semiconductors. Under galvanostatic control both systems are unstable with respect to the formation of stationary large amplitude current domains. The current domains as well as the homogeneous steady state exhibit oscillatory instabilities for slow dynamics of the potential drop across the double layer, or across the semiconductor device, respectively. The interplay of the different instabilities leads to complex spatio-temporal behavior. We find breathing current domains and chaotic spatio-temporal dynamics in the electrochemical system. Comparing these findings with the results obtained earlier for the semiconductor system, we outline bifurcation scenarios leading to complex dynamics in globally coupled bistable systems with subcritical spatial bifurcations.Comment: 13 pages, 11 figures, 70 references, RevTex4 accepted by PRE http://pre.aps.or

Automatic multiplanar CT reformatting from trans-axial into left ventricle short-axis view

International audienceThe short-axis view defined such that a series of slices are perpendicular to the long-axis of the left ventricle (LV) is one of the most important views in cardiovascular imaging. Raw trans-axial Computed Tomography (CT) images must be often reformatted prior to diagnostic interpretation in short-axis view. The clinical importance of this refor-matting requires the process to be accurate and reproducible. It is often performed after manual localization of landmarks on the image (e.g. LV apex, centre of the mitral valve, etc.) being slower and not fully reproducible as compared to automatic approaches. We propose a fast, automatic and reproducible method to reformat CT images from original trans-axial orientation to short-axis view. A deep learning based seg-mentation method is used to automatically segment the LV endocardium and wall, and the right ventricle epicardium. Surface meshes are then obtained from the corresponding masks and used to automatically detect the shape features needed to find the transformation that locates the cardiac chambers on their standard, mathematically defined, short-axis position. 25 datasets with available manual reformatting performed by experienced cardiac radiologists are used to show that our reformatted images are of equivalent quality

Microbial contamination and management scenarios in a Mediterranean coastal lagoon (Etang de Thau, France): application of a Decision Support System within the Integrated Coastal Zone Management context

1 - In the Thau lagoon (Southern Mediterranean Coast) the main anthropogenic pressure is represented by the urban development in the watershed, whilst oyster and mussel farming represents one of the main economical activities in the region. 2 - During the last decade, the increasing organic loads from watershed and urban settlements in the lagoon surroundings have caused a diffuse contamination by faecal bacteria. Also toxic algal blooms have been occurring, impairing water quality with major impacts on shellfish farming, fishery and bathing. 3 - In this study, indicators and scenarios identified for the lagoon have been integrated in a Decision Support System (DSS) to evaluate the best solutions for reducing pressures and improving both water quality and ecosystem status. 4 - The watershed has been analysed with reference to indicators of pollution sources and transfer rates to the lagoon. In parallel, socio-economic indicators and descriptors of urban growth and development have been assessed. Numerical models have been run in order to simulate the lagoon hydrodynamics in relation to both meteorological factors and watershed runoff. The impact of faecal bacteria contamination has been evaluated in terms of economical losses and social conflicts, arising from the restriction of shellfish farming and marketing during contamination events. Finally, the DSS prototype has been applied to the lagoon in support to management and future planning