Crise de l’euro et divergences économiques : les conséquences du marché unique pour l’unité européenne

The real causes of the euro crisis (2010-2013) are still questioned. For the European authorities, it is mainly due to the imperfection of the national institutions of the affected countries. In response, the policies implemented in these countries were to correct these imperfections by reforming deeply their national institutions in a move towards a balanced budget and improved competitiveness. In this article, it is argued that the origins of the crisis lie in the very functioning of the Single Market. By organizing the European economy according to the principles of free competition and by promoting the circulation of mobile production factors, the Single Market has strengthened the agglomeration mechanisms, which has led to a European industrial polarization. Although this dynamic has been beneficial for the core European countries, it accelerated the deindustrialization of peripheral economies. Moreover, the policies pursued since 2010 in the countries affected by the euro crisis have failed to correct the economic imbalances. It then appears that only a profound reconsideration of the rules that organize the functioning of the European Single Market would be likely to stop the current divergence dynamics of European economies

Collective secondary instabilities: an application to three-dimensional boundary-layer flow

In some linearly unstable flows, secondary instability is found to have a much larger wavelength than that of the primary unstable modes, so that it cannot be recovered with a classical Floquet analysis. In this work, we apply a new formulation for capturing secondary instabilities coupling multiple length scales of the primary mode. This formulation, based on two-dimensional stability analysis coupled with a Bloch waves formalism originally described in Schmid et al. (2017), allows to consider high-dimensional systems resulting from several repetitions of a periodic unit, by solving an eigenproblem of much smaller size. Collective instabilities coupling multiple periodic units can be thus retrieved. The method is applied on the secondary stability of a swept boundary-layer flow subject to stationary cross-flow vortices, and compared with Floquet analysis. Two multi-modal instabilities are recovered: for streamwise wavenumber $\alpha_v$ close to zero, approximately twelve sub-units are involved in large-wavelength oscillations; whereas a staggered pattern, characteristic of subharmonic instabilities, is observed for $\alpha_v = 0.087$

Turbulent transition in a channel with superhydrophobic walls: the effect of roughness anisotropy

Superhydrophobic surfaces dramatically reduce skin friction of overlying liquid flows. These surfaces are complex and numerical simulations usually rely on models for reducing this complexity. One of the simplest consists in finding an equivalent boundary condition through an homogenisation procedure, which in the case of channel flow over oriented riblets, leads to the presence of a small spanwise component in the homogenized base flow velocity. This work aims at investigating the influence of such a three-dimensionality of the base flow on stability and transition in a channel with walls covered by oriented riblets. Linear stability for this base flow is investigated: a new instability region, linked to cross-flow effects, is observed. Tollmien-Schlichting waves are also retrieved but the most unstable are three-dimensional. Transient growth is also affected as oblique streaks with non-zero streamwise wavenumber become the most amplified perturbations. When transition is induced by Tollmien-Schlichting waves, after an initial exponential growth regime, streaky structures with large spanwise wavenumber rapidly arise. Modal mechanisms appear to play a leading role in the development of these structures and a secondary stability analysis is realised to retrieve successfully some of their characteristics. The second scenario, initiated with crossflow vortices, displays a strong influence of nonlinearities. The flow develops into large quasi spanwise-invariant structures before breaking down to turbulence. Secondary stability on the saturated cross-flow vortices sheds light on this stage of transition. In both cases, cross-flow effects dominate the flow dynamics, suggestings the need to consider these effects when modelling superhydrophobic surfaces

Contribution au pronostic d'une pile à combustible de type PEMFC - approche par filtrage particulaire.

The development of new energy converters, more efficient and environment friendly, such as fuelcells, tends to accelerate. Nevertheless, their large scale diffusion supposes some guaranties in termsof safety and availability. A possible solution to do so is to develop Prognostics and HealthManagement (PHM) on these systems, in order to monitor and anticipate the failures, and torecommend the necessary actions to extend their lifetime. In this spirit, this thesis deals with theproposal of a prognostics approach based on particle filtering dedicated to PEMFCs.The reasoning focuses first on setting a formalization of the working framework and theexpectations. This is pursued by the development of a physic-based modelling enabling a state ofhealth estimation and its evolution in time. The state estimation is made thanks to particle filtering.Different variants of filters are considered on the basis of the literature and new proposals adaptedto PHM are proposed and compared to existing ones. State of health estimates given by the filter areused to predict the future state of the system and its remaining useful life. All the proposals arevalidated on four datasets from PEMFC following different mission profiles. The results show goodperformances for predictions and remaining useful life estimates before failure.Le développement de nouveaux convertisseurs d’énergie, plus efficients et plus respectueux del’environnement, tels que les piles à combustibles, tend à s’accélérer. Leur diffusion à grande échellesuppose cependant des garanties en termes de sécurité et de disponibilité. Une solution possiblepour ce faire est de développer des solutions de Prognostics and Health Management (PHM) de cessystèmes, afin de mieux les surveiller, anticiper les défaillances et recommander les actionsnécessaires à l’allongement de leur durée de vie. Dans cet esprit, cette thèse porte sur la propositiond’une approche de pronostic dédiée aux piles à combustibles de types PEMFC à l’aide de filtrageparticulaire.Le raisonnement s’attache tout d’abord à mettre en place une formalisation du cadre de travailainsi que des exigences de mise en. Ceci se poursuit par le développement d’un modèle basé sur laphysique permettant une estimation d’état de santé et de son évolution temporelle. L’estimationd’état est réalisée grâce à du filtrage particulaire. Différentes variantes de filtres sont considérées surla base d’une de la littérature et de nouvelles propositions adaptées au PHM sont formulées etcomparées à celles existantes. Les estimations d’état de santé fournies par le processus de filtragesont utilisées pour réaliser des prédictions de l’état de santé futur du système, puis de sa durée devie résiduelle. L’ensemble des propositions est validé sur 4 jeux de données obtenus sur des PEMFCsuivant des profils de mission variés. Les résultats montrent de bonnes performances deprédictions et d’estimations de durée de vie résiduelle avant défaillance

Acid geopolymer materials based on different aluminosilicate sources

Geopolymers synthetized from the reaction of metakaolin (or alumino-silicate) in an alkali medium are studied since decades [1]. However, in order to develop composites, alkali medium is undesirable due to the detrimental effect of alkali ions on fibers. As an alternative, the use of an acid medium seems promising as some authors demonstrated an increase of mechanical properties with acid-based geopolymers [2, 3]. The aim of this work is to investigate the various formulations and to understand the reactional mechanisms. The work is based on the activation of an alumino-silicate source with phosphoric acid to obtain geopolymer The various formulations consist to determine the Al/P ratio leading to consolidation at various temperatures (from 20 to 70°C). The samples were characterized by Fourier Transform Infrared and Nuclear Magnetic Resonance spectroscopies and X-Ray Diffraction measurements in order to study their structure. The thermal and mechanical properties were correlated with the microstructure [4]. Consolidated geopolymers were synthetized with different Al/P ratios. The consolidation time decreases with increasing Al/P ratio. For instance, the material realized with Si/Al=1,17 consolidates at 20°C in 15 and 8 days with Al/P=4 and 1, respectively. Tow behaviors can be distinguished samples presenting good fire resistance (Si/Al=1,17 and Al/P=1) or presenting poorly water resistant (Si/Al=1,17 and Al/P=4). Consequently, the impact of the reactivity of the alumino-silicate source on the geopolymerisation kinetics leads to different types of structures (secondary and metastable phases) in relation with the phosphor content. References: [1] J.Davidovits, J. Therm. Anal. 37 (1991) 1633-1656. [2] D. S. Perrera, J Mater Sci, vol. 3, pp. 6562-6566, 2008. [3] H. K. Tchakouté and C. Rüscher, Applied Clay Science, vol. 140, pp. 81-87,2017. [4] H.Celerier and al., under submission

Introduction

Dans les années 1980 et 1990, le concept de communauté était au cœur des débats entre les communautariens et les libéraux anglo-saxons. En France, il a joué (et joue encore) un rôle important dans les débats sur la république et le « communautarisme ». Le contexte dans lequel il est remis en scène aujourd’hui est celui de la résurgence du nationalisme et des revendications identitaires. La crise de l’idéal cosmopolitique et de l’idée du multicul..

Prognostics of PEM fuel cell in a particle filtering framework.

International audienceProton Exchange Membrane Fuel Cells (PEMFC) suffer from a limited lifespan, which impedes their uses at a large scale. From this point of view, prognostics appears to be a promising activity since the estimation of the Remaining Useful Life (RUL) before a failure occurs allows deciding from mitigation actions at the right time when needed. Prognostics is however not a trivial task: 1) underlying degradation mechanisms cannot be easily measured and modeled, 2) health prediction must be performed with a long enough time horizon to allow reaction. The aim of this paper is to face these problems by proposing a prognostics framework that enables avoiding assumptions on the PEMFC behavior, while ensuring good accuracy on RUL estimates. Developments are based on a particle filtering approach that enables including non-observable states (degradation through time) into physical models. RUL estimates are obtained by considering successive probability distributions of degrading states. The method is applied on 2 data sets, where 3 models of the voltage drop are tested to compare predictions. Results are obtained with an accuracy of 90 hours around the real RUL value (for a 1000 hours lifespan), clearly showing the significance of the proposed approach