416 research outputs found
Convergence of a Vector Penalty Projection Scheme for the Navier-Stokes Equations with moving body
In this paper, we analyse a Vector Penalty Projection Scheme (see [1]) to
treat the displacement of a moving body in incompressible viscous flows in the
case where the interaction of the fluid on the body can be neglected. The
presence of the obstacle inside the computational domain is treated with a
penalization method introducing a parameter . We show the stability of
the scheme and that the pressure and velocity converge towards a limit when the
penalty parameter , which induces a small divergence and the time
step t tend to zero with a proportionality constraint =
t. Finally, when goes to 0, we show that the problem
admits a weak limit which is a weak solution of the Navier-Stokes equations
with no-sleep condition on the solid boundary. R{\'e}sum{\'e} Dans ce travail
nous analysons un sch{\'e}ma de projection vectorielle (voir [1]) pour traiter
le d{\'e}placement d'un corps solide dans un fluide visqueux incompressible
dans le cas o` u l'interaction du fluide sur le solide est n{\'e}gligeable. La
pr{\'e}sence de l'obstacle dans le domaine solide est mod{\'e}lis{\'e}e par une
m{\'e}thode de p{\'e}nalisation. Nous montrons la stabilit{\'e} du sch{\'e}ma
et la convergence des variables vitesse-pression vers une limite quand le param
etre qui assure une faible divergence et le pas de temps t
tendent vers 0 avec une contrainte de proportionalit{\'e} =
t. Finalement nous montrons que leprob{\`i} eme converge au
sens faible vers une solution des equations de Navier-Stokes avec une condition
aux limites de non glissement sur lafront{\`i} ere immerg{\'e}e quand le param
etre de p{\'e}nalisation tend vers 0
Le rĂŽle de lâĂtat et des bourgeoisies urbaines dans la production dâespace de loisir au QuĂ©bec
Dans un espace rĂ©gional pĂ©riphĂ©rique, le processus de valorisation/appropriation spatiale est vif. Il s'inscrit et s'interprĂšte aux deux degrĂ©s suivants de l'Ă©chelle socio-spatiale : l'espace des relations centre-pĂ©riphĂ©rie, d'une part, oĂč les impulsions partent du centre et trouvent leur expression spatiale par Ătat et technocratie interposĂ©s. Et d'autre part, l'espace des relations ville-campagne oĂč les bourgeoisies d'origine urbaine dĂ©veloppent et imposent de nouvelles pratiques spatiales. L'utilisation de l'espace en vue d'une production sociale implique des moyens et des fins qui sont induites par la logique du systĂšme productif et les conditions de sa survie. L'organisation du contraste est l'une des formes spatiales que commande cette logique.In a peripheral region, the process of spatial valorization/appropriation is vigorous. It can be inscribed in and explained by the two following degrees of the sociospatial scale : the space of heartland-hinterland relations, on the one hand, where the impetus comes from the core and finds its spatial expression via State and technocracy. On the other hand, we find the space of urban-rural relations where urban bourgeoisies develop and impose new spatial practices. The use of space for social production implies means, and purposes induced by the logic of the System of production and by its conditions for survival. The organization of contrast is one of the spatial forms which is commanded by this logic
Les réseaux de villes en France : quels acteurs? Quelles finalités? Quel avenir?
En cette fin de siĂšcle, la France nâĂ©chappe pas aux diktats de la mondialisation des marchĂ©s pas plus quâĂ celui de lâintĂ©gration europĂ©enne. Le nouveau contexte exacerbe la compĂ©tition Ă toutes les Ă©chelles gĂ©ographiques mais interpelle particuliĂšrement les villes moyennes et petites situĂ©es Ă lâĂ©cart des grands courants dâĂ©change. La mise en rĂ©seau est lâune des stratĂ©gies spatiales retenues par ces derniĂšres. Câest la voie choisie par la rĂ©gion Poitou-Charentes qui sâest dotĂ©e rĂ©cemment dâun rĂ©seau de villes moyennes puis dâun rĂ©seau de petites villes. Lâobjectif visĂ© ici est de dĂ©crire ces expĂ©riences de dĂ©veloppement rĂ©gional, dâen montrer la justification au plan thĂ©orique et dâen faire une Ă©valuation critique dans le contexte français et europĂ©en. Nous posons, notamment, quâau-delĂ de la perspective amĂ©nagiste, lâavenir des rĂ©seaux de villes passe par la survie Ă©conomique.Nowadays, France must deal at the same time with marketâs globalization and European integration. The new context increases competition at every territorial scale, but concerns especially small and medium sized cities located away from mainstream exchanges. The creation of urban networks is one of the spatial strategies chosen by French cities, particularly in the Poitou-Charentes region where two of these networks have recently emerged: one of medium sized cities followed by one of small sized cities. The goal we pursue here is to describe these experiences in regional development, to discuss their theoretical basis and to assess their relevance in the French and European contexts. Among other things, we believe that urban networking will survive through jobs creation, not only spatial planning
Le rĂŽle dâune ville moyenne pĂ©riphĂ©rique dans la production dâespace : Ă©tude de cas
De moins en moins territoire, de plus en plus espace, l'hinterland rimouskois est un produit social. Objet d'un enjeu, il entre dans des stratĂ©gies qui dĂ©neutralisent l'espace. On observe l'appropriation â par expropriation â d'un milieu de vie par des acteurs d'origine rimouskoise monopolisant un savoir fortement valorisĂ© socialement. On peut dĂ©crire le processus ainsi: appropriation fonciĂšre Ă caractĂšre absentĂ©iste, utilisation et frĂ©quentation d'un espace Ă des fins de loisirs, cristallisation de telles pratiques par l'Ătat. Ceux qui enclavent l'espace, et qui l'organisent, sont aussi ceux qui le consomment. Dans le cadre de la division du travail et par opposition aux « exĂ©cutants », ils se rattachent pour la plupart Ă une mĂȘme strate sociale, celle des « compĂ©tents ». C'est Ă travers les relations ville-campagne, centre-pĂ©riphĂ©rie, voire les rapports sociaux qu'est menĂ©e l'analyse de la production d'espace.The land around Rimouski is less and less a territory for productive activities and more and more a space for leisure activities. Thus the hinterland of Rimouski can be considered a social product. As an object of considerable and diverse market forces, this product is part of strategies which deneutralize space. Appropriation-expropriation of a milieu of life is achieved by interveners originating from Rimouski and monopolizing a know-how strongly valued by society. The process is as follows : land appropriation by absentee land holders, utilization and frequentation of a space for leisure purposes, crystallization of such practices by the State. Those who enclose space, and those who organize it, are those who consume it. From the point of view of the division of labor, in opposition to the « executants », most of them participate in the same social stratum, the « competents ». It is through these urban-rural and hearthland-hinterland relations, and even in a greater sense, through social structure that analysts will interpret major changes in space production
Palladium-acetate catalyst for regioselective direct arylation at C2 of 3-furanyl or 3-thiophenyl acrylates with inhibition of Heck type reaction
International audiencePd(OAc)2/KOAc was found to be an efficient catalytic system for the direct arylation of thiophene and furan derivatives bearing an acrylate at C3. The selectivity of the reaction strongly depends on the nature of the coordinating base. Na2CO3 and Li2CO3 favours the Heck type reaction; whereas the use of KOAc or CsOAc promotes regioselective arylation at C2 of the heteroarene and inhibits the Heck type reaction. The direct arylation products were obtained in moderate to good yields using only 0.1 mol % of catalyst. Electron-withdrawing substituent on aryl bromide, such as acetyl, formyl, ester, nitrile or nitro, favours the reaction; whereas electron-donating ones are unfavourable
Indicateurs de durabilité pour la conception préliminaire de bureaux du point de vue énergétique
The building sector currently represents 40% of the energy consumption and one of the major emitters of greenhouse gases in the world. This, combined with the characteristic long lifespan of buildings, means that the decisions behind building design have long-term and multidimensional impacts on both society and the environment. As a result, there is a growing interest in the assessment of buildings based on the concept of sustainability, considering its three basic dimensions: economic, ecological and social. However, current evaluation systems are usually developed in the context of the declaration or certification of buildings, while only a limited number are designed to provide decision-support during the preliminary design phase. It is during these early design stages that key decisions such as construction principles and operation strategies are defined, usually with a limited amount of information available. In order to assist in decision-making during the preliminary building design, a set of indicators is proposed in this present work to evaluate early design alternatives by following a life-cycle analysis approach and according to the three pillars of sustainability. Indicator selection is based on consensus from the international projects and initiatives that compose the state of the art, as well as operational aspects such as database availability for calculation parameters, the evolution of information available and of specific design decisions at every stage of the design process. The conclusions of this study are focused on the energy design of commercial buildings, specifically offices, in the French context
Analyse expĂ©rimentale et modĂ©lisation dâun Ă©changeur-stockeur contenant des matĂ©riaux Ă changement de phase
Un outil de simulation dynamique a Ă©tĂ© dĂ©veloppĂ© afin dâĂ©tudier le comportement thermique dâun Ă©changeur-stockeur contenant des matĂ©riaux Ă changement de phase dĂ©diĂ© au rafraĂźchissement de lâair dans le bĂątiment. Ce modĂšle prend en compte le phĂ©nomĂšne de fonte par contact induit par la variation de densitĂ© entre les phases solide et liquide du MCP. Les rĂ©sultats expĂ©rimentaux sont prĂ©sentĂ©s et analysĂ©s afin de dĂ©gager le comportement dynamique de lâĂ©changeur-stockeur soumis Ă un Ă©coulement dâair Ă vitesse constante et Ă tempĂ©rature dâentrĂ©e constant
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