492 research outputs found
A Study of Induced Drag and Spanwise Lift Distribution for Three-Dimensional Inviscid Flow Over a Wing
Numerical results for an untwisted, finite rectangular wing (NACA 0012, AR = 6.7) using no flap deflections are compared against theoretical lifting line predictions. The numerical approach used an Euler-based computational fluid dynamic (CFD) solver. A span-wise lift distribution was extracted from the CFD solution. The comparison between the predicted numerical and lifting-line span-wise lift distributions shows good agreement with a maximum deviation of only 2.4% over the wing span. The induced drag was extracted from the downstream wake using a wake integral technique referred to as Trefftz plane analysis. The predictions for induced drag based on surface integration, wake integration and lifting line methods are compared. Near wake and compressible flow corrections were applied to improve the induced drag predictions by wake integration. The study details an initial effort to identify and to quantify the numerical uncertainties associated with the induced drag prediction
The imprint of the disc dispersal phase on the demographics of giant planets
JĂŒngste Beobachtungsprogramme von Exoplaneten haben die Existenz einer beeindruckenden Vielfalt von Planetensystemen aufgezeigt. Dies wirft daher die Frage auf, wie Planetensysteme wie das Unsere entstehen und sich entwickeln können. Der SchlĂŒssel zur ErklĂ€rung dieser Vielfalt liegt im VerstĂ€ndnis der statistischen Trends, die sich aus der jĂŒngsten FĂŒlle von Exoplanetendaten abzeichnen. Einer davon ist ein Peak in der Halbwertsachsenverteilung von Gasriesen, die sich bevorzugt bei Bahnradien von etwa 1â2 astronomischen Einheiten anhĂ€ufen. Es wurde kĂŒrzlich die Hypothese aufgestellt, dass dieses charakteristische Merkmal wĂ€hrend der Zeit der Planetenmigration in der gasreichen protoplanetaren Scheibe entsteht, die durch die Auflösung der Scheibe mittels röntgengetriebener Photoevaporation gestoppt wird. In dieser Dissertation untersuche ich den Einfluss der Dispersionsphase der Scheibe auf den Migrationsprozess von Gasriesen, was zu einem besseren VerstĂ€ndnis ihrer beobachteten Demografie fĂŒhrt. Zu diesem Zweck habe ich mehrdimensionale, numerische Simulationen der Scheiben-Planeten-Wechselwirkung und eine als Planetenpopulationssynthese bekannte Methode verwendet. AnschlieĂend untersuche ich, ob diese Wechselwirkung zwischen der Scheibendispersion und Planetenentwicklung einen möglichen Abdruck in der beobachteten Demografie von Gas- riesen hinterlassen kann. Indem wir die beobachteten RöntgenleuchtkrĂ€fte von Sternen mit der Halbwertsachsenverteilung ihrer Gasriesen korrelieren, identifizieren wir ein auffĂ€lliges Merkmal, das auch qualitativ von unseren Simulationen vorhergesagt wird. Dies festigt daher unsere Anfangshypothese, dass Röntgen-Photoevaporation tatsĂ€chlich die Architektur von Planetensystemen prĂ€gt. Die Ergebnisse dieser umfangreichen Studie stellen wichtige Bedingungen fĂŒr aktuelle Modelle der Planetenentstehung und -entwicklung dar und geben Orientierung fĂŒr zukĂŒnftige Modelle, die eine genaue Behandlung der Dispersionsphase der protoplanetaren Scheibe berĂŒcksichtigen mĂŒssen.Recent exoplanet surveys have highlighted the existence of an impressive diversity of planetary systems, raising the question of how systems like our own can form and develop. The key to explaining their diversity lies in the understanding of the statistical trends that are now emerging from the recent wealth of exoplanet data. One of these trends is a peak in the semi-major axis distribution of gas giants that preferentially clump up at orbital radii of 1â2 astronomical units. It has recently been suggested that this characteristic feature may be established during the time of planetary migration. The migration of giant planets in the gas-rich protoplanetary disc is halted by disc dispersal via X-ray driven photoevaporation. In this thesis I aim at studying the impact of the disc dispersal phase on the migration process of gas giants, leading to a better understanding of their observed demographics. For this purpose, I have used multi-dimensional numerical simulations of disc-planet interactions and a method known as planet population synthesis. I am then investigating if this interaction between disc dispersal and planet evolution can leave any potential diagnostics in the observed demographics of giant planets. By correlating the observed X-ray luminosities of giant planet host stars with the semi-major axis distribution of their giant planets, we find a prominent feature that is also predicted qualitatively by our simulations, further strengthening the conclusion that X-ray-driven photoevaporation is indeed shaping the architecture of planetary systems. The results obtained from this extensive study pose important limitations on current models of planet formation and evolution and provide guidance for future models that need to take an accurate treatment of the disc dispersal phase into account
La dimension externe de l'action éducative : vers une politique intégrée de l'Union européenne
This study reveals the strong potential of the EUâs intervention to deal with the current international challenges and it aims to recognize a shared competence of the EU in the field of education. Based on multiple foundations, the EUâs external education measures are substantially more important than they may appear. The EUâs external education policy is, at the same time, mainstreamed by its cross-disciplinary nature, and integrative by its contribution to the deepening of the European project. The EUâs external education policy is not confined to sporadic measures and was based from the outset on the use of the flexibility clause and connectivity of the EUâs areas of expertise. It is built on holistic concepts and coherent goals pursued within the framework of external long-term strategies, which implied the EUâs enhanced competence in the field of education, beyond that of support established in the Treaty. The progressive extension of the EUâs scope of competence in the field of education is closely linked with the higher added value of the EU in the management of a knowledge-based economyâs impact on education services and its effective contribution to international measures in the field of education for all. This research aims to gather and analyse legal, technical, socio-political and financial elements, which offer conclusive evidence of the existence of the EUâs external education policy and present its main features. It is hoped this will lead to an adjustment of the EUâs competences and powers, so as to take into account the development of institutional practice that cannot be overlooked for the sake of legal certainty, transparency and effectiveness of EUlaw.Tendant vers la reconnaissance dâune compĂ©tence partagĂ©e de lâUE en matiĂšre dâĂ©ducation, cette Ă©tude vise Ă rĂ©vĂ©ler le fort potentiel de lâintervention de lâUE dans la gestion des nouveaux dĂ©fis Ă©ducatifs mondiaux. FondĂ©e sur un faisceau de compĂ©tences intriquĂ©es, lâaction externe de lâUE dans le secteur Ă©ducatif est substantiellement plus dĂ©veloppĂ©e quâelle ne le laisse a priori paraĂźtre. Elle constitue une politique extĂ©rieure Ă©ducative, qui se rĂ©vĂšle Ă la fois intĂ©grĂ©e, par sa nature transversale, et intĂ©grative, par sa contribution Ă lâapprofondissement du projet europĂ©en. L'extension progressive du champ de compĂ©tence de lâUE en matiĂšre dâĂ©ducation est liĂ©e Ă la valeur ajoutĂ©e, sans cesse accrue, de lâUE pour gĂ©rer lâimpact de lâĂ©conomie mondialisĂ©e de la connaissance sur les services dâĂ©ducation et contribuer efficacement au dĂ©veloppement dâactions internationales de grande envergure en matiĂšre dâĂ©ducation pour tous. Ces travaux de recherches ont pour finalitĂ© de rassembler et analyser les Ă©lĂ©ments juridiques, techniques, sociopolitiques et financiers, plaidant en faveur de lâĂ©tablissement dâune politique extĂ©rieure Ă©ducative de lâUE et dâen apprĂ©hender les principales caractĂ©ristiques. Ils visent Ă impulser un ajustement des compĂ©tences et pouvoirs de lâUE afin de prendre en compte lâĂ©volution de la pratique institutionnelle, que lâon ne peut occulter dans un souci de sĂ©curitĂ© juridique, de transparence et de prĂ©servation de lâeffet utile du droit europĂ©en
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