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Search Results: 1 - 10 of 4068 matches for " Jacques Crovisier "
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Astronomy and astronomers in Jules Verne's novels
Jacques Crovisier
Physics , 2009,
Abstract: Almost all the "Voyages Extraordinaires" written by Jules Verne refer to astronomy. In some of them, astronomy is even the leading theme. However, Jules Verne was basically not learned in science. His knowledge of astronomy came from contemporaneous popular publications and discussions with specialists among his friends or his family. In this article, I examine, from the text and illustrations of his novels, how astronomy was perceived and conveyed by Jules Verne, with errors and limitations on the one hand, with great respect and enthusiasm on the other hand. This informs us on how astronomy was understood by an "honn\^ete homme" in the late 19th century.
Observations of the 18-cm OH lines of comet 103P/Hartley 2 at Nan?ay in support to the EPOXI and Herschel missions
Jacques Crovisier,Pierre Colom,Nicolas Biver,Dominique Bockelée-Morvan,Jérémie Boissier
Physics , 2012, DOI: 10.1016/j.icarus.2012.03.033
Abstract: The 18-cm radio lines of the OH radical were observed in comet 103P/Hartley 2 with the Nan\c{c}ay radio telescope in support to its flyby by the EPOXI mission and to observations with the Herschel Space Observatory. The OH lines were detected from 24 September to 15 December 2010. These observations are used to estimate the gas expansion velocity within the coma to 0.83 \pm 0.08 km/s in October 2010. The water production increased steeply but progressively before perihelion, and reached 1.9 \pm 0.3 X 10E28 s-1 just before the EPOXI flyby.
Birth of homoclinic intersections: a model for the central dynamics of partially hyperbolic systems
Sylvain Crovisier
Mathematics , 2006,
Abstract: We prove a conjecture of J. Palis: any diffeomorphism of a compact manifold can be C1-approximated by a Morse-Smale diffeomorphism or by a diffeomorphism having a transverse homoclinic intersection. ----- Cr'eation d'intersection homoclines : un mod`ele pour la dynamique centrale des syst`emes partiellement hyperboliques. Nous montrons une conjecture de J. Palis : tout diff'eomorphisme d'une vari'et'e compacte peut ^etre approch'e en topologie C1 par un diff'eomorphisme Morse-Smale ou par un diff'eomorphisme ayant une intersection homocline transverse.
Perturbation de la dynamique de difféomorphismes en topologie C^1 / Perturbation of the dynamics of diffeomorphisms in the C^1-topology
Sylvain Crovisier
Mathematics , 2009,
Abstract: Les travaux pr\'esent\'es dans ce m\'emoire portent sur la dynamique de diff\'eomorphismes de vari\'et\'es compactes. Pour l'\'etude des propri\'et\'es g\'en\'eriques ou pour la construction d'exemples, il est souvent utile de savoir perturber un syst\`eme. Ceci soul\`eve g\'en\'eralement des probl\`emes d\'elicats : une modification locale de la dynamique peut engendrer un changement brutal du comportement des orbites. En topologie C^1, nous proposons diverses techniques permettant de perturber tout en contr\^olant la dynamique : mise en transversalit\'e, connexion d'orbites, perturbation de la dynamique tangente, r\'ealisation d'extensions... Nous en tirons diverses applications \`a la description de la dynamique des diff\'eomorphismes C^1-g\'en\'eriques.

This memoir deals with the dynamics of diffeomorphisms of compact manifolds. For the study of generic properties or for the construction of examples, it is often useful to be able to perturb a system. This generally leads to delicate problems: a local modification of the dynamic may cause a radical change in the behavior of the orbits. For the C^1 topology, we propose various techniques which allow to perturb while controlling the dynamic: setting in transversal position, connection of orbits, perturbation of the tangent dynamics,... We derive various applications to the description of the C^1-generic diffeomorphisms.

Perturbations of C1-diffeomorphisms and dynamics of generic conservative diffeomorphisms of surface
Sylvain Crovisier
Mathematics , 2010,
Abstract: In the first part of this text we give a survey of the properties satisfied by the C1-generic conservative diffeomorphisms of compact surfaces. The main result that we will discuss is that a C1-generic conservative diffeomorphism of a connected compact surface is transitive. It is obtain as a consequence of a connecting lemma for pseudo-orbits. In the last parts we expose some recent developments of the C1-perturbation technics and the proof of this connecting lemma. We are not aimed to deal with technicalities nor to give the finest available versions of these results. Besides this theory exists also in higher dimension and in the non-conservative setting, we restricted the scope of this presentation to the conservative case on surfaces, since it offers some simplifications which allow to explain in an easier way the main ideas of the subject.
Partial hyperbolicity far from homoclinic bifurcations
Sylvain Crovisier
Mathematics , 2008,
Abstract: We prove that any diffeomorphism of a compact manifold can be C^1-approximated by a diffeomorphism which exhibits a homoclinic bifurcation (a homoclinic tangency or a heterodimensional cycle) or by a diffeomorphism which is partially hyperbolic (its chain-recurrent set splits into partially hyperbolic pieces whose centre bundles have dimensions less or equal to two). We also study in a more systematic way the central models introduced in arXiv:math/0605387.
Dynamics of $C^1$-diffeomorphisms: global description and prospects for classification
Sylvain Crovisier
Mathematics , 2014,
Abstract: We are interested in finding a dense part of the space of $C^1$-diffeomorphisms which decomposes into open subsets corresponding to different dynamical behaviors: we discuss results and questions in this direction. In particular we present recent results towards a conjecture by J. Palis: any system can be approximated either by one which is hyperbolic (and whose dynamics is well understood) or by one which exhibits a homoclinic bifurcation (a simple local configuration involving one or two periodic orbits).
Ethyl alcohol and sugar in comet C/2014Q2 (Lovejoy)
Nicolas Biver,Dominique Bockelée-Morvan,Rapha?l Moreno,Jacques Crovisier,Pierre Colom,Dariusz C. Lis,Aage Sandqvist,Jérémie Boissier,Didier Despois,Stefanie N. Milam
Physics , 2015,
Abstract: The presence of numerous complex organic molecules (COMs; defined as those containing six or more atoms) around protostars shows that star formation is accompanied by an increase of molecular complexity. These COMs may be part of the material from which planetesimals and, ultimately, planets formed. Comets represent some of the oldest and most primitive material in the solar system, including ices, and are thus our best window into the volatile composition of the solar protoplanetary disk. Molecules identified to be present in cometary ices include water, simple hydrocarbons, oxygen, sulfur, and nitrogen-bearing species, as well as a few COMs, such as ethylene glycol and glycine. We report the detection of 21 molecules in comet C/2014 Q2 (Lovejoy), including the first identification of ethyl alcohol (ethanol, C2H5OH) and the simplest monosaccharide sugar glycolaldehyde (CH2OHCHO) in a comet. The abundances of ethanol and glycolaldehyde, respectively 5 and 0.8% relative to methanol (0.12 and 0.02% relative to water), are somewhat higher than the values measured in solar- type protostars. Overall, the high abundance of COMs in cometary ices supports the formation through grain-surface reactions in the solar system protoplanetary disk.
On the density of singular hyperbolic three-dimensional vector fields: a conjecture of Palis
Sylvain Crovisier,Dawei Yang
Mathematics , 2014,
Abstract: In this note we announce a result for vector fields on three-dimensional manifolds: those who are singular hyperbolic or exhibit a homoclinic tangency form a dense subset of the space of $C^1$-vector fields. This answers a conjecture by Palis. The argument uses an extension for local fibered flows of Ma\~n\'e and Pujals-Sambarino's theorems about the uniform contraction of one-dimensional dominated bundles. Sur la densit\'e de l'hyperbolicit\'e singuli\`ere pour les champs de vecteurs en dimension trois : une conjecture de Palis Dans cette note, nous annon\c{c}ons un r\'esultat portant sur les champs de vecteurs des vari\'et\'es de dimension $3$ : ceux qui v\'erifient l'hyperbolicit\'e singuli\`ere ou qui poss\`edent une tangence homocline forment un sous-ensemble dense de l'espace des champs de vecteurs $C^1$. Ceci r\'epond \`a une conjecture de Palis. La d\'emonstration utilise une g\'en\'eralisation pour les flots fibr\'es locaux des th\'eor\`emes de Ma\~n\'e et Pujals-Sambarino traitant de la contraction uniforme de fibr\'es unidimensionnels domin\'es.
Recurrence and genericity
Christian Bonatti,Sylvain Crovisier
Mathematics , 2003, DOI: 10.1007/s00222-004-0368-1
Abstract: We prove a C^1-connecting lemma for pseudo-orbits of diffeomorphisms on compact manifolds. We explore some consequences for C^1-generic diffeomorphisms. For instance, C^1-generic conservative diffeomorphisms are transitive.
Nous montrons un lemme de connexion C^1 pour les pseudo-orbites des diffeomorphismes des varietes compactes. Nous explorons alors les consequences pour les diffeomorphismes C^1-generiques. Par exemple, les diffeomorphismes conservatifs C^1-generiques sont transitifs.
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