245 research outputs found
Non-hyperbolic chain recurrence classes of C¹ diffeomorphisms
No full textLa dynamique d'un difféomorphisme d'une variété compacte est essentiellement concentrée sur l'ensemble récurrent par chaînes, qui est partitionné en classes de récurrence par chaînes, disjointes et indécomposables. Le travail de Bonatti et Crovisier [BC] montre que, pour les difféomorphismes C¹-génériques, une classe de récurrence par chaînes ou bien est une classe homocline, ou bien ne contient pas de point périodique. Une classe de récurrence par chaînes sans point périodique est appelée classe apériodique.Il est clair qu'une classe homocline hyperbolique ni contient d'orbite périodique faible ni supporte de mesure non hyperbolique.Cette thèse tente de donner une caractérisation des classes homoclines non hyperboliques en montrant qu'elles contiennent des orbites périodiques faibles ou des mesures ergodiques non hyperboliques. Cette thèse décrit également les décompositions dominées sur les classes apériodiques.Le premier résultat de cette thèse montre que, pour les difféomorphismes C¹-génériques, si les orbites périodiques contenues dans une classe homocline H(p) ont tous leurs exposants de Lyapunov bornés loin de zéro, alors H(p) doit être (uniformément) hyperbolique. Ceci est dans l'esprit des travaux sur la conjecture de stabilité, mais il y a une différence importante lorsque la classe homocline H(p) n'est pas isolée. Par conséquent, nous devons garantir que des orbites périodiques "faibles'', crées par perturbations au voisinage de la classe homocline, sont contenues dans la classe. En ce sens, le problème est de nature "intrinsèque'', et l'argument classique de la conjecture de stabilité est impraticable.Le deuxième résultat de cette thèse prouve une conjecture de Díaz et Gorodetski [DG]: pour les difféomorphismes C¹-génériques, si une classe homocline n'est pas hyperbolique, alors elle porte une mesure ergodique non hyperbolique. C'est un travail en collaboration avec C. Cheng, S. Crovisier, S. Gan et D. Yang. Dans la démonstration, nous devons appliquer une technique introduité dans [DG], et qui améliore la méthode de [GIKN], pour obtenir une mesure ergodique comme limite d'une suite de mesures périodiques.Le troisième résultat de cette thèse énonce que, génériquement, une décomposition dominée non-triviale sur une classe apériodique stable au sens de Lyapunov est en fait une décomposition partiellement hyperbolique. Plus précisément, pour les difféomorphismes C¹-génériques, si une classe apériodique stable au sens de Lyapunov a une décomposition dominée non-triviale Eoplus F, alors, l'un des deux fibrés est hyperbolique: soit E contracté, soit F dilaté.Dans les démonstrations des résultats principaux, nous construisons des perturbations qui ne sont pas obtenues directement à partir des lemmes de connexion classiques. En fait, il faut appliquer le lemme de connexion un grand nombre (et même un nombre infini) de fois. Nous expliquons les méthodes de connexions multiples dans le Chapitre 3.The dynamics of a diffeomorphism of a compact manifold concentrates essentially on the chain recurrent set, which splits into disjoint indecomposable chain recurrence classes. By the work of Bonatti and Crovisier [BC], for C¹-generic diffeomorphisms, a chain recurrence class either is a homoclinic class or contains no periodic point. A chain recurrence class without a periodic point is called an aperiodic class.Obviously, a hyperbolic homoclinic class can neither contain weak periodic orbit or support non-hyperbolic ergodic measure.This thesis attempts to give a characterization of non-hyperbolic homoclinic classes via weak periodic orbits inside or non-hyperbolic ergodic measures supported on it. Also, this thesis gives a description of the dominated splitting on Lyapunov stable aperiodic classes.The first result of this thesis shows that for C¹-generic diffeomorphisms, if the periodic orbits contained in a homoclinic class H(p) have all their Lyapunov exponents bounded away from 0, then H(p) must be (uniformly) hyperbolic. This is in spirit of the works of the stability conjecture, but with a significant difference that the homoclinic class H(p) is not known isolated in advance. Hence the "weak'' periodic orbits created by perturbations near the homoclinic class have to be guaranteed strictly inside the homoclinic class. In this sense the problem is of an "intrinsic" nature, and the classical argument of the stability conjecture does not pass through.The second result of this thesis proves a conjecture by Díaz and Gorodetski [DG]: for C¹-generic diffeomorphisms, if a homoclinic class is not hyperbolic, then there is a non-hyperbolic ergodic measure supported on it. This is a joint work with C. Cheng, S. Crovisier, S. Gan and D. Yang. In the proof, we have to use a technic introduced in [DG], which developed the method of [GIKN], to get an ergodic measure by taking the limit of a sequence of periodic measures.The third result of this thesis states that, generically, a non-trivial dominated splitting over a Lyapunov stable aperiodic class is in fact a partially hyperbolic splitting. To be precise, for C¹-generic diffeomorphisms, if a Lyapunov stable aperiodic class admits a non-trivial dominated splitting Eoplus F, then one of the two bundles is hyperbolic: either E is contracted or F is expanded.In the proofs of the main results, we construct several perturbations which are not simple applications of the connecting lemmas. In fact, one has to apply the connecting lemma several (even infinitely many) times. We will give the detailed explanations of the multi-connecting processes in Chapter 3
Comet 88P/HOWELL
No full texteditorial reviewedJ. Crovisier, P. Colom, N. Biver, D. Bockelee-Morvan, LESIA, Observatoire de Paris; and I. Cognard, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, Universite d'Orleans, report: "While monitoring the 18-cm lines of OH in comet 88P/Howell at the Nancay radio telescope, we serendipitously observed the occultation of the radio source PKS 1416-15 by the comet on Aug. 15.69 UT. This point radio source, which has a flux of about 2 Jy at 18 cm, was then 2'.2 from the comet nucleus, corresponding to a projected distance of 125000 km. The 1667-MHz line area was then observed to be -250 +/- 25 mJy*km/s, enhanced by a factor of 5 with respect to the signal as averaged for +/- 6 days before/after the event. This can be explained by the OH maser amplification of the background radio source radiation. The OH production rate averaged before/after the occultation was estimated to be 3.3 x 10**28 molecules/s. A similar event was observed on 1989 Oct. 13 for comet C/1989 Q1 (Crovisier et al. 1989, IAUC 4882; Crovisier et al. 1992, A.Ap. 253, 286)." E. Jehin, STAR Institute, University of Liege, reports (together with Y. Moulane, J. Manfroid, F. Pozuelos, and D. Hutsemekers) that they obtained narrowband photometry of comet 88P with the robotic 0.6-m "Transiting Planets and Planetesimals Small Telescope" (TRAPPIST-North) at Oukaimden, Morocco, on Aug. 17 (with the comet at r = 1.42 AU and Delta = 1.31 AU), using the HB comet filters (cf. Farnham et al. 2000, Icarus 147, 180) that focus on seven cometary emissions and four continuum bands. Using a Haser model (with V_p = V_d = 1 km/s, for 10000 km and correcting for the phase angle) they computed the dust-production rate proxy (as explained on CBET 4691) by profile fitting and correcting for the phase angle: A(0)f[rho](R) = 372 +/- 9 cm. They determined the following molecular production rates: Q(OH) = 2.97 (+/- 0.17) x 10**28 molecules/s, Q(CN) = 4.86 (+/- 0.10) x 10**25 molecules/s, Q(C_2) = 5.59 (+/- 0.12) x 10**25 molecules/s. Selected recent visual total-magnitude and coma-diameter estimates: Apr. 15.46 UT, 14.4, 0'.8 (C. Wyatt, Walcha, NSW, Australia, 0.40-m reflector); 18.48, 13.9, 1' (P. Camilleri, Katherine, NT, Australia, 0.40-m reflector); May 10.39, 13.6, 0'.8 (Wyatt, 25-cm reflector); 21.87, 13.0, 0'.3 (W. Hasubick, Buchloe, Germany, 44-cm reflector); June 9.48, 12.2, 3' (Camilleri); 16.37, 11.7, 3' (Wyatt, 25-cm reflector); 20.94, 10.7, 4' (J. J. Gonzalez, Leon, Spain, 0.20-m reflector); July 12.98, 11.2, 2' (M. Goiato, Aracatuba, Brazil, 0.22-m reflector); 18.43, 10.6, 3' (Camilleri); 24.91, 10.1, 3'.5 (Gonzalez); 30.37, 10.3, 4' (Wyatt, 25-cm reflector; moonlight); Aug. 8.98, 10.3, 3' (Goiato); 13.88, 9.4, 7' (Gonzalez); 19.48, 9.3, 4' (K. Yoshimoto, Yamaguchi, Japan, 20x100 binoculars); 23.92, 9.6, -- (J. G. de S. Aguiar, Campinas, Brazil, 25x100 binoculars; moonlight); 27.92, 9.4, -- (Aguiar, 0.27-m reflector)
Submillimetre observations of comets with Odin: 2001-2005
No full textThe Odin satellite, launched in February 2001, is equipped with a 1.1-m submillimetre telescope. Odin was used to observe the 557 GHz line of water with high spectral resolution in 12 comets between 2001 and 2005. Line shapes and spatial mapping provide information on the anisotropy of the outgassing and constraints on water excitation, enabling accurate measurements of the water production rate. Five comets were regularly observed over periods of more than one month to monitor the variation of their water outgassing rate with heliocentric distance. Observing campaigns have been generally coordinated with ground-based observations of molecular lines at Nançay, CSO or IRAM 30-m telescopes to obtain molecular abundances relative to water. Thanks to Odin's frequency coverage, it was also possible to detect the H 2 18O 548 GHz line, first in comet 153P/Ikeya-Zhang in April 2002 [Lecacheux, A., Biver, N., Crovisier, J. et al., 2003, Observations of water in comets with Odin. Astron. Astrophys. 402, L55-L58.] and then in comets C/2002 T7 (LINEAR), C/2001 Q4 (NEAT) and C/2004 Q2 (Machholz). The 16O/ 18O isotopic ratio (≈ 450) is consistent with the terrestrial value. Ammonia has been searched for in three comets through its J K = 1 0 - 0 0 line at 572 GHz and was tentatively detected in C/2001 Q4 and C/2002 T7. The derived abundances of NH 3 relative to water are 0.5% and 0.3%, respectively, similar to values obtained in other comets with different techniques. © 2006 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex
Classes de récurrence par chaînes non hyperboliques des difféomorphismes C¹
No full textThe dynamics of a diffeomorphism of a compact manifold concentrates essentially on the chain recurrent set, which splits into disjoint indecomposable chain recurrence classes. By the work of Bonatti and Crovisier [BC], for C¹-generic diffeomorphisms, a chain recurrence class either is a homoclinic class or contains no periodic point. A chain recurrence class without a periodic point is called an aperiodic class.Obviously, a hyperbolic homoclinic class can neither contain weak periodic orbit or support non-hyperbolic ergodic measure.This thesis attempts to give a characterization of non-hyperbolic homoclinic classes via weak periodic orbits inside or non-hyperbolic ergodic measures supported on it. Also, this thesis gives a description of the dominated splitting on Lyapunov stable aperiodic classes.The first result of this thesis shows that for C¹-generic diffeomorphisms, if the periodic orbits contained in a homoclinic class H(p) have all their Lyapunov exponents bounded away from 0, then H(p) must be (uniformly) hyperbolic. This is in spirit of the works of the stability conjecture, but with a significant difference that the homoclinic class H(p) is not known isolated in advance. Hence the "weak'' periodic orbits created by perturbations near the homoclinic class have to be guaranteed strictly inside the homoclinic class. In this sense the problem is of an "intrinsic" nature, and the classical argument of the stability conjecture does not pass through.The second result of this thesis proves a conjecture by Díaz and Gorodetski [DG]: for C¹-generic diffeomorphisms, if a homoclinic class is not hyperbolic, then there is a non-hyperbolic ergodic measure supported on it. This is a joint work with C. Cheng, S. Crovisier, S. Gan and D. Yang. In the proof, we have to use a technic introduced in [DG], which developed the method of [GIKN], to get an ergodic measure by taking the limit of a sequence of periodic measures.The third result of this thesis states that, generically, a non-trivial dominated splitting over a Lyapunov stable aperiodic class is in fact a partially hyperbolic splitting. To be precise, for C¹-generic diffeomorphisms, if a Lyapunov stable aperiodic class admits a non-trivial dominated splitting Eoplus F, then one of the two bundles is hyperbolic: either E is contracted or F is expanded.In the proofs of the main results, we construct several perturbations which are not simple applications of the connecting lemmas. In fact, one has to apply the connecting lemma several (even infinitely many) times. We will give the detailed explanations of the multi-connecting processes in Chapter 3.La dynamique d'un difféomorphisme d'une variété compacte est essentiellement concentrée sur l'ensemble récurrent par chaînes, qui est partitionné en classes de récurrence par chaînes, disjointes et indécomposables. Le travail de Bonatti et Crovisier [BC] montre que, pour les difféomorphismes C¹-génériques, une classe de récurrence par chaînes ou bien est une classe homocline, ou bien ne contient pas de point périodique. Une classe de récurrence par chaînes sans point périodique est appelée classe apériodique.Il est clair qu'une classe homocline hyperbolique ni contient d'orbite périodique faible ni supporte de mesure non hyperbolique.Cette thèse tente de donner une caractérisation des classes homoclines non hyperboliques en montrant qu'elles contiennent des orbites périodiques faibles ou des mesures ergodiques non hyperboliques. Cette thèse décrit également les décompositions dominées sur les classes apériodiques.Le premier résultat de cette thèse montre que, pour les difféomorphismes C¹-génériques, si les orbites périodiques contenues dans une classe homocline H(p) ont tous leurs exposants de Lyapunov bornés loin de zéro, alors H(p) doit être (uniformément) hyperbolique. Ceci est dans l'esprit des travaux sur la conjecture de stabilité, mais il y a une différence importante lorsque la classe homocline H(p) n'est pas isolée. Par conséquent, nous devons garantir que des orbites périodiques "faibles'', crées par perturbations au voisinage de la classe homocline, sont contenues dans la classe. En ce sens, le problème est de nature "intrinsèque'', et l'argument classique de la conjecture de stabilité est impraticable.Le deuxième résultat de cette thèse prouve une conjecture de Díaz et Gorodetski [DG]: pour les difféomorphismes C¹-génériques, si une classe homocline n'est pas hyperbolique, alors elle porte une mesure ergodique non hyperbolique. C'est un travail en collaboration avec C. Cheng, S. Crovisier, S. Gan et D. Yang. Dans la démonstration, nous devons appliquer une technique introduité dans [DG], et qui améliore la méthode de [GIKN], pour obtenir une mesure ergodique comme limite d'une suite de mesures périodiques.Le troisième résultat de cette thèse énonce que, génériquement, une décomposition dominée non-triviale sur une classe apériodique stable au sens de Lyapunov est en fait une décomposition partiellement hyperbolique. Plus précisément, pour les difféomorphismes C¹-génériques, si une classe apériodique stable au sens de Lyapunov a une décomposition dominée non-triviale Eoplus F, alors, l'un des deux fibrés est hyperbolique: soit E contracté, soit F dilaté.Dans les démonstrations des résultats principaux, nous construisons des perturbations qui ne sont pas obtenues directement à partir des lemmes de connexion classiques. En fait, il faut appliquer le lemme de connexion un grand nombre (et même un nombre infini) de fois. Nous expliquons les méthodes de connexions multiples dans le Chapitre 3
Data for: The Surface Distributions of the Production of the Major Volatile Species, H2O, CO2, CO and O2, from the Nucleus of Comet 67P/Churyumov-Gerasimenko throughout the Rosetta Mission as Measured by the ROSINA Double Focusing Mass Spectrometer
No full textThe file MIRO_Columns.txt contains the column densities and their uncertainties corresponding to the results published previously in the paper by Marshall, D.W., Hartogh, P. Rezac, L. von Allmen, P., Biver, N., Bockelée-Morvan, D., Crovisier, J., Encrenaz, P. Bulkis, S. Hofstadter, M. Ip, W.-H., Jarchow, C. Lee, S., Lellouch, E. 2017. Spatially resolved evolution of the local H2O production rates of coet 67P/Churyumov,Gerasimenko, from the MIRO instrument of Rosetta. Astronomy & Astrophysics 603, A87. The format containes space delimited columns corresponding to Date, UT time, Heliocentric Distance (AU), column density (cm^-2), column density error (cm^-2)
Data for: The Surface Distributions of the Production of the Major Volatile Species, H2O, CO2, CO and O2, from the Nucleus of Comet 67P/Churyumov-Gerasimenko throughout the Rosetta Mission as Measured by the ROSINA Double Focusing Mass Spectrometer
No full textThe file MIRO_Columns.txt contains the column densities and their uncertainties corresponding to the results published previously in the paper by Marshall, D.W., Hartogh, P. Rezac, L. von Allmen, P., Biver, N., Bockelée-Morvan, D., Crovisier, J., Encrenaz, P. Bulkis, S. Hofstadter, M. Ip, W.-H., Jarchow, C. Lee, S., Lellouch, E. 2017. Spatially resolved evolution of the local H2O production rates of coet 67P/Churyumov,Gerasimenko, from the MIRO instrument of Rosetta. Astronomy & Astrophysics 603, A87. The format containes space delimited columns corresponding to Date, UT time, Heliocentric Distance (AU), column density (cm^-2), column density error (cm^-2)
Data for: The Surface Distributions of the Production of the Major Volatile Species, H2O, CO2, CO and O2, from the Nucleus of Comet 67P/Churyumov-Gerasimenko throughout the Rosetta Mission as Measured by the ROSINA Double Focusing Mass Spectrometer
No full textThe file MIRO_Columns.txt contains the column densities and their uncertainties corresponding to the results published previously in the paper by Marshall, D.W., Hartogh, P. Rezac, L. von Allmen, P., Biver, N., Bockelée-Morvan, D., Crovisier, J., Encrenaz, P. Bulkis, S. Hofstadter, M. Ip, W.-H., Jarchow, C. Lee, S., Lellouch, E. 2017. Spatially resolved evolution of the local H2O production rates of coet 67P/Churyumov,Gerasimenko, from the MIRO instrument of Rosetta. Astronomy & Astrophysics 603, A87. The format containes space delimited columns corresponding to Date, UT time, Heliocentric Distance (AU), column density (cm^-2), column density error (cm^-2).THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV
Conjugacy class of homeomorphisms and distortion elements in groups of homeomorphisms
No full textLet S be a compact connected surface and let f be an element of the group Homeo_0(S) of homeomorphisms of S isotopic to the identity. Denote by \tilde{f} a lift of f to the universal cover of S. Fix a fundamental domain D of this universal cover. The homeomorphism f is said to be non-spreading if the sequence (d_{n}/n) converges to 0, where d_{n} is the diameter of \tilde{f}^{n}(D). Let us suppose now that the surface S is orientable with a nonempty boundary. We prove that, if S is different from the annulus and from the disc, a homeomorphism is non-spreading if and only if it has conjugates in Homeo_{0}(S) arbitrarily close to the identity. In the case where the surface S is the annulus, we prove that a homeomorphism is non-spreading if and only if it has conjugates in Homeo_{0}(S) arbitrarily close to a rotation (this was already known in most cases by a theorem by Béguin, Crovisier, Le Roux and Patou). We deduce that, for such surfaces S, an element of Homeo_{0}(S) is distorted if and only if it is non-spreading
Replacement and late formation of atmospheric N2 on undifferentiated Titan by impacts
No full textSaturn’s moon, Titan, has remarkable surface features—a massive N2 atmosphere and hydrological cycle of CH4—that are often compared with that of Earth^1^. However, the origin and evolution of Titan’s atmosphere remains largely unknown. The proposed formation mechanisms for Titan’s N2 require a prolonged, warm proto-atmosphere during accretion^2-4^. These mechanisms accordingly would not have worked efficiently if Titan stayed cold, as indicated by the incompletely differentiated interior observed by Cassini^5^. Because formation of a massive secondary atmosphere on a planetary body would associate with a major differentiation of its sold body during accretion^6–8^, the presence of such an atmosphere on undifferentiated cold Titan poses a serious dilemma on our view of how planetary bodies develop atmospheres. Here we propose a new mechanism for the post-accretion formation of Titan’s N2 to resolve this problem: conversion and replenishment of N2 from NH3 contained in Titan by impacts during the late heavy bombardment (LHB)^9^. Our results show that Titan, regardless of its thermal history, would acquire sufficient N2 to account for the current atmosphere during the LHB and that most of the pre-LHB atmosphere would have replaced by impact-induced N2. This is the first scenario capable of generating a N2-rich and nearly primordial Ar-free atmosphere on undifferentiated cold Titan. We also suggest that Titan’s N2 was delivered from a different source in the solar nebula compared with Earth and that the origins of N2 on Titan and Triton are fundamentally different with that of N2 on Pluto
Alteration of Si-B-Na-Al model glass in water at 90°C: experiments and thermodynamic modelling
No full textABSTRACTAn attempt to model the alteration process of a model glass (Si-B-Al-Na), similar to the French reference SON68 glass, by using the geochemical code KINDIS, was developed. This simulation study was compared with experiments carried out in parallel: glass samples were placed at 90°C in pure water for 30 to 180 days, at two different S/V ratios (1 and 80 cm-1).The formation of the alteration layer was simulated by the precipitation of an ideal solid solution. The cases of oxides, hydroxides and metasilicates as end-members were tested. The considered solid solution always contains a siliceous end-member, which consists of amorphous silica, chalcedony or quartz.The relative thermodynamic stability of the chosen end-members (especially siliceous ones) influences directly the composition of the predicted gel and thus the composition of the solution. The results obtained by using chalcedony and hydroxides as end-members show a good agreement between the experimental and modelled silicon contents in solutions and in alteration gels, whatever the S/V ratio.The gel layer of the glass contains significant amounts of Na and Al, which are equimolar on average, what would probably correspond to the compensation of AlO4- charges by Na+.</jats:p
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