1,720,975 research outputs found
Rigorous estimates for the relegation algorithm
No full textWe revisit the relegation algorithm by Deprit et al. (Celest. Mech. Dyn. Astron. 79:157–182, 2001) in the light of the rigorous Nekhoroshev’s like theory. This relatively recent algorithm is nowadays widely used for implementing closed form analytic perturbation theories, as it generalises the classical Birkhoff normalisation algorithm. The algorithm, here briefly explained by means of Lie transformations, has been so far introduced and used in a formal way, i.e. without providing any rigorous convergence or asymptotic estimates. The overall aim of this paper is to find such quantitative estimates and to show how the results about stability over exponentially long times can be recovered in a simple and effective way, at least in the non-resonant case
EFFECTIVE STABILITY OF HAMILTONIAN PLANETARY SYSTEMS
Full text linkThe stability of the Solar System is a classical, long standing and challenging problem, already pointed out by Newton. In this thesis we revisit the problem in the light of Kolmogorov and Nekhoroshev theorems, with the aim of proving that they apply to realistic approximations of the Sun-Jupiter-Saturn and Sun-Jupiter-Saturn-Uranus systems. The present thesis is devoted to the study of three main problems, namely: (i) the applicability of Kolmogorov and Nekhoroshev theories to the problem of three bodies; (ii) the stability of the secular evolution of the planar Sun-Jupiter-Saturn-Uranus system; (iii) the explicit construction of the normal form for elliptic tori in planetary systems. This work gives an original contribution on the methods for studying the stability of planetary systems. It contains an analytical contribution, namely the proof of the existence of low dimensional elliptic tori for the planetary system obtained via an algorithmic constructive method, and the explicit calculation of the stability time for the Sun-Jupiter-Saturn system and for the planar secular Sun-Jupiter-Saturn-Uranus system. We emphasize that we obtain the first realistic estimates for these problems based on a well established theoretical framework
Effective stability around the Cassini state in the spin-orbit problem
No full textWe investigate the long-time stability in the neighborhood of the Cassini state in the conservative spin-orbit problem. Starting with an expansion of the Hamiltonian in the canonical Andoyer-Delaunay variables, we construct a high-order Birkhoff normal form and give an estimate of the effective stability time in the Nekhoroshev sense. By extensively using algebraic manipulations on a computer, we explicitly apply our method to the rotation of Titan. We obtain physical bounds of Titan's latitudinal and longitudinal librations, finding a stability time greatly exceeding the estimated age of the Universe. In addition, we study the dependence of the effective stability time on three relevant physical parameters: the orbital inclination, i, the mean precession of the ascending node of Titan orbit, Ω, and the polar moment of inertia, C
On the continuation of degenerate periodic orbits via normal form : full dimensional resonant tori
Full text linkWe reconsider the classical problem of the continuation of degenerate periodic orbits in Hamiltonian systems. In particular we focus on periodic orbits that arise from the breaking of a completely resonant maximal torus. We here propose a suitable normal form construction that allows to identify and approximate the periodic orbits which survive to the breaking of the resonant torus. Our algorithm allows to treat the continuation of approximate orbits which are at leading order degenerate, hence not covered by classical averaging methods. We discuss possible future extensions and applications to localized periodic orbits in chains of weakly coupled oscillators
Methods of algebraic manipulation in perturbation theory
Full text linkWe give a short introduction to the methods of representing
polynomial and trigonometric series that are often used in Celestial
Mechanics. A few applications are also illustrated
On the relativistic Lagrange-Laplace secular dynamics for extrasolar systems
Full text linkWe study the secular dynamics of extrasolar planetary systems by extending the Lagrange-Laplace theory to high order and by including the relativistic effects. We investigate the long-term evolution of the planetary eccentricities via normal form and we find an excellent agreement with direct numerical integrations. Finally we set up a simple analytic criterion that allows to evaluate the impact of the relativistic effects in the long-time evolution
Effective resonant stability of Mercury
Full text linkMercury is the unique known planet that is situated in a 3:2 spin-orbit resonance nowadays. Observations and models converge to the same conclusion: the planet is presently deeply trapped in the resonance and situated at the Cassini state 1, or very close to it. We investigate the complete non-linear stability of this equilibrium, with respect to several physical parameters, in the framework of Birkhoffnormal form and Nekhoroshev stability theory. We use the same approach we have adopted for the 1:1 spin-orbit case with a peculiar attention to the role of Mercury's non-negligible eccentricity. The selected parameters are the polar moment of inertia, the Mercury's inclination and eccentricity and the precession rates of the perihelion and node. Our study produces a bound to both the latitudinal and longitudinal librations (of 0.1 rad) for a long but finite time (greatly exceeding the age of the Solar system). This is the so-called effective stability time. Our conclusion is that Mercury, placed inside the 3:2 spin-orbit resonance, occupies a very stable position in the space of these physical parameters, but not the most stable possible one
On the stability of the secular evolution of the planar Sun–Jupiter–Saturn–Uranus system
No full textWe investigate the long time stability of the Sun-Jupiter-Saturn-Uranus system by considering the planar, secular model. Our method may be considered as an extension of Lagrange's theory for the secular motions. Indeed, concerning the planetary orbital revolutions, we improve the classical circular approximation by replacing it with a torus which is invariant up to order two in the masses; therefore, we investigate the stability of the elliptic equilibrium point of the secular system for small values of the eccentricities. For the initial data corresponding to a real set of astronomical observations, we find an estimated stability time of 107 years, which is not extremely smaller than the lifetime of the Solar System (∼5 Gyr)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
