Excentricité orbitale

L’excentricité orbitale définit, en mécanique céleste et en mécanique spatiale, la forme des orbites des objets célestes. Notation et types d'orbites L'excentricité est couramment notée e. Elle exprime l'écart de forme entre l'orbite et le cercle parfait dont l'excentricité est nulle. Lorsque e < 1, la trajectoire est fermée : l'orbite est périodique. Dans ce cas :

lorsque e = 0, l'objet décrit un cercle et son orbite est dite circulaire ;
lorsque 0 < e < 1, l'objet décrit une ellipse et son orbite est dite elliptique.

Lorsque e \geqslant 1, la trajectoire est ouverte. Dans ce cas :

lorsque e = 1, l'objet décrit une parabole et sa trajectoire est dite parabolique ;
lorsque e > 1, l'objet décrit la branche d'une hyperbole et sa trajectoire est dite hyperbolique.

Lorsque e \rightarrow +\infty, la branche de l'hyperbole dégénère en une droite. Avec les conventi

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Is ram-pressure stripping an efficient mechanism to remove gas in galaxies?

Elena Ricciardelli

We study how the gas in a sample of galaxies (M-* > 10(9) M-circle dot) in clusters, obtained in a cosmological simulation, is affected by the interaction with the intracluster medium (ICM). The dynamical state of each elemental parcel of gas is studied using the total energy. At z similar to 2, the galaxies in the simulation are evenly distributed within clusters, later moving towards more central locations. In this process, gas from the ICM is accreted and mixed with the gas in the galactic halo. Simultaneously, the interaction with the environment removes part of the gas. A characteristic stellar mass around M-* > 10(10) M-circle dot appears as a threshold marking two differentiated behaviours. Below this mass, galaxies are located at the external part of clusters and have eccentric orbits. The effect of the interaction with the environment is marginal. Above, galaxies are mainly located at the inner part of clusters with mostly radial orbits with low velocities. In these massive systems, part of the gas, strongly correlated with the stellar mass of the galaxy, is removed. The amount of removed gas is subdominant compared with the quantity of retained gas, which is continuously influenced by the hot gas coming from the ICM. The analysis of individual galaxies reveals the existence of a complex pattern of flows, turbulence and a constant fuelling of gas to the hot corona from the ICM, which could mean that the global effect of the interaction of galaxies with their environment is substantially less dramatic than previously expected.

Oxford Univ Press2017

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Analysis of Spiral-Grooved Gas Journal Bearings by the Narrow-Groove Theory and the Finite Element Method At Large Eccentricities

Eliott Philippe Guenat, Elia Iseli, Jürg Alexander Schiffmann

A finite groove approach (FGA), based on the finite element method (FEM), is used for analyzing the static and dynamic behavior of spiral-grooved aerodynamic journal bearings at different eccentricities, number of grooves, and compressibility numbers. The results of the FGA are compared with the narrow-groove theory (NGT) solutions. For the rotating-groove case, a novel time-periodic solution method is presented for computing the quasi-steady-state and dynamic pressure profiles. The new method offers the advantage of avoiding time-consuming transient integration, while resolving a finite number of grooves. The static and dynamic solutions of the NGT and FGA approach are compared, and they show good agreement, even at large eccentricities (⁠ε=0.8⁠) and high compressibility numbers (Λ = 40). Stability maps at different eccentricities are presented. At certain operation points, a stability decrease toward larger eccentricities is observed. The largest stability deviations of the NGT from the FGA solutions occur at large groove angle, low number of grooves, and large compressibility numbers.

2020

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Spin-orbital separation in the quasi-one-dimensional Mott insulator Sr2CuO3

Jean-Sebastien Caux, Martin Mourigal, Henrik Moodysson Rønnow, Thorsten Schmitt

When viewed as an elementary particle, the electron has spin and charge. When binding to the atomic nucleus, it also acquires an angular momentum quantum number corresponding to the quantized atomic orbital it occupies. Even if electrons in solids form bands and delocalize from the nuclei, in Mott insulators they retain their three fundamental quantum numbers: spin, charge and orbital(1). The hallmark of one-dimensional physics is a breaking up of the elementary electron into its separate degrees of freedom(2). The separation of the electron into independent quasi-particles that carry either spin (spinons) or charge (holons) was first observed fifteen years ago(3). Here we report observation of the separation of the orbital degree of freedom (orbiton) using resonant inelastic X-ray scattering on the one-dimensional Mott insulator Sr2CuO3. We resolve an orbiton separating itself from spinons and propagating through the lattice as a distinct quasi-particle with a substantial dispersion in energy over momentum, of about 0.2 electronvolts, over nearly one Brillouin zone.

2012

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PHYS-401: Astrophysics III : stellar and galactic dynamics

The aim of this course is to acquire the basic knowledge on specific dynamical phenomena related to the origin, equilibrium, and evolution of star clusters, galaxies, and galaxy clusters.

PHYS-460: Nonlinear dynamics, chaos and complex systems

The course provides students with the tools to approach the study of nonlinear systems and chaotic dynamics. Emphasis is given to concrete examples and numerical applications are carried out during the exercise sessions.

MATH-126: Geometry for architects II

Ce cours traite des 3 sujets suivants : la perspective, la géométrie descriptive, et une initiation à la géométrie projective.

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