Data: 15/03/2019

Ora: 14:30:00

Descrizione:

Data: 22/02/2019

Ora: 11:30:00

Descrizione:

The physical life of a comet near the Sun is relatively short. Therefore, in order to provide the actual flow of comets, there should be cometary reservoirs in the solar system where comets do not feel the heat of the Sun. For long period comets, i.e. comets with an orbital period greater than 200 years, this reservoir is believed to be at more than 10,000 times the Earth-Sun distance, known as the Oort Cloud. However, the shape, density and formation of this Oort cloud remains an open question.

The problem is that cometary dynamics is highly chaotic, so it is useless to investigate the origin of comets by backward propagation of their movement. We are therefore reduced to massive simulations where huge samples of synthetic comets are propagated forward over a long time span. The Oort cloud informations are then obtained by comparing the final results with the observations.

I will first introduce how we have built our model for the long-term propagation of long-lived comets. This model takes into account the gravitational attraction of the whole galaxy on the Sun and the comets, which induces an quasi-integrable dynamic, the passage of the stars close to the Sun and the planetary scattering by the four giant planets of our solar system. These last two effects are stochastic.

Then, I will present how this model has allowed us to investigate the memory of the Oort cloud and should give us crucial informations about its formation.

Data: 18/12/2018

Ora: 15:00:00

Descrizione: ]]>

Data: 30/10/2018

Ora: 09:00:00

Descrizione:

After giving some basic examples of Lie groupoids, we will explain the rule of convolution of distributions on a Lie groupoid G and its relationship with the symplectic groupoid structure on T^*G found by Coste-Dazord-Weinstein. Secondly, we will explain how to develop a calculus for Fourier Integral Operators on a groupoid G. Finally, we will show that the one parameter group e^{itP}, t ∈ **R**, where P is a first order elliptic positive G-pseudodifferential operator, consists of G-FIOs in a weaker sense.

Data: 26/10/2018

Ora: 11:30:00

Descrizione:

In the restricted three-body problem, consecutive collision orbits arethose orbits which start and end at collisions with one of theprimaries. Interests for such orbits arise not only from mathematics butalso from various engineering problems. In this talk we shall discussthe existence of such orbits via the use of Rabinowitz-Floer theory.This is a joint work with Urs Frauenfelder.

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