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Theses

Systèmes dynamiques sur réseaux : Applications au milieu interstellaire et à la transition vers la turbulence

Abstract : The general framework of this thesis is the study and the modeling of spatially-extended systems. We have been more specifically interested by systems where a natural length exists which allows for spatial discretisation. Processes numerically too costly to be incorporated in a continuous model can then be taken into account. Specifically, we have considered the dynamics of dark molecular clouds and the transition to turbulence {\it via} spatio-temporal intermittency. Detailed models of molecular clouds have shown that there is no dominating process in the inner regions. A realistic description must include a hundred of chemical species reacting within a turbulent fluid. Moreover, the local thermal balance imposes the resolution of the radiative transfer equations. We have developed a minimal ``Coupled Map Lattice'' model including those processes at a phenomenological level. Its study has shown that one must consider those processes simultaneously to properly describe the global evolution of the system. In 1986, Y. Pomeau predicted the existence of a specific and ``universal'' scenario for transition to turbulence {\it via} spatio-temporal intermittency. We have studied the role of the propagative structures commonly observed in numerical models and experiments, which can a priori limit the validity of this equivalence between stochastic and deterministic systems. Using a minimal CML model of spatio-temporal intermittency, we have shown that these propagative structures play an active role in the emergence of a specific turbulent regime.
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https://tel.archives-ouvertes.fr/tel-00001079
Contributor : Guillaume Rousseau <>
Submitted on : Thursday, January 31, 2002 - 5:43:47 PM
Last modification on : Wednesday, September 23, 2020 - 4:36:50 AM
Long-term archiving on: : Friday, April 2, 2010 - 7:50:55 PM

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Guillaume Rousseau. Systèmes dynamiques sur réseaux : Applications au milieu interstellaire et à la transition vers la turbulence. Physique [physics]. Université Paris-Diderot - Paris VII, 1998. Français. ⟨tel-00001079⟩

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