Personne : Doyon, Bernard
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Faculté des sciences et de génie, Université Laval
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Voici les éléments 1 - 6 sur 6
- PublicationAccès libreTargeting unknown and unstable periodic orbits(American Institute of Physics, 2002-03-07) Dubé, Louis J.; Doyon, BernardWe present a method to target and subsequently control (if necessary) orbits of specified period but otherwise unknown stability and position. For complex systems where the dynamics is often mixed [e.g., coexistence of regular and chaotic regions in area-preserving (Hamiltonian) systems], this targeting algorithm offers a way to not only gently bring the system from the chaotic domain to an unstable periodic orbit (where control is applied), but also to access stable regions of phase space (where control is not necessary) from within the stochastic regions. The technique is quite general and applies equally well to dissipative or conservative discrete maps and continuous flows.
- PublicationAccès libreOn Jacobian matrices for flows(American Institute of Physics, 2005-02-10) Dubé, Louis J.; Doyon, BernardWe present a general method for constructing numerical Jacobian matrices for flows discretized on a Poincaré surface of section. Special attention is given to Hamiltonian flows where the additional constraint of energy conservation is explicitly taken into account. We demonstrate the approach for a conservative dynamical flow and apply the technique for the general detection of periodic orbits.
- PublicationRestreintNew laser induced spatio–temporal transition in nematics(Elsevier Science, 2002-05-07) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Doyon, BernardWe report the observation of a new light-induced spatio–temporal transition in homeotropically aligned nematic liquid crystals under the action of circularly polarized light. We believe that the competition of symmetric and asymmetric excitation modes is at the origin of this abrupt transition. A theoretical model explaining the main features of the observation is proposed
- PublicationAccès libreOptically induced dynamics in nematic liquid crystals : the role of twist deformation and asymmetry(American Physical Society, 2003-03-26) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Doyon, BernardWe present a theoretical study of optically induced dynamics in a homeotropic nematic liquid crystal excited at normal incidence. By retaining the first symmetric and antisymmetric reorientation modes, the dynamical equations are reduced to a four-dimensional problem. The main advantage of this minimal approach is to emphasize the role of twisted mode and asymmetry of the light-induced molecular reorientation in a manner suitable for a clear physical interpretation. Theoretical results are compared with experiments in the particular case of circularly polarized light beams to show the physical origin of mode competition and of the breakdown of chiral and longitudinal symmetry. The model successfully describes previous experimental studies such as time-dependent three-dimensional molecular dynamics, light-induced stabilized helical reorientation, and in-plane precession regime in achiral nematics. While a recent experiment has revealed a new spatiotemporal transition, the model succeeds to describe all the features of such a bifurcation pointing out anew the importance of asymmetry. Finally, the first quantitative description of the appearance of a giant mirrorless optical bistability when twisted reorientation modes are excited is demonstrated. A qualitative physical interpretation is suggested for all these phenomen
- PublicationAccès libreOptically induced dynamics in nematic liquid crystals : the role of finite beam size(American Physical Society, 2004-02-10) Brasselet, Étienne.; Galstian, Tigran; Dubé, Louis J.; Doyon, BernardWe report on the influence of a finite beam size on the molecular reorientation dynamics when a nematic liquid crystal film is excited by a laser beam. We present experimental evidence of a new class of nonlinear dynamics when the excitation is a Gaussian shaped, circularly polarized laser beam at normal incidence. Various nonlinear regimes, periodic, quasiperiodic, intermittent, and possibly chaotic, are observed. A physical interpretation based on walk-off effects is proposed and its implications on current research in the field are discussed
- PublicationRestreintThe control of hamiltonian chaos(Canadian association of physicists, 2001-03-01) Pourbohloul, Babak; Després, Philippe; Dubé, Louis J.; Doyon, BernardWe demonstrate the control of the chaotic dynamics of Hamiltonian systems. This ability offers the possibility to select (stabilize) at will regular behavior(s) within the chaotic regime and to make efficient use of the richness and diversity of chaos.