154 research outputs found
A mechanism explaining the metamorphoses of KAM islands in nonhyperbolic chaotic scattering
In the context of nonhyperbolic chaotic scattering, it has been shown that the evolution of the KAM islands exhibits four abrupt metamorphoses that strongly affect the predictability of Hamiltonian systems. It has been suggested that these metamorphoses are related to significant changes in the structure of the KAM islands. However, previous research has not provided an explanation of the mechanisms underlying the metamorphoses. Here, we show that they occur due to the formation of a homoclinic or heteroclinic tangle that breaks the internal structure of the main KAM island. We obtain similar qualitative results in a two-dimensional Hamiltonian system and a two-dimensional area-preserving map. The equivalence of the results obtained in both systems suggests that the same four metamorphoses play an important role in conservative systems
Attractor-repeller collision and the heterodimensional dynamics
We study the heterodimensional dynamics in a simple map on a
three-dimensional torus. This map consists of a two-dimensional driving Anosov
map and a one-dimensional driven M\"obius map, and demonstrates the collision
of a chaotic attractor with a chaotic repeller if parameters are varied. We
explore this collision by following tangent bifurcations of the periodic
orbits, and establish a regime where periodic orbits with different numbers of
unstable directions coexist in a chaotic set. For this situation, we construct
a heterodimensional cycle connecting these periodic orbits. Furthermore, we
discuss properties of the rotation number and of the nontrivial Lyapunov
exponent at the collision and in the heterodimensional regime
A singular perturbation analysis for the Brusselator
In this work we study the Brusselator - a prototypical model for chemical
oscillations - under the assumption that the bifurcation parameter is of order
for positive . The dynamics of this mathematical
model exhibits a time scale separation visible via fast and slow regimes along
its unique attracting limit cycle. Noticeably this limit cycle accumulates at
infinity as , so that in polar coordinates ,
and by doing a further change of variable , we analyse the
dynamics near the line at infinity, corresponding to the set . This
object becomes a nonhyperbolic invariant manifold for which we use a
desingularising rescaling, in order to study the closeby dynamics. Further use
of geometric singular perturbation techniques allows us to give a decomposition
of the Brusselator limit cycle in terms of four different fully quantified time
scales
Bifurcation diagram for saddle/source bimodal linear dynamical systems
We continue the study of the structural stability and the bifurcations of planar bimodal linear dynamical systems (BLDS) (that is, systems consisting of two linear dynamics acting on each side of a straight line, assuming continuity along the separating line). Here, we enlarge the study of the bifurcation diagram of saddle/spiral BLDS to saddle/source BLDS and in particular we study the position of the homoclinic bifurcation with regard to the new improper node bifurcationPostprint (published version
Discontinuity induced bifurcations of non-hyperbolic cycles in nonsmooth systems
We analyse three codimension-two bifurcations occurring in nonsmooth systems,
when a non-hyperbolic cycle (fold, flip, and Neimark-Sacker cases, both in
continuous- and discrete-time) interacts with one of the discontinuity
boundaries characterising the system's dynamics. Rather than aiming at a
complete unfolding of the three cases, which would require specific assumptions
on both the class of nonsmooth system and the geometry of the involved
boundary, we concentrate on the geometric features that are common to all
scenarios. We show that, at a generic intersection between the smooth and
discontinuity induced bifurcation curves, a third curve generically emanates
tangentially to the former. This is the discontinuity induced bifurcation curve
of the secondary invariant set (the other cycle, the double-period cycle, or
the torus, respectively) involved in the smooth bifurcation. The result can be
explained intuitively, but its validity is proven here rigorously under very
general conditions. Three examples from different fields of science and
engineering are also reported
Enharmonic motion: Towards the global dynamics of negative delayed feedback
In this thesis, we establish a new method for describing the qualitative dynamics of the so-called Hopf-Smale attractors in scalar delay differential equations with symmetric negative delayed feedback.
The dynamics of Hopf-Smale attractors are robust under regular perturbations. Qualitatively, the attractor consists of an equilibrium, periodic orbits, and connections between them. We describe the mechanism that produces the periodic orbits and show how their formation creates new connecting orbits via sequences of Hopf bifurcations. As a result, we obtain an enumeration of all the phase diagrams, that is, the directed graphs encoding the equilibrium and periodic orbits as vertices and the connections as edges.
In particular, we have obtained a prototype, the so-called enharmonic oscillator, that realizes all Hopf-Smale phase diagrams. Besides describing the Hopf-Smale attractors, our method also sheds insight into the formation process of certain global attractors with positive delayed feedback.In dieser Arbeit wird eine neue Methode zur Beschreibung der qualitativen Dynamik der sogenannten Hopf-Smale-Attraktoren in skalaren retardierten Differentialgleichung mit symmetrischer negativer verzögerter Rückkopplung entwickelt.
Die Dynamik von Hopf-Smale-Attraktoren ist robust gegenüber regelmäßigen Störungen. Qualitativ besteht der Attraktor aus einem Gleichgewicht, periodischen Orbits und Orbits zwischen diesen. Wir beschreiben den Mechanismus, der die periodischen Orbits erzeugt und zeigen, wie dieser neue verbindende Orbits über Sequenzen von Hopf-Bifurkationen erzeugt. Als Ergebnis erhalten wir eine Aufzählung aller Phasendiagramme, d.h. der gerichteten Graphen, die die Gleichgewichts- und periodischen Bahnen als Knoten und die Verbindungen als Kanten kodieren.
Insbesondere haben wir einen Prototyp, den sogenannten enharmonischen Oszillator, gefunden, der alle Hopf-Smale-Phasendiagramme verwirklicht. Neben der Beschreibung der Hopf-Smale-Attraktoren gibt unsere Methode auch Aufschluss über den Entstehungsprozess bestimmter globaler Attraktoren mit positiver verzögerter Rückkopplung
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