## Journals

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### Open Access Journals

DCDS

This paper deals with normal forms about contact points (`turning points') of nilpotent type that one frequently encounters in the study of planar slow-fast systems. In case the contact point of an analytic slow-fast vector field is of order two, we prove that the slow-fast vector field can locally be written as a slow-fast Liénard equation up to exponentially small error. The proof is based on the use of Gevrey asymptotics. Furthermore, for slow-fast jump points, we eliminate the exponentially small remainder.

CPAA

We consider an Ackerberg-O'Malley singular perturbation problem
$\epsilon y'' + f(x,\epsilon)y' + g(x,\epsilon)y=0, y(a)=A, y(b)=B$ with a single turning point
and study the nature of resonant solutions $y=\varphi(x,\epsilon)$, i.e. solutions for which
$\varphi(x,\epsilon)$ tends to a nontrivial solution of $f(x,0)y'+ g(x,0)y=0$ as $\epsilon\to 0$.
Many techniques have been applied to the study of this problem
(WKBJ, invariant manifolds, asymptotic methods, spectral methods, variational techniques)
and they have been successful in characterizing these resonant solutions when $f(x,0)$ has a simple
zero at the origin. When the order of zero is higher the increase in complexity of the problem
is significant. The existence of a nonzero formal power series solution is no longer necessary
for resonance and resonant solutions are in general not smooth at the origin. We
apply the method of blow up to study the nature of resonant solutions in this setting, using
techniques from invariant manifold theory and planar singular perturbation theory. The main result
is the sufficiency of the Matkowsky condition for turning points of arbitrary order (based on
Gevrey-asymptotics), but we also give a characterization of the location of the boundary layer in
resonant solutions.

DCDS

This paper deals with the study of limit cycles that appear in a class of planar slow-fast systems, near a "canard'' limit periodic set of FSTS-type.
Limit periodic sets of FSTS-type are closed orbits, composed of a Fast branch, an attracting Slow branch, a Turning point, and
a repelling Slow branch. Techniques to bound the number of limit cycles near a FSTS-l.p.s. are based on the study of the so-called
slow divergence integral, calculated along the slow branches. In this paper, we extend the technique to the case where the slow dynamics has singularities of any (finite) order that accumulate to the turning point, and in which case the slow divergence integral becomes unbounded.
Bounds on the number of limit cycles near the FSTS-l.p.s. are derived by examining appropriate derivatives of the slow divergence integral.

keywords:
singular perturbations
,
blow-up
,
slow-fast cycle
,
generalized Liénard equation.
,
turning point
,
canards

DCDS-B

We give sufficient conditions on the spectrum at the equilibrium point such that a Gevrey-$s$ family can be
Gevrey-$s$ conjugated to a simplified form, for $0\le s\le 1$. Local analytic results (i.e. $s=0$) are obtained
as a special case, including the classical Poincaré theorems and the analytic stable and unstable manifold
theorem. As another special case we show that certain center manifolds of analytic vector fields are of
Gevrey-$1$ type. We finally study the asymptotic properties of the conjugacy on a polysector with opening angles
smaller than $s\pi$ by considering a Borel-Laplace summation.

DCDS-S

The theory of slow-fast systems is a challenging field both from the
viewpoint of theory and applications. Advances made over the last
decade led to remarkable new insights and we therefore decided that
it is worthwhile to gather snapshots of results and achievements in
this field through invited experts. We believe that this volume of
DCDS-S contains a varied and interesting overview of different
aspects of slow-fast systems with emphasis on 'bifurcation delay'
phenomena. Unfortunately, as could be expected, not all invitees
were able to sent a contribution due to their loaded agenda, or the
strict deadlines we had to impose.

Slow-fast systems deal with problems and models in which different (time- or space-) scales play an important role. From a dynamical systems point of view we can think of studying dynamics expressed by differential equations in the presence of curves, surfaces or more general varieties of singularities. Such sets of singularities are said to be critical. Perturbing such equations by adding an $\varepsilon$-small movement that destroys most of the singularities can create complex dynamics. These perturbation problems are also called singular perturbations and can often be presented as differential equations in which the highest order derivatives are multiplied by a parameter $\varepsilon$, reducing the order of the equation when $\varepsilon\to 0$.

For more information please click the “Full Text” above.

Slow-fast systems deal with problems and models in which different (time- or space-) scales play an important role. From a dynamical systems point of view we can think of studying dynamics expressed by differential equations in the presence of curves, surfaces or more general varieties of singularities. Such sets of singularities are said to be critical. Perturbing such equations by adding an $\varepsilon$-small movement that destroys most of the singularities can create complex dynamics. These perturbation problems are also called singular perturbations and can often be presented as differential equations in which the highest order derivatives are multiplied by a parameter $\varepsilon$, reducing the order of the equation when $\varepsilon\to 0$.

For more information please click the “Full Text” above.

keywords:

CPAA

In this paper we continue the study of ``large" small-amplitude limit cycles in slow-fast codimension 3 elliptic bifurcations which is initiated in [8].
Our treatment is based on blow-up and good normal forms.

## Year of publication

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