351 research outputs found
Characteristics of in-out intermittency in delay-coupled FitzHugh-Nagumo oscillators
We analyze a pair of delay-coupled FitzHugh-Nagumo oscillators exhibiting
in-out intermittency as a part of the generating mechanism of extreme events.
We study in detail the characteristics of in-out intermittency and identify the
invariant subsets involved --- a saddle fixed point and a saddle periodic orbit
--- neither of which are chaotic as in the previously reported cases of in-out
intermittency. Based on the analysis of a periodic attractor possessing in-out
dynamics, we can characterize the approach to the invariant synchronization
manifold and the spiralling out to the saddle periodic orbit with subsequent
ejection from the manifold. Due to the striking similarities, this analysis of
in-out dynamics explains also in-out intermittency.Comment: 15 pages, 6 figure
Generalized models as a universal approach to the analysis of nonlinear dynamical systems
We present a universal approach to the investigation of the dynamics in
generalized models. In these models the processes that are taken into account
are not restricted to specific functional forms. Therefore a single generalized
models can describe a class of systems which share a similar structure. Despite
this generality, the proposed approach allows us to study the dynamical
properties of generalized models efficiently in the framework of local
bifurcation theory. The approach is based on a normalization procedure that is
used to identify natural parameters of the system. The Jacobian in a steady
state is then derived as a function of these parameters. The analytical
computation of local bifurcations using computer algebra reveals conditions for
the local asymptotic stability of steady states and provides certain insights
on the global dynamics of the system. The proposed approach yields a close
connection between modelling and nonlinear dynamics. We illustrate the
investigation of generalized models by considering examples from three
different disciplines of science: a socio-economic model of dynastic cycles in
china, a model for a coupled laser system and a general ecological food web.Comment: 15 pages, 2 figures, (Fig. 2 in color
Self-induced switchings between multiple space-time patterns on complex networks of excitable units
We report on self-induced switchings between multiple distinct space--time
patterns in the dynamics of a spatially extended excitable system. These
switchings between low-amplitude oscillations, nonlinear waves, and extreme
events strongly resemble a random process, although the system is
deterministic. We show that a chaotic saddle -- which contains all the patterns
as well as channel-like structures that mediate the transitions between them --
is the backbone of such a pattern switching dynamics. Our analyses indicate
that essential ingredients for the observed phenomena are that the system
behaves like an inhomogeneous oscillatory medium that is capable of
self-generating spatially localized excitations and that is dominated by
short-range connections but also features long-range connections. With our
findings, we present an alternative to the well-known ways to obtain
self-induced pattern switching, namely noise-induced attractor hopping,
heteroclinic orbits, and adaptation to an external signal. This alternative way
can be expected to improve our understanding of pattern switchings in spatially
extended natural dynamical systems like the brain and the heart
What Determines Size Distributions of Heavy Drops in a Synthetic Turbulent Flow?
We present results from an individual particle based model for the collision,
coagulation and fragmentation of heavy drops moving in a turbulent flow. Such a
model framework can help to bridge the gap between the full hydrodynamic
simulation of two phase flows, which can usually only study few particles and
mean field based approaches for coagulation and fragmentation relying heavily
on parameterization and are for example unable to fully capture particle
inertia. We study the steady state that results from a balance between
coagulation and fragmentation and the impact of particle properties and flow
properties on this steady state. We compare two different fragmentation
mechanisms, size-limiting fragmentation where particles fragment when exceeding
a maximum size and shear fragmentation, where particles break up when local
shear forces in the flow exceed the binding force of the particle. For
size-limiting fragmentation the steady state is mainly influenced by the
maximum stable particle size, while particle and flow properties only influence
the approach to the steady state. For shear fragmentation both the approach to
the steady state and the steady state itself depend on the particle and flow
parameters. There we find scaling relationships between the steady state and
the particle and flow parameters that are determined by the stability condition
for fragmentation.Comment: 14 pages, 7 figure
Relevant knowledge concerning the derivative concept for students of economics - A normative point of view and students' perspectives
International audienceThe concept of the derivative plays a major role in economics. A proper understanding of the concept and its application in economics is therefore important for students of economics. In this paper two perspectives on the relevant knowledge concerning the derivative for students of economics are presented: a normative point of view based on literature and the students' perspectives identified in an empirical study. It can be seen that the students' perspectives differed from the normative point of view. An interesting result is that, although emphasized in the course, the students of economics seemed to consider the economic interpretation of the derivative and the corresponding mathematical background knowledge to be much less important than pure mathematical procedures like differentiation rules.</p
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