733 research outputs found
Excitable Delaunay triangulations
In an excitable Delaunay triangulation every node takes three states
(resting, excited and refractory) and updates its state in discrete time
depending on a ratio of excited neighbours. All nodes update their states in
parallel. By varying excitability of nodes we produce a range of phenomena,
including reflection of excitation wave from edge of triangulation, backfire of
excitation, branching clusters of excitation and localized excitation domains.
Our findings contribute to studies of propagating perturbations and waves in
non-crystalline substrates
Bifurcation analysis of a normal form for excitable media: Are stable dynamical alternans on a ring possible?
We present a bifurcation analysis of a normal form for travelling waves in
one-dimensional excitable media. The normal form which has been recently
proposed on phenomenological grounds is given in form of a differential delay
equation. The normal form exhibits a symmetry preserving Hopf bifurcation which
may coalesce with a saddle-node in a Bogdanov-Takens point, and a symmetry
breaking spatially inhomogeneous pitchfork bifurcation. We study here the Hopf
bifurcation for the propagation of a single pulse in a ring by means of a
center manifold reduction, and for a wave train by means of a multiscale
analysis leading to a real Ginzburg-Landau equation as the corresponding
amplitude equation. Both, the center manifold reduction and the multiscale
analysis show that the Hopf bifurcation is always subcritical independent of
the parameters. This may have links to cardiac alternans which have so far been
believed to be stable oscillations emanating from a supercritical bifurcation.
We discuss the implications for cardiac alternans and revisit the instability
in some excitable media where the oscillations had been believed to be stable.
In particular, we show that our condition for the onset of the Hopf bifurcation
coincides with the well known restitution condition for cardiac alternans.Comment: to be published in Chao
Soliton-like phenomena in one-dimensional cross-diffusion systems: a predator-prey pursuit and evasion example
We have studied properties of nonlinear waves in a mathematical model of a
predator-prey system with pursuit and evasion. We demonstrate a new type of
propagating wave in this system. The mechanism of propagation of these waves
essentially depends on the ``taxis'', represented by nonlinear
``cross-diffusion'' terms in the mathematical formulation. We have shown that
the dependence of the velocity of wave propagation on the taxis has two
distinct forms, ``parabolic'' and ``linear''. Transition from one form to the
other correlates with changes in the shape of the wave profile. Dependence of
the propagation velocity on diffusion in this system differs from the
square-root dependence typical of reaction-diffusion waves. We demonstrate also
that, for systems with negative and positive taxis, for example, pursuit and
evasion, there typically exists a large region in the parameter space, where
the waves demonstrate quasisoliton interaction: colliding waves can penetrate
through each other, and waves can also reflect from impermeable boundaries.Comment: 15 pages, 18 figures, submitted to Physica
Termination of Reentry in an Inhomogeneous Ring of Model Cardiac Cells
Reentrant waves propagating in a ring or annulus of excitable media model is
the basic mechanism underlying a major class of irregular cardiac rhythms known
as anatomical reentry. Such reentrant waves are terminated by rapid electrical
stimulation (pacing) from an implantable device. Because the mechanisms of such
termination are poorly understood, we study pacing of anatomical reentry in a
one-dimensional ring of model cardiac cells. For realistic off-circuit pacing,
our model-independent results suggest that circuit inhomogeneities, and the
electrophysiological dynamical changes they introduce, may be essential for
terminating reentry in some cases.Comment: 8 pages, 2-column LaTex (7 eps figures included); v2 includes
additional results and figures as in published versio
Nonlinear physics of electrical wave propagation in the heart: a review
The beating of the heart is a synchronized contraction of muscle cells
(myocytes) that are triggered by a periodic sequence of electrical waves (action
potentials) originating in the sino-atrial node and propagating over the atria and
the ventricles. Cardiac arrhythmias like atrial and ventricular fibrillation (AF,VF)
or ventricular tachycardia (VT) are caused by disruptions and instabilities of these
electrical excitations, that lead to the emergence of rotating waves (VT) and turbulent
wave patterns (AF,VF). Numerous simulation and experimental studies during the
last 20 years have addressed these topics. In this review we focus on the nonlinear
dynamics of wave propagation in the heart with an emphasis on the theory of pulses,
spirals and scroll waves and their instabilities in excitable media and their application
to cardiac modeling. After an introduction into electrophysiological models for action
potential propagation, the modeling and analysis of spatiotemporal alternans, spiral
and scroll meandering, spiral breakup and scroll wave instabilities like negative line
tension and sproing are reviewed in depth and discussed with emphasis on their impact
in cardiac arrhythmias.Peer ReviewedPreprin
Traveling waves in the Baer and Rinzel model of spine studded dendritic tissue
The Baer and Rinzel model of dendritic spines uniformly distributed along a dendritic
cable is shown to admit a variety of regular traveling wave solutions including
solitary pulses, multiple pulses and periodic waves. We investigate numerically the
speed of these waves and their propagation failure as functions of the system parameters
by numerical continuation. Multiple pulse waves are shown to occur close to
the primary pulse, except in certain exceptional regions of parameter space, which
we identify. The propagation failure of solitary and multiple pulse waves is shown to
be associated with the destruction of a saddle-node bifurcation of periodic orbits.
The system also supports many types of irregular wave trains. These include waves
which may be regarded as connections to periodics and bursting patterns in which
pulses can cluster together in well-defined packets. The behavior and properties of
both these irregular spike-trains is explained within a kinematic framework that is
based on the times of wave pulses. The dispersion curve for periodic waves is important
for such a description and is obtained in a straightforward manner using the
numerical scheme developed for the study of the speed of a periodic wave. Stability
of periodic waves within the kinematic theory is given in terms of the derivative
of the dispersion curve and provides a weak form of stability that may be applied
to solutions of the traveling wave equations. The kinematic theory correctly predicts
the conditions for period doubling bifurcations and the generation of bursting states. Moreover, it also accurately describes the shape and speed of the traveling
front that connects waves with two different periods
- …