3,480 research outputs found
Dichotomy results for delay differential equations with negative Schwarzian
We gain further insight into the use of the Schwarzian derivative to obtain
new results for a family of functional differential equations including the
famous Wright's equation and the Mackey-Glass type delay differential
equations. We present some dichotomy results, which allow us to get easily
computable bounds of the global attractor. We also discuss related conjectures,
and formulate new open problems.Comment: 16 pages, submitted to Chaos,Solitons,Fractal
Existence of global attractor for a nonautonomous state-dependent delay differential equation of neuronal type
The analysis of the long-term behavior of the mathematical model of a neural
network constitutes a suitable framework to develop new tools for the dynamical
description of nonautonomous state-dependent delay equations (SDDEs).
The concept of global
attractor is given, and some results which establish properties ensuring
its existence and providing a description of its shape, are proved.
Conditions for the exponential stability of the global attractor
are also studied. Some properties
of comparison of solutions constitute a key in
the proof of the main results, introducing methods of monotonicity
in the dynamical analysis of nonautonomous SDDEs.
Numerical simulations of some illustrative models show
the applicability of the theory.Ministerio de Economía y Competitividad / FEDER, MTM2015-66330-PMinisterio de Ciencia, Innovación y Universidades, RTI2018-096523-B-I00European Commission, H2020-MSCA-ITN-201
Delay Equations and Radiation Damping
Starting from delay equations that model field retardation effects, we study
the origin of runaway modes that appear in the solutions of the classical
equations of motion involving the radiation reaction force. When retardation
effects are small, we argue that the physically significant solutions belong to
the so-called slow manifold of the system and we identify this invariant
manifold with the attractor in the state space of the delay equation. We
demonstrate via an example that when retardation effects are no longer small,
the motion could exhibit bifurcation phenomena that are not contained in the
local equations of motion.Comment: 15 pages, 1 figure, a paragraph added on page 5; 3 references adde
Global dynamics of a novel delayed logistic equation arising from cell biology
The delayed logistic equation (also known as Hutchinson's equation or
Wright's equation) was originally introduced to explain oscillatory phenomena
in ecological dynamics. While it motivated the development of a large number of
mathematical tools in the study of nonlinear delay differential equations, it
also received criticism from modellers because of the lack of a mechanistic
biological derivation and interpretation. Here we propose a new delayed
logistic equation, which has clear biological underpinning coming from cell
population modelling. This nonlinear differential equation includes terms with
discrete and distributed delays. The global dynamics is completely described,
and it is proven that all feasible nontrivial solutions converge to the
positive equilibrium. The main tools of the proof rely on persistence theory,
comparison principles and an -perturbation technique. Using local
invariant manifolds, a unique heteroclinic orbit is constructed that connects
the unstable zero and the stable positive equilibrium, and we show that these
three complete orbits constitute the global attractor of the system. Despite
global attractivity, the dynamics is not trivial as we can observe long-lasting
transient oscillatory patterns of various shapes. We also discuss the
biological implications of these findings and their relations to other logistic
type models of growth with delays
A delay differential model of ENSO variability, Part 2: Phase locking, multiple solutions, and dynamics of extrema
We consider a highly idealized model for El Nino/Southern Oscillation (ENSO)
variability, as introduced in an earlier paper. The model is governed by a
delay differential equation for sea surface temperature in the Tropical
Pacific, and it combines two key mechanisms that participate in ENSO dynamics:
delayed negative feedback and seasonal forcing. We perform a theoretical and
numerical study of the model in the three-dimensional space of its physically
relevant parameters: propagation period of oceanic waves across the Tropical
Pacific, atmosphere-ocean coupling, and strength of seasonal forcing. Phase
locking of model solutions to the periodic forcing is prevalent: the local
maxima and minima of the solutions tend to occur at the same position within
the seasonal cycle. Such phase locking is a key feature of the observed El Nino
(warm) and La Nina (cold) events. The phasing of the extrema within the
seasonal cycle depends sensitively on model parameters when forcing is weak. We
also study co-existence of multiple solutions for fixed model parameters and
describe the basins of attraction of the stable solutions in a one-dimensional
space of constant initial model histories.Comment: Nonlin. Proc. Geophys., 2010, accepte
On Norm-Based Estimations for Domains of Attraction in Nonlinear Time-Delay Systems
For nonlinear time-delay systems, domains of attraction are rarely studied
despite their importance for technological applications. The present paper
provides methodological hints for the determination of an upper bound on the
radius of attraction by numerical means. Thereby, the respective Banach space
for initial functions has to be selected and primary initial functions have to
be chosen. The latter are used in time-forward simulations to determine a first
upper bound on the radius of attraction. Thereafter, this upper bound is
refined by secondary initial functions, which result a posteriori from the
preceding simulations. Additionally, a bifurcation analysis should be
undertaken. This analysis results in a possible improvement of the previous
estimation. An example of a time-delayed swing equation demonstrates the
various aspects.Comment: 33 pages, 8 figures, "This is a pre-print of an article published in
'Nonlinear Dynamics'. The final authenticated version is available online at
https://doi.org/10.1007/s11071-020-05620-8
Dynamics of FitzHugh-Nagumo excitable systems with delayed coupling
Small lattices of nearest neighbor coupled excitable FitzHugh-Nagumo
systems, with time-delayed coupling are studied, and compared with systems of
FitzHugh-Nagumo oscillators with the same delayed coupling. Bifurcations of
equilibria in N=2 case are studied analytically, and it is then numerically
confirmed that the same bifurcations are relevant for the dynamics in the case
. Bifurcations found include inverse and direct Hopf and fold limit cycle
bifurcations. Typical dynamics for different small time-lags and coupling
intensities could be excitable with a single globally stable equilibrium,
asymptotic oscillatory with symmetric limit cycle, bi-stable with stable
equilibrium and a symmetric limit cycle, and again coherent oscillatory but
non-symmetric and phase-shifted. For an intermediate range of time-lags inverse
sub-critical Hopf and fold limit cycle bifurcations lead to the phenomenon of
oscillator death. The phenomenon does not occur in the case of FitzHugh-Nagumo
oscillators with the same type of coupling.Comment: accepted by Phys.Rev.
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