21 research outputs found
Linear response theory for coupled phase oscillators with general coupling functions
We develop a linear response theory by computing the asymptotic value of the order parameter from the linearized equation of continuity around the nonsynchronized reference state using the Laplace transform in time. The proposed theory is applicable to a wide class of coupled phase oscillator systems and allows for any coupling functions, any natural frequency distributions, any phase-lag parameters, and any values for the time-delay parameter. This generality is in contrast to the limitation of the previous methods of the Ott鈥揂ntonsen ansatz and the self-consistent equation for an order parameter, which are restricted to a model family whose coupling function consists of only a single sinusoidal function. The theory is verified by numerical simulations
Macroscopic Models and Phase Resetting of Coupled Biological Oscillators
This thesis concerns the derivation and analysis of macroscopic mathematical models for coupled biological oscillators. Circadian rhythms, heart beats, and brain waves are all examples of biological rhythms formed through the aggregation of the rhythmic contributions of thousands of cellular oscillations. These systems evolve in an extremely high-dimensional phase space having at least as many degrees of freedom as the number of oscillators. This high-dimensionality often contrasts with the low-dimensional behavior observed on the collective or macroscopic scale. Moreover, the macroscopic dynamics are often of greater interest in biological applications.
Therefore, it is imperative that mathematical techniques are developed to extract low-dimensional models for the macroscopic behavior of these systems. One such mathematical technique is the Ott-Antonsen ansatz. The Ott-Antonsen ansatz may be applied to high-dimensional systems of heterogeneous coupled oscillators to derive an exact low-dimensional description of the system in terms of macroscopic variables. We apply the Ott-Antonsen technique to determine the sensitivity of collective oscillations to perturbations with applications to neuroscience.
The power of the Ott-Antonsen technique comes at the expense of several limitations which could limit its applicability to biological systems. To address this we compare the Ott-Antonsen ansatz with experimental measurements of circadian rhythms and numerical simulations of several other biological systems. This analysis reveals that a key assumption of the Ott-Antonsen approach is violated in these systems. However, we discover a low-dimensional structure in these data sets and characterize its emergence through a simple argument depending only on general phase-locking behavior in coupled oscillator systems. We further demonstrate the structure's emergence in networks of noisy heterogeneous oscillators with complex network connectivity. We show how this structure may be applied as an ansatz to derive low-dimensional macroscopic models for oscillator population activity. This approach allows for the incorporation of cellular-level experimental data into the macroscopic model whose parameters and variables can then be directly associated with tissue- or organism-level properties, thereby elucidating the core properties driving the collective behavior of the system.
We first apply our ansatz to study the impact of light on the mammalian circadian system. To begin we derive a low-dimensional macroscopic model for the core circadian clock in mammals. Significantly, the variables and parameters in our model have physiological interpretations and may be compared with experimental results. We focus on the effect of four key factors which help shape the mammalian phase response to light: heterogeneity in the population of oscillators, the structure of the typical light phase response curve, the fraction of oscillators which receive direct light input and changes in the coupling strengths associated with seasonal day-lengths. We find these factors can explain several experimental results and provide insight into the processing of light information in the mammalian circadian system.
In a second application of our ansatz we derive a pair of low-dimensional models for human circadian rhythms. We fit the model parameters to measurements of light sensitivity in human subjects, and validate these parameter fits with three additional data sets. We compare our model predictions with those made by previous phenomenological models for human circadian rhythms. We find our models make new predictions concerning the amplitude dynamics of the human circadian clock and the light entrainment properties of the clock. These results could have applications to the development of light-based therapies for circadian disorders.PHDApplied and Interdisciplinary MathematicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138766/1/khannay_1.pd
Phase reduction beyond the first order: The case of the mean-field complex Ginzburg-Landau equation
Phase reduction is a powerful technique that makes possible to describe the dynamics of a weakly perturbed limit-cycle oscillator in terms of its phase. For ensembles of oscillators, a classical example of phase reduction is the derivation of the Kuramoto model from the mean-field complex Ginzburg-Landau equation (MF-CGLE). Still, the Kuramoto model is a first-order phase approximation that displays either full synchronization or incoherence, but none of the nontrivial dynamics of the MF-CGLE. This fact calls for an expansion beyond the first order in the coupling constant. We develop an isochron-based scheme to obtain the second-order phase approximation, which reproduces the weak-coupling dynamics of the MF-CGLE. The practicality of our method is evidenced by extending the calculation up to third order. Each new term of the power-series expansion contributes with additional higher-order multibody (i.e., nonpairwise) interactions. This points to intricate multibody phase interactions as the source of pure collective chaos in the MF-CGLE at moderate coupling.We acknowledge support by MINECO (Spain) under Project No. FIS2016-74957-P. IL acknowledges support by Universidad de Cantabria and Government of Cantabria under the Concepci贸n Arenal programme
Volcano Transition in a System of Generalized Kuramoto Oscillators with Random Frustrated Interactions
In a system of heterogeneous (Abelian) Kuramoto oscillators with random or
`frustrated' interactions, transitions from states of incoherence to partial
synchronization were observed. These so-called volcano transitions are
characterized by a change in the shape of a local field distribution and were
discussed in connection with an oscillator glass. In this paper, we consider a
different class of oscillators, namely a system of (non-Abelian) SU(2)-Lohe
oscillators that can also be defined on the 3-sphere, i.e., an oscillator is
generalized to be defined as a unit vector in 4D Euclidean space. We
demonstrate that such higher-dimensional Kuramoto models with reciprocal and
nonreciprocal random interactions represented by a low-rank matrix exhibit a
volcano transition as well. We determine the critical coupling strength at
which a volcano-like transition occurs, employing an Ott-Antonsen ansatz.
Numerical simulations provide additional validations of our analytical findings
and reveal the differences in observable collective dynamics prior to and
following the transition. Furthermore, we show that a system of unit 3-vector
oscillators on the 2-sphere does not possess a volcano transition
A minimal model of peripheral clocks reveals differential circadian re-entrainment in aging
The mammalian circadian system comprises a network of cell-autonomous
oscillators, spanning from the central clock in the brain to peripheral clocks
in other organs. These clocks are tightly coordinated to orchestrate rhythmic
physiological and behavioral functions. Dysregulation of these rhythms is a
hallmark of aging, yet it remains unclear how age-related changes lead to more
easily disrupted circadian rhythms. Using a two-population model of coupled
oscillators that integrates the central clock and the peripheral clocks, we
derive simple mean-field equations that can capture many aspects of the rich
behavior found in the mammalian circadian system. We focus on three
age-associated effects which have been posited to contribute to circadian
misalignment: attenuated input from the sympathetic pathway, reduced
responsiveness to light, and a decline in the expression of neurotransmitters.
We find that the first two factors can significantly impede re-entrainment of
the clocks following a perturbation, while a weaker coupling within the central
clock does not affect the recovery rate. Moreover, using our minimal model, we
demonstrate the potential of using the feed-fast cycle as an effective
intervention to accelerate circadian re-entrainment. These results highlight
the importance of peripheral clocks in regulating the circadian rhythm and
provide fresh insights into the complex interplay between aging and the
resilience of the circadian system
Erosion of synchronization in networks of coupled oscillators
We report erosion of synchronization in networks of coupled phase
oscillators, a phenomenon where perfect phase synchronization is unattainable
in steady-state, even in the limit of infinite coupling. An analysis reveals
that the total erosion is separable into the product of terms characterizing
coupling frustration and structural heterogeneity, both of which amplify
erosion. The latter, however, can differ significantly from degree
heterogeneity. Finally, we show that erosion is marked by the reorganization of
oscillators according to their node degrees rather than their natural
frequencies.Comment: 5 pages, 4 figure
The Kuramoto model: A simple paradigm for synchronization phenomena
Synchronization phenomena in large populations of interacting elements are the subject of intense research efforts in physical, biological, chemical, and social systems. A successful approach to the problem of synchronization consists of modeling each member of the population as a phase oscillator. In this review, synchronization is analyzed in one of the most representative models of coupled phase oscillators, the Kuramoto model. A rigorous mathematical treatment, specific numerical methods, and many variations and extensions of the original model that have appeared in the last few years are presented. Relevant applications of the model in different contexts are also included
The mathematics behind chimera states
Chimera states are self-organized spatiotemporal patterns of coexisting coherence and incoherence. We give an overview of the main mathematical methods used in studies of chimera states, focusing on chimera states in spatially extended coupled oscillator systems. We discuss the continuum limit approach to these states, Ott--Antonsen manifold reduction, finite size chimera states, control of chimera states and the influence of system design on the type of chimera state that is observed