Spiral Waves

Spiral waves are observed in a variety of natural systems, including cardiac arrhythmias and chemical oscillations, both of which are commonly modeled with reaction-diffusion systems. We are interested in the stability of spiral waves, and how spectral properties of spirals on bounded domains can provide insight into understanding the instabilities from a mathematical perspective.


Alternans in the Karma Model

Alternans Instability


Ventricular tachycardia, a dangerous fast-paced heart rate, is a result of a sustained spiral wave rotating on the surface of the heart. After the spiral destabilizes, unorganized electrical activity can lead to ventricular fibrillation and sudden cardiac arrest (SCA) – the leading natural cause of death in the US. Clinically, the onset of SCA has been linked to the alternans instability, a beat-to-beat alteration in the action potential duration of the spiral bands. We seek to understand the role of spectra in the formation of the alternans instability.

Related Poster: Spectral Properties of Spiral Waves in the Karma Model, SIAM Conference on Applications of Dynamical Systems, May 2017, Snowbird, UT.


Spectra in zero-diffusion limit

Spectra of Spirals in Reaction-Diffusion Systems with Diffusion-less Species


Reaction-diffusion systems often have one or more diffusion-less species (such as ion-channel models). Numerical results indicate that removing diffusion from a slowly diffusing component dramatically changes the spectra of a 2D spiral; a property that is not observed in 1D. The figure shows the change in the spectra of a spiral in the Barkley model from the slow species slightly diffusing (δ = 0.2) to not diffusing (δ = 0). We are working to analytically and numerically understand why these differences occur and what the implications are.

Related Posters:


Stationary Line Defect in Rössler Model

Line Defects in the Rössler Model


Spiral waves in the Rössler Model exhibit stationary line defects. It has been hypothesized that these defects emerged from instabilities of the boundary sink, but until now, this theory has not been directly tested. A comparison of the spectra of spiral waves and the boundary sinks suggests that the line defects are a result of unstable point eigenvalues from the boundary.


A Model for Electrically Excitable Tissue

iOS-HEK Cells


In collaboration with the Cohen Lab at Harvard University, we developed a PDE model for isradipine Optopatch Spiking Human Embrionic Kidney Cells (iOS-HEK cells), a synthetic excitable tissue. The iOS-HEK cells have simple and well understood ionic channels, but exhibit complex electrical activity similar to cardiac cells. Additionally, the model and experiment highlight how the geometry of the tissue impacts the behavior of propagating electrical waves.

Preprint available on bioRxiv:


Migratory Patterns of Blue Whales

Blue Whale Simulation: Background
indicates prey concentration with yellow high.



Through the 2018 NSF Graduate Research Internship Program, I began working with Dr. Elliott Hazen and Dr. Steven Bograd at the NOAA Environmental Research Division to study the spatiotemporal distribution of blue whales off the California coast. Blue whales are a highly dynamic species, and we developed an agent-based model to investigate how environmental and prey conditions impact the migratory behavior. The model accurately captures the spring-summer northward migration and yearly differences in the spatiotemporal distribution driven by variations in prey abundance. We are now exploring drivers of the fall southward migration.


Publications


Reading Group

Dr. Sandstede's reseach group participates in weekly meetings and each semester discusses a topic in dynamical systems. The topics covered are below, as well as my contributions.

Semester Topic My Subtopic Notes
Spring 2016 Nonlinear Waves: Spatial Dynamics and Fredholm Approaches
Fall 2016 Vegetation Patterns Localised pattern formation in a model for dryland vegetation Slides
Spring 2017 Data Science Data Science in Cooking Slides
Fall 2017 Dynamics and Statistics Introduction to Parameter Estimation
Spring 2018 Probability and Statistics Information Theory
Fall 2018 Agent-Based Models