Faculty Publications
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Item Dynamics of Chemical Excitation Waves Subjected to Subthreshold Electric Field in a Mathematical Model of the Belousov-Zhabotinsky Reaction(Springer Science and Business Media B.V., 2022) Sebastian, A.; Amrutha, S.V.; Punacha, S.; Shajahan, T.K.We present a numerical study of the dynamics of spiral waves in a weak external electric field, using the Oregonator model of the Belousov-Zhabotinky (BZ) reaction. Both free and pinned spiral waves are studied in two types of electric fields: unidirectional (DC) and Circularly Polarised Electric Field (CPEF). Both free spirals and pinned spiral waves rotate faster in the DC field. The CPEF can help a free spiral to be spatially confined. A pinned spiral period can be controlled by varying the period of the CPEF. Both DC and CPEF can unpin the pinned spiral wave, but the minimum electric field required to unpin is much less with CPEF compared to DC. Thus, CPEF is more energy efficient to unpin a pinned spiral wave. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Drift and Annihilation of a Counter-Rotating Spiral Pair in Belousov-Zhabotinsky Reaction Under a DC Electric Field(Springer Science and Business Media Deutschland GmbH, 2024) Mishra, P.R.; Sebastian, A.; Shajahan, T.K.We present a numerical study of the dynamics of the counter-rotating spiral pair in the presence of a DC electric field using the Oregonator model of the Belousov-Zhabotinky (BZ) reaction. The dynamics of the counter-rotating pair is investigated by changing the strength and direction of the electric field. The dynamics can change from meander to drift with increasing field strength. The drift velocity increases with the field strength, and its direction depends on the direction of the field. Finally, the spiral pair is annihilated when the applied field is above a threshold value. With further increase in field strength, the annihilation is followed by generation of a new counter-rotating pair oriented opposite to the initial pair. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.Item Spiral wave unpinning facilitated by wave emitting sites in cardiac monolayers(Royal Society Publishing, 2019) Punacha, S.; Berg, S.; Sebastian, A.; Krinski, V.I.; Luther, S.; Shajahan, T.K.Rotating spiral waves of electrical activity in the heart can anchor to unexcitable tissue (an obstacle) and become stable pinned waves. A pinned rotating wave can be unpinned either by a local electrical stimulus applied close to the spiral core, or by an electric field pulse that excites the core of a pinned wave independently of its localization. The wave will be unpinned only when the pulse is delivered inside a narrow time interval called the unpinning window (UW) of the spiral. In experiments with cardiac monolayers, we found that other obstacles situated near the pinning centre of the spiral can facilitate unpinning. In numerical simulations, we found increasing or decreasing of the UW depending on the location, orientation and distance between the pinning centre and an obstacle. Our study indicates that multiple obstacles could contribute to unpinning in experiments with intact hearts. © 2019 The Author(s) Published by the Royal Society. All rights reserved.Item Mechanism of Spiral Wave Unpinning in the Belousov-Zhabotinsky Reaction with a DC Electric Field(American Chemical Society, 2022) Amrutha, S.V.; Sebastian, A.; Sibeesh, P.; Punacha, S.; Shajahan, T.K.We study the mechanism of spiral wave unpinning in the Belousov-Zhabotinsky (BZ) reaction with a DC electric field. The unpinning is characterized by the phase of the spiral tip around the obstacle boundary at the time of unpinning. We systematically measure the unpinning phase as a function of the chirality of spiral rotation, the initial phase of the spiral, the size of the pinning obstacle, the direction, and the strength of the applied electric field. In both BZ experiments and simulations using the Oregonator model, we observe that the spiral wave always unpins at a fixed position with respect to the applied field. The wave unpins when the electric field component in the direction of the tip velocity of the spiral waves becomes equal to a threshold field strength. From these observations, we deduce a relation between the phase of unpinning, the size of the pinning obstacle, the strength, and the direction of the electric field, and it agrees with our observations. We conclude from our observations that a retarding 'electric force' on the chemical wave is responsible for the unpinning in the BZ medium. Our results indicate that the 'electric force' is more effective in unpinning when the wave moves away from the anode than when it is moving toward it. © 2022 American Chemical Society.Item Theory and experiments of spiral unpinning in the Belousov-Zhabotinsky reaction using a circularly polarized electric field(American Institute of Physics Inc., 2023) Amrutha, S.V.; Sebastian, A.; Sibeesh, P.; Punacha, S.; Shajahan, T.K.We present the first experimental study of unpinning an excitation wave using a circularly polarized electric field. The experiments are conducted using the excitable chemical medium, the Belousov-Zhabotinsky (BZ) reaction, which is modeled with the Oregenator model. The excitation wave in the chemical medium is charged so that it can directly interact with the electric field. This is a unique feature of the chemical excitation wave. The mechanism of wave unpinning in the BZ reaction with a circularly polarized electric field is investigated by varying the pacing ratio, the initial phase of the wave, and field strength. The chemical wave in the BZ reaction unpins when the electric force opposite the direction of the spiral is equal to or above a threshold. We developed an analytical relation of the unpinning phase with the initial phase, the pacing ratio, and the field strength. This is then verified in experiments and simulations. © 2023 Author(s).Item Effect of electric field chirality on the unpinning of chemical waves in the Belousov–Zhabotinsky reaction(Elsevier Ltd, 2024) Sebastian, A.; Sibeesh, P.; Amrutha, S.V.; Punacha, S.; Shajahan, T.K.We investigate the unpinning of chemical spiral waves attached to obstacles in the Belousov–Zhabotinsky (BZ) reaction using a Circularly Polarized Electric Field (CPEF). The unpinning is quantified by measuring the angle at which the spiral leaves the obstacle. Previously, we had found that the wave can unpin when the electric field along the direction of the spiral is above a threshold value. When we apply a DC field, this condition can be satisfied for a range of spiral phases, which we call the unpinning window (UW). With a CPEF, this UW moves either along the direction of the spiral (co-rotating) or against the spiral (counter-rotating). We find that when the field is co-rotating, it can take several rotations of the spiral to get unpinned. With a counter-rotating field, the spiral always unpins during the first rotation. We analyze how unpinning with CPEF depends on the electric field's relative speed, chirality, and strength using experiments and the Oregonator model. Our work helps to understand and control chemical waves. © 2024 Elsevier LtdItem Influence of Oil Density on Self-Propelled Motion of Belousov-Zhabotinsky Reaction Droplet(Binghamton University Libraries, 2025) Meshram, V.B.; Sebastian, A.; Sibeesh, P.; Shajahan, T.K.Belousov-Zhabotinsky reaction serves as an example of the nonlinear chemical oscillator in which the reacting substance undergoes sequential oxidation and re-duction. A droplet containing the BZ reaction, when placed within the oily envi-ronment, can self-propel. In this experimental work, we explore the effect of oil medium density on the BZ reaction droplet dynamics. In an oil medium with lower density, the BZ droplet exhibits higher speed and effective diffusivity but a shorter lifetime. Both the distance and speed of the droplet initially increase with droplet volume. However, beyond a critical volume, the distance decreases while the speed stays constant. Interestingly, the critical volumes for distance and speed are not the same. This experimental work might help researchers understand the self-propelled motion of active matter in different media. © 2025, Binghamton University Libraries. All rights reserved.