Faculty Publications
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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 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 Ltd