Excitable Chemical Systems Research Articles

Electromechanical vortex filaments during cardiac fibrillation.

The self-organized dynamics of vortex-like rotating waves, which are also known as scroll waves, are the basis of the formation of complex spatiotemporal patterns in many excitable chemical and biological systems. In the heart, filament-like phase singularities that are associated with three-dimensional scroll waves are considered to be the organizing centres of life-threatening cardiac arrhythmias. The mechanisms that underlie the onset, maintenance and control of electromechanical turbulence in the heart are inherently three-dimensional phenomena. However, it has not previously been possible to visualize the three-dimensional spatiotemporal dynamics of scroll waves inside cardiac tissues. Here we show that three-dimensional mechanical scroll waves and filament-like phase singularities can be observed deep inside the contracting heart wall using high-resolution four-dimensional ultrasound-based strain imaging. We found that mechanical phase singularities co-exist with electrical phase singularities during cardiac fibrillation. We investigated the dynamics of electrical and mechanical phase singularities by simultaneously measuring the membrane potential, intracellular calcium concentration and mechanical contractions of the heart. We show that cardiac fibrillation can be characterized using the three-dimensional spatiotemporal dynamics of mechanical phase singularities, which arise inside the fibrillating contracting ventricular wall. We demonstrate that electrical and mechanical phase singularities show complex interactions and we characterize their dynamics in terms of trajectories, topological charge and lifetime. We anticipate that our findings will provide novel perspectives for non-invasive diagnostic imaging and therapeutic applications.

Optical Communication among Oscillatory Reactions and Photo‐Excitable Systems: UV and Visible Radiation Can Synchronize Artificial Neuron Models

AbstractNeuromorphic engineering promises to have a revolutionary impact in our societies. A strategy to develop artificial neurons (ANs) is to use oscillatory and excitable chemical systems. Herein, we use UV and visible radiation as both excitatory and inhibitory signals for the communication among oscillatory reactions, such as the Belousov–Zhabotinsky and the chemiluminescent Orban transformations, and photo‐excitable photochromic and fluorescent species. We present the experimental results and the simulations regarding pairs of ANs communicating by either one or two optical signals, and triads of ANs arranged in both feed‐forward and recurrent networks. We find that the ANs, powered chemically and/or by the energy of electromagnetic radiation, can give rise to the emergent properties of in‐phase, out‐of‐phase, anti‐phase synchronizations and phase‐locking, dynamically mimicking the communication among real neurons.

Optical Communication among Oscillatory Reactions and Photo-Excitable Systems: UV and Visible Radiation Can Synchronize Artificial Neuron Models.

Neuromorphic engineering promises to have a revolutionary impact in our societies. A strategy to develop artificial neurons (ANs) is to use oscillatory and excitable chemical systems. Herein, we use UV and visible radiation as both excitatory and inhibitory signals for the communication among oscillatory reactions, such as the Belousov-Zhabotinsky and the chemiluminescent Orban transformations, and photo-excitable photochromic and fluorescent species. We present the experimental results and the simulations regarding pairs of ANs communicating by either one or two optical signals, and triads of ANs arranged in both feed-forward and recurrent networks. We find that the ANs, powered chemically and/or by the energy of electromagnetic radiation, can give rise to the emergent properties of in-phase, out-of-phase, anti-phase synchronizations and phase-locking, dynamically mimicking the communication among real neurons.

On Emulation of Flueric Devices in Excitable Chemical Medium.

Flueric devices are fluidic devices without moving parts. Fluidic devices use fluid as a medium for information transfer and computation. A Belousov-Zhabotinsky (BZ) medium is a thin-layer spatially extended excitable chemical medium which exhibits travelling excitation wave-fronts. The excitation wave-fronts transfer information. Flueric devices compute via jets interaction. BZ devices compute via excitation wave-fronts interaction. In numerical model of BZ medium we show that functions of key flueric devices are implemented in the excitable chemical system: signal generator, and, xor, not and nor Boolean gates, delay elements, diodes and sensors. Flueric devices have been widely used in industry since late 1960s and are still employed in automotive and aircraft technologies. Implementation of analog of the flueric devices in the excitable chemical systems opens doors to further applications of excitation wave-based unconventional computing in soft robotics, embedded organic electronics and living technologies.

On computing in fine-grained compartmentalised Belousov–Zhabotinsky medium

We introduce results of computer experiments on information processing in a hexagonal array of vesicles filled with Belousov–Zhabotinsky (BZ) solution in a sub-excitable mode. We represent values of Boolean variables by excitation wave-fragments and implement basic logical gates by colliding the wave-fragments. We show that a vesicle filled with BZ mixture can implement a range of basic logical functions. We cascade BZ-vesicle logical gates into arithmetic circuits implementing addition of two one-bit binary numbers. We envisage that our theoretical results will be applied in chemical laboratory designs of massive-parallel computers based on fine-grained compartmentalisation of excitable chemical systems.

Towards constructing one-bit binary adder in excitable chemical medium

The light-sensitive modification (ruthenium catalysed) of the Belousov–Zhabotinsky reaction exhibits various excitability regimes depending on the level of illumination. Within a narrow range of applied illumination levels the medium is in a sub-excitable state. When in this state an asymmetric perturbation of the medium leads to formation of a travelling localized excitation (wave-fragment) which moves along a predetermined trajectory, ideally preserving its shape and velocity over an extended time period. Collision-based computing can be implemented with these wave-fragments whereby values of Boolean variables are represented as the presence/absence of a wave-fragment at specific sites. When two wave-fragments collide they either annihilate, or form new wave-fragments. The trajectories of the wave-fragments after the collision represent the result of a computation, e.g. construction of a simple logical gate. However, wave-fragments in sub-excitable chemical media are difficult to control. Therefore, we adopted a hybrid procedure in order to construct collision-based logical gates. We used channels of low light intensity projected onto the excitable media in order to subtly tune and stabilise the propagating wave-fragments allowing them to collide at the junctions between channels. Using this methodology we were able to implement both in theoretical models (using the Oregonator) and in experiment two interaction-based logical gates and assemble the gates into a basic one-bit binary adder. We present the first ever experimental approach towards constructing arithmetic circuits in spatially-extended excitable chemical systems where light is used to impart functionality.

Routing Physarum with repellents

Plasmodium of Physarum polycephalum is a single cell with many nuclei. Plasmodium is an easy-to-experiment-with biological substrate, a multi-functional bio-material used to implement novel and future computing architectures. The plasmodium exhibits typical features of excitable chemical systems and capable for distributed sensing, parallel information processing and decentralized actuation. Plasmodium of P. polycephalum is proved to be a universal storage modification machine. Actively growing zones of the plasmodium are considered to be elementary processors of the growing computing machine, as well as messages traveling in the spatially extended non-linear medium. Controlling propagation of the messages and computing processes is a prerequisite for a successful implementation of working prototypes of plasmodium machines. In laboratory experiments and computer simulation we show that active growing zones of plasmodium can be precisely routed using repelling diffusion gradients generated by crystals of sodium chloride. We demonstrate how to achieve controllable reflection, splitting/multiplication and merging of plasmodium's active zones.

One Dimensional Chemical Signal Diode Constructed with Two Nonexcitable Barriers

Excitable chemical systems can process information coded in excitation pulses. Here we demonstrate the simplest realization of a chemical signal diode that transmits pulses in one direction only. It is constructed with only two different nonexcitable barriers. The proposed diode has been tested in numerical simulations and in experiments with Ru-catalyzed Belousov-Zhabotinsky reaction.

Motion of phase singularities in a class-B laser

We investigate the circling motion of phase singularities in a small Fresnel number CO 2-laser. This occurs whenever modes with singly or multiply charged phase singularities are simultaneously excited with rotationally symmetric modes. From the helical bistability of modes containing phase singularities follows bistability of the circling motion. Up to three simultaneously circling singularities are demonstrated. The slowly relaxing inversion of class-B lasers has as a consequence the nonstationarity of phase singularities which results in motion even when all mode frequencies are equal. Evidence of this nonstationarity, which relates class-B lasers to excitable chemical systems, is given.

Phase mappings from diffusion-coupled excitable chemical systems

Dynamics of a cascade of two diffusion-coupled excitable units periodically perturbed by pulses applied to the first cell is examined. Firing sequences experimentally found in a chemical system constituted by two coupled stirred cells with the Belousov-Zhabotinskii (BZ) reaction are modelled on two levels. A phase mapping of an abstract piecewise linear excitable two-cell system is derived and its dynamics examined in detail. The functional form of this map combined with local excitation dynamics extracted from a realistic model of the BZ kinetics is used to formulate a semi-empirical model directly applicable to the experimental BZ system. The frequency of firings in the second cell can be either equal to that in the first cell - a complete propagation of the excitation, or smaller - a propagation failure. Complex patterns of transitions between the two dynamic modes found in experiments are well predicted by the semi-empirical model and, surprisingly, by the abstract model as well, pointing to a generic nature of the patterns.

Origin of spontaneous wave generation in excitable chemical systems

We investigate the origin of spontaneous chemical wave generation in an excitable Beloubov-Zhabotinskii system. We solve one-dimensional reaction-diffusion equations of an Oregonator model with the initial profiles possessing an excitation of varying concentration of either HBrO 2 or Br - , and the excitation occurs within a region of different length. The concentration of the threshold excitation necessary for a wave to propagate depends on the length within which the initial excitation is applied

Excitable chemical reaction systems in a continuous stirred tank reactor

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExcitable chemical reaction systems in a continuous stirred tank reactorJ. Finkeova, M. Dolnik, B. Hrudka, and M. MarekCite this: J. Phys. Chem. 1990, 94, 10, 4110–4115Publication Date (Print):May 1, 1990Publication History Published online1 May 2002Published inissue 1 May 1990https://doi.org/10.1021/j100373a042RIGHTS & PERMISSIONSArticle Views122Altmetric-Citations30LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (704 KB) Get e-Alerts

The bifurcation structure of waves in excitable chemical systems

We report the results of a numerical study of how traveling wave branches originate and terminate in a prototypical excitable chemical system, viz. the Kernevez model. These results furnish a qualitative understanding of recent experimental observations on sustained spiral waves in a continuously fed unstirred reactor [W. Y. Tam et al., J. Chem. Phys. 88, 3395 (1988)], in particular of the hysteretic nature of the transition between the wave state and the homogeneous steady state.

Excitable chemical reaction systems. II. Several pulses on the ring fiber.

The parameters of the Field, Noyes and Körös model for the Belousov-Zhabotinskii reaction were chosen in such a way that the given system is excitable. It is shown by simulation that several pulses on the ring fiber, contrary to experience with known excitable media, may arrange themselves in a non-symmetrical manner while the equilibrium distances are stable. The condition for such behavior is the non-monotonic dependence of the propagation velocity, v, on the time, T, elpased since the previous excitation at that point.

Excitable chemical reaction systems I. Definition of excitability and simulation of model systems

Using a computer program based on the well-known Crank-Nicolson method, a number of onedimensional chemical reaction-diffusion systems showing “regenerative excitability” are simulated, both on a finite interval and on a circle. Hereby several phenomena known from nerve physiology as travelling trains and pulse omissions have been reproduced.