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Oliver Steinbock

Publications and source records attributed to Oliver Steinbock.

16 recordsLinked to original sources
PubMed2006

Nucleation and collapse of scroll rings in excitable media.

We describe a novel nucleation mechanism of scroll rings in three-dimensional reaction-diffusion systems with anomalous dispersion. The vortices form after the collision of two spherical wave fronts from a third, trailing wave that only partially annihilates in the wake of its predecessor. Depending on the relative positions of the three relevant wave sources, one obtains untwisted or twisted scroll rings. The formation of both vortex structures is demonstrated for a modified Belousov-Zhabotinsky reaction.

Colloids↗
PubMed2006

Compositional analysis of copper-silica precipitation tubes.

Silica gardens consist of hollow tubular structures that form from salt crystals seeded into silicate solution. We investigate the structure and elemental composition of these tubes in the context of a recently developed experimental model that allows quantitative analyses based on predetermined reactant concentrations and flow rates. In these experiments, cupric sulfate solution is injected into large volumes of waterglass. The walls of the resulting tubular structures have a typical width of 10 microm and are gradient materials. Micro-Raman spectroscopy along with energy dispersive X-ray fluorescence data identify amorphous silica and copper(ii) hydroxide as the main compounds within the inner and outer tube surfaces, respectively. Upon heating the blueish precipitates to approximately 150 degrees C, the material turns black as copper(ii) hydroxide decomposes to copper(ii) oxide. Moreover, we present high resolution transmission electron micrographs that reveal polycrystalline morphologies.

Journal Article↗
PubMed2006

Propagation failure dynamics of wave trains in excitable systems.

We report experimental and numerical results on temporal patterns of propagation failures in reaction-diffusion systems. Experiments employ the 1,4-cyclohexanedione Belousov-Zhabotinsky reaction. The propagation failures occur in the frontier region of the wave train and can profoundly affect its expansion speed. The specific rhythms observed vary from simple periodic to highly complex and possibly chaotic sequences. All but the period-1 sequences are found in the transition region between "merging" and "tracking" dynamics, which correspond to wave behavior caused by two qualitatively different types of anomalous dispersion relations.

Journal Article↗
PubMed2006

Propagation failures, breathing pulses, and backfiring in an excitable reaction-diffusion system.

We report results from experiments with a pseudo-one-dimensional Belousov-Zhabotinsky reaction that employs 1,4-cyclohexanedione as its organic substrate. This excitable system shows traveling oxidation pulses and pulse trains that can undergo complex sequences of propagation failures. Moreover, we present examples for (i) breathing pulses that undergo periodic changes in speed and size and (ii) backfiring pulses that near their back repeatedly generate new pulses propagating in opposite direction.

Animals↗
PubMed2006

Introduction: Self-organization in nonequilibrium chemical systems.

The field of self-organization in nonequilibrium chemical systems comprises the study of dynamical phenomena in chemically reacting systems far from equilibrium. Systematic exploration of this area began with investigations of the temporal behavior of the Belousov-Zhabotinsky oscillating reaction, discovered accidentally in the former Soviet Union in the 1950s. The field soon advanced into chemical waves in excitable media and propagating fronts. With the systematic design of oscillating reactions in the 1980s and the discovery of Turing patterns in the 1990s, the scope of these studies expanded dramatically. The articles in this Focus Issue provide an overview of the development and current state of the field.

Biophysics↗
PubMed2005

Front aggregation in multiarmed excitation vortices.

Using the Belousov-Zhabotinsky reaction, we study the pinning of multiarmed spiral waves to nonexcitable obstacles. With increasing obstacle size, the individual arms switch from a repulsive to an attractive state. This transition yields densely aggregated spiral arms and is caused by anomalous dispersion. A kinematic model reproduces the measurements quantitatively and identifies the transition as a supercritical pitchfork bifurcation.

Journal Article↗
PubMed2005

Bubble guidance of tubular growth in reaction-precipitation systems.

Numerous types of reaction-precipitation systems involve the growth of tubular structures similar to those formed in "silica gardens". As a model case for this phenomenon, we investigate the rapid growth of hollow tubes in the reaction between sodium silicate and cupric sulfate. The latter solution is injected hydrodynamically at constant flow rates of 1-20 mL h(-1) into a large reservoir of waterglass. In this study, the growth is templated and guided by single, buoyant gas bubbles. The resulting tubes can be several decimetres long and have constant radii in the range of 100-600 microm. Systematic measurements show that bubble size governs the tube radius. According to this radius, the system selects its growth velocity following volume conservation of the injected solution. Moreover, scanning electron microscopy reveals intricate ring patterns on the tube walls. We also show evidence for the existence of a minimal and a maximal tube radius. Finally, we report an intriguing collapse of tubes created at high silicate concentrations, which yields twisted ribbon-like structures. Critical radii and tube collapse are discussed in terms of simple competing forces.

Chemical Precipitation↗
PubMed2004

Dynamics of excitation pulses with attractive interaction: kinematic analysis and chemical wave experiments.

We present a theoretical analysis of stacking and destacking wave trains in excitable reaction-diffusion systems with anomalous velocity-wavelength dependence. For linearized dispersion relations, kinematic analysis yields an analytical function that rigorously describes front trajectories. The corresponding accelerations have exactly one extremum that slowly decays with increasing pulse number. For subsequent pulses these maxima occur with a lag time equal to the inverse slope of the linearized dispersion curve. These findings are reproduced in experiments with chemical waves in the 1,4-cyclohexanedione Belousov-Zhabotinsky reaction but should be also applicable to step bunching on crystal surfaces and certain traffic phenomena.

Journal Article↗
PubMed2004

Quantized spiral tip motion in excitable systems with periodic heterogeneities.

Meandering spiral tips in homogeneous reaction-diffusion systems are characterized by two generically incommensurate radii and frequencies. Here, we create periodic perturbations in space to induce a transition to commensurate radii and frequencies that exhibit a devil's staircase. The plateaus of the staircase correspond to pinned or complex periodic orbits of the spiral tip.

Cell Physiological Phenomena↗
PubMed2003

Oscillatory growth of silica tubes in chemical gardens.

We report distinct growth regimes of hollow silica fibers formed by hydrodynamic injection of cupric sulfate into silicate solution. The tubes grow either steadily along a continuous jet of buoyant solution or through relaxation oscillations that are governed by chemo-mechanical processes. The dependence of the oscillation period on flow rate and copper concentration is explained in the framework of a simple model. Tailored flow patterns allow the directional control of the tubes and their use as miniature connectors. Our findings are applicable to the understanding of chemical gardens, promise a wealth of nonlinear phenomena, and offer possible applications in microfluidics.

Journal Article↗
PubMed2002

Traveling fronts of copper deposition.

We report the experimental observation of traveling fronts during the electroless deposition of copper on passive steel substrates. The low-carbon steel samples are passivated in nitric acid prior to the plating experiment, thus creating a thin, protective oxide layer on the steel surface. The deposition experiments are carried out from slightly acidic (pH 3.2) copper sulfate solution and copper nitrate solution with the latter showing front propagation only in the presence of chloride ions. For up to 30 s, fronts propagate with constant velocities in the range from 0.5 to 5 mm/s depending on the experimental conditions. This phase of constant-speed propagation gives way to accelerating fronts and very rapid, spatially unstructured deposition. Front-mediated plating is observed over a wide range of cupric ion concentration and constitutes a striking and unexpected example for pattern formation in electrochemical systems.

Copper↗
PubMed2002

Excitable front geometry in reaction-diffusion systems with anomalous dispersion.

Two-dimensional excitable systems with anomalous dispersion provide a discrete set of interpulse distances for the stable propagation of planar wave trains. Numerical simulations show that the trailing front of a pulse pair can undergo transitions between these stable distances. In response to localized perturbations, the trailing front converges towards one of numerous, sigmoidal shapes. Their transition segments move at constant speeds and can collide and fuse with each other. A complementing kinematic analysis of the front dynamics yields a reaction-diffusion-like equation.

Action Potentials↗
PubMed2002

Shock structures and bunching fronts in excitable reaction-diffusion systems.

We report experimental results on the dynamics of excitation waves in a modified Belousov-Zhabotinsky reaction. The waves in this system obey nonmonotonic dispersion relations. This anomaly induces the stacking of excitation fronts into patterns with stable interpulse distances. The stacking process creates either a traveling shock structure or a cascade of bunching events in which metastable wave packets are formed. The direction and the speed of the shock are explained in terms of a simple geometrical analysis. We also present experimental evidence for the corresponding instabilities in two-dimensional systems. Here, wave stacking generates atypical structures in the collision of target patterns and wave bunching is accompanied by complex front deformations.

Cyclohexanones↗
PubMed2002

Nonlinear analysis of dynamic binding in affinity capillary electrophoresis demonstrated for inclusion complexes of beta-cyclodextrin.

The stability of the molecular host-guest inclusion complexes of beta-cyclodextrin with benzoate and four different hydroxybenzoates is investigated. For the measurement of the binding constants an experimental method is devised that is based on affinity capillary electrophoresis (ACE) with indirect UV absorbance detection. We derive an explicit equation for effective mobilities in ACE experiments without violation of rigorous mass balance. This equation is employed in the nonlinear least-squares analyses of the experimental data yielding binding constants of 48+/-2 M(-1) for benzoate, 299+/-38 M(-1) for 2-hydroxybenzoate, 37+/-1 M(-1) for 3-hydroxybenzoate, 228+/-9 M(-1) for 4-hydroxybenzoate, and 895+/-110 M(-1) in the case of 2,4-dihydroxybenzoate.

Cyclodextrins↗
PubMed1994

External forcing of spiral waves.

The effect of an external rhythm on rotating spiral waves in excitable media is investigated. Parameters of the unperturbed medium were chosen, such that the organizing spiral tip describes meandering (hypocyclic) trajectories, which are the most general shape for the experimentally observed systems. Periodical modulation of excitability in a model of the Belousov-Zhabotinsky (BZ) reaction forces meandering spiral tips to describe trajectories that are not found at corresponding stationary conditions. For different modulation periods, two types of resonance drift, phase-locked tip motion, a spectrum of hypocyclic trajectories, and complex multifrequency patterns were computed. The computational results are complemented by experimental data obtained for periodically changing illumination of the photosensitive BZ reaction. The observed drastic deformation of the tip trajectory is considered as an efficient means to study and to control wave processes in excitable media.

Journal Article↗