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Biomedical subjects

Vladimir K Vanag

Publications and source records attributed to Vladimir K Vanag.

13 recordsLinked to original sources
PubMed2006

Designing an enzymatic oscillator: bistability and feedback controlled oscillations with glucose oxidase in a continuous flow stirred tank reactor.

The reaction of glucose with ferricyanide catalyzed by glucose oxidase from Aspergillus niger gives rise to a wide range of bistability as the flow rate is varied in a continuous flow stirred tank reactor. Oscillations in pH can be obtained by introducing a negative feedback on the autocatalytic production of H+ that drives the bistability. In our experiments, this feedback consists of an inflow of hydroxide ion at a rate that depends on [H+] in the reactor as k0[OH-]0[H+]/(K+[H+]). pH oscillations are found over a broad range of enzyme and ferricyanide concentrations, residence times (k0 (-1)), and feedback parameters. A simple mathematical model quantitatively accounts for the experimentally found oscillations.

Aspergillus niger↗
PubMed2006

Resonance-induced oscillons in a reaction-diffusion system.

A new type of oscillon that arises from interaction between subcritical Turing and wave instabilities is found in a system of reaction-diffusion equations. These oscillons can be induced resonantly by localized external periodic perturbations. This phenomenon may be useful for frequency selection and/or information processing.

Journal Article↗
PubMed2005

Out-of-phase oscillatory Turing patterns in a bistable reaction-diffusion system.

A new type of out-of-phase oscillatory Turing pattern is found in simulations of a simple two-variable model of a bistable reaction-diffusion system consisting of an autocatalytic activator reacting with a substrate that is replenished by a flow. This class of models can describe pH oscillators or enzymatic reactions. No Hopf instability is necessary for this type of oscillatory Turing pattern.

Journal Article↗
PubMed2005

"Black spots" in a surfactant-rich Belousov-Zhabotinsky reaction dispersed in a water-in-oil microemulsion system.

The Belousov-Zhabotinsky (BZ) reaction dispersed in water-in-oil aerosol OT (AOT) microemulsion has been studied at small radius R(d) of water nanodroplets (R(d) (nm) congruent with0.17omega,omega = [H(2)O][AOT] = 9). Stationary spotlike and labyrinthine Turing patterns are found close to the fully oxidized state. These patterns, islands of high concentration of the reduced state of the Ru(bpy)(3) (2+) catalyst, can coexist either with "black" reduction waves or, under other conditions, with the "white" oxidation waves usually observed in the BZ reaction. The experimental observations are analyzed with the aid of a new Oregonator-like model and qualitatively reproduced in computer simulations.

Journal Article↗
PubMed2005

Complex patterns in reactive microemulsions: self-organized nanostructures?

In a reverse microemulsion consisting of water, oil (octane), an anionic surfactant [aerosol OT (AOT)], and the reactants of the oscillating Belousov-Zhabotinsky (BZ) reaction, a variety of complex spatiotemporal patterns appear. These include traveling and standing waves, spirals that move either toward or away from their centers, spatiotemporal chaos, Turing patterns, segmented waves, and localized structures, both stationary and oscillatory. The system consists of nanometer-sized droplets of water containing the BZ reactants surrounded by a monolayer of AOT, swimming in a sea of oil, through which nonpolar BZ intermediates can diffuse rapidly. We present experimental and computational results on this fascinating system and comment on possible future directions for research.

Computer Simulation↗
PubMed2004

Subcritical wave instability in reaction-diffusion systems.

We report an example of subcritical wave instability in a model of a reaction-diffusion system and discuss the potential implications for localized patterns found in experiments on the Belousov-Zhabotinsky reaction in a microemulsion.

Journal Article↗
PubMed2004

Stationary and oscillatory localized patterns, and subcritical bifurcations.

Stationary and oscillatory localized patterns (oscillons) are found in the Belousov-Zhabotinsky reaction dispersed in Aerosol OT water-in-oil microemulsion. The experimental findings are analyzed in terms of subcritical Hopf instability, subcritical Turing instability, and their combination.

Journal Article↗
PubMed2003

From the Cover: Segmented spiral waves in a reaction-diffusion system.

Pattern formation in reaction-diffusion systems is often invoked as a mechanism for biological morphogenesis. Patterns in chemical systems typically occur either as propagating waves or as stationary, spatially periodic, Turing structures. The spiral and concentric (target) waves found to date in spatially extended chemical or physical systems are smooth and continuous; only living systems, such as seashells, lichens, pine cones, or flowers, have been shown to demonstrate segmentation of these patterns. Here, we report observations of segmented spiral and target waves in the Belousov-Zhabotinsky reaction dispersed in water nanodroplets of a water-in-oil microemulsion. These highly ordered chemical patterns, consisting of short wave segments regularly separated by gaps, form a link between Turing and trigger wave patterns and narrow the disparity between chemistry and biology. They exhibit aspects of such fundamental biological behavior as self-replication of structural elements and preservation of morphology during evolutionary development from a simpler precursor to a more complex structure.

Biophysical Phenomena↗
PubMed2003

Translational and nontranslational motion of perturbed Turing patterns.

When the front and rear boundaries of a Turing pattern with nonzero flux boundary conditions move synchronously, several modes of motion of the pattern are found. Traveling boundaries can be obtained experimentally by illuminating a Turing-unstable system through a moving mask consisting of a single dark stripe with a light intensity sufficient to suppress pattern formation. All structured moving patterns belong to two general types: smooth translation at low mask velocity v(x) and nontranslational ("hopping") at intermediate v(x). At high v(x), Turing patterns are unable to form, and an unstructured striped image of the mask is seen. When the mask width exceeds the Turing wavelength, bistability between different types of moving patterns can occur as v(x) is varied.

Journal Article↗
PubMed2003

Dash waves in a reaction-diffusion system.

Patterns in reaction-diffusion systems generally consist of smooth traveling waves or of stationary, discontinuous Turing structures. Hybrid patterns that blend the properties of waves and Turing structures have not previously been observed. We report observation of dash waves, which consist of wave segments regularly separated by gaps, moving coherently in the Belousov-Zhabotinsky system dispersed in water-in-oil microemulsion. Dash waves emerge from the interaction between excitable and pseudo-Turing-unstable steady states. We are able to generate dash waves in simulations with simple models.

Journal Article↗
PubMed2002

Packet waves in a reaction-diffusion system.

The finite-wavelength instability gives rise to a new type of wave in reaction-diffusion systems: packet waves, which propagate only within a wave packet, are found in experiments on the Belousov-Zhabotinsky reaction dispersed in water-in-oil AOT microemulsion (BZ-AOT) as well as in model simulations. Inwardly moving packet waves with negative curvature occur in experiments and in a model of the BZ-AOT system when the dispersion d omega(k)/dk is negative at the characteristic wave number k(0). This result sheds light on the origin of anti-spirals.

Journal Article↗