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The mechanism of development of superlattice Turing structures from photochemically generated hexagonal patterns of spots with wavelengths several times larger than the characteristic wavelength of the Turing patterns is studied. Comparison of the experiment with numerical simulations shows that interaction of the photochemical periodic forcing with the Turing instability results in generation of multiple resonant triplets of wave vectors.

The influence of the intensity of light and the wavelength of an imposed parallel striped mask on the development of striped Turing patterns is studied. It is found that stripes develop parallel or perpendicular to the orientation of the mask depending on the ratio of the R=lambda(sub F)/lambda(sub p) of the wavelength of the mask to the wavelength of the natural pattern and on the amplitude of forcing.

Molecular switches have been implicated in the storage of information in biological systems. For small structures such as synapses, these switches are composed of only a few molecules and stochastic fluctuations are therefore of importance. Such fluctuations could potentially lead to spontaneous switch reset that would limit the lifetime of information storage. We have analyzed a model of the calcium/calmodulin-dependent protein kinase II (CaMKII) switch implicated in long-term memory in the nervous system. The bistability of this switch arises from autocatalytic autophosphorylation of CaMKII, a reaction that is countered by a saturable phosphatase-1-mediated dephosphorylation. We sought to understand the factors that control switch stability and to determine the functional relationship between stability and the number of molecules involved. Using Monte Carlo simulations, we found that the lifetime of states of the switch increase exponentially with the number of CaMKII holoenzymes. Switch stability requires a balance between the kinase and phosphatase rates, and the kinase rate must remain high relative to the rate of protein turnover. Thus, a critical limit on switch stability is set by the observed turnover rate (one per 30 h on average). Our computational results show that, depending on the timescale of fluctuations in enzyme numbers, for a switch composed of about 15 CaMKII holoenzymes, the stable persistent activation can span from a few years to a human lifetime.

Dibromomalonic acid (Br2MA) oxidizes the photo excited state of the Ru(bpy)(sub 3)(super 2+) complex producing Br2.the first of these reactions play an important part in the mechanism of photoinhibition of the Belousov-Zhabotinsky reaction.

Research was conducted to demonstrate that illumination of the chlorine dioxide-iodine-malonic acid reaction with visible light suppresses oscillations and shifts the steady state of the reaction to lower concentrations of iodide ions. In the system with starch, illumination causes a large reduction in the steady-state concentration of the triiodide-starch complex. A simple mechanism is proposed, in which iodine atoms produced by photodissociation of molecular iodine initiate reduction of chlorine dioxide to chlorite and oxidation of iodide ions to iodine. This results in a reduced amplitude of oscillations and, at more intense illumination, the total elimination of oscillations.

Research was conducted to examine pattern formation during polymerization of acrylamide in the presence of sulfide ions. The preparation of the thin gel layer was done using a mixture of acrylamide, N,N'-methylene-bisacrylamide and triethanolamine with a peroxodisulfate initiator in the presence of sulfide. When water was spread over the gel after solidifying, spatial pattern formation was observed in the gel. Results reveal that sulfide ion terminates the polymer chain elongation while retaining the overall exothermic chain reaction.

The application of various redox indicators on bromate oscillators to visualize batch oscillations and patterns was examined. Although a variety of reagents were used to broaden the range of systems for observation, focus was on cyclohexanedione which was used as a substrate. Results indicate that by using carefully chosen indicators, spatial structures can be visualized in systems in which oscillations could previously only be sensed instrumentally and their formation could not be seen at all.

A variety of standing waves in a two-dimensional reaction-diffusion model with short-wave instability was studied at low degrees of supercriticality. These include patterns with rotational symmetry in systems with circular geometry, plain and modulated stripes, squares and rhombi in systems with square and rectangular geometry. The short-wave instability can lead to a greater variety of spatio-temporal patterns. However, simple hexagonal patterns in matched rectangular systems were not obtained.

The occurrence of spatial domains of large amplitude oscillation on a background of small amplitude oscillation in a reaction–diffusion system is called localization. We study, analytically and numerically, the mechanism of localization in a model of the Belousov–Zhabotinsky reaction subject to global feedback. This behavior is found to arise from the canard phenomenon, in which a limit cycle suddenly undergoes a significant change in amplitude as a bifurcation parameter, in this case the feedback strength, is varied. In the system studied here, the oscillations arise via a supercritical Hopf bifurcation, but our analysis suggests that the same mechanism is relevant for systems undergoing a subcritical Hopf bifurcation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We study pattern formation arising from the interaction of the stationary Turing and wave (oscillatory Turing) instabilities. Interaction and competition between these symmetry-breaking modes lead to the emergence of a large variety of spatiotemporal patterns, including modulated Turing structures, modulated standing waves, and combinations of Turing structures and spiral waves. Spatial resonances are obtained near codimension-two Turing-wave bifurcations. Far from bifurcation lines, we obtain inwardly propagating spiral waves with Turing spots at their tips. We demonstrate that the coexistence of Turing spots and traveling waves is a result of interaction between Turing and oscillatory modes, while the inwardly propagating waves (antispirals) do not require this interaction; they can arise from the wave instability combined with a negative group velocity. [ABSTRACT FROM AUTHOR]

Pattern formation is studied numerically in a three-variable reaction-diffusion model with onset of the oscillatory instability at a finite wavelength. Traveling and standing waves, asymmetric standing-traveling wave patterns, and target patterns are found. With increasing overcriticality or system length, basins of attraction of more symmetric patterns shrink, while less symmetric patterns become stable. Interaction of a defect with an impermeable boundary results in displacement of the defect. Fusion and splitting of defects are observed. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The photoresponse was examined of the chlorine dioxide-iodine-malonic acid (CDIMA) reaction. A new mechanism was proposed or the effect of visible light on the CDIMA reaction and simulations based on the proposed mechanism accurately describe the experimentally observed kinetics.