New types of complex motion of a simple camphor boat

We discuss the motion of a rectangular camphor boat, considering the position of a camphor pill in relation to the boat's stern as the control parameter. The boat moves because the pill releases surface active molecules that decrease the surface tension and support the motion. We introduce a new experimental system in which the boat rotates on a long arm around the axis located at the centre of a Petri dish; thus, the motion is restricted to a circle and can be studied under stationary conditions for a long time. The experiments confirmed two previously reported modes of motion: continuous motion when the pill was located at the boat edge and pulsating (intermittent) motion if it was close to the boat centre (Suematsu et al., J. Phys. Chem. C, 2010, 114(21), 9876-9882). For intermediate pill locations, we observed a new, unreported type of motion characterised by oscillating speed (i.e. oscillating motion). Different modes of motion can be observed for the same pill location. The experimental results are qualitatively confirmed using a simple reaction-diffusion model of the boat evolution used in the above-mentioned paper.

Dynamic ordering caused by a source-sink relation between two droplets

Two droplets composed of different chemicals, 1-decanol and liquid paraffin, floating on the water surface show characteristic co-responsive behavior. The presence of two different types of droplets in the system imposes an asymmetry that would not be possible with single droplets alone. The self-propulsion and interactions between droplets appear because surface active 1-decanol molecules provided by the source are absorbed by the paraffin sink thus generating an asymmetric surface tension gradient. This source-sink relation between droplets stabilizes and enhances the self-propulsion, and leads to a variety of dynamic structures including oscillations in the inter-droplet distance. We found that the character of time evolution also depends on the concentration of dye, Sudan Black B, initially used just to stain the decanol droplet. A simple mathematical model explains the transition between the stationary state and the oscillations as a Hopf bifurcation.

Complexity and bifurcations in the motion of a self-propelled rectangle confined in a circular water chamber

We consider the motion of a self-propelled object of rectangular shape inside a circular water chamber. The mathematical model of self-motion includes equations for the orientation and location of the rectangle and reaction-diffusion equation with an effective diffusion coefficient for the time evolution of the surface concentration of active molecules. Numerical simulations of motion were performed for different values of the ratio between the supply rate S and the evaporation rate a of active molecules. Treating S₀ = S/a as a control parameter, we found the critical behavior in variables characterizing the trajectory and identified different types of motion. If the value of S₀ is small, the rectangle rests at the chamber center. For larger S₀, a reciprocal motion during which the rectangle passes through the center is observed. At yet higher supply rates, the star-polygonal motion appears, and the trajectory remains at a distance from the chamber center. In the experiments with a rectangle made of camphor-camphene-polypropylene plastic moving in a Petri dish, we observed the transition from the star-polygonal motion to the reciprocal motion in time. This transition can be understood on the basis of the developed model if we assume that the supply rate decreases in time.

Method development and validation for total mercury determination in coke oven gas combining a trap sampling method with CVAAS detection

Coke oven gas is one of the by-products of the coal coking process. It is used as a fuel in the coking plant, but also as a raw material in the chemical industry to produce methanol, syngas or environment-friendly, low-CO₂ hydrogen fuel. Due to the reasons mentioned above, the knowledge of coke oven gas pollutants such as mercury is a key issue. To determine the mercury in the cleaned coke oven gas a trap sampling method combined with CVAAS mercury detection was developed, optimized and validated. In order to perform the sampling process the traps filled with activated carbon were used. The determination of mercury in the traps material was performed by means of an MA-2 mercury analyzer. During the optimization of the method one selected the trap material, sample volume and flow rate. The optimal volume of the coke oven gas sample was 3 dm³ and the flow rate was 18 dm³/h (per one trap). The developed method was validated according to the Eurachem recommendation and was applied to determine mercury in the clean coke oven gas. The coke oven gas sampling was performed in a coking plant in Poland. The average concentration of mercury in the clean coke oven gas was 3.2 ± 0.3 μg/m³_N (k = 2) for n = 18.

Discrimination of time-dependent inflow properties with a cooperative dynamical system

Many physical, chemical, and biological systems exhibit a cooperative or sigmoidal response with respect to the input. In biochemistry, such behavior is called an allosteric effect. Here, we demonstrate that a system with such properties can be used to discriminate the amplitude or frequency of an external periodic perturbation. Numerical simulations performed for a model sigmoidal kinetics illustrate that there exists a narrow range of frequencies and amplitudes within which the system evolves toward significantly different states. Therefore, observation of system evolution should provide information about the characteristics of the perturbation. The discrimination properties for periodic perturbation are generic. They can be observed in various dynamical systems and for different types of periodic perturbation.

Pinwheel-like structures resulting from interaction of plane pulses of excitation

We demonstrate that complex spatiotemporal structures may appear in an excitable system as the result of interaction between two plane pulses. Such behavior has been obtained for FitzHugh-Nagumo type of dynamics by numerical integration of reaction-diffusion equations.

Complex transformations of chemical signals passing through a passive barrier

It has been recently observed that a passive barrier separating two excitable chemical media may transform the frequency of a train of incoming pulses. In this work we apply the FitzHugh-Nagumo-type model to study this phenomenon in a detailed way. Our numerical calculations demonstrate that at the barrier a periodic train of pulses may be transformed into a complex output signal. The ratio of frequencies of the output and the input signals, plotted as a function of the barrier's width or as a function of the input signal frequency, has a devil's-staircase-like shape.