49 research outputs found
Rearrangement dynamics of fishbonelike Turing patterns generated by spatial periodic forcing
No full textExternal forcing can greatly affect the evolution of Turing patterns in reaction-diffusion (RD) media. Here, we employ spatially periodic illumination in a photosensitive RD system to create Turing structures that are repetitive in one direction. We then study their relaxation in the absence of light. These unforced, fishbonelike configurations undergo self-reorganization and establish stationary arrangements, some of which fully exhibit, while others partially or completely lose, the symmetry of the initially imposed pattern
“Photochemical Oscillator”: Colored Hydrodynamic Oscillations and Waves in a Photochromic System
No full textA vertical thermal gradient is generated in a solution of a thermoreversible photochromic spiro-oxazine in methanol or acetone by UV irradiation at the bottom of the solution and evaporation of solvent at the top. When the gradient is sufficiently high, it triggers color oscillations and waves due to hydrodynamic convective motion of the solution. Experiments on such systems in several configurations are presented and simulated with a reaction-diffusion-convection model, which yields good agreement with the experiments. The photoexcitable system described in this work constitutes a prototype of a "photochemical oscillator" which, analogously to an electronic oscillator, converts the continuous UV energy into alternating optical visible and UV signals with periods between 15 and 70 s
Locking of Turing patterns in the chlorine dioxide–iodine–malonic acid reaction with one-dimensional spatial periodic forcing
No full textWe use the photosensitive chlorine dioxide–iodine–malonic acid reaction–diffusion system to study wavenumber locking of Turing patterns with spatial periodic forcing. Wavenumber-locked stripe patterns are the typical resonant structures that labyrinthine patterns exhibit in response to one-dimensional forcing by illumination when images of stripes are projected on a working medium. Our experimental results reveal that segmented oblique, hexagonal and rectangular patterns can also be obtained. However, these two-dimensional resonant structures only develop in a relatively narrow range of forcing parameters, where the unforced stripe pattern is in close proximity to the domain of hexagonal patterns. Numerical simulations based on a model that incorporates the forcing by illumination using an additive term reproduce well the experimental observations. These findings confirm that additive one-dimensional forcing can generate a two-dimensional resonant response. However, such a response is considerably less robust than the effect of multiplicative forcing
Communication with chemical chaos in the presence of noise. Chaos, 8(3):702–710 Control of Chaotic Systems 23
No full textWe use control of chaos to encode information into the oscillations of the Belousov-Zhabotinsky reaction. An arbitrary binary message is encoded by forcing the chaotic oscillations to follow a specified trajectory. The information manipulating control requires only small perturbations to vary the binary message. In this paper we extend our recent theoretical work ͓Bollt and Dolnik, Phys. Rev. E 64, 1196 ͑1990͔͒ by introducing a new and simplified encoding technique which can be utilized in the presence of experimental noise. We numerically and theoretically study several practical aspects of controlling symbol dynamics including: modeling noisy time-series, learning underlying symbol dynamics, and evaluation of derivatives for control by observing system responses to an intelligent and deliberate sequence of input parameter variations. All of the modeling techniques incorporated here are ultimately designed to learn and control symbol dynamics of experimental data known only as an observed time-series; the simulation assumes no global model. We find that noise affects reliability of encoding information and may cause coding errors. But, if the level of noise is confined to relatively small values, which are achievable in experiments, the control mechanism is robust to the noise. Thus we can still produce a desired symbolic code. However, scarce errors in encoding may occur due to rare but large fluctuations. These errors may be corrected during the decoding process by a variation of the filtering technique suggested by Rosa et al. ͓Phys. Rev. Lett. 78, 1247 ͑1997͔͒. © 1998 American Institute of Physics. ͓S1054-1500͑98͒01402-5͔ Recent applications of controlling chaotic dynamical systems focus on manipulation of information flow, for communications, encryption, and targeting. A particularly interesting possibility concerns encoding information into a chemical system. We propose an alternative to a popular and intuitive, but not well founded belief which is an analogy to electronic computers, that information is stored in a biological version of physical switching devices. In contrast, an analogy between chemical systems and biological systems 1 implies an interesting possibility that living systems may store information in underlying dynamics. In our previous work, 2,3 we demonstrated the possibility of encoding information into chemical chaos utilizing a model of the Belousov-Zhabotinsky "BZ… reaction. In this work, we extend and improve these methods with the aim of successfully implementing a message into a controlled oscillatory reaction in a ''real world'' noisy laboratory environment. We have therefore included numerical stochastic studies to argue that the improved technique promises success given measurement tolerances within laboratory feasible levels
Excitability and bursting in the chlorine dioxide–iodide reaction in a forced open system
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Conducting Field Research on Terrorism: a Brief Primer
No full textThis article focuses on the practical aspects of field research on terrorism. Firstly, it outlines some issues involved in the process of attaining a human research ethics/institutional review board clearance in order to be able to even begin the field research. It suggests some ways in which researchers can positively influence this review process in their favor. Secondly, the article focuses on the real and perceived dangers of field research, identifying practical steps and preparatory activities that can help researchers manage and reduce the risks involved. The article also covers the formalities and dilemmas involved in gaining access to the field. It then provides some insights into the topic of operating in conflict zones, followed by a section covering the ways of gaining access to sources, effective communication skills and influence techniques and addresses key issues involved in interviewing sources in the field. The final section focuses on identifying biases and interfering factors which researchers need to take into account when interpreting the data acquired through interviews. This article is a modest attempt to fill a gap in the literature on terrorism research by outlining some of the key issues involved in the process of doing field research. It incorporates insights from diverse disciplines as well as the author’s personal experiences of conducting field research on terrorism in places like Afghanistan, Pakistan, Chechnya, Ingushetia, Colombia, Mindanao, Uganda, Indonesia, Democratic Republic of Congo, Sudan, and India.</p
Electrophoretic separations of proteins in capillaries with hydrolytically-stable surface structures
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