Exploring the computational potential of simple chemical reactions
A large number of human activities rely on conventional computing devices producing huge quantities of data. These “traditional computers” may eventually fail to deal with such demands. Therefore, there is a need to develop novel computing paradigms, this project aims to fabricate and explore the potential of novel computing devices, based on the space-time dynamics of travelling waves in non-linear media. The designed prototype computing devices are all experimentally implemented in chemical reaction-diffusion media.
A light sensitive Belousov-Zhabotinsky (BZ) reaction was used to construct a number of logic gates and arithmetic circuits. A 1-bit half adder was constructed using the collisions of wave fragments within channels in a weakly excitable analogue of the BZ reaction. The excitability of the reaction is controlled by altering the light levels projected onto an immobilised light sensitive catalyst within an open reactor fed with fresh BZ reagents. This approach was extended by projecting a series of interconnected discs with differing connection weight and size. Using this approach an inverter gate, an AND gate, a NAND gate, a NXOR gate, an XOR gate and a diode were created in addition to a compact 1-bit half adder circuit and memory circuits.. Using an excitable BZ analogue a 4-bit input, 2-bit output integer square root circuit has been implemented. This utilises the principal of constant speed wave propagation and the annihilation of colliding wave fronts coupled with light controlled valves. The light sensitive BZ reaction was also used as a substrate for exploring the potential of applying co-evolutionary algorithms coupled with memory to control the dynamics in order to solve specific computational tasks. It was shown that learnt solutions from simulation experiments could be directly applied to experimental systems. A “gas free” cyclohexadione analogue of the BZ reaction was encapsulated in 3-D lipid stabilised vesicles. The transfer of excitation between adjacent vesicles could be induced by altering the reaction chemistry. It was also possible to selectively initiate waves using lasers at selected wavelengths. Light activation is important because it will enable initiation in required position of computational schemes.
In addition there is a need to study pattern formations in simple inorganic systems in order to gain a better understanding of pattern formation and the control thereof in order to synthesise functional materials and implement computation by utilising the inherent self-assembly mechanisms. Therefore, a simple reaction between aluminium chloride and sodium hydroxide was studied; a phase diagram was constructed of the reaction. A controllable region was found where circular wave, target waves, cardioid like double spiral, simple Voronoi and additively weighted Voronoi diagrams could be constructed.
In addition, a group of simple chemical reactions capable of geometric calculations (Generalised and Weighted Voronoi diagrams) are presented. Drops of metal ion solution were placed on either potassium ferrocyanide or ferricyanide gel to construct complex tessellations of the plane (sometimes calculating multiple Voronoi diagrams in parallel).The reactions were utilised to reconstruct natural tessellations such as those observed on animal coat patterns. Therefore, these simple reactions may be valuable in helping understand natural pattern formation.
Jahan, I. (2014). Exploring the computational potential of simple chemical reactions. (Thesis). University of the West of England
|Publication Date||May 1, 2014|
|Keywords||unconventional computing, chemical computing, B-Z reactions chemical tessellations,inorganic pattern forming reactions, natural pattern formation|