Benjamin de Lacy Costello

Novel composite organic–inorganic semiconductor sensors for the quantitative detection of target organic vapours

Composites of tin dioxide (an n-type semiconductor) and derivatives of the conducting polymer polypyrrole (a p-type semiconductor) gave reversible changes in electrical resistance at room temperature when exposed to a range of organic vapours. The optimum amount of polymer giving highest sensitivity was found by experiment to be 2.5% by mass for the polypyrrole chloride-tin dioxide composite. Composites containing 2.5% polymer by mass but differing in polymer derivative, were fabricated and exposed to low concentrations of ethanol, methanol, acetone, methyl acetate and ethyl acetate. All were found to give significant and reversible decreases in electrical resistance. Direct comparison with sensors constructed solely of tin dioxide or polypyrrole at room temperature showed the composites to be more sensitive. The gas sensitivity of the composite materials depended on the type of polymer derivative incorporated and the dopant anion associated with the polymer. The composites were simple to fabricate and gave differing response profiles to a range of organic vapours.

Experimental reaction–diffusion pre-processor for shape recognition☆

Abstract We have produced an experimental implementation of a massively-parallel reaction–diffusion processor which performs one of the most essential parts of shape recognition—construction of a skeleton. A skeleton is a unique, stable and invariant representation of a shape, therefore computation of the skeleton is an essential tool of computer vision. Skeleton computation is a typical ‘natural’ spatial problem that can be solved with the use of biological, chemical or physical phenomena. One possible approach—a reaction–diffusion based computation—is explored in this Letter. A contour is represented by a concentration profile of one reagent, a planar substrate is mixed with another reagent. The reagent, representing the original contour diffuses to form a coloured phase in a reaction with the substrate-reagent. However, at sites where two diffusion wave fronts meet no coloured phase is formed and the substrate retains its uncoloured state. These loci of the computation space represent a skeleton of the given contour. In the Letter we only describe a laboratory prototype of a reaction–diffusion processor that computes a skeleton, no further tasks of image processing are undertaken, one could say we have designed an unconventional chemical pre-processor for shape recognition.

Experimental Reaction–Diffusion Chemical Processors for Robot Path Planning

In this paper we discuss the experimental implementation of a chemical reaction–diffusion processor for robot motion planning in terms of finding the shortest collision-free path for a robot moving in an arena with obstacles. These reaction–diffusion chemical processors for robot navigation are not designed to compete with existing silicon-based controllers. These controllers are intended for the incorporation into future generations of soft-bodied robots built of electro- and chemo-active polymers. In this paper we consider the notion of processing as being implicit in the physical medium constituting the body of a ‘soft’ robot. This work therefore represents some early steps in the employment of excitable media controllers. An image of the arena in which the robot is to navigate is mapped onto a thin-layer chemical medium using a method that allows obstacles to be represented as local changes in the reactant concentrations. Disturbances created by the ‘objects’ generate diffusive and phase wave fronts. The spreading waves approximate to a repulsive field generated by the obstacles. This repulsive field is then inputted into a discrete model of an excitable reaction–diffusion medium, which computes a tree of shortest paths leading to a selected destination point. Two types of chemical processors are discussed: a disposable palladium processor, which executes arena mapping from a configuration of obstacles, given before an experiment and, a reusable Belousov–Zhabotinsky processor which allows for online path planning and adaptation for dynamically changing configurations of obstacles.

The synthesis of novel 3-substituted pyrrole monomers possessing chiral side groups: a study of their chemical polymerisation and the assessment of their chiral discrimination properties

Novel 3-substituted pyrrole monomers possessing chiral side groups were synthesised. These compounds were successfully polymerised with ferric salts and the polymer materials fabricated into sensors. The sensors were found to elicit differential changes in electrical resistance and mass, when exposed to different chiral enantiomers in the vapour phase.

Reaction–diffusion path planning in a hybrid chemical and cellular-automaton processor

Abstract To find the shortest collision-free path in a room containing obstacles we designed a chemical processor and coupled it with a cellular-automaton processor. In the chemical processor obstacles are represented by sites of high concentration of potassium iodide and a planar substrate is saturated with palladium chloride. Potassium iodide diffuses into the substrate and reacts with palladium chloride. A dark coloured precipitate of palladium iodide is formed almost everywhere except sites where two or more diffusion wavefronts collide. The less coloured sites are situated at the furthest distance from obstacles. Thus, the chemical processor develops a repulsive field, generated by obstacles. A snapshot of the chemical processor is inputted to a cellular automaton. The automaton behaves like a discrete excitable media; also, every cell of the automaton is supplied with a pointer that shows an origin of the cell’s excitation. The excitation spreads along the cells corresponding to precipitate depleted sites of the chemical processor. When the destination-site is excited, waves travel on the lattice and update the orientations of the pointers. Thus, the automaton constructs a spanning tree, made of pointers, that guides a traveler towards the destination point. Thus, the automaton medium generates an attractive field and combination of this attractive field with the repulsive field, generated by the chemical processor, provides us with a solution of the collision-free path problem.

Investigation of faecal volatile organic metabolites as novel diagnostic biomarkers in inflammatory bowel disease.

The aetiology of inflammatory bowel disease (IBD) remains poorly understood. Recent evidence suggests an important role of gut microbial dysbiosis in IBD, and this may be associated with changes in faecal volatile organic metabolites (VOMs).

On some limitations of reaction-diffusion chemical computers in relation to Voronoi diagram and its inversion

Abstract A reaction–diffusion chemical computer in this context is a planar uniform chemical reactor, where data and results of a computation are represented by concentration profiles of reactants and the computation itself is implemented via the spreading and interaction of diffusive and phase waves. This class of chemical computers are efficient at solving problems with a ‘natural’ parallelism where data sets are decomposable onto a large number of geographically neighboring domains which are then processed in parallel. Typical problems of this type include image processing, geometrical transformations and optimisation. When chemical based devices are used to solve such problems questions regarding their reproducible, efficiency and the accuracy of their computations arise. In addition to these questions what are the limitations of reaction–diffusion chemical processors—what type of problems cannot currently and are unlikely ever to be solved? To answer the questions we study how a Voronoi diagram is constructed and how it is inverted in a planar chemical processor. We demonstrate that a Voronoi diagram is computed only partially in the chemical processor. We also prove that given a specific Voronoi diagram it is impossible to reconstruct the planar set (from which diagram was computed) in the reaction–diffusion chemical processor. In the Letter we open the first ever line of enquiry into the computational inability of reaction–diffusion chemical computers.

Voronoi diagrams generated by regressing edges of precipitation fronts

Reaction-diffusion systems where one of the reagents (outer electrolyte) penetrates into a gel by diffusion and forms a precipitate with the other reagent (inner electrolyte) homogenized in the gel, are able to produce various complex precipitation patterns. The previously studied NaOH + AgNO3 and recently discovered CuCl2 + K3[Fe(CN)6] processes, (where the first reagent is the outer electrolyte and the other is the inner electrolyte homogenized in the gel), when reacted using the above mentioned method, are able to generate tessellations of a plane by a mechanism dependant on the dynamics of so-called regressing edges of the reaction fronts. The spontaneous partitioning of the reacted phases results in the construction of a pattern analogous to a Voronoi diagram or one of their generalizations.

Towards evolving spiking networks with memristive synapses

This paper presents a spiking neuro-evolutionary system which implements memristors as neuromodulatory connections, i.e. whose weights can vary during a trial. The evolutionary design process exploits parameter self-adaptation and a constructionist approach, allowing the number of neurons, connection weights, and inter-neural connectivity pattern to be evolved for each network. We demonstrate that this approach allows the evolution of networks of appropriate complexity to emerge whilst exploiting the memristive properties of the connections to reduce learning time. We evaluate two phenomenological real-world memristive implementations against a theoretical “linear memristor”, and a system containing standard connections only. Our networks are evaluated on a simulated robotic navigation task.

Preparation of polypyrrole composites and the effect of volatile amines on their electrical properties

Composites of polypyrrole were produced using thermoplastic binders, polypyrrole and a proprietary glass-fibre paper. The polypyrrole was chemically polymerized using iron(III) chloride in aqueous conditions. It was then finely ground and dip coated with a binder on to paper to produce a gas-sensitive resistor. The performance of such sensors was evaluated by measuring the resistance change that occurred during exposure to the headspace of a number of organic vapours and against a range of volatile amines in the concentration range 1–1000 ppm.