Reaction Diffusion Behaviour in Bronze Route Cu-Nb-Sn Superconducting Wires

2006 ◽  
pp. 152-157
Author(s):  
S.C. Hopkins ◽  
K.S. Tan ◽  
I. Pong ◽  
Bartek A. Glowacki
Keyword(s):  
Reaction Diffusion ◽  
Superconducting Wires ◽  
Diffusion Behaviour

Reaction Diffusion Behaviour in Bronze Route Cu-Nb-Sn Superconducting Wires

2006 ◽  
Vol 258-260 ◽  
pp. 152-157
Author(s):  
Simon C. Hopkins ◽  
K.S. Tan ◽  
I. Pong ◽  
Bartek A. Glowacki
Keyword(s):  
Heat Treatment ◽  
Reaction Diffusion ◽  
Heat Treatments ◽  
Matrix Composition ◽  
Superconducting Wires ◽  
Reaction Diffusion Model ◽  
Wire Cross Section ◽  
The Wire ◽  
Diffusion Behaviour

The bronze process is a mature technology for the production of Nb3Sn superconducting wires exploiting reaction diffusion behaviour in the Cu-Nb-Sn system. However, the superconducting properties depend strongly on the applied heat treatment, and optimisation of the heat treatment is still largely by trial and improvement. Modelling of the reaction-diffusion behaviour would allow improved heat treatments to be designed; combination of this with a nondestructive in situ characterisation technique would also permit improved superconducting wires to be produced. A finite difference reaction diffusion model has been designed to permit rapid calculation of the bronze matrix composition and Nb3Sn layer thickness profiles across the wire cross-section as a function of time for any applied heat treatment. The model has also been designed to calculate the electrical resistivity of the wire, which has previously been demonstrated as a suitable in situ characterisation technique. This model has been applied to isothermal and more complex heat treatments and compared with experimental results. Good qualitative agreement has been found, and plans for further improvement of the model are described in detail.

Excitability, wave reflection, and wave splitting in a cubic autocatalysis reaction-diffusion system

1994 ◽  
Vol 347 (1685) ◽  
pp. 631-642 ◽  
Keyword(s):  
Wave Front ◽  
Wave Reflection ◽  
Reaction Diffusion ◽  
Turing Patterns ◽  
Chemical Oscillations ◽  
One Dimensional ◽  
Wave Splitting ◽  
Successive Wave ◽  
Diffusion Behaviour ◽  
Cubic Autocatalysis

The excitability properties of a two-variable cubic autocatalysis model for chemical oscillations are examined. The reaction-diffusion behaviour of this model is studied in a one-dimensional configuration with differing relative diffusivities of the species. Wave reflection at no-flux boundaries is examined and described in terms of reactant depletion in the wave front and reactant influx in the wave back. Waves are also reflected upon collision with other waves. Wave splitting, the spontaneous initiation of a wave from the trailing edge of another wave, is found to occur for some relative diffusivities. Successive wave splittings give rise to stationary Turing patterns at long times.

Dynamics of Particle-Based Reaction-Diffusion Computing

2011 ◽  
pp. 194-222
Author(s):  
Jeff Jones
Keyword(s):  
Surface Tension ◽  
Physical Properties ◽  
Physarum Polycephalum ◽  
Reaction Diffusion ◽  
Front Propagation ◽  
Chemical Systems ◽  
Emergent Behaviour ◽  
Active Approach ◽  
Similarities And Differences ◽  
Diffusion Behaviour

Reaction-diffusion computing utilises the complex auto-catalytic and diffusive interactions underlying self-organising systems for practical computing tasks – developing variants of classical logical computing devices, or direct spatial embodiments of problem representations and solutions. We investigate the concept of passive and active approaches to reaction-diffusion computing. Passive approaches use front propagation as a carrier signal for information transport and computation. Active approaches can both sense and modify the propagation of the underlying carrier signal. We also consider the differences in attraction and repulsion behaviour for both passive and active approaches. Using particle approximations of reaction-diffusion behaviour in chemical systems, and the plasmodium of Physarum polycephalum, we demonstrate the similarities and differences between the passive and active approaches using both attraction and repulsion behaviour. We provide examples of how the approaches can be used for complex spatially represented computational tasks. We note that the active approach results in second-order emergent behaviour, exhibiting complex quasi-physical properties such as apparent surface tension effects and network minimisation which may have utility in future physical implementations of reaction-diffusion computing devices.

Surface reactions observed by photoemission electron microscopy (PEEM)

1992 ◽  
Vol 50 (1) ◽  
pp. 286-287
Author(s):  
H.H. Rotermund
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Work Function ◽  
Chemical Reactions ◽  
Reaction Diffusion ◽  
Dynamic Processes ◽  
Clean Surface ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Photoemission Electron

Chemical reactions at a surface will in most cases show a measurable influence on the work function of the clean surface. This change of the work function δφ can be used to image the local distributions of the investigated reaction,.if one of the reacting partners is adsorbed at the surface in form of islands of sufficient size (Δ>0.2μm). These can than be visualized via a photoemission electron microscope (PEEM). Changes of φ as low as 2 meV give already a change in the total intensity of a PEEM picture. To achieve reasonable contrast for an image several 10 meV of δφ are needed. Dynamic processes as surface diffusion of CO or O on single crystal surfaces as well as reaction / diffusion fronts have been observed in real time and space.

On a Nonlinear System of Reaction-Diffusion Equations

2006 ◽  
Vol 11 (2) ◽  
pp. 115-121 ◽  
Author(s):  
G. A. Afrouzi ◽  
S. H. Rasouli
Keyword(s):  
Weak Solution ◽  
Dirichlet Boundary ◽  
Smooth Boundary ◽  
Reaction Diffusion ◽  
Reaction Diffusion Equations ◽  
Dirichlet Boundary Conditions ◽  
Nonlinear Elliptic System ◽  
Positive Parameter ◽  
Nonlinear Elliptic ◽  
Positive Weak Solution

The aim of this article is to study the existence of positive weak solution for a quasilinear reaction-diffusion system with Dirichlet boundary conditions,− div(|∇u1|p1−2∇u1) = λu1α11u2α12... unα1n,   x ∈ Ω,− div(|∇u2|p2−2∇u2) = λu1α21u2α22... unα2n,   x ∈ Ω, ... , − div(|∇un|pn−2∇un) = λu1αn1u2αn2... unαnn,   x ∈ Ω,ui = 0,   x ∈ ∂Ω,   i = 1, 2, ..., n,  where λ is a positive parameter, Ω is a bounded domain in RN (N > 1) with smooth boundary ∂Ω. In addition, we assume that 1 < pi < N for i = 1, 2, ..., n. For λ large by applying the method of sub-super solutions the existence of a large positive weak solution is established for the above nonlinear elliptic system.

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