Abstract

We consider two singular limits: a fast reaction limit with a non-monotone nonlinearity and a regularization of the forward-backward diffusion equation. We derive pointwise identities satisfied by the Young measure generated by these problems. As a result, we obtain an explicit formula for the Young measure even without the non-degeneracy assumption used in the previous works. The main new idea is an application of the Radon–Nikodym theorem to decompose the Young measure.

Highlights

  • We are interested in the limiting behavior of the following problems: for the reaction-diffusion system

  • By a small abuse of notation, we extend functions Si by a constant value to the whole of R

  • For monotone F the problem is fairly classical and has been studied for a great variety of reaction-diffusion systems, with more than two components [5, 6, 14, 29] or reaction-diffusion equation coupled with an ODE [21]

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Summary

Presentation of the problem

We are interested in the limiting behavior (as ε → 0) of the following problems: for the reaction-diffusion system. Let S1(λ) ≤ S2(λ) ≤ S3(λ) be the solutions of equation F (Si (λ)) = λ (see Figure 1) For monotone F the problem is fairly classical and has been studied for a great variety of reaction-diffusion systems, with more than two components [5, 6, 14, 29] or reaction-diffusion equation coupled with an ODE [21]. -called nonstandard analysis was used to study the limit problem in the space of grid functions [7, 8]. It is known [33, 35] that both systems exhibit the following surprising phenomenon: as ε → 0, F (uε) → v and vε → v converge strongly without any known a priori estimates allowing to conclude so. The non-degeneracy condition excludes piecewise affine functions used in more explicit computations as in [26]

Main results and outline of the paper
Compensated compactness lemma
Support of a measure
Young measures

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