159 research outputs found
Relaxation of the incompressible porous media equation
It was shown recently by Cordoba, Faraco and Gancedo that the 2D porous media
equation admits weak solutions with compact support in time. The proof, based
on the convex integration framework, uses ideas from the theory of laminates,
in particular T4 configurations. In this note we calculate the explicit
relaxation of IPM, thus avoiding T4 configurations. We then use this to
construct weak solutions to the unstable interface problem (the Muskat
problem), as a byproduct shedding new light on the gradient flow approach
introduced by Otto.Comment: 19 pages, no figures, some misprints correcte
The failure of spectral synthesis on some types of discrete Abelian groups
AbstractThe problem of spectral synthesis on arbitrary Abelian groups is solved in the negative
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