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A strong unique continuation theorem for parabolic equations. (English) Zbl 0990.35028
The main result of the paper is the strong unique continuation for solutions in \(W^{2,1} _{p; \text{loc}}\) of the system of linear second-order inequalities \[ \Biggl|{{\partial u} \over {\partial t}} - D \Delta u\Biggr|\leq M_1 |\nabla u|+ M_0 |u| \] defined in a finite strip \(\mathbb R^n \times (T_1,T_2)\). As a consequence the author obtains upper bounds in the parabolic Hausdorff dimension for the nodal set of \(u\) and for the set where both \(u=0\) and \(\nabla u =0,\) and for the standard Hausdorff dimension of the set of \(x \in \mathbb R^n\) such that \(u(x,t)=0\) for fixed \(t \in (T_1, T_2).\) The method of proof relies on the classification (in self-similar variables) of the local asymptotics of the solution. Related results can be found in Q. Han and F. H. Lin [Commun. Pure Appl. Math. 47, 1219–1238 (1994; Zbl 0807.35052)], and C. C. Poon [Commun. Partial Differ. Equations 21, 521–539 (1996; Zbl 0852.35055)].

MSC:
35B60 Continuation and prolongation of solutions to PDEs
35K40 Second-order parabolic systems
35R45 Partial differential inequalities and systems of partial differential inequalities
35K10 Second-order parabolic equations
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