# Seminar on Qualitative Theory of Differential Equations - Jin Takahashi (13.10.2016)

## Thursday 13.10.2016 at 14:00, Lecture room M/223

**Jin Takahashi **(Tokyo Institute of Technology):*Time-dependent singularities in a semilinear heat equation*

*Abstract:*

We consider the following semilinear heat equation$u_t-\Delta u=u^p$, $x\in \mathbf{R}^N\setminus\{\xi(t)\}$, $t\in I$,where $N\geq3$, $p>1$, $I\subset\mathbf{R}$ is an open interval and $\xi:\overline{I}\rightarrow\mathbf{R}^N$ is a prescribed curve which is smooth enough.

The aim of this talk is to study time-dependent singularities of nonnegative solutions of the above equation under the assumption that $1<p<N/(N-2)$.

In the first part of this talk, we prove that every solution $u$can be extended as a distributional solution of the following equation$u_t-\Delta u=u^p +(\delta_0\otimes\mu)\circ\mathcal{T}$ in ${\cal D}'(\mathbf{R}^N \times I)$. Here $\mathcal{T} (\varphi) (x,t):=\varphi(x+\xi(t),t)$, $\delta_0$ is the Dirac measure on $\mathbf{R}^N$ concentrated at the origin and $\mu$ is a Radon measure on $I$ determined by the solution $u$.

In addition, we show relations between the exponent $p$ and the local growth rate of $\mu$ and specify the behavior of solutions at the time-dependent singularity.

In the second part of this talk, we give sharp conditions on $\mu$ for the existence and the nonexistence of solutions of the above extended equation.

This is a joint work with Dr. Toru Kan (Tokyo Institute of Technology).