Asymptotic behavior of global solutions of the $u_t=\Delta u + u^{p}$
  We study the asymptotic behavior of nonnegative solutions of the semilinear parabolic problem   {u_t=\Delta u + u^{p}, x\in\mathbb{R}^{N}, t>0   u(0)=u_{0}, x\in\mathbb{R}^{N}, t=0.   It is known that the nonnegative solution $u(t)$ of this problem blows up in finite time for $1<p\leq 1+ 2/N$. Moreover, if $p> 1+ 2/N$ and the norm of $u_{0}$ is small enough, the problem admits global solution. In this work, we use the entropy method to obtain the decay rate of the global solution $u(t)$. 
Oscar A. Barraza and Laura B. Langoni