Gradient estimates for a nonlinear parabolic equation under Ricci flow
  Let $(M,g(t))$, $0\le t\le T$, be a n-dimensional complete noncompact manifold, $n\ge 2$, with bounded curvatures and metric $g(t)$ evolving by the Ricci flow $\frac{\partial g_{ij}}{\partial t}=-2R_{ij}$. We will extend the result of L. Ma and Y. Yang and prove a local gradient estimate for positive solutions of the nonlinear parabolic equation $\frac{\1 u}{\1 t}=\Delta u-au\log u-qu$ where $a\in\R$ is a constant and $q$ is a smooth function on $M\times [0,T]$. 
Shu-Yu Hsu