\begin{table}%t1
      %\centering
\par
      \caption{\label{t1}Numerical parameters for the simulations.}
      \begin{tabular}{llll}
      \hline\hline
      & numerical grid
      & physical grid
      & resolution \\
      Model
      & cell$^2$
      & pc$^2$
      & pc cell$^{-1}$ \\ \hline  
      U & $640 \times 200$ & $800 \times 250$ & 1.25 \\
      K & $640 \times 200$ & $80 \times 25$ & 0.125 \\
      E & $640 \times 200$ & $50 \times 15.625$ & $7.8 \times 10^{-2}$ \\
      \hline
      \end{tabular}
      \end{table}