\begin{table}%t2
%\centering
\par
\caption{ 
We compare the characteristic time-scales of gravity torques
($T_{\rm grav}$), dynamical friction ($T_{\rm df}$) and  viscosity ($T_{\rm visc}$) in the nuclear disks of
NGC~4321 , NGC~4826, NGC~4579 and NGC~6951. Time-scales are given in units of 
rotation periods ($T_{\rm rot}$).
\label{time-scales}}
\begin{tabular}{lccc}
\hline\hline
\multicolumn{1}{l}{Galaxy} &
\multicolumn{1}{c}{$T_{\rm grav}$} &
\multicolumn{1}{c}{$T_{\rm df}$} &
\multicolumn{1}{c}{$T_{\rm visc}$}  \\
\multicolumn{1}{c}{} &
\multicolumn{1}{c}{($T_{\rm rot}$)} &
\multicolumn{1}{c}{($T_{\rm rot}$)} &
\multicolumn{1}{c}{($T_{\rm rot}$)}  \\
\hline 
{NGC~4321}($r=200$~pc) & 8 & 30 & 20  \\
{NGC~4826}($r=50$~pc) & 70 & 5 & 5   \\
{NGC~4579}($r=200$~pc) & 8 & 30 & 22   \\
{NGC~6951}($r=200$~pc) & 50--100 & 30 & 20    \\
\hline
\end{tabular}
\end{table}