  We consider Euclidean D4 and D6-branes filling the whole ${\bf R}^4$ and
${\bf R}^6$ space, respectively. In both cases, with a constant background
B-field turned on for D4-branes, we propose actions which are the same as the
DBI actions up to some constant or total derivative terms. These extra terms
allow us to write the action as a square of nonlinear instanton equations. As
such, the actions can easily be supersymmetrized using the methods of
topological field theory.
