  Sen has shown that tachyon condensation in Dbrane-anti-Dbrane configurations
can lead to remarkable connections between string theories. A consequence of
his results is that there is a minimal value of the radial coordinate $r_{c}
\propto \sqrt{\alpha'} (gN)^{1/(9-p)}$ such that N units of D$p$brane charge
cannot be localized to values smaller than $r_{c}.$ At this value of $r_{c}$
the curvature and the gradient of the Ramond-Ramond field strength are of order
$1/\alpha',$ and the vacuum, regarded as a Dbrane-anti-Dbrane configuration
with a tachyon condensate, is rendered unstable, leading to a separation of the
Dbrane and the anti-Dbrane. This value of $r_{c}$ lies in the region
intermediate between the near-horizon regime and the asymptotic regime for
Dbrane classical solutions for small $g$. This vacuum stability bound on the
curvature can be interpreted as an uncertainty relation for Dbrane charge.
