  The dynamical properties of double-stranded DNA are studied in the framework
of the Peyrard-Bishop-Dauxois model using Langevin dynamics. Our simulations
are analyzed in terms of two probability functions describing coherently
localized separations ("bubbles") of the double strand. We find that the
resulting bubble distributions are more sharply peaked at the active sites than
found in thermodynamically obtained distributions. Our analysis ascribes this
to the fact that the bubble life-times significantly afects the distribution
function. We find that certain base-pair sequences promote long-lived bubbles
and we argue that this is due to a length scale competition between the
nonlinearity and disorder present in the system.
