  Mechanically induced protein unfolding in the force-clamp apparatus is shown,
in a coarse-grained model of ubiquitin, to have lognormal statistics above a
treshold force and exponential below it. Correspondingly, the mean unfolding
time is slowly varying and exponentially decreases as a function of the force.
The time dependencies of the end-to-end distances are also distinct. The time
sequence of unfolding events weakly depends on force and much of it resembles
that for stretching at constant speed. A more complicated time dependence
arises for integrin.
