  We study $I$-$V$ characteristics of periodic square Nb wire networks as a
function of temperature in a transverse magnetic field, with a focus on three
fillings 2/5, 1/2, and 0.618 that represent very different levels of
incommensurability. For all three fillings, a scaling behavior of $I$-$V$
characteristics is found, suggesting a finite temperature continuous
superconducting phase transition. The low-temperature $I$-$V$ characteristics
are found to have an exponential form, indicative of the domain-wall
excitations.
