  We present numerical results on the temperature dependence of the
distribution of bubble lengths in DNA segments of various guanine-cytosine (GC)
concentrations. Base-pair openings are described by the Peyrard-Bishop-Dauxois
model and the corresponding thermal equilibrium distributions of bubbles are
obtained through Monte Carlo calculations for bubble sizes up to the order of a
hundred base pairs. The dependence of the parameters of bubble length
distribution on temperature and the GC content is investigated. We provide
simple expressions which approximately describe these relations. The variation
of the average bubble length is also presented. We find a temperature
dependence of the exponent c that appears in the distribution of bubble
lengths. If an analogous dependence exists in the loop entropy exponent of real
DNA, it may be relevant to understand overstretching in force-extension
experiments.
