  We numerically examine the properties of a two-dimensional system of
particles which have competing long range repulsive and short range attractive
interactions as a function of density and temperature. For increasing density,
there are well defined transitions between a low density clump phase, an
intermediate stripe phase, an anticlump phase, and a high density uniform
phase. To characterize the transitions between these phases we propose several
measures which take into account the different length scales in the system. For
increasing temperature, we find an intermediate phase that is liquid-like on
the short length scale of interparticle spacing but solid-like on the larger
length scale of the clump, stripe, or anticlump pattern. This intermediate
phase persists over the widest temperature range in the stripe state when the
local particle lattice within an individual stripe melts well below the
temperature at which the entire stripe structure breaks down, and is
characterized by intra-stripe diffusion of particles without inter-stripe
diffusion. This is followed at higher temperatures by the onset of inter-stripe
diffusion in an anisotropic diffusion phase, and then by breakup of the stripe
structure. We identify the transitions between these regimes through diffusion,
specific heat, and energy fluctuation measurements, and find that within the
intra-stripe liquid regime, the excess entropy goes into disordering the
particle arrangements within the stripe rather than affecting the stripe
structure itself. The clump and anticlump phases also show multiple
temperature-induced diffusive regimes which are not as pronounced as those of
the stripe phase.
