  A self-organized system composed of classical particles confined in a
two-dimensional parabolic trap and interacting through a potential with a
short-range attractive part and long-range repulsive part is studied as
function of temperature. The influence of the competition between the
short-range attractive part of the inter-particle potential and its long-range
repulsive part on the melting temperature is studied. Different behaviors of
the melting temperature are found depending on the screening length ($\kappa$)
and the strength ($B$) of the attractive part of the inter-particle potential.
A re-entrant behavior and a thermal induced phase transition is observed in a
small region of ($\kappa,B$)-space. A structural hysteresis effect is observed
as a function of temperature and physically understood as due to the presence
of a potential barrier between different configurations of the system.
