  In my PhD thesis I studied cooperative phenomena arise in complex systems
using the methods of statistical and computational physics. The aim of my work
was also to study the critical behaviour of interacting many-body systems
during their phase transitions and describe their universal features
analytically and by means of numerical calculations. In order to do so I
completed studies in four different subjects. My first investigated subject was
a study of non-equilibrium phase transitions in weighted scale-free networks.
The second problem I examined was the ferromagnetic random bond Potts model
with large values of q on evolving scale-free networks which problem is
equivalent to an optimal cooperation problem. The third examined problem was
related to the large-q sate random bond Potts model also and I examined the
critical density of clusters which touched a certain border of a perpendicular
strip like geometry and expected to hold analytical forms deduced from
conformal invariance. The last investigated problem was a study of the
non-equilibrium dynamical behaviour of the antiferromagnetic Ising model on
two-dimensional triangular lattice at zero temperature in the absence of
external field and at the Kosterlitz-Thouless phase transition point.
