Investigating the stellar system's life-time and the evolution of their
  mass function using N-body simulation
  In this thesis we study several aspects of dynamical evolution of stellar
clusters. The results of more than 200 simulations of single-mass star clusters
with different initial total mass, half-mass radius and galactocentric
distance, are reported. Recent studies of star clusters show a linear relation
between a star cluster's dissolution time and its two-body relaxation time in
logarithmic scale. We found that the single-mass star clusters do not show such
a linear relation. We present new modified initial parameters to obtain a
linear relation for single-mass star clusters. Also the evolution of multi-mass
clusters and their lifetime, in the presence of the Galaxy is investigated. We
simulate about 90 multi-mass star clusters with the Nbody6 code. These clusters
have different initial total mass, half-mass radius and galactocentric
distance. Finally we investigate the evolution of the stellar mass function and
show that the slopes of the mass functions decrease with time. In addition we
study the effect of galactocentric distance of star clusters on the evolution
of the mass function.
