High velocity clumps and cluster of galaxies evolution
  We study the effect of the interaction between small scale clumps having velocities larger than the average escape velocity v_{\rm esc} and bound clumps (having v<v_{\rm esc}), on clusters of galaxies evolution. We find that the collapse of the bound clumps is accelerated with respect to the homogeneous case (Gunn & Gott's model - Gunn & Gott 1972). A comparison between the acceleration produced by this effect to the slowing down effect studied in Del Popolo & Gambera (1998) shows that the magnitude of the slowing down effect is larger than the acceleration produced by the effect studyed in this paper, only in the outskirts of the cluster. 
A. Del Popolo (1,2,3), M. Gambera (1) ((1) Bergamo University, Italy,   (2) Feza Gursey Institute, Istanbul, Turkey, (3) Bog...