Vortex Interaction with Mesoscopic Irregularities in High Temperature   Superconductors
  The conformal mapping method is used to study the problem of flux line interaction with surface cavities having cylindrical profile and characteristic size much less than the penetration length, i.e, within mesoscopic scale. It is shown that the metastable states are achieved when the dimensions of the surface irregularities do not exceed the coherence length. Our study shows that the surface barrier may vanished at some weak point at which the surface irregularities have mesoscopic scales. On the other hand, the surface barrier is completely disappeared when the surface defects size is more greater than penetration length. Our results are compared with the available experimental data and theoretical results. 
L. N. Shehata and A. Y. Afram