@unpublished{ChenYu2008,
  author  = {Hua Chen and Chun Yu},
  title   = {Asymptotic behaviour of the trace for Schr{\"o}dinger operator on fractal drums},
  institution = {Institut f{\"u}r Mathematik},
  series    = {Preprint},
  number    = {(2001) 32},
  year    = {2008},
}