@article{SoffRafelskiGreiner2006,
  author    = {Gerhard Soff and Johann Rafelski and Walter Greiner},
  title     = {Lower bound to limiting fields in nonlinear electrodynamics},
  journal   = {Physical review A},
  volume    = {7},
  number    = {3},
  pages     = {903 -- 907},
  year      = {2006},
}