@article{Porcu:2010,
  author  = "E. Porcu and J. Matkowski and J. Mateu",
  title   = "On the non-reducibility of non-stationary correlation functions to stationary ones under a class of mean-operator transformations",
  journal = "Stochastic Environmental Research and Risk Assessment",
  volume  = "Vol. 24",
  pages   = "599--610",
  year    = "2010",
}