@article {IOPORT.50160362,
    author       = {Porcu, Emilio and Zastavnyi, Viktor},
    title        = {Characterization theorems for some classes of covariance functions associated to vector valued random fields},
    year         = {2011},
    journal      = {J. Multivariate Analysis},
    volume       = {102},
    number       = {9},
    pages        = {1293-1301},
    doi          = {10.1016/j.jmva.2011.04.013},
    identifier   = {50160362},
}