@article{FCAA_2005_8_2_a6,
     author = {Mart{\'\i}nez, Celso and Sanz, Miguel and Redondo, Antonia},
     title = {Fractional {Powers} of {Almost} {Non-Negative} {Operators}},
     journal = {Fractional calculus and applied analysis},
     pages = {201--230},
     publisher = {mathdoc},
     volume = {8},
     number = {2},
     year = {2005},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/FCAA_2005_8_2_a6/}
}