@article{JEMS_2005_7_2_a1,
     author = {Henri Berestycki and Fran\c{c}ois Hamel and Nikolai Nadirashvili},
     title = {The speed of propagation for {KPP} type problems. {I:} {Periodic} framework},
     journal = {Journal of the European Mathematical Society},
     pages = {173--213},
     publisher = {mathdoc},
     volume = {7},
     number = {2},
     year = {2005},
     doi = {10.4171/jems/26},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/jems/26/}
}