@article{10_4171_ifb_12,
     author = {Hans Wilhelm Alt and C J van Duijn},
     title = {A free boundary problem involving a cusp: breakthrough of salt water},
     journal = {Interfaces and free boundaries},
     pages = {21--72},
     year = {2000},
     volume = {2},
     number = {1},
     doi = {10.4171/ifb/12},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ifb/12/}
}