@article{IM_1990__99_1_143761,
     author = {J. Harris and I. Morrison},
     title = {Slopes of effective divisors on the moduli space of stable curves.},
     journal = {Inventiones mathematicae},
     pages = {321--356},
     year = {1990},
     volume = {99},
     number = {1},
     zbl = {0705.14026},
     url = {http://geodesic.mathdoc.fr/item/IM_1990__99_1_143761/}
}