1. Alt, H.W., Caffarelli, L.A.: Existence and regularity for a minimum problem with free boundary. J. Reine Angew. Math. 325, 105–144 (1981)
2. Alt, H.W., Caffarelli, L.A., Friedman, A.: Axially symmetric jet flows. Arch. Rational Mech. Anal. 81(2), 97–149 (1983)
3. Alt, H.W., Caffarelli, L.A., Friedman, A.: A free boundary problem for quasilinear elliptic equations. Ann. Scuola Norm. Sup. Pisa Cl. Sci. 11, 1–44 (1984)
4. Alt, H.W., Caffarelli, L.A., Friedman, A.: Jets with two fluids. I. One free boundary. Indiana Univ. Math. J. 33(2), 213–247 (1984)
5. Alt, H.W., Caffarelli, L.A., Friedman, A.: Jets with two fluids. II. Two free boundaries. Indiana Univ. Math. J. 33(3), 367–391 (1984)