1. Brezis, H., Turner, R.: On a class of superlinear elliptic problems. Comm. Partial Differ. Equ. 2, 601–614 (1977)
2. Caldwell, S., Castro, A., Shivaji, R., Unsurangsie, S.: Positive solutions for classes of multiparameter elliptic semipositone problems. Electron. J. Differen. Equ. 96, 10 pp (2007)
3. Cañada, A., Magal, P., Montero, J.A.: Optimal control of harvesting in a nonlinear elliptic system arising from population dynamics. J. Math. Anal. Appl. 254, 571–586 (2001)
4. Chabrowski, J., Yang, J.: Multiple solutions of a nonlinear elliptic equation involving Neumann conditions and a critical Sobolev exponent. Rend. Sem. Mat. Univ. Padova. 110, 1–24 (2003)
5. Corrêa, F.J.: On the existence and multiplicity of positive solutions of a semilinear elliptic system. An. Acad. Bras. Ciênc. 60, 266–270 (1988)