Some generalized results on subquadratic Lane-Emden elliptic systems with weights in unbounded domains

We study a nonlinear elliptic system of Lane-Emden type in RN, N >2, which is equivalent to a fourth order quasilinear elliptic equation involving a suitable \sublinear" term. Thanks to some compact imbeddings in weighted L^p-spaces, existence and multiplicity results are proved by means of a generalized Weierstrass Theorem and a variant of the Symmetric Mountain Pass Theorem. These results, which generalize previous ones stated by the authors, apply in particular to a biharmonic equation under Navier conditions in R^N.