“…A well studied problem in the geometry of the Laplacian is the relation between the first eigenvalue/fundamental tone of open sets of a Riemannian manifold and its geometric invariants; see [2], [3], [8] and the references therein. Another interesting problem is to give bounds for the the first eigenvalue/fundamental tone of open sets of minimal submanifolds of Riemannian manifolds; see [4], [5], [7], [9], [10]. There has recently been increasing interest in the study of minimal surfaces (constant mean curvature) in product spaces N × R, after the discovery of many beautiful examples in those spaces; see [16], [17].…”