2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/124812We consider the Dirichlet Laplacian in infinite two-dimensional strips defined as uniform tubular neighbourhoods of curves on ruled surfaces. We show that the negative Gauss curvature of the ambient surface gives rise to a Hardy inequality and use this to prove certain stability of spectrum in the case of asymptotically straight strips about mildly perturbed geodesics.LaTeX, 10 pages; to appear in Journal of Inequalities and ApplicationsSpectral TheoryMathematical PhysicsDifferential Geometry58J50; 35P99; 81Q10text