We study the periodic and Neumann boundary value problems associated with the second order nonlinear differential equation u''+cu'+λa(t)g(u)=0, where g:[0,+∞[→[0,+∞[ is a sublinear function at infinity having superlinear growth at zero. We prove the existence of two positive solutions when ∫a(t)dt 0 is sufficiently large. Our approach is based on Mawhin's coincidence degree theory and index computations.

%B Proc. Roy. Soc. Edinburgh Sect. A 146 (2016), 449–474. %I Cambridge University Press %G en %U http://urania.sissa.it/xmlui/handle/1963/35262 %1 35566 %2 Mathematics %4 1 %# MAT/05 %$ Approved for entry into archive by Maria Pia Calandra (calapia@sissa.it) on 2016-11-21T07:33:12Z (GMT) No. of bitstreams: 0 %R 10.1017/S0308210515000621