Wc. Lian et Fh. Wong, EXISTENCE OF POSITIVE SOLUTIONS FOR NONLINEAR SINGULAR BOUNDARY-VALUE-PROBLEMS, Mathematical and computer modelling, 24(9), 1996, pp. 69-78
Under suitable conditions on f(t,u), the two-point boundary value prob
lem u ''(t) + lambda f(t,u(t)) = 0 in (0,1) u(0) = u(1) = 0 has at lea
st one positive solution for lambda belonging to a compatible interval
.