EXISTENCE OF MULTIPLE POSITIVE RADIAL SOLUTIONS TO ELLIPTIC EQUATIONS IN AN ANNULUS

In this paper, we use Leggett-Williams multiple fixed point theorems to obtain  sufficient conditions for the existence of at least one or  two positive radial solutions of the equation

$$-\Delta u=\lambda g(|x|)f(u), \,\,\, R_{1}<|x|<R_{2},$$

$x \in R^{N}, \, N \geq 2$ subject to a linear mixed boundary condition at $R_{1}$ and $R_{2}$.