Abstract
We study the positive solutions to boundary value problems of the form
;
,
;
, where
is a bounded domain in
with
,
is the Laplace operator,
is a positive parameter,
is a continuous function which is sublinear at
,
is the outward normal derivative, and
is a smooth function nondecreasing in
. In particular, we discuss the existence of at least two positive radial solutions
for
when
is an annulus in
. Further, we discuss the existence of a double S-shaped bifurcation curve when
,
, and
with
.
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