Let $Omega subset {mathbb R}^N$ ($N geq 3$) be a $C^2$ bounded domain and $F subset partial Omega$ be a $C^2$ submanifold of dimension $0 leq k leq N-2$. Put $delta_F(x)=dist(x,F)$, $V=delta_F^{-2}$ in $Omega$ and $L_{gamma V}=Delta + gamma V$. Denote by $C_H(V)$ the Hardy constant relative to $V$ in $Omega$. We study positive solutions of equations (LE) $-L_{gamma V} u = 0$ and (NE) $-L_{gamma V} u+ f(u) = 0$ in $Omega$ when $gamma < C_H(V)$ and $f in C({mathbb R})$ is an odd, monotone increasing function. We establish the existence of a normalized boundary trace for positive solutions of (LE) - first studied by Marcus and Nguyen for the case $F=partial Omega$ - and employ it to investigate the behavior of subsolutions and super solutions of (LE) at the boundary. Using these results we study boundary value problems for (NE) and derive a-priori estimates. Finally we discuss subcriticality of (NE) at boundary points of $Omega$ and establish existence and stability results when the data is concentrated on the set of subcritical points.
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