Let $\Omega$ be a bounded simply connected domain in the complex plane, $ℂ$. Let $N$ be a neighborhood of $\partial \Omega$, let $p$ be fixed, $1\<p\<\infty ,$ and let $\widehat{u}$ be a positive weak solution to the $p$ Laplace equation in $\Omega \cap N.$ Assume that $\widehat{u}$ has zero boundary values on $\partial \Omega$ in the Sobolev sense and extend $\widehat{u}$ to $N\setminus \Omega$ by putting $\widehat{u}\equiv 0$ on $N\setminus \Omega .$ Then there exists a positive finite Borel measure $\widehat{\mu }$ on $ℂ$ with support contained in $\partial \Omega$ and such that$$\begin{array}{c}\hfill \int |\nabla \widehat{u}{|}^{p-2}\langle \nabla \widehat{u},\nabla \phi \rangle dA=-\int \phi d\widehat{\mu }\end{array}$$whenever $\phi \in C_0^{\infty }\left(N\right).$ If $p=2$ and if $\widehat{u}$ is the Green function for $\Omega$ with pole at $x\in \Omega \setminus \overline{N}$ then the measure $\widehat{\mu }$ coincides with harmonic measure...

When $1\<p\<\infty$ and $p\ne 2$ the $p$-harmonic measure on the boundary of the half plane ${ℝ}_{+}^2$ is not additive on null sets. In fact, there are finitely many sets $E_1$, $E_2$,...,$E_{\kappa }$ in $ℝ$, of $p$-harmonic measure zero, such that $E_1\cup E_2\cup ...\cup E_{\kappa }=ℝ$.

Via critical point theory we establish the existence and regularity of solutions for the quasilinear elliptic problem ⎧ $div(x,\nabla u)+{a\left(x\right)\left|u\right|}^{p-2}u={g\left(x\right)\left|u\right|}^{p-2}u+h\left(x\right){\left|u\right|}^{s-1}u$ in ${ℝ}^N$ ⎨ ⎩ u > 0, $li{m}_{\left|x\right|\to \infty }u\left(x\right)=0$, where 1 < p < N; a(x) is assumed to satisfy a coercivity condition; h(x) and g(x) are not necessarily bounded but satisfy some integrability restrictions.

In the paper we present an identity of the Picone type for a class of nonlinear differential operators of the second order involving an arbitrary norm $H$ in ${ℝ}^n$ which is continuously differentiable for $x\ne 0$ and such that $H^p$ is strictly convex for some $p>1$. Two important special cases are the $p$-Laplacian and the so-called pseudo $p$-Laplacian. The identity is then used to establish a variety of comparison results concerning nonlinear degenerate elliptic equations which involve such operators. We also get criteria...

Let $u$ be a weak solution of a quasilinear elliptic equation of the growth $p$ with a measure right hand term $\mu$. We estimate $u\left(z\right)$ at an interior point $z$ of the domain $\Omega$, or an irregular boundary point $z\in \partial \Omega$, in terms of a norm of $u$, a nonlinear potential of $\mu$ and the Wiener integral of ${𝐑}^n\setminus \Omega$. This quantifies the result on necessity of the Wiener criterion.

We study the existence and nonexistence of positive solutions of the nonlinear equation $$-{\Delta }_{p\left(x\right)}u=\lambda k\left(x\right)u^q\pm h\left(x\right)u^r\text{in}\Omega ,u=0\text{on}\partial \Omega$$ where $\Omega \subset {ℝ}^N$, $N\ge 2$, is a regular bounded open domain in ${ℝ}^N$ and the $p\left(x\right)$-Laplacian $${\Delta }_{p\left(x\right)}u:={\text{div}\left(\right|\nabla u|}^{p\left(x\right)-2}\nabla u)$$ is introduced for a continuous function $p\left(x\right)>1$ defined on $\Omega$. The positive parameter $\lambda$ induces the bifurcation phenomena. The study of the equation (Q) needs generalized Lebesgue and Sobolev spaces. In this paper, under suitable assumptions, we show that some variational methods still work. We use them to prove the existence of positive solutions...

We consider the existence of positive solutions of -pu=g(x)|u|p-2u+h(x)|u|q-2u+f(x)|u|p*-2u(1) in ${ℝ}^N$, where $\lambda ,\alpha \in ℝ$, $1<p<N$, $p^{*}=Np/(N-p)$, the critical Sobolev exponent, and $1<q<p^{*}$, $q\ne p$. Let ${\lambda }_1^{+}>0$ be the principal eigenvalue of -pu=g(x)|u|p-2u    in ,        g(x)|u|p>0, (2) with $u_1^{+}>0$ the associated eigenfunction. We prove that, if ${\int }_{{ℝ}^N}f{\left|u_1^{+}\right|}^{p^{*}}<0$, ${\int }_{{ℝ}^N}h{\left|u_1^{+}\right|}^q>0$ if $1<q<p$ and ${\int }_{{ℝ}^N}h{\left|u_1^{+}\right|}^q<0$ if $p<q<p^{*}$, then there exist ${\lambda }^{*}>{\lambda }_1^{+}$ and ${\alpha }^{*}>0$, such that for $\lambda \in [{\lambda }_1^{+},{\lambda }^{*})$ and $\alpha \in [0,{\alpha }^{*})$, (1) has at least one positive solution.