In this paper, we consider a critical elliptic system in $\mathbb{R}^N$. We obtain a positive solution of the system with high energy by variational methods.

Our purpose in this paper is to provide a self-contained account of the inhomogeneous Dirichlet problem ${\Delta_\infty} u=f(x,u)$ where $u$ represents prescribed continuous data on the boundary of bounded domains. We employ a combination of Perron's method and a priori estimates to give general sufficient conditions on the right-hand side $f$ that would ensure existence of viscosity solutions to the Dirichlet problem. Examples show that these sufficient conditions may not be relaxed. We also identify a class of inhomogeneous terms for which the corresponding Dirichlet problem has no solution in any domain with large in-radius. Several results, which are of independent interest, are developed to build towards the main results. The existence theorems provide a substantial improvement of previous results, including our earlier results [7] on this topic.

We study the Cauchy problem for a quasilinear wave equation with low-regularity data. A space-time $L^2$ estimate for the variable coefficient wave equation plays a central role for this purpose. Assuming radial symmetry, we establish the almost global existence of a strong solution for every small initial data in $H^2 \times H^1$. We also show that the initial-value problem is locally well posed.

We give a sufficient condition for nonexistence of nontrivial nonnegative solutions to the partial differential inequality involving $A$-Laplacian: $-\Delta_A u\ge \Phi (u)$, where $u$ is defined on ${{\mathbb{R}^{n}}}$. The condition obtained relies on the rate of decay at infinity of certain functions involving $A$ and $\Phi$. The techniques, based on methods due to Mitidieri and Pohozaev, exploit suitable a priori estimates in the framework of Orlicz-Sobolev spaces. The result is illustrated by logarithmic $A$-Laplacians and logarithmic functions $\Phi$.

We consider the Cauchy problem for the $L^{2}$-critical damped nonlinear Schrödinger equation. We prove existence and stability of finite time blow-up dynamics with the log-log blow-up speed for $\|\nabla u(t)\|_{L^2}.$

In this paper, we study the solutions to the following singular elliptic problem of exponential type growth posed in a bounded smooth domain $\Omega \subset {{\mathbb R}}^2$: \begin{eqnarray*}( P_\lambda)\qquad \left\{\begin{array} {ll} & - \Delta u = \lambda (u^{-\delta}+h(u)e^{u^\alpha}) \quad\mbox{ in }\,\Omega,\\ & u> 0\quad\mbox{ in }\,\Omega, \;\;u\vert_{\partial\Omega} = 0. \end{array}\right. \end{eqnarray*} Here, $1\leq\alpha\leq 2$, $0<\delta<3$, ${\lambda}\geq 0$ and $h(t)$ is assumed to be a smooth ``perturbation" of $e^{t^{\alpha}}$ as $t \rightarrow \infty$ (see ${\bf (H1)-(H2)}$ below). We show the existence of an unbounded connected branch of solutions to $(P_{\lambda})$ emanating from the trivial solution at ${\lambda}=0$. In the radial case (i.e., when $\Omega =B_1$ and $u$ is radially symmetric) we make a detailed study of the blow-up/convergence of the solution branch as it approaches the asymptotic bifurcation point at infinity. In the critical case $\alpha=2$, we interpret the multiplicity results in terms of the corresponding bifurcation diagrams and the asymptotic profile of large solutions along the branch at infinity.