Consider the Dirichlet problem for elliptic and parabolic equations in non-divergence form with variable coefficients in convex bounded domains of $\mathbb R^n$. We prove solvability of the elliptic problem and maximal $L^q$-$L^p$-estimates for the solution of the parabolic problem provided the coefficients $a_{ij} \in L^\infty$ satisfy a Cordes condition and $p \in (1,2]$ is close to $2$. This implies that in two dimensions, i.e., $n=2$, the elliptic Dirichlet problem is always solvable if the associated operator is uniformly strongly elliptic, and $p \in (1,2]$ is close to $2$, for maximal $L^q$-$L^p$-regularity in the parabolic case an additional assumption on the growth of the coefficients is needed.

We prove some space-time estimates with homogeneous weight functions for the wave equation with radially symmetric data in order to explain a connection between the Morawetz-type space-time estimate and the Strichartz-type space-time estimate. As an application of such linear estimates, we give a new proof of global existence of small radial solutions to semilinear wave equations. Local existence of radial solutions is also studied for low-regularity data.

In this article we consider the Boussinesq system supplemented with some dissipation terms. These equations model the propagation of a water wave in shallow water. We prove the existence of a global smooth attractor for the corresponding dynamical system.

The paper investigates the well posedness of the quasi-stationary Stefan problem with the Gibbs-Thomson correction. The main result proves the existence of unique weak solutions provided the initial surface belongs to the $W^{2-3/p}_p$-Sobolev-Slobodeckij class for $p>n+3$, only. The proof is based on Schauder-type estimates in $L_p$-type spaces for a linearization of the original system in a rigid domain.

We study some of the properties of bounded, asymptotically almost-periodic or pseudo almost-periodic solutions of the Liénard equation, $$x'' + f(x)x' + g(x) = p(t) ,$$ where $p : \mathbb R \longrightarrow \mathbb R$ is a continuous, bounded, asymptotically almost-periodic or pseudo almost-periodic function, $f$ and $g : (a,b) \longrightarrow \mathbb R$ are continuous and $g$ is strictly decreasing. Notably, we describe the set of initial conditions of the bounded solutions on $( 0 , + \infty )$ and we state some results of existence of pseudo almost-periodic solutions.

The main result of this paper concerns the limit of the solution of the Ostrovsky equation as the rotation parameter $\gamma $ goes to zero. We are interested also in the ill-posedness of the Cauchy problem associated with this equation. First, using a compactness method, we show that the initial-value problem of Ostrovsky equation is locally well-posed in $H^s(\mathbb R)$ for $s>3/4$. The compactness method is essentially used to prove that the solution of the Ostrovsky equation converges to that of the Korteweg-de Vries equation, as $\gamma $ tends to zero, locally in time, in $ H^s(\mathbb R)$ for $ s>3/4$. Thanks to some conservation laws and estimates, we will prove a persistence property of the solutions. Therefore, we show the convergence of the solutions in $ L^{\infty}_{loc}(\mathbb R, H^s(\mathbb R))$ for $ s \geq 3/4$. In the case of positive dispersion, we gain a strong convergence in $ C(\mathbb R, H^1(\mathbb R))$. The last section is devoted to studying the ill-posedness of the Cauchy problem associated with the Ostrovsky equation.