We prove that the global attractor for a weakly damped nonlinear Schrödinger equation in a suitable energy space is in fact included and compact in a more regular energy space.

We study the large-time behaviour of nonnegative solutions of the problem $$ \begin{cases} u_t - (u^m)_x = u_{xx} \quad& \hbox{in }\; \mathbb{R}^+\times\mathbb{R}^+ \cr u_x=0 & \hbox{in }\; \{0\}\times\mathbb{R}^+ \cr u=u_0 & \hbox{in }\; \mathbb{R}^+\times\{0\}, \end{cases} $$ where $m>1$ and $u_0$ is a nonnegative function in $L^\infty(\mathbb{R}^+)$. We investigate the competition between the diffusion and the convection terms with respect to the concentration of the initial data controlled by the condition $$ \lim_{x\to +\infty} x^\alpha u_0(x) = A >0. $$ Convergence results are proved rescaling the equation and using Bernstein-type methods to obtain the necessary estimates.

We provide two abstract direct proofs on the analyticity of the s.c. contraction semigroups, which arise in thermo-elastic systems under a variety of physical boundary conditions. A fortiori, the semigroups are then uniformly stable. Several examples illustrate the theory.

We prove local integral (entropy) estimates for nonnegative solutions of the fourth-order degenerate parabolic equation $$ u_t+ \div (u^n\nabla\Delta u)=0 $$ in space dimensions two and three. These estimates enable us to show that solutions have finite speed of propagation if $n\in(\frac 18,2)$ and that the support cannot shrink if the growth exponent $n$ is larger than $3/2$. In addition, we prove decay estimates for solutions of the Cauchy problem and a growth estimate for their support.

Consider the semilinear Schrödinger equation (*) $-\Delta u + V(x)u = f(x,u)$, $u\in H^1(\mathbf {R} ^N)$. It is shown that if $f$, $V$ are periodic in the $x$-variables, $f$ is superlinear at $u=0$ and $\pm\infty$ and 0 lies in a spectral gap of $-\Delta+V$, then (*) has at least one nontrivial solution. If in addition $f$ is odd in $u$, then (*) has infinitely many (geometrically distinct) solutions. The proofs rely on a degree-theory and a linking-type argument developed in this paper.

We study the Cauchy problem for two systems of equations (Maxwell--Debye and Maxwell--Bloch) describing laser-matter interaction phenomena. We show that these problems are locally-in-time well-posed for initial data in different Sobolev spaces. In the case of the Maxwell--Debye system, which contains some delay term, we study the limit of the solutions when this delay tends to 0. We also consider an adiabatic approximation of the Maxwell--Bloch system.