We propose a new formulation of the 3D Boltzmann non linear operator, without assuming Grad's angular cutoff hypothesis, and for intermolecular laws behaving as 1/rs, with s> 2. It involves natural pseudo differential operators, under a form which is analogous to the Landau operator. It may be used in the study of the associated equations, and more precisely in the non homogeneous framework.

We establish the continuity of bounded local solutions of the equation $\beta {\left(u\right)}_t=\mathrm{\Delta }u$. Here $\beta$ is any coercive maximal monotone graph in $\mathbb{R}\times \mathbb{R}$, bounded for bounded values of its argument. The multiphase Stefan problem and the Buckley-Leverett model of two immiscible fluids in a porous medium give rise to such singular equations.

We prove the existence of uniform attractors ${}_{\epsilon }$ in the space $H¹\left({ℝ}^N\right)$ for the nonautonomous nonclassical diffusion equation $u_t-\epsilon \Delta u_t-\Delta u+f(x,u)+\lambda u=g(x,t)$, ε ∈ [0,1]. The upper semicontinuity of the uniform attractors ${{}_{\epsilon }}_{\epsilon \in [0,1]}$ at ε = 0 is also studied.

We give some results on the existence, uniqueness and regularity of a nonlinear evolution system. This system models the viscoelastic behaviour of unicellular marine alga Acetabularia mediterrania when the calcium concentration varies. We show (with the aid of a fixed-point theorem) that the system admits a unique local solution in time.

Abbiamo considerato il problema della regolarità interna delle soluzioni deboli della seguente equazione differenziale $$\stackrel{m_0}{\sum _{i,j=1}}{\partial }_{x_i}\left(a_{i,j}\left(x,t\right){\partial }_{x_j}u\right)+\stackrel{N}{\sum _{i,j=1}}{b}_{i,j}{x}_i{\partial }_{x_j}u-{\partial }_{t}u=\stackrel{m_0}{\sum _{j=1}}{\partial }_{x_j}{F}_j\left(x,t\right),$$ dove $\left(x,t\right)\in {\mathbb{R}}^{N+1}$, $0<m_0\le N$ ed $F_j\in L_{\text{loc}}^p\left({\mathbb{R}}^{N+1}\right)$ per $j=1,\mathrm{\dots },m_0$. I nostri principali risultati sono una stima a priori interna del tipo $$\stackrel{m_0}{\sum _{j=1}}{∥{\partial }_{x_j}u∥}_p\le c\left(\stackrel{m_0}{\sum _{j=1}}{∥F_j∥}_p+{∥u∥}_p\right),$$ e la regolarità hölderiana di $u$. La stima a priori delle derivate viene ottenuta utilizzando una tecnica analoga a quella introdotta da Chiarenza, Frasca e Longo in [3], per gli operatori ellittici in forma di non divergenza, supponendo che i coefficienti $a_{i,j}$ verifichino una condizione...

We study the existence and the uniqueness of the weak solution of an inverse problem for a semilinear higher order ultraparabolic equation with Lipschitz nonlinearity. The main aim is to determine the weak solution of the equation and some functions that depend on the time variable, appearing on the right-hand side of the equation. The overdetermination conditions introduced are of integral type. In order to prove the solvability of this problem in Sobolev spaces we use the Galerkin method and the...