The Helfrich variational problem is the minimizing problem of the bending energy among closed surface with prescribed area and enclosed volume. This is one of the models for shape transformation theory of human red blood cells. Here the associated gradient flow, called the Helfrich flow, is studied. The existence of this geometric flow is proved locally for arbitrary initial data, and globally near spheres. Furthermore its center manifold near spheres is investigated.

In this work we study the existence, multiplicity and concentration of positive solutions for the following class of problem \begin{equation} - \epsilon^{p} \Delta_{p}u + V(z)|u|^{p-2}u=f(u), \,\,\, u(z) > 0, \forall \ z \in \mathbb R^N , \tag*{$(P_{\epsilon})$} \end{equation} where $\Delta_{p}u$ is the p-Laplacian operator, $\epsilon$ is a positive parameter, $2 \leq p < N, V:\mathbb R^N \to \mathbb R$ is a continuous functions and $f:\mathbb R \to \mathbb R$ is a function of $C^{1}$ class.

We consider the generalized Korteweg-de Vries equations : \[ u_t + (u_{xx} + u^p)_x =0, \quad t,x \in \mathbb R, \] for $p \in (3,\infty)$. Let $U(t)$ be the associated linear group. Given $V$ in the weighted Sobolev space $H^{2,2} = \{ f \in L^2 : (1+|x|)^2(1-\partial_x^2)f \|_{L^2} < \infty\}$, possibly large, we construct a solution $u(t)$ of the generalized Korteweg-de Vries equation such that : \[ \lim_{t \to \infty} \| u(t) - U(t) V \|_{H^1} =0. \] We also prove uniqueness of such a solution in an adequate space. In the $L^2$-critical case ($p=5$), this result can be improved to any possibly large function $V$ in $L^2$ (with convergence in $L^2$).

The kernel of a continuous positive integral operator on an interval $I$ is a Moore matrix on $I$. We show that, under minimal differentiability assumptions, this implies that the kernel satisfies a 2-parameter family of differential inequalities. These inequalities ensure that, for unbounded $I$, the corresponding integral operator is exceptionally well behaved: it is compact and thus the eigenfunctions for its discrete spectrum have the differentiability of the kernel and satisfy sharp Sobolev bounds, the symmetric mixed partial derivatives are again kernels of positive operators and the differentiated eigenfunction series converge uniformly and absolutely. Converse results are derived.

We prove global existence for the Dirac-Klein-Gordon equations in one space dimension with $\psi\in L^2$ (charge class) and $\phi\in H^{1/4}$. This improves the global existence result of Fang [7] by $1/4 + \epsilon$ derivatives in $\phi$. The proof relies on bilinear estimates for solutions of the Dirac equation and a decomposition of the spinor field into `left' and `right' spinors.

In this paper we study the existence of positive solutions for nonlinear elliptic problems driven by the $p$-Laplacian differential operator and with a nonsmooth potential (hemivariational inequalities). The hypotheses, in the case $p=2$ (semilinear problems), incorporate in our framework of analysis the so-called asymptotically linear problems. The approach is degree theoretic based on the fixed-point index for nonconvex-valued multifunctions due to Bader [3].