is a solvable linear equation in a Hilbert space H , A is a linear, closed, densely defined, unbounded operator in H , which is not boundedly invertible, so problem (1) is ill-posed. It is proved that the closure of the operator (AA + α I )−1A∗, with the domain D(A), where α > 0 is a constant, is a linear bounded everywhere defined operator with norm ≤ 1 2 √ α . This result is applied to the va...

Ocean (T, S) data analysis/assimilation, conducted in the three-dimensional physical space, is a generalized average of purely observed data (data analysis) or of modeled/observed data (data assimilation). Because of the high nonlinearity of the equation of the state of the seawater and nonuniform vertical distribution of the observational profile data, false static instability may be generated...

For Schrödinger maps fromR2×R+ to the 2-sphere S2, it is not known if finite energy solutions can form singularities (blow up) in finite time. We consider equivariant solutions with energy near the energy of the two-parameter family of equivariant harmonic maps. We prove that if the topological degree of the map is at least four, blowup does not occur, and global solutions converge (in a disper...

Continuing research in [13] and [14] on well-posedness of the optimal time control problem with a constant convex dynamics (in a Hilbert space), we adapt one of the regularity conditions obtained there to a slightly more general problem, where nonaffine additive term appears. We prove existence and uniqueness of a minimizer in this problem as well as continuous differentiability of the value fu...

This paper is concerned with the one-dimensional stationary linear Wigner equation, a kinetic formulation of quantum mechanics. Specii-cally, we analyze the well-posedness of the boundary value problem on a slab of the phase-space with given innow data for a discrete-velocity model. We nd that the problem is uniquely solvable if zero is not a discrete velocity. Otherwise one obtains a diierenti...

In this article we prove local well-posedness in lowregularity Sobolev spaces for general quasilinear Schrödinger equations. These results represent improvements of the pioneering works by Kenig-Ponce-Vega and Kenig-Ponce-Rolvung-Vega, where viscosity methods were used to prove existence of solutions in very high regularity spaces. Our arguments here are purely dispersive. The function spaces i...

We study the higher-order nonlinear dispersive equation ∂tu+ ∂ 2j+1 x u = ∑ 0≤j1+j2≤2j aj1,j2∂ j1 x u∂ j2 x u, x, t ∈ R. where u is a real(or complex-) valued function. We show that the associated initial value problem is well posed in weighted Besov and Sobolev spaces for small initial data. We also prove ill-posedness results when a0,k 6= 0 for some k > j, in the sense that this equation cann...

We describe traveling waves in a basic model for three-dimensional water-wave dynamics in the weakly nonlinear long-wave regime. Small solutions that are periodic in the direction of translation (or orthogonal to it) form an infinite-dimensional family. We characterize these solutions through spatial dynamics, by reducing a linearly ill-posed mixed-type initial-value problem to a center manifol...

A version of the Dynamical Systems Method (DSM) for solving ill-posed nonlinear equations F (u) = f with monotone operators F in a Hilbert space is studied in this paper under less restrictive assumptions on the nonlinear operators F than the assumptions used earlier. A new method of proof of the basic results is used. An a posteriori stopping rule, based on a discrepancy-type principle, is pro...

By using tools of time-frequency analysis, we obtain some improved local well-posedness results for the NLS, NLW and NLKG equations with Cauchy data in modulation spaces M 0,s .