2,185 research outputs found
Modulational Instability in Equations of KdV Type
It is a matter of experience that nonlinear waves in dispersive media,
propagating primarily in one direction, may appear periodic in small space and
time scales, but their characteristics --- amplitude, phase, wave number, etc.
--- slowly vary in large space and time scales. In the 1970's, Whitham
developed an asymptotic (WKB) method to study the effects of small
"modulations" on nonlinear periodic wave trains. Since then, there has been a
great deal of work aiming at rigorously justifying the predictions from
Whitham's formal theory. We discuss recent advances in the mathematical
understanding of the dynamics, in particular, the instability of slowly
modulated wave trains for nonlinear dispersive equations of KdV type.Comment: 40 pages. To appear in upcoming title in Lecture Notes in Physic
Nondegeneracy and Stability of Antiperiodic Bound States for Fractional Nonlinear Schr\"odinger Equations
We consider the existence and stability of real-valued, spatially
antiperiodic standing wave solutions to a family of nonlinear Schr\"odinger
equations with fractional dispersion and power-law nonlinearity. As a key
technical result, we demonstrate that the associated linearized operator is
nondegenerate when restricted to antiperiodic perturbations, i.e. that its
kernel is generated by the translational and gauge symmetries of the governing
evolution equation. In the process, we provide a characterization of the
antiperiodic ground state eigenfunctions for linear fractional Schr\"odinger
operators on with real-valued, periodic potentials as well as a
Sturm-Liouville type oscillation theory for the higher antiperiodic
eigenfunctions.Comment: 46 pages, 2 figure
An Integrable Shallow Water Equation with Linear and Nonlinear Dispersion
We study a class of 1+1 quadratically nonlinear water wave equations that
combines the linear dispersion of the Korteweg-deVries (KdV) equation with the
nonlinear/nonlocal dispersion of the Camassa-Holm (CH) equation, yet still
preserves integrability via the inverse scattering transform (IST) method.
This IST-integrable class of equations contains both the KdV equation and the
CH equation as limiting cases. It arises as the compatibility condition for a
second order isospectral eigenvalue problem and a first order equation for the
evolution of its eigenfunctions. This integrable equation is shown to be a
shallow water wave equation derived by asymptotic expansion at one order higher
approximation than KdV. We compare its traveling wave solutions to KdV
solitons.Comment: 4 pages, no figure
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