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In this paper, it is shown that all non-trivial solutions of a wide class of dispersive equations, defined by a dispersion relation with minimal hypotheses on its regularity, are compactly supported for at most one time element. With plane waves of different frequencies traveling at different speeds, the finite speed of propagation is not expected for dispersive phenomena, and this intuition is made rigorous by complex-analytic arguments. Furthermore the method developed here applies to time fractional-order systems given by the Caputo derivative where the generalized space-time fractional Schr\"odinger equation is considered for concreteness. When the energy operator $i\partial_t$ and the Riesz derivative $(-\Delta)^{\frac{\beta}{2}}$ are fractionalized to the same order, it is shown that the sharp frequency-localized dispersive estimates yield the time decay of solutions that depends on both the spatial dimension and the long-memory effect. Asymptotically in time, the solution operator strongly, but not uniformly, converges in $L^2(\mathbb{R}^d)$ to the half-wave operator.

We prove the existence and uniqueness of the complexified Nonlinear Poisson-Boltzmann Equation (nPBE) in a bounded domain in $\mathbb{R}^3$. The nPBE is a model equation in nonlinear electrostatics. The standard convex optimization argument to the complexified nPBE no longer applies, but instead, a contraction mapping argument is developed. Furthermore, we show that uniqueness can be lost if the hypotheses given are not satisfied. The complixified nPBE is highly relevant to regularity analysis of the solution of the real nPBE with respect to the dielectric (diffusion) and Debye-H\"uckel coefficients. This approach is also well-suited to investigate the existence and uniqueness problem for a wide class of semi-linear elliptic Partial Differential Equations (PDEs).

Motivated by the appearance of the fractional Laplacian in many physical processes, recent work has emerged in particular on the properties of the fractional nonlinear Schr��dinger equation. Specific to models in optics and photonics a variant of mixed degrees of fractionality prove to be of interest. This paper presents first results in this new regime.

We consider the compact case of one-dimensional quantum Zakharov system, as an initial-value problem with periodic boundary conditions. We apply the Bourgain norm method to show low regularity local well-posedness for a certain class of Sobolev exponents that are sharp up to the boundary, under the condition that Schr\"odinger Sobolev regularity is non-negative. Using the conservation law and energy method, we show global well-posedness for sufficiently regular initial data, without any smallness assumption. Lastly we show the semi-classical limit as $\epsilon \to 0$ on a compact time interval, whereas the quantum perturbation proves to be singular on an infinite time interval., Comment: 18 pages

We consider Carleson's problem regarding small time almost everywhere convergence to initial data for the Schr��dinger equation, both linear and nonlinear. We show that the (sharp) result proved by Dahlberg and Kenig for initial data in Sobolev spaces still holds when one considers the full Schr��dinger equation with a certain class of potentials. We also show the same technique used to bound such potential functions works for certain types of nonlinearities as well. As for $s, 20 pages

We prove modified Strichartz estimates on the one-dimensional torus, that are adapted to a fourth-order dispersion relation, and use them to show global well-posedness of nonlinear fourth-order Schr\"odinger equations. This extends the (low regularity) existence theory of the adiabatic transition of the Quantum Zakharov system to NLS. We show that the solutions behave continuously with respect to the quantum parameter in every compact time interval. Globally in time, however, we also show that such continuous dependence is generally not uniform., Comment: 15pg

In this paper, we prove the low-regularity global well-posedness of the adibatic limit of the Quantum Zakharov system and consider its semi-classical limit, i.e., the convergence of the model equation as the quantum parameter tends to zero. We also show ill-posedness in negative Sobolev spaces and discuss the existence of ground-state soliton solutions in high spatial dimensions., Comment: Few Edits