Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · 0708.2193

Focusing waves in unknown media by modified time reversal iteration

Matias Dahl·Anna Kirpichnikova·Matti Lassas
View original source ↗Read source document ↗Export metadata ↓

Abstract

We study the wave equation in a bounded domain or on a compact Riemannian manifold with boundary. Assume that we are given the hyperbolic Neumann-to-Dirichlet map on the boundary corresponding to physical boundary measurements. We consider how to focus waves, that is, how to find Neumann boundary values so that at a given time the corresponding wave converges to a delta distribution $δ_y$ while the time derivative of the wave converges to zero. Such boundary value are generated by an iterative sequence of measurements. In each iteration step we apply time reversal and other simple operators to measured data and compute boundary values for the next iteration step. The key feature of the algorithm is that it does not require knowledge of the coefficients in the wave equation, that is, the material parameters inside the media. However, we assume that the point $y$ where the wave focuses is known in travel time coordinates.

Explore related subjects

math.APmath.OC

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Matias Dahl, Anna Kirpichnikova, Matti Lassas. 2007-08-16. Focusing waves in unknown media by modified time reversal iteration. https://arxiv.org/abs/0708.2193

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Large friction limit of compressible Navier--Stokes equations with Navier boundary conditions in a half-space

We study the large-friction limit for the three-dimensional barotropic compressible Navier-Stokes equations in a half-space. The velocity satisfies a Navier boundary condition with friction coefficient $α>0$, while the limiting problem satisfies the no-slip boundary condition. We establish estimates for local-in-time smooth solutions that are uniform in $α$ and prove strong convergence of the density and velocity as $α\to\infty$. For weak solutions, we use the Lagrangian flow maps associated with the two velocities to compare the densities and construct suitable transported test functions. This yields weak convergence to the no-slip solution. Our results provide a compressible counterpart of the large-friction limit for incompressible flows.

math.AP↗
arXiv2026

Bochner-Riesz means for critical magnetic Schrödinger operators in ${\mathbb R^2}$

We study $L^p$-boundedness of the Bochner-Riesz means for critical magnetic Schrödinger operators $\LL_{\A}$ in ${\mathbb R^2}$, which involve the {physical} Aharonov-Bohm potential. We show that for $1\leq p\leq +\infty$ and $p\not= 2$, the Bochner-Riesz operator $S_λ^δ(\LL_{\A})$ of order $δ$ is bounded on $L^p(\R^2)$ if and only if $δ>\max\big\{0, 2\big|1/2-1/p\big|-1/2\big\}$. The new ingredient {in} the proof is to obtain the localized $L^4(\R^2)$ estimate of $S_λ^δ(\LL_{\A})$, whose kernel is heavily affected by the physical magnetic diffraction, and more singular than the classical Bochner-Riesz means $S_λ^δ(Δ)$ for the Laplacian $Δ$ in ${\mathbb R}^2$.

math.AP↗
arXiv2026

Solitons, scattering and blow-up for the nonlinear Schrödinger equation with combined power-type nonlinearities on $\mathbb{R}^d\times\mathbb{T}$

We investigate the long time dynamics of the nonlinear Schrödinger equation (NLS) with combined powers on the waveguide manifold $\mathbb{R}^d\times\mathbb{T}$. Different from the previously studied NLS-models with single power on the waveguide manifolds, where the non-scale-invariance is mainly due to the mixed nature of the underlying domain, the non-scale-invariance of the present model is both geometrical and structural. By considering different combinations of the nonlinearities, we establish both qualitative and quantitative properties of the soliton, scattering and blow-up solutions. As one of the main novelties of the paper compared to the previous results for the NLS with single power, we particularly construct two different rescaled families of variational problems, which leads to an NLS with single power in different limiting profiles respectively, to establish the periodic dependence results.

math.AP↗