Stable determination of conductivity by boundary measurements

We consider the problem of determining the scalar coefficient γ in the elliptic equation div(γ grad u) = 0 in ω when, for every Dirichlet datum u = ? on ?ω , the Neumann datum γ(?/ ? n)u = ∧._γ? is known. We prove a continuous dependence result     

Uniqueness for the determination of sound-soft defects in an inhomogeneous planar medium by acoustic boundary measurements

We consider the inverse problem of determining shape and location of sound-soft defects inside a known planar inhomogeneous and anisotropic medium through acoustic imaging at low frequency. In order to determine the defects, we perform acoustic boundary measurements, with prescribed boundary conditions of different types. We prove that at most two, suitably chosen, measurements allow us to uniquely determine multiple defects under minimal regularity assumptions on the defects and the medium containing them. Finally, we treat applications of these results to the case of inverse scattering.

     

Stable determination of an inclusion in a layered medium

We consider the inverse problem of detecting an inclusion in conductor through electrostatic measurements taken on the boundary. We analyze in particular the stability issue showing that the solution depends from the available data with a rate of continuity of logarithmic type.     

Reconstruction of the shape of the inclusion by boundary measurements

We give a formula for the reconstruction of the shape of the unknown inclusion by means of the Dirichlet to Neumann map.     

Stable methods for an inverse problem in acoustic scattering by an obstacle and an inhomogeneous medium

We consider (in two-dimensional Euclidean space) the scattering of a plane, time-harmonic acoustic wave by an inhomogeneous medium Ω with compact support and a bounded obstacle D lying completely outside of the inhomogeneous medium. We show that one may determine the shape of D and the local speed of sound in Ω from a knowledge of the asymptotic behavior of the scattered wave (i.e. the far field). This is done by considering a constrained optimization problem and employing integral equation and conformal mapping techniques. By assuming a priori that the functions which determine the shape of D and the local speed of sound in Ω lie in given compact sets, we show that the problem is stable, in the sense that the solution of the inverse scattering problem depends continuously on the far field data.     

A boundary blow-up elliptic problem with an inhomogeneous term

By a perturbation method and constructing comparison functions, we reveal how the inhomogeneous term h$h$ affects the exact asymptotic behaviour of solutions near the boundary to the problem △u=b(x)g(u)+λh(x)$△u=b\left(x\right)g\left(u\right)+\lambda h\left(x\right)$, u>0$u>0$ in Ω$\Omega$, u_|∂Ω=∞$u{|}_{\partial \Omega }=\infty$, where Ω$\Omega$ is a bounded domain with smooth boundary in R^N${\mathbb{R}}^N$, λ>0$\lambda >0$, g∈C¹[0,∞)$g\in C^1[0,\infty )$ is increasing on [0,∞)$[0,\infty )$, g(0)=0$g\left(0\right)=0$, g^′$g^{\prime }$ is regularly varying at infinity with positive index ρ$\rho$, the weight b$b$, which is non-trivial and non-negative in Ω$\Omega$, may be vanishing on the boundary, and the inhomogeneous term h$h$ is non-negative in Ω$\Omega$ and may be singular on the boundary.     

Nonlinear boundary stabilization of an inhomogeneous and anisotropic thermoelasticity system

We study the nonlinear boundary stabilization of an inhomogeneous and anisotropic thermoelasticity system. We generalize a result of Rivera-Oliveira [1] to the nonlinear case. Our main tool is the use of the perturbed energy functional introduced by Komornik-Zuazua [2].     

Determining conductivity by boundary measurements

In [2], A. P. Caldéron posed the following question: can one determine the heat conductivity of an object from static temperature and heat flux measurements at the boundary? We show that such measurements uniquely determine the conductivity and all of its derivatives at the boundary.     

Solvability of an inhomogeneous boundary value problem for steady MHD equations

In this paper, we consider the steady MHD equations with inhomogeneous boundary conditions for the velocity and the tangential component of the magnetic field. Using a new construction of the magnetic lifting, we obtain existence of weak solutions under sharp assumption on boundary data for the magnetic field.     

The inclusion of Stekloff eigenvalues by boundary data approximation

We give eigenvalue inclusion theorems allowing the computation of both-sided Stekloff-eigenvalue bounds from a given approximate eigenpair. We demonstrate in numerical examples the possibility to get close bounds for even higher eigenvalues using the boundary collocation method. A good choice for trial functions are singularity functions allowing a control for the numerical stability and—in theory—an eigenvalue inclusion in an arbitrary small interval.The inclusion theorems may be interpreted as a priori norm inequalities, too.

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Zusammenfassung Wir stellen Eigenwerteinschlußsätze vor, welche die Berechnung beiderseitiger Eigenwertschranken in Abhängigkeit von vorgelegten Näherungseigenpaaren gestatten. Wir demonstrieren an numerischen Beispielen, daß es mit dem Kollokationsverfahren möglich ist, sehr gute Einschlüsse selbst höherer Eigenwerte zu erhalten. Als Ansatzfunktionen bewähren sich Singularitätenfunktionen, welche eine Steuerbarkeit der numerischen Stabilität ermöglichen. Zudem erlauben diese Funktionen in der Theorie einen Einschluß in beliebiger Güte.Die Einschlußsätze können auch als a priori Norm-Ungleichungen angesehen werden.

     

A boundary-only treatment by singular boundary method for two-dimensional inhomogeneous problems

In this study, an effective singular boundary method (SBM) in conjunction with the recursive multiple reciprocity method (MRM) is developed and validated for inhomogeneous problems. It avoids the inner nodes or domain discretizations to evaluate the particular solution, and preserves the boundary-only property of the SBM. Rather than using only polyharmonic operators in the traditional MRM, a recursive MRM is proposed to annihilate source terms with different partial differential operators recursively. Nevertheless, high-order fundamental solutions are involved in the recursive MRM. The absence of the origin intensity factors of higher order fundamental solutions is a major bottleneck in applying the SBM. In order to remedy this difficulty, the origin intensity factors of higher order fundamental solutions are derived with simple formulas. Numerical examples are presented to illustrate the accuracy and efficiency of the proposed method.     

Phase transition layers with boundary intersection for an inhomogeneous Allen–Cahn equation

We consider the nonlinear problem of inhomogeneous Allen–Cahn equation

${?}^2\mathrm{\Delta }u+V(y)u(1?u^2)=0\text{in}\mathrm{\Omega },\frac{?u}{?\nu }=0\text{on}?\mathrm{\Omega },$

where Ω is a bounded domain in ${\mathbb{R}}^2$ with smooth boundary, ? is a small positive parameter, ν denotes the unit outward normal of ?Ω, V is a positive smooth function on $\overline{\mathrm{\Omega }}$. Let Γ be a curve intersecting orthogonally with ?Ω at exactly two points and dividing Ω into two parts. Moreover, Γ satisfies stationary and non-degenerate conditions with respect to the functional ${\int }_{\mathrm{\Gamma }}{V}^{1/2}$. We can prove that there exists a solution $u_{?}$ such that: as $?\to 0$, $u_{?}$ approaches +1 in one part of Ω, while tends to ?1 in the other part, except a small neighborhood of Γ.     

Methods of boundary control theory in the nonstationary inverse problem for an inhomogeneous string

An approach to inverse problems based on the boundary control theory is developed. The dynamic problem to recover a density of an inhomogeneous string via its free endopoint oscillations generated by an instantaneous force source is proposed. The problem is to determine the coefficient ρ(x)>0 in the equation ρ(x)u_tt(x, t)−u_xx(x, t)=0(x, t>0) with the conditions u|_<0=0, u_x(0, t)=δ(t) by using a known function (response) u(0, t)=r(t) (t>0). The authors propose an algorithm based upon the approach and demonstrate its numerical efficiency in the test problems including those for nonmonotone ρ(x)'s. Bibliography: 12 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 186, pp. 37–49, 1990. Translated by T. N. Surkova.     

On the complete damping of oscillations of an inhomogeneous rod by means of a boundary control at one end

The process of damping oscillations of a rod consisting of two dissimilar segments and fixed at one end is considered. The damping is carried out by means of a boundary control at the other end of the rod.     

X-ray tomographic determination of the chemical composition and structure of an inhomogeneous medium

The chemical composition of an inhomogeneous body consisting of several homogeneous parts is determined by x-ray tomography. At the first stage, an indicator of inhomogeneities is used to determine the internal structure of the body. Next, under certain additional assumptions about the properties of the parts, a method is proposed for partial or complete determination of the chemical composition of each part as based on the results of the previous stage. Mathematically, the problem is reduced to solving the radiative transfer equation and systems of linear algebraic equations. Numerical experiments are performed via computer simulation. The numerical results are illustrated by graphs and tomograms.     

The methods of boundary control theory in the inverse spectral problem for an inhomogeneous string

The inverse spectral problem for an inhomogeneous string is solved by means of the methods of boundary control theory. A numerical algorithm is described and computations of the density of the string are presented for a number of model examples.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, Vol. 179, pp. 14–22, 1989.