V. Bacchelli, M. Di Cristo, E. Sincich, S. Vessella
We consider the problem of determining an unaccessible part of the boundary of a conductor by mean of thermal measurements. We study a problem of corrosion where a Robin type condition is prescribed on the damaged part and we prove logarithmic stability estimate.
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We consider an inverse problem arising in corrosion detection. We prove a stability result of logarithmic type for the determination of the corroded portion of the boundary and impedance by two measurements on the accessible portion of the boundary.
In this paper we will review the main results concerning the issue of stability for the determination unknown boundary portion of a thermic conducting body from Cauchy data for parabolic equations. We give detailed and selfcontained proofs. We prove that such problems are severely ill-posed in the sense that under a priori regularity assumptions on the unknown boundaries, up to any finite order of differentiability, the continuous dependence of unknown boundary from the measured data is, at best, of logarithmic type.
Energy Dissipative Solution to a Nonlinear Parabolic Systems with Unknown Dependent Coefficients
本文研究了整合图像处理中各向异性取向自适应去噪过程和材料科学中晶界运动相场模型的非线性抛物型偏微分方程组，提出能量耗散解概念以解决统一分析框架的问题。
Variational inequalities, formulated on unknown dependent convex sets, are called quasi-variational inequalities (QVI). This paper is concerned with the abstract approach to a class of parabolic QVIs arising in many biochemical/mechanical problems, based on a compactness theorem for parabolic variational inequalities (cf. [9]). The prototype of our model for QVIs of parabolic type is formulated in a reflexive Banach space as the sum of the time-derivative operator under unknown convex constraints and a semimonotone operator, including a feedback system which selects a convex constraint. The ma…
We consider the two-dimensional version of Calderòn's problem. When the D-N map is assumed to be known up to an error level $\varepsilon_0$, we investigate how the resolution in the determination of the unknown conductivity deteriorates the farther one goes from the boundary. We provide explicit formulas for the resolution, which apply to conductivities which are perturbations, concentrated near an interior point $q$, of the homogeneous conductivity.
An inverse boundary value problem for the Helmholtz equation in a bounded domain is considered. The problem is to extract information about an unknown obstacle embedded in the domain with unknown impedance boundary condition (the Robin condition) from the associated Dirichlet-to-Neumann map. The main result is a characterization of the unknown obstacle via the sequences that are constructed by the Dirichlet-to-Neumann map, under smallness conditions on the wave number and the upper bound of the impedance. Moreover two alternative simple proofs of a previous result of Cheng-Liu-Nakamura which a…
Stability Estimate for an Inverse Stochastic Parabolic Problem of Determining Unknown Time-varying Boundary
本文研究随机抛物型方程中未知时变边界的反问题，利用新的Carleman估计证明未知边界对数依赖于内部测量，从而可从任意内部区域观测跟踪边界行为。
In this paper we investigate the boundary value problem ${div(γ\nabla u)=0 in Ω, u=f on \partialΩ$ where $γ$ is a complex valued $L^\infty$ coefficient, satisfying a strong ellipticity condition. In Electrical Impedance Tomography, $γ$ represents the admittance of a conducting body. An interesting issue is the one of determining $γ$ uniquely and in a stable way from the knowledge of the Dirichlet-to-Neumann map $Λ_γ$. Under the above general assumptions this problem is an open issue. In this paper we prove that, if we assume a priori that $γ$ is piecewise constant with a bounded known number o…
This note presents a regularity result with proof for an initial-boundary value problem of a linear parabolic system involving curl of the unknown vector field, subjected to the boundary condition of prescribing the tangential component of the solution.
A 2D problem of acoustic wave scattering by a segment bearing impedance boundary conditions is considered. In the current paper (the first part of a series of two) some preliminary steps are made, namely, the diffraction problem is reduced to two matrix Riemann-Hilbert problems with exponential growth of unknown functions (for the symmetrical part and for the antisymmetrical part). For this, the Wiener--Hopf problems are formulated, they are reduced to auxiliary functional problems by applying the embedding formula, and finally the Riemann-Hilbert problems are formulated by applying the Hurd's…
We deal with the problem of determining the shape of an inclusion embedded in a homogenous background medium. The multifre-quency electrical impedance tomography is used to image the inclusion. For different frequencies, a current is injected at the boundary and the resulting potential is measured. It turns out that the potential solves an elliptic equation in divergence form with discontinuous leading coefficient. For this inverse problem we aim to establish a logarithmic type stability estimate. The key point in our analysis consists in reducing the original problem to that of determining an…
In this paper, we study inverse boundary problems associated with semilinear parabolic systems in several scenarios where both the nonlinearities and the initial data can be unknown. We establish several simultaneous recovery results showing that the passive or active boundary Dirichlet-to-Neumann operators can uniquely recover both of the unknowns, even stably in a certain case. It turns out that the nonlinearities play a critical role in deriving these recovery results. If the nonlinear term belongs to a general $C^1$ class but fulfilling a certain growth condition, the recovery results are …
Classical results of second order parabolic quasi-linear equations always require that the nonlinear terms are controlled by a power of the unknown functions and their first derivatives. We improve the previous results. More precisely, in the present article the upper bound of nonlinear term can be extended to a power series.
We deal with the problem of determining a time varying inclusion within a thermal conductor. In particular we study the continuous dependance of the inclusion from the Dirichlet-to-Neumann map. Under a priori regularity assumptions on the unknown defect we establish logarithmic stability estimates.
Conditional stability in determining source terms of semilinear parabolic partial differential equations
本文提出了一种非线性反源问题的条件Hölder稳定性方法，结合广义微分算子线性化和Carleman估计，用于确定半线性抛物型方程的源项。
A semilinear parabolic problem of second order with an unknown time-convolution kernel is considered. The missing kernel is recovered from an additional integral measurement. The existence, uniqueness and regularity of a weak solution is addressed. We design a numerical algorithm based on Rothe's method, derive a priori estimates and prove convergence of iterates towards the exact solution.
Let $u_t-u_{xx}=h(t)$ in $0\leq x \leq π, t\geq 0.$ Assume that $u(0,t)=v(t)$, $u(π,t)=0$, and $u(x,0)=g(t)$. The problem is: {\it what extra data determine the three unknown functions $\{h, v, g\}$ uniquely?}. This question is answered and an analytical method for recovery of the above three functions is proposed.
In this paper we will focus on a parabolic degenerate system with respect to unknown functions u and w on a bounded domain of the two-dimensional Euclidean space. This system appears as a mathematical model for some biological processes. Global existence and uniqueness of a nonnegative classical Hölder continuous solution are proved. The last part of the paper is devoted to the study of the asymptotic behavior of the solutions.
The paper study a possibility to recover a parabolic diffusion from its time-average when the values at the initial time are unknown. This problem can be reformulated as a new boundary value problem where a Cauchy condition is replaced by a prescribed time-average of the solution. It is shown that this new problem is well-posed in certain classes of solutions. The paper establishes existence, uniqueness, and a regularity of the solution for this new problem and its modifications, including problems with singled out terminal values.
Let $u_t-a(t)u_{xx}=f(x, t)$ in $0\leq x \leq π,\,\,t\geq 0.$ Assume that $u(0,t)=u_1(t)$, $u(π,t)=u_2(t)$, $u(x,0)=h(x)$, and the extra data $u_x(0,t)=g(t)$ are known. The inverse problem is: {\it How does one determine the unknown $a(t)$?} The function $a(t)>a_0>0$ is assumed continuous and bounded. This question is answered and a method for recovery of $a(t)$ is proposed. There are several papers in which sufficient conditions are given for the uniqueness and existence of $a(t)$, but apparently there was no method proposed for calculating of $a$. The method given in this paper for proving t…
Assigning boundary conditions, such as acoustic impedance, to the frequency domain thermoviscous wave equations (TWE), derived from the linearized Navier-Stokes equations (LNSE) poses a Helmholtz problem, solution to which yields a discrete set of complex eigenfunctions and eigenvalue pairs. The proposed method -- the inverse Helmholtz solver (iHS) -- reverses such procedure by returning the value of acoustic impedance at one or more unknown impedance boundaries (IBs) of a given domain, via spatial integration of the TWE for a given real-valued frequency with assigned conditions on other bound…
Stably Determining a generalised Impedance Obstacle from a Single Far-Field Pattern
本文提出了一种新的Artificial Test Domain框架，用于单测量逆散射问题，通过微局分析揭示了广义阻抗超平面排除机制和定性-定量原则，实现了对多面体障碍物的稳定性估计，并统一了现有单测量唯一性结果。
Reconstruction of the initial condition in parabolic equations with Log-Lipschitz coefficients
针对系数关于时间Log-Lipschitz连续、关于空间Lipschitz连续的抛物方程，结合条件稳定性结果与适定变分问题，实现了从终值粗糙测量数据出发的初值重构。
In this article we study an inverse problem for the space-time fractional parabolic operator $(\partial_t-Δ)^s+Q$ with $0<s<1$ in any space dimension. We uniquely determine the unknown bounded potential $Q$ from infinitely many exterior Dirichlet-to-Neumann type measurements. This relies on Runge approximation and the dual global weak unique continuation properties of the equation under consideration. In discussing weak unique continuation of our operator, a main feature of our argument relies on a Carleman estimate for the associated fractional parabolic Caffarelli-Silvestre extension. Furthe…
A time-dependent inverse source problem for a semilinear pseudo-parabolic equation with Neumann boundary condition
本文针对带Neumann边界条件的半线性伪抛物方程时变逆源问题，基于Rothe方法建立弱解存在唯一性，设计数值时间离散格式并证明收敛性，通过多项式正则化处理含噪数据，数值实验验证理论结果。
Well-posedness of parabolic KWC-systems with variable-dependent mobilities
本文通过改进解的正则性，建立了抛物型KWC系统的适定性理论。
We study systems of nonlinear partial differential equations of parabolic type, in which the elliptic operator is replaced by the first order divergence operator acting on a flux function, which is related to the spatial gradient of the unknown through an additional implicit equation. This setting, broad enough in terms of applications, significantly expands the paradigm of nonlinear parabolic problems. Formulating four conditions concerning the form of the implicit equation, we first show that these conditions describe a maximal monotone $p$-coercive graph. We then establish the global-in-tim…
We consider fully nonlinear obstacle-type problems of the form \begin{equation*} \begin{cases} F(D^{2}u,x)=f(x) & \text{a.e. in}B_{1}\capΩ,|D^{2}u|\le K & \text{a.e. in}B_{1}\backslashΩ, \end{cases} \end{equation*} where $Ω$ is an unknown open set and $K>0$. In particular, structural conditions on $F$ are presented which ensure that $W^{2,n}(B_1)$ solutions achieve the optimal $C^{1,1}(B_{1/2})$ regularity when $f$ is Hölder continuous. Moreover, if $f$ is positive on $\overline B_1$, Lipschitz continuous, and $\{u\neq 0\} \subset Ω$, then we obtain local $C^1$ regularity of the free boundary …
The one dimensional wave equation serves as a basic model for imaging modalities such as seismic which utilize acoustic data reflected back from a layered medium. In 1955 Peterson et al. described a single scattering approximation for the one dimensional wave equation that relates the reflection Green's function to acoustic impedance. The approximation is simple, fast to compute and has become a standard part of seismic theory. The present paper re-examines this classical approximation in light of new results concerning the (exact) measurement operator for reflection imaging of layered media, …
This paper studies asymptotic behavior of solutions of a free boundary problem modeling the growth of tumors with two species of cells: proliferating cells and quiecent cells. In previous literatures it has been proved that this problem has a unique stationary solution which is asymptotically stable in the limit case $\varepsilon=0$. In this paper we consider the more realistic case $0<\varepsilon<<1$. In this case, after suitable reduction the model takes the form of a coupled system of a parabolic equation and a hyperbolic system, so that it is more difficult than the limit case $\varepsilon…
In this paper we are concerned with the initial boundary value problems of linear and semi-linear parabolic equations with mixed boundary conditions on non-cylindrical domains in spatial-temporal space. We obtain the existence of a weak solution to the problem. In the case of the linear equation the parts for every type of boundary condition are any open subsets of the boundary being nonempty the part for Dirichlet condition at any time. Due to this it is difficult to reduce the problem to one on a cylindrical domain by diffeomorphism of the domain. By a transformation of unknown function and …
An Euler-type hyperbolic-parabolic system of chemotactic aggregation describing the vascular network formation is investigated in the critical regularity setting. For small initial data around a constant equilibrium state, the well-posedness of the global classical solution to the Cauchy problem with general pressure laws is established in homogeneous hybrid Besov spaces. Then, the optimal time-decay rates of the global solution are analyzed under an additional regularity assumption on the initial data. Furthermore, the relaxation limit (large friction limit) of the hyperbolic-parabolic system…
Identifying unknown time delay and spatially varying coefficients in a reaction-diffusion equation from boundary measurements
针对含多个延迟项的线性反应-扩散系统，利用边界通量测量和奇异时间行为，同时恢复未知时滞和空间变化系数，并建立Lipschitz稳定性估计，为首个此类结果。
We present an analytic approach to solve a degenerate parabolic problem associated to the Heston model, which is widely used in mathematical finance to derive the price of an European option on an risky asset with stochastic volatility. We give a variational formulation, involving weighted Sobolev spaces, of the second order degenerate elliptic operator of the parabolic PDE. We use this approach to prove, under appropriate assumptions on some involved unknown parameters, the existence and uniqueness of weak solutions to the parabolic problem on unbounded subdomains of the half-plane.
We study the behaviour of solutions to a class of nonlinear degenerate parabolic problems when the data are perturbed. The class includes the Richards equation, Stefan problem and the parabolic $p$-Laplace equation. We show that, up to a subsequence, weak solutions of the perturbed problem converge uniformly-in-time to weak solutions of the original problem as the perturbed data approach the original data. We do not assume uniqueness or additional regularity of the solution. However, when uniqueness is known, our result demonstrates that the weak solution is uniformly temporally stable to pert…
Boundary symmetry breaking via logistic damping in a chemotaxis-growth system
研究在1D领域内具有对数敏感性的趋化-生长模型的全局稳定性，分析抛物线-抛物线和抛物线-双曲线系统，通过引入动态参考轮廓处理时间依赖的边界数据，证明能量估计、解的有界性和扰动的全局渐进行为。
In this paper we consider the fully nonlinear parabolic free boundary problem $$ \left\{\begin{array}{ll} F(D^2u) -\partial_t u=1 & \text{a.e. in}Q_1 \cap Ω\\ |D^2 u| + |\partial_t u| \leq K & \text{a.e. in}Q_1\setminusΩ, \end{array} \right. $$ where $K>0$ is a positive constant, and $Ω$ is an (unknown) open set. Our main result is the optimal regularity for solutions to this problem: namely, we prove that $W_x^{2,n} \cap W_t^{1,n} $ solutions are locally $C_x^{1,1}\cap C_t^{0,1} $ inside $Q_1$. A key starting point for this result is a new BMO-type estimate which extends to the parabolic sett…
Rothe's method in direct and time-dependent inverse source problems for a semilinear pseudo-parabolic equation
本文利用罗特方法研究半线性伪抛物方程的反源问题，证明了解的存在性和唯一性，并提出数值方案验证其准确性与稳定性。
On quasilinear parabolic systems and FBSDEs of quadratic growth
本文使用概率方法为两类具有二次梯度增长的拟线性抛物PDE系统建立先验估计，证明了其经典解的存在性，并由此推断出相应前向-后向随机微分方程解的存在性。
Uniqueness in determining multidimensional domains with unknown initial data
本文研究了初始数据未知的线性抛物型系统的几何反问题，通过边界或内部观测结合半群理论等工具，证明了多维子区域判定的唯一性并推导出初始数据信息。
On behavior of free boundaries to generalized two-phase Stefan problems for parabolic partial differential equation systems
本文研究了广义双相Stefan问题中自由边界的行为，通过提升解的正则性，克服了自由边界增长速率依赖于水分含量以及水分含量边界条件包含温度的困难，建立了局部时间内的解的存在性和唯一性，并在某些初始数据符号条件下推导了解存在最大区间的结果。
Interpolation of missing electrode data in electrical impedance tomography
本文提出了一种新的插值方法，用于从更可靠的电流自由电极测量中预测电流驱动电极上的电压，以在差分电阻抗断层成像设置中恢复导电性变化。该方法利用导电性变化的上界，以与差分电阻抗断层成像数据的特殊几何光滑性一致的方式进行插值，且计算成本低，适合实时应用。
We consider elliptic operators with operator-valued coefficients and discuss the associated parabolic problems. The unknowns are functions with values in a Hilbert space $W$. The system is equipped with a general class of coupled boundary conditions of the form $f_{|\partialΩ}\in \mathcal Y$ and $\frac{\partial f}{\partial ν}\in {\mathcal Y}^\perp$, where $\mathcal Y$ is a closed subspace of $L^2(\partialΩ;W)$. We discuss well-posedness and further qualitative properties, systematically reducing features of the parabolic system to operator-theoretical properties of the orthogonal projection on…
The size estimates approach for Electrical Impedance Tomography (EIT) allows for estimating the size (area or volume) of an unknown inclusion in an electrical conductor by means of one pair of boundary measurements of voltage and current. In this paper we show by numerical simulations how to obtain such bounds for practical application of the method. The computations are carried out both in a 2D and a 3D setting.
Convexity for a parabolic fully nonlinear free boundary problem with singular term
本文针对带奇异项的外部区域抛物型完全非线性自由边界问题，在初始值适当条件下证明了非负拟凹解的存在性，并揭示其随时间单调非减的性质。
Inverse source problem for the parabolic equation with sparse moving observations
本文研究了通过稀疏边界测量反演抛物方程源项的问题，提出了一种基于移动传感器的数据定位方法，并通过数值实验验证了算法的有效性。
Lipschitz stability for an elliptic inverse problem with two measurements
本文研究通过包围区域边界上的测量值反演椭圆方程外部未知边界值的问题，在可容许函数类上证明了Lipschitz稳定性，并将结果推广到内部问题和抛物情形。
This paper deals with a semilinear parabolic system with free boundary in one space dimension. We suppose that unknown functions $u$ and $v$ undergo nonlinear reactions $u^q$ and $v^p$, and exist initially in a interval $\{0\leq x\leq s(0)\}$, but expand to the right with spreading front $\{x=s(t)\}$, with $s(t)$ evolving according to the free boundary condition $s'(t)=-μ(u_x+ρv_x)$, where $p,\, q,\, μ, \,ρ$ are given positive constants. The main purpose of this paper is to understand the existence, uniqueness, regularity and long time behavior of positive solution or maximal positive solution…
Regularization operators for identifying the unknown source in the time-fractional convection-diffusion-reaction equation
本文研究了基于噪声时间依赖测量在任意位置确定时间依赖源项的问题，采用傅里叶方法解析求解，发现解不稳定，提出三种正则化算子以克服不稳定性，并引入新的正则化参数选择规则和误差界。
Cancer Detection via Electrical Impedance Tomography and Optimal Control of Elliptic PDEs
本文提出利用 EIT 与椭圆型 PDE 约束最优控制早期检测癌症，通过排列电流-电压测量扩充数据，并用 GPM 反演电导率，显著提升肿瘤成像分辨率。
We consider a non-linear parabolic partial differential equation (PDE) on $\mathbb R^d$ with a distributional coefficient in the non-linear term. The distribution is an element of a Besov space with negative regularity and the non-linearity is of quadratic type in the gradient of the unknown. Under suitable conditions on the parameters we prove local existence and uniqueness of a mild solution to the PDE, and investigate properties like continuity with respect to the initial condition and blow-up times. We prove a global existence and uniqueness result assuming further properties on the non-li…
In this paper, we consider an inverse conductivity problem on a bounded domain $Ω\subset\mathbb{R}^n$, $n\geq2$, also known as Electrical Impedance Tomography (EIT), for the case where unknown impenetrable obstacles are embedded into $Ω$. We show that a piecewise-constant conductivity function and embedded obstacles can be simultaneously recovered in terms of the local Dirichlet-to-Neumann map defined on an arbitrary small open subset of the boundary of the domain $Ω$. The method depends on the well-posedness of a coupled PDE-system constructed for the conductivity equations in the $H^1$-space…
This paper considers the inverse problem of recovering both the unknown, spatially-dependent conductivity $a(x)$ and the nonlinear reaction term $f(u)$ in a reaction-diffusion equation from overposed data. These measurements can consist of: the value of two different solution measurements taken at a later time $T$; time-trace profiles from two solutions; or both final time and time-trace measurements from a single forwards solve data run. We prove both uniqueness results and the convergence of iteration schemes designed to recover these coefficients. The last section of the paper shows numeric…
We consider the inverse source problem in the parabolic equation, where the unknown source possesses the semi-discrete formulation. Theoretically, we prove that the flux data from any nonempty open subset of the boundary can uniquely determine the semi-discrete source. This means the observed area can be extremely small, and that is why we call the data as sparse boundary data. For the numerical reconstruction, we formulate the problem from the Bayesian sequential prediction perspective and conduct the numerical examples which estimate the space-time-dependent source state by state. To better …
We prove the well-posedness results, i.e. existence, uniqueness, and stability, of the solutions to a class of nonlocal fully nonlinear parabolic partial differential equations (PDEs), where there is an external time parameter $t$ on top of the temporal and spatial variables $(s,y)$ and thus the problem could be considered as a flow of equations. The nonlocality comes from the dependence on the unknown function and its first- and second-order derivatives evaluated at not only the local point $(t,s,y)$ but also at the diagonal line of the time domain $(s,s,y)$. Such equations arise from time-in…
A Geometric Inverse Source Problem for Stochastic Parabolic Equations
本文针对随机抛物方程，提出形状梯度重建方法，通过部分边界通量测量首次同时恢复漂移项和扩散项中的两个未知源支撑，数值实验验证了其区分源通道的有效性。
Reconstruction in the Calderón problem on a fixed partition from finite and partial boundary data
本文改进了Calderón问题中从有限和部分边界数据重建分段常数电导率的方法，无需层状假设和电导率边界限制。
Well-posedness and numerical reconstruction of a source term for linear parabolic problems with an integral constraint
该研究针对带积分约束的线性抛物型方程源项识别问题，建立解对的适定性，开发结合有限元与隐式时间步长的数值算法，采用导数罚项Tikhonov正则化等实现准确鲁棒的源项重建。
We present a general framework to study uniqueness, stability and reconstruction for infinite-dimensional inverse problems when only a finite-dimensional approximation of the measurements is available. For a large class of inverse problems satisfying Lipschitz stability we show that the same estimate holds even with a finite number of measurements. We also derive a globally convergent reconstruction algorithm based on the Landweber iteration. This theory applies to nonlinear ill-posed problems such as electrical impedance tomography, inverse scattering and quantitative photoacoustic tomography…
Uniqueness and regularization for unknown spacewise lower-order coefficient and source for the heat type equation
本文通过伴随问题的密度性质给出了抛物型偏微分方程中未知空间系数和热源同时唯一识别的充分条件，并采用非线性Landweber迭代与迭代Tikhonov正则化耦合方法获得近似解序列，证明了参数到解映射的稳定性和收敛性，最后应用于热成像肿瘤区域识别。
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