HaiGang Li, YanYan Li, ZhuoLun Yang
In the perfect conductivity problem of composite material, the gradient of solutions can be arbitrarily large when two inclusions are located very close. To characterize the singular behavior of the gradient in the narrow region between two inclusions, we capture the leading term of the gradient and give a fairly sharp description of such asymptotics.
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In this paper, we study the perfect and the insulated conductivity problems with multiple inclusions imbedded in a bounded domain in $\mathbb{R}^n, n\ge 2$. For these two extreme cases of the conductivity problems, the gradients of their solutions may blow up as two inclusions approach each other. We establish the gradient estimates for the perfect conductivity problems and an upper bound of the gradients for the insulated conductivity problems in terms of the distances between any two closely spaced inclusions.
We study the perfect conductivity problem when two perfectly conducting inclusions are closely located to each other in an anisotropic background medium. We establish optimal upper and lower gradient bounds for the solution in any dimension which characterize the singular behavior of the electric field as the distance between the inclusions goes to zero.
The insulated and perfect conductivity problems arising from high-contrast composite materials are considered in all dimensions. The solution and its gradient, respectively, represent the electric potential and field. The novelty of this paper lies in finding exact solutions for the insulated and perfect conductivity problems with concentric balls. Our results show that there appears no electric field concentration for the insulated conductivity problem, while the electric field for the perfect conductivity problem exhibits sharp singularity with respect to the small distance between interfaci…
Gradient Estimates for the Perfect Conductivity Problem
本文研究具有密界面的理想电导率问题解的最优梯度估计。问题来自复合材料。我们的估计表现出不同的吹胀率的梯度，夹杂物之间的距离为零，在尺寸n=2，n=3和n \ge 4，这变得更高的尺寸增加。
Asymptotics of the solution to the perfect conductivity problem with $p$-Laplacian
研究具有 $p$-Laplacian 的完美导电问题中紧密排列导体间解梯度的奇异行为，首次捕获了非线性问题中梯度的首阶渐近项。
We consider the problem of recovering an isotropic conductivity outside some perfectly conducting or insulating inclusions from the interior measurement of the magnitude of one current density field $|J|$. We prove that the conductivity outside the inclusions, and the shape and position of the perfectly conducting and insulating inclusions are uniquely determined (except in an exceptional case) by the magnitude of the current generated by imposing a given boundary voltage. We have found an extension of the notion of admissibility to the case of possible presence of perfectly conducting and ins…
In the perfect conductivity problem of composite material, the electric field concentrates in a narrow region in between two inclusions and always becomes arbitrarily large when the distance between inclusions tends to zero. To characterize such singular behavior, we capture the leading term of the gradient and reveal that the blow-up rates are determined by their relative convexity of the two adjacent inclusions. On the other hand, a blow-up factor, which is a linear functional of boundary data, is found to determine the blow-up will occur or not.
We study the stress concentration, which is the gradient of the solution, when two smooth inclusions are closely located in a possibly anisotropic medium. The governing equation may be degenerate of $p-$Laplace type, with $1<p \leq N$. We prove optimal $L^\infty$ estimates for the blow-up of the gradient of the solution as the distance between the inclusions tends to zero.
In the perfect conductivity problem, it is interesting to study whether the electric field can become arbitrarily large or not, in a narrow region between two adjacent perfectly conducting inclusions. In this paper, we show that the relative convexity of two adjacent inclusions plays a key role in the blowup analysis of the electric field and find some new phenomena. By energy method, we prove the boundedness of the gradient of the solution if two adjacent inclusions fail to be locally relatively strictly convex, namely, if the top and bottom boundaries of the narrow region are partially "flat…
The perfect conductivity problem with arbitrary vanishing orders and non-trivial topology
本文研究完全电导率问题，推广Bao-Li-Yin的梯度估计以处理任意零化阶边界和非平凡拓扑的狭窄区域，并证明了估计关于导体间距的尖锐性。
In composite materials, the inclusions are frequently spaced very closely. The electric field concentrated in the narrow regions between two adjacent perfectly conducting inclusions will always become arbitrarily large. In this paper, we establish an asymptotic formula of the electric field in the zone between two spherical inclusions with different radii in three dimensions. An explicit blowup factor relying on radii is obtained, which also involves the digamma function and Euler-Mascheroni constant, and so the role of inclusions' radii played in such blowup analysis is identified.
Gradient estimates for the $p$-Laplacian perfect conductivity problem with partially flat and $C^{1,γ}$ inclusions
本文研究了$p$-Laplacian完美导电问题中部分平坦和$C^{1,γ}$包含体的梯度估计，证明了梯度有界性并给出了最优发散速率。
When a convex perfectly conducting inclusion is closely spaced to the boundary of the matrix domain, a bigger convex domain containing the inclusion, the electric field can be arbitrary large. We establish both the pointwise upper bound and the lower bound of the gradient estimate for this perfect conductivity problem by using the energy method. These results give the optimal blow-up rates of electric field for conductors with arbitrary shape and in all dimensions. A particular case when a circular inclusion is close to the boundary of a circular matrix domain in dimension two is studied earli…
We consider a large number of randomly dispersed spherical, identical, perfectly conducting inclusions (of infinite conductivity) in a bounded domain. The host medium's conductivity is finite and can be inhomogeneous. In the dilute limit, with some boundedness assumption on a large number (proportional to the global volume fraction raised to the power of -1/2) of marginal probability densities, we prove convergence in H^1 norm of the expectation of the solution of the steady state heat equation, to the solution of an effective medium problem, where the conductivity is given by the Clausius-Mos…
In high-contrast composite materials, the electric field concentration is a common phenomenon when two inclusions are close to touch. It is important from an engineering point of view to study the dependence of the electric field on the distance between two adjacent inclusions. In this paper, we derive the upper and lower bounds of the gradient of solutions to the conductivity problem where two perfectly conducting inclusions are located very close to each other. To be specific, we extend the known results of Bao-Li-Yin (ARMA 2009) in two folds: First, we weaken the smoothness of the inclusion…
When inclusions with extreme conductivity (insulator or perfect conductor) are closely located, the gradient of the solution to the conductivity equation can be arbitrarily large. And computation of the gradient is extremely challenging due to its nature of blow-up in a narrow region in between inclusions. In this paper we characterize explicitly the singular term of the solution when two circular inclusions with extreme conductivities are adjacent. Moreover, we show through numerical computations that the characterization of the singular term can be used efficiently for computation of the gra…
We consider the one-dimensional compressible Navier-Stokes system with constant viscosity and the nonlinear heat conductivity being proportional to a positive power of the temperature which may be degenerate. This problem is imposed on the stress-free boundary condition, which reveals the motion of a viscous heat-conducting perfect polytropic gas with adiabatic ends putting into a vacuum. We prove that the solution of one dimensional compressible Navier-Stokes system with the stress-free boundary condition shares the same large-time behavior as the case of constant heat conductivity.
Optimal gradient estimates for conductivity problems with imperfect low-conductivity interfaces
本文研究了由Robin边界条件建模的几乎接触导体间不完美低电导率界面的场集中问题，建立了显式依赖于界面参数$γ$和分离距离$\varepsilon$的最优逐点梯度估计，统一了梯度有界与奇异爆破情形，并提供了完整连续的刻画。
Reconstruction of cracks in Calderón's inverse conductivity problem using energy comparisons
针对Calderón反电导率问题中的Lipschitz超曲面型裂纹，提出两种重构方法：一种可通过算子不等式收缩上界得到精确位置，能同时处理两类裂纹；另一种针对单一类型裂纹生成保证为未知裂纹子集的近似结果，填补了相关严格重构方法的空白。
We study the insulated conductivity problem with inclusions embedded in a bounded domain in $\mathbb R^n$, for $n \ge 3$. The gradient of solutions may blow up as $\varepsilon$, the distance between inclusions, approaches to $0$. We established in a recent paper optimal gradient estimates for a class of inclusions including balls. In this paper, we prove such gradient estimates for general strictly convex inclusions. Unlike the perfect conductivity problem, the estimates depend on the principal curvatures of the inclusions, and we show that these estimates are characterized by the first non-ze…
Large-Time Behavior of Solutions to Compressible Navier-Stokes System in Unbounded Domains with Degenerate Heat-Conductivity and Large Data
研究无界域中具有退化热传导的可压缩Navier-Stokes系统大初始数据解的大时间行为，证明比容和温度有界且全局解渐近稳定。
The multifrequency electrical impedance tomography is considered in order to image a conductivity inclusion inside a homogeneous background medium by injecting one current. An original spectral decomposition of the solution of the forward conductivity problem is used to retrieve the Cauchy data corresponding to the extreme case of perfect conductor. Using results based on the unique continuation we then prove the uniqueness of multifrequency electrical impedance tomography and obtain rigorous stability estimates. Our results in this paper are quite surprising in inverse conductivity problem si…
In this paper, we present a high-order expansion for elliptic equations in high-contrast media. The background conductivity is taken to be one and we assume the medium contains high (or low) conductivity inclusions. We derive an asymptotic expansion with respect to the contrast and provide a procedure to compute the terms in the expansion. The computation of the expansion does not depend on the contrast which is important for simulations. The latter allows avoiding increased mesh resolution around high conductivity features. This work is partly motivated by our earlier work in \cite{ge09_1} wh…
On the singular layer for the 1-D steady Euler system with heat conductivity in a finite nozzle as the heat conduction coefficient vanishes
本文研究有限喷管中带热传导的一维稳态Euler系统在热传导系数趋于零时的奇异极限，建立了热传导解的存在性，发现端点边界层，按入口状态和出口压力将解分类为纯超声速、纯亚声速和跨声速解，并推导了边界层方程。
We study a two dimensional collision problem for a rigid solid immersed in a cavity filled with a perfect fluid. We are led to investigate the asymptotic behavior of the Dirichlet energy associated to the solution of a Laplace Neumann problem as the distance $\varepsilon>0$ between the solid and the cavity's bottom tends to zero. Denoting by $α>0$ the tangency exponent at the contact point, we prove that the solid always reaches the cavity in finite time, but with a non zero velocity for $α<2$ (real shock case), and with null velocity for $α\geqslant 2$ (smooth landing case). Our proof is base…
We present a procedure for recovering the conformal factor of an anisotropic conductivity matrix in a known conformal class in a domain in Euclidean space of dimension greater than or equal to 2. The method requires one internal measurement, together with a priori knowledge of the conformal class (local orientation) of the conductivity matrix. This problem arises in the coupled-physics medical imaging modality of Current Density Impedance Imaging (CDII) and the assumptions on the data are suitable for measurements determinable from cross-property based couplings of the two imaging modalities C…
We study the well-posedness and the spatial behavior at infinity of perfect fluid flows on $\R^d$ with initial data in a scale of weighted Sobolev spaces that allow spatial growth/decay at infinity as $|x|^β$ with $β<1/2$. In particular, we show that the solution of the Euler equation generically develops an asymptotic expansion at infinity with non-vanishing asymptotic terms that depend analytically on time and the initial data. We identify the evolution space for initial data in the Schwartz class with a certain space of symbols.
The conductivity problem with imperfect bonding interfaces and finite internal conductivities
本文研究有限电导率夹杂物间不完美粘接界面导致的场集中，揭示梯度爆破依赖于粘接参数γ，并确定阈值、最优爆破速率及临界值处的对数爆破现象。
On Outer Pressure Problem of Compressible Navier-Stokes System with Degenerate Heat-Conductivity in Unbounded Domains
针对一维无界区域中带退化热传导的可压缩Navier-Stokes系统外压问题，证明比容和温度的时空上下界后得到强解整体存在性，并建立其时间无穷时的渐近稳定性。
An inverse problem for a stationary heat transfer process is studied for a totally isolated bar on its lateral surface, made up of two consecutive sections of different, isotropic and homogeneous materials, perfectly assembly, where one of the materials, that is unreachable and unknown, has to be identified. The length of the bar is assumed to be much greater that the diameter so that a 1D heat transfer process is considered. A constant temperature is assumed at the end of the unknown part of the rod while the other end is let free for convection. We propose a procedure to identify the unknown…
Gradient estimates for the conductivity problem with imperfect bonding interfaces
本文研究具有不完美键合界面的电导率问题中的场集中现象，发现梯度有界性依赖于键合参数，并确定了阈值与最优爆破速率，提出了适用于多种椭圆方程的通用估计框架。
In the perfect conductivity problem of composites, the electric field may become arbitrarily large as $\varepsilon$, the distance between the inclusions and the matrix boundary, tends to zero. The main contribution of this paper lies in developing a clear and concise procedure to establish a boundary asymptotic formula of the concentration for perfect conductors with arbitrary shape in all dimensions, which explicitly exhibits the singularities of the blow-up factor $Q[φ]$ introduced in [29] by picking the boundary data $φ$ of $k$-order growth. In particular, the smoothness of inclusions requi…
Asymptotic analysis and design of shell-based thermal lattice metamaterials
本文提出了一个严格的渐近分析框架，通过引入渐近方向热导率（ADC）指标，研究了壳晶格超材料在厚度趋于零时的热导率，并开发了离散优化算法，为三周期极小曲面的最优热导率提供了首个理论证明。
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