Morteza Fotouhi

Morteza Fotouhi
Sharif University of Technology | SHARIF · Department of Mathematical Science

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22
Publications
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88
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Publications

Publications (22)
Article
Full-text available
In this paper we study the following parabolic system $$\begin{aligned} \Delta \mathbf{u }-\partial _t \mathbf{u }=|\mathbf{u }|^{q-1}\mathbf{u }\,\chi _{\{ |\mathbf{u }|>0 \}}, \qquad \mathbf{u }= (u^1, \cdots , u^m) \ , \end{aligned}$$ Δ u - ∂ t u = | u | q - 1 u χ { | u | > 0 } , u = ( u 1 , ⋯ , u m ) , with free boundary $$\partial \{|\mathbf{u...
Article
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This work is devoted to study a class of singular perturbed elliptic systems and their singular limit to a phase segregating system. We prove existence and uniqueness and study the asymptotic behavior of limiting problem as the interaction rate tends to infinity. The limiting problem is a free boundary problem such that at each point in the domain...
Preprint
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In this paper we study the following parabolic system \begin{equation*} \Delta \u -\partial_t \u =|\u|^{q-1}\u\,\chi_{\{ |\u|>0 \}}, \qquad \u = (u^1, \cdots , u^m) \ , \end{equation*} with free boundary $\partial \{|\u | >0\}$. For $0\leq q<1$, we prove optimal growth rate for solutions $\u $ to the above system near free boundary points, and show...
Article
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We study solutions and the free boundary ∂{|u|>0} of the sublinear systemΔu=λ+(x)|u+|q−1u+−λ−(x)|u−|q−1u−, from a regularity point of view. For λ±(x)>0 and Hölder, and 0<q<1, we apply the epiperimetric inequality approach and show C1,β-regularity for the free boundary at asymptotically flat points.
Article
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The purpose of this note is to present a “new” approach to the decay rate of the solutions to the no-sign obstacle problem from the free boundary, based on Weiss-monotonicity formula. In presenting the approach we have chosen to treat a problem which is not touched earlier in the existing literature. Although earlier techniques may still work for t...
Article
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We consider the homogenization of a Robin boundary value problem in a locally periodic perforated domain which is also time-dependent. We aim at justifying the homogenization limit, that we derive through asymptotic expansion technique. More exactly, we obtain the so-called corrector homogenization estimate that specifies the convergence rate. The...
Article
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We study existence, structure, uniqueness and regularity of solutions of the obstacle problem infu∈BVf(Ω)∫Ωϕ(x,Du),where BVf(Ω)={u∈BV(Rn):u≥ψinΩandu|∂Ω=f|∂Ω}, f∈W01,1(Rn), ψ is the obstacle, and ϕ(x,ξ) is a convex, continuous and homogeneous function of degree one with respect to the ξ variable. We show that every minimizer of this problem is also...
Preprint
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We study existence, structure, uniqueness and regularity of solutions of the obstacle problem \begin{equation*} \inf_{u\in BV_f(\Omega)}\int_{\mathbb{R}^n}\phi(x,Du), \end{equation*} where $BV_f(\Omega)=\{u\in BV(\Omega): u\geq \psi \text{ in }\Omega\text{ and } u|_{\partial \Omega}=f|_{\partial \Omega}\}$, $f \in W^{1,1}_0(\mathbb{R}^n)$, $\psi$ i...
Article
Let Ω = R ² \ B(0 , 1) ¯ be the exterior of the closed unit ball. We prove the existence of extremal constant-sign solutions as well as sign-changing solutions of the following boundary value problem -Δu=a(x)f(u)inΩ,u=0on∂Ω=∂B(0,1),where the nonnegative coefficient a satisfies a certain integrability condition. We are looking for solutions in the s...
Article
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We study the regularity of solutions of the following semilinear problem $$\Delta u=-\lambda_+(x) (u^+)^{q}+\lambda_- (x) (u^-)^{q} \qquad \hbox{in } \ B_1,$$ where $B_1$ is the unit ball in $\bR^n$, $0<q<1 $ and $\lambda_\pm$ satisfy a H\"older continuity condition. Our main results concern local regularity analysis of solutions and their nodal s...
Article
We study the seminilinear problem $$\Delta u=\lambda_+(x) (u^+)^{q-1}-\lambda_- (x) (u^-)^{q-1} \qquad \hbox{in } \ B_1,$$ from a regularity point of view for solutions and the free boundary $\partial\{\pm u>0\}$. Here $B_1$ is the unit ball, $1< q<2 $ and $\lambda_\pm$ are Lipschitz. Our main results concern local regularity analysis of solution...
Article
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The purpose of this paper is to address the question of well-posedness and spectral controllability of the wave equation perturbed by potential on networks which may contain unbounded potentials in the external edges. It has been shown before that in the absence of any potential, there exists an optimal time T∗ (which turns out to be simply twice t...
Article
We present a universal model of brain tissue microstructure that dynamically links osmosis and diffusion with geometrical parameters of brain extracellular space (ECS). Our model robustly describes and predicts the nonlinear time dependency of tortuosity (?=D/D*) changes with very high precision in various media with uniform and nonuniform osmolari...
Article
As long as the size of the embedded scatterer in comparison to the internal length scale of its surrounding elastic matrix is large, then the linear sampling method (LSM) and singular sources method (SSM) can be used in conjunction with classical theory of elasticity to reconstruct the size of the scatterer with reasonable accuracy. On the other ha...
Article
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We introduce an extension of the classical neural field equation where the dynamics of the synaptic kernel satisfies the standard Hebbian type of learning (synaptic plasticity). Here, a continuous network in which changes in the weight kernel occurs in a specified time window is considered. A novelty of this model is that it admits synaptic weight...
Article
The purpose of this paper is to provide a full analysis of the null controllability problem for the one dimensional degenerate/singular parabolic equation u t − (a(x)u x) x − λ x β u = 0, (t, x) ∈ (0, T) × (0, 1), where the diffusion coefficient a(·) is degenerate at x = 0. Also the boundary conditions are considered to be Dirichlet or Neumann type...
Article
The purpose of this paper is to provide a full analysis of the null controllability problem for the one dimensional degenerate/singular parabolic equation $ {u_t} - {\left( {a(x){u_x}} \right)_x} - \frac{\lambda }{{{x^\beta }}}u = 0 $ , (t, x) ∈ (0, T) × (0, 1), where the diffusion coefficient a(∙) is degenerate at x = 0. Also the boundary condit...
Article
Full-text available
We introduce a modified-firing-rate model based on Hebbian-type changing synaptic connections. The existence and stability of solutions such as rest state, bumps, and traveling waves are shown for this type of model. Three types of kernels, namely exponential, Mexican hat, and periodic synaptic connections, are considered. In the former two cases,...
Article
The singular sources method is given to detect the shape of a thin infinitely cylindrical obstacle from a knowledge of the TM-polarized scattered electromagnetic field in large distance. The basic idea is based on the singular behaviour of the scattered field of the incident point source on the cross-section of the cylinder. We assume that the scat...
Article
We use the singular sources method to detect the shape of the obstacle in a mixed boundary value problem. The basic idea of the method is based on the singular behavior of the scattered field of the incident point-sources on the boundary of the obstacle. Moreover we take advantage of the scattered field estimate by the backprojection operator. Also...
Article
In this paper, we use Conley index theory to examine the Poincare index of an isolated invariant set. We obtain some limiting conditions on a critical point of a planar vector field to be an isolated invariant set. As a result we show the existence of infinitely many homoclinic orbits for a critical point with the Poincare index greater than one.

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