Linear Dynamical Systems.- Semigroups, Generators, and Resolvents.- Perturbation and Approximation of Semigroups.- Spectral Theory for Semigroups and Generators.- Asymptotics of Semigroups.- Semigroups Everywhere.- A Brief History of the Exponential Function.

https://www.springer.com/productFlyer_978-0-387-98463-6.pdf?SGWID=0-0-1297-1590487-0

One-Parameter Semigroups for Linear Evolution Equations

Fractional Differential Equations

关于Semigroups of Linear Operators and Applications to Partial Differential Equations的两个注解

A criterion is given for the convergence of numerical solutions of the Navier-Stokes equations in two dimensions under steady conditions. The criterion applies to all cases, of steady viscous flow in two dimensions and shows that if the local ' mesh Reynolds number ', based on the size of the mesh used in the solution, exceeds a certain fixed value, the numerical solution will not converge.

On the Navier-Stokes equations

The evolution of the state of many systems modeled by linear partial diﬁerentialequations (PDEs) or linear delay-diﬁerential equations can be described by operatorsemigroups. The state of such a system is an element in an inﬂnite-dimensionalnormed space, whence the name \inﬂnite-dimensional linear system".The study of operator semigroups is a mature area of functional analysis, which isstill very active. The study of observation and control operators for such semigroupsis relatively more recent. These operators are needed to model the interactionof a system with the surrounding world via outputs or inputs. The main topicsof interest about observation and control operators are admissibility, observability,controllability, stabilizability and detectability. Observation and control operatorsare an essential ingredient of well-posed linear systems (or more generally systemnodes). Inthisbookwedealonlywithadmissibility, observabilityandcontrollability.We deal only with operator semigroups acting on Hilbert spaces.This book is meant to be an elementary introduction into the topics mentionedabove. By \elementary" we mean that we assume no prior knowledge of ﬂnite-dimensional control theory, and no prior knowledge of operator semigroups or ofunbounded operators. We introduce everything needed from these areas. We doassume that the reader has a basic understanding of bounded operators on Hilbertspaces, diﬁerential equations, Fourier and Laplace transforms, distributions andSobolev spaces on

Observation and Control for Operator Semigroups

We consider a system with a suitable boundary condition, where is a bounded domain, is a uniformly elliptic operator of the second order whose coefficients are suitably regular for , is fixed, and a function satisfies Our inverse problems are determinations of g using overdetermining data or , where and . Our main result is the Lipschitz stability in these inverse problems. We also consider the determination of , in the case of with given R satisfying on . Finally, we discuss an upper estimation of our overdetermining data by means of f.

https://iopscience.iop.org/article/10.1088/0266-5611/14/5/009/pdf

Lipschitz stability in inverse parabolic problems by the Carleman estimate

For the solution u(p) = u(p)(x,t) to ∂t2u(x,t)-Δu(x,t)-p(x)u(x,t) = 0 in Ω×(0,T) and (∂u/∂ν)|∂Ω×(0,T) = 0 with given u(,0) and ∂tu(,0), we consider an inverse problem of determining p(x), xΩ, from data u|ω×(0,T). Here Ω⊂n, n = 1,2,3, is a bounded domain, ω is a sub-domain of Ω and T>0. For suitable ω⊂Ω and T>0, we prove an upper and lower estimate of Lipschitz type between ||p-q||L2(Ω) and ||∂t(u(p)-u(q))||L2(ω×(0,T)) + ||∂t2(u(p)-u(q))||L2(ω×(0,T)).

https://iopscience.iop.org/article/10.1088/0266-5611/17/4/310/pdf

Global Lipschitz stability in an inverse hyperbolic problem by interior observations

We consider a backward problem in time for a time-fractional partial differential equation in one-dimensional case, which describes the diffusion process in porous media related with the continuous time random walk problem. Such a backward problem is of practically great importance because we often do not know the initial density of substance, but we can observe the density at a positive moment. The backward problem is ill-posed and we propose a regularizing scheme by the quasi-reversibility with fully theoretical analysis and test its numerical performance. With the help of the memory effect of the fractional derivative, it is found that the property of the initial status of the medium can be recovered in an efficient way. Since our solution is established on the eigenfunction expansion of elliptic operator, the method proposed in this article can be used to higher dimensional case with variable coefficients.

A backward problem for the time-fractional diffusion equation

We consider an inverse problem of determining p(x), x ∈ Ω in (∂2 u/∂t 2)(x, t) − Δu(x, t) − p(x)u(x, t) = 0 in Ω × (0, T) and (∂u/∂ν)|∂Ω×(0, T) = 0 with given u(·, 0) and (∂u/∂t)(·, 0). Here Ω ⊂ R n , n = 1, 2, 3, is a bounded domain. We prove the Lipschitz stability in determining p from u|∂Ω×(0,T), under the assumption that T is greater than the diameter of Ω and u(·,0) > 0 on . Our stability holds over Ω without any knowledge of boundary values of p. The proof is based on the Carleman estimate.

Global uniqueness and stability in determining coefficients of wave equations

We prove for a two dimensional bounded domain that the Cauchy data for the Schrodinger equation measured on an arbitrary open subset of the boundary determines uniquely the potential. This implies, for the conductivity equation, that if we measure the current fluxes at the boundary on an arbitrary open subset of the boundary produced by voltage potentials supported in the same subset, we can determine uniquely the conductivity. We use Carleman estimates with degenerate weight functions to construct appropriate complex geometrical optics solutions to prove the results.

/pdf/the-calderon-problem-with-partial-data-in-two-dimensions-2asgumji61.pdf

Masahiro Yamamoto

Papers

Lipschitz stability in inverse parabolic problems by the Carleman estimate

Global Lipschitz stability in an inverse hyperbolic problem by interior observations

A backward problem for the time-fractional diffusion equation

Global uniqueness and stability in determining coefficients of wave equations

The Calderón problem with partial data in two dimensions