651 research outputs found
Conditional stability of unstable viscous shocks
Continuing a line of investigation initiated by Texier and Zumbrun on
dynamics of viscous shock and detonation waves, we show that a linearly
unstable Lax-type viscous shock solution of a semilinear strictly parabolic
system of conservation laws possesses a translation-invariant center stable
manifold within which it is nonlinearly orbitally stable with respect to small
perturbatoins, converging time-asymptotically to a translate of
the unperturbed wave. That is, for a shock with unstable eigenvalues, we
establish conditional stability on a codimension- manifold of initial data,
with sharp rates of decay in all . For , we recover the result of
unconditional stability obtained by Howard, Mascia, and Zumbrun
Hyperbolic Relaxation of Reaction Diffusion Equations with Dynamic Boundary Conditions
Under consideration is the hyperbolic relaxation of a semilinear
reaction-diffusion equation on a bounded domain, subject to a dynamic boundary
condition. We also consider the limit parabolic problem with the same dynamic
boundary condition. Each problem is well-posed in a suitable phase space where
the global weak solutions generate a Lipschitz continuous semiflow which admits
a bounded absorbing set. We prove the existence of a family of global
attractors of optimal regularity. After fitting both problems into a common
framework, a proof of the upper-semicontinuity of the family of global
attractors is given as the relaxation parameter goes to zero. Finally, we also
establish the existence of exponential attractors.Comment: to appear in Quarterly of Applied Mathematic
Mild solutions of semilinear elliptic equations in Hilbert spaces
This paper extends the theory of regular solutions ( in a suitable
sense) for a class of semilinear elliptic equations in Hilbert spaces. The
notion of regularity is based on the concept of -derivative, which is
introduced and discussed. A result of existence and uniqueness of solutions is
stated and proved under the assumption that the transition semigroup associated
to the linear part of the equation has a smoothing property, that is, it maps
continuous functions into -differentiable ones. The validity of this
smoothing assumption is fully discussed for the case of the Ornstein-Uhlenbeck
transition semigroup and for the case of invertible diffusion coefficient
covering cases not previously addressed by the literature. It is shown that the
results apply to Hamilton-Jacobi-Bellman (HJB) equations associated to infinite
horizon optimal stochastic control problems in infinite dimension and that, in
particular, they cover examples of optimal boundary control of the heat
equation that were not treatable with the approaches developed in the
literature up to now
A unified framework for parabolic equations with mixed boundary conditions and diffusion on interfaces
In this paper we consider scalar parabolic equations in a general non-smooth
setting with emphasis on mixed interface and boundary conditions. In
particular, we allow for dynamics and diffusion on a Lipschitz interface and on
the boundary, where diffusion coefficients are only assumed to be bounded,
measurable and positive semidefinite. In the bulk, we additionally take into
account diffusion coefficients which may degenerate towards a Lipschitz
surface. For this problem class, we introduce a unified functional analytic
framework based on sesquilinear forms and show maximal regularity for the
corresponding abstract Cauchy problem.Comment: 27 pages, 4 figure
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