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In this paper, we study the nonstationary Stokes equation with Neumann boundary condition in a bounded or an exterior domain in ℝⁿ, which is the linearized model problem of the free boundary value problem. Mainly, we prove estimates for the semigroup of the Stokes operator. Comparing with the non-slip boundary condition case, we have the better decay estimate for the gradient of the semigroup in the exterior domain case because of the null force at the boundary.
The Yosida approximation is treated as an inversion formula for the Laplace transform.
Given a family of (W) contractions on a reflexive Banach space X we discuss unrestricted sequences . We show that they converge weakly to a common fixed point, which depends only on x and not on the order of the operators if and only if the weak operator closed semigroups generated by are right amenable.
Soit un espace localement compact. Tout opérateur dissipatif de domaine dense dans est limite d’opérateurs dissipatifs bornés. Ce résultat permet, dans le cas où est un espace homogène, de démontrer que tout opérateur dissipatif, de domaine dense et invariant sur se prolonge en le générateur infinitésimal d’un semi-groupe à contraction invariant sur .À tout opérateur vérifiant le principe du maximum positif sur et de domaine assez riche, on associe un opérateur bilinéaire , appelé...
In questo lavoro, motivati dalla teoria di Fredholm in spazi di Banach e dalla cosiddetta teoria degli ideali di operatori nel senso di Pietsch, viene definito un nuovo concetto di semigruppo di operatori. Questa nuova definizione include quella di molte classi di operatori già studiate in letteratura, come la classe degli operatori di semi-Fredholm, quella degli operatori tauberiani ed altre ancora. Inoltre permette un nuovo ed unificante approccio ad una serie di problemi in teoria degli operatori...
We study several aspects of a generalized Perron-Frobenius and Krein-Rutman theorems concerning spectral properties of a (possibly unbounded) linear operator on a cone in a Banach space. The operator is subject to the so-called tangency or weak range assumptions implying the resolvent invariance of the cone. The further assumptions rely on relations between the spectral and essential spectral bounds of the operator. In general we do not assume that the cone induces the Banach lattice structure into...
On obtient un théorème général concernant la perturbation multiplicative par un opérateur (linéaire borné, mais pas forcément d’inverse borné), du générateur d’un semi-groupe fortement continu sur un espace de Banach. On en déduit un résultat intimement lié au changement de temps dans les processus de Markov, qui étend un théorème de Dorroh (et résout par l’affirmative la seule situation qui restait en doute dans le contexte du théorème de Dorroh cité). Comme exemple d’autres possibilités d’application,...
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