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Given a dissipative operator $A$ on a complex Hilbert space $mathcal{H}$ such that the quadratic form $fmapsto mbox{Im}langle f,Afrangle$ is closable, we give a necessary and sufficient condition for an extension of $A$ to still be dissipative. As applications, we describe all maximally accretive extensions of strictly positive symmetric operators and all maximally dissipative extensions of a highly singular first-order operator on the interval.
Let $A$ and $(-widetilde{A})$ be dissipative operators on a Hilbert space $mathcal{H}$ and let $(A,widetilde{A})$ form a dual pair, i.e. $Asubsetwidetilde{A}^*$, resp. $widetilde{A}subset A^*$. We present a method of determining the proper dissipativ
In our article [15] description in terms of abstract boundary conditions of all $m$-accretive extensions and their resolvents of a closed densely defined sectorial operator $S$ have been obtained. In particular, if ${mathcal{H},Gamma}$ is a boundary
Let $x_0$ be a possibly-unbounded self-adjoint random variable, $tildesigma_alpha$ and $sigma_beta$ are semicircular variables with variances $alphageq 0$ and $beta>0$ respectively (when $alpha = 0$, $tildesigma_alpha = 0$). Suppose $x_0$, $sigma_alp
We investigate minimal operator corresponding to operator differential expression with exit from space, study its selfadjoint extensions, also for one particular selfadjoint extension corresponding to boundary value problem with some rational functio
Building on techniques developed by Cowen and Gallardo-Guti{e}rrez, we find a concrete formula for the adjoint of a composition operator with rational symbol acting on the Hardy space $H^{2}$. We consider some specific examples, comparing our formula with several results that were previously known.