This paper is devoted to studying the effects of a vanishing structural damping on the controllability properties of the one dimensional linear beam equation. The vanishing term depends on a small parameter $\epsilon \in (0,1)$. We study the boundary controllability properties of this perturbed equation and the behavior of its boundary controls $v_{\epsilon }$ as $\epsilon$ goes to zero. It is shown that for any time $T$ sufficiently large but independent of $\epsilon$ and for each initial data in a suitable space there exists a uniformly bounded...

This article considers the linear 1-d Schrödinger equation in (0,π) perturbed by a vanishing viscosity term depending on a small parameter ε > 0. We study the boundary controllability properties of this perturbed equation and the behavior of its boundary controls vε as ε goes to zero. It is shown that, for any time T sufficiently large but independent of ε and for each initial datum in H−1(0,π), there exists a uniformly...

This article considers the linear 1-d Schrödinger equation in (0,π) perturbed by a vanishing viscosity term depending on a small parameter ε > 0. We study the boundary controllability properties of this perturbed equation and the behavior of its boundary controls vε as ε goes to zero. It is shown that, for any time T sufficiently large but independent of ε and for each initial datum in H−1(0,π), there exists a uniformly...

Let $C$ be the extended complex plane; $G\subset C$ a finite Jordan with $0\in G$; $w=\varphi \left(z\right)$ the conformal mapping of $G$ onto the disk $B\left(0;{\rho }_0\right):=\left\}w\left|w\right|<{\rho }_0\right\{$ normalized by $\varphi \left(0\right)=0$ and ${\varphi }^{\text{'}}\left(0\right)=1$. Let us set ${\varphi }_p\left(z\right):={\int }_0^z{\left[{\varphi }^{\text{'}}\left(\zeta \right)\right]}^{2/p}\mathrm{d}\zeta$, and let ${\pi }_{n,p}\left(z\right)$ be the generalized Bieberbach polynomial of degree $n$ for the pair $(G,0)$, which minimizes the integral $\underset{G}{\int \int }{\left|{\varphi }_p^{\text{'}}\left(z\right)-P_n^{\text{'}}\left(z\right)\right|}^p\mathrm{d}{\sigma }_z$ in the class of all polynomials of degree not exceeding $\le n$ with $P_n\left(0\right)=0$, $P_n^{\text{'}}\left(0\right)=1$. In this paper we study the uniform convergence of the generalized Bieberbach polynomials ${\pi }_{n,p}\left(z\right)$ to ${\varphi }_p\left(z\right)$ on $\overline{G}$ with interior and exterior zero angles and determine its dependence on the...

We discuss relations between uniform minimality, unconditionality and interpolation for families of reproducing kernels in backward shift invariant subspaces. This class of spaces contains as prominent examples the Paley-Wiener spaces for which it is known that uniform minimality does in general neither imply interpolation nor unconditionality. Hence, contrarily to the situation of standard Hardy spaces (and of other scales of spaces), changing the size of the space seems necessary to deduce unconditionality...

Let $H\left(K\right)$ be the Hilbert space with reproducing kernel $K$. This paper characterizes some sufficient conditions for a sequence to be a universal interpolating sequence for $H\left(K\right)$.

We prove the existence of sequences ${\varrho ₙ}_{n=1}^{\infty }$, ϱₙ → 0⁺, and ${zₙ}_{n=1}^{\infty }$, |zₙ| = 1/2, such that for every α ∈ ℝ and for every meromorphic function G(z) on ℂ, there exists a meromorphic function $F\left(z\right)=F_{G,\alpha }\left(z\right)$ on ℂ such that $\varrho {ₙ}^{\alpha }F(nzₙ+n\varrho ₙ\zeta )$ converges to G(ζ) uniformly on compact subsets of ℂ in the spherical metric. As a result, we construct a family of functions meromorphic on the unit disk that is $Q_m$-normal for no m ≥ 1 and on which an extension of Zalcman’s Lemma holds.

A holomorphic function $f$ on a simply connected domain $\Omega$ is said to possess a universal Taylor series about a point in $\Omega$ if the partial sums of that series approximate arbitrary polynomials on arbitrary compacta $K$ outside $\Omega$ (provided only that $K$ has connected complement). This paper shows that this property is not conformally invariant, and, in the case where $\Omega$ is the unit disc, that such functions have extreme angular boundary behaviour.

We prove some conditions on a sequence of functions and on a complex domain for the existence of universal functions with respect to sequences of certain derivative and antiderivative operators related to them. Conditions for the equicontinuity of those families of operators are also studied. The conditions depend upon the "size" of the domain and functions. Some earlier results about multiplicative complex sequences are extended.

A universal optimal in order approximation of a general functional in the space of continuous periodic functions is constructed and its fundamental properties and some generalizations are investigated. As an application the approximation of singular integrals is considered and illustrated by numerical results.