A factorization result for generalized Nevanlinna functions of the classN k

LetQN _k. It is shown that if is a nonreal pole or a real generalized pole of nonpositive type and is a nonreal zero or a real generalized zero of nonpositive type of the functionQ then the function

The closure of unitary orbit for strongly irreducible operators in a class of nest algebras

A linear operatorT L(H) is called a strongly irreducible, if there is no non-trivial idempotent linear operator commuting withT. In this paper, denote the set of all strongly irreducible operators by (SI). Let be a nest with infinite dimensional atoms, be the nest algebra associated with and be the closure of , then the following result is proved

Nevanlinna inequality for intersection of divisors

A Nevanlinna-type inequality is proved for holomorphic mapf:C ^m →M and for intersection of sections of a line bundle overM, in which the intersection may not be pure dimensional and the map may be degenerate. Partial financial support was provided by the NSF under grant number DMS-8922760.     

Higher order recurrences for analytical functions of Tchebysheff type

Relation of hyperbolons of volume one to generalized Clifford algebras is described in [1b] and there some applications are listed. In this note which is an extension of [8] we use the one parameter subgroups of the group of hyperbolons of volume one in order to define and investigate generalization of Tchebysheff polynomial system. Parallely functions of roots of polynomials of any degree are studied as possible generalization of symmetric functions considered by Eduard Lucas. It is found how functions of roots of polynomial of any degree are related to this generalization of Tchebysheff polynomials. The relation is explicit. In a primary sense the considered generalization is in passing fromZ ₂ toZ _n group decomposition of the exponential. We end up with an application of the discovered generalization to quite large class of dynamical systems with iteration.     

On universal entire functions with zero-free derivatives

We prove in this note a generalization of a theorem due to G. Herzog on zero-free universal entire functions. Specifically, it is shown that, if a nonnegative integer q and a nonconstant entire function φ of subexponential type are given, then there is a residual set in the class of entire functions with zero-free derivatives of orders q and q + 1, such that every member of that set is universal with respect to φ (D), where D is the differentiation operator. This work is supported in part by DGICYT grant PB93-0926.     

A note on the congruences of the nakano superlattice and some properties of the associated quotients

In this paper we explore theNakano superlattice (H, ⊔, ⊓), where ⊔, ⊓ are the Nakanohyperoperations x⊔y={z:x∨z=y∨z=x∨y},x⊓y={z:x∧z=y∧z=x∧y}. In particular, we study the properties of congruences on the Nakano superlattice and the associated quotients. New hyperoperations are introduced on the quotient and their properties studied.     

Interpolating varieties for spaces of meromorphic functions

We consider in this paper interpolation problems for weighted spaces of entire and meromorphic functions. Various (analytic and geometric) conditions necessary and sufficient for multiplicity varieties to be interpolating varieties will be given. This research is supported in part by NSF Grants DMS-90-00616 and CDR 88-03012.     

Toeplitz operators and arguments of analytic functions

For a Toeplitz operator T _φ , we study the interrelationship between smoothness properties of the symbol φ and those of the functions annihilated by T _φ . For instance, it follows from our results that if φ is a unimodular function on the circle lying in some Lipschitz or Zygmund space Λ^α with 0 < α < ∞, and if f is an H ^p -function (p ≥ 1) with T _φ f = 0, then f ∈ Λ^α and

Fixed points of asymptotically regular semigroups in Banach spaces

In this paper we study in Banach spaces the existence of fixed points of (nonlinear) asymptotically regular semigroups. We establish for these semigroups some fixed point theorems in spaces with weak uniform normal structure, in a Hilbert space, inL ^p spaces, in Hardy spacesH ^p and in Sobolev spacesW ^r.p for 1<p<∞ andr≥0, in spaces with Lifshitz’s constant greater than one. These results are the generalizations of [8, 10, 16].     

Properties of generalized Toeplitz operators

An operatorX: is said to be a generalized Toeplitz operator with respect to given contractionsT ₁ andT ₂ ifX=T ₂XT₁ ^*. The purpose of this line of research, started by Douglas, Sz.-Nagy and Foia, and Pták and Vrbová, is to study which properties of classical Toeplitz operators depend on their characteristic relation. Following this spirit, we give appropriate extensions of a number of results about Toeplitz operators. Namely, Wintner's theorem of invertibility of analytic Toeplitz operators, Widom and Devinatz's invertibility criteria for Toeplitz operators with unitary symbols, Hartman and Wintner's theorem about Toeplitz operator having a Fredholm symbol, Hartman and Wintner's estimate of the norm of a compactly perturbed Toeplitz operator, and the non-existence of compact classical Toeplitz operators due to Brown and Halmos.Dedicated to our friend Cora Sadosky on the occasion of her sixtieth birthday     

The spectral property of dual matrix strings as a consequence of the existence of spectral matrix functions for canonical systems

The term dual string for scalar strings was introduced in [KK1], where some connections between the spectra of a string and its dual were studied. In [KK2] it was shown that if () is a spectral function of a scalar stringS ₁ with nonnegative spectrum (in the sense of [KK2]), then the function

An improvement of the Ivanov bound

Let be a distance-regular graph of diameterd, valencyk andr=max{i|(c _i ,b _i )=(c ₁,b ₁)}. In this paper, we prove that

Crowding for analytic functions with elongated range

Letf be a function analytic in the unit diskD. If the rangef(D) off is contained in a rectangleR with sidesa andb withba such thatf(D) touches both small sides ofR, then the supremum norm of the derivative satisfies f b·(b/a). We derive tight bounds for the best possible function in this estimate. In particular, we show that for small .Communicated by Dieter Gaier.     

A characterization of the interpolation spaces ofH 1 andL ∞ on the line

The Calderón-Mitjagin theorem characterizes all interpolation spaces of the pair of Lebesgue spaces (L ¹,L ) as the rearrangement-invariant spaces. The results of this paper show that the interpolation spaces ofH ¹(R) andL (R) consist of elements whose nontangential maximal functions lie in rearrangement-invariant spaces.Communicated by Jaak Peetre.     

Unitary invariants of spectral measures with the CGS-property

A «CGS-property» for the spectral measures is introduced and the classical results of determining complete systems of unitary invariants for self-adjoint and bounded normal operators on separable Hilbert spaces are extended to the class of spectral measures with this property. As a consequence, the above mentioned results are extended to unbounded normal operators on separable Hilbert spaces. Moreover, three different kinds of multiplicity are defined and it is shown that for the measures with the «CGS-property» they all coincide. In the last section some analogues of the multiplicity functions defined by Stone [14] are related to the total multiplicity.     

A Characterization of Mixed Branching Greedoids

Branching greedoids have been defined and characterized for both directed and undirected rooted graphs. Such greedoids can be extended to rooted mixed graphs – graphs with both directed and undirected edges. These greedoids are characterized by a list of forbidden minors. If Ω is a rooted mixed graph, its mixed branching greedoid has the edges of Ω as its ground set and the collection of arborescences as its feasible sets. The set of mixed branching greedoids is exactly the set of local forest greedoids without

A sharp form of Nevanlinna's second fundamental theorem

Letf be meromorphic in the plane. We find a sharp upper bound for the error term

Lyapunov modular functions

We prove a Lyapunov type theorem for modular functions on complemented lattices.     

Feedback stabilization of some classes of nonlinear transport systems

It is shown that for some cases, the control system of the linearized transport equation with a controllable unstable part is exponentially stabilizable. The same result holds true for nonlinear transport phenomena if it can be found as simulation orbit of perturbed transport equation.     

Rational approximation in the real Hardy spaceH 2 and Stieltjes integrals: A uniquencess theorem

The paper deals with rational approximation over the real Hardy spaceH _{2, R}(V), whereV is the complement of the closed unit disk. The results concern Stieltjes functions