On BV-Solutions of Some Nonlinear Integral Equations

In this paper we prove uniqueness theorems for bounded variation (shortly: BV) solutions and continuous BV-solutions of the Hammerstein and the Volterra-Hammerstein integral equations. We investigate real-valued functions and functions with values in a Banach space. Submitted: August 16, 2001?Revised: September 13, 2002     

Integral Equations on Function Spaces and Dichotomy on the Real Line

The purpose of this paper is to give new and general characterizations for uniform dichotomy and uniform exponential dichotomy of evolution families on the real line. We consider two general classes denoted and and we prove that if V,W are Banach function spaces with and , then the admissibility of the pair for an evolution family implies the uniform dichotomy of . In addition, we consider a subclass and we prove that if , then the admissibility of the pair implies the uniform exponential dichotomy of the family . This condition becomes necessary if . Finally, we present some applications of the main results.     

On Stability of Negative Index Singular Integral Equations over an Interval

By normalization of the negative index singular integral equations with Cauchy kernel over (-1,1), the stability of the equations is proved, and the error estimate of the perturbed solutions is precisely investigated. Submitted: September 5, 2000? Revised: December 6, 2001.     

Solvability and Fredholm Properties of Integral Equations on the Half-Line in Weighted Spaces

The solvability of integral equations of the form and the behaviour of the solution x at infinity are investigated. Conditions on k and on a weight function w are obtained which ensure that the integral operator K with kernel k is bounded as an operator on X_w, where X_w denotes the weighted space of those continuous functions defined on the half-line which are O(w(s)) as We also derive conditions on w and k which imply that the spectrum and essential spectrum of K on X_w are the same as on BC[0,). In particular, the results apply when when the integral equation is of Wiener-Hopf type. In this case we show that our results are particularly sharp.     

Measures on the Product of Compact Spaces

 If K is an uncountable metrizable compact space, we prove a “factorization” result for a wide variety of vector valued Borel measures μ defined on K ⁿ . This result essentially says that for every such measure μ there exists a measure μ′ defined on K such that the measure μ of a product A ₁ × ⋯ × A _n of Borel sets of K equals the measure μ′ of the intersection A ₁′∩⋯∩A _n ′, where the A _i ′’s are certain transforms of the A _i ’s. Partially supported by DGICYT grant PB97-0240. Received August 23, 2001; in revised form March 21, 2002     

Remarks on the uniqueness of comparable renormalized solutions of elliptic equations with measure data

We give a partial uniqueness result concerning comparable renormalized solutions of the nonlinear elliptic problem -div(a(x,Du))=μ in Ω, u=0 on ∂Ω, where μ is a Radon measure with bounded variation on Ω. Received: December 27, 2000 Published online: December 19, 2001     

A Note on Wiener-Hopf Determinants and the Borodin-Okounkov Identity

The continuous analogue of a Toeplitz determinant identity for Wiener-Hopf operators is proved. An example which arises from random matrix theory is studied and an error term for the asymptotics of the determinant is computed. Submitted: October 15, 2001? Revised: January 3, 2002.     

Berezin Forms on Line Bundles over Complex Hyperbolic Spaces

We consider complex hyperbolic spaces where and , line bundles , over them and representations of in smooth sections of (the representation is induced by a character of ). We define a Berezin form $, associated with , and give an explicit decomposition of this form into invariant Hermitian (sesqui-linear) forms for irreducible representations of the group for all and . It is the main result of the paper. Besides it, we give the Plancherel formula for . As it turns out, this formula is, en essence, one of the particular cases of the Plancherel formula for the quasiregular representation for rank one semisimple symmetric spaces, see [20], it can be obtained from the quasiregular Plancherel formula for hyperbolic spaces (complex, quaternion, octonion) by analytic continuation in the dimension of the root subspaces. The decomposition of the Berezin form allows us to define and study the Berezin transform, - in particular, to find out an explicit expression of this transform in terms of the Laplacian. Using that, we establish the correspondence principle (an asymptotic expansion as ). At last, considering , we observe an interpolation in the spirit of Neretin between Plancherel formulae for and for the similar representation for a compact form of the space . Submitted: July 12, 2001?Revised: February 12, 2002     

Multipliers between $ BMO $ Spaces on Open Unit Ball

and spaces consist of all those locally integrable functions on the open unit ball such that their mean oscillations on any Bergman ball are, respectively, bounded and vanishing to zero as the Bergman ball approaches the boundary of the unit ball. The harmonic (or analytic) versions of the and spaces are the Bloch space and the little Bloch space, respectively. The study of these spaces plays an important role in modern analysis, especially in the the area of operator theory and holomorphic spaces. In this paper, we characterize systematically the multipliers of and spaces. Submitted: January 9, 2001?Revised: October 16, 2002     

Small Transitive Families of Dense Operator Ranges

In complex, separable, infinite-dimensional Hilbert space there exist 5 proper dense operator ranges with the property that every operator leaving each of them invariant is a scalar multiple of the identity. The algebra of operators leaving a pair of proper dense operator ranges invariant can have an infinite nest of invariant subspaces. A slight extension of Foiaş' Theorem shows that it can also have a non-trivial reducing subspace. Submitted: July 13, 2001? Revised: December 6, 2001.     

Continuity of the Norm of a Composition Operator

We explore the continuity of the map which, given an analytic selfmap of the disk, takes as its value the norm of the associated composition operator on the Hardy space . We also examine the continuity the functions which assign to a self-map of the disk the Hilbert-Schmidt norm or the essential norm of the associated composition operator and show these to be discontinuous. Additionally, we characterize when the norm of a composition operator is minimal. Submitted: January 3, 2002? Revised: March 1, 2002.     

A Bitangential Interpolation Problem on the Closed Unit Ball for Multipliers of the Arveson Space

We solve a bitangential interpolation problem for contractive multipliers on the Arveson space with an arbitrary interpolating set in the closed unit ball . The solvability criterion is established in terms of positive kernels. The set of all solutions is parametrized by a Redheffer transform. Submitted: February 2, 2002.     

On Vector Integral Inequalities

The first author introduced an integration theory of vector functions with respect to an operator-valued measure in complete bornological locally convex vector spaces. In this paper some important results behind this Dobrakov-type integration technique in non-metrizable spaces are given. Received: December 10, 2007., Accepted: May 6, 2008.     

Orthogonal decompositions of Sobolev spaces in Clifford analysis

The space L ₂(G;ℂ _m ) of Clifford-algebra-valued functions in bounded domains G of ℝ ^m is decomposed into the orthogonal sum of the subspace of poly-left-monogenic functions of arbitrary order k≥1 and its orthogonal complement and as well into the orthogonal sum of the subspace of polyharmonic functions of arbitrary order k≥1 and its orthogonal complement. The complementary subspaces are given explicitly. In the particular case m=2, complex functions are involved. Although this case has to be treated separately, the results are as before. The proofs are based on proper higher-order Cauchy–Pompeiu formulas and Green functions for powers of the Laplacian. Received: July 4, 2000; in final form: January 7, 2001?Published online: December 19, 2001     

Oscillation constant of second-order non-linear self-adjoint differential equations

Our concern is to solve the oscillation problem for the non-linear self-adjoint differential equation (a(t)x’)’+b(t)g(x)=0, where g(x) satisfies the signum condition xg(x)>0 if x≠0, but is not assumed to be monotone. Sufficient conditions and necessary conditions are given for all non-trivial solutions to be oscillatory. The obtained results show that the number 1/4 is a critical value for this problem. This paper takes a different approach from most of the previous research. Proof is given by means of phase plane analysis of systems of Liénard type. Examples are included to illustrate the relation between our theorems and results which were given by Cecchi, Marini and Villari. Received: January 5, 2001?Published online: June 11, 2002     

Existence of minimizers for a class of quasi-convex functionals with non-standard growth

We study the lower semicontinuity properties of non-autonomous variational integrals whose energy densities satisfy general growth conditions. We apply these results to solve Dirichlet’s boundary value problems for such functionals. Received: June 14, 2000; in final form: November 25, 2000 Published online: December 19, 2001     

Eigenvalues of Integral Operators Defined by Smooth Positive Definite Kernels

We consider integral operators defined by positive definite kernels , where X is a metric space endowed with a strictly-positive measure. We update upon connections between two concepts of positive definiteness and upgrade on results related to Mercer like kernels. Under smoothness assumptions on K, we present decay rates for the eigenvalues of the integral operator, employing adapted to our purposes multidimensional versions of known techniques used to analyze similar problems in the case where X is an interval. The results cover the case when X is a subset of endowed with the induced Lebesgue measure and the case when X is a subset of the sphere S^m endowed with the induced surface Lebesgue measure. The first author was partially supported by FAPESP, grants # 2005/56694–4, # 2007/58086–7.     

Recombination Semigroups on Measure Spaces

The dynamics of recombination in genetics leads to an interesting nonlinear differential equation, which has a natural generalization to a measure valued version. The latter can be solved explicitly under rather general circumstances. It admits a closed formula for the semigroup of nonlinear positive operators that emerges from the forward flow and is, in general, embedded in a multi-parameter semigroup.     

A characterization of bielliptic curves and applications to their moduli spaces

We deal with the covers of degree 4 naturally associated to a bielliptic curve of genus g≥6, giving a proof of the unirationality of the moduli space ? _g ^be of such curves, of the rationality of the Hurwitz scheme ℌ ^be _{4, g} of bielliptic curves of even genus g, whereas, when g is odd, we construct a finite map ℂ^{2 g -2}→? _g ^be and compute its degree. Received: March 25, 2000; in final form: March 10, 2001?Published online: May 29, 2002