Recent Advances in Operator Theory The Israel Gohberg Anniversary Volume International Workshop in Groningen, June 1998

This volume contains a selection of papers in modern operator theory and its applications. Most of them are directly related to lectures presented at the Inter­ national Workshop on Operator Theory and its Applications held at the University of Groningen (IWOTA-98) in Groningen, the Netherlands, from June 30-July 3, 1998. The workshop was attended by 97 mathematicians-of which 12 were PhD or postdoctoral students-from 19 countries. The program consisted of 19 plenary lectures of 40 minutes and 72 lectures of 30 minutes in 4 parallell sessions. The present volume reflects the wide range and rich variety of topics presented and discussed at the workshop. The papers deal with operator polynomials and analytic operator functions, with spectral problems of (partial) differential oper­ ators and related operator matrices, with interpolation, completion and extension problems, with commutant lifting and dilation, with Ricatti equations and real­ ization problems, with scattering theory, with problems from harmonic analysis, and with topics in the theory of reproducing kernel spaces and of spaces with an indefinite metric. All papers underwent the usual refereeing process.

On the spectral theory of degenerate quadratic operator pencils.- Two-sided tangential interpolation for Hilbert-Schmidt operator functions on polydisks.- Nonstationary analogs of the Herglotz representation theorem: realizations centered at an arbitrary point.- Characteristic functions of maximal sectorial operators.- Similarity between Krein space bicontractions and Hilbert space contractions.- Classification of cyclic invariant subspaces of Jordan operators.- Elliptic spectral problems of higher order with eigenparameter dependent boundary conditions.- About scattering on the ring.- Dilation of generalized Toeplitz kernels on lexicographic ? × R.- On Riccati equations and reproducing kernel spaces.- A status report on the asymptotic behavior of Toeplitz determinants with Fisher—Hartwig singularities.- On the spectrum of unbounded off-diagonal 2 × 2 operator matrices in Banach spaces.- Multithreshold spectral phase transitions for a class of Jacobi matrices.- Positive extensions and diagonally connected patterns.- Parametrized Furuta inequality and its applications.- J-symmetric factorizations and algebraic Riccati equations.- Scattering of waves by periodic gratings and factorization problems.- Corner of numerical ranges.- On some classes of extensions of sectorial operators and dual pairs of contractions.- Liftings of intertwining operators.- Some estimates for the resolvent and for the lengths of Jordan chains of an analytic operator function.- The Parrott problem for singular values.- Unconditional decompositions and Schur-type multipliers.- Scattering in a loop-shaped waveguide.- Pseudospectra of operator polynomials.