14 citations · 28 across the 7 of their papers we have counts for
7 papers
Dirac-Krein systems on star graphs
Vadym Adamyan, Heinz Langer, Christiane Tretter +1
We study the spectrum of a self-adjoint Dirac-Krein operator with potential on a compact star graph with a finite number of edges. This operator is defined by a Di…
Transfer functions and local spectral uniqueness for Sturm-Liouville operators, canonical systems and strings
Heinz Langer
It is shown that transfer functions, which play a crucial role in M.G. Krein's study of inverse spectral problems, are a proper tool to formulate local spectral uniqueness conditio…
Non-linear eigenvalue problems and applications to photonic crystals
Christian Engström, Heinz Langer, Christiane Tretter
We establish new analytic and numerical results on a general class of rational operator Nevanlinna functions that arise e.g. in modelling photonic crystals. The capability of these…
Essential spectrum of systems of singular differential equations
Orif O. Ibrogimov, Heinz Langer, Matthias Langer +1
In this paper we develop a new method to determine the essential spectrum of coupled systems of singular differential equations. Applications to problems from magnetohydrodynamics…
Mark Krein's Method of Directing Functionals and Singular Potentials
Charles Fulton, Heinz Langer, Annemarie Luger
It is shown that M. Krein's method of directing functionals can be used to prove the existence of a scalar spectral measure for certain Sturm-Liouville equations with two singular…
On the spectrum of the magnetohydrodynamic mean-field alpha^2-dynamo operator
Uwe Guenther, Heinz Langer, Christiane Tretter
The existence of magnetohydrodynamic mean-field alpha^2-dynamos with spherically symmetric, isotropic helical turbulence function alpha is related to a non-self-adjoint spectral pr…