Ibrogimov, Orif O.; Langer, Heinz; Langer, Matthias; Tretter, Christiane Essential spectrum of systems of singular differential equations. (English) Zbl 1324.47029 Acta Sci. Math. 79, No. 3-4, 423-465 (2013). Reviewer: Catalin Badea (Lille) MSC: 47A53 55R10 47A10 34L05 47A55 76E99 PDFBibTeX XMLCite \textit{O. O. Ibrogimov} et al., Acta Sci. Math. 79, No. 3--4, 423--465 (2013; Zbl 1324.47029) Full Text: arXiv
Fulton, Charles; Langer, Heinz; Luger, Annemarie Mark Krein’s method of directing functionals and singular potentials. (English) Zbl 1259.34017 Math. Nachr. 285, No. 14-15, 1791-1798 (2012). Reviewer: Aleksey Kostenko (Donetsk) MSC: 34B20 34B24 34L05 47B25 47E05 PDFBibTeX XMLCite \textit{C. Fulton} et al., Math. Nachr. 285, No. 14--15, 1791--1798 (2012; Zbl 1259.34017) Full Text: DOI arXiv
Adamyan, V.; Langer, H.; Mennicken, R. Eigenvalues of a Sturm-Liouville problem depending rationally on the eigenvalue parameter. (English) Zbl 0813.34068 Helmke, Uwe (ed.) et al., Systems and networks: mathematical theory and applications. Proceedings of the 10th international symposium on the mathematical theory of networks and systems, MTNS ’93, held in Regensburg, Germany, August 2-6, 1993. Volume II: Invited and contributed papers. Berlin: Akademie Verlag. Math. Res. 79, 589-594 (1994). Reviewer: M.Möller (Regensburg) MSC: 34L05 34L15 34B24 PDFBibTeX XMLCite \textit{V. Adamyan} et al., in: Systems and networks: mathematical theory and applications. Proceedings of the 10th international symposium on the mathematical theory of networks and systems, MTNS '93, held in Regensburg, Germany, August 2-6, 1993. Volume II: Invited and contributed papers. Berlin: Akademie Verlag. 589--594 (1994; Zbl 0813.34068)
Dijksma, Aad; Langer, Heinz; de Snoo, Henk Eigenvalues and pole functions of Hamiltonian systems with eigenvalue depending boundary conditions. (English) Zbl 0795.34070 Math. Nachr. 161, 107-154 (1993). MSC: 34L05 34B15 37J99 PDFBibTeX XMLCite \textit{A. Dijksma} et al., Math. Nachr. 161, 107--154 (1993; Zbl 0795.34070) Full Text: DOI
Atkinson, F. V.; Langer, H.; Mennicken, R. Sturm-Liouville problems with coefficients which depend analytically on the eigenvalue parameter. (English) Zbl 0792.34024 Acta Sci. Math. 57, No. 1-4, 25-44 (1993). Reviewer: M.Möller (Regensburg) MSC: 34B24 34L05 PDFBibTeX XMLCite \textit{F. V. Atkinson} et al., Acta Sci. Math. 57, No. 1--4, 25--44 (1993; Zbl 0792.34024)
Langer, Heinz; Mennicken, Reinhard; Möller, Manfred On Floquet eigenvalue problems for first order differential systems in the complex domain. (English) Zbl 0752.34004 J. Reine Angew. Math. 425, 87-121 (1992). Reviewer: W.D.Evans (Cardiff) MSC: 34M99 34L05 PDFBibTeX XMLCite \textit{H. Langer} et al., J. Reine Angew. Math. 425, 87--121 (1992; Zbl 0752.34004) Full Text: Crelle EuDML
Langer, H.; Mennicken, R.; Möller, M. A second order differential operator depending nonlinearly on the eigenvalue parameter. (English) Zbl 0734.34070 Topics in operator theory. Ernst D. Hellinger Mem. Vol., Oper. Theory, Adv. Appl. 48, 319-332 (1990). Reviewer: G.Moroşanu (Iaşi) MSC: 34L05 PDFBibTeX XML