Publications
1. Books 

[1]  On λNonlinear Boundary Eigenvalue Problems; Mathematical Research Vol. 71, Akademie Verlag, Berlin 1993, 124 pp. (94i:34042) [785.34054] 
[2]  Spectral theory of block operator matrices and applications; Imperial College Press, London 2008, xxxii+264 pp. 
2. Articles 

[3] 
Asymptotic boundary conditions for expansion theorems for boundary
eigenvalue problems of the form N(y) = λP(y) with λdepending
Boundary Conditions;
ZAMM
73
(1993) 7/8,
T769–T773
(1 237 866) [801.41026] 
[4] 
Kamke problems. Properties of the eigenfunctions;
Math. Nachr.
170
(1994),
251–275
(with A.A.Shkalikov)
(95j:34025) [813.34071] 
[5] 
Kamke's problem – properties of the eigenfunctions;
in: Systems and Networks: Mathematical Theory and Applications, Mathematical Research,
Vol. 79,
Akademie Verlag,
Berlin 1994,
885–888
[813.34072] 
[6] 
On fundamental systems for differential equations of Kamke type;
Math. Z.
219
(1995),
609–629
(96g:34031) [827.34004] 
[7] 
Boundary eigenvalue problems of Orr–Sommerfeld type;
ZAMM
75
(1995) SII,
417–420
(with A.A.Shkalikov)
[837.34084] 
[8] 
Spectral analysis for linear pencils N  λP of ordinary differential operators;
Math. Nachr.
179
(1996),
275–305
(with A.A. Shkalikov)
(97b:34091) [862.34058] 
[9] 
A selfadjoint linear pencil Q  λP of ordinary differential operators;
Methods Funct. Anal. Topology
2:1
(1996),
38–54
(with H. Langer, R. Mennicken)
(97f:47046) 
[10] 
Nonselfadjoint spectral problems for linear pencils N  λP of ordinary differential operators
with λ–linear boundary conditions: Completeness results;
Integral Equations Operator Theory
26:2
(1996),
222–248
(97f:47047) [862.34057] 
[11] 
Spectral properties of a compactly perturbed linear span of projections;
Integral Equations Operator Theory
26:3
(1996),
353366
(with H. Langer, V. Pivovarchik)
(97j:47008) [865.47009] 
[12] 
Spectral properties of the Orr–Sommerfeld problem;
Proc. Roy. Soc. Edinburgh A
127:6
(1997),
12451261
(with H. Langer)
(99e:34119) [897.34070] 
[13] 
Spectral decomposition of some nonselfadjoint block operator matrices;
J. Operator Theory
39:2
(1998),
339359
(with H. Langer)
(99d:47004) 
[14] 
Lyapunov stability of a perturbed multiplication operator;
in: Contributions to Operator Theory in Spaces with an Indefinite Metric, Operator Theory: Adv. Appl.
106
(1998),
309–326
(with S. Naboko)
[990.05639] (pdf version) 
[15]  On buckling problems; ZAMM 80 (2000), 633639 
[16]  Nonclassical boundary eigenvalue problems: Linearization, spectral properties and applications; Habilitationsschrift, Regensburg 1998, 110 S. 
[17]  A linearization for a class of λnonlinear boundary eigenvalue problems; J. Math. Anal. Appl. 247 (2000), 331–355. 
[18]  Linear Operator Pencils with discrete spectrum; Integral Equations Operator Theory 37:3 (2000). 
[19]  Spectral problems for systems of differential equations y' + A_{0} y = λA_{1} y with λ–polynomial boundary conditions; Math. Nachr. 214 (2000), 129–172. 
[20]  Spectral issues for block operator matrices; in: R. Weikard, G. Weinstein (Eds.), Differential Equations and Mathematical Physics, AMS/IP Studies in Advanced Mathematics 16 (2000), 407–423 
[21]  Diagonalization of certain block operator matrices and applications to Dirac operators; Operator Theory: Adv. Appl. 122 (2001), 331–358 (with H. Langer) 
[22]  Corners of numerical ranges; Operator Theory: Adv. Appl. 124 (2001), 385400 (with H. Langer, A. Markus) 
[23]  Boundary eigenvalue problems for differential equations N η = λPη with λ–polynomial boundary conditions; J. Differential Equations 170:2 (2001), 408–471 
[24]  Existence and Uniqueness of Contractive Solutions of some Riccati Equations; J. Funct. Anal. 179:2 (2001), 448–473 (with V. Adamjan, H. Langer) 
[25]  A new concept for block operator matrices: The quadratic numerical range; Linear Algebra Appl. 330 (2001), 89–112 (with H. Langer, A. Markus, V. Matsaev) 
[26]  Direct and inverse spectral problem for a system of differential equations depending rationally on the spectral parameter; Duke Math. J. 109:3 (2001), 413–449 (with R. Mennicken, A.L. Sakhnovich) 
[27]  Essential spectrum of a system of singular differential operators; Proc. Amer. Math. Soc. 130:6 (2002), 1699–1710 (with R. Mennicken, S. Naboko) 
[28]  The spectrum of the multiplication operator associated with a family of operators; J. London Math. Soc. 65:2 (2002), 483–492 (with R. Denk, M. Möller) 
[29]  Singular Dirac systems and SturmLiouville problems nonlinear in the spectral parameter; J. Differential Equations 181:2 (2002), 511–542 (with H. Schmid) 
[30]  On a class of nonselfadjoint quadratic matrix operator pencils arising in elasticity theory; J. Operator Theory 47:2 (2002), 325341 (with V. Adamjan, V. Pivovarchik) 
[31]  Variational principles for eigenvalues of block operator matrices; Indiana Univ. Math. J. 51:6 (2002), 1427–1459 (with H. Langer, M. Langer) 
[32]  The block numerical range of an n × n block operator matrix; SIAM J. Matrix Anal. Appl. 24:4 (2003), 10031017 (with M. Wagenhofer) 
[33]  Selfadjoint block operator matrices with nonseparated diagonal entries and their Schur complements; J. Funct. Anal. 199:2 (2003), 427451 (with H. Langer, A. Markus, V. Matsaev) 
[34]  Eigenvalue bounds for the singular SturmLiouville problem with a complex potential; J. Phys. A: Math. Gen 36:13 (2003), 37733787 (with B.M. Brown, M. Langer, M. Marletta, M. Wagenhofer) 
[35]  Asymptotic separation of the spectrum of quadratic operator pencils associated with damped dynamical systems; Asymptot. Anal. 36:1 (2003), 112 (with V. Pivovarchik) 
[36]  A new method for eigenvalue estimates for Dirac operators on certain manifolds with S^{k}symmetry; Differential Geom. Appl. 19:1 (2003), 114 (with M. Kraus) 
[37]  Pencils of differential operators containing the eigenvalue parameter in the boundary conditions; Proc. Roy. Soc. Edinburgh Sect. A 133:4 (2003), 893917 (with M. Marletta, A.A. Shkalikov) 
[38]  Variational principles and eigenvalue estimates for unbounded block operator matrices and applications; J. Comp. Appl. Math. 171 (2004), 311334 (with M. Kraus, M. Langer) 
[39]  Complete second order linear differential operator equations in Hilbert space and applications in hydrodynamics; Trans. Amer. Math. Soc. 356:12 (2004), 47374766 (with N. Kopachevsky, Ju. Pashkova, R. Mennicken) 
[40]  Eigenvalue accumulation for Dirac operators with spherically symmetric potential; J. Phys. A 37:36 (2004), 86578674 (with H. Schmid) 
[41]  A Krein space approach to PTsymmetry; Czechoslovak J. Phys. 54:10 (2004), 11131120 (with H. Langer) 
[42]  Spectrum of definite type of selfadjoint operators in Krein spaces; Linear Multilinear Algebra 53:2 (2005), 115136 (with H. Langer, M. Langer, A. Markus) 
[43]  Spectral theory of the KleinGordon equation in Pontryagin spaces; Comm. Math. Phys. 267:1 (2006), 159180 (with H. Langer, B. Najman) 
[44]  The spectrum of the multiplication operator associated with a family of operators in a Banach space; Oper. Theory Adv. Appl. 162 (2006), 103116 (with R. Denk, M. Möller) 
[45]  Corrigendum to: "A Krein space approach to PT symmetry" [Czechoslovak J. Phys. 54:10 (2004), no. 10, 11131120]; Czechoslovak J. Phys. 56:9 (2006), 10631064 (with H. Langer) 
[46]  Variational principles for eigenvalues of the KleinGordon equation; J. Math. Phys. 47:10 (2006), 103506, 18 pp. (with M. Langer) 
[47]  Essential spectra of coupled systems of differential equations and applications in hydrodynamics; J. Differential Equations 243:1 (2007), 3669 (with M. Marletta) 
[48]  The VirozubMatsaev condition and spectrum of definite type for selfadjoint operator functions; Complex Anal. Oper. Theory 2:1 (2008), 99134 (with H. Langer, M. Langer, M. Alexander) 
[49]  Spectral theory of the KleinGordon equation in Krein spaces; Proc. Edinb. Math. Soc. (2) 51:3 (2008), 711750 (with H. Langer, N. Branko) 
3. Editorial Work 

[50] 
Differential and Integral Operators;
Operator Theory: Adv. Appl. Vol. 102,
Birkhäuser Verlag,
Basel 1998,
324 S.
(with I.C. Gohberg, R. Mennicken) (99d:47001)) [883.00019] 
[51] 
Recent Progress in Operator Theory;
Operator Theory: Adv. Appl. Vol. 103,
Birkhäuser Verlag,
Basel 1998,
283 S.
(with I.C. Gohberg, R. Mennicken) (99d:47002) [883.00020] 