Trotter-Kato product formula for unitary groups (2009)
Exner, Pavel, Neidhardt, Hagen
Let $A$ and $B$ be non-negative self-adjoint operators in a separable Hilbert space such that its form sum $C$ is densely defined. It is shown that the Trotter product formula holds for imaginary...
On the unitary equivalence of absolutely continuous parts of self-adjoint extensions (2009)
Malamud, Mark M., Neidhardt, Hagen
The classical Weyl-von Neumann theorem states that for any self-adjoint operator $A$ in a separable Hilbert space $\mathfrak H$ there exists a (non-unique) Hilbert-Schmidt operator $C = C^*$ such...
Finite Rank Perturbations, Scattering Matrices and Inverse Problems (2009)
Behrndt, Jussi, Malamud, Mark M., Neidhardt, Hagen
In this paper the scattering matrix of a scattering system consisting of two selfadjoint operators with finite dimensional resolvent difference is expressed in terms of a matrix Nevanlinna function....
Behrndt, Jussi, Malamud, Mark M., Neidhardt, Hagen
In this paper the scattering matrix of a scattering system consisting of two selfadjoint operators with finite dimensional resolvent difference is expressed in terms of a matrix Nevanlinna function....
A Kohn-Sham system at zero temperature (2008)
Cornean, Horia, Hoke, Kurt, Neidhardt, Hagen, Racec, Paul N., Rehberg, Joachim
An one-dimensional Kohn-Sham system for spin particles is considered which effectively describes semiconductor {nano}structures and which is investigated at zero temperature. We prove the existence...
Evanescent channels and scattering in cylindrical nanowire heterostructures (2008)
Racec, Paul N., Racec, Roxana, Neidhardt, Hagen
We investigate the scattering phenomena produced by a general finite range non-separable potential in a multi-channel two-probe cylindrical nanowire heterostructure. The multi-channel current...
Scattering matrices and Weyl functions (2008)
Behrndt, Jussi, Malamud, Mark M., Neidhardt, Hagen
For a scattering system {AΘ, A0} consisting of self-adjoint extensions AΘ and A0 of a symmetric operator A with finite deficiency indices, the scattering matrix {SΘ(λ)} and a spectral shift...
Trace formulae for dissipative and coupled scattering systems (2007)
Behrndt, Jussi, Malamud, Mark M., Neidhardt, Hagen
For scattering systems consisting of a (family of) maximal dissipative extension(s) and a selfadjoint extension of a symmetric operator with finite deficiency indices, the spectral shift function is...
Potential approximations to 0: an inverse Klauder (2007)
Pavel Exner, Hagen Neidhardt, Valentin A. Zagrebnov
a;b
Hagen Neidhardt, Joachim Rehberg
Classical solutions of quasilinear parabolic systems on two dimensional domains Hans--Christoph Kaiser
Hans-christoph Kaiser, Hagen Neidhardt, Joachim Rehberg
Macroscopic current induced boundary
Dissipative Schrdinger-type operator as a model for generation and recombination
Universit de la Mditerrane (Aix-Marseille II) (2007)
Takashi Ichinose, Hagen Neidhardt, Valentin A. Zagrebnov
product formula and fractional powers of self-adjoint generators
Vincent Cachia, Hagen Neidhardt, Valentin A. Zagrebnov
Let A be a positive self-adjoint operator and let B be an m-accretive operator which is A-small with a relative bound less than one. Let H = A+B, then H is well-defined on dom(H) = dom(A) and...
Linear non-autonomous Cauchy problems and evolution semigroups (2007)
Neidhardt, Hagen, Zagrebnov, Valentin A.
The paper is devoted to the problem of existence of propagators for an abstract linear non-autonomous evolution Cauchy problem of hyperbolic type in separable Banach spaces. The problem is solved...
The effect of time-dependent coupling on non-equilibrium steady states (2007)
Cornean, Horia D., Neidhardt, Hagen, Zagrebnov, Valentin A.
Consider (for simplicity) two one-dimensional semi-infinite leads coupled to a quantum well via time dependent point interactions. In the remote past the system is decoupled, and each of its...
Zeno product formula revisited (2007)
Exner, Pavel, Ichinose, Takashi, Neidhardt, Hagen, Zagrebnov, Valentin A.
We introduce a new product formula which combines an orthogonal projection with a complex function of a non-negative operator. Under certain assumptions on the complex function the strong convergence...
Classical solutions of drift-diffusion equations for semiconductor devices: the 2d case (2007)
Kaiser, Hans-Christoph, Neidhardt, Hagen, Rehberg, Joachim
We regard drift-diffusion equations for semiconductor devices in Lebesgue spaces. To that end we reformulate the (generalized) van Roosbroeck system as an evolution equation for the potentials to the...
3 Weierstraß-Institut für Angewandte Analysis und Stochastik (2007)
Jussi Behrndt, Mark M. Malamud, Hagen Neidhardt
Trace formulae for dissipative and coupled scattering systems
Université de laMéditerranée (Aix-Marseille II) Centre de Physique Théorique- UMR 6207 (2007)
Hagen Neidhardt, Valentin A. Zagrebnov
The paper is devoted to the problem of existence of propagators for an abstract linear non-autonomous evolution Cauchy problem of hyperbolic type in separable Banach spaces. The problem is solved...
Scattering matrices and Weyl functions (2006)
Behrndt, Jussi, Malamud, Mark M., Neidhardt, Hagen
For a scattering system $\{A_\Theta,A_0\}$ consisting of selfadjoint extensions $A_\Theta$ and $A_0$ of a symmetric operator $A$ with finite deficiency indices, the scattering matrix $\{S_\gT(\gl)\}$...
Zeno product formula revisited (2004)
Exner, Pavel, Ichinose, Takashi, Neidhardt, Hagen, Zagrebnov, Valentin A.
We introduce a new product formula which combines an orthogonal projection with a complex function of a non-negative operator. Under certain assumptions on the complex function the strong convergence...
Baro, Michael, Neidhardt, Hagen, Rehberg, Joachim
A 1D coupled drift-diffusion dissipative Schr?dinger model (hybrid model), which is capable to describe the transport of electrons and holes in semi-conductor devices in a non-equilibrium situation,...
Kaiser, Hans-Christoph, Neidhardt, Hagen, Rehberg, Joachim
Let H be a semi-bounded self-adjoint operator in a separable Hilbert space. For a certain class of positive, continuous, decreasing, and convex functions F we show the convexity of trace functionals...
Johannes F. Brasche, Mark Malamud, Hagen Neidhardt
We characterize the spectra of self-adjoint extensions of a symmetric operator with equal deciency indices in terms of boundary values of their Weyl functions. A complete description is obtained for...
Exner, Pavel, Neidhardt, Hagen, Zagrebnov, Valentin
We show that there is a family Schroedinger operators with scaled potentials which approximates the $\delta'$-interaction Hamiltonian in the norm-resolvent sense. This approximation, based on a...
Weyl function and spectral properties of self-adjoint extensions (2000)
Brasche, Johannes Friedemann, Malamud, Mark M., Neidhardt, Hagen
On the Right Hamiltonian for Singular Perturbations: General Theory (1997)
Hagen Neidhardt, Valentin Zagrebnov
Let a pair of self-adjoint operators fA 0; W 0g be such that (a) there is a dense domain D ` dom(A) " dom(W ) that H = (A + W )jD is semibounded from below (stability domain), (b) the symmetric...
On Inverse Spectral Theory for Self-Adjoint Extensions: Mixed Types of Spectra (1996)
Sergio Albeverio, Johannes Brasche, Hagen Neidhardt
Let H be a symmetric operator in a separable Hilbert space H. Suppose that H has some gap J . We shall investigate the question about what spectral properties the self--adjoint extensions of H can...