Andreas Ruffing

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We present new oscillation criteria for the second order nonlinear neutral delay differential equation ( a (t) (y (t)+ p (t) y (t − τ))′)′ + q (t) |y (σ (t))|α−1 y (σ (t)) = 0, where t ≥ t0, τ, and α are positive constants and the functions p, q, a, σ ∈ C ([t0,∞) ,R) . Our results generalize and improve some known results for oscillation of second order(More)
The q-deformed harmonic oscillator is studied in the light of q-deformed phase space variables. This allows a formulation of the corresponding Hamiltonian in terms of the ordinary canonical variables x and p. The spectrum shows unexpected features such as degeneracy and an additional part that cannot be reached from the ground state by creation operators.(More)
The propagation differential for bosonic strings on a complex torus with three symmetric punctures is investigated. We study deformation aspects between two point and three point differentials as well as the behaviour of the corresponding KricheverNovikov algebras. The structure constants are calculated and from this we derive a central extension of the(More)
We report on the observation of a giant spin-orbit splitting of quantum-well states in the unoccupied electronic structure of a Bi monolayer on Cu(111). Up to now, Rashba-type splittings of this size have been reported exclusively for surface states in a partial band gap. With these quantum-well states we have experimentally identified a second class of(More)
We employ a recently developed purpose-made technique based on spin-resolved two-photon photoemission spectroscopy to study the influence of alkali-metal doping (Cs and Na) on the spin functionality of the interface between a cobalt thin film and the organic semiconductor copper phthalocyanine. We find two alkali-metal-induced effects. First, alkali-metal(More)
In this article, discrete versions of diffusion equations are presented on basic adaptive grids. These equations stem from originally considering discrete versions of exponential functions which have zeros on the negative axis. As a main result, similarity solutions to these difference equations are developed which reduce in the transition to the real axis(More)
Capturing the dynamic electronic band structure of a correlated material presents a powerful capability for uncovering the complex couplings between the electronic and structural degrees of freedom. When combined with ultrafast laser excitation, new phases of matter can result, since far-from-equilibrium excited states are instantaneously populated. Here,(More)
The orthogonal polynomials with recurrence relation (λn + μn − z)Fn(z) = μn+1 Fn+1(z) + λn−1 Fn−1(z) with two kinds of cubic transition rates λn and μn, corresponding to indeterminate Stieltjes moment problems, are analyzed. We derive generating functions for these two classes of polynomials, which enable us to compute their Nevanlinna matrices. We discuss(More)
Throughout the paper we discuss results related to the class of entire functions φN (z) ≡ φN (z; λ, q) for N ∈ N, defined by φN (0) = 1 and φ′ N (z) = λNz N−1φN (qz) for all z ∈ C, where λ 6= 0 and while the basic parameter q ∈ (0, 1) assigns a fixed delay. In that sense the functions φN may be regarded as q-delayed analogs of the standard exponentials(More)
A generalization of the ladder operator formalism for the harmonic oscillator in one-dimensional Schrödinger theory to time scales T shall be considered. Stemming from a fundamental decomposition of the Hamiltonian H into ladder operators A and A†, this can be achieved at least on unitary lattices — characterized by a constant growth of graininess. In fact,(More)