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 ≥ t 0 , τ, and α are positive constants and the functions p, q, a, σ ∈ C ([t 0 , ∞) , R). Our results generalize and improve some known results for oscillation of second order(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)
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 Krichever-Novikov algebras. The structure constants are calculated and from this we derive a central extension of the(More)
Throughout the paper we discuss results related to the class of entire functions ϕ N (z) ≡ ϕ N (z; λ, q) for N ∈ N, defined by ϕN (0) = 1 and ϕ N (z) = λN z N −1 ϕN (qz) for all z ∈ C, where λ = 0 and while the basic parameter q ∈ (0, 1) assigns a fixed delay. In that sense the functions ϕ N may be regarded as q-delayed analogs of the standard exponentials(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)
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)
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(More)
Starting from supersymmetric quantum mechanics and related supermodels within Schrödinger theory, we review the meaning of self-similar superpotentials which exhibit the spectrum of a geometric series. We construct special types of discretizations of the Schrödinger equation on time scales with particular symmetries. This discretization leads to the same(More)
Mixed linear birth–and–death processes with killing are investigated in view of their spectral representation. Having discussed the relations of linear/q-linear rate structures to Meixner/Al-Salam–Chihara polynomials, six special types of such mixed rate structures shall be encountered. Half of them can be understood as perturbations of pure birth–and–death(More)