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)
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)
The angle resolved photoelectron spectroscopy (ARPES) has emerged as a leading technique in identifying static key properties of complex systems such as the electronic band structure of adsorbed molecules, ultrathin quantum-well films or high temperature superconductors. We efficiently combined ARPES by using a two-dimensional analyzer for parallel energy(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)
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)
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)