The German Stage in 1944

Picture of stage during last season before war closur

Anomalous Behavior of Ru for Catalytic Oxidation: A Theoretical Study of the Catalytic Reaction CO + 1/2 O_2 --> CO_2

Recent experiments revealed an anomalous dependence of carbon monoxide oxidation at Ru(0001) on oxygen pressure and a particularly high reaction rate. Below we report density functional theory calculations of the energetics and reaction pathways of the speculated mechanism. We will show that the exceptionally high rate is actuated by a weakly but nevertheless well bound (1x1) oxygen adsorbate layer. Furthermore it is found that reactions via scattering of gas-phase CO at the oxygen covered surface may play an important role. Our analysis reveals, however, that reactions via adsorbed CO molecules (the so-called Langmuir-Hinshelwood mechanism) dominate.Comment: 5 pages, 4 figures, Phys. Rev. Letters, Feb. 1997, in prin

Ab initio Quantum and ab initio Molecular Dynamics of the Dissociative Adsorption of Hydrogen on Pd(100)

The dissociative adsorption of hydrogen on Pd(100) has been studied by ab initio quantum dynamics and ab initio molecular dynamics calculations. Treating all hydrogen degrees of freedom as dynamical coordinates implies a high dimensionality and requires statistical averages over thousands of trajectories. An efficient and accurate treatment of such extensive statistics is achieved in two steps: In a first step we evaluate the ab initio potential energy surface (PES) and determine an analytical representation. Then, in an independent second step dynamical calculations are performed on the analytical representation of the PES. Thus the dissociation dynamics is investigated without any crucial assumption except for the Born-Oppenheimer approximation which is anyhow employed when density-functional theory calculations are performed. The ab initio molecular dynamics is compared to detailed quantum dynamical calculations on exactly the same ab initio PES. The occurence of quantum oscillations in the sticking probability as a function of kinetic energy is addressed. They turn out to be very sensitive to the symmetry of the initial conditions. At low kinetic energies sticking is dominated by the steering effect which is illustrated using classical trajectories. The steering effects depends on the kinetic energy, but not on the mass of the molecules. Zero-point effects lead to strong differences between quantum and classical calculations of the sticking probability. The dependence of the sticking probability on the angle of incidence is analysed; it is found to be in good agreement with experimental data. The results show that the determination of the potential energy surface combined with high-dimensional dynamical calculations, in which all relevant degrees of freedon are taken into account, leads to a detailed understanding of the dissociation dynamics of hydrogen at a transition metal surface.Comment: 15 pages, 9 figures, subm. to Phys. Rev.

Ensemble-averaged Rabi oscillations in a ferromagnetic CoFeB film

Rabi oscillations describe the process whereby electromagnetic radiation interacts coherently with spin states in a non-equilibrium interaction. To date, Rabi oscillations have not been studied in one of the most common spin ensembles in nature: spins in ferromagnets. Here, using a combination of femtosecond laser pulses and microwave excitations, we report the classical analogue of Rabi oscillations in ensemble-averaged spins of a ferromagnet. The microwave stimuli are shown to extend the coherence-time resulting in resonant spin amplification. The results we present in a dense magnetic system are qualitatively similar to those reported previously in semiconductors which have five orders of magnitude fewer spins and which require resonant optical excitations to spin-polarize the ensemble. Our study is a step towards connecting concepts used in quantum processing with spin-transport effects in ferromagnets. For example, coherent control may become possible without the complications of driving an electromagnetic field but rather by using spin-polarized currents

High-dimensional quantum dynamics of adsorption and desorption of H2_2 at Cu(111)

We performed high-dimensional quantum dynamical calculations of the dissociative adsorption and associative desorption of hydrogen on Cu(111). The potential energy surface (PES) is obtained from density functional theory calculations. Two regimes of dynamics are found, at low energies sticking is determined by the minimum energy barrier, at high energies by the distribution of barrier heights. Experimental results are well-reproduced qualitatively, but some quantitative discrepancies are identified as well.Comment: 4 two column pages, revtex, 4 figures, to appear in Phys. Rev. Let

Betriebswirtschaftliche und marktbezogene Analyse von Hoffesten als Instrument der Regionalvermarktung

Vor allem im ökologischen Landbau werden Hoffeste, also Veranstaltungen auf bäuerlichen Bio-Betrieben, sehr oft eingesetzt. Wegen des Fehlens offizieller Zahlen ist jedoch schwer einzuschätzen, welchen Beitrag diese Feste zu einer erfolgreichen Regionalvermarktung leisten. Hieran setzt die vorliegende Studie an, die sich folgendermaßen gliedert. Im ersten Teil wird eine betriebswirtschaftliche Analyse von 19 Hoffest-Veranstaltern durchgeführt, die eine sehr breite Streuung der Kennzahlen aufweist. Im Allgemeinen wird den Betriebsleitern empfohlen, sich Transparenz über Aufwand und Ertrag ihrer Veranstaltung zu verschaffen und die betriebswirtschaftlichen Ergebnisse im Hinblick auf die für das Fest formulierten Marketingziele zu bewerten. Der zweite Teil der Studie beschäftigt sich mit der Wahrnehmung der Hoffeste durch die Besucher. Hierfür wurden diese zunächst auf dem Hoffest selbst (n=788) und nochmals nach sechs Monaten (n=73) befragt. Die Gäste auf Hoffesten zeichnen sich durch eine sehr positive Wahrnehmung der Hoffeste aus. Während bei den Stammgästen das Biokauf-Verhalten durch Hoffeste bestätigt wird, bleibt die Langzeitwirkung auf Neukunden unklar. Die Studie zeigt Maßnahmen auf, durch die das Leistungsspektrum von Hoffesten erfolgreich zur Geltung kommt. Insgesamt zeigen die Ergebnisse eine hohe Individualität von Hoffesten auf ökologisch wirtschaftenden Betrieben auf. Aufgrund der Besucherwahrnehmung lässt sich sagen, dass die Hoffeste ein wirksames Kommunikationsinstrument mit hohem Glaubwürdigkeitsfaktor und Erlebnischarakter für die Direktvermarkter sind