W. Meyer

Substoichiometric cobalt oxide monolayer on Ir(100)-(1 × 1).

A substoichiometric monolayer of cobalt oxide has been prepared by deposition and oxidation of slightly less than one monolayer of cobalt on the unreconstructed surface of Ir(100). The ultrathin film was investigated by scanning tunnelling microscopy (STM) and quantitative low-energy electron diffraction (LEED). The cobalt species of the film reside in or near hollow positions of the substrate with, however, unoccupied sites (vacancies) in a 3 × 3 arrangement. In the so-formed 3 × 3 supercell the oxides oxygen species are both threefold and fourfold coordinated to cobalt, forming pyramids with a triangular and square cobalt basis, respectively. These pyramids are the building blocks of the oxide. Due to the reduced coordination as compared to the sixfold one in the bulk of rock-salt-type CoO, the Co-O bond lengths are smaller than in the latter. For the threefold coordination they compare very well with the bond length in oxygen terminated CoO(111) films investigated recently. The substoichiometric 3 × 3 oxide monolayer phase transforms to a stoichiometric c(10 × 2)-periodic oxide monolayer under oxygen exposure, in which, however, cobalt and oxygen species are in (111) orientation and so form a CoO(111) layer.

Berechnung der Netzrückwirkungen von Stromrichteranlagen mit Raumzeigern

ÜbersichtDynamische Netzberechnungen lassen sich vorteilhaft in Drehstrom-Modalkomponenten durchführen. Das Beispiel der meistgebräuchlichen Drehstrom-Brückenschaltung zeigt, daß auch Stromrichter mit Raumzeigern beschrieben werden können. Unter Berücksichtigung der Eigenschaften stromführender Ventile werden die Ersatzschaltpläne sowie die Zünd- und Löschbedingungen in Modalkomponenten hergeleitet. Die Ergebnisse numerischer Berechnungen stimmen mit Messungen überein. Eine Parameterstudie zeigt die für Brückenschaltungen typischen Stromortskurven in Modalkomponenten.ContentsCalculating transients in power systems it is advantageous to use symmetrical components. The example of the most common three-phase bridge converter shows that also current converters can be described in space phasors. With respect to the characteristics of conducting valves the networks and the conditions of firing and commutation ending are deduced. Numerically calculated results agree with measurements. A parameter study shows the typical space phasor curves of bridge converter currents.

Hidden Markov Models for Classification of Heart Rate Variability in RR Time Series

Discrete hidden Markov models (HMM) are trained in order to differentiate between RR series of persons in normal sinus rhythm and of post-myocardial infarct patients with six or more ventricular premature complexes per hour during 24 hour Holter ECG recording.

Dynamische Kurzschlußbeanspruchung in Gleichstromanlagen

ÜbersichtDie Zeitverläufe der Kurzschlußströme und daher auch der elektromagnetischen Kurzschlußkräfte in Gleichstromanlagen sind sehr vielfältig und können nur mit einer größeren Anzahl von Parametern beschrieben werden. Für jeden dieser Verläufe kann eine einfache Ersatzfunktion — Rechteck oder Sinusquadrat — bestimmt werden, die annähernd den gleichen maximalen Momentanwert der mechanischen Beanspruchung wie die ursprüngliche elektromagnetische Kraft verursacht, wenn die Kurzschlußdauer kleiner als die halbe mechanische Periodendauer ist. Nach geeigneter Modifikation kann das Ersatzrechteck auch dann verwendet werden, wenn die Kurzschlußdauer größer ist als die halbe mechanische Periodendauer.ContentsThe time patterns of short-circuit currents and therefore of the electromagnetic short-circuit forces in DC bus systems are very manifold; they only can be expressed by use of several parameters. For each of these patterns a substitute time function can be determined (rectangle or sinussquare) which causes about the same maximum instantaneous value of mechanical strength, like the original electromagnetic force, if the short-circuit duration is less than the half period of the mechanical oscillation. After suitable modification the rectangle function can also be used if the short-circuit duration is greater than the half period of the mechanical oscillation.

Erweiterung der Teilleitermethode auf Anordnungen mit magnetischen Gebieten

ÜbersichtDie Teilleitermethode ist auf Anordnungen mit unterschiedlich permeablen Gebieten erweiterbar. Hierzu werden Ähnlichkeitsbezichungen angegeben, die das Original in ein Modell konstanter Permeabilität überführen. Die in diesem Modell auftretenden Sprünge der magnetischen Feldstärke ergeben Strombeläge in den Grenzflächen der Gebiete. Die derart erweiterte Teilleitermethode wird auf die Berechnung des Stromes im Mantel eines Rohrleiters angewandt und mit der analytischen Näherungslösung verglichen.ContentsThe method of current splitting can be extended for arrangements with diversified permeable spaces. Accordingly, model equations are put foreward, which transfer the original to a model of constant permeability. Discontinuities of magnetic field strength, occuring in this model, yield to distributed currents in the boundary surface. The method of current splitting extended in this way, is applied to the current calculations of a metal-clad conductor and compared with the analytical approximation.

Ligand Effect in Hydrogen Adsorption on Epitaxial Nickel Films

Abstract The adsorption structure of hydrogen on ultrathin epitaxial nickel films in pseudomorphic arrangement on the unreconstructed Ir(100) surface is investigated by quantitative low-energy electron diffraction (LEED). This is highly interesting in the light of the fact that on Ni(100) adsorption is in hollow sites whilst on unreconstructed Ir(100) it is exclusively in bridge sites. On Ni films thicker than 1 monolayer (ML) the adsorption is in 4-fold coordinated hollow sites as it is on Ni(100). This is in spite of the considerable tensile strain of the Ni film (+8.9%) and is interpreted by the dominance of ensemble effects in the hydrogen bonding. In contrast, on the 1 ML Ni film on Ir(100), with iridium atoms being nearest neighbours to nickel atoms, there is occupation of both bridge and hollow sites of the nickel layer – a clear indication for the presence of ligand effects.

Non-stationary Langevin equation in cardiology

As a model for RR-interval time series, a nonstationary linear Langevin equation is used. Approximating the time-dependent point of equilibrium by a piecewise constant function, an algorithm is presented to reconstruct the amplitudes of this trend. From these quantities a measure of activity is defined, which is shown to be an indicator of a deterioration of cardiac performance such as involved by congestive heart failure.