14 Externe wissenschaftliche Einrichtungen
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Item Open Access Cohesive properties of bcc and fcc rubidium from ab initio pseudopotentials(1985) Maysenhölder, Waldemar; Louie, Steven G.; Cohen, Marvin L.Total-energy calculations have been performed for Rb at zero temperature using a self-consistent ab initio pseudopotential approach within a local-density-functional scheme. The energy difference between fcc and bcc Rb, and the energy barrier between these structures, are found to be extremely small near the equilibrium volume. Agreement of the calculated cohesive properties of bcc Rb with experimental values is good in view of the softness of the material. A transition from bcc to fcc has been calculated to occur at a pressure of about 52 kbar for T=0 K, which compares favorably with the observed value of 70 kbar for this transition at room temperature.Item Open Access Some didactical and some practical remarks on free plate waves(1987) Maysenhölder, WaldemarIt is recalled how wave equations can be generated from dispersion relations. The bending wave equation for thin plates including some higher-order terms is obtained by this general method and compared to the corresponding equation of Timoshenko. Further, the dispersion of free plate waves is derived in a concise and elementary manner without using a scalar potential and a vector potential for the displacements. Finally, as a matter of practical interest, exact and approximate expressions for the ratio of parallel to perpendicular displacements at a plate surface are calculated. Under favourable circumstances measurement of this ratio allows decomposing an observed wave into its quasi-longitudinal and bending components.Item Open Access Calculations of point-defect properties in copper, silver, and gold based on three-body interactions(1982) Bauer, Rolf; Maysenhölder, Waldemar; Seeger, AlfredLong-term trends in the calculation of defect properties in the noble metals are criticezed. On physical grounds it is argued that the model potentials used should allow for many-body interactions. Results based on potentials which include three-body interaction terms are presented for Cu, Ag, and Au.Item Open Access Vergleich von Reifen-Luftschallmessungen und Schwingungsmessungen mit Hilfe von laseroptischen Verfahren(1981) Eberspächer, Ralph Peter; Liedl, Werner; Tiziani, Hans J.; Litschel, Reinhold; Pfister, Berthold; Zeller, AlbertReifenschwingungen werden als primäre Ursache für die Geräuschemission von Pkw-Reifen angesehen. Es werden drei im Labor erprobte laseroptische Meßverfahren vorgestellt, die für Schwingungsuntersuchungen an auf dem Trommelprüfstand laufenden Reifen geeignet sind: Doppelpuls-Holografie, Doppelpuls-Specklefotografie und Laser-Doppler-Vibrometrie (LDV). Die Doppelpuls-Holografie liefert im Zusammenwirken mit einem Bild-Derotator das Schwingungsmuster des rotierenden Reifens. Die LDV ermöglicht die Messung der Schwingschnelle eines reifenfesten Punktes bzw. an einem raumfesten Punkt der Reifenoberfläche. Mit Rüfe der LDV kann eine gute Korrelation zwischen Laufflächenschwingungen und Reifenabrollgeräusch nachgewiesen werden.Item Open Access On the determination of interaction parameters from correlations in binary alloys(1987) Maysenhölder, WaldemarThe determination of interaction parameters from correlation functions in binary alloys is discussed by means of high-temperature expansions for the correlations. The inherent nonlinearity of this "inverse problem" of statistical mechanics leading to non-unique solutions is emphasized. The formulation includes pair and triplet interactions. Some results of a specific "inverse Monte Carlo calculation" are criticized. The paper provides a collection of formulae, especially for probabilities and correlations, which should prove useful for clarifying the subject.Item Open Access Körperschallausbreitung in Gebäuden : Untersuchungen mit einem Intensitätsmeßverfahren(1988) Maysenhölder, WaldemarBauakustische Körperschallmessungen haben sich bisher fast ausschließlich auf die Messung von Schwingungsamplituden beschränkt ("Körperschallpegel"). Die für einen wirksamen Schallschutz so wichtige Frage, wie sich die Schwingungsenergie ausbreitet, wird aber durch eine reine Pegelmessung meistens nicht zuverlässig beantwortet. Zu diesem Zweck muß die Körperschallintensität gemessen werden. Unter gewissen Bedingungen läßt sich die Körperschallintensität relativ einfach aus dem Kreuzspektrum zweier Beschleunigungssignale bestimmen. Die Grundzüge dieser in der Bauakustik noch neuen Meßtechnik werden erläutert. Ihr Einsatz bei der Lokalisierung von Schallbrücken und beim Studium der Schalllängsdämmung zeigt die deutliche Überlegenheit gegenüber reinen Körperschallpegelmessungen.Item Open Access Two subroutines for calculating lattice sums and the distortion field due to a point force in hexagonal systems(1981) Maysenhölder, WaldemarThe subroutines ARRANGE and DISPL contained in HEXALAT have been developed for application of solid state theory to hexagonal crystals, in particular to the hexagonal closed packed (hcp) structures. ARRANGE generates the coordinates of a roughly estispherical arrangement of atoms which occupy regular sites of an hcp structure, and thus provides a means for calculating lattice sums very easily.Item Open Access The Eshelby factor for cubic crystals with arbitrary elastic anisotropy(1984) Maysenhölder, WaldemarThe Eshelby factor for cubic crystals has been calculated for arbitrary anisotropy. One of the two integrations needed could be performed analytically. An expansion up to 4th order in the anisotropy and exact results for special cases are also given.Item Open Access Effect of three-body interactions on the formation entropy of monovacancies in copper, silver and gold(1985) Maysenhölder, Waldemar; Bauer, Rolf; Seeger, AlfredThe vacancy formation entropy in Cu, Ag and Au is estimated from model calculations with explicit treatment of three-body interactions. The three-body interactions cause a rather strong relaxation around the vacancies and therefore lead to lower values for the formation entropy than usual pair-potential calculations.Item Open Access Lowest-order approximations to relaxation volumes of monovacancies in cubic metals from pair potentials and Finnis-Sinclair potentials(1986) Maysenhölder, WaldemarRelaxation volumes of point defects in cubic metals can be conveniently estimated by differentiating approximate formation energies with respect to the lattice constant. Lowest-order analytical expressions for monovacancies have been derived for equilibrium pair potentials and for the N-body potentials of Finnis and Sinclair (1984). These expressions may be evaluated with little effort and prove far superior to other lowest-order approximations to vacancy relaxation volumes.