Flow measurements near a Reynolds ridge

The Reynolds ridge is a well-known phenomenon first observed in 1854 by Henry David Thoreau. It was then rediscovered by Langton in 1872, but Reynolds was the first to recognize that the surface tension difference was the physical mechanism behind its formation and saw the equality between the case of a spreading film and that of a stagnant film met by oncoming flow. However, it wasn't until McCutchen in 1970 that the prediction of a boundary layer forming beneath the film was introduced as the cause of the surface deformation rise ahead of the film due to the retardation of the flow. The first quantitative theory of the ridge was formed by Harper and Dixon (1974), who stated that the surface tension gradient balances the viscous shear stress generated in the boundary layer. Experimental studies of the ridge so far include Schlieren visualizations by Sellin (1968) as well as by Scott (1982) who measured the surface slope across the ridge and found good comparisons between the theoretical results of Harper and Dixon. Finally, it was Scott who recognized that even at very low levels of surface contamination the Reynolds ridge is found to exist

Amplitude measurements of Faraday waves

A light reflection technique is used to measure quantitatively the surface elevation of Faraday waves. The performed measurements cover a wide parameter range of driving frequencies and sample viscosities. In the capillary wave regime the bifurcation diagrams exhibit a frequency independent scaling proportional to the wavelength. We also provide numerical simulations of the full Navier-Stokes equations, which are in quantitative agreement up to supercritical drive amplitudes of 20%. The validity of an existing perturbation analysis is found to be limited to 2.5% overcriticaly.Comment: 7 figure

Pfad-Operatoralgebren in Konformen Quantenfeldtheorien

Two different kinds of path algebras and methods from noncommutative geometry are applied to conformal field theory: Fusion rings and modular invariants of extended chiral algebras are analyzed in terms of essential paths which are a path description of intertwiners. As an example, the ADE classification of modular invariants for minimal models is reproduced. The analysis of two-step extensions is included. Path algebras based on a path space interpretation of character identities can be applied to the analysis of fusion rings as well. In particular, factorization properties of character identities and therefore of the corresponding path spaces are - by means of K-theory -related to the factorization of the fusion ring of Virasoro- and W-algebras. Examples from nonsupersymmetric as well as N=2 supersymmetric minimal models are discussed. (orig.)Available from TIB Hannover: RN 4852(2000-15) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Pfaddarstellungen minimaler Modelle

An introduction to path spaces and AF-algebras over graphs is given. Statistical models over graphs are considered and the spectrum of the corner transfer matrix hamiltonian is given at zero temperature as well as at the critical point. Results are compared to the superselection structure of the corresponding conformal field theories. Path representations of certain sectors of conformal minimal models are obtained from factorizing Virasoro characters. Operator K-theory is applied to the path algebra to derive the fusion of the maximally extended chiral algebra. By generalized Rogers-Ramanujan-Identities the factorizing characters are related to sum forms allowing for a quasiparticle interpretation. The latter can be used for the construction of lattice Virasoro algebras. First results in this direction are given. (orig.)SIGLEAvailable from TIB Hannover: RN 4852(93-24) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman