Probing liquid surface waves, liquid properties and liquid films with light diffraction

Surface waves on liquids act as a dynamical phase grating for incident light. In this article, we revisit the classical method of probing such waves (wavelengths of the order of mm) as well as inherent properties of liquids and liquid films on liquids, using optical diffraction. A combination of simulation and experiment is proposed to trace out the surface wave profiles in various situations (\emph{eg.} for one or more vertical, slightly immersed, electrically driven exciters). Subsequently, the surface tension and the spatial damping coefficient (related to viscosity) of a variety of liquids are measured carefully in order to gauge the efficiency of measuring liquid properties using this optical probe. The final set of results deal with liquid films where dispersion relations, surface and interface modes, interfacial tension and related issues are investigated in some detail, both theoretically and experimentally. On the whole, our observations and analyses seem to support the claim that this simple, low--cost apparatus is capable of providing a wealth of information on liquids and liquid surface waves in a non--destructive way.Comment: 25 pages, 12 figures, to appear in Measurement Science and Technology (IOP

Finite-Size Effects and Dynamical Scaling in Two-Dimensional Josephson Junction Arrays

In recent years many groups have used Fisher, Fisher, and Huse (FFH) dynamical scaling to investigate and demonstrate details of the superconducting phase transition. Some attention has been focused on two dimensions where the phase transition is of the Kosterlitz-Thouless-Berezinskii (KTB) type. Pierson et al. used FFH dynamical scaling almost exclusively to suggest that the dynamics of the two-dimensional superconducting phase transition may be other than KTB-like. In this work we investigate the ability of scaling behavior by itself to yield useful information on the nature of the transition. We simulate current-voltage (IV) curves for two-dimensional Josephson junction arrays with and without finite-size-induced resistive tails. We find that, for the finite-size effect data, the values of the scaling parameters, specifically the transition temperature and the dynamical scaling exponent z, depend critically on the magnitude of the contribution that the resistive tails make to the IV curves. In effect, the values of the scaling parameters depend on the noise floor of the measuring system.Comment: 24 pages, 8 figures; submitted to Physical Review

Determination of nutrient salts by automatic methods both in seawater and brackish water: the phosphate blank

9 páginas, 2 tablas, 2 figurasThe main inconvenience in determining nutrients in seawater by automatic methods is simply solved: the preparation of a suitable blank which corrects the effect of the refractive index change on the recorded signal. Two procedures are proposed, one physical (a simple equation to estimate the effect) and the other chemical (removal of the dissolved phosphorus with ferric hydroxide).Support for this work came from CICYT (MAR88-0245 project) and Conselleria de Pesca de la Xunta de GaliciaPeer reviewe

Experimentelle Untersuchung von Wandkonturierung in einem vierstufigen Axialverdichter Abschlussbericht zum Vorhaben 1.121

One of the most prominent trends in the development of axial compressors during the last decades was research on higher aerodynamic loading and lower aspect ratio. Further improvements in regard to these both aspects require a more detailed understanding of the flow phenomena at hub and tip of the blades. These phenomena are characterised by three dimensional boundary layers in the endwall regions of the blades. Additionally, numerical investigations of this area have to be provided with experimental data for validation purposes. To contribute to this research a four stage transsonic axial compressor with controlled diffusion airfoils (CDA) was build at the Institute of Turbomachinery. The CDA blades were produced in-house on a four axes milling machine. The experimental investigation presented in this study compares the basis configuration with a special set of stator blades with modified endwall contours at the hub. First, the overall performace of the compressor with both configurations was measured at four engine speeds. The modified stators showed an improvement in efficiency up to 0.5 points without affecting the stall margin. In addition the pressure rise was slightly higher at low speeds. In a second step, the flowfield of each rotor and stator was investigated at two operation points using a pneumatic probe. The flowfield in the hub region of each modified stator showed improvement in both, pressure rise and efficiency, while the upper half of the span indicated no significant differences. (orig.)Der Trend in der Axialverdichterentwicklung wird durch die Steigerung des Stufendruckverhaeltnisses gepraegt. Zur Beherrschung der hieraus resultierenden hohen aerodynamischen Belastung der Schaufelprofile ist es noetig die reibungsbehaftete Stroemung in den Wandbereichen zu kennen. Um diese zu untersuchen, wurde ein vierstufiger Axialverdichter moderner Auslegung errichtet. Um die Beschaffung der Beschaufelung qualitaets- und kostenmaessig zu optimieren, wurde eine Schaufelfertigung im Hause aufgebaut. Es wurde eine konturierte Leitbeschaufelung im Vergleich zur Basisbeschaufelung untersucht. Die Konturierung umfasste den Nabenbereich der vier Leitraeder. Die Kennfeldmessung zeigte im Bereich geringer Drosselung einen hoeheren Druckaufbau und Wirkungsgrad der konturierten Beschaufelung. Die Schluckgrenze wurde zu hoeheren Massenstroemen verschoben. Im stark angedrosselten Betriebszustand zeigten sich keine Unterschiede zwischen der Basisbeschaufelung und der konturierten Beschaufelung. Die Stabilitaetsgrenze wurde nicht verschoben. Die Stufenabstastung mit einer pneumatischen Vierlochsonde zeigte, dass die deutlichen Auswirkungen der Nabenkonturierung bei den Groessen Druck, Temperatur und Winkel auf die Nabennahen Bereich beschraenkt bleiben. Bei den abgeleiteten Stroemungsgroessen konnten Veraenderungen bis in die Kanalmitte festgestellt werden. Da die Nabenkonturierung einen Wirkungsgradgewinn ohne Fertigungsmehraufwand ermoeglicht ist sie ein interessantes Konstruktionsmerkmal zur Optimierung der Verdichterstroemung. (orig.)SIGLEAvailable from TIB Hannover: F00B972+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSiemens AG Energieerzeugung KWU, Erlangen (Germany); Bundesministerium fuer Wirtschaft und Technologie (BMWi), Berlin (Germany); ABB Reaktor GmbH, Mannheim (Germany); Rolls-Royce Deutschland GmbH, Oberursel (Germany); Maschinen- und Turbinen-Union G.m.b.H. (MTU), Muenchen (Germany)DEGerman