3 results
Flow past a rotationally oscillating cylinder
- S. Kumar, C. Lopez, O. Probst, G. Francisco, D. Askari, Y. Yang
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- Journal:
- Journal of Fluid Mechanics / Volume 735 / 25 November 2013
- Published online by Cambridge University Press:
- 24 October 2013, pp. 307-346
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Flow past a circular cylinder executing sinusoidal rotary oscillations about its own axis is studied experimentally. The experiments are carried out at a Reynolds number of 185, oscillation amplitudes varying from
$\mathrm{\pi} / 8$ to
$\mathrm{\pi} $, and at non-dimensional forcing frequencies (ratio of the cylinder oscillation frequency to the vortex-shedding frequency from a stationary cylinder) varying from 0 to 5. The diagnostic is performed by extensive flow visualization using the hydrogen bubble technique, hot-wire anemometry and particle-image velocimetry. The wake structures are related to the velocity spectra at various forcing parameters and downstream distances. It is found that the phenomenon of lock-on occurs in a forcing frequency range which depends not only on the amplitude of oscillation but also the downstream location from the cylinder. The experimentally measured lock-on diagram in the forcing amplitude and frequency plane at various downstream locations ranging from 2 to 23 diameters is presented. The far-field wake decouples, after the lock-on at higher forcing frequencies and behaves more like a regular Bénard–von Kármán vortex street from a stationary cylinder with vortex-shedding frequency mostly lower than that from a stationary cylinder. The dependence of circulation values of the shed vortices on the forcing frequency reveals a decay character independent of forcing amplitude beyond forcing frequency of
${\sim }1. 0$ and a scaling behaviour with forcing amplitude at forcing frequencies
${\leq }1. 0$. The flow visualizations reveal that the far-field wake becomes two-dimensional (planar) near the forcing frequencies where the circulation of the shed vortices becomes maximum and strong three-dimensional flow is generated as mode shape changes in certain forcing parameter conditions. It is also found from flow visualizations that even at higher Reynolds number of 400, forcing the cylinder at forcing amplitudes of
$\mathrm{\pi} / 4$ and
$\mathrm{\pi} / 2$ can make the flow field two-dimensional at forcing frequencies greater than
${\sim }2. 5$.
EURECA – The Future of Cryogenic Dark Matter Detection in Europe
- E. Pécontal, T. Buchert, Ph. Di Stefano, Y. Copin, H. Kraus, E. Armengaud, M. Bauer, I. Bavykina, A. Benoit, A. Bento, J. Blümer, L. Bornschein, A. Broniatowski, G. Burghart, P. Camus, A. Chantelauze, M. Chapellier, G. Chardin, C. Ciemniak, C. Coppi, N. Coron, O. Crauste, F.A. Danevich, M. De Jésus, P. de Marcillac, E. Daw, X. Defay, G. Deuter, J. Domange, P. Di Stefano, G. Drexlin, L. Dumoulin, K. Eitel, F. von Feilitzsch, D. Filosofov, P. Gandit, E. Garcia, J. Gascon, G. Gerbier, J. Gironnet, H. Godfrin, S. Grohmann, M. Gros, M. Hannewald, D. Hauff, F. Haug, S. Henry, P. Huff, J. Imber, S. Ingleby, C. Isaila, J. Jochum, A. Juillard, M. Kiefer, M. Kimmerle, H. Kluck, V.V. Kobychev, V. Kozlov, V.M. Kudovbenko, V.A. Kudryavtsev, T. Lachenmaier, J.-C. Lanfranchi, R.F. Lang, P. Loaiza, A. Lubashevsky, M. Malek, S. Marnieros, R. McGowan, V. Mikhailik, A. Monfardini, X.-F. Navick, T. Niinikoski, A.S. Nikolaiko, L. Oberauer, E. Olivieri, Y. Ortigoza, E. Pantic, P. Pari, B. Paul, G. Perinic, F. Petricca, S. Pfister, C. Pobes, D.V. Poda, R.B. Podviyanuk, O.G. Polischuk, W. Potzel, F. Pröbst, J. Puimedon, M. Robinson, S. Roth, K. Rottler, S. Rozov, C. Sailer, A. Salinas, V. Sanglard, M.L. Sarsa, K. Schäffner, S. Scholl, S. Scorza, A. Smolnikov, W. Seidel, S. Semikh, M. Stern, L. Stodolsky, M. Teshima, V. Tomasello, A. Torrento, L. Torres, V.I. Tretyak, J.A. Villar, M.A. Verdier, I. Usherov, J. Wolf, E. Yakushev
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- Journal:
- European Astronomical Society Publications Series / Volume 36 / 2009
- Published online by Cambridge University Press:
- 30 May 2009, pp. 249-255
- Print publication:
- 2009
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EURECA (European Underground Rare Event Calorimeter Array) is an astro-particle physics facility aiming to directly detect galactic dark matter. The Laboratoire Souterrain de Modane has been selected as host laboratory. The EURECA collaboration unites CRESST, EDELWEISS and the Spanish-French experiment ROSEBUD, thus concentrating and focussing effort on cryogenic detector research in Europe into a single facility. EURECA will use a target mass of up to one ton, enough to explore WIMP – nucleon scalar scattering cross sections in the region of 10-9 – 10-10 picobarn. A major advantage of EURECA is the planned use of more than just one target material (multi target experiment for WIMP identification).
Advanced Stacked Elemental Layer Process for Cu(InGa)Se2 Thin Film Photovoltaic Devices
- V. Probst, F. Karg, J. Rimmasch, W. Riedl, W. Stetter, H. Harms, O. Eibl
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- Journal:
- MRS Online Proceedings Library Archive / Volume 426 / 1996
- Published online by Cambridge University Press:
- 10 February 2011, 165
- Print publication:
- 1996
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Targeting large area and low cost processing of highly efficient thin film solar modules an advanced stacked elemental layer process for Cu(InGa)Se2 (CIGS) thin films is presented. Key process steps are i) barrier coating of the soda lime glass substrate combined with the addition of a sodium compound to the elemental Cu/In/Ga/Se-precursor stack and ii) rapid thermal processing (RTP) to form the CIGS compound.
By this strategy exact impurity control is achieved and the advantageous influence of sodium on device performance and on CIGS film formation is demonstrated unambiguously by means of electrical characterisation, XRD, SEM, TEM and SIMS. Sodium enriched and sodium free precursor stacks were heated to intermediate states (300°C–500°C) of the RTPreaction process. The experiment clearly reveals that on the reaction pathway to the chalcopyrite semiconductor increased amounts of copper-selenide are formed, if sodium is added to the precursor films. TEM-electron diffraction unambiguously identifies the CuSe-phase which is localised at the surface of the forming CIGS-film. These experimental findings propose a sodium assisted quasi liquid growth model for the CIS formation taking into account that sodium promotes the existence of CuSe at higher temperatures and its effect as a flux agent. The model contributes to a better understanding of the observed superior crystal qualitiy for sodium enriched in contrast to sodium free CIGS films.
Application of these experimental findings in the technique of the optimized and controlled sodium incorporation significantly improves process reproducibility, CIGS film homogenity over larger substrate areas and shifts the average efficiency of cells and modules to a significantly higher level. This is demonstrated by a 12-cell integrated series connected minimodule with an aperture area of 51 cm2 and a confirmed efficiency of 11.75 %.
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