2 results
3 - Patterns
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- By G. E. Koppenwallner, D. Etling, C.-W. Leong, J. M. Ottino, E. Villermaux, J. Duplat, P. D. Weidman, V. O. Afenchenko, A. B. Ezersky, S. V. Kiyashko, M. I. Rabinovich, E. Bodenschatz, S. W. Morris, J. R. De bruyn, D. S. Cannell, G. Ahlers, C. F. Chen, F. Zoueshtiagh, P. J. Thomas, G. Gauthier, P. Gondret, F. Moisy, M. Rabaud, M. Fermigier, P. Jenffer, E. Tan, S. T. Thoroddsen, B. Vukasinovic, A. Glezer, M. K. Smith, N. J. Zabusky, W. Townsend, R. A. Hess, N. J. Brock, B. J. Weber, L. W. Carr, M. S. Chandrasekhara
- M. Samimy, Ohio State University, K. S. Breuer, Brown University, Rhode Island, L. G. Leal, University of California, Santa Barbara, P. H. Steen, Cornell University, New York
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- Book:
- A Gallery of Fluid Motion
- Published online:
- 25 January 2010
- Print publication:
- 12 January 2004, pp 28-41
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Summary
Vortex flows paint themselves
The artistlike pictures of vortex flows presented here have been produced by the flow itself. The method of this “natural” flow visualization can be described briefly as follows: The working fluid is water mixed with some paste in order to increase the viscosity. Vortex flows are produced by pulling a stick or similar devices through the fluid or by injecting fluid through a nozzle into the working tank.
The flow visualization is performed in the following way: the surface of the fluid at rest is sparkled with oil paint of different colors diluted with some evaporating chemical. After the vortex structures have formed due to wakes or jets, a sheet of white paper is placed on the surface of the working fluid, where the oil color is attached to the paper immediately. The final results are artistlike paintings of vortex flows which exhibit a rich variety of flow structures.
Mixing in regular and chaotic flows
These photographs show the time evolution of two passive tracers in a low Reynolds number two-dimensional timeperiodic flow. The initial condition corresponds to two blobs of dye, green and orange, located below the free surface of a cavity filled with glycerine. The flow is induced by moving the top and bottom walls of the cavity while the other two walls are fixed. In this experiment the top wall moves from left to right and the bottom wall moves from right to left; both velocities are of the form Usin2(2πt/T), with the same U and the same period T, but with a phase shift of 90°.
Tunability of τf in perovskites and related compounds
- P. L. Wise, I. M. Reaney, W. E. Lee, D. M. Iddles, D. S. Cannell, T. J. Price
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- Journal:
- Journal of Materials Research / Volume 17 / Issue 8 / August 2002
- Published online by Cambridge University Press:
- 31 January 2011, pp. 2033-2040
- Print publication:
- August 2002
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- Article
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Tuning the temperature coefficient of resonant frequency (τf) in microwave dielectrics has been attributed to two main mechanisms: (i) dilution of the average ionic polarizability; (ii) the onset of an octahedral tilt transition above room temperature. The contributions of each mechanism have been isolated using ceramics in the Srn+1TinO3n+1, SrxCa1−x)3Ti2O7, and (SrxCa1−x)TiO3 series. In the Srn+1TinO3n+1 series, relative permittivity (εr) and τf are linearly proportional over a broad range of values, 100–37 and 800–140 ppm/°C, n = 4 and 1, respectively. No structural phase transitions occur on cooling from the prototype symmetry, and the mechanism of tuning is attributed solely to dilution of the average ionic polarizability as the SrO:SrTiO3 ratio increases. Exchanging Ca for Sr in the (SrxCa1−x)3Ti2O7 series resulted in an 80% reduction in the magnitude of τf from +320 to +50 ppm/°C but only 21% in permittivity (58 to 46). The effect was nonlinear and attributed primarily to the onset of a phase transition involving rotations of the octahedra on cooling. Superlattice reflections associated with the octahedral tilt transition have been identified.