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  • 1
    Electronic Resource
    Electronic Resource
    Phenomenological model of chaotic mode competition in surface waves (1985)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 6 (1985), S. 309-316 
    Details
    ISSN: 0392-6737
    Keywords: Turbulent flows, convection and heat transfer ; Hydrodynamic waves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Description / Table of Contents: Riassunto Si presenta un modello a quattro variabili (due oscillatori accoppiati forzati parametricamente) che descrive molti dei fenomeni visti in un esperimento sulle onde di superficie nel quale la competizione fra le configurazioni spaziali produce un comportamento caotico. Il modello riproduce la via al caos, la dimensione dell'attrattore, l'entropia di Kolmogorov e (approssimativamente) il diagramma di fase.
    Notes: Summary We present a four-variable model (two coupled parametrically forced oscillators) that describes many of the phenomena seen in an experiment on surface waves in which the competition between spatial patterns produces chaotic behaviour. The model reproduces the route to chaos, the dimension of the attractor, the Kolmogorov entropy and (approximately) the phase diagram.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02450690
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  • 2
    Electronic Resource
    Electronic Resource
    Geometry of isothermal and isoconcentration surfaces in thermal turbulence (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 647-661 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The geometry of isothermal surfaces for Rayleigh–Bénard convection at Rayleigh numbers R in the range 107 to 3×108 (close to the soft to hard turbulence transition) are measured. The measurements were made by imaging the color of light scattered from chiral nematic particles suspended in the fluid. Although the isotherms are multiply connected and convoluted, they do not display fractal scaling. The minimum scale for convolutions can be understood as resulting from the competition between folding and thermal diffusion. The isotherms are characterized statistically by the probability distribution of the local curvature, which may be described approximately as a stretched exponential. The distribution is essentially independent of the position and orientation of the plane of observation, and of R over the range explored. The geometry of the isotherms is compared to that of isoconcentration surfaces for dye injected into the flow; the latter do show a limited range of approximate fractal scaling because of the smaller diffusivity of the dye. The thermal measurements are supplemented by simultaneous measurements of the velocity field obtained by particle image velocimetry. Unstable waves often form on the thermal boundary layers in regions of high horizontal velocity gradient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858891
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  • 3
    Electronic Resource
    Electronic Resource
    Stability boundaries and phase-space measurement for spatially extended dynamical systems (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 280-284 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Automated methods of studying the stability boundaries and phase-space dynamics of a spatially extended dynamical system are presented. The stability boundaries are determined accurately as a function of external parameters in an automated search. The amplitudes of the individual spatial modes are measured in real time in order to determine the structure of the attractors in phase space. Some control over initial conditions allows the basins of attraction and the transients leading to the attractors to be studied as well. The methods are applied specifically to interacting waves on a fluid surface, but should also be useful to other extended dynamical systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140241
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  • 4
    Electronic Resource
    Electronic Resource
    Chaos and threshold for irreversibility in sheared suspensions (2005)
    [s.l.] : Nature Publishing Group
    Nature 438 (2005), S. 997-1000 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Systems governed by time reversible equations of motion often give rise to irreversible behaviour. The transition from reversible to irreversible behaviour is fundamental to statistical physics, but has not been observed experimentally in many-body systems. The flow of a newtonian fluid at low ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature04380
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  • 5
    Electronic Resource
    Electronic Resource
    Nonlinear dynamics Chaos in space and time (2000)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 404 (2000), S. 710-711 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Many aspects of nature are essentially unpredictable over the long term, even when quantum effects are completely absent. A frequent cause is chaotic dynamics, which can arise when the rates of change of important dynamical variables depend in a nonlinear fashion on the variables themselves. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35008168
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  • 6
    Electronic Resource
    Electronic Resource
    Persistent patterns in transient chaotic fluid mixing (1999)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 770-772 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Chaotic advection of a fluid can cause an initially inhomogeneous impurity (a passive scalar field) to develop complex spatial structure as the elements of the fluid are stretched and folded, even if the velocity field is periodic in time. The effect of chaotic advection on the transient mixing ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/44529
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  • 7
    Electronic Resource
    Electronic Resource
    Inverting chaos: Extracting system parameters from experimental data (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 6 (1996), S. 528-533 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Given a set of experimental or numerical chaotic data and a set of model differential equations with several parameters, is it possible to determine the numerical values for these parameters using a least-squares approach, and thereby to test the model against the data? We explore this question (a) with simulated data from model equations for the Rossler, Lorenz, and pendulum attractors, and (b) with experimental data produced by a physical chaotic pendulum. For the systems considered in this paper, the least-squares approach provides values of model parameters that agree well with values obtained in other ways, even in the presence of modest amounts of added noise. For experimental data, the "fitted'' and experimental attractors are found to have the same correlation dimension and the same positive Lyapunov exponent. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.166200
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  • 8
    Electronic Resource
    Electronic Resource
    Probability distributions and thermal transport in a turbulent grid flow (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2255-2263 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent theoretical proposals concerning non-Gaussian statistics of passive scalars in random velocity fields are tested experimentally, by measuring the probability distributions of fluctuating temperature in an oscillating grid flow across which a steady temperature gradient is maintained. Pronounced exponential tails occur at sufficiently high Reynolds number R, and predominantly Gaussian statistics at low R. When the extended tails are present for the passive scalar, the corresponding velocity power spectrum shows reasonable scaling, and the velocity distribution is not far from Gaussian. The present paper provides a more complete characterization of the flow field than an earlier brief report [Phys. Rev. Lett. 67, 3507 (1991)], and also contains a description of additional features, such as the skewness of the distributions. Finally, the effective or eddy diffusivity of both heat and a molecular impurity are measured and compared.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858564
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  • 9
    Electronic Resource
    Electronic Resource
    Transport by capillary waves. Part II: Scalar dispersion and structure of the concentration field (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1344-1350 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments on the transport of passive scalar tracers on capillary waves generated by the Faraday instability are presented. A spot of fluorescent dye is placed just below the fluid surface and the evolution of the dye concentration field is studied. Substantial transport is found over large distances, consistent with earlier observations of particle motion on the fluid surface. The time evolution of the radial distribution of impurity is characterized on a coarse-grained scale. At large driving amplitudes ε, where the wave pattern is time-dependent with only short-range spatial correlations, the diffusion may be described as a normal Brownian process. At lower ε, where the patterns are well ordered (but modulated), this approximation fails though there is still significant transport. For large ε, the isoconcentration contours are well described as fractals with a dimension that approaches 1.40±0.05 at long times. The scalar gradient field may be described as a multifractal. These results are surprisingly similar to those obtained for transport in turbulent shear flows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858063
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  • 10
    Electronic Resource
    Electronic Resource
    Transport by capillary waves. Part I. Particle trajectories (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 1955-1965 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transport of particles on capillary waves generated by the Faraday instability is studied experimentally. The motion of a single particle on the fluid surface is determined over 4×104 wave periods by particle tracking. Erratic particle motion over large distances occurs even for small wave amplitudes, where the pattern is ordered, though spatially modulated. This implies that the wave field is accompanied by significant flows with velocities approximately 30 times smaller than the instantaneous local fluid velocities. The particle motion is characterized statistically. The displacements of the particle in the two orthogonal directions follow independent Gaussian distributions. It is found that the variance of the particle's displacement grows with the elapsed time interval as V(τ)∼τ2H over times long compared with the correlation time of the motion. The exponent H depends on the wave amplitude, decreasing gradually from about 0.7 to an asymptotic value of 0.5 (corresponding to classical Brownian motion) at large wave amplitudes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857671
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