Image correlation velocimetry

Tokumaru, P. T.; Dimotakis, Paul E.

doi:10.1007/bf00192228

Cited by 147 publications

(78 citation statements)

References 17 publications

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“…By averaging the CCD signal over horizontal rows of pixels, we are able to measure accurately the time, t, and height, z, dependence of the volume fraction, ϕ(z, t), with a spatial resolution of about 100 µm. We obtain the evolution of the local sedimentation velocity profiles, v(z, t), using an Image Correlation Velocimetry (ICV) algorithm [20] that we apply to rectangular Regions Of Interest (ROIs) of the CCD images corresponding to the width of the sample and a height ∆z = 0.5 mm. To quantify the microscopic dynamics, we measure space and time-resolved intensity correlation functions (ICFs) [19],…”

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Highly Nonlinear Dynamics in a Slowly Sedimenting Colloidal Gel

et al. 2011

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We use a combination of original light scattering techniques and particles with unique optical properties to investigate the behavior of suspensions of attractive colloids under gravitational stress, following over time the concentration profile, the velocity profile, and the microscopic dynamics. During the compression regime, the sedimentation velocity grows nearly linearly with height, implying that the gel settling may be fully described by a (time-dependent) strain rate. We find that the microscopic dynamics exhibit remarkable scaling properties when time is normalized by strain rate, showing that the gel microscopic restructuring is dominated by its macroscopic deformation.PACS numbers: 47.57.ef, 64.70.pv, 82.70.Dd Gels and attractive glasses resulting from the aggregation of colloidal particles are the subject of extensive studies because their physical behavior often results from a complex interplay between equilibrium thermodynamics and nonequibrium dynamic processes [1][2][3], and because they are relevant for understanding networkforming biological systems [4] and for industrial applications. Although they exhibit solid-like mechanical properties, colloidal gels are easily disrupted by small perturbations, such as gravitational forces. While a large body of macroscopic observations of gels under gravitational stress exists [5][6][7][8][9][10][11][12][13], very little is known on the microscopic processes at play during sedimentation, thus limiting our ability to understand and predict the behavior of sedimenting gels.Here, we use a novel light scattering method to gain access to the dynamics of a slowly settling colloidal system from the macroscopic deformation of the sample down to the relaxational behavior at the particle scale. We find that the very slow macroscopic deformation occurs via irreversible plastic events at the microscopic scale. Remarkably, the gel behavior at all scales is controlled by a single parameter, the time-dependent compression rate, in striking analogy with recent observations on deformed polymer [14] and colloidal [15] glasses.We study gels formed by attractive colloidal hard spheres with radius R = 82 ± 3 nm, suspended in an aqueous solvent at an initial volume fraction ϕ 0 = 0.123 (more details can be found in [16][17][18]). Gelation is induced by attractive depletion forces obtained by adding micelles of a nonionic surfactant. The interaction between colloids is well described by the Asakura-Oosawa depletion potential [16], with a range r ≈ 3 nm. The potential can be mapped on the Adhesive Hard Sphere model, with a stickiness parameter τ ≃ 0.01 [16,17]. The density mismatch between the particles and the solvent is ∆ρ = 1.12 g/cm 3 . The particles have an intrinsic optical anisotropy; accordingly, they scatter light with polarization both parallel and perpendicular ("depolarized") to that of the incident radiation. The depolarized scattered intensity is an accurate probe of the local particle concentration [16].To probe the sedimentation process in great detail, we use...

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Highly Nonlinear Dynamics in a Slowly Sedimenting Colloidal Gel

et al. 2011

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“…Among those attempts Tokumaru & Dimotakis (1995) proposed a semilocal approach (Ritz method see section 3.1.2) -involving a parametric cubic model and insuring a global spatial consistency-appropriate for both scalar and particle images. The integral form (7) of the equation of motion (6) is employed in this method.…”

Section: First-and Second-order Regularization Robust Normsmentioning

confidence: 99%

Variational fluid flow measurements from image sequences: synopsis and perspectives

2009

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Variational approaches to image motion segmentation has been an active field of study in image processing and computer vision for two decades. We present a short overview over basic estimation schemes and report in more detail recent modifications and applications to fluid flow estimation. Key properties of these approaches are illustrated by numerical examples. We outline promising research directions and point out the potential of variational techniques in combination with correlation-based PIV methods, for improving the consistency of fluid flow estimation and simulation.

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“…• image deformation techniques (Astarita, 2007;2008;Jambunathan et al, 1995;Lecuona et al, 2002;Nogueira et al, 1999;Nogueira, Lecuona, Rodriguez, Alfaro & Acosta, 2005;Scarano, 2004;Schrijer & Scarano, 2008;Tokumaru & Dimotakis, 1995), where the entire images are deformed accordingly to the assumed velocity field before the sub-division into interrogation windows to be correlated, also using different image interpolation techniques.…”

Section: Introductionmentioning

confidence: 99%

Limits in Planar PIV Due to Individual Variations of Particle Image Intensities

Nobach¹

2012

The Particle Image Velocimetry - Characteristics, Limits and Possible Applications

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Image correlation velocimetry

Cited by 147 publications

References 17 publications

Highly Nonlinear Dynamics in a Slowly Sedimenting Colloidal Gel

Highly Nonlinear Dynamics in a Slowly Sedimenting Colloidal Gel

Variational fluid flow measurements from image sequences: synopsis and perspectives

Limits in Planar PIV Due to Individual Variations of Particle Image Intensities

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