References of "Vandewalle, Nicolas"
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See detailGranular spirals on erodible sand bed submitted to a circular fluid motion
Caps, Hervé ULg; Vandewalle, Nicolas ULg

in Physical Review E (2003), 68(3, Pt 1), 31303

An experimental study of a granular surface submitted to a circular fluid motion is presented. The appearance of an instability along the sand-water interface is observed beyond a critical radius r(c ... [more ▼]

An experimental study of a granular surface submitted to a circular fluid motion is presented. The appearance of an instability along the sand-water interface is observed beyond a critical radius r(c). This creates ripples with a spiral shape on the granular surface. A phase diagram of such patterns is constructed and discussed as a function of the rotation speed omega of the flow and as a function of the height of water h above the surface. The study of r(c) as a function of h, omega, and r parameters is reported. Thereafter, r(c) is shown to depend on the rotation speed according to a power law. The ripple wavelength is found to decrease when the rotation speed increases and is proportional to the radial distance r. The azimuthal angle epsilon of the spiral arms is studied. It is found that epsilon scales with homegar. This lead to the conclusion that epsilon depends on the fluid momentum. Comparison with experiments performed with fluids allows us to state that the spiral patterns are not the signature of an instability of the boundary layer. [less ▲]

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See detailLong lasting instabilities in granular mixtures
Caps, Hervé ULg; Michel, Renaud; Lecocq, N. et al

in Physica A: Statistical Mechanics and its Applications (2003), 326(3-4), 313-321

We have performed experiments of axial segregation in the Oyama's drum. We have tested binary granular mixtures during very long times. The segregation patterns have been captured by a CCD camera and ... [more ▼]

We have performed experiments of axial segregation in the Oyama's drum. We have tested binary granular mixtures during very long times. The segregation patterns have been captured by a CCD camera and spatio-temporal graphs are created. We report the occurrence of instabilities which can last several hours! We stress that those instabilities originate from the competition between axial and radial segregations. We put into evidence the occurrence of giant fluctuations in the fraction of grain species along the surface during the unstable periods. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

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See detailLimit current density in 2D metallic granular packings
Dorbolo, Stéphane ULg; Ausloos, Marcel ULg; Vandewalle, Nicolas ULg

in European Physical Journal B -- Condensed Matter (2003), 34(2), 201-204

The electrical properties of a 2D packed metallic pentagons have been studied. The electrical characterization of such metallic pentagon heaps, like i - V measurements, has been achieved. Two distinct ... [more ▼]

The electrical properties of a 2D packed metallic pentagons have been studied. The electrical characterization of such metallic pentagon heaps, like i - V measurements, has been achieved. Two distinct regimes have been shown. They are separated by a transition line along which the system exhibits a memory effect behavior due to the irreversible improvement of electrical contacts between pentagons (hot spots). A limit current density has been found. [less ▲]

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See detailDynamics of crack opening in a one-dimensional desiccation experiment
Lecocq, N.; Vandewalle, Nicolas ULg

in Physica A: Statistical Mechanics and its Applications (2003), 321(3-4), 431-441

We used a simple one-dimensional experiment to investigate the dynamical aspects of crack opening that occurs in clay exposed to shrinkage induced by desiccation. The opening rate of single cracks is ... [more ▼]

We used a simple one-dimensional experiment to investigate the dynamical aspects of crack opening that occurs in clay exposed to shrinkage induced by desiccation. The opening rate of single cracks is obtained. A simple model is introduced to account for the observed behavior. Interaction between adjacent cracks is put into evidence and a collective behavior is observed. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailReexamination of the Branly effect
Dorbolo, Stéphane ULg; Ausloos, Marcel ULg; Vandewalle, Nicolas ULg

in Physical Review E (2003), 67(4, Pt 1), 40302

The electrical resistance of a metallic granular packing has been recorded at room temperature. A nearby burster between which sparks are produced, induces a decrease in the resistance of the granular ... [more ▼]

The electrical resistance of a metallic granular packing has been recorded at room temperature. A nearby burster between which sparks are produced, induces a decrease in the resistance of the granular packing as described in the works of Branly. Our measurements emphasize that the decrease is continuous and the resistance variations behave like a stretched exponential law due to the creation of new electrical paths as in nucleation-growth soldering processes. This behavior has been identified to be a diffusionlike process. [less ▲]

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See detailStripe patterns in self-stratification experiments
Lecocq, N.; Vandewalle, Nicolas ULg

in Fractals-Complex Geometry Patterns and Scaling in Nature and Society (2003), 11(Suppl. S), 259-269

We report pattern formation of complex stripes with binary and ternary granular mixtures. Ternary mixtures lead to a particular ordering of the strates which was not accounted for in former explanations ... [more ▼]

We report pattern formation of complex stripes with binary and ternary granular mixtures. Ternary mixtures lead to a particular ordering of the strates which was not accounted for in former explanations. Bouncing grains are found to have an important effect on strate formation. A complementary mechanism for self-stratification of binary and ternary granular mixtures is proposed. This mechanism leads to a simple model. Eventually we report the observation of self-stratification for a binary mixture of grains of the same size but with different shapes. [less ▲]

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See detailFoam imbibition in microgravity - An experimental study
Caps, Hervé ULg; Decauwer, H.; Chevalier, M. L. et al

in European Physical Journal B -- Condensed Matter (2003), 33(1), 115-119

We report an experimental study of aqueous foam imbibition in microgravity with strict mass conservation. The foam is in a Hele-Shaw cell. The bubble edge width l is measured by image analysis. The ... [more ▼]

We report an experimental study of aqueous foam imbibition in microgravity with strict mass conservation. The foam is in a Hele-Shaw cell. The bubble edge width l is measured by image analysis. The penetration of the liquid in the foam, the foam imbibition, the foam inflation, and the rigidity loss are shown all to obey strict diffusion processes. The motion of bubbles needed for the foam inflation is a slow two-dimensional process with respect to the one-dimensional capillary rise of liquid. The foam is found to imbibes faster than it inflates. [less ▲]

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See detailA Modified Tetris Model Including The Effect of Friction
Ludewig, François ULg; Dorbolo, Stéphane ULg; Caps, Hervé ULg et al

in Traffic and Granular Flow'03 (2003)

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See detailCascades of popping bubbles
Vandewalle, Nicolas ULg; Caps, Hervé ULg; Dorbolo, Stéphane ULg

in Physica A: Statistical Mechanics and its Applications (2002), 314(1-4), 320-324

We study the intermittent dynamics of collapsing foams. Avalanches of popping bubbles are observed. Although correlations between successive popping bubbles are emphasized, film raptures at the air/foam ... [more ▼]

We study the intermittent dynamics of collapsing foams. Avalanches of popping bubbles are observed. Although correlations between successive popping bubbles are emphasized, film raptures at the air/foam interface seem to be independent of the bubble size. Possible mechanisms for cascades of bubble pops are proposed and discussed. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailPatterns in hydraulic ripples with binary granular mixtures
Caps, Hervé ULg; Vandewalle, Nicolas ULg

in Physica A: Statistical Mechanics and its Applications (2002), 313(3-4), 357-364

An experimental study of a binary granular mixture submitted to a transient shear flow in a cylindrical container is reported. The formation of ripples with a spiral shape is observed. The appearance of ... [more ▼]

An experimental study of a binary granular mixture submitted to a transient shear flow in a cylindrical container is reported. The formation of ripples with a spiral shape is observed. The appearance of phase segregation in those spiral patterns is shown. The relative grain size between sand species is found to be a relevant parameter leading to phase segregation. However, the relative repose angle is an irrelevant parameter. The formation of sedimentary structures is also presented. They result from a ripple climbing process. The "sub-critical" or "super-critical" character of the lamination patterns is shown to depend on the rotation speed of the container. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailElectrical investigations of granular arches
Dorbolo, Stéphane ULg; Vandewalle, Nicolas ULg

in Physica A: Statistical Mechanics and its Applications (2002), 311(3-4), 307-312

Compaction dynamics and granular arches have been studied using the electrical resistance of a packing. An exponential decay of the resistance is found whatever the electrical current is. A fluctuation ... [more ▼]

Compaction dynamics and granular arches have been studied using the electrical resistance of a packing. An exponential decay of the resistance is found whatever the electrical current is. A fluctuation regime is then encountered. A characteristic relaxation time has been pointed out and is linked to the arch formation in the system. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

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See detailHysteretic behavior in metallic granular matter
Dorbolo, Stéphane ULg; Ausloos, Marcel ULg; Vandewalle, Nicolas ULg

in Applied Physics Letters (2002), 81(5), 936-938

Various packings made of metallic grains have been electrically characterized. Electrical breakdown is observed in I-V curves. A well defined critical point separates the insulating and the conducting ... [more ▼]

Various packings made of metallic grains have been electrically characterized. Electrical breakdown is observed in I-V curves. A well defined critical point separates the insulating and the conducting regime of the packing. The breakdown is reversible by submitting the packing to a small tap. This unusual property leads to hysteretic loops in I-V diagrams. The study of the behavior of I-V curves allows us to describe the system as a network of weak lossy contacts. The key parameter is the inner electrical field controlling the diode-like or diffusion-like state of the packing. (C) 2002 American Institute of Physics. [less ▲]

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See detailExperimental study of cracking induced by desiccation in 1-dimensional systems
Lecocq, N.; Vandewalle, Nicolas ULg

in European Physical Journal E -- Soft Matter (2002), 8(4), 445-452

We designed a simple experiment to study both the dynamical and statistical properties of cracking that occurs in a one-dimensional system composed of wet clay (or similar material) exposed to shrinkage ... [more ▼]

We designed a simple experiment to study both the dynamical and statistical properties of cracking that occurs in a one-dimensional system composed of wet clay (or similar material) exposed to shrinkage induced by desiccation. We study both the dynamical formation of cracks and the statistical characteristics of the final cracks pattern. We observe that the drying rate has a strong influence on the way cracks appear and grow. We find that the final crack width is related to the order of apparition of the cracks. We discuss the statistical distributions of cracks width and separation between two adjacent cracks. We also study the correlations between these two quantities. Our results are compared to the predictions of existing models. Finally, a comparison with another kind of clay is made. [less ▲]

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See detailLabyrinthine Granular Landscapes
Caps, Hervé ULg; Vandewalle, Nicolas ULg

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2001), 64(5, Pt 1), 52301

We have numerically studied a model of granular landscape eroded by wind. We show the appearance of labyrinthic patterns when the wind orientation turns by 90 degrees. The occurrence of such structures is ... [more ▼]

We have numerically studied a model of granular landscape eroded by wind. We show the appearance of labyrinthic patterns when the wind orientation turns by 90 degrees. The occurrence of such structures is discussed. Moreover, we introduce the density n(k) of "defects" as the dynamic parameter governing the landscape evolution. A power-law behavior of n(k) is found as a function of time. In the case of wind variations, the exponent (drastically) shifts from two to one. The presence of two asymptotic values of n(k) implies the irreversibility of the labyrinthic formation process. [less ▲]

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See detailRipple and Kink Dynamics
Caps, Hervé ULg; Vandewalle, Nicolas ULg

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2001), 64(4, Pt 1), 41302

We propose a relevant modification of the Nishimori-Ouchi model [Phys. Rev. Lett. 71, 197 (1993)] for granular landscape erosion. We explicitly introduce an additional parameter: the angle of repose ... [more ▼]

We propose a relevant modification of the Nishimori-Ouchi model [Phys. Rev. Lett. 71, 197 (1993)] for granular landscape erosion. We explicitly introduce an additional parameter: the angle of repose straight theta(r), and an additional process: avalanches. We show that the straight theta(r) parameter leads to an asymmetry of the ripples, as observed in natural patterns. The temporal evolution of the maximum ripple height h(max) is limited and not linear according to recent observations. The ripple symmetry and the kink dynamics are studied and discussed. [less ▲]

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See detailCascades of Popping Bubbles Along Air/Foam Interfaces
Vandewalle, Nicolas ULg; Lentz, J. F.

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2001), 64(2, Pt 1), 21507

We report image analysis of popping bubbles during the collapsing of two-dimensional (2D) and 3D aqueous foams. Although temporal and spatial correlations between successive popping bubbles within ... [more ▼]

We report image analysis of popping bubbles during the collapsing of two-dimensional (2D) and 3D aqueous foams. Although temporal and spatial correlations between successive popping bubbles within avalanches are emphasized, the breaking of a soap film at the air/foam interface seems to be independent of (i) the topology, (ii) the local curvature, and (iii) the size of the popping bubble. Possible mechanisms for cascades of pops are proposed and discussed. [less ▲]

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See detailGiant electrical fluctuations in metallic disordered packings
Vandewalle, Nicolas ULg; Dorbolo, Stéphane ULg

in European Physical Journal E -- Soft Matter (2001), 5(2), 129-131

We have experimentally studied granular arches through electrical measurements. The packing is composed of 2d metallic pentagons and is submitted to small taps. Large electrical fluctuations are observed ... [more ▼]

We have experimentally studied granular arches through electrical measurements. The packing is composed of 2d metallic pentagons and is submitted to small taps. Large electrical fluctuations are observed and they are distributed along power laws. The indicates the presence of long-time memory effects event the packing density remains constant around a value rho = 0.72 +/- 0.02. Large electrical fluctuations should be associated with the breaking/creation of granular arches. [less ▲]

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See detailAvalanches of Popping Bubbles in Collapsing Foams
Vandewalle, Nicolas ULg; Lentz, J. F.; Dorbolo, Stéphane ULg et al

in Physical Review Letters (2001), 86(1), 179-82

We report acoustic measurements of popping bubbles during the collapsing of aqueous foams. The sound pattern is analyzed using classical methods of statistical physics. It is found that membrane rupture ... [more ▼]

We report acoustic measurements of popping bubbles during the collapsing of aqueous foams. The sound pattern is analyzed using classical methods of statistical physics. It is found that membrane rupture concerns a wide variety of situations: small and large membranes at the air/foam interface. Avalanches of popping bubbles are put into evidence. Time durations in between successive pops seem to be distributed on a universal power law. [less ▲]

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See detailNon-Gaussian electrical fluctuations in a quasi-2d packing of metallic beads
Vandewalle, Nicolas ULg; Lenaerts, Cedric ULg; Dorbolo, Stéphane ULg

in Europhysics Letters [=EPL] (2001), 53(2), 197-201

The electrical properties of a two-dimensional packing of metallic beads are studied. Small mechanical perturbations of the packing lead to giant voltage fluctuations. Fluctuations are found to be non ... [more ▼]

The electrical properties of a two-dimensional packing of metallic beads are studied. Small mechanical perturbations of the packing lead to giant voltage fluctuations. Fluctuations are found to be non-Gaussian and seem to belong to Levy stable distributions. Anticorrelations have been also found for the sign of these fluctuations. [less ▲]

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See detailTaxonomy of stock market indices
Bonanno, G.; Vandewalle, Nicolas ULg; Mantegna, R. N.

in Physical Review. E : Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (2000), 62(6),

We investigate sets of financial nonredundant and nonsynchronously recorded time series. The sets are composed by a number of stock market indices located all over the world in five continents. By ... [more ▼]

We investigate sets of financial nonredundant and nonsynchronously recorded time series. The sets are composed by a number of stock market indices located all over the world in five continents. By properly selecting the time horizon of returns and by using a reference currency we find a meaningful taxonomy. The detection of such a taxonomy proves that interpretable information can be stored in a set of nonsynchronously recorded time series. [less ▲]

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