References of "Vandewalle, Nicolas"
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See detailFoamability and structure analysis of foams in Hele-Shaw cell
Caps, Hervé ULg; Vandewalle, Nicolas ULg; Broze, Guy ULg et al

in Applied Physics Letters (2007), 90(21),

The authors have generated two-dimensional foams by imposing an intermittent drainage in a Hele-Shaw cell partially filled with a detergent/water mixture. The foam generation associated with this process ... [more ▼]

The authors have generated two-dimensional foams by imposing an intermittent drainage in a Hele-Shaw cell partially filled with a detergent/water mixture. The foam generation associated with this process is reproducible and depends on the surfactant molecules composing the solution. A kinetic model can be proposed for the foam evolution. The structure of the foam is also investigated: the average bubble side number and correlation functions are measured. Distinguishable behaviors are observed for different surfactant molecules. This way of producing a foam is thus adequate for applied foam structure characterizations and fundamental studies. (c) 2007 American Institute of Physics. [less ▲]

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See detailCritical parameters for the partial coalescence of a droplet
Gilet, Tristan ULg; Mulleners, Karen; Lecomte, Jean-Paul et al

in Physical Review E (2007), 75(3, Pt 2), 36303

The partial coalescence of a droplet onto a planar liquid-liquid interface is investigated experimentally by tuning the viscosities of both liquids. The problem mainly depends on four dimensionless ... [more ▼]

The partial coalescence of a droplet onto a planar liquid-liquid interface is investigated experimentally by tuning the viscosities of both liquids. The problem mainly depends on four dimensionless parameters: The Bond number (gravity vs surface tension), the Ohnesorge numbers (viscosity in both fluids vs surface tension), and the density relative difference. The ratio between the daughter droplet size and the mother droplet size is investigated as a function of these dimensionless numbers. Global quantities such as the available surface energy of the droplet have been measured during the coalescence. The capillary waves propagation and damping are studied in detail. The relation between these waves and the partial coalescence is discussed. Additional viscous mechanisms are proposed in order to explain the asymmetric role played by both viscosities. [less ▲]

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See detailThe role of deformation in the bouncing droplet problem
Terwagne, Denis ULg; Gilet, Tristan ULg; Dorbolo, Stéphane ULg et al

Poster (2007, March)

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See detailThe influence of grain shape, friction and cohesion on granular compaction dynamics
Vandewalle, Nicolas ULg; Lumay, Geoffroy ULg; Gerasimov, O. et al

in European Physical Journal E -- Soft Matter (2007), 22(3), 241-248

This article is a review of our recent and new experimental works on granular compaction. The effects of various microscopic parameters on the compaction dynamics are addressed, in particular the ... [more ▼]

This article is a review of our recent and new experimental works on granular compaction. The effects of various microscopic parameters on the compaction dynamics are addressed, in particular the influence of the grain shape, the friction and the cohesion between the grains. Two dimensional and three dimensional systems are analysed. And the role of dimensionality will be emphasized. Theoretical and numerical investigations provide additional informations about that phenomenon. Indeed numerical models permit us to study the influence of some parameters not easily accessible experimentally. Our results show that the above mentioned parameters have a deep impact on the compaction dynamics. Anisotropic grains lead to two different compaction regimes separated by a "burst" of the packing fraction. Friction is observed to modify how the grains are arranged in the pile. This is confirmed by numerical simulations. Cohesive forces between particles inhibit compaction and lead to extremely low values of the packing fraction. [less ▲]

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See detailThe role of deformation in the bouncing droplet problem
Terwagne, Denis ULg; Gilet, Tristan ULg; Dorbolo, Stéphane ULg et al

Poster (2007, February)

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See detailEffects of electromagnetic waves on the electrical properties of contacts between grains
Dorbolo, Stéphane ULg; Merlen, A.; Creyssels, M. et al

in Europhysics Letters [=EPL] (2007), 79(5),

A DC electrical current is injected through a chain of metallic beads. The electrical resistance of each bead- bead contacts is measured. At low current, the distribution of these resistances is large and ... [more ▼]

A DC electrical current is injected through a chain of metallic beads. The electrical resistance of each bead- bead contacts is measured. At low current, the distribution of these resistances is large and log- normal. At high enough current, the resistance distribution becomes sharp and Gaussian due to the creation of microweldings between some beads. The action of nearby electromagnetic waves ( sparks) on the electrical conductivity of the chain is also studied. The spark effect is to lower the resistance values of the more resistive contacts, the best conductive ones remaining unaffected by the spark production. The spark is able to induce through the chain a current enough to create microweldings between some beads. This explains why the electrical resistance of a granular medium is so sensitive to the electromagnetic waves produced in its vicinity. [less ▲]

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See detailInvestigation of SDS, DTAB and CTAB micelle microviscosities by electron spin resonance
Bahri, Mohamed Ali ULg; Hoebeke, Maryse ULg; Grammenos, Angeliki ULg et al

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2006), 290(1-3), 206-212

Electron spin resonance spectroscopy (ESR) of the nitroxide labelled fatty acid probes (5-, 16-doxyl stearic acid) was used to monitor the micelle microviscosity of three surfactants at various ... [more ▼]

Electron spin resonance spectroscopy (ESR) of the nitroxide labelled fatty acid probes (5-, 16-doxyl stearic acid) was used to monitor the micelle microviscosity of three surfactants at various concentrations in aqueous solution: sodium dodecyl sulphate (SDS), dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB). At low surfactant concentration, there is no micelle, the ESR probe is dissolved in water/surfactant homogeneous phase and gives his microviscosity. At higher surfactant concentration, an abrupt increase in microviscosity indicates the apparition of micelles and, the solubilization of the probes in micelles. The microviscosity of the three surfactants, in a large surfactant range, was obtained as well as the critical micelle concentration (CMC). The microviscosity increased slightly with the increase in surfactant concentration. Phosphate buffer lowered the CMC value and generally increased the microviscosity. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

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See detailPrecursors to avalanches in a granular monolayer
Scheller, T.; Huss, C.; Lumay, Geoffroy ULg et al

in Physical Review E (2006), 74(3, Pt 1), 31311

We investigate the stability of a granular monolayer composed of spherical grains on an inclined plate. When the tilt angle alpha increases, some reorganizations are observed throughout the pile. The ... [more ▼]

We investigate the stability of a granular monolayer composed of spherical grains on an inclined plate. When the tilt angle alpha increases, some reorganizations are observed throughout the pile. The packing fraction rho of the packing evolves by successive jumps. Those discontinuous events precede the collapse of the pile at a critical angle alphac. The occurrence of precursors before avalanches is modeled by stop-and-go motions of blocks due to the competition between sliding friction and the Janssen effect [J. Durand, (Springer-Verlag, New York, 2000)]. [less ▲]

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See detailSchool fish behaviour
Becco, Christophe ULg; Vandewalle, Nicolas ULg; Delcourt, Johann ULg et al

Conference (2006, September)

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See detailLinking compaction dynamics to the flow properties of powders
Lumay, Geoffroy ULg; Vandewalle, Nicolas ULg; Delattre, Luc ULg et al

in Applied Physics Letters (2006), 89(9),

The authors have investigated the flow properties of powders by using two classical techniques based on the shear stress measurements and the count of intermittent avalanches, respectively. Results are ... [more ▼]

The authors have investigated the flow properties of powders by using two classical techniques based on the shear stress measurements and the count of intermittent avalanches, respectively. Results are compared with measurements of the compaction dynamics. Strong correlations are evidenced between compaction relaxation parameters and free flow characteristics. Those correlations are given by semiempirical laws based on physical arguments. This work opens perspectives in powder technology and the knowledge on granular matter. (c) 2006 American Institute of Physics. [less ▲]

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See detailExperimental study of the compaction dynamics for two-dimensional anisotropic granular materials
Lumay, Geoffroy ULg; Vandewalle, Nicolas ULg

in Physical Review E (2006), 74(2, Pt 1), 21301

We present an experimental study of the compaction dynamics for two-dimensional anisotropic granular systems. The compaction dynamics of rods is measured at three different scales: (i) the macroscopic ... [more ▼]

We present an experimental study of the compaction dynamics for two-dimensional anisotropic granular systems. The compaction dynamics of rods is measured at three different scales: (i) the macroscopic scale through the packing fraction rho, (ii) the mesoscopic scale through both fractions of aligned grains phi(a) and ideally ordered grains phi(io), and (iii) the microscopic scale through both rotational and translational grain mobilities mu(r,t). At the macroscopic scale, we have observed two stages during the compaction process, suggesting different characteristic time scales for grain relaxation. At the mesoscopic scale, we have observed the formation and the growth of domains made of aligned grains during the first stage of compaction. At the late stage, these domains of aligned grains are sheared to form ideally ordered domains. From a microscopic point of view, measurements reveal that the beginning of the compaction process is essentially related to translational motions of the grains. The grain rotations drive mainly the process during the late stages of compaction. [less ▲]

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See detailAir bubbles under vertical vibrations
Zoueshtiagh, F.; Caps, Hervé ULg; Legendre, M. et al

in European Physical Journal E -- Soft Matter (2006), 20(3), 317-325

This paper reports on an experimental study of the splitting instability of an air bubble a few centimetres in diameter placed in a sealed cylindrical cell filled with liquid and submitted to vertical ... [more ▼]

This paper reports on an experimental study of the splitting instability of an air bubble a few centimetres in diameter placed in a sealed cylindrical cell filled with liquid and submitted to vertical oscillations. The response of the bubble to the oscillations is observed with a high-speed video camera. It is found that the bubble dynamics is closely associated with the acceleration of the cell Gamma. For small acceleration values, the bubble undergoes minor shape deformations. With increasing acceleration values, these deformations are amplified and for sufficiently large Gamma the bubble becomes toroidal. The bubble may then become unstable and split into smaller parts. The onset of bubble division is studied and its dependency on physical parameters such as the fluid viscosity, the fluid surface tension and the initial size of the bubble is presented. It is found that the criterion for the bubble splitting process is associated with a threshold based on the acceleration of the oscillations. Above this threshold, the number of bubbles present in the cell is observed to grow until a final steady state is reached. Data analysis reveals that the final bubble size may be characterized in terms of Bond number. [less ▲]

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See detailFoaming dynamics in Hele-Shaw cells
Caps, Hervé ULg; Vandewalle, Nicolas ULg; Broze, Guy ULg

in Physical Review E (2006), 73(6, Pt 2), 65301

We have studied foaming dynamics in Hele-Shaw cells partially filled with a soap and water mixture. A series of upside-down flips produces an intermittent wetting of the cell and leads to foam formation ... [more ▼]

We have studied foaming dynamics in Hele-Shaw cells partially filled with a soap and water mixture. A series of upside-down flips produces an intermittent wetting of the cell and leads to foam formation. As a function of the number of flips, an increasing number of bubbles composes the foam, until saturation is observed. Statistical analysis shows that the bubble size follows a Gamma distribution. Contrary to common belief, this foaming dynamics by "shaking" creates homogeneous foam, even though the system may pass through transient heterogeneous configurations. A mechanistic interpretation is proposed and included into a theoretical model. [less ▲]

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See detailCompaction of granular mixtures
Ludewig, François ULg; Vandewalle, Nicolas ULg; Dorbolo, Stéphane ULg

in Granular Matter (2006), 8(2), 87-91

We propose a lattice model for studying the compaction of granular mixtures under taps. Two granular species are considered: small grains with low mobilities and T-shaped grains characterized by a larger ... [more ▼]

We propose a lattice model for studying the compaction of granular mixtures under taps. Two granular species are considered: small grains with low mobilities and T-shaped grains characterized by a larger ability to move. When those grains are mixed together, the compaction dynamics is mainly controlled by the volume fraction x of the small grains. Segregation have been found on the top layers of the pile. The grain mobilities have been studied for different values of the volume fraction x. An effective grain mobility has been defined for the mixture. This mobility is given by the linear combination of the mobility of both pure species minus a non-linear interaction term. Finally, the compaction speed depends on the fraction of the anisotropic grains. [less ▲]

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See detailDense bubble flow in a silo: An unusual flow of a dispersed medium
Bertho, Y.; Becco, Christophe ULg; Vandewalle, Nicolas ULg

in Physical Review E (2006), 73(5, Pt 2), 56309

The dense flow of air bubbles in a two-dimensional silo (through an aperture D) filled with a liquid is studied experimentally. A particle tracking technique has been used to bring out the main properties ... [more ▼]

The dense flow of air bubbles in a two-dimensional silo (through an aperture D) filled with a liquid is studied experimentally. A particle tracking technique has been used to bring out the main properties of the flow: displacements of the bubbles, transverse, and axial velocities. The behavior of the air bubbles is observed to present similarities with nondeformable solid grains in a granular flow. Nevertheless, a correlation between the bubble velocities and their deformations has been evidenced. Moreover, a new discharge law (Beverloo like) must be considered for such a system, where the flow rate is observed to vary as D-1/2 and depends on the deformability of the particles. [less ▲]

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