References of "Dorbolo, Stéphane"
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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 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 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 detailDancing droplets onto liquid surfaces
Vandewalle, Nicolas ULg; Terwagne, Denis ULg; Mulleners, K. et al

Poster (2006, March)

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See detailDancing droplets onto liquid surfaces
Vandewalle, Nicolas ULg; Terwagne, Denis ULg; mulleners, karin et al

in Physics of Fluids (2006), 18

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See detailDynamics of a bouncing dimer
Dorbolo, Stéphane ULg; Volfson, D.; Tsimring, L. et al

in Physical Review Letters (2005), 95(4),

We investigate the dynamics of a dimer bouncing on a vertically oscillated plate. The dimer, composed of two spheres rigidly connected by a light rod, exhibits several modes depending on initial and ... [more ▼]

We investigate the dynamics of a dimer bouncing on a vertically oscillated plate. The dimer, composed of two spheres rigidly connected by a light rod, exhibits several modes depending on initial and driving conditions. The first excited mode has a novel horizontal drift in which one end of the dimer stays on the plate during most of the cycle, while the other end bounces in phase with the plate. The speed and direction of the drift depend on the aspect ratio of the dimer. We employ event-driven simulations based on a detailed treatment of frictional interactions between the dimer and the plate in order to elucidate the nature of the transport mechanism in the drift mode. [less ▲]

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See detailStability limit of a granular monolayer
Dorbolo, Stéphane ULg

in European Physical Journal E -- Soft Matter (2005), 17(1), 77-81

A granular monolayer is composed by spherical grains on a horizontal plate. The plate is then tilted until the monolayer breaks down. This critical angle has been measured for different widths and heights ... [more ▼]

A granular monolayer is composed by spherical grains on a horizontal plate. The plate is then tilted until the monolayer breaks down. This critical angle has been measured for different widths and heights of the rectangular monolayer. The highest critical angles are found when one of these two characteristic lengths is less than about 30 bead diameters. When the polydispersity is less than one percent, the monolayer may be stable till angles close to 90 degrees. Arches induce large critical angles. On the other hand, for a large and high monolayer, the critical angle saturates towards a lower value. This angle is related to the static friction of a grain on the plate. A model based on the block dynamics is proposed to describe the behavior of the avalanche angle as a function of the size of the monolayer and the polydispersity of the beads. [less ▲]

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See detailAging of an antibubble
Dorbolo, Stéphane ULg; Reyssat, E.; Vandewalle, Nicolas ULg et al

in Europhysics Letters [=EPL] (2005), 69(6), 966-970

Antibubbles are unusual fluid objects consisting of a thin spherical air shell surrounding a liquid globule. Here we study and analyze the aging of these inverted bubbles. The lifetime is found to be ... [more ▼]

Antibubbles are unusual fluid objects consisting of a thin spherical air shell surrounding a liquid globule. Here we study and analyze the aging of these inverted bubbles. The lifetime is found to be distributed along an exponential law. Moreover, the breakdown of the air film is observed to be the analogue of dewetting by spinodal decomposition. We interpret the long lifetime of the antibubbles as resulting from the slow drainage of the air until the film reaches a critical thickness. Then, van der Waals forces act, leading to the collapse of the film. [less ▲]

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See detailBubble and granular flows: differences and similarities
Caps, Hervé ULg; Trabelsi, Samy ULg; Dorbolo, Stéphane ULg et al

in Physica A: Statistical Mechanics and its Applications (2004), 344(3-4), 424-430

We have experimentally studied the dense flow of identical bubbles below planes inclined at an angle theta. The flow is driven by the fast motion of dislocations. As a function of the density of ... [more ▼]

We have experimentally studied the dense flow of identical bubbles below planes inclined at an angle theta. The flow is driven by the fast motion of dislocations. As a function of the density of dislocations (controlled by the parameter theta), a transition occurs between a simple collective block motion and a granular-like surface flow regime. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailEffect of friction in a toy model of granular compaction
Ludewig, François ULg; Dorbolo, Stéphane ULg; Vandewalle, Nicolas ULg

in Physical Review E (2004), 70(5, Pt 1), 51304

A toy model of granular compaction which includes some resistance due to granular arches is proposed. In this model, the solid/solid friction of contacting grains is a key parameter and a slipping ... [more ▼]

A toy model of granular compaction which includes some resistance due to granular arches is proposed. In this model, the solid/solid friction of contacting grains is a key parameter and a slipping threshold omega(c) is defined. Realistic compaction behaviors have been obtained. Two regimes separated by a critical point omega(c)* of the slipping threshold have been emphasized: (i) a slow compaction with lots of paralyzed regions and (ii) an inverse logarithmic dynamics with a power-law scaling of grain mobility. Below the critical point omega(c)*, the physical properties of this frozen system become independent of omega(c). Above the critical point omega(c)*-i.e., for low friction values-the packing properties behave as described by the classical Janssen theory for silos. [less ▲]

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See detailRolling and slipping motion of Euler's disk
Caps, Hervé ULg; Dorbolo, Stéphane ULg; Ponte, S. et al

in Physical Review E (2004), 69(5, Pt 2), 56610

We present an experimental study of the motion of a circular disk spun onto a table. With the help of a high speed video system, the temporal evolution of (i) the inclination angle alpha, (ii) the angular ... [more ▼]

We present an experimental study of the motion of a circular disk spun onto a table. With the help of a high speed video system, the temporal evolution of (i) the inclination angle alpha, (ii) the angular velocity omega, and (iii) the precession rate Omega are studied. The influence of the mass of the disk as well as the friction between the disk and the supporting surface are considered. Both inclination angle and angular velocity are observed to decrease according to a power law. We also show that the precession rate diverges as the motion stops. Measurements are performed very near the collapse as well as on long range times. Times to collapse have been also measured. Results are compared with previous theoretical and experimental works. The major source of energy dissipation is found to be the slipping of the disk on the plane. [less ▲]

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See detailEffects of silicon addition on the electrical and magnetic properties of copper-doped (La,Ca)MnO3 compounds
Vertruyen, Bénédicte ULg; Rulmont, André ULg; Cloots, Rudi ULg et al

in Journal of Magnetism and Magnetic Materials (2004), 268(3), 364-373

In this paper we report about the electrical properties of La0.7Ca0.3MnO3 compounds substituted by copper on the manganese site and/or deliberately contaminated by SiO2 in the reactant mixture. Several ... [more ▼]

In this paper we report about the electrical properties of La0.7Ca0.3MnO3 compounds substituted by copper on the manganese site and/or deliberately contaminated by SiO2 in the reactant mixture. Several phenomena have been observed and discussed. SiO2 addition leads to the formation of an apatite-like secondary phase that affects the electrical conduction through the percolation of the charge carriers. On the other hand, depending on the relative amounts of copper and silicon, the temperature dependence of the electrical resistivity can be noticeably modified: our results enable us to compare the effects of crystallographic vacancies on the A and B sites of the perovskite with the influence of the copper ions substituted on the manganese site. The most original result occurs for the compounds with a small ratio Si/Cu, which display double-peaked resistivity vs. temperature curves. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

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See detailAnalysis of experimental conditions for simultaneous measurements of transport and magnetotransport coefficients of high temperature superconductors
Mucha, J.; Dorbolo, Stéphane ULg; Bougrine, Hassan ULg et al

in Cryogenics (2004), 44(3), 145-149

Experimental conditions for simultaneous measurements of transport coefficients of high temperature superconductors in zero and non-zero magnetic fields are analysed. Test measurements of the thermal ... [more ▼]

Experimental conditions for simultaneous measurements of transport coefficients of high temperature superconductors in zero and non-zero magnetic fields are analysed. Test measurements of the thermal conductivity, the thermoelectric power and the Nernst-Ettingshausen effect of a textured Bi2212 sample are reported in an external magnetic field of 2 T. Errors related to parameters of the thermocouple used and to the spurious heat flows are discussed for a new experimental set-up built based on a closed cycle helium refrigerator. Possible optimising of experimental conditions is suggested. (C) 2003 Elsevier Ltd. All rights reserved. [less ▲]

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See detailFluid instabilities in the birth and death of antibubbles
Dorbolo, Stéphane ULg; Caps, Hervé ULg; Vandewalle, Nicolas ULg

in New Journal of Physics (2003), 5

Antibubbles have been produced and studied with the help of a high-speed camera. An antibubble is defined as a fluid object constituted by a thin air shell surrounding a liquid and surrounded by the same ... [more ▼]

Antibubbles have been produced and studied with the help of a high-speed camera. An antibubble is defined as a fluid object constituted by a thin air shell surrounding a liquid and surrounded by the same liquid. Images reveal some key physical processes and fluid instabilities which take place when an antibubble forms and dies. The collapsing speed of the air film has been measured. Culik's theory does not apply. A new mechanism has been introduced. [less ▲]

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See detailAging process of electrical contacts in granular matter
Dorbolo, Stéphane ULg; Ausloos, Marcel ULg; Vandewalle, Nicolas ULg et al

in Journal of Applied Physics (2003), 94(12), 7835-7838

The electrical resistance decay of a metallic granular packing has been measured as a function of time. This measurement gives information about the size of the conducting cluster formed by the well ... [more ▼]

The electrical resistance decay of a metallic granular packing has been measured as a function of time. This measurement gives information about the size of the conducting cluster formed by the well connected grains. Several regimes have been encountered. Chronologically, the first one concerns the growth of the conducting cluster and is identified to belong to diffusion processes through a stretched exponential behavior. The relaxation time is found to be simply related to the initial injected power. This regime is followed by a reorganization process due to thermal dilatation. For the long-term behavior of the decay, an aging process occurs and enhances the electrical contacts between grains through microsoldering. (C) 2003 American Institute of Physics. [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 detailBehavior of bulk melt-textured YBCO single domains subjected to crossed magnetic fields
Vanderbemden, Philippe ULg; Dorbolo, Stéphane ULg; Hari-Babu, N. et al

in IEEE Transactions on Applied Superconductivity (2003), 13(2, Part 3), 3746-3749

We have experimentally investigated the crossed magnetic field effects on bulk melt-processed YBCO single domains. The samples were first permanently magnetized along their c-axis and then subjected to ... [more ▼]

We have experimentally investigated the crossed magnetic field effects on bulk melt-processed YBCO single domains. The samples were first permanently magnetized along their c-axis and then subjected to several cycles of a transverse magnetic field parallel to the ab planes. The magnetic properties along the c and ab directions were simultaneously measured using a couple of orthogonal pick-up coils as well as a Hall probe placed against the sample surface. The effects of both sweep amplitude and polarity were investigated. Field sweeps of alternate polarities are shown to affect the decay of the c-axis magnetization much more strongly than field sweeps of unique polarity do. However, the c-axis magnetization does not show any saturation even after a large number of field sweeps. Next, a micro-Hall probe scanning system was used to measure the distribution of magnetic induction over the top surface of the single domain subjected to the same combination of magnetic fields. The results are shown to be consistent with those determined with the sensing coils and bring out the role played by geometric effects. (C) 2003 IEEE. [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 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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