References of "Physical Review E"
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See detailControlled flow of smart powders
Lumay, Geoffroy ULg; Vandewalle, Nicolas ULg

in Physical Review E (2008), 78(6),

The flow properties of powders are mainly due to the interplay of cohesive forces and intergrain frictional forces. We have experimentally investigated a "smart granular system" for which the ... [more ▼]

The flow properties of powders are mainly due to the interplay of cohesive forces and intergrain frictional forces. We have experimentally investigated a "smart granular system" for which the interparticle cohesion can be tuned by a magnetic field B. We show that the rheological features of such a system can be controlled. Indeed, the granular flow can be controlled or even stopped by the magnetic field. Depending on the orientation of B, different dynamical regimes can be obtained like a "dry liquid state" forming conical droplets as well as a "layered soft state". Scaling lows are given for the flow rate outside a funnel as a function of B and for the stopping threshold of the flow as a function of the funnel output diameter D. From this analysis, it appears that the flowing properties are related to the dimensionality of the magnetic aggregates. [less ▲]

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See detailLifetime of a Bouncing Droplet
Terwagne, Denis ULg; Vandewalle, Nicolas ULg; Dorbolo, Stéphane ULg

in Physical Review E (2007), 76(5, Pt 2), 56311

When a droplet is gently laid onto the surface of the same liquid, it stays at rest for a moment before coalescence. The coalescence can be delayed and sometimes inhibited by injecting fresh air under the ... [more ▼]

When a droplet is gently laid onto the surface of the same liquid, it stays at rest for a moment before coalescence. The coalescence can be delayed and sometimes inhibited by injecting fresh air under the droplet. This can happen when the surface of the bath oscillates vertically. In this case the droplet basically bounces on the interface. The lifetime of the droplet has been studied with respect to the amplitude and the frequency of the excitation. The lifetime decreases when the acceleration increases. The thickness of the air film between the droplet and the bath has been investigated using interference fringes obtained when the system is illuminated by low-pressure sodium lamps. Moreover, both the shape evolution and the motion of the droplet center of mass have been recorded in order to evidence the phase offset between the deformation and the trajectory. A short lifetime is correlated to a small air-film thickness and to a large phase offset between the maximum of deformation and the minimum of the vertical position of the center of mass. [less ▲]

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See detailControlling the partial coalescence of a droplet on a vertically vibrated bath
Gilet, Tristan ULg; Vandewalle, Nicolas ULg; Dorbolo, Stéphane ULg

in Physical Review E (2007), 76(3, Pt 2), 35302

A method is proposed to stop the cascade of partial coalescences of a droplet laid on a liquid bath. The strategy consists of vibrating the bath in the vertical direction in order to keep small droplets ... [more ▼]

A method is proposed to stop the cascade of partial coalescences of a droplet laid on a liquid bath. The strategy consists of vibrating the bath in the vertical direction in order to keep small droplets bouncing. Since large droplets are not able to bounce, they partially coalesce until they reach a critical size. The system behaves as a low pass filter: droplets smaller than the critical size are selected. This size has been investigated as a function of the acceleration and the frequency of the bath vibration. Results suggest that the limit size for bouncing is related to the first mode of the droplet deformation. [less ▲]

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See detailBifractality of human DNA strand-asymmetry profiles results from transcription
Nicolay, Samuel ULg; Brodie, E. B.; Touchon, M. et al

in Physical Review E (2007), 75(3), 032902

We use the wavelet transform modulus maxima method to investigate the multifractal properties of strand-asymmetry DNA walk profiles in the human genome. This study reveals the bifractal nature of these ... [more ▼]

We use the wavelet transform modulus maxima method to investigate the multifractal properties of strand-asymmetry DNA walk profiles in the human genome. This study reveals the bifractal nature of these profiles, which involve two competing scale-invariant (up to repeat-masked distances less than or similar to 40 kbp) components characterized by Holder exponents h(1)=0.78 and h(2)=1, respectively. The former corresponds to the long-range-correlated homogeneous fluctuations previously observed in DNA walks generated with structural codings. The latter is associated with the presence of jumps in the original strand-asymmetry noisy signal S. We show that a majority of upward (downward) jumps colocate with gene transcription start (end) sites. Here 7228 human gene transcription start sites from the refGene database are found within 2 kbp from an upward jump of amplitude Delta S >= 0.1 which suggests that about 36% of annotated human genes present significant transcription-induced strand asymmetry and very likely high expression rate. [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 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 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 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 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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See detailMesoscopic fluctuations of the Loschmidt echo
Petitjean, Cyril ULg; Jacquod, P.

in PHYSICAL REVIEW E (2005), 71(3), 036223-6

We investigate the time-dependent variance of the fidelity with which an initial narrow wave packet is reconstructed after its dynamics is time reversed with a perturbed Hamiltonian. In the semiclassical ... [more ▼]

We investigate the time-dependent variance of the fidelity with which an initial narrow wave packet is reconstructed after its dynamics is time reversed with a perturbed Hamiltonian. In the semiclassical regime of perturbation, we show that the variance first rises algebraically up to a critical time t(c), after which it decays. To leading order in the effective Planck's constant h(eff), this decay is given by the sum of a classical term similar or equal to exp[-2 lambda t], a quantum term similar or equal to 2h(eff) exp[-Gamma t], and a mixed term similar or equal to 2 exp[-(Gamma+lambda)t]. Compared to the behavior of the average fidelity, this allows for the extraction of the classical Lyapunov exponent lambda in a larger parameter range. Our results are confirmed by numerical simulations. [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 detailCompaction of anisotropic granular materials: Experiments and simulations
Lumay, Geoffroy ULg; Vandewalle, Nicolas ULg

in Physical Review E (2004), 70(5, Pt 1), 51314

We present both experimental and numerical investigations of compaction in granular materials composed of rods. As a function of the particles size and with respect to the container diameter, we have ... [more ▼]

We present both experimental and numerical investigations of compaction in granular materials composed of rods. As a function of the particles size and with respect to the container diameter, we have observed large variations of the asymptotic packing volume fraction. The relevant parameter is the ratio between the rod length l and the tube diameter D. Even the compaction dynamics remains unchanged for various particle lengths, and a transition between 3d and 2d ordering for grain orientations is observed for l/D= 1. A toy model for the compaction of needles on a lattice is also proposed. This toy model gives a complementary view of our experimental results and leads to behaviors similar to experimental ones. [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 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 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 detailAmplitude equations for Rayleigh-Benard convective rolls far from threshold
Dauby, Pierre ULg; Desaive, Thomas ULg; Bragard, J. et al

in Physical Review E (2001), 64(6), 66301

An extension of the amplitude method is proposed. An iterative algorithm is developed to build an amplitude equation model that is shown to provide precise quantitative results even far from the linear ... [more ▼]

An extension of the amplitude method is proposed. An iterative algorithm is developed to build an amplitude equation model that is shown to provide precise quantitative results even far from the linear instability threshold. The method is applied to the study of stationary Rayleigh-Benard thermoconvective rolls in the nonlinear regime. In particular, the generation of second and third spatial harmonics is analyzed. Comparison with experimental results and direct numerical calculations is also made and a very good agreement is found. [less ▲]

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See detailCoupled capillary and gravity-driven instability in a liquid film overlying a porous layer
Desaive, Thomas ULg; Lebon, Georgy ULg; Hennenberg, M.

in Physical Review E (2001), 64(6, Pt 2), 66304

In this work, we study the problem of onset of thermal convection in a fluid layer overlying a porous layer, the whole system being heated from below. We use Brinkman's model to describe the porous medium ... [more ▼]

In this work, we study the problem of onset of thermal convection in a fluid layer overlying a porous layer, the whole system being heated from below. We use Brinkman's model to describe the porous medium and determine the corresponding linear stability equations. The eigenvalue problem is solved by means of a modified Galerkin method. The behavior of the critical wave number and temperature gradient is discussed in terms of the various parameters of the system. We also emphasize the influence of the boundary conditions at the upper surface of the fluid layer; in particular, we examine the role of a free surface whose surface tension is temperature dependent (Marangoni effect). Comparison with earlier works is also made. [less ▲]

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See detailConstruction and properties of fractal trees with tunable dimension: The interplay of geometry and physics
Vandewalle, Nicolas ULg; Ausloos, Marcel ULg

in Physical Review E (1997), 55(1), 94-98

In this paper, we emphasize three different techniques for the growth of fractal trees with a desired fractal dimension D-f. The three different growths are due to the influence of (i) stretched branches ... [more ▼]

In this paper, we emphasize three different techniques for the growth of fractal trees with a desired fractal dimension D-f. The three different growths are due to the influence of (i) stretched branches, (ii) dead ends, or (iii) a variable branching rate. Several examples are given. We point out that geometrical and physical properties (skeleton dimension, percolation exponents, self-avoiding walk) of fractal tress depend strongly on their type. The most striking result is that the critical exponents at the percolation transition are nonuniversal since they depend on the tree type. The critical exponents depend on D-f for trees of types (ii) and (iii). [less ▲]

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