arXiv subjects

S. Dorbolo

Publications and source records attributed to S. Dorbolo.

32 records · Page 2Linked to original sources

arXiv2007

About the lifetime of a bouncing droplet

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 centre of mass.

nlin.CD↗

arXiv2006

Critical parameters for the partial coalescence of a droplet

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 has 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.

physics.flu-dyn↗

arXiv2005

Dynamics of a bouncing dimer

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.

physics.class-ph↗

arXiv2004

Effect of friction in a toy model of granular compaction

We proposed a toy model of granular compaction which includes some resistance due to granular arches. In this model, the solid/solid friction of contacting grains is a key parameter and a slipping threshold Wc is defined. Realistic compaction behaviors have been obtained. Two regimes separated by a critical point Wc* 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 Wc*, the physical properties of this frozen system become independent of Wc. Above the critical point Wc*, i.e. for low friction values, the packing properties behave as described by the classical Janssen theory for silos.

cond-mat.other↗

arXiv2004

Rolling/Slipping Motion of Euler's Disk

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 evolutions of (i) the inclination angle $α$, (ii) the angular velocity $ω$ and (iii) the precession rate $Ω$ are studied. The influence of the mass of the disk and the friction between the disk and the supporting surface are considered. %The motions of disks with different masses and over different surfaces are studied. The inclination angle $α$ and the angular velocity are observed to decrease according to a power law. We also show that the precession rate $Ω$ diverges as the disk stops. Exponents are measured very near the collapse as well as on long range times. Collapsing times have been also measured. The 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.

cond-mat.stat-mech↗

arXiv2003

Aging process of electrical contacts in granular matter

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 reorganisation 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.

cond-mat.mtrl-sci↗

arXiv2003

Analysis of Experimental Conditions for Simultaneous Measurements of Transport and Magnetotransport Coefficients of High Temperature Superconductors

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 2T. 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.

cond-mat.supr-con↗

arXiv2003

Antibubbles: evidences of a critical pressure

We present experimental investigations of antibubbles. Such an unusual fluid object is a thin spherical air shell surrounding a liquid globule. We explain how to produce them and we study their stability. By overweighting antibubbles with a small amount of salt, they sink and pop at a definite depth. A critical depth related to a critical pressure has been found. A modified Laplace law describes the air shell thickness evolution with respect to pressure. This law combined with surfactant layers interaction allows to explain the critical depth for antibubble stability.

cond-mat.soft↗

arXiv2003

Limit current density in 2D metallic granular packings

The electrical properties 2D of packed metallic pentagons have been studied. The characterization of such metallic pentagon heaps (like $i-V$ measurements) has been achieved and has allowed to point out two distinct conduction regimes. 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.

cond-mat.stat-mech↗

arXiv2002

Magnon-polaron and Spin-polaron Signatures in the Specific Heat and Electrical Resistivity of $La_{0.6}Y_{0.1}Ca_{0.3}MnO_3$ in Zero Magnetic Field, and the Effect of $Mn-O-Mn$ Bond Environment

$La_{0.6}Y_{0.1}Ca_{0.3}MnO_{3}$, an $ABO_{3}$ perovskite manganite oxide, exhibits a non trivial behavior in the vicinity of the sharp peak found in the resistivity $ρ$ as a function of temperature $T$ in zero magnetic field. The various features seen on $dρ/dT$ are discussed in terms of competing phase transitions. They are related to the $Mn-O-Mn$ bond environment depending on the content of the $A$ crystallographic site. A Ginzburg-Landau type theory is presented for incorporating concurrent phase transitions. The specific heat $C$ of such a compound is also examined from 50 till 200 K. A log-log analysis indicates different regimes. In the low temperature conducting ferromagnetic phase, a collective magnon signature ($C \simeq T^{3/2}$) is found as for what are called magnon-polaron excitations. A $C \simeq T^{2/3}$ law is found at high temperature and discussed in terms of the fractal dimension of the conducting network of the weakly conducting (so-called insulating) phase and Orbach estimate of the excitation spectral behaviors. The need of considering both independent spin scattering and collective spin scattering is thus emphasized. The report indicates a remarkable agreement for the Fisher-Langer formula, i.e. $C$ $\sim$ $dρ/dT$ at second order phase transitions. Within the Attfield model, we find an inverse square root relationship between the critical temperature(s) and the total local $Mn-O-Mn$ strain.

cond-mat↗

arXiv2002

Influence of a low magnetic field on the thermal diffusivity of Bi-2212

The thermal diffusivity of a Bi-2212 polycrystalline sample has been measured under a 1T magnetic field applied perpendicularly to the heat flux. The magnetic contribution to the heat carrier mean free path has been extracted and is found to behave as a simple power law. This behavior can be attributed to a percolation process of electrons in the vortex lattice created by the magnetic field.

cond-mat↗

arXiv2001

Quasiparticle contribution to heat carriers relaxation time in DyBa$_2$Cu$_3$O$_{7-x}$ from heat diffusivity measurements

It is shown that the controversy on phonons or electrons being the most influenced heat carriers below the critical temperature of high-T$_c$ superconductors can be resolved. Electrical and thermal properties of the same DyBa$_2$Cu$_3$O$_{7-x}$ monodomain have been measured for two highly different oxygenation levels. While the oxygenated sample DyBa$_2$Cu$_3$O$_{7}$ has very good superconducting properties ($T_c=90$ K), the DyBa$_2$Cu$_3$O$_{6.3}$ sample exhibits an insulator behavior. A careful comparison between measurements of the {\bf thermal diffusivity} of both samples allows us to extract the electronic contribution. This contribution to the relaxation time of heat carriers is shown to be large below $T_c$ and more sensitive to the superconducting state than the phonon contribution.

cond-mat.supr-con↗

arXiv2000

Avalanches of popping bubbles in collapsing foams

We report acoustic experiments on foam systems. We have recorded the sound emitted by crackling cells during the collapsing of foams. The sound pattern is then analyzed using classical methods of statistical physics. Fundamental processes at the surface of the collapsing foam are found. In particular, size is not a relevant parameter for exploding bubbles.

cond-mat.stat-mech↗

arXiv2000

Non-gaussian electrical fluctuations in a quasi-2d packing of metallic beads

The electrical properties of a two-dimensional packing of metallic beads are studied. Small mechanical perturbations of the packing leads to giant electrical 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.

cond-mat.stat-mech↗