38 research outputs found
Effect of an electric field on a Leidenfrost droplet
We experimentally investigate the effect of an electric field applied between
a Leidenfrost droplet and the heated substrate on which it is levitating. We
quantify the electro-Leidenfrost effect by imaging the interference fringes
between the liquid-vapour and vapour-substrate interfaces. The increase of the
voltage induces a decrease of the vapour layer thickness. Above a certain
critical voltage the Leidenfrost effect is suppressed and the drop starts
boiling. Our study characterizes this way to control and/or to avoid the
Leidenfrost effect that is undesirable in many domains such as metallurgy or
nuclear reactor safety.Comment: 6 pages, 6 figures, 2 movie
Jet impact on a soap film
We experimentally investigate the impact of a liquid jet on a soap film. We
observe that the jet never breaks the film and that two qualitatively different
steady regimes may occur. The first one is a refraction-like behavior obtained
at small incidence angles when the jet crosses the film and is deflected by the
film-jet interaction. For larger incidence angles, the jet is absorbed by the
film, giving rise to a new class of flow in which the jet undulates along the
film with a characteristic wavelength. Besides its fundamental interest, this
study presents a new way to guide a micro-metric flow of liquid in the inertial
regime and to probe foam stability submitted to violent perturbations at the
soap film scale.Comment: 6 pages, 5 figure
Stretching an adsorbed polymer globule
Using molecular dynamic simulation, we study the stretching of an adsorbed
homopolymer in a poor solvent with one end held at a distance from the
substrate. We measure the vertical force on the end of the chain as a
function of the extension and the substrate interaction energy . The
force reaches a plateau value at large extensions. In the strong adsorption
limit, we show that the plateau value increase linearly in in good
agreement with a theoretical model. In the weak adsorption limit, a polymer
globule with a layered structure is formed and elastically deformed when
stretched. In both cases a simple theoretical model permits us to predict the
relation between the necessary force to fully detach the polymer and its
critical extension.Comment: Accepted for publication in Phys. Rev.
Take-off of small Leidenfrost droplets
We put in evidence the unexpected behaviour of Leidenfrost droplets at the
later stage of their evaporation. We predict and observe that, below a critical
size , the droplets spontaneously take-off due to the breakdown of the
lubrication regime. We establish the theoretical relation between the droplet
radius and its elevation. We predict that the vapour layer thickness increases
when the droplets become smaller. A satisfactory agreement is found between the
model and the experimental results performed on droplets of water and of
ethanol.Comment: Accepted for publication in Phys. Rev. Lett. (2012
Realistic grand canonical Monte Carlo surface simulation: application to Ar(111)
Most realistic, off-lattice surface simulations are done canonically---
conserving particles. For some applications, however, such as studying the
thermal behavior of rare gas solid surfaces, these constitute bad working
conditions. Surface layer occupancies are believed to change with temperature,
particularly at preroughening, and naturally call for a grand canonical
approach, where particle number is controlled by a chemical potential. We
report preliminary results of novel realistic grand canonical Monte Carlo
simulations of the Lennard-Jones (LJ) fcc(111) surface, believed to represent a
quantitative model of e.g. Ar(111). The results are successful and highly
informative for temperatures up to roughly 0.8 T_m, where clear precursor
signals of preroughening are found. At higher temperatures, convergence to
equilibrium is hampered by large fluctuations.Comment: 4 pages, REVTeX, 3 PostScript figure
Hole growth dynamics in a two dimensional Leidenfrost droplet
International audienceWe studied the behaviors of Leidenfrost droplets confined in a Hele-Shaw cell. These droplets are unstable above a critical size and a hole grows at their center. We experimentally investigate two different systems for which the hole growth dynamics exhibits peculiar features that are driven by capillarity and inertia. We report a first regime characterized by the liquid reorganization from a liquid sheet to a liquid torus with similarities to the burst of micron-thick soap films. In the second regime the liquid torus expands and thins before fragmentation. Finally we propose models to account for the experimental results
Modelling the Distribution of Multidimensional Poverty Scores: Evidence from Mexico
The main purpose of this paper is to explore a new methodology already developed by Berenger and Celestini (2006). This theoretical method based on fuzzy sets approach makes it possible to define a multidimensional poverty score lying, as for income, between 0 and infinity in order to characterize the organization of poverty. This method is applied using the data from the XII Census of Mexico, 2000 (INEGI). The results obtained enable us to build a typology of poverty. And we derive public policy implications.fuzzy sets approach, multidimensional measures of poverty, unsatisfied basic needs
Dynamics of a ball bouncing on a vibrated elastic membrane
International audienceWe investigate the dynamics of a ball bouncing on a vibrated elastic membrane. Beyond the classical solid/solid case, we study the effect of introducing new degrees of freedom by allowing substrate oscillations. The forcing frequency of the vibration strongly influences the different thresholds between the dynamical states. The simple model proposed gives a good agreement between the experiments and the analytical expression for the threshold at which the ball begins to bounce. Numerical simulations permit to qualitatively recover the experimental phase diagram. Finally, we discuss how this simple system can give new insights in the recent experimental studies on bouncing droplets