1,509 research outputs found
A new conjecture extends the GM law for percolation thresholds to dynamical situations
The universal law for percolation thresholds proposed by Galam and Mauger
(GM) is found to apply also to dynamical situations. This law depends solely on
two variables, the space dimension d and a coordinance numberq. For regular
lattices, q reduces to the usual coordination number while for anisotropic
lattices it is an effective coordination number. For dynamical percolation we
conjecture that the law is still valid if we use the number q_2 of second
nearest neighbors instead of q. This conjecture is checked for the dynamic
epidemic model which considers the percolation phenomenon in a mobile
disordered system. The agreement is good.Comment: 8 pages, latex, 3 figures include
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 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.Comment: 4 pages, 6 figure
A New Universality for Random Sequential Deposition of Needles
Percolation and jamming phenomena are investigated for random sequential
deposition of rectangular needles on square lattices. Associated
thresholds and are determined for various needle
sizes. Their ratios are found to be a constant for all sizes. In addition the ratio of jamming thresholds for
respectively square blocks and needles is also found to be a constant . These constants exhibit some universal connexion in the geometry of
jamming and percolation for both anisotropic shapes (needles versus square
lattices) and isotropic shapes (square blocks on square lattices). A universal
empirical law is proposed for all three thresholds as a function of .Comment: 9 pages, latex, 4 eps figures include
Controlling the partial coalescence of a droplet on a vertically vibrated bath
A new method is proposed to stop the cascade of partial coalescences of a
droplet laid on a liquid bath. The strategy consists in 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.Comment: 4 pages, 3 figures, accepted in Phys. Rev.
Resonant and antiresonant bouncing droplets
When placed onto a vibrating liquid bath, a droplet may adopt a permanent
bouncing behavior, depending on both the forcing frequency and the forcing
amplitude. The relationship between the droplet deformations and the bouncing
mechanism is studied experimentally and theoretically through an asymmetric and
dissipative bouncing spring model. Antiresonance effects are evidenced.
Experiments and theoretical predictions show that both resonance at specific
frequencies and antiresonance at Rayleigh frequencies play crucial roles in the
bouncing mechanism. In particular, we show that they can be exploited for
droplet size selection.Comment: 4 pages, 4 figures and 1 vide
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.Comment: 16 pages, 14 figures, submitted to Physical Review
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