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

Labyrinthic granular landscapes

We have numerically studied a model of granular landscape eroded by wind. We show the appearance of labyrinthic patterns when the wind orientation turns by $90^\circ$. The occurence of such structures are discussed. Morever, we introduce the density $n_k$ of ``defects'' as the dynamic parameter governing the landscape evolution. A power law behavior of $n_k$ is found as a function of time. In the case of wind variations, the exponent (drastically) shifts from 2 to 1. The presence of two asymptotic values of $n_k$ implies the irreversibility of the labyrinthic formation process.Comment: 3 pages, 3 figure, RevTe

Domino effect for world market fluctuations

In order to emphasize cross-correlations for fluctuations in major market places, series of up and down spins are built from financial data. Patterns frequencies are measured, and statistical tests performed. Strong cross-correlations are emphasized, proving that market moves are collective behaviors.Comment: 8 pages, 5 figures, submitted to EPJ

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.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 $d=2$ square lattices. Associated thresholds $p_c^{perc}$ and $p_c^{jam}$ are determined for various needle sizes. Their ratios $p_c^{perc} / p_c^{jam}$ are found to be a constant $0.62 \pm 0.01$ for all sizes. In addition the ratio of jamming thresholds for respectively square blocks and needles is also found to be a constant $0.79 \pm 0.01$. 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 $a$.Comment: 9 pages, latex, 4 eps figures include

Compaction of anisotropic granular materials : experiments and simulations

We present both experimental and numerical investigations of compaction in granular materials composed of rods. As a function of the aspect ratio of the particles, we have observed large variations of the asymptotic packing volume fraction in vertical tubes. The relevant parameter is the ratio between the rod length $\ell$ and the tube diameter $D$. Even the compaction dynamics remains unchanged for various particle lengths, a 3d/2d phase transition for grain orientations is observed for $\ell/D = 1$. 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.Comment: 5 pages, 10 figure

Strings of droplets propelled by coherent waves

Bouncing walking droplets possess fascinating properties due to their peculiar wave/particule interaction. In order to study such walkers in a 1d system, we considered the case of one or more droplets in an annular cavity. We show that, in this geometry, walking droplets form a string of synchronized bouncing droplets that share a common coherent wave propelling the group at a speed faster than single walkers. The formation of this coherent wave and the collective behavior of droplets is captured by a model.Comment: 5 Pages, 5 Figures, 2 supplementary movies (identical), supplementary .pdf fil