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

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

Construction and Comparison of Genetic Linkage Maps of Four F1 Populations of Italian Ryegrass (\u3cem\u3eLolium Multiflorum\u3c/em\u3e Lam.)

The objective of this work was to integrate genetic maps and QTL-positions within 4 two-way pseudo-testcross F1 populations (each 110 genotypes) of Italian ryegrass (Lolium multiflorum) To integrate genetic maps and QTL-positions within the 4 populations and to the ILGI reference map, the maps used for initial QTL-analysis and marker assisted selection for yield and for different quality traits were further evaluated

The conundrum of stock versus bond prices

In a general way, stock and bond prices do not display any significant correlation. Yet, if we concentrate our attention on specific episodes marked by a crash followed by a rebound, then we observe that stock prices have a strong connection with interest rates on the one hand, and with bond yield spreads on the other hand. That second relationship is particularly stable in the course of time having been observed for over 140 years. Throughout the paper we use a quasi-experimental approach. By observing how markets respond to well-defined exogenous shocks (such as the shock of September 11, 2001) we are able to determine how investors organize their ``flight to safety'': which safe haven they select, how long their collective panic lasts, and so on. As rebounds come to an end the correlation of stock and bond prices fades away, a clear sign that the collective behavior of investors loses some of its coherence; this observation can be used as an objective criterion for assessing the end of a market rebound. Based on the behavior of investors, we introduce a distinction between ``genuine stock market rallies'', as opposed to spurious rallies such as those brought about by the buyback programs implemented by large companies. The paper ends with a discussion of testable predictions.Comment: 19 pages, 8 figures, 3 tables. To appear in "Physica A

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

Diffusive foam wetting process in microgravity

We report the experimental study of aqueous foam wetting in microgravity. The liquid fraction $\ell$ along the bubble edges is measured and is found to be a relevant dynamical parameter during the capillary process. The penetration of the liquid in the foam, the foam inflation, and the rigidity loss are shown all to obey strict diffusion processes.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let

Multifractal nature of stock exchange prices

The multifractal structure of the temporal dependence of the Deutsche Aktienindex (DAX) is analyzed. The $q$-th order moments of the structure functions and the singular measures are calculated. The generalized Hurst exponent $H(q)$ and the $h(\gamma(q))$ curve indicate a hierarchy of power law exponents. This approach leads to characterizing the nonstationarity and intermittency pertinent to such financial signals, indicating differences with turbulence data. A list of results on turbulence and financial markets is presented for asserting the analogy.Comment: 6 pages, 3 figures; an invited talk at: Conference on Computational Physics 2001, Sept 5-8, Aachen, German