Force chains and contact network topology in packings of elongated particles

By means of contact dynamic simulations, we investigate the contact network topology and force chains in two-dimensional packings of elongated particles modeled by rounded-cap rectangles. The morphology of large packings of elongated particles in quasistatic equilibrium is complex due to the combined effects of local nematic ordering of the particles and orientations of contacts between particles. We show that particle elongation affects force distributions and force/fabric anisotropy via various local structures allowed by steric exclusions and the requirement of force balance. As a result, the force distributions become increasingly broader as particles become more elongated. Interestingly, the weak force network transforms from a passive stabilizing agent with respect to strong force chains to an active force-transmitting network for the whole system. The strongest force chains are carried by side/side contacts oriented along the principal stress direction.Comment: Soumis a Physical Review

Single superpartner production at Tevatron Run II

We study the single productions of supersymmetric particles at Tevatron Run II which occur in the $2 \to 2-body$ processes involving R-parity violating couplings of type \l'_{ijk} L_i Q_j D_k^c. We focus on the single gaugino productions which receive contributions from the resonant slepton productions. We first calculate the amplitudes of the single gaugino productions. Then we perform analyses of the single gaugino productions based on the three charged leptons and like sign dilepton signatures. These analyses allow to probe supersymmetric particles masses beyond the present experimental limits, and many of the \l'_{ijk} coupling constants down to values smaller than the low-energy bounds. Finally, we show that the studies of the single gaugino productions offer the opportunity to reconstruct the $\tilde \chi^0_1$, $\tilde \chi^{\pm}_1$, $\tilde \nu_L$ and $\tilde l^{\pm}_L$ masses with a good accuracy in a model independent way.Comment: 47 pages, epsfi

Stress-strain behavior and geometrical properties of packings of elongated particles

We present a numerical analysis of the effect of particle elongation on the quasistatic behavior of sheared granular media by means of the Contact Dynamics method. The particle shapes are rounded-cap rectangles characterized by their elongation. The macroscopic and microstructural properties of several packings subjected to biaxial compression are analyzed as a function of particle elongation. We find that the shear strength is an increasing linear function of elongation. Performing an additive decomposition of the stress tensor based on a harmonic approximation of the angular dependence of branch vectors, contact normals and forces, we show that the increasing mobilization of friction force and the associated anisotropy are key effects of particle elongation. These effects are correlated with partial nematic ordering of the particles which tend to be oriented perpendicular to the major principal stress direction and form side-to-side contacts. However, the force transmission is found to be mainly guided by cap-to-side contacts, which represent the largest fraction of contacts for the most elongated particles. Another interesting finding is that, in contrast to shear strength, the solid fraction first increases with particle elongation, but declines as the particles become more elongated. It is also remarkable that the coordination number does not follow this trend so that the packings of more elongated particles are looser but more strongly connected.Comment: Submited to Physical Review

Taphonomical and chronological studies of a concentration of European glass trade beads from Ashuapmushuan, Central Quebec (Canada)

As early as the sixteenth century, glass beads were among the several categories of goods brought from Europe to be traded to Northeastern North American Indians. Attempts to set up a chronological framework on the basis of the chemistry of these beads has been recently enhanced by the application of neutron activation analysis of turquoise blue glass beads from many sites in Southwestern Ontario and Central Quebec. Subsequently, in the Quebec site of Ashuapmushuan was found a collection of 515 beads excavated from a very restricted area, indicating that they pertain to a single depositional event. This suggestion is tested through taphonomical studies , in particular on the basis of the spatial distributions of the beads. Chronological placement is also assessed on the basis of neutron activation of 122 turquoise blue glass beads. These taphonomical and chronological observations lead to some challenging cultural interpretations

Internet and the ‘Long Tail versus superstar effect’ debate: evidence from the French book market

From a comprehensive database of monthly sales of comic books and literature books in France over the period 2003 to 2007, we show that (i) bestsellers got smaller market shares online than offline, contrary to medium- and low-sellers; (ii) both online and offline sales shift from the head of the distribution to the tail with increasing magnitude over the period; and (iii) the Long Tail appears to be more than just a short-lived phenomenon caused by the specific preferences of early adopters of e-commerce. These three results suggest that online information and distribution tools, whose use increased over the period 2003 to 2007, do have an impact on book distribution and on consumers\u27 purchase decisions