9,258 research outputs found
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 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 , , and 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
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