We study the internal dynamical processes taking place in a granular packing below yield stress. At all packing fractions and down to vanishingly low applied shear, a logarithmic creep is observed. The experiments are analyzed using a viscoelastic model which introduces an internal, time-dependent, fluidity variable. For all experiments, the creep dynamics can be rescaled onto a unique curve wh...

In this paper we consider the two-dimensional rectangular packing problem, where a fixed set of items have to be allocated on a single object. Two heuristics, which belong to the class of packing procedures that preserve bottom-left stability, are hybridised with three meta-heuristic algorithms (genetic algorithms, simulated annealing, naïve evolution) and local search heuristic (hill-climbing)...

We present the densest known packing of regular tetrahedra with density φ = 4000 4671 = 0.856347 . . . . Like the recently discovered packings of Kallus et al. and Torquato–Jiao, our packing is crystalline with a unit cell of four tetrahedra forming two triangular dipyramids (dimer clusters). We show that our packing has maximal density within a three-parameter family of dimer packings. Numeric...

This paper examines the constructive Hausdorff and packing dimensions of weak truth-table degrees. The main result is that every infinite sequence S with constructive Hausdorff dimension dimH(S) and constructive packing dimension dimP(S) is weak truth-table equivalent to a sequence R with dimH(R) ≥ dimH(S)/dimP(S)− ǫ, for arbitrary ǫ > 0. Furthermore, if dimP(S) > 0, then dimP(R) ≥ 1− ǫ. The re...

We explore adhesive loose packings of small dry spherical particles of micrometer size using 3D discrete-element simulations with adhesive contact mechanics and statistical ensemble theory. A dimensionless adhesion parameter (Ad) successfully combines the effects of particle velocities, sizes and the work of adhesion, identifying a universal regime of adhesive packings for Ad > 1. The structura...

The densest amorphous packing of rigid particles is known as random close packing. It has long been appreciated that higher densities are achieved by using collections of particles with a variety of sizes. For spheres, the variety of sizes is often quantified by the polydispersity of the particle size distribution: the standard deviation of the radius divided by the mean radius. Several prior s...

The regime transitions of granular flow in a model shear cell are investigated numerically with a stress-controlled boundary condition. The correlations between the elastically and kinetically scaled stresses and the packing fraction are examined, and two packing fractions (0.58 and 0.50) are identified for the quasistatic to intermediate and intermediate to inertial regime transitions. The pro...