We study the origin of scaling behavior in frictionless granular media above jamming transition by analyzing their linear response. The response to local forcing is non-self-averaging and fluctuates over a length scale that diverges at transition. global becomes increasingly nonaffine near This due proximity floppy modes, influence which we characterize show also governs anomalous elastic constants contact number.

Shear induced alignment of elongated particles is studied experimentally and numerically. We show that shear ensembles macroscopic comparable even on a quantitative level to simple molecular systems, despite the completely different types particle interactions. demonstrate for dry grains preferred orientation forms small angle with streamlines, independent rate across three decades. For given shape, this decreases increasing aspect ratio particles. The shear-induced results in considerable...

We present numerical simulations of acoustic wave propagation in confined granular systems consisting particles interacting with the three-dimensional Hertz-Mindlin force law. The response to a short mechanical excitation on one side system is found be propagating coherent wavefront followed by random oscillations made multiply scattered waves. find that insensitive details packing: chains do not play an important role determining this wavefront. propagates linearly time, and its amplitude...

We probe the nature of jamming transition frictional granular media by studying their vibrational properties as a function applied pressure $p$ and friction coefficient $\ensuremath{\mu}$. The density states exhibits crossover from plateau at frequencies $\ensuremath{\omega}\ensuremath{\gtrsim}{\ensuremath{\omega}}^{*}(p,\ensuremath{\mu})$ to linear growth for $\ensuremath{\omega}\ensuremath{\lesssim}{\ensuremath{\omega}}^{*}(p,\ensuremath{\mu})$. show that ${\ensuremath{\omega}}^{*}$ is...

We report scanning tunneling microscopy observations, which imply that all atoms in a Cu(001) surface move frequently, even at room temperature. Using low density of embedded indium "tracer" atoms, we visualize the diffusive motion atoms. Surprisingly, seem to make concerted, long jumps. Responsible for this is an ultralow vacancies, diffusing rapidly within surface. This interpretation supported by detailed analysis displacement distribution reveals shape characteristic vacancy mediated...

The alignment, ordering, and rotation of elongated granular particles was studied in shear flow. time evolution the orientation a large number monitored laboratory experiments by particle tracking using optical imaging x-ray computed tomography. were complemented discrete element simulations. develop an orientational order. In steady state time- ensemble-averaged direction main axis encloses small angle with streamlines. This alignment is independent applied rate, it decreases increasing...

We study the rheology of dense granular flows for frictionless spherocylinders by means 3D numerical simulations. As in case spherical particles, effective friction $\ensuremath{\mu}$ is an increasing function inertial number $I$, and we systematically investigate dependence on particle aspect ratio $Q$, as well that normal stress differences, volume fraction, coordination number. show particular quasistatic coefficient nonmonotonic with $Q$: from $Q=1$, it first sharply increases, reaches a...

We have performed DEM simulations of elongated grains in a shear cell for various particle aspect ratios and contact frictions, with an additional heterogeneous force perturbation the flow direction. For form single Fourier mode, we show that response system consists transverse secondary flows average onto pattern four vortices. also theoretically studied this phenomenon by generalizing granular rheology $\mu(I)$ to case computing linear such perturbation. Even if agreement between theory...

A granular material exposed to shear shows a variety of unique phenomena: Reynolds dilatancy, positional order and orientational effects may compete in the zone. We study packing consisting macroscopic prolate, oblate spherical grains compare their behaviour. X-ray tomography is used determine particle positions orientations cylindrical split bottom cell. Packing densities arrangements individual particles zone are evaluated. For anisometric particles, we observe competition two opposite...

Granular material flowing through bottlenecks like the openings of silos tend to clog and inhibit further flow. We study this phenomenon in a three-dimensional hopper for spherical shape-anisotropic particles by means X-ray tomography. The tomograms provide information on bulk granular filling, allows determine particle positions orientations inside silo. In addition, it calculate local packing densities different parts container. find that zone silo show preferred orientation thereby higher...

We report the first experimental demonstration of bulk segregation in a shear-driven dry granular mixture, where particles only differ their surface friction coefficients. found that smoother tend to sink bottom shear zone, while rough migrate top sample. This phenomenon is similar well known kinetic sieving particle mixtures with size heterogeneity. In present case smooth have higher probability penetrate into voids created by shearing than ones. Discrete element simulations were carried...

The creation of fractal clusters by diffusion limited aggregation (DLA) is studied using iterated stochastic conformal maps following the method proposed recently Hastings and Levitov. object interest function ${\ensuremath{\Phi}}^{(n)}$ which conformally exterior unit circle to an n-particle DLA. map obtained from n iterations a $\ensuremath{\varphi}$ that with bump. scaling properties usually in literature on DLA appear new light this language. dimension cluster determined linear...

Solids deform and fluids flow, but soft glassy materials, such as emulsions, foams, suspensions, pastes, exhibit an intricate mix of solid- liquid-like behavior. We show that two distinct softening yielding scenarios unfold depending on the material's packing density.

We propose a coarse-grained theory for the formation of river network in form Langevin equation erosion landscape coupled to conservation law surface water flow. claim that this is universal large-scale behavior. show by simulations discrete model represents same dynamics slope-area law, basin size distribution and Horton's laws agree with real rivers. discuss relationship optimal channel networks self-organized criticality.

The shear response of soft solids can be modeled with linear elasticity, provided the forcing is slow and weak. Both these approximations must break down when material loses rigidity, such as in foams emulsions at their (un)jamming point – suggesting that window elastic near jamming exceedingly narrow. Yet precisely how this breakdown occurs remains unclear. To answer questions, we perform computer simulations stress relaxation start-up tests athermal sphere packings, canonical model for...

An experimental evidence for kinetic roughening in a micromodel of mountain ranges is presented. We have observed that during the watering an initially smooth ridge made mixture silica sand and earthy soil surface evolves into shape analogous to actual profiles with self-affine geometry. For exponents describing respectively temporal spatial scaling width \ensuremath{\beta}\ensuremath{\approxeq}0.9 \ensuremath{\alpha}=0.78\ifmmode\pm\else\textpm\fi{}0.05 been obtained. The latter value very...

We discuss the scaling of characteristic lengths in diffusion limited aggregation (DLA) clusters light recent developments using conformal maps. are led to conjecture that apparently anomalous is due one slow crossover. This supported by an analytical argument for penetration depth newly arrived random walkers, and numerical evidence on Laurent coefficients which uniquely determine each cluster. find a single crossover exponent -0.3 all DLA. gives hint about structure renormalization group...

In this paper we report experiments where shear granular rods in split-bottom geometries, and find that a significant heap of height least 40% the filling can form at particle surface. We show heaping is caused by secondary flow, absent for spherical particles. Flow reversal transiently reverses leading to quick collapse slower regeneration heap. present symmetry argument experimental data generation flow driven misalignment mean orientation with streamlines flow. This general mechanism...

The influence of the local contact network on interparticle forces and effective particle weights is studied in simulations two-dimensional packings frictionless, Hertzian spheres. weight distribution P(w) changes qualitatively when approaching a boundary differs for regular irregular packings, while force P(f) robust. We provide examples where at boundary, which quantity probed experimentally, deviates substantially from bulk. Discrepancies between P(w)'s predicted by q model measured...

The relation between packing geometry and force network statistics is studied for granular media. Based on simulations of two-dimensional packings Hertzian spheres, we develop a geometrical framework relating the distribution interparticle forces P(f) to weight P(w), which measured in experiments. We apply this reinterpret recent experimental data strongly deformed suggest that observed changes P(w) are dominated by contact while remains relatively unaltered. furthermore investigate role...