Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Granular materials flow like complex fluids   Granular materials such as sand, powders, foams etc. are ubiquitous in our
daily life, as well as in industrial and geotechnical applications. Although
these disordered systems form stable structures if unperturbed, in practice
they do relax because of the presence of unavoidable external influences such
as tapping or shear. Often it is tacitly assumed that for granular systems this
relaxation dynamics is similar to the one of thermal glass-formers, but in fact
experimental difficulties have so far prevented to determine the dynamic
properties of three dimensional granular systems on the particle level. This
lack of experimental data, combined with the fact that in these systems the
motion of the particles involves friction, makes it very challenging to come up
with an accurate description of their relaxation dynamics. Here we use X-ray
tomography to determine the microscopic relaxation dynamics of hard granular
ellipsoids that are subject to an oscillatory shear. We find that the
distribution function of the particle displacement can be described by a Gumbel
law with a shape parameter that is independent of time and the strain amplitude
$\gamma$. Despite this universality, the mean squared displacement of a tagged
particle shows power-laws as a function of time with an exponent that depends
on $\gamma$ and the time interval considered. We argue that these results are
directly related to the existence of the microscopic relaxation mechanisms that
involve friction and memory effects. These observations demonstrate that on the
particle level the dynamical behavior of granular systems is qualitatively
different from the one of thermal glass-formers and instead more similar to the
one of complex fluids. Thus we conclude that granular materials can relax even
when the driving is weak, an insight which impacts our understanding of the
nature of granular solids.

31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph