Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The stress field in granular systems: Loop forces and potential
  formulation   The transmission of stress through a marginally stable granular pile in two
dimensions is exactly formulated in terms of a vector field of loop forces, and
thence in terms of a single scalar potential.
  The loop force formulation leads to a local constitutive equation coupling
the stress tensor to {\it fluctuations} in the local geometry. For a disordered
pile of rough grains (even with simple orientational order) this means the
stress tensor components are coupled in a frustrated manner, analogous to a
spin glass.
  If the local geometry of the pile of rough grains has long range staggered
order, frustration is avoided and a simple linear theory follows. Known exact
lattice solutions for rough grains fall into this class.
  We show that a pile of smooth grains (lacking friction) can always be mapped
into a pile of unfrustrated rough grains. Thus it appears that the problems of
rough and smooth grains may be fundamentally distinct.

10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
0
The categories of this paper are: hep-ph
1
The categories of this paper are: cs
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
6
The categories of this paper are: astro-ph