Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The role of initial speed in projectile impacts into light granular
  media   Projectile impact into a light granular material composed of expanded
polypropylene (EPP) particles is investigated systematically with various
impact velocities. Experimentally, the trajectory of an intruder moving inside
the granular material is monitored with a recently developed non-invasive
microwave radar system. Numerically, discrete element simulations together with
coarse-graining techniques are employed to address both dynamics of the
intruder and response of the granular bed. Our experimental and numerical
results of the intruder dynamics agree with each other quantitatively and are
in congruent with existing phenomenological model on granular drag. Stepping
further, we explore the `microscopic' origin of granular drag through
characterizing the response of granular bed, including density, velocity and
kinetic stress fields at the mean-field level. In addition, we find that the
dynamics of cavity collapse behind the intruder behaves qualitatively different
with different impact velocities. Moreover, the kinetic pressure ahead of the
intruder decays exponentially in the co-moving system of the intruder. Its
scaling gives rise to a characteristic length scale, which is in the order of
intruder size. This finding is in perfect agreement with the long-scale
inertial dissipation type that we find in all cases.

17
The categories of this paper are: q-fin
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
13
The categories of this paper are: quant-ph
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
25
The categories of this paper are: patt-sol
5
The categories of this paper are: gr-qc
7
The categories of this paper are: hep-th