Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On pressure impulse of a laser-induced underwater shock wave   We experimentally examine a laser-induced underwater shock wave with a
special attention to pressure impulse, the time integral of pressure evolution.
%total pressure variation associated with the shock wave. Plasma formation,
shock-wave expansion, and pressure in water are observed simultaneously using a
combined measurement system that obtains high-resolution nanosecond-order image
sequences. These detailed measurements reveal a non-spherically-symmetric
distribution of pressure peak. In contrast, remarkably, pressure impulse is
found to distribute symmetrically for a wide range of experimental parameters
even when the shock waves are emitted from an elongated region. The structure
is determined to be a collection of multiple spherical shock waves originated
from point-like plasmas in the elongated region.

2
The categories of this paper are: math
13
The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph