Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Modulational and filamentational instabilities of two electromagnetic
  pulses in a radiation background   The nonlinear interaction, due to quantum electrodynamical (QED) effects,
between two electromagnetic pulses and a radiation gas is investigated. It is
found that the governing equations admit both modulational and filamentational
instabilities. The instability growth rates are derived, and the results are
discussed.

25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
19
The categories of this paper are: eess
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
2
The categories of this paper are: math
16
The categories of this paper are: stat
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
24
The categories of this paper are: dg-ga
18
The categories of this paper are: econ