Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Current self-oscillations, spikes and crossover between charge monopole
  and dipole waves in semiconductor superlattices
5
The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
6
The categories of this paper are: astro-ph
31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
37
The categories of this paper are: supr-con
33
The categories of this paper are: plasm-ph
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas