Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Thermal emissivity for finite three-dimensional photonic band gap
  crystals   We discuss the results of computer model for the thermal emissivity of a
three-dimensional photonic band gap (PBG) crystal, specifically an inverted
opal structure. The thermal emittance for a range of frequencies and angles is
calculated.

20
The categories of this paper are: acc-phys
4
The categories of this paper are: cond-mat
21
The categories of this paper are: adap-org
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
22
The categories of this paper are: chao-dyn