Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Negative index of refraction and distributed Bragg reflectors   The Bragg regime shifts when conventional materials in a multilayer
distributed Bragg reflector (DBR) are replaced by artificial materials with the
so-called negative index of refraction. This provides an avenue for
characterizing the latter class of materials.

0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
32
The categories of this paper are: atom-ph
7
The categories of this paper are: hep-th
27
The categories of this paper are: comp-gas