Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On 2D Periodic Hexagonal Cells   Graphene, the new wondrous material, is a perfect example of a
two-dimensional hexagonal crystal unlike any other. Here we exhibit some of the
characteristic directional features associated with hexagonal cells,
emphasising the sixfold symmetry. We depict the X-ray, vibrational and
electronic band structures to be expected in such systems via 2 dimensional
contour plots.

2
The categories of this paper are: math
17
The categories of this paper are: q-fin
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
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
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat
25
The categories of this paper are: patt-sol
5
The categories of this paper are: gr-qc