Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Group velocity of the acoustic eigen-modes in sonic crystals   In this brief report, the group velocity of the eigen-modes in sonic crystals
is derived, and shown to equal the averaged energy velocity of the eigen-modes.
How the group velocity can be used to describe acoustic energy flows in sonic
crystals is discussed.

22
The categories of this paper are: chao-dyn
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
19
The categories of this paper are: eess
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
1
The categories of this paper are: cs
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg