Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: "Barchan" dunes in the lab   We demonstrate the feasibility of studying dunes in a laboratory experiment.
It is shown that an initial sand pile, under a wind flow carrying sand,
flattens and gets a shape recalling barchan dunes. An evolution law is proposed
for the profile and the summit of the dune. The dune dynamics is shown to be
shape invariant. The invariant shape, the ``dune function'' is isolated.

1
The categories of this paper are: cs
2
The categories of this paper are: math
3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
16
The categories of this paper are: stat
5
The categories of this paper are: gr-qc
34
The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex