Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microscopic calculation of expanding nuclear matter   Quantum Molecular Dynamics (QMD) calculations are used to study the expansion
phase in central collisions between heavy nuclei. The final state of such a
reaction can be understood as the result of a entropy conserving expansion
starting from a compact source. The properties of this hypothetic source,
however, are in conflict with the assumptions used in fireball models.
Moreover, this hypothetical source is not formed in the dynamical evolution of
the system.

2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
13
The categories of this paper are: quant-ph
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
18
The categories of this paper are: econ
6
The categories of this paper are: astro-ph
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
10
The categories of this paper are: q-bio
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom