Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Adiabatic and isothermal sound waves: the case of supercritical nitrogen   The acoustic sound dispersion of nitrogen in its liquid and supercritical
phases has been studied by Inelastic X-Ray Scattering. Approaching
supercritical conditions, the gradual disappearance of the positive sound
dispersion, characteristic of the low temperature liquid, is observed. In the
supercritical state, evidence for a crossover between adiabatic and isothermal
sound propagation regimes is inferred by an analysis of the dynamic structure
factor based on generalized hydrodynamics.

3
The categories of this paper are: physics
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
26
The categories of this paper are: bayes-an
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
35
The categories of this paper are: mtrl-th
7
The categories of this paper are: hep-th