Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Interaction with thermal radiation in the free expansion and mixing of
  ideal gases and Gibbs' paradox in classical thermodynamics   The standard theory of ideal gases ignores the interaction of the gas
particles with the thermal radiation (photon gas) that fills the otherwise
vacuum space between them. This is an unphysical feature of the theory since
every material in this universe, and hence also the particles of a gas, absorbs
and radiates thermal energy. The interaction with the thermal radiation that is
contained within the volume of the body may be important in gases since the
latter, unlike solids and liquids, are capable of undergoing conspicuous volume
changes. Taking this interaction into account makes the behaviour of the ideal
gases more realistic and removes Gibbs' paradox.

15
The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph