Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Inelastic collisions as a source of entropy?   Activation/deactivation by inelastic collisions have been extensively studied
at unimolecular reactions in gas phase where they are crucial for
equilibration. As equilibration means an increase of entropy, the mechanism can
also be considered responsible for entropy production. Theoretical treatments
show a remarkable agreement with experiments. They rest upon the assumption of
stochastic quantum transitions. Under this premise, master equations have been
used that are known to deliver equilibria and entropy production.
  Here we examine the hypothesis that the ubiquitous inelastic interactions in
gas and liquid phase may represent a source of entropy beyond chemical
reactions, rotational activation/deactivation being the prevailing mechanism in
gas dynamics at room temperature. For a quantum mechanical two-state model the
master equations are formulated which yield entropy production and
equilibration in translational degrees of freedom until, at conserved energy, a
stationary Maxwell-Boltzmann distribution is reached.
  The relaxation rates show features that can be checked by monitoring thermal
relaxation in gas phase. Depending on the composition, first or second order
processes are predicted. The temperature dependence is determined by the
activation energy of the lowest transition. Thus, experimental verification
will allow to decide to which extent this hypothesis describes thermal
relaxation. It would support a connection between the macroscopic second law of
thermodynamics and the microscopic stochastic collapse in quantum mechanics,
both experimentally secured facts which in theory emerge as special elements
beyond Hamiltonian dynamics.
  It is also shown that inelastic collisions are connected with
velocity-dependent forces and result in a new analog of the Fokker-Planck
equation where they replace Langevin dynamics as a non-Hamiltonian dissipative
mechanism.

22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
37
The categories of this paper are: supr-con
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
17
The categories of this paper are: q-fin