Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Onsager relations and hydrodynamic balance equations   In this paper we clarify the role of heat flux in the hydrodynamic balance
equations, facilitating the formulation of an Onsager relation within the
framework of this theory. Previously thought to be unobtainable from the
present form of the theory [X.L. Lei, J. Cai, and L.M. Xie, Phys. Rev. B {\bf
38},1529 (1988)], our verification of the Onsager relation for linear particle
and heat flux currents driven by electric fields and temperature gradients
resolves a puzzling issue of long standing. Our results show that, for any
temperature, when electron density is sufficiently high, the linear predictions
of balance equation theory exactly satisfy the Onsager relation. The condition
of high density is consonant with the requirement of strong electron-electron
interactions for the validity of the Lei-Ting balance equations. Our results
support the validity of this theory for a weakly nonuniform system. We also
discuss a possible method of extending this theory to a system further removed
from thermal equilibrium.

23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
34
The categories of this paper are: chem-ph
7
The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
22
The categories of this paper are: chao-dyn
32
The categories of this paper are: atom-ph
21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex