Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Kinetic energy of Bose systems and variation of statistical averages   The problem of defining the average kinetic energy of statistical systems is
addressed. The conditions of applicability for the formula, relating the
average kinetic energy with the mass derivative of the internal energy, are
analysed. It is shown that incorrectly using this formula, outside its region
of validity, leads to paradoxes. An equation is found for a parametric
derivative of the average for an arbitrary operator. A special attention is
paid to the mass derivative of the internal energy, for which a general formula
is derived, without invoking the adiabatic approximation and taking into
account the mass dependence of the potential-energy operator. The results are
illustrated by the case of a low-temperature dilute Bose gas.

2
The categories of this paper are: math
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
20
The categories of this paper are: acc-phys
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
6
The categories of this paper are: astro-ph