Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Perpendicular electron collisions in drift and acoustic wave
  instabilities   Perpendicular electron dynamics and the associated collisions are discussed
in relation to the collisional drift wave instability. In addition, the limit
of small parallel wave numbers of this instability is studied and it is shown
to yield a reduced wave frequency. It is also shown that in this case the
growth rate in fact {\em decreases} for smaller parallel wave numbers, instead
of growing proportional to $1/k_z^2$. As a result, the growth rate appears to
be angle dependent and to reach a maximum for some specific direction of
propagation. The explanation for this strange behavior is given. A similar
analysis is performed for acoustic perturbations in plasmas with unmagnetized
ions and magnetized electrons, in the presence of a density gradient.

24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
4
The categories of this paper are: cond-mat
25
The categories of this paper are: patt-sol
6
The categories of this paper are: astro-ph
28
The categories of this paper are: alg-geom
35
The categories of this paper are: mtrl-th