Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Calculation of Electric Unit charge   Considering the stresses due to the vacuum fluctuation and the electric
charge loaded over the surface of a spherical cavity, we estimate the maximum
value of the charge. Since this value is independent of the cavity size and
parameter free, it is regarded as the electric unit charge. Our result is $Q=
1.55\times 10^{-19}$ Coulomb which implies the relevant fine structure constant
$\alpha=1/145.90$.

14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
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The categories of this paper are: patt-sol
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
4
The categories of this paper are: cond-mat