Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Inductive measurements of third-harmonic voltage and critical current
  density in bulk superconductors   We propose an inductive method to measure critical current density $J_c$ in
bulk superconductors. In this method, an ac magnetic field is generated by a
drive current $I_0$ flowing in a small coil mounted just above the flat surface
of superconductors, and the third-harmonic voltage $V_3$ induced in the coil is
detected. We present theoretical calculation based on the critical state model
for the ac response of bulk superconductors, and we show that the
third-harmonic voltage detected in the inductive measurements is expressed as
$V_3= G_3\omega I_0^2/J_c$, where $\omega/2\pi$ is the frequency of the drive
current, and $G_3$ is a factor determined by the configuration of the coil. We
measured the $I_0$-$V_3$ curves of a melt-textured $\rm YBa_2Cu_3O_{7-\delta}$
bulk sample, and evaluated the $J_c$ by using the theoretical results.

10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
24
The categories of this paper are: dg-ga