Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The dynamic expansion of positive leaders observed using Mach-Zehnder
  interferometry in a 1-m air gap   The leader plays an important role in long-air-gap discharges. In this paper,
Mach-Zehnder interferometry and a high-speed video camera were used to observe
the dynamic expansion process of positive leaders near the anode in a 1 m air
gap. The leader diameters under lightning and switching impulse are obtained
through the analysis of interference fringes. The influences of the applied
voltage, including the amplitude and the front time, as well as the electrode
sizes on leader expansion are obtained and analysed. For a 0.5-cm-diameter cone
electrode, when the applied voltage amplitudes are 330-419 kV, the diameters of
the leaders are 1.5-2.5 mm at time scales of less than 195 {\mu}s, and the
diameters increase as the voltage rises. The diameters of the leaders are
larger and the expansion rates are higher for shorter front times. The average
expansion rates are 72.30-9.54, 28.09-5.05, 14.38-3.02 and 5.73-1.44 m/s for
front times of 1.2, 40, 100 and 250 {\mu}s for a 0.5-cm-diameter cone
electrode. A larger electrode size leads to a wider diameter. A numerical model
was employed to analyse the expansion of the leaders, and the calculated
results are in good agreement with the experimental data. Based on the model,
the mechanism underlying the leader expansion is discussed in detail.

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The categories of this paper are: cond-mat
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The categories of this paper are: cmp-lg
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The categories of this paper are: acc-phys
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
32
The categories of this paper are: atom-ph
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The categories of this paper are: stat
37
The categories of this paper are: supr-con
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The categories of this paper are: hep-ex
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The categories of this paper are: math
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The categories of this paper are: hep-th
12
The categories of this paper are: nucl-th