Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: New reconstruction of the sunspot group number since 1739 using the
  direct calibration and "backbone" methods   Group sunspot number (GSN) series constitute the longest instrumental
astronomical database providing information on solar activity. It is a
compilation of observations by many individual observers, and their
inter-calibration has usually been performed using linear rescaling. There are
multiple published series that show different long-term trends for solar
activity. We aim at producing a GSN series, with a non-linear non-parametric
calibration. The only underlying assumptions are that the differences between
the various series are due to different acuity thresholds of the observers, and
that the threshold of each observer remains constant throughout the observing
period. We use a daisy chain process with backbone (BB) observers and calibrate
all overlapping observers to them. The calibration of each individual observer
is performed with a probability distribution function (PDF) matrix, constructed
considering all daily values for the overlapping period with the BB. The
calibration of the BBs is done in a similar manner. Propagation of errors is
modelled with Monte Carlo simulations. The final series extends back to 1739
and includes data from 314 observers. It suggests moderate activity during the
18th and 19th century, which is significantly lower than the high level of
solar activity predicted by other recent reconstructions applying linear
regressions. The new series provides a robust reconstruction, based on modern
and non-parametric methods, of sunspot group numbers since 1739, and it
confirms the existence of the Modern grand maximum of solar activity in the
second half of the 20th century.

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The categories of this paper are: stat
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The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
5
The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
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The categories of this paper are: econ
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio
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The categories of this paper are: nlin
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The categories of this paper are: bayes-an