Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Correlations in magnitude series to assess nonlinearities: application
  to multifractal models and heartbeat fluctuations   The correlation properties of the magnitudes of a time series (sometimes
called volatility) are associated with nonlinear and multifractal properties
and have been applied in a great variety of fields. Here, we have obtained
analytically the expression of the autocorrelation of the magnitude series of a
linear Gaussian noise as a function of its correlation as well as several
analytical relations involving them. For both, models and natural signals, the
deviation from these equations can be used as an index of non-linearity that
can be applied to relatively short records and that does not require the
presence of scaling in the time series under study. We apply this approach to
show that the heart-beat records during rest show higher non-linearities than
the records of the same subject during moderate exercise. This behavior is also
achieved on average for the analyzed set of 10 semiprofessional soccer players.
This result agrees with the fact that other measures of complexity are
dramatically reduced during exercise and can shed light on its relationship
with the withdrawal of parasympathetic tone and/or the activation of
sympathetic activity during physical activity.

34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
17
The categories of this paper are: q-fin
32
The categories of this paper are: atom-ph
16
The categories of this paper are: stat
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con