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Universality in the pair contact process with diffusion
The pair contact process with diffusion is studied by means of multispin
Monte Carlo simulations and density matrix renormalization group calculations.
Effective critical exponents are found to behave nonmonotonically as functions
of time or of system length and extrapolate asymptotically towards values
consistent with the directed percolation universality class. We argue that an
intermediate regime exists where the effective critical dynamics resembles that
of a parity conserving process.Comment: 8 Pages, 9 figures, final version as publishe
Size matters: some stylized facts of the stock market revisited
We reanalyze high resolution data from the New York Stock Exchange and find a
monotonic (but not power law) variation of the mean value per trade, the mean
number of trades per minute and the mean trading activity with company
capitalization. We show that the second moment of the traded value distribution
is finite. Consequently, the Hurst exponents for the corresponding time series
can be calculated. These are, however, non-universal: The persistence grows
with larger capitalization and this results in a logarithmically increasing
Hurst exponent. A similar trend is displayed by intertrade time intervals.
Finally, we demonstrate that the distribution of the intertrade times is better
described by a multiscaling ansatz than by simple gap scaling.Comment: 10 pages, 13 figures, 2 tables, accepted to Eur. Phys. J. B, updated
references, fixed some minor error
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