Abstract
Recent developments have made it possible to understand the origin
of $1/f$ -noise in several non-equilibrium systems exhibiting avalanches.
For Barkhausen noise, it has been shown 1 that the power spectrum
exponent $\alpha$ is related to the scaling of average avalanche sizes with
their duration. Our work shows that the equality of $\alpha$ to
$\gamma_st$, from the size-duration scaling $s(T) \sim
T^\gamma_st$, is applicable to a wide class of systems from
sandpile models of self-organized criticality (SOC) 2,
to dislocation avalanches in plastically deforming crystals
3 to fluid invasion into disordered media 4.
In the case of SOC, our observation is that the noise exponent of the
activity time series $V(t)$ follows from the avalanche scaling and
therefore from the underlying universality class of the model and
spatial dimension at hand. This implies that for $d<d_c$ (with $d_c$ the
upper critical dimension), the power spectrum $P(f) f^-\alpha$
scales with a non-trivial $\alpha<2$, instead of the long-standing belief
that sandpile models should lead to a Lorentzian power spectrum
(i.e. $\alpha=2$) independent of $d$ 5,6.
For two specific, experimentally relevant applications we consider
two apparently very different systems. First, the collective velocity or
deformation time series of dislocations in a plastically deforming
crystal, as obtained from a simple two-dimensional discrete dislocation
dynamics model, is shown to follow $\alpha=\gamma_st$ -scaling as well
3.
Second, this conclusion is also found for the fluctuations of a two-phase
interface velocity in fluid invasion into disordered, porous media, by
simulating a phase-field model of the problem 4.\\
1) M. C. Kuntz and J. P. Sethna, Phys. Rev. B 62, 11699 (2000).\\
2) L. Laurson, M. J. Alava, and S. Zapperi, J. Stat. Mech. 0511, L11001
(2005).\\
3) L. Laurson, M. J. Alava, Phys. Rev. E 74, 066106 (2006).\\
4) M. Rost, L. Laurson, M. Dubé and M. J. Alava, Phys. Rev. Lett. 98,
054502 (2007).\\
5) H. J. Jensen, K. Christensen, and H. C. Fogedby, Phys. Rev. B 40, R7425 (1989).\\
6) J. Kertesz and L. B. Kiss, J. Phys. A: Math. Gen. 23, L433 (1990).
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