609 research outputs found
Self-similar aftershock rates
In many important systems exhibiting crackling noise --- intermittent
avalanche-like relaxation response with power-law and, thus, self-similar
distributed event sizes --- the "laws" for the rate of activity after large
events are not consistent with the overall self-similar behavior expected on
theoretical grounds. This is in particular true for the case of seismicity and
a satisfying solution to this paradox has remained outstanding. Here, we
propose a generalized description of the aftershock rates which is both
self-similar and consistent with all other known self-similar features.
Comparing our theoretical predictions with high resolution earthquake data from
Southern California we find excellent agreement, providing in particular clear
evidence for a unified description of aftershocks and foreshocks. This may
offer an improved way of time-dependent seismic hazard assessment and
earthquake forecasting
Interacting Elastic Lattice Polymers: a Study of the Free-Energy of Globular Rings
We introduce and implement a Monte Carlo scheme to study the equilibrium
statistics of polymers in the globular phase. It is based on a model of
"interacting elastic lattice polymers" and allows a sufficiently good sampling
of long and compact configurations, an essential prerequisite to study the
scaling behaviour of free energies. By simulating interacting self-avoiding
rings at several temperatures in the collapsed phase, we estimate both the bulk
and the surface free energy. Moreover from the corresponding estimate of the
entropic exponent we provide evidence that, unlike for swollen and
-point rings, the hyperscaling relation is not satisfied for globular
rings.Comment: 8 pages; v2: typos removed, published versio
Complex networks of earthquakes and aftershocks
We invoke a metric to quantify the correlation between any two earthquakes.
This provides a simple and straightforward alternative to using space-time
windows to detect aftershock sequences and obviates the need to distinguish
main shocks from aftershocks. Directed networks of earthquakes are constructed
by placing a link, directed from the past to the future, between pairs of
events that are strongly correlated. Each link has a weight giving the relative
strength of correlation such that the sum over the incoming links to any node
equals unity for aftershocks, or zero if the event had no correlated
predecessors. A correlation threshold is set to drastically reduce the size of
the data set without losing significant information. Events can be aftershocks
of many previous events, and also generate many aftershocks. The probability
distribution for the number of incoming and outgoing links are both scale free,
and the networks are highly clustered. The Omori law holds for aftershock rates
up to a decorrelation time that scales with the magnitude, , of the
initiating shock as with .
Another scaling law relates distances between earthquakes and their aftershocks
to the magnitude of the initiating shock. Our results are inconsistent with the
hypothesis of finite aftershock zones. We also find evidence that seismicity is
dominantly triggered by small earthquakes. Our approach, using concepts from
the modern theory of complex networks, together with a metric to estimate
correlations, opens up new avenues of research, as well as new tools to
understand seismicity.Comment: 12 pages, 12 figures, revtex
Nonequilibrium temperature response for stochastic overdamped systems
The thermal response of nonequilibrium systems requires the knowledge of
concepts that go beyond entropy production. This is showed for systems obeying
overdamped Langevin dynamics, either in steady states or going through a
relaxation process. Namely, we derive the linear response to perturbations of
the noise intensity, mapping it onto the quadratic response to a constant small
force. The latter, displaying divergent terms, is explicitly regularized with a
novel path-integral method. The nonequilibrium equivalents of heat capacity and
thermal expansion coefficient are two applications of this approach, as we show
with numerical examples.Comment: 23 pages, 2 figure
On the Characteristic Isolation of Compact Subgroups within Loose Groups of Galaxies
We have explored the hypothesis that compact subgroups lying within dense
environments as loose groups of galaxies, at a certain stage of their
evolutionary history, could be influenced by the action of the tidal field
induced by the gravitational potential of the whole system. We argue that empty
rings observed in projection around many compact subgroups of galaxies embedded
in larger hosts originate around the spherical surface drawn by the tidal
radius where the internal binding force of the compact subgroup balances the
external tidal force of the whole system. This effect would torn apart member
galaxies situated in this region determining a marked isolation of the
subgroups from the rest of the host groups. If so, subsequent evolution of
these subgroups should not be affected by external influences as the infall of
new surrounding galaxies on them. Following this idea we have developed a
statistical method of investigation and performed an application to show
evidences of such effect studying a loose group of galaxies hosting a compact
group in its central region. The system UZC 578 / HCG 68 seems to be a fair
example of such hypothesized process.Comment: 12 pages, match version accepted for publication in TOAJ, corrected
typo
Models of DNA denaturation dynamics: universal properties
We briefly review some of the models used to describe DNA denaturation
dynamics, focusing on the value of the dynamical exponent , which governs
the scaling of the characteristic time as a function of the
sequence length . The models contain different degrees of simplifications,
in particular sometimes they do not include a description for helical
entanglement: we discuss how this aspect influences the value of , which
ranges from to . Connections with experiments are also
mentioned
Inflow rate, a time-symmetric observable obeying fluctuation relations
While entropy changes are the usual subject of fluctuation theorems, we seek
fluctuation relations involving time-symmetric quantities, namely observables
that do not change sign if the trajectories are observed backward in time. We
find detailed and integral fluctuation relations for the (time integrated)
difference between "entrance rate" and escape rate in mesoscopic jump systems.
Such "inflow rate", which is even under time reversal, represents the
discrete-state equivalent of the phase space contraction rate. Indeed, it
becomes minus the divergence of forces in the continuum limit to overdamped
diffusion. This establishes a formal connection between reversible
deterministic systems and irreversible stochastic ones, confirming that
fluctuation theorems are largely independent of the details of the underling
dynamics.Comment: v3: published version, slightly shorter title and abstrac
A thermodynamic uncertainty relation for a system with memory
We introduce an example of thermodynamic uncertainty relation (TUR) for
systems modeled by a one-dimensional generalised Langevin dynamics with memory,
determining the motion of a micro-bead driven in a complex fluid. Contrary to
TURs typically discussed in the previous years, our observables and the entropy
production rate are one-time variables. The bound to the signal-to-noise ratio
of such state-dependent observables only in some cases can be mapped to the
entropy production rate. For example, this is true in Markovian systems. Hence,
the presence of memory in the system complicates the thermodynamic
interpretation of the uncertainty relation
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