1,721,020 research outputs found
The kink-counting problem: Equilibrium densities and nucleation rates
No full textThe longstanding problem of thermal pair nucleation in the
presence of global reflection symmetry (viz. no
external biases) is investigated numerically for a
classical string coupled to a viscous heat bath. Our numerics
agree within a few percent with the theoretical estimates for the
low-temperature kink (antikink) density; as a result,
finite-temperature corrections could be assessed quantitatively.
More importantly, the relevant pair nucleation rates, too, have
been computed numerically, thus confirming the predictions of the
kinetic model: Local symmetry breaking by pre-existing
kinks (antikinks) assists the nucleation of new kink-antikink
pairs in the stationary regime and determines their lifetime
Ordering Phenomena in Cooling Granular Mixtures
No full textWe report two phenomena, induced by dynamical correlations, that occur during the free cooling of a
two-dimensional mixture of inelastic hard disks. First, we show that, due to the onset of velocity
correlations, the ratio of the kinetic energies associated with the two species changes from the value
corresponding to the homogeneous cooling state to a value approximately given by the mass ratio
m1
=m2
of the two species. Second, we report a novel segregation effect that occurs in the late stage of
cooling, where interconnected domains appear. Spectral analysis of the composition field reveals the
emergence of a growing characteristic lengt
Semiotic dynamics and collaborative tagging
Full text linkCollaborative tagging has been quickly gaining ground because of its ability to recruit the activity of web users into effectively organizing and sharing vast amounts of information. Here we collect data from a popular system and investigate the statistical properties of tag cooccurrence. We introduce a stochastic model of user behavior embodying two main aspects of collaborative tagging: (i) a frequency-bias mechanism related to the idea that users are exposed to each other's tagging activity; (ii) a notion of memory, or aging of resources, in the form of a heavy-tailed access to the past state of the system. Remarkably, our simple modeling is able to account quantitatively for the observed experimental features with a surprisingly high accuracy. This points in the direction of a universal behavior of users who, despite the complexity of their own cognitive processes and the uncoordinated and selfish nature of their tagging activity, appear to follow simple activity patterns
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