780 research outputs found

### Avalanche Mixing of Granular Solids

Mixing of two fractions of a granular material in a slowly rotating
two-dimensional drum is considered. The rotation is around the axis of the
upright drum. The drum is filled partially, and mixing occurs only at a free
surface of the material. We propose a simple theory of the mixing process which
describes a real experiment surprisingly well. A geometrical approach without
appealing to ideas of self-organized criticality is used. The dependence of the
mixing time on the drum filling is calculated. The mixing time is infinite in
the case of the half-filled drum. We describe singular behaviour of the mixing
near this critical point.Comment: 9 pages (LaTeX) and 2 Postscript figures, to be published in
Europhys. Let

### Complex networks created by aggregation

We study aggregation as a mechanism for the creation of complex networks. In
this evolution process vertices merge together, which increases the number of
highly connected hubs. We study a range of complex network architectures
produced by the aggregation. Fat-tailed (in particular, scale-free)
distributions of connections are obtained both for networks with a finite
number of vertices and growing networks. We observe a strong variation of a
network structure with growing density of connections and find the phase
transition of the condensation of edges. Finally, we demonstrate the importance
of structural correlations in these networks.Comment: 12 pages, 13 figure

### Evolution of a sandpile in a thick flow regime

We solve a one-dimensional sandpile problem analytically in a thick flow
regime when the pile evolution may be described by a set of linear equations.
We demonstrate that, if an income flow is constant, a space periodicity takes
place while the sandpile evolves even for a pile of only one type of particles.
Hence, grains are piling layer by layer. The thickness of the layers is
proportional to the input flow of particles $r_0$ and coincides with the
thickness of stratified layers in a two-component sandpile problem which were
observed recently. We find that the surface angle $\theta$ of the pile reaches
its final critical value ($\theta_f$) only at long times after a complicated
relaxation process. The deviation ($\theta_f - \theta$) behaves asymptotically
as $(t/r_{0})^{-1/2}$. It appears that the pile evolution depends on initial
conditions. We consider two cases: (i) grains are absent at the initial moment,
and (ii) there is already a pile with a critical slope initially. Although at
long times the behavior appears to be similar in both cases, some differences
are observed for the different initial conditions are observed. We show that
the periodicity disappears if the input flow increases with time.Comment: 14 pages, 7 figure

### Language as an Evolving Word Web

Human language can be described as a complex network of linked words. In such
a treatment, each distinct word in language is a vertex of this web, and
neighboring words in sentences are connected by edges. It was recently found
(Ferrer and Sol\'e) that the distribution of the numbers of connections of
words in such a network is of a peculiar form which includes two pronounced
power-law regions. Here we treat language as a self-organizing network of
interacting words. In the framework of this concept, we completely describe the
observed Word Web structure without fitting.Comment: 4 pages revtex, 2 figure

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