12 research outputs found
Numerical modeling of the wind flow over a transverse dune
Transverse dunes, which form under unidirectional winds and have fixed
profile in the direction perpendicular to the wind, occur on all celestial
objects of our solar system where dunes have been detected. Here we perform a
numerical study of the average turbulent wind flow over a transverse dune by
means of computational fluid dynamics simulations. We find that the length of
the zone of recirculating flow at the dune lee --- the {\em{separation bubble}}
--- displays a surprisingly strong dependence on the wind shear velocity,
: it is nearly independent of for shear velocities within
the range between ms and $0.8\,$ms but increases linearly with
for larger shear velocities. Our calculations show that transport in
the direction opposite to dune migration within the separation bubble can be
sustained if is larger than approximately ms, whereas a
larger value of $u_{\ast}$ (about $0.49\,$ms) is required to initiate this
reverse transport.Comment: 11 pages, 8 figure
Nonequilibrium Zaklan model on Apollonian Networks
The Zaklan model had been proposed and studied recently using the equilibrium
Ising model on Square Lattices (SL) by Zaklan et al (2008), near the critica
temperature of the Ising model presenting a well-defined phase transition; but
on normal and modified Apollonian networks (ANs), Andrade et al. (2005, 2009)
studied the equilibrium Ising model. They showed the equilibrium Ising model
not to present on ANs a phase transition of the type for the 2D Ising model.
Here, using agent-based Monte-Carlo simulations, we study the Zaklan model with
the well-known majority-vote model (MVM) with noise and apply it to tax evasion
on ANs, to show that differently from the Ising model the MVM on ANs presents a
well defined phase transition. To control the tax evasion in the economics
model proposed by Zaklan et al, MVM is applied in the neighborhood of the
critical noise to the Zaklan model. Here we show that the Zaklan model
is robust because this can be studied besides using equilibrium dynamics of
Ising model also through the nonequilibrium MVM and on various topologies
giving the same behavior regardless of dynamic or topology used here.Comment: 11 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1204.0386 and arXiv:0910.196
Patterns formed by chains of magnetic beads
Magnetic beads attract each other forming rather stable chains. We consider such chains formed by magnetic beads and push them into a Hele-Shaw cell either from the boundary or from the center. When such a chain is pushed into a cavity, it bends and folds spontaneously forming interesting unreported patterns. These patterns are self-similar and an effective fractal dimension can be defined. As found experimentally and with numerical simulations, the numbers of beads, loops and contacts follow power laws as a function of packing fraction and, depending on the injection procedure, even energetically less favorable triangular configurations can be stabilized
Patterns formed by chains of magnetic beads
Magnetic beads attract each other forming rather stable chains. We consider such chains formed by magnetic beads and push them into a Hele-Shaw cell either from the boundary or from the center. When such a chain is pushed into a cavity, it bends and folds spontaneously forming interesting unreported patterns. These patterns are self-similar and an effective fractal dimension can be defined. As found experimentally and with numerical simulations, the numbers of beads, loops and contacts follow power laws as a function of packing fraction and, depending on the injection procedure, even energetically less favorable triangular configurations can be stabilized