13,459 research outputs found
Model for erosion-deposition patterns
We investigate through computational simulations with a pore network model
the formation of patterns caused by erosion-deposition mechanisms. In this
model, the geometry of the pore space changes dynamically as a consequence of
the coupling between the fluid flow and the movement of particles due to local
drag forces. Our results for this irreversible process show that the model is
capable to reproduce typical natural patterns caused by well known erosion
processes. Moreover, we observe that, within a certain range of porosity
values, the grains form clusters that are tilted with respect to the horizontal
with a characteristic angle. We compare our results to recent experiments for
granular material in flowing water and show that they present a satisfactory
agreement.Comment: 8 pages, 12 figures, submitted to Phys. Rev.
On bare masses in time-symmetric initial-value solutions for two black holes
The Brill-Lindquist time-symmetric initial-value solution for two uncharged
black holes is rederived using the Hamiltonian constraint equation with Dirac
delta distributions as a source for the binary black-hole field. The bare
masses of the Brill-Lindquist black holes are introduced in a way which is
applied, after straightforward modification, to the Misner-Linquist binary
black-hole solution.Comment: LaTeX, 4 page
Non-nequilibrium model on Apollonian networks
We investigate the Majority-Vote Model with two states () and a noise
on Apollonian networks. The main result found here is the presence of the
phase transition as a function of the noise parameter . We also studies de
effect of redirecting a fraction of the links of the network. By means of
Monte Carlo simulations, we obtained the exponent ratio ,
, and for several values of rewiring probability . The
critical noise was determined and also was calculated. The
effective dimensionality of the system was observed to be independent on ,
and the value is observed for these networks. Previous
results on the Ising model in Apollonian Networks have reported no presence of
a phase transition. Therefore, the results present here demonstrate that the
Majority-Vote Model belongs to a different universality class as the
equilibrium Ising Model on Apollonian Network.Comment: 5 pages, 5 figure
Physical regularization for the spin-1/2 Aharonov-Bohm problem in conical space
We examine the bound state and scattering problem of a spin-one-half particle
undergone to an Aharonov-Bohm potential in a conical space in the
nonrelativistic limit. The crucial problem of the \delta-function singularity
coming from the Zeeman spin interaction with the magnetic flux tube is solved
through the self-adjoint extension method. Using two different approaches
already known in the literature, both based on the self-adjoint extension
method, we obtain the self-adjoint extension parameter to the bound state and
scattering scenarios in terms of the physics of the problem. It is shown that
such a parameter is the same for both situations. The method is general and is
suitable for any quantum system with a singular Hamiltonian that has bound and
scattering states.Comment: Revtex4, 5 pages, published versio
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
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