164 research outputs found
Microscopic Theory of Damon-Eshbach Modes in Ferromagnetic Films
The surface spin wave branches in ferromagnetic films are studied using a
microscopic theory which considers both magnetic dipole-dipole and Heisenberg
exchange interactions. The dipole terms are expressed in a Hamiltonian
formalism, and the dipole sums are calculated in a rapidly convergent form. The
Damon-Eshbach surface modes are analyzed for different directions of the
spin-wave propagation and also for different ratios of the strength of the
dipole interactions relative to the exchange interactions. Numerical results
are presented using parameters for Fe and GdCl.Comment: 9 pages including figures, Revtex, to appear in the proceedings of
the ICM 200
Brazilian elections: voting for a scaling democracy
The proportional elections held in Brazil in 1998 and 2002 display identical
statistical signatures. In particular, the distribution of votes among
candidates includes a power-law regimen. We suggest that the rationale behind
this robust scaling invariance is a multiplicative process in which the voter's
choice for a candidate is governed by a product of probabilities.Comment: 4 pages, 2 figure
Spatial correlations in vote statistics: a diffusive field model for decision-making
We study the statistics of turnout rates and results of the French elections
since 1992. We find that the distribution of turnout rates across towns is
surprisingly stable over time. The spatial correlation of the turnout rates, or
of the fraction of winning votes, is found to decay logarithmically with the
distance between towns. Based on these empirical observations and on the
analogy with a two-dimensional random diffusion equation, we propose that
individual decisions can be rationalised in terms of an underlying "cultural"
field, that locally biases the decision of the population of a given region, on
top of an idiosyncratic, town-dependent field, with short range correlations.
Using symmetry considerations and a set of plausible assumptions, we suggest
that this cultural field obeys a random diffusion equation.Comment: 18 pages, 5 figures; added sociophysics references
Antisymmetric Tensor Fields in Randall Sundrum Thick Branes
In this article we study the issue of localization of the three-form field in
a Randall-Sundrum-like scenario. We simulate our membrane by kinks embedded in
D=5, describing the usual case (not deformed) and new models coming from a
specific deformation procedure. The gravitational background regarded includes
the dilaton contribution. We show that we can only localize the zero-mode of
this field for a specific range of the dilaton coupling, even in the deformed
case. A study about resonances is presented. We use a numerical approach for
calculations of the transmission coefficients associated to the quantum
mechanical problem. This gives a clear description of the physics involved in
the model. We find in this way that the appearance of resonances is strongly
dependent on the coupling constant. We study the cases and 5 for
and . The first value of give us one
resonance peak for and no resonances for . The second value of
give us a very rich structure of resonances, with number deppending on
the value of .Comment: 7 pages, 3 figure
Pattern Selection in a Phase Field Model for Directional Solidification
A symmetric phase field model is used to study wavelength selection in two
dimensions. We study the problem in a finite system using a two-pronged
approach. First we construct an action and, minimizing this, we obtain the most
probable configuration of the system, which we identify with the selected
stationary state. The minimization is constrained by the stationary solutions
of stochastic evolution equations and is done numerically. Secondly, additional
support for this selected state is obtained from straightforward simulations of
the dynamics from a variety of initial states.Comment: 7 pages, 6 figures, to appear in Physica
Variational Principle underlying Scale Invariant Social Systems
MaxEnt's variational principle, in conjunction with Shannon's logarithmic
information measure, yields only exponential functional forms in
straightforward fashion. In this communication we show how to overcome this
limitation via the incorporation, into the variational process, of suitable
dynamical information. As a consequence, we are able to formulate a somewhat
generalized Shannonian Maximum Entropy approach which provides a unifying
"thermodynamic-like" explanation for the scale-invariant phenomena observed in
social contexts, as city-population distributions. We confirm the MaxEnt
predictions by means of numerical experiments with random walkers, and compare
them with some empirical data
Unravelling the size distribution of social groups with information theory on complex networks
The minimization of Fisher's information (MFI) approach of Frieden et al.
[Phys. Rev. E {\bf 60} 48 (1999)] is applied to the study of size distributions
in social groups on the basis of a recently established analogy between scale
invariant systems and classical gases [arXiv:0908.0504]. Going beyond the ideal
gas scenario is seen to be tantamount to simulating the interactions taking
place in a network's competitive cluster growth process. We find a scaling rule
that allows to classify the final cluster-size distributions using only one
parameter that we call the competitiveness. Empirical city-size distributions
and electoral results can be thus reproduced and classified according to this
competitiveness, which also allows to correctly predict well-established
assessments such as the "six-degrees of separation", which is shown here to be
a direct consequence of the maximum number of stable social relationships that
one person can maintain, known as Dunbar's number. Finally, we show that scaled
city-size distributions of large countries follow the same universal
distribution
Potts model with q=3 and 4 states on directed Small-World network
Monte Carlo simulations are performed to study the two-dimensional Potts
models with q=3 and 4 states on directed Small-World network. The disordered
system is simulated applying the Heat bath Monte Carlo update algorithm. A
first-order and second-order phase transition is found for q=3 depending on the
rewiring probability , but for q=4 the system presents only a first-order
phase transition for any value . This critical behavior is different from
the Potts model on a square lattice, where the second-order phase transition is
present for and a first-order phase transition is present for q>4.Comment: 5 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1001.184
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