212 research outputs found
Chaotic, staggered and polarized dynamics in opinion forming: the contrarian effect
We revisit the no tie breaking 2-state Galam contrarian model of opinion
dynamics for update groups of size 3. While the initial model assumes a
constant density of contrarians a for both opinions, it now depends for each
opinion on its global support. Proportionate contrarians are thus found to
indeed preserve the former case main results. However, restricting the
contrarian behavior to only the current collective majority, makes the dynamics
more complex with novel features. For a density a<a_c=1/9 of one-sided
contrarians, a chaotic basin is found in the fifty-fifty region separated from
two majority-minority point attractors, one on each side. For 1/9<a< 0.301 only
the chaotic basin survives. In the range a>0.301 the chaotic basin disappears
and the majority starts to alternate between the two opinions with a staggered
flow towards two point attractors. We then study the effect of both, decoupling
the local update time sequence from the contrarian behavior activation, and a
smoothing of the majority rule. A status quo driven bias for contrarian
activation is also considered. Introduction of unsettled agents driven in the
debate on a contrarian basis is shown to only shrink the chaotic basin. The
model may shed light to recent apparent contradictory elections with on the one
hand very tied results like in US in 2000 and in Germany in 2002 and 2005, and
on the other hand, a huge majority like in France in 2002.Comment: 17 pages, 10 figure
Self-consistency and Symmetry in d-dimensions
Bethe approximation is shown to violate Bravais lattices translational
invariance. A new scheme is then presented which goes over the one-site Weiss
model yet preserving initial lattice symmetry. A mapping to a one-dimensional
finite closed chain in an external field is obtained. Lattice topology
determines the chain size. Using recent results in percolation, lattice
connectivity between chains is argued to be where is the
coordination number and is the space dimension. A new self-consistent
mean-field equation of state is derived. Critical temperatures are thus
calculated for a large variety of lattices and dimensions. Results are within a
few percent of exact estimates. Moreover onset of phase transitions is found to
occur in the range . For the Ising hypercube it yields the Golden
number limit .Comment: 16 pages, latex, Phys. Rev. B (in press
From GM Law to A Powerful Mean Field Scheme
A new and powerful mean field scheme is presented. It maps to a
one-dimensional finite closed chain in an external field. The chain size
accounts for lattice topologies. Moreover lattice connectivity is rescaled
according to the GM law recently obtained in percolation theory. The associated
self-consistent mean-field equation of state yields critical temperatures which
are within a few percent of exact estimates. Results are obtained for a large
variety of lattices and dimensions. The Ising lower critical dimension for the
onset of phase transitions is . For the Ising hypercube it
becomes the Golden number . The scheme recovers the
exact result of no long range order for non-zero temperature Ising triangular
antiferromagnets.Comment: 3M Conference Proceedings, San Jose, California (November, 1999
Opinion dynamics: rise and fall of political parties
We analyze the evolution of political organizations using a model in which
agents change their opinions via two competing mechanisms. Two agents may
interact and reach consensus, and additionally, individual agents may
spontaneously change their opinions by a random, diffusive process. We find
three distinct possibilities. For strong diffusion, the distribution of
opinions is uniform and no political organizations (parties) are formed. For
weak diffusion, parties do form and furthermore, the political landscape
continually evolves as small parties merge into larger ones. Without diffusion,
a pattern develops: parties have the same size and they possess equal niches.
These phenomena are analyzed using pattern formation and scaling techniques.Comment: 5 pages, 5 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
The Galam Model of Minority Opinion Spreading and the Marriage Gap
In 2002, Serge Galam designed a model of a minority opinion spreading. The
effect is expected to lead a conservative minority to prevail if the issue is
discussed long enough. Here we analyze the marriage gap, i.e. the difference in
voting for Bush and Kerry in 2004 between married and unmarried people. It
seems possible to interpret this marriage gap in terms of the Galam model.Comment: 6 page
Voting and Catalytic Processes with Inhomogeneities
We consider the dynamics of the voter model and of the monomer-monomer
catalytic process in the presence of many ``competing'' inhomogeneities and
show, through exact calculations and numerical simulations, that their presence
results in a nontrivial fluctuating steady state whose properties are studied
and turn out to specifically depend on the dimensionality of the system, the
strength of the inhomogeneities and their separating distances. In fact, in
arbitrary dimensions, we obtain an exact (yet formal) expression of the order
parameters (magnetization and concentration of adsorbed particles) in the
presence of an arbitrary number of inhomogeneities (``zealots'' in the
voter language) and formal similarities with {\it suitable electrostatic
systems} are pointed out. In the nontrivial cases , we explicitly
compute the static and long-time properties of the order parameters and
therefore capture the generic features of the systems. When , the problems
are studied through numerical simulations. In one spatial dimension, we also
compute the expressions of the stationary order parameters in the completely
disordered case, where is arbitrary large. Particular attention is paid to
the spatial dependence of the stationary order parameters and formal
connections with electrostatics.Comment: 17 pages, 6 figures, revtex4 2-column format. Original title ("Are
Voting and Catalytic Processes Electrostatic Problems ?") changed upon
editorial request. Minor typos corrected. Published in Physical Review
Noisy continuous--opinion dynamics
We study the Deffuant et al. model for continuous--opinion dynamics under the
influence of noise. In the original version of this model, individuals meet in
random pairwise encounters after which they compromise or not depending of a
confidence parameter. Free will is introduced in the form of noisy
perturbations: individuals are given the opportunity to change their opinion,
with a given probability, to a randomly selected opinion inside the whole
opinion space. We derive the master equation of this process. One of the main
effects of noise is to induce an order-disorder transition. In the disordered
state the opinion distribution tends to be uniform, while for the ordered state
a set of well defined opinion groups are formed, although with some opinion
spread inside them. Using a linear stability analysis we can derive approximate
conditions for the transition between opinion groups and the disordered state.
The master equation analysis is compared with direct Monte-Carlo simulations.
We find that the master equation and the Monte-Carlo simulations do not always
agree due to finite-size induced fluctuations that we analyze in some detail
Bayesian Updating Rules in Continuous Opinion Dynamics Models
In this article, I investigate the use of Bayesian updating rules applied to
modeling social agents in the case of continuos opinions models. Given another
agent statement about the continuous value of a variable , we will see that
interesting dynamics emerge when an agent assigns a likelihood to that value
that is a mixture of a Gaussian and a Uniform distribution. This represents the
idea the other agent might have no idea about what he is talking about. The
effect of updating only the first moments of the distribution will be studied.
and we will see that this generates results similar to those of the Bounded
Confidence models. By also updating the second moment, several different
opinions always survive in the long run. However, depending on the probability
of error and initial uncertainty, those opinions might be clustered around a
central value.Comment: 14 pages, 5 figures, presented at SigmaPhi200
Contemporary management of genitourinary injuries in a tertiary trauma centre in Nigeria
Background: The genitourinary system has been shown to be involved in 10% of patients presenting after trauma and is therefore a significant factor in trauma induced morbidity and mortality. It affects all age groups and both sexes. The aim of this study is to determine the aetiology, mechanism of injury and management of genitourinary injuries in a tertiary trauma centre.Methods: This is a prospective study carried out at the Jos University Teaching Hospital between 2012 and 2017. All patients who presented at the A and E with genitourinary trauma were recruited into the study. Initial assessment involved taking an AMPLE history and resuscitation, using the Advanced Trauma Life Support (ATLS) protocol of the American College of Surgeons. Physical examination and investigation were carried out to localize and determine extent of injury. Investigations carried out were complete blood count, blood grouping, serum electrolyte, urea and creatinine and radiography where applicable. Surgical intervention was carried out where indicated.Results: A total of 104 patients were involved in this study. The mean age was 32.14±15.5 years with a range of 3 to 75yrs. Median age was 28yrs. Eighty-nine (85.6%) were males while fifteen (14.4%) were females. The genitalia were the most affected in 34% (n=35) of the patients. Gunshot was the commonest mechanism of injury (37.5%, n=39). Operative and non-operative management were employed depending on mechanism and extent of injury.Conclusions: Gunshot was the commonest cause of genitourinary trauma. These injuries require specialized attention for proper assessment and management.
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