568 research outputs found
Cultural propagation on social networks
In this work we present a model for the propagation of culture on networks of
different topology and by considering different underlying dynamics. We extend
a previous model proposed by Axelrod by letting a majority govern the dynamics
of changes. This in turn allows us to define a Lyapunov functional for the
system.Comment: 8 pages, 9 figures include
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Certainty in ascending sensory signals - The unexplored driver of analgesic placebo response.
Previous frameworks have failed to adequately explain the observed correlation between within-subject variability in pain reporting and analgesic placebo response. These relationships have been observed in both clinical and experimental setups. Within-subject variability of clinical pain scores is traditionally assessed based on daily pain diaries collected during the pre-intervention stage. Experimental variability can be assessed by the Focused Analgesia Selection Test (FAST), which calculates the relationship between noxious stimuli administrated at various intensities and pain reports. The variability, either clinical or experimental, has been shown to predict the placebo response. In explaining the placebo response, Bayesian Brain Hypothesis (BBH) posits that pain perception (posterior), is composed of certainty (precision) of expectations (priors due to belief or conditioning) and incoming sensory information (likelihood), with the bulk of research focused on the precision of priors. Virtually all placebo analgesia research has focused on the priors and their certainty, rather than on the certainty of the likelihood, mainly because it cannot be assessed directly. We propose that the within-subject variability, as encapsulated by the FAST, is a proxy for certainty in (or, precision of) ascending sensory signals, and our results suggest that it could not only be assessed, but also manipulated. If true, our hypothesis will facilitate new lines of research and could potentially promote precision analgesic medicine by use of variability of pain scores as a diagnostic method to identify pain patients who will benefit from specific treatments
Comparison of voter and Glauber ordering dynamics on networks
We study numerically the ordering process of two very simple dynamical models
for a two-state variable on several topologies with increasing levels of
heterogeneity in the degree distribution. We find that the zero-temperature
Glauber dynamics for the Ising model may get trapped in sets of partially
ordered metastable states even for finite system size, and this becomes more
probable as the size increases. Voter dynamics instead always converges to full
order on finite networks, even if this does not occur via coherent growth of
domains. The time needed for order to be reached diverges with the system size.
In both cases the ordering process is rather insensitive to the variation of
the degreee distribution from sharply peaked to scale-free.Comment: 12 pages, 12 figure
Effects of Mass Media and Cultural Drift in a Model for Social Influence
In the context of an extension of Axelrod's model for social influence, we
study the interplay and competition between the cultural drift, represented as
random perturbations, and mass media, introduced by means of an external
homogeneous field. Unlike previous studies [J. C. Gonz\'alez-Avella {\it et
al}, Phys. Rev. E {\bf 72}, 065102(R) (2005)], the mass media coupling proposed
here is capable of affecting the cultural traits of any individual in the
society, including those who do not share any features with the external
message. A noise-driven transition is found: for large noise rates, both the
ordered (culturally polarized) phase and the disordered (culturally fragmented)
phase are observed, while, for lower noise rates, the ordered phase prevails.
In the former case, the external field is found to induce cultural ordering, a
behavior opposite to that reported in previous studies using a different
prescription for the mass media interaction. We compare the predictions of this
model to statistical data measuring the impact of a mass media vasectomy
promotion campaign in Brazil.Comment: 10 pages, 3 figures; minor changes; added references. To appear in
IJMP
Opinion and community formation in coevolving networks
In human societies opinion formation is mediated by social interactions,
consequently taking place on a network of relationships and at the same time
influencing the structure of the network and its evolution. To investigate this
coevolution of opinions and social interaction structure we develop a dynamic
agent-based network model, by taking into account short range interactions like
discussions between individuals, long range interactions like a sense for
overall mood modulated by the attitudes of individuals, and external field
corresponding to outside influence. Moreover, individual biases can be
naturally taken into account. In addition the model includes the opinion
dependent link-rewiring scheme to describe network topology coevolution with a
slower time scale than that of the opinion formation. With this model
comprehensive numerical simulations and mean field calculations have been
carried out and they show the importance of the separation between fast and
slow time scales resulting in the network to organize as well-connected small
communities of agents with the same opinion.Comment: 10 pages, 5 figures. New inset for Fig. 1 and references added.
Submitted to Physical Review
Experimental evidence of stochastic resonance without tuning due to non Gaussian noises
In order to test theoretical predictions, we have studied the phenomenon of
stochastic resonance in an electronic experimental system driven by white non
Gaussian noise. In agreement with the theoretical predictions our main findings
are: an enhancement of the sensibility of the system together with a remarkable
widening of the response (robustness). This implies that even a single resonant
unit can reach a marked reduction in the need of noise tuning.Comment: 4 pages, 3 figure
Halting viruses in scale-free networks
The vanishing epidemic threshold for viruses spreading on scale-free networks
indicate that traditional methods, aiming to decrease a virus' spreading rate
cannot succeed in eradicating an epidemic. We demonstrate that policies that
discriminate between the nodes, curing mostly the highly connected nodes, can
restore a finite epidemic threshold and potentially eradicate a virus. We find
that the more biased a policy is towards the hubs, the more chance it has to
bring the epidemic threshold above the virus' spreading rate. Furthermore, such
biased policies are more cost effective, requiring less cures to eradicate the
virus
How strongly do word reading times and lexical decision times correlate? Combining data from eye movement corpora and megastudies
We assess the amount of shared variance between three measures of visual word recognition latencies: eye movement latencies, lexical decision times and naming times. After partialling out the effects of word frequency and word length, two well-documented predictors of word recognition latencies, we see that 7-44% of the variance is uniquely shared between lexical decision times and naming times, depending on the frequency range of the words used. A similar analysis of eye movement latencies shows that the percentage of variance they uniquely share either with lexical decision times or with naming times is much lower. It is 5 – 17% for gaze durations and lexical decision times in studies with target words presented in neutral sentences, but drops to .2% for corpus studies in which eye movements to all words are analysed. Correlations between gaze durations and naming latencies are lower still. These findings suggest that processing times in isolated word processing and continuous text reading are affected by specific task demands and presentation format, and that lexical decision times and naming times are not very informative in predicting eye movement latencies in text reading once the effect of word frequency and word length are taken into account. The difference between controlled experiments and natural reading suggests that reading strategies and stimulus materials may determine the degree to which the immediacy-of-processing assumption and the eye-mind assumption apply. Fixation times are more likely to exclusively reflect the lexical processing of the currently fixated word in controlled studies with unpredictable target words rather than in natural reading of sentences or texts
Small world effect in an epidemiological model
A model for the spread of an infection is analyzed for different population
structures. The interactions within the population are described by small world
networks, ranging from ordered lattices to random graphs. For the more ordered
systems, there is a fluctuating endemic state of low infection. At a finite
value of the disorder of the network, we find a transition to self-sustained
oscillations in the size of the infected subpopulation
Scaling Properties of Random Walks on Small-World Networks
Using both numerical simulations and scaling arguments, we study the behavior
of a random walker on a one-dimensional small-world network. For the properties
we study, we find that the random walk obeys a characteristic scaling form.
These properties include the average number of distinct sites visited by the
random walker, the mean-square displacement of the walker, and the distribution
of first-return times. The scaling form has three characteristic time regimes.
At short times, the walker does not see the small-world shortcuts and
effectively probes an ordinary Euclidean network in -dimensions. At
intermediate times, the properties of the walker shows scaling behavior
characteristic of an infinite small-world network. Finally, at long times, the
finite size of the network becomes important, and many of the properties of the
walker saturate. We propose general analytical forms for the scaling properties
in all three regimes, and show that these analytical forms are consistent with
our numerical simulations.Comment: 7 pages, 8 figures, two-column format. Submitted to PR
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