149 research outputs found
Risk aversion in economic transactions
Most people are risk-averse (risk-seeking) when they expect to gain (lose).
Based on a generalization of ``expected utility theory'' which takes this into
account, we introduce an automaton mimicking the dynamics of economic
operations. Each operator is characterized by a parameter q which gauges
people's attitude under risky choices; this index q is in fact the entropic one
which plays a central role in nonextensive statistical mechanics. Different
long term patterns of average asset redistribution are observed according to
the distribution of parameter q (chosen once for ever for each operator) and
the rules (e.g., the probabilities involved in the gamble and the indebtedness
restrictions) governing the values that are exchanged in the transactions.
Analytical and numerical results are discussed in terms of how the sensitivity
to risk affects the dynamics of economic transactions.Comment: 4 PS figures, to appear in Europhys. Let
Exact results for the Barabasi queuing model
Previous works on the queuing model introduced by Barab\'asi to account for
the heavy tailed distributions of the temporal patterns found in many human
activities mainly concentrate on the extremal dynamics case and on lists of
only two items. Here we obtain exact results for the general case with
arbitrary values of the list length and of the degree of randomness that
interpolates between the deterministic and purely random limits. The
statistically fundamental quantities are extracted from the solution of master
equations. From this analysis, new scaling features of the model are uncovered
Single-species fragmentation: the role of density-dependent feedbacks
Internal feedbacks are commonly present in biological populations and can
play a crucial role in the emergence of collective behavior. We consider a
generalization of Fisher-KPP equation to describe the temporal evolution of the
distribution of a single-species population. This equation includes the
elementary processes of random motion, reproduction and, importantly, nonlocal
interspecific competition, which introduces a spatial scale of interaction.
Furthermore, we take into account feedback mechanisms in diffusion and growth
processes, mimicked through density-dependencies controlled by exponents
and , respectively. These feedbacks include, for instance, anomalous
diffusion, reaction to overcrowding or to rarefaction of the population, as
well as Allee-like effects. We report that, depending on the dynamics in place,
the population can self-organize splitting into disconnected sub-populations,
in the absence of environment constraints. Through extensive numerical
simulations, we investigate the temporal evolution and stationary features of
the population distribution in the one-dimensional case. We discuss the crucial
role that density-dependency has on pattern formation, particularly on
fragmentation, which can bring important consequences to processes such as
epidemic spread and speciation
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