2,588 research outputs found
Evolutionary prisoner's dilemma games with optional participation
Competition among cooperators, defectors, and loners is studied in an
evolutionary prisoner's dilemma game with optional participation. Loners are
risk averse i.e. unwilling to participate and rather rely on small but fixed
earnings. This results in a rock-scissors-paper type cyclic dominance of the
three strategies. The players are located either on square lattices or random
regular graphs with the same connectivity. Occasionally, every player
reassesses its strategy by sampling the payoffs in its neighborhood. The loner
strategy efficiently prevents successful spreading of selfish, defective
behavior and avoids deadlocks in states of mutual defection. On square
lattices, Monte Carlo simulations reveal self-organizing patterns driven by the
cyclic dominance, whereas on random regular graphs different types of
oscillatory behavior are observed: the temptation to defect determines whether
damped, periodic or increasing oscillations occur. These results are compared
to predictions by pair approximation. Although pair approximation is incapable
of distinguishing the two scenarios because of the equal connectivity, the
average frequencies as well as the oscillations on random regular graphs are
well reproduced.Comment: 6 pages, 7 figure
Benefits of a marketing cooperative in transition agriculture: Mórakert purchasing and service co-operative
The paper analyses the potential benefits of marketing cooperatives in Hungary, employing a transaction cost economics framework. We found that the purchased quantity, the existence of contracts, flexibility and trust are the most important factors farmers consider when selling their products via a cooperative. The most striking result is that diversification has positive influences on the share of cooperatives in farmers’ sale. Furthermore, farmers with larger bargaining power have less willingness to sell their product to the cooperative. Surprisingly, asset specificity has rather negative effects on the share of cooperatives in members’ sales
Causation, Measurement Relevance and No-conspiracy in EPR
In this paper I assess the adequacy of no-conspiracy conditions employed in
the usual derivations of the Bell inequality in the context of EPR
correlations. First, I look at the EPR correlations from a purely
phenomenological point of view and claim that common cause explanations of
these cannot be ruled out. I argue that an appropriate common cause explanation
requires that no-conspiracy conditions are re-interpreted as mere common
cause-measurement independence conditions. In the right circumstances then,
violations of measurement independence need not entail any kind of conspiracy
(nor backwards in time causation). To the contrary, if measurement operations
in the EPR context are taken to be causally relevant in a specific way to the
experiment outcomes, their explicit causal role provides the grounds for a
common cause explanation of the corresponding correlations.Comment: 20 pages, 1 figur
Main-Belt Asteroids in the K2 Engineering Field of View
Unlike NASA's original Kepler Discovery Mission, the renewed K2 Mission will
stare at the plane of the Ecliptic, observing each field for approximately 75
days. This will bring new opportunities and challenges, in particular the
presence of a large number of main-belt asteroids that will contaminate the
photometry. The large pixel size makes K2 data susceptible to the effect of
apparent minor planet encounters. Here we investigate the effects of asteroid
encounters on photometric precision using a sub-sample of the K2 Engineering
data taken in February, 2014. We show examples of asteroid contamination to
facilitate their recognition and distinguish these events from other error
sources. We conclude that main-belt asteroids will have considerable effects on
K2 photometry of a large number of photometric targets during the Mission, that
will have to be taken into account. These results will be readily applicable
for future space photometric missions applying large-format CCDs, such as TESS
and PLATO.Comment: accepted for publication in AJ, 6 page
Cooperation enhanced by inhomogeneous activity of teaching for evolutionary Prisoner's Dilemma games
Evolutionary Prisoner's Dilemma games with quenched inhomogeneities in the
spatial dynamical rules are considered. The players following one of the two
pure strategies (cooperation or defection) are distributed on a two-dimensional
lattice. The rate of strategy adoption from a randomly chosen neighbors are
controlled by the payoff difference and a two-value pre-factor
characterizing the players whom the strategy learned from. The reduced teaching
activity of players is distributed randomly with concentrations at the
beginning and fixed further on. Numerical and analytical calculations are
performed to study the concentration of cooperators as a function of and
for different noise levels and connectivity structures. Significant
increase of cooperation is found within a wide range of parameters for this
dynamics. The results highlight the importance of asymmetry characterizing the
exchange of master-follower role during the strategy adoptions.Comment: 4 pages, 5 figures, corrected typo
Phase transition and selection in a four-species cyclic Lotka-Volterra model
We study a four species ecological system with cyclic dominance whose
individuals are distributed on a square lattice. Randomly chosen individuals
migrate to one of the neighboring sites if it is empty or invade this site if
occupied by their prey. The cyclic dominance maintains the coexistence of all
the four species if the concentration of vacant sites is lower than a threshold
value. Above the treshold, a symmetry breaking ordering occurs via growing
domains containing only two neutral species inside. These two neutral species
can protect each other from the external invaders (predators) and extend their
common territory. According to our Monte Carlo simulations the observed phase
transition is equivalent to those found in spreading models with two equivalent
absorbing states although the present model has continuous sets of absorbing
states with different portions of the two neutral species. The selection
mechanism yielding symmetric phases is related to the domain growth process
whith wide boundaries where the four species coexist.Comment: 4 pages, 5 figure
Motion of influential players can support cooperation in Prisoner's Dilemma
We study a spatial Prisoner's dilemma game with two types (A and B) of players located on a square lattice. Players following either cooperator or defector strategies play Prisoner's Dilemma games with their 24 nearest neighbors. The players are allowed to adopt one of their neighbor's strategy with a probability dependent on the payoff difference and type of the given neighbor. Players A and B have different efficiency in the transfer of their own strategies; therefore the strategy adoption probability is reduced by a multiplicative factor (w < 1) from the players of type B. We report that the motion of the influential payers (type A) can improve remarkably the maintenance of cooperation even for their low densitie
Vortex dynamics in a three-state model under cyclic dominance
The evolution of domain structure is investigated in a two-dimensional voter
model with three states under cyclic dominance. The study focus on the dynamics
of vortices, defined by the points where three states (domains) meet. We can
distinguish vortices and antivortices which walk randomly and annihilate each
other. The domain wall motion can create vortex-antivortex pairs at a rate
which is increased by the spiral formation due to the cyclic dominance. This
mechanism is contrasted with a branching annihilating random walk (BARW) in a
particle antiparticle system with density dependent pair creation rate.
Numerical estimates for the critical indices of the vortex density
() and of its fluctuation () improve an earlier
Monte Carlo study [Tainaka and Itoh, Europhys. Lett. 15, 399 (1991)] of the
three-state cyclic voter model in two dimensions.Comment: 5 pages, 6 figures, to appear in PR
Semiclassical model for calculating fully differential ionization cross sections of the H molecule
Fully differential cross sections are calculated for the ionization of H
by fast charged projectiles using a semiclassical model developed previously
for the ionization of atoms. The method is tested in case of 4 keV electron and
6 MeV proton projectiles. The obtained results show good agreement with the
available experimental data. Interference effects due to the two-center
character of the target are also observed and analyzed.Comment: 11 pages, 4 figure
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