1,910 research outputs found
Conditional strategies and the evolution of cooperation in spatial public goods games
The fact that individuals will most likely behave differently in different
situations begets the introduction of conditional strategies. Inspired by this,
we study the evolution of cooperation in the spatial public goods game, where
besides unconditional cooperators and defectors, also different types of
conditional cooperators compete for space. Conditional cooperators will
contribute to the public good only if other players within the group are likely
to cooperate as well, but will withhold their contribution otherwise. Depending
on the number of other cooperators that are required to elicit cooperation of a
conditional cooperator, the latter can be classified in as many types as there
are players within each group. We find that the most cautious cooperators, such
that require all other players within a group to be conditional cooperators,
are the undisputed victors of the evolutionary process, even at very low
synergy factors. We show that the remarkable promotion of cooperation is due
primarily to the spontaneous emergence of quarantining of defectors, which
become surrounded by conditional cooperators and are forced into isolated
convex "bubbles" from where they are unable to exploit the public good. This
phenomenon can be observed only in structured populations, thus adding to the
relevance of pattern formation for the successful evolution of cooperation.Comment: 7 two-column pages, 7 figures; accepted for publication in Physical
Review
Correlation of Positive and Negative Reciprocity Fails to Confer an Evolutionary Advantage: Phase Transitions to Elementary Strategies
Economic experiments reveal that humans value cooperation and fairness. Punishing unfair behavior is therefore common, and according to the theory of strong reciprocity, it is also directly related to rewarding cooperative behavior. However, empirical data fail to confirm that positive and negative reciprocity are correlated. Inspired by this disagreement, we determine whether the combined application of reward and punishment is evolutionarily advantageous. We study a spatial public goods game, where in addition to the three elementary strategies of defection, rewarding, and punishment, a fourth strategy that combines the latter two competes for space. We find rich dynamical behavior that gives rise to intricate phase diagrams where continuous and discontinuous phase transitions occur in succession. Indirect territorial competition, spontaneous emergence of cyclic dominance, as well as divergent fluctuations of oscillations that terminate in an absorbing phase are observed. Yet, despite the high complexity of solutions, the combined strategy can survive only in very narrow and unrealistic parameter regions. Elementary strategies, either in pure or mixed phases, are much more common and likely to prevail. Our results highlight the importance of patterns and structure in human cooperation, which should be considered in future experiments
Self-Organized Ordering of Nanostructures Produced by Ion-Beam Sputtering
We study the self-organized ordering of nanostructures produced by ion-beam
sputtering (IBS) of targets amorphizing under irradiation. By introducing a
model akin to models of pattern formation in aeolian sand dunes, we extend
consistently the current continuum theory of erosion by IBS. We obtain new
non-linear effects responsible for the in-plane ordering of the structures,
whose strength correlates with the degree of ordering found in experiments. Our
results highlight the importance of redeposition and surface viscous flow to
this nanopattern formation process.Comment: 4 pages, 2 figure
Note and Comment
The Law School; Pleading Estoppel; Libels on Person and on Property; The Conflict Between a Patentee\u27s Right to Monopoly and a State Anti-Monopoly Statut
Dynamical charge and spin density wave scattering in cuprate superconductor
We show that a variety of spectral features in high-T_c cuprates can be
understood from the coupling of charge carriers to some kind of dynamical order
which we exemplify in terms of fluctuating charge and spin density waves. Two
theoretical models are investigated which capture different aspects of such
dynamical scattering. The first approach leaves the ground state in the
disordered phase but couples the electrons to bosonic degrees of freedom,
corresponding to the quasi singular scattering associated with the closeness to
an ordered phase. The second, more phenomological approach starts from the
construction of a frequency dependent order parameter which vanishes for small
energies. Both theories capture scanning tunneling microscopy and angle-resoved
photoemission experiments which suggest the protection of quasiparticles close
to the Fermi energy but the manifestation of long-range order at higher
frequencies.Comment: 27 pages, 13 figures, to appear in New J. Phy
Phase separation in the vicinity of "quantum critical" doping concentration: implications for high temperature superconductors
A general quantitative measure of the tendency towards phase separation is
introduced for systems exhibiting phase transitions or crossovers controlled by
charge carrier concentration. This measure is devised for the situations when
the quantitative knowledge of various contributions to free energy is
incomplete, and is applied to evaluate the chances of electronic phase
separation associated with the onset of antiferromagnetic correlations in
high-temperature cuprate superconductors. The experimental phenomenology of
lanthanum- and yittrium-based cuprates was used as input to this analysis. It
is also pointed out that Coulomb repulsion between charge carriers separated by
the distances of 1-3 lattice periods strengthens the tendency towards phase
separation by accelerating the decay of antiferromagnetic correlations with
doping. Overall, the present analysis indicates that cuprates are realistically
close to the threshold of phase separation -- nanoscale limited or even
macroscopic with charge density varying between adjacent crystal planes
The Structure on Invariant Measures of generic diffeomorphisms
Let be an isolated non-trival transitive set of a generic
diffeomorphism f\in\Diff(M). We show that the space of invariant measures
supported on coincides with the space of accumulation measures of
time averages on one orbit. Moreover, the set of points having this property is
residual in (which implies the set of irregular points is also
residual in ). As an application, we show that the non-uniform
hyperbolicity of irregular points in with totally 0 measure
(resp., the non-uniform hyperbolicity of a generic subset in )
determines the uniform hyperbolicity of
A Two-Player Game of Life
We present a new extension of Conway's game of life for two players, which we
call p2life. P2life allows one of two types of token, black or white, to
inhabit a cell, and adds competitive elements into the birth and survival rules
of the original game. We solve the mean-field equation for p2life and determine
by simulation that the asymptotic density of p2life approaches 0.0362.Comment: 7 pages, 3 figure
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