5,859 research outputs found
Adaptive simulation using mode identification
Adaptive simulation using modal clustering and method of potential function
Social diversity and promotion of cooperation in the spatial prisoner's dilemma game
The diversity in wealth and social status is present not only among humans,
but throughout the animal world. We account for this observation by generating
random variables that determ ine the social diversity of players engaging in
the prisoner's dilemma game. Here the term social diversity is used to address
extrinsic factors that determine the mapping of game pay offs to individual
fitness. These factors may increase or decrease the fitness of a player
depending on its location on the spatial grid. We consider different
distributions of extrin sic factors that determine the social diversity of
players, and find that the power-law distribution enables the best promotion of
cooperation. The facilitation of the cooperative str ategy relies mostly on the
inhomogeneous social state of players, resulting in the formation of
cooperative clusters which are ruled by socially high-ranking players that are
able to prevail against the defectors even when there is a large temptation to
defect. To confirm this, we also study the impact of spatially correlated
social diversity and find that coopera tion deteriorates as the spatial
correlation length increases. Our results suggest that the distribution of
wealth and social status might have played a crucial role by the evolution of
cooperation amongst egoistic individuals.Comment: 5 two-column pages, 5 figure
Similarity based cooperation and spatial segregation
We analyze a cooperative game, where the cooperative act is not based on the
previous behaviour of the co-player, but on the similarity between the players.
This system has been studied in a mean-field description recently [A. Traulsen
and H. G. Schuster, Phys. Rev. E 68, 046129 (2003)]. Here, the spatial
extension to a two-dimensional lattice is studied, where each player interacts
with eight players in a Moore neighborhood. The system shows a strong
segregation independent on parameters. The introduction of a local conversion
mechanism towards tolerance allows for four-state cycles and the emergence of
spiral waves in the spatial game. In the case of asymmetric costs of
cooperation a rich variety of complex behavior is observed depending on both
cooperation costs. Finally, we study the stabilization of a cooperative fixed
point of a forecast rule in the symmetric game, which corresponds to
cooperation across segregation borders. This fixed point becomes unstable for
high cooperation costs, but can be stabilized by a linear feedback mechanism.Comment: 7 pages, 9 figure
Einstein Radii from Binary Lensing Events
We show that the Einstein ring radius and transverse speed of a lens
projected on the source plane, and , can be
determined from the light curve of a binary-source event, followed by the
spectroscopic determination of the orbital elements of the source stars. The
determination makes use of the same principle that allows one to measure the
Einstein ring radii from finite-source effects. For the case when the orbital
period of the source stars is much longer than the Einstein time scale, , there exists a single two-fold degeneracy in determining
. However, when the degeneracy can
often be broken by making use of the binary-source system's orbital motion.
%Once , and thus are determined, one can
%distinguish self-lensing events in the Large Magellanic Cloud %from Galactic
halo events. For an identifiable 8\% of all lensing events seen toward the
Large Magellanic Cloud (LMC), one can unambiguously determine whether the
lenses are Galactic, or whether they lie in the LMC itself. The required
observations can be made after the event is over and could be carried out for
the events seen by Alcock et al.\ and Aubourg et al.. In addition, we
propose to include eclipsing binaries as sources for gravitational lensing
experiments.Comment: 18 pages, revised version, submitted to Ap
Algebraic Characterization of Vector Supersymmetry in Topological Field Theories
An algebraic cohomological characterization of a class of linearly broken
Ward identities is provided. The examples of the topological vector
supersymmetry and of the Landau ghost equation are discussed in detail. The
existence of such a linearly broken Ward identities turns out to be related to
BRST exact antifield dependent cocycles with negative ghost number.Comment: 30 pages, latex2e file, subm. to Journ. of Math. Phy
Emotional Strategies as Catalysts for Cooperation in Signed Networks
The evolution of unconditional cooperation is one of the fundamental problems
in science. A new solution is proposed to solve this puzzle. We treat this
issue with an evolutionary model in which agents play the Prisoner's Dilemma on
signed networks. The topology is allowed to co-evolve with relational signs as
well as with agent strategies. We introduce a strategy that is conditional on
the emotional content embedded in network signs. We show that this strategy
acts as a catalyst and creates favorable conditions for the spread of
unconditional cooperation. In line with the literature, we found evidence that
the evolution of cooperation most likely occurs in networks with relatively
high chances of rewiring and with low likelihood of strategy adoption. While a
low likelihood of rewiring enhances cooperation, a very high likelihood seems
to limit its diffusion. Furthermore, unlike in non-signed networks, cooperation
becomes more prevalent in denser topologies.Comment: 24 pages, Accepted for publication in Advances in Complex System
Residential segregation and cultural dissemination: An Axelrod-Schelling model
In the Axelrod's model of cultural dissemination, we consider mobility of
cultural agents through the introduction of a density of empty sites and the
possibility that agents in a dissimilar neighborhood can move to them if their
mean cultural similarity with the neighborhood is below some threshold. While
for low values of the density of empty sites the mobility enhances the
convergence to a global culture, for high enough values of it the dynamics can
lead to the coexistence of disconnected domains of different cultures. In this
regime, the increase of initial cultural diversity paradoxically increases the
convergence to a dominant culture. Further increase of diversity leads to
fragmentation of the dominant culture into domains, forever changing in shape
and number, as an effect of the never ending eroding activity of cultural
minorities
A Proper Motion Survey for White Dwarfs with the Wide Field Planetary Camera 2
We have performed a search for halo white dwarfs as high proper motion
objects in a second epoch WFPC2 image of the Groth-Westphal strip. We identify
24 high proper motion objects with mu > 0.014 ''/yr. Five of these high proper
motion objects are identified as strong white dwarf candidates on the basis of
their position in a reduced proper motion diagram. We create a model of the
Milky Way thin disk, thick disk and stellar halo and find that this sample of
white dwarfs is clearly an excess above the < 2 detections expected from these
known stellar populations. The origin of the excess signal is less clear.
Possibly, the excess cannot be explained without invoking a fourth galactic
component: a white dwarf dark halo. We present a statistical separation of our
sample into the four components and estimate the corresponding local white
dwarf densities using only the directly observable variables, V, V-I, and mu.
For all Galactic models explored, our sample separates into about 3 disk white
dwarfs and 2 halo white dwarfs. However, the further subdivision into the thin
and thick disk and the stellar and dark halo, and the subsequent calculation of
the local densities are sensitive to the input parameters of our model for each
Galactic component. Using the lowest mean mass model for the dark halo we find
a 7% white dwarf halo and six times the canonical value for the thin disk white
dwarf density (at marginal statistical significance), but possible systematic
errors due to uncertainty in the model parameters likely dominate these
statistical error bars. The white dwarf halo can be reduced to around 1.5% of
the halo dark matter by changing the initial mass function slightly. The local
thin disk white dwarf density in our solution can be made consistent with the
canonical value by assuming a larger thin disk scaleheight of 500 pc.Comment: revised version, accepted by ApJ, results unchanged, discussion
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