16,244 research outputs found
Emergence of order in selection-mutation dynamics
We characterize the time evolution of a d-dimensional probability
distribution by the value of its final entropy. If it is near the
maximally-possible value we call the evolution mixing, if it is near zero we
say it is purifying. The evolution is determined by the simplest non-linear
equation and contains a d times d matrix as input. Since we are not interested
in a particular evolution but in the general features of evolutions of this
type, we take the matrix elements as uniformly-distributed random numbers
between zero and some specified upper bound. Computer simulations show how the
final entropies are distributed over this field of random numbers. The result
is that the distribution crowds at the maximum entropy, if the upper bound is
unity. If we restrict the dynamical matrices to certain regions in matrix
space, for instance to diagonal or triangular matrices, then the entropy
distribution is maximal near zero, and the dynamics typically becomes
purifying.Comment: 8 pages, 8 figure
Modeling the X-ray Contribution of X-ray Binary Jets
Astrophysical jets exist in both XRBs and AGN, and seem to share common
features, particularly in the radio. While AGN jets are known to emit X-rays,
the situation for XRB jets is not so clear. Radio jets have been resolved in
several XRBs in the low/hard state, establishing that some form of outflow is
routinely present in this state. Interestingly, the flat-to-inverted radio
synchrotron emission associated with these outflows strongly correlates with
the X-ray emission in several sources, suggesting that the jet plasma plays a
role at higher frequencies. In this same state, there is increasing evidence
for a turnover in the IR/optical where the flat-to-inverted spectrum seems to
connect to an optically thin component extending into the X-rays. We discuss
how jet synchrotron emission is likely to contribute to the X-rays, in addition
to inverse Compton up-scattering, providing a natural explanation for these
correlations and the turnover in the IR/optical band. We present model
parameters for fits to several sources, and address some common misconceptions
about the jet model.Comment: 4 pages, 1 Table, conference proceedings for "The Physics of
Relativistic Jets in the Chandra and XMM Era, Bologna, 2002", Eds. G.
Brunetti, D. E. Harris, R. M. Sambruna & G. Sett
Coevolution of dynamical states and interactions in dynamic networks
We explore the coupled dynamics of the internal states of a set of
interacting elements and the network of interactions among them. Interactions
are modeled by a spatial game and the network of interaction links evolves
adapting to the outcome of the game. As an example we consider a model of
cooperation, where the adaptation is shown to facilitate the formation of a
hierarchical interaction network that sustains a highly cooperative stationary
state. The resulting network has the characteristics of a small world network
when a mechanism of local neighbor selection is introduced in the adaptive
network dynamics. The highly connected nodes in the hierarchical structure of
the network play a leading role in the stability of the network. Perturbations
acting on the state of these special nodes trigger global avalanches leading to
complete network reorganization.Comment: 4 pages, 5 figures, for related material visit
http:www.imedea.uib.es/physdept
Topological enslavement in evolutionary games on correlated multiplex networks
Governments and enterprises strongly rely on incentives to generate favorable
outcomes from social and strategic interactions between individuals. The
incentives are usually modeled by payoffs in evolutionary games, such as the
prisoner's dilemma or the harmony game, with imitation dynamics. Adjusting the
incentives by changing the payoff parameters can favor cooperation, as found in
the harmony game, over defection, which prevails in the prisoner's dilemma.
Here, we show that this is not always the case if individuals engage in
strategic interactions in multiple domains. In particular, we investigate
evolutionary games on multiplex networks where individuals obtain an aggregate
payoff. We explicitly control the strength of degree correlations between nodes
in the different layers of the multiplex. We find that if the multiplex is
composed of many layers and degree correlations are strong, the topology of the
system enslaves the dynamics and the final outcome, cooperation or defection,
becomes independent of the payoff parameters. The fate of the system is then
determined by the initial conditions
Disordered Environments in Spatial Games
The Prisoner's dilemma is the main game theoretical framework in which the
onset and maintainance of cooperation in biological populations is studied. In
the spatial version of the model, we study the robustness of cooperation in
heterogeneous ecosystems in spatial evolutionary games by considering site
diluted lattices. The main result is that due to disorder, the fraction of
cooperators in the population is enhanced. Moreover, the system presents a
dynamical transition at , separating a region with spatial chaos from
one with localized, stable groups of cooperators.Comment: 6 pages, 5 figure
Parity Doubling and SU(2)_L x SU(2)_R Restoration in the Hadron Spectrum
We construct the most general nonlinear representation of chiral SU(2)_L x
SU(2)_R broken down spontaneously to the isospin SU(2), on a pair of hadrons of
same spin and isospin and opposite parity. We show that any such representation
is equivalent, through a hadron field transformation, to two irreducible
representations on two hadrons of opposite parity with different masses and
axial couplings. This implies that chiral symmetry realized in the
Nambu-Goldstone mode does not predict the existence of degenerate multiplets of
hadrons of opposite parity nor any relations between their couplings or masses.Comment: 4 pages, 1 figure; v3: Note added to clarify implications for hadrons
that do not couple to pions: Chiral symmetry can be realized linearly on such
states, leading to parity doubling. To the extent that they are parity
doubled, these hadrons must decouple from pions, a striking prediction that
can be tested experimentally. This applies to the work of L. Glozman and
collaborator
The supermassive black hole in NGC4486a detected with SINFONI at the VLT
The near-infrared integral field spectrograph SINFONI at the ESO VLT opens a
new window for the study of central supermassive black holes. With a near-IR
spatial resolution similar to HST optical and the ability to penetrate dust it
provides the possibility to explore the low-mass end of the M-sigma relation
(sigma<120km/s) where so far very few black hole masses were measured with
stellar dynamics. With SINFONI we observed the central region of the
low-luminosity elliptical galaxy NGC4486a at a spatial resolution of ~0.1arcsec
in the K band. The stellar kinematics was measured with a maximum penalised
likelihood method considering the region around the CO absorption band heads.
We determined a black hole mass of M_BH=1.25^{+0.75}_{-0.79} x 10^7 M_sun (90%
C.L.) using the Schwarzschild orbit superposition method including the full
2-dimensional spatial information. This mass agrees with the predictions of the
M-sigma relation, strengthening its validity at the lower sigma end.Comment: 7 pages, 7 figures. Accepted by MNRA
Evolutionary instability of Zero Determinant strategies demonstrates that winning isn't everything
Zero Determinant (ZD) strategies are a new class of probabilistic and
conditional strategies that are able to unilaterally set the expected payoff of
an opponent in iterated plays of the Prisoner's Dilemma irrespective of the
opponent's strategy, or else to set the ratio between a ZD player's and their
opponent's expected payoff. Here we show that while ZD strategies are weakly
dominant, they are not evolutionarily stable and will instead evolve into less
coercive strategies. We show that ZD strategies with an informational advantage
over other players that allows them to recognize other ZD strategies can be
evolutionarily stable (and able to exploit other players). However, such an
advantage is bound to be short-lived as opposing strategies evolve to
counteract the recognition.Comment: 14 pages, 4 figures. Change in title (again!) to comply with Nature
Communications requirements. To appear in Nature Communication
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