4,622 research outputs found
Evolutionary Markovian Strategies in 2 x 2 Spatial Games
Evolutionary spatial 2 x 2 games between heterogeneous agents are analyzed
using different variants of cellular automata (CA). Agents play repeatedly
against their nearest neighbors 2 x 2 games specified by a rescaled payoff
matrix with two parameteres. Each agent is governed by a binary Markovian
strategy (BMS) specified by 4 conditional probabilities [p_R, p_S, p_T, p_P]
that take values 0 or 1. The initial configuration consists in a random
assignment of "strategists" among the 2^4= 16 possible BMS. The system then
evolves within strategy space according to the simple standard rule: each agent
copies the strategy of the neighbor who got the highest payoff. Besides on the
payoff matrix, the dominant strategy -and the degree of cooperation- depend on
i) the type of the neighborhood (von Neumann or Moore); ii) the way the
cooperation state is actualized (deterministically or stochastichally); and
iii) the amount of noise measured by a parameter epsilon. However a robust
winner strategy is [1,0,1,1].Comment: 18 pages, 8 figures (7 of these figures contain 4 encapsulapted
poscript files each
Prisoner's Dilemma cellular automata revisited: evolution of cooperation under environmental pressure
We propose an extension of the evolutionary Prisoner's Dilemma cellular
automata, introduced by Nowak and May \cite{nm92}, in which the pressure of the
environment is taken into account. This is implemented by requiring that
individuals need to collect a minimum score , representing
indispensable resources (nutrients, energy, money, etc.) to prosper in this
environment. So the agents, instead of evolving just by adopting the behaviour
of the most successful neighbour (who got ), also take into account if
is above or below the threshold . If an
individual has a probability of adopting the opposite behaviour from the one
used by its most successful neighbour. This modification allows the evolution
of cooperation for payoffs for which defection was the rule (as it happens, for
example, when the sucker's payoff is much worse than the punishment for mutual
defection). We also analyse a more sophisticated version of this model in which
the selective rule is supplemented with a "win-stay, lose-shift" criterion. The
cluster structure is analyzed and, for this more complex version we found
power-law scaling for a restricted region in the parameter space.Comment: 15 pages, 8 figures; added figures and revised tex
Biomass-Dependent Diet Shifts in Omnivorous Gizzard Shad: Implications for Growth, Food Web, and Ecosystem Effects
Microbial Decontamination and Weight of Carcass Beef as Affected by Automated Washing Pressure and Length of Time of Spray
Carcass beef has traditionally been washed by hand to remove foreign material such as hair, soil particles, and microbiological organisms that have contaminated the surfaces. These carcasses are inspected by the Food Safety Inspection Service (FSIS)to detect defects related to carcass cleanliness. Recent research and development of technology have emphasized automated machine washing.
At pressures above that normally used, it is conceivable that water could penetrate tissue surfaces and be absorbed by the carcasses. Also, longer wash periods may enhance water uptake by carcasses. According to the ASH RAE Handbook and Product Directory, the average shrinkage of carcass beef using good current practices was 1.3% at 20 hr postmortem. USDA meat inspection regulations required that carcasses sustain no net increase in weight due to absorption of water during the washing process. There is no available literature on the effects of various automated washing techniques on carcass weights after a 20-hr chill.
The objectives of the study reported presently were to determine the effects of nozzle pressure and length of time washed on the microflora and weights of carcass beef at 20 hr postmortem
Finite Size Scaling Analysis of Exact Ground States for +/-J Spin Glass Models in Two Dimensions
With the help of EXACT ground states obtained by a polynomial algorithm we
compute the domain wall energy at zero-temperature for the bond-random and the
site-random Ising spin glass model in two dimensions. We find that in both
models the stability of the ferromagnetic AND the spin glass order ceases to
exist at a UNIQUE concentration p_c for the ferromagnetic bonds. In the
vicinity of this critical point, the size and concentration dependency of the
first AND second moment of the domain wall energy are, for both models,
described by a COMMON finite size scaling form. Moreover, below this
concentration the stiffness exponent turns out to be slightly negative \theta_S
= -0.056(6) indicating the absence of any intermediate spin glass phase at
non-zero temperature.Comment: 7 pages Latex, 5 postscript-figures include
On the ratio of consecutive gaps between primes
In the present work we prove a common generalization of Maynard-Tao's recent
result about consecutive bounded gaps between primes and on the
Erd\H{o}s-Rankin bound about large gaps between consecutive primes. The work
answers in a strong form a 60 years old problem of Erd\"os, which asked whether
the ratio of two consecutive primegaps can be infinitely often arbitrarily
small, and arbitrarily large, respectively
Adaptation and enslavement in endosymbiont-host associations
The evolutionary persistence of symbiotic associations is a puzzle.
Adaptation should eliminate cooperative traits if it is possible to enjoy the
advantages of cooperation without reciprocating - a facet of cooperation known
in game theory as the Prisoner's Dilemma. Despite this barrier, symbioses are
widespread, and may have been necessary for the evolution of complex life. The
discovery of strategies such as tit-for-tat has been presented as a general
solution to the problem of cooperation. However, this only holds for
within-species cooperation, where a single strategy will come to dominate the
population. In a symbiotic association each species may have a different
strategy, and the theoretical analysis of the single species problem is no
guide to the outcome. We present basic analysis of two-species cooperation and
show that a species with a fast adaptation rate is enslaved by a slowly
evolving one. Paradoxically, the rapidly evolving species becomes highly
cooperative, whereas the slowly evolving one gives little in return. This helps
understand the occurrence of endosymbioses where the host benefits, but the
symbionts appear to gain little from the association.Comment: v2: Correction made to equations 5 & 6 v3: Revised version accepted
in Phys. Rev. E; New figure adde
Building Cooperative Networks
We study the cooperation problem in the framework of evolutionary game theory
using the prisoner's dilemma as metaphor of the problem. Considering the
growing process of the system and individuals with imitation capacity, we show
conditions that allow to form highly cooperative networks of any size and
topology. Introducing general considerations of real systems, we reduce the
required conditions for cooperation to evolve approaching the benefit-cost
ratio r to the theoretical minimum r=1, when the mean connectivity of the
individuals is increased. Through the paper, we distinguish different
mechanisms that allow the system to maintain high levels of cooperation when
the system grows by incorporation of defectors. These mechanisms require
heterogeneity among individuals for cooperation to evolve. However, the
required conditions and heterogeneities are drastically reduced as compared to
those required for static networks.Comment: 24 pages, 8 figure
Quantum mechanics gives stability to a Nash equilibrium
We consider a slightly modified version of the Rock-Scissors-Paper (RSP) game
from the point of view of evolutionary stability. In its classical version the
game has a mixed Nash equilibrium (NE) not stable against mutants. We find a
quantized version of the RSP game for which the classical mixed NE becomes
stable.Comment: Revised on referee's criticism, submitted to Physical Review
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