40,451 research outputs found
Rocket exhaust effluent modeling for tropospheric air quality and environmental assessments
The various techniques for diffusion predictions to support air quality predictions and environmental assessments for aerospace applications are discussed in terms of limitations imposed by atmospheric data. This affords an introduction to the rationale behind the selection of the National Aeronautics and Space Administration (NASA)/Marshall Space Flight Center (MSFC) Rocket Exhaust Effluent Diffusion (REED) program. The models utilized in the NASA/MSFC REED program are explained. This program is then evaluated in terms of some results from a joint MSFC/Langley Research Center/Kennedy Space Center Titan Exhaust Effluent Prediction and Monitoring Program
The collapse of cooperation in evolving games
Game theory provides a quantitative framework for analyzing the behavior of
rational agents. The Iterated Prisoner's Dilemma in particular has become a
standard model for studying cooperation and cheating, with cooperation often
emerging as a robust outcome in evolving populations. Here we extend
evolutionary game theory by allowing players' strategies as well as their
payoffs to evolve in response to selection on heritable mutations. In nature,
many organisms engage in mutually beneficial interactions, and individuals may
seek to change the ratio of risk to reward for cooperation by altering the
resources they commit to cooperative interactions. To study this, we construct
a general framework for the co-evolution of strategies and payoffs in arbitrary
iterated games. We show that, as payoffs evolve, a trade-off between the
benefits and costs of cooperation precipitates a dramatic loss of cooperation
under the Iterated Prisoner's Dilemma; and eventually to evolution away from
the Prisoner's Dilemma altogether. The collapse of cooperation is so extreme
that the average payoff in a population may decline, even as the potential
payoff for mutual cooperation increases. Our work offers a new perspective on
the Prisoner's Dilemma and its predictions for cooperation in natural
populations; and it provides a general framework to understand the co-evolution
of strategies and payoffs in iterated interactions.Comment: 33 pages, 13 figure
Small games and long memories promote cooperation
Complex social behaviors lie at the heart of many of the challenges facing
evolutionary biology, sociology, economics, and beyond. For evolutionary
biologists in particular the question is often how such behaviors can arise
\textit{de novo} in a simple evolving system. How can group behaviors such as
collective action, or decision making that accounts for memories of past
experience, emerge and persist? Evolutionary game theory provides a framework
for formalizing these questions and admitting them to rigorous study. Here we
develop such a framework to study the evolution of sustained collective action
in multi-player public-goods games, in which players have arbitrarily long
memories of prior rounds of play and can react to their experience in an
arbitrary way. To study this problem we construct a coordinate system for
memory- strategies in iterated -player games that permits us to
characterize all the cooperative strategies that resist invasion by any mutant
strategy, and thus stabilize cooperative behavior. We show that while larger
games inevitably make cooperation harder to evolve, there nevertheless always
exists a positive volume of strategies that stabilize cooperation provided the
population size is large enough. We also show that, when games are small,
longer-memory strategies make cooperation easier to evolve, by increasing the
number of ways to stabilize cooperation. Finally we explore the co-evolution of
behavior and memory capacity, and we find that longer-memory strategies tend to
evolve in small games, which in turn drives the evolution of cooperation even
when the benefits for cooperation are low
The evolution of complex gene regulation by low specificity binding sites
Transcription factor binding sites vary in their specificity, both within and
between species. Binding specificity has a strong impact on the evolution of
gene expression, because it determines how easily regulatory interactions are
gained and lost. Nevertheless, we have a relatively poor understanding of what
evolutionary forces determine the specificity of binding sites. Here we address
this question by studying regulatory modules composed of multiple binding
sites. Using a population-genetic model, we show that more complex regulatory
modules, composed of a greater number of binding sites, must employ binding
sites that are individually less specific, compared to less complex regulatory
modules. This effect is extremely general, and it hold regardless of the
regulatory logic of a module. We attribute this phenomenon to the inability of
stabilising selection to maintain highly specific sites in large regulatory
modules. Our analysis helps to explain broad empirical trends in the yeast
regulatory network: those genes with a greater number of transcriptional
regulators feature by less specific binding sites, and there is less variance
in their specificity, compared to genes with fewer regulators. Likewise, our
results also help to explain the well-known trend towards lower specificity in
the transcription factor binding sites of higher eukaryotes, which perform
complex regulatory tasks, compared to prokaryotes
Coriolis effects during pitch and roll maneuvers in a piloted flight simulator
Effect of suprathreshold value of Coriolis acceleration on pilot of flight simulator - reference to perception of illusory motion and position in spac
Cost analysis of new and retrofit hot-air type solar assisted heating systems
A detailed cost analysis/cost improvement study was performed on two Department of Energy/National Aeronautics and Space Administration operational test sites to determine actual costs and potential cost improvements of new and retrofit hot air type, solar assisted heating and hot water systems for single family sized structures. This analysis concentrated on the first cost of a system which included procurement, installation, and integration of a solar assisted heating and hot water system on a new or retrofit basis; it also provided several cost projections which can be used as inputs to payback analyses, depending upon the degree of optimism or future improvements assumed. Cost definitions were developed for five categories of cost, and preliminary estimates were developed for each. The costing methodology, approach, and results together with several candidate low cost designs are described
A Compilation of the Property Differences of Ortho and Para Hydrogen or Mixtures of Ortho and Para Hydrogen
Chemical and physical properties of ortho and para hydrogen or mixtures of ortho and para hydroge
Evolutionary consequences of behavioral diversity
Iterated games provide a framework to describe social interactions among
groups of individuals. Recent work stimulated by the discovery of
"zero-determinant" strategies has rapidly expanded our ability to analyze such
interactions. This body of work has primarily focused on games in which players
face a simple binary choice, to "cooperate" or "defect". Real individuals,
however, often exhibit behavioral diversity, varying their input to a social
interaction both qualitatively and quantitatively. Here we explore how access
to a greater diversity of behavioral choices impacts the evolution of social
dynamics in finite populations. We show that, in public goods games, some
two-choice strategies can nonetheless resist invasion by all possible
multi-choice invaders, even while engaging in relatively little punishment. We
also show that access to greater behavioral choice results in more "rugged "
fitness landscapes, with populations able to stabilize cooperation at multiple
levels of investment, such that choice facilitates cooperation when returns on
investments are low, but hinders cooperation when returns on investments are
high. Finally, we analyze iterated rock-paper-scissors games, whose
non-transitive payoff structure means unilateral control is difficult and
zero-determinant strategies do not exist in general. Despite this, we find that
a large portion of multi-choice strategies can invade and resist invasion by
strategies that lack behavioral diversity -- so that even well-mixed
populations will tend to evolve behavioral diversity.Comment: 26 pages, 4 figure
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