729 research outputs found
The Role of Behavioral Dynamics in Determining the Patch Distributions of Interacting Species
The effect of the behavioral dynamics of movement on the population dynamics of interacting species in multipatch systems is studied. The behavioral dynamics of habitat choice used in a range of previous models are reviewed. There is very limited empirical evidence for distinguishing between these different models, but they differ in important ways, and many lack properties that would guarantee stability of an ideal free distribution in a single-species system. The importance of finding out more about movement dynamics in multispecies systems is shown by an analysis of the effect of movement rules on the dynamics of a particular two-species–two-patch model of competition, where the population dynamical equilibrium in the absence of movement is often not a behavioral equilibrium in the presence of adaptive movement. The population dynamics of this system are explored for several different movement rules and different parameter values, producing a variety of outcomes. Other systems of interacting species that may lack a dynamically stable distribution among patches are discussed, and it is argued that such systems are not rare. The sensitivity of community properties to individual movement behavior in this and earlier studies argues that there is a great need for empirical investigation to determine the applicability of different models of the behavioral dynamics of habitat selection
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Ecological theatre and the evolutionary game: how environmental and demographic factors determine payoffs in evolutionary games
In the standard approach to evolutionary games and replicator dynamics, differences in fitness can be interpreted as an excess from the mean Malthusian growth rate in the population. In the underlying reasoning, related to an analysis of "costs" and "benefits", there is a silent assumption that fitness can be described in some type of units. However, in most cases these units of measure are not explicitly specified. Then the question arises: are these theories testable? How can we measure "benefit" or "cost"? A natural language, useful for describing and justifying comparisons of strategic "cost" versus "benefits", is the terminology of demography, because the basic events that shape the outcome of natural selection are births and deaths. In this paper, we present the consequences of an explicit analysis of births and deaths in an evolutionary game theoretic framework. We will investigate different types of mortality pressures, their combinations and the possibility of trade-offs between mortality and fertility. We will show that within this new approach it is possible to model how strictly ecological factors such as density dependence and additive background fitness, which seem neutral in classical theory, can affect the outcomes of the game. We consider the example of the Hawk-Dove game, and show that when reformulated in terms of our new approach new details and new biological predictions are produced
Energy flux fluctuations in a finite volume of turbulent flow
The flux of turbulent kinetic energy from large to small spatial scales is
measured in a small domain B of varying size R. The probability distribution
function of the flux is obtained using a time-local version of Kolmogorov's
four-fifths law. The measurements, made at a moderate Reynolds number, show
frequent events where the flux is backscattered from small to large scales,
their frequency increasing as R is decreased. The observations are corroborated
by a numerical simulation based on the motion of many particles and on an
explicit form of the eddy damping.Comment: 10 Pages, 5 figures, 1 tabl
Mesoscale modeling of molecular machines: Cyclic dynamics and hydrodynamical fluctuations
Proteins acting as molecular machines can undergo cyclic internal conformational motions that are coupled to ligand binding and dissociation events. In contrast to their macroscopic counterparts, nanomachines operate in a highly fluctuating environment, which influences their operation. To bridge the gap between detailed microscopic and simple phenomenological descriptions, a mesoscale approach, which combines an elastic network model of a machine with a particle-based mesoscale description of the solvent, is employed. The time scale of the cyclic hinge motions of the machine prototype is strongly affected by hydrodynamical coupling to the solvent
Design Study for the Asteroid Redirect Vehicle (ARV) Composite Primary Bulkhead
A design study was undertaken of a carbon fiber primary bulkhead for a large solar electric propulsion (SEP) spacecraft. The bulkhead design, supporting up to 16 t of xenon propellant, progressed from one consisting of many simple parts with many complex joints, to one consisting of a few complex parts with a few simple joints. The unique capabilities of composites led to a topology that transitioned loads from bending to in-plane tension and shear, with low part count. This significantly improved bulkhead manufacturability, cost, and mass. The stiffness-driven structure utilized high-modulus M55J fiber unidirectional prepregs. A full-scale engineering demonstration unit (EDU) of the concept was used to demonstrate manufacturability of the concept. Actual labor data was obtained, which could be extrapolated to a full bulkhead. The effort demonstrated the practicality of using high-modulus fiber (HMF) composites for unique shape topologies that minimize mass and cost. The lessons are applicable to primary and secondary aerospace structures that are stiffness driven
Backwards-induction outcome in a quantum game
In economics duopoly is a market dominated by two firms large enough to
influence the market price. Stackelberg presented a dynamic form of duopoly
that is also called `leader-follower' model. We give a quantum perspective on
Stackelberg duopoly that gives a backwards-induction outcome same as the Nash
equilibrium in static form of duopoly also known as Cournot's duopoly. We find
two qubit quantum pure states required for this purpose.Comment: Revised in the light of referee's comments. Latex, 16 pages, 2
figures, To appear in Phy. Rev.
Mass Spectrometry Imaging Characterization of Ethiodized Oil, a Radiopaque Hydrophobic Multipurpose Liquid Used in Cancer Therapy
https://openworks.mdanderson.org/sumexp21/1226/thumbnail.jp
Effects of intertidal oyster reefs on water quality in a tidal creek ecosystem
The importance of oyster filtering in moderating aspects of water quality has
received increased attention over the past several years. With population growth and
increasing development in coastal watersheds come increased runoff and pollution of
tidal creeks. It has been suggested that bivalves may play an important role in controlling
phytoplankton levels in shallow coastal areas, with several laboratory studies and models
estimating the potential filtration effects of these organisms. However, few field studies
have been undertaken to quantify these effects. This study examined the influence of
intertidal oyster reefs on chlorophyll a, fecal coliform bacteria and total suspended solid
concentrations under field conditions in a tidal creek estuary. Oyster reefs of varying live
oyster density were sampled during summer 2002, winter 2003 and spring 2003. Water
samples were taken upstream and downstream of each reef as well as over a mudflat
control area on an ebb tide and analyzed for concentrations of these water column
constituents. Summer data showed consistent and statistically significant decreases in
chlorophyll a concentrations as water moved over the reef, usually by 10-25%. Fecal
coliform counts were frequently lower downstream, by up to 45%, but were much more
variable and not statistically different in most cases. Data taken in winter, when
temperatures and oyster feeding rates are lower, show less consistency in upstream vs.
downstream patterns. In spring, chlorophyll a decreases were less frequent than in
summer, but significant fecal coliform decreases were more frequent. Data from this
study indicate that feeding by oysters and changes in water flow caused by the presence
of reefs may both play a role in reducing particulate loads in the water column
Cooperation enhanced by inhomogeneous activity of teaching for evolutionary Prisoner's Dilemma games
Evolutionary Prisoner's Dilemma games with quenched inhomogeneities in the
spatial dynamical rules are considered. The players following one of the two
pure strategies (cooperation or defection) are distributed on a two-dimensional
lattice. The rate of strategy adoption from a randomly chosen neighbors are
controlled by the payoff difference and a two-value pre-factor
characterizing the players whom the strategy learned from. The reduced teaching
activity of players is distributed randomly with concentrations at the
beginning and fixed further on. Numerical and analytical calculations are
performed to study the concentration of cooperators as a function of and
for different noise levels and connectivity structures. Significant
increase of cooperation is found within a wide range of parameters for this
dynamics. The results highlight the importance of asymmetry characterizing the
exchange of master-follower role during the strategy adoptions.Comment: 4 pages, 5 figures, corrected typo
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