27,367 research outputs found
Group Chase and Escape
We describe here a new concept of one group chasing another, called "group
chase and escape", by presenting a simple model. We will show that even a
simple model can demonstrate rather rich and complex behavior. In particular,
there are cases in which an optimal number of chasers exists for a given number
of escapees (or targets) to minimize the cost of catching all targets. We have
also found an indication of self-organized spatial structures formed by both
groups.Comment: 13 pages, 12 figures, accepted and to appear in New Journal of
Physic
Four bugs on a rectangle
The problem of four bugs in cyclic pursuit starting from a 2-by-1 rectangle is considered, and asymptotic formulas are derived to describe the motion. In contrast to the famous case of four bugs on a square, here the trajectories quickly freeze to essentially one dimension. After the first rotation about the centre point, the scale of the configuration has shrunk by a factor of 10^427907250, and this number is then exponentiated four more times with each successive cycle. Relations to Knuthās double-arrow notation and level-index arithmetic are discussed
Long Memory, Heterogeneity and Trend Chasing
Long-range dependence in volatility is one of the most prominent examples of applications in financial market research involving universal power laws. Its characterization has recently spurred attempts at theoretical explanation of the underlying mechanism. This paper contributes to this recent development by analyzing a simple market fraction asset pricing model with two types of traders fundamentalists who trade on the price deviation from estimated fundamental value and trend followers who follow a trend which is updated through a geometric learning process. Our analysis shows that the heterogeneity, trend chasing through learning, and the interplay of noisy processes and a stable deterministic equilibrium can be the source of power-law distributed fluctuations. Statistical analysis based on Monte Carlo simulations are conducted to characterize the long memory. Realistic estimates of the power-law decay indices and the (FI)GARCH parameters are found.asset pricing; fundamentalists and trend followers; market fraction; stability; learning; long memory
Pursuit-evasion predator-prey waves in two spatial dimensions
We consider a spatially distributed population dynamics model with excitable
predator-prey dynamics, where species propagate in space due to their taxis
with respect to each other's gradient in addition to, or instead of, their
diffusive spread. Earlier, we have described new phenomena in this model in one
spatial dimension, not found in analogous systems without taxis: reflecting and
self-splitting waves. Here we identify new phenomena in two spatial dimensions:
unusual patterns of meander of spirals, partial reflection of waves, swelling
wavetips, attachment of free wave ends to wave backs, and as a result, a novel
mechanism of self-supporting complicated spatio-temporal activity, unknown in
reaction-diffusion population models.Comment: 15 pages, 15 figures, submitted to Chao
Coevolutionary dynamics of a variant of the cyclic Lotka-Volterra model with three-agent interactions
We study a variant of the cyclic Lotka-Volterra model with three-agent
interactions. Inspired by a multiplayer variation of the Rock-Paper-Scissors
game, the model describes an ideal ecosystem in which cyclic competition among
three species develops through cooperative predation. Its rate equations in a
well-mixed environment display a degenerate Hopf bifurcation, occurring as
reactions involving two predators plus one prey have the same rate as reactions
involving two preys plus one predator. We estimate the magnitude of the
stochastic noise at the bifurcation point, where finite size effects turn
neutrally stable orbits into erratically diverging trajectories. In particular,
we compare analytic predictions for the extinction probability, derived in the
Fokker-Planck approximation, with numerical simulations based on the Gillespie
stochastic algorithm. We then extend the analysis of the phase portrait to
heterogeneous rates. In a well-mixed environment, we observe a continuum of
degenerate Hopf bifurcations, generalizing the above one. Neutral stability
ensues from a complex equilibrium between different reactions. Remarkably, on a
two-dimensional lattice, all bifurcations disappear as a consequence of the
spatial locality of the interactions. In the second part of the paper, we
investigate the effects of mobility in a lattice metapopulation model with
patches hosting several agents. We find that strategies propagate along the
arms of rotating spirals, as they usually do in models of cyclic dominance. We
observe propagation instabilities in the regime of large wavelengths. We also
examine three-agent interactions inducing nonlinear diffusion.Comment: 22 pages, 13 figures. v2: version accepted for publication in EPJ
Coerced transitions in Timor-Leste and Kosovo
Statebuilding under the aegis of international administrations has faced various hurdles and obstacles in Kosovo and Timor-Leste. One of these hurdles is related to the specific mandate of these missions, which created a specific conflict of objectives for the international presence ā between democracy promotion and institution-building. The piece analyzes specifically the strategies of international and local elites in this context. After trying to prioritize institution-building while paying lip service to democratization imperatives, international officials had to readjust their strategy following contestation and resistance from local partners. Facing practical consequences of the conflict of objectives, international officials then proceeded to prioritize democracy promotion imperatives and reduced their institution-building role. The paper concludes on the implications of these experiences for the debate concerning democracy promotion and highlights the possibilities of the āparticipatory interventionā framework put forth by Chopra and Hohe
Take Me Out to the Ball Game (And Away From Camp): How Soldiers Used Sports to Cope During War Time
Snowball fights during the Civil War were a pretty big deal.
In fact, sports and fitness in general played a role in shaping ideals of honor, courage, and idolization among the Armies of the Potomac and Northern Virginia, and they proved to have an impact on the life of the individual soldier by distracting him (or possibly her) from the monotonous routine of camp life and establishing bonds of comradeship. [excerpt
Cooperative Physics of Fly Swarms: An Emergent Behavior
We have simulated the behavior of several artificial flies, interacting visually with each other. Each fly is described by a simple tracking system (Poggio and Reichardt, 1973; Land and Collett, 1974) which summarizes behavioral experiments in which individual flies fixate a target. Our main finding is that the interaction of theses implemodules gives rise to a variety of relatively complex behaviors. In particular, we observe a swarm-like behavior of a group of many artificial flies for certain reasonable ranges of our tracking system parameters
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