29,920 research outputs found
Coherence and incoherence in extended broad band triplet interaction
In the present analysis we study the transition from coherent to incoherent
dynamics in a nonlinear triplet of broad band combs of waves. Expanding the
analysis of previous works, this paper investigates what happens when the band
of available modes is much larger than that of the initial narrower combs
within which the nonlinear interaction is not subjected to selection rules
involving wave momenta. Here selection rules are present and active, and we
examine how and when coherence can be defined.Comment: 6 pages, 2 figure
Death by starvation in May-Leonard models
We consider the dynamics of spatial stochastic May-Leonard models with mutual
predation interactions of equal strength between any two individuals of
different species. Using two-dimensional simulations, with two and three
pecies, we investigate the dynamical impact of the death of individuals after a
given threshold number of successive unsuccessful predation attempts. We find
that the death of these individuals can have a strong impact on the dynamics of
population networks and provide a crucial contribution to the preservation of
coexistence.Comment: 7 pages, 9 figure
Phase transitions in dependence of apex predator decaying ratio in a cyclic dominant system
Cyclic dominant systems, like rock-paper-scissors game, are frequently used
to explain biodiversity in nature, where mobility, reproduction and
intransitive competition are on stage to provide the coexistence of
competitors. A significantly new situation emerges if we introduce an apex
predator who can superior all members of the mentioned three-species system. In
the latter case the evolution may terminate into three qualitatively different
destinations depending on the apex predator decaying ratio . In particular,
the whole population goes extinct or all four species survive or only the
original three-species system remains alive as we vary the control parameter.
These solutions are separated by a discontinuous and a continuous phase
transitions at critical values. Our results highlight that cyclic dominant
competition can offer a stable way to survive even in a predator-prey-like
system that can be maintained for large interval of critical parameter values.Comment: version to appear in EPL. 7 pages, 7 figure
Invasion controlled pattern formation in a generalized multi-species predator-prey system
Rock-scissors-paper game, as the simplest model of intransitive relation
between competing agents, is a frequently quoted model to explain the stable
diversity of competitors in the race of surviving. When increasing the number
of competitors we may face a novel situation because beside the mentioned
unidirectional predator-prey-like dominance a balanced or peer relation can
emerge between some competitors. By utilizing this possibility in the present
work we generalize a four-state predator-prey type model where we establish two
groups of species labeled by even and odd numbers. In particular, we introduce
different invasion probabilities between and within these groups, which results
in a tunable intensity of bidirectional invasion among peer species. Our study
reveals an exceptional richness of pattern formations where five quantitatively
different phases are observed by varying solely the strength of the mentioned
inner invasion. The related transition points can be identified with the help
of appropriate order parameters based on the spatial autocorrelation decay, on
the fraction of empty sites, and on the variance of the species density.
Furthermore, the application of diverse, alliance-specific inner invasion rates
for different groups may result in the extinction of the pair of species where
this inner invasion is moderate. These observations highlight that beyond the
well-known and intensively studied cyclic dominance there is an additional
source of complexity of pattern formation that has not been explored earlier.Comment: 8 pages, 8 figures. To appear in PR
Nematic liquid crystal dynamics under applied electric fields
In this paper we investigate the dynamics of liquid crystal textures in a
two-dimensional nematic under applied electric fields, using numerical
simulations performed using a publicly available LIquid CRystal Algorithm
(LICRA) developed by the authors. We consider both positive and negative
dielectric anisotropies and two different possibilities for the orientation of
the electric field (parallel and perpendicular to the two-dimensional lattice).
We determine the effect of an applied electric field pulse on the evolution of
the characteristic length scale and other properties of the liquid crystal
texture network. In particular, we show that different types of defects are
produced after the electric field is switched on, depending on the orientation
of the electric field and the sign of the dielectric anisotropy.Comment: 7 pages, 12 figure
Water activity in lamellar stacks of lipid bilayers: "Hydration forces" revisited
Water activity and its relationship with interactions stabilising lamellar
stacks of mixed lipid bilayers in their fluid state are investigated by means
of osmotic pressure measurements coupled with small-angle x-ray scattering. The
(electrically-neutral) bilayers are composed of a mixture in various
proportions of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic
cosurfactant with an ethoxylated polar head. For highly dehydrated samples the
osmotic pressure profile always exhibits the "classical" exponential decay as
hydration increases but, depending on Simulsol to lecithin ratio, it becomes
either of the "bound" or "unbound" types for more water-swollen systems. A
simple thermodynamic model is used for interpreting the results without
resorting to the celebrated but elusive "hydration forces"Comment: 24 pages, 12 figures. Accepted for publication in The European
Physical Journal
- …