8,089 research outputs found
Competition/Enhancement of Two Probe Order Parameters in the Unbalanced Holographic Superconductor
We introduce and study a simple unbalanced holographic superconductor model
with two scalar order parameters. The attention is focused on the possibility
of coexisting orderings corresponding to the concomitant condensation of two
scalar operators. Through a probe analysis we show that an attractive or
repulsive direct interaction between the two bulk scalars leads respectively to
competition and enhancement of the associated condensates. The system at hand
is a toy model for studying generic multiple ordering in a strongly coupled
context and some comments are given about its applicability to the
ferromagnetic unconventional superconductors.Comment: 17 pages, 8 figure
Maintenance of Microbial Cooperation Mediated by Public Goods in Single- and Multiple-Trait Scenarios
Microbes often form densely populated communities, which favor competitive and cooperative interactions. Cooperation among bacteria often occurs through the production of metabolically costly molecules produced by certain individuals that become available to other neighboring individuals; such molecules are called public goods. This type of cooperation is susceptible to exploitation, since nonproducers of a public good can benefit from it while saving the cost of its production (cheating), gaining a fitness advantage over producers (cooperators). Thus, in mixed cultures, cheaters can increase in frequency in the population, relative to cooperators. Sometimes, and as predicted by simple game-theoretic arguments, such increases in the frequency of cheaters cause loss of the cooperative traits by exhaustion of the public goods, eventually leading to a collapse of the entire population. In other cases, however, both cooperators and cheaters remain in coexistence. This raises the question of how cooperation is maintained in microbial populations. Several strategies to prevent cheating have been studied in the context of a single trait and a unique environmental constraint. In this review, we describe current knowledge on the evolutionary stability of microbial cooperation and discuss recent discoveries describing the mechanisms operating in multiple-trait and multiple-constraint settings. We conclude with a consideration of the consequences of these complex interactions, and we briefly discuss the potential role of social interactions involving multiple traits and multiple environmental constraints in the evolution of specialization and division of labor in microbes.info:eu-repo/semantics/publishedVersio
Diversity, competition, extinction: the ecophysics of language change
As early indicated by Charles Darwin, languages behave and change very much
like living species. They display high diversity, differentiate in space and
time, emerge and disappear. A large body of literature has explored the role of
information exchanges and communicative constraints in groups of agents under
selective scenarios. These models have been very helpful in providing a
rationale on how complex forms of communication emerge under evolutionary
pressures. However, other patterns of large-scale organization can be described
using mathematical methods ignoring communicative traits. These approaches
consider shorter time scales and have been developed by exploiting both
theoretical ecology and statistical physics methods. The models are reviewed
here and include extinction, invasion, origination, spatial organization,
coexistence and diversity as key concepts and are very simple in their defining
rules. Such simplicity is used in order to catch the most fundamental laws of
organization and those universal ingredients responsible for qualitative
traits. The similarities between observed and predicted patterns indicate that
an ecological theory of language is emerging, supporting (on a quantitative
basis) its ecological nature, although key differences are also present. Here
we critically review some recent advances lying and outline their implications
and limitations as well as open problems for future research.Comment: 17 Pages. A review on current models from statistical Physics and
Theoretical Ecology applied to study language dynamic
Lattice Models of Ionic Systems
A theoretical analysis of Coulomb systems on lattices in general dimensions
is presented. The thermodynamics is developed using Debye-Huckel theory with
ion-pairing and dipole-ion solvation, specific calculations being performed for
3D lattices. As for continuum electrolytes, low-density results for sc, bcc and
fcc lattices indicate the existence of gas-liquid phase separation. The
predicted critical densities have values comparable to those of continuum ionic
systems, while the critical temperatures are 60-70% higher. However, when the
possibility of sublattice ordering as well as Debye screening is taken into
account systematically, order-disorder transitions and a tricritical point are
found on sc and bcc lattices, and gas-liquid coexistence is suppressed. Our
results agree with recent Monte Carlo simulations of lattice electrolytes.Comment: 25 pages, 3 figures, ReVTeX 4, Submitted to J. Chem. Phy
Coexistence and asymptotic periodicity in a competitor–competitor–mutualist model
AbstractIn this paper, the competitor–competitor–mutualist three-species Lotka–Volterra model is discussed. Firstly, by Schauder fixed point theory, the coexistence state of the strongly coupled system is given. Applying the method of upper and lower solutions and its associated monotone iterations, the true solutions are constructed. Our results show that this system possesses at least one coexistence state if cross-diffusions and cross-reactions are weak. Secondly, the existence and asymptotic behavior of T-periodic solutions for the periodic reaction–diffusion system under homogeneous Dirichlet boundary conditions are investigated. Sufficient conditions which guarantee the existence of T-periodic solution are also obtained
Fairy circle landscapes under the sea
Short-scale interactions yield large-scale vegetation patterns that, in turn,
shape ecosystem function across landscapes. Fairy circles, which are circular
patches bare of vegetation within otherwise continuous landscapes, are
characteristic features of semiarid grasslands. We report the occurrence of
submarine fairy circle seascapes in seagrass meadows and propose a simple model
that reproduces the diversity of seascapes observed in these ecosystems as
emerging from plant interactions within the meadow. These seascapes include two
extreme cases, a continuous meadow and a bare landscape, along with
intermediate states that range from the occurrence of persistent but isolated
fairy circles, or solitons, to seascapes with multiple fairy circles, banded
vegetation, and "leopard skin" patterns consisting of bare seascapes patterns
consisting of bare seascapes dotted with plant patches. The model predicts that
these intermediate seascapes extending across kilometers emerge as a
consequence of local demographic imbalances along with facilitative and
competitive interactions among the plants with a characteristic spatial scale
of 20 to 30 m, consistent with known drivers of seagrass performance. The
model, which can be extended to clonal growth plants in other landscapes
showing fairy rings, reveals that the different seascapes observed hold
diagnostic power as to the proximity of seagrass meadows to extinction points
that can be used to identify ecosystems at risks
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