Apex predator and the cyclic competition in a rock-paper-scissors game of three species

This work deals with the effects of an apex predator on the cyclic competition among three distinct species that follow the rules of the rock-paper-scissors game. The investigation develops standard stochastic simulations but is motivated by a novel procedure which is explained in the work. We add the apex predator as the fourth species in the system that contains three species that evolve following the standard rules of migration, reproduction and predation, and study how the system evolves in this new environment, in comparison with the case in the absence of the apex predator. The results show that the apex predator engenders the tendency to spread uniformly in the lattice, contributing to destroy the spiral patterns, keeping biodiversity but diminishing the average size of the clusters of the species that compete cyclically.Comment: 7 pages, 7 figures. To appear in PR

Benefícios das coberturas vegetais para melhorar a sustentabilidade do mamoeiro.

O solo em interação com o ambiente está sempre coberto com vegetação. As exceções são os desertos ou as interferências antrópicas em determinada área, no intervalo entre os cultivos. Nos estágios iniciais de sua formação o solo já está sendo coberto por líquens, algas e fungos em um processo de interação da flora e da fauna com os minerais, onde ambas as partes se beneficiam. A evolução milenar da formação de um solo será acompanhada por um sistema vegetal, também em evolução, cobrindo sua superfície. Quando bem desenvolvido, definido em profundidade, o solo estará coberto por uma vegetação pouco ou muito diversificada, mas extremamente adaptada àquela condição edafoclimática. A melhor cobertura - a que mais conserva o solo - é a vegetação nativa que se estabeleceu de forma espontânea como a Mata Atlântica, a Caatinga, o Cerrado, a Floresta Amazônica, o Pampa gaúcho etc. O solo sob essas plantas, que aí nasceram de forma competitiva e predominando sobre as demais, está protegido dos impactos diretos da chuva, do vento e da insolação, o que manterá suas características e capacidade de sustentar essas plantas durante longo tempo. Na medida em que se remove a vegetação nativa (desmatamento) para realizar os necessários cultivos agrícolas, tem início o processo mais lento ou mais rápido de degradação do solo.PDF. P4_3

Species richness and beta-diversity of aquatic macrophytes assemblages in three floodplain tropical lagoons: evaluating the effects of sampling size and depth gradients

Using aquatic macrophyte data gathered in three lagoons of the Paraná River floodplain we showed a strong effect of sample size on species richness. Incidence-based species richness estimators (Chao 2, jackknife 1, jackknife 2, incidence-based coverage estimator and bootstrap) were compared to evaluate their performance in estimating the species richness throughout transect sampling rnethod. Our results suggest that the best estimate of the species richness was gave by jackknife 2 estimator. Nevertheless, the transect sampling design was considered inappropriate to estimate aquatic macrophytes species richness. Depth gradient was not a good predictor of the species richness and species turnover (beta diversity). The dynamics of these environments, subject to high water-level fluctuation prevents the formation and permanence of a clear floristic depth-related gradient

Impact of Power Allocation and Antenna Directivity in the Capacity of a Multiuser Cognitive Ad Hoc Network

This paper studies the benefits that power control and antenna directivity can bring to the capacity of a multiuser cognitive radio network. The main objective is to optimize the secondary network sum rate under the capacity constraint of the primary network. Exploiting location awareness, antenna directivity, and the power control capability, the cognitive radio ad hoc network can broaden its coverage and improve capacity. Computer simulations show that by employing the proposed method the system performance is significantly enhanced compared to conventional fixed power allocation

Differential interferometric phases at high spectral resolution as a sensitive physical diagnostic of circumstellar disks

Context. The circumstellar disks ejected by many rapidly rotating B stars (so-called Be stars) offer the rare opportunity of studying the structure and dynamics of gaseous disks at high spectral as well as angular resolution. Aims. This paper explores a newly identified effect in spectro-interferometric phase that can be used for probing the inner regions of gaseous edge-on disks on a scale of a few stellar radii. Methods. The origin of this effect (dubbed central quasi-emission phase signature, CQE-PS) lies in the velocity-dependent line absorption of photospheric radiation by the circumstellar disk. At high spectral and marginal interferometric resolution, photocenter displacements between star and isovelocity regions in the Keplerian disk reveal themselves through small interferometric phase shifts. To investigate the diagnostic potential of this effect, a series of models are presented, based on detailed radiative transfer calculations in a viscous decretion disk. Results. Amplitude and detailed shape of the CQE-PS depend sensitively on disk density and size and on the radial distribution of the material with characteristic shapes in differential phase diagrams. In addition, useful lower limits to the angular size of the central stars can be derived even when the system is almost unresolved. Conclusions. The full power of this diagnostic tool can be expected if it can be applied to observations over a full life-cycle of a disk from first ejection through final dispersal, over a full cycle of disk oscillations, or over a full orbital period in a binary system

Effects of random pinning on the potential energy landscape of a supercooled liquid

We use energy landscape methods to investigate the response of a supercooled liquid to random pinning. We classify the structural similarity of different energy minima using a measure of overlap. This analysis reveals a correspondence between distinct particle packings (which are characterised via the overlap) and funnels on the energy landscape (which are characterised via disconnectivity graphs). As the number of pinned particles is increased, we find a crossover from glassy behavior at low pinning to a structure-seeking landscape at high pinning, in which all thermally accessible minima are structurally similar. We discuss the consequences of these results for theories of randomly pinned liquids. We also investigate how the energy landscape depends on the fraction of pinned particles, including the degree of frustration and the evolution of distinct packings as the number of pinned particles is reduced.Comment: Supporting research data may be found at https://doi.org/10.17863/CAM.3098

Reducing the parameter space for Unparticle-inspired models using white dwarf masses

Based on astrophysical constraints derived from Chandrasekhar's mass limit for white-dwarfs, we study the effects of the model on the parameters of unparticle-inspired gravity, on scales $\Lambda_U > 1 \; TeV$ and $d_U \approx 1$.Comment: 4 pp., 4 Fig., to appear in PR