Emergence of Hierarchy on a Network of Complementary Agents

Complementarity is one of the main features underlying the interactions in biological and biochemical systems. Inspired by those systems we propose a model for the dynamical evolution of a system composed by agents that interact due to their complementary attributes rather than their similarities. Each agent is represented by a bit-string and has an activity associated to it; the coupling among complementary peers depends on their activity. The connectivity of the system changes in time respecting the constraint of complementarity. We observe the formation of a network of active agents whose stability depends on the rate at which activity diffuses in the system. The model exhibits a non-equilibrium phase transition between the ordered phase, where a stable network is generated, and a disordered phase characterized by the absence of correlation among the agents. The ordered phase exhibits multi-modal distributions of connectivity and activity, indicating a hierarchy of interaction among different populations characterized by different degrees of activity. This model may be used to study the hierarchy observed in social organizations as well as in business and other networks.Comment: 13 pages, 4 figures, submitte

Impacto do aumento da concentração de dióxido de carbono no ar sobre a comunidade microbiana da rizosfera de mudas de eucalipto.

Resumo: O aumento significativo da concentração de dióxido de carbono atmosférico, em decorrência das atividades antrópicas, pode provocar modificações na morfologia e fisiologia das plantas e no ciclo dos patógenos, hospedeiros e antagonistas. Estufas de topo aberto (?open-top chambers?, OTC) foram utilizadas para verificar o impacto do aumento da concentração de CO2 do ar sobre a comunidade microbiana da rizosfera de mudas de eucalipto. Mudas cultivadas em OTCs com injeção de CO2 puro até atingir a concentração de 550 ?mol mol-1 (tratamento E+CO2) foram comparadas com mudas em OTCs sem injeção de CO2 (tratamento E) e em parcelas sem a estufa (tratamento T), em três repetições. Após 30 dias do plantio, amostras compostas de 10g de solo da rizosfera de 5 plantas escolhidas aleatoriamente foram colhidas. Depois foram feitas três diluições para cada amostra: 10-1, 10-2 e 10-3, com três repetições cada. Alíquotas das suspensões obtidas foram transferidas para placas de Petri contendo meios de cultura BDA e NA. A obtenção de colônias de Trichoderma spp. e Bacillus spp. foi maior para os tratamentos (T) e (E), diferindo significativamente do tratamento (E+CO2). Os resultados demonstram que o aumento de CO2 atmosférico pode causar alterações na comunidade microbiana da rizosfera

Quantum Monte Carlo Study of Strongly Correlated Electrons: Cellular Dynamical Mean-Field Theory

We study the Hubbard model using the Cellular Dynamical Mean-Field Theory (CDMFT) with quantum Monte Carlo (QMC) simulations. We present the algorithmic details of CDMFT with the Hirsch-Fye QMC method for the solution of the self-consistently embedded quantum cluster problem. We use the one- and two-dimensional half-filled Hubbard model to gauge the performance of CDMFT+QMC particularly for small clusters by comparing with the exact results and also with other quantum cluster methods. We calculate single-particle Green's functions and self-energies on small clusters to study their size dependence in one- and two-dimensions.Comment: 14 pages, 18 figure

Immunization and Aging: a Learning Process in the Immune Network

The immune system can be thought as a complex network of different interacting elements. A cellular automaton, defined in shape-space, was recently shown to exhibit self-regulation and complex behavior and is, therefore, a good candidate to model the immune system. Using this model to simulate a real immune system we find good agreement with recent experiments on mice. The model exhibits the experimentally observed refractory behavior of the immune system under multiple antigen presentations as well as loss of its plasticity caused by aging.Comment: 4 latex pages, 3 postscript figures attached. To be published in Physical Review Letters (Tentatively scheduled for 5th Oct. issue

Projeto e desenvolvimento de um sistema sobre demandas em software agropecuário.

A demanda em software é um fator essencial para tomada de decisão no que se refere ao desenvolvimento de novos softwares agropecuários. Em 2009, a Embrapa Informática Agropecuária realizou uma pesquisa sobre a demanda desse tipo de software, em que foram levantadas questões referentes às necessidades e aos perfis de Cooperativas e Ematers (escritórios de extensão rural) em relação à informática. Visando obter análises de dados de forma automatizada, foi desenvolvido um sistema para o gerenciamento dos questionários respondidos na pesquisa

Experimental analysis of lateral impact on planar brittle material: spatial properties of the cracks

The breakup of glass and alumina plates due to planar impacts on one of their lateral sides is studied. Particular attention is given to investigating the spatial location of the cracks within the plates. Analysis based on a phenomenological model suggests that bifurcations along the cracks' paths are more likely to take place closer to the impact region than far away from it, i. e., the bifurcation probability seems to lower as the perpendicular distance from the impacted lateral in- creases. It is also found that many observables are not sensitive to the plate material used in this work, as long as the fragment multiplicities corresponding to the fragmentation of the plates are similar. This gives support to the universal properties of the fragmentation process reported in for- mer experiments. However, even under the just mentioned circumstances, some spatial observables are capable of distinguishing the material of which the plates are made and, therefore, it suggests that this universality should be carefully investigated

Controle integrado da broca da haste da mandioca Sternocoelus spp.

Consideradas pragas secundárias, as brocas da haste da mandioca Sternocoelus spp. (Coleoptera: Curculionidae) são problema fitossanitário em algumas áreas produtoras (RODRIGUEZ et al., 2009). O controle dessa praga é difícil, pois o dano ocorre quando ao eclodir e se alimentar no interior da haste as larvas interrompem o fluxo de seiva na planta levando-a à morte (CARVALHO et al. 2009)