Continuous and discontinuous absorbing-state phase transitions on Voronoi-Delaunay random lattices

We study absorbing-state phase transitions in two-dimensional Voronoi-Delaunay (VD) random lattices with quenched coordination disorder. Quenched randomness usually changes the criticality and destroys discontinuous transitions in low-dimensional nonequilibrium systems. We performed extensive simulations of the Ziff-Gulari-Barshad (ZGB) model, and verified that the VD disorder does not change the nature of its discontinuous transition. Our results corroborate recent findings of Barghatti and Vojta [Phys. Rev. Lett. {\bf 113}, 120602 (2014)] stating the irrelevance of topological disorder in a class of random lattices that includes VD and raise the interesting possibility that disorder in nonequilibrium APT may, under certain conditions, be irrelevant for the phase coexistence. We also verify that the VD disorder is irrelevant for the critical behavior of models belonging to the directed percolation and Manna universality classes.Comment: 7 pages, 6 figure

Contact process on a Voronoi triangulation

We study the continuous absorbing-state phase transition in the contact process on the Voronoi-Delaunay lattice. The Voronoi construction is a natural way to introduce quenched coordination disorder in lattice models. We simulate the disordered system using the quasistationary simulation method and determine its critical exponents and moment ratios. Our results suggest that the critical behavior of the disordered system is unchanged with respect to that on a regular lattice, i.e., that of directed percolation

Cosmological constant constraints from observation-derived energy condition bounds and their application to bimetric massive gravity

Among the various possibilities to probe the theory behind the recent accelerated expansion of the universe, the energy conditions (ECs) are of particular interest, since it is possible to confront and constrain the many models, including different theories of gravity, with observational data. In this context, we use the ECs to probe any alternative theory whose extra term acts as a cosmological constant. For this purpose, we apply a model-independent approach to reconstruct the recent expansion of the universe. Using Type Ia supernova, baryon acoustic oscillations and cosmic-chronometer data, we perform a Markov Chain Monte Carlo analysis to put constraints on the effective cosmological constant $\Omega^0_{\rm eff}$. By imposing that the cosmological constant is the only component that possibly violates the ECs, we derive lower and upper bounds for its value. For instance, we obtain that $0.59 < \Omega^0_{\rm eff} < 0.91$ and $0.40 < \Omega^0_{\rm eff} < 0.93$ within, respectively, $1\sigma$ and $3\sigma$ confidence levels. In addition, about 30\% of the posterior distribution is incompatible with a cosmological constant, showing that this method can potentially rule it out as a mechanism for the accelerated expansion. We also study the consequence of these constraints for two particular formulations of the bimetric massive gravity. Namely, we consider the Visser's theory and the Hassan and Roses's massive gravity by choosing a background metric such that both theories mimic General Relativity with a cosmological constant. Using the $\Omega^0_{\rm eff}$ observational bounds along with the upper bounds on the graviton mass we obtain constraints on the parameter spaces of both theories.Comment: 11 pages, 4 figures, 1 tabl

Observational Constraints on Visser's Cosmological Model

Theories of gravity for which gravitons can be treated as massive particles have presently been studied as realistic modifications of General Relativity, and can be tested with cosmological observations. In this work, we study the ability of a recently proposed theory with massive gravitons, the so-called Visser theory, to explain the measurements of luminosity distance from the Union2 compilation, the most recent Type-Ia Supernovae (SNe Ia) dataset, adopting the current ratio of the total density of non-relativistic matter to the critical density ($\Omega_m$) as a free parameter. We also combine the SNe Ia data with constraints from Baryon Acoustic Oscillations (BAO) and CMB measurements. We find that, for the allowed interval of values for $\Omega_m$, a model based on Visser's theory can produce an accelerated expansion period without any dark energy component, but the combined analysis (SNe Ia + BAO + CMB) shows that the model is disfavored when compared with $\Lambda$CDM model.Comment: 6 pages, 4 figure

Plantios comerciais de cupuaçuzeiro são fontes de novas cultivares?

A procura por novos materiais é uma prática incessante em qualquer programa de melhoramento genético. Os pomares de cupuaçuzeiro do município de Tomé Açu - Pará, por apresentarem alta variabilidade, oferecem oportunidade de que sejam selecionadas matrizes com boas características de produção de frutos. O objetivo desta pesquisa foi avaliar clones de cupuaçuzeiro oriundos de plantios comerciais, para identificar e selecionar matrizes interessantes para o programa de melhoramento genético da espécie. Dezoito matrizes foram, inicialmente, identificadas nos pomares comerciais, e depois clonadas. O experimento foi instalado a campo, em fevereiro/1999, no delineamento blocos inteiramente casualizados, com dez repetições, sendo uma planta por parcela. Foram coletados dados do número de frutos produzidos por planta, bem como, o peso do fruto, peso de sementes e polpa por fruto. Os dados revelaram boa variabilidade entre os clones no tocante ao número de frutos, entretanto, houve pouca variação para as características componentes do fruto. O clone 378 destacou-se como o material mais promissor para todas as variáveis estudadas. Quanto à produção de frutos também merece destaque o clone 366 e para produção de sementes o clone 375. Este clone também teve bom desempenho na produção de polpa, assim como os clones 366 e 415. Pelo comportamento apresentado neste ensaio, os clones 378, 375 e 366 deverão ser aproveitados pelo programa de melhoramento genético. Entretanto, necessitam ser testados numa escala experimental ampliada, antes da seleção final.PIBIC-2011

A cuiarana como matéria-prima papeleira.

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Biogás: uma alternativa de energia no meio rural.

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