Revisiting the nonequilibrium phase transition of the triplet-creation model

The nonequilibrium phase transition in the triplet-creation model is investigated using critical spreading and the conservative diffusive contact process. The results support the claim that at high enough diffusion the phase transition becomes discontinuous. As the diffusion probability increases the critical exponents change continuously from the ordinary directed percolation (DP) class to the compact directed percolation (CDP). The fractal dimension of the critical cluster, however, switches abruptly between those two universality classes. Strong crossover effects in both methods make it difficult, if not impossible, to establish the exact location of the tricritical point.Comment: 7 pages, 12 figure

Bioeconomic Model for Decision-Making on Fattening Beef-Cattle

Profitability and competitiveness of agricultural systems it is closely related with the technology used. Economic and financial appraisal of investments on pasture improvements, facilities, feed and management plans, etc. are often required in order to make decisions. A bio-economic simulation model was developed in order to support decision making on beef-cattle grazing fattening. The aim of the model is to show the relationship between the technological alternative analysed in physical terms as well as financial and economic. By this way it is possible to asset and relate the bio-economic impact of the different animal and pasture management alternative technologies. Results show that the model could be used to support decision making when using stocking rates between 0.8 and 2.5 heads/ha

Diffusive epidemic process: theory and simulation

We study the continuous absorbing-state phase transition in the one-dimensional diffusive epidemic process via mean-field theory and Monte Carlo simulation. In this model, particles of two species (A and B) hop on a lattice and undergo reactions B -> A and A + B -> 2B; the total particle number is conserved. We formulate the model as a continuous-time Markov process described by a master equation. A phase transition between the (absorbing) B-free state and an active state is observed as the parameters (reaction and diffusion rates, and total particle density) are varied. Mean-field theory reveals a surprising, nonmonotonic dependence of the critical recovery rate on the diffusion rate of B particles. A computational realization of the process that is faithful to the transition rates defining the model is devised, allowing for direct comparison with theory. Using the quasi-stationary simulation method we determine the order parameter and the survival time in systems of up to 4000 sites. Due to strong finite-size effects, the results converge only for large system sizes. We find no evidence for a discontinuous transition. Our results are consistent with the existence of three distinct universality classes, depending on whether A particles diffusive more rapidly, less rapidly, or at the same rate as B particles.Comment: 19 pages, 5 figure

Aeromonas no processamento de queijos tipos Minas Frescal e Colonial.

Resumo: Com o objetivo de estabelecer, durante o processamento do queijo Minas Frescal e Colonial os possíveis pontos de contaminação e a forma de disseminação de bactérias do gênero Aeromonas, foram analisados, quanto à presença do micro-organismo, diferentes produtos e pontos do fluxograma de produção. Para o Queijo Minas Frescal, Aeromonas spp. foram isoladas no leite cru, leite pasteurizado, ambiente de produção e nas mãos dos manipuladores. A. caviae foi a espécie mais frequentemente identificada, sendo também isoladas A. sobria e A. schubertii. Durante o processamento do queijo Colonial, as espécies A. hydrophila, A. caviae, A. sobria, A. veronii e A. jandaei foram isoladas a partir da água, mãos dos manipuladores, utensílios, leite cru e após tratamento térmico e de massa coagulada. Os resultados demonstram que o gênero Aeromonas encontra-se disseminado nas diferentes etapas do processamento de queijos, destacando-se o leite cru como principal fonte de contaminação para o processamento industrial e artesanal. [Aeromonas in processing line of Minas Frescal and Colonial cheeses]. Abstract: The aim of this study is to establish possible contamination points and dissemination forms of the bacteria genus Aeromonas during the processing of the Brazilian cheeses Minas Frescal and Colonial. Therefore, different products and production points of the process were analyzed to determine the presence of the microorganism. In Minas Frescal cheese, Aeromonas spp. was isolated in raw and pasteurized milk, in the environment and on the handlers? hands. A. caviae was the most frequently identified species, but A. sobria and A. schubertii were also isolated. During the processing of Colonial cheese, the species A. hydrophila, A. caviae, A. sobria, A. veronii and A. jandaei were isolated in the water, raw milk, after thermal treatment and curd, as well as on the handlers' hands and utensils. The results showed that the genus Aeromonas is disseminated throughout different stages of both cheese processes while the raw milk stands out as the main source of contamination in the industrial and handmade processing

Obstáculos en el aprendizaje del concepto de respiracion

Se presentan los modelos explicativos expresados por estudiantes sobre el campo conceptual de la respiración. Se identificaron diferentes tipos de obstáculos frente a la enseñanza y el aprendizaje de la respiración. Se realizó análisis cualitativo de la información recolectada con el uso de la herramienta Atlas-Ti. La identificación de los modelos de los estudiantes y de los obstáculos frente al aprendizaje nos permitirá orientar acciones de enseñanza con el propósito de lograr aprendizajes en profundidad de los diferentes temas enseñados