Phase transitions and crossovers in reaction-diffusion models with catalyst deactivation

The activity of catalytic materials is reduced during operation by several mechanisms, one of them being poisoning of catalytic sites by chemisorbed impurities or products. Here we study the effects of poisoning in two reaction-diffusion models in one-dimensional lattices with randomly distributed catalytic sites. Unimolecular and bimolecular single-species reactions are considered, without reactant input during the operation. The models show transitions between a phase with continuous decay of reactant concentration and a phase with asymptotic non-zero reactant concentration and complete poisoning of the catalyst. The transition boundary depends on the initial reactant and catalyst concentrations and on the poisoning probability. The critical system behaves as in the two-species annihilation reaction, with reactant concentration decaying as t^{-1/4} and the catalytic sites playing the role of the second species. In the unimolecular reaction, a significant crossover to the asymptotic scaling is observed even when one of those parameters is 10% far from criticality. Consequently, an effective power-law decay of concentration may persist up to long times and lead to an apparent change in the reaction kinetics. In the bimolecular single-species reaction, the critical scaling is followed by a two-dimensional rapid decay, thus two crossovers are found.Comment: 8 pages, 7 figure

Segurança em Laboratórios de Análises Químicas: estudo de caso na Embrapa Florestas.

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Riscos microbianos na produção integrada de morango.

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Cooperation between university and industry in the research of the suitability of agile methodologies in software development

Choosing a proper approach to manage a software development project is critical to increasing the chances to succeed in the venture. One of the great dilemmas nowadays concerns the option for an Agile or a traditional approach. There are several characteristics of software projects and the business environment in which they are carried out that must be considered while choosing the most appropriate development process. Although Agile development methodologies have been increasingly expanding and consolidating worldwide as an effective way of building software in the last two decades, they are not a one-size-fits-all approach. Knowing when to use Agile and which methodology is most suitable are the great questions that we aimed to answer in this study. In this paper, through a comprehensive revision of the Agile literature and an exploratory study, with the realization of focus group sessions with Agile practitioners and an interview with an Agile expert actively engaged in the software industry, we explored the characteristics of software development projects and organisational environments, identifying those that favour the use of an Agile approach. We also studied the main aspects that lead Agile teams to opt for one of the common Agile frameworks: Scrum, Extreme Programming (XP), Kanban, or Lean Software Development (LSD). The major goal of our study, clarifying the main aspects to be considered in the choice of an Agile methodology, is to support the decision-maker in the process of selecting an appropriate development approach.info:eu-repo/semantics/acceptedVersio

Cultivo de arroz irrigado orgânico no Rio Grande do Sul.

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Atividade inibitória de óleos fixos e essenciais no crescimento de isolados de Salmonella sp. e Salmonella typhimurium.

Neste trabalho foi avaliada a atividade antimicrobiana dos óleos essenciais de Cymbopogon wiinterianus, Pogostemon cablin, Ocimum basilicum, Ocimum gratissimum, Mentha arvensis, Eucalyptus spp., Ocimum basilicum var. Maria Bonita, Romarinus officinalis, Lippia sidoides, Cymbopogon citratus, Zingiber officinale, Azadirachta indica, Allium sativum contra Salmonella sp., e óleos de Pogostemon cablin, Ocimum basilicum var. Maria Bonita, Lippia sp., Lippia sidoides, Cymbopogon cytratus, Zingiber officinale e Ocimum gratissimum para Salmonella typhimurium

Potencial dendrocronológico de espécies arbóreas da caatinga.

Resumo

Avaliação de genótipos de trigo e de outros cereais de inverno ao crestamento, em solo com e sem aplicação de calcário.

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Distribuição diamétrica de Erisma unicatum e Qualea sp. em floresta natural do Mato Grosso.

Editores técnicos: Marcílio José Thomazini, Elenice Fritzsons, Patrícia Raquel Silva, Guilherme Schnell e Schuhli, Denise Jeton Cardoso, Luziane Franciscon. EVINCI. Resumos