Living bacteria rheology: population growth, aggregation patterns and cooperative behaviour under different shear flows

The activity of growing living bacteria was investigated using real-time and in situ rheology -- in stationary and oscillatory shear. Two different strains of the human pathogen Staphylococcus aureus -- strain COL and its isogenic cell wall autolysis mutant -- were considered in this work. For low bacteria density, strain COL forms small clusters, while the mutant, presenting deficient cell separation, forms irregular larger aggregates. In the early stages of growth, when subjected to a stationary shear, the viscosity of both strains increases with the population of cells. As the bacteria reach the exponential phase of growth, the viscosity of the two strains follow different and rich behaviours, with no counterpart in the optical density or in the population's colony forming units measurements. While the viscosity of strain COL keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the population stabilizes, the viscosity of the mutant strain decreases steeply, still in the exponential phase, remains constant for some time and increases again, reaching a constant plateau at a maximum value for the late phase of growth. These complex viscoelastic behaviours, which were observed to be shear stress dependent, are a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. The viscous and elastic moduli of strain COL, obtained with oscillatory shear, exhibit power-law behaviours whose exponent are dependent on the bacteria growth stage. The viscous and elastic moduli of the mutant have complex behaviours, emerging from the different relaxation times that are associated with the large molecules of the medium and the self-organized structures of bacteria. These behaviours reflect nevertheless the bacteria growth stage.Comment: 9 pages, 10 figure

Interacting Particles and Strings in Path and Surface Representations

Non-relativistic charged particles and strings coupled with abelian gauge fields are quantized in a geometric representation that generalizes the Loop Representation. We consider three models: the string in self-interaction through a Kalb-Ramond field in four dimensions, the topological interaction of two particles due to a BF term in 2+1 dimensions, and the string-particle interaction mediated by a BF term in 3+1 dimensions. In the first case one finds that a consistent "surface-representation" can be built provided that the coupling constant is quantized. The geometrical setting that arises corresponds to a generalized version of the Faraday's lines picture: quantum states are labeled by the shape of the string, from which emanate "Faraday`s surfaces". In the other models, the topological interaction can also be described by geometrical means. It is shown that the open-path (or open-surface) dependence carried by the wave functional in these models can be eliminated through an unitary transformation, except by a remaining dependence on the boundary of the path (or surface). These feature is closely related to the presence of anomalous statistics in the 2+1 model, and to a generalized "anyonic behavior" of the string in the other case.Comment: RevTeX 4, 28 page

Respiratory hospital admission risk near large composting facilities

AbstractBackgroundLarge-scale composting can release bioaerosols in elevated quantities, but there are few studies of health effects on nearby communities.MethodsA cross-sectional ecological small area design was used to examine risk of respiratory hospital admissions within 2500m of all 148 English large-scale composting facilities in 2008–10. Statistical analyses used a random intercept Poisson regression model at Census Output Area (COA) level (mean population 310). Models were adjusted for age, sex, deprivation and tobacco sales.ResultsAnalysing 34,963 respiratory hospital admissions in 4656 COAs within 250–2500m of a site, there were no significant trends using pre-defined distance bands of >250–750m, >750–1500m and >1500–2500m. Using a continuous measure of distance, there was a small non-statistically significant (p=0.054) association with total respiratory admissions corresponding to a 1.5% (95% CI: 0.0–2.9%) decrease in risk if moving from 251m to 501m. There were no significant associations for subgroups of respiratory infections, asthma or chronic obstructive pulmonary disease.ConclusionThis national study does not provide evidence for increased risks of respiratory hospital admissions in those living beyond 250m of an outdoor composting area perimeter. Further work using better measures of exposure and exploring associations with symptoms and disease prevalence, especially in vulnerable groups, is recommended to support regulatory approaches

Densidade e composição florística de vegetação de caatinga em áreas ocupadas por algarobeira (Prosopis juliflora (SW) D.C.) em Petrolina-PE, Dormentes-PE, Juazeiro-BA e Jaguarari-BA.

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Viabilidade econômica do sistema agroflorestal grevílea x café na Região Norte do Paraná.

Na década de 70, o Instituto Brasileiro do Café - IBC incentivou a introdução de Grevillea robusta nos cafezais da região Norte do Paraná, na forma de quebra-ventos, apesar de sua implantação não haver seguido padrões técnicos adequados. Para a análise da viabilidade econômica da utilização desses quebra-ventos, foram comparados os benefícios diretos (custos x renda) do Sistema Puro Café e do Sistema Agroflorestal Grevílea x Café, utilizando um aplicativo de apropriação e análise de custos, o SAAC florestal (Hildebrandt, 1995). As planilhas do aplicativo foram preenchidas separadamente para os dois sistemas. O Sistema Puro Café contou com dados secundários de custos de produção e rendas fornecidos por órgãos públicos e privados. Para a análise do Sistema Agroflorestal, foram utilizados os mesmos dados referentes à produção monocultural de café, acrescidos dos dados de custos de produção e rendas da espécie florestal obtidos por meio de questionários aplicados junto a proprietários rurais e serrarias da região de estudo. Os resultados obtidos permitiram constatar que a espécie florestal introduzida no sistema representa um custo adicional insignificante para o produtor rural e ocupa uma área mínima, ou seja, uma média de 58 árvores por hectare. A renda obtida com a venda da madeira para serrarias gera um aumento significativo da renda no último ano, de 32,22%, permitindo o pagamento dos custos de implantação ou grande parte dos custos de reforma da atividade. Portanto, a utilização da grevílea nos cafezais é altamente positiva do ponto de vista do aumento da rentabilidade da atividade e da tranquilidade do produtor, pois pode representar uma poupança ao longo do ciclo da cultura cafeeira, assegurando a continuidade desta atividade por meio do pagamento da reforma com o corte da madeira

A Roadmap to Gamify Programming Education

Learning programming relies on practicing it which is often hampered by the barrier of difficulty. The combined use of automated assessment, which provides fast feedback to the students experimenting with their code, and gamification, which provides additional motivation for the students to intensify their learning effort, can help pass the barrier of difficulty in learning programming. In such environment, students keep receiving the relevant feedback no matter how many times they try (thanks to automated assessment), and their engagement is retained (thanks to gamification). While there is a number of open software and programming exercise collections supporting automated assessment, up to this date, there are no available open collections of gamified programming exercises, no open interactive programming learning environment that would support such exercises, and even no open standard for the representation of such exercises so that they could be developed in different educational institutions and shared among them. This gap is addressed by Framework for Gamified Programming Education (FGPE), an international project whose primary objective is to provide necessary prerequisites for the application of gamification to programming education, including a dedicated gamification scheme, a gamified exercise format and exercises conforming to it, software for editing the exercises and an interactive learning environment capable of presenting them to students. This paper presents the FGPE project, its architecture and main components, as well as the results achieved so far. 2012 ACM Subject Classification Social and professional topics ! Computer science education

Utilização do fosfato de tapira em dietas de frangos de corte.

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