Concretos secos produzidos com agregados reciclados de RCD separados por densidade

ResumoO uso de agregados reciclados de resíduos de construção e demolição (RCD) em blocos de concreto permite compatibilizar as diferentes características de composição e porosidade desses agregados com os diferentes níveis de exigência mecânica em uso dos blocos. Paralelamente, concretos secos são pouco estudados porque a energia de prensagem obtida em vibroprensas não é facilmente reprodutível em escala de laboratório; porém, parte dessa limitação pode ser superada, realizando-se a avaliação do comportamento da mistura (sob confinamento) com prensas de laboratório com controle de deformação. Assim, o objetivo deste artigo foi analisar o comportamento do concreto seco (no estado fresco e endurecido) produzido com agregados de RCD (separados ou não por densidade), empregando-se esse método laboratorial de prensagem. Com substituição total do agregado natural pelo agregado reciclado misto obtido por processo de jigagem obteve-se resistências à compressão comparáveis às dos concretos de referência. A influência das características dos agregados e das formulações de concretos secos foi identificada pela técnica de compactação laboratorial. A redução da porosidade do agregado reciclado e a otimização da granulometria da mistura seca (cimento e agregados) foram os parâmetros mais importantes para o incremento de resistência observado

In vitro phosphorylation as tool for modification of silk and keratin fibrous materials

An overview is given of the recent work on in vitro enzymatic phosphorylation of silk fibroin and human hair keratin. Opposing to many chemical "conventional" approaches, enzymatic phosphorylation is in fact a mild reaction and the treatment falls within "green chemistry" approach. Silk and keratin are not phosphorylated in vivo, but in vitro. This enzyme-driven modification is a major technological breakthrough. Harsh chemical chemicals are avoided, and mild conditions make enzymatic phosphorylation a real "green chemistry" approach. The current communication presents a novel approach stating that enzyme phosphorylation may be used as a tool to modify the surface charge of biocompatible materials such as keratin and silk

Variability in the analysis of a single neuroimaging dataset by many teams

Data analysis workflows in many scientific domains have become increasingly complex and flexible. To assess the impact of this flexibility on functional magnetic resonance imaging (fMRI) results, the same dataset was independently analyzed by 70 teams, testing nine ex-ante hypotheses. The flexibility of analytic approaches is exemplified by the fact that no two teams chose identical workflows to analyze the data. This flexibility resulted in sizeable variation in hypothesis test results, even for teams whose statistical maps were highly correlated at intermediate stages of their analysis pipeline. Variation in reported results was related to several aspects of analysis methodology. Importantly, meta-analytic approaches that aggregated information across teams yielded significant consensus in activated regions across teams. Furthermore, prediction markets of researchers in the field revealed an overestimation of the likelihood of significant findings, even by researchers with direct knowledge of the dataset. Our findings show that analytic flexibility can have substantial effects on scientific conclusions, and demonstrate factors related to variability in fMRI. The results emphasize the importance of validating and sharing complex analysis workflows, and demonstrate the need for multiple analyses of the same data. Potential approaches to mitigate issues related to analytical variability are discussed

Variability in the analysis of a single neuroimaging dataset by many teams

Data analysis workflows in many scientific domains have become increasingly complex and flexible. To assess the impact of this flexibility on functional magnetic resonance imaging (fMRI) results, the same dataset was independently analyzed by 70 teams, testing nine ex-ante hypotheses. The flexibility of analytic approaches is exemplified by the fact that no two teams chose identical workflows to analyze the data. This flexibility resulted in sizeable variation in hypothesis test results, even for teams whose statistical maps were highly correlated at intermediate stages of their analysis pipeline. Variation in reported results was related to several aspects of analysis methodology. Importantly, meta-analytic approaches that aggregated information across teams yielded significant consensus in activated regions across teams. Furthermore, prediction markets of researchers in the field revealed an overestimation of the likelihood of significant findings, even by researchers with direct knowledge of the dataset. Our findings show that analytic flexibility can have substantial effects on scientific conclusions, and demonstrate factors related to variability in fMRI. The results emphasize the importance of validating and sharing complex analysis workflows, and demonstrate the need for multiple analyses of the same data. Potential approaches to mitigate issues related to analytical variability are discussed

Réseaux de réactions dans l'oxydation catalytique de composés organiques : utilité et limitations

Des réseaux de réactions-aussi détaillés que nécessaire mais aussi simples que possible- sont utilisés pour quantifier des cinétiques réactionnelles complexes dans le but d'améliorer la conduite du réacteur et de garantir un dimensionnement fiable. L'approche est illustrée à l'aide d'exemples, à savoir : - la postcombustion catalytique de composés organiques volatiles ; - l'oxydation partielle de composés organiques

Theoretical Interpretation of Residence-Time Distribution Measurements in Industrial Processes

International audienceThe Residence-Time Distribution (RTD) is a chemical engineering concept introduced by Danckwerts in 1953. It has been described in a multitude of scientific papers and applied for various industrial processes. The development of Computer Fluid Dynamics will improve the comprehension and optimisation of such processes. However, this approach remains difficult in case of complex industrial processes. Therefore, the extension of the RTD concept is an alternative way to obtain hydrodynamic data and help for improvement of the processes. Actually, the models derived from tracer experiments are often restricted to the use of simple elementary reactors such as perfect mixing cells in series or plug flow with axial dispersion. The resulting information is often not sufficient for the understanding of complex processes. Better understanding may be obtained by the creation of complex networks of interconnected elementary reactors. However, that can lead to two problems to be solved: the first one is the possibility to realise an easy simulation of any complex network, the second one is to create realistic models on a sound physical basis. Indeed, complex models contain so many parameters that two different models may give the same result or the same model may give an identical result with different sets of parameters. A software package has been developed to simulate the response to an input of any complex network of elementary reactors properly interconnected. Processes with multiple inlets or outlets can be modelled by convolution and optimisation procedures. The software may equally be used to determine the parameters of different models giving the same response, and the subsequent examination of the physical soundness of these parameters leads to the choice of a realistic model. In addition, local measurements may be validated through the possibility to simulate the local response within the model and to optimise the corresponding parameters. Also, a general procedure has been developed to optimise the different flow rates of models in complex industrial processes with many undetermined recirculation flow rates. Future developments including RTD under transient state and automatic generation of flow models are also presented. They are illustrated through experiments and literature analysis. Finally, different perspectives of recent concepts are suggested