Role of the cell-wall structure in the retention of bacteria by microfiltration membranes

This experimental study investigates the retention of bacteria by porous membranes. The transfer of bacteria larger than the nominal pore size of microfiltration track-etched membranes has been studied for several kinds of bacterial strains. This unexpected transfer does not correlate to the hydrophobicity,neither to the surface charge of the microorganism, as suggested in previous reports. We conclude that,in our conditions, the kind of bacteria (Gram-positive or Gram-negative) is finally the most important parameter. As the distinction between those two types of bacteria is related to the cell-wall structure, we provide an experimental evidence, via the action of an antibiotic, that the cell-wall flexibility triggers the transfer of the bacteria through artificial membranes, when the pores are smaller in size than the cell

Effects of membrane alterations on bacterial retention

The study shows the respective roles of skin and support of an ultrafiltration membrane in the retention mechanisms of bacteria (Escherichia coli). For this, pinholes defects of 5–200 μm in diameter were performed through ultrafiltration polymeric membranes and their impact was assessed on bacterialretention in a stirred cell when the transmembrane pressure is set at 0.5 bars. Various techniques have been used to make the defects such as a microhardness tester or femtosecond lasers. As long as the selective skin is not altered through its whole thickness, the membrane keeps a retention efficiency equivalent to the one of an uncompromised membrane. The retention by the macroporous support is also investigated. In case of membrane with defects of cylindrical geometry, experimental results are compared to calculated data obtained with a pore flow model, and the validity of this model is discussed

Potable water production by membrane processes: membrane characterization using a series of bacterial strains

The aim of this study was to develop a method for characterizing membranes (ultrafiltration and microfiltration) used in drinking water production. The method accounts for the specific behaviour of microorganisms during filtration, namely their deformation under mechanical stress. The leaks of microorganisms are linked to the presence of a small number of defects or abnormally large pores in the membrane structure. Assuming that the defects are cylindrical capillaries, the range of pore diameters concerned by the method lies between 0.05 and 1.2mm

When are Stochastic Transition Systems Tameable?

A decade ago, Abdulla, Ben Henda and Mayr introduced the elegant concept of decisiveness for denumerable Markov chains [1]. Roughly speaking, decisiveness allows one to lift most good properties from finite Markov chains to denumerable ones, and therefore to adapt existing verification algorithms to infinite-state models. Decisive Markov chains however do not encompass stochastic real-time systems, and general stochastic transition systems (STSs for short) are needed. In this article, we provide a framework to perform both the qualitative and the quantitative analysis of STSs. First, we define various notions of decisiveness (inherited from [1]), notions of fairness and of attractors for STSs, and make explicit the relationships between them. Then, we define a notion of abstraction, together with natural concepts of soundness and completeness, and we give general transfer properties, which will be central to several verification algorithms on STSs. We further design a generic construction which will be useful for the analysis of {\omega}-regular properties, when a finite attractor exists, either in the system (if it is denumerable), or in a sound denumerable abstraction of the system. We next provide algorithms for qualitative model-checking, and generic approximation procedures for quantitative model-checking. Finally, we instantiate our framework with stochastic timed automata (STA), generalized semi-Markov processes (GSMPs) and stochastic time Petri nets (STPNs), three models combining dense-time and probabilities. This allows us to derive decidability and approximability results for the verification of these models. Some of these results were known from the literature, but our generic approach permits to view them in a unified framework, and to obtain them with less effort. We also derive interesting new approximability results for STA, GSMPs and STPNs.Comment: 77 page

Context and Keyword Extraction in Plain Text Using a Graph Representation

Document indexation is an essential task achieved by archivists or automatic indexing tools. To retrieve relevant documents to a query, keywords describing this document have to be carefully chosen. Archivists have to find out the right topic of a document before starting to extract the keywords. For an archivist indexing specialized documents, experience plays an important role. But indexing documents on different topics is much harder. This article proposes an innovative method for an indexing support system. This system takes as input an ontology and a plain text document and provides as output contextualized keywords of the document. The method has been evaluated by exploiting Wikipedia's category links as a termino-ontological resources

Les valeurs scientifiques au travail

Cet article a pour objet les valeurs ayant cours aujourd’hui dans le monde de la science européenne, dégagées à partir d’entretiens semi-directifs avec des lauréats d’un grand prix de médecine et de biologie. Centrée sur la question, particulièrement révélatrice, des prix scientifiques et de leurs effets sur la vie professionnelle, relationnelle ou privée, cette enquête visait la socialisation de la vie scientifique, dans la perspective d’une sociologie compréhensive et empirique des valeurs. L’analyse inductive du corpus nous a permis de distinguer deux grands couples d’oppositions : d’une part, entre « valeurs fondamentales » et « valeurs contextuelles » et, d’autre part, entre « valeurs publiques » (susceptibles d’être publiquement revendiquées, en tant que valeurs de références) et « valeurs privées » (qui orientent effectivement l’action mais d’une façon difficilement revendicable en public). L’article présente un répertoire des valeurs contextuelles, sous la forme d’une quinzaine de couples de qualificatifs opposés (du type individuel/collectif), dont le statut axiologique varie selon les contextes.This article addresses the values prevailing today in the sphere of European science, identified through semi-directive interviews with the winners of a grand prize in medicine and biology. Focussing on the particularly revealing question of scientific prizes and their effects on professional, relational or private life, this survey addressed the socialization of scientific life from the perspective of a comprehensive and empirical sociology of values. An inductive analysis of the data revealed two main pairs of oppositions — on the one hand, between ‘fundamental values’ and ‘contextual values’ and, on the other, between ‘public values’ (that can be publicly proclaimed, as reference values) and ‘private values’ (which effectively guide the action but can hardly be proclaimed publicly). The article presents a list of contextual values in the form of some fifteen pairs of opposites (e.g. individual/collective) whose axiological status varies according to context.Este artículo tiene por objeto los valores que tienen curso hoy en el mundo de la ciencia europea, logrados a partir de entrevistas semidirigidas con laureados de un gran premio de medicina y biología. Centrada en la cuestión, especialmente reveladora, de los premios científicos y de sus efectos sobre la vida profesional, relacional o privada, esta investigación contemplaba la socialización de la vida científica, en la perspectiva de una sociología comprensiva y empírica de los valores. El análisis inductivo del corpus nos permitió distinguir dos grandes pares de oposiciones : por una parte, entre “valores fundamentales” y “valores del contexto” y, por otra parte, entre “valores públicos” (susceptibles de reivindicarse públicamente, como valores de referencia) y “valores privados” (que orientan efectivamente la acción pero de una manera difícilmente reivindicables en público). El artículo presenta un repertorio de los valores del contexto, en forma de una quincena de pares de calificativos opuestos (del tipo individual /colectivo), cuyo estatuto axiológico varía según los contextos

Short-term Farm Level Adaptations of EU15 Agricultural Supply to Climate Change

Assessing climate change impact on agriculture is a complex task involving a wide range of economical and physical processes, leading to significant uncertainties. At European scale, climate change impacts on agricultural supply have been appraised to be of relatively less important driver by the end of century compared to other global drivers. However these diagnoses are incomplete due to a limited representation of both spatial heterogeneity in important determinants of agricultural supply (soil, management practices and producer typology) and fine scale processes such as farm scale autonomous adaptation. We propose a complementary approach based on a modeling framework including a spatially explicit representation of productivity and producer behavior with regard to heterogeneity in soil, climate, and producer socio-economic context to appraise climate change impacts including autonomous farm-scale adaptations of EU15 agricultural supply to climate change. Our results suggest that without accounting for autonomous adaptation European agricultural supply may have interesting resilience properties at an aggregated scale despite significant heterogeneity at smaller resolution. Accounting for autonomous adaptations result in significant yield gains, and may lead to (i) a significant increase in the relative profitability of crops compared to other land-covers, thus possibly increasing its agricultural land-use share over other land covers, and (ii) an increase in total European production which may have impacts on agricultural goods markets, thus highlighting the need for integrating fine scale processes such as autonomous adaptation.Environmental Economics and Policy, Farm Management,