Experimental study of the effects of viscosity and viscoelasticity on a line vortex cavitation

This paper investigates the influence of viscosity and viscoelasticity on the structure of the flow in a line vortex in view of understanding their effects on cavitation inception. Experiments were conducted in a vortex chamber where the fluid injection speed and the liquid properties can be easily controlled. Measurements of the velocities, pressures, and thus the cavitation number were conducted using a PIV system, pressure gauges, and Pitot tubes. Experiments were performed using water, different dilute concentrations of polymer (POLYOX WSR 301) solutions, and solutions with different concentrations of corn syrup for a large range of Reynolds numbers. The measurements and observations showed that cavitation inception at the vortex center was delayed when polymer and corn syrup solutions are used as compared to the experiments in water. However, contrary to reported observations with tip vortices, here the large scale vortex was found to rotate faster in the polymer and corn syrup solutions. This did not match with our observations of cavitation inception delay in the case of polymers and the conventional thinking about the relationship between pressures and velocities in a vortex line. This may be due to the observations that the velocity fluctuations and the turbulent kinetic energy in the viscous core region increased significantly in the polymer and corn syrup solutions and could question the validity of a pressure computation based on a single vortex.http://deepblue.lib.umich.edu/bitstream/2027.42/84322/1/CAV2009-final152.pd

Culture-independent methods for identifying microbial communities in cheese

International audienceThis review focuses on the culture-independent methods available for the description of both bacterial and fungal communities in cheese. Important steps of the culture-independent strategy, which relies on bulk DNA extraction from cheese and polymerase chain reaction (PCR) amplification of selected sequences, are discussed. We critically evaluate the identification techniques already used for monitoring microbial communities in cheese, including PCR-denaturing gradient gel electrophoresis (PCR-DGGE), PCR-temporal temperature gradient gel electrophoresis (PCR-TTGE) or single-strand conformation polymorphism-PCR (SSCP-PCR) as well as some other techniques that remain to be adapted to the study of cheese communities. Further, our analysis draws attention to the lack of data available on suitable DNA sequences for identifying fungal communities in cheese and proposes some potential DNA targets

Use of response surface methodology to optimise environmental stress conditions on Penicillium glabrum, a food spoilage mould

International audienceFungi are ubiquitous micro-organisms often associated with spoilage and biodeterioration of a large variety of foods and feedstuffs. Their growth may be influenced by temporary changes in intrinsic or environmental factors such as temperature, water activity, pH, preservatives, atmosphere composition, all of which may represent potential sources of stress. Molecular-based analyses of their physiological responses to environmental conditions would help to better manage the risk of alteration and potential toxicity of food products. However, before investigating molecular stress responses, appropriate experimental stress conditions must be precisely defined. Penicillium glabrum is a filamentous fungus widely present in the environment and frequently isolated in the food processing industry as a contaminant of numerous products. Using response surface methodology, the present study evaluated the influence of two environmental factors (temperature and pH) on P. glabrum growth to determine ‘optimised' environmental stress conditions. For thermal and pH shocks, a large range of conditions was applied by varying factor intensity and exposure time according to a two-factorial central composite design. Temperature and exposure duration varied from 30 to 50°C and from 10 min to 230 min, respectively. The effects of interaction between both variables were observed on fungal growth. For pH, the duration of exposure, from 10 to 230 min, had no significant effect on fungal growth. Experiments were thus carried out on a range of pH from 0.15 to 12.50 for a single exposure time of 240 min. Based on fungal growth results, a thermal shock of 120 min at 40°C or a pH shock of 240 min at 1.50 or 9.00 may therefore be useful to investigate stress responses to non-optimal conditions

A novel approach for electric load curve holistic modelling and simulation

International audienceThis paper presents a novel approach of an electric load curve simulator using a set of grey box models that results to an efficient trade-off between complete and complex physical models and fast simplified statistical models. The input parameters are macroscopic data coming from large databases such as national census, DSO’s client information and meteorological data such as temperature or irradiation data. The problem of matching between the different databases is investigated to assess comparable load curves. Validation is performed using load measurements at the medium voltage level. Once the model is calibrated it can be turned into a good prediction tool useful for planning studies since it permits easily to incorporate the evolution of usages, the characteristics of consumption devices, as well as the evolution of the building’s characteristics

Visualisation Focus+Contexte pour l'Exploration Interactive de Maillages Tétraèdriques

in Revue Électronique Francophone d'Informatique Graphique (REFIG) , Vol 2, Num 1, http://www.irit.fr/REFIG/index.php/refig/issue/view/2National audienceL'exploration et l'analyse visuelle de grands maillages tétraédriques restent des tâches coûteuses en temps lorsque les ensembles de données sont affichés dans leur globalité. Pourtant, dans la plupart des cas, l'utilisateur n'explorera que de petites zones compactes où se concentrent les informations qu'il juge remarquables. Se basant sur ce constat, nous proposons une approche focus+contexte reposant sur une double résolution des données. Dans l'espace objet, une Région Locale d'Intérêt (RLI) - le focus - est extraite du maillage précis originel et est entourée par une représentation grossière globale - le contexte. Pour unir les deux résolutions, une connexion topologiquement valide est créée interactivement. Les techniques de rendu classiques y sont intégrées. De plus, quand le focus est déplacé, l'extraction de la RLI ainsi que son affichage sont accélérés en utilisant la cohérence temporelle. Les dernières cartes graphiques sont utilisées afin d'accélérer le Rendu Volumique Direct. Notre approche focus+contexte réduit de manière significative le nombre de primitives affichées ce qui permet une exploration interactive de grands maillages tétraédriques

Marine culturable yeasts in deep-sea hydrothermal vents: species richness and association with fauna

The definitive version is available at ww3.interscience.wiley.com. Post-print en libre-accès sur Archimer : http://archimer.ifremer.fr/doc/00006/11704/8475.pdfInternational audienceInvestigations of the diversity of culturable yeasts at deep-sea hydrothermal sites have suggested possible interactions with endemic fauna. Samples were collected during various oceanographic cruises at the Mid-Atlantic Ridge, South Pacific Basins and East Pacific Rise. Cultures of 32 isolates, mostly associated with animals, were collected. Phylogenetic analyses of 26S rRNA gene sequences revealed that the yeasts belonged to Ascomycota and Basidiomycota phyla, with the identification of several genera: Rhodotorula, Rhodosporidium, Candida, Debaryomyces and Cryptococcus. Those genera are usually isolated from deep-sea environments. To our knowledge, this is the first report of yeasts associated with deep-sea hydrothermal animals

Rapport scientifique de synthèse de la recherche Cahier numérique de l'élève chercheur (CNEC)

Le texte qui suit est fondé sur un travail collectif mené pendant 3 années au sein du projet EFRAN Les savanturiers du numérique