Simulation of the discharge propagation in a capillary tube in air at atmospheric pressure

International audienceThis paper presents simulations of an air plasma discharge at atmospheric pressure initiated by a needle anode set inside a dielectric capillary tube. We have studied the influence of the tube inner radius and its relative permittivity ε r on the discharge structure and dynamics. As a reference, we have used a relative permittivity ε r = 1 to study only the influence of the cylindrical constraint of the tube on the discharge. For a tube radius of 100 µm and ε r = 1, we have shown that the discharge fills the tube during its propagation and is rather homogeneous behind the discharge front. When the radius of the tube is in the range 300 to 600 µm, the discharge structure is tubular with peak values of electric field and electron density close to the dielectric surface. When the radius of the tube is larger than 700 µm, the tube has no influence on the discharge which propagates axially. For a tube radius of 100 µm, when ε r increases from 1 to 10, the discharge structure becomes tubular. We have noted that the velocity of propagation of the discharge in the tube increases when the front is more homogeneous and then, the discharge velocity increases with the decrease of the tube radius and ε r. Then, we have compared the relative influence of the value of tube radius and ε r on the discharge characteristics. Our simulations indicate that the geometrical constraint of the cylindrical tube has more influence than the value of ε r on the discharge structure and dynamics. Finally, we have studied the influence of photoemission processes on the discharge structure by varying the photoemission coefficient. As expected, we have shown that photoemission, as it increases the number of secondary electrons close to the dielectric surface, promotes the tubular structure of the discharge

The psychology of mountaineering: A systematic review

Research on the psychology of mountaineering has received widespread attention over many decades. Therefore, to clarify scientific findings in the area, provide future research directions, and enable the development of applied recommendations to enhance performance and safety, the purpose of this systematic mixed studies review was to identify, appraise, and synthesise research on the psychology of mountaineering. After systematically searching 10 electronic databases and undertaking manual searches up to April 2020, 69 studies published over 54 years (1966-2020) were included in the review. Thematic synthesis was undertaken and generated 11 descriptive themes, which were captured by two analytical themes, (i) personality characteristics of mountaineers, and (ii) psychological experiences in mountaineering. The synthesis generated novel insights into connections between different research topics in the psychology-specific literature in mountaineering, thus providing a more advanced understanding of current knowledge in this area. The review highlights that considerable progress has been made in this field, but further high-quality studies are required across all facets of this literature. Future avenues for research include: group dynamics; cognitive mechanisms underlying decision-making; and coping with setbacks and traumatic events

Magnetite as a precursor for green rust through the hydrogenotrophic activity of the iron-reducing bacteria Shewanella putrefaciens

International audienceMagnetite ((FeFe2O4)-Fe-II-O-III) is often considered as a stable end product of the bioreduction of Fe-III minerals (e.g., ferrihydrite, lepidocrocite, hematite) or of the biological oxidation of Fe-II compounds (e.g., siderite), with green rust (GR) as a mixed Fe-II-Fe-III hydroxide intermediate. Until now, the biotic transformation of magnetite to GR has not been evidenced. In this study, we investigated the capability of an iron-reducing bacterium, Shewanella putrefaciens, to reduce magnetite at circumneutral pH in the presence of dihydrogen as sole inorganic electron donor. During incubation, GR and/or siderite ((FeCO3)-C-II) formation occurred as secondary iron minerals, resulting from the precipitation of Fe-II species produced via the bacterial reduction of Fe-III species present in magnetite. Taking into account the exact nature of the secondary iron minerals and the electron donor source is necessary to understand the exergonic character of the biotic transformation of magnetite to GR, which had been considered to date as thermodynamically unfavorable at circumneutral pH. This finding reinforces the hypothesis that GR would be the cornerstone of the microbial transformations of iron-bearing minerals in the anoxic biogeochemical cycle of iron and opens up new possibilities for the interpretation of the evolution of Earth's history and for the understanding of biocorrosion processes in the field of applied science

IMPACTS DE L'HYDRODYNAMIQUE SUR LES AMIBES LIBRES DE BIOFILMS DE CIRCUITS DE REFROIDISSEMENT

International audienceNaturellement présentes dans les eaux de rivière qui alimentent les circuits de refroidissement (CRFs), les amibes libres (FLA) peuvent épisodiquement rencontrer des conditions favorables à leur multiplication lors de l’échauffement des eaux et représenter un risque sanitaire. Pour contrôler et anticiper les développements de telles amibes il est nécessaire d’identifier les facteurs influençant leur installation, leur croissance et leur survie dans les circuits d'eau. Longtemps oublié de la liste des niches écologiques potentielles des amibes libres, le biofilm est à ce jour décrit par la littérature scientifique comme une matrice privilégiée des pathogènes en raison de l’abondance de nutriments et de la stabilité des conditions hydrauliques (Puzon et al., 2009). Il est considéré que 95% de l’activité microbienne dans les eaux douces a lieu dans les biofilms (à l’interface eau-solide). La densité bactérienne et des températures au-delà de 32°C sont des conditions nécessaires mais pas suffisantes pour expliquer la croissance des amibes Naegleria fowleri dans les biofilms (Goudot et al., 2012). En effet, les équilibres microbiologiques sont encore méconnus et peuvent dans certaines conditions favoriser ou non l’apparition, le développement voire la disparition de N. fowleri. La complexité des circuits de refroidissement, notamment en termes de conditions hydrodynamiques (matériaux et hydraulique), sont aussi susceptibles d’influencer le comportement des amibes dans les biofilms et des biofilms eux-mêmes.Aussi, l’objectif de ce travail est d’étudier les effets des conditions hydrodynamiques représentatives des CRFs sur le comportement des FLA, et du pathogène Naegleria fowleri en particulier, dans les biofilms d’eau de rivière.Pour ce faire, il a été nécessaire de concevoir un réacteur qui permet la formation de biofilms en présence d’amibes libres, en laboratoire de type P3, sous différentes contraintes hydrodynamiques pariétales (caractérisées par de grands nombre de Reynolds et de grands taux de cisaillement) représentatives des CRFs. Le choix s’est porté sur un réacteur à disque tournant (Mathieu et al., 2014; Pelleïeux et al., 2012) qu’il a fallu modifier pour l’adapter à l’étude des amibes et pour des taux de cisaillement variant de 136 à 63698 s-1 à 42°C (optimum de croissance de N. fowleri). Ce réacteur est ainsi optimisé pour une étude inédite du développement aux interfaces solide-eau de microorganismes de taille supérieure à 20 μm en milieu turbulent et sous de fortes contraintes de cisaillement. Les biofilms et la qualité de l’eau, aux différents taux de cisaillement, seront caractérisées selon des approches physicochimiques et microbiologiques (quantification de la flore totale par marquage SYBR et numération des amibes cultivables) et par biologie moléculaire (qPCR 16S et amibiennes).Les premiers essais ont permis de valider le réacteur et les méthodes de caractérisation des biofilms d’eaux de rivière sous des taux de cisaillements de 9971 à 33238 s-1. D’autres essais, nous permettrons de balayer l’ensemble des taux de cisaillement possibles dans ce réacteur soit de 136 à 63698 s-1 avec l’implantation de notre amibe d’intérêt N. fowleri.En conclusion, nos travaux vont nous permettre d’évaluer l’impact de fortes conditions hydrodynamiques en proche paroi telles que retrouvées dans les circuits de refroidissement sur l’implantation, la croissance et la survie des amibes libres au sein de biofilms générés à 42°C

Design of a rotating disk reactor to assess the colonization of biofilms by free-living amoebae under high shear rates

<p>The present study was aimed at designing and optimizing a rotating disk reactor simulating high hydrodynamic shear rates (<i>γ</i>), which are representative of cooling circuits. The characteristics of the hydrodynamic conditions in the reactor and the complex approach used to engineer it are described. A 60 l tank was filled with freshwater containing free-living amoebae (FLA) and bacteria. Adhesion of the bacteria and formation of a biofilm on the stainless steel coupons were observed. FLA were able to establish in these biofilms under <i>γ</i> as high as 85,000 s⁻¹. Several physical mechanisms (convection, diffusion, sedimentation) could explain the accumulation of amoeboid cells on surfaces, but further research is required to fully understand and model the fine mechanisms governing such transport under <i>γ</i> similar to those encountered in the industrial environment. This technological advance may enable research into these topics.</p

Pseudo-first-order reaction of chemically and biologically formed green rusts with HgII and C15H15N3O2: effects of pH and stabilizing agents (phosphate, silicate, polyacrylic acid, and bacterial cells)

International audienceThe kinetics of Hg(II) and methyl red (MR) reduction by hydroxycarbonate green rust (GR1) and by hydroxysulfate green rust (GR2) were studied in the presence of naturally occurring organic and inorganic ligands (phosphate, polyacrylic acid, bacterial cells, silicate). The reducing ability of biogenic hydroxycarbonate green rust (GR1bio), obtained after microbial reduction of lepidocrocite by Shewanella putrefaciens, was also investigated and compared to those of chemically synthesized GR1 and GR2 (GR1ab and GR2ab). Pseudo first-order rate constants (kobs) of Hg(II) reduction (at pH 7.0, 8.2, and 9.5) and MR reduction (at pH 7.0) were determined and were normalized to the structural Fe(II) content of GRs (kFeII) and to the estimated concentration of surface Fe(II) sites (kS). The kS values ranged from 0.3 L mmol(-1) min(-1) to 43 L mmol(-1) min(-1) for the Hg reduction, and from 0.007 L mmol(-1) min(-1) to 3.4 L mmol(-1) min(-1) for the MR reduction. No significant discrepancy between GRab and GRbio was observed in term of reactivity. However, the reduction kinetics of MR was generally slower than the Hg(II) reduction kinetics for all tested GRs. While a slight difference in Hg(II) reduction rate was noted whatever the pH values (7.0, 8.2, or 9.5), the reduction of MR was significantly affected in the presence of ligands. A decrease by a factor of 2-200, depending on the type of ligand used, was observed. These data give new insights into the reactivity of GRs in the presence of co-occurring organic and inorganic ligands, and have major implications in the characterization of contaminated systems as well as water treatment processes.[on SciFinder (R)