Particle transport in neutral xenon: 2D modelling approach for the contribution of recombination processes to VUV emissions

International audienceThis paper constitutes a first step in studying transport phenomena, consecutive to a very brief 2-photon excitation of the Xe(3 P 2) metastable state in neutral xenon, followed by absorption of a further photon leading to ionisation, in Two-Photon Absorption Laser-Induced Fluorescence (TALIF) experiments. Here, the laser beam simply defines the column volume in which electrons and atomic ions are initially confined. Performing a numerical approach, we only consider the reactions occurring once electrons and atomic ions are produced by the incident laser pulse. All metastable atoms initially present are discarded, thus allowing evaluation of the contribution of only recombination processes to the VUV emissions. Besides kinetics of collisional and radiative processes, we also account for diffusion and possible drift phenomena (in presence of a Laplacian electric field). We provide spatial distributions of the number densities of the various species as well as temporal profiles of both their total number and the different VUV emissions. The influence of the external electric field and xenon pressure is discussed as well

Plasmas Froids : Systèmes d'analyse, Modélisation et Rayonnement

I - Physique et applications atmosphériques des filaments de plasma générés par des impulsions laser ultrabrèves (Jérôme Kasparian, Jean Pierre Wolf) Spectroscopie d'émission optique sur plasma induit par laser : Principe et applications (Patrick Mauchien, Catherine Gallou, Jean Luc Lacour, Laurent Salmon) II-2. Spectroscopie de fluorescence induite par diodes laser : Application au diagnostic des plasmas (Stéphane Mazouffre) II-3. Un capteur de flux d'énergie dans les plasmas (A.-L. Thomann, N. Semmar, R. Dussart, L. Bedra, J. Mathias, Y. Tessier et S. Mazouffre) III-1. Modélisation de la photoionisation dans les plasmas d'air non-thermiques à la pression atmosphérique (Anne Bourdon, Sébastien Célestin, Julien Capeillère et Pierre Ségur) III-2. Modélisation des plasmas produits par interaction laser-matière (Tatiana E. Itina) IV-1. Propriétés et transferts radiatifs dans les plasmas (M.Y. Perrin, A. Soufiani, Ph. Riviere) IV-2. Modifications induites en surface de polymères par traitement laser (Patricia Laurens, Sophie Petit) IV-3. Lampes fluorescentes sans mercure, à la recherche de l'efficacité énergétique (Eric Robert, Sébastien Point, Sébastien Dozias, Christophe Cachoncinlle, Raymond Viladrosa et Jean Michel Pouvesle) IV-4. Sources plasmas de rayonnement X créées par laser (Fabien Dorchies) Importance du rayonnement dans les procédés thermiques industriels (Yann Cressault, Philippe Teulet, Jean-Jacques Gonzalez, Alain Gleizes) La spectroscopie optique appliquée à l'étude des disjoncteurs (Dunpin Hong, Jean-Marc Bauchire et François Gentils) Exemples de micro plasmas à haute densité : Électroérosion et ouverture de contacts électriques (Jean-Luc Dorier, Antoine Descoeudres, Christoph Hollenstein) Chauffage et génération de courant par ondes dans les tokamaks (Gérard Bonhomme

Proton-assisted two-electron transfer in natural variants of tetraheme cytochromes from Desulfomicrobium Sp

The tetraheme cytochrome c(3) isolated from Desulfomicrobium baculatum (DSM 1743) (Dsmb) was cloned, and the sequence analysis showed that this cytochrome differs in just three amino acid residues from the cytochrome c(3) isolated from Desulfomicrobium norvegicum (Dsmn): (DsmnXXDsmb) Thr-37 --> Ser, Val-45 --> Ala, and Phe-88 --> Tyr. X-ray crystallography was used to determine the structure of cytochrome c(3) from Dsmb, showing that it is very similar to the published structure of cytochrome c(3) from Dsmn. A detailed thermodynamic and kinetic characterization of these two tetraheme cytochromes c(3) was performed by using NMR and visible spectroscopy. The results obtained show that the network of cooperativities between the redox and protonic centers is consistent with a synergetic process to stimulate the hydrogen uptake activity of hydrogenase. This is achieved by increasing the affinity of the cytochrome for protons through binding electrons and, reciprocally, by favoring a concerted two-electron transfer assisted by the binding of proton(s). The data were analyzed within the framework of the differences in the primary and tertiary structures of the two proteins, showing that residue 88, close to heme I, is the main cause for the differences in the microscopic thermodynamic parameters obtained for these two cytochromes c(3). This comparison reveals how replacement of a single amino acid can tune the functional properties of energy-transducing proteins, so that they can be optimized to suit the bioenergetic constraints of specific habitats