Curing and post-curing luminescence in an epoxy resin

A spontaneous luminescence is reported when epoxy resin samples are heated in air. This phenomenon is very sensitive to the nature of the atmosphere. The same treatment in nitrogen leads to an extinction of the luminescence. The emission process is restored when samples are kept for a sufficient time in air. In order to better understand this phenomenon, we have investigated the luminescence of the elementary constituents of the epoxy (resin and hardener) when heated in air and nitrogen, as well as during resin curing in the same atmospheres. It appears that the emission process is linked with the presence of oxygen. Although the kinetics of the luminescence can differ depending on the nature of the sample (cured resin, resin during curing, liquid components), the emission spectra are the same during resin curing and upon heating of the cured resin and hardener. The emission spectrum of the base resin is different. It is concluded that the light results from a chemiluminescence process during oxidation.Comment: p. 1

Liquid fuel spray atomisation, ignition and combustion dynamics

Turbulent spray ames are increasingly found in industrial combustion devices due to greater demand for fuel exibility. However, a comprehensive model of the underlying physics involved into this is still lacking due to the great complexity of the problem. The importance of numerical studies in this context is related to the possible savings in experimental testing both in terms of time and resources. A detailed yet a ordable numerical tool is therefore required to the development of less polluting and more e cient devices. This work aims at the validation of existing models and developing methods focusing on the atomisation, evaporation, ignition, and combustion dynamics of spray fuelled burners. Here, extensive simulations are performed in the context of Large Eddy Simulation (LES) where the scalar elds are modelled using a transported pdf approach. The solution of the latter is obtained by means of the Eulerian stochastic eld method, a exible and comprehensive combustion model. The liquid phase is treated in a discrete Lagrangian fashion, where the sub-grid-scale uctuations from the LES are accounted for by the stochastic parcel method for dispersion, break-up and evaporation. Di erent atomisation and evaporation models of increasing complexity are tested and greater insight on the e ect of this choice is provided. This is achieved while exploring the applicability of the method to various state of the art techniques for pollutants reduction. Several test cases have been simulated: the Sandia constant volume chamber, the DELFT hot co- ow burner and two of the burners from CORIA laboratories. For all cases good reproduction of the aerodynamic elds as well as the qualitative ame shapes is acheived. Three evaporation model have been tested, and three break-up models used for the simulations and the e ects of this choice are explored in this work. The stochastic break-up model tested allows for reduced a priori assumption on the calculation providing results comparable with other methods. The Abramzon-Sirignano evaporation model appears to be a valid evaporation model to be employed in dilute spray LES calculations. Validation is achieved by comparing both gas and liquid phase properties with the available experimental data. An important dependency of the quality of the predictions on the choice of the chemical mechanism describing the oxidation process is observed. As a conclusion of the study, future directions are suggested together with some preliminary illustrative results.Open Acces

Médecin de bord sur le Marion Dufresne (pathologies incidentes de 2004 à 2007)

BORDEAUX2-BU Santé (330632101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Etude de la charge d'espace et des phénomènes luminescents comme précurseurs du vieillissement électrique d'une résine époxy utilisée dans l'isolation haute tension

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Large eddy simulation of an ethanol spray flame with secondary droplet breakup

A computational investigation of three configurations of the Delft Spray in Hot-diluted Co-flow (DSHC) is presented. The selected burner comprises a hollow cone pressure swirl atomiser, injecting an ethanol spray, located in the centre of a hot co-flow generator, with the conditions studied corresponding to Moderate or Intense Low-oxygen Dilution (MILD) combustion. The simulations are performed in the context of Large Eddy Simulation (LES) in combination with a transport equation for the joint probability density function (pdf) of the scalars, solved using the Eulerian stochastic field method. The liquid phase is simulated by the use of a Lagrangian point particle approach, where the sub-grid-scale interactions are modelled with a stochastic approach. Droplet breakup is represented by a simple primary breakup model in combination with a stochastic secondary breakup formulation. The approach requires only a minimal knowledge of the fuel injector and avoids the need to specify droplet size and velocity distributions at the injection point. The method produces satisfactory agreement with the experimental data and the velocity fields of the gas and liquid phase both averaged and ‘size-class by size-class’ are well depicted. Two widely accepted evaporation models, utilising a phase equilibrium assumption, are used to investigate the influence of evaporation on the evolution of the liquid phase and the effects on the flame. An analysis on the dynamics of stabilisation sheds light on the importance of droplet size in the three spray flames; different size droplets play different roles in the stabilisation of the flames

Large eddy simulation of an opposed jet turbulent flame

A Large Eddy Simulation (LES) of a turbulent premixed flame in a counter-flow configuration is performed. This burner is a benchmark for the analysis of turbulent flames with particularly the turbulence-chemistry interaction. In the simulations combustion is modelled by means of the evolution of the joint sub-grid-scale (sgs) probability density function. The solution of the transport equation for the scalars is obtained by the stochastic field method. The results presented are a comparison with the experimental data for a reacting and non reacting case and they include axial and radial velocities as well as OH plots

Large Eddy Simulation of an ethanol spray flame under MILD combustion with the stochastic fields method

A combustion device operating in Moderate or Intense Low-oxygen Dilution (MILD) condition is numerically simulated. The burner consists of a cylindrical hot co-flow generator with an injector installed on the central axis. The hot co-flow is obtained by the lean combustion of Dutch Natural Gas (DNG). The spray is injected through an industrial pressure swirl atomiser using liquid ethanol as fuel. MILD combustion consists in burning the fuel in a high temperature environment so that the temperature gradients are limited and the production of pollutants such as NOx reduced. MILD combustion has been investigated for furnace applications and for various gaseous fuels, recently it has also been explored for spray combustion. The simulation is performed in the context of Large Eddy Simulation (LES) and the transported pdf equation for the scalars is solved using the stochastic fields approach. The validation of the results is based on the comparison with experimental data. The characteristics of the injector are obtained a posteriori by the use of the measurements at downstream location. The simulation correctly reproduces the velocity profiles of the particles within their size classes and the integral particle size distribution which is represented by the Sauter Mean Diameter (SMD). The gas phase temperature and velocity are also in good agreement with the measurements, however, some discrepancies are observed, presumably because of the lack of modelling of primary atomisation. The model employed appears to reliably reproduce the behaviour of the spray combustion system under MILD conditions

Comparative genomics of Chrysochromulina Ericina Virus (CeV) and other microalgae-infecting large DNA viruses highlight their intricate evolutionary relationship with the established Mimiviridae family.

International audienceChrysochromulina Ericina Virus CeV-01B (CeV) was isolated from Norwegian coastal waters in 1998. Its icosahedral particle is 160 nm in diameter and encloses a 474-kb dsDNA genome. This virus, although infecting a microalgae (the haptophyceae Haptolina ericina, formerly Chrysochromulina ericina), is phylogenetically related to members of the Mimiviridae family, initially established with the acanthamoeba-infecting Mimivirus and Megavirus as prototypes. This family was latter split into two genera (Mimivirus and Cafetariavirus) following the characterization of a virus infecting the heterotrophic stramenopile Cafeteria roenbergensis (CroV). CeV, as well as two of its close relatives infecting the unicellular photosynthetic eukaryotes Phaeocystis globosa (PgV) and Aureococcus anophagefferens (AaV), are currently unclassified by ICTV. The detailed comparative analysis of the CeV genome presented here confirms the phylogenetic affinity of this emerging group of microalgae-infecting viruses with the Mimiviridae, but argues in favor of their classification inside a distinct clade within the family. Although CeV, PgV, AaV share more common features between them than with the larger Mimiviridae, they also exhibit a large complement of unique genes attesting to their complex evolutionary history. We identified several gene fusion events and cases of convergent evolution involving independent lateral gene acquisitions. Finally, CeV possesses an unusual number of inteins, some of which are closely related despite been inserted in non-homologous genes. This appears to contradict the paradigm of allele-specific inteins and suggests that Mimiviridae might be especially efficient in spreading inteins while enlarging their repertoire of homing genes

Giant viruses at the core of microscopic wars with global impacts

International audienceThe unicellular eukaryotes (also called protists) that inhabit the contemporary oceans have large impacts on major biogeochemical cycles. Populations of oceanic protists are to a large extent regulated by their viral parasites, especially nucleocytoplasmic large DNA viruses (NCLDVs). NCLDVs can themselves be the prey of smaller viruses called virophages and can also be infected by transposable elements termed transpovirons. These entangled parasitisms have fostered the emergence of sophisticated infection and defence strategies. In addition persistent contact has facilitated the exchange of genes between different parties. Recent advances shed light on the strategies that govern such microbial wars. Endogenous virophage-like elements found in the genome of a marine alga could for instance provide the host acquired immunity against NCLDVs. In return, it was recently speculated that virophage sequences can be hijacked by NCLDVs and used as genetic weapons against virophages