Direct Numerical Simulation and Wall-Resolved Large Eddy Simulation in Nuclear Thermal Hydraulics

International audienceThe critical review discusses the most accurate methods for description of turbulent flows: the computationally very expensive direct numerical simulation (DNS) and slightly less accurate and slightly less expensive large eddy simulation (LES) methods. Both methods have found their way into nuclear thermal hydraulics as tools for studies of the fundamental mechanisms of turbulence and turbulent heat transfer. In the first section of this critical review, both methods are briefly introduced in parallel with the basic properties of the turbulent flows. The focus is on the DNS method, the so-called quasi-DNS approach, and the coarsest turbulence modeling approach discussed in this work, which is still on the very small-scale, wall-resolved LES. Other, coarser turbulence modeling approaches (such as wall-modeled LES, Reynolds Averaged Navier-Stokes (RANS)/LES hybrids, or RANS) are beyond the scope of the present work. Section II answers the question: "How do the DNS and LES methods work?" A short discussion of the computational requirements, numerical approaches, and computational tools is included. Section III is about the interpretation of the DNS and LES results and statistical uncertainties. Sections IV and V give some examples of the DNS and wall-resolved LES results relevant for nuclear thermal hydraulics. The last section lists the conclusions and some of the challenges that might be tackled with the most accurate techniques like DNS and LES

Le choix lexical en français langue seconde : fondements empiriques et réflexions didactiques

Ce mémoire propose des pistes pour l'enseignement du choix lexical en français langue seconde au niveau intermédiaire-avancé fondées sur une analyse de corpus d'apprenants. L'analyse des erreurs lexicales dans un corpus de productions écrites a permis de dégager des catégories d'erreurs de choix lexical. Cinq catégories d'erreurs de nature sémantique sont caractérisées à l'aide de notions linguistiques, pour être utilisées dans une séquence didactique. Cette séquence comprend la présentation d’un « espace de décision » pour le choix lexical associée à une prise de conscience des paramètres intervenant dans le choix lexical, une démarche d'autocorrection avec utilisation des codes issus de l'analyse du corpus et de stratégies d'autocorrection et enfin un travail sur des champs lexicaux. En effet, la compétence dans le choix lexical dépend à la fois des mots considérés individuellement et des mots insérés dans un réseau lexical

Création de bases de données fines par simulation directe pour les effets de la turbulence sur les transferts thermiques pariétaux

This study focuses on the turbulent heat transfer in the turbulent channel flow configuration. Our Direct Numerical Simulations are performed using the open-source code Incompact3d. As our target is to produce data for RANS models validation, the budgets of the turbulent heat fluxes and of the temperature variance are extracted. Two-point correlations for the temperature and wall-normal heat flux are also presented to deepen our analysis. Regarding the thermal field, 2 configurations are considered: with and without conjugate heat transfer (thermal coupling between the fluid and solid domains). For conjugate heat transfer cases, a novel compatiblity condition, expressed in the spectral space, connects the temperature and wall-normal heat flux at the fluid-solid interface. For non-conjugate cases, our study is limited to boundary conditions that impose a linear combination of the temperature and wall-normal heat flux at the wall using constant coefficients (Dirichlet, Neumann, Robin). For such simple boundary conditions, a novel compatibility condition is obtained which connects the wall-value of the temperature variance and the wall-normal part of the associated dissipation rate. On one hand, this condition highlights the limitations of an imposed temperature or heat-flux at the wall. On the other, it allows us to build tailored Robin boundary conditions able to reproduce satisfactorily present conjugate heat-transfer results in the channel flow configuration.Cette étude porte sur le transfert thermique pariétal dans un canal plan turbulent. L’étude est théorique et numérique. Nos simulations directes (DNS) sont effectuées avec le code de calcul Incompact3d. On a porté un intérêt particulier aux grandeurs que l’on trouve dans les bilans des flux thermiques turbulents et de la variance de la température : ces données permettent de valider les modèles de type RANS. On analyse également nos simulation à l’aune de statistiques plus fines, telles que les corrélations en 2 points. On distingue 2 traitements de la thermique dans le cas ducanal plan turbulent : avec ou sans prise en compte du transfert thermique conjugué (couplage thermique fluide/solide). Pour les cas avec transfert thermique conjugué, on a mis en évidence une condition de compatibilité dans l’espace spectral entre la température et le flux de chaleur à l’interface fluide-solide. En l’absence de transfert thermique conjugué, notre étude se borne aux conditions limites qui sont une combinaison linéaire à coefficients constants de la température et du flux de chaleur à la paroi (Dirichlet, Neumann, Robin). Pour ces conditions aux limites simples, on met en évidence une condition de compatibilité entre les valeurs pariétales de la variance de la température et la partie normale de la dissipation associée. D’une part, cette relation souligne les limites des simulations avec une température ou un flux imposé à la paroi. D’autre part, elle permet de construire des conditions de type Robin sur-mesure qui donnent des résultats proches de ceux obtenus avec transfert thermique conjugué pour la configuration du canal plan turbulent

The 2DECOMP&FFT library: an update with new CPU/GPU capabilities

The 2DECOMP&FFT library is a software framework written in modern Fortran to build large-scale parallel applications. It is designed for applications using three-dimensional structured meshes with a particular focus on spatially implicit numerical algorithms. However, the library can be easily used with other discretisation schemes based on a structured layout and where pencil decomposition can apply. It is based on a general-purpose 2D pencil decomposition for data distribution and data Input Output (I/O). A 1D slab decomposition is also available as a special case of the 2D pencil decomposition. The library includes a highly scalable and efficient interface to perform three-dimensional Fast Fourier Transforms (FFTs). The library has been designed to be user-friendly, with a clean application programming interface hiding most communication details from application developers, and portable with support for modern CPUs and NVIDIA GPUs (support for AMD and Intel GPUs to follow)

Diffuse cutaneous mastocytosis with novel somatic KIT mutation K509I and association with tuberous sclerosis.

Diffuse cutaneous mastocytosis (DCM) is a rare but potentially fatal condition when diagnosis and targeted treatments are delayed. This case illustrates the life-threatening complications in DCM and reviews the currently available treatments. To our knowledge, this is the first report of mastocytosis with somatic K509I mutation and concomitant tuberous sclerosis

Vallée de la Cèze

En 2015, les prospections diachroniques menées par le CFRA, se sont poursuivies sur la commune de Verfeuil (Gard). L’étude de deux nouvelles sections cadastrales (OD et OE) a permis de recenser cinq sites du Moyen Âge : les vestiges du village médiéval : château, beffroi, posterle, remparts (mentionnés en 1121) ; le site de surface de la Terre de l’Aire (probable emplacement de l’ancien prieuré et de son cimetière) ; la Tour de Marcuel (mentionnée en 1211) Cette tour encore en élévation est i..

Transient Increase in Intrahepatic Pressure Mediates Successful Treatment of the Gunn Rat with Reduced Doses of Lentiviral Vector

Lentiviral vectors can stably transduce hepatocytes and are promising tools for gene therapy of hepatic diseases. Although hepatocytes are accessible to blood-borne viral vectors through fenestrations of the hepatic endothelium, improved liver transduction after delivery of vectors to the blood stream is needed. As the normal endothelial fenestration and lentiviral vectors are similar in size (150 nm), we hypothesized that a transient increase in hepatic blood pressure may enhance in vivo gene transfer to hepatocytes. We designed a simple surgical procedure, by which the liver is temporarily excluded from blood flow. Lentiviral vectors were injected in a large volume to increase intrahepatic pressure. We demonstrated that in the Gunn rat, a model of Crigler–Najjar disease, the administration of low vector doses (corresponding to a multiplicity of infection of 0.2) by this procedure resulted in therapeutic correction of hyperbilirubinemia, without toxicity. The correction was sustained for 10 months (end of study). The same vector amounts yielded only partial correction after intraportal delivery. We believe that this new and clinically applicable strategy may broaden the range of genetic liver diseases accessible to gene therapy

On the origin of leprosy.

International audienceLeprosy, a chronic human disease with potentially debilitating neurological consequences, results from infection with Mycobacterium leprae. This unculturable pathogen has undergone extensive reductive evolution, with half of its genome now occupied by pseudogenes. Using comparative genomics, we demonstrated that all extant cases of leprosy are attributable to a single clone whose dissemination worldwide can be retraced from analysis of very rare single-nucleotide polymorphisms. The disease seems to have originated in Eastern Africa or the Near East and spread with successive human migrations. Europeans or North Africans introduced leprosy into West Africa and the Americas within the past 500 years

Infectious Bronchitis Coronavirus: Genome Evolution in Vaccinated and Non-Vaccinated SPF Chickens

Infectious Bronchitis virus (IBV) continues to cause significant economic losses for the chicken industry despite the use of many live IBV vaccines around the world. Several authors have suggested that vaccine-induced partial protection may contribute to the emergence of new IBV strains. In order to study this hypothesis, three passages of a challenge IBV were made in SPF chickens sham inoculated or vaccinated at day of age using a live vaccine heterologous to the challenge virus. All birds that were challenged with vaccine heterologous virus were positive for viral RNA. NGS analysis of viral RNA in the unvaccinated group showed a rapid selection of seven genetic variants, finally modifying the consensus genome of the viral population. Among them, five were non-synonymous, modifying one position in NSP 8, one in NSP 13, and three in the Spike protein. In the vaccinated group, one genetic variant was selected over the three passages. This synonymous modification was absent from the unvaccinated group. Under these conditions, the genome population of an IBV challenge virus evolved rapidly in both heterologous vaccinated and non-vaccinated birds, while the genetic changes that were selected and the locations of these were very different between the two groups

Lentiviral Vectors That Express UGT1A1 in Liver and Contain Mir-142 Target Sequences Normalize Hyperbilirubinemia in Gunn Rats

Background & AimsCrigler–Najjar type 1 (CN-I) is an inherited liver disease caused by an absence of bilirubin–uridine 5′-diphosphate–glucuronosyltransferase (UGT1A1) activity. It results in life-threatening levels of unconjugated bilirubin, and therapeutic options are limited. We used adult Gunn rats (an animal model of the disease) to evaluate the efficiency of lentiviral-based gene therapy to express UGT1A1 in liver. Methods Gunn rats were given intraportal injections of VSVG-pseudotyped lentiviral vectors that encode UGT1A1 under the control of a liver-specific transthyretin promoter (mTTR.hUGT1A1); this vector does not contain target sequences for miR-142, a microRNA that is expressed specifically in hematopoietic cells. Rats were also injected with the vector mTTR.hUGT1A1.142T, which contains 4 copies of the miR-142 target sequences; its messenger RNA should be degraded in antigen-presenting cells. Bilirubinemia was monitored, and the presence of transduced hepatocytes was analyzed by quantitative polymerase chain reaction. Vector expression was tested in vitro in rat hematopoietic cells. Results In Gunn rats, bilirubin levels normalized 2 weeks after administration of mTTR.hUGT1A1. However, hyperbilirubinemia resumed 8 weeks after vector administration, concomitant with the induction of an immune response. In contrast, in rats injected with mTTR-UGT1A1.142T, bilirubin levels normalized for up to 6 months and transduced cells were not eliminated. Conclusions Lentiviral vectors that express UGT1A1 reduce hyperbilirubinemia in immunocompetent Gunn rats for at least 6 months. The immune response against virally expressed UGT1A1 can be circumvented by inclusion of miR-142 target sequences, which reduce vector expression in antigen-presenting cells. This lentiviral-based gene therapy approach might be developed to treat patients with CN-I