Strongly coupled fluid-particle flows in vertical channels. II. Turbulence modeling

In Part I, simulations of strongly coupled fluid-particle flow in a vertical channel were performed with the purpose of understanding, in general, the fundamental physics of wall-bounded multiphase turbulence and, in particular, the roles of the spatially correlated and uncorrelated components of the particle velocity.The exact Reynolds-averaged (RA) equations for high-mass-loading suspensions were presented, and the unclosed terms that are retained in the context of fully developed channel flow were evaluated in an Eulerian–Lagrangian (EL) framework. Here, data from the EL simulations are used to validate a multiphase Reynolds-stress model (RSM) that predicts the wall-normal distribution of the two-phase, one-point turbulence statistics up to second order. It is shown that the anisotropy of the Reynolds stresses both near the wall and far away is a crucial component for predicting the distribution of the RA particle-phase volume fraction. Moreover, the decomposition of the phase-average (PA) particle-phase fluctuating energy into the spatially correlated and uncorrelated components is necessary to account for the boundary conditions at the wall. When these factors are properly accounted for in the RSM, the agreement with the EL turbulence statistics is satisfactory at first order (e.g., PA velocities) but less so at second order (e.g., PA turbulent kinetic energy). Finally, an algebraic stress model for the PA particle-phase pressure tensor and the Reynolds stresses is derived from the RSM using the weak-equilibrium assumption

Identification of Cryptic MHC I–restricted Epitopes Encoded by HIV-1 Alternative Reading Frames

Human immunodeficiency virus (HIV) 1 major histocompatibility complex (MHC) I–restricted epitopes are widely believed to be derived from viral proteins encoded by primary open reading frames. However, the HIV-1 genome contains alternative reading frames (ARFs) potentially encoding small polypeptides. We have identified a panel of epitopes encoded by ARFs within the gag, pol, and env genes. The corresponding epitopic peptides were immunogenic in mice humanized for MHC-I molecules. In addition, cytotoxic T lymphocytes recognizing these epitopes were found in HIV-infected patients. These results reveal the existence of atypical mechanisms of HIV-1 epitope generation. They indicate that the repertoire of epitopes recognized by the cellular anti–HIV-1 immune response is broader than initially thought. This should be taken into account when designing vaccine strategies aimed at activating these responses

X-point and divertor filament dynamics from Gas Puff Imaging on TCV

A new Gas Puff Imaging (GPI) diagnostic has been installed on the TCV tokamak, providing two-dimensional insights into Scrape-Off-Layer (SOL) turbulence dynamics above, at and below the magnetic X-point. A detailed study in L-mode, attached, lower single-null discharges shows that statistical properties have little poloidal variations, while vast differences are present in the 2D behaviour of intermittent filaments. Strongly elongated filaments, just above the X-point and in the divertor far-SOL, show a good consistency in shape and dynamics with field-line tracing from filaments at the outboard midplane, highlighting their connection. In the near-SOL of the outer divertor leg, shortlived, high frequency and more circular (diameter $\sim$15 sound Larmour radii) filaments are observed. These divertor-localised filaments appear born radially at the position of maximum density and display a radially outward motion with velocity $\approx$400\,m/s that is comparable to radial velocities of upstream-connected filaments. Conversely, in these discharges ($B\times\nabla B$ pointing away from the divertor), these divertor filaments' poloidal velocities differ strongly from those of upstream-connected filaments. The importance of divertor-localised filaments upon radial transport and profile broadening is explored using filament statistics and in-situ kinetic profile measurements along the divertor leg. This provides evidence that these filaments contribute significantly to electron density profile broadening in the divertor.Comment: This is the version of the article before peer review or editing, as submitted by an author to IOPScience Nuclear Fusion. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. 15 pages, 15 figure

Pediatric Measles Vaccine Expressing a Dengue Antigen Induces Durable Serotype-specific Neutralizing Antibodies to Dengue Virus

Dengue disease is an increasing global health problem that threatens one-third of the world's population. Despite decades of efforts, no licensed vaccine against dengue is available. With the aim to develop an affordable vaccine that could be used in young populations living in tropical areas, we evaluated a new strategy based on the expression of a minimal dengue antigen by a vector derived from pediatric live-attenuated Schwarz measles vaccine (MV). As a proof-of-concept, we inserted into the MV vector a sequence encoding a minimal combined dengue antigen composed of the envelope domain III (EDIII) fused to the ectodomain of the membrane protein (ectoM) from DV serotype-1. Immunization of mice susceptible to MV resulted in a long-term production of DV1 serotype-specific neutralizing antibodies. The presence of ectoM was critical to the immunogenicity of inserted EDIII. The adjuvant capacity of ectoM correlated with its ability to promote the maturation of dendritic cells and the secretion of proinflammatory and antiviral cytokines and chemokines involved in adaptive immunity. The protective efficacy of this vaccine should be studied in non-human primates. A combined measles–dengue vaccine might provide a one-shot approach to immunize children against both diseases where they co-exist

Modélisation globale du contrôle des îlots magnétiques dans les tokamaks

Magneto-Hydro-Dynamic (MHD) instabilities are susceptible to develop within a tokamak plasma. These instabilities manifest themselves as magnetic islands which reduce the plasma confinement. The islands can however be controlled by driving current inside them. In this thesis, we consider the modeling of the magnetic islands and their control using first principle approaches, which rely on a global MHD description of the plasma. We have detailed the inclusion a RF-driven current like source term in an MHD code, which requires special care to be given to the modeling of the current density evolution. The implementation has been benchmarked against the asymptotic models, allowing us to retrieve the influence of parameters such as deposition width or misalignment with respect to the island width and position. Beyond these aspects, we have evidenced new effects, linked to the 3D nature of the current deposition. We have observed a flip instability in which an island, reduced by the ECCD, brutally inverse its phase so that its X-Point faces the current deposition, allowing the mode the grow further. We then moved on to the topic of the best suitable control strategies for the control of the island. We have implemented in XTOR a control system that mimics the experimental ones and adapt the current deposition in function of a preset strategy. Nonlinear MHD simulations have been carried out using different control schemes, allowing us to quantify the gain to expect from each of these methods depending on the characteristics of the current deposition.Dans les plasmas de tokamak peuvent se développer des instabilités MHD (Magneto-Hydro-Dynamiques) se manifestant sous la forme d’îlots magnétiques qui réduisent le confinement. Ces îlots peuvent être contrôlés par la génération localisée de courant dans le plasma. Dans cette thèse, nous nous intéressons à la modélisation des îlots magnétiques et de leur contrôle en utilisant une description fluide (MHD) du plasma, à l’aide du code XTOR. Nous détaillons l'inclusion d'une source de courant au sein du modèle MHD, ce qui nécessite l'ajout d'une équation supplémentaire pour modéliser la propagation de la densité de courant le long des lignes de champ magnétique. Cette implémentation est ensuite vérifiée sur la base de modèles analytiques, nous permettant de retrouver l'influence de paramètres tels que la largeur du dépôt ou son désalignement. Nous avons mis en évidence des effets non-décrits par les modèles asymptotiques, liés à la nature de la localisation spatiale de la source de courant. Nous nous sommes ensuite intéressés aux stratégies de contrôle envisageable pour la suppression des îlots. Nous avons ajouté au sein du code XTOR un système de contrôle qui ajuste le dépôt de courant selon les stratégies choisies. Des simulations MHD non-linéaires des différents schémas de contrôle ont été effectuées, et les différentes stratégies comparées, permettant de préciser pour chacune une gamme d’intérêt

Les dirigeants de collectivités territoriales françaises confrontés à la gestion opérationnelle des cybermenaces : une approche typologique

Data assessing the extent to which local authority managers take into account the security of theirinformation systems (IS) are rare in general andnon-existent in France. Yet this security is a major strategic imperative that goes beyond the local level, as shown by the constant increase in cyberattacks against local authorities - including small ones - since the beginning of the Covid crisis19.The theoretical underpinnings of this article are based on the work related to the adoption and appropriation of digital tools in TOE mode by Tor-natzky and Fleischer (1990), on that related to digital risks in public organisations by Norris et al. (2019) as well as on that related to cyberattacksby Février (2020). It is empirically based on data from the only survey specifically carried out to date on cybersecurity among 67 managers of local au-thorities with fewer than 3,500 inhabitants, with a statistical treatment that is successively descriptive and by hierarchical classification. The articleasks the question of the 'why' of this vulnerability by deciphering the obstacles delaying the deployment of a real IS security policy for local autho-rities. The analysis carried out tends to highlight worrying gaps in the awareness of the reality of digital risks by territorial decision-makers and pro-poses a typology of the profiles of local authorities’ leaders in relation to digital risk management. The objective is to contribute to the operationalization by the public authorities of a proactive approach of structural security of territorial IS as well as of citizens' personal data.Les données évaluant la prise en compte par les dirigeants de collectivités territoriales de la Sécurité de leurs Systèmes d’Information (SSI) sont rares en général et quasiment inexistantes en France. Dans le même temps, cette sécurisation constitue un impératif stratégique majeur qui dépasse le simple cadre local au regard de l’augmentation constante des cyberattaques contre des collectivités – y compris de taille modeste – depuis le début de la crise sanitaire. Cet article s’intéresse en partie à ce paradoxe et tente de combler ce gap. Les fondements théoriques de cette recherche reposent sur trois piliers, les travaux liés à l’adoption et à l’appropriation des outils numériques en mode TOE de Tornatzky et Fleischer (1990), les travaux sur les risques numériques en organisation publique de Norris et al. (2019) et les travaux liés à la prévention des cyberattaques de Février (2020). Il est empiriquement fondé sur les données de l’unique enquête spécifiquement réalisée à ce jour en cybersécurité auprès de 67 dirigeants de collectivités de moins de 3 500 habitants avec un traitement statistique successivement descriptif puis par classification hiérarchique. L’article pose la question du « pourquoi » de cette vulnérabilité en décryptant les freins retardant le déploiement d’une véritable politique de sécurisation des SI des collectivités territoriales. L’analyse menée tend à mettre en évidence certaines lacunes en matière de prise de conscience de la réalité des risques numériques par les décideurs territoriaux et propose une typologie des profils de dirigeants de collectivités relativement au management des risques numériques. L’objectif poursuivi est de contribuer à l’opérationnalisation par les pouvoirs publics d’une démarche volontariste de sécurisation structurelle des SI territoriaux ainsi que des données à caractère personnel des citoyens

Stratégies de stabilisation des îlots magnétiques établies par des simulations Magnéto-Hydro-Dynamiques

International audienceThe degradation of plasma confinement in tokamaks by magnetic islands motivates to better understand their possible suppression using Electron Cyclotron Current Drive (ECCD) and to investigate the various strategies relevant for this purpose. In this work, we evaluate the efficiency of several control methods through nonlinear simulations of this process with the toroidal MHD code XTOR Lütjens and Luciani (2010), which has been extended to incorporate in Ohm's law a source term model-ing the RF driven current resulting from the interaction of the RF waves with the plasma. A basic control system has been implemented in the code, allowing testing advanced strategies that require feedback on island position or phase. We focus in particular on the robustness of the control strategies towards the uncertainties that apply on the control and ECCD systems, such as the risk of misalignment of the current deposition or the possible inability to generate narrow current deposition

Non-Linear Simulations of Neoclassical Tearing Mode Control by Externally Driven RF Current and Heating, with application to ITER

International audienceNeoclassical Tearing Modes (NTM) must be controlled or suppressed to prevent a degradation of the energy confinement in tokamak plasmas. This can be done applying RF-current via Electron Cyclotron Current Drive (ECCD) and-heating (ECRH) at the rational surface where the instability appears. Both the current and heating generated by the RF waves are known to provide a stabilizing effect on the magnetic island. In the present work, we address the issue of Neoclassical Tearing Mode stabilization by Heating and Current Drive in an ITER-like configuration, using a stiff transport model. From a revised Generalized Rutherford Equation, we revisit the criterion on the RF current and power required to stabilize an NTM, showing that the level of plasma background heating (residual heat sources) in ITER significantly lowers the benefit of the RF heating contribution. Nonlinear MagnetoHydroDynamic simulations with the XTOR code, where a stiff transport model as well as RF-power and-current drive are implemented, are performed to compute the NTM stabilization efficiency. The stabilization efficiency due to the RF current contribution is found to be less than theoretically predicted in the case of continuous application, but consistent with theory in the modulated control scheme, suggesting an enhanced destabilization at the X-point. The role of RF heating for continuous application is found to be moderate for the range of power envisaged in ITER, essentially because of the detrimental effect of residual heat sources. This numerical work confirms the capability of the ITER RF system to control the (3, 2) NTM, with a larger confidence for the modulated control scheme

Stabilization of a magnetic island by localized heating in a tokamak with stiff temperature profile

International audienceIn tokamaks plasmas, turbulent transport is triggered above a threshold in the temperature gradient and leads to stiff profiles. This particularity, neglected so far in the problem of magnetic island stabilization by a localized heat source, is investigated analytically in the present paper. We show that the efficiency of the stabilization is deeply modified compared to previous estimates due to the strong dependence of the turbulence level on the additional heat source amplitude inside the island