Multi-Fluid Simulations of Upper Chromospheric Magnetic Reconnection with Helium-Hydrogen mixture

Our understanding of magnetic reconnection (MR) under chromospheric conditions remains limited. Recent observations have demonstrated the important role of ion-neutral interactions in the dynamics of the chromosphere. Furthermore, the comparison between spectral profiles and synthetic observations of reconnection events suggest that current MHD approaches appear to be inconsistent with observations. First, collisions and multi-thermal aspects of the plasma play a role in these regions. Second, hydrogen and helium ionization effects are relevant to the energy balance of the chromosphere. This work investigates multi-fluid multi-species (MFMS) effects on MR in conditions representative of the upper chromosphere using the multi-fluid Ebysus code. We compare an MFMS approach based on a helium-hydrogen mixture with a two-fluid MHD model based on hydrogen only. The simulations of MRs are performed in a Lundquist number regime high enough to develop plasmoids and instabilities. We study the evolution of the MR and compare the two approaches including the structure of the current sheet and plasmoids, the decoupling of the particles, the evolution of the heating mechanisms, and the composition. The presence of helium species leads to more efficient heating mechanisms than the two-fluid case. This scenario, which is out of reach of the two-fluid or single-fluid models, can reach transition region temperatures starting from upper chromospheric thermodynamic conditions, representative of a quiet Sun scenario. The different dynamics between helium and hydrogen species could lead to chemical fractionation and, under certain conditions, enrichment of helium in the strongest outflows. This could be of significance for recent observations of helium enrichment in the solar wind in switchbacks and CMEs

Study of the compatibility between criteria in a set of materials requirements: Application to a machine tool.

International audienceThis contribution to materials selection theory aims at developing methodological methods and tools to analyse a complex set of material requirements with the objective of forecast whether there are materials that can fulfil it, or alternatively, if multi-materials selection is more likely to provide a solution. This "pre-analysis" of requirements examines the two main reasons which may prevent a single material solution: nonuniformity of materials space filling, or intrinsic contradiction between properties. A variety of statistical tools is used, based on Multivariate Analysis Methods as Principal Component Analysis (PCA) and the estimation of density distribution in the materials space. These tools allow to evaluate the "statistical compatibility" between the requirements and the available materials, and provides an estimate of the likelihood to find a single material solution or not. The methodology is applied to the research of a material for a machine tool frame

Tolerance synthesis of fastened metal-composite joints based on probabilistic and worst case approaches

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Determination of Materials Selection Performance Indices Through the Combination of Numerical Modeling and Optimization Methods.

International audienceAfter translation, the first stages traditionally involved in the materials selection are filtration and classification, which require formulation of criteria (constraints or objectives) deduced from information written in the set Of material requirements. These criteria, which are representative of the behavior of the material and the studied structure, must be formulated analytically in order to be used during selection stage. However, for complex behavior, analytical processing of models is no longer possible and it can be replaced by a combination of numerical resolution methods and an optimization method which make it possible to obtain approximate formal expressions of the criteria. In this paper, a complete selection method is proposed. The method is applied to the constraints as well as the objectives, in order to carry out the filtration and classification stages at the same time. The study of the thermomechanical behavior of a machine tool frame has been used to demonstrate the validity of the proposed method

Proposal for a multi-material design procedure

International audienceThis paper describes a proposal for a multi-material design procedure. First, the context of the study and the requirements of the multi-material must be clearly defined in order to specify the parameters that the designer must select or optimise in order to produce the design: the components and their volume fraction, the architecture and morphology at different scales, etc. The general design procedure proposed here starts with the reasons why the designer has turned to multi-materials, from which a multi-material concept with fixed parameters can be defined. In this first stage the design problem can be made less complex by reducing the number of unknown parameters and guiding the designer towards the appropriate selection or optimisation tools: (i) subdivision of requirements, guided by applying statistical analysis tools to the materials database to search for appropriate multi-material components, (ii) tools to filter the materials database and search for multi-material components and their volume fraction, (iii) optimisation tools to search for the appropriate architecture when components are known or to search for architecture and components simultaneously. The paper demonstrates how these tools can be applied to different design concepts

Mycobacteriosis in the compromised host

The studies of rare genetic defects, the preliminary results of population-based studies, being validated by the experimental immunocompromised animal models and the current observations accumulated in immunocompromised patients with mycobacterial diseases provide us with insights into the importance of the macrophage activation pathway in controlling human infection with pathogenic and non pathogenic intracellular multiplying mycobacteria. Initial cytokine production by infected macrophages and/or dendritic cells could be crucial in the overall regulation of self cure, acquired protection or immunopathological sequelae expressing the disease. Knowledge of molecular and genetic cross-talks between phagocytic and specialized antigen presenting cells and different mycobacterial products associated with persistence or replication of the intracellular bacteria, could provide further informations on the global immune regulation of the early host responses to infection and the following events. It seems likely that the development of mycobacterial infections in humans will turn out to be as much dependent on the genetic make up of the host as or the virulence of the bacteria

Multifluid Simulations of Upper-chromospheric Magnetic Reconnection with Helium–Hydrogen Mixture

Our understanding of magnetic reconnection (MR) under chromospheric conditions remains limited. Recent observations have demonstrated the important role of ion–neutral interactions in the dynamics of the chromosphere. Furthermore, the comparison between the spectral profiles and synthetic observations of reconnection events suggests that current MHD approaches appear to be inconsistent with observations. First, collisions and multithermal aspects of the plasma play a role in these regions. Second, hydrogen and helium ionization effects are relevant to the energy balance of the chromosphere. This work investigates the multifluid multispecies (MFMS) effects on MR in conditions representative of the upper chromosphere using the multifluid Ebysus code. We compare an MFMS approach based on a helium–hydrogen mixture with a two-fluid MHD model based on hydrogen only. The simulations of MR are performed in a Lundquist number regime high enough to develop plasmoids and instabilities. We study the evolution of the MR and compare the two approaches including the structure of the current sheet and plasmoids, the decoupling of the particles, the evolution of the heating mechanisms, and the composition. The presence of helium species leads to more efficient heating mechanisms than the two-fluid case. This scenario, which is out of reach of the two-fluid or single-fluid models, can reach transition region temperatures starting from upper-chromospheric thermodynamic conditions, representative of a quiet Sun scenario. The different dynamics between helium and hydrogen species could lead to chemical fractionation and, under certain conditions, enrichment of helium in the strongest outflows. This could be of significance for recent observations of helium enrichment in the solar wind in switchbacks and coronal mass ejections

The Impact of Multifluid Effects in the Solar Chromosphere on the Ponderomotive Force under SE and NEQ Ionization Conditions

The ponderomotive force has been suggested to be the main mechanism to produce the so-called first ionization potential (FIP) effect—the enrichment of low-FIP elements observed in the outer solar atmosphere, in the solar wind, and in solar energetic events. It is well known that the ionization of these elements occurs within the chromosphere. Therefore, this phenomenon is intimately tied to the plasma state in the chromosphere and the corona. For this study, we combine IRIS observations, a single-fluid 2.5D radiative magnetohydrodynamics (MHD) model of the solar atmosphere, including ion–neutral interaction effects and nonequilibrium (NEQ) ionization effects, and a novel multifluid multispecies numerical model (based on the Ebysus code). Nonthermal velocities of Si iv measured from IRIS spectra can provide an upper limit for the strength of any high-frequency Alfvén waves. With the single-fluid model, we investigate the possible impact of NEQ ionization within the region where the FIP may occur, as well as the plasma properties in those regions. These models suggest that regions with strongly enhanced network and type II spicules are possible sites of large ponderomotive forces. We use the plasma properties of the single-fluid MHD model and the IRIS observations to initialize our multifluid models to investigate the multifluid effects on the ponderomotive force associated with Alfvén waves. Our multifluid analysis reveals that collisions and NEQ ionization effects dramatically impact the behavior of the ponderomotive force in the chromosphere, and existing theories may need to be revisited

Phobos photometric properties from Mars Express HRSC observations

International audienceThis study aims to analyze Phobos’ photometric properties using Mars Express mission observations to support the MartianMoons eXploration mission (MMX) devoted to the investigation of the Martian system and to the return of Phobos samples.Methods. We analyzed resolved images of Phobos acquired between 2004 and 2022 by the High Resolution Stereo Camera (HRSC)on board the Mars Express spacecraft at a resolution ranging from ∼ 30 m px−1 to 330 m px−1. We used data acquired with theblue, green, red, and IR filters of HRSC and the panchromatic data of the Super Resolution Channel (SRC). The SRC data areunique because they cover small phase angles (0.2-10o), permitting the investigation of the Phobos opposition effect. We simulatedillumination and geometric conditions for the different observations using the Marx Express and the camera spice kernels providedby the HRSC team. We performed photometric analysis using the Hapke model for both integrated and disk-resolved data.Results. The Phobos phase function is characterized by a strong opposition effect due to shadow hiding, with an amplitude and a half-width of the opposition surge of 2.28±0.03 and 0.0573±0.0001, respectively. Overall, the surface of Phobos is dark, with a geometricalbedo of 6.8 % in the green filter and backscattering. Its single-scattering albedo (SSA) value (7.2% in the green filter) is much higherthan what has been found for primitive asteroids and cometary nuclei and is close to the values reported in the literature for Ceres. Wealso found a surface porosity of 87%, indicating the presence of a thick dust mantle or of fractal aggregates on the top surface. TheSSA maps revealed high reflectance variability, with the blue unit area in the northeast Stickney rim being up to 65% brighter thanaverage, while the Stickney floor is among the darkest regions, with reflectance 10 to 20% lower than average. Photometric modelingof the regions of interest selected in the red and blue units indicates that red unit terrains have a stronger opposition effect and asmaller SSA value than the blue ones, but they have similar porosity and backscattering properties.Conclusions. The HRSC data provide a unique investigation of the Phobos phase function and opposition surge, which is valuableinformation for the MMX observational planning. The Phobos opposition surge, surface porosity, phase integral, and spectral slopeare very similar to the values observed for the comet 67P and for Jupiter family comets in general. Based on these similarities, weformulate a hypothesis that the Mars satellites might be the results of a binary or bilobated comet captured by Mars