Semi-implicit two-speed Well-Balanced relaxation scheme for Ripa model

In this paper, we propose a semi-implicit well-balanced scheme for the Ripa model based on a two-speed relaxation. The method both preserves equilibria and has an implicit step that reduces to the inversion of a constant Laplacian. Numerical simulations show that the scheme well capture low-Froude flows

Simulation of a liquid-vapour compressible flow by a Lattice Boltzmann Method

International audienceThis work is devoted to the numerical resolution of a compressible three-phase flow with phase transition by a Lattice-Boltzmann Method (LBM). The flow presents complex features and large variations of physical quantities. The LBM is a robust numerical method that is entropy stable and that can be extended to second order accuracy without additional numerical cost. We present preliminary numerical results, which confirm its competitiveness compared to other Finite Volume methods

DMTs and Covid-19 severity in MS: a pooled analysis from Italy and France

We evaluated the effect of DMTs on Covid-19 severity in patients with MS, with a pooled-analysis of two large cohorts from Italy and France. The association of baseline characteristics and DMTs with Covid-19 severity was assessed by multivariate ordinal-logistic models and pooled by a fixed-effect meta-analysis. 1066 patients with MS from Italy and 721 from France were included. In the multivariate model, anti-CD20 therapies were significantly associated (OR = 2.05, 95%CI = 1.39–3.02, p < 0.001) with Covid-19 severity, whereas interferon indicated a decreased risk (OR = 0.42, 95%CI = 0.18–0.99, p = 0.047). This pooled-analysis confirms an increased risk of severe Covid-19 in patients on anti-CD20 therapies and supports the protective role of interferon

Search for dark matter candidates and large extra dimensions in events with a jet and missing transverse momentum with the ATLAS detector

Open Access, Copyright CERN, for the benefit of the ATLAS collaboration. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited

Kinetic simulations of the Chodura and Debye sheaths for magnetic fields with grazing incidence

International audienceWhen an unmagnetized plasma comes in contact with a material surface, the difference in mobility between the electrons and the ions creates a nonneutral layer known as the Debye sheath (DS). However, in magnetic fusion devices, the open magnetic field lines intersect the structural elements of the device with near grazing incidence angles. The magnetic field tends to align the particle flow along its own field lines, thus counteracting the mechanism that leads to the formation of the DS. Recent work using a fluid model [P. Stangeby, Nucl. Fusion 52, 083012 (2012)] showed that the DS disappears when the incidence angle is smaller than a critical value (around 5 • for ITER-like parameters). Here, we study this transition by means of numerical simulations of a kinetic model both in the collisionless and weakly collisional regimes. We show that the main features observed in the fluid model are preserved: for grazing incidence, the space charge density near the wall is reduced, the ion flow is subsonic, and the electric field and plasma density profiles are spread out over several ion Larmor radii instead of a few Debye lengths as in the unmagnetized case. As there is no singularity at the DS entrance in the kinetic model, this phenomenon depends smoothly on the magnetic field incidence angle and no particular critical angle arises. The simulation results and the predictions of the fluid model are in good agreement, although some discrepancies subsist, mainly due to the assumptions of isothermal closure and diagonality of the pressure tensor in the fluid model

Microbial Evolution Drives Adaptation of Substrate Degradation on Decadal to Centennial Time Scales Relevant to Global Change

International audienceUnderstanding microbial adaptation is crucial for predicting how soil carbon dynamics and global biogeochemical cycles will respond to climate change. This study employs the DEMENT model of microbial decomposition, along with empirical mutation and dispersal rates, to explore the roles of mutation and dispersal in the adaptation of soil microbial populations to shifts in litter chemistry, changes that are anticipated with climate-driven vegetation dynamics. Following a change in litter chemistry, mutation generally allows for a higher rate of litter decomposition than dispersal, especially when dispersal predominantly introduces genotypes already present in the population. These findings challenge the common idea that mutation rates are too low to affect ecosystem processes on ecological timescales. These results demonstrate that evolutionary processes, such as mutation, can help maintain ecosystem functioning as the climate changes.</div

Implicit time schemes for compressible fluid models based on relaxation methods

International audienceIn this work, we are interested in the implicit discretization of compressible fluid models. When applied to this type of models, standard implicit schemes suffer from a lack of efficiency due to the ill-conditioning of the associated matrices. In this paper we propose an alternative strategy based on a relaxation method coupled with an implicit scheme. This method allows us to approximate the full complex problem by a collection of simpler ones than we can solve with standard methods. We obtain eventually a second order implicit method with some additional parallelism able to treat hyperbolic systems with small diffusion

Laser Ultrasonics NDE of Two-Layered Samples

The new structures developed in industry are more and more complex (special coatings, smart materials, etc⋯) and often need to be investigated by non-contact methods. Laser Based Ultrasound technique (LBU) offers for several years an efficient alternative to conventional ultrasound (piezoelectric transducers), especially for the nondestructive evaluation (NDE) and the material characterization [1]. Many structures encountered in aeronautics such as painted metals or composites are made of two layers of completely different materials and the control of such specimens may be intricate. Thus, it is useful to develop a theoretical model able to predict the laser induced acoustic response of a two-layered material [2,3]. So, this paper presents a new and original model adapted to that kind of structures which are homogeneous and transversely isotropic. The cylindrical symmetry of the model allows fast calculation and observation of the displacements over a long duration. The simulations are compared to the experimental results performed with a Nd: Yag laser for the generation and a heterodyne interferometer. Moreover, the NonDestructive Testing (NDT) of metallic structures is difficult because of the very large optical reflection coefficient of the laser light on the surface. A paint covering the surface of the metal allows to improve the ultrasound generation around the normal incidence and then improves the control of the material. The two-layer model is used to characterize this paint and to optimize its thickness in order to ensure the way of testing such as the detection of effects due to corrosion.</p