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Euclid preparation. Review of forecast constraints on dark energy and modified gravity
No full textInternational audienceThe Euclid mission has been designed to provide, as one of its main deliverables, information on the nature of the gravitational interaction, which determines the expansion of the Universe and the formation of structures. Thus, Euclid has the potential to test deviations from general relativity that will allow us to shed light on long-lasting problems in the standard cosmological model, CDM. Euclid will mainly do this by using two complementary probes: weak gravitational lensing and galaxy clustering. In this paper we review pre-launch Euclid analyses for dark energy and modified gravity. These include forecast constraints with future Euclid data on cosmological parameters for different cosmological models, such as a time-varying dark energy component, phenomenological modifications of the perturbation sector and specific modified gravity models, with further extensions that include neutrino physics and the coupling to the electromagnetic sector through the fine-structure constant. We review the study of the impact of nonlinear clustering methods on beyond-CDM constraints with Euclid. This is of fundamental importance to efficiently predict the large-scale clustering of matter and dark matter halos, given that we will have access to a wealth of information on scales beyond the linear regime. We inspect the extension of theoretical predictions for observable quantities in alternative cosmologies to CDM at fully nonlinear scales by means of -body simulations. We discuss the impact of relativistic corrections in extended cosmological models. Overall, this review highlights the significant potential of the Euclid mission to tightly constrain parameters of dark energy and modified gravity models, or perhaps to detect possible signatures of a CDM failure
Mixing induced by Faraday surface waves
No full textWe investigate how surface waves enhance mixing across the interface between two miscible fluids with a small density contrast. Imposing a vertical, time-periodic acceleration, we excite Faraday waves both experimentally and numerically. In systems with a shallow density gradient, these standing waves advect the interface and can trigger secondary instabilities. When driven beyond the linear regime, large Faraday crests collapse to form cavities, injecting bubbles and lighter fluid deep into the heavier layer. Together, these mechanisms gradually homogenize the upper layer, diminish the interfacial density jump, and drive the interface downward until it decouples from surface forcing. We report a non-monotonic mixing rate -- first increasing as the interfacial energy barrier lowers, then decreasing as less energy is injected into the weakened surface -- revealing a balance between barrier reduction and energy input. Based on these observations, we introduce a one-dimensional model incorporating a turbulent diffusivity coefficient that depends on depth and the internal Richardson number, which captures the qualitative evolution of the system
Interaction entre une bulle oscillante et une particule sphérique viscoélastique
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An alternative approach for the mean-field behaviour of weakly self-avoiding walks in dimensions
No full textInternational audienceThis article proposes a new way of deriving mean-field exponents for the weakly self-avoiding walk model in dimensions d>4. Among other results, we obtain up-to-constant estimates for the full-space and half-space two-point functions in the critical and near-critical regimes. A companion paper proposes a similar analysis for spread-out Bernoulli percolation in dimensions d>6
A step beyond the tryptic of acoustic streaming
No full textInternational audienceThe path followed since Faraday’s first observations of acoustic streaming has led to a modern picture of this field as split into separate panels of a tryptic: standing acoustic waves in a channel with uniform background density, known as Rayleigh–Schlichting streaming, with stratified background density, known as baroclinic streaming, and acoustic waves progressing far from the walls under the shape of an attenuated beam, known as Eckart streaming. In their theoretical work, Mushthaq et al. (2025 J. Fluid Mech. 1017 , A32) describe in a single continuous parameter space both Rayleigh–Schlichting and baroclinic streaming, thus making a decisive step forward in the frontier between two of these panels. Dealing with a stratification of thermal origin, they identify the level of heating above which baroclinic streaming becomes of the same order of magnitude or greater than Rayleigh–Schlichting streaming. They also depict the major part played by the channel size to wavelength ratio in this problem. This work will be of great help in designing the next generation of experiments concerning acoustic streaming and acoustic management of heat transfer. It is of interest for engineering fields like microfluidics, electronics cooling and biomedical applications. It can also serve as an inspiring basis for academic works in which waves are crossed with stratification
Energy cascades in rotating and stratified turbulence in anisotropic domains
No full textInternational audienceThe concept of inverse energy cascades has played a central role in the development of turbulence theory, with applications in two-dimensional and quasi-two-dimensional flows. We examine the presence or absence of inverse energy cascades in rotating stably stratified flows constrained to anisotropic yet fully three-dimensional domains, in a range of parameters that are relevant for planetary atmospheres. In particular, we focus on regimes with aspect ratios, Rossby, and Froude numbers similar to those found in the Earth's and other planets atmospheres. Our results show that, under certain conditions, inverse energy cascades can indeed emerge from the dry fluid dynamics solely, suggesting that this process can play a role in intermediate-scale atmospheric self-organization processes
On Alfvénic turbulence of solar wind streams observed by Solar Orbiter during March 2022 perihelion and their source regions
No full textInternational audienceContext. It has been recently accepted that the standard classification of the solar wind solely according to flow speed is outdated, and particular interest has been devoted to the study of the origin and evolution of so-called Alfvénic slow solar wind streams and to what extent such streams resemble or differ from fast wind. Aims. In March 2022, Solar Orbiter completed its first nominal phase perihelion passage. During this interval, it observed several Alfvénic streams, allowing for characterization of fluctuations in three slow wind intervals (AS1-AS3) and comparison with a fast wind stream (F) at almost the same heliocentric distance. Methods. This work makes use of Solar Orbiter plasma parameters from the Solar Wind Analyzer (SWA) and magnetic field measurements from the magnetometer (MAG). The magnetic connectivity to the solar sources of selected solar wind intervals was reconstructed using a ballistic extrapolation based on measured solar wind speed down to the (spherical) source surface at 2.5 R s below which a potential field extrapolation was used to map back to the Sun. The source regions were identified using SDO/AIA observations. A spectral analysis of in situ measured magnetic field and velocity fluctuations was performed to characterize correlations, Alfvénicity, normalized cross-helicity, and residual energy in the frequency domain as well as intermittency of the fluctuations and spectral energy transfer rate estimated via mixed third-order moments. A machine learning technique was used to separate proton core, proton beam, and alpha particles and to study v − b correlations for the different ion populations in order to evaluate the role played by each population in determining the Alfvénic content of solar wind fluctuations. Results. The comparison between fast wind and Alfvénic slow wind intervals highlights the differences between the two solar wind regimes: The fast wind is characterized by larger amplitude fluctuations, and magnetic and velocity fluctuations are closer to equipartition of energy. In fact the Alfvénic slow wind streams appear to be on a spectrum of wind types, with AS1, originating from open field lines neighboring active regions and displaying similarities with the fast wind in terms of fluctuation amplitude and turbulence characteristics, but not with respect to the alpha particles and proton beams. The other two slow streams differed both in their sources as well as plasma characteristics, with AS2 coming from the expansion of a narrow coronal hole corridor and AS3 from a region straddling a pseudostreamer. The latter displayed the coldest and highest density but the slowest stream with the smallest fluctuation amplitude and greatest magnetic energy excess. It also showed the largest scatter in proton beam speeds and the greatest difference in speed between proton beam and alpha particles. Conclusions. This study shows how the old fast–slow solar wind dichotomy, already called into question by the observations of slower Alfvénic solar wind streams, should further be refined, as the Alfvénic slow wind, originating in different solar wind regions, show significant differences in density, temperature, and proton and alpha-particle properties in the inner heliosphere. The observations presented here provide the starting point for a better understanding of the origin and evolution of different solar wind streams as well as the evolving turbulence contained within
Caractérisation électrique de modules photovoltaïques en conditions contrôlées
No full textNational audienceLes énergies renouvelables représentent une opportunité majeure de remplacer les énergies fossiles par une solution vertueuse et durable pour l’avenir. Dans ce cadre, l’énergie solaire photovoltaïque, appelée à devenir l’une des principales sources d’électricité d’ici 2050, jouera un rôle central dans la décarbonation de l’industrie de l’énergie,du transport, du bâtiment ainsi que du tertiaire [1]. Il est donc primordial de modéliser avec précision la production d’électricité des systèmes photovoltaïques afin de faciliter la prise de décision lors du déploiement de nouveaux projets. Toutefois, cette modélisation est évaluée dans des "Standard Test Conditions" en laboratoire (STC), avec une température fixe du module photovoltaïque à 25°C et un rayonnement incident normalisé sous un spectre AM1.5. De plus, les conditions de "Normal Operating Cell Temperature" (NOCT), avec une température ambiante de 20°C, demeurent elles aussi éloignées des conditions réelles de fonctionnement observées en extérieur.Dans ce travail, nous présentons un banc de caractérisation de modules photovoltaïques en conditions contrôlées, soumis à des contraintes thermiques et hydriques, afin de mieux modéliser la production électrique des panneaux solaires dans des conditions réelles. Si l’effet de la température a déjà été largement documenté [2], l’impact de l’humidité reste en revanche peu étudié dans la littérature, que ce soit pour des modules en silicium ou de nouvelles technologies, telles que les modules pérovskites et organiques qui feront l’objet de travaux futurs.Le banc de caractérisation, développé à l’INL, est composé d’une enceinte climatique équipée d’un simulateur solaire capable de simuler des conditions environnementales variées. Il offre la possibilité d’acquérir les données environnementales (température et humidité de l’enceinte, température du module photovoltaïque) ainsi que les données électriques (tension et courant du module photovoltaïque). Ces mesures permettent de tracer les courbes courant-tension nécessaires à la comparaison des performances des modules sous différentes conditions environnementales simulées. [1] IEA. 2021. ‘Net Zero by 2050 – Analysis’. https://www.iea.org/reports/net-zero-by-2050.[2] Singh, Priyanka, and N. M. Ravindra. 2012. ‘Temperature Dependence of Solar Cell Performance—an Analysis’. Solar Energy Materials and Solar Cells 101 : 36–45.https://doi.org/10.1016/j.solmat.2012.02.019
Vers une photonique reconfigurable dans les plateformes à base de germanium pour les sources non linéaires à large bande dans l'infrarouge moyen
No full textInternational audienceMid-infrared (MIR 3-15 µm) photonics is a burgeoning scientific and technological field with wide potential application domains including pollution detection, environmental monitoring, security, safety, astrophysics and many more...One of the key aspect is that many important molecules have fundamental ro-vibrational absorption lines in the MIR. An appealing approach, to create power efficient, sensitive, precise, compact molecular sensing devices is to develop an on-chip MIR platform integrating a bright and broadband light source, such as an integrated supercontinuum or a Kerr micro-comb. Gebased platform (e.g. silicon germanium) has emerged as an attractive platform for nonlinear MIR photonics. We report on our latest progress on reconfigurable Ge-based photonics for bright and broadband MIR sources. We demonstrate that Phase change materials, like Sb2S3, are suitable for reconfigurable supercontinuum generation. We also report Ge-based ring resonators with quality factors reaching up to one million which is highly promising for power efficient MIR microcomb generation
Security layers for neuromorphic photonic accelerators
No full textInternational audienceSecurity layers for neuromorphic photonic accelerators Fabio Pavanello and co-authors discuss the importance of security layers in computer systems, particularly in the context of the Horizon Europe NEUROPULS project, which focuses on innovative security solutions based on novel neuromorphic architectures and PUF-based security layers. Security layers are critical to protecting computer systems from threats. They often rely on cryptographic protocols that use secret keys, which are typically stored in memory. However, storing such sensitive data in non-volatile digital memory can pose risks, especially if exploited through hardware vulnerabilities. To address this, the Horizon Europe NEUROPULS project is exploring novel solutions based on integrated photonic