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Rescaled equations for well-conditioned direct numerical simulations of rapidly rotating convection
No full textInternational audienceConvection is a ubiquitous process driving geophysical/astrophysical fluid flows, which are typically strongly constrained by planetary rotation on large scales. A celebrated model of such flows, rapidly rotating Rayleigh-Bénard convection, has been extensively studied in direct numerical simulations (DNS) and laboratory experiments, but the parameter values attainable by state-of-the-art methods are limited to moderately rapid rotation (Ekman numbers Ek ≳ 10 -8 ), while realistic geophysical/astrophysical Ek are significantly smaller. Asymptotically reduced equations of motion, the nonhydrostatic quasi-geostrophic equations (NHQGE), describing the flow evolution in the limit Ek → 0, do not apply at finite rotation rates. The geophysical/astrophysical regime of small but finite Ek therefore remains currently inaccessible. Here, we introduce a new, numerically advantageous formulation of the Navier-Stokes-Boussinesq equations informed by the scalings valid for Ek → 0, the Rescaled Rapidly Rotating incompressible Navier-Stokes Equations (RRRiNSE). We solve the RRRiNSE using a spectral quasi-inverse method resulting in a sparse, fast algorithm to perform efficient DNS in this previously unattainable parameter regime. We validate our results against the literature across a range of Ek, and demonstrate that the algorithmic approaches taken remain accurate and numerically stable at Ek as low as 10 -15 . Like the NHQGE, the RRRiNSE derive their efficiency from adequate conditioning, eliminating spurious growing modes that otherwise induce numerical instabilities at small Ek. We show that the time derivative of the mean temperature is inconsequential for accurately determining the Nusselt number in the stationar
Photonic bandgap properties of hyperuniform systems self-assembled in a microfluidic channel
No full textTraditional self-assembly methods often rely on densely packed colloidal crystalline structures and have inherent limitations in generating materials with isotropic photonic bandgaps (PBG). This study explores the photonic properties of materials structured according to hyperuniform disordered patterns (HUDS) generated via a hydrodynamic process in a microchannel. This research employs simulations to characterize optical bandgaps and determine the minimum dielectric contrast required for PBG formation in structures based on the templates experimentally formed under various conditions during the hydrodynamic process. The optimal conditions in the hydrodynamic process for realizing PBG have been identified. The findings offer a promising avenue for the large-scale production of isotropic photonic bandgap materials
Anelastic approximation for the degenerate compressible Navier--Stokes equations revisited
No full textIn this paper, we revisit the joint low-Mach and low-Frode number limit for the compressible Navier-Stokes equations with degenerate, density-dependent viscosity. Employing the relative entropy framework based on the concept of -entropy, we rigorously justify the convergence of weak solutions toward the generalized anelastic system in a three-dimensional periodic domain for well-prepared initial data. For general ill-prepared initial data, we establish a similar convergence result in the whole space, relying essentially on dispersive estimates for acoustic waves. Compared with the work of Fanelli and Zatorska [Commun. Math. Phys., 400 (2023), pp. 1463-1506], our analysis is conducted for the standard isentropic pressure law, thereby eliminating the need for the cold pressure term that played a crucial role in the previous approach. To the best of our knowledge, this is the first rigorous singular limit result for the compressible Navier-Stokes equations with degenerate viscosity that requires no additional regularization of the system
Closed-form solutions for simplified fretting wear profiles prediction incorporating an inverse identification of local wear rates
No full textInternational audienceThis paper proposes a method for estimating the local wear rates operating within a flat-on-flat contact subjected to fretting wear through an inverse identificationapproach. Using an error minimization strategy involving a limited number of experimental tests, it is possible to identify the wear rate coefficients associated withadhesive or abrasive wear domains observed within the fretting interface. This work is then extended by the development of an analytical formulation for thecalculation of simplified surface wear profiles. This model shows that the wear increment profile tends towards a flat distribution. In other words, the materialremoval increment is inclined towards a constant value over the entire fretting interface, regardless of the varying wear coefficients operating within the contact. Agood correlation is observed between the proposed model and the experimental results, not only for predicting the total wear volumes, but also for predicting thewear profiles, and particularly the evolution of the maximum wear depth. Contrary to the iterative FEM approaches, which are time consuming and demanding, thisanalytical formulation provides a quasi-instantaneous estimation of the wear profiles, which can be very interesting for fast and efficient fretting wear design
Influence of K4Nb6O17 secondary phase on ferroelectric behavior of K0.5Na0.5NbO3 thin films
No full textInternational audienceKxNa1-xNbO3 (KNN) perovskite thin films deposition by various methods poses significant challenges due to alkali cations losses, which result in vacancies or secondary phases. In this study, KNN thin films were obtained by pulsed laser deposition using a stoichiometric commercial target and a 60% potassium-enriched target on platinized silicon substrates. Potassium-enrichment target was used as an alternative to obtain a pure perovskite phase and enhance piezoelectric and ferroelectric behavior of the thin films. It was observed that the alkali losses during the deposition of KNN thin films mainly promote the formation of the secondary phase K4Nb6O17 and its hydrated form. Importantly, K4Nb6O17 adversely affects ferroelectric and piezoelectric properties owing to its high sensitivity to moisture. It was observed that these KNN films grown from a stoichiometric commercial target (denoted as KNNs) present a perovskite structure and K4Nb6O17 secondary phase presence, while thin films deposited with a K-enriched target (denoted as KNNe) show a single perovskite structure. The topography and piezoresponse force microscopy amplitude exhibit topographic differences and a null-piezoelectric response in large and flat grains in KNNs, disrupting the distribution of small and rounded grains associated with piezoelectric signal. Meanwhile KNNe films present strong piezoelectric behavior. Null-piezoelectric response in KNNs agree with scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis, where areas exhibiting such large and flat grains displayed a pronounced deficiency in alkali cations. In addition, characterization by using X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopy coupled to energy dispersive X-ray spectroscopy showed the presence of low amount of sodium incorporated into the K4Nb6O17 structure during KNN films deposition, although only the K4Nb6O17 was reported. On the other hand, thin films deposited from a K-enriched target presents a single perovskite phase devoid of any secondary phase. Their electrical measurements, performed on 0.25 x 0.25 mm2 capacitors, show a d33,f value similar to 40 pm V-1 and typical ferroelectric behavior with saturation polarization = 20 mu C cm-2, remnant polarization (2Pr) = 17.5 mu C cm-2 and coercive voltage (2Vc) = 3 V, comparable to earlier works reported in the literature, making KNNe thin films suitable candidates for further engineering applications through their optimization, contrary to KNNs thin films
A methodological approach for design of Collaborative Assistive Systems
No full textInternational audienceCollaborative Assistive Systems (CAS) are a category of Computer Supported Collaborative Systems (CSCW) which objective is to provide collaborative, multi user, interactive, mobile, integrated applications which are working in smart environment using in the field communicating objects (senders and receivers). Design and Development of these systems need appropriated framework and elaboration processes. We present this framework with specification model and language, generic architecture and associated development approaches related to concrete situation in respect of particular behaviors. Elaborated specifications are projected to generic software architecture. This framework speeds-up implementation of specialized CAS. A case study shows the use of this approach
Mesure d'ondes de choc périodiques en guide d'onde par un interféromètre à rétroaction optique
No full textExpérimentation en acoustique : conception, mise en oeuvre, validation de dispositifs expérimentaux; EXACT - Expérimentations en AcoustiqueNational audienceUn interféromètre à rétroaction optique ("optical feedback interferometer" ou "Self-Mixing Interferometer") est un interféromètre exploitant les propriétés des diodes Laser. Il nécessite seulement trois composants optiques : une capsule contenant une diode Laser, une photodiode embarquée, et une surface rétro-réfléchissante. Il présente l’avantage d’être auto-aligné et ne nécessite pas l’utilisation de miroirs mais seulement d'une surface rétro-réfléchissante pour renvoyer une portion des photons vers la diode. Déjà utilisé en mode vibromètre, son usage comme microphone est moins documenté. Considérant la faible sensibilité des méthodes optiques, son usage en acoustique est à réserver aux domaines de l'acoustique à niveau élevé, voire à la propagation non linéaire, et aux hautes fréquences. Nous présenterons le principe de fonctionnement d'un dispositif de mesure acoustique basé sur un interféromètre à rétroaction optique, une méthode de calibration, et un exemple d'exploitation pour la mesure d'ondes de choc en guide d'onde et l'estimation de la réponse en hautes fréquences d'un microphone 1/8" en incidence rasante
Emergence of supercoiling-mediated regulatory networks through the evolution of bacterial chromosome organization
No full textInternational audienceDNA supercoiling-the level of twisting and writhing of the DNA molecule around itselfplays an important role in the regulation of gene expression in bacteria by modulating promoter activity. The level of DNA supercoiling is a dynamic property of the chromosome which varies both at local and global scales, in response to both external factors such as environmental perturbations and internal factors including gene transcription. As such, local variations in supercoiling could in theory couple the expression levels of neighboring genes by creating feedback loops at the transcriptional level. However, the impact of such supercoiling-mediated interactions on the regulation of gene expression still remains uncertain. In this work, we study how this coupling between transcription and supercoiling could shape genome organization and help regulate gene transcription. We present a model of genome evolution in which individuals whose gene transcription rates are coupled to local supercoiling must adapt to two environments that induce different global supercoiling levels. In this model, we observe the evolution of whole-genome regulatory networks that provide control over gene expression by leveraging the transcriptionsupercoiling coupling, and show that the structure of these networks is underpinned by the organization of genes along the chromosome at several scales. Local variations in DNA supercoiling could therefore help jointly shape both gene regulation and genome organization during evolution.</div