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Dispersion and ellipticity of Rayleigh waves in a soil substrate supporting resonant beams and plates
No full textInternational audienceThe behavior of surface waves in a soil supporting an array of beams in three dimensions, or an array of plates in two dimensions, with compressional and flexural resonances is examined both theoretically and numerically. Our findings demonstrate that Love waves, characterized by displacements perpendicular to the sagittal plane, can propagate even without a homogeneous guiding layer, owing to the influence of flexural resonances in beams. Within the sagittal plane, hybridized Rayleigh waves exhibit a dispersion that is notably altered by the presence of the array, with their properties emerging from the interaction between flexural and compressional resonances. Notably, we uncover the coexistence of two Rayleigh waves with distinct wave numbers within specific frequency ranges, corresponding to prograde and retrograde motions. Additionally, both waves significantly amplify ground motion, either horizontally or vertically. Similar physics, yet quantitatively different, is demonstrated in the case of plate arrays
Templex-detected patterns and their connection to elephant seal behavior in the South Atlantic Ocean
No full textInternational audienceThe "templex" topological approach (Charó et al., 2022) utilizes a cell complex equipped with a directed graph to characterize flow structures within phase space. Templex attributes are shared among fluid particles that demonstrate particular qualitative behaviors, making it useful for detecting Lagrangian patterns. For individual particles, this approach necessitates extended observation periods to reconstruct phase-space flow accurately. To address the limited long-term stability of oceanic particle motion, we propose a method involving multiple particles within a localized area. Applying this strategy to surface geostrophic velocity fields derived from satellite altimetry allows for the identification of eddies and other patterns, which have been analyzed in relation to elephant seal movements. Our findings indicate that templex-detected patterns along an elephant seal's path in the South Atlantic correlate with prey capture attempts and that the animal’s foraging behavior is significantly influenced by ocean currents (Allice Della Penna et al., 2015)
Joint determination of Venus gravity and atmospheric density through EnVision radio science investigation
No full textInternational audienceThe ESA mission EnVision will address its main scientific questions through a detailed mapping of the surface and interior properties of Venus. A precise reconstruction of the spacecraft trajectory is a key requirement for the EnVision scientific investigations, including radio science. To precisely constrain the orbit evolution, refined models of the dynamical forces are included in the Precise Orbit Determination (POD) process. We developed a methodology based on a batch-sequential filter that enables a joint estimation of Venus gravity and atmospheric density. Our approach yields an accurate compensation of atmospheric mismodeling, simulated through semi-empirical predictions of the atmospheric density provided by general circulation models (GCM), e.g., Venus Climate Database (VCD). Numerical simulations of the EnVision radio science investigation were carried out by using a perturbative analysis of the dynamical forces, which accounts for atmospheric density errors ≥ 200%. By adjusting a set of atmospheric scale factors, our proposed strategy enables an estimation of the atmospheric density at the spacecraft altitudes with an accuracy of 25%. The improved dynamical model yields accuracies in the orbit reconstruction of 1-2 m, 30-40 m and 20-30 m in the radial, transverse and normal directions
Carbon Dot Synthesis in CYTOP Optical Fiber Using IR Femtosecond Laser Direct Writing and Its Luminescence Properties
No full textInternational audienceLuminescent carbon dots (CDs) were locally synthesized in the core of CYTOP fibers using IR femtosecond laser direct writing (FLDW), a one-step simple method serving as a post-treatment of the pristine fiber. This approach enables the creation of several types of modifications such as ellipsoid voids. The CDs and photoluminescence (PL) distribute at the periphery of the voids. The PL spectral properties were studied through the excitation/emission matrix in the visible range and excitation/emission spectra in the UV/visible range. Our findings reveal the presence of at least three distinct luminescent species, facilitating a broad excitation range extending from UV to green, and light emission spanning from blue to red. The average laser power and dose influence the quantity and ratio of these luminescent CD species. Additionally, we measured the spatially resolved lifetime of the luminescence during and after the irradiation. We found longer lifetimes at the periphery of the laser-induced modified regions and shorter ones closer to the center, with a dominant lifetime ~2 ns. Notably, unlike many other luminophores, these laser-induced CDs are insensitive to oxygen, enhancing their potential for display or data storage applications
Modèles de filaments pour la natation à l'échelle microscopique
No full textThe mathematics associated with swimming at the microscopic scale has been an active research area for about fifteen years, with numerous applications in biology and physics. Indeed, microorganisms moving in water play a crucial role in the origin and maintenance of life, and the physical principles governing their movements differ greatly from those that govern human swimming. Research in this field can also be applied to the design of micro-robots, paving the way for innovative applications in medicine, such as non-invasive surgery.This thesis deals with the study of such microorganisms in a context where inertial forces are negligible compared to viscous forces in the surrounding fluid, a phenomenon characterized by a low Reynolds number.The first two parts present new mathematical models of swimmers, composed of active arms, spheres, and passive springs. These models circumvent Purcell's scallop theorem, which states that a swimmer doing a reciprocal stroke cannot move, as it always returns to its initial position in the absence of inertia. The first model developed in this thesis is a four-sphere swimmer with two passive elastic arms. By varying the oscillation frequency of the active arm, the direction of the swimmer’s displacement can be changed, making the system controllable with only one active degree of freedom. The model studied in the second chapter involves a large number of springs. A limiting model of this swimmer, where the number of springs tends to infinity, was then considered, transforming the swimmer into an elastic tail that compresses and extends along one single dimension.In the third chapter, a proof of the convergence and well-posedness of a discrete model of an elastic microfilament at low Reynolds numbers is presented. This model consists of N rigid filaments immersed in a fluid, studied in 3D and whose movement is in two dimensions.Finally, in the last chapter, models of activation mechanisms along a flagellum are introduced. Biologically, these activation mechanisms exist in the flagellum in an internal structure called the axoneme, in the form of molecular motors arranged in several rows. Based on a model of these motors from biophysics, two new systems are then studied. The first one represents a projection of the axoneme with two rows of motors and is analyzed both theoretically and numerically. The second one takes into account all rows of motors in the axoneme; its behavior is illustrated by numerical simulations.Les mathématiques associées à la natation à l'échelle microscopique constituent un domaine de recherche actif depuis une quinzaine d'années, avec de nombreuses applications en biologie et en physique. En effet, les micro-organismes se déplaçant dans l'eau jouent un rôle crucial dans l'origine et le maintien de la vie, et les principes physiques régissant leurs mouvements diffèrent grandement de ceux qui gouvernent la natation humaine. Les recherches dans ce domaine peuvent aussi être appliquées à la conception de micro sous-marins, ouvrant la voie à des applications innovantes en médecine, comme la chirurgie non-invasive.Cette thèse porte sur l'étude de tels micro-organismes, dans un contexte où les forces inertielles sont négligeables par rapport aux forces visqueuses dans le fluide environnant, phénomène caractérisé par un faible nombre de Reynolds.Les deux premières parties traitent de modèles mathématiques de nageurs, composés de bras actifs, sphères, et ressorts passifs. Ces modèles permettent de contourner le théorème de la coquille Saint-Jacques de Purcell, qui garantit qu'un nageur dont la brassée est un mouvement réciproque ne pourra jamais se déplacer, car il revient toujours à sa position initiale en l'absence d'inertie.Le premier modèle conçu au cours de cette thèse est un nageur à quatre sphères avec deux bras élastiques passifs. Faire varier la fréquence d'oscillation du bras actif permet de changer le signe du déplacement du nageur, rendant le système contrôlable, tout en n'ayant qu'un seul degré de liberté actif. Le modèle étudié dans le deuxième chapitre comporte, quant à lui, un grand nombre de ressorts. Un modèle limite de ce nageur où le nombre de ressorts tend vers l'infini a ensuite été considéré, transformant le nageur en une queue élastique se compressant et s'étendant unidimensionnellement.Au cours du troisième chapitre, on présente une preuve de la convergence et du caractère bien posé d'un modèle discret de micro-filament élastique à bas nombre de Reynolds. Ce modèle en trois dimensions est composé de N filaments rigides, dont le mouvement est en deux dimensions.Enfin, dans le dernier chapitre, des modèles des mécanismes d'activation le long d'un flagelle sont présentés. Du point de vue de la biologie, ces mécanismes d'activation sont présents dans le flagelle dans une structure interne, appelée axonème, sous la forme de moteurs moléculaires arrangés en plusieurs rangées.En se basant sur un modèle de ces moteurs issu de la biophysique, deux nouveaux systèmes sont ensuite étudiés. Le premier représente une projection de l'axonème dans laquelle deux rangées de moteurs sont présentes, et est étudié aussi bien théoriquement que numériquement. Le second prend en compte la totalité des rangées de moteurs dans l'axonème, son comportement est illustré par des simulations numériques
Dynamiques des organisations: Les décrypter pour un monde plus durable et équitable
No full textInternational audienceOrganizations shape our world... for better or for worse. But how can we design organizations that respond to societal challenges for a more sustainable world? By deciphering their complex world. What forces set organizations in motion or paralyze them? How are power dynamics and decision-making shaped? How are they structured, and how can they evolve? In six chapters, this book puts simple words and images to work on the essential mechanisms of organizations, exploring their structure, culture, power relationships, incentive systems, processes and processes of change. incentive systems, decision-making processes and capacity for innovation. Complemented by illustrations and real-life case studies, it is a real tool for appropriating the keys to design, implement and test conditions conducive to sustainable organizational environments. Deciphering the dynamics of organizations and what falls within the scope of individual or collective action will enable every professional and manager to build a more equitable and sustainable future. and sustainable future.Les organisations façonnent notre monde… pour le meilleur et pour le pire. Mais comment pouvons-nous concevoir des organisations qui répondent aux défis sociétaux pour un monde plus durable ? En décryptant leur monde complexe. Quelles sont les forces qui mettent en mouvement ou paralysent les organisations ? Comment se construisent les dynamiques de pouvoir et les prises de décision ? Quelle est leur structure et comment peuvent-elles évoluer ? À travers six chapitres, ce livre pose des mots et des images simples sur les mécanismes essentiels des organisations, en explorant leur structure, leur culture, les rapports de pouvoir en leur sein, leurs systèmes d’incitation, leurs processus décisionnels ou encore leur capacité d’innovation. Complété d’illustrations et de cas d’entreprises concrets, il est un véritable outil pour s’approprier les clés afin de concevoir, mettre en place et tester des conditions favorables à des environnements organisationnels soutenables. Décrypter les dynamiques des organisations et ce qui relève de l’action individuelle ou collective permettra à chaque professionnel et dirigeant de bâtir un avenir plus équitable et durable
Does leadership in policy setting reduce pollution and make countries better off?
No full textIn light of the ongoing debate on Common But Differentiated Responsibilities (CBDR), we wonder whether it is worthwile for industrialized countries to take the lead in reducing emissions, rather than acting simultaneously with less advanced countries. To do this, we compare national payoffs and global emissions in each situation. We also examine whether industrial leakage is an inevitable outcome of asymmetric policies with differentiated abatement responsibilities and, if so, whether unambigously hurts the more industrialized countries. We show that leadership can improve payoffs while reducing global emissions, even though these goals appear to be at odds.</div
Multi-objective calibration and evaluation of the ORCHIDEE land surface model over France at high resolution
No full textInternational audienceHere we present a strategy to obtain a reliable hydrological simulation over France with the ORCHIDEE land surface model. The model is forced by the SAFRAN atmospheric reanalysis at 8 km resolution and hourly time steps from 1959 to 2020 and by a high-resolution DEM (around 1.3 km in France). Each SAFRAN grid cell is decomposed into a graph of hydrological transfer units (HTUs) based on the higher-resolution DEM to better describe lateral water movements. In particular, it is possible to accurately locate 3507 stations among the 4081 stations collected from the national hydrometric network HydroPortail (filtered to drain an upstream area larger than 64 km2). A simple trial-and-error calibration is conducted by modifying selected parameters of ORCHIDEE to reduce the biases of the simulated water budget compared to the evapotranspiration products (the GLEAM and FLUXCOM datasets) and the HydroPortail observations of river discharge. The simulation that is eventually preferred is extensively assessed with classic goodness-of-fit indicators complemented by trend analysis at 1785 stations (filtered to have records for at least 8 entire years) across France. For example, the median bias of evapotranspiration is −0.5 % against GLEAM (−4.3 % against FLUXCOM), the median bias of river discharge is 6.3 %, and the median Kling–Gupta efficiency (KGE) of square-rooted river discharge is 0.59. These indicators, however, exhibit a large spatial variability, with poor performance in the Alps and the Seine sedimentary basin. The spatial contrasts and temporal trends of river discharge across France are well represented with an accuracy of 76.4 % for the trend sign and an accuracy of 62.7 % for the trend significance. Although it does not yet integrate human impacts on river basins, the selected parameterization of ORCHIDEE offers a reliable historical overview of water resources and a robust configuration for climate change impact analysis at the nationwide scale of France
Attribution of summer 2022 extreme wildfire season in Southwest France to anthropogenic climate change
No full textInternational audienceSummer 2022 was exceptionally hot and dry in Europe and especially in Southwest France, where the most important wildfires since 1949 had serious environmental and socio-economic impacts. Here we conduct an impact-oriented climate change attribution study by first investigating which climate indices are the most correlated with the burnt area between 2003 and 2022. We find that an index combining soil moisture integrated over 6 months and temperature and vapour pressure deficit integrated over 3 months is correlated with large burnt areas. Using the index developed, we estimate that anthropogenic climate change made climate conditions propitious for wildfire development, such as the ones of July 2022, two times more likely, with a return period of 13 years in the current climate. Our study raises the question of the sustainability of the Landes Forest and stresses the urgent need to mitigate greenhouse gas emissions and adapt to climate change
Identifying and quantifying the impact of climatic and non-climatic drivers on river discharge in Europe
No full textOur water resources have changed over the last century through a combination of water management evolutions and climate change. Understanding and decomposing these drivers of discharge changes is essential to preparing and planning adaptive strategies. We propose a methodology combining a physical-based model to reproduce the natural behavior of river catchments and a parsimonious model to serve as a framework of interpretation, comparing the physical-based model outputs to observations of discharge trends. We show that over Europe, especially in the South, the dominant explanations for discharge trends are non-climatic factors. Still, in some catchments of Northern Europe, climate change seems to be the dominating driver of change.We hypothesize that the dominating non-climatic factors are irrigation development, groundwater pumping and other human water usage, which need to be taken into account in physical-based models to understand the main drivers of discharge and project future changes