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A multi-sourced assessment of the spatiotemporal dynamics of soil moisture in the MARINE flash flood model
Get PDFThe MARINE (Model of Anticipation of Runoff and INundations for Extreme events) hydrological model is a distributed model dedicated to flash flood simulation. Recent developments of the MARINE model are explored in this work. On one hand, transfers of water through the subsurface, formerly relying on water height, now take place in a homogeneous soil column based on the soil saturation degree (SSF model). On the other hand, the soil column is divided into two layers, which represent, respectively, the upper soil layer and the deep weathered rocks (SSF–DWF model). The aim of the present work is to assess the accuracy of these new representations for the simulation of soil moisture during flash flood events. An exploration of the various products available in the literature for soil moisture estimation is performed. The efficiency of the models for soil saturation degree simulation is estimated with respect to several products either at the local scale or spatially distributed: (i) the gridded soil moisture product provided by the operational modeling chain SAFRAN-ISBA-MODCOU; (ii) the gridded soil moisture product provided by the LDAS-Monde assimilation chain, which is based on the ISBA-A-gs land surface model and assimilating satellite derived data; (iii) the upper soil water content hourly measurements taken from the SMOSMANIA observation network; and (iv) the Soil Water Index provided by the Copernicus Global Land Service (CGLS), which is derived from Sentinel-1 C-SAR and ASCAT satellite data. The case study is performed over two French Mediterranean catchments impacted by flash flood events over the 2017–2019 period. The local comparison of the MARINE outputs with the SMOSMANIA measurements, as well as the comparison at the basin scale of the MARINE outputs with the gridded LDAS-Monde and CGLS data, lead to the following conclusion: both the dynamics and the amplitudes of the soil saturation degree simulated with the SSF and SSF–DWF models are better correlated with both the SMOSMANIA measurements and the LDAS-Monde data than the outputs of the base model. Finally, the soil saturation degree simulated by the two-layers model for the deep layer is compared to the soil saturation degree provided by the LDAS-Monde product at corresponding depths. In conclusion, the developments presented for the representation of subsurface flow in the MARINE model enhance the soil saturation degree simulation during flash floods with respect to both gridded data and local soil moisture measurements
Multi-scale two-domain numerical modeling of stationary positive DC corona discharge/drift-region coupling
Get PDFCorona discharge modeling mostly relies on two, mostly distinct, approaches: high-fidelity, numerically challenging, unsteady simulations having high-computational cost or low-fidelity simulations based on empirical assumptions such as constant electric field at the emitter electrode. For the purpose of steady discharge current predictions, high-fidelity models are very costly to use whilst empirical models have limited range of validity owing the subtle use of tuned parameters. We propose an intermediate approach: an asymptotic multi-scale/two-domain numerical modeling based upon generalizing previous asymptotic axi-symmetrical analysis [1,2]. We show how the initial elliptic (electric potential), hyperbolic (charge transport), non-local (photo-ionization) problem can be formulated into two local problems coupled by matching conditions. The approach relies on a multipole expansion of the radiative photo-ionization source term (in two dimensions for cylindrical emitters). The analytical asymptotic matching conditions derived in [2]result in flux continuity conditions at the boundary of the two domains. These coupling conditions are enforced by Lagrange multipliers, within a variational formulation, leading to a hierarchy of non-linear coupled problems. The proposed approach is both monolithic and two-domains: two asymptotic regions, an inner-one associated with corona discharge, and an outer-one, the ion drift region. Numerical convergence and validations of the finite element implementation is provided. A comparison with various experimental results convincingly demonstrate the applicability of the method, which avoids tuning parameters dedicated to each specific configuration, but, on the contrary, exclusively relies on known and measurable physical quantities (e.g.,ion mobilities, photo-ionization coefficient, ionization electric field, Townsend discharge coefficient, etc...)
Numerical simulation of mass transfer dynamics in Taylor flows
Get PDFDirect Numerical Simulations of mass transfer within Taylor flows are carried out using the periodic unit-cell approach by means of the Level-Set method, under the axisymmetric assumption. The considered cases are based on the experimental study of Butler et al. (2018) (absorption of gaseous species) for bubbles of Reynolds numbers Re_b>200 and capillary numbers Ca>10^{-3}. Firstly, the hydrodynamics of five cases are calculated up to steady state, after which the bubble shape, lubrication film thickness and velocity profiles are compared to experimental and theoretical results. Using these converged hydrodynamics, the transient mass transfer between the gas and liquid phases is then simulated, assuming no change in bubble volume. The Péclet number is varied between 10 and 900 by changing the diffusion coefficient, allowing for new insight into local phenomena of mass transfer. In this way, the maximal transfer fluxes at the interface are observed to be (i) close to the stagnation point at the film entrance, and (ii) at the rear cap where the tangential velocity is greatest. As once as the mass transfer coefficient becomes constant, the fluxes across the part of the interface in contact with the film and around the bubble caps are each characterised by a local Sherwood number. The latter evolves by Pe_{film}^{1/2} across the film and is found to be predictable by a simple model when Pe_{film} > 1, where Pe_{film} is the film Péclet number. Concerning the caps, it evolves by Pe^{1/2} but only in a finite range of Pe, contrary to the common assumption of similarity of transfer around the caps with that around a rising unconfined spherical bubble. Such local analyses could be further used in multizone models of mass transfer for Taylor flows.
Finally, a correlation is proposed to scale the global Sherwood number Sh_{\infty} far from channel inlet, defined as a function of both a Péclet number Pe_R based on the relative velocity between the bubble and the two-phase flow and the gas volume fraction in the unit cell. Its predictions are discussed against experimental results at much higher Péclet numbers, after showing that Sh_{\infty} is independent on the initial concentration distribution in the liquid (the latter being sensitive to the injection conditions in experiments)
An hybrid resolution method for the aircraft predictive maintenance and routing problem
No full textAircraft routing and maintenance planning still represents a challenging research topic. Aircraft routing, or aircraft tail assignment, optimises fleet allocation to predefined routes.
Maintenance is optimized by accordingly making decisions based on aircraft preventive or condition-based needs. These two problems can lead to separate optimization processes. Nevertheless, a combined optimization problem should produce better results, as routes should impact maintenance costsand vice-versa. One issue is how to scale the problem such that many aircraft could fly at the same time from one airport to another and make maintenance decisions in an uncertain environment due to health indicators dynamics. In this work, we propose a unified model for this problem based on Markov Decision Processes (MDP). Two limiting factors impact our search of solution: the number of maintenance actions to be considered in planning that increases with the number of aircraft, as well as, the number of possible allocations that in turn is affected by the number of aircraft and airports. We propose a hybrid planning solution which decomposes the problem in such way it performs aircraft tail assignment optimisation combined with maintenance policy. The maintenance policies are computed for several independent MDPs (e.g. one per aircraft) in a robust manner by considering several possible aircraft locations. Then, a solution for the aircraft tail allocation problem is obtained by using aircraft maintenance policies. Finally, we empirically show that this method scales better than a unified (and possibly huge) MDP approach
Tuning the Reduction of Graphene Oxide Nanoflakes Differently Affects Neuronal Networks in the Zebrafish
Get PDFThe increasing engineering of biomedical devices and the design of drug-delivery platforms enriched by graphene-based components demand careful investigations of the impact of graphene-related materials (GRMs) on the nervous system. In addition, the enhanced diffusion of GRM-based products and technologies that might favor the dispersion in the environment of GRMs nanoparticles urgently requires the potential neurotoxicity of these compounds to be addressed. One of the challenges in providing definite evidence supporting the harmful or safe use of GRMs is addressing the variety of this family of materials, with GRMs differing for size and chemistry. Such a diversity impairs reaching a unique and predictive picture of the effects of GRMs on the nervous system. Here, by exploiting the thermal reduction of graphene oxide nanoflakes (GO) to generate materials with different oxygen/carbon ratios, we used a high-throughput analysis of early-stage zebrafish locomotor behavior to investigate if modifications of a specific GRM chemical property influenced how these nanomaterials affect vertebrate sensory-motor neurophysiology—exposing zebrafish to GO downregulated their swimming performance. Conversely, reduced GO (rGO) treatments boosted locomotor activity. We concluded that the tuning of single GRM chemical properties is sufficient to produce differential effects on nervous system physiology, likely interfering with different signaling pathways
Phase Retrieval With Bregman Divergences and Application to Audio Signal Recovery
Get PDFPhase retrieval (PR) aims to recover a signal from the magnitudes of a set of inner products. This problem arises in many audio signal processing applications which operate on a short-time Fourier transform magnitude or power spectrogram, and discard the phase information. Recovering the missing phase from the resulting modified spectrogram is indeed necessary in order to synthesize time-domain signals. PR is commonly addressed by considering a minimization problem involving a quadratic loss function. In this paper, we adopt a different standpoint. Indeed, the quadratic loss does not properly account for some perceptual properties of audio, and alternative discrepancy measures such as beta-divergences have been preferred in many settings. Therefore, we formulate PR as a new minimization problem involving Bregman divergences. We consider a general formulation that actually addresses two problems, since it accounts for the non-symmetry of these divergences in general. To optimize the resulting objective, we derive two algorithms based on accelerated gradient descent and alternating direction method of multiplier. Experiments conducted on audio signal recovery from either exact or modified spectrograms highlight the potential of our proposed methods for audio restoration. In particular, leveraging some of these Bregman divergences induce better performance than the quadratic loss when performing PR from highly degraded spectrograms
AI can fool us humans, but not at the psycho-physiological level: a hyperscanning and physiological synchrony study
Get PDFThis study aims at investigating the neural
and physiological correlates of human-human and human-AI
interactions under ecological settings. We designed a scenario in which a ground controller had to guide his/her pilot to
reach a location. We also implemented a Controller-Bot and
a Pilot-Bot using AI techniques to behave like real human
operators. The cooperation between controllers and pilots were
either genuine (‘Coop scenarios’ – four missions), explicitly
notified as pilot-Bot and controller-Bot interactions (‘No coop
scenarios’ – two missions), or with no notification that they
were actually collaborating with their AI counterparts (‘fake
coop scenarios’ – two missions). Sixteen participants (8 dyads)
equipped with EEG and ECG took part in this experiment.
Our findings disclosed that Human-Human dyads exhibited
similar performance to Human-Bots dyads whether the human
participants were aware that they were playing with a bot or
not. Our participants declared that they did not realize they
were playing with an AI in the fake cooperation condition.
These findings indicate that 1) humans can be fooled by AI,
and that 2) humans can behave in a natural way with AI.
Interestingly enough, our analyses revealed that the cardiac
activity of controllers and pilots was more synchronized when
they were collaborating together than when they were playing
with AI (being aware or not). Similarly, EEG analyses disclosed
a higher cerebral efficiency and connectivity between the two
brains when teammates were interacting together than when
cooperating with AI
A comparative study of the crystallinity of polyetheretherketone by using density, DSC, XRD, and Raman spectroscopy techniques
Get PDFA comparative study of the crystallinity of Polyetheretherketone by using density, DSC, XRD, and Raman spectroscopy techniques. In this work, the microstructure of Polyetheretherketone is first analyzed with usual techniques such as density, Differential Scanning Calorimetry, X-ray Diffraction, and secondly, compared with Raman Spectroscopy. Assessing the degree of crystallinity of PEEK is challenging because of the different interpretation of the crystallinity according to each technique. The density measurement gives the highest most trusted absolute uncertainty for the degree of crystallinity, around 4, compared to the other techniques. The Differential Scanning Calorimetry, usually used by the polymer community, overestimates up to 18 the degree of crystallinity due to a competitive phenomenon between crystallization and melting of PEEK over the same temperature range, and a fast crystallization. When Analyzing the X-ray Diffraction data, the degree of crystallinity is underestimated up to 11 as a consequence of the broad amorphous halo. Lastly, our investigation proves that Raman microspectroscopy is appropriate to determine the local crystallinity on the sample surface and compares 18 indicators in the same study. The 1651 cm-1 band shift has the highest correlation coefficient of 0.92 with the degree of crystallinity determined by density. This work attempts to correlate the results of degree of crystallinity of PEEK obtained by these four techniques in order to establish the best evaluation of this fundamental property for numerous applications
Contribution à l'étude de l'éthogramme du chien de compagnie (canis lupus familiaris) à l'aide de colliers accélérométres : étude expérimentale
Get PDFChez le chien de compagnie, les données relatives à l’activité spontanée font défaut dans la littérature scientifique, en raison de la difficulté de trouver un système de mesure adapté. L’utilisation de colliers accéléromètres semble représenter une solution prometteuse. Notre étude expérimentale avait pour objectif de mesurer et de décrire l’activité spontanée de dix chiens de compagnie, dans leurs conditions de vie habituelles, au cours de deux périodes d’enregistrement de deux semaines. Pour cela, ils ont été équipés du capteur INVOXIA LWT 200 GPS TRACKER (Invoxia SAS, Issy-les-moulineaux, France), dont la fiabilité, pour ce type d’utilisation a été testée, à cette occasion. Les résultats montrent que les chiens passent en moyenne 86% de leur temps immobile, 7% à marcher et 2% à courir. Cette répartition de l’activité est relativement homogène au sein de notre échantillon (9/10 chiens) et est stable entre les deux périodes d’enregistrement, malgré une variation modérée du rythme de vie, liée aux activités du propriétaire. Il n’a cependant pas été possible de distinguer les temps de promenades, du temps passé au domicile à partir des données, faisant douter de la sensibilité du capteur à détecter les mouvements sur des intervalles de temps restreints
Checking SysML Models against Safety and Security Properties
Get PDFSystems Engineering, or engineering in general, has long been relying on document-centric approaches. Switching to Model Based Systems Engineering, or MBSE for short, has extensively been discussed over the past three decades. Since about two decades, MBSE has been commonly associated with the modelling language SysML (Systems Modeling Language), that offers a standardized notation, not a methodology of using it. SysML needs therefore to be associated with a methodology supported by tools. In this paper, a methodology supported by the free and open-source software TTool is associated with SysML. This paper focuses discussion on methodological issues, leading the authors to share their experience in real-time systems modeling. Modeling with SysML is more than just drawing the different diagrams. Associated tools offer possibilities to analyze SysML models for specific properties. In this paper, verification addresses both safety and security properties. The TTool model checker inputs the SysML model enriched with safety properties to be verified and outputs a yes-no answer for each property. Security verification checks SysML models against confidentiality, integrity and authenticity properties. As an illustration of the proposed approach, an aircraft cockpit door control system is modeled in SysML and verified against safety and security properties