Prise en compte de la transition laminaire/turbulent dans un code Navier-Stokes éléments finis non structurés

This thesis present the state-of-the-art of the transition prediction numerical chain which has been developed at Dassault Aviation in the RANS solver AETHER. Two strategies for transition location estimations exist. First, AETHER is coupled with the ONERA boundary layer code 3C3D. Second, the transition location is computed by using directly the RANS velocity profiles. Both methods were preliminarily tested in subsonic and transonic. The issues of the influence of the numerical solvers, transition onset criteria and coupling process are studied. The influence of higher order numerical method, are also considered.La thèse vise à intégrer des critères de transition dans le solveur Navier-Stokes non structuré Aether utilisé chez Dassault Aviation. Une méthodologie de prévision de la transition laminaire/turbulent a été élaborée et implémentée dans le solveur RANS Aether. Deux stratégies de calcul de transition ont été testées. Soit Aether est couplé avec le code de couche limite de l’ONERA 3C3D. Soit la position de transition est calculée en utilisant directement les profils de vitesse RANS. Les deux méthodes ont été testées pour des écoulements subsoniques et transsoniques. L’influence des solveurs numériques, des critères de transition et du processus de couplage sont étudiés. L’utilisation de schémas numériques d’ordre élevé est également considérée

Recursive decomposition of electromyographic signals with a varying number of active sources: Bayesian modelling and filtering

International audienceThis paper describes a sequential decomposition algorithm for single channel intramuscular electromyography (iEMG) generated by a varying number of active motor neurons. As in previous work, we establish a Hidden Markov Model of iEMG, in which each motor neuron spike train is modeled as a renewal process with inter-spike intervals following a discrete Weibull law and motor unit action potentials are modeled as impulse responses of linear time-invariant systems with known prior. We then expand this model by introducing an activation vector associated to the state vector of the Hidden Markov Model. This activation vector represents recruitment/derecruitment of motor units and is estimated together with the state vector using Bayesian filtering. Non-stationarity of the model parameters is addressed by means of a sliding window approach, thus making the algorithm adaptive to variations in contraction force and motor unit action potential waveforms. The algorithm was validated using simulated and experimental iEMG signals with varying number of active motor units. The experimental signals were acquired from the tibialis anterior and abductor digiti minimi muscles by fine wire and needle electrodes. The decomposition accuracy in both simulated and experimental signals exceeded 90% and the recruitment/derecruitment was successfully tracked by the algorithm. Because of its parallel structure, this algorithm can be efficiently accelerated, which lays the basis for its future real-time applications in human-machine interfaces, e.g. for prosthetic control

Towards an ultra efficient kinetic scheme. Part I: basics on the BGK equation

In this paper we present a new ultra efficient numerical method for solving kinetic equations. In this preliminary work, we present the scheme in the case of the BGK relaxation operator. The scheme, being based on a splitting technique between transport and collision, can be easily extended to other collisional operators as the Boltzmann collision integral or to other kinetic equations such as the Vlasov equation. The key idea, on which the method relies, is to solve the collision part on a grid and then to solve exactly the transport linear part by following the characteristics backward in time. The main difference between the method proposed and semi-Lagrangian methods is that here we do not need to reconstruct the distribution function at each time step. This allows to tremendously reduce the computational cost of the method and it permits for the first time, to the author's knowledge, to compute solutions of full six dimensional kinetic equations on a single processor laptop machine. Numerical examples, up to the full three dimensional case, are presented which validate the method and assess its efficiency in 1D, 2D and 3D

Muscle activation during gait in children with Duchenne muscular dystrophy

The aim of this prospective study was to investigate changes in muscle activity during gait in children with Duchenne muscular Dystrophy (DMD). Dynamic surface electromyography recordings (EMGs) of 16 children with DMD and pathological gait were compared with those of 15 control children. The activity of the rectus femoris (RF), vastus lateralis (VL), medial hamstrings (HS), tibialis anterior (TA) and gastrocnemius soleus (GAS) muscles was recorded and analysed quantitatively and qualitatively. The overall muscle activity in the children with DMD was significantly different from that of the control group. Percentage activation amplitudes of RF, HS and TA were greater throughout the gait cycle in the children with DMD and the timing of GAS activity differed from the control children. Significantly greater muscle coactivation was found in the children with DMD. There were no significant differences between sides. Since the motor command is normal in DMD, the hyper-activity and co-contractions likely compensate for gait instability and muscle weakness, however may have negative consequences on the muscles and may increase the energy cost of gait. Simple rehabilitative strategies such as targeted physical therapies may improve stability and thus the pattern of muscle activity

An essential role for Clp1 in assembly of polyadenylation complex CF IA and Pol II transcription termination

Polyadenylation is a co-transcriptional process that modifies mRNA 3′-ends in eukaryotes. In yeast, CF IA and CPF constitute the core 3′-end maturation complex. CF IA comprises Rna14p, Rna15p, Pcf11p and Clp1p. CF IA interacts with the C-terminal domain of RNA Pol II largest subunit via Pcf11p which links pre-mRNA 3′-end processing to transcription termination. Here, we analysed the role of Clp1p in 3′ processing. Clp1p binds ATP and interacts in CF IA with Pcf11p only. Depletion of Clp1p abolishes transcription termination. Moreover, we found that association of mutations in the ATP-binding domain and in the distant Pcf11p-binding region impair 3′-end processing. Strikingly, these mutations prevent not only Clp1p-Pcf11p interaction but also association of Pcf11p with Rna14p-Rna15p. ChIP experiments showed that Rna15p cross-linking to the 3′-end of a protein-coding gene is perturbed by these mutations whereas Pcf11p is only partially affected. Our study reveals an essential role of Clp1p in CF IA organization. We postulate that Clp1p transmits conformational changes to RNA Pol II through Pcf11p to couple transcription termination and 3′-end processing. These rearrangements likely rely on the correct orientation of ATP within Clp1p

Increasing crop heterogeneity enhances multitrophic diversity across agricultural regions

International audienceAgricultural landscape homogenization has detrimental effects on biodiversity and key ecosystem services. Increasing agricultural landscape heterogeneity by increasing seminatural cover can help to mitigate biodiversity loss. However, the amount of seminatural cover is generally low and difficult to increase in many intensively managed agricultural landscapes. We hypothesized that increasing the heterogeneity of the crop mosaic itself (hereafter “crop heterogeneity”) can also have positive effects on biodiversity. In 8 contrasting regions of Europe and North America, we selected 435 landscapes along independent gradients of crop diversity and mean field size. Within each landscape, we selected 3 sampling sites in 1, 2, or 3 crop types. We sampled 7 taxa (plants, bees, butterflies, hoverflies, carabids, spiders, and birds) and calculated a synthetic index of multitrophic diversity at the landscape level. Increasing crop heterogeneity was more beneficial for multitrophic diversity than increasing seminatural cover. For instance, the effect of decreasing mean field size from 5 to 2.8 ha was as strong as the effect of increasing seminatural cover from 0.5 to 11%. Decreasing mean field size benefited multitrophic diversity even in the absence of seminatural vegetation between fields. Increasing the number of crop types sampled had a positive effect on landscape-level multitrophic diversity. However, the effect of increasing crop diversity in the landscape surrounding fields sampled depended on the amount of seminatural cover. Our study provides large-scale, multitrophic, cross-regional evidence that increasing crop heterogeneity can be an effective way to increase biodiversity in agricultural landscapes without taking land out of agricultural production

Converging Intracranial Markers of Conscious Access

We compared conscious and nonconscious processing of briefly flashed words using a visual masking procedure while recording intracranial electroencephalogram (iEEG) in ten patients. Nonconscious processing of masked words was observed in multiple cortical areas, mostly within an early time window (<300 ms), accompanied by induced gamma-band activity, but without coherent long-distance neural activity, suggesting a quickly dissipating feedforward wave. In contrast, conscious processing of unmasked words was characterized by the convergence of four distinct neurophysiological markers: sustained voltage changes, particularly in prefrontal cortex, large increases in spectral power in the gamma band, increases in long-distance phase synchrony in the beta range, and increases in long-range Granger causality. We argue that all of those measures provide distinct windows into the same distributed state of conscious processing. These results have a direct impact on current theoretical discussions concerning the neural correlates of conscious access

Automatic prediction of laminar/turbulent transition in an unstructured finite element Navier-Stokes solver

La thèse vise à intégrer des critères de transition dans le solveur Navier-Stokes non structuré Aether utilisé chez Dassault Aviation. Une méthodologie de prévision de la transition laminaire/turbulent a été élaborée et implémentée dans le solveur RANS Aether. Deux stratégies de calcul de transition ont été testées. Soit Aether est couplé avec le code de couche limite de l’ONERA 3C3D. Soit la position de transition est calculée en utilisant directement les profils de vitesse RANS. Les deux méthodes ont été testées pour des écoulements subsoniques et transsoniques. L’influence des solveurs numériques, des critères de transition et du processus de couplage sont étudiés. L’utilisation de schémas numériques d’ordre élevé est également considérée.This thesis present the state-of-the-art of the transition prediction numerical chain which has been developed at Dassault Aviation in the RANS solver AETHER. Two strategies for transition location estimations exist. First, AETHER is coupled with the ONERA boundary layer code 3C3D. Second, the transition location is computed by using directly the RANS velocity profiles. Both methods were preliminarily tested in subsonic and transonic. The issues of the influence of the numerical solvers, transition onset criteria and coupling process are studied. The influence of higher order numerical method, are also considered

Modulation of muscle activity in children’s gait : towards a modelling of dynamic electromyography

La marche des enfants atteints de paralysie cérébrale est explorée dans des structures appelées laboratoires d’analyse quantifiée du mouvement depuis environ 30 ans. L’interprétation des données acquises dans ces laboratoires est difficile en raison d’obstacles méthodologiques, statistiques, et parce que la physiologie motrice n’est pas totalement connue. L’étude des signaux électromyographiques, indicateurs des activations musculaires dynamiques, fait l’objet de cette thèse. Nous avons effectué deux séries d’expérimentations aboutissant à quatre études de recherche sur la marche des enfants à développement typique et des enfants atteints de paralysie cérébrale unilatérale. L’effet de la vitesse de marche sur la coactivation musculaire, le lien entre cette coactivation et l’amplitude des mouvements du membre inférieur pendant la marche, les adaptations musculaires lors de la marche en virage, et les spécificités de ces adaptations chez les enfants paralysés cérébraux, ont été successivement étudiées. Ces résultats nous ont permis de préciser le rôle de facteurs physiologiques liés à la commande motrice, tels que la vitesse ou le changement de direction, mais également l’effet de la pathologie sur les activations musculaires observées. Les difficultés métrologiques et statistiques liées aux signaux étudiés ont cependant constitué des obstacles importants à l’interprétation de ces données en termes de contrôle moteur. La réflexion progressive sur ces problèmes méthodologiques a permis le développement par étapes de traitements statistiques spécifiques, parfois innovants, et l’émergence de propositions concernant la métrologie de l’électromyographie dynamique.Children with cerebral palsy benefit from gait analyses in motion labs for approximately thirty years. The interpretation of the numerous data that can be obtained during such evaluations still remains cautious, because of methodological and statistical reasons, and because of the lack of an exhaustive knowledge regarding the motor control of gait. This Ph D thesis focused on the study of electromyographic signals, which are representative of the dynamic muscle activations during gait. We designed two series of experiments, leading to four studies into the dynamic electromyography during gait in children with unilateral cerebral palsy and their typically developing peers. The effect of gait speed on muscle coactivation, the impact of this coactivation on the range of motion during gait, the muscle adaptations to turning gait, and finally the specificities of these adaptations in children with cerebral palsy were investigated successively. The results of the studies give insight into the role of physiological factors linked to the motor control of gait, such as speed or change of direction, but also into the impact of pathology on the muscle activations, which are the parameters of interest. Some methodological and statistical difficulties, linked to the nature of the signals that are studied, compromise the possibility to interpret the data with respect to motor control. The continuous reflection on these methodological limitations allows the development of specific, appropriate statistical analyses, and the emergence of propositions regarding the metrology of dynamic electromyography

What causes increased passive stiffness of plantarflexor muscle–tendon unit in children with spastic cerebral palsy?

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