Numerical solution of Cauchy problems in linear elasticity in axisymmetric situations

International audienceAn iterative method for solving axisymmetric Cauchy problems in linear elasticity is presented. This kind of problem consists in recovering missing displacements and forces data on one part of a domain boundary from the knowledge of overspecified displacements and forces data on another part of this boundary. Numerical simulations using the finite element method highlight the algorithm's efficiency, accuracy and robustness to noisy data as well as its ability to deblur noisy data. An application of the inverse technique to the identification of a friction coefficient is also presented

Importance of the model selection for processing dynamic three-point bending tests

International audienceThe Split-Hopkinson Pressure Bar apparatus remains the standard test to investigate high strain rate materials properties. To determine the tensile strength of quasi-brittle materials three-point bending tests are frequently employed. In this paper, we compare different analytical models for processing the recorded experimental wave signals. It is concluded that only the semi-infinite beam model and the modal superposition analysis with several modes are relevant to get precise strain rate and material dynamic characteristic

Gaze Behavior During Simulated Driving: Elements for a Visual Driving Aid

Analyses of optic flow due to observer self-motion and analyses ofthe driver’s gazing behavior during curve driving have suggested that the driverhas a tendency to look at a location close to the tangent point on the inside edge ofthe road. Psychophysical experiments have further demonstrated that this visualstrategy can be partly explained as an optimization of information pick-up. Themain objective of the present study was to investigate, in an interactive simulationcontext, if this perceptual strategy might be used to define a visual aid for curvedriving. In the framework of the French ARCOS project (Research action forsecure driving; www.arcos2004.com), we used a mini-simulator developed byINRETS (MSIS-CIR group) in collaboration with FAROS company, with twomain original characteristics: (1) during curve driving, the tangent point can becalculated and inserted in the visual scene in real-time and (2) a real-time eyerecordingsystem (EYELINK,® SMI) allows us to evaluate the relationshipsbetween driving performance, gaze direction and the on-line presentation of thetangent point

The odor context facilitates the perception of low-intensity facial expressions of emotion

It has been established that the recognition of facial expressions integrates contextual information. In this study, we aimed to clarify the influence of contextual odors. The participants were asked to match a target face varying in expression intensity with non-ambiguous expressive faces. Intensity variations in the target faces were designed by morphing expressive faces with neutral faces. In addition, the influence of verbal information was assessed by providing half the participants with the emotion names. Odor cues were manipulated by placing participants in a pleasant (strawberry), aversive (butyric acid), or no-odor control context. The results showed two main effects of the odor context. First, the minimum amount of visual information required to perceive an expression was lowered when the odor context was emotionally congruent: happiness was correctly perceived at lower intensities in the faces displayed in the pleasant odor context, and the same phenomenon occurred for disgust and anger in the aversive odor context. Second, the odor context influenced the false perception of expressions that were not used in target faces, with distinct patterns according to the presence of emotion names. When emotion names were provided, the aversive odor context decreased intrusions for disgust ambiguous faces but increased them for anger. When the emotion names were not provided, this effect did not occur and the pleasant odor context elicited an overall increase in intrusions for negative expressions. We conclude that olfaction plays a role in the way facial expressions are perceived in interaction with other contextual influences such as verbal information

Stabilisation progressive

International audienceCet article est un résumé étendu de (Altisen et al., Euro-Par 2016) dans lequel nous nous intéressons à des réseaux pouvant subir des changements topologiques transitoires. Nous proposons une nouvelle spécialisation de l'autostabilisation adaptée à ce type de réseau : la stabilisation progressive. Un algorithme est progressivement stabilisant sous hypothèse de (τ, ρ)-dynamicité s'il est autostabilisant et satisfait la propriété supplémentaire suivante : après au plus τ pas dynamiques vérifiant la condition ρ et se produisant à partir d'une configuration légitime, l'algorithme converge rapidement vers une configuration où une spécification plus faible est satisfaite ; puis il continue à converger progressivement vers des configurations où des spécifications de plus en plus fortes sont vérifiées, et ce, jusqu'à retrouver une configuration légitime vérifiant la spécification initiale du problème. Nous illustrons cette nouvelle propriété en proposant un algorithme progressivement stabilisant de synchronisation d'horloges

Stabilisation progressive

International audienceCet article est un résumé étendu de (Altisen et al., Euro-Par 2016) dans lequel nous nous intéressons à des réseaux pouvant subir des changements topologiques transitoires. Nous proposons une nouvelle spécialisation de l'autostabilisation adaptée à ce type de réseau : la stabilisation progressive. Un algorithme est progressivement stabilisant sous hypothèse de (τ, ρ)-dynamicité s'il est autostabilisant et satisfait la propriété supplémentaire suivante : après au plus τ pas dynamiques vérifiant la condition ρ et se produisant à partir d'une configuration légitime, l'algorithme converge rapidement vers une configuration où une spécification plus faible est satisfaite ; puis il continue à converger progressivement vers des configurations où des spécifications de plus en plus fortes sont vérifiées, et ce, jusqu'à retrouver une configuration légitime vérifiant la spécification initiale du problème. Nous illustrons cette nouvelle propriété en proposant un algorithme progressivement stabilisant de synchronisation d'horloges

Caractérisation du comportement à l'interface entre un matériau agrégataire et un acier sous forte pression et à grande vitesse

Un essai a été développé pour étudier l'interface entre un matériau énergétique et de l'acier. Le domaine d'intérêt est celui des fortes pressions (10-100 MPa) et des grandes vitesses relatives (10-100 m/s). Un dispositif consiste à faire glisser un cylindre constitué du matériau dans un tube en acier. Une précontrainte est réalisée. Elle permet de créer la contrainte normale au contact et de maintenir l'intégrité du corps d'épreuve lors de l'essai. Le déplacement relatif rapide est obtenu par des barres de Hopkinson. Les mesures permettent d'accéder au comportement local recherché

Plasmodium vivax-like genome sequences shed new insights into Plasmodium vivax biology and evolution

Although Plasmodium vivax is responsible for the majority of malaria infections outside Africa, little is known about its evolution and pathway to humans. Its closest genetic relative, P. vivax-like, was discovered in African great apes and is hypothesized to have given rise to P. vivax in humans. To unravel the evolutionary history and adaptation of P. vivax to different host environments, we generated using long- and short-read sequence technologies 2 new P. vivax-like reference genomes and 9 additional P. vivax-like genotypes. Analyses show that the genomes of P. vivax and P. vivax-like are highly similar and colinear within the core regions. Phylogenetic analyses clearly show that P. vivax-like parasites form a genetically distinct clade from P. vivax. Concerning the relative divergence dating, we show that the evolution of P. vivax in humans did not occur at the same time as the other agents of human malaria, thus suggesting that the transfer of Plasmodium parasites to humans happened several times independently over the history of the Homo genus. We further identify several key genes that exhibit signatures of positive selection exclusively in the human P. vivax parasites. Two of these genes have been identified to also be under positive selection in the other main human malaria agent, P. falciparum, thus suggesting their key role in the evolution of the ability of these parasites to infect humans or their anthropophilic vectors. Finally, we demonstrate that some gene families important for red blood cell (RBC) invasion (a key step of the life cycle of these parasites) have undergone lineage-specific evolution in the human parasite (e.g., reticulocyte-binding proteins [RBPs])

Analytical Approach to the Local Contact Potential Difference on (001) Ionic Surfaces: Implications for Kelvin Probe Force Microscopy

An analytical model of the electrostatic force between the tip of a non-contact Atomic Force Microscope (nc-AFM) and the (001) surface of an ionic crystal is reported. The model is able to account for the atomic contrast of the local contact potential difference (CPD) observed while nc-AFM-based Kelvin Probe Force Microscopy (KPFM) experiments. With the goal in mind to put in evidence this short-range electrostatic force, the Madelung potential arising at the surface of the ionic crystal is primarily derived. The expression of the force which is deduced can be split into two major contributions: the first stands for the coupling between the microscopic structure of the tip apex and the capacitor formed between the tip, the ionic crystal and the counter-electrode; the second term depicts the influence of the Madelung surface potential on the mesoscopic part of the tip, independently from its microscopic structure. These short-range electrostatic forces are in the range of ten pico-Newtons. When explicitly considering the crystal polarization, an analytical expression of the bias voltage to be applied on the tip to compensate for the local CPD, i.e. to cancel the short-range electrostatic force, is derived. The compensated CPD has the lateral periodicity of the Madelung surface potential. However, the strong dependence on the tip geometry, the applied modulation voltage as well as the tip-sample distance, which can even lead to an overestimation of the real surface potential, makes quantitative KPFM measurements of the local CPD extremely difficult