Caractérisation de matériaux électrooptiques

National audienceLe problème posé est la caractérisation d'un matériau disponible en très petite quantité. Nous utilisons les propriétés d'une cavité électromagnétique. Nous mesurons la fréquence de résonance de cette structure en présence et en absence de l'échantillon dont nous cherchons la constante diélectrique

Impact-Aware Multi-Contact Balance Criteria

Intentionally applying impacts while maintaining balance is challenging for legged robots. This study originated from observing experimental data of the humanoid robot HRP-4 intentionally hitting a wall with its right arm while standing on two feet. Strangely, violating the usual zero moment point balance criteria did not systematically result in a fall. To investigate this phenomenon, we propose the zero-step capture region for non-coplanar contacts, defined as the center of mass (CoM) velocity area, and validated it with push-recovery experiments employing the HRP-4 balancing on two non-coplanar contacts. To further enable on-purpose impacts, we compute the set of candidate post-impact CoM velocities accounting for frictional-impact dynamics in three dimensions, and restrict the entire set within the CoM velocity area to maintain balance with the sustained contacts during and after impacts. We illustrate the maximum contact velocity for various HRP-4 stances in simulation, indicating potential for integration into other task-space whole-body controllers or planners. This study is the first to address the challenging problem of applying an intentional impact with a kinematic-controlled humanoid robot on non-coplanar contacts

Identification and expression of differentially expressed genes in the hard clam, Mercenaria mercenaria, in response to quahog parasite unknown (QPX)

<p>Abstract</p> <p>Background</p> <p>The hard clam, <it>Mercenaria mercenaria</it>, has been affected by severe mortality episodes associated with the protistan parasite QPX (Quahog Parasite Unknown) for several years. Despite the commercial importance of hard clams in the United States, molecular bases of defense mechanisms in <it>M. mercenaria</it>, especially during QPX infection, remain unknown.</p> <p>Results</p> <p>Our study used suppression subtractive hybridization (SSH), as well as the construction of cDNA libraries from hemocytes to identify genes related to the defense of the hard clam against its parasite. Hard clams were experimentally infected with QPX and SSH was performed on mRNA samples extracted from mantle and gill tissues at different times post-challenge. A total of 298 clones from SSH libraries and 1352 clones from cDNA libraries were sequenced. Among these sequences, homologies with genes involved in different physiological processes related to signal transduction, stress response, immunity and protein synthesis were identified. Quantitative PCR revealed significant changes in the expression of several of these genes in response to QPX challenge and demonstrated significant correlations in terms of levels of gene expression between intermediates of signalling pathways and humoral defense factors, such as big defensin and lysozyme.</p> <p>Conclusion</p> <p>Results of this study allowed the detection of modifications caused by QPX at the transcriptional level providing insight into clam immune response to the infection. These investigations permitted the identification of candidate genes and pathways for further analyses of biological bases of clam resistance to QPX allowing for a better understanding of bivalve immunity in general.</p

Impact-Aware Task-Space Quadratic-Programming Control

Generating on-purpose impacts with rigid robots is challenging as they may lead to severe hardware failures due to abrupt changes in the velocities and torques. Without dedicated hardware and controllers, robots typically operate at a near-zero velocity in the vicinity of contacts. We assume knowing how much of impact the hardware can absorb and focus solely on the controller aspects. The novelty of our approach is twofold: (i) it uses the task-space inverse dynamics formalism that we extend by seamlessly integrating impact tasks; (ii) it does not require separate models with switches or a reset map to operate the robot undergoing impact tasks. Our main idea lies in integrating post-impact states prediction and impact-aware inequality constraints as part of our existing general-purpose whole-body controller. To achieve such prediction, we formulate task-space impacts and its spreading along the kinematic tree of a floating-base robot with subsequent joint velocity and torque jumps. As a result, the feasible solution set accounts for various constraints due to expected impacts. In a multi-contact situation of under-actuated legged robots subject to multiple impacts, we also enforce standing stability margins. By design, our controller does not require precise knowledge of impact location and timing. We assessed our formalism with the humanoid robot HRP-4, generating maximum contact velocities, neither breaking established contacts nor damaging the hardware

Caractérisation de matériaux diélectriques anisotropes

International audienceDe nos jours, le fonctionnement de la grande majorité des convertisseurs hertzien/optique repose sur les propriétés électrooptiques d'un matériau anisotrope cristallin, le niobate de lithium. Lorsqu'une onde optique pénètre dans le matériau, sa vitesse de propagation varie en fonction de l'intensité du champ électrique appliqué suivant l'effet Pockels (variation d'indice dépendante de l'intensité de champ). En général, cette variation est transformée en modulation d'intensité dans un interféromètre de type Mach-Zender ou à l'aide de polariseurs qui transforment la rotation de la polarisation en une variation d'intensité. La principale différence entre les deux méthodes est que dans le premier cas la structure de modulation est planaire, et qu'elle est volumique dans l'autre cas. Bien que déjà très répandu, le niobate de lithium a plusieurs inconvénients non négligeables : son coût de fabrication est très élevé, son coefficient électrooptique est faible et sa constante diélectrique haute fréquence est élevée. Pour pallier ces inconvénients, des matériaux à base de polymères sont actuellement développés. Nous nous intéressons à la caractérisation et à l'utilisation de ce type de matériaux. Dans cet article, nous présentons la méthode de mesure mise en œuvre pour déterminer la partie réelle de la constante diélectrique de ces matériaux en tenant compte de l'anisotropie

Characterization of electrooptic polymer applied to microwave sensing

International audienceIn this paper we present electrooptic measurement of a crosslinked side chain PGMA/DR1 polymer. Measured values are as high as 11 pm/V at 1310 nm, we present measurement as a function of incident beam reflexion point and show dependance between the reflexion point location over the sample and the measured electrooptic coefficient. We present low frequency relative dielectric constant using a capacitance measurement method. Using this method, we found a relative permittivity of 4.46plusmn0.38 for our polymer. We present a new electrooptic microwave sensor, where we enhance the electrooptical interaction by increasing the optical path length using a Fabry-Perot cavity and we concentrate the electric field inside our device using a microstrip resonator. Expected interaction enhancement value is expected to be as high 310deg compared to the simple reflexion case at low frequenc

Electrooptic microwave antenna using organic poled polymers

International audienceWe propose a new electrooptic antenna design using organic polymer to receive microwave signals. In this paper we present the characterization of an electrooptic organic polymer. We measured the dielectric constant at microwave frequencies, and the electrooptic coefficient. We measured values of r33 of 3.35 pm/V at 1310 nm and 1.98 pm/V at 1550 nm. The goal of the electrooptic antenna design is to obtain maximum microwave and optical interaction. We propose a novel approach based on resonance effect in both optical and microwave domain. For the optical resonance effect we use a Fabry-Perot cavity, and a patch structure as microwave resonator

Passive electro-optic antenna using polymer material

International audienceThe experimental results of a polymer microwave electro-optic antenna are reported. The device amplitude-modulates an optical input beam with a free-space propagating electromagnetic wave. By using a new dipole printed antenna, the electromagnetic energy is concentrated inside the device. An antenna factor of 168 dB/m is achieved with only 1 mum of electro-optic polyme