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Proximity Effect of Metallic Environments on Cylindrical Dielectric Resonator Antenna for Smart Metering Applications
No full textInternational audienceDielectric resonator antennas (DRA), that is antennas where the radiating element is constituted by a block of dielectric material, have been effectively used for several applications, including wireless communications radar and satellite systems. In this paper, we present design of an environment independent cylindrical DRA for smart metering application. Numerical simulations displaying the fundamental antenna parameters for a cylindrical DRA have been carried out for three excitation modes (HEM11δ, TE01δ and TM01δ). The three modes are compared in order to demonstrate and reveal the robustness of dielectric resonators to the effects of close environment variations. The comparative study relies on numerical results obtained using Ansoft High Frequency Structure Simulator (HFSS). The obtained results give a better understanding of the impact of the excited mode on the environment independence of cylindrical DRAs
SHG using different combination of modal and quasi- phase matching in PPLN waveguides
No full textInternational audienceTheoretically, increasing the mode confinement is the way to go to improve the nonlinear efficiency, and we are actively working in this direction [1], but up to know there are still fabrications issues to solve to get low loss, highly confining waveguides with preserved nonlinearities in PPLN. Therefore, we are still intensively studying the SPE technique and despite our experience and the numerous devices we have been able to develop for Quantum Communications [2], precisely controlling the spectrum and the efficiency in SHG experiments is still an issue. Our devices are designed to be used at low CW power, but in order to characterise them more precisely, we add a characterisation step using a pulsed OPO NT242 from EKSPLA which emits 5ns pulses at 1kHz rep. rate and is tuneable from 210 to 2600 nm. Using a 1.5 cm long sample in which the PPLN section obtained by e-beam writing [3] was 1.5mm long and the waveguides produced by the SPE process using a proton source composed of Benzoic Acid and 3.1% Lithium Benzoate melted at 300°C, we obtained the normalized spectra reported in fig.1a. In this picture, we can see that we obtained the same results with the OPO and with a tuneable monomode CW laser (Tunics T100S-HP). (a) (b) Fig. 1. (a) Comparison of the SHG normalized spectra obtained with the OPO and a CW monomode tunable laser and (b) SHG spectra showing the harmonic signal obtained with different combinations of modal and quasi-phase matching. Using an intense broadly tuneable source, we expected to find the different combinations of modal and quasi-phase matching which can be observed in fig. 1b. The signal observed for a pump wavelength of 1.55 µm correspond to the interactio
A stabilized Powell-Sabin finite-element method for the 2D Euler equations in supersonic regime
No full textIn this paper is presented a Powell-Sabin finite-elements scheme (PS-FEM) for the solution of the 2D Euler equations in supersonic regime. The spatial dis-cretization is based on PS splines, that are piecewise quadratic polynomials with a global C 1 continuity, defined on conforming triangulations. Some geometrical issues related the practical construction of the PS elements are discussed, in particular, the generation of the control triangles and the imposition of the boundary conditions. A stabilized formulation is considered, and a novel shock-capturing technique in the context of continuous finite-elements is proposed to reduce oscillations around the discontinuity, and compared with the classic technique proposed by Tedzuyar [1]. The code is verified using manufactured solutions and validated using two challenging numerical examples, which allows to evaluate the performance of the PS discretization in capturing the shocks
Vers une source UV à partir de la génération d'harmonique dans des guides GaN
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GÉNÉRATION D'HARMONIQUE EFICACE, EN UTILISANT POUR L'HARMONIQUE DES MODES D'ORDRE ÉLEVÉ DANS LES GUIDES SUR PPLN
No full textInternational audienceDans cette étude, pour nous assurer que la fabrication des guides n'induise aucun effet parasites comme la création de nanodomaines, la réductions du coefficient non linéaire ou le coupage des polarisations ordinaires et extra-ordinaire induit par les contraintes mécaniques, nous avons utilisé des guides à gradient d'indice présentant une très faible variation d'indice et un profil a gradient. Dans ce cas, nous avons pu constater qu'il était plus intéressant de travailler avec des modes d'ordre élevé pour l'harmonique. Ces modes présentent en effet un meilleur recouvrement avec le mode de pompe et une dispersion très semblable à celle du mode de pompe ce qui rend l'interaction efficace et peu sensible aux variations des paramètres géométriques du guide. MOTS-CLEFS : Optique non linéaire, Optique Intégrée, PPLN, Echange protoniqu
A coupled PDE-ODE model for bounded acceleration in macroscopic traffic flow models
No full textIn this paper, we propose a new mathematical model accounting for the boundedness of traffic acceleration at a macroscopic scale. Our model is built on a first order macroscopic PDE model coupled with an ODE describing the trajectory of the leader of a platoon accelerating at a given constant rate. We use Wave Front Tracking techniques to construct approximate solutions to the Initial Value Problem. We present some numerical examples including the case of successive traffic signals on an arterial road and we compare the solution to our model with the solution given by the classical LWR equation in order to evaluate the impact of bounded acceleration
The dynamics of populist mobilization in the 2017 French presidential election
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Reconstructing the social constructionist view of emotions: from language to culture, including nonhuman culture
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Two genomes of highly polyphagous lepidopteran pests (Spodoptera frugiperda, Noctuidae) with different host-plant ranges
No full textInternational audienceEmergence of polyphagous herbivorous insects entails significant adaptation to recognize, detoxify and digest a variety of host-plants. Despite of its biological and practical importance - since insects eat 20% of crops - no exhaustive analysis of gene repertoires required for adaptations in generalist insect herbivores has previously been performed. The noctuid moth Spodoptera frugiperda ranks as one of the world’s worst agricultural pests. This insect is polyphagous while the majority of other lepidopteran herbivores are specialist. It consists of two morphologically indistinguishable strains (“C” and “R”) that have different host plant ranges. To describe the evolutionary mechanisms that both enable the emergence of polyphagous herbivory and lead to the shift in the host preference, we analyzed whole genome sequences from laboratory and natural populations of both strains. We observed huge expansions of genes associated with chemosensation and detoxification compared with specialist Lepidoptera. These expansions are largely due to tandem duplication, a possible adaptation mechanism enabling polyphagy. Individuals from natural C and R populations show significant genomic differentiation. We found signatures of positive selection in genes involved in chemoreception, detoxification and digestion, and copy number variation in the two latter gene families, suggesting an adaptive role for structural variation