Piezoelectric Phononic Plates: Retrieving the Frequency Band Structure via All-electric Experiments

We propose an experimental technique based on all-electric measurements to retrieve the frequency response of a one-dimensional piezoelectric phononic crystal plate, structured periodically with millimeter-scaled metallic strips on its two surfaces. The metallic electrodes, used for the excitation of Lamb-like guided modes in the plate, ensure at the same time control of their dispersion by means of externally loaded electric circuits that offer non-destructive tunability in the frequency response of these structures. Our results, in very good agreement with finite-element numerical predictions, reveal interesting symmetry aspects that are employed to analyze the frequency band structure of such crystals. More importantly, Lamb-like guided modes interact with electric-resonant bands induced by inductance loads on the plate, whose form and symmetry are discussed and analyzed in depth, showing unprecedented dispersion characteristics.Comment: This is the version of the article before peer review or editing, as submitted by an author to Smart Materials and Structures. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-665X/ab4aa

Efficient occupancy model-fitting for extensive citizen-science data

Appropriate large-scale citizen-science data present important new opportunities for biodiversity modelling, due in part to the wide spatial coverage of information. Recently proposed occupancy modelling approaches naturally incorporate random effects in order to account for annual variation in the composition of sites surveyed. In turn this leads to Bayesian analysis and model fitting, which are typically extremely time consuming. Motivated by presence-only records of occurrence from the UK Butterflies for the New Millennium data base, we present an alternative approach, in which site variation is described in a standard way through logistic regression on relevant environmental covariates. This allows efficient occupancy model-fitting using classical inference, which is easily achieved using standard computers. This is especially important when models need to be fitted each year, typically for many different species, as with British butterflies for example. Using both real and simulated data we demonstrate that the two approaches, with and without random effects, can result in similar conclusions regarding trends. There are many advantages to classical model-fitting, including the ability to compare a range of alternative models, identify appropriate covariates and assess model fit, using standard tools of maximum likelihood. In addition, modelling in terms of covariates provides opportunities for understanding the ecological processes that are in operation. We show that there is even greater potential; the classical approach allows us to construct regional indices simply, which indicate how changes in occupancy typically vary over a species’ range. In addition we are also able to construct dynamic occupancy maps, which provide a novel, modern tool for examining temporal changes in species distribution. These new developments may be applied to a wide range of taxa, and are valuable at a time of climate change. They also have the potential to motivate citizen scientists

Surfométrie appliquée à la caractérisation des matériaux

Le système proposé et réalisé est un profilomètre hybride fonctionnant en lumière monochromatique, double longueur d'onde, et en lumière blanche. Il comprend essentiellement un microscope métallographique, auquel on a intégré un interféromètre de Mirau, une caméra CCD matricielle, ainsi qu'un micro-ordinateur. Trois techniques d'interférométrie intégrées dans le même dispositif seront proposées : La première est basée sur la microscopie interférentielle à décalage de phase (Phase Shifting Interferometry) qui a les avantages de rapidité d'acquisition et de bonne résolution verticale tant que les défauts de surface ne dépassent pas quelques micromètres en profil continu. Afin de lever l'ambiguïté sur la phase, une deuxième technique a été mise en œuvre. Elle consiste à utiliser deux longueurs d'onde voisines l'une de l'autre et opérant dans le même interféromètre. La troisième méthode faisant appel à l'interférométrie en lumière blanche (White Light Interferometry) est avantageuse du point de vue de la dynamique verticale puisqu'on peutmesurer des motifs dont la hauteur peut aller jusqu'à plusieurs dizaines de micromètres.Néanmoins cette méthode présente l'inconvénient d'être moins rapide que les précédentes àcause du nombre élevé d'images à traiter.On présente dans cet article les performances du système en termes de résolutions latérale, longitudinale, précision, gamme de mesure, et de rapidité. Afin de valider cette étude, une étude comparative a été établie entre PSM, WLI, et par microscopie à forces atomiques AFM

Tunable phononic structures using Lamb waves in a piezoceramic plate

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