Wigner islands with electrons over helium

We present here the first experimental study of Wigner islands formed by electrons floating over helium. Electrons are trapped electrostatically in a mesoscopic structure covered with a helium film, behaving as a quantum dot. By removing electrons one by one, we are able to find the addition spectrum, i.e. the energy required to add (or extract) one electron from the trap with occupation number $N$. Experimental addition spectra are compared with Monte Carlo simulations for the actual trap geometry, confirming the ordered state of electrons over helium in the island.Comment: 12 pages, 13 figures, draft pape

A strategy for multimodal canopy images registration

Registration of complex and self-similar images such as plant canopy images is a challenge in plant sciences. Yet, this is often a required step for multimodal imaging, where unaligned sensors yield unregistered image pairs. We propose a pipeline adapted to such constraints, applied to apple tree canopies. Specifically, we apply an intensity-based registration on downscaled and/or Gaussian blurred versions of the targeted images. This helps to eliminate spurious details, which smooths the optimization landscape and also helps to reduce differences between the modalities. Results show better registration than with standard feature-based or intensity-based methods

On the value of the Kullback-Leibler divergence for cost-effective spectral imaging of plants by optimal selection of wavebands

The practical value of a criterion based on statistical information theory is demonstrated for the selection of optimal wavelength and bandwidth of low-cost lighting systems in plant imaging applications. Kullback–Leibler divergence is applied to the problem of spectral band reduction from hyperspectral imaging. The results are illustrated on various plant imaging problems and show similar results to the one obtained with state-of-the-art criteria. A specific interest of the proposed approach is to offer the possibility to integrate technological constraints in the optimization of the spectral bands selected

ElonCam : instrumentation et analyse d'images pour le suivi automatisé individualisé du développement de semences et de plantules

Le système ElonCam est en cours de développement dans le cadre d\u27une collaboration entre le LARIS, le GEVES-SNES et l\u27INRA d\u27Angers - IRHS. Il s’agit d’un système de vision, constitué d’un système d’acquisition d’images piloté par ordinateur, et d’un logiciel de traitement et d\u27analyse d\u27images couleur RVB, qui permet de réaliser des mesures automatisées sur les semences et les plantules au cours de leur développement. Le système d’acquisition peut incorporer différentes modalités d\u27imagerie, et il est actuellement employé en imagerie visible (voir Fig. 1). L\u27acquisition des images est effectuée en lumière verte inactinique (censée simuler l\u27obscurité et ne pas influencer le développement des plantules). Afin de minimiser l\u27apport d\u27énergie lumineuse l\u27éclairage intermittent est synchronisé avec la prise de vue. Les graines sont semées dans une boîte de Pétri contenant de la gélose (milieu de culture transparent) placée à la verticale afin de respecter le géotropisme. Le logiciel de traitement d\u27images détecte, isole, labellise puis mesure les semences et les plantules. L\u27analyse numérique des images permet d\u27aboutir à la mesure individuelle automatisée des semences au cours de la germination puis des plantules et de leurs organes d\u27intérêt en fonction du temps, selon les conditions de la croissance. Afin de gérer les croisements de plantules, un algorithme de suivi de structures arborescentes a été développé. Le système de vision vise à contribuer au phénotypage automatisé haut-débit des semences et plantules, afin de tester la capacité à germer et la vitesse de croissance pour différentes espèces et différents génotypes, et en vue d\u27améliorer leurs propriétés et rendement. Le système a été testé pour la caractérisation de différentes espèces comme Medicago truncatula, colza, blé, tournesol, et également la betterave dans le cadre du programme ANR Investissements d\u27Avenir AKER où les coauteurs sont impliqués et qui concerne l\u27amélioration de la betterave sucrière pour laquelle la France est l\u27un des premiers producteurs mondiaux. Ce travail a bénéficié d\u27une aide de l\u27État gérée par l\u27Agence Nationale de la Recherche au titre du programme "Investissements d\u27Avenir" portant la référence ANR-11-BTBR-0007 (programme AKER)

Différentes modalités d'imagerie (visible, thermographie, hyperspectrale) pour le phénotypage des semences et plantules

Différentes modalités d\u27imagerie (visible, thermographie, hyperspectrale) pour le phénotypage des semences et plantules

A Reanalysis of theUltraviolet Extinction from Interstellar Dust in the Large Magellanic Cloud

We have reanalyzed the Large Magellanic Cloud's (LMC) ultraviolet (UV) extinction using data from the IUE final archive. Our new analysis takes advantage of the improved signal--to--noise of the IUE NEWSIPS reduction, the exclusion of stars with very low reddening, the careful selection of well matched comparison stars, and an analysis of the effects of Galactic foreground dust. Differences between the average extinction curves of the 30 Dor region and the rest of the LMC are reduced compared to previous studies. We find that there is a group of stars with very weak 2175 Ang. bumps that lie in or near the region occupied by the supergiant shell, LMC 2, on the southeast side of 30 Dor. The average extinction curves inside and outside LMC 2 show a very significant difference in 2175 Ang. bump strength, but their far--UV extinctions are similar. While it is unclear whether or not the extinction outside the LMC 2 region can be fit with the relation of Cardelli, Clayton and Mathis (CCM), sightlines near LMC 2 cannot be fit with CCM due to their weak 2175 Ang. bumps. While the extinction properties seen in the LMC lie within the range of properties seen in the Galaxy, the correlations of UV extinction properties with environment seen in the Galaxy do not appear to hold in the LMC.Comment: 29 pages, 10 figures, to be published in Ap

3D multimodal simulation of image acquisition by X-Ray and MRI for validation of seedling measurements with segmentation algorithms

3D multimodal simulation of image acquisition by X-Ray and MRI for validation of seedling measurements with segmentation algorithms

Low-cost vision machine for high-throughput automated monitoring of heterotrophic seedling growth on wet paper support

In this communication, we propose a fully automated vision system to monitor the germination and elongation of seedlings positioned in a petri dish. While most existing systems use agar gel as transparent nutritive medium imaged in backlight, we demonstrate that although it provides a reduced contrast, not fully opaque paper can serve as efficient lower-cost medium preventing the well-known problem of seedling joining during elongation. Automatic tracking of elongating seedlings is realized with a minimal pathalgorithm. The three organs (radicle, hypocotyl, and cotyledon) are then segmented. Validation of the accuracy of the system is provided on sugar beet seedling by comparison with the expert-based ground truth

Vortex density spectrum of quantum turbulence

The fluctuations of the vortex density in a turbulent quantum fluid are deduced from local second-sound attenuation measurements. These measurements are performed with a micromachined open-cavity resonator inserted across a flow of turbulent He-II near 1.6 K. The power spectrum of the measured vortex line density is compatible with a (-5/3) power law. The physical interpretation, still open, is discussed.Comment: Submitted to Europhys. Let