Détection de contours | EPFL Graph Search

En et en vision par ordinateur, on appelle détection de contours les procédés permettant de repérer les points d'une qui correspondent à un changement brutal de l'intensité lumineuse. Ces changements de propriétés de l' indiquent en général des éléments importants de structure dans l'objet représenté. Ces éléments incluent des discontinuités dans la profondeur, dans l'orientation d'une surface, dans les propriétés d'un matériau et dans l'éclairage d'une scène. La détection des contours dans une image réduit de manière significative la quantité de données en conservant des informations qu'on peut juger plus pertinentes. Il existe un grand nombre de méthodes de détection des contours de l'image mais la plupart d'entre elles peuvent être regroupées en deux catégories. La première recherche les extremums de la dérivée première, en général les maximums locaux de l'intensité du gradient. La seconde recherche les annulations de la dérivée seconde, en général les annulations du laplacien ou

Asymmetric Metal-Dielectric Metacylinders and Their Potential Applications From Engineering Scattering Patterns to Spatial Optical Signal Processing

Romain Christophe Rémy Fleury, Ali Momeni, Mahdi Safari

We propose a bianisotropic hybrid metal-dielectric structure comprising dielectric and metallic cylindrical wedges wherein the composite metacylinder enables advanced control of electric, magnetic, and magnetoelectric resonances. We establish a theoretical framework in which the electromagnetic response of this meta-atom is described through the electric and magnetic multipole moments. The complete dynamic polarizability tensor, expressed in a compact form, is derived as a function of the Mie-scattering coefficients. Further, the constitutive parameters—determined analytically—illustrate the tunability of the structure’s frequency and strength of resonances in light of its high degree of geometric freedom. Flexibility in the design makes the proposed metacylinder a viable candidate for various applications in the microscopic (single meta-atom) and macroscopic (metasurface) levels. We show that the highly versatile bianisotropic meta-atom is amenable to being designed for the desired electromagnetic response, such as electric dipole-free and zero or near-zero (backward and forward) scattering at the microscopic level. In addition, we show that the azimuthal asymmetry gives rise to normal polarizability components, which are vital elements in synthesizing asymmetric optical transfer function at the macroscopic level. We conduct a precise inspection, from the microscopic to the macroscopic level, of the metasurface synthesis for emphasizing on the role of normal polarizability components for spatial optical signal processing. It is shown that this simple two-dimensional asymmetric meta-atom can perform first-order differentiation and edge detection at normal illumination. The results reported herein contribute toward improving the physical understanding of wave interaction with artificial materials composed of asymmetric elongated metal-dielectric inclusions and open the potential of its application in spatial signal and image processing.

2021

Gold nanoparticles mediated label-free capacitance detection of cardiac troponin I

Sandro Carrara, Priyanka Sharma

It has been already proved that electrical capacitance increases at the electrode surface due to binding of highly charged antigens on the biointerface. In this paper, this capacitance change was used to demonstrate a novel detection for cardiac troponin I (cTnI). Citrate-capped gold nanoparticles (GNPs) were deposited on screen printed electrodes using an innovative one-step electrochemical technique. The gold (Au) nanostructuration onto the electrode surface was characterized by atomic force and field emission scanning electron microscopies. The highly specific anti-cTnI antibodies were immobilized onto the Au matrix, and characterized by confocal microscopy. The interaction of cTnI with its corresponding antibody was studied with respect to electrical capacitance changes as deduced by using the Randles model of the equivalent circuit of the electrochemical cell. The sensor-to-sensor measurements error was registered less than 2% on the average measured capacitance. cTnI was successfully detected in a label-free manner with a limit of detection equal to 0.2 ng mL(-1). This obtained result was one order of magnitude better than that obtained with ELISA tests performed by using the same antibodies, with a detection limit of 4.3 ng mL(-1). (C) 2011 Elsevier B.V. All rights reserved.

2012

Asymmetric Metal-Dielectric Metacylinders and Their Potential Applications From Engineering Scattering Patterns to Spatial Optical Signal Processing

Romain Christophe Rémy Fleury, Ali Momeni, Mahdi Safari

2021