ABSTRACT
In this paper, we investigate the unusual color effect exhibited by the plumage of the heads of Cyanerpes cyaneus males, whose color turns from green to turquoise as the angle between the illumination and observation directions is increased. This singular color effect is characteristic of species that have quasi-ordered nanostructures of short-range order within the feather barbs. However, among species of the same family and even within feather patches of the same individual, one can find barbs with different characteristics, both macroscopic (curvature, shape, cross-sectional area) and in their internal microstructure. We apply the Korringa-Kohn-Rostoker method with the averaging technique to model the reflectance spectra for different angles of incidence and explain the dependence of the observed color with the incidence-collection angle. To investigate the influence of the disorder in the optical response of the spongy matrix, we apply the integral method for a two-dimensional cylinder system that simulates the distribution of air cavities within the $ \beta $ß-keratin medium. The experimental reflectance was interpreted as the result of multiple reflections in the internal interfaces generated by large air voids present within the spongy matrix. The application of rigorous methods to the study of natural photonic structures is of fundamental relevance for the design of efficient bioinspired artificial materials.
Subject(s)
Feathers/physiology , Pigmentation/physiology , Pigments, Biological/metabolism , Animals , Birds , Color , Male , Models, Biological , Nanostructures/chemistry , Optical Phenomena , Optics and Photonics , Spectrophotometry , beta-Keratins/metabolismABSTRACT
In this paper, we numerically demonstrate a refraction index sensor based on phase resonance excitation in a subwavelength-slit structure with a double period. The sensor consists of a metal layer with subwavelength slots arranged in a bi-periodic form, separated from a high refraction index medium. Between the metallic structure and the incident medium, a dielectric waveguide is formed whose refraction index is going to be determined. Variations in the refraction index of the waveguide are detected as shifts in the peaks of transmitted intensity originated by resonant modes supported by the compound metallic structure. At normal incidence, the spectral position of these resonant peaks exhibits a linear or a quadratic dependence with the refraction index, which permits us to obtain the unknown refraction index value with a high precision for a wide range of wavelengths. Since the operating principle of the sensor is due to the morphological resonances of the slits' structure, this device can be scaled to operate in different wavelength ranges while keeping similar characteristics.
ABSTRACT
The possibility of controlling the diffracted response of a periodic structure is investigated by using dual-period arrays, i.e., periodic arrays with a compound unit cell. We consider wire gratings in which each period comprises several cylinders with circular cross sections and all the cylinder axes are contained in the same plane. It is shown that this kind of structure permits one to control the diffracted response, regardless of the cylinder material and the incident polarization. Our numerical results suggest that the effect produced by wire gratings with dual-period characteristics is basically a geometric effect, and it can be present for other shapes of individual scatterers within each subarray.
ABSTRACT
Se describen brevemente los aspectos fundamentales de la mamografía digital, el estado actual de desarrollo y los avances que se esperan concretar en los próximos años. Mediante el empleo del filtro IRIS para la detección de masas incipientes se ilustra la contribución del diagnóstico asistido por computadora (CAD) a la reducción de falsos negativos (AU)
Subject(s)
Humans , Female , Mammography/methods , Radiographic Image Enhancement/methods , Ultrasonography, Mammary/methods , Filters , Breast Neoplasms/diagnosis , Breast Diseases/diagnosis , Mammography/instrumentation , Filtration MediaABSTRACT
Se describen brevemente los aspectos fundamentales de la mamografía digital, el estado actual de desarrollo y los avances que se esperan concretar en los próximos años. Mediante el empleo del filtro IRIS para la detección de masas incipientes se ilustra la contribución del diagnóstico asistido por computadora (CAD) a la reducción de falsos negativos
