Effect of extinction on the high-energy optical response of photonic crystals

An analysis of the optical response of photonic crystals in the high-order band energy range is herein presented. High and abruptly fluctuating specular reflectance is predicted for perfect lattices at those energies even in the absence of any photonic gap or pseudogap. As optical extinction is gradually introduced, it is possible to reproduce experimental results found in the literature and which have recently been the subject of an intense debate. Band structure calculations demonstrate that extinction is extraordinarily amplified in the high-energy range and is responsible for the features so far observed in that range in real crystalsConsejo Superior de Investigaciones Científicas 2005AR0070Universidad de Buenos Aires ANPCYT-BID 802Agencia Nacional de Promoción Científica y Tecnológica OC-AR03-14099Ministerio de Educación y Ciencia MAT2005-0302

Towards a full understanding of the growth dynamics and optical response of self-assembled photonic colloidal crystal films

Recent advances in the comprehension of the growth dynamics of colloidal crystal films opens the door to rational design of experiments aiming at fabricating lattices in which the density of intrinsic defects is minimized. Since such imperfections have a dramatic effect on scattered light of wavelength smaller than the lattice constant, the evaluation of the experimental optical response at those energy ranges, based on the comparison to rigorous calculations, is identified as the most sensitive guide to accurately evaluate the progress towards the actual realization of defect-free colloidal crystals.Ministerio de Ciencia y Educación MAT200503028Consejo Superior de Investigaciones Científicas 2005AR007

Interplay between crystal-size and disorder effects in the high-energy optical response of photonic crystal slabs

Experimental reflectance spectra have been obtained for colloidal crystals whose widths ranged from one to several sphere monolayers, and their features in the higher order band energy range have been reproduced theoretically. In order to fit the measured data, optical extinction has been introduced in the theoretical model, which accounts for structure imperfections and disorder, the main sources of losses in an actual measurement. A complex spectrum in the high frequency region is observed even for one ordered monolayer, being this peak structure gradually modified as more layers are piled up. This allowed us to identify which peaks are reminiscent of the optical reflectance features of a single close-packed layer and which are the result of building up a three dimensional periodicity. A clear correlation between the amount of extinction introduced in the fitting and the slab width has been found, which demonstrates that wider real crystals produce less diffusely scattered light. At the same time, we find that the optical response of thinner crystals is more robust against the introduction of extinction than that of thicker ones, for which the effect is dramatic.Consejo Superior de Investigaciones Científicas 2005AR0070Universidad de Buenos Aires ANPCYT-BID 802Agencia Nacional de Promoción Científica y Tecnológica OC-AR03-14099Ministerio de Ciencia y Educación MAT2005-0302

Physical origin of the high energy optical response of three-dimensional photonic crystals

The physical origin of the optical response observed in three-dimensional photonic crystals when the photon wavelength is equal or lower than the lattice parameter still remains unsatisfactorily explained and is the subject of an intense and interesting debate. Herein we demonstrate for the first time that all optical spectra features in this high energy region of photonic crystals arise from electromagnetic resonances within the ordered array, modified by the interplay between these resonances with the opening of diffraction channels, the presence of imperfections and finite size effects. AU these four phenomena are taken into account in our theoretical approach to the problem, which allows us to provide a full description of the observed optical response based on fundamental phenomena as well as to attain fair fittings of experimental results.Consejo Superior de Investigaciones Científicas 2005AR0070Universidad de Buenos Aires ANPCYT-BID 802Agencia Nacional de Promoción Científica y Tecnológica OC-AR03-14099Ministerio de Ciencia y Educación MAT2005-0302

Dante en Colombia

Coral Dorado, R. (2001). Dante en Colombia. La madriguera. (41):65-66. http://hdl.handle.net/10251/41995.Importación Masiva65664

Structural and Phylogenetic Analysis of Rhodobacter capsulatus NifF: Uncovering General Features of Nitrogen-fixation (nif)-Flavodoxins

Analysis of the crystal structure of NifF from Rhodobacter capsulatus and its homologues reported so far reflects the existence of unique structural features in nif flavodoxins: a leucine at the re face of the isoalloxazine, an eight-residue insertion at the C-terminus of the 50’s loop and a remarkable difference in the electrostatic potential surface with respect to non-nif flavodoxins. A phylogenetic study on 64 sequences from 52 bacterial species revealed four clusters, including different functional prototypes, correlating the previously defined as “short-chain” with the firmicutes flavodoxins and the “long-chain” with gram-negative species. The comparison of Rhodobacter NifF structure with other bacterial flavodoxin prototypes discloses the concurrence of specific features of these functional electron donors to nitrogenase.Fil: Perez Dorado, Inmaculada. Consejo Superior de Investigaciones Cientificas; EspañaFil: Bortolotti, Ana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Cortez, Nestor Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Hermoso, Juan A.. Consejo Superior de Investigaciones Cientificas; Españ

Anomalous Light Propagation, Finite Size-Effects and Losses in Real 3D Photonic Nanostructures

The propagation of light through 3D ordered photonic nanostructures is strongly affected by real aspects of actual crystals, especially at the spectral range where the wavelength of light is on the order of the lattice parameter. We perform a theoretical study on anomalous light propagation in finite thin artificial opal slabs made of a reduced number of layers. The vector KKR method we use accounts for the finite character of the structure and for different sources of losses. We show that an interplay between finite-size effects and losses engineers group velocity at this high energy range. Only depending on the crystal size and extinction, light propagation can either be superluminal (positive or negative) or approach zero for certain frequencies. The numerically calculated group index is in good agreement with experimental results some of which remained partially unexplainedPeer reviewe

Implementación de una metodología de aprendizaje del idioma inglés basado en la música como recurso didáctico

Incentivar a un estudiante a aprender una segunda lengua es parte del quehacer del educador, en el cual se debe tratar que el estudiante caiga en cuenta que se encuentra en un contexto comunicativo global, esperando sembrar de este modo, la necesidad de su aprendizaje, no obstante, el no ser capaces como formadores de estimular y hacer imperativa dicha necesidad, hará difícil la asimilación, al menos de los conceptos básicos de una lengua extranjera. Desde otra perspectiva, la enseñanza de una lengua extranjera por medio de la gramática ha funcionado de manera parcial, ya que el énfasis que se hace en lo escrito y en la estructura gramatical, ha dejado de lado la expresión oral y por consiguiente el entendimiento del nuevo idioma no es completo, presentándose deficiencias que se hacen evidentes cuando el estudiante, una vez finalizado el colegio, no se desenvuelve con un nivel de comunicación básica en segunda lengua, y menos aún se hace entender con propieda