Anisotropic diffraction of stratified volume holographic grating in photorefractive media

We have studied the anisotropic diffraction properties of the stratified volume holographic gratings recorded in photorefractive media using the anisotropic coupled wave theory. It is shown that the diffraction efficiency of such system exhibit the uniform periodic Bragg selectivity properties. In addition the dependence of the stratified volume holographic optical elements (SVHOEs) diffraction properties on the buffer-layer thickness, grating-layer thickness, number of modulation layers, and total thickness of system are discussed in detail. (c) 2005 Elsevier GrnbH. All rights reserved.

The resolution of the thermodynamic paradox and the theory of guided wave propagation in anisotropic media

The resolution of the so-called thermodynamic paradox is presented in this paper. It is shown, in direct contradiction to the results of several previously published papers, that the cutoff modes (evanescent modes having complex propagation constants) can carry power in a waveguide containing ferrite. The errors in all previous “proofs” which purport to show that the cutoff modes cannot carry power are uncovered. The boundary value problem underlying the paradox is studied in detail; it is shown that, although the solution is somewhat complicated, there is nothing paradoxical about it.

The general problem of electromagnetic wave propagation through rectangular guides filled inhomogeneously in cross-section with transversely magnetized ferrite is also studied. Application of the standard waveguide techniques reduces the TM part to the well-known self-adjoint Sturm Liouville eigenvalue equation. The TE part, however, leads in general to a non-self-adjoint eigenvalue equation. This equation and the associated expansion problem are studied in detail. Expansion coefficients and actual fields are determined for a particular problem.

Microscopic Origin of Macroscopic Strength in Granular Media: A Numerical and Analytical Approach

Constitutive modeling in granular materials has historically been based on macroscopic experimental observations that, while being usually effective at predicting the bulk behavior of these type of materials, suffer important limitations when it comes to understanding the physics behind grain-to-grain interactions that induce the material to macroscopically behave in a given way when subjected to certain boundary conditions.

The advent of the discrete element method (DEM) in the late 1970s helped scientists and engineers to gain a deeper insight into some of the most fundamental mechanisms furnishing the grain scale. However, one of the most critical limitations of classical DEM schemes has been their inability to account for complex grain morphologies. Instead, simplified geometries such as discs, spheres, and polyhedra have typically been used. Fortunately, in the last fifteen years, there has been an increasing development of new computational as well as experimental techniques, such as non-uniform rational basis splines (NURBS) and 3D X-ray Computed Tomography (3DXRCT), which are contributing to create new tools that enable the inclusion of complex grain morphologies into DEM schemes.

Yet, as the scientific community is still developing these new tools, there is still a gap in thoroughly understanding the physical relations connecting grain and continuum scales as well as in the development of discrete techniques that can predict the emergent behavior of granular materials without resorting to phenomenology, but rather can directly unravel the micro-mechanical origin of macroscopic behavior.

In order to contribute towards closing the aforementioned gap, we have developed a micro-mechanical analysis of macroscopic peak strength, critical state, and residual strength in two-dimensional non-cohesive granular media, where typical continuum constitutive quantities such as frictional strength and dilation angle are explicitly related to their corresponding grain-scale counterparts (e.g., inter-particle contact forces, fabric, particle displacements, and velocities), providing an across-the-scale basis for better understanding and modeling granular media.

In the same way, we utilize a new DEM scheme (LS-DEM) that takes advantage of a mathematical technique called level set (LS) to enable the inclusion of real grain shapes into a classical discrete element method. After calibrating LS-DEM with respect to real experimental results, we exploit part of its potential to study the dependency of critical state (CS) parameters such as the critical state line (CSL) slope, CSL intercept, and CS friction angle on the grain's morphology, i.e., sphericity, roundness, and regularity.

Finally, we introduce a first computational algorithm to ``clone'' the grain morphologies of a sample of real digital grains. This cloning algorithm allows us to generate an arbitrary number of cloned grains that satisfy the same morphological features (e.g., roundness and aspect ratio) displayed by their real parents and can be included into a DEM simulation of a given mechanical phenomenon. In turn, this will help with the development of discrete techniques that can directly predict the engineering scale behavior of granular media without resorting to phenomenology.

Corrections to the paraxial approximation solutions in transversely nonuniform refractive-index media

The coupled differential recurrence equations for the corrections to the paraxial approximation solutions in transversely nonuniform refractive-index media are established in terms of the perturbation method. All the corrections (including the longitudinal field corrections) to the paraxial approximation solutions are presented in the weak-guidance approximation. As a concrete application, the first-order longitudinal field correction and the second-order transverse field correction to the paraxial approximation of a Gaussian beam propagating in a transversely quadratic refractive index medium are analytically investigated. (C) 1999 Optical Society of America [S0740-3232(99)00310-5].

Spatiotemporal instabilities in nonlinear Kerr media in the presence of arbitrary higher-order dispersions

Spatiotemporal instabilities in nonlinear Kerr media with arbitrary higher-order dispersions are studied by use of standard linear-stability analysis. A generic expression for instability growth rate that unifies and expands on previous results for temporal, spatial, and spatiotemporal instabilities is obtained. It is shown that all odd-order dispersions contribute nothing to instability, whereas all even-order dispersions not only affect the conventional instability regions but may also lead to the appearance of new instability regions. The role of fourth-order dispersion in spatiotemporal instabilities is studied exemplificatively to demonstrate the generic results. Numerical simulations confirm the obtained analytic results. (C) 2002 Optical Society of America.

Los linajes de Bizkaia en la Baja Edad Media: poder, parentesco y conflicto

Este libro se ocupa del principal protagonista de la historia medieval de Bizkaia: el hidalgo. Como en el resto de Europa Occidental, la nobleza del Señorío, organizada social y políticamente en linajes, acapara las fuentes de renta y traza sus estrategias sobre la alianza y la violencia. Sin embargo, en Bizkaia, la violencia feudal alcanzará cotas extremas en lo que se conoce como "luchas de bandos". La competencia entre los hidalgos se fundamenta en un argumento tan sólido como simple: el "más valer". "Más valer" en rentas y atreguados, "más valer" en descendencia bastarda o legítima, "más valer" que mueve a matar al vecino como forma extrema de sometimiento. En este contexto el linaje destaca como una referencia existencial paralela a tan extrema ideología de la competencia. En él se desarrolla la vida, se revelan los signos del poder y se conforma la imagen propia sobre la de los antepasados. Al filo del 1500, esta manifestación local de la honra tendrá tal éxito que contagiará al resto de los vizcaínos de la época forzando la implantación de la "hidalguía universal"

Optical parameters and absorption of copper (II)-azo complexes thin films as optical recording media

Smooth thin films of three kinds of azo dyes of 2-(5'-tert-butyl-3'-azoxylisoxazole)-1, 3-diketones and their copper (II)-azo complexes were prepared by the spin-coating method. Absorption spectra of the thin films on a glass substrate in the 300-600 nm wavelength region were measured. Optical constants (complex refractive index N=n+ik) and thickness of the thin films prepared on single-crystal silicon substrate in the 300-600 nm wavelength region were investigated on rotating analyzer-polarizer type of scanning ellipsometer, and dielectric constants epsilon(epsilon=epsilon(1)+i epsilon(2)), absorption coefficients alpha as well as reflectance R of thin films were then calculated. In addition, one of the copper (II)-azo complex thin film prepared on glass substrate with an Ag reflective layer was also studied by atomic force microscopy (AFM) and static optical recording. AFM study shows that the copper (II)-azo complex thin film is very smooth and has a root mean square surface roughness of 1.89 nm. Static optical recording shows that the recording marks on the copper (II)-azo complex thin film are very clear and circular, and the size of the minimal recording marks can reach 200 nm. (c) 2004 Elsevier B.V. All rights reserved.

Optical properties of nickel(II)-azo complexes thin films for potential application as high-density recordable optical recording media

Smooth thin films of three kinds of nickel(II)-azo complexes were prepared by the spin-coating method. Absorption spectra of the thin films on K9 glass substrate in the 300-600 nn wavelength region were measured. Optical constants (complex refractive index N = n + ik) and thickness of the thin films prepared on single-crystal silicon substrate in the 300-600 nm wavelength region were investigated on rotating analyzer-polarizer type of scanning ellipsometer, and dielectric constants epsilon (epsilon = epsilon(1) + i epsilon(2)), absorption coefficients a as well as reflectance R of thin films were then calculated at 405 nm. In addition, in order to examine the possible use of nickel(II)-azo complex thin film as an optical recording medium, one of the nickel(II)-azo complex thin film prepared on K9 glass substrate with an Ag reflective layer was also studied by atomic force microscopy and static optical recording. The results show that the nickel(II)-azo complex thin film is smooth and has a root mean square surface roughness of 2.25 nm, and the recording marks on the nickel(II)-azo complex thin film are very clear and circular, and their size can reach 200 nn or less. (c) 2006 Elsevier Ltd. All rights reserved.

O papel da imprensa na qualidade democrática : uma análise de possibilidades nos principais jornais nacionais

Esta tese avalia como se dá a atuação da imprensa brasileira em relação a aspectos importantes para a qualidade de uma democracia, considerando o conceito de embedded democracy, segundo o qual democracias constitucionais são formadas por cinco regimes parciais: direitos civis; liberdade política; accountability horizontal; poder efetivo para governar; e regime eleitoral democrático, todos ligados a esferas externas responsáveis pela viabilização de condições para essas democracias, dentre elas, os media. Neste contexto, a imprensa teria algumas funções ser fórum de discussões; dar voz à opinião pública; servir de olhos e ouvidos dos cidadãos; fiscalizar e mostrar irregularidades , que podem ser prejudicadas pela mercantilização dos media e aspectos da produção da rotina jornalística. Para verificar isso, busco evidências empíricas da cobertura da imprensa escrita sobre a política nacional, especialmente sobre os dois principais atores, Legislativo e Executivo, por meio da análise de 1.768 notícias

Social Media Marketing como herramienta del mix de comunicación

[ES]El presente TFG plantea un análisis de la utilización de las redes sociales dentro de la estrategia de comunicación de las organizaciones empresariales. Para ello, se estudia el contexto comunicacional actual, caracterizado por la fragmentación y dispersión de las audiencias, la saturación, la pérdida de la eficacia de la publicidad tradicional, los nuevos hábitos de consumo de medios y la explosión de la conectividad, y el papel de las distintas herramientas de comunicación en entornos digitales: página web, blog corporativo, email marketing, gestión multimedia, mobile marketing, E-commerce y Social Media Marketing. En este contexto y por su relevancia, nos centramos en el estudio de las estrategias de Social Media Marketing. Para ello abordamos las ventajas e inconvenientes de la utilización de redes sociales, cómo efectuar la planificación de la comunicación en redes sociales (objetivos, público, contenidos, plataformas, plan de acción e indicadores), y las nuevas profesiones ligadas a su gestión. Un aspecto relevante que también se analiza es la gestión de la reputación online y las implicaciones que el uso de redes sociales tiene sobre ella, así como los protocolos de actuación ante posibles crisis derivadas de la presencia en estos canales. En las redes sociales se encuentran prácticamente todos los stakeholders de las empresas/marcas, fuente de información continua para mejorar sus negocios. Su utilización, dentro de una comunicación integral de marketing, permite fortalecer la imagen corporativa y lograr un posicionamiento claro y a largo plazo.