Group velocity and dispersion model of coupled-cavity waveguides in photonic crystals

A theoretical model of the group velocity, dispersion parameter, and dispersion slope of coupled-cavity waveguides in photonic crystals is reported. Results arising from closed-form expressions show a good agreement with simulation results obtained by employing a plane-wave expansion method. Coupled-cavity waveguides present interesting dispersion properties that may be employed in applications such as optical signal processing, dispersion compensation, and optical delay lines.     

Planar photonic crystal structure with inherently single-mode waveguides

A planar photonic crystal that allows inherently gap-guided single-mode waveguides is proposed and discussed. This novel structure consists of a two-dimensional lattice of silicon rods embedded on a thin silica slab sandwiched between two silica claddings whose refractive indices are slightly lower than the index of the silica core. The physical parameters of the structure, i.e., rod radius and core thickness, are optimized to maximize the bandgap width for odd modes. Lossless guided modes inside the bandgap and below the claddings' light cone are obtained by reducing the radius of a row of rods. The waveguide bandwidth can be increased by inserting a thin silicon dielectric waveguide instead of the row of rods. The proposed approach may overcome many of the common drawbacks in conventional holes-on-dielectric planar photonic crystal waveguides.     

Effect of pH on the precipitation of hydroxyapatite on silica gels

Silica-HAp composites have been produced with particle size ranging from several nm to few μm, through control of the pH of the solution, which also controls morphology. A calcium ions reservoir has been made available as a Ca/EDTA soluble complex allowing the production of HAp at low temperature and short periods of time (hours). The presence of silica seems to promote the formation of HAp under these conditions. Electronic Publication     

New analytical techniques in food science

In this review, some of the latest analytical techniques that are being used for the study and characterization of food are examined. This work intends to provide an updated overview (including works published up to June 1999) on the principal applications of such techniques together with their main advantages and drawbacks in food analysis. Some future developments of these systems and their foreseeable application in food characterization are also discussed. The reviewed techniques are those based on spectroscopic, biological, separation, and electrochemical procedures. Moreover, some relevant facts on new systems for sample preparation and on-line couplings are also given.     

Enhancing the experience of 3D virtual worlds with a cartographic generalization approach

In this work we propose a new approach for fast visualization and exploration of virtual worlds based on the use of cartographic concepts and techniques. Versions of cartographic maps with different levels of details can be created by using a set of operations named cartographic generalization. Cartographic generalization employs twelve operators and domain-specific knowledge, being the contribution of this work their transposition to 3D virtual worlds. The architecture of a system for 3D generalization is proposed and the system is implemented. Differently from traditional cartographic processes, we use artificial intelligence for both selecting the key objects and applying the operators. As a case study, we present the simplification of the historical quarter of Recife (Brazil).     

Ultrasound image segmentation with shape priors: application to automatic cattle rib-eye area estimation.

Automatic ultrasound (US) image segmentation is a difficult task due to the quantity of noise present in the images and the lack of information in several zones produced by the acquisition conditions. In this paper, we propose a method that combines shape priors and image information to achieve this task. In particular, we introduce knowledge about the rib-eye shape using a set of images manually segmented by experts. A method is proposed for the automatic segmentation of new samples in which a closed curve is fitted taking into account both the US image information and the geodesic distance between the evolving curve and the estimated mean rib-eye shape in a shape space. This method can be used to solve similar problems that arise when dealing with US images in other fields. The method was successfully tested over a database composed of 610 US images, for which we have the manual segmentations of two experts.     

Bilinear Control for Three-Phase Microgrids: A Proportional-Integral Passivity-Based Design

Abstract

A bilinear PI control based on passivity theory for the adequate integration of distributed energy resources (DERs) in ac microgrids is presented in this paper. DERs are integrated into the grid by voltage source converters (VSC), the most common and suitable technology for this type of application. The proposed control guarantees asymptotically stable operation for the dynamical system under closed-loop operating scenarios via Hamiltonian and Lyapunov formulations. ZP load models and π-model of the transmission lines are considered in the stability analysis of the microgrid. Conventional PI control is also implemented for comparative purposes. Simulation results in Matlab/Simulink demonstrate the effectiveness and stability of the proposed control’s performance in a radial microgrid composed of a photovoltaic generator, a supercapacitor energy storage (SCES) system and unbalanced loads.     

HYBRID METAHEURISTICS FOR THE DESIGN OF COUPLED RESONATOR FILTERS

The design of coupled resonator filters used in many telecommunication applications poses an optimization problem that can be tackled with heuristic methods. In many configurations, simple heuristic methods do not give satisfactory results, and the combination in hybrid metaheuristics of local and global search methods is a better approach. This article analyzes the systematic development of hybrid metaheuristic methods for the design of coupled resonator filters. Engineers normally use the MATLAB computing environment to work on the design of these devices, so the available MATLAB optimization toolboxes are used here as a basis to address those optimization problems. The results obtained are in general satisfactory, and the best results are obtained in the experiments with memetic algorithms in which methods based in populations (Genetic Algorithms and Scatter Search) are combined with local search methods to improve individuals in the population at different parts of the metaheuristic.     

Towards a journalist-based news recommendation system: The Wesomender approach

The present paper introduces a context-aware recommendation system for journalists to enable the identification of similar topics across different sources. More specifically a journalist-based recommendation system that can be automatically configured is presented to exploit news according to expert preferences. News contextual features are also taken into account due to the their special nature: time, current user interests, location or existing trends are combined with traditional recommendation techniques to provide an adaptive framework that deals with heterogeneous data providing an enhanced collaborative filtering system. Since the Wesomender approach is able to generate context-aware recommendations in the journalism field, a quantitative evaluation with the aim of comparing Wesomender results with the expectations of a team of experts is also performed to show that a context-aware adaptive recommendation engine can fulfil the needs of journalists daily work when retrieving timely and primary information is required.