Browsing by Issue Date, starting with "2009-08"
Now showing 1 - 10 of 21
Results Per Page
Sort Options
- Optimization of Scaffolds in Alginate for Biofabrication by Genetic AlgorithmsPublication . Rezende, Rodrigo; Rezende, Mylene; Bártolo, Paulo; Mendes, Ausenda; Filho, Rubens Maciel; Bartolo, Paulo; Mendes, AusendaWith an increasing in the rate of transplants due to damaged or affected tissues or organs by accidents or diseases and also by the aging of the population in many countries as Brazil, have motivated the research of some novel and alternative ways focused on restoring and replacing tissues. Biofabrication by means of Rapid Prototyping techniques can help in the fashioning and final production of scaffolds devoted to support and stimulate the growth of new tissues. For soft tissues, a biomaterial known as Alginate has been studied and used as raw-material for scaffolds fabrication. A scaffold must guarantee good strength and stiffness at the same time the material degrades gradually. In this work, a single mathematical model experimentally obtained that describes an interesting mechanical behavior of the degradation of alginated-scaffolds is developed. The optimization process scheme using Genetic Algorithms to maximize the elastic modulus and therefore to aid the design of scaffolds in alginate is proposed. The optimization is very welcome to tissue engineering and Biofabrication.
- Portugal as a Semi‐peripheral Country in the Global Migration SystemPublication . Góis, Pedro; Marques, José Carlos; Carlos Marques, JoséAlthough Portugal has traditionally produced many emigrants, the last 30 years have also shown increasing immigration. This increase in immigration has drawn attention away from the fact that significant emigration from Portugal continues. In this article, some of the main characteristics of migrations to and from Portugal are highlighted from a systemic perspective. The article shows that Portugal is both a receiving country and a sending country in the global migration system, and that it integrates several of the main migration systems at different levels. It is suggested that Portugal's participation in existing migration systems is best captured and explained by conceptualizing it as a semi-peripheral society, one that is part of a core region of the world system (the European Union) and displays a number of characteristics of both central and peripheral countries. The concept of semi-periphery enables one to recognize the existence of what could be termed a quasi or emergent migratory system: the Lusophone migration system, which one can conceive as communicating intensively with other macro migratory systems. Observing the country's migratory dynamics from the last two decades, and especially the migration flows that bond the Portuguese-speaking countries, one may view the Lusophone migration system as able to combine different levels of centers that (in some moments, and given certain conditions) could evolve into a bicephalous, or even tricephalous, center. These centers function as bonds among several other migration systems, and it is in the middle of this Lusophone migration system that the semi-peripheral role of Portugal becomes evident, as it can be core and periphery at the same time.
- Benchmarking a Wide Spectrum of Metaheuristic Techniques for the Radio Network Design ProblemPublication . Mendes, S.P.; Molina, G.; Vega-Rodriguez, M.A.; Gomez-Pulido, J.A.; Saez, Y.; Miranda, G.; Segura, C.; Alba, E.; Isasi, P.; Leon, C.; Sanchez-Perez, J.M.; Mendes, SilvioThe radio network design (RND) is an NP-hard optimization problem which consists of the maximization of the coverage of a given area while minimizing the base station deployment. Solving RND problems efficiently is relevant to many fields of application and has a direct impact in the engineering, telecommunication, scientific, and industrial areas. Numerous works can be found in the literature dealing with the RND problem, although they all suffer from the same shortfall: a noncomparable efficiency. Therefore, the aim of this paper is twofold: first, to offer a reliable RND comparison base reference in order to cover a wide algorithmic spectrum, and, second, to offer a comprehensible insight into accurate comparisons of efficiency, reliability, and swiftness of the different techniques applied to solve the RND problem. In order to achieve the first aim we propose a canonical RND problem formulation driven by two main directives: technology independence and a normalized comparison criterion. Following this, we have included an exhaustive behavior comparison between 14 different techniques. Finally, this paper indicates algorithmic trends and different patterns that can be observed through this analysis.
- Spatio-temporal structure of diatom assemblages in a temperate estuary. A STATICO analysisPublication . Mendes, Susana; Fernández-Gómez, Maria José; Resende, Paula; Pereira, Mário Jorge; Galindo-Villardón, Maria Purificación; Azeiteiro, Ulisses MirandaThis study examines the spatio-temporal structure of diatom assemblages in a temperate estuary (Ria de Aveiro, Western Portugal). Eighteen monthly surveys were conducted, from January 2002 to June 2003, at three sampling sites (at both high and low tide) along the estuarine salinity gradient. The relationship of diatom assemblages and environmental variables was analysed using the STATICO method, which has been designed for the simultaneous analysis of paired ecological tables. This method allowed examination of the stable part of the environment-diatom relationship, and also the variations of this relationship through time. The interstructure factor map showed that the relationship between the 11 environmental variables and the abundance of the 231 diatom species considered was strongest in the months May and September 2002 and January, February and May 2003. The stable part of the species-environment relationships mainly consisted of a combined phosphate, chlorophyll a and salinity gradient linked to a freshwater-marine species gradient. A more pronounced gradient was observed in January, February and May 2003. Diatom assemblages showed clear longitudinal patterns due to the presence of both marine and freshwater components. May and September 2002 had the least structured gradients with marine-estuarine species appearing in the freshwater side of the gradient. The most complete gradient in February 2003 could be considered, in terms of bio-ecological categories, as the most structured period of the year, with a combination of strong marine influence in the lower zone and freshwater influence in the upper. The best-structured gradients were during periods of a diatom bloom. Stable diatom assemblages (with a strong structure and a good fit between the diatoms and environment) are described and characterized. This study shows the efficiency of the STATICO analysis. The inclusion of space-time data analysis tools in ecological studies may therefore improve the knowledge of the dynamics of species-environmental assemblages.
- An Artificial Immune System for Temporal Anomaly Detection Using Cell Activation Thresholds and Clonal Size Regulation with HomeostasisPublication . Antunes, Mário; Correia, Manuel E.This paper presents an Artificial Immune System (AIS) based on Grossman's Tunable Activation Threshold (TAT) for anomaly detection. We describe the immunological metaphor and the algorithm adopted for T-cells, emphasizing two important features: the temporal dynamic adjustment of T-cells clonal size and its associated homeostasis mechanism. We present some promising results obtained with artificially generated data sets, aiming to test the appropriateness of using TAT in dynamic changing environments, to distinguish new unseen patterns as part of what should be detected as normal or as anomalous.
- Use of Co-occurrences for Temporal Expressions AnnotationPublication . Craveiro, Olga; Macedo, Joaquim; Madeira, HenriqueThe annotation or extraction of temporal information from text documents is becoming increasingly important in many natural language processing applications such as text summarization, information retrieval, question answering, etc.. This paper presents an original method for easy recognition of temporal expressions in text documents. The method creates semantically classified temporal patterns, using word co-occurrences obtained from training corpora and a pre-defined seed keywords set, derived from the used language temporal references. A participation on a Portuguese named entity evaluation contest showed promising effectiveness and efficiency results. This approach can be adapted to recognize other type of expressions or languages, within other contexts, by defining the suitable word sets and training corpora.
- M-Ary Mutually Orthogonal Complementary Gold CodesPublication . Pereira, João; Silva, Henrique J.A. daA method to obtain large sets of periodic conjugate symmetric sequences with perfect periodic autocorrelation functions is presented. Each of these perfect sequences can be transformed into two real sequences which are perfectly orthogonal for any cyclic shift. In this way, mutually orthogonal complementary (MOC) sequences derived from bipolar Gold codes can be transformed into M-ary MOC Gold codes. Ternary MOC Gold codes are the simpler implementation case and exist in large number. These Ternary MOC Gold codes provide a greater immunity to multi-path interferences than other codes, like Hadamard codes, Orthogonal Gold codes, Gold codes, and Complementary Golay codes, when a periodic or aperiodic autocorrelation function is used for asynchronous bit detection.
- A hierarchical broad-class classification to enhance phoneme recognitionPublication . Lopes, Carla, Alexandra Calado Lopes; Perdigão, FernandoIn this paper a hierarchical classification of different levels of phonetic information is proposed in order to improve phone recognition. In this paradigm several intermediate classifiers give posterior probability predictions for broad phonetic classes, achieving phone detail in the last layer. Class membership probabilities are weighted and combined in order to get a more robust phoneme prediction. A method for finding the best set of weights is also proposed based on discriminative training in a hybrid MLP/HMM system. Experiments show that the use of broad-class information enhances phone recognition. Relative improvements of 8% in Correctness and 5% in Accuracy were achieved in phoneme recognition on the TIMIT database compared to a baseline system.
- On the formability, geometrical accuracy, and surface quality of sheet metal parts produced by SPIFPublication . Alves, Maria; Silva, M. B.; Alves, L. M.; Martins, P. A. F.; Xiaoyuan He; Huimin Xie; YiLan KangConventional sheet metal forming processes are not suitable for flexible small-batch production and, therefore, are not appropriate for the growing agile manufacturing trends requiring very short life-cycles, development and production lead times. In fact, the present need for flexible sheet metal forming techniques requires the development of innovative technological solutions that are capable of reducing the fixed and capital costs of sheet metal forming to a level where small-batch production becomes economically feasible. Single point incremental forming (SPIF) is a new sheet metal forming process with a high potential economic payoff for rapid prototyping applications and for small quantity production. In general terms a typical SPIF set-up makes use of a small number of low cost active tools components; (i) a blankholder, (ii) a backing plate and (iii) a single point forming tool. The tool path is generated in a CNC machining center and during the process there is no backup die supporting the back surface of the sheet. Despite the contributions of many researchers on the development of industrial applications and better characterization of the forming limits of the process, several key topics related to the mechanics of deformation, likely mode of failure, geometric accuracy and surface quality of the formed parts remain little understood and scarcely systematized. This paper attempts to provide new contributions about the abovementioned issues by means of a comprehensive experimental investigation performed under laboratory controlled conditions.
- Métodos de evaluación de las reacciones álcali-sílice en hormigones con áridos recicladosPublication . Barreto Santos, Miguel; Brito, Jorge; Silva, António SantosAlkali-silica reactions (ASR) are one of the causes of chemical degradation of concrete with natural aggregates (CNA) that compromise its durability. The introduction of recycled aggregates (RA) in concrete creates changes in their properties and differences in the results of the evaluation tests of ASR. Existing bibliography emphasizes special care in the evaluation of RA and concrete with recycled aggregate (CRA) for ASR and changes are proposed to the existing test methods. There are proposals to change the accelerated test of mortar and concrete with RA to accelerate the reactions and recommendations to prevent changes in the characteristics of the RA, during the preparation of samples. Some articles recommend the pre-saturation of the AR, due to its absorption of water, to avoid significant variations in the results of expansion of concrete samples from early ages. This article aims to briefly describe the characteristics of CRA and ASR presenting comments from existing bibliography to the evaluation methods of ASR in CRA and CNA. Las reacciones álcali-sílice son una de las causas químicas de la degradación de los hormigones con áridos pétreos (HAP) que comprometen su durabilidad. La introducción de áridos reciclados (AR) en los hormigones produce alteraciones en sus propiedades y diferencias en los resultados de los ensayos de evaluación de las RAS. Se encuentran en la bibliografía algunos cuidados en la evaluación de los AR y de los hormigones con áridos reciclados (HAR) en cuanto a la RAS, así como propuestas de modificación de las metodologías de ensayo existentes. Existen propuestas de modificación del ensayo acelerado de mortero y hormigón con AR para acelerar las reacciones y recomendaciones para evitar alteraciones en las características del AR grueso, durante la preparación de probetas. Algunos artículos recomiendan la pre-saturación del AR, debido a su absorción de agua, para evitar variaciones en los resultados de expansión de probetas de hormigón a edades prematuras. El presente artículo pretende describir sucintamente las características de los HAR y de las RAS presentando observaciones de la bibliografía en cuanto a los métodos de evaluación de las RAS en HAR y en HAP.
- «
- 1 (current)
- 2
- 3
- »