Rio de Janeiro, Brazil
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Peixoto A.,CEFET RJ | De Moura C.A.,State University of Rio de Janeiro
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2014

Two discretization methods for implicit surfaces are presented: the Non-Compact Dual Simplification and the Sewing Octree. They work with surfaces polygonalized with Dual Contouring, an adaptive method which uses an octree. The Non-Compact Dual Simplification (NDS) preserves the topology of simplified non-compact surfaces. This method can be used for non-compact as well as for compact surfaces in the case the polygonalization region does not contain the latter ones. The Sewing Octree is a method to glue two or more octrees that share faces or edges and contain portions of the surface polygonalized with Dual Contouring. These methods can be employed either independently or coupled, by dividing the original cube in two or more cubes, making the polygonalization, simplifying these regions with NDS, if necessary, and glueing the resulting surfaces with the Sewing Octree. We assure that, with this procedure, the resulting surface and the original one share the same topology. © 2014 Springer International Publishing.

Campos R.S.,CEFET RJ | Campos R.S.,Federal University of Rio de Janeiro | Lovisolo L.,State University of Rio de Janeiro | De Campos M.L.R.,Federal University of Rio de Janeiro
Expert Systems with Applications | Year: 2014

This paper focuses on the positioning of Wi-Fi nodes in multi-floor indoor environments. A target radio-frequency (RF) fingerprint - measured by the MS to be localized - is compared with georeferenced RF fingerprints, previously stored in a correlation database (CDB). Therefore, this strategy lies within the so-called Database Correlation Methods (DCM) used to locate mobile stations (MS) in wireless networks. To obtain best matches in terms of architectural structures such as floors, doors, aisles, among others, the authors apply two combined techniques that improve localization accuracy: unsupervised clustering (K-medians and Kohonen layer) and majority voting committees of backpropagation artificial neural networks (ANNs). The unsupervised clustering is employed to allow collected data (the fingerprints) to group freely in their natural space, without precluding - through the imposition of architectural constraints - any natural arrangement of the collected fingerprints. The proposed combined strategy improves floor identification accuracy, which in indoor multi-floor positioning must be high. The effects of the proposed solution on the DCM positioning accuracy are experimentally evaluated using actual measured data. In the trial the floor identification accuracy ranged from 91% to 97%, and the average 2D positioning error ranged from 4.5 to 1.7 m, depending on the size of the measurement window (from 1 to 25 samples).n © 2014 Elsevier Ltd. All rights reserved.

Aguiar R.A.A.,CEFET RJ | Savi M.A.,Federal University of Rio de Janeiro | Pacheco P.M.C.L.,CEFET RJ
Journal of Intelligent Material Systems and Structures | Year: 2013

Smart materials have a growing technological importance due to their unique thermomechanical characteristics. Shape memory alloys belong to this class of materials being easy to manufacture, relatively lightweight, and able to produce high forces or displacements with low power consumption. These aspects could be exploited in different applications including vibration control. Nevertheless, literature presents only a few references concerning the experimental analysis of shape memory alloy dynamical systems. This contribution deals with the experimental analysis of shape memory alloy dynamical systems by considering an experimental apparatus consisted of low-friction cars free to move in a rail. A shaker that provides harmonic forcing excites the system. The vibration analysis reveals that shape memory alloy elements introduce complex behaviors to the system and that different thermomechanical loadings are of concern showing the main aspects of the shape memory alloy dynamical response. Special attention is dedicated to the analysis of vibration reduction that can be achieved by considering different approaches exploiting either temperature variations promoted by electric current changes or vibration absorber techniques. The results establish that adaptability due to temperature variations is defined by a competition between stiffness and hysteretic behavior changes. © The Author(s) 2012.

Petraglia M.R.,Federal University of Rio de Janeiro | Haddad D.B.,CEFET RJ
Proceedings of the 2010 7th International Symposium on Wireless Communication Systems, ISWCS'10 | Year: 2010

The convergence of the classical adaptive filtering algorithms becomes slow when the number of coefficients is very large. However, in many applications, such as digital network and acoustical echo cancelers, the system being modeled presents sparse impulse response, that is, most of its coefficients have small magnitudes. In order to improve the convergence for these applications, several algorithms have been proposed recently, which employ individual step-sizes for the updating of the different coefficients. The adaptation step-sizes are made larger for the coefficients with larger magnitudes, resulting in a faster convergence for the most significant coefficients. In this paper, we give an overview of the most important adaptive algorithms developed for the fast identification of systems with sparse impulse responses. Their convergence rates are compared through computer simulations for the identification of the channel impulse responses in a digital network echo cancellation application. A theoretical analysis of an improved version of the PNLMS algorithm is presented. © 2010 IEEE.

Aguiar R.A.A.,CEFET RJ | Savi M.A.,Federal University of Rio de Janeiro | Pacheco P.M.C.L.,CEFET RJ
Smart Materials and Structures | Year: 2010

Shape memory alloys (SMAs) belong to the class of smart materials and have been used in numerous applications. Solid phase transformations induced either by stress or temperature are behind the remarkable properties of SMAs that motivate the concept of innovative smart actuators for different purposes. The SMA element used in these actuators can assume different forms and a spring is an element usually employed for this aim. This contribution deals with the modeling, simulation and experimental analysis of SMA helical springs. Basically, a one-dimensional constitutive model is assumed to describe the SMA thermomechanical shear behavior and, afterwards, helical springs are modeled by considering a classical approach for linear-elastic springs. A numerical method based on the operator split technique is developed. SMA helical spring thermomechanical behavior is investigated through experimental tests performed with different thermomechanical loadings. Shape memory and pseudoelastic effects are treated. Numerical simulations show that the model results are in close agreement with those obtained by experimental tests, revealing that the proposed model captures the general thermomechanical behavior of SMA springs. © 2010 IOP Publishing Ltd.

Andrade D.P.P.,University of Paraíba Valley | De barros A.L.F.,CEFET RJ | Pilling S.,University of Paraíba Valley | Domaracka A.,CNRS Center for Research on Ions, Materials and Photonics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We studied the effects produced by the interaction of heavy ion cosmic rays with interstellar and cometary organic molecules in the solid phase. Formic acid (HCOOH) ice at 15 K was irradiated by 267-MeV 56Fe22+ ions and the chemical evolution was analysed using Fourier transform infrared spectroscopy. The destruction cross-section of HCOOH and the formation cross-sections of the produced molecular species have been determined; the sputtering yield values are also discussed. The most abundant chemical species formed by Fe ion irradiation are CO, CO2 and H2O. The half-life of frozen formic acid molecules in the interstellar medium, as a result of interaction with the different cosmic ray constituents, is evaluated to be 108 yr, considering that the destruction cross-section σd of heavy ions is ruled by a power law as a function of the electronic stopping power Se (i.e. σd ∼ S3/2 e). Moreover, a complementary study based on mass spectrometry data from the literature has been performed, in order to understand the HCOOH molecule radiolysis, the desorption of its product and the chemical reaction pathways in ice. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Vignoli L.L.,Pontifical Catholic University of Rio de Janeiro | Kenedi P.P.,CEFET RJ
Latin American Journal of Solids and Structures | Year: 2016

A human femur model, submitted to static loads, is analyzed through the utilization of three material constitutive relationships, namely: isotropic, transversally isotropic and orthotropic. The influence of bone anisotropy with respect to principal stress/strain distribution on human femur external surface was accessed through the use of analytical and finite element approaches. The models results show that the principal angles at a medial path bone surface have a good correlation with human femur bone lamellae angles. © 2016, Brazilian Association of Computational Mechanics. All rights reserved.

De Barros A.L.F.,CEFET RJ | De Barros A.L.F.,CNRS Center for Research on Ions, Materials and Photonics | Domaracka A.,CNRS Center for Research on Ions, Materials and Photonics | Andrade D.P.P.,University of Paraíba Valley | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

The chemical and physical effects induced by fast heavy ion irradiation on frozen pure methanol (CH3OH) at 15K were studied. These energetic ions can simulate the energy transfer processes that occur by cosmic ray irradiation of interstellar ices, comets and icy Solar system bodies. The analysis was made by infrared spectroscopy (Fourier transform infrared) before and after irradiation, with 16-MeV 16O5+, 220-MeV 16O7+, 606-MeV 65Zn20+ and 774-MeV 86Kr31+ ion beams. Integrated values of the absorbance of the main methanol bands were determined. The induced CH3OH dissociation gives rise to the formation of molecular species, particularly H2CO, CH2OH, CH4, CO, CO2, HCO and HCOOCH3. Their formation and dissociation cross-sections were determined. H2CO and CH4 molecules are in general the most abundant new products of the four beams analysed. Except for the HCO and CH2OH species, cross-sections increased with the electronic stopping power, roughly as σ∼S3/2 e. The G values for CH3OH destruction by fast heavy ion irradiation with Zn and Kr beams were found to be considerably larger than those for oxygen, helium or hydrogen. As an astrophysical implication, the S3/2 e power law should be very helpful for predicting the CH3OH formation and dissociation cross-sections for other ion beam projectiles and energies. As astrophysical point of view, the analysis of the predictions reveals the unexpected importance of iron and some other heavy ion constituents of cosmic rays in astrochemistry. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Thome R.C.A.,CEFET RJ | Yang H.M.,University of Campinas | Esteva L.,National Autonomous University of Mexico
Mathematical Biosciences | Year: 2010

We present a mathematical model to describe the dynamics of mosquito population when sterile male mosquitoes (produced by irradiation) are introduced as a biological control, besides the application of insecticide. In order to analyze the minimal effort to reduce the fertile female mosquitoes, we search for the optimal control considering the cost of insecticide application, the cost of the production of irradiated mosquitoes and their delivery as well as the social cost (proportional to the number of fertilized females mosquitoes). The optimal control is obtained by applying the Pontryagin's Maximum Principle. © 2009 Elsevier Inc. All rights reserved.

De Souza C.G.,CEFET RJ | Barbastefano R.G.,CEFET RJ
International Journal of Life Cycle Assessment | Year: 2011

Purpose: The interest in life cycle assessment (LCA) studies has increased over the years, and one of the main ways of disseminating these studies is through the publication of articles in scientific journals. Coauthorship relations form a social network where it is possible to identify how research is organized and structured in a specific field of knowledge. This paper aims to show the spread of these studies and the configuration of a collaboration network based on coauthorship relations between researchers of LCA considering some properties of social networks. Methods: The research was based on a bibliometric approach of 1,386 articles related to LCA and published in journals indexed in the ISI/Web of Science until 2008. A free software, Pajek, which has been largely used for the representation and analysis of social networks, was employed in this work. The properties of social networks analyzed in this study were power law, degrees of separation, giant component, and clustering. Results and discussion: The research showed a social network formed by 2,598 authors from 60 countries, 88% of coauthored articles, a mean of 1.87 authors per article; the distribution of articles per author follows a power law (f (z)=2,134.3×z -2.544) with a high regression coefficient (R 2=0.9704), a degree of separation of 6.5, a giant component embracing 37% of the authors, and a clustering coefficient of 0.75. The LCA coauthorship network has properties following power law patterns similar to other nets such as WWW. The community forms a giant component which is still small, but which, nevertheless, might experience considerable growth in the near future. The average distance between authors follows the small-world hypothesis. The clustering degree was also coherent with other scientific communities. Conclusions: In spite of being an area with less than 20 years of publications registered in the ISI/Web of Science, LCA is now experiencing fast dissemination involving a large number of articles, authors, and institutions. The LCA's coauthorship network can be characterized as a scientific community with properties verified in other networks of more consolidated academic collaboration. © 2011 Springer-Verlag.

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