Recursos de colección

Repositório do Instituto Politénico de Castelo Branco (13.941 recursos)

O Repositório Científico do Instituto Politécnico de Castelo Branco tem como objectivos fundamentais a divulgação, a preservação em formato digital e a partilha do conhecimento científico gerado na instituição, constituindo-se numa ferramenta de valor acrescentado porque permite aumentar a visibilidade e o impacto da investigação desenvolvida.

ESTCB - Escola Superior de Tecnologia

Mostrando recursos 1 - 20 de 391

  1. Estudo e implementação de sistema de gestão de credenciais de autenticação de alta disponibilidade

    Reis, Fernando Emanuel Azevedo
    Dissertação apresentada à Escola Superior de Tecnologia de Castelo Branco do Instituto Politécnico de Castelo Branco para cumprimento dos requisitos necessários à obtenção do grau de Mestre em Desenvolvimento de Software e Sistemas Interativos, realizada sob a orientação científica do Professor Doutor Osvaldo Arede dos Santos, do Instituto Politécnico de Castelo Branco.

  2. Experimentation with radio environment maps for resources optimisation in dense wireless scenarios

    Dionísio, Rogério; Alves, T. F.; Ribeiro, J. M. A.
    The rapidly increasing popularity of WiFi has created unprecedent levels of congestion in the unlicensed frequency bands, especially in densely populated urban areas. This results mainly because of the uncoordinated operation and the unmanaged interference between WiFi access points. Recently, Radio Environment Maps (REM) have been suggested as a support for coordination strategies that optimize the overall WiFi network performance. Despite some theoretical work done in this area, there are no clear experimental evidences of the benefit brought by WiFi coordination. In this context, the main objective of this experiment is to assess the benefit of a coordinated management of radio resources in dense WiFi networks using REMs for indoor scenarios. This...

  3. Empirical model for plasticity-induced crack closure based on Kmax and ΔK

    Antunes, F.V.; Chegini, A.G.; Camas, D.; Correia, L.
    The mean stress has a significant effect on crack propagation life and must be included in prediction models. However, there is no consensus in the fatigue community regarding the dominant mechanism explaining the mean stress effect. The concept of crack closure has been widely used and several empirical models can be found in literature. The stress ratio, R, is usually the main parameter of these models, but present numerical results showed a significant influence of Kmax. A new empirical model is therefore proposed here, dependent on Kmax and ΔK, with four empirical constants. The model also includes the effect of material's yield stress, and two...

  4. Potential toxic elements in stream sediments, soils and waters in an abandoned radium mine (central Portugal)

    Antunes, I. M. H. R.; Neiva, A. M. R.; Albuquerque, M. T. D.; Carvalho, P. C. S.; Santos, A. C. T.; Cunha, P. P.
    The final publication is available at Springer via http://dx.doi.org/10.1007/s10653-017-9945-2

  5. A numerical study of non-linear crack tip parameters

    Antunes, F.V.; Branco, R.; Correia, L.; Ramalho, A.L.
    Crack closure concept has been widely used to explain different issues of fatigue crack propagation. However, different authors have questioned the relevance of crack closure and have proposed alternative concepts. The main objective here is to check the effectiveness of crack closure concept by linking the contact of crack flanks with non-linear crack tip parameters. Accordingly, 3D-FE numerical models with and without contact were developed for a wide range of loading scenarios and the crack tip parameters usually linked to fatigue crack growth, namely range of cyclic plastic strain, crack tip opening displacement, size of reversed plastic zone and total plastic dissipation per cycle, were...

  6. Effect of compressive loads on plasticity induced crack closure

    Antunes, F. V.; Correia, L.; Camas, D.; Branco, R.
    Compressive stresses play an important role on tension-compression fatigue which can be attributed to plasticity induced crack closure (PICC). The objective here is to study numerically the effect of compressive stresses on PICC and to discuss the applicability of PICC to explain the effect of negative stress ratios on fatigue crack growth rate. The compression produces reversed plastic deformation at the crack tip, reducing linearly the crack opening level. The incursion to negative stress ratios did not produce sudden changes in the behavior of PICC and no saturation with the decrease of minimum load was observed for δKeff. Crack closure was able to collapse da/dN-δK...

  7. Finite element meshes for optimal modelling of plasticity induced crack closure

    Antunes, F. V.; Camas, D.; Correia, L.; Branco, R.
    The main goal here is to optimise the finite element mesh used to predict plasticity induced crack closure (PICC). A numerical model was developed for a M(T) specimen made of 6016-T4 aluminium alloy. The parameters studied were the size of most refined region perpendicularly to crack flank (ym) and along propagation direction (xr), the size of finite elements near crack tip (L1) and the vertical size of refinement close to crack flank (yA/B). A maximum size of about 1.3mm was found for ym, but a smaller value has a limited impact on PICC. An analytical expression was proposed for xr, dependent on δK and...

  8. Effect of crack closure on non-linear crack tip parameters

    Antunes, F.V.; Sousa, T.; Branco, R.; Correia, L.
    Crack closure concept has been widely used to explain different issues of fatigue crack propagation. However, some authors have questioned the relevance of crack closure and have proposed alternative concepts. The main objective here is to check the effectiveness of crack closure concept by linking the contact of crack flanks with non-linear crack tip parameters. Accordingly, 3D-FE numerical models with and without contact were developed for a wide range of loading scenarios and the crack tip parameters usually linked to fatigue crack growth, namely range of cyclic plastic strain, crack tip opening displacement, size of reversed plastic zone and total plastic dissipation per cycle were...

  9. A parameter for quantitative analysis of plasticity induced crack closure

    Antunes, F.V.; Correia, L.; Ramalho, A.L.
    Numerical models have been successfully developed to predict plasticity induced crack closure (PICC). However, despite the large research effort a full understanding of the links between physical parameters, residual plastic wake and PICC has not been achieved yet. The plastic extension of material behind crack tip, Dyp, obtained by the integration of vertical plastic deformation perpendicularly to crack flank, is proposed here to quantify the residual plastic field. The values of Dyp and PICC were obtained numerically in a M(T) specimen using the finite element method. An excellent correlation was found between PICC and Dyp which indicates that this parameter controls the phenomenon, and can be...

  10. Innovation and entrepreneuship networks as global competitiveness drivers

    Farinha, Luís Manuel do Carmo
    The main aim of this thesis is to analyze the relationship between innovation, entrepreneurship and competitiveness, following the triple helix network approach to regional economies, considering their impact on socio-economic development. This correspondingly involved a mixed research typology, as advocated in chapters 2 to 5, alternating between quantitative methodologies, deploying descriptive statistics, structural equation modelling (SEM) and hierarchical cluster analysis; and the qualitative methodology underpinning the case studies. The socio-economic prosperity of triple helix spaces (Academia-Industry-Political Decision regional spaces of interaction) depends on competitive advantages, including their positioning in terms of innovation and entrepreneurship factors, local endogenous resources and the...

  11. ETSI opportunistic spectrum sharing technology for (TV) white spaces

    Mueck, Markus Dominik; Sato, Naotaka; Sun, Chen; Freda, Martino; Ojanen, Pekka; Zhou, Dong; Xiao, Junfeng; Dionísio, Rogério; Marques, Paulo
    This chapter provides an overview on European Telecommunications Standards Institute (ETSI) activities related to opportunistic spectrum sharing technology with a specific focus on (TV) white spaces. Key use cases are outlined and a novel approach for a coordinated and an uncoordinated approach for accessing the spectrum resource is given. A spectrum coordinator is indeed introduced in order to handle resource management. Furthermore, database system design and inter-database communication solutions are discussed as they are introduced by ETSI. Finally, various sensing mechanisms are detailed, which allow to monitor the radio environment and to feed decision-making components correspondingly.

  12. TV white spaces with geo-location database access: practical considerations and trials in Europe

    Dionísio, Rogério; Ribeiro, José; Ribeiro, Jorge; Marques, Paulo; Rodriguez, Jonathan
    This chapter describes outdoor transmission tests and field measurements in TV white spaces (TVWS) carried out in Europe. TVWS Measurements in Germany showed that the extended Hata model is appropriate to describe the path loss over distances up to a few kilometers. During the TVWS trial in Slovenia, we combine infrastructure sensing with geo-location database access to protect not only DVB-T, but also wireless microphone (WM) signals from TVWS devices interference.

  13. Inovação Didática no Ensino Superior através do Projeto ROBOT@ESCOLA: escola de robótica

    Gonçalves, P.J.S.; Torres, P.M.B.; Farinha, R.A.A.
    A Robótica é uma área multidisciplinar que tem contribuído significativamente no processo educativo dos jovens nos últimos anos. O modelo pedagógico de aprender fazendo é uma alavanca fundamental para cativar e manter os alunos interessados nas áreas tecnológicas. O projeto ROBOT@ESCOLA – Escola de Robótica, foi desenvolvido com base em componentes básicos para a construção de robôs, plataformas Arduino para programação, bem como dispositivos móveis com sistemas operativos Android, tornando a experimentação de ciência e tecnologia acessível a todos. O projeto foi desenvolvido em parceria com várias instituições de ensino da região da Beira Interior. Desta cooperação resultou uma plataforma...

  14. Inovação Didática no Ensino Superior através do Projeto ROBOT@ESCOLA: escola de robótica

    Gonçalves, P.J.S.; Torres, P.M.B.; Farinha, R.A.A.
    A Robótica é uma área multidisciplinar que tem contribuído significativamente no processo educativo dos jovens nos últimos anos. O modelo pedagógico de aprender fazendo é uma alavanca fundamental para cativar e manter os alunos interessados nas áreas tecnológicas. O projeto ROBOT@ESCOLA – Escola de Robótica, foi desenvolvido com base em componentes básicos para a construção de robôs, plataformas Arduino para programação, bem como dispositivos móveis com sistemas operativos Android, tornando a experimentação de ciência e tecnologia acessível a todos. O projeto foi desenvolvido em parceria com várias instituições de ensino da região da Beira Interior. Desta cooperação resultou uma plataforma...

  15. Uncalibrated eye-to-hand visual servoing using inverse fuzzy models

    Gonçalves, P.J.S.; Mendonça, L.F.; Sousa, J.M.C.; Pinto, J.R.C.
    (c) 2007 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.

  16. Delimitação de perímetros de protecção em sistemas aquíferos fissurados: caso de estudo na Serra da Gardunha, Centro de Portugal

    Albuquerque, M.T.D.; Antunes, I.M.H.R; Sousa, Miguel
    A crescente necessidade e importância das águas subterrâneas exige uma protecção adequada deste recurso através da delimitação de perímetros de protecção em torno das captações. Para tal, torna-se necessária uma abordagem específica e ajustada às caraterísticas locais para obter soluções mais adequadas. Os métodos analíticos permitem a delimitação das zonas de protecção utilizando parâmetros hidrogeológicos. Neste trabalho são comparados dois métodos analíticos - método do raio fixo e de Wyssling - na definição dos peímetros de proteção de duas captações localizadas na Serra da Gardunha. As captações de Eirinhas nº 1 e Eirinhas Nº2 estão incluídas no subsistema de Casal...

  17. Interferometry applications in all-optical communications networks

    Dionísio, Rogério
    Throughout the years, the expanded search and flow of information led to an expansion of traffic intensity in today’s optical communication systems. Coherent communications, using the amplitude and phase of the optical wave, resurface as one of the transmission methods to increase the effective bandwidth of optical channels. In this framework, this chapter presents a study on all-optical format conversion of modulated signals, using exclusively interferometric techniques through wavelength conversion, based on Mach-Zehnder interferometers with semiconductor optical amplifiers (MZI-SOA). This technique, when applied in interconnection nodes between optical networks with different bit rates and modulation formats, allows a better efficiency...

  18. Influência dos procedimentos de determinação da baridade em misturas betuminosas densas e stone mastic asphalt

    Gardete, Dinis; Picado-Santos, Luís; Capitão, Silvino
    Neste trabalho realiza-se uma avaliação da utilização de diferentes procedimentos de determinação das baridades de misturas betuminosas. Utilizou-se uma mistura densa, do tipo AC 20, e uma mistura de granulometria descontínua do tipo SMA 12,5. Fabricaram-se em laboratório provetes Marshall, com compactação por impactos, e provetes SUPERPAVE, obtidos por compactação giratória. Os resultados indicam que a mistura SMA 12,5 apresenta uma textura superficial significativa mas o seu interior é fechado e os vazios não apresentam interligação significativa. Existe uma variação significativa das propriedades determinadas para as misturas com os diferentes procedimentos, com impacto significativo nos resultados da sua formulação.

  19. Módulo para o ensino das telecomunicações com rádios definidos por software

    Albardeiro, D. J. C.; Rocha, E. M. R.; Dionísio, Rogério
    Este artigo apresenta duas aplicações desenvolvidas em Software Labview com rádios definidos por Software USRP2, destinadas às aulas laboratoriais no ensino das Telecomunicações. Uma das aplicações é um analisador de espectro, com uma gama espectral entre 50 MHz e 2.2 GHz, na qual podem ser visualizados e analisados sinais no domínio do tempo e da frequência. Este módulo possui uma interface intuitiva e vários parâmetros fundamentais para análise espectral, o que permite o seu uso em aulas práticas laboratoriais. A outra aplicação implementada foi um rádio analógico FM; para além de permitir desmodular os sinais FM e ouvir as emissões rádio na gama de frequências entre 87,5MHz a 108MHz, é também possível...

  20. Numerical evaluation of the behavior of tubular columns in the connections to I beams with welded reverse channel

    Magalhães, Luís; Rebelo, Carlos; Jordão, Sandra
    This paper presents results of numerical study on the behaviour of tubular columns in the connections to I beams with U-profiles, effected on the basis of a parametric variation of the most significant characteristics of tubular profiles. The parameters considered are the thicknesses, the widths and the diameters of the tubular columns, the filling with concrete. The main purpose is the characterisation of the nonlinear behaviour of this type of steel joints. The results of the parametric study with numerical models allow correlate the parameters considered with the structural behaviour of the connection, defined by the resistance, the stiffness and...

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