José Duarte Marafona, Arlindo Araújo,
The aim of this research is to show the influence of the hardness of the alloy steel on the material removal rate and on the workpiece surface roughness. The Taguchi methodology was used to study that influence. The result of the verification test for workpiece surface roughness was a strong confirmation. This type of outcome allows the use of the additive model to predict the workpiece surface roughness with an average error of 0.4%. The result of the verification test for material removal rate ...
Tópico(s): Advanced machining processes and optimization
2009 - Elsevier BV | International Journal of Machine Tools and Manufacture
Tópico(s): Advanced Surface Polishing Techniques
2008 - Springer Science+Business Media | The International Journal of Advanced Manufacturing Technology
This article gives a new proposal about the electrode wear ratio (EWR) in the die-sinking electrical discharge machining (EDM) process. During the machining of a work piece (BS 4695 D2), a black layer is produced on the tool surface (W/Cu). The black colour is due to the migrated carbon from the dielectric during the electrical discharge. This article shows that a bi-dimensional laminate of carbon crystals with random phases forms the black layer, which is strongly attached to the tool. Moreover, it ...
Tópico(s): Advanced Surface Polishing Techniques
2006 - Elsevier BV | Journal of Materials Processing Technology
José Duarte Marafona, J.A.G. Chousal,
A thermal–electrical model was developed for sparks generated by electrical discharge in a liquid media. A cylindrical shape has been used for the discharge channel created between the electrodes. The discharge channel being an electrical conductor will dissipate heat, which can be explained by the Joule heating effect. The amount of heat dissipated varies with the thermal–physical properties of the conductor; as a result, the maximum temperature reached is different. In the present model, the radii ...
Tópico(s): Advanced Surface Polishing Techniques
2005 - Elsevier BV | International Journal of Machine Tools and Manufacture
José Duarte Marafona, C. Wykes,
Tópico(s): Advanced Surface Polishing Techniques
2000 - Elsevier BV | International Journal of Machine Tools and Manufacture
Joaquím Fonseca, José Duarte Marafona,
Tópico(s): Advanced machining processes and optimization
2013 - Springer Science+Business Media | The International Journal of Advanced Manufacturing Technology
João D.M. Marafona, Pedro M.T. Marques, Ramiro C. Martins, J. Seabra,
This work presents the development and dynamic analysis of Constant Mesh Stiffness Gears. First, a study of the contact length variation between gears is conducted since it has great influence on the gear mesh stiffness. Following that, an algorithm capable of generating Constant Mesh Stiffness Gears (CMSGears) was developed while considering the gears’ safety factors and mesh efficiency. The dynamic performance of these gears was evaluated resorting to a single degree of freedom dynamic model which ...
Tópico(s): Tribology and Lubrication Engineering
2019 - Elsevier BV | Mechanism and Machine Theory
Pedro M.T. Marques, João D.M. Marafona, Ramiro C. Martins, J. Seabra,
In this work a continuous analytical model for the estimation of the mesh stiffness, load sharing and friction torque for parallel axis involute spur and helical gears is presented. The model has no limitations in the admissible range for the overlap and contact ratios. The main novelty of the work lies on the mathematical approach that allows the continuous description of the gearing phenomena without using functions by domains. At first, a model for the mesh stiffness and load sharing ratio for ...
Tópico(s): Tribology and Lubrication Engineering
2021 - Elsevier BV | Mechanism and Machine Theory
João D.M. Marafona, Pedro M.T. Marques, Ramiro C. Martins, J. Seabra,
Gear transmissions have always been a subject of study for many different reasons which change due to the constant evolution of technology. Consequently, new topics must be addressed and different ways to solve the upcoming problems must be discovered. Gear mesh stiffness is a central topic for both gear design and gear dynamic modeling due to its ability to represent the gears’ behavior, making it a subject of high interest in the field of gear transmissions. Different types of models are used ...
Tópico(s): Tribology and Lubrication Engineering
2021 - Elsevier BV | Mechanism and Machine Theory
Filipa Martins, Ana M. Marafona, Cátia D. Pereira, Thorsten Müller, Christina Looße, Katharina Kolbe, Odete A. B. da Cruz e Silva, Sandra Rebelo,
BRI family proteins are ubiquitous type II transmembrane proteins but BRI2 is highly expressed in some neuronal tissues. Possible BRI2 functions include neuronal maturation and differentiation. Protein complexes appear to be important in mediating its functions. Previously described BRI2 interactors include the Alzheimer's amyloid precursor protein and protein phosphatase 1, but clearly the identification of novel interactors provides an important tool to understand the role and function of BRI2. ...
Tópico(s): Genetics and Neurodevelopmental Disorders
2018 - Nature Portfolio | Scientific Reports
José Almacinha, António M. Lopes, P.A.R. Rosa, José Duarte Marafona,
An electro-thermal model based on the Joule heating effect is proposed to simulate a single discharge in an electric discharge machining process. Normally, the dielectric strength of the hydrocarbons oil is approximately 20 MV/m, but it varies with both the thickness of the film and its decomposition. After the breakdown, the hydrocarbon oil has an average dielectric strength value of 2 MV/m. This value is close to the dielectric strength of the hydrogen, which is the main gas that results from ...
Tópico(s): Advanced Surface Polishing Techniques
2018 - Multidisciplinary Digital Publishing Institute | Micromachines
Abílio M.P. De Jesus, Gisela F.S. Ramos, Vítor M. G. Gomes, María José Marqués, M. Figueiredo, José Duarte Marafona,
Non-conventional machining processes, such as the Electrical Discharging Machining (EDM) offers the possibility to machine very hard materials with great potential to generate complex geometries. However, the EDM process involves significant microstructural changes in the as machined surfaces, which are known to have a significant impact on fatigue behaviour of mechanical parts. This study aims at investigating the fatigue behaviour of the AISI D2 tool steel subjected to EDM machining. Both smooth ...
Tópico(s): Advanced Surface Polishing Techniques
2020 - Elsevier BV | International Journal of Fatigue
João D.M. Marafona, Pedro M.T. Marques, Stéphane Portron, Ramiro C. Martins, J. Seabra,
There are certainly a lot of different gear mesh stiffness models in the literature, nonetheless, it is not possible to find comprehensive and in-depth gear parametric studies that sweep the gear geometrical domain. To do so, it is required to have a fast and accurate gear mesh stiffness model, which is precisely one of the main developments of this work. By taking advantage of this new model, a parametric study on the influence of tooth pair structural stiffness asymmetry is conducted. This investigation ...
Tópico(s): Tribology and Lubrication Engineering
2023 - Elsevier BV | Mechanism and Machine Theory
João D.M. Marafona, Pedro M.T. Marques, Ramiro C. Martins, J. Seabra,
In many gear mesh stiffness models, the single tooth pair mesh stiffness is commonly approximated as having a parabolic-like symmetric shape along the path of contact with a fixed or contact ratio dependent amplitude. Even though this is a valid approximation under certain conditions, there is an asymmetry being disregarded and an amplitude being roughly approximated. In this work, a new straightforward analytical expression for the single tooth pair slice mesh stiffness is defined resorting to ...
Tópico(s): Tribology and Lubrication Engineering
2023 - Elsevier BV | Mechanism and Machine Theory
Joaquím Fonseca, José Duarte Marafona,
Abstract It is known that the servo reference voltage affects the material removal rate. However, its effect on the tool wear rate is not well known. In this study was used an electro-thermal model to simulate a single electrical discharge. Therefore, this numerical and experimental study not only shows the effect of servo reference voltage on the material removal rate but also on the tool wear rate. The effect of servo reference voltage on the material removal rate is multiplicative, in the generality ...
Tópico(s): Advanced Surface Polishing Techniques
2013 - Elsevier BV | Procedia CIRP
João D.M. Marafona, Gonçalo Carneiro, Pedro M.T. Marques, Ramiro C. Martins, Carlos Alberto Conceição António, J. Seabra,
Optimization is a flexible methodology for gear design since it allows for diverse approaches according to current demands. Thus, lightweight, efficient, small, quiet or robust gears can all be achieved according to the designers' needs. However, these problems can easily become a computational burden due to the large amount of calculations necessary. In this work, a macro-geometry gear design optimization problem solved by a genetic algorithm is investigated to find the best approach to reach minimum ...
Tópico(s): Iterative Learning Control Systems
2023 - Elsevier BV | Mechanism and Machine Theory
José Almacinha, Alice M. G. Fernandes, D.A. Maciel, Ricardo Seca, José Duarte Marafona,
In this article, a finite element (FE) thermal–electrical model with a trunk-conical discharge channel is employed to simulate individual EDM discharges with a time-on of 18 μs up to 320 μs, which are subsequently compared with the experimental results to validate the model. The discharge channel is a trunk-conical electrical conductor which dissipates heat by the Joule heating effect, being the correspondent factor equal to 1. Instead of the usual copper–iron electrode combination, steel (DIN CK45) ...
Tópico(s): Additive Manufacturing and 3D Printing Technologies
2021 - Multidisciplinary Digital Publishing Institute | Materials
Humberto S Machado, Ana Sofia Marafona, Joana Patricia Meireles, Catarina S. Nunes, Ana Laura Esteves, Sofia Marques, Bruno Bragança, Daniela Bento,
Background:The contact with antibiotics at an early age may lead to a number of nefarious consequences.Nevertheless, the amount of literature available on the usage of antibiotics in children is scarce.Taking into account the increasing emergence of resistant bacterial strains, it is imperative to study and make society aware of the excessive exposure of children to antibiotics.The purpose of this study was to evaluate the incidence of antibiotic therapy in children under the age of six, in the ...
Tópico(s): Antibiotic Use and Resistance
2016 - OMICS Publishing Group | Journal of Pregnancy and Child Health
... in linguistic impertinence, what the sole narrator—the "marafona floozy"—describes in the end as the weave ... in the string of diminutives ad absurdum the marafona floozy reserves for her little dog Brinksy (Brinks' ... fitting that the narrator of Paraguayan Sea, a marafona floozy—"catin trollop, the biggest trashy flooze in ... Simultaneously "witch [and] guru," "fate and fortune," the marafona floozy provokes mixed feelings of admiration, fear, and ...
Tópico(s): Indigenous Studies in Latin America
2019 - University of Nebraska Press | American book review/The American book review
Miguel Oliveira, Antônio Ricardo Calazans Duarte, P.M. Coelho, José Duarte Marafona,
Tópico(s): Metal Alloys Wear and Properties
2014 - Springer Science+Business Media | The International Journal of Advanced Manufacturing Technology
Ana Sofia Marafona, Humberto S Machado,
Background: Nowadays, intraoperative evoked potentials are recommended in a variety of procedures but there is still a lack of standard protocols and consensus about warning criteria. Moreover, studies are now being made to fundament its risk-beneficial ratio through recordings’ predictive value for short and long term outcomes. Furthermore, wake up test limitations encouraged intraoperative evoked potentials research, a reliable monitoring technology. Objectives: This literature revision aims to ...
Tópico(s): Intracranial Aneurysms: Treatment and Complications
2017 - OMICS Publishing Group | Journal of Anesthesia & Clinical Research
Produção Nacional
Rosana Cristina Zanelatto Santos,
... a maestria da composição da trágica narradora, uma marafona nascida no país vizinho e radicada no nosso, ...
Tópico(s): Linguistics and Education Research
2014 - UNIVERSIDADE FEDERAL DO RIO DE JANEIRO | Fórum de Literatura Brasileira Contemporânea
Pedro M.T. Marques, João D.M. Marafona, J. Seabra,
Flank line crowning is a gear surface geometry modification that can be applied as a measure to accommodate contact imperfections along the gear teeth facewidth, that are a consequence of misalignment from either geometric defects or elastic deflection. Due to flank line crowning, the contact stiffness between the teeth of an ideal spur gear changes, thus modifying the gear mesh stiffness. Gear mesh stiffness fluctuations are one of the main driving factors behind gear performance, such as transmission ...
Tópico(s): Mechanical Engineering and Vibrations Research
2023 - Elsevier BV | Mechanism and Machine Theory
Pitawas Siriprayook, P.M. Coelho, José Duarte Marafona,
The article aims to show that the electrical discharge machining plasma can be developed in solid or gaseous medium, through the numerical and experimental evaluation of process performance. The plasma channel developed in gaseous medium is based on an electrical discharge developed in a gas bubble and the plasma channel developed in solid medium is based on underwater explosions. The main electrical difference between both mediums is on its electrical resistivity. However, if the radius of plasma ...
Tópico(s): Advanced Surface Polishing Techniques
2015 - SAGE Publishing | Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture
Pedro Miguel Horta Sousa, Ivo M. F. Bragança, Abílio M.P. De Jesus, José Duarte Marafona, P.A.R. Rosa,
Electrical discharge machining (EDM) involves the generation of micro-plasmas subjected to high temperature and pressure to promote the material removal.Hence, to understand the material removal mechanism it is of great importance the knowledge of the interaction plasma-solid.Knowing how physical and chemical properties of materials affect heat transfer at the electrode surface, how this eventually affects electrical properties of the plasma channel over the discharge time are key issues to achieve ...
Tópico(s): Advanced Surface Polishing Techniques
2018 - CENTRO FEDERAL DE EDUCAÇÃO TECN. CELSO SUCKOW DA FONSECA | Revista Produção e Desenvolvimento
Produção Nacional
Rafaela Vieira Costa, Ana Sofia Marafona, Andreia Oliveira Martins,
N/a.
Tópico(s): Maternal and Neonatal Healthcare
2023 - Ordem dos Médicos | Acta Médica Portuguesa
Rita Correia, Carla Vissolela Nachilovo Adelino António, Raquel Palhau, Rita Marafona,
Introduction Accidents at work resulted from sharp injuries are frequent and preventable events among health care professionals. The prevalence of secondary infection depends on several factors related to the patient itself, the health care worker and the adherence to preventive protocols. In this article, the authors pretend to present a case report of an accident involving a primary health care professional that suffered a sharp injury and, also, to alert about the significance of appropriately ...
Tópico(s): Infection Control in Healthcare
2023 - | Revista Portuguesa de Saúde Ocupacional
Tiago Francisco da Cunha Costa, Ana Filipa Paraíso, Daniela Marafona Pereira, Maria João Coelho,
Objetivos: Rever a evidência existente quanto à eficácia, tolerabilidade e segurança do hipericão no tratamento da perturbação depressiva (PD). Fontes de dados: NICE, Canadian Medical Association Infobase, PubMed – Clinical Queries, The Cochrane Library, BMJ, Bandolier e DARE – Centre for Reviews and Dissemination. Método: Foi realizada a pesquisa de artigos científicos em plataformas online de medicina baseada na evidência, com as palavras-chave Hypericum e Depressive Disorder. A seleção dos artigos ...
Tópico(s): Maternal Mental Health During Pregnancy and Postpartum
2021 - | Revista Portuguesa de Clínica Geral