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Sökning: WFRF:(Ferreira Rafael)

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21.
  • Dutra, Thiago, 1985, et al. (författare)
  • Identification of Representative Equivalent Volumes on the Microstructure of 3D-Printed Fiber-Reinforced Thermoplastics Based on Statistical Characterization
  • 2022
  • Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 14:5
  • Tidskriftsartikel (refereegranskat)abstract
    • The present work describes a methodology to compute equivalent volumes representing the microstructure of 3D-printed continuous fiber-reinforced thermoplastics, based on a statistical characterization of the fiber distribution. In contrast to recent work, the methodology herein presented determines the statistically equivalent fiber distribution directly from cross-section micrographs, instead of generating random fiber arrangements. For this purpose, several regions, with different sizes and from different locations, are cropped from main cross-section micrographs and different spatial descriptor functions are adopted to characterize the microstructures in terms of agglomeration and periodicity of the fibers. Detailed information about the adopted spatial descriptors and the algorithm implemented to identify the fiber distribution, as well as to define the location of cropped regions, are given. From the obtained statistical characterization results, the minimum size of the equivalent volume required to be representative of the fiber distribution, which is found in the cross-section micrographs of 3D-printed composite materials, is presented. To support the findings, as well as to demonstrate the effectiveness of the proposed methodology, the homogenized properties are also computed using representative equivalent volumes obtained in the statistical characterization and the results are compared to those experimentally measured, which are available in the literature.
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22.
  • Dutra, Thiago, 1985, et al. (författare)
  • Mechanism based failure of 3D-printed continuous carbon fiber reinforced thermoplastic composites
  • 2021
  • Ingår i: Composites Science and Technology. - : Elsevier BV. - 0266-3538. ; 231
  • Tidskriftsartikel (refereegranskat)abstract
    • The present work describes a computational mechanism based failure analysis conducted for 3D-printed continuous carbon fiber reinforced thermoplastic composites (CFRTPCs), which could not be seen in the available literature. The material failure is investigated based on intraply failure evaluation and adopts different failure criteria for the material constituents. The micromechanical modeling employs the Asymptotic Homogenization technique and comprises the selection of a representative volume element statistically equivalent to the microstructure of the material, which is identified from cross-section micrographs. In contrast to recent work, it is demonstrated that an additional relation is required for the macroscopic deviatoric stresses acting over the matrix. This avoids an overestimation of the matrix failure when the reinforced lamina is subjected to longitudinal and shear loads. The resulting failure envelopes are presented and compared to those provided by analytical failure theories available in the literature. The results obtained by the micromechanical approach showed its ability to predict failure of 3D-printed CFRTPCs, in addition to bring different elements for the discussion that could not be captured with analytical models. In this context, it is believed that the characteristics inherent to the microstructure reproduced in the RVE,  articularly contributed to obtaining more realistic failure envelopes.
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23.
  • Ferreira, Rafael A., et al. (författare)
  • Ferrimagnetism and spin excitation in a Ni-Mn partially inverted spinel prepared using a modified polymeric precursor method
  • 2014
  • Ingår i: Materials Chemistry and Physics. - : Elsevier BV. - 0254-0584. ; 146:1-2, s. 58-64
  • Tidskriftsartikel (refereegranskat)abstract
    • We demonstrate that a Ni-Mn oxide partially inverted spinel (Ni1-pMnv)[NivMn2-v]O-4 having inversion degree v approximate to 0.8 and produced by a modified polymeric precursor method exhibits behaviour previously reported only in monophased samples. The structure of the specimen was determined using Rietveld analysis of X-ray and neutron powder diffraction data, showing that at room temperature the material crystallizes in the Fd3(over bar)m space group with a lattice constant a = 8.392 angstrom. Combining magnetization measurements with neutron powder diffraction, we show that the magnetic structure of this spinel is associated with the interplay between the ferromagnetic and antiferromagnetic lattices which coexist due to the cations' presence on both tetrahedral and octahedral sites. Our analysis of the neutron diffraction data confirms the postulated magnetic structure involving a star-like moment arrangement, arising from competition for the B (octahedral) spinel sites by the Ni and Mn cations. Finally, we show that strong magnetic fluctuations are observed in the inelastic neutron scattering data. (C) 2014 Elsevier B.V. All rights reserved.
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24.
  • Ferreira, Rafael Pereira, et al. (författare)
  • Development and implementation of a software for wire arc additive manufacturing preprocessing planning : trajectory planning and machine code generation
  • 2022
  • Ingår i: Welding in the World. - : Springer Science and Business Media Deutschland GmbH. - 0043-2288 .- 1878-6669.
  • Tidskriftsartikel (refereegranskat)abstract
    • To overcome a shortage of flexible and low-cost solutions for wire arc additive manufacturing (WAAM) preprocessing, this work´s objective was to develop and validate an in-house computational programme in an open-source environment for WAAM preprocessing planning. Algorithms for reading STL (stereolithography) files and implementing rotation, slicing, trajectory planning, and machine code generation were elaborated and implemented in the Scilab environment (free and open-source). A graphical interface was developed to facilitate user interaction, with 5 options for path planning. The functionality of each work step is detailed. For validation of the software, single and multiple-layer prints, with different geometrical complexity and printing challenges, were built in a CNC table geared by the generated machine code. The validation criteria were deposition imperfection, morphological, and dimensional tolerances. The outputs showed that the parts were successfully printed. Therefore, this work demonstrates that Scilab provides the necessary resources for companies and universities to implement and/or develop algorithms for planning and generating trajectories for WAAM. Moreover, emerging ideas can be reasonably easily implemented in such software, not always possible in commercial packages. 
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25.
  • Hudson, Lawrence N, et al. (författare)
  • The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project
  • 2017
  • Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 7:1, s. 145-188
  • Tidskriftsartikel (refereegranskat)abstract
    • The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.
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26.
  • In ’t Veld, Sjors G.J.G., et al. (författare)
  • Detection and localization of early- and late-stage cancers using platelet RNA
  • 2022
  • Ingår i: Cancer Cell. - : Elsevier. - 1535-6108 .- 1878-3686. ; 40:9, s. 999-1009.e6
  • Tidskriftsartikel (refereegranskat)abstract
    • Cancer patients benefit from early tumor detection since treatment outcomes are more favorable for less advanced cancers. Platelets are involved in cancer progression and are considered a promising biosource for cancer detection, as they alter their RNA content upon local and systemic cues. We show that tumor-educated platelet (TEP) RNA-based blood tests enable the detection of 18 cancer types. With 99% specificity in asymptomatic controls, thromboSeq correctly detected the presence of cancer in two-thirds of 1,096 blood samples from stage I–IV cancer patients and in half of 352 stage I–III tumors. Symptomatic controls, including inflammatory and cardiovascular diseases, and benign tumors had increased false-positive test results with an average specificity of 78%. Moreover, thromboSeq determined the tumor site of origin in five different tumor types correctly in over 80% of the cancer patients. These results highlight the potential properties of TEP-derived RNA panels to supplement current approaches for blood-based cancer screening.
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27.
  • Jones, Benedict C, et al. (författare)
  • To which world regions does the valence-dominance model of social perception apply?
  • 2021
  • Ingår i: Nature Human Behaviour. - : Springer Science and Business Media LLC. - 2397-3374. ; 5:1, s. 159-169
  • Tidskriftsartikel (refereegranskat)abstract
    • Over the past 10 years, Oosterhof and Todorov's valence-dominance model has emerged as the most prominent account of how people evaluate faces on social dimensions. In this model, two dimensions (valence and dominance) underpin social judgements of faces. Because this model has primarily been developed and tested in Western regions, it is unclear whether these findings apply to other regions. We addressed this question by replicating Oosterhof and Todorov's methodology across 11 world regions, 41 countries and 11,570 participants. When we used Oosterhof and Todorov's original analysis strategy, the valence-dominance model generalized across regions. When we used an alternative methodology to allow for correlated dimensions, we observed much less generalization. Collectively, these results suggest that, while the valence-dominance model generalizes very well across regions when dimensions are forced to be orthogonal, regional differences are revealed when we use different extraction methods and correlate and rotate the dimension reduction solution. PROTOCOL REGISTRATION: The stage 1 protocol for this Registered Report was accepted in principle on 5 November 2018. The protocol, as accepted by the journal, can be found at https://doi.org/10.6084/m9.figshare.7611443.v1 .
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28.
  • Kehoe, Laura, et al. (författare)
  • Make EU trade with Brazil sustainable
  • 2019
  • Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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29.
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30.
  • Pereira Ferreira, Rafael, et al. (författare)
  • Concept of a Novel Path Planning Strategy for Wire + Arc Additive Manufacturing of Bulky Parts : Pixel
  • 2021
  • Ingår i: Metals. - : MDPI. - 2075-4701. ; 11:3, s. 1-20
  • Tidskriftsartikel (refereegranskat)abstract
    • An innovative trajectory strategy was proposed and accessed for wire arc additive manufacturing (WAAM), applicable to different and more complex geometries, rather than being a single solution. This strategy, named Pixel, can be defined as a complex multitask procedure to carry out optimized path planning, whose operation is made through computational algorithms (heuristics), with accessible computational resources and tolerable computational time. The model layers are fractioned in squared grids, and a set of dots is systematically generated and distributed inside the sliced outlines, resembling pixels on a screen, over which the trajectory is planned. The Pixel strategy was based on creating trajectories from the technique travelling salesman problem (TSP). Unlike existing algorithms, the Pixel strategy uses an adapted greedy randomized adaptive search procedure (GRASP) metaheuristic, aided by four concurrent trajectory planning heuristics, developed by the authors. Interactions provide successive trajectories from randomized initial solutions (global search) and subsequent iterative improvements (local search). After all recurrent loops, a trajectory is defined and written in machine code. Computational evaluation was implemented to demonstrate the effectof each of the heuristics on the final trajectory. An experimental evaluation was eventually carried out using two different not easily printable shapes to demonstrate the practical feasibility of the proposed strategy.
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