Papers by Manuel F C Pereira
Applied Catalysis A: General, 2008
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International audienc
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Microscopy and Microanalysis, 2015
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Buildings, 2021
The present study aims at evaluating the impact of anobiid damage on pine timber elements. Anobii... more The present study aims at evaluating the impact of anobiid damage on pine timber elements. Anobiid attack produces a diffuse damage of the elements with a set of tunnels in random directions and sizes, thus confusing quantification. Therefore, a method was developed based on X-ray micro-computed tomography (μ-XCT) to obtain, for naturally infested timber samples, an empirical correlation between lost material percentage (consumed by beetles) and timber apparent density (original, before degradation—OTD and residual, after degradation—RTD). The quantified density loss can then be used in further assessment of the structure. The results of the tests performed showed high correlation between original apparent density and lost material percentage (r2 = 0.60) and between residual apparent density and lost material percentage (r2 = 0.83), which confirms μ-XCT as a valuable tool to the required quantification. The loss of density results can be further applied on the definition of an asses...
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Microscopy Research and Technique, 2013
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ABSTRACT Materials with a cellular structure are common in nature and an example of natural solid... more ABSTRACT Materials with a cellular structure are common in nature and an example of natural solid foam is trabecular bone. As for other materials, the microstructural features of cellular solids affect their mechanical response. The aim of this work is to study how the trabecular bone microarchitecture affects the mechanical properties of two types of bone and compare the results with models existing on the literature for solid cellular materials. In spite of several works which make a more medical analysis, this type of materials-science approach is rare.Two types of trabecular bone were studied, namely from male and female patients with osteoporotic (fragility) fractures and patients with coxarthrosis, that were submitted to total hip arthroplasty. Each sample was first analyzed with micro-computed tomography, micro‑CT, for structural assessment. Several parameters used to characterize the three-dimensional structure of trabecular bone were obtained, including the bone volume fraction. Cylinder samples were also tested under uniaxial compression and the Young’s modulus and the ultimate stress were determined.No statistical differences between the two bone groups in respect to the structural and mechanical properties were found. The structural parameters that correlate better with the mechanical properties are different for each bone assembly, being the trabecular separation on the coxarthrosis group and the trabecular number on the osteoporotic group. However, both trabecular separation and trabecular number are strongly correlated with the bone volume fraction, i.e., to the bone relative density.The existing models of Gibson and Ashby were adapted to the relationship between stiffness and strength with the bone volume fraction. In both bone groups, the Young’s modulus is reduced with the decrease of the bone volume fraction following a quadratic law as happens in bending dominated open-cell foams. The ultimate strength is related to the bone volume fraction by a relationship with an exponent between 1 and 2, which indicates that during cell collapse, there is a mixture of two mechanisms: elastic buckling and brittle crushing.
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Bio-Design and Manufacturing
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Materials and Structures
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Archaeometry
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Agricultural and Forest Entomology
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Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada, Jun 1, 2017
Lithotripsy methods show relatively low efficiency in the fragmentation of sialoliths compared wi... more Lithotripsy methods show relatively low efficiency in the fragmentation of sialoliths compared with the success rates achieved in the destruction of renal calculi. However, the information available on the mechanical behavior of sialoliths is limited and their apparently tougher response is not fully understood. This work evaluates the hardness and Young's modulus of sialoliths at different scales and analyzes specific damage patterns induced in these calcified structures by ultrasonic vibrations, pneumoballistic impacts, shock waves, and laser ablation. A clear correlation between local mechanical properties and ultrastructure/chemistry has been established: sialoliths are composite materials consisting of hard and soft components of mineralized and organic nature, respectively. Ultrasonic and pneumoballistic reverberations damage preferentially highly mineralized regions, leaving relatively unaffected the surrounding organic matter. In contrast, shock waves leach the organic c...
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International journal of paleopathology, Mar 1, 2017
Calcification, or mineralisation, can occur as part of a natural process, or by pathological proc... more Calcification, or mineralisation, can occur as part of a natural process, or by pathological processes. The purpose of this work is to examine an unidentified semi-spherical and perforate hollow mass, found near the pelvis of an adult female, dated 12th-13th century AD, exhumed of the Church of Santo Domingo de Silos (Prádena del Ricón, Madrid, Spain). The mass was examined by SEM and Energy Dispersive X-Ray Spectroscopy. These procedures revealed a heterogeneous inner surface with both smooth and irregular areas. A larger spherical and several smaller crescent-shaped perforations were noticed. X-ray microanalysis revealed the presence of the elements C, K, P, Ca, Al, Si, Fe, and Mg. The co-localisation of Ca and P suggests that they may be combined in a mineral matrix, likely formed in vivo. Other minerals probably came from the soil, although Fe could be related to the presence of blood. The macroscopic and microscopic appearances, chemical composition, and location of the calcifi...
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Mineral Processing and Extractive Metallurgy Review, 2016
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International Journal of Minerals, Metallurgy, and Materials, 2016
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Environmental Earth Sciences, 2013
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Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy, 2013
Two sherds representative of the Portuguese faience production of the first and second halves of ... more Two sherds representative of the Portuguese faience production of the first and second halves of the 17th century were studied carefully with the use of non-invasive spectroscopies, namely: Ground State Diffuse Reflectance Absorption (GSDR), micro-Raman, Fourier-Transform Infrared (FT-IR), Laser Induced Luminescence (LIL) and Proton Induced X-ray (PIXE). These results were compared with the ones obtained for a Chinese Ming porcelain, Wanli period (16th/beginning of the 17th centuries), which served as an influence for the initial Lisbon's faience production. By combining information of the different non-destructive spectroscopic techniques used in this work, it was possible to conclude that: Co(3)O(4) (Co II and Co III) can be found in the silicate matrix and is the blue pigment in the "Especieiro" sample (1st half of the 17th C.). Cobalt olivine silicate (Co(2)SiO(4), Co II only) was clearly identified as the blue pigment in "Aranhões" sample (2nd half of the 17th C.) - 824 cm(-1) band in the micro-Raman-spectrum. Cobalt aluminate (CoAl(2)O(4), Co II only) is the blue pigment in the Wanli plate - 203 and 512 cm(-1) bands in the micro-Raman spectrum. The blue pigment in the 1st half 17th century of Lisbon's production was obtained by addition of a cobalt ore in low concentrations, which gives no specific Raman signature, because of complete dissolution in the glass. However, in most cases of the 2nd half 17th century, the Raman signature was quite evident, from a cobalt silicate. These findings point to the use of higher temperature kilns in the second case.
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Journal of Applied Polymer Science, 2014
ABSTRACT Cellulose acetate (CA)–silver (Ag) nanocomposite asymmetric membranes were prepared via ... more ABSTRACT Cellulose acetate (CA)–silver (Ag) nanocomposite asymmetric membranes were prepared via the wet-phase inversion method by dispersing polyvinylpirrolydone-protected Ag nanoparticles in the membrane casting solutions of different compositions. Silver nanoparticles were synthesized ex situ and added to the casting solution as a concentrated aqueous colloidal dispersion. The effects of the dispersion addition on the structure and on the selective permeation properties of the membranes were studied by comparing the nanocomposites with the silver-free materials. The casting solution composition played an important role in the adequate dispersion of the silver nanoparticles in the membrane. Incorporation of nanoscale silver and the final silver content resulted in structural changes leading to an increase in the hydraulic permeability and molecular weight cut-off of the nanocomposite membranes. © 2014 Wiley
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Microscopy and Microanalysis, 2012
This article presents a detailed study of the microstructure of Iberian expanded clay lightweight... more This article presents a detailed study of the microstructure of Iberian expanded clay lightweight aggregates (LWA). Other than more commonly used mercury porosimetry (MP) and water absorption methods, the experimental study involves optical microscopy, scanning electron microscopy (SEM), and microtomography (μ-CT). Pore connectivity and how it is deployed are shown to some degree, and the pore size spectrum is estimated. LWA are in general characterized by a dense outer shell up to 200 μm thick, encasing an inner cellular structure of 10–100 times bigger pore size. Aggregate pore sizes may span from some hundreds of nanometers up to over 1 mm, though the range of 1–25 μm is more typical. A noteworthy fraction of these pores is closed, and they are mainly up to 1 μm. It is also shown that macropore spatial arrangement is affected by the manufacturing process. A step forward is given to understanding how the outer shell and the inner pore network influence the mechanical and physical ...
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Microscopy and Microanalysis, 2013
Theories have been put forward on the etiology of sialoliths; however, a comprehensive understand... more Theories have been put forward on the etiology of sialoliths; however, a comprehensive understanding of their growth mechanisms is lacking. In an attempt to fill this gap, the current study has evaluated the internal architecture and growth patterns of a set of 30 independent specimens of sialoliths characterized at different scales by computed microtomography and electron microscopy. Tomography reconstructions showed cores in most of the sialoliths. The cores were surrounded by concentric or irregular patterns with variable degrees of mineralization. Regardless of the patterns, at finer scales the sialoliths consisted of banded and globular structures. The distribution of precipitates in the banded structures is compatible with a Liesegang–Ostwald phenomenon. On the other hand, the globular structures appear to arise from surface tension effects and to develop self-similar features as a result of a viscous fingering process. Electron diffraction patterns demonstrated that Ca- and P...
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Journal of Performance of Constructed Facilities, 2014
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Papers by Manuel F C Pereira