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Your search keyword '"Manuel F.C. Pereira"' showing total 3 results
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3 results on '"Manuel F.C. Pereira"'

1. Organic geochemistry and mineralogy suggest anthropogenic impact in speleothem chemistry from volcanic show caves of the Galapagos

Author

Ana Z. Miller, Nicasio T. Jiménez-Morillo, Mathilda L. Coutinho, Fernando Gazquez, Vera Palma, Francesco Sauro, Manuel F.C. Pereira, Fernando Rull, Theofilos Toulkeridis, Ana T. Caldeira, Paolo Forti, and José M. Calaforra

Subjects
Earth sciences, Geochemistry, Geology, Volcano, Science
Abstract

Summary: The network of lava tubes is one of the most unexploited natural wonders of the Galapagos Islands. Here, we provide the first morphological, mineralogical, and biogeochemical assessment of speleothems from volcanic caves of the Galapagos to understand their structure, composition, and origin, as well as to identify organic molecules preserved in speleothems. Mineralogical analyses revealed that moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves were composed of calcite, opal-A, and minor amounts of clay minerals. Extracellular polymeric substances, fossilized bacteria, silica microspheres, and cell imprints on siliceous minerals evidenced microbe-mineral interactions and biologically-mediated silica precipitation. Alternating depositional layers between siliceous and carbonate minerals and the detection of biomarkers of surface vegetation and anthropogenic stressors indicated environmental and anthropogenic changes (agriculture, human waste, and cave visits) on these unique underground resources. Stable isotope analysis and Py-GC/MS were key to robustly identify biomarkers, allowing for implementation of future protection policies.

Published
2022
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3. X-ray microtomography applied to mortars: Review of microstructural visualization and parameterization

Author

Rafael Travincas, Manuel F.C. Pereira, Isabel Torres, António Maurício, Dora Silveira, and Inês Flores-Colen

Subjects
Structural Biology, General Physics and Astronomy, General Materials Science, Cell Biology
Abstract

The objective of the present work is to review the main applications of X-ray microtomography in the microstructural study of mortars, based on a literature search related to the subject, and to enable the development of more innovative and sustainable mortar formulations. This three-dimensional non-destructive microscopy allows qualitative visualization down to micrometric scales, visualization of the spatial distribution of the interior of samples of objects relatively opaque to visible light and the measurement of quantitative microstructural parameters. Furthermore, the combination of X-ray microtomography with other microstructural and compositional techniques can result in data at different scales of observation. Particularly, in the study of mortars, there are benefits in using this technique to better characterize materials in terms of the spatial structure of pores and other voids, aiding in the formulation of new mortars and in the characterization of mortar behavior, for example, after leaching and carbonation processes. This paper intends to contribute to the discussion of the potentials and drawbacks of this advanced technique, allowing a better characterization of mortars and enabling the development of more innovative and sustainable formulations.

Published
2022

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