Browsing by Issue Date, starting with "2014-06"
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- Biomineralization studies on cellulose membrane exposed to biological fluids of Anodonta cygneaPublication . Lopes, Anabela; Lima, Manuel Lopes; Ferreira, Jorge Amaral; Araújo, Sandra; Hinzmann, Mariana F.; Oliveira, José; Rocha, António; Domingues, Bernardo; Bobos, Iuliu; Machado, JorgeThe present work proposes to analyse the results obtained under in vitro conditions where cellulose artificial membranes were incubated with biological fluids from the freshwater bivalve Anodonta cygnea. The membranes were mounted between two half ‘Ussing chambers’ with different composition solutions in order to simulate epithelial surfaces separating organic fluid compartments. The membrane surfaces were submitted to two synthetic calcium and phosphate solutions on opposite sides, at pH 6.0, 7.0 or 9.0 during a period of 6 hours. Additional assays were accomplished mixing these solutions with haemolymph or extrapallial fluid from A. cygnea, only on the calcium side. A selective ion movement, mainly dependent on the membrane pore size and/or cationic affinity, occurred with higher permeability for calcium ions to the opposite phosphate chamber supported by calcium diffusion forces across the cellulose membrane. In general, this promoted a more intense mineral precipitation on the phosphate membrane surface. A strong deposition of calcium phosphate mineral was observed at pH 9.0 as a primary layer with a homogeneous microstructure, being totally absent at pH 6.0. The membrane showed an additional crystal phase at pH 7.0 exhibiting a very particular hexagonal or cuttlebone shape, mainly on the phosphate surface. When organic fluids of A. cygnea were included, these crystal forms presented a high tendency to aggregate under rosaceous shapes, also predominantly in the phosphate side. The cellulose membrane was permeable to small organic molecules that diffused from the calcium towards the phosphate side. In the calcium side, very few similar crystals were observed. The presence of organic matrix from A. cygnea fluids induced a preliminary apatite–brushite crystal polymorphism. So, the present results suggest that cellulose membranes can be used as surrogates of biological epithelia with preferential ionic diffusion from the calcium to the phosphate side where the main mineral precipitation events occurred. Additionally, the organic fluids from freshwater bivalves should be also thoroughly researched in the applied biomedical field, as mineral nucleators and crystal modulators on biosynthetic systems.
- Deciphering a multi-event in a non-complex set of detrital zircon U-Pb ages from Carboniferous graywackes of SW IberiaPublication . Ferreira, A.; Lopes, C.; Chichorro, Martim; Pereira, M. Francisco; Solá, A. RitaThe determination of U–Pb ages from detrital zircons of sedimentary rocks using LA-ICP-MS has been widely used for the purpose of provenance analysis. One problem that frequently arises is finding a population that appears to be non-complex despite several perceptible age peaks in its spectrum. These peaks are qualitatively defined by means of relative probability diagrams, or PDFs, but it is difficult to quantify their statistical significance relative to a zircon forming multi-event. Thus, can a multi-event in a non-complex set of detrital zircon U–Pb ages be deciphered and characterized? The aim of this study is to attempt to provide an answer to this question by means of statistical analysis. Its objectives are: a) to determine the best minimum number of zircon age populations (peaks), BmPs, b) for the characterization of each peak in terms of age and event duration; c) to compare the results obtained from two datasets showing similar zircon ages; and d) to demonstrate the usefulness of deciphering these BmPs. First, cluster analysis is carried out, aimed at grouping zircon ages into a set of consistent clusters. A Gaussian Kernel function is then fitted to each cluster and summed to obtain a theoretical PDFm (modeled probability density function). Finally, the selected modeled PDFm (that built on the BmPs) is that which reports the lowest number of peaks for which the difference as compared with the original gPDF (global probability density function) is equal to or below 5%. Deciphered BmP peaks can be characterized and used for characterizing and providing an understanding of related event(s). A geological interpretation, based on the results obtained, is attempted. This includes a robust measure for maximum age of deposition for both Cabrela and Mértola graywackes.
- The recovery of scarce critical metals in environmental treatments of mining residues : rhenium in Panasqueira tungsten mine tailingsPublication . Figueiredo, M. Ondina; Silva, Teresa; Veiga, JP; Batista, Maria Joao; Salas-Colera, Eduardo; de Oliveira, Daniel Pipa Soares
- Incorporating descriptive metadata into seismic source zone models for seismic-hazard assessment : a case study of the Azores-West Iberian RegionPublication . Vilanova, Susana P.; Nemser, Eliza S.; Besana-Ostman, Glenda M.; Bezzeghoud, Mourad; Borges, José Fernando; Silveira, António Brum da; Cabral, João; Carvalho, João; Cunha, Pedro Proença e; Dias, Ruben Pereira; Madeira, José; Lopes, Fernando Carlos; Oliveira, Carlos Sousa; Perea, Hector; García-Mayordomo, Julián; Wong, Ivan G.; Arvidsson, Ronald; Fonseca, João F. B. D.In probabilistic seismic-hazard analysis (PSHA), seismic source zone (SSZ) models are widely used to account for the contribution to the hazard from earthquakes not directly correlated with geological structures. Notwithstanding the impact of SSZ models in PSHA, the theoretical framework underlying SSZ models and the criteria used to delineate the SSZs are seldom explicitly stated and suitably documented. In this paper, we propose a methodological framework to develop and document SSZ models, which includes (1) an assessment of the appropriate scale and degree of stationarity, (2) an assessment of seismicity catalog completeness-related issues, and (3) an evaluation and credibility ranking of physical criteria used to delineate the boundaries of the SSZs. We also emphasize the need for SSZ models to be supported by a comprehensive set of metadata documenting both the unique characteristics of each SSZ and the criteria used to delineate its boundaries. This procedure ensures that the uncertainties in the model can be properly addressed in the PSHA and that the model can be easily updated whenever new data are available. The proposed methodology is illustrated using the SSZ model developed for the Azores–West Iberian region in the context of the Seismic Hazard Harmonization in Europe project (project SHARE) and some of the most relevant SSZs are discussed in detail.
- Intra-crustal recycling and crustal-mantle interactions in North Gondwana revealed by oxygen isotopic composition of Neoproterozoic to Ordovician zircons from SW Iberia rocksPublication . Chichorro, Martim; Solá, A. Rita; Pereira, M. Francisco; Sánchez-García, Teresa; Ferreira, A.; Silva, J. Brandão; Armstrong, R.