79 research outputs found
Crystal chemistry of Mg-, Fe-bearing muscovites-2M(1)
No full textPhengitic muscovite-2M(1), crystals [([12])(K0.88-0.99Na0.01-0.09Ca0.Ba-00-0.06(0.00-0.01))([6])(Al1.64-1.88Fe0.06-0.292+Fe0.01-0.163+Mg0.00-0.16Mn0.00-0.07Ti0.00-0.06)([4])(Si2.87-3.30Al0.70-1.13)(OH)(1.56-2.07)F0.00-0.41O9.91-10.25] from peg matites and peraluminous granites were refined to investigate the influence of phengitic substitution on the mica structure. Single-crystal X-ray diffraction data were collected for eleven crystals in the C2/c space-group (agreement factor 2.1% less than or equal to R-obs less than or equal to 3.9%). Tetrahedral Si and Al cation disorder was found for each sample, with the mean tetrahedral cation-oxygen distances ranging from 1.639 Angstrom less than or equal to less than or equal to 1.647 Angstrom and 1.640 Angstrom less than or equal to less than or equal to 1.646 Angstrom. As phengitic substitution increases, the octahedral sheet expands and requires a less distorted (more hexagonal) tetrahedral ring (7.70 degrees less than or equal to alpha less than or equal to 11.38 degrees) and low corrugation of the basal O plane (0.1796 Angstrom less than or equal to Delta z less than or equal to 0.2296 Angstrom). The electron density at the M2 site is greater than that required for the ideal muscovite-2M(1), structure, and a small excess of electron density is found in the M1 site. The inner sixfold coordination of the interlayer (A) cation is elongated along c*, which is consistent with the high or values and the long A-O11 bond length
Factors affecting the transport and recovery of heavy metals and organic pollutants in smectitic soils
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Crystal chemistry of Al-rich biotites coexisting with muscovites in peraluminous granites
No full textA comparison was made between single-crystal structure refinements, electron microprobe analy ses and octahedral site populations of seven biotite crystals and data obtained previously for coexisting muscovite in peraluminous granites using the same methods. Both micas, From several plutons of Northern Victoria Land (Antarctica) and Sardinia (Italy), show significant octahedral substitutions: biotite has a composition characterized by relatively high Al-[6] content (0.32 less than or equal to Al-[6] less than or equal to 0.59 apfu), whereas muscovite is characterized by phengite-like substitutions [0.12 less than or equal to ([6])(Mg + Fe + Ti + Mn) less than or equal to 0.35]. Mean bond-lengths and electron count data for six biotites-1M (space group C2/m. agreement factor 2.7% less than or equal to R-obs less than or equal to 3.6%) and a biotite-2M(1) (space group C2/c, R-obs = 2.8%) show that Al substitutes for divalent cations in the octahedral M2 site and that the Fe and Mg distribution is disordered. The mean tetrahedral bond lengths determined for biotite-2M(1) reflect Al-Si disorder. In coexisting muscovite-2M(1) crystals, small positive electron density residuals close to M1 site position as well as the increase in M2 mean atomic number is in agreement with the presence of a significant phengitic component. Reduction in biotite unit-cell dimensions with the increase of Al follows a pattern similar to that of associated muscovites. and the octahedral site volumes of both micas are influenced by the Al saturation index (ASI) of the rock. These results, and the calculated partition coefficients between biotite and muscovite for elements in M sites, are consistent with continuous reaction and re-equilibration of biotite and muscovite during crystallization of peraluminous granitic melts
Case of stroke in a 7-year-old male after parvovirus B19 infection
No full textA 7-year-old male presented sudden-onset left hemiparesis, left-sided paresthesia, central paralysis of the left VII cranial nerve, and subsequent headache. Magnetic resonance scans were obtained 24 hours after admission. T-2-weighted images disclosed hyperintensities located mainly in the posterior portion of the lenticular nucleus and in the head and body of the right caudate nucleus. A diagnosis of ischaemic stroke was made on the basis of neuroradiologic findings. Laboratory tests undertaken to establish the cause of stroke revealed parvovirus B19 infection preceding the neurologic abnormalities. In the absence of other known risk factors for stroke the possibility of parvovirus B19's being correlated with stroke onset is discussed. (C) 2003 by Elsevier Science Inc. All rights reserved
La conoscenza del patrimonio culturale attraverso l’uso della tecnologia. Obiettivi e metodologie
No full textCon il motto "Open future" Matera ha iniziato il 2019 quale rappresentante del Patrimonio Europeo della Cultura. Questa è un'occasione per compiere riflessioni ed elaborare strategie per una "valorizzazione" sostenibile, in relazione al carattere identitario e alla storia di una realtà urbana complessa, stratificata nei secoli, unica al mondo. Il contributo intende compiere alcune considerazioni sul rinnovato valore della "conoscenza dei luoghi", fondamento critico ad ogni tipo di "operatività" sui beni culturali. Oggi l'uso di sistemi integrati di rilevamento tridimensionale tecnologicamente avanzati offre la possibilità di documentare, in tempi assai rapidi, il patrimonio culturale in ogni sua forma: dal singolo monumento, a intere porzioni di città, da realtà archeologiche fino a contesti paesaggistici o naturalistici, ottenendo correttezza geometrica e completezza di restituzione. Si presenta, attraverso alcuni episodi nella città di Matera, tale processo metodologico della conoscenza, in grado di fornire il supporto scientifico per la comprensione della preesistenza storica, la sua valorizzazione e "comunicazione".With the slogan "Open future" Matera started 2019 as a European Capital of Culture. This is an opportunity to make reflections and development strategies for sustainable "valorisation", in relation to the identity character and history of a complex urban reality, stratified over the centuries, unique in the world. The contribution intends to make some considerations on the renewed value of "knowledge of places", a critical base for all types of "operations" on cultural heritage. Today the use of advanced technologies offers the possibility of documenting the cultural heritage in all its forms in a very short time, obtaining geometrical correctness and completeness of restitution: from the single monument, to entire portions of the city, from archaeological realities up to natural-landscape context. Through some episodes in the city of Matera, the methodological process of knowledge is able to provide scientific support for the understanding of historical pre-existence, and therefore to design
Comparison between zeolite and sepiolite in the treatment of heavy metal polluted waters
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