379 research outputs found
Natural nanomaterials : reappraising the elusive structure of the nano-sized mineral ferrihydrite through X-Ray absorption spectroscopy at the iron K-edge
Ferrihydrite is natural ferric oxyhydroxide occurring exclusively nanocrystalline. With ideal formula 5 Fe2 O3 . 9 H2 O,
ferrihydrite is quite abundant in sediments, weathering crusts and mine wastes, being characteristic of red pre-soils
formed by loose weathered rock plus mineral debris (regoliths) and commonly designated as “2-line” or “6-line” on the
basis of the broadened maxima observed in the X-ray diffraction pattern. Synthetic nanocrystalline “6-line” ferrihydrite
was recently studied through methods based on atomic-pair distribution functions disclosing the possible occurrence
of icosahedral clusters formed by twelve octahedra centred by an inner tetrahedron, all filled by Fe 3+ ions. However,
Mössbauer studies were inconclusive about the existence of 4-coordinated iron, thus suggesting that the tetrahedral
cation may well be Si4+. In view of such structural uncertainty, a XANES study at the Fe K-edge was undertaken on
ferrihydrite from a regolith to ascertain the occurrence of tetrahedral iron. Comparison with data collected from well
crystallized iron oxide and hydroxide minerals where Fe 3+/2+ ions occur in octahedral and tetrahedral coordination is
described and the results so far obtained are discussed, showing that supplementary study is needed on the elusive
structure of ferrihydrite
Cultural Heritage analysis using Synchrotron Radiaon: case studies in Ceramics, Glasses, and Lithologic Materials
ABSTRACT: Synchrotron radiaton is a powerful tool for non‐destructve analysis of materials in cultural
heritage research. It has revolutonized our ability to understand the compositon, structure, and
history of cultural heritage objects, leading to significant advances in fields such as archaeology, art
conservation, and materials science. Dedicated beamlines for cultural heritage research are available at synchrotron facilites around the world, such as the European Synchrotron Radiation Facility (ESRF), SOLEIL synchrotron, and ALBA synchrotron, providing specialized support and instrumentation for high‐resolution analysis of cultural heritage objects using various techniques, such as X‐ray absorption spectroscopy, X‐ray fluorescence, X‐ray diffraction, and X‐ray imaging.N/
Leigh Syndrome with Atypical Cerebellum Imaging Features
info:eu-repo/semantics/publishedVersio
Leigh syndrome with atypical cerebellar lesions
Leigh Syndrome is a neurodegenerative disorder caused by mitochondrial dysfunction, with significant phenotypic and genetic heterogeneity. It usually presents in early life, with a severe prognosis. It can be caused by more than 75 different gene mutations, of nuclear and mitochondrial origin, involving all respiratory chain complexes, with less than 25% of Leigh syndrome having mitochondrial DNA mutations. The typical pathologic hallmarks are focal, bilateral, and symmetric lesions in the basal ganglia, thalamus, cerebellum, cerebral white matter and spinal cord gray matter, usually with T2WI and FLAIR hyperintensity. The basal ganglia and thalami frequently present with a pattern of cytotoxic edema. We present one case with clinical and analytical features consistent with Leigh Syndrome, with peculiar imaging features, showing dominant cerebellar edematous changes with unexpected petechial component suggestive of microangiopathy. To our knowledge, these features are unreported and suggest the existence of microvascular lesions. Based on the reported imaging findings, we propose that Leigh Syndrome should be added to the differential diagnosis of acute cerebellitis.info:eu-repo/semantics/publishedVersio
Molybdenite as a rhenium carrier : first results of a spectroscopic approach using synchrotron radiation
The chemical and physical properties of rhenium render it a highly demanded metal for advanced applications in important industrial fields. This very scarce
element occurs mainly in ores of porphyry copper-molybdenum deposits associated with the mineral molybdenite, MoS2, but it has also been found in granite
pegmatites and quartz veins as well as in volcanic gases. Molybdenite is a typical polytype mineral which crystal structure is based on the stacking of [S-Mo-S]
with molybdenum in prismatic coordination by sulphide anions; however, it is not yet clearly established if rhenium ions replace Mo4+ cations in a disordered
way or else, if such replacement gives rise to dispersed nanodomains of a rhenium-rich phase. As a contribution to clarify this question, an X-ray absorption
spectroscopy (XANES) study using synchrotron radiation was performed at the Re L3-edge of rhenium-containing molybdenite samples. Obtained results are
described and discussed supporting the generally accepted structural perspective that rhenium is mainly carried by molybdenite through the isomorphous
replacement of Mo, rather than by the formation of dispersed Re-specific nanophase(s)
- …