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Crystal structure of the hydrated sulphate pickeringite (MgAl2(SO4)4. 22H2O): X-ray powder diffraction study
No full textThe crystal structure of pickeringite (ideal formula MgAl2(SO4)4. 22H2O) from Roccalumera (Messina, Italy), a hydrated sulphate of the halotrichite group, has been determined by X-ray powder diffraction with the Rietveld method. The space group has been confirmed to be P21/c with unit cell parameters: a = 6.1844(2) Å, b = 24.2715(9) Å, c = 21.2265(7) Å and β = 100.326(4)°. The comparison of these powder data with those reported in the PDF-2 database (12-299) evidences strong differences in both the cell parameters and Bragg reflection positions, suggesting the redefinition of the PDF card for this mineral. The results of the Rietveld refinement confirm the close correspondence between the structures of pickeringite and apjohnite (MnAl2(SO4)4 · 22H2O)
Orthopyroxene as a Geospeedometer: Thermal History of Kapoeta, Old Homestead 001 and Hughes 002 Howardites
No full textSingle crystals of orthopyroxene from small fragments of the Kapoeta, Old Homestead 001, and
Hughes 002 howardites were studied by x-ray diffraction and microprobe analyses. The Fe-Mg equilibrium
distribution coefficients k~ of the crystals were used to calculate the closure temperatures (T,) using the
calibration by Stimpfl et al. (1 999). The compositions, the presence of exsolved augite lamellae, and the T,
values (from 365 to 385 "C) obtained for Kapoeta orthopyroxenes suggest that our fragment comes from a
diogenitic cumulate clast. The more Fe-rich composition, the absence of exsolved lamellae, and the higher
T, values (from 583 to 605 "C) measured in the Old Homestead 001 orthopyroxenes suggest that this
fragment comes from a cumulitic clast affected by fast cooling at high temperature. For the Hughes 002
orthopyroxenes, close in composition to Old Homestead 001, the different T, values (339, 358, and 607 "C)
recorded by the various crystals and the presence of augite lamellae in the crystals with the lowest T, support
the hypothesis that this howardite sample is an unheated breccia containing a mixture of cumulitic
orthopyroxenes with different thermal histories
ORTHOPYROXENE AS GEOSPEEDOMETER:THERMAL HISTORY OF KAPOETA OLD HOMESTEAD 001 AND HUGHES 002 HOWARDITES.
No full textIl vetro opaco in epoca romana: studi spettroscopici in luce di sincrotrone su reperti da Pompei e siti siciliani
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The effects of anthropogenic particulate emissions on roadway dust and Nerium oleander leaves in Messina (Sicily, Italy)
No full textComplementary studies on the inorganic chemical composition of Nerium oleander leaves collected in the town of Messina (Sicily, Italy) and seven grain-size fractions of local roadway dust have been carried out. Data and maps are presented to show that the particulate matter present in the air of Messina contains trace elements significantly in excess with respect to the average continental earth crust. The anomalies follow the outline of the urban area, the highest concentrations of trace elements being observed where traffic density is highest. Chemical and isotopic analyses of both road dust and Nerium oleander leaves indicate that Pb contamination still characterizes roads with heavy traffic. In addition to Pb, other metals such as Pt, Pd, Sb, Au, Br, Zn, Cu, Mo, and Cd are significantly enriched in roadway dust, indicating their common anthropogenic origin, especially from traffic. SEM/EDS study of some roadway dust particles has shown the presence of gypsum probably of secondary origin, mixed particles formed by coagulation or gas-to-particle conversion, and porous spherical particles apparently emanating from combustion processes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The opaque Roman Glass: synchrotron radiation studies on tesserae from Pompeii and Sicily
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