The MgCr2O4–MgFe2O4 solid solution series: effects of octahedrally coordinated Fe3+ on T–O bond lengths     

Davide Lenaz  Henrik Skogby  Francesco Princivalle  Ulf Hålenius 《Physics and Chemistry of Minerals》2006,33(7):465-474

The influence on the spinel structure of Fe³⁺ → Cr substitution was studied in flux-grown synthetic single crystals of the magnesiochromite–magnesioferrite (MgCr₂O₄–MgFe₂O₄) solid solution series. Samples were analysed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption and Mössbauer spectroscopy. With the exception of iron-poor samples (3–12 mol-% MgFe₂O₄), optical absorption and Mössbauer spectra show that iron occurs almost exclusively as trivalent Fe in the present samples. A very intense and broad absorption band at ca 7,800 cm^?1 dominates the optical absorption spectra of samples with higher Fe-contents. The appearance of this band is related to a distinct structural disorder of Fe³⁺ and a development of magnetic ordering as demonstrated by Mössbauer spectra. Profound composition-related changes are observed in the Mössbauer spectra, which are magnetically unsplit in the range 2–41 mol-% magnesioferrite, but become magnetically split in the range 59–100 mol-% magnesioferrite. Structural parameters a ₀ and M–O increase with magnesioferrite content and inversion degree, while u and T–O decrease. Our study confirms the previously reported (Lavina et al. 2002) influence of Fe³⁺ at the M site on T–O bond lengths in the spinel structure.  相似文献   

Comparing predictive capability of statistical and deterministic methods for landslide susceptibility mapping: a case study in the northern Apennines (Reggio Emilia Province, Italy)   总被引：5，自引：3，他引：2  

Federico Cervi  Matteo Berti  Lisa Borgatti  Francesco Ronchetti  Federica Manenti  Alessandro Corsini 《Landslides》2010,7(4):433-444

Statistical and deterministic methods are widely used in geographic information system based landslide susceptibility mapping. This paper compares the predictive capability of three different models, namely the Weight of Evidence, the Fuzzy Logic and SHALSTAB, for producing shallow earth slide susceptibility maps, to be included as informative layers in land use planning at a local level. The test site is an area of about 450 km² in the northern Apennines of Italy where, in April 2004, rainfall combined with snowmelt triggered hundreds of shallow earth slides that damaged roads and other infrastructure. An inventory of the landslides triggered by the event was obtained from interpretation of aerial photos dating back to May 2004. The pre-existence of mapped landslides was then checked using earlier aerial photo coverage. All the predictive models were run on the same set of geo-environmental causal factors: soil type, soil thickness, land cover, possibility of deep drainage through the bedrock, slope angle, and upslope contributing area. Model performance was assessed using a threshold-independent approach (the ROC plot). Results show that global accuracy is as high as 0.77 for both statistical models, while it is only 0.56 for SHALSTAB. Besides the limited quality of input data over large areas, the relatively poorer performance of the deterministic model maybe also due to the simplified assumptions behind the hydrological component (steady-state slope parallel flow), which can be considered unsuitable for describing the hydrologic behavior of clay slopes, that are widespread in the study area.  相似文献   

Tectono‐sedimentary evolution of the ‘Numidian Formation’ and Lateral Facies (southern branch of the western Tethys): constraints for central‐western Mediterranean geodynamics     

Francesco Guerrera  Agustín Martín‐Algarra  Manuel Martín‐Martín 《地学学报》2012,24(1):34-41

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A simple but effective cellular automaton for earthquakes   总被引：1，自引：0，他引：1  

Silvia Castellaro  Francesco Mulargia 《Geophysical Journal International》2001,144(3):609-624

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Retrospective selection bias (or the benefit of hindsight)   总被引：2，自引：0，他引：2  

Francesco Mulargia 《Geophysical Journal International》2001,146(2):489-496

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Gezira Scheme between state and market: some remarks on the privatization of irrigation in Sudan   总被引：1，自引：0，他引：1  

Francesco Bicciato  Pierpaolo Faggi 《GeoJournal》1995,37(1):101-104

This paper is a study of so-called privatization of the great Sudanese Gezira Scheme, under the structural and budgetary problems of the country. Nothwithstanding the official declaration, in reality privatization affected the project just in nominal way. Indeed, two factors play against it: the resistance of the State, which wants to hold the management of the national strategic resources, and the resistance of the territory itself which — as autopoietic system — reacts against any attempt to change its own structure. The islamic renewal(tajdid) can be considered as a way to solve the dilemma between development and social consent, under these new conditions.  相似文献   

Reply to Takayama's comment     

Francesco Mulargia  Paolo Gasperini 《Geophysical Journal International》1993,115(3):1199-1201

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Size distribution models of stratospheric particles in terms of the modified gamma function     

Dr. Francesco Tampieri  Dr. Claudio Tomasi 《Meteorology and Atmospheric Physics》1976,25(1):47-54

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Velocity and runout simulation of destructive debris flows and debris avalanches in pyroclastic deposits,Campania region,Italy   总被引：7，自引：0，他引：7  

Paola?Revellino  Oldrich?Hungr  Francesco?M.?GuadagnoEmail author  Stephen?G.?Evans 《Environmental Geology》2004,45(3):295-311

The Campanian Apennines are characterized by the presence of monocline ridges, mainly formed by limestone. During the periods of volcanic activity of the Somma-Vesuvius and Phlegrean Fields, the ridges were mantled with pyroclastic materials in varying thickness. The pyroclastics have been involved in destructive landslides both in historical time and in the recent past (1997, 1998, 1999). The landslides occur following intense and prolonged rainfalls. In some cases, landslides extended up to 4 km into the surrounding lowlands and reached towns, causing severe destruction and over 200 deaths. Generally, the landslides begin as small debris slides that develop into large, shallow debris avalanches or debris flows involving pyroclastic horizons and colluvial soils (0.5–2 m thick) on steep and vegetated slopes, often at the heads of gullies. During motion, the landslide materials eroded vegetation and soils from the slope, so that the moving material volume tended to increase. Then, proceeding towards and beyond the base of the slopes, the phenomena evolved into hyperconcentrated streamflow due to dilution by incorporating water. The results of motion analyses are described. An empirical rheological relationship was used including two principal terms that depend on the total normal stress and on the flow velocity. On this basis, the model has simulated the velocity and duration of debris avalanches and the distribution of the deposits. The selected areas were those of Sarno/Quindici and Cervinara, where a large amount of data is available both on the material properties and geomorphological setting. It was found that the majority of the cases at the two sites can be simulated successfully with only one specific pair of rheologic parameters. This provides the possibility for first-order predictions to be made of the motion of future landslides. Such predictions will be a valuable tool for outlining potential hazard areas and designing remedial measures.  相似文献   

High-temperature rapid pyrometamorphism induced by a charcoal pit burning: The case of Ricetto,central Italy     

Flavio?CapitanioEmail author  Francesco?Larocca  Salvatore?Improta 《International Journal of Earth Sciences》2004,93(1):107-118

Bulk chemistry and mineralogy of the peculiar rock of Ricetto (Carseolani Mts., Central Apennines, Italy) was studied to resolve its controversial origin: igneous dyke or anthropic product. This hybrid rock consists of a colorless, felsic component made up of glass plus quartz, and a brown, femic component made up of fans and spherulites of diopside, calcic plagioclase, wollastonite, and melilite. Textural relationships indicate very rapid cooling and immiscibility phenomena. The bulk chemistry of the rock is the same as that of the surrounding siliciclastic sandstone. The ¹⁴C analysis of a coal fragment from bottom of the body yields the conventional age of 227(±50) years. The Ricetto occurrence is an example of pyrometamorphism of a siliceous limestone induced by a charcoal pit burning. The small size of the heat source at Ricetto caused an intense but short-lived melting of the country rock. Prograde metamorphism caused a temperature increase up to 1,000–1,100 °C when melilite crystallization conditions were reached at appreciable P(CO₂) and high f(O₂). Melting occurred in a close system represented by the simplified equation: 3Cal+16.5Qtz+Ms+BtMel+Melt+2H₂O+3CO₂+0.5O₂. Diopside+calcic plagioclase+wollastonite formed by melilite breakdown during rapid cooling, through the reaction: 6Mel+6Qtz+0.5O₂3Di+2An+7Wo. Liquid immiscibility caused the separation between the felsic melt component and the femic melilite-bearing component. Immiscibility was characterized by different fractionation of alumina and alkalies between these two phases. Differences in bulk, glass, and mineral chemistry between the Ricetto and other melilite-bearing pyrometamorphic rocks can be attributed mainly to different protoliths.An erratum to this article can be found at  相似文献