Effect of XFe and fO2 on the FTIR and Mössbauer spectra of richterites in the system K2O-Na2O-CaO-MgO-FeO-Fe2O3-TiO2-SiO2-H2O     

J. Sergent  J. -L. Robert  B. Boukili  G. Della Ventura 《Physics and Chemistry of Minerals》1996,23(4-5):308-308

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An alternative model for positive shifts in shallow-marine carbonate δ¹³C and δ¹⁸O     

Adrian Immenhauser  Giovanna Della Porta  Jeroen A. M. Kenter  Juan R. Bahamonde† 《Sedimentology》2003,50(5):953-959

Abstract Positive shifts in global seawater δ¹³C_DIC are related to changes in the ratio of organic relative to inorganic carbon burial in oceanic basins, whereas factors such as climatic cooling and the accumulation of polar ice are known to cause positive shifts in δ¹⁸O. Here, an alternative model is proposed for the formation of local positive isotope shifts in shallow-marine settings. The model involves geochemically altered platform-top water masses and the effects of early meteoric diagenesis on carbonate isotopic composition. Both mechanisms are active on modern (sub)tropical carbonate platforms and result in low carbonate δ¹³C and δ¹⁸O relative to typical oceanic values. During high-amplitude transgressive events, the impact of isotopically light meteoric fluids on the carbonate geochemistry is much reduced, and ¹³C-depleted platform-top water mixes with open oceanic water masses having higher isotope values. Both factors are recorded as a transient increase in carbonate ¹³C and ¹⁸O relative to low background values. These processes must be taken into consideration when interpreting the geochemical record of ancient epeiric seas.  相似文献   

A crystal-chemical investigation of Cr substitution in muscovite by XANES spectroscopy     

A. Cardelli  G. Cibin  M. Benfatto  S. Della Longa  M. F. Brigatti  A. Marcelli 《Physics and Chemistry of Minerals》2003,30(1):54-58

 This work introduces a novel procedure to fit the scattering features of XANES spectra. The procedure was applied and validated on a chromium-containing muscovite for which structural and crystal-chemical characterization is available from literature. The simulation, which involved clusters formed by up to 90 atoms, proved to be effective in representing the Cr local environment, even if the system is characterized by a very low metal content, as demonstrated by the extremely good correspondence with experimental data. Received: 23 May 2002 / Accepted: 6 November 2002  相似文献   

On core-collapse supernovae in normal and in Seyfert galaxies     

A.Bressan  M.Della Valle  P.Marziani 《Monthly notices of the Royal Astronomical Society》2002,331(3):L25-L29

This paper estimates the relative frequency of different types of core-collapse supernovae, in terms of the ratio between the number of Type Ib–Ic and of Type II supernovae. We estimate independently for all normal and Seyfert galaxies whose radial velocity is ≤14 000 km s⁻¹, and which had at least one supernova event recorded in the Asiago catalogue from 1986 January to 2000 August. We find that the ratio is  ≈0.23±0.05  in normal galaxies. This value is consistent with constant star formation rate and with a Salpeter initial mass function and an average binary rate ≈50 per cent. On the contrary, Seyfert galaxies exceed the ratio in normal galaxies by a factor ≈4 at a confidence level ≳2 σ . A caveat is that the numbers for Seyferts are still small (six of Type Ib–Ic and six of Type II supernovae discovered as yet). Assumed to be real, this excess of Type Ib/c supernovae may indicate a burst of low-age star formation  ( τ ≲20 Myr)  , a high incidence of binary systems in the inner regions  ( r ≲0.4 R ₂₅)  of Seyfert galaxies, or a top-loaded mass function.  相似文献   

A Mössbauer and FTIR study of synthetic amphiboles along the magnesioriebeckite – ferri-clinoholmquistite join     

Giancarlo Della Ventura  Günther J. Redhammer  Gianluca Iezzi  Frank C. Hawthorne  Arnaud Papin  Jean-Louis Robert 《Physics and Chemistry of Minerals》2005,32(2):103-113

A series of amphiboles along the magnesioriebeckite—Na₂Mg₃Fe³⁺ ₂Si₈O₂₂(OH)₂– ferri-clinoholmquistite—Li₂Mg₃Fe³⁺ ₂Si₈O₂₂(OH)2 - join, defined by the ^BLi^B Na_–1 exchange vector, were hydrothermally synthesized at 700°C, 0.4 GPa, NNO + 1 redox conditions. Powder XRD and SEM-EDAX showed a very high (> 90%) amphibole yield for all samples. X-ray patterns were indexed in the C2/m space group; refined cell-parameters show a linear decrease of a and as a function of chemistry. IR spectra in the OH-stretching region show four main and rather sharp bands; these are assigned to Mg and Fe²⁺ at M(1,3), and indicate that the obtained amphiboles depart from the nominal octahedral composition (^M1,3Mg₃). The IR spectra also show that there is an increasing filling-up of the A-site for increasing Na in the system (increasing solid-solution toward, arfvedsonite). Mössbauer spectra show four well-defined quadrupole doublets which are assigned to Fe³⁺ at M2 and to Fe²⁺ at M1, M3 and M4, respectively. The Fe³⁺/Fe²⁺ content derived from fitted peak areas show variable Fe³⁺ concentration along the series. Mössbauer spectra also show a distinct alteration of ⁵⁷Fe hyperfine parameters with changing Na–Li at M4. The most evident variation is observed for the quadrupole splitting of Fe³⁺ at M2, which increases by 50% from ferri-clinoholmquistite to magnesio-riebeckite; this suggest that the M2 octahedron in ferri-clinoholmquistite is much closer to the ideal geometry than the M2 octahedron in magnesio-riebeckite. Mössbauer spectra show also a well-defined increase in the Fe²⁺ quadrupole splitting of the M1 and M3 octahedra, which is attributed to the Na–Li distribution at the B-sites.  相似文献   

Seasonal changes and biochemical composition of the labile organic matter flux in the Cretan Sea     

Roberto Danovaro  Norberto Della Croce  Antonio Dell'Anno  Mauro Fabiano  Daniela Marrale  Daniela Martorano 《Progress in Oceanography》2000,46(2-4)

Downward fluxes of labile organic matter (lipids, proteins and carbohydrates) at 200 (trap A) and 1515 m depth (trap B), measured during a 12 months sediment trap experiment, are presented, together with estimates of the bacterial and cyanobacterial biomasses associated to the particles. The biochemical composition of the settling particles was determined in order to provide qualitative and quantitative information on the flux of readily available organic carbon supplying the deep-sea benthic communities of the Cretan Sea. Total mass flux and labile carbon fluxes were characterised by a clear seasonality. Higher labile organic fluxes were reported in trap B, indicating the presence of resuspended particles coming from lateral inputs. Particulate carbohydrates were the major component of the flux of labile compounds (on annual average about 66% of the total labile organic flux) followed by lipids (20%) and proteins (13%). The biopolymeric carbon flux was very low (on annual average 0.9 and 1.2 gC m⁻² y⁻¹, at trap A and B). Labile carbon accounted for most of the OC flux (on annual average 84% and 74% in trap A and B respectively). In trap A, highest carbohydrate and protein fluxes in April and September, corresponded to high faecal pellet fluxes. The qualitative composition of the organic fluxes indicated a strong protein depletion in trap B and a decrease of the bioavailability of the settling particles as a result of a higher degree of dilution with inorganic material. Quantity and quality of the food supply to the benthos displayed different temporal patterns. Bacterial biomass in the sediment traps (on average 122 and 229 μgC m⁻² d⁻¹ in trap A and B, respectively) was significantly correlated to the flux of labile organic carbon, and particularly to the protein and carbohydrate fluxes. Cyanobacterial flux (on average, 1.1 and 0.4 μgC m⁻² d⁻¹, in trap A and B, respectively) was significantly correlated with total mass and protein fluxes only in trap A. Bacterial carbon flux, equivalent to 84.2 and 156 mgC m⁻² y⁻¹, accounted for 5–6.5% of the labile carbon flux (in trap A and B respectively) and for 22–41% protein pool of the settling particles. These results suggest that in the Cretan Sea, bacteria attached to the settling particles represent a potential food source of primary importance for deep-sea benthic communities.  相似文献   

The role of petrography on the thermal decomposition and burnability of limestones used in industrial cement clinker     

Nicoletta Marinoni  Andrea Bernasconi  Giovanna Della Porta  Maurizio Marchi  Alessandro Pavese 《Mineralogy and Petrology》2015,109(6):719-731

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Structural and geodynamic study in central Tunisia using field and geophysical data: new structural interpretation of the N–S axis and associated Atlassic structures     

Ferid Dhahri  Dorra Tanfous  Hakim Gabtni  Noureddine Boukadi 《International Journal of Earth Sciences》2015,104(7):1819-1835

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A laboratory study of the initial structure and the overconsolidation effects on the undrained monotonic behavior of sandy soil from Chlef region in northern Algeria   总被引：2，自引：1，他引：1  

Noureddine Della  Ahmed Arab  Mostefa Belkhatir 《Arabian Journal of Geosciences》2011,4(5-6):983-991

The effects of initial state of the samples and the overconsolidation ratio (OCR) on the behavior of Chlef sand were studied in this article. For this purpose, the results of two series of undrained monotonic triaxial compression tests on medium dense sand are presented. In the first test series, the influence of the specimen's fabric and confining pressure has been studied. The tests were conducted at initial confining pressure of 50, 100, and 200 kPa. Two methods of sample preparation, which included the dry funnel pluviation and the wet deposition, were utilized. All the samples were subjected to a monotonic loading after consolidation phase. The results of the tests demonstrate that an increase in initial confining pressure leads to an increase in the resistance to liquefaction. The results also show that the samples prepared with the dry funnel pluviation method exhibit a greater resistance to liquefaction than those prepared with the wet deposition method. In the second series of tests, the overconsolidation influence on the resistance to the sand liquefaction has been realized on samples at an effective stress of 100 kPa for OCR varying between 1 and 8. The tests show that the increase of OCR improves the stiffness of sand and accelerates the appearance of dilatancy.  相似文献   

Two refractory Wild 2 terminal particles from a carrot‐shaped track characterized combining MIR/FIR/Raman microspectroscopy and FE‐SEM/EDS analyses     

A. Rotundi  F. J. M. Rietmeijer  M. Ferrari  V. Della Corte  G. A. Baratta  R. Brunetto  E. Dartois  Z. Djouadi  S. Merouane  J. Borg  J. R. Brucato  L. Le Sergeant d'Hendecourt  V. Mennella  M. E. Palumbo  P. Palumbo 《Meteoritics & planetary science》2014,49(4):550-575

We present the analyses results of two bulk Terminal Particles, C2112,7,171,0,0 and C2112,9,171,0,0, derived from the Jupiter‐family comet 81P/Wild 2 returned by the Stardust mission. Each particle embedded in a slab of silica aerogel was pressed in a diamond cell. This preparation, as expected, made it difficult to identify the minerals and organic materials present in these particles. This problem was overcome using a combination of three different analytical techniques, viz. FE‐SEM/EDS, IR, and Raman microspectroscopy that allowed identifying the minerals and small amounts of amorphous carbon present in both particles. TP2 and TP3 were dominated by Ca‐free and low‐Ca, Mg‐rich, Mg,Fe‐olivine. The presence of melilite in both particles is supported by IR microspectroscopy, but is not confirmed by Raman microspectroscopy, possibly because the amounts are too small to be detected. TP2 and TP3 show similar silicate mineral compositions, but Ni‐free and low‐Ni, subsulfur (Fe,Ni)S grains are present in TP2 only. TP2 contains indigenous amorphous carbon hot spots; no indigenous carbon was identified in TP3. These nonchondritic particles probably originated in a differentiated body. This work found an unanticipated carbon contamination following the FE‐SEM/EDS analyses. It is suggested that organic materials in the embedding silica aerogel are irradiated during FE‐SEM/EDS analyses creating a carbon gas that develops a strong fluorescence continuum. The combination of the selected analytical techniques can be used to characterize bulk Wild 2 particles without the need of extraction and removal of the encapsulating aerogel. This approach offers a relatively fast sample preparation procedure, but compressing the samples can cause spurious artifacts, viz. silica contamination. Because of the combination of techniques, we account for these artifacts.  相似文献