Sulphate reduction in the sediment of the Venice canals (Italy)     

Zaggia L  Rosso J  Zonta R 《Marine pollution bulletin》2007,55(10-12):415-424

The sulphur cycle in the sediment of the Venice canal network was investigated by considering the sulphate reduction rate (SRR) and the distribution of sulphur compounds, in both pore water and sediment. Sulphate reduction (SR) is the main process in the metabolism of the organic matter supplied to the network by untreated urban effluents. Although it might account for the decomposition of only a limited percentage of the total organic-C inputs, the estimated rates are among the highest observed in coastal sediments. Measured rates range from 0.26 to 0.99 micromolcm(-3)d(-1), while mean annual values, estimated by a diagenetic model, vary from 0.16 to 0.43 micromolcm(-3)d(-1). The speciation of S in the sediment reveals that pyrite-S is the most abundant component of the total reduced S pool, whereas acid volatile sulphides and elemental sulphur together account for less than 45%. A preliminary budget indicates that the rate of burial of solid-phase S is small compared to the S produced by SR (from 10 to 25%). A large amount of reduced S is then lost from the canal deposits to be re-oxidised at the sediment-water interface or in the overlying water column.  相似文献   

A Fe K-edge XAS study of amethyst     

Francesco Di Benedetto  Francesco D’Acapito  Gabriele Fornaciai  Massimo Innocenti  Giordano Montegrossi  Luca A. Pardi  Silvia Tesi  Maurizio Romanelli 《Physics and Chemistry of Minerals》2010,37(5):283-289

An X-ray absorption spectroscopy (XAS) study of the Fe local environment in natural amethyst (a variety of α-quartz, SiO₂) has been carried out. Room temperature measurements were performed at the Fe K-edge (7,112 eV), at both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. Experimental results were then compared with DFT calculations. XANES experimental spectra suggest Fe to occur mainly in the trivalent state, although a fraction of Fe²⁺ is identified. EXAFS spectra, on the other hand, reveal an unusual short distance for the first coordination shell:  = 1.78(2) Å, the coordination number being 2.7(5). These results allow to establish that Fe replaces Si in its tetrahedral site, and that numerous local distortions are occurring as a consequence of the presence of Fe³⁺ variably compensated by protons and/or alkaline ions, or uncompensated. The formal valence of Fe, on the basis of both experimental and DFT structural features, can be either 4+ or 3+. Taking into account the XANES evidences, we suggest that Fe mainly occurs in the trivalent state, compensated by protons, and that a minor fraction of Fe⁴⁺ is stabilised by the favourable local structural arrangement.  相似文献   

An improved processing sequence for uncorrelated Chirp sonar data     

Luca?BaradelloEmail author 《Marine Geophysical Researches》2014,35(4):337-344

Chirp sonar systems can be used to obtain high resolution seismic reflection images of the sub-seafloor during marine surveys. The exact knowledge of the Chirp signature allows the use of deterministic algorithms to process the data, similarly to that applied to Vibroseis data on land. Here, it is described an innovative processing sequence to be applied to uncorrelated Chirp data, which can improve vertical and lateral resolution compared to conventional methods. It includes application of a Wiener filter to transform a frequency-modulated sweep into a minimum-phase pulse sequence. In this way, the data become causal and can undergo predictive deconvolution to reduce ringing and enhance vertical resolution. Afterwards, FX-deconvolution and Stolt migration can be applied to obtain an improved imaging of the subsurface. The result of this procedure is a seismic reflection image with higher resolution than traditional ones, which are normally represented using the envelope function of the signal. This technique can be particularly useful for engineering-geotechnical surveys and archaeological investigations that require a fine detail imaging of the uppermost meters of the sub-seafloor.  相似文献   

Chromium solubility in MgSiO3 ilmenite at high pressure     

Luca Bindi  Ekaterina A. Sirotkina  Andrey V. Bobrov  Tetsuo Irifune 《Physics and Chemistry of Minerals》2014,41(7):519-526

The crystal structure and chemical composition of crystals of (Mg_1?x Cr _x )(Si_1?x Cr _x )O₃ ilmenite (with x = 0.015, 0.023 and 0.038) synthesized in the model system Mg₃Cr₂Si₃O₁₂–Mg₄Si₄O₁₂ at 18–19 GPa and 1,600 °C have been investigated. Chromium was found as substitute for both Mg at the octahedral X site and Si at the octahedral Y site, according to the reaction Mg²⁺ + Si⁴⁺ = 2Cr³⁺. Such substitutions cause a shortening of the <X–O> and a lengthening of the <Y–O> distances with respect to the values typically observed for pure MgSiO₃ ilmenite and eskolaite Cr₂O₃. Although no high Cr contents are considered in the pyrolite model, Cr-bearing ilmenite may be the host for chromium in the Earth’s transition zone. The successful synthesis of ilmenite with high Cr contents and its structural characterization are of key importance because the study of its thermodynamic constants combined with the data on phase relations in the lower-mantle systems can help in the understanding of the seismic velocity and density profiles of the transition zone and the constraining composition and mineralogy of pyrolite in this area of the Earth.  相似文献   

X-ray single-crystal and Raman study of knorringite,Mg3(Cr1.58Mg0.21Si0.21)Si3O12, synthesized at 16 GPa and 1,600 °C     

Elena A. Bykova  Andrey V. Bobrov  Ekaterina A. Sirotkina  Luca Bindi  Sergey V. Ovsyannikov  Leonid S. Dubrovinsky  Yuriy A. Litvin 《Physics and Chemistry of Minerals》2014,41(4):267-272

The crystal structure of a knorringite-type compound, Mg₃(Cr_1.58Mg_0.21Si_0.21)Si₃O₁₂, synthesized in a multi-anvil press at P = 16 GPa and T = 1,600 °C, was refined from single-crystal X-ray diffraction data up to R = 2.36 % for 314 independent reflections. Garnet was found to be cubic and have space group Ia $\overline{3}$ d, with the unit cell parameters a = 11.5718 (1) Å, V = 1,549.54 (2) Å³. The knorringite crystal studied contains 21 mol% of majorite end-member. The structural characterization of knorringitic garnet is important because the study of its thermodynamic constants provides new constraints on thermobarometry of peridotitic garnet assemblages of the lowermost upper mantle. The Raman spectra of synthetic knorringite have been obtained for the first time.  相似文献   

Predictive Power Evaluation of a Physically Based Model for Shallow Landslides in the Area of Oltrepò Pavese,Northern Italy   总被引：2，自引：0，他引：2  

Roberto Valentino  Claudia Meisina  Lorella Montrasio  Gian Luca Losi  Davide Zizioli 《Geotechnical and Geological Engineering》2014,32(4):783-805

The use of real-time landslide early warning systems is attracting the attention of the scientific community, since it allows to assess “where” and “when” a shallow rainfall-induced landslide might occur by coupling rainfall amounts, hydrological models and slope-stability analysis. The paper deals with the main results of a back analysis, which refers to the application of a physically based stability model [Shallow Landslides Instability Prediction (SLIP)] on regional scale. The analysis concerns the occurrence of some recent rainfall-induced shallow landslides in the municipal territory of Broni, in the area of Oltrepò Pavese (Northern Italy). The study area is a hilly region 2.4 km² wide, where more than 40 % of the territory has slopes steeper than 15° and altitudes are between 90 and 250 m a.s.l. As regards the geologic setting, clayey-silty shallow colluvial deposits, with a maximum thickness of about 3 m, overlap a bedrock made of clayey shales, calcareous flysch and marls. The SLIP model is based on the limit equilibrium method applied to an infinite slope and on the Mohr–Coulomb strength criterion for the soil. By assuming that the main hydro-geotechnical process that leads to failure is the saturation of parts of the soil, the model allows to take into account the condition of partial saturation of the soil. The safety factor (F _S ) of a slope is also function of previous rainfalls. After the implementation of the model at territory scale, the input data have been introduced through a geographic information systems platform. In the current paper we mainly intend to evaluate the performance of SLIP at catchment scale, by comparison to (1) observed landslide events and (2) another well-established physically based model (TRIGRS). Further, we want to assess the suitability of the model as early warning tool. The results produced by the model are analyzed both in terms of safety factor maps, corresponding to some particular rainfall events, and in terms of the time-varying percentage of unstable areas over a 2-year span period. The paper shows the comparison between observed landslide localizations and model predictions. A quantitative comparison between the SLIP model and TRIGRS is presented, only for the most important event that occurred during the analyzed period. Overall, the results of the stability analyses based on observed rainfalls show the capability of the SLIP model to predict, in real-time and on a wide area, the occurrence of the analyzed phenomena.  相似文献   

Discussion of ‘Influence of diaphragm wall installation on the numerical analysis of deep excavation’, by Burlon S., Mroueh H. & I. Shahrour     

Riccardo Conti  Luca de Sanctis  Giulia M.B. Viggiani 《国际地质力学数值与分析法杂志》2013,37(11):1685-1687

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Assessment of coastal flooding hazard along the Emilia Romagna littoral,IT     

Luca Martinelli  Barbara Zanuttigh  Corinne Corbau 《Coastal Engineering》2010,57(11-12):1042-1058

Aim of this paper is to develop simple tools for mapping — at regional and local scale — coastal areas exposed at flooding risk. A two-step simplified procedure for coastal management purposes is presented and is applied to Emilia Romagna (Italy), whose low and sandy coast faces the relatively mild Northern Adriatic Sea. The procedure is composed by a 1D conceptual model to determine flooding probability along wide coastal stretches and by a more detailed 2D Level II reliability method, that provides local quantitative statistical maps of inland flooding propagation. Qualitative maps obtained by literature approaches and quantitative results of flooding probability along the littoral show a good agreement. A coastal flood state indicator is proposed to rapidly assess coastal hazard.  相似文献   

JP3D compression of solar data-cubes: Photospheric imaging and spectropolarimetry     

Dario Del Moro  Luca Giovannelli  Ermanno Pietropaolo  Francesco Berrilli 《Experimental Astronomy》2017,43(1):23-37

Hyperspectral imaging is an ubiquitous technique in solar physics observations and the recent advances in solar instrumentation enabled us to acquire and record data at an unprecedented rate. The huge amount of data which will be archived in the upcoming solar observatories press us to compress the data in order to reduce the storage space and transfer times. The correlation present over all dimensions, spatial, temporal and spectral, of solar data-sets suggests the use of a 3D base wavelet decomposition, to achieve higher compression rates. In this work, we evaluate the performance of the recent JPEG2000 Part 10 standard, known as JP3D, for the lossless compression of several types of solar data-cubes. We explore the differences in: a) The compressibility of broad-band or narrow-band time-sequence; I or V Stokes profiles in spectropolarimetric data-sets; b) Compressing data in [x,y, λ] packages at different times or data in [x,y,t] packages of different wavelength; c) Compressing a single large data-cube or several smaller data-cubes; d) Compressing data which is under-sampled or super-sampled with respect to the diffraction cut-off.  相似文献   

Dissipationless collapse, weak homology and central cores of elliptical galaxies     

Carlo Nipoti  Pasquale Londrillo  Luca Ciotti 《Monthly notices of the Royal Astronomical Society》2006,370(2):681-690

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