Centrifuge modelling of the seismic performance of soft buried barriers     

Valeria Nappa  Emilio Bilotta  Alessandro Flora  S. P. Gopal Madabhushi 《Bulletin of Earthquake Engineering》2016,14(10):2881-2901

The paper presents the results of an experimental work carried out in a geotechnical centrifuge at the Schofield Centre of Cambridge University. Two reduced scale models of soft barriers in a sand layer underwent a series of ground shaking. In the first model a thin horizontal layer made of latex balloons filled with a cross-linked gel was created at about mid-height of the sand layer. In the second, the same balloons were deployed to form a V-shaped barrier aimed at isolating a relatively shallow volume of sand. The aim of the study was to get experimental evidence of the capability of such soft barriers to isolate a volume of soil thus reducing amplification of ground motion during severe seismic events. The experimental results were compared with FE numerical analyses of the same models, carried out also in free field to have a benchmark condition. By validating the FE modelling via the comparison with the experimental results, a robust model has been built, aimed at being used for carrying out a wider parametric numerical testing. The experimental results confirm the effectiveness of such soft barriers to reduce amplification in the isolated volumes during seismic events.  相似文献   

Denitrification and the stoichiometry of nutrient regeneration in Waquoit Bay, Massachusetts     

Michael G. LaMontagne  Valeria Astorga  Anne E. Giblin  Ivan Valiela 《Estuaries and Coasts》2002,25(2):272-281

To determine the removal of regenerated nitrogen by estuarine sediments, we compared sediment N₂ fluxes to the stoichiometry of nutrient and O₂ fluxes in cores collected in the Childs River, Cape Cod, Massachusetts. The difference between the annual PO₄ ³⁻ (0.2 mol P m⁻² yr⁻¹) and NH₄ ⁺ (1.6 mol N m⁻² yr⁻¹) flux and the Redfield N∶P ratio of 16 suggested an annual deficit of 1.5 mol N m⁻² yr⁻¹. Denitrification predicted from O₂∶NH₄ ⁺ flux ratios and measured as N₂ flux suggested a nitrogen sink of roughly the same magnitude (1.4 mol N m⁻² yr⁻¹). Denitrification accounted for low N∶P ratios of benthic flux and removed 32–37% of nitrogen inputs entering the relatively highly nutrient loaded Childs River, despite a relatively brief residence time for freshwater in this system. Uptake of bottom water nitrate could only supply a fraction of the observed N₂ flux. Removal of regenerated nitrogen by denitrification in this system appears to vary seasonally. Denitrification efficiency was inversely correlated with oxygen and ammonium flux and was lowest in summer. We investigated the effect of organic matter on denitrification by simulating phytoplankton deposition to cores incubated in the lab and by deploying chambers on bare and macroaglae covered sediments in the field. Organic matter addition to sediments increased N₂ flux and did not alter denitrification efficiency. Increased N₂ flux co-varied with O₂ and NH₄ ⁺ fluxes. N₂ flux (261±60 μmol m⁻² h⁻¹) was lower in chambers deployed on macroalgal beds than deployed on bare sediments (458±70 μmol m⁻² h⁻¹), and O₂ uptake rate was higher in chambers deployed on macroalgal beds (14.6±2.2 mmol m⁻² h⁻¹) than on bare sediments (9.6±1.5 mmol m⁻² h⁻¹). Macroalgal cover, which can retain nitrogen in the system, is a link between nutrient loading and denitrification. Decreased denitrification due to increasing macroalgal cover could create a positive feedback because decreasing denitrification would increase nitrogen availability and could increase macroalgae cover.  相似文献   

Uncertainties on elastic parameters and occupancy factors: how do they affect the accuracy of the calculated Gibbs energy of minerals at ( P , T ) conditions? The case of 3 T - versus 2 M ₁-phengite     

Alessandro Pavese  Valeria Diella 《Physics and Chemistry of Minerals》2007,34(9):637-645

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A principal component analysis approach to assess CHIRPS precipitation dataset for the study of climate variability of the La Plata Basin,Southern South America     

Cerón  Wilmar Loaiza  Molina-Carpio  Jorge  Ayes Rivera  Irma  Andreoli  Rita Valeria  Kayano  Mary Toshie  Canchala  Teresita 《Natural Hazards》2020,103(1):767-783

Natural Hazards - This article assesses the consistency of the satellite precipitation estimate CHIRPS v.2 to describe the spatiotemporal rainfall variability in the La Plata Basin (LPB), the...  相似文献   

Analysis of waves observed by synthetic aperture radar across ocean fronts     

Shao  Weizeng  Jiang  Xingwei  Nunziata  Ferdinando  Marino  Armando  Yang  Zhehao  Zhang  Youguang  Corcione  Valeria 《Ocean Dynamics》2020,70(11):1397-1407

Ocean Dynamics - In this study, synthetic aperture radar (SAR) imaging of waves across ocean fronts was investigated using C-band Sentinel-1 VV-polarized SAR imagery collected over the Yangtze and...  相似文献   

Trace element behaviour during interaction between basalt and crustal rocks at 0.5–0.8 GPa: an experimental approach     

Silvio Mollo  Valeria Misiti  Piergiorgio Scarlato 《Central European Journal of Geosciences》2010,2(2):188-198

We experimentally investigate the major and trace elements behavior during the interaction between two partially molten crustal rocks (meta-anorthosite and metapelite) and a basaltic melt at 0.5–0.8 GPa. Results show that a hybrid melt is formed at the basalt-crust contact, where plagioclase crystallizes. This contact layer is enriched in trace elements which are incompatible with plagioclase crystals. Under these conditions, the trace element diffusion coefficients are one order of magnitude larger than those expected. Moreover, the HFSE diffusivity in the hybrid melt is surprisingly higher than the REE one. Such a feature is related to the plagioclase crystallization that changes the trace elements liquid-liquid partitioning (i.e. diffusivity) over a transient equilibrium that will persist as long as the crystal growth proceeds. These experiments suggests that the behaviour of the trace elements is strongly dependent on the crystallization at the magma-crust interface. Diffusive processes like those investigated can be invoked to explain some unusual chemical features of contaminated magmatic suites.  相似文献   

Chronic oil pollution harms Magellanic penguins in the Southwest Atlantic     

García-Borboroglu P  Boersma PD  Ruoppolo V  Reyes L  Rebstock GA  Griot K  Rodrigues Heredia S  Adornes AC  da Silva RP 《Marine pollution bulletin》2006,52(2):193-198

Petroleum pollution is a problem for seabirds along the Southwest Atlantic coast. Twenty-five groups from Salvador, Brazil (12 degrees 58'S) to San Antonio Oeste, Argentina (40 degrees 43'S) survey or rehabilitate sick or oiled seabirds. Four groups, one each in Brazil and Uruguay, and two in Argentina, kept counts of birds found alive and in need of rehabilitation. An average of 63.7% of the seabirds found were Magellanic penguins (Spheniscus magellanicus), with 3869 reported since 1987. Mainly adult penguins were found in Argentina (1605 of 2102 penguins of known age class) and Uruguay (158 of 197). Juveniles were most common in Brazil (234 of 325). Oil fouling was the most frequent cause of injury or sickness. The number of oiled penguins reported in their wintering range has greatly increased since the early 1990s and is strongly correlated with petroleum exports from Argentina. Our results show that chronic petroleum pollution is a problem for wildlife from Southern Brazil through Northern Argentina, and regulations and enforcement are failing to protect living resources.  相似文献   

Experimental Study of Pollutant Dispersion Within a Network of Streets   总被引：2，自引：2，他引：0  

Valeria Garbero  Pietro Salizzoni  Lionel Soulhac 《Boundary-Layer Meteorology》2010,136(3):457-487

We investigate the dispersion of a passive scalar within an idealised urban district made up of a building-like obstacle array. We focus on a street network in which the lateral dimension of the buildings exceeds the street width, a geometry representative of many European cities. To investigate the effect of different geometries and wind directions upon the pollutant dispersion process, we have performed a series of wind-tunnel experiments. Concentration measurements of a passive tracer have enabled us to infer the main features characterising its dispersion within the street network. We describe this by focusing on the roles of different transfer processes. These are the channelling of the tracer along the street axes, the mixing at street intersections, and the mass exchange between the streets and the overlying atmospheric flow. Our experiments provide evidence of the dependence of these processes on the geometrical properties of the array and the direction of the overlying atmospheric flow.  相似文献   

Carbonate assimilation in magmas: A reappraisal based on experimental petrology     

Silvio Mollo  Mario Gaeta  Carmela Freda  Tommaso Di Rocco  Valeria Misiti  Piergiorgio Scarlato 《Lithos》2010,114(3-4):503-514

The main effect of magma–carbonate interaction on magma differentiation is the formation of a silica-undersaturated, alkali-rich residual melt. Such a desilication process was explained as the progressive dissolution of CaCO₃ in melt by consumption of SiO₂ and MgO to form diopside sensu stricto. Magma chambers emplaced in carbonate substrata, however, are generally associated with magmatic skarns containing clinopyroxene with a high Ca-Tschermak activity in their paragenesis. Data are presented from magma–carbonate interaction experiments, demonstrating that carbonate assimilation is a complex process involving more components than so far assumed. Experimental results show that, during carbonate assimilation, a diopside–hedenbergite–Ca-Tschermak clinopyroxene solid solution is formed and that Ca-Tschermak/diopside and hedenbergite/diopside ratios increase as a function of the progressive carbonate assimilation. Accordingly, carbonate assimilation reaction should be written as follows, taking into account all the involved magmatic components:CaCO₃^solid + SiO₂^melt + MgO^melt + FeO^melt + Al₂O₃^melt → (Di–Hd–CaTs)_ss^solid + CO₂^fluidThe texture of experimental products demonstrates that carbonate assimilation produces three-phases (solid, melt, and fluid) whose main products are: i) diopside–hedenbergite–Ca-Tschermak clinopyroxene solid solution; ii) silica-undersaturated CaO-rich melt; and iii) C–O–H fluid phase. The silica undersaturation of the melt and, more importantly, the occurrence of a CO₂-rich fluid phase, must be taken into account as they significantly affect partition coefficients and the redox state of carbonated systems, respectively.  相似文献   

Modelling of thermo-chemical properties over the sub-solidus MgO–FeO binary,as a function of iron spin configuration,composition and temperature     

Marcello Merli  Luciana Sciascia  Alessandro Pavese  Valeria Diella 《Physics and Chemistry of Minerals》2015,42(5):347-362

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