Micromechanical inspection of incremental behaviour of crushable soils     

Ciantia  Matteo O.  Arroyo  Marcos  O’Sullivan  Catherine  Gens  Antonio 《Acta Geotechnica》2019,14(5):1337-1356

In granular soils grain crushing reduces dilatancy and stress obliquity enhances crushability. These are well-supported specimen-scale experimental observations. In principle, those observations should reflect some peculiar micromechanism associated with crushing, but which is it? To answer that question the nature of crushing-induced particle-scale interactions is here investigated using an efficient DEM model of crushable soil. Microstructural measures such as the mechanical coordination number and fabric are examined while performing systematic stress probing on the triaxial plane. Numerical techniques such as parallel and the newly introduced sequential probing enable clear separation of the micromechanical mechanisms associated with crushing. Particle crushing is shown to reduce fabric anisotropy during incremental loading and to slow fabric change during continuous shearing. On the other hand, increased fabric anisotropy does take more particles closer to breakage. Shear-enhanced breakage appears then to be a natural consequence of shear-enhanced fabric anisotropy. The particle crushing model employed here makes crushing dependent only on particle and contact properties, without any pre-established influence of particle connectivity. That influence does not emerge, and it is shown how particle connectivity, per se, is not a good indicator of crushing likelihood.

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Spatial distribution pattern analysis of subtidal macroalgae assemblages by a non-destructive rapid assessment method     

Xabier Guinda  José Antonio JuanesAraceli Puente  Beatriz Echavarri-Erasun 《Journal of Sea Research》2012,67(1):34-43

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The science of European marine reserves: Status,efficacy, and future needs     

Phillip B. Fenberg  Jennifer E. Caselle  Joachim Claudet  Michaela Clemence  Steven D. Gaines  Jose Antonio García-Charton  Emanuel J. Gonçalves  Kirsten Grorud-Colvert  Paolo Guidetti  Stuart R. Jenkins  Peter J.S. Jones  Sarah E. Lester  Rob McAllen  Even Moland  Serge Planes  Thomas K. Sørensen 《Marine Policy》2012

The ecologically and socio-economically important marine ecosystems of Europe are facing severe threats from a variety of human impacts. To mitigate and potentially reverse some of these impacts, the European Union (EU) has mandated the implementation of the Marine Strategy Framework Directive (MSFD) in order to achieve Good Environmental Status (GES) in EU waters by 2020. The primary initiative for achieving GES is the implementation of coherent networks of marine protected areas (MPAs). Marine reserves are an important type of MPA in which no extraction is allowed, but their usefulness depends upon a number of ecological, management, and political factors. This paper provides a synthesis of the ecological effects of existing European marine reserves and the factors (social and ecological) underlying their effectiveness. Results show that existing European marine reserves foster significant positive increases in key biological variables (density, biomass, body size, and species richness) compared with areas receiving less protection, a pattern mirrored by marine reserves around the globe. For marine reserves to achieve their ecological and social goals, however, they must be designed, managed, and enforced properly. In addition, identifying whether protected areas are ecologically connected as a network, as well as where new MPAs should be established according to the MSFD, requires information on the connectivity of populations across large areas. The adoption of the MSFD demonstrates willingness to achieve the long-term protection of Europe's marine ecosystems, but whether the political will (local, regional, and continent wide) is strong enough to see its mandates through remains to be seen. Although the MSFD does not explicitly require marine reserves, an important step towards the protection of Europe's marine ecosystems is the establishment of marine reserves within wider-use MPAs as connected networks across large spatial scales.  相似文献   

Taxonomic distinctness in Mediterranean marine nematodes and its relevance for environmental impact assessment     

Bevilacqua S  Sandulli R  Plicanti A  Terlizzi A 《Marine pollution bulletin》2012,64(7):1409-1416

Taxonomic distinctness has been applied successfully for the exploration of biodiversity patterns, yet its relevance in environmental impact assessment is far from being unquestioned. In this study, we assessed the potential of taxonomic distinctness to discern perturbed and unperturbed sites by analysing Mediterranean nematode assemblages. Geographic and habitat-related effects on the performance of the index were also explored. Above all, our findings do not corroborate the conjecture that taxonomic distinctness could be largely unaffected by natural variability, habitat features, and biogeographic context, casting doubts on potential generalization concerning its application as an indicator of environmental stress. Taxonomic distinctness represents an excellent metric to identifying taxonomic properties of ecological systems but, as for other ecological indices, it should be viewed as a complementary tool in environmental impact assessment, due to its sensitiveness to specific environmental features of systems being investigated.  相似文献   

Groundwater connections under a barrier beach: A case study in the Venice Lagoon     

John Rapaglia  Eloisa Di Sipio  Henry Bokuniewicz  Gian Maria Zuppi  Luca Zaggia  Antonio Galgaro  Aaron Beck 《Continental Shelf Research》2010

The flow of groundwater beneath barrier islands has been cited as a possible pathway for salt water and chemical exchange between a protected embayment and the open sea. Evidence is presented that identifies an exchange of groundwater through a highly permeable paleoinlet along the barrier beach of Cavallino, which separates the northern Venice Lagoon from the Adriatic Sea. We utilized both point measurements of submarine groundwater discharge (SGD) and a geophysical investigation of the subsurface resistivity to analyze the movement of saline groundwater. Discharge of groundwater and associated nutrients, was higher at the site of a former inlet than at a similar site along the barrier and modulated by the difference in tidal water level between the lagoon and Adriatic Sea. If the measured conditions are typical, storm surge barriers could potentially result in a saline groundwater flow of up to 1.5×10⁶ m³ d⁻¹ into the lagoon.  相似文献   

From regional- to local-scale seismic hazard assessment: examples from Southern Spain     

Jorge M. Gaspar-Escribano  Manuel Navarro  Belén Benito  Antonio García-Jerez  Francisco Vidal 《Bulletin of Earthquake Engineering》2010,8(6):1547-1567

An approach that relates results from a regional seismic hazard assessment study with local-scale site-effect characterizations in an area of low-to-moderate seismic activity such as Andalusia (southern Spain), is presented. Results of a previous probabilistic seismic hazard analysis of Andalusia on rock conditions are disaggregated to infer hazard controlling earthquakes for different target motions. A collection of controlling magnitude-distance pairs and the corresponding site-specific response spectra at main capital cities of the region are obtained. These spectra are first-order approximations to expected seismic actions required in local earthquake risk assessments. In addition, results of independent, local-scale studies developed in Almeria City (SE Andalusia) are used to derive an updated seismic zonation of the city. These include predominant soil period estimates and shear-wave velocity profiles at different locations. If a local seismic risk assessment study or an earthquake-resistant structural design is to be developed, it may be recommended the use of different seismic actions on sites characterized by distinct response to seismic shaking (as derived from the seismic zonation). The seismic action related to worst-case scenarios may be modeled through a hazard-consistent response spectrum, obtained by hazard disaggregation at the spectral acceleration with period matching the prevailing resonant period of the target site or structure.  相似文献   

Testing the sensitivity of geomorphic indices in areas of low-rate active folding (eastern Betic Cordillera, Spain)   总被引：2，自引：0，他引：2  

Antonio Pedrera  Jos Vicente Prez-Pea  Jesús Galindo-Zaldívar  Jos Miguel Azan  Antonio Azor 《Geomorphology》2009,105(3-4):218-231

Active deformation structures have an incidence in topography that can be quantified by using geomorphic indices. Most of these indices have been checked in faulted regions with high-deformation rates. The application of several geomorphic indices (hypsometric curve analysis, normalized stream-length gradient, and valley width-to-valley height ratio) to the drainage network of the southern limb of the Sierra de Las Estancias antiform (Internal Zones, eastern Betic Cordillera), where low-rate active folding has been recognized, allows us to investigate the suitability of these indices to identify active structures in such a scenario. Hypsometric curves clearly identify regions with recent uplift and young topography, but they do not provide any constraint on the location of active folds. Local valley width-to-valley height index variations have been detected just coinciding whit the position of ENE–WSW active folds. Normalized stream-length gradient index serves to locate active folds in areas of hard rock substratum, but not in those areas with soft sediments (Neogene-Quaternary sedimentary basins). This is most likely due to the fact that in the basins erosion is much more intense than in the hard rock sectors. In view of these results, we consider that geomorphic indices constitute a valuable tool for identifying sectors affected by low-rate uplift related to active folding, with the best results obtained in hard rock areas.  相似文献   

Intra-annual variation and baseline concentrations of dissolved trace metals in the Vigo Ria and adjacent coastal waters (NE Atlantic Coast)     

Juan Santos-Echeandía  Antonio Cobelo-García 《Marine pollution bulletin》2009,58(2):298-58

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Use of Chitosan with Different Deacetylation Degrees for the Adsorption of Food Dyes in a Binary System          下载免费PDF全文

Janaína O. Gonçalves  Diana A. Duarte  Guilherme L. Dotto  Luiz Antonio A. Pinto 《洁净——土壤、空气、水》2014,42(6):767-774

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Representivity of incompletely sampled fall deposits in estimating eruption source parameters: a test using the 12–13 January 2011 lava fountain deposit from Mt. Etna volcano,Italy     

Daniele Andronico  Simona Scollo  Antonio Cristaldi  Maria Deborah Lo Castro 《Bulletin of Volcanology》2014,76(10):1-14

The Southeast Crater (SEC) of Mt. Etna, Italy, is renowned for its high activity, mainly long-lived eruptions consisting of sequences of individual paroxysmal episodes which have produced more than 150 eruptive events since 1998. Each episode typically forms eruption columns followed by tephra fallout over distances of up to about 100 km from the vent. One of the last sequences consisted of 25 lava fountaining events, which took place between January 2011 and April 2012 from a pit-vent on the eastern flank of the SEC and built a new scoria cone renamed New Southeast Crater. The first episode on 12–13 January 2011 produced tephra fallout which was unusually dispersed toward to the South extending out over the Mediterranean Sea. The southerly deposition of tephra permitted an extensive survey at distances between ~1 and ~100 km, providing an excellent characterization of the tephra deposit. Here, we document the stratigraphy of the 12–13 January fallout deposit, draw its dispersal, and reconstruct its isopleth map. These data are then used to estimate the main eruption source parameters. The total erupted mass (TEM) was calculated by using four different methodologies which give a mean value of 1.5?±?0.4?×?10⁸ kg. The mass eruption rate (MER) is 2.5?±?0.7?×?10⁴ kg/s using eruption duration of 100 min. The total grain-size (TGS) distribution, peaked at ?3 phi, ranges between ?5 and 5 phi and has a median value of ?1.4 phi. Further, for the eruption column height, we obtained respective values of 6.8–13.8 km by using the method of Carey and Sparks (1986) and 3.4?±?0.3 km by using the methods of Wilson and Walker (1987), Mastin et al. (2009), and Pistolesi et al. (2011) and considering the mean value of MER from the deposit. We also evaluated the uncertainty and reliability of TEM and TGS for scenarios where the proximal and distal samples are not obtainable. This is achieved by only using a sector spanning the downwind distances between 6 and 23 km. This scenario is typical for Etna when the tephra plume is dispersed eastward, i.e., in the prevailing wind direction. Our results show that, if the analyzed deposit has poorer sample coverage than presented in this study, the TEM (3.4?×?10⁷ kg) is 22 % than the TEM obtained from the whole deposit. The lack of the proximal (<6 km) deposit may cause more significant differences in the TGS estimations.  相似文献