Characterization of wrench tectonics from dating of syn- to post-magmatism in the north-western French Massif Central     

C. Cartannaz  P. Rolin  A. Cocherie  D. Marquer  O. Legendre  C. M. Fanning  P. Rossi 《International Journal of Earth Sciences》2007,96(2):271-287

This work establishes the relative timing of pluton emplacement and regional deformation from new dating and structural data. (1) Monazite and (2) zircon dating show Tournaisian ages for the Guéret granites [Aulon granite 352 ± 5 Ma (1), 351 ± 5 Ma (2) and Villatange tonalite 353 ± 6 Ma (1)] and Viseo-Namurian ages for the north Millevaches granites [Chavanat granite 336 ± 4 Ma (1), Goutelle granite 336 ± 3 Ma (1), Royère granite 323 ± 2 Ma (1) and 328 ± 6 Ma (2), Courcelles granite 318 ± 3 Ma (1)]. The Guéret and Millevaches granites are separated by the N110 Arrènes–la Courtine Shear Zone (ACSZ), composed from West to East by the Arrènes Fault (AF), the North Millevaches Shear Zone (NMSZ) and the la Courtine Shear Zone (CSZ), respectively. Tournaisian Guéret granites experienced a non-coaxial dextral shearing (NMSZ) recorded by the Villatange granite while the Aulon granite (Guéret granite) cuts across this dextral shear zone which thus stopped shearing during Tournaisian time. Visean to Namurian Millevaches granites experienced a coaxial deformation. Therefore, low displacements along the NMSZ and the CSZ occurred at the emplacement time of Chavanat and Pontarion-Royère granites (336–323 Ma). The structural analyses of Goutelle granite emphasizes a deformation related to the dextral Creuse Fault System (CFS) oriented N150–N160. From 360 to 300 Ma, the Z strain axis is always horizontal inferring a wrench setting for these granite emplacements. During this tectonic evolution, the Argentat zone acted as a minor normal fault and is related with a local Middle Visean (340–335 Ma) syn-orogenic extension on the western border of the Millevaches massif.  相似文献   

Cadmium transport in sediments by tubificid bioturbation: An assessment of model complexity     

Sebastien Delmotte  Filip J.R. Meysman  Alain Boudou  Magali Gerino 《Geochimica et cosmochimica acta》2007,71(4):844-862

Biogeochemistry of metals in aquatic sediments is strongly influenced by bioturbation. To determine the effects of biological transport on cadmium distribution in freshwater sediments, a bioturbation model is explored that describes the conveyor-belt feeding of tubificid oligochaetes. A stepwise modelling strategy was adopted to constrain the many parameters of the model: (i) the tubificid transport model was first calibrated on four sets of microspheres (inert solid tracer) profiles to constrain tubificid transport; (ii) the resulting transport coefficients were subsequently applied to simulate the distribution of both particulate and dissolved cadmium. Firstly, these simulations provide quantitative insight into the mechanism of tubificid bioturbation. Values of transport coefficients compare very well with the literature, and based on this, a generic model of tubificid bioturbation is proposed. Secondly, the application of the model to cadmium dataset sheds a light on the behaviour of cadmium under tubificid bioturbation. Cadmium enters the sediment in two ways. In one pathway, cadmium enters the sediment in the dissolved phase, is rapidly absorbed onto solid particles, which are then rapidly transported to depth by the tubificids. In the other pathway, cadmium is adsorbed to particles in suspension in the overlying water, which then settle on the sediment surface, and are transported downwards by bioturbation. In a final step, we assessed the optimal model complexity for the present dataset. To this end, the two-phase conveyor-belt model was compared to two simplified versions. A solid phase-only conveyor-belt model also provides good results: the dissolved phase should not be explicitly incorporated because cadmium adsorption is fast and bioirrigation is weak. Yet, a solid phase-only biodiffusive model does not perform adequately, as it does not mechanistically capture the conveyor-belt transport at short time-scales.  相似文献   

Transaction links through cities: ‘decision cities’ and ‘service cities’ in outsourcing by leading Brazilian firms   总被引：2，自引：0，他引：2  

Eliana C. Rossi  Peter J. Taylor 《Geoforum》2007,38(4):628-642

Most world city studies focus on where the provision of advanced producer services takes place, but in this study the location of the service clients are also taken into account. Production-service transactions are identified as links between ‘service city’ and ‘decision city’ (client HQ) and classified as intra-city (where a firms uses local (same city) services) and inter-city which may be domestic or foreign depending on whether the client uses services in or out of the country. Sampling the leading firms in Brazil, 218 transaction links are described and analysed in terms of cities, firm sectors, ownership and market. The analyses are used to inform a rereading of gateway city functions that takes into account the concentration/dispersal nexus in economic globalization. Thus, whereas the dominance of Sao Paulo in the Brazilian economy is confirmed, this is not interpreted as a simple gateway function with this one city ‘articulating’ the national economy into the world economy. A much more complex situation is revealed with by-passing of the gateway also much in evidence. The conclusion is that this shows concentration and dispersion of economic activity happening simultaneously in Brazil.  相似文献   

A design procedure for tied braced frames     

Pier Paolo Rossi 《地震工程与结构动力学》2007,36(14):2227-2248

The paper deals with the analysis of the seismic behaviour and design of tied braced frames (TBFs). The behavioural properties of TBFs are described and a comparison drawn with standard eccentrically braced frames. A design procedure is then proposed that aims to achieve optimal collapse seismic behaviour, i.e. a global collapse mechanism characterized by uniform plastic rotations of links. The procedure is based on the displacement‐based approach so as to achieve direct and efficient control of the peak ground acceleration of collapse. Applications are carried out on systems with different numbers of storeys and lengths of links to obtain confirmation of the accuracy of the design hypotheses and methodologies. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Attenuation tomography: An application to gas-hydrate and free-gas detection   总被引：1，自引：0，他引：1  

Giuliana Rossi  Davide Gei  Gualtiero Böhm  Gianni Madrussani  José M. Carcione 《Geophysical Prospecting》2007,55(5):655-669

We estimate the quality factor (Q) from seismic reflections by using a tomographic inversion algorithm based on the frequency‐shift method. The algorithm is verified with a synthetic case and is applied to offshore data, acquired at western Svalbard, to detect the presence of bottom‐simulating reflectors (BSR) and gas hydrates. An array of 20 ocean‐bottom seismographs has been used. The combined use of traveltime and attenuation tomography provides a 3D velocity–Q cube, which can be used to map the spatial distribution of the gas‐hydrate concentration and free‐gas saturation. In general, high P‐wave velocity and quality factor indicate the presence of solid hydrates and low P‐wave velocity and quality factor correspond to free‐gas bearing sediments. The Q‐values vary between 200 and 25, with higher values (150–200) above the BSR and lower values below the BSR (25–40). These results seem to confirm that hydrates cement the grains, and attenuation decreases with increasing hydrate concentration.  相似文献   

A comparative analysis of three habitat suitability models for commercial yield estimation of Tapes philippinarum in a North Adriatic coastal lagoon (Sacca di Goro, Italy)   总被引：1，自引：0，他引：1  

Simone Vincenzi  Graziano Caramori  Remigio Rossi  Giulio A. De Leo   《Marine pollution bulletin》2007,55(10-12):579

Habitat Suitability (HS) models have been extensively used by conservation planners to estimate the spatial distribution of threatened species and of species of commercial interest. In this work we compare three HS models for the estimation of commercial yield potential and the identification of suitable sites for Tapes philippinarum rearing in the Sacca di Goro lagoon (Italy) on the basis of six environmental factors. The habitat suitability index (HSI) is based on expert opinion while the habitat suitability conditional (HSC) is calibrated on observational data. The habitat suitability mixed (HSM) model is a two-part model combining expert knowledge and regression analysis: the first component of the model uses logistic regression to identify the areas in which clams are likely to be present; the second part applies the same parameter-specific suitability functions of the HSI model only in the areas previously identified as productive by the logistic component.The HS models were validated on an independent data set and estimates of potential yield of the Goro lagoon were compared. The effectiveness of the three approaches is then discussed in terms of predicted yield and identification of suitable sites for farming.  相似文献   

Association of riparian features and water chemistry with reed litter breakdown in a volcanic lake (Lake Vico,Italy)     

Maria Letizia Costantini  Loreto Rossi  Fabrizio Scialanca  Giuseppe Nascetti  David Rossi  Letizia Sabetta 《Aquatic Sciences - Research Across Boundaries》2007,69(4):503-510

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On the MHD Acceleration of Astrophysical Jets     

Claudio Zanni  Attilio Ferrari  Silvano Massaglia  Gianluigi Bodo  Paola Rossi 《Astrophysics and Space Science》2004,293(1-2):99-106

We present a 2.5D magnetohydrodynamic (MHD) simulation of the acceleration of a collimated jet from a magnetized accretion disk. We employ a MHD Adaptive Mesh Refinement (AMR) code (FLASH—University of Chicago). Thanks to this tool we can follow the evolution of the system for many dynamical timescales with a high-spatial resolution. Assuming an initial condition in which a Keplerian disk, thus with no accretion motions, is threaded by a uniform poloidal magnetic field, we show how both the accretion flow and the acceleration of the outflow occur, and we present in detail which are the forces responsible for the jet launching and collimation. Our simulation also shows how the collimating forces due to the self-generated toroidal magnetic field can produce some peculiar knotty features.  相似文献   

Ecological evaluation of an experimental beneficial use scheme for dredged sediment disposal in shallow tidal waters     

van der Wal D  Forster RM  Rossi F  Hummel H  Ysebaert T  Roose F  Herman PM 《Marine pollution bulletin》2011,62(1):99-108

An experiment was performed to test an alternative dredging strategy for the Westerschelde estuary. Clean sand dredged from the navigation channel was disposed seawards of an eroding intertidal flat in order to modify morphology and hydrodynamics, improving the multi-channel system with ecologically productive shallow water habitat. Five years of intensive monitoring revealed that part of the disposed sediment moved slowly towards the flat, increasing the very shallow subtidal and intertidal area, as planned. The sand in the impact zone became gradually finer after disposal, possibly due to reduced current velocities. Nevertheless, no changes in macrobenthic biomass, density, species richness and composition were detected in the subtidal zone, also demonstrating rapid macrobenthic recovery. In the intertidal zone, no ecological effects could be revealed superimposed on trends associated with long-term sediment fining. Thus, despite morphological success and absence of detected negative ecological impacts of the experiment, new beneficial habitat was not created.  相似文献   

Seismic characterization of rigid sites in the ITACA database by ambient vibration monitoring and geological surveys     

Domenico Pileggi  David Rossi  Enrico Lunedei  Dario Albarello 《Bulletin of Earthquake Engineering》2011,9(6):1839-1854

The problem of seismic characterization of rock-mass or stiff-soil outcrops by the use of passive seismic prospecting techniques is discussed. Difficulties in the application of this kind of procedure in the presence of rugged morphology, high surface wave velocities and low ambient vibration powers, typical of stiff-soil/rock-mass sites are examined. A methodology to face these problems is here proposed, which is based on the strict synergy of detailed geologic surveys and application of robust seismic prospecting techniques, jointly considering single-station and multi-station tools. The application of this approach for the characterization of a number of sites belonging to the Italian Accelerometric Network is described, focusing on two representative case histories.  相似文献