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41.
Angelo Paone 《International Journal of Earth Sciences》2008,97(3):635-650
A compilation of B–Be–Li data on rocks that cover the entire eruptive history of Somma-Vesuvius is presented and interpreted
in the light of evolution models for the Somma-Vesuvius rocks. Using major and trace element data, fractional crystalllization
models are presented for different geochemical units. These data were used to constrain the source mineralogy of the Somma-Vesuvius
rocks (ol-opx-cpx-gar-amp of 0.4-0.3-0.1-0.1-0.1), the amount of sediment added (5–10%) and the melt fraction from batch partial
melting computations (0.05–0.1). From the B–Li data it is inferred that the main process responsible for the B isotopic signature
is sediment recycling. However, the B–Li data show a major variation in Li abundances respect to B which is explained with
Li dehydration before the fluid enriched the mantle wedge that produced the arc magmas. The Somma-Vesuvius B isotope composition
is intermediate between that of the Campi Flegrei and the broad field of the Eolian Island arc. A low Be isotopes in the recent
volcanic rocks can be explained as: (a) the top 1–22 m of the incoming sediment is accreted, (b) large amounts of sediment
erosion, (c) a slow rate of subduction which have provoked a long magmatic history for the Vesuvius magma, (d) the sediment
component takes several Myr longer than the subducting plate to reach the magma source region beneath Italy. 相似文献
42.
Roberto F. Viotti Lucio Angelo Antonelli Sonja Rebecchi Corinne Rossi 《Journal of Astrophysics and Astronomy》2002,23(1-2):19-22
We have investigated with BeppoSAX the long term behaviour of the harder X-ray component of the supposed supermassive binary
system η Car along its 5.52 year cycle. We have found that in March 1998 during egress from the last December 1997 eclipse,
this component was the same as outside eclipse, but for a large (×3.5) increase of NH
h
, that can be attributed to the presence or formation of opaque matter in front of the source near periastron. Unexpectedly,
at that time the iron 6.7 keV emission line was 40% stronger. BeppoSAX has for the first time found ahard X-ray tail extending to at least 50 keV, that cannot be adequately fitted with an additional hotter thermal component. The 2–100 keV
spectrum of η Car is instead well fitted with an absorbed powerlaw spectrum with photon index 2.53, suggesting non-thermal
emission as an alternative model for the core source. 相似文献
43.
Abstract. Deltaic populations of Conopeum seurati from diverse environmental settings have variable phenotypes related to strong competitive regimes and to dissolved oxygen minima. Under extremely stressful conditions, the poorly canalized phenotype of C. seurati displays new additional features such as kleistozooids ( kleistós = closed) and chaotic celleporoid layers. Kleistozooids are clearly distinguishable polymorphs characterized by the presence of a compact, imperforate frontal membrane and by a strongly reduced lumen of the "opesium". They commonly aggregate in clusters of regularly-arranged individuals that store a large quantity of proteic material. The inferred function of these cell-like structures is to supply nutrients for basic colony activities. Celleporoid layers are, possibly, a developmental relaxation of the colony of C. seurati for a more efficient use of space in competitive interactions.
Both celleporoid layers and kleistozooids reveal the magnitude of intracolony variability of a widespread opportunistic bryozoan species. 相似文献
Both celleporoid layers and kleistozooids reveal the magnitude of intracolony variability of a widespread opportunistic bryozoan species. 相似文献
44.
Carlotta Nonnis Marzano Maria Flavia Gravina Alessandra Fianchini Giuseppe Portacci Myriam Gherardi Angelo Tursi Giuseppe Corriero 《Marine Ecology》2010,31(4):622-632
The macrozoobenthic assemblage from the Karavasta lagoon system, the main wetland of Albania, was studied on soft bottoms and artificial hard substrates. Three different communities were identified: the typical ‘brackish‐water community’, an ‘outlet community’ dominated by filter‐feeders, and a typical ‘marine community’, inhabiting fine sandy bottoms, where polychaetes are dominant, together with a few species of tunicates and bivalves, which colonize hard substrates. The occurrence of build‐ups of the bryozoan Conopeum seurati, settled on the upper portion of long submerged wooden poles, was the main feature of faunistic interest. The faunistic affinity between the zoobenthic assemblage recorded in the hyperhaline lagoon of Karavasta and the assemblages from two Italian lagoons, the brackish Lake of Lesina and the euhaline Lake of Fogliano, was considered according to the different hydrological conditions and the geographical location. Hydrological confinement and salinity were likely to be the leading factors influencing the benthic community composition in the Karavasta wetland area. Therefore, on a vaster spatial scale, the isolation and geographical proximity of the ecosystems and colonizing ability and dispersal changes of the species appear to be the main factors liable to produce faunal variations. 相似文献
45.
New records of cold‐water coral sites and fish fauna characterization of a potential network existing in the Mediterranean Sea 下载免费PDF全文
Gianfranco D'Onghia Crescenza Calculli Francesca Capezzuto Roberto Carlucci Angela Carluccio Porzia Maiorano Alessio Pollice Pasquale Ricci Letizia Sion Angelo Tursi 《Marine Ecology》2016,37(6):1398-1422
New cold‐water coral (CWC) sites were recorded along the Apulian margin (Central Mediterranean). The species composition and depth distribution of CWCs were updated. A distribution of the CWC sites coincident with the course of the dense‐water masses that flow between the Southern Adriatic and Northern Ionian was confirmed. The faunal assemblages of five of these CWC sites were investigated and compared using experimental longlines during the spring–summer and autumn–winter seasons, between 2010 and 2014. Differences in ecological variables amongst the sites in each season were evaluated by means of a set of univariate and multivariate methods (analysis of variance, permutational multivariate analysis of variance, non‐metric multidimensional scaling). Although some differences were detected in relation to the different depths examined during spring–summer, the CWC sites showed similar features in terms of species richness and diversity as well as in the abundance of the same fish species (Galeus melastomus, Conger conger, Helicolenus dactylopterus, Merluccius merluccius, Phycis blennoides and Pagellus bogaraveo) most probably because of the distribution of adult specimens in structurally complex and heterogeneous habitats, which act as a potential ‘refuge network’ with respect to commercial fishing. The presence of maturing and mature individuals as well as post‐reproductive females indicates that these CWC sites also act as spawning areas, representing a potential ‘renewal network’ for the fish populations. The term ‘network’ used here refers to several similar subsystems (CWC sites) that play the same ecological role in a wider system (Apulian margin). These CWC communities need coherent conservation measures and management strategies according to the Ecosystem Approach to Fisheries. 相似文献
46.
In recent years, a number of constitutive models have been proposed to describe mathematically the mechanical response of natural clays. Some of these models are characterized by complex formulations, often leading to non‐trivial problems in their numerical integration in finite elements codes. The paper describes a fully implicit stress‐point algorithm for the numerical integration of a single‐surface mixed isotropic–kinematic hardening plasticity model for structured clays. The formulation of the model stems from a compromise between its capability of reproducing the larger number of features characterizing the behaviour of structured clays and the possibility of developing a robust integration algorithm for its implementation in a finite elements code. The model is characterized by an ellipsoid‐shaped yield function, inside which a stress‐dependent reversible stiffness is accounted for by a non‐linear hyperelastic formulation. The isotropic part of the hardening law extends the standard Cam‐Clay one to include plastic strain‐driven softening due to bond degradation, while the kinematic hardening part controls the evolution of the position of the yield surface in the stress space. The proposed algorithm allows the consistent linearization of the constitutive equations guaranteeing the quadratic rate of asymptotic convergence in the global‐level Newton–Raphson iterative procedure. The accuracy and the convergence properties of the proposed algorithm are evaluated with reference to the numerical simulations of single element tests and the analysis of a typical geotechnical boundary value problem. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
47.
Probabilistically controlled design values of the nonlinear seismic response of reinforced concrete frames are obtained using a method previously proposed by the authors. The method allows to calculate conservative design values characterized by a predefined non‐exceedance probability, using a limited number of spectrum‐fitting generated accelerograms. Herein the method is applied to elastic‐strain hardening single degree of freedom systems representative of RC framed structures and is then assessed with reference to four reinforced concrete model frames designed according to EC8. The frames are characterized by different natural periods and aspect ratios. The results, compared with those obtained applying current EC8 recommendations, show the effectiveness of the proposed method. EC8 provides for design values of the seismic response of a structure with a nonlinear behavior computed as the mean value of the responses to seven accelerograms or as the maximum value of the responses to three accelerograms. These two criteria lead to design values characterized by very different and uncontrolled non‐exceedance probability levels, while the proposed method allows the analyst to directly control the non‐exceedance probability level of the calculated design values. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
48.
49.
May-Linn Paulsen Andreas J. Andersson Lihini Aluwihare Tyler Cyronak Sydney D’Angelo Charlie Davidson Hany Elwany Sarah N. Giddings Heather N. Page Magali Porrachia Stephen Schroeter 《Estuaries and Coasts》2018,41(4):1050-1068
Estuaries are important subcomponents of the coastal ocean, but knowledge about the temporal and spatial variability of their carbonate chemistry, as well as their contribution to coastal and global carbon fluxes, are limited. In the present study, we measured the temporal and spatial variability of biogeochemical parameters in a saltmarsh estuary in Southern California, the San Dieguito Lagoon (SDL). We also estimated the flux of dissolved inorganic carbon (DIC) and total organic carbon (TOC) to the adjacent coastal ocean over diel and seasonal timescales. The combined net flux of DIC and TOC (FDIC?+?TOC) to the ocean during outgoing tides ranged from ??1.8±0.5?×?103 to 9.5±0.7?×?103?mol C h?1 during baseline conditions. Based on these fluxes, a rough estimate of the net annual export of DIC and TOC totaled 10±4?×?106?mol C year?1. Following a major rain event (36 mm rain in 3 days), FDIC?+?TOC increased and reached values as high as 29.0 ±?0.7?×?103?mol C h?1. Assuming a hypothetical scenario of three similar storm events in a year, our annual net flux estimate more than doubled to 25 ±?4?×?106?mol C year?1. These findings highlight the importance of assessing coastal carbon fluxes on different timescales and incorporating event scale variations in these assessments. Furthermore, for most of the observations elevated levels of total alkalinity (TA) and pH were observed at the estuary mouth relative to the coastal ocean. This suggests that SDL partly buffers against acidification of adjacent coastal surface waters, although the spatial extent of this buffering is likely small. 相似文献
50.
Potassic and ultrapotassic magmas and their origin 总被引:38,自引:0,他引:38