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21.
G.L. Granato L. Silva P. Monaco P. Panuzzo P. Salucci G. De Zotti L. Danese 《Monthly notices of the Royal Astronomical Society》2001,324(3):757-768
Direct and indirect observational evidence leads to the conclusion that high-redshift QSOs did shine in the core of early-type protogalaxies during their main episode of star formation. Exploiting this fact, we derive the rate of formation of this kind of stellar system at high redshift by using the QSO luminosity function. The elemental proportions in elliptical galaxies, the descendants of the QSO hosts, suggest that the star formation was more rapid in more massive objects. We show that this is expected to occur in dark matter haloes, when the processes of cooling and heating are considered. This is also confirmed by comparing the observed submm counts with those derived by coupling the formation rate and the star formation rate of the spheroidal galaxies with a detailed model for their SED evolution. In this scenario SCUBA galaxies and Lyman-break galaxies are early-type protogalaxies forming the bulk of their stars before the onset of QSO activity. 相似文献
22.
23.
E. Jacques C. Monaco P. Tapponnier L. Tortorici T. Winter 《Geophysical Journal International》2001,147(3):499-516
24.
Rutger de Wit Lucas J. Stal Bente Aa. Lomstein Rodney A. Herbert Hans van Gemerden Pierluigi Viaroli Victor-Ugo Cecherelli Francisco Rodríguez-Valera Marco Bartoli Gianmarco Giordani Roberta Azzoni Bart Schaub David T. Welsh Andrew Donnelly Ana Cifuentes Josefa Antn Kai Finster Lise B. Nielsen Anne-Grethe Underlien Pedersen Anne Turi Neubauer Marina A. Colangelo Sander K. Heijs 《Continental Shelf Research》2001,21(18-19)
“Buffer capacities” has been defined in ecology as a holistic concept (e.g., Integration of Ecosystem Theories: A Pattern, second ed. Kluwer, Dordrecht, 1997, 388pp), but we show that it can also be worked out in mechanistic studies. Our mechanistic approach highlights that “buffering capacities” can be depleted progressively, and, therefore, we make a distinction between current and potential “buffering capacities”. We have applied this concept to understand the limited “local stability” in seagrass ecosystems and their vulnerability towards structural changes into macro-algal dominated communities. We explored the following processes and studied how they confer buffering capacities to the seagrass ecosystem: (i) net autotrophy is persistent in Zostera noltii meadows where plant assimilation acts as a sink for nutrients, this contrasted with the Ulva system that shifted back and forth between net autotrophy and net heterotrophy; (ii) the Z. noltii ecosystem possesses a certain albeit rather limited capacity to modify the balance between nitrogen fixation and denitrification, i.e., it was found that in situ nitrogen fixation always exceeded denitrification; (iii) the nitrogen demand of organoheterotrophic bacteria in the sediment results in nitrogen retention of N in the sediment and hence a buffer against release of nitrogen compounds from sediments, (iv) habitat diversification in seagrass meadows provides shelter for meiofauna and hence buffering against adverse conditions, (v) sedimentary iron provides a buffer against noxious sulfide (note: bacterial sulfide production is enhanced in anoxic sediment niches by increased organic matter loading). On the other hand, in the coastal system we studied, sedimentary iron appears less important as a redox-coupled buffer system against phosphate loading. This is because most inorganic phosphate is bound to calcium rather than to iron. In addition, our studies have highlighted the importance of plant–microbe interactions in the seagrass meadows. 相似文献
25.
Federico Murrone Fabio Rossi Pierluigi Claps 《Stochastic Hydrology and Hydraulics》1997,11(6):483-510
A conceptual-stochastic approach to short time runoff data modelling is proposed, according to the aim of reproducing the
hydrological aspects of the streamflow process and of preserving as much as possible the dynamics of the process itself. This
latter task implies preservation of streamflow characteristics at higher scales of aggregation and, within a conceptual framework,
involves compatibility with models proposed for the runoff process at those scales. At a daily time scale the watershed response
to the effective rainfall is considered as deriving from the response of three linear reservoirs, respectively representing
contributions to streamflows of large deep aquifers, with over-year response lag, of aquifers which run dry by the end of
the dry season and of subsurface runoff. The surface runoff component is regarded as an uncorrelated point process. Considering
the occurrences of effective rainfall events as generated by an independent Poisson process, the output of the linear system
represents a conceptually-based multiple shot noise process. Model identification and parameter estimation are supported by
information related to the aggregated runoff process, in agreement to the conceptual framework proposed, and this allows parameter
parsimony, efficient estimation and effectiveness of the streamflow reproduction. Good performances emerged from the model
application and testing made with reference to some daily runoff series from Italian basins. 相似文献
26.
27.
Seasonal nitrogen and phosphorus dynamics during benthic clam and suspended mussel cultivation 总被引:1,自引:0,他引:1
Effects of suspended mussel and infaunal clam cultivation on sediment characteristics, and benthic organic and inorganic nitrogen and phosphorus fluxes were compared in a shallow coastal lagoon. The two species had different impacts on sediment features, but both created “hotspots” of nutrient fluxes with annual N and P regeneration rates being 4.9 and 13.5 (mussel) and 4.5 and 14.9 (clams) fold greater than those of unfarmed control sediments. Mussel farming also caused considerable nutrient regeneration within the water column with the mussel ropes contributing ∼25% of total inorganic N and P production and at times dominating the sediments (e.g. 95% of SRP production in summer and 45% of DIN production in winter). Such nutrient regeneration rates seriously question the proposal that suspension-feeding bivalves act as a eutrophication buffer, especially during summer when nutrient regeneration rates are maximal, but other nutrient sources (freshwater run-off and unfarmed sediments) are at their lowest. 相似文献
28.
Net autotrophy in a fluvial lake: the relative role of phytoplankton and floating-leaved macrophytes
Monica Pinardi Marco Bartoli Daniele Longhi Pierluigi Viaroli 《Aquatic Sciences - Research Across Boundaries》2011,73(3):389-403
This study combined water- and sediment flux measurements with mass balances of dissolved gas and inorganic matter to determine
the importance of pelagic and benthic processes for whole-system metabolism in a eutrophic fluvial lake. Mass balances of
dissolved O2, inorganic carbon (DIC), nitrogen (DIN), phosphorous (SRP), particulate N (PN) and P (PP) and Chl a were calculated at a nearly monthly frequency by means of repeated sampling at the lake inlet and outlet. Simultaneously,
benthic fluxes of gas and nutrients, including denitrification rates, and the biomass of the dominant pleustophyte (Trapa natans) were measured, and fluxes of O2 and CO2 across the water–atmosphere interface were estimated from diel changes in outlet concentrations. On an annual scale, Middle
Lake exhibited CO2 supersaturation, averaging 313% (range 86–562%), but was autotrophic with a net O2 production (6.35 ± 2.05 mol m−2 y−1), DIC consumption (−31.18 ± 18.77 mol m−2 y−1) and net export of Chl a downstream (8.38 ± 0.95 mol C m−2 y−1). Phytoplankton was the main driver of Middle Lake metabolism, with a net primary production estimated at 33.24 mol O2 m−2 y−1, corresponding to a sequestration of 4.18 and 0.26 mol m−2 y−1 of N and P, respectively. At peak biomass, T. natans covered about 18% of Middle Lake’s surface and fixed 2.46, 0.17 and 0.02 mol m−2 of C, N and P, respectively. Surficial sediments were a sink for O2 (−14.47 ± 0.65 mol O2 m−2 y−1) and a source of DIC and NH4
+ (18.84 ± 2.80 mol DIC m−2 y−1 and 0.83 ± 0.16 mol NH4
+ m−2 y−1), and dissipated nitrate via denitrification (1.44 ± 0.11 mol NO3
− m−2 y−1). Overall, nutrient uptake by primary producers and regeneration from sediments were a minor fraction of external loads.
This work suggests that the creation of fluvial lakes can produce net autotrophic systems, with elevated rates of phytoplanktonic
primary production, largely sustained by allochtonous nutrient inputs. These hypereutrophic aquatic bodies are net C sinks,
although they simultaneously release CO2 to the atmosphere. 相似文献
29.
Paola Monaco Filippo Santucci de Magistris Salvatore Grasso Silvano Marchetti Michele Maugeri Gianfranco Totani 《Bulletin of Earthquake Engineering》2011,9(1):231-261
This paper describes a case-history of liquefaction occurred near the village of Vittorito after the April 6, 2009 L’Aquila
earthquake (moment magnitude Mw = 6.3), approximately 45 km far from the epicentre. In the document, first, an estimation of the seismic motion in the area
has been made. Thereafter, the performed geotechnical investigation is described, followed by the application of some fast
assessment criteria for the occurrence of liquefaction, recently proposed by the new Italian Building Code. A careful assessment
of all the parameters involved in conventional Seed and Idriss (1971) liquefaction analyses is considered. The cyclic resistance ratio CRR is evaluated by cone penetration tests CPT and by in
situ seismic dilatometer tests SMDT; in the latter case CRR is evaluated by different empirical correlations with shear wave
velocity Vs and horizontal stress index KD. Analytical data confirmed the observed occurrence of the liquefaction in Vittorito, even if the acceleration field in the
area, produced by the L’Aquila earthquake, was very low. 相似文献
30.
Chelli Stefano Maponi Pierluigi Campetella Giandiego Monteverde Paolo Foglia Monica Paris Eleonora Lolis Andreas Panagopoulos Thomas 《Natural Hazards》2015,75(2):1795-1810
Natural Hazards - The Canadian Fire Weather Index (FWI) is one of the most used tools to forecast forest fire hazard. In this paper, we propose an adaptation of the FWI to take into account the... 相似文献