Limits on dust and metallicity evolution of Lyα forest clouds from COBE     

Andrea Ferrara  Biman Nath  Shiv K. Sethi  Yuri Shchekinov 《Monthly notices of the Royal Astronomical Society》1999,303(2):301-308

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The Hubble Deep Field North reveals a supernova at z∼0.95     

F. Mannucci  A. Ferrara 《Monthly notices of the Royal Astronomical Society》1999,305(3):L55-L58

We report the discovery of a variable object in the Hubble Deep Field North (HDF-N) which brightened, during the 8.5 d sampled by the data, by more than 0.9 mag in I ₈₁₄ and about 0.7 mag in V ₆₀₆, remaining stable in B ₄₅₀. Subsequent observations of the HDF-N show that two years later this object has dimmed to about its original brightness in I ₈₁₄. The colours of this object, its brightness, its time behaviour in the various filters and the evolution of its morphology are consistent with it being a Type Ib supernova in a faint galaxy at z .  相似文献   

Cosmological reionization around the first stars: Monte Carlo radiative transfer     

B. Ciardi  A. Ferrara  S. Marri  G. Raimondo 《Monthly notices of the Royal Astronomical Society》2001,324(2):381-388

We study the evolution of ionization fronts around the first protogalaxies by using high-resolution numerical cosmological (Λ+ cold dark matter, CDM, model) simulations and Monte Carlo radiative transfer methods. We present the numerical scheme in detail and show the results of test runs from which we conclude that the scheme is both fast and accurate. As an example of interesting cosmological application, we study the reionization produced by a stellar source of total mass M =2×10⁸ M_⊙ turning on at z ≈12, located at a node of the cosmic web. The study includes a spectral energy distribution of a zero-metallicity stellar population, and two initial mass functions (IMFs; Salpeter/Larson). The expansion of the ionization front (I-front) is followed as it breaks out from the galaxy and is channelled by the filaments into the voids, assuming (in a 2D representation) a characteristic butterfly shape. The ionization evolution is very well tracked by our scheme, as realized by the correct treatment of the channelling and shadowing effects resulting from overdensities. We confirm previous claims that both the shape of the IMF and the ionizing power metallicity dependence are important to correctly determine the reionization of the Universe.  相似文献   

Limitations of an Eddy-Covariance System in Measuring Low Ammonia Fluxes     

Ferrara  Rossana Monica  Di Tommasi  Paul  Famulari  Daniela  Rana  Gianfranco 《Boundary-Layer Meteorology》2021,180(1):173-186

Green manuring of legume crops can improve soil fertility and sustainability. To evaluate its agronomic and environmental effectiveness, gaseous losses of ammonia (NH₃) in the surface layer need to be quantified by direct measurements in the field. However, the application of the eddy-covariance technique to atmospheric NH₃ is challenging: its high reactivity, water solubility, and low background concentrations all hinder the response time of closed-path sensors for fast measurements of NH₃ concentration. Ammonia emissions following green manuring were measured for 21 days using a flux system equipped with a fast-pulsed quantum-cascade tunable-infrared-laser spectrometer. The noisy cross-covariance function for this configuration indicates flux measurements are close to the limit of detection; the low signal-to-noise ratio further increases the uncertainties, introducing a mirroring effect on the fluxes, which results in the rapid alternation between emission and deposition, within the limit of detection (around 13 and 20 ng m^?2 s^?1, at the 95 and 99% confidence limits, respectively). An evaluation of the measurement errors is presented, focussing on three technical aspects of the eddy-covariance system: (1) time lag, (2) random error, and (3) limit of detection. The NH₃ fluxes measured by the spectrometer are close to its limit of detection, with a random error of the same order as the flux.

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Copper complexing capacity of phytoplanktonic cell exudates     

Alfredo Seritti  David Pellegrini  Elisabetta Morelli  Corrado Barghigiani  Romano Ferrara 《Marine Chemistry》1986,18(2-4)

Copper complexing capacity of cell exudates of Dunaliella salina in natural seawater culture medium was investigated in order to evaluate the influence of this organism on speciation of trace metals in seawater.Seawater samples were collected at 200 m and 2 miles off the coast and immediately filtered. Copper complexing capacity (CC_Cu) and stability constants (K′) of related cupric complexes were then measured. They were, respectively, 27.1 × 10⁻⁸ mol l⁻¹ and 0.56 × 10⁷ l mol⁻¹ for the samples collected at 200 m and 12.8 × 10⁻⁸ mol l⁻¹ and 6.10 × 10⁷ l mol⁻¹ for those collected 2 miles off the coast. A stock culture (20 ml, 10⁶ cells ml⁻¹) in log-phase was inoculated in 2 l of each sample of filtered natural seawater. The trend of cell influence was estimated on filtered culture medium by measuring CC_Cu and K′ after 1 h, 3 and 7 days. From the results it appears that CC_Cu increased with respect to time and this was related to the growth rate, indicating a certain relationship with cell metabolic activity.It can be concluded that a comparison between the culture referring to 200 m and 2 miles, respectively, shows that the former presents a CC_Cu two times higher than the latter while the K′ is ten times higher at 2 miles than that at 200 m.  相似文献   

The effect of minihaloes on cosmic reionization   总被引：1，自引：0，他引：1  

B. Ciardi  E. Scannapieco  F. Stoehr  A. Ferrara  I. T. Iliev  P. R. Shapiro 《Monthly notices of the Royal Astronomical Society》2006,366(2):689-696

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Winds and infalling gas in Lyman break galaxies     

Andrea Ferrara  Massimo Ricotti 《Monthly notices of the Royal Astronomical Society》2006,373(2):571-576

A model for gas outflows is proposed which simultaneously explains the correlations between the (i) equivalent widths of low-ionization and Lyα lines, (ii) outflow velocity, and (iii) star formation rate observed in Lyman break galaxies (LBGs). Our interpretation implies that LBGs host short-lived (30 ± 5 Myr) starburst episodes observed at different evolutionary phases. Initially, the starburst powers a hot wind bound by a denser cold shell, which after ≈5 Myr becomes dynamically unstable and fragments; afterwards the fragment evolution is approximately ballistic while the hot bubble continues to expand. As the fragments are gravitationally decelerated, their screening ability of the starlight decreases as the ultraviolet (UV) starburst luminosity progressively dims. LBG observations sample all these evolutionary phases. Finally, the fragments fall back on to the galaxy after ≈60 Myr. This phase cannot be easily probed as it occurs when the starburst UV luminosity has already largely faded; however, galaxies dimmer in the UV than LBGs should show infalling gas.  相似文献   

Suppression of dwarf galaxy formation by cosmic shocks     

Filippo Sigward  rea Ferrara  Evan Scannapieco 《Monthly notices of the Royal Astronomical Society》2005,358(3):755-764

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Effects of dust grains on early galaxy evolution     

Hiroyuki Hirashita †  Andrea Ferrara 《Monthly notices of the Royal Astronomical Society》2002,337(3):921-937

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Fluid flow modeling of a coastal fractured karstic aquifer by means of a lumped parameter approach     

Claudia Cherubini  Concetta Giasi  Nicola Pastore 《Environmental Earth Sciences》2013,70(5):2055-2060

Fluid flow and solute transport phenomena in fractured and karstic aquifers remain an open issue that calls the attention of numerous researchers belonging to different disciplinary fields as far as the aspects linked both to shallow and to deep phenomena are concerned. The hydrogeologic knowledge of these phenomena proves to be of high importance especially if considered in relationship with water resource exploitation, with the problems linked to contamination and the ones linked to urban and industrial development of the territory. In the examined area, characterized by a dismissed contaminated site, the realization of the landfill has required the development of a 3D flow model supported by a detailed local scale geologic model in order to evaluate the effects on groundwater flow and subsequently on contaminant propagation. The results of the flow model prove to be coherent with the fractured and karstic nature of the site in that they show at higher depths the presence of a subterranean stream channel that would speed up pollutant propagation. The obtained results represent the fundamental basis to implement a transport model that will permit to achieve a more in depth knowledge of the subsoil transport phenomena, and therefore to optimize any anthropic intervention that can involve the site.  相似文献