Is primordial ⁴He truly from the Big Bang?     

R. Salvaterra  A. Ferrara 《Monthly notices of the Royal Astronomical Society》2003,340(3):L17-L20

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Detecting the first objects in the mid-infrared with the Next Generation Space Telescope     

Benedetta Ciardi †  rea Ferrara 《Monthly notices of the Royal Astronomical Society》2001,324(3):648-652

We calculate the expected mid-infrared (MIR) molecular hydrogen line emission from the first objects in the Universe. As a result of their low masses, the stellar feedback from massive stars is able to blow away their gas content and collect it into a cooling shell where H₂ rapidly forms and IR roto-vibrational (as for example the rest-frame 2.12 μm) lines carry away a large fraction (up to 10 per cent) of the explosion energy. The fluxes from these sources are in the range 10⁻²¹–10⁻¹⁷ erg s⁻¹ cm⁻² . The highest number counts are expected in the 20-μm band, where about 10⁵ sources deg⁻² are predicted at the limiting flux of 3×10⁻¹⁸ erg s⁻¹ cm⁻². Among the planned observational facilities, we find that the best detection perspectives are offered by the Next Generation Space Telescope ( NGST ), which should be able to reveal about 200 first objects in one hour observation time at its limiting flux in the above band. Therefore, mid-IR instruments appear to represent perfect tools to trace star formation and stellar feedback in the high ( z ≳5) redshift Universe.  相似文献   

Molecular hydrogen in damped Lyα systems: spatial distribution     

H. Hirashita  †  A. Ferrara  K. Wada  P. Richter 《Monthly notices of the Royal Astronomical Society》2003,341(3):L18-L22

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Focal mechanism inversion in the Giudicarie–Lessini seismotectonic region (Southern Alps, Italy): Insights on tectonic stress and strain     

Alfio Vigan  Gianni Bressan  Giorgio Ranalli  Silvana Martin 《Tectonophysics》2008,460(1-4):106-115

A set of 41 focal mechanisms (1989–2006) from P-wave first polarities is computed from relocated seismic events in the Giudicarie–Lessini region (Southern Alps). Estimated hypocentral depths vary from 3.1 to 20.8 km, for duration magnitudes (M_D) in the range 2.7–5.1. Stress and strain inversions are performed for two seismotectonic zones, namely G (Giudicarie) and L (Lessini). This subdivision is supported by geological evidence, seismicity distribution, and focal mechanism types. The available number of data (16 in G, 22 in L) does not make possible any further subdivisions. Seismotectonic zones G and L are undergoing different kinematic regimes: thrust with strike-slip component in G, and strike-slip in L. Principal stress and strain axes in each sub-region show similar orientations. The direction of maximum horizontal compressive stress is roughly perpendicular to the thrust fronts along the Giudicarie Belt in zone G, and compatible with right-lateral strike-slip reactivation of the faults belonging to the Schio-Vicenza system in zone L. On the whole, kinematic regimes and horizontal stress orientations show a good fit with other stress data from focal mechanisms and breakouts and with geodetic strain rate axes.  相似文献   

Models of natural and human dynamics in forest landscapes: Cross-site and cross-cultural synthesis   总被引：1，自引：0，他引：1  

Miguel F. Acevedo  J. Baird Callicott  Donald Lyons  Judith Rosales  Magdiel Ablan  Giorgio Tonella  Emilio Vilanova 《Geoforum》2008,39(2):846-866

We synthesize the study of coupled natural and human systems across sites and cultures through a process of simplification and abstraction based on multiple dimensions of human-nature connectedness: satisfaction of basic needs, psycho-cultural connectedness and regulation of use of natural resources. We thus provide both a place-based and general understanding of value-driven anthropogenic environmental change and response. Two questions guide this research: what are the crucial stakeholder values that drive land use decisions and thus land cover change? And how can knowledge of these values be used to make decisions and policies that sustain both the human and natural systems in a place? To explore these questions we build simulation models of four study sites, two in the State of Texas, United States, and two in Venezuela. All include protected areas, though they differ in the specifics of vegetation and land use. In the Texas sites, relatively affluent individuals are legally converting forests to residential, commercial, and industrial uses, while in Venezuela landless settlers are extra-legally converting forests for purposes of subsistence agriculture. Contemporary modeling techniques now facilitate simulations of stakeholder and ecosystem dynamics revealing emergent patterns. Such coupled human and natural systems are currently recognized as a form of biocomplexity. Our modeling framework is flexible enough to allow adaptation to each of the study sites, capturing the essential features of the respective natural and anthropogenic land use changes and stakeholder reactions. The interactions between human stakeholders are simulated using multi-agent models that act on forest landscape models, and receive feedback of the effects of these actions on ecological habitats and hydrological response. The multi-agent models employ a formal logic-based method for the Venezuelan sites and a decision analysis approach using multi-attribute utility functions for the Texas sites, differing more in style and emphasis than in substance. Our natural-systems models are generic and can be tailored according to site-specific conditions. Similar models of tree growth and patch transitions are used for all the study sites and the differing responses to environmental variables are specified for each local species and terrain conditions.  相似文献   

Sediment-activation depth values for gentle and steep beaches     

Giorgio Anfuso   《Marine Geology》2005,220(1-4):101-112

This paper analyzes methods and terminologies used in literature for the determination and characterization of vertical distribution of sediment-activation depth, which is bottom sediment layer affected by hydrodynamic processes. Studies on this topic include assessments carried out during short time spans, from minutes to few hours or longer periods, from a tidal cycle to several days. In the first case, activation is generally named “mixing depth” and is calculated by evaluating vertical distribution of fluorescent tracers. In the second case, it is referred to as “disturbance depth” and is generally evaluated using plugs of marked sand and rods, or rods with a loose-fitting washer. Vertical cross and longshore distribution of mixing and disturbance depth values, recorded in different works with different techniques, were also analyzed highlighting the conceptual differences between used methods and obtained results. In a further step, a data set from literature on this topic was gathered to obtain new formulations between disturbance depth and beach and wave characteristics as well as morphodynamic beach state, expressed throughout the surf scaling parameter and the surf similarity index. Good linear regressions were observed between these variables, obtaining expressions that can be easily used in a wide range of beach states, from dissipative and intermediate to reflective ones.  相似文献   

Contribution of Sponge Spicules to the Composition of Biogenic Silica in the Ligurian Sea     

Giorgio  Bavestrello  Riccardo  Cattaneo-Vietti  Carlo  Cerrano  Stefania  Cerutti Michele  Sará 《Marine Ecology》1996,17(1-3):41-50

Abstract. The importance of sponge spicules in the turnover of biogenic silica (BSi) in the detritic bottoms of the Eastern Ligurian Riviera was evaluated by studying sediment cores and the detrital matter collected by a trap over a one year period.
This study made evident that: i) Sponge spicules represent the main component of the BSi both in the sediments and in the trapped matter; ii) A correlation exists between the sponge biomass present on the overhanging cliff and the amount of sponge spicules found in the sediment below; iii) Inside the sediments, a superficial layer (10 cm deep) characterized by intensive silica dissolution processes can be observed; and iv) The amount of spicules collected using the trap is not constant throughout the year, but shows a characteristic trend with low values in spring and summer and high values in autumn and winter.  相似文献   

Dynamics and Variability of Terra Nova Bay Polynya   总被引：1，自引：0，他引：1  

Giannetta Fusco  Daniela Flocco  Giorgio Budillon  Giancarlo Spezie  Enrico Zambianchi 《Marine Ecology》2002,23(S1):201-209

Abstract. We present a process study on the dynamics and variability of the Terra Nova Bay polynya in the western sector of the Ross Sea. The air-sea heat exchange is known to be particularly large in polynya during the winter, when differences between air and sea temperatures are large. We apply a 1-D model (Pease, 1987; Van Woert, 1999a, 1999b), which is modified in the latent heat parameterisation in order to account for time-dependent relative humidity and cloud coverage. Furthermore, the Ice Collection Depth is correlated linearly with a variable wind speed. The model is forced with two different meteorological data sets: the operational analysis of the European Center for Medium Range Weather Forecasts atmospheric data set and the meteorological parameters measured by an Automatic Weather Station located on the coast of Terra Nova Bay. The results are compared in terms of polynya extension, ice, and High Salinity Shelf Water production. According to the two different wind velocities, the results obtained from the different data sets clearly differ. Qualitatively, however, the results are in good agreement.  相似文献   

An Assessment of Surface – Dynamics Observed Offshore Ancona with HF Radar     

Giorgio Budillon  Federica Grilli  Annalisa Ortona  Aniello Russo  Marco Tramontin 《Marine Ecology》2002,23(S1):21-37

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A real-time spectrum analyser with on-line definition of the confidence levels     

Paolo Santin  Giorgio Sedmak 《Astrophysics and Space Science》1977,48(1):57-63

This paper describes a real-time spectrum analyser with on-line definition of the confidence levels built at Trieste Observatory for a research program on periodical components of unknown period in optical sources. The system is realized by a photon counting photometer on-line to a computer that elaborates in real-time the data from the photometer and displays the spectrum of the source measured. The spectrum is normalized to unity mean value and the display is calibrated by the confidence levels relative to the distribution of the spectrum displayed. Some experimental data show the performance of the machine that operates in real-time at full efficiency up to 160 Hz. Work supported by Consiglio Nazionale delle Ricerche, Gruppo Nazionale di Astronomia, Settore Tecnologie Astronomiche. Trieste Observatory — Instruments and Data Processing Group (1/76).  相似文献