Assessment of gas hydrate and free gas distribution on the South Shetland margin (Antarctica) based on multichannel seismic reflection data   总被引：4，自引：0，他引：4  

Emanuele Lodolo  Angelo Camerlenghi  Gianni Madrussani  Umberta Tinivella  Giuliana Rossi 《Geophysical Journal International》2002,148(1):103-119

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Orbital forcing in a stochastic resonance model of the Late-Pleistocene climatic variations     

Gianni Matteucci 《Climate Dynamics》1989,3(4):179-190

Applying a number of simplifying assumptions, we have used a zero-dimensional energy balance climate model (EBM) of the Budyko-Sellers type to investigate the degree to which the climatic variability of the Late Pleistocene can be explained by the mechanism of stochastic resonance. As a logical extension of an earlier version of this model we have included a more complete representation for the orbital forcings to show that a reasonably good agreement with the paleoclimatic record can be obtained. This zerodimensional EBM is appealing because of its simplicity and its ability to reproduce some of the most striking qualitative features of the observed climatic variability with a very limited number of parameters, several of which can be derived from either the observations or general circulation model (GCM) simulations of ice-age conditions.  相似文献   

The structure and intensity evolution of a solar burst at 2.8 cm and the relation with the soft X-ray emitting region     

Marcello Felli  Roberto Pallavicini  Gianni Tofani 《Solar physics》1975,44(1):135-147

The decay phase of a microwave burst was observed with a one-dimensional angular resolution of 16″ at 2.8 cm. The structure was found to be composed of several bursting regions with different evolution. The event was also observed in soft X-rays by full-disk detectors. The joint analysis of these data suggests that the complete event has thermal origin and that the soft X-ray emission is associated with the rapidly varying component of the radio structure. From these results the average values of the electron temperatures and densities were computed for each component.  相似文献   

The impact of commercial and recreational harvesting for Paracentrotus lividus on shallow rocky reef sea urchin communities in North-western Sardinia, Italy     

Antonio Pais  Lorenzo A. Chessa  Simone Serra  Alberto Ruiu  Gianni Meloni  Yuri Donno 《Estuarine, Coastal and Shelf Science》2007,73(3-4):589-597

The fishery for the edible sea urchin Paracentrotus lividus is of great importance to many European regions, although in some of them this species has shown a wide scale decline in recent years. This paper reports on direct (on P. lividus) and indirect (on the co-occurring but not fished echinoid, Arbacia lixula) effects of sea urchin harvesting in shallow rocky reefs in North-western Sardinia (Italy, central-western Mediterranean Sea), where this activity is intensively practised. Density, size (test diameter), and biomass of both species were assessed in autumn 2004 at two locations impacted by P. lividus fishery, and at two controls within an adjacent Marine Protected Area. Density of P. lividus and A. lixula was significantly greater at the controls than at the exploited locations. The average test diameter of P. lividus was also significantly larger at the controls, where large-sized specimens (i.e. >5 cm) were notably more abundant. The average size of A. lixula did not significantly differ between the impacted locations and the controls. The average biomass of P. lividus was significantly greater at the controls than at the exploited locations, whereas no differences were detected for A. lixula. These results reveal the existence of a heavy fishing impact on P. lividus in North-western Sardinia and the need for regulation of its harvesting to prevent severe direct effects on its populations. Since no indirect effects on A. lixula have been detected, it could be hypothesized that this species did not benefit from P. lividus fishery due to an only moderate competition for habitat and resources between these two echinoids. Implications for management of edible sea urchin fishery are also discussed.  相似文献   

Chemistry and sulfur isotopic composition of precipitation at Bologna, Italy   总被引：2，自引：0，他引：2  

Pasquale Panettiere  Gianni Cortecci  Enrico Dinelli  Alberto Bencini  Massimo Guidi 《Applied Geochemistry》2000,15(10):2127

Individual and monthly precipitation samples from the polluted atmosphere of Bologna (Emilia-Romagna province) were collected during March 1996 to May 1997 and analyzed for major ions in solution and S isotopes in dissolved SO₄.Weighted mean enrichment factors relative to seawater are found to be 1.0 for Na, 15.2 for K, 105 for Ca, 3.3 for Mg, 17.3 for SO₄ and 663 for HCO⁻₃. Very good positive correlations are observed for the Ca²⁺–Mg²⁺–HCO⁻₃–SO²⁻₄–NO⁻₃ system, indicating that dissolution of Ca (±Mg)-carbonate particles by H₂SO₄ and HNO₃ from combustion of oil and gas is a major process controlling the chemical composition of rain and snow. Na⁺ and Cl⁻ in monthly precipitation derive essentially from sea spray, but the contribution of Na⁺ from continental sources is appreciable in a number of individual rains. NH⁺₄ appears to be on average more abundant in spring and summer precipitation, its main sources being microbial activity in soils and application of fertilizers. K⁺ is probably of continental origin from soil dust.The S isotopic composition of SO₄ is systematically positive, with mean δ³⁴S values of +3.2±1.6‰ (n=40) in individual precipitation and +2.8±1.4‰ (n=12) in monthly precipitation. These isotopic compositions are interpreted in terms of a dominant contribution of S from anthropogenic emissions and subordinate contributions from biogenic and marine sources. Pollutant SO₄ is estimated to have a δ³⁴S value in the range +2.5 to +4.5‰, whereas a distinctive δ³⁴S of −4.5‰ or lower indicates SO₄ from oxidation of biogenic gases.The isotopic and chemical compositions of SO₄ do not depend on wind direction, thus testifying to a mostly local source for pollutant S in the Bologna atmosphere.  相似文献   

Crop yield model validation for Cameroon     

Munang Tingem  Mike Rivington  Gianni Bellocchi  Jeremy Colls 《Theoretical and Applied Climatology》2009,96(3-4):275-280

A crop simulation model must first be capable of representing the actual performance of crops grown in any region before it can be applied to the prediction of climate variability and change impacts. A cropping systems model (CropSyst) simulations of crop productivity in the sub-Saharan Central African (using Cameroon as the case study) region, under the current climate were compared with observed yields of maize, sorghum, groundnut, bambara groundnut and soybean from eight sites. The model produced both over-and-under estimates, but with a mean percentage difference of only –2.8%, ranging from –0.6% to –4.5%. Based on these results, we judged the CropSyst simulations sufficiently reliable to justify use of the model in assessing crop growth vulnerability to climatic changes in Cameroon and else where.  相似文献   

Key problems in cool-star astrophysics     

Isabella Pagano  Thomas R. Ayres  Alessandro C. Lanzafame  Jeffrey L. Linsky  Benjamín Montesinos  Marcello-Rodonò 《Astrophysics and Space Science》2006,303(1-4):17-31

Selected key problems in cool-star astrophysics are reviewed, with emphasis on the importance of new ultraviolet missions to tackle the unresolved issues.UV spectral signatures are an essential probe of critical physical processes related to the production and transport of magnetic energy in astrophysical plasmas ranging, for example, from stellar coronae, to the magnetospheres of magnetars, and the accretion disks of protostars and Active Galactic Nuclei. From an historical point of view, our comprehension of such processes has been closely tied to our understanding of solar/stellar magnetic activity, which has its origins in a poorly understood convection-powered internal magnetic dynamo. The evolution of the Sun's dynamo, and associated magnetic activity, affected the development of planetary atmospheres in the early solar system, and the conditions in which life arose on the primitive Earth. The gradual fading of magnetic activity as the Sun grows old likewise will have profound consequences for the future heliospheric environment. Beyond the Sun, the magnetic activity of stars can influence their close-in companions, and vice versa.Cool star outer atmospheres thus represent an important laboratory in which magnetic activity phenomena can be studied under a wide variety of conditions, allowing us to gain insight into the fundamental processes involved. The UV range is especially useful for such studies because it contains powerful diagnostics extending from warm (∼ 10⁴ K) chromospheres out to hot (1–10 MK) coronae, and very high-resolution spectroscopy in the UV has been demonstrated by the GHRS and STIS instruments on HST but has not yet been demonstrated in the higher energy EUV and X-ray bands. A recent example is the use of the hydrogen Lyα resonance line—at 110 000 resolution with HST STIS—study, for the first time, coronal winds from cool stars through their interaction with the interstellar gas. These winds cannot be detected from the ground, for lack of suitable diagnostics; or in the X-rays, because the outflowing gas is too thin.A 2m class UV space telescope with high resolution spectroscopy and monitoring capabilities would enable important new discoveries in cool-star astronomy among the stars of the solar neighborhood out to about 150 pc. A larger aperture facility (4–6 m) would reach beyond the 150 pc horizon to fainter objects including young brown dwarfs and pre-main sequence stars in star-forming regions like Orion, and magnetic active stars in distant clusters beyond the Pleiades and α Persei. This would be essential, as well, to characterize the outer atmospheres of stars with planets, that will be discovered by future space missions like COROT, Kepler, and Darwin.Deceased October 23, 2005  相似文献   

New photometric models of galactic evolution applied to the HDF     

Gian Luigi Granato  Laura Silva  Luigi Danese  Giulia Rodighiero  Alberto Franceschini  Gianni Fasano  Alessandro Bressan 《Astrophysics and Space Science》2001,276(2-4):973-978

We summarize our modelling of galaxy photometric evolution (the GRASIL code). By including the effects of dust grains and PAH molecules in a two-phase clumpy medium, where clumps are associated with star-forming regions, we reproduce the observed UV to radio SEDs of galaxies with star formation rates from zero to several hundred M _⊙ yr^-1.GRASIL is a powerful tool for investigating star formation, the initial mass function and the supernova rate in nearby starbursts and normal galaxies, as well as for predicting the evolution of luminosity functions of different types of galaxies at wavelengths covering six decades. It may be interfaced with any device to provide the star formation and metallicity histories of a galaxy. As an application, we have investigated the properties of early-type galaxies in the HDF, tracking the contribution of this population to the cosmic star formation history, which has a broad peak between z = 1.5 and 4.To explain the absence of objects at z ≳ 1.3, we suggest a sequence of dust-enshrouded merger-driven starbursts in the first few Gyr of galaxy lifetimes. We are at present working on a complementary sample of late-type objects selected in a similar way. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Climate control on snowfall days in peninsular Italy     

Nazzareno Diodato  Gianni Bellocchi 《Theoretical and Applied Climatology》2020,140(3):951-961

The advent of instrumental and digital weather observatories has not eliminated the substantial gaps within surface meteorological time series. In particular, the lack of long-term homogeneous snowfall records may be a major impediment for hydrologic studies. We tested the hypothesis that reliable estimates of snowy days per year (SDY) can be produced for peninsular Italy, based on weather and site measurements from a limited set of stations centrally located in the Central Mediterranean Area. The core weather data are those from three observatories: Naples (40° 51′ N, 14° 15′ E, 150 m a.s.l.), Rome (41° 53′ N, 12° 28′ E, 100 m a.s.l.) and Montevergine (40° 56′ N, 14° 43′ E, 1280 m a.s.l.). A linear multivariate regression model (LMRM) was developed with candidate predictors (elevation, snowfall days and winter temperatures) for SDY reconstructions in the Benevento Valley (calibration site), whose homogenised SDY time series covers the period 1869–2018 (the longest in Southern Italy, extending back to 1832 thanks to documentary proxies but with missing values from 1911 to 1949). Three validation sites across peninsular Italy were considered: Vesuvius (40° 49′ N, 14° 24′ E, 605 m a.s.l.), Perugia (43° 05′ N, 12° 30′ E, 205 m a.s.l.) and Padua (45° 23′ N, 11° 51′ E, 15 m a.s.l.). The percent relative mean absolute error (%RMAE) for Benevento Valley was 20.2%, and though higher model errors were encountered at validation sites, they were in an acceptable range (32.6, 39.3 and 39.5% at Vesuvius, Perugia and Padua, respectively). Our SDY reconstruction in the Benevento Valley parallels, the pattern of water discharge occurred in the region during the same period, whose fluctuations result in changes of the pattern of snowfall days (i.e. decreasing snowfall days in recent times was accompanied by decreasing groundwater levels). This corroborates that the approach used to reconstruct SDY data takes dominant climate controlling factors of hydrological changes. We conclude that the LMRM, a statistically developed model, is physically meaningful and may be reasonably used for estimating SDY in peninsular Italy roughly down from the sub-Alpine range.  相似文献   

A modeling language to support the interoperability of global navigation satellite systems     

Daniele Gianni  Joachim Fuchs  Pierluigi De Simone  Marco Lisi 《GPS Solutions》2013,17(2):175-198

The availability of multiple Global Navigation Satellite Systems (GNSS) will offer the opportunity to provide seamless navigation services and improved positioning performance. However, before this opportunity can be exploited, a number of issues need to be solved to ensure the compatibility and interoperability of existing GNSS. In particular, the GNSS interoperability can be technically defined as the capability of receivers to compute their global position using two or more GNSS signals. This capability can be more effectively achieved if Signal-In-Space interface specifications are available in a consistent, unambiguous, and possibly standard format, which can support engineers to design interoperable receivers. We aim to support the design of interoperable receivers with the introduction of the Interface Communication Modeling Language (ICML), a graphical language for the formal specification of Signal-In-Space interfaces. The ICML language enables receiver engineers to specify these interfaces at different levels of abstraction, such as analog signal or binary data. In addition, the ICML language also supports the specification of conversion routines between adjacent levels, for the representation of the dynamic aspects—e.g., convolution and encryption processes—of the interface specification. As such, the ICML language proposes an alternative format to textual-based interface specifications and can possibly integrate with the ongoing trend of the Model-based Systems Engineering approaches. We present the structure of the framework implementing the language and an example ICML-based specification for a simplified and reduced version of the Galileo Freely Accessible Navigation (F/NAV) message. The language metamodel is also attached for technical reference. An important caveat: no endorsement is made for the use of the ICML language for the official Galileo Signal-In-Space interface specification.  相似文献