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111.
During the last few decades, the combined effects of natural and human activities acting on the Mediterranean Sea basin have caused a reduction in the swordfish (Xiphias gladius, L. 1758) population. In this project, we investigated the accumulation of lead (Pb), cadmium (Cd) and mercury (Hg) levels in the Atlantic and Mediterranean populations of swordfish during a five-year survey. In the marine environment, top predators such as swordfish accumulate high concentrations of toxic metals, and thus, potentially incur a high toxicological risk. Furthermore, heavy metals, such as chemical pollutants, have strong long-term effects on fish, and thus, constitute a high risk for the resource and humans that consume it. The aim of this work is to contribute to the assessment of the state of European swordfish population health. We analyzed muscle tissue from 56 specimens captured in Mediterranean and Atlantic areas for trace elements. Mean concentrations of Hg, Cd, and Pb were in the following ranges: 0.66-2.41, 0.04-0.16, and 0.97-1.36 mg/kg ww, respectively. These data suggest a need for continuous monitoring to avoid reductions in the population of this fish species of high commercial and ecological interest. 相似文献
112.
Three small-scale paroxysmal explosions (also called major explosions) interrupted ordinary mild Strombolian activity at Stromboli
on May 3, November 8 and 24, 2009. Products were largely confined to the summit area, except in the November 24 event, during
which coarse pumiceous lapilli reached the coast. Emission of crystal-poor pumice closely mingled with crystal-rich products
characterized the three events. The textural and chemical study of minerals and glassy matrices revealed that the two end-members
are mingled together physically in the May 3 and November 24 pumice, whereas November 8 products contain heterogeneous glass
with intermediate compositions derived from chemical mixing between crystal-rich and crystal-poor magmas. We here discuss
the different degrees of interaction between the two magmas in the three explosions in terms of magma dynamics during small-scale
paroxysms. 相似文献
113.
Petko Nenovski Maria Chamati Umberto Villante Marcello De Lauretis Patrizia Francia 《Acta Geophysica》2013,61(2):311-337
We apply detrended fluctuation analysis (DFA) on fluxgate and search-coil data in ULF range (scales 10–90 s or 0.1–0.011 Hz) for the months January–April 2009 available from the South European GeoMagnetic Array stations: Castello Tesino (CST), Ranchio (RNC), and L’Aquila (AQU) in Italy; Nagycenk (NCK) in Hungary; and Panagyuriste (PAG) in Bulgaria. DFA is a data processing method that allows for the detection of scaling behaviors in observational time series even in the presence of non-stationarities. The H and Z magnetic field components at night hours (00-03 UT, 01–04 LT) and their variations at the stations CST, AQU, NCK, and PAG have been examined and their scaling characteristics are analyzed depending on geomagnetic and local conditions. As expected, the scaling exponents are found to increase when the K p index increases, indicating a good correlation with geomagnetic activity. The scaling exponent reveals also local changes (at L’Aquila), which include an increase for the Z (vertical) component, followed by a considerable decrease for the X (horizontal) component in the midst of February 2009. Attempts are made to explain this unique feature with artificial and/or natural sources including the enhanced earthquake activity in the months January–April 2009 at the L’Aquila district. 相似文献
114.
Monica Tosi 《Astrophysics and Space Science》2003,284(2):651-660
This is a summary of a general discussion held during the third EuroConference on galaxy evolution. Various observational
features of the stellar populations in present-day dwarf galaxies were presented to introduce the discussion on the possibility
that these systems be the main building blocks of spiral and elliptical galaxies. Many people in the audience turned out to
think that the inconsistencies among the observed properties of large and dwarf galaxies are too many to believe that the
former are built up only by means of successive accretions of the latter. However, theorists of hierarchical galaxy formation
suggested that present-day dwarfs are not representative of the galactic building blocks, which may be completely invisible
nowadays. Some of them suggested that, contrary to what is usually assumed in hierarchical modelling, the actual building
blocks were still fully gaseous systems when their major mergers occurred. If this is the case, then most of the inconsistencies
can be overcome, and the scenario of hierarchical galaxy formation becomes not too different from that of a slow gas accretion.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
115.
To understand the role of dwarfs in the context of galaxy formation and evolution, we are studying the star-formation history
of some representative irregular and blue compact dwarf galaxies by comparing the observed colour–magnitude diagrams with
synthetic ones based on homogeneous sets of stellar evolutionary tracks. Here we present the results obtained for the blue
compact I Zw 18, the most metal-poor galaxy known. Our simulations suggest star-formation activity started around 1–0.3 Gyr
ago, with evidence of an intense burst around 15–20 Myr ago. I Zw 18 has turned out not to be a young object as previously
suggested.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
116.
In the context of the application of WFD, a scientific debate is growing about the applicability of biotic indices in coastal and transitional waters. In the present work, the question about the discriminating power of different biotic indices and the relationships with the structure and functioning of the macrobenthic community in a transitional environment is discussed. A time series of samples collected during the last 70 years in the lagoon of Venice, reflecting different environmental conditions (a sort of 'pristine state' in 1935, the distrophic crisis in 1988 and subsequent modifications in 1990, the invasion by an alien species and the developing of high impacting fishery in 1999) has been used. The comparison of results obtained by applying different biotic indices, such as AMBI, Bentix and BOPA, shows differences in the discriminating power of indices and a general overestimation of environmental conditions. Discrepancies between environmental status as indicated by biotic indices and the structure and functioning of the benthic community have been highlighted. 相似文献
117.
Inspection of near-infrared images from Cassini’s Imaging Science Subsystem and Visual and Infrared Mapping Spectrometer have revealed a new feature in Titan’s haze structure: a narrow band of increased scattering by haze south of the equator. The band seems to indicate a region of very limited mixing in the lower stratosphere, which causes haze particles to be trapped there. This could explain the sharp separation between the two hemispheres, known as the north-south asymmetry, seen in images. The separation of the two hemispheres can also be seen in the stratosphere above 150 km using infrared spectra measured by Cassini’s Composite Infrared Spectrometer. Titan’s behaviour in the lower tropical stratosphere is remarkably similar to that of the Earth’s tropical stratosphere, which hints at possible common dynamical processes. 相似文献
118.
G. Filacchione F. Capaccioni J.N. Cuzzi A. Coradini P.D. Nicholson R.H. Brown F. Tosi R. Jaumann 《Icarus》2010,206(2):507-523
We report the detailed analysis of the spectrophotometric properties of Saturn’s icy satellites as derived by full-disk observations obtained by visual and infrared mapping spectrometer (VIMS) experiment aboard Cassini. In this paper, we have extended the coverage until the end of the Cassini’s nominal mission (June 1st 2008), while a previous paper (Filacchione, G., and 28 colleagues [2007]. Icarus 186, 259-290, hereby referred to as Paper I) reported the preliminary results of this study.During the four years of nominal mission, VIMS has observed the entire population of Saturn’s icy satellites allowing us to make a comparative analysis of the VIS-NIR spectral properties of the major satellites (Mimas, Enceladus, Tethys, Dione, Rhea, Hyperion, Iapetus) and irregular moons (Atlas, Prometheus, Pandora, Janus, Epimetheus, Telesto, Calypso, Phoebe). The results we discuss here are derived from the entire dataset available at June 2008 which consists of 1417 full-disk observations acquired from a variety of distances and inclinations from the equatorial plane, with different phase angles and hemispheric coverage. The most important spectrophotometric indicators (as defined in Paper I: I/F continua at 0.55 μm, 1.822 μm and 3.547 μm, visible spectral slopes, water and carbon dioxide bands depths and positions) are calculated for each observation in order to investigate the disk-integrated composition of the satellites, the distribution of water ice respect to “contaminants” abundances and typical regolith grain properties. These quantities vary from the almost pure water ice surfaces of Enceladus and Calypso to the organic and carbon dioxide rich Hyperion, Iapetus and Phoebe. Janus visible colors are intermediate between these two classes having a slightly positive spectral slope. These results could help to decipher the origins and evolutionary history of the minor moons of the Saturn’s system. We introduce a polar representation of the spectrophotometric parameters as function of the solar phase angle (along radial distance) and of the effective longitude interval illuminated by the Sun and covered by VIMS during the observation (in azimuth) to better investigate the spatial distribution of the spectrophotometric quantities across the regular satellites hemispheres. Finally, we report the observed spectral positions of the 4.26 μm band of the carbon dioxide present in the surface material of three outermost moons Hyperion, Iapetus and Phoebe. 相似文献
119.
D. Turrini F. Marzari F. Tosi 《Monthly notices of the Royal Astronomical Society》2009,392(1):455-474
The origin of the irregular satellites of the giant planets has been long debated since their discovery. Their dynamical features argue against an in situ formation suggesting that they are captured bodies, yet there is no global consensus on the physical process at the basis of their capture. In this paper, we explore the collisional capture scenario, where the actual satellites originated from impacts occurred within Saturn's influence sphere. By modelling the inverse capture problem, we estimated the families of orbits of the possible parent bodies and the specific impulse needed for their capture. The orbits of these putative parent bodies are compared to those of the minor bodies of the outer Solar system to outline their possible region of formation. Finally, we tested the collisional capture hypothesis on Phoebe by taking advantage of the data supplied by Cassini on its major crater, Jason. Our results presented a realistic range of solutions matching the observational and dynamical data. 相似文献
120.
E. Sabbi A. Nota J. S. Gallagher M. Tosi L. R. Carlson M. Sirianni M. Meixner L. J. Smith M. S. Oey R. Walterbos A. Pasquali L. Angeretti 《Astrophysics and Space Science》2009,324(2-4):101-107
We combined optical Hubble Space Telescope ACS images with mid-infrared Spitzer data of the two young star clusters NGC346 and NGC602 in the Small Magellanic Cloud, to study how local and global conditions may affect the process of star formation. We found that, while general conditions such as metallicity, or the mass or morphological type of the parent galaxy do not strongly affect the process of star formation, local conditions such as the gas and stellar density can affect both how star formation occurs and propagates, and also the evolution of a star cluster from early times. 相似文献