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1.
Distribution and sources of aliphatic hydrocarbons in surface sediments of Sergipe River estuarine system 总被引：1，自引：0，他引：1
The assessment of aliphatic hydrocarbons was performed in the Sergipe River estuarine system, northeastern Brazil. Aliphatic hydrocarbons concentration ranged from 9.9 ug g?1 up to 30.8 ug g?1 of dry sediment. The carbon preference index (CPI, based on nC?? to nC?? range), indicated predominance of petrogenic input in two of the sites analyzed (P4 and P5). The unresolved complex mixture (UCM) was found to be present in seven of the nine sites sampled (except for P4 and P5). Overall, the results of this work suggest that there is a mix of organic matter sources to the sediment. Although the coast of Sergipe has an intense off shore petroleum exploration and the Sergipe River crosses the entire city of Aracaju, the capital city of Sergipe, non-significant anthropogenic fingerprint was assessed. 相似文献
2.
Thermohaline Anomalies in the Spring and Early Summer of 2000 in the Gulf of Trieste 总被引：1，自引：0，他引：1
Abstract. In the framework of the Interreg II Project (July 1998 - June 2001), hydro-logical, chemical and biological data were collected in the Gulf of Trieste.
During spring and summer 2000, some particular thermohaline anomalies were observed in the Gulf of Trieste. Especially in May and June the water body showed: a very strong thermohaline stratification, an increase of advective salt water coming from the south and the presence of sharp pycnoclines. In July the temperature was higher than usual in the whole water column. Moreover, in late May and in June, massive mucilaginous aggregates were observed along the water column and at the surface.
In order to highlight these particular thermohaline features the hydrological data of 16 stations were analysed (Fig. 1). Two stations, in particular, were considered: one offshore (St. AA1, average depth 20 m) and one close to the coast (St. C1, average depth 17 m). For these two stations a best-fit analysis, computed over 11 and 7 years, respectively, was performed on temperature, salinity and density excess data.
Moreover, the hydrological features were compared with the rainfall, air temperature, wind speed data (Istituto Sperimentale Talassografico di Trieste - ISTT) and the Isonzo River's flow rate (Direzione Regionale dell'Ambiente - Regione F. V. G.) collected from January 1998 to December 2000. 相似文献
During spring and summer 2000, some particular thermohaline anomalies were observed in the Gulf of Trieste. Especially in May and June the water body showed: a very strong thermohaline stratification, an increase of advective salt water coming from the south and the presence of sharp pycnoclines. In July the temperature was higher than usual in the whole water column. Moreover, in late May and in June, massive mucilaginous aggregates were observed along the water column and at the surface.
In order to highlight these particular thermohaline features the hydrological data of 16 stations were analysed (Fig. 1). Two stations, in particular, were considered: one offshore (St. AA1, average depth 20 m) and one close to the coast (St. C1, average depth 17 m). For these two stations a best-fit analysis, computed over 11 and 7 years, respectively, was performed on temperature, salinity and density excess data.
Moreover, the hydrological features were compared with the rainfall, air temperature, wind speed data (Istituto Sperimentale Talassografico di Trieste - ISTT) and the Isonzo River's flow rate (Direzione Regionale dell'Ambiente - Regione F. V. G.) collected from January 1998 to December 2000. 相似文献
3.
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
4.
Antonio C. da Silva rea Catalano Ludovic Montier Etienne Pointecouteau Joseph Lanoux Martin Giard 《Monthly notices of the Royal Astronomical Society》2009,396(2):849-859
We investigate the effect of dust on the scaling properties of galaxy clusters based on hydrodynamic N -body simulations of structure formation. We have simulated five dust models plus radiative cooling and adiabatic models using the same initial conditions for all runs. The numerical implementation of dust was based on the analytical computations of Montier & Giard. We set up dust simulations to cover different combinations of dust parameters that make evident the effects of size and abundance of dust grains. Comparing our radiative plus dust cooling runs with a purely radiative cooling simulation, we find that dust has an impact on cluster scaling relations. It mainly affects the normalization of the scalings (and their evolution), whereas it introduces no significant differences in their slopes. The strength of the effect critically depends on the dust abundance and grain size parameters as well as on the cluster scaling. Indeed, cooling due to dust is effective in the cluster regime and has a stronger effect on the 'baryon driven' statistical properties of clusters such as L X – M , Y – M , S – M scaling relations. Major differences, relative to the radiative cooling model, are as high as 25 per cent for the L X – M normalization, and about 10 per cent for the Y – M and S – M normalizations at redshift zero. On the other hand, we find that dust has almost no impact on the 'dark matter driven' T mw – M scaling relation. The effects are found to be dependent in equal parts on both dust abundances and grain size distributions for the scalings investigated in this paper. Higher dust abundances and smaller grain sizes cause larger departures from the radiative cooling (i.e. with no dust) model. 相似文献
5.
Richard L. Gibson Walter R. Turpening rea Born & Roger M. Turpening 《Geophysical Prospecting》1997,45(1):1-20
Theoretical results show that the amplitude of a borehole source is reduced when the well in which it is operated is cased and cemented. This reduction is a strong function of the formation velocity and is more weakly dependent on the direction of propagation of the wave travelling from source to receiver and on the diameter of the borehole itself. We have tested these predictions with data gathered in a cross-hole seismic experiment conducted in two stages in 1990 and 1991. The source and receivers were located in the MIT/Stech 1-21A and MIT/Burch 1-20B wells at the Earth Resources Laboratory (ERL) test site in Michigan (USA). Though the source well (MIT/Stech 1-21A) was uncased in 1990, a steel casing and cement were added prior to the collection of data in 1991. Several receiver positions were reoccupied to compare data collected with the source in open and cased holes. Using a velocity model for this area and borehole diameter measurements from a calliper log, a compensation factor can be computed that will adjust the data collected in 1991 to have amplitudes comparable to that collected in the first stage of the experiment. The accuracy of the results demonstrates the validity of the theory, which can be very useful in better understanding seismic waveforms recorded in cross-hole experiments. 相似文献
6.
Magnetic anisotropy produced by magma flow: theoretical model and experimental data from Ferrar dolerite sills (Antarctica) 总被引：3，自引：0，他引：3
Volcanic rocks forming sills, dykes or lava flows may display a magnetic anisotropy derived from the viscous flow during their emplacement. We model a sill as a steady-state flow of a Bingham fluid, driven by a pressure gradient in a horizontal conduit. The magma velocity as a function of depth is calculated from the motion and constitutive equations. Vorticity and strain rate are determined for a reference system moving with the fluid. The angular velocity and the orientation of an ellipsoidal magnetic grain immersed in the fluid are calculated as functions of time or strain. Magnetic susceptibility is then calculated for a large number of grains with a uniform distribution of initial orientations. It is shown that the magnetic lineation oscillates in the vertical plane through the magma flow direction, and that the magnetic foliation plane changes periodically from horizontal to vertical. The results are compared with the magnetic fabric of Ferrar dolerite sills (Victoria Land, East Antarctica) derived from low-field susceptibility measurements. 相似文献
7.
8.
Abstract. In the Sicilian lagoon Stagnone di Marsala, Tethya aurantium and T. citrina show different ecological distributions, although some overlapping occurs. The first species reaches its highest density where linear currents are maximal, and in this habitat it is particularly frequent on Posidonia oceanica rhizomes. The second species is more abundant in still water locations and is equally common on Posidonia rhizomes and on calcareous concretions. Such distributions can be related to water movement, Posidonia shoot density, and associated factors such as sedimentation and food availability. These observations are consistent with an adaptive interpretation of the morphofunctional features distinguishing the two species. 相似文献
9.
Massimo Azzali rea De Felice Manlio Luna Giulio Cosimi Flavio Parmiggiani 《Marine Ecology》2002,23(S1):78-91
Abstract. The paper provides an overview of the state of the small pelagic fish in the Adriatic Sea. The North Adriatic is reviewed for the 1976–1998 period and the South Adriatic for the 1987–1998 period. First the fluctuations in time and in space of the pelagic biomass, as a whole and per species, are presented. Then the dramatic collapse of anchovy stock and its apparent association with the decrease of surface temperature is discussed. Finally the changes of the anchovy and sardine catches are compared and analysed with respect to their abundances in the sea. The conclusion is that acoustic and satellite methods are able to provide a large amount of information on the variability in the pelagic populations; this is essential for an appropriate management of these resources. There is still a need, however, to refine the methods and to integrate this kind of information with further environmental data (including natural predators). 相似文献
10.
Ilian T. Iliev Benedetta Ciardi Marcelo A. Alvarez Antonella Maselli rea Ferrara Nickolay Y. Gnedin Garrelt Mellema Taishi Nakamoto Michael L. Norman Alexei O. Razoumov Erik-Jan Rijkhorst Jelle Ritzerveld Paul R. Shapiro Hajime Susa Masayuki Umemura Daniel J. Whalen 《Monthly notices of the Royal Astronomical Society》2006,371(3):1057-1086
Radiative transfer (RT) simulations are now at the forefront of numerical astrophysics. They are becoming crucial for an increasing number of astrophysical and cosmological problems; at the same time their computational cost has come within reach of currently available computational power. Further progress is retarded by the considerable number of different algorithms (including various flavours of ray tracing and moment schemes) developed, which makes the selection of the most suitable technique for a given problem a non-trivial task. Assessing the validity ranges, accuracy and performances of these schemes is the main aim of this paper, for which we have compared 11 independent RT codes on five test problems: (0) basic physics; (1) isothermal H ii region expansion; (2) H ii region expansion with evolving temperature; (3) I-front trapping and shadowing by a dense clump and (4) multiple sources in a cosmological density field. The outputs of these tests have been compared and differences analysed. The agreement between the various codes is satisfactory although not perfect. The main source of discrepancy appears to reside in the multifrequency treatment approach, resulting in different thicknesses of the ionized-neutral transition regions and the temperature structure. The present results and tests represent the most complete benchmark available for the development of new codes and improvement of existing ones. To further this aim all test inputs and outputs are made publicly available in digital form. 相似文献