Foreword     

Silvano Massaglia  Gianluigi Bodo  Paola Rossi 《Astrophysics and Space Science》2004,293(1-2):vii-viii

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Experiments and Numerical Simulations on the Mid-Term Evolution of Hypersonic Jets     

Marco Belan  Sergio de Ponte  Silvano Massaglia  Daniela Tordella 《Astrophysics and Space Science》2004,293(1-2):225-232

The experiment described here is focussed to the observation of underexpanded, hypersonic turbulent jets. The experiment is relevant to a few aspects concerning the dynamics of astrophysical phenomena such as the Herbig-Haro jets and to the interaction between the large-scale vortices and the system of shocks that determine the spreading and entrainment properties of highly compressible free-flows. A number of orifice jets with a ratio between the stagnation pressure and the ambient pressure of the order 10³-10⁴ have been studied by changing the stagnation/ambient density ratio. This has been realized using dissimilar gases in the jet and in the ambient medium: by using He, Ar and air the stagnation/ambient density ratio can be changed by one order of magnitude while keeping fixed the pressure ratio. It has been possible to visualize the near and mid-term evolution of the jets and measure the axial and transversal density distributions. A comparison relevant to the shock waves configuration in between the nozzle exit and the first Mach's disk is shown for an air in air laboratory jet and its numerical simulation.  相似文献   

The operational sex ratio of the sea urchin Paracentrotus lividus populations: the case of the Mediterranean marine protected area of Ustica Island (Tyrrhenian Sea, Italy)     

Paola Gianguzza  Fabio Badalamenti  Fabrizio Gianguzza  Chiara Bonaviri  & Silvano Riggio 《Marine Ecology》2009,30(1):125-132

We investigated, with a series of field and laboratory observations, the possible effect of the starfish Marthasteria glacialis predation on the operational sex ratio (OSR), i.e. the number of sexually mature males divided by the total number of sexually mature adults of both sexes at any one time, of the edible sea urchin Paracentrotus lividus . The OSR was estimated three times during the sea urchin summer spawning period (July 2004, June 2005 and July 2006) on barren substrates of Ustica Island Marine Protected Area (Southern Tyrrhenian Sea, Italy). Four sites were selected: two characterized by high M. glacialis density (take zone C) and two controls with low starfish density (no-take zone A). Mature sea urchins were independently collected by SCUBA diving and sexed. The adult sex ratio was skewed towards males at high M. glacialis density sites, whereas it was balanced (1:1) at predator low-density sites. Results of sex-selective feeding experiments in the laboratory showed that females of P. lividus were more vulnerable to M. glacialis predation. These outcomes underline the possible importance of M. glacialis in regulating the OSR of P. lividus populations.  相似文献   

Mixed function oxidase activity and cytochrome P-450 forms in black-headed gulls feeding in different areas     

Cristina Fossi  Claudio Leonzio  Silvano Focardi 《Marine pollution bulletin》1986,17(12):546-548

The aim of the present study was to evaluate the mixed function oxidase (MFO) system and the forms of supposed cytochrome P-450 in the liver of black-headed gulls (Larus ridibundus) feeding in a lagoon and on a garbage dump. Tissue levels of polychlorinated biphenyls (PCBs) were also determined. Ethoxyresorufin 10-deethylase (EROD) and aldrin epoxidase activities were higher in the dump gulls than in the lagoon gulls. A marked thickening of the proteins in the cytochrome P-450 area, particularly of P-450c and P-450d, was also found in the dump gulls. No relationship was found between MFO activity and tissue chlorinated hydrocarbon levels.  相似文献   

Cholinesterase activities in the Antarctic scallop Adamussium colbecki: Tissue expression and effect of ZnCl₂ exposure     

I. Corsi  S. Bonacci  G. Santovito  M. Chiantore  L. Castagnolo  S. Focardi 《Marine environmental research》2004,58(2-5):401

Biochemical characterization of cholinesterase activity (ChE) was carried out on the Antarctic scallop Adamussium colbecki collected in winter 2000 from Campo Icaro (Ross Sea, Antarctica) in order to increase its suitability as a sentinel organism for monitoring the Antarctic environment. The digestive gland, gills and adductor muscle were investigated for substrate specificity and inhibitors sensitivity using acetylthiocholine iodide (ASCh) and butyrylthiocholine iodide (BSCh) as substrates and tetra (monoisopropyl)pyrophosphor-tetramide (Iso-OMPA), 1,5-bis(4-allyldimethylammoniumphenyl)-penthan-3-one dibromide (BW284c51) and the insecticide chlorpyrifos as inhibitors. Effect of in vivo exposure to ZnCl₂ was also investigated. All the tissues expressed ChE activity (gill > adductor muscle > digestive gland) and low substrates specificity throughout the hydrolysis of both ASCh and BSCh substrates. Partial (25–29%) and total inhibition (100%) of ChE activity in gills was demonstrated following in vitro incubation with Iso-OMPA and BW284c51 (3 mM), respectively. Concentration-dependent inhibition was also evident with chlorpyrifos in the range 10⁻⁴–10⁻¹⁰ M (IC₅₀ 10⁻⁶) while in vivo exposure to ZnCl₂ did not seem to affect ChE activity in the scallop. The potential use of ChE in the A. colbecki as biomarker for monitoring water contamination in the marine Antarctic environment is discussed.  相似文献   

Mixed-function oxidase activity and conjugating enzymes in two species of antarctic fish   总被引：1，自引：0，他引：1  

Silvano Focardi  Cristina Fossi  Claudio Leonzio  Paolo Di Simplicio 《Marine environmental research》1989,28(1-4)

Enzyme activities of phase I and phase II of the hepatic detoxication system were investigated in two species of fish from the Ross Sea in Antarctica. The fish had extremely low phase I enzyme (BPMO and aldrin epoxidase). The reductase regenerating enzyme activities were comparable to those found in fish of temperate seas. Transferases of cytosol showed highest activity in the conjugation of 1-chloro-2,4-dinitrobenzene (CDNB) and little or no conjugation of other substrates. The GSSG reductase and the glutathione transferase with peroxidase activity (CuOOH substrate) were low; the Sedependent glutathione peroxidase activity was not detectable. Interspecific differences were found for most of the enzymes tested.  相似文献   

XMM-EPIC observation of MCG–6-30-15: direct evidence for the extraction of energy from a spinning black hole?     

Jörn Wilms  Christopher S. Reynolds †  Mitchell C. Begelman  James Reeves  Silvano Molendi  Rüdiger Staubert  Eckhard Kendziorra 《Monthly notices of the Royal Astronomical Society》2001,328(3):L27-L31

We present XMM-Newton European Photon Imaging Camera (EPIC) observations of the bright Seyfert 1 galaxy MCG–6-30-15, focusing on the broad Fe K α line at ∼6 keV and the associated reflection continuum, which is believed to originate from the inner accretion disc. We find these reflection features to be extremely broad and redshifted, indicating an origin in the very central regions of the accretion disc. It seems likely that we have caught this source in the 'deep minimum' state first observed by Iwasawa et al. The implied central concentration of X-ray illumination is difficult to understand in any pure accretion disc model. We suggest that we are witnessing the extraction and dissipation of rotational energy from a spinning black hole by magnetic fields connecting the black hole or plunging region to the disc.  相似文献   

Propagation of microwaves in pulsar magnetospheres     

Gianluigi Bodo  Attilio Ferrari  Silvano Massaglia 《Astrophysics and Space Science》1981,80(2):261-266

We discuss the dispersion relation of linearly-polarized waves, propagating along a strong background magnetic field embedded in an electron-positron plasma. The results are then applied to the study of the propagation conditions of coherent curvature radio radiation inside neutron stars magnetospheres, as produced by electric discharges following current pulsar models.  相似文献   

Mediterranean Talitrus saltator (Crustacea, Amphipoda) as a biomonitor of heavy metals contamination     

Ugolini A  Borghini F  Calosi P  Bazzicalupo M  Chelazzi G  Focardi S 《Marine pollution bulletin》2004,48(5-6):526-532

The use of sandhoppers and beachfleas as biomonitors of heavy metals contamination is relatively recent. Using adult individuals of Talitrus saltator from nine localities on the northern Mediterranean Sea, we studied the concentrations of eight trace elements: Al, Cd, Cr, Fe, Hg, Pb, Cu, Zn, both in the substratum and in the individuals. We also carried out a preliminary investigation of the correspondence between the sandhoppers' genetic variability and heavy metal contamination at the sampling sites. T. saltator accumulated Cd, Cu, Zn and Hg (at higher concentrations than in the sand) and also Al and Fe (at lower concentrations than in the sand). It seems that Mediterranean sandhoppers do not accumulate Pb and Cr. An intraspecific comparison between northern European (Baltic) and Mediterranean populations of T. saltator was made. Finally, we observed a tendency to a positive correlation between the sandhoppers' genetic variability and heavy metals contamination.  相似文献   

Sensitivity analysis of pounding between adjacent structures          下载免费PDF全文

Vincent Crozet  Ioannis Politopoulos  Mingguan Yang  Jean‐Marc Martinez  Silvano Erlicher 《地震工程与结构动力学》2018,47(1):219-235

This article deals with sensitivity of the response of pounding buildings with respect to structural and earthquake excitation parameters. A comprehensive sensitivity analysis is carried out by means of Monte Carlo simulations of adjacent single degree of freedom impacting oscillators. This sensitivity analysis, based on Sobol's method, computes sensitivity indexes which provide a consistent measure of the relative importance of parameters such as the dimensionless main excitation frequency, the mass and frequency ratios of the structures, and the coefficient of restitution. Moreover, the influence of nonlinear behavior of the impacting structures is also considered. The consequences of pounding on the structures themselves are analyzed in terms of maximum force and nonlinear demand amplification compared with the case without pounding. As for the influence of pounding on the floor response spectra, the quantity of interest is the maximum impact impulse. The overall conclusions of this analysis are that the frequency ratio is the most important parameter as far as the maximum force and nonlinear demand are concerned. Regarding the maximum impact impulse, the mass and frequency ratios are, in general, the most influential parameters, the mass ratio being predominant for low frequencies of the oscillator of interest.  相似文献