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排序方式: 共有136条查询结果,搜索用时 31 毫秒
81.
Ericsson D. Lopez Elisabete M. de Gouveia Dal Pino 《Astrophysics and Space Science》2008,314(1-3):129-136
We here investigate the dispersion properties of radiation in the SS433 relativistic jets. We assume that the jet is composed
of cold electron-proton plasma immersed in a predominantly parallel magnetic field to the jet axis. We find that for the mildly
relativistic source SS433 (for which 〈ψ〉≃79°), the bulk velocity is too small (v≃0.26c) to produce significant changes in the dispersion properties of the medium. Nonetheless, in the rarefied outer regions of
the jets, where radio emission dominates, even a weak magnetic field has some influence on the dispersion properties and there
appear two different electromagnetic branches that are slightly sensitive to the bulk relativistic motion. In the inner, X-ray
region, the magnetic field is much stronger, but in this region the high electron density preserves the isotropic character
of the local plasma and no branch separation occurs. In the region of the jet where the IR and optical emission dominates,
the cold plasma may be also considered isotropic, i.e., neither the magnetic field nor the bulk velocity is able to affect
the propagation of the radiation. Finally, we find that the Doppler line displacement in SS433 is affected by plasma dispersion
only in a narrow frequency range in the far IR. As a consequence, although the shift (z) modulation due to precession of the SS433 jets is well described by previous work, it has to be corrected by plasma dispersion
effects in the far-IR range. 相似文献
82.
Levels and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in superficial sediment from 15 Italian marine protected areas (MPA) 总被引:5,自引:0,他引:5
Perra G Pozo K Guerranti C Lazzeri D Volpi V Corsolini S Focardi S 《Marine pollution bulletin》2011,62(4):874-877
Surface sediment from 15 Italian marine protected areas (MPA) were analysed for polycyclic aromatic hydrocarbons (PAHs). The organic carbon percentage was also determined. Total PAH concentrations (ng g−1 d.w.) ranged from 0.71 (Penisola del Sinis) to 1550 (Miramare). Individual PAH analysis showed that three and four rings PAHs were the most frequently detected isomers and accounted for 60-70% of the PAH total concentrations. PAH ratio analysis showed a prevalence of pyrolytic PAH origin at most of the MPAs with exception of Porto Cesareo and Ustica where a petrogenic origin was detected. Results for organic carbon percentages ranged from 0.3% (Capo Rizzuto) to 2% (Punta Campanella). These results are comparable to other Mediterranean marine environments. However, our results shows that some MPAs, such as Miramare, Porto Cesareo, Isola Capo Rizzuto and Punta Campanella, are subject to strong pressure from urban and industrial activities where high PAH levels were detected. 相似文献
83.
84.
Levels and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in sediments from Lenga Estuary, central Chile 总被引:1,自引:0,他引:1
Pozo K Perra G Menchi V Urrutia R Parra O Rudolph A Focardi S 《Marine pollution bulletin》2011,62(7):1572-1576
The Lenga Estuary is a small brackish wetland located southwest of San Vicente Bay, Region VIII, Chile. Surface sediment from nine sites in the estuary were analysed for PAHs and compared to Sediment Quality Guidelines (SQG). Sediment samples were freeze dried and soxhlet extracted for 16 h using DCM. Identification and quantification was carried out by HPLC. Organic carbon was also determined. Results showed total PAH concentrations ranged from 290 to 6118 (2025 ± 1975) ng g−1 d.w. (2025 ± 1975). Results for organic carbon percentages ranged from 1% to 7%. Statistical analysis showed a significant positive correlation (Pearson test) between organic carbon percentage PAHs. Comparison of contaminant levels and international Sediment Quality Guidelines (SQG) (ERL and ER) suggested that sediment of the Lenga estuary did not show any ecotoxicologial risk for benthic organisms where high levels of PAHs were detected. Monitoring of this and other contaminants is recommended in Chile. 相似文献
85.
86.
Gianluigi Bodo Claudio Zanni Giuseppe Murante Paola Rossi Silvano Massaglia Attilio Ferrari 《Astrophysics and Space Science》2004,293(1-2):247-254
We study, by numerical simulations, the propagation of an axisymmetric supersonic jet in an isothermal King atmosphere and we analyse the evolution of the resulting X-ray properties and their dependence on the jet physical parameters. We show the existence of two distinct regimes of interaction, with strong and weak shocks. In the first case shells of enhanced X-ray emission are to be expected, whereas in the second case we expect deficit of X-ray emission coincident with the cocoon. Analysing the results of our simulations we find that the jet kinetic power is the main parameter controlling the transition between the two regimes. We also discuss, in the same scheme, the ICM heating induced by the jet propagation, considering its effects on the observed relations between the cluster X-ray luminosity and temperature and between cluster entropy and temperature. 相似文献
87.
88.
Jaramillo Natalia Andrea Durán dos Santos Ferreira José Wilson Malko José Adriano Cardoso Casagrande Michéle Dal Toé 《Geotechnical and Geological Engineering》2022,40(6):3365-3378
Geotechnical and Geological Engineering - The volume of discarded tires continues to increase each year, becoming a major topic of concern for society. Motivated by this environmental issue, this... 相似文献
89.
90.
Paola Rossi Gianluigi Bodo Silvano Massaglia Attilio Ferrari Andrea Mignone 《Astrophysics and Space Science》2004,293(1-2):149-155
Extragalactic radio sources are separated in two classes according to their specific luminosity: Fanaroff-Riley I and II. The origin of this dichotomy can be due either to intrinsec different properties of the AGN or to interaction of the jet with different enviroments. We assume that jets are always relativistic and supersonic close to their source, as recent observations suggest, and we explore the conditions in which the jets decelerate assuming FR I morphology. We have carried out high resolution 3D simulations for a set of parameters and in this paper we concentrate our discussion on two extreme cases. 相似文献