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121.
Ricardo Cesar Silvia Egler Helena Polivanov Zuleica Castilhos Ana Paula Rodrigues 《Environmental Earth Sciences》2011,64(1):211-222
Mercury, zinc and copper contamination was evaluated in soils and fluvial sediments from an abandoned gold mining site at
Descoberto Municipality (southern Minas Gerais State, Brazil). Metals bioavailability and potential mobility were studied
through physical, chemical and mineralogical characterization, geoaccumulation indexes calculations, mercury speciation and
determination of potentially bioavailable contents of zinc and copper. Values of pH were in the neutral range, while organic
matter concentrations were very low. Mineralogical characterization, in the total samples, indicated the presence of quartz,
kaolinite and gibbsite for all samples. Total mercury, zinc and cooper concentrations were higher than the limits recommended
by Brazilian documents. Geoaccumulations indexes revealed that most of the sediment samples were low to moderately polluted
by zinc and copper, while just one sample was very strongly polluted by mercury. Mercury speciation revealed the predominance
of the elementary form for all samples, and low concentrations for exchangeable, strongly bound and residual fractions. Zinc
and copper behavior was strongly controlled by iron and aluminum concentrations, while their bioavailable contents were very
low in comparison with the total concentrations. 相似文献
122.
Emmanoel V. Silva-Filho Christian J. Sanders Michel Bernat Ana M. G. Figueiredo Silvia M. Sella Julio Wasserman 《Environmental Earth Sciences》2011,64(5):1257-1267
Elemental contents were determined in two mangrove habitats along Sepetiba Bay, SE Brazil, an area impacted by local industrial activities, as well as hinterland water diversion networks. This study demonstrates how specific REEs (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) may be used as a sediment source tracer to mangrove-dominated coastlines. From the two stations studied, a pair of cores was collected, one in the mangrove forest and the other in the tidal flat. Station 1 results show a general enrichment in most of the fractioned patterns of the REEs normalised by Post-Archean Australian Shale. The relatively light rare earth elements are similarly enriched in the generally more polluted Station 1. Despite the probable difference in background sediment characteristics, a common sharp increase in mud contents patterns in the upper part of the mangrove sediment core was related to a lower REE content as well as Eu anomalies. With existing knowledge of clockwise water circulation in the bay, these patterns can be explained by man-made water diversion from the São Francisco and Guandu rivers, initiated more than 30 years ago, whereby suspended matter with relatively large contents of REEs and material originating from industrial sources accumulate in the eastern sector of the bay. This is the first comprehensive assessment of REEs as sedimentary tracers in a mangrove ecosystem in Brazil. 相似文献
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125.
Gianluca Masi 《Icarus》2003,163(2):389-397
The likely existence of bodies orbiting the Sun with aphelia Q < 0.983 AU has been suggested by numerical simulations of the dynamical evolution of the near-Earth objects (NEOs) population. For obvious reasons, these hypothetical minor bodies are called inner-Earth objects (IEOs). While much progresses has been made in learning more about the Amor, Apollo, and Aten population from surveys optimized for their discovery, no large, systematic, and similar observation projects devoted to the search of IEOs have been started. For their own orbital nature, IEOs can be observed only at small solar elongations (<90°), corresponding to regions of the sky currently neglected by the modern, ongoing surveys. This paper discusses a possible ground-based approach to look for IEOs, providing some useful tricks and the results of simulated surveys devoted to their discovery. It will be shown that such a search promises interesting results, the setup of a dedicated project being highly recommended. 相似文献
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127.
Recent Chandra and XMM–Newton observations of a number of X-ray 'dim' pulsating neutron stars have revealed quite unexpected features in the emission from these sources. Their soft thermal spectrum, believed to originate directly from the star surface, shows evidence for a phase-varying absorption line at some hundred eVs. The pulse modulation is relatively large (pulsed fractions in the range ∼12–35 per cent), the pulse shape is often non-sinusoidal, and the hard X-ray colour appears to be anticorrelated in phase with the total emission. Moreover, the prototype of this class, RX J0720.4−3125, has been found to undergo rather sensible changes in both its spectral and timing properties over a time-scale of a few years. All these new findings seem difficult to reconcile with the standard picture of a cooling neutron star endowed with a purely dipolar magnetic field, at least if surface emission is produced in an atmosphere on top of the crust. In this paper we explore how a dipolar+quadrupolar star-centred field influences the properties of the observed light curves. The phase-resolved spectrum has been evaluated accounting for both radiative transfer in a magnetized atmosphere and general relativistic ray-bending. We computed over 78 000 light curves, varying the quadrupolar components and the viewing geometry. A comparison of the data with our model indicates that higher-order multipoles are required to reproduce the observations. 相似文献
128.
J-Ph. Bernard P. Ade Y. André J. Aumont L. Bautista N. Bray P. de Bernardis O. Boulade F. Bousquet M. Bouzit V. Buttice A. Caillat M. Charra M. Chaigneau B. Crane J.-P. Crussaire F. Douchin E. Doumayrou J.-P. Dubois C. Engel P. Etcheto P. Gélot M. Griffin G. Foenard S. Grabarnik P. Hargrave A. Hughes R. Laureijs Y. Lepennec B. Leriche Y. Longval S. Maestre B. Maffei J. Martignac C. Marty W. Marty S. Masi F. Mirc R. Misawa J. Montel L. Montier B. Mot J. Narbonne J-M. Nicot F. Pajot G. Parot E. Pérot J. Pimentao G. Pisano N. Ponthieu I. Ristorcelli L. Rodriguez G. Roudil M. Salatino G. Savini O. Simonella M. Saccoccio P. Tapie J. Tauber J.-P. Torre C. Tucker 《Experimental Astronomy》2016,42(2):199-227
Future cosmology space missions will concentrate on measuring the polarization of the Cosmic Microwave Background, which potentially carries invaluable information about the earliest phases of the evolution of our universe. Such ambitious projects will ultimately be limited by the sensitivity of the instrument and by the accuracy at which polarized foreground emission from our own Galaxy can be subtracted out. We present the PILOT balloon project, which aims at characterizing one of these foreground sources, the polarized continuum emission by dust in the diffuse interstellar medium. The PILOT experiment also constitutes a test-bed for using multiplexed bolometer arrays for polarization measurements. This paper presents the instrument and its expected performances. Performance measured during ground calibrations of the instrument and in flight will be described in a forthcoming paper. 相似文献
129.
Claudius M. Pirkenseer Silvia Spezzaferri Claudio Stalder 《Swiss Journal of Geoscience》2018,111(3):549-560
The ostracod assemblages from sediment core TTR17-401G recovered from the Melilla cold-water coral mound field in the eastern Alboran Sea spanning the last 13 ka are analysed quantitatively, taxonomically and palaeoecologically. The core can be subdivided in three distinct assemblages linked to environmental shifts during the Younger Dryas and the Bølling–Allerød interstadial. A total of 9 ostracod species is recorded, Paracypris polita is dominant throughout the core. Common accessory taxa Cytherella robusta, Echinocythereis vidua and Macromckenziea ligustica characterize the well-oxygenated ostracod assemblage 2 affected by the Younger Dryas. Favourable growth conditions for ostracods during the latter are indicated by large-sized Krithe praetexta specimens. 相似文献
130.
Akram El Kateb Claudio Stalder Christoph Neururer Robin Fentimen Jorge E. Spangenberg Silvia Spezzaferri 《Swiss Journal of Geoscience》2018,111(3):589-606
The eastern edge of the Djerba Island represents an important tourist pole. However, studies describing the environmental processes affecting this Island are scarce. Although never studied before, the peculiar Djerba lagoon is well known by the local population and by tourists. In July 2014, surface sediment and seawater samples were collected in this lagoon to measure grain size, organic matter content and living foraminiferal assemblages to describe environmental conditions. Seawater samples were also collected and the concentration of 17 chemical elements were measured by ICP-OES. The results show that a salinity gradient along the studied transect clearly impacts seagrass distribution, creating different environmental conditions inside the Djerba lagoon. Biotic and abiotic parameters reflect a transitional environment from hypersaline to normal marine conditions. Living benthic foraminifera show an adaptation to changing conditions within the different parts of the lagoon. In particular, the presence of Ammonia spp. and Haynesina depressula correlates with hypersaline waters, whilst Brizalina striatula characterizes the parts of the lagoon colonized by seagrass. Epifaunal species, such as Rosalina vilardeboana and Amphistegina spp. colonize hard substrata present at the transition between the lagoon and the open sea. 相似文献