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861.
Roberto Capuzzo-Dolcetta 《Astrophysics and Space Science》2004,294(1-2):95-100
Globular cluster systems evolve, in galaxies, due to internal and external dynamics and tidal phenomena. One of the causes
of evolution, dynamical friction, is responsible for the orbital decay of massive clusters into the innermost galactic regions.
It is found that these clusters are effective source of matter to feed a central galactic black hole such to make it grow
and shine as an AGN. 相似文献
862.
Luca Zampieri Roberto Turolla Ewa Szuszkiewicz 《Monthly notices of the Royal Astronomical Society》2001,325(3):1266-1274
Transonic discs with accretion rates relevant to intrinsically bright Galactic X-ray sources ( L ≈1038 –1039 erg s−1 ) exhibit a time-dependent cyclic behaviour due to the onset of a thermal instability driven by radiation pressure. In this paper we calculate radiation spectra emitted from thermally unstable discs to provide detailed theoretical predictions for observationally relevant quantities. The emergent spectrum has been obtained by solving self-consistently the vertical structure and radiative transfer in the disc atmosphere. We focus on four particular stages of the disc evolution, the maximal evacuation stage and three intermediate stages during the replenishment phase. The disc is found to undergo rather dramatic spectral changes during the evolution, emitting mainly in the 1–10 keV band during outburst and in the 0.1–1 keV band off-outburst. Local spectra, although different in shape from a blackbody at the disc effective temperature, may be characterized in terms of a hardening factor f . We have found that f is more or less constant, both in radius and in time, with a typical value ∼ 1.65. 相似文献
863.
864.
Will J. Percival Daniel Burkey Alan Heavens y Taylor Shaun Cole John A. Peacock Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Peder Norberg Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,353(4):1201-1218
865.
IsabelSalamanca Roberto J.Terlevich GuillermoTenorio-Tagle 《Monthly notices of the Royal Astronomical Society》2002,330(4):844-854
We report the detection of a very narrow P Cygni profile on top of the broad emission H α and H β lines of the Type IIn Supernova 1997eg. A similar feature has been detected in SN 1997ab, SN 1998S and SN 1995G . The detection of the narrow P Cygni profile indicates the existence of a dense circumstellar material (CSM), into which the ejecta of the supernova is expanding. From the analysis of the spectra of SN 1997eg we deduce (i) that such CSM is very dense ( n ≳5×107 cm-3 ) , (ii) that it has a low expanding velocity of about 160 km s−1 . The origin of such dense CSM can be either a very dense progenitor wind ( M˙ ∼10-2 M⊙ yr-1 ) or a circumstellar shell product of the progenitor wind expanding into a high-pressure environment. 相似文献
866.
Mechanical Testing in Unsaturated Soils 总被引:1,自引:0,他引:1
Laureano R. Hoyos Lyesse Laloui Roberto Vassallo 《Geotechnical and Geological Engineering》2008,26(6):675-689
The state-of-the-art report presented herein is aimed at documenting, to the largest extent possible, some of the recent advances
in laboratory testing of unsaturated soils for stress–strain–strength–stiffness characterization under suction-controlled
isotropic, axisymmetric, and true triaxial stress states. The report is intended to be neither comprehensive nor fully inclusive,
offering plenty of room for further discussion on recent refinements and techniques not yet reported in the literature. The
main sections in this report are devoted to describing current methods and technologies using cylindrical triaxial systems,
including advances in volume change measurements; resonant column/torsional shear systems; bender element-based systems; and
suction-controlled testing under true triaxial stress states. Concluding remarks are included in the last section of the report. 相似文献
867.
Juan Reynerio Fagundo-Castillo Joel José Carrillo-Rivera Iñaki Antigüedad-Auzmendi Patricia González-Hernández Roberto Peláez-Díaz Rebeca Hernández-Díaz Dámaso Cáceres-Govea José Ramón Hernández-Santana Margaret Suárez-Muñoz Clara Melián-Rodríguez Mónica Rodríguez-Piña 《Environmental Geology》2008,55(2):247-267
Flows of different hierarchy, which travel through limestone, schist, sandstone and ultra-basic rocks, with ages from the
Paleocene to the Jurassic, at Sierra del Rosario, Pinar del Río, Cuba, were characterized. The waters were sampled from 1984
until 2004 and the data were statistically processed by means of chemical equilibrium and physico-chemical models, under a
flow system view of interpretation. Results demonstrate that the physico-chemical properties of the water are controlled by
water–rock interaction resulting from residence time since rainwater infiltrate and the path it follows to the discharge zone
and the type of aquifer material the different groundwater flows are in contact with. Geochemical indices allow the definition
of the different types of flow (local, intermediate, regional) to be characterized, permitting a further definition of the
different flow systems and rock type involved, as well as its use for water supply and medical use. The main geochemical processes
which control the chemical composition acquisitions mode are: congruent dissolution of calcite, dolomite, and halite; incongruent
dissolution of plagioclase and microcline minerals; pyrite oxidation, sulphate reduction, and silica dissolution at the surface
or silica precipitation at deep saturation and circulation zones. 相似文献
868.
Bringing GEOSS Services into Practice: A Capacity Building Resource on Spatial Data Infrastructures (SDI) 下载免费PDF全文
Gregory Giuliani Pierre Lacroix Yaniss Guigoz Roberto Roncella Lorenzo Bigagli Mattia Santoro Paolo Mazzetti Stefano Nativi Nicolas Ray Anthony Lehmann 《Transactions in GIS》2017,21(4):811-824
Data discoverability, accessibility, and integration are frequent barriers for scientists and a major obstacle for favorable results on environmental research. To tackle this issue, the Group on Earth Observations (GEO) is leading the development of the Global Earth Observation System of Systems (GEOSS), a voluntary effort that connects Earth Observation resources world‐wide, acting as a gateway between producers and users of environmental data. GEO recognizes the importance of capacity building and education to reach large adoption, acceptance and commitment on data sharing principles to increase the capacity to access and use Earth Observations data. This article presents “Bringing GEOSS services into practice” (BGSIP), an integrated set of teaching material and software to facilitate the publication and use of environmental data through standardized discovery, view, download, and processing services, further facilitating the registration of data into GEOSS. So far, 520 participants in 10 countries have been trained using this material, leading to numerous Spatial Data Infrastructure implementations and 1,000 tutorial downloads. This workshop lowers the entry barriers for both data providers and users, facilitates the development of technical skills, and empowers people. 相似文献
869.