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Giorgio Matt Enrico Costa Marco Feroci Tomaso Belloni Marco Tavani 《New Astronomy Reviews》1998,42(9-10)
Results from a BeppoSAX observational campaign on GRS 1915+105, performed in October/November 1996, are presented. The source was observed 10 times (nine 10 ksec snapshots, one 100 ksec long observation). The broad band spectral analysis reveals a complex spectrum, including Compton reflection and an iron emission line, probably originating from a relativistic disc. 相似文献
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Beike Hiemstra Paolo Soleri Mariano Méndez Tomaso Belloni Reham Mostafa Rudy Wijnands 《Monthly notices of the Royal Astronomical Society》2009,394(4):2080-2088
We analysed simultaneous archival XMM–Newton and Rossi X-ray Timing Explorer observations of the X-ray binary and black hole candidate Swift J 1753.5−0127 . In a previous analysis of the same data, a soft thermal component was found in the X-ray spectrum, and the presence of an accretion disc extending close to the innermost stable circular orbit was proposed. This is in contrast with the standard picture in which the accretion disc is truncated at large radii in the low/hard state. We tested a number of spectral models and found that several of them fit the observed spectra without the need of a soft disc-like component. This result implies that the classical paradigm of a truncated accretion disc in the low/hard state cannot be ruled out by these data. We further discovered a broad iron emission line between 6 and 7 keV in these data. From fits to the line profile we found an inner disc radius that ranges between ∼6 and 16 gravitational radii, which can be in fact much larger, up to ∼250 gravitational radii, depending on the model used to fit the continuum and the line. We discuss the implications of these results in the context of a fully or partially truncated accretion disc. 相似文献
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Jo De Waele Ilenia M. D'Angeli Tomaso Bontognali Paola Tuccimei Denis Scholz Klaus Peter Jochum Andrea Columbu Stefano M. Bernasconi Joan J. Fornós Esteban R. Grau González Nicola Tisato 《地球表面变化过程与地形》2018,43(11):2313-2326
A flight of marine terraces along the Cuban coast records Quaternary sea‐level highstands and a general slowly uplifting trend during the Pleistocene. U/Th dating of these limestone terraces is difficult because fossil reef corals have been affected by open system conditions. Terrace ages are thus often based on geological and geomorphological observations. In contrast, the minimum age of the terraces can be constrained by dating speleothems from coastal mixing (flank margin) caves formed during past sea‐level highstands and carving the marine limestones. Speleothems in Santa Catalina Cave have ages >360 ka and show various cycles of subaerial–subaqueous corrosion and speleothem growth. This suggests that the cave was carved during the MIS 11 sea‐level highstand or earlier. Some stalagmites grew during MIS 11 through MIS 8 and were submerged twice, once at the end of MIS 11 and then during MIS 9. Phreatic overgrowths (POS) covering the speleothems suggest anchialine conditions in the cave during MIS 5e. Their altitude at 16 m above present sea level indicates a late Pleistocene uplift rate of <0.1 mm/ka, but modelling also shows uplift to have been insignificant over a long timespan during the middle Pleistocene since the cave was carved. Our study shows that some flank margin caves in the region of Matanzas are older than commonly believed (i.e. MIS 11 rather than MIS 5). These caves not only can be preserved but are good markers of interglacial sea‐level highstands, more reliable than marine abrasion surfaces. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
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Michele Palermo Stefano Silvestri Giada Gasparini Tomaso Trombetti 《Bulletin of Earthquake Engineering》2013,11(5):1467-1491
This paper gives a new insight into the linear dynamic behavior of one-storey eccentric systems, with particular attention devoted to provide a comprehensive physically-based formulation of the maximum corner displacement magnification, which involves three contributions (translational response, torsional response and their combination). It is shown that the largest magnifications, which mainly occur for the class of torsionally-flexible systems, are due to the translational contribution which is caused by the shift of the fundamental period of the eccentric system with respect to that of the equivalent not-eccentric system. A simplified method for the estimation of the maximum corner displacement under seismic excitation, based on the physical properties of the eccentric system, is finally proposed. 相似文献
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Francesco Sauro Nicola Tisato Jo De Waele Stefano M. Bernasconi Tomaso R. R. Bontognali Ermanno Galli 《Sedimentology》2014,61(5):1433-1451
Gypsum (CaSO4·2H2O), alunite (KAl3(SO4)2(OH)6), and rare phosphate–sulphate sanjuanite Al2(PO4)(SO4)(OH) 9(H2O) and rossiantonite (Al3(PO4)(SO4) 2(OH)2(H2O)14) have recently been identified as secondary mineral deposits in different quartz‐sandstone caves in the Gran Sabana region, Venezuela. Due to the extended time scale required for speleogenesis in the hard and barely soluble quartz‐sandstone lithology, these caves are considered to be as old as 20 to 30 My. The study of these peculiar secondary mineral deposits potentially reveals important insights for understanding the interaction between deep, superficial and atmospheric processes over thousands to perhaps millions of years. In this study, chemical and petrographic analyses of potential host rock sources, sulphur and oxygen isotope ratios, and meteorological, hydrological and geographical data are used to investigate the origin of sulphates and phospho–sulphates. The results suggest that the deposition of sulphates in these caves is not linked to the quartz‐sandstone host rock. Rather, these mineral deposits originate from an external atmospheric sulphate source, with potential contributions of marine non‐sea salt sulphates, terrestrial dimethyl sulphide and microbially reduced H2S from the forests or peatbogs within the watershed. Air currents within the caves are the most plausible means of transport for aerosols, driving the accumulation of sulphates and other secondary minerals in specific locations. Moreover, the studied sulphate minerals often co‐occur with silica speleothems of biological origin. Although this association would suggest a possible biogenic origin for the sulphates as well, direct evidence proving that microbes are involved in their formation is absent. Nonetheless, this study demonstrates that these quartz‐sandstone caves accumulate and preserve allogenic sulphates, playing a yet unrecognized role in the sulphur cycle of tropical environments. 相似文献
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We discuss the evolution of black hole transients on the basis of a few systems that were intensively observed with the Rossi X-ray Timing Explorer (rxte). We focus on the global evolution and the observed state transitions. Rather than giving a numerical recipe for classifying observations, we try to identify times during outbursts at which clear changes occur in the X-ray variability, X-ray spectral, or multi-wavelength properties. 相似文献