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Tomaso R. R. Bontognali Judith A. McKenzie Rolf J. Warthmann Crisogono Vasconcelos 《地学学报》2014,26(1):72-77
Some species of sulphate‐reducing bacteria (SRB) are known to mediate the formation of dolomite and Mg‐calcite. However, their exact role in the mineralization process remains elusive. Here, we present the result of a laboratory experiment that was designed to test whether formation of carbonate minerals by SRB can occur in the absence of living cells, through passive mineralization of their exopolymeric substances (EPS). SRB capable of mediating dolomite were cultivated in the laboratory, allowing them to secrete EPS. Microbial activity within the cultures was subsequently inhibited with antibiotics. Only after this step, Ca2+ and Mg2+ were added to the solution and carbonate minerals could form. Mg‐calcite and disordered Ca‐dolomite precipitated in association with EPS. The mol.% of Mg2+ in the crystals increased with longer incubation times. This result demonstrates that organic compounds produced by SRB can mediate the formation of Ca‐Mg carbonates in the absence of an active metabolism. 相似文献
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Stefano Silvestri Salvador Ivorra Laura Di Chiacchio Tomaso Trombetti Dora Foti Giada Gasparini Luca Pieraccini Matt Dietz Colin Taylor 《地震工程与结构动力学》2016,45(1):69-89
According to Eurocode 8, the seismic design of flat‐bottom circular silos containing grain‐like material is based on a rough estimate of the inertial force imposed on the structure by the ensiled content during an earthquake: 80% of the mass of the content multiplied by the peak ground acceleration. A recent analytical consideration of the horizontal shear force mobilised within the ensiled material during an earthquake proposed by some of the authors has resulted in a radically reduced estimate of this load suggesting that, in practice, the effective mass of the content is significantly less than that specified. This paper describes a series of laboratory tests that featured shaking table and a silo model, which were conducted in order to obtain some experimental data to verify the proposed theoretical formulations and to compare with the established code provisions. Several tests have been performed with different heights of ensiled material – about 0.5 mm diameter Ballotini glass – and different magnitudes of grain–wall friction. The results indicate that in all cases, the effective mass is indeed lower than the Eurocode specification, suggesting that the specification is overly conservative, and that the wall–grain friction coefficient strongly affects the overturning moment at the silo base. At peak ground accelerations up to around 0.35 g, the proposed analytical formulation provides an improved estimate of the inertial force imposed on such structures by their contents. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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We have recently put forward a ‘unified’ semi-empirical model for the coupling between accretion and jet production in galactic
black hole X-ray binaries. In this paper, we summarise this model and briefly discuss relevant considerations that have arisen
since its publication. 相似文献
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Guobao Zhang Mariano Méndez Diego Altamirano Tomaso M. Belloni Jeroen Homan 《Monthly notices of the Royal Astronomical Society》2009,398(1):368-374
We have discovered a triple-peaked X-ray burst from the low-mass X-ray binary (LMXB) 4U 1636−53 with the Rossi X-ray Timing Explorer ( RXTE ). This is the first triple-peaked burst reported from any LMXB using RXTE , and it is only the second burst of this kind observed from any source. (The previous one was also from 4U 1636−53, and was observed with EXOSAT .) From fits to time-resolved spectra, we find that this is not a radius-expansion burst, and the same triple-peaked pattern seen in the X-ray light curve is also present in the bolometric light curve of the burst. Similar to what was previously observed in double-peaked bursts from this source, the radius of the emitting area increases steadily during the burst, with short periods in between during which the radius remains more or less constant. The temperature first increases steeply, and then decreases across the burst also showing three peaks. The first and last peak in the temperature profile occur, respectively, significantly before and after the first and last peaks in the X-ray and bolometric light curves. We found no significant oscillations during this burst. This triple-peaked burst, as well as the one observed with EXOSAT and the double-peak bursts in this source, all took place when 4U 1636−53 occupied a relatively narrow region in the colour–colour diagram, corresponding to a relatively high (inferred) mass-accretion rate. No model presently available is able to explain the multiple-peaked bursts. 相似文献
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Luca Salvati Sofia Bajocco Tomaso Ceccarelli Luigi Perini 《The Professional geographer》2013,65(4):647-663
This article analyzes the territorial disparities in the level of land vulnerability (TDLV) to soil degradation caused by five processes (soil erosion, salinization, sealing, contamination, and compaction) as well as by climate variations in Italy in 1990 and 2000. The analysis reveals, for each soil degradation process, a typical spatial distribution across Italy. Three processes (soil salinization, compaction, and sealing) contribute significantly to the increase in land vulnerability, which is mainly concentrated in risky areas. The observed disparities highlight a growing environmental divide between northern Italy (an economically developed region, not at risk of desertification) and southern Italy and the two main islands (dry, disadvantaged regions at risk of desertification). The knowledge of such a territorial divide and of the underlying soil degradation processes is regarded as important for environmental policies at the country and regional scales aimed at sustaining the economic and socioenvironmental cohesion between areas that are either vulnerable or nonvulnerable to soil degradation. The proposed approach should be seen as part of a decision-making tool informing policies and supporting the design of management solutions, hopefully reversing disparities in land vulnerability to soil degradation. 相似文献
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Coastal uplift rate at Matanzas (Cuba) inferred from MIS5e phreatic overgrowths on speleothems 
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下载免费PDF全文 Jo De Waele Ilenia M. D'Angeli Nicola Tisato Paola Tuccimei Michele Soligo Joaquín Ginés Angel Ginés Joan J. Fornós Igor M. Villa Esteban R. Grau González Stefano M. Bernasconi Tomaso R. R. Bontognali 《地学学报》2017,29(2):98-105
Many morphological elements in Cuba's landscape (e.g. marine terraces, tidal notches) demonstrate that coastal uplift has taken place, but the rate at which this occurs is not known. Carbonate phreatic overgrowths on speleothems have been found in a cave in Central North Cuba, ~1 km from the present coastline at 16 m asl. They form exceptional and unique mushroom‐shaped speleothems and balconies decorating the walls of the rooms. These phreatic overgrowths on speleothems (POS) formed at the oscillating air–water interface in sea‐level controlled anchialine lakes. U/Th dating of these overgrowths suggests ages that are compatible with the Marine Isotope Stage 5e (i.e. 130–115 ka). These POS have fixed this sea‐level highstand and demonstrate that this part of Cuba has been subjected to a much lower uplift rate than previously reported, that is, less than 0.1 mm/year since the last interglacial. 相似文献
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Is there a link between the neutron-star spin and the frequency of the kilohertz quasi-periodic oscillations? 总被引：1，自引：0，他引：1
Mariano Méndez Tomaso Belloni 《Monthly notices of the Royal Astronomical Society》2007,381(2):790-796
There is a general consensus that the frequencies of the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron-star low-mass X-ray binaries are directly linked to the spin of the neutron star. The root of this idea is the apparent clustering of the ratio of the frequency difference of the kHz QPOs, and the neutron-star spin frequency, Δν/νs , at around 0.5 and 1 in 10 systems for which these two quantities have been measured. Here, we re-examine all available data of sources for which there exist measurements of two simultaneous kHz QPOs and spin frequencies, and we advance the possibility that Δν and νs are not related to each other. We discuss ways in which this possibility could be tested with current and future observations. 相似文献
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Tomaso Belloni 《New Astronomy Reviews》1998,42(9-10)
The X-ray properties of the two galactic microquasars GRS 1915+105 and GRO J1655−40 are rather perculiar. In particular, GRS 1915+105 displays a richness of variability never observed in any other source. Nevertheless, many characteristics of these two sources are not unlike those expected from black-hole candidates on the basis of other known sources. I discuss these similarities and suggest that the connection between these and other more “conventional” systems can potentially lead to a better understanding of accretion around black holes. 相似文献