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61.
Madhusoodhan Satish-Kumar Hisayoshi Yurimoto Shoichi Itoh Bernardo Cesare 《Contributions to Mineralogy and Petrology》2011,162(4):821-834
High-spatial resolution carbon isotope analyses of natural graphite using secondary ion mass spectrometry (SIMS), together
with conventional mass spectrometry techniques, demonstrate isotopic heterogeneity within single graphite crystals precipitated
from a partially melted metamorphic rock. SIMS 13C/12C measurements were calibrated using an internal graphite standard previously analyzed by conventional isotope ratio mass
spectrometry, which gave a reproducibility of 0.3‰ (1σ) at a spatial resolution of 2–3 μm. This resolution helped to identify
an unusual carbon isotope distribution in a single graphite crystal from a metapelitic leucosome, showing remarkable core
to rim variations with sharp δ13C steps up to 10‰. The results suggest that the graphite crystal grew from one edge to other forming layers perpendicular
to the c-axis. The sharp isotopic steps indicate the presence of disequilibrium carbon isotope zoning in graphite and points to the
possible existence of carbon isotope sector zoning. Intra-crystalline carbon isotope disequilibrium in graphite is believed
to have resulted from the difference in diffusivity between 12C and 13C in the growth medium to the interface of graphite precipitation in different growth sectors. 相似文献
62.
Shun Nomura Giovanni De Cesare Mikito Furuichi Yasushi Takeda Hide Sakaguchi 《国际泥沙研究》2022,37(3):299-306
A turbidity current is a turbulent, particle-laden gravity current that is driven by density differences resulting from the presence of suspended sediment particles. The current travels downslope, bearing a large amount of sediment over a great distance, and forms fluvial and submarine bedforms. Knowledge of the spatio-temporal deposition profile of turbidity-deposited sediment is important for a better understanding of sediment transport by turbidity currents. In the current study, the depositi... 相似文献
63.
Nicola Gretter Ausonio Ronchi Antonio Langone Cesare R. Perotti 《International Journal of Earth Sciences》2013,102(5):1181-1202
The Val Daone Conglomerate (VDC) is a continental clastic unit that crops out eastwards of the central Southern Alps, from the NE sector of the Collio Basin to the W as far as the Tione Basin to the E. This significant but as yet relatively unknown formation lies just above the regional unconformity that marks the boundary between the two Permian major tectono-sedimentary cycles (TSU1 and TSU2) and grades upwards paraconformably (?) to the fluvial red beds of Verrucano Lombardo/Val Gardena Sandstone, generally associated with Late Permian times. Recent palynological investigations on the VDC suggested a Guadalupian age (late Roadian–early Wordian), owing to the remarkable presence of diversified pollen associations; therefore, this sedimentary unit is to date the first one ascribed, on a palaeontological basis, to the Middle Permian in the entire Southern Alps domain. A detailed facies analysis of VDC shows deposition in amalgamated alluvial fan-braided and fluvial environments with wide channels and longitudinal bars. In its type area and Val Rendena, the VDC rests unconformably above the last volcanic episode of the TSU1. LA ICP-MS U–Pb dating on zircon from two samples of such topmost Lower Permian volcanic rocks, known as Ponte Murandin dacitic lava and Malga Plan rhyodacitic Ignimbrites (Tione Basin), provided Concordia ages of 278 ± 2 Ma (MSWD = 0.01) and 279 ± 2 Ma (MSWD = 0.16), respectively. As well as allowing us to better define the duration of the time gap between the two Permian megacycles in the central Southern Alps in almost 10 Ma, these radiometric age determinations are also significant because they enable us to regionally link the coeval volcanic bodies which crop out in the Collio Basin to the SW and in the “Athesian Volcanic Group” to the NE, respectively. 相似文献
64.
65.
Cesare Cecchi-Pestellini & David A. Williams 《Monthly notices of the Royal Astronomical Society》1998,296(2):414-418
High brightness temperatures ( T b ) implied by quasar intraday variability may be explained by coherent emission, or else by physically implausible bulk relativistic Lorentz factors Γ ≥ 100. Previous theory asserts that various absorption mechanisms will block escape of such coherent, high-brightness sources. Yet this same theory fails to account for laboratory experiments detecting collective emission. Probably this is because present theory is inadequate, and should not be used to rule out collective radiation processes. 相似文献
66.
Governing urban vacancy in post-crash dublin: contested property and alternative social projects 总被引:1,自引:1,他引:0
The scale and severity of property crashes following the global financial crisis has made vacancy a more visible and politically significant feature of cities. Although research has focused on urban experiments in vacant spaces, there has been less emphasis on how the contested property relations around vacancy remake urban governance. In this paper, we argue that debates about vacancy have been a central concern in post-crisis urban governance. In the first part of the paper we draw two conceptual approaches into a dialogue and apply them to an analysis of vacant space: that of Nicholas Blomley on property and Elizabeth Povinelli on “alternative social projects”. In the second part of the paper, we critically analyse how three groups discursively construct the need to “activate” and “re-use” vacant spaces in Dublin: grassroots groups, urban policy-makers, and financial actors. We argue that governing vacancy will be a key feature of post-crisis urbanisation. 相似文献
67.
B. Cesare 《Contributions to Mineralogy and Petrology》1995,122(1-2):25-33
Equilibrium C–O–H fluid speciation calculations predict that graphite will precipitate from initially graphite saturated
fluid inclusions during cooling and exhumation of metamorphic rocks. In the case that no mass is gained or lost by the inclusions,
the original X
O ratio [O/(O+H)] of the fluid phase must be maintained. Given this closed system constraint, the down-temperature progress
of graphite precipitation can easily be monitored as a function of the varible X
O, and produces some effects that are of significance to fluid inclusion studies: 1. Variation of the H2O : CO2 : CH4 relationship in the graphite-saturated COH fluid, namely increase of X
H2
O and decrease of the carbonic fraction; 2. Decrease of fluid density due to precipitation of graphite, which is denser than
the residual fluid; 3. Alteration of the CO2 : CH4 ratio of the fluid, depending on the initial O : H ratio of the fluid: for X
O>1/3, fluids increase their CO2 : CH4 ratio with decreasing temperature, and vice-versa. This implies that the CO2 : CH4 ratio measured at room T will not represent the trapping value, which is in any case closer to unity. As a consequence of density reduction, isochores
extrapolated from densities observed at room temperature do not pass through the pressure-temperature conditions at which
the inclusion was trapped, with pressure underestimates of up to 2 kbar. Actual P-T trapping conditions are located along the equilibrium “bulk isochore” (curve of constant-X
O, constant-volume) of the fluid. Alteration of the CO2 : CH4 ratio is a mechanism by which a CO2-rich or CH4-rich carbonic phase can be formed from aqueous fluids that are slightly off the neutral X
O=1/3 value. Subsequent segregation of this phase from the aqueous counterpart may account for the formation of pure CO2 and CH4 fluids in the upper crust.
Received: 15 March 1995 / Accepted: 1 June 1995 相似文献
68.
18O/16O and14C analysis of deep-sea cores from the Gulf of Mexico revealed a 2.4% isotopic anomaly between 12,000 and 11,000 years ago. This value, together with estimates of the oxygen isotopic composition of ice meltwater and rates of mixing within the Gulf of Mexico indicates that the average yearly discharge of the Mississippi River was between 100,000 and 230,000 m3/s (as compared to 57,000 m3/s for the peak flood of February 17, 1937), with probable yearly peak floods twice as large. Corresponding sea-level rise was between 1 and 2 m per century. 相似文献
69.
Trapping of long water waves that are induced by submarine earthquakes and that attack circular islands is studied by applying a theoretical model (Tinti andVannini, 1994) that is based on the linear shallow water approximation. The solution is computed as the superposition of the eigenmodes of the water basin. The tsunami trapping is seen in terms of the capability of the source to excite the trapped eigenmodes of the basin. The bottom depth dependence around the island is shown to be quite important in determining the trapping capability of the island: a depth profile that is downwardly concave as the distance from the island coasts increases is substantially more efficient in amplifying the incoming waves and in trapping their energy than a profile exhibiting an upward concavity. 相似文献