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911.
912.
Daniele Pedretti Roger D. Beckie 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(7):1933-1946
Two-station pairing approaches are routinely used to infill missing information in incomplete rainfall databases. We evaluated the performance of three simple methodologies to reconstruct incomplete time series in presence of variable nonlinear correlation between data pairs. Nonlinearity stems from the statistics describing the marginal peak-over-threshold (POT) values of rainfall events. A Monte Carlo analysis was developed to quantitatively assess expected errors from the use of chronological pairing (CP) with linear and nonlinear regression and frequency pairing (FP). CP is based on a priori selection of regression functions, while FP is based on matching the probability of non-exceedance of an event from one time series with the probability of non-exceedance of a similar event from another time series. We adopted a generalized Pareto (GP) model to describe POT events, and a t-copula algorithm to generate reference nonlinearly correlated pairs of random temporal distributions distributed according with the GP model. The results suggest that the optimal methodology strongly depends on GP statistics. In general, CP seems to provide the lowest errors when GP statistics were similar and correlation became linear; we found that a power-2 function performs well for the selected statistics when the number of missing points is limited. FP outperforms the other methods when POT statistics are different and variables are markedly nonlinearly correlated. Ensemble-based results seem to be supported by the analysis of observed precipitation at two real-world gauge stations. 相似文献
913.
In the frame of the UPStrat-MAFA “Urban Disaster Prevention Strategies Using MAcroseismic Fields and FAult Sources” project, seismic hazard has been assessed in Portugal in terms of macroseismic intensity. Assessment has been performed by using a probabilistic approach based on the statistical analysis of local seismic histories (i.e., the record of seismic effects at each locality) performed by a new version of the SASHA code (D’Amico and Albarello in Res Lett 79(5):663–671, 2008) on purpose modified to account for this specific area of study. Local seismic histories are reconstructed by considering documented effects or indirect estimates deduced from epicentral information or numerical simulations. All these pieces of evidence are combined taking into account relevant uncertainty and statistical completeness of information locally available. Distribution of expected maximum intensity (i.e., the maximum intensity characterized by a fixed exceedance probability for a exposure time of 50 years) has been obtained and compared with the one deduced from alternative approaches. 相似文献
914.
Field data, collected by the authors during winter expedition studies in Kaliningrad Bay, are analyzed. Notwithstanding the presence of ice cover, considerable advective processes are shown to be taking place in the bay. Seawater enters the bay, spreading in the bottom horizon all over the water area. Suspended sediment concentration in under-ice period is on the average three times less than that in the ice-free period. The space and time variations of its quantitative and qualitative composition under ice are mostly governed by two factors—the effect of the sea and river runoff. The values of vertical fluxed of eolian material to the bay surface in winter vary from 0.5 to 2.9 with the average of 1.7 mg m–2 day–1. 相似文献
915.
A problem of convective cooling of both freshwater and saltwater lake is formulated. A transient one-dimensional turbulent model with variable layer depth is proposed to describe the process of freezing. The dependence of layer depth on time is determined by a universal equation describing the propagation of Deardorff convective layer. A combination of the main form of equations of Kolmogorov–Obukhov theory and available experimental data is shown to allow the construction of a universal profile of turbulent exchange coefficient, depending on the height. 相似文献
916.
The age and thermal history of Cerro Rico de Potosi, Bolivia 总被引:1,自引:0,他引:1
C. G. Cunningham R. E. Zartman E. H. McKee R. O. Rye C. W. Naeser O. Sanjinés V G. E. Ericksen F. Tavera V 《Mineralium Deposita》1996,31(5):374-385
Cerro Rico de Potosi, Bolivia, is the world’s largest silver deposit and has been mined since the sixteenth century for silver,
and for tin and zinc during the twentieth century, together with by-product copper and lead. The deposit consists primarily
of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and
explosion breccia. The deposit is compositionally and thermally zoned, having a core of cassiterite, wolframite, bismuthinite,
and arsenopyrite surrounded by a peripheral, lower-temperature mineral assemblage consisting principally of sphalerite, galena,
lead sulfosalt, and silver minerals. The low-temperature assemblage also was superimposed on the high-temperature assemblage
in response to cooling of the main hydrothermal system. Both the dacite dome and the ore fluids were derived from a larger
magmatic/hydrothermal source at depth. The dome was repeatedly fractured by recurrent movement on the fault system that guided
its initial emplacement. The dome was extruded at 13.8±0.2 Ma (2σ), based on U-Th-Pb dating of zircon. Mineralization and
alteration occurred within about 0.3 my of dome emplacement, as indicated by a 40Ar/39Ar date of 13.76±0.10 Ma (1σ) for sericite from the pervasive quartz-sericite-pyrite alteration associated with the main-stage,
high-temperature, mineralization. The last thermal event able to reset zircon fission tracks occurred no later than 12.5±1.1 Ma
(1σ), as indicated by fission-tract dating. Minor sericite, and magmatic-steam alunite veins, were episodically formed around
11 Ma and between 8.3 and 5.7 Ma; the younger episodes occurring at the time of extensional fracturing at Cerro Rico and widespread
volcanism in the adjacent Los Frailes volcanic field. None of these younger events appear to be significant thermal/mineralizing
events; the exceptionally flat thermal release pattern of 39Ar from sericite and the results of the fission-tract dating of zircon show that none of the younger events was hot enough,
and lasted long enough, to cause significant loss of Ar or annealing of zircon fission tracks. U-Th-Pb dating of zircon cores
indicates a Precambrian progenitor for some zircons, and REE analyses of dated samples of hydrothermally altered dacite show
the presence of a prominent positive Eu anomaly, which constrains interpretations of the origin and evolution of the magmatic/hydrothermal
system.
Received: 14 October 1995/Accepted: 29 January 1996 相似文献
917.
Studies of macrophytes in the coastal zone of the Artic Seas, including the White Sea, have shown the essential role of these
algae in the activity of the coastal half-latitude ecosystems. In summer, during the macrophyte reproduction period, a great
number of reproduction products are released into the water. For a short time, this considerably affects the ratio of the
nanoplankton in the populations that inhibit the vast and shallow coastal areas. At different coastal sites in Chernorechenskaya
Inlet, Kadalaksha Bay, during the period of intensive reproduction of Ascophyllum nodosum and Fucus vesiculosus, 42 plankton samples were collected in 2005. During this period the concentration of antherozoids in the water reached 55000
cells/ml (216 mg C/m3). The number of eggs was within the range of 0.05–0.7 cells/ml. The proportion of antherozoids in the total biomass of nanoplankton
varied at different coastal sites from 0.37 to 99%, with a mean of 46% for the reproduction period of A. nodosum, and only 7% for the reproduction period of F. vesiculosus. As was shown by counts of F. vesiculosus female gametes in sedimentation traps, 1 m2 of the macrophyte bed (assuming 100% coverage) produces 18000–108000 eggs per day (0.33–2 mg C). The calculated flux of the
reproductive material from the brown algae beds to the coastal water shows good agreement with the sample counts. 相似文献
918.
919.
The magnetic-field distribution outside a flat, infinitely conductive unbounded disk in the field of a point magnetic dipole is determined. A relationship is established between the problem of magnetic-field determination and the problem of the flow of an ideal incompressible fluid around an infinitely thin disk. 相似文献
920.
Churyumov Klim I. Luk'yanyk Igor V. Berezhnoi Alexei A. Chavushyan Vahram H. Sandoval Lourdes S. Palma Alejandro A. 《Earth, Moon, and Planets》2002,90(1-4):361-368
We present a preliminary analysis of medium resolution optical spectra of comet C/2000 WM1 (LINEAR) obtained on 22 November
2001. Theemission lines of the molecules C2, C3, CN, NH2,H2O+ and presumably CO (Asundi and triplet bands) and C2
-were identified in these spectra. By analysing the brightnessdistributions of the C2, C3, CN emission lines along theslit of the spectrograph we determined some physical parameters of theseneutrals, such as their
lifetimes and expansion velocities inthe coma. The Franck–Condon factors for the CO Asundi bands and C2
- bands were calculated using a Morse potential model. 相似文献