Natural Hazards - The ability to forecast extreme precipitation events has become increasingly important over the last decades due to their significant impacts on society and properties. In this... 相似文献
The Breves deposit in the Carajás Copper-Gold Belt, Brazil, a member of the Cu-Au-(W-Bi-Sn) group of deposits, contains about 50 Mt of 1.22% Cu, 0.75 g/t Au, 2.4 g/t Ag, 1,200 g/t W, 70 g/t Sn, 175 g/t Mo and 75 g/t Bi. It is hosted by sandstones and siltstones of the Águas Claras Formation (minimum age of 2,681±5 Ma) in the roof zone of a complex, highly altered granite intrusion. The mineralisation is disseminated in a greisenized zone, resulting from alteration of probable monzogranites and syenogranites. The ore-bearing greisen contains abundant xenomorphic quartz in association with Fe-chlorite and muscovite. The gangue assemblage also includes fluorite, tourmaline, and minor amounts of monazite, xenotime, chlorapatite, thorite, zircon, calcite, siderite and bastnäesite. Copper mineralisation is dominated by chalcopyrite associated with pyrite, arsenopyrite, pyrrhotite and molybdenite. Gold particles, in equilibrium with native bismuth, are common as inclusions in chalcopyrite. The greisen contains sub-economic concentrations of tungsten and niobium that are related to the presence of ferberite, qitianlingite and Nb-rutile. SHRIMP II zircon dating of the host granites gives 207Pb/206Pb ages of 1,878±8 and 1,880±9 Ma for two phases, and a combined age of 1,879±6 Ma. SHRIMP II dating of monazite and xenotime grains in late- to post-mineralisation veins gives a combined 207Pb/206Pb age of 1,872±7 Ma, indistinguishable from the ages of the granites. This provides a genetic connection between the Breves deposit and the ca. 1.88 Ga A-type granite magmatism that typifies the Carajás Belt as part of a much larger, intracratonic magmatic province that extends over much of the Amazonian Craton. The recognition of this association has exploration implications, not only for the geophysical signature of the granite roof zones, but also for likely geochemical dispersion around the deposits of this type.Editorial handling: G. Beaudoin 相似文献
This paper presents a thermo‐hydro‐mechanical framework to model the drying behavior of Boom clay. First, the experimental campaign conducted Noémie Prime is briefly presented because it is used to validate the model. The data acquisition and processing is emphasized because of the use of X‐ray microtomography to be able to more accurately compare experimental and numerical strain fields. The different submodels are introduced. Numerical simulations are performed to illustrate the capability of the proposed model to reproduce the observed behavior. Finally, a comprehensive sensitivity study on several key model parameters associated with the water retention curve, and the permeability of the medium, is performed to get a better understanding of the physics behind the coupled model. 相似文献
In the present paper, an ensemble approach is proposed to estimate possible modifications caused by climate changes in the extreme precipitation regime, with the rain gauge Napoli Servizio Idrografico (Naples, Italy) chosen as test case. The proposed research, focused on the analysis of extremes on the basis of climate model simulations and rainfall observations, is structured in several consecutive steps. In the first step, all the dynamically downscaled EURO‐CORDEX simulations at about 12 km horizontal resolution are collected for the current period 1971–2000 and the future period 2071–2100, for the RCP4.5 and the RCP8.5 concentration scenarios. In the second step, the significance of climate change effects on extreme precipitation is statistically tested by comparing current and future simulated data and bias‐correction is performed by means of a novel approach based on a combination of simple delta change and quantile delta mapping, in compliance with the storm index method. In the third step, two different ensemble models are proposed, accounting for the variabilities given by the use of different climate models and for their hindcast performances. Finally, the ensemble models are used to build novel intensity–duration–frequency curves, and their effects on the early warning system thresholds for the area of interest are evaluated. 相似文献
Riassunto Richiamate brevemente le conoscenze fondamentali sulla scintillizzazione stellare, si espongono i principi generali di un procedimento inteso a ricavare elementi d'integrazione alle osservazioni sinottiche per la formulazione del presagio meteorico locale, partendo dalla accurata e sistematica misura della scintillazione stessa. Lo studio ha carattere preliminare, contenendo considerazioni generali la cui applicazione dovrà trovare conferma dallo sviluppo delle relative osservazioni.
Zusammenfassung Nach einem Überblick über die Entwicklung unserer Kenntnissen zur Erklärung des Funkelns der Sterne, gibt der Verf. die allgemeinen Richtlinien einer Methode, welche, stützend auf systematischen Beobachtungen dieser Erscheinung, die synoptischen Verfahren der Wettervorhersage unterstützen und ergänzen kann. Die Schrift gilt als vorläuflge Mitteilung, besonders in Anbetrachtung der Notwendigkeit einer entsprechenden Entwicklung und Verfeinerung der Beobachtungen.
Stochastic optimization methods, such as genetic algorithms, search for the global minimum of the misfit function within a given parameter range and do not require any calculation of the gradients of the misfit surfaces. More importantly, these methods collect a series of models and associated likelihoods that can be used to estimate the posterior probability distribution. However, because genetic algorithms are not a Markov chain Monte Carlo method, the direct use of the genetic‐algorithm‐sampled models and their associated likelihoods produce a biased estimation of the posterior probability distribution. In contrast, Markov chain Monte Carlo methods, such as the Metropolis–Hastings and Gibbs sampler, provide accurate posterior probability distributions but at considerable computational cost. In this paper, we use a hybrid method that combines the speed of a genetic algorithm to find an optimal solution and the accuracy of a Gibbs sampler to obtain a reliable estimation of the posterior probability distributions. First, we test this method on an analytical function and show that the genetic algorithm method cannot recover the true probability distributions and that it tends to underestimate the true uncertainties. Conversely, combining the genetic algorithm optimization with a Gibbs sampler step enables us to recover the true posterior probability distributions. Then, we demonstrate the applicability of this hybrid method by performing one‐dimensional elastic full‐waveform inversions on synthetic and field data. We also discuss how an appropriate genetic algorithm implementation is essential to attenuate the “genetic drift” effect and to maximize the exploration of the model space. In fact, a wide and efficient exploration of the model space is important not only to avoid entrapment in local minima during the genetic algorithm optimization but also to ensure a reliable estimation of the posterior probability distributions in the subsequent Gibbs sampler step. 相似文献
Acoustic emission (AE) technique that is capable of diagnosing the failure process of stressed materials has rarely reported its application to sandy soils subjected to triaxial compression. In this paper, drained triaxial compression tests incorporating with a high-performance AE measurement system were conducted for dry sands with different confining stresses and initial relative densities. Generally, an increased confining stress or initial relative density generates more acoustic emissions, while there also exist exceptions due to different failure patterns. A good resemblance between stress–strain and AE hit rate–strain relations was observed, and power functions between the mechanical parameters and AE hit rate were well established regardless of different confining stresses and initial relative densities. Besides, the behavioral state of yield and peak during compression could be also evaluated by AE hit rate, compared with conventional stress–strain determination. Particularly, the peak AE hit rate is found not always synchronous to but fluctuating at around the peak stress depending on different failure patterns, which might provide beneficial insights into the incipient failure of sands. The present good consistencies suggest that AE characteristics could be used as alternative parameters to evaluate and even predict the mechanical behavior of dry sands.