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51.
Moment equation methods are popular and powerful tools for modeling transport processes in randomly heterogeneous porous media, but the application of these methods to advection-dispersion equations often leads to erroneous oscillations. Perturbative methods, required to close systems of moment equations, become inaccurate for large perturbations; however, little quantitative theory exists for determining when this occurs for advection-dispersion equations. We consider three different methods (asymptotic approximation, Eulerian truncation, and iterative solution) for closing and solving advection-dispersion moment equations describing transport in stratified porous media with random permeability. We obtain approximate analytical expressions for time above which the asymptotic approximation to the mean diverges, in particular quantifying the impact that dispersion has on delaying—but not eliminating—divergence. We demonstrate that Eulerian truncation and iterative solution methods do not eliminate divergent behavior either. Our divergence criteria provide a priori estimates that signal a warning to the practitioner of stochastic advection-dispersion equations to carefully consider whether to apply perturbative approaches. 相似文献
52.
Alexandre de Oliveira Chaves 《Central European Journal of Geosciences》2013,5(3):354-373
New evidence supported by petrography (including mineral chemistry), lithogeochemistry, U-Pb geochronology by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and physicochemical study of fluid and melt inclusions by LA-ICP-MS and microthermometry, point to an orogenic setting of Lagoa Real (Bahia-Brazil) involving uraniferous mineralization. Unlike the previous models in which uraniferous albitites represent Na-metasomatised 1.75 Ga anorogenic granitic rocks, it is understood here that they correspond to metamorphosed sodium-rich and quartz-free 1.9 Ga late-orogenic syenitic rocks (Na-metasyenites). These syenitic rocks are rich not only in albite, but also in U-rich titanite (source of uranium). The interpretation of geochemical data points to a petrogenetic connection between alkali-diorite (local amphibolite protolith) and sodic syenite by fractional crystallization through a transalkaline series. This magmatic differentiation occurred either before or during shear processes, which in turn led to albitite and amphibolite formation. The metamorphic reactions, which include intense recrystallization of magmatic minerals, led uraninite to precipitate at 1.87 Ga under Oxidation/Reduction control. A second population of uraninites was also generated by the reactivation of shear zones during the 0.6 Ga Brasiliano Orogeny. The geotectonic implications include the importance of the Orosirian event in the Paramirim Block during paleoproterozoic S?o Francisco Craton edification and the influence of the Brasiliano event in the Paramirim Block during the West-Gondwana assembly processes. The regional microcline-gneiss, whose protolith is a 2.0 Ga syn-collisional potassic granite, represents the albitite host rock. The microcilne-gneiss has no petrogenetic association to the syenite (albitite protolith) in magmatic evolutionary terms. 相似文献
53.
Gabriel A. Pinto Adrien Tavernier Jérôme Gattacceca Alexandre Corgne Millarca Valenzuela Béatrice Luais Laura Flores Felipe Olivares Yves Marrocchi 《Meteoritics & planetary science》2024,59(2):351-367
In the last 15 years, more than 2700 meteorites have been recovered and officially classified from the Atacama Desert. Although the number of meteorites collected in the Atacama has risen, the physical and climatic properties of the dense collection areas (DCAs) have not been fully characterized. In this article, we compiled the published data of all classified meteorites found in the Atacama Desert to (i) describe the distribution by meteorite groups, (ii) compare the weathering degree of chondrites among different Atacama DCAs and other hot and cold deserts, and (iii) determine the preservation conditions of chondrites in the main Atacama DCAs in relation with the local climatic conditions. The 35 DCAs so far identified in the Atacama Desert are located in three main morphotectonic units: The Coastal Range (CR), Central Depression (CD), and Pre-Andean Range/Basement. A comparison with reported weathering data from other cold and hot deserts indicates that the mean terrestrial weathering of Atacama chondrites (W1–2), displays less alteration than other hot deserts (W2–3) and resembles the weathering distribution of the Antarctic meteorites (W1–2). The highest abundance of Atacama chondrites with low weathering (≤W2) is localized in the CD (78.8%, N = 1435), which is protected from the coastal fog influence and seasonal rainfalls and displays the oldest surfaces in the Atacama Desert. The morphogenetic classification based on present-day temperatures and precipitations of the main Atacama DCAs reveals similar regional/subregional climatic conditions in the most productive areas and a truly productive surface for meteorite recovery between 5% and 58% of the quadrangles formally defined for each Atacama DCA. Our morphogenetic classification lacks consideration of some meteorological parameters such as the coastal fog, so it cannot fully explain the differences in weathering patterns among CR chondrites. Future studies of chondrite preservation in the Atacama DCAs should consider other meteorological variables such as relative humidity, specific humidity, or dew point, in combination with exposure ages of meteorites and its surfaces. 相似文献
54.
Alexandre C. M. Correia Jacques Laskar Fran?ois Farago Gwena?l Bou�� 《Celestial Mechanics and Dynamical Astronomy》2011,111(1-2):105-130
We investigate the dynamical evolution of hierarchical three-body systems under the effect of tides, when the ratio of the orbital semi-major axes is small and the mutual inclination is relatively large (greater than 20°). Using the quadrupolar non-restricted approximation for the gravitational interactions and the viscous linear model for tides, we derive the averaged equations of motion in a vectorial formalism which is suitable to model the long-term evolution of a large variety of exoplanetary systems in very eccentric and inclined orbits. In particular, it can be used to derive constraints for stellar spin-orbit misalignment, capture in Cassini states, tidal-Kozai migration, or damping of the mutual inclination. Because our model is valid for the non-restricted problem, it can be used to study systems of identical mass or for the outer restricted problem, such as the evolution of a planet around a binary of stars. Here, we apply our model to various situations in the HD 11964, HD 80606, and HD 98800 systems. 相似文献
55.
Long‐term sediment yield from a small catchment in southern Brazil affected by land use and soil management changes 下载免费PDF全文
Jean P.G. Minella Gustavo H. Merten Claúdia A.P. Barros Rafael Ramon Alexandre Schlesner Robin T. Clarke Michele Moro Leandro Dalbianco 《水文研究》2018,32(2):200-211
Sediments produced from eroding cultivated land can cause on‐site and off‐site effects that cause considerable economic and social impacts. Despite the importance of soil conservation practices (SCP) for the control of soil erosion and improvements in soil hydrological functions, limited information is available regarding the effects of SCP on sediment yield (SY) at the catchment scale. This study aimed to investigate the long‐term relationships between SY and land use, soil management, and rainfall in a small catchment. To determine the effects of anthropogenic and climatic factors on SY, rainfall, streamflow, and suspended sediment concentration were monitored at 10‐min intervals for 14 years (2002–2016), and the land use and soil management changes were surveyed annually. Using a statistical procedure to separate the SY effects of climate, land use, and soil management, we observed pronounced temporal effects of land use and soil management changes on SY. During the first 2 years (2002–2004), the land was predominantly cultivated with tobacco under a traditional tillage system (no cover crops and ploughed soil) using animal traction. In that period, the SY reached approximately 400 t·km?2·year?1. From 2005 to 2009, a soil conservation programme introduced conservation tillage and winter cover crops in the catchment area, which lowered the SY to 50 t·km?2·year?1. In the final period (2010–2016), the SCP were partially abandoned by farmers, and reforested areas increased, resulting in an SY of 150 t·km?2·year?1. This study also discusses the factors associated with the failure to continue using SCP, including structural support and farmer attitudes. 相似文献
56.
Benoît Dewandel Yvan Caballero Jérôme Perrin Alexandre Boisson Fabrice Dazin Sylvain Ferrant Subash Chandra Jean‐Christophe Maréchal 《水文研究》2017,31(12):2277-2295
An innovative approach for regionalizing the 3‐D effective porosity field is presented and applied to two large, overexploited, and deeply weathered crystalline aquifers located in southern India. The method derives from earlier work on regionalizing a 2‐D effective porosity field in that part of an aquifer where the water table fluctuates, which is now extended over the entire aquifer using a 3‐D approach. A method based on geological and geophysical surveys has also been developed for mapping the weathering profile layers (saprolite and fractured layers). The method for regionalizing 3‐D effective porosity combines water table fluctuation and groundwater budget techniques at various cell sizes with the use of satellite‐based data (for groundwater abstraction), the structure of the weathering profile, and geostatistical techniques. The approach is presented in detail for the Kudaliar watershed (983 km2) and tested on the 730 km2 Anantapur watershed. At watershed scale, the effective porosity of the aquifer ranges from 0.5% to 2% in Kudaliar and between 0.3% and 1% in Anantapur, which agrees with earlier works. Results show that (a) depending on the geology and on the structure of the weathering profile, the vertical distribution of effective porosity can be very different and that the fractured layers in crystalline aquifers are not necessarily characterized by a rapid decrease in effective porosity and (b) that the lateral variations in effective porosity can be larger than the vertical ones. These variations suggest that within a same weathering profile, the density of open fractures and/or degree of weathering in the fractured zone may significantly vary from a place to another. The proposed method provides information on the spatial distribution of effective porosity that is of prime interest in terms of flux and contaminant transport in crystalline aquifers. Implications for mapping groundwater storage and scarcity are also discussed, which should help in improving groundwater resource management strategies. 相似文献
57.
The recent study and classification of over 200 cadastral maps created in the nineteenth century in Catalonia have provided a valuable source of information about the agricultural landscape country’s past, but by linking them with data recorded in tax books known as amillaramientos, it is possible to gain a better knowledge of the past. By applying this method to the 1861 cadastral map of Horta and its corresponding amillaramiento, a planimetric map showing the land use distribution in the town was created. The resulting land use map was subsequently overlaid on top of a digital elevation model to create 3D visualizations which show the altitudinal distribution of crops and other features. Finally, the article explores a way of distributing the results online, making them accessible to the public and increasing the research impact of future findings. Therefore, the method described in this article allows the systematic recreation and distribution of past landscapes by using Catalan cadastral maps of the nineteenth century, something which can help enrich the scientific knowledge of many disciplines. 相似文献
58.
Effects of the October 25, 2010, Mentawai tsunami in La Réunion Island (France): observations and crisis management 总被引:1,自引:1,他引:0
On October 25, 2010, a Mw = 7.7 magnitude earthquake was recorded in the Kepulauan Mentawai archipelago, in Indonesia. Following the earthquake, the Pacific Tsunami Warning Center issued a tsunami bulletin to the countries of the Indian Ocean informing them that a local tsunami watch was in effect for Indonesia. La Réunion Island, a French territory located 5,000 km southwest of the seismic source, did not trigger its tsunami early warning protocol, but did suffer the impact of this tsunami 7h20 post-earthquake. This paper presents the post-tsunami survey conducted in La Réunion Island a few days after the event, providing run-up measurements that reach 1.72 m locally as well as information about the material losses and the crisis management. It provides a time sequence of the observations along the coast and the reactions of the population and authorities in dealing with this crisis. This paper also shows the local authorities’ lack of action in managing this event—thus increasing human and material vulnerabilities—the consequences for victims and the impact on the credibility of the local early warning system. These results provide geophysicists with information to better describe the source of this tsunami through far-field inversion and provide local decision makers with a comprehensive assessment of the weaknesses of the local early warning system and protocols. 相似文献
59.
Rainfall on the subtropical east coast of Australia has declined at up to 50?mm per decade since 1970. Wavelet analysis is used to investigate eight station and four station-averaged rainfall distributions along Australia??s subtropical east coast with respect to the El Ni?o-Southern Oscillation (ENSO), the inter-decadal Pacific oscillation (IPO) and the southern annular mode (SAM). The relationships are examined further using composite atmospheric circulation anomalies. Here we show that the greatest rainfall variability occurs in the 15?C30?year periodicity of the 1948?C1975 or ??cool?? phase of the IPO when the subtropical ridge is located sufficiently poleward for anomalous moist onshore airflow to occur together with high ENSO rainfall variability and high, negative phase, SAM variability. Thus, the mid-latitude westerlies are located at their most equatorward position in the Australian region. This maximizes tropospheric interaction of warm, moist tropical air with enhanced local baroclinicity over the east coast, and hence rainfall. 相似文献
60.
Alexandre Raphael Cabral Michael Wiedenbeck Francisco Javier Rios Ant?nio Augusto Seabra Gomes Jr Orlando Garcia Rocha Filho Richard David Jones 《Mineralium Deposita》2012,47(4):411-424
Talc mineralisation occurs as hematite–talc schist between soft hematite ore and dolomitic itabirite at Gongo Soco, Quadrilátero
Ferrífero of Minas Gerais, Brazil. The hematite–talc schist and soft hematite have a prominent tectonic foliation of tabular
hematite. Tabular hematite without preferential orientation is superimposed on the tectonic foliation. The talcose schist
is enriched in F and has a constant Fe/S ratio. Electron-microprobe analyses indicate trace amounts of S in different generations
of hematite. The whole-rock Fe/S ratio possibly represents sulfate S from hematite-hosted fluid inclusions. Fluid inclusions
in foliation-overprinting hematite and chlorite geothermometry from talcose rocks suggest, respectively, temperatures from
<200°C to ~300°C. Tourmaline, a rarely observed mineral in the hematite–talc schist, belongs to the alkali group and falls
in the dravite compositional field. Boron-isotope determinations of tourmaline crystals, using secondary ion mass spectrometry,
vary from −20‰ to −12‰ δ11B. This compositional isotopic range and the tourmaline chemical composition suggest a meta-evaporitic origin. A non-marine
evaporitic setting is the most likely source of acidic, highly oxidising fluids, which resulted in the abundant F-bearing
talc and the presence of otherwise immobile Ti in hematite. Oxidising brines were channelled along shear zones and converted
dolomitic itabirite into the Gongo Soco soft hematite and the talc mineralisation. The latter is envisaged as the hydrothermal
wall-rock alteration of dolomitic itabirite, which gave rise to the soft hematite ore. 相似文献