Crossover from Nonlinearity Controlled to Heterogeneity Controlled Mixing in Two-Phase Porous Media Flows     

Frederico Furtado  Felipe Pereira 《Computational Geosciences》2003,7(2):115-135

We use high resolution Monte Carlo simulations to study the dispersive mixing in two-phase, immiscible, porous media flow that results from the interaction of the nonlinearities in the flow equations with geologic heterogeneity. Our numerical experiments show that distinct dispersive regimes occur depending on the relative strength of nonlinearity and heterogeneity. In particular, for a given degree of multiscale heterogeneity, controlled by the Hurst exponent which characterizes the underlying stochastic model for the heterogeneity, linear and nonlinear flows are essentially identical in their degree of dispersion, if the heterogeneity is strong enough. As the heterogeneity weakens, the dispersion rates cross over from those of linear heterogeneous flows to those typical of nonlinear homogeneous flows.  相似文献   

The abundance of ammonium in the granites of central Spain,and the behaviour of the ammonium ion during anatexis and fractional crystallization     

A. Hall  M. D. Pereira  F. Bea 《Mineralogy and Petrology》1996,56(1-2):105-123

Summary The granites of the Sistema Central Espanol are richer in ammonium than those of most other regions, and have a mean NH₄ ⁺ content of 84 ppm (range = 1–243 ppm). Among the possible causes for the high level of ammonium, a high proportion of organic-rich pelitic protolith and reducing conditions during anatexis are considered to be the most significant. The behaviour of the ammonium ion during magmatic differentiation is discussed by reference to its distribution in the Pedrobernardo layered intrusion: ammonium is depleted in the final liquid fraction, but there is no relative fractionation of NH₄ ⁺ and K⁺. The depletion of the melt in NH₄ ⁺ during crystallization is attributed to its removal by biotite and to a lesser extent by K-feldspar. The behaviour of the ammonium ion during anatexis is discussed with reference to the Peña Negra migmatite complex. It is shown that large amounts of NH₄ ⁺ are present in these high grade metamorphic rocks, and that NH₄ ⁺ is preferentially partitioned into the restite fraction during partial melting. These relationships are attributed to the preferential incorporation of NH₄ ⁺ into potassic host minerals in the order: biotite > muscovite > K-feldspar.

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Ammonium in Zentralspanischen Graniten, und das Verhalten des Ammonium-Ions während Anatexis und fraktionierter Kristallisation

Zusammenfassung Die Granite des Sistema Central Espanol sind reicher an Ammonium als die der meisten anderen Regionen, und haben einen durchschnittlichen NH₄ ⁺ Gehalt von 84 ppm (von 1-243 ppm). Der hohe Ammoniumgehalt könme auf einen hohen Anteil peiitischer Ausgangsgesteine, die reich an organischen Material sind, and auf reduzierende Bedingungen während der Anatexis zurückgehen. Das Verhalten des Ammonium-Ions während magmatischer Differentiation wind in Hinblick seiner Verteilung in der geschichteten Intrusion von Pedrobernardo diskutiert: Ammonium ist in der finalen Schmelzfraktion angereichert, aber es gibt keine relative Fraktionierung von NH₄ ⁺ and K⁺. Die Verarmung der Schmelze an NH₄ ⁺ wahrend der Kristallisation geht darauf zurück, daß NH₄ ⁺ von Biotit and in einem geringen Ausmaß von K-Feldspat aufgenommen wird. Das Verhalten des Ammonium-Ions während der Anatexis wird am Peña Negra Migmatit-Komplex diskutiert. Es zeigt rich, daß große Mengen von NH₄ ⁺ in diesen hochgradig metamorphen Gesteinen vorkommen, and das NH₄ ⁺ während teilweiser Aufschmelzung vorzugsweise in der Restit-Fraktion angereichert wird. Diese Beziehungen gehen auf die vorzugsweise Aufnahme von NH₄ ⁺ in Kali-führenden Gastmineralen zurück, and zwar in folgender Ordnung: Biotit > Muskovit > K-Feldspat.

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With 5 Figures  相似文献   

The impact of hydrological changes on travertine deposits related to thermal springs in the Pamukkale area (SW Turkey)   总被引：2，自引：0，他引：2  

Dilsiz  Cüneyt  Marques  José Manuel  Carreira  Paula Maria Mimo 《Environmental Geology》2004,45(6):808-817

Pamukkale thermal waters (35 °C), exhibiting calcium-bicarbonate-sulfate composition and high carbon dioxide concentration, are of a predominantly meteoric origin. The meteoric fluid, circulating through faults and fractures, is heated by magmatic intrusions at great depth, and ascends from deep reservoirs to the surface. Mixing with relatively cold groundwater in the near surface zone promotes different saturation conditions with respect to calcium carbonate that later precipitates at depth and/or the surface. Dissolution-deposition processes of calcium carbonate both at surface and depth environments may help to reconstruct past climate direction in the field. During wet climate conditions a high-rate of calcium carbonate accumulation would be expected to occur at the surface because thermal fluid would be under-saturated with respect to calcium carbonate at depth because of a relatively higher mixing ratio with cold groundwater. During dry climate conditions the thermal fluid would be super-saturated at depth because of the highly acidic environment. Hydrometeorological studies reveal that the annual precipitation at the Pamukkale hydrothermal field tends to decrease with time. This climatic change in the area was also detected from geological records. While humid climate conditions prevailed during the late Quaternary, the area has recently been affected by arid/semi-arid climate conditions, followed by some episodic transitions. This study has shown how the system has possibly reacted to different climate conditions since antiquity.  相似文献   

Long‐term monitoring of a mercury contaminated estuary (Ria de Aveiro,Portugal): the effect of weather events and management in mercury transport          下载免费PDF全文

J. P. Coelho  P. Pato  B. Henriques  A. Picado  A. I. Lillebø  J. M. Dias  A. C. Duarte  M. E. Pereira  M. A. Pardal 《水文研究》2014,28(2):352-360

The main aim of this research was to assess the mercury transport from an estuarine basin with a background of anthropogenic contamination during a spring tidal cycle (year 2009) and compare it with two previous tidal cycles (years 1994 and 1999), as part of a long‐term monitoring program. Results showed that effective mercury transport occurs both in the dissolved and particulate fractions (0.18 and 0.20 kg per tidal cycle, respectively), and despite an overall decrease in environmental contamination, results more than double previous findings on particulate transport in the system. These findings result essentially from changes in the tidal prism (net export of 2 million m³ of water), given that both dissolved and particulate concentrations did not increase over time. Hydrodynamic simulations were performed to evaluate the effect of physical disturbance (dredging) and weather events (increased freshwater flow) in these processes, and results suggest the increased freshwater flow into the system as the main forcing function for the mercury transport increment. These results highlight the importance of long‐term monitoring programs, since despite an overall improvement in local contamination levels, the enhancement of transport processes through hydrological changes increases environmental pressure away from the contamination source. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Provenance of Holocene beach sand in the Western Iberian margin: the use of the Kolmogorov–Smirnov test for the deciphering of sediment recycling in a modern coastal system          下载免费PDF全文

Manuel Francisco Pereira  Luís Albardeiro  Cristina Gama  Martim Chichorro  Mandy Hofmann  Ulf Linnemann 《Sedimentology》2016,63(5):1149-1167

Detrital zircons from Holocene beach sand and igneous zircons from the Cretaceous syenite forming Cape Sines (Western Iberian margin) were dated using laser ablation – inductively coupled plasma – mass spectrometry. The U–Pb ages obtained were used for comparison with previous radiometric data from Carboniferous greywacke, Pliocene–Pleistocene sand and Cretaceous syenite forming the sea cliff at Cape Sines and the contiguous coast. New U–Pb dating of igneous morphologically simple and complex zircons from the syenite of the Sines pluton suggests that the history of zircon crystallization was more extensive (ca 87 to 74 Ma), in contrast to the findings of previous geochronology studies (ca 76 to 74 Ma). The U–Pb ages obtained in Holocene sand revealed a wide interval, ranging from the Cretaceous to the Archean, with predominance of Cretaceous (37%), Palaeozoic (35%) and Neoproterozoic (19%) detrital‐zircon ages. The paucity of round to sub‐rounded grains seems to indicate a short transportation history for most of the Cretaceous zircons (ca 95 to 73 Ma) which are more abundant in the beach sand that was sampled south of Cape Sines. Comparative analysis using the Kolmogorov–Smirnov statistical method, analysing sub‐populations separately, suggests that the zircon populations of the Carboniferous and Cretaceous rocks forming the sea cliff were reproduced faithfully in Quaternary sand, indicating sediment recycling. The similarity of the pre‐Cretaceous ages (>ca 280 Ma) of detrital zircons found in Holocene sand, as compared with Carboniferous greywacke and Pliocene–Pleistocene sand, provides support for the hypothesis that detritus was reworked into the beach from older sedimentary rocks exposed along the sea cliff. The largest percentage of Cretaceous zircons (<ca 95 Ma) found in Holocene sand, as compared with Pliocene–Pleistocene sand (secondary recycled source), suggests that the Sines pluton was the one of the primary sources that became progressively more exposed to erosion during Quaternary uplift. This work highlights the application of the Kolmogorov–Smirnov method in comparison of zircon age populations used to identify provenance and sediment recycling in modern and ancient detrital sedimentary sequences.  相似文献   

Using a regional numerical weather prediction model for GNSS positioning over Brazil     

Daniele Barroca Marra Alves  Luiz Fernando Sapucci  Haroldo Antonio Marques  Eniuce Menezes de Souza  Tayná Aparecida Ferreira Gouveia  Jackes Akira Magário 《GPS Solutions》2016,20(4):677-685

The global navigation satellite system (GNSS) can provide centimeter positioning accuracy at low costs. However, in order to obtain the desired high accuracy, it is necessary to use high-quality atmospheric models. We focus on the troposphere, which is an important topic of research in Brazil where the tropospheric characteristics are unique, both spatially and temporally. There are dry regions, which lie mainly in the central part of the country. However, the most interesting area for the investigation of tropospheric models is the wet region which is located in the Amazon forest. This region substantially affects the variability of humidity over other regions of Brazil. It provides a large quantity of water vapor through the humidity convergence zone, especially for the southeast region. The interconnection and large fluxes of water vapor can generate serious deficiencies in tropospheric modeling. The CPTEC/INPE (Center for Weather Forecasting and Climate Studies/Brazilian Institute for Space Research) has been providing since July 2012 a numerical weather prediction (NWP) model for South America, known as Eta. It has yield excellent results in weather prediction but has not been used in GNSS positioning. This NWP model was evaluated in precise point positioning (PPP) and network-based positioning. Concerning PPP, the best positioning results were obtained for the station SAGA, located in Amazon region. Using the NWP model, the 3D RMS are less than 10 cm for all 24 h of data, whereas the values reach approximately 60 cm for the Hopfield model. For network-based positioning, the best results were obtained mainly when the tropospheric characteristics are critical, in which case an improvement of up to 7.2 % was obtained in 3D RMS using NWP models.  相似文献   

Observer presence may alter the behaviour of reef fishes associated with coral colonies          下载免费PDF全文

Pedro Henrique Cipresso Pereira  Isabela Carolina Silva Leal  Maria Elisabeth de Araújo 《Marine Ecology》2016,37(4):760-769

Although underwater visual census (UVC) is the most frequently used technique for quantifying reef fish assemblages, remote video analysis has been gaining attention as a potential alternative. In the South Atlantic Ocean, Millepora spp. (class Hydrozoa) are the only branching coral species; however, little is known about the ecological role that they play for reef fish communities. We compared these two observation methods (remote video and UVC) to estimate reef fish abundance and species richness associated with colonies of the fire‐coral Millepora alcicornis at Tamandaré Reefs, Northeast Brazil. Additionally, the two different techniques were used to compare species behaviour in association with fire‐corals in order to examine the biases associated with each technique and provide useful information for behavioural ecologists studying fish–coral associations. There were no differences in reef fish abundance or species richness sampled by remote video or UVC. However, a significant difference in the behaviour of associated fish was recorded between the two methods. In the presence of a diver carrying out a UVC, fish were observed spending more time sheltered amongst the coral branches compared with passively swimming on coral colonies with the remote video technique. Specifically, on the remote video recordings agonistic interactions between fish and passive swimming accounted for 33.3% and 22.2% of the census time, respectively. By comparison, when observed by a diver fish spent 34.8% of their time sheltering amongst the coral branches. We demonstrate that both techniques are similarly effective for recording fish abundance and species richness associated with fire‐corals. However, differences were observed in the ability of each method to detect the behaviour of coral‐associated fishes. Our findings show that behavioural ecologists studying complex fish–coral associations need to ensure that their aims are clearly defined and that they choose the most appropriate technique for their study in order to minimize methodological biases.  相似文献   

High-dimensional geostatistical history matching     

João Carneiro  Leonardo Azevedo  Maria Pereira 《Computational Geosciences》2018,22(2):607-622

Hydrocarbon reservoir modelling and characterisation is a challenging subject within the oil and gas industry due to the lack of well data and the natural heterogeneities of the Earth’s subsurface. Integrating historical production data into the geo-modelling workflow, commonly designated by history matching, allows better reservoir characterisation and the possibility of predicting the reservoir behaviour. We present herein a geostatistical-based multi-objective history matching methodology. It starts with the generation of an initial ensemble of the subsurface petrophysical property of interest through stochastic sequential simulation. Each model is then ranked according the match between its dynamic response, after fluid flow simulation, and the observed available historical production data. This enables building regionalised Pareto fronts and the definition of a large ensemble of optimal subsurface Earth models that fit all the observed production data without compromising the exploration of the uncertainty space. The proposed geostatistical multi-objective history matching technique is successfully implemented in a benchmark synthetic reservoir dataset, the PUNQ-S3, where 12 objectives are targeted.  相似文献   

Three-dimensional numerical and analytical study of horizontal group of square anchor plates in sand     

Hicham Mokhbi  Mekki Mellas  Abdelhak Mabrouki  Jean-Michel Pereira 《Acta Geotechnica》2018,13(1):159-174

In this paper, numerical and analytical methods are used to evaluate the ultimate pullout capacity of a group of square anchor plates in row or square configurations, installed horizontally in dense sand. The elasto-plastic numerical study of square anchor plates is carried out using three-dimensional finite element analysis. The soil is modeled by an elasto-plastic model with a Mohr–Coulomb yield criterion. An analytical method based on a simplified three-dimensional failure mechanism is developed in this study. The interference effect is evaluated by group efficiency η, defined as the ratio of the ultimate pullout capacity of group of N anchor plates to that of a single isolated plate multiplied by number of plates. The variation of the group efficiency η was computed with respect to change in the spacing between plates. Results of the analyses show that the spacing between the plates, the internal friction angle of soil and the installation depth are the most important parameters influencing the group efficiency. New equations are developed in this study to evaluate the group efficiency of square anchor plates embedded horizontally in sand at shallow depth (H = 4B). The results obtained by numerical and analytical solutions are in excellent agreement.  相似文献   

Characterization and rehabilitation of the “Porta Férrea” stone materials,University of Coimbra,Portugal     

Lídia Catarino  Francisco P. S. C. Gil  Mário Quinta-Ferreira  Fernando Marques 《Environmental Earth Sciences》2018,77(11):416

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