Salinity effect on the liquid limit of soils     

Ying  Zi  Cui  Yu-Jun  Duc  Myriam  Benahmed  Nadia  Bessaies-Bey  Hela  Chen  Bo 《Acta Geotechnica》2021,16(4):1101-1111

Acta Geotechnica - Previous studies stated that, with increasing salinity, the decreased liquid limit for expansive soils was attributed to the shrinkage of diffuse double layer, while the...  相似文献   

Amazonian magnetostratigraphy: Dating the first pulse of the Great American Faunal Interchange     

Kenneth E. Campbell  Donald R. Prothero  Lidia Romero-Pittman  Fritz Hertel  Nadia Rivera 《Journal of South American Earth Sciences》2010,29(3):619-626

The chronostratigraphy of the youngest Neogene deposits of the Amazon Basin, which comprise the Madre de Dios Formation in eastern Peru, remains unresolved. Although ⁴⁰Ar/³⁹Ar dates on two volcanic ashes from this formation in Peru provide critical baseline data points, stratigraphic correlations among scattered riverine outcrops in adjacent drainage basins remain problematic. To refine the chronostratigraphy of the Madre de Dios Formation, we report here the magnetostratigraphy of an outcrop on the Madre de Dios River in southeastern Peru. A total of 18 polarity zones was obtained in the ～65-m-thick Cerro Colorado section, which we correlate to magnetozones Chrons C4Ar to C2An (9.5–3.0 Ma) based on the prior ⁴⁰Ar/³⁹Ar dates. These results confirm the late Miocene age of a gomphothere recovered from the Ipururo Formation, which underlies the late Miocene Ucayali Unconformity at the base of the Cerro Colorado outcrop. The results also support earlier interpretations of a late Miocene age for other fossils of North American mammals recovered from basal conglomeratic deposits of the Madre de Dios Formation immediately above the Ucayali Unconformity. These mammals include other gomphotheres, peccaries, and tapirs, and their presence in South America in the late Miocene is recognized as part of the first pulse of the Great American Faunal Interchange.  相似文献   

Reduction of The Stellar Three – Body Problem     

Nadia A. Saad 《Astrophysics and Space Science》2003,284(3):1001-1012

The stellar problem of three bodies is studied. A Lie transform is used to eliminate the short and intermediate periodic terms from Harrington's Hamiltonian. The resulting system is a one of two degrees of freedom whose further reduction requires recourse to numerical procedures. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The origin of major talc deposits in the Eastern Desert of Egypt: relict fragments of a metamorphosed carbonate horizon?     

Eva S. Schandl  Michael P. Gorton  Nadia A. Sharara 《Journal of African Earth Sciences》2002,34(3-4)

Detailed geochemical and mineralogical investigation of four talc deposits in the Eastern Desert of Egypt (Atshan, Abu Gurdi, Darhib and Kashira) suggests that the deposits form a distinct lithological unit within the Shadli metavolcanic rocks. The talc crystallized from the replacement of siliceous carbonate beds locally intercalated with clastic sediments. Th/Yb vs. Ta/Yb ratios of the rocks suggest that the sediments and the host volcanic rocks formed in an active continental margin (ACM) environment. Thus, the talc deposits may represent relict fragments of an ancient, regionally extensive carbonate horizon within the arc-related metavolcanics. The talc-rich rocks, which contain relict carbonate, serpentinized olivine and tremolite, have low (<3 wt%) Al₂O₃, Cr, Ni (<20 ppm), Co and Sc (<15 ppm) concentrations, precluding mafic or felsic igneous protoliths. The deposits were locally affected by contact metamorphism, giving rise to pyroxene-hornfels and granulite facies assemblages, and by regional metamorphism which produced greenschist-amphibolite grade assemblages. Disseminated sulfides commonly occur in the talc-tremolite-rich rocks (having low Al₂O₃ concentrations), suggesting that the metals were probably present in the original carbonate beds, but were remobilized and reconcentrated during the various metamorphic events.  相似文献   

OH-bearing planar defects in olivine produced by the breakdown of Ti-rich humite minerals from Dabie Shan (China)   总被引：2，自引：0，他引：2  

Jörg Hermann  John D. Fitz Gerald  Nadia Malaspina  Andrew J. Berry  Marco Scambelluri 《Contributions to Mineralogy and Petrology》2007,153(4):417-428

The partial breakdown of Ti-chondrodite and Ti-clinohumite during exhumation from ultra-high pressure to amphibolite facies conditions in garnet-pyroxenites from Dabie Shan (China) produces coronas of olivine coexisting with ilmenite blebs. Fourier transform infrared (FTIR) spectra of this newly formed olivine exhibit absorption bands in the hydroxyl-stretching region. Two intense peaks were observed at 3,564 and 3,394 cm⁻¹, identical in energy to peaks in Ti-clinohumite. Transmission electron microscopy (TEM) of the same olivine domains revealed the presence of a complex (001) planar intergrowth. These interlayers have a 1.35 nm repeat distance, which is characteristic of clinohumite. Such interlayers are also enriched in Ti with respect to the adjacent olivine as shown by energy dispersive spectrometry. The combined evidence from FTIR spectroscopy and TEM indicates that OH is incorporated along Ti-clinohumite planar defects. This study provides evidence that the nominally anhydrous phase olivine may contain OH as a humite-type defect beyond the breakdown of the hydrous humite minerals and confirms earlier suggestions that Ti plays a key role in OH incorporation in mantle olivine. We suggest that olivine containing Ti-clinohumite defects is an important phase for water transport in subduction zones and for the storage of water in cold subcontinental mantle. However, these defects are unlikely to be stable in hotter parts of the oceanic mantle such as where basaltic magmas are generated.  相似文献   

Stable elements of radioecological importance in certain echinoderm species     

Catherine Papadopoulou  George D. Kanias  Elli Moraitopoulou-Kassimati 《Marine pollution bulletin》1976,7(8):143-144

Echinoderms may present variations in their elementary composition according to the surrounding medium and to their food sources. The accumulation of certain trace elements by these organisms is of radioecological interest, besides the biological one. The elements cobalt, zinc, chromium, caesium, silver, tin, iron, rubidium, selenium and scandium were determined in seven echinoderm species by neutron activation analysis and γ-ray spectroscopy. In this work the calculated values of the concentration factors of the determined elements are reported and discussed from the radioecological point of view.  相似文献   

Artificial neural networks as an alternative approach to groundwater numerical modelling and environmental design     

Ioannis K. Nikolos  Maria Stergiadi  Maria P. Papadopoulou  George P. Karatzas 《水文研究》2008,22(17):3337-3348

Classical optimization methodologies based on mathematical theories have been developed for the solution of various constrained environmental design problems. Numerical models have been widely used to represent an environmental system accurately. The use of methodologies such as artificial neural networks (ANNs), which approximate the complicated behaviour and response of physical systems, allows the optimization of a large number of case scenarios with different set of constraints within a short period of time, whereas the corresponding simulation time using a numerical model would be prohibitive. In this paper, a combination of an ANN with a differential evolution algorithm is proposed to replace the classical finite‐element numerical model in water resources management problems. The objective of the optimization problem is to determine the optimal operational strategy for the productive pumping wells located in the northern part of Rhodes Island in Greece, to cover the water demand and maintain the water table at certain levels. The conclusions of this study show that the use of ANN as an approximation model could (a) significantly reduce the computational burden associated with the accurate simulation of complex physical systems and (b) provide solutions very close to the optimal ones for various constrained environmental design problems. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

疏浚污泥资源化处理试验研究     

杨媛媛  胡黎明  Ange Nzihou  Nadia Yacoubi 《岩土力学》2009,30(5):1323-1327

疏浚污泥的处理与处置是世界性的环保难题,资源化处理技术的研究有重要的工程应用价值。通过化学处理技术,在疏浚污泥中加入磷酸,将其中的重金属转变成难溶的金属磷酸盐固化在处理产物中,加入FeCl3试剂与水作用,改善处理后污泥的物理力学性质;通过热处理技术大大降低有机物的含量,使固体残留物无害化。研究了不同磷酸含量和不同FeCl3含量对其物理力学和热学性质的影响。试验结果表明,处理后的疏浚污泥污染物活动性降低,并有可能用作建筑材料。  相似文献   

Field observations of an evolving rip current on a meso-macrotidal well-developed inner bar and rip morphology   总被引：1，自引：0，他引：1  

Nicolas Bruneau  Bruno Castelle  Philippe Bonneton  Rodrigo Pedreros  Rafael Almar  Natalie Bonneton  Patrice Bretel  Jean-Paul Parisot  Nadia Snchal 《Continental Shelf Research》2009,29(14):1650-1662

The Aquitanian Coast (France) is a high-energy meso-macrotidal environment exhibiting a highly variable double sandbar system. The inner and the outer bar generally exhibit a bar and rip morphology and persistent crescentic patterns, respectively. In June 2007, an intense five-day field experiment was carried out at Biscarrosse Beach. A large array of sensors was deployed on a well-developed southward-oriented bar and rip morphology. Daily topographic surveys were carried out together with video imaging to investigate beach morphodynamic evolution. During the experiment, offshore significant wave height ranged from 0.5 to 3 m, with a persistent shore-normal angle. This paper identifies two types of behavior of an observed rip current: (1) for low-energy waves, the rip current is active only between low and mid tide with maximum mean rip current velocity reaching 0.8 m/s for an offshore significant wave height (H_s) lower than 1 m; (2) for high-energy waves (H_s≈ 2.5–3 m), the rip current was active over the whole tide cycle with the presence of persistent intense offshore-directed flows between mid and high tide. For both low and high-energy waves, very low-frequency pulsations (15–30 min) of the mean currents are observed on both feeder and rip channels.A persistent slow shoreward migration of the sandbar was observed during the experiment while no significant alongshore migration of the system was measured. Onshore migration during the high-energy waves can be explained by different sediment transport processes such as flow velocity skewness, wave asymmetry or bed ventilation. High-frequency local measurements of the bed evolution show the presence of significant (in the order of 10 cm) fluctuations (in the order of 1 h). These fluctuations, observed for both low- and high-energy waves, are thought to be ripples and megaripples, respectively and may play an important but still poorly understood role in the larger scale morphodynamics. The present dataset improves the knowledge of rip dynamics as well as the morphological response of strongly alongshore non-uniform meso-macrotidal beaches.  相似文献   

Eddy diffusivity derived from drifter data for dispersion model applications   总被引：2，自引：1，他引：1  

Michela De Dominicis  Giovanni Leuzzi  Paolo Monti  Nadia Pinardi  Pierre-Marie Poulain 《Ocean Dynamics》2012,62(9):1381-1398

Ocean transport and dispersion processes are at the present time simulated using Lagrangian stochastic models coupled with Eulerian circulation models that are supplying analyses and forecasts of the ocean currents at unprecedented time and space resolution. Using the Lagrangian approach, each particle displacement is described by an average motion and a fluctuating part. The first one represents the advection associated with the Eulerian current field of the circulation models while the second one describes the sub-grid scale diffusion. The focus of this study is to quantify the sub-grid scale diffusion of the Lagrangian models written in terms of a horizontal eddy diffusivity. Using a large database of drifters released in different regions of the Mediterranean Sea, the Lagrangian sub-grid scale diffusion has been computed, by considering different regimes when averaging statistical quantities. In addition, the real drifters have been simulated using a trajectory model forced by OGCM currents, focusing on how the Lagrangian properties are reproduced by the simulated trajectories.  相似文献