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Most mathematical models for radiometric dating of recent sediments are particular solutions of a unique physical problem: the advective?Cdiffusive transport of a particle-bound radiotracer within a sediment profile that undergoes accretion. Regardless of the particular assumptions about fluxes, sedimentation rates and the diffusion term, all models assume ideal deposition as a boundary condition at the sediment water interface, i.e. new radioactive input will be deposited above the previously existing material. In sediments with very high porosities, this assumption may be unrealistic, because a fraction of the incoming flux may penetrate rapidly through the connected pore spaces. This process will be referred to as non-ideal deposition. This paper reviews evidence from literature data, discusses the basic processes involved, and establishes the mathematical basis to incorporate non-ideal deposition into one-phase radiometric dating models, as depth-distributed local sources. Through analytical and numerical solutions, this work demonstrates that such penetration patterns can explain excess 210Pb subsurface maxima, often observed in sediment cores, as well as penetration of 137Cs to depths greater than expected from sedimentation rates and diffusion. These ideas are illustrated using examples from the literature in which sediment porosities were >90?%. Implications for radiometric dating include: (1) spurious accelerations in sedimentation rate inferred when applying the constant rate of supply model, and (2) erroneous chronologies, developed when using the maximum depth at which 137Cs can be measured as a chronostratigraphic marker. 相似文献
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Hend Askri Fatma Gharbi Saloua Rejeb Ahmed Mliki Abdelwahed Ghorbel 《Arabian Journal of Geosciences》2017,10(11):246
Salinity problems for vineyards are in concerns, especially in coastal areas where several aquifers are reported to be affected by seawater intrusion and agricultural contamination. Saline irrigation affects growth, yield, and fruit quality of grapevines. Exploring germplasm base through wild ancestors of the target species is a novel adopted strategy to increase crop tolerance to irrigation with saline water. The effects of salt on growth, organic and inorganic solute accumulations, and chlorophyll florescence were studied on 3-month-old plants of six Tunisian wild grapevines with the objective to identify salt tolerance mechanisms and select tolerant genotypes. Potted plants were grown under controlled conditions and irrigated for 14 days with 0, 100, and 150 mM NaCl nutrient solution. Parameters analyzed were related to growth, water relations, mineral nutrition, and chlorophyll fluorescence. Several processes are operating either at the whole plant or at cell level. They appear to be involved in salt tolerance of wild grapevines and are more efficient in tolerant accessions. Salt adversely affects plant growth and plant nutrition. Reductions of shoot growth rate (relative growth rate, day?1) reached 49% of control since 100 mM NaCl. They were assigned to stomatal closure and alteration of potassium nutrition and photochemistry. There were significant differences (P < 0.05) within accessions, Tebaba was the most tolerant and Houamdia the most sensitive, while the others were intermediate. 相似文献
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Understanding the hydrological response of small and large river basins is crucial for regional climate and hydrology studies. Also, rainfall space–time variability (Known in semi arid climate) has a major influence on hydrological dynamics. As consequent, we developed a software application (with MATLAB) in order to take into account the rainfall space-time variability, and that open a major prospects of studying hydrometeorological effects such scale effect and moving storms. In this context, in order to asses scale and dynamic rainy events effect in hydrologic modelling, this study focuses on instantaneous rainy data in central Tunisia (Merguellil and Skhira watershed): a rainfall runoff modelling was done to investigate basins responses and a developed geomorphology-based transfer function, was applied. A systematic hydro-meteorological analysis have been implemented to understand different types of variability and rainy fields dynamic, the relevance of rainfall network and scale effects. As result, two different behaviours of studied basins are detected. Responses of studied areas are much related to event dynamic (East/West and West/East) and hydrographs change according to event direction. 相似文献
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Mehdi A. Guemache Djamel Machane Hamoud Beldjoudi Sofiane Gharbi Leila Djadia Sihem Benahmed Hayet Ymmel 《Natural Hazards》2010,54(2):273-288
On March 20, 2006, an earthquake (M
w = 5.3; SED) struck the mountainous region of the Babors chain (Wilaya of Bejaia, northeast Algeria). The seismic epicenter
was located near the Kherrata village. This earthquake was felt on a large area of the northeastern part of Algeria. It reached
an intensity of VII (EMS scale) at the Laalam village, situated at about 20 km northeast of Kherrata. Here, many old and recent
houses were damaged or collapsed totally, four people died and 68 were injured. Field investigations revealed that these casualties
were caused by a landslide triggered by the earthquake. Many fissures were visible on ground throughout the site. They were
generated by both sliding and settling phenomena. The Laalam site is prone to landslide, as revealed by some evidences on
old instabilities. This is due to two main factors: local geomorphology and geology. These factors intervene synchronously
for reducing the slope instability at the Laalam village. The March 20, 2006 Kherrata earthquake was the trigger that released
the Laalam landslide. 相似文献
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The use of mud motors and other tools to accomplish forward motion of the bit in extended reach and horizontal wells allows avoiding large amounts of torque caused by rotation of the whole drill string. The forward motion of the drill string, however, is resisted by excessive amount of friction. In the presence of large compressive axial loads, the drill pipe or coiled tubing tends to buckle into a helix in horizontal boreholes. This causes additional frictional drag resisting the transmission of axial load (resulting from surface slack‐off force) to the bit. As the magnitude of the frictional drag increases, a buckled pipe may become ‘locked‐up’ making it almost impossible to drill further. In case of packers, the frictional drag may inhibit the transmission of set‐up load to the packer. A prior knowledge of the magnitude of frictional drag for a given axial load and radial clearance can help avoid lock‐up conditions and costly failure of the tubular. In this study a neural network model, for the prediction of frictional drag and axial load transmission in horizontal wellbores, is presented. Several neural network architectures were designed and tested to obtain the most accurate prediction. After cross‐validation of the Back Propagation Neural Network (BPNN) algorithm, a two‐hidden layer model was chosen for simultaneous prediction of frictional drag and axial load transmission. A comparison of results obtained from BPNN and General Regression Neural Network (GRNN) algorithms is also presented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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The alluvial aquifer of Upper Cheliff (northern Algeria) is known for its intensive agricultural activities, which is based especially on groundwater exploitation. This aquifer is now facing a dual problem of quantity and quality, with a decrease in the groundwater levels and an increase in mineralization. Twenty monitoring samples were collected and analyzed for major ion during the dry season 2014. In the present study, we try to characterize the hydrogeochemical processes and to assess the impact of natural and anthropogenic conditions on groundwater mineralization. The analytical results of the dry season 2014 show a groundwater quality slightly alkaline (pH > 7) and indicate that the majority of samples have a values exceeding the limits of potability fixed by WHO in 2008, due to the various sources of anthropogenic pollution. The Piper diagram shows the dominance of groundwater types: Ca–Cl, the mixed facies (Cl–SO4–Ca–Mg), and Ca–HCO3: The mineralization process in this aquifer is mainly controlled by the lithology of the aquifer (exchange water–rock and weathering of calcareous crust dissolution in the unsaturated zone), by anthropogenic factors (discharges of untreated urban sewage, intensive use of fertilizers in agriculture and the use of domestic septic tanks by rural inhabitants) and also by geoclimatic conditions (semiarid climate). Suitability of groundwater shows more than 80% of samples have very poor quality for drinking and more than 20% of samples indicate a quality unsuitable for irrigation. 相似文献
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Coastal and bank erosion along the St. Lawrence River Waterway in Quebec, Canada, represents a hazard to local communities
living along the river banks, as well as to the local fauna habitat. The purpose of this study is to assess the potential
impact of the waves generated by long containerships on riverbank erosion and recession at critical sites along the St. Lawrence
River Waterway, which have already experienced significant damage. A field study was carried out to investigate the ship-generated
hydrodynamics and the various driving mechanisms of the erosion process induced by ship waves. The field measurements provided
an assessment of the influence of the length of large vessels by comparing the characteristics of the hydrodynamics fields
induced by the passage of two containerships of different lengths. The potential for bank erosion and recession is assessed
in terms of the wake erosive energy incident to the shoreline. The field data are compared against analytical results predicted
by an empirical model, as well as against a ship-generated hydrodynamics model. Several numerical simulations for quantifying
the ship’s drawdown and its effects are also presented. 相似文献
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Abed Salih Al Dulaymie Bayan Muhie Hussien Moshtaq Ahmed Gharbi Husam Naji Mekhlif 《Arabian Journal of Geosciences》2013,6(3):801-816
This research examined the balneological characteristics of spring waters within the area of Abu-Jir Fault Zone throughout the hydrogeologic aspects explained by the setting of the hydrogeologic units including the water-bearing horizons of Euphrates, Ana, and Baba Formations. The groundwater flow in the hydrogeologic system correlated with the trends of enrichment or depletion case processes of mineralization (spatial distribution maps of TDS and other components) show different phenomena of groundwater source and interconnection, which helps in the classification springs into two potential site. The physicochemical characteristics of the water flow from springs indicate a hydrochemical approach throughout the spatial variation of important parameters (using Rockware software) related to the balneological study. The monitoring network of the spring waters performed by seven field measurements and 33 variables (totaling to 720 detected measurements) in 18 springs approved the after desk study and water point inventory using a GPS apparatus (GARMIN SUMMIT-e TREX). The study examined the integrated hydrogeological aspects and spring water properties for evolutions and the classification of minero-medicinal water. The traditional hydrochemical information of the spring waters and their sediment properties correlated with balneological limits (standards and definitions) are used in the selection of springs characterized by balneotherapeutic applications. A suggested screening and ranking technique has been developed for evaluating preferable springs selected for natural therapy. The application of ranking technique indicates four graded consequent preferable springs for balneotherapeutic investment: first grade spring represented by Kubaiysa spring (S-4); second grade springs represented by Tawila spring (S-12); third grade springs represented by Mamora spring (S-15), Arnab spring (S-10), Zazoe spring (S-5), and Maqtoom spring (S-13); and fourth grade springs represented by Khalidiya spring (S-16) and Layeg spring (S-7). 相似文献