Modelling Subsurface Heterogeneity by Coupled Markov Chains: Directional Dependency,Walther’s Law and Entropy     

A.?M.?M.?ElfekiEmail author  F.?M.?Dekking 《Geotechnical and Geological Engineering》2005,23(6):721-756

This paper is an extension of the two-dimensional coupled Markov chain model developed by Elfeki and Dekking (2001) supplemented with extensive simulations. We focus on the development of various coupled Markov chains models: the so-called fully forward Markov chain, fully backward Markov chain and forward–backward Markov chain models. We addressed many issues such as: sensitivity analysis of optimal sampling intervals in horizontal and lateral directions, directional dependency, use of Walther’s law to describe lateral variability, effect of conditioning on number of boreholes on the model performance, stability of the Monte Carlo realizations, various implementation strategies, use of cross validation techniques to evaluate model performance and image division for statistically non-homogeneous deposits are addressed. The applications are made on three sites; two sites are located in the Netherlands, and the third is in the USA. The purpose of these applications is to show under which conditions the Markov models can be used, and to provide some guidelines for the practice. Entropy maps are good tools to indicate places where high uncertainty is present, so can be used for designing sampling networks to reduce uncertainty at these locations. Symmetric and diagonally dominant horizontal transition probabilities with proper sampling interval show plausible results (fits with geologists prediction) in terms of delineation of subsurface heterogeneous structures. Walther’s law can be utilised with a proper sampling interval to account for the lateral variability.  相似文献   

Cyanobacterial blooms in estuarine ecosystems: characteristics and effects on Laeonereis acuta (Polychaeta, Nereididae)     

da Rosa CE  de Souza MS  Yunes JS  Proença LA  Nery LE  Monserrat JM 《Marine pollution bulletin》2005,50(9):956-964

In January of 2003, a cyanobacterial bloom in the Patos' Lagoon (Southern Brazil) (32 degrees 05'S-52 degrees 12'W) was observed. Water samples were taken to identify the composition and abundance of the bloom, as well as the occurrence of toxins. The effects of this occurrence on the estuarine worm Laeonereis acuta (Polychaeta, Nereididae) was also evaluated. Predominance of cyanobacteria, particularly Anabaena trichomes ( approximately 2.5.10(6) individuals per liter) was observed, and low concentrations of microcystins and anticholinesterasic toxins were detected. Augmented levels of lipid hydroperoxides (LPO) and glutathione-S-transferase activity, and lowering of total protein content were also observed in organisms collected during the bloom event. Although non-toxic, the cyanobacterial bloom could augment the cycle of hyper-oxygenation and hypoxia in the water. During hyperoxia, L. acuta, an oxyconformer, should consume more oxygen, thus augmenting the rate of reactive oxygen species generation. A repeated cycle of hyper-oxygenation and hypoxia would finally induce oxidative stress, as evidenced by the high levels of LPO and glutathione-S-transferase activity.  相似文献   

Effects of artificial and natural recharge on chemical equilibrium in the Cerro Prieto reservoirs, Baja California, México     

Enrique Portugal  Rosa María Barragn  Jesús de Len 《Journal of Geochemical Exploration》2006,89(1-3):339

Chemical equilibrium modeling studies of two aquifers in the western part of the Cerro Prieto (CP-I) geothermal field were performed to obtain the activities of the main ions and complexes by using the EQQYAC program. The results provided a pH of 6.44 for the deep aquifer, which is slightly higher than the value of 5.5 found for the shallower reservoir. In the northern part of the field, the reservoir pH has decreased up to 1.5 units compared to that modeled for 1990. Variations of pH with respect to time were also found to occur in the southern part of the field. In spite of the large changes in hydrodynamic conditions occurring in the reservoir due to exploitation, the equilibrium between both K- and Na-feldspars and between K-feldspar and K-mica seems to control the chemical composition of the fluids, in both reservoirs.  相似文献   

Hydrothermal alteration and fluid inclusion study of the Lower Cretaceous porphyry Cu–Au deposit of Tiámaro, Michoacán, Mexico     

Carlos Garza-Gonzlez  Antoni Camprubí  Eduardo Gonzlez-Partida  Germn Arriaga-García  Fernando Rosique-Naranjo 《Journal of Geochemical Exploration》2006,89(1-3):124

The Tiámaro deposit in Michoacán state has been dated as Lower Cretaceous (Valanginian), though most of the porphyry deposits in central Mexico were dated or have an attributed Eocene–Oligocene age. The host rocks belong to a volcanoplutonic complex overlain by red conglomerates. These rocks were intruded by pre-Valanginian plutonic and hypabissal rocks. Propylitic, phyllic, and argillic alteration assemblages developed, and their superimposition draws the evolution of the deposit. Stage I is represented by propylitic assemblages, stage II contains the main ore forming stockworks and both phyllic and argillic assemblages, and stage III contains late carbonatization assemblages. The obtained temperatures and salinities from inclusion fluids are low for a porphyry-type deposit, but we interpret that the known part of the deposit represents the shallow portion of a bigger deposit. The evolution of mineralizing fluids draws a dilution trend of brines from “porphyry-like” to “epithermal-like” stages. The richest ore zone is roughly located between the 300 and 350 °C isotherms, though unnoticed resources may occur at depth.  相似文献   

Fluoride pollution in French rivers and estuaries     

Jean-Marie Martin  François Salvadori 《Estuarine, Coastal and Shelf Science》1983,17(3):231-242

Fluoride concentrations have been determined in major French rivers and estuaries. The unpolluted estuary in the Loire has been compared with the Seine, Gironde and Charente where important discharges occur. Natural dissolved concentration can be multiplied by a factor of 30. Particulate fluorine concentration reach almost 2000 ppm in the Seine estuary. The percentage between free and complexed dissolved fluoride is not affected by the anthropic discharge. The present French rivers discharge of fluoride is 700% higher than the pristine value. At a global scale, dissolved fluoride has probably increased by 25% compared with the natural situation.  相似文献   

Compact Groups of Galaxies: Evolution of the Stellar Population     

I. García De La Rosa  R. Coziol  R.R. De Carvalho  S. Zepf 《Astrophysics and Space Science》2001,276(2-4):717-723

We present a study focusing on the nature of compact groups (CGs) through the study of their elliptical (E) galaxies. Parameters describing the internal dynamics and the stellar populations of the galaxies are compared with their counterparts in other environments. Our sample has24 bright E galaxies located in the core of Hickson CGs and 11 bright ‘bona fide’ Es, located in the field or very loose groups. Their spectra were obtained with the 2.1 m Telescope at KPNO and have a 4.1 Å resolution over the wavelength range 3500–7000 Å. We have found that, from the dynamical point of view, E galaxies in CGs are essentially similar to those in dense clusters. Moreover, the stellar populations of Es in CGs seem to be older and less metal rich than those in the field, behaviour which has also been observed by Rose et al. (1994).  相似文献   

Assessing the geochemical reactivity of inorganic phosphorus along estuaries by means of laboratory simulation experiments     

Enrique García‐Luque  Jesús M. Forja Pajares  Abelardo Gmez‐Parra 《水文研究》2006,20(16):3555-3566

Phosphate behaviour in natural estuarine systems can be studied by performing field measurements and by undertaking laboratory simulation experiments. Thus, in this paper we describe the use of a dynamic automated estuarine simulator to characterize the geochemical reactivity of phosphate in varying salinity gradients in order to study possible mechanisms of phosphate removal from the dissolved phase (e.g. formation of some kind of apatite) and how changes in pH and salinity values influence this removal. Six laboratory assays, representing various salinity and pH gradients (average pH values between 7 and 8), were carried out. The geochemical equilibrium model MINTEQA2 was employed to characterize removal of phosphate. Among the minerals from which dissolved phosphate can originate, it seems that hydroxyapatite is by far the mineral that shows the greatest saturation indexes in the experiments. Thus, there is evidence that a type of calcium phosphate (hydroxyapatite) is involved in phosphate removal in the assays. Phosphate removal by Ca²⁺ occurs sharply at salinity values of 1–2, whereas by Fe³⁺ it is relatively gradual, at least until a salinity value of 7. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Structural and metamorphic evolution of the northern Nile province of Sudan     

A.S. Dawoud  S.M. El-Raba&#x;a 《Precambrian Research》1978,6(1):A12-A13

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Basement control of deposition and subsequent deformation of early Palaeozoic sediments in Sudan     

S.M. El-Raba&#x;a 《Precambrian Research》1978,6(1):A18

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Auf dem Wege zur internationalen Seekarte     

Ltd. Reg. Dir. a. D. Hans Ermel 《Ocean Dynamics》1976,29(2):51-57

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