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411.
412.
Javier Palarea-Albaladejo Josep A. Martín-Fernández Juan Gómez-García 《Mathematical Geology》2007,39(7):625-645
In this work, a parametric approach for replacing data below the detection limit, also known as rounded zeros, in compositional
data sets is proposed. Compositional rounded zeros correspond to small proportions of some whole that cannot be reliably detected
by the analytical instruments under given operating conditions. This kind of zeros appear frequently in the data collection
process in geosciences. They must be treated in an adequate way before some multivariate analysis can be applied. Our procedure
results from a modification of the Expectation-Maximization (EM) algorithm and is based on the additive log-ratio transformation.
Its coherence with the nature of compositional data and with basic operations in the simplex sample space is checked. Using
real data sets, we find that this approach improves other parametric and non-parametric techniques for compositional rounded
zeros. 相似文献
413.
María Gabriela García Ondra Sracek Diego Sebastián Fernández Margarita del Valle Hidalgo 《Environmental Geology》2007,52(7):1261-1275
The concentration of arsenic measured in groundwater from three aquifers in the study area located in the Eastern Tucuman
province, Argentina, mostly depends on the lithology, but the spatial and temporal variations of concentrations seem to be
also controlled by pH changes, climatic factors, and human perturbations. The highest concentrations of As (more than 1,000 μg
L−1) were found in the shallow aquifer, made of As-rich loess, while the lowest concentrations were measured in the deep confined
aquifer, consisting of alternating layers of alluvial sands/gravels and clays. Intermediate values were measured in the semiconfined
aquifer made of the fluvial sediments deposited in the Salí River valley, that alternate in the upper part of the sedimentary
sequence with layers of loess. Because most of As in the loess is considered to be adsorbed onto Fe-oxyhydroxide coatings,
the increase of pH in the flow direction (west-east) leads to increasing arsenic concentrations towards the eastern border
of the study area. The decomposition of organic wastes poured into the Salí River or associated with local and diffuse sources
of contamination in the eastern part of the study area depletes dissolved oxygen, which leads to the reductive dissolution
of Fe and Mn oxyhydroxides, and to the subsequent release of the adsorbed and co-precipitated As. This process mainly affects
shallow groundwater and the upper part of the semiconfined aquifer. Geochemical and hydrological data also suggest that rising
water table levels at the end of the wet season may also lead to reductive dissolution of As-rich Fe oxyhydroxides in the
shallow aquifer. 相似文献
414.
The distribution of platinum group elements (PGEs) in massive sulfides and hematite–magnetite±pyrite assemblages from the
recently discovered basalt-hosted Turtle Pits hydrothermal field and in massive sulfides from the ultramafic-hosted Logatchev
vent field both on the Mid-Atlantic Ridge was studied and compared to that from selected ancient volcanic-hosted massive sulfide
(VHMS) deposits. Cu-rich samples from black smoker chimneys of both vent fields are enriched in Pd and Rh (Pd up to 227 ppb
and Rh up to 149 ppb) when compared to hematite–magnetite-rich samples from Turtle Pits (Pd up to 10 ppb, Rh up to 1.9 ppb).
A significant positive correlation was established between Cu and Rh in sulfide samples from Turtle Pits. PGE chondrite-normalized
patterns (with a positive Rh anomaly and Pd and Au enrichment), Pd/Pt and Pd/Au ratios close to global MORB, and high values
of Pd/Ir and Pt/Ir ratios indicate mafic source rock and seawater involvement in the hydrothermal system at Turtle Pits. Similarly
shaped PGE chondrite-normalized patterns and high values of Pd/Pt and Pd/Ir ratios in Cu-rich sulfides at Logatchev likely
reflect a similar mechanism of PGE enrichment but with involvement of ultramafic source rocks. 相似文献
415.
J. P. Cárcomo Lobo Ferreira Maria da Conceição Cunha A. G. Chachadi Kai Nagel Catarina Diamantino Manuel Mendes Oliveira 《Hydrogeology Journal》2007,15(6):1147-1155
Using the hydrogeological and socio-economic data derived from a European Commission research project on the measurement,
monitoring and sustainability of the coastal environment, two optimization models have been applied to satisfy the future
water resources needs of the coastal zone of Bardez in Goa, India. The number of tourists visiting Goa since the 1970s has
risen considerably, and roughly a third of them go to Bardez taluka, prompting growth in the tourist-related infrastructure
in the region. The optimization models are non-linear mixed integer models that have been solved using GAMS/DICOPT++ commercial
software. Optimization models were used, firstly, to indicate the most suitable zones for building seaside resorts and wells
to supply the tourist industry with an adequate amount of water, and secondly, to indicate the best location for wells to
adequately supply pre-existing hotels. The models presented will help to define the optimal locations for the wells and the
hydraulic infrastructures needed to satisfy demand at minimum cost, taking into account environmental constraints such as
the risk of saline intrusion.
Résumé A l’aide de données hydrogéologiques et socio-économiques, dérivées d’un projet de recherche de la Commission Européenne sur l’étude, la surveillance et la durabilité de l’environnement c?tier, deux modèles d’optimisation ont été appliqués en vue de satisfaire les besoins futurs en ressources en eau de la zone c?tière de Bardez au Goa en Inde. Le nombre de touristes qui visitent le Goa depuis les années 70 a considérablement augmenté et environ un tiers d’entre eux se rend à Bardez taluka, ce qui encourage la croissance des infrastructures liées au tourisme dans la région. Les modèles d’optimisation sont des modèles non linéaires mixtes en nombres entiers qui ont été résolus en utilisant le logiciel commercial GAMS/DICOPT++. Les modèles d’optimisation ont été utilisés pour indiquer premièrement les zones les plus appropriées pour construire des stations balnéaires et des puits pour approvisionner en quantité d’eau suffisante l’industrie touristique, et deuxièmement pour indiquer la meilleure localisation de puits pour l’alimentation des h?tels préexistants. Les modèles présentés aideront à définir les localisations optimales des puits et des infrastructures hydrauliques nécessaires à la satisfaction de la demande à un co?t minimum, tout en prenant en compte les contraintes environnementales, tel que le risque d’intrusion saline.
Resumen Se han aplicado dos modelos de optimización en base a datos socio-económicos e hidrogeológicos derivados de un proyecto de investigación de la Comisión Europea sobre medición, monitoreo y sostenibilidad del ambiente costero para satisfacer las necesidades futuras de recursos hídricos de la zona costera de Bardez en Goa, India. El número de turistas que visita Goa desde la década de 1970′s ha subido considerablemente y cerca de un tercio de ellos van a Bardez taluka impulsando el crecimiento en la infraestructura turística de la región. Los modelos de optimización son modelos de números enteros mixtos no-lineales que se han resuelto usando el programa comercial GAMS/DICOPT++. Los modelos de optimización se usaron, primero para indicar las zonas más adecuadas para la construcción de centros de diversión en las márgenes del océano y pozos para abastecer la industria turística con una adecuada cantidad de agua, y segundo, para indicar la mejor localización de pozos para el abastecimiento de hoteles pre-existentes. Los modelos que se presentan ayudarán a definir las localizaciones óptimas para los pozos y las infraestructuras hidráulicas necesarias para satisfacer la demanda al mínimo costo, tomando en consideración restricciones ambientales tal como el riesgo de intrusión salina.相似文献
416.
Facies reconstructions are used in hydrogeology to improve the interpretation of aquifer permeability distribution. In the absence of sufficient data to define the heterogeneity due to geological processes, uncertainties in the distribution of aquifer hydrofacies and characteristics may appear. Geometric and geostatistical methods are used to understand and model aquifer hydrofacies distribution, providing models to improve comprehension and development of aquifers. However, these models require some input statistical parameters that can be difficult to infer from the study site. A three-dimensional reconstruction of a kilometer scale fine-grain dominated Cenozoic alluvial fan derived from more than 200 continuously cored, closely spaced, and regularly distributed wells is presented. The facies distributions were reconstructed using a genetic stratigraphic subdivision and a deterministic geostatistical algorithm. The reconstruction is only slightly affected by variations in the geostatistical input parameters because of the high-density data set. Analysis of the reconstruction allowed identification in the proximal to medial alluvial fan zones of several laterally extensive sand bodies with relatively higher permeability; these sand bodies were quantified in terms of volume, mean thickness, maximum area, and maximum equivalent diameter. These quantifications provide trends and geological scenarios for input statistical parameters to model aquifer systems in similar alluvial fan depositional settings. 相似文献
417.
O'Leary González Leonardo Alvarez Mariangela Guidarelli Giuliano F. Panza 《Pure and Applied Geophysics》2007,164(10):1985-2007
An overview of the crust and upper mantle structure of Central America and the Caribbean region is presented as a result of
the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. Group
velocity dispersion curves are obtained in the period range from 10s to 40s by FTAN analysis of the fundamental mode of the
Rayleigh waves; the error of these measurements varies from 0.06 and 0.09 km/s. From the dispersion curve, seven tomographic
maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification
techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each
one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region
are extended to 150s by adding data from a larger-scale tomographic study (Vdovin et al., 1999) and inverted using a nonlinear procedure. A set of models of the S-wave velocity vs. depth in the crust and upper
mantle is found as a result of the inversion process. In six regions we identify a typically oceanic crust and upper mantle
structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located
over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and
upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth. 相似文献
418.
P. Novák 《Studia Geophysica et Geodaetica》2007,51(3):351-367
Satellite missions CHAMP and GRACE dedicated to global mapping of the Earth’s gravity field yield accurate satellite-to-satellite
tracking (SST) data used for recovery of global geopotential models usually in a form of a finite set of Stokes’s coefficients.
The US-German Gravity Recovery And Climate Experiment (GRACE) yields SST data in both the high-low and low-low mode. Observed
satellite positions and changes in the intersatellite range can be inverted through the Newtonian equation of motion into
values of the unknown geopotential. The geopotential is usually approximated in observation equations by a truncated harmonic
series with unknown coefficients. An alternative approach based on integral inversion of the SST data of type GRACE into discrete
values of the geopotential at a geocentric sphere is discussed in this article. In this approach, observation equations have
a form of Green’s surface integrals with scalar-valued integral kernels. Despite their higher complexity, the kernel functions
exhibit features typical for other integral kernels used in geodesy for inversion of gravity field data. The two approaches
are discussed and compared based on their relative advantages and intended applications. The combination of heterogeneous
gravity data through integral equations is also outlined in the article.
panovak@kma.zcu.cz 相似文献
419.
Analysis of the weightiness of site effects on reinforced concrete (RC) building seismic behaviour: The Adra town example (SE Spain) 总被引:1,自引:0,他引:1
Manuel Navarro Francisco Vidal Takahisa Enomoto Francisco J. Alcalá Antonio García‐Jerez Francisco J. Sánchez Norio Abeki 《地震工程与结构动力学》2007,36(10):1363-1383
The damage distribution in Adra town (south‐eastern Spain) during the 1993 and 1994 Adra earthquakes (5.0 magnitude), that reached a maximum intensity degree of VII (European Macroseismic Scale (EMS scale)), was concentrated mainly in the south‐east zone of the town and the most relevant damage occurred in reinforced concrete (RC) buildings with four or five storeys. In order to evaluate the influence of ground condition on RC building behaviour, geological, geomorphological and geophysical surveys were carried out, and a detailed map of ground surface structure was obtained. Short‐period microtremor observations were performed in 160 sites on a 100m × 100m dimension grid and Nakamura's method was applied in order to determine a distribution map of soil predominant periods. Shorter predominant periods (0.1–0.3 s) were found in mountainous and neighbouring zones and larger periods (greater than 0.5 s) in thicker Holocene alluvial fans. A relationship T = (0.049 ± 0.001)N, where T is the natural period of swaying motion and N is the number of storeys, has been empirically obtained by using microtremor measurements at the top of 38 RC buildings (ranging from 2 to 9 storeys). 1‐D simulation of strong motion on different soil conditions and for several typical RC buildings were computed, using the acceleration record in Adra town of the 1993 earthquake. It is noteworthy that all the aforementioned results show the influence of site effects in the degree and distribution of observed building damage. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
420.
A methodology has been proposed which can be used to reduce the number of ground motion records needed for the reliable prediction of the median seismic response of structures by means of incremental dynamic analysis (IDA). This methodology is presently limited to predictions of the median IDA curve only. The reduction in the number of ground motion records needed to predict the median IDA curve is achieved by introducing a precedence list of ground motion records. The determination of such a list is an optimization problem, which is solved in the paper by means of (1) a genetic algorithm and (2) a proposed simple procedure. The seismic response of a simple, computationally non‐demanding structural model has been used as input data for the optimization problem. The presented example is a three‐storey‐reinforced concrete building, subjected to two sets of ground motion records, one a free‐field set and the other a near‐field set. It is shown that the median IDA curves can be predicted with acceptable accuracy by employing only four ground motion records instead of the 24 or 30 records, which are the total number of ground motion records for the free‐field and near‐field sets, respectively. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献