Attenuation of a Mixed Chromium and Chlorinated Etjeme Ground Wate Plume in Estuarine Influenced Glaciated Sediments     

Lucas A. Hellerich  Matthew A. Poneiera  Nikolaos P. Nikolaidis  Barth F. Smets  Gregory M. Dobbs 《Ground Water Monitoring & Remediation》2003,23(3):74-84

The natural attenuation behavior of a ground water contaminant plume containing chromium and chlorinated ethenes in glaciated sediments was assessed using traditional and nontraditional methods. The mixed waste is transported through and attenuated within an estuarine influenced ground water aquifer of spatially varying redox character and organic carbon content. Contaminant fate and speciation were assessed as a function of geochemical conditions. Total, speciation-based, and sequential chemical extraction analyses were performed to determine contaminant partitioning and the redox capacity of the aquifer. Chromium speciation and partitioning were correlated with the reductive capacity and redox conditions of the aquifer sediments spatially distributed within the aquifer. Reductive dechlorination and partitioning of chlorinated ethenes were correlated with the organic carbon content and redox conditions of the aquifer sediments. The data showed that sharp redox gradients existed within the aquifer. Active reduction and retardation of both chromium and chlorinated ethenes was exhibited. The aqueous hexavalent chromium concentrations decreased to near nondetect levels in the vicinity of the receptor, whereas degradation products of higher-order chlorinated ethenes increased as a fraction of the total chlorinated ethene concentrations along the length of the plume. The potential for competition for reducing power under specific cases within the aquifer was suggested by the data, highlighting the need to include contaminant interactions in natural attenuation assessments.  相似文献   

A frequency‐dependent and intensity‐dependent macroelement for reduced order seismic analysis of soil‐structure interacting systems          下载免费PDF全文

Nikolaos Lesgidis  Anastasios Sextos  Oh‐Sung Kwon 《地震工程与结构动力学》2018,47(11):2172-2194

The computational demand of the soil‐structure interaction analysis for the design and assessment of structures, as well as for the evaluation of their life‐cycle cost and risk exposure, has led the civil engineering community to the development of a variety of methods toward the model order reduction of the coupled soil‐structure dynamic system in earthquake regions. Different approaches have been proposed in the past as computationally efficient alternatives to the conventional finite element model simulation of the complete soil‐structure domain, such as the nonlinear lumped spring, the macroelement method, and the substructure partition method. Yet no approach was capable of capturing simultaneously the frequency‐dependent dynamic properties along with the nonlinear behavior of the condensed segment of the overall soil‐structure system under strong earthquake ground motion, thus generating an imbalance between the modeling refinement achieved for the soil and the structure. To this end, a dual frequency‐dependent and intensity‐dependent expansion of the lumped parameter modeling method is proposed in the current paper, materialized through a multiobjective algorithm, capable of closely approximating the behavior of the nonlinear dynamic system of the condensed segment. This is essentially the extension of an established methodology, also developed by the authors, in the inelastic domain. The efficiency of the proposed methodology is validated for the case of a bridge foundation system, wherein the seismic response is comparatively assessed for both the proposed method and the detailed finite element model. The above expansion is deemed a computationally efficient and reliable method for simultaneously considering the frequency and amplitude dependence of soil‐foundation systems in the framework of nonlinear seismic analysis of soil‐structure interaction systems.  相似文献   

An algorithm developed in Matlab for the automatic selection of cut-off frequencies,in the correction of strong motion data     

Georgios Sakkas  Nikolaos Sakellariou 《Acta Geophysica》2018,66(4):425-448

Strong motion recordings are the key in many earthquake engineering applications and are also fundamental for seismic design. The present study focuses on the automated correction of accelerograms, analog and digital. The main feature of the proposed algorithm is the automatic selection for the cut-off frequencies based on a minimum spectral value in a predefined frequency bandwidth, instead of the typical signal-to-noise approach. The algorithm follows the basic steps of the correction procedure (instrument correction, baseline correction and appropriate filtering). Besides the corrected time histories, Peak Ground Acceleration, Peak Ground Velocity, Peak Ground Displacement values and the corrected Fourier Spectra are also calculated as well as the response spectra. The algorithm is written in Matlab environment, is fast enough and can be used for batch processing or in real-time applications. In addition, the possibility to also perform a signal-to-noise ratio is added as well as to perform causal or acausal filtering. The algorithm has been tested in six significant earthquakes (Kozani-Grevena 1995, Aigio 1995, Athens 1999, Lefkada 2003 and Kefalonia 2014) of the Greek territory with analog and digital accelerograms.  相似文献   

Setting,sulfur isotope variations,and metamorphism of Jurassic massive Zn‐Pb‐Ag sulfide mineralization associated with arc‐type volcanism (Skra,Vardar zone, Νorthern Greece)     

Nikolaos Skarpelis 《Resource Geology》2020,70(4):311-335

Massive Zn‐Pb‐Ag sulfide mineralization appears conformable with felsic volcanism, developed in an Upper Jurassic volcanic arc to the Southwest (SW) of the Serbo‐Macedonian continent in Northern Greece. The host volcanic sequence of the mineralization comprises mylonitized rhyolitic to rhyodacitic lavas, pyroclastics, quartz‐feldspar porphyries, and cherty tuffs. A “white mica—quartz—pyrite” mineral assemblage characterizes the volcanic rocks in the footwall and hanging‐wall of massive sulfide ore layers, formed as a result of greenschist‐grade regional metamorphism on “clay‐quartz‐pyrite” hydrothermal alteration haloes. Massive ore lenses are usually underlain by deformed Cu‐pyrite and quartz‐pyrite stockworks. Most of the sulfide ore bodies have proximal‐type features. Ductile deformation and regional metamorphism have transformed many of the stockwork structures. The mineralization is characterized by high Zn, Pb, and Ag contents, while Cu and critical metals are low. Primary depositional textures, for example, layering, clastic pyrite, colloform, and atoll textures were identified. The overall textural features of the mineralization indicate it has undergone mechanical deformation. The most prominent features of the effects of metamorphism, folding and shearing, are modification of the ore body morphology toward flattened and boudinage structures and transformation of the ore textures toward the dominance of planar fabrics. Sulfur isotope analyses of sulfides along with textural observations are consistent with a dual source of sulfide sulfur. Sulfur isotope values for sphalerite, non‐colloform pyrite, galena, and chalcopyrite fall in a limited range from ?1.6 to +4.8‰ (mean δ³⁴S + 2‰), indicating a hydrothermal source derived from the reduction of coeval seawater sulfate in the convective system. Pyrites with colloform and atoll textures are characterized by a ³⁴S depletion, indicating a bacterial reduction of coeval seawater sulfate. The morphology of ore beds, the mineralogy, sulfide textures, and ore chemistry along with the petrology and tectonic setting of the host rocks can be attributed to typical of a bimodal‐felsic metallogenesis. Although similar in many respects to classic Kuroko‐type volcanogenic massive sulfide mineralization, it has some atypical features, like the absence of barite ore, which is possibly a result of significant temporal depletion in sulfate due to bacterial reduction, a conclusion supported by the widespread occurrence of colloidal and atoll textures of pyrite.  相似文献   

Porting of a wildfire risk and fire spread application into a cloud computing environment     

Kostas Kalabokidis  Nikolaos Athanasis  Christos Vasilakos  Palaiologos Palaiologou 《International journal of geographical information science》2014,28(3):541-552

Effective wildfire management is an essential part of forest firefighting strategies to minimize damage to land resources and loss of human lives. Wildfire management tools often require a large number of computing resources at a specific time. Such computing resources are not affordable to local fire agencies because of the extreme upfront costs on hardware and software. The emerging cloud computing technology can be a cost- and result-effective alternative. The purpose of this paper is to present the development and the implementation of a state-of-the-art application running in cloud computing, composed of a wildfire risk and a wildfire spread simulation service. The two above applications are delivered within a web-based interactive platform to the fire management agencies as Software as a Service (SaaS). The wildfire risk service calculates and provides daily to the end-user maps of the hourly forecasted fire risk for the next 112 hours in high spatiotemporal resolution, based on forecasted meteorological data. In addition, actual fire risk is calculated hourly, based on meteorological conditions provided by remote automatic weather stations. Regarding the wildfire behavior simulation service, end users can simulate the fire spread by simply providing the ignition point and the projected duration of the fire, based on the HFire algorithm. The efficiency of the proposed solution is based on the flexibility to scale up or down the number of computing nodes needed for the requested processing. In this context, end users will be charged only for their consumed processing time and only during the actual wildfire confrontation period. The system utilizes both commercial and open source cloud resources. The current prototype is applied in the study area of Lesvos Island, Greece, but its flexibility enables expansion in different geographical areas.  相似文献   

Human impacts on soils: Tipping points and knowledge gaps     

Nikolaos P. Nikolaidis 《Applied Geochemistry》2011

Soil ecosystem functions are derived from plant, animal and microorganism communities and the non-living environment interacting as a unit. Human activities have affected soil ecosystem functions and in many cases caused soil ecosystem collapse. This review provides a synthesis of current knowledge of human impacts on soil ecosystems, with a special focus on knowledge gaps regarding soil ecosystem shifts and tipping points, using the island of Crete, Greece as an example. Soil ecosystem shifts are abrupt changes that occur at “tipping points” and have long-lasting effects on the landscape and both the biotic and abiotic structure of the soil. These shifts can occur due to climate change, land use change, fertilization, or above-ground biodiversity decline. The environmental pressures in the agricultural land of Crete, place the island very close to tipping points, and make it an “ideal” area for soil ecosystem shifts. Reversing the trend of the shift while using the soil ecosystem services, means that significantly more organic matter needs to be added to the soil compared to the amount added under set-aside conditions. Potential nutrient supply and demand calculations indicate that fertilizer demand in Crete can be satisfied by recycling of bio-residue and livestock excreta produced on the island. Soil fertility improves faster if, in addition to bio-fertilization, farmers use traditional agricultural practices such as crop rotations and legume row plantings within olive trees and orchards. A renewed soil fertility paradigm shift requires a “holistic” management of biotic-soil–water resources in order to provide sufficient and an appropriate type of organic matter to the plant–microorganism system to maximize food production.  相似文献   

Meiobenthic diversity in space and time: The case of harpacticoid copepods in two Mediterranean microtidal sandy beaches     

Katerina Sevastou  Nikolaos Lampadariou  Anastasios Eleftheriou 《Journal of Sea Research》2011,66(3):205-214

Meiobenthic data from two microtidal sandy beaches of the eastern Mediterranean (Crete, Greece) were used to investigate patterns of both alpha and beta diversity in space and time. Copepod assemblages and environmental variables related to sediment characteristics, morphodynamics and food were studied over a year at four distinct habitats at each beach; the retention, resurgence and saturation zones of Salvat's intertidal scheme (midlittoral zone), and the surf zone of the sublittoral. Αlpha diversity analysis indicated similar species richness at both beaches when the whole 13-month data set was considered but was higher at the sheltered site when each sampling period was examined separately. Both beaches supported higher diversity in the sublittoral zone. Species richness increased seawards at the midlittoral zone of the sheltered site whereas, no pattern was evident at the exposed site, where the intense hydrodynamic conditions homogenized the sediments. Beta diversity increased markedly towards the sublittoral, indicating greater differences in alpha diversity between the sublittoral and the midlittoral zone. Species turnover was more variable at the exposed beach and at the most landward stations, where environmental conditions change often between extremes. A proportion of the variation in alpha diversity was explained by food availability at both beaches and additionally by grain size at the sheltered site. However, no environmental variable explained beta diversity patterns. Although the results of our study support the hypothesis of Multicausal Environmental Severity proposed for sandy beach macrofauna, we believe the classic Intermediate Disturbance Hypothesis is a more appropriate framework for the meiofauna communities of the studied sites.  相似文献   

Using detrital garnets to determine provenance: a case study from the Vertiskos Unit (Serbomacedonian Massif,N. Greece)     

Ioannis K. Georgiadis  Antonios Koroneos  Lamprini Papadopoulou  Nikolaos Kantiranis  Alexios E. Tamparopoulos  Ananias Tsirambides 《Mineralogy and Petrology》2014,108(2):187-206

Garnet single crystals of several millimeters in diameter were collected from the uppermost horizon of a soil profile developing immediately on the gneissic rocks of the Vertiskos Unit of the Serbomacedonian Massif in northern Greece. The garnets were analyzed for major elements by EDS analyzer mounted on a scanning electron microscope, and the obtained data were utilized to determine their source rocks. Bivariate diagrams, spider diagrams as well as statistical analysis were used in order to correlate and compare the garnet composition of the basement rocks of the Vertiskos Unit with the existing reference data. This case study demonstrates the difficulty in assigning a source rock to sediment, using only the chemical compositional of detrital garnet. Direct linking of the detrital garnets and the outcropping rocks is not always possible despite well documented outcrop lithologies. This is largely due to a complex metamorphic evolution that leads to overlapping compositions between garnets originating from different lithologies that have undergone similar metamorphic processes and alteration effects.  相似文献   

Field survey and modelling of irrigation water quality indices in a Mediterranean island catchment: a comparison between spatial interpolation methods     

Nikolaos Malamos  Demetris Koutsoyiannis 《水文科学杂志》2013,58(10):1447-1467

ABSTRACT

A biannual survey of physico-chemical quality indices of 104 irrigation-water wells located in a cultivated plain of a Mediterranean island catchment was conducted using a multi-parameter probe. The campaign was planned so as to differentiate between the dry and wet seasons. The acquired data constituted the test bed for evaluating the results and the features of four spatial interpolation methods, i.e. ordinary kriging, universal kriging, inverse distance weighted and nearest neighbours, against those of the recently introduced bilinear surface smoothing (BSS). In several cases, BSS outperformed the other interpolation methods, especially during the two-fold cross-validation procedure. The study emphasizes the fact that both in situ measurements and good mathematical techniques for studying the spatial distribution of water quality indices are pivotal to agricultural practice management. In the specific case studied, the spatio-temporal variability of water quality parameters and the need for monitoring were evident, as low irrigation water quality was encountered throughout the study area.  相似文献   

The species of Silene compacta Fischer as indicator of zinc,iron and copper mineralization     

Anestis Filippidis  Georgios Papastergios  Nikolaos Kantiranis  Kleopas Michailidis  Athanasios Chatzikirkou  Kostas Katirtzoglou 《Chemie der Erde / Geochemistry》2012,72(1):71-76

The possibility of using the species Silene compacta Fischer (Caryophyllaceae) as a plant indicator for Zn, Fe and Cu is discussed in this paper. Rock and plant samples were collected from an area near Essimi, north-eastern Greece, which is known for its Cu–Pb–Zn mineralization and analyzed for their content in 14 elements (Fe, Mn, Ag, As, Cd, Co, Cu, Mo, Ni, Pb, Sb, Sn, Zn and V). The data illustrate positive linear correlation between the concentrations of Zn, Fe and Cu in plant ash and rock samples. In particular, these correlations are 0.99 for Zn, 0.97 for Fe and 0.97 for Cu and are significant at the 99.9% confidence level. Therefore, S. compacta could be used as a plant indicator for Zn, Fe and Cu mineralization.  相似文献