Simulation of DNAPL infiltration and spreading behaviour in the saturated zone at varying flow velocities and alternating subsurface geometries   总被引：3，自引：1，他引：2  

Katharina Erning  Sibylle Grandel  Andreas Dahmke  Dirk Schäfer 《Environmental Earth Sciences》2012,65(4):1119-1131

The influence of varying groundwater flow velocities on DNAPL infiltration and spreading behaviour was investigated by multiphase modelling using TMVOC and PetraSim. The multiphase models were calibrated by results of previously conducted laboratory experiments for the complete spatio-temporal range of the experiments. The small scale 2D scenario modelling was applied to qualify and quantify changes in position, architecture, geometry and dissolution of a TCE body in a fully saturated homogeneous sandy medium. The applied flow velocities ranging from 0.05 up to 40.00 m/day exhibited that the DNAPL TCE is affected even at the lowest flow velocity in its position, its size and its architecture. Additionally, several impermeable lenses with simple geometry were assumed in the model, to investigate the influence of stratified subsoil. In the experimental set-ups, the DNAPL body reacts more sensitive to the applied groundwater flow velocities than to the geometrical set-up of the scenarios. A possible consequence can be the transportation and displacement of a DNAPL pool due to natural or anthropogenic induced high groundwater flow velocities, as by Pump and Treat facilities, complicating site investigation process and planning of remediation activities.  相似文献   

Investigating sediments and rock structures beneath a river using underwater ERT     

Jannis Epting  Andreas Wüest  Peter Huggenberger 《Central European Journal of Geosciences》2012,4(1):81-93

This article presents hydrogeophysical investigations performed in a well-developed, long-term hydrogeological gypsum karst research site where subsurface evaporite dissolution has led to the subsidence of a river dam and an adjacent highway; both constructed on gypsum-containing rock, southeast of Basel, Switzerland. An observation system was set up to improve the protection of surface and subsurface water resources during remedial construction measures of the highway and in order to understand the processes, as well as the temporal evolution, of rock water interaction (flow and dissolution). However, no detailed hydrogeological information beneath the river could be derived from the previous investigations. To supplement the basic knowledge on this area, underwater Electrical Resistivity Tomography (ERT) measurements were conducted in the river bed upstream of the dam. The ERT-data are interpreted together with drill-core information and a conceptual 3D-Model of the area behind the dam and beneath the river. Results help to delineate weathered zones, associated faults and the thickness of sediment deposits behind the dam, as well as to locate voids within the local karst system. The combination of the ERT and modeling allows the optimization of future site-specific remedial construction measures.  相似文献   

Skyline-based registration of 3D laser scans     

Andreas Nüchter  Stanislav Gutev  Dorit Borrmann  Jan Elseberg 《地球空间信息科学学报》2011,14(2):85-90

Acquisition and registration of terrestrial 3D laser scans is a fundamental task in mapping and modeling of cities in three dimensions. To automate this task marker-free registration methods are required. Based on the existence of skyline features, this paper proposes a novel method. The skyline features are extracted from panoramic 3D scans and encoded as strings enabling the use of string matching for merging the scans. Initial results of the proposed method in the old city center of Bremen are pre-sented.  相似文献   

Physical and economic bias in climate change research: a scientometric study of IPCC Third Assessment Report     

Andreas Bjurstr?m  Merritt Polk 《Climatic change》2011,108(1-2):1-22

This study demonstrates that IPCC Third Assessment Report is strongly dominated by Natural sciences, especially the Earth sciences. The Social sciences are dominated by Economics. The IPCC assessment also results in the separation of the Earth, Biological and Social sciences. The integration that occurs is mainly between closely related scientific fields. The research community consequently imposes a physical and economic bias and a separation of scientific fields that the IPCC reproduces in the policy sphere. It is argued that this physical and economic bias distorts a comprehensive understanding of climate change and that the weak integration of scientific fields hinders climate change from being fully addressed as an integral environmental and social problem. If climate change is to be understood, evaluated and responded to in its fullness, the IPCC must broaden its knowledge base and challenge the anthropocentric worldview that places humans outside of nature.  相似文献   

Reversed North Atlantic gyre dynamics in present and glacial climates     

Marisa Montoya  Andreas Born  Anders Levermann 《Climate Dynamics》2011,36(5-6):1107-1118

The dynamics of the North Atlantic subpolar gyre (SPG) are assessed under present and glacial boundary conditions by investigating the SPG sensitivity to surface wind-stress changes in a coupled climate model. To this end, the gyre transport is decomposed in Ekman, thermohaline, and bottom transports. Surface wind-stress variations are found to play an important indirect role in SPG dynamics through their effect on water-mass densities. Our results suggest the existence of two dynamically distinct regimes of the SPG, depending on the absence or presence of deep water formation (DWF) in the Nordic Seas and a vigorous Greenland?CScotland ridge (GSR) overflow. In the first regime, the GSR overflow is weak and the SPG strength increases with wind-stress as a result of enhanced outcropping of isopycnals in the centre of the SPG. As soon as a vigorous GSR overflow is established, its associated positive density anomalies on the southern GSR slope reduce the SPG strength. This has implications for past glacial abrupt climate changes, insofar as these can be explained through latitudinal shifts in North Atlantic DWF sites and strengthening of the North Atlantic current. Regardless of the ultimate trigger, an abrupt shift of DWF into the Nordic Seas could result both in a drastic reduction of the SPG strength and a sudden reversal in its sensitivity to wind-stress variations. Our results could provide insight into changes in the horizontal ocean circulation during abrupt glacial climate changes, which have been largely neglected up to now in model studies.  相似文献   

Comparison of models calculating the sky view factor used for urban climate investigations     

Martin H?mmerle  Tam��s G��l  J��nos Unger  Andreas Matzarakis 《Theoretical and Applied Climatology》2011,105(3-4):521-527

The sky view factor (SVF) describes the surface geometry and is a commonly used and important measure in urban climate investigations whose aim is the exploration of effects of a complex urban surface on climatological processes in built-up areas. A selection of methods and models for calculating the SVF was compared. For this purpose, fish eye images were taken at several locations in the city of Szeged, southern Hungary. The fish eye images equidistantly follow linear transects to cover a range of SVF values and to analyze the reaction of the methods to a continuously changing environment. The fish eye pictures were evaluated by three methods: the method according to Steyn (Atmos-Ocean 18(3):245?C258, 1980) implemented in a GIS-Script, the ??Edit free sky view factor?? tool of the RayMan model and BMSkyView. The SVF values at the coordinates of the fish eye pictures were calculated with three numerical models (SkyHelios, ArcView SVF extension, and SOLWEIG) with a 3D building data base as input. After comparing the results of the first run, a deviation occurs. The deviation disappears after implementing an option to include a weighting factor in some of the models.  相似文献   

Human-biometeorological assessment of heat waves in Athens   总被引：1，自引：1，他引：0  

Andreas Matzarakis  Panagiotis T. Nastos 《Theoretical and Applied Climatology》2011,105(1-2):99-106

The goal of this study is the analysis of heat waves and their impact on humans, using human biometeorological indices, which are based on the energy balance of the human body. The implications for humans are not only described through the intensity of the heat waves, but also through their duration over consecutive days. Both intensity and duration were analyzed for the Greater Athens Area during the period 1955 to 2001. The analysis was carried out using the daily physiologically equivalent temperature and the daily minimum air temperature. Based on these two parameters, the results showed an increase in the average duration of heat waves. Furthermore, the use of the Gaussian filter revealed the intra-annual variation of heat stress conditions and their relevance to humans. The results could be used for the management of the negative consequences of heat waves in cities suffering from environmental pollution and also for climate impact studies.  相似文献   

Total least-squares adjustment of condition equations     

Burkhard Schaffrin  Andreas Wieser 《Studia Geophysica et Geodaetica》2011,55(3):529-536

The usual least-squares adjustment within an Errors-in-Variables (EIV) model is often described as Total Least-Squares Solution (TLSS), just as the usual least-squares adjustment within a Random Effects Model (REM) has become popular under the name of Least-Squares Collocation (without trend). In comparison to the standard Gauss-Markov Model (GMM), the EIV-Model is less informative whereas the REM is more informative. It is known under which conditions exactly the GMM or the REM can be equivalently replaced by a model of condition equations or, more generally, by a Gauss-Helmert Model. Similar equivalency conditions are, however, still unknown for the EIV-Model once it is transformed into such a model of condition equations. In a first step, it is shown in this contribution how the respective residual vector and residual matrix look like if the TLSS is applied to condition equations with a random coefficient matrix to describe the transformation of the random error vector. The results are demonstrated using a numeric example which shows that this approach may be valuable in its own right.  相似文献   

The chemical composition including the Rare Earth Elements of the three major glass types of Europe and the Orient used in late antiquity and the Middle Ages     

Karl Hans Wedepohl  Klaus Simon  Andreas Kronz 《Chemie der Erde / Geochemistry》2011,71(3):289-296

Sets of 20 soda ash glasses, 16 soda lime glasses and 23 wood ash glasses mainly from excavations in Europe (additional soda ash glasses from Egypt) were analysed on 61 chemical elements. Average SiO₂ is about 62% in soda glasses and 50% in wood ash glasses. The three groups of glasses contain on average 13% Na₂O, 18% Na₂O and 13% K₂O as fluxes to lower the melting temperature of quartz at their production. The starting materials beside quartz were halophytic plant ash for soda ash glass, trona (Na₃H(CO₃)₂·2H₂O) and lime (clamshells) for soda lime glass and beech ash for wood ash glass. Each of the three major glass types contains specific Rare Earth Element (REE) concentrations mainly contained in quartz and its intergrown minerals. 50 Paleozoic and Mesozoic sandstones from Central Europe represent the quartz composition. The REE pattern of these glasses apparently indicates major compositional stages of the Continental Earth's Crust. The boron to lithium and sodium to potassium ratios as in seawater suggest reactions of materials for soda glass with seawater. Negative Ce anomalies in the three glasses are caused by reactions of quartz with seawater.  相似文献   

Dimensional analysis of the earthquake-induced pounding between inelastic structures     

Elias G. Dimitrakopoulos  Nicos Makris  Andreas J. Kappos 《Bulletin of Earthquake Engineering》2011,9(2):561-579

In this paper the seismic response of inelastic structures with unilateral contact is revisited with dimensional analysis. All physically realizable contact types are captured via a non-smooth complementarity approach. The implementation of formal dimensional analysis leads to a condensed presentation of the response and unveils remarkable order even though two different types of non-linearity coexist in the response: the boundary non-linearity of unilateral contact and the inelastic behaviour of the structure itself. It is shown that regardless the intensity and frequency content of the excitation, all response spectra become self-similar when expressed in the appropriate dimensionless terms. The proposed approach hinges upon the notion of the energetic length scale of an excitation which measures the persistence of ground shaking to impose deformation demands. Using the concept of persistency which is defined for excitations with or without distinct pulses, the response is scaled via meaningful novel intensity measures: the dimensionless gap and the dimensionless yield displacement. The study confirms that contact may have a different effect on the response displacements of inelastic structures depending on the spectral region. In adjacent inelastic structures, such as colliding buildings or interacting bridge segments, contact is likely to alter drastically the excitation frequencies’ at which the system is most vulnerable. Finally, it is shown that the proposed approach yields maximum response displacements which correlate very well with the persistency of real earthquakes for a bridge system with considerably complex behaviour.  相似文献