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181.
Flow and diffusion of water in natural porous media, quartz sand, and calcareous gravel were measured using a 1.5-T clinical magnetic resonance tomograph. The spatial resolution of the dynamic measurements was 1.32 x 1.32 x 5 mm3, and the time between two cross-sectional measurements was approximately 10 s. The measured coefficients of molecular diffusion for water were in good agreement with theoretical data. Flow was measured without any tracer at velocities between 0.15 and 6.67 mm/s. The results, based on a calibration within one part of the column, were in good agreement with data obtained from a tracer experiment and from a numerical model. It was possible to measure the flow velocity in larger pores and preferential flow paths directly. The results of the flow measurements in smaller pores reflected the mean velocity within that volume element. In that case the obtained values were close to the average linear velocity. Since the time resolution is high a monitoring of flow processes is possible. The pore space was imaged with a spatial resolution of 0.5 x 0.5 x 0.5 mm3. Here, the porosity of pores that are larger than 0.2 mm can be measured directly; for smaller pores a calibration is necessary. 相似文献
182.
Linking socio-economic factors, environment and land cover in the German Highlands, 1945-1999 总被引:4,自引:0,他引:4
Land-cover changes are caused by human activities and natural ecological processes. Thus, our study uses an interdisciplinary approach to research land-cover changes. We present a method to (i) link socio-economic/environmental factors and land-cover changes, (ii) identify indicators of land-cover changes, and (iii) distinguish between socio-economic and environmental indicators associated with local types of overall land-cover changes. The study was conducted in the Lahn-Dill Highlands, Germany, a typical marginal rural landscape. In this region, we investigated land-cover changes occurring over the period 1945-1999. Land-cover data were derived from multi-temporal aerial photographs. Types of overall land-cover changes characterising the districts within the study area were differentiated. With the help of redundancy analysis (RDA), we analysed the relationships between land-cover changes and widely available socio-economic/environmental factors. The results reveal that both individual land-cover changes at patch level and types of overall land-cover changes characterising districts are correlated with socio-economic and environmental factors. Whereas the stable environmental factors are drivers of land-cover changes in our rural study area, socio-economic factors introduced into the analysis mostly result from land-cover changes. We identified correlative socio-economic indicators that cannot explain land-cover changes, but that in combination with the environmental factors can be used to greatly facilitate the reconstruction of past land-cover changes and thus lead to a better knowledge of land-cover history. Based on the types of overall land-cover changes, the results of the study can be adopted for the study of land-cover changes in other regions. 相似文献
183.
Development of Environmental Indicator Systems: Experiences from Germany 总被引:44,自引:0,他引:44
Walz R 《Environmental management》2000,25(6):613-623
ABSTACT / Environmental indicator systems aim to improve both the information and communication on the state of the environment and the environmental policy making. They have to fulfill scientific, functional and pragmatic requirements, e.g., consideration of ecological context, transparency and reproducibility, comprehensibility, policy relevance, international comparability, and justifiable expenditure. This paper analyzes the experiences made with the development of the German environmental indicator system and draws general conclusions toward further improvements. For Germany, an indicator system has been developed that uses the pressure-state-response approach proposed by the OECD, together with a classification in 14 environmental themes. According to the general requirements, the main criteria used for selecting the indicators are the ecological significance of the indicator, its quantifiability and data availability, and its comprehensibility and policy relevance. Altogether, about 140 indicators are selected. This high number stresses the need for further high-level aggregation, e.g., using methods developed for the valuation process in LCA. Further improvement is also needed, especially for the development of response indicators and in the area of data systematization. 相似文献
184.
Robert Blanchard Detlef Arndt Rainer Grätz Marco Poli Swen Scheider 《Journal of Loss Prevention in the Process Industries》2010,23(2):253-259
There is a general lack of information on the effects of full-bore obstacles on combustion in the literature, these obstacles are prevalent in many applications and knowledge of their effects on phenomena including burning rate, flame acceleration and DDT is important for the correct placing of explosion safety devices such as flame arresters and venting devices. In this work methane, propane, ethylene and hydrogen–air explosions were investigated in an 18 m long DN150 closed pipe with a 90 degree bend and various baffle obstacles placed at a short distance from the ignition source. After carrying out multiple experiments with the same configuration it was found that a relatively large variance existed in the measured flame speeds and overpressures, this was attributed to a stochastic element in how flames evolved and also how they caused and interacted with turbulence to produce flame acceleration. This led to several experiments being carried out for one configuration in order to obtain a meaningful average. It was shown that a 90 degree bend in a long tube had the ability to enhance flame speeds and overpressures, and shorten the run-up distance to DDT to a varying degree for a number of gases. In terms of the qualitative effects on these parameters they were comparable to baffle type obstacles with a blockage ratios of between 10 and 20%. 相似文献
185.
As it is practically impossible in an industrial society to reduce impacts into ecosystems to a level that would preclude any damages, the need for damage valuation arises. One of the available valuation tools is the economic approach. Subsequent publications present this approach using the example of soils. In this second part, two methods are presented for monetarising ecosystem services, the contingent valuation method, the valuation on the basis of restoration and replacement costs. Common arguments against the monetarisation of ecosystems, like the omission of intrinsic values or the incomplete information of individuals, are then discussed. In conclusion, limits and possibilities of monetarising ecosystem services are described. 相似文献
186.
Ethylarsine dichloride was used during WW I as a chemical warfare agent. Residues of this chemical warfare agent and its metabolites
are still present today and continue to contaminate soil and water.
A gas Chromatographic method for the detection and determination of ethylarsine dichloride is shown. Six dithiols were tested
as possible derivatization reagents for ethylarsine dichloride. With selection of the dithiol, matrix interferences can be
eliminated because of the different retention times of the derivatives. 相似文献
187.
Rainer W. Sieke Günter Lippke Alfred Krippendorf Rainer Haas Sven Lüdtke 《Environmental science and pollution research international》1998,5(4):199-201
The new technology of Plasmazon® uses the extremely strong oxidation of radicals to break up the compocunds of organic connections, e.g. chemical warfare agents like Clark I. In making a comparison of oxidation to normal ozone, the factor of the Plasmazon® -technology is available up to 103. The investigation in an experimental test shows that it is possible to destroy the warfare agent character of Clark I. As the possibility of a large-lot application this technology is the method of choice for other chemical or biological warfare agents. 相似文献
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