Numerical Homogenization of the Rigidity Tensor in Hooke's Law Using the Node-Based Finite Element Method

Combining a geological model with a geomechanical model, it generally turns out that the geomechanical model is built from units that are at least a 100 times larger in volume than the units of the geological model. To counter this mismatch in scales, the geological data model's heterogeneous fine-scale Young's moduli and Poisson's ratios have to be “upscaled” to one “equivalent homogeneous” coarse-scale rigidity. This coarse-scale rigidity relates the volume-averaged displacement, strain, stress, and energy to each other, in such a way that the equilibrium equation, Hooke's law, and the energy equation preserve their fine-scale form on the coarse scale. Under the simplifying assumption of spatial periodicity of the heterogeneous fine-scale rigidity, homogenization theory can be applied. However, even then the spatial variability is generally so complex that exact solutions cannot be found. Therefore, numerical approximation methods have to be applied. Here the node-based finite element method for the displacement as primary variable has been used. Three numerical examples showing the upper bound character of this finite element method are presented.     

Ocean acidification: Separating evidence from judgment – A reply to Dupont et al.

Recently ocean acidification as a major threat for marine species has moved from a consensus statement into a much discussed and even challenged conception. A simple meta-analysis of Hendriks et al. (2010) showed that based on results of pooled experimental evidence, marine biota may turn out to be more resistant than hitherto believed. Dupont et al. (in press) indicate the importance of evaluating the most vulnerable stages in the life cycle of organisms instead of only adult stages. Here we evaluate additional material, composed of experimental evidence of the effect of ocean acidification on marine organisms during adult, larval, and juvenile stages, and show that the observed effects are within the range predicted by Hendriks et al. (2010). Species-specific differences and a wide variance in the reaction of organisms might obscure patterns of differences between life stages. Future research should be aimed to clarify underlying mechanisms to define the effect ocean acidification will have on marine biodiversity. Conveying scientific evidence along with an open acknowledgment of uncertainties to help separate evidence from judgment should not harm the need to act to mitigate ocean acidification and should pave the road for robust progress in our understanding of how ocean acidification impacts biota of the ocean.     

Carbon dioxide recovery from industrial processes

The ongoing human-induced emission of carbon dioxide (CO₂) threatens to change the earth's climate. One possible way of decreasing CO₂ emissions is to apply CO₂ removal, which involves recovering of carbon dioxide from energy conversion processes and storing it outside the atmosphere. Since the 1980's, the possibilities for recovering CO₂ from thermal power plants received increasing attention.In this study possible techniques of recovering CO₂ from large-scale industrial processes are assessed.In some industrial processes, e.g. ammonia production, CO₂ is recovered from the process streams to prevent it from interfering with the production process. The CO₂ thus recovered can easily be dehydrated and compressed, at low cost. In the iron and steel industry, carbon dioxide can be recovered from blast furnace gas. In the petrochemical industry CO₂ can be recovered from flue gases, using low-temperature heat for the separation process.Carbon dioxide can be recovered from large-scale industrial processes and in some cases the cost of recovery is significantly less than CO₂ recovery from thermal power plants. Therefore this option should be studied further and should be considered if carbon dioxide removal is introduced on a wide scale.     

Does upward seepage of river water and storm water runoff determine water quality of urban drainage systems in lowland areas? A case study for the Rhine–Meuse delta

The water quality of urban drainage ditches in lowlands in the Rhine‐Meuse delta was analysed with principal component analysis (PCA) during a dry period and a rain storm, and related to the seepage of polluted river water and effective impervious area (EIA). This was done in order to test the hypothesis that seepage of river water and storm water runoff from impervious areas strongly determine the water quality of urban drainage systems along large lowland rivers. Our analysis revealed that upward seepage of groundwater originating from rivers Rhine and Meuse was positively correlated with nitrate, potassium, sodium and chloride and negatively correlated with alkalinity, calcium, magnesium and iron. EIA was correlated with very few environmental variables (i.e. phosphate, pH and iron in the dry period and iron during the rain storm). Nickel and zinc concentrations generally exceeded the maximum allowable concentrations (MAC), while lead and phosphorus concentrations were just above the nutrient standards and MAC in a few locations during the rain storm. To optimize water quality in urban water systems, attention should be paid to all sources of pollution and not only to EIA. The impact of local groundwater seepage originating from large rivers in lowlands on the chemistry of urban water systems is often underestimated and should be taken into account when assessing water quality and improving water quality status. Copyright © 2009 John Wiley & Sons, Ltd.     

Accumulation of organochlorines and brominated flame retardants in estuarine and marine food chains: field measurements and model calculations

Food chain accumulation of organochlorines and brominated flame retardants in estuarine and marine environments is compared to model estimations and fresh water field data. The food chain consists of herbivores, detritivores and primary and secondary carnivores i.e. fish, fish-eating birds and marine mammals. Accumulation of polychlorinated biphenyls is predicted well by OMEGA for herbi-detritivores and primary and secondary carnivorous fish. Ratios are similar to those found for fresh water species. Accumulation ratios for fish-eating birds and mammals are overestimated by the model, which is attributed partly to biotransformation of meta-para unsubstituted congeners. Additionally, birds may feed in other less polluted areas. For brominated diphenylethers (BDE) accumulation patterns are highly species and congener specific. Accumulation depends on both K(ow) and metabolization capacities. BDE47 is the predominant congener in lower trophic levels. For marine birds and mammals accumulation ratios of BDE99 and 100 are similar to or higher than ratios of persistent PCBs.     

Effects of lithology and land use on storm run-off in east luxembourg

For a large part of the year, the forested catchments in the Keuper formation of east Luxembourg produce more direct run-off on a storm basis than paired cultivated catchments. The occurrence of shrinkage cracks, their pronounced opening and closing, and the occurrence of natural pipes in the forested environment play a major role in explaining this phenomenon. The effect of land use on storm run-off is studied in relation to that found for lithology in the same area.     

Organotin accumulation in an estuarine food chain: comparing field measurements with model estimations

The bioaccumulation model OMEGA (optimal modelling for ecotoxicological applications) is used to explore accumulation of organotins in the Western Scheldt food chain, consisting of herbi-detritivores, primary and secondary carnivorous fish and a piscivorous bird. Organotins studied are tributyltin (TBT) and triphenyltin (TPT) and the respective di- and mono-organotin metabolites. Empirical elimination rate constants are compared to model predictions for organic substances and metals. It is found that field bioaccumulation ratios are higher than predicted based on elimination kinetics relevant for organic compounds. The results indicate that uptake of organotins mainly occurs via hydrophobic mechanisms, whereas elimination may occur via metal-like kinetics. This results in very low elimination rates, which are comparable to model predictions for metals.     

Reconsidering the definition of a spatial data infrastructure

The great interest in spatial data infrastructures (SDIs) has led to a wealth of SDI definitions in SDI debates. The article aims to contribute to both theory-oriented and practice-oriented SDI research by providing a critical re-examination of the SDI literature. Ashby's formal theory of regulation, which sees infrastructures as regulatory devices, is used to identify the strengths and weaknesses of several SDI definitions. This exercise shows how debates of the SDI objectives and the roles of users get caught in mantraps and also opens the door for a way out of this confusion by distinguishing between functional and adoption objectives. It also highlights the emphasis on technological components in the SDI definitions, which sidestep the importance of structural and human resource components in SDI.