Management of Biesboch reservoirs for quality control with special reference to eutrophication

The three Biesbosch Reservoirs are pumped storage reservoirs, fed with rather polluted and highly eutrophic water from the River Meuse. Air injection at the bottom of the reservoirs prevents thermal stratification, which would otherwise result in serious water quality deterioration. Reservoir mixing also serves as an economic algal control measure; mixing over sufficient depth causes light to play the role of limiting factor and this, combined with zooplankton grazing, keeps the biomass of phytoplankton at acceptable levels. Special problems are caused by benthic, geosmin-producing Oscillatoria species growing on the inner embankment. Rooting up the bottom with a harrow is used as the method of control, based on underwater observations by biological staff trained as SCUBA-divers. With regard to pollutant behaviour the three reservoirs act as a series of fully mixed reactors. This enables the application of kinetic models to describe their behaviour and allows the use of a selective intake policy, e.g. for suspended solids with associated contaminants, ammonia and polynuclear aromatic hydrocarbons. A combination of selective intake and self- purification processes - enhanced by the compartmentalisation of the storage volume in three reservoirs - leads to a striking improvement for many water-quality parameters

Contact mechanics in glassy polymers

Polymers, primarily semi-crystalline, are widely used in applications where low friction is required; examples are cups in artificial hip joints, bearings and gears. Until now there is no clear indication why some polymers display low friction and others don’t. In this thesis a systematic identification of the role of the intrinsic properties of glassy polymers on singleasperity sliding friction experiments is performed. The problem is analysed using a hybrid numerical/experimental technique. In the numerical part the interaction between indenter and polymer is studied by means of a constitutive model capturing the intrinsic behaviour of glassy polymers, where the interaction between tip and polymer can be influenced by the incorporation of existing friction models. The experimental section concerns the development of reproducible sliding friction experiments, which in a later stage can be compared with simulations before conclusions can be drawn. Starting point is the constitutive model developed in our group over the last decade, which accurately captures the deformation response of glassy polymers, including strain localization phenomena as well as life time predictions. The choice for glassy polymers is, therefore, clearly not motivated by their relevance in low friction applications, but only because they represent a well-characterized class of polymers that allow quantitative predictions. First however some drawbacks of the existing model must be removed. The pre-yield regime itself is highly non-linear and thus correct modelling thereof is important in all simulations where non-homogeneous deformation is applied, like e.g. in indentation and sliding friction. Nevertheless, at present the pre-yield region is modelled as a compressible linear elastic solid and, as a result, details of indentation and unloading are not described quantitatively. The straightforward solution is to extend the existing model to include a spectrum of relaxation times in the pre-yield regime, via use of a multi-mode approach. The thus improved model now indeed also quantitatively predicts the indentation response of polycarbonate for different types of indenter geometries. A second drawback of the existing model is that it cannot deal with multiple relaxation mechanisms, as occur in cases where more than one molecular transition contributes to the stress. This behaviour typically manifests itself when high strain rates are applied, demonstrating a change in slope in the dependence of yield stress on the logarithm of strain rate. Solution of this problem requires a model extension by incorporation of a second, additional, flow process with its own non-linearity, that is, a multiprocess approach. A material which manifests this type of mechanical response is poly(methyl methacrylate); a quantitative prediction of its indentation response is achieved. Generally the friction force is regarded to be an additive composition of a deformationand an adhesion-related component, suggesting that components operate and contribute independently. Although decomposition in independent contributions is impossible to verify in an experimental set-up, it can be conveniently studied by using a numerical approach. Simulations with no adhesive interaction between tip and polymer show almost no influence of sliding velocity on friction force, whereas experiments show a significant influence. In case of an additive decomposition, this would imply a rate-dependence of the adhesive component. By inclusion of the Amontons-Coulomb friction law, which creates an interaction between tip and polymer, the suggested additive decomposition is proved not to be applicable and the large macroscopic deformation response proves to be the result of small changes in local processes. When interaction is taken into account, a bow wave is formed in front of the sliding tip, which leads to an increase in contact area between tip and polymer and results in an increase in friction force. As a consequence the experimentally observed time-dependent behaviour of the friction force can solely be attributed to a polymer’s intrinsic deformation response. Furthermore the influence of a polymer’s intrinsic material properties, such as strain hardening and the thermodynamic state, on the friction force can be studied conveniently

The Age of the Sept Iles layered mafic intrusion, Canada: implications for the Late Neoproterozoic/Cambrian history of southeastern Canada

The large Sept Iles layered mafic intrusion of eastern Canada has been precisely dated by U‐Pb zircon methods at 565 ± 4 Ma. Consideration of other magmatic events at that time in southeastern Canada reveals three different phases of magmatism. The first phase was composed of two tholeiitic dike swarms, at 615 Ma and 590 Ma. The second, including the Sept Iles intrusion, comprised a widespread series of mostly alkaline intrusions, emplaced around 575–565 Ma, along the rift faults of the St Lawrence graben. The last phase was composed predominantly of alkali and transitional basalts, now exposed in the Appalachians, erupted during the latest Neoproterozoic and early Cambrian. The second and third phases are best accounted for by the arrival of a major mantle plume near the town of Sept Iles 565 million years ago. The widespread, but volumetrically minor, alkali magmatism that peaked 10 m.y. earlier is typical of other plumes elsewhere. The plume model is reinforced by sedimentological evidence for a crustal dome centered near the town of Sept Iles that persisted for 80 m.y. The positions of the earlier dike swarms are problematical. They may represent vertical and/or lateral transport of magmas into the crust from earlier independent plumes or precursors to the Sept Iles plume

Rock-eating mycorrhizas: their role in plant nutrition and biogeochemical cycles

A decade ago, tunnels inside mineral grains were found that were likely formed by hyphae of ectomycorrhizal (EcM) fungi. This observation implied that EcM fungi can dissolve mineral grains. The observation raised several questions on the ecology of these ¿rock-eating¿ fungi. This review addresses the roles of these rock-eating EcM associations in plant nutrition, biogeochemical cycles and pedogenesis. Research approaches ranged from molecular to ecosystem level scales. Nutrient deficiencies change EcM seedling exudation patterns of organic anions and thus their potential to mobilise base cations from minerals. This response was fungal species-specific. Some EcM fungi accelerated mineral weathering. While mineral weathering could also increase the concentrations of phytotoxic aluminium in the soil solution, some EcM fungi increase Al tolerance through an enhanced exudation of oxalate. Through their contribution to Al transport, EcM hyphae could be agents in pedogenesis, especially podzolisation. A modelling study indicated that mineral tunnelling is less important than surface weathering by EcM fungi. With both processes taken together, the contribution of EcM fungi to weathering may be significant. In the field vertical niche differentiation of EcM fungi was shown for EcM root tips and extraradical mycelium. In the field EcM fungi and tunnel densities were correlated. Our results support a role of rock-eating EcM fungi in plant nutrition and biogeochemical cycles. EcM fungal species-specific differences indicate the need for further research with regard to this variation in functional traits

Endothelin-Induced Sarcoplasmic Reticulum Calcium Depletion Waves in Vascular Smooth Muscle Cells

Agonist-stimulated waves of elevated cytoplasmic Ca2+ concentration ([Ca2+]i ) regulate blood vessel tone and vasomotion in vascular smooth muscle. Previous studies employing cytoplasmic Ca2+ indicators revealed that these Ca2+ waves were generated by a combination of inositol 1,4,5-trisphosphate (IP3) and Ca2+ induced Ca2+ release (CICR) from the sarcoplasmic reticulum (SR); although, some of the mechanistic details remain uncertain. However, these findings were derived indirectly from observing agonist-induced [Ca2+]i fluctuations in the cytoplasm.
Here, for the first time, we have recorded Endothelin-1 (ET-1) induced waves of Ca2+ depletion from the SR lumen in vascular smooth muscle cells (VSMCs) using a calsequestrin-targeted Ca2+ indicator. Our findings show that these waves: (1) are due to regenerative CICR by the receptors for IP3 (IP3R), (2) have a marked latency period, (3) are characterized by a transient increase in SR Ca2+ ([Ca2+]SR ) both at the point of origin and at the wave front, (4) proceed with diminishing velocity, and (5) are arrested by the nuclear envelope. Our quantitative model indicates that the gradual decrease in the velocity of the SR depletion wave, in the absence of external Ca2+, results from continuity of the SR luminal network