Interactions between dodecyl phosphates and hydroxyapatite or tooth enamel: relevance to inhibition of dental erosion.

Tooth surface modification is a potential method of preventing dental erosion, a form of excessive tooth wear facilitated by softening of tooth surfaces through the direct action of acids, mainly of dietary origin. We have previously shown that dodecyl phosphates (DPs) effectively inhibit dissolution of native surfaces of hydroxyapatite (the type mineral for dental enamel) and show good substantivity. However, adsorbed saliva also inhibits dissolution and DPs did not augment this effect, which suggests that DPs and saliva interact at the hydroxyapatite surface. In the present study the adsorption and desorption of potassium and sodium dodecyl phosphates or sodium dodecyl sulphate (SDS) to hydroxyapatite and human tooth enamel powder, both native and pre-treated with saliva, were studied by high performance liquid chromatography-mass Spectrometry. Thermo gravimetric analysis was used to analyse residual saliva and surfactant on the substrates. Both DPs showed a higher affinity than SDS for both hydroxyapatite and enamel, and little DP was desorbed by washing with water. SDS was readily desorbed from hydroxyapatite, suggesting that the phosphate head group is essential for strong binding to this substrate. However, SDS was not desorbed from enamel, so that this substrate has surface properties different from those of hydroxyapatite. The presence of a salivary coating had little or no effect on adsorption of the DPs, but treatment with DPs partly desorbed saliva; this could account for the failure of DPs to increase the dissolution inhibition due to adsorbed saliva.

Minor inheritance inhibits the calibration of the 10Be production rate from the AD 1717 Val Ferret rock avalanche, European Alps

To calibrate the in situ 10Be production rate, we collected surface samples from nine large granitic boulders within the deposits of a rock avalanche that occurred in AD 1717 in the upper Ferret Valley, Mont Blanc Massif, Italy. The 10Be concentrations were extremely low and successfully measured within 10% analytical uncertainty or less. The concentrations vary from 4829 ± 448 to 5917 ± 476 at g−1. Using the historical age exposure time, we calculated the local and sea level-high latitude (i.e. ≥60°) cosmogenic 10Be spallogenic production rates. Depending on the scaling schemes, these vary between 4.60 ± 0.38 and 5.26 ± 0.43 at g−1 a−1. Although they correlate well with global values, our production rates are clearly higher than those from more recent calibration sites. We conclude that our 10Be production rate is a mean and an upper bound for production rates in the Massif region over the past 300 years. This rate is probably influenced by inheritance and will yield inaccurate (e.g. too young) exposure ages when applied to surface-exposure studies in the area. Other independently dated rock-avalanche deposits in the region that are approximately 103 years old could be considered as possible calibration sites.

Benchmark problems for reactive transport modeling of the generation and attenuation of acid rock drainage

Acid rock drainage (ARD) is a problem of international relevance with substantial environmental and economic implications. Reactive transport modeling has proven a powerful tool for the process-based assessment of metal release and attenuation at ARD sites. Although a variety of models has been used to investigate ARD, a systematic model intercomparison has not been conducted to date. This contribution presents such a model intercomparison involving three synthetic benchmark problems designed to evaluate model results for the most relevant processes at ARD sites. The first benchmark (ARD-B1) focuses on the oxidation of sulfide minerals in an unsaturated tailing impoundment, affected by the ingress of atmospheric oxygen. ARD-B2 extends the first problem to include pH buffering by primary mineral dissolution and secondary mineral precipitation. The third problem (ARD-B3) in addition considers the kinetic and pH-dependent dissolution of silicate minerals under low pH conditions. The set of benchmarks was solved by four reactive transport codes, namely CrunchFlow, Flotran, HP1, and MIN3P. The results comparison focused on spatial profiles of dissolved concentrations, pH and pE, pore gas composition, and mineral assemblages. In addition, results of transient profiles for selected elements and cumulative mass loadings were considered in the intercomparison. Despite substantial differences in model formulations, very good agreement was obtained between the various codes. Residual deviations between the results are analyzed and discussed in terms of their implications for capturing system evolution and long-term mass loading predictions.

Local adaptations in populations of rock-dwelling haplochromines (Pisces:Cichlidae) from southern Lake Victoria

The radiation of cichlid fishes in the African great lakes is often described as adaptive, because, at a superficial level, cichlid fishes seem adapted to the ecological niches they occupy. However, adaptiveness has rarely been studied. We investigated to what extent island populations of three species of the rock-dwelling genus Neochromis, endemic to Lake Victoria, are adapted anatomically to exploit locally abundant resources. Specifically, we asked whether different resource environments were reflected in differences in the feeding apparatus, both within species and between species. In populations of two specialized biters, the algae scrapers N. rufocaudalis and N. omnicaeruleus, the biting force of the lower jaw increased with increasing amount of items that require biting in the diet. N. greenwoodi is a less specialized biter; we found differences between two populations in the hyoid position and in the premaxilla that enhance suction feeding. These adaptations were related to the amount of items requiring suction. Comparing across three sympatric pairs of species, in each case different diets were reflected in differences in anatomy.

Die politischen Flickschneider: Der Rock des heiligen Römischen oder Deutschen Reiches war schon vor längerer Zeit mürbe geworden ...

Welsch (Projektbearbeiter): Vergleich der politischen Verfaßtheit Deutschlands mit einem alten, mottenzerfressenen Rock, der aus 38 Flicken besteht und den die politischen Flickschneider nicht zusammenzunähen in der Lage sind. Die Lösung dieser verfahrenen Situation liegt darin, daß der deutsche Michel die Flickschneider davonjagt, die Flicken zusammenwalkt und sich daraus einen neuen, gut sitzenden Rock schneidert

Patterns of landscape form in the upper Rhône basin, Central Swiss Alps, predominantly show lithologic controls despite multiple glaciations and variations in rock uplift rates

The development of topography depends mainly on the interplay between uplift and erosion. These processes are controlled by various factors including climate, glaciers, lithology, seismic activity and short-term variables, such as anthropogenic impact. Many studies in orogens all over the world have shown how these controlling variables may affect the landscape's topography. In particular, it has been hypothesized that lithology exerts a dominant control on erosion rates and landscape morphology. However, clear demonstrations of this influence are rare and difficult to disentangle from the overprint of other signals such as climate or tectonics. In this study we focus on the upper Rhône Basin situated in the Central Swiss Alps in order to explore the relation between topography, possible controlling variables and lithology in particular. The Rhône Basin has been affected by spatially variable uplift, high orographically driven rainfalls and multiple glaciations. Furthermore, lithology and erodibility vary substantially within the basin. Thanks to high-resolution geological, climatic and topographic data, the Rhône Basin is a suitable laboratory to explore these complexities. Elevation, relief, slope and hypsometric data as well as river profile information from digital elevation models are used to characterize the landscape's topography of around 50 tributary basins. Additionally, uplift over different timescales, glacial inheritance, precipitation patterns and erodibility of the underlying bedrock are quantified for each basin. Results show that the chosen topographic and controlling variables vary remarkably between different tributary basins. We investigate the link between observed topographic differences and the possible controlling variables through statistical analyses. Variations of elevation, slope and relief seem to be linked to differences in long-term uplift rate, whereas elevation distributions (hypsometry) and river profile shapes may be related to glacial imprint. This confirms that the landscape of the Rhône Basin has been highly preconditioned by (past) uplift and glaciation. Linear discriminant analyses (LDAs), however, suggest a stronger link between observed topographic variations and differences in erodibility. We therefore conclude that despite evident glacial and tectonic conditioning, a lithologic control is still preserved and measurable in the landscape of the Rhône tributary basins.

Der blutige Rock Josefs [Illustration]

H. Vernet