Basal slip and texture development in calcite: new results from torsion experiments

The deformation behavior of calcite has been of longstanding interest. Through experiments on single crystals, deformation mechanisms were established such as mechanical twinning on in the positive sense and slip on and both in the negative sense. More recently it was observed that at higher temperatures slip in both senses becomes active and, based on slip line analysis, it was suggested that slip may occur. So far there had been no direct evidence for basal slip, which is the dominant system in dolomite. With new torsion experiments on calcite single crystals at 900 K and transmission electron microscopy, this study identifies slip unambiguously by direct imaging of dislocations and diffraction contrast analysis. Including this slip system in polycrystal plasticity simulations, enigmatic texture patterns observed in compression and torsion of calcite rocks at high temperature can now be explained, resolving a long-standing puzzle.     

Biodiversity in the high ranges of the Alps: Ethnobotanical and climate change perspectives

Alpine plants, those predominantly occurring above a treeline, contribute significantly to biodiversity in mountain systems. Thus, one might expect a considerable part of the Alpine flora to be ethnobotanically relevant as has been documented for the Eastern Himalaya. As climate change, especially global warming, may lead to the extinction of Alpine plants, at least locally, loss of alpine species might be important to local people who rely on traditional medicine. How this holds for the Alps will be discussed in this contribution.The Alps are different from the Himalayas in that land use has changed dramatically during the past century. Rural life and culture has changed and much land has been abandoned or is under modern land use systems (industrial farming, tourism, urbanisation). Though much traditional knowledge has disappeared, traditional medicinal practices are still popular as supplemental to modern medicine. In a representative region in the Central Alps, traditional healers use 268 plants species of which 158 can be considered native to that area. Of the 25 predominantly Alpine species three are restricted to the highest Alps where warming might lead to their extinction. In the Alps some ornamental plants are of particular interest from an ethnobotanical point of view. People are apparently much more interested in what happens to Edelweiss (Leontopodium alpinum) than to medicinal plants. Other famous ornamentals (Leontopodium, Rhododendron, Gentiana, Anemone species) do not grow at critical high elevations, but could disappear locally from mountains which are too low in elevation.     

A two‐mechanism elastoplastic model for shakedown of unbound granular materials and DEM simulations

An elastoplastic model has been developed for the finite elements modelling of repeated load triaxial tests. This model is based on the shakedown theory established by Zarka for metallic structures. To the previous works, which were based on the Drucker–Prager yield surface and the plastic potential of Von Mises, a compression cap has been added to each one. The model straightforwardly determines the purely elastic state or the elastic shakedown state or the plastic shakedown state and calculates the deviatoric and the volumetric plastic strains. The calibration of the elastoplastic model has been carried out with DEM simulations and an unbound granular material for roads under repeated load triaxial tests using finite element method. The calculations underline the capabilities of the model to take into account, with a unique formalism, the accumulation of the deviatoric and volumetric plastic strains along the loading cycles. Copyright © 2011 John Wiley & Sons, Ltd.     

Carrier phase wind-up in GPS reflectometry

Changes in GPS transmitter and receiver antenna orientations induce variations in observed carrier phase values. An analytic formula for this well-known carrier phase wind-up correction is derived which generalizes a previous result. In addition, it is shown that in GPS reflectometry the wind-up values of direct and coherently reflected rays may differ by up to several centimeters. The results are discussed on the basis of simulated measurements.