Paul Scherrer Institute

About: Paul Scherrer Institute is a facility organization based out in Villigen, Switzerland. It is known for research contribution in the topics: Neutron & Large Hadron Collider. The organization has 9248 authors who have published 23984 publications receiving 890129 citations. The organization is also known as: PSI.

Restoring dense vegetation can slow mountain erosion to near natural benchmark levels

Abstract: Tropical mountain areas may undergo rapid land degradation as demographic growth and intensified agriculture cause more people to migrate to fragile ecosystems. To assess the extent of the resulting damage, an erosion rate benchmark against which changes in erosion can be evaluated is required. Benchmarks reflecting natural erosion rates are usually not provided by conventional sediment fluxes, which are often biased due to modern land use change, and also miss large, episodic events within the measuring period. To overcome this, we combined three independent assessment tools in the southern Ecuadorian Andes, an area that is severely affected by soil erosion. First, denudation rates from cosmogenic nuclides in river sediment average over time periods of 1–100 k.y. and establish a natural benchmark of only 150 ± 100 t km −2 yr −1 . Second, we find that land use practices have increased modern sediment yields as derived from reservoir sedimentation rates, which average over periods of 10–100 yr to as much as 15 × 10 3 t km −2 yr −1 . Third, our land cover analysis has shown us that vegetation cover exerts first-order control over present-day erosion rates at the catchment scale. Areas with high vegetation density erode at rates that are characteristically similar to those of the natural benchmark, regardless of whether the type of vegetation is native or anthropogenic. Therefore, our data suggest that even in steep mountain environments sediment fluxes can slow to near their natural benchmark levels with suitable revegetation programs. A set of techniques is now in place to evaluate the effectiveness of erosion mitigation strategies.

A Two‐Dimensional Porphyrin‐Based Porous Network Featuring Communicating Cavities for the Templated Complexation of Fullerenes

Abstract: An unprecedented two-dimensional porphyrin network featuring dynamic pores capable of hosting fullerenes is realized following a bottom-up approach at a single-crystal silver surface. Surface- and porphyrin-driven long-range interactions between the C-60 guest molecules and porphyrin layer result in the formation of exceptionally large supramolecular hybrid chains and islands (see Figure and Cover).

LUCIA, a microfocus soft XAS beamline

Abstract: The beamline “LUCIA” (line for ultimate characterization by imaging and absorption) is a “tender” (0.8–8 keV) X-ray microprobe with capabilities for chemical speciation by micro-X-ray absorption spectroscopy (μ-XAS) and for elemental mapping by X-ray micro-fluorescence (μ-XRF). It allows the possibility to study heterogeneous samples at a micrometer scale and to combine these two element-specific and non-destructive techniques. A monochromatic beam of a few micrometer in size is incident on a sample which is mounted on a scanning x–y–z stage. μ-XRF shows the location of the elements, their relative abundances, and their association with other elements. One can take advantage of the monochromatic beam which allows separating out different elements by their absorption edges. After mapping the fluorescence, spots of interest can be analysed by XAS to determine the speciation (local chemistry, quantitative determination of the local geometric structure around the absorbing atom) of the elements and how they depend on the different components. Installed at first at the SLS of the Paul Scherrer Institute (Switzerland), the LUCIA beamline will be transferred to SOLEIL by the beginning of 2008. The energy range offered by the beamline corresponds to the best performances of SLS and SOLEIL in terms of brightness. It allows XAS experiments at the K edge of elements ranging from Na to Fe, L edges from Ni to Gd, and M edges of rare earths and actinides.

Increase of human over natural erosion rates in tropical highlands constrained by cosmogenic nuclides

Abstract: We quantify the difference between the human-caused sediment yield and the natural rates of soil production and bedrock erosion in a now largely deforested tropical highland. The present-day rate of soil loss in the Upper Mahaweli catchment, Sri Lanka, is calculated by using suspended river-load fluxes. These data provide spatially averaged sediment yields of 130-2100 t-km - 2 .yr - 1 . Local rates of soil loss from agricultural plots on hillslopes are as high as 7000 t.km - 2 .yr - 1 . By comparison, natural rates of sediment generation, as determined by measuring cosmogenic 1 0 Be in quartz from sediments and soils, are only 13-30 t.km - 2 .yr - 1 . The natural rates presented here provide a benchmark against which recent erosion rates, determined by various sediment gauging techniques, can be referenced. In the Sri Lankan highlands, these results suggest that soil is now being lost 10-100 times faster from agriculturally utilized areas than it is being produced.