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.

Neutron Phase Imaging and Tomography

Abstract: We report how a setup consisting of three gratings yields quantitative two- and three-dimensional images depicting the quantum-mechanical phase shifts of neutron de Broglie wave packets induced by the influence of macroscopic objects. Since our approach requires only a little spatial and chromatic coherence it provides a more than 2 orders of magnitude higher efficiency than existing techniques. This dramatically reduces the required measurement time for computed phase tomography and opens up the way for three-dimensional investigations of previously inaccessible quantum-mechanical phase interactions of neutrons with matter.

Quantitative x-ray dark-field computed tomography

Abstract: The basic principles of x-ray image formation in radiology have remained essentially unchanged since Rontgen first discovered x-rays over a hundred years ago. The conventional approach relies on x-ray attenuation as the sole source of contrast and draws exclusively on ray or geometrical optics to describe and interpret image formation. Phase-contrast or coherent scatter imaging techniques, which can be understood using wave optics rather than ray optics, offer ways to augment or complement the conventional approach by incorporating the wave-optical interaction of x-rays with the specimen. With a recently developed approach based on x-ray optical gratings, advanced phase-contrast and dark-field scatter imaging modalities are now in reach for routine medical imaging and non-destructive testing applications. To quantitatively assess the new potential of particularly the grating-based dark-field imaging modality, we here introduce a mathematical formalism together with a material-dependent parameter, the so-called linear diffusion coefficient and show that this description can yield quantitative dark-field computed tomography (QDFCT) images of experimental test phantoms.

Investigation of the Transversal Water Profile in Nafion Membranes in Polymer Electrolyte Fuel Cells

Abstract: The in situ resistance of Nafion membranes with different thickness was measured in one-dimensional fuel cells as a function of current density. Except for the thin Nation I 12 membrane, an increase of the ionic resistance with current density (in the range 0 to I A/cm 2 ) was found. The thicker the membrane, the stronger the increase in the same current density interval. The resistance distribution across the thickness of membranes was determined by using membranes composed from several thin sheets with interlying thin gold wires as potential probes. It was found that the increase of the resistance is always confined to the membrane sheet contacting the anode electrode. These measurements, combined with the results from experiments with membranes of different water content, lead to the conclusion that the resistance increase at the anode side is due to the insufficient compensation of the electro-osmotic drag by the hack transport of water to the anode. Based on a solution diffusion mechanism of the water motion in the membrane, the experimental results may he explained by a mechanism whereby the electro-osmotic drag coefficient is independent of the local membrane hydration and the water diffusion coefficient D H2O , is a strong function of the local membrane water content. The experimental data would, qualitatively, also he in line with a model proposing hack transport of water to the anode by convection of water in the submicropores of the membrane.

Gluon-induced W-boson pair production at the LHC

Abstract: Pair production of W bosons constitutes an important background to Higgs boson and new physics searches at the Large Hadron Collider LHC. We have calculated the loop-induced gluon-fusion process gg → W ∗ W ∗ → leptons, including intermediate light and heavy quarks and allowing for arbitrary invariant masses of the W bosons. While formally of next-to-next-to-leading order, the gg → W ∗ W ∗ → leptons process is enhanced by the large gluon flux at the LHC and by experimental Higgs search cuts, and increases the next-to-leading order W W background estimate for Higgs searches by about 30%. We have extended our previous calculation to include the contribution from the intermediate top- bottom massive quark loop and the Higgs signal process. We provide updated results for cross sections and differential distributions and study the interference between the different gluon scattering contributions. We describe important analytical and numerical aspects of our calculation and present the public GG2WW event generator.