Neutron backscattering spectroscopy with sub-μeV energy resolution has profited over recent years from intensity gains enabled by a phase space transformation (PST) chopper, which is a fast-moving neutron optical component first proposed by Schelten and Alefeld (Internal Report No. Jül1954, KFA Jülich, 1984). Here, we present its principle, the considerations for our technical layout, the related challenges, the mechanical and neutron optical aspects, and tests related to the graphite mosaic crystals, moving with a center velocity of 243 m/s in the scattering plane perpendicular to the reciprocal lattice vector of the reflection. The reported tests of the graphite crystal quality are informative for other neutron optical applications. Our mechanically innovative, most compact PST chopper layout has proven its reliability during user operation in the backscattering spectrometer IN16B, and certain aspects of its design have already been adopted for another backscattering spectrometer. We report the relative intensity gain measured on the backscattering spectrometer IN16B, ILL. ... Read more

Non-periodic homogenization has proved to be an accurate asymptotic method for
computing long-wavelength equivalent media for the seismic wave equation, turning
small-scale heterogeneities and geometric complexity into smooth elastic properties.
Using homogenized media allows i) decreasing the computation cost of wave propagation
simulation and ii) studying the apparent, small-scale-induced anisotropy. After illustrating
these two aspects briefly, we propose to analyze in great detail the accuracy of body waves
simulated in homogenized 3D models of the subsurface. First, the behaviour of head-,
reflected and refracted waves with respect to source-receiver o\set, maximum frequency
and velocity contrast across a planar interface, is investigated. Then, we consider the SEGEAGE overthrust model to exemplify how the accuracy of simulated body waves anticorrelates with the distance to seismic source and the amount of apparent anisotropy. In
high apparent anisotropy regions, we show that the first-order correction provided by the
homogenization theory significantly improves the computed wavefield. The overall results
of this analysis better frame the use of homogenized media in seismic wave simulation. ... Read more