2,396 research outputs found
X-ray Resonant Magnetic Scattering : Polarisation Dependence in the non-spherical case
We develop a simple tensorial contraction method to obtain analytical formula
for X-ray resonant magnetic scattering. We apply the method considering first
electric dipole-dipole and electric quadrupole-quadrupole scattering in the
isolated atom approximation and compare the results with previous works. Then
we apply the method to derive phenomenological original formulas which account
also for non-spherical systems and for dipole-quadrupole mixing.Comment: typo corrections : -- P_b^{\prime} has been changed to P_b^{\prime *}
-- a sign changed in formula 3
PyHST2: an hybrid distributed code for high speed tomographic reconstruction with iterative reconstruction and a priori knowledge capabilities
We present the PyHST2 code which is in service at ESRF for phase-contrast and
absorption tomography. This code has been engineered to sustain the high data
flow typical of the third generation synchrotron facilities (10 terabytes per
experiment) by adopting a distributed and pipelined architecture. The code
implements, beside a default filtered backprojection reconstruction, iterative
reconstruction techniques with a-priori knowledge. These latter are used to
improve the reconstruction quality or in order to reduce the required data
volume and reach a given quality goal. The implemented a-priori knowledge
techniques are based on the total variation penalisation and a new recently
found convex functional which is based on overlapping patches.
We give details of the different methods and their implementations while the
code is distributed under free license.
We provide methods for estimating, in the absence of ground-truth data, the
optimal parameters values for a-priori techniques
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