12,387 research outputs found
Compensation for the setup instability in ptychographic imaging
The high-frequency vibration of the imaging system degrades the quality of
the reconstruction of ptychography by acting as a low-pass filter on ideal
diffraction patterns. In this study, we demonstrate that by subtracting the
deliberately blurred diffraction patterns from the recorded patterns and adding
the properly amplified subtraction to the original data, the high-frequency
components lost by the vibration of the setup can be recovered, and thus the
image quality can be distinctly improved. Because no prior knowledge regarding
the vibrating properties of the imaging system is needed, the proposed method
is general and simple and has applications in several research fields.Comment: 13pages, 10figure
Stable Recovery from the Magnitude of Symmetrized Fourier Measurements
In this note we show that stable recovery of complex-valued signals
up to global sign can be achieved from the magnitudes of
Fourier measurements when a certain "symmetrization and zero-padding" is
performed before measurement ( is possible in certain cases). For real
signals, symmetrization itself is linear and therefore our result is in this
case a statement on uniform phase retrieval. Since complex conjugation is
involved, such measurement procedure is not complex-linear but recovery is
still possible from magnitudes of linear measurements on, for example,
.Comment: 4 pages, will be submitted to ICASSP1
Three-dimensional coherent X-ray diffraction imaging of a ceramic nanofoam: determination of structural deformation mechanisms
Ultra-low density polymers, metals, and ceramic nanofoams are valued for
their high strength-to-weight ratio, high surface area and insulating
properties ascribed to their structural geometry. We obtain the labrynthine
internal structure of a tantalum oxide nanofoam by X-ray diffractive imaging.
Finite element analysis from the structure reveals mechanical properties
consistent with bulk samples and with a diffusion limited cluster aggregation
model, while excess mass on the nodes discounts the dangling fragments
hypothesis of percolation theory.Comment: 8 pages, 5 figures, 30 reference
Three-dimensional coherent X-ray diffraction imaging of a ceramic nanofoam: determination of structural deformation mechanisms
Ultra-low density polymers, metals, and ceramic nanofoams are valued for
their high strength-to-weight ratio, high surface area and insulating
properties ascribed to their structural geometry. We obtain the labrynthine
internal structure of a tantalum oxide nanofoam by X-ray diffractive imaging.
Finite element analysis from the structure reveals mechanical properties
consistent with bulk samples and with a diffusion limited cluster aggregation
model, while excess mass on the nodes discounts the dangling fragments
hypothesis of percolation theory.Comment: 8 pages, 5 figures, 30 reference
Dose, exposure time, and resolution in Serial X-ray Crystallography
The resolution of X-ray diffraction microscopy is limited by the maximum dose
that can be delivered prior to sample damage. In the proposed Serial
Crystallography method, the damage problem is addressed by distributing the
total dose over many identical hydrated macromolecules running continuously in
a single-file train across a continuous X-ray beam, and resolution is then
limited only by the available molecular and X-ray fluxes and molecular
alignment. Orientation of the diffracting molecules is achieved by laser
alignment. We evaluate the incident X-ray fluence (energy/area) required to
obtain a given resolution from (1) an analytical model, giving the count rate
at the maximum scattering angle for a model protein, (2) explicit simulation of
diffraction patterns for a GroEL-GroES protein complex, and (3) the frequency
cut off of the transfer function following iterative solution of the phase
problem, and reconstruction of an electron density map in the projection
approximation. These calculations include counting shot noise and multiple
starts of the phasing algorithm. The results indicate counting time and the
number of proteins needed within the beam at any instant for a given resolution
and X-ray flux. We confirm an inverse fourth power dependence of exposure time
on resolution, with important implications for all coherent X-ray imaging. We
find that multiple single-file protein beams will be needed for sub-nanometer
resolution on current third generation synchrotrons, but not on fourth
generation designs, where reconstruction of secondary protein structure at a
resolution of 0.7 nm should be possible with short exposures.Comment: 19 pages, 7 figures, 1 tabl
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