206 research outputs found
Phase retrieval by coherent modulation imaging
Phase retrieval is a long-standing problem in imaging when only the intensity of the wavefield can be recorded. Coherent diffraction imaging is a lensless technique that uses iterative algorithms to recover amplitude and phase contrast images from diffraction intensity data. For general samples, phase retrieval from a single-diffraction pattern has been an algorithmic and experimental challenge. Here we report a method of phase retrieval that uses a known modulation of the sample exit wave. This coherent modulation imaging method removes inherent ambiguities of coherent diffraction imaging and uses a reliable, rapidly converging iterative algorithm involving three planes. It works for extended samples, does not require tight support for convergence and relaxes dynamic range requirements on the detector. Coherent modulation imaging provides a robust method for imaging in materials and biological science, while its single-shot capability will benefit the investigation of dynamical processes with pulsed sources, such as X-ray free-electron lasers
Multi-slice ptychographic tomography
Ptychography is a form of Coherent Diffractive Imaging, where diffraction patterns are processed by iterative algorithms to recover an image of a specimen. Although mostly applied in two dimensions, ptychography can be extended to produce three dimensional images in two ways: via multi-slice ptychography or ptychographic tomography. Ptychographic tomography relies on 2D ptychography to supply projections to conventional tomographic algorithms, whilst multi-slice ptychography uses the redundancy in ptychographic data to split the reconstruction into a series of axial slices. Whilst multi-slice ptychography can handle multiple-scattering thick specimens and has a much smaller data requirement than ptychographic tomography, its depth resolution is relatively poor. Here we propose an imaging modality that combines the benefits of the two approaches, enabling isotropic 3D resolution imaging of thick specimens with a small number of angular measurements. Optical experiments validate our proposed method
Ptychographic X-ray nanotomography quantifies mineral distributions in human dentine
Bones are bio-composites with biologically tunable mechanical properties,
where a polymer matrix of nanofibrillar collagen is reinforced by apatite
mineral crystals. Some bones, such as antler, form and change rapidly, while
other bone tissues, such as human tooth dentine, develop slowly and maintain
constant composition and architecture for entire lifetimes. When studying
apatite mineral microarchitecture, mineral distributions or mineralization
activity of bone-forming cells, representative samples of tissue are best
studied at submicrometre resolution while minimizing sample-preparation
damage. Here, we demonstrate the power of ptychographic X-ray tomography to
map variations in the mineral content distribution in three dimensions and at
the nanometre scale. Using this non-destructive method, we observe
nanostructures surrounding hollow tracts that exist in human dentine forming
dentinal tubules. We reveal unprecedented quantitative details of the
ultrastructure clearly revealing the spatially varying mineralization density.
Such information is essential for understanding a variety of natural and
therapeutic effects for example in bone tissue healing and ageing
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Experimental observation of vortex rings in a bulk magnet
Vortex rings are remarkably stable structures occurring in numerous systems:
for example in turbulent gases, where they are at the origin of weather
phenomena [1]; in fluids with implications for biology [2]; in electromagnetic
discharges [3]; and in plasmas [4]. While vortex rings have also been predicted
to exist in ferromagnets [5], they have not yet been observed. Using X-ray
magnetic nanotomography [6], we imaged three-dimensional structures forming
closed loops in a bulk micromagnet, each composed of a vortex-antivortex pair.
Based on the magnetic vorticity, a quantity analogous to hydrodynamic
vorticity, we identify these configurations as magnetic vortex rings. While
such structures have been predicted to exist as transient states in exchange
ferromagnets [5], the vortex rings we observe exist as stable, static
configurations, whose stability we attribute to the dipolar interaction. In
addition, we observe stable vortex loops intersected by magnetic singularities
[7], at which the magnetisation within the vortex and antivortex cores
reverses. We gain insight into the stability of these states through field and
thermal equilibration protocols. These measurements pave the way for the
observation of complex three-dimensional solitons in bulk magnets, as well as
for the development of applications based on three-dimensional magnetic
structures
Hard X-ray grazing incidence ptychography: Large field-of-view nanostructure imaging with ultra-high surface sensitivity
We demonstrate a technique that allows highly surface sensitive imaging of
nanostructures on planar surfaces over large areas, providing a new avenue for
research in materials science, especially for \textit{in situ} applications.
The capabilities of hard X-ray grazing incidence ptychography combine aspects
from imaging, reflectometry and grazing incidence small angle scattering in
providing large field-of-view images with high resolution transverse to the
beam, horizontally and along the surface normal. Thus, it yields data with
resolutions approaching electron microscopy, in two dimensions, but over much
larger areas and with a poorer resolution in the third spatial dimension, along
the beam propagation direction. Similar to grazing incidence small angle X-ray
scattering, this technique facilitates the characterization of nanostructures
across statistically significant surface areas or volumes within potentially
feasible time frames for \textit{in situ} experiments, while also providing
spatial information.Comment: 8 pages, 6 figure
A three-dimensional view of structural changes caused by deactivation of fluid catalytic cracking catalysts
Since its commercial introduction three-quarters of a century ago, fluid catalytic cracking has been one of the most important conversion processes in the petroleum industry. In this process, porous composites composed of zeolite and clay crack the heavy fractions in crude oil into transportation fuel and petrochemical feedstocks. Yet, over time the catalytic activity of these composite particles decreases. Here, we report on ptychographic tomography, diffraction, and fluorescence tomography, as well as electron microscopy measurements, which elucidate the structural changes that lead to catalyst deactivation. In combination, these measurements reveal zeolite amorphization and distinct structural changes on the particle exterior as the driving forces behind catalyst deactivation. Amorphization of zeolites, in particular, close to the particle exterior, results in a reduction of catalytic capacity. A concretion of the outermost particle layer into a dense amorphous silica–alumina shell further reduces the mass transport to the active sites within the composite
3D nanoscale analysis of bone healing around degrading Mg implants evaluated by X-ray scattering tensor tomography
The nanostructural adaptation of bone is crucial for its biocompatibility with orthopedic implants. The bone nanostructure also determines its mechanical properties and performance. However, the bone\u27s temporal and spatial nanoadaptation around degrading implants remains largely unknown. Here, we present insights into this important bone adaptation by applying scanning electron microscopy, elemental analysis, and small-angle X-ray scattering tensor tomography (SASTT). We extend the novel SASTT reconstruction method and provide a 3D scattering reciprocal space map per voxel of the sample\u27s volume. From this reconstruction, parameters such as the thickness of the bone mineral particles are quantified, which provide additional information on nanostructural adaptation of bone during healing. We selected a rat femoral bone and a degrading ZX10 magnesium implant as model system, and investigated it over the course of 18 months, using a sham as control. We observe that the bone\u27s nanostructural adaptation starts with an initially fast interfacial bone growth close to the implant, which spreads by a re-orientation of the nanostructure in the bone volume around the implant, and is consolidated in the later degradation stages. These observations reveal the complex bulk bone-implant interactions and enable future research on the related biomechanical bone responses. Statement of significance: Traumatic bone injuries are among the most frequent causes of surgical treatment, and often require the placement of an implant. The ideal implant supports and induces bone formation, while being mechanically and chemically adapted to the bone structure, ensuring a gradual load transfer. While magnesium implants fulfill these requirements, the nanostructural changes during bone healing and implant degradation remain not completely elucidated. Here, we unveil these processes in rat femoral bones with ZX10 magnesium implants and show different stages of bone healing in such a model system
Live cell X-ray imaging of autophagic vacuoles formation and chromatin dynamics in fission yeast
Seeing physiological processes at the nanoscale in living organisms without labeling is an ultimate goal in life sciences. Using X-ray ptychography, we explored in situ the dynamics of unstained, living fission yeast Schizosaccharomyces pombe cells in natural, aqueous environment at the nanoscale. In contrast to previous X-ray imaging studies on biological matter, in this work the eukaryotic cells were alive even after several ptychographic X-ray scans, which allowed us to visualize the chromatin motion as well as the autophagic cell death induced by the ionizing radiation. The accumulated radiation of the sequential scans allowed for the determination of a characteristic dose of autophagic vacuole formation and the lethal dose for fission yeast. The presented results demonstrate a practical method that opens another way of looking at living biological specimens and processes in a time-resolved label-free setting
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