Simulation of diffraction and scattering using the Wigner Distribution Function

X-ray phase-contrast imaging enhances soft tissue visualization by leveraging the phase shift of X-rays passing through materials. It permits to minimize radiation exposure due to high contrast, as well as high resolution imaging limited by the wavelength of the X-rays. Phase retrieval extracts the phase shift computationally, but simulated images fail to recreate low-frequency noise observed in experimental images. To this end, we propose a new method to simulate phase contrast images using the Wigner Distribution Function. This permits the simulation of wave and particle effects simultaneously and simulates images photon by photon. Here, we give a first demonstration of the method by simulating the Gaussian double-slit experiment. It has the potential for realistic simulation of low-dose imaging.Comment: 4 pages, 5 figure

Laser powder bed fusion recoater selection guide: comparison of resulting powder bed properties and part quality

Spreading devices used to create powder layers in the laser powder bed fusion of metals (PBF-LB/M) were found to have a significant impact on the additive manufacturing process. However, previous research primarily focused on theoretical investigations, including recoater concepts that are not available on the market, while no comprehensive comparison of commercially available spreading devices currently exists. The aim of this study is therefore to examine the powder bed properties and part qualities that can be achieved with the three most common types of recoater: carbon fiber brushes, polymer lips, and high speed steel (HSS) blades. Identical build jobs were produced using each of the spreading devices. Their capabilities were assessed by nine evaluation criteria, including dimensional, metallurgical, and mechanical properties and criticality of particles abraded from the spreading devices. Based on these quantitative findings, a spreading device selection guide was compiled for the benefit of PBF-LB/M practitioners. All recoaters yielded processes with high stability and part properties that were on a par with or even outperformed the nominal values from the literature. However, the HSS blade was found to provide higher accuracy and stability in steady-state processes. In turn, the brush and lip are better suited for parameter development and design studies. Additionally, the lip was found to have economic benefits over the brush, while the brush was deemed an effective all-rounder

Mastzellen und gestörte männliche Fertilität

In der vorliegenden Arbeit konnte mittels Durchflusszytometrie nachgewiesen werden, dass Mastzellen im Ejakulat von Männern mit Infertilität vorhanden sind. Weiterhin konnte gezeigt werden, dass auch eine signifikante Korrelation zwischen erhöhten Mastzellzahlen und IgA-Antikörpern besteht, und zwar sowohl in der Patientengruppe des Gesamtkollektivs (n = 23) als auch in der Gruppe der Patienten mit Normozoospermie (n = 19). Keine Korrelation konnte in der Gruppe der Patienten mit Oligozoospermie (n = 4) festgestellt werden, da die Gruppengröße zu klein für eine signifikante Aussage ist. Nicht bekannt ist, wie die Korrelation in der Gruppe des Gesamtkollektivs und der Gruppe der Normozoospermiepatienten zustande kommt. Als Möglichkeiten kommen in Betracht, dass eine Erhöhung der Mastzellzahlen eine Erhöhung der IgA-Antikörper nach sich zieht oder der umgekehrte Fall ursächlich ist. Als weitere Möglichkeit wäre zu untersuchen, ob evtl. ein dritter Parameter existiert, welcher in Korrelation zu Mastzellen und IgAAntikörpern gleichermaßen steht. Die Korrelation von Mastzellen und IgA-Antikörpern lässt eine Spekulation über einen immunologischen-pathologischen Prozess zu. Eine Korrelation zu IgG-Antikörpern besteht nicht und auch in verschiedenen vorhergegangenen Studien ist bisher lediglich nachgewiesen worden, dass männliche Infertilität vorrangig mit IgA-Antikörpern in Verbindung gebracht wird. Des Weiteren ist keine Korrelation der Mastzellen zu den anderen untersuchten Parametern wie Spermienzahl, Beweglichkeit, Morphologie oder Vitalität, sowie auch zu den Entzündungsparametern (Elastase, Peroxidase) festzustellen

Endocast of the Late Triassic (Carnian) dinosaur Saturnalia tupiniquim: implications for the evolution of brain tissue in Sauropodomorpha

The evolutionary history of dinosaurs might date back to the first stages of the Triassic (c. 250-240 Ma), but the oldest unequivocal records of the group come from Late Triassic (Carnian -c. 230 Ma) rocks of South America. Here, we present the first braincase endocast of a Carnian dinosaur, the sauropodomorph Saturnalia tupiniquim, and provide new data regarding the evolution of the floccular and parafloccular lobe of the cerebellum (FFL), which has been extensively discussed in the field of palaeoneurology. Previous studies proposed that the development of a permanent quadrupedal stance was one of the factors leading to the volume reduction of the FFL of sauropods. However, based on the new data for S. tupiniquim we identified a first moment of FFL volume reduction in non-sauropodan Sauropodomorpha, preceding the acquisition of a fully quadrupedal stance. Analysing variations in FFL volume alongside other morphological changes in the group, we suggest that this reduction is potentially related to the adoption of a more restricted herbivore diet. In this context, the FFL of sauropods might represent a vestigial trait, retained in a reduced version from the bipedal and predatory early sauropodomorphs

Registration of phase contrast images in propagation-based X-ray phase tomography

International audienceX-ray phase tomography aims at reconstructing the 3D electron density distribution of an object. It offers enhanced sensitivity compared to attenuation-based X-ray absorption tomography. In propagation-based methods, phase contrast is achieved by letting the beam propagate after interaction with the object. The phase shift is then retrieved at each projection angle, and subsequently used in tomographic reconstruction to obtain the refractive index decrement distribution, which is proportional to the electron density. Accurate phase retrieval is achieved by combining images at different propagation distances. For reconstructions of good quality, the phase-contrast images recorded at different distances need to be accurately aligned. In this work, we characterise the artefacts related to misalignment of the phase-contrast images, and investigate the use of different registration algorithms for aligning in-line phase-contrast images. The characterisation of artefacts is done by a simulation study and comparison with experimental data. Loss in resolution due to vibrations is found to be comparable to attenuation-based computed tomography. Further, it is shown that registration of phase-contrast images is nontrivial due to the difference in contrast between the different images, and the often periodical artefacts present in the phase-contrast images if multilayer X-ray optics are used. To address this, we compared two registration algorithms for aligning phase-contrast images acquired by magnified X-ray nanotomography: one based on cross-correlation and one based on mutual information. We found that the mutual information-based registration algorithm was more robust than a correlation-based method

Caractérisation expérimentale de l'endommagement dans les minicomposites SiC/SiC

National audienceLes composites SiC/SiC sont étudiés pour leur usage potentiel comme matériau de gainage dans les réacteurs nucléaires de génération future. Afin de valider un modèle multiéchelle d'endommagement à l'échelle microscopique, une caractérisation expérimentale de l'endommagement à l'échelle du toron est mise en œuvre. Des essais de traction in-situ sur minicomposite permettent d'obtenir des données statistiques sur la cinétique d'apparition des fissures matricielles et l'évolution de leur ouverture en fonction de la contrainte. Ces observations de surface sont complétées par des observations microtomographiques réalisées à l'ESRF sur un minicomposite en traction. L'analyse des images 3D permet alors d'étudier la propagation des fissures matricielles au sein du minicomposite. Les ruptures de fibres sont également observables grâce à cette technique d'observation