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Mechanochemical synthesis and transformation of the polymorphic double carbonates fairchildite and buetschliite, (KCa(CO)): an in situ X-ray powder diffraction study
No full textThis study presents the mechanochemical synthesis of the two K2Ca(CO3)2 polymorphs, fairchildite and buetschliite, from CaCO3 and K2CO3 using a shaker mill. Unlike previous methods requiring high temperatures and prolonged heating, fairchildite, a high-temperature polymorph, is formed initially in all experiments, adhering to Ostwald's rule of stages. Notably, the transformation to the stable buetschliite phase can be achieved by varying milling parameters, particularly frequency and moisture content. The results suggest that pressure, rather than temperature, plays a significant role in this phase transition, with moisture further accelerating the transformation. These findings offer a new, efficient route for the synthesis of these polymorphs, highlighting the critical influence of milling conditions on the reaction pathway
Computed tomography imaging analysis of a fused filament fabrication (FFF) 3D printed neck-thyroid phantom for multidisciplinary purposes
No full textThe application of the 3D printing technique for the development of low-cost phantoms is being investigatedrecently and requires a complex study of the interaction of printed materials with different types and qualities ofradiation, as well as the characterization of printing filaments to correctly simulate human tissue attenuation.This study aims to present the Computed Tomography (CT) Imaging analysis of a fused filament fabrication (FFF)3D printed anthropomorphic neck-thyroid phantom. The commercial phantom ATOM MAX 711 from CIRS wasused as anatomy of reference for the 3D modeling base of the neck-thyroid phantom. Commercially available PLAand ABS XCT-A validated at IPEN were used in the 3D printing process in order to simulate soft and bone tissuesrespectively. The printing process was done using the RAISE3D PRO 2 FFF printer from IPEN. The imaging studyof the phantom was performed through the analysis of images from a CT acquisition, comparing the HounsfieldUnits (HU) numbers of the tissues between both CIRS and 3D printed phantoms. The developed phantom is afeasible alternative and presents some desirable characteristics for applications in radiation protection, measurements of radioisotopes incorporated in the thyroid (both contamination counters and nuclear medicinedetectors) and training of techniques of acquisition of images with X rays
Accurate measurements of slice electron beam parameters at the undulator in seeded Free Electron Lasers
No full textThe operation of modern Free Electron Lasers (FELs) necessitates precise knowledge of electron beam properties at the undulator to ensure the level of control required by increasingly demanding experiments. In seeded FELs, where only electrons inter- acting with the seed laser contribute to the process, it is crucial to determine the local values of these properties. We present a novel method, based on accurate modeling of the FEL process in High-Gain Harmonic Generation (HGHG), to accurately retrieve the electron beam energy spread, current, and laser-induced energy modulation. Understanding these values is essential for enabling advanced FEL schemes and optimally setting advanced seeding schemes such as Echo Enabled Harmonic Generation (EEHG). We describe the method and provide an experimental application to the FERMI FEL-1, where an energy spread in the range of 40-100 keV with a fewkeV accuracy is measured
Machine learning for the reconstruction and analysis of synchrotron-radiation tomography data
No full textThe Helmholtz-Zentrum Hereon is operating imaging beamlines for X-ray tomography (P05 IBL, P07 HEMS) for academic and industrial users at the synchrotron-radiation source PETRA III at DESY in Hamburg, Germany. The high flux density and coherence of synchrotron radiation enable high-resolution in situ/operando/in vivo tomography experiments and phase-contrast imaging techniques, respectively. Large amounts of 3D and 4D data are collected that are difficult to process and analyze. Recently, we have explored machine learning approaches for the reconstruction, processing and analysis of synchrotron-radiation tomography data. Here, we report on the application of supervised learning for multimodal data analysis to generate a virtual 3D histology, digital volume correlation of 4D in situ tomography data, and instance segmentation. Furthermore, we present findings related to unsupervised learning in the context of semantic segmentation
P21.1 at PETRA III - a high energy x-ray diffraction beamline for physics and chemistry
No full textBeamline P21.1 at PETRA III uses high-energy photons for the investigation of materials structure by diffraction methods. The instrumentation is particularly suited for probing ordering phenomena on a local scale in chemistry and physics. A detailed description of the instrumentation and detectors for such experiments is given. The beamline supports a number of sample environments for investigations under in situ and operando conditions, e.g. cryostats, furnaces, chemical reactors. Recent examples of measurements on amorphous, single-crystalline and thin film samples are described
Femtosecond charge and spin dynamics in a CoPt alloy
No full textThe use of advanced X-ray sources plays a key role in the study of dynamic processes in magnetically ordered materials. The progress in X-ray free electron lasers enables the direct and simultaneous observation of the femtosecond evolution of the electrons and spins through transient X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). Such experiments allow us to resolve how the population of the valence states evolves in magnetic solids upon optical excitation. Here, we utilize the new FLASH2 helical afterburner undulator’s circularly polarized ultrashort soft X-ray pulses from the FLASH free-electron laser FLASH to study the femtosecond dynamics of a laser-excited CoPt alloy at the Co L edge. We find a comparable demagnetization for lower electronic excitation of Co 3d-states in CoPt compared to previous measurements on CoPd. This points to a more efficient demagnetization depending on orbital hybridization and spin-orbit coupling between 3d and 4d or 5d elements in an alloys and multilayers
Thermal evolution of solid solution of silica-embedded AgPt alloy NPs in the large miscibility gap
No full textUnderstanding the phase behavior of immiscible elements in bimetallic nanomaterials is essential for controlling their structure and properties. At the nanoscale, the miscibility of these immiscible elements often deviates from their behavior in bulk materials. Despite its significance, comprehensive and quantitative experimental insights into the dynamics of the immiscible-to-miscible transition, and vice versa, remain limited. In this study, we investigate the nucleation and growth kinetics of silica-embedded AgPt nanoparticles (NPs) across a wide range of annealing temperatures (25 °C to 900 °C) to elucidate temperature-dependent nanoalloy phase transitions and NP size distribution. Our findings reveal that the alloy phase persists up to 400 °C, with a corresponding average NP size of ∼2 nm. Beyond this temperature, phase instability begins to occur. We propose a three-stage process of nucleation and growth: (1) initial AgPt nanoalloy formation during deposition, (2) growth via thermal energy-assisted diffusion up to 400 °C, and (3) Ag atom emission from the nanoalloy above 500 °C, indicating Ag diffusion towards the surface, followed by partial sublimation of Ag atoms at 900 °C. These results provide crucial insights into the thermal limits for the dealloying of NPs, growth kinetics, and phase stability or instability under varying thermal conditions
Unravelling the cracking mechanism in wire-based laser-directed energy deposition processing high-strength aluminum alloy
No full textHigh-strength aluminum alloys exhibit high cracking susceptibility in laser-based additive manufacturing. Understanding the mechanisms behind cracking and identifying the primary factors are crucial to preventing cracking, especially when dealing with difficult-to-process materials. Therefore, it is necessary to uncover the cracking mechanisms during successive deposition. In this study, the cracking mechanism is investigated in laser-directed energy deposition processing AA7075 alloy in terms of solidification conditions, microstructure, and residual stress. Based on the results, the cracking phenomenon observed during successive deposition is induced by insufficient backfilling to solidification shrinkage leading to solidification cracking. The melt-pool lifetime and the maximum melt-pool temperature are the primary factors determining the solidification cracking susceptibility. After the initiation, the cracks grow in two directions parallel to the building direction. The growth downwards is attributed to the liquation cracking mechanism, while the growth upwards results from the solidification cracking mechanism. The delayed cracking (cracking after a certain number of layers have been deposited) is identified as the consequence of the competitive growth between grains with preferential growth direction and highly misaligned grains
Discrete Gauging of 6d SCFTs and Wreathed 3d Quivers
No full textWe study the Higgs branch moduli space of certain 6d SCFTs after gauging their Green--Schwarz automorphism. We explain how to read the flavor symmetry of such SCFTs directly from the 6d construction, and we confirm the expectation by computing the Coulomb branch Hilbert series of their -wreathed 3d magnetic quiver. To perform the latter computation, we explicitly introduce a methodology to determine such Hilbert series for -wreathed orthosymplectic quivers