Journal of Applied Crystallography最新文献

Proteins are ubiquitous in biological membranes and have a significant impact on their scattering properties. In this contribution, we introduce a general mathematical construction to add proteins to any pre-existing membrane model and to calculate the resulting elastic and/or inelastic scattering cross section. The model is a low-resolution one, which describes the proteins as made up of regions of homogeneous scattering length density that extend through an arbitrary fraction of the membrane and possibly protrude out of it. In this construction, the protein characteristics that are relevant to scattering are their space and time correlation functions in the two-dimensional plane of the membrane. The results are particularized to a static bilayer model and to a Gaussian model of a fluctuating membrane. The models are then applied to the joint analysis of small-angle neutron and X-ray scattering of red blood cell membranes, of which transmembrane proteins constitute 25% of the volume, and to neutron spin-echo data measured on the same systems.

Far-field high-energy diffraction microscopy (ff-HEDM) bridges a critical gap between microscale and macroscale plasticity by enabling three-dimensional (3D) time-resolved observations of grain-scale deformation. It can be used to measure the grain-averaged elastic strain tensor, crystallographic orientation, centroid and relative volume of each individual grain. Researchers have also proposed methods to extract information about grain-scale plastic deformation from time-resolved ff-HEDM measurements, using e.g. signature changes in a grain's equivalent or resolved shear stress, orientation or diffraction peak width. However, the accuracy of these different methods is largely unexplored due to the absence of an independent ground truth, particularly for plastic deformation that occurs prior to the macroscopic yield point. In the present work, we evaluate four methods for detecting grain-scale plastic deformation events using ff-HEDM: (i) equivalent stress relaxation, (ii) resolved shear stress relaxation, (iii) orientation change and (iv) diffraction peak shape evolution. Using ff-HEDM data from room-temperature creep tests of a Ti-7Al alloy, we cross-validate these approaches. The achieved high validation rates support confidence in the identified events. Two types of stress relaxation are observed among the detected events - fast and large versus gradual and small - suggesting different deformation mechanisms. The spatiotemporal distribution of plastic events is also captured, revealing clustered activity and intergranular propagation. These findings open avenues for future studies to explore the initiation and propagation of plasticity among grains.

Small- and wide-angle X-ray scattering tensor tomography are powerful methods for studying anisotropic nanostructures in a volume-resolved manner and are becoming increasingly available to users of synchrotron facilities. The analysis of such experiments requires advanced procedures and algorithms, which creates a barrier for the wider adoption of these techniques. Here, in response to this challenge, we introduce the MUMOTT package. It is written in Python, with computationally demanding tasks handled via just-in-time compilation using both CPU and GPU resources. The package has been developed with a focus on usability and extensibility, while achieving a high computational efficiency. Following a short introduction to the common workflow, we review key features, outline the underlying object-oriented framework and demonstrate the computational performance. By developing the MUMOTT package and making it generally available, we hope to lower the threshold for the adoption of tensor tomography and to make these techniques accessible to a larger research community.

We start from an analytical formulation for the coherent multiple scattering treatment - similar to Mie scattering - for spherical particles. Then, we revisit the Born approximation with an approximation for all higher-order terms. Finally, we draw conclusions from those calculations and formulate an approximative model to describe ultra-small-angle neutron scattering and ultra-small-angle X-ray scattering data. In all calculations, we can specify the conditions for coherent multiple scattering. Several examples are provided to show the quality of the simple approximation in comparison with exact calculations and experiments.

Resonant elastic X-ray scattering (REXS) is an experimental technique that can be highly valuable for studying magnetic structures in certain scenarios. In this paper, we introduce MagStREXS, a crystallographic program designed to determine magnetic structures from REXS data. This software makes use of the key concepts and computational tools already established in the field of magnetic crystallography. Here, we present the fundamental equations implemented in MagStREXS, derived for the two methods used to describe magnetic models: the representation analysis and the symmetry-based approach. We illustrate the capabilities of MagStREXS with a case study. The software is under active development, with the aim of benefiting both specialists and non-specialists in the field.

A three-term equation for phenomenological absorption of electron beams in materials is derived for use in quantitative transmission electron microscopy simulations. This is motivated by differential quantitative convergent-beam electron diffraction (QCBED) using CBED patterns that have not been electron-optically energy filtered. As a starting point, this three-parameter function reproduces inelastic scattering factors generated by the ubiquitous ATOM subroutine of Bird & King [Acta Cryst. (1990), A46, 202-208] to within a few per cent, spanning elements Z = 1 to 98, Debye-Waller parameters from B = 0.05 Ų to B = 2.0 Ų, scattering angles from s = 0 Å^-1 to s = 6.0 Å^-1 and electron energies from E ₀ = 1 keV to E ₀ = 1 MeV. As such, it is applicable to zero-energy-loss electron-optically filtered pattern matching for which the Bird and King ATOM subroutine was designed. Crucially, the coefficients of the three terms in the present equation can be refined to produce inelastic scattering factors with differing local and non-local contributions, which are better suited to unfiltered differential QCBED pattern matching.

The LibraEDT software has been developed to enhance and automate 3D electron diffraction (3D-ED) experiments by addressing key challenges such as crystal tracking, low-fluence data acquisition and better data management. This tool significantly improves both the accuracy and efficiency of ED workflows, particularly when applied to beam-sensitive materials. The utility of this approach is demonstrated through the structural analysis of a known beam-sensitive organic crystal, as well as a novel and previously unreported zinc-based metal-organic framework incorporating protocatechuic acid.

Non-stochiometric crystals, such as solid solutions, represent a valid strategy for fine-tuning the properties of materials from inorganic pigments to active pharma-ceutical ingredients. The change is achieved by substitution of structurally similar compounds within the crystal structure, resulting in a minor variation of cell parameters, and it can be experimentally observed as a shift of the X-ray diffraction profile, with the shift depending on the substitutional amount. After proper alignment of the diffraction data, chemometric methods can detect the evolution of the solid solution profile and correlate it to the molar composition, creating rapid quantitative models. The solid solutions chosen for this work are NA₂·FA _x SA_1-x and IN₂·FA _x SA_1-x , i.e. co-crystals of nicotin-amide (NA) and isonicotinamide (IN) with fumaric acid (FA) and succinic acid (SA) in different proportions; they are used as model systems for the development of principal component regression and partial least-squares models for the quantification of solid solution composition. Different alignment strategies are presented, and the results obtained from test samples show the prediction efficacy of the proposed approach.

We demonstrate that small-angle neutron scattering (SANS) can resolve the architecture of photosynthetic thylakoid membranes in live symbiotic algal cells, both extracted from and living inside their respective hosts (ex hospite and in hospite, respectively). This enables a new non-destructive approach to probing thylakoid organization in coral symbioses, relevant to understanding the mechanisms of coral bleaching. A biologically realistic triple-vesicle model, guided by electron microscopy and established biochemical constraints, was fitted to SANS data from live Symbiodinium associated with both the coral analogue Aiptasia and the reef-building coral Acropora. The resulting compartment scattering length densities, together with established biochemical constraints, define a limited compositional range that supports the plausibility of the structural solution. These fits capture key scattering features and yield dimensional parameters, including inter-thylakoid (IT) gap widths, with uncertainties small enough to test models of stress-related membrane rearrangement. A focused covariance analysis shows that this SANS framework can resolve an IT-gap expansion of ∼2.4 nm with >7σ sensitivity, sufficient to distinguish structural changes proposed in thylakoid stress-response models. This provides a robust baseline for future live-cell studies.

The virtual special issue related to the 19th International Small Angle Scattering Conference (SAS2024, Taipei, Taiwan) is introduced. The articles included here were originally published in recent regular issues of Journal of Applied Crystallography and Journal of Synchrotron Radiation. The SAS2024 special issue is available at https://journals.iucr.org/special_issues/2025/sas2024/.