Nanostructure determination from the pair distribution function: A parametric study of the INVERT approach

We present a detailed study of the mechanism by which the INVERT method [Phys. Rev. Lett. 104, 125501] guides structure refinement of disordered materials. We present a number of different possible implementations of the central algorithm and explore the question of algorithm weighting. Our analysis includes quantification of the relative contributions of variance and fit-to-data terms during structure refinement, which leads us to study the roles of density fluctuations and configurational jamming in the RMC fitting process. We present a parametric study of the pair distribution function solution space for C60, a-Si and a-SiO2, which serves to highlight the difficulties faced in developing a transferable weighting scheme.Comment: 15 pages, 7 figures, formatted for JPCM (RMC issue

The diffusion of cholera in Egypt, 1947: a time-space analysis of one of the largest single outbreaks in the twentieth century

The epidemic of cholera that spread through Egypt in the latter months of 1947 was one of the largest single outbreaks of the disease in the twentieth century. Using a swash–backwash model, this paper examines the geographical wave-like spread and subsequent retreat of the epidemic from an apparent origin in the settlements and prisoner-of-war camps of the Nile Delta area to reach its maximum geographical extent some six weeks later at Aswan (850 km away). Our results demonstrate the very rapid spatial advance of the epidemic wave through the provinces and governorates of Egypt, with an approximately linear sequence of progression up the Nile. Superimposed on this national pattern are pronounced differences in the rate of epidemic advance in the traditional geographical divisions of Lower and Upper Egypt. Alternative visualisations of the cholera spaces of Egypt, using techniques of multidimensional scaling (MDS) and cluster analysis, underscore the differential patterns of cholera transmission in these areas of the country. The patterns are interpreted in relation to a vigorous control effort that included restrictions on public transport, patient isolation, contact tracing and mass vaccination of the entire population exposed to risk of infection

Structure determination of disordered materials from diffraction data

We show that the information gained in spectroscopic experiments regarding the number and distribution of atomic environments can be used as a valuable constraint in the refinement of the atomic-scale structures of nanostructured or amorphous materials from pair distribution function (PDF) data. We illustrate the effectiveness of this approach for three paradigmatic disordered systems: molecular C60, a-Si, and a-SiO2 . Much improved atomistic models are attained in each case without any a-priori assumptions regarding coordination number or local geometry. We propose that this approach may form the basis for a generalised methodology for structure "solution" from PDF data applicable to network, nanostructured and molecular systems alike.Comment: 4 pages, 3 figures, set out as for PR

Design of crystal-like aperiodic solids with selective disorder--phonon coupling

Functional materials design normally focuses on structurally-ordered systems because disorder is considered detrimental to many important physical properties. Here we challenge this paradigm by showing that particular types of strongly-correlated disorder can give rise to useful characteristics that are inaccessible to ordered states. A judicious combination of low-symmetry building unit and high-symmetry topological template leads to aperiodic "procrystalline" solids that harbour this type of topological disorder. We identify key classes of procrystalline states together with their characteristic diffraction behaviour, and establish a variety of mappings onto known and target materials. Crucially, the strongly-correlated disorder we consider is associated with specific sets of modulation periodicities distributed throughout the Brillouin zone. Lattice dynamical calculations reveal selective disorder-phonon coupling to lattice vibrations characterised by these same periodicities. The principal effect on the phonon spectrum is to bring about dispersion in energy rather than wave-vector, as in the poorly-understood "waterfall" effect observed in relaxor ferroelectrics. This property of procrystalline solids suggests a mechanism by which strongly-correlated topological disorder might allow new and useful functionalities, including independently-optimised thermal and electronic transport behaviour as required for high-performance thermoelectrics.Comment: 4 figure

Variola minor in coalfield areas of England and Wales, 1921–34: geographical determinants of a national smallpox epidemic that spread out of effective control

This paper uses techniques of binary logistic regression to identify the spatial determinants of the last national epidemic of smallpox to spread in England and Wales, the variola minor epidemic of 1921–34. Adjusting for age and county-level variations in vaccination coverage in infancy, the analysis identifies a dose-response gradient with increasing odds of elevated smallpox rates in local government areas with (i) medium (odds ratio [OR] = 5.32, 95% Confidence Interval [95% CI] 1.96–14.41) and high (OR = 11.32, 95% CI 4.20–31.59) coal mining occupation rates and (ii) medium (OR = 16.74, 95% CI 2.24–125.21) and high (OR = 63.43, 95% CI 7.82–497.21) levels of residential density. The results imply that the spatial transmission of variola virus was facilitated by the close spatial packing of individuals, with a heightened transmission risk in coal mining areas of the country. A syndemic interaction between common respiratory conditions arising from exposure to coal dust and smallpox virus transmission is postulated to have contributed to the findings. We suggest that further studies of the geographical intersection of coal mining and acute infections that are transmitted via respiratory secretions are warranted

Defect-dependent colossal negative thermal expansion in UiO-66(Hf) metal-organic framework

Thermally-densified hafnium terephthalate UiO-66(Hf) is shown to exhibit the strongest isotropic negative thermal expansion (NTE) effect yet reported for a metal-organic framework (MOF). Incorporation of correlated vacancy defects within the framework affects both the extent of thermal densification and the magnitude of NTE observed in the densified product. We thus demonstrate that defect inclusion can be used to tune systematically the physical behaviour of a MOF.Comment: 8 pages, 4 figures, revise

Inorganic Metal Thiocyanates

Metal thiocyanates were some of the first pseudohalide compounds to be discovered and adopt a diverse range of structures. This review describes the structures, properties, and syntheses of the known binary and ternary metal thiocyanates. It provides a categorization of their diverse structures and connects them to the structures of atomic inorganic materials. In addition to this description of characterized binary and ternary thiocyanates, this review summarizes the state of knowledge for all other binary metal thiocyanates. It concludes by highlighting opportunities for future materials development

PASCal Python: A Principal Axis Strain Calculator

The response of crystalline materials to external stimuli: whether temperature, pressure or electrochemical potential, is critical for both our understanding of materials and their use. This information can be readily obtained through in-situ diffraction experiments, however if the intrinsic anisotropy of crystals is not taken into account, the true behaviour of crystals can be overlooked. This is particularly true for anomalous mechanical properties of great topical interest, such as negative linear or area compressibility (Cairns & Goodwin, 2015; Hodgson et al., 2014), negative thermal expansion (Chen et al., 2015) or strongly anisotropic electrochemical strain (Kondrakov et al., 2017). We have developed PASCal, Principal Axis Strain Calculator, a widely used web tool that implements the rapid calculation of principal strains and fitting to many common models for equations of state. It provides a simple web form user interface designed to be able to be used by all levels of experience. This new version of PASCal is written in Python using the standard scientific Python stack (Harris et al., 2020; Virtanen et al., 2020), is released open source under the MIT license, and significantly extends the feature set of the original closed-source Fortran, Perl and Gnuplot webtool (Cliffe & Goodwin, 2012). Significant additional attention has been paid to testing, documentation, modularisation and reproducibility, enabling the main app functionality to now also be accessed directly through a Python API. The web app is deployed online at https://www.pascalapp.co.uk with the associated source code and documentation available on GitHub at MJCliffe/PASCal

SquidLab—A user-friendly program for background subtraction and fitting of magnetization data

We present an open-source program free to download for academic use with a full user-friendly graphical interface for performing flexible and robust background subtraction and dipole fitting on magnetization data. For magnetic samples with small moment sizes or sample environments with large or asymmetric magnetic backgrounds, it can become necessary to separate background and sample contributions to each measured raw voltage measurement before fitting the dipole signal to extract magnetic moments. Originally designed for use with pressure cells on a Quantum Design MPMS3 SQUID magnetometer, SquidLab is a modular object-oriented platform implemented in Matlab with a range of importers for different widely available magnetometer systems (including MPMS, MPMS-XL, MPMS-IQuantum, MPMS3, and S700X models) and has been tested with a broad variety of background and signal types. The software allows background subtraction of baseline signals, signal preprocessing, and performing fits to dipole data using Levenberg–Marquardt non-linear least squares or a singular value decomposition linear algebra algorithm that excels at picking out noisy or weak dipole signals. A plugin system allows users to easily extend the built-in functionality with their own importers, processes, or fitting algorithms. SquidLab can be downloaded, under Academic License, from the University of Warwick depository (wrap.warwick.ac.uk/129665)