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Here we determine the compressional and shear wave velocities ( v p and v s ) of hexagonal close-packed iron, a candidate for the main constituent of the Earth’s inner core, to pressures above 300 gigapascals using a newly designed diamond anvil cell and inelastic X-ray scattering combined with X-ray diffraction. The present results reveal that the v p and v s of the Preliminary reference Earth model (PREM) inner core are 4(±2)% and 36(±17)% slower than those of the pure iron, respectively at the centre of the core. The density and sound velocity of the PREM inner core can be explained by addition of 3(±1) wt% silicon and 3(±2) wt% sulphur to iron‒5 wt% nickel alloy. Our suggested inner core composition is consistent with the existing outer core model with oxygen, as the growth of the inner core may have created a secular enrichment of the element in the outer core. New constraints on the composition of Earth’s inner core are provided by experimental verification of Birch’s law for hexagonal close-packed iron to pressure above 300 gigapascals, about double the pressure achieved in previous investigations

While charge density wave (CDW) instabilities are ubiquitous to superconducting cuprates, the different ordering wave vectors in various cuprate families have hampered a unified description of the CDW formation mechanism. Here, we investigate the temperature dependence of the low-energy phonons in the canonical CDW-ordered cuprateLa1.875Ba0.125CuO4. We discover that the phonon softening wave vector associated with CDW correlations becomes temperature dependent in the high-temperature precursor phase and changes from a wave vector of 0.238 reciprocal lattice units (r.l.u.) below the ordering transition temperature to 0.3 r.l.u. at 300 K. This high-temperature behavior shows that “214”-type cuprates can host CDW correlations at a similar wave vector to previously reported CDW correlations in non-214-type cuprates such asYBa2Cu3O6+δ. This indicates that cuprate CDWs may arise from the same underlying instability despite their apparently different low-temperature ordering wave vectors.

Antiferroelectrics are essential ingredients for the widely applied piezoelectric and ferroelectric materials: the most common ferroelectric, lead zirconate titanate is an alloy of the ferroelectric lead titanate and the antiferroelectric lead zirconate. Antiferroelectrics themselves are useful in large digital displacement transducers and energy-storage capacitors. Despite their technological importance, the reason why materials become antiferroelectric has remained allusive since their first discovery. Here we report the results of a study on the lattice dynamics of the antiferroelectric lead zirconate using inelastic and diffuse X-ray scattering techniques and the Brillouin light scattering. The analysis of the results reveals that the antiferroelectric state is a ‘missed’ incommensurate phase, and that the paraelectric to antiferroelectric phase transition is driven by the softening of a single lattice mode via flexoelectric coupling. These findings resolve the mystery of the origin of antiferroelectricity in lead zirconate and suggest an approach to the treatment of complex phase transitions in ferroics. Although antiferroelectric lead zirconate is a principal component in the most widely used piezoelectric ceramics, the nature of its antiferroelectricticity has been unclear. Here Tagantsev et al. reveal how this phenomenon arises from the softening of a single lattice mode.

We investigated the compressional and shear velocities, VP and VS, of the HH1‐phase by combining the inelastic x‐ray scattering and x‐ray diffraction experiments. In the pressure range of 64.7–79.6 GPa and at room temperature, the VP and VS were measured to be 9.66–11.05 and 4.9–6.4 km·s⁻1, respectively. We employed a simplified model to quantitatively discuss the sound velocity differences between hydrous and anhydrous phase assemblages in the mid‐lower mantle, revealing that the hydrous assemblage exhibits increased VS and a reduced VP/VS ratio compared to its anhydrous counterpart. This suggests formation of seismic scatterers in the mid‐lower mantle exhibiting high VS anomalies may be related to the heterogeneous distribution of water. Moreover, the interpretation of a large VP/VS ratio as indicating the presence of water in the upper mantle and crust may not be applicable for detecting water in the lower mantle. Plain Language Summary Water, which is heterogeneously distributed in the Earth's interior, is one of the most important volatiles of our planet. Incorporation of water into a multicomponent system of the Earth's lower mantle can dramatically alter its phase relations. In particular, the formation of hydrous phases can lead to changes in the seismic velocities of the system. The HH1‐phase is an iron‐rich hydrous hexagonal phase of Fe16.72O18Hx (x∼4.5), which can be formed through reactions in basaltic or peridotitic compositions with water under the pressure and temperature conditions of the deep lower mantle. We have performed inelastic X‐ray scattering and X‐ray diffraction experiments in diamond anvil cells, and measured the sound velocities of HH1‐phase. We thus investigate the sound velocity differences between hydrous and anhydrous phase assemblages in the mid‐lower mantle. Our study can provide a better understanding of the seismic anomalies in the lower mantle. Key Points VP and VS of the HH1‐phase were obtained by inelastic x‐ray scattering and x‐ray diffraction measurements at 64.7–79.6 GPa and 300 K Some hydrous regions of pyrolite lower mantle may exhibit higher VS and lower VP/VS ratio than the dry regions Heterogeneous distribution of water may provide an explanation for the seismic scatterers in the lower mantle

The relative abundance of light elements in the Earth’s core has long been controversial. Recently, the presence of carbon in the core has been emphasized, because the density and sound velocities of the inner core may be consistent with solid Fe 7 C 3 . Here we report the longitudinal wave velocity of liquid Fe 84 C 16 up to 70 GPa based on inelastic X-ray scattering measurements. We find the velocity to be substantially slower than that of solid iron and Fe 3 C and to be faster than that of liquid iron. The thermodynamic equation of state for liquid Fe 84 C 16 is also obtained from the velocity data combined with previous density measurements at 1 bar. The longitudinal velocity of the outer core, about 4% faster than that of liquid iron, is consistent with the presence of 4–5 at.% carbon. However, that amount of carbon is too small to account for the outer core density deficit, suggesting that carbon cannot be a predominant light element in the core. The composition of the Earth's core, particularly the light elements present, is not well constrained. Here, the authors report sound velocities of liquid iron-carbon alloy as measured at very high pressures using inelastic X-ray scattering and suggest that carbon cannot be predominant in the outer core.

Background Contact tracing (CT) is a key strategy when dealing with outbreaks of infectious diseases such as COVID-19. The scale of the COVID-19 pandemic has often left public health professionals (PHPs), who are responsible for the execution of CT, unable to keep up with the rapid and largescale spread of the virus. To enhance or support its execution, and potentially lower the workload for PHPs, citizens may be more actively involved in CT-tasks that are commonly executed by PHPs (referred to as ‘self-led CT’). There is limited insight into citizens’ perspectives on and needs for self-led CT for COVID-19. This study aims to explore the perspectives and needs of Dutch citizens on taking more responsibilities in the execution of CT for COVID-19, potentially through the use of digital tools. Methods An exploratory qualitative study was performed, in which online semi-structured interviews were conducted. Questions were based on the Reasoned Action Approach and Health Belief Model. Interviews were audio-recorded and transcribed verbatim. A thematic analysis was conducted to identify citizens’ perspectives and needs to participate in self-led CT. Results We conducted 27 interviews with Dutch citizens. Seven main themes were identified from the interviews: 1) ‘Citizens’ perspectives on self-led CT are influenced by prior experiences with regular CT’, 2) ‘Citizens’ felt responsibilities and the perceived responsibilities of the PHS in CT shape their perspectives on self-led CT’, 3) ‘Anticipated impacts of self-led CT on the CT-process’, 4) ‘Citizens’ attitude towards the application of self-led CT depends on their own perceived skills and the willingness and skills of others’, 5) ‘Shame and social stigma may hamper participation in self-led CT’, 6) ‘Concerns about privacy and data security: a barrier for self-led CT’, and 7) ‘Citizens’ perspectives and anticipated needs for the implementation and application of self-led CT in practice’. Conclusions Most interviewees hold a positive attitude towards self-led CT and using digital tools for this purpose. However, their intention for self-led CT may depend on various factors, such as prior experiences with regular CT, and their perceived self-efficacy to participate. Perspectives and needs of citizens should be considered for the future implementation of self-led CT in practice.

Complex regional pain syndrome (CRPS) is the result of changes to the somatosensory systems that process noxious, tactile, and thermal information; to the sympathetic systems that innervate skin (blood vessels, sweat glands); and to the somatomotor systems. The changes suggest that the CNS representations of the systems have been altered. Patients with CRPS also have peripheral changes (eg, oedema, signs of inflammation, sympathetic-afferent coupling [the basis for sympathetically maintained pain], and trophic changes) that cannot be explained by central changes. On the basis of clinical observation and research in human beings and animals, we hypothesise that CRPS is a systemic disease involving the CNS and peripheral nervous system. The most important question for future research is what causes CRPS? In this article, we suggest a change to the focus of research efforts and treatment. We also suggest there be diagnostic reclassification and redefinition of CRPS.

Background Autoimmune pancreatitis (AIP) is an uncommon form of chronic pancreatitis. Whilst being corticosteroid responsive, AIP often masquerades radiologically as pancreatic neoplasia. Our aim is to appraise demographic, radiological and histological features in our cohort in order to differentiate AIP from pancreatic malignancy. Methods Clinical, biochemical, histological and radiological details of all AIP patients 1997–2016 were analysed. The initial imaging was re-reviewed according to international guidelines by three blinded independent radiologists to evaluate features associated with autoimmune pancreatitis and pancreatic cancer. Results There were a total of 45 patients: 25 in type 1 (55.5%), 14 type 2 (31.1%) and 6 AIP otherwise not specified (13.3%). The median (IQR) age was 57 (51–70) years. Thirty patients (66.6%) were male. Twenty-six patients (57.8%) had resection for suspected malignancy and one for symptomatic chronic pancreatitis. Three had histologically proven malignancy with concurrent AIP. Two patients died from recurrent pancreatic cancer following resection. Multidisciplinary team review based on radiology and clinical history dictated management. Resected patients (vs. non-resected group) were older (64 vs. 53, p  = 0.003) and more frequently had co-existing autoimmune pathologies (22.2 vs. 55.6%, p  = 0.022). Resected patients also presented with less classical radiological features of AIP, which are halo sign (0/25 vs. 3/17, p  = 0.029) and loss of pancreatic clefts (18/25 vs. 17/17, p  = 0.017). There were no differences in demographic features other than age. Conclusion Despite international guidelines for diagnosing AIP, differentiation from pancreatic cancer remains challenging. Resection remains an important treatment option in suspected cancer or where conservative treatment fails.

A diffusion model for the analysis of chronoamperometric data in response to a concentration step is developed for amperometric gas sensors. This analysis avoids the difficulties with standard potentiodynamic measurements at the large specific area, high capacitance electrodes employed in these sensors. Despite the fact that typical devices comprise multiple layers with varying thicknesses and diffusivities, we show that typical chronoamperometric traces can be fitted to a simple diffusion model with a single parameter τ=L2D${\\tau ={{{L}^{2}}\\over{D}}}$where L is an overall effective thickness of the diffusion barrier and D is an effective diffusion coefficient. Through a comparison of the transient and steady‐state current, independent estimates of L and D in the devices can be made. The model is also extended to cover cases with interfacial kinetic barriers; such kinetic limitations lead to a change in the effective values L and D, but the simple diffusion model remains a good fit to the data. This analysis shows that transient sensor responses can be characterised by a single parameter τ and conversely that deviations from this regression model cannot be assigned to (i) complex layer architectures or (ii) interlayer kinetic barriers. Instead, we show that non‐uniform accessibility effects arising from a distribution of diffusion rates across the device lead to deviations from the simple regression model, but that they may be captured approximately by a more complex model in which τ has a probability distribution. Diffusion models for the response of commercial amperometric gas sensors to a concentration step of the analyte are analysed. Effective values of barrier thickness and diffusion coefficient can be extracted for devices with complex layered architectures and possible interfacial phase transfer barriers. Small deviations of the experimental data from the model reflect a distribution of diffusivities in the devices.

This paper examines the phonon dispersion and static local atomic distortion of iron-manganese-based Elinvar alloys using high-resolution inelastic X-ray scattering, magnetization, neutron diffraction, and neutron total scattering. In this study, nonlinear phonon dispersion was observed for a transverse acoustic mode near zone center, associated with elastic constants, over a wide temperature range along the to X (310) points of the face-centered cubic system, indicating lattice instability coupled with tetragonal distortions in the long-wavelength limit. Bulk magnetization and neutron diffraction measurements suggest that the conventional ferromagnetic magnetostriction scenario is not the origin of Elinvar characteristics. Instead, the martensitic transformation and lattice instabilities underlie these phenomena. The reduced pair distribution function reveals a significant discrepancy between local and global (averaged) structures suggesting the influence of atomic-scale lattice disorder and instability in FeMn-based Elinvar alloys.