Interstitial-mediated dislocation climb and the weakening of particle-reinforced alloys under irradiation

Dislocations can climb out of their glide plane by absorbing (or emitting) point defects [vacancies and self-interstitial atoms (SIAs)]. In contrast with conservative glide motion, climb relies on the point defects' thermal diffusion and hence operates on much longer timescales, leading to some forms of creep. While equilibrium point defect concentrations allow dislocations to climb to relieve nonglide stresses, point defect supersaturations also lead to osmotic forces, driving dislocation motion even in the absence of external stresses. Self-interstitial atoms typically have significantly higher formation energies than vacancies, so their contribution to climb is usually ignored. However, under irradiation conditions, both types of defect are athermally created in equal numbers. In this paper, we use simple thermodynamic arguments to show that the contribution of interstitials cannot be neglected in irradiated materials and that the osmotic force they induce on dislocations is many orders of magnitude larger than that caused by vacancies. This explains why the prismatic dislocation loops observed by in situ transmission electron microscope irradiations are more often of interstitial rather than vacancy character. Using discrete dislocation dynamics simulations, we investigate the effect on dislocation-obstacle interactions and find reductions in the depinning time of many orders of magnitude. This has important consequences for the strength of particle-reinforced alloys under irradiation

Performance and Cost Assessment of Machine Learning Interatomic Potentials.

Machine learning of the quantitative relationship between local environment descriptors and the potential energy surface of a system of atoms has emerged as a new frontier in the development of interatomic potentials (IAPs). Here, we present a comprehensive evaluation of machine learning IAPs (ML-IAPs) based on four local environment descriptors-atom-centered symmetry functions (ACSF), smooth overlap of atomic positions (SOAP), the spectral neighbor analysis potential (SNAP) bispectrum components, and moment tensors-using a diverse data set generated using high-throughput density functional theory (DFT) calculations. The data set comprising bcc (Li, Mo) and fcc (Cu, Ni) metals and diamond group IV semiconductors (Si, Ge) is chosen to span a range of crystal structures and bonding. All descriptors studied show excellent performance in predicting energies and forces far surpassing that of classical IAPs, as well as predicting properties such as elastic constants and phonon dispersion curves. We observe a general trade-off between accuracy and the degrees of freedom of each model and, consequently, computational cost. We will discuss these trade-offs in the context of model selection for molecular dynamics and other applications

Structure of the protective nematode protease complex H-gal-GP and its conservation across roundworm parasites

Roundworm parasite infections are a major cause of human and livestock disease worldwide and a threat to global food security. Disease control currently relies on anthelmintic drugs to which roundworms are becoming increasingly resistant. An alternative approach is control by vaccination and ‘hidden antigens’, components of the worm gut not encountered by the infected host, have been exploited to produce Barbervax, the first commercial vaccine for a gut dwelling nematode of any host. Here we present the structure of H-gal-GP, a hidden antigen from Haemonchus contortus, the Barber’s Pole worm, and a major component of Barbervax. We demonstrate its novel architecture, subunit composition and topology, flexibility and heterogeneity using cryo-electron microscopy, mass spectrometry, and modelling. Importantly, we demonstrate that complexes with the same architecture are present in other Strongylid roundworm parasites including human hookworm. This suggests a common ancestry and the potential for development of a unified hidden antigen vaccine

ATLASGAL - physical parameters of dust clumps associated with 6.7 GHz methanol masers

We have constructed the largest sample of dust-associated class II 6.7 GHz methanol masers yet obtained. New measurements from the Methanol Multibeam (MMB) survey were combined with the 870 μm APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) and the 850 μm JCMT Plane Survey (JPS). Together with two previous studies we have now identified the host clumps for 958 methanol masers across the Galactic Plane, covering approximately 99 per cent of the MMB catalogue and increasing the known sample of dust-associated masers by over 30 per cent. We investigate correlations between the physical properties of the clumps and masers using distances and luminosities drawn from the literature. Clumps hosting methanol masers are significantly more compact and have higher volume densities than the general population of clumps. We determine a minimum volume density threshold of n(H2) ≥ 104 cm−3 for the efficient formation of intermediate- and high-mass stars. We find 6.7 GHz methanol masers are associated with a distinct part of the evolutionary process (Lbol/Mfwhm ratios of between 100.6 and 102.2) and have well-defined turning on and termination points. We estimate the lower limit for the mass of embedded objects to be ≥6 M⊙ and the statistical lifetime of the methanol maser stage to be ∼3.3 × 104 yr. This suggests that methanol masers are indeed reliable tracers of high-mass star formation, and indicates that the evolutionary period traced by this marker is relatively rapid

Spirometry reference equations for central European populations from school age to old age.

Spirometry reference values are important for the interpretation of spirometry results. Reference values should be updated regularly, derived from a population as similar to the population for which they are to be used and span across all ages. Such spirometry reference equations are currently lacking for central European populations. To develop spirometry reference equations for central European populations between 8 and 90 years of age. We used data collected between January 1993 and December 2010 from a central European population. The data was modelled using "Generalized Additive Models for Location, Scale and Shape" (GAMLSS). The spirometry reference equations were derived from 118'891 individuals consisting of 60'624 (51%) females and 58'267 (49%) males. Altogether, there were 18'211 (15.3%) children under the age of 18 years. We developed spirometry reference equations for a central European population between 8 and 90 years of age that can be implemented in a wide range of clinical settings

A systematic review of the neurobiological underpinnings of borderline personality disorder (BPD) in childhood and adolescence

Contemporary theories for the aetiology of borderline personality disorder (BPD) take a lifespan approach asserting that inborn biological predisposition is potentiated across development by environmental risk factors. In this review, we present and critically evaluate evidence on the neurobiology of BPD in childhood and adolescence, compare this evidence to the adult literature, and contextualise within a neurodevelopmental framework. A systematic review was conducted to identify studies examining the neurobiological (i.e. genetic, structural neuroimaging, neurophysiological, and neuropsychological) correlates of BPD symptoms in children and adolescents aged 19 years or under. We identified, quality assessed, and narratively summarised 34 studies published between 1980 and June 2016. Similar to findings in adult populations, twin studies indicated moderate to high levels of heritability of BPD, and there was some evidence for gene-environment interactions. Also consistent with adult reports is that some adolescents with BPD demonstrated structural (grey and white matter) alterations in frontolimbic regions and neuropsychological abnormalities (i.e. reduced executive function and disturbances in social cognition). These findings suggest that neurobiological abnormalities observed in adult BPD may not solely be the consequence of chronic morbidity or prolonged medication use. They also provide tentative support for neurodevelopmental theories of BPD by demonstrating that neurobiological markers may be observed from childhood onwards and interact with environmental factors to increase risk of BPD in young populations. Prospective studies with a range of repeated measures are now required to elucidate the temporal unfurling of neurobiological features and further delineate the complex pathways to BPD