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In this work, we study vacancy energetics in the equiatomic Nb-Mo-Ta-W alloy, especially vacancy formation and migration energies, using molecular statics calculations based on a spectral neighbor analysis potential specifically developed for Nb-Mo-Ta-W. We consider vacancy properties in bulk environments as well as near edge dislocation cores, including the effect of short-range order (SRO) by preparing supercells through Metropolis Monte-Carlo relaxations and temperature on the calculation. The nudged elastic band (NEB) method is applied to study vacancy migration energies. Our results show that both vacancy formation energies and vacancy migration energies are statistically distributed with a wide spread, on the order of 1.0 eV in some cases, and display a noticeable dependence on SRO. We find that, in some cases, vacancies can form with very low energies at edge dislocation cores, from which we hypothesize the formation of stable 'superjogs' on edge dislocation lines. Moreover, the large spread in vacancy formation energies results in an asymmetric thermal sampling of the formation energy distribution towards lower values. This gives rise to effective vacancy formation energies that are noticeably lower than the distribution averages. We study the effect that this phenomenon has on the vacancy diffusivity in the alloy and discuss the implications of our findings on the structural features of Nb-Mo-Ta-W.

The compound La 2-2 x Sr 1+2 x Mn 2 O 7 , x = 0.30-0.40, consists of bilayers of ferromagnetic metallic MnO 2 sheets that are separated by insulating layers. The materials show colossal magnetoresistance-a reduction in resistivity of up to two orders of magnitude in a field of 7 T-at their three-dimensional ordering temperatures, T C = 90-126 K, and are the layered analogues of the widely studied pseudo-cubic perovskite manganites, R 1- x A x MnO 3 (R = rare earth, A = Ca, Sr, Ba, Pb). Two distinct short-range orderings-antiferromagnetic fluctuations and correlated polarons, which are related to the magnetic and the lattice degrees of freedom respectively-have previously been discovered in La 2-2 x Sr 1+2 x Mn 2 O 7 , x = 0.40, and have each been qualitatively connected to the resistivity. Here, in a comprehensive study as a function of both temperature and magnetic field for the different hole-concentrations per Mn site of x = 0.30 and 0.35, we show that antiferromagnetic fluctuations also appear at temperatures just above T C , and that the intensities of both the antiferromagnetic fluctuations and polaron correlations closely track the resistivity. In particular, for x = 0.35 we show that there is a simple scaling relation between the intensities of the antiferromagnetic fluctuations and the in-plane resistivity that applies for the temperatures and magnetic fields used in the experiments. The results show that antiferromagnetic fluctuations are a common feature ofLa 2-2 x Sr 1+2 x Mn 2 O 7 with ferromagnetic bilayers, and that there is a close connection between the antiferromagnetic fluctuations and polarons in these materials., (© 2020 IOP Publishing Ltd.)

Bioactive glasses have potential applications in the field of regenerative medicine due to their bioactivity that permits interaction with both hard and soft tissues. In the same way, mesenchymal stromal cells (MSCs) have been experimentally tested as part of engineered constructs considering their self-renewal and multipotent capacities. However, to design an association, it is crucial to investigate the physical properties of bioglass 45S5, as well as its biocompatibility. Therefore, we investigated the structural short range order of the stoichiometric 45S5, by obtaining its total structure factors (S(K)) and total pair distribution function G(r). The in vitro compatibility of human MSCs with 45S5 was verified by viability, morphometry and osteoinduction assays, F-actin staining and scanning electron (SEM) analysis. The compatibility outcome was verified through a subcutaneous implantation in a murine model by grafting the 45S5 as a scaffold for allogeneic MSCs. The cell-substrate modulation includes the maintenance of the MSC viability and osteoinduction potential after being exposed to the 45S5 extract. A low spreading during cell adhesion was detected. Both normal actin cytoskeleton organization and nuclei irregularities were observed, besides an increase of hydroxyapatite (HA) depositions around cells. Cells showed satisfactory compatibility patterns when growing over 45S5 for 7, 30 and 90 days. The implant did not show any apparent toxicity for organs, or strong immunogenic reactions, and it was accompanied by a dense capsule formation around the graft. Our results indicate that MSCs can grow in the long term on the 45S5 while maintaining their characteristics. This fact, together with a non-toxicity to animals means that the 45S5 can be implemented in pre-clinical trials aiming MSC's transplantation leading to further bone and tissue repair., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Element clustering and structural features of liquid lead-bismuth eutectic (LBE) alloy have been investigated up to 720 °C by means of high temperature X-ray diffraction (HT-XRD), X-ray Photoemission Spectroscopy (XPS) and Scanning Photoemission Microscopy (SPEM) at the Elettra synchrotron in Trieste. The short-range order in liquid metal after melting corresponds to the cuboctahedral atomic arrangement and progressively evolves towards the icosahedral one as temperature increases. Such process, that involve a negative expansion of the alloy, is mainly connected to the reduction of atom distance in Pb-Pb pairs which takes place from 350 °C to 520 °C. On an atomic scale, it is observed a change of the relative number of Bi-Bi, Pb-Pb, and Pb-Bi pairs. The Pb-Bi pairs are detected only at a temperature above ~350 °C, and its fraction progressively increases, giving rise to a more homogeneous distribution of the elements. SPEM results showed evidence that the process of chemical homogenization on an atomic scale is preceded and accompanied by homogenization on micro-scale. Clusters rich of Bi and Pb, which are observed after melting, progressively dissolve as temperature increases: Only a few residuals remain at 350 °C, and no more clusters are detected a 520 °C.

We demonstrated that the immunological identity of variant peptides may be accurately predicted on the basis of atomic coordination of both unprotonated and protonated tertiary structures, provided that the structure of the native peptide (index) is known. The metric which was discovered to account for this discrimination is the coordination difference between the variant and the index; we also showed that increasing coordination difference in respect to the index was correlated to a correspondingly weakening immunological outcome of the variant. Additionally, we established that this metric quickly seizes to operate beyond the peptide scale, e.g., within a coordination shell inclusive of atoms up to a distance of 7 Å away from the peptide or over the entire pMHC-TCR complex. Analysis of molecular orbital interactions for a range of formal charges further revealed that the N-terminus of the agonists was always able to sustain a stable ammonium (NH[Formula: see text]) group which was consistently absent in antagonists. We deem that the presence of NH[Formula: see text] constitutes a secondary observable with a biological consequence, signifying a change in T cell activation. While our analysis of protonated structures relied on the quantum chemical relaxation of the H species, the results were consistent across a wide range of peptide charge and spin polarization conditions.

Whilst atom probe tomography (APT) is a powerful technique with the capacity to gather information containing hundreds of millions of atoms from a single specimen, the ability to effectively use this information creates significant challenges. The main technological bottleneck lies in handling the extremely large amounts of data on spatial-chemical correlations, as well as developing new quantitative computational foundations for image reconstruction that target critical and transformative problems in materials science. The power to explore materials at the atomic scale with the extraordinary level of sensitivity of detection offered by atom probe tomography has not been not fully harnessed due to the challenges of dealing with missing, sparse and often noisy data. Hence there is a profound need to couple the analytical tools to deal with the data challenges with the experimental issues associated with this instrument. In this paper we provide a summary of some key issues associated with the challenges, and solutions to extract or "mine" fundamental materials science information from that data., (Copyright © 2015. Published by Elsevier B.V.)

The coordination difference between the unprotonated tertiary structures of a native (Tax) peptide and a number of its variants - all peptides presented by HLA-A201 and bound to the human A6 T cell receptor-was discovered to constitute a metric of pMHC-TCR functional avidity. Moreover, increasing coordination deviations from the index were found to flag correspondingly weakening immunological outcomes of the variant peptides. The prognostic utility of the coordination difference of unprotonated tertiary structure was established to operate strictly on the peptide scale, seizing to be of relevance either to the immediate peptide environment (i.e. within the realm of peptide short range order, within 7 Å of any peptide atom) or over the entirety of the pMHC-TCR complex. Additionally, the imprint of peptide immunological identity was expressed both by the total coordination as well as by its C-C partial.

A combination of atomic correlation statistics and quantum chemical calculations are shown to predict biological function. In the present study, various antigenic peptide-Major Histocompatibility Complex (pMHC) ligands with near-identical stereochemistries, in complexation with the same T cell receptor (TCR), were found to consistently induce distinctly different quantum chemical behavior, directly dependent on the peptide's electron spin density and intrinsically expressed by the protonation state of the peptide's N-terminus. Furthermore, the cumulative coordination difference of any variant in respect to the native peptide was found to accurately reflect peptide biological function and immerges as the physical observable which is directly related to the immunological end-effect of pMHC-TCR interaction.