Atomic order and cluster energetics of a 17 w.t.% Si-based glass versus the liquid phase

Aerodynamic levitation of a multi component 17 w.t.% Si glass formed by rapid quenching of the melt phase was studied by high resolution X-ray diffraction (XRD) and Reverse Monte Carlo (RMC) modeling. The main local atomic order features comprised of interactions between Si, Fe and Mg polyhedra, the stereochemistry of which was on a par with literature. Both the glass and the liquid state appeared to consist of the same fundamental Si-O, Fe-O and Mg-O clusters, with only the relative number of each varying between the two. Transition from liquid to the glass involved a 3-fold decrease in uncoordinated O (to within the first minimum of the total g(r)) and a marked increase of Fe-Si-Mg polyhedra bridging O. Octahedral Fe coordination was not suggested by the RMC data. All-electron open-shell Density Functional Theory (DFT) calculations of the most prominent clusters suggested independence between the Fe oxidation state and its polyhedra O-coordination. Of secondary thermodynamic importance were indications of network-forming Fe2+ and Fe3+ distorted trigonal and tetrahedral polyhedra. In all occasions, the Fe ferrous and ferric states involved comparable binding energies within similar clusters which indicate a dynamic equilibrium between the two

Human Cytomegalovirus variant peptides adapt by decreasing their total coordination upon binding to a T cell receptor

The tertiary structure of the native Cytomegalovirus peptide (NLV) presented by HLA-A2 and bound to the RA14 T cell receptor was used as a reference for the calculation of atomic coordination differences of both the NLV as well as of a number of singly substituted NLV variants in the absence of TCR. Among the pMHC complexes, the native peptide was found to exhibit the highest total coordination difference in respect to the reference structure, suggesting that it experienced the widest structural adaptation upon recognition by the TCR. In addition, the peptide on the isolated NLV-MHC complex was over-coordinated as compared to the rest of the variants. Moreover, the trend was found to account for a set of measured dissociation constants and critical concentrations for target-cell lysis for all variants in complexation with RA14: functionally, all variant peptides were established to be either weak agonists or null peptides, while, at the same time, our current study established that they were also under-coordinated in respect to NLV. It could, thus, be argued that the most 'efficient' structural adaptation upon pMHC recognition by the TCR requires of the peptide to undergo the widest under-coordination possible. The main structural characteristic which differentiated the NLV in respect to the variants was a the presence of 16 oxygen atoms (waters) in the former[U+05F3]s second coordination shell which accounted for over-coordination of roughly 100% and 30% in the O-O and C-O partials respectively. In fact, in the absence of second shell oxygens, the NLV peptide was decidedly under-coordinated in respect to all of the variants, as also suggested by the C-C partial. © 2015 The Authors. Published by Elsevier Inc

Data from: Pragmatic analysis of the electric submerged arc furnace continuum

A transient mathematical model was developed for the description of fluid flow, heat transfer and electromagnetic phenomena involved in the production of ferronickel in electric arc furnaces. The key operating variables considered were the thermal and electrical conductivity of the slag and the shape, immersion depth and applied electric potential of the electrodes. It was established that the principal stimuli of the velocities in the slag bath were the electric potential and immersion depth of the electrodes and the thermal and electrical conductivities of the slag. Additionally, it was determined that, under the set of operating conditions examined, the maximum slag temperature ranged between 1756 and 1825 K, which is in accordance with industrial measurements. Moreover, it was affirmed that contributions to slag stirring due to Lorentz forces and momentum forces due to the release of carbon monoxide bubbles from the electrode surface were negligibl

Electronic structure of nickel porphyrin NiP: Study by X-ray photoelectron and absorption spectroscopy

Energy distributions and properties of the occupied and empty electronic states for a planar complex of nickel porphyrin NiP are studied by X-ray photoemission and absorption spectroscopy techniques. As a result of the analysis of the experimental spectra of valence photoemission, the nature and energy positions of the highest occupied electronic states were determined: the highest occupied state is formed mostly by atomic states of the porphine ligand; the following two states are associated with 3d states of the nickel atom. It was found that the lowest empty state is specific and is described by the σ-type b 1g MO formed by empty Ni3dx2−y2 -states and occupied 2p-states of lone electron pairs of nitrogen atoms. This specific nature of the lowest empty state is a consequence of the donor–acceptor chemical bond in NiP