High-pressure X-ray near-edge absorption study of thallium rhenium oxide up to 10.86 GPa

High-pressure X-ray near-edge absorption measurements have been performed on thallium rhenium oxide (TlReO₄) up to 10.86?GPa at room temperature and in a diamond-anvil cell. At ～10?GPa, TlReO₄ undergoes a large volume collapse and a striking optical transition, changing from transparent to opaque. A model has been proposed by Jayaraman et al. that the high-pressure phase transition is associated with a charge transfer from the thallium to rhenium atom; Tl¹⁺(Re⁷⁺O₄)^?1?→?Tl³⁺(Re⁵⁺O₄)^?3 and an accompanying truly octahedral coordination of the rhenium atom with respect to the surrounding oxygen cage. In this article, we find a significant broadening of ～1.5?eV of the white-line feature at the rhenium L₃(2p_3/2?→?5d) absorption-edge above this transition, and no evidence for the proposed valence change.     

A CFD model for the prediction of haemolysis in micro axial left ventricular assist devices

This paper describes the development and application of a computational model based upon Computational Fluid Dynamics (CFD) software simulation technology to predict haemolysis in micro Left Ventricular Assist Devices (μ$\mathrm{\mu }$LVAD). A CFD model, capturing the full three dimensional geometry of the device, together with an explicit representation of the rotating machinery based upon a rotating reference frame, is solved transiently. Mixed meshes with the order of a million elements are required to resolve the flow adequately and so to enable solutions in a reasonable time (e.g., 3 h) the model is solved on a high performance parallel cluster. Haemolysis is a measure of damage occurring in the blood and is conceived as accumulating as it passes through parts of the device where it encounters high shear forces. As such, the haemolysis model is based upon tracking the behaviour of particles released at the inlet throughout the flow domain and calculating the damage accumulated by each individual particle as it traverses the device. In order to ensure the model predictions of haemolysis are noise free from a statistically significant perspective then it is demonstrated that the number of particles to be tracked must exceed 20 000 in any simulation experiment. Comparisons with experimental data from a companion paper demonstrate the effectiveness of the CFD simulation embedding the haemolysis model.     

Incorporating dust lift-off into a CFD model of a blast furnace gravity dust-catcher

A gravity dust-catcher separates a mixture of dusts from the spent top gas flow of a blast furnace. These dusts are predominantly made up of limestone, iron ore and coke/coal. As a result of the turbulent gas flow patterns within a dust-catcher, modelling of the flow pattern can be very complex, attributed to the turbulent vortices that can be formed within the main body of the structure. Using data from an experimental prototype test rig, a simple model to capture the lift-off characteristics of particle lift-off from dust pile surfaces is created and incorporated into a computational fluid dynamics (CFD) model of the dust-catcher.The variation of particle separation performance over a typical blast furnace (BF) operational cycle is analysed. An attempt is made to explain the observed phenomena in terms of particle–fluid interaction. It is found that particle separation efficiency is largely unaffected by dust lift-off at low dust-catcher hopper fullness levels, but is significant at higher levels. It is found that the topography of the dust surface is important when predicting particle lift-off trends. It is concluded that this is due to the exposure experienced by a given particle when subjected to a surface velocity.     

Magnetic‐Structure‐Stabilized Polarization in an Above‐Room‐Temperature Ferrimagnet

Above‐room‐temperature polar magnets are of interest due to their practical applications in spintronics. Here we present a strategy to design high‐temperature polar magnetic oxides in the corundum‐derived A₂BB′O₆ family, exemplified by the non‐centrosymmetric (R3) Ni₃TeO₆‐type Mn²⁺₂Fe³⁺Mo⁵⁺O₆, which shows strong ferrimagnetic ordering with T_C=337 K and demonstrates structural polarization without any ions with (n?1)d¹⁰ns⁰, d⁰, or stereoactive lone‐pair electrons. Density functional theory calculations confirm the experimental results and suggest that the energy of the magnetically ordered structure, based on the Ni₃TeO₆ prototype, is significantly lower than that of any related structure, and accounts for the spontaneous polarization (68 μC cm^?2) and non‐centrosymmetry confirmed directly by second harmonic generation. These results motivate new directions in the search for practical magnetoelectric/multiferroic materials.     

Evolution of structure and magnetic properties in electron-doped double perovskites, Sr2−xLaxMnWO6 (0?x?1)

Powder neutron and X-ray diffraction studies show that the double perovskites in the region 0?x?1 exhibit two crystallographic modifications at room temperature: monoclinic P2₁/n and tetragonal I4/m, with a boundary at 0.75<x<0.9. Magnetic susceptibility measurements indicate that for x=0 and 0.5 Sr_2−xLa_xMnWO₆ orders antiferromagnetically (AFM) at 15 and 25 K, respectively, for 0.75?x<1.0, a contribution of weak ferromagnetism (FM), probably due to canted-AFM order, increases with increasing x. The end point compound SrLaMnWO₆ shows the strongest FM cluster effect; however, no clear evidence of magnetic order is discernable down to 4.2 K. X-ray absorption spectroscopy (XAS) confirms Mn²⁺ and mixed-valent W^6+/5+ formal oxidation states in Sr_2−xLa_xMnWO₆.     

Flux line lattice symmetries in the borocarbide superconductor LuNi2B2C

We compare the results of small angle neutron scattering on the flux line lattice (FLL) obtained in the borocarbide superconductor LuNi₂B₂C with the applied field along the c- and a-axes. For H‖c the temperature dependence of the FLL structural phase transition from square to hexagonal symmetry was investigated. Above 10 K the transition onset field. H ₂(T), rises sharply, bending away from H _c2(T) in contradiction to theoretical predictions of the two merging. For H‖a a first order FLL reorientation transition is observed at H _tr=3–3.5 kOe. Below H _tr the FLL nearest neighbor direction is parallel to the b-axis, and above H _tr to the c-axis. This transition cannot be explained using nonlocal corrections to the London model.