Director alignment at the nematic–isotropic interface: elastic anisotropy and active anchoring

Activity in nematics drives interfacial flows that lead to preferential alignment that is tangential or planar for extensile systems (pushers) and perpendicular or homeotropic for contractile ones (pullers). This alignment is known as active anchoring and has been reported for a number of systems and described using active nematic hydrodynamic theories. The latter are based on the one-elastic constant approximation, i.e. they assume elastic isotropy of the underlying passive nematic. Real nematics, however, have different elastic constants, which lead to interfacial anchoring. In this paper, we consider elastic anisotropy in multiphase and multicomponent hydrodynamic models of active nematics and investigate the competition between the interfacial alignment driven by the elastic anisotropy of the passive nematic and the active anchoring. We start by considering systems with translational invariance to analyse the alignment at flat interfaces and, then, consider two-dimensional systems and active nematic droplets. We investigate the competition of the two types of anchoring over a wide range of the other parameters that characterize the system. The results of the simulations reveal that the active anchoring dominates except at very low activities, when the interfaces are static. In addition, we found that the elastic anisotropy does not affect the dynamics but changes the active length that becomes anisotropic. This article is part of the theme issue ‘Progress in mesoscale methods for fluid dynamics simulation’.

Fate of titanium in alkaline electro-reduction of sintered titanomagnetite

Direct electrochemical reduction of iron ore in concentrated NaOH electrolyte has been proposed as a potential route to substantially reducing the global steel industry’s CO2 emissions. Here, we report the solid-state electro-reduction of sintered pellets formed from titanomagnetite ironsand. This commercial iron ore contains ∼4 wt.% Ti which is directly incorporated within the magnetite lattice. At 110 °C, these pellets are electrochemically reduced and exhibit a well-defined reaction front which moves into the pellet as the reaction progresses. The electro-reduction process selectively produces iron metal, whilst the Ti content is not reduced. Instead, Ti becomes enriched in segregated oxide inclusions, which are subsequently transformed to a sodium iron titanate phase through taking up Na+ from the electrolyte. These inclusions adopt an elongated shape and appear to exhibit locally preferential alignment. This suggests that they may nucleate from the microscopic titanohematite lamellae which naturally occur within the original ironsand particles. The expulsion of contaminant Ti-oxides from the final reduced metal matrix has implications for the potential to development of an industrial electrochemical iron-making process utilising titanomagnetite ore. © 2020 The Author(s). Published by IOP Publishing Ltd.

Fate of titanium in alkaline electro-reduction of sintered titanomagnetite

Direct electrochemical reduction of iron ore in concentrated NaOH electrolyte has been proposed as a potential route to substantially reducing the global steel industry’s CO2 emissions. Here, we report the solid-state electro-reduction of sintered pellets formed from titanomagnetite ironsand. This commercial iron ore contains ∼4 wt.% Ti which is directly incorporated within the magnetite lattice. At 110 °C, these pellets are electrochemically reduced and exhibit a well-defined reaction front which moves into the pellet as the reaction progresses. The electro-reduction process selectively produces iron metal, whilst the Ti content is not reduced. Instead, Ti becomes enriched in segregated oxide inclusions, which are subsequently transformed to a sodium iron titanate phase through taking up Na+ from the electrolyte. These inclusions adopt an elongated shape and appear to exhibit locally preferential alignment. This suggests that they may nucleate from the microscopic titanohematite lamellae which naturally occur within the original ironsand particles. The expulsion of contaminant Ti-oxides from the final reduced metal matrix has implications for the potential to development of an industrial electrochemical iron-making process utilising titanomagnetite ore. © 2020 The Author(s). Published by IOP Publishing Ltd.

Velocity anisotropy and trend in Niger Delta, Nigeria

In geophysical data interpretation, matching the vertical velocity direction from seismic data with borehole-derived velocities is a challenging task because seismic-derived velocities are faster than borehole recorded velocities. This geophysical phenomenon is caused by velocity anisotropy. In this study, we used an empirical approach to estimate the degree of velocity anisotropy in the study area. The results showed that the delta anisotropy in sandstone beds varies from − 2.5% to 7.2% while most of them concentrate between 3.2% and 6.1%. The epsilon ranges between -6.4% and 9.3% while many of them concentrate between 3.2% and 7.2%. The gamma varies from − 6.3% to 7.3% while most of them concentrate between 1.2% and 5%. At shale beds, delta anisotropy varies from − 11.2% to 11.1% but most of them concentrate between 4.3% and 10.5%. The epsilon varies from − 7.2% to 14.5% while most of them concentrate between 4.5% and 10.5%. The gamma varies from 6.4% to 8.2% while majority of them concentrate between 2% and 5.3%. The results indicate that the study area is weakly to moderately anisotropic with shale beds having higher anisotropy values than sandstone beds. This probably results from preferential alignment of clay mineral orientations which also affect in situ velocity propagation. Three distinct velocity gradients (low, moderate and very high) were identified in the study area. These velocities vary erratically but showed northeast–southwest increase in velocities. Thus, the need to derive correction factors for individual wells for improved exploration success.

Dense shearing flows of soft, frictional cylinders

We perform discrete numerical simulations at constant volume of dense, steady, homogeneous flows of true cylinders interacting via Hertzian contacts, with and without friction, in the absence of preferential alignment....