Effects of solute content on grain refinement in an isothermal melt

This is the port-print version of the article. The official published version can be obtained from the link below - Copyright @ 2011 Acta Materialia Inc. Published by Elsevier LtdIt is well accepted in the literature that for effective grain refinement some solute is required in the melt to restrict the growth of the solid even if potent nucleating particles with a favourable physical nature are present. In this paper we investigate the effect of the solute on grain initiation in an isothermal melt, and an analytical model is developed to account for the effect of solute elements on grain size. This study revealed that the solute elements in the liquid ahead of the growing crystals reduce the growth velocity of the nucleated crystals and increase the maximum undercooling achievable before recalescence. This allows more particles to be active in nucleation and, consequently, increases the number density of active particles, giving rise to a finer grain size. The analytical model shows that the final grain size can be related to the maximum undercooling, average growth velocity and solid fraction at the moment of recalescence. Further analysis using the free growth model and experimental data in the literature revealed that for a given alloy system solidified under similar conditions the grain size can be empirically related to 1/Q (Q is the growth restriction factor) to a power of 1/3, which is considerably different from the empirical linear relationship in the literature. It is demonstrated that the 1/3 power law can describe the experimental data more accurately than a linear relationship.The EPSRC is gratefully acknowledged for providing financial support under Grant EP/H026177/1

Effects of lattice mismatch on interfacial structures of liquid and solidified Al in contact with hetero-phase substrates: MD simulations

Published under licence in IOP Conference Series: Material Science and Engineering by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.In this study, the effects of the misfit on in-plane structures of liquid Al and interfacial structure of solidified Al in contact with the heterophase substrates have been investigated, using molecular dynamics (MD) simulations. The MD simulations were conducted for Al/fcc (111) substrates with varied misfits. The order parameter and atomic arrangement indicated that the in-plane ordering of the liquid at the interface decreases significantly with an increase of the misfit, i.e., solid-like for small misfit and liquid-like for large misfit. Further, our MD simulation results revealed that a perfect orientation relationship forms at the interface between the substrate and the solidified Al for a misfit of less than -3% and the boundary is coherent. With an increase in the misfit, Shockley partial and extended dislocations form at the interface, and the boundary becomes a semi-coherent or low-angle twist boundary.EPSR

Subjective Annotation for a Frame Interpolation Benchmark using Artefact Amplification

Current benchmarks for optical flow algorithms evaluate the estimation either directly by comparing the predicted flow fields with the ground truth or indirectly by using the predicted flow fields for frame interpolation and then comparing the interpolated frames with the actual frames. In the latter case, objective quality measures such as the mean squared error are typically employed. However, it is well known that for image quality assessment, the actual quality experienced by the user cannot be fully deduced from such simple measures. Hence, we conducted a subjective quality assessment crowdscouring study for the interpolated frames provided by one of the optical flow benchmarks, the Middlebury benchmark. We collected forced-choice paired comparisons between interpolated images and corresponding ground truth. To increase the sensitivity of observers when judging minute difference in paired comparisons we introduced a new method to the field of full-reference quality assessment, called artefact amplification. From the crowdsourcing data, we reconstructed absolute quality scale values according to Thurstone's model. As a result, we obtained a re-ranking of the 155 participating algorithms w.r.t. the visual quality of the interpolated frames. This re-ranking not only shows the necessity of visual quality assessment as another evaluation metric for optical flow and frame interpolation benchmarks, the results also provide the ground truth for designing novel image quality assessment (IQA) methods dedicated to perceptual quality of interpolated images. As a first step, we proposed such a new full-reference method, called WAE-IQA. By weighing the local differences between an interpolated image and its ground truth WAE-IQA performed slightly better than the currently best FR-IQA approach from the literature.Comment: arXiv admin note: text overlap with arXiv:1901.0536

Infrastructure Quality in Deregulated Industries: Is there an Underinvestment Problem?

We investigate how various institutional settings affect a network provider’s incentives to invest in infrastructure quality. Under reasonable assumptions on demand, investment incentives turn out to be smaller under vertical separation than under vertical integration, though we also provide counter-examples. The introduction of downstream competition for the market can sometimes improve incentives. With suitable non-linear access prices investment incentives under separation become identical to those under integration.investment incentives, networks, quality, vertical externality.