Ab-initio elastic tensor of cubic Ti0.5_{0.5}Al0.5_{0.5}N alloy: the dependence of the elastic constants on the size and shape of the supercell model

In this study we discuss the performance of approximate SQS supercell models in describing the cubic elastic properties of B1 (rocksalt) Ti$_{0.5}$Al$_{0.5}$N alloy by using a symmetry based projection technique. We show on the example of Ti$_{0.5}$Al$_{0.5}$N alloy, that this projection technique can be used to align the differently shaped and sized SQS structures for a comparison in modeling elasticity. Moreover, we focus to accurately determine the cubic elastic constants and Zener's type elastic anisotropy of Ti$_{0.5}$Al$_{0.5}$N. Our best supercell model, that captures accurately both the randomness and cubic elastic symmetry, results in $C_{11}=447$ GPa, $C_{12}=158$ GPa and $C_{44}=203$ GPa with 3% of error and $A=1.40$ for Zener's elastic anisotropy with 6% of error. In addition, we establish the general importance of selecting proper approximate SQS supercells with symmetry arguments to reliably model elasticity of alloys. In general, we suggest the calculation of nine elastic tensor elements - $C_{11}$, $C_{22}$, $C_{33}$, $C_{12}$, $C_{13}$, $C_{23}$, $C_{44}$, $C_{55}$ and $C_{66}$, to evaluate and analyze the performance of SQS supercells in predicting elasticity of cubic alloys via projecting out the closest cubic approximate of the elastic tensor. The here described methodology is general enough to be applied in discussing elasticity of substitutional alloys with any symmetry and at arbitrary composition.Comment: Submitted to Physical Review

Community mapping by non-literate citizen scientists in the rainforest

Supporting local communities to share their environmental knowledge by utilizing scientifically accepted tools and methodologies can lead to improvement in environmental governance, environmental justice and management practices. Mbendjele hunter-gatherers in the rainforests of Congo are collaborating with the ExCiteS Research Group at University College London to record their local knowledge about illegal poaching activities, which will improve the control of commercial hunters and diminish the harassment they often experience at the hands of 'eco-guards' who enforce hunting regulations. Developing and deploying a system for non-literate users introduces a range of challenges that we have tried to tackle with our Anti-Poaching data collection platform

Making local knowledge matter: Supporting non-literate people to monitor poaching in Congo

This paper describes a project initiated by non-literate indigenous people to equip their own “citizen scientists” with rugged smartphones running adapted software that enable them to share some of their detailed environmental knowledge in ways that improve the sustainable management of their forest. Supporting local people to share their environmental knowledge in scientifically valid and strategically targeted ways can lead to improvement in environmental governance, environmental justice and management practices. Mbendjele hunter-gatherers in the rainforests of Congo are working together with the ExCiteS Research Group at University College London to make their local knowledge about commercial hunters’ activities improve the control of commercial hunters and diminish the harassment they often experience at the hands of “eco-guards” who enforce hunting regulations. Developing and deploying a system for non-literate users introduces a range of challenges that we have tried to solve. Our Anti-Poaching data collection platform, running on Android smartphones, is based on a decision tree of pictorial icons and employs various smartphone sensors to augment observations. We describe its development here

Supporting collaboration with non-literate forest communities in the congo-basin

Providing indigenous communities with ICT tools and methods for collecting and sharing their Traditional Ecological Knowledge is increasingly recognised as an avenue for improvements in environmental governance and socialenvironmental justice. In this paper we show how we carried out a usability engineering effort in the “wild” context of the Congolese rainforest – designing, evaluating and iteratively improving novel collaborative data collection interfaces for non-literate forest communities that can subsequently be used to facilitate communication and information sharing with logging companies. Working in this context necessitates adopting a thoroughly flexible approach to the design, development, introduction and evaluation of technology and the modes of interaction it offers. We show that we have improved participant accuracy from about 75% towards 95% and provide a set of guidelines for designing and evaluating ICT solutions in “extreme circumstances” – which hold lessons for CSCW, HCI and ICT4D practitioners dealing with similar challenges

Transmission through correlated Cun_nCoCun_n heterostructures

The effects of local electronic interactions and finite temperatures upon the transmission across the Cu$_4$CoCu$_4$ metallic heterostructure are studied in a combined density functional and dynamical mean field theory. It is shown that, as the electronic correlations are taken into account via a local but dynamic self-energy, the total transmission at the Fermi level gets reduced (predominantly in the minority spin channel), whereby the spin polarization of the transmission increases. The latter is due to a more significant $d$-electrons contribution, as compared to the non-correlated case in which the transport is dominated by $s$ and $p$ electrons.Comment: 29 pages, 7 figures, submited to PR