Nanomechanical testing of bcc micropillars – power laws and lattice resistance correlations

It is now well established that the compression plastic flow stress, sp, of metallic micropillars increases with decreasing sample diameter. With fcc metals, if the pillar flow stress and pillar diameter are normalised by the shear modulus resolved onto the active slip system, m, and Burgers’ vector, b, respectively, the data follows an empirical relation of Please click Additional Files below to see the full abstract

Using Sparse Semantic Embeddings Learned from Multimodal Text and Image Data to Model Human Conceptual Knowledge

Distributional models provide a convenient way to model semantics using dense embedding spaces derived from unsupervised learning algorithms. However, the dimensions of dense embedding spaces are not designed to resemble human semantic knowledge. Moreover, embeddings are often built from a single source of information (typically text data), even though neurocognitive research suggests that semantics is deeply linked to both language and perception. In this paper, we combine multimodal information from both text and image-based representations derived from state-of-the-art distributional models to produce sparse, interpretable vectors using Joint Non-Negative Sparse Embedding. Through in-depth analyses comparing these sparse models to human-derived behavioural and neuroimaging data, we demonstrate their ability to predict interpretable linguistic descriptions of human ground-truth semantic knowledge.Comment: Proceedings of the 22nd Conference on Computational Natural Language Learning (CoNLL 2018), pages 260-270. Brussels, Belgium, October 31 - November 1, 2018. Association for Computational Linguistic

Graphene-Based Transparent Flexible Strain Gauges with Tunable Sensitivity and Strain Range

Flexible strain gauges with 88% optical transmittance, of reduced graphene oxide (rGO) on poly dimethylsiloxne membranes, are produced form monolayers of graphene oxide assembled into densely packed sheets at an immiscible hexane/water interface and subsequently reduced in HI vapor to increase electrical conductivity. Pre-straining and relaxing the membranes introduces a population of cracks into the rGO film. Subsequent straining opens these cracks, inducing piezoresistivity. Reduction for 30 s forms an array of parallel cracks that do not individually span the membrane and results in a strain gauge with a usable strain range > 0.2 and gauge factor of 20 - 100 at low strain levels that increases with increasing pre-strain. In all cases the gauge facto decreases with increasing applied strain and asymptotes to a value of about 3, as it approaches the pre-strain value. If the rGO is reduced for 60 s, the cracks fully span the width of the membrane, leading to an increased gauge resistance but a much more sensitive strain gauge with GF ranging from 1000 - 16000. However, the usable strain range reduces to < 0.01. A simple equivalent resistor model is proposed to describe the behaviour of both gauge types. The gauges show a repeatable and stable response with loading frequencies up to 1 kHz and have been used to detect human body motion in a simple e-skin demonstration.Comment: 24 Pages, 9 Figures plus Supporting Information 11 page

In-situ bending tests of penta-twinned Ag NWs and their structure analyses

Ag nanowires (NWs) are readily available for applications in flexible electronics because of their excellent electrical and optical performance. Research into the mechanical properties and deformation mechanisms of NWs is important to understand the durability of these devices. The polyol process used to fabricate Ag NWs leads to a penta-twinned structure containing five {111} twin planes sharing a common axis along the [110] direction. Here we study the microstructures of the twinned NWs after plastic deformation in bending (Fig 1 (a)-(c))1. When deformation is highly spatially confined a clear grain boundary is observed under dark filed imaging (Fig 1 (d)). To further characterize the deformed penta-twinned wires, scanning precession nano-beam diffraction was used to map their structure and determine the crystal orientations. The diffraction signal and corresponding physical localization for every sub-crystal were isolated from the data using non-negative matrix factorization (NMF) 2. For example in Fig 1. (e)-(f), the crystal orientation is confirmed to be [110] albeit with an in-plane rotation of the pattern corresponding to the bend in the wire. The same approach was applied to other sub-crystals. The structure of penta-twinned Ag nanowire and the direction of incident electron beam are illustrated in Fig 1. (h). From the outlined shape of the subcrystals in the bent penta-twinned Ag NWs (Fig 1. (e), (f)), it was observed that the sub-crystals can expand or contract when approaching the bending Interface. To explain these behaviors, a coincident site lattice (CSL) was used to model the structure of grain boundaries formed during the bending process3. The change in orientation within a sub-crystal across the bending interface could be assigned in many cases to a particular highly coherent planar interface. This study is a clear example of how nano-materials with complex structure can be explored under advanced TEM experiments to provide insight into the deformation mechanisms of nanostructures. Please click Additional Files below to see the full abstract

Solution Processing of Two-Dimensional Black Phosphorus

This feature article discusses solution-phase routes to semiconducting two-dimensional black phosphorus (‘phosphorene’) and highlights challenges in processing the material as well as illuminating new avenues and opportunities in the area.</p