Size effects in dislocation depinning models for plastic yield

Typically, the plastic yield stress of a sample is determined from a stress-strain curve by defining a yield strain and reading off the stress required to attain it. However, it is not a priori clear that yield strengths of microscale samples measured this way should display the correct finite size scaling. Here we study plastic yield as a depinning transition of a 1+1 dimensional interface, and consider how finite size effects depend on the choice of yield strain, as well as the presence of hardening and the strength of elastic coupling. Our results indicate that in sufficiently large systems, the choice of yield strain is unimportant, but in smaller systems one must take care to avoid spurious effects.Comment: 7 pages, 8 figure

Diversity enabling equilibration: disorder and the ground state in artificial spin ice

We report a novel approach to the question of whether and how the ground state can be achieved in square artificial spin ices where frustration is incomplete. We identify two types of disorder: quenched disorder in the island response to fields and disorder in the sequence of driving fields. Numerical simulations show that quenched disorder can lead to final states with lower energy, and disorder in the driving fields always lowers the final energy attained by the system. We use a network picture to understand these two effects: disorder in island responses creates new dynamical pathways, and disorder in driving fields allows more pathways to be followed.Comment: 5 pages, 5 figure

Disorder regimes and equivalence of disorder types in artificial spin ice

The field-induced dynamics of artificial spin ice are determined in part by interactions between magnetic islands, and the switching characteristics of each island. Disorder in either of these affects the response to applied fields. Numerical simulations are used to show that disorder effects are determined primarily by the strength of disorder relative to inter-island interactions, rather than by the type of disorder. Weak and strong disorder regimes exist and can be defined in a quantitative way.Comment: The following article has been submitted to J. Appl. Phys. After it is published, it will be found at http://link.aip.org/link/?ja

Vertex dynamics in finite two dimensional square spin ices

Local magnetic ordering in artificial spin ices is discussed from the point of view of how geometrical frustration controls dynamics and the approach to steady state. We discuss the possibility of using a particle picture based on vertex configurations to interpret time evolution of magnetic configurations. Analysis of possible vertex processes allows us to anticipate different behaviors for open and closed edges and the existence of different field regimes. Numerical simulations confirm these results and also demonstrate the importance of correlations and long range interactions in understanding particle population evolution. We also show that a mean field model of vertex dynamics gives important insights into finite size effects.Comment: 4 pages, 4 figures; v2: minor changes to text and figures. Accepted to Phys. Rev. Let

Protein accumulation in the endoplasmic reticulum as a non-equilibrium phase transition

Several neurological disorders are associated with the aggregation of aberrant proteins, often localized in intracellular organelles such as the endoplasmic reticulum. Here we study protein aggregation kinetics by mean-field reactions and three dimensional Monte carlo simulations of diffusion-limited aggregation of linear polymers in a confined space, representing the endoplasmic reticulum. By tuning the rates of protein production and degradation, we show that the system undergoes a non-equilibrium phase transition from a physiological phase with little or no polymer accumulation to a pathological phase characterized by persistent polymerization. A combination of external factors accumulating during the lifetime of a patient can thus slightly modify the phase transition control parameters, tipping the balance from a long symptomless lag phase to an accelerated pathological development. The model can be successfully used to interpret experimental data on amyloid-\b{eta} clearance from the central nervous system

Avoidance and Coalescence of Delamination Patterns

Delamination of coatings and thin films from substrates generates a fascinating variety of patterns, from circular blisters to wrinkles and labyrinth domains, in a way that is not completely understood. We report on large-scale numerical simulations of the universal problem of avoidance and coalescence of delamination wrinkles, focusing on a case study of graphene sheets on patterned substrates. By nucleating and growing wrinkles in a controlled way, we are able to characterize how their interactions, mediated by long-range stress fields, determine their formation and morphology. We also study how the interplay between geometry and stresses drives a universal transition from conformation to delamination when sheets are deposited on particle-decorated substrates. Our results are directly applicable to strain engineering of graphene and also uncover universal phenomena observed at all scales, as for example in geomembrane deposition

Avalanches, loading and finite size effects in 2D amorphous plasticity: results from a finite element model

Crystalline plasticity is strongly interlinked with dislocation mechanics and nowadays is relatively well understood. Concepts and physical models of plastic deformation in amorphous materials on the other hand - where the concept of linear lattice defects is not applicable - still are lagging behind. We introduce an eigenstrain-based finite element lattice model for simulations of shear band formation and strain avalanches. Our model allows us to study the influence of surfaces and finite size effects on the statistics of avalanches. We find that even with relatively complex loading conditions and open boundary conditions, critical exponents describing avalanche statistics are unchanged, which validates the use of simpler scalar lattice-based models to study these phenomena.Comment: Journal of Statistical Mechanics: Theory and Experiment, 2015, P0201

Indigenous online creative responses to the COVID-19 pandemic lockdown in Western Australia

In response to the worldwide COVID-19 pandemic in 2020, many communities of endangered Indigenous languages have utilised digital technologies and created online language resources with renewed motivation. In this article we explore the ways that Noongar community members have shifted, adapted and persisted in creating new language revitalisation resources for their endangered Aboriginal language, describing three case studies of video content created and shared online through social media as localised responses to the pressing need for easily produced, accessible and engaging online approaches to support Indigenous communities and their languages

‘Keep the music going’: How the isolation tour 2020 maintained community and cultural connectedness during the 2020 COVID-19 lockdown in Western Australia

The COVID-19 pandemic and subsequent social isolation measures had a profound impact on communities worldwide. In regional and remote Western Australia, the use of online platforms has become increasingly important for maintaining social and emotional well-being. This article examines the role of ‘The Isolation Tour 2020’ Facebook page in providing a lifeline for its mostly Aboriginal audience to stay connected with culture, Country, and one another during the 2020 COVID-19 lockdown in Western Australia. The authors conducted an in-depth interview with one of the administrators of the page and supplemented this with a thematic analysis of publicly available Facebook data. Data were analysed using NVivo qualitative analysis software and common themes were identified. The findings show that ‘The Isolation Tour 2020’ provided an effective virtual platform for people to interact with loved ones and feel a sense of belonging and comfort in the uncertainty of the pandemic. This research highlights the importance of online spaces for supporting social and emotional well-being during extended periods of social isolation and offers insights into how similar initiatives can be supported in future