An atomistic investigation of the effect of strain on frictional properties of suspended graphene

We performed molecular dynamics (MD) simulations of a diamond probe scanned on a suspended graphene to reveal the effect of strain on the fictional properties of suspended graphene. The graphene was subjected to some certain strain along the scanning direction. We compared the friction coefficient obtained from different normal loads and strain. The results show that the friction coefficient can be decreased about one order of magnitude with the increase of the strain. And that can be a result of the decreased asymmetry of the contact region which is caused by strain. The synthetic effect of potential energy and the fluctuation of contact region were found to be the main reason accounting for the fluctuation of the friction force. The strain can reduce the fluctuation of the contact region and improve the stability of friction

Insight into perovskite antiferroelectric phases: Landau theory and phase field study

Understanding the appearance of commensurate and incommensurate modulations in perovskite antiferroelectrics (AFEs) is of great importance for material design and engineering. The dielectric and elastic properties of the AFE domain boundaries are lack of investigation. In this work, a novel Landau theory is proposed to understand the transformation of AFE commensurate and incommensurate phases, by considering the coupling between the oxygen octahedral tilt mode and the polar mode. The derived relationship between the modulation periodicity and temperature is in good agreement with the experimental results. Using the phase field study, we show that the polarization is suppressed at the AFE domain boundaries, contributing to a remnant polarization and local elastic stress field in AFE incommensurate phases

Kinetics of amino sugar formation from organic residues of different quality

A

A Novel Multimodal Approach for Studying the Dynamics of Curiosity in Small Group Learning

Curiosity is a vital metacognitive skill in educational contexts, leading to creativity, and a love of learning. And while many school systems increasingly undercut curiosity by teaching to the test, teachers are increasingly interested in how to evoke curiosity in their students to prepare them for a world in which lifelong learning and reskilling will be more and more important. One aspect of curiosity that has received little attention, however, is the role of peers in eliciting curiosity. We present what we believe to be the first theoretical framework that articulates an integrated socio-cognitive account of curiosity that ties observable behaviors in peers to underlying curiosity states. We make a bipartite distinction between individual and interpersonal functions that contribute to curiosity, and multimodal behaviors that fulfill these functions. We validate the proposed framework by leveraging a longitudinal latent variable modeling approach. Findings confirm a positive predictive relationship between the latent variables of individual and interpersonal functions and curiosity, with the interpersonal functions exercising a comparatively stronger influence. Prominent behavioral realizations of these functions are also discovered in a data-driven manner. We instantiate the proposed theoretical framework in a set of strategies and tactics that can be incorporated into learning technologies to indicate, evoke, and scaffold curiosity. This work is a step towards designing learning technologies that can recognize and evoke moment-by-moment curiosity during learning in social contexts and towards a more complete multimodal learning analytics. The underlying rationale is applicable more generally for developing computer support for other metacognitive and socio-emotional skills.Comment: arXiv admin note: text overlap with arXiv:1704.0748

Evolution of surface grain structure and mechanical properties in orthogonal cutting of titanium alloy

In this study, a mesoscale dislocation simulation method was developed to study the orthogonal cutting of Titanium alloy. The evolution of surface grain structure and its effects on the surface mechanical properties were studied by using two-dimensional climb assisted dislocation dynamics technology. The motions of edge dislocations such as dislocation nucleation, junction, interaction with obstacles and grain boundaries, and annihilation were tracked. The results indicated that the machined surface has a microstructure composed of refined grains. The fine-grains bring appreciable scale effect and a mass of dislocations are piled up in the grain boundaries and persistent slip bands. In particular, dislocation climb can induce a perfect softening effect, but this effect is significantly weakened when grain size is less than 1.65 μm. In addition, a Hall-Petch type relation was predicted according to the arrangement of grain, the range of grain sizes and the distribution of dislocations